Attenuation of reperfusion arrhythmias by selective inhibition of angiotensin-converting enzyme/kininase II in the ischemic zone: mediated by endogenous bradykinin?

Extracellular and intracellular proteases in cardiac dysfunction due to ischemia-reperfusion injury

Various procedures such as angioplasty, thrombolytic therapy, coronary bypass surgery, and cardiac transplantation are invariably associated with ischemia-reperfusion (I/R) injury. Impaired recovery of cardiac function due to I/R injury is considered to be a consequence of the occurrence of both oxidative stress and intracellular Ca(2+)-overload in the myocardium. These changes in the ischemic myocardium appear to activate both extracellular and intracellular proteases which are responsible for the cleavage of extracellular matrix and subcellular structures involved in the maintenance of cardiac function. It is thus intended to discuss the actions of I/R injury on several proteases, with a focus on calpain, matrix metalloproteinases, and cathepsins as well as their role in inducing alterations both inside and outside the cardiomyocytes. In addition, modifications of subcellular organelles such as myofibrils, sarcoplasmic reticulum and sarcolemma as well as extracellular matrix, and the potential regulatory effects of endogenous inhibitors on protease activities are identified. Both extracellular and intracellular proteolytic activities appear to be imperative in determining the true extent of I/R injury and their inhibition seems to be of critical importance for improving the recovery of cardiac function. Thus, both extracellular and intracellular proteases may serve as potential targets for the development of cardioprotective interventions for reducing damage to the heart and retarding the development of contractile dysfunction caused by I/R injury.

Reperfusion-induced arrhythmias are suppressed by inhibition of the angiotensin II type 1 receptor

We examined antiarrhythmic effects of drugs, including renin-angiotensin system (RAS) inhibitors, on reperfusion arrhythmias in rats in vivo. Anesthetized rats were subjected to 5 min of coronary occlusion and 30 min of reperfusion. Arrhythmia scores, calculated as the product of the type of arrhythmia (1 for ventricular tachycardia, 2 for ventricular fibrillation) and its duration (in seconds), were adopted to evaluate the severity of arrhythmias. Reperfusion arrhythmias were suppressed by Na(+)/H(+) exchange inhibitor, Na(+)/Ca(2+) exchange inhibitor and L-type Ca channel antagonist by more than 90%. Angiotensin-converting enzyme inhibitor and angiotensin II (Ang II) type 1 receptor (AT(1)) antagonist also modestly (by 60-70%) but significantly decreased reperfusion arrhythmias. These effects were not reversed by co-administration of bradykinin B(2) receptor antagonist or AT(2) antagonist, respectively. Effects of superoxide dismutase (SOD) were also examined, but SOD proved ineffective. Effects of Na(+)/H(+) exchange inhibitor, Na(+)/Ca(2+) exchange inhibitor and L-type Ca channel antagonist suggest a causative relationship of Ca overload in reperfusion arrhythmias. These transport systems are known to be activated by Ang II. Thus, the antiarrhythmic action of RAS inhibitors might be attributable to the inhibition of the action of Ang II via AT(1).

Impact of myocardial angiotensin-converting enzyme activity on coronary vascular resistance and serum brain natriuretic peptide concentration in coronary bypass surgery

Angiotensin-converting enzyme (ACE) inhibitors have cardioprotective effects in animals, but whether that occurs in humans is still controversial. The effect of myocardial ACE activity on coronary vascular resistance during coronary artery bypass surgery and on serum brain natriuretic peptide (BNP) concentration after surgery was studied in myocardial tissue sampled from the right atrium of patients during cardiac surgery (n=20). Tissue enzyme activity (nmol/min per mg protein) was measured using a photometric technique, and the flow rate and pressure upon antegrade infusion of a crystalloid cardioplegic solution was measured for calculating the coronary vascular resistance (mmHg. ml(-1). min(-1)). Serum BNP concentration (pg/ml) was measured on days 0 and 5 after the surgery. Linear regression between tissue ACE activity and coronary vascular resistance (y = 0.46x + 0.56, r=0.85) as well as serum BNP concentration on days 0 (y = 129x + 30, r=0.59) and 5 (y = 347x + 180, r=0.73) after the surgery was significant (x: ACE activity; y: coronary vascular resistance/serum BNP concentration). The results indicate that inhibition of myocardial ACE activity might improve coronary circulation during surgery and hence, cardiac function after surgery.

