Characterizing responses to gamma radiation by a highly clonogenic fish brain endothelial cell line

X-ray-induced bio-acoustic emissions from cultured cells

PURPOSE

We characterize for the first time the emission of acoustic waves from cultured cells irradiated with X-ray photon radiation.

METHODS AND MATERIALS

Human cancer cell lines (MCF-7, HL-60) and control cell-free media were exposed to 1 Gy X-ray photons while recording the sound generated before, during and after irradiation using custom large-bandwidth ultrasound transducer. The effects of dose rate and cell viability were investigated.

RESULTS

We report the first recorded acoustic signals captured from a collective pressure wave response to ionizing irradiation in cell culture. The acoustic signal was co-terminous with the radiation pulse, its magnitude was dependent on radiation dose rate, and live and dead cells showed qualitatively and quantitatively different acoustic signal characteristics. The signature of the collective acoustic peaks was temporally wider and with higher acoustic power for irradiated HL-60 than for irradiated MCF-7.

CONCLUSIONS

We show that X-ray irradiation induces two cultured cancer cell types to emit a characteristic acoustic signal for the duration of the radiation pulse. The rapid decay of the signal excludes acoustic emissions themselves from contributing to the inter-organism bystander signal previously reported in intact animals, but they remain a potential component of the bystander process in tissues and cell cultures. This preliminary study suggests that further work on the potential role of radiation-induced acoustic emission (RIAE) in the inter-cellular bystander effect is merited.

A pilot study of radiation-induced bystander effect in radio-adapting frogs at a radiologically contaminated site located on the chalk river laboratories property

PURPOSE

To measure medium borne bystander effects, to study the influence of radioadaptive response (RAR) on bystander response, and to discover reliable radioresponsive biomarkers in radio-adapting frogs from Duke Swamp contaminated with an above-background radiation level and in naïve frogs from Twin Lake as the background control site.

MATERIALS AND METHODS

Frogs were captured at Duke Swamp and Twin Lake and brought to the lab at the Canadian Nuclear Laboratories facility. Half of the frogs from each site were irradiated with 4 Gy while the other half of the frogs were left with no further radiation treatment. Frog bladders were removed and placed in sterile culture media. Upon arrival at McMaster University, the bladders were processed for tissue cultures. After 48 h, the culture media conditioned by the bladder explants were harvested for clonogenic reporter survival assay and calcium flux measurements for assessing bystander effects. HPV-G cells were used as bystander reporter cells in all radiation-induced bystander effect (RIBE) assays. The frog bladder cultures were incubated for another 10-12 days followed by immunochemical staining for bcl-2 and c-myc expressions to analyze cellular anti-apoptotic (pro-survival) and pro-apoptotic (pro-death) responses, respectively.

RESULTS

Only culture media conditioned by bladders from 4-Gy-irradiated naïve frogs from Twin Lake induced bystander effects (reduction of HPV-G reporter cells' clonogenic survival and presence of strong calcium flux activities). The 4 Gy irradiation dose increased pro-apoptotic c-myc expression in naïve frogs' bladder explants. Culture media conditioned by bladders from radio-adapting frogs from Duke Swamp enhanced HPV-G's clonogenic survival and a 4 Gy irradiation challenge did not change the enhanced clonogenic survival nature nor induce calcium flux. In bladder explants from both control and 4-Gy-irradiated radio-adapting frogs, anti-apoptotic bcl-2 expression for pro-survival responses was ubiquitous while c-myc expression for pro-death responses was limited to a small fraction of cells.

CONCLUSION

The clonogenic RIBE reporter assay using HPV-G and calcium flux measurements are useful diagnostic tools for RIBE assessment of field biological samples, specifically those from frogs. RAR induced by environmentally relevant low-dose radiation induces protective bystander response. Bcl-2 and c-myc are reliable biomarkers for evaluating low dose radiation responses in wild populations of amphibians. Overall, this pilot study emphasizes the importance of looking at non-targeted effects (NTEs) in natural populations of non-human biota that could be vulnerable to chronic low-dose radiation exposures.

