Development of a porcine skin injury model and characterization of the dose-dependent response to high-dose radiation.

A porcine skin model was developed to characterize the dose-dependent response to high-dose radiation. The dorsal skin of a mini pig was divided into four paraspinal sections, with 11 small irradiation fields (2 cm × 2 cm) in each section, and a single fraction of 15, 30, 50 or 75 Gy was delivered to each section using a 6 MeV electron beam. A spectrophotometer measured gross skin changes, and a biopsy for each radiation dose was performed in the 1st, 2nd, 4th, 6th and 9th weeks for histology, immunostaining with anti-CD31, and western blotting with IL-6 and TGF-β1 to determine the degree of skin damage. After a 4-week latency period, erythema and dry desquamation, moist desquamation, and ulceration appeared at 4, 6 and 9 weeks, respectively. Gross skin toxicity was more pronounced, occurred early and continued to progress with irradiation >50 Gy, whereas complete healing was observed 12 weeks after 15 Gy. Spectrophotometry showed erythema indices rapidly increased during the first 4 weeks after irradiation. The number of eosinophils began rising sharply at 4 weeks and normalized after reaching peaks at 7-8 weeks. Microvessel density showed a biphasic pattern with a transient peak at 1 week, a nadir at 4-6 weeks, and maximum recovery at 9 weeks. Increase in the levels of IL-6 and TGF-β1 was detected soon after irradiation. Most of these parameters indicated complete healing of the skin 12 weeks after 15 Gy. Our porcine skin model provides an effective platform for studying high-dose radiation-induced skin injury, in particular histologic and molecular changes, during the early latency period.