Cell-density dependent effects of low-dose ionizing radiation on E. coli cells

The changes in genome conformational state (GCS) induced by low-dose ionizing radiation in E. coli cells were measured by the method of anomalous viscosity time dependence (AVTD) in cellular lysates. Effects of X-rays at doses 0.1 cGy--1 Gy depended on post-irradiation time. Significant relaxation of DNA loops followed by a decrease in AVTD. The time of maximum relaxation was between 5-80 min depending on the dose of irradiation. U-shaped dose response was observed with increase of AVTD in the range of 0.1-4 Gy and decrease in AVTD at higher doses. No such increase in AVTD was seen upon irradiation of cells at the beginning of cell lysis while the AVTD decrease was the same. Significant differences in the effects of X-rays and gamma-rays at the same doses were observed suggesting a strong dependence of low-dose effects on LET. Effects of 0.01 cGy gamma-rays were studied at different cell densities during irradiation. We show that the radiation-induced changes in GCS lasted longer at higher cell density as compared to lower cell density. Only small amount of cells were hit at this dose and the data suggest cell-to-cell communication in response to low-dose ionizing radiation. This prolonged effect was also observed when cells were irradiated at high cell density and diluted to low cell density immediately after irradiation. These data suggest that cell-to-cell communication occur during irradiation or within 3 min post-irradiation. The cell-density dependent response to low-dose ionizing radiation was compared with previously reported data on exposure of E. coli cells to electromagnetic fields of extremely low frequency and extremely high frequency (millimeter waves). The body of our data show that cells can communicate in response to electromagnetic fields and ionizing radiation, presumably by reemission of secondary photons in infrared-submillimeter frequency range.     

Observations on the effect of X-ray alone and in combination with ultrasound on human chromosomes

Summary Human peripheral blood was treated with ultrasound either before or after irradiation, and chromosome aberrations in lymphocytes of peripheral blood cultures compared to those resulting from an equivalent dose of irradiation given alone.When peripheral blood is sonicated at a high intensity (3 W/cm²) for 10 min after irradiation, there is an increase in aberration frequency as compared to control samples receiving the equivalent radiation dose alone. However, should the blood be sonicated at the same frequency and for the same time period before radiation there is no significant increase in total chromosome aberrations over the irradiated controls. On the contrary a significant decreases occurs in certain classes of aberration.When sonification with a lower intensity (20 mW/cm²) was used in combination with irradiation the reverse effect was noted. Ultrasound administered for 10 min after radiation caused no significant increase in aberrations. On the contrary increasing the period of sonification to one hour resulted in a lowering of all types of aberration, significant in the case of dicentrics and total chromosome aberrations, when compared to irradiation alone. Reversing the order of treatment again resulted in the opposite effect to that achieved with comparable experiments at high intensities of sonification. Ultrasound before radiation did not produce lower breakage rates. Instead, when the period of sonification was increased to one hour, the number of aberrant cells, fragments, and total aberrations rose significantly over controls.It is suggested that sonification produces chemical changes affecting cellular repair systems, which when combined with ionising radiation, results in an increased or decreased repair effect depending on the dose, duration, and order of treatment.Dedicated to Prof. Dr. Felix Mainx on the occasion of his 80th birthday     

Chronic low‐dose radiation inhibits cisplatin‐induced formation of tumorous clones in Drosophila melanogaster wts/ + heterozygotes

Ionizing radiation is one of the most extensively studied carcinogens. In contrast to the detrimental effects of high‐dose radiation in carcinogenesis, the biological effects of low‐dose radiation remains poorly understood. In this study, we introduced adult wts/ + heterozygotes of Drosophila melanogaster as transgenic model organisms to determine the tumorigenic activity of low‐dose radiation. The warts (wts) gene is a tumor suppressor gene in mice and humans that is directly involved in cell cycle regulation. Fruit flies at the first larval stage were subjected to ionizing radiation, and then tumorigenic activity was evaluated as the frequency of observed warts tumorous mosaic clones in adult flies. Low‐dose irradiation alone did not cause tumorigenesis in our system. In combined treatment with a chemical carcinogen, chronic irradiation at 0.2 Gy decreased the frequency of tumorous clones induced by cisplatin. These results suggest that low‐dose radiation alone is not deleterious but beneficial in tumorigenesis induced by a chemical carcinogen.     

