Biological Effects of Tritium Radiation Quantitatively Estimated Using Mouse Fetal Cell Damage

研究了甲基-^3H-胸苷等4种有机结合氚化合物（OBT）对培养的小鼠胚胎中脑细胞（MBC）的β辐射效应。结果表明，β射线与X射线在其ID 50（50%X射线剂量）下对细胞增殖和分化的抑制作用以及对培养物DNA和蛋白质含量的降低作用的相对生物学效应（RBE）值为4.6 ~ 8.7。低至5 cGy的剂量从混合曝光导致可检测的抑制effects.Induction细胞凋亡的氚曝光进行了研究，在MBC和脑切片的胚胎和新生儿的小鼠。在MBC培养物中，与ID 50剂量的X射线照射相比，加入甲基-^3 H-胸苷（^3 H-TdR）（21 kBq ml^<-1>）和氚水（HTO）（5.616 MBq ml^<-1>）诱导的凋亡出现较晚，凋亡百分比较低。孕鼠在妊娠第12.5天腹腔注射HTO 481.8kBq/g体重<-1>，子代出现处理行为改变。从注射后1天到出生后1周，在胚胎神经管中观察到凋亡细胞增加。X射线诱导的细胞凋亡在照射后2 h出现，4 h达高峰。新生儿脑皮质凋亡细胞增多。产前HTO暴露小鼠脑细胞凋亡的百分比高于产前X射线照射小鼠。细胞凋亡的可能机制及其与氚β射线的较高相对生物学效应（RBE）值的关系进行了讨论。

Effects of beta-radiation from 4 kinds of organically bound tritium compounds (OBTs) including methyl-^3H-thymidine were investigated on cultured mouse embryonic mid brain cells (MBC). The relative biological effectiveness (RBE) values, ranging from 4.6 to 8.7, of beta ray from OBTs were obtained when compared with X-irradiation at their ID5Os (50 % inhibiton dose) on the inhibition of cell proliferation and differentiation, and on the decrease of DNA and protein contents of the cultures. Doses as low as 5 cGy from a mixed exposure resulted in detectable inhibitory effects.Induction of apoptosis by tritium exposure was investigated in both MBC and brain sections of embryos and of newborns in mice. In the cultures of MBC, addition of methyl-^3H-thymidine (^3H-TdR) (21 kBq ml^<-1>) and tritiated water (HTO) (5.616 MBq ml^<-1>) induced late appearances and low percentages of apoptosis when compared to X-irradiation at the ID50 dose. The pregnant mice were given an intraperitoneal injection of HTO at the concentration of 481.8 kBq g^<-1> of body weight on gestation day 12.5, by which treatment behavioral changes in the offspring occurred. Increased apoptotic cells were observed in the neural tube of embryos from 1 day after the injection to 1 week postnatal age. Apoptosis induced by X-rays appeared 2 h after irradiation, with a peak at 4 h. Increase of apoptotic cells was also found in the brain cortexes of newborns. The percentage of apoptosis in the brain was higher in the prenatal HTO exposed mice than in the prenatal X-irradiated mice. Possible mechanisms on apoptosis and its relation to the higher relative biological effectiveness (RBE) value of tritium beta-rays are discussed.