Effect of low-level radiation on the death of male germ cells

Hormetic and adaptive responses induced by low-level radiation in hematopoietic and immune systems have been observed, as shown by stimulatory effects on cell growth and resistance to subsequent radiation-induced cytogenetic damage. However, in terms of cell death by apoptosis, the effects of low-level radiation are controversial: Some studies showed decreased apoptosis in response to low-level radiation while others showed increased apoptosis. This controversy may be related to the radiation doses or dose rates and also, more importantly, to the cell types. Testes are one of the most radiosensitive organs. The loss of male germ cells after exposure to ionizing radiation has been attributed to apoptosis. In the present study, the effects of low-level radiation at doses up to 200 mGy on mouse male germ cells in terms of apoptosis and the expression of apoptosis-related proteins were examined at different times after whole-body exposure of mice to low-level radiation. In addition, the effect of pre-exposure to low-level radiation on subsequent cell death induced by high doses of radiation was examined to explore the possibility of low-level radiation-induced adaptive response. The results showed that low-level radiation in the dose range of 25-200 mGy induced significant increases in apoptosis in both spermatogonia and spermatocytes, with the maximal effect at 75 mGy. The increased apoptosis is most likely associated with Trp53 protein expression. Furthermore, 75 mGy low-level radiation given pre-irradiation led to an adaptive response of seminiferous germ cells to subsequent high-level radiation-induced apoptosis. These results suggest that low-level radiation induces increased apoptosis in male germ cells but also induces a significant adaptive response that decreases cell death after a subsequent high-dose irradiation.     

Cytogenetic adaptive response induced by pre-exposure in human lymphocytes and marrow cells of mice

The frequencies of chromosomal aberrations bith in human lymphocytes and in mouse marrow cells exposed to low-level radiation were higher than in their unexposed controls. However, the frequencies of chromosomal aberrations in two kinds of cells pre-exposed to low-level radiation induced by a subsequent high dose of X-rays or γ-rays were lower than those of the groups only exposed to high-level radiation. This implies that adaptive responses for cytogenetic indicators might be induced by pre-exposure to low-level radiation. The results also show the existence of possible variations between individual lymphocytes.     

Response of the glutathione system to chronic irradiation of human population after the Chernobyl accident

A complex relationship between glutathione level in plasma in human population (children living in radionuclide-contaminated regions and the Chernobyl liquidators) exposed to chronic low-level radiation after the Chernobyl accident was demonstrated. The obtained experimental data indicate different responses of the human glutathione system to low (from 0.1 to 20 cSv) and high (from 20 to 150 cSv) doses of ionizing radiation.Translated from Izvestiya Akademii Nauk, Seriya Biologicheskaya, No. 1, 2005, pp. 9–17.Original Russian Text Copyright © 2005 by Ivanenko, Burlakova.     

The action of atomic radiation in low doses on the biota

The radiobiological studies carried out in conditions of lower and slightly increased natural radiation background have prompted an idea of "low doses" in radiobiology which is proposed for discussion. The author emphasizes that the difference between the leading molecular and cellular mechanisms that come into play under the effect of high- and low-level atomic radiation makes it incorrect to assess the risk from low radiation doses on the basis of the regularities obtained with high doses.     

The biological effects of space radiation during long stays in space.

Many space experiments are scheduled for the International Space Station (ISS). Completion of the ISS will soon become a reality. Astronauts will be exposed to low-level background components from space radiation including heavy ions and other high-linear energy transfer (LET) radiation. For long-term stay in space, we have to protect human health from space radiation. At the same time, we should recognize the maximum permissible doses of space radiation. In recent years, physical monitoring of space radiation has detected about 1 mSv per day. This value is almost 150 times higher than that on the surface of the Earth. However, the direct effects of space radiation on human health are currently unknown. Therefore, it is important to measure biological dosimetry to calculate relative biological effectiveness (RBE) for human health during long-term flight. The RBE is possibly modified by microgravity. In order to understand the exact RBE and any interaction with microgravity, the ISS centrifugation system will be a critical tool, and it is hoped that this system will be in operation as soon as possible.     

