Protective effects of vitamins and selenium compounds in yeast

Effect of Selenium on the Growth and Lipid Accumulation of Yarrowia lipolytica Yeast

Nowadays, there is an increase attention on the effect of selenium (Se) on metabolic processes of microorganisms. Strains belonging to the genus of Yarrowia are of great biotechnological interest for various industries. In this study, we evaluated the effect of 10 mg/L of Se on the growth and lipid production of two Yarrowia lipolytica strains: the ACA DC 50109 and one more with increased oleagenicity, derived after ALE methodology (referred here as Y. lipolytica ALE_70). The presence of Se in the growth medium negatively affected both cell mass production and total lipid accumulation, for both Y. lipolytica strains. Fractionation of total lipids showed an inhibition on neutral lipid (NL) synthesis and consequently, an increase of polar lipids (glycolipids plus sphingolipids, and phospholipids) on the lipids of the Se-enriched ACA DC 50109 strain; however, the NL/polar ratio of the Se-enriched ALE_70 indicated that Se, apart from the inhibition of NL synthesis, provoked also the accumulation of polar lipids in this strain. In addition, the fatty acid (FA) composition was differently affected by Se. Se-enriched total lipids of the ALE_70 strain were enriched in linoleic acid (C18:2 n-6), which resulted in increase of the unsaturated index. On the other hand, Se-enriched lipids of the ACA DC 50109 strain were more saturated, as the percentage of palmitic (C16:0) and stearic (C18:0) acids increased in the total FAs. Moreover, it seems that Se influenced the activity or the expression of desaturases and elongase in both strains. Finally, the supplementation of growth medium with Se affected cell morphology, as well as the size and distribution of lipid droplets inside the yeast cells. According to our opinion, Se caused stress conditions and the consequence of that was the occurrence of metabolic disorders that affected cell mass, lipid content, and/or morphological structures. The results of the present study suggest that further research should be carried out to understand the background of the lipogenesis process in yeast cells cultured under stress conditions.

Utility of Galleria mellonella larvae for evaluating nanoparticle toxicology

The use of nanoparticles in consumer products is currently on the rise, so it is important to have reliable methods to predict any associated toxicity effects. Traditional in vitro assays fail to mimic true physiological responses of living organisms against nanoparticles whereas murine in vivo models are costly and ethically controversial. For these reasons, this study aimed to evaluate the efficacy of Galleria mellonella as an alternative, non-rodent in vivo model for examining nanoparticle toxicity. Silver, selenium, and functionalized gold nanoparticles were synthesized, and their toxicity was assessed in G. mellonella larvae. The degree of acute toxicity effects caused by each type of NP was efficiently detected by an array of indicators within the larvae: LD₅₀ calculation, hemocyte proliferation, NP distribution, behavioral changes, and histological alterations. G. mellonella larvae are proposed as a nanotoxicological model that can be used as a bridge between in vitro and in vivo murine assays in order to obtain better predictions of NP toxicity.

Effect of selenium on growth and antioxidative system of yeast cells

Selenium exhibits health-promoting properties in humans and animals. Therefore, the development of selenium-enriched dietary supplements has been growing worldwide. However, it may also exhibit toxicity at higher concentrations, causing increased oxidative stress. Different species of yeasts may exhibit different tolerances toward selenium. Therefore, in this study, we aimed to determine the effect of selenium on growth and on the antioxidative system in Candida utilis ATCC 9950 and Saccharomyces cerevisiae ATCC MYA-2200 yeast cells. The results of this study have demonstrated that high doses of selenium causes oxidative stress in yeasts, thereby increasing the process of lipid peroxidation. In addition, we obtained an increased level of GSSG from aqueous solutions of yeast biomass grown with selenium supplementation (40-60 mg/L). Increased levels of selenium in aqueous solutions resulted in an increase in the activity of antioxidant enzymes, including glutathione peroxidase and glutathione reductase. These results should encourage future research on the possibility of a thorough understanding of antioxidant system functioning in yeast cells.

A Case-Control Study of the Risk of Cutaneous Melanoma Associated with Three Selenium Exposure Indicators

Aims and background

A direct association between exposure to the metalloid selenium and risk of cutaneous melanoma has been suggested by some observational and experimental cohort studies, whereas other studies have yielded inconsistent results. Since some of the inconsistencies may be due to exposure misclassification arising from the use of exposure indicators that do not adequately reflect body tissue selenium content or the levels of the biologically relevant species of this metalloid, we examined this issue using multiple indicators of exposure.

Methods

We analyzed the relation of selenium exposure with risk of cutaneous melanoma using two different biomarkers, plasma and toenail selenium concentration, and estimated dietary selenium intake in a population-based case-control series (54 cases, 56 controls) from an Italian community.

Results

In unmatched and matched logistic regression models as well as nonparametric generalized additive models, higher plasma selenium levels were strongly associated with excess disease risk. In contrast, toenail and dietary selenium exhibited little relation with melanoma risk. The pattern of correlation among indicators of exposure differed by disease status, with dietary intake associated with plasma selenium levels in patients but not in controls.

Conclusions

Our data showed that different selenium exposure indicators can yield different inferences about melanoma risk. Although the series was small, our results are consistent with a positive association between circulating levels of selenium and melanoma risk. Further investigation of the exposure classification performance of various selenium biomarkers and of metabolic patterns of the metalloid and of its speciation are needed to help elucidate the relation between selenium exposure and human health.

