Showing papers on "Dehydroascorbic acid published in 2017"
TL;DR: Calculated pKa's and reduction potentials show that the most stable form of dehydroascorbic acid in water is the bicyclic hydrated structure, in agreement with NMR studies and the possible oxidation reactions at different pH conditions can be understood.
Abstract: Ascorbic acid is a well-known antioxidant and radical scavenger. It can be oxidized by losing two protons and two electrons, but normally loses only one electron at a time. The reactivity of the ascorbate radical is unusual, in that it can either disproportionate or react with other radicals, but it reacts poorly with non-radical species. To explore the oxidation mechanism of ascorbic acid, the pKa's and reduction potentials have been calculated using the B3LYP/6-31+G(d,p) and CBS-QB3 levels of theory with the SMD implicit solvent model and explicit waters. Calculations show that the most stable form of dehydroascorbic acid in water is the bicyclic hydrated structure, in agreement with NMR studies. The possible oxidation reactions at different pH conditions can be understood by constructing a potential-pH (Pourbaix) diagram from the calculated pKa's and standard reduction potentials. At physiological pH disproportionation of the intermediate radical is thermodynamically favored. The calculations show that disproportionation proceeds via dimerization of ascorbate radical and internal electron transfer, as suggested by Bielski. In the dimer, one of the ascorbate units cyclizes. Then protonation and dissociation yields the fully reduced and bicyclic fully oxidized structures. Calculations show that this mechanism also explains the reaction of the ascorbic acid radical with other radical species such as superoxide. Ascorbate radical combines with the radical, and intramolecular electron transfer followed by cyclization and hydrolysis yields dehydroascorbic acid and converts the radical to its reduced form.
96 citations
TL;DR: The nature of degradation products using [14 C]ascorbate labelling in tomato, a model plant for fleshy fruits, are revealed; oxalate and threonate are accumulated in leaves, as is oxalyl Threonate.
Abstract: Ascorbate content in plants is controlled by its synthesis from carbohydrates, recycling of the oxidized forms and degradation. Of these pathways, ascorbate degradation is the least studied and represents a lack of knowledge which could impair improvement of ascorbate content in fruits and vegetables as degradation is non-reversible and leads to a depletion of the ascorbate pool. The present study revealed the nature of degradation products using [14C]ascorbate labelling in tomato, a model plant for fleshy fruits; oxalate and threonate are accumulated in leaves, as is oxalyl threonate. Carboxypentonates coming from diketogulonate degradation were detected in relatively insoluble (cell wall-rich) leaf material. No [14C]tartaric acid was found in tomato leaves. Ascorbate degradation was stimulated by darkness, and the degradation rate was evaluated at 63% of the ascorbate pool per day, a percentage that was constant and independent of the initial ascorbate or dehydroascorbic acid concentration over periods of 24h or more. Furthermore, degradation could be partially affected by the ascorbate recycling pathway, as lines under-expressing monodehydroascorbate reductase showed a slight decrease in degradation product accumulation.
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46 citations
TL;DR: Water-washing of spinach leaves and leaf discs increased ascorbate loss and Oxalate was the major [14C]ascorbate by-product, indicating oxidative stress.
34 citations
TL;DR: The results show that the rate of DHA reduction depends not only on the level of reduced glutathione, but also on the rates of NADPH production, contradicting the conclusions of some previous studies.
33 citations
TL;DR: The mitochondrial fraction of l-ascorbic acid is of critical importance for the regulation of the redox status of these organelles and for cell survival and is conditioned by possible cell culture effects as overexpression of SVCT2 in the plasma membrane and mitochondria.
Abstract: Significance: The mitochondrial fraction of l-ascorbic acid (AA) is of critical importance for the regulation of the redox status of these organelles and for cell survival. Recent Advances: Most cell types take up AA by the high-affinity sodium-dependent vitamin C transporter 2 (SVCT2) sensitive to inhibition by dehydroascorbic acid (DHA). DHA can also be taken up by glucose transporters (GLUTs) and then reduced back to AA. DHA concentrations, normally very low in biological fluids, may only become significant next to superoxide-releasing cells. Very little is known about the mechanisms mediating the mitochondrial transport of the vitamin. Critical Issues: Information on AA transport is largely derived from studies using cultured cells and is therefore conditioned by possible cell culture effects as overexpression of SVCT2 in the plasma membrane and mitochondria. Mitochondrial SVCT2 is susceptible to inhibition by DHA and transports AA with a low affinity as a consequence of the restrictive ionic...