A multifactorial study on the relative postradiation changes in various categories of behavioral reactions in rats

The use of the methods of multifactor, orthogonal and composition planning in studying the behavioural disturbances in rats after gamma irradiation with doses of 0.258 to 1.29 C/kg and the application of the proposed method of discrimination of effects by empirical models permitted to establish the informative and adequate dependences of the probability of these disturbances on dose of nonuniform irradiation and the degree of strengthening of the conditioned reflex. It was shown that the effect of radiation decreased, in a discrete manner, the probability of making the first decision by rats in a behavioural task (here we deal with the "dose-response" function). The average time of making the first decision after irradiation was invariable within the dose range under study. Within the range of the studied factors both the value of the dose of whole-body irradiation and the degree of strengthening of the conditioned reflex significantly affected the probability of fulfilling the task by the animals the significance of the radiation dose being several times higher. The effects of the interaction of the two factors, that is, irradiation and the degree of the radiation affection, were insignificant in changing the behavioural reactions under study.     

Combined Effect of Neutron and Proton Radiations on the Growth of Solid Ehrlich Ascites Carcinoma and Remote Effects in Mice

Doklady Biochemistry and Biophysics - The combined effect of the irradiation with a proton pencil scanning beam (PBS) at a total dose of 80 Gy and neutron radiation at a dose of 5 Gy on the growth...     

Dynamics of hybrid dysgenesis frequency in Drosophila melanogaster in controlled terms of protracted radiation exposure

The dynamics of hybrid dysgenesis frequency in F ₁ descendants of two lines of Drosophila melanogaster (lines Santon-s and radius incompletus (ri) brining P-mobile element), which was maintained for 20 generations were under the conditions of chronic radiation with three dose rate (1.2 × 10^?8; 0.3 × 10^?8; 0.12 × 10^?8 Gy/s), have been studied. Gradual changes have been shown in the dose dependences of the hybrid dysgenesis frequency for F ₁ descendants of every 20 generations from parents exposed to radiation. The complicated dynamics of the transitional process of the appearance of gonadal dysgenesis depending on the duration and dose rate of irradiation in ancestors, has been found. The cumulative effect of the prolonged irradiation appears in the form of adaptation at the lowest dose rate of irradiation and at exhaustion at the highest used dose rate. Problem of the transitional process peculiarities, including the hierarchy of protective and adaptive reactions under the conditions of the chronic irradiation has been discussed.     

The effect of prolonged gamma irradiation at a decreasing dose rate on survivability and gene mutation induction in cultured Chinese hamster cells

Continuous gamma irradiation at decreasing dose rate was shown to be less effective than acute exposure with regard to the lethal effect and frequency of mutations of resistance to 6-thioguanine in cultured Chinese hamster cells. The cell population subjected to continuous irradiation was more radioresistant than the intact one. Lethal and genetic effects of continuous irradiation at decreasing dose rate were mainly determined by the contribution of the radiation dose received during the first 24 h of exposure.     

Characteristics of the radiation-induced changes in the content of sterols and squalene in the lymphoid system tissues and erythrocyte membranes of rats

Ionizing radiation causes considerable changes in the content of sterols and squalene in the lymphoid system tissues and erythrocyte membranes which is in accordance with the concept of high radiosensitivity of haemopoietic tissue. The processes of cholesterol conversion to its oxy-derivatives are increased under the effect of radiation. The content of some lipid components in the lymphoid system tissues and erythrocyte membranes is changed depending on the dose and time after irradiation. There is a relationship between the changes in the sterol composition and in the properties of erythrocyte membranes.     

