Comparison of the antioxidant properties of HYAFF®-11p75, AQUACEL® and hyaluronan towards reactive oxygen species in vitro

In chronic wounds, a number of host factors are released which perpetuate the inflammatory process, including polymorphonuclear leukocyte (PMN)-derived reactive oxygen species (ROS), such as superoxide radical (O2√−) and hydroxyl radical (√OH) species. The glycosaminoglycan, hyaluronan, has been shown to act as an antioxidant towards ROS, although the potential for biomaterials, such as HYAFF®-11p75 (the 75% benzyl ester of hyaluronan) and AQUACEL® (carboxymethylcellulose), to act in this manner has yet to be elucidated. This study compared the antioxidant properties of high and low molecular weight hyaluronan (HMWT HA and LMWT HA), HYAFF®-11p75, AQUACEL® and an AQUACEL®/hyaluronan composite (AQUACEL®/HA) against O2√− and √OH. The antioxidant capacities of each material were assessed by their ability to inhibit cytochrome C reduction by O2√− fluxes, generated via the oxidation of hypoxanthine by xanthine oxidase, and their inhibition of 2-deoxy- -ribose degradation by √OH fluxes, generated by the reaction of hydrogen peroxide (H2O2) and iron (Fe2+). All materials studied possessed dose dependent antioxidant properties towards O2√−, with HYAFF®-11p75 having the greatest antioxidant potential towards these species, followed by AQUACEL®, HMWT HA, AQUACEL®/HA and LMWT HA. Only HMWT HA exhibited dose dependent antioxidant properties towards √OH at the fluxes examined. Gas chromatography/mass spectrometry analysis implied that ester bonds between the hyaluronan backbone and benzyl groups of HYAFF®-11p75 are highly susceptible to O2√− hydrolysis, with the de-esterified benzyl alcohol being rapidly degraded in the presence of √OH. This data supports the hypothesis that HYAFF®-11p75 has greater antioxidant capacity towards O2√−, due to the esterified benzyl groups providing alternative sites for O2√− attack other than the hyaluronan backbone of HYAFF®-11p75 itself and explains the inability of HYAFF®-11p75 to scavenge √OH, due to benzyl alcohol degradation by √OH. The antioxidant activities of these biomaterials, particularly HYAFF®-11p75 and AQUACEL®, towards O2√− could be beneficial, as the scavenging of PMN-derived O2√− may remove initial sources of O2√− and further prevent the secondary formation of √OH. These ROS are thought to be a primary causal factor for the extensive degradation and metabolic alterations observed in chronic wounds.