Decrease, Coupling of oxidative phosphorylation

51-28-5

UFBJCMHMOXMLKC-UHFFFAOYSA-N

2,4-Dinitrophenol

DNP 1,3-Dinitro-4-hydroxybenzene 1-Hydroxy-2,4-dinitrobenzene 2,4-dinitrofenol Aldifen Dinitrophenol DINITROPHENOL, 2,4- Dinofan Fenoxyl Carbon N NSC 1532 Phenol, α-dinitro- UN 1320 UN 1599 α-Dinitrophenol Phenol, 2,4-dinitro-

DTXSID0020523

87-86-5

IZUPBVBPLAPZRR-UHFFFAOYSA-N

Pentachlorophenol

PCP Phenol, pentachloro- 1-Hydroxy-2,3,4,5,6-pentachlorobenzene 1-Hydroxypentachlorobenzene Chlorophenasic acid CHLOROPHENATE Dowicide EC 7 Dura Treet II Fungifen Grundier Arbezol Lauxtol Liroprem NSC 263497 Penchlorol Pentachlorphenol Perchlorophenol Permasan Phenol, 2,3,4,5,6-pentachloro- Pole topper Pole topper fluid Preventol P Santophen 20 Satophen UN 3155 Witophen P Woodtreat A 2,3,4,5,6-Pentachlorophenol

DTXSID7021106

3380-34-5

XEFQLINVKFYRCS-UHFFFAOYSA-N

Triclosan

5-Chloro-2-(2,4-dichlorophenoxy)phenol Phenol, 5-chloro-2-(2,4-dichlorophenoxy)- 2, 4, 4'-Trichloro-2'-hydroxydiphenylether 2,2'-Oxybis(1',5'-dichlorophenyl-5-chlorophenol) 2,4,4'-TRICHLORO-2'-HYDROXY DIPHENYLETHER 2',4',4-Trichloro-2-hydroxydiphenyl ether 2',4,4'-Trichloro-2-hydroxydiphenyl ether 2,4,4'-Trichloro-2'-hydroxydiphenyl ether 2'-Hydroxy-2,4,4'-trichlorodiphenyl ether 2-Hydroxy-2',4,4'-trichlorodiphenyl ether 3-Chloro-6-(2,4-dichlorophenoxy)phenol 4-Chloro-2-hydroxyphenyl 2,4-dichlorophenyl ether 5-Chloro-2-(2', 4'-dichlorophenoxy) phenol Aquasept Bacti-Stat soap Cansan TCH DIPHENYL ETHER, 2,4,4'-TRICHLORO-2'-HYDROXY- Irgacare MP Irgacide LP 10 Irgaguard B 1000 Irgaguard B 1325 Irgasan Irgasan CH 3565 Irgasan DP 30 Irgasan DP 300 Irgasan DP 3000 Irgasan DP 400 Irgasan PE 30 Irgasan PG 60 Microban Additive B Microban B Oletron Phenol, 5-chloro-2-(2,4-dichlorophenoxy) Phenol, 5-chloro-2-(2,4-dichlorophenoxy)-, dihydrogen phosphate Sanitized XTX Sapoderm SterZac Tinosan AM 100 Tinosan AM 110 TRICLOSAM Ultra Fresh NM 100 Ultrafresh NM-V 2 Vinyzene DP 7000 Yujiexin Zilesan UW

DTXSID5032498

518-82-1

RHMXXJGYXNZAPX-UHFFFAOYSA-N

Emodin

9,10-Anthracenedione, 1,3,8-trihydroxy-6-methyl- 1,3,8-trihidroxi-6-metilantraquinona 1,3,8-Trihydroxy-6-methyl-9,10-anthraquinone 1,3,8-Trihydroxy-6-methylanthrachinon 1,3,8-trihydroxy-6-methylanthraquinone 1,6,8-Trihydroxy-3-methylanthraquinone 3-Methyl-1,6,8-trihydroxyanthraquinone 4,5,7-Trihydroxy-2-methylanthraquinone Anthraquinone, 1,3,8-trihydroxy-6-methyl- Frangula emodin Frangulic acid NSC 408120 NSC 622947 Rheum emodin Schuttgelb

DTXSID5025231

10537-47-0

MZOPWQKISXCCTP-UHFFFAOYSA-N

Malonoben

DTXSID1042106

GO:0005739

GO mitochondrion

CHEBI:15422

CHEBI ATP

UBERON:0000468

UBERON multicellular organism

GO:1901691

GO proton binding

GO:0017077

GO oxidative phosphorylation uncoupler activity

GO:0051881

GO regulation of mitochondrial membrane potential

GO:0006754

GO ATP biosynthetic process

GO:0008219

GO cell death

GO:0040007

GO growth

WIKI increased

WIKI decreased

2,4-Dinitrophenol

2016-11-29T18:42:27

Carbonyl cyanide-p-trifluoromethoxyphenylhydrazone

2020-11-12T17:59:28

Carbonyl cyanide m-chlorophenyl hydrazone

2020-11-12T17:59:47

Pentachlorophenol

2020-11-12T17:59:12

Triclosan

2020-11-12T18:00:07

Emodin

2020-11-20T13:48:58

Malonoben

2020-11-27T14:43:47

WCS_7955

common ecological species zebrafish

WCS_9606

common toxicological species human

10090

NCBI mouse

10116

NCBI rat

WCS_4472

common ecological species Lemna minor

WikiUser_25

Wikiuser: Cyauk human and other cells in culture

10116

NCBI Rattus norvegicus

WCS_90988

common ecological species fathead minnow

WCS_35525

common ecological species Daphnia magna

WCS_9606

common toxicological species humans

WikiUser_17

mammals

WikiUser_6

ApacheUser fish

WCS_35525

common ecological species crustaceans

WCS_63659

common ecological species green algae

Decrease, Coupling of oxidative phosphorylation

Decrease, Coupling of OXPHOS

Cellular

Decreased coupling of oxidative phosphorylation (OXPHOS), or uncoupling of OXPHOS, describes dissipation of protonmotive force (PMF) across the inner mitochondrial membrane (IMM) by environmental stressors. In eukaryotes, the mitochondrial electron transport chain mediates a series of redox reactions to create a PMF across the IMM. The PMF is used as energy to drive adenosine triphosphate (ATP) synthesis through phosphorylation of adenosine diphosphate (ADP). These processes are coupled and referred to as OXPHOS. A number of chemicals can dissipate the PMF, leading to uncoupling of OXPHOS. This key event describes the main outcome of the interactions between an uncoupler and the transmembrane PMF. An uncoupler can bind to a proton in the mitochondrial inter membrane space, transport the proton to the matrix side of the IMM, release the proton and move back to the inter membrane space. These processes are repeated until the transmembrane PMF is dissipated. This KE is therefore a lumped term of these processes and represents the final consequence of the interactions.

Uncoupling of oxidative phosphorylation can be indicated by reduced mitochondrial membrane potential, increased proton leak and/or increased oxygen consumption rate. <ul> <li>Mitochondrial membrane potential can be determined using ToxCast high-throughput screening bioassays such as “APR_HepG2_MitoMembPot”, “APR_Hepat_MitoFxnI”, and “APR_Mitochondrial_membrane_potential”, and the Tox21 high-throughput screening assay “tox21-mitotox-p1”.</li> <li>Mitochondrial membrane potential can also be measured using commercially available fluorescent probes such as TMRM (tetramethylrhodamine, methyl ester, perchlorate), TMRE (tetramethylrhodamine, ethyl ester, perchlorate) and JC-1 (Perry 2011).</li> <li>Proton leak and oxygen consumption rate can be measured using a high-resolution respirometry (Affourtit 2018) or a Seahorse XF analyzer (Divakaruni 2014).</li> </ul>

Taxonomic applicability domain This key event is in general considered applicable to most eukaryotes, as the mitochondrion and oxidative phosphorylation are highly conserved (Roger 2017).     Life stage applicability domain This key event is considered applicable to all life stages, as ATP synthesis by oxidative phosphorylation is an essential biological process for most living organisms.   Sex applicability domain This key event is considered sex-unspecific, as both males and females use oxidative phosphorylation as a main process to generate ATP.

