The arresting phase determines the total healing time of

Abstract

【Abstract】Objective: Radiation is an important cause of delayed wound healing, and there still exist many questions regarding the patterns and mechanisms of wound healing. This study investigated the characteristics of wound healing after varying doses of local radiation and explored possible causes of the delay in healing caused by radiation. Methods: A full-thickness dorsal longitudinal skin tissue, 2 cm in diameter, was excised after local irradiation on one side of the back of swine, and the other side was wounded as a control. The size of the wound area was re-corded every two days after injury. Pathological changes, proliferating cell nuclear antigen (PCNA, immunohisto-chemistry) and apoptosis levels (TUNEL assay) were mea-sured at different time points after wounding. Results: The course of wound healing can be divided into four phases, namely: the arresting phase, the healing priming phase, the fast healing phase, and the healed phase. Although the total wound healing time was closely corre-lated to the dose of irradiation (R 2 = 0.9758), it was more dependent on the length of the arresting phase (R 2 =0.9903) because once the arresting phase ended, the wound healed at a similar speed regardless of radiation doses. Pathologi-cal analysis showed that compared with the control side there were more necrotic tissues, slower epithelial crawling, as well as fewer blood vessels and cellular components in the irradiated side at the arresting phase, while other phases revealed no significant difference concerning these measurements. Immunohistochemistry showed that the ir-radiated wounds had significantly less PCNA-positive and more TUNEL-positive labeling of cells in the arresting phase than in other phases. Moreover, the changes were posi-tively related to the radiation doses, but there was no obvi-ous difference in cell proliferation or apoptosis among the healing priming phase, fast healing phase or healed phase, whether on the control side or on the irradiated side. Conclusions: After local irradiation, the length of the arresting phase determines the wound healing time. In-creased apoptosis and decreased cell proliferation might be an important reason for the formation of the arresting phase. Key words: Apoptosis; Cell proliferation; Radiation; Wound healing