SS31, a Mitochondrially Targeted Antioxidant, Prevents Sepsis Induced Reductions in Diaphragm Strength and Endurance.J Appl Physiol (1985) 2020JA
Sepsis-induced diaphragm dysfunction contributes to respiratory failure and mortality in critical illness. There are no treatments for this form of diaphragm weakness. Studies show that sepsis-induced muscle dysfunction is triggered by enhanced mitochondrial free radical generation. We tested the hypothesis that SS31, a mitochondrially-targeted antioxidant, would attenuate sepsis-induced diaphragm dysfunction. Four groups of mice were studied: (a) sham operated controls, (b) sham operated+SS31 (10 mg/kg/day), (c) cecal ligation puncture (CLP), and (d) CLP+SS31. Forty-eight hours post-operatively, diaphragm strips with attached phrenic nerves were isolated and the following assessed: muscle field stimulated force-frequency curves, nerve stimulated force-frequency curves, and muscle fatigue. We also measured calpain activity, 20S proteasomal activity, myosin heavy chain (MHC) levels, mitochondrial function and aconitase activity, an index of mitochondrial superoxide generation. Sepsis markedly reduced diaphragm force generation; SS31 prevented these decrements. Diaphragm specific force generation averaged 30.2±1.4, 9.4±1.8, 25.5±2.3, and 27.9±0.6 N/cm2 for sham, CLP, sham+SS31, and CLP+SS31 groups (p<0.001). Similarly, with phrenic nerve stimulation, CLP depressed diaphragm force generation, effects prevented by SS31. During endurance trials, force was significantly reduced with CLP and SS31 prevented these reductions (p<0.001). Sepsis also increased diaphragm calpain activity, increased 20S proteasomal activity, decreased MHC levels, reduced mitochondrial function (state 3 rates and ATP generation), and reduced aconitase activity; SS31 prevented each of these sepsis-induced alterations (p≤0.017 for all indices). SS31 prevents sepsis-induced diaphragm dysfunction, preserving force generation, endurance and mitochondrial function. Compounds with similar mechanisms of action may be useful therapeutically to preserve diaphragm function in septic, critically ill patients.