Role of alpha-macroglobulin-elastase complexes in the pathogenesis of elastase-induced emphysema in hamsters.

Radiolabeled, enzymatically active or chloromethyl ketone-inactivated porcine pancreatic elastase was endotracheally instilled into hamsters. Gel filtration of the bronchopulmonary lavage fluid revealed two major radioactive fractions: one, eluting at 780,000 daltons, corresponding to an alpha-macroglobulin-pancreatic elastase complex, and another, at 68,000 daltons, corresponding to an alpha-1-protease inhibitor-pancreatic elastase complex. Elastolytic activity was recovered in the bronchopulmonary lavage fluid up to 4 d after elastase instillation and was associated with the alpha-macroglobulin-pancreatic elastase complex. Small amounts of this complex were recovered 14 d after instillation. When less than 1% (1.5--1.7 micrograms) of the usual dose of elastase was instilled into hamsters, the major radioactive complex was alpha-1-protease inhibitor-pancreatic elastase complex, and little or no elastolytic activity was found in the lavage fluid. In contrast to the instillation of 220 micrograms of elastase, no disease or hemorrhagic reaction was detected with this low dose, and without hemorrhage only insignificant amounts of alpha-macroglobulin-pancreatic elastase complexes were recovered from the lungs. To study the interaction of circulating antiproteases with elastase, hamster plasma was allowed to interact directly with the radiolabeled elastase; alpha-macroglobulin bound much more of the elastase than alpha-1-protease inhibitor, confirming the findings in the lung lavage experiments. The hamster's susceptibility to pancreatic elastase-induced emphysema may depend on the preferential binding of elastase to alpha-macroglobulin, which protects the elastolytic potential, rather than to alpha-1-protease inhibitor, which inactivates elastase. We speculate that if even a fraction of the residual radioactivity found in the hamster lungs as long as 144 d after instillation of elastase represents enzymatically active alpha-macroglobulin-pancreatic elastase complex, this could serve as a source of persistent elastolytic activity, which might explain the progressive nature of the pulmonary lesion.