Toxic Effects Of Long-term And Low-dose Exposure To Cadmium In Diabetic Mice

Objective:To investigate the toxic effects of long-term and low-dose exposure to cadmium in diabetic mice.Methods:This study included four parts:Firstly,we have established a mouse model with diabetes mellitus(DM).The mice were intraperitoneal injected with STZ solution(40 mg/kg body weight)for 5 days.Five days after the last injection,fasting plasma glucose was measured.The mice were defined as diabetic mice only if the concentrations of fasting plasma glucose were equal or greater than 11.1 mmol/L.Secondly,the effects of long-term and low-dose cadmium exposure on glucose/lipid metabolism in diabetic mice were evaluated.Diabetic mice were randomly divided into two groups:diabetic control(DM),diabetic mice treated with cadmium(DM+Cd).And the control mice were also divided into two groups:sham control(con)and cadmium control(Cd,1 mg/kg ip,twice a week).Each group contained 5 mice.Cd and DM+Cd group mice were intraperitoneal injected with CdCl2 for 24 weeks,con and DM group mice were injected with the same volume of saline.After 24 weeks injection,IPGTT(intraperitoneal glucose tolerance test)and EPITT(intraperitoneal insulin tolerance test)were performed and levels of fasting plasma glucose and insulin were detected.And then,HOMA-IR and HOMA-? were calculated.Finally,levels of plasma lipids were measured and the HE staining was carried out to observe the pathological changes of the islets in mice.Thirdly,effects of long-term and low-dose cadmium exposure on kidney in diabetic mice were determined.Twenty-four weeks later,all the mice were sacrificed.Weights of each organs were recorded and the ratio of organ were calculated.Levels of blood creatinine and urea nitrogen were detected by automatic biochemical analyzer.Then,pathological changes of renal were observed by H-E staining.The glomerular and mesangial areas and the renal fibrosis were finally detected by PAS staining and MT staining,respectively.Finally,effects of long-term and low-dose cadmium exposure on bone in diabetic mice were investigated.We separated the femurs and tibias from skeletal muscles and ligaments.Then,the wet weight of femurs and tibias was measured by analytical balance and the length of femurs and tibias was measured by Vernier caliper.The Micro-CT were used to analyze the bone mineral density,bone volume/tissue volume,trabecular number,trabecular thickness,trabecular separation and structure model index.Finally,changes in bone metabolism were determined by comparing the bone structure and morphology among different groups of mice.Results:(1)Twenty-four diabetic model mice was established in 44 mice,and the success rate was 55.6%.The body weight of diabetic model mice was significantly decreased as compared with the control mice.(2)Although significant decreases in plasma insulin were reported con mice with cadmium treatment were reported,we did not observed significant changes in fasting plasma glucose.As compared with the con mice,the islets atrophy in pancreas and the islet area in Cd mice was decreased.Long-term and low-dose cadmium exposure induced decreases in high density lipoprotein but increases in low density lipoprotein in mice.Significant decreases in fasting insulin level and fasting blood glucose were observed in diabetic mice treated with cadmium.Compared with the DM mice,the HOMA-IR decreased but the ? cell function index increased in DM+Cd mice.The number of islets in per pancreas and the area of islets were significantly increasing in DM+Cd mice.Moreover,long-term and low-dose cadmium exposure could significantly decrease levels of HDL(high density lipoprotein)but increase LDL(low density lipoprotein)in DM+Cd mice compared with DM mice.(3)Ratio of kidney weight and body weight was increased in Cd and DM mice as compared with con group mice.Cr in Cd mice and BUN in DM mice were increased.After HE and PAS staining,different degree of structural damages and renal tubular stenosis were observed in kidneys of Cd and DM group mice.Collage fibers were detected by MT staining in DM and Cd group mice.While,renal tubular stenosis and severe epithelial cells edema were observed in DM+Cd group mice.The pathological architecture damages in kidney were aggravated in DM+Cd mice as compared with DM mice.MT staining showed more collage fibers in DM+Cd mice compared with DM mice.Long-term and low-dose cadmium exposure could aggravated fibrosis lesions in renal tubules in diabetic mice.In all four groups of mice,more severe injury in renal tubular than in glomeruli were observed.(4)Compared with the con group,the tibia wet weights,tibial cancellous BV/TV and trabecular number decreased significantly in Cd group mice,Tibia bone mass loss,bone metabolism disorders were observed in Cd group mice.Similar changes in tibia cancellous were founded in both Cd group and DM group,and the bone metabolism disorders in tibia cancellous were observed in DM mice.Bone damages were exhibited in DM+Cd mice,however,long-tern and low-dose cadmium did not aggravate bone loss in diabetic eice.Compared with injuries in tibia,the injuries in femur were less obvious in all the groups.However,no significant injuries in femur and tibia cortical bone were obseved in four groups of mice.Conclusions:1,Long-term and low-dose cadmium exposLre could decrease levels of fasting insulin in normal mice but had no obviously effect in fasting blood glucose.Although no aggravation of glucose metabolism disorders was observed after long-term and low-dose cadmium exposure,decreases in high density lipoprotein cholesterol and increases in low density lipoprotein cholesterol were detected in diabetic mice.2,Long-tern and low-dose cadmium exposure could accelerate k:idney fibrosis and aggravate renal injury,especially in renal tubules,in diabetic mice.3,Long-term cadmium exposure with low-dose and diabetes mellitus could both induce bone loss in the mice tibia and lead to bone metabolism disorders.However,no significant pathological changes in femur bones were observed in diabetic mice after long-term and low-dose cadmium exposure.