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BACKGROUND Intrinsic resistance of cancer cells is a major concern for the success of chemotherapy, and this undesirable feature stimulates further research into the design of new compounds and/or alternative multiple drug chemotherapy... more
BACKGROUND Intrinsic resistance of cancer cells is a major concern for the success of chemotherapy, and this undesirable feature stimulates further research into the design of new compounds and/or alternative multiple drug chemotherapy protocols. METHODS In this study, we investigated the antitumoral potential of the coordination compounds [Cu(HPClNOL)Cl]Cl (1), [Fe(HPClNOL)Cl2]NO3(2) and [Mn(HPClNOL)Cl2] (3). Using the human, MCF-7 and A549, and the murine melanoma, B16-F10, cell lines, we determined the cytotoxicity, DCFH oxidation, disruption of mitochondrial membrane potential (ΔΨm), Sub-G1 and TUNEL positive cells, and caspase 8 and 9 activities. Fractional inhibitory concentration (FIC) and xenograft models were also assessed to evaluate the efficacy of antitumoral potential. RESULTS We observed that only complex 1 was cytotoxic. The treatment of cancer cells with complex 1 triggered ROS generation and promoted the disruption of ΔΨm. Complex 1 increased the number of Sub-G1 and TUNEL positive cells, and the measurement of caspase 8 and 9 activity confirmed that apoptosis was triggered by the intrinsic pathway. FIC demonstrated that the combination of complex 1 with cisplatin was additive for the A549 cells whilst it was synergic for MCF-7 and B16-F10. Treatment with complex 1, either alone or combined with cisplatin, reduced tumor growth on xenograft models. CONCLUSIONS The present study brings new clues regarding the mechanism of action of [Cu(HPClNOL)Cl]Cl, either alone or in combination with cisplatin. GENERAL SIGNIFICANCE These results indicate that complex 1, administered either singly or in combination with current drugs, has real potential for use in cancer therapy.
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Aiming to investigate the use of tridentate ligands to develop new bireductively activated prodrugs, two N2O-donor ligands (HL1:[(2-hydroxybenzyl)(2-(imidazol-2-yl) ethyl)] amine; and HL2:[(2-hydroxybenzyl)(2-(pyridil-2-yl) ethyl] amine)... more
Aiming to investigate the use of tridentate ligands to develop new bireductively activated prodrugs, two N2O-donor ligands (HL1:[(2-hydroxybenzyl)(2-(imidazol-2-yl) ethyl)] amine; and HL2:[(2-hydroxybenzyl)(2-(pyridil-2-yl) ethyl] amine) were used to synthesize new Co ...
Research Interests: Chemistry, Inorganic Chemistry, Electrochemistry, Mass Spectrometry, NMR Spectroscopy, and 14 moreInorganic, Molecular modeling, Saccharomyces cerevisiae, X Rays, Anaerobic Metabolism, Cell Death, Electronic properties, Imidazole, Pyridine, Inorganic Biochemistry, Biological activity, Redox, X Ray Crystallography, and Redox Potential
Research Interests: Biochemistry, Microbiology, Medical Microbiology, Biology, Enzyme Inhibitors, and 13 moreToxoplasma, Transmission Electron Microscopy, Medicine, Toxoplasma gondii, Antioxidants, Cell line, Reactive Oxygen Species, Animals, Catalase, Superoxide Dismutase, Macaca Mulatta, Ferric Compounds, and Pharmacology and pharmaceutical sciences
The ability to undergo morphological changes during adaptation to distinct environments is exploited byCandida albicansand has a direct impact on virulence. In this study, we investigated the influence of fungal extracellular vesicles... more
The ability to undergo morphological changes during adaptation to distinct environments is exploited byCandida albicansand has a direct impact on virulence. In this study, we investigated the influence of fungal extracellular vesicles (EVs) during yeast growth, biofilm formation, and morphogenesis inC. albicans. Addition ofC. albicansEVs (CaEVs) to the culture medium positively affected yeast growth. Using crystal violet staining and scanning electron microscopy (SEM), we demonstrated thatCaEVs inhibited biofilm formation byC. albicans in vitro. By time-lapse microscopy and SEM, we showed thatCaEV-treatment stops filamentation promoting pseudohyphae formation with multiple sites for yeast budding. The ability ofCaEVs to regulate dimorphism was further compared to EVs isolated from differentC. albicansstrains,Saccharomyces cerevisiae, andHistoplasma capsulatum.CaEVs from distinct strains robustly inhibited yeast-to-hyphae differentiation with morphological changes occurring in less t...
