Effects of phthalates on 3β-hydroxysteroid dehydrogenase and 17β-hydroxysteroid dehydrogenase 3 activities in human and rat testes

The 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and 17 beta-hydroxysteroid dehydrogenase 3 (17 beta-HSD3) are involved in the reactions that culminate in androgen biosynthesis in Leydig cells. Human and rat testis microsomes were used to investigate the inhibitory potencies on 3 beta-HSD and 17 beta-HSD3 activities of 14 different phthalates with various carbon numbers in the ethanol moiety. The results demonstrated that the half-maximal inhibitory concentrations (IC(50)s) of dipropyl (DPrP), dibutyl (DBP), dipentyl (DPP), bis(2-but-oxyethyl) (BBOP) and dicyclohexyl (DCHP) phthalate were 123.0, 24.1, 25.5, 50.3 and 25.5 mu M for human 3 beta-HSD activity, and 62.7, 30.3, 33.8, 82.6 and 24.7 mu M for rat 3 beta-HSD activity, respectively. However, only BBOP and DCHP potently inhibited human (IC(50)s, 23.3 and 8.2 mu M) and rat (IC(50)s, 30.24 and 9.1 mu M) 17 beta-HSD3 activity. Phthalates with 1-2 or 7-8 carbon atoms in ethanol moieties had no effects on both enzyme activities even at concentrations up to 1 mM. The mode of action of DCHP on 3 beta-HSD activity was competitive with the substrate pregnenolone but noncompetitive with the cofactor NAD+. The mode of action of DCHP on 17 beta-HSD3 activity was competitive with the substrate androstenedione but noncompetitive with the cofactor NADPH. In summary, our results showed that there are clear structure-activity responses for phthalates in the inhibition of both 3 beta-HSD and 17 beta-HSD3 activities. The length of carbon chains in the ethanol moieties of phthalates may determine the potency to inhibit these two enzymes. (C) 2012 Published by Elsevier Ireland Ltd.