DNA damage in frog erythrocytes after in vitro exposure to a high peak-power pulsed electromagnetic field

Repeated exposure to nanosecond high power pulsed microwaves increases cancer incidence in rat

High-power microwaves are used to inhibit electronics of threatening military or civilian vehicles. This work aims to assess health hazards of high-power microwaves and helps to define hazard threshold levels of modulated radiofrequency exposures such as those emitted by the first generations of mobile phones. Rats were exposed to the highest possible field levels, under single acute or repetitive exposures for eight weeks. Intense microwave electric fields at 1 MV m-1 of nanoseconds duration were applied from two sources at different carrier frequencies of 10 and 3.7 GHz. The repetition rate was 100 pps, and the duration of train pulses lasted from 10 s to twice 8 min. The effects on the central nervous system were evaluated, by labelling brain inflammation marker GFAP and by performing different behavioural tests: rotarod, T-maze, beam-walking, open-field, and avoidance test. Long-time survival was measured in animals repeatedly exposed, and anatomopathological analysis was performed on animals sacrificed at two years of life or earlier in case of precocious death. Control groups were sham exposed. Few effects were observed on behaviour. With acute exposure, an avoidance reflex was shown at very high thermal level (22 W kg-1); GFAP was increased some days after exposure. Most importantly, with repeated exposures, survival time was 4-months shorter in the exposed group, with eleven animals exhibiting a large sub-cutaneous tumour, compared to two in the sham group. A residual X-ray exposure was also present in the beam (0.8 Gy), which is probably not a bias for the observed result. High power microwaves below thermal level in average, can increase cancer prevalence and decrease survival time in rats, without clear effects on behaviour. The parameters of this effect need to be further explored, and a more precise dosimetry to be performed.

The comet assay in animal models: From bugs to whales - (Part 2 Vertebrates)

The comet assay has become one of the methods of choice for the evaluation and measurement of DNA damage. It is sensitive, quick to perform and relatively affordable for the evaluation of DNA damage and repair at the level of individual cells. The comet assay can be applied to virtually any cell type derived from different organs and tissues. Even though the comet assay is predominantly used on human cells, the application of the assay for the evaluation of DNA damage in yeast, plant and animal cells is also quite high, especially in terms of biomonitoring. The present extensive overview on the usage of the comet assay in animal models will cover both terrestrial and water environments. The first part of the review was focused on studies describing the comet assay applied in invertebrates. The second part of the review, (Part 2) will discuss the application of the comet assay in vertebrates covering cyclostomata, fishes, amphibians, reptiles, birds and mammals, in addition to chordates that are regarded as a transitional form towards vertebrates. Besides numerous vertebrate species, the assay is also performed on a range of cells, which includes blood, liver, kidney, brain, gill, bone marrow and sperm cells. These cells are readily used for the evaluation of a wide spectrum of genotoxic agents both in vitro and in vivo. Moreover, the use of vertebrate models and their role in environmental biomonitoring will also be discussed as well as the comparison of the use of the comet assay in vertebrate and human models in line with ethical principles. Although the comet assay in vertebrates is most commonly used in laboratory animals such as mice, rats and lately zebrafish, this paper will only briefly review its use regarding laboratory animal models and rather give special emphasis to the increasing usage of the assay in domestic and wildlife animals as well as in various ecotoxicological studies.

The level of DNA damage in mouse hematopoietic cells and in frog and human blood cells, as induced by the action of reactive oxygen species in vitro

Comparative studies of the level of DNA damage induced in vitro by X-rays (0-8 Gy) or hydrogen peroxide (0-300 µM) in cells of blood, spleen, and bone marrow of mice and in blood cells of frogs and humans were performed using the alkaline comet assay. For both agents, the levels of induced DNA damage in leucocytes/splenocytes of mice were higher than those in blood cells of frogs and humans, while in human leucocytes, they were comparable with those in frog blood cells. The rate of DNA repair in frog blood cells was very slow. The results suggest that the levels of radiation-induced DNA damage are not in accordance with species radiosensitivity (according to LD_50/30) but rather with the intrinsic peculiarities of cells.

