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PubMed1976

Changes in Ascorbic Acid Content during Growth and Development of Panicum miliaceum.

The present paper deals with changes in the ascorbic acid content of the shoot apex during its transformation from the vegetative to the reproductive state and its further development in Panicum miliaceum var. Samai Co. 1. Seedlings were exposed to 24-hour illumination, natural day, and 8 hours of illumination per day. Ascorbic acid was determined for the growing apex, stem, and leaf of the main shoot and for the individual branches produced on it at successive developmental stages.A several-fold increase in ascorbic acid content of the growing apex of the main shoot of plants grown under 8-hour illumination synchronizes with its transformation from the vegetative to the reproductive state. In plants grown under natural day and continuous illumination, which continue to grow vegetatively, the ascorbic acid content remains at a low level. Moving these plants to 8-hour illumination results in floral initiation and an increase in the ascorbic acid content. The high level of ascorbic acid is maintained through the gametogenic and embryogenic phases, but decreases during seed formation. A rise in ascorbic acid content of branch apices always occurs later than that in the main shoot but the increase again coincides with floral initiation in the branch apex. The ascorbic acid contents of stem and leaf are not significantly affected by the photoperiod. Hence, a massive upsurge in ascorbic acid content synchronizes with the transformation of the vegetative branch and shoot apices to the reproductive state.

Journal Article↗
PubMed1976

Ascorbic acid metabolism in rats fed high fat cholesterol diet.

The synthesis and catabolism of ascorbic acid has been studied in rats fed an atherogenic diet as also has the relation between the concentration of ascorbic acid and concentration of lipids in the tissues. The concentration of ascorbic acid was found to decrease in the serum, liver, spleen and adrenals, but not in the kidney, in the animals fed an atherogenic diet when compared with those fed normal diet. An inverse relationship was found between the concentration of ascorbic acid in the tissue and the concentration of lipids. The synthesis of ascorbic acid from D-glucuronalactone did not significantly differ in the liver and kidney, but decreased in the spleen in the animals fed the atherogenic diet. On the other hand, the catabolism of ascorbic acid significantly increased in the liver and spleen.

2,3-Diketogulonic Acid↗
PubMed2003

Ascorbic acid dynamics in the seriously ill and injured.

BACKGROUND: In addition to the known beneficial effects of ascorbic acid on wound healing and the immune response, it is also a potent extracellular antioxidant. Recent work in septic rats suggests that high-dose ascorbic acid total parenteral nutrition (TPN) supplementation may protect cells from free radical injury and improve survival. In this study, we determined ascorbic acid levels in the immediate post-injury/illness period and evaluated the ability of early short-term high levels of ascorbic acid in TPN to normalize plasma levels. MATERIALS AND METHODS: Ascorbic acid levels were determined in 12 critically injured patients and 2 patients with severe surgical infections. Each patient received TPN supplemented with increasing doses of ascorbic acid over a 6-day period. Therapeutic responses were determined by plasma and urine measurements using high-pressure liquid chromatography. RESULTS: The initial mean +/- SEM baseline plasma ascorbic acid concentration was depressed (0.11 +/- 0.03 mg/dl) and unresponsive following 2 days on 300 mg/day supplementation (0.14 +/- 0.03; P = 1.0) and only approached low normal plasma levels following 2 days on 1000 mg/day (0.32 +/- 0.08; P = 0.36). A significant increase was noted following 2 days on 3000 mg/day (1.2 +/- 0.03; P = 0.005). CONCLUSION: We confirmed extremely low plasma levels of ascorbic acid following trauma and infection. Maximal early repletion of this vitamin requires rapid pool filling early in the post-injury period using supraphysiologic doses for 3 or more days.

Adult↗
PubMed1988

Inhibitory effect of l-ascorbic acid on the growth of astrocytes in cell culture.

The effect of l-ascorbic acid on the growth of astrocytic cells in culture was investigated. l-Ascorbic acid produced a concentration-dependent reduction of the growth of astrocytes, both in normal and tumor cells. The effect of l-ascorbic acid was similar to that of the relative acidification of the medium, except in treated concentrations greater than 10(-6) M. The effects produced by both l- and d-forms of ascorbic acid were the same. The inhibitory effect of l-ascorbic acid at greater concentrations was partially prevented by oxidized glutathione and increased by the large concentration of reduced glutathione. This result suggests that l-ascorbic acid possesses the ability to inhibit the growth of astrocytic cells in culture through the acidification of the medium at small concentrations and/or the antioxidative properties of this compound at larger concentrations.

