Role of xanthine oxidase in thermal injury of skin.

These studies were designed to assess pathophysiologic factors responsible for increased vascular permeability occurring in rat skin that has been thermally injured in vivo. Under the conditions employed, permeability changes and edema formation progressed over time, with peak changes occurring 60 minutes after thermal trauma. The plasma of thermally injured rats showed dramatic increases in levels of xanthine oxidase activity, with peak values appearing as early as 15 minutes after thermal trauma. Excision of the burned skin immediately after thermal injury significantly diminished the increase in plasma xanthine oxidase activity. The skin permeability changes were attenuated by treatment of animals with antioxidants (catalase, superoxide dismutase [SOD], dimethyl sulfoxide [DMSO], dimethylthiourea [DMTU]) or an iron chelator (deferoxamine), supporting the role of oxygen radicals in the development of vascular injury as defined by greatly increased vascular permeability. Studies employing laser Doppler velocimetry in thermally injured skin revealed a pronounced and sustained decrease in blood flow after thermal trauma, a pattern not affected by protective interventions. The failure of neutrophil depletion to protect against the vascular permeability changes and the protective effects of the xanthine oxidase inhibitors (allopurinol and lodoxamide tromethamine) suggest that xanthine oxidase is the most likely source of the oxygen radicals involved in edema formation. Lodoxamide was found to have some hydroxyl radical (HO.) scavenging ability (greater than that of allopurinol) but no iron chelating activity. Some of the protective effects of lodoxamide and allopurinol may be linked to their HO. scavenging ability. These data suggest that, in this model of thermal trauma, vascular injury defined by increased vascular permeability is, in part, related to the activation of xanthine oxidase and the generation of toxic oxygen metabolites that damage microvascular endothelial cells.