Radiation induced bystander effects What? Why? And How? Carmel Mothersill Colin Seymour McMaster University
Outline Bystander effects and genomic instability In vivo relevance and evidence The fish model Mechanisms Multiple stressor issues Why do these effects happen?
Take home messages Target theory, LNT and DNA centric ideas of low dose effects are dead Chronic (background) exposure to radiation is in no way related, even by elaborate fudge factors to acute exposure Environmental effects are not simple and multiple stressor exposure HAS to be part of the discussion Evolution is all about adaptation (or not?) to changed conditions
The bystander effect Ionizing radiation, UVA, UVB, ELF EMF and heavy metals induce affected cell to signal to others. Responses to the signals include apoptosis, micronucleus formation, transformation, mutation, induction of stress and adaptive pathways. Serotonin (5HT) and Calcium ions known to be involved in signal production. GJIC connexins Ca 2+ 1 o and 2 o response 5HT bystander factor molecules ROS/Nitric oxide/cytokines Biogenic amines,tgfb, p53???? response Ca 2+ response Ca 2+ Amplification/ Cascade effects? response Ca 2+
Bystander and direct dose survival curves over six orders of magnitude 60 Co with calcium data 140 120 100 80 60 ICCM Irradiat 40 No Ca 2+ Ca 2+ 20 0 0.01 0.1 1 10 100 1000 10000 Dose (m
The link between bystander effects and genomic instability twin pillars of the new paradigm Old view clonal outcome Hit Progeny are all i.e. identical and mutation is passed to all progeny New view non clonal, population determined outcome Hit? Cells continue to be produced with non clonal changes Progeny cells are non clonal and may give rise to a variety of mutations or die
In vivo relevance
In vivo evidence Clastogenic factors in blood of irradiated people and experimental animals Abscopal effects in distant organs Bone marrow ablated mice receiving opposite sex marrow transplant show instability in the regenerating marrow Soluble factors from explanted tissues after in vivo exposure
The fish model for studying bystander effects
Measuring radiation induced bystander response in vivo Irradiate fish ±Metals in water Dissect fresh tissue from animal Do proteomics Chop tissue to provide explant pieces Culture of explants Harvest culture medium containing stress signal molecules/metabolomics Examine explant outgrowth/immunocytoche mistry Add to unirradiated clonogenic cell line and determine survival or other stress endpoints
INDUCTION OF THE BYSTANDER EFFECT IN A DIFFERENT FISH X rayed fish Waterborne bystander effect Partner bystander effect
BYSTANDER EFFECT INDUCED IN VIVO IN RAINBOW TROUT, MEDAKA & ZEBRAFISH 0.5Gy X ray dose Water soluble bystander signals Non X rayed fish Rainbow trout (Mothersill et al 2006) 0.5Gy X ray dose Non X rayed fish Zebrafish (Mothersill et al 2007) 0.5Gy X ray dose Non X rayed fish Medaka (Mothersill et al 2009)
X RAY AND BYSTANDER EFFECT INDUCED CHANGES TO THE TROUT GILL PROTEOME 76.0 66.2 Hemopexin like protein Molecular size (kda) 43.0 36.0 31.0 21.5 Annexin II Pyruvate dehydrogenase (PDH) RhoGDP dissociation inhibitor (RhoGDI) Chromosome 1 SCAF protein 17.5 4.5 5.1 5.4 5.6 6.0 7.0 8.5 Isoelectric point (ph units) SCAF = SR like CTD associated factor (SR = Serine argenine Rich, CTD = C Terminal Domain)
Medaka gill proteins affected 76.0 66.2 Complement component C3 Chromosome 5 SCAF protein Warm temperature acclimation related 65 kda protein (Wap65) Molecular size (kda) 43.0 36.0 31.0 Annexin A1 Creatine kinase Lactate dehydrogenase Annexin A4 21.5 ABC transporter 17.5 4.5 5.1 5.4 5.6 6.0 7.0 8.5 pi (ph units)
Bystander effect proteomics Protective response against reactive oxygen species Bystander effect proteomic changes are transcriptionally regulated (SCAF proteins) Virtually identical proteomic response in rainbow trout and medaka Is the bystander effect an immediate protective response (Smith et al 2007) or an adaptation to possible future radiation damage (Kadhim et al 2004)? Evidence from trout and medaka suggests the bystander effect is immediately protective Additionally the induction of an adaptive response may be species specific and apply particularly in radiosensitive biological systems
Legacy effect of single acute 0.5Gy X ray exposure to eggs
Transgenerational study (in progress)
