Elucidation of the biochemical role of ascorbic acid.
Explore the source record for details and available documents.
Animals↗
SEARCH · Search PubMed
Results for “Dehydroascorbic Acid”
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Ascorbic acid stimulates chloride transport in the amphibian cornea.
The cornea of the toad, Bufo marinus, actively transports chloride from the endothelial to the epithelial surface. This transport process has been related to the maintenance of the normal transparency of the cornea. Ion transport, as evidenced by the short-circuit current (SCC), is markedly stimulated by physiologic concentrations of ascorbic acid. Measurement of the unidirectional fluxes of 36Cl and 22Na shows that the increase in SCC is due primarily to a stimulation of the active transport of chloride.
Animals↗
Influence of Drought-Induced Water Stress on Soybean and Spinach Leaf Ascorbate-Dehydroascorbate level and Redox Status.
We examined the influence of water stress (water deficit) induced by drought on the steady state levels of ascorbic acid (ASC), dehydroascorbate (DHA), and the ASC&rcolon;DHA redox status in leaflets of Glycine max (soybean) and leaves of Spinacia oleracea (spinach). Two soybean cultivars (cv. Essex and cv. Forrest) and one spinach cultivar (cv. Nordic) were grown in high-light growth chambers ( approximately 1000-1200 µmol m-2 s-1) or in the greenhouse during May, June, and July 1999. The cultivars were supplied with water until approximately 25-29 d postemergence, at which time one-half of the plants were not watered for a period of from 4.5 to 7.5 d; the other half of the plants were provided water daily and served as controls. On designated days, leaf water potential (PsiLeaf) was measured, and leaf disks of constant area were excised in the period between approximately 1230 and 1330 hours. Leaf disk samples were immediately frozen in liquid N2, samples were extracted, and ASC and DHA levels were measured and expressed as µmol per gram dry mass per time point. For the soybean cultivars, low PsiLeaf values ( approximately -3.00 to -3.95 MPa) were accompanied by slight decreases in ASC levels and slight increases in DHA levels per gram dry mass. In some cases, leaflet ASC levels of water-stressed soybeans were similar to controls or were even increased by as much as 1.2 times. In soybeans, the mole fraction of ASC remained at 93-99 mol% of the total ascorbate (ASC+DHA), indicating that most of the total ascorbate remained in the reduced form even at low water potential. In spinach plants subjected to water stress (-1.8 to -2.6 MPa), leaf ASC decreased as much as 38%, but the ASC remained at 96-99 mol% of the total ascorbate. It is concluded that during water stress, enzymes of the ascorbate-glutathione cycle in leaf mesophyll cells, as well as in the system that generates reductant to support DHA to ASC recycling, e.g., photosynthetic electron transport in chloroplasts, is able to remain active enough to maintain reduction of DHA to ASC.
Journal Article↗
Redox regulation of copper-metallothionein.
Copper (Cu) is an essential element whose localization within cells must be carefully controlled to avoid Cu-dependent redox cycling. Metallothioneins (MTs) are cysteine-rich metal-binding proteins that exert cytoprotective effects during metal exposure and oxidative stress. The specific role of MTs, however, in modulating Cu-dependent redox cycling remains unresolved. Our studies utilized a chemically defined model system to study MT modulation of Cu-dependent redox cycling under reducing (Cu/ascorbate) and mild oxidizing (Cu/ascorbate + H2O2) conditions. In the presence of Cu and ascorbate, MT blocked Cu-dependent lipid oxidation and ascorbyl radical formation with a stoichiometry corresponding to Cu/MT ratios </=12. In the presence of H2O2 the degree of protection by MT was less and biological oxidations and radical formation were inhibited only up to Cu/MT ratios of 6. Physical interaction of MT and Cu was measured by using low-temperature EPR of free Cu2+ in solution. The maximal amount of EPR-silent Cu1+ (presumably in complex with MT) corresponded to 12 molar equivalents of Cu/MT under reducing conditions, but only 9 in the presence of H2O2. H2O2 modulated the ability of MT to protect HL-60 cells from Cu-induced cell death in a manner that correlated with the ability of MT to mitigate Cu-redox cycling in cell-free systems. Thus, optimal binding of Cu to MT is achieved under reducing conditions; however, a portion of this Cu appears releasable under oxidizing conditions. Release of free Cu from MT during oxidative stress could enhance the formation of reactive oxygen species and potentiate cellular damage.
Animals↗
Vitamin E supplementation does not increase the vitamin C radical concentration at rest and after exhaustive exercise in healthy male subjects.
