Nitric oxide and wound healing

Nitric oxide (NO) is a free radical with a multitude of tissue specific functions. Its expanding range of functions includes host defense, signal transduction, vasodilation, and neurotransmission. Many wound resident cells including macrophages synthesize NO, which is subsequently metabolized to NO\sb3-. The present study was designed to further clarify the level of NO production during wound healing. Rats fed low NO\sb3- diets were wounded, following the establishment of baseline urinary NO\sb3- levels. The rate of wound closure was measured using computer based video imaging analysis (VIA), while urinary NO\sb3- levels were monitored for several weeks post-wounding. After wounding, both arginine-free diet and arginine fed animals responded with a many-fold increase in the urinary NO \sb3- levels, demonstrating that dietary arginine is not necessary for the sudden increase in NO\sb3- output immediately after wounding. It was found that rats fed arginine-free diet responded to LPS challenge with a typical increase in NO\sb3- output. Lack of dietary arginine apparently does not prevent the NO producing activity of macrophages during the early phase of healing, but NO synthesis suppressed in the later stages of tissue repair. Post-wound urinary NO\sb3- levels in both steroid-treated and diabetic rats were significantly lower compared to controls. Steroid-treated and diabetic rats also demonstrated suppressed NO\sb3- response to LPS challenge. VIA analysis confirmed impaired wound healing in the early post-wound period with both models. In addition, topical application of nitric oxide synthase (NOS) inhibitors, L-NMMA and L-NO\sb2A, caused reduced NO synthesis during wound healing, indicating that post-wound increase in urinary NO\sb3- levels were due to enhanced NO synthesis primarily at the wound site. Topical delivery of NO releasing polymer (PEIC-NO) resulted in a significant enhancement of the healing process (p < 0.05) in normal wounded rats. No hypotensive effects of PEIC-NO application were observed, probably due to the controlled release of NO from PEIC-NO. NO was also shown to be delivered transdermally through the use of NONOates. Results obtained from experiments in this dissertation reveal that delayed wound healing is associated with attenuated NO production, and that site specific delivery of NO via NONOates may overcome healing impairment.