CL:0000000

CL cell

High Unspecific

High

Embryo

High

Juvenile

Moderate

Adult, reproductively mature

High High High High High

Affourtit C, Wong H-S, Brand MD. 2018. Measurement of proton leak in isolated mitochondria. In Palmeira CM, Moreno AJ, eds, Mitochondrial Bioenergetics: Methods and Protocols. Springer New York, New York, NY, pp 157-170. Attene-Ramos MS, Huang R, Sakamuru S, Witt KL, Beeson GC, Shou L, Schnellmann RG, Beeson CC, Tice RR, Austin CP, Xia M. 2013. Systematic study of mitochondrial toxicity of environmental chemicals using quantitative high throughput screening. Chemical Research in Toxicology 26:1323-1332. DOI: 10.1021/tx4001754. Attene-Ramos MS, Huang RL, Michael S, Witt KL, Richard A, Tice RR, Simeonov A, Austin CP, Xia MH. 2015. Profiling of the Tox21 chemical collection for mitochondrial function to identify compounds that acutely decrease mitochondrial membrane potential. Environ Health Persp 123:49-56. DOI: 10.1289/ehp.1408642. Divakaruni AS, Paradyse A, Ferrick DA, Murphy AN, Jastroch M. 2014. Chapter Sixteen - Analysis and Interpretation of Microplate-Based Oxygen Consumption and pH Data. In Murphy AN, Chan DC, eds, Methods in Enzymology. Vol 547. Academic Press, pp 309-354. Dreier DA, Denslow ND, Martyniuk CJ. 2019. Computational in vitro toxicology uncovers chemical structures impairing mitochondrial membrane potential. J Chem Inf Model 59:702-712. DOI: 10.1021/acs.jcim.8b00433. Escher BI, Schwarzenbach RP. 2002. Mechanistic studies on baseline toxicity and uncoupling of organic compounds as a basis for modeling effective membrane concentrations in aquatic organisms. Aquatic Sciences 64:20-35. DOI: 10.1007/s00027-002-8052-2. Legradi J, Dahlberg A-K, Cenijn P, Marsh G, Asplund L, Bergman Å, Legler J. 2014. Disruption of Oxidative Phosphorylation (OXPHOS) by Hydroxylated Polybrominated Diphenyl Ethers (OH-PBDEs) Present in the Marine Environment. Environmental Science & Technology 48:14703-14711. DOI: 10.1021/es5039744. Naven RT, Swiss R, Klug-Mcleod J, Will Y, Greene N. 2012. The development of structure-activity relationships for mitochondrial dysfunction: Uncoupling of oxidative phosphorylation. Toxicol Sci 131:271-278. DOI: 10.1093/toxsci/kfs279. Perry SW, Norman JP, Barbieri J, Brown EB, Gelbard HA. 2011. Mitochondrial membrane potential probes and the proton gradient: a practical usage guide. BioTechniques 50:98-115. DOI: 10.2144/000113610. Roger AJ, Munoz-Gomez SA, Kamikawa R. 2017. The origin and diversification of mitochondria. Curr Biol 27:R1177-R1192. DOI: 10.1016/j.cub.2017.09.015. Russom CL, Bradbury SP, Broderius SJ, Hammermeister DE, Drummond RA. 1997. Predicting modes of toxic action from chemical structure: Acute toxicity in the fathead minnow (Pimephales promelas). Environ Toxicol Chem 16:948-967. DOI: <a href="https://doi.org/10.1002/etc.5620160514">https://doi.org/10.1002/etc.5620160514</a>. Schultz TW, Cronin MTD. 1997. Quantitative structure-activity relationships for weak acid respiratory uncouplers to Vibrio fisheri. Environ Toxicol Chem 16:357-360. DOI: <a href="https://doi.org/10.1002/etc.5620160235">https://doi.org/10.1002/etc.5620160235</a>. Shim J, Weatherly LM, Luc RH, Dorman MT, Neilson A, Ng R, Kim CH, Millard PJ, Gosse JA. 2016. Triclosan is a mitochondrial uncoupler in live zebrafish. J Appl Toxicol 36:1662-1667. DOI: 10.1002/jat.3311. Sugiyama Y, Shudo T, Hosokawa S, Watanabe A, Nakano M, Kakizuka A. 2019. Emodin, as a mitochondrial uncoupler, induces strong decreases in adenosine triphosphate (ATP) levels and proliferation of B16F10 cells, owing to their poor glycolytic reserve. Genes to Cells 24:569-584. DOI: <a href="https://doi.org/10.1111/gtc.12712">https://doi.org/10.1111/gtc.12712</a>. Terada H. 1990. Uncouplers of oxidative phosphorylation. Environ Health Perspect 87:213-218. DOI: 10.1289/ehp.9087213. Troger F, Delp J, Funke M, van der Stel W, Colas C, Leist M, van de Water B, Ecker GF. 2020. Identification of mitochondrial toxicants by combined in silico and in vitro studies – A structure-based view on the adverse outcome pathway. Computational Toxicology 14:100123. DOI: <a href="https://doi.org/10.1016/j.comtox.2020.100123">https://doi.org/10.1016/j.comtox.2020.100123</a>. Weatherly LM, Shim J, Hashmi HN, Kennedy RH, Hess ST, Gosse JA. 2016. Antimicrobial agent triclosan is a proton ionophore uncoupler of mitochondria in living rat and human mast cells and in primary human keratinocytes. Journal of Applied Toxicology 36:777-789. DOI: <a href="https://doi.org/10.1002/jat.3209">https://doi.org/10.1002/jat.3209</a>. Xia M, Huang R, Shi Q, Boyd WA, Zhao J, Sun N, Rice JR, Dunlap PE, Hackstadt AJ, Bridge MF, Smith MV, Dai S, Zheng W, Chu PH, Gerhold D, Witt KL, DeVito M, Freedman JH, Austin CP, Houck KA, Thomas RS, Paules RS, Tice RR, Simeonov A. 2018. Comprehensive analyses and prioritization of Tox21 10K chemicals affecting mitochondrial function by in-depth mechanistic studies. Environ Health Perspect 126:077010. DOI: 10.1289/EHP2589.  AOPWiki 2017-06-29T08:05:51

2025-11-07T05:15:58

Decrease, Adenosine triphosphate pool

Decrease, ATP pool

Cellular

Decreased adenosine triphosphate (ATP) pool describes the loss of balance between ATP synthesis and ATP consumption, leading to reduced total ATP. As a primary form of biological energy, ATP is used by many biological processes (Bonora 2012). Decrease in ATP level normally attributes to metabolic disorders in major ATP synthetic pathways, such as mitochondrial oxidative phosphorylation, fatty acid β-oxidation, glycolysis and plant photophosphorylation.

-The ATP pool in cells or tissue can be quantified using a well-established ATP bioluminescent assay (Lemasters 1978; Wibom 1990). Assay principles: ATP can react with luciferase and luciferin from firefly and the luminescence emitted from the reaction is proportional to the ATP concentration:   ATP + D-Luciferin + O2 è Oxyluciferin + AMP + PPi + CO2 + Light -ToxCast high-throughput screening bioassays, such as “NCCT_HEK293T_CellTiterGLO” and “NIS_HEK293T_CTG_Cytotoxicity” can be used to measure this KE.

Taxonomic applicability domain This key event is in general considered applicable to all eukaryotes utilizing ATP as a direct source of energy and signaling molecule.   Life stage applicability domain This key event is considered applicable to all life stages, as all developmental stages require energy supply to maintain necessary physiological processes.   Sex applicability domain This key event is considered sex-unspecific, as both males and females use ATP as an essential energy molecule.

CL:0000000

CL cell

High Unspecific

High

Embryo

High

Juvenile

Moderate

Adult, reproductively mature

High High High High High

Bonora M, Patergnani S, Rimessi A, De Marchi E, Suski JM, Bononi A, Giorgi C, Marchi S, Missiroli S, Poletti F, Wieckowski MR, Pinton P. 2012. ATP synthesis and storage. Purinergic Signalling 8:343-357. DOI: 10.1007/s11302-012-9305-8. Lemasters JJ, Hackenbrock CR. 1978. [4] Firefly luciferase assay for ATP production by mitochondria. Methods in Enzymology. Vol 57. Academic Press, pp 36-50. Wibom R, Lundin A, Hultman E. 1990. A sensitive method for measuring ATP-formation in rat muscle mitochondria. Scandinavian Journal of Clinical and Laboratory Investigation 50:143-152. DOI: 10.1080/00365519009089146.  AOPWiki 2020-04-30T12:42:35

2021-06-14T13:40:17

Increase, Cell injury/death

Cell injury/death

Cellular

Two types of cell death can be distinguished by morphological features, although it is likely that these are two ends of a spectrum with possible intermediate forms. Apoptosis involves shrinkage, nuclear disassembly, and fragmentation of the cell into discrete bodies with intact plasma membranes. These are rapidly phagocytosed by neighbouring cells. An important feature of apoptosis is the requirement for adenosine triphosphate (ATP) to initiate the execution phase. In contrast, necrotic cell death is characterized by cell swelling and lysis. This is usually a consequence of profound loss of mitochondrial function and resultant ATP depletion, leading to loss of ion homeostasis, including volume regulation, and increased intracellular Ca2+. The latter activates a number of nonspecific hydrolases (i.e., proteases, nucleases, and phospholipases) as well as calcium dependent kinases. Activation of calpain I, the Ca2+-dependent cysteine protease cleaves the death-promoting Bcl-2 family members Bid and Bax which translocate to mitochondrial membranes, resulting in release of truncated apoptosis-inducing factor (tAIF), cytochrome c and endonuclease in the case of Bid and cytocrome c in the case of Bax. tAIF translocates to cell nuclei, and together with cyclophilin A and phosphorylated histone H2AX (γH2AX) is responsible for DNA cleavage, a feature of programmed necrosis. Activated calpain I has also been shown to cleave the plasma membrane Na+–Ca2+ exchanger, which leads to build-up of intracellular Ca2+, which is the source of additional increased intracellular Ca2+. Cytochrome c in cellular apoptosis is a component of the apoptosome. DNA damage activates nuclear poly(ADP-ribose) polymerase-1(PARP-1), a DNA repair enzyme. PARP-1 forms poly(ADP-ribose) polymers, to repair DNA, but when DNA damage is extensive, PAR accumulates, exits cell nuclei and travels to mitochondrial membranes, where it, like calpain I, is involved in AIF release from mitochondria. A fundamental distinction between necrosis and apoptosis is the loss of plasma membrane integrity; this is integral to the former but not the latter. As a consequence, lytic release of cellular constituents promotes a local inflammatory reaction, whereas the rapid removal of apoptotic bodies minimizes such a reaction. The distinction between the two modes of death is easily accomplished in vitro but not in vivo. Thus, although claims that certain drugs induce apoptosis have been made, these are relatively unconvincing. DNA fragmentation can occur in necrosis, leading to positive TUNEL staining (see explanation below). Conversely, when apoptosis is massive, it can exceed the capacity for rapid phagocytosis, resulting in the eventual appearance of secondary necrosis. Two alternative pathways - either extrinsic (receptor-mediated) or intrinsic (mitochondria-mediated) - lead to apoptotic cell death. The initiation of cell death begins either at the plasma membrane with the binding of TNF or FasL to their cognate receptors or within the cell. The latter is due to the occurrence of intracellular stress in the form of biochemical events such as oxidative stress, redox changes, covalent binding, lipid peroxidation, and consequent functional effects on mitochondria, endoplasmic reticulum, microtubules, cytoskeleton, or DNA. The intrinsic mitochondrial pathway involves the initiator, caspase-9, which, when activated, forms an “apoptosome” in the cytosol, together with cytochrome c, which translocates from mitochondria, Apaf-1 and dATP. The apoptosome activates caspase-3, the central effector caspase, which in turn activates downstream factors that are responsible for the apoptotic death of a cell (Fujikawa, 2015). Intracellular stress either directly affects mitochondria or can lead to effects on other organelles, which then send signals to the mitochondria to recruit participation in the death process (Fujikawa, 2015; Malhi et al., 2010). Constitutively expressed nitric oxide synthase (nNOS) is a Ca2+-dependent cytosolic enzyme that forms nitric oxide (NO) from L-arginine, and NO reacts with the free radical such as superoxide (O2−) to form the very toxic free radical peroxynitrite (ONOO−). Free radicals such as ONOO−, O2 − and hydroxyl radical (OH−) damage cellular membranes and intracellular proteins, enzymes and DNA (Fujikawa, 2015; Malhi et al., 2010; Kaplowitz, 2002; Kroemer et al., 2009).

