Analysis of radioprotection and antimutagenic effects of Ilex paraguariensis infusion and its component rutin.

DNA repair pathways, cell cycle checkpoints, and redox protection systems are essential factors for securing genomic stability. The aim of the present study was to analyze the effect of Ilex paraguariensis (Ip) infusion and one of its polyphenolic components rutin on cellular and molecular damage induced by ionizing radiation. Ip is a beverage drank by most inhabitants of Argentina, Paraguay, Southern Brazil, and Uruguay. The yeast Saccharomyces cerevisiae (SC7Klys 2-3) was used as the eukaryotic model. Exponentially growing cells were exposed to gamma rays (γ) in the presence or absence of Ip or rutin. The concentrations used simulated those found in the habitual infusion. Surviving fractions, mutation frequency, and DNA double-strand breaks (DSB) were determined after treatments. A significant increase in surviving fractions after gamma irradiation was observed following combined exposure to γ+R, or γ+Ip. Upon these concomitant treatments, mutation and DSB frequency decreased significantly. In the mutant strain deficient in MEC1, a significant increase in γ sensitivity and a low effect of rutin on γ-induced chromosomal fragmentation was observed. Results were interpreted in the framework of a model of interaction between radiation-induced free radicals, DNA repair pathways, and checkpoint controls, where the DNA damage that induced activation of MEC1 nodal point of the network could be modulated by Ip components including rutin. Furthermore, ionizing radiation-induced redox cascades can be interrupted by rutin potential and other protectors contained in Ip.

Analysis of radioprotection and antimutagenic effects of Ilex paraguariensis infusion and its component rutin

DNA repair pathways, cell cycle checkpoints, and redox protection systems are essential factors for securing genomic stability. The aim of the present study was to analyze the effect of Ilex paraguariensis (Ip) infusion and one of its polyphenolic components rutin on cellular and molecular damage induced by ionizing radiation. Ip is a beverage drank by most inhabitants of Argentina, Paraguay, Southern Brazil, and Uruguay. The yeast Saccharomyces cerevisiae (SC7Klys 2-3) was used as the eukaryotic model. Exponentially growing cells were exposed to gamma rays (γ) in the presence or absence of Ip or rutin. The concentrations used simulated those found in the habitual infusion. Surviving fractions, mutation frequency, and DNA double-strand breaks (DSB) were determined after treatments. A significant increase in surviving fractions after gamma irradiation was observed following combined exposure to γ+R, or γ+Ip. Upon these concomitant treatments, mutation and DSB frequency decreased significantly. In the mutant strain deficient in MEC1, a significant increase in γ sensitivity and a low effect of rutin on γ-induced chromosomal fragmentation was observed. Results were interpreted in the framework of a model of interaction between radiation-induced free radicals, DNA repair pathways, and checkpoint controls, where the DNA damage that induced activation of MEC1 nodal point of the network could be modulated by Ip components including rutin. Furthermore, ionizing radiation-induced redox cascades can be interrupted by rutin potential and other protectors contained in Ip.

Mutagenicity induced by hyperthermia, hot mate infusion, and hot caffeine in Saccharomyces cerevisiae.

Mate, an infusion containing caffeine (3 g/liter), is drunk hot by most Uruguayan, North Argentinian, and South Brazilian people. This beverage has been recently associated with esophageal cancer in Brazil and Uruguay. To test the mutagenic and lethal effects of mate infusion, caffeine, hyperthermia, and their combinations, we used Saccharomyces cerevisiae as an eucaryotic model system measuring lys to LYS reversions. We showed that mate infusion was not mutagenic, whereas caffeine at the same concentration contained in mate, produced a 5-fold increase in the spontaneous mutation rate. The highest observed mutagenic rate corresponded to hyperthermia (54 degrees C at 60 min). Hot caffeine also produced a time-dependent mutagenic effect, whereas hot mate infusion determined a significantly lower mutagenic effect than hot caffeine. The differential lethality produced by the tested agents plays an important role in the expression of the induced mutagenic damage. Caffeine and mate infusion could decrease the mutagenic effect of hyperthermia through the channeling of part of the induced DNA lesions into an error-free repair pathway.

The mutagenic effect of elevated temperatures in yeast is blocked by a previous heat shock.

We have analyzed the mutagenic effect of elevated temperatures (hyperthermia: HT) either upon direct exposure or after a previous heat shock (HS) in the haploid auxotrophic Saccharomyces cerevisiae strain SC7K lys2-3 in the logarithmic phase of growth. We demonstrated a significant antimutagenic effect of HS (38 degrees C for 1 h) followed by hyperthermia (48 degrees C, up to 60 min). Using cycloheximide (CHM) during the HS exposure we reversed the antimutagenic effect. We suggest that, upon HS, the enzymes involved in repair of premutational damage are more resistant to denaturation, i.e., by the induced HSP genes, and could work efficiently to prevent damage fixation in critical targets. CHM blocks the antimutagenic effect of the HS treatment by inhibiting the inducible synthesis of HSP.

Survival of diploid yeast cells to bleomycin in combination with UV-light or hyperthermia.

In the present work we have investigated the possible interaction between Bleomycin (B) and UV light or hyperthermia (HT) in the induction of lethal events in diploid yeast populations in the stationary phase of growth. UV and B acting as single agents determine sigmoid survival curves. The combination of UV + B produces different degrees of sensitization depending on dose ranges. For [B] = 7.5 micrograms/ml combined with different UV fluences an exponential course is observed, suggesting overlapping lesion specificity of the involved repair pathways (excision and recombination). The hyperthermia plus Bleomycin treatment produces different degrees of inactivation depending on the sequences. Maximal inactivation effect was obtained for the sequence B + HT. In the case of HT + B ([B] greater than 7.5 micrograms/ml) the obtained sensitization is lower.

Common repair pathways acting upon U.V.- and X-ray induced damage in diploid cells of Saccharomyces cerevisiae.

Studies on X-ray sensitive mutants of Saccharomyces cerevisiae (Benathen 1973, Benathen and Beam 1977) show that the XS6, XS8 and XS9 genes are not only involved in the repair of X-ray-induced damage but also in the repair of U.V.-induced damage. Analysis of the U.V. sensitivity of multiple xs mutants indicates the participation of three repair pathways which differ from excision repair. Under conditions which can influence repair, such as plating of the U.V.-irradiated cells in the presence of caffeine, followed or not by hyperthermic incubation, the wild type strain shows a diphasic survival curve, consisting of an exponential component for low doses and a sigmoidal one for higher doses. Comparison with the survival curves obtained for the sensitive mutants suggests that the first component of the wild type survival curve corresponds to the inhibition of the XS6 and XS8 gene products while the appearance of a radio-resistant fraction in the population relies on the induction of another repair pathway. A sequential model of repair with two branching points is proposed to explain the results.