Healing of Mid-Dermal Burns in a Diabetic Porcine Model

Abstract

Wound healing is delayed in diabetic patients. We developed a diabetic-porcine burn model and compared the healing of partial-thickness burns in normal and diabetic pigs. We hypothesized that wound healing would be delayed in the diabetic swine. Diabetes mellitus was chemically induced in three domestic pigs (25-50 kg) by intravenous injection of streptozotocin 130 mg/kg over 30 minutes. Glucose levels were maintained between 250 and 500 mg/dl by injecting short-acting or long-acting insulin 1 unit/kg daily as needed. Three weeks later, 14 partial-thickness burns were created on the backs and flanks of each of the anesthetized pigs with a 2.5 x 2.5-cm aluminum bar preheated to 80 degrees C and applied for 20 seconds. A similar number of burns were created on three control nondiabetic pigs. The burns were treated with a topical antibiotic, and 3-mm full-thickness biopsies were taken from all wounds at 7, 10, 14, and 21 days for histomorphologic evaluation using hematoxylin and eosin staining by a board-certified dermatopathologist masked to the type of pig. The main outcome was the percentage of the wound in cross section that was reepithelialized. Comparison of outcomes between normal and diabetic pigs was performed with Student's t-tests. The diabetic pigs gained less weight, and their skin was considerably thinner than in the control pigs. Although the absolute depth of the burns was similar, the relative depth was greater in the diabetic pigs. The percentage of wound reepithelialization was lower in diabetic than in normal pigs at 7 days (1.8% [95% CI: 0-5.5] vs 65.0% [95% CI: 54.2-75.9]; P < .001) as well as at 10 days (19.2% [95% CI: 6.0-32.4] vs 76.9% [95% CI: 59.8-94.0]; P < .001) and 14 days (43.9% [95% CI: 30.4-57.4] vs 99.9% [95% CI: 92.6-100]; P < .001). All burns were completely reepithelialized at 21 days, and none of the wounds were infected. Reepithelialization of partial-thickness burns is delayed in streptozotocin-induced diabetic pigs when compared with normal pigs. It is unclear whether the delay in healing is due to the thinner skin or the metabolic consequences of diabetes or their combination.