Study On The Hepatotoxicity And Biochemical Mechanism Of Paraquat On Commom Carp

Application of pesticide on a large scale in agriculture inevitably causes the entrance of pesticides into the water environment,which consequently induces the adverse impact of toxicity to non-target organisms on growth and health and triggers a series of environmental problems.Paraquat(PQ)is a nonselective herbicide used worldwide and it has been demonstrated to be highly toxic to animals and humans.Owing to its high water solubility and extensive usage,many cases of acute poisoning and death have been reported in human over the past few decades.For the first time since 1966,PQ poisoning with its high mortality has attracted wide attention around the world.Studies on the acute toxicity of PQ in global pesticides has been received more and more concerns in recent years.Although there have been many reports and new insights about the lung toxicity of PQ,however,the hepatotoxicity of PQ,especially the toxicity mechanism of PQ to aquatic animals is still not completely known.This study used common carp as experimental animal and aimed first to determine the acute toxicity of PQ on commom carp and then to evaluate the possible effects of PQ-exposure on the biochemical indexes and immulogical response in the liver of fish to the stress at the levels of transpritioan,protein content,and enzymatic activity by using qPCR and ELISA.In addition,histopathological observation was also conducted to evaluate the damage of PQ-exposure on the liver of fish.The main results obtained in the present study are as follows:(1)The result of the acute toxicity test showed that the 72 and 96 h LC50 values of PQ for common carp were 15.962 and 15.106 mg/L,respectively,suggesting that the PQ has medium toxicity to common carp.(2)The results of biochemical assays showed that PQ-exposure significantly increased the level of MDA,generally reduced the levels or activities of T-AOC and GSH,SOD and CAT in fish liver,indicating that the excessive ROS and lipid peroxidation may be involved in the hepatotoxicity of PQ on common carp.(3)The result of qPCR showed that iNOS mRNA level in the liver of common carp were increased by PQ-exposure,and ELISA detection revealed that PQ significantly increased the activity of NOS in fish liver,suggesting that the high level of NOS might be induced in the liver of common carp exposed to PQ.(4)The result of qPCR in proinflammatory cytokines and anti-inflammatory cytokines in the liver of common carp showed that IL-1? and TNF-? mRNA expressional levels were first downregulated but then upregulated when compared to the control throughout the period of exposure.ELISA assays showed that TNF-? content significantly increased in the liver of common carp in all PQ-treated groups throughout the period of exposure in comparison with that of control fish while IL-1? content increased at the early time of PQ-exposure but then remained unchanged.Moreover,transcription level and content of IL-6 were significantly higher than that of control fish throughout the period of exposure.However,IL-8 expression level significantly increased in all PQ-treatment groups except for the group of 1.596 mg/L PQ treatment at 1 d.Regarding the anti-inflammatory cytokines,IL-10 mRNA level was first upregulated but subsequently downregulated in PQ treatment group(1.596 mg/L);however,it was remarkably decreased in PQ treated group(3.192 mg/L).TGF-? mRNA level and content in PQ-treatment groups increased first but then decreased significantly.This result suggests that PQ-exposure can cause inflammation reaction in common carp liver.(5)ELISA assays indicated that PQ-exposure generally promoted the enzymic activities of Caspase-3 and Caspase-9 in fish liver and Caspase-8 enzymic activity was also promoted in the high concentration of PQ group,suggesting that PQ may induce apoptosis in the liver of PQ-exposed fish.This result suggests that the death receptor signaling pathway as well as mitochondrial-mediated apoptosis pathway may be invoved in the hepatotoxicity of PQ in common carp.(6)The results of histopathological examinations showed that PQ-exposure at 1.596 mg/L caused slight necrosis of fish liver such as spreading,cavitation,and degeneration of hepatocytes.However,remarkable damage such as height cellular swelling,nucleus distortion and pyknosis,and intracytoplasmic vacuolization were observed in 3.192 mg/L PQ group.This result further confirms that PQ has induced liver damage in common carp.The results of this study showed that PQ-exposure caused oxidative stress and inflammation in the liver of common carp.Our results confirm that PQ has hepatotoxicity on common carp.The study further enriches and perfects the mechanism theory of PQ-hepatotoxicity to fish,which may be valuable for the risk assessment of PQ.