Down-regulation of cytochrome P450 2C family members and positive acute- phase response gene expression by peroxisome proliferator chemicals

In this study, we show that peroxisome proliferator chemical (PPC) exposure leads to alterations in the expression of genes in rat liver regulated by the sex-specific growth hormone secretory pattern and induced during inflammation. Expression of the male-specific cytochrome P450 (P450) 2011 and α2 urinary globulin (α2u) genes and the female-specific P450 2C12 gene was down-regulated by some PPC. Expression of P450 2C13, also under control by the sex-specific growth hormone secretory pattern, was not altered by PPC treatment, indicating that regulation of CYP2C family members does not involve perturbation of the growth hormone secretory pattern. In contrast to the increases in expression observed when inflammation was induced in male rats, two positive acute-phase response genes, α₁-acid glycoprotein and β- fibrinogen, were decreased by PPC exposure. The down-regulation of the P450 2C11 by WY-14,643 could be reproduced in cultured rat hepatocytes, indicating the down-regulation is a direct effect. Experiments in wild-type mice and mice that lacked a functional peroxisome proliferator-activated receptor-α gene showed that down-regulation by WY of α₁-acid glycoprotein, β- fibrinogen, and a mouse homologue of α2u was dependent on peroxisome proliferator-activated receptor-α expression. Our results demonstrate that PPC exposure leads to down-regulation of diverse liver-specific genes, including CYP2C family members important in hormonal homeostasis and acute- phase response genes important in inflammatory responses.