Vitamin E: Not only a single stereoisomer.

The recent publication by Azzi and colleagues puts forth the argument that only RRR-α-tocopherol should be considered as vitamin E from a physiological point of view. They base their argument primarily on the assertion that only this form has been used to treat stark vitamin E deficiency in humans (known as AVED, or Ataxia with Vitamin E Deficiency). Azzi et al. also argue that other chemically similar molecules, such as tocopherols other than α-tocopherol and tocotrienols do not provide vitamin E activity. Azzi and colleagues are correct on this second point. An investigation into the biological activities of vitamin E, and the mechanisms behind these activities, confirms that physiological vitamin E activity is limited to certain α-tocopherol forms. However, it is also clear that these activities are not restricted only to the RRR-form but include other 2R-forms as well. Indeed, the α-tocopherol transfer protein (α-TTP), which is critical to mediate vitamin E trafficking and biological activity, and genetic defects of which lead to vitamin E deficiency, binds well to all 2R-forms of α-tocopherol. Furthermore, both RRR-α-tocopherol and the other 2R-forms are maintained in human plasma and distributed to tissues and organs, whereas the 2S-stereoisomers are excreted quickly. As such, in recent years the definition of vitamin E including both 2R- and RRR-α-tocopherol has gained both broad scientific and regulatory acceptance. Consistent with this understanding, we provide evidence that AVED has indeed been treated successfully with forms in addition to RRR-α-tocopherol, again arguing against the restriction of the definition to RRR-α-tocopherol only. Finally, we provide evidence against any safety concerns utilizing the currently accepted definition of vitamin E.

GPX4 and vitamin E cooperatively protect hematopoietic stem and progenitor cells from lipid peroxidation and ferroptosis.

Ferroptosis, a newly defined mode of regulated cell death caused by unbalanced lipid redox metabolism, is implicated in various tissue injuries and tumorigenesis. However, the role of ferroptosis in stem cells has not yet been investigated. Glutathione peroxidase 4 (GPX4) is a critical suppressor of lipid peroxidation and ferroptosis. Here, we study the function of GPX4 and ferroptosis in hematopoietic stem and progenitor cells (HSPCs) in mice with Gpx4 deficiency in the hematopoietic system. We find that Gpx4 deletion solely in the hematopoietic system has no significant effect on the number and function of HSPCs in mice. Notably, hematopoietic stem cells (HSCs) and hematopoietic progenitor cells lacking Gpx4 accumulated lipid peroxidation and underwent ferroptosis in vitro. α-Tocopherol, the main component of vitamin E, was shown to rescue the Gpx4-deficient HSPCs from ferroptosis in vitro. When Gpx4 knockout mice were fed a vitamin E-depleted diet, a reduced number of HSPCs and impaired function of HSCs were found. Furthermore, increased levels of lipid peroxidation and cell death indicated that HSPCs undergo ferroptosis. Collectively, we demonstrate that GPX4 and vitamin E cooperatively maintain lipid redox balance and prevent ferroptosis in HSPCs.

Hidden Hunger of Vitamin E among Healthy College Students: A Cross- Sectional Study.

BACKGROUND: College students may have a risk of fat-soluble vitamin deficiencies due to unhealthy dietary habits, especially for vitamin A and E. They are important members of the human antioxidant network; deficiencies of these vitamins may increase the risk of many critical diseases. OBJECTIVE: The current study was undertaken to determine the status of vitamin A and E in college students. METHODS: Healthy college students were recruited, and fasting blood samples of them were collected and used for determining serum levels of retinol and α-tocopherol by the HPLC method. RESULTS: We found that there was no vitamin A deficiency in college students. However, vitamin E deficiency existed in 34.5% of college students, especially in males. All the students had no vitamin E adequacy. In addition, our findings showed that BMI was inversely associated with serum α-- tocopherol, but not serum retinol. CONCLUSION: These results suggest that vitamin E deficiency in college students should be given more attention, and it is necessary to consider using vitamin E supplements.

First Recognized Patient with Genetic Vitamin E Deficiency Stable after 36 Years of Controlled Supplement Therapy.

