The role of α-tocopherol in motor hypofunction with aging in α-tocopherol transfer protein knockout mice as assessed by oxidative stress biomarkers

α-Tocopherol Transfer Protein-Null Mice with Very Low α-Tocopherol Status Do Not Have an Enhanced Lipopolysaccharide-Induced Acute Inflammatory Response

Background

The α-tocopherol transfer protein-null (Ttpa-/-) mouse model is a valuable tool for studying the molecular and functional consequences of vitamin E (α-tocopherol, αT) deficiency. Because αT has been associated with reduced oxidative stress and improved immune function, we hypothesized that depleted αT concentration would exacerbate LPS-induced acute inflammatory response in the brain and heart of Ttpa-/- mice fed a vitamin E deficient (VED) diet.

Objectives

The objective was to investigate how extremely low αT status, followed by exposure to LPS, altered the acute inflammatory response to LPS in Ttpa-/- and wild-type (Ttpa+/+) mice.

Methods

Three-week-old male Ttpa+/+ and Ttpa-/- littermates (n = 36/genotype) ingested a VED diet ad libitum for 4 wk. At week 7, mice received an intraperitoneal LPS (1 or 10 μg/mouse) or saline (control) injection and were killed 4 h postinjection. Brain and heart IL-6 protein concentrations and tissue and serum αT concentrations were measured via ELISA and HPLC with photodiode array detection, respectively. Hippocampal Il-6, Tnf, and Gpx1 gene expression were measured via reverse transcriptase-quantitative polymerase chain reaction, and blood immune cell profiles were measured via a hematology analyzer.

Results

αT accumulation in analyzed tissues and serum of Ttpa-/- mice was substantially lower than Ttpa+/+ mice. Circulating white blood cell concentration, particularly lymphocytes, were lower in all LPS groups compared with controls (P < 0.01). The 10 μg LPS groups had elevated IL-6 in the cerebellum and heart compared with controls, confirming an acute inflammatory response (P < 0.01). Hippocampal and heart Il-6 gene expression in the LPS-treated Ttpa-/- mice was upregulated in a dose-dependent manner (P < 0.05).

Conclusions

The 10 μg LPS dose enhanced inflammatory markers in the brain, heart, and serum in each genotype but the lower αT status in Ttpa-/- mice did not further impact the acute immune responses.

Vitamin A and Vitamin E: Will the Real Antioxidant Please Stand Up?

Vitamin A, acting through its metabolite, all-trans-retinoic acid, is a potent transcriptional regulator affecting expression levels of hundreds of genes through retinoic acid response elements present within these genes. However, the literature is replete with claims that consider vitamin A to be an antioxidant vitamin, like vitamins C and E. This apparent contradiction in the understanding of how vitamin A acts mechanistically within the body is a major focus of this review. Vitamin E, which is generally understood to act as a lipophilic antioxidant protecting polyunsaturated fatty acids present in membranes, is often proposed to be a transcriptional regulator. The evaluation of this claim is another focus of the review. We conclude that vitamin A is an indirect antioxidant, whose indirect function is to transcriptionally regulate a number of genes involved in mediating the body's canonical antioxidant responses. Vitamin E, in addition to being a direct antioxidant, prevents the increase of peroxidized lipids that alter both metabolic pathways and gene expression profiles within tissues and cells. However, there is little compelling evidence that vitamin E has a direct transcriptional mechanism like that of vitamin A. Thus, we propose that the term antioxidant not be applied to vitamin A, and we discourage the use of the term transcriptional mediator when discussing vitamin E.

Natural and Synthetic α-Tocopherol Modulate the Neuroinflammatory Response in the Spinal Cord of Adult Ttpa-null Mice

BACKGROUND

Vitamin E (α-tocopherol, α-T) deficiency causes neurological pathologies. α-T supplementation improves outcomes, but the relative bioactivities of dietary natural and synthetic α-T in neural tissues are unknown.

OBJECTIVE

The aim was to assess the effects of dietary α-T source and dose on oxidative stress and myelination in adult α-tocopherol transfer protein-null (Ttpa- / - ) mouse cerebellum and spinal cord.

