Direct Cleavage of Soluble Collagen by Ozone or Hydroxyl Radicals: Possible Mechanism of Emphysema Produced by Exposure to Oxidant Gases

Emphysema is produced in animals several weeks after exposure to oxidant gases. Oxidant gases are known to damage the alveolar walls and capillary bed of the lung. We have shown a decrease in the content of lung collagen, but not elastin, at the end of a period of hyperoxic exposure in rats (Fed Proc 1982; 41:488), suggesting that early destruction of collagen may be related to the late emphysema found in this model. This destruction was followed by deposition of excess collagen which appeared structurally and functionally abnormal. Our hypothesis is outlined in Figure 1. We hypothesize that exposure to highly reactive oxygen species causes the direct degradation of collagen. Collagenous peptides are known to be chemotactic for inflammatory cells which release both active O2 radicals and proteinases which are believed to degrade connective tissue.