Apoptosis and necrosis in the ischemic zone adjacent to third degree burns

Objectives: Burns are characterized by a central zone of necrosis surrounded by a zone of potentially reversible ischemia. The authors explored the contribution of necrosis and apoptosis to cell death in the zone of ischemia. Methods: A previously established rat contact thermal injury model that utilizes a brass comb to produce four distinctive burns sites separated by three "interspaces" of unburned skin was used. The interspaces represent the zone of stasis or ischemia while the burn sites represent the zone of coagulation. With this model, most unburned interspaces progress to necrosis over 2 to 3 days. Full-thickness 3-mm biopsies were obtained from the interspaces, burns, and normal skin controls at 30 minutes, 24 hours, and 48 hours after injury. Slides were stained with hematoxylin and eosin as well as activated cleaved caspase-3 (CC3a) for evidence of apoptosis and high-mobility group box 1 (HMGB1) for evidence of necrosis. Results: Necrosis was not seen at 30 minutes, but was found in a large number of cells within the epidermis, sebaceous glands, and follicles at 24 and 48 hours. Faint nuclear CC3a staining indicative of apoptosis was present in a minority of cells within the epidermis, dermal fibroblasts, dermal follicles, and dermal sebaceous glands at 30 minutes and to a lesser degree at 24 and 48 hours. Conclusions: Both early apoptosis and delayed necrosis are present in the zone of ischemia, contributing to injury progression. Necrosis appears to play a larger role than apoptosis in injury progression in the comb burn model.