Kidney Cell DNA Damage Caused By Combined Exposure To Volatile Anaesthetics and 1 Gy Or 2 Gy Radiotherapy Dose in Vivo

Patient immobilisation with volatile anaesthetics (VA) during radiotherapy is sometimes unavoidable. Although it is known that both VAs and ionising radiation can have nephrotoxic effects, there are no studies of their combined effects on DNA damage. The aim of this in vivo study was to address this gap by investigating whether 48 groups of healthy Swiss albino mice (totalling 240) would differ in kidney cell DNA damage response (alkaline comet assay) to isoflurane, sevoflurane, or halothane anaesthesia and exposure to 1 Gy or 2 Gy of ionising radiation. We took kidney cortex samples after 0, 2, 6, and 24 h of exposure and measured comet parameters: tail length and tail intensity. To quantify the efficiency of the cells to repair and re-join DNA strand breaks, we also calculated cellular DNA repair index. Exposure to either VA alone increased DNA damage, which was similar between sevoflurane and isoflurane, and the highest with halothane. In combined exposure (VA and irradiation with 1 Gy) DNA damage remained at similar levels for all time points or was even lower than damage caused by radiation alone. Halothane again demonstrated the highest damage. In combined exposure with irradiation of 2 Gy sevoflurane significantly elevated tail intensity over the first three time points, which decreased and was even lower on hour 24 than in samples exposed to the corresponding radiation dose alone. This study confirmed that volatile anaesthetics are capable of damaging DNA, while combined VA and 1 Gy or 2 Gy treatment did not have a synergistic damaging effect on DNA. Further studies on the mechanisms of action are needed to determine the extent of damage in kidney cells after longer periods of observation and how efficiently the cells can recover from exposure to single and multiple doses of volatile anaesthetics and radiotherapy.Key words: DNA repair index, comet assay, halothane, isoflurane, sevoflurane, tail intensity, tail length     

Exposure to strong magnetic fields at power frequency potentiates X-ray-induced DNA strand breaks

We examined the effect of an extremely low-frequency magnetic field (ELFMF) at 5, 50 and 400 mT on DNA strand breaks in human glioma MO54 cells. A DNA damage analysis was performed using the method of alkaline comet assay. The cells were exposed to X-rays alone (5 Gy), ELFMF alone, or X-rays followed by ELFMF at 4 degrees C or on ice. No significant difference in the tail moment was observed between control and ELFMF exposures up to 400 mT. X-ray irradiation increased DNA strand breaks. When cells were exposed to X-rays followed by ELFMF at 50 and 400 mT, the tail moment increased significantly compared with that for X-rays alone. When the exposure of cells was performed at 37 degrees C, no significant change was observed between X-rays alone and X-rays plus 400 mT. We previously observed that exposure to 400 mT ELFMF for 2 h increased X-ray-induced mutations (Miyakoshi et al, Mutat. Res., 349: 109-114, 1996). Additionally, an increase in the mutation by exposure to the ELFMF was observed in cells during DNA-synthesizing phase (Miyakoshi et al., Int. J. Radiat. Biol., 71: 75-79, 1997). From these results, it appears that exposure to the high density ELFMF at more than 50 mT may potentiate X-ray-induced DNA strand breaks.     

手机模拟电磁信号对人眼晶状体上皮细胞DNA损伤及修复的影响

目的 检测手机微波辐照2 h后人眼晶状体上皮细胞（human lens epithelial cells,LECs）的DNA损伤及其修复情况.方法 LECs分为辐照组和假辐照组,置于sXc-1800细胞辐照（发射217 Hz脉冲调制的1.8 GHz微波）系统内连续波辐照2 h,辐照强度比吸收率（specific absorption rate,SAR）分别为0、1、2、3、4W/kg,辐照后0、30、60、120、240min分别进行彗星试验检测尾长和尾相,以判定细胞DNA的损伤及其修复情况.结果 1和2 W/kg辐照诱导的DNA损伤与假辐照组相比,在各个检测时段的差异均无统计学意义（P＞0.05）;辐照后即刻进行的检测发现,3和4W/kg组DNA损伤与假辐照组相比,差异有统计学意义（P＜0.01）,3 W/kg组的差异在修复30 min后仍然存在,修复60min后消失,而4 W/kg组的差异在各检测时段持续存在.结论 SAR≤3 W/kg的1.8 GHz手机微波辐照2 h对体外培养的人眼晶状体上皮细胞不产生或产生可修复DNA损伤,4 W/kg的辐照剂量可导致细胞DNA不可逆性损伤.     

