Analysis of oxidative DNA damage and HPRT mutant frequencies in cancer patients before and after radiotherapy.

Various markers of radiation-induced DNA damage including DNA oxidation were investigated in peripheral lymphocytes of 23 cancer patients prior to and one week after receiving radiotherapy with a cumulative dose of 54-70 Gy. Exposure to ionizing radiation nonsignificantly increased the ratio 2'deoxy-7-dihydro-8-oxoguanosine/2'deoxyguanosine (8-oxodG/dG) from 1.73 x 10(-5) to 3.33 x 10(-5). Frequencies of micronuclei significantly (p = 0.0003) increased from 6.4 to 38.9 per 1000 cells. The frequency of hypoxanthine-guanine-phosphoribosyltransferase (HPRT) mutant lymphocytes measured as 6-thioguanine resistant variant cells by 5-bromodeoxyuridine labeling, was elevated eight-fold, from 4.7 x 10(-6) to 36.2 x 10(-6) (p = 0.008) after termination of the radiotherapy, thus showing a clear response to the radiation treatment. No correlation between levels of oxidative DNA damage and frequencies of HPRT mutant lymphocytes or micronuclei could be established.

Oxidative DNA damage and cytogenetic effects in flight engineers exposed to cosmic radiation.

This study set out to analyze biomarkers for genotoxic events, e.g., oxidative DNA damage, chromosomal damage and hprt mutations, among flight personnel, who are known to be occupationally exposed to ionizing radiation of cosmic origin. Twenty-three flight engineers were recruited while ground personnel served as a matched control group. Cumulative radiation doses during flight were calculated on the basis of subjects' flight records assuming an exposure rate of 6 microSv per hour of flight. Oxidative DNA damage in peripheral lymphocytes from flight engineers appeared significantly increased in comparison with controls and was associated with cumulative exposure to cosmic radiation. Frequencies of peripheral lymphocyte chromosome aberrations, micronuclei and hprt mutations appeared also to be increased in flight engineers, but not significantly. It was also observed that DNA damage was higher in flight engineers with a relatively shorter flight history in comparison with flight engineers with higher cumulative exposures to radiation, suggesting adaptation to DNA damage caused by ionizing radiation. DNA repair activities measured as unscheduled DNA synthesis were clearly increased in the higher-exposed subgroup of flight engineers, and appeared significantly correlated with cumulative radiation dose, as well as inversely with oxidative DNA damage. The implications for cancer risk assessment in relation to exposure to cosmic radiation are discussed.

B[a]P-DNA adduct formation and induction of human epithelial lung cell transformation.

In this study we tested the suitability of the human epithelial lung cell line BEAS-2B for in vitro studies of lung carcinogenesis. The human bronchial epithelial lung cell line BEAS-2B, immortalized with an SV-40/Ad-12 hybrid virus construct, was treated for 24 hours with five different concentrations of the lung carcinogen benzo(a)pyrene (B[a]P) to assess the relationship between DNA adduct levels, cell cycle distribution, micronuclei formation (MN), colony forming efficiency (CFE), and anchorage independent growth (AIG). There appeared to be a strong linear correlation between B[a]P concentration and DNA adduct formation, but no difference in cell cycle distribution was observed after incubation with various concentrations of B[a]P. In the incubation range of 4 to 100 nM B[a]P, the number of DNA adducts was linearly correlated with colony formation in AIG and with the number of cells within individual colonies but not the number of colonies in the CFE test. At higher B[a]P concentrations, the clonal expansion of cells in the CFE and the number of colonies in the AIG declined. Also, the number of micronuclei increased with the formation of DNA adducts. It is concluded that after 24 hours of incubation with 100 nM B[a]P, the formation of BPDE-DNA adducts in the human epithelial lung cells BEAS-2B results in maximal induction of cell transformation. Because of this correlation between DNA adduct formation and lung epithelial cell transformation, the BEAS-2B cells seem suitable for in vitro studies on lung carcinogens.