EXP3174, the AII antagonist human metabolite of losartan, but not losartan nor the angiotensin-converting enzyme inhibitor captopril, prevents the development of lethal ischemic ventricular arrhythmias in a canine model of recent myocardial infarction

Testing the Translational Power of the Zebrafish: An Interspecies Analysis of Responses to Cardiovascular Drugs

The zebrafish is rapidly emerging as a promising alternative in vivo model for the detection of drug-induced cardiovascular effects. Despite its increasing popularity, the ability of this model to inform the drug development process is often limited by the uncertainties around the quantitative relevance of zebrafish responses compared with nonclinical mammalian species and ultimately humans. In this test of concept study, we provide a comparative quantitative analysis of the in vivo cardiovascular responses of zebrafish, rat, dog, and human to three model compounds (propranolol, losartan, and captopril), which act as modulators of two key systems (beta-adrenergic and renin–angiotensin systems) involved in the regulation of cardiovascular functions. We used in vivo imaging techniques to generate novel experimental data of drug-mediated cardiovascular effects in zebrafish larvae. These data were combined with a database of interspecies mammalian responses (i.e., heart rate, blood flow, vessel diameter, and stroke volume) extracted from the literature to perform a meta-analysis of effect size and direction across multiple species. In spite of the high heterogeneity of study design parameters, our analysis highlighted that zebrafish and human responses were largely comparable in >80% of drug/endpoint combinations. However, it also revealed a high intraspecies variability, which, in some cases, prevented a conclusive interpretation of the drug-induced effect. Despite the shortcomings of our study, the meta-analysis approach, combined with a suitable data visualization strategy, enabled us to observe patterns of response that would likely remain undetected with more traditional methods of qualitative comparative analysis. We propose that expanding this approach to larger datasets encompassing multiple drugs and modes of action would enable a rigorous and systematic assessment of the applicability domain of the zebrafish from both a mechanistic and phenotypic standpoint. This will increase the confidence in its application for the early detection of adverse drug reactions in any major organ system.

Angiotensin II type 1a receptor signalling directly contributes to the increased arrhythmogenicity in cardiac hypertrophy

BACKGROUND AND PURPOSE

Angiotensin II has been implicated in the development of various cardiovascular ailments, including cardiac hypertrophy and heart failure. The fact that inhibiting its signalling reduced the incidences of both sudden cardiac death and heart failure in several large-scale clinical trials suggests that angiotensin II is involved in increased cardiac arrhythmogenicity during the development of heart failure. However, because angiotensin II also promotes structural remodelling, including cardiomyocyte hypertrophy and cardiac fibrosis, it has been difficult to assess its direct contribution to cardiac arrhythmogenicity independently of the structural effects.

EXPERIMENTAL APPROACH

We induced cardiac hypertrophy in wild-type (WT) and angiotensin II type 1a receptor knockout (AT1aR-KO) mice by transverse aortic constriction (TAC). The susceptibility to ventricular tachycardia (VT) assessed in an in vivo electrophysiological study was compared in the two genotypes. The effect of acute pharmacological blockade of AT1R on the incidences of arrhythmias was also assessed.

KEY RESULTS

As described previously, WT and AT1aR-KO mice with TAC developed cardiac hypertrophy to the same degree, but the incidence of VT was much lower in the latter. Moreover, although TAC induced an increase in tyrosine phosphorylation of connexin 43, a critical component of gap junctional channels, and a reduction in ventricular levels of connexin 43 protein in both genotypes, the effect was significantly ameliorated in AT1aR-KO mice. Acute pharmacological blockade of AT1R also reduced the incidence of arrhythmias.

CONCLUSIONS AND IMPLICATIONS

Our findings demonstrate that AT1aR-mediated signalling makes a direct contribution to the increase in arrhythmogenicity in hypertrophied hearts independently of structural remodelling.

Prevention of atrial fibrillation by Renin-Angiotensin system inhibition a meta-analysis

OBJECTIVES

The authors reviewed published clinical trial data on the effects of renin-angiotensin system (RAS) inhibition for the prevention of atrial fibrillation (AF), aiming to define when RAS inhibition is most effective.

BACKGROUND

Individual studies examining the effects of RAS inhibition on AF prevention have reported controversial results.