Adaptive response in human blood lymphocytes exposed to non-ionizing radiofrequency fields: resistance to ionizing radiation-induced damage

The aim of this preliminary investigation was to assess whether human peripheral blood lymphocytes which have been pre-exposed to non-ionizing radiofrequency fields exhibit an adaptive response (AR) by resisting the induction of genetic damage from subsequent exposure to ionizing radiation. Peripheral blood lymphocytes from four healthy donors were stimulated with phytohemagglutinin for 24 h and then exposed for 20 h to 1950 MHz radiofrequency fields (RF, adaptive dose, AD) at an average specific absorption rate of 0.3 W/kg. At 48 h, the cells were subjected to a challenge dose (CD) of 1.0 or 1.5 Gy X-irradiation (XR, challenge dose, CD). After a 72 h total culture period, cells were collected to examine the incidence of micronuclei (MN). There was a significant decrease in the number of MN in lymphocytes exposed to RF + XR (AD + CD) as compared with those subjected to XR alone (CD). These observations thus suggested a RF-induced AR and induction of resistance to subsequent damage from XR. There was variability between the donors in RF-induced AR. The data reported in our earlier investigations also indicated a similar induction of AR in human blood lymphocytes that had been pre-exposed to RF (AD) and subsequently treated with a chemical mutagen, mitomycin C (CD). Since XR and mitomycin-C induce different kinds of lesions in cellular DNA, further studies are required to understand the mechanism(s) involved in the RF-induced adaptive response.     

The Comet Assay as Biomarker of Heavy Metal Genotoxicity in Earthworms

The ubiquitous occurring earthworm species, Eisenia fetida, were exposed to nickel chloride to determine whether the heavy metal Ni caused DNA damage, as measured by the comet (single cell gel electrophoresis) assay. Primary cell cultures of earthworm coelomocytes were exposed in vitro and whole animals either in spiked artificial soil water or in spiked cattle manure substrates. Comets formed were scored using mean tail lengths as well as comparing percentages of damage in five different damage classes. The exposure concentrations used for the in vitro exposure (2, 6, and 12 g/ml) caused the formation of comets of which the mean tail lengths differed significantly (p < 0.05) from those of unexposed controls but not from each other. Coelomocytes from worms exposed in artificial soil water at concentrations of 0.0049, 0.0078, 0.0175, and 0.025 mg/ml formed comets of which the mean tail lengths differed significantly (p < 0.05) between the exposure groups with increasingly longer tail lengths with higher concentration (dose-related response). The tail length means of the comets of the three highest exposure concentrations also differed significantly (p < 0.05) from the controls. No dose-related response was found between comet tail lengths of the three exposure concentrations (60, 240, and 480 mg/kg) used for the worms in the cattle manure substrates, but the mean tail lengths of comets from all three exposure groups differed significantly (p > 0.05) from the controls. The comets formed in cells from animals exposed in artificial soil water and in cattle manure substrates, scored within damage classes, indicated a clear shift with increasing exposure concentrations from low to high damage. Our results indicated DNA single-strand breaks in soil invertebrate cells caused by exposure to a nickel compound, verifying previous findings for mammals which indicated that this heavy metal has genotoxic potential. These results therefore suggest that earthworms may be useful indicator organisms to assess the genotoxic risks of nickel pollution to terrestrial environments and that the comet assay is a useful tool to use as biomarker of genotoxic effects on invertebrates in soil.     

Evaluation of genotoxic and/or co-genotoxic effects in cells exposed in vitro to extremely-low frequency electromagnetic fields

