Ascorbic acid, glutathione and synthetic antioxidants prevent the oxidation of vitamin E in platelets

Sc(OTf)3 catalyzed intramolecular single-electron transfer of 2-alkyl-1,4-benzoquinones: synthesis of 6-chromanols from donor-acceptor cyclopropanes

A Sc(OTf)3 catalyzed intramolecular cyclization reaction of 2-alkyl-1,4-benzoquinone derived from D-A cyclopropane was discovered. This reaction involves single-electron transfer, proton-transfer, an aromatization driven spin center shift, and radical coupling processes, and offers an efficient method for the synthesis of 6-chromanols from D-A cyclopropanes.

Platelet storage: Progress so far

There is a crucial need for platelet transfusion during an emergency-surgery and treatment of platelet disorders. The unavailability of donors has furthermore increased the demand for platelet storage. Platelets have limited shelf life due to bacterial contamination and storage lesions. Temperature, materials, oxygen availability, media, platelet processing and manufacturing methods influence the platelet quality and viability during storage. The conception of various platelet additive solutions along with the advent of plastic storage during the 1980s led to enormous developments in platelet storage strategies. Cold storage of platelets gained attention despite its inability to contribute to platelet survival post-transfusion as it offers faster haemostasis. Several developments in platelet storage strategies over the years have improved the quality and shelf-life of stored platelets. Despite the progress, the efficacy of platelets during storage beyond a week has not been achieved. Antioxidants as additives have been explored in platelet storage and have proven to enhance the efficacy of platelets during prolonged storage. However, the molecular interactions of antioxidants in platelets can provide a better understanding of their mechanism of action. Optimization of dosage concentrations of antioxidants is also a critical parameter to be considered as they tend to exhibit toxicity at certain levels. This review provides comprehensive insights into the critical factors affecting platelet storage and the evolution of platelet storage. It also emphasizes the role of antioxidants as additives in platelet storage solutions and their future prospects towards better platelet banking.

Dietary Antioxidant-Constructed Nanodrugs Can High-Efficiently Kill Cancer Cells while Protecting Noncancer Cells

Despite great advances, the development of cancer drugs that can efficiently kill cancer cells while protecting noncancer cells has not been achieved. By using only dietary antioxidants vitamin C (VC) and (R)-(+)-lipoic acid (LA), we herein develop a nanodrug VC@cLAV featuring the above function. After entering cells, cLAV dissociates into LA and DHLA (dihydrolipoic acid, reduced form of LA) and releases VC and DHA (dehydroascorbate, oxidized form of VC). In cancer cells, the two redox pairs recycle each other and dramatically promote the intracellular reactive oxygen species production to kill cancer cells at low doses comparable to cytotoxic drugs. Oppositely in noncancer cells, the LA/DHLA and VC/DHA pairs exert anti-oxidant action to actively protect the organism by preventing the normal cells from oxidative stress and repairing cells suffering from oxidative stress. When compared with the first-line cytotoxic drug, VC@cLAV displayed superior therapeutic outcomes yet without side effects in diverse tumor models including patient-derived xenograft (PDX). This drug with efficient cancer cell killing and noncancer cell protection represents a new cancer therapy.

Propargyl Chalcones' Radical Annulation/Sulfonation Reaction: Efficient Synthesis of Benzo[b]oxepin-5(2H)-one and Chromane Derivatives

A novel and facile methodology for the synthesis of sulfonated benzo[b]oxepinone and chromane derivatives was reported by the reaction of propargyl chalcones with arylsulfonyl chloride via radical cascade annulation/sulfonation under laboratory conditions. Readily available propargyl chalcones, commercialized arylsulfonyl chloride, and simple reaction conditions make this six(seven)-membered oxygen-containing heterocycles' synthetic strategy more attractive and with significant application values.

Antireduction: an ancient strategy fit for future

While antioxidants are on everyone's lips, antireductants are their much less-known counterparts. Following an antioxidant's definition, an antireductant prevents the chemical reduction of another compound by undergoing reduction itself. Antireductants have been traced back as far as the origin of life, which they facilitated by removal of atmospheric dihydrogen, H2 Moreover, as electron acceptors, antireductants equipped the first metabolic pathways, enabling lithoautotrophic microbial growth. When the Earth's atmosphere became more oxidizing, certain antireductants revealed their Janus-face by acting as antioxidants. Both capacities, united in one compound, were detected in primary as well as plant secondary metabolites. Substantiated by product identification, such antireductants comprise antiradicals (e.g. carotenoids) up to diminishers of ruminal methane emission (e.g. fumarate, catechin or resveratrol). Beyond these Janus-faced, multifunctional compounds, the spectrum of antireductants extends to pure electron-attractors (e.g. atmospheric triplet oxygen, O2, for plant root and gut protection). Current and prospective fields of antireductant application range from health promotion over industrial production to environmental sustainability.