METHODS

All published randomized controlled trials reporting the effects of treatment with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers in the primary or secondary prevention of AF were included.

RESULTS

A total of 23 randomized controlled trials with 87,048 patients were analyzed. In primary prevention, 6 trials in hypertension, 2 trials in myocardial infarction, and 3 trials in heart failure were included (some being post-hoc analyses of randomized controlled trials). In secondary prevention, 8 trials after cardioversion and 4 trials assessing the medical prevention of recurrence were included. Overall, RAS inhibition reduced the odds ratio for AF by 33% (p < 0.00001), but there was substantial heterogeneity among trials. In primary prevention, RAS inhibition was effective in patients with heart failure and those with hypertension and left ventricular hypertrophy but not in post-myocardial infarction patients overall. In secondary prevention, RAS inhibition was often administered in addition to antiarrhythmic drugs, including amiodarone, further reducing the odds for AF recurrence after cardioversion by 45% (p = 0.01) and in patients on medical therapy by 63% (p < 0.00001).

CONCLUSIONS

This analysis supports the concept of RAS inhibition as an emerging treatment for the primary and secondary prevention of AF but acknowledges the fact that some of the primary prevention trials were post-hoc analyses. Further areas of uncertainty include potential differences among specific RAS inhibitors and possible interactions or synergistic effects with antiarrhythmic drugs.

Mast cell degranulation mediates bronchoconstriction via serotonin and not via renin release

To verify the recently proposed concept that mast cell-derived renin facilitates angiotensin II-induced bronchoconstriction bronchial rings from male Sprague-Dawley rats were mounted in Mulvany myographs, and exposed to the mast cell degranulator compound 48/80 (300 microg/ml), angiotensin I, angiotensin II, bradykinin or serotonin (5-hydroxytryptamine, 5-HT), in the absence or presence of the renin inhibitor aliskiren (10 micromol/l), the ACE inhibitor captopril (10 micromol/l), the angiotensin II type 1 (AT1) receptor blocker irbesartan (1 micromol/l), the mast cell stabilizer cromolyn (0.3 mmol/l), the 5-HT2A/2C receptor antagonist ketanserin (0.1 micromol/l) or the alpha1-adrenoceptor antagonist phentolamine (1 micromol/l). Bath fluid was collected to verify angiotensin generation. Bronchial tissue was homogenized to determine renin, angiotensinogen and serotonin content. Compound 48/80 contracted bronchi to 24+/-4% of the KCl-induced contraction. Ketanserin fully abolished this effect, while cromolyn reduced the contraction to 16+/-5%. Aliskiren, captopril, irbesartan and phentolamine did not affect this response, and the angiotensin I and II levels in the bath fluid after 48/80 exposure were below the detection limit. Angiotensin I and II equipotently contracted bronchi. Captopril shifted the angiotensin I curve approximately 10-fold to the right, whereas irbesartan fully blocked the effect of angiotensin II. Bradykinin-induced constriction was shifted approximately 100-fold to the left with captopril. Serotonin contracted bronchi, and ketanserin fully blocked this effect. Finally, bronchial tissue contained serotonin at micromolar levels, whereas renin and angiotensinogen were undetectable in this preparation. In conclusion, mast cell degranulation results in serotonin-induced bronchoconstriction, and is unlikely to involve renin-induced angiotensin generation.

Angiotensin II inhibition during myocardial ischemia–reperfusion in dogs: effects on leukocyte infiltration, nitric oxide synthase isoenzymes activity and left ventricular ejection fraction