Necrosis: Lactate dehydrogenase (LDH) is a soluble cytoplasmic enzyme that is present in almost all cells and is released into extracellular space when the plasma membrane is damaged. To detect the leakage of LDH into cell culture medium, a tetrazolium salt is used in this assay. In the first step, LDH produces reduced nicotinamide adenine dinucleotide (NADH) when it catalyzes the oxidation of lactate to pyruvate. In the second step, a tetrazolium salt is converted to a colored formazan product using newly synthesized NADH in the presence of an electron acceptor. The amount of formazan product can be colorimetrically quantified by standard spectroscopy. Because of the linearity of the assay, it can be used to enumerate the percentage of necrotic cells in a sample (Chan et al., 2013).  The MTT assay is a colorimetric assay for assessing cell viability. NAD(P)H-dependent cellular oxidoreductase enzymes may reflect the number of viable cells present. These enzymes are capable of reducing the tetrazolium dye MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide to its insoluble formazan, which has a purple color. Other closely related tetrazolium dyes include XTT, MTS and the WSTs. Tetrazolium dye assays can also be used to measure cytotoxicity (loss of viable cells) or cytostatic activity (shift from proliferation to quiescence) of potential medicinal agents and toxic materials. MTT assays are usually done in the dark since the MTT reagent is sensitive to light (Berridgeet al.,2005). Propidium iodide (PI) is an intercalating agent and a fluorescent molecule used to stain necrotic cells. It is cell membrane impermeant so it stains only those cells where the cell membrane is destroyed. When PI is bound to nucleic acids, the fluorescence excitation maximum is 535 nm and the emission maximum is 617 nm (Moore et al.,1998) Alamar Blue (resazurin) is a fluorescent dye. The oxidized blue non fluorescent Alamar blue is reduced to a pink fluorescent dye in the medium by cell activity (O'Brien et al., 2000) (12). Neutral red uptake, which is based on the ability of viable cells to incorporate and bind the supravital dye neutral red in lysosomes (Repetto et al., 2008)(13). Moreover, quantification of ATP, signaling the presence of metabolically active cells, can be performed (CellTiter-Glo; Promega). ATP assay: Quantification of ATP, signaling the presence of metabolically active cells (CellTiter-Glo; Promega). Apoptosis: TUNEL is a common method for detecting DNA fragmentation that results from apoptotic signalling cascades. The assay relies on the presence of nicks in the DNA which can be identified by terminal deoxynucleotidyl transferase or TdT, an enzyme that will catalyze the addition of dUTPs that are secondarily labeled with a marker. It may also label cells that have suffered severe DNA damage. Caspase activity assays measured by fluorescence. During apoptosis, mainly caspase-3 and -7 cleave PARP to yield an 85 kDa and a 25 kDa fragment. PARP cleavage is considered to be one of the classical characteristics of apoptosis. Antibodies to the 85 kDa fragment of cleaved PARP or to caspase-3 both serve as markers for apoptotic cells that can be monitored using immunofluorescence (Li, Peng et al., 2004). Hoechst 33342 staining: Hoechst dyes are cell-permeable and bind to DNA in live or fixed cells. Therefore, these stains are often called supravital, which means that cells survive a treatment with these compounds. The stained, condensed or fragmented DNA is a marker of apoptosis (Loo, 2002; Kubbies and Rabinovitch, 1983).  Acridine Orange/Ethidium Bromide staining is used to visualize nuclear changes and apoptotic body formation that are characteristic of apoptosis. Cells are viewed under a fluorescence microscope and counted to quantify apoptosis.   Update - non-endorsed (by You Song, 02/09/2026) ToxCast/Tox21 assays (invitrodb v4.3): APR_HepG2_CellLoss_*; ATG_XTT_Cytotoxicity; LTEA_HepaRG_LDH_cytotoxicity

Cell death is an universal event occurring in cells of any species (Fink and Cookson,2005).

CL:0000255

CL eukaryotic cell

Not Specified Unspecific

Not Specified

All life stages

High High High High

<ul> <li>Fujikawa, D.G. (2015), The role of excitotoxic programmed necrosis in acute brain injury, Comput Struct Biotechnol J, vol. 13, pp. 212-221.</li> <li>Malhi, H. et al. (2010), Hepatocyte death: a clear and present danger, Physiol Rev, vol. 90, no. 3, pp. 1165-1194.</li> <li>Kaplowitz, N. (2002), Biochemical and Cellular Mechanisms of Toxic Liver Injury, Semin Liver Dis, vol. 22, no. 2, <a class="external free" href="http://www.medscape.com/viewarticle/433631" rel="nofollow" target="_blank">http://www.medscape.com/viewarticle/433631</a> (accessed on 20 January 2016).</li> <li>Kroemer, G. et al., (2009), Classification of cell death: recommendations of the Nomenclature Committee on Cell Death, Cell Death Differ, vol. 16, no. 1, pp. 3-11.</li> <li>Chan, F.K., K. Moriwaki and M.J. De Rosa (2013), Detection of necrosis by release of lactate dehydrogenase (LDH) activity, Methods Mol Biol, vol. 979, pp. 65–70.</li> <li>Berridge, M.V., P.M. Herst and A.S. Tan (2005), Tetrazolium dyes as tools in cell biology: new insights into their cellular reduction. Biotechnology Annual Review, vol. 11, pp 127-152.</li> <li>Moore, A, et al.(1998), Simultaneous measurement of cell cycle and apoptotic cell death,Methods Cell Biol, vol. 57, pp. 265–278.</li> <li>Li, Peng et al. (2004), Mitochondrial activation of apoptosis, Cell, vol. 116, no. 2 Suppl,pp. S57-59, 2 p following S59.</li> <li>Loo, D.T. (2002), TUNEL Assay an overview of techniques, Methods in Molecular Biology, vol. 203: In Situ Detection of DNA Damage, chapter 2, Didenko VV (ed.), Humana Press Inc.</li> <li>Kubbies, M. and P.S. Rabinovitch (1983), Flow cytometric analysis of factors which influence the BrdUrd-Hoechst quenching effect in cultivated human fibroblasts and lymphocytes, Cytometry, vol. 3, no. 4, pp. 276–281.</li> <li>Fink, S.L. and B.T. Cookson (2005), Apoptosis, pyroptosis, and necrosis: mechanistic description of dead and dying eukaryotic cells, Infect Immun, vol. 73, no. 4, pp.1907-1916.</li> <li>O'Brien J, Wilson I, Orton T, Pognan F. 2000. Investigation of the Alamar Blue (resazurin) fluorescent dye for the assessment of mammalian cell cytotoxicity. European journal of biochemistry / FEBS 267(17): 5421-5426.</li> <li>Repetto G, del Peso A, Zurita JL. 2008. Neutral red uptake assay for the estimation of cell viability/cytotoxicity. Nature protocols 3(7): 1125-1131.</li> </ul> AOPWiki 2016-11-29T18:41:22

2026-09-02T04:23:51

Decrease, Growth

Individual

Decreased growth refers to a reduction in size and/or weight of a tissue, organ or individual organism. Growth is normally controlled by growth factors and mainly achieved through cell proliferation (Conlon 1999).

Growth can be indicated by measuring weight, length, total volume, and/or total area of a tissue, organ or individual organism.   Revised version (non-endorsed, added by You Song, 02/09/2026) Growth can be measured as a change in size, mass, biomass, length, area, volume, or growth rate of a tissue, organ, or whole organism over a defined exposure period. The appropriate measurement depends on the biological system, life stage, and test species. At the organism level, growth is commonly assessed by measuring body weight, wet weight, dry weight, body length, standard length, total length, shell length, shoot height, root length, frond number, frond area, cell density, biomass, or relative growth rate. Growth inhibition is typically expressed as a statistically significant reduction relative to the control, or as an effect concentration causing a defined percentage reduction in growth, such as ECx, ErCx, EyCx, LOEC, NOEC, or benchmark concentration/dose values. For unicellular algae and cyanobacteria, growth is commonly quantified from changes in biomass over time. Biomass may be estimated using direct cell counts, electronic particle counters, microscopy, optical density, fluorescence, chlorophyll-related measurements, or other validated biomass proxies. Growth inhibition is commonly calculated from average specific growth rate and yield. For aquatic macrophytes such as Lemna spp., growth is typically quantified using frond number and at least one additional growth-related variable, such as total frond area, dry weight, fresh weight, or image-based area measurements. Digital imaging, flatbed scanning, stereomicroscopy, or automated image-analysis tools can be used to quantify frond area and related morphological endpoints. For terrestrial plants, growth can be measured using seedling emergence, survival, shoot height, root length, fresh or dry biomass, leaf area, and visual signs of phytotoxicity such as chlorosis, necrosis, deformation, or delayed development. Measurements may be made using rulers or calipers, analytical balances, scanners, digital imaging, or plant image-analysis software. For aquatic invertebrates, growth may be assessed using body length, body area, wet weight, dry weight, developmental stage, or size at defined time points. In small organisms such as Daphnia, body length is often measured from microscope or stereomicroscope images using calibrated image-analysis software. For fish and amphibians, growth is commonly assessed using wet weight, dry weight, standard length, total length, snout–vent length, condition factor, developmental stage, and specific growth rate. Measurements may be obtained using balances, calipers, digital imaging, or stereomicroscopy, depending on organism size and life stage. For mammals and other vertebrates in repeated-dose or reproductive/developmental toxicity studies, growth-related endpoints are typically evaluated using body weight, body-weight gain, food and water consumption, pup or offspring weight, litter growth, organ weight, and developmental landmarks. These endpoints are usually interpreted together with clinical observations, survival, pathology, and reproductive or developmental parameters. Because growth is an integrative apical endpoint, measurement should be performed over a biologically appropriate time window and interpreted in relation to survival, developmental delay, nutritional status, reproductive output, and general toxicity. Direct measurements of organismal size, biomass, or growth rate provide the strongest evidence for this key event, whereas indirect indicators such as altered morphology, reduced condition factor, or reduced organ weight may provide supporting evidence depending on biological context. Relevant OECD Test Guidelines include, but are not limited to: <ul> <li> OECD TG 201: Freshwater Alga and Cyanobacteria, Growth Inhibition Test. This guideline directly assesses inhibition of algal or cyanobacterial growth, typically using average specific growth rate and yield as response variables. </li> <li> OECD TG 208: Terrestrial Plant Test: Seedling Emergence and Seedling Growth Test. This guideline assesses effects on seedling emergence and early growth of terrestrial plants, including biomass, shoot height, and visible phytotoxic effects. </li> <li> OECD TG 211: Daphnia magna Reproduction Test. Although the primary endpoint is reproductive output, the test can provide chronic organism-level information relevant to population performance, and growth-related observations such as body size may be reported as supporting endpoints when included in the study design. </li> <li> OECD TG 212: Fish, Short-term Toxicity Test on Embryo and Sac-Fry Stages. This guideline assesses toxicity during early fish development from fertilized egg to the end of the sac-fry stage. Growth-related developmental observations may support interpretation of early-life-stage impairment. </li> <li> OECD TG 215: Fish, Juvenile Growth Test. This guideline directly evaluates effects on juvenile fish growth. Effects are expressed using growth rate, and concentration-response analysis can be used to estimate concentrations causing a defined percentage change in growth rate. </li> <li> OECD TG 221: Lemna sp. Growth Inhibition Test. This guideline directly assesses effects on vegetative growth of Lemna spp. using average specific growth rate and yield, commonly based on frond number and additional variables such as frond area or biomass. </li> <li> OECD TG 228: Determination of Developmental Toxicity to Dipteran Dung Flies. This guideline is relevant where chemical exposure affects development and growth-related performance in terrestrial invertebrates. </li> <li> OECD TG 241: Larval Amphibian Growth and Development Assay. This guideline evaluates growth and development in amphibians from fertilization through the early juvenile period. </li> <li> OECD TG 407: Repeated Dose 28-day Oral Toxicity Study in Rodents. This guideline includes body weight and food/water consumption measurements as part of the assessment of repeated-dose systemic toxicity. </li> <li> OECD TG 408: Repeated Dose 90-day Oral Toxicity Study in Rodents. This guideline includes body weight and related clinical observations as part of subchronic systemic toxicity assessment. </li> <li> OECD TG 416: Two-Generation Reproduction Toxicity. This guideline evaluates effects on reproduction as well as growth and development of offspring across generations. </li> <li> OECD TG 422: Combined Repeated Dose Toxicity Study with the Reproduction/Developmental Toxicity Screening Test. This guideline includes body weight, food/water consumption, offspring observations and measurements, and developmental parameters. </li> <li> OECD TG 443: Extended One-Generation Reproductive Toxicity Study. This guideline evaluates reproductive and developmental effects, including health, growth, development, and function of offspring following pre- and postnatal exposure. </li> <li> OECD TG 453: Combined Chronic Toxicity/Carcinogenicity Studies. This guideline includes body weight and body-weight gain as part of the evaluation of chronic systemic toxicity and carcinogenicity. </li> </ul>

Taxonomic applicability domain This key event is in general applicable to all eukaryotes.   Life stage applicability domain This key event is applicable to early life stages such as embryo and juvenile.   Sex applicability domain This key event is sex-unspecific.

