Subchronic Cadmium Exposure Up-regulates The MRNA Level Of Genes Associated To Hepatic Lipid Metabolism In Adult Female CD1 Mice

Backgrounds and ObjectivesCadmium is a persistent environmental and occupational pollutant,and the liver is one of the main organs of human cadmium accumulation.Cadmium exposure has a detrimental effect on the liver.Studies have shown that cadmium exposure is associated with liver lipid deposition and metabolic changes in adult male mice.However,it is still unknown whether cadmium exposure induced liver lipid accumulation and metabolic changes in female mice.The purpose of this study was to investigate the effects of subchronic cadmium exposure on glucose tolerance,insulin sensitivity,insulin resistance,liver lipid accumulation and related metabolic pathways in adult female CD1 mice.MethodsFemale CD1 mice（8 weeks old,26g-28g）were randomly assigned into three groups（20 animals each group）as follows.In the control group,mice were treated with 0 mg/L CdCl₂ in drinking water.In the Cd-treated groups,mice were treated with10 mg/L and 100 mg/L CdCl₂ respectively in drinking water.The animals were poisoned by water with free access to water and food.From the two week,the blood glucose of the tail tip was measured.After eight weeks of cadmium exposure,six mice were randomly selected for glucose tolerance test,and the insulin tolerance test was conducted after 4 days.After 9 weeks of cadmium exposure,4 mice were randomly selected from each group,two of which were directly killed and liver tissues were isolated.The other two mice were injected intraperitoneally with insulin（1 U/kg）and isolated the liver tissues 5 minutes later.The expression level of hepatic insulin signal related protein phosphorylation protein kinase B（pAKT）and protein kinase B（AKT）was detected with Western blotting.After 10 weeks of exposure to cadmium,the remaining mice were killed,and the serum and liver were retained.Part of the liver tissues were nitrified,the cadmium concentration in serum and the cadmium content of liver were detected with graphite furnace atomic absorption method.Serum levels of Triglycerides（TG）,Total cholesterol（TCHO）,High density lipoprotein（HDL）,Low density lipoprotein（LDL）and Very Low density lipoprotein（VLDL）content and Alanine aminotransferase（ALT）were detected by automatic biochemical analyzer.The mRNA levels of hepatic lipid metabolism related genes and glucose metabolism related genes detected by RT-PCR.The liver tissues were prepared with paraffin sections or frozen sections to detect lipid deposition in the liver,with H&E staining and oil red O staining,respectively.Results（1）In this study,cadmium exposure had no effect on the food intake and weight gain of CD1 female mice,but the amount of water in the Cd 100 mg/L group was significantly reduced.（2）The serum cadmium content increased significantly and the content of cadmium in the liver was also increased significantly.（3）Cadmium exposure did not cause elevated blood glucose,increased glucose tolerance,and reduced insulin sensitivity.On the contrary,the area under the curve of the glucose tolerance test in Cd 100 mg/L group was markedly reduced.（4）We also found that the expression levels of pAKT protein in the cadmium treatment groups were elevated to different degrees.The mRNA level of Irs-1 was elevated in Cd 100 mg/L group,but the level of Irs-2 mRNA was not affected.The mRNA level of Pepck,a gene in the downstream of the insulin signaling pathway,was elevated after cadmium exposure,while the mRNA level of G6pc was not affected（5）Cadmium exposure had no effect on the liver weight and liver/body weight.No significant fat vacuoles were observed by H&E staining.The results of oil red O staining showed a slight lipid deposition in the Cd 10 mg/L group,while the lipid deposition was not observed in the Cd 100mg/L group.（6）Cadmium exposure had no effect on the mRNA levels of Srebp-1 and Acc in lipid synthesis.The mRNA level of Fasn was elevated in Cd 10 mg/L group.Cadmium exposure increased the mRNA level of scd-1.Cadmium exposure had no effect on the mRNA levels of Pparγ,Apob and Mttp in hepatic lipid transport.In the Cd 100 mg/L group,the mRNA level of Cd36 was elevated.The mRNA levels of Fabp1 and Fabp4 were elevated after cadmium exposure.Cadmium exposure had no effect on Cpt1 and Lipe,two genes of lipid degradation related genes.In the Cd 10mg/L group,the mRNA level of Cyp4a10 was reduced.In the Cd 100 mg/L group,the mRNA level of Lpl was elevated.ConclusionsThe results of this study showed that cadmium exposure did not cause elevated blood glucose,increased glucose tolerance,and reduced insulin sensitivity and hepatic lipid deposition in the adult female CD1 mice.Cadmium exposure of different levels elevated the mRNA levels of hepatic lipid synthesis,lipid transport and lipid degradation related genes,which kept the hepatic lipid metabolism in a state of balance.