Does single-dose cell resistance to the radio-mimetic zeocin correlate with a zeocin-induced adaptive response in Chlamydomonas reinhardtii strains?

DNA susceptibility of Saccharomyces cerevisiae to Zeocin depends on the growth phase

The aim of this study was to evaluate the level of Zeocin-induced double-strand breaks (DSBs) in Saccharomyces cerevisiae cells in a different growth phase, using constant-field gel electrophoresis (CFGE). Saccharomyces cerevisiae diploid strain D7ts1 with enhanced cellular permeability was used. The effects of growth phase and treatment time were evaluated based on Zeocin-induced DSBs, measured by CFGE. Survival assay was also applied. No protoplast isolation was necessary for the detection of DSBs in strain D7ts1. Differences in the response of cells depending on the growth phase were obtained. Cells in exponential growth phase had increased DSB levels only after Zeocin treatment with concentrations equal or higher than 200 μgml^-1. Increasing treatment time did not result in higher DSB levels. Oppositely, treatment of cells at the beginning of stationary phase with Zeocin concentrations resulted in more than 1.5-fold increase in DSB levels in comparison with those in untreated cells. Increased DSB levels were measured for all the treatment times. A dose-dependent decrease in cell survival was observed after Zeocin treatment with concentrations in the range of lethality LD₂₀-LD₅₀. A strong negative correlation was calculated between the levels of DSBs and cell survival. New information is provided concerning DNA susceptibility depending on the growth phase. DNA susceptibility is higher in cells at the beginning of stationary phase than those in exponential phase. Data presented here illustrate that the optimized by us CFGE protocol is sensitive and could be used successfully for DSB measurement in Saccharomyces cerevisiae strains with enhanced cellular permeability.

Lilium compounds kaempferol and jatropham can modulate cytotoxic and genotoxic effects of radiomimetic zeocin in plants and human lymphocytes In vitro

Organisms are constantly exposed to the detrimental effect of environmental DNA-damaging agents. The harmful effects of environmental genotoxins could be decreased in a viable way by antimutagenesis. One of the modern approaches to reduce the mutagenic burden is based on exogenous natural and synthetic compounds that possess protective and antimutagenic potential against genotoxins. The natural compounds kaempferol and jatropham isolated from Lilium candidum were tested with respect to their potential to protect cells against the radiomimetic zeocin, as well as to their cytotoxic and genotoxic activities in two types of experimental eukaryotic test systems: Hordeum vulgare and human lymphocytes in vitro. Mitotic index (MI) was used as an endpoint for cytotoxicity; the frequency of chromosome aberrations (MwA) and the number of induced micronuclei (MN), as endpoints for genotoxicity/clastogenicity. Formation of aberration "hot spots" was also used as an indicator for genotoxicity in H. vulgare. Both kaempferol and jatropham were shown to possess a potential to modulate and decrease the cytotoxic and genotoxic/clastogenic effect of zeocin depending on the experimental design and the test system. Our data could be useful for health research programs, particularly in clarifying the pharmacological potential and activity of natural plant compounds. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 751-764, 2016.

Ionizing radiation-induced adaptive response in fibroblasts under both monolayer and 3-dimensional conditions

To observe the adaptive response (AR) induced by ionizing radiation in human fibroblasts under monolayer and 3-dimensional (3-D) condition. Three kinds of fibroblasts were cultured under both monolayer and 3-D condition. Immunofluorescent staining was used to detect the γ-H2AX foci and the morphological texture. Trypan blue staining was used to detect the cell death. Western blot was used to detect the expressions of γ-H2AX, p53 and CDKN1A/p21 (p21). We found that DNA damage increased in a dose-dependent and time-dependent manner after high doses of radiation. When cells were pretreated with a priming low dose of radiation followed by high dose radiation, DNA damage was attenuated under both monolayer and 3-D condition, and the adaptive response (AR) was induced. Additionally, the morphology of cells under monolayer and 3-D conditions were different, and radiation also induced AR according to morphological texture analysis. Priming low dose radiation induced AR both under monolayer and 3-D condition. Interestingly, 3-D microenvironment made cells more sensitive to radiation. The expression of p53 and p21 was changed and indicated that they might participate in the regulation of AR.

Antioxidant, antimutagenic, and anticarcinogenic effects of Papaver rhoeas L. extract on Saccharomyces cerevisiae

The aim of this work was to analyze the antioxidant and antimutagenic/anticarcinogenic capacity of Papaver rhoeas L. water extract against standard mutagen/carcinogen methyl methanesulfonate (MMS) and radiomimetic zeocin (Zeo) on a test system Saccharomyces cerevisiae. The following assays were used: 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, quantitative determination of superoxide anion (antireactive oxygen species [antiROS test]), DNA topology assay, D7ts1 test--for antimutagenic--and Ty1 transposition test--for anticarcinogenic effects. Strong pro-oxidative capacity of Zeo was shown to correlate with its well-expressed mutagenic and carcinogenic properties. The mutagenic and carcinogenic effects of MMS were also confirmed. Our data concerning the antioxidant activity of P. rhoeas L. extract revealed that concentration corresponding to IC(50) in the DPPH assay possessed the highest antioxidant activity in the antiROS biological assay. It was also observed that a concentration with 50% scavenging activity expressed the most pronounced antimutagenic properties decreasing Zeo-induced gene conversion twofold, reverse mutation fivefold, and total aberrations fourfold. The same concentration possessed well-expressed anticarcinogenic properties measured as reduction of MMS-induced Ty1 transposition rate fivefold and fourfold when Zeo was used as an inductor. Based on the well-expressed antioxidant, antimutagenic, and anticarcinogenic properties obtained in this work, the P. rhoeas L. extract could be recommended for further investigations and possible use as a food additive.