High Unspecific

High

Embryo

High

Juvenile

Moderate Moderate Moderate High High High Moderate

Conlon I, Raff M. 1999. Size control in animal development. Cell 96:235-244. DOI: 10.1016/s0092-8674(00)80563-2.  AOPWiki 2018-05-24T15:24:11

2026-09-02T03:23:17

<upstream-id>983ed406-e440-4341-ae8d-fbf88f32a063</upstream-id> <downstream-id>6c7a2777-5834-489c-b345-a8a55a89fd08</downstream-id> This key event relationship describes the dissipation of protonmotive force across the inner mitochondrial membrane by uncouplers (uncoupling of oxidative phosphorylation), leading to reduced total adenosine triphosphate (ATP) pool in cells or organisms.

The overall evidence supporting Relationship 2203 is considered high.

The biological plausibility of Relationship 2203 is considered high. Rationale: In eukaryotic cells, the major metabolic pathways responsible for ATP production are OXPHOS, citric acid (TCA) cycle, glycolysis and photosynthesis. Oxidative phosphorylation is much (theoretically 15-18 times) more efficient than the rest due to high energy derived from oxygen during aerobic respiration (Schmidt-Rohr 2020). As the ATP level is relatively balanced between production and consumption (Bonora 2012), ATP depletion is a plausible consequence of reduced ATP synthetic efficiency following uncoupling of OXPHOS.

The empirical support of Relationship 2203 is considered high. Rationale: The majority of relevant studies show good incidence, temporal and/or dose concordance in different organisms and cell types after exposure to known uncouplers, with relatively few exceptions. Evidence: <ul> <li>Temporal concordance: Exposure of zebrafish embryos to 0.5 µM of the classical uncoupler 2,4-DNP led to significantly uncoupling of OXPHOS after 21h, whereas significant reduction in ATP was only observed after 45h (Bestman 2015). </li> <li>Dose concordance: The uncoupler triclosan induced significant uncoupling of OXPHOS in zebrafish embryos at 15 µM, whereas higher (30 µM) concentration was required to caused significant ATP depletion  (Shim 2016).</li> <li>Dose concordance: Exposure to 1 µM of of the uncoupler CCCP led to 40% uncoupling of OXPHOS in rat RBL-2H3 cells, whereas the same magnitude of effect for ATP reduction required 1.6 µM of CCCP (Weatherly 2016).</li> <li>Dose concordance: Exposure to 10 µM of the uncoupler triclosan caused significant uncoupling of OXPHOS in rat RBL-2H3 cells, whereas significant reduction in ATP was observed at a higher concentration (30 µM)  (Weatherly 2018).</li> <li>Dose concordance: Significant effect on uncoupling of OXPHOS required  2 µM FCCP, whereas a significant reduction in ATP required 20 µM FCCP in human RD cells  (Kuruvilla 2003).</li> <li>Incidence concordance: In human colon cancer cells (SW480), exposure to 150 µM of the uncoupler flavanoid morin caused 60% reduction in MMP, whereas only around 35% decrease in ATP  (Sithara 2017).</li> <li>Incidence concordance: Exposure of rat RBL-2H3 cells to 10 µM  of the uncoupler triclosan led to 50% uncoupling of OXPHOS, whereas only 40% reduction in ATP (Weatherly 2016).</li> <li>Incidence concordance: Exposure to 5 µM of the uncoupler CCCP caused 71% uncoupling of OXPHOS, whereas only 64% reduction of ATP in human HL-60 cells (Sweet 1999).</li> <li>Incidence concordance: Exposure of human HeLa cells to 50 µM of the uncoupler CCCP for 1h led to 77% uncoupling of OXPHOS and 25% reduction in ATP (Koczor 2009).</li> <li>Incidence concordance: Exposure of the nematode Caenorhabditis elegans to 50 µM Arsenite for 1h led to approximately 45% uncoupling of OXPHOS and 20% reduction in ATP (Luz 2016).</li> </ul>

<ul> <li style="text-align:justify">A significant decrease followed by a significant increase in total ATP was observed in human RD cells during a 48h exposure to the uncoupler FCCP (Kuruvilla 2003), possibly due to the enhancement of other ATP synthetic pathways (e.g., glycolysis) as a compensatory action to impaired OXPHOS (Jose 2011</li> </ul>

The quantitative understanding of Relationship 2203 is high. Rationale: Multiple mathematical models have been developed for describing the quantitative relationships between uncoupling of OXPHOS and ATP synthesis in vertebrates (Beard 2005; Schmitz 2011; Heiske 2017; Kubo 2020). These models, however, are highly complex metabolic or systems biological models and warrant further simplification to be used for this AOP.

A regression based quantitative response-response relationship between uncoupling of OXPHOS and ATP depletion was proposed for the crustacean Daphnia magna under UVB stress (Song 2020).

<ul> <li style="text-align:justify">It is known that mild uncoupling of oxidative phosphorylation can enhance the activity of the mitochondrial electron transport chain to produce more ATP, and/or activate other ATP synthetic pathways (e.g., glycolysis) as a compensatory action to impaired OXPHOS (Jose 2011).</li> </ul>

High Unspecific

High

Embryo

High

Juvenile

High High High High

Taxonomic applicability Relationship 2203 is considered applicable to eukaryotes, as mitochondrial oxidative phosphorylation and ATP synthesis are highly conserved in these organisms. Uncoupling of oxidative phosphorylation leading to ATP depletion is a well-documented relationship in many taxa, such as human, rodents and fish.   Sex applicability Relationship 2203 is considered applicable to all genders, as mitochondrial oxidative phosphorylation and ATP synthesis are fundamental biological processes and are not sex-pecific.   Life-stage applicability Relationship 2203 is considered applicable to all life-stages, as mitochondrial oxidative phosphorylation and ATP synthesis are essential energy production processes for maintaining basic biological activities.

Beard DA. 2005. A biophysical model of the mitochondrial respiratory system and oxidative phosphorylation. PLOS Computational Biology 1:e36. DOI: 10.1371/journal.pcbi.0010036. Bestman JE, Stackley KD, Rahn JJ, Williamson TJ, Chan SS. 2015. The cellular and molecular progression of mitochondrial dysfunction induced by 2,4-dinitrophenol in developing zebrafish embryos. Differentiation 89:51-69. DOI: 10.1016/j.diff.2015.01.001. Bonora M, Patergnani S, Rimessi A, De Marchi E, Suski JM, Bononi A, Giorgi C, Marchi S, Missiroli S, Poletti F, Wieckowski MR, Pinton P. 2012. ATP synthesis and storage. Purinergic Signalling 8:343-357. DOI: 10.1007/s11302-012-9305-8. Heiske M, Letellier T, Klipp E. 2017. Comprehensive mathematical model of oxidative phosphorylation valid for physiological and pathological conditions. The FEBS Journal 284:2802-2828. DOI: <a href="https://doi.org/10.1111/febs.14151">https://doi.org/10.1111/febs.14151</a>. Jose C, Bellance N, Rossignol R. 2011. Choosing between glycolysis and oxidative phosphorylation: A tumor's dilemma? Biochimica et Biophysica Acta (BBA) - Bioenergetics 1807:552-561. DOI: <a href="https://doi.org/10.1016/j.bbabio.2010.10.012">https://doi.org/10.1016/j.bbabio.2010.10.012</a>. Koczor CA, Shokolenko IN, Boyd AK, Balk SP, Wilson GL, Ledoux SP. 2009. Mitochondrial DNA damage initiates a cell cycle arrest by a Chk2-associated mechanism in mammalian cells. J Biol Chem 284:36191-36201. DOI: 10.1074/jbc.M109.036020. Kubo S, Niina T, Takada S. 2020. Molecular dynamics simulation of proton-transfer coupled rotations in ATP synthase FO motor. Scientific Reports 10:8225. DOI: 10.1038/s41598-020-65004-1. Kuruvilla S, Qualls CW, Jr., Tyler RD, Witherspoon SM, Benavides GR, Yoon LW, Dold K, Brown RH, Sangiah S, Morgan KT. 2003. Effects of minimally toxic levels of carbonyl cyanide P-(trifluoromethoxy) phenylhydrazone (FCCP), elucidated through differential gene expression with biochemical and morphological correlations. Toxicol Sci 73:348-361. DOI: 10.1093/toxsci/kfg084. Luz AT, Godebo TR, Bhatt DP, Ilkayeva OR, Maurer LL, Hirschey MD, Meyer JN. 2016. Arsenite Uncouples Mitochondrial Respiration and Induces a Warburg-Like Effect in Caenorhabditis elegans. Toxicol Sci 154:195-195. DOI: 10.1093/toxsci/kfw185. Schmidt-Rohr K. 2020. Oxygen is the high-energy molecule powering complex multicellular life: fundamental corrections to traditional bioenergetics. ACS Omega 5:2221-2233. DOI: 10.1021/acsomega.9b03352. Schmitz JPJ, Vanlier J, van Riel NAW, Jeneson JAL. 2011. Computational modeling of mitochondrial energy transduction.  39:363-377. DOI: 10.1615/CritRevBiomedEng.v39.i5.20. Shim J, Weatherly LM, Luc RH, Dorman MT, Neilson A, Ng R, Kim CH, Millard PJ, Gosse JA. 2016. Triclosan is a mitochondrial uncoupler in live zebrafish. J Appl Toxicol 36:1662-1667. DOI: 10.1002/jat.3311. Sithara T, Arun KB, Syama HP, Reshmitha TR, Nisha P. 2017. Morin inhibits proliferation of SW480 colorectal cancer cells by inducing apoptosis mediated by reactive oxygen species formation and uncoupling of Warburg effect. Frontiers in Pharmacology 8. DOI: 10.3389/fphar.2017.00640. Song Y, Xie L, Lee Y, Tollefsen KE. 2020. De novo development of a quantitative adverse outcome pathway (qAOP) network for ultraviolet B (UVB) radiation using targeted laboratory tests and automated data mining. Environmental Science & Technology 54:13147-13156. DOI: 10.1021/acs.est.0c03794. Sweet S, Singh G. 1999. Changes in mitochondrial mass, membrane potential, and cellular adenosine triphosphate content during the cell cycle of human leukemic (HL-60) cells. Journal of Cellular Physiology 180:91-96. DOI: <a href="https://doi.org/10.1002/(SICI)1097-4652(199907)180:1">https://doi.org/10.1002/(SICI)1097-4652(199907)180:1</a><91::AID-JCP10>3.0.CO;2-6. Weatherly LM, Nelson AJ, Shim J, Riitano AM, Gerson ED, Hart AJ, de Juan-Sanz J, Ryan TA, Sher R, Hess ST, Gosse JA. 2018. Antimicrobial agent triclosan disrupts mitochondrial structure, revealed by super-resolution microscopy, and inhibits mast cell signaling via calcium modulation. Toxicol Appl Pharmacol 349:39-54. DOI: 10.1016/j.taap.2018.04.005. Weatherly LM, Shim J, Hashmi HN, Kennedy RH, Hess ST, Gosse JA. 2016. Antimicrobial agent triclosan is a proton ionophore uncoupler of mitochondria in living rat and human mast cells and in primary human keratinocytes. Journal of Applied Toxicology 36:777-789. DOI: <a href="https://doi.org/10.1002/jat.3209">https://doi.org/10.1002/jat.3209</a>. AOPWiki 2020-11-12T17:57:43