Leukocyte infiltration and activation in myocardial reperfusion injury may be modulated by nitric oxide synthase isoforms. Angiotensin II influences leukocyte activation directly or by nitric oxide generation mechanisms. The effects of angiotensin II inhibition before reperfusion on myocardial function, leukocyte accumulation and nitric oxide synthase were evaluated on three groups of eight dogs. They were submitted to occlusion of the left anterior descending coronary artery for 90 min, followed by 120 min of reperfusion. The first group received captopril, the second losartan and the third received normal saline solution. Left ventricular ejection fraction significantly improved after reperfusion in the groups under captopril (15+/-5.1%, p=0.029) and losartan (16+/-4.3%, p=0.014) when compared to the control group (7+/-2.5%). Myeloperoxidase activity was significantly lower in captopril group (6.6+/-1.0 U/100 mg, p=0,036) and losartan (6.8+/-1.7 U/100 mg, p=0.044) than in the control group (12.5+/-4.7 U/100 mg). Significant difference on constitutive nitric oxide synthase activity was not observed when all three groups were compared simultaneously (10.1+/-1.8 versus 8.5+/-1.3 versus 7.3+/-1.9 fM/mg/min, p=0.447). Inducible nitric oxide synthase activity was significantly lower in the losartan group (9.0+/-4.1 fM/mg/min) than in the captopril (29.2+/-5.1 fM/mg/min, p=0.0001) and control groups (26.2+/-4.6 fM/mg/min, p=0.0001). Angiotensin II inhibition reduced leukocyte infiltration and improved left ventricular ejection fraction during reperfusion by angiotensin-converting enzyme inhibition or by angiotensin II type 1 receptor blocker. This was observed without influencing the constitutive nitric oxide synthase activity. Only losartan reduced inducible nitric oxide synthase activity but did not influence the leukocyte infiltration and myocardial contractile function.

Losartan but not enalaprilat acutely reduces reperfusion ventricular tachyarrhythmias in hypertrophied rat hearts after low-flow ischaemia

Based on clinical and experimental studies, angiotensin II receptor blockers and angiotensin converting enzyme inhibitors have been proposed to exert acute anti-arrhythmic effects in heart failure patients. Therefore, the goal of this study was to assess acute anti-arrhythmic effects of losartan and enalaprilat in hypertrophied rat hearts during low-flow ischaemia and reperfusion. In dose-finding experiments in non-hypertrophied isolated perfused hearts, we performed dose-response curves of losartan and enalaprilat studying monophasic action potential duration at 90% repolarisation (MAPD(90%)) and ventricular fibrillation (VF) threshold. Subsequently, we determined the effects of losartan and enalaprilat (in therapeutically relevant concentrations) on ventricular tachyarrhythmias induced by low-flow ischaemia/reperfusion in hearts demonstrating left ventricular (LV) hypertrophy 70 days after aortic banding. We found that neither drug significantly affected MAPD(90%) (1 nM-1 mM) or VF threshold (1 microM losartan and 10 microM enalaprilat) in non-hypertrophied hearts. Similarly in hypertrophied hearts, neither drug significantly affected the incidence or the duration of ventricular tachyarrhythmias (ventricular tachycardia and VF) during low-flow ischaemia. However, 1 microM losartan significantly reduced the duration of ventricular tachyarrhythmias during reperfusion. In conclusion, neither losartan nor enalaprilat is acutely anti-arrhythmic in hypertrophied rat hearts during low-flow ischaemia. During reperfusion, however, losartan but not enalaprilat exerts acute anti-arrhythmic effects.

Left ventricular dysfunction is associated with prolonged average ventricular fibrillation cycle length in patients with implantable cardioverter defibrillators

OBJECTIVES

In cellular studies, ventricular refractoriness (ERP) is prolonged in heart failure (CHF), but clinical evidence is lacking. The average ventricular fibrillation cycle length (VFCL) has been shown to correlate with local ERP. We hypothesized that the VFCL increases with left ventricular (LV) dysfunction. Therefore, we evaluated intracardiac VFCL recorded by implantable defibrillators (ICD) in patients with and without LV dysfunction.

METHODS

We analyzed intracardiac VFCL recorded by sensing leads of Ventak MINI (Guidant) ICD in 49 patients (35 men; age 54 +/- 13 years; 25 (51%) with coronary artery disease; mean LV ejection fraction (EF) 41 +/- 17%, range 76-10) from the European Ventak MINI Investigator Group. No patients were receiving antiarrhythmic drugs, including beta-blockers. Mean and median VFCL were obtained at predischarge testing during first charge time (4.5 +/- 2.7 s, range 1.4-11).