The Comet Assay and its applications in the field of ecotoxicology: a mature tool that continues to expand its perspectives

Since Singh and colleagues, in 1988, launched to the scientific community the alkaline Single Cell Gel Electrophoresis (SCGE) protocol, or Comet Assay, its uses and applications has been increasing. The thematic areas of its current employment in the evaluation of genetic toxicity are vast, either in vitro or in vivo, both in the laboratory and in the environment, terrestrial or aquatic. It has been applied to a wide range of experimental models: bacteria, fungi, cells culture, arthropods, fishes, amphibians, reptiles, mammals, and humans. This document is intended to be a comprehensive review of what has been published to date on the field of ecotoxicology, aiming at the following main aspects: (i) to show the most relevant experimental models used as bioindicators both in the laboratory and in the field. Fishes are clearly the most adopted group, reflecting their popularity as bioindicator models, as well as a primary concern over the aquatic environment health. Amphibians are among the most sensitive organisms to environmental changes, mainly due to an early aquatic-dependent development stage and a highly permeable skin. Moreover, in the terrestrial approach, earthworms, plants or mammalians are excellent organisms to be used as experimental models for genotoxic evaluation of pollutants, complex mix of pollutants and chemicals, in both laboratory and natural environment. (ii) To review the development and modifications of the protocols used and the cell types (or tissues) used. The most recent developments concern the adoption of the enzyme linked assay (digestion with lesion-specific repair endonucleases) and prediction of the ability to repair of oxidative DNA damage, which is becoming a widespread approach, albeit challenging. For practical/technical reasons, blood is the most common choice but tissues/cells like gills, sperm cells, early larval stages, coelomocytes, liver or kidney have been also used. (iii) To highlight correlations with other biomarkers. (iv) To build a constructive criticism and summarize the needs for protocol improvements for future test applications within the field of ecotoxicology. The Comet Assay is still developing and its potential is yet underexploited in experimental models, mesocosmos or natural ecosystems.

The effect of 900 and 1800 MHz GSM-like radiofrequency irradiation and nicotine sulfate administration on the embryonic development of Xenopus laevis

The aim of this study was to investigate the effects of GSM-like radiofrequency electromagnetic radiation (RF EMR) and nicotine sulfate (NS) exposure on Xenopus embryonic development.The developmental effects of GSM-like RF-EMR (900-1800 MHz, at a SAR value of 1W/kg and NS on Xenopus laevis embryos were investigated). Following the application of radiofrequency radiation and/or NS administration, the embryos were closely examined in order to determine their possible teratogenic effects. Xenopus frogs obtained from the Department of Physiology of the Cukurova University, in accordance described by the Standard Guide of the American Society for Testing and Materials (ASTM). Following the exposure of Xenopus embryos to RF-EMR at 900 and 1800 MHz (1.0W/kg) for 4, 6 and 8h; the whole body specific energy absorption rate (SAR) of the embryos was calculated. With the exception of irradiation at 1800 MHz no dramatic developmental anomalies were observed in the Xenopus embryos in association with RF-EMR applications. Combined RF-EMR and NS applications resulted in dramatic abnormalities and death among the Xenopus embryos. The study results indicated that GSM-like RF-EMR (e.g. radiation from cell phones) was not as harmful to Xenopus embryos as might have been expected. However, the combined effects of GSM-like RF-EMR and NS on Xenopus embryos were more severe than the effect of RF-EMR or NS alone. In conclusion, the study results appear to suggest that the combined use of nicotine and cell phones might result in more pronounced detrimental effects on the health of smokers.

Extremely low-frequency electromagnetic fields cause DNA strand breaks in normal cells

BACKGROUND

Extremely low frequency electromagnetic fields aren't considered as a real carcinogenic agent despite the fact that some studies have showed impairment of the DNA integrity in different cells lines. The aim of this study was evaluation of the late effects of a 100 Hz and 5.6 mT electromagnetic field, applied continuously or discontinuously, on the DNA integrity of Vero cells assessed by alkaline Comet assay and by cell cycle analysis. Normal Vero cells were exposed to extremely low frequency electromagnetic fields (100 Hz, 5.6 mT) for 45 minutes. The Comet assay and cell cycle analysis were performed 48 hours after the treatment.

