Inter- and intra-individual variation in plasma and red blood cell vitamin E after supplementation

Alpha-Tocopherol Metabolites (the Vitamin E Metabolome) and Their Interindividual Variability during Supplementation

The metabolism of α-tocopherol (α-TOH, vitamin E) shows marked interindividual variability, which may influence the response to nutritional and therapeutic interventions with this vitamin. Recently, new metabolomics protocols have fostered the possibility to explore such variability for the different metabolites of α-TOH so far identified in human blood, i.e., the “vitamin E metabolome”, some of which have been reported to promote important biological functions. Such advances prompt the definition of reference values and degree of interindividual variability for these metabolites at different levels of α-TOH intake. To this end, a one-week oral administration protocol with 800 U RRR-α-TOH/day was performed in 17 healthy volunteers, and α-TOH metabolites were measured in plasma before and at the end of the intervention utilizing a recently validated LC-MS/MS procedure; the expression of two target genes of α-TOH with possible a role in the metabolism and function of this vitamin, namely pregnane X receptor (PXR) and the isoform 4F2 of cytochrome P450 (CYP4F2) was assessed by immunoblot in peripheral blood leukocytes. The levels of enzymatic metabolites showed marked interindividual variability that characteristically increased upon supplementation. With the exception of α-CEHC (carboxy-ethyl-hydroxychroman) and the long-chain metabolites M1 and α-13′OH, such variability was found to interfere with the possibility to utilize them as sensitive indicators of α-TOH intake. On the contrary, the free radical-derived metabolite α-tocopheryl quinone significantly correlated with the post-supplementation levels of α-TOH. The supplementation stimulated PXR, but not CYP4F2, expression of leucocytes, and significant correlations were observed between the baseline levels of α-TOH and both the baseline and post-supplementation levels of PXR. These findings provide original analytical and molecular information regarding the human metabolism of α-TOH and its intrinsic variability, which is worth considering in future nutrigenomics and interventions studies.

Ageing, age-related diseases and oxidative stress: What to do next?

Among other mechanisms, oxidative stress has been postulated to play an important role in the rate of ageing. Oxidative damage contributes to the hallmarks of ageing and essential components in pathological pathways which are thought to drive multiple age-related diseases. Nonetheless, results from studies testing the hypothesis of oxidative stress in ageing and diseases showed controversial results. While observational studies mainly found detrimental effects of high oxidative stress levels on disease status, randomized clinical trials examining the effect of antioxidant supplementation on disease status generally showed null effects. However, re-evaluations of these counterinitiative observations are required considering the lack of reliability and specificity of traditionally used biomarkers for measuring oxidative stress. To facilitate these re-evaluations, this review summarizes the basic knowledge of oxidative stress and the present findings regarding the role of oxidative damage in ageing and age-related diseases. Meanwhile, two approaches are highlighted, namely proper participants selection, together with the development of reliable biomarkers. We propose that oxidized vitamin E metabolites may be used to accurately monitor individual functional antioxidant level, which might serve as promising key solutions for future elucidating the impact of oxidative stress on ageing and age-related diseases.

Targeting mitochondrial responses to intra-articular fracture to prevent posttraumatic osteoarthritis

We tested whether inhibiting mechanically responsive articular chondrocyte mitochondria after severe traumatic injury and preventing oxidative damage represent a viable paradigm for posttraumatic osteoarthritis (PTOA) prevention. We used a porcine hock intra-articular fracture (IAF) model well suited to human-like surgical techniques and with excellent anatomic similarities to human ankles. After IAF, amobarbital or N-acetylcysteine (NAC) was injected to inhibit chondrocyte electron transport or downstream oxidative stress, respectively. Effects were confirmed via spectrophotometric enzyme assays or glutathione/glutathione disulfide assays and immunohistochemical measures of oxidative stress. Amobarbital or NAC delivered after IAF provided substantial protection against PTOA at 6 months, including maintenance of proteoglycan content, decreased histological disease scores, and normalized chondrocyte metabolic function. These data support the therapeutic potential of targeting chondrocyte metabolism after injury and suggest a strong role for mitochondria in mediating PTOA.

GC-MS Based Metabolomics and NMR Spectroscopy Investigation of Food Intake Biomarkers for Milk and Cheese in Serum of Healthy Humans

The identification and validation of food intake biomarkers (FIBs) in human biofluids is a key objective for the evaluation of dietary intake. We report here the analysis of the GC-MS and 1H-NMR metabolomes of serum samples from a randomized cross-over study in 11 healthy volunteers having consumed isocaloric amounts of milk, cheese, and a soy drink as non-dairy alternative. Serum was collected at baseline, postprandially up to 6 h, and 24 h after consumption. A multivariate analysis of the untargeted serum metabolomes, combined with a targeted analysis of candidate FIBs previously reported in urine samples from the same study, identified galactitol, galactonate, and galactono-1,5-lactone (milk), 3-phenyllactic acid (cheese), and pinitol (soy drink) as candidate FIBs for these products. Serum metabolites not previously identified in the urine samples, e.g., 3-hydroxyisobutyrate after cheese intake, were detected. Finally, an analysis of the postprandial behavior of candidate FIBs, in particular the dairy fatty acids pentadecanoic acid and heptadecanoic acid, revealed specific kinetic patterns of relevance to their detection in future validation studies. Taken together, promising candidate FIBs for dairy intake appear to be lactose and metabolites thereof, for lactose-containing products, and microbial metabolites derived from amino acids, for fermented dairy products such as cheese.

Alpha-Tocopherol Concentration in Colostrum and Serum of Women With Premature Labor

OBJECTIVE

The aim of the study was to evaluate and compare the levels of alpha-tocopherol in colostrum milk and serum of mothers with premature birth, classified as severe prematurity and moderate prematurity.

METHODS

Cross-sectional study with 65 women, 18 births classified as severe prematurity (<32 weeks of gestation) and 47 as moderate prematurity (≥32 weeks of gestation). The study only included mothers without any conditions associated with pregnancy and who had a single conception without any malformation. Samples of serum and colostrum were collected during fasting in the immediate postpartum, and alpha-tocopherol was analyzed by high-performance liquid chromatography. To determine the biochemical nutritional status of vitamin E, a serum cutoff (11.6 μmol/L) was adopted. The Student t test for independent variables compared the average concentrations of alpha-tocopherol in serum and colostrum among prematurity groups. Differences were considered significant when P < 0.05.

RESULTS

The alpha-tocopherol concentrations in colostrum were similar in both groups, being 34.5 ± 20.2 μmol/L for women with severe prematurity and 35.1 ± 16.3 μmol/L for moderate prematurity. For the serum of puerperal women with severe prematurity, alpha-tocopherol concentration was, however, lower than in women with moderate prematurity, 22.2 ± 4.4 μmol/L versus 27.1 ± 8.6 μmol/L (P < 0.05). The serum levels of alpha-tocopherol indicated nutritional risk at 5.6% (n = 1) of women with severe prematurity and 4.3% (n = 2) for those with moderate prematurity.

CONCLUSIONS

Severe prematurity affected the levels of alpha-tocopherol in maternal serum; however, the level of prematurity did not change the concentration of vitamin E in colostrum.