INTRODUCTION: Familial isolated deficiency of vitamin E (VED or AVED; MIM #277460) is a progressive neurodegenerative disorder resembling Friedreich ataxia. It is caused by the deficiency of α-tocopherol transfer protein that prevents patients from retaining vitamin E. Oral vitamin E supplements are an accepted treatment, but detailed dosage recommendations and reports on long-term therapeutic results are scarce. METHODS: The first patient with VED was discovered at our institution at the age of 12 years and has since been followed with clinical, neurophysiological, neuroradiological, and biochemical investigations to his present age of 52 years. For the last 36 years, the patient has scrupulously followed a custom-made high-dose vitamin E supplement regimen that we devised on the basis of studies of his metabolism of vitamin E. RESULTS: Over the long period of observation, the patient has remained in good general health and has not shown progression of neurological symptoms and signs. His vitamin E plasma levels were always moderately above the normal range. During short interruptions of vitamin E supplements, vitamin E levels fell rapidly, even after years of massive supplementation. DISCUSSION: In this VED patient, a specified and carefully controlled high-dose vitamin E therapy has prevented any recognizable progression of the neurodegenerative process over more than 3 decades of observation.

Vitamin A deficiency exacerbates extrinsic atopic dermatitis development by potentiating type 2 helper T cell-type inflammation and mast cell activation.

BACKGROUND: Vitamin A deficiency (VAD) has been hypothesized to play a role in the pathophysiology of atopic dermatitis (AD). OBJECTIVE: We sought to verify whether VAD can exacerbate AD development, and explore the possible pathophysiologic mechanism. METHODS: We detected serum vitamin A (VA) concentration in different phenotypes of AD infants (intrinsic AD, iAD and extrinsic AD, eAD), and established ovalbumin (OVA) percutaneous sensitized AD model and passive cutaneous anaphylaxis (PCA) model on VAD and vitamin A supplementation (VAS) model in wild-type mice (C57BL/6) and established AD model on both normal VA (VAN) and VAD feeding mast cell deficiency mice (ckitw-sh/w-sh ). RESULTS: The average serum VA concentration of eAD was significantly lower than that of iAD, as well as healthy controls. In OVA-induced C57BL/6 mouse AD model, compared with VAN group, VAD mice manifested significantly more mast cells accumulation in the skin lesions, more severe Th2-mediated inflammation, including higher serum IgG1 and IgE levels, more IL-4, IL-13 mRNA expression in OVA-sensitized skin, and lower Th1 immune response, including lower serum IgG2a and IFN-γ mRNA expression in the skin. But there was no significant difference in the expression of IL-17 mRNA between OVA-treated skin of VAN and VAD mice. However, in OVA-induced ckitw-sh/w-sh mouse AD model, we did not find any significant differences in the above measurements between VAD and VAN group. In PCA model, VAD mice showed remarkable more blue dye leakage than that in VAN mice. Compared with VAD group, the above-mentioned inflammatory measurements in VAS group and VAN group were similar in OVA-induced AD model mice. CONCLUSIONS AND CLINICAL RELEVANCE: VAD can exacerbate extrinsic AD by augmenting Th2-mediated inflammation and mast cell activation. Therapeutic VAS can rescue VAD-aggravated eAD. It may provide a new strategy for future prevention or treatment of atopic dermatitis.

Multiple Micronutrient Powder Reduces Vitamin E Deficiency in Brazilian Children: A Pragmatic, Controlled Clinical Trial.

Multiple micronutrient powder supplementation is a health promotion strategy, but data on its effectiveness regarding vitamin E are rare. The objective was to evaluate the impact of home fortification with powdered micronutrients on α-tocopherol concentrations, growth, and inflammation in Brazilian children aged 6-15 months. This is a pragmatic, controlled clinical trial, in which the intervention group received micronutrient powder sachets for up to 3 months. Vitamin E deficiency was considered when α-tocopherol was less than 11.6 µmol/L. The Poisson regression model was used to estimate adjusted values for prevalence ratios (PR) for the outcome variable. A total of 224 children participated in the study. The intervention group had a higher median α-tocopherol level (17.2 versus 3.6 µmol/L; p < 0.001) and an 82.0% reduction in the prevalence of vitamin deficiency (PR = 0.18; 95% CI 0.11-0.30) when compared with the control group. Consumption of multiple micronutrients in powder increases serum α-tocopherol concentrations, promotes better linear growth, and reduces morbidity in children.