Animals↗
PubMed2006

Mechanistic insights and functional determinants of the transport cycle of the ascorbic acid transporter SVCT2. Activation by sodium and absolute dependence on bivalent cations.

We characterized the human Na(+)-ascorbic acid transporter SVCT2 and developed a basic model for the transport cycle that challenges the current view that it functions as a Na(+)-dependent transporter. The properties of SVCT2 are modulated by Ca(2+)/Mg(2+) and a reciprocal functional interaction between Na(+) and ascorbic acid that defines the substrate binding order and the transport stoichiometry. Na(+) increased the ascorbic acid transport rate in a cooperative manner, decreasing the transport K(m) without affecting the V(max), thus converting a low affinity form of the transporter into a high affinity transporter. Inversely, ascorbic acid affected in a bimodal and concentration-dependent manner the Na(+) cooperativity, with absence of cooperativity at low and high ascorbic acid concentrations. Our data are consistent with a transport cycle characterized by a Na(+):ascorbic acid stoichiometry of 2:1 and a substrate binding order of the type Na(+):ascorbic acid:Na(+). However, SVCT2 is not electrogenic. SVCT2 showed an absolute requirement for Ca(2+)/Mg(2+) for function, with both cations switching the transporter from an inactive into an active conformation by increasing the transport V(max) without affecting the transport K(m) or the Na(+) cooperativity. Our data indicate that SVCT2 may switch between a number of states with characteristic properties, including an inactive conformation in the absence of Ca(2+)/Mg(2+). At least three active states can be envisioned, including a low affinity conformation at Na(+) concentrations below 20 mM and two high affinity conformations at elevated Na(+) concentrations whose Na(+) cooperativity is modulated by ascorbic acid. Thus, SVCT2 is a Ca(2+)/Mg(2+)-dependent transporter.

Amino Acid Sequence↗
PubMed2003

Enhancement of neurite outgrowth in PC12 cells stimulated with cyclic AMP and NGF by 6-acylated ascorbic acid 2-O-alpha-glucosides (6-Acyl-AA-2G), novel lipophilic ascorbate derivatives.

It has been shown that ascorbate (AsA) and its stable derivative, ascorbic acid 2-O-alpha-glucoside (AA-2G), do not elicit neurite outgrowth in PC12 cells. However, these ascorbates are synergistically enhanced by both dibutyryl cyclic AMP (Bt(2)cAMP)- and nerve growth factor (NGF)-induced neurite outgrowth in this model. In the present study, the effects of a series of novel lipophilic ascorbate derivatives, 6-acylated ascorbic acid 2-O-alpha-glucosides (6-Acyl-AA-2G), on neurite outgrowth induced by Bt(2)cAMP and NGF were examined in PC12 cells. We found that all the tested acylated ascorbate derivatives enhanced neurite formation induced by both agents in a dose-dependent manner. Of the 6-Acyl-AA-2G derivatives, 6-octanoyl ascorbic acid 2-O-alpha-glucoside (6-Octa-AA-2G) enhanced the Bt(2)cAMP-induced phosphorylated MAPK p44 and p42 expression. A alpha-glucosidase inhibitor, castanospermine, completely abrogated the promotion of neurite outgrowth and MAPK expression by 6-Octa-AA-2G. Addition of 6-Octa-AA-2G (0.5 mM) to PC12 cells caused a rapid and significant increase in intracellular AsA content, which reached a maximum and was maintained from 12 to 24 h after the culture. These findings suggest that 6-Acyl-AA-2G is rapidly hydrolyzed to AsA within the cell and enhances neurite differentiation through the interaction with the inducer-activated MAPK pathway.

Acylation↗
PubMed1996

Ascorbic acid deficiency reduces hepatic apolipoprotein A-I mRNA in scurvy-prone ODS rats.