Bioavailability of vitamin E in humans: an update

Vitamin E is essential for human health and may play a role in the prevention of some degenerative diseases. Its bioavailability, however, is wide ranging and is affected by numerous factors. Recent findings showing that the intestinal absorption of vitamin E involves proteins have raised new relevant questions about factors that can affect bioavailability. It is, therefore, opportune to present a current overview of this topic. This review begins by exploring what is known, as well as what is unknown, about the metabolization of vitamin E in the human upper gastrointestinal tract and then presents a methodical evaluation of factors assumed to affect vitamin E bioavailability. Three main conclusions can be drawn. First, the proteins ABCA1, NPC1L1, and SR-BI are implicated in the absorption of vitamin E. Second, the efficiency of vitamin E absorption is widely variable, though not accurately known (i.e., between 10% and 79%), and is affected by several dietary factors (e.g., food matrix, fat, and fat-soluble micronutrients). Finally, numerous unanswered questions remain about the metabolization of vitamin E in the intestinal lumen and about the factors affecting the efficiency of vitamin E absorption.

Expression of the α-tocopherol transfer protein gene is regulated by oxidative stress and common single-nucleotide polymorphisms

Vitamin E (α-tocopherol) is the major lipid-soluble antioxidant in most animal species. By controlling the secretion of vitamin E from the liver, the α-tocopherol transfer protein regulates whole-body distribution and levels of this vital nutrient. However, the mechanism(s) that regulates the expression of this protein is poorly understood. Here we report that transcription of the TTPA gene in immortalized human hepatocytes is induced by oxidative stress and by hypoxia, by agonists of the nuclear receptors PPARα and RXR, and by increased cAMP levels. The data show further that induction of TTPA transcription by oxidative stress is mediated by an already-present transcription factor and does not require de novo protein synthesis. Silencing of the cAMP response element-binding (CREB) transcription factor attenuated transcriptional responses of the TTPA gene to added peroxide, suggesting that CREB mediates responses of this gene to oxidative stress. Using a 1.9-kb proximal segment of the human TTPA promoter together with a site-directed mutagenesis approach, we found that single-nucleotide polymorphisms that are commonly found in healthy humans dramatically affect promoter activity. These observations suggest that oxidative stress and individual genetic makeup contribute to vitamin E homeostasis in humans. These findings may explain the variable responses to vitamin E supplementation observed in human clinical trials.

Double-balloon jejunal perfusion to compare absorption of vitamin E and vitamin E acetate in healthy volunteers under maldigestion conditions

BACKGROUND/OBJECTIVES

The vitamin E derivative, α-tocopheryl acetate, is often included in formulations used in enteral nutrition. In this respect, we compared α-tocopherol and α-tocopheryl acetate absorption under 'maldigestion' conditions, such as occurring during enteral tube feeding, using differentially labeled RRR-[5,7-methyl-((2)H(6))]-α-tocopherol and RRR-[5-methyl-(2)H(3)]-α-tocopheryl acetate allowing direct comparison between free and esterified forms.

SUBJECTS/METHODS

The two derivatives were given together in a single dose to six volunteers directly into the jejunum using a double-balloon perfusion system. Perfusion lasted for 1 h, and the collected blood and effluent samples were analyzed by liquid chromatography-mass spectrometry.

RESULTS

In the isolated 20-cm length of exposed jejunum, on average ~ 6% of the two vitamin E forms were absorbed >1 h based on subtraction of effluent from influent. There was substantial difference in the absolute absorbed quantity between individuals, but no significant differences were observed in the absorption between the two labeled forms as assessed in the plasma. (2)H(3)-α-tocopherol was not present in the influent, but appeared in the effluent, indicating that the acetylated form of vitamin E is cleaved by brush border enzymes in the small intestine.

CONCLUSIONS

This study shows that even in the absence of digestive enzymes and bile salts, the appropriately solubilized acetylated form of α-tocopherol exhibits the same bioavailability as free α-tocopherol. This suggests that both forms can be absorbed equally under maldigestion conditions such as present clinically during enteral tube feeding.

Effects of antioxidants on rapeseed oil oxidation in an artificial digestion model analyzed by UHPLC-ESI-MS

A normal diet contains large quantities of oxidized fatty acids, glycerolipids, cholesterol, and their cytotoxic degradation products because many foods in the diet are fried, heated, or otherwise processed and consumed often after long periods of storage. There is also evidence that the acid medium of the stomach promotes lipid peroxidation and that the gastrointestinal tract is a major site of antioxidant action, as demonstrated by various colorimetric methods. The identity and yields of specific products of lipid transformation have seldom been determined. The present study describes the molecular species profiles of all major gastrointestinal lipids formed during digestion of autoxidized rapeseed oil in an artificial digestion model in the presence of L-ascorbic acid, 6-palmitoyl-O-L-ascorbic acid, 3,5-di-tert-butyl-4-hydroxytoluene (BHT), DL-α-tocopherol, and DL-α-tocopheryl acetate. Differences in oxidized lipid profiles were detected in the samples digested in the presence of different antioxidants, but none of them could prevent the formation of oxidized lipids or promote their degradation in a gastric digestion model. The lack of effect is attributed to the inappropriate nature of the gastrointestinal medium for the antioxidant activity of these vitamins and BHT. A fast ultrahigh performance liquid chromatographic-electrospray ionization-mass spectrometric method was developed for the analysis of lipolysis products, including epoxy, hydroperoxy, and hydroxy fatty acids, and acylglycerols, utilizing lithium as ionization enhancer.

Vitamin E deficiency in developing countries

In addition to its role as a potent antioxidant, vitamin E is involved in a wide range of physiological processes, ranging from immune function and control of inflammation to regulation of gene expression and cognitive performance. Results from multiple studies suggest that poor nutritional status and higher prevalence of other oxidative stressors such as malaria and HIV infection predispose populations in developing countries for vitamin E deficiency. Although direct comparison between study outcomes is complicated by varied definitions of vitamin E deficiency, data trends indicate that children and the elderly are more vulnerable age groups and that men may be at higher risk for deficiency than women. Public health initiatives aimed at improving the vitamin E status of high-risk populations in developing countries would be prudent to counteract oxidative stress, improve immune function, and protect against neurologic and cognitive deficits. Additional research is needed to establish dose-response relationships of various interventions and to develop cost-effective, culturally-appropriate, and targeted programs.

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.

γ-Tocopherol biokinetics and transformation in humans

BACKGROUND

The uptake and biotransformation of gamma-tocopherol (gamma-T) in humans is largely unknown. Using a stable isotope method we investigated these aspects of gamma-T biology in healthy volunteers and their response to gamma-T supplementation.

METHODS

A single bolus of 100 mg of deuterium labeled gamma-T acetate (d(2)-gamma-TAC, 94% isotopic purity) was administered with a standard meal to 21 healthy subjects. Blood and urine (first morning void) were collected at baseline and a range of time points between 6 and 240 h post-supplemetation. The concentrations of d(2) and d(0)-gamma-T in plasma and its major metabolite 2,7,8-trimethyl-2-(b-carboxyethyl)-6-hydroxychroman (-gamma-CEHC) in plasma and urine were measured by GC-MS. In two subjects, the total urine volume was collected for 72 h post-supplementation. The effects of gamma-T supplementation on alpha-T concentrations in plasma and alpha-T and gamma-T metabolite formation were also assessed by HPLC or GC-MS analysis.

