Oxidative stress responses in rainbow trout (Oncorhynchus mykiss) hepatocytes exposed to pro-oxidants and a complex environmental sample

A wide range of pollutants in the aquatic environment have the capacity to induce toxic effects expressed as cellular oxidative stress. In the current study, the potential of an in vitro toxicity testing system was therefore investigated using rainbow trout (Oncorhynchus mykiss) hepatocytes to assess different endpoints of oxidative stress. The pro-oxidants CuSO4 and paraquat were used as models for comparison to a complex environmental sample. Results following 6, 24, 48 and 96 h exposure to different concentrations of these substances show cellular effects on intracellular ROS formation, glutathione levels and redox status, expression of the antioxidant enzymes superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, γ-glutamyl-cysteine synthetase (GCS) and thioredoxin, as well as cytotoxicity parameters. The most consistent effects (maximum values within brackets), observed in dose and time parameters for both model compounds and environmental sample, were the depletion of total glutathione (9.4% of control), induced levels of oxidized glutathione (695% of control), and gene expression regulation depicted relative to the control gene beta-actin of GCS mRNA (239% of control) and catalase (29% of control). In conclusion, the responses on several antioxidant defence system parameters demonstrated the validity of the in vitro toxicity testing system. Not only could multiple effects be detected at sub-lethal exposure concentrations, but these effects also gave valuable insight to the toxic mechanisms at the molecular level.