29 citations
TL;DR: It is concluded that the post-flowering temperature has marked effects on the concentration of important chemical compounds responsible for taste and nutritional value of black currant berries, whereas photoperiod has no such effect in the studied cultivars.
Abstract: BACKGROUND
Marked effects of the climatic environment on fruit chemical composition have often been demonstrated in field experiments. However, complex covariations of several climatic factors in the natural environment complicate the interpretation of such experiments and the identification of the causal factors. This can be better achieved in a phytotron where the various climatic factors can be varied systematically. Therefore, we grew four black currant cultivars of contrasting origin in a phytotron under controlled post-flowering temperature and photoperiod conditions and analysed the berries for their ascorbic acid, sugar and organic acid contents.
RESULTS
The analyses revealed significant effects of genotype on all investigated compounds. Particularly large cultivar differences were observed in the concentrations of l-ascorbic acid (AA) and sucrose. The concentrations of both AA and dehydroascorbic acid (DHAA), as well as the concentrations of all major sugars, decreased consistently with an increasing temperature over the temperature range 12–24 °C. Fructose and glucose were the predominant sugars with concentrations several fold higher than that for sucrose. AA was the main contributor to the total ascorbate pool in black currant berries. The AA/DHAA ratio varied from 5.6 to 10.3 among the studied cultivars. The concentration of citric acid, which was the predominant organic acid in black currant berries, increased with an increasing temperature, whereas the opposite trend was observed for malic and shikimic acid. Quninic acid was always present at relatively low concentrations. By contrast, photoperiod had no significant effect on berry content of any of the investigated compounds.
CONCLUSION
It is concluded that the post-flowering temperature has marked effects on the concentration of important chemical compounds responsible for taste and nutritional value of black currant berries, whereas photoperiod has no such effect in the studied cultivars. © 2016 Society of Chemical Industry
25 citations
TL;DR: While AA and A2P were capable of modulating HIF-1α protein accumulation/activity, DHA supplementation resulted in minimal intracellular vitamin C activity with decreased ability to inhibit Hif-1 α activity and malignant potential in advanced melanoma.
24 citations
TL;DR: Key findings with clinical implications were that RBCs in vitro transported dehydroascorbic acid but not bromo-dehydroasc orbic acid; RBC ascorbate in vivo was obtained only via DHA transport; and internal RBCAscorbates was essential to maintain asCorbate plasma concentrations in vitro/in vivo.
23 citations
TL;DR: In this paper, 2,3-diketogulonate (DKG) is used to generate apoplastic H2O2 and delay cell-wall crosslinking.
21 citations
TL;DR: The hypothesis that genetically determined local dysregulation of dietary vitamin C or antioxidants transport contributes to IBD development is strengthened, as these transporter proteins are targetable by dietary interventions.
19 citations
TL;DR: In this paper, the authors assessed oxygen availability in different media during heat treatment and the related vitamin C loss and found that oxygen depletion stabilized completely vitamin C, independently of the medium tested.
Abstract: Oxygen availability in different media during heat treatment (8 h at 80 °C) and the related vitamin C loss was assessed. Dissolved oxygen in water containing 3 mmol kg−1 of ascorbic acid decreased initially and seemed to be replaced by oxygen from the headspace in the course of time, as oxygen values increased again. In apple puree and carrot puree in contrast, oxygen was depleted within 60 min. Vitamin C in ultrapure water was stable even in the presence of oxygen. A trigger seemed to be crucial to launch vitamin C degradation. Fe3+ ions added to water, but also the media Mc Ilvaine citrate-phosphate buffer (pH 3.5) or apple puree, initiated degradation. Adding Fe3+ ions to apple puree did not accelerate vitamin C degradation but shifted the equilibrium between ascorbic acid and dehydroascorbic acid to the latter. Oxygen deprivation stabilized completely vitamin C, independently of the medium tested. A temperature decrease to 70 or 60 °C, in contrast, had no effect on the degradation extent of vitamin C in water containing 20 μmol kg−1 Fe3+ ions but led to complete stability in apple puree.