RESULTS

At baseline, mean plasma alpha-T concentration was approximately 15 times higher than gamma-T (28.3 vs. 1.9 micromol/l). In contrast, plasma gamma-CEHC concentration (0.191 micromol/l) was 12 fold greater than alpha-CEHC (0.016 micromol/l) while in urine it was 3.5 fold lower (0.82 and 2.87 micromol, respectively) suggesting that the clearance of alpha-CEHC from plasma was more than 40 times that of gamma-CEHC. After d(2)-gamma-TAC administration, the d(2) forms of gamma-T and gamma-CEHC in plasma and urine increased, but with marked inter-individual variability, while the d(0) species were hardly affected. Mean total concentrations of gamma-T and gamma-CEHC in plasma and urine peaked, respectively, between 0-9, 6-12 and 9-24 h post-supplementation with increases over baseline levels of 6-14 fold. All these parameters returned to baseline by 72 h. Following challenge, the total urinary excretion of d(2)-gamma-T equivalents was approximately 7 mg. Baseline levels of gamma-T correlated positively with the post-supplementation rise of (d(0) + d(2)) - gamma - T and gamma-CEHC levels in plasma, but correlated negatively with urinary levels of (d(0) + d(2))-gamma-CEHC. Supplementation with 100 mg gamma-TAC had minimal influence on plasma concentrations of alpha-T and alpha-T-related metabolite formation and excretion.

CONCLUSIONS

Ingestion of 100mg of gamma-TAC transiently increases plasma concentrations of gamma-T as it undergoes sustained catabolism to CEHC without markedly influencing the pre-existing plasma pool of gamma-T nor the concentration and metabolism of alpha-T. These pathways appear tightly regulated, most probably to keep high steady-state blood ratios alpha-T to gamma-T and gamma-CEHC to alpha-CEHC.

Dosage and formulation issues: oral vitamin E therapy in children

PURPOSE

Oral vitamin E is used in several childhood diseases, but dosage recommendations differ. Few oral products have a marketing authorization for therapeutic use in children. Preliminary data indicate differences in bioavailability among the various vitamin E compounds. Our objective was to review published data on oral vitamin E therapy in neonates and children in order to establish dosage recommendations at a local level.

METHODS

A literature search was conducted, including Medline Ovid, EMBASE (1980-Feb 2008), Cochrane databases, product monographs, handbooks, and textbooks.

RESULTS

The main vitamin E compounds being used in children are alpha-tocopherol, alpha-tocopheryl acetate, and tocofersolan. The most data are available on tocopheryl acetate, both in neonates and older children. In children with malabsorption disorders, tocofersolan appears to have an increased bioavailability compared to tocopherol or tocopheryl acetate. Published data on pharmacokinetics and dosages for clinical use are few and heterogeneous. No pharmacokinetic studies were found for tocofersolan in neonates and infants. There are few comparative studies on pharmacokinetics, therapeutic use, and adverse drug reactions (ADRs) in children. Dosages used in clinical studies and dosage recommendations in handbooks differ considerably.

CONCLUSIONS

The differences in dosing recommendations in children may be due to lack of systematic studies. Existing published data on oral vitamin E do not provide a basis for evaluation of dosage recommendations in children. Comparative clinical studies are required for scientific evaluation of pharmacokinetics, dosage regimens, and efficacy/ADR assessments in children.

Oral a-tocopherol Supplementation Inhibits Lipid Oxidation in Established Human Atherosclerotic Lesions

BACKGROUND

Much experimental evidence suggests that lipid oxidation is important in atherogenesis and in epidemiological studies dietary antioxidants appear protective against cardiovascular events. However, most large clinical trials failed to demonstrate benefit of oral antioxidant vitamin supplementation in high-risk subjects. This paradox questions whether ingestion of antioxidant vitamins significantly affects lipid oxidation within established atherosclerotic lesions.

METHODS AND RESULTS

This placebo-controlled, double blind study of 104 carotid endarterectomy patients determined the effects of short-term alpha-tocopherol supplementation (500 IU/day) on lipid oxidation in plasma and advanced atherosclerotic lesions. In the 53 patients who received alpha-tocopherol there was a significant increase in plasma alpha-tocopherol concentrations (from 32.66 +/- 13.11 at baseline to 38.31 +/- 13.87 (mean +/- SD) micromol/l, p < 0.01), a 40% increase (compared with placebo patients) in circulating LDL-associated alpha-tocopherol (p < 0.0001), and their LDL was less susceptible to ex vivo oxidation than that of the placebo group (lag phase 115.3 +/- 28.2 and 104.4 +/- 15.7 min respectively, p < 0.02). Although the mean cholesterol-standardised alpha-tocopherol concentration within lesions did not increase, alpha-tocopherol concentrations in lesions correlated significantly with those in plasma, suggesting that plasma alpha-tocopherol levels can influence lesion levels. There was a significant inverse correlation in lesions between cholesterol-standardised levels of alpha-tocopherol and 7beta-hydroxycholesterol, a free radical oxidation product of cholesterol.

CONCLUSIONS

These results suggest that within plasma and lesions alpha-tocopherol can act as an antioxidant. They may also explain why studies using < 500 IU alpha-tocopherol/day failed to demonstrate benefit of antioxidant therapy. Better understanding of the pharmacodynamics of oral antioxidants is required to guide future clinical trials.

Absorption, transport, and tissue delivery of vitamin E

Vitamin E is one of the most abundant lipid-soluble antioxidant agents found in plasma and cells of higher mammals. The uptake, transport and tissue delivery of alpha-tocopherol, a key vitamin E form, involves molecular, biochemical, and cellular processes closely related to overall lipid and lipoprotein homeostasis. This review highlights recent findings that have led to a better understanding of vitamin E transport, including intestinal absorption, hepatic transport, and cellular uptake of alpha-tocopherol in vivo. This new information may be critical for manipulation of vitamin E homeostasis in a variety of oxidative stress-related disease conditions in humans.

The absorption of vitamin E is influenced by the amount of fat in a meal and the food matrix

Vitamin E absorption requires the presence of fat; however, limited information exists on the influence of fat quantity on optimal absorption. In the present study we compared the absorption of stable-isotope-labelled vitamin E following meals of varying fat content and source. In a randomised four-way cross-over study, eight healthy individuals consumed a capsule containing 150 mg 2H-labelled RRR-α-tocopheryl acetate with a test meal of toast with butter (17·5 g fat), cereal with full-fat milk (17·5 g fat), cereal with semi-skimmed milk (2·7 g fat) and water (0 g fat). Blood was taken at 0, 0·5, 1, 1·5, 2, 3, 6 and 9 h following ingestion, chylomicrons were isolated, and 2H-labelled α-tocopherol was analysed in the chylomicron and plasma samples. There was a significant time (P<0·001) and treatment effect (P<0·001) in 2H-labelled α-tocopherol concentration in both chylomicrons and plasma between the test meals. 2H-labelled α-tocopherol concentration was significantly greater with the higher-fat toast and butter meal compared with the low-fat cereal meal or water (P<0·001), and a trend towards greater concentration compared with the high-fat cereal meal (P=0·065). There was significantly greater 2H-labelled α-tocopherol concentration with the high-fat cereal meal compared with the low-fat cereal meal (P<0·05). The 2H-labelled α-tocopherol concentration following either the low-fat cereal meal or water was low. These results demonstrate that both the amount of fat and the food matrix influence vitamin E absorption. These factors should be considered by consumers and for future vitamin E intervention studies.

