Hepatotoxicity And Immunotoxicity Of MC-LR On Silver Carp (Hypophthalmichthys Molitrix)

Environmental pollution has received much attention from the public due to the rapid development of social industrialization and the increase of population,of which the water pollution is closely related to human life.In the freshwater,the formation of eutrophication leads to overgrowth of algae,i.e.,algal blooms.Recently,there have more and more reports of the poisoning and even death of living creature caused by outbreak of algal blooms.Particularly,Microcystis bloom has a much greater influence than others.Microcystins?MCs?produced by toxic cyanobacteria are toxic to a wide range of organisms and their target organ of toxicity has been proved to be liver.Human,aquatic organisms,poultry and livestock may develop symptoms of poisoning through direct contact with or consumption of the water containing the toxin.In natural waters,silver carp and other filter-feeding fish fed on algae and other plankton and they have to directly suffer from the toxicitly of the toxin.MC-LR is the most toxic among these MCs,and therefore it has attracted great attention in the recent years.Untill now,the mechanism of MC-LR toxicity has not completely clear,especially very few reports about the immunotoxicity of MCs on silver carp can be available now.In this study,silver carp was used as experimental animal to first determine the acute toxicity of MC-LR by using the improved up-and-down method.Therewith the indexes of blood physiology and biochemistry,inflammatory factors,and other immunological indexes of silver carp following MC-LR exposure at 104.9?g/kg(1/5 of LD₅₀)and 262.1?g/kg(1/2 LD₅₀)for 168 hours were determined and evaluated at protein level using the method of ELISA according to the result of the acute toxicity test.The main results obtained are as follows:1.The LD₅₀ of MC-LR on silver carp at 24 h was calculated to be 524.32?g/kg according to the resut of acute toxicity test,indicating that MC-LR was highly toxic to silver carp.2.The results of organ weight ratio and serum aminotransferase assay showed that the activities of ALT and AST in the serum of silver carp after intraperitoneal injection of MC-LR were siginificantly promoted,suggesting the serious and persistent damage to fish hepatocytes by the toxin.After toxin exposure,The liver index of silver carp was also increased,especially at 12 h and 72 h,indicating that MC-LR caused damage to fish liver.3.The results of white blood cell count showed that after exposure of MC-LR,fish white blood cells significantly increased when compared to that of control group,indicating that MC-LR exposure induced acute inflammation in silver carp.4.The assay results of serum complement and lysozyme level of silver carp showed that serum C3levels were significantly increased in comparation with the control group,suggesting that the complement system of silver carp may be activated following MC-LR exposure.Meanwhile,serum lysozyme activity increased at the early period of exposure,but decreased at the late time.This result indicates that MC-LR exposure probably induces the stress of fish serum lysozyme.5.The IgM concentration in the serum of MC-LR treated silver carp increased significantly within a short time after MC-LR treatment,but it decreased with the prolongation of MC-LR exposure time.However,a persistent higher level of IgM was observed in head kidney,suggesting that MC-LR exposure may stimulate the head kidney and induce immune response.6.The contents of inflammatory factors including TNF-?,IL-1?,and IFN-?in MC-LR treated silver carp serum were promoted when compared to theose of control groups.The results inducate that MC-LR exposure induces inflammatory response in silver carp.In conclusion,our results revealed that MC-LR exposure caused various changes of physiological and biochemical indexes of silver carp,damages of fish liver and immue system,and hepatic inflammatory response,indicating that MC-LR has hepatotoxicity and immunotoxicity on silver carp.These results not only conform the hepatotoxicity of MC-LR on silver carp,but also reveal that MC-LR is toxic to both the innate immune system and the adaptive immune system of silver carp.The result will make the MC-LR toxicology enriched and also supply basic experimental evidences for the future study of MC-LR toxicology.