Selenium and Cancer Stem Cells

Selenium (Se) is an essential micronutrient that functions as "redox gatekeeper" and homeostasis factor of normal and cancer cells. Epidemiology and experimental studies, in the last years suggested that both inorganic and organic forms of Se may have favorable health effects. In this regard, a protective action of Se on cellular systems that may help preventing cancer cell differentiation has been demonstrated, while the hypothesis that Se compounds may cure cancer and its metastatic diffusion appears speculative and is still a matter of investigation. Indeed, the overall actions of Se compounds in carcinogenesis are controversial. The recognition that cancer is a stem cell disease instigated major paradigm shifts in our basic understanding of cancer and attracted a great deal of interest. Although current treatment approaches in cancer are grounded in the need to kill the majority of cancer cells, targeting cancer stem cells (CSCs) may hold great potential in improving cancer treatment. In this respect, Se compounds have been demonstrated modulating numerous signaling pathways involved in CSC biology and these findings are now stimulating further research on optimal Se concentrations, most effective and cancer-specific Se compounds, and inherent pathways involved in redox and metabolic regulation of CSCs. In this review, we summarize the current knowledge about the effects of Se compounds on CSCs, by focusing on redox-dependent pathways and main gene regulation checkpoints that affect self-renewal, differentiation, and migration responses in this subpopulation of cancer cells.

Effect of selenium on growth and antioxidant enzyme activities of wine related yeasts

The use of supplements in the diet is a common practice to address nutritional deficiencies. Selenium is an essential micronutrient with an antioxidant and anti-carcinogenic role in human and animal health. There is increasing interest in developing nutritional supplements such as yeast cells enriched with selenium. The possibility of producing beverages, namely wine, with selenium-enriched yeasts, led us to investigate the selenium tolerance of six wine related yeasts. The production of such cells may hamper selenium toxicity problems. Above certain concentrations selenium can be toxic inducing oxidative stress and yeast species can show different tolerance. This work aimed at studying selenium tolerance of a diversity of wine related yeasts, thus antioxidant response mechanisms with different concentrations of sodium selenite were evaluated. Viability assays demonstrated that the yeast Torulaspora delbrueckii showed the highest tolerance for the tested levels of 100 µg mL(-1) of sodium selenite. The evaluation of antioxidative enzyme activities showed the best performance for concentrations of 250 and 100 µg mL(-1), respectively for the yeast species Saccharomyces cerevisiae and Hanseniaspora guilliermondii. These results encourage future studies on the possibility to use pre-enriched yeast cells as selenium supplement in wine production.

Heavy Metals and Human Health: Mechanistic Insight into Toxicity and Counter Defense System of Antioxidants

Heavy metals, which have widespread environmental distribution and originate from natural and anthropogenic sources, are common environmental pollutants. In recent decades, their contamination has increased dramatically because of continuous discharge in sewage and untreated industrial effluents. Because they are non-degradable, they persist in the environment; accordingly, they have received a great deal of attention owing to their potential health and environmental risks. Although the toxic effects of metals depend on the forms and routes of exposure, interruptions of intracellular homeostasis include damage to lipids, proteins, enzymes and DNA via the production of free radicals. Following exposure to heavy metals, their metabolism and subsequent excretion from the body depends on the presence of antioxidants (glutathione, α-tocopherol, ascorbate, etc.) associated with the quenching of free radicals by suspending the activity of enzymes (catalase, peroxidase, and superoxide dismutase). Therefore, this review was written to provide a deep understanding of the mechanisms involved in eliciting their toxicity in order to highlight the necessity for development of strategies to decrease exposure to these metals, as well as to identify substances that contribute significantly to overcome their hazardous effects within the body of living organisms.

Selenium and Human Health: Witnessing a Copernican Revolution?

In humans, selenium was hypothesized to lower the risk of several chronic diseases, mainly due to the antioxidant activity of selenium-containing proteins. Recent epidemiologic and laboratory studies, however, are changing our perception of the biological effects of this nutritionally essential trace element. We reviewed the most recent epidemiologic and biochemical literature on selenium, synthesizing the findings from these studies into a unifying view. Randomized trials have shown that selenium did not protect against cancer and other chronic diseases, but even increased the risk of specific neoplasms such as advanced prostate cancer and skin cancer, in addition to type 2 diabetes. Biochemical studies indicate that selenium may exert a broad pattern of toxic effects at unexpectedly low concentrations. Furthermore, its upregulation of antioxidant proteins (selenium-dependent and selenium-independent) may be a manifestation of self-induced oxidative stress. In conclusion, toxic effects of selenium species occur at lower concentrations than previously believed. Those effects may include a large range of proteomic changes and adverse health effects in humans. Since the effects of environmental exposure to this element on human health still remain partially unknown, but are potentially serious, the toxicity of selenium exposure should be further investigated and considered as a public health priority.

Tolerance of pentose utilising yeast to hydrogen peroxide-induced oxidative stress

Background

Bioethanol fermentations follow traditional beverage fermentations where the yeast is exposed to adverse conditions such as oxidative stress. Lignocellulosic bioethanol fermentations involve the conversion of pentose and hexose sugars into ethanol. Environmental stress conditions such as osmotic stress and ethanol stress may affect the fermentation performance; however, oxidative stress as a consequence of metabolic output can also occur. However, the effect of oxidative stress on yeast with pentose utilising capabilities has yet to be investigated.

