Effect of high doses of dietary vitamin E on the concentrations of vitamin E in several brain regions, plasma, liver, and adipose tissue of rats

The object of this study was to assess the influence of high levels of dietary vitamin E on vitamin E concentrations in specific areas of the brain. Four-week-old male rats were fed vitamin E-deficient, control, and high-vitamin E (1,000 IU/kg) diets for 4 months. Concentrations of alpha-tocopherol in serum, adipose tissue, liver, cerebrum, cerebellum, and striatum were determined by liquid chromatography with fluorescence detection. In the high-vitamin E group, alpha-tocopherol concentrations in cerebrum, cerebellum, and striatum increased uniformly to 1.4-fold of values in controls; serum, adipose tissue, and liver attained even higher concentrations: 2.2-, 2.2-, and 4.6-fold, respectively, of control values. As observed before, brain levels of alpha-tocopherol were somewhat resistant to vitamin E deficiency, in contrast to the peripheral tissues.

Concentrations of vitamin E in various neuroanatomical regions and subcellular fractions, and the uptake of vitamin E by specific areas, of rat brain

Vitamin E concentrations were determined by high-performance liquid chromatography in different anatomical regions of the brain from 3-month-old Fischer 344 rats. Gray matter from cerebellum and cervical spinal cord contained the lowest concentrations, while gray matter from the frontal cortex and thalamus had the highest concentrations of vitamin E. Radioactive alpha-tocopherol injected intravenously into the rat was readily taken up by brain although the level of uptake was very low compared with the liver. The ratios of brain-to-serum radioactivities ranged from 0.011 to 0.016 depending upon the brain region. Cerebellar gray matter is characterized by a low concentration of unlabeled alpha-tocopherol and a high level of uptake of radioactive alpha-tocopherol and thus is particularly active in the metabolism of vitamin E. Concentrations of unlabeled alpha-tocopherol were highest in microsomal and mitochondrial fractions and were the lowest in cytosol and nuclear fractions.

High doses of vitamin E in the treatment of disorders of the central nervous system in the aged

Oxidative stress is a putative factor in the pathogenesis of many human disorders of the central nervous system. Therefore, antioxidants such as vitamin E have become attractive as therapeutic agents in the treatment of several diseases. In addition, vitamin E seems to play a specific role in the nervous system. As a result, vitamin E has been used in pharmacologic doses in the treatment of disorders such as Parkinson disease, Alzheimer disease, and tardive dyskinesia. One investigation showed that the use of 2000 IU all-rac-alpha-tocopheryl acetate is beneficial in the treatment of Alzheimer disease. Similar doses of vitamin E, however, were not beneficial for delaying the progression of Parkinson disease. In other studies, dosages >/=400 IU vitamin E/d were found to be beneficial in the treatment of tardive dyskinesia, although this finding was not confirmed in a larger cooperative study conducted by the Veterans Administration. Even though the efficacy of vitamin E in the management of cardiovascular disease has been shown, the potential role of vitamin E in the treatment of cerebrovascular disease remains essentially unknown. The experience from 2 large clinical trials involving the oral intake of 2000 IU vitamin E/d suggests that vitamin E is relatively safe at this dosage for periods <2 y. However, the safety and efficacy of supplemental vitamin E over periods of many years in the prevention of neurologic diseases has not been adequately explored.

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

An earlier report from this laboratory showed that tocopherol in human platelets is oxidized when the platelets are incubated in vitro in Tyrode medium with arachidonate (or other oxidants). Arachidonate is a more potent oxidizing agent in 50 mM potassium phosphate buffer at pH 7.4 with 0.1 mM ethylenediaminetetraacetic acid (EDTA) than in Tyrode medium. Forty to fifty percent of total platelet tocopherol was oxidized upon incubation with 40-50 microM arachidonate in the phosphate-buffered medium. The tocopherol oxidation took place within 15 min after the addition of arachidonate. Preincubation of platelets with ascorbate blocked the oxidation of tocopherol. This is one of the first direct in vitro demonstrations of the vitamin E-sparing action of vitamin C in media containing biological cellular material. Other compounds which blocked the oxidation of platelet tocopherol were ascorbyl palmitate, propyl gallate, butylated hydroxytoluene, hydroquinone and glutathione. If ascorbate or glutathione was added after the tocopherol was oxidized to the quinone there was no reversal of the oxidation.

