Late-life enalapril administration induces nitric oxide-dependent and independent metabolic adaptations in the rat skeletal muscle

Abstract

Recently, we showed that administration of the angiotensin-converting enzyme inhibitor enalapril to aged rats attenuated muscle strength decline and mitigated apoptosis in the gastrocnemius muscle. The aim of the present study was to investigate possible mechanisms underlying the muscle-protective effects of enalapril. We also sought to discern the effects of enalapril mediated by nitric oxide (NO) from those independent of this signaling molecule. Eighty-seven male Fischer 344 × Brown Norway rats were randomly assigned to receive enalapril (n = 23), the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; n = 22), enalapril + L-NAME (n = 19), or placebo (n = 23) from 24 to 27 months of age. Experiments were performed on the tibialis anterior muscle. Total NOS activity and the expression of neuronal, endothelial, and inducible NOS isoforms (nNOS, eNOS, and iNOS) were determined to investigate the effects of enalapril on NO signaling. Transcript levels of tumor necrosis factor-alpha (TNF-α) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) were assessed to explore actions of enalapril on inflammation and mitochondrial biogenesis, respectively. Protein expression of energy-sensing and insulin signaling mediators, including protein kinase B (Akt-1), phosphorylated Akt-1 (pAkt-1), mammalian target of rapamycin (mTOR), AMP-activated protein kinase subunit alpha (AMPKα), phosphorylated AMPKα (pAMPKα), and the glucose transporter GLUT-4, was also determined. Finally, the generation of hydrogen peroxide (H2O2) was quantified in subsarcolemmal (SSM) and intermyofibrillar (IFM) mitochondria. Enalapril increased total NOS activity, which was prevented by L-NAME co-administration. eNOS protein content was enhanced by enalapril, but not by enalapril + L-NAME. Gene expression of iNOS was down-regulated by enalapril either alone or in combination with L-NAME. In contrast, protein levels of nNOS were unaltered by treatments. The mRNA abundance of TNF-α was reduced by enalapril relative to placebo, with no differences among any other group. PCG-1α gene expression was unaffected by enalapril and lowered by enalapril + L-NAME. No differences in protein expression of Akt-1, pAkt-1, AMPKα, pAMPKα, or GLUT-4 were detected among groups. However, mTOR protein levels were increased by enalapril compared with placebo. Finally, all treatment groups displayed reduced SSM, but not IFM H2O2 production relative to placebo. Our data indicate that enalapril induces a number of metabolic adaptations in aged skeletal muscle. These effects result from the concerted modulation of NO and angiotensin II signaling, rather than from a dichotomous action of enalapril on the two pathways. Muscle protection by enalapril administered late in life appears to be primarily mediated by mitigation of oxidative stress and pro-inflammatory signaling.

Effect of Angiotensin-Converting Enzyme Inhibitors on Physical Function in Elderly Subjects: A Systematic Review and Meta-Analysis

“…The mechanisms for effects of ACEIs on skeletal muscle may be concluded as muscle fiber type effect which determines a shift of the myosin-heavy chains of leg skeletal muscle from type II toward type I, Anti-inflammatory effect, nutritional effect, effects on angiogenesis and metabolic effect [54]. Our result showed that ACEIs could not improve gait speed and grip strength significantly, indicating that ACEIs could not improve physical function in elderly, which was inconsistent with the results from animal experiments [55][56][57][58]. The reasons for this phenomenon may relate to the short tintervening time and limitations of this meta-analyses.…”

Angiotensin II blockade: how its molecular targets may signal to mitochondria and slow aging. Coincidences with calorie restriction and mTOR inhibition

“…However, ACE inhibitors increase mTOR protein levels in rat skeletal muscle (274), which is consistent with the observed ACE-induced impairment of mTOR signaling in mouse myoblast cells that overexpress ACE (292). Furthermore, data demonstrating a key role for arrestin-dependent signaling in AT 1 R-mediated regulation of mTORC1 (211) suggest that, by favoring proliferation, cell growth, and hyperplasia, arrestin-dependent signaling may result in adverse cardiovascular effects.…”

Hypertension and aging

“…Moreover, in addition to effects in mitigating hypertension, several antihypertensive drugs are also thought to have pleiotropic physiologic effects that extend beyond lowering blood pressure (Sica, 2011; Zoccali and Mallamaci, 2014). For instance, prior work has demonstrated the effects of angiotensin converting enzyme (ACE) inhibitors in endocrine signaling, regulation to tissue-specific oxidative stress and inflammation, and in the regulation of body composition (Carter et al, 2011; Giovannini et al, 2010; Marzetti et al, 2012). Epidemiological studies have also suggested that use of ACE inhibitors may indeed slow functional decline among seniors (Gambassi et al, 2000; Onder et al, 2002), though subsequent evidence suggests that these benefits may only exist when combined with physical exercise (Buford et al, 2012; Carter et al, 2012).…”