Inhibition of angiotensin-converting enzyme reduces susceptibility of hypertrophied rat myocardium to ventricular fibrillation

Left ventricular (LV) hypertrophy increases susceptibility to reperfusion arrhythmias and the angiotensin-converting enzyme inhibitor, ramipril, may reduce that susceptibility via regression of LV hypertrophy. Rats (n=12 per group) were subjected to abdominal aortic constriction (AC) or sham-operation (SH) and from 3 to 6 weeks after surgery, 3 AC groups received ramipril (0.01, 0.1, or 1 mg/kg per day p.o.) while the SH and 1 AC group received vehicle. Six weeks after surgery (ie after 3 weeks of treatment), the hearts were excised and subjected to independent Langendorf perfusion of left and right coronary beds. The left coronary bed was then subjected to ischemia (7 min) and reperfusion (5 min). Hypertrophied hearts from the vehicle AC group showed a significant increase in the incidence of reperfusion-induced ventricular fibrillation (VF) compared with control hearts from the SH group (92%* vs 33%: *p<0.05); this difference was abolished by ramipril (42%, 50%, and 42%, at 0.01, 0.1, or 1 mg/kg per day, respectively). The LV weight/body weight ratio was significantly increased in all AC groups (regardless of ramipril treatment) relative to the SH group. At the cellular level, myocyte length was significantly increased in the vehicle AC group, but was normalized by ramipril treatment (1 mg/kg per day). At the molecular level, atrial natriuretic factor (ANF) mRNA expression was also significantly increased in the vehicle AC group, but was again normalized by ramipril treatment (1 mg/kg per day). In conclusion, short-term treatment with ramipril reduced susceptibility to severe ventricular arrhythmias in hypertrophied rat hearts. This protection was achieved in the absence of a significant reduction in LV weight, but was accompanied by regression of myocyte hypertrophy, as reflected by reductions in cell size and ANF expression.

Insulin potentiates bradykinin-induced inositol 1,4,5-triphosphate in neonatal rat cardiomyocytes

This study investigated whether cross-talk between insulin and the bradykinin receptor exists to modulate bradykinin-induced increase in inositol 1,4,5-triphosphate (IP3) in neonatal rat cardiomyocytes. Treatment of the cultures with 1, 2, and 20 nM of insulin for 90 min before adding bradykinin increased the IP3 response to the same bradykinin dose to 372.0 +/- 17.8, 413.7 +/- 17.7, and 457.3 +/- 18.2 pmol/mg protein, respectively. Tyrphostine A23 and genistein (tyrosine kinase inhibitors) decreased the bradykinin (10 nM)-induced IP3 production potentiated by 2 nM insulin from 400.7 +/- 19.4 pmol/mg protein to 297.3 +/- 42.4 and 314.3 +/- 37.5 pmol/mg protein, respectively. Administration of 100 nM N-(6-aminohexyl)-5-chloro-naphthalenesulfonamide (W7, a calmodulin antagonist) significantly increased the bradykinin (10 nM)-induced IP3 production from 311.7 +/- 13.0 pmol/mg protein in the absence of insulin to 457.8 +/- 19.9, 578.2 +/- 25.9, and 665.2 +/- 16.0 pmol/mg protein in the presence of 1, 2, and 20 nM insulin, respectively. These results demonstrate that cross-talk between the insulin receptor and the bradykinin signaling system may exist in neonatal rat cardiomyocytes. Tyrosine kinase appears to play an important role in the cross-talking. Calmodulin controls the IP3 response to bradykinin by a negative feedback mechanism.

Bradykinin for the treatment of cardiovascular disease

Bradykinin is a vasoactive kinin known to be involved in many biologic processes. Levels of bradykinin have been shown to be elevated in a number of cardiac diseases. It is thought that these elevated levels play a protective role in cardiovascular diseases. Preliminary studies have demonstrated that bradykinin may have beneficial effects on a wide spectrum of cardiovascular disorders. Though much study is still required, bradykinin augmentation represents an exciting new target for the treatment of cardiovascular disease.

The D allele of the angiotensin-converting enzyme gene and reperfusion-induced ventricular arrhythmias in patients with acute myocardial infarction