Water-Soluble Vitamin E-Tocopheryl Phosphate.

The hydrophobicity of vitamin E poses transport and metabolic challenges to regulate its bioavailability and to prevent its accumulation in lipid-rich tissues such as adipose tissue, brain, and liver. Water-soluble precursors of vitamin E (α-tocopherol, αT), such as its esters with acetate (αTA), succinate (αTS), or phosphate (αTP), have increased solubility in water and stability against reaction with free radicals, but they are rapidly converted during their uptake into the lipid-soluble vitamin E. Therefore, the bioavailability of these precursors as intact molecules is low; nevertheless, at least for αTS and αTP, the recent research has revealed unique regulatory effects on signal transduction and gene expression and the modulation of cellular events ranging from proliferation, survival/apoptosis, lipid uptake and metabolism, phagocytosis, long term potentiation, cell migration, telomere maintenance, and angiogenesis. Moreover, water-soluble derivatives of vitamin E including some based on αTP are increasingly used as components of nanocarriers for enhanced and targeted delivery of drugs and other molecules (vitamins, including αT and αTP itself, vitamin D3, carnosine, caffeine, docosahexaenoic acid (DHA), insulin) and cofactors such as coenzyme Q10. In this review, the chemical characteristics, transport, metabolic pathways, and molecular mechanisms of action of αTP in cells and tissues are summarized and put into perspective with its possible role in the prevention of a number of diseases.

Effects of feeding two RRR-α-tocopherol formulations on serum, cerebrospinal fluid and muscle α-tocopherol concentrations in horses with subclinical vitamin E deficiency.

BACKGROUND: Alpha-tocopherol (α-TP) supplementation is recommended for the prevention of various equine neuromuscular disorders. Formulations available include RRR-α-TP acetate powder and a more expensive but rapidly water-dispersible liquid RRR-α-TP (WD RRR-α-TP). No cost-effective means of rapidly increasing serum and cerebrospinal fluid (CSF) α-TP with WD RRR-α-TP and then sustaining concentrations with RRR-α-TP acetate has yet been reported. OBJECTIVES: To evaluate serum, CSF and muscle α-TP concentrations in an 8-week dosing regimen in which horses were transitioned from WD RRR-α-TP to RRR-α-TP acetate. STUDY DESIGN: Non-randomised controlled trial. METHODS: Healthy horses with serum α-TP of <2 µg/mL were divided into three groups and followed for 8 weeks. In the control group (n = 5), no α-TP was administered. In the second group (Group A; n = 7), 5000 IU/day RRR-α-TP acetate was administered. In the third group (Group WD-A; n = 7), doses of 5000 IU/day of WD RRR-α-TP were administered over 3 weeks, followed by a 4-week transition from WD RRR-α-TP to RRR-α-TP acetate, and a final 1 week of treatment with RRR-α-TP acetate. Serum samples were obtained weekly; muscle biopsies were obtained before, at 2.5 weeks and after supplementation. CSF samples were obtained before and after the 8-week period of supplementation. RESULTS: Serum α-TP increased significantly in Group WD-A at week 1 and remained significantly higher than in Group A and the control group throughout the transition, with inter-individual variation in response. Serum α-TP increased significantly by week 7 in Group A. CSF α-TP increased significantly in Group WD-A only. Muscle α-TP concentrations did not differ significantly across groups. Serum and CSF α-TP were closely correlated (r = 0.675), whereas serum and muscle-α-TP concentrations were not correlated. MAIN LIMITATIONS: The study duration was short and data on pre-transition CSF was lacking. CONCLUSIONS: The administration of 5000 IU/day of water-dispersible RRR-α-TP rapidly increases serum α-TP. Serum and CSF α-TP concentrations are sustained with a gradual transition to 5000 IU/day of RRR-α-TP acetate. Periodic evaluation of serum α-TP concentrations is recommended because responses vary among individuals.

Oral Tocofersolan Corrects or Prevents Vitamin E Deficiency in Children With Chronic Cholestasis.

