Substance P has a role in neurogenic mediation of human burn wound healing

Knowledge of biochemical and molecular events during burn wound healing may optimize treatment of patients with thermal injuries. Substance P (SP), a neuropeptide present in C fibers of the skin, has been implicated as a mediator of inflammation and wound healing. This neuropeptide induces vasodilitation and vascular permeability by stimulating endothelial cells to round up, vascular smooth cells to relax, and mast cells to release histamine. SP also induces cytokine release by macrophages and neutrophils. Because many of the functions of SP seemed relevant to wound repair in burns, we used immunocytochemistry to characterize SP+ nerve fibers in healing human burn wounds. Deep partial-thickness burns collected from 20 patients at the time of excision and grafting were formalin fixed, paraffin-embedded, sectioned, and labeled with a monoclonal antibody to SP with use of an immunoperoxidase technique. Our tissue samples included normal skin and 20 specimens from postburn days 2 through 49. In normal adult skin, SP+ nerve fibers surrounded vessels throughout the skin and extended from the papillary dermis into the epidermis. SP+ fibers were absent in early wound beds. SP immunostaining did occur in the advancing epidermis, endothelial cells, and mast cells. SP+ fibers could be identified in the deep dermis and subjacent to the advancing epithelium before the wound beds. Maximum numbers of SP+ fibers were present subjacent to the advancing epithelium at 2 weeks after burn injury. After 4 weeks, the distribution of SP+ fibers in reepithelialized areas was similar to that of normal skin. Our data corroborate published reports of SP+ fiber regeneration in guinea pig burns and correlates with clinical observations of pain and pruritus in patients with thermal injuries. The absence of SP+ fibers in the early wounds with SP immunostaining in the epidermis and extracellular matrix suggests that SP may be released from injured nerves and supports neurogenic mediation of inflammation and vasodilitation in early wound repair. Repopulation of the wound beds with SP+ fibers appeared to follow neovascularization originating in the deep reticular dermis and wound edge.