Infrared exposure induces an angiogenic switch in human skin that is partially mediated by heat

Abstract

BACKGROUND: Angiogenesis plays an important role in physiological and pathological conditions of the skin. Although acute ultraviolet-induced skin angiogenesis has been investigated, little is known about the distinct effects of acute infrared (IR) radiation on angiogenesis in human skin. OBJECTIVES: To elucidate the molecular regulation of the angiogenic switch by acute near-IR radiation or by a single heat treatment in human skin in vivo. METHODS: We subjected 16 healthy volunteers to near-IR irradiation (six minimal heating doses) and 14 healthy volunteers to heat treatment (43 degrees C for 90 min), and skin specimens were obtained by punch biopsy for immunohistochemical, Western blot and reverse transcription-polymerase chain reaction analyses. RESULTS: We observed that CD31-stained vessels in the upper dermis were increased after acute near-IR exposure, and that this was associated with the upregulation of vascular endothelial growth factor (VEGF) and the downregulation of thrombospondin (TSP)-2. During the application of near-IR to buttock skin, skin temperatures immediately increased from 32 degrees C up to 42 degrees C, as measured using a digital thermometer. Moreover, the expression of inducible heat shock protein 70 was increased after near-IR irradiation in human skin. Therefore, we investigated the effects of a single heat treatment on angiogenesis and on the expression of VEGF and TSP-2 in skin, and found that vascularization and VEGF expression were increased, whereas TSP-2 expression was reduced. CONCLUSIONS: Our results suggest that IR radiation plays an important role in skin angiogenesis via regulation of the balance between the angiogenic inducer VEGF and the angiogenic inhibitor TSP-2, and that IR-induced skin angiogenesis might be partially caused by the effects of heat in human skin in vivo.