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Post-cardiac transplant arteriopathy in piglets is associated with fragmentation of elastin and increased activity of a serine elastase.

In experimental piglets after heterotopic heart transplant, we observed an immune/inflammatory response in the coronary arteries with increased expression of interleukin-1 beta and accumulation of fibronectin and smooth muscle cells in the subendothelium (N. Clausell, S. Molossi, M. Rabinovitch, Am J Pathol 1993, 142, 1772-1786). Proteolytic enzymes including elastases regulate cytokine activity and are associated with the development of neointimal proliferation. We now report ultrastructural evidence of elastolytic activity in the donor compared to host coronary arteries judged by a fivefold increase in the breaks in the internal elastic lamina, (P < 0.01) correlating with a 10-fold increase in elastase activity per mg tissue (P < 0.01). The enzyme activity is serine elastase, i.e., inhibited by phenylmethyl sulfonyl fluoride, and elafin but not EDTA. Using a novel strategy that greatly increases the activity extractable from the tissue, we resolved the enzyme on an elastin substrate gel as a protein of approximately 23 kd. Ours is the first report and characterization of increased elastase activity associated with the development of the post-cardiac transplant coronary arteriopathy. The source may be inflammatory or smooth muscle cells, and elastase may play a pathophysiological role in neointimal proliferation by activating cytokines and growth factors and by release of chemotactic peptides.