OBJECTIVES: D-Alpha-tocopheryl polyethylene glycol 1000 succinate (Tocofersolan, Vedrop), has been developed in Europe to provide an orally bioavailable source of vitamin E in children with cholestasis. The aim was to analyze the safety/efficacy of Vedrop in a large group of children with chronic cholestasis. METHODS: Two hundred seventy-four children receiving Vedrop for vitamin E deficiency or for its prophylaxis were included from 7 European centers. Median age at treatment onset was 2 months and median follow-up was 11 months. Vedrop was prescribed at a daily dose of 0.34 mL/kg (25 IU/kg) of body weight. Three methods were used to determine a sufficient serum vitamin E status: vitamin E, vitamin E/(total cholesterol), vitamin E/(total cholesterol + triglycerides). RESULTS: Before Vedrop therapy, 51% of children had proven vitamin E deficiency, 30% had normal vitamin E status and 19% had an unknown vitamin E status. During the first months of treatment, vitamin E status was restored in the majority of children with insufficient levels at baseline (89% had a normal status at 6 months). All children with a normal baseline vitamin E status had a normal vitamin E status at 6 months. Among children with an unknown vitamin E status at baseline, 93% had a normal vitamin E status at 6 months. A sufficient vitamin E status was observed in 80% of children with significant cholestasis (serum total bilirubin >34.2 µmol/L). No serious adverse reaction was reported. CONCLUSIONS: Vedrop seems a safe and effective oral formulation of vitamin E that restores and/or maintains sufficient serum vitamin E level in the majority of children with cholestasis, avoiding the need for intramuscular vitamin E injections.

Suplementacion con vitaminas liposolubles en pacientes con fibrosis quistica: ¿es suficiente con Aquadek’s®? / Fat-soluble vitamins supplementation in patients with cystic fibrosis: is enough Aquadek’s®?

Introducción y objetivo: Conocer si la suplementación un nuevo polivitamínico (Aquadek’s®) durante 12 meses es segura y eficaz en pacientes con Fibrosis Quística (FQ). Material y Métodos: Estudio prospectivo, longitudinal y no controlado en pacientes con FQ insuficientes pancreáticos, clínicamente estables, que recibieron suplementación con Aquadek’s® (2 comprimidos masticables) durante 12 meses en lugar de su suplementación habitual. Se evaluaron niveles séricos de retinol, betacarotenos, 25 OH vitamina D y α-tocoferol un año antes, al inicio y tras un año de tratamiento. Análisis estadístico: Pruebas t para datos pareados. Resultados: Se incluyeron 28 pacientes entre 6 y 39 años (mediana 18,5 años). La suplementación con Aquadek’s® supuso un incremento en la dosis de vitaminas A y una disminución del número de comprimidos administrados. Al inicio, un 89% presentaban algún tipo de dé- ficit vitamínico: (61% pro-Vitamina A y 54% vitamina D). Tras un año, se produjo un incremento de los niveles de betacarotenos: 160 mcg/l (IC 95% 98-222) (p<0,001) y disminuyó el porcentaje de pacientes con deficiencia de dicha pro-vitamina un 46% (IC 95% 22-64) (p<0,001). Vitamina D aumentaron un 18% (IC 95% 2-32) (p=0,025). En ningún caso los niveles séricos sobrepasaron los límites indicativos de toxicidad. Conclusiones: La suplementación con Aquadek’s® en el formato de comprimidos masticables es segura y eficaz para mantener el estatus de las vitaminas A y E en pacientes con FQ mayores de 6 años, aunque es insuficiente para mantener niveles séricos de 25 OH vitamina D dentro de las recomendaciones para esta enfermedad (AU)