Comparative2H-labelled α-tocopherol biokinetics in plasma, lipoproteins, erythrocytes, platelets and lymphocytes in normolipidaemic males

The biokinetics of newly absorbed vitamin E in blood components was investigated in normolipidaemic males. Subjects (n12) ingested encapsulated 150 mg2H-labelledRRR-α-tocopheryl acetate with a standard meal. Blood was collected at 3, 6, 9, 12, 24 and 48 h post-ingestion.2H-Labelled and pre-existing unlabelled α-tocopherol (α-T) was determined in plasma, lipoproteins, erythrocytes, platelets and lymphocytes by LC–MS. In all blood components, labelled α-T concentration significantly increased while unlabelled decreased following ingestion (P<0·0001). Significant differences in labelled α-T biokinetic parameters were found between lipoproteins. Time of maximum concentration was significantly lower in chylomicrons, while VLDL had a significantly greater maximum α-T concentration and area under the curve (AUC) (P<0·05). The largest variability occurred in chylomicron α-T transport. Erythrocyte labelled α-T concentrations increased gradually up to 24 h while α-T enrichment of platelets and lymphocytes was slower, plateauing at 48 h. Platelet enrichment with labelled α-T was biphasic, the initial peak coinciding with the labelled α-T peak in chylomicrons. Erythrocyte and HDL AUC were significantly correlated (P<0·005), as was platelet and HDL AUC (P<0·05). There was a lower turnover of pre-existing α-T in platelets and lymphocytes (maximum 25 % labelled α-T) compared to plasma and erythrocytes (maximum 45 % labelled α-T). These data indicate that different processes exist in the uptake and turnover of α-T by blood components and that chylomicron α-T transport is a major determinant of inter-individual variation in vitamin E response. This is important for the understanding of α-T transport and uptake into tissues.

Long-term effects of nutritional programming of the embryo and fetus: mechanisms and critical windows

The maternal nutritional and metabolic environment is critical in determining not only reproduction, but also long-term health and viability. In the present review, the effects of maternal nutritional manipulation at defined stages of gestation coinciding with embryogenesis, maximal placental or fetal growth will be discussed. Long-term outcomes from these three developmental windows appear to be very different, with brain and cardiovascular function being most sensitive to influences in the embryonic period, the kidney during placental development and adipose tissue in the fetal phase. In view of the similarities in fetal development, number and maturity at birth, there are close similarities in these outcomes between findings from epidemiological studies in historical human cohorts and nutritional manipulation of large animals, such as sheep. One key nutrient that may modulate the long-term metabolic effects is the supply of glucose from the mother to the fetus, because this is sensitive to both global changes in food intake, maternal glucocorticoid status and an increase in the carbohydrate content of the diet. The extent to which these dietary-induced changes may reflect epigenetic changes remains to be established, especially when considering the very artificial diets used to induce these types of effects. In summary, the maintenance of a balanced and appropriate supply of glucose from the mother to the fetus may be pivotal in ensuring optimal embryonic, placental and fetal growth. Increased or decreased maternal plasma glucose alone, or in conjunction with other macro- or micronutrients, may result in offspring at increased risk of adult diseases.

The α‐Tocopherol Transfer Protein

Almost a century ago, plant extracts were documented to be critical for the fertility of rodents. This activity was later ascribed to vitamin E, a term comprising a number of structurally related plant lipids that function as fat soluble antioxidants. The alpha-tocopherol transfer protein (TTP) is a critical regulator of vitamin E status that stimulates the movement of vitamin E between membrane vesicles in vitro and facilitates the secretion of tocopherol from hepatocytes. Heritable mutations in the ttpA gene cause ataxia with vitamin E deficiency (AVED), an autosomal recessive disorder characterized by low plasma vitamin E levels and progressive neurodegeneration. This chapter summarizes recent advances in our understanding of the molecular and physiological aspects of TTP activity.

Effect of vitamin E on tamoxifen-treated breast cancer cells

BACKGROUND

Induction of apoptosis by tamoxifen has been postulated to involve oxidative stress. Tamoxifen (TAM) may act on estrogen receptors (ER) located in the plasma membrane. Our hypothesis that supplemental antioxidant vitamin E (alpha-tocopherol) acts at the plasma membrane to alter the effectiveness of tamoxifen was tested in ER-positive breast cancer cell lines, MCF-7 and T47D.

METHODS

Cells were treated in vitro with 20-muM TAM alone and in combination with 10-muM alpha-tocopherol (AT). Estrogen growth signals were quantified by immunohistochemical staining for the mitogen-activated protein kinase p-ERK. Rapid changes in intracellular calcium were detected in TAM-treated MCF-7 and T-47D cells by fluorescence microscopy of cells loaded with the calcium-sensitive dye Fluo 4AM. Apoptosis was assayed by flow cytometry.

RESULTS

Proliferating cells in normal medium exhibited strong p-ERK staining. Addition of TAM abolished p-ERK staining and caused cell rounding and death. The addition of AT led to the restoration of cell proliferation and p-ERK expression even in the presence of high-dose TAM. Intracellular calcium rapidly increased in MCF-7 and T47D cells upon exposure to TAM, followed by an increase in caspase activation and eventual apoptosis. The increase in intracellular calcium was abolished by the addition of 10muM AT to TAM, and pan-caspase staining decreased at 5 hours from 72% to 41%.

CONCLUSIONS

These studies suggest that supplemental vitamin E decreases the inhibitory effect of TAM on the proliferation of ER+ breast cancer cells and eliminates the rapid rise in intracellular calcium that leads to apoptosis stimulated by TAM. The use of vitamin E acetate supplements may be inadvisable for women taking tamoxifen.

Vitamin supplementation does not protect against symptoms in ozone-responsive subjects

Vitamin supplements have been reported to reduce the magnitude of symptoms in subjects exposed to oxidant air pollution. To confirm whether supplementation with vitamins C and E could reduce lung function decrements, airway inflammation, and epithelial injury in subjects sensitive to ozone, a double-blinded, crossover control study was performed. Fourteen ozone-responsive subjects were randomly exposed to both air and ozone (0.2 ppm for 2 h) after 7 days of either placebo treatment or supplementation with vitamin C (500 mg/day) and E (100 mg/day). Lung function was assessed pre- and immediately postexposure and blood samples were taken at set intervals. Inflammatory, tissue injury, and antioxidant responses were examined in lavage fluid obtained by bronchoscopy 6 h postexposure. Exposure to ozone resulted in significant (P < 0.01) decrements in FEV1 with no protection observed following vitamin supplementation (-8.5%) versus placebo (-7.3%) treatment. Similarly, ozone-induced neutrophilia were of a similar magnitude after both treatments (P < 0.05). This lack of protection was observed despite elevated plasma vitamin C (+60.1%) and vitamin E (+51.4%) concentrations following supplementation, and increased vitamin C concentrations in the airways after supplementation following ozone exposure. These data do not therefore support the contention that acute ozone-induced symptoms can be attenuated through the use of dietary antioxidants in well-nourished individuals.