Results

Assaying for the effect of hydrogen peroxide-induced oxidative stress on Candida, Pichia and Scheffersomyces spp. has demonstrated that these yeast tolerate hydrogen peroxide-induced oxidative stress in a manner consistent with that demonstrated by Saccharomyces cerevisiae. Pichia guillermondii appears to be more tolerant to hydrogen peroxide-induced oxidative stress when compared to Candida shehatae, Candida succiphila or Scheffersomyces stipitis.

Conclusions

Sensitivity to hydrogen peroxide-induced oxidative stress increased in the presence of minimal media; however, addition of amino acids and nucleobases was observed to increase tolerance. In particular adenine increased tolerance and methionine reduced tolerance to hydrogen peroxide-induced oxidative stress.

New natural diterpene-type abietane from Tetradenia riparia essential oil with cytotoxic and antioxidant activities

Tetradenia riparia (Hochstetter) Codd belongs to the Lamiaceae family and it was introduced in Brazil as an exotic ornamental plant. A previous study showed its antimicrobial, acaricidal and analgesic activities. Two compounds were isolated from essential oil of T. riparia leaves and identified as 9β,13β-epoxy-7-abietene (1), a new one, and 6,7-dehydroroyleanone (2), already reported for another plant. The structure of these compounds was determined by spectroscopic analysis and by comparison with literature data. The cytotoxic activities of the essential oil and compounds 1 and 2 were determined by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, and by tumor cells MDA-MB-435 (human breast carcinoma), HCT-8 (human colon), SF-295 (human nervous system) and HL-60 (human promyelocytic leukemia). The essential oil and compound 1 showed high cytotoxic potential of the cell lines SF-295 (78.06% and 94.80%, respectively), HCT-8 (85.00% and 86.54%, respectively) and MDA-MB-435 (59.48% and 45.43%, respectively). Compound 2 had no cytotoxic activity. The antioxidant activity was determined by 2,2-diphenyl-1-picryl-hydrazyl (DPPH), β-carotene-linoleic acid system and 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays. The inhibitory concentration (IC50 in µg mL-1) for essential oil and compound 2 was, respectively 15.63 and 0.01 for DPPH; 130.1 and 109.6 for β-carotene-linoleic acid and 1524 and 1024 for ABTS. Compound 1 had no antioxidant activity. By fractioning the oil, it was possible to identify two unpublished compounds: 1 with high cytotoxic potential and 2 with high antioxidant potential.

Mechanism-oriented controllability of intracellular quantum dots formation: the role of glutathione metabolic pathway

Microbial cells have shown a great potential to biosynthesize inorganic nanoparticles within their orderly regulated intracellular environment. However, very little is known about the mechanism of nanoparticle biosynthesis. Therefore, it is difficult to control intracellular synthesis through the manipulation of biological processes. Here, we present a mechanism-oriented strategy for controlling the biosynthesis of fluorescent CdSe quantum dots (QDs) by means of metabolic engineering in yeast cells. Using genetic techniques, we demonstrated that the glutathione metabolic pathway controls the intracellular CdSe QD formation. Inspired from this mechanism, the controllability of CdSe QD yield was realized through engineering the glutathione metabolism in genetically modified yeast cells. The yeast cells were homogeneously transformed into more efficient cell-factories at the single-cell level, providing a specific way to direct the cellular metabolism toward CdSe QD formation. This work could provide the foundation for the future development of nanomaterial biosynthesis.

The need for a reassessment of the safe upper limit of selenium in drinking water

Results of recent epidemiologic studies suggest the need to reassess the safe upper limit in drinking water of selenium, a metalloid with both toxicological and nutritional properties. Observational and experimental human studies on health effects of organic selenium compounds consumed through diet or supplements, and of inorganic selenium consumed through drinking water, have shown that human toxicity may occur at much lower levels than previously surmised. Evidence indicates that the chemical form of selenium strongly influences its toxicity, and that its biological activity may differ in different species, emphasizing the importance of the few human studies on health effects of the specific selenium compounds found in drinking water. Epidemiologic studies that investigated the effects of selenate, an inorganic selenium species commonly found in drinking water, together with evidence of toxicity of inorganic selenium at low levels in from in vitro and animal studies, indicate that health risks may occur at exposures below the current European Union and World Health Organization upper limit and guideline of 10 and 40 μg/l, respectively, and suggest reduction to 1 μg/l in order to adequately protect human health. Although few drinking waters are currently known to have selenium concentrations exceeding this level, the public health importance of this issue should not be overlooked, and further epidemiologic research is critically needed in this area.

A case-control study of the risk of cutaneous melanoma associated with three selenium exposure indicators

AIMS AND BACKGROUND

A direct association between exposure to the metalloid selenium and risk of cutaneous melanoma has been suggested by some observational and experimental cohort studies, whereas other studies have yielded inconsistent results. Since some of the inconsistencies may be due to exposure misclassification arising from the use of exposure indicators that do not adequately reflect body tissue selenium content or the levels of the biologically relevant species of this metalloid, we examined this issue using multiple indicators of exposure.

