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Results for “Dehydroascorbic Acid”

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PubMed1996

Protection by ascorbate against apoptosis of thymocytes: implications of ascorbate-induced nonlethal oxidative stress and poly(ADP-ribosyl)ation.

Apoptosis can be triggered in thymocytes with stimuli (6alpha-methylprednisolone, thapsigargin, and etoposide) acting by different mechanisms. In each of these instances cell death is extensively prevented until 5 h of incubation when cells are preincubated with 250 microM ascorbic acid (AA) for 1 h, then washed, and incubated in fresh medium containing the above mentioned apoptotic stimuli. In addition, the degree of spontaneous apoptosis of untreated thymocytes is somewhat lower in the AA-preincubated cells. The protection against apoptosis does not seem to be dependent on the intracellular enrichment of AA, as measured at the end of the preincubation period. On the contrary, such a protection is strictly related to a partial loss of ascorbate in the medium (possibly due to its autooxidation), is catalase-inhibitable, and is reproduced by a preincubation of the cells with nontoxic concentrations of hydrogen peroxide. The AA-supplemented cells show a remarkable decrease in NAD+ levels and a significant increase of poly(ADP-ribose) polymerase (PARP) activity. Consistently with these results, the addition of PARP inhibitors, such as thymidine and 3-aminobenzamide, during the preincubation with AA, prevents NAD+ depletion and abolishes the protective effect of AA against apoptosis. The possibility is discussed that an early activation of PARP by stimuli which are nontoxic per se makes the cells able to withstand subsequent apoptotic stimuli which are otherwise lethal.

Animals↗
PubMed1993

Cerebral metabolism of oxidized ascorbate.

The brain has a high level of ascorbic acid which is thought to act as a reducing agent, e.g. in protecting tissues against oxidative stress. The mechanism by which ascorbate is maintained in the useful, reduced state in the CNS is evaluated herein. Cerebrum from rat or calf was minced and homogenized in buffer. The endogenous levels of ascorbic acid, dehydro-L-ascorbic acid (DHAA) and reduced glutathione (GSH) were determined by HPLC with coulometric electrochemical detection. We also quantitated tissue capacity to regenerate ascorbic acid from DHAA, which is a product of electron transfer reactions of ascorbic acid. The homogenate was fractionated by centrifugation in steps up to 110,000 x g and dialyzed free of low molecular weight components. The activity for reducing DHAA was approximately equal in the various supernatants; resuspended pellets had little activity. The active component has several properties of a protein, including being precipitated by solid ammonium sulfate addition to the tissue extract; most activity appeared in the 40-80% saturated fraction. The activity was stable up to a temperature of 80 degrees C, but was lost at 95 degrees C. The protein was digested by trypsin. The results suggest that a cytosolic component of cerebrum regenerates ascorbic acid in a step that preferentially uses GSH and NADPH as reducing cofactors. At least one form of DHAA reductase exists in brain.

Animals↗
PubMed1995

Vitamin C redox reactions in blood of normal and malaria-infected mice studied with isoascorbate as a nonisotopic marker.

It has been suggested that the host antimalarial response depends in part on phagocyte-derived oxidants and that the parasite itself exerts an oxidative stress on its erythrocytic environment. Intraerythrocytic malaria parasites are particularly susceptible to being damaged by oxidative drugs, several of which are under development as chemotherapeutic agents. Thus the antioxidant status and associated regulatory mechanisms of the blood during malaria infection are of great interest. The important antioxidant ascorbate (AH-) and isoascorbate (IAH-), an isomer that does not occur naturally in animals, were found to have similar redox properties. We therefore assessed the usefulness of IAH- as a marker for studies of AH- handling in vivo and in vitro under normal conditions and in murine malaria infection. DHIA added to whole blood from normal or Plasmodium vinckei-infected mice in vitro was rapidly taken up into blood cells and reduced to IAH-. Intracellular IAH- derived from the exogenous DHIA was released into the plasma by blood cells from malaria-infected mice but not those from normal mice. Uptake and reduction of DHIA had no effect on plasma or cellular levels of AH- under these conditions. IAH- injected i.v. into either normal or P. vinckei-infected mice was rapidly cleared in both cases and led to an increase in plasma levels of AH-; this suggested displacement of the latter from some intracellular site, presumably not associated with blood cells. DHIA administered as an intravascular bolus into either normal or malaria-infected mice was rapidly reduced. However, in contrast to the in vitro situation, the concentration of plasma IAH- derived from the injected DHIA was approximately the same in both the infected and control animals. The IAH- so formed disappeared quickly from the plasma. Intravenous injection of DHIA into malaria-infected mice caused a rapid, prolonged increase in the proportion of plasma vitamin C in the form of DHA, whereas in uninfected mice there was a transient decrease in plasma DHA followed by normalisation. The changes in plasma AH- and DHA following IV injection of a single dose of DHA closely paralleled those seen after DHIA administration. These observations indicate that: (i) blood cells from normal and malaria-infected mice take up and reduce DHIA in a similar fashion, but they have different ways of handling the resulting IAH-; (ii) cells other than blood cells are important in the reduction of plasma DHIA and DHA in vivo; (iii) malaria-infected mice are less capable of handling oxidative challenge than normal ones; (iv) in some circumstances IAH- and DHIA may be useful nonisotopic markers for studies of vitamin C handling in vitro and in vivo.