METHODS

Three-week-old male Ttpa- / - mice (n = 56) were fed 1 of 4 AIN-93G-based diets for 37 wk: vitamin E-deficient (VED; below α-T limit of detection); natural α-T, 600 mg/kg diet (NAT); synthetic α-T, 816 mg/kg diet (SYN); or high synthetic α-T, 1200 mg/kg diet (HSYN). Male Ttpa+/+ littermates (n = 14) fed AIN-93G (75 mg synthetic α-T/kg diet; CON) served as controls. At 40 wk of age, total and stereoisomer α-T concentrations and oxidative stress markers were determined (n = 7/group). Cerebellar Purkinje neuron morphology and white matter areas in cerebellum and spinal cord were assessed in a second subset of animals (n = 7/group).

RESULTS

Cerebral cortex α-T concentrations were undetectable in Ttpa- / - mice fed the VED diet. α-T concentrations were increased in NAT (4.6 ± 0.3 nmol/g), SYN (8.0 ± 0.7 nmol/g), and HSYN (8.5 ± 0.3 nmol/g) mice, but were significantly lower than in Ttpa+/+ mice fed CON (27.8 ± 1.9 nmol/g) (P < 0.001). 2R stereoisomers constituted the majority of α-T in brains of Ttpa+/+ mice (91%) and Ttpa- / - mice fed NAT (100%), but were substantially lower in the SYN and HSYN groups (∼53%). Neuroinflammatory genes were increased in the spinal cord, but not cerebellum, of VED-fed animals; NAT, SYN, and HSYN normalized their expression. Cerebellar Purkinje neuron atrophy and myelin pathologies were not visible in Ttpa- / - mice.

CONCLUSIONS

Natural and synthetic α-T supplementation normalized neuroinflammatory markers in neural tissues of 10-mo-old Ttpa- / - mice. α-T prevents tissue-specific molecular abnormalities, which may prevent severe morphological changes during late adulthood.

Preadministration of high-dose alpha-tocopherol improved memory impairment and mitochondrial dysfunction induced by proteasome inhibition in rat hippocampus

Objective: The ubiquitin-proteasome system plays a key role in memory consolidation. Proteasome inhibition and free radical-induced neural damage were implicated in neurodegenerative states. In this study, it was tested whether alpha-tocopherol (αT) in low and high doses could improve the long-term memory impairment induced by proteasome inhibition and protects against hippocampal oxidative stress. Methods: Alpha-tocopherol (αT) (60, 200 mg/kg, i.p. for 5 days) was administered to rats with memory deficit and hippocampal oxidative stress induced by bilateral intra-hippocampal injection of lactacystin (32 ng/μl) and mitochondrial evaluations were performed for improvement assessments. Results: The results showed that lactacystin significantly reduced the passive avoidance memory performance and increased the level of malondialdehyde (MDA), reactive oxygen species (ROS) and diminished the mitochondrial membrane potential (MMP) in the rat hippocampus. Furthermore, Intraperitoneal administration of αT significantly increased the passive avoidance memory, glutathione content and reduced ROS, MDA levels and impaired MMP. Conclusions: The results suggested that αT has neuroprotective effects against lactacystin-induced oxidative stress and memory impairment via the enhancement of hippocampal antioxidant capacity and concomitant mitochondrial sustainability. This finding shows a way to prevent and also to treat neurodegenerative diseases associated with mitochondrial impairment.

