The induction of reciprocal translocations in mouse germ cells by chemicals and ionizing radiations. III. Differential effect of two doses of adriamycin combined with 5 or 9 Gy of gamma-rays

The induction of reciprocal translocations in mouse germ cells by combined treatments with chemicals and ionizing radiations has been studied. Male mice were intraperitoneally injected with doses of 5 or 10 mg/kg of adriamycin (ADR) and irradiated with doses of 5 or 9 Gy of gamma-rays 24 h later. Three types of response were found after analyzing diakinesis-metaphase I multivalent configurations: potentiation, with the dose of 5 mg/kg of ADR plus 9 Gy; subadditivity, with the dose of 5 mg/kg of ADR plus 5 Gy; and additivity, with the dose of 10 mg/kg of ADR plus 5 or 9 Gy. According to these results, the subadditive effect observed with the lower dose of ADR plus 5 Gy cannot be explained under the assumption that depletion of any kind of spermatogonia is sufficient for modifying the chromosomal response of stem cells to ionizing radiations. The role of DNA repair mechanisms modulating the response of spermatogonial cells to combined treatments is discussed under the assumption that some repair mechanisms can be triggered by treatment with a low dose of a chemical and these repair mechanisms can reduce cell mortality. Consequently, a higher frequency of more radioresistant cells can survive.     

The induction of reciprocal translocations in mouse germ cells by chemicals and ionizing radiations. I. Dose-response relationships and combined effects of bleomycin with thio-tepa and gamma-rays

The effect of bleomycin (BLM) on mouse stem cells has been analysed using the spermatocyte test. The dose-response relationships after treatment with doses of 20, 40 and 60 mg/kg of the compound as well as the combined effect of BLM and gamma-rays and BLM and thio-tepa (TT) were studied. A positive, significant correlation between the dose of BLM and the frequency of translocations was found. Two different responses were found when the yields of translocations induced after combined treatments, separated by a lapse of 24 h, were compared with the sum of translocation frequencies induced after the corresponding single treatments: (1) Potentiation, in the treatments with 1 Gy plus 9 Gy and 60 mg/kg of BLM plus 9 Gy; (2) additivity, in the treatments with 60 mg/kg of BLM plus 1 Gy, 1 Gy plus 60 mg/kg of BLM, and 0.2 mg of TT plus 60 mg/kg of BLM. In mice irradiated with 1 Gy plus 9 Gy and mice treated with 60 mg/kg of BLM plus 9 Gy, similar translocation yields were found. The potentiating effect of BLM is similar to that obtained with non-radiomimetic compounds such as triethylenemelamine, cyclophosphamide and adriamycin. These results are discussed taking into account the hypothesis of germ cell selection, and the dose of radiation employed.     

Theoretical models for estimating dose-effect relationships after combined exposure to cytotoxicants

Two classes of dose-effect models for cell killing (additive damage and independent effects) are developed under alternative hypotheses about the damage that leads to cell death. Generalized models, along with specific models for cell killing after exposure to a specific cytotoxicant, are used to make predictions about the effects of sequential or simultaneous exposure to different cytotoxicants. It is demonstrated that with the additive damage models developed one can adequately account for the combined effects of the cytotoxicants considered. Theoretical results are presented which suggest that after simultaneous exposure of cells to low total doses (<0.1 Gy) of different ionizing radiations, use of the conventional relative biological effectiveness approach to predict cell killing risks is unnecessary; cell killing risks can adequately be determined by assuming the effects of the different radiations to be independent. Also, for simultaneous exposure of cells to total doses of different radiations much larger than 0.1 Gy, use of the conventional RBE approach to arrive at cell killing risk could lead to overestimation of the risk.     

