Depolymerization of hyaluronic acid by autoxidants and radiatiions.

Abstract

Hyaluronic acid, a linear polymer of alternating N-acetyl-D-glucosamine and D-glucuronic acid units with a molecular weight of 105 to 107, is known to be degraded by X-rays, ultraviolet radiation, and ultrasonic waves (1-6). This substance and other natural and synthetic polymers are also degraded by autoxidants such as ascorbic acid or ferrous or cuprous ions in the presence of oxygen (7), by mechanisms probably involving free radicals (5, 8, 9) similar to those involved in their degradation by radiations. This latter reaction has been described as the oxidativereductive depolymerization (ORD) reaction (10). Alexander et al. (8, 11) noted degradations of polymethacrylic acid by both X-rays and several autoxidants such as cysteine, but the present study is the first formal comparison of the effects of radiations and autoxidants on hyaluronic acid. The present work was carried out in order to compare the effects of radiation on hyaluronic acid with those produced by autoxidants under closely similar conditions. A semiquantitative comparison of the effects of X-rays, ,B-rays (P32, internally), and autoxidants is reported. The effect of visible light with riboflavin as sensitizer was also studied. For the ORD reaction, the results of a survey of possible autoxidants and antioxidants are included. Viscometric measurements were used as the criterion of the degree of degradation of hyaluronic acid.