Topical insulin application improves healing by regulating the wound inflammatory response

Inflammation, the initiating stage of wound healing, is characterized by increased endothelial permeability, infiltration of inflammatory cells, and secretion of numerous growth factors and chemokines. By controlling wound contamination and infection, as well as inducing the repairing process, inflammatory response plays an irreplaceable role during wound healing. We utilized a variety of approaches to observe the effect of insulin on wound inflammatory response, specifically the effect of insulin on the function of wound macrophages. We also investigated whether insulin-regulated inflammatory response contributed to insulin-induced healing. Mice excisional wounds treated with insulin showed advanced infiltration and resolution of macrophages, which correlated with the expression of monocyte chemotactic protein-1, a potent chemotactic factor for macrophages. Blockage of monocyte chemotactic protein-1 resulted in reduced macrophages infiltration and impaired wound healing despite the presence of insulin. In vitro studies showed insulin-facilitated monocytes/macrophages chemotaxis, pinocytosis/phagocytosis, and secretion of inflammatory mediators as well. Our study strongly suggests that insulin is a potent healing accelerant. Regulating wound inflammatory response, especially the quantity and function of macrophages, is one of the mechanisms explaining insulin-induced accelerated wound healing.