Effects of methoxychlor and 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane on 3β-hydroxysteroid dehydrogenase and 17β-hydroxysteroid dehydrogenase-3 activities in human and rat testes

P>Human and rat testis microsomes were used to investigate direct inhibitory activities of methoxychlor (MXC) and its metabolite 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE) on 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and 17 beta-hydroxysteroid dehydrogenase type 3 (17 beta-HSD3). The 3 beta-HSD and 17 beta-HSD3 enzymes are involved in the reactions that culminate in androgen biosynthesis in Leydig cells. The results demonstrated that MXC and HPTE inhibited human 3 beta-HSD activity at a concentration of 10 nm. The half maximal inhibitory concentration (IC50) for MXC inhibition of 3 beta-HSD was 53.21 +/- 15.52 mu m (human) and 46.15 +/- 17.94 mu m (rat), and for HPTE, it was 8.29 +/- 2.49 mu m (human) and 13.82 +/- 2.26 mu m (rat). At the higher concentration of 100 mu m, MXC did not affect human and rat 17 beta-HSD3 activity. However, the IC50 for HPTE inhibition of 17 beta-HSD3 was 12.1 +/- 1.9 mu m (human) and 32 .0 +/- 8.6 mu m (rat). The mode of action of MXC and HPTE on 3 beta-HSD activity was non-competitive with the substrate pregnenolone, but was competitive with the cofactor NAD+. The mode of HPTE inhibition of 17 beta-HSD3 was non-competitive with the substrate androstenedione, but was competitive with the cofactor NADPH. In summary, our results showed that HPTE, which is the biologically active metabolite of MXC, has the capacity for direct inhibition of 3 beta-HSD and 17 beta-HSD3 enzyme activity. Inhibition of enzyme activity is presumably associated with suppression of steroidogenesis in gonadal tissues and has implications for testis function.