Showing papers on "Ascorbic acid published in 1983"

Implications of water stress‐induced changes in the levels of endogenous ascorbic acid and hydrogen peroxide in Vigna seedlings

Abstract: Vigna cutjang Endl. cv. Pusa Barsati seedlings, subjected to increasing degrees of water stress (−0.5, −1.0, −1,5 MPa), produced an approximately proportional increase in glycolate oxidase activity, hydrogen peroxide (H2O2) and proline content but a decrease in catalase activity, ascorbic acid and protein content. Leaf water potential (leaf ψ) and relative water content (RWC) were also lowered with increasing stress. Pretreatment with l-cysteine and reduced glutathione (10-3 M) decreased glycolate oxidase activity, H2O2 content, ascorbic acid oxidase activity, proline content and also slightly improved the water status of leaves stressed (−1.0 MPa) for 2 days. Pretreatment of non-stressed seedlings with these antioxidants had little or no effect. These studies indicate that treatment with antioxidants makes the plant tolerant against water stress by modulating the endogenous levels of H2O2 and ascorbic acid in stressed tissue.

Glutathione and ascorbic acid in spinach (Spinacia oleracea) chloroplasts. The effect of hydrogen peroxide and of Paraquat.

Abstract: The stroma of spinach chloroplasts contains ascorbic acid and glutathione at millimolar concentrations. [Reduced glutathione]/[oxidized glutathione] and [ascorbate]/[dehydroascorbate] ratios are high under both light and dark conditions and no evidence for a role of oxidized glutathione or dehydroascorbate in the dark-deactivation of fructose bisphosphatase could be obtained. Addition of H2O2 to chloroplasts in the dark decreases the above ratios, an effect that is reversed on illumination. Addition of Paraquat to illuminated chloroplasts caused a rapid oxidation of reduced glutathione and ascorbate, and apparent loss of dehydroascorbate. Paraquat rapidly inactivated fructose bisphosphatase activity, as assayed under physiological conditions.

In vivo measurement of dopamine and its metabolites by intracerebral dialysis: changes after d-amphetamine.

Abstract: By using a new technique, intracerebral dialysis, in combination with high performance liquid chromatography and electrochemical detection, it was possible to recover and measure endogenous extracellular dopamine, together with its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) from the striatum and nucleus accumbens of anaesthetized or freely moving rats. In addition, measurements of extracellular 5-hydroxyindoleacetic acid, ascorbic acid, and uric acid were made. Basal extracellular concentrations of dopamine and DOPAC in the striatum were estimated to be 5 X 10(-8) M and 5 X 10(-6) M, respectively. d-Amphetamine (2 mg/kg s.c.) increased dopamine levels in the striatum perfusates by 14-fold, whereas levels of DOPAC and HVA decreased by 77% and 66%, respectively.

The effects of organic acids, phytates and polyphenols on the absorption of iron from vegetables.