BACKGROUND: Extensive exercise may promote the formation of reactive oxygen species and subsequently contribute to tissue damage. A compound which can protect cells and tissues is vitamin E. The vitamin E radical, formed during the radical scavenging process, can be reduced by vitamin C resulting in a higher level of the vitamin C radical (semidehydroascorbate free radical). An increase of the vitamin C radical, however, is assumed to exert prooxidative effects. AIM OF THE STUDY: To elucidate whether supplementation of vitamin E and exhaustive exercise lead to an increase of the vitamin C radical in human plasma. METHODS: A placebo controlled, cross over study with 13 male volunteers was carried out. After an 8 day supplementation period with 500 I.U. D-alpha-tocopherol, the subjects performed two exhaustive treadmill runs. Blood samples were collected at rest, 0, 0.25, 1, 3, 24 and 48 h after exercise. Serum was separated and concentrations of D-alpha-tocopherol and ascorbic acid were determined by HPLC. Vitamin C radical levels in plasma were assessed by electron paramagnetic resonance (EPR). RESULTS: Vitamin E and C both showed a tendency to decrease between 3 h and 24 h after exercise. Vitamin C radical level remained stable during the whole period. Neither vitamin E supplementation nor exercise had any influence on the plasma concentration of the vitamin C radical. CONCLUSIONS: Vitamin E supplementation under conditions of mild oxidative stress does not result in an increased vitamin C radical concentration.
Adult↗
Transport of L-ascorbic acid and dehydro-L-ascorbic acid across renal cortical basolateral membrane vesicles.
The uptake of L-ascorbic acid and dehydro-L-ascorbic acid into renal cortical basolateral membrane vesicles has been characterized. The uptake systems for both solutes demonstrate saturation kinetics. The presence of structural analogs of L-ascorbic acid and dehydro-L-ascorbic acid results in cis-inhibition and trans-stimulation. Uptake of each substrate is Na+-independent, proceeding to an endpoint of substrate equilibrium across the vesicular membrane. The transport mechanism(s) for L-ascorbic acid and dehydro-L-ascorbic acid appears to be facilitated diffusion.
Animals↗
Chondrocyte transport and concentration of ascorbic acid is mediated by SVCT2.
Collagen II is the major protein component of articular cartilage and forms the collagen fibril network, which provides the tensile strength of cartilage. Collagen II synthesis is enhanced by ascorbic acid (vitamin C) at both a transcriptional and post-transcriptional level. While the importance of ascorbic acid in the synthesis of collagen has been established, the mechanism by which this essential nutrient is transported into chondrocytes has not been investigated previously. We have characterized the transport of the reduced form of ascorbic acid in passaged primary human chondrocytes to discern the physiologically relevant pathways of ascorbic acid transport in cartilage. We have found that chondrocytes are robust concentrators of ascorbic acid, capable of transporting the reduced form, and concentrating total ascorbic acid, in the reduced form and its metabolites, 960-fold over the concentration in the extracellular milieu. Chondrocyte transport of ascorbic acid was sodium and temperature dependent, stereoselective for the L-forms, and inhibited by the anion transport inhibitor, sulfinpyrazone. Chondrocytes preferentially expressed the full-length and functional isoform of sodium-dependent vitamin C transporter 2 (SVCT2). When this transcript was suppressed with sequence-specific siRNAs, the active transport component of ascorbic acid was abolished. Thus, we provide the first evidence that SVCT2 mediates the secondary active and concentrative transport of ascorbic acid in human chondrocytes.
Amino Acids↗
Impaired ascorbic acid metabolism in streptozotocin-induced diabetic rats.
Ascorbic acid (AA) metabolism in streptozotocin (STZ)-induced diabetic rats was determined by examining urinary excretion, renal reabsorption, reductive regeneration, and biosynthesis of AA at 3 and 14 days after STZ administration. AA concentrations in the plasma, liver, and kidney of the diabetic rats were significantly lower than those of controls on d 3, and decreased further as the diabetic state continued. Hepatic AA regeneration significantly decreased in the diabetic rats on d 3 in spite of increased gene expressions of AA regenerating enzymes and was further reduced on d 14. Hepatic activity of L-gulono-gamma-lactone oxidase, a terminal enzyme of hepatic AA biosynthesis, also decreased significantly on d 3 and decreased further on d 14. Urinary excretion of AA was significantly increased on d 3, with an increase in urine volume but no change in gene expressions of renal AA transporters (SVCT1 and SVCT2). Urinary excretion of AA was normalized on d 14. The results suggest that impaired hepatic and renal regeneration, as well as increased urinary excretion and impaired hepatic biosynthesis of AA, contributed to the decrease in AA in plasma and tissues of STZ-induced diabetic rats.