A liquid chromatographic method for the simultaneous determination of alpha-tocopherol and tocopherolquinone in human red blood cells and other biological samples where tocopherol is easily oxidized during sample treatment

A liquid chromatographic method for the simultaneous determination of alpha-tocopherol and tocopherolquinone in human red blood cells is described. Tocopherols in the red cell membrane are very susceptible to oxidation during sample processing. Red cell samples are saponified in the presence of a mixture of butylated hydroxytoluene, ascorbic acid, and pyrogallol and then extracted with hexane. The tocopherol compounds are separated on a C-18 column using a mobile phase containing 12% acetonitrile, 83% methanol, and 5% buffer (NaH2PO4.H2O, 7.5 mM final concentration) and are detected electrochemically. The mixture of antioxidants is essential to avoid loss of the tocopherol compounds during processing of samples. The use of acetonitrile in the mobile phase results in the separation of tocopherolquinone from delta-tocopherol. The proposed method may be generally suitable for the analysis of biological samples where tocopherols are especially vulnerable to oxidation. The levels of tocopherolquinone and delta-tocopherol in normal red cells are quite small (less than 1% of alpha-tocopherol). The ratio of tocopherol and tocopherolquinone concentrations might serve as a useful index of the redox status of red cell membranes, particularly under in vitro conditions.

Changes in vitamin E concentrations in human plasma and platelets with age

It has been postulated that vitamin E compounds (tocopherols) can retard the aging process. Therefore, changes in concentrations of tocopherols in human plasma and platelets with aging were studied. Fasting blood samples were obtained from 48 healthy male volunteers aged 24-91 years. Concentrations of the tocopherols in plasma and platelets were determined by a liquid chromatographic method. Alpha and gamma tocopherols were the major forms of vitamin E found in both plasma and platelets. The concentrations of alpha and total tocopherols in plasma did not change significantly with age. However, the plasma gamma tocopherol and the platelet alpha, gamma, and total tocopherol concentrations decreased significantly with age. The platelet to plasma ratios of tocopherol concentrations also decreased with age.

In vitro oxidation of vitamin E, vitamin C, thiols and cholesterol in rat brain mitochondria incubated with free radicals

The kinetics of oxidation of endogenous antioxidants such as vitamins C and E and thiols as well as membrane cholesterol in isolated rat brain mitochondria were studied. Oxidation was induced by incubating the mitochondria at 37 degrees C with the free radical generators 2,2' azobis (2'-amidinopropane) dihydrochloride (ABAPH) and 2,2' azobis (2,4-dimethyl) valeronitrile (ABDVN) which undergo thermal decomposition to yield free radicals. An approximate order for the in vitro ease of oxidation was: ascorbate >> alpha-tocopherol > sulfhydryls >> cholesterol. However, small amounts of ascorbate were present in the mitochondria when alpha-tocopherol and sulfhydryl compounds were getting oxidized. This observation is different from those with more homogeneous biological substrates like blood plasma or serum. The order of oxidation of the various compounds is a function of not only the redox potentials but also the (a) concentrations of the oxidized and reduced species, (b) compartmentation of the compounds and (c) enzymatic and nonenzymatic systems for the repair or regeneration of the individual antioxidants. Even though ascorbate levels are quite low within mitochondria this nutrient may play a major role as a first line of defense against oxidative stress. The lipid-soluble ABDVN was much more potent in oxidizing membrane alpha-tocopherol and thiols than the water-soluble ABAPH. With both free radical generators the rate of oxidation of the antioxidants consisted of two phases. The initial phase, that is more rapid, may represent a pool of antioxidant that is involved in immediate antioxidant protection of the organelle with the slower compartment being responsible for replenishing the faster pool whenever needed.(ABSTRACT TRUNCATED AT 250 WORDS)