α-Tocomonoenol Is Bioavailable in Mice and May Partly Be Regulated by the Function of the Hepatic α‑Tocopherol Transfer Protein

Tocomonoenols are vitamin E derivatives present in foods with a single double bond at carbon 11' in the sidechain. The α-tocopherol transfer protein (TTP) is required for the maintenance of normal α-tocopherol (αT) concentrations. Its role in the tissue distribution of α-11'-tocomonoenol (αT₁) is unknown. We investigated the tissue distribution of αT₁ and αT in wild-type (TTP^+/+) and TTP knockout (TTP^-/-) mice fed diets with either αT or αT₁ for two weeks. αT₁ was only found in blood, not tissues. αT concentrations in TTP^+/+ mice were in the order of adipose tissue > brain > heart > spleen > lungs > kidneys > small intestine > liver. Loss of TTP function depleted αT in all tissues. αT₁, contrary to αT, was still present in the blood of TTP^-/- mice (16% of αT₁ in TTP^+/+). Autoclaving and storage at room temperature reduced αT and αT₁ in experimental diets. In conclusion, αT₁ is bioavailable, reaches the blood in mice, and may not entirely depend on TTP function for secretion into the systemic circulation. However, due to instability of the test compounds in the experimental diets, further in vivo experiments are required to clarify the role of TTP in αT₁ secretion. Future research should consider compound stability during autoclaving of rodent feed.

Synthetic α-Tocopherol, Compared with Natural α-Tocopherol, Downregulates Myelin Genes in Cerebella of Adolescent Ttpa-null Mice

BACKGROUND

Vitamin E (α-tocopherol; α-T) deficiency causes spinocerebellar ataxia. α-T supplementation improves neurological symptoms, but little is known about the differential bioactivities of natural versus synthetic α-T during early life.

OBJECTIVE

We assessed the effects of dietary α-T dose and source on tissue α-T accumulation and gene expression in adolescent α-tocopherol transfer protein-null (Ttpa-/-) mice.

METHODS

Three-week-old male Ttpa-/- mice (n  = 7/group) were fed 1 of 4 AIN-93G-based diets for 4 wk: vitamin E deficient (VED; below α-T limit of detection); natural α-T, 600 mg/kg diet (NAT); synthetic α-T, 816 mg/kg diet (SYN); or high synthetic α-T, 1200 mg/kg diet (HSYN). Male Ttpa+/+ littermates fed AIN-93G [75 mg synthetic α-T (CON)] served as controls (n  = 7). At 7 wk of age, tissue α-T concentrations and stereoisomer profiles were measured for all groups. RNA-sequencing was performed on cerebella of Ttpa-/- groups.

RESULTS

Ttpa-/- mice fed VED had undetectable brain α-T concentrations. Cerebral cortex α-T concentrations were greater in Ttpa-/- mice fed NAT (9.1 ± 0.7 nmol/g), SYN (10.8 ± 1.0 nmol/g), and HSYN (13.9 ± 1.6 nmol/g) compared with the VED group but were significantly lower than in Ttpa+/+ mice fed CON (24.6 ± 1.2 nmol/g) (P < 0.001). RRR-α-T was the predominant stereoisomer in brains of Ttpa+/+ mice (∼40%) and Ttpa-/- mice fed NAT (∼94%). α-T stereoisomer composition was similar in brains of Ttpa-/- mice fed SYN and HSYN (2R: ∼53%; 2S: ∼47%). Very few of the 16,774 genes measured were differentially expressed. However, compared with the NAT diet, HSYN significantly downregulated 20 myelin genes, including 2 transcription factors: SRY-box transcription factor 10 (Sox10) and myelin regulatory factor (Myrf), and several downstream target genes (false discovery rate <0.05).

CONCLUSIONS

High-dose synthetic α-T compared with natural α-T alters myelin gene expression in the adolescent mouse cerebellum, which could lead to morphological and functional abnormalities later in life.

Bone Mineral Density in Premenopausal Women Is Associated with the Dietary Intake of α-Tocopherol: A Cross-Sectional Study

