Persistence of genetic damage in mice exposed to low dose of X rays

PURPOSE: The aim of this work was to evaluate the persistence of genetic damage in CBA/J mice treated with a single irradiation of 0.1 or 1 Gy of X rays. MATERIALS AND METHODS: Peripheral blood was collected from irradiated and control mice after 30 min, 24 h, 7 days, 1, 3 and 6 months from exposure and analysed by comet assay. To investigate if the whole-body irradiation affect DNA repair, half of the sampled blood cells were in vitro-irradiated with additional 4 Gy and immediately analysed. Six months from exposure haematopoietic organs were sampled for measuring apoptotic index. RESULTS: In mice exposed to 1 Gy genetic damage was initially high and decreased during the experimental-time, while in the 0.1 Gy group damage, at first low, persisted and slightly increased. The 0.1 Gy-irradiated mice showed also a time-dependent increasing sensitivity to the in vitro-irradiation. Six months after whole-body irradiation, the percentage of apoptotic cells observed in haematopoietic compartments from 0.1 Gy-irradiated mice was significantly higher compared to controls and to 1 Gy mice. CONCLUSIONS: Results demonstrated that a single exposure to low-dose might induce long-term damage. Persistence of genetic damage might have relevant implications for estimating risk for low doses.     

Involvement of MAPK signalling in radioadaptive response in BALB/c mice exposed to low dose ionizing radiation

To investigate low dose ionizing radiation (LDIR)-induced adaptive response in lymphocytes of BALB/c mice and to elucidate related molecular mechanisms. Mice were exposed to a priming dose (PD) of 0.1?Gy and challenge dose (CD) of 2?Gy ionizing radiation. Proliferation response to mitogen concanavalin A was assessed using ³H thymidine incorporation and carboxyfluoresceinsuccinamidylester (CFSE) dye dilution. Early activation markers were assessed by flow cytometry, cytokines by ELISA, DNA damage by comet assay and mitogen activated protein kinase (MAPK) signaling by Western blotting. Radioadaptive response was observed in lymphocytes of mice exposed to PD prior to CD of ionizing radiation in terms of DNA damage, early activation markers CD69, CD71, cytokines IL-2, IFN-γ as well as proliferation. This effect was transient and observed 24?h after CD and not after 0?h or 72?h. Hyper activation of MAPK signaling pathways in lymphocytes from LDIR-exposed mice and abrogation by ERK and p38 inhibitors suggests the involvement of MAPK signaling in radioadaptive response. Our study demonstrates that LDIR-induced transient adaptive response was due to hyper activation of MAPK signaling. Our findings contribute towards the understanding of LDIR-induced adaptive response.     

低剂量电离辐射诱发小鼠显性致死突变的适应性反应

须先给予雄性小鼠０．０５Ｇｙ照射，随后给予２．０Ｇｙ照射，观察精子发生不同阶段显性致死突变率，受孕率．结果表明精原干细胞阶段、分化型精原细胞阶段预先照射０．０５Ｇｙ组，平均植入胚胎数、活胎数均明显高于单纯２．０Ｇｙ组，显性致死突变率明显低于单纯２．０Ｇｙ照射组，表现出适应性反应．同时还观察到预先给予小剂量处理组与雌鼠交配的受孕率也高于单纯大剂量组。统计学检验差异有非常显著性．     

Genetic instability induced by low doses of x-rays in hamster cells

Purpose:?Genomic instability involves time delayed events and can be manifested as elevated rates of heritable changes in the progeny of irradiated cells. To study the induction of chromosomal instability by very low doses of radiation Chinese Hamster Ovary (CHO) cells were exposed to 10 – 50 milisieverts (mSv) (≈10 – 50 miligrays (mGy)) of x-rays.

Materials and methods:?Control and irradiated cell populations were assayed for chromosomal aberrations and assessed using a micronucleus test and anaphase-telophase analysis at the first cell division post-irradiation and at every four population doublings thereafter up to 16 population doublings post-irradiation.

