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|AHFS/Drugs.com||International Drug Names|
|Molar mass||316.483 g/mol|
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Pregnenolone (3β-hydroxypregn-5-en-20-one), also known as P5, is an endogenous steroid hormone. It is the precursor of the progestogens, mineralocorticoids, glucocorticoids, androgens, and estrogens, as well as the neuroactive steroids. In addition, pregnenolone is biologically active in its own right, acting as a neurosteroid.
Like other steroids, pregnenolone consists of four interconnected cyclic hydrocarbons. It contains ketone and hydroxyl functional groups, two methyl branches, and a double bond at C5, in the B cyclic hydrocarbon ring. Like many steroid hormones, it is hydrophobic. The sulfated derivative, pregnenolone sulfate, is water-soluble.
Pregnenolone is synthesized from cholesterol. This conversion involves hydroxylation at the side-chain at C20 and C22 positions, with cleavage of the side-chain. The enzyme performing this task is cytochrome P450scc, located in the mitochondria, and controlled by anterior pituitary tropic hormones, such as ACTH, FSH, LH.
Pregnenolone undergoes further steroid metabolism in one of three ways.
- Pregnenolone can be converted to progesterone. The critical enzyme step is two-fold using a 3-beta-hydroxysteroid dehydrogenase and a delta 4-5 isomerase. The latter transfers the double bond from C5 to C4 on the A ring. Progesterone is the entry into the delta-4-pathway, resulting in production of 17-hydroxy progesterone and androstenedione, precursor to testosterone and estrone. Aldosterone and corticosteroids are also derived from progesterone or its derivatives.
- Pregnenolone can be converted to 17-hydroxy-pregnenolone by the enzyme 17α-hydroxylase (CYP17A1). Using this pathway, termed delta-5 pathway, the next step is conversion to dehydroepiandrosterone (DHEA) using a desmolase. DHEA is the precursor of androstenedione.
- Pregnenolone can be converted to androsta-5,16-dien-3 beta-ol by 16-ene synthetase.
Pregnenolone and its sulfate, like DHEA and its sulfate and progesterone, belong to the group of neurosteroids that are found in high concentrations in certain areas of the brain, and are synthesized there. Neurosteroids affect synaptic functioning, are neuroprotective, and enhance myelinization. Pregnenolone and its sulfate ester are under investigation for their potential to improve cognitive and memory functioning. Pregnenolone is also being considered as a potential treatment for schizophrenia.
Interestingly, unlike pregnenolone, pregnenolone sulfate is a negative allosteric modulator of the GABAA receptor as well as a positive allosteric modulator of the NMDA receptor. In addition, it has been shown to activate the transient receptor potential M3 (TRPM3) ion channel in hepatocytes and pancreatic islets causing calcium entry and subsequent insulin release.
Pregnenolone, a molecule produced by the brain, is involved in a natural negative feedback loop against CB1 receptor activation in animals. Pregnenolone prevents CB1 agonists like THC, the main active principle in cannabis, from fully activating the CB1 receptor, that when stimulated by THC causes the psychological effects of cannabis.
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- Majewska MD, Mienville JM, Vicini S (August 1988). "Neurosteroid pregnenolone sulfate antagonizes electrophysiological responses to GABA in neurons". Neuroscience Letters. 90 (3): 279–84. doi:10.1016/0304-3940(88)90202-9. PMID 3138576.
- Wu FS, Gibbs TT, Farb DH (September 1991). "Pregnenolone sulfate: a positive allosteric modulator at the N-methyl-D-aspartate receptor". Molecular Pharmacology. 40 (3): 333–6. PMID 1654510.
- Irwin RP, Maragakis NJ, Rogawski MA, Purdy RH, Farb DH, Paul SM (July 1992). "Pregnenolone sulfate augments NMDA receptor mediated increases in intracellular Ca2+ in cultured rat hippocampal neurons". Neurosci Lett. 141 (1): 30–4. doi:10.1016/0304-3940(92)90327-4. PMID 1387199.
- Wagner TF, Loch S, Lambert S, et al. (December 2008). "Transient receptor potential M3 channels are ionotropic steroid receptors in pancreatic beta cells". Nature Cell Biology. 10 (12): 1421–30. doi:10.1038/ncb1801. PMID 18978782.