British Journal of Radiology (2005) Supplement_27, 128-131
© 2005 British Institute of Radiology
doi: 10.1259/bjr/69849747
British Journal of Radiology Supplement_27 (2005),128-131 © 2005 The British Institute of Radiology
Bystander and other delayed effects and multi-organ involvement and failure following high dose exposure to ionising radiation
C Mothersill, PhD1,
M J Moriarty, MD2 and
C B Seymour, PHD1
1 Medical Physics and Applied Radiation Sciences Unit, McMaster University, Hamilton, Ontario, Canada L8S 4K1 and 2 Saint Luke's Institute of Cancer Research, Rathgar, Dublin 6, Ireland
Correspondence: Prof. Carmel Mothersill. E-mail: mothers@mcmaster.ca
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Abstract
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There is no doubt that ionising radiation damages DNA and that certain organs in the body are more vulnerable than others to the effects of radiation. However, the reasons for the different sensitivities vary and there are now known to be many late expressed effects of exposure that cannot simply be explained on the basis of direct DNA damage. Examples include transmissible genomic instability, bystander effects and adaptive responses, which seem to be interrelated phenomena occurring even at low doses and affecting very high numbers of cells in the exposed organ or organism. Clinically, systemic effects such as fatigue and mental confusion are well known side effects of radiotherapy. Accident victims are also known to exhibit systemic effects that involve general system failure and cannot easily be attributed to effects on particular targeted tissues or organs. There is also evidence for emergent properties of systems that involve communication within and between organs, and concerted responses that are not predictable using reductionist approaches in radiotoxicology. This paper reviews and analyses data regarding delayed or late expressed effects, with particular reference to how they might impact on the understanding and treatment of multi-organ involvement and failure following exposure to accidental or deliberate releases of radiation.
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Introduction
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Since Bergonie and Tribondeau showed in 1906 [1] that radiation destroyed the reproductive capacity of the cell, radiobiology has developed a highly structured approach which assumes that radiation energy damages DNA, either directly or through secondary damage caused by radicals, leading to loss of function, death or mutation of the individual cell [2]. Application of radiobiological ideas to radiotherapy was often unsuccessful and radiotherapy therefore developed empirically [3–5]. For example, radiosensitisers developed and tested using in vitro radiobiological techniques often did not work well in practice [6–8]. References to delayed or late effects, or to abscopal or clastogenic effects, tended to get forgotten because they could not be explained [9–12]. Now, however, the multitude of radiation-induced changes detectable at low doses using modern molecular biological probes and antibodies means that delayed and systemic effects not only cannot be ignored but may actually be explained. What is occurring is a shift from dose-based radiation biology to effect-based radiation biology [13–15]. This paradigm shift opens new and exciting opportunities for modelling radiation effects, treating accident victims and planning radiotherapy. The clinical applications will follow the science only slowly, but the potential is there.
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Brief history of the radiobiology of delayed and bystander effects
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The literature has references to delayed, abscopal and clastogenic effects in humans back to 1954 ([16], and reviewed in [14]). These effects have also been detected in animals [17]. Mainly the effects were ignored or not considered because they were not understood in the prevailing paradigm and were not regarded as important in radiotherapy or risk assessment. The effects were mainly systemic, such as fatigue, or were out-of-field effects, for example effects in the contralateral organ to the one exposed to the dose, and were rightly or wrongly attributed to experimental error, human variation, inflammatory responses to radiation-induced cell death, or the physiology of the tissue being irradiated [18–22]. However, in the light of new insights into the effects of low doses of radiation on cells, these effects are perhaps more explicable. The key change in thinking is to shift from a dose-driven view to an effect- or response-driven view. If dose is the only parameter of importance, then "scatter", "noise" or "background" are regarded as an unfortunate experimental error, but in a response-driven view this error is actually what is important. It means that genetic or lifestyle factors can modify the outcome of exposure to a dose of radiation, however large or small. There is considerable evidence of this in the literature regarding the delayed effects such as genomic instability or bystander effects. Both are known to vary in genetically different strains of mice [23–25]. In humans, variation in the type of delayed effect or the extent and nature of the bystander effect also occurs [25–27], but here it is not easy to decide on the relative importance of genetic or lifestyle factors. Our group has evidence that smoking can modify radiation response [26, 28]. The mechanism appears to involve a shift in the balance of the pro-and anti-apoptotic proteins induced in cells within minutes to hours post exposure.