Using the ODS rat (genotype od/od) as a model, we investigated the effect of ascorbic acid deficiency on the expression of the apolipoprotein A-I gene. Male ODS rats (7 wk old, body weight approximately 140 g) were fed a basal diet containing ascorbic acid (300 mg/kg) or a diet without ascorbic acid for 14 d. Ascorbic acid deficiency lowered the serum apolipoprotein A-I concentration. The apolipoprotein A-I mRNA level in the liver of ascorbic acid-deficient rats was lowered to about 40% (P < 0.05) of that of control rats fed sufficient ascorbic acid. The mRNA level in jejunum was not affected by ascorbic acid deficiency. Ascorbic acid deficiency did not change the transcriptional rate of the hepatic apolipoprotein A-I gene, suggesting that post-transcriptional regulation was involved in lowering the mRNA level. The low level of hepatic apolipoprotein A-I mRNA was restored to the control level within 3 d after the administration of sufficient ascorbic acid. These data indicate that ascorbic acid deficiency lowers serum apolipoprotein A-I concentration through lowering its mRNA level and subsequent depression of its synthesis in liver.

Animals↗
PubMed1999

Ascorbic acid in buffalo ovary in relation to oestrous cycle.

Concentration of ascorbic acid was determined in different parts of buffalo ovary at four different stages of oestrous cycle viz. early luteal, mid luteal, late luteal and follicular. The stages were decided from the physical and morphological examinations of corpora lutea. The ovary was dissected in three components viz. corpus luteum, follicular fluid and ovarian stromal tissue for ascorbic acid assay. Corpus luteum showed significant change in concentration of ascorbic acid with the advancement of oestrous cycle, value being highest in late- luteal stage. Follicular fluid and ovarian stromal tissue did not show significant changes in ascorbic acid at any stage of the oestrous cycle. Small follicles, irrespective of the stage of oestrous cycle had, however, significantly higher ascorbic acid content than large follicles.

Animals↗
PubMed1989

Intestinal absorption of L-ascorbic acid in rats with renal failure.

We studied L-ascorbic acid absorption in rats subjected to subtotal nephrectomy (renal failure (RF) group) and compared the results with those obtained in sham-operated normal animals and those pair-fed with their azotemic counterparts (PF group). In vivo recirculating perfusion and in vitro everted sac techniques were employed. The in vitro experiments were repeated substituting buffer within the serosal compartment with pooled sera from uremic and normal individuals. L-Ascorbic acid absorption in vivo in the RF group was significantly lower than those found in normal control and PF groups. In contrast, the in vitro mucosal to serosal transport was increased in the RF and PF groups when compared with the normal control group, suggesting increased permeability to L-ascorbic acid in the former groups. The disparity between in vivo and in vitro results in the RF animals is indicative of some inhibitory influence present in the intact uremic animals. However, experiments comparing the effect of uremic with normal sera on in vitro transport failed to reveal any suppressive effect of uremic chemical environment. In addition, serum ascorbic acid was reduced in PF and RF groups when compared with the normal control animals, thereby excluding elevated blood level as a cause of impaired absorption in intact animals with RF. In conclusion, in vivo jejunal absorption of L-ascorbic acid is impaired in rats with RF despite evidence of increased in vitro permeability. The latter appears to be mediated by reduced nutrient intake and weight loss. The inhibitory influence present in vivo could not be reproduced by incubation with uremic sera in vitro.

Animals↗
PubMed1999

Ascorbic acid is a potent inhibitor of various forms of T cell apoptosis.

This study was designed to examine the effect of ascorbic acid (vitamin C) on various death pathways of mouse T cells. Unlike humans, mice produce their own ascorbic acid and our study tested the effect of additional ascorbic acid on murine T cells. Our data show that three T cell death pathways (growth factor withdrawal-, spontaneous-, and steroid-induced death) were inhibited when T cells were incubated with ascorbic acid. The data show that both activated and resting T cells were responsive to ascorbic acid since both populations were resistant to death stimuli when treated with ascorbic acid. Additionally, effector T cells were more likely to enter S phase if treated with ascorbic acid. Our data implicate ascorbic acid as a potent inhibitor of various forms of T cell death and suggest that vitamin C may function as an immune booster through this mechanism.

Animals↗
PubMed1998

Relation of serum ascorbic acid to serum lipids and lipoproteins in US adults.