During the last two decades, concerns have arisen regarding a possible association between extremely-low frequency (ELF) electromagnetic fields (EMF) exposure and cancer incidence (e.g. childhood acute leukaemia, cancer of the nervous system, and lymphomas). In 1979, Wertheimer and Leeper firstly reported an excess of cancer mortality among children living in homes located near power lines and presumably exposed to elevated magnetic fields. Subsequently, a large number of epidemiological studies investigated the possible association between residential or occupational exposure to ELF-EMF and cancer. Several in vivo and in vitro models have been investigated with the effort to determine a link, if any, between such fields and mutagenesis and to determine the possible mechanism of cancer risk. However, a causal relationship between exposure to ELF-EMF and cancer has been suggested but has not been unequivocally demonstrated. In 1998, following an analysis of the results retrieved in the literature, the U.S. National Institute of Environmental Health Sciences proposed to apply a "possible human carcinogen" category (Group 2B) to ELF-EMF. More recently, in 2002, the same classification for ELF-MF was proposed by the International Agency for Research on Cancer. In this in vitro approach, to test the genotoxic and/or co-genotoxic potency of ELF-MF, we used the alkaline single-cell microgel-electrophoresis (comet) assay and the cytokinesis block micronucleus test. Co-exposure assays were performed in the presence of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), 4-nitroquinoline N-oxide (4NQO), benzene, 1,4-benzenediol (1,4-BD), or 1,2,4-benzenetriol (1,2,4-BT). An ELF-MF (50 Hz, 5 mT) was obtained by a system composed of capsulated induction coils. ELF-MF alone was unable to cause direct primary DNA damage. Whereas, an increased extent of DNA damage was observed in cells co-exposed to ELF-MF and MNNG, 1,4-BD, or 1,2,4-BT. An opposite trend was observed in cells treated with 4NQO and co-exposed to ELF-MF. Moreover, the frequency of micronucleated cells in ELF-MF-exposed cells was higher than in control cultures. Our findings suggest that the tested ELF-MF (50 Hz, 5 mT) possess genotoxic (micronucleus test) and co-genotoxic (comet assay) capabilities. The possibility that ELF-MF might interfere with the genotoxic activity of xenobiotics has important implications, since human populations are likely to be exposed to a variety of genotoxic agents concomitantly with exposure to this type of physical agent.     

Comet assay with the fish cell line rainbow trout gonad-2 for in vitro genotoxicity testing of xenobiotics and surface waters

The present study examines the potential of the comet assay using the rainbow trout gonad cell line-2 (RTG-2) as an in vitro indicator test for genotoxicity assessment of aquatic contaminants and native surface waters. Initially, the comet assay protocol was adapted to the RTG-2 cell line. An exposure period of 2 h was found to be optimal, because DNA damage decreased when exposure was prolonged. Then, the sensitivity of the comet assay with RTG-2 cells toward six genotoxic reference substances was evaluated. The lowest-observed-effect concentration values for the directly acting genotoxins, 4-nitroquinoline-N-oxide and N-methyl-N'-nitro-N-nitrosoguanidine, were in the low nanomolar range. The RTG-2 test system clearly was less sensitive for the indirectly acting genotoxins benzo[a]pyrene, nitrofurantoin, 2-acetylaminofluorene, and dimethylnitrosamine, despite the presence of xenobiotic metabolic capacities in RTG-2 cells. The two effect endpoints used, tail length (TL) and tail moment (TM), did not differ with respect to sensitivity, but the linearity of the concentration-response curve was better with TM than with TL. The overall reproducibility of the assay results was good. Finally, the applicability of the comet assay with RTG-2 cells for genotoxicity screening of native surface water samples was studied. The assay tolerated the use of nonsterile water samples and was able to detect genotoxic potentials in native water samples; that is, extraction and concentration of the samples were not needed. The results of the present study indicate the suitability of the comet assay with the fish cell line, RTG-2, as in vitro screen for detecting genotoxic potencies of xenobiotics and environmental samples.     

Genotoxic effects of strong static magnetic fields in DNA-repair defective mutants of Drosophila melanogaster

To assess the possibility that strong static magnetic fields cause DNA damage and mutation, we examined the genotoxic effects of magnetic field exposure by using the somatic mutation and recombination test system in DNA repair-proficient and -deficient strains of Drosophila melanogaster. A postreplication repair-defective mutation mei-41D5 and/or a nucleotide excision repair-defective mutation mei-9(a) was introduced into the conventional loss of the heterozygosity assay system by the use of mwh +/ + flr transheterozygotes, and were exposed to static magnetic fields of up to 14 Tesla (T). We found that exposure to 2, 5, or 14 T fields for 24 h caused a statistically significant enhancement in somatic recombination frequency in the postreplication repair-deficient flies, whereas the frequency remained unchanged in the nucleotide excision repair-deficient flies and in the DNA repair-proficient flies after exposure. An increase linearly dependent on the flux density was observed between 0.5 T and 2 T, but it was saturated at exposure levels over 2 T. These findings suggest that exposure to high-density magnetic fields induce somatic recombination in Drosophila and that the dose-response relationship is not linear.     

