Free radical depolymerization of hyaluronan by Maillard reaction products: role in liquefaction of aging vitreous.

The degradation of hyaluronan was followed by viscosimetry and by HPLC in order to study the possible role of Maillard products (lysine-glucose) on the alteration of the vitreous gel in aging and diabetes. Lysine-glucose generated Maillard products produced a decrease of viscosity and of the number average molecular weight (Mn) of hyaluronan during a 1 h incubation at 37 degrees C. This effect was comparable to that produced by 1 U/ml of testicular hyaluronidase but was weaker than the effect of a Fenton-type reagent (Udenfriend's reagent). The polydispersity of hyaluronan incubated with Maillard products appeared higher than with hyaluronidase suggesting a more random reaction. Antioxydant enzymes (SOD, catalase), the iron chelators (desferrioxamine, transferrin) and the free radical scavengers (uric acid, carnosine) inhibited the degradation by Maillard products confirming its free radical nature and the intervention of trace metals. Maillard products have been detected in diabetic vitreous and may play a role in its accelerated modifications (liquefaction) in diabetes as compared to normal aging.