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PubMed1999

Hormone-regulated and glucose-sensitive transport of dehydroascorbic acid in immature rat granulosa cells.

Ascorbic acid is concentrated in granulosa cells of the follicle, and ascorbate deficiency causes follicular atresia. Dehydroascorbic acid (DHAA), the oxidized form of ascorbic acid, serves as an important source for the recycling of ascorbate. As we previously demonstrated endocrine up-regulation of ascorbic acid transport by granulosa cells, we investigated DHAA as an alternate source of ascorbate in the follicle. Granulosa cells were cultured for 24 h, and DHAA uptake was initiated by the addition of 14C-labeled ascorbic acid (300 microM) in the presence of ascorbic acid oxidase (2 U/ml), which catalyzes DHAA production. Almost 90% of accumulated DHAA was present as ascorbic acid within 2 h. Preculture of cells for 24 h with FSH (50 ng/ml) and IGF-I (30 ng/ml) significantly stimulated DHAA uptake compared with the control (158 +/- 16 vs. 43 +/- 8 pmol/10(6) cells, respectively). DHAA uptake by granulosa cells was inhibited by D-glucose (ID50, approximately 2.5 mM) and by the glucose transport inhibitors phloretin (200 microM) and cytochalasin B (10 microM), which reduced uptake to 13 +/- 2% and 8 +/- 3% of the control, respectively. Northern and Western analysis of GLUT1 in granulosa cells following 24 h coincubation with FSH and IGF-I revealed up-regulation of GLUT1 at both the messenger RNA and protein levels (1.6- and 1.3-fold of control, respectively), suggesting that the stimulatory effects of FSH and IGF-I on DHAA transport are mediated by the induction of GLUT1. GLUT4 protein was not detectable by Western analysis. Endocrine-regulated DHAA transport may represent an important mechanism for maintaining adequate antioxidant tone within the developing follicle.

Animals↗
PubMed1997

Inactivation of intracellular proteolysis and cathepsin B enzyme activity by dehydroascorbic acid and reactivation by dithiothreitol in perfused rat heart.

The selective inhibition of some subcomponents of intracellular protein degradation was characterized under exposure to the cyclic multiketone thiol oxidizing agents dehydroascorbic acid (DHA) and alloxan. Proteins of the isolated perfused rat heart were labeled in vitro with a 10-min infusion of [3H] leucine, and subsequent release of radiolabeled amino acid from cell proteins was measured. As determined previously, four subcomponents of total proteolysis can be distinguished; the first three subcomponents are reversibly inhibited by the thiol-reactive agent diamide: (a) The rapid turnover proteins comprise most of the [3H] leucine release from 20 min to 3 hr after labeling. (b) Following 3 hr of degradation, the lysosomal (insulin-responsive) subcomponent comprises 35-40% of [3H] leucine release. (c) A third nonlysosomal (adrenergic-responsive) subcomponent comprises 35%. (d) A fourth nonlysosomal subcomponent consisting of 25% of [3H] leucine release is uninhibited by diamide. Infusion of supraphysiologic DHA (1 mM) or alloxan (1.5 mM) promptly mimicked the proteolytic inhibitory action of diamide on the first three subcomponents, but did not inhibit the diamide-resistant subcomponent. Infusion of a physiologic extracellular DHA concentration of 5 microM caused little or no change in proteolysis. The proteolytic inhibitory action of DHA (1 mM) could be reversed by concurrent infusion of dithiothreitol (DTT, 1.5 mM) simultaneously with continued DHA. DHA (1 mM) caused direct inhibition of the purified sulfhydryl proteinase cathepsin B (EC 3.4.22.1), which was reversible by subsequent excess DTT (5 mM). Results indicate that a nontoxic endogenous multiketone thiol oxidant can reversibly inhibit some proteolytic processes in viable tissue; however, approximately 25% of the observed proteolysis is uninhibited. Reversible inactivation of sulfhydryl proteinases, including cathepsin B, is among the possible multiple mechanisms of this DHA action.

Alloxan↗
PubMed1994

A note on distribution of human plasma levels of ascorbic and dehydroascorbic acid.

Ascorbic acid concentrations in 102 human plasma samples ranged from 1 to 15 micrograms ml-1 with a mean concentration at about 8 micrograms ml-1, corresponding to the results of other authors. Dehydroascorbic acid was found only in traces, independent of ascorbic acid concentrations. The ascorbic acid concentrations in plasma of four persons, examined twice with a four-years interim period revealed no obvious differences over time. It is suggested that the variability of plasma ascorbic acid concentrations is mainly determined by long-term dietary habits.

