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The moderate consumption of alcoholic beverages has been associated with protection against the development of coronary heart disease. Although alcohol itself can help prevent coronary heart disease through a number of mechanisms, red wine appears to offer protection above and beyond that attributable to alcohol alone. Red wine is a complex fluid containing grape, yeast, and wood-derived phenolic compounds, the majority of which have been recognized as potent antioxidants. The aim of this study was to investigate the major phenolic contributors to the antioxidant activity of wine. To this end, four wines were followed during the first 7-9 days of vinification. Individual phenolic compounds were quantified by HPLC, and antioxidant activity was determined by electron spin resonance spectroscopy. The extraction of the phenolics was found to be influenced by vinification procedure, grape quality, and grape variety. Although fermenting wines reached a total phenolic content comparable to that of a bottled wine after 9 days of vinification, the antioxidant activity was significantly lower than that of a finished wine. This suggests that the larger polyphenolic complexes and condensation products that appear during aging make a sizable contribution to the overall antioxidant activity of red wines.

The health benefit of fruit juices have been ascribed, in part, to phenolic antioxidants. The antioxidant potential of a range of fruit juices was assessed by measurement of their ability to reduce a synthetic free radical, potassium nitrosodisulphonate, and also by their ability to reduce Fe(III). Vitamin C was found to account for 65–100% of the antioxidant potential of beverages derived from citrus fruit but less than 5% of apple and pineapple juice. The contribution of carotenoids to antioxidant potential was negligible. Although phenolics appear to be major contributors to the antioxidant potential of the non-citrus juices, their identity and bio-availability requires further investigation.

Antioxidant nutrients are important for limiting damaging oxidative reactions in cells, which may predispose to the development of major clinical conditions such as heart disease and cancer. There is great interest in the possibility that the antioxidant potential of plant-derived phenolic compounds, such as flavonoids, may reduce the risk of developing these conditions. Antioxidant effectiveness in vivo depends on the bioavailability of these compounds, which was assumed to be low. However, recent studies with improved methodology indicate that some plant phenolics appear in plasma and body tissues and, thus, may be important nutritional antioxidants. However, this cannot be established with certainty until their effects on biomarkers of oxidative stress are established.

Quercetin is a plant polyphenol which is present in the diet as an aglycone and as sugar conjugates. Despite potent vasodilatory and antioxidant effects in vitro, destruction by intestinal organisms has been assumed to limit its nutritional relevance in the rat. However, we have refined extraction techniques using beta-glucuronidase followed by acid hydrolysis. Following this with HPLC methodology with post-column derivatisation, we have detected significant concentrations of quercetin and its metabolite, isorhamnetin, in tissues of rats maintained on quercetin-rich diets. Percentage recoveries are greater than 95% and intra-batch variation does not exceed 7% suggesting that the method may be useful in further studies of the biological role of this flavonoid.

Health benefits of red wine have been ascribed in part to the antioxidant properties of quercetin and other flavonols. Red wines, however, contain many other polyphenolic compounds with antioxidant potential. The present study has assessed the antioxidant capacity of seven red wines using electron spin resonance spectrometry to measure their ability to donate hydrogen atoms to a stable Fremy's radical. Antioxidant capacity of the wines was strongly related to the total phenol content (r = 0.872, P

Effects of three highly saturated fat diets containing either palm fat (RBDPO), hydrogenated soya fat (HSO) or hydrogenated rapeseed fat (HRSO), on short-term indicators of coronary heart disease (CHD) risk in healthy Scottish volunteers were compared. “Free living” subjects (53) were randomly assigned to one of three experimental diets or the “wild” habitual diet group for eight week periods. Fasting blood samples were collected at week 0 (baseline) and at two week intervals. Plasma lipoprotein-cholesterol, triglycerides and indices of lipid peroxidation were assessed. RBDPO diets increased plasma total-, LDL- and HDL-cholesterol (i.e. both beneficial and detrimental effects); HRSO and HSO diets decreased total- and HDL-cholesterol. Changes in cholesterol in ‘wild’ volunteers were similar (0.4m.mol./L) to those in experimental groups (0.4–0.5m.mol./L) with similar absolute values. Plasma triglycerides were reduced after four weeks RBDPO but not HSO or HRSO; values in the “wild” group did not differ from baseline or from other groups. RBDPO reduced indices of lipid peroxidation. HSO increased whole-blood aggregation and plasma conjugated dienes (CD). Physiological relevance of such small changes in indices of CHD risk elicited by the saturated diets are questionable.

Substantial in vitro and animal model evidence implicates the free radical-mediated oxidation of low density lipoprotein and its subsequent preferential uptake by macrophages in the arterial intima as an important factor in the development of vascular disease. In addition, antioxidants which prevent the oxidation of LDL in vitro also reduce the severity of vascular disease in animal models. Although some epidemiological studies also suggest that inadequate antioxidant status is related to the development of vascular disease, particularly cardiovascular disease, results from intervention trials have been contradictory. Whereas vitamin E may have a role in reducing the incidence of vascular disease, evidence is less strong for vitamin C, flavonoids and beta-carotene. Additionally, supplementation with some antioxidants such as beta-carotene may increase the incidence of cancer in high risk groups. Although increasing antioxidant intake is generally beneficial for health, this should perhaps be achieved by an increased dietary intake of antioxidant-rich foods rather than by use of supplements.

Objective: To assess whether consumption of 100 ml of whisky or red wine by healthy male subjects increased plasma total phenol content and antioxidant capacity. Design: A Latin square arrangement to eliminate ordering effects whereby, after an overnight fast, nine volunteers consumed 100 ml of red wine, malt whisky or unmatured ‘new make’ spirit. Each volunteer participated on three occasions one week apart, consuming one of the beverages each time. Blood samples were obtained from the anticubital vein at intervals up to 4h after consumption of the beverages when a urine sample was also obtained. Results: Within 30 min of consumption of the wine and whisky, there was a similar and significant increase in plasma total phenol content and antioxidant capacity as determined by the ferric reducing capacity of plasma (FRAP). No changes were observed following consumption of ‘new make’ spirit. Conclusions: Consumption of phenolic-containing alcoholic beverages transiently raises total phenol concentration and enhances the antioxidant capacity of plasma. This is compatible with suggestions that moderate alcohol usage and increased antioxidant intake decrease the risk of coronary heart disease. Sponsorship: Funded by the Scottish Office Agriculture, Environment and Fisheries Department (SOAEFD), the ERASMUS exchange program, the EC-Fair program and the Scotch Whisky Research Institute.

