Do angiotensin converting enzyme inhibitors limit myocardial infarct size?

Preconditioning the Myocardium: From Cellular Physiology to Clinical Cardiology

Yellon, Derek M., and James M. Downey. Preconditioning the Myocardium: From Cellular Physiology to Clinical Cardiology. Physiol Rev 83: 1113-1151, 2003; 10.1152/physrev.00009.2003.—The phenomenon of ischemic preconditioning, in which a period of sublethal ischemia can profoundly protect the cell from infarction during a subsequent ischemic insult, has been responsible for an enormous amount of research over the last 15 years. Ischemic preconditioning is associated with two forms of protection: a classical form lasting ∼2 h after the preconditioning ischemia followed a day later by a second window of protection lasting ∼3 days. Both types of preconditioning share similarities in that the preconditioning ischemia provokes the release of several autacoids that trigger protection by occupying cell surface receptors. Receptor occupancy activates complex signaling cascades which during the lethal ischemia converge on one or more end-effectors to mediate the protection. The end-effectors so far have eluded identification, although a number have been proposed. A range of different pharmacological agents that activate the signaling cascades at the various levels can mimic ischemic preconditioning leading to the hope that specific therapeutic agents can be designed to exploit the profound protection seen with ischemic preconditioning. This review examines, in detail, the complex mechanisms associated with both forms of preconditioning as well as discusses the possibility to exploit this phenomenon in the clinical setting. As our understanding of the mechanisms associated with preconditioning are unravelled, we believe we can look forward to the development of new therapeutic agents with novel mechanisms of action that can supplement current treatment options for patients threatened with acute myocardial infarction.

The kallikrein-kininogen-kinin system: lessons from the quantification of endogenous kinins

The purpose of the present review is to describe the place of endogenous kinins, mainly bradykinin (BK) and des-Arg(9)-BK in the kallikrein-kininogen-kinin system, to review and compare the different analytical methods reported for the assessment of endogenous kinins, to explain the difficulties and the pitfalls for their quantifications in biologic samples and finally to see how the results obtained by these methods could complement and extend the pharmacological evidence of their pathophysiological role.

Possible mechanism of cardioprotective effect of angiotensin preconditioning in isolated rat heart

The present study is designed to investigate the mechanism of cardioprotective effect of angiotensin II preconditioning. Isolated perfused rat heart was subjected to global ischaemia for 30 min followed by reperfusion for 120 min. Coronary effluent was analysed for lactate dehydrogenase and creatine kinase enzyme release to assess the degree of cardiac injury. Myocardial infarct size was estimated macroscopically using triphenyltetrazolium chloride staining. Four episodes of angiotensin II preconditioning markedly reduced lactate dehydrogenase and creatine kinase release in the coronary effluent and decreased myocardial infarct size. Administration of prazosin (alpha(1)-adrenoceptor antagonist) before global ischaemia reduced the extent of ischaemia-reperfusion-induced myocardial injury. Moreover, administration of prazosin during angiotensin II preconditioning or depletion of biogenic amines by reserpinisation (0.5 mg/kg i.p.) did not affect the cardioprotective effect of angiotensin II preconditioning. On the other hand, colchicine (5 mg/kg i.p.) or polymyxin B (50 microM) treatment markedly attenuated the cardioprotective effect of angiotensin II preconditioning. On the basis of these results, it may be concluded that the cardioprotective effects of angiotensin II preconditioning may be mediated through protein kinase C and may not involve release of norepinephrine or activation of alpha(1)-adrenoceptor.

Differential effects of long-term renin-angiotensin system blockade on limitation of infarct size in cholesterol-fed rabbits

We evaluated the effects of chronic inhibition of angiotensin-converting enzyme (ACE) or receptor blockade of angiotensin II type I on the size of myocardial infarcts induced by coronary occlusion-reperfusion in rabbits fed a high-cholesterol or normal diet for 10 weeks. In treated rabbits, myocardial infarction occurred 24 h after the last dose of enalapril or L-158809, an angiotensin II type I receptor antagonist, because of the drugs' waning effects on hemodynamic parameters. The size of the infarct was significantly larger in cholesterol-fed rabbits than in rabbits fed a normal diet. This augmentation of infarct size in cholesterol-fed rabbits was reversed by long-term treatment with enalapril, but not L-158809. The favorable effects of enalapril treatment disappeared after pretreatment with the bradykinin B(2) receptor blocker HOE 140. Long-term enalapril or L-158809 administration did not reduce the size of the infarct in rabbits fed a normal diet. ACE activity in ischemic myocardium significantly exceeded that in nonischemic myocardium and was further increased in cholesterol-fed rabbits, but was significantly reduced by long-term enalapril, but not L-158809. Moreover, treatment with enalapril, but not L-158809, restored acetylcholine-induced endothelium-dependent relaxation of aortic rings from cholesterol-fed rabbits. These results demonstrate that long-term ACE inhibition, but not angiotensin II type I receptor blockade, effectively reduces the size of myocardial infarcts in cholesterol-fed rabbits. The favorable effects of enalapril treatment may involve primarily a bradykinin B(2) receptor-mediated pathway.

Amelioration by quinapril of myocardial infarction induced by coronary occlusion/reperfusion in a rabbit model of atherosclerosis: possible mechanisms

BACKGROUND

The increased severity of the myocardial injury produced by coronary occlusion-reperfusion in models of atherosclerosis is associated with an increase in leukocyte accumulation in the ischemic myocardium. Expression of P-selectin, an adhesion molecule involved in the interaction between leukocytes and endothelium, is increased in atherosclerotic vessels. Long-term angiotensin-converting enzyme (ACE) inhibition has been shown to reduce atherosclerotic vascular change in experimental models.

