Brain Metabolism of Allopregnanolone and Isoallopregnanolone in Male Rat Brain

Allopregnanolone (allo) and isoallopregnanolone (isoallo) are neuroactive steroid epimers that differ in hydroxyl orientation at carbon three. Allo is a potent GABA-A receptor agonist, while isoallo acts as an antagonist, influencing brain function through their interconversion. Their metabolism var...

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Bibliographic Details
Published in:International journal of molecular sciences Vol. 26; no. 17; p. 8559
Main Authors: Öfverman, Charlotte, Hill, Martin, Johansson, Maja, Bäckström, Torbjörn
Format: Journal Article
Language:English
Published: Switzerland MDPI AG 03.09.2025
Subjects:
17β-hydroxysteroid dehydrogenases
aldoketoreductases
allopregnanolone
Animals
Brain
Brain - metabolism
circulation
Conversion
Enzymes
GABA
GC-MS
hippocampus
isoallopregnanolone
Liver
Male
Metabolism
Metabolites
neuroactive steroids
Neurophysiology
Physiological aspects
Pregnanolone - analogs & derivatives
Pregnanolone - metabolism
rat
Rats
Rats, Sprague-Dawley
Steroids
striatum
Sweden
GC-MS
neuroactive steroids
hippocampus
rat
striatum
17β-hydroxysteroid dehydrogenases
circulation
isoallopregnanolone
allopregnanolone
brain
aldoketoreductases
ISSN:1422-0067, 1661-6596, 1422-0067
Online Access:Get full text
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Summary:Allopregnanolone (allo) and isoallopregnanolone (isoallo) are neuroactive steroid epimers that differ in hydroxyl orientation at carbon three. Allo is a potent GABA-A receptor agonist, while isoallo acts as an antagonist, influencing brain function through their interconversion. Their metabolism varies across brain regions due to enzyme distribution, with AKR1C1–AKR1C3 active in the brain and AKR1C4 restricted to the liver. In rats, AKR1C9 (liver) and AKR1C14 (intestine) perform similar roles. Beyond AKR1Cs, HSD17Bs regulate steroid balance, with HSD17B6 active in the liver, thyroid, and lung, while HSD17B10, a mitochondrial enzyme, influences metabolism in high-energy tissues. Our current data obtained using the GC-MS/MS platform show that allo and isoallo in rats undergo significant metabolic conversion, suggesting a regulatory role in neurosteroid action. High allo levels following isoallo injection indicate brain interconversion, while isoallo clears more slowly from blood and undergoes extensive conjugation. Metabolite patterns differ between brain and plasma—allo injection leads to 5α-DHP and isoallo production, whereas isoallo treatment primarily yields allo. Human plasma contains mostly sulfate/glucuronided steroids (2.4–6% non-sulfate/glucuronided), whereas male rats exhibit much higher free steroid levels (29–56%), likely due to the absence of zona reticularis. These findings highlight tissue-specific enzymatic differences, which may impact neurosteroid regulation and CNS disorders.
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ISSN:1422-0067
1661-6596
1422-0067
DOI:10.3390/ijms26178559