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Multi-organ involvement and failure (MOIF) and radiation-induced bystander effects
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In relation to MOIF, it is important to recognise that the type of delayed effect seen often reflects what is being measured. Many types of delayed effects may occur in a given system but often only one is measured. For example, a clonogenic "survival" curve tells us nothing about the state of the survivors, it measures only the death of a proportion of the exposed population. Similarly, a "% delayed apoptosis" or "% of micronucleated cells" end-point measures just those features of the exposed population. No judgment can be made from such data regarding the overall effect of these responses. It is not even possible to say whether they are even harmful in a tissue or organism context. This awareness of the limitations of biological assays for revealing outcomes following radiation exposure is becoming more important since so many sophisticated molecular probes and tools are available. It is now very easy to show effects of radiation, even at really low doses, but it is virtually impossible to relate such effects to "harm" at any relevant level. This is a problem that leads to much of the uncertainty and mistrust regarding radiation effects.
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Multicellular responses to irradiation
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It is often said that death of a cell is not a problem because individual cells can be replaced through recruitment or repopulation. If this is true, then obviously the control of tissue function post exposure to any dose of radiation must be at the multicellular level. It must be co-ordinated and monitored by systemic signals. This is well accepted in cell biology, and mechanisms such as cytokine cascades and immune or inflammatory responses are well understood (reviewed in [29]). In radiation biology however, up until recently little attention was generally paid to systemic responses, and both radiation protection research and radiotherapy research are even now more concerned with concepts such as cancer stem cell kill or carcinogenic transformation [30–34]. These concepts are very dependent on dose-driven paradigms where more cells are inactivated or transformed as the dose is increased. The recent upsurge in research on bystander effects and genomic instability has changed this focus and now cell communication, cell signalling, and gene and protein expression post irradiation to any dose are vibrant areas for research, particularly following low doses where these processes dominate the response (reviewed in [35–37]).
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Multi-organ or multi-tissue responses
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What has been rather ignored up to now is how these newly popular effects impact after high dose exposures either for therapy or as a result of accidents. Clearly they are important after low dose exposure because not every cell is damaged or hit and the argument is that bystander effects and delayed expression of damage due to induced genomic instability amplify the dose or, strictly speaking, the effect of the dose. However, at higher doses where all cells receive some energy deposition, there is likely to be a more deterministic response. After high doses, certainly all cells in the field will get multiple hits and therefore the amplification will be due to systemic damage or temporal extension of the effective dose owing to the consequences of genomic instability.
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For the future?
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Intriguing questions of relevance to MOIF after high doses might include the following. Does the dead or lethally irradiated cell induce a bystander effect in other irradiated cells or does the signal only induce a response in unirradiated cells? This question has not been answered satisfactorily and will probably require clonal isolation of targeted and untargeted cells, which would then have to be exposed to medium from dead or lethally irradiated cells.
Do cells receiving bystander signals initiate a bystander signalling response themselves, leading to a cascade effect? The evidence in vitro is confusing. Certainly Azzam et al [38] have evidence for clustering of cells expressing their end-point of p21 expression, but Belyakov et al [39] found that apoptotic cells appeared randomly and not in clusters when he targeted a single cell in a quadrant and measured apoptosis in all the quadrants. Using low-LET (linear energy transfer) and the medium harvest technique, our group showed that repeated harvesting of media was possible and that the effect of the putative signal did not diminish even after subculture of the cells [40]. This means that, once induced, the signal appears to be permanently expressed and this suggests that cells receiving signals can in turn produce signals.
Is there a relative biological effectiveness (RBE) for bystander and delayed effects induced by various types of radiation? Some evidence in the literature suggests a RBE of 1 for neutrons and 
particles when apoptosis is the end-point measured in genomic instability experiments [41, 42]. No one appears to have published data for neutron-induced bystander effects. It is a moot point whether RBE has any meaning if a single -particle track can induce genomic instability in the population or when the lowest dose at which 
-irradiation produces genomic instability has not yet been established.
Is there a dose–response at high doses? There is much evidence that the effects saturate at very low doses [43, 44] but no one appears to have looked at very high doses.
