Chromosome aberrations in lymphocytes and clastogenic factors in plasma detected in Belarus children 10 years after Chernobyl accident

LONG/TERM GENETIC AND EPIGENETIC DISORDERS IN PERSONS EXPOSED TO IONIZING RADIATION AND THEIR DESCENDANTS (review)

The review is devoted to long-term genetic and epigenetic disorders in exposed individuals and their descendants,namely to cytogenetic effects in the Chornobyl NPP accident clean-up workers and their children, DNA methylation as an epigenetic modification of human genome. Data presented in review expand the understanding of risk of the prolonged exposure for the present and future generations, which is one of key problems posed by fundamental radiation genetics and human radiobiology.

Radioactively contaminated areas: Bioindicator species and biomarkers of effect in an early warning scheme for a preliminary risk assessment

Concerns about the impacts on public health and on the natural environment have been raised regarding the full range of operational activities related to uranium mining and the rest of the nuclear fuel cycle (including nuclear accidents), nuclear tests and depleted uranium from military ammunitions. However, the environmental impacts of such activities, as well as their ecotoxicological/toxicological profile, are still poorly studied. Herein, it is discussed if organisms can be used as bioindicators of human health effects, posed by lifetime exposure to radioactively contaminated areas. To do so, information was gathered from several studies performed on vertebrates, invertebrate species and humans, living in these contaminated areas. The retrieved information was compared, to determine which are the most used bioindicators and biomarkers and also the similarities between human and non-human biota responses. The data evaluated are used to support the proposal for an early warning scheme, based on bioindicator species and on the most sensitive and commonly shared biomarkers, to perform a screening evaluation of radioactively contaminated sites. This scheme could be used to support decision-making for a deeper evaluation of risks to human health, making it possible to screen a large number of areas, without disturbing and alarming local populations.

Aspermy, sperm quality and radiation in Chernobyl birds

BACKGROUND

Following the Chernobyl nuclear power plant accident, large amounts of radionuclides were emitted and spread in the environment. Animals living in such contaminated areas are predicted to suffer fitness costs including reductions in the quality and quantity of gametes.

METHODOLOGY/PRINCIPAL FINDINGS

We studied whether aspermy and sperm quality were affected by radioactive contamination by examining ejaculates from wild caught birds breeding in areas varying in background radiation level by more than three orders of magnitude around Chernobyl, Ukraine. The frequency of males with aspermy increased logarithmically with radiation level. While 18.4% of males from contaminated areas had no sperm that was only the case for 3.0% of males from uncontaminated control areas. Furthermore, there were negative relationships between sperm quality as reflected by reduced sperm velocity and motility, respectively, and radiation.

CONCLUSIONS/SIGNIFICANCE

Our results suggest that radioactive contamination around Chernobyl affects sperm production and quality. We are the first to report an interspecific difference in sperm quality in relation to radioactive contamination.

Responses to ionizing radiation mediated by inflammatory mechanisms

Since the early years of the twentieth century, the biological consequences of exposure to ionizing radiation have been attributed solely to mutational DNA damage or cell death induced in irradiated cells at the time of exposure. However, numerous observations have been at variance with this dogma. In the 1950s, attention was drawn to abscopal effects in areas of the body not directly irradiated. In the 1960s reports began appearing that plasma factors induced by irradiation could affect unirradiated cells, and since 1990 a growing literature has documented an increased rate of DNA damage in the progeny of irradiated cells many cell generations after the initial exposure (radiation-induced genomic instability) and responses in non-irradiated cells neighbouring irradiated cells (radiation-induced bystander effects). All these studies have in common the induction of effects not in directly irradiated cells but in unirradiated cells as a consequence of intercellular signalling. Recently, it has become clear that all the various effects demonstrated in vivo may reflect an ongoing inflammatory response to the initial radiation-induced injury that, in a genotype-dependent manner, has the potential to contribute primary and/or ongoing damage displaced in time and/or space from the initial insult. Importantly, there is direct evidence that non-steroidal anti-inflammatory drug treatment reduces such damage in vivo. These new findings highlight the importance of tissue responses and indicate additional mechanisms of radiation action, including the likelihood that radiation effects are not restricted to the initiation stage of neoplastic diseases, but may also contribute to tumour promotion and progression. The various developments in understanding the responses to radiation exposures have implications not only for radiation pathology but also for therapeutic interventions.

