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EN
A report is presented on the advantages of the rapid interphase chromosome assay (RICA) and the difficulties that may be met while implementing this method for application in biological dosimetry. The RICA test can be applied on unstimulated human lymphocytes; this is an advantage in comparison with the dicentric chromosomes or micronucleus tests. In the former two tests, stimulated lymphocytes are examined and hence, 48 h more are needed to obtain cells traversing the cell cycle. Due to the use of unstimulated nondividing cells, higher numbers of cells are available for RICA analysis than for dicentric chromosomes or micronuclei tests. Moreover, the method can be applied after exposure to ionizing radiation doses in excess of 5 Gy. Such doses cause a significant cell cycle delay or result in the loss of G2 phase and mitotic cells because of apoptosis. Therefore, the traditional biodosimetry based on the evaluation of the incidence of damage to chromosomes is very difficult to carry out. This is due to the lack of an adequate number of mitotic cells for analysis. RICA is free of this disadvantage. An automatic microscope can be used to retrieve cell images; automatic image analysis can also be used.
EN
Sirtuins (type III histone deacetylases) are an important member of a group of enzymes that modify chromatin conformation. We investigated the role of sirtuin inhibitor, GPI 19015, in double strand break (DSB) repair in CHO-K1 wt and xrs-6 mutant cells. The latter is defective in DNA-dependent protein kinase (DNA-PK)-mediated non-homologous end-joining (D-NHEJ). DSB were estimated by the neutral comet assay and histone γH2AX foci formation. We observed a weaker effect of GPI 19015 treatment on the repair kinetics in CHO wt cells than in xrs6. In the latter cells the increase in DNA repair rate was most pronounced in G1 phase and practically absent in S and G2 cell cycle phases. The decrease in the number of histone γH2AX foci was faster in xrs6 than in CHO-K1 cells. The altered repair rate did not affect survival of X-irradiated cells. Since in G1 xrs6 cells DNA-PK-dependent non-homologous end-joining, D-NHEJ, does not operate, these results indicate that inhibition of sirtuins modulates DNA-PK-independent (backup) non-homologous end-joining, B-NHEJ, to a greater extent than the other DSB repair system, D-NHEJ.
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