2022-07-06T07:39:36

<upstream-id>6c7a2777-5834-489c-b345-a8a55a89fd08</upstream-id> <downstream-id>0389f740-377e-4dce-9e2c-ac7ef571a422</downstream-id> This key event relationship describes the causal and predictive link by which a decrease in the cellular adenosine triphosphate (ATP) pool leads to increased cell injury and/or cell death. ATP is required to maintain ion gradients, plasma membrane integrity, mitochondrial homeostasis, macromolecular repair, vesicular trafficking, and regulated cell death programs. When ATP depletion is sufficiently severe or prolonged, energy-dependent adaptive and repair processes fail, calcium and sodium homeostasis are disrupted, mitochondrial permeability transition may be promoted, and cells may undergo apoptosis, necrosis, necroptosis-like injury or mixed forms of cell death depending on cellular context and residual ATP availability (Nieminen et al., 1994; Leist et al., 1997; Bonora et al., 2012). The direction of this KER is from reduced ATP availability to increased cell injury/death. The KER is not intended to specify a single mode of cell death. Rather, it captures the general biological principle that loss of cellular energy supply increases the probability of irreversible cellular injury and death, with the exact death phenotype depending on cell type, severity of ATP depletion, duration of exposure, and availability of death-execution pathways.

The evidence base was assembled using the same structured strategy applied across the ROS-growth AOP network. Existing AOP-Wiki pages and OECD AOP reports were reviewed first to identify reusable KEs and related KERs. Particular attention was given to the mitochondrial energetic AOP series, including AOP 263 and AOP 264, because these AOPs contain the upstream event decreased ATP pool and downstream cellular or organismal outcomes relevant to growth inhibition and cell injury/death. Targeted literature searches were then conducted using combinations of terms related to ATP depletion, cellular ATP, energetic failure, mitochondrial dysfunction, metabolic inhibition, apoptosis, necrosis, cytotoxicity, cell viability, cell injury, mitochondrial permeability transition, calcium electroporation, rotenone, FCCP, CCCP, paraquat, cadmium, algae, bivalves, fish, mammalian cells and human cells. Primary studies were prioritized when they measured ATP levels and cell viability, cytotoxicity, apoptosis or necrosis in the same biological system and reported dose/concentration or time-course information. Mechanistic reviews were used to support biological plausibility, while primary experimental studies were used for empirical concordance and quantitative understanding. The evidence was curated for weight-of-evidence indicators including biological plausibility, temporal concordance, dose-response concordance, incidence concordance, evidence of threshold behavior, and intervention or rescue information. Studies were considered most informative when ATP depletion preceded or occurred at lower or similar exposure levels than cytotoxicity or cell death, or when restoration of energy metabolism reduced the downstream injury response.

The overall evidence supporting this KER is considered moderate to high. Biological plausibility is high because ATP is indispensable for cellular homeostasis and because severe ATP depletion is a well-established trigger of irreversible cell injury and death. Empirical support is moderate to high because multiple studies in mammalian cells, algae, aquatic organisms and cancer cell systems demonstrate concordance between ATP depletion and cell injury/death; however, the exact quantitative threshold varies substantially across biological systems and exposure conditions.

Biological plausibility is high. ATP depletion compromises core cellular maintenance processes including ion pumping, membrane integrity, cytoskeletal dynamics, protein turnover, DNA repair, and mitochondrial function. When ATP supply falls below the level required for homeostasis, cells lose the ability to maintain electrochemical gradients and to execute energy-dependent adaptive responses. Severe energetic collapse promotes necrotic injury, while partial ATP depletion may permit regulated apoptotic execution depending on residual ATP availability and caspase competence (Nieminen et al., 1994; Leist et al., 1997; Nicotera et al., 1998; Zong and Thompson, 2006). The mechanistic relationship is also supported by mitochondrial cell-death biology. ATP depletion often accompanies mitochondrial membrane depolarization, permeability transition, impaired oxidative phosphorylation, calcium dysregulation, and increased reactive oxygen species generation. These processes can amplify cellular injury and increase the probability of cell death (Kroemer et al., 1998; Green and Kroemer, 2004; Halestrap, 2009; Bonora et al., 2012).

Empirical support is moderate to high. In mammalian systems, ATP depletion has been directly linked to cell killing after metabolic inhibition, and experimental work has shown that ATP depletion rather than mitochondrial depolarization can mediate hepatocyte death under some conditions (Nieminen et al., 1994). A widely cited study demonstrated that intracellular ATP concentration influences whether cells die by apoptosis or necrosis, supporting both causality and phenotype dependence (Leist et al., 1997). Calcium electroporation studies provide dose-dependent evidence that ATP depletion is associated with reduced cancer cell survival and increased cell death (Hansen et al., 2015). Evidence from environmental and ecotoxicological systems is consistent with this relationship. In   Chlamydomonas reinhardtii, herbicide exposure produced ATP depletion and cell injury/death in a multiple-endpoint assay, demonstrating concordance between energetic disruption and cellular toxicity in an algal model (Nestler et al., 2012). In eastern oysters, cadmium exposure affected mitochondrial bioenergetics and was associated with cellular damage endpoints, supporting applicability of energetic failure to cell injury in aquatic invertebrates (Sokolova et al., 2005). In ROS-growth concordance data, mitochondrial toxicants and oxidative stressors including paraquat, rotenone, cadmium and hydrogen peroxide frequently produce decreased ATP or mitochondrial dysfunction together with cytotoxicity or tissue injury, although direct measurement of both KEs in the same study is not always available. <table align="center" cellspacing="0" class="MsoTableGrid" style="border-collapse:collapse; border:none"> <thead> <tr> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:144px"> Evidence type </td> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:384px"> Summary </td> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:192px"> Representative references </td> </tr> </thead> <tbody> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:144px"> Biological plausibility </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:384px"> ATP is required for ion homeostasis, membrane maintenance, repair, and regulated cell death execution; severe ATP depletion promotes irreversible cell injury/death. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:192px"> Nieminen et al. 1994; Leist et al. 1997; Bonora et al. 2012 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:144px"> Temporal concordance </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:384px"> ATP depletion can occur rapidly after metabolic inhibition or mitochondrial impairment and precedes detectable loss of viability or death execution in several cell systems. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:192px"> Nieminen et al. 1994; Hansen et al. 2015 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:144px"> Dose-response concordance </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:384px"> Increasing intensity of energetic perturbation or calcium electroporation increases ATP depletion and cell killing. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:192px"> Hansen et al. 2015 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:144px"> Incidence concordance </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:384px"> Systems showing marked ATP depletion commonly show increased cytotoxicity, cell injury or cell death, although moderate ATP depletion may be compensated in some contexts. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:192px"> Leist et al. 1997; Nestler et al. 2012; Sokolova et al. 2005 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:144px"> Essentiality / intervention </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:384px"> Experimental data indicate that ATP availability influences the form and occurrence of cell death; restoration or maintenance of energy status can reduce injury in some systems, but direct rescue evidence across taxa remains limited. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:192px"> Leist et al. 1997; Nicotera et al. 1998 </td> </tr> </tbody> </table>

The main uncertainty is that ATP depletion is not the only cause of cell injury/death. Cell death may also be initiated by DNA damage, receptor-mediated apoptosis, oxidative damage, calcium overload, lysosomal injury, proteotoxic stress or inflammatory signaling. Consequently, the presence of cell injury/death does not uniquely imply ATP depletion. The KER is strongest when ATP decline occurs before or at lower concentrations than cell death and when the upstream energetic perturbation is mechanistically established.     Another uncertainty concerns severity thresholds. Moderate ATP depletion may be reversible or may shift cells into cell-cycle arrest, reduced proliferation, or adaptive metabolic compensation rather than death. Conversely, very severe ATP depletion may prevent the energy-requiring execution of apoptosis and produce necrotic injury instead. Therefore, the downstream phenotype depends on the magnitude and duration of ATP depletion and on cellular metabolic reserve (Leist et al., 1997; Nicotera et al., 1998). Empirical evidence across environmental species remains less dense than evidence from mammalian cell systems. Many ecotoxicological studies measure ATP, mitochondrial dysfunction, or cytotoxicity separately rather than measuring both KEs in the same time- and dose-resolved experiment. This limits the strength of concordance assessment across the full taxonomic applicability domain.

<table align="center" cellspacing="0" class="MsoTableGrid" style="border-collapse:collapse; border:none"> <thead> <tr> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:154px"> Modulating factor </td> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:211px"> Details </td> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:259px"> Effect on this KER </td> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:163px"> References </td> </tr> </thead> <tbody> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:154px"> Magnitude and duration of ATP depletion </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:211px"> Transient or moderate ATP depletion versus severe, sustained ATP depletion. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:259px"> Severe and sustained ATP depletion increases probability of irreversible injury/death. Partial depletion may cause reversible stress or cell-cycle arrest. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:163px"> Nieminen et al. 1994; Leist et al. 1997 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:154px"> Metabolic flexibility / glycolytic capacity </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:211px"> Ability to compensate for mitochondrial ATP loss by glycolysis or alternative ATP-generating pathways. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:259px"> Higher metabolic flexibility may reduce sensitivity of the downstream cell death response. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:163px"> Bonora et al. 2012; Zong and Thompson 2006 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:154px"> Cell type and proliferative/metabolic demand </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:211px"> Highly energy-demanding or poorly glycolytic cells may have lower tolerance to ATP depletion. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:259px"> Alters threshold and time-scale for transition from ATP depletion to injury/death. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:163px"> Bonora et al. 2012; Green and Kroemer 2004 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:154px"> Mitochondrial permeability transition and calcium homeostasis </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:211px"> Calcium overload and permeability transition can amplify ATP depletion and membrane failure. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:259px"> Can accelerate progression to necrotic or mixed cell injury phenotypes. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:163px"> Halestrap 2009; Nieminen et al. 1994 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:154px"> Apoptotic execution machinery </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:211px"> Caspase competence and residual ATP availability influence whether death is apoptotic or necrotic. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:259px"> Determines cell death mode rather than the existence of injury/death per se. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:163px"> Leist et al. 1997; Nicotera et al. 1998 </td> </tr> </tbody> </table>

The quantitative understanding of this KER is considered moderate. Quantitative evidence supports a general response-response relationship in which larger or longer decreases in ATP increase the probability and severity of cell injury/death. However, a single universal threshold cannot be defined because ATP demand, ATP reserve, glycolytic capacity, cell type, death pathway, and exposure duration vary substantially among biological systems. Several studies support threshold-like behavior. In hepatocytes, ATP depletion mediated killing after metabolic inhibition, supporting a causal threshold relationship between energetic collapse and cell death (Nieminen et al., 1994). Experiments in human T cells showed that intracellular ATP concentration can act as a switch influencing apoptotic versus necrotic death phenotypes (Leist et al., 1997). Calcium electroporation studies showed dose-dependent ATP depletion and reduced survival, supporting a quantitative relationship between the upstream energetic disturbance and the downstream cell death outcome (Hansen et al., 2015).