Chromosome aberration assays in Pisum for the study of environmental mutagens

From a literature survey, 117 chemicals are tabulated that have been assayed in 179 assays for their clastogenic effects in Pisum. Of the 117 chemicals that have been assayed, 65 are reported at giving a positive reaction (i.e. causing chromosome aberrations), 30 positive with a dose response, five borderline positive. Seventeen chemicals gave a negative response. Eighty-one percent of the chemicals gave a definite positive response. A c-mitotic effect was detected from treatment with 17 chemicals. In addition to the above tabulation of chemicals, 39 chemicals have been reported with an antimitotic effect. Thirteen assays have been recorded for five types of radiation, which with the exception of ultrasound reacted positively. The results of assays with 38 chemicals and/or radiations in combined treatments, as well as 15 chemicals and three types of radiations that induce somatic mutations are tabulated. The Pisum sativum (2n=14) bioassay has been shown to be a very good plant bioassay for assessing chromosome damage both in mitosis and meiosis for somatic mutations induced by chemicals, radiations, and environmental pollutants. For some chemicals, the Pisum assay is not as sensitive in assessing clastogenicity as the Allium assay, although this should be considered in relative terms. Pisum fulvum (2n=14) has been used in clastogenic studies also, but to a much lesser extent.     

Specific-locus mutation response to unequal, 1 + 9 Gy X-ray fractionations at 24-h and 4-day fraction intervals

The specific-locus mutation frequency obtained from mouse spermatogonial stem cells following unequal, 1 + 9 Gy X-ray fractionation with a 24-h fractionation interval is low, and consistent with the two fractions acting additively. The response is therefore markedly different from the augmented mutation frequencies obtained with 500 + 500 R and 100 + 500 R, 24-h fractionations. The lower yield compared with the 100 + 500 R response also indicates a clear difference from the translocation data which demonstrate increases in yield with increasing second dose over the same dose range. The decline in specific locus mutation yield with the increase in the second dose from 500 R to 9 Gy suggests that the stem cells surviving the first fraction are heterogeneous in their sensitivities to this class of genetic damage. A similar, additive specific locus mutation frequency is obtained with unequal, 1 + 9 Gy X-irradiation when the interval between fractions is 4 days. This is consistent with 500 + 500 R, 4-day and 7-day interval responses obtained previously but again differs from the sub-additive translocation responses obtained with such X-ray fractionation. Taken together with the data from previous studies the present results suggest that (1) 24 h after the first fraction, (a) the surviving stem cell have two components; survivors of the formerly radiosensitive, cycling component of the normal stem cell population and the formerly radioresistant, G0 or arrested G1 cells, which are being 'triggered' into a rapid cell cycle to achieve repopulation of the testis; (b) these two components are of near-equal sensitivity to translocation induction and cell killing, hence the additive translocation yields with equal X-ray fractionations and yields consistent with those extrapolated from lower doses with higher, unequal fractionations, e.g. 1 + 7 Gy, 1 + 9 Gy; but (c) the formerly radioresistant, triggered component is much more sensitive than the surviving cycling component to specific locus mutation and cell killing, hence the augmented mutation response with 500 + 500 R fractionation and the drop in yield with 1 + 9 Gy compared with 100 + 500 R X-irradiation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Sequential exposures of mammalian cells to low- and high-LET radiations. II. As a function of cell-cycle stages

The synergistic effects of low- and high-LET radiations were further studied with partially synchronized Chinese hamster V79 cells. Principally, nearly monoenergetic 425 MeV/u neon ions and 570 MeV/u argon ions produced near the Bragg peak were employed as the high-LET radiations and 225 kVp X rays as the low-LET counterpart. It was found that the killing effect due to damage interaction after sequential irradiations with the particle beam and X rays varies throughout the cell cycle. The greatest effect was observed in late-S phase which was most resistant to either of the radiations. The effect was quantitatively less in the G1/S border and in G2. Effects on pure mitotic cells have not been investigated in this study. For all cell stages studied, a dose of high-LET particles modified the shape of the X-ray survival curve in a way similar to the modification predicted by an appropriately selected X-ray dose. This finding suggests that the mechanism for the synergistic effects is similar to that operating for sequential treatments with X rays alone. Experiments with an S population, either incubated at 37 degrees C or room temperature between fractionation of high- and low-LET radiation treatments further verified that the damage involved is a repairable type. At a certain fractionation interval (6 to 8 h) following a dose of high-LET treatment, initially asynchronous cells were found to be very sensitive to X-irradiation. It is noteworthy that the net killing measured at this "radiosensitive window" was as effective as the killing observed by "immediately" sequential treatments with the same doses of high- and low-LET radiations. Such a time window also existed when the order of the treatment sequence was reversed except that the time of occurrence was earlier and the window was broader. This sensitization effect may be explained by radiation-induced G2 arrest together with an increase of radiosensitivity as the previously irradiated cells progress into S phase. Radiotherapy strategies using combined high-LET and low-LET radiations for rapidly proliferative tumors are presented.     

