Bioaccumulation, oxidative stress and HSP70 expression in Cyprinus carpio L. exposed to microcystin-LR under laboratory conditions

Microcystin-LR (MC-LR) produced by cyanobacteria are potent specific hepatotoxins. So far the pathogenesis of environmental MC-LR toxicity to aquatic organisms has not been fully elucidated. In the present study the accumulation of MC-LR was investigated in various organs/tissues of Cyprinus carpio L. (C. carpio) following exposure to MC-LR for 14 d at environmentally relevant concentrations (0.1 to 10 μg L− 1). Results showed that the presence of MC-LR enhanced toxin accumulation in all investigated organs and the highest accumulation was found in the liver of fish exposed to 5.0 μg L− 1 of MC-LR. An EPR analysis indicated ·OH intensity in liver was significantly induced at 0.1 μg L− 1 of MC-LR and then restored when the MC-LR concentration was greater than 0.1 μg L− 1. After 14-day exposure, MC-LR (1.0-10.0 μg L− 1 of MC-LR) caused a pronounced promotion of glutathione S-transferase (GST) activity and a depletion of reduced glutathione (GSH) content in fish liver, which indicated that GSH was involved in detoxification of MC-LR and the conjugation reaction of MC-LR and GSH occurred. A mild oxidative damage was evidenced by the accumulation of malondialdehyde (MDA) level at 5.0 μg L− 1 of MC-LR exposure, but which was restored when the MC-LR concentration was increased to 10.0 μg L− 1. The responses of antioxidant enzymes and the induction of HSP70 expression might contribute to MC-LR tolerance of C. carpio. However, the protein phosphatase (PP) activities were strikingly inhibited in all treated groups. Thus, the overall toxicity of environmental MC-LR on C. carpio seems to be initiated in the liver via both the ROS pathway and the PP inhibition pathway, and the latter might be more important when ambient MC-LR concentration is greater than 0.1 μg L− 1. More importantly, these results can help to support the evaluation on the potential effects of MC-LR under common environmental concentrations.