Prolonging action of imidapril on the lifespan expectancy of cardiomyopathic hamsters

Na+-H+ exchanger and proton channel in heart failure associated with Becker and Duchenne muscular dystrophies

Cardiomyopathy is found in patients with Duchenne (DMD) and Becker (BMD) muscular dystrophies, which are linked muscle diseases caused by mutations in the dystrophin gene. Dystrophin defects are not limited to DMD but are also present in mild BMD. The hereditary cardiomyopathic hamster of the UM-X7.1 strain is a particular experimental model of heart failure (HF) leading to early death in muscular dystrophy (dystrophin deficiency and sarcoglycan mutation) and heart disease (δ-sarcoglycan deficiency and dystrophin mutation) in human DMD. Using this model, our previous work showed a defect in intracellular sodium homeostasis before the appearance of any apparent biochemical and histological defects. This was attributed to the continual presence of the fetal slow sodium channel, which was also found to be active in human DMD. Due to muscular intracellular acidosis, the intracellular sodium overload in DMD and BMD was also due to sodium influx through the sodium-hydrogen exchanger NHE-1. Lifetime treatment with an NHE-1 inhibitor prevented intracellular Na⁺ overload and early death due to HF. Our previous work also showed that another proton transporter, the voltage-gated proton channel (Hv1), exists in many cell types including heart cells and skeletal muscle fibers. The Hv1 could be indirectly implicated in the beneficial effect of blocking NHE-1.

Cardiomyopathic Syrian hamster as a model of congestive heart failure

Cardiomyopathic Syrian hamsters (Bio TO-2 dilated strain) constitute an animal model of congestive heart failure, which progressively develops an alteration of cardiac function leading to decreased arterial blood pressure and musculo-cutaneous blood flow associated with a complex process of cardiac remodeling including left ventricle dilation, wall thinning, and greater collagen density. The protocols described in this unit are designed to assess the pharmacological effects of new therapeutic strategies on cardiac and systemic hemodynamics, morphometry (body and target organs weight), cardiac remodeling (left ventricle dilation and collagen density), and survival in this model of dilated cardiomyopathy. Examples of results obtained with enalapril, an angiotensin I converting enzyme inhibitor, are provided for illustrative purposes.

ACE inhibition actively promotes cell survival by altering gene expression

We tested the effect of ACE inhibition on the survival of bovine retinal (REC) and choroidal (CEC) endothelial cells (EC) in culture. The ACE inhibitor captopril delayed the apoptotic tube collapse of REC on Matrigel for >15 days. Captopril treatment of confluent monolayers (2-8 weeks) followed by slow starvation (2-4 weeks) increased EC viability by approximately 200%. Two-week captopril exposures were sufficient to confer maximal protection. Only vehicle-treated EC demonstrated apoptotic features such as membrane blebbing and DNA laddering. By RT-PCR, the starvation marker p202 was upregulated only in starved cells. In REC, captopril upregulated the pro-survival proteins mortalin-2, uPA, and uPAR while downregulating the anti-growth sprouty-4 and tPA. In CEC, captopril also upregulated tPA and its inhibitor PAI-1. Amiloride (uPA inhibitor) blocked the captopril-induced increase in EC survival, secondary sprouting, and invasion in Matrigel. The pro-survival effects of captopril involve the reprogramming of genes involved in cell survival and immortalization.

T-1032, a novel phosphodiesterase type 5 inhibitor, increases the survival of cardiomyopathic hamsters

To evaluate the influence of T-1032 (methyl2-(4-aminophenyl)-1,2-dihydro-1-oxo-7-(2-pyridylmethoxy)-4-(3,4,5-trimethoxyphenyl)-3-isoquinoline carboxylate sulfate), a potent and relatively selective phosphodiesterase 5 inhibitor, on chronic heart failure, we examined the acute hemodynamic profile of T-1032 and its chronic effect on the survival of Bio 14.6 cardiomyopathic hamsters. In the acute study, T-1032 (1, 10, 100 microg/kg) was administered intravenously by means of a dose-escalating procedure in 55-week-old hamsters. T-1032 significantly reduced both the right and left ventricular end-diastolic pressure in a dose-dependent manner. T-1032 modestly reduced the systemic arterial pressure at the highest dose (100 microg/kg i.v.). T-1032 did not change the heart rate or left ventricular dp/dt(max). In the survival study, chronic administration of T-1032 (50 and 500 ppm in a diet) increased survival, and the survival rate was 24.2%, 45.4% and 48.5% in the control, 50 and 500 ppm-treated groups, respectively. The median survival was 55, 58 and 58 weeks in control, 50 and 500 ppm-treated groups, respectively. Analysis of the survival curves revealed that T-1032 (500 ppm) significantly increased the survival of these hamsters (P<0.05 vs. control). It was concluded that T-1032 had beneficial hemodynamic effects on heart failure in Bio 14.6 cardiomyopathic hamsters, and the favorable hemodynamic changes induced by T-1032 were partly related to the increase in the survival of these hamsters. Phosphodiesterase type 5 inhibitors may have therapeutic potential for the treatment of chronic heart failure.