Gold catalysis in total synthesis – recent achievements

The most recent achievements of gold catalysed transformations applied in total synthesis of natural products are reviewed and analysed.

Genetic determinants of dietary antioxidant status

Oxidative stress refers to a physiological state in which an imbalance between pro-oxidants and antioxidants results in oxidative damage. Oxidative stress has been associated with the development of numerous chronic diseases such as type 2 diabetes, cardiovascular disease (CVD), osteoporosis, and cancer. Endogenous production of free radicals occurs during normal physiological processes, such as aerobic metabolism, oxidation of biological molecules, and enzymatic activity. Environmental factors such as ultraviolet radiation, air pollution, and cigarette smoking can also contribute to the accumulation of free radicals in the body. Excess free radicals can damage tissues and promote the upregulation of disease-related pathways such as inflammation. Modulating oxidative stress by dietary supplementation with antioxidant micronutrients such as vitamins C and E or phytochemicals such as different carotenoids may help prevent or delay the development of certain diseases. However, research on antioxidant supplementation and disease has yielded inconsistent findings, which may be due, in part, to interindividual genetic variation. Polymorphisms in genes coding for endogenous antioxidant enzymes or proteins responsible for the absorption, transport, distribution, or metabolism of dietary antioxidants have been shown to affect antioxidant status and response to supplementation. These genetic variants may also interact with environmental factors, such as diet, to determine an individual's overall antioxidant status. This chapter examines current knowledge of the relationship between genetic variation and dietary antioxidant status.

Preventive effect of Ganoderma amboinense on acetaminophen-induced acute liver injury

In vivo preventive effects of Ganoderma amboinense against acetaminophen-induced hepatotoxicity in Balb/cA mice were studied. G. amboinense powder at 1% and 2% was mixed with standard diet and supplied to mice for 6 weeks, and followed by acetaminophen (350 mg/kg body weight) intraperitoneal injection. In normal mice (without acetaminophen treatment), the consumption of G. amboinense significantly increased hepatic glutathione (GSH) level. Acetaminophen treatment significantly elevated both alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities; however, the pre-intake of G. amboinense significantly and dose-dependently protected liver against the subsequent acetaminophen-induced elevation of ALT and AST activities. Acetaminophen treatment also caused significant GSH depletion, malondialdehyde (MDA) and reactive oxygen species (ROS) increase, and activity reduction of glutathione peroxidase (GPX) and catalase. However, the pre-intake of G. amboinense significantly diminished the subsequent acetaminophen-induced GSH depletion, MDA and ROS increase, and retarded the loss of catalase and GPX activities, in which the effect of G. amboinense on GPX activity, and formation of MDA and ROS was dose-dependent. These results support that G. amboinense may be considered as a preventive agent for acute liver injury.

To What Extent Does Ozone Therapy Need a Real Biochemical Control System? Assessment and Importance of Oxidative Stress

Ozone therapy is not officially allowed in many countries, but private medical services are using this therapy worldwide. However, appropriate control systems to assess the benefits and risks of systemic ozone therapy are not always used and in such cases the treatment is based on anecdotal reports. Oxidative stress phenomenon is becoming a highlighted biological process for ozone therapy because it is deeply involved in its mechanism of action. On the contrary, ozone therapy is an efficient regulator of the oxidative stress processes. In terms of therapeutic effects, it is convenient to know the metabolic status of the organism to face new oxidative challenges before and during ozone therapy applications. Oxidative stress is also important because it is involved as a cause or effect of many diseases. Since the 1990s, there has been the necessity of developing reliable systems for measuring oxidative stress in humans. In this sense, we have proposed a system for oxidative stress diagnosis that can serve as a control system for systemic ozone therapy applications. The system is based on the blood measurement of eight biomarkers (GSH, GPx, GST, SOD, CAT, DC, SRATB, and HPT) and the interpretation of these values by a computer-developed algorithm yielding four new indices (total antioxidant activity, total prooxidant activity, redox index and grade of oxidative stress). The system shows the patient's redox status and estimation of the oxidative stress level, with this information being relevant regarding implications on dosage and therapeutic effectiveness of ozone therapy.

