Effects of oxygen-derived free radicals on the molecular weight and the polydispersity of hyaluronan solutions

Depolymerization of high-molecular-weight sodium hyaluronan by superoxide anions and hydroxyl free radicals was studied. The changes in number-average and weight-average molecular weight, molecular-weight distribution, polydispersity, and concentration were measured over time by high-performance liquid chromatography on a TSK 6000 PW size-exclusion column coupled to multiangle laser light scattering and refractive index detection. There was no significant change in the elution profile and in the peak height of the refractive index chromatogram for either of the radical species at different reaction times. Furthermore, the weight-average molecular weight of hyaluronan decreased from 1.3 × 106 to 3.0 × 105 g/mol; however, the polydispersity did not significantly increase. These experimental results indicate that superoxide anions and hydroxyl free radicals do not have different modes of action on hyaluronan. Also, both radical species seem to attack hyaluronan randomly from the end of the molecule. Depolymerization studies on sodium hyaluronate by superoxide anions and hydroxyl free radicals indicate similar modes of action for both species.