L-Arginine supplementation enhances diabetic wound healing: involvement of the nitric oxide synthase and arginase pathways.

Diabetes impairs wound healing and there are few therapeutic options to reverse it. Previous work has demonstrated the importance of nitric oxide for successful wound healing. In diabetes, NO synthesis is reduced in the wound milieu. The amino acid L-arginine is the only substrate for NO synthesis. We hypothesized that L-arginine supplementation would enhance wound healing by restoring NO synthesis. Thirty-six male Sprague-Dawley rats (body weight, 225 to 250 g) were separated in 4 groups: 20 rats were rendered diabetic 7 days prior to wounding by intraperitoneal streptozotocin (STZ) injection (70 mg/kg). Sixteen rats served as controls. Half of the animals of each group received 1 g/kg supplemental L-arginine administered by gavage twice daily. Control rats were gavaged with water. Treatment was started 3 days before wounding. All rats underwent a dorsal skin incision and subcutaneous implantation of polyvinyl alcohol (PVA) sponges. The rats were killed 10 days post wounding and wound breaking strength, hydroxyproline content of the sponges, nitrite/nitrate (NO(x)) concentration, arginase activity, and amino acid composition of the wound fluid and plasma were analyzed. Wound fluid NO(x) concentrations and wound breaking strength were significantly reduced in the diabetic group compared to the controls. L-Arginine treatment restored diabetic NO(x) levels toward normal values and significantly enhanced wound breaking strength. Wound fluid arginase activity and ornithine concentrations were significantly lower in the diabetic animals but unaffected by treatment. The data demonstrate that the impaired NO synthesis in the diabetic wound milieu can at least partially be reversed by arginine supplementation. In view of previous results on the importance of NO for wound healing, the data suggest that arginine supplementation restores impaired healing in this acute wound model by normalizing the NO pathway but without affecting arginase activity.