Activation of the DNA repair system in tissues of mice subjected to chronic gamma irradiation

Mice exposed to gamma-quanta during 47 and 82 days at a dose-rate of 1.3 mGy/h and cumulative doses of 1.45 and 2.54 Gy, respectively, were subsequently subjected to a single acute irradiation with a dose of 20 Gy. Repair of DNA damages induced by the acute exposure was shown to proceed in the brain, pulmonary and splenic tissues of chronically exposed mice more readily than in the tissues of mice not subjected to chronic irradiation. The data obtained indicate that the induced adaptive response activates DNA repair in tissues of mice exposed to long-term low-level radiation.     

Assessment of radiation-induced DNA damage in human blood lymphocytes using the single-cell gel electrophoresis technique.

The ability of the alkaline single-cell gel (SCG) electrophoresis technique to detect single-strand breaks and alkali-labile DNA damage in human cells induced by low doses of radiation was evaluated. Peripheral blood lymphocytes were irradiated with gamma-rays from a 137Cs source at doses from 0.01 to 1 Gy and exposed to alkali (pH greater than 13) for 20, 40 or 60 min and then electrophoresed at 25 V and 300 mA for either 20 or 40 min. The extent of DNA damage that was expressed and detected as DNA migration depended directly on the dose of radiation, the duration of exposure to alkali and the length of electrophoresis. At all experimental conditions tested, it was possible to detect a significant increase in DNA damage induced by a radiation dose as low as 0.05 Gy. Based on an analysis of the ratio of the range to the standard deviation for each radiation dose and experimental condition, the distribution of damage among cells for all doses was neither excessively homogeneous nor heterogeneous. Furthermore, the distribution was independent of radiation treatment. The SCG technique is rapid and sensitive, and useful for investigations concerned with effects of low doses of radiation.     

Comparison of structural changes in skin and amnion tissue grafts for transplantation induced by gamma and electron beam irradiation for sterilization

Sterilization is an important step in the preparation of biological material for transplantation. The aim of the study is to compare morphological changes in three types of biological tissues induced by different doses of gamma and electron beam radiation. Frozen biological tissues (porcine skin xenografts, human skin allografts and human amnion) were irradiated with different doses of gamma rays (12.5, 25, 35, 50 kGy) and electron beam (15, 25, 50 kGy). Not irradiated specimens served as controls. The tissue samples were then thawn and fixed in 10 % formalin, processed by routine paraffin technique and stained with hematoxylin and eosin, alcian blue at pH 2.5, orcein, periodic acid Schiff reaction, phosphotungstic acid hematoxylin, Sirius red and silver impregnation. The staining with hematoxylin and eosin showed vacuolar cytoplasmic changes of epidermal cells mainly in the samples of xenografts irradiated by the lowest doses of gamma and electron beam radiation. The staining with orcein revealed damage of fine elastic fibers in the xenograft dermis at the dose of 25 kGy of both radiation types. Disintegration of epithelial basement membrane, especially in the xenografts, was induced by the dose of 15 kGy of electron beam radiation. The silver impregnation disclosed nuclear chromatin condensation mainly in human amnion at the lowest doses of both radiation types and disintegration of the fine collagen fibers in the papillary dermis induced by the lowest dose of electron beam and by the higher doses of gamma radiation. Irradiation by both, gamma rays and the electron beam, causes similar changes on cells and extracellular matrix, with significant damage of the basement membrane and of the fine and elastic and collagen fibers in the papillary dermis, the last caused already by low dose electron beam radiation.     