Synthesis of natural products and analogs using multiple Pd-catalyzed transformations

Palladium-catalyzed transformations are of great importance in modern synthetic organic chemistry. The vast number of reactions that can be catalyzed by Pd0- as well as Pd2+-complexes in combination with the relative stability of the intermediates offers the intriguing opportunity of carrying out multiple consecutive bond-forming processes. They can be even performed in a domino fashion and in the presence of chiral ligands to allow the efficient preparation of almost enantiopure compounds. In this article, the use of double Heck, Tsuji-Trost-Heck, and Wacker-Heck reactions for the total syntheses of estradiol, spinosyn A analogs, cephalotaxine, and vitamin E is described.

Enantioselective Palladium-Catalyzed Total Synthesis of Vitamin E by Employing a Domino Wacker–Heck Reaction

An enantioselective total synthesis of vitamin E in which a novel palladium-catalyzed domino reaction was employed as the key step is described. This reaction allows the formation of the chiral chroman framework and the concurrent introduction of part of the side chain of vitamin E. The sequence comprises an enantioselective Wacker cyclization and a subsequent Heck reaction. Accordingly, reaction of alkenylphenol 12 with methyl vinyl ketone (13) in the presence of catalytic amounts of Pd(OTFA)(2) (TFA = trifluoroacetate), the enantiopure ligand (S,S)-Bn-BOXAX (8 b; Bn = benzyl, BOXAX = 2,2'-bis(oxazolyl)-1,1'-binaphthyl, and p-benzoquinone (9) as an oxidant gives access to chiral chroman 10 with an enantioselectivity of 97 % ee in 84 % yield. Chroman 10 is then converted into 24 by an aldol condensation reaction with (3R)-3,7-dimethyloctanal (11). Subsequent 1,2-addition of methyllithium, elimination of water, and hydrogenation yields vitamin E.

Ascorbate compartmentalization in the CNS

Ascorbic acid, found physiologically as the ascorbate anion, is an abundant water-soluble antioxidant. It is concentrated in the intracellular compartment of all tissues in the body. The CNS has particularly high levels of ascorbate. Recent data from this laboratory indicate that ascorbate is distinctly compartmentalized between neurons and glia, with an average intracellular concentration of 10 mM in neurons and 1 mM in glial cells. These data can be contrasted with those for another important low molecular weight antioxidant, glutathione, which is somewhat more concentrated in glia than in neurons. The present review summarizes evidence for ascorbate compartmentalization between neurons and glia and considers these data in light of evidence for the roles of ascorbate as a neuroprotective antioxidant and as a neuromodulator in the CNS.

Use of ascorbate in the preparation and maintenance of brain slices

Ascorbate and glutathione (GSH) are normally concentrated in brain cells at millimolar levels. However, both of these low-molecular-weight antioxidants are washed out of mammalian brain tissue during slice preparation and subsequent incubation. Ascorbate, which is not synthesized in the brain, can be added back to slices by active uptake from the incubation medium. Levels of GSH, on the other hand, are regulated by synthesis rather than uptake, and cannot be readily maintained in slices. Importantly, maintenance of brain slice ascorbate content at at least 50% of that in vivo, prevents the increase in slice water content that normally occurs during incubation. Slices with maintained ascorbate levels also have better histological characteristics than ascorbate-depleted tissue. The medium concentration of ascorbate sufficient to maintain content and inhibit edema formation is 400 microM, which is the normal concentration in brain extracellular fluid. This paper describes methods to maintain ascorbate levels in brain slices, including procedures to minimize oxidation in oxygenated incubation media. Also described is an HPLC analysis for ascorbate and GSH that is based on direct injection rather than extraction of samples.

