Effect of topical insulin application on wound neutrophil function.

UNLABELLED This study observed the quantity and functions of wound neu- trophils after topical insulin treatment and investigated the effect of insulin on the wound inflammatory response, as well as the mechanism of insulin-induced wound healing. METHODS Full-thickness excisional wounds were made on the dorsal symmetrical site of C57BL/6J mice. The wounds were treated with either 0.03U insulin/20 μL saline or 20 μL saline. The healing times and healing rates of the wounds were recorded. The wounds and adjacent tissues were collected during the first 3 consecutive days after the injury. Quantification of myeloid dif- ferentiation antigen Gr-1, myeloperoxidase (MPO), malondialdehyde (MDA), and macrophage inflammatory protein-2 (MIP-2) were mea- sured by Western blotting, biochemical analysis, and real-time poly- merase chain reaction (PCR), respectively. RESULTS The healing time of insulin-treated wounds was significantly decreased compared with the saline-treated wounds. The wound closure rates at days 5 and 7 after injury were significantly higher with insulin treatment than with saline treatment. Additionally, wound neutrophil infiltration was suppressed by insulin treatment within the first 2 days after injury. Real-time PCR revealed insulin treatment significantly inhibited MIP-2 expression within 2 days after injury (P P <0.05), whereas MIP-2 expression in both groups decreased to a similar level at 3 days after injury. There was no statistical difference in MPO or MDA content between the insulin treatment and control group. CONCLUSION Topical insulin application decreased neutrophil infiltration by inhibiting MIP-2 expression and advanced neutrophil resolution. It has been reported that insulin pro- motes neutrophil functions; therefore, the present results, along with previous findings, suggest there is a delicate regulation of insulin on wound inflammatory response during the healing process.