Effect of high-salt diet or chronic captopril treatment on exercise capacity in normotensive rats

Angiotensin-Converting Enzyme Inhibition as an Adjunct to Pulmonary Rehabilitation in Chronic Obstructive Pulmonary Disease

RATIONALE

Epidemiological studies in older individuals have found an association between the use of angiotensin-converting enzyme (ACE) inhibition (ACE-I) therapy and preserved locomotor muscle mass, strength, and walking speed. ACE-I therapy might therefore have a role in the context of pulmonary rehabilitation (PR).

OBJECTIVES

To investigate the hypothesis that enalapril, an ACE inhibitor, would augment the improvement in exercise capacity seen during PR.

METHODS

We performed a double-blind, placebo-controlled, parallel-group randomized controlled trial. Patients with chronic obstructive pulmonary disease, who had at least moderate airflow obstruction and were taking part in PR, were randomized to either 10 weeks of therapy with an ACE inhibitor (10 mg enalapril) or placebo.

MEASUREMENTS AND MAIN RESULTS

The primary outcome measurement was the change in peak power (assessed using cycle ergometry) from baseline. Eighty patients were enrolled, 78 were randomized (age 67 ± 8 years; FEV₁ 48 ± 21% predicted), and 65 completed the trial (34 on placebo, 31 on the ACE inhibitor). The ACE inhibitor-treated group demonstrated a significant reduction in systolic blood pressure (Δ, -16 mm Hg; 95% confidence interval [CI], -22 to -11) and serum ACE activity (Δ, -18 IU/L; 95% CI, -23 to -12) versus placebo (between-group differences, P < 0.0001). Peak power increased significantly more in the placebo group (placebo Δ, +9 W; 95% CI, 5 to 13 vs. ACE-I Δ, +1 W; 95% CI, -2 to 4; between-group difference, 8 W; 95% CI, 3 to 13; P = 0.001). There was no significant between-group difference in quadriceps strength or health-related quality of life.

CONCLUSIONS

Use of the ACE inhibitor enalapril, together with a program of PR, in patients without an established indication for ACE-I, reduced the peak work rate response to exercise training in patients with chronic obstructive pulmonary disease.

A randomized controlled trial of angiotensin-converting enzyme inhibition for skeletal muscle dysfunction in COPD

BACKGROUND

Skeletal muscle impairment is a recognized complication of COPD, predicting mortality in severe disease. Increasing evidence implicates the renin-angiotensin system in control of muscle phenotype. We hypothesized that angiotensin-converting enzyme (ACE) inhibition would improve quadriceps function and exercise performance in COPD.

METHODS

This double-blind, randomized placebo-controlled trial investigated the effect of the ACE inhibitor, fosinopril, on quadriceps function in patients with COPD with quadriceps weakness. Primary outcomes were change in quadriceps endurance and atrophy signaling at 3 months. Quadriceps maximum voluntary contraction (QMVC), mid-thigh CT scan of the cross-sectional area (MTCSA), and incremental shuttle walk distance (ISWD) were secondary outcomes.

RESULTS

Eighty patients were enrolled (mean [SD], 65 [8] years, FEV1 43% [21%] predicted, 53% men). Sixty-seven patients (31 fosinopril, 36 placebo) completed the trial. The treatment group demonstrated a significant reduction in systolic BP (Δ-10.5 mm Hg; 95% CI, -19.9 to -1.1; P = .03) and serum ACE activity (Δ-20.4 IU/L; 95% CI, -31.0 to -9.8; P < .001) compared with placebo. No significant between-group differences were observed in the primary end points of quadriceps endurance half-time (Δ0.5 s; 95% CI, -13.3-14.3; P = .94) or atrogin-1 messenger RNA expression (Δ-0.03 arbitrary units; 95% CI, -0.32-0.26; P = .84). QMVC improved in both groups (fosinopril: Δ1.1 kg; 95% CI, 0.03-2.2; P = .045 vs placebo: Δ3.6 kg; 95% CI, 2.1-5.0; P < .0001) with a greater increase in the placebo arm (between-group, P = .009). No change was shown in the MTCSA (P = .09) or ISWD (P = .51).

CONCLUSIONS

This randomized controlled trial found that ACE inhibition, using fosinopril for 3 months, did not improve quadriceps function or exercise performance in patients with COPD with quadriceps weakness.

TRIAL REGISTRY

Current Controlled Trials; No.: ISRCTN05581879; URL: www.controlled-trials.com.

Keeping pace with ACE: are ACE inhibitors and angiotensin II type 1 receptor antagonists potential doping agents?