Involvement of mismatch repair proteins in adaptive responses induced by N-methyl-N'-nitro-N-nitrosoguanidine against γ-induced genotoxicity in human cells

As humans are exposed to a variety of chemical agents as well as radiation, health effects of radiation should be evaluated in combination with chemicals. To explore combined genotoxic effects of radiation and chemicals, we examined modulating effects of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), a direct-acting methylating agent, against genotoxicity of γ-radiation. Human lymphoblastoid TK6 cells and its mismatch-deficient derivative, i.e., MT1 cells, were treated with MNNG for 24h before they were exposed to γ-irradiation at a dose of 1.0 Gy, and the resulting genotoxicity was examined. In TK6 cells, the pretreatments with MNNG at low doses suppressed frequencies of the thymidine kinase (TK) gene mutation and micronucleus (MN) formation induced by γ-irradiation and thus the dose responses of TK and MN assays were U-shaped along with the pretreatment doses of MNNG. In contrast, the genotoxic effects of MNNG and γ-irradiation were additive in MT1 cells and the frequencies of TK mutations and MN induction increased along with the doses of MNNG. Apoptosis induced by γ-radiation was suppressed by the pretreatments in TK6 cells, but not in MT1 cells. The expression of p53 was induced and cell cycle was delayed at G2/M phase in TK6, but not in MT1 cells, by the treatments with MNNG. These results suggest that pretreatments of MNNG at low doses suppress genotoxicity of γ-radiation in human cells and also that mismatch repair proteins are involved in the apparent adaptive responses.     

Variability of the adaptive response to ionizing radiations in humans

Human lymphocytes exposed to low doses of ionizing radiations from incorporated tritiated thymidine ([3H]dThd) or from X-rays become less susceptible to the induction of chromatid aberrations by high doses of X-rays. This indicates that low doses of ionizing radiation can produce an effect similar to the adaptive response observed with alkylating agents in prokaryotes, animal and plant cells. To determine whether there is individual variability in the adaptive response to ionizing radiations we exposed human lymphocytes from 18 different healthy donors to 'adapting' doses of [3H]dThd (0.01 microCi/ml) or X-rays (0.01 Gy) and subsequently to a 'challenge' treatment of 0.75 Gy of X-rays delivered 2 h before fixation. Four of the 18 donors did not show an adaptive response; in some cases in these individuals a synergistic response of increased, rather than decreased, damage was found. Two of these 4 donors showed no adaptive response in 3 subsequent experiments separated by 4-month intervals. This suggests that the human population exhibits a heterogeneity in the adaptive response to ionizing radiations which might be, at least in part, genetically determined.     

