| IntroductionInsulin resistance and insulin deficiency are major factors in the pathogenesis of type 2 diabetes,but the mechanism by which they occur is unknown.There has been a recent explosion of interest in the notion that chronic low-grade inflammation and activation of innate immune system are closely involved in the pathogenesis of type 2 diabetes.It says that many factors such as nutrition excess,age,smoking,inactivity,stress,genetics can activate markers of inflammation,which include immune cells,acute-phase protein as C-reactive protein,cytokine as TNF-α.Growing evidence show that inflammatory mediators can influence the sensitivity of insulin and the function ofβcell in pancreas through circulation or paracrine,furthermore cause insulin resistance and insulin deficiency,this eventually mediate incurrence of type 2 diabetes.These findings provide insights that anti-inflammatory agents may prevent the activation of inflammatory mediators and reduce the risk of developing type 2 diabetes.Recently Yuan et al hypothesized that salicylate may improve insulin resistance and protectβcell opposed to inhibition of cyclooxygenases,but the mechanism is still unclear.Our study aim at examining the influence of sodium salicylate on insulin sensitivity in lipid infusion rats and the mechanism.Methods(1) Infusion of saline,intralipid,intralipid +sodium salicylate for 7 hours in awake rats.(2) Hyperinsulinemic-euglycemic clamp in awake rats to estimate insulin resistance.(3) Plasma glucose was measured at the bedside with a Beckman Instruments Inc.BIOSEN5030,Germany.Plasma insulin and C-peptide were determined by RIA. We determined plasma concentration of cytokines,including IL-6,TNF-α,HsCRP and adiponectin using enzyme-linked immunosorbent assay.Plasma free fatty acids and MDA in liver,muscle and the activity of GSH-PX in liver and muscle were detected by colorimetric method.(4) NFκB in lipocytes,skelecton muscle cells and iNOS in hepatocytes,lipocytes,skelecton muscle cells were measured by immunhistochemistry methods.(5) We examined the gene expression of IL-6,TNF-α,SOCS-3 and adiponectin in liver,skelecton muscle,white adipose tissue by RT-PCR.(6) The levels of serine phosporylation of insulin receptor substrate 1 and insulin receptor substrate 1 in liver and skelecton muscle were detected by Western blotting.Results(1) Compared with SAL group,there was elevated plasma FFA levels by 2 times in 2h IH group while GIR decreased 27%,GIR decreased 52%in 5h IH group, GIR decreased 56%in rats with IH for 7h,GIR decreased 58%in 48h IH group, however there was no significant difference among 5h,7h and 48h IH group.(2) Infusion of sodium salicylate for 7 hours in rats can decrease plasma FFA levels gently.Compared with SAL group,there was decreased 30%in glucose,39% in insulin and 32%in C-peptide in rats with SI.During hyperinsulinemic-euglycemic clamp test,infusion of intralipid resulted in a 55% reduction in GIR,while Compared with IH group,GIR increased 1.3 times in rats with infusion of sodium salicylate.(3) Compared with SAL group,there were elevated plasma IL-6 levels by 1.2 times and were elevated plasma TNF-αlevels by 1.3 times,and HsCRP levels by 1.5 times,adiponectin levels by 1.3 times in IH group.The levels of IL-6,TNF-α,HsCRP in rats with infusion of sodium salicylate decreased 19%,20%,20% respectively compared with rats in IH group,however there was no significant difference in adiponectin levels between IH and SI group.(4) Compared with SAL group,NF-κB relative expression in lipocyte elevated nearly 1 time in SI group,sodium salicylate treatment resulted in a 35% reduction.There was no significant difference of NF-κB relative expression in skelecton muscle cell among three groups.(5) In white adipose tissue,inflammation cytokines including IL-6,SOCS-3,TNF-αgene expression increased 0.9,1.6 and 3 times respectively in IH group compared with SI group,infusion of sodium salicylate resulted in 30%,50%and 50% decrease.In skelecton muscle tissue,SOCS-3mRNA levels in IH group is 3.5 times compared with SAL group,There was no significant difference of IL-6 and TNF-αmRNA relative expression in skelecton muscle among three groups.In liver,the relative expression of IL-6,SOCS-3,TNF-αmRNA increased 1,1.9 and 1 times respectively in IH group compared with SI group,infusion of sodium,the relative expression ofIL-6,SOCS-3,TNF-αmRNA salicylate decrease 38%,40%and 50% respectively.(6) The levels of serine phosporylation of insulin receptor substrate 1 in liver and skelecton muscle increased 2.8 and 2 times in rats with IH compared with SAL group,sodium salicylate treatment resulted in 20%and 45%reduction,and there was no significant difference of insulin receptor substrate 1 in liver and skelecton muscle among three groups.(7) Compared with SAL group,there were elevated 2-4 times of MDA in plasma,liver,muscle and pancreas in rats with IH,and the activity of GSH-PX in liver,muscle and pancreas decreased 45%-50%.Compared with IH group,the levels of MDA in plasma,liver,muscle and pancreas decreased 62%-66%,the activity of GSH-PX increased 35-38%in rats with SI.Conclusion(1) The model of insulin resistance of lipotoxicity may be established after the concentration of FFA reached 3 times of basic level that induced by intravenously infused intralipid,and insulin resistance would keep steady until it reached some degree.(2) The elevation of FFA can cause a reduction of GIR,sodium salicylate treatment resulted in a increase of GIR,these data support the hypothesis that anti-inflammatory drug sodium salicylate can improve insulin resistance induced by intravenously infused intralipid.(3) The mechanism of insulin resistance induced by intravenously infused intralipid and the mechanism of sodium salicylate action:(4) There have been activation of NF-κB and downstream cytokine production in liver,skelecton muscle,white adipose tissue,which induced by intravenously infused intralipid.This cause the insulin resistance both locally and systemically,sodium salicylate can suppress the activation of NF-κB and downstream cytokine production in liver,skelecton muscle,white adipose tissue,at same time decrease the levels of inflammatory reactions systemically.(5) The increase of serine phosporylation of insulin receptor substrate 1 in liver and skelecton muscle which induced by intravenously infused intralipid result in the insulin resistance,sodium salicylate can decrease insulin resistance by reversing the elevation of the serine phosporylation of insulin receptor substrate 1 in liver and skelecton muscle(6) Oxidative stress may be one of the mechanisms of insulin resistance induced by elevation of FFA,and there were decrease of oxidative stress and insulin resistance in rats with sodium salicylate.Perhaps sodium salicylate improved insulin resistance and protectedβcell through decreasing oxidative stress in rats.
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