Introduction and objective: Evaluate the safety and efficacy of a novel polyvitaminic (Aquadek’s®) in patients with Cystic Fibrosis (CF). Material and Methods: Prospective, longitudinal and non-randomized study. CF patients with pancreatic insufficiency and clinically stable were given Aquadek’s® (two chewable tablets) daily for 12 months. Serum levels of retinol, beta-carotene, 25 OH vitamin D and α-tocopherol were evaluated twelve months before, at baseline and 12 months after. Statistical analysis: paired ttests. Results: 28 patients aged 6 to 39 years (median 18.5 years) were included. Aquadek’s® supplementation led to an increase in vitamin A dose and a decrease in the number of tablets administered. At baseline, 89% had at least one vitamin deficiency (61% pro-Vitamin A and 54% vitamin D). After one year, serum beta-carotene levels were increases 160 (95% CI 98-222) mcg/l (p<0,001) and decreased the percentage of patients with pro-vitamin A deficiency 46% (95% CI 22-64) (p<0,001). The proportion of patients with vitamin D insufficiency increased 18% (95% CI 2-32) (p =0.025). In any case serum levels exceeded the upper limits used to assess the risk of toxicity. Conclusions: Two daily Aquadek’s® chewable tablets are safe and effective for maintaining vitamin A and E status of CF patients older than 6 years, although it is insufficient to normalize serum 25OHvitaminD according to the current recommendations for this disease (AU)

Vitamin E inadequacy in humans: causes and consequences.

It is estimated that >90% of Americans do not consume sufficient dietary vitamin E, as α-tocopherol, to meet estimated average requirements. What are the adverse consequences of inadequate dietary α-tocopherol intakes? This review discusses health aspects where inadequate vitamin E status is detrimental and additional vitamin E has reversed the symptoms. In general, plasma α-tocopherol concentrations <12 µmol/L are associated with increased infection, anemia, stunting of growth, and poor outcomes during pregnancy for both the infant and the mother. When low dietary amounts of α-tocopherol are consumed, tissue α-tocopherol needs exceed amounts available, leading to increased damage to target tissues. Seemingly, adequacy of human vitamin E status cannot be assessed from circulating α-tocopherol concentrations, but inadequacy can be determined from "low" values. Circulating α-tocopherol concentrations are very difficult to interpret because, as a person ages, plasma lipid concentrations also increase and these elevations in lipids increase the plasma carriers for α-tocopherol, leading to higher circulating α-tocopherol concentrations. However, abnormal lipoprotein metabolism does not necessarily increase α-tocopherol delivery to tissues. Additional biomarkers of inadequate vitamin E status are needed. Urinary excretion of the vitamin E metabolite α-carboxy-ethyl-hydroxychromanol may fulfill this biomarker role, but it has not been widely studied with regard to vitamin E status in humans or with regard to health benefits. This review evaluated the information available on the adverse consequences of inadequate α-tocopherol status and provides suggestions for avenues for research.

Brown bowel syndrome: a rare complication in diseases associated with long-standing malabsorption.

BACKGROUND/AIMS: Longtime chronic malabsorption may among other things cause a lack of liposoluble vitamins. Vitamin E deficiency can lead to formation of lipofuscin aggregates. Its deficiency is also associated with an increased lipofuscinosis of the bowel, i.e. brown bowel syndrome. METHODS: Systematic research via Medline on brown bowel syndrome, lipofuscinosis, and vitamin E deficiency was performed. We combined our own clinical experience and a review of the literature for this paper. Its goal is to inform about the possible consequences of severe malabsorption and brown bowel syndrome. RESULTS: Systematic data about the occurrence of severe malabsorption and brown bowel syndrome are rare. Only about 27 scientific reports can be found on this subject. Brown bowel syndrome is found mostly in conjunction with vitamin E deficiency and lipofuscinosis of the bowel. The clinical findings are caused by both malabsorption and lipofuscinosis. Case reports show a therapeutic effect of vitamin E. CONCLUSION: Vitamin deficiency caused by longtime chronic malabsorption can lead to the development of brown bowel syndrome, which is seen as the expression of lipofuscinosis of the bowel, and can cause further clinical disorders. Patients with malabsorption should therefore be monitored regarding their vitamin E levels.

Serum tocopherol levels in very preterm infants after a single dose of vitamin E at birth.