The expected response-response relationship is generally monotonic but non-linear. Small or transient ATP reductions may be tolerated or compensated. Larger reductions increase the probability of cell stress, impaired repair, loss of membrane integrity, and cell death. At extreme ATP depletion, necrotic injury is favored, whereas intermediate depletion may permit energy-dependent apoptosis depending on cell type and execution machinery (Leist et al., 1997; Nicotera et al., 1998).

The time scale of ATP depletion can range from minutes to hours following direct mitochondrial inhibition, uncoupling, metabolic inhibition, or membrane-disrupting interventions. Observable downstream cell injury/death may occur within hours to days depending on cell type, severity of ATP loss, and endpoint measured. In whole organisms, cell death may contribute to tissue injury or growth impairment over longer time frames.

Feedback and feedforward processes may influence this linkage. ATP depletion can impair ion pumps, causing calcium dysregulation and mitochondrial permeability transition, which further suppresses ATP production and amplifies injury. Loss of mitochondrial function may also increase ROS generation, further damaging mitochondrial and cellular components. Conversely, glycolytic compensation and stress-response activation may temporarily buffer ATP depletion and delay cell death.

Moderate Unspecific

Moderate

All life stages

High High High High High

The biological domain of applicability is broad because ATP-dependent homeostasis is a conserved property of living cells. The KER is most directly applicable to eukaryotic cells and tissues in which mitochondrial and/or glycolytic ATP supply maintains cellular viability. It is particularly relevant to metabolically active tissues and developing organisms where energy demand is high. It is applicable to both sexes and to multiple life stages, although sensitivity may differ with developmental status, tissue type, temperature, oxygen availability, and metabolic reserve. The chemical and stressor applicability domain includes stressors that reduce cellular ATP through mitochondrial inhibition, OXPHOS uncoupling, oxidative stress, membrane disruption, calcium overload, metabolic poisons, hypoxia or other mechanisms that impair ATP synthesis or increase ATP demand beyond compensatory capacity. In the ROS-growth AOP network, this KER is most relevant downstream of OXPHOS impairment caused by lipid peroxidation or protein oxidation, where energetic failure contributes to increased cell injury/death.

Bonora M, Patergnani S, Rimessi A, De Marchi E, Suski JM, Bononi A, Giorgi C, Marchi S, Missiroli S, Poletti F, Wieckowski MR, Pinton P. 2012. ATP synthesis and storage. Purinergic Signaling 8:343-357. https://doi.org/10.1007/s11302-012-9305-8. Green DR, Kroemer G. 2004. The pathophysiology of mitochondrial cell death. Science 305:626-629. https://doi.org/10.1126/science.1099320. Halestrap AP. 2009. What is the mitochondrial permeability transition pore? Journal of Molecular and Cellular Cardiology 46:821-831. https://doi.org/10.1016/j.yjmcc.2009.02.021. Hansen EL, Sozer EB, Romeo S, Frandsen SK, Vernier PT, Gehl J. 2015. Dose-dependent ATP depletion and cancer cell death following calcium electroporation, relative effect of calcium concentration and electric field strength. PLoS ONE 10:e0122973. https://doi.org/10.1371/journal.pone.0122973. Kroemer G, Dallaporta B, Resche-Rigon M. 1998. The mitochondrial death/life regulator in apoptosis and necrosis. Annual Review of Physiology 60:619-642. https://doi.org/10.1146/annurev.physiol.60.1.619. Leist M, Single B, Castoldi AF, Kuhnle S, Nicotera P. 1997. Intracellular adenosine triphosphate (ATP) concentration: a switch in the decision between apoptosis and necrosis. Journal of Experimental Medicine 185:1481-1486. https://doi.org/10.1084/jem.185.8.1481. Lemasters JJ, Qian T, Bradham CA, Brenner DA, Cascio WE, Trost LC, Nishimura Y, Nieminen AL, Herman B. 1999. Mitochondrial dysfunction in the pathogenesis of necrotic and apoptotic cell death. Journal of Bioenergetics and Biomembranes 31:305-319. https://doi.org/10.1023/A:1005419617371. Nestler H, Groh KJ, Schonenberger R, Behra R, Schirmer K, Eggen RIL, Suter MJF. 2012. Multiple-endpoint assay provides a detailed mechanistic view of responses to herbicide exposure in Chlamydomonas reinhardtii. Aquatic Toxicology 110-111:214-224. https://doi.org/10.1016/j.aquatox.2012.01.014. Nicotera P, Leist M, Ferrando-May E. 1998. Intracellular ATP, a switch in the decision between apoptosis and necrosis. Toxicology Letters 102-103:139-142. https://doi.org/10.1016/S0378-4274(98)00298-7. Nieminen AL, Saylor AK, Herman B, Lemasters JJ. 1994. ATP depletion rather than mitochondrial depolarization mediates hepatocyte killing after metabolic inhibition. American Journal of Physiology - Cell Physiology 267:C67-C74. https://doi.org/10.1152/ajpcell.1994.267.1.C67. OECD. 2022. Uncoupling of oxidative phosphorylation leading to growth inhibition via decreased cell proliferation. OECD Series on Adverse Outcome Pathways No. 28. Paris: OECD Publishing. Sokolova IM, Sokolov EP, Ponnappa KM. 2005. Cadmium exposure affects mitochondrial bioenergetics and gene expression of key mitochondrial proteins in the eastern oyster Crassostrea virginica Gmelin (Bivalvia: Ostreidae). Aquatic Toxicology 73:242-255. https://doi.org/10.1016/j.aquatox.2005.03.016. Zong WX, Thompson CB. 2006. Necrotic death as a cell fate. Genes & Development 20:1-15. https://doi.org/10.1101/gad.1376506. AOPWiki 2022-09-27T13:24:52

2026-06-23T07:40:42

<upstream-id>0389f740-377e-4dce-9e2c-ac7ef571a422</upstream-id> <downstream-id>d44e0d40-341d-4096-87a6-142e58288689</downstream-id> This KER describes the causal and predictive relationship whereby an increase in cell injury and/or cell death leads to a decrease in growth. The upstream KE, cell injury/death, represents loss of cellular viability or severe cellular damage resulting in apoptosis, necrosis, or other forms of lethal cellular injury. The downstream KE, decreased growth, represents reduced accumulation of biomass, body size, length, cell density, tissue mass, or other growth-related endpoints at organ, organism, or population levels. The biological logic of the KER is that growth requires a positive balance between production of new cellular material and loss of existing cells. When cell injury/death is sufficiently frequent, persistent, or spatially distributed across growth-relevant tissues, net cell accumulation is reduced and tissue or organismal growth is impaired. In unicellular systems, increased cell death directly reduces viable cell density and biomass accumulation. In multicellular organisms, the relationship depends on the affected tissue, the ability to compensate through proliferation or regeneration, and the timing of injury relative to developmental or growth windows. This relationship is not intended to imply that all decreases in growth are caused by cell death. Growth can also decrease through reduced cell proliferation, altered energy allocation, endocrine disruption, nutrient limitation, or developmental delay without overt lethality. Rather, the KER applies when increased cell injury/death is of sufficient magnitude or duration to reduce the viable cellular pool needed for growth or to damage growth-relevant tissues. Within the ROS-growth AOP network, this KER provides a terminal convergence relationship for pathways in which oxidative stress, DNA strand breaks, or ATP depletion produce cytotoxicity that contributes to reduced growth.

Evidence for this KER was assembled using the same AI-human hybrid strategy applied across the ROS-growth AOP network. Initial evidence identification used AOP-Wiki relationship and key event mapping, prior ROS-growth concordance tables, and targeted literature searches. Search terms combined upstream and downstream concepts such as “cell death”, “cell injury”, “cytotoxicity”, “apoptosis”, “necrosis”, “viability”, “growth inhibition”, “growth retardation”, “developmental delay”, “biomass”, “cell density”, “condition index”, and “organism growth”, together with taxa and stressor terms including algae, Daphnia, copepod, bivalve, fish embryo, mammalian embryo, paraquat, cadmium, methanol, rotenone, gamma radiation, and oxidative stress. AOP-Wiki was consulted to confirm that Relationship 2767 links Event 55 to Event 1521 and to identify related AOP reuse contexts. Candidate studies were prioritized when they measured both cell injury/death and a growth-related outcome in the same biological system, reported dose or concentration and exposure duration, or provided information relevant to temporal, dose-response, or incidence concordance. Large language model assistance was used only as an auxiliary screening and structuring tool to extract study metadata, identify potentially relevant endpoints, and prioritize records for expert review. Final inclusion decisions, interpretation of endpoints, and weight-of-evidence judgments were made by manual expert curation against the original article text. Mechanistic reviews were used to support biological plausibility, while primary experimental studies were used preferentially to support empirical concordance.

Overall call: High. Growth at the level of a tissue, organ, organism, or cell population depends on net accumulation of cells and cellular biomass. Increased cell death directly lowers the number of viable cells and can reduce tissue mass, disrupt morphogenesis, or impair the capacity for biomass accumulation. This relationship is strongly supported by developmental and cell-size control principles showing that final tissue and organism size depend on the balance among cell growth, cell division, and cell death (Conlon and Raff, 1999). In embryos and developing organisms, excessive cell death can reduce cell number available for organ formation and growth, whereas in unicellular populations and cell cultures, cytotoxicity directly reduces viable cell density. The KER is therefore mechanistically plausible across taxa, although the magnitude of growth impairment depends on the tissue affected, compensatory proliferation, regeneration, and exposure duration.