Results:?Frequencies of micronuclei, anaphase-telophase alterations and chromosomal aberrations were increased when the cells were analysed immediately after x-ray exposure. Micronuclei and anaphase-telophase alterations showed significantly increased frequencies when they were analysed at 12 and 16 population doublings after exposure to 50 mSv. Chromosomal aberrations increased significantly at 12 and 16 population doublings after exposure to 10 mSv and 50 mSv.

Conclusions:?Our results are consistent with the presence of a phenomenon by which the initial DNA damage in the surviving cells is memorized. Micronuclei and achromatic lessions were the main cytogenetic damage observed in cells exposed to very low doses of x-rays, indicating that these low doses are able to induce genetic instability.     

Transcriptomic profiling suggests a role for IGFBP5 in premature senescence of endothelial cells after chronic low dose rate irradiation

Abstract

Purpose: Ionizing radiation has been recognized to increase the risk of cardiovascular diseases (CVD). However, there is no consensus concerning the dose-risk relationship for low radiation doses and a mechanistic understanding of low dose effects is needed.

Material and methods: Previously, human umbilical vein endothelial cells (HUVEC) were exposed to chronic low dose rate radiation (1.4 and 4.1 mGy/h) during one, three and six weeks which resulted in premature senescence in cells exposed to 4.1 mGy/h. To gain more insight into the underlying signaling pathways, we analyzed gene expression changes in these cells using microarray technology. The obtained data were analyzed in a dual approach, combining single gene expression analysis and Gene Set Enrichment Analysis.

Results: An early stress response was observed after one week of exposure to 4.1 mGy/h which was replaced by a more inflammation-related expression profile after three weeks and onwards. This early stress response may trigger the radiation-induced premature senescence previously observed in HUVEC irradiated with 4.1 mGy/h. A dedicated analysis pointed to the involvement of insulin-like growth factor binding protein 5 (IGFBP5) signaling in radiation-induced premature senescence.

Conclusion: Our findings motivate further research on the shape of the dose-response and the dose rate effect for radiation- induced vascular senescence.     

Increased susceptibility to delayed genetic effects of low dose X-irradiation in DNA repair deficient cells

Abstract

Purpose: To examine whether the levels of micronuclei induction, as a marker for genomic instability in the progeny of X-irradiated cells, correlates with DNA repair function.

Materials and methods: Two repair deficient cell lines (X-ray repair cross-complementing 1 [XRCC1] deficient cell line [EM9] and X-ray repair cross complementing 5 [XRCC5; Ku80] deficient X-ray sensitive Chinese hamster ovary [CHO] cell line [xrs5]) were used in addition to wild-type CHO cells. These cells were irradiated with low doses of X-rays (up to 1 Gy). Seven days after irradiation, micronuclei formed in binucleated cells were counted. To assess the contribution of the bystander effect micronuclei induction was measured in progeny of non-irradiated cells co-cultured with cells that had been irradiated with 1Gy.

Results: The delayed induction of micronuclei in 1 Gy-irradiated cells was observed in normal CHO and EM9 but not in xrs5. In the clone analysis, progenies of xrs5 under bystander conditions showed significantly higher levels of micronuclei, while CHO and EM9 did not.

Conclusion: Genomic instability induced by X-irradiation is associated with DSB (double-strand break) repair, even at low doses. It is also suggested that bystander signals, which lead to genomic instability, may be enhanced when DSB repair is compromised.     

低剂量辐射适应性反应对辐射诱发小鼠胸腺淋巴瘤的影响

目的 探讨低剂量辐射对致癌剂量辐射诱发小鼠胸腺淋巴瘤的影响及其免疫学机理。方法 采用4次1.75GyX射线全身照射C57BL/6J小鼠诱发胸腺淋巴瘤模型, 观察不同剂量照后6个月小鼠胸腺淋巴瘤发生率, 照后1个月脾脏NK细胞毒活性、IL-2和γIFN分泌活性、腹腔巨噬细胞吞噬功能及其TNFα分泌活性以及胸腺细胞分化的变化。结果 每次1.75Gy照射前6h或12h接受25mGy或75mGy全身照射均可降低胸腺淋巴瘤发生率, 且预先接受75mGy全身照射的作用效果更为明显; 每次1.75Gy照射前12h接受75mGy照射小鼠, 上述免疫指标均比单纯1.75Gy照射组增强, 且多数指标接近假照射组; 其胸腺CD4^-CD8^-和CD4^-CD8⁺细胞较单纯1.75Gy照射组减少、CD4⁺CD8⁺细胞增多。结论 低剂量辐射可诱导辐射诱发胸腺淋巴瘤适应性反应, 对致癌剂量辐射诱发小鼠胸腺淋巴瘤有抑制作用, 其抑制作用的免疫学机理可能与低剂量辐射的免疫增强效应及诱导的免疫学适应性反应, 减轻致癌剂量辐射对机体免疫功能的损伤, 使胸腺淋巴瘤前体细胞在形成胸腺淋巴瘤之前被免疫系统清除有关。     