Bystander apoptosis in human cells mediated by irradiated blood plasma

Following exposure to high doses of ionizing radiation, due to an accident or during radiotherapy, bystander signalling poses a potential hazard to unirradiated cells and tissues. This process can be mediated by factors circulating in blood plasma. Thus, we assessed the ability of plasma taken from in vitro irradiated human blood to produce a direct cytotoxic effect, by inducing apoptosis in primary human peripheral blood mononuclear cells (PBM), which mainly comprised G(0)-stage lymphocytes. Plasma was collected from healthy donors' blood irradiated in vitro to 0-40Gy acute γ-rays. Reporter PBM were separated from unirradiated blood with Histopaque and held in medium with the test plasma for 24h at 37°C. Additionally, plasma from in vitro irradiated and unirradiated blood was tested against PBM collected from blood given 4Gy. Apoptosis in reporter PBM was measured by the Annexin V test using flow cytometry. Plasma collected from unirradiated and irradiated blood did not produce any apoptotic response above the control level in unirradiated reporter PBM. Surprisingly, plasma from irradiated blood caused a dose-dependent reduction of apoptosis in irradiated reporter PBM. The yields of radiation-induced cell death in irradiated reporter PBM (after subtracting the respective values in unirradiated reporter PBM) were 22.2±1.8% in plasma-free cultures, 21.6±1.1% in cultures treated with plasma from unirradiated blood, 20.2±1.4% in cultures with plasma from blood given 2-4Gy and 16.7±3.2% in cultures with plasma from blood given 6-10Gy. These results suggested that irradiated blood plasma did not cause a radiation-induced bystander cell-killing effect. Instead, a reduction of apoptosis in irradiated reporter cells cultured with irradiated blood plasma has implications concerning oncogenic risk from mutated cells surviving after high dose in vivo irradiation (e.g. radiotherapy) and requires further study.

Clastogenic plasma factors: a short overview

A large number of studies have revealed that irradiated subjects produce soluble factors found in their blood plasma which, when transferred into cell cultures from non-irradiated individuals, show clastogenic (chromosome breaking) activity. Increased yields of chromatid-type aberrations have been characteristic in most of these studies. Exposed cohorts of various origins have revealed to possess this feature: from A-bomb survivors to patients treated with radiotherapy. It is apparent that the plasma factors are sustainable for long time periods. On the other hand, they seem to be produced very fast after exposure. Considerable variation in the effect has been found between individuals with similar radiation exposure. Further, the phenomenon is not restricted to irradiated populations. Clastogenic plasma has also been observed in patients with inflammatory diseases or congenital chromosome breakage syndromes as well in subjects exposed to other agents than ionizing radiation. Chromosomal aberration inducing substances have been detected not only in vivo, but also in vitro. A common feature to all the conditions is that they are associated with oxidative stress. Studies on the biochemical nature of the clastogenic factor(s) have been conducted, and tumor necrosis factor alpha and lipid peroxidation products, among others, have been suggested as good candidates. The relevance of the plasma factors to health effects remains open. The aim of the paper is to give a short overview on the phenomenon of clastogenic factors--their occurrence and formation as well as possible effectors.

Transgenerational genomic instability in children of irradiated parents as a result of the Chernobyl Nuclear Accident

The study of families irradiated as a result of the accident at the Chernobyl Nuclear Power Plant revealed significantly increased aberrant genomes frequencies (AGFs) not only in irradiated parents (n=106, p<0.01), but also in their children born after the accident (n=159, p<0.05). This is an indicative of the phenomenon of transgenerational genomic instability. To elucidate this phenomenon, experiments were undertaken to model genomic instability by using single and fractional in vitro gamma-irradiation ((137)Cs) of peripheral blood samples from the children and their parents at doses of 0.1, 0.2 and 0.3 Gy. The spectrum and frequency of chromosome aberrations were studied in the 1st and 2nd cell generations. The average AGF was significantly increased at all doses (except 0.1 Gy) in children of irradiated parents, as compared to children born from non-irradiated parents. Amplification of cells with single-break chromosome aberrations in mitosis 2, as compared to mitosis 1, suggests the replication mechanism of realization of potential damage in DNA and the occurrence of genomic instability in succeeding cell generations.