Vitamin E effects on nasal symptoms and serum specific IgE levels in patients with perennial allergic rhinitis

BACKGROUND

Studies have shown that vitamin E intake may reduce IgE production.

OBJECTIVE

To evaluate the effects of vitamin E supplementation on the severity of nasal symptoms and the serum levels of specific IgE in patients with perennial allergic rhinitis.

METHODS

Sixty-three patients (mean +/- SD age, 12 +/- 2.4 years) with a history of perennial allergic rhinitis participated in this study. None of the patients had evidence of acute infectious disease or used tobacco, corticosteroids, antihistamines, or vitamins. Patients were randomized to receive either vitamin E (400 IU/d) or placebo for 4 weeks, with loratadine-pseudoephedrine (0.2/0.5 mg/kg) during the first 2 weeks of treatment. The severity of nasal symptoms was evaluated using a validated questionnaire, which was administered weekly for 4 weeks. The serum concentrations of specific IgE to 5 common inhalant allergens and lipid peroxides were measured before treatment and at the end of the study.

RESULTS

Before, during, and after treatment, the symptom severity scores were similar in the 2 groups; within each group, a significant decrease was observed after the first week of follow-up (P < .05), with no further changes. Serum levels of specific IgE and lipid peroxides did not show any significant changes related to vitamin E intake within and between groups.

CONCLUSIONS

In patients with perennial allergic rhinitis, vitamin E supplementation (400 IU/d) did not have any significant effects on nasal symptom severity or on serum concentrations of specific IgE to 5 common allergens.

Noncompetitive plasma biokinetics of deuterium-labeled natural and synthetic alpha-tocopherol in healthy men with an apoE4 genotype

Previous studies comparing the biokinetics of deuterated natural (RRR) and synthetic (all-rac) alpha-tocopherol (vitamin E) used a simultaneous ingestion or competitive uptake approach and reported relative bioavailability ratios close to 2:1, higher than the accepted biopotency ratio of 1.36:1. The aim of the current study was to compare the biokinetics of deuterated natural and synthetic vitamin E using a noncompetitive uptake model both before and after vitamin E supplementation in a distinct population. Healthy men (n = 10) carrying the apolipoprotein (apo)E4 genotype completed a randomized crossover study, comprised of two 4-wk treatments with 400 mg/d (RRR-alpha-tocopheryl and all-rac-alpha-tocopheryl acetate) with a 12-wk washout period between treatments. Before and after each treatment period, the subjects consumed a capsule containing 150 mg deuterated alpha-tocopheryl acetate in either the RRR or all-rac form depending on their treatment regimen. Blood was obtained up to 48 h after ingestion, and tocopherols analyzed by LC/MS. After deuterated all-rac administration, plasma deuterated tocopherol maximum concentrations and area under the concentration vs. time curves (AUC) were lower than those following RRR administration. The RRR:all-rac ratios determined from the deuterated biokinetic profiles (maximum concentration; C(max)) and AUCs were 1.35:1 +/- 0.17 and 1.33:1 +/- 0.18, respectively. The 4-wk supplementation with either RRR or all-rac significantly increased plasma alpha-tocopherol concentrations (P < 0.001), but decreased the plasma response to newly absorbed deuterated RRR or all-rac alpha-tocopherol. Using a noncompetitive uptake approach, the relative bioavailability of natural to synthetic vitamin E in apoE4 males was close to the currently accepted biopotency ratio of 1.36:1.

Inter- and intra-individual vitamin E uptake in healthy subjects is highly repeatable across a wide supplementation dose range

Vitamin E uptake after supplementation varies widely in the healthy population, and preliminary studies have indicated that individual responses are relatively stable over periods in excess of 1 year. This phenotypic stability suggests a genetic basis to this observed variation. To examine this issue further, we examined the repeatability of both baseline plasma alpha-tocopherol and urinary alpha-tocopherol metabolite concentrations, as well as individual responses of these parameters after vitamin E supplementation. In the first study, 65 subjects (33 males, 32 females, aged 30.7 +/- 7.4 years) provided three plasma and urine samples for alpha-tocopherol and metabolite analysis with each collection separated by at least 2 weeks. Plasma alpha-tocopherol concentrations were found to be highly repeatable over this short interval (intra-class correlation coefficient [ICC] = 0.85), although the association deteriorated once values were corrected for plasma cholesterol (ICC = 0.64). Similarly, urinary alpha-tocopherol metabolites 2(2'-carboxyethyl)-6-hydroxychroman acid (alpha-CEHC) and quinone lactone (QL) concentration were found to display a moderate degree of intra-subject repeatability: ICC = 0.65 and 0.58, respectively. In a second study, plasma alpha-tocopherol and urinary metabolite responses were investigated in 18 healthy, nonsmoking subjects (12 males, 6 females, aged 33.1 +/- 9.1 years) after successive 6-week periods of vitamin E (RRR-alpha-tocopherol acetate) supplementation at 15, 100, 200, and 400 mg/day. Plasma and urine samples were obtained on days 0, 7, 14, 21, and 28 (7 days after the final supplement) of each dosing period and the strength of the underlying association between responses determined using Kendall's tau_b test. Individual plasma alpha-tocopherol responses at the 100, 200, and 400 mg/day doses were found to be highly associated: tau, 0.51, P = 0.02 [100 vs. 200] and tau, 0.49, P = 0.03 [100 vs. 400] and tau, 0.56, P = 0.005 [200 vs. 400]. Together these data support the contention that alpha-tocopherol uptake is a stable individual phenotype under genetic regulation.

Physiological factors influencing vitamin E biokinetics

Limited information is available on factors that can influence vitamin E bioavailability. In several studies we have investigated the influence of dietary, biochemical, and genetic factors on vitamin E biokinetics. In these studies, subjects ingested a capsule containing 150 mg deuterated RRR-alpha-tocopheryl acetate, blood was taken up to 48 hr, and tocopherols were analyzed by liquid chromatography and mass spectroscopy. There was significantly greater plasma-labeled alpha-tocopherol concentrations when the capsule was consumed with a high-fat meal (17.5 g) versus a low-fat meal (2.7 g), and there was also a difference between a high-fat toast and butter and a cereal with full-fat milk meal (both 17.5 g fat), indicating that both the amount of fat and food matrix is important for vitamin E absorption. Dyslipidemic subjects displayed a reduced plasma uptake of newly absorbed alpha-tocopherol, and differences were also apparent in individual lipoproteins. A decreased uptake of labeled alpha-tocopherol was also observed in erythrocytes, platelets, and lymphocytes of dyslipidemics. Following vitamin E supplementation (400 mg/day, 4 weeks), the uptake of newly absorbed alpha-tocopherol was decreased, presumably because of saturation of alpha-tocopherol transfer protein. We also found that apoE3 subjects displayed a considerably reduced uptake of newly absorbed labeled alpha-tocopherol compared to apoE4 subjects, which may be a consequence of the reduced low-density lipoprotein catabolic rate in these subjects. Taken together, these data show that several physiological factors influence the uptake of newly absorbed alpha-tocopherol, and that this is an important consideration in the design of future vitamin E supplementation studies.