Effects of single gamma-irradiation on the activity of ornithine decarboxylase in the thymus and pulmonary tissue]

In studying the dose (0.1-6 Gy) and time (2 h to 180 days) dependence of ornithine decarboxylase activity, it was found that deviations from the control were more pronounced in the thymus than in the pulmonary tissue. The radiation effect was a function of dose and time after irradiation. A nonmonotonous type of the dose-response curve was observed 7 days after irradiation: the radiation effect with a low dose (0.1 Gy) was opposite to that with sublethal doses (1-6 Gy).     

Combined application of misonidazole and piotron pions on mouse embryos

Mouse embryos on day 8 of gestation were irradiated with negative pions (12.5-100 rad) or 200 kV X-rays (12.5-150 rad). Misonidazole (MISO), a hypoxic cell radiosensitizer, was applied 30 min before exposure. On day 13 the fetuses were examined for lethality, growth retardation and malformation. No significant embryolethal effects were observed after irradiation alone in the dose range of 12.5-100 rad (X-rays or pions). However, MISO alone and in combination with radiation led to high rates of lethality. The frequency of growth retardation was significantly increased at 100 rad and in combined treatments at low radiation doses. MISO and irradiation with 50 rad and more induced complex damages consisting of multiple and severe malformations and growth retardation. The relative biological effectiveness (RBE) for teratogenic effects was 1.6. In conclusion, the combined application of MISO and radiation of different LET revealed a strong enhancing action compared to single treatments. The extent of enhancement depends on both radiation quality and dose.     

The repair of DNA damage induced in human lymphocytes by gamma rays and fast neurons

When Go human lymphocytes are exposed either to gamma-rays or to d(50)-Be neutrons and then immediately incubated in presence of cytosine arabinoside, the frequency of chromosomal aberrations which is normally observed after radiation exposure only is sharply increased. This enhancement of the aberrations, particularly the dicentrics, is, however, less marked when cytosine arabinoside is administered at longer intervals of time after irradiation. For gamma-rays, the treatment with cytosine arabinoside has no effect on the dicentrics yield when given 5 h after irradiation, indicating that the repair is completed within the 5 h after irradiation and that the lesions are not anymore available to produce exchange aberrations. For d(50)-Be neutrons, the time of repair takes approximately 5 h after a dose of 2.0 Gy, whereas it appears to be shorter (3 h) after a dose of 0.5 Gy.     

Radiation-induced bystander effects in the Atlantic salmon (salmo salar L.) following mixed exposure to copper and aluminum combined with low-dose gamma radiation

Very little is known about the combined effects of low doses of heavy metals and radiation. However, such “multiple stressor” exposure is the reality in the environment. In the work reported in this paper, fish were exposed to cobalt 60 gamma irradiation with or without copper or aluminum in the water. Doses of radiation ranged from 4 to 75 mGy delivered over 48 or 6 h. Copper doses ranged from 10 to 80 μg/L for the same time period. The aluminum dose was 250 μg/L. Gills and skin were removed from the fish after exposure and explanted in tissue culture flasks for investigation of bystander effects of the exposures using a stress signal reporter assay, which has been demonstrated to be a sensitive indicator of homeostatic perturbations in cells. The results show complex synergistic interactions of radiation and copper. Gills on the whole produce more toxic bystander signals than skin, but the additivity scores show highly variable results which depend on dose and time of exposure. The impacts of low doses of copper and low doses of radiation are greater than additive, medium levels of copper alone have a similar level of effect of bystander signal toxicity to the low dose. The addition of radiation stress, however, produces clear protective effects in the reporters treated with skin-derived medium. Gill-derived medium from the same fish did not show protective effects. Radiation exposure in the presence of 80 μg/L led to highly variable results, which due to animal variation were not significantly different from the effect of copper alone. The results are stressor type, stressor concentration and time dependent. Clearly co-exposure to radiation and heavy metals does not always lead to simple additive effects.     

