Ketoconazole, an antifungal imidazole, increases the sensitivity of rainbow trout to 17alpha-ethynylestradiol exposure

This study focuses on effects of two classes of xenobiotics, azole fungicides and xenoestrogens, both of which have been detected in the aquatic environment. We hypothesize that azoles and estrogenic compounds are metabolized by cytochrome P450 (CYP) enzymes, and in particular CYP1A and CYP3A, to more readily excreted metabolites. We exposed rainbow trout (Oncorhynchus mykiss) to two different pharmaceutical representatives of theses two classes, such as the imidazole ketoconazole and the synthetic estrogen analogue, 17alpha-ethynylestradiol (EE(2)). Juvenile rainbow trout were i.p. injected with a single low dose of EE(2) (2.5 microg/kg), alone or in combination with ketoconazole (100mg/kg). Hepatic microsomal CYP1A and CYP3A protein expressions were analyzed in Western blots using polyclonal antibodies (PAb) and enhanced cheminoluminescence. CYP1A activities were analyzed using the ethoxyresorufin-O-deethylase (EROD) assay and CYP3A activities were analyzed using the benzyloxy-4-[trifluoromethyl]-coumarin-O-debenzyloxylase (BFCOD) assay. Plasma vitellogenin (vtg) and sex steroid hormones (i.e. 17beta-estradiol, testosterone and 11-keto-testosterone) were analyzed using commercially available ELISA-kits. The vtg mRNA expression was analyzed using quantitative (Q)-PCR. The dose of EE(2) selected had little or no effect on the estrogen receptor (ER) mediated vtg induction. However, in combination with ketoconazole this threshold-dose of EE(2) resulted in significantly elevated plasma vtg levels, 6 days post injection. Exposure to ketoconazole resulted in up to nine-fold induction of CYP1A after 3 days. However, this nine-fold induction was not reflected on the CYP1A catalytic activity, where exposure to ketoconazole resulted only in a two-fold increase in activity. Ketoconazole increased CYP3A protein levels 1.5-fold and decreased BFCOD activities by 80% at days 3 and 6. Treatment with ketoconazole and EE(2) alone and in combination had no significant effect on sex steroid hormones, compared to vehicle-treated fish. This study demonstrates that exposure to ketoconazole compromises the function of key enzymes involved in metabolic clearance of xenobiotics and steroids, and increases the sensitivity to EE(2) exposure in juvenile rainbow trout.