Age-related chemical changes in human elastins from non-atherosclerotic areas of thoracic aorta

Elastins from normal appearing areas of human thoracic aortae with varying degrees of mineralization were taken from subjects of different ages and purified by autoclaving their amino acid compositon, Ca and P contents and N terminal profiles were determined before and after EDTA decalcification. (1) Decrease in desmosine concentration with increasing age was accounted for by dilution of the elastin by autoclave-resistant polar glycoproteins. (2) The appearance and growth of a mineral phase with a Ca/P molar ratio typical of apatites was accompanied by an increased association of polar contaminants with elastin. (3) After 24 h EDTA treatment, small and constant amounts of Ca were still apparent although P was absent, in elastins from all age groups. (4) The undialyzable fraction of the material solubilised by EDTA consisted mainly of elastin fragments, glycoproteins and Ca. (5) All the elastin samples showed the same type of N-terminal amino acids. In low and medium mineralized samples the concentration of amino end-groups was slightly increased, while in highly mineralized elastin the content of N-terminal residues was three times greater than in normal young elastin. Extraction with EDTA reduced the amount of end-groups to a normal level. It is suggested that in the initial stages of elastin fibre mineralization, an increased amount of autoclave-resistant glycoproteins becomes associated with elastin; and that with ageing, degradative changes involving peptide-bond cleavage may occur. However, evidence of degradation is found only in old and highly mineralized elastin samples.