RESULTS

Exposed samples presented an increase of the number of cells with high damaged DNA as compared with non-exposed cells. Quantitative evaluation of the comet assay showed a significantly (<0.001) increase of the tail lengths, of the quantity of DNA in tail and of Olive tail moments, respectively. Cell cycle analysis showed an increase of the frequency of the cells in S phase, proving the occurrence of single strand breaks. The most probable mechanism of induction of the registered effects is the production of different types of reactive oxygen species.

CONCLUSIONS

The analysis of the registered comet indices and of cell cycle showed that extremely low frequency electromagnetic field of 100 Hz and 5.6 mT had a genotoxic impact on Vero cells.

A method of low-temperature storing of agarose slides with lysed cells

A method has been developed for a long-term low-temperature storage (-10 to -15°C) of the agarose slides with nucleoids (lysed eukaryotic cells). After lysis of agarose-immobilized cells, the slides were incubated for 30 min in phosphate buffer with 50% glycerol and 100 mM EDTA, thereupon they were stored in a freezer at -10 to -15°C. After long-term storage, the slides were re-incubated for 30 min in lysing solution. The measurements of the baseline and in vitro induced DNA damage in nucleoids of the human and mouse leukocytes, which had been stored in agarose slides at low temperature, showed that DNA damage level determined after a 40-day storage did not significantly differ from that of the fresh slides. The advanced storage method is simple and reliable; it opens the way to avoid cryopreservation of the biological samples and to process little by little a great number of the identically prepared slides.

Changes in the level of spontaneous DNA damage in whole blood leukocytes during storage

We evaluated structural damage to DNA (%TDNA) in blood leukocytes from healthy donors of different age at different periods (0-6 days) of blood storage at 4-8°C. It was found that the basal level of DNA damage increased and intracellular antioxidant level decreased during storage. Mean %TDNA was 6.8±3.3% in the fresh blood and 19.2±8.1% after 5-day storage. The experiments with exposure to reactive oxygen species induced by irradiation suggest that depletion of low-molecular-weight endogenous antioxidants occurs as soon as after 5-h storage. Our results suggest that storage time should be taken into account when assessing the basal and induced levels of leukocyte DNA damage by the comet assay.

In vitro and in vivo genotoxicity of radiofrequency fields

There has been growing concern about the possibility of adverse health effects resulting from exposure to radiofrequency radiations (RFR), such as those emitted by wireless communication devices. Since the introduction of mobile phones many studies have been conducted regarding alleged health effects but there is still some uncertainty and no definitive conclusions have been reached so far. Although thermal effects are well understood they are not of great concern as they are unlikely to result from the typical low-level RFR exposures. Concern rests essentially with the possibility that RFR-exposure may induce non-thermal and/or long-term health effects such as an increased cancer risk. Consequently, possible genetic effects have often been studied but with mixed results. In this paper we review the data on alleged RFR-induced genetic effects from in vitro and in vivo investigations as well as from human cytogenetic biomonitoring surveys. Attention is also paid to combined exposures of RFR with chemical or physical agents. Again, however, no entirely consistent picture emerges. Many of the positive studies may well be due to thermal exposures, but a few studies suggest that biological effects can be seen at low levels of exposure. Overall, however, the evidence for low-level genotoxic effects is very weak.

Protection of mice against X-ray injuries by the post-irradiation administration of guanosine and inosine

PURPOSE

To examine the radioprotective action of guanosine (Guo) and inosine (Ino) administered to mice after irradiation with X-rays.

MATERIALS AND METHODS

Survival of mice exposed to lethal and sublethal doses of X-rays was studied. Peripheral blood cells were counted using a light microscope. The damage to bone marrow cells was assessed by micronucleus (MN) test. Damage and repair of DNA in blood leukocytes were estimated using the comet assay.

RESULTS

Mice injected intraperitoneally (i.p.) with Guo or Ino ( approximately 30 microg g(-1), i.e., approximately 0.6 mg per 20-g mouse) 15 min after acute whole-body irradiation with 7 Gy recovered from X-ray injury. On the 30th day after irradiation, 50 and 40% of mice injected with Guo and Ino, respectively, remained alive. The dose reduction factor (DRF) was 1.23 for Guo and 1.15 for Ino. The protective effect gradually decreased as the time interval between the irradiation and injection was increased to 3, 5, 8 h. Guo and Ino facilitated the restoration of peripheral blood cell counts. These compounds protected bone marrow cells from damage and normalized erythropoiesis. Guo and Ino contributed to a more rapid and complete repair of DNA in mouse leukocytes irradiated both in vitro and in vivo.

