No abstract

The first objective of our study was to analyse whether biomarkers for genotoxic effects (DNA breaks and alkali-labile sites and micronucleus and non-disjunction frequencies) could be fully validated for biomonitoring workers chronically exposed to ionizing radiation (IR). Blood samples of controls and individuals chronically exposed to IR were analysed. The interindividual variation was reduced when the comet data were adjusted for interexperimental variation, but remained statistically significant. No differences were found between groups, either for smoking or for exposure status. The second objective was to determine whether the Comet assay can be used to evaluate global repair phenotype as a susceptibility biomarker for IR-induced DNA damage in nuclear workers. A pilot study was performed and blood from workers exposed or not to radiation was submitted to a challenging dose of gamma-rays. The repair kinetics of each individual donor were analysed by Comet assay at different time points and compared with the frequencies of biomarkers of genotoxic effects. There was a statistically significant interaction between biomarkers assessing the same damage (micronucleus and Comet assays). Multivariate analysis showed that micronucleus frequencies were positively influenced by age and the percentage of residual tail length was negatively influenced by the interaction between smoking and exposure status. The general conclusions from our study are: (i) a positive correlation exists between mechanistically related biomarkers; (ii) multivariate regression analysis confirmed that the interaction between smoking and exposure to IR negatively and statistically significantly influenced residual tail length; (iii) use of the Comet assay for the estimation of global repair phenotype with respect to IR is recommended because it is simple, fast and differences in in vitro repair capacity can be detected.

The aim of the present work was to examine in human lymphocytes, firstly, whether in vitro gamma-rays as compared with X-rays also induce chromatid malsegregation and at higher frequencies than chromosome loss and, secondly, whether the cytokinesis-blocked micronucleus assay combined with fluorescence in situ hybridization might be useful for the biomonitoring of individuals exposed to ionizing radiation. After irradiation, the relative frequencies of centromere-positive micronuclei decreased from 39.2% at 0.1 Gy to 21. 63% at higher doses. There was no statistically significant increase in MNCen+ frequencies at doses below 1 Gy (0.1, 0.25 and 0.5 Gy), but a statistically significant increase at 1 (P < 0.05) and 2 Gy (P < 0.001) was observed for all the donors. No significant differences in baseline and gamma-ray-induced non-disjunction frequencies for chromosomes 1 (P = 0.9) and 17 (P = 0.8) between individuals were detected. For radiation-induced non-disjunction, lower doses (0.1, 0. 25 and 0.5 Gy) of gamma-rays did not induce a statistically significant increase in non-disjunction frequencies whereas 1 Gy and above clearly induced a statistically significant increase in the total non-disjunction frequencies for all the donors (P < 0.05 at 1 Gy and P < 0.0001 at 2 Gy). The aneugenic effect of radiation is less clearly dose dependent at the lower doses, suggesting an apparent threshold below which no change could be demonstrated. At high radiation doses the major mechanism for gamma-ray-induced aneuploidy is related to chromosome loss through non-disjunction, as has been demonstrated using X-rays, and not through the formation of micronuclei.

No abstract

The aim of the present study was to observe the induction and repair of single strand breaks (Ssbs) and double strand breaks (Dsbs) in mesophyll protoplasts of Nicotiana plumbaginifolia, irradiated with UV-C and cultured under light or dark conditions. DNA damage and repair was determined by the neutral and alkaline comet assay to reveal Dsbs and Ssbs respectively.Subculturing protoplasts for 4 h at low temperature was essential to reduce the amount of Dsbs to the detection limit of the assay procedure.Light-cultured protoplasts showed a significant increase of Ssbs and Dsbs compared to dark cultured protoplasts, in which the number of Ssbs and Dsbs remained very constant throughout the experiments.UV treatment significantly enhanced the levels of Ssbs and Dsbs in light and dark cultured protoplasts. On average, equal levels of DNA damage were observed under light or dark conditions. Formulations introduced to evaluate the contribution of UV-C or light treatment in repair kinetics of DNA damage, showed that the number of Ssbs, but not of Dsbs, evolved differently for light and dark cultured protoplasts. DNA repair was more rapidly observed under light conditions and occurred in different repair phases. Observations are discussed in relation to the involvement of chromatin remodelling, photosynthetic active radiation and DNA repair mechanisms.