OBJECTIVE: To examine the relation of serum ascorbic acid level to serum lipid and lipoprotein levels among a random sample of the US adult population. METHODS: Using linear regression, the relation of serum ascorbic acid level to serum lipid and lipoprotein levels was examined among 5,412 women and 5,116 men enrolled in the Second National Health and Nutrition Examination Survey (NHANES II), 1976-1980. Age, race, body mass index, level of physical activity, level of education, alcohol intake, and dietary energy, cholesterol, and fat intakes, and other potential confounders were included in the multivariate models. RESULTS: Serum ascorbic acid level was independently associated with high-density lipoprotein cholesterol (HDL-C) among women; each 1 mg/dl increase in serum ascorbic acid level (range 0.1 to 2.7 mg/dl) was associated with a 2 mg/dl increase in HDL-C level (p = 0.001). Because other investigators have demonstrated an inverse relation between ascorbic acid intake or blood levels and total serum cholesterol in individuals with elevated total serum cholesterol levels, we analyzed four subgroups of NHANES II participants with total serum cholesterol levels > 200 mg/dl. Among women with total serum cholesterol levels > or = 200 mg/dl, each 1 mg/dl increase in serum ascorbic acid level was independently associated with an increase of 2 to 3 mg/dl in HDL-C level (p < or = 0.05). Serum ascorbic acid level was not significantly associated with other serum lipids or lipoproteins. CONCLUSIONS: If the observed associations are linked causally, they would suggest that ascorbic acid is a factor in cholesterol homeostasis among women and may be particularly important for women at increased risk for coronary heart disease.

Adolescent↗
PubMed2005

Enhanced oxidative stress by L-ascorbic acid within cells challenged by hydrogen peroxide.

It has been amply documented that L-ascorbic acid added to the medium of a cell culture increases oxidative damage, and this effect of L-ascorbic acid has been ascribed to the generation of reactive oxygen intermediates in the medium during its auto-oxidation. We have here questioned whether such an effect is exerted inside the cell as well, and if so, what its mechanism is. To assess thiol oxidation in the cell, we manipulated CHO cells so that they could express bacterial alkaline phosphatase in the cytoplasm. Alkaline phosphatase activity, which requires the formation of intramolecular disulfide bridges, was shown to appear when the cells were exposed to H2O2. This H2O2-induced activity increased more than 1.5 fold when L-ascorbic acid had been loaded in the cells by incubation with L-ascorbic acid-2-O-phosphate. Similar enhancing effects were also observed by assessing oxidation of glutathione, formation of protein carbonyls, and generation of reactive oxygen intermediates. Interestingly, the effects by the L-ascorbic acid-2-O-phosphate treatment were totally suppressed by addition of the membrane-permeable chelator deferoxamine to the medium, indicating the involvement of iron ions. Because the apoprotein of conalbumin, which binds iron ions with a high affinity, had no effect and because the same deferoxamine effect was observed with the cells incubated in balanced salt solution with no metal salts added, it was concluded that L-ascorbic acid acts as a pro-oxidant within the cell suffering oxidative stress, and that this effect is elicited through increased redox-cycling of iron in combination with L-ascorbic acid.

Alkaline Phosphatase↗
PubMed1977

The microdetermination of ascorbic acid with N-chlorosuccinimide.

New methods for the microdetermination of ascorbic acid are described. The 3 proposed methods based on the fact that N-chlorosuccinimide in acid, alkaline or neutral medium readily oxidizes ascorbic acid. The mechanism of the reaction is discussed. The proposed methods are simple rapid, and sufficiently accurate to determine concentrations as low as 10 micrograms of ascorbic acid. The experimental error does not exceed +/- 2%. The methods were also used for the determination of ascorbic acid in such biological fluids as bloody, urine or edible fruits with an error not exceeding +/- 5%.

Ascorbic Acid↗
PubMed2003

Vitamin C activity in guinea pigs of 6-O-acyl-2-O-alpha-D-glucopyranosyl-L- ascorbic acids with a branched-acyl chain.

A series of novel acylated ascorbic acid derivatives, 6-O-acyl-2-O-alpha-D-glucopyranosyl-L-ascorbic acids with a branched-acyl chain (6-bAcyl-AA-2G) were recently developed in our laboratory as stable and lipophilic ascorbate derivatives. In this study, the bioavailability of 6-bAcyl-AA-2G was investigated in guinea pigs. Various tissue homogenates from guinea pigs hydrolyzed 6-bAcyl-AA-2G to give ascorbic acid (AA), 2-O-alpha-D-glucopyranosyl-L-ascorbic acid (AA-2G), and 6-O-acyl AA. The releasing pattern of the three hydrolysates suggested that 6-bAcyl-AA-2G was hydrolyzed via 6-O-acyl AA to AA as a main pathway and via AA-2G to AA as a minor pathway. The former pathway seems to be of advantage, because 6-O-acyl AA, as well as AA, can have vitamin C activity. In addition, we found that a derivative with an acyl chain of C(12), 6-bDode-AA-2G, had a pronounced therapeutic effect in scorbutic guinea pigs by its repeated oral administrations. These results indicate that 6-bAcyl-AA-2G is a readily available source of AA in vivo, and may be a promising antioxidant for skin care and treatment of diseases associated with oxidative stress.