TL;DR: It is demonstrated that adding Ce3+ could significantly promote seedling growth, and alleviate morphological and structural damage of leaf, decrease oxidative stress and increase antioxidative capacity in maize leaves caused by different stresses.
Abstract: It had been indicated that cerium (Ce) could promote maize growth involving photosynthetic improvement under potassium (K) deficiency, salt stress, and combined stress of K+ deficiency and salt stress. However, whether the improved growth is related to leaf morphological structure, oxidative stress in maize leaves is not well understood. The present study showed that K+ deficiency, salt stress, and their combined stress inhibited growth of maize seedlings, affecting the formation of appendages of leaf epidermal cells, and stomatal opening, which may be due to increases in H2O2 and malondialdehyde levels, and reductions in Ca2+ content, ratios of glutathione/oxidized glutathione, ascorbic acid/dehydroascorbic acid, and the activities of superoxide dismutase, catalase, ascorbic acid peroxidase, guaiacol peroxidase, and glutathione reductase in leaves under different stresses. The adverse effects caused by combined stress were higher than those of single stress. Furthermore, our findings demonstrated that ad...
TL;DR: In this article, the reactivity of cob(II)alamin (Cbl(II)) toward reduction of dehydroascorbic (DHA) to ascorbic acid (AA) mediated by sulfur-containing compounds such as glutathione (GSH) and thiocyanate was reported.
01 Jan 2017
TL;DR: Vitamin C is a dietary essential for only a few species, including humans, and functions as a cosubstrate for a series of enzymes, including those responsible for collagen synthesis.
Abstract: Vitamin C is a dietary essential for only a few species, including humans. Vitamin C is the generic descriptor for all compounds exhibiting qualitatively the biological activity of ascorbic acid. For animals that cannot synthesize vitamin C, the best dietary sources include fruits and vegetables. Vitamin C is water soluble and is absorbed through active and passive transport. It functions as a water-soluble antioxidant by reacting with free radicals and reducing reactive oxygen species to protect against the oxidation of lipids, proteins, and DNA. It also functions as a cosubstrate for a series of enzymes, including those responsible for collagen synthesis. Vitamin C deficiency results in scurvy, which is manifested by poor appetite, hemorrhaging, impaired wound healing, and skeletal muscle atrophy.
TL;DR: It is demonstrated that vitamin C is a nutritional stimulator of autophagy, and transporter inhibitor studies in an AsA deficient ODS model rat revealed more accurately that the enhancing effect on autophagic proteolysis still existed, even though the intracellular influx of AsA was blocked.
01 Jan 2017
TL;DR: Co-treatment of methotrexate with AA or DHA showed synergism and enhanced cytotoxicity of the anti-folate towards MDA-MB-231 breast cancer cells, which might be useful for reducing MTX-related oxidativestress.
Abstract: Aims: To examine the effects of ascorbic acid (AA), dehydroascorbic acid (DHA) and methotrexate(MTX) combined treatments on (MDA-MB-231) breast cancer cell viability and intracellular reactive oxygen species (ROS).Study Design: In-vitro method.Place and Duration of Study: Biomedical Sciences Research Institute, University of Ulster, Coleraine, BT52 1SA, United Kingdom. September 2016-2017Methodology: Cytotoxicity tests were performed with MTX (0.01- 1000 µmol/l) alone or in combination with AA or DHA, for 72 h. Cell viability was measured by 3-4,5 dimethylthiazol-2,5 diphenyl tetrazolium bromide (MTT) or Sulforhodamine B (SRB) assays. Intracellular ROS was measured by 2’,7’-dichlorofluroscein diacetate assay.Results: Treatments of MDA-MB231 cells with single agents, showed dose dependent response with 50% inhibition of cell viability (IC50) of 110.5-201.4 µmol/l (MTX), 2237-5703 µmol/l (AA) or 2474 µmol/l (DHA). Combination studies showed clear synergisms for MTX (~10 µmol/l) and DHA or AA (1100 µmol/l) but weak or no interactions at other concentrations. Three days combination treatment of DHA showed decrease of ROS, which was reversed by MTX (>10 µmol/l).Conclusions: Co-treatment of methotrexate with AA or DHA showed synergism (C1<1.0) and enhanced cytotoxicity of the anti-folate towards MDA-MB-231 breast cancer cells. Intracellular ROSdecreased with AA and DHA treatment, which might be useful for reducing MTX-related oxidativestress.