Abstract: 1. Non-haem iron absorption from a variety of vegetable meals was studied in parous Indian Women, using the erythrocyte utilization of radioactive Fe method.2. The studies were undertaken to establish whether Fe absorption could be correlatedwith the chemical composition of the foodstuff.3. Addition of the following organic acids commonly found in vegetables, improved the geometric mean Fe absorption from a basic rice meal as follows: from 0·028 to 0·085 with 1 g citric acid, from 0·031 to 0·081 with 15 mg ascorbic acid, from 0·048 to 0·095 with 1 g L-malic acid, from 0·041 to 0·096 with 1 g tartaric acid. The only exception was oxalic acid; the addition of 1 g calciumoxalate to cabbage (Brassica oleraceae) was associated with some depression in Fe absorption from 0·320 to 0·195.4. There was a marked inhibition of the geometric mean absorption when 500 mg tannic acid was added to a broccoli (Brassica oleraceae) meal (0·015 v. 0·297). Sodium phytate (2 g) caused a similar, though less profound inhibition (0·035 to 0·152).5. When 3 mg ferrous sulphate was added to different vegetables the geometric mean absorption varied widely. Vegetables of low Fe bioavailability were wheat germ (Triticum aestivum) 0·007, aubergine (Solanum melongena) 0·007, butter beans (Phaseolus lunatus) 0·012, spinach (Spinacea oleraceae) 0·014, brown lentils (Lens culinaris) 0·024, beetroot greens (Beta vulgaris) 0·024 and green lentils (Lens culinaris) 0·032. In contrast, bioavailability was moderate or good with carrot (Daucus carota) 0·098, potato (Solanum tuberosum) 0·115, beetroot (Beta vulgaris) 0·185, pumpkin (Cucurbita mixta) 0·206, broccoli 0·260, tomato (Lycopersicon esculentum) 0·224, cauliflower (Brassica oleraceae) 0·263, cabbage 0·320, turnip (Brassica rapa) 0·327 and sauerkraut 0·327.6. All the vegetables associated with moderate or good Fe bioavailability contained appreciable amounts of one or more of the organic acids, malic, citric and ascorbic acids.7. Poor Fe bioavailability was noted in vegetables with high phytate contents (e.g. wheat germ 0·007, butter beans 0·012, brown lentils 0·024 and green lentils 0·032).8. The fact that a number of vegetables associated with low Fe-absorption turned bluish-black when Fe was added to them, suggested that the total polyphenol content in them was high. The vegetables included aubergine spinach, brown lentils, green lentils and beetroot greens. When the total polyphenol content in all the vegetables tested was formally measured, there was a significant inverse correlation (r 0·859, P < 0·001) between it and Fe absorption. The inverse correlation between the non-hydrolysable polyphenol content and Fe absorption was r 0·901 (P < 0·001).9. The major relevance of these findings is the fact that the total absorption of non-haem-Fe from a mixed diet may be profoundly influenced by the presence of single vegetables with either marked enhancing or inhibiting effects on Fe bioavailability.

Inhibition of neoplasia by minor dietary constituents

Abstract: Food contains a large number of inhibitors of carcinogenesis, including phenols, indoles, aromatic isothiocyanates, methylated flavones, coumarins, plant sterols, selenium salts, protease inhibitors, ascorbic acid, tocopherols, retinol, and carotenes. The diversity and widespread occurrence of these compounds in food make it virtually impossible to consume a diet that does not contain inhibitors of carcinogenesis. Inhibitors can be classified as to the time in the carcinogenic process at which they act. Some prevent formation of carcinogens. Others, termed "blocking agents," prevent carcinogens from reaching or reacting with critical target sites. A third group called "suppressing agents" are effective when fed subsequent to administration of carcinogens. Some compounds inhibit at more than one time point. The major emphasis in this paper is on blocking agents, in particular those that act by enhancing host detoxification systems. Mary blocking agents produce a coordinated enhancement of multiple detoxification systems. Two distinctive patterns termed type A and type B have been identified. One enzyme system commonly induced by blocking agents is glutathione S-transferase. On the basis of this information, induction of glutathione S-transferase activity is being used to detect the presence of blocking agents in complex natural products. Green coffee beans induce increased glutathione S-transferase activity and inhibit mammary neoplasia in the rat resulting from administration of 7,12-dimethylbenz(a)anthracene. Two potent inducers of increased glutathione S-transferase activity have been isolated from green coffee beans. These are kahweol palmitate and cafestol palmitate. In recent work, several plant materials have been found to inhibit carcinogenesis when fed after carcinogen exposure. The identification and further investigation of inhibitors present in food are of importance so that their impact on the occurrence of neoplasia in humans can be ascertained.