The sine qua non of the fish invitrome today and tomorrow in environmental radiobiology

Fish cell lines, collectively referred to as the fish invitrome, are useful diagnostic tools to study radiation impacts on aquatic health and elucidate radiation mechanisms in fish. This paper will highlight the advantages, discuss the challenges, and propose possible future directions for uses of the fish invitrome in the field of environmental radiobiology. The fish invitrome contains at least 714 fish cell lines. However, only a few of these cell lines have been used to study radiation biology in fish and they represent only 10 fish species. The fish invitrome is clearly not yet explored for its full potential in radiation biology. Evidence suggests that they are useful and, in some cases, irreplaceable in making underlying theories and fundamental concepts in radiation responses in fish. The debate of whether environmental radiation is harmful, presents risks, has no effect on health, or is beneficial is on-going and is one that fish cell lines can help address in a time-effective fashion. Any information obtained with fish cell lines is useful in the framework of environment radiation risk assessments. Radiation threats to aquatic health will continue due to the very likely rise of nuclear energy and medicine in the future. The fish invitrome, in theory, lives forever and can meet new challenges at any given time to provide diagnostic risk analyses pertaining to aquatic health and environmental radiation protection.

One-Decade-Spanning transgenerational effects of historic radiation dose in wild populations of bank voles exposed to radioactive contamination following the chernobyl nuclear disaster

The concept of historic radiation doses associated with accidental radioactive releases and their role in leading to radiation-induced non-targeted effects on affected wild animals are currently being evaluated. Previous research studying Fukushima butterfly, Chernobyl bird and fruit fly populations shows that the effects are transgenerational, underlined by the principles of genomic instability, and varied from one species to another. To further expand on the responses of and their sensitivity in different taxonomically distinct groups, the present study sought to reconstruct historic radiation doses and delineate their effects on bank voles (Clethrionomys glareolus) found within a 400-km radius of the Chernobyl Nuclear Power Plant meltdown site. Historic dose reconstruction from the whole-body dose rates for the bank vole samples for their parental generation at the time of radioactive release was performed. Relationships between the historic doses and cytogenetic aberrations and embryonic lethality were examined via graphical presentations. Results suggest that genomic instability develops at the historic dose range of 20-51 mGy while a radioadaptive response develops at the historic dose range of 51-356 mGy. The Linear No-Threshold (LNT) relationship was absent at historic doses of lower than 356 mGy at all generations. However, LNT was apparent when the very high historic dose of 10.28 Gy in one sampling year was factored into the dose response curve for the bank vole generation 21-22. It is worth being reminded that natural mutation accumulation and other environmental stressors outside the realm of dose effects could contribute to the observed effects in a multiple-stressor environment. Nevertheless, the consistent development of genomic instability and radio-adaptive response across generations and sampling sites unearths the utmost fundamental radiobiological principle of transgenerational non-targeted effects. As a result, it calls for better attention and regulation from global governing bodies of environmental health protection.

An investigation into neutron-induced bystander effects: How low can you go?

Neutron radiation is very harmful to both individual organisms and the environment. A n understanding of all aspects of both direct and indirect effects of radiation is necessary to accurately assess the risk of neutron radiation exposure. This review seeks to review current evidence in the literature for radiation-induced bystander effects and related effects attributable to neutron radiation. It also attempts to determine if the suggested evidence in the literature is sufficient to justify claims that neutron-based radiation can cause radiation-induced bystander effects. Lastly, the present paper suggests potential directions for future research concerning neutron radiation-induced bystander effects. Data was collected from studies investigating radiation-induced bystander effects and was used to mathematically generate pooled datasets and putative trends; this was done to potentially elucidate both the appearance of a conventional trend for radiation-induced bystander effects in studies using different types of radiation. Furthermore, literature review was used to compare studies utilizing similar tissue models to determine if neutron effects follow similar trends as those produced by electromagnetic radiation. We conclude that the current understanding of neutron-attributable radiation-induced bystander effects is incomplete. Various factors such as high gamma contamination during the irradiations, unestablished thresholds for gamma effects, different cell lines, energies, and different dose rates affected our ability to confirm a relationship between neutron irradiation and RIBE, particularly in low-dose regions below 100 mGy. It was determined through meta-analysis of the data that effects attributable to neutrons do seem to exist at higher doses, while gamma effects seem likely predominant at lower dose regions. Therefore, whether neutrons can induce bystander effects at lower doses remains unclear. Further research is required to confirm these findings and various recommendations are made to assist in this effort. With these recommendations, we hope that research conducted in the future will be better equipped to explore the indirect effects of neutron radiation as they pertain to biological and ecological phenomena.

