Isolation of the effects of alpha-related components from total effects of radium at low doses.

PURPOSE: Radium is the most common source of alpha radiation exposure to humans and non-human species in the environment but the dosimetry is complicated by the decay chain which involves gamma exposure due to radon daughters. This paper seeks to determine the separate contributions of alpha and gamma doses to the total dose and total direct and non-targeted effect in a fish and a human cell line. MATERIALS AND METHODS: This study aimed to isolate the effect of alpha particles following exposure to low doses of radium in cells, and their progeny which received no further exposure. This was initially done by comparing the survival values of a human keratinocyte cell line (HaCaT) and an embryonic Chinook salmon cell line (CHSE-214) exposed to gamma radiation, from survival of the same cell lines exposed to mixed alpha and gamma radiation through exposure to Ra-226 and its decay products. A Monte Carlo simulation was later performed to determine the contributions of radium decay products including radon daughters. RESULTS: The human cell line showed increased radioresistance when exposed to low doses of alpha particles. In contrast the fish cell line, which demonstrated radioresistance to low dose gamma radiation, showed increased lethality when exposed to low doses of alpha particles. Significant and complex levels of non-targeted effects were induced in progeny of irradiated cells. The simulation showed that gamma and beta decay products did not contribute significant dose and the highest beta dose was below the threshold for inducing non-targeted effects. CONCLUSIONS: The results confirm the need to consider the dose-response relationship when developing radiation weighting factors for low dose exposures, as well as the need to be aware of possible cell line and species differences.

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.

From tangled banks to toxic bunnies; a reflection on the issues involved in developing an ecosystem approach for environmental radiation protection.

The objective of this paper is to present the results of discussions at a workshop held as part of the International Congress of Radiation Research (Environmental Health stream) in Manchester UK, 2019. The main objective of the workshop was to provide a platform for radioecologists to engage with radiobiologists to address major questions around developing an Ecosystem approach in radioecology and radiation protection of the environment. The aim was to establish a critical framework to guide research that would permit integration of a pan-ecosystem approach into radiation protection guidelines and regulation for the environment. The conclusions were that the interaction between radioecologists and radiobiologists is useful in particular in addressing field versus laboratory issues where there are issues and challenges in designing good field experiments and a need to cross validate field data against laboratory data and vice versa. Other main conclusions were that there is a need to appreciate wider issues in ecology to design good approaches for an ecosystems approach in radioecology and that with the capture of 'Big Data', novel tools such as machine learning can now be applied to help with the complex issues involved in developing an ecosystem approach.

Quantifying Biophoton Emissions From Human Cells Directly Exposed to Low-Dose Gamma Radiation.

Biophoton emission leading to bystander effects (BEs) was shown in beta-irradiated cells; however, technical challenges precluded the analysis of the biophoton role in gamma-induced BEs. The present work was to design an experimental approach to determine if, what type, and how many biophotons could be produced in gamma-irradiated cells. Photon emission was measured in HCT116 p53+/+ cells irradiated with a total dose of 22 mGy from a cesium-137 source at a dose rate of 45 mGy/min. A single-photon detection unit was used and shielded with lead to reduce counts from stray gammas reaching the detector. Higher quantities of photon emissions were observed when the cells in a tissue culture vessel were present and being irradiated compared to a cell-free vessel. Photon emissions were captured at either 340 nm (in the ultraviolet A [UVA] range) or 610 nm. At the same cell density, radiation exposure time, and radiation dose, HCT116 p53+/+ cells emitted 2.5 times more UVA biophotons than 610-nm biophotons. For the first time, gamma radiation was shown to induce biophoton emissions from biological cells. As cellular emissions of UVA biophotons following beta radiation lead to BEs, the involvement of cellular emissions of the same type of UVA biophotons in gamma radiation-induced BEs is highly likely.

Serotonin and 5-HT3 receptors sensitize human skin cells to direct irradiation cell death but not to soluble radiation-induced bystander signals.