Osteoblasts Isolated from Mouse Calvaria Initiate Matrix Mineralization in Culture

Abstract: A method is presented for isolating osteoblasts from newborn mouse calvaria without the use of digestive enzymes. The procedure is based on the ability of osteoblasts to migrate from bone onto small glass fragments (Jones, S.J., and A. Boyde, 1977, Cell Tissue Res., 184:179-193). The isolated cells were cultured for up to 14 d in Dulbecco's modified Eagle's medium supplemented with 10% fetal calf serum and 50 micrograms/ml of ascorbic acid. 7-d cultures were incubated for 24 h with [3H]proline. High levels of collagen synthesis relative to total protein were found, as measured by collagenase digestion of medium and cell layer proteins. Analysis of pepsin-digested proteins from the same cultures by SDS PAGE showed that type I collagen was predominantly produced with small amounts of type III and V (alpha 1 chains) collagens. Osteoblasts grown in the presence of beta-glycerophosphate were able to initiate mineral deposition in culture. Electron microscopic analysis of the cultures revealed the presence of needle-shaped apatite-like crystals associated with collagen fibrils and vesicles in the extracellular space. Mouse skin fibroblasts cultured under identical conditions failed to initiate mineralization. Electron histochemical studies revealed the presence of alkaline phosphatase activity, associated with osteoblast membranes, matrix vesicles and on or near collagen fibrils. Thus these isolated osteoblasts retained in culture their unique property of initiating mineralization and therefore represent a model of value for studying the mineralization process in vitro.

Identification in pituitary tissue of a peptide alpha-amidation activity that acts on glycine-extended peptides and requires molecular oxygen, copper, and ascorbic acid

Abstract: An enzymatic activity capable of producing an alpha-amidated peptide product from its glycine-extended precursor has been identified in secretory granules of rat anterior, intermediate, and neural pituitary and bovine intermediate pituitary. High levels of endogenous inhibitors of this alpha-amidation activity have also been found in tissue homogenates. The alpha-amidation activity is totally inhibited by addition of divalent metal ion chelators such as diethyldithiocarbamate, o-phenanthroline, and EDTA; alpha-amidation activity is restored to above control levels upon addition of copper. The alpha-amidation reaction requires the presence of molecular oxygen. Of the various cofactors tested, ascorbic acid was the most potent stimulator of alpha-amidation. The alpha-amidation activity has a neutral pH optimum and is primarily soluble following several cycles of freezing and thawing. Kinetic studies with the bovine intermediate pituitary granule-associated activity demonstrated a linear Lineweaver-Burk plot when D-Tyr-Val-Gly was the varied substrate; the apparent Km and Vmax varied with the concentration of ascorbic acid. The substrate specificity of the alpha-amidation activity appears to be quite broad; the conversion of D-Tyr-Val-Gly into D-Tyr-Val-NH2 is inhibited by the addition of a variety of glycine-extended peptides.

On the cytotoxicity of vitamin C and metal ions. A site-specific Fenton mechanism.

Abstract: The toxicity of ascorbate towards phage lambda and the phages T2–T7 has been investigated. At room temperature the T-odd and lambda bacteriophages are highly susceptible to ascorbate-induced damage, whereas the T-even phages are practically resistant. The toxicity of ascorbate is dependent on the presence of copper (or iron) and oxygen, although oxygen is not required in the presence of H2O2. Hydrogen peroxide is essential for the ascorbate-induced phage inactivation and the damage is prevented by catalase. At the concentrations used, most of the copper ions are bound to the phage particles. Chelating agents such as EDTA or histidine fully protect the phages, whereas salicylate only reduces the rate of phage inactivation. OH scavengers such as sucrose, formate, mannitol, tert-butyl alcohol or poly(ethylene glycol) have no protective effect. Experiments with DNA labeled phages indicate that both phage adsorption and DNA injection are impaired as a result of the exposure to ascorbate and copper. The failure to express the viral genetic information as a result of single and double-strand breaks in the DNA, probably also contribute to the loss of the plaque-forming ability of the phages. The results are interpreted in terms of a ‘site-specific’ Fenton mechanism according to which the binding of the transition metal ions to the biological target is a prerequisite for the production of damage. The bound metal ion is reduced either by O−2, ascorbate or other reductants and is subsequently reoxidized by H2O2 yielding OH˙ radicals. This cyclic redox reaction of the metal generates OH˙ radicals which react with vital macromolecules with a high probability of causing ‘multi-hit’ damage. This ‘site-specific’ formation of OH˙ radicals, which takes place near the target molecules, accounts both for the high damaging efficiency and for the failure of OH˙ scavengers to protect against it.

