Age-related changes in the elastic tissue of the human thoracic aorta

Thirty human aortas with varying degrees of atheroma graded macroscopically according to the WHO classification were taken at autopsy from subjects of different ages (24-86 years). Study by light microscopy showed aortas with an intact wall (4 subjects, 25-46 years) with a thin intima and regular elastic layers, and aortas with varying degrees of modification of the wall, where the intima was of varying thickness and the elastic fibers showed varying degrees of damage (moderate lesions: 5 subjects, 35-52 yrs; severe lesions: 21 subjects, 26-86 yrs). From each aorta, a 4-cm segment from the tunica media, free of atheromatous lesions, was defatted and subjected to successive treatment with EDTA-Tris, 6 M guanidine-HCl-Tris, 6 M guanidine-HCl-Tris-DTE and collagenase. The residues (EP residues) were subjected to amino acid (AA) analysis and transmission electron microscopy (TEM) study. In the young subject, the AA composition was similar to that of elastin and the TEM images were characteristic of this substance. In the aging subject, an increase in polar AA and a parallel decrease in apolar AA and crosslinks was noted. By TEM, the elastin was seen to be associated with abundant fibrillar material. Trypsin treatment of EP residues gave E residues, whose composition and TEM appearance were similar in all samples, corresponding to the standard composition of elastin and its classic appearance by electron microscopy. We suggest that the fibrillar material removed by trypsin is the morphological reflection of the chemical variations observed in the EP residues. These correspond to contamination of the elastin by a polar protein fraction. This contamination is closely correlated with age but not with the degree of atheroma. Thus the age-related chemical changes in elastin appear to be independent of the onset and evolution of atheromatous lesions. The 10-15 nm diameter of the contaminating fibrillar material suggests that may be the microfibrillar fraction of elastic tissue.