CONCLUSION

Guo and Ino introduced shortly after irradiation reduce leukopenia and thrombocytopenia and offer promise as therapeutic agents for treatment of radiation injuries.

DNA damage in human mononuclear cells induced by bacterial endotoxin

Damage to nuclear DNA in human peripheral blood mononuclear cells was studied after in vitro treatment with bacterial endotoxin by alkaline comet assay. It was found that LPS induced DNA damage as soon as over the first 30 min of incubation, while by the 4th hour of incubation DNA damage was found in more than 95% cells. Exogenous superoxide dismutase completely protected DNA, which suggests that superoxide radical is the primary extracellular damaging agent. Polyphenol antioxidant (water-soluble lignin) and specific NADPH oxidase inhibitor (diphenyleneiodonium chloride) also produced a protective effect. Our results show that LPS-activated mononuclear cells can be used ex vivo as a convenient and adequate experimental system for evaluation of the efficiency of various substances in protection of lymphocyte DNA from the damaging effect of reactive oxygen species of LPS-stimulated monocytes.

Spontaneous DNA damage in peripheral blood leukocytes from donors of different age

Spontaneous DNA damage in peripheral blood cells was studied in healthy donors of different age (23-70 years). Alkaline comet assay was used to evaluate total DNA damage in individual cells. The individual variability in venous blood samples was higher than in capillary blood samples. The advantage of analysis of DNA damage in nucleated cells from the whole blood is more preferable compared to experiments with isolated lymphocytes because all cell populations in the sample are analyzed. Study of blood cells from healthy donors showed that the mean percent of DNA in the comet tail tended to decrease with age. However, correlation analysis revealed no relationship was found between donor age and degree of spontaneous DNA damage.

DNA damage (comet assay) and 8-oxodGuo (HPLC-EC) in relation to oxidative stress in the freshwater bivalveUnio tumidus

The relationships between DNA damage and oxidative stress in the digestive gland, gills and haemocytes of the freshwater bivalve Unio tumidus were investigated. Two markers of genotoxicity were measured: DNA breaks by means of the comet assay, and oxidative DNA lesions by means of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) measured using high-performance liquid chromatography (HPLC) coupled to electrochemical detection. Lipid peroxidation was evaluated by measuring malondialdehyde (MDA) tissue levels. Effects were studied after exposure of bivalves for 6 days to benzo[a]pyrene (B[a]P) (50 and 100 microg l(-1)) and ferric iron (20 and 40 mg l(-1)), applied alone or in combination. Lipid peroxidation in the digestive gland and gills resulted from exposure to Fe3+ or B[a]P whatever the concentrations tested. DNA oxidatively formed lesions were induced in the two tissues at a higher level after B[a]P exposure than after Fe3+ treatment. No significant dose-response relationship was found with the two compounds and no synergistic effect was observed between Fe3+ and B[a]P. The gills appeared less sensitive than the digestive gland to DNA lesions expressed as 8-oxodGuo and comet results. Good correlations were noted between 8-oxodGuo and comet. MDA and DNA damage did not correlate as well, although it was stronger in the digestive gland than in the gills. Production of mucus by the gills likely served to prevent lesions by reducing the bioavailability of the chemicals tested, which could explain that dose-effect relationships and synergistic effects were not observed.

Comet assay: a reliable tool for the assessment of DNA damage in different models

New chemicals are being added each year to the existing burden of toxic substances in the environment. This has led to increased pollution of ecosystems as well as deterioration of the air, water, and soil quality. Excessive agricultural and industrial activities adversely affect biodiversity, threatening the survival of species in a particular habitat as well as posing disease risks to humans. Some of the chemicals, e.g., pesticides and heavy metals, may be genotoxic to the sentinel species and/or to non-target species, causing deleterious effects in somatic or germ cells. Test systems which help in hazard prediction and risk assessment are important to assess the genotoxic potential of chemicals before their release into the environment or commercial use as well as DNA damage in flora and fauna affected by contaminated/polluted habitats. The Comet assay has been widely accepted as a simple, sensitive, and rapid tool for assessing DNA damage and repair in individual eukaryotic as well as some prokaryotic cells, and has increasingly found application in diverse fields ranging from genetic toxicology to human epidemiology. This review is an attempt to comprehensively encase the use of Comet assay in different models from bacteria to man, employing diverse cell types to assess the DNA-damaging potential of chemicals and/or environmental conditions. Sentinel species are the first to be affected by adverse changes in their environment. Determination of DNA damage using the Comet assay in these indicator organisms would thus provide information about the genotoxic potential of their habitat at an early stage. This would allow for intervention strategies to be implemented for prevention or reduction of deleterious health effects in the sentinel species as well as in humans.