Cytogenetic observations in human peripheral blood leukocytes following in vitro exposure to THz radiation: a pilot study

Emerging technologies are considering the possible use of Terahertz radiation in different fields ranging from telecommunications to biology and biomedicine. The study of the potential effects of Terahertz radiation on biological systems is therefore an important issue in order to safely develop a variety of applications. This paper describes a pilot study devoted to determine if Terahertz radiation could induce genotoxic effects in human peripheral blood leukocytes. For this purpose, human whole blood samples from healthy donors were exposed for 20 min to Terahertz radiation. Since, to our knowledge, this is the first study devoted to the evaluation of possible genotoxic effects of such radiation, different electromagnetic conditions were considered. In particular, the frequencies of 120 and 130 GHz were chosen: the first one was tested at a specific absorption rate (SAR) of 0.4 mW g-1, while the second one was tested at SAR levels of 0.24, 1.4, and 2 mW g-1. Chromosomal damage was evaluated by means of the cytokinesis block micronucleus technique, which also gives information on cell cycle kinetics. Moreover, human whole blood samples exposed to 130 GHz at SAR levels of 1.4 and 2 mW g-1 were also tested for primary DNA damage by applying the alkaline comet assay immediately after exposure. The results obtained indicate that THz exposure, in the explored electromagnetic conditions, is not able to induce either genotoxicity or alteration of cell cycle kinetics in human blood cells from healthy subjects.     

Impacts of two perfluorinated compounds (PFOS and PFOA) on human hepatoma cells: cytotoxicity but no genotoxicity?

Perfluorinated compounds (PFCs) and particularly two of them, perfluoroctanoate (PFOA) and perfluorooctanesulfonate (PFOS), have been widely produced and used since 1950. They both persist in the environment and accumulate in wildlife and humans. The toxicity of PFOS and PFOA has been studied extensively in rodents with several adverse effects mainly a hepatocarcinogenic potential. Carcinogenic effects are not highlighted in humans' studies. In this study, we investigated the cytotoxic and genotoxic effects of PFOA and PFOS using human HepG2 cells after 1 or 24h of exposure. The cytotoxic and genotoxic potential was evaluated by MTT assay, single cell gel electrophoresis (SCGE) assay and micronucleus assay respectively. We measured the intracellular generation of reactive oxygen species (ROS) using dichlorofluorescein diacetate to identify a potential mechanism of toxicity. We observed a cytotoxic effect of PFOA and PFOS after 24h of exposure starting from a concentration of 200 μM (MTT: -14.6%) and 300 μM (MTT: -51.2%) respectively. We did not observe an increase of DNA damage with the comet assay or micronucleus with the micronucleus assay after exposure to the two PFCs. After 24h of exposure, both PFOA and PFOS highlight a decrease of ROS generation (-5.9% to -23%). We did not find an effect after an hour of exposure. Our findings show that PFOA and PFOS exert a cytotoxic effect on the human cells line HepG2 but nor PFOA or PFOS could induce an increase of DNA damage (DNA strand breaks and micronucleus) or reactive oxygen species at the range concentration tested. Our results do not support that oxidative stress and DNA damage are relevant for potential adverse effects of PFOA and PFOS. These results tend to support epidemiological studies that do not show evidence of carcinogenicity.     

Detection of DNA damage by alkaline single cell gel electrophoresis in 2,4-dichlorophenoxyacetic-acid- and butachlor-exposed erythrocytes of Clarias batrachus

The alkaline single cell gel electrophoresis, also known as comet assay, is a rapid, simple and sensitive technique for measuring DNA strand breaks in individual cells. The present study was undertaken to evaluate the genotoxic potential of two widely used herbicides; 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-chloro-2,6-diethyl-N-(butoxymethyl) acetanilide (butachlor) in erythrocytes of freshwater catfish, Clarias batrachus. Fish were exposed by medium treatment with three sub-lethal concentrations of 2,4-D (25, 50, and 75ppm) and butachlor (1, 2, and 2.5ppm) and alkaline comet assay was performed on nucleated erythrocytes after 48, 72, and 96h. The amount of DNA damage in cells was estimated from comet tail length as the extent of migration of the genetic material. A significant increase in comet tail length indicating DNA damage was observed at all concentrations of both the herbicides compared with control (P<0.05). The mean comet tail length showed a concentration-related and time-dependent increase as the maximum tail length recorded at highest concentration and longer duration of 2,4-D (9.59microm) and butachlor (9.28microm). This study confirmed that the comet assay applied on the fish erythrocyte is a useful tool in determining potential genotoxicity of water pollutants and might be appropriate as a part of a monitoring program.     

