Relationship between radiation induced dicentric chromosome aberrations and micronucleus formation in human lymphocytes.

Chromosome damage measured by the chromosome aberration technique is a reliable method to assess the radiation dose absorbed by cells. However, this technique has some disadvantages. Scoring is difficult and requires skill and experience which of these lead low number of cell counts. The micronucleus (MN) technique which also measures chromosome losses has easy scoring criteria leading high numbers of cell counts and therefore holds more statistical power. In this study, the relationship between the results of the micronucleus technique and those obtained by the chromosome aberration technique was investigated after radiation doses of 1Gy, 2Gy, 3Gy and 4Gy to peripheral blood lymphocytes of 3 healthy individuals. Increases in the chromosome damage after radiation were observed in both techniques. When the dicentric aberration frequencies that were measured in the chromosome aberration technique and the micronucleus frequencies were compared, no difference (p > 0.05) between these two independent measures of radiation damage was reported. The relationship between the micronuclei and the free acentric chromosome aberrations measured in the chromosome aberration technique was not significant as well as that between the dicentrics and micronuclei. On the basis of the relationship between the dicentric aberrations and the micronucleus frequencies, the micronucleus technique with an easy and short-term application and with an easy scoring can be used as an alternative to the chromosome aberration technique.

The use of chromosome aberrations in predicting breast cancer risk.

In order to assess the usefulness of chromosome aberrations in predicting breast cancer risk, 10 patients with breast cancer diagnosis and appropriately matching 10 healthy controls were chosen. Spontaneous and radiation induced unstable chromosome aberrations in peripheral blood lymphocytes were compared in the two groups. When the spontaneous aberration frequencies were compared, acentric chromosome frequency, scored in the group of patients was significantly higher than that found in the control group (p<0.01). Absolute aberration frequencies as a determinant of radiosensitivity were calculated by subtracting spontaneous aberration frequencies from the frequencies that were obtained following 2 Gy of Co-60 gamma irradiation. Absolute dicentric chromosome frequency significantly increased in the patients1 group (p<0.01) as compared to that observed in the control group. Increases in either spontaneous acentric chromosome frequency or dicentric chromosome frequency as a determinant of an enhanced radiosensitivity in the group of patients may be valuable in predicting breast cancer risk. The studies involving unstable chromosome aberrations can be easily performed and can facilitate cancer diagnosis with minor effort and low cost.

Biological Dosimetry of Co-60 Gamma Irradiation.

Development of radiation technology has resulted in increasing numbers of people working with it. Therefore it has increasingly been important to monitor the radiation in order to ensure public safety. Physical dosimetry plays an important role in monitoring. But a need arise for biological dosimetry where physical dosimetry is absent or its presence is insufficient. In this study Co-60 gamma radiation dose-response curves for chromosome aberrations were determined for use as controls in biological dosimetry. Peripheral blood that were taken from healthy individuals not working with radiation were irradiated at different radiation doses. The relationship between unstable chromosome aberrations in metaphaseblocked cells and radiation dose were drawn by using the linear-quadratic (LQ) formula. The absorbed radiation doses of the test group consisting of five people that had been working with Co-60 teletherapy machines were estimated using the LQ parameters of control dose-response curves in the Qdr method. Estimated radiation doses were below the permissible radiation dose-limits for four workers, but one worker's estimated dose was higher than these limits.

Chromatin structure and cellular radiosensitivity: a comparison of two human tumour cell lines.

The role of variation in susceptibility to DNA damage induction was studied as a determinant for cellular radiosensitivity. Comparison of the radiosensitive HX142 and radioresistant RT112 cell lines previously revealed higher susceptibility to X-ray-induced DNA damage in the sensitive cell line using non-denaturing elution, but not when using alkaline unwinding. The present data also show that no difference in the amount of initial damage is seen when pulsed-field gel electrophoresis (PFGE) or comet analysis are used for DNA damage assessment. However, using the halo assay or a modified version of PFGE in which the higher DNA architecture remained partially intact, the radiosensitive cells showed steeper dose-response curves for initial DNA damage than the radioresistant cells. Analysis of the protein composition, of DNA-nucleoid structures revealed substantial differences when isolated from HX142 or RT112 cells. From our data, it is concluded that HX142 and RT112 differ in their structural organization of chromatin. As no differences in the kinetics of DNA damage rejoining were found, it is hypothesized that the same amount of lesions have a different impact in the two cell lines in that the 'presentation' of DNA damage alters the ratio of repairable to non-repairable DNA damage.

Glutathione determination by the Tietze enzymatic recycling assay and its relationship to cellular radiation response.

Large fluctuations in glutathione content were observed on a daily basis using the Tietze enzyme recycling assay in a panel of six human cell lines of varying radiosensitivity. Glutathione content tended to increase to a maximum during exponential cell proliferation, and then decreased at different rates as the cells approached plateau phase. By reference to high-performance liquid chromatography and flow cytometry of the fluorescent bimane derivative we were able to verify that these changes were real. However, the Tietze assay was occasionally unable to detect glutathione in two of our cell lines (MGH-U1 and AT5BIVA), although the other methods indicated its presence. The existence of an inhibitory activity responsible for these anomalies was confirmed through spiking our samples with known amounts of glutathione. We were unable to detect a direct relationship between cellular glutathione concentration and aerobic radiosensitivity in our panel of cell lines.

Glutathione manipulation and the radiosensitivity of human tumour and fibroblast cell lines.

We have studied the role of glutathione (GSH) in determining radiation response in five human tumour and one human fibroblast cell line. GSH concentration was measured using the Tietze assay and compared with clonogenic survival following gamma-irradiation. No relationship between GSH concentration and aerobic radiosensitivity was observed. The addition of 10 mM extracellular cysteamine produced protection factors in all cell lines, ranging from 1.6 to 2.1, but had little influence on cellular GSH concentration. Depletion of GSH by buthionine sulphoximine (0.1 mM for 18 h) had negligible effect on cell survival, though moderate radiosensitization resulted from extreme GSH depletion after 30-min treatment with 1 mM dimethylfumarate. The degree of aerobic sensitization did not correlate with GSH levels. Irradiation under hypoxia produced oxygen enhancement ratios varying from 1.6 to 2.6, with no relationship to GSH content.