Investigation Of The Protective Effects Of Recombined Human Neuregulin On Cardiac Muscle In Pacing-induced Heart Failure Of Rhesus Monkey And The Mechanisms Involved

Background Congestive hear failure (CHF) is a cardia insufficiency syndrome, caused by diverse cardiac diseases. The main mechanism is that the reduced contractile function of cardiac muscle can't provide enough blood flow to surpport the metabolism of whole body. So the main symptoms of CHF are due to insufficient blood flow in organs and tissues, and present severe congestion in pulmonary circulation and systemic circulation. CHF is the final symptom of many cardiac diseases, and attracts worldwide attention for its high mortality. Clinicians have taken efforts to discover new therapy and new medicine to improve the cardiac function and hypoxia situation of patients, which is also the ideal aim of pharmaceutical researchers. Neuregulins is a endothelia derived epidermal growth factor, a excitomotor of tyrosine protein kinase receptor family (ErBb). Many investigations have shown Neuregulins-ErbB signal system plays important roles in cardiac development and adaption of myocardium to pathological and physiological load and injure, and also is significant in CHF pathogenesis. Treatment of exogenous Neuregulins has been proved to be efficient way to improve CHF in rat model. So, carrying on researchs on the therapeutic effect of Neuregulins in primate model and investigating the possible mechanism will gain light on the molecular pathogenesis of CHF and benefit the exploitation novel drug for CHF.Objective To investigate the roles of neuregulin receptor ErbB₂ and protein kinase B (PKB) in Pacing-induced heart failure of rhesus monkey, to evaluate the effects of recombined human Neuregulin on contractibility of cardiac muscle in Pacing-induced heart failure of Rhesus Monkey and to clarify the possible mechanisms therein involved.Methods Twenty four rhesus monkeys were randomly divided into three groups (shame operated group,heart failure group and Neuregulin treated group), each with 8 monkeys. Heart failure were induced by rapid pacing(240 heartbeats/min). Neuregulin treated group received Neuregulin 3μg/kg intravenously for 10 days. Hemodynamic measurements such as the peak positive rate of change in left ventricular blood pressure (+ dP/dtmax) and Left ventricular systolic, end-diastolic blood pressures (LVSP and LVEDP, respectively) were performed. Ejection fraction was measured by echocardiogram. N-Terminal Pro-Brain Natriuretic Peptide (BNP), one of the most important molecular marker of heart failure, was also measured by the method of electrochemical luminescence immunoassay. The apoptosis of cardiac myocyte was observed by Tunel method. Using real-time quantitative RT-PCR was used to detect the expression of myosin heavy chain mRNA in left ventricular cardiac muscle.The mRNA expression of ErbB₂, PKB, Bcl-xl and Glut1 were detected in the left ventricular free walls by RT-PCR method. The expression of phospho-PKB and Bcl-xl on protein level was also detected by Western blotting.Results The contractibility of cardiac muscle was significantly decreased, which consisted with the increase of BNP after rapid pacing. Increase of the collagen fibers were found in heart failure group. Rapid pacing was shown to induce cardiac myocyte apoptosis in rhesus monkey. The mRNA expression of a-myosin heavy chain, ErbB2, PKB, Bcl-xl and Glut1 were depressed in heart failure group, and the similar results was also found in the protein expression analysis of phospho-PKB and Bcl-xl. However the contractibility of cardiac muscle was significantly increased with the decrease of BNP treated with 3μg·Kg^-1 Neuregulin. In addition, the levels of mean expression of a-myosin heavy chain and Glut1 mRNA in Neuregulin treated group were significantly higher than that in heart failure. The apoptotic index was obviously lower in Neuregulin treated group. It also showed increase of Bcl-xl and more activity of PKB in those animals treated with 3μg.Kg^-1 Neuregulin.Conelution1 The expression of ErbB2, PKB, Bcl-xl and Glut1 were down-regulated during heart failure in rhesus monkey which suggested the important roles of ErbB₂ receptor and PKB in the mechanism of heart failure. 2 Recombined human Neuregulin can enhance the contractibility of cardiac muscle, relieve the heart failure syndrome.3 Through reversing the falling of a-myosin heavy chain induced by rapid ventricular pacing, recombined human Neuregulin can enhance the contractibility of cardiac muscle.4 Neuregulin protects against pacing-induced apoptosis in heart failure of rhesus monkey and the mechanism might be attributed to its increase of the activity of PKB and Bcl-xl protein.5 The improved effect of neuregulin on cardiac function might be attributed to the increase of the glut1 expression.