Complete processing of type III collagen in atherosclerotic plaques

The extent of processing of type III collagen is assessed, and the proportions of type I and III collagens are estimated in atherosclerotic plaques obtained from the carotid artery, common femoral artery, and aorta. The fraction of type III collagen that had retained its amino-terminal propeptide (pN-collagen) was 42% in the soluble extract but only 0.0081% in the insoluble residue. Taken together, only 0.011% of the type III collagen in whole plaques was in the form of type III pN-collagen. Together with the small amounts of the free propeptides of type I procollagen, this finding indicates a low rate of collagen turnover. The amounts of solubilized telopeptides of type I and III collagens were measured, after heat denaturation and trypsin digestion of the collagenous helix, by specific immunoassays for the corresponding trypsin-generated antigens. The mean proportion of type III collagen was 61% (95% confidence interval, 58% to 65%) in the carotid and femoral artery plaques and 56% (95% confidence interval, 44% to 68%) in the aortic specimens. The completely processed and cross-linked type III collagen seems to be the major collagen type in atherosclerotic plaques.