Decreased, Pregnenolone levels

Pregnenolone is the precursor for all steroid hormones and its expression and conversion depends on tissue and cell type, as well as availability and activity of various steroid enzymes. Pregnenolone is expressed in all tissues with steroidogenic activity, where it is converted from cholesterol by cytochrome P-450 enzyme (P450scc or CYP11A1) in the inner mitochondrial membrane and exits the mitochondria to be available for production of downstream steroid hormones (DM et al., 2017). Pregnenolone has other roles besides being the precursor to all steroids. For example, expression of 

pregnenolone in the brain is essential for cognitive functions, regulation of neurotransmission, is an important neuromodulator, and is neuroprotective (Lin et al., 2022; Vallée, 2016). 

Pregnenolone can be converted into 17-OH pregnenolone by CYP17A1 (expressed mainly in gonads and adrenal cortex in humans (Z et al., 2019)) or progesterone by 3-beta-hydroxysteroid dehydrogenase (3-beta-HSD) (membrane-bound enzyme (Q et al., 2019)). 

Two main pathways, Δ4 in rodents, hamsters and guinea pigs and Δ5 in humans and bovine, both in other species, can determine what downstream hormones will be synthesized from pregnenolone (Flück et al., 2003). Pregnenolone is converted to progesterone by 3-beta-HSD then to 17-OH-progesterone and androstenedione by CYP17A1 enzyme for the Δ4 pathway. More commonly in humans, pregnenolone is converted to 17-OH-pregnenolone and to dehydroepiandrosterone (DHEA), by CYP17A1, following the Δ5 pathway (Z et al., 2019). 

Reduction of pregnenolone synthesis, or inhibition of CYP11A1 for example, can lead to a decrease in pregnenolone levels. This will impact all of steroidogenesis as all downstream steroid hormones are synthesized from pregnenolone.

There is no standardised test guideline available for the measurement of pregnenolone. However, the H295R cell line can be used in a high throughput assay to measure pregnenolone using LC-MS/MS (Haggard et al., 2018; Karmaus et al., 2016). LC-MS/MS has also been used recently to measure steroid hormones including pregnenolone in rat plasma and tissue (Evangelista et al., 2024). ELISA or RIA immunoassays can be used to measure tissue or serum levels of pregnenolone.

Taxonomic applicability. 

Pregnenolone is conserved from amphibians to mammals, even plants (Batth et al., 2020; DM et al., 2017; Tarkowská, 2019; V et al., 2018), but in the case of this KER, it is focused on mammals. 

Life stage applicability 

It is also applicable for all life stages as it plays roles during development and adulthood (DM et al., 2017; V et al., 2018). 

Sex applicability 

Both sexes produce pregnenolone as it is the precursor to all other steroid hormones necessary for correct development, reproduction and general homeostasis (DM et al., 2017; V et al., 2018).

Batth, R., Nicolle, C., Cuciurean, I. S., & Simonsen, H. T. (2020). Biosynthesis and Industrial Production of Androsteroids. Plants, 9(9), 1144. https://doi.org/10.3390/plants9091144 

DM, S., AH, Z., LN, T., K, M., & V, S. (2017). A brief history of the search for the protein(s) involved in the acute regulation of steroidogenesis. Molecular and Cellular Endocrinology, 441, 7–16. https://doi.org/10.1016/j.mce.2016.07.036 

Evangelista, S., Vazakidou, P., Koekkoek, J., Heinzelmann, M. T., Lichtensteiger, W., Schlumpf, M., Tresguerres, J. A. F., Linillos-Pradillo, B., van Duursen, M. B. M., Lamoree, M. H., & Leonards, P. E. G. (2024). High throughput LC-MS/MS method for steroid hormone analysis in rat liver and 

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Flück, C. E., Miller, W. L., & Auchus, R. J. (2003). The 17, 20-Lyase Activity of Cytochrome P450c17 from Human Fetal Testis Favors the Δ 5 Steroidogenic Pathway. The Journal of Clinical Endocrinology & Metabolism, 88(8), 3762–3766. https://doi.org/10.1210/jc.2003-030143 

Haggard, D. E., Karmaus, A. L., Martin, M. T., Judson, R. S., Setzer, R. W., & Paul Friedman, K. (2018). High-Throughput H295R Steroidogenesis Assay: Utility as an Alternative and a Statistical Approach to Characterize Effects on Steroidogenesis. Toxicological Sciences, 162(2), 509–534. https://doi.org/10.1093/toxsci/kfx274 

Karmaus, A. L., Toole, C. M., Filer, D. L., Lewis, K. C., & Martin, M. T. (2016). High-Throughput Screening of Chemical Effects on Steroidogenesis Using H295R Human Adrenocortical Carcinoma Cells. Toxicological Sciences, 150(2), 323–332. https://doi.org/10.1093/toxsci/kfw002 

Lin, Y. C., Cheung, G., Espinoza, N., & Papadopoulos, V. (2022). Function, regulation, and pharmacological effects of pregnenolone in the central nervous system. Current Opinion in Endocrine and Metabolic Research, 22, 100310. https://doi.org/10.1016/j.coemr.2021.100310 

Q, Z., P, P., X, C., Y, W., S, Z., J, M., X, L., & RS, G. (2019). Human placental 3β-hydroxysteroid dehydrogenase/steroid Δ5,4-isomerase 1: Identity, regulation and environmental inhibitors. Toxicology, 425, 152253. https://doi.org/10.1016/j.tox.2019.152253 

Tarkowská, D. (2019). Plants are Capable of Synthesizing Animal Steroid Hormones. Molecules, 24(14), 2585. https://doi.org/10.3390/molecules24142585 

V, S., DM, S., & BJ, C. (2018). Current knowledge on the acute regulation of steroidogenesis. Biology of Reproduction, 99(1), 13–26. https://doi.org/10.1093/biolre/ioy102 

Vallée, M. (2016). Neurosteroids and potential therapeutics: Focus on pregnenolone. The Journal of Steroid Biochemistry and Molecular Biology, 160, 78–87. https://doi.org/10.1016/j.jsbmb.2015.09.030 

Z, P., G, X., W, C., & S, X. (2019). Environmental inhibitors of the expression of cytochrome P450 17A1 in mammals. Environmental Toxicology and Pharmacology, 69, 16–25. https://doi.org/10.1016/j.etap.2019.02.007