Food preservative composition

Abstract: This invention resides in a composition for treatment of meat, poultry, fruit and vegetables to maintain the color and to preserve same. The composition comprises as essential constituents between about 10 and 40% each of the following materials: (1) ascorbic acid and/or the sodium or potassium salts thereof; (2) citric acid and/or the sodium or potassium salts thereof; (3) sodium or potassium carbonate; and (4) sulfite, bisulfite or metabisulfite of sodium or potassium. These materials represent a synergistic combination which preserves the color and freshness of these products for a surprisingly long period of time.

Diet in the Epidemiology of Carcinoma of the Prostate Gland

Abstract: In vivo, in vitro, prospective, and retrospective epidemiologic inquiries have suggested that retinoids inhibit cancer, and fats have been hypothesized to enhance and ascorbic acid to reduce cancer risk. Comparison of 260 patients from Buffalo with cancer of the prostate gland was made with two different control series of similar size and age distribution. Regardless of the control group, risk of prostate cancer gained with increases in ingestion of retinoids, animal fats, and vitamin C. These anomalous findings may be due to peculiarities in methodology. From the possible specificity of effect of the nutrients studied, as shown in experimental animals and in vitro, a hypothesis could be made that a substance like vitamin A or C, which may inhibit certain cancers, also may enhance risk of other cancer types or have neither effect.

Metabolism of the carcinogen chromate by cellular constituents

Abstract: The redox chemistry of chromium(VI) is discussed with respect to the cellular metabolism of the carcinogen chromate in vivo. Possible sites for cellular reduction of chromium(VI) to chromium(III) are considered. The reactions of amino acids, ascorbic acid, carboxylic acids, thiol-containing mole-cules and other small molecules with chromate under physiological conditions are presented. In general only ascorbate and those molecules containing sulfhydryl groups are capable of easily reducing chromate at pH 7.4. Thus, in the cytoplasm, glutathione, cysteine and ascorbate are likely candidates to react with chromate. While most proteins are unreactive toward chromate, certain redox proteins are active in reducing chromate. The heme proteins hemoglobin and cytochrome P-450 possess chromate-reductase activity, whereas cytochrome c and myoglobin are inactive. The NADPH-dependent flavoenzymes glutathione reductase and NADPH-cytochrome P-450 reductase also possess chromate-reductase activity. However, the NAD(P)H enzymes, isocitrate dehydrogenase, glutamate dehyrogenase and malate dehydrogenase do not reduce chromate. Both microsomes and mitochondria possess chromate-reductase activity. The microsomal activity is accounted for by the NADPH-cytochrome P-450 reductase/cytochrome P-450 system. The enzyme(s) responsible for the mitochondrial reduction of chromate have not been identified. Chromium(VI) and its metabolite chromium(III) inhibit the normal activities of enzymes which bind chromium(III) or reduce chromate. The metabolism of chromate involves the generation of reactive intermediates which ultimately bind to cellular constituents and damage their function in the cell.

Studies on the activities of tannins and related compounds from medicinal plants and drugs. I. Inhibitory effects on lipid peroxidation in mitochondria and microsomes of liver.

Abstract: The inhibitory effects of 25 tannins and related compounds on the lipid peroxidation induced by adenine 5'-diphosphate (ADP) and ascorbic acid in rat liver mitochondria, and on that induced in rat liver microsomes by ADP and nicotinamide adenine dinucleotide phosphate (NADPH), were determined. All of the tannins, except for some polyphenols of low molecular weight and methylated polyphenols, showed significant inhibition in these two systems at the concentration of 1μg/ml. Almost complete inhibition of the lipid peroxidation in the two systems was shown by some ellagitannins such as pedunculagin, isoterchebin, etc., at the dose of 5μg/ml. Marked differences of the inhibitory activities were observed among the tannins depending on the tannin structure, including the stereoisomerism in the monomer of condensed tannin, and on the experimental system used. The inhibitory effects of most of the hydrolyzable tannins were higher than those of the condensed tannins in both systems. Some monomeric polyphenols, represented by (-)-epigallocatechin gallate, showed inhibitory effects stronger than those of the condensed tannins in these systems, particularly on the lipid peroxidation induced by ADP and NADPH. The inhibitory effects of these tannins in both systems were very much stronger than that of α-tocopherol.

