Relationship between proteolytic enzymes and atherosclerosis in aortic aneurysms

Aortic elastase and aortic collagenase were assayed in 38 patients who underwent an operation for thoracic or infrarenal aneurysm or infrarenal aortic occlusive disease and in 15 control patients (heart or kidney donors). Elastase was elevated in normal aortas of the infrarenal region (1.10 milliunits per gram, p less than 0.05), and in atherosclerotic descendens aneurysms (1.24 milliunits per gram, p less than 0.05), compared with the ascending aorta, when normal; aneurysmatic specimens revealed similar low elastolytic activities (0.10 milliunits per gram). The highest elastase content was found in infrarenal aneurysms (4.65 milliunits per gram). Collagenase assays yielded no significant differences, although higher activities were extracted from aortas of the infrarenal region. Coexistent atherosclerosis and wall destruction were evaluated by macroscopic and histologic investigation. All infrarenal specimens demonstrated severe atherosclerotic wall degeneration with depletion of elastic fibers. As the atherosclerotic specimens did not differ from normal aortas by protease assay, the higher elastase of infrarenal samples compared with the thoracic aorta suggests a more rapid fiber metabolism in the infrarenal region. The significantly elevated elastolytic activity of infrarenal aneurysms points to the decisive role of elastase in infrarenal aneurysm formation.