Showing papers on "Ascorbic acid published in 1976"

The presence of glutathione and glutathione reductase in chloroplasts: A proposed role in ascorbic acid metabolism.

Abstract: Both glutathione and an NADPH-dependent glutathione reductase are present in spinach (Spinacia oleracea L.) chloroplasts. It is proposed that glutathione functions to stabilise enzymes of the Calvin cycle, and it may also act to keep ascorbic acid in chloroplasts in the reduced form.

The flavonoids. A class of semi-essential food components: their role in human nutrition.

Abstract: A review of flavonoids discusses their chemistry, the fate of food flavonoids, (in the gastrointestinal tract) and their nutritional effects. These materials are comprised of flavanones, flavones, flavonols, flavandiols, catechins, and flavylium compounds. The antioxidant activity of food flavonoids is described and discussed, as well as their metal-chelating capacity and its effect on the activity of enzyme and membrane function. Vegetable foods rich in flavonoids are marked by an unusual stability of their Vitamin C content. The antibiotic and/or bacteriostatic effects of flavonoids are discussed, as well as their contribution to both the maintenance of body cell integrity and defense against malignant degeneration (via an anti-carcinogenic activity). (wz)

Supplemental ascorbate in the supportive treatment of cancer: Prolongation of survival times in terminal human cancer.

Abstract: Ascorbic acid metabolism is associated with a number of mechanisms known to be involved in host resistance to malignant disease. Cancer patients are significantly depleted of ascorbic acid, and in our opinion this demonstrable biochemical characteristic indicates a substantially increased requirement and utilization of this substance to potentiate these various host resistance factors. The results of a clinical trial are presented in which 100 terminal cancer patients were given supplemental ascorbate as part of their routine management. Their progress is compared to that of 1000 similar patients treated identically, but who received no supplemental ascorbate. The mean survival time is more than 4.2 times as great for the ascorbate subjects (more than 210 days) as for the controls (50 days). Analysis of the survival-time curves indicates that deaths occur for about 90% of the ascorbate-treated patients at one-third the rate for the controls and that the other 10% have a much greater survival time, averaging more than 20 times that for the controls. The results clearly indicate that this simple and safe form of medication is of definite value in the treatment of patients with acvanced cancer.

Flavonols and flavones in food plants: a review†

Abstract: Summary In this review the qualitative and quantitative occurrence of flavonols and flavones, particularly in fruit and vegetables, are considered. They occur practically in all plants. Their formation normally depends on light so that they are mainly concentrated in the outer tissues. the concentration of flavonols in free standing leaves exceeds that in other parts of the same plant considerably, except in onions. Flavonols act as antioxidants and protect the ascorbic acid from auto-oxidation, for example in fruit juices. On the other hand, flavonols can lead to discolourations. Beneficial effects on the human organism have also been described.

Vitamin dificiencies and neural tube defects.

Abstract: Serum folate, red cell folate, white blood cell vitamin C, riboflavin saturation index, and serum vitamin A were determined during the first trimester of pregnancy in over 900 cases. For each of these there was a social classes I + II showed the highest levels which differed significantly from other classes, except for serum folate. In 6 mothers who gave birth to infants with neural tube defects, first trimester serum folate, red cell folate, white blood cell vitamin C, and riboflavin values were lower than in controls. In spite of small numbers the differences were significant for red cell folate (P less than 0-001) and white blood cell vitamin C (P less than 0-05). These findings are compatible with the hypothesis that nutritional deficiencies are significant in the causation of congenital defects of the neural tube in man.

Human epidermal growth factor and the proliferation of human fibroblasts.