Ascorbic Acid↗
PubMed1998

Deficient transport of dehydroascorbic acid in the glucose transporter protein syndrome.

The glucose transporter protein syndrome (GTPS) is caused by defective transport of glucose across the blood-brain barrier via the glucose transporter GLUT1, resulting in hypoglycorrhachia, infantile seizures, and developmental delay. Recent reports indicated that GLUT1 is a multifunctional transporter. We investigated the transport of vitamin C in its oxidized form (dehydroascorbic acid) via GLUT1 into erythrocytes of 2 patients with GTPS. In both patients, uptake of oxidized vitamin C was 61% of the mothers' values. Our findings are consistent with recent observations that vitamin C is transported in its oxidized form via GLUT1. We speculate that impaired transport of this substrate and perhaps other substrates in GTPS might contribute to the pathophysiology of this condition.

Adult↗
PubMed2000

Interaction of respiratory burst and uptake of dehydroascorbic acid in differentiated HL-60 cells.

HL-60 cells differentiated with DMSO increased their rates of uptake of ascorbate when they were activated with PMA. The rates observed after this activation were essentially the same as those with dehydroascorbic acid as the original transport substrate. The effect of activation was sensitive to the antioxidant enzymes superoxide dismutase and catalase. When ascorbate was oxidized in situ by chemical or enzymic oxidation, the rates of uptake were similar to those after activation of the cells by phorbol ester; however, in the latter case the extracellular vitamin remained largely in the reduced form and there was very little loss by degradation, whereas after immediate oxidation no more reduced ascorbate could be found outside the cells after a few minutes and a significant part of the total vitamin was lost. The generation of superoxide by xanthine/xanthine oxidase stimulated the uptake of ascorbate much less than the activation by phorbol ester; H(2)O(2) was even less effective. Stimulation of the uptake by phorbol ester was also insensitive to GSH, in contrast with stimulation by the chemical oxidation of ascorbate. Stimulation of ascorbate uptake by phorbol ester was sensitive to the respiratory-burst inhibitor diphenyliodonium as well as the protein kinase C inhibitor staurosporine, indicating the respiratory burst as the cause of stimulation. Activation of the cells by the phorbol ester also stimulated the uptake of dehydroascorbate as the original substrate, in a manner insensitive to antioxidants or inhibitors of the respiratory burst. In all cases the intracellular vitamin was completely in the reduced form. Kinetic characterization by the calculation of maximal velocities and apparent K(m) values and assaying for the dependence of uptake rates on the ionic milieu and for inhibition by glucose analogues and inhibitors of glucose transport revealed that after treatment with phorbol ester the uptake of total vitamin C in differentiated HL-60 cells was largely due to the low-affinity high-capacity glucose transporter. In contrast, in non-stimulated cells reduced ascorbate was taken up by the Na(+)-dependent high-affinity low-capacity ascorbate transporter. This change was probably due to the oxidation of ascorbate and, simultaneously, the recruitment of additional transporter molecules to the cell surface.

Biological Transport↗
PubMed1996

Protective action of dehydroascorbic acid on the Ah receptor-dependent and receptor-independent induction of lipid peroxidation in adipose tissue of male guinea pig caused by TCDD administration.

The effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on lipid peroxidation, 3H-Me-glucose (3H-Me-glu), and 14C-dehydroascorbic acid (14C-DHA) uptakes were studied in adipose tissue of male guinea pig. Under in vitro test conditions, using isolated adipose tissue in a culture medium (explant culture), TCDD reduced the uptake of 3H-Me-glu and 14C-DHA in a dose- and time-dependent fashion. The IC50 values of TCDD's action were 0.04 and 2 nM on 14C-DHA and 3H-Me-glu uptakes, respectively. TCDD (10 nM) also suppressed glucose transporting activity within 15 minutes in explant-cultured adipocytes. Cytochalasin B (CB) and nonlabeled D-glucose inhibited 14C-DHA uptake also in a dose-dependent manner. In addition, TCDD was found to induce lipid peroxidation in explant-cultured adipose tissue. This effect of TCDD was similar to that of a typical lipid peroxidation inducer, CCl4, and it was dose and time dependent. TCDD caused a statistically significant rise in lipid peroxidation at a concentration as low as 0.1 nM after 60 minutes of treatment in explant culture. Unexpectedly, the Ah receptor partial antagonists, 4,7-phenanthroline and alpha-naphthoflavone, did not fully antagonize TCDD-induced lipid peroxidation in explant-cultured adipocytes. In vivo treatment of TCDD also induced lipid peroxidation. Among seven organs of male guinea pig tested, the levels of lipid peroxidation in adipose tissue and in liver increased at 1 and 40 days following a single i.p. dose of TCDD (1 microgram/kg). The results of an in vivo time-course study indicated that such an effect of TCDD was most pronounced after 40 days of treatment. Finally, we have tested the protective role of some antioxidants on TCDD-induced lipid peroxidation under explant-culture conditions. The results indicated that DHA, but not ascorbic acid, could completely abolish TCDD-induced lipid peroxidation. The protective effect of DHA on TCDD-induced lipid peroxidation was stronger than that of alpha-tocopherol and uric acid, and this effect was blocked by CB. We conclude from these studies that TCDD acts in this guinea pig tissue through two different routes: one is the Ah receptor-dependent route causing the reduction of the level of glucose transporters and subsequent decrease of cellular uptake of DHA and the other, the Ah receptor-independent route causing the overall lipid peroxidation. Nevertheless, it appears likely that both events are antagonized by DHA.

Adipose Tissue↗
PubMed1984

Effects of ascorbic and dehydroascorbic acid on the multiplication of tumor ascites cells in vitro.

The effects of AA and DHA on ATP C+ cell multiplication in vitro were studied by measuring incorporation of 3H thymidine into DNA. The results obtained demonstrate that both AA and DHA have the same effects: they favor cell multiplication at low doses and inhibit it at high doses. Experiments carried out with serial doses of both these substances revealed that AA is more efficient in determining both stimulating and inhibiting effects. The lesser efficiency of DHA may be attributed to its limited stability in culture medium. Studies on the effect of high doses of AA and DHA added to the culture medium in single or fractionated doses revealed that fractionated administration is more efficient in inhibiting cell multiplication than single administration.

Animals↗
PubMed1975

Determination of vitamin C (ascorbic and dehydroascorbic acids) in foods and feeds.

Ascorbic acid (ASC) is separated by percolating the extract solution through an anionic Sephadex column. After one or two washings with water, the vitamin is oxidized on the column by a p-benzoquinone solution to dehydroascorbic acid (DASC). This latter being actually no acid is eluted as it is formed. The DASC containing eluate is treated with a new colorimetric reagent: 4-Nitro-1,2-Phenylenediamine (NPD). After extraction of the excess reagent with ethyl acetate, the optical extinction is measured at 375 nm. DASC, if present in the extract solution, can be reduced to ASC by dimercaptopropanol prior to chromatography. The method is very specific. The rather simple chromatographic purification can be effected semi-automatically with series of 10 colums (or more).

Ascorbic Acid↗
PubMed1999

Identification of the dehydroascorbic acid reductase and thioltransferase (Glutaredoxin) activities of bovine erythrocyte glutathione peroxidase.

Bovine erythrocyte glutathione (GSH) peroxidase (GPX, EC 1.11.1.9) was examined for GSH-dependent dehydroascorbate (DHA) reductase (EC 1.8.5.1) and thioltransferase (EC 1.8.4.1) activities. Using the direct assay method for GSH-dependent DHA reductase activity, GPX had a kcat (app) of 140 +/- 9 min-1 and specificity constants (kcat/Km(app)) of 5.74 +/- 0.78 x 10(2) M-1s-1 for DHA and 1.18 +/- 0.17 x 10(3) M-1s-1 for GSH based on the monomer Mr of 22,612. Using the coupled assay method for thioltransferase activity, GPX had a kcat (app) of 186 +/- 9 min-1 and specificity constants (app) of 1. 49 +/- 0.14 x 10(3) M-1s-1 for S-sulfocysteine and 1.51 +/- 0.18 x 10(3) M-1s-1 for GSH based on the GPX monomer molecular weight. GPX has a higher specificity constant for S-sulfocysteine than DHA, and both assay systems gave nearly identical specificity constants for GSH. The DHA reductase and thioltransferase activities of GPX adds to the repertoire of functions of this enzyme as an important protector against cellular oxidative stress.

Animals↗