RESULTS

Mean median VFCL was 186 +/- 21ms (range 150-230 ms). Patients with LVEF >/= 50% (n = 14) had shorter median VFCL than patients with LVEF < 50% (n = 35), (171 +/- 14 vs. 191 +/- 20 ms; p = 0.002). Median VFCL correlated with LVEF (r = -0.41; p = 0.003) and age (r = 0.28, p = 0.04), but was not significantly associated with charge time and defibrillation threshold at implant. Similar results occurred with mean VFCL. In multiple linear regression and correlation models, only LVEF% was a significant predictor (p < 0.05 for all models) of median VFCL.

CONCLUSIONS

LV dysfunction prolongs averaged VFCL in patients at risk for malignant ventricular arrhythmias who have implantable cardioverter defibrillators. This phenomenon might be related to alterations in the ventricular refractory period.

Cardioprotection after angiotensin II type 1 blockade involves angiotensin II type 2 receptor expression and activation of protein kinase C-epsilon in acutely reperfused myocardial infarction in the dog. Effect of UP269-6 and losartan on AT1 and AT2-receptor expression and IP3 receptor and PKCepsilon proteins

To determine whether cardioprotection after chronic angiotensin II (Ang II) type 1 (AT(1)) receptor blockade involves Ang II type 2 (AT(2)) receptor expression and protein kinase C-epsilon (PKC(epsilon)) activation, we measured in vivo haemodynamics and left ventricular (LV) remodelling and dysfunction (echocardiogram/ Doppler) and ex vivo AT(1)/AT(2)-receptor expression, IP(3)R (1, 4, 5-inositol trisphosphate type 2 receptor) and PKC(epsilon) proteins in dogs with acutely reperfused (90 minutes ischaemia, 90 minutes reperfusion) myocardial infarction (MI) following seven days of AT(1)-receptor blockade with oral losartan or UP269-6. The animals were randomised to sham; sham + losartan or UP269-6; MI alone; MI + losartan; MI + UP269-6. More marked AT(1)-receptor blockade with UP269-6 (greater inhibition of Ang II pressor responses) was associated with a smaller increase in preload, less systolic and diastolic dysfunction, less infarct expansion, and smaller LV diastolic and systolic volumes. However, both AT(1)-receptor antagonists decreased infarct size. Importantly, MI decreased AT(1)-receptor and AT(2)-receptor expression while MI after AT(1)-receptor antagonism increased AT(1)-receptor (mRNA, not protein) and AT(2)-receptor (mRNA and protein) expression as well as IP(3)R and PKC(epsilon) proteins and cyclic guanosine 3', 5' monophosphate (cGMP). These results suggest that cardioprotection induced by chronic AT(1)-receptor antagonism involves enhanced AT(2)-receptor expression and possibly downstream signalling through IP(3)R, PKC(epsilon) and cGMP.

Effect of losartan compared with captopril on mortality in patients with symptomatic heart failure: randomised trial--the Losartan Heart Failure Survival Study ELITE II

BACKGROUND

The ELITE study showed an association between the angiotensin II antagonist losartan and an unexpected survival benefit in elderly heart-failure patients, compared with captopril, an angiotensin-converting-enzyme (ACE) inhibitor. We did the ELITE II Losartan Heart Failure Survival Study to confirm whether losartan is superior to captopril in improving survival and is better tolerated.

METHODS

We undertook a double-blind, randomised, controlled trial of 3,152 patients aged 60 years or older with New York Heart Association class II-IV heart failure and ejection fraction of 40% or less. Patients, stratified for beta-blocker use, were randomly assigned losartan (n=1,578) titrated to 50 mg once daily or captopril (n=1,574) titrated to 50 mg three times daily. The primary and secondary endpoints were all-cause mortality, and sudden death or resuscitated arrest. We assessed safety and tolerability. Analysis was by intention to treat.

FINDINGS

Median follow-up was 555 days. There were no significant differences in all-cause mortality (11.7 vs 10.4% average annual mortality rate) or sudden death or resuscitated arrests (9.0 vs 7.3%) between the two treatment groups (hazard ratios 1.13 [95.7% CI 0.95-1.35], p=0.16 and 1.25 [95% CI 0.98-1.60], p=0.08). Significantly fewer patients in the losartan group (excluding those who died) discontinued study treatment because of adverse effects (9.7 vs 14.7%, p<0.001), including cough (0.3 vs 2.7%).