Acylation↗
PubMed2003

Certification of standard reference material 970, ascorbic acid in serum, and analysis of associated interlaboratory bias in the measurement process.

BACKGROUND: The accurate and reproducible measurement of ascorbic acid is essential in delineating the role of ascorbic acid as a diagnostic tool for human disease and for the comparison of data acquired by different laboratories. A stabilized pair of standards of ascorbic acid in human serum, which is compatible with most analytical methods, have been prepared. METHODS: The certification was based on the gravimetric addition of ascorbic acid to metaphosphoric acid-stabilized, ascorbic acid-depleted serum and NIST liquid chromatography-electrochemical measurements. The NIST results were analyzed statistically for homogeneity, and the expanded uncertainty of each SRM was calculated using all of the NIST data. An interlaboratory comparison exercise was also performed. RESULTS: These materials, Standard Reference Material (SRM) 970 Ascorbic Acid in Serum, Level I and Level II, are homogeneous and are certified to contain (10.07 +/- 0.21) and (30.57 +/- 0.28) mmol ascorbic acid/L of solution (expanded uncertainty), respectively. In the interlaboratory comparison (n = 17), the relative SDs for the two materials were 22% and 19%. CONCLUSIONS: Two lots of serum, each containing different amounts of ascorbic acid stabilized in metaphosphoric acid, have been prepared and characterized. Many laboratories provide inaccurate results.

Ascorbic Acid↗
PubMed1970

Urinary hydroxyproline in the elderly with low leucocyte ascorbic acid levels.

Fourteen elderly patients aged 58 to 91 with varying leucocyte ascorbic acid levels had urinary hydroxyproline/creatinine ratios measured before, during, and after treatment with ascorbic acid 1 g. daily for six days. The ratio increased during treatment in those patients whose initial ascorbic acid levels were below 15mug./10(8) white blood cells. It is suggested that collagen metabolism may be impaired in these patients, and that all such patients should receive ascorbic acid supplements.

Aged↗
PubMed1992

Comparison of ascorbic acid levels in the eye and remainder of the chicken embryo during development.

Ascorbic acid was not detectable in egg white and egg yolk of fertilized eggs prior to incubation. It was demonstrated in the embryo at 5 days of incubation and its content in the eyes and other parts of the embryo increased with the embryo's age. Ascorbic acid of the eyes rose rapidly after day 6 during maximal eye growth and reached a peak by days 10-14 when the expansion of the eyes began to level off. Ascorbic acid content of the eyes decreased thereafter, while ascorbic acid in the head and the body tissues continued to rise up to the time of hatching. Whether this rapid increase of ascorbic acid concurrent with the increase of eye diameter indicates a role for ascorbic acid in the growth of the embryonic eye remains to be determined.

Animals↗
PubMed2001

The protective effects of high dose ascorbic acid and diltiazem on myocardial ischaemia-reperfusion injury.

In this study, we aimed to compare the myocardial protective effects of high dose ascorbic acid with the effects obtained by adding diltiazem to high dose ascorbic acid. We studied 30 elective cardiac surgery patients prospectively. In ascorbic acid group (group AA), ascorbic acid was given after induction and just before aortic declamping, 50 mg.kg-1 each time. In ascorbic acid + diltiazem group (group AA + D), diltiazem was added to ascorbic acid (0.3 mg.kg-1, i.v. after induction and then 2 micrograms.kg-1 min-1 i.v. infusion until declamping). Group C was the control group. There was no significant difference between groups in terms of cardiac enzyme levels. After declamping, the arterial and coronary sinus malondialdehyde levels, measured as a marker of lipid peroxidation, were increased significantly in the group C while remained stable in the other two groups. Ventricular fibrillation (VF) after declamping was positive in 3, 1 and 6 patients in the groups AA, AA + D and C respectively. In this study, we observed the prevention of lipid peroxidation in the group AA and group AA + D. The only positive result obtained by addition of diltiazem to high dose ascorbic acid was the decrease in the frequency of VF after declamping. We concluded that the prevention of lipid peroxidation in the groups AA and AA + D provided no measurable protection over myocardial ischaemia-reperfusion injury.

Adult↗