Vitamin E concentrations in human blood plasma and platelets

Vitamin E (tocopherol), cholesterol, triglyceride, and total lipid concentrations were determined in the plasma of 49 healthy, human, male subjects ranging in age from 24 to 91 yr. Tocopherol concentrations in the blood platelets of these subjects were also determined. alpha and gamma tocopherol accounted for nearly all of the vitamin E compounds in plasma and platelet samples. The mean gamma tocopherol concentration was one-fourth of that of alpha in both plasma and platelets. The alpha and gamma tocopherol concentrations in plasma showed statistically significant positive correlations with total lipid, cholesterol, and triglyceride concentrations. However, the platelet alpha and gamma tocopherol concentrations were not significantly correlated with plasma lipid, cholesterol, or triglyceride concentrations. Thus platelet vitamin E concentrations do not passively reflect plasma lipid changes and are postulated to be better indicators of vitamin E nutritional status than plasma tocopherol concentrations.

Determination of alpha-tocopherolquinone (vitamin E quinone) in human serum, platelets, and red cell membrane samples

A high-performance liquid chromatographic method for the determination of alpha-tocopherolquinone in a few selected biological samples is reported. Samples of human serum, blood platelets, or red cell membranes were saponified and extracted with hexane. A measured aliquot of the extract was evaporated under a stream of nitrogen, and the residue was reconstituted with mobile phase (methanol:water, 98:2) and used directly for liquid chromatography. alpha-Tocopherolquinone was separated on Zorbax C-18 columns (25 cm X 4.6 mm, 5-microns particles) and detected by its absorption at 265 nm. The addition of high levels of base during saponification as well as exposure to fluorescent light results in loss of the quinone. Concentrations of alpha-tocopherolquinone in normal human serum are exceedingly small constituting only 0.02-0.05% of the alpha-tocopherol concentration. The technique is particularly useful in the quantitation of the oxidation of alpha-tocopherol in biological samples under in vitro conditions. For example, incubation of human platelets with diamide or arachidonate resulted in oxidation of alpha-tocopherol and the alpha-tocopherolquinone produced accounted for 11.8 and 30.6%, respectively of the alpha-tocopherol lost.

Effect of age on vitamin E concentrations in various regions of the brain and a few selected peripheral tissues of the rat, and on the uptake of radioactive vitamin E by various regions of rat brain

The concentrations of tocopherols in selected areas of the brains and a few peripheral tissues of 3-, 14-, and 30-month-old male Fischer 344 rats were determined by a high-performance liquid chromatographic method. Throughout the time period studied, alpha-tocopherol was the only tocopherol detected in the brain. Concentrations of alpha-tocopherol increased significantly with age in medulla and spinal cord whereas no such change was seen in other brain areas. Among the peripheral tissues, total tocopherol concentrations increased with age in the liver and adipose tissue while no significant changes were observed in the heart. The pattern of uptake of radioactive alpha-tocopherol from the serum by the various areas of the brain was similar for the 3- and 14-month-old animals even though the brains from the 14-month-old animals took up less of the radioactive compound. Measurable amounts of tocopherol esters were not present in the tissues of the 30-month-old animals.

Vitamin E concentrations in the brains and some selected peripheral tissues of selenium-deficient and vitamin E-deficient mice

Weanling male CD-l mice were fed control, vitamin E-deficient or selenium-deficient diets for periods of 12 to 20 weeks. alpha-Tocopherol concentrations in plasma, liver, and testes, as well as in three specific areas in the brain (cerebral hemisphere, cerebellum, and medulla plus pons) were determined by high performance liquid chromatography. Significant concentrations of alpha-tocopherol were found in all brain samples from vitamin E-deficient animals long after the peripheral tissues were depleted, indicating that brain is more resistant to vitamin E deficiency than peripheral tissues. Cerebellar concentrations of alpha-tocopherol were consistently lower than those of cerebral hemisphere and medulla-pons. Furthermore, the cerebellar alpha-tocopherol concentration sustained a larger decline than the other two brain areas within 6 weeks of vitamin E deficiency treatment. These and other data suggest that cerebellum may be more susceptible to damage from vitamin E deficiency than other parts of the brain. Selenium deficiency did not affect brain alpha-tocopherol concentrations during the 12 weeks of the study.