Dotting the eyes: mouse strain dependency of the lens epithelium to low dose radiation-induced DNA damage

Purpose: Epidemiological evidence regarding the radiosensitivity of the lens of the eye and radiation cataract development has led to changes in the EU Basic Safety Standards for protection of the lens against ionizing radiation. However, mechanistic details of lens radiation response pathways and their significance for cataractogenesis remain unclear. Radiation-induced DNA damage and the potential impairment of repair pathways within the lens epithelium, a cell monolayer that covers the anterior hemisphere of the lens, are likely to be involved.

Materials and Methods: In this work, the lens epithelium has been analyzed for its DNA double-strand break (DSB) repair response to ionizing radiation. The responses of epithelial cells located at the anterior pole (central region) have been compared to at the very periphery of the monolayer (germinative and transitional zones). Described here are the different responses in the two regions and across four strains (C57BL/6, 129S2, BALB/c and CBA/Ca) over a low dose (0–25 mGy) in-vivo whole body X-irradiation range up to 24?hours post exposure.

Results: DNA damage and repair as visualized through 53BP1 staining was present across the lens epithelium, although repair kinetics appeared non-uniform. Epithelial cells in the central region have significantly more 53BP1 foci. The sensitivities of different mouse strains have also been compared.

Conclusions: 129S2 and BALB/c showed higher levels of DNA damage, with BALB/c showing significantly less inter-individual variability and appearing to be a more robust model for future DNA damage and repair studies. As a result of this study, BALB/c was identified as a suitable radiosensitive lens strain to detect and quantify early low dose ionizing radiation DNA damage effects in the mouse eye lens specifically, as an indicator of cataract formation.     

低剂量辐射适应性反应对辐射诱发小鼠胸腺淋巴瘤 …

目的 探讨低剂量对致癌剂量辐射诱发小鼠胸腺淋巴瘤的影响及其免疫学机理。方法 采用４次１．７５ＧｙＸ射线全身照射Ｃ５７ＢＬ／６Ｊ小鼠诱发胸腺淋巴瘤模型,观察不同剂量照后６个月小鼠胸腺淋巴瘤发生率,照后１个月脾脏ＮＫ细胞毒活性、ＩＬ－２和γ－ＩＦＮ分泌活性、腹腔巨噬细胞吞洚功能及其ＴＮＦ６分泌活性以及胸腺细胞分化的变化。结果 每次１．７５Ｇｙ照射前６ｈ、１２ｈ接受２５ｍＧｙ、７５ｍＧｙ全身照射均可降你     

山东济宁辐射事故受照人员生物剂量估算及彗星电泳检测分析

目的探索特大剂量照射后外周血和骨髓染色体培养方法，拟合6Gy以上大剂量照射染色体双着丝点＋环剂量-效应曲线，对山东济宁“10．21”事故受照者进行准确生物剂量估算和DNA损伤检测。方法采集2例受照者外周血和骨髓细胞，制备染色体标本，计数双（多）着丝点＋环数目；用正常离体人血拟合6～22Gy双＋环剂量效应曲线及数学方程；对2例事故受照者进行生物剂量估算。用碱性单细胞凝胶电泳方法检测受照者外周血DNA损伤。结果B的外周血染色体双＋环平均数为4．47个／细胞；A的外周血培养无分裂细胞，骨髓染色体双＋环平均数为9．15个／细胞。用6—22Gy剂量效应方程估算全身平均受照剂量，B为9．4Gy，A为19．5Gy。单细胞凝胶电泳可见2例受照者的多数彗星细胞呈小头大尾形状。结论用新建立的6～22Gy染色体畸变剂量效应曲线估算2例受照者的生物剂量，已分别达到极重度骨髓型放射病和肠型放射病水平。     