The accumulation of chromosome aberrations and Dlb-1 mutations in mice with highly fractionated exposure to gamma radiation

The dichotomy between the doses at which experimental measurements of genetic effects can be made and the doses to which people are exposed is often different by two or more orders of magnitude. This presents a significant problem when determining the effects of low doses of radiation or chemicals. The solution has usually involved extrapolating the data by curve-fitting or by applying theoretical considerations. Both approaches are unsatisfactory due to uncertainties of the assumptions used in each process. The alternative solution has been to increase the sample size enormously at the lower doses. This is impractical beyond a certain point due to the variation in the spontaneous frequency and the need to quadruple the sample size for a doubling of precision. The development of new methods for measuring stable genetic effects, however, permits a simple and effective approach to this problem: if the genetic events being detected have no effect on survival, i.e., are selectively neutral, then the effects of multiple independent treatments will be additive. If the independent treatments are identical, then the effect of each is easily calculated by dividing the total effect by the number of treatments. Here we report a limited test of this approach using mice. Chromosome aberrations induced in lymphocytes and Dlb-1 mutations induced in the small intestine were measured after daily doses of 0.64, 1.85 or 5.5 cGy ¹³⁷Cs gamma rays administered for 21, 42 or 63 days. The dose response curve for chromosome translocations obtained in this way, combined with the data from single larger acute doses, shows no evidence for a threshold over a 500-fold dose range. Dlb-1 mutations were increased at each dose and time but the results do not permit reliable extrapolations. The results suggest that translocations might be useful for quantifying the effect of doses below 0.05 cGy and that the effect of dose rate and dose fractionation at much lower doses than reported here could be investigated.     

Detection of ionizing radiations with the SOS Chromotest, a bacterial short-term test for genotoxic agents

The effects of 3 types of ionizing radiation, gamma-rays, neutrons and accelerated alpha-particles, were examined using the SOS Chromotest, a bacterial colorimetric assay for genotoxic agents based on the measurement of the SOS response in Escherichia coli. The SOS Chromotest appeared to be a sensitive and simple assay to detect quantitatively these radiations as well as their biological effects. The range of adsorbed doses for which induction was observed was similar for the 3 types of radiation, the minimum inducing doses being in the order of 2.5-5 Gy. We discuss the possible use of these observations to study the molecular action of radiations and to compare their genotoxic effects with those of chemicals.     

Relationship between radiation induced adaptive response in human fibroblasts and changes in chromatin conformation

Chromatin conformation changes in the normal human fibroblasts VH-10 were studied by the method of anomalous viscosity time dependence (AVTD). Gamma-irradiation of cells in a dose range of 0.1–3 Gy caused an increase in maximal viscosity of cell lysates. Conversely, irradiation of cells with low doses of 0.5 or 2 cGy resulted in a decrease in the AVTD peaks with a maximum effect approximately 40 min after irradiation. The same exposure conditions were used to study a possible adaptive effect of low doses, measured by changes in cell survival. A primary dose of 2 cGy caused significant modification of cell response to a challenge dose. Approximately 20% protection to challenge doses of 0.5 Gy (p < 0.003), 2 Gy (p < 0.02) and 2.5 Gy (p < 0.002) was observed. However, the direction of this effect (adaptation or synergism) was found to be dependent on a challenge dose. The combined effect of 2 cGy and 1 Gy was significantly synergistic, while no modification was observed for 1.5 Gy and 3 Gy. A partial correlation was found between the AVTD changes and cell survival when the combined effect of a primary dose of 2 cGy and challenge dose was examined. The dose of 2 cGy alone increased survival by 16% (p < 0.0003). These results suggest that the low-dose induced effects on survival may be related to chromatin reorganization.     

Distinct response of adult neural stem cells to low versus high dose ionising radiation

Radiosusceptibility is the sensitivity of a biological organism to ionising radiation (IR)-induced carcinogenesis, an outcome of IR exposure relevant following low doses. The tissue response is strongly influenced by the DNA damage response (DDR) activated in stem and progenitor cells. We previously reported that in vivo exposure to 2 Gy X-rays activates apoptosis, proliferation arrest and premature differentiation in neural progenitor cells (transit amplifying cells and neuroblasts) but not in neural stem cells (NSCs) of the largest neurogenic region of the adult brain, the subventricular zone (SVZ). These responses promote adult quiescent NSC (qNSC) activation after 2 Gy. In contrast, neonatal (P5) SVZ neural progenitors continue proliferating and do not activate qNSCs. Significantly, the human and mouse neonatal brain is radiosusceptible.Here, we examine the response of stem and progenitor cells in the SVZ to low IR doses (50–500 mGy). We observe a linear dose-response for apoptosis but, in contrast, proliferation arrest and neuroblast differentiation require a threshold dose of 200 or 500 mGy, respectively. Importantly, qNSCs were not activated at doses below 500 mGy. Thus, full DDR activation in the neural stem cell compartment in vivo necessitates a threshold dose, which can be considered of significance when evaluating IR-induced cancer risk and dose extrapolation.     