Effects of Dose Rate on the Reproductive Cell Death and Early Mitochondrial Membrane Potential in Different Human Epithelium-Derived Cells Exposed to Gamma Rays

Dose rate is one of the most varied experimental parameters in radiation biology research. In this study, effects of dose rates on the radiation responses of 2 different types of human epithelium-derived cells, immortalized keratinocytes (HaCaT), and colorectal cancer cells (HCT116 p53^+/+ and HCT116 p53^-/-) were systematically studied. Cells were γ-irradiated at one of the 4 dose rates (24.6, 109, 564, and 1168 mGy/min) to a total dose of 0.5 to 2 Gy. Clonogenic survival and mitochondrial membrane potential (MMP) were measured to assess the levels of reproductive cell death and damage to mitochondrial physiology, respectively. It was found that clonogenic survival was similar at all 4 tested dose rates in the 3 cell lines. The loss of MMP occurred at all tested dose rates in all 3 cell lines except for one case where the MMP increased in HCT116 p53^+/+cells after exposure to 0.5 Gy at 24.6 mGy/min. In HCT116 cells, the loss of MMP was the most severe at high dose/dose rate combination exposure and when p53 was expressed. In contrast, no effect in dose rate was observed with HaCaT cells as the reduction level of MMP was similar at the tested dose rates.

Effects of historic radiation dose on the frequency of sex-linked recessive lethals in Drosophila populations following the Chernobyl nuclear accident

Contrary to the effects of high doses of radiation, the effects of low doses of radiation are still being investigated. Low doses and their non-targeted effects in particular are of special interest for researchers. The accident that occurred at the Chernobyl Nuclear Power Plant (NPP) gives researchers the opportunity to view these effects outside of a laboratory environment. For this paper, the relationship between low historic radiation doses and the persistent genetic damage observed in populations of fruit flies (Drosophila melanogaster) around the Chernobyl NPP over 3 years will be investigated. Data from Zainullin et al. (1992) on the frequency of sex-linked recessive lethals (SLRLs) in D. melanogaster around the Chernobyl NPP. To calculate the absorbed historic external dose, a method based on the Gaussian plume model was used to find the external dose from both plume shine and ground shine. The dose attributed to the ground shine dose made a greater contribution to the overall absorbed external historic radiation dose than the plume shine dose. For earlier generations of Drosophila living in the radioactive contaminated sites, the SLRL frequencies appeared to correlate with the dose in a linear no-threshold relationship. The later descendent generations appeared to have developed a radio-adaptive-like response. This work contributes to the understanding of historic dose effects on wildlife health following the accidental release of high mount of radioactive materials into the environment.

The common field lampricide 3-trifluoromethyl-4-nitrophenol is a potential radiosensitizer in fish cells

PURPOSE

To evaluate if the common field lampricide 3-trifluoromethyl-4-nitrophenol (TFM) that is intended to eradicate the invasive species sea lampreys in the Great Lakes has the potential to sensitize radiation responses in cells from non-targeted native fish MATERIALS AND METHODS: The TFM toxicity was assessed acutely and chronically with the clonogenic fish cell line eelB. The acute toxicity (24-h exposure) was determined by the fluorescent cell viability probe Alamar Blue. The chronic toxicity was determined either by Alamar Blue (7-d exposure) or the clonogenic survival assay (14-d exposure). Pre- and post-exposure of fish cells to environmentally relevant TFM concentrations following gamma irradiation were performed. Clonogenic survival was determined to assess the damage level of radiation-induced reproductive cell death.

RESULTS

The chronic toxicity tests were more sensitive than the acute toxicity tests. The 14-d EC₅₀ using the clonogenic survival endpoint was 2.09 ± 0.28 μg/mL and was statistically similar to the 7-d EC₅₀ (1.85 ± 0.07 μg/mL) based on the Alamar Blue-based cytotoxicity endpoint. Post-exposure of cells to environmentally relevant TFM concentrations following irradiation did not have any effect as compared to the irradiation alone group. In contrast, pre-exposure of cells to TFM following irradiation had a negative additive effect when the total radiation dose was 2 Gy, but not 0.1 or 0.5 Gy.

CONCLUSION

Our results suggest that the common field lampricide TFM is a potential radiation sensitizer in cells from non-targeted native fish. This could be a health problem of concern for non-targeted native fish if a large accidental radioactive release occurs.

Radiobiological characteristics of descendant progeny of fish and amphibian cells that survive the initial ionizing radiation dose

PURPOSE

To evaluate the development of delayed lethal mutations, the production of medium borne lethal bystander signals, and the acquirement of radiosensitive or radioresistant traits in distant descendant progeny of fish and amphibian cells surviving ionizing radiation MATERIALS AND METHODS: American eel brain endothelial cells (eelB) and African clawed frog epithelial cells (A6) were initially irradiated with gamma rays at 0.5 Gy or 2 Gy. Ionizing radiation (IR)-surviving cells were grown for 27 population doublings (PDs) for eelB and 43 PDs for A6. Reproductive cell death as quantified by clonogenic survival assays was used to determine the development of delayed lethal mutations, the production of medium borne lethal bystander signals, and the acquirement of radiosensitive or radioresistant traits in the progeny survivors.