Overall call: Moderate. Empirical support is moderate because multiple studies report concordance between cell injury/death and growth-related effects, but the evidence is heterogeneous and not always designed specifically to test this KER. In several systems, cell injury/death and growth inhibition are measured at different time points, and growth can be affected by mechanisms other than cell death. Nevertheless, the available data support the expected direction of effect across algae, fish embryos, mollusks, and mammalian embryo models.   <table align="center" cellspacing="0" class="MsoTableGrid" style="border-collapse:collapse; border:none"> <thead> <tr> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:112px"> Biological system </td> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:112px"> Stressor / context </td> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:112px"> Upstream evidence: cell injury/death </td> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:112px"> Downstream evidence: decreased growth </td> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:112px"> Concordance interpretation </td> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:112px"> Reference </td> </tr> </thead> <tbody> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Chlamydomonas reinhardtii </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Paraquat </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Loss of membrane integrity measured by SYTOX Green; cell death observed at approximately 0.5 uM after 24 h. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Reduced cell density/growth after 72 h; growth LOEC approximately 0.1 uM and EC50 approximately 0.26 uM. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Partial temporal and endpoint concordance. Growth effects occurred at or below cytotoxicity thresholds, indicating that cell death contributes but is not the only driver of growth inhibition. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Jamers and De Coen, 2010 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Chlamydomonas reinhardtii </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Paraquat and herbicides </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> SYTOX Green cell death observed with paraquat; cell injury occurred alongside ATP depletion and other stress endpoints. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Assay system reported reduced growth/cell density and multiple mechanistic endpoints following herbicide exposure. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Supports association between cytotoxicity and reduced population growth, but includes multiple parallel mechanisms. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Nestler et al., 2012 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Mouse and rat whole-embryo culture </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Methanol </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Cell death markedly elevated in embryos at growth-relevant concentrations. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Mouse and rat embryo growth reduction observed in exposed cultures. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Supports developmental concordance between increased embryonic cell death and growth impairment, with species differences in sensitivity. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Abbott et al., 1995 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Eastern oyster, Crassostrea virginica </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Cadmium and temperature interaction </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Hemocyte mortality, lysosomal destabilization, and cellular energy disruption observed under cadmium stress. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Reduced condition index and increased mortality under combined cadmium and elevated temperature. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Supports linkage between cellular injury and reduced growth/condition, although growth is modified by temperature and energy budget effects. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Sokolova et al., 2005; Cherkasov et al., 2006 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Fish embryos and juveniles </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Rotenone </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Histological lesions and tissue injury observed at low concentrations. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Developmental delay and growth-related impairment reported after short-term exposure. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Supports association between cellular/tissue injury and developmental growth impairment; direct measurement of cell death was limited. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Melo et al., 2015 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Marine copepod, Paracyclopina nana </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Gamma radiation </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Radiation induced oxidative stress and impaired survival/development. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Growth retardation and failure of nauplii to develop to adults observed. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Supports an adverse sequence from stress-induced cellular injury to growth retardation, although cell death was not always measured directly. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:112px"> Won and Lee, 2014 </td> </tr> </tbody> </table> <h2> </h2>

The main uncertainty is that decreased growth is an integrative endpoint and can arise through several mechanisms that do not require overt cell death. Reduced proliferation, ATP depletion, endocrine disruption, altered energy allocation, nutrient limitation, delayed development, or behavioral effects can all reduce growth. For this reason, cell injury/death should be interpreted as a sufficient but not always necessary contributor to decreased growth. A second uncertainty is that many studies measure cytotoxicity and growth at different times or in different tissues, which limits direct evaluation of temporal concordance. In some algal studies, growth inhibition occurs at lower concentrations than overt cell death, suggesting that non-lethal impairment of proliferation, photosynthesis, or energy metabolism may precede cell death. Conversely, mild or localized cell injury may be compensated by repair or proliferation and may not lead to measurable growth reduction. These uncertainties support a moderate, rather than high, empirical call for this KER.

<table align="center" cellspacing="0" class="MsoTableGrid" style="border-collapse:collapse; border:none"> <thead> <tr> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:168px"> Modulating factor </td> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:168px"> Relevant details </td> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:168px"> Effect on the KER </td> <td style="background-color:#d9eaf7; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:168px"> Supporting references </td> </tr> </thead> <tbody> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Developmental stage </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Embryonic and larval stages, rapid growth phases </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Increases sensitivity because rapid tissue growth requires high net cell accumulation; cell death during development can disproportionately impair growth. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Abbott et al., 1995; Conlon and Raff, 1999 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Tissue regenerative capacity </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Capacity for compensatory proliferation or tissue repair </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Reduces probability that cell death will translate into growth impairment when surviving cells can replace lost cells. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Conlon and Raff, 1999 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Exposure duration and timing </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Acute versus chronic exposures; timing relative to growth window </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Longer or developmentally timed exposures increase probability of growth effects from cell loss. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Jamers and De Coen, 2010; Melo et al., 2015 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Energy and nutritional status </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Energy budget, food availability, metabolic reserve </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Can increase or decrease impact of cell death on growth by altering compensatory capacity and resource allocation. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Sokolova, 2013; Cherkasov et al., 2006 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Environmental stressors </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Temperature, oxygen availability, salinity, co-exposures </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Can amplify cytotoxicity or reduce compensatory growth responses, modifying downstream growth effects. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:168px"> Cherkasov et al., 2006; Won and Lee, 2014 </td> </tr> </tbody> </table>

Overall call: Low to moderate. Quantitative understanding is limited because the relationship between cell injury/death and growth depends on the proportion of cells affected, tissue location, developmental timing, compensatory proliferation, regenerative capacity, and organismal energy allocation. At a conceptual level, the linkage is quantitative: growth rate reflects the balance between biomass accumulation and biomass or cell loss, so increasing the frequency or magnitude of cell death should reduce net growth if cell replacement or compensatory growth is insufficient. However, few studies provide response-response models that predict growth reduction from a measured degree of cell injury/death across taxa or stressors.

In cell populations and unicellular organisms, the quantitative relationship can be relatively direct because viable cell density is part of the growth measurement. In multicellular organisms, the relationship is less direct because growth can continue despite localized cell death if compensatory proliferation or tissue repair occurs. Some data show concordance between cytotoxicity and growth inhibition, but these data are generally insufficient to define universal thresholds. Therefore, quantitative understanding should be considered low to moderate for broad AOP-Wiki application, with higher confidence possible for specific model systems where cell viability and growth rate are measured in the same assay and time course.

Moderate Unspecific

Moderate

All life stages

Moderate Moderate Moderate Moderate Moderate

The KER is applicable to biological systems in which growth depends on maintenance or expansion of viable cell number or biomass. This includes unicellular populations, developing embryos, juvenile organisms, growing tissues, and adult organisms in which tissue condition or somatic growth is assessed. Taxonomic applicability is broad across eukaryotes, but empirical support is strongest for algae, aquatic invertebrates, mollusks, fish, and mammalian embryo or cell models. The KER is not sex-specific, but sex, endocrine status, life stage, and environmental context may modulate sensitivity. The relationship is most relevant when cell injury/death is sufficiently extensive, sustained, or located in growth-relevant tissues. It is less predictive when growth is reduced by upstream mechanisms that suppress proliferation or metabolism without substantial cell death.

Abbott, B. D., Harris, M. W., & Birnbaum, L. S. (1995). Cell death in rat and mouse embryos exposed to methanol in whole embryo culture: Evaluation of the role of the p53 tumor suppressor gene. Teratogenesis, Carcinogenesis, and Mutagenesis, 15(3), 147–169. Cherkasov, A. S., Biswas, P. K., Ridings, D. M., Ringwood, A. H., & Sokolova, I. M. (2006). Effects of acclimation temperature and cadmium exposure on cellular energy budgets in the marine mollusk Crassostrea virginica: Linking cellular and mitochondrial responses. Journal of Experimental Biology, 209(7), 1274–1284. Conlon, I., & Raff, M. (1999). Size control in animal development. Cell, 96(2), 235–244. Jamers, A., & De Coen, W. (2010). Effect assessment of the herbicide paraquat on a green alga using differential gene expression and biochemical biomarkers. Environmental Toxicology and Chemistry, 29(4), 893–901. Knops, M., Altenburger, R., & Segner, H. (2001). Alterations of physiological energetics, growth and reproduction of Daphnia magna under toxicant stress. Aquatic Toxicology, 53(2), 79–90. Melo, K. M., Oliveira, R., Grisolia, C. K., Domingues, I., Pieczarka, J. C., de Souza Filho, J., & Nagamachi, C. Y. (2015). Short-term exposure to low doses of rotenone induces developmental, biochemical, behavioral, and histological changes in fish. Environmental Science and Pollution Research, 22(18), 13926–13938. Nestler, H., Groh, K. J., Schönenberger, R., Eggen, R. I. L., & Suter, M. J.-F. (2012). Multiple-endpoint assay provides a detailed mechanistic view of responses to herbicide exposure in Chlamydomonas reinhardtii. Aquatic Toxicology, 110–111, 214–224. Organisation for Economic Co-operation and Development (OECD). (2018). Users’ handbook supplement to the guidance document for developing and assessing adverse outcome pathways. OECD Series on Adverse Outcome Pathways No. 1. OECD Publishing, Paris. Organisation for Economic Co-operation and Development (OECD). (2021). Guidance document for the scientific review of adverse outcome pathways. OECD Series on Testing and Assessment No. 344. OECD Publishing, Paris. Sokolova, I. M. (2013). Energy-limited tolerance to stress as a conceptual framework to integrate the effects of multiple stressors. Integrative and Comparative Biology, 53(4), 597–608. Sokolova, I. M., Sokolov, E. P., & Ponnappa, K. M. (2005). Cadmium exposure affects mitochondrial bioenergetics and gene expression of key mitochondrial proteins in the eastern oyster Crassostrea virginica Gmelin (Bivalvia: Ostreidae). Aquatic Toxicology, 73(3), 242–255. Won, E. J., & Lee, J. S. (2014). Gamma radiation induces growth retardation, impaired egg production, and oxidative stress in the marine copepod Paracyclopina nana. Aquatic Toxicology, 150, 17–26. AOPWiki 2022-09-27T13:22:59

2026-06-23T07:54:07

Uncoupling of oxidative phosphorylation leading to growth inhibition via ATP depletion associated cell death

Uncoupling of OXPHOS leading to growth inhibition via ATP depletion associated cell death

You Song

You Song Norwegian Institute for Water Research (NIVA), Økernveien 94, NO-0579 Oslo, Norway   Acknowledgement This project was funded by the Research Council of Norway (RCN), grant no. 301397 “RiskAOP - Quantitative Adverse Outcome Pathway assisted risk assessment of mitochondrial toxicants” (<a href="https://www.niva.no/en/projectweb/riskaop">https://www.niva.no/en/projectweb/riskaop</a>), and supported by the NIVA Computational Toxicology Program, NCTP (<a href="http://www.niva.no/nctp">www.niva.no/nctp</a>). Dan Villeneuve