Culture of quiescent arterial smooth muscle cells in a defined serum-free medium

Abstract: An ideal medium for metabolic studies would maintain cultured vascular smooth muscle cells in a quiescent, viable state, as they are in normal arteries in vivo, and would be chemically defined so that the concentrations of hormones and nutrients could be manipulated precisely. In unsupplemented serum-free media these cultures lose protein and DNA, indicating impaired viability. Addition of maximally effective concentrations of insulin (10(-6) M) and transferrin (5 micrograms/ml) prevents loss of DNA and produces near neutral protein balance. Further addition of ascorbic acid (10(-4) M) actually promotes net gain of protein with little or no increase in DNA. Ascorbate consistently increased noncollagen protein synthesis by cultured aortic smooth muscle cells. This novel action of the vitamin did not require insulin but was additive to the effect of this hormone, and was produced by isoascorbate, but not by a variety of other reducing agents. Thus, vascular smooth muscle cells can be maintained in a quiescent but noncatabolic state in simple chemically defined culture media. This finding should facilitate studies of the effects of nutrients and hormones on the metabolism of these cells under conditions that resemble those in the normal artery in vivo. Such an approach may also prove valuable for culture of other differentiated cell types that do not usually divide in the intact organism.

Metabolic Fate of an Oral Dose of 15N-labeled Nitrate in Humans: Effect of Diet Supplementation with Ascorbic Acid

Abstract: The metabolic fate of a po dose of 35 mmol 15N-labeled nitrate has been investigated in 12 healthy young adults Samples of urine, saliva, plasma, and feces were collected over a period of 48 hr following administration of the dose Subjects received either 60 mg of ascorbic acid, 2 g of ascorbic acid, or 2 g of sodium ascorbate per day An average of 60% of the 15NO3- dose appeared in the urine as nitrate within 48 hr Less than 01% appeared in the feces The 15N label of nitrate was also found in the urine (3%) and feces (02%) in the form of ammonia or urea The fate of the remaining 35% of the 15NO3- dose administered is unknown No effect of ascorbic acid or sodium ascorbate on the nitrate and nitrite levels of plasma, saliva, urine, or feces was observed A one-compartment pharmacokinetic model was used to describe the relationships between intake, plasma concentration, and urinary excretion of nitrate The half-life of nitrate in the body was found to be approximately 5 hr, and its volume of distribution was about 30% of body weight Daily endogenous biosynthesis of nitrate was estimated to be about 1 mmol/day

A Case-Control Study of Dietary and Nondietary Factors in Ovarian Cancer

Abstract: A case-control study is presented that estimates ovarian cancer risk for various factors, including diet. Data collected by interview between 1957 and 1965 for 274 white women aged 30-79 years with epithelial carcinoma of the ovary are compared to data similarly collected for 1,034 hospital controls. Relative risk estimates are presented for the total group as well as for premonopausal (ages 30-49) and postmenopausal (ages 50-79) are groups. In the total group, cancer risk increased with increasing age at first marriage (P less than .01) and previous history of benign breast disease (P less than 0.1), and risk decreased with increasing number of previous pregnancies (P less than .01). In the 50- to 79-year age group, a marginally significant trend for decreasing risk with increasing obesity was observed (P less than .10). There was no significant risk (i.e., P less than .10) associated with the consumption of alcohol, cigarettes, coffee, tea, total dietary protein, vitamin C, or fat at any age. In the 30- to 49-year age group only, increased risk (P less than .01) was seen in women reporting diets low in fiber and vitamin A from fruit and vegetable sources. Multiple regression analysis demonstrated that the apparent protective effect of vitamin A in the 30- to 49-year age group (but not dietary fiber) was independent of the nondietary factors analyzed in this study (P less than .05).

Pulse radiolytic study of the interaction of thiols and ascorbate with OH adducts of dGMP and dG: implications for DNA repair processes.

