Dehydroepiandrosterone 7α‐ and 7β‐Hydroxylation in Mouse Brain Microsomes. Effects of Cytochrome P450 Inhibitors and Structure‐Specific Inhibition by Steroid Hormones

Abstract

Presently, several works question the effects of dehydroepiandrosterone (DHEA) reported in vivo and designate its 7-hydroxylated metabolites as native antiglucocorticoids and potent mediators in the triggering of immune response. Among mouse tissues and organs, and second to liver, the largest production of 7alpha-and 7beta-hydroxylated derivatives of DHEA takes place in brain microsomes. To contribute to identification of cytochromes P450 (CYPs) responsible for 7alpha- and 7beta-hydroxy-DHEA production, effects of CYP inhibitors and of several steroid hormones on DHEA 7-hydroxylation were examined. Using mouse brain microsomes as a source of enzyme, we report now that strong and smaller inhibitions of DHEA 7alpha-hydroxylation were obtained with ketoconazole and alpha-naphthoflavone, respectively, and that neither changed DHEA 7beta-hydroxylation. Metyrapone and antipyrine also inhibited 7alpha-hydroxylation, but by contrast, significantly increased 7beta-hydroxylation of DHEA. This indicated that at least, two different CYPs were responsible for 7alpha- and 7beta-hydroxylation of DHEA. Steroids sharing a 3beta-hydroxylated structure with DHEA, namely pregnenolone, 5-androstene-3beta,17beta-diol and 3beta-hydroxy-5alpha-androstan-17-one, were strong inhibitors of DHEA 7alpha-hydroxylation (non-competitive inhibition with pregnenolone, Ki=2.0 +/- 0.3 microM). In contrast, 7beta-hydroxylation yields were not decreased by the 3beta-hydroxysteroids tested. Moderate inhibition of 7alpha- and 7beta-hydroxylation was obtained with 3-oxosteroids, namely testosterone, progesterone, corticosterone and 4-androsten-3,17-dione. Taken together, these data indicate specific inhibition patterns of DHEA 7alpha- and 7beta-hydroxylation by CYP inhibitors and steroid hormones in mouse brain microsomes and may be used as criteria necessary for identification of the responsible CYP species.

Characterization of the dehydroepiandrosterone (DHEA) metabolism via oxysterol 7α‐hydroxylase and 17‐ketosteroid reductase activity in the human brain

“…The verified occurrence of DHEA 7a-hydroxylase and DHEA 17-ketosteroid reductase activity in the human temporal lobe (Figs 2, 4 and 5) is in accordance with results obtained from rodent brain tissue experiments (Akwa et al 1992;Doostzadeh et al 1997;Rose et al 1997;Fig. 6).…”

“…3b). The cytochrome P450 inhibitor ketoconazole was shown to be a potent inhibitor of microsomal mouse brain 7a-hydroxylase activity (Doostzadeh et al 1997). According to these findings, the present study revealed that ketoconazole is also a strong inhibitor of human brain tissue 7a-hydroxylase activity (Fig.…”

“…Within the rodent brain, DHEA is also known to be converted into 7b-hydroxy-DHEA (Akwa et al 1992;Doostzadeh et al 1997). According to this, we observed the formation of low amounts of a third polar metabolite when investigating mouse brain tissue homogenates (Fig.…”

Neurosteroid Hydroxylase CYP7B

“…In rodent brain, 7␣-hydroxylation is the major ex vivo metabolic route for DHEA, pregnenolone, and A/enediol (24,25,29,31,(33)(34)(35) and, in brain and other tissues, for oxysterols/bile acids (25-and 27-hydroxycholesterol, 3␤-hydroxy-5-cholestenoic acid, 3␤-hydroxy-5-cholenoic acid; Ref. 29), although 7␤-and 6␣-hydroxylation have also been recorded.…”

7-oxygenated Derivatives of Dehydroepiandrosterone and Obesity

“…7-hydroxylation in rat liver homogenate microsomes was characterized (Stárka and Kutová, 1962) and the 7-hydroxylation of dehydroepiandrosterone was discovered in various tissues, including of the brain (Akwa et al, 1992(Akwa et al, , 1993Doostzadeh and Morfin, 1996;Doostzadeh et al, 1997;Rose et al, 1997). Numerous authors paid attention to the presence and role of 7-oxygenated dehydroepiandrosterone derivatives in the brain (Morfin and Stárka, 2001).…”