We analyzed the antioxidant properties of Ilex paraguariensis infusion (Ip) popularly known as mate (mä'tā), by using two experimental models: the induction of DNA double-strand breaks (DSB) by hydrogen peroxide (H(2)O(2)) and lethality in Saccharomyces cerevisiae, as well as peroxide and lipoxygenase-induced human low-density lipoprotein (LDL) oxidation. Diploid yeast cells were exposed to different concentrations of H(2)O(2) (5-10 mmol/L) in the absence or presence of Ip infusion (10(-1) v/v) or alpha-tocopherol (10(-2) mol/L). Both mate infusion and alpha-tocopherol significantly decreased the dose dependent DSB number, and the lethality induced by H(2)O(2). Peroxynitrite and lipoxygenase-induced human LDL oxidation are inhibited by Ip extracts in a potent, dose-dependent fashion. Dilutions of 5 x 10(-3) v/v provide 50% +/- 10% inhibition. Finally, Ip extracts are potent direct quenchers of the free radical 1,1-diphenyl-2-picrylhydrazyl. Dilutions of 2 x 10(-2) v/v produced quenching of more than 30%, which was comparable to that obtained with 0.5-1 mmol/L alpha-tocopherol or the quercetin aglycone, respectively. For comparison, total polyphenol content of Ip, green, and black tea (Camelia sinensis) were 6.5 +/- 0.8; 1.8 +/- 0.5; and 1.13 +/- 0.3 mmol of quercetin equivalents per liter, respectively. Their respective free radical quenching activities at dilutions of 1 x 10(-1) v/v were 75% +/- 5%; 35% +/- 5%; and 2% +/- 5%. Ip is thus a rich source of polyphenols and has antioxidant properties comparable to those of green tea which merit further in vivo intervention and cross-sectional studies.

In order to analyze the roles of some repair genes in the processing of bleomycin-induced DNA damage and, especially, the interrelationships among the involved repair pathways, we investigated the potentially lethal effect of bleomycin on radiosensitive mutants of Saccharomyces cerevisiae defective in recombination, excision, and R4D6-dependent DNA repair. Using single, double, and triple rad mutants, we analyzed growth kinetics and survival curves as a function of bleomycin concentration. Our results indicate that genes belonging to the three epistasis groups interact in the repair of bleomycin-induced DNA damage to different degrees depending on the concentration of bleomycin. The most important mechanisms involved are recombination and postreplication repair. The initial action of a potentially inducible excision repair gene could provide intermediate substrates for the R4D6-and RAD52-dependent repair processes. Interaction between R4D6 and RADS2 genes was epistatic for low bleomycin concentrations. RA1D3 and RAD52 genes act independently in processing DNA damage induced by high concentrations of bleomycin. The synergistic interaction observed at high concentrations in the triple mutant rad2-6 rad6-1 rad52-1 indicates partial independence of the involved repair pathways, with possible common substrates. On the basis of the present results, we propose a heuristic model of bleomycin-induced DNA damage repair.Bleomycin (BLM) is a radiomimetic glycopeptide antibiotic used extensively in tumor therapy (32,48). This drug binds to DNA and through a free-radical-based mechanism produces DNA base loss and single-and double-strand breaks (43,44). In different lines of eukaryotic cells, BLM produces inhibition of DNA synthesis (10) as well as cell cycle G2 delay (19,38). With phages, bacteria, and yeast cells, it was demonstrated that this drug is recombinogenic and mutagenic (11,23,39,42). Analysis of BLM-induced mutagenesis in repackaged lambda phage suggests SOS repair dependence (33).BLM-induced DNA damage in prokaryotic and eukaryotic cells is partially reparable (3,22,27,40). For human fibroblasts, a long-patch mode of excision repair of BLM-induced damage was recently described (4, 5). Using haploid and diploid radiosensitive strains of Saccharomyces cerevisiae, Moore (22) showed that all rad single mutants sensitive to BLM tested, with the exception of rad1S, are sensitive to X rays. Likewise, BLM-sensitive (blm) mutants exhibit crosssensitivity to ionizing radiation and hydrogen peroxide (26). These results suggest that some aspects of the repair of BLM and ionizing radiation DNA damage in yeast cells may be similar. Furthermore, DNA ligase (the product of the CDC9 gene) is required in the overall process of restoring full-size DNA molecules from DNA fragments produced by BLM (24, 25).We have recently shown that BLM induces at least one error-prone type of repair in S. cerevisiae and that the PS04 (XS9) gene acts as a mutation-triggering factor (39). Furthermore, the combination of UV light and BLM produces di...

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Mutants of the RAD9 gene of Saccharomyces cerevisiae are defective in cell cycle checkpoint arrest in G1 and G2 after treatment with DNA-damaging agents. It is demonstrated that the pronounced G1 arrest observed in yeast after hyperthermia treatment or exposure to paraquat-generated superoxide radicals does not depend on a functional RAD9 gene. For both types of treatments, the mechanism of cell cycle arrest must be considered different from the activation of the DNA damage checkpoint response.