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PubMedDate not supplied

Chemical stability of selenious acid in total parenteral nutrition solutions containing ascorbic acid.

Reduction of selenious acid (H2SeO3) to elemental Se by ascorbic acid was investigated in regard to the stability of selenite in total parenteral nutrition (TPN) solutions. [75Se] H2SeO3 (100 micrograms Se/liter) was incubated at 25 degrees C with pure ascorbic acid (100 or 500 mg/liter) or added to complete TPN solutions containing similar levels of ascorbate. The mixtures were subjected to thin layer electrophoresis at pH 5.3 to separate HSeO3- from Se degree. In complete TPN formulas, little or no reduction of HSeO3- to Se degree occurred over a 24-hr period, whereas complete reduction occurred with pure ascorbic acid. Further experiments showed that the amino acid component of the TPN formula was preventing the reduction of selenite, and that reduction of selenite by ascorbate did not occur in buffered solutions having a pH of 5 or greater. These results show that reduction of selenite is strongly influenced by pH. At the concentrations of H2SeO3 and ascorbic acid commonly used, reduction to elemental Se is unlikely to be a practical problem in TPN solutions in the near-neutral pH range.

Ascorbic Acid↗
PubMed2000

Riboflavin-sensitized photochemical changes in beta-lactoglobulin in an aqueous buffer solution as affected by ascorbic acid.

The effects of ascorbic acid on the riboflavin-sensitized photochemical changes in beta-lactoglobulin in an aqueous buffer solution as determined by high performance gel permeation liquid chromatography (HPGPLC), insoluble protein content, and individual amino acid content during fluorescent light illumination were studied. The riboflavin-sensitized photochemical degradation of beta-lactoglobulin was effectively inhibited by ascorbic acid, and its inhibitory effectiveness was concentration dependent. The 0.1% ascorbic acid treatment showed 74.4% inhibition of beta-lactoglobulin degradation as determined by a HPGPLC during 6 h light illumination. Insolubility of beta-lactoglobulin in a buffer solution during light illumination was also effectively decreased by ascorbic acid treatment. The riboflavin-sensitized photochemical reduction of cysteine, histidine, lysine, methionine, and tryptophan in beta-lactoglobulin was high during 6 h fluorescent light illumination. The 0.1% ascorbic acid treatment exhibited 20.8% inhibition of total amino acid degradation in beta-lactoglobulin during 6 h light illumination, showing strong inhibitory activity against the degradation of arginine, aspartic acid, cystein, glycine, histidine, phenylalanine, proline, serine, and tryptophan.

Ascorbic Acid↗
PubMed1998

Acylated ascorbate stimulates collagen synthesis in cultured human foreskin fibroblasts at lower doses than does ascorbic acid.

Acylated derivatives of ascorbic acid were found to be active in a number of biochemical and physiological processes. In the present study we investigated the effects of 6-O-palmitoyl ascorbate on collagen synthesis by cultured foreskin human fibroblasts. Our observations indicate a marked stimulatory effect on collagen synthesis by 6-O-palmitoyl ascorbate in the concentration range of 5-20 microM, while the synthesis stimulated by ascorbic acid was maximal at concentrations of 20-100 microM. Cells treated with 10 microM palmitoyl ascorbate for 36 h exhibited a production of collagen threefold greater than those in the presence of 10 microM ascorbic acid, and it was about the same as in cells treated with 100 microM ascorbic acid. By 48 h differences were not significant. Acylated ascorbate impaired vitality of the treated fibroblasts at concentrations exceeding 20 microM in media supplemented with 0.5% FCS. However, most of the cytotoxic effect was neutralized by FCS at a concentration of 10%. The resistance of acylated ascorbate against oxidative degradation as well as the role of free radicals in the modulation of collagen synthesis by ascorbic acid and by its derivatives is discussed.

Acylation↗
PubMed1986

Ascorbic acid transport in mammalian kidney.

Ascorbic acid is known to circulate free in the plasma of several species and is therefore filtered in the kidney; reabsorption subsequently takes place and prevents urinary loss. However, no specific mechanism of renal ascorbic acid transport has previously been presented. In the present study, rat and guinea pig kidney were incubated as slices or as isolated tubules in vitro in the presence of low concentrations of [14C]ascorbic acid. The kidneys of both species handle ascorbic acid similarly. Ascorbic acid accumulates in the renal tissue to a concentration three to four times that present in the bathing media. Recently absorbed ascorbic acid diffuses freely from the kidney and is predominantly nonmetabolized during absorption. Uptake is reduced following replacement of bathing solution sodium by lithium or cesium, or when incubation is performed in the presence of metabolic inhibitors or at low temperatures. The results indicate that ascorbic acid is reabsorbed in the kidney by a sodium-dependent active transport mechanism that operates by concentrating ascorbic acid in the cellular fluid. Renal slices and tubules both appear to transport ascorbic acid and galactose across the brush-border membrane; this indicates that the tubular lumens in these preparations are not collapsed or sealed off.

Animals↗
PubMed1995

Ascorbic acid inhibits chemically induced uroporphyria in ascorbate-requiring rats.

