Invited Review HIGHLIGHTED TOPIC Free Radical Biology in Skeletal Muscle Ventilatory muscle activation and inflammation: cytokines, reactive oxygen species, and nitric oxide

Vassilakopoulos T, Hussain SN. Ventilatory muscle activation and inflammation: cytokines, reactive oxygen species, and nitric oxide. J Appl Physiol 102: 1687–1695, 2007. First published December 21, 2006; doi:10.1152/japplphysiol.01273.2006.— Strenuous diaphragmatic contractions that are induced by inspiratory resistive breathing initiate an inflammatory response that involves the elevation of proand anti-inflammatory cytokines within the diaphragm, which may then spill into the circulation. The production of reactive oxygen species within working respiratory muscles increases in response to these strenuous diaphragmatic contractions. At the same time, diaphragmatic nitric oxide (NO) production declines significantly, despite a time-dependent increase in NO synthase isoform protein expression. The increase in adhesion molecule expression and infiltration of granulocytes and macrophages that follows may contribute to the contraction-induced diaphragm injury. Enhanced generation of reactive oxygen species, oxidative stress augmentation, reduced NO production, and glycogen depletion are potential stimuli for the cytokine induction that is secondary to strenuous diaphragmatic contractions. This production of cytokines within the diaphragm may contribute to the diaphragmatic muscle fiber injury that occurs with strenuous contractions or to the expected repair process. TNFis a cytokine that compromises diaphragmatic contractility and may contribute to muscle wasting. IL-6 is a cytokine that may have beneficial systemic effects by mobilizing glucose from the liver and free fatty acids from the adipose tissue and providing them to the strenuously working respiratory muscles. Thus cytokine upregulation within the working diaphragm may be adaptive and maladaptive.