Environmental Hormone Disruptors: Evidence That Vinclozolin Developmental Toxicity Is Mediated by Antiandrogenic Metabolites

Recent studies with vinclozolin, a dicarboximide fungicide, demonstrate that perinatal exposure to 100 mg vinclozolin/kg/day from Gestational Day 14 through Postnatal Day 3 inhibits morphological sex differentiation. At 1 year, treated male rats exhibited hypospadias, cleft phallus, suprainguinal ectopic testes, a vaginal pouch, epididymal and testicular granulomas, and atrophic seminal vesicles and ventral prostate glands. This pattern of malformations suggests that this fungicide possesses antiandrogenic activity. To test this hypothesis, we examined the ability of vinclozolin to inhibit the conversion of testosterone to the more potent androgen 5α-dihydrotestosterone via 5α-reductase (EC 1.3.1.22) and to compete with androgen for binding to the androgen receptor. The results indicate that neither vinclozolin nor its degradation products, 2-[[(3,5-dichlorophenyl)-carbamoyl]oxy]-2-methyl-3-butenoic acid (M1) and 3′,5′-dichloro-2-hydroxy-2-methylbut-3-enanilide (M2), inhibit 5α-reductase activity. Although the ability of vinclozolin to compete with androgen for binding to the androgen receptor was weak ( K i > 700 μM), the two vinclozolin metabolites, M1 and M2, were effective antagonists of androgen receptor binding ( K i = 92 and 9.7 μM, respectively). As the concentrations of M1 in the serum of pregnant rats and their pups on Postnatal Day 3 meet or exceed the in vitro K i for androgen receptor inhibition, we suggest that the demasculinizing effects of vinclozolin exposure in vivo also may be mediated via the antiandrogenic metabolites M1 and/or M2.