Health promotion by flavonoids, tocopherols, tocotrienols, and other phenols: direct or indirect effects? Antioxidant or not?

Foods and beverages rich in phenolic compounds, especially flavonoids, have often been associated with decreased risk of developing several diseases. However, it remains unclear whether this protective effect is attributable to the phenols or to other agents in the diet. Alleged health-promoting effects of flavonoids are usually attributed to their powerful antioxidant activities, but evidence for in vivo antioxidant effects of flavonoids is confusing and equivocal. This may be because maximal plasma concentrations, even after extensive flavonoid intake, may be low (insufficient to exert significant systemic antioxidant effects) and because flavonoid metabolites tend to have decreased antioxidant activity. Reports of substantial increases in plasma total antioxidant activity after flavonoid intake must be interpreted with caution; findings may be attributable to changes in urate concentrations. However, phenols might exert direct effects within the gastrointestinal tract, because of the high concentrations present. These effects could include binding of prooxidant iron, scavenging of reactive nitrogen, chlorine, and oxygen species, and perhaps inhibition of cyclooxygenases and lipoxygenases. Our measurements of flavonoids and other phenols in human fecal water are consistent with this concept. We argue that tocopherols and tocotrienols may also exert direct beneficial effects in the gastrointestinal tract and that their return to the gastrointestinal tract by the liver through the bile may be physiologically advantageous.

Hyperlipidemic subjects have reduced uptake of newly absorbed vitamin E into their plasma lipoproteins, erythrocytes, platelets, and lymphocytes, as studied by deuterium-labeled alpha-tocopherol biokinetics

Vitamin E homeostasis in hyperlipidemia is poorly understood. The biokinetics of deuterated alpha-tocopherol (alpha-T) in blood components was investigated in normolipidemic (N; total cholesterol < 5.5 mmol/L and triglycerides < 1.5 mmol/L, n = 9), hypercholesterolemic (HC; total cholesterol > 6.5 mmol/L and triglycerides < 1.5 mmol/L, n = 10), and combined hypercholesterolemic and hypertriglyceridemic (HCT; total cholesterol > 6.5 mmol/L and triglycerides > 2.5 mmol/L, n = 6) subjects. Subjects ingested 150 mg hexadeuterated RRR-alpha-tocopheryl acetate, and blood was collected up to 48 h after ingestion. Labeled alpha-T was measured in plasma, lipoproteins, erythrocytes, platelets, and lymphocytes by liquid chromatography/mass spectroscopy. In plasma, HC had an earlier time of maximum concentration (6 h) compared with N and HCT (12 h) (P < 0.05). HCT had a lower uptake of labeled alpha-T (P < 0.005) and a longer half-life (P < 0.05). In chylomicrons, the maximum labeled alpha-T concentration was higher in HC compared with N and HCT (P < 0.00005); however, HCT had a lower uptake of labeled alpha-T in LDL. In all groups, the lowest density LDL subfraction contained more labeled alpha-T than denser subfractions (P < 0.05). In platelets, lymphocytes, and erythrocytes, the areas under the labeled alpha-T concentration vs. time curves were in the order N > HC > HCT. In lymphocytes, differences in labeled alpha-T were found at 6 and 48 h (P < 0.05). These data demonstrate that there are differences in the uptake of newly absorbed alpha-T into blood components in hyperlipidemia. Because these blood components are functionally affected by vitamin E, reduced uptake of alpha-T may be relevant to the pathogenesis of atherosclerosis.

Anti-atherosclerotic effects of vitamin E--myth or reality?

Atherosclerosis and its complications such as coronary heart disease, myocardial infarction and stroke are the leading causes of death in the developed world. High blood pressure, diabetes, smoking and a diet high in cholesterol and lipids clearly increase the likelihood of premature atherosclerosis, albeit other factors, such as the individual genetic makeup, may play an additional role. Several epidemiological studies and intervention trials have been performed with vitamin E, and some of them showed that it prevents atherosclerosis. For a long time, vitamin E was assumed to act by decreasing the oxidation of LDL, a key step in atherosclerosis initiation. However, at the cellular level, vitamin E acts by inhibition of smooth muscle cell proliferation, platelet aggregation, monocyte adhesion, oxLDL uptake and cytokine production, all reactions implied in the progression of atherosclerosis. Recent research revealed that these effects are not the result of the antioxidant activity of vitamin E, but rather of precise molecular actions of this compound. It is assumed that specific interactions of vitamin E with enzymes and proteins are at the basis of its non-antioxidant effects. Vitamin E influences the activity of several enzymes (e.g. PKC, PP2A, COX-2, 5-lipooxygenase, nitric oxide synthase, NADPH-oxidase, superoxide dismutase, phopholipase A2) and modulates the expression of genes that are involved in atherosclerosis (e.g. scavenger receptors, integrins, selectins, cytokines, cyclins). These interactions promise to reveal the biological properties of vitamin E and allow designing better strategies for the protection against atherosclerosis progression.

Re-evaluation of the relative potency of synthetic and natural α-tocopherol: experimental and clinical observations

Nutritionists generally consider all-rac-alpha-tocopherol and RRR-alpha-tocopherol equivalent in vitamin E activity but disagree whether equivalency requires a dosage ratio of 1.36:1 or 2:1. In contrast, we hypothesize that all-rac- and RRR-alpha-tocopherols are not equivalent in any dosage ratio. Previous observations that all-rac- and RRR-alpha-tocopherols are distributed and eliminated via saturable and stereospecific pathways imply that their relative bioavailability varies with the saturation of these pathways and therefore varies with dosage. Indeed, previous studies observed that the relative bioavailability of all-rac- and RRR-alpha-tocopherols varies between tissues as well as with dose, time after dosing, and duration of dosing. This non-constant relative bioavailability predicts non-constant relative activity (i.e., non-parallel dose-concentration curves predict non-parallel dose-effect curves). Non-constant relative bioavailability suggests that a fixed dosage ratio of all-rac- and RRR-alpha-tocopherols cannot produce a fixed ratio of effects on all processes in all tissues at all times after all dosages. However, previous studies suggest that all-rac- and RRR-alpha-tocopherols have equivalent effects (parallel dose-effect curves) in vitamin E-deficient animals and non-vitamin E-deficient humans. We re-evaluate the data from these animal studies and find non-parallel dose-effect and concentration-effect curves. We discuss pharmacokinetic and pharmacodynamic reasons why previous studies in non-vitamin E-deficient humans did not find non-parallel dose-effect curves for all-rac- and RRR-alpha-tocopherols. We note that saturable elimination predicts that all-rac- and RRR-alpha-tocopherols might inhibit and/or induce elimination of other compounds (including 30-40% of prescription drugs) eliminated via the same saturable pathways, and stereospecific elimination predicts that all-rac- and RRR-alpha-tocopherol have non-parallel dose-effect curves for these interactions.