Comparison of the protective effect of garlic extract and cell defense during adaptive response

The resistance of human cell DNA to damaging doses of CdCl2 or gamma radiation has been investigated after pretreatment with garlic extract (GE) or with adaptive doses of the same mutagens. The adaptive response (AR) and pretreatment with GE stabilize the DNA structure in a similar way. In experiments with 4-nitroquinoline-1-oxide (4-NQO), GE does not stabilize DNA structure but increases the rate and volume of repair of induced breaks. 3-Aminobenzamide (3-AB) increases the number of DNA breaks induced in experiments with CdCl2, gamma radiation, and 4-NQO. This suggests that poly(ADP-ribose)polymerase participates defense of cells from mutagens. Thus, it has been demonstrated that cell defense from CdCl2 or gamma radiation in experiments with GE and AO is mediated by stabilization of DNA structure and in experiments with 4-NQO, by activation of repair of DNA breaks induced.     

Possible Relationships between Plasma Glutathione Levels and Cytogenetic Indices in Peripheral Blood Lymphocytes of Children Exposed to Low Doses of Radiation

An analysis of correlations between cytogenetic indices in lymphocytes and levels of reduced glutathione in the plasma of peripheral blood in children born after the Chernobyl accident is presented. The studied systems in the child population demonstrated different responses to low-level radiation of their mothers living in conditions of radionuclide contamination (1–20 Ci/km² of ¹³⁷Cs). Low doses of radiation accumulated by mothers (below 30 cSv) proved to have a more pronounced effect on the studied systems in children as compared to high doses (from 30 to 60 cSv).     

The biological effects in animals in relation to the accident at the Chernobyl Atomic Electric Power Station. 9. The morphofunctional indices of the immunocompetent organs in mice]

The permanent action of small doses of low-intensity radiation on the immune status of 2.5-3.5 month CC57W mice has been investigated. Total doses of internal and external irradiation were about few cGy. The permanent action of low-level radiation on the experimental animals of the first and fourth generations was shown to change spleen and lymph nodes weights and the count of lymphocytes isolated from these organs. Cellularity and DNA synthesis in the lymph-node lymphocytes and their proliferative response to polyclonal mitogens also changed. The alterations in the parameters that characterized T-lymphocyte population were statistically significant.     

Adaptive response of human lymphocytes for the repair of radon-induced chromosomal damage

In human lymphocytes low doses of X-rays can decrease the number of chromatid deletions induced by subsequent high doses of sparsely ionizing X-rays. Because of the concern with the carcinogenic effects of low doses of -particles from radon in homes, experiments were carried out to see if low doses of X-rays could also decrease the yield of chromosomal aberrations induced by subsequent exposure to radon. Human peripheral blood lymphocytes were irradiated with low doses of X-rays (2 cGy) at 48 h of culture, exposed to radon at 72 h of culture, and analyzed for the presence of chromatid aberrations at subsequent intervals. The frequency of chromatid aberrations induced by radon alone increased with time after exposure, indicating exaggerated differences in the stage sensitivity of cell cycle stages to high-LET radiation. Furthermore, the numbers of aberrations per cell did not follow a Poisson distribution but were over dispersed, as might be expected since high-LET radiations have a high relative biological effectiveness compared with low-LET radiations. Nevertheless, lymphocytes exposed to 2 cGy of X-rays before radon exposure contained approximately one-half the number of chromatid deletions compared with lymphocytes treated with radon alone and analzed at the same time. Thus, the putative chromosomal repair mechanism induced by low doses of sparsely ionizing radiation is also effective in reducing chromosomal aberrations induced by radon, which hitherto had been thought to be relatively independent of repair processes.     

Up‐Regulation and Redistribution of Bax in Ultraviolet B‐Irradiated Melanocytes

Ultraviolet B (UVB) radiation may activate or deteriorate cultured human epidermal melanocytes, depending on the doses and culture conditions. It is also reported that cultured human epidermal melanocytes derived from different pigmentary phenotypes showed different responses to UVB radiation. In this study, we examined whether apoptosis of melanocytes can be induced by physiologic doses of UVB irradiation using cultured human epidermal melanocytes derived from oriental males of skin types III and IV. Propidium iodide staining for DNA condensation and flow cytometric analyses demonstrated the apoptotic cell death of melanocytes following UVB irradiation (0–30 mJ/cm²). The levels of p53, Bax, and Bcl‐2, determined by immunoblotting, revealed a dose‐dependent increase in p53 and Bax, but the level of Bcl‐2 remained unchanged. Confocal microscopic examination showed that Bax moved from a diffuse to a punctate distribution after UVB irradiation. However, there were no changes in the pattern of distribution of Bcl‐2. These data suggest that the high constitutional level of Bcl‐2 may protect melanocytes from UVB‐induced injury, and that apoptotic death of melanocytes may be induced by the elevation and redistribution of Bax.     