Vitamin E in plasma and platelets of human diabetic patients and control subjects

Vitamin E concentrations were determined in plasma and platelet samples from 23 diabetic and 30 control human subjects. The mean concentrations of alpha and total tocopherols in the plasma and platelets of the diabetics were higher than that of the controls. The mean gamma tocopherol concentrations in both plasma and platelets were similar in diabetics and controls. The platelet vitamin E concentrations decreased significantly with age in only the controls and not in the diabetics. Thus diabetics have higher concentrations of tocopherols in blood platelets and plasma. The total plasma tocopherol concentrations correlated significantly with total plasma cholesterol, triglyceride, and total lipid concentrations in both diabetic and control groups. However, no significant correlations were observed between platelet tocopherol levels and plasma lipids in either group. In five subjects plasma and platelet vitamin E concentrations remained unchanged during standard glucose tolerance tests.

Oxidation of vitamin E in red cell membranes by fatty acids, hydroperoxides and selected oxidants

Our laboratory previously reported that vitamin E (tocopherol) in human blood platelets was oxidized in vitro by various oxidants. This paper shows that diamide, superoxide, hydroperoxides and polyunsaturated fatty acids induce oxidation of tocopherols in red cell membranes. In contrast to platelets, red cell membrane tocopherol was oxidized by hydrogen peroxide and tertiary butyl hydroperoxide. Alpha tocopherolquinone was one of the products of oxidation. Among the fatty acids, the cis polyunsaturated acids were the most potent oxidizing agents with monounsaturated and trans compounds relatively ineffective. The oxidation is not a detergent effect of the fatty acids since neither the detergents Brij and Lubrol, when present in concentrations under 0.5 mM, nor sodium arachidonate (1.25 mM), could oxidize the membrane tocopherol. When red cell membrane samples were incubated with 0.5 mM arachidonate, 47 +/- 11% (S.D.) of the tocopherol lost was converted to tocopherolquinone. Unlike arachidonate, oxidants such as diamide, hydrogen peroxide and tertiary butylhydroperoxide are unable to oxidize all of the membrane tocopherol and produce less tocopherolquinone from oxidation (10-15%) under the experimental conditions of this study. Linoleic acid hydroperoxide is a much more potent oxidant and produces less quinone than arachidonate. The mechanisms of tocopherol oxidations induced by the various compounds seem to be different since the yields of quinone during oxidation vary with the nature of the oxidant. Tocopherol is consumed by oxidation as it protects the membrane from oxidant damage induced by compounds such as unsaturated fatty acids and hydroperoxides.

Alpha tocopherol in CSF of subjects taking high-dose vitamin E in the DATATOP study. Parkinson Study Group

Alpha-Tocopherol concentrations were determined in the CSF of patients with early untreated Parkinson's disease receiving 2,000 IU vitamin E orally per day. After treatment the concentrations increased significantly (p < 0.001) by 76+/-10 (SE)%. The net increases in CSF alpha-tocopherol concentrations after treatment showed a significant positive correlation with the number of days of vitamin E ingestion (p < 0.001). Thus, high-dose vitamin E treatment results in elevating CSF vitamin E levels and possibly brain vitamin E levels.