Estrogen-dependent modulation of rat brain ascorbate levels and ischemia-induced ascorbate loss

Brain ascorbate levels in young adult female rat are lower than those in males. Loss of ascorbate during ischemia is also less in females, suggesting lower oxidative stress. After ovariectomy, however, ischemia-induced loss equals that in males. In the present study, we determined ascorbate levels in maturing male and female rat brain to establish when the gender difference in content arises. We further investigated whether 17beta-estradiol and/or progesterone treatment modulate levels and ischemia-induced loss in ovariectomized females and compared these data with those from normal females in proestrus and estrus. Gender differences in brain ascorbate content were absent before puberty and persisted only in cortex in aging rats. Chronic estradiol treatment, whether alone or in combination with progesterone, prevented an ovariectomy-induced ascorbate increase in hippocampus and caused levels in cortex and cerebellum to fall below those of randomly sampled normal females. These same low levels were found during proestrus and estrus. Estradiol replacement after ovariectomy prevented enhanced ischemia-induced ascorbate loss in hippocampus, but not in cortex or cerebellum. Ischemia-induced losses in proestrus and estrus were similar to those in normal controls. Progesterone had little effect in any region. These data indicate that ascorbate content and redox balance in female brain are influenced postpubertally by estrogens in a region-selective manner.

Vitamin E combined with selenium inhibits atherosclerosis in hypercholesterolemic rabbits independently of effects on plasma cholesterol concentrations

Several antioxidants inhibit atherosclerosis. This study investigated the hypothesis that combining vitamin E, a lipophilic antioxidant, with vitamin C, a hydrophilic antioxidant, and/or selenium, a cofactor of peroxidases that detoxify lipid peroxides, would inhibit atherosclerosis more effectively than vitamin E alone. We also considered whether regional variation in inhibition of atherosclerosis by antioxidants would be associated with regional variation in aortic lipophilic antioxidants. Rabbits were fed an atherogenic diet (control) or an atherogenic diet supplemented with vitamin E, vitamins E and C, vitamin E+selenium, vitamins E and C+selenium, or probucol (positive control). Supplements were as follows: vitamin E, 146 IU/d; vitamin C, 791 mg/d; selenium, 22 microg/d; or probucol, 406 mg/d. Vitamin C did not influence atherosclerosis. After 22 weeks of treatment, rank order of aortic atherosclerosis was control>vitamin E (with or without vitamin C)>vitamin E+selenium (with or without vitamin C)>probucol. Antioxidant treatment reduced aortic cholesterol concentrations 21% to 56%, 29% to 86%, and 19% to 75% for the aortic arch, descending thoracic aorta, and abdominal aorta, respectively (P<0.025 to P<0.0003 by ANOVA), with slightly greatly reductions for areas of atherosclerotic lesions. Some treatments reduced plasma cholesterol concentrations, but none altered the distribution of cholesterol among lipoproteins. Corrected for differences in plasma cholesterol concentrations, aortic cholesterol concentrations were reduced up to 72% (P<0.02) by the antioxidant treatments, with equal reductions by vitamin E+selenium and by probucol. Aortic alpha-tocopherol standardized by aortic cholesterol as a measure of aortic lipids was lower in the abdominal aorta than in the aortic arch of rabbits not given alpha-tocopherol and increased relatively more in the abdominal aorta than in the aortic arch with alpha-tocopherol supplementation. The results of this study suggest that vitamin E+ selenium inhibited atherosclerosis as effectively as an equally hypocholesterolemic dose of probucol by a mechanism(s) that is in part independent of effects on plasma and lipoprotein cholesterol concentrations. The tendency for greater efficacy of antioxidant treatments in the abdominal aorta than aortic arch may relate to the lower concentrations of alpha-tocopherol in the abdominal aorta of unsupplemented rabbits.

Vitamins E plus C and interacting conutrients required for optimal health. A critical and constructive review of epidemiology and supplementation data regarding cardiovascular disease and cancer

Antioxidants are crucial components of fruit/vegetable rich diets preventing cardiovascular disease (CVD) and cancer: plasma vitamins C, E, carotenoids from diet correlate prevalence of CVD and cancer inversely, low levels predict an increased risk of individuals which is potentiated by combined inadequacy (e.g., vitamins C + E, C + carotene, A + carotene); self-prescribed rectification of vitamins C and E at adequacy of other micronutrients reduce forthcoming CVD, of vitamins A, C, E, carotene and conutrients also cancer; randomized exclusive supplementation of beta-carotene +/- vitamin A or E lack benefits except prostate cancer reduction by vitamin E, and overall cancer reduction by selenium; randomized intervention with synchronous rectification of vitamins A + C + E + B + minerals reduces CVD and counteracts precancerous lesions; high vitamin E supplements reveal potentials in secondary CVD prevention. Plasma values desirable for primary prevention: > or = 30 mumol/l lipid-standardized vitamin E (alpha-tocopherol/cholesterol > or = 5.0 mumol/mmol); > or = 50 mumol/l vitamin C aiming at vitamin C/vitamin E ratio > 1.3-1.5; > or = 0.4 mumol/l beta- (> or = 0.5 mumol/l alpha+ beta-) carotene.