The renin-angiotensin system may play a pivotal role in reperfusion ventricular arrhythmias (RVA). The purpose of this study was to investigate the association between angiotensin-converting enzyme (ACE) gene polymorphism and RVA in patients with acute myocardial infarction (AMI) in a case-control study. Patients who had undergone successful coronary intervention for AMI were enrolled (n= 127, male/female: 97/30, mean age, 62.6 years). The incidence of RVA was continuously monitored by ECG at a coronary care unit. The severity of ventricular arrhythmias was evaluated in terms of the Lown's grade and patients with a high risk of ventricular arrhythmias that may cause sudden cardiac death (Lown's grade > or =2) within 5 h of coronary intervention were defined as cases (n=59), and otherwise as controls (n=68). A receiver operating characteristic curve was used to determine the discriminatory ability of continuous variables and to produce dummy variables for use in a logistic regression analysis. Cases had a significantly higher body mass index, higher maximal levels of serum creatine kinase, and a shorter time preceding coronary intervention than controls. The severity of coronary atherosclerosis was similar between the 2 groups. The frequency distribution of ACE genotypes in cases differed from that in controls (II/ID/DD: 22.0%/52.6%/25.4% vs 44.1%/41.4%/14.7%, p<0.05, by the Mantel-Haenzel chi-square test). The ACE-D allele had additive and dominant effects with regard to the occurrence of significant ventricular arrhythmias after adjusting for other risk factors. The ACE-D allele may play a pivotal role in sudden cardiac death in patients with AMI.

Effects of the aminopeptidase P inhibitor apstatin on bradykinin-induced inositol 1,4,5-triphosphate in neonatal rat cardiomyocytes

We investigated the effect of apstatin (an aminopeptidase P inhibitor) on bradykinin-induced inositol 1,4,5-triphosphate (IP3) formation and glucose uptake in isolated neonatal rat cardiomyocytes. Apstatin enhanced bradykinin-induced IP3 formation in a dose-dependent manner. We found that 1 microM Hoe 140 (a bradykinin B2-receptor antagonist) significantly decreased the potentiation of bradykinin-induced IP3 production by 5 microM apstatin from 781.8+/-67.2 to 127.4+/-33.0 pmol/mg protein; 5 microM apstatin increased bradykinin-induced glucose uptake from 197.0+/-25.5 to 297.3+/-64.0 pmol/h per milligram of protein. The stimulation of glucose uptake with apstatin was blocked to 132.5+/-26.2 pmol/h per milligram of protein by 1 microM Hoe 140. We conclude that apstatin stimulates bradykinin-induced IP3 formation and glucose uptake by preventing the degradation of bradykinin.

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.

The effects of Z13752A, a combined ACE/NEP inhibitor, on responses to coronary artery occlusion; a primary protective role for bradykinin

The effects on the responses to coronary artery occlusion of a combined ACE/NEP inhibitor (Z13752A) were examined in anaesthetized dogs. A 1 h infusion of Z13752A (128 microgram kg(-1) min(-1) intravenously) decreased arterial blood pressure (by 11+/-3%; P<0. 05) and increased coronary blood flow (by 12+/-4%, P<0.05). There were no other significant haemodynamic changes. Z13752A inhibited both NEP and ACE enzymes both in dog plasma and in tissue (lung ACE; kidney NEP). Pressor responses to angiotensin I in vivo were inhibited and systemic vasodilator responses to bradykinin were potentiated. When the left anterior descending coronary artery was occluded for 25 min, Z13752A markedly reduced the severity of the resultant ventricular arrhythmias. No ventricular fibrillation (VF) occurred (compared to 7/16 in the controls; P<0.05), and ventricular tachycardia (VT) was reduced (VT in 2/9 dogs treated with Z13752A cp. 16/16 of controls; episodes of VT 0.2+/-0.1 c.p. 10.7+/-3.3; P<0. 05). Reperfusion of the ischaemic myocardium led to VF in all control dogs but occurred less frequently in dogs given Z13752A (survival from the combined ischaemia-reperfusion insult 67% c.p. 0% in controls; P<0.05). Z13752A reduced two other indices of ischaemia severity; epicardial ST-segment elevation and inhomogeneity of electrical activation. These protective effects of Z13752A during ischaemia and reperfusion were abolished by the administration of icatibant (0.3 mg kg(-1), i.v.) a selective antagonist of bradykinin at B(2) receptors; the ischaemic changes in dogs given both icatibant and Z13752A were similar to those in the controls. We conclude that this ACE/NEP inhibitor is effective at reducing the consequences of coronary artery occlusion in this canine model and that this protection is primarily due to potentiation of released bradykinin. British Journal of Pharmacology (2000) 129, 671 - 680

Cardioprotective effects of the aminopeptidase P inhibitor apstatin: studies on ischemia/reperfusion injury in the isolated rat heart