Animals↗
The antioxidant status of patients subjected to total body irradiation.
BACKGROUND AND PURPOSE: Total body irradiation (TBI) is a routine preconditioning procedure for the treatment of leukemia and aplastic anemia, prior to bone marrow transplantation (BMT). Ionizing radiation generates reactive oxygen derived species (ROS) that can be removed by antioxidants. Our purpose is to determine the antioxidant status of patients undergoing TBI by evaluating the oxidant stress and their antioxidant capacity. MATERIAL AND METHODS: We evaluated by cyclic voltammetry (CV) the total antioxidant capacity (TAC) in plasma of 14 patients undergoing TBI prior to BMT. The levels of the antioxidants, ascorbic acid (AA) and uric acid (UA) were determined by HPLC-ECD. The oxidant stress level was calculated by the ratio [dehydro ascorbic acid]/total ascorbic acid]. RESULTS: TAC was reduced by 36% (p < 0.02) but after 4 months recovered to a level 22% higher than before the treatment (p < 0.05). Both, AA and UA, decreased following irradiation by 84% (p < 0.02) and 24% (p < 0.05) respectively, but returned to a level of 21% and 320% after 4 months compared to baseline values. The changes in [UA] were affected by Allopurinol (xanthine oxidase inhibitor), given as a routine pretransplant therapy until day -1. The [dehydroascorcbic acid]/[total ascorbic acid] (%) was 45% (range of normal controls = 13.2 +/- 1.5%) and increased by 69% following TBI. In order to obtain a decrease in the TAC of plasma in vitro, comparable to that in vivo, a 1000 fold higher dose of irradiation was required. CONCLUSIONS: TBI caused a pronounced decrease in antioxidant capacity and an excessive increase in oxidant stress. We assume that TBI alters antioxidant homeostasis greatly enhancing the stress damage. CV measurements may lead to a better understanding of the balance between oxidant stress and antioxidant utilization, and to a reconsideration of the routine use of Allopurinol as pretreatment for TBI, and antioxidant support before and/or after TBI.
Adolescent↗
Ascorbic acid uptake and metabolism by corneal endothelium.
Ascorbic acid is concentrated in various ocular compartments where it is thought to protect diurnal animal species against damaging effects of ultraviolet radiation. The authors evaluated the possibility that corneal endothelial cells have specific transport and/or metabolic properties that deliver ascorbic acid to the stroma. Bovine corneal endothelial cells were grown to confluence in multiple-well plates. Individual groups of cells (approximately 10(4)) were then incubated at various times at 34 degrees C in a physiologic buffer that contained a 10 microM level of 14C-labeled ascorbic acid or the oxidized product, dehydro-L-ascorbic acid. Endothelial cells take up dehydro-L-ascorbic acid at least seven times as rapidly as they take up ascorbic acid. After 30 sec of incubation with 14C-dehydro-L-ascorbic acid, most of the label accumulated in the cell is in the reduced form. Uptake is inhibited by cyanide and iodoacetamide but is unaffected by ouabain. Exposure of cultured cells to various intermediates in the energy metabolism pathways reduced uptake of ascorbic acid but had a minor effect on uptake of the oxidized molecule. These results suggest that the cornea has transport and metabolic capacity to extract dehydro-L-ascorbic acid from aqueous humor and reduce it, thus providing a source of ascorbic acid for corneal protection. This also would maintain "total" ascorbic acid of aqueous humor in the reduced state.
2,3-Diketogulonic Acid↗
Analyses of vitamin C in biological samples with an emphasis on recent chromatographic techniques.
AA analyses are rife with problems - but primarily stability of the sample AA and specificity are the most prevalent shortcomings of the assays reviewed. Should one desire to quantify AA alone with no consideration for DHAA or DKG, chromatographic separations such as those described by Nahrwold (1981) with reductants added to samples and standards using UV detection, or Iwata et al. (1985) with fluorescence or Tsao and Salimi (1982) with EC detection would probably be appropriate depending upon the equipment available. The initial preparation of sample must be tested to ensure that no spontaneous oxidation of AA occurs during the sample preparation. The main advantage of these chromatographic assays is simply that one is measuring AA directly. On the other hand, manual assays such as that proposed by Zannoni et al. (1974) or Samyn (1983) have apparently demonstrated sufficient specificity and sensitivity to be used as well. When other vitamin C compounds need to be quantified, chromatographic assays should be considered but the selection is largely dependant on the sample size (and thus sensitivity required), the possible interfering compounds, and the detector available. Ideally HPLC should ensure the specificity by resolving the compounds of interest from artifacts. However, the optical characteristics of DHAA and DKG which are quite different from that of AA and detection limitations have fostered a number of complicated manipulations to quantify the former.
