Depolymerisation products of hyaluronic acid after exposure to oxygen-derived free radicals

Preparative chromatographic fractions of human umbilical cord hyaluronic acid (HA) of a molecular weight of 10(6) were subjected to graded oxygen-derived free radical (oxy radical) fluxes produced by: (a) the autoxidation of ferrous ions; (b) the action of xanthine oxidase (XO) on hypoxanthine (HX); and (c) by peripheral blood polymorphonuclear leucocytes that had been stimulated by phorbol myristate acetate (PMA). Analysis by gel chromatography of the products obtained with each of the oxy radical generating systems showed polydispersity in size. The smallest molecules detected had a molecular weight of 10(4). This limiting size was not reduced further by exposure to a second oxy radical flux. The relative proportions of large, medium, and small degradation products were established for various levels of oxy radical flux. Consistently a relatively rapid transition from large to small material was seen on Sepharose 2B chromatography, suggesting an ordered element to the breakdown process. Although the decrease in molecular weight after oxy radical exposure was confirmed by analytical ultracentrifugation, this procedure showed that those samples of lowest viscosity did not have the lowest sedimentation values, possibly reflecting oxy radical-induced repolymerisation. If the size and possibly the conformational characteristics of HA are altered, oxy radical exposure might be expected to alter its biological properties.