Electron spin resonance methodology has been used to assess the hydrogen-donating (antioxidant) ability of catechins and extracts of green and black tea to Fremy's radical and galvinoxyl radical in aqueous and organic solutions, respectively. Catechin flavanols accounted for 77-82% of the total antioxidant activity of green tea but only 47-58% of that of black tea. The radical quenching ability of the green tea was 21-24% more effective than that of the black tea in both aqueous and lipophilic systems. Epigallocatechin gallate was the most effective at reducing the two radical species, whereas epigallocatechin was least effective in the galvinoxyl/ethanol system, and catechin least effective in the Fremy's radical/water system. In a model system comprising a mixture of the flavanols in ethanolic or aqueous solution, in the same concentrations as they were present in the tea extracts, the antioxidant potential was a simple summation of the activity of the individual components indicating no synergistic or antagonistic side reactions. Results demonstrate that flavanol components of teas exhibit potent antioxidant activity in both aqueous and organic media. This will be of physiological relevance if such compounds partition into both the aqueous and lipid compartment of cells.

Objective: Adequate dietary intakes of vitamin E and essential polyunsaturated fatty acids are important to maintain cell membrane integrity, and deficiencies have been associated with smoking related cardiovascular disease. Sufficient vitamin E is required to prevent free radical mediated peroxidation of membrane lipids. Consequently, smokers may have a greater requirement for this antioxidant. To investigate, we assessed the concurrent influences of smoking, vitamin E supplementation and red blood cell (RBC) PUFA composition on the susceptibility of the cells to lipid peroxidation in adult males. Design and subjects: Thirty male smokers and thirty male non-smokers were randomly ascribed to daily 280 mg vitamin E or placebo supplements for 10 weeks. RBC were analysed at weeks 0 and 10 for fatty acid methyl esters, vitamin E, and their susceptibility to in vitro H2O2 induced lipid peroxidation. Results: Concentrations of essential fatty acids (EFA) in RBC were lower in smokers than in non-smokers. Supplementation with vitamin E increased levels of RBC EFA in smokers to match those of non-smokers. Furthermore, the ratio of vitamin E to PUFA in RBC from smokers and non-smokers was inversely correlated with their susceptibility to peroxidation. Conclusions: An adequate vitamin E to PUFA ratio is required to protect cell membranes from oxidative damage. The significant correlation between susceptibility to peroxidation and the PUFA content of RBC before supplementation suggests an inadequate intake of vitamin E in relation to PUFA intake. Moreover, the requirement for vitamin E appears to be greater in smokers than in non-smokers. Sponsorship: BASF Germany, Tobacco Products Research Trust, Scottish Office Agriculture, Environment, and Fisheries Department.

The effects of the flavonoids quercetin and myricetin, and the antihepatotoxic agent silymarin, on hydrogen peroxide-mediated DNA damage in human lymphocytes were determined using alkaline single-cell gel electrophoresis (the comet assay). Treatment with hydrogen peroxide increased the levels of DNA strand breaks and oxidised pyrimidine bases in these cells. Quercetin was protective at concentrations above 10 microM and myricetin decreased oxidant-induced DNA strand breakage at concentrations of 100 microM. Cellular metabolism may alter the antioxidant efficacy of the flavonoids. Silymarin had no protective effect at any of the concentrations tested. None of these flavonoids was itself genotoxic. Neither alpha-tocopherol nor beta-carotene decreased hydrogen peroxide-induced DNA breakage. The differences in effectiveness of these dietary compounds against oxidative DNA damage may be explained by differences in their chemical structure or location within the cell.

Many human degenerative diseases involve free radical processes that nutritional antioxidants may ameliorate or prevent, but the optimum intake of such nutrients has yet to be established. Requirement will depend in part on the level of exposure to exogenous and endogenous reactive oxygen species. Smokers incur a sustained degree of oxidant stress from both of these sources, increasing their requirements for vitamins E and C. Male smokers (n = 50) from a Scottish population with habitually low vitamin E and vitamin C intakes consistently had lower plasma ascorbate concentrations (P < 0.02) and greater susceptibility to hydrogen peroxide-stimulated erythrocyte peroxidation in vitro (P < 0.001) than did nonsmokers (n = 50) from the same population. Erythrocyte vitamin E concentrations increased in a dose-dependent manner during 20 wk of supplementation with 70, 140, 560, and 1050 mg D-alpha-tocopherol/d. In smokers each dose was associated with a significant decrease in susceptibility of erythrocytes to peroxidation (P < 0.001). However, red cells of nonsmokers receiving the 1050-mg supplement had an increased susceptibility to peroxidation. Moreover, prolonged supplementation with D-alpha-tocopherol in nonsmokers induced a decline in plasma ascorbate concentration (P < 0.02) in association with an increasing erythrocyte vitamin E uptake (P < 0.001), and in nonsmokers receiving 1050 mg, the susceptibility to peroxidation also increased (P < 0.001). Thus, vitamin E may have prooxidant activity in nonsmokers at high and prolonged intakes.

Despite high plasma levels of vitamin E, red blood cell membranes contain relatively low levels of vitamin E. This suggests the existence of a selective vitamin E uptake/regeneration system in human red blood cell membranes. alpha-Tocopherol binding sites on human red blood cells are thought to be involved in the uptake of alpha-tocopherol from the plasma. To understand the role of the uptake system we have compared the alpha-tocopherol content and binding activity of red blood cells from smokers and non-smokers. The specific binding of [3H] alpha-tocopherol to pure red blood cell preparations from smokers (n = 7, 28.4 +/- 2.8 years) was 30.6 +/- 3.2 fmoles per 3 x 10(8) red blood cells and for non-smokers (n = 17, 27.9 +/- 1.3 years) was 41.7 +/- 3.7 fmoles per 3 x 10(8) red blood cells. Thus alpha-tocopherol uptake activity was significantly lower in smokers (P = 0.05). Red blood cells from smokers contained less (1.8 +/- 0.4 micrograms/gHb) alpha-tocopherol than non-smokers (2.8 +/- 0.3 micrograms/gHb), (P0.05), despite plasma levels of alpha-tocopherol being similar: 12.9 +/- 0.8 microM in non-smokers vs. 12.7 +/- 0.5 microM in smokers. However, adjusting plasma alpha-tocopherol for total plasma cholesterol plus triacylglycerols showed alpha-tocopherol levels were higher (P0.01) in non-smokers (2.84 +/- 0.10 mumol alpha-tocopherol/ mmol [cholesterol+triacylglycerol]) than in smokers (2.36 +/- 0.11 mumol alpha-tocopherol/mmol [cholesterol+triacylglycerol]). The reduced alpha-tocopherol levels in red blood cells from smokers may be due to impairment of alpha-tocopherol uptake activity. The reduced levels of alpha-tocopherol in smokers red blood cells was not associated with any changes in cell membrane fluidity. At present it is not known whether supplementation of smokers with vitamin E would normalise the alpha-tocopherol uptake activity of red blood cells.

