Ramiprilat attenuates hypoxia/reoxygenation injury to cardiac myocytes via a bradykinin-dependent mechanism

Protective Role of Ramipril and Candesartan against Myocardial Ischemic Reperfusion Injury: A Biochemical and Transmission Electron Microscopical Study

The present study was designed to investigate the role of combined administration of Ramipril and Candesartan against in vitro myocardial ischemic reperfusion injury in rat. Male Wistar albino rats were divided into five groups (n = 6) and treated with saline (10 mL/kg), Ramipril (2 mg/kg), Candesartan (1 mg/kg), and the combination of both drugs, respectively 24 h before induction of global ischemia (5 min of stabilization, 9 min of global ischemia, and 12 min of reflow). Combination of Ramipril and Candesartan when compared to the monotherapy significantly increased the levels of superoxide dismutase, reduced glutathione, catalase, and nitric oxide and decreased the levels of thiobarbituric acid reactive substances. In addition, the superior protective role of combination of Ramipril and Candesartan on ischemia induced myocardial damage was further confirmed by well preserved myocardial tissue architecture in light microscopy and transmission electron microscopy analysis studies. The combination was proved to be effective in salvaging the myocardial tissue against ischemic reperfusion injury when compared to the monotherapy of individual drugs and further investigations on protective mechanism of drugs by increasing the nitric oxide level at molecular levels are needed.

Serum ACE predicts severe hypoglycemia in children and adolescents with type 1 diabetes

OBJECTIVE

To investigate whether risk of severe hypoglycemia is related to serum (S) ACE level during intensive treatment in type 1 diabetic children.

RESEARCH DESIGN AND METHODS

A cohort of 86 intensively treated type 1 diabetic patients was studied during 1999-2000. In 1999, the age range was 7-19 years (median 12.8), diabetes duration was 1.2-14.7 years (5.3), insulin dose was 0.4-1.7 units x kg(-1) x 24 h(-1) (1.0), and the HbA(1c) year mean was 4.7-10.2% (6.8). HbA(1c), insulin doses, and events of severe hypoglycemia (needing assistance from another person) were prospectively registered at regular visits, scheduled quarterly. S-ACE was determined once.

RESULTS

Severe hypoglycemia was correlated to S-ACE (r = 0.22, 95% CI 0.01-0.41, P = 0.0093). The square root of severe hypoglycemia was correlated to S-ACE (r = 0.27, 95% CI 0.06-0.45, P = 0.0093). Patients with S-ACE at the median level or above (n = 44) reported a mean of 3.0 yearly events of severe hypoglycemia compared with 0.5 events in patients with S-ACE lower than the median (n = 42) (P = 0.0079). Of the patients with an S-ACE at the median level or above, 27 (61%) reported severe hypoglycemia, compared with 17 (40%) patients with an S-ACE lower than the median (P = 0.0527). Insulin dose, HbA(1c), age, onset age, duration, C-peptide, and sex did not differ between these two groups. S-ACE was negatively correlated with age (r = -0.27, 95% CI -0.46 to 0.07, P = 0.0265) but not with HbA(1c), duration, or blood pressure.

CONCLUSIONS

The elevated rate of severe hypoglycemia among patients with higher S-ACE suggests, among other factors, that a genetic determinant for severe hypoglycemia exists. Further evaluation is needed before the clinical usefulness of this test can be elucidated.

Myocardial bradykinin following acute angiotensin-converting enzyme inhibition, AT1 receptor blockade, or combined inhibition in congestive heart failure

BACKGROUND

The present study examined the effects of acute angiotensin-converting enzyme inhibition (ACEI), AT(1) receptor blockade (AT(1) block), or combined treatment on in vitro and in vivo bradykinin (BK) levels.

METHODS

BK levels were measured in isolated porcine myocyte preparations (n = 13) in the presence of exogenous BK (10(-8) M); with an ACEI (benezaprilat; 0.1 mM) and BK; an AT(1) block (valsartan; 10(-5) M) and BK; and combined treatment and BK. In a second study, myocardial microdialysis was used to measure porcine interstitial BK levels in both normal (n = 14) and pacing-induced congestive heart failure (CHF) (240 beats/min, 3 weeks, n = 16) under the following conditions: baseline, following ACEI (benezaprilat, 0.0625 mg/kg) or AT(1) block (valsartan, 0.1 mg/kg), and a combined treatment (benezaprilat, 0.0625 mg/kg; valsartan, 0.1 mg/kg).

RESULTS

In the left ventricular myocyte study, BK levels increased over 93% with all treatments compared to untreated values (P < 0.05). In the in vivo study, basal interstitial BK values were lower in the CHF group than in controls (2.64 +/- 0.57 vs 5.91 +/- 1.4 nM, respectively, P < 0.05). Following acute infusion of the ACEI, BK levels in the CHF state increased from baseline (57% +/- 22; P < 0.05). Following combined ACEI/AT(1) block, BK levels increased from baseline in both control (42% +/- 11) and CHF groups (60% +/- 22; P < 0.05 for both).

