Nitric oxide synthase inhibitors appear to improve wound healing in endotoxemic rats: An investigator-blinded, controlled, experimental study

Abstract

Background: Although inflammation is a normal part of wound healing, if the inflammatory response is excessive the repair process might be prolonged. Nitric oxide (NO) has been implicated in healing inflammation and wounds.

Objective: Endotoxins and cytokines associated with sepsis induce NO synthesis in the tissues. This study used tensile strength and tissue hydroxyproline levels as proxies for wound healing to determine whether wound healing in the presence of endotoxemia is improved when NO synthase is inhibited by N-nitro-l-arginine methyl ester (L-NAME) or N (5)-(1-Imino-methyl)-l-ornithine (L-NIO).

Methods: In this investigator-blinded, controlled, experimental study, male Wistar albino rats (275-300 g) were divided into 4 groups. The first group received an intraperitoneal (IP) injection of Escherichia coli endotoxin 10 mg/kg and an SC injection of 0.9% sodium cloride (NaCl). The second group received IP E coli 10 mg/kg and SC L-NAME 2 mg/kg. The third group received IP E coli 10 mg/kg and L-NIO 10 mg/kg. The control group was administered an IP and an SC injection of 0.9% NaCl. Each group received both injections at 24 and 16 hours before surgery. All rats underwent a 3-cm dorsal midline incision, which was subsequently closed. Five days after surgery, all rats were euthanized and skin from the healing wound was excised. Hydroxyproline levels and tensile strength were then measured.

Results: Forty-four male rats (mean age, 16 weeks; mean [SD] weight, 284 [16] g) were included in the study. Each of the groups receiving endotoxin (endotoxin, L-NAME, and L-NIO groups) had 12 rats; the control group consisted of 8 rats. All the groups that received endotoxin showed significant declines in hydroxyproline levels versus controls (P < 0.001, P = 0.001, and P = 0.002, respectively). Compared with the control group, the endotoxin-only group had a significant reduction in both mean (SD) hydroxyproline levels and mean (SD) wound tensile strength (298.27 [17.66] vs 175.82 [18.73] g/cm2 and 7.16 [0.51] vs 4.01 [0.29] μg/mg wet tissue; both, P < 0.001). Compared with the endotoxin- only group, rats that received L-NIO had significantly greater mean (SD) hydroxyproline levels and mean (SD) wound tensile strength (6.44 [0.34] vs 4.01 [0.29] μg/mg wet tissue and 280.12 [14.38] vs 175.82 [18.73] g/cm(2); both, P < 0.001). Wound tensile strength in the L-NIO group was not significantly different from that in the control group. A significant difference was observed between the L-NIO and L-NAME groups in wound tensile strength (280.12 [14.38] vs 241.38 [20.69] g/cm(2); P = 0.001), but not in tissue hydroxyproline levels.

Conclusion: Inhibition of NO synthesis might improve wound tensile strength, which suggests a possible role for NO inhibitors in improved wound healing in the presence of endotoxemia.

Keywords: endotoxemia; nitric oxide; nitric oxide synthase inhibitors; wound healing.