Whole-grain diets are linked to reduced risk of several chronic diseases (heart disease, cancer, diabetes, metabolic syndrome) and all-cause mortality. There is increasing evidence that these benefits are associated with the gut microbiota and that release of fibre-related phenolic metabolites in the gut is a contributing factor. Additional sources of these metabolites include fruits and vegetables, but the evidence for their protective effects is less well established. With respect to the availability of bound phytophenols, ready-to-eat cereals are compared with soft fruits (considered rich in antioxidants) and other commonly consumed fruits and vegetables. The results demonstrated that when compared with an equivalent serving of fruits or vegetables, a recommended portion of whole-grain cereals deliver substantially higher amounts of bound phytophenols, which are available for metabolism in the colon. The increased amount of these phenolic metabolites may, in part, explain the evidence for the protective effects of whole-grain cereals.

Objectives of this study were (a) to assess the extent of oxidative stress elicited in human endothelial cells by n-3, n-6 and n-9 mono- and polyunsaturated fatty acids and by interleukin-1 beta and (b) to determine how such stress influenced glutathione peroxidase (GSHPx) activity. Fatty acids were co-incubated with human vascular endothelial cells (HUVEC) for 24 h. Lipid peroxidation, monitored as conjugated diene (CD) formation, increased 3-4-fold with increasing eicosapentaenoic and docosahexaenoic acids: 2-3-fold with linoleic acid; decreased by 50% with arachidonic acid and was unchanged with oleic acid. Changes in glutathione peroxidase activity mirrored conjugated diene formation in the HUVEC incubated with fatty acids. Interleukin-1 beta also increased glutathione peroxidase and conjugated diene formation; the latter increased enzyme activity dose-dependently suggesting a possible role for this oxidation product in the induction of glutathione peroxidase activity. The ability of fish oil fatty acids to induce antioxidant enzymes, particularly those of the glutathione redox system, may be an important mechanism protecting cells and tissues against oxidative and inflammatory cytokine elicited damage.

1. During all aerobic metabolism, free radicals generated by the partial reduction of oxygen are potentially injurious to cells. Highly efficient antioxidant defence systems exist to inhibit oxidative damage to cellular lipids and proteins. Specific enzymes have a crucial role in these antioxidant defences, and their activity may be induced by regulatory mechanisms that respond to oxygen metabolite concentration. 2. To assess whether smoking induces an additional adaptive response, we compared antioxidant defence systems in erythrocytes from smokers and non-smokers and assessed whether a high intake of vitamin E (280 mg/day), a major lipophilic free-radical-scavenging antioxidant, affects the activity of antioxidant enzymes. 3. A total of 100 men, 50 smokers and 50 non-smokers, were allocated to four treatment groups in a 2 × 2 factorial design (smokers versus non-smokers and placebo versus vitamin E). For 10 weeks each subject took one capsule per day of either 280 mg dl-α-tocopherol acetate or a visually identical placebo (hydrogenated coconut oil with negligible vitamin E content). 4. Despite increased erythrocyte cytosolic antioxidant enzyme activities in smokers compared with non-smokers, erythrocytes from smokers were more susceptible to hydrogen peroxide-induced lipid peroxidation in vitro. 5. Vitamin E supplementation further increased erythrocyte catalase (EC 1.11.1.6) activity in both smokers and non-smokers (P > 0.001) and erythrocyte glutathione peroxidase (EC 1.11.1.9) and glutathione reductase (EC 1.6.4.2) activities in non-smokers (P > 0.001). After supplementation with vitamin E there was a concomitant fall in erythrocyte superoxide dismutase (EC 1.15.1.1) activity (P > 0.001) and total glutathione concentration (P > 0.01). Furthermore, in both smokers and non-smokers there was a significant decrease in the susceptibility of erythrocytes to peroxidation (P > 0.001). 6. Various endogenous and exogenous factors exert control over cellular protection against reactive oxygen species, and our data suggest that one such factor is the supply of vitamin E.

Inflammatory disorders of the bowel and colon cancer are associated with elevated indices of oxidative stress. Analogous elevations in markers of oxidative stress and loss of cell-membrane integrity are also observed in the colons of rats deficient in vitamin E (D-α-tocopherol), the major lipid-soluble antioxidant in biological systems. The causal relationship between colon pathologies associated with oxidative stress and dietary deficiency in antioxidant vitamins such as vitamin E is still uncertain. Investigation of potential mechanisms by which lack of dietary vitamin E may lead to clinically relevant pathological changes in colon tissue was conducted using gene expression profiling strategies on vitamin E-sufficient and -deficient rats. Morphological changes and increased indices of lipid peroxidation were linked to vitamin E deficiency. These changes in colon tissue are potentially important in disease pathogenesis of the colon linked with oxidative stress or other direct consequences of inadequate levels of vitamin E.

