Effect Of Carvedilol On Toll-like Receptor4Signal And Cardiomyocytes Apoptosis In Rats After Acute Myocardial Infarction

Background＆Objective：Toll-like receptor4(TLR4), a class of pattern recognition receptors, has recentlyemerged key to inflammation and innate immunity, including innate immune responses,antigen presentation, and most importantly cytokine gene expression. ConventionalTLR4signaling recognizes ligands, activates nuclear factor-κB (NF-κB) pathway, andsufficiently trigger on inflammatory response. TLR4-NF-κB pathways is markedlyactivated in failing and ischemic myocardium, and is important in cardiac myocytesapoptosis.It is well known that cardiomyocyte apoptosis is an important event after acutemyocardial infarction (AMI) and may be responsible for a significant portion ofmyocyte death during the acute ischemic stage. The observation document reported thatapoptotic and necrotic myocyte cell death are independent contributing variables ofinfarct size, but apoptosis accounted for86%of the total loss of myocytes and necrosisfor only14%. The loss of cardiac myocytes is one of the mechanisms involved inMI-related heart failure, so inhibition of cardiomyocyte apoptosis after MI may improveleft ventricular (LV) remodeling and cardiac function.Carvedilol is a non-selective α1-and β-receptor blocker initially used in thetreatment of hypertension. Besides the effect of antihypertension, carvedilol was alreadydemonstrated to significantly reduce morbidity and mortality in heart failure andpost-AMI patients. The protective effects of carvedilol on the ischemic myocardiuminclude inhibition of apoptosis of cardiomyocytes in an experimental model ofischemia/reperfusion. Molecular mechanisms underlying carvedilol suppresses apoptosis have not beenwell explored. Whether TLR4signalling pathway was involved in the antiapoptoticeffect of carvedilol hadn’t been reported up to now. we hypothesized that part of theeffects are mediated through TLR4-mediated signaling.Methods:Forty-eight rats were randomized to the following groups before surgury:①sham-operated group (n=8),②MI group (n=10),③2mg/kg carvedilol-treatment group(n=10),④10mg/kg carvedilol-treatment group (n=10),⑤30mg/kg carvedilol-treatmentgroup (n=10). Sham and MI groups were given vehicle, and carvedilol groups receiveddifferent dose of carvedilol by direct gastric gavage for7days, respectively. In thefourth day of drug or vehicle administration, MI model was produced by ligating theleft anterior descending coronary artery. The sham-operated rats underwent the sameoperative procedure, but the suture was loosely tied to avoid coronary artery occlusion.On day4after MI, apoptosis was assessed by TUNEL assay, the levels of expression ofBax, Bcl-2, TLR4and NF-κB P50in infarcted myocardium were analyzed byimmunohistochemistry.Results:(1)The number of TUNEL-positive myocytes was approximately undetectable inSham, but significant increased in MI (p<0.05vs. Sham). In contrast to MI,carvedilol-treatment showed a significant reduction in the number of TUNEL-positivemyocyte nuclei (p<0.05vs. MI group).(2)The expression of Bax was higher in MIgroup than that in Sham group (p<0.05). Carvedilol-treatment could inhibit theincreased expression of Bax (p<0.05). The expression of Bcl-2was increased in MI,and three Car groups (p<0.05vs. Sham). But there was not statistical differencebetween MI and carvedilol-treatment groups. The ratio of Bax to Bcl-2was increased inMI group（1.57） compared with Sham group（0.89）, but decreased in carvedilol treatment groups (1.11for2mg/kg,1.00for10mg/kg and0.88for30mg/kg).(3)Theexpression of TLR4protein in MI group was obviously more than that in Sham groups(P<0.05vs. MI groups). Carvedilol-treatment could all decrease the excessiveexpression of TLR4protein induced by MI (P<0.05vs. MI group).(4)The expressionof NF-ΚB P50protein in MI group was obviously more than that in Sham groups(P<0.05vs. MI groups). Carvedilol treatment groups could inhibit NF-ΚB P50expression induced by MI (P<0.05), especially in Car30mg/kg group.Conclusion:Short term administration of carvedilol significantly inhibited cardiomyocyteapoptosis and decrease the ratio of a pro-apoptotic protein Bax to an anti-apoptoticprotein Bcl-2in infracted area probably via inhibiting the excessive expression of TLR4and NF-κB protein induced by myocardial infarction.