Showing papers on "Ascorbic acid published in 2009"

Electrochemical sensing and biosensing platform based on chemically reduced graphene oxide.

Abstract: In this paper, the characterization and application of a chemically reduced graphene oxide modified glassy carbon (CR-GO/GC) electrode, a novel electrode system, for the preparation of electrochemical sensing and biosensing platform are proposed. Different kinds of important inorganic and organic electroactive compounds (i.e., probe molecule (potassium ferricyanide), free bases of DNA (guanine (G), adenine (A), thymine (T), and cytosine (C)), oxidase/dehydrogenase-related molecules (hydrogen peroxide (H2O2)/β-nicotinamide adenine dinucleotide (NADH)), neurotransmitters (dopamine (DA)), and other biological molecules (ascorbic acid (AA), uric acid (UA), and acetaminophen (APAP)) were employed to study their electrochemical responses at the CR-GO/GC electrode, which shows more favorable electron transfer kinetics than graphite modified glassy carbon (graphite/GC) and glassy carbon (GC) electrodes. The greatly enhanced electrochemical reactivity of the four free bases of DNA at the CR-GO/GC electrode compare...

Antioxidants prevent health-promoting effects of physical exercise in humans.

Abstract: Exercise promotes longevity and ameliorates type 2 diabetes mellitus and insulin resistance. However, exercise also increases mitochondrial formation of presumably harmful reactive oxygen species (ROS). Antioxidants are widely used as supplements but whether they affect the health-promoting effects of exercise is unknown. We evaluated the effects of a combination of vitamin C (1000 mg/day) and vitamin E (400 IU/day) on insulin sensitivity as measured by glucose infusion rates (GIR) during a hyperinsulinemic, euglycemic clamp in previously untrained (n = 19) and pretrained (n = 20) healthy young men. Before and after a 4 week intervention of physical exercise, GIR was determined, and muscle biopsies for gene expression analyses as well as plasma samples were obtained to compare changes over baseline and potential influences of vitamins on exercise effects. Exercise increased parameters of insulin sensitivity (GIR and plasma adiponectin) only in the absence of antioxidants in both previously untrained (P < 0.001) and pretrained (P < 0.001) individuals. This was paralleled by increased expression of ROS-sensitive transcriptional regulators of insulin sensitivity and ROS defense capacity, peroxisome-proliferator-activated receptor gamma (PPARγ), and PPARγ coactivators PGC1α and PGC1β only in the absence of antioxidants (P < 0.001 for all). Molecular mediators of endogenous ROS defense (superoxide dismutases 1 and 2; glutathione peroxidase) were also induced by exercise, and this effect too was blocked by antioxidant supplementation. Consistent with the concept of mitohormesis, exercise-induced oxidative stress ameliorates insulin resistance and causes an adaptive response promoting endogenous antioxidant defense capacity. Supplementation with antioxidants may preclude these health-promoting effects of exercise in humans.

A Systematic Review of the Evidence Supporting a Causal Link Between Dietary Factors and Coronary Heart Disease

Abstract: Background: Although a wealth of literature links dietaryfactorsandcoronaryheartdisease(CHD),thestrength oftheevidencesupportingvalidassociationshasnotbeen evaluated systematically in a single investigation. Methods: We conducted a systematic search of MEDLINE for prospective cohort studies or randomized trials investigating dietary exposures in relation to CHD. We used the Bradford Hill guidelines to derive a causation score based on 4 criteria (strength, consistency, temporality, and coherence) for each dietary exposure in cohort studies and examined for consistency with the findings of randomized trials. Results:Strongevidencesupportsvalidassociations(4criteriasatisfied)ofprotectivefactors,includingintakeofvegetables,nuts,and“Mediterranean”andhigh-qualitydietary patternswithCHD,andassociationsofharmfulfactors,includingintakeoftrans–fattyacidsandfoodswithahighglycemicindexorload.Amongstudiesofhighermethodologic quality,therewasalsostrongevidenceformonounsaturated fatty acids and “prudent” and “western” dietary patterns. Moderateevidence(3criteria)ofassociationsexistsforintakeoffish,marine-3fattyacids,folate,wholegrains,dietary vitamins E and C, beta carotene, alcohol, fruit, and fiber. Insufficient evidence (2 criteria) of association is present for intake of supplementary vitamin E and ascorbic acid (vitamin C); saturated and polyunsaturated fatty acids;totalfat;-linolenicacid;meat;eggs;andmilk.Among thedietaryexposureswithstrongevidenceofcausationfrom cohortstudies,onlyaMediterraneandietarypatternisrelated to CHD in randomized trials. Conclusions: The evidence supports a valid association of a limited number of dietary factors and dietary patterns with CHD. Future evaluation of dietary patterns, including their nutrient and food components, in cohort studies and randomized trials is recommended.