Lactate-mediated changes in growth morphology and transformation frequency of irradiated C3H 10T1/2 cells

Treatment of mammalian cells with lactate or inhibitors of glycolysis alters their radiation response, particularly in the low dose region of the dose response curve. The occurrence of both high lactate levels and high glycolytic metabolism in tumours is well known and therefore the effect of lactate on a cell line sensitive to radiation induced transformation was examined using a single exposure to Cobalt 60 gamma rays as the carcinogen challenge. The results indicate that cells treated with 5mM lactate before irradiation exhibit changes in morphology and growth rate and that the transformation frequency is increased by three to ten fold following 24 hours lactate treatment just prior to irradiation. Examination of radiation survival curves showed a positive correlation between transformation frequency and size of the shoulder, but increasing transformation frequency was associated with a decrease in Do. A mechanism involving altered Redox potential in lactate treated cells is suggested. The results are discussed in terms of their possible significance for radiotherapy.     

Radioprotective effect of melatonin assessed by measuring chromosomal damage in mitotic and meiotic cells.

This study was taken to evaluate the radioprotective effects of melatonin. Male adult albino mice were treated (intraperitoneal, i.p.) with 10 mg/kg melatonin either 1 h before or 1/2 h after exposure to 1.5 Gy of gamma-irradiation. Control, melatonin, irradiated and melatonin plus irradiation groups were sacrificed 24 h following treatment. The incidence of micronuclei (MN) in bone marrow cells was determined in all groups. The results show that melatonin caused a significant reduction in micronuclei polychromatic erythrocytes (MNPCE) when animals were treated with melatonin before and not after exposure to radiation. Mitotic and meiotic metaphases were prepared from spermatogonial and primary spermatocytes, respectively. Examination and analysis of metaphases showed no mutagenic effect of melatonin on chromosomal aberration (CA) frequency in spermatogonial chromosomes. Administration of one single dose of melatonin to animals before irradiation lowered total CA from 46 to 32%. However, no significant effect was observed when melatonin was given after irradiation. Similarly, the frequency of CA in meiotic metaphases decreased from 43.5% in the irradiated group to 31.5% in the irradiated group treated with melatonin 1 h before irradiation, but no change was observed when melatonin was administered after irradiation. The data obtained in this study suggest that melatonin administration confers protection against damage inflicted by radiation when given prior to exposure to irradiation and not after, and support the contention that melatonin radioprotection is achieved by its ability as a scavenger for free radicals generated by ionizing radiation.     

Frequency of dominant lethal mutations induced by combined exposure to incorporated 137Cs and external gamma-irradiation in mice

The genetic effect of combined exposure to incorporated 137Cs and external gamma-irradiation was studied in germ cells of male mice. The activity of incorporated 137Cs was 3.7 x 10(4) Bq/g. The dose of external gamma-irradiation was 1.5 Gy. In the case of combined exposure, mice were treated with a cesium solution immediately after irradiation. The genetic effect was estimated by the frequency of dominant lethal mutations (DLM) induced at different stages of spermatogenesis. Upon combined exposure to external and internal irradiation, the frequency of DLM in premeiotic cells significantly exceeded the total frequency of DLM induced by separate exposure to external and internal irradiation; i.e., a marked synergistic interaction of external and internal irradiation was observed.     

Reduced oxygen enhancement ratio at low doses of ionizing radiation

A decreased oxygen enhancement ratio (OER) at lower radiation doses has been previously reported (B. Palcic, J. W. Brosing, and L. D. Skarsgard, Br. J. Cancer 46, 980-984 (1984]. The question remained whether or not this effect is due to a possible oxygen contamination at low doses, which was not the case at high doses. To ensure a sufficient degree of hypoxia prior to the start of irradiation, Chinese hamster cells (CHO) were made hypoxic by gas exchange combined with metabolic consumption of oxygen at 37 degrees C. At the same time oxygen levels in cell suspension were measured using a Clark electrode. It was found that under experimental conditions used in this laboratory for hypoxic irradiations, the oxygen levels before the start of irradiation are always below the levels which could give any significant enhancement to radiation inactivation by X rays. Full survival curves were determined in the dose range 0-30 Gy using the conventional survival assay and in the dose range 0-3 Gy using the low dose survival assay. The results confirmed the earlier finding that the OER decreases at low doses. It is therefore believed that the dose-dependent OER is a true radiobiological phenomenon and not an artifact of the experimental method used in the low dose survival assay.     