Induction of specific locus mutations in mouse spermatogonial stem cells by combined chemical X-ray treatments

Data that demonstrate how the biology of spermatogenesis plays an important role in determining the yield of genetic damage from ionizing radiation are briefly reviewed. It is suggested that for valid extrapolations of data from mouse mutation experiments to man detailed knowledge of the spermatogonial stem cell systems in the two species is required. Two new sets of mouse specific mutation data are presented. (1) When a 2 mg/kg dose of triethylenemelamine (TEM) was used as a conditioning dose and followed 24 h later by 6 Gy X-rays, the mutation yield from spermatogonial stem cells was over twice as high (30.20 X 10(-5)/locus/gamete) as that when the X-ray dose was given alone (13.75 X 10(-5)/locus/gamete). No such effect was found when the TEM was given only 3 h prior to the X-irradiation. Since TEM at the dose used is inefficient at inducing specific-locus mutations, an augmentation of the X-ray response is indicated. It has therefore been concluded that the augmented mutation responses obtained with equal 24 h X-ray fractionations at high doses are attributable to mutation induction by the second dose. The responsive cells would be the formerly resistant component of the stem cell population that had survived the TEM treatment and that had been 'triggered' into a radiosensitive phase by the population depletion. (2) When 2 doses of 500 mg/kg hydroxyurea (HU) were given 3 h apart 3 h prior to 6 Gy X-rays to reduce the numbers of stem cells in the S and G2 phases of the cell cycle exposed to the radiation, the mutation responses was greatly enhanced to a level that is the highest yet recorded per unit X-ray dose (7.10 X 10(-5)/locus/gamete/Gy). No such effect was obtained when the intervals between the HU and X-ray treatments were either shorter (less than 0.5 h) or longer (24 h). It was concluded that X-ray-induced specific-locus mutations derive principally from stem cells in the G1 phase of the cell cycle. The reasons why the X-ray-induced mutation-yields from repopulating stem cells (with a short cell cycle and, hence, short G1 phase) are similar to those from undamaged stem cell populations, in contrast to translocation yields, therefore remains unresolved.     

Interaction of post harvest disease control treatments and gamma irradiation on mangoes

The effects of gamma irradiation and disease control treatments on disease severity and post harvest quality of several mango cultivars were investigated.
In mangoes cv. Kensington Pride, irradiation doses ranging from 300–1200 Gy reduced disease, but the level of control was not commercially acceptable. Hot benomyl immediately followed by irradiation provided effective control of anthracnose (Colletotrichum gloeosporioides) and stem end rot (Dothiorella dominicana) during short-term storage (15 days at 20°C). The effects of the two treatments were additive.
Satisfactory disease control was achieved during long term controlled atmosphere storage when mangoes were treated with hot benomyl followed by prochloraz and then irradiated. Effects of fungicide treatment and irradiation were additive. Fungicide, or irradiation treatments alone, were unsatisfactory.
Irradiation of cv. Kensington Pride at doses in excess of 600 Gy caused unacceptable surface damage (i.e. lenticel spotting, surface discolouration and retardation of degreening) which was particularly severe after long-term controlled atmosphere storage.
In a separate short-term storage trial, several other mango cultivars were assessed. Hot benomyl followed by prochloraz controlled anthracnose on all cultivars and stem end rot on some. Irradiation at 600 Gy contributed only minor improvements to disease control. The severity of surface damage that developed following irradiation and fungicide treatment varied with cultivars.     