Genotoxicity of acute and chronic gamma-irradiation on zebrafish cells and consequences for embryo development

The effects of radiation on biological systems have been studied for many years, and it is now accepted that direct damage to DNA from radiation is the triggering event leading to biological effects. In the present study, DNA damage induced by acute or chronic irradiation was compared at the cellular (zebrafish [Danio rerio] cell line ZF4) and developmental (embryo) levels. Zebrafish ZF4 cells and embryos (at 3 h postfertilization) were exposed within ranges of acute doses (0.3-2 Gy/d) or chronic dose rates (0.1-0.75 Gy/d). DNA damage was assessed by immunodetection of γ-H2AX and DNA-PK (DNA double-strand breaks) and the alkaline comet assay (DNA single-strand breaks). Zebrafish embryo development and DNA damage were examined after 120 h. At low doses, chronic irradiation induced more residual DNA damage than acute irradiation, but embryo development was normal. From 0.3 Gy, a hyper-radiosensitivity phenomenon compared to other species was shown for acute exposure with an increase of DNA damage, an impairment of hatching success, and larvae abnormalities. These results suggest a dose-dependent correlation between unrepaired DNA damage and abnormalities in embryo development, supporting the use of DNA repair proteins as predictive biomarkers of ionizing radiation exposure. This could have important implications for environmental protection.     

Assessment of DNA damage in Japanese nurses handling antineoplastic drugs by the comet assay

To clarify genotoxic effects of occupational exposure to antineoplastic drugs in Japan, we examined DNA damage, assessed by the comet assay, in 121 female nurses and 46 female clerks working at three hospitals in the northeast of Japan. The comet assay is considered to be a sensitive and rapid method for DNA strand break detection in individual cells, and tail length and tail moment are used as the comet parameters. Concerning the basal characteristics, the 46 control subjects had higher rates of smoking and coffee-drinking habits and lower hemoglobin than the 121 nurses (p<0.05). The log-transformed tail length in the nurses was significantly longer than that in the control subjects after adjusting for possible covariates such as age and smoking habit (p<0.05). Also, the log-transformed tail length was significantly longer, in the 57 nurses who had handled antineoplastic drugs in the last six months, than that in the 46 control subjects (p<0.05); but, no significant difference in tail length or tail moment was seen between the two nurse groups with and without experience of handling hazardous drugs (p>0.05). These results suggest that Japanese nurses who have worked at hospitals using antineoplastic drugs may have a potential risk of DNA damage. To minimize this risk in Japan, use of biological safety cabinet and appropriate protective equipment, in addition to staff education and training, should be implemented in the healthcare environment.     

Genotoxicity analysis of two halonitromethanes, a novel group of disinfection by-products (DBPs), in human cells treated in vitro

Halonitromethanes (HNMs) constitute an emerging class of disinfection by-products (DBPs) produced when chlorine and/or ozone are used for water treatment. The HNMs are structurally similar to halomethanes, but have a nitro-group in place of hydrogen bonded to the central carbon atom. Since little information exists on the genotoxic potential of HNMs, a study has been carried out with two HNM compounds, namely trichloronitromethane (TCNM) and bromonitromethane (BNM) by using human cells. Primary damage induction has been measured with the Comet assay, which is used to determine both the repair kinetics of the induced damage and the proportion of induced oxidative damage. In addition, the fixed DNA damage has been evaluated by using the micronucleus (MN) assay. The results obtained indicate that both compounds are genotoxic, inducing high levels of DNA breaks in the Comet assay, and that this DNA damage repairs well over time. In addition, oxidized bases constitute a high proportion of DNA-induced damage (50-75%). Contrarily, no positive effects were observed in the frequency of micronucleus, which measures both clastogenic and aneugenic effects, neither using TK6 cells nor peripheral blood lymphocytes. This lack of fixed genetic damage would minimize the potential mutagenic risk associated with HNMs exposure.     

