Experimental nonenzymatic glycosylation of vitreous collagens occurs by two pathways.

PURPOSE: To study the process of nonenzymatic glycosolation of vitreous collagen in vitro to determine the contributions of the classic Maillard pathway and the oxidative pathway, as well as to evaluate possible inhibitors of both pathways.
METHODS: Bovine vitreous collagen was extracted and then incubated with hexoses in vitro. The amount of advanced glycosylation end (AGE) products was measured by fluorometry under varying conditions in the presence and absence of glycosolation inhibitors. Oxygen consumption studies and electron spin resonance spectroscopy with and without free-radical inhibitors were performed to differentiate oxidative from nonoxidative glycosolation.
RESULTS: Vitreous collagen undergoes nonenzymatic glycosolation in the presence of glucose or galactose in vitro. Oxygen consumption data show that oxygen is consumed in glucose and galactose solutions. Oxygen consumption is decreased by known free-radical inhibitors and rutin but not aminoguanidine. Electron spin resonance spectroscopy demonstrated the presence of a carbon-centered radical, and known free-radical inhibitors decreased the carbon-centered signal.
CONCLUSIONS: Nonenzymatic glycosolation of vitreous collagen can occur not only by the classic nonoxidative pathway, but also by a second oxidative pathway that is susceptible to a number of inhibitors.