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Horie, S.,Ansari, B.,Masterson, C.,Devaney, J.,Scully, M.,O'Toole, D.,Laffey, J. G.
2016
December
Intensive Care Med Expintensive Care Med Exp
Hypercapnic acidosis attenuates pulmonary epithelial stretch-induced injury via inhibition of the canonical NF-kappaB pathway
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4
11
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BACKGROUND: Hypercapnia, with its associated acidosis (HCA), is a consequence of respiratory failure and is also seen in critically ill patients managed with conventional "protective" ventilation strategies. Nuclear factor kappa-B (NF-kappaB), a pivotal transcription factor, is activated in the setting of injury and repair and is central to innate immunity. We have previously established that HCA protects against ventilation-induced lung injury in vivo, potentially via a mechanism involving inhibition of NF-kappaB signaling. We wished to further elucidate the role and mechanism of HCA-mediated inhibition of the NF-kappaB pathway in attenuating stretch-induced injury in vitro. METHODS: Initial experiments examined the effect of HCA on cyclic stretch-induced inflammation and injury in human bronchial and alveolar epithelial cells. Subsequent experiments examined the role of the canonical NF-kappaB pathway in mediating stretch-induced injury and the mechanism of action of HCA. The contribution of pH versus CO2 in mediating this effect of HCA was also examined. RESULTS: Pulmonary epithelial high cyclic stretch (22 % equibiaxial strain) activated NF-kappaB, enhanced interleukin-8 (IL-8) production, caused cell injury, and reduced cell survival. In contrast, physiologic stretch (10 % strain) did not activate inflammation or cause cell injury. HCA reduced cyclic mechanical stretch-induced NF-kappaB activation, attenuated IL-8 production, reduced injury, and enhanced survival, in bronchial and alveolar epithelial cells, following shorter (24 h) and longer (120 h) cyclic mechanical stretch. Pre-conditioning with HCA was less effective than when HCA was applied after commencement of cell stretch. HCA prevented the stretch-induced breakdown of the NF-kappaB cytosolic inhibitor IkappaBalpha, while IkappaBalpha overexpression "occluded" the effect of HCA. These effects were mediated by a pH-dependent mechanism rather than via CO2 per se. CONCLUSIONS: HCA attenuates adverse mechanical stretch-induced epithelial injury and death, via a pH-dependent mechanism that inhibits the canonical NF-kappaB activation by preventing IkappaBalpha breakdown.BACKGROUND: Hypercapnia, with its associated acidosis (HCA), is a consequence of respiratory failure and is also seen in critically ill patients managed with conventional "protective" ventilation strategies. Nuclear factor kappa-B (NF-kappaB), a pivotal transcription factor, is activated in the setting of injury and repair and is central to innate immunity. We have previously established that HCA protects against ventilation-induced lung injury in vivo, potentially via a mechanism involving inhibition of NF-kappaB signaling. We wished to further elucidate the role and mechanism of HCA-mediated inhibition of the NF-kappaB pathway in attenuating stretch-induced injury in vitro. METHODS: Initial experiments examined the effect of HCA on cyclic stretch-induced inflammation and injury in human bronchial and alveolar epithelial cells. Subsequent experiments examined the role of the canonical NF-kappaB pathway in mediating stretch-induced injury and the mechanism of action of HCA. The contribution of pH versus CO2 in mediating this effect of HCA was also examined. RESULTS: Pulmonary epithelial high cyclic stretch (22 % equibiaxial strain) activated NF-kappaB, enhanced interleukin-8 (IL-8) production, caused cell injury, and reduced cell survival. In contrast, physiologic stretch (10 % strain) did not activate inflammation or cause cell injury. HCA reduced cyclic mechanical stretch-induced NF-kappaB activation, attenuated IL-8 production, reduced injury, and enhanced survival, in bronchial and alveolar epithelial cells, following shorter (24 h) and longer (120 h) cyclic mechanical stretch. Pre-conditioning with HCA was less effective than when HCA was applied after commencement of cell stretch. HCA prevented the stretch-induced breakdown of the NF-kappaB cytosolic inhibitor IkappaBalpha, while IkappaBalpha overexpression "occluded" the effect of HCA. These effects were mediated by a pH-dependent mechanism rather than via CO2 per se. CONCLUSIONS: HCA attenuates adverse mechanical stretch-induced epithelial injury and death, via a pH-dependent mechanism that inhibits the canonical NF-kappaB activation by preventing IkappaBalpha breakdown.
2197-425X (Print) 2197-42
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