Oxidative Stress Responses To Microcystin MC-LR In Tilapia Fish (Oreochromis Niloticus)

Water bloom is a serious problem caused by eutrophication. As a causative alage, Microcystis aeruginosa can metabolize microcystin. A toxicant may pose a very stress on fish and other aquatic animals. It also can become a potential risk to human health with a food chain by bioaccumulation and bioamplification. Great deals of attention have focused on microcystin. This thesis discussed oxidative stress responses to microcysrin in tilapia fish (Oreochromis niloticus).The experiment detected liver damage to microcystin in tilapia fish using glutamic-pyruvic transaminase (ALT) and glutamic-oxalacetic transaminase (AST) as bio-indicators. The results showed that the activities of ALT and AST had maximum values in 24 hours, and its values have time-depend effect and dose-depend effect. It indicated that microcysrin could be metabolized into live and caused liver damage, and we can use ALT and AST as biomarkers to monitor the toxicity of microcrstin to tilapia fish.The experiment discussed detoxification of microcystin in phase ? reaction in terms of variation of cytochrome P450 enzymes (P450 1A2, P450 2E1, P450 3A1).The results showed that P450 enzymes varied subtly without marked diffidence compared to control treatment in different time. Microcystin may not have detoxification in phase ? reaction.Then, the experiment discussed detoxification of microcystin in phase ? reaction. Antioxidtion defence system, combined with endogenous antioxidation enzymes (catalase, CAT and superoxidedismutase, SOD) and glutathione and its related enzymes, played a very important role in this reaction. The results showed that microcystin could cause surplus reactive oxygen species (ROS) in liver and gill. It could reach the maximum values in 24 hours and 36 hours respectively, and the activity values of CAT and SOD had time-depend effect and dose-depend effect. In the respect of glutathione system, microcystin could deplete glutathione when combined with it. Glutathione reductase (GR) and glutathione peroxidase (GPx) regulated reduced glutathione (GSH) and oxidized glutathione (GSSG) which is a very important buffer pair in vivo. The depletion of glutathione also could trigger its de novo synthesis. The results also showed that liver had the most ability in antioxidant defence system, kidney better, and gill worse. May microcystin be transported into kidney for excretion and/or reabsorption? It is still a question.Phase ? reaction played an essential role in detoxification of microcystin. It is believed that toxicant can be metabolitized in phase ? reaction, providing essential metabolite for phase ? reaction, or be excreted by kidney. Our results show a contrary detoxification process. Microcystin only processed in phase ? reaction.