In the decade since the angiotensin-converting enzyme (ACE) gene was first proposed to be a 'human gene for physical performance', there have been numerous studies examining the effects of ACE genotype on physical performance phenotypes such as aerobic capacity, muscle function, trainability, and athletic status. While the results are variable and sometimes inconsistent, and corroborating phenotypic data limited, carriers of the ACE 'insertion' allele (the presence of an alu repeat element in intron 16 of the gene) have been reported to have higher maximum oxygen uptake (VO2max), greater response to training, and increased muscle efficiency when compared with individuals carrying the 'deletion' allele (absence of the alu repeat). Furthermore, the insertion allele has been reported to be over-represented in elite athletes from a variety of populations representing a number of endurance sports. The mechanism by which the ACE insertion genotype could potentiate physical performance is unknown. The presence of the ACE insertion allele has been associated with lower ACE activity (ACEplasma) in number of studies, suggesting that individuals with an innate tendency to have lower ACE levels respond better to training and are at an advantage in endurance sporting events. This could be due to lower levels of angiotensin II (the vasoconstrictor converted to active form by ACE), higher levels of bradykinin (a vasodilator degraded by ACE) or some combination of the two phenotypes. Observations that individuals carrying the ACE insertion allele (and presumably lower ACEplasma) have an enhanced response to training or are over-represented amongst elite athletes raises the intriguing question: would individuals with artificially lowered ACEplasma have similar training or performance potential? As there are a number of drugs (i.e. ACE inhibitors and angiotensin II type 1 receptor antagonists [angiotensin receptor blockers--ARBs]) that have the ability to either reduce ACEplasma activity or block the action of angiotensin II, the question is relevant to the study of ergogenic agents and to the efforts to rid sports of 'doping'. This article discusses the possibility that ACE inhibitors and ARBs, by virtue of their effects on ACE or angiotensin II function, respectively, have performance-enhancing capabilities; it also reviews the data on the effects of these medications on VO2max, muscle composition and endurance capacity in patient and non-patient populations. We conclude that, while the direct evidence supporting the hypothesis that ACE-related medications are potential doping agents is not compelling, there are insufficient data on young, athletic populations to exclude the possibility, and there is ample, albeit indirect, support from genetic studies to suggest that they should be. Unfortunately, given the history of drug experimentation in athletes and the rapid appropriation of therapeutic agents into the doping arsenal, this indirect evidence, coupled with the availability of ACE-inhibiting and ACE-receptor blocking medications may be sufficiently tempting to unscrupulous competitors looking for a shortcut to the finish line.

Inhibition of angiogenesis by high salt diet is associated with impaired muscle performance following chronic muscle stimulation

OBJECTIVE

High dietary salt has been demonstrated to inhibit angiogenesis in skeletal muscle. The purpose of this study was to determine whether high salt impairs steady state muscle performance following a chronic stimulation protocol.

METHODS

Sprague-Dawley rats were placed on a control diet (CD, 0.4% NaCl) or high salt diet (HSD, 4.0% NaCl) prior to implantation of an electrical muscle stimulator. In chronically stimulated animals, hind limb muscles were stimulated to contract eight hours daily for seven days. Sham animals received a stimulator that was never activated.

RESULTS

Following chronic stimulation, tibialis anterior (TA) muscles of animals on CD demonstrated an 84.6% increase in force of contraction at the end of an acute stimulation bout relative to sham animals fed CD. Decreased muscle fatigue was associated with an increase in capillaries per TA fiber (C:F). Chronic stimulation in HSD rats induced a smaller improvement (52.2%) in final force compared to HSD sham rats. This impairment of muscle performance in high salt-fed rats correlated with inhibited angiogenesis. Infusion of angiotensin II in HSD animals restored angiogenesis and muscle fatigue to CD levels.

CONCLUSIONS

This study suggests that angiogenic inhibition by high salt is associated with impaired skeletal muscle performance following chronic stimulation.

Effect of angiotensin-converting enzyme inhibition on skeletal muscle oxidative function and exercise capacity in streptozotocin-induced diabetic rats

