Ratio of acentrics to dicentrics in human lymphocytes exposed to X rays and misonidazole

A 0.8 mM concentration of misonidazole was added to human blood samples before exposure to graded X-ray single doses, in order to investigate the dependence of the frequency ratio of acentrics to dicentrics, produced in lymphocytes, on treatment with radiation, the substance and the combination of the 2 agents. The results confirm the findings of a previous experiment carried out using sodium iothalamate, showing that this ratio is markedly influenced by the relative action of the physical and the chemical agents, especially at low radiation doses, because of the enhancement of the frequency of acentrics, and not of dicentrics, caused by the presence of the drug compared to the spontaneous level.     

Chromosome aberrations in human lymphocytes induced by fission neutrons

The dose-response relationships of dicentrics and excess acentrics were analysed after exposure of human lymphocytes to a mixed fission neutron-gamma-ray beam. From the analysis of exclusively first division cells a linear-quadratic relation was obtained for dicentrics with the ratio of linear and quadratic components, zeta, equal to 2.76 Gy. Over the range of doses studied (0.04-1.97 Gy) intratrack events therefore predominated. This also applied to acentrics which were linearly related to dose. At the lowest level of observed effect and dose, r.b.e. values with respect to 60Co gamma-rays of up to about 11 were derived for dicentrics and acentrics. With increasing neutron dose the r.b.e. decreased.     

Application of conventional and FPG staining for the analysis of chromosome aberrations induced by low levels of dose in human lymphocytes

Human peripheral lymphocytes were irradiated with 0.05-0.5 Gy of 220 keV X-rays. After application of either a conventional or the fluorescence plus Giemsa (FPG) staining technique, the dose response for dicentrics and acentrics was studied. The analysis of exclusively first-division cells (M1), carried out by the FPG method, revealed significantly higher aberration yields as compared with the results of the conventional method. The data from M1 cells support the assumption of a linear dose response for both dicentrics and acentrics. The results are discussed with regard to the application of chromosome analyses for a cytogenetic dosimetry after exposure to low levels of ionizing radiation.     

Chromosome alterations in cleanup workers sampled years after the Chernobyl accident

Cytogenetic analysis performed 4-13 years after the Chernobyl accident showed an elevated frequency of acentrics, chromatid exchanges, dicentrics and rings in Chernobyl cleanup workers compared to the control group. Cytogenetic data were analyzed according to the information on exposure to radiation (the year when the cleanup workers worked at the Chernobyl station, doses rates, time elapsed since exposure to radiation, and cytogenetic examination) and some lifestyle factors. The data obtained suggested that some types of chromosome aberrations could be influenced by the action of different environmental factors or lifestyle factors. The frequency of acentrics was correlated with the age of the cleanup workers, and the increased chromatid exchange frequency was attributed to smoking. The numbers of dicentrics and rings suggested a genotoxic effect of ionizing radiation that is still present over 13 years after the exposure.     

The induction of chromosome aberrations during the course of radiation therapy for morbus Hodgkin

In a patient with Morbus Hodgkin, structural aberrations of the chromosome type in peripheral lymphocytes were analyzed during radiation therapy (accumulated target dose 44.6 Gy: 22 fractions of 1.8 Gy each and 2 fractions of 2.5 Gy each at the end of the therapy). The blood was sampled about 5 min after a fraction and/or 24, 48, or 72 h thereafter. The frequency of dicentric chromosomes:acentric fragments:centric ring chromosomes is 37:14:1 throughout the therapy. Independent of the time of blood sampling after a fraction, the distributions of dicentrics and acentrics are overdisperse and represent negative binomial distributions. The yields from these aberrations, as determined during the course of radiotherapy, are best fitted to a linear-quadratic function with a negative quadratic term. The two dose-effect curves (blood sampling about 5 min and 24 to 72 h after a fraction) of dicentrics and acentrics do not differ significantly. Up to an accumulated target dose of about 20 Gy the percentages of cells with chromosome aberrations increase to about 48 to 65% and, at this level, remain constant until the end of therapy.     

Cytogenetic analysis of peripheral blood lymphocytes of occupational workers exposed to low levels of ionising radiation.

