Age-related changes in non-enzymatic glycosylation of human basement membranes

Age and diabetes-related changes in the extent of non-enzymatic glycosylation of two anatomically distinct human basement membranes were examined. The amount of glucose in ketoamine linkage to glomerular basement membrane, measured by the thiobarbituric acid reaction, correlated positively and significantly with age. For analysis of lens capsule basement membrane, adsorption to agarose-linked phenylboronate was used. The ability of this resin to completely discriminate non-glycosylated from glycosylated residues was first documented by separating synthetic preparations of radioactive glucitol-lysine and glucitol-hydroxylysine, the glucosylamines formed with non-enzymatic glycosylation of collagen, from the respective free amino acids by affinity chromatography on and batch adsorption to phenylboronate. The extent of non-enzymatic glycosylation of lens capsule basement membranes correlated with age in both non-diabetic and diabetic samples, and the slopes of the lines for age versus glycosylation were similar in both groups. The calculated line for diabetic specimens, however, was displaced about 15 years to the left, compatible with premature aging. The results indicate that non-enzymatic glycosylation can be accurately assessed in minute amounts of tissue by phenylboronate adsorption, and provide evidence that human basement membrane is subject to increased glycosylation with aging and diabetes.