Analysis of the mechanism underlying radiation-induced jaw bone necrosis

用小鼠骨髓来源的成骨细胞样细胞研究了辐射诱导骨坏死的机制。对此类坏死的预防性药物治疗也进行了研究。辐射后仍存活的成骨细胞样细胞的百分比与DNA含量的减少有关，DNA数量的减少与辐射剂量有关。荧光法测得的DNA裂解率随照射剂量的增加而增加。当用BrdU标记的酶免疫分析法检测DNA片段时，培养上清液中的DNA片段数量随着时间的推移而增加，表明这些片段代表了与细胞活力丧失相关的细胞膜破坏。用琼脂糖凝胶电泳法对DNA裂解模式的分析显示，在所检测的所有辐射剂量水平下，单线体链都发生了非特异性裂解。这些结果表明，辐射诱导的成骨细胞的非特异性DNA裂解导致的活性丧失是辐射诱导的骨坏死的基础。单独使用时，依普列酮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Hachimijiogan的草药制剂联合使用时，也具有类似的效果。当检测这些药物对DNA断裂的影响时，发现所有经Hachimijiogan处理的细胞在照射后失去活力的细胞膜都保持完好。依普黄酮处理后，5Gy射线照射所致的细胞坏死与细胞膜损伤无关。另一方面，维生素D_3处理后，在所有辐射剂量水平下，辐射所致的细胞坏死与细胞膜损伤有关。这些结果表明，依普列酮或维生素D_3和哈奇密交感合用对预防放射性骨坏死可能是有效的。

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.