Enhancement of wound repair with a topically applied nitric oxide-releasing polymer

Nitric oxide is an important cytotoxic agent for host defense which also regulates gene expression, signal transduction, and vasodilation. In normal wounds, nitric oxide synthesis and metabolism are significantly increased during inflammation and tissue remodeling. However, nitric oxide production is suppressed in wounds where healing is impaired by diabetes or steroid-treatment. Topical delivery of nitric oxide in therapeutic amounts may alleviate this deficiency and thereby enhance wound repair. Consequently, we developed polyethyleneimine cellulose NONOate polymer, a nonsoluble, nontoxic, polymer-based NONOate--one of a new class of compounds that spontaneously release nitric oxide in a controlled fashion in aqueous media. Polyethyleneimine cellulose NONOate polymer was synthesized from polyethyleneimine cellulose to provide extended nitric oxide release with a half-life of 16 hours. Polyethyleneimine cellulose NONOate polymer or a control polymer was applied topically on full-thickness dermal wounds of rats at the time of wounding and days 3, 7, 10, 14, 17, and 21. Nitric oxide delivery was determined indirectly by measuring urinary nitrate. The first two polyethyleneimine cellulose NONOate polymer applications increased urinary nitrate output twofold to fourfold, whereas urinary nitrate output of control rats did not significantly increase. Nitrate output in polyethyleneimine cellulose NONOate polymer-treated rats was elevated compared with controls after each application, although this was attenuated in later applications. Rate of wound closure was measured with computer-based video imaging. Polyethyleneimine cellulose NONOate polymer-treated wounds were significantly smaller (p < 0.05) on days 7, 10, and 17 relative to controls, based on percentage of wound open relative to initial wound area. In a second experiment, telemetry-implanted rats were wounded to detect potential hypotensive effects as a result of polyethyleneimine cellulose NONOate polymer application. Topical polyethyleneimine cellulose NONOate polymer application to wounds showed no prolonged hypotensive effects, in contrast to a soluble NONOate which suppressed systolic blood pressure for over 6 hours. These results show that a nonsoluble, polymeric NONOate can provide topical nitric oxide delivery to wounds in a controlled manner, which may enhance wound healing. Further studies are in progress with other promising NONOate candidates to establish dose-response effects and therapeutic limits of exogenous nitric oxide release in impaired wound models.