Analysis and Optimization of Copper-Catalyzed Azide–Alkyne Cycloaddition for Bioconjugation

Abstract: Since its discovery in 2002, the copper-catalyzed azide-alkyne cycloaddition (CuAAC)[1] reaction—the most widely recognized example of click chemistry[2]—has been rapidly embraced for applications in myriad fields.[3] The attractiveness of this procedure (and its copper-free strained-alkyne variant[4]) stems from the selective reactivity of azides and alkynes only with each other. Because of the fragile nature and low concentrations at which biomolecules are often manipulated, bioconjugation presents significant challenges for any ligation methodology. Several different CuAAC procedures have been reported to address specific cases involving peptides, proteins, polynucleotides, and fixed cells, often with excellent results,[5] but also occasionally with somewhat less satisfying outcomes.[6] We describe here a generally applicable procedure that solves the most vexing click bioconjugation problems in our laboratory, and therefore should be of use in many other situations. The CuAAC reaction requires the copper catalyst, usually prepared with an appropriate chelating ligand,[7] to be maintained in the CuI oxidation state. Several years ago we developed a system featuring a sulfonated bathophenanthroline ligand,[8] which was optimized into a useful bioconjugation protocol.[9] A significant drawback was the catalyst’s acute oxygen sensitivity, requiring air-free techniques which can be difficult to execute when an inert-atmosphere glove box is unavailable or when sensitive biomolecules are used in small volumes of aqueous solution. We also introduced an electrochemical method to generate and protect catalytically active CuI–ligand species for CuAAC bioconjugation and synthetic coupling reactions with miminal effort to exclude air.[10] Under these conditions, no hydrogen peroxide was produced in the oxygen-scrubbing process, resulting in protein conjugates that were uncontaminated with oxidative byproducts. However, this solution is also practical only for the specialist with access to the proper equipment. Other protocols have employed copper(I) sources such as CuBr for labeling fixed cells[11] and synthesizing glycoproteins.[12] In these cases, the instability of CuI in air imposes a requirement for large excesses of Cu (greater than 4 mm) and ligand for efficient reactions, which raises concerns about protein damage or precipitation, plus the presence of residual metal after purification. The most convenient CuAAC procedure involves the use of an in situ reducing agent. Sodium ascorbate is the reductant of choice for CuAAC reactions in organic and materials synthesis, but is avoided in bioconjugation with a few exceptions.[13] Copper and sodium ascorbate have been shown to be detrimental to biological[14] and synthetic[15] polymers due to copper-mediated generation of reactive oxygen species.[16] Moreover, dehydroascorbate and other ascorbate byproducts can react with lysine amine and arginine guanidine groups, leading to covalent modification and potential aggregation of proteins.[6a,17] We hoped that solutions to these problems would allow ascorbate to be used in fast and efficient CuAAC reactions using micromolar concentration of copper in the presence of atmospheric oxygen. This has now been achieved, allowing demanding reactions to be performed with biomolecules of all types by the nonspecialist. For purposes of catalyst optimization and reaction screening, the fluorogenic coumarin azide 1 developed by Wang et al. has proven to be invaluable (Scheme 1).[18] The progress of cycloaddition reactions between mid-micromolar concentrations of azide and alkyne in aqueous buffers was followed by the increase in fluorescence at 470 nm upon formation of the triazole 2. Scheme 1 Top: Reaction used for screening CuAAC catalysts and conditions. Below: Accelerating ligand 3 and additive 4 used in these studies. DMSO=dimethylsulfoxide.

