| Background: With the changes in human diet and lifestyle,the prevalence of metabolic diseases such as diabetes has increased dramatically,which seriously threatens human physical and mental health.Microvascular and macrovascular complications caused by diabetes are the main reasons for the high incidence and mortality of diabetes.Studies have found that vascular endothelial dysfunction is the initiating factor for diabetic vascular disease and is closely related to the pathogenesis of vascular complications in diabetes.Fenofibrate is a classic cholesterol-lowering drug.In recent years,large-scale clinical trials have found that fenofibrate can reduce vascular complications of diabetic patients.Studies have found that the vascular protection effect of fenofibrate on diabetes may be independent of its lipid-lowering effect,but the specific mechanism of the protection is not completely clear.Objective: This study was aimed to investigate whether fenofibrate can improve vascular function in diabetic mice and to understand the protective mechanism of fenofibrate in vascular function of diabetic mice.Materials and methods: 1.In this experiment,C57BL/6 mice were intraperitoneally injected with streptozotocin(STZ,50 mg/kg/d)for five consecutive days to induce a mouse model of diabetes.The control group was injected with an equal volume of citrate-sodium citrate solution.Fenofibrate(100 mg/kg/d)was administered intragastrically to mice for eight weeks.The control group was given an equal volume of sodium carboxymethyl cellulose solution.The mice were random Ly divided into four groups: control group,fenofibrate-treated control group,diabetic group,and fenofibrate-treated diabetic group.2.Renal afferent arterioles were isolated from the four groups and the micro-perfusion technique was used to study the response and tension changes of the arterioles to acetylcholine and compare the differences of vascular function among the four groups.3.Aorta were isolated from the four groups,and a wire myograph system(model 620 M,Danish Myo Technology)was used to measure the aortic vascular tone to vasoactive drugs and compare the differences of vascular function in the four groups.4.Serum urea,creatinine,renal injury factor-1,neutrophil gelatinase-associated lipocalin were measured by enzyme-linked immunosorbent assay(ELISA)to compare renal function among the four groups.5.Total nitric oxide(NO)levels in the aorta and serum of the four groups were measured by a nitric oxide detection kit.6.Levels of superoxide dismutase,catalase and hydrogen peroxide in the aortic tissue were measured by special kits to compare the differences of oxidative stress in the four groups.7.Serum prostaglandin E2 and thromboxane A2 levels were measured by ELISA kit in four groups.8.The protein of aorta was extracted with RIPA protein lysis solution contained protease inhibitor.The protein concentration was determined by BCA method.The relative expression of PPARα,p-LKB1/LKB1,p-AMPK/AMPK,p-e NOS/e NOS,NF-κB and COX-2 was detected by western blot.9.Aorta were isolated from the four groups,incubated with e NOS antagonist,PPARα agonist or antagonist,AMPK agonist or antagonist,peroxidase dismutase analogues or COX-2 andantagonist,then a wire myograph system was used to measure the aortic vascular tone and compare the differences of vascular function in the four groups.10.Aorta of normal mice were incubated with a physiological salt solution containing normal glucose medium(11.5 mmol/L)or high glucose medium(44 mmol/L),with or without fenofibrate pre-incubation,then a wire myograph system was used to measure the aortic vascular tone to vasoactive drugs and compare the differences of vascular function among different treatment groups.Result: 1.Body weights of mice were markedly lower and blood glucose levels were higher in the diabetic mice compared with the control mice.Fenofibrate treatment did not affect body weights or blood glucose in diabetic mice.2.Eight-week fenofibrate treatment significantly improved endothelium-dependent relaxation by acetylcholine in diabetic aortas without affecting responses in control mice.3.Endothelium-independent relaxation by the NO donor sodium nitroprusside was similar in all four groups.4.Fenofibrate administration markedly improved endothelium-dependent relaxation in renal afferent arteriole without affecting responses in control mice.5.Compared with the control group,levels of NO in the serum and aorta were significantly lower in diabetic mice,and this change was prevented with treatment of fenofibrate.6.Diabetes-associated oxidative stress and renal injury were inhibited by fenofibrate treatment.7.Compared with the control group,the levels of vasoconstriction substances,namely prostaglandin E2 and thromboxane A2,were significantly increased in the serum of diabetic mice,and this change was prevented with treatment of fenofibrate.8.Western blots showed that protein expression of PPARα,p-AMPK,p-LKB1,and p-e NOS phosphorylation were decreased in diabetic mice,whereas fenofibrate treatment upregulated them.9.Western blots showed that protein expression of NF-κB and COX-2 were increased in diabetic mice,whereas fenofibrate treatment reduced them.10.Protective effect of fenofibrate on vascular relaxation was abolished by incubation with antagonist of e NOS,PPARα or AMPK.11.Incubation with the PPARα agonist,AMPK agonist or permeable superoxide mimetic tempol all increased the vasodilatory response to acetylcholine in vehicle-treated diabetic mice.12.Incubation with the COX-2 antagonist or permeable superoxide mimetic tempol both improved the vasoconstriction response in vehicle-treated diabetic mice.13.Compared with normal concentrations of glucose,the vasodilation was markedly impaired and the contractile responses were increased in aortas incubated with hyperglycemic concentrations,while incubation with fenofibrate improved vascular relaxation and constriction under high glucose concentration.Conclusion: 1.Fenofibrate could improve vascular endothelial dysfunction in diabetic mice,mainly by balancing endothelium-dependent relaxation and contractility in diabetes mellitus.2.The effect of fenofibrate on increasing endothelium-dependent relaxation in diabetic mice was via activating the PPARα/LKB1/AMPK/e NOS pathway,thus increasing endogenous NO generation and preventing oxidative stress.3.Protective effect of fenofibrate on contractile responses were related to the inhibition of NF-κB/COX-2 pathway and thus suppressing vasoconstrictor prostaglandin and oxidative stress. |
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