Aminopeptidase P and angiotensin-converting enzyme (ACE) are responsible for the metabolism of exogenously administered bradykinin in the coronary circulation of the rat. It has been shown that ACE inhibitors decrease cytosolic enzyme release from the ischemic rat heart and reduce reperfusion-induced ventricular arrhythmias by increasing endogenous levels of bradykinin. It was hypothesized that the aminopeptidase P inhibitor apstatin could do the same. In an isolated perfused rat heart preparation subjected to global ischemia and reperfusion, both apstatin and ramiprilat (an ACE inhibitor) significantly decreased creatine kinase (CK) and lactate dehydrogenase (LDH) release. The difference between the postischemia and preischemia levels of released CK was reduced 68% by apstatin and 68% by ramiprilat compared with control. The corresponding reductions in LDH release were 74% for apstatin and 81% for ramiprilat. A combination of the inhibitors was not significantly better than either one alone. Apstatin and ramiprilat also significantly reduced the duration of reperfusion-induced ventricular fibrillation by 69 and 61%, respectively. The antiarrhythmic effect of apstatin was reversed by HOE140, a bradykinin B2-receptor antagonist, suggesting that apstatin is acting by potentiating endogenously formed bradykinin. The results demonstrate that the aminopeptidase P inhibitor apstatin is cardioprotective in this model of cardiac ischemia/ reperfusion injury.

Pharmacology and cardiovascular implications of the kinin-kallikrein system

Kinins are peptide hormones that can exert a significant influence on the regulation of blood pressure and vascular tone due to their vasodilatatory, natriuretic and growth modulating activity. Their cardiovascular involvement in physiological and pathophysiological situations has been studied intensively since inhibitors for angiotensin I-converting enzyme and selective receptor antagonists have become available for pharmacologically potentiating or inhibiting kinin-mediated reactions. Molecular biological analysis and the establishment of genetically modified animal models have also allowed newer information to be acquired on this subject. In this review, the components and cardiovascularly relevant mechanisms of the kinin-kallikrein system shall be described. Organ-specific effects concerning the kidneys, the vascular system, the heart and nervous tissue shall also be illustrated. On this issue, the physiological functions and pathophysiological implications of the kinin-kallikrein system should be clearly distinguished from the many, mostly endothelium-mediated protective effects which occur during ACE inhibition due to the potentiation of kinin effects. Finally, a view shall also be cast upon newly discovered targets of action, which could be exploited for therapeutically altering the kinin-kallikrein system.

ACE inhibition, endothelial function and coronary artery lesions. Role of kinins and nitric oxide

In healthy coronary arteries, the endothelium plays an important role in the regulation of vascular smooth muscle growth and contractility. Furthermore, the endothelium inhibits overt platelet aggregation and prevents the adhesion of white blood cells to, and their infiltration into, the vascular wall. Among the mediators of these functions of endothelial cells, nitric oxide (NO) plays a central role. Moreover, the presence of local kinin-generating enzymatic systems associated with endothelial cells, vascular smooth muscle, platelets, neutrophils and monocytes suggests that bradykinin stimulates endothelial cells to release NO locally. The activation of endothelial cells by bradykinin is inhibited by kininase II, best known as angiotensin converting enzyme (ACE). Hence, ACE inhibitors, in addition to reducing the levels of angiotensin II (a potent stimulus to vascular smooth muscle growth and contraction), cause an amplification of the release of NO and other endothelial mediators that is induced by bradykinin. Independent risk factors for coronary artery disease such as hypertension, diabetes and hypercholesterolaemia reduce the NO-dependent regulation of vascular smooth muscle contractility and growth in otherwise normal coronary arteries. This endothelial dysfunction probably also affects the inhibitory role of NO with regard to platelet aggregation and monocyte infiltration into the vascular wall. In atherosclerotic vessels, the role of NO is severely reduced. In animal models, as well as in patients with coronary artery disease, endothelial dysfunction is improved by treatment with ACE inhibitors. Although in humans the mechanism of the restoration of endothelial function is not known, in animals endogenous kinins and NO are involved. However, it is clear that this process is multifactorial, and thus probably involves both the prevention of the deleterious actions of angiotensin II and the potentiation of bradykinin.

Beneficial effects of bradykinin on myocardial energy metabolism and infarct size

There is growing evidence for a local kallikrein-kinin system in the heart. In the ischemic heart the enhanced generation and release of kinins seem to have cardioprotective actions. In isolated rat hearts with ischemia-reperfusion injuries, perfusion with bradykinin reduces the duration and incidence of ventricular fibrillations, improves cardiodynamics, reduces release of cytosolic enzymes, and preserves energy-rich phosphates and glycogen stores. In anesthetized animals, intracoronary infusion of bradykinin is followed by comparable beneficial changes and limits infarct size. Inhibition of breakdown of bradykinin and related peptides induces similar beneficial cardiac effects. Treatment with angiotensin-converting enzyme (ACE) inhibitors such as ramipril increases cardiac kinins and reduces postischemic reperfusion injuries in isolated rat hearts as well as infarct size and remodeling in postinfarcted animals, respectively. Blockade of B2 kinin receptors increases ischemia-induced effects. In isolated hearts, ischemia-reperfusion injuries intensify with the B2 kinin receptor antagonist icatibant, which also abolishes the cardioprotective effects of ACE inhibitors and of exogenous bradykinin. Infarct size reduction by ACE inhibitors and bradykinin in anesthetized animals is reversed by icatibant. Kinins contribute to the cardioprotective effects associated with ischemic preconditioning. Preconditioning or bradykinin-induced antiarrhythmic and infarct size-limiting effects are attenuated by icatibant.