What are the operational thresholds that govern cell and tissue responses? Our group has considered for many years that sectoring decisions such as whether a cell lives or dies, and the factors that control them, are key to understanding radiation responses (reviewed in [45, 46]). Much of the effort needed to resolve these questions is experimental and requires an acceptance of emergent systems biology. Whilst very useful, reductionist approaches will not ultimately resolve complex problems involving tissue salvage responses or "function versus growth" decisions. Figure 1
is a possible model describing the problem. The figure attempts to demonstrate the interplay between factors involved in the biology of MOIF from the time the dose is received through to the final outcome. Depending on the timing of critical events, different outcomes may be possible.
Can we identify a series of "change points" (suggested in Figure 1
) that are not radiation doses but are more akin to saturation points where a particular function ceases and another begins to dominate the response? This would give a range of discontinuities in the radiation response depending on which cellular response systems were saturated. It is possible that this would lead to variable responses at doses approaching discontinuity points, and areas of relative stability in response at doses removed from average discontinuity points.
How relevant is persistent oxidative stress, a feature of MOIF that is also known to be induced during the bystander process and that appears to drive genomic instability [47–50]?
Finally, and most importantly, can we modulate bystander and other related effects and apply the knowledge to the treatment of MOIF? Our group has identified a monoamine oxidase inhibitor (l-deprenyl) that can abolish the death effect of irradiated-cell-conditioned medium. It appears to act by preventing Bcl 2 induction post irradiation [51]. It is important to stress that it prevents expression of the death end-point of the bystander effect. This does not mean it prevents the signal from being produced. It prevents a death response to that signal. Other likely modulators are anti-oxidants and calcium channel blockers. Gap junction inhibitors have also been shown to prevent bystander effects [52, 53].
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Conclusions
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MOIF is a newly recognised syndrome that follows high dose exposure to ionising radiation. The mechanisms involved are not understood, but radiation-induced bystander effects leading to systemic genomic instability, persistent elevation of reactive oxygen species and persistent delayed cell death are certainly a candidate mechanism. Future research on the mechanisms underlying bystander effects and in particular on ways of controlling them may provide new drugs for treatment of normal tissue injury, however caused.
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Acknowledgments
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We acknowledge the generous support of the Science Foundation Ireland, The Irish Cancer Society and St Luke's Institute of Cancer Research.
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References
|
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- Interprétation de quelques résultats de la radiothérapie et essai de fixation d'une technique rationnelle. Note de J Bergonié et L Tribondeau, présentée par d'Arsonval. [n.p.] 1906. Extract from Académie des sciences. Séance du 10 Décembre 1906.
- Hall EJ. Radiobiology for the radiologist. Philadelphia, PA: Lippincott Williams & Wilkins, 2000.
- Hall EJ, Fowler JF. Review: total doses in fractionated radiotherapy — implications of new radiobiological data. Int J Radiat Biol Relat Stud Phys Chem Med 1984;46:103–20.[Medline]
- Ulmer W. On a foundation of the Ellis-formula and Strandqvist-function with kinetic equations. Strahlentherapie 1983;159:427–34.[Medline]
- Sinclair JA, Oates JP, Dale RG. BED–time charts and their application to the problems of interruptions in external beam radiotherapy treatments. Int J Radiat Oncol Biol Phys 1999;44:381–9.[Medline]
- Jennings MT, Iyengar S. Pharmacotherapy of malignant astrocytomas of children and adults: current strategies and future trends. CNS Drugs 2001;15:719–43.[Medline]
- Sims EC, Plowman PN. Stereotactic radiosurgery XII. Large AVM and the failure of the radiation response modifier gamma linolenic acid to improve the therapeutic ratio. Br J Neurosurg 2001;15:28–34.[Medline]
- Adams GE, Dische S, Fowler JF, Thomlinson RH. Hypoxic cell sensitisers in radiotherapy. Lancet 1976;1:186–8.[Medline]
- Camphausen K, Moses MA, Menard C, Sproull M, Beecken WD, Folkman J, et al. Radiation abscopal antitumor effect is mediated through p53. Cancer Res 2003;63:1990–3.[Abstract/Free Full Text]