This work evaluated the strategies to increase the oxidative stability and the potential health benefits of Brassica napus L. var. oleifera (rapeseed) oil enriched with natural compounds. The effect of storage, light, and heating on the oxidative stability of rapeseed oil was compared with olive oil. Oxidative stability was assessed by using Rancimat and thiobarbituric acid reactive-substances assay (TBARS) production. Different concentrations of individual phenol compounds, extracts, and vegetable powders were added to the cold-pressed rapeseed oil. The most positive effects were observed with addition of freeze dried powders. The rapeseed oil chemical profile was analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) and the antioxidant effects of rapeseed oil fortified with vegetable powders were investigated with different in vitro assays. Results suggested that beetroot, carrot, tomato, and swede can offer effective alternatives or adjuncts to synthetic antioxidants during frying and storage of rapeseed oil. Practical applications: Brassica napus L. var. oleifera (rapeseed) oil is one of the most consumed oil. In this study, we evaluated the possible approaches to increase rapeseed oil oxidative stability and potential health benefits by using different natural products (beetroot, broccoli, carrot, celery, green pea, onion, red pepper, spinach, swede, tomato, and yellow pea). Results clearly showed that natural products may increase the stability of rapeseed oil, particularly when within a matrix rather than as an extract or pure compound. These evidences are significant for both consumers and oil industry. Rapeseed oil oxidative stability is investigated. Rapeseed oil composition is determined by GC-MS. Increased antioxidant activity of rapeseed oil with powders supplementation is evidenced. Vegetable powders can offer effective alternative to synthetic antioxidants during frying and storage of rapeseed oil. Rapeseed oil oxidative stability is investigated. Rapeseed oil composition is determined by GC-MS. Increased antioxidant activity of rapeseed oil with powders supplementation is evidenced. Vegetable powders can offer effective alternative to synthetic antioxidants during frying and storage of rapeseed oil.

Acknowledgment This work is part of the Strategic Research 2011–2016 and is funded by the Scottish Government's Rural and Environment Science and Analytical Services Division (RESAS).

We previously reported the identification of a new alpha-tocopherol-binding protein (approximately 15 kDa) in the cytosol of rat liver and heart and in rabbit heart (A.K. Dutta-Roy et al., J. Nutr. Biochem. 5, 562-570, 1994). This protein specifically binds alpha-tocopherol and enhances its transfer between separate membranes. In the present paper we have purified and characterized the alpha-tocopherol-binding protein from bovine heart cytosol and compared its various structural and functional properties with the similar size (approximately 15 kDa) cytosolic fatty acid-binding protein of this tissue. alpha-Tocopherol-binding protein was purified to electrophoretic homogeneity from bovine heart cytosol by a procedure involving precipitation with 70% ammonium sulfate, followed sequentially by gel filtration chromatography and chromatofocusing. The purified protein migrated as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an apparent molecular mass of 16 kDa. Isoelectric focusing of the purified protein showed that the pI value is around 4.5. The binding of alpha-tocopherol to the purified protein was rapid, reversible, and saturable. The alpha-tocopherol-binding protein did not bind oleate as assessed by direct radiolabeled fatty acid binding and fluorescence enhancement assay. Amino acid analysis showed the presence of a large number of Ala, Gly, Ser, Lys, and Pro residues and a lesser number of aromatic residues in this protein. Anti-bovine heart fatty acid-binding protein antibody did not recognize the alpha-tocopherol-binding protein in the Western blot. The Western blot, ligand affinity, molecular size, and amino acid analysis data suggest that the alpha-tocopherol-binding protein is different from the cytosolic fatty acid-binding protein and that it may be involved in intracellular transport and metabolism of alpha-tocopherol.

cope We examined whether flavan-3-ol-enriched dark chocolate, compared with standard dark and white chocolate, beneficially affects platelet function in healthy subjects, and whether this relates to flavan-3-ol bioavailability. Methods and results A total of 42 healthy subjects received an acute dose of flavan-3-ol-enriched dark, standard dark or white chocolate, in random order. Blood and urine samples were obtained just before and 2 and 6 h after consumption for measurements of platelet function, and bioavailability and excretion of flavan-3-ols. Flavan-3-ol-enriched dark chocolate significantly decreased adenosine diphosphate-induced platelet aggregation and P-selectin expression in men (all p ≤ 0.020), decreased thrombin receptor-activating peptide-induced platelet aggregation and increased thrombin receptor-activating peptide-induced fibrinogen binding in women (both p ≤ 0.041), and increased collagen/epinephrine-induced ex vivo bleeding time in men and women (p ≤ 0.042). White chocolate significantly decreased adenosine diphosphate-induced platelet P-selectin expression (p = 0.002) and increased collagen/epinephrine-induced ex vivo bleeding time (p = 0.042) in men only. Differences in efficacy by which flavan-3-ols affect platelet function were only partially explained by concentrations of flavan-3-ols and their metabolites in plasma or urine. Conclusion Flavan-3-ols in dark chocolate, but also compounds in white chocolate, can improve platelet function, dependent on gender, and may thus beneficially affect atherogenesis.

Epicatechin is a widely consumed dietary flavonoid and there is substantial evidence that it contributes to the health benefits reported for flavanol-rich cocoa products including dark chocolate. Numerous reports have described the appearance of epicatechin and epicatechin phase-2 conjugates (sulfates and glucuronides of epicatechin and methylepicatechin) in blood and urine samples of subjects following ingestion of epicatechin. The most widely reported method of quantifying total epicatechin in plasma and urine samples involves hydrolysis with a mixture of β-glucuronidase and sulfatase to convert the conjugates to epicatechin aglycone which is subsequently quantified. We observed a lack of hydrolysis of epicatechin sulfates and methylepicatechin sulfates using commercial sulfatases and investigated this further. Samples of urine or plasma from subjects who had consumed epicatechin were subjected to enzyme hydrolysis and then analysed using LC-MS/MS, or analysed without enzyme hydrolysis. Attempts to increase the extent of hydrolysis of epicatechin conjugates were made by increasing the amount of enzyme, hydrolysis pH and length of incubations, and using alternative sources of enzyme. The standard hydrolysis conditions failed to hydrolyse the majority of epicatechin sulfates and methylepicatechin sulfates. Even when the quantity of enzyme and incubation period was increased, the pH optimised, or alternative sources of sulfatases were used, epicatechin monosulfates and methylepicatechin monosulfates remained as major peaks in the chromatograms of the samples. An assessment of literature data strongly suggested that the majority of reports where enzyme hydrolysis was used had significantly underestimated epicatechin bioavailability in humans. Methods for quantifying epicatechin concentrations in blood and urine need to take account of the lack of hydrolysis of (methyl)epicatechin-sulfates, for example by quantifying these directly using LC-MS/MS.