Ascorbate was previously shown to suppress accumulation of uroporphyrin (URO) in cultured chick embryo hepatocytes and to competitively inhibit microsomal oxidation of uroporphyrinogen catalyzed by cytochrome P4501A2. Here we used the Osteogenic Disorder Shionogi (ODS) mutant rat, which cannot synthesize ascorbic acid, to examine the in vivo effect of ascorbic acid on hepatic URO accumulation caused by treatment with 3-methylcholanthrene (MC) and 5-aminolevulinate (ALA). Female mutant rats maintained on three levels of dietary ascorbate (15,200, and 800 ppm) were treated for a total of 24 days. On the 11th and 16th days, rats were administered 3-methylcholanthrene, and 5-aminolevulinate was present continuously in the drinking water from day 14. Hepatic URO accumulated at the two lowest ascorbate levels, but not at 800 ppm ascorbate. The latter dose produced normal hepatic ascorbate levels. Plasma ascorbate levels were proportional to the hepatic values. Male rats also accumulated URO at the low dietary dose of ascorbic acid. The methylcholanthrene-induced increase in microsomal levels of CYP1A1 and CYP1A2, total cytochrome P450, and activities of uroporphyrinogen oxidation and ethoxyresorufin deethylase were not affected by the dietary level of ascorbate. Neither male nor female Fischer 344 rats accumulated URO when treated with the MC/ALA regime. Hepatic ascorbate concentrations in these rats were five-fold to seven-fold higher than they were in mutant rats that developed uroporphyria on 150 ppm dietary ascorbate. In ODS rats fed ascorbate at 90 but not 900 ppm in the diet, hexachlorobenzene caused hepatic URO accumulation, indicating that the effect of ascorbic acid is not unique to the regimen using methylcholanthrene.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminolevulinic Acid↗
PubMed1983

Decalcification for electron microscopy with L-ascorbic acid.

L-Ascorbic acid decalcification was used for electron microscopy of mammalian tooth germs and bone after fixation in a glutaraldehyde-paraformaldehyde mixture. The recommended decalcifying solution is 2% with respect to L-ascorbic acid and 0.9% with respect to sodium chloride. The method has the advantage that decalcification is complete within a quarter of the time required with EDTA. The fine structure of ameloblasts and hard tissue is preserved as well as with EDTA.

Ameloblasts↗
PubMedDate not supplied

Titrimetric determination of ascorbic acid using chloranil.

Ascorbic acid is oxidized and quantitatively titrated with chloranil (2,3,5,6-tetrachloro-1,4-benzoquinone) in the presence of hexamethylenetetramine in acetone-water; the end point is determined visually by the appearance of a golden yellow color. Colored solutions are assayed by setting the initial absorbance at 451 nm to zero or the minimum, titrating with chloranil solution, and measuring absorbance after each increment of titrant. A plot of the volume of chloranil added against the absorbance gives a straight line with the volume intercept as the end point. Interference by the thiol group of cysteine, glutathione, etc., is avoided by masking with acrylamide; interference by iron(II) is masked with ammonium thiocyanate and sodium potassium tartrate. Hydrogen sulfite and thiourea (which do not interfere) are added as antioxidants during extraction of ascorbic acid from drugs and fruits.

Ascorbic Acid↗
PubMed2000

Tolerance of a field grown soybean cultivar to elevated ozone level is concurrent with higher leaflet ascorbic acid level, higher ascorbate-dehydroascorbate redox status, and long term photosynthetic productivity.

We examined the characteristics of ascorbic acid (ASC) level, dehydroascorbate (DHA) level, and the ASC-DHA redox status in the leaflets of two soybean cultivars grown in a field environment and exposed to elevated ozone (O(3)) levels. These two cultivars, one that preliminary evidence indicated to be O(3)-tolerant (cv Essex), and one that was indicated to be O(3)-sensitive (cv Forrest), were grown in open-top chambers during the summer of 1997. The plants were exposed daily to a controlled, moderately high O(3) level ( approximately 58 nl l(-1) air) in the light, beginning at the seedling stage and continuing to bean maturity. Concurrently, control plants were exposed to carbon-filtered, ambient air containing a relatively low O(3) level ( approximately 24 nl l(-1) air) during the same period. Elevated O(3) did not affect biomass per plant, mature leaf area accretion, or bean yield per plant of cv Essex. In contrast, elevated O(3) level decreased the biomass and bean yield per plant of cv Forrest by approximately 20%. Daily leaflet photosynthesis rate and stomatal conductance per unit area did not decrease in either cultivar as a result of prolonged O(3) exposure. A 10% lower mature leaflet area in O(3)-treated cv Forrest plants contributed to an ultimate limitation in long-term photosynthetic productivity (vegetative and bean yield). Possible factors causing cv Essex to be more O(3) tolerant than cv Forrest were: 1) mature leaflets of control and O(3)-treated cv Essex plants consistently maintained a higher daily ASC level than leaflets of cv Forrest plants, and 2) mature leaflets of cv Essex plants maintained a higher daily ASC-DHA redox status than leaflets of cv Forrest plants.

Journal Article↗
PubMed2002

Serum ascorbic acid concentrations in previously unsupplemented greyhounds after administration of a single dose of ascorbic acid intravenously or per os.

Plasma vitamin C concentrations (mean + SD) were measured after a large (1 g) dose of vitamin C was administered orally or intravenously to each of four trained greyhounds in a randomized cross-over design. Concentrations increased (p<0.05) for 2 h but returned to baseline by 6 h after supplementation. Peak concentrations were greater (p<0.01) after intravenous than oral administration (6.1+/-1.2 vs. 0.54+/-0.23 mg/dl). This suggests that vitamin C must be administered many times daily to maintain plasma concentrations above normal.

Administration, Oral↗