Influence Of Environmental Factors And Vitamins On Toxicity Of Polychlorinated Biphenyls On Eriocheir Sinensis

Polychlorinated biphenyls（PCBs）are a class of persistent and highly toxic organic pollutants,which spread throughout the aquatic system with a widely hazards to aquatic animals.Crustaceans such as shrimps and crabs are important economic species of aquatic animals facing the threat of PCBs.However,the studies of effects of PCBs on crustaceans are still weak.In this paper,the effects of polychlorinated biphenyls on crustaceans was studied systematically,by using the techniques of nutrition,physiology,biochemistry,molecular biology and cell biology.The influence of environmental factors on PCB-induced toxicity in crustaceans and the regulation of vitamin on PCBs in Eriocheir sinensis have been studied.The main results and conclusions of this paper are as follows:1.Toxicity of PCBs on Eriocheir sinensisThe toxicity of PCBs comes from I-phase detoxification metabolism controlled by cytochrome P450.In present study,to further understand the metabolic pathway of polychlorinated biphenyls in crustacean,we cloned two gene fragments in the P450family（CYP2E1 and CYP4C）.Then,a phylogenetic tree was constructed with NCBI blast and MEGA.It proved that the CYP2E1 and CYP4C were moderate homologous with those cloned from Portunus trituberculatus（95%,84%）.Megalopae were selected to study on the acute toxicity of PCBs,because the crabs in this period are susceptible to stress.The LC₅₀ of Aroclor 1254 after 48h,72h and 96h exposure in megalopae of Eriocheir sinensis were 3.19 mg L^-1,2.84 mg L^-1 and 2.22 Mg L^-1.In present research,the effects of PCBs on hemocytes,Megalopae and juvenile crabs of Eriocheir sinensis were studied.The result revealed that the toxicity of PCBs on crustaceans is attributed to ROS production,which is caused by the upregulation of CYP gene.In this process,the activities of antioxidant enzymes,including SOD and CAT,increased to respond the oxidative stress caused by ROS.Upregulation of CYP gene induced cell apoptosis of hemocytos of Eriocheir sinensis.And cell apoptosis induced the decline of immune function in Eriocheir sinensis.In addition,the gene expression of intracellular lipolytic enzyme was upregulated by PCBs,which would increase the decomposition of lipid droplets in hepatopancreas of Eriocheir sinensis,and affect the energy metabolism of crustaceans.These effects would lead to tissue damage,growth retardation and death of Eriocheir sinensis eventually.2.Effects of Environmental Factors on the Exposure Toxicity of PCBs in Eriocheir sinensisIn this study,all three environmental factors（salinity,pH and persistent organic pollutants）were found to affect the toxicity of PCB exposure.The main effect of salinity stress is that it reduces the activity of ERND and APND during high-concentration Aroclor 1254 exposure,which would reduce the remove of PCBs and eventually lead the growth disorders or death.In acidic environment,the activity of I phase and II phase detoxification enzymes decreased and the PCBs metabolism were reduced.Moreover,the pH stress also consumes the antioxidant enzymes what increased oxidative stress caused by PCBs.All there reslults indicated that the salinity,low-toxic substances and pH stress in the natural environment would influence the toxicity of PCBs.As a low-toxic substances of persistent organic pollutants,the polybrominated biphenyl（BDE-209）can neither induce the increase of the CYP expression nor induce a significant weight loss or death during PCBs exposure.However,as an endocrine disrupter,BDE 209 significantly inhibited the molting of megalopae by significantly upregulating molt-inhibiting hormones gene（MIH）.3.Effects of Dietary Vitamin Supplementation on the Toxicity of PCBs in Eriocheir sinensis.Vitamin E and vitamin A were selected as the supplement to study the effects of vitamins on the toxicity of PCBs in Eriocheir sinensis.The results after 8 weeks of culture showed that,a certain amount of dietary vitamin E and vitamin A significantly relieve the toxicity caused by PCBs exposure.vitamin E reduced the PCBs-induced toxicity in the animals by reducing the ROS levels.Vitamin A is not only involved in the antioxidant effect,but also regulate the peroxisome proliferators-activated receptors（PPAR）through the retinoic acid pathway.All the results indicated that addition of 100 mg kg^-1 vitamin E in the feed could relive the damage caused by PCBs exposure;240000 IU kg-1 dietary vitamin A would help promote the lipid accumulation while 80000 IU kg^-11 vitamin A is better for the toxicity relief in Eriocheir sinensis.