This study aimed to investigate the relationship between the consumption of various nutrients and bone mineral density (BMD) in middle-aged women. This cross-sectional survey was conducted based on the clinical records of 157 women aged 38–76. Their lumbar spine BMD was measured with dual-energy X-ray absorptiometry and dietary habits were assessed with the brief-type self-administered diet history questionnaire. Participants were divided into premenopausal (n = 46) and postmenopausal (n = 111) groups and the correlation between the BMD Z-score (Z-score) and the intakes of 43 nutrients was investigated separately for each group. In premenopausal women, the daily intake of ash, calcium, and α-tocopherol was positively correlated with the Z-score (Pearson’s correlation coefficient, R = 0.31, 0.34, 0.33, p = 0.037, 0.020, 0.027, respectively). When dividing the consumption of ash, calcium, and α-tocopherol into low, middle, and high tertiles, the Z-score significantly differed only between the α-tocopherol tertiles. After adjustment for age, body mass index, and lifestyle factors, daily intake of α-tocopherol remained significantly associated with the Z-score (regression coefficient = 0.452, p = 0.022). No nutrient was found to be significantly correlated with the Z-score in postmenopausal women. Increase in the intake of α-tocopherol could help maintain bone mass in premenopausal women.

Vitamin E: Regulatory Role on Signal Transduction

Vitamin E modulates signal transduction pathways by several molecular mechanisms. As a hydrophobic molecule located mainly in membranes it contributes together with other lipids to the physical and structural characteristics such as membrane stability, curvature, fluidity, and the organization into microdomains (lipid rafts). By acting as the main lipid-soluble antioxidant, it protects other lipids such as mono- and poly-unsaturated fatty acids (MUFA and PUFA, respectively) against chemical reactions with reactive oxygen and nitrogen species (ROS and RNS, respectively) and prevents membrane destabilization and cellular dysfunction. In cells, vitamin E affects signaling in redox-dependent and redox-independent molecular mechanisms by influencing the activity of enzymes and receptors involved in modulating specific signal transduction and gene expression pathways. By protecting and preventing depletion of MUFA and PUFA it indirectly enables regulatory effects that are mediated by the numerous lipid mediators derived from these lipids. In recent years, some vitamin E metabolites have been observed to affect signal transduction and gene expression and their relevance for the regulatory function of vitamin E is beginning to be elucidated. In particular, the modulation of the CD36/FAT scavenger receptor/fatty acids transporter by vitamin E may influence many cellular signaling pathways relevant for lipid homeostasis, inflammation, survival/apoptosis, angiogenesis, tumorigenesis, neurodegeneration, and senescence. Thus, vitamin E has an important role in modulating signal transduction and gene expression pathways relevant for its uptake, distribution, metabolism, and molecular action that when impaired affect physiological and patho-physiological cellular functions relevant for the prevention of a number of diseases. © 2018 IUBMB Life, 71(4):456-478, 2019.

An innate immune response and altered nuclear receptor activation defines the spinal cord transcriptome during alpha-tocopherol deficiency in Ttpa-null mice

Mice with deficiency in tocopherol (alpha) transfer protein gene develop peripheral tocopherol deficiency and sensory neurodegeneration. Ttpa^-/- mice maintained on diets with deficient α-tocopherol (α-TOH) had proprioceptive deficits by six months of age, axonal degeneration and neuronal chromatolysis within the dorsal column of the spinal cord and its projections into the medulla. Transmission electron microscopy revealed degeneration of dorsal column axons. We addressed the potential pathomechanism of α-TOH deficient neurodegeneration by global transcriptome sequencing within the spinal cord and cerebellum. RNA-sequencing of the spinal cord in Ttpa^-/- mice revealed upregulation of genes associated with the innate immune response, indicating a molecular signature of microglial activation as a result of tocopherol deficiency. For the first time, low level Ttpa expression was identified in the murine spinal cord. Further, the transcription factor liver X receptor (LXR) was strongly activated by α-TOH deficiency, triggering dysregulation of cholesterol biosynthesis. The aberrant activation of transcription factor LXR suppressed the normal induction of the transcription factor retinoic-related orphan receptor-α (RORA), which is required for neural homeostasis. Thus we find that α-TOH deficiency induces LXR, which may lead to a molecular signature of microglial activation and contribute to sensory neurodegeneration.