Abstract: The effect of human epidermal growth factor (hEGF), a 5,400 molecular weight polypeptide isolated from human urine, on the growth of human foreskin fibroblasts (HF cells) was studied by measuring cell numbers and the incorporation of labeled thymidine. The addition of hEGF to HF cells growing in a medium containing 10% calf serum resulted in a 4-fold increase in the final density. The presence of hEGF also promoted the growth of HF cells in media containing either 1% calf serum or 10% gamma globulin-free serum. The addition of hEGF to quiescent confluent monolayers of HF cells, maintained in a medium with 1% calf serum for 48 hours, resulted in a 10- to 20-fold increase in the amount of 3H-thymidine incorporation after 20-24 hours. The stimulation of thymidine incorporation was maximal at an hEGF concentration of 2 ng/ml, was dependent on the presence of serum, and was enhanced by the addition of ascorbic acid. In confluent cultures of HF cells, subject to density dependent inhibition of growth, hEGF was able to stimulate DNA synthesis more effectively than fresh calf serum. Human EGF stimulated DNA synthesis in quiescent cultures, however, regardless of cell density. The addition of rabbit anti-hEGF inhibited all effects of this growth factor on HF cells.

The particulate superoxide-forming system from human neutrophils. Properties of the system and further evidence supporting its participation in the respiratory burst.

Abstract: Studies were performed to characterize the previously reported particulate O2--forming system from human neutrophils. Of eight reducing agents examined, including glutathione, ascorbic acid, and intermediates of the glycolytic and hexose monophosphate shunt pathways, only the pyridine nucleotides could serve as electron donors. At 0.1 mM pyridine nucleotide, O2- production was relatively independent of pH. The Km for NADH was approximately 0.7 mM regardless of pH, while with NADPH the Km varied from 0.02 mM at pH 6.0 to 0.3 mM at pH 7.5. The molar ratio of NADPH oxidized to O2- produced was consistent with the reaction: NADPH + 2 O2- leads to NADP+ H+; the product nucleotide was shown enzymatically to be NADP. O2- production was not inhibited by CN-, Na-, EDTA, or 1,10-phenanthroline. Particulate O2- production accounted for 35% of the oxygen taken up during the respiratory burst by an equivalent number of intact neutrophils. Greatly diminished O2- production was seen with particles prepared from cells obtained from three patients with chronic granulomatous disease, with 2.5 mM NADPH as electron donor. With 5.0 mM NADH similar observations were made with particles from two of the patients, but with this nucelotide, O2- production was only slightly reduced in the third case. The evidence available suggests that this particulate O2- -forming system is the one responsible for the respiratory burst in activated neutrophils. The relationship between this system and other O2- -forming system found in human neutrophils is discussed.

Sensitive fluorometric method for tissue tocopherol analysis.

Abstract: A sensitive, highly reproducible method for tissue tocopherol analysis that combines saponification in the presence of large amounts of ascorbic acid to remove interfering substances, extraction of the nonsaponifiable lipids with hexane, and fluorometric measurement of the tocopherol is presented. The nonsaponifiable lipid phase contained only one fluorochrome in the 290 nm excitation and 330 nm emission range, and it was identified as tocopherol by thin layer and column chromatography. Column chromatography of the hexane extract of a saponified,14C-tocopherolspiked microsomal fraction showed that no measurable oxidation to tocopherylquinone has occurred. The fluorometric method for tocopherol analysis was applied to homogenates and subcellular fractions from rat liver, kidney, lung, and heart and red blood cells. The heavy mitochondrial and microsomal fractions had the highest subcellular concentrations of tocopherol.

Simultaneous synthesis of types I and III collagen by fibroblasts in culture.

Abstract: Specific antibodies against types I and III collagens and procollagens were used to localize these proteins in cultured human cells. These studies indicate that the same cell makes both proteins. No type III procollagen synthesis was observed in cells from two patients with two patients with the Ehlers-Danlos type IV syndrome.

Ascorbic acid, metal ions and the superoxide radical.

Abstract: 1. No evidence could be found for production of the superoxide radical, O2-, during autoxidation of ascorbic acid at alkaline pH values. Indeed, ascorbate may be important in protection against O2- genat-d in vivo. 2. Oxidation of ascorbate at pH 10.2 was stimulated by metal ions. Stimulation by Fe2+ was abolished by superoxide dismutase, probably because of generation of O2-- during reduction of O2 by Fe2+, followed by reaction of O2-- with ascorbate. EDTA changed the mechanism of Fe2+-stimulated ascorbate oxidation. 3. Stimulation of ascorbate oxidation by Cu2+ was also decreased by superoxide dismutase, but this appears to be an artifact, since apoenzyme or bovine serum albumin showed similar effects.