OBJECTIVE: Our aim was to examine the impact of a single enteral dose of vitamin E on serum tocopherol levels. The study was undertaken to see whether a single dose of vitamin E soon after birth can rapidly increase the low α-tocopherol levels seen in very preterm infants. If so, this intervention could be tested as a means of reducing the risk of intracranial hemorrhage. METHODS: Ninety-three infants <27 weeks' gestation and <1000 g were randomly assigned to receive a single dose of vitamin E or placebo by gastric tube within 4 hours of birth. The vitamin E group received 50 IU/kg of vitamin E as dl-α-tocopheryl acetate (Aquasol E). The placebo group received sterile water. Blood samples were taken for measurement of serum tocopherol levels by high-performance liquid chromatography before dosing and 24 hours and 7 days after dosing. RESULTS: Eighty-eight infants received the study drug and were included in the analyses. The α-tocopherol levels were similar between the groups at baseline but higher in the vitamin E group at 24 hours (median 0.63 mg/dL vs. 0.42 mg/dL, P = .003) and 7 days (2.21 mg/dL vs 1.86 mg/dL, P = .04). There were no differences between groups in γ-tocopherol levels. At 24 hours, 30% of vitamin E infants and 62% of placebo infants had α-tocopherol levels <0.5 mg/dL. CONCLUSIONS: A 50-IU/kg dose of vitamin E raised serum α-tocopherol levels, but to consistently achieve α-tocopherol levels >0.5 mg/dL, a higher dose or several doses of vitamin E may be needed.

Liver X receptor up-regulates α-tocopherol transfer protein expression and α-tocopherol status.

Fat-soluble vitamin E (α-tocopherol) has antioxidant activity. α-Tocopherol transfer protein (α-TTP), a hepatic cytosolic protein, selectively binds α-tocopherol and has an important role regulating circulatory α-tocopherol levels. However, only a few studies have shown the transcriptional regulation of the α-TTP gene. Here, we demonstrate that liver X receptor (LXR) regulates α-TTP expression through direct interaction with the α-TTP gene promoter, and it modulates circulating α-tocopherol levels. LXR belongs to the nuclear receptor superfamily, acts as a ligand-dependent transcription factor for oxysterols and plays an important role in cholesterol metabolism and lipogenesis. We identified an LXR response element (LXRE; DR4, a direct repeat with four-nucleotides spacing) of the human α-TTP gene promoter by using luciferase and electrophoretic mobility shift assays. Mutations in this element abolished activation of this promoter. Moreover, treatment of vitamin E-deficient rats with T0901317, a synthetic LXR ligand, increased α-TTP expression in the liver and cerebrum and increased the plasma α-tocopherol levels. These results indicate that the LXR signaling pathway modulates α-TTP gene expression and plasma α-tocopherol levels. Our observations imply that the LXR signaling pathway might be a useful target for antioxidant properties by controlling the vitamin E status.

Vitamin E attenuates homocysteine and cholesterol induced damage in rat aorta.

BACKGROUND: The aim of this study was to investigate the effect of vitamin E on homocysteine and cholesterol-induced damage of rat aorta. METHODS: Wistar rats (all fed with a vitamin E poor diet) were divided into five groups. Control group was fed with the diet only, the second group received 1 mg kg(-1) day(-1) L-methionine in drinking water, the third group was fed with 2% cholesterol containing diet, the fourth group received L-methionine and cholesterol together, and the fifth group was fed with L-methionine and cholesterol and received intramuscular injections of vitamin E. After 4 weeks serum homocysteine, cholesterol and vitamin E levels were measured; aortas were removed; collagen and elastin and the major extracellular matrix components were evaluated microscopically as indicators of aortic degeneration. Aortic collagen content was measured by a colorimetric hydroxyproline assay. RESULTS: Four-week diet supplementation with methionine and cholesterol caused a twofold increase in serum homocysteine and 22% increase in serum cholesterol levels; endothelial damage and degenerative alterations in the aortic media were observed, as indicated by the dissociation of elastic fibers and accumulation of collagen. Vitamin E completely prevented the accumulation of collagen and largely prevented aorta damage as shown by the morphological data. CONCLUSION: The results indicate that, even moderate increases in homocysteine and cholesterol levels are sufficient to induce vascular degeneration that may be prevented by vitamin E supplementation.

Vitamin-responsive disorders: cobalamin, folate, biotin, vitamins B1 and E.