METHODS

We analyzed the relation of selenium exposure with risk of cutaneous melanoma using two different biomarkers, plasma and toenail selenium concentration, and estimated dietary selenium intake in a population-based case-control series (54 cases, 56 controls) from an Italian community.

RESULTS

In unmatched and matched logistic regression models as well as nonparametric generalized additive models, higher plasma selenium levels were strongly associated with excess disease risk. In contrast, toenail and dietary selenium exhibited little relation with melanoma risk. The pattern of correlation among indicators of exposure differed by disease status, with dietary intake associated with plasma selenium levels in patients but not in controls.

CONCLUSIONS

Our data showed that different selenium exposure indicators can yield different inferences about melanoma risk. Although the series was small, our results are consistent with a positive association between circulating levels of selenium and melanoma risk. Further investigation of the exposure classification performance of various selenium biomarkers and of metabolic patterns of the metalloid and of its speciation are needed to help elucidate the relation between selenium exposure and human health.

Intracellular scavenging activity of Trolox (6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid) in the fission yeast, Schizosaccharomyces pombe

The ability of Trolox (6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid), a water-soluble vitamin E analogue, to prevent oxidative damages is well characterized, but the mechanisms underlying it remain unclear. The protective effect of Trolox pre-treatment on H₂O₂-induced toxicity might be attributed to the decreased cellular permeability to H₂O₂ or in vitro scavenging activity of Trolox, induction of antioxidant enzymes or the direct scavenging activity of Trolox. The results obtained rule out the first and second possibilities and intracellular scavenging activity was found to be the mechanism whereby Trolox confers protection. This was confirmed by measuring protein oxidation (levels), and the observed decrease in proteasomal activity indicated that the decrease in protein carbonyls was due to Trolox scavenging activity rather than proteasome activation. In conclusion, the intracellular scavenging activity of Trolox is a key protective mechanism against H₂O₂. These findings obtained in Schizosaccharomyces pombe, a good model organism for eukaryotic cells, can be used as standard protocols for investigating the antioxidant activity of pure or complex potential antioxidants.

Genotoxicity evaluation of effluents from textile industries of the region Fez-Boulmane, Morocco: a case study

In order to investigate the biological hazard of effluents from textile industries of Fez-Boulmane region in Morocco, mutagenicity and phytotoxicity tests were performed on different biological systems. Moreover, the efficiency of a Sequencing Batch Reactor (SBR) system, working by activated sludge on a laboratory scale, was estimated by comparing the ecotoxicity results observed before and after wastewater treatment. Evaluation of the genotoxic potential was investigated by means of classic mutagenicity tests on D7 strain of Saccharomyces cerevisiae and by phytotoxicity tests on Allium sativum L., Vicia faba L. and Lactuca sativa L., estimating micronuclei presence, mitotic index and cytogenetic anomalies. The results obtained by testing untreated wastewater demonstrated major genotoxicity effects in S. cerevisiae and various levels of phytotoxicity in the three plant systems, while after SBR treatment no more ecotoxicological consequences were observed. These data confirm the effectiveness of the SBR system in removing toxic substances from textile wastewaters in Fez-Boulmane region.

Inhibitory effect of grapefruit juice on the genotoxicity induced by hydrogen peroxide in human lymphocytes

By means of the comet assay we demonstrated a strong effect by hydrogen peroxide (HP) and no damage by grapefruit juice (GJ) in human lymphocytes. Cells exposed to HP and treated with three concentrations of GJ (10-90 min) showed an increase of DNA damage by HP over the control level, and a decrease of such damage by GJ. With the comet assay plus formamidopyrimidine-DNA-glycosylase we found the strongest increase of DNA damage by HP over the control level, and the strongest reduction of such damage by GJ. By applying the comet/FISH method we determined 98% of the p53 gene signals in the comet head of control cells along the experiment (10-90 min), in contrast with about 90% signals in the comet tail of cells exposed to HP. Cells treated with both agents showed a significant, concentration/time dependent return of p53 signals to the head, suggesting enhancement of the gene repair. Finally, with the annexin V assay we found an increase in apoptosis and necrosis by HP, and no effect by GJ; when GJ was added to HP treated cells no modification was observed in regard to apoptosis, although a decrease of necrosis was observed.

Use of Saccharomyces cerevisiae and Caenorhabditis elegans as model organisms to study the effect of cocoa polyphenols in the resistance to oxidative stress

Developing functional foods to improve the quality of life for elderly people has great economic and social impact. Searching for and validating ingredients with in vivo antioxidant effects is one of the key steps in developing this kind of food. Here we describe the combined use of simple biological models and transcriptomics to define the functional intracellular molecular targets of a polyphenol-enriched cocoa powder. Cocoa powder supplemented culture medium led to increased resistance to oxidative stress, in both the budding yeast Saccharomyces cerevisiae and the nematode Caenorhabditis elegans, and, in the latter, lifespan was also increased. These effects are fully dependent on the polyphenols present in the cocoa powder and on the sirtuins Hst3 (yeast) and SIR-2.1 (worm). The transcription factor DAF-16 also plays an important role in the case of the nematode, indicating that the insulin/IGF-1 (insulin-like growth factor) signaling pathway is related with the antioxidative effect of cocoa polyphenols. All in all, these results confirm that this polyphenol-enriched cocoa powder, with antioxidant activity, has great potential use as a functional food ingredient for elderly people. Furthermore, this work reveals the value of using simple biological models to screen for compounds that are of interest for the food and pharmacological industry.