Animals↗
PubMed1994

Ascorbyl free radical: a noninvasive marker of oxidative stress in human open-heart surgery.

To assess the development of oxidative stress in cardiac ischemia/reperfusion, the resulting depletion of plasma ascorbate was monitored by electron spin resonance spectroscopic detection of ascorbyl free radical (AFR) in a homogeneous group of 12 patients undergoing aortic valve replacement. Dimethyl sulfoxide (DMSO) was used as an enhancer and stabilizer for AFR in plasma separated from blood samples collected 15 min before incision, 10 min before aortic declamping, and sequentially during the initial 30 min of reperfusion. Plasma DMSO/AFR levels of patients were found to be significantly lower than in healthy subjects (-25%), further decreased upon ischemia (-35%), dropped to their lowest values within the first 10 min of reperfusion (-46%), and did not recover their initial values within 30 min following reflow. Cardiac index measurements revealed a still depressed heart function 4 h postdeclamping and a more delayed tissue injury was evidenced by cardiac myosin and myoglobin release in plasma. DMSO/AFR levels at early reperfusion were slightly (+ 12%) higher in plasma obtained from coronary sinus samples than in plasma from peripheral blood, suggesting an extra ascorbate release from the injured heart tissue. The close analogy between these results and the reported measurements of other plasma markers of oxidative stress, including ascorbate, indicates that the present method could be of great value in clinical practice.

Aortic Valve↗
PubMed2004

Direct fluorimetric determination of ascorbic acid by the supramolecular system of AA with beta-cyclodextrin derivative.

We established a simple and selective fluorimetric method for the determination of ascorbic acid (AA) with the novel mono-[6-N(4-carboxy-phenyl)]-beta-cyclodextrin (ACD). The method is based on the fluorescence intensity of ACD decreases as the ACD-AA supramolecular complexes form. The fluorescence intensity is measured at excitation and emission wavelengths of 270 and 352 nm, respectively. Under optimum condition, a linear relationship is obtained between the fluorescence intensity and the concentration of AA in the range of 0.05-8.0 microgml(-1). The detection limit is 0.012 microgml(-1). The method has been applied to the direct analysis of AA in real samples with satisfactory results.

Absorption↗
PubMed1986

Ascorbate regeneration in bovine ocular tissues by NADH-dependent semidehydroascorbate reductase.

Despite its fast autoxidation in vitro, ascorbate remains in its reduced form in vivo, indicating a special mechanism may be involved in its regeneration. The presence of an NADH-dependent reductase system, semidehydroascorbate reductase (SDR), for regeneration of ascorbate from its partially oxidized form, semidehydroascorbate (SDA), was demonstrated in bovine ocular tissues after extraction in Triton X-100. Highest SDR activity was detected in retinal extracts in the order of retina greater than pigment epithelium-choroid = ciliary body greater than iris. Minimal or no activity was observed in lens extracts or in aqueous fluid. Freezing and thawing, or boiling, destroyed the NADH-dependent SDR activity. NADH oxidation was significantly reduced (22% of total activity) when assays with retinal extracts were performed at 5 degrees C. Treatment with 4 mM, N-ethylmaleimide reduced the rate of NADH oxidation to 73 or 42% compared with control values with retinal or ciliary body extracts, respectively.

Animals↗
PubMed2003

Effects of processing treatment and sorbate addition on the flavor characteristics of apple cider.

Processing treatments used to produce a microbiologically "safe" apple cider were evaluated to determine the impact of these treatments on the overall flavor characteristics. Apple cider with (0.1%) and without (0%) potassium sorbate was subjected to four processing treatments: untreated, irradiated at 2 kGy, irradiated at 4 kGy, and pasteurized. Volatile flavor compounds were isolated from the cider using solid-phase microextraction methods with gas chromatographic analysis. A trained descriptive analysis panel evaluated sensory attributes. The effects of the processing treatment were dependent on the presence of sorbate in the apple cider. Irradiation treatments resulted in a decrease in the content of esters characteristic of apple flavor and an increase in the content of alcohols and aldehydes formed through lipid oxidation reactions. The presence of sorbate reduced the effects of the irradiation treatments on these volatile flavor compounds. Sensory panelists, however, detected higher intensities of undesirable flavor attributes, including "cardboard flavor", and lower intensities of the desirable "apple flavor" in irradiated cider with added sorbate.

Alcohols↗
PubMed2000

Product and redox potential analysis of sauerkraut fermentation.

The relationships between the redox potential of the brine, during fermentation of white cabbage into sauerkraut of two early and two late fermentation processes, and the changes in the amount of sugars, organic acids, the redox potential of the brine and of the ascorbic acid redox couple, and pH are described. The trend in the change of the redox potential of the brine is the same for all four fermentation processes studied. In the first phase a sharp decrease in redox potential is followed by an increase in redox potential. In the second phase the redox potential is rather constant. This second phase is followed by another decrease in redox potential, which stabilizes at a minimum value, the third phase. It was observed that sugar fermentation and acid production mainly took place during the first and third phases, probably representing, respectively, the heterogeneous and homogeneous fermentation processes.

Ascorbic Acid↗