The role of poly(ADP)ribose synthetase in lung ischemia-reperfusion injury

Abstract

The activation of poly(ADP)ribose synthetase (PARS), in response to free radical and oxidant induced DNA strand breaks triggers an energy consuming cycle ultimately resulting in cell death. Previous studies have reported that inhibition of PARS pharmacologically or by genetic deficiency confer protection in models of endotoxic shock and ischemia-reperfusion injury (heart and gut). The purpose of this study was to determine the role of PARS inhibition in lung ischemia-reperfusion injury (LIRI). Left lungs of Long Evans rats were rendered ischemic for ninety minutes and reperfused for up to four hours. Treated animals received 3mg/kg IV of a PARS inhibitor (INO-1001) 30 minutes prior to ischemia. Injury was assessed in terms of tissue neutrophil accumulation (MPO content), vascular permeability (125-I BSA extravasation) and bronchoalveolar lavage (BAL) leukocyte count. Cytokine and chemokine content in BAL fluid was determined by ELISA. Separate tissue samples were processed for nuclear transcriptional factor activation by EMSA and apoptosis by TUNEL assay. Lung vascular permeability was reduced in treated animals by 73% compared to controls (p<0.009). The protective effects of PARS inhibition correlated with a 46% decrease in tissue MPO content (p<0.008) and a 56% reduction in BAL leukocyte counts (p<0.01). This positively correlated with diminshed expression of pro-inflammatory mediators. TNFα was decreased by 96%, MIP-1α by 99%, MIP-2 by 75%, and CINC by 70%.The expression of nuclear transcription factors and the degree of apoptosis were also reduced. The deleterious effects of LIRI are initiated by formation of free radicals and superoxides which in turn leads to DNA strand breaks. Consequently activation of PARS causes cellular energy depletion and ultimately cell death, as well as pro-inflammatory nuclear transcription factor activation. Amelioration of these mechanisms likely contributes to the protective effects of PARS inhibition in LIRI.