Collagen stability and collagenolytic activity in the normal and aneurysmal human abdominal aorta

Two issues were addressed in this study. The first was whether a bona fide collagenase exists within the wall of the aorta. The second was whether the activity of this putative collagenase is greater in aneurysmal tissue. No collagenase could be extracted from the wall of the aorta under nondenaturing conditions. However, hydroxyproline was liberated from tissue samples allowed to autolyze at neutral pH under reaction conditions favoring the activity of collagenase. Such an activity was probably enzymic as it occurred in a time- and temperature-dependent fashion and was suppressed by chelators. In normal and stenotic tissue, activity was increased by adding aminophenylmercuric acetate, an activator of latent collagenase. Examination of the blanks revealed that the collagen of aneurysmal aorta was more soluble than normal. Furthermore, its digestion kinetics differed in a way that suggested that aneurysmal aorta possessed a labile component that was absent from normal tissue. Although the activity of the putative aortic collagenase was higher than normal in the aneurysmal tissue, our assays do not distinguish between changes in the amount or activity of the enzyme and alterations in the collagen.