Vitamin E (RRR-α-tocopherol) is a lipid-soluble antioxidant that is present in the membranes of intracellular organelles. There it plays an important role in the suppression of free radical-induced lipid peroxidation. There are eight naturally occurring homologues of vitamin E that differ in their structure and in biological activity in vivo and in vitro. Although γ-tocopherol is a more effective free radical scavenger than α-tocopherol in vitro, the reverse is true in vivo, suggesting that the tocopherol distribution systems favor the localization of α-tocopherol at the sites where it is required. Vitamin E is transported in plasma primarily by lipoproteins, but little is known of how it is transported intracellularly. A 30 kDa α-tocopherol-binding protein in the liver cytoplasm may regulate plasma vitamin E concentrations by preferentially incorporating the vitamin E homologue, RRR-α-tocopherol (α-tocopherol), into nascent very low density lipoproteins. However, this α-tocopherol-binding protein is unique to the hepatocyte, whereas α-tocopherol is present in the cells of all major tissues. Moreover α-tocopherol accumulates at those sites within the cell where oxygen radical production is greatest and thus where it is most required; in the membranes of heavy mitochondria, light mitochondria, and endoplasmic reticulum. This raises the question of how the lipid-soluble α-tocopherol is transported intracellularly in different tissues. We have identified a new α-tocopherol-binding protein of molecular mass 14.2 kDa in the cytosol of heart and liver. This protein specifically binds α-tocopherol in preference to the δ- and γ-homologues but does not bind oleate. Studies on immunoreactivity and ligand specificity of the protein suggest that it is not a fatty acid-binding protein. The 14.2 kDa α-tocopherol-binding protein stimulates the transfer of α-tocopherol from liposomes to mitochondria in vitro by 8 to 10 fold. We suggest that this low molecular mass TBP may be responsible for the intracellular transport and distribution of α-tocopherol in the tissues.

Smokers incur a sustained free radical load that may increase their vitamin E requirement. Erythrocytes of male smokers from a Scottish population with a habitually low vitamin E intake were more susceptible to hydrogen peroxide-stimulated peroxidation than were those from nonsmokers (P < 0.001). Plasma concentrations of lipid peroxides, thiobarbituric acid re- active substances, and conjugated dienes were also elevated in smokers compared with nonsmokers (P < 0.05). These indexes of oxidative stress were markedly decreased (P < 0.001) in the smokers and nonsmokers after consumption of 280 mg dl-a to- copherol acetate/d for 10 wk. Platelet numbers in serum of both smokers and nonsmokers were also decreased by vitamin E sup- plementation (P < 0.02). Although the clinical significance of the results is unclear, elevated indexes of lipid peroxidation are associated with the pathogenesis of atherosclerosis, and platelets are involved with fibrinolysis. Therefore, both smokers and non- smokers may benefit from increased vitamin E intakes. Am J Clin Nutr l994;60:383-7.

Scope: Olive products are rich in phenolic compounds, which are natural antioxidants in vitro. We tested the in vivo effects of alperujo, an olive production by-product, as well as hydroxytyrosol and 3,4-dihydroxyphenylglycol (DHPG) isolated from alperujo, on indices and pathways of oxidative and metabolic stress in a vitamin E-deficient rat model. Methods and results: Rats were fed a vitamin E-deficient diet for 10 weeks, followed by this diet supplemented with either 100 mg/kg diet dα-tocopherol, alperujo extract, hydroxytyrosol, or 10 mg/kg diet DHPG, for a further 2 weeks. We detected alperujo phenolics in tissues and blood, indicating they are bioavailable. Alperujo extract partially ameliorated elevated plasma levels of thiobarbituric acid reactive substances and also lowered plasma cholesterol levels, whereas hydroxytyrosol increased plasma triglyceride levels. Proteomics and subsequent network analysis revealed that hepatic mitochondrial aldehyde dehydrogenase (ALDH2), of which protein and activity levels were regulated by dα-tocopherol and olive phenolics, represents a novel central regulatory protein hub affected by the dietary interventions. Conclusion: The in vivo free radical scavenging properties of olive phenolics appear relatively modest in our model. But alternative mechanisms, including regulation of ALDH2, may represent relevant antioxidant mechanisms by which dietary olive phenolics could have beneficial impact on cardiovascular health. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Salicylic acid and related compounds are produced by plants as part of their defence systems against pathogen attack and environmental stress. First identified in myrtle and willow, the medical use of salicylate-rich preparations as anti-inflammatory and antipyretic treatments may date back to the third millennium BC. It is now known that salicylates are widely distributed throughout the plant kingdom, and they are therefore present in plant products of dietary relevance. In the UK, major food sources are tomato-based sauces, fruit and fruit juice, tea, wine, and herbs and spices. In mammalian cells, salicylic acid demonstrates several bioactivities that are potentially disease-preventative, including the inhibition of production of potentially neoplastic prostaglandins, which arise from the COX-2 mediated catalysis of arachidonic acid. Moreover, it appears to be readily absorbed from the food matrix. This has led some to suggestions that the recognised effects of consuming fruit and vegetables on lowering the risk of several diseases may be due, in part, to salicylates in plant-based foods. However, published estimates of daily salicylic acid intake vary markedly, ranging from 0.4 to 200 mg day(-1), so it is unclear whether the Western diet can provide sufficient salicylates to exert a disease-preventative activity. Some ethnic cuisines that are associated with lowered disease risk may contain considerably more salicylic acid than is obtainable from a Western diet. However known protective effects of acetylsalicylic acid (Aspirin™) may have lead to an over-emphasis on the importance of dietary salicylates compared with other bioactive plant phenolics in the diet.

Plant-based diets contain a plethora of secondary metabolites that may impact on health and disease prevention. Much attention has been focused on the potential bioactivity and nutritional relevance of several classes of phytochemicals such as flavonoids, carotenoids, phyto-oestrogens and glucosinolates. Less attention has been paid to simple phenolic acids that are widely found in fruit, vegetables, herbs, spices and beverages. Daily intakes may exceed 100 mg. In addition, bacteria in the gut can perform reactions that transform more complex plant phenolics such as anthocyanins, procyanidins, flavanones, flavonols, tannins and isoflavones into simple phenolic metabolites. The colon is thus a rich source of potentially active phenolic acids that may impact both locally and systemically on gut health. Both the small and large intestine (colon) contain absorption sites for phenolic acids but low post-prandial concentrations in plasma indicate minimal absorption early in the gastrointestinal tract and/or rapid hepatic metabolism and excretion. Therefore, any bioactivity that contributes to gut health may predominantly occur in the colon. Several phenolic acids affect the expression and activity of enzymes involved in the production of inflammatory mediators of pathways thought to be important in the development of gut disorders including colon cancer. However, at present, we remain largely ignorant as to which of these compounds are beneficial to gut health. Until we can elucidate which pro-inflammatory and potentially carcinogenetic changes in gene expression can be moderated by simple phenolic acids, it is not possible to recommend specific plant-based foods rich in particular phenolics to optimise gut health.