Validity of the 24-hr. recall. Analysis of data obtained from elderly subjects.

Abstract: Tests of the validity of the 24-hr. dietary recall were done by comparing actual with recalled intakes for eight nutrients and the MAR (mean adequacy ratio) for a sample of seventy-six subjects age sixty years or older. Validity was tested by using paired-t tests and regression analysis. In the paired-t test, no significant difference was found between the mean recalled and the mean actual intake of nutrients, with the exception of calories. Using regression analysis, results indicated that for three of the eight nutrients considered (calories, protein, and vitamin A), small intakes tend to be over-reported and large intakes under-reported (p less than .05). Thus, for these three nutrients, the recall seems to be statistically conservative for group comparisons; it would seldom, if ever, indicate a difference in intake where no difference exists. But, it could yield a false negative, i.e., an indication of no significant difference, when, in fact, a difference does exist. Clearly, more research is needed, both to replicate this study and to develop techniques with greater internal validity for comparing the dietary intakes of groups.

Oxidation of alpha-methyldopa and other catechols by cytochrome P-450-generated superoxide anion: possible mechanism of methyldopa hepatitis.

Abstract: Renewed interest in the hepatic injury produced by α-methyldopa has been stimulated by recent reports that the antihypertensive drug may initiate chronic active liver disease, occasionally with a fatal outcome. To determine whether the toxicity might be due to a reactive metabolite, [3H]α-methyldopa was incubated with rat liver microsomes in the presence of an NADPH-generating system. A large amount of covalent binding occurred, but only in the presence of NADPH and oxygen (Vmax = 0.5 nmol/mg/min; Km = 50 µM). The binding was inhibited by a CO-O2 atmosphere (9:1), indicating the involvement of cytochrome P-450. However, α-methyldopa did not show P-450 binding spectra (type I, II, or III), and its covalent binding was inhibited by superoxide dismutase, ascorbic acid (1 mM), ethylenediamine (20 mM), and glutathione (1 mM). This indicated that α-methyldopa was being oxidized by cytochrome P-450-generated superoxide anion to a reactive semiquinone and/or quinone. The covalent binding was inhibited by analogues such as l-dopa, dopamine, epinephrine, norepinephrine, and catechol, but not by 3-O-methyldopa, indicating a requirement for the unsubstituted catechol nucleus. Additional studies demonstrated that the rat microsomal system could be replaced by human hepatic microsomes or by a xanthine oxidase system and the binding was again inhibited by superoxide dismutase. Metabolic activation by superoxide anion may play a role in the hepatotoxicity of this and other catechols, including hydroxylated estrogens.

Mutagaenic action of ascorbic acid

Abstract: MICROBIAL1, mammalian2,3 and human4,5 bioassays are being applied to uncover the mutagenic action of synthetic compounds which have been introduced accidently or intentionally into the environment. Somewhat less attention has been given to the potential genetic hazard of chemicals which are an essential part of human nutrition or are formed within mammalian tissues and organs. Ascorbic acid belongs to this group of “neglected” naturally occurring compounds, although its capacity to form radicals and its interaction with viral6 and bacterial7 DNA should have raised suspicion about its possible mutagenic capacity. Considering the large daily intake of ascorbic acid, its addition to many food products8 and its potential use as an inhibitor of the intragastric formation of N-nitroso compounds8,9 and nitrosamine formation in food products10, its action on the genome of human cells requires investigation. We here present evidence, from several experimental systems, suggesting that vitamin C, particularly in the presence of copper, has a mutagenic effect.

The mechanism of DNA strand breakage by vitamin C and superoxide and the protective roles of catalase and superoxide dismutase.

