In Vitro Assessment of the Impact of Ultraviolet B Radiation on Oral Healthy and Tumor Cells

Abstract

Ultraviolet radiation (UVR) is generally considered a primary tumorigenic agent. While UVR exposure has been studied, especially at the skin level, the impact of UV exposure on internal tissues and its effect on the appearance and the development of tumors has not yet been fully examined. Although there are maximum limits for UVR exposure on external tissues, other internal tissues, such as oral tissue, can be exposed to UVR as well. Over the course of diagnosis and treatment, oral cells may be exposed to ultraviolet radiation; however, there has not been an established limit for UV radiation exposure. Therefore, the aim of the current study was to examine the effects of ultraviolet-B (UVB) radiation at two doses (2.5 and 5 J/cm2) on tumor cells (pharyngeal carcinoma and tongue carcinoma) and healthy cells (gingival fibroblasts). The viability of the cells and their morphology, actin filaments, and nuclei structures; the expression of anti-apoptotic (Bcl-2) and pro-apoptotic (Bax) genes; and the roles of caspases-3/7, 8, and 9 were determined after the cells had been exposed to UVB. The experiments revealed that both types of cell lines showed reductions in viability, especially at a dose of 5 J/cm2. Additionally, apoptotic-like changes (rounding of the cells, the condensation of the nuclei, the re-organization of the actin filaments) were observed in all analyzed cells. The expression of anti-apoptotic (Bcl-2) and pro-apoptotic (Bax) genes revealed that UVB (5 J/cm2) may induce apoptosis in both oral tumor and healthy cells. Moreover, an analysis of caspases-3/7, 8, and 9 showed that UVB exposure enhanced their activity, suggesting that cell death could be caused by both intrinsic and extrinsic apoptosis. Accordingly, UVB exposure at the maximum doses used in dental practices (5 J/cm2) induced nonselective apoptotic changes, thereby reducing both tumor and healthy cell viability.