Up-Regulation and redistribution of Bax in ultraviolet B-irradiated melanocytes

Ultraviolet B (UVB) radiation may activate or deteriorate cultured human epidermal melanocytes, depending on the doses and culture conditions. It is also reported that cultured human epidermal melanocytes derived from different pigmentary phenotypes showed different responses to UVB radiation. In this study, we examined whether apoptosis of melanocytes can be induced by physiologic doses of UVB irradiation using cultured human epidermal melanocytes derived from oriental males of skin types III and IV. Propidium iodide staining for DNA condensation and flow cytometric analyses demonstrated the apoptotic cell death of melanocytes following UVB irradiation (0-30 mJ/cm2). The levels of p53, Bax, and Bcl-2, determined by immunoblotting, revealed a dose-dependent increase in p53 and Bax, but the level of Bcl-2 remained unchanged. Confocal microscopic examination showed that Bax moved from a diffuse to a punctate distribution after UVB irradiation. However, there were no changes in the pattern of distribution of Bcl-2. These data suggest that the high constitutional level of Bcl-2 may protect melanocytes from UVB-induced injury, and that apoptotic death of melanocytes may be induced by the elevation and redistribution of Bax.     

Cellular responses to DNA double-strand breaks after low-dose γ-irradiation

DNA double-strand breaks (DSBs) are a serious threat to genome stability and cell viability. Although biological effects of low levels of radiation are not clear, the risks of low-dose radiation are of societal importance. Here, we directly monitored induction and repair of single DSBs and quantitatively analyzed the dynamics of interaction of DNA repair proteins at individual DSB sites in living cells using 53BP1 fused to yellow fluorescent protein (YFP-53BP1) as a surrogate marker. The number of DSBs formed was linear with dose from 5 mGy to 1 Gy. The DSBs induced by very low radiation doses (5 mGy) were repaired with efficiency similar to repair of DSBs induced at higher doses. The YFP-53BP1 foci are dynamic structures: 53BP1 rapidly and reversibly interacted at these DSB sites. The time frame of recruitment and affinity of 53BP1 for DSB sites were indistinguishable between low and high doses, providing mechanistic evidence for the similar DSB repair after low- and high-dose radiation. These findings have important implications for estimating the risk associated with low-dose radiation exposure on human health.     

Effect of small doses of gamma radiation on the activity of marker enzymes in the plasma membranes of chick embryo liver

A study was made of marker enzyme activity in plasma membranes of chick liver during embryogenesis in normal conditions and after exposure to ionizing radiation. It was shown that irradiation with small doses of eggs prior to incubation and of chick embryos during different periods of the prenatal ontogenesis caused essential changes in activity of membrane-bound enzymes of liver plasmolemma. Stimulation with small radiation doses was most effective with preincubation irradiation of eggs and most manifest at later stages of the prenatal ontogenesis. Thus, the marker enzymes were shown to play a significant role in the realization of the stimulatory effect of low-level radiation.     