Since exercise capacity is related to the mitochondrial respiration rate in skeletal muscle and both parameters are potentially modulated by the onset of diabetes and by inhibition of the angiotensin-converting enzyme (ACE), we investigated whether skeletal muscle oxidative functions and exercise capacities are impaired in chronic streptozotocin-induced diabetic (STZ) rats and whether ACE inhibition could reverse such abnormalities. The ACE inhibitor perindopril (2 mg kg(-1) day(-1)) was given for a period of 5 weeks to 7-month-old STZ rats (DIA-PE, n = 8) whose haemodynamic function, skeletal muscle mitochondrial function and exercise capacity were compared with those of untreated diabetic (DIA, n = 8) and control rats (CONT, n = 8). Increased arterial blood pressure (157 +/- 12 versus 130 +/- 6 mmHg, P < 0.05) and reduced exercise capacity (29 +/- 2 versus 91 +/- 2 min, respectively, P < 0.01) were observed in DIA compared with CONT. The oxidative capacity of the gastrocnemius muscle was significantly reduced in DIA compared with CONT rats (5.4 +/- 0.5 versus 10.6 +/- 0.7 micromol O(2) min(-1)(g dry weight)(-1), respectively, P < 0.001). Moreover, the coupling between oxidation and phosphorylation was significantly impaired in DIA (-52%, P < 0.001). Angiotensin-converting enzyme inhibition (ACEi) normalized blood pressure without improving mitochondrial function (4.3 +/- 0.8 micromol O(2) min(-1) (g dry weight)(-1) in DIA-PE rats) but reduced exercise capacity to even lower levels (10 +/- 1 min, P < 0.01). Exercise capacity correlated positively with blood pressure in DIA-PE (r = 0.79, P < 0.05). In experimental type 1 diabetic rats, both skeletal muscle mitochondrial respiration and exercise capacity are impaired. The ACEi failed to restore the muscular function and worsened exercise capacity. Further studies will be useful to determine whether an inadequate muscular blood flow secondary to the reduction in mean systemic blood pressure can explain these results.

Effects of angiotensin-converting enzyme inhibitor and exercise training on exercise capacity and skeletal muscle

OBJECTIVE

Physical fitness is closely related with cardiovascular health. We examined the effects of angiotensin-converting enzyme inhibitor, exercise training and their combination on exercise capacity as well as skeletal muscle fiber type and capillarity in spontaneously hypertensive rats (SHR).

METHODS

Seven-week-old male SHR were allocated to four groups: sedentary control (C), treatment with perindopril (3 mg/kg per day) (Per), exercise training on a treadmill (EX), and their combination (Per + EX). Following 8-week interventions, rats were submitted to a stepwise exercise test on a treadmill. After experiments, fiber type and capillarity in soleus muscle were examined.

RESULTS

Exercise capacity significantly increased in Per compared with in C. Combination of exercise training and perindopril further increased exercise capacity compared with perindopril alone, whereas there was no significant difference in exercise capacity between EX and Per + EX. Capillary density increased similarly in Per and EX compared with in C. Combination of exercise training and perindopril further increased capillary density compared with exercise training alone. The percentage of type I fiber increased only in Per + EX.

CONCLUSIONS

We found that in growing SHR, chronic treatment with perindopril enhances untrained exercise capacity, while it does not affect acquired exercise capacity as a result of exercise training. We also found that perindopril promotes adaptive changes of skeletal muscle in response to exercise such as increases in capillary density and percentage of type I fiber.

Cardioprotective Effects of a Novel Iron Chelator, Pyridoxal 2-Chlorobenzoyl Hydrazone, in the Rabbit Model of Daunorubicin-Induced Cardiotoxicity

Iron chelation is the only pharmacological intervention against anthracycline cardiotoxicity whose effectiveness has been well documented both experimentally and clinically. In this study, we aimed to assess whether pyridoxal 2-chlorobenzoyl hydrazone (o-108, a strong iron chelator) can provide effective protection against daunorubicin (DAU)-induced chronic cardiotoxicity in rabbits. First, using the HL-60 leukemic cell line, it was shown that o-108 has no potential to blunt the antiproliferative efficacy of DAU. Instead, o-108 itself moderately inhibited cell proliferation. In vivo, chronic DAU treatment (3 mg/kg weekly for 10 weeks) induced mortality (33%), left ventricular (LV) dysfunction, a troponin T rise, and typical morphological LV damage. In contrast, all animals treated with 10 mg/kg o-108 before DAU survived without a significant drop in the LV ejection fraction (63.2 +/- 0.5 versus 59.2 +/- 1.0%, beginning versus end, not significant), and their cardiac contractility (dP/dt(max)) was significantly higher than in the DAU-only group (1131 +/- 125 versus 783 +/- 53 kPa/s, p < 0.05), which corresponded with histologically assessed lower extent and intensity of myocardial damage. Although higher o-108 dose (25 mg/kg) was well tolerated when administered alone, in combination with DAU it led to rather paradoxical and mostly negative results regarding both cardioprotection and overall mortality. In conclusion, we show that shielding of free intracellular iron using a potent lipophilic iron chelator is able to offer a meaningful protection against chronic anthracycline cardiotoxicity. However, this approach lost its potential with the higher chelator dose, which suggests that iron might play more complex role in the pathogenesis of this disease than previously assumed.