Diabetes-impaired healing and reduced wound nitric oxide synthesis: a possible pathophysiologic correlation

Nitric oxide (NO) is synthesized in wounds, but its role in the healing process is not fully understood. The inhibition of NO production during wound healing is accompanied by decreased wound reparative collagen deposition. To further define the role of NO in reparative collagen accumulation, we studied its production during diabetes-induced wound healing impairment.

Male Sprague-Dawley rats (290 to 310 gm) were rendered diabetic by intraperitoneal streptozotocin administration. Seven days after induction of diabetes (blood glucose greater than 300 mg/dl), the rats underwent dorsal skin incision and subcutaneous implantation of polyvinyl alcohol sponges. Beginning on the day of wounding, 21 diabetic animals were treated with 3 units/day insulin via intraperitoneally implanted miniosmotic pumps. Ten days after injury, wound breaking strength was determined, and wound collagen accumulation and types I and III collagen gene expression were measured in subcutaneously implanted polyvinyl alcohol sponges. NO-synthesis, as measured by nitrite/nitrate accumulation, was determined in wound fluid and in supernatants of wound cell cultures.

Streptozotocin-induced diabetes markedly impaired wound breaking strength and collagen deposition. A parallel decrease occurred in wound NO synthesis as reflected by decreased nitrite/nitrate concentration in wound fluid and in diminished ex vivo NO production by wound cells. Insulin treatment partially but significantly improved wound mechanical strength (p < 0.01) and collagen accumulation (p < 0.001). Decreased wound NO accumulation and ex vivo NO production by wound cells were also partially restored by insulin treatment.

Impaired diabetic wound healing is paralleled by decreased wound NO synthesis, supporting the hypothesis that NO plays a significant role in wound reparative collagen accumulation.