Vitamin E delivery to human skin: studies using deuterated alpha-tocopherol measured by APCI LC-MS

Enrichment of skin surface lipids with deuterium-labeled alpha-tocopherol was compared with plasma enrichment to evaluate kinetics of the delivery of vitamin E to skin surface lipids. For 7 d, subjects consumed 75 mg each of RRR-alpha-[5-(C2H3)]- (d3) and all rac-alpha-[5,7-(C2H3)2]- (d6) tocopheryl acetates with breakfast. Blood was drawn and skin lipids were collected daily for 2 weeks, then every other day for 2 weeks. A liquid chromatography-mass spectrometry atmospheric pressure chemical ionization method for quantification of deuterium labeled (d3, d6, d9-alpha-tocopherols) and unlabeled (d0-) alpha- and gamma-tocopherols was developed. Tocopherols were quantified at their m/z [M-1] using single ion recording. alpha-Tocopherol detection was linear from 1 to 100 pmol with a detection limit of 40 pg (93 fmol). Detection of gamma-tocopherol was twice as sensitive due to greater ionization efficiency. Though d3- and d6-alpha-tocopherols appeared in plasma within 24 h of the first dose, d3-alpha-tocopherol was not detected in skin surface lipids until approximately 1 week. Plasma percentage d3 peaked at day 8, while skin surface lipid percentage d3 increased on average until day 19. Apparently skin employs a mechanism to deliver alpha-tocopherol into skin via lipid secretions.

Vitamin E bioavailability from fortified breakfast cereal is greater than that from encapsulated supplements

BACKGROUND

Conflicting results from vitamin E intervention studies suggest supplemental vitamin E malabsorption.

OBJECTIVE

We compared vitamin E bioavailability from a supplement with that from a fortified breakfast cereal.

DESIGN

Vitamin E bioavailability was evaluated by using deuterium-labeled all-rac-alpha-tocopherol in three 4-d trials (2 wk apart). Five fasting subjects sequentially consumed the following (with 236 mL fat-free milk): 400 IU d(9)-alpha-tocopheryl acetate (400-IU capsule), 41 g ready-to-eat wheat cereal containing 30 IU d(9)-alpha-tocopheryl acetate (30-IU cereal), and 45 g cereal containing 400 IU d(9)-alpha-tocopheryl acetate (400-IU cereal). Five months later (trial 4), they consumed a 400-IU capsule with 41 g vitamin E-free cereal. Blood was obtained up to 72 h after the start of each trial.

RESULTS

The mean (+/-SD) vitamin E bioavailabilities of the 30-IU cereal and the 400-IU cereal were 6 +/- 2 and 26 +/- 8 times, respectively, the vitamin E bioavailability of the 400-IU capsule. The areas under the 0-72-h d(9)-alpha-tocopherol curves for the 400-IU capsule, the 30-IU cereal, and the 400-IU cereal were 30 +/- 7, 153 +/- 43, and 765 +/- 164 micro mol. h/L (all trial comparisons, P < 0.0001). In trial 4, 3 subjects barely responded and 2 subjects had areas under the curve that were similar to their 400-IU cereal responses.

CONCLUSION

The low bioavailability of vitamin E from the 400-IU capsule and the variability observed when the capsule was consumed with cereal suggest that encapsulated vitamin E is poorly absorbed when consumed with a low-fat meal and that bioavailability can be enhanced by food fortification with vitamin E.

Factors affecting intestinal absorption of highly lipophilic food microconstituents (fat-soluble vitamins, carotenoids and phytosterols)

Highly lipophilic food microconstituents (HLFMs) with octanol-water partition coefficients log10 P(c) > 8 include the fat-soluble vitamins (A, E, D and K) and phytochemicals with potential health benefits, the carotenoids and phytosterols. It has been assumed that these compounds have the same metabolism in the human upper gastrointestinal tract and that they follow the same fate as lipids. However, a literature review shows that the metabolism of HLFMs in the upper gastrointestinal tract depends on each HLFM species. For example, some HLFM esters are hydrolyzed mainly by pancreatic lipase, others by bile salt-stimulated lipase; some HLFMs are apparently absorbed by passive diffusion, others by a transporter. Also, although some factors (HLFM molecular species, fat, food matrix) affect absorption efficiency of most HLFMs, other factors (fibers, microconstituents) apparently affect absorption only of some HLFMs. The mnemonic acronym SLAMENGHI, previously proposed to list the factors affecting the bioavailability of carotenoids, was used here to review current knowledge of the factors suspected to affect the intestinal absorption of HLFMs. The available data reveal numerous gaps in the knowledge of the metabolism of HLFMs and the factors that affect their absorption. These gaps need to be filled to be able to formulate HLFMs so as to promote greater absorption efficiency.

Development of a liquid chromatographic time-of-flight mass spectrometric method for the determination of unlabelled and deuterium-labelled alpha-tocopherol in blood components

A method is described for the analysis of deuterated and undeuterated alpha-tocopherol in blood components using liquid chromatography coupled to an orthogonal acceleration time-of-flight (TOF) mass spectrometer. Optimal ionisation conditions for undeuterated (d0) and tri- and hexadeuterated (d3 or d6) alpha-tocopherol standards were found with negative ion mode electrospray ionisation. Each species produced an isotopically resolved single ion of exact mass. Calibration curves of pure standards were linear in the range tested (0-1.5 microM, 0-15 pmol injected). For quantification of d0 and d6 in blood components following a standard solvent extraction, a stable-isotope-labelled internal standard (d3-alpha-tocopherol) was employed. To counter matrix ion suppression effects, standard response curves were generated following identical solvent extraction procedures to those of the samples. Within-day and between-day precision were determined for quantification of d0- and d6-labelled alpha-tocopherol in each blood component and both averaged 3-10%. Accuracy was assessed by comparison with a standard high-performance liquid chromatography (HPLC) method, achieving good correlation (r(2) = 0.94), and by spiking with known concentrations of alpha-tocopherol (98% accuracy). Limits of detection and quantification were determined to be 5 and 50 fmol injected, respectively. The assay was used to measure the appearance and disappearance of deuterium-labelled alpha-tocopherol in human blood components following deuterium-labelled (d6) RRR-alpha-tocopheryl acetate ingestion. The new LC/TOFMS method was found to be sensitive, required small sample volumes, was reproducible and robust, and was capable of high throughput when large numbers of samples were generated.

Modulation of cell proliferation and cell cycle regulators by vitamin E in human prostate carcinoma cell lines

PURPOSE

Vitamin E has been identified as a candidate agent for the prevention of prostate cancer. We hypothesize that the mechanism for this effect is in part a result of cell cycle inhibition rather than only due to a reduction in reactive oxygen species. We tested whether vitamin E induces cell cycle arrest in prostate carcinoma, mediated by alterations in cell cycle regulatory proteins, including cyclin E, cdk2 and p27.

MATERIALS AND METHODS

Cells were incubated with and without vitamin E (alpha-tocopherol succinate, 20 microg./ml.), fixed and stained with propidium iodide for flow cytometry analysis. In parallel experiments total protein was extracted, immunoprecipitated with cyclin E antibody and analyzed by Western blot for the expression of cell cycle markers.

RESULTS

Flow cytometry analysis revealed a dramatic reduction in the S phase percent of LNCaP and PC3 cells in response to vitamin E (69% and 95%, respectively). It was accompanied by over expression of p27 (3-fold increase) with vitamin E treatment.