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The overproduction of reactive oxygen species (ROS) induces oxidative stress, a well-known process associated with aging and several human pathologies, such as cancer and neurodegenerative diseases. A large number of synthetic compounds... more
The overproduction of reactive oxygen species (ROS) induces oxidative stress, a well-known process associated with aging and several human pathologies, such as cancer and neurodegenerative diseases. A large number of synthetic compounds have been described as antioxidant enzyme mimics, capable of eliminating ROS and/or reducing oxidative damage. In this study, we investigated the antioxidant activity of a water-soluble 1,10-phenantroline-octanediaoate Mn2+-complex on cells under oxidative stress, and assessed its capacity to attenuate alpha-synuclein (aSyn) toxicity and aggregation, a process associated with increased oxidative stress. This Mn2+-complex exhibited a significant antioxidant potential, reducing intracelular oxidation and increasing oxidative stress resistance in S. cerevisiae cells and in vivo, in G. mellonella, increasing the activity of the intracellular antioxidant enzymes superoxide dismutase and catalase. Strikingly, the Mn2+-complex reduced both aSyn oligomerizat...
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Photosensitizers (PS) are compounds that can generate reactive oxygen species under irradiation of appropriate light and are widely used in photodynamic therapy (PDT). Currently, topical PDT is an effective treatment for several skin... more
Photosensitizers (PS) are compounds that can generate reactive oxygen species under irradiation of appropriate light and are widely used in photodynamic therapy (PDT). Currently, topical PDT is an effective treatment for several skin diseases, including bacterial infections, fungal mycoses and psoriasis. In addition, PDT is also used to treat nonmelanoma skin cancer and can be a potential tool for melanoma, associated with other treatments. In this work, we evaluated the antitumor photoactivity of a new pyrene‐based PS (TPPy) by using the murine melanoma cell line (B16F10). The in vitro permeation/retention tests in porcine ear skin were also performed in order to evaluate the potential application of the PS for topical use in skin cancer. Moreover, to determine the toxicity in vivo, we used the Galleria mellonella as an alternative animal model of study. The results showed that TPPy is a promising PS for application in PDT, with potential antitumor photoactivity (IC50 6.5 μmol L‐1)...
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Research Interests: Biochemistry, Biomarkers, Biology, Oxidative Stress, Medicine, and 15 moreManganese, Biological Sciences, Copper, Reactive Oxygen Species, Catalase, Iron, Biochemical, CHEMICAL SCIENCES, Hydrogen Peroxide, Biomimetic materials, Oxidative phosphorylation, Pyridines, Lipid Droplets, Microbial Viability, and Medical and Health Sciences
Cryptococcus neoformans is an environmental fungus that can cause lethal meningoencephalitis in immunocompromised individuals. The mechanisms by which environmental microbes become pathogenic to mammals are still obscure, but different... more
Cryptococcus neoformans is an environmental fungus that can cause lethal meningoencephalitis in immunocompromised individuals. The mechanisms by which environmental microbes become pathogenic to mammals are still obscure, but different studies suggest that fungal virulence evolved from selection imposed by environmental predators. The soil-living Acanthamoeba castellanii is a well-known predator of C. neoformans. In this work, we evaluated the participation of C. neoformans virulence-associated structures in the interaction of fungal cells with A. castellanii. Fungal extracellular vesicles (EVs) and the polysaccharide glucuronoxylomannan (GXM) were internalized by A. castellanii with no impact on the viability of amoebal cells. EVs, but not free GXM, modulated antifungal properties of A. castellanii by inducing enhanced yeast survival. Phagocytosis of C. neoformans by amoebal cells and the pathogenic potential in a Galleria mellonella model were not affected by EVs, but previous int...