CONCLUSIONS

In CVD vitamin E acts as first risk discriminator, vitamin C as second one; optimal health requires synchronously optimized vitamins C + E, A, carotenoids and vegetable conutrients.

Ascorbate promotes low density lipoprotein oxidation in the presence of ferritin

Whilst catalytic iron has been implicated in the development of atherosclerosis by initiating low density lipoprotein (LDL) oxidation, the source of such iron remains uncertain. Here, we show that LDL oxidation in the presence of ferritin was stimulated by ascorbate (15-60 microM), whilst this effect was inhibited by the iron chelator desferrioxamine. Ascorbate also showed an antioxidant activity at high concentrations (125-250 microM). Our results suggest that the combination of ascorbate with ferritin may supply free iron for LDL oxidation in vivo.

In vitro oxidation of vitamins C and E, cholesterol, and thiols in rat brain synaptosomes

Free radical-induced oxidation of vitamins C, E, sulfhydryl compounds, and cholesterol in brain synaptosomes from Fisher 344 rats was studied. The synaptosomes were incubated at 37 degrees C with 2,2'-azobis-(2-amidinopropane) dihydrochloride (AAPH), which undergoes thermal decomposition to yield free radicals. After incubation, the synaptosomes were sedimented, saponified, and extracted with hexane to isolate tocopherol and cholesterol. Ascorbate and tocopherol were assayed by liquid chromatography, cholesterol by gas chromatography, and total sulfhydryls by spectrophotometry. Under the in vitro conditions used in this study, the approximate order for the ease of oxidation of the various compounds was: ascorbate >>tocopherol > sulfhydryl compounds >>> cholesterol. However, tocopherol and sulfhydryl oxidation occurred even before all of the ascorbate had been consumed. Therefore, the fate of a specific antioxidant at a particular cellular location cannot be predicted with complete accuracy using the in vitro order for ease of oxidation shown here. Ascorbate may play a major role in protecting brain against oxidative damage because: (i) ascorbate concentration is high in brain, (ii) it can regenerate vitamin E from its radical oxidation product, and (iii) it is one of the first antioxidants to be consumed during oxidative reactions.

Alterations in the bioantioxidants following thrombosis

The role of free radicals in rat thrombosis has been demonstrated by studying its scavenging enzyme system. Changes in the bio-antioxidants (GSH-redox cycle, total thiol groups, vitamins E and C) that also offer protection against the free radicals, have, however, not been studied so far. This investigation was undertaken to understand the involvement of these antioxidants during thrombosis. The tissues investigated following thrombosis were blood, platelets, polymorphonuclear leukocytes (PMNLs), heart, and lung. Glutathione (GSH) content in the platelets was observed to be depleted. However, oxidized glutathione (GSSG) contents in the platelets, PMNLs, and blood remain unaltered. In addition, in the whole blood GSH levels were increased significantly, whereas there was no change in the GSSG level. Activity of glutathione reductase (GR) was decreased significantly in platelets and lungs with an increase in the total thiol groups in the lung homogenate. Activity of Glutathione peroxidase (Gpx) remained unaltered in all the tissues studied. In addition, 24% and 15% decrease in the alpha-tocopherol concentration was observed in thrombocytes and PMNLs, respectively, with no change in the ascorbate levels in these cells. Results of this investigation suggest alterations in the GSH-redox cycle in blood, platelets, and lung after thrombosis in the rat.

Effect of [dl]-alpha-tocopherol on FeCl2-induced lipid peroxidation in rat amygdala

Peroxidative injury of neural membrane lipids can be initiated by iron-containing blood products, chelated ferrous or ferric ions, and low valence iron in aqueous solution. Lipid peroxidation was measured following focal injection of 3 microliters of 100 mM FeCl2 into rat amygdala. Acute parenteral administration of [dl]-alpha-tocopherol as the alcohol limited the quantity of peroxidation products generated. These data suggest a potential role for alpha-tocopherol administration in limiting brain injury responses.