The effect of low dose rate on recovery of hemopoietic and stromal progenitor cells in gamma-irradiated mouse bone marrow

Long-term recovery of mouse hemopoietic stem cells (CFU-S and CFU-S per colony), granulocyte-macrophage precursor cells (GM-CFC), and stromal colony-forming units (CFU-F) after doses up to 12.5 Gy was almost complete by 1 year when the dose rate was reduced to 0.0005 Gy/min compared to incomplete recovery after doses up to only 6.5 Gy given at greater than 0.7 Gy/min. This sparing effect of dose rate on long-term hemopoietic recovery is in contrast to the generally reported lack of dependence on dose rate for acute survival of hemopoietic progenitors after doses up to 5 Gy. The present results are compatible with the hypothesis that good recovery of the stroma should be reflected in the long-term recovery of hemopoiesis.     

Quantitative analyses of the induction of chromosome aberrations and sister-chromatid exchanges in human lymphocytes exposed to gamma-rays and mitomycin-C in combination

Most chemicals are S-dependent and are potent inducers of SCE, but do not produce chromosome-type aberrations in the first metaphases after exposure. Ionizing radiation, which is an S-independent agent, produces chromosome-type aberrations, especially dicentrics and rings, but inefficiently produces chromatid-type aberrations. A series of experiments has been performed to investigate whether cytogenetic damage induced by ionizing radiation (gamma-rays) might be assessed separately from that induced by the alkylating chemical, mitomycin C (MMC), when human lymphocytes were exposed to these 2 agents in combination. Whole-blood cultures of human lymphocytes in G0 phase were exposed to gamma-rays and MMC in combination or separately. Cytogenetic analyses were done for both chromosome aberrations (CA), analyzed in cultures incubated for 56 h without BrdUrd, and sister-chromatid exchanges (SCEs) in cultures incubated for 72 h with BrdUrd. The frequency of chromosome-type aberrations (dicentrics and rings) increased with increasing doses of gamma-rays from 0.5 to 4.0 Gy. The dose-response relationships were the same with or without concomitant treatment with MMC (10(-6) M). Although the SCE frequency increased with increasing doses of MMC, the increase was nearly the same as when cells were treated with both MMC and gamma-rays (2 Gy). There was no interaction between MMC and gamma-rays concerning these 2 endpoints.     

Analysis of in vitro chemoprevention of genotoxic damage by phytochemicals, as single agents or as combinations

Cancer chemoprevention with low-dose combinations of bioactive phytochemicals instead of single agents has been suggested to induce less toxicity and improve efficacy. In this study, we selected four plant food-based phytochemicals, viz. chlorogenic acid (CLA), pelargonidin (PEL), resveratrol (RES) and epigallocatechin gallate (EGCG) to evaluate the in vitro chemoprevention of genotoxic damage in HL-60 cells. These agents were tested either individually or as a combination at two concentrations (with a 10-fold difference) against the genotoxins mitomycin C (MMC), diepoxybutane (DEB) and patulin (PAT). Our preliminary ferric reducing antioxidant power (FRAP) assay demonstrated additive effects when PEL, CLA, RES and EGCG were combined. Results of the cytokinesis-block micronucleus test showed significant protection against genotoxic damage induced by PAT, DEB and MMC when CLA, PEL, RES and EGCG were tested individually. This protective effect of the phytochemicals was not concentration-related. Both low- and high-concentration combinations of CLA, PEL, RES and EGCG showed significant reducing effects on the frequencies of micronuclei induced by PAT, DEB and MMC. However, the micronucleus test did not provide indications of additive or synergistic effects with this combination of phytochemicals. In conclusion, the chemo-preventive effects of PEL, CLA, RES and EGCG against genotoxic damage induced by MMC, DEB and PAT are indicative of a 'saturation effect' when higher concentrations and combinations of these phytochemicals are used.     