Genotoxicity of 4-nonylphenol and nonylphenol ethoxylate mixtures by the use of Saccharomyces cerevisiae D7 mutation assay and use of this text to evaluate the efficiency of biodegradation treatments

Nonylphenol ethoxylates (NPnEOs, where n is the number of ethoxylic units in the molecule) are non-ionic surfactants widely used for domestic and industrial purposes. 4-Nonylphenol (4-NP), the main product of NPnEO biodegradation, is a toxic xenobiotic compound classified as endocrine disrupter. While numerous studies reported the toxicity and oestrogenic activity of nonylphenols, little is known about the mutagenicity of these compounds. In this paper, the genotoxicity of 4-NP and NPnEO mixtures was evaluated by using the D7 strain of Saccharomyces cerevisiae as experimental model. The same genotoxicity tests were applied to effluents deriving from experimental packed-bed bioreactors, developed for the treatment of NPnEO contaminated wastewater, in order to evaluate the residual genotoxic potential with respect to the influent waste. The target compounds fed to the bioreactors were 4-NP and NPnEO mixtures possessing an average of 5 or 1.5 ethoxylic units (Igepal CO-520 and Igepal CO-210, respectively). The results showed that 4-NP induced significant cytotoxic effect on S. cerevisiae cells at 50 mg/L, as well as mutagenic effects at the lowest tested concentrations (12 and 25 mg/L). 4-NP was the most genotoxic compound among those assayed, followed by Igepal CO-210, whereas Igepal CO-520 did not induce genotoxicity at any of the assayed concentrations. The genotoxic effects of 4-NP on yeast cells disappeared after the treatment of 4-NP artificially contaminated water in the bioreactor. This indicates that the biological treatment is capable of removing not only the pollutant, but also the toxicity associated to the compound and its degradation metabolites. This study represents, to the best of our knowledge, the first report that evaluates the genotoxicity of both 4-NP, NPnEOs and their potential aerobic degradation products on an eukaryotic organism. The obtained results suggest that the S. cerevisiae D7 strain is a very effective model microorganism to study the induction of genotoxic damage by the compounds under study. Moreover, this yeast assay has been proved effective to evaluate the detoxification effect deriving from biotreatment processes.

Inhibitory effect of grapefruit juice on the genotoxic damage induced by ifosfamide in mouse

The consumption of grapefruit juice (GJ) has been associated with various activities potentially beneficial for human health, including protection against the DNA damage produced by various compounds. In the present report, we evaluated the capability of this juice to inhibit the rate of micronucleated polychromatic erythrocytes (MNPE) and sister chromatid exchanges (SCE) induced by the antineoplastic alkylating agent ifosfamide (IF). We tested the effect of administering 100, 500, and 1000 mg/kg of GJ in mouse and obtained the following results: a) with the high dose, a reduction of 72% in the rate of SCE induced by IF; b) a mean reduction of 65.3% in the rate of MNPE compared with the damage induced by IF at 48 h post-administration; c) no modification induced by GJ either on the cellular proliferation kinetics or in the mitotic index; and d) neither induction of bone marrow cytotoxicity by GJ nor a protective effect of the juice against the cytotoxicity induced by IF. These data showed a significant inhibitory effect of GJ against the chromosome damage induced by the tested agent; they also suggest the relevance of carrying out studies to clarify the involved mechanism of action as well as to determine the cancer chemopreventive capacity of the juice.

Protective effects of selenium against sister chromatid exchange induced by AFG 1 in human lymphocytes in vitro

Aflatoxins have been shown to be hepatotoxic, carcinogenic, mutagenic and teratogenic to different species of animals. Besides, at low concentrations, Selenium (Se(4+)) is antimutagenic and anticarcinogenic while it is toxic, mutagenic and carcinogenic at high concentrations. In this study, we aimed to evaluate the effect of Se(4+) against aflatoxin GAFG(1) (AFG(1)) on blood cultures in relation to induction of sister chromatid exchange (SCE). The results showed that at 0.4 and 0.8 parts per million (ppm) concentration of AFG(1), the frequency of SCE increased in cultured human lymphocytes. When different concentration of Se(4+) (0.08 and 8 ppm) were added to AFG(1), the frequencies of SCE decreased. Howewer, when 800 ppm concentration of Se(4+) together with 0.08 ppm AFG(1) were added to cell division inhibited in the cultures. Results suggested that Se(4+) could effectively inhibit AFG(1)-induced SCE. Besides, the protective role of Se(4+) against AFG(1)-induced SCE is probably related to its doses.

