A Preliminary Study On Nuclear Logs As Radiation Biomarkers

Nucleoplasmic bridge (NPB) is a continuous DNA-containing structure linking nuclei in a binucleated cell and is an indicator of DNA mis-repair, chromosome rearrangement and telomere end fusions. Studies have shown that NPB frequency was enhanced with the increased absorbed dose of ionizing radiation. And there was a strong correlation between NPB frequencies and dicentic chromosome plus centic ring (dic+r) in the metaphases at the same lymphocyte cultures. NPB has a low level of background frequency, so it can be easily identified and efficiently scored. Therefore, NPB has the fundamental characteristics of radiation biodosimeter.Objective:This paper is a preliminary study of NPB as a radiation biomarker and aimed to provide a new biomarker in radiation damage field as well as to provide scientific evidence for the NPB eventually become a rapid and accurate radiation biodosimetre.Materials and methods:The dose-range and dose-response of radiation-induced NPB, its background frequency, the influence of different dose-rates and radiation quality were analyzed by cytokinesis-block micronucleus (CBMN) cytome assay. The frequencies of dic+r and acentric fragments in the metaphases were analyzed by chromosomal aberration (CA) assay. The mechanism of NPB was analyzed by Fluorescence in situ hybridization (FISH).Results:(1) The NPB frequency and number of NPB cells in human peripheral blood lymphocytes was significantly increased with the increased absorbed dose of60Co y-rays. The dose-response relationship between the NPB frequency and the absorbed doses (0～6Gy and0～1Gy) followed the linear-quadratic model, and the regression equations were as follows:y=(1.39×10-3)x2+(4.94×10-3)x (R2=0.981, P<0.01), y=-(2.48×10-2)x2+(5.62×10-2)x+0.336(R2=0.960, P<0.01), respectively, where y is NPB per cell induced by absorbed dose, x in Gy. (2) CA assay were simultaneously carried out after human peripheral blood samples were exposed to the same60Co γ-ray dose (0,2, and5Gy). The frequencies of dic+r and acentric fragments also increased with the increased absorbed dose of60Co y-ray. The background frequency of NPB was higher than that of dic+r. However, after exposure to2Gy or5Gy60Co γ-rays, the NPB frequencies at each dose level were much lower than those of dic+r frequencies. The dic+r/NPB ratios at0,2, and5Gy60Co γ-rays were0.725,23.1, and33.5, respectively. Positive correlations were observed between the frequencies of NPB and dic+r as well as between the frequencies of MN and ace.(3) Nuclei and NPB staining by DAPI in FISH specimen were blue, and centromere probes signal labeled by Cy3were red. In the merged image, the red dot centromere probe signal was observed on NPB in binucleated cells.(4) The spontaneous frequency of NPB in population was (0.56±0.69)×10-3/cell. The subjects were grouped by gender, NPB spontaneous frequency of male was (0.65±0.74) x10-3/cell, which was higher than that of female was (0.46±0.62)×10-3/cell (P>0.05). The subjects were grouped by age, and the lowest NPB spontaneous frequency was found in the age20-29group,(0.36±0.66) x10-3/cells and the highest was found in the age40～49group,(0.92±0.76) x10-3/cells.(5) Human peripheral blood sample were exposed to5Gy60Co γ-rays at different dose-rates. The NPB frequency had a decreased trend with the increased dose-rate of60Co γ-rays. NPB frequencies in5.0and10.0Gy/min groups were lower than those of in0.2,0.5,1.0,3.0Gy/min groups (P<0.01); NPB frequencies among0.2,0.5,1.0,3.0Gy/min groups and between5.0and10.0Gy/min were not statistical significant (P>0.05).(6) The NPB frequency and number of NPB cells in human peripheral blood lymphocytes significantly increased with the increased absorbed dose of12C6+ion. The dose-response relationship between the NPB frequency and the absorbed doses followed a linear-quadratic model, and the regression equation was as follows:y=-(1.73×10-3)x2+(3.51×10-2)x(R2=0.934, P<0.01), wherey is NPB per cell induced by absorbed dose, x in Gy. The relative biological effect (RBE) values of12C6+ion to 60Co y-ray were between5.86and2.47when the NPB frequencies between0.005and0.07/cell, and the average value was3.72.Conclusion:the NPB background frequency in normal population was very low. And it was not influenced by gender, but has an increased trend with the increased age. NPB has a well dose-response manner after exposed to60Co γ-ray and high LET radiation (12C6+ion). NPB frequencies in higher dose-rate groups were lower than those of in lower groups. The centromere probe signal was observed on NPB in binucleated cells, so it suggested that NPB formation may origin from dicentic chromosome. Therefore, NPB has the potential to become an ideal radiation biodosimeter, but it still needs further research.