Melanin decreases clastogenic effects of ionizing radiation in human and mouse somatic cells and modifies the radioadaptive response

Melanin’s influence on the chromosome aberration frequency induced by radiation in human lymphocytes and mouse bone marrow cells has been studied. We revealed earlier that melanin significantly decreases the frequencies of different radiation-induced mutations in animal germ cells. Melanin protection in somatic cells has been found to be less effective. The melanin effect in somatic cells depends on radiation dose: the lower the damage level, the better the melanin protection. In order to determine the influence of melanin at low radiation doses, the adaptive response was investigated in mouse bone marrow cells in vivo. The level of chromosome aberrations in these cells after fractionated irradiation of 0.2 Gy+1.5 Gy with a 4-h interval was about half that after a single dose of 1.7 Gy. If melanin was injected prior to irradiation, the aberration level decreased by a factor of about two in both cases. This observed result may be due to the potential radioprotective effect of melanin and to the absence of any adaptive response, whereas in the case of melanin application between the priming and challenge doses, the combined effect of the adaptive response as well as melanin protection resulted in a 4-fold decrease of chromosome aberrations. These results allow us to draw the following conclusions: adaptive response can be prevented by a radioprotector such as melanin, and melanin is capable of completely removing low-dose radiation effects. Received: 2 December 1998 / Accepted in revised form: 15 September 1999     

The effect of high energy irradiation on the membrane potential and impulse activity of neurons in the brain of Helix pomatia

In electrophysiological experiments with a preparation of the isolated Helix pomatia brain, a study was made of the effect of pulsed irradiation with high-energy electrons (20 MeV) on membrane potentials and pulse activity of "silent", pacemaking and postsynaptic neurons. It was shown that after irradiation with 150 and 300 Gy (dose rate 5 Gy/s and pulse frequency 50 Hz) "silent" neurons retain their excitability. Pacemaking neurons responded to radiation by a drastic increase in spontaneous pulse activity followed by its transfer to a clipped then to an irregular one. At the same time, the discharge frequency increased in the postsynaptic neurons.     

In vivo synergistic effect of the immunomodulator AS101 and the PKC inducer bryostatin.

The immunomodulator AS101 has recently been found to have radioprotective properties when injected prior to sublethal and lethal doses of irradiation. In addition, this compound was found to protect mice from hemopoietic damage caused by sublethal doses of cyclophosphamide (CYP) and to increase the rate of survival of mice treated with lethal doses of CYP. AS101 was previously shown to exert a synergistic effect with the PKC-inducer bryostatin in cytokine secretion in vitro. The present studies were designed to evaluate the effects of in vivo combined treatment with AS101 and bryostatin on bone marrow and spleen cellularity and on the number of committed progenitors in the bone marrow at various points of time after their treatment with a sublethal dose of CYP or irradiation. In addition, the combined effect was tested on the survival of mice irradiated with a lethal dose of irradiation. Our data show the presence of synergism which greatly enhances the number of bone marrow and spleen cells 48 hr and 9 days after CYP treatment or irradiation. The combined effect was also demonstrated when bone marrow colony-forming units granulocyte-macrophage (CFU-GM) progenitor cells were evaluated. Moreover, AS101 and bryostatin synergized in their protective effects against lethal damages of irradiation. These results strongly suggest that bryostatin, which lacks tumor-promoting activity, is a particularly good candidate in combination with AS101 for treatment in vivo in counteracting chemotherapy- or radiation-induced hematopoietic suppression or in generally improving the restoration of immune response under conditions involving immune or hemopoietic damage.