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Research Interests: Chemical Engineering, Biochemistry, Chemistry, Inorganic Chemistry, Oxidative Stress, and 14 moreInorganic, Medicine, Saccharomyces cerevisiae, Antioxidants, Reactive Oxygen Species, Antioxidant, Catalase, Iron, Superoxide Dismutase, Hydrogen Peroxide, Superoxide, Protein Binding, Ligands, and Molecular Structure
Research Interests: Chemistry, Photochemistry, Scanning Electron Microscopy, Nanoparticles, Transmission Electron Microscopy, and 15 moreMedicine, Nuclear Chemistry, Photodynamic Therapy, Humans, Phototoxicity, Anthraquinones, Fourier transform infrared spectroscopy, Singlet Oxygen, Drug Carriers, Silicon Dioxide, Biochemistry and cell biology, Adenocarcinoma, Anthraquinone, Rose Bengal, and lung neoplasms
Among the familial forms of amyotrophic lateral sclerosis (fALS), 20% are associated with the Cu,Zn-superoxide dismutase (Sod1). fALS is characterized by the accumulation of aggregated proteins and the increase in oxidative stress... more
Among the familial forms of amyotrophic lateral sclerosis (fALS), 20% are associated with the Cu,Zn-superoxide dismutase (Sod1). fALS is characterized by the accumulation of aggregated proteins and the increase in oxidative stress markers. Here, we used the non-invasive bimolecular fluorescence complementation (BiFC) assay in human H4 cells to investigate the kinetics of aggregation and subcellular localization of Sod1 mutants. We also studied the effect of the different Sod1 mutants to respond against oxidative stress by following the levels of reactive oxygen species (ROS) after treatment with hydrogen peroxide. Our results showed that only 30% of cells transfected with A4VSod1 showed no inclusions while for the other Sod1 mutants tested (L38V, G93A and G93C), this percentage was at least 70%. In addition, we found that 10% of cells transfected with A4VSod1 displayed more than five inclusions per cell and that A4V and G93A Sod1 formed inclusions more rapidly than L38V and G93C Sod...
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Alzheimer's and Parkinson's diseases share similar amyloidogenic mechanisms, in which metal ions might play an important role. In this last neuropathy, misfolding and aggregation of α-synuclein (α-Syn) are crucial pathological... more
Alzheimer's and Parkinson's diseases share similar amyloidogenic mechanisms, in which metal ions might play an important role. In this last neuropathy, misfolding and aggregation of α-synuclein (α-Syn) are crucial pathological events. A moderate metal-binding compound, namely, 8-hydroxyquinoline-2-carboxaldehyde isonicotinoyl hydrazone (INHHQ), which was previously reported as a potential 'Metal-Protein Attenuating Compound' for…
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We investigated the involvement of the autophagy protein 7 (Atg7) in physiology and pathogenic potential of Cryptococcus neoformans. The C. neoformans gene encoding Atg7 was deleted by biolistic transformation for characterization of... more
We investigated the involvement of the autophagy protein 7 (Atg7) in physiology and pathogenic potential of Cryptococcus neoformans. The C. neoformans gene encoding Atg7 was deleted by biolistic transformation for characterization of autophagy mechanisms, pigment formation, cell dimensions, interaction with phagocytes and pathogenic potential in vivo. ATG7 deletion resulted in defective autophagy mechanisms, enhanced pigmentation and increased cellular size both in vitro and in vivo. The atg7Δ mutant had decreased survival in the lung of infected mice, higher susceptibility to the killing machinery of different host phagocytes and reduced ability to kill an invertebrate host. These results connect Atg7 with mechanisms of pathogenicity in the C. neoformans model.
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The complexes [Ag2(OOC-(CH2)n-COO)] (n=1-10) (1-10) were synthesised and reacted with 1,10-phenanthroline (phen) to yield derivatives formulating as [Ag2(phen)x(OOC-(CH2)y-COO)]·zH2O (x=2 or 3; y=1-10; z=1-4) (11-20) which are highly... more
The complexes [Ag2(OOC-(CH2)n-COO)] (n=1-10) (1-10) were synthesised and reacted with 1,10-phenanthroline (phen) to yield derivatives formulating as [Ag2(phen)x(OOC-(CH2)y-COO)]·zH2O (x=2 or 3; y=1-10; z=1-4) (11-20) which are highly water-soluble and photo-stable in aqueous solution. The phen derivatives 11-20 exhibit chemotherapeutic potential against Candidaalbicans, Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa and against cisplatin-sensitive breast (MCF-7) and resistant ovarian (SKOV-3) cancer cell lines. Cyclic voltammetric analysis and DNA binding and intercalation studies indicate that the mechanism of action of 11-20 is significantly different to that of their silver(I) dicarboxylate precursors and they do not induce DNA damage or ROS generation in mammalian cells. The representative complexes 9 and 19 (containing the undecanedioate ligand) were both found to significantly reduce superoxide and hydrogen peroxide induced oxidative stress in the yeast S. cerevisiae.