CONCLUSIONS

This study demonstrates that at physiological concentrations vitamin E induced profound cell cycle arrest mediated by up-regulation of p27. This observation provides a theoretical basis for the putative chemopreventive effect of vitamin E.

The European perspective on vitamin E: current knowledge and future research

Vitamin E is indispensible for reproduction in female rats. In humans, vitamin E deficiency primarily causes neurologic dysfunctions, but the underlying molecular mechanisms are unclear. Because of its antioxidative properties, vitamin E is believed to help prevent diseases associated with oxidative stress, such as cardiovascular disease, cancer, chronic inflammation, and neurologic disorders. However, recent clinical trials undertaken to prove this hypothesis failed to verify a consistent benefit. Given these findings, a group of European scientists met to analyze the most recent knowledge of vitamin E function and metabolism. An overview of their discussions is presented in this article, which includes considerations of the mechanisms of absorption, distribution, and metabolism of different forms of vitamin E, including the alpha-tocopherol transfer protein and alpha-tocopherol-associated proteins; the mechanism of tocopherol side-chain degradation and its putative interaction with drug metabolism; the usefulness of tocopherol metabolites as biomarkers; and the novel mechanisms of the antiatherosclerotic and anticarcinogenic properties of vitamin E, which involve modulation of cellular signaling, transcriptional regulation, and induction of apoptosis. Clinical trials were analyzed on the basis of the selection of subjects, the stage of disease, and the mode of intake, dosage, and chemical form of vitamin E. In addition, the scarce knowledge on the role of vitamin E in reproduction was summarized. In conclusion, the scientists agreed that the functions of vitamin E were underestimated if one considered only its antioxidative properties. Future research on this essential vitamin should focus on what makes it essential for humans, why the body apparently utilizes alpha-tocopherol preferentially, and what functions other forms of vitamin E have.

Role of free radicals in the neurodegenerative diseases: therapeutic implications for antioxidant treatment

Free radicals and other so-called 'reactive species' are constantly produced in the brain in vivo. Some arise by 'accidents of chemistry', an example of which may be the leakage of electrons from the mitochondrial electron transport chain to generate superoxide radical (O2*-). Others are generated for useful purposes, such as the role of nitric oxide in neurotransmission and the production of O2*- by activated microglia. Because of its high ATP demand, the brain consumes O2 rapidly, and is thus susceptible to interference with mitochondrial function, which can in turn lead to increased O2*- formation. The brain contains multiple antioxidant defences, of which the mitochondrial manganese-containing superoxide dismutase and reduced glutathione seem especially important. Iron is a powerful promoter of free radical damage, able to catalyse generation of highly reactive hydroxyl, alkoxyl and peroxyl radicals from hydrogen peroxide and lipid peroxides, respectively. Although most iron in the brain is stored in ferritin, 'catalytic' iron is readily mobilised from injured brain tissue. Increased levels of oxidative damage to DNA, lipids and proteins have been detected by a range of assays in post-mortem tissues from patients with Parkinson's disease, Alzheimer's disease and amyotrophic lateral sclerosis, and at least some of these changes may occur early in disease progression. The accumulation and precipitation of proteins that occur in these diseases may be aggravated by oxidative damage, and may in turn cause more oxidative damage by interfering with the function of the proteasome. Indeed, it has been shown that proteasomal inhibition increases levels of oxidative damage not only to proteins but also to other biomolecules. Hence, there are many attempts to develop antioxidants that can cross the blood-brain barrier and decrease oxidative damage. Natural antioxidants such as vitamin E (tocopherol), carotenoids and flavonoids do not readily enter the brain in the adult, and the lazaroid antioxidant tirilazad (U-74006F) appears to localise in the blood-brain barrier. Other antioxidants under development include modified spin traps and low molecular mass scavengers of O2*-. One possible source of lead compounds is the use of traditional remedies claimed to improve brain function. Little is known about the impact of dietary antioxidants upon the development and progression of neurodegenerative diseases, especially Alzheimer's disease. Several agents already in therapeutic use might exert some of their effects by antioxidant action, including selegiline (deprenyl), apomorphine and nitecapone.

HPLC and GC/MS determination of deuterated vitamin K (phylloquinone) in human serum after ingestion of deuterium-labeled broccoli

The ability to intrinsically label plant constituents with stable isotopes has the potential to advance the study of vitamin K-absorption and metabolism in humans. Broccoli, a primary food source of phylloquinone (VK-1), was grown hydroponically using 31 atom % deuterium oxide in order to label VK-1 within the food matrix. Deuterium-labeled broccoli (115 g; 168 &mgr;g VK-1) was fed to one male subject in a single serving. Multiple serum samples were drawn throughout the subsequent 24-hr period. Reversed-phase HPLC was used to extract and purify VK-1 in both broccoli and serum. Ion abundances of the deuterium-labeled and unlabeled (endogenous) VK-1 were determined using GC/MS in negative chemical ionization mode. No sample derivatization was required. Endogenous VK-1 produced isotopomers from m/z 450 to m/z 453. The labeled VK-1 isotopomers in the broccoli were from m/z 452 to m/z 467, with the most abundant isotopomer being m/z 458 (14.1% of total labeled VK-1). The GC/MS chromatograms from serum revealed both endogenous VK-1 and VK-1 derived from the deuterium-labeled broccoli. The profile of labeled VK-1 isotopomers in serum was identical to the VK-1 isotopomer profile in labeled broccoli, indicating that no deuterium was lost due to exchange either in the body or in sample preparation. At 4 hr following broccoli intake, there was an 81.1% enrichment of phylloquinone in serum; labeled VK-1 was no longer detectable in serum at 24 hr. Use of isotope labeled vegetables enables one to discriminate exogenous intake of VK-1 from endogenous pools and ultimately to determine bioavailability of VK-1 from foods.

Vitamin E kinetics in smokers and nonsmokers

Does cigarette smoking increase vitamin E utilization in vivo? A trial was carried out in 6 smokers and 5 nonsmokers of comparable ages and serum lipids. Subjects consumed 75 mg each d(3)-RRR and d(6)-all rac-alpha-tocopheryl acetates (natural and synthetic vitamin E, respectively) daily for 7 d with a standardized breakfast. Fasting blood samples were drawn on days -7, -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 9, 14, 21 (negative days indicate supplementation). In both groups, plasma d(3)-alpha-tocopherol concentrations were approximately double of d(6)-alpha-tocopherol. At day 0, the %d(3) alpha-tocopherols (d(3)-alpha-tocopherol/total-alpha-tocopherol x 100) were similar in both smokers and nonsmokers. Subsequently, there was a trend toward a faster exponential disappearance of the plasma %d(3) alpha-tocopherol in smokers compared with nonsmokers (0.30 +/- 0.04 compared with 0.24 +/- 0.05, p =.0565). The calculated %d(3) half-lives were 55.6 +/- 7.4 h in smokers and 72.1 +/- 17.3 h in nonsmokers (p =.0630). By day 21, the %d(3) in smokers had decreased to 1.4% +/- 0.3% while it was 2.2% +/- 0.7% (p =.0418) in the nonsmokers. These data suggest that smoking increases plasma vitamin E disappearance, but further studies are needed to confirm this finding and to assess its cause.