Misreporting of energy and micronutrient intake estimated by food records and 24 hour recalls, control and adjustment methods in practice

Abstract: In order to assess nutritional adequacy, valid estimates of nutrient intake are required. One of the main errors in dietary assessment is misreporting. The objective was to review the extent, nature and determinants of misreporting in dietary assessment, how this affects reported intakes of micronutrients and how this is identified and measured, and to identify the best ways of dealing with misreporting when interpreting results. A systematic literature search was conducted for studies of misreporting of dietary intake in adults by 24 hour recalls or by estimated or weighed food records, published up to March 2008. Thirty-seven relevant studies were identified. Possible causes of misreporting were identified. Methods most used to identify misreporting were the Goldberg cut-off (46 % studies) and the doubly labelled water technique (24 % studies). The magnitude of misreporting of energy intake was similar in all three dietary assessment methods. The percentage of under-reporters was about 30 % and energy intake was underestimated by approximately 15 %. Seven papers presented usable data for micronutrient intake. Absolute intakes of Fe, Ca and vitamin C (the three micronutrients addressed in all papers) were on average 30 % lower in low-energy reporters (LER) than that in non-LER and, although results were not consistent, there was a tendency for micronutrient density to be higher in LER. Excluding underreporters or using energy adjustment methods for micronutrient intakes is discussed. Residual method of energy adjustment seems to be a good tool for practice to decrease an influence of misreporting when interpreting results of studies based on food records and 24 hour recalls.

Antioxidants in Wild Mushrooms

Abstract: Maintenance of equilibrium between free radical production and antioxidant defences (enzymatic and non enzymatic) is an essential condition for normal organism functioning. When this equilibrium has a tendency for the production of free radicals we say that the organism is in oxidative stress. In this situation, excess free radicals may damage cellular lipids, proteins and DNA, affecting normal function and leading to various diseases. In aerobic organisms, the free radicals are constantly produced during the normal cellular metabolism, mainly in the form of Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS). Exposition of the organism to free radicals has led to the development of endogenous defence mechanisms to eliminate them. These defences were the response of evolution to the inevitability of ROS production in aerobic conditions. Natural products with antioxidant activity may help the endogenous defence system. In this perspective the antioxidants present in the diet assume a major importance as possible protector agents reducing oxidative damage. Particularly, the antioxidant properties of wild mushrooms have been extensively studied by our research group and by others, and many antioxidant compounds extracted from these sources have been identified, such as phenolic compounds, tocopherols, ascorbic acid, and carotenoids. We will review the compounds identified so far in mushrooms, as well as the mechanism of action involved in their antioxidant properties. Wild mushrooms might be used directly in diet and promote health, taking advantage of the additive and synergistic effects of all the bioactive compounds present.

Sustained release systems of ascorbic acid phosphate

Abstract: A novel method of preparing a controlled release composition is disclosed. Specifically, the present invention relates to a method of preparing controlled release compositions of ascorbic acid phosphate and absorbable polymers. Also disclosed is a novel controlled release composition of ascorbic acid phosphate made by the method of the present invention.

Impact of high pressure processing on total antioxidant activity, phenolic, ascorbic acid, anthocyanin content and colour of strawberry and blackberry purées.

Abstract: The present study was undertaken to assess the effect of high pressure treatments and conventional thermal processing on antioxidant activity, levels of key antioxidant groups (polyphenols, ascorbic acid and anthocyanins) and the colour of strawberry and blackberry purees. Bioactive compounds (cyanidin-3-glycoside, pelargonidin-3-glucoside, ascorbic acid) and antioxidant activity were measured in strawberry and blackberry purees subjected to high pressure treatment (400, 500, 600 MPa/15 min/10–30 °C) and thermal treatments (70 °C/2 min). Samples were assessed immediately after processing. Different pressure treatments did not cause any significant change in ascorbic acid (p > 0.05). In contrast, following thermal processing (P70 ≥ 2 min) ascorbic acid degradation was 21% (p 0.05), whereas conventional thermal treatments significantly reduced the levels (p Industrial relevance This research paper provides scientific evidence of the potential benefits of high pressure processing in comparison to thermal treatments in retaining important bioactive compounds. Antioxidant activity (ARP), ascorbic acid, and anthocyanins after exposure to high pressure treatments (400–600 MPa) were well retained. Our results also show that redness and colour intensity of strawberry and blackberry purees were better preserved by high pressure processing than conventional thermal treatment. From a nutritional perspective, high pressure processing is an attractive food preservation technology and offers opportunities for horticultural and food processing industries to meet the growing demand from consumers for healthier food products. Therefore high pressure processed foods could be sold at a premium than their thermally processed counterparts as they will have retained their fresh-like properties.

