Hepatic CYP1A, 2B, 2C, 2E and 3A regulation by methoxychlor in male and female rats

The effect on liver cytochrome P450 (CYP) by i.p. injections of methoxychlor (MXC) in corn oil at 0, 100, 150, 200 or 250 mg/kg twice daily for 3 days was investigated in adult male and female Wistar rats. The MXC injection (100 mg/kg b.w.) caused a similar increase of total CYP content in males and females as compared with controls who received the vehicle only. In males, this increase continued up to 250 mg/kg. As to the induction of specific CYP activities, the effect of MXC was found to be sex dependent with three different patterns. Males showed the greatest increases of ethoxy- and methoxyresorufin-O-dealkylase (EROD and MROD, respectively), two CYP1A1/1A2-related activities. On the contrary, females were more responsive than males for pentoxyresorufin-O-dealkylase (PROD) and benzyloxyresorufin-O-dearylase (BROD), two CYP2B-related activities. Finally, p-nitrophenol hydroxylase (PNPH), a CYP2E1-related activity, showed a similar small, although statistically significant, increase for both sexes. As to CYP apoprotein levels, CYP1A1 and CYP2B1/2B2 showed greater increases in females than in males; whereas, interestingly, CYP2E1 induction was higher in males than in females. These results indicate overall that gender modulates CYP expression after MXC injection both qualitatively and quantitatively, and, therefore, this pesticide is not a pure PB inducer. Moreover, the statistically significant increase of CYP3A2 apoprotein expression observed in females and also, to a lower extent, in males, and the decrease of CYP2C11 apoprotein found in males, two sex-related enzymes, may explain the reported endocrine disrupting effect of MXC. The relevance of the different patterns of rat liver CYP induction observed after MXC treatment, in relationship to the speculated endocrine disrupting potential of MXC in humans potentially exposed to this pesticide, needs further investigation. (C) 2003 Elsevier Ireland Ltd. All rights reserved.