The role of metal-catalyzed oxidation in the formation of advanced glycation end products: an in vitro study on collagen.

The present study investigates the role of metal catalysed oxidation in the formation of Advanced Glycation End products (AGEs). Rat tail tendon collagen was incubated with glucose (250 mM) and increasing concentrations of copper ions (5-500 microM) under physiological conditions of temperature and pH. After 1 and 3 weeks of incubation the level of AGEs in collagen samples were estimated by enzyme linked immunoassay, using antibodies raised against AGE ribonuclease. It was observed that the presence of metal ions significantly increased the rate of accumulation of AGEs. The increase was dependent on the concentration of metal ions present in the incubation medium. Free radical scavengers such as mannitol, benzoate, catalase, and the antiglycating agent aminoguanidine almost completely inhibited the formation of AGEs. Incubation of collagen with copper ions alone did not show any increase in crosslinking, as detected by cyanogen bromide digestion, and AGEs formation. Further it was also noted that glycoxidation, i.e., oxidation of glycated collagen, was the major pathway that leads to increased formation of AGEs. These results indicate that metal-catalyzed oxidation and free radicals play a major role in the formation of AGEs. This work also strongly suggests that increased oxidative stress in diabetes may accelerate the formation of AGEs and thus contribute to the pathogenesis of diabetic complications.