Interference of chromium with biological systems in yeasts and fungi: a review

This paper deals with the interactions of chromium (Cr) with biological systems, focusing in particular on yeasts and fungi. These interactions are analysed with primarily regard to biochemical functions, but higher levels of organization are also considered. Thus, the morphological and cytological characteristics of selected microorganisms in response to exposure to chromium ions are evaluated. The different oxidation states of chromium and reactive oxygen species (ROS) generated in redox reactions with chromium ions are presented and characterized. The interactions of the most exposed subcellular structures, including the cell wall, plasma membrane and nuclei, have been deeply investigated in recent years, for two major reasons. The first is the toxicity of chromium ions and their strong impact on the metabolism of many species, ranging from microbes to humans. The second is the still disputed usefulness of chromium ions, and in particular trivalent chromium, in the glucose and fat metabolisms. Chromium pollution is still an important issue in many regions of the world, and various solutions have been proposed for the bioremediation of soil and water with selected microbial species. Yeasts and especially moulds have been most widely investigated from this aspect, and the biosorption and bioaccumulation of chromium for bioremediation purposes have been demonstrated. Accordingly, the mechanisms of chromium tolerance or resistance of selected microbes are of particular importance in both bioremediation and waste water treatment technologies. The mechanisms of chromium toxicity and detoxification have been studied extensively in yeasts and fungi, and some promising results have emerged in this area.

Inhibition of cyclophoshamide-induced mutagenicity by microsized powder of selenium-enriched green tea in mice

Previously, the antioxidant activity of Se-enriched green tea extracts has been studied in vitro. In the present study, an in vivo micronuclei test was employed to assess the antimutagenic effect of microsized Se-enriched green tea powder (MSTP) in mice bone marrow. Pretreatments of MSTP, micrometer-sized regular tea powder (MRTP), selenite, and MRTP + selenite were given by gavage for 29 consecutive days prior to cyclophoshamide (CP) treatment. Certain key antioxidant enzymes were also investigated to elucidate the mechanism of antimutagenic effect. Results indicated that MSTP and MRTP or selenite alone did not significantly induce micronuclei at either concentration, confirming its nonmutagenicity. In the CP-treated groups, significant suppressions in the micronuclei were recorded following pretreatment with MSTP, MRTP, and selenite administration. The antimutagenic effect of MSTP was evidently observed by significant reduction in the frequencies of micronuclei in bone marrow cells when compared to a positive control group. The administration of MSTP, selenite, and MRTP + selenite also increased the levels of selenium concentration, glutathione peroxidase (GPx), and superoxide dismutase (SOD) enzymes in both blood and liver. However, no pronounced differences in activities of GPx and SOD were found among MSTP, selenite, and MRTP + selenite. The present findings demonstrate that the antimutagenic potential of MSTP could not be solely related to the enhancment of antioxidant enzymes of GPx and SOD.

Toxicity and mutagenicity of selenium compounds in Saccharomyces cerevisiae

Selenium (Se) is an essential trace element for humans, animals and some bacteria which is important for many cellular processes. Se's bio-activity is mainly influenced by its chemical form and dose. The use of Se supplements in the human diet emphasizes the need to establish both the beneficial and detrimental doses of each Se compound. We have evaluated three different Se compounds, sodium selenite (SeL), selenomethionine (SeM) and Se-methylselenocysteine (SeMC), with respect to their potential DNA damaging effects. The budding yeast Saccharomyces cerevisiae was used as a model system to test the toxic and mutagenic effects as well as the DNA double-strand breakage potency of these Se compounds in both exponentially growing and stationary yeast cells. Only SeL manifested any significant toxic effects in the yeast which were more pronounced in the exponentially growing cells than in those cells in the stationary phase of growth. The toxic effects of SeL were however accompanied with the pro-mutagenic effects in the stationary cell phase of growth. The toxic and mutagenic effects of SeL are likely associated with the ability of this compound to generate DNA double-strand breaks (DSB). We also show that SeL significantly increased frame-shift mutations, especially 1-4 bp deletions, in the CAN1 mutational spectrum of the yeast genome when compared to untreated control. We propose that SeL is acting as an oxidizing agent in S. cerevisiae producing superoxide and oxidative damage to DNA accounting for the observed DSB and cell death.

Biological effects of essential oils--a review

Since the middle ages, essential oils have been widely used for bactericidal, virucidal, fungicidal, antiparasitical, insecticidal, medicinal and cosmetic applications, especially nowadays in pharmaceutical, sanitary, cosmetic, agricultural and food industries. Because of the mode of extraction, mostly by distillation from aromatic plants, they contain a variety of volatile molecules such as terpenes and terpenoids, phenol-derived aromatic components and aliphatic components. In vitro physicochemical assays characterise most of them as antioxidants. However, recent work shows that in eukaryotic cells, essential oils can act as prooxidants affecting inner cell membranes and organelles such as mitochondria. Depending on type and concentration, they exhibit cytotoxic effects on living cells but are usually non-genotoxic. In some cases, changes in intracellular redox potential and mitochondrial dysfunction induced by essential oils can be associated with their capacity to exert antigenotoxic effects. These findings suggest that, at least in part, the encountered beneficial effects of essential oils are due to prooxidant effects on the cellular level.