Ionizing radiation (IR) is an environmental carcinogen and the biological damages it elicits are mechanistically distinct between high and low doses. Non-targeted effects occurring in nonirradiated cells such as the radiation-induced bystander effect predominate at low doses of IR. However, the role of non-targeted effects in environmental radiation protection is often overlooked because the governing mechanisms are complex and multifactorial. An improved understanding of the signaling molecules and their capacity to sensitize specific cell types are essential in establishing environmental IR risks. In particular, serotonin (5-HT) has been identified to exacerbate both direct irradiation and bystander-induced cell death (CD) in certain cell types, although not all cell types are responsive to 5-HT in this respect. In this study, we further characterize the role of 5-HT and 5-HT receptors (5-HTR) in the amplification of CD following IR exposure in human keratinocytes. We examined the survival of HaCaT cells treated with 5-HT and the 5-HTR antagonists ketanserin (5-HT2A) and ondansetron (5-HT3) following exposure to direct IR and irradiated cell condition medium (ICCM). Nonirradiated cell survival was consistent with the vehicle control among 5-HT concentrations ranging from 0.001 to 100 µM. Significant 5-HT concentration-dependent increases in CD occurred following direct IR exposure. Nonirradiated ICCM-recipient CD was not altered by 5-HT (0.001-100 µM) when present during donor cell irradiation among all IR doses. Increases in direct irradiation CD evoked by 5-HT were significantly attenuated by ondansetron, blocking the effect of 5-HT, whereas ketanserin did not alter CD. Western blotting of these target 5-HTRs revealed protein expression of the 5-HT3 receptor, while the 5-HT2A receptor was not detected. We have demonstrated a definitive role for 5-HT in the exacerbation of CD following direct IR exposure and identified the 5-HT3 receptor as a potential target for ameliorating radiation damage in keratinocytes.

5-HT2A and 5-HT3 receptors contribute to the exacerbation of targeted and non-targeted effects of ionizing radiation-induced cell death in human colon carcinoma cells.

Purpose: Serotonin (5-HT) is implicated in the underlying mechanisms which mediate cell death following ionizing radiation exposure, however, effects appear to be cell type-dependent. We sought to further characterize the role of 5-HT and 5-HT receptors (5-HTRs) in the exacerbation of cell death following ionizing radiation exposure in human colon carcinoma cells.Materials and methods: We examined the clonogenic survival of colon carcinoma HCT116 cells treated with 5-HT and the selective 5-HTR antagonists ketanserin (5-HT2A) and ondansetron (5-HT3), following exposure to direct ionizing radiation and irradiated cell-conditioned medium (ICCM). The relative expression of these target receptors was measured using western blotting.Results: Western blotting results revealed that relative protein levels of the 5-HT2A and 5-HT3 receptors were similar. 5-HT concentration-dependent increases in cell death that occurred following direct ionizing radiation exposure were abolished by both 5-HTR antagonists. Death of nonirradiated cells recipient of ICCM was increased in a concentration-dependent manner by 5-HT when present during donor cell irradiation. Both 5-HTR antagonists completely abolished the increases in bystander-induced cell death generated by 5-HT. Finally, we show that exposure of cells to 5-HT prior to receipt of ICCM can also dictate the degree of bystander-induced cell death.Conclusions: Our findings demonstrate a definitive role for 5-HT in the exacerbation of cell death following ionizing radiation exposure in colon carcinoma cells and highlight 5-HTRs as potential markers for predicting cellular radiosensitivity.

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.

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.

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 ±â€¯0.28 µg/mL and was statistically similar to the 7-d EC50 (1.85 ±â€¯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.

Cell Line-Specific Direct Irradiation and Bystander Responses are Influenced by Fetal Bovine Serum Serotonin Concentrations.

The radiation-induced bystander effect is mechanistically complex, involving many different signaling components. Serotonin, present in fetal bovine serum (FBS), has been implicated in the modulation of cellular responses to radiation. However, the role of this ubiquitous signaling molecule has yet to be elucidated with regard to cell line-specific radiation responses. In this study, cell survival was measured in HCT116 p53 wild-type (HCT116+/+) and HaCaT cell cultures treated with media containing serotonin-depleted FBS and compared to our standard FBS-supplemented media, using clonogenic assays. We utilized an enzyme-linked immunosorbent assay to quantify the difference (4.3 ± 1.3 ng/ml) in serotonin concentrations among the media. Serotonin-depleted media significantly reduced survival in both nonirradiated cell lines. Furthermore, we sought to determine the effects to cells in this media exposed to direct irradiation as well as bystander media from irradiated cells. Cell survival was significantly increased when HCT116+/+ cells were directly irradiated in serotonin-depleted media, while HaCaT cells showed no significant difference in survival between the media. Bystander investigations demonstrated that HCT116+/+ cells were only able to generate a bystander effect when cultured in standard media conditions containing greater serotonin levels. Conversely, HaCaT cells were unaffected by the different media in terms of producing a bystander response, generating bystander effects irrespective of the media. Previous research linking serotonin receptors to the bystander effect, together with our results, indicate that receptor heterogeneity among cell types may underlie serotonin sensitivity in direct irradiation and bystander responses through serotonin receptor-mediated cell signaling cascades.

Irradiation of rainbow trout at early life stages results in a proteomic legacy in adult gills. Part B; the effect of a second radiation dose, after one year, on the proteomic responses in the irradiated and non-irradiated bystander fish.