低剂量辐射兴奋效应及其机制

国内外有关低剂量辐射兴奋效应的研究始于70年代末,近年来已从低剂量诱导蛋白生成、基因调控方面研究其机制。本文分别从流行病学调查和放射生物学研究两大领域对低剂量辐射兴奋效应及其机制加以综述。     

低剂量辐射诱导细胞遗传学适应性反应的某些规律

10mGyX射线可诱导人外周血淋巴细胞和家兔外周血淋巴细胞产生对相继较大剂量(1.5Gy)X射线诱发染色体畸变的抗性, 称之为适应性反应。在离体和整体条件下, 该反应广泛存在于体细胞和生殖细胞中, 其反应程度与低剂量辐射的剂量呈负相关, 即辑先照射的剂量愈低, 诱导的适应性反应愈明显。同时还发现该反应也受许多因素的影响, 如: 低剂量辐射的剂量、剂量率, 照射时间以及生物个体差异等因素。     

The effect of genetic background and dose on non-targeted effects of radiation

Abstract

Purpose: This work investigates the hypothesis that genetic background plays a significant role in the signalling mechanisms underlying induction and perpetuation of genomic instability following radiation exposure.

Materials and methods: Bone marrow from two strains of mice (CBA and C57) were exposed to a range of X-ray doses (0, 0.01, 0.1, 1 and 3 Gy). Different cellular signalling endpoints: Apoptosis, cytokine levels and calcium flux, were evaluated at 2 h, 24 h and 7 d post-irradiation to assess immediate and delayed effects.

Results: In CBA (radiosensitive) elevated apoptosis levels were observed at 24 h post X-irradiation, and transforming growth factor-β (TGF-β) levels which increased with time and dose. C57 showed a higher background level of apoptosis, and sustained apoptotic levels 7 days after radiation exposure. Levels of tumor necrosis factor-α (TNF-α were increased in C57 at day 7 for higher X-ray doses. TGF-β levels were higher in CBA, whilst C57 exhibited a greater TNF-α response. Calcium flux was induced in reporter cells on exposure to conditioned media from both strains.

Conclusions: These results show genetic and dose specific differences in radiation-induced signalling in the initiation and perpetuation of the instability process, which have potential implications on evaluation of non-targeted effects in radiation risk assessment.     

第二届低和很低剂量电离辐射对人体健康效应国际会议中有关容许剂量的介绍

概要介绍了第二届低和很低剂量辐射对人体健康效应国际会议中有关容许剂量照射对人体效应的内容:根据对放射性工作者所受职业照射出现的变化,对ICRP制订的容许剂量限值提出了某些异议,但也有持不同观点者。     

低剂量辐射的细胞遗传适应性反应机理研究现状

很多学者对LDR(低剂量辐射)可以在体内及体外培养的细胞中诱导出适应性反应的机理进行了深入的研究,发现适应性反应的诱导与很多因素有关,这些因素包括LDR诱导的DNA修复系统的激活、LDR诱导的基因和蛋白的作用、抗氧化物酶的作用、细胞信号转导以及与p53蛋白有关的细胞周期阻滞的影响等。     

