Pharmacological targeting of mitochondrial reactive oxygen species counteracts diaphragm weakness in chronic heart failure

Abstract

Diaphragm muscle weakness in chronic heart failure (CHF) is caused by elevated oxidants and exacerbates breathing abnormalities, exercise intolerance, and dyspnea. However, the specific source of oxidants that cause diaphragm weakness is unknown. We examined whether mitochondrial reactive oxygen species (ROS) cause diaphragm weakness in CHF by testing the hypothesis that CHF animals treated with a mitochondria-targeted antioxidant have normal diaphragm function. Rats underwent CHF or sham surgery. Eight weeks after surgeries, we administered a mitochondrial-targeted antioxidant (MitoTEMPO; 1 mg·kg(-1)·day(-1)) or sterile saline (Vehicle). Left ventricular dysfunction (echocardiography) pre- and posttreatment and morphological abnormalities were consistent with the presence of CHF. CHF elicited a threefold (P < 0.05) increase in diaphragm mitochondrial H2O2 emission, decreased diaphragm glutathione content by 23%, and also depressed twitch and maximal tetanic force by ∼20% in Vehicle-treated animals compared with Sham (P < 0.05 for all comparisons). Diaphragm mitochondrial H2O2 emission, glutathione content, and twitch and maximal tetanic force were normal in CHF animals receiving MitoTEMPO. Neither CHF nor MitoTEMPO altered the diaphragm protein levels of antioxidant enzymes: superoxide dismutases (CuZn-SOD or MnSOD), glutathione peroxidase, and catalase. In both Vehicle and MitoTEMPO groups, CHF elicited a ∼30% increase in cytochrome c oxidase activity, whereas there were no changes in citrate synthase activity. Our data suggest that elevated mitochondrial H2O2 emission causes diaphragm weakness in CHF. Moreover, changes in protein levels of antioxidant enzymes or mitochondrial content do not seem to mediate the increase in mitochondria H2O2 emission in CHF and protective effects of MitoTEMPO.

Diaphragm Abnormalities in Patients with End-Stage Heart Failure: NADPH Oxidase Upregulation and Protein Oxidation

“…These results corroborate previous findings in animals with severe HF induced by aortic stenosis (Coirault et al, 2007) or in the early stages post-myocardial infarction (Supinski and Callahan, 2005; Bowen et al, 2015a), but disagrees with data from our group in rats and mice with moderate HF in the later stages post-myocardial infarction (Ahn et al, 2015; Laitano et al, 2016). We speculate that the increase in diaphragm protein carbonyls in chronic HF is related to disease severity.…”

“…Regarding protein function, carbonylation of sarcomeric proteins in vitro impairs actomyosin cross- bridge kinetics and, in general, exposure to oxidants depresses diaphragm force and shortening velocity (Perkins et al, 1997; Callahan et al, 2001; Coirault et al, 2007). These functional outcomes are consistent with impaired diaphragm contractile properties in HF animals (Lecarpentier et al, 1998; Coirault et al, 2007; van Hees et al, 2007, 2008b; Empinado et al, 2014; Ahn et al, 2015), which are prevented by pharmacologic antioxidants (Supinski and Callahan, 2005; Laitano et al, 2016) or knockout of p47 phox (Ahn et al, 2015). …”

“…This outcome is likely due to our limited sample size and large variability in the human diaphragm data. In animal models of HF with reduced ejection fraction, diaphragm levels of SOD1 or SOD2 were either unchanged (Ahn et al, 2015; Laitano et al, 2016) or elevated (Mangner et al, 2015), whereas the activity of GPX was increased (Mangner et al, 2015) and catalase was unchanged (Mangner et al, 2015). Nonetheless, diaphragm catalase activity was increased in a model of HF with preserved ejection fraction (Bowen et al, 2015b).…”

Regulation of NADPH oxidases in skeletal muscle

“…Mechanical ventilation elevates diaphragm ROS, which can be prevented by either apocynin or a mitochondria-targeted antioxidant [123, 148]. Similarly, the increase in diaphragm ROS elicited by chronic heart failure or exposure to exogenous sphingomyelinase are prevented by knockout of Nox2 subunits (Nox2 −/y [158], p47 phox−/− [38]) or mitochondria-targeted antioxidants [159]. Finally, repetitive contraction induces a rapid rise in cytosolic superoxide mediated by Nox, which is followed by a slower rise in mitochondrial ROS [18, 160].…”

Skeletal muscle bioenergetics in aging and heart failure

“…Recent work demonstrates that mitochondrial oxidative stress plays an important role in skeletal muscle dysfunction in both conditions. Skeletal muscle mitochondria from aged mice and those with heart failure have an increased capacity to produce H 2 O 2 [53,95]. This increased mitochondrial oxidative stress can control mitochondrial function both in vivo [22,23] and ex vivo [96,97].…”