Alpha tocopherol levels in various regions of the central nervous systems of the rat and guinea pig

The alpha tocopherol contents of various discrete anatomical regions in the central nervous system of adult rats and guinea pigs were assayed using a liquid chromatographic method. All parts of the guinea pig nervous system had lower alpha tocopherol contents per gram wet, dry orlipid weights than the corresponding areas in the rat. In both animals the distribution of alpha tocopherol did not correspond to the distribution pattern of total lipid. There was also a rostral to caudal concentration gradient with respect to alpha tocopherol content; gray matter from cerebral hemisphere has the highest concentration and cervical spinal cord the least. In both animals alpha tocopherol content per gram dry weight or lipid weight were higher in gray matter areas when compared with white matter areas. The low concentration of alpha tocopherol in spinal cord could make this region more susceptible to damage from deficiency than the rest of the central nervous system.

Oxidation of vitamin E, vitamin C, and thiols in rat brain synaptosomes by peroxynitrite

Peroxynitrite is formed by the reaction of superoxide with nitric oxide, an important neurotransmitter. Incubation of rat brain synaptosomes with peroxynitrite resulted in the consumption of antioxidant substances such as alpha-tocopherol, ascorbate, and thiols. Membrane cholesterol was not oxidized under the same conditions. alpha-Tocopherol and ascorbate in synaptosomes were oxidized very rapidly by peroxynitrite. In contrast, previous reports in the literature have shown that peroxynitrite treatment did not oxidize tocopherol in human plasma. Peroxynitrite in sufficient concentrations oxidized all of the tocopherol and ascorbate in synaptosomes. Thus, the oxidant is able to diffuse to the different membranes in synaptosomes and oxidize tocopherol in all of them. alpha-Tocopherol is converted quantitatively to tocopherolquinone during the oxidation. Significant amounts of thiols (at least 30% of the total thiols) do not seem to be accessible to oxidation by peroxynitrite. However, the concentration of thiols is much higher than those of tocopherol and ascorbate. Addition of the hydroxyl radical quenchers benzoate or mannitol or the enzymes superoxide dismutase or catalase (alone or together) did not affect the oxidation of tocopherol and ascorbate by peroxynitrite, whereas cysteine and glutathione blocked the oxidation. Therefore, reactive oxygen species may not be directly involved as intermediates in oxidations induced by peroxynitrite. The latter is a potent oxidizing agent that can oxidize substances such as tocopherols, ascorbate, and thiols in the immediate vicinity of its formation. The antioxidant nutrients ascorbate and tocopherol could play important roles in protecting brain from oxidative damage induced by peroxynitrite.

Aging is associated with a decrease in synaptosomal glutamate uptake and an increase in the susceptibility of synaptosomal vitamin E to oxidative stress

We examined the influence of aging upon the uptake of glutamate by synaptosomes, and the oxidation of synaptosomal vitamin E. Synaptosomes isolated from the cerebral hemispheres of Fischer 344 rats, 4 and 24 months old, were suspended at 37 degrees C in buffer (pH 7.4) simulating extracellular fluid containing 10 mM glucose. The Km for the high affinity uptake of tritium labeled glutamate was approximately 10 microM. The uptake of glutamate was lower in synaptosomes from older animals than those from younger animals for periods of up to 20 minutes. Upon incubation with a mixture of ferrous iron and ascorbate, more of the alpha tocopherol in synaptosomes derived from older rats was oxidized than in those derived from younger ones. Older animals may be more susceptible to excitotoxicity because: a) synaptosomal reuptake of glutamate is less efficient and b) oxidative stress induced by various agents including glutamate may be higher in synaptosomes from the older animal.

A sensitive assay of transthyretin (prealbumin) in human cerebrospinal fluid in nanogram amounts by ELISA

A sensitive ELISA method for determining transthyretin (prealbumin) in human cerebrospinal fluid (CSF) is described. The method utilizes goat antihuman transthyretin antibody (IgG fraction) for capture and peroxidase conjugated antibody for color development. The assay has a linear range of 1-4 ng transthyretin added per well. The within-day and between-day coefficients of variation are 5.1 and 6.1%, respectively. The concentration of transthyretin in CSF (ranging from 5 to 20 mg per L) correlated significantly with the corresponding serum concentrations (range 170-420 mg/l). This suggests that synthesis of transthyretin in the brain and peripheral tissues is under similar biological control in normal subjects. The transthyretin concentrations in CSF did not correlate with total CSF protein concentration or age of the subject.

