Effects Of Liraglutide Combined With Metformin On Insulin Resistance And Thoracic Aorta Fibrosis In Diabetic Rats

Objective: To observe the effects of liraglutide combined with metformin on blood glucose,blood lipid and insulin resistance,and on thoracic aorta protection and it’s possible mechanism.Methods: Nine SPF grade SD male rats were randomly chosen as normal group(NG,distilled water 5 ml·kg-1·d-1 i.g.),and the remaining rats were made for the diabetic model,which was established by keeping on high sugar high fat diet and intraperitoneal injection with STZ(35mg/kg).Rats with fasting blood glucose(FBG)levels exceeding 11.1mmol/L were considered diabetic rats and randomly divided into diabetes mellitus group(DM,distilled water 5 ml·kg-1·d-1,i.g.),metformin group(Met,100 mg·kg-1·d-1,i.g.),liraglutide group(Lir,0.2 mg·kg-1·d-1,i.p.),liraglutide with metformin group(Lir+Met,0.1 mg·kg-1·d-1,i.p.+50 mg·kg-1·d-1,i.g.),and gliclazide with metformin group(Gli+Met,10 mg·kg-1·d-1+50 mg·kg-1·d-1,i.g.).Rat in all groups were lavaged or intraperitoneally injected with these dosages from 8:00 to 10:00 AM daily for 6 weeks.During treatment,body weight(BW)and FBG was measured and recorded every two weeks.After 6 weeks of treatment,rats were subjected to an oral glucose tolerance test(OGTT)and the values of area under curve(AUC)were calculated.Following collection of blood sample from abdominal aorta,triglyceride(TG),total cholesterol(TC),low density lipoprotein cholesterol(LDL-C),high density lipoprotein cholesterol(HDL-C),glycosylated hemoglobin(HbA1c)and fasting insulin(FINS)were measured and the extents of insulin resistance(IR)were calculated.The levels of tumor necrosis factor alpha(TNF-a),vascular endothelial growth factor(VEGF),and von willebrand factor(VWF)in serum were determined with commercially available kits.Histopathological injuries in rat thoracic aorta were observed by HE staining.The changes in rat thorax aortic collagen fibers were observed by Masson staining,and the collagen volume fraction(CVF)was calculated.Rat vascular permeability experiment was used to observe injuries in rat thoracic aorta.The mRNA expression of TNF-a,VEGF,and mitogen-activated protein kinase p38(P38MAPK)were determined by RT-PCR method.Results:(1)Compared with the normal group,body weight and high density lipoprotein cholesterol(HDL-C)decreased obviously(P<0.01)in diabetes mellitus group,while fasting blood glucose(FBG),fasting insulin(FINS),triglyceride(TG),total cholesterol(TC),low density lipoprotein cholesterol(LDL-C),glycosylated hemoglobin(HbA1c)increased obviously(P<0.01 or P<0.05),displaying obvious insulin resistance.The levels of TNF-a,VEGF,and VWF in serum increased(P<0.01 or P<0.05).HE staining displayed that the thoracic arteria intimal thickened,endothelial cells and smooth muscle disorganized,inflammatory substances disordered,showing obvious pathological injury.Masson staining displayed that collagen deposited,thoracic arteria thickened,and CVF increased obviously(P<0.01).The mRNA expression of TNF-α,VEGF,and P38 MAPK was increased.(2)Compared with rats in diabetes mellitus group,the body weight and HDL-C of the dosage group rats increased(P<0.01 or P<0.05),while FBG,FINS,TG,LDL-C,HbA1 c decreased(P<0.01 or P<0.05),displaying a decrease in insulin resistance(P<0.01 or P<0.05).The liraglutide with metformin group is better than the single metformin drug treatment group.The levels of TNF-a,VEGF,and VWF in serum decreased(P<0.01 or P<0.05),and those in the liraglutide with metformin group decreased more significantly(P<0.01 or P<0.05).HE staining displayed that the thoracic arteria intimal’s thickening,endothelial cells and smooth muscle’s disorganization,and inflammatory substances disorder have improved in different degrees,the pathological injuries were improved.The rats liraglutide with metformin group improved better than the single drug groups.Masson staining displayed collagen deposition,thoracic arteria thickening,and CVF decreased obviously in the dosage groups(P<0.01).The liraglutide with metformin treatment had the same effect on the CVF compared with the group gliclazide combined with metformin.The decreased m RNA expression of TNF-α,VEGF,and P38 MAPK was observed in liraglutide combined with metformin group.Conclusion:(1)Using liraglutide combined with metformin on diabetic model rats,which were induced by high-sugar high-fat and STZ,can decrease fasting blood glucose,improve the abnormal metabolism of serum lipids,reduce insulin levels in serum to improve insulin resistance,and has the better effect than single metformin drug treatment.(2)Using liraglutide combined with metformin on diabetic model rats can decrease the levels of TNF-a,VEGF,and VWF in serum,and has the better effect than single drug treatment.(3)Using liraglutide combined with metformin on diabetic model rats can decrease CVF,improve the thoracic arteria intimal pathological injury,and decrease levels of vascular fibrosis.The mechanism may be related to the down regulation of the expression of TNF-a,VEGF,and P38 MAPK.