Induction of chromatid-type aberrations in peripheral lymphocytes of hospital workers exposed to very low doses of radiation

Radiological personnel represent workers exposed to low cumulative doses of radiation. As their surveillance is generally based on physical dosimetry, there is little or inconclusive information on biological effects due to radiation exposure at these doses. We aimed to explore the extent of chromosomal damage in circulating lymphocytes of hospital workers (technicians, nurses and physicians) chronically exposed to a very low level of radiation using conventional and molecular cytogenetic analyses (chromosome painting with chromosomes #2, #3 and #10 as probe cocktail). Compared with controls, exposed workers displayed a significant increase in the frequency of aberrant lymphocytes (1.26+/-0.11/100 cells versus 1.63+/-0.17/100 cells). In particular, exposed technicians showed significantly higher mean values than nurses or physicians (3.68+/-1.17/100 cells versus 1.36+/-0.18/100 cells and 1.36+/-0.09/100 cells, respectively). Interestingly, we found that the chromosomal damage was prevalently expressed as chromatid-type aberrations. Chromosome painting indicated that the frequency of chromosome rearrangements (CR; translocations and dicentrics pooled together) was approximately comparable between radiological workers and the control group. Moreover, we did not detect any significant difference due to radiation exposure when CR rates were considered separately for each of the three chromosomes in the probe cocktail.

Non-targeted bystander effects induced by ionizing radiation

Radiation-induced bystander effects refer to those responses occurring in cells that were not subject to energy deposition events following ionizing radiation. These bystander cells may have been neighbors of irradiated cells, or physically separated but subject to soluble secreted signals from irradiated cells. Bystander effects have been observed in vitro and in vivo and for various radiation qualities. In tribute to an old friend and colleague, Anthony V. Carrano, who would have said "well what are the critical questions that should be addressed, and so what?", we review the evidence for non-targeted radiation-induced bystander effects with emphasis on prevailing questions in this rapidly developing research field, and the potential significance of bystander effects in evaluating the detrimental health effects of radiation exposure.

Differential induction of micronuclei in peripheral lymphocytes and exfoliated urothelial cells of workers exposed to 4,4'-methylenebis-(2-chloroaniline) (MOCA) and bitumen fumes

Cytogenetic end-points used to estimate risk of genotoxic events in workers include the measurement of micronuclei (MN) in exfoliated cells, lymphocytes, and other tissues. Micronuclei are chromatin-containing bodies outside the cell nucleus resulting from contaminant-induced DNA damage. A review of 71 reports of human genotoxic responses to chemical or physical agents published between 1999 and 2001 revealed that 14% of such studies measured genotoxicity endpoints in specific target tissues relevant to the site of disease for the agent examined; 18% used endpoints in surrogate or non-target tissues but considered the relations between endpoints in surrogate and disease target tissues, and 68% measured genotoxicity endpoints in accessible tissues without reference to specific targets for disease. Methylenebis-(2-chloroaniline) (MOCA), used in polyurethane manufacture, is a suspected bladder carcinogen. Bitumen, used in road surfacing, contains skin and lung carcinogens. In this study, we aimed to compare genotoxicity in urothelial cells and in lymphocytes of workers exposed to these materials. Twelve men employed in polyurethane manufacture, twelve bitumen road layers, and eighteen hospital stores personnel (controls) were recruited and all provided blood and urine samples on the same day. Blood cultures were prepared using a cytochalasin B-block method. Exfoliated urothelial cells were collected from urine and stained for light microscopy. The number of MN in urothelial cells was higher in MOCA-exposed (14.27 +/- 0.56 MN/1000, 9.69 +/- 0.32 MN cells/1000) than in bitumen exposed workers (11.99 +/- 0.65 MN/1000, 8.66 +/- 0.46 MN cells/1000) or in control subjects (6.88 +/- 0.18 MN/1000, 5.17 +/- 0.11 MN cells/1000). Conversely, in lymphocytes, MN were higher in bitumen-exposed (16.24 +/- 0.63 MN/1000, 10.65 +/- 0.24 MN cells/1000) than in MOCA-exposed workers (13.25 +/- 0.48 MN/1000, 8.54 +/- 0.14 MN cells/1000) or in control subjects (9.24 +/- 0.29 MN/ 1000, 5.93 +/- 0.13 MN cells/1000). The results of this study suggest that genotoxins can cause different rates of micronuclei formation in different tissues. Thus, the sensitivity and relevance to cancer risk may be greater if the tissues selected for genotoxicity studies reflect the target tissue for the chemicals concerned.

