Effects Of Combined Exposure To Low Dose Cadmium And High-fat Diet On Bone Quality And Glucose-lipid Metabolism In Mice And Protective Role Of Vitamin D For The Effects

Objective:Dietary habits have been changed with the development of economy,and excessive energy intake leads to obesity and metabolic diseases.Obesity is a risk factor of glucose-lipid metabolism disorder.However,the relationship between obesity and bone quality is unclear.Recently,low dose cadmium exposure becomes widespread due to environmental pollution,the effects of low dose cadmium exposuer attract more and more attention.Low dose cadmium cloud cause bone loss,but its influences on glucose-lipid metabolism is still unclear.Vitamin D plays an important role inprevention and treatment of bone diseases.Recent studies show that vitamin D also plays an important role in glucose-lipid metabolism.Therefore,the study characterized effects of combined exposure to low dose cadmium and high-fat diet on bone quality and glucose-lipid metabolism in mice and further to explore the influences of vitamin D on these effects.Methods:The main work of this study includes three sections.(1)Effects of combined exposure to low dose cadmium and high-fat diet on bone quality in mice.Eight-week-old male SPF C57BL/6J mice were randomly divided into 8 groups:Normal control group(Con,N=7),low dose cadmium group(Cd,N=7),high-fat diet group(HFD,N=7),low dose vitamin D group(VD125,N=6),high dose vitamin D group(VD1000,N=6),high-fat diet plus low dose cadmium group(HFD+Cd,N=7),high-fat diet plus low dose cadmium with low dese vitamin D group(VD125+HFD+Cd,N=7),high-fat diet plus low dose cadmium with high dose vitamin D group(VD0000+HFD+Cd,N=7).Mice with low dose cadmium exposure were treated intraperitoneally with CdCl2(1.0 mg/kg body weight)two times per week for 20 weeks,and the exposure level of Cd was close to human environment exposure.Femurs,tibias and vertebraes were harvested with isolating soft tissues.The right femurs were scanned by Micro-CT,and left femurs was used to evaluate biomechanical strength by three points bending test.The levels of calcium,phosphorus and ALP in serum and the content of calcium,phosphorus and cadmium in left femurs were measured.The mRNA expression of OPG and RANKL were detected by RT-qPCR to investigate the mechanism in right tibias.(2)Effects of combined exposure to low dose cadmium and high-fat diet on glucose-lipid metabolism in mice.The experiment mice models were the same as mice in Part One.The body weight of mice was measured weekly.IPGTT and ITT were performed at 18th week and 19th week.Body length and abdominal circumference were recored after anaesthesia.The weight of white adipose tissue was recorded.White adipose tissue,pancreas and liver were performed HE staining.Liver was also performed oil red O staining,Masson staining and PAS staining.Serum biochemistry was measured with the automatic biochemistry analyzer.Serum insulin level was measured by ELISA.(3)Effects of vitamin D on toxicity of combined exposure to low dose cadmium and high-fat diet in mice.Mice were treated with intramuscular injection vitamin D once a week for 20 weeks.The tests of bone referred to Part One,and the tests of glucose-lipid metabolism referred to Part two.Results:(1)Effects of combined exposure to low dose cadmium and high-fat diet on bone quality in mice.The femur weight was significantly reduced in HFD+Cd group compared to others(p<0.01);there was no obvious difference in cortical BMD among each group.However,Ct.Th was significantly decreased in HFD+Cd group compared to control(p<0.01).The microstructure of cancellous bone was significantly damaged in HFD+Cd group compared to control.BMD,BV/TV,Conn.D and Tb.N were lower in HFD+Cd group compared to control.For SMI,Tb.Pf,Tb.Th and Tb.Sp,which significant increased in HFD+Cd group compared to control.Based on biomechanical analysis,femoral strength was decreased,being more brittle and less resistant to biomechanical forces in the HFD plus Cd mice.HFD plus Cd reduced the serum level ALP and Ca content in bone.HFD plus Cd mice had lower OPG mRNA expression and higher RANKL mRNA expression than others.(2)Effects of combined exposure to low dose cadmium and high-fat diet on glucose-lipid metabolism in mice.High-fat diet alone increased abdominal circumference of mice compared to control(p<0.05),others was no difference.Although low dose cadmium alone had no influence on weight on normal mice,body weight of HFD plus Cd mice was obviously lower than HFD mice(p<0.01).The weight of white adipose tissue was significantly increased in HFD mice compare to control.The weight of white adipose tissue of HFD+Cd mice significantly decreased compared to HFD mice(p<0.01),but which was higher than control mice(p<0.01).Low dose cadmium had no significant effects on glucose-lipid metabolism in normal mice,high-fat diet resulted in disorder of glucose-lipid metabolism.Low dose cadmium alleviated impaired glucose tolerance and insulin resistance in HFD mice.The AUC of IPGTT in HFD+Cd group was significantly lower than HFD group(p<0.05).Low dose cadmium decreased the lipid droplets in liver and significantly increased hepatic glycogen in mice fed with high-fat diet(p<0.01).Low dose cadmium alone led to structural disorders and light fibration in liver.(3)Effects of vitamin D on toxicity of combined exposure to low dose cadmium and high-fat diet in mice.Neither high nor low dose vitamin D affected the accumulation of cadmium in mice.High and low dose vitamin D had no effect on the length,weight,cortical and cancellous of femur in normal mice.After HFD+Cd mice were treated with high and low dose vitamin D,the femoral BMD was increased,the microstructure was ameliorated and the bone strength was increased by up-regular expression of OPG mRNA and down-regular RANKL mRNA.Vitamin D supplementation had significant effects on femur damage,and no difference exsited between high and low dose vitamin D.Neight high nor low dose vitamin D had effect on the body length,abdominal circumference,white adipose tissue,blood lipid levels,liver function and structure,IPGTT,ITT and serum insulin level in normal mice;After intervention with high and low dose vitamin D in HFD+Cd group,the disorder of glucose-lipid metabolism was ameliorated in mice,but the effects were not significant.There was no difference in the protective effect on disorder of glucose-lipid metabolism between high and low dose vitamin D.Conclusions:1.Combined exposure to low dose cadmium and high-fat diet aggravated bone damage by regulating the mRNA expression of RANKL/OPG in mice.2.Low dose cadmium ameliorated disorder of glucose-lipid metabolism resulted from high-fat diet,further studies are needed to clarify the underlying mechanisms.3.Vitamin D ameliorated bone damage and disorder of glucose-lipid metabolism resulted from combined exposure to low dose cadmium and high-fat diet.