Effects And Mechanism Of Different DHA/EPA Ratios On Insulin Resistance In Mice

Objective:Insulin resistance(IR)is a one of the key factors in the development of chronic noncommunicable diseases.It has been suggested that both docosahexaenoic acid(DHA)and eicosapentaenoic acid(EPA)could improve IR,but their effects vary in many aspects.Besides,the effect of diary DHA and EPA with different ratios on IR remains unclear:Therefore,this study aimed to investigate the regulation effect of different DHA/EPA ratios on IR in mice to explore the optimal ratio.Meanwhile,the underling mechanism was inspected by testing the key molecular about insulin signaling pathway in adipose tissue.Material and Methods:A total of 108 male C57BL/6J mice were fed with high fat diet for 16 weeks to establish IR model and then the IR mice were randomly assigned into six groups,namely a high fat diet control(HFD)group and 5 DHA/EPA intervention groups with different ratios(3:1,1.5:1,1:1,1:1.5 and 1:3,respectively).Mice fed with basic diet were continued to be used as negative control(CON).All mice were fed for another 12 weeks.The food intake and body weight were measured weekly during the intervention period.After intervention,the glucose tolerance and insulin tolerance in mice were detected.The visceral adipose tissue and liver were weighed.The fasting serum glucose(FBG),serum insulin levels(FINS)were assayed and homeostasis model assessment of insulin resistance(HOMA-IR),insulin sensitive index(ISI)were calculated.Moreover,the serum lipid level,MDA content and SOD and GSH-Px activity were determined using the enzymatic kit,while the serum adipoectin and leptin level were detected by ELISA.The epididymal adipose tissue and liver were used for H&E staining.The GLUT4 translocation on epididymal adipocyte was detected by immunohistochemistry.The mRNA expression of adiponectin,leptin,UCP-1,FAS,ACC,HSL,ATGL,IRS-1,PI3K,AKT and GLUT4 in epididymal adipose tissue were detected by RT-PCR.The protein expression of IRS-1,PI3K,p-AKT(Ser473),AKT,GLUT4 and adiponectin epididymal adipose tissue were detected by Western Blot.Results:1、The insulin sensitivity were significantly impaired and the HOMA-IR was significantly increased in mice after high-fat diet for 16 weeks,suggesting successful establishment of IR model in mice.2、After intervention with different DHA/EPA ratios for IR mice,we found:(1)There was no significant difference in the food intake and body weight between the intervention groups and HDF group.The FBG and FINS levels of mice in the DHA/EPA intervention groups tended to decrease,but only the FBG in the 1.5:1 group was significantly lower than that of the HFD group.Moreover,the AUC value of intraperitoneal insulin tolerance test of mice in the 1.5:1 group was the lowest among DHA/EPA intervention groups.Except for the 1:1 group,HOMA-IR in other intervention groups dramatically decreased,especially in the 1.5:1 group.(2)Mice serum LDL-C level in all the intervention groups,especially the 1.5:1 group dramatically decrease.The levels of serum TG,TC,FFA and the content of visceral fat in mice were significantly decreased only in the 3:1,1:5:1 and 1:3 groups.A significantly reduction in adipocytes sizes was observed in different DHA/EPA ratios groups,except for the 1:1 group.The DHA/EPA ratio of 3:1 exerted the most positive effect in improving dyslipidemia,reducing fat accumulation and cell hypertrophy.The mRNA expressions of ACC in adipose tissue in the DHA/EPA intervention groups were decreased except for the 1:3 group,while the mRNA expressions of HSL and ATGL in the 1:1 and 1:1.5 groups were also significantly decreased.(3)The serum GSH-Px activity was significantly increased only in the 1:1 group.Except for the 1:1 group,the serum MDA level of the DHA/EPA intervention groups were significantly decreased,especially in the 1:3 group.(4)Compared to HFD group,the protein expression of adiponectin in mice were significantly increased after DHA/EPA intervention.Only the 1.5:1 group had signifcant up-regulation effect on the gene expression of adiponectin and the serum level of adiponectin.Although the mRNA expression and the serum levels of leptin in mice tended to decreased in all the intervention groups,statistical differences only occurred in the 3:1 and 1.5:1 groups when compared with the HFD group.(5)Only the 1.5:1 and 1:3 groups,especially the former,remarkablely up-regulated the IRS-1 mRNA level in mice.All the DHA/EPA intervention groups had a positive effect on the protein expression of IRS-1.The mRNA expression of PI3K was significantly increased only in the 1:1 group,but the corresponding protein expression was not significantly up-regulated.The AKT mRNA levels was significantly increased in the 1.5:1,1:1.5 and 1:3 groups,especially in the 1.5:1 group.The protein expressions of p-AKT and AKT tended to increase in all the intervention groups,but significant difference was observed only in the expression of p-AKT protein in the 1:3 group when compared to the HFD group.The GLUT4 membrane translocation in adipose tissue were significantly improved by DHA/EPA supplement with the ratio of 3:1,1.5:1 and 1:3,especially in the 3:1 group.Conclusions1、Different DHA/EPA ratios presented different effects on the regulation of glucose and lipid metabolism disorders,adipocytokine and oxidative stress in IR mice,and DHA/EPA supplement with the ratio of 1.5:1 exerted the most dramatic effect on increasing insulin sensitivity and improving insulin resistance.2、Different DHA/EPA ratios exerted different effects on IR in mice,which might be related to the up-regulation of the IRS-1/PI3K/AKT/GLUT4 expression in adipose tissue and the improvement of GLUT4 membrane translation.