The redox couple between glutathione and ascorbic acid: a chemical and physiological perspective

This article provides a comprehensive analysis of the redox reaction between glutathione/glutathione disulfide and ascorbic acid/dehydroascorbic acid. It includes an historical perspective of the progression of the experiments, first begun more than 60 years ago and continuing today with heightened importance. Indeed, the antioxidant capacity of glutathione and ascorbic acid, whether singly or in combination, linked via the redox couple, is a subject of intense interest for studies by bench scientists and clinicians, particularly because a growing body of evidence suggests that free radicals may be involved in a variety of diseases. The authors begin with a detailed summary of "test tube" experiments (the chemical perspective) that have revealed the conditions that regulate the rate of the redox coupling between glutathione and dehydroascorbic acid and that promote or inhibit the decomposition of dehydroascorbic acid in ordinary, buffered aqueous media; results obtained in the authors' laboratory are used for illustration purposes and uniformity of presentation. The authors then proceed to a critical examination of the extent to which the redox couple between glutathione and ascorbic acid operates in a cell, using the often published antioxidant cascade (See Fig. 1) as the model for the analysis (the physiological perspective). The evidence for and the evidence against the presence of the enzyme dehydroascorbate reductase in animal cells is outlined in a balanced way in an attempt to make sense of this continuing controversy. Next, the authors carefully document the many studies showing that exogenous dehydroascorbic acid is transported into cells where it is reduced to ascorbic acid by glutathione. Finally, they probe the functional significance and efficiency of the redox couple in monolayer cultures of human retinal pigment epithelial (RPE) cells, as a prototypical cellular model. The authors include the results of new experiments showing that incubation of RPE cells with a nitroxide, TEMPOL, leads to the selective oxidation of intracellular ascorbic acid. This approach is desirable because it dissects the cascade at a specific site and permits measurements of the levels of ascorbic acid and glutathione in the cells before, during, and after oxidation. The results show that only partial regeneration of ascorbic acid is obtained when control conditions are restored. However, if either ascorbic acid or dehydroascorbic acid is added to the media during the recovery period following treatment of cells with TEMPOL, then full recovery of ascorbic acid is observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Apolipoprotein oxidation in the absence of lipid peroxidation enhances LDL uptake by macrophages

A characteristic of the antioxidant, probucol, is its inability to inhibit apolipoprotein B fragmentation in low density lipoprotein (LDL), despite a pronounced ability to inhibit lipid oxidation on relatively lengthy exposure to Cu(II). Here we show that a short exposure of LDL to hydrogen peroxide and Cu(II) leads to 125I-labelled apolipoprotein B fragmentation, the production of malondialdehyde and hydroperoxides and leads to increased uptake by macrophages on subsequent culture. However, pre-loading LDL with probucol protects LDL from lipid oxidation but not protein fragmentation or macrophage uptake. The use of probucol to conduct studies on apolipoprotein B oxidation without extensive lipid oxidation may prove useful when studying LDL apolipoprotein damage on exposure to an aqueous free radical insult.

High-performance liquid chromatography-electrochemical detection of antioxidants in vertebrate lens: glutathione, tocopherol, and ascorbate

The HPLC-EC method has good specificity for the analysis of glutathione, tocopherol, and ascorbate. The same HPLC system can be used for all three analysis with changes of mobile phase and the electrode cell to match the procedure required. The same C18 reversed-phase column has been used with a refillable guard column for 3 years with no noticeable loss of resolving power. The main advantage of the glutathione procedure was the ability to monitor both GSH and GSSG, which allowed us to confirm that loss of GSH in the diabetic rat lens does not result in the appearance of GSSG. The main benefit of the tocopherol procedure was the ability to measure the tocopherol content of a single rat lens. Our previous experience with UV or fluorescence detection showed those methods to be not sensitive enough for a single lens determination. The mammalian lens has the lowest tocopherol content of the tissues of the eye, 10 to 40 times less than most body tissues as measured by gas chromatography-mass spectrometry (GC-MS). The better sensitivity of electrochemical detection has allowed for a single lens determination, keeping the number of experimental animals to a minimum. An advantage of the ASC analysis procedure was the extra specificity imparted by both the chromatography and the detector as well as the ability to estimate the total ascorbate (ASC plus DHAA) and DHAA content. Other reducing agents such as GSH and uric acid can interfere in colorimetric methods that rely on the reducing action of ASC. The very high GSH content of the mammalian lens was a concern when choosing a procedure. GSH levels exceeding 10 times the level of lens samples were found to yield no response using the HPLC-EC procedure for ASC. The only disadvantage with electrochemical detection was that the electrode response could drift with time, requiring more frequent calibration with standards. We continue to utilize these methods to examine the prevacuole loss of ASC and GSH in the diabetic rat lens model of cataract.