This study extends the investigation of the legacy effects of exposure to a single radiation dose at one of four early life stages, in adult rainbow trout (Part A), by examining the effects of a second identical dose after one year; i.e. egg 48 h after fertilisation (48 h egg) + 1 year, eyed egg + 1 year, yolk sac larvae (YSL) + 1 year and first feeder + 1 year. This included the induction of a bystander effect in non-irradiated trout which had swam with the irradiated fish. The second radiation dose negated any beneficial proteomic responses following early life stage irradiation only, particularly irradiation of 48 h eggs and eyed eggs (Part A). Instead the responses after early life stage + 1 year irradiation are consistently associated with tumorigenesis, cancer progression, or are otherwise damaging: upregulation of alpha-globin 1 (YSL + 1 year and first feeders + 1 year) and downregulation of histone H1, type II keratin, malate dehydrogenase 2-2, Na/K ATPase alpha subunit isoform 1b, nucleoside diphosphate kinase (48 h egg + 1 year), electron transfer flavoprotein subunit alpha (eyed egg + 1 year), 60 S ribosomal protein L30 (YSL + 1 year) and haemoglobin subunit beta-4 (first feeder + 1 year). Most significantly the second radiation dose also negated the overwhelmingly beneficial bystander effect proteomic responses induced by trout irradiated at an early life stage only (Part A). Instead the bystander effect proteomic changes induced by trout irradiated at an early life stage and again at 1 year have been associated with uncertain, with respect to tumorigenesis, or detrimental effects; upregulation of alpha-globin 1 (YSL + 1 year and first feeder + 1 year) and downregulation of malate dehydrogenase 2-2, nucleoside diphosphate kinase (48 h egg + 1 year), transferrin precursor (eyed egg + 1 year), 60 S ribosomal protein L30 (YSL + 1 year) and serine / threonine-protein phosphatase 2 A 65 kDa (first feeder + 1 year). This difference between the bystander effect induced proteomic changes following early life stage irradiation only and early life stage + 1 year irradiation may indicate a fundamental change in the non-targeted effects of radiation following multiple exposure to radiation.

Modulation of oxidative phosphorylation (OXPHOS) by radiation- induced biophotons.

Radiation-induced biophotons are an electromagnetic form of bystander signalling. In human cells, biophoton signalling is capable of eliciting effects in non-irradiated bystander cells. However, the mechanisms by which the biophotons interact and act upon the bystander cells are not clearly understood. Mitochondrial energy production and ROS are known to be involved but the precise interactions are not known. To address this question, we have investigated the effect of biophoton emission upon the function of the complexes of oxidative phosphorylation (OXPHOS). The exposure of bystander HCT116 p53 +/+ cells to biophoton signals emitted from ß-irradiated HCT116 p53 +/+ cells induced significant modifications in the activity of Complex I (NADH dehydrogenase or NADH:ubiquinone oxidoreductase) such that the activity was severely diminished compared to non-irradiated controls. The enzymatic assay showed that the efficiency of NADH oxidation to NAD+ was severely compromised. It is suspected that this impairment may be linked to the photoabsorption of biophotons in the blue wavelength range (492-455 nm). The photobiomodulation to Complex I was suspected to contribute greatly to the inefficiency of ATP synthase function since it resulted in a lower quantity of H+ ions to be available for use in the process of chemiosmosis. Other reactions of the ETC were not significantly impacted. Overall, these results provide evidence for a link between biophoton emission and biomodulation of the mitochondrial ATP synthesis process. However, there are many aspects of biological modulation by radiation-induced biophotons which will require further elucidation.

Irradiation of rainbow trout at early life stages results in a proteomic legacy in adult gills. Part A; proteomic responses in the irradiated fish and in non-irradiated bystander fish.