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.

Spectrophotofluorometry of serotonin in blood platelets

A rapid sensitive, and reproducible assay for determination of platelet serotonin is reported. Serotonin in extracted into an ascorbic acid solution by freezing and thawing and sonication. Ascorbic acid stabilizes the serotonin in the extract, and added ethanol enhances the final fluorescence of serotonin, which is measured in a concentrated hydrochloric acid medium (activation at 295 nm and emission at 540 nm). The method has an average coefficient of variation of 4.1%; 95% of added standards is accounted for. The average serotonin content of platelets from 15 men, ages 30-65 years, was 0.67 (SE 0.03) microgram/10(9) platelets, which compares favorably with previously reported values. 5-Hydroxyindole compounds such as 5-hydroxyindole-3-acetic acid and 5-hydroxytryptophan interfere with the assay, but there is relatively little of these compounds in platelets.

Determination of trazodone and its metabolite, 1-m-chlorophenyl-piperazine, in human plasma and red blood cell samples by HPLC

OBJECTIVES

To develop an HPLC method for the analysis of trazodone and its metabolite, 1-m-chlorophenyl-piperazine (m-CPP), in human plasma and red blood cells.

DESIGN AND METHODS

The analytes were extracted by heptane containing 1.5% isoamyl alcohol, back extracted into phosphoric acid and analyzed by reverse phase HPLC with UV detection.

RESULTS

In seven randomly selected, male, human subjects plasma concentrations (nmol/l) were 380-5841 for trazodone and 14-237 for m-CPP while those in packed red blood cells were 98-634 for trazodone and 15-155 for m-CPP. Plasma trazodone concentrations were 4-11-fold higher than those in red blood cells while those of m-CPP were about equal. This may be the first report on concentrations of trazodone and m-CPP in human red blood cells.

CONCLUSIONS

This sensitive method can be used for monitoring trazodone and m-CPP in human plasma and red blood cells.

Oxidation of cholesterol in synaptosomes and mitochondria isolated from rat brains

Cholesterol and alpha-tocopherol oxidations were studied in brain subcellular fractions isolated from cerebral hemispheres of 4-month-old, male Fischer 344 rats. The fractions were suspended in buffered media (pH 7.4, 37 degrees C0 and oxidized by adding (i) ferrous iron (Fe2+) with or without ascorbate or (ii) peroxynitrite (an endogenous oxidant produced by the reaction of superoxide and nitric oxide). Treatment of subcellular fractions with Fe2+ in the presence or absence of ascorbate produced primarily 7-keto- and 7-hydroxy-cholesterols and small amounts of 5 alpha, 6 alpha-epoxycholesterol. Since brain contains high levels of ascorbate, and release of iron could result in oxysterol formation. Peroxynitrite oxidized alpha-tocopherol but not cholesterol. Hence, the toxicity of peroxynitrite or nitric oxide could not be due to cytotoxic oxysterols. When synaptosomes were incubated for 5 min in the presence of 0.5 to 2 microM Fe2+ and ascorbate, alpha-tocopherol was oxidized while cholesterol remained unchanged. Thus, alpha-tocopherol is functioning as an antioxidant, protecting cholesterol. Diethylenetriaminepentaacetic acid blocked production of oxysterols, whereas citrate, ADP and EDTA did not. A significant percentage of mitochondrial cholesterol was oxidized by treatment with Fe2+ and ascorbate. Hence, mitochondrial membrane properties dependent on cholesterol could be particularly susceptible to oxidation. The oxysterols formed were retained within the membranes of synaptosomes and mitochondria. The 7-oxysterols produced are known to be inhibitors of membrane enzymes and also can modify membrane permeability. Hence, oxysterols may plan an important role in brain tissue damage during oxidative stress.