PURPOSE: Previous work in our lab has shown that short-term inhalation of nitric oxide (NO) before ischemia/reperfusion (I/R) ameliorates the detrimental I/R-induced consequences on lung function. In consideration of the major role of proteolysis in lung I/R, the effects of preconditioning with NO on proteases and inhibitors in a rat model of in situ I/R of the left lung were investigated.
METHODS: Left lung ischemia was maintained for 60 min, followed by reperfusion for up to 4 h. In the NO group, inhalation of NO (10 min, 15 ppm) preceded I/R. Animals in the control group underwent sham surgery without NO inhalation and ischemia. The extent of I/R injury was assessed in terms of oxygenation (arterial pO2), lung albumin permeability (Evans blue extravasation), and myeloperoxidase (MPO) activity in lung tissue. Matrix metalloproteinases (MMP), elastase, and tissue inhibitors of MMP (TIMP) were measured in bronchoalveolar lavage fluid (BALF), in tissue extracts, and in plasma, using Western blots and zymograms.
RESULTS: The animals in the I/R group showed symptoms of severe pulmonary I/R injury, including reduction of arterial pO2 and increased Evans blue extravasation. After 30 min reperfusion, a massive accumulation of MMP-2 and MMP-7 in left lung BALF was observed. The increased activities of elastase and MMP-9 in tissue extracts of the left lung were correlated with an increase in MPO activity. The levels of TIMP-1, TIMP-2, TIMP-4, MMP-1 and MMP-3 in both lungs did not vary among treatment groups. Short-term NO inhalation ameliorated the I/R-induced effects on oxygenation and lung permeability. The treatment also prevented the secretion of MMP-2 and MMP-7, but the tissue levels of MPO, MMP-9 and elastase were not affected.
CONCLUSION: Preconditioning of the rat lung with inhaled NO prevents the I/R-induced loss of function and the secretion of epithelial MMP activity, but there is no effect on the invasion of neutrophils and the release of neutrophil proteases.
CLINICAL IMPLICATIONS: The results support the view that short-term NO inhalation is sufficient to ameliorate I/R injury of the lung.
DISCLOSURE: Wolfgang Witt, No Product/Research Disclosure Information; Grant monies (from sources other than industry) FR Germany, InnoRegio Research Grant