Impairment of antioxidant mechanisms in Japanese Medaka (Oryzias latipes) by acute exposure to aluminum

Increasing aluminum (Al) concentrations in aquatic habitats as a result of anthropogenic acidification and industrialization is a global issue. Moreover, in extensive areas of the humid tropics and subtropics, high Al concentrations in freshwater are observed because of both naturally low pH and high Al concentrations in soil. Al increases production of reactive oxygen species and enhances oxidative damage in mammals. However, no studies have examined the effect of environmentally relevant concentrations of Al at low pH on oxidative stress in fish. This study assessed Al-induced effects on enzymatic and non-enzymatic antioxidants, lipid peroxidation, and on expression of oxidative stress-related genes at low pH using Japanese Medaka (Oryzias latipes). Larval fish were exposed to dissolved Al concentrations of 0, 1.7, 6.2 and 16.7 μg L^{− 1} for 4 days at pH 5.3 in soft water. Al caused a significant reduction in activity of glutathione peroxidase at 6.2 and 16.7 μg L^{− 1}, and of glutathione reductase at 16.7 μg L^{− 1} in whole body homogenates. No changes were observed in the expression of the glutathione peroxidase gene, and expression levels of the glutathione reductase gene were too low to be quantitated. Even though there was an overall decrease in the activity of catalase and in the concentration of glutathione, differences were not significant compared to the control. Changes in lipid peroxidation were not found. This study showed that exposure to environmentally relevant concentrations of Al at low pH impairs antioxidant defense mechanisms of Medaka.