Low levels of cadmium exposure induce DNA damage and oxidative stress in the liver of Oujiang colored common carp Cyprinus carpio var. color

Cadmium (Cd) compounds are widely distributed toxic environmental and industrial pollutants, and they may bring danger to growth and development of aquatic organisms. In China, the Oujiang color common carp, Cyprinus carpio var. color, is a very important fish, from an economic point of view, and is well used for fish culture in paddy fields. The purpose of this study was to show the low concentrations of cadmium-induced oxidative stress response and DNA damage in the livers of Cyprinus carpio var. color. Superoxide dismutase (SOD), malondialdehyde (MDA), and glutathione (GSH) in liver were measured after exposure to Cd levels (0.41, 0.52, 0.69, 1.03 and 2.06 mg/L, respectively) for 7 days and compared with the control groups. DNA damage, including indicators of damage percentage, DNA tail length (TL) and DNA tail moment (TM) were also analyzed by comet assays. Results showed that MDA and GSH levels in all treatment groups increased significantly relative to the controls (P < 0.01). Treatment with Cd at concentration of 0.41 mg/L increased SOD activity, while treatment with Cd at concentrations >0.41 mg/L inhibited SOD activities. DNA damage percentage, TL and TM also significantly increased when the Cd level was >0.41 mg/L. Positive correlations were also found between DNA damage levels and MDA levels (r = 0.74 for DNA damage percentage, r = 0.83 for TL, r = 0.84 for TM; P < 0.01 for all) as well as between GSH and MDA levels (r = 0.77, P < 0.01). These results strongly suggested that Cd-induced DNA damage in the livers of Cyprinus carpio var. color was due to lipid peroxidation and oxidative stress.