Are the inotropic and antiarrhythmic effects of bradykinin due to increases in coronary flow?

The purpose of this research was to test whether the positive inotropic and antiarrhythmic effects of bradykinin are due solely to increases in coronary flow. Rat hearts were perfused at constant pressure (75 cm H2O) and temperature (37 degrees C). Coronary flow was measured using an electronic drop counter. Contractile force was assessed using a left ventricular balloon catheter. Bradykinin (10 nmol/L) significantly increased coronary flow by 55 +/- 8% above the control level of 4.8 +/- 0.5 mL/min (n = 20), while force was increased by 23.1 +/- 3% (n = 20). Ramiprilat (10 nmol/L) potentiated the vasodilatory and inotropic responses to 10 nmol/L bradykinin by 58 +/- 8% (n = 5). When hearts were perfused at constant flow, bradykinin no longer produced a positive inotropic effect. Bradykinin, 10 or 100 nmol/L, under these conditions actually caused a negative inotropic effect of -24.8 +/- 5% (n = 8) and -35 +/- 11% (n = 3), respectively. In another 2 groups of hearts, also perfused at constant pressure, reperfusion arrhythmias were elicited after a 20-min period of complete global ischemia. In control hearts, the mean period of fibrillation was 7.3 +/- 1.8 min (n = 10). This period was significantly reduced to 2.7 +/- 0.7 min (n = 10) in hearts receiving 10 nmol/L bradykinin. In untreated hearts, the coronary flow during the reperfusion period increased over the baseline flow by a factor of 1.8 +/- 0.2, and this factor was not significantly effected by bradykinin. These results suggest that only the positive inotropic, but not the antiarrhythmic, action of bradykinin is due to coronary vasodilation.

Attenuation of epinephrine-induced dysrhythmias by bradykinin: role of nitric oxide and prostaglandins

Cardiac dysrhythmias are common during anesthesia and surgery. An important precipitating factor of clinically relevant arrhythmias is the introoperative use of epinephrine. Bradykinin acts as an endogenous cardioprotective substance because it suppresses ventricular dysrhythmias induced by ischemia. In this study, we investigated whether bradykinin has a protective effect, preventing the development of dysrhythmias after epinephrine infusion in rats. Because kinins are potent stimulators of the release of nitric oxide and prostaglandins from the endothelium, we investigated whether the protective effect of bradykinin is mediated by these 2 autacoids. Male Sprague-Dawley rats anesthetized with sodium pentobarbital had catheters placed into a carotid artery and both jugular veins. Arterial blood pressure and lead II of the electrocardiogram (ECG) were continuously monitored and recorded. After a steady state was achieved, 1 mg/kg enalapril, an inhibitor of angiotensin I-converting enzyme/kininase II, was given intravenously to all groups except the one treated with losartan. Bradykinin was infused at the initial rate of 0.5 microg/kg per min. Cardiac arrhythmia was induced with 7.5 microg/kg epinephrine intravenously. Dysrhythmia was assessed by counting the number of premature ventricular contractions (PVCs), runs of ventricular tachycardia (V Tach), and missing beats during the first minute after epinephrine. In untreated, control rats, epinephrine caused 10.8 +/- 2.7 PVCs, 0.8 +/- 0.2 runs of V tach, and 11.6 +/- 7.4 missing beats/min. In rats pretreated with bradykinin, the same dose of epinephrine elicited 1.2 +/- 0.5 PVCs, no runs of V tach, and 0.4 +/- 0.4 missing beats/min. This beneficial effect of bradykinin was partially reversed by N-nitro-L-arginine methyl ester (L-NAME) or indomethacin, and completely by L-NAME plus indomethacin or icatibant, but it was not affected by des-Arg9[Leu8]-bradykinin. We conclude that bradykinin, acting on the B2 receptor, attenuates epinephrine-induced dysrhythmia via a mechanism that involves the release of NO and prostaglandins. Although the mechanism is not clear, NO and prostaglandins may prevent epinephrine-induced dysrhythmia and protect the myocardium via a direct action on cardiac neurons.