Relationship between the content of lysyl oxidase-dependent cross-links in skin collagen, nonenzymatic glycosylation, and long-term complications in type I diabetes mellitus.

Many abnormalities in collagen have been reported in insulin-dependent diabetes mellitus, some or all of which have been attributed to increased cross-linking. Although recent work has focused on the role of glucose-derived collagen cross-links in the pathogenesis of diabetic complications, relatively few studies have investigated the role of lysyl oxidase-dependent (LOX) cross-links. In the present study, LOX cross-links and nonenzymatic glycosylation were quantified in skin collagen from diabetic subjects. There was an increase in the difunctional cross-link dihydroxylysinonorleucine (DHLNL) as well as in one of its trifunctional maturation products, hydroxypyridinium. All other LOX crosslinks were normal. Nonenzymatic glycosylation was increased in diabetic skin collagen, and this increase was correlated with increases in DHLNL (P less than 0.001). The biochemical results were examined for correlations with clinical data from the same subjects. Increases in DHLNL content were associated with duration of diabetes (P less than 0.003), glycohemoglobin levels (P less than 0.001), hand contractures (P less than 0.05), skin changes (P less than 0.005), and microalbuminuria (P less than 0.01). In nondiabetic subjects age was not correlated with collagen cross-link content with the exception that his-HLNL increased with age (r = 0.79, P less than 0.02). In diabetic subjects, PA levels decreased with age (r = 0.51, P less than 0.02). With increased duration of diabetes, DHLNL content was increased (r = 0.55, P less than 0.003) and OHP was increased (r = 0.59, P less than 0.01), whereas PA levels were decreased (r = -0.48, P less than 0.04). Nonenzymatic glycosylation of collagen was also increased with increased duration of diabetes (hex-lys, r = 0.47, P less than 0.02; hex-hyl, r = 0.39, P less than 0.05). We conclude that: (a) lysyl oxidase-dependent cross-linking is increased in skin collagen in diabetes and (b) that these changes in skin collagen are correlated with duration of diabetes, glycemic control, and long-term complications.