BY-SA

Under Development

1.92

2.0

Uncoupling of oxidative phosphorylation (OXPHOS) is a well-known mechanism of action of many chemicals. Mitochondrial uncoupler-mediated energetic dysfunction is known to affect growth, a critical process in most organisms and a chronic toxicity endpoint included in many OECD test guidelines. This adverse outcome pathway (AOP) causally links uncoupling of OXPHOS to growth inhibition, through ATP depletion and reduced cell proliferation as the intermediate key events (KEs), with strong weight of evidence support. The AOP is generalized to reflect its expected applicability to a broad range of taxa, ranging from microalga to human. Three out of four KEs included can be quantified using high-throughput methods, making this AOP particularly useful for screening, prioritization and hazard assessment of mitochondrial uncouplers as potential growth inhibiting chemicals. This AOP is of high regulatory relevance, as it is considered applicable to both human health and ecological risk assessments. The AOP also forms the core of a larger AOP network addressing uncoupling of OXPHOS mediated growth inhibition (AOP 263-268). The mitochondrial OXPHOS machinery is a key physiological process responsible for producing the primary cellular energy, adenosine triphosphate (ATP). During OXPHOS, a series of redox reactions (oxidation) are mediated by protein complexes in an electron transport chain to create a protonmotive force (PMF) across the inner mitochondrial membrane (Liberman 1969). The PMF acts as a driving force of ATP synthesis through phosphorylation of adenosine diphosphate (ADP). Mitochondrial oxidation and phosphorylation are coupled to ensure continuous ATP supply for various physiological processes. A number of chemicals can bind to the inner mitochondrial membrane and dissipate the PMF, thus leading to uncoupling of OXPHOS and reduction in ATP synthetic efficiency. Classical “uncouplers” are normally protonophores with major characteristics of bulky hydrophobic moiety, an acid dissociable group and a strong electron-withdrawing group (Terada 1990). With the rapid development of in silico (Russom 1997; Schultz 1997; Naven 2012; Dreier 2019; Troger 2020) and in vitro (Escher 2002; Attene-Ramos 2013; Attene-Ramos 2015; Xia 2018) approaches, more and more uncouplers have been identified. However, their hazards to biota remain to be assessed. Uncoupling of OXPHOS can affect many ATP-dependent biological functions. In particular, cell proliferation as a major process to achieve organismal growth is positively correlated with the cellular ATP level and highly susceptible to energy depletion (Ramaiah 1964; Bonora 2012). Therefore, a link between uncoupling of OXPHOS and growth inhibition can be established with ATP depletion and reduced cell proliferation as the intermediate steps.

Decreased coupling of oxidative phosphorylation can be directly triggered by “uncouplers” as a molecular initiating event. <ul> <li style="text-align:justify">Most of the chemical uncouplers are protonophores, a type of proton binders that can translocate protons across membranes. These protonophores share several common structural characteristics, such as bulky hydrophobic moiety, an acid dissociable group and a strong electron-withdrawing group (Terada 1990). Weak acids such as phenols, benzimidazoles and salicylic acids are considered potential protonophores.</li> <li style="text-align:justify">Classical uncouplers, such as carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP), carbonyl cyanide m-chlorophenyl hydrazone (CCCP), 2,4-dinitrophenol (DNP), pentachlorophenol (PCP) and SF-6847 (Terada 1990).</li> <li style="text-align:justify">Newer uncouplers, such as triclosan (Shim 2016; Weatherly 2016), emodin (Sugiyama 2019), and hydroxylated polybrominated diphenyl ethers (PBDEs) (Legradi 2014) have been widely investigated in vertebrates.</li> <li style="text-align:justify">Computational predictions based on quantitative structure-activity relationships (Russom 1997; Schultz 1997; Naven 2012; Dreier 2019; Troger 2020) and in vitro high-throughput screening (Escher 2002; Attene-Ramos 2013; Attene-Ramos 2015; Xia 2018) have facilitated the identification and classification of potential uncouplers from a large list of chemicals.   </li> </ul>

Growth is a regulatory relevant chronic toxicity endpoint for almost all organisms. Multiple OECD test guidelines have included growth either as a main endpoint of concern, or as an additional endpoint to be considered in the toxicity assessments. Relevant test guidelines include, but not only limited to:   -Test No. 201: Freshwater Alga and Cyanobacteria, Growth Inhibition Test -Test No. 208: Terrestrial Plant Test: Seedling Emergence and Seedling Growth Test -Test No. 211: Daphnia magna Reproduction Test -Test No. 212: Fish, Short-term Toxicity Test on Embryo and Sac-Fry Stages -Test No. 215: Fish, Juvenile Growth Test -Test No. 221: Lemna sp. Growth Inhibition Test -Test No. 228: Determination of Developmental Toxicity to Dipteran Dung Flies (Scathophaga stercoraria L. (Scathophagidae), Musca autumnalis De Geer (Muscidae)) -Test No. 241: The Larval Amphibian Growth and Development Assay (LAGDA) -Test No. 407: Repeated Dose 28-day Oral Toxicity Study in Rodents -Test No. 408: Repeated Dose 90-Day Oral Toxicity Study in Rodents -Test No. 416: Two-Generation Reproduction Toxicity -Test No. 422: Combined Repeated Dose Toxicity Study with the Reproduction/Developmental Toxicity Screening Test -Test No. 443: Extended One-Generation Reproductive Toxicity Study -Test No. 453: Combined Chronic Toxicity/Carcinogenicity Studies

adjacent

Not Specified

Moderate adjacent

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Moderate adjacent

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Moderate

The weight of evidence (WoE) assessment of the AOP was conducted based on the evolved Bradford-Hill considerations (Becker 2015) and according to the criteria in OECD’s Guidance Document for Developing and Assessing AOPs (OECD 2018). In terms of evidence for the essentiality of the key events, the MIE (Event 1446) and KE1 (Event 1771) were scored as high, whereas KE2 (Event 1821) was scored as moderate due to a lack of solid evidence to support its essentiality. The overall WoE of KER1 (Relationship 2203) is considered high, as strong biological plausibility, empirical evidence and fairly good quantitative understanding were evidenced from multiple studies. The overall WoE of KER2 (Relationship 2204) is considered moderate, due to high biological plausibility, acceptable empirical concordance and some biological understanding. The overall WoE of KER3 (Relationship 2205) is scored as moderate, mainly due to biological plausibility, but there is presently a lack of empirical evidence and quantitative understanding to further support causality. The AOP is considered applicable to a wide range of species as well as a broad domain of chemicals. The rationales for making these judgements will be discussed in detail in the following sections. The taxonomic application domain of the AOP potential covers all animals, plants and some microorganisms such as fungus and protists, as mitochondrial OXPHOS is highly conserved in eukaryotes (Roger 2017). The life stage applicability domain of the AOP mainly contains embryos and juveniles, as growth is more relevant to developing organisms. It should be noted that fully grown adults are also susceptible to uncouplers, as tissue/organ (e.g., adipose tissue) growth and regeneration still occur in adults (Yun 2015; Demine 2019). Classical uncouplers such as 2,4-DNP have been reported to cause weight loss in adult humans (Grundlingh 2011). In fact, 2,4-DNP was sold for weight loss until its legal sale was banned over toxicity and abuse concerns (Baker 2020). These suggest that adults are in the applicability domain of this AOP.  The sex applicability domain of the AOP is unspecific, as the AOP is mainly targeting growth effects in sexually immature organisms and the KEs are therefore harmonized between male and females. However, male and females may have different sensitivities to OXPHOS uncoupling, as strategies for allocating energy for developmental processes may be gender specific (Demarest 2015). The chemical applicability domain of the AOP mainly includes weak acids, such as phenols, benzimidazoles, N-phenylanthranilates, salicylanilides, phenylhydrazones, salicylic acids, acyldithiocarbazates, cumarines, and aromatic amines, which are well-known protonophoric uncouplers. Uncouplers typically have properties as both weak acids and hydrophobic substances. As weak acids, they are capable of gaining and losing an electron. As hydrophobic substances, they are capable of distributing a negative charge over a number of atoms (often by π-orbitals which delocalize a proton's charge when it attaches to the molecule), so that they can diffuse back and forth across the inner mitochondrial membrane in either the charged or uncharged state, thus moving protons back across the concentration gradient generated by the electron transport chain. Classical uncouplers, such as 2,4-dinitrophenol (2,4-DNP), carbonyl cyanide-p-trifluoromethoxyphenyl hydrazone (FCCP), carbonyl cyanide m-chlorophenyl hydrazone (CCCP), pentachlorophenol (PCP), 3,5-dichlorophenol (3,5-DCP), 6-sec-butyl-2,4-dinitrophenol (dinoseb), SF 6847 (3,5-di-t-butyl-4-hydroxybenzylidinemalononitrile) have been widely used as positive controls in (eco)toxicological tests, whereas the hazards of “new” uncouplers, such as triclosan, emodin and metabolites of polybrominated diphenyl ethers (PBDEs) are also under extensive assessments. Other types of uncouplers that are SH-reactive chemicals or hydrophobic ions may also be in the applicability domain of this AOP. A number of potential uncouplers have been identified by in silico (Russom 1997; Schultz 1997; Naven 2012; Dreier 2019; Troger 2020) and in vitro (Escher 2002; Attene-Ramos 2013; Attene-Ramos 2015; Xia 2018) approaches, and are considered in the chemical applicability domain of the AOP.

<div> <table class="table table-bordered table-fullwidth"> <thead> <tr> <th>Modulating Factor (MF)</th> <th>Influence or Outcome</th> <th>KER(s) involved</th> </tr> </thead> <tbody> <tr> <td> </td> <td> </td> <td> </td> </tr> </tbody> </table> </div>

The present AOP has several potential applications. First, the AOP anchors a recognized endpoint of regulatory concern (i.e., growth), at least in OECD member countries, and is directly relevant for a number of OECD test guidelines (e.g., TG206, 208, 201, 210, 211, 212, 215, 221, 228, 241, 407, 408, 416, 422, 443 and 453). These guidelines cover a diversity of taxonomic groups including mammals, birds, fish, amphibians, terrestrial plants, aquatic plants and algae, and various invertebrates. Second, the AOP anchors an important molecular initiating event (e.g., uncoupling of oxidative phosphorylation) and can be used to support several initiatives (e.g., Tox21 and ToxCast) for identification of mitochondrial toxicants. The present AOP helps establish the utility of such assays for identifying chemicals with potential to cause growth impacts. Third, three out of four key events in this AOP can be measured using high-throughput in vitro assays, hence offering a tiered testing strategy (i.e., in silico→in vitro→in vivo) or integrated approaches to testing and assessment (IATA) for efficient screening, classification and assessment of potential mitochondrial uncouplers and growth-regulating chemicals. The key events can be considered as useful biomarkers in (eco)toxicological studies. However, it is not recommended to use a single key event (e.g., ATP level alone) as a biomarker for classification and hazard assessment of chemicals, as key events such as decreased ATP pool and cell proliferation can also be the consequences of other biological processes.  A combined measurement of 2-3 key events can normally yield more reliable results.  Finally, the quantitative relationships of the key events in this AOP have been relatively well defined, allowing it to be further developed into quantitative prediction models for higher tier assessments. This is a range of potential applications that were conceived during the development of the present AOP. However, it is neither an exhaustive list of potential applications, nor can explicit examples of these applications in practice be cited at this time.  We invite users of this AOP to share their applications of this AOP via the Discussion so that practical examples of use can be added.

AOPWiki 2018-05-24T14:16:25

2024-06-20T02:54:56