Angiotensin-converting enzyme inhibitor therapy for ventricular dysfunction in infants, children and adolescents: a review

Angiotensin-converting enzyme (ACE) inhibitors have become an important part of the pharmacologic armamentarium in the battle against treatment of ventricular dysfunction. There have been a number of large controlled, randomized trials in adults with both asymptomatic and symptomatic ventricular dysfunction, which confirm the safety and efficacy of this category of drugs for the treatment of this potentially lethal condition. ACE inhibitors may be used to treat infants, children and adolescents with asymptomatic and symptomatic ventricular dysfunction as well. The data supporting their use in children is less complete than that concerning the treatment of adults. We review here the various causes of ventricular dysfunction and congestive heart failure (CHF) in infants, children, and adolescents; the data available regarding treatment of these conditions with ACE inhibitors, and the safety and efficacy of these drugs for the various conditions. The pharmacokinetics and proposed mechanisms of action of ACE inhibitors in children are reviewed, as are speculated long-term results of ACE inhibitor use in cohorts of growing children. Recommendations are made for future studies.

MCI-154, a Ca2+ sensitizer, increases survival in cardiomyopathic hamsters

To assess the long-term efficacy of a Ca2+ sensitizer MCI-154, 6-[4-(4'-pyridylamino)phenyl]-4,5-dihydro-3(2H)-pyridazinone hydrochloride trihydrate, on chronic heart failure, we studied the effects of the agent on the life span of cardiomyopathic hamsters of the BIO-14.6 strain. At approximately 150 days of age, 210 male hamsters were randomly divided into three groups: MCI-154 0.1 mg kg(-1), day(-1)(MCI-154-low), MCI-154 1 mg kg(-1) day(-1) (MCI-154-high), and control group. The median survival time in control, MCI-154-low and MCI-154-high groups was 227, 243 and 260 days after the start of treatment, respectively. Final survival rate at 284 days in control, MCI-154-low and MCI-154-high groups was 0, 17.1 and 38.6%, respectively. The cumulative survival times in the two MCI-154 treated groups were significantly prolonged in comparison with that in the control group (P < 0.0001). Thus, the present study clearly showed that MCI-154 prolonged the life span of cardiomyopathic hamsters, suggesting that long-term therapy with MCI-154 would be promising in the treatment of congestive heart failure.

High- versus low-dose ACE inhibition in chronic heart failure: a double-blind, placebo-controlled study of imidapril

OBJECTIVES

To determine dose-related clinical and neurohumoral effects of angiotensin-converting enzyme (ACE) inhibitors in patients with chronic heart failure (CHF), we conducted a double-blind, placebo-controlled, randomized study of three doses (2.5 mg, 5 mg and 10 mg) of the long-acting ACE inhibitor imidapril.

BACKGROUND

The ACE inhibitors have become a cornerstone in the treatment of CHF, but whether high doses are more effective than low doses has not been fully elucidated, nor have the mechanisms involved in such a dose-related effect.

METHODS

In a parallel group comparison, the effects of three doses of imidapril were examined. We studied 244 patients with mild to moderate CHF (New York Heart Association class II-III: +/-80%/20%), who were stable on digoxin and diuretics. Patients were treated for 12 weeks, and the main end points were exercise capacity and plasma neurohormones.

RESULTS

At baseline, the four treatment groups were well-matched for demographic variables. Of the 244 patients, 25 dropped out: 3 patients died, and 9 developed progressive CHF (3/182 patients on imidapril vs. 6/62 patients on placebo, p < 0.05). Exercise time increased 45 s in the 10-mg group (p = 0.02 vs. placebo), but it did not significantly change in the 5-mg (+16 s), and 2.5-mg (+11 s) imidapril group, compared to placebo (+3 s). Physical working capacity also increased in a dose-related manner. Plasma brain and atrial natriuretic peptide decreased (p < 0.05 for linear trend), while (nor)epinephrine, aldosterone and endothelin were not significantly affected. Renin increased in a dose-related manner, but plasma ACE activity was suppressed similarly (+/-60%) on all three doses.

CONCLUSIONS

Already within 3 months after treatment initiation, high-dose ACE inhibition (with imidapril) is superior to low-dose. This is reflected by a more pronounced effect on exercise capacity and some of the neurohormones, but it does not appear to be related to the extent of suppression of plasma ACE.

Cardioprotective effects of an angiotensin-converting-enzyme inhibitor, imidapril, and Ca2+ channel antagonist, amlodipine, in spontaneously hypertensive rats at established stage of hypertension

The present study was performed to compare cardioprotective effects of an angiotensin-converting-enzyme inhibitor, imidapril, and of a Ca2+ channel antagonist, amlodipine, against the cardiac hypertrophy in male spontaneously hypertensive rats (SHRs) at the established stage of hypertension. Fifteen-week-old SHRs were given imidapril (2 and 5 mg/kg/day) or amlodipine (10 mg/kg/day) by gavage for 8 weeks. Three hours after the 1st treatment, imidapril moderately reduced blood pressure without changing heart rate, while amlodipine caused a marked reduction in blood pressure accompanied by transient tachycardia. At the end of the treatments, ventricular weight in the imidapril-treated groups was markedly lower, but that in the amlodipine-treated group was only slightly lower than that in the vehicle-treated group. Myocardial collagen content in the imidapril-treated group tended to be decreased, and significant reduction was observed in the low-dose group. In another experiment, the isolated heart of the imidapril-treated animals demonstrated better cardiac compliance than that in the vehicle-treated animals. In contrast, amlodipine failed to improve cardiac function. The present results suggest that imidapril possesses advantageous effects to prevent cardiac hypertrophy and deteriorated cardiac function in SHRs of established stage of hypertension as compared with amlodipine.