Role of Vitamin E in the Treatment of Alzheimer's Disease: Evidence from Animal Models

Alzheimer's disease (AD) is a neurodegenerative disorder representing the major cause of dementia. It is characterized by memory loss, and cognitive and behavioral decline. In particular, the hallmarks of the pathology are amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs), formed by aggregated hyperphosphorylated tau protein. Oxidative stress plays a main role in AD, and it is involved in initiation and progression of AD. It is well known that Aβ induced oxidative stress, promoting reactive oxygen species (ROS) production and consequently lipid peroxidation, protein oxidation, tau hyperphosphorylation, results in toxic effects on synapses and neurons. In turn, oxidative stress can increase Aβ production. For these reasons, the administration of an antioxidant therapy in AD patients was suggested. The term vitamin E includes different fat-soluble compounds, divided into tocopherols and tocotrienols, that possess antioxidant action. α-Tocopherol is the most studied, but some studies suggested that tocotrienols may have different health promoting capacities. In this review, we focused our attention on the effects of vitamin E supplementation in AD animal models and AD patients or older population. Experimental models showed that vitamin E supplementation, by decreasing oxidative stress, may be a good strategy to improve cognitive and memory deficits. Furthermore, the combination of vitamin E with other antioxidant or anti-inflammatory compounds may increase its efficacy. However, even if some trials have evidenced some benefits, the effects of vitamin E in AD patients are still under debate.

Therapies targeting lipid peroxidation in traumatic brain injury

Lipid peroxidation can be broadly defined as the process of inserting a hydroperoxy group into a lipid. Polyunsaturated fatty acids present in the phospholipids are often the targets for peroxidation. Phospholipids are indispensable for normal structure of membranes. The other important function of phospholipids stems from their role as a source of lipid mediators - oxygenated free fatty acids that are derived from lipid peroxidation. In the CNS, excessive accumulation of either oxidized phospholipids or oxygenated free fatty acids may be associated with damage occurring during acute brain injury and subsequent inflammatory responses. There is a growing body of evidence that lipid peroxidation occurs after severe traumatic brain injury in humans and correlates with the injury severity and mortality. Identification of the products and sources of lipid peroxidation and its enzymatic or non-enzymatic nature is essential for the design of mechanism-based therapies. Recent progress in mass spectrometry-based lipidomics/oxidative lipidomics offers remarkable opportunities for quantitative characterization of lipid peroxidation products, providing guidance for targeted development of specific therapeutic modalities. In this review, we critically evaluate previous attempts to use non-specific antioxidants as neuroprotectors and emphasize new approaches based on recent breakthroughs in understanding of enzymatic mechanisms of lipid peroxidation associated with specific death pathways, particularly apoptosis. We also emphasize the role of different phospholipases (calcium-dependent and -independent) in hydrolysis of peroxidized phospholipids and generation of pro- and anti-inflammatory lipid mediators. This article is part of a Special Issue entitled SI:Brain injury and recovery.

Vitamin E and neurodegeneration

Alpha-tocopherol (vitamin E) is a plant-derived antioxidant that is essential for human health. Studies with humans and with animal models of vitamin E deficiency established the critical roles of the vitamin in protecting the central nervous system, and especially the cerebellum, from oxidative damage and motor coordination deficits. We review here the established roles of vitamin E in protecting cerebellar functions, as well as emerging data demonstrating the critical roles of alpha-tocopherol in preserving learning, memory and emotive responses. We also discuss the importance of vitamin E adequacy in seemingly unrelated neurological disorders.