Radiation protection by diethyldithiocarbamate: protection of membrane and DNA in vitro and in vivo against gamma-radiation

Diethyldithiocarbamate (DDTC) is studied for its antioxidant and radioprotective abilities. DDTC at a concentration of 0.5 mM reduced DPPH radical. DDTC reduced the damage to deoxyribose resulting from hydroxyl radicals generated by Fenton reaction, indicating that the radioprotective abilities of this compound could be due to the free radical scavenging. DDTC protected rat liver microsomal membranes in vitro from peroxidative damage in lipids (measured as TBARS) resulting from 50 Gy gamma-radiation. It also protected plasmid pBR322 DNA from radiation-induced strand breaks. An oral administration of DDTC to mice before whole body gamma-radiation exposure (4 Gy) resulted in a reduction of radiation-induced lipid peroxides in the liver homogenates. An administration of DDTC to mice before gamma-radiation reduced the radiation-induced DNA damage as studied by single cell gel-electrophoresis (comet assay). The comet parameters such as tail length, tail moment, and percent of DNA in tail were found to increase in the blood leukocytes of mice exposed to 4 Gy gamma-radiation. When DDTC was administered to mice before the radiation exposure, the increase in the comet parameters as a result of radiation was prevented, indicating a protection of cellular DNA. The present study has implication for the potential use of DDTC as a radioprotector.     

Evaluation of early DNA damage in healthcare workers handling antineoplastic drugs

Objectives: This study evaluates by comet assay the induction of early DNA damage in healthcare workers of an oncology hospital regularly handling antineoplastic drug mixtures. The aim was to identify a suitable biomarker of DNA damage by exposure to low levels of such drugs. Methods: We studied 12 day hospital nurses and 13 oncology ward nurses who performed up to 300 and up to 35 drug administrations per week, respectively, and five pharmacy employees who regularly prepared mixtures of antineoplastic agents. Thirty healthy subjects were selected as controls. For exposure evaluation, we performed environmental monitoring of 5-fluorouracil, cytarabine, gemcitabine, cyclophosphamide, and ifosfamide in selected work areas of pharmacy and day hospital units and biological monitoring of urine for the 5-fluorouracile metabolite, α-fluoro-β-alanine. We evaluated early DNA damage in lymphocytes and exfoliated buccal cells by comet assay measuring tail moment (TM) parameter that indirectly indicates the presence of DNA damage. Results: Environmental monitoring detected cyclophosphamide, 5-fluorouracil and ifosfamide, with higher levels of contamination in day hospital unit. The biological monitoring measured detectable levels of α-fluoro-β-alanine only in three nurses. Comet assay showed an increase on exfoliated buccal cells, even if not statistically significant, of mean TM with respect to controls in day hospital nurses (43.2 vs. 28.6, respectively) while ward nurses and pharmacy technicians did not show differences. Comet assay performed on lymphocytes did not show appreciable differences between exposed and controls. Conclusions: The employment of the sensitive comet assay, which is able to detect early the effects of a recent exposure to genotoxic substances, allowed us to find a slight DNA damage, only on exfoliated buccal cells of day hospital nurses, the group handling the highest amount of drugs during the administration process. This finding suggests that comet assay on exfoliated buccal cells could represent a useful tool to evaluate early and still repairable genotoxic effects of exposure to antineoplastic drug mixtures and then contribute to the improvement of the hospital safety practices.     

Neutron-induced adaptive response studied in go human lymphocytes using the comet assay