- Petrovic N, Perovic J, Karanovic D, Todorovic L, Petrovic V. Abscopal effects of local fractionated X-irradiation of face and jaw region. Strahlentherapie 1982;158:40–2.[Medline]
- Robin HI, AuBuchon J, Varanasi VR, Weinstein AB. The abscopal effect: demonstration in lymphomatous involvement of kidneys. Med Pediatr Oncol 1981;9:473–6.[Medline]
- Denham JW, Kron T. Extinction of the weakest. Int J Radiat Oncol Biol Phys 2001;51:807–19.[Medline]
- Morgan WF. Non-targeted and delayed effects of exposure to ionizing radiation: I. Radiation-induced genomic instability and bystander effects in vitro. Radiat Res 2003;159:567–80.[Medline]
- Mothersill C, Seymour C. Radiation-induced bystander effects: past history and future directions. Radiat Res 2001;155:759–67.[Medline]
- Mothersill C, Seymour C. Low-dose radiation effects: experimental hematology and the changing paradigm. Exp Hematol 2003;31:437–45.[Medline]
- Parsons WB Jr, Watkins CH, Pease GL, Childs DS Jr. Changes in sternal marrow following roentgen-ray therapy to the spleen in chronic granulocytic leukemia. Cancer 1954;7:179–89.[Medline]
- Moment GB. Recovery and abscopal effects after inhibitory X-irradiation in earthworm regeneration. J Exp Zool 1972;181:33–9.[Medline]
- Jansen CR, Bond VP, Rai KR, Lippincott SW. Abscopal effects of localized irradiation by accelerator beams. Ann N Y Acad Sci 1964;114:302–15.[Medline]
- Law AW, Mole RH. Direct and abscopal effects of x-radiation on the thymus of the weanling rat. Int J Radiat Biol 1961;3:233–48.[Medline]
- Raventos A. An abscopal effect of x-ray upon mouse spleen weight. Radiat Res 1954;1:381–7.[Medline]
- Moiseenko VV, Battista JJ, Hill RP, Travis EL, Van Dyk J. In-field and out-of-field effects in partial volume lung irradiation in rodents: possible correlation between early DNA damage and functional endpoints. Int J Radiat Oncol Biol Phys 2000;48:1539–48.[Medline]
- Denham JW, Hamilton CS, Simpson SA, Ostwald PM, O'Brien M, Kron T, et al. Factors influencing the degree of erythematous skin reactions in humans. Radiother Oncol 1995;36:107–20.[Medline]
- Watson GE, Lorimore SA, Clutton SM, Kadhim MA, Wright EG. Genetic factors influencing alpha-particle-induced chromosomal instability. Int J Radiat Biol 1997;71:497–503.[Medline]
- Ponnaiya B, Cornforth MN, Ullrich RL. Radiation-induced chromosomal instability in BALB/c and C57BL/6 mice: the difference is as clear as black and white. Radiat Res 1997;147:121–5.[Medline]
- Mothersill CE, O'Malley KJ, Murphy DM, Seymour CB, Lorimore SA, Wright EG. Identification and characterization of three subtypes of radiation response in normal human urothelial cultures exposed to ionizing radiation. Carcinogenesis 1999;20:2273–8.[Abstract/Free Full Text]
- Mothersill C, Rea D, Wright EG, Lorimore SA, Murphy D, Seymour CB, et al. Individual variation in the production of a ‘bystander signal’ following irradiation of primary cultures of normal human urothelium. Carcinogenesis 2001;22:1465–71.[Abstract/Free Full Text]
- Kadhim MA, Lorimore SA, Townsend KM, Goodhead DT, Buckle VJ, Wright EG. Radiation-induced genomic instability: delayed cytogenetic aberrations and apoptosis in primary human bone marrow cells. Int J Radiat Biol 1995;67:287–93.[Medline]
- Harney JV, Seymour CB, Murphy DM, Mothersill C. Variation in the expression of p53, c-myc, and bcl-2 oncoproteins in individual patient cultures of normal urothelium exposed to cobalt 60 gamma-rays and N-nitrosodiethanolamine. Cancer Epidemiol Biomarkers Prev 1995;4:617–25.[Abstract]
- Dainiak N, Waselenko JK, Armitage JO, MacVittie TJ, Farese AM. The hematologist and radiation casualties. Hematology (Am Soc Hematol Educ Program) 2003:473–96.
- Dugan LC, Bedford JS. Are chromosomal instabilities induced by exposure of cultured normal human cells to low- or high-LET radiation? Radiat Res 2003;159:301–11.[Medline]
- Curtis SB, Luebeck EG, Hazelton WD, Moolgavkar SH. A new perspective of carcinogenesis from protracted high-LET radiation arises from the two-stage clonal expansion model. Adv Space Res 2002;30:937–44.[Medline]
- Holt PD. Consideration of tissue response in the application of the two-mutation model to radiation carcinogenesis. Int J Radiat Biol 1997;71:203–13.[Medline]
- Trosko JE. Role of low-level ionizing radiation in multi-step carcinogenic process. Health Phys 1996;70:812–22.[Medline]
- Trott DA, Cuthbert AP, Overell RW, Russo I, Newbold RF. Mechanisms involved in the immortalization of mammalian cells by ionizing radiation and chemical carcinogens. Carcinogenesis 1995;16:193–204.[Abstract/Free Full Text]
- Trosko JE. Biomarkers for low-level exposure causing epigenetic responses in stem cells. Stem Cells 1995;13 (Suppl. 1):231–9.
