Study Of The Effect And Mechanisms Of Atorvastatin On Gap Junction Remodelling In Hypertrophic Myocardium

Cardiac hypertrophy is an adaptive response of the heart to pressure overload, prolonged cardiac hypertrophy may result in cardiac dysfunction leading to subsequent cardio- vascular events, such as congestive heart failure and sudden death. The molecular response to pressure overload is complex and may include modulation of various intracellular signal pathways, such as activation of many protein kinases (mitogen-activated protein kinase and phosphatidylinositol-3 kinase), expression of cardiac fetal genes (atrial natriuretic factor), and increase of protein synthesis. Furthermore, pressure overload leads to the release of secretion and production of vasoactive peptides, such as angiotensin II and endothelin-1, which play pivotal roles in the induction of these hypertrophic responses. A characteristic consequence of hypertrophic remodeling as a result of pathological stress is the increased risk for fatal ventricular arrhythmias. One of these changes is the remodeling of myocardial gap junctions, which provide for electrical coupling of adjacent cardiomyocytes. The predominant isoform in the ventricles is connexin 43 (Cx43). A derangement in the intercellular electrical coupling and expression and distribution of connexins may have profound effects on cardiac electrophysiology and arrhythmogenesis. Furthermore, disruption of the side-to-side cell connections in hypertrophy by interstitial fibrosis, for instance, has been shown to impair cellular impulse propagation. Study suggested that agents with the regression of ventricular hypertrophy have been shown to decrease the susceptibility of ventricular arrhythmias.The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or"statins", are agents that inhibit the rate-limiting enzyme of cholesterol synthesis in the liver, thereby decreasing the hepatic production of cholesterol, increasing the expression of low-density lipoprotein (LDL) receptors, and lowering the circulating levels of LDL cholesterol. Although it is widely accepted that the majority of clinical benefitobtained with statins is a direct result of their lipid-lowering properties, these agents appear to display additional cholesterol-independent or "pleiotropic" effects on -various aspects of cardiovascular disease. Strong experimental evidence and some recent clinical studies indicate that statins can prevent cardiac hypertrophy, irrespective of serum cholesterol levels. Meanwhile, it was suggested that statins have direct or indirect antiarrhythmic effects in large scale clinical lipid-lowering trials and some experimental study, irrespective of serum cholesterol levels. So we hypothesize that statins can improve the gap junction remodeling in hypertrophic myocardium for its inhibition to cardiac hypertrophy. Now we illustrate this question in three parts as follows:Part I Effect of Atorvastatin on Cardiac Hypertrophy Induced by Pressure-overloadObjective: To investigate the effect and possible mechanism of atorvastatin on cardiac hypertrophy induced by pressure-overload.Methods: Thirty male SD rats were divided into three groups randomly: ① abdominal aortic constriction(AC) group; ②abdominal aortic constriction + atorvastatin group(AA); ③sham operation(SO) group. With abdominal aortic constriction operation make cardiac hypertrophy model. To measure the thickness of left ventricular wall with echocardiography and cardiac tissue collagen type I and III with immunohistochemistry, and measure plasma cholesterol levels by automated method.Results: Left ventricular mass index (LVMI) of AC group was higher than SO group's (2.60±0.37 vs 2.05 ± 0.08, P<0.01), while LVMI of AA group was 2.21 ± 0.14, lower than AC group's (P<0.05). The level of collagen type I and collagen type III of A group was higher than SO group's markedly (2.45 ± 0.36 vs 0.50 ± 0.06, 0.82 ± 0.10 vs 0.37 ± 0.03, P< 0.01), while that of the AA group was 1.20 ± 0.10 and 0.47 ± 0.06 respectively, lower than AC group's (P<0.01). The plasma cholesterol levels did not differ among of the three groups (P>0.05).Conclusion: Atorvastatin can inhibit cardiac hypertrophy induced by pressureoverload and prevent myocardial fibrosis. And the data indicate the non-lipid effect of statin on cardiac hypertrophy.Part II Effect of Atorvastatin on the Change of Extracellular Signal-regulated Kinase in CardiacHypertrophyObjective: To investigate the effect of atorvastatin on the extracellular signal-regulated kinase (ERK) in cardiac hypertrophy and the possible mechanism.Methods: Twenty-four male SD rats were divided into three groups randomly: ①abdominal aortic constriction(AC) group; ②abdominal aortic constriction + atorvastatin group(AA);③sham operation(SO) group. With abdominal aortic constriction operation make cardiac hypertrophy model. To measure the levels of plasma and cardiac tissue angiotensin II (Ang II), endothelin-1(ET-1) by radioimmunoassay, and ERK content with immunoblotting techniques.Results: The level of plasma Ang II and ET-1 of AC group was higher than SO group's markedly, while that of the AA group was lower than AC group's (P<0.01or P<0.05). The level of myocardial Ang II and ET-1 of AC group was higher than SO group's markedly, while that of the AA group was lower than AC group's (P<0.01). There was no statistical difference in the amount of total ERK among of the three groups (P>0.05), but the content of phospho-ERK of AC group was higher than SO group's and the phosphor-ERK content of AA group was lower than AC group's (P<0.05).Conclusion: Ang II and ET-1 may be contribute to cardiac hypertrophy through ERK pathway. Atorvastatin can inhibit this pathway to prevent cardiac hypertrophyPart III Effect of Atorvastatin on Gap Junction Remodelling in Hypertrophic MyocardiumObjective: To investigate the effect of atorvastatin on gap junction remodeling in hypertrophied myocardium induced by pressure-overload.Methods: Twenty-four male SD rats were divided into three groups randomly:①abdominal aortic constriction(AC) group; ②abdominal aortic constriction + atorvastatin group(AA); ③sham operation(SO) group. With abdominal aortic -constriction operation make cardiac hypertrophy model. The change of connexin43 was observed with immunohistochemistry and western blotting techniques.Results: In contrast to SO group, which showed connexin 43 distributed regularly, ventricular myocardium from AC group, showed that the distribution of connexin 43 was markedly disorganized. Compared with AC group, the disorganization of connexin 43 was improved in AA group. There was no statistical difference in the amount of connexin43 among of the three groups (P>0.05).Conclusion: Atorvastatin can prevent partly gap junction remodeling of hypertrophied myocardium induced by pressure-overload.