RESULTS

Only medium borne bystander signals produced by 2-Gy-irradiated eelB progeny survivors at 12 PDs could reduce the clonogenic survival of the bystander reporter cells. IR-induced delayed lethal mutations occurred in irradiated eelB cells at 15-18 PDs; however, subsequently propagated progeny cells retained normal replicative abilities. No IR-induced delayed lethal mutations developed in progeny of irradiated A6 cells at up to 43 PDs. eelB progeny survivors did not develop new radiosensitive or radioresistant traits while A6 progeny survivors acquired a new radiosensitive characteristic.

CONCLUSION

This study enriches the current literature on the radiobiological characteristics of distant surviving progeny of irradiated fish and amphibian cells and highlights cell-type/species-dependent differential responses to IR. This study is the first to examine the potential transgenerational effects of progenitor irradiation in amphibian cells.

Parallel comparison of pre-conditioning and post-conditioning effects in human cancers and keratinocytes upon acute gamma irradiation

PURPOSE

To determine and compare the effects of pre-conditioning and post-conditioning towards gamma radiation responses in human cancer cells and keratinocytes.

MATERIAL AND METHODS

The clonogenic survival of glioblastoma cells (T98G), keratinocytes (HaCaT), and colorectal carcinoma cells (HCT116 p53^+/+ and p53^-/-) was assessed following gamma ray exposure from a Cs-137 source. The priming dose preceded the challenge dose in pre-conditioning whereas the priming dose followed the challenge dose in post-conditioning. The priming dose was either 5 mGy or 0.1 Gy. The challenge dose was 0.5-5 Gy.

RESULTS

In both pre- and post-conditioning where the priming dose was 0.1 Gy and the challenge dose was 4 Gy, RAR developed in T98G but not in HaCaT cells. In HCT116 p53^+/+, pre-conditioning had either no effect or a radiosensitizing effect and whereas post-conditioning induced either radiosensitizing or radioadaptive effect. The different observed outcomes were dependent on dose, the time interval between the priming and challenge dose, and the time before the first irradiation. Post-conditioning effects could occur with a priming dose as low as 5 mGy in HCT116 p53^+/+ cells. When HCT116 cells had no p53 protein expression, the radiosensitizing or radioadaptive response by the conditioning effect was abolished.

CONCLUSIONS

The results suggest that radiation conditioning responses are complex and depend on at least the following factors: the magnitude of priming/challenge dose, the time interval between priming and challenge dose, p53 status, cell seeding time prior to the first radiation treatment. This work is the first parallel comparison demonstrating the potential outcomes of pre- and post-conditioning in different human cell types using environmentally and medically relevant radiation doses.

Transgenerational effects of historic radiation dose in pale grass blue butterflies around Fukushima following the Fukushima Dai-ichi Nuclear Power Plant meltdown accident

Low dose radiation effects have been investigated in Chernobyl for many years but there is uncertainty about initial doses received by many animal species. However, the Fukushima Dai-ichi Nuclear Power Plant accident opens an opportunity to study the effects of the initial low historic dose on directly exposed species and their progeny during a time where the contaminating radionuclides are decaying. In this paper, it is proposed that historic acute exposure and its resulting non-targeted effects (NTEs) may be partially involved in the high mortality/abnormality rates seen across generations of pale grass blue butterflies (Zizeeria maha) around Fukushima. Data from Hiyama et al. (2012) on the morphological abnormality frequencies in Z. maha collected around Fukushima and their progeny were used in this paper. Two dose reconstruction methods based on the Gaussian plume model were used to determine the external absorbed dose to the first exposed generation from both ground shine and plume shine. One method involved the use of the dose rate recorded at the time of collection and only took Cs-137 into account. The other involved using release rates and atmospheric conditions to determine the doses and considered Cs-137 and Cs-134. The reconstructed doses were plotted against the mortality rates and abnormality frequencies across generations. The mortality rates of the progeny from irradiated progenitors increased linearly with the increasing historic radiation doses reconstructed using both Cs-137 and Cs-134 sources. Additionally, a higher level of morphological abnormalities was observed in progeny than in the progenitors. The mean abnormality frequencies also increased throughout generations. As these results are a sign of NTEs being involved, it can be suggested that increasing mutation levels across generations may result, in part, from NTEs induced by the initial low dose received by the first exposed generation. However, continual accumulation of mutations over generations in their natural contaminated habitats remains a likely contributor into the observed outcome.