There are concerns that weight-loss (WL) diets based on very low carbohydrate (LC) intake have a negative impact on antioxidant status and biomarkers of cardiovascular and metabolic health. Obese men (n 16) participated in a randomised, cross-over design diet trial, with food provided daily, at approximately 8·3 MJ/d (approximately 70 % of energy maintenance requirements). They were provided with two high-protein diets (30 % of energy), each for a 4-week period, involving a LC (4 % carbohydrate) and a moderate carbohydrate (MC, 35 % carbohydrate) content. Body weight was measured daily, and weekly blood samples were collected. On average, subjects lost 6·75 and 4·32 kg of weight on the LC and MC diets, respectively (P sed 0·350). Although the LC and MC diets were associated with a small reduction in plasma concentrations of retinol, vitamin E (α-tocopherol) and β-cryptoxanthin (P P P P

Background: Diets that are high in protein but reduced in carbohydrate contents provide a common approach for achieving weight loss in obese humans. However, the effect of such diets on microbiota-derived metabolites that influence colonic health has not been established. Objective: We designed this study to assess the effect of diets with reduced carbohydrate and increased protein contents on metabolites considered to influence long-term colonic health, in particular the risk of colorectal disease. Design: We provided 17 obese men with a defined weight-maintenance diet (85 g protein, 116 g fat, and 360 g carbohydrate/d) for 7 d followed by 4 wk each of a high-protein and moderate-carbohydrate (HPMC; 139 g protein, 82 g fat, and 181 g carbohydrate/d) diet and a high-protein and low-carbohydrate (HPLC; 137 g protein, 143 g fat, and 22 g carbohydrate/d) diet in a crossover design. Fecal samples were analyzed to determine concentrations of phenolic metabolites, short-chain fatty acids, and nitrogenous compounds of dietary and microbial origin. Results: Compared with the maintenance diet, the HPMC and HPLC diets resulted in increased proportions of branched-chain fatty acids and concentrations of phenylacetic acid and N-nitroso compounds. The HPLC diet also decreased the proportion of butyrate in fecal short-chain fatty acid concentrations, which was concomitant with a reduction in the Roseburia/Eubacterium rectale group of bacteria, and greatly reduced concentrations of fiber-derived, antioxidant phenolic acids such as ferulate and its derivatives. Conclusions: After 4 wk, weight-loss diets that were high in protein but reduced in total carbohydrates and fiber resulted in a significant decrease in fecal cancer-protective metabolites and increased concentrations of hazardous metabolites. Long-term adherence to such diets may increase risk of colonic disease. Am J Clin Nutr doi: 10.3945/ajcn.110.002188.

An alpha-tocopherol-binding protein (TBP) with a molecular mass of 14.2 kDa has been identified from the cytosol of rat heart and liver and purified to electrophoretic homogeneity by precipitation with 70% ammonium sulphate, followed by gel filtration and ion-exchange chromatography. In addition to the 14.2 kDa TBP, liver also contains the previously described 30 kDa TBP. The concentrations of the 14.2 kDa TBP in heart and liver were 12.3 micrograms and 17.5 micrograms per g of tissue, respectively. The purified protein specifically binds d alpha-tocopherol in preference to the delta- and gamma-homologues but does not bind oleate. The TBP stimulated the transfer of d alpha-tocopherol from liposomes to mitochondria in vitro by 8-10 fold. These results suggest that low molecular mass TBPs may play a role in intracellular vitamin E transport.

Finnish Landrace sheep with a genetic lesion which results in restricted cysteine transport across the red cell membrane have total glutathione concentrations in their red blood cells that are approximately 40% of those in normal sheep of the same breed. However, dimethyldisulphide-challenged red blood cells from both phenotypes produce an ESR-spin adduct at similar rates. The resistance of the low glutathione phenotype red cells to oxidant challenge is reflected by increases in the activities of antioxidant enzymes. Sheep with a genotypic disorder in cysteine transport may be a suitable model for studying the genetic expression of antioxidant enzymes in response to oxidant loads.

A simple, fast and reliable method to quantify, simultaneously, 3,4-dihydroxyphenylglycol (DHPG), hydroxytyrosol (HT) and tyrosol (Ty) extracted and purified successfully from olive oil by-product, called alperujo, in animal plasma and tissues samples has been developed using a high-performance liquid chromatographic (HPLC) method with UV-Vis detection. Extraction of compounds is based on solid-phase extraction for plasma and homogenisation with zirconia beads and centrifugation for tissues. Calibration curves were linear for all three phenols at a relatively low concentration range (0.05-50 μg/mL). This method has acceptable accuracy (91-95% in plasma and 63-100% in tissues), precision (1.11-8.26% intra-day and 0.32-9.5% inter-day) and sensitivity for detecting low concentrations of these phenols in small plasma volumes and several animal tissues such as liver, heart, kidney, muscle, testes, white adipose tissue (WAT) and brain. © 2010 Elsevier Ltd. All rights reserved., This study was funded by the Scottish Government Rural and Environment Research and Analysis Directorate (RERAD).

Several studies suggest that natural salicylates in plant-based foods may benefit health. However, large variation in published values of the salicylate content of foods means that relating dietary intakes to disease risk is problematical. Consequently, we have systematically reviewed the available literature using prescribed selection criteria. By combining these literature values with in-house analysis, we have constructed a food composition database describing median salicylate values for 27 different types of fruits, 21 vegetables, 28 herbs, spices and condiments, 2 soups and 11 beverages. Application of a validated food frequency questionnaire estimated median dietary intakes of 4.42 (range 2.90-6.27) and 3.16 (2.35-4.89) mg/day for Scottish males and females, respectively. Major dietary sources of salicylates were alcoholic beverages (22%), herbs and spices (17%), fruits (16%), non-alcoholic beverages including fruit juices (13%), tomato-based sauces (12%) and vegetables (9%). Application of the database to populations with differing dietary habits and disease risk profiles may provide further evidence for the role of dietary salicylates in the prevention of chronic diseases.

