Protective Effect Of Vitamin D On Glucose Metabolism Disorder Induced By Low Concentration Cadmium In Mice

Objective:To investigate the effects of long-term low concentration cadmium exposure on the function of pancreatic?cells and the effect of vitamin D on cadmium induced pancreatic?cells toxicity.Methods:1.The dose-response meta-analysis of urinary cadmium levels below the threshold limits and the risk of DM:A systematic literature search was conducted via PubMed,MEDLINE and the Cochrane Library to identify eligible studies published before December 2016.We combined odds ratio?OR?for the highest vs.lowest category of urinary cadmium level from each study.Dose-response relationship was assessed by restricted cubic spline model with three knots.2.Effects of vitamin D on pancreatic islet beta cell damage induced by low concentration of cadmium:Mouse NIT-1 cells were cultured in RPMI medium 1640supplemented with 10%fetal bovine serum?FBS?.Cdcl₂ was added into the culture medium with the final concentration of 0.05?M.1,25?OH?₂D₃ was added into the culture medium with the final concentration of 1nM.Enzyme linked immunosorbent assay?ELISA?was used to detect the insulin content in the supernatant of the culture medium.Flow cytometry was used to detect the intracellular reactive oxygen species?ROS?and the changes of insulin related genes were detected by real time Q-PCR.Western blotting was used to detect the insulin receptor substrate-1?IRS-1?and insulin receptor substrate-2?IRS-2?.3.Effects of vitamin D on mouse exposed to low dose of cadmium:?1?The cadmium accumulation experiment:10 mice were randomly divided into two groups,one group was injected with 2.5mg/kg Cdcl₂ via the caudal vein.After 48h,the mice were killed and the kidneys and pancreas were isolated.Using concentrated nitric acid to digest organs.Flame atomic absorption spectrometry?FAAS?was used for the determination of cadmium in solution.?2?15 mice were randomly divided into three groups.One group was given normal drinking water,and the other two groups were treated with Cdcl₂.CdCl2 was added to the drinking water to yield 162.5 ppm Cd,and this water was then continuously provided to the mice until the end of the study.A cadmium exposure group was randomly selected,followed by intramuscular injection of vitamin D₃?1000 IU/w?.The body weight was measured every week.After eighth weeks of intervention,fasting serum glucose was measured weekly.After 16 weeks of intervention,the body weight,organ coefficient,bone wet weight and blood biochemical parameters were measured.The serum insulin was detected by ELISA.The content of ROS in pancreatic tissue was detected,and the pathological sections of mouse pancreas were analyzed.Results:1.The meta-analysis included 6 studies of 28402 participants from Europe,North America and Asia.The result showed that there is positive significant association between urine cadmium level and risk of DM?OR=1.24;95%CI,1.03-1.49?.The dose-response analysis results showed a significant correlation between urinary cadmium levels and DM risk when urinary cadmium was greater than 1.16?g/g creatinine.2.We used CCK-8 method to select a Cdcl₂ concentration?0.05?M?which had no significant effect on cell viability.1?,25?OH?₂D₃ concentrations?1nM?were also selected to reduce the toxicity of cadmium.The ability of NIT-1 cells to secrete insulin was measured.The results showed that the insulin secretion of NIT-1 cells increased at the first 4 days of low concentration of cadmium exposure?P<0.05?.With the increase of cadmium exposure time,the insulin secretion of NIT-1 cells decreased?P<0.05?.However,1?,25?OH?₂D₃ intervention increased the insulin secretion?P<0.05?of cadmium exposed cells.At the transcriptional level,long-term low concentration cadmium exposure did not significantly change the expression of insulin gene.Long term low concentration cadmium exposure can significantly increase the ROS content in NIT-1 cells?P<0.001?.The intervention of 1?,25?OH?₂D₃ can reduce the content of ROS?P<0.001?in cadmium treated cells.At the protein level,low concentration of cadmium exposure could decrease the expression of IRS-1 in NIT-1 cells?P<0.05?.3.Cadmium accumulation experiment showed that compared with the control group,the volume of cadmium in kidney and pancreas of Cdcl₂ group was significantly higher than that of control group?P<0.05?.Among them,the cadmium accumulation in the pancreas was less than that in the kidney.In the experiment of cadmium exposure in drinking water,the body weight and fasting blood glucose did not change significantly during the whole experiment.Compared with the control group,the levels of fasting insulin in the mice exposed to cadmium increased,the pancreatic beta cell function index decreased significantly,and the level of active oxygen in the pancreas increased significantly.Pathological examination showed that,compared with the control group,the islet cells in the cadmium exposed group were bundle and narrow,and the volume became larger.Compared with the cadmium exposure group,the islet cells of mice exposed to cadmium which were injected with vitamin D₃,is in a regular shape or oval shape.Conclusion:1.This meta-analysis indicates that urine cadmium is significantly associated with an increased risk of DM,and urinary cadmium may lead to DM at a low level.2.Early exposure to low concentrations of cadmium led to an increase in insulin secretion in pancreatic beta cells,and insulin secretion decreased as the cadmium exposure time prolonged.1?,25?OH?₂D₃ intervention has an impact on this change.Low dose of cadmium exposure increased the level of serum insulin in mice,resulting in an increase in the size of pancreatic beta cells.And long-term vitamin D₃ intervention might be helpful to improve the cadmium induced islet beta cell injury in mice.