Effect of gamma radiation on the production of bystander signals from three earthworm species irradiated in vivo

The effect of gamma radiation delivered over 24 h on the induction of bystander signals of three earthworm species exposed in vivo was investigated: A. chlorotica, A. caliginosa, and E. tetraedra. Worms were exposed to external gamma irradiation (Co-60 source) for 24 h and samples of head, body, and clitellum were dissected from exposed and control worms and placed in culture medium for 24 h at 19 C. The harvested medium was filtered and assayed for expression of bystander signals using both clonogenic and mitochondrial reporter assays. Different responses were observed in the different species and in the different tissues. A. chlorotica worm-treated reporters show insignificant mitochondrial response for all sections, yet a significant clonogenic reduction in survival for body sections. A. caliginosa worm-treated reporters show a significant mitochondrial response for some sections and insignificant mitochondrial response and insignificant reduction in clonogenic survival for the rest. E. tetraedra worms from a control site show significant evidence of bystander signalling, measured by mitochondrial response in reporter cells, for all sections while those harvested from a contaminated site show insignificant changes in baseline signalling when exposed to the challenge dose. In vivo exposure of earthworm species shows evidence of bystander signalling using two different reporter assays. This effect varied between the different species and tissues. There is also evidence of attenuated bystander signalling in worms harvested from a site contaminated with radiation.

Assessing off-target cytotoxicity of the field lampricide 3-trifluoromethyl-4-nitrophenol using novel lake sturgeon cell lines

Lampricides are currently being applied to streams and rivers to control the population of sea lamprey, an invasive species, in the Great Lakes. The most commonly used lampricide agent used in the field is 3-trifluoromethyl-4-nitrophenol (TFM), which targets larval sea lamprey in lamprey-infested rivers and streams. The specificity of TFM is due to the relative inability of sea lamprey to detoxify the agent relative to non-target fishes. There is increasing concern, however, about non-target effects on fishes, particularly threatened populations of juvenile lake sturgeon (LS; Acipenser fulvescens). There is therefore a need to develop models to better define lake sturgeon's response to TFM. Here we report the establishment of five LS cell lines derived from the liver, gill, skin and intestinal tract of juvenile LS and some of their cellular characteristics. All LS cell lines grew well at 25 °C in Leibovitz's (L)- 15 medium supplemented with 10% FBS. All cell lines demonstrated high senescence-associated β-galactosidase activity and varying levels of Periodic acid Schiff-positive polysaccharides, indicating substantial production of glycoproteins and mucosubstances by the cells. Comparative toxicity of TFM in the five LS cell lines was assessed by two fluorescent cell viability dyes, Alamar Blue and CFDA-AM, in conditions with and without serum and at 24 or 72 h exposure. Deduced EC₅₀ values were compared between the cell lines and to the reported in vivo LC₅₀s. Tissues sensitive to the effects of TFM in vivo correlated with cell lines from the same tissues being most sensitive to TFM in vitro. EC₅₀ values for the LSliver-e cells was significantly lower than the EC₅₀ for the rainbow trout (RBT) liver cells RTL-W1, reaffirming the in vivo observation that LS was generally more TFM-sensitive than rainbow trout. Our data suggests that whole-fish sensitivity of LS to TFM is likely attributable to sensitivity at the cellular level. Thus, LS cell lines, as well as those of RBT, can be used to screen and evaluate the toxicity of the next generation of lampricides on non-target fish such as lake sturgeon.

Dose rate effects of low-LET ionizing radiation on fish cells

Radiobiological responses of a highly clonogenic fish cell line, eelB, to low-LET ionizing radiation and effects of dose rates were studied. In acute exposure to 0.1-12 Gy of gamma rays, eelB's cell survival curve displayed a linear-quadratic (LQ) relationship. In the LQ model, α, β, and α/β ratio were 0.0024, 0.037, and 0.065, respectively; for the first time that these values were reported for fish cells. In the multi-target model, n, D _o, and D _q values were determined to be 4.42, 2.16, and 3.21 Gy, respectively, and were the smallest among fish cell lines being examined to date. The mitochondrial potential response to gamma radiation in eelB cells was at least biphasic: mitochondria hyperpolarized 2 h and then depolarized 5 h post-irradiation. Upon receiving gamma rays with a total dose of 5 Gy, dose rates (ranging between 83 and 1366 mGy/min) had different effects on the clonogenic survival but not the mitochondrial potential. The clonogenic survival was significantly higher at the lowest dose rate of 83 mGy/min than at the other higher dose rates. Upon continuous irradiation with beta particles from tritium at 0.5, 5, 50, and 500 mGy/day for 7 days, mitochondria significantly depolarized at the three higher dose rates. Clearly, dose rates had differential effects on the clonogenic survival of and mitochondrial membrane potential in fish cells.