Synergistic Effect of Hydrogen Peroxide and Elastase on Elastic Fiber Injury In Vitro

This laboratory has previously shown that hyperoxia enhances 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 activity was studied in vitro, using a radiolabeled elastic fiber matrix derived from rat pleural mesothelial cells. Matrix samples were treated with either 0.1%, 1%, 3%, or 10% hydrogen peroxide (H₂O₂) for 1 hr, then incubated with 1.0 μg/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 markedly enhanced elastolysis compared to enzyme treatment alone. A 22% increase in elastolysis was seen with 0.1% H₂O₂ (325 vs. 396 cpm; P < 0.05), whereas samples pretreated with 1%, 3%, and 10% H₂O₂ showed increases of 53% (274 vs. 420 cpm; P < 0.05), 71% (381 vs. 653 cpm; P < 0.01), and 38% (322 vs. 443 cpm; P < 0.01), respectively. Exposure to various concentrations of H₂O₂ alone (0.1% to 10%) produced only minimal elastolysis (<20 cpm). However, 1% H₂O₂ was capable of degrading peptide-free desmosine and isodesmosine, suggesting that exposure to this oxidant may reduce the stability of the elastic fiber matrix. With regard to lung diseases such as emphysema, H₂O₂ and other oxidants derived from inflammatory cells or the environment could possibly act as priming agents for elastase-mediated breakdown of elastic fibers, resulting in amplification of lung injury.