Abstract: Using the technique of pulse radiolysis, the interaction of .OH radicals with 2'-deoxyguanosine (dG) and dG-5'-monophosphate (dGMP) has been shown to result in the production of intermediates with different redox properties as demonstrated by their reactions with tetranitromethane (TNM) and N,N,N',N'-tetramethyl-p-phenylenediamine. The ratio of the yields of oxidizing to reducing-type .OH radical adducts of dGMP was determined to be about 1:1 and independent of pH (6-11). The nature of the intermediates produced on reaction of .OH with dGMP are discussed. The thiols, cysteine, glutathione, mercaptoacetic acid, and ascorbate have been shown to interact with those .OH adducts of dGMP and dG with oxidizing properties preferentially via an electron transfer process (k approximately 3 X 10(7)-1.4 X 10(9) dm3 mole-1 sec-1) as implied from the pH dependence of the rate constants. It is further demonstrated that oxygen and TNM do not interact with those .OH adducts of the purines with oxidizing properties. The implications of these findings are discussed with reference to the mechanistic aspects of radioprotection and especially of radiosensitization.

Promoting Effects of Sodium l-Ascorbate on Two-Stage Urinary Bladder Carcinogenesis in Rats

Abstract: The promoting effect of sodium l-ascorbate on two-stage urinary bladder carcinogenesis in F344 rats initiated with N-butyl-N-(4-hydroxybutyl)nitrosamine at levels of 0.01 and 0.05% in drinking water was studied. Administration of 5.0% but not of 1.0% sodium l-ascorbate in the diet significantly increased the incidence and number of preneoplastic lesions, papillary or nodular hyperplasia, papilloma, and cancer of the urinary bladder. In groups given 5.0% sodium l-ascorbate, the urine was characterized by an apparent elevation of pH, a decrease of osmolality, and an increase of MgNH4PO4 crystalline. Addition of sodium l-ascorbate to the diet also resulted in increase in the content of ascorbic acid and its metabolite, dehydroascorbic acid, in the urine. These results show that an extremely high dose of sodium l-ascorbate (5.0%) promotes urinary bladder carcinogenesis under the present experimental conditions, while a high dose (1.0%) does not.

VARIATION IN GLUTATHIONE AND ASCORBIC ACID CONTENT AMONG SELECTED CULTIVARS OF Phaseolus vulgaris PRIOR TO AND AFTER EXPOSURE TO OZONE

Abstract: Measurements of reduced glutathione (GSH) and ascorbic acid (AA) concentrations in the primary leaves of four bean cultivars, two ozone-sensitive (S) and two ozone-insensitive (I), have revealed that GSH concentrations were not significantly different in all four cultivars prior to the exposure to ozone (0.28–0.32 ppm for 8 h); however, after ozone exposure GSH concentrations were significantly lower in the two sensitive cultivars, PHR and 0669, while in the two insensitive tolerants, FH and Nep-2, the drop in GSH concentrations was slight. The assay of glutathione reductase (GR), the enzyme which catalyzed the reduction of oxidized glutathione (GSSG) to its reduced form, namely GSH, indicated that its specific activity in the two insensitive cultivars was almost twice as high as in the two sensitive cultivars. The drop in AA concentration after 8 h of fumigation was moderate (although significant) in all four cultivars, whereas the concentrations of AA in all four cultivars prior to ozone fumigation were...

Effects of Cooking and Chemical Treatment on Heme and Nonheme Iron in Meat

Abstract: Treatment of ground beef samples with heat (conventional and microwave), ascorbic acid, or H2O2 increased nonheme iron concentrations. The increases ranged from less than 10% to more than 100% depending on the type, length, and severity of the treatment. Cooking of fresh beef round using common household methods (braising, roasting, microwave cooking) resulted in nonheme iron increases that were generally less than 10%. Treatment of hemin and meat extract solutions with heat and H2O2 resulted in destruction of the iron-porphyrin complex. Oxidative cleavage of the porphyrin ring followed by release of the iron is probably the mechanism for the observed increases in nonheme iron.