Biomarkers of DNA damage in leukocytes

129 Differential effects of theophylline on MMS- and MNNG-induced mutagenesis in V79 hamster cells Cytotoxic and genotoxic effects of methylxanthine theophylline as well as the effects of sublethal concentrations of this drug on toxicity and mutagenicity of MMS and MNNG have been studied using V79 hamster cells. From the results of the mutagenicity test we conclude that theophylline does not possess any significant genotoxic effect. Growth activity of V79 cells was not depressed significantly at concentrations < 0.3 mg/ml; however, we found that sublethal concentrations of theophylline cause inhibition of DNA synthesis probably as a result of inhibition of the process of elongation of short segments of newly synthesized DNA. In contrast to the situation seen in cells affected by theophylline itself, the toxic effects of MMS and MNNG were substantially enhanced in cells pretreated with a sublethal concentration of theophylline over the effect observed in commonly cultured cells. It is noteworthy that in the case of MMS enhanced cytotoxicity was accompanied by reduction and in the case of MNNG by elevation of the mutagenic effect. The diversity of biological effects of theophylline in combination with MMS or MNNG probably consists in: (1) different ways of DNA repair responsible for the level of mutations induced by MMS and MNNG and (2) pleiotropic effects of theophylline on the enzymes having different roles in DNA repair.

33 Sledziewska-G6jska, E., Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw (Poland) The level of GC---, AT transitions induced by methyl methanesulfonate is not affected by adaptive response Most of the GC--* AT transitions induced by alkylating agents are due to the miscoding effect of O6-alkylated DNA-guanine. These mutations are successfully avoided in Escherichia coli cells adapted by low levels of alkylating agents. Induction of adaptive response causes a dramatic de-

crease in the level of GC ~ AT transitions induced by MNNG, MNU or EMS. Our results show that this is not the case with MMS. GC--* AT transitions form only a small fraction of MMS-induced mutations in bacteria proficient in DNA repair. However, in m u t S - or r n u t L ~ strains, deficient in mismatch repair, the level of GC--* AT transitions increases 10 times and those transitions form a major group of mutations induced. In both m u t S - ( m u t L - ) and m u t ÷ strains adaptive response has little or no effect on the level of GC ~ AT transitions. In the control experiments we observed a dramatic decrease in MNNG-induced mutagenesis in adopted cells until they were treated with MMS 5-10 min before a challenging dose of MNNG. This treatment completely abolished the effect of the adaptive response on MNNG-induced mutagenesis.

34 Verhagen, H. 1, W.R. Leeman 1 and G.P. van der Schans 2, l TNO Toxicology and Nutrition Institute, Zeist and 2 TNO Medical Biological Laboratory, Rijswijk (The Netherlands) Biomarkers of DNA damage in leukocytes Interindividual variations in DNA damage may reflect different levels of exposure to genotoxic compounds and hence differences in possibility of tumor development. In the past, biomarkers of DNA damage have been developed which measure, for instance, DNA adducts, point mutations or chromosomal mutations. In addition to differences in exposure, variations among humans exist in susceptibility to tumor development due to (acquired or inherited) host factors such as interindividual differences in DNA repair capacity (DNA-RC). We are currently developing simple methods, potential biomarkers, for the assessment of individual differences in overall DNA damage and its repair in humans. A simple, sensitive and fast immunochemical method to quantify the amount of DNA damage in human white blood cells (WBC) after in vitro exposure to ionizing radiation has been found to be also applicable to detect mutagen-induced