低剂量电离辐射对雄性糖尿病模型大鼠生殖损伤的影响

目的 探讨75 mGy照射对12周糖尿病(DM)大鼠睾丸生精细胞凋亡及抗氧化和性激素水平的影响。方法 随机将Wistar大鼠分为3组:健康对照组、75 mGy＋DM组及DM组,12周末记录其存活率和体重。采用流式细胞术和TUNEL染色法检测生精细胞凋亡率,应用试剂盒分别检测血清及睾丸抗氧化和激素水平的变化。结果 12周后,DM组大鼠存活率为25%,健康对照组为100%(χ²=15.938, P<0.01);75 mGy＋DM组大鼠存活率为56.25%,与DM组比较差异有统计学意义(χ²=4.00,P<0.05)。糖尿病大鼠生精细胞凋亡率较健康对照组明显增加,亦高于75 mGy+DM组(F＝5.496,P<0.05)。与健康对照组比较,糖尿病大鼠血清和睾丸组织中丙二醛(MDA)及NO含量不同程度增加,而75 mGy＋DM组大鼠血清和睾丸MDA含量显著低于单纯DM组,以睾丸组织中尤为明显(F=10.644,P<0.01);75 mGy照射显著降低了DM组大鼠血清NO含量(F=14.379, P<0.05),同时增加了DM组大鼠血清中的一氧化氮合酶(NOS)活性及睾丸酮(TS)和促滤泡激素(FSH)含量(F值分别为9.676、43.194和5.282,P<0.05或P<0.01)。结论 低剂量辐射显著降低睾丸组织及血清MDA和NO含量,增加抗氧化酶活性和TS及FSH含量,可能与其抑制糖尿病大鼠生精细胞凋亡增多所致生精障碍有关。     

低剂量全身照射抑制小鼠癌细胞播散

小鼠受５０，７５，１００和１５０ｍＧｙＸ射线全身照射后２４小时经球后静脉注入Ｌｅｗｉｓ肺癌或Ｂ１６黑色素瘤细胞。注后１４天以计数肺肿瘤结节数为指标，发现受照小鼠癌细胞播散明显低于假照射对照小鼠。Ｌｅｗｉｓ肺癌细胞注入前２４小时接受７５ｍＧｙ全身照射小鼠与注入相同癌细胞数的假照射小鼠比较，发现照后２～６天脾脏ＮＫ细胞活性和ＩＬ－２分泌均增高。提示低剂量辐射可能通过增强免疫反应抑制癌细胞播散。     

Gene set enrichment analysis highlights different gene expression profiles in whole blood samples X-irradiated with low and high doses

Abstract

Purpose: Health risks from exposure to low doses of ionizing radiation (IR) are becoming a concern due to the rapidly growing medical applications of X-rays. Using microarray techniques, this study aims for a better understanding of whole blood response to low and high doses of IR.

Materials and methods: Aliquots of peripheral blood samples were irradiated with 0, 0.05, and 1 Gy X-rays. RNA was isolated and prepared for microarray gene expression experiments. Bioinformatic approaches, i.e., univariate statistics and Gene Set Enrichment Analysis (GSEA) were used for analyzing the data generated. Seven differentially expressed genes were selected for further confirmation using quantitative real-time PCR (RT-PCR).

Results: Functional analysis of genes differentially expressed at 0.05 Gy showed the enrichment of chemokine and cytokine signaling. However, responsive genes to 1 Gy were mainly involved in tumor suppressor protein 53 (p53) pathways. In a second approach, GSEA showed a higher statistical ranking of inflammatory and immune-related gene sets that are involved in both responding and/or secretion of growth factors, chemokines, and cytokines. This indicates the activation of the immune response. Whereas, gene sets enriched at 1 Gy were ‘classical’ radiation pathways like p53 signaling, apoptosis, DNA damage and repair. Comparative RT-PCR studies showed the significant induction of chemokine-related genes (PF4, GNG11 and CCR4) at 0.05 Gy and DNA damage and repair genes at 1 Gy (DDB2, AEN and CDKN1A).

Conclusions: This study moves a step forward in understanding the different cellular responses to low and high doses of X-rays. In addition to that, and in a broader context, it addresses the need for more attention to the risk assessment of health effects resulting from the exposure to low doses of IR.     

低剂量辐射诱导适应性反应的分子机制研究现状

低剂量辐射(low dose radiation,LDR)可以增强细胞对随后进行的攻击性剂量(challenge dose)照射的抵抗能力,从而降低攻击性照射引起的染色体畸变和DNA损伤。人们把LDR的这种效应称之为"低剂量辐射诱导的适应性反应"。低剂量辐射诱导适应性反应的分子机制主要涉及细胞信号转导、ROS(活性氧物质)的作用和DNA修复兴奋效应等方面。