The evaluation of protective effect of lycopene against genotoxic influence of X-irradiation in human blood lymphocytes

Many studies suggest that exogenous antioxidants may protect cells against DNA damage caused with ionizing radiation. One of the most powerful antioxidants is lycopene (LYC), a carotenoid derived from tomatoes. The aim of this study was to investigate, using the comet assay, whether LYC can act as protectors/modifiers and prevent DNA damage induced in human blood lymphocytes, as well as to mitigate the effects of radiation exposure. In this project, LYC, dissolved in DMSO at a concentration of 10, 20 or 40 μM/ml of cell suspension, was added to the isolated lymphocytes from human blood at appropriate intervals before or after the X-irradiation at doses of 0.5, 1 and 2 Gy. Cell viability in all groups was maintained at above 70%. The results showed the decrease of DNA damage in cells treated with various concentrations of LYC directly and 1 h before exposure to X-rays compared to the control group exposed to irradiation alone. Contrary results were observed in cells exposed to LYC immediately after exposure to ionizing radiation. The studies confirmed the protective effect of LYC against DNA damage induced by ionizing radiation, but after irradiation the carotenoid did not stimulate of DNA repair and cannot act as modifier. However, supplementation with LYC, especially at lower doses, may be useful in protection from radiation-induced oxidative damage.     

The biological effects in animals in relation to the accident at the Chernobyl Atomic Electric Power Station. 5. Longevity and the carcinogenic effects]

Remote effects in laboratory animals living in conditions of exposure to a mixture of external and internal radiation resulted from the Chernobyl A.P.S. disaster have been investigated. It has been found that the rate of deaths from non-tumor illnesses grows, the incidence of neoplasms increases and their latency time decreases. The redistribution within the spectrum of benign and malignant tumors and the increase in the multiplicity coefficient have been revealed. It is concluded that chronic exposure of animals to low-level radiation from the radionuclides, resulted from the accident, brings about a much larger number of negative stochastic and nonstochastic remote effects as compared to those expected from the extrapolation of the effects produced by high radiation doses.     

Exposure to low dose of gamma radiation enhances the excision repair in Saccharomyces cerevisiae

The effect of low doses of ionizing and nonionizing radiation on the radiation response of yeast Saccharomyces cerevisiae toward ionizing and nonionizing radiation was studied. The wild-type strain D273-10B on exposure to 54 Gy gamma radiation (resulting in about 10% cell killing) showed enhanced resistance to subsequent exposure to UV radiation. This induced UV resistance increased with the incubation time between the initial gamma radiation stress and the UV irradiation. Exposure to low doses of UV light on the other hand showed no change in gamma or UV radiation response of this strain. The strains carrying a mutation at rad52 behaved in a way similar to the wild type, but with slightly reduced induced response. In contrast to this, the rad3 mutants, defective in excision repair, showed no induced UV resistance. Removal of UV-induced pyrimidine dimers in wild-type yeast DNA after UV irradiation was examined by analyzing the sites recognized by UV endonuclease from Micrococcus luteus. The samples that were exposed to low doses of gamma radiation before UV irradiation were able to repair the pyrimidine dimers more efficiently than the samples in which low gamma irradiation was omitted. The nature of enhanced repair was studied by scoring the frequency of induced gene conversion and reverse mutation at trp and ilv loci respectively in strain D7, which showed similar enhanced UV resistance induced by low-dose gamma irradiation. The induced repair was found to be essentially error-free. These results suggest that irradiation of strain D273-10B with low doses of gamma radiation enhances its capability for excision repair of UV-induced pyrimidine dimers.     

Establishment of dose-response relationships between doses of Cs-137 gamma-rays and frequencies of micronuclei in human peripheral blood lymphocytes

It has been suggested that the yield of micronuclei in human peripheral blood lymphocytes could be used as a biological dosimeter in cases of radiation exposure. In the present study micronuclei were induced in lymphocytes by exposing human blood samples in vitro to various doses of Cs-137 gamma-rays. The blood samples were then cultivated using the cytokinesis block method. Coded programs were employed to establish the relationships between the frequencies of micronuclei and various doses of gamma-rays. The best fit was obtained by the linear-quadratic model, Y = c + aD + bd2, where Y is the yield of micronuclei, D is the dose in Gy and c, a, b, are constants. It seems there is a correlation between the yields of MN in mononuclear cells and the corresponding doses of radiation. Therefore an attempt was made to include these MN in the calculation of the dose-response relationship.