Anticlastogenic and antigenotoxic effects of selenomethionine on doxorubicin-induced damage in vitro in human lymphocytes

The use of antioxidants during chemotherapy has been shown to reduce or prevent the undesirable effects experienced by healthy cells. Micronutrient selenium is well known for its antioxidant properties; however, selenium exhibits a bimodal nature in that both its beneficial and toxic properties lie within a limited and narrow dose range. The present study investigated the possible protective effects of selenomethionine (SM) on the cytotoxicity, genotoxicity and clastogenicity of the chemotherapic doxorubicin (DXR), a key chemotherapic used in cancer treatment. Human peripheral lymphocytes were treated in vitro with varying concentrations of SM (0.25 microM, 0.5 microM, 1.0 microM and 2.0 microM), tested in combination with DXR (0.15 microg/mL). SM alone was not cytotoxic and when combined with DXR treatment, reduced the DNA damage index significantly, the frequency of chromosomal aberrations, the number of aberrant metaphases and the frequency of apoptotic cells. The mechanism of chemoprotection of SM may be related to its antioxidant properties as well as its ability to interfere with DNA repair pathways. Therefore this study showed that SM is effective in reducing the genetic damage induced by the antitumoral agent DXR.

Extracellular Production of Hydrogen Selenide Accounts for Thiol-assisted Toxicity of Selenite against Saccharomyces cerevisiae

Administration of selenium in humans has anticarcinogenic effects. However, the boundary between cancer-protecting and toxic levels of selenium is extremely narrow. The mechanisms of selenium toxicity need to be fully understood. In Saccharomyces cerevisiae, selenite in the millimolar range is well tolerated by cells. Here we show that the lethal dose of selenite is reduced to the micromolar range by the presence of thiols in the growth medium. Glutathione and selenite spontaneously react to produce several selenium-containing compounds (selenodiglutathione, glutathioselenol, hydrogen selenide, and elemental selenium) as well as reactive oxygen species. We studied which compounds in the reaction pathway between glutathione and sodium selenite are responsible for this toxicity. Involvement of selenodiglutathione, elemental selenium, or reactive oxygen species could be ruled out. In contrast, extracellular formation of hydrogen selenide can fully explain the exacerbation of selenite toxicity by thiols. Indeed, direct production of hydrogen selenide with D-cysteine desulfhydrase induces high mortality. Selenium uptake by S. cerevisiae is considerably enhanced in the presence of external thiols, most likely through internalization of hydrogen selenide. Finally, we discuss the possibility that selenium exerts its toxicity through consumption of intracellular reduced glutathione, thus leading to severe oxidative stress.

In vivo effects of adding singular or combined anti-oxidative vitamins and/or minerals to diets on the immune system of tilapia (Oreochromis hybrids) peripheral blood monocyte-derived, anterior kidney-derived, and spleen-derived macrophages

Macrophage function is an important factor for resistance to infection and anti-oxidative vitamins and minerals can affect how macrophages function in fish. We report the in vivo effect of adding singular or combined vitamins (A, C, and E) and/or minerals (Se, Zn, Cu, Mn, and Fe) in diets on the immune system of tilapia (Oreochromis hybrids) peripheral blood monocyte-derived, anterior kidney-derived, and spleen-derived macrophages. An optimal dose of vitamins and/or minerals in diets increased macrophage proliferation and protective activity, maintained macrophage viability, increased body weight and length, and increased lysozyme activity, however, at improper doses and combinations of vitamins or minerals a decrease was observed. Furthermore, vitamins and/or minerals at any doses and combinations in diets decreased superoxide and nitric oxide production. Therefore, appropriate doses and combinations of vitamins and/or minerals in diets may increase tilapia macrophages immunity.

The oxidative stress response of the yeastCandida intermedia to copper, zinc, and selenium exposure

The yeast Candida intermedia, as a model organism, was used to examine the links between the metal ions exposure, reactive oxygen species generation and oxidative stress response. To estimate intracellular peroxide and superoxide levels, the fluorescence indicators dihydrorhodamine 123 and dihydroethidium were used, respectively. Antioxidant defence systems were investigated by measuring the activity of catalase, glutathione peroxidase and superoxide dismutase and the content of reduced glutathione. Altered superoxide, peroxide, glutathione levels, and the catalase activity were perceived after the treatment with copper. In the samples treated with selenium and zinc the altered peroxide and superoxide levels, and the glutathione peroxidase activity were perceived. The results indicate that the tolerance of the yeast C. intermedia to different metal ions was correlated with the reactive oxygen species generation in the cells and with the efficiency of antioxidative defence systems.

Antigenotoxic and antioxidant effect of grapefruit juice in mice treated with daunorubicin

Grapefruit juice (GJ) is widely consumed in many countries. Several of its constituents possess nutritive value, as well as antigenotoxic and antioxidant effects. Therefore, the aim of this investigation was to evaluate the capacity of GJ to inhibit the micronucleated polychromatic erythrocytes (MNPE) produced by daunorubicin (Dau) in an acute assay in mice, as well as to determine its antioxidant potential in mouse hepatic microsomes, and its capacity to trap free radicals in vitro. In regard to the first point, GJ produced no toxic or genotoxic damage; on the contrary, it generated a significant reduction of the MNPE formed by Dau. The effect was found throughout the examined schedule (from 24 to 96 h). The two high doses produced inhibition of about 60% at 48 h, 86% at 72 h and 100% at 96 h after the treatment. With respect to the GJ antioxidant potential, a 50% decrease in liver microsomal lipid peroxidation produced by Dau was found by quantifying malondialdehyde formation. Finally, a strong GJ scavenging activity evaluated with the 1,1-diphenyl-2-picryl-hydrazyl (DPPH) was observed, giving rise to a concentration-dependent curve with a correlation coefficient of 0.98. Overall, our results established an efficient anticlastogenic potential of GJ, probably related to its antioxidant capacity, or to alterations of Dau metabolism, suggesting the pertinence of extending research on the matter using other mutagens and biological models.

