Recent studies indicate that the diaphragm becomes profoundly weak in critically ill patients. Diaphragm weakness, in turn, increases the duration of mechanical ventilation, increases patient mortality, and is a major contributor to the high cost of taking care of critically ill, mechanically ventilated patients in the VA health care system. Our own work indicates that infections are a major cause of the development of severe diaphragm weakness in critically ill patients. It is also known that infections elicit increases in diaphragm free radical generation, and that heightened free radical generation contributes to the development of weakness. The precise mechanism(s) by which infections activate free radical generation in skeletal muscle are not known, however. Moreover, currently there is no pharmacological treatment to prevent or reverse infection induced diaphragm weakness in critically ill patients. The purpose of the present project is to discover the mechanisms by which infections increase diaphragm free generation and to employ this mechanistic information to define novel translatable pharmacological treatments that can be used to prevent and reverse diaphragm weakness in critically patients. Our central hypothesis is that infection induced diaphragm dysfunction is primarily a consequence of the sequential activation of neutral sphingomyelinase 2, cytosolic phospholipase A2 (cPLA2), mitochondrial free radical generation, and proteolytic pathways (e.g. calpain). The planned studies will test this hypothesis and use this information to define new therapies that can be quickly translated into clinical usage.
Aim 1 experiments will delineate the specific mechanism(s) by which infections induce heightened free radical generation in skeletal muscle. Experiment 1.1 will test the hypothesis that infections first activate neutral sphingomyelinase 2 in skeletal muscle. Experiment 1.2 will test the hypothesis that infection induced activation of neutral sphingomyelinase 2 subsequently activates skeletal muscle cPLA2, which, in turn, induces an increase in mitochondrial free radical production.
Aim 2 experiments will determine the specific skeletal muscle proteolytic pathways activated (Experiment 2.1) and cellular proteins degraded (Experiment 2.2) as a consequence of infection induced activation of cPLA2 and mitochondrial free radical generation.
Aim 3 experiments will determine if novel pharmacological agents which block cPLA2 activation and mitochondrial free radical generation prevent loss of diaphragm function in the cecal ligation perforation animal model of sepsis. We will study an agent which blocks activation of cPLA2 (taurine) in Experiment 3.1, a direct cPLA2 inhibitor (CDIBA) in Experiment 3.2, and an inhibitor of mitochondrial free radical generation (SS31) in Experiment 3.3.

Public Health Relevance

The long term goal of this proposal is to identify treatments to prevent weakness in critically ill patients. The novel pharmacological agents that will be tested in Aim 3 studies of the current proposal were found to approximately double diaphragm strength in an animal model of infection. If these same agents can produce comparable effects on diaphragm strength in humans, then administration of these therapies to critically ill VA MICU patients should reduce the duration of mechanical ventilation by more than 60%. A therapy with this large of an impact should cut VA MICU costs by as much as $850 Million dollars per year and save 2400 lives per year. As a result, if the present work leads to the discovery of a new treatment for diaphragm weakness in MICU patients, this discovery has the potential to markedly reduce VA MICU costs, save thousands of lives, and reduce long term disability by improving skeletal muscle strength.

National Institute of Health (NIH)
Veterans Affairs (VA)
Non-HHS Research Projects (I01)
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VA Medical Center - Lexington, KY
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Supinski, Gerald S; Morris, Peter E; Dhar, Sanjay et al. (2018) Diaphragm Dysfunction in Critical Illness. Chest 153:1040-1051
Supinski, Gerald S; Alimov, Alexander P; Wang, Lin et al. (2016) Calcium-dependent phospholipase A2 modulates infection-induced diaphragm dysfunction. Am J Physiol Lung Cell Mol Physiol 310:L975-84
Supinski, Gerald S; Westgate, Phillip; Callahan, Leigh A (2016) Correlation of maximal inspiratory pressure to transdiaphragmatic twitch pressure in intensive care unit patients. Crit Care 20:77
Callahan, Leigh A; Supinski, Gerald S (2016) Early Mobilization in the ICU: Help or Hype? Crit Care Med 44:1239-40
Supinski, Gerald S; Alimov, Alexander P; Wang, Lin et al. (2015) Neutral sphingomyelinase 2 is required for cytokine-induced skeletal muscle calpain activation. Am J Physiol Lung Cell Mol Physiol 309:L614-24
Supinski, Gerald S; Callahan, Leigh A (2015) How Important is Diaphragm Function as a Determinant of Outcomes for MICU Patients in Respiratory Failure? Physiology (Bethesda) 30:336-7
Supinski, Gerald S; Wang, Lin; Song, Xiao-Hong et al. (2014) Muscle-specific calpastatin overexpression prevents diaphragm weakness in cecal ligation puncture-induced sepsis. J Appl Physiol (1985) 117:921-9
Callahan, Leigh A; Supinski, Gerald S (2014) Hyperglycemia-induced diaphragm weakness is mediated by oxidative stress. Crit Care 18:R88
Supinski, Gerald S; Callahan, Leigh A (2014) ?-hydroxy-?-methylbutyrate (HMB) prevents sepsis-induced diaphragm dysfunction in mice. Respir Physiol Neurobiol 196:63-8
Supinski, Gerald S; Callahan, Leigh Ann (2013) Diaphragm weakness in mechanically ventilated critically ill patients. Crit Care 17:R120