Relationship between collagen synthesis and expression of the osteoblast phenotype in MC3T3-E1 cells.

Abstract: The MC3T3-E1 mouse calvaria-derived cell line has been used to study the role of collagen synthesis in osteoblast differentiation. MC3T3-E1 cells, like several previously characterized osteoblast culture systems, expressed osteoblast markers and formed a mineralized extracellular matrix only after exposure to ascorbic acid. Mineralization was stimulated further by β-glycerol phosphate. Ultrastructural observations indicated that the extracellular matrix produced by ascorbic acid-treated cells was highly organized and contained well-banded collagen fibrils. Expression of osteoblast markers followed a clear temporal sequence. The earliest effects of ascorbic acid were to stimulate type I procollagen mRNA and collagen synthesis (24 h after ascorbate addition), followed by induction of alkaline phosphatase (48–72 h) and osteocalcin (96–144 h) mRNAs. Procollagen mRNA, which was expressed constitutively in the absence of ascorbate, increased only twofold after vitamin C addition. In contrast, alkaline phosphatase and osteocalcin mRNAs were undetectable in untreated cultures. Actions of ascorbic acid on osteoblast marker gene expression are mediated by increases in collagen synthesis and/or accumulation because (1) parallel dose-response relationships were obtained for ascorbic acid stimulation of collagen accumulation and alkaline phosphatase activity, and (2) the specific collagen synthesis inhibitors, 3,4-dehydroproline and cis-4-hydroxyproline, reversibly blocked ascorbic acid-dependent collagen synthesis and osteoblast marker gene expression.

Mechanisms of Antioxidants in the Oxidation of Foods

Abstract: Antioxidants delay or inhibit lipid oxidation at low concentration. Tocopherols, ascorbic acid, carotenoids, flavonoids, amino acids, phospholipids, and sterols are natural antioxidants in foods. Antioxidants inhibit the oxidation of foods by scavenging free radicals, chelating prooxidative metals, quenching singlet oxygen and photosensitizers, and inactivating lipoxygenase. Antioxidants show interactions, such as synergism (tocopherols and ascorbic acids), antagonism (α-tocopherol and caffeic acid), and simple addition. Synergism occurs when one antioxidant is regenerated by others, when one antioxidant protects another antioxidant by its sacrificial oxidation, and when 2 or more antioxidants show different antioxidant mechanisms.

Potatoes and Human Health

Abstract: The potato (Solanum tuberosum L.) tuber follows only rice and wheat in world importance as a food crop for human consumption. Cultivated potatoes have spread from the Andes of South America where they originated to 160 countries around the world. Consumption of fresh potatoes has declined while processed products have increased in popularity. As the potato becomes a staple in the diets of an increasing number of humans, small differences in potato nutritional composition will have major impacts on population health. The potato is a carbohydrate-rich, energy-providing food with little fat. Potato protein content is fairly low but has an excellent biological value of 90-100. Potatoes are particularly high in vitamin C and are a good source of several B vitamins and potassium. The skins provide substantial dietary fiber. Many compounds in potatoes contribute to antioxidant activity and interest in cultivars with pigmented flesh is growing. This review will examine the nutrient and bioactive compounds in potatoes and their impact on human health.

