Effects of ACE Inhibition on Myocardial Apoptosis in an Ischemia–Reperfusion Rat Heart Model

Abstract

Myocardial ischemia-reperfusion injury involves necrosis and apoptosis. The inhibition of angiotensin-converting enzyme (ACE) has been reported to suppress infarct size. In this study, it was investigated whether an ACE inhibitor affected myocardial apoptosis and apoptosis-related proteins in rats with experimental myocardial infarction. Anesthetized Sprague-Dawley rats were divided into four groups. Group I underwent 30 minutes of left coronary artery occlusion followed by 24 hours of reperfusion (control group); Group II underwent oral administration of the ACE inhibitor quinapril (10 mg/kg/day) before coronary occlusion (quinapril group); Group III underwent administration of the bradykinin B(2)-receptor antagonist Hoe 140 (250 microg/kg/day, subcutaneously) with quinapril (quinapril + Hoe 140 group); and Group IV underwent administration of Hoe 140 alone (Hoe 140 group). After reperfusion, myocardial infarct size was determined by triphenyltetrazolium chloride staining. Myocardial apoptosis was detected immunohistologically using terminal deoxynucleotidyl transferase-mediated nick end labeling staining and DNA electrophoresis. Myocardial caspase-3 activation was analyzed by Western blot and the expressions of Bcl-xL and Bax proteins were detected immunohistochemically. Quinapril significantly reduced the ratio of myocardial infarct size in the ischemic area at risk. In addition, quinapril significantly suppressed the incidence of apoptotic myocytes around the necrotic region (from 18.9 +/- 0.8% to 8.6 +/- 1.0%; P < 0.0001), the intensity of DNA ladder formation, and the activation of caspase-3. Hoe 140 attenuated these protective effects of quinapril. In the immunohistochemical study, Bax and Bcl-xL were expressed in myocytes, and ischemia-reperfusion abolished both proteins in the center region of ischemia. The Bax staining was equally observed among all groups. However, Bcl-xL staining remained in the ischemic area widely after quinapril treatment. In addition, Hoe 140 also depleted this effect of quinapril. These results suggest that inhibition of ACE reduces myocardial infarction and apoptosis via the bradykinin B(2) receptor in part. The antiapoptotic effect of the ACE inhibitor is attributed to the changing expression of Bcl-xL.

Aliskiren Reduces Myocardial Ischemia–Reperfusion Injury by a Bradykinin B 2 Receptor– and Angiotensin AT 2 Receptor–Mediated Mechanism

“…In contrast to the findings for the kidney by Siragy et al, 35 we found that PD123319 did not modify basal cardiac bradykinin levels nor prevent the aliskiren-induced increase in bradykinin levels. Our study demonstrates that B 2 receptor-mediated cardioprotection is dependent on a functional AT 2 receptor, although the exact nature of the interaction between the B 2 and AT 2 receptors remains to be determined (Figure 4).In contrast to the reduction in infarct size produced by short-term ACE inhibitor and ARB administration, [23][24][25][26][27][28][29] we and others 39 showed that short-term aliskiren administration did not produce cardioprotection, despite reduction in angiotensin peptide levels. Rather, a longer period of aliskiren administration, sufficient to increase tissue kallikrein protein and mRNA and bradykinin levels, 12 was required to produce cardioprotection.…”

“…In contrast to the reduction in infarct size produced by short-term ACE inhibitor and ARB administration, [23][24][25][26][27][28][29] we and others 39 showed that short-term aliskiren administration did not produce cardioprotection, despite reduction in angiotensin peptide levels. Rather, a longer period of aliskiren administration, sufficient to increase tissue kallikrein protein and mRNA and bradykinin levels, 12 was required to produce cardioprotection.…”

“…12 Bradykinin has well-established cardioprotective activity [13][14][15][16][17][18][19][20][21][22] and is implicated in the reduction of myocardial ischemiareperfusion (I/R) injury by both ACE inhibitors and ARBs. The bradykinin receptor type 2 (B 2 ) receptor antagonist icatibant prevents the reduction in I/R injury produced by ACE inhibitors, [23][24][25][26] whereas both icatibant and the angiotensin II receptor type 2 (AT 2 ) receptor antagonist PD123319 attenuate cardioprotection by ARBs. 25,[27][28][29] Our finding that aliskiren increases cardiac bradykinin levels 12 raised the possibility of cardioprotection, independent of any effect of aliskiren on renin.…”

Spironolactone Modulates Expressions of Cardiac Mineralocorticoid Receptor and 11.BETA.-Hydroxysteroid Dehydrogenase 2 and Prevents Ventricular Remodeling in Post-Infarct Rat Hearts

“…MI were produced as described previously ( 21 ). Briefly, male Sprague-Dawley rats weighing 220 to 240 g were anesthetized with intraperitoneal sodium pentobarbital (30 mg/kg body weight).…”

“…The terminal deoxynucleotide transferase-mediated dUTP nick end labeling (TUNEL) assay was performed to detect apoptotic cells (ApopTag kit, Chemicon International, Temecula, USA), as previously described ( 21 ). Myocytes were immunohistochemically stained with anti-myosin heavy chain antibody (CLA67/1; BD Transduction Laboratories, San Jose, USA) using Histofine Simple Stain MAX PO ® as a secondary antibody (Nichirei, Tokyo, Japan).…”