Peroxide Enhances Elastase-Mediated Injury In Vitro
Jerome O. Cantor, Department of Pharmaceutical Sciences, College of Pharmacy and Health Sciences
Bronislava Shteyngart and Joseph M. Cerreta
Pulmonary emphysema is characterized by destruction of elastic fibers, resulting in dilatation and rupture of airspaces. Our laboratory has studied the mechanisms responsible for this lung damage, particularly the interaction of oxidants with enzymes known to degrade these fibers (elastases). Previously we have shown that oxidants present in hyperoxia enhance airspace enlargement in a hamster model of elastase-induced emphysema. To further understand the mechanism responsible for this finding, the effect of oxidants on elastase was studied in vitro, using a radiolabeled elastic fiber matrix derived from rat pleural mesothelial cells. Matrix samples were treated with 1%, 3%, or 10% H2O2 for 1 hr, then incubated with 1.0 g/ml porcine pancreatic elastase for 2 hrs. Radioactivity released from the matrix was used as a measure of elastolysis. Results indicate that sequential exposure to H2O2 and elastase synergistically enhanced elastolysis compared to separate enzyme and oxidant treatment. In contrast, exposure to 1%, 3%, or 10% H2O2 alone produced only minimal elastolysis (<20 cpm). When elastase and 3% H2O2 were given concomitantly, elastolysis was actually reduced compared to elastase treatment alone (263 vs 311 cpm). While the precise mechanism(s) responsible for these findings still remain unclear, preliminary studies indicate that H2O2 may degrade the isodesmosine crosslinks of elastin, thereby reducing the stability of the elastic fiber matrix and increasing its susceptibility to elastase injury. With regard to lung diseases such as emphysema, these results suggest that H2O2 and other oxidants from inflammatory cells or the environment could act as priming agents for enzyme-mediated breakdown of elastic fibers. This would help explain why cigarette smoke and other pollutants increase the rate of progression of pulmonary emphysema.