Transgenerational memory of irradiation calcium signal 1.05 sham Sample # 28 1.35 Sample #1 Irradiated YSL stage parents 1.30 Ratio of Flourescence 1.04 1.03 1.02 1.01 1.00 Ratio of Fluorescence 1.25 1.20 1.15 1.10 1.05 1.00 0.99 0.98 0 200 400 600 800 1000 0.95 0 100 200 300 400 500 600 Time (s) Time (s) Sham Sample # 10 Sample # 11 Bystander to above parents 1.10 1.08 1.6 Ratio of Flourescence 1.06 1.04 1.02 Ratio of Flourescence 1.4 1.2 1.00 1.0 0.98 0 100 200 300 400 500 600 Time (s) 0.8 0 100 200 300 400 500 Time (s)
Some mechanistic questions Role of DNA repair Role of serotonin Role of p53
DNA repair is important in vivo and in vitro Reduced reproductive survival in vitro 140 120 100 Increased apoptosis in vivo 80 60 0Gy 0.5Gy 5Gy 40 20 0 HPV-G SW48 GS3 1Br3 ATBr1 180Br CHO-K1 XRS 5 XR-1 Burkitts control Raji 9 Raji 10 Cell Lin DNA repair deficient cell lines and transgenic medaka both produce highly toxic bystander signals after low dose irradiation
Serotonin important in vivo and in vitro Serotonin bound by irradiated cells In vitro, leading to Calcium pulse. Reserpine inhibits serotonin binding and prevents the bystander effect in vitro and in vivo
Role of p53 in response to signal but not in generation of signal HCT / Reporters HCT +/+ Reporters PE 120 100 80 60 Direct 0Gy "Direct 0.1Gy" "Direct 0.5Gy" got / 0Gy PE 120 100 80 60 Direct 0Gy Direct 0.1Gy Direct 0.5Gy got / 0Gy 40 got / 0.1Gy 40 got / 0.1Gy 20 got / 0.5 Gy 20 got / 0.5Gy 0 1 got +/+ 0Gy 0 1 got +/+ 0Gy Treatments got +/+ 0.1Gy Treatments got +/+ 0.1Gy got +/+ 0.5Gy got +/+ 0.5Gy
Multiple stressors Radiation seldom acts alone Isotopes are by definition a radioactive chemical Little information on synergistic effects Little low dose information Little in vivo information
What the multiple stressor problem does to radiation protection Multiple inducers of stress effects therefore dose and effect are not simply linked Response based approach needed How to link biological effect with adverse outcome at the organism, population and ecosystem level Mechanistic uncertainty at low doses Non targeted effect predominate at low doses
Examples of complex senarios Radiation induces a cell to undergo apoptosis, removing it from the potentially carcinogenic pool. Substance 2 (eg Cd) interferes with the signaling cascade and the cell lives survival assay suggests protective effect of interaction? Radiation induces an adaptive response in population A, a further stressor has little effect but pristine population B has no adaption and is devastated by the same stressor.
Fish irradiation in Norway: (lets get some low dose data!) Exposure of fish in aerated tanks to mgy doses over 5 48 hours Metals in the water
Comparison of in vivo mgy radiation exposure±metals on production of bystander signals Co60 Al+Cd
Proposed dose response relationship for radiation in the context of non-targeted effects Purple arrows indicate mechanistic break points where new, more appropriate, response pathways emerge saturation Blue line represents old LNT model Effect saturatio n Zone of linearity Zone of uncertainty tolerance New coping mechanisms induced Dose Hormesis area Natural background
Unifying Theory: transduction of bystander effect Serotonin (nm range) binds - Activation of calcium channel Low dose stimulation of system Ca2+ Activated system NOTES : good response at one level in system may be bad at another level Links stress even mental stress, physiological response and outcome response In system
So why do these effects happen?
WHY ARE THESE MECHANISMS SO WIDESPREAD AND PERSISTENT? In terms of evolution there is conservation of the mechanism and bystander pathway across species and this suggests a very primitive origin in the vertebrates since teleost fish split from the main vertebrate line early in vertebrate evolution.
Population based response? Are non targeted effects a reflection of population level regulation to optimise population fitness (tissue or individual level)? Is the function of radiation induced bystander signaling to co ordinate behaviour at higher hierarchical levels of organisation? Quorum sensing in bacteria is an example of this at the population level as are hormones at the organism level
SUMMARY Non targeted effects exist They manifest at high frequency in many ways They cause stress like symptoms We know a lot about the mechanisms but little about the reasons why they are tolerated The underlying debate about purpose or chance is as old as Plato and Aristotle
Acknowledgements Thanks to Colin Seymour, husband and long time collaborator Richard Smith and all the Salbu Lab NOTE EU IP collaborators Funded by The Canada Research Chairs and NSERC IRC Chairs programmes