Spatio-temporal localization of HIF-1α and COX-2 during irradiation-induced oral mucositis in a rat model system

Purpose: Oral mucositis is a common side effect of radiotherapy for head and neck cancer. The purpose of this study was to examine the significance of and the relationship between hypoxia inducible factor-1 alpha (HIF-1 alpha) and cyclooxygenase-2 (COX-2) gene expression and the corresponding protein levels in irradiated rat mucosa. Material and methods: A Sprague-Dawley rat model of irradiation-induced oral mucositis was generated. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to evaluate the HIF-1 alpha and COX-2 mRNA level in rat buccal mucosa exposed to a fractionated irradiation regime. The Streptavidin-Biotin-Complex method was applied to delineate the in situ localization, intensity, and distribution of both proteins. The right buccal mucosa was not irradiated and used as control tissue. Results: The RT-PCR analyses demonstrated that, upon irradiation, HIF-1 alpha and COX-2 expression was significantly induced in the left buccal mucosa in contrast to control buccal mucosa. Based on immunohistochemical analyses, the HIF-1 alpha and COX-2 level, in situ localization, and the type of cells exhibiting the highest HIF-1 alpha and COX-2 amounts appear to correlate. Conclusions: The expression and protein levels of HIF-1 alpha and COX-2 are substantially enhanced in irradiated rat mucosa and correlate with each other and with the severity of irradiation-induced oral mucositis.