Abstract: Vitamin C breaks DNA only in the presence of oxygen. Superoxide dismutase has no effect on the reaction but catalase suppresses it. Superoxide also gives rise to breaks in DNA suppressible by both superoxide dismutase and catalase. The hydroxyl radical seems to be the agent responsible for strand cleavage itself.

Ascorbic acid-induced uricosuria. A consequency of megavitamin therapy.

Abstract: The effect of ascorbic acid on the serum and urinary uric acid was studied in 14 subjects. Two to 6 h after the ingestion of 4.0 g of ascorbic acid, the fractional clearance of uric acid increased to 202% +/- 41% of the control value. This uricosuria was inhibited by pyrazinamide and by low-dose acetylsalicylic acid, but was not accompanied by an increase of the creatinine clearnace. Ascorbic acid did not diminish protein-bound uric acid. In 3 subjects who ingested 8.0 g of ascorbic acid for 3 to 7 days the serum uric acid decreased by 1.2 to 3.1 mg/dl as a result of a sustained uricosuria. These results suggest that ascorbic acid could invalidate studies involving the measurement of uric acid and obscure the diagnosis of gout in some cases. Theoretically it could precipitate attacks of gouty arthritis or renal calculi in predisposed persons. These observations show a pharmacologic effect of megadoses of a simple vitamin.

Lipid Peroxides in Spermatozoa; Formation, Role of Plasmalogen, and Physiological Significance

Abstract: In view of the high content of unsaturated fatty acids in the phospholipids of mammalian spermatozoa, the possibility was investigated that during aerobic incubation of spermatozoa these fatty acids, in particular arachidonic (20:4) and docosahexanoic (22:6) acid, undergo peroxidation, which in turn is responsible for the decline in viability of spermatozoa. The formation of lipid peroxides was followed by the thiobarbituric acid (TBA) reaction, iodometry and fluorimetry; it was found that during aerobic incubation of washed ram spermatozoa at 37 degrees C in the presence of ascorbic acid (0.1 mg/ml) and ferrous iron (2.8 $\mu $g Fe/ml), peroxides became detectable after 30 min incubation and their level reached a maximum after 60 min. Coincident with the formation of peroxides motility declined and the spermatozoa became agglutinated, but their oxygen uptake was not grossly different from that of motile spermatozoa in mixtures free of ascorbic acid or Fe. Peroxide formation could be prevented by the addition of either chelating agents, such as EDTA and sodium citrate, or antioxidants, such as tocopherol and butylated hydroxyanisole, to the incubation medium. Conclusive evidence that the substrate for the peroxidation reaction is a lipid, was obtained by extracting lipids from spermatozoa with chloroform: methanol and incubating aerobically in the presence of catalytic amounts of ascorbate and Fe, two fractions: the extracted lipid and the 'defatted' sperm residue; very high peroxide values were recorded in the former, but not the latter fraction. Examination by thin-layer and gas-liquid chromatography of the phospholipid and neutral lipid fractions obtained from spermatozoa, revealed that peroxidation caused a loss of approximately 50% in the content of plasmalogens, 20:4 and 22:6 fatty acids, and palmitaldehyde. Changes in the other phospholipids and their bound fatty acids were relatively small, but there was some increase in the amount of a substance which behaved chromatographically as lysolecithin. The content of cholesterol and glycerides in the neutral lipid fraction was not appreciably different in non-peroxidized and peroxidized spermatozoa, but the latter contained a higher proportion of free fatty acids. Our results indicate that under aerobic conditions the lipids in spermatozoa, in particular the plasmalogens, are susceptible to peroxidation. The peroxidation reaction apparently takes place within the lipoprotein, and is associated with a decline in the viability of spermatozoa. This decline could be due either to an increase in cellular permeability resulting from changes in membrane-bound lipids, or to a direct toxic effect of lipid peroxides on spermatozoa. Development of means for the prevention of adverse effects of the peroxidation reaction, may be of practical importance in relation to the problem of long-term storage of semen for artificial insemination.

Enhanced synthesis and extracellular accumulation of hyaluronic acid during stimulation of quiescent human fibroblasts by mouse epidermal growth factor.