2,3-Diketogulonic Acid↗
Markers for cytogenetic damage in smokers: associations with plasma antioxidants and glutathione S-transferase mu.
Biomarkers for increased cytogenetic damage in smokers include sister chromatid exchanges (SCE) in peripheral lymphocytes and micronuclei in sputum cells. These markers may reflect increased cancer risk. Increased cancer risk has also been associated with lower blood levels of the antioxidants beta-carotene and vitamin C and with genetic deficiency of the detoxification enzyme glutathione S-transferase mu (GST-mu). We therefore evaluated the associations of plasma antioxidants, GST-mu phenotype, and indices for tobacco exposure with SCEs and micronuclei in a group of 156 male cigarette smokers and 38 nonsmokers. As expected, smokers as compared with nonsmokers had higher SCE levels (5.08 versus 4.71 SCE/lymphocyte) and lower levels of plasma beta-carotene (0.31 versus 0.48 mumol/liter) and blood vitamin C (36.6 versus 33.8 mumol/liter). In smokers, SCEs were weakly correlated with plasma cotinine (r = 0.186) but not with plasma antioxidants (all r < 0.04). Micronuclei in smokers were not correlated with either cotinine or antioxidants (all r < 0.14). As reported previously, SCEs were higher (5.24 versus 4.97 SCE/lymphocyte) in GST-mu-deficient smokers than in nondeficient smokers. Micronuclei, however, were similar in both GST-mu phenotypes (4.3 versus 4.9 micronuclei/3000 cells). No correlation was observed between micronuclei and SCEs (r = -0.025). Large random variations in both SCEs and micronuclei make it difficult to interpret the absence of relations unambiguously. The results indicate that SCEs and micronuclei have only limited sensitivity to variations in cigarette smoke exposure. The association between GST-mu and cancer risk may be mediated through increases in certain forms of smoking-induced DNA damage in GST-mu deficiency.
Adult↗
Hydrogen peroxide cytotoxicity. Low-temperature enhancement by ascorbate or reduced lipoate.
The principal mechanism of H2O2 toxicity is thought to involve the generation of hydroxyl (HO.) radicals through its interactions with Fe2+ ions by the Fenton reaction. Of particular interest has been the demonstration by Ward, Blakely & Joner [(1985) Radiat. Res. 103, 383-392] that the cytotoxicity of H2O2 is diminished at low temperature. We have now examined this phenomenon further with a mammalian epithelial cell line (CNCMI-221). Resistance of these cells to 100 microM-H2O2 added extracellularly exhibits a transition in the temperature range between 27 degrees C and 22 degrees C. We have found that the low-temperature resistance to cytotoxic concentrations of H2O2 is abolished by preincubation of cells with reductants such as ascorbate or reduced lipoic acid. This implies that the low-temperature resistance to H2O2 cytotoxicity may be due to inhibition of cellular reductive processes. The restoration of the cytotoxic action of H2O2 at 4 degrees C by ascorbate is prevented by pre-exposure of cells to desferrioxamine. This is evidence that transition-metal ions (such as iron ions) are involved in the cytotoxicity and is consistent with a mechanism of cell damage that depends on the Fenton reaction and a metal ion in the reduced state. Restoration of H2O2 cytotoxicity at low temperature by ascorbate is consistent with the artificial production of an intracellular reducing environment that at normal temperatures is sustained by cellular metabolism.
Animals↗
Furan precursors in food: a model study and development of a simple headspace method for determination of furan.
Furan was previously detected in foods that had undergone thermal treatment. Because furan is now classified as a possible human carcinogen, a model system was developed to investigate the origins of furan. Also, a simple, rapid isotope dilution (d4-furan) headspace method was developed to measure furan. Two pathways of furan formation have been identified in the model systems tested so far. The first is the oxidation of polyunsaturated fatty acids at elevated temperatures, and the second is linked to the decomposition of ascorbic acid derivatives. The analytical procedure, based on the use of a 50 microL injection (from the headspace of a 1.5 mL vial containing 0.5 mL water) into the split/splitless injection port of a gas chromatograph/mass spectrometer (electron ionization, selected-ion monitoring), showed linearity in the 10-1000 ng/g range with a limit of detection of 1 ng/g.
