Mechanical stress activates xanthine oxidoreductase through MAP kinase-dependent pathways

1 Division of Pulmonary and Critical Care Medicine, 2 Department of Medicine, Department of Environmental Health Sciences, Bloomberg School of Public Health, and 3 Division of Cardiopulmonary Pathology and Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and 4 Pulmonary and Critical Care Division, Tupper Research Institute, Tufts-New England Medical Center, Tufts University School of Medicine, Boston, Massachusetts Submitted 27 October 2005 ; accepted in final form 7 April 2006 ABSTRACT Xanthine oxidoreductase (XOR) plays a prominent role in acute lung injury because of its ability to generate reactive oxygen species. We investigated the role of XOR in ventilator-induced lung injury (VILI). Male C57BL/6J mice were assigned to spontaneous ventilation (sham) or mechanical ventilation (MV) with low (7 ml/kg) and high tidal volume (20 ml/kg) for 2 h after which lung XOR activity and expression were measured and the effect of the specific XOR inhibitor allopurinol on pulmonary vascular leakage was examined. In separate experiments, rat pulmonary microvascular endothelial cells (RPMECs) were exposed to cyclic stretch (5% and 18% elongation, 20 cycles/min) for 2 h before intracellular XOR activity measurement. Lung XOR activity was significantly increased at 2 h of MV without changes in XOR expression. There was evidence of p38 MAP kinase, ERK1/2, and ERK5 phosphorylation, but no change in JNK phosphorylation. Evans blue dye extravasation and bronchoalveolar lavage protein concentration were significantly increased in response to MV, changes that were significantly attenuated by pretreatment with allopurinol. Cyclic stretch of RPMECs also caused MAP kinase phosphorylation and a 1.7-fold increase in XOR activity, which was completely abrogated by pretreatment of the cells with specific MAP kinase inhibitors. We conclude that XOR enzymatic activity is significantly increased by mechanical stress via activation of p38 MAP kinase and ERK and plays a critical role in the pathogenesis of pulmonary edema associated with VILI. mechanical ventilation; acute lung injury; mitogen-activated protein kinase Address for reprint requests and other correspondence: P. M. Hassoun, Div. of Pulmonary and Critical Care Medicine, 5501 Hopkins Bayview Circle, Baltimore, MD 21224 (e-mail: phassoun{at}jhmi.edu )