CONCLUSION

These findings suggest that ACEI, or combined ACEI/AT(1) block increased BK at the level of the myocyte and potentiated BK levels in the CHF myocardial interstitium.

Activity of angiotensin-converting enzyme and risk of severe hypoglycaemia in type 1 diabetes mellitus

BACKGROUND

The insertion (I) allele of the angiotensin-converting-enzyme (ACE) gene occurs at increased frequency in endurance athletes. This association suggests that low ACE activity is favourable for performance in conditions with limited substrate availability. Such conditions occur in endurance athletes during competition and in diabetic patients during insulin-induced hypoglycaemia. Patients rely on preserved functional capacity to recognise hypoglycaemic episodes and avoid progression by self-treatment. We studied whether ACE activity is related to the risk of severe hypoglycaemia in type 1 diabetes.

METHODS

Consecutive adult outpatients with type 1 diabetes, untreated with ACE inhibitors or angiotensin-II-receptor antagonists (n=207) reported their experience of mild and severe hypoglycaemia during the previous 1 year and 2 years. The patients were further characterised by diabetes history, degree of hypoglycaemia awareness, measurement of C-peptide, haemoglobin A(1c), and serum ACE concentrations, and determination of ACE genotype.

FINDINGS

Patients with the DD genotype had a relative risk of severe hypoglycaemia in the preceding 2 years of 3.2 (95% CI 1.4-7.4) compared with those who had the II genotype. There was a significant relation between serum ACE activity and the rate of severe hypoglycaemia (relative risk per 10 U/L increment 1.4 [1.2-1.6]), corresponding to a 3.5 times higher risk for patients in the highest quartile than for those in the lowest quartile. Multiple regression analysis showed that the effect of the ACE genotype was explained by its influence on serum ACE activity and that the only other significant determinants of the risk of severe hypoglycaemia were the degree of hypoglycaemia awareness, b-cell function, and duration of diabetes of more than 20 years.

INTERPRETATION

ACE activity is a clinically significant marker of the risk of severe hypoglycaemia in patients with type 1 diabetes, especially in those with impaired defence against hypoglycaemia. These findings need to be confirmed in prospective studies.

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.

Expression of kininogen, kallikrein and kinin receptor genes by rat cardiomyocytes

To ascertain the existence of the kallikrein-kinin system in the heart, we have studied in vivo and in vitro whether rat cardiac tissue expresses kininogen, kallikrein and kinin receptor mRNAs. The reverse transcription-polymerase chain reaction demonstrated that the ventricular myocardium of adult male rats expressed mRNAs for T- and low-molecular-weight (L-) kininogens, tissue kallikreins such as true kallikrein and T-kininogenase, and bradykinin B2 receptor, but not those for high-molecular-weight kininogen and B1 receptor. Lipopolysaccharide (LPS; 0.5 mg/kg, i.v.) increased the levels of mRNA for T-kininogen at 12 h and the bradykinin B1 receptor at 24 h without affecting that for other components. All of these mRNAs for the kallikrein-kinin system were also detected in cultured cardiomyocytes derived from neonatal rat ventricles; dibutyryl cyclic AMP, LPS or inflammatory cytokines such as interleukin-1 and tumor necrosis factor, up-regulated mRNA expression of T-kininogen, T-kininogenase, or B1 receptor in these cells in vitro. These results suggest that there are two kinin-generating systems in rat myocardium comprising T-kininogen/T-kininogenase and L-kininogen/true kallikrein respectively, and that the former may be relatively important in inflammatory diseases or conditions in which cAMP levels increase in cardiomyocytes.

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.

Modification by bradykinin B2 receptor blockade of protection by pacing against ischaemia-induced arrhythmias

In dogs, rapid cardiac pacing, by way of a pacing electrode in the right ventricle, protects against ventricular arrhythmias when a coronary artery is occluded immediately after cessation of the pacing period. This represents a form of ischaemic preconditioning. The role of bradykinin in mediating the protective effects of rapid cardiac pacing in this model was investigated using a selective antagonist of bradykinin at B2 receptors (icatibant; HOE 140). In the presence of icatibant cardiac pacing (220 beats min(-1)) resulted in more severe ischaemia (as assessed by ST-segment elevation from the pacing electrode at the end of the stimulus) and to a higher incidence of ventricular arrhythmias during the pacing protocol. When the coronary artery was occluded under such conditions the antiarrhythmic protection afforded by cardiac pacing was not seen although other indices of reduced ischaemia severity (epicardial ST-segment mapping; changes in the degree of inhomogeneity of electrical activation within the ischaemic area) were not affected by icatibant treatment. These results suggest that bradykinin is an important trigger mediator involved in the protective effects of cardiac pacing. Whether this is due to the generation of endothelium-derived protective substances (such as nitric oxide and prostacyclin) or whether it results from a direct effect on B2 receptors in cardiac myocytes is unclear.