Investigation of direct and bystander effects following neutron irradiation of skin cells

研究中子照射皮肤细胞后的直接效应和旁观者效应

• 批准号: RGPIN-2014-05542
• 负责人: Seymour, Colin
• 金额: $ 3.06万
• 依托单位: McMaster University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=611696
• 关键词: Investigation; direct; bystander; effects; following

The aim of this proposal is to discover why non-targeted effects (NTE) of ionising radiation including bystander effects (BE) and genomic instability (GI) are not seen following exposure of cells or organisms to neutrons. Several experiments over the last 30 years by the applicant and others using different neutron sources have confirmed this but no systematic study has been done to understand why. BE - i.e. effects in neighbouring cells and GI i.e. effects in the distant progeny, not targeted by direct irradiation are very well characterised low dose effects of ionising radiation and UV. They predominate in the dose range 2mGy-0.5Gy of acute low LET radiation exposure and are thought to be mediated by oxidative stress generation (ROS) in exposed cells which turns on signalling mechanisms activating stress responses in un-hit cells. There are many endpoints for determining that bystander signalling has occurred such as measurement of cell death, chromosome damage, calcium flux, up-regulation of DNA repair mechanisms and over production of ROS. The current proposal will investigate three hypotheses built around 5 questions, to try to determine why neutrons do not produce bystander effects. Q1. Is it true that neutrons NEVER produce NTE or have we just missed the effective window? Q2. What is stopping neutron exposed cells from producing NTE? Is signal production affected? If so at what point in the mechanism? Q3. Most neutron beams have a gamma component - does the presence of neutrons cancel or otherwise neutralise any gamma-produced signal? Q4. Neutron radiobiology shows an “inverse dose rate effect” for radiation transformation (in vitro assay for carcinogenic potential) where, lower dose rates are more effective at producing damage than high dose rates. Is the lack of NTE responsible for this? Q5. Neither neutron nor alpha particle cell survival curves have a shoulder (low dose sparing) but alpha particles are reported to produce NTE, protons effects are equivocal. Is this true and what are the implications for understanding neutron NTE radiobiology? These questions have been distilled into 3 testable hypotheses briefly listed here: A. The dose to the individual cell receiving a neutron hit is so high that it cannot generate a signal. This will be tested using dosimetric and biological approaches to determine the dose to the cell and whether that dose blocks mechanisms involved in signal production such as calcium ion flux, ROS and serotonin binding. Testing this will employ 3 PhD students and will address questions 1,2,3 and 4. B. In addition to a low LET, low dose threshold for triggering NTE there is also a high dose threshold above which signal production is inhibited. This will be tested using systematic approaches aimed at comparing different radiation qualities. This will employ one additional PhD student and will address questions 3 and 5. C. The interaction of x- and gamma rays with cell membranes causes direct excitation and ionisation of the membrane and activates ion-gated membrane pumps to trigger the signalling cascade. Some types of neutrons may not cause this excitation depending on whether they cause indirect ionisation or not. This will be tested by treating cells before exposure to gamma rays or thermal or fast neutrons, with membrane stabilising agents. This will also address question 2 and 3. These approaches should answer the question of why neutrons do not produce NTE and should provide mechanistic information of importance in low dose radiobiology in general and neutron radiobiology in particular. Because neutrons are a by-product in CANDU reactors, the results may also benefit those concerned with radiation protection issues in the nuclear power industry.

该提案的目的是发现为什么在细胞或生物体暴露于中子后没有观察到电离辐射的非靶效应（NTE），包括旁观者效应（BE）和基因组不稳定性（GI）。申请人和其他人在过去30年中使用不同中子源进行的几次实验已经证实了这一点，但没有进行系统的研究来了解原因。BE -即在邻近细胞中的效应和GI-即在远距离子代中的效应，不被直接照射靶向，是电离辐射和UV的低剂量效应的非常好的特征。它们在急性低LET辐射暴露的剂量范围2 mGy-0.5Gy中占主导地位，并且被认为是由暴露细胞中的氧化应激产生（ROS）介导的，其开启激活未击中细胞中的应激反应的信号传导机制。存在许多用于确定旁观者信号传导已经发生的终点，例如测量细胞死亡、染色体损伤、钙通量、DNA修复机制的上调和ROS的过度产生。目前的建议将调查围绕5个问题建立的三个假设，试图确定为什么中子不产生旁观者效应。 Q1.中子真的从来没有产生过NTE吗？或者我们只是错过了有效的窗口？ Q2.是什么阻止中子暴露细胞产生NTE？信号产生是否受到影响？如果是，在机制的哪个点？ Q3.大多数中子束都有伽马成分--中子的存在会抵消或中和伽马产生的信号吗？ Q4.中子放射生物学显示出辐射转化的“反向剂量率效应”（体外致癌潜力测定），其中较低剂量率比高剂量率更有效地产生损害。这是否因为缺乏NTE？ Q5.中子和α粒子细胞存活曲线都没有肩部（低剂量保留），但据报道α粒子会产生NTE，质子效应是不确定的。这是真的吗？对于理解中子NTE放射生物学有什么意义？ 这些问题已经被提炼成3个可测试的假设，简要地列在这里： A.接受中子撞击的单个细胞的剂量如此之高，以至于它不能产生信号。这将使用剂量测定和生物学方法进行测试，以确定细胞的剂量以及该剂量是否会阻断参与信号产生的机制，如钙离子通量、ROS和血清素结合。测试将雇用3名博士生，并将解决问题1，2，3和4。 B。除了触发NTE的低LET、低剂量阈值外，还存在高剂量阈值，高于该阈值信号产生就会被抑制。这将使用旨在比较不同辐射质量的系统方法进行测试。这将雇用一名额外的博士生，并将解决问题3和5。 C. X射线和伽马射线与细胞膜的相互作用导致膜的直接激发和电离，并激活离子门控膜泵以触发信号级联。某些类型的中子可能不会引起这种激发，这取决于它们是否引起间接电离。这将通过在暴露于伽马射线或热中子或快中子之前用膜稳定剂处理细胞来测试。这也将解决问题2和3。 这些方法应该回答的问题，为什么中子不产生NTE，并应提供机械信息的重要性，在低剂量放射生物学一般和中子放射生物学特别是。由于中子是CANDU反应堆的副产品，因此这些结果也可能使那些关注核电工业辐射防护问题的人受益。