Genotoxicity of diphenyl diselenide in bacteria and yeast

Diphenyl diselenide (DPDS) is an electrophilic reagent used in the synthesis of a variety of pharmacologically active organic selenium compounds. This may increase the risk of human exposure to the chemical at the workplace. We have determined its mutagenic potential in the Salmonella/microsome assay and used the yeast Saccharomyces cerevisiae to assay for putative genotoxicity, recombinogenicity and to determine whether DNA damage produced by DPDS is repairable. Only in exponentially growing cultures was DPDS able to induce frameshift mutations in S. typhimurium and haploid yeast and to increase crossing over and gene conversion frequencies in diploid strains of S. cerevisiae. Thus, DPDS presents a behavior similar to that of an intercalating agent. Mutants defective in excision-resynthesis repair (rad3, rad1), in error-prone repair (rad6) and in recombinational repair (rad52) showed higher than WT-sensitivity to DPDS. It appears that this compound is capable of inducing single and/or double strand breaks in DNA. An epistatic interaction was shown between rad3-e5 and rad52-1 mutant alleles, indicating that excision-resynthesis and strand-break repair may possess common steps in the repair of DNA damage induced by DPDS. DPDS was able to enhance the mutagenesis induced by oxidative mutagens in bacteria. N-acetylcysteine, a glutathione biosynthesis precursor, prevented mutagenesis induced by DPDS in yeast. We have shown that DPDS is a weak mutagen which probably generates DNA strand breaks through both its intercalating action and pro-oxidant effect.

Glutathione, Altruistic Metabolite in Fungi

Glutathione (GSH; gamma-L-glutamyl-L-cysteinyl-glycine), a non-protein thiol with a very low redox potential (E'0 = 240 mV for thiol-disulfide exchange), is present in high concentration up to 10 mM in yeasts and filamentous fungi. GSH is concerned with basic cellular functions as well as the maintenance of mitochondrial structure, membrane integrity, and in cell differentiation and development. GSH plays key roles in the response to several stress situations in fungi. For example, GSH is an important antioxidant molecule, which reacts non-enzymatically with a series of reactive oxygen species. In addition, the response to oxidative stress also involves GSH biosynthesis enzymes, NADPH-dependent GSH-regenerating reductase, glutathione S-transferase along with peroxide-eliminating glutathione peroxidase and glutaredoxins. Some components of the GSH-dependent antioxidative defence system confer resistance against heat shock and osmotic stress. Formation of protein-SSG mixed disulfides results in protection against desiccation-induced oxidative injuries in lichens. Intracellular GSH and GSH-derived phytochelatins hinder the progression of heavy metal-initiated cell injuries by chelating and sequestering the metal ions themselves and/or by eliminating reactive oxygen species. In fungi, GSH is mobilized to ensure cellular maintenance under sulfur or nitrogen starvation. Moreover, adaptation to carbon deprivation stress results in an increased tolerance to oxidative stress, which involves the induction of GSH-dependent elements of the antioxidant defence system. GSH-dependent detoxification processes concern the elimination of toxic endogenous metabolites, such as excess formaldehyde produced during the growth of the methylotrophic yeasts, by formaldehyde dehydrogenase and methylglyoxal, a by-product of glycolysis, by the glyoxalase pathway. Detoxification of xenobiotics, such as halogenated aromatic and alkylating agents, relies on glutathione S-transferases. In yeast, these enzymes may participate in the elimination of toxic intermediates that accumulate in stationary phase and/or act in a similar fashion as heat shock proteins. GSH S-conjugates may also form in a glutathione S-transferases-independent way, e.g. through chemical reaction between GSH and the antifugal agent Thiram. GSH-dependent detoxification of penicillin side-chain precursors was shown in Penicillium sp. GSH controls aging and autolysis in several fungal species, and possesses an anti-apoptotic feature.

Protective effect of lipoic acid against hydrogen peroxide in yeast cells

Lipoic acid (LA) is found in all kinds of cells, it is widely used in medicine and as a dietary supplement, and it is involved in different physiological functions. Even if there are many papers regarding therapeutic effects of LA, medical research does not always support its effectiveness and little is known about LA metabolism in eukaryotic cells. In this work the probable protective effect of LA was investigated employing five strains of yeast Saccharomyces cerevisiae through short term assays. In particular LA behaviour in oxidative stress conditions was studied. For this purpose hydrogen peroxide was used as oxidant. In D7 strain, LA showed antimutagenic effects against hydrogen peroxide and decreased significantly cytochrome P450. To better elucidate the effect of LA the following yeast strains carrying deletions in superoxide dismutase genes (SOD) were employed: EG-103 (wild type), EG-110 strain (without mytochondrial SOD), EG-118 (without cytoplasmatic SOD) and EG-133 (without both enzymes). LA increased the number of mitotic divisions in EG-103, EG-110 and EG-133 and in growing cells (EG-103, EG-110, EG-118) it increased survival percentage with respect to hydrogen peroxide. The positive action was evident in D7 and in EG strains and it showed that LA can be protective and antimutagenic against oxidants in yeast cells, via its antioxidant activity.