The incidence of chromosomal aberrations was analysed in peripheral blood lymphocytes of occupationally exposed people having cumulative doses of 500 mSv. The exposed individuals showed higher frequencies of dicentrics as well as acentrics than normal controls. Absorbed radiation dose was calculated by using in vitro dose response curve established for Cobalt-60 gamma rays. In the control constituting 17 healthy individuals, two dicentrics were detected among 3700 metaphases analysed. In the exposed group 27 dicentrics and one centric ring was detected among 8400 metaphases analysed. Due to small number of dicentrics scored in each individual, the dose estimate suffers from a large statistical uncertainty. The collective dose was found to be 1.89 Gy. This is in good agreement with the corrected physical doses, assuming a mean life of 10 years for the disappearance of lymphocytes. The physical doses accumulated during the last 10 years of occupation were also in good agreement with the biological dose estimate.     

Distribution pattern and dose-response-relationship of chromosome aberrations in human lymphocytes induced in vitro by 60Co gamma-rays and 110 kV X-rays.

Peripheral blood lymphocyte culture system was used to construct reference dose-response curves for 60Co gamma-rays and 110 kV X-ray-induced chromosome aberrations at 6 dose points ranging from 0.25 to 4.0 Gy. Qualitative and quantitative differences between these two types of radiation for the yield of induced aberrations and their distribution pattern were analysed. Experimental data of aberration yields were compared after fitting them to five different dose-response models. The yields of chromosome aberrations in particular dicentrics, gave a good fit to linear-quadratic besides linear and power models. In this model, single-track events predominated over double-track events for both the qualities of radiation used. The pattern of distribution was mainly Poisson for dicentrics but gave a conflicting result for acentrics which was in excess.     

Radiation induced chromosome aberrations and the poisson distribution

Summary Data on the distribution of dicentrics and acentrics observed when human lymphocytes are cultured for 48 h after irradiation by X-rays,-rays, and neutrons are presented. Analysis shows that for dicentrics, the observed distribution for X-rays,-rays, and fission neutrons may be described by Poisson statistics but for higher energy neutrons overdispersion is observed. The phenomenon of overdispersion is also observed for acentrics irrespective of the radiation used. The possibility that overdispersion results from the variations of dose in sensitive sites leads to the conclusion that for dicentrics the site size is considerably larger than the 1–2 µm diameter derived by applying the dual action theory to the dose effect relationships. This larger site may well be the cell nucleus.     

Genotoxic effects of radiotherapy and chemotherapy on the circulating lymphocytes of breast cancer patients. II. Alteration of DNA repair and chromosome radiosensitivity

Lymphocytes from 43 breast cancer patients were tested for their DNA-repair ability and in vitro chromosomal radiosensitivity. Lymphocytes were collected before and after treatment with radiotherapy or chemotherapy or both, and then irradiated in vitro. The aim was to detect alterations of these 2 indicators of radiosensitivity, in relation to cancer status or medical treatment. Patients before treatment were significantly deficient in DNA-repair ability but had a normal chromosomal radiosensitivity as compared to healthy donors. When assessed after treatment, DNA-repair ability and the frequency of in vitro-induced chromosome anomalies were modified according to the type of treatment. A reduced DNA-repair ability was observed for patients after radiotherapy but not after chemotherapy. In vitro-induced dicentrics and acentrics were not modified to the same extent according to the treatment. A decreased number of acentrics (the most frequently observed alteration) was preferentially associated with a more reduced DNA-repair ability. Interindividual differences of response to in vitro irradiation tested by both assays were observed between patients who had undergone similar treatments. The possibility that these assays could be used for predicting individual susceptibility to radiation or chemotherapy drug exposure is discussed.     

Chromosomal damage induced in human lymphocytes by low doses of D-T neutrons

Unstable chromosome aberrations induced by in vitro irradiation with zero plus seven low doses of 14.8 MeV D-T neutrons in the range 3.55-244 mGy have been analysed in human peripheral blood lymphocytes. In order to obtain the required large numbers of scored cells for such low doses, fourteen laboratories participated in the experiment. The dose responses for dicentrics, excess acentrics and total aberrations, fitted well to the Y = alpha D model. The alpha coefficient of yield for dicentrics, 1.60 +/- 0.07 X 10(-2) Gy-1, compares well with the values obtained in previous studies with D-T neutrons at somewhat higher doses. Results from a previous collaborative study using 250 kVp X-rays over a comparable dose range indicated the possible existence of a threshold below 50 mGy. In the present study there is no clear evidence for neutrons for such a threshold. However, the data were insufficient to permit the rejection of a possible threshold below approximately 10 mGy.     

