Toxicokinetics As Well As The Damages Of Liver And Kidney In Cadmium-treated Freshwater Turtle Chinemys Reevesii

Cadmium in the aquatic ecosystem mainly comes from industrial activities such as mining,metallurgy,electroplating,leather manufacturing and agricultural activities such as pesticides and chemical fertilizers.Moreover,the pollution of cadmium in aquatic ecological environment is a serious challenge with the rapid development of industry and agriculture.In recent years,the pollution of heavy metal cadmium occurred frequently.Rice with elevated cadmium level,which was put to market,was reported.Serious cadmium pollution occurred in Longjiang River of Guangxi province,which casted threats to humans.There is an urgent need to find an ideal biological indicator to monitor the pollution of cadmium and other heavy metals in the water environment.Turtle chinemys reevesii is widely distributed in freshwater in China,which is sensitive to cadmium pollution.They are located on the upper layer of the food chain.Moreover,their omnivorous characteristic makes them easy to enrich cadmium and have a biomagnification effect on cadmium pollution.So they are ideal indicator organisms.In this context,in my Ph.D.study,I studied the toxicokinetics of cadmium in the turtles administrated by a single intraperitoneal injection of cadmium chloride,and investigated the toxicity of cadmium using various methods.In particular,the toxic effects of cadmium to the turtles' liver and kidney were examined at the levels of physiology,biochemistry,pathology and molecular biology.These results provided a theoretical basis for the turtle as an ideal environmental monitoring indicator organism.Therefore,my study has important scientific value.MethodsTurtles were exposed a single dose of 15mg/kg of cadmium chloride by intraperitoneal injection to study the toxicokinetics such as the absorption of cadmium,the distribution of cadmium in different tissues and organs,and the excretion of cadmium in different ways.Moreover,the dynamic changes ofthe activities of SOD,CAT,ALT,AST and the contents of GSH,MDA and TP in plasma were quantified.In order to investigate the effect of cadmium on the structure,ultrastructure,oxidative damage and the function of liver and kidney of turtles,the turtles weighing approximately 130±10 g were exposed to gradient cadmium(7.5 mg/kg,15 mg/kg,30 mg/kg)and 5 turtles were taken from each group after one week(1 w),two weeks(2 w)and three weeks(3 w)after the exposure.The entire lesion of liver and kidney was observed,and then the histological structure and ultrastructure of liver and kidney were examined with microscope and transmission electron microscope.Biochemical and molecular biological methods were used to show the cadmium-induced lipid peroxidation damages(such as the activities of SOD,CAT and the content of GSH,MDA)as well as the differential expression of related genes MT,SOD,CAT,Gpx and PNKP in liver of turtles.The indicators relating renal lipid peroxidation(such as the activities of SOD,CAT and the content of GSH,MDA)as well as renal impairment were analyzed.Results1.The results of toxicokinetics showed that cadmium injected i.p.was rapidly absorbed into the blood,which peaked at the third hour.The highest amount of cadmium was found in the liver,followed by the pancreas.There were different degrees of cadmium accumulations in spleen,kidney,intestine,lung,stomach,heart,brain and muscle.Cadmium in feces,urine,and bile was also found.There was a small amount of cadmium in the feces,while the level of cadmium in urine and bile was very low.The dynamic changes of SOD and CAT activities in the plasma of exposed turtles were significantly different from those in the control group.The activities of SOD in the plasma significantly decreased at 3 hour,1 week,2 week,and 4 week in the treated turtles,but significantly increased in 8 week.The activities of CAT in the plasma significantly increased at 3 hour,6 hour,12 hour,and 1 day in the treated turtles,but significantly decreased in 1 week,2 week,and 4 week.The GSH content fluctuated at a lower level than that in the control groupduring the whole experiment period,and the dynamic changes of MDA content significantly increased compared with that in the control during the entire experiment period.Compared with the control group,the ALT and AST activities in the plasma of the treated turtles showed significantly a trend of volatile increase.2.The liver from the treated turtles showed congestion,hepatomegaly and turned to yellowish in color.Under the microscope,turtles' liver cells had various degrees of swelling,degeneration and necrosis.Under electronic microscope,nucleus,mitochondria and rough endoplasmic reticulum presented various degrees of lesions in a dose-dependent manner.The nuclei of the hepatocytes were deformed.The nuclear membrane was missing and the chromosome edge sets were altered.The mitochondria of the cells were severely damaged and swollen;the membrane was missing or even disintegrated.The endoplasmic reticulums were swelling,twisting and breaking,with a large number of ribosome shedding.There was a significant increase of lipid droplets and lysosome,and the liver villus was lost.The activity of SOD and the contents of GSH in liver tissue increased at lower concentration of cadmium and then decreased when cadmium concentration was increased.The activity of CAT was decreased,while the content of MDA was increased.The expression level of mRNA of MT,SOD,CAT,Gpx4 and PNKP genes in turtle liver cells were detected at 2 weeks after cadmium exposure.The mRNA expression of MT and SOD gene in the treatment group of 30 mg/kg was significantly higher than that of the control group.3.The results showed that there were various degrees of congestion and darken color in the kidney in a dose-dependent manner.Under the microscope,in the 7.5mg/kg group and 15mg/kg group,some turtles' tubular cells showed various degrees of swelling,degeneration and vacuolization.In the 30mg/kg group,more serious morphological changes in vacuolization,severe degeneration and necrosis of the tubular cells appeared.The boundary of the renal tubular cells was blurred;glomerular congested and capsular space narrowed.Under transmission electron microscope,in the 7.5 mg/kgand 15 mg/kg groups,there were various degrees of increases in lipid droplets,irregular brush borders.Changes in mitochondria and endoplasmic reticulum in the kidney cells were noted.In the 30mg/kg group,the intercellular space of turtle kidney cells were widened;the mitochondria were swelling,lacking of film,the matrix density reduced,and even ruptured;rough endoplasmic reticulum expanded and distorted,and a large number of ribosomes fell off.Autolysosomes increased significantly,and the cell villi were broken or missing.The activities of SOD and CAT as well as the contents of GSH and MDA in the homogenate of kidney tissue of the turtles were altered.The results showed that the activity of SOD in kidney tissue increased first and then decreased,and it was in dose-dependent manner.However,the activity of CAT and the content of GSH were decreased in a dose-dependent manner.There was a significant dose-and time-dependent increase in MDA content.The contents of CRE and BUN in the plasma of the treated turtle increased in a dose-dependent manner.Conclusions1.Toxicokinetic studies showed that cadmium was absorbed rapidly into the blood,which peaked at the third of treatment.Liver and pancreas were the target organs for cadmium accumulation,and the feces might be the main route of cadmium excretion.Cadmium reduced the antioxidant capacity of the body and increased the number of lipid peroxidation products in plasma,which indicating that cadmium causes oxidative stress and damage.The increases in ALT,AST activities indicate that cadmium causes liver damages.2.The experimental results showed that there were changes in the histopathological and microstructure of liver,which occurred in dose–dependent manner.Cadmium induced lipid peroxidation damage of liver tissue in turtles.Cadmium had a significant effect on the mRNA expression of MT and SOD genes in liver tissue of turtles.Apparently,cadmium causes live damages.3.The experimental results showed that there were changes in the histopathological and microstructure of renal tissue,which occurred indose-dependent manner.Cadmium induced lipid peroxidation in the kindey tissue in turtles.Cadmium damaged the function of turtle's kidneys.It is suggested that cadmium causes structural and functional damages to the kidney.