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Cobalt(III) complexes are well-suited systems for cytotoxic drug release under hypoxic conditions. Here, we investigate the effect of cytotoxic azide release by cobalt-containing carrier-prototypes for antitumoral prodrugs. In addition,... more
Cobalt(III) complexes are well-suited systems for cytotoxic drug release under hypoxic conditions. Here, we investigate the effect of cytotoxic azide release by cobalt-containing carrier-prototypes for antitumoral prodrugs. In addition, we study the species formed after reduction of Co(3+)→Co(2+) in the proposed models for these prodrugs. Three new complexes, [Co(III)(L)(N3)2]BF4(1), [{Co(II)(L)(N3)}2](ClO4)2(2), and [Co(II)(L)Cl]PF6(3), L=[(bis(1-methylimidazol-2-yl)methyl)(2-(pyridyl-2-yl)ethyl)amine], were synthesized and studied by several spectroscopic, spectrometric, electrochemical, and crystallographic methods. Reactivity and spectroscopic data reveal that complex 1 is able to release N3(-) either after reduction with ascorbic acid, or by ambient light irradiation, in aqueous phosphate buffer (pH6.2, 7.0 and 7.4) and acetonitrile solutions. The antitumoral activities of compounds 1-3 were tested in normoxia on MCF-7 (human breast adenocarcinoma), PC-3 (human prostate) and A-549 (human lung adenocarcinoma epithelial) cell lines, after 24h of exposure. Either complexes or NaN3 presented IC50 values higher than 200μM, showing lower cytotoxicity than the clinical standard antitumoral complex cisplatin, under the same conditions. Complexes 1-3 were also evaluated in hypoxia on A-549 and results indicate high IC50 data (>200μM) after 24h of exposure. However, an increase of cancer cell susceptibility to 1 and 2 was observed at 300μM. Regarding complex 3, no cytotoxic activity was observed in the same conditions. The data presented here indicate that the tridentate ligand L is able to stabilize both oxidation states of cobalt (+3 and +2). In addition, the cobalt(III) complex generates the low cytotoxic cobalt(II) species after reduction, which supports their use as as carrier prototypes for antitumoral prodrugs.
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It has been shown that the activation of cytosolic superoxide dismutase (Sod1) in Saccharomyces cerevisiae is only dependent on Ccs1, which is responsible for insertion of copper into the enzyme catalytic center, and that glutathione... more
It has been shown that the activation of cytosolic superoxide dismutase (Sod1) in Saccharomyces cerevisiae is only dependent on Ccs1, which is responsible for insertion of copper into the enzyme catalytic center, and that glutathione (GSH) is not necessary for this process. In this work, we addressed an important role of GSH in Sod1 activation by a Ccs1-dependent mechanism during oxidative stress and its role in yeast lifespan. Exponential cells of Saccharomyces cerevisiae, treated or not with 0.5 mM menadione for 1 h, were used for evaluation of the effect of a mild oxidative stress pre-treatment on chronological lifespan. The results showed that menadione induced a lifespan extension in the wild-type (WT) strain but this adaptive response was repressed in gsh1 and in sod1 strains. Interestingly, menadione treatment increased SOD1 and CCS1 gene expression in both WT and gsh1 strains. However, while these strains showed the same Sod1 activity before treatment, only the WT presented an increase of Sod1 activity after menadione exposure. Glutathionylation seems to be essential for Sod1 activation since no increase in activity was observed after menadione treatment in grx1 and grx2 null mutants. Our results suggest that GSH and glutathionylation are fundamental to protect Sod1 sulfhydryl residues under mild oxidative stress, enabling Sod1 activation and lifespan extension.
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Research Interests: Complementary and Alternative Medicine, Traditional Medicine, Plant Biology, Phytomedicine, Saccharomyces cerevisiae, and 15 moreAntioxidants, Lipid peroxidation, Hydrogen Peroxide, Antioxidant Activity, Mode of action, Phenols, Plant extracts, Quercetin, Ginkgo Biloba, Medicinal Plant, Oxidants, HYPTIS, Protein carbonylation, Neurodegenerative disorder, and Pharmacology and pharmaceutical sciences
Moderate consumption of red wine reduces the risk of heart disease and extends lifespan, but the relative contribution of wine polyphenols to these effects is unclear. In this work, the capacity of resveratrol and catechin to protect the... more
Moderate consumption of red wine reduces the risk of heart disease and extends lifespan, but the relative contribution of wine polyphenols to these effects is unclear. In this work, the capacity of resveratrol and catechin to protect the eukaryotic microorganism Saccharomyces cerevisiae against oxidative stress caused by different agents, hydrogen peroxide, carbon tetrachloride, and cadmium, was evaluated. Under all stress conditions, both polyphenols increased tolerance, although their protection was more evident under peroxide exposure. By using mutant strains deficient in specific antioxidant defense systems (superoxide dismutases, catalase, or glutathione), it was observed that increased H2O2 tolerance produced by both polyphenols was associated with catalase, as well as the rise in survival rates caused by resveratrol under CCl4. The acquisition of tolerance was correlated with a reduction in lipid peroxidation, indicating that the antioxidant property of resveratrol and catechin involves protection against membrane oxidation.