Peculiarities of the effect of low-dose-rate radiation simulating high-altitude flight conditions on mice in vivo

In the present work, the effect of a low-dose rate of high-LET radiation in polychromatic erythrocytes of mice bone marrow was investigated in vivo. The spectral and component composition of the radiation field used was similar to that present in the atmosphere at an altitude of about 10 km. The dose dependence, adaptive response, and genetic instability in the F1 generation born from males irradiated under these conditions were examined using the micronucleus test. Irradiation of the mice was performed for 24 h per day in the radiation field behind the concrete shield of the Serpukhov accelerator. Protons of 70 GeV were used over a period of 15-31 days, to accumulate doses of 11.5-31.5 cGy. The experiment demonstrated that irradiation of mice in vivo in this dose range leads to an increase in cytogenetic damage to bone marrow cells, but does not induce any adaptive response. In mice pre-irradiated with a dose of 11.5 cGy, an increase in sensitivity was observed after an additional irradiation with a dose of 1.5 Gy. The absence of an adaptive response suggests existence of genetic instability.

Cytogenetic Studies in Human Blood Lymphocytes ExposedIn Vitroto 2.45 GHz or 8.2 GHz Radiofrequency Radiation

Peripheral blood samples collected from healthy human volunteers were exposed in vitro to 2.45 GHz or 8.2 GHz pulsed-wave radiofrequency (RF) radiation. The net forward power, average power density, mean specific absorption rate, and the temperature maintained during the 2-h exposure of the cells to 2.45 GHz or 8.2 GHz were, respectively, 21 W or 60 W, 5 mW/cm(2) or 10 mW/cm(2), 2.13 W/kg or 20.71 W/kg, and 36.9 +/- 0.1 degrees C or 37.5 +/- 0.2 degrees C. Aliquots of the same blood samples that were either sham-exposed or exposed in vitro to an acute dose of 1.5 Gy gamma radiation were used as unexposed and positive controls, respectively. Cultured lymphocytes were examined to determine the extent of cytogenetic damage assessed from the incidence of chromosomal aberrations and micronuclei. Under the conditions used to perform the experiments, the levels of damage in RF-radiation-exposed and sham-exposed lymphocytes were not significantly different. Also, there were no significant differences in the response of unstimulated lymphocytes and lymphocytes stimulated with phytohemagglutinin when exposed to 8.2 GHz RF radiation. In contrast, the positive control cells that had been subjected to gamma irradiation exhibited significantly more damage than RF-radiation- and sham-exposed lymphocytes.

Lack of direct DNA damage in human blood leukocytes and lymphocytes after in vitro exposure to high power microwave pulses

Currently, the potential genotoxicity of high power microwave pulses (HPMP) is not clear. Using the alkaline single cell gel electrophoresis assay, also known as the alkaline comet assay, we studied the effects of HPMP (8.8 GHz, 180 ns pulse width, peak power 65 kW, pulse repetition frequency 50 Hz) on DNA of human whole-blood leukocytes and isolated lymphocytes. The cell suspensions were exposed to HPMP for 40 min in a rectangular waveguide. The average SAR calculated from the temperature kinetics was about 1.6 kW/kg (peak SAR was about 300 MW/kg). The steady-state temperature rise in the 50 microl samples exposed to HPMP was 3.5 +/- 0.1 degrees C. In independent experiments, we did not find any statistically significant DNA damage manifested immediately after in vitro HPMP exposure of human blood leukocytes or lymphocytes or after HPMP exposure of leukocytes subsequently incubated at 37 degrees C for 30 min. Our results indicate that HPMP under the given exposure conditions did not induce DNA strand breaks, alkali-labile sites, and incomplete excision repair sites, which could be detected by the alkaline comet assay.