Effects of benzo[a]pyrene on whole cytochrome P450-involved molecular responses in the marine medaka Oryzias melastigma.

Despite being a strong toxicant for aquatic ecosystems, the effect of benzo[a]pyrene (B[a]P) on whole cytochrome P450 (CYP) biotransformation mechanisms has not been deeply investigated in aquatic organisms. To understand the mode of action of B[a]P on CYP molecular responses in fish, we analyzed the full spectrum of cyp genes and the activities of enzymes that are involved in detoxification and antioxidant defense systems after exposure to different concentrations of B[a]P over different time courses in the marine medaka, Oryzias melastigma. Upon B[a]P exposure, we found significant downregulation of cyp genes associated with steroidogenesis with decreased concentrations of actual hormones including estradiol (E2) and testosterone (11-KT), indicating that B[a]P-treated groups were closely associated with the dysfunction of hormone synthesis in a dose-dependent manner. In addition, B[a]P exposure strongly influenced transcriptional levels of antioxidant-related genes and their enzyme activities. Based on these results, we suggest that B[a]P induced the CYPs-involved systematic biotransformation mechanism with oxidative stress in the juvenile marine medaka, resulting in changes of endogenous hormonal levels and transcriptional levels of several steroidogenic metabolism-related CYPs.