Enhanced frequency of chromosome aberrations in workers occupationally exposed to diagnostic X-rays

To estimate the level of radiation exposure of personnel handling diagnostic X-ray machines, the yield of chromosomal aberrations was analysed in peripheral blood lymphocyte cultures. These occupationally exposed individuals showed higher frequencies of dicentrics as well as acentrics than normal controls. Absorbed radiation doses calculated by extrapolating reference in vitro dose-response curve for dicentrics ranged between 0.13 and 0.17 Gy. This implies exposure beyond the permissible limit of 0.05 Gy/year for the whole body. However, no obvious trend of increased aberrations as a function of either duration of employment or age was noticed. The increase in the aberration yields in this personnel underscores the need of adopting measures to avoid or minimise such overexposure.     

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.     

Effect of storage duration on cell cycle kinetics and yield of chromosomal aberrations in PHA-responsive human peripheral blood lymphocytes.

Phytohaemagglutinin (PHA)-responsive lymphocytes from human peripheral blood samples, either irradiated or un-irradiated, showed increased frequency of first division metaphase cells (detected by fluorescence plus Giemsa (FPG) staining) as a function of duration of storage. Irradiated and subsequently stored samples showed small but significant increase for the yield of dicentrics. The yield of aberrant metaphases and deletions (excess acentrics) remained unchanged. Increasing Bromodeoxyuridine (BrdU) concentrations slowed down the cell cycle progression but did not influence the yield of aberrations including that of dicentrics.     

Results of dynamic cytogenetic study of children and teenagers living in areas, radioactive by contaminated after the Chernobyl accident

Results of multiyear cytogenetic study of children and teenagers living in areas, radioactive by contaminated after Chernobyl accident, were adduced. Mean density of 137Cs contamination in two compared living areas were 111 and 200 kBq/m2 and mean external doses accumulated for 1986-2001 were 6.7 and 11.4 mGy correspondingly. Averaged thyroid doses receives by subjects of all age groups in the second area were approximately 1.5 times higher than in the first area; in the youngest group (0-1 year) the doses were 114.3 and 174.3 mGy. During 17 years cytogenetic investigation approximately from 30% to 60% of examined persons were observed the increased level of chromosome aberrations in lymphocytes of peripheral blood. Average frequency of unstable aberrations (acentrics, dicentrics and centric rings) constituted about 0.4 per 100 cells (0.22 per 100 cells in controls) during all period of observation. Level of marker aberrations (dicentrics and centric rings) was increased almost all times of study and varied within 0.04-0.19 per 100 cell (0.03 in control group). The parallel investigation of frequency of stable aberrations by FISH method showed up their level about 3 times exceeding observed dicentrics level. Comparably higher indexes of cytogenetic disturbances were revealed in group exposed in utero during period of accident.     

The production of chromosome aberration in Chinese hamster fibroblasts exposed to 24 keV neutrons

A filtered reactor beam, consisting mainly of 24 keV neutrons, was used to study the induction of chromosome aberrations in the V79/4(AH1) Chinese hamster cell line. The yields of both dicentrics and acentrics were linear with dose and the value of relative biological effectiveness (RBE) for dicentrics at low doses was 6.5 +/- 1.4. This value was similar to that found previously for a neutron spectrum with mean energy 2.1 MeV, and suggests that the RBE of neutrons does not increase to very high values in the energy region below 100 keV. This result does not support the suggestions of Davy (1969) and Key (1971) that the neutron RBE rises to very high values in the intermediate energy range.     

Cytogenetic effect in peripheral blood lymphocytes of children living in villages in the Ovruch District, Zhitomir Region of the Ukraine contaminated by radionuclides]

For the purpose of genetic indication of low level of chronic radiation exposure the cytogenetic monitoring of some critical children groups living in two contaminated Ukrainian villages was carried out. In all the groups the mean frequency of aberrant cells and chromosome type aberrations (including dicentrics, centric rings, chromosome translocations as well as polyploid cells) significantly exceeded control level. During the repeated examination of children from Vistupovichi (in 13 months after the first one) the striking increase of cytogenetic effect was revealed. Dicentrics and rings were registered in 79% of persons with the individual rate 0.5-1.5 and mean group frequency 0.57 per 100 cells. The authors tried to evaluate the average cumulative doses of radiation for examined groups using G. Littlefield equation for dicentric outcome under the low dose rate Cs-137 source and taking into account the assumption about the reducing of 50% dicentrics per year. According to this rough calculation, the revealed cytogenetic effect can correspond to the mean total dose of 33 cSv for Vistupovichi children.     