- Lorimore SA, Wright EG. Radiation-induced genomic instability and bystander effects: related inflammatory-type responses to radiation-induced stress and injury? A review. Int J Radiat Biol 2003;79:15–25.
- Mothersill C, Seymour C. Radiation-induced bystander effects, carcinogenesis and models. Oncogene 2003;22:7028–33.[Medline]
- Azzam EI, de Toledo SM, Little JB. Expression of CONNEXIN43 is highly sensitive to ionizing radiation and other environmental stresses. Cancer Res 2003;63:7128–35.[Abstract/Free Full Text]
- Belyakov OV, Folkard M, Mothersill C, Prise KM, Michael BD. Bystander-induced apoptosis and premature differentiation in primary urothelial explants after charged particle microbeam irradiation. Radiat Prot Dosimetry 2002;99:249–51.[Abstract]
- Mothersill C, Seymour CB. Cell–cell contact during gamma irradiation is not required to induce a bystander effect in normal human keratinocytes: evidence for release during irradiation of a signal controlling survival into the medium. Radiat Res 1998;149:256–62.[Medline]
- Vral A, Cornelissen M, Thierens H, Louagie H, Philippe J, Strijckmans K, et al. Apoptosis induced by fast neutrons versus 60Co gamma-rays in human peripheral blood lymphocytes. Int J Radiat Biol 1998;73:289–95.[Medline]
- Hendry JH, Potten CS, Merritt A. Apoptosis induced by high- and low-LET radiations. Radiat Environ Biophys 1995;34:59–62.[Medline]
- Seymour CB, Mothersill C. Relative contribution of bystander and targeted cell killing to the low-dose region of the radiation dose–response curve. Radiat Res 2000;153(5 Pt 1):508–11.
- Prise KM, Folkard M, Michael BD. A review of the bystander effect and its implications for low-dose exposure. Radiat Prot Dosimetry 2003;104:347–55.[Abstract]
- Mothersill C, Seymour C. Lethal mutations and genomic instability. Int J Radiat Biol 1997;71:751–8.[Medline]
- Mothersill C, Seymour CB. Radiation-induced bystander effects – implications for cancer. Nat Rev Cancer 2004;4:158–64.[Medline]
- Lyng FM, Seymour CB, Mothersill C. Oxidative stress in cells exposed to low levels of ionizing radiation. Biochem Soc Trans 2001;29(Pt 2):350–3.
- Clutton SM, Townsend KM, Walker C, Ansell JD, Wright EG. Radiation-induced genomic instability and persisting oxidative stress in primary bone marrow cultures. Carcinogenesis 1996;17:1633–9.[Abstract/Free Full Text]
- Limoli CL, Giedzinski E, Morgan WF, Swarts SG, Jones GD, Hyun W. Persistent oxidative stress in chromosomally unstable cells. Cancer Res 2003;63:3107–11.[Abstract/Free Full Text]
- Azzam EI, de Toledo SM, Little JB. Oxidative metabolism, gap junctions and the ionizing radiation-induced bystander effect. Oncogene 2003;22:7050–7.[Medline]
- Seymour CB, Mothersill C, Mooney R, Moriarty M, Tipton KF. Monoamine oxidase inhibitors l-deprenyl and clorgyline protect nonmalignant human cells from ionising radiation and chemotherapy toxicity. Br J Cancer 2003;89:1979–86.[Medline]
- Bishayee A, Hill HZ, Stein D, Rao DV, Howell RW. Free radical-initiated and gap junction-mediated bystander effect due to nonuniform distribution of incorporated radioactivity in a three-dimensional tissue culture model. Radiat Res 2001;155:335–44.[Medline]
- Nagasawa H, Cremesti A, Kolesnick R, Fuks Z, Little JB. Involvement of membrane signaling in the bystander effect in irradiated cells. Cancer Res 2002;62:2531–4.[Abstract/Free Full Text]
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Abstract
Introduction