Prevention of platelet dysfunction by vitamin E in diabetic atherosclerosis

Premature atherosclerosis and other vascular disorders are serious complications of diabetes mellitus. Contributing factors include (i) increased peroxidation of LDL leading to foam cell formation, fatty streaks and plaque formation in the arterial wall, and (ii) hyperreactivity of blood platelets leading to increased platelet adhesion and aggregation. Vitamin E may play a protective role as an antioxidant and/or membrane stabilizing agent in either mechanism. In platelets it appears to regulate arachidonic acid metabolism. Decreased vitamin E levels in platelets are associated with increased aggregation. This is reversible by correction of the vitamin E status. In diabetics, platelet vitamin E levels tend to be reduced with concomitant increase in platelet aggregation. Several studies in patients with insulin-dependent diabetes mellitus and, to some extent, in those with non-insulin-dependent diabetes mellitus have shown that supplementation with several hundred IU vitamin E significantly reduced platelet aggregation and lipid peroxidation. In healthy volunteers high-dose supplementation had no notable effect on platelet aggregation. However, doses as low as 200 IU vitamin E significantly reduced platelet adhesion and inhibited the formation of protruding pseudopods typically occurring in activated platelets. In diabetic patients a decrease in the nonenzymatic glycation of proteins by vitamin E supplementation has been observed. Controlled studies are needed to confirm the effect of vitamin E on platelet function in well-defined groups of diabetics, followed by large-scale trials investigating the prevention of diabetic vascular complications as clinical end point.

Oxidation of alpha-tocopherol in subcellular fractions from rat brain and its possible involvement in nerve function

The turnover rate of vitamin E is slow in nerve tissue. Therefore, we have developed in vitro techniques to study the biochemical reactions of this nutrient in brain. Subcellular fractions were isolated from the cerebral hemispheres of 4-month-old, male, Fisher 344 rats. Aliquots of fractions (500 micrograms protein) were suspended in 50 mM phosphate buffer at pH 7.4 and incubated at room temperature (20-22 degrees) or 37 degrees for 2 hr in the presence or absence of the following oxidizing agents: 1 mM tertiary butyl hydroperoxide, 10 microM linoleic acid hydroperoxide, 0.5 to 50 mM 2,2'-azobis (2-amidinopropane) dihydrochloride (ABAPH) or 0.1 to 2 mM 2,2'-azobis (2,4-dimethyl) valeronitrile (ABDVN). The latter two compounds generate free radicals upon heating. After oxidation, the subcellular fractions were sedimented, saponified and assayed for tocopherol by liquid chromatography. Linoleic acid hydroperoxide was the most potent oxidizing agent, suggesting that endogenous fatty acid peroxides (e.g. eicosanoid intermediates) are very powerful oxidizing agents. Vitamin E may play an important role in providing antioxidant protection for membranes against excessive oxidation induced by these peroxides. Tocopherol in mitochondria and microsomes was much more susceptible to oxidation than synaptosomal tocopherol. The possible reasons for this observation are: (a) mitochondria and microsomes may contain less of the other reducing agents such as sulfhydryl compounds than synaptosomes, and/or (b) the electron transport structures in the former two subcellular fractions may be facilitating oxidation of tocopherol induced by free radicals. A portion of tocopherol remained unoxidized in all subcellular fractions even at high concentrations of ABAPH, suggesting that tocopherol exists in labile and nonlabile biochemical compartments or complexes.

Ascorbic acid oxidation: a potential cause of the elevated severity of atherosclerosis in diabetes mellitus?

The exposure of mouse peritoneal macrophages to cholesterol linoleate-containing artificial lipoproteins can lead to intracellular ceroid accumulation. This can be used as a model to study the role of oxidation in macrophage uptake of lipoproteins containing unsaturated fatty acids, considered by many as a primary event in atherosclerotic plaque formation. Our studies show that ascorbic acid can both inhibit and promote the formation of ceroid in such a model system. The transition metal copper (Cu(II)) further elevates ceroid accumulation and EDTA, a metal chelator, inhibits it. When trace levels of transition metals are present, low concentrations of ascorbic acid can elevate ceroid formation. This pro- and antioxidant characteristic of ascorbic acid was confirmed by monitoring the generation of oxidants by various concentrations of ascorbic acid, assessed by benzoic acid hydroxylation or the fragmentation of BSA. We discuss these observations in the context of an apparent increase in ascorbic acid oxidation and elevated severity of atherosclerosis in diabetes mellitus.

