Cadmium-induced antioxidant defense mechanism in freshwater teleost Oreochromis mossambicus (Tilapia)

Antioxidant defenses consisting of catalase, superoxide dismutase (SOD), xanthine oxidase (XOD), glutathione peroxidase (GPX), and glutathione S-transferase were estimated in liver and kidney of freshwater fish subjected to a sublethal concentration of cadmium chloride (Cd2+), i.e., 5 ppm. The aim of the study was to evaluate the role of antioxidant defenses during cadmium-induced oxidative stress. Significant elevations in liver and kidney of all of the above detoxification enzymes were evident from the 7th day onward, were maintained until the 15th day, and then decreased slightly on the 30th day of exposure to cadmium stress. Between the two tissues studied, liver recorded higher activity for all enzymes except GPX, which was elevated significantly in kidney (82.85%). Both liver and kidney recorded more or less similar increases of SOD (86.61% and 86.32%, respectively), and XOD (86.41% and 84.19%, respectively). The findings indicate that tissue glutathione-dependent enzymes as well as other antioxidant enzymes function in protection against Cd2+ toxicity and that these antioxidants provide a first line of defense against Cd2+ before the induction of any metallothionein synthesis occurs.