Protein Analysis of Dentin After γ-rays Irradiation

Objective: Radiotherapy for oral cancer causes adverse effects to the oral tissues. Understanding the radiation effects on dentin will be beneficial to practitioner in providing dental treatment for radiotherapy patient. The objectives of this in vitro study were to evaluate the effect of ionizing irradiation on protein profile of dentin using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Methods: Three pairs of bovine mandibular central incisors were used. One from each pair was irradiated with γ-rays from a cobalt 60 therapeutic machine at a dose of 60 Gy in one fraction while another was served as control. Within two weeks after irradiation, the root dentin was powdered at -196 °C. The obtained dentin powder was decalcified using 0.5M EDTA at pH 7.4 at 4 °C for 7 days. The decalcified pellet was digested using pepsin (1,090 units per mg wet weight of pellet) at pH 2 at 4°C for 24 hours and was analyzed using 15% SDS-PAGE. The obtained gel was photographed and relative amounts of proteins were examined from densitograms using image analysis software (ImageJ, NIH, USA). The experiment was repeated three times. Results: The protein profiles of irradiated dentin were the same as those of non-irradiated dentin. For both conditions, two bands corresponding to alpha 1(I) and alpha 2(I) chains at around 100 kDa were demonstrated in addition to pepsin bands at around 40 kDa. Significant difference of the amount of alpha chains was not found between irradiated and non-irradiated dentin by paired-t test (P>0.05). Conclusion: Irradiation with γ-rays at a dose of 60 Gy has no effects on protein profile of dentin after short period of irradiation at least under in vitro conditions.