Antioxidant and HSP70B responses in Chlamydomonas reinhardtii genotypes with different resistance to oxidative stress

Today, the information from model species that differ in their resistance to oxidative stress and the determination of suitable plant markers for screening stress-resistant genotypes are essential for better understanding of plant stress responses and for selection. Here we aimed to assess the differences in antioxidant and HSP70B responses to paraquat treatment between genotypes susceptible and resistant to oxidative stress. Four genotypes of Chlamydomonas reinhardtii were chosen as a model of plant cells: two susceptible genotypes: wild type and paraquat-sensitive; and two paraquat-resistant genotypes: with high and moderate resistance. Varying responses to paraquat treatment were found depending on the genotype and paraquat concentrations. High paraquat concentrations (>50μM) were shown to be very stressful for all C. reinhardtii genotypes, leading to inhibition of enzyme activity. Only the paraquat-sensitive genotype responded to low-level paraquat treatment with a marked enhancement of SOD, CAT, GST activities. The lack of statistically significant response measured as SOD, CAT, GST activities in WT and resistant genotypes could be considered as an indication of absence of strong oxidative stress. This could relate to higher levels of endogenous SOD and CAT activities characteristic of moderately and highly paraquat-resistant genotypes. The response to lower paraquat concentrations evaluated as HSP70B accumulation was proportional to the level of genotype susceptibility to PQ. New evidence is provided that low-level oxidative stress impacts the antioxidant and HSP70B responses differently depending on the genotype resistance. In light of the still unresolved challenge for identification of reliable characters for screening of genotype resistance/susceptibility to oxidative stress, our study demonstrates that HSP70B accumulation could be used as an early marker for induced oxidative stress in the studied genotypes. The obtained results that the most pronounced differences in the antioxidant and HSP70B response were found between the two susceptible genotypes provoke us to convey future experiments with other susceptible genotypes.

Extract of Lillium candidum L. can modulate the genotoxicity of the antibiotic zeocin

Lilium candidum L. extract (LE) is well known in folk medicine for the treatment of burns, ulcers, inflammations and for healing wounds. This work aims to clarify whether the genotoxic potential of the radiomimetic antibiotic zeocin (Zeo) could be modulated by LE. Our results indicate that LE exerts no cytotoxic, DNA-damaging and clastogenic activity in in Chlamydomonas reinhardtii, Pisum sativum L. and Hordeum vulgare L. test systems over a broad concentration range. Weak but statistically significant clastogenic effects due to the induction of micronuclei and chromosome aberrations have been observed in H. vulgare L. after treatment with 200 and 300 μg/mL LE. To discriminate protective from adverse action of LE different experimental designs have been used. Our results demonstrate that the treatment with mixtures of LE and Zeo causes an increase in the level of DNA damage, micronuclei and "metaphases with chromatid aberrations" (MwA). Clear evidence has been also obtained indicating that pretreatment with LE given 4 h before the treatment with Zeo accelerates the rejoining kinetics of Zeo-induced DNA damage in P. sativum L. and C. reinhardtii, and can decrease clastogenic effect of Zeo measured as frequencies of micronuclei and MwA in H. vulgare L. Here, we show for the first time that LE can modulate the genotoxic effects of zeocin. The molecular mode of action strongly depends on the experimental design and varies from synergistic to protective effect (adaptive response-AR). Our results also revealed that LE-induced AR to zeocin involves up-regulation of DSB rejoining in C. reinhardtii and P. sativum L. cells.

Role of nuclear factor-kappaB and P53 in radioadaptive response in Chang live cells

Understanding the mechanism governing radioadaptive response (RAR) has important implication for cancer risk assessment of a low-dose radiation (LDR). However the related knowledge especially the key gene of RAR is still limited. In this study, Chang liver cells were irradiated with a priming dose of 0.016 Gy, 0.08 Gy, or 0.16 Gy of gamma-rays, and with 4 h interval, they were irradiated again with a challenging dose of 2 Gy or 3 Gy. It was found that only 0.08 Gy, but not 0.016 Gy or 0.16 Gy, induced RAR of micronuclei induction to the challenging irradiation. This RAR could be slightly reduced by pifithrin-alpha, an inhibitor of P53, however it was completely suppressed by BAY11-7082, an inhibitor of nuclear factor-kappaB (NF-kappaB). Further assays using western blotting and luciferase reporter gene found that nuclear NF-kappaB and its activity could be triggered by the priming irradiation of 0.08 Gy so that the expressions of them in the primed cells were higher than those in the cells exposed to the challenging dose alone. In contrast, LDR neither influenced the expressions of both P53 and phospho-P53 (ser15) nor enhanced P53 activity; the expression of phospho-P53 and the activity of P53 in the primed cells were lower than that in the non-primly challenged cells. Our results demonstrate that the induction of RAR relays on an optimum priming irradiation dose and it is NF-kappaB rather than P53 that contributes to RAR.