Alpha-1 antitrypsin inhibits caspase-1 and protects from acute myocardial ischemia–reperfusion injury

Abstract

Alpha-1-antitrypsin (AAT) possesses anti-inflammatory and tissue-protective properties. Here, we studied the effects of exogenously administered AAT on caspase-1 activity and on the outcome of ischemia–reperfusion injury (I/R) in a mouse model of acute myocardial infarction (AMI). Adult male mice underwent 30 min of coronary artery ligation followed by reperfusion and were randomly assigned to receive clinical-grade AAT or albumin at reperfusion. Infarct size was evaluated after 1 and 7 days. Caspase-1 activity was measured in homogenates of heart tissue. Left ventricular (LV) end-diastolic diameter (EDD) and end-systolic diameter (ESD) were measured and LV fractional shortening (FS) and ejection fraction (EF) were calculated using transthoracic echocardiography. The effect of AAT on caspase-1 activity was determined in cultures of mouse HL-1 cardiomyocytes stimulated with LPS and triggered with nigericin or when HL-1 cells were exposed to simulated ischemia. AAT-treated mice had significantly smaller infarct sizes (− 30% day 1 and − 55% day 7) compared with mice treated with albumin. AAT treatment resulted in > 90% reduction in caspase-1 activity in homogenates of hearts 24 h after I/R. Seven days after AMI, AAT-treated mice exhibited a > 90% smaller increase in LVEDD and LVESD and smaller reduction in LVEF. The increase in caspase-1 activity in HL-1 cells induced by LPS and nigericin or following exposure to simulated ischemia was reduced by > 80% and AAT similarly reduced cell death by > 50%. In conclusion, exogenous administration of clinical grade AAT reduces caspase-1 activity in the ischemic myocardium leading to preservation of viable myocardium and prevention of adverse cardiac remodeling.

Introduction

Acute myocardial infarction (AMI) and heart failure represent leading causes of mortality worldwide [1]. AMI is associated with an inflammatory response promoting cell death, cardiac dysfunction and heart failure [2]. Alpha-1-antitrypsin (AAT) is an abundant serine protease inhibitor circulating in health and increasing in most inflammatory diseases as an acute phase reactant [3]. Subjects with AAT deficiency are prone to emphysema thought to be due to unopposed elastase activity in the alveoli [3]. However, there are also data that suggest the cellular protective effect as well as the anti-inflammatory properties of AAT are independent of the serine protease inhibiting activity [4], [5], [6]. AAT plasma levels are increased in patients with AMI, reflecting a likely natural protective role of AAT in the tissue response to ischemic injury [7], [8]. Accordingly, human AAT given to mice during renal ischemia–reperfusion (I/R) injury lessened tissue injury and attenuated organ dysfunction [9]. Upon examination of renal tissues, it was found that AAT had significantly reduced caspase-1 activity[9]. Caspase-1 has indeed emerged as a key modulator of the inflammatory response to ischemia and tissue injury and participates in the amplification of the inflammatory response and promotion of cell death [10], [11]. Experimental studies in mice with genetic deletion of caspase-1 have identified caspase-1 inhibition as a potential target for intervention in AMI and heart failure (HF) [12], [13]. Here, we examine whether administration of clinical grade AAT to animals during experimental AMI at a clinically relevant time frame would inhibit caspase-1 activity and prevent cell death, thus limiting infarct size, cardiac enlargement and dysfunction.