METHODS AND RESULTS

We examined changes in the size of the infarct resulting from coronary occlusion/reperfusion in normally fed and cholesterol-fed rabbits that were chronically treated with quinapril. Infarct size was significantly larger in the cholesterol-fed versus normally fed rabbits. ACE activity in the ischemic and nonischemic myocardium was significantly reduced by quinapril. Chronic quinapril administration significantly ameliorated the increased myocardial injury in cholesterol-fed rabbits. Quinapril administration markedly increased the myocardial cGMP content and reduced the myeloperoxidase activity in the border region of the ischemic myocardium in cholesterol-fed rabbits. The enhanced expression of P-selectin in myocardial tissue of cholesterol-fed rabbits was also effectively reduced by quinapril treatment. The above effects of quinapril were eliminated by blockade of bradykinin B2 receptors or inhibition of nitric oxide synthesis.

CONCLUSIONS

Chronic quinapril treatment ameliorated the severity of myocardial injury produced by coronary occlusion/reperfusion in cholesterol-fed rabbits, possibly because of reversal of the enhanced interaction between leukocytes and endothelium in the ischemic myocardium via a bradykinin-related pathway.

Angiotensin-converting enzyme inhibitors potentiate preconditioning through bradykinin B2 receptor activation in human heart

OBJECTIVES

This study was designed to determine whether angiotensin-converting enzyme (ACE) inhibitors play a role in cardioprotection in a human model of preconditioning.

BACKGROUND

Recent studies have suggested that bradykinin may contribute to the protective effects of preconditioning in animal models. ACE inhibitors are known to inhibit the degradation of bradykinin and hence may be able to potentiate the effect of preconditioning.

METHODS

We examined the effects of the ACE inhibitors captopril and lisinopril in combination with a subthreshold preconditioning stimulus (i.e., insufficient to have any protective effects alone). Human atrial trabeculae were superfused with Krebs buffer and paced at 1 Hz. They were subjected to a full or subthreshold preconditioning stimulus consisting of either 3 or 1.5 min of simulated ischemia and 7 min of reoxygenation. In each instance, this stimulus was followed by 90 min of simulated ischemia and 2 h of reoxygenation. In addition, the subthreshold preconditioned group had 20 min of previous ACE inhibitor treatment.

RESULTS

Recovery of contractile function (percent of baseline) was 22 +/- 1% (mean +/- SEM) in the control group versus 61 +/- 1% in the preconditioned group. The subthreshold preconditioned group and the ACE inhibitor-alone groups did not exhibit any protection; however, in combination, the protection was significant (71 +/- 4% in the captopril group, 58 +/- 8% in the lisinopril group, p < 0.005) compared with the control group. There was no significant difference between these values and recovery after the full preconditioning stimulus. Furthermore, Hoe 140, a specific bradykinin B2 receptor antagonist, abolished the protection.

CONCLUSIONS

To our knowledge, these are the first results in human muscle to suggest that ACE inhibitors may augment ischemic preconditioning, possibly through B2 receptor activation.

Captopril potentiates the myocardial infarct size-limiting effect of ischemic preconditioning through bradykinin B2 receptor activation

OBJECTIVES

To investigate the role of kinin in preconditioning against infarction, the present study assessed the effect of captopril, a kininase II inhibitor, on preconditioning and arterial plasma kinin levels.

BACKGROUND

Recent studies suggest a possible contribution of kinin to preconditioning against infarction. However, its role and the site of kinin production remain uncharacterized.

METHODS

Six groups of rabbits (n = 6 to 13) underwent 30-min coronary occlusion and 3-h reperfusion. The infarct size and area at risk were determined by tetrazolium staining and fluorescent particles, respectively. Arterial blood was sampled under baseline conditions, before the 30-min ischemia and after reperfusion for radioimmunoassay of the kinin level.

RESULTS

Infarct size expressed as a percentage of area at risk (%IS/AR) was 42.9 +/- 2.9% (mean +/- SEM) in the control group, 34.5 +/- 3.3% in the group preconditioned with 2 min of ischemia/5 min of reperfusion and 41.7 +/- 5.1% in the group given captopril (1 mg/kg body weight) alone before the 30-min ischemia. These %IS/AR values were not significantly different between the three groups. However, a combination of captopril and subsequent preconditioning with 2 min of ischemia markedly limited %IS/AR to 21.2 +/- 2.4%. This potentiation of 2 min of preconditioning by captopril was not observed when 2 micrograms/kg body weight of Hoe 140, a specific bradykinin B2 receptor antagonist, was administered before preconditioning (%IS/AR = 41.2 +/- 5.7%), whereas Hoe 140 alone did not modify infarct size (%IS/AR = 38.5 +/- 5.1%). Arterial plasma kinin levels were comparable between the control rabbits, the group given captopril alone and the group that received captopril plus 2 min of preconditioning at baseline (3.8 +/- 1.0, 6.3 +/- 1.9 and 5.2 +/- 1.7 pg/ml, respectively), and there was no significant change in kinin levels after the captopril injection or the combination of captopril plus 2 min of preconditioning.

CONCLUSIONS

The present results indicate that captopril is capable of potentiating preconditioning without increasing the arterial kinin level and that the beneficial effect of captopril can be inhibited by Hoe 140. These findings support the hypothesis that kinin produced locally in the heart during preconditioning may contribute to the cardioprotective mechanism through bradykinin receptor activation.