Diagnosis, natural history, and management of Charcot–Marie–Tooth disease

Abstract: Summary Charcot–Marie–Tooth disease is the most common inherited neuromuscular disorder. There have been substantial advances in elucidating the molecular bases of this genetically heterogeneous neuropathy and, in most cases, molecular diagnosis is now possible. The diagnostic approach requires careful assessment of clinical presentation and mode of inheritance, nerve-conduction studies, and DNA testing, and current research is focused on assessing natural history and finding effective treatments. Disease course is variable because of genotypic and phenotypic heterogeneity. At present, there is no drug therapy for Charcot–Marie–Tooth disease, and rehabilitation therapy and surgical procedures for skeletal deformities are the only available treatments, although best practice has not been defined. Animal models are proving useful for the identification of therapeutic targets and approaches. Progesterone antagonists, neurotrophic factors, ascorbic acid, and curcumin have shown promising results in experimental models, and ascorbic acid is being studied in large randomised controlled trials.

Transgenic multivitamin corn through biofortification of endosperm with three vitamins representing three distinct metabolic pathways.

Abstract: Vitamin deficiency affects up to 50% of the world's population, disproportionately impacting on developing countries where populations endure monotonous, cereal-rich diets. Transgenic plants offer an effective way to increase the vitamin content of staple crops, but thus far it has only been possible to enhance individual vitamins. We created elite inbred South African transgenic corn plants in which the levels of 3 vitamins were increased specifically in the endosperm through the simultaneous modification of 3 separate metabolic pathways. The transgenic kernels contained 169-fold the normal amount of β-carotene, 6-fold the normal amount of ascorbate, and double the normal amount of folate. Levels of engineered vitamins remained stable at least through to the T3 homozygous generation. This achievement, which vastly exceeds any realized thus far by conventional breeding alone, opens the way for the development of nutritionally complete cereals to benefit the world's poorest people.

Effects of ascorbic acid on collagen matrix formation and osteoblast differentiation in murine MC3T3-E1 cells.

Abstract: Treatment of mouse MC3T3-E1 cells with ascorbic acid initiates the formation of a collagenous extracellular matrix and synthesis of several osteoblast-related proteins. We recently showed that ascorbic acid dramatically increases alkaline phosphatase and osteocalcin mRNAs and that this induction is blocked by inhibitors of collagen triple-helix formation (Franceschi and Iyer, J Bone Miner Res 7:235). In the present study, the relationship between collagen matrix formation and osteoblast-specific gene expression is explored in greater detail. Kinetic studies revealed that ascorbic acid increased proline hydroxylation in the intracellular procollagen pool within 1 h and stimulated the cleavage of type I collagen propeptides beginning at 2.5 h. Mature alpha 1(I) and alpha 2(I) collagen components were first detected at 10 h and continued to increase in both cell layer and culture medium for up to 72 h. Ascorbic acid also increased the rate of procollagen secretion from cell layers to culture medium. The secretion of another matrix protein, fibronectin, was only slightly affected. Alkaline phosphatase or its mRNA was first detected 2-3 days after ascorbic acid addition, but osteocalcin mRNA was not seen until day 6. Two inhibitors of collagen triple-helix formation, ethyl-3,4-dihydroxybenzoate and 3,4-dehydroproline, inhibited procollagen hydroxylation and alkaline phosphatase induction. 3,4-Dehydroproline also inhibited the induction of alkaline phosphatase and osteocalcin mRNAs. Surprisingly, induction was not blocked if cells were exposed to ascorbic acid before inhibitor addition. Alkaline phosphatase was also partially inhibited if cells were grown in the presence of purified bacterial collagenase. These results indicate that the induction of osteoblast markers by ascorbic acid does not require the continuous hydroxylation and processing of procollagens and suggest that a stable, possibly matrix-associated signal is generated at early times after ascorbic acid addition that allows subsequent induction of osteoblast-related genes.