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In Saccharomyces cerevisiae, accumulation of cadmium-glutathione complex in cytoplasm inhibits cadmium absorption, glutathione transferase 2 is required for the formation of the complex and the vacuolar gamma-glutamyl transferase... more
In Saccharomyces cerevisiae, accumulation of cadmium-glutathione complex in cytoplasm inhibits cadmium absorption, glutathione transferase 2 is required for the formation of the complex and the vacuolar gamma-glutamyl transferase participates of the first step of glutathione degradation. Here, we proposed that Lap4, a vacuolar amino peptidase, is involved in glutathione catabolism under cadmium stress. Saccharomyces cerevisiae cells deficient in Lap4 absorbed almost 3-fold as much cadmium as the wild-type strain (wt), probably due to the lower rate of cadmium-glutathione complex synthesis in the cytoplasm. In wt, but not in lap4 strain, the oxidized/reduced GSH ratio and the Gtt activity increased in response to cadmium, confirming that the mutant is deficient in the synthesis of the complex probably because the degradation of vacuolar glutathione is impaired. Thus, under cadmium stress, Lap4 and gamma-glutamyl transferase seem to work together to assure an efficient glutathione turnover stored in the vacuole.
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Eukaryotic cells have developed mechanisms to rapidly respond towards the environment by changing the expression of a series of genes. There is increasing evidence that reactive oxygen species (ROS), besides causing damage, may also... more
Eukaryotic cells have developed mechanisms to rapidly respond towards the environment by changing the expression of a series of genes. There is increasing evidence that reactive oxygen species (ROS), besides causing damage, may also fulfill an important role as second messengers involved in signal transduction. Recently, we have demonstrated that deletion of SOD1 is beneficial for the acquisition of tolerance towards heat and ethanol stresses. The present report demonstrates that a sod1 mutant was the only one capable of acquiring tolerance against a subsequent stress produced by menadione, although this mutant strain had exhibited high sensitivity to oxidative stress. By measuring the level of intracellular oxidation, lipid peroxidation as well as glutathione metabolism, we have shown that in the SOD1-deleted strain, an unbalance occurs in the cell redox status. These results indicated that the capacity of acquiring tolerance to oxidative stress is related to a signal given by one or all of the above factors.
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Aiming to investigate the use of tridentate ligands to develop new bireductively activated prodrugs, two N2O-donor ligands (HL1: [(2-hydroxybenzyl)(2-(imidazol-2-yl)ethyl)]amine; and HL2: [(2-hydroxybenzyl)(2-(pyridil-2-yl)ethyl]amine)... more
Aiming to investigate the use of tridentate ligands to develop new bireductively activated prodrugs, two N2O-donor ligands (HL1: [(2-hydroxybenzyl)(2-(imidazol-2-yl)ethyl)]amine; and HL2: [(2-hydroxybenzyl)(2-(pyridil-2-yl)ethyl]amine) were used to synthesize new Co(III) complexes, 1 and 2. Both complexes were characterized by X-ray crystallography, mass spectrometry, electrochemistry, IR, UV–visible and 1H NMR spectroscopies. Electrochemical data in methanol revealed that the Co(III)→Co(II) reduction of 1 (−0.84V
Research Interests: Chemistry, Analytical Chemistry, Inorganic Chemistry, Organic Chemistry, Water, and 28 moreFungi, Nanotechnology, Magnetic Resonance Spectroscopy, Atomic Force Microscopy, Apoptosis, Macromolecular X-Ray Crystallography, DNA, Humans, Escherichia coli, Organotin Compounds, Animals, Bacteria, Anti-inflammatory agents, Solubility, Anti-Bacterial Agents, Rats, Transition metal chemistry, Edema, Spectrum analysis, Pyridines, Streptococcus, Wistar Rats, Carboxylic Acids, Molecular Conformation, Inorganic Biochemistry, Cell Proliferation, Antineoplastic Agents, and Biochemistry and cell biology
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Research Interests: Oxidative Stress, Transcription Factors, Gene expression, Manganese, Biocatalysis, and 14 moreSaccharomyces cerevisiae, Antioxidants, Copper, Catalase, Iron, Superoxide Dismutase, Lipid peroxidation, Hydrogen Peroxide, Biomimetic materials, SOD mimics, Microbial Viability, CAT Mimics, Superoxides, and Biochemistry and cell biology
