The Research Of The Mechanism That Oxidative Stress Mediates Myocardiac Fibrosis In Diabetic Rats

Objective Diabetic cardiomyopathy is characterized by myocardial fibrosis. Oxidative stress has been demonstrated to contribute to such structural remodeling. The underlying mechanisms,however,remain to be elucidated.This study researches the mechanism by which oxidative stress mediates myocardiac fibrosis in diabetic rats.It also examines the effects of alpha lipoic acid(α-LA) which prevents the oxidative damage induced by hyperglycemia in experimental models.Methods 1.Diabetes was induced in Wistar rats by a single intravenous tail injection of streptozotocin(45mg/g body weight).2.Experimental animals were randomly divided into 3 groups:control,STZ and STZ+LA group.Diabetic rats in the STZ+LA group were treated withα-LA (100mg/kg) by intraperitoneal injection every day for 12 weeks.3.Plasma glucose,body weight,heart weight and heart weight to body weight ratio were assayed.LVESP,LVEDP,dp/dtmax and dp/dtmin were measured to assess LV function.4.The content of MDA in LV myocardium was assayed by thiobarbituric acid.5.LV total collagen,collagen typeâ… andâ…¢content were analyzed and quantified by digital image analysis.6.Population of myofibroblasts in LV was immunohistochemically assessed.7.Expression of procollagenα₂(â… ),procollagenα₁(â…¢),MMP-2,MMP-9,TIMP-2 and TGFβ₁,mRNA were determined by SQ-RT-PCR.8.TGFβ₁ and a-SMA protein levels were assayed by Western blot.9.Pro-MMP-2,active MMP-2 and pro-MMP-9 levels were analyzed by zymography.Results 1.The incidence of STZ-induced diabetes was 80%.2.STZ and STZ plus LA rats showed significantly increased plasma glucose levels and decrease in body weight compared with control group.The levels of body weight and plasma glucose showed no difference between STZ and STZ plus LA rats.The heart to body weight ratio in STZ and STZ plus LA groups were 1.17-fold and 1.74-fold increased versus controls,respectively.3.LV function:STZ rats showed significant impairment in LVESP,LVEDP, dp/dtmax and dp/dtmin,which were attenuated in the STZ plus LA rats.4.The content of MDA in STZ and STZ plus LA groups were 1.48-fold and 1.14-fold increased versus controls,respectively.The content of MDA in the STZ plus LA group was significantly lower than the STZ group.5.Total collagen,collagenâ… and Collagenâ…¢in the STZ group were 1.67-fold, 1.38-fold and 1.80-fold increased versus controls,respectively.They were 1.52-fold, 1.32-fold and 1.70-fold increased in the STZ plus LA group versus controls, respectively.α-LA treatment of STZ rats significantly reduced the deposition of collagen.A linear regression analysis showed a significant positive correlation between total collagen and MDA.6.Procollagenα₂(â… ) and procollagenα₁(â…¢) mRNA in the STZ group were 1.66-fold and 1.73-fold increased versus controls,respectively.Procollagenα₂(â… ) and procollagenα₁(â…¢) mRNA in the STZ group were 1.17-fold and 1.27-fold increased versus controls,respectively.α-LA treatment of STZ rats significantly reduced the synthesis of the two types of collagen.7.The content ofα-SMA in STZ and STZ plus LA groups were 1.26-fold and 1.09-fold increased versus controls,respectively.α-LA treatment of STZ rats significantly reduced the transformation of cardiac fibroblasts to myofibroblasts.8.TGFβ₁ mRNA in the STZ and STZ plus LA groups were 1.26-fold and 1.09-fold increased versus controls,respectively.The content of TGFβ₁ in the STZ and STZ plus LA groups were 2.28-fold and 1.85-fold increased versus controls,respectively.α-LA treatment significantly reduced TGFβ₁ in STZ rats.9.MMP-2 mRNA in the STZ and STZ plus LA groups were 2.08-fold and 1.67-fold reduced versus controls,respectively.Latent MMP-2 levels in the STZ and STZ plus LA groups were 1.25-fold and 1.09-fold reduced versus controls,respectively.Active MMP-2 in the STZ plus LA group was 2-fold decreased versus controls,whereas it was decreased to undetectable levels in the STZ group.MMP-9 mRNA in the STZ group was 1.17-fold increased versus controls.MMP-9 mRNA in the STZ plus LA group was similar to controls and significantly lower than the STZ group.Latent MMP-9 activity was similar in all three groups.10.TIMP-2 mRNA in the STZ and STZ plus LA groups was 2.14-fold and 1.27-fold increased versus controls,respectively.α-LA treatment of STZ rats significantly reduced the synthesis of TIMP-2.Conclusion Under STZ-diabetic conditions,cardiac fibrosis is associated with a dysregulation in extracellular matrix synthesis and degradation.Oxidative stress promotes the development of cardiac fibrosis by enhancing cardiac collagen synthesis and suppressing collagen degradation in diabetic rats.The antioxidantα-LA treatment can attenuate myocardiac fibrosis in diabetic rats.