Dietary factors and cancer mortality among atomic-bomb survivors

Dietary factors such as fruit and vegetables are thought to reduce the risk of cancer incidence and mortality. We investigated the effect of a diet rich in fruit and vegetables against the long-term effects of radiation exposure on the risk of cancer. A cohort of 36,228 atomic-bomb survivors of Hiroshima and Nagasaki, for whom radiation dose estimates were currently available, had their diet assessed in 1980. They were followed for a period of 20 years for cancer mortality. The joint-effect of fruit and vegetables intake and radiation exposure on risk of cancer death was examined, in additive (sum of effects of diet alone and radiation alone) and multiplicative (product of effects of diet alone and radiation alone) models. In the additive model, a daily intake of fruit and vegetables significantly reduced the risk of cancer deaths by 13%, compared to an intake of once or less per week. Radiation exposure of 1 Sievert (Sv) increased significantly the risk of cancer death by 48-49%. The additive joint-effects showed a lower risk of cancer among those exposed to 1 Sv who had a diet rich in vegetables (49%-13%=36%) or fruit (48%-13%=35%). The multiplicative model gave similar results. The cancer risk reduction by vegetables in exposed persons went from 52% (effect of radiation alone) to 32% (product of effect of vegetables and radiation), and cancer risk reduction by fruit was 52% (radiation alone) to 34% (product of effect of fruit and radiation). There was no significant evidence to reject either the additive or the multiplicative model. A daily intake of fruit and vegetables was beneficial to the persons exposed to radiation in reducing their risks of cancer death.

Non-targeted and delayed effects of exposure to ionizing radiation: II. Radiation-induced genomic instability and bystander effects in vivo, clastogenic factors and transgenerational effects

The goal of this review is to summarize the evidence for non-targeted and delayed effects of exposure to ionizing radiation in vivo. Currently, human health risks associated with radiation exposures are based primarily on the assumption that the detrimental effects of radiation occur in irradiated cells. Over the years a number of non-targeted effects of radiation exposure in vivo have been described that challenge this concept. These include radiation-induced genomic instability, bystander effects, clastogenic factors produced in plasma from irradiated individuals that can cause chromosomal damage when cultured with nonirradiated cells, and transgenerational effects of parental irradiation that can manifest in the progeny. These effects pose new challenges to evaluating the risk(s) associated with radiation exposure and understanding radiation-induced carcinogenesis.

Bystander effects in radiation-induced genomic instability

Exposure of GM10115 hamster-human hybrid cells to X-rays can result in the induction of chromosomal instability in the progeny of surviving cells. This instability manifests as the dynamic production of novel sub-populations of cells with unique cytogenetic rearrangements involving the "marker" human chromosome. We have used the comet assay to investigate whether there was an elevated level of endogenous DNA breaks in chromosomally unstable clones that could provide a source for the chromosomal rearrangements and thus account for the persistent instability observed. Our results indicate no significant difference in comet tail measurement between non-irradiated and radiation-induced chromosomally unstable clones. Using two-color fluorescence in situ hybridization we also investigated whether recombinational events involving the interstitial telomere repeat-like sequences in GM10115 cells were involved at frequencies higher than random processes would otherwise predict. Nine of 11 clones demonstrated a significantly higher than expected involvement of these interstitial telomere repeat-like sequences at the recombination junction between the human and hamster chromosomes. Since elevated levels of endogenous breaks were not detected in unstable clones we propose that epigenetic or bystander effects (BSEs) lead to the activation of recombinational pathways that perpetuate the unstable phenotype. Specifically, we expand upon the hypothesis that radiation induces conditions and/or factors that stimulate the production of reactive oxygen species (ROS). These reactive intermediates then contribute to a chronic pro-oxidant environment that cycles over multiple generations, promoting chromosomal recombination and other phenotypes associated with genomic instability.