Like nonylphenol genistein affected reductase
Like nonylphenol, genistein affected 5α-reductase,CYP3A and CYP2C11. Genistein treatment resulted in a significant decrease in CYP2C11 activity at the 1250 ppm dose that was accompanied by a non-significant decrease in CYP2C11 protein. CYP3A1/2 protein was also decreased at the highest dose of genistein. Although no decrease in the activity normally associated with CYP3A1 (6β-hydroxylase activity) was observed, this might be explained by the fact that CYP1A1 can also catalyze this reaction (Sonderfan et al., 1987). The effects of genistein on 5α-reductase activity differed from those of nonylphenol in that a significant effect was seen in both sexes and the dose response appeared to be non-monotonic, with the greatest increase in activity at the intermediate (250 ppm) dose and a decrease (significant in males only) in activity at the highest (1250 ppm) dose. Apparent non-monotonic effects of genistein were also found for CYP3A expression in this study and have been reported in other studies. For example, lower genistein concentrations (10 nm–1 μm) stimulated growth of MCF-7 cells, while higher concentrations (10–100 μm) inhibited growth (Wang et al., 1996). In the MCF-7 study, the low dose effects appeared to be mediated through the mct2 inhibitor receptor, whereas the high-dose effects appeared to be independent of the estrogen receptor. It is possible that genistein is either inhibiting or down-regulating 5α-reductase at the high dose. While Evans et al. (1995) have shown that 100 μm genistein inhibits 5α-reductase activity in tissue homogenates, this explanation seems unlikely since genistein and metabolites have been reported to reach higher concentrations in female rat liver than male rat liver (Chang, Churchwell, Delclos, Newbold, & Doerge, 2000, Coldham, & Sauer, 2000) and no inhibition of 5α-reductase activity was observed in female liver microsomes in our studies. The potent estrogen EE2 induced a decrease in CYP2C11 activity (reduction in 2α-OH and 16α-OH testosterone) and protein at the 200 ppb dose and in this respect was similar to nonylphenol and genistein. This result agrees qualitatively with the results of Hallstrom et al. (1996) who exposed male rats to higher doses of EE2 (160–210 μg/kg/day vs approximately 45 μg/kg/day in the present study) via subcutaneous implants. On the other hand, unlike the exposures to nonylphenol and genistein, no significant effects on 5α-reductase or CYP3A were observed in the EE2-treated animals. EE2 may be covalently binding CYP2C11, resulting in degradation of the enzyme, rather than regulating expression of the enzyme. Indeed, early studies suggested that EE2 causes loss of CYP450 in the rat liver in vitro and in vivo (White and Müller-Eberhard, 1977), presumably due to mechanism-based inactivation with subsequent destruction of CYP450 (Ortiz de Montellano et al., 1979). The decrease in the female-predominant 7α-OH testosterone metabolite observed at the 25 and 200 ppb EE2 doses in our studies further argues against feminization and for destruction of CYP450. Nevertheless, it is noteworthy that the 200 ppb EE2 dose did have effects in the males in these studies (e.g. decreased testes weight, stimulation of male mammary gland, mineralization of renal tubules; Delclos et al., unpublished) that could be related to estrogenic activity and that were equivalent or more pronounced than the potentially estrogenic effects of genistein (Delclos et al., 2001) and nonylphenol (unpublished data) in males.