Alpha-tocopherol levels in brain are not altered in Parkinson's disease

alpha-Tocopherol (vitamin E) levels in normal brain were lower in the cerebellum than in the cerebral cortex or basal ganglia. There was no difference in alpha-tocopherol levels in the cerebellum, basal ganglia, or cerebral cortex between control subjects and patients with Parkinson's disease.

Vitamin E. Neurochemistry and implications for neurodegeneration in Parkinson's disease

Recently there has been a great deal of interest in the potential therapeutic use of supplemental vitamin E in amelioration of diseases of the nervous system. Even though many studies have provided encouraging results, the mechanism of any beneficial effect remains elusive. Experimental studies suggest that the presence of high levels of vitamin E in tissues prior to injury is essential for biological efficacy because administration of the vitamin after insult is often ineffective. The rationale for this phenomenon is unknown at present. Some of the remaining areas of investigation include the biochemical interaction of vitamin E with other biological antioxidant substances such as vitamin C and sulfhydryl compounds; the relative potencies of different molecular forms of tocopherols, such as trienols and various optical isomers; and the optimal dosage and mode of administration of the most potent tocopherol molecule. Future research on these and other topics will shed more light on the effective use of vitamin E in neurodegeneration.

Regeneration of vitamin E in rat polymorphonuclear leucocytes

The objectives of this study were to determine whether the recycling of tocopherol occurs in elicited rat polymorphonuclear leukocytes and if so, whether the recycling process is enzymic or chemical. When incubated with hemoglobin, tocopherol was oxidized in cell homogenates in a time- and concentration-dependent manner. The oxidized tocopherol could be regenerated by addition of ascorbate, glutathione or nordihydroguaiaretic acid. Time course studies showed a rapid regeneration of tocopherol which peaked at 1 min after the addition of reductants. Determination of the regeneration reaction in the presence of CHCl3 and MeOH indicated that under these enzyme-denaturing conditions, a considerable amount of tocopherol was still regenerated, suggesting that the regeneration reaction is predominantly a chemical reaction. This study provided direct evidence from mass analysis that oxidized vitamin E can be regenerated by cellular water-soluble reductants such as ascorbate and glutathione.

Vitamin C and vitamin E--synergistic interactions in vivo?

The synergistic relationship between ascorbic acid (vitamin C) and alpha-tocopherol (vitamin E) in the inhibition of lipid peroxidation has been known for some time and is now well established in vitro systems. The possibility that ascorbic acid may also reduce tocopheroxyl radicals in vivo is a subject of some interest and speculation. Although not all experiments have failed to suggest a synergistic antioxidant interaction, recent data indicate that the postulated synergism between these vitamins might be relatively unimportant compared with other metabolic processes.

Effect of vitamin E on arachidonic acid peroxidation and its binding to Chinese hamster V79 cell DNA

Following 24 h incubation in standard culture medium (containing 2 microM of arachidonic acid, AA), and 10 and 20 microM supplemented AA, approx. 55, 40 and 33%, respectively, of the fatty acid was incorporated into Chinese hamster V79 cell lipids. The AA content of cells increased 5 to 7-fold with the 10 and 20 microM supplementations of AA and, there was a correspondingly marked decrease in the proportion of AA incorporated into phospholipids (94 vs. 50 and 32%), whereas an increased percentage of AA was recovered in triacylglycerols (1 vs. 30 and 50%) and free fatty acids (1 vs. 3 and 8%). AA at 12 and 22 microM induced a 50 and 80% increase, respectively, in cellular content of thiobarbituric acid reactive substances (TBARS), an indication of increased peroxidation of cell lipids. This formation of TBARS was inhibited by vitamin E but not by indomethacin or SKF-525. Binding of [3H]AA-derived counts to DNA increased in parallel to the levels of cellular lipid peroxidation. Vitamin E added to the culture medium at 10(-4) M was readily taken up by the cells within 48 h and significantly reduced both lipid peroxidation and binding of AA-derived counts to DNA, without affecting AA uptake. Cell vitamin E content was significantly reduced following 24 h incubation in the presence of 10 and 20 microM supplemented AA. This study indicates that products of lipid peroxidation can bind to DNA in cultured cells, and points to a potential cyto- and geno-toxic risk posed by increased cellular AA content relative to anti-oxidant defenses.