The F value for chromosome aberrations in atomic bomb survivors does not provide evidence for a primary contribution of neutrons to the dose in Hiroshima.

Brenner and Sachs (Radiat. Res. 140, 134-142, 1994) proposed that the ratio of interchromosomal to intrachromosomal exchanges, termed the F value, can be a cytogenetic fingerprint of exposure to radiations of different linear energy transfer (LET). Using published data, they suggested that F values are over 10 for low-LET radiations and approximately 6 for high-LET radiations. Subsequently, as F values for atomic bomb survivors were reported to be around 6, Brenner suggested that the biological effects of atomic bomb radiation in Hiroshima are due primarily to neutrons. However, the F values used for the survivors were means from individuals exposed to various doses. As the F-value hypothesis predicts a radiation fingerprint at low doses, we analyzed our own data for the survivors in relation to dose. G-banding data for the survivors showed F values varying from 5 to 8 at DS86 doses of 0.2 to 5 Gy in Hiroshima and around 6 in Nagasaki with no evidence of a difference between the two cities. The results are consistent with our in vitro data that the F values are invariably around 6 for X and gamma rays at doses of 0.5 to 2 Gy as well as two types of fission-spectrum neutrons at doses of about 0.2 to 1 Gy. Thus, apart from a possible effect at even lower doses, current data do not provide evidence to support the proposition that the biological effects of atomic bomb radiation in Hiroshima are caused mainly by neutrons.     

The in vivo effects of culture medium. I. Radioprotective effects of vitamins, amino acids and inorganic salts of culture medium in mice.

It has been shown that pretreatment of mice with a five-fold condensed culture medium before irradiation increased the number of multipotential haemopoietic stem cells in the spleen. The degree of cyto- and radioprotection is dependent on both the time of administration and the dose of the culture medium. The administration of culture medium in twofold doses in a volume of 1 ml intraperitoneally 18 h and 8 h before irradiation with a dose of 9 Gy protected 95% of C57Bl/6 mice. On the other hand, no therapeutic effect of different doses of the culture medium was found. Our observation suggests that the culture medium can mediate a radioprotective effect. The possible mechanisms participating in this effect are discussed.     

Assessment of DNA base oxidation and glutathione level in patients with type 2 diabetes

Genetic instability resulting from the disturbances in various mechanisms of DNA-repair is the characteristic feature of cancer cells. One of the possibilities to evaluate the effectiveness of DNA-repair system is the adaptive response (AR) analysis. The AR is a phenomenon by which cells exposed to low, non-genotoxic doses of a mutagen become significantly resistant to a subsequent higher dose of the same or another genotoxic agent. Generally, it is postulated that AR is related to a reduction of damage by the induction of free radical detoxification and/or DNA-repair systems.The existence of various DNA-repair mechanisms poses the question whether there are differences in AR induced by chemicals causing DNA-damage that requires different pathways for its repair. In this paper we present the study on the AR induced by two chemical mutagens, bleomycin (BLM) and mitomycin C (MMC), which differ in their action on DNA. BLM is a radiomimetic agent causing mainly single-strand breaks (SSB) and double-strand breaks (DSB) and, thus, inducing chromosomal aberrations (CA). MMC is a potent bifunctional mutagen acting as an alkylating agent, causing DNA cross-links and inducing sister chromatid exchanges (SCEs).The protective effect induced by low doses of tested chemicals was analysed in whole blood human lymphocytes using cytogenetic endpoints (CA for BLM and SCE for MMC, respectively) as a measure of chromosomal instability. There was a significant difference between the protective effects induced by BLM and MMC in the lymphocytes of the same group of donors. The pre-treatment with a low dose of BLM-induced almost 50% decrease in the frequency of CA induced by challenging dose (CD), while the protective effect of MMC was below 20%. The higher AR induced by BLM may be related to the repair processing of BLM-induced DNA-damages. There was also a variability in ARs among individuals, which may reflect the differences in individual DNA-repair capacity.