Analysis of the mechanism underlying radiation-induced jaw bone necrosis

利用小鼠骨髓源性成骨细胞样细胞研究了辐射诱导骨坏死的机制。对这种坏死的预防性药物治疗也进行了研究。研究发现，受辐射后仍能存活的成骨细胞的百分比与DNA数量的减少有关，而DNA数量的减少又与辐射剂量有关。荧光法测定的DNA裂解率随辐射剂量的增加而增加。当使用BrdU标记的酶免疫分析法检测DNA片段时，培养上清中DNA片段的数量随着时间的推移而增加，这表明这些片段代表了与细胞活力丧失相关的细胞膜破坏。琼脂糖凝胶电泳分析显示，在所有辐射剂量水平下，单线链的切割都是非特异性的。这些结果表明，由于辐射诱导的非特异性DNA切割导致成骨细胞活力丧失是辐射诱导的骨坏死的基础。单独使用时，依普利黄酮可显著提高成骨样细胞的细胞存活率。维生素D_3与一种名为八目健肝的草药制剂联合使用时，也有类似的效果。当检查这些药物对DNA断裂的影响时，发现在所有的八氏菌根处理的细胞中，细胞膜保持完整，在照射后失去了活力。经异丙黄酮治疗后，5gy辐射诱导的细胞坏死与细胞膜损伤无关。另一方面，在接受维生素D_3治疗后，在所有检测的辐射剂量水平下，辐射引起的细胞坏死与细胞膜损伤有关。这些结果表明，用异丙黄酮治疗或维生素D_3和八目肝联合治疗可能有助于预防辐射引起的骨坏死。

The mechanism underlying radiation-induced bone necrosis was studied using mouse marrow- derived osteoblast-like cells. Prophylactic drug therapy for such necrosis was also studied.The percentage of osteoblast-like cells that remained viable after radiation exposure was found to correlate with a decrease in the amount of DNA, and the decrease in amount of DNA was correlated with the radiation dose. The DNA cleavage rate, as measured by the fluorescence method, increased as the radiation dose increased. When DNA fragmentation was examined by enzyme immunoassay using BrdU labeling, the amount of DNA fragments in the culture supernatants increased with time, suggesting that the fragments represented cell membrane destruction associated with the loss of cell viability. Analysis of the DNA cleavage patterns using agarose gel electrophoresis revealed nonspecific cleavage of the singlet chain at all radiation dose levels examined. These results suggest that the loss of viability of osteoblasts due to non-specific DNA cleavage induced by radiation underlies radiation-induced bone necrosis. When used independently, ipriflavone markedly elevated the cell viability rate of osteoblast-like cells. Vitamin D_3 exerted a similar effect when used in combination with a herbal preparation named Hachimijiogan. When the effects of these drugs on DNA fragmentation were examined, it was found that the cell membrane remained intact in all of the Hachimijiogan-treated cells which lost their viability following irradiation. Following treatment with ipriflavone, cell necrosis induced by 5 Gy radiation was not associated with cell membrane damage. On the other hand, following treatment with vitamin D_3, cell necrosis induced by radiation was associated with cell membrane damage at all the radiation dose levels examined. These results suggest that treatment with ipriflavone or a combination of vitamin D_3 and Hachimijiogan may be useful for the prevention of radiation-induced bone necrosis.