Background: Three daily portions of whole-grain foods could lower cardiovascular disease risk, but a comprehensive intervention trial was needed to confirm this recommendation. Objectives: We aimed to assess the effects of consumption of 3 daily portions of whole-grain foods (provided as only wheat or a mixture of wheat and oats) on markers of cardiovascular disease risk in relatively high-risk individuals. Design: This was a randomized controlled dietary trial in middleaged healthy individuals. After a 4-wk run-in period with a refined diet, we randomly allocated volunteers to a control (refined diet), wheat, or wheat + oats group for 12 wk. The primary outcome was a reduction of cardiovascular disease risk factors by dietary intervention with whole grains, which included lipid and inflammatory marker concentrations, insulin sensitivity, and blood pressure. Results: We recruited a total of 233 volunteers; 24 volunteers withdrew, and 3 volunteers were excluded. Systolic blood pressure and pulse pressure were significantly reduced by 6 and 3 mm Hg, respectively, in the whole-grain foods groups compared with the control group. Systemic markers of cardiovascular disease risk remained unchanged apart from cholesterol concentrations, which decreased slightly but significantly in the refined group. Conclusions: Daily consumption of 3 portions of whole-grain foods can significantly reduce cardiovascular disease risk in middle-aged people mainly through blood pressure‐lowering mechanisms. The observed decrease in systolic blood pressure could decrease the incidence of coronary artery disease and stroke by 15% and 25%, respectively. This trial was registered at clinicaltrials.gov as ISRCTN27657880. Am J Clin Nutr 2010;92:733‐40.

We have measured coronary heart disease (CHD) risk factors, dietary antioxidant intakes, plasma antioxidant concentrations, activities of blood antioxidant enzymes and plasma indices of lipid peroxidation in current smokers, past-smokers and those who have never smoked (sample size=242; mean age±SE=54±lyr). Compared with non-smokers, both current smokers and past-smokers had increased plasma concentrations of low density lipoproteins (LDL) (P=0.027) and triglycerides (P

Diets rich in flavonoids may reduce the risk of developing colorectal cancer. Flavonoids are widely distributed in foods of plant origin, though in the UK tea is the main dietary source. Our objective was to evaluate any independent associations of total dietary and non-tea intake of four flavonoid subclasses and the risk of developing colorectal cancer in a tea-drinking population with a high colorectal cancer incidence. A population-based case ‐ control study (264 cases with histologically confirmed incident colorectal cancer and 408 controls) was carried out. Dietary data gathered by FFQ were used to calculate flavonoid intake. Adjusted OR and 95 % CI were estimated by logistic regression. No linear association between risk of developing colorectal cancer and total dietary flavonol, procyanidin, flavon-3-ol or flavanone intakes was found, but non-tea flavonol intake was inversely associated with colorectal cancer risk (OR 0·6; 95 % CI 0·4, 1·0). Stratification by site of cancer and assessment of individual flavonols showed a reduced risk of developing colon but not rectal cancer with increasing non-tea quercetin intake (OR 0·5; 95 % CI 0·3, 0·8; Ptrend , 0·01). We concluded that flavonols, specifically quercetin, obtained from non-tea components of the diet may be linked with reduced risk of developing colon cancer. Flavonoids: Flavonols: Quercetin: Colorectal cancer: Case‐control studies: Epidemiology

1. Blood antioxidants were measured in venous blood samples from 20 runners and six sedentary individuals. All subjects were male, between 20 and 40 years old, and in steady state with respect to body weight and physical activity patterns. Dietary analysis was undertaken using a 7-day weighed food intake. Correlations were sought between antioxidants in blood and (1) weekly training distance and (2) maximum oxygen uptake. In addition, 12 runners could be classified into two groups undertaking either low (range 16–43 km, n = 6) or high (80–147 km, n = 6) weekly training. 2. Body weight (range 55.3–90.0 kg) and percentage body fat (range 7–19%) both showed negative correlations with the weekly training distance (both P < 0.001). Energy intake and maximum oxygen uptake were both correlated with the weekly training distance (both P < 0.001). 3. Plasma creatine kinase activity, an indicator of muscle damage, was significantly correlated with the weekly training distance (P < 0.01), whereas the plasma concentration of thiobarbituric acid-reactive substances, an indicator of free-radical-mediated lipid peroxidation, decreased with increased maximum oxygen uptake (P < 0.01). 4. Erythrocyte α-tocopherol content was greater in the two running groups (P < 0.05) compared with the sedentary group, and lymphocyte ascorbic acid concentration was significantly elevated in the high-training group (P < 0.01) compared with the low-training group. 5. Erythrocyte activities of the antioxidant enzymes, glutathione peroxidase and catalase, were significantly and positively correlated with the weekly training distance (P < 0.01 and P < 0.05, respectively). Total erythrocyte glutathione content was higher in the two training groups, and was accounted for by an increase in reduced glutathione content. 6. These results indicate that there is an increase in blood antioxidant defence mechanisms associated with endurance training or the related life style, but despite this there is a degree of muscle damage in the training individuals.

NADPH-induced lipid peroxidation of hepatic microsomes from vitamin E-deficient rats has been used to assess the antioxidant effectiveness of dl alpha, d alpha- and gamma-tocopherol. When the tocopherols were added in ethanol to microsomes, the degree of inhibition of formation of thiobarbituric acid reactive substances (TBARS) decreased in the order dl alpha- greater than d alpha- greater than gamma-tocopherol. This reflected the difference in the solubility of the tocopherols in the microsomes, dl alpha-tocopherol being the most soluble and gamma-tocopherol the least. Using inhibition of TBARS produced per tocopherol content in microsome as a measure of antioxidant potency, the effectiveness of the isomers was gamma- greater than d alpha- greater than dl alpha. Despite addition of pharmacological concentrations of the isomers, it was not possible to inhibit lipid peroxidation to the same levels as were found in microsomes from vitamin E sufficient animals. Use of ethanol as a vehicle may not allow optimum orientation of the tocopherols into the lipid bilayer.