Exposure to a single 0.5 Gy X-ray dose of eggs at 48 h after fertilisation (48 h egg), eyed eggs, yolk sac larvae (YSL) and first feeders induces a legacy effect in adult rainbow trout. This includes the transmission of a bystander effect to non-irradiated adult trout which had swam with the irradiated fish. The aim of this study was to investigate this legacy by analysing the gill proteome of these irradiated and bystander fish. Irradiation at all of the early life stages resulted in changes to proteins which play a key role in development but are also known to be anti-tumorigenic and anti-oxidant: upregulation of haemoglobin subunit beta (48 h egg), haemoglobin, serum albumin 1 precursor (eyed eggs), clathrin heavy chain 1 isoform X10 (eyed eggs and first feeders), and actin-related protein 2/3 complex subunit 4 (first feeders), downregulation of pyruvate dehydrogenase, histone 1 (48 h egg), triosephosphate isomerase (TPI), collagen alpha-1(1) chain like proteins (YSL), pyruvate kinase PKM-like protein (YSL and first feeders), ubiquitin-40S ribosomal proteins S27 and eukaryotic translation initiation factor 4 A isoform 1B (first feeders). However irradiation of YSL and first feeders (post hatching early life stages) also induced proteomic changes which have a complex relationship with tumorigenesis or cancer progression; downregulation of alpha-1-antiprotease-like protein precursor, vigilin isoform X2 and nucleoside diphosphate kinase (YSL) and upregulation of hyperosmotic glycine rich protein (first feeders). In bystander fish some proteomic changes were similar to those induced by irradiation: upregulation of haemoglobin subunit beta (48 h egg), haemoglobin (eyed eggs), actin-related protein 2/3 complex subunit 4, hyperosmotic glycine rich protein (first feeders), and downregulation of alpha-1-antiprotease-like protein, vigilin isoform X2, nucleoside diphosphate kinase (YSL), pyruvate kinase PKM-like protein and ubiquitin-40S ribosomal protein S27a-like (first feeders). Other proteomic changes were unique to bystander fish; downregulation of TPI, ubiquitin-40S ribosomal protein S2 (eyed egg), cofilin-2, cold-inducible RNA-binding protein B-like isoform X3 (YSL) and superoxide dismutase (first feeder), and upregulation of haemoglobin subunit alpha, collagen 1a1 precursor, apolipoprotein A-1-1 and A-1-2 precursor (first feeders). These bystander effect proteomic changes have been shown to be overwhelmingly anti-tumorigenic or protective of the fish gill.

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, ß, and α/ß 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.

Influence of chronic low-dose/dose-rate high-LET irradiation from radium-226 in a human colorectal carcinoma cell line.

PURPOSE: To evaluate potential damages of chronic environmentally relevant low-dose/dose-rate high-LET irradiation from a naturally occurring alpha-emitting radionuclide (radium-226, 226Ra) on a human colorectal carcinoma HCT116 p53+/+ cell line. METHODS: Clonogenic survival assays and mitochondrial membrane potential (MMP) measurement with a sensitive fluorescent MMP probe JC-1 were performed in HCT116 p53+/+ cells chronically exposure to low doses/dose rates of 226Ra with high-LET. Comparisons were made with the human non-transformed keratinocyte HaCaT cell line and acute low-dose direct low-LET gamma radiation. RESULTS AND CONCLUSION: The chronic low-dose/dose-rate alpha radiation (CLD/DRAR) did not reduce the clonogenic survival of HCT116 p53+/+ cells over the period of 70 days of exposure. Only one significant reduction in the HCT116 p53+/+ cells' clonogenic survival was when cells were grown with 10,000mBq/mL 226Ra for 40 days and progeny cells were clonogenically assessed in the presence of 10,000mBq/mL 226Ra. The cumulative doses that cells received during this period ranged from 0.05 to 46.2mGy. The mitochondrial membrane potential (MMP) dropped initially in both HCT116 p53+/+ and HaCaT cells in response to CLD/DRAR. The MMP in HCT116 p53+/+ cells recovered more quickly at all dose points than and that in HaCaT cells until the end of the exposure period. The highest dose rate of 0.66mGy/day depolarized the HaCaT's mitochondria more consistently during the exposure period. The faster recovery status of the MMP in HCT116 p53+/+ cells than that in HaCaT cells was also observed after exposure to acute low-dose gamma rays. Overall, it was found that CLD/DRAR had little impact on the MMP of human colorectal cancer and keratinocyte cell lines.

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

PURPOSE: The clonogenic property and radiobiological responses of a fish brain endothelial cell line, eelB, derived from the American eel were studied. METHODS: Clonogenic assays were performed to determine the plating efficiency of the eelB cells and to evaluate the clonogenic survival fractions after direct irradiation to low-dose low-LET gamma radiation or receiving irradiated cell conditioned medium in the bystander effect experiments. RESULT: eelB had the second highest plating efficiency ever reported to date for fish cell lines. Large eelB macroscopic colonies could be formed in a short period of time and were easy to identify and count. Unlike with other fish clonogenic cell lines, which had a relatively slow proliferation profile, clonogenic assays with the eelB cells could be completed as early as 12 days in culture. After direct irradiation with gamma rays at low doses ranging from 0.1Gy to 5Gy, the dose-clonogenic survival curve of the eelB cell line showed a linear trend and did not develop a shoulder region. A classical radio-adaptive response was not induced with the clonogenic survival endpoint when the priming dose (0.1 or 0.5Gy) was delivered 6h before the challenge dose (3 or 5Gy). However, a radio-adaptive response was observed in progeny cells that survived 5Gy and developed lethal mutations. eelB appeared to lack the ability to produce damaging radiation-induced bystander signals on both eelB and HaCaT recipient cells. CONCLUSION: eelB cell line could be a very useful cell model in the study of radiation impacts on the aquatic health.