Induction of detoxification processes in Oncorhynchus mykiss by trace levels of contaminants

Abstract

In order to study the variability of detoxification activities associated with the cytochromes P450 1A (CYP1A) and 3A (CYP3A), several continental fish farms of Oncorhynchus mykiss were routinely sampled. In fish, CYP1A plays a key role in the biotransformation of awide variety of pollutants. This cytochrome is induced after ligand-activation of the aryl hydrocarbon receptor. CYP3A is also implicated in themetabolismof a wide variety of xenobiotics, including pharmaceuticals however its activity is mediated by the pregnane-X-receptor. CYP1A and CYP3A inductions have been widely used as biomarkers of environmental pollution in aquatic systems, in particular when measured at the enzymatic level through ethoxyresorufin-O-deethylase (EROD) and benzyloxy-4-[trifluoromethyl]-coumarin-O-debenzyloxylase (BFCOD) activities, respectively. In one of the monitored fish farms, EROD activity, which initially showed basal levels, exhibited a sharp increase difficult to explain by seasonal variability. In order to confirm the increased induction of the cytochrome activities, 32 animals were transferred to a control farm and maintained for one month. Periodic samplings of eight animals at days 0, 7, 15 and 30 were performed and both EROD and BFCOD activities in the livers measured. Under these controlled conditions, enzymatic activities associated with detoxification processes gradually decreased to basal levels indicating thepresence of some factor in the fish farm inducing the cytochromes. In order to investigate possible causes of such induction both water and sediment samples, along the river feeding the fish farm, were taken and analysed byaGCxGC-TOFMS system. This systemprovedveryuseful and allowed us to identify non-target compounds in some samples, among them personal care, pharmaceutical products, and industrial chemicals (i.e. PAHs, phthalates, alkylphenolic compounds) that couldbe related to the observed induction.