Certain dietary antioxidants such as vitamin E and vitamin C are important for maintaining optimum health. There is now much interest in polyphenolic products of the plant phenylpropanoid pathway as they have considerable antioxidant activityin vitroand are ubiquitous in our diet. Rich sources include tea, wine, fruits and vegetables although levels are affected by species, light, degree of ripeness, processing and storage. This confounds the formulation of databases for the estimation of dietary intakes. Most attention to date has focused on the flavonoids, a generic term which includes chalcones, flavones, flavanones, flavanols and anthocyanins. There is little convincing epidemiological evidence that intakes of polyphenols are inversely related to the incidence of cancer whereas a number of studies suggest that high intakes of flavonoids may be protective against CHD. In contrast, numerous cell culture and animal models indicate potent anticarcinogenic activity by certain polyphenols mediated through a range of mechanisms including antioxidant activity, enzyme modulation, gene expression, apoptosis, upregulation of gap junction communication and P-glycoprotein activation. Possible protective effects against heart disease may be due to the ability of some polyphenols to prevent the oxidation of LDL to an atherogenic form although anti-platelet aggregation activity and vasodilatory properties are also reported. However, some polyphenols are toxic in mammalian cells. Thus, until more is known about their bioavailability, metabolism and intracellular location, increasing intakes of polyphenols by supplements or food fortification may be unwise.

Due to the success of therapeutic anti-inflammatory compounds to inhibit, retard, and reverse the development of colon cancer, the identification of dietary compounds as chemopreventives is being vigorously pursued. However, an important factor often overlooked is the metabolic transformation of the food-derived compounds in the gut that may affect their bioactivity. Commonly consumed dietary phenolics (esterified ferulic acid and its 5-5'-linked dimer), which have the potential to undergo predominant microbial transformations (de-esterification, hydrogenation, demethylation, dehydroxylation, and dimer cleavage), were incubated with human microbiota. The metabolites were identified (high-performance liquid chromatography and nuclear magnetic resonance) and confirmed to be present in fresh fecal samples from 4 human volunteers. The potential anti-inflammatory properties were compared by measuring the ability of the parent compounds and their metabolites to modulate prostanoid production in a cell line in which the inflammatory pathways were stimulated following a cytokine-induced insult. The compounds were readily de-esterified and hydrogenated, but no dimer cleavage occurred. Only the monomer underwent demethylation and selective de-hydroxylation. The resultant metabolites had differing effects on prostanoid production ranging from a slight increase to a significant reduction in magnitude. This suggests that the microbial transformation of dietary compounds will have important inflammatory implications in the chemoprevention of colon cancer.

Background: Alkali provision may explain why fruit and vegetables benefit bone health. Objective: We aimed to determine the effects of alkali-providing potassium citrate (double-blind) and fruit and vegetable intake (single-blind) on bone turnover over 2 y. Design: We conducted a randomized placebo-controlled trial in 276 postmenopausal women (aged 55– 65 y). Women were randomly assigned to 4 groups: high-dose potassium citrate (55.5 mEq/d), low-dose potassium citrate (18.5 mEq/d), placebo, and 300 g additional fruit and vegetables/d (equivalent of 18.5 mEq alkali). Serum and fasted urine for bone markers were collected at baseline and at 3, 6, 12, 18, and 24 mo. An additional urine sample was collected at 4 – 6 wk. Bone mineral density (BMD) was measured at baseline and 2y . Results: Repeated-measures ANOVA showed no difference between groups for urinary free deoxypyridinoline cross-links relative to creatinine (fDPD/Cr), serum N-terminal propeptide of type 1 collagen, or beta C-terminal telopeptide, although, at 4 – 6 wk, fDPD/Cr was lower in the high-dose potassium citrate group (P 0.04). Mean SD spine BMD loss in the placebo group (1.8 3.9%) did not differ significantly from that in the treatment groups (2.1 3.2%;P 0.88). Hip BMD loss in the placebo and low-dose potassium citrate groups was 1.3 2.3% and 2.2 2.3%, respectively (P 0.14). Conclusions: Two-year potassium citrate supplementation does not reduce bone turnover or increase BMD in healthy postmenopausal women, which suggests that alkali provision does not explain any long-term benefit of fruit and vegetable intake on bone. Am J Clin Nutr 2008;88:465–74.

In 1988 over half of the deaths in the world were due to heart disease. The recognised risk factors for coronary heart disease are smoking, plasma cholesterol levels and hypertension. These factors, however, account only for some 50‐60 per cent of the variance in incidence of the disease between countries; so other factors must contribute. Recent biochemical evidence suggests that in conditions of oxidant stress a relative deficiency in antioxidants, in conjunction with a relatively high concentration of oxidisable substrates such as cholesterol, may play an important role in the development of atheroma. The efficiency of the human antioxidant defence system depends in part on an adequate intake of foods containing antioxidants such as vitamins C and E. Until intervention trials with these antioxidants show positive effects in reducing coronary heart disease, advising the general population to increase intake of Vitamin C and E is contentious. On the other hand increasing consumption of fruit and vegetables is unlikely to do any harm, and may do us some good.

The fate of anthocyanins and ellagitannins in rats was monitored following ingestion of raspberry juice. After 1 h low nM concentrations of unmetabolised anthocyanins were present in plasma but these declined by 2 h and after 4 h they were no longer detectable. For the first 2 h there was an almost full recovery of anthocyanins as they passed from the stomach through the duodenum/jejunum and into the ileum. After 3 h less than 50% were recovered, and the levels declined rapidly thereafter. Excretion of raspberry anthocyanins in urine over a 24 h period was equivalent to 1.2% of the amount ingested. Trace quantities of anthocyanins were detected in the caecum, colon and faeces and they were absent in extracts of liver, kidneys and brain. Urine also contained a number of phenolic acids but most were present in quantities well in excess of the 918 nmol of anthocyanins present in the ingested juice. These findings indicate that raspberry anthocyanins per se are poorly absorbed, probably prior to reaching the ileum, and that substantial amounts pass from the small to the large intestine where they are degraded by colonic bacteria. Ellagitannins disappeared in the stomach without accumulation of ellagic acid.

Elevated levels of phospholipases, prostaglandin synthases and lipoxygenases in colonic cells at various stages of malignancy indicate a strong link between dietary lipids and colon cancer. Lipoxygenase-catalysed arachidonic acid metabolism plays a key role in colorectal carcinogenesis and has the potential to be modulated by phenolic compounds. Plant-based foods are rich sources of phenolic compounds and in the human colon they are predominantly available as simple phenolics such as the benzoic acids. Benzoic acids were determined in faecal waters from four volunteers consuming a western-style diet. Structure-activity relationships were established for the lipoxygenase-catalysed oxygenation of arachidonic acid using an oxygen electrode. All compounds studied inhibited this reaction (21-73%; p