The catalytic properties of many enzymes depend on the participation of vitamins as obligatory cofactors. Vitamin B12 (cobalamin) and folic acid (folate) deficiencies in infants and children classically present with megaloblastic anemia and are often accompanied by neurological signs. A number of rare inborn errors of cobalamin and folate absorption, transport, cellular uptake, and intracellular metabolism have been delineated and identification of disease-causing mutations has improved our ability to diagnose and treat many of these conditions. Two inherited defects in biotin metabolism are known, holocarboxylase synthetase and biotinidase deficiency. Both lead to multiple carboxylase deficiency manifesting with metabolic acidosis, neurological abnormalities, and skin rash. Thiamine-responsive megaloblastic anemia is characterized by megaloblastic anemia, non-type I diabetes, and sensorineural deafness that responds to pharmacological doses of thiamine (vitamin B1). Individuals affected with inherited vitamin E deficiencies including ataxia with isolated vitamin E deficiency and abetalipoproteinemia present with a spinocerebellar syndrome similar to patients with Friedreich's ataxia. If started early, treatment of these defects by oral or parenteral administration of the relevant vitamin often results in correction of the metabolic defect and reversal of the signs of disease, stressing the importance of early and correct diagnosis in these treatable conditions.

Vitamin E deficiency impairs the somatostatinergic receptor-effector system and leads to phosphotyrosine phosphatase overactivation and cell death in the rat hippocampus.

Vitamin E plays an essential role in maintaining the structure and function of the nervous system, and its deficiency, commonly associated with fat malabsorption diseases, may reduce neuronal survival. We previously demonstrated that the somatostatinergic system, implicated in neuronal survival control, can be modulated by α-tocopherol in the rat dentate gyrus, increasing cyclic adenosine monophosphate response element binding protein phosphorylation. To gain a better understanding of the molecular actions of tocopherols and examine the link among vitamin E, somatostatin and neuronal survival, we have investigated the effects of a deficiency and subsequent administration of tocopherol on the somatostatin signaling pathway and neuronal survival in the rat hippocampus. No changes in somatostatin expression were detected in vitamin-E-deficient rats. These rats, however, showed a significant increase in the somatostatin receptor density and dissociation constant, which correlated with a significant increase in the protein levels of somatostatin receptors. Nevertheless, vitamin E deficiency impaired the ability of the somatostatin receptors to couple to the effectors adenylyl cyclase and phosphotyrosine phosphatase by diminishing Gi protein functionality. Furthermore, vitamin E deficiency significantly increased phosphotyrosine phosphatase activity and PTPη expression, as well as PKCδ activation, and decreased extracellular-signal-regulated kinase phosphorylation. All these changes were accompanied by an increase in neuronal cell death. Subsequent α-tocopherol administration partially or completely reversed all these values to control levels. Altogether, our results prove the importance of vitamin E homeostasis in the somatostatin receptor-effector system and suggest a possible mechanism by which this vitamin may regulate the neuronal cell survival in the adult hippocampus.

A history of vitamin E.

Vitamin E (α-tocopherol) was discovered nearly 100 years ago because it was required to prevent fetal resorption in pregnant, vitamin E-deficient rats fed lard-containing diets that were easily oxidizable. The human diet contains eight different vitamin E-related molecules synthesized by plants; despite the fact that all of these molecules are peroxyl radical scavengers, the human body prefers α-tocopherol. The biological activity of vitamin E is highly dependent upon regulatory mechanisms that serve to retain α-tocopherol and excrete the non-α-tocopherol forms. This preference is dependent upon the combination of the function of α-tocopherol transfer protein (α-TTP) to enrich the plasma with α-tocopherol and the metabolism of non-α-tocopherols. α-TTP is critical for human health because mutations in this protein lead to severe vitamin E deficiency characterized by neurologic abnormalities, especially ataxia and eventually death if vitamin E is not provided in large quantities to overcome the lack of α-TTP. α-Tocopherol serves as a peroxyl radical scavenger that protects polyunsaturated fatty acids in membranes and lipoproteins. Although specific pathways and specific molecular targets have been sought in a variety of studies, the most likely explanation as to why humans require vitamin E is that it is a fat-soluble antioxidant.