Abstract: The effect of mouse epidermal growth factor (mEGF) on the synthesis of glycosaminoglycans and glycoproteins by human fibroblasts has been studied The addition of physiological concentrations (10(-9)M) of mEGF to quiescent cultures preincubated in the absence of serum was found to elicit an increased incorporation of 3H-glucosamine into the glycosaminoglycans and glycoproteins of both the cellular and extracellular fractions Although the growth response to the factor, as measured by DNA replication, was minimal under these conditions as compared with the effect of serum, the mEGF-induced incorporation of glucosamine into these cellular constituents and into the extracellular glycoproteins was comparable to that elicited by serum shift-up Serum, however, caused a significantly larger incorporation of glucoasimine into extracellular, acid-soluble glycosaminoglycans, which were shown to contain hyaluronic acid as the major component As previously demonstrated, the growth response to mEGF can be enhanced several fold by an mEGF-binding arginine esterase, which is normally associated with the factor in vivo, and by ascorbate The esterase was found to increase markedly the mEGF-induced incorporation of glucosamine into extracellular hyaluronic acid, while the addition of ascorbic acid did not significantly alter glucosamine incorporation

Induction of human fibroblast proliferation by epidermal growth factor (EGF): enhancement by an EGF-binding arginine esterase and by ascorbate.

Abstract: The effect of mouse epidermal growth factor (mEGF) and an mEGF-binding arginine esterase on the growth of cultured human fibroblasts has been studied Physiological concentrations (10(-9)-10(-10) M) of the growth factor were found to stimulate DNA replication and cell proliferation in quiescent cultures, and the arginine esterase, which is normally associated with mEGF in vivo, was shown to enhance this growth effect synergistically The cellular response to mEGF was dependent upon a low, growth-limiting concentration of serum in the extracellular medium Ascorbic acid, which alone exhibited no growth-promoting effect, could partially replace this requirement, and was found to elicit a rapid and marked increase in proline hydroxylation Quiescent cultures in serum-free medium containing ascorbic acid were stimulated by the combination of mEGF and the esterase in a manner comparable to that achieved with serum shift-up The possible requirement of a collagen-containing extracellular matrix for the growth response to mEGF is discussed

Ascorbic acid prevents corneal ulceration and perforation following experimental alkali burns.

Abstract: Depressed aqueous humor glucose and ascorbic acid levels returned to control values within 14 days following a 20 sec, 6 mm. diameter, 1N sodium hydroxide burn of the rabbit cornea. These corneas did not ulcerate or perforate. After a 20 sec., 12 mm. diameter, 1N sodium hydroxide burn, aqueous humor glucose levels returned to normal values, but ascorbic acid levels remained significantly depressed for up to 30 days. These corneas became markedly ulcerated in about 60 per cent of animals and frequently perforated. Following 12 mm. alkali burns, rabbits treated daily with 1.5 Gm. of subcutaneous ascorbic acid rarely developed corneal ulcerations and the corneas did not perforate. It is suggested that exogenous maintenance of adequate aqueous humor levels of ascorbic acid overcomes the relatively scorbutic state of the anterior segment induced by a 12 mm. alkali burn, thereby impairing the development of corneal ulceration and perforation. Elevated aqueous humor levels of ascorbic acid had no influence on corneal epithelial cell migration patterns following alkali burns.

Rapid chemical analysis of some plant constituents

Abstract: Simple reproducible methods using a minimum of equipment are described for the routine analysis of soluble sugars, starch, total nitrogen and phosphorus in plant material. Soluble sugars are extracted with 62.5% methanol and the sugars estimated by the phenol–sulphuric acid technique. Starch in the residual tissue is digested by an amyloglucosidase and glucose is determined by a glucose oxidase method. Both nitrogen and phosphorus are assayed after wet ashing the plant tissue—nitrogen by the phenol–hypochlorite reaction and phosphorus after reduction of the phosphomolybdic acid with ascorbic acid/antimony potassium tartrate.