Differential Proliferative Responses to Low-Dose Irradiation between Human Submandibular and Parotid Salivary Ductal Cell Lines

Abstract

Objective: Salivary glands are frequently exposed to X-radiation during dental radiography. The present study aimed to investigate the proliferative and apoptotic effects of low-dose irradiation on human salivary cell lines in vitro. Materials and Methods: Two distinct ductal cell lines, HSG and HSY, were first characterized by expressions of carcinoembryonic antigen (CEA) and lactoferrin (LF), compared to those in human oral keratinocytes (HOKs), and then examined for their doubling times. They were exposed to periapical radiography for 5, 10, or 20 times, and incubated further for 1, 3, or 5 cycles of their cell division. Cell proliferation was examined by a BrdU assay and immunoblot analysis of Ki-67 expression. Cell apoptosis was determined by the presence of human active caspase 3. Results: The mean degrees of CEA and LF expressions were significantly higher in HSG and HSY than in HOKs (p<0.01). The doubling time of HSG was significantly shorter than that of HSY (p=0.009). Upon repeated exposures to dental X-ray, the proliferation of HSG was significantly increased at the first cycle, whereas that of HSY was significantly decreased (p<0.05). At the third cycle, Ki-67 expression was significantly increased in HSG, while it was significantly decreased in HSY (p=0.037). However, the proliferative effect was temporarily presented in both cells. No active caspase 3 was detected upon exposure to any doses or in any cycles. Conclusion: The two ductal cell lines demonstrated adaptive response to low-dose irradiation by either increased or decreased cell proliferation, but no apoptosis was found in both cell lines. Keywords: Bromodeoxyuridine assay; Cell apoptosis; Cell proliferation; Dental X-ray; Salivary ductal cells