Induction of complete and incomplete chromosome aberrations by bleomycin in human lymphocytes

Bleomycin (BLM) is a clastogenic compound, which due to the overdispersion in the cell distribution of induced dicentrics has been compared to the effect of high-LET radiation. Recently, it has been described that in fibroblast derived cell lines BLM induces incomplete chromosome elements more efficiently than any type of ionizing radiation. The objective of the present study was to evaluate in human lymphocytes the induction of dicentrics and incomplete chromosome elements by BLM. Peripheral blood samples have been treated with different concentrations of BLM. Two cytogenetic techniques were applied, fluorescence plus Giemsa (FPG) and FISH using pan-centromeric and pan-telomeric probes. The observed frequency of dicentric equivalents increases linearly with the BLM concentration, and for all BLM concentrations the distribution of dicentric equivalents was overdispersed. In the FISH study the ratio between total incomplete elements and multicentrics was 0.27. The overdispersion in the dicentric cell distribution, and the linear BLM-concentration dependence of dicentrics can be compared to the effect of high-LET radiation, on the contrary the ratio of incomplete elements and multicentrics is similar to the one induced by low-LET radiation (~0.40). The elevated proportion of interstitial deletions in relation to total acentric fragments, higher than any type of ionizing radiation could be a characteristic signature of the clastogenic effect of BLM.     

Chromosome aberrations produced in human lymphocytes by in vivo and in vitro irradiation

The production of chromosome aberrations in vivo has been studied in lymphocytes from a patient undergoing a wholebody treatment with gamma-radiation up to a cumulative dose of 1.4 Gy. These results were compared with the observations performed on whole blood samples irradiated in vitro with doses from 0.05 up to 2 Gy of gamma-rays. The frequency of chromosome aberrations, particularly the dicentrics, was found to be similar in vivo and in vitro. The yield of dicentrics could be best related to the dose by using a linear-quadratic model in both cases, the ratio of the coefficients a/b being of 0.56 and 0.69 Gy, respectively in vivo and in vitro. These observations confirm that in vitro dose response curves may be used to evaluate accurately an in vivo absorbed dose.     

Stable and unstable chromosome aberrations in humans and other mammals in relation to the problems of biological dosimetry

Literature data of long-term cytogenetic follow-up of people exposed to radiation as a results of different radiation accidents are considered for the purpose of discussing of some problems of biological dosimetry. The results obtained for mammals are also presented. Of particular interest is a decrease in the level of dicentrics and symmetrical translocations in peripheral blood lymphocytes with the time after acute exposure depending on the dose of irradiation. The frequency of dicentrics decreases in accordance to the exponential law passing the fast and slow phases of elimination. In different radiation situations the values of the parameter which defines the half-life period of lymphocytes characterizing 50% reduction of cells with dicentrics markedly vary. However a general regularity is a decrease in the parameter value as the exposure dose increases. The level of stable translocations estimates by the EISH method remains relatively constant at doses below 1-2 Gy. At higher doses their level in peripheral blood lymphocytes declines with time due to which the retrospective dose appears to be underestimated. The reasons of such regularity, the role of various factors affecting the scoring of translocations, criteria of analysis of the given chromosome aberrations are discussed in the context of common agreements between leading European laboratories on the use of FISH for improving biological dosimetric estimates.     

The significance of cytogenetic investigation for the estimation of Chernobyl accident consequences

The results of the cytogenetic investigation of people, which were exposed to radiation in the result of the Chernobyl NPP accident, were presented. Also the possibilities of the application of cytogenetic findings for dose estimations and for the prediction of the radiation influence consequences were examined. During the period of time since 1986 till 2004 the cytogenetic investigations of 1724 liquidators participating in the liquidation works after the Chernobyl accident were carried out. The radiation dose estimated by the frequency of dicentrics in 1986 was about 0.16 Gy. The doses for liquidators were determined by the frequency of translocations (FISH method) during the period from 1992 till 1995. For liquidators who worked in Chernobyl only in 1986 the average dose of radiation was about 0.19 Gy and for liquidators who worked repeatedly during the period from 1986 till 1995 - 0.39 Gy. There was shown that during the whole period of investigation (1986-2004) the frequency of dicentrics in peripheral blood lymphocytes was significantly higher than the control level. The cytogenetic investigation of Bryansk region inhabitants which was carried out in 1992-1994 discovered heightened value in 5 times than the control one. Findings are of great importance for the prediction of ill effects of radiation and for the development of sensitive criterions for early exposure disturbances in state of health.