Effects of Methoxychlor and Its Metabolite Hydroxychlor on Human Placental 3β-Hydroxysteroid Dehydrogenase 1 and Aromatase in JEG-3 Cells

Progesterone and estradiol produced by the human placenta are critical for maintenance of pregnancy and fetal development. In the human placenta, 3β-hydroxysteroid dehydrogenase 1 (HSD3B1) is responsible for the formation of progesterone from pregnenolone and aromatase (CYP19A1) for the production of estradiol from androgen. Insecticide methoxychlor (MXC) and its metabolite hydroxychlor (HPTE) may disrupt the activities of these 2 enzymes. In this study, we investigated the effects of MXC and HPTE on steroid production in human placental JEG-3 cells and on HSD3B1 and CYP19A1 activities. MXC and HPTE inhibited progesterone and estradiol production in JEG-3 cells. MXC and HPTE were potent HSD3B1 inhibitors with the half maximal inhibitory concentration (IC₅₀) values of 2.339 ± 0.096 and 1.918 ± 0.078 μmol/l, respectively. MXC had no inhibition on CYP19A1 at 100 μmol/l, while HPTE was a weak inhibitor with IC₅₀ of 97.16 ± 0.10 μmol/l. When pregnenolone was used to determine the inhibitory mode, MXC and HPTE were found to be competitive inhibitors of HSD3B1. When cofactor NAD⁺ was used, MXC and HPTE were the noncompetitive inhibitors of HSD3B1. When testosterone was used, HPTE was a mixed inhibitor of CYP19A1. In conclusion, MXC and HPTE are potent inhibitors of human HSD3B1, and HPTE is a weak CYP19A1 inhibitor.