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Research Interests: Inorganic Chemistry, Catalysis, Kinetics, Macromolecular X-Ray Crystallography, DNA, and 13 moreSaccharomyces cerevisiae, Antioxidants, Copper, Antioxidant, Temperature, Superoxide Dismutase, Magnetics, Biomimetic materials, DNA Cleavage, Molecular Conformation, Hydrogen-Ion Concentration, Ligands, and Heterocyclic compounds
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Living cells constantly sense and adapt to redox shifts by the induction of genes whose products act to maintain the cellular redox environment. In the eukaryote Saccharomyces cerevisiae, while stationary cells possess a degree of... more
Living cells constantly sense and adapt to redox shifts by the induction of genes whose products act to maintain the cellular redox environment. In the eukaryote Saccharomyces cerevisiae, while stationary cells possess a degree of constitutive resistance towards oxidants, treatment of exponential phase cultures with sub-lethal stresses can lead to the transient induction of protection against subsequent lethal oxidant conditions. The sensors of oxidative stress and the corresponding transcription factors that activate gene expression under these conditions have not yet been completely identified. We report the role of SOD1, SOD2 and TPS1 genes (which encode the cytoplasmic Cu/Zn-superoxide dismutase, the mitochondrial Mn-isoform and trehalose-6-phosphate synthase, respectively) in the development of resistance to oxidative stress. In all experimental conditions, the cultures were divided into two parts, one was immediately submitted to severe stress (namely: exposure to H2O2, heat s...
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Saccharomyces uvarum var. carlsbergensis is heat sensitive and when dried by usual procedures exhibits very poor survival. Our results demonstrate that these cells are capable of accumulating trehalose when submitted to an osmotic... more
Saccharomyces uvarum var. carlsbergensis is heat sensitive and when dried by usual procedures exhibits very poor survival. Our results demonstrate that these cells are capable of accumulating trehalose when submitted to an osmotic treatment using 20% solutions of either sorbitol or dextrin endowing them with the capacity of surviving posterior dehydration.
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Our group has recently initiated a study on the development of new prototypes for bioreductive prodrugs, based on Co(III) complexes with the ligand... more
Our group has recently initiated a study on the development of new prototypes for bioreductive prodrugs, based on Co(III) complexes with the ligand 2,2'-bis(3-hydroxy-1,4-naphthoquinone), H2bhnq. The focus of this work is to investigate the dissociation of bhnq(-2) from the complex upon reduction, and the effects of pH, redox potential, oxygen concentration and nature of the auxiliary ligands on this reaction. The bhnq(2-) ligand is a "non-cytotoxic" agent that was chosen as a probe for the reactivity studies due to its suitable chromophoric properties, at the same time that it resembles more cytotoxic naphthoquinones relevant for cancer therapy. In this way, two Co(III) complexes [Co(bhnq)(L1)]BF4·H2O (1) and [Co(bhnq)(L2)]BF4·H2O (2) (L1=N,N'-bis(pyridin-2-ylmethyl)ethylenediamine and L2=N,N'-dimethyl-N,N'-bis(pyridin-2-ylmethyl)ethylenediamine) were synthesized and fully characterized. The gallium analogs [Ga(bhnq)(L1)]NO3·3H2O (3) and [Ga(bhnq)(L2)]NO3·3H2O (4) were also prepared for helping with the assignments of the redox properties of the cobalt complexes and the structure of 2. Cyclic voltammetry analysis revealed a pH-independent quasi-reversible Co(III)/Co(II) process at -0.22 and -0.08V vs NHE for 1 and 2, respectively. An O2-dependent dissociation of bhnq(2-) was observed for the reaction of 1 with ascorbic acid. For 2, the dissociation of bhnq(2-) was found to be independent on the concentration of O2 and faster than in 1, with little influence of the pH on both complexes. The difference in reactivity between 1 and 2 and their redox properties, among other factors, suggests that 1 undergoes redox cycling, pointed out as a key feature for a prodrug to achieve hypoxic selectivity.