Effects of 17 beta-estradiol and testosterone on hepatic mRNA/protein levels and catalytic activities of CYP2M1, CYP2K1, and CYP3A27 in rainbow trout(Oncorhynchus mykiss)

There is growing concern that exposure to chemicals in the environment can disrupt the endocrine systems of wildlife and humans, causing reproductive problems or other adverse effects. The expression of many cytochrome P450s (CYPs) is under hormonal control, hence, levels of these enzymes can be aff ected by exposure to endocrine-disrupting chemicals. Previous research has reported that treatment of fish and other animals with the estrogenic and a ndrogenic hormones 17 beta -estradiol (E2) and testosterone (T) alters the P450 content or enzyme activities in the treated animals. However, the resu lts of many of these studies are either incomplete or in disagreement and i n most cases the effect on specific P450 forms has not been determined. The refore, to better understand the effects of gonadal hormones on the express ion of P450s and their associated enzyme activities, it was of interest to undertake a comprehensive investigation of the transcriptional and translat ional expression of three constitutive hepatic P450s in the rainbow trout ( Oncorhynchus mykiss) following hormone exposure. Accordingly, juvenile trou t were injected intraperitoneally with propylene glycol vehicle and the mos t active estrogenic and androgenic hormones E2 (3 mg/kg) or T (3 mg/kg) on days 1, 4, 7, 13, and 15 and euthanized on day 19. After treatment with E2, hepatic microsomes showed significantly lower levels (percentage of contro l) in total P450 contents (52%), lauric acid hydroxylase (32%), and 6 beta -progesterone hydroxylase activities (27%), [H-3]aflatoxin-DNA binding (31% ), and the protein levels of individual cytochrome P450s (CYPs) LMC1 (CYP2M 1), LMC2, (CYP2K1), and LMC5 (CYP3A27) (average for three isoforms a reduct ion to 29% of control values) with only minor differences between sexes. Tr eatment with T had either no effect or resulted in small increases in total P450 in males (42%), in lauric acid hydroxylase in females (24%), and in 6 beta -progesterone hydroxylase activity in males (21%). Biological variabi lities among fish were high and a polymorphic or new LMC2-like form was detected at about 52 kDa in some live r microsomal samples after exposure of fish to either hormone. Female liver RNAs were analyzed through Northern blots and an average decrease of 94% i n CYP2 M1, CYP2K1, and CYP3A27 mRNA levels occurred in the E2-treated trout . In livers from T-treated trout, the changes of mRNA levels of CYP2M1 and CYP3A27 were negligible, but CYP2K1 mRNA level decreased by about 60%. Addi tional CYP2K1 cDNA hybridizable mRNAs were seen in some fish as faint bands at about 2.8 kb for both hormone treatments. Results of this study, theref ore, indicated that E2 down-regulated while T produced small but variable e ffects on the hepatic mRNA/protein levels of CYP2K1, CYP2M1, and CYP3A27 in juvenile rainbow trout. This study, therefore, suggests that exposure of f ish and other wildlife to environmental endocrine disrupters, especially es trogen mimics, can adversely affect a number of physiological processes thr ough mechanisms involving altered levels of expression of specific P450 iso zymes. (C) 2000 Academic Press.