Antioxidant defense responses: physiological plasticity in higher plants under abiotic constraints

Abstract: Environmental stresses (salinity, drought, heat/cold, light and other hostile conditions) may trigger in plants oxidative stress, generating the formation of reactive oxygen species (ROS). These species are partially reduced or activated derivatives of oxygen, comprising both free radical $$ ( {\text{O}}_{2}^{\cdot - } ,{\text{OH}} \cdot , {\text{OH}}_{ 2} \cdot ) $$ and non-radical (H2O2) forms, leading to cellular damage, metabolic disorders and senescence processes. In order to overcome oxidative stress, plants have developed two main antioxidants defense mechanisms that can be classified as non-enzymatic and enzymatic systems. The first class (non-enzymatic) consists of small molecules such as vitamin (A, C and E), glutathione, carotenoids and phenolics that can react directly with the ROS by scavenging them. Second class is represented by enzymes among them superoxide dismutase, peroxidase and catalase which have the capacity to eliminate superoxide and hydrogen peroxide. In this review, we have tried to explore the related works, which have revealed the changes in the basic antioxidant metabolism of plants under various abiotic constraints.

Fruit and Vegetable Consumption and Its Relation to Markers of Inflammation and Oxidative Stress in Adolescents

Abstract: Background Fruits and vegetables, foods rich in flavonoids and antioxidants, have been associated with lower risk of stroke, coronary heart disease, and markers of inflammation and oxidative stress in adults. Markers of inflammation and oxidative stress are predictors of coronary heart disease risk; however, it is unknown whether these markers are related to dietary flavonoid and antioxidant intake in youth. Objective To determine whether greater intakes of fruit and vegetables, antioxidants, folate, and total flavonoids were inversely associated with markers of inflammation and oxidative stress in 285 adolescent boys and girls aged 13 to 17 years. Design In this cross-sectional study conducted between February 1996 and January 2000, diet was assessed by a 127-item food frequency questionnaire. Height and weight measurements were obtained and a fasting blood sample drawn. Spearman partial correlation analyses evaluated the relation of intakes of fruit and vegetables, antioxidants, folate, and flavonoids with markers of inflammation (C-reactive protein, interleukin-6, tumor necrosis factor-α, and 15-keto-dihydro-PGF 2α metabolite and oxidative stress (urinary 8-iso prostaglandin F 2α , an F 2 -isoprostane), adjusting for age, sex, race, Tanner stage, energy intake, and body mass index. Results Urinary F 2 -isoprostane was inversely correlated with intakes of total fruit and vegetables, vitamin C, beta carotene, and flavonoids. Serum C-reactive protein was significantly inversely associated with intakes of fruit ( r =−0.19; P =0.004), vitamin C ( r =−0.13, P =0.03), and folate ( r =−0.18; P =0.004). Serum interleukin-6 was inversely associated with intakes of legumes, vegetables, beta carotene, and vitamin C. Serum tumor necrosis factor-α was inversely associated with beta carotene ( r =−0.14, P =0.02) and luteolin ( r =−0.15, P =0.02). Conclusion Study results show that the beneficial effects of fruit and vegetable intake on markers of inflammation and oxidative stress are already present by early adolescence and provide support for the Dietary Guidelines for Americans "to consume five or more servings per day" of fruits and vegetables to promote beneficial cardiovascular health.

Nutrient content of tropical edible seaweeds, Eucheuma cottonii, Caulerpa lentillifera and Sargassum polycystum

Abstract: The proximate composition, vitamin C, α-tocopherol, dietary fibers, minerals, fatty acid and amino acid profiles of three tropical edible seaweeds, Eucheuma cottonii (Rhodophyta), Caulerpa lentillifera (Chlorophyta) and Sargassum polycystum (Phaeophyta) were studied. The seaweeds were high in ash (37.15–46.19%) and dietary fibers (25.05–39.67%) and low in lipid content (0.29–1.11%) on dry weight (DW) basis. These seaweeds contained 12.01–15.53% macro-minerals (Na, K, Ca and Mg) and 7.53–71.53 mg.100 g−1 trace minerals (Fe, Zn, Cu, Se and I). The crude protein content of E. cottonii (9.76% DW) and C. lentillifera (10.41% DW) were higher than that of S. polycystum (5.4% DW), and protein chemical scores are between 20 and 67%. The PUFA content of E. cottonii was 51.55%, C. lentillifera 16.76% and S. polycystum 20.34%. Eicosapentaenoic acid (EPA), accounted for 24.98% of all fatty acids in E. cottonii. These seaweeds have significant vitamin C (∼35 mg.100 g−1) and α-tocopherol (5.85–11.29 mg.100 g−1) contents.