Binge Ethanol Leads to Decreased Macrophage Accumulation in Infected Cutaneous Wounds

Trauma patients who consumed alcohol prior to sustaining injuries have higher rates of morbidity and mortality than those with comparable injuries who did not drink. Additionally, those who drank had impaired wound healing and increased susceptibility to infection. Despite these clinical observations, few studies have explored the effect of ethanol on the innate immune cell function in a healing wound or how this may alter resolution of cutaneous infection. A murine model of ethanol and cutaneous wound infection was used to examine bacterial growth and recruitment of innate immune cells. Mice were given either ethanol (2.2 g/kg) or saline 30 minutes prior to being subjected to six 3 mm dorsal punch wounds and Staphylococcus aureus (104 CFU/wound). At 24 hours after injury and infection, wound tissue was collected. There was a 3.6 fold increase in bacterial growth in the infected wounds of ethanol-exposed mice relative to those given vehicle prior to wound infection. This elevated bacterial growth was accompanied by an increase in the percentage of open wound area realative to wounds from mice that were immediately sacrificed after being injured (p\u3c0.0001). To determine the contribution of ethanol-related alterations in the innate immune response to this heightened bacterial colonization, we examined wound neutrophil and macrophage accumulation in the wounds by immunofluorescent imaging. At 24 hours, no differences were observed in the number of neutrophils at the infected wound site regardless of ethanol exposure. In contrast, macrophage accumulation was 45% lower in wounds from ethanol-exposed mice relative to vehicle-treated animals (p\u3c0.05). This decrease in macrophage recruitement was accompanied by a 24% reduction in the level of macrophage chemoattractant protein-1 (MCP-1) in wound homogenates from ethanol exposed mice, however, this differences was not significant. Consistent with the lack of change in the number of wound neutrophils, we also failed to detect a difference in the wound content of neutrophil chemokines, KC and macrophage inflammatory protein-2 (MIP-2). To further explore differences in innate immune response due to alcohol, we examined phagocytosis of S. aureus by neutrophils and macrophages in the wound. However, no evidence of phagocytosis by either cell was observed due to a lack of bacterial dissemination into the tissue adjacent to the wound. Together, these data show that ethanol impairs macrophage accumulation at the infected wound site 24 hours after injury and suggest that the reduction in these cells in ethanol-exposed mice could contribute to reduced bacterial clearance and increased wound size