Ascorbic Acid↗
Effect of the type of serum in the medium on sodium ascorbate-induced cytotoxicity.
Sodium ascorbate induced cytotoxicity against human glioblastoma T98G cells in RPMI1640 medium supplemented with fetal bovine serum or human serum samples was studied. Several human serum samples significantly reduced the cytotoxic activity of sodium ascorbate, regardless of sex, age or the disease of the serum donor with or without heat-inactivation of the serum. ESR spectroscopy revealed that this serum effect was not simply due to the alteration of the ascorbyl radical intensity, produced from sodium ascorbate. The present study suggests that the apoptosis-inducing activity of sodium ascorbate might be significantly affected by human serum.
Adult↗
Ascorbate is regenerated by HL-60 cells through the transplasmalemma redox system.
Ascorbate was maintained in the media during a long-term culture by HL-60 cells. The chemical oxidation of ascorbate was reversed in vitro by living HL-60 cells and was related to the amount of cells added. The increase of NADH concentration by lactate addition to cells was accompanied by an increase of both ascorbate regeneration and ferricyanide reduction. Further, plasma membrane enriched fractions from HL-60 cells revealed enhancement of both ascorbate regeneration and ferricyanide reduction in the presence of NADH when previously treated with detergent. The blockage of cell surface carbohydrates by wheat germ agglutinin (WGA) and Concanavalina ensiformis (Con A) lectins significantly inhibited the regeneration of ascorbate caused by the cells. These results support the idea that ascorbate is externally regenerated by the NADH-ascorbate free radical reductase as a part of the transplasma membrane redox system.
Ascorbic Acid↗
Transport and intracellular accumulation of vitamin C in endothelial cells: relevance to collagen synthesis.
Endothelial cells preserve vascular integrity in part by synthesizing type IV collagen for the basement membrane of blood vessels. Vitamin C, which at physiologic pH is largely the ascorbate mono-anion, both protects these cells from oxidant stress and is required for collagen synthesis. Therefore, cultured endothelial cells were used to correlate intracellular concentrations of ascorbate with its uptake and ability to stimulate collagen release into the culture medium. The kinetics and inhibitor specificity of ascorbate transport into EA.hy926 endothelial cells were similar to those observed in other cell types, indicative of a specific high affinity transport process. Further, transport of the vitamin generated intracellular ascorbate concentrations that were 80-100-fold higher than concentrations in the medium following overnight culture, and transport inhibition with sulfinpyrazone and phloretin partially prevented such ascorbate accumulation. On the other hand, low millimolar intracellular concentrations of ascorbate impaired its transport measured after overnight culture. Synthesis and release of type IV collagen into the culture medium was markedly stimulated by ascorbate in a time-dependent manner, and was saturable with increasing medium concentrations of the vitamin. Optimal rates of collagen synthesis required intracellular concentrations of the vitamin up to 2 mM. Since such concentrations can only be generated by the ascorbate transporter, these results show the necessity of transport for this crucial function of the vitamin in endothelium.
Ascorbic Acid↗
Glucose oxidase-produced H2O2 induces Ca2+-dependent DNA damage in human peripheral blood lymphocytes.
DNA of lymphocytes from human peripheral blood was analyzed by using the single cell gel electrophoresis technique (comet assay). The cells were used either as received from the donors or after treatment with various concentrations of the H2O2-generating enzyme glucose oxidase, in order to achieve a continuous flow of H2O2. The formation of single strand breaks (SSB) was dose-related but the time course of the induction of SSB by relatively low concentrations of glucose oxidase was of a biphasic mode with a fast increase 2 to 5 min after the addition of glucose oxidase followed by a gradual decrease toward the original base level during the next 35 to 60 min. This response of the cells appears to be based on the activation of already existing defense system(s) because it was shown that H2O2 is continuously released during the reaction time and the inhibition of protein synthesis does not affect the observed pattern. Supplementation of the growth medium with various antioxidants resulted in substantial protection only when the agents were taken up by the cells. The presence of the intracellular calcium chelator BAPTA protected the cells from H2O2-induced DNA damage in a dose-dependent manner. Only at the higher rate of H2O2-generation considerable DNA damage was observed in the presence of BAPTA. These results suggest that H2O2, at low concentrations induces DNA damage through intracellular Ca2+ -mediated processes, which lead to DNA strand breaks possibly by endonuclease activation.
Antioxidants↗