title: Substrate specificity of human 3(20)alpha-hydroxysteroid dehydrogenase for neurosteroids and its inhibition by benzodiazepines.
abstract: In this report, we compared kinetic constants and products in the reduction of the neurosteroids, 3alpha,5alpha-tetrahydroprogesterone (3alpha,5alpha THP) and 3alpha,5alpha-tetrahydrodeoxycorticosterone (3alpha,5alpha-THDOC), and their precursors, 5alpha-dihydroprogesterone (5alpha-DHP), 5alpha-dihydrodeoxycorticosterone (5alpha-DHDOC) and progesterone, by three isoenzymes (AKR1C1, AKR1C2 and AKR1C3) of human 3alpha-hydroxysteroid dehydrogenase. AKR1C1 efficiently reduced 3alpha,5alpha-THP, 5alpha-DHP and progesterone to their 20alpha-hydroxy metabolites, and slowly converted 5alpha-DHDOC to 3alpha,5alpha-THDOC. AKR1C2 exhibited low 20-ketoreductase activity for 3alpha,5alpha-THP and moderate 3-ketoreductase activity for 5alpha-DHP and 5alpha-DHDOC. 3alpha,5alpha-THDOC was not reduced by the two isoenzymes. No significant activity for the steroids was detected with AKR1C3. The results suggest that AKR1C2 is involved in the neurosteroid synthesis, but AKR1C1 decreases the neurosteroid concentrations in human brain by inactivating 3alpha,5alpha-THP and eliminating the precursors from the synthetic pathways. In addition, we found that the several benzodiazepines inhibited the three isoenzymes noncompetitively with respect to the substrate. Although cloxazolam was a potent and specific inhibitor of AKR1C3, diazepam, estazolam, flunitrazepam, medazepam and nitrazepam, that inhibited AKR1C1 and AKR1C2, may influence the neurosteroid metabolism.
authors: Laboratory of Biochemistry, Gifu Pharmaceutical University, Japan.
authors: Noriyuki
authors: N
authors: Usami
authors: Tomohiro
authors: T
authors: Yamamoto
authors: Syunichi
authors: S
authors: Shintani
authors: Shuhei
authors: S
authors: Ishikura
authors: Yu
authors: Y
authors: Higaki
authors: Yoshihiro
authors: Y
authors: Katagiri
authors: Akira
authors: A
authors: Hara
mesh_terms: D015096:3-Hydroxysteroid Dehydrogenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D045002:3-alpha-Hydroxysteroid Dehydrogenase (B-Specific); D043582:5-alpha-Dihydroprogesterone; D001569:Benzodiazepines / Q000737:chemistry / Q000378:metabolism*; D003345:Corticosterone / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D011277:Pregnanediones / Q000737:chemistry / Q000378:metabolism*; D011280:Pregnanolone / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: C454687:5-dihydrodeoxycorticosterone; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D011277:Pregnanediones; D001569:Benzodiazepines; D043582:5-alpha-Dihydroprogesterone; D011280:Pregnanolone; D015096:3-Hydroxysteroid Dehydrogenases; D045002:3-alpha-Hydroxysteroid Dehydrogenase (B-Specific); D003345:Corticosterone