This study demonstrates that cells adapted to ionizing radiation developed reduced initial DNA damage when compared to non-adapted cells. The results were obtained by subjecting in vitro irradiated whole blood from 10 healthy volunteers (including 2 A-bomb survivors carrying 1.5-2 Gy in vivo exposure) in an unstimulated condition (G0) using the comet assay. The intensity of DNA damage was assessed by computing the 'tail moment'. Adaptive response (AR) was noticed in only donor 3, as indicated by reduced tail moment when the blood samples received priming + challenging doses over a 4 h interval. The priming dose was either 0.01 Gy 137Cs gamma-rays or 0.0025 Gy 252Cf neutrons. The delivered challenging dose was either 1 Gy 60Co g-rays or 0.25 Gy 252Cf neutrons. The irradiation was conducted using the HIRRAC facility. A prior exposure to 0.0025 Gy 252Cf neutrons nullified the excess tail moment caused by 0.25 Gy neutrons given during a 4 h gap. In a similar way, 0.01 Gy 137Cs gamma-rays offered a cross-adaptive response to the neutron challenging dose. The tail moment of A-bomb survivors after in vitro irradiation was less than that of the age-matched control and, at the same time, was not influenced by the priming dose. An altered subset and the immunological status of blood after A-bomb exposure were cited as possible factors. Because AR can affect the outcome of RBE, its individual variability only emphasizes the need to have individual biodosimetry for better risk assessment, especially in planning for a long space voyage.     

Genotoxicity of fecal water in a free-living Irish population

The alkaline single-cell gel electrophoresis (comet) assay was used to investigate the genotoxicity of fecal water (FW) isolated from 47 Irish subjects using Caco-2 colonocytes as target cells. Two methods of comet assay analysis were compared to determine the extent of DNA damage and to categorize the samples as having no, low-to-moderate, or high genotoxicity. FW was isolated from stool samples by centrifugation and tested for its ability to induce DNA damage in Caco-2 cells. DNA damage was assessed using the comet assay by measuring the extent of DNA migration from the nucleus (microns, tail length) or by classifying the nuclei into five different categories depending on their morphology. Data collected from the two methods were used to categorize the FW samples on the basis of their genotoxic activity. Both methods showed good agreement. There was an approximately 50:50 split, with half the samples having some level of genotoxic activity and half having no genotoxicity. About one-third of the samples were considered to be highly genotoxic. There was a trend for low pH of the FW to be associated with increased DNA damage, but this was not significant. The results presented in this report show a relatively high incidence of genotoxic FW in samples derived from a free-living Irish population. Our data demonstrate the suitability of classifying nuclei on the basis of their morphology as a means of determining DNA damage. This procedure is very rapid and, therefore, advantageous in analyzing a large number of slides in the absence of an image analysis system.     

线粒体损伤在镉诱导肝细胞凋亡和DNA损伤中的作用

目的探讨活性氧(reactive oxidative species, ROS)介导的线粒体损伤在镉(cadmium, Cd)暴露诱导肝L02细胞凋亡和DNA损伤中的作用。方法以肝L02细胞为研究对象,利用0～90μmol/L的Cd处理细胞24 h,采用噻唑兰法检测Cd暴露对细胞生存率的影响;以0、20和40μmol/L的Cd染毒细胞24 h,分别采用克隆形成实验、流式细胞术、彗星实验、2′,7′-二氯荧光黄双乙酸盐非标记性氧化敏感的荧光探针、线粒体红色荧光探针(Mitotracker Red CMXRos)和10-N-壬基-吖啶橙等荧光探针标记、线粒体膜电位检测试剂盒(JC-1)、ATP测定试剂盒以及Western Blot等方法,检测Cd暴露对细胞克隆形成能力、细胞凋亡、DNA损伤、ROS水平、线粒体形态、线粒体膜电位(mitochondrial membrane potential, MMP/Δψm)、线粒体质量、ATP含量及相关蛋白的影响;利用90μmol/L抗氧化剂维生素C预处理细胞1 h后给予40μmol/L Cd处理细胞24 h,检测ROS水平、Δψm、线粒体质量、ATP...     

Genotoxicity of heavy metals to the larvae of Chironomus kiiensis Tokunaga after short-term exposure

The genotoxic effects of increasing concentrations (below lethal concentration [LC??]) of cadmium ([Cd] 0.1, 1 and 10 mg/L), copper ([Cu] 0.2, 2 and 20 mg/L) and zinc ([Zn] 0.5, 5 and 50 mg/L) on Chironomus kiiensis were evaluated using alkaline comet assay after exposure for 24 h. Both the tail moment and the olive tail moment showed significant differences between the control and different concentrations of Cd, Cu and Zn (Kruskal-Wallis, p < 0.05). The highest concentration of Cd was associated with higher DNA damage to C. kiiensis larvae compared with Cu and Zn. The potential genotoxicity of these metals to C. kiiensis was Cd > Cu > Zn.