Vitamin E is essential for Purkinje neuron integrity

α-Tocopherol (vitamin E) is an essential dietary antioxidant with important neuroprotective functions. α-Tocopherol deficiency manifests primarily in neurological pathologies, notably cerebellar dysfunctions such as spinocerebellar ataxia. To study the roles of α-tocopherol in the cerebellum, we used the α-tocopherol transfer protein for the murine version (Ttpa(-/)(-)) mice which lack the α-tocopherol transfer protein (TTP) and are a faithful model of vitamin E deficiency and oxidative stress. When fed vitamin E-deficient diet, Ttpa(-/)(-) mice had un-detectable levels of α-tocopherol in plasma and several brain regions. Dietary supplementation with α-tocopherol normalized plasma levels of the vitamin, but only modestly increased its levels in the cerebellum and prefrontal cortex, indicating a critical function of brain TTP. Vitamin E deficiency caused an increase in cerebellar oxidative stress evidenced by increased protein nitrosylation, which was prevented by dietary supplementation with the vitamin. Concomitantly, vitamin E deficiency precipitated cellular atrophy and diminished dendritic branching of Purkinje neurons, the predominant output regulator of the cerebellar cortex. The anatomic decline induced by vitamin E deficiency was paralleled by behavioral deficits in motor coordination and cognitive functions that were normalized upon vitamin E supplementation. These observations underscore the essential role of vitamin E and TTP in maintaining CNS function, and support the notion that α-tocopherol supplementation may comprise an effective intervention in oxidative stress-related neurological disorders.

Evaluation of long-term vitamin E insufficiency or excess on bone mass, density, and microarchitecture in rodents

High dietary α-tocopherol levels reportedly result in osteopenia in growing rats, whereas α-tocopherol deficiency in α-tocopherol transfer protein-knockout (α-TTP-KO) mice results in increased cancellous bone mass. Because osteoporosis is a disease associated primarily with aging, we hypothesized that age-related bone loss would be attenuated in α-TTP-KO mice. Cancellous and cortical bone mass and microarchitecture were assessed using dual-energy X-ray absorptiometry and micro-computed tomography in 2-year-old α-TTP-KO and wild-type (WT) male and female mice fed dl-α-tocopherol acetate. In contrast to our expectations, differences in cancellous bone were not detected between WT and α-TTP-KO mice of either gender, and α-TTP-KO males had lower (p<0.05) cortical bone mass than WT males. We therefore evaluated bone mass, density, and microarchitecture in proximal femur of skeletally mature (8.5-month-old) male Sprague-Dawley rats fed diets containing low (15 IU/kg diet), adequate (75 IU/kg diet), or high (500 IU/kg diet) dl-α-tocopherol acetate for 13 weeks. Low dietary α-tocopherol did not increase bone mass. Furthermore, no reductions in cancellous or cortical bone mass were detected with high dietary α-tocopherol. Failure to detect increased bone mass in aged α-TTP-KO mice or bone changes in skeletally mature rats fed either low or high levels of α-tocopherol does not support the hypothesis that α-tocopherol has a negative impact on bone mass, density, or microarchitecture in rodents.

Vitamin E trafficking in neurologic health and disease

Vitamin E was identified almost a century ago as a botanical compound necessary for rodent reproduction. Decades of research since then established that of all members of the vitamin E family, α-tocopherol is selectively enriched in human tissues, and it is essential for human health. The major function of α-tocopherol is thought to be that of a lipid-soluble antioxidant that prevents oxidative damage to biological components. As such, α-tocopherol is necessary for numerous physiological processes such as permeability of lipid bilayers, cell adhesion, and gene expression. Inadequate levels of α-tocopherol interfere with cellular function and precipitate diseases, notably ones that affect the central nervous system. The extreme hydrophobicity of α-tocopherol poses a serious thermodynamic barrier for proper distribution of the vitamin to target tissues and cells. Although transport of the vitamin shares some steps with that of other lipids, selected tissues evolved dedicated transport mechanisms involving the α-tocopherol transfer protein (αTTP). The critical roles of this protein and its ligand are underscored by the debilitating pathologies that characterize human carriers of mutations in the TTPA gene.

Recent applications of engineered animal antioxidant deficiency models in human nutrition and chronic disease

Dietary antioxidants are essential nutrients that inhibit the oxidation of biologically important molecules and suppress the toxicity of reactive oxygen or nitrogen species. When the total antioxidant capacity is insufficient to quench these reactive species, oxidative damage occurs and contributes to the onset and progression of chronic diseases, such as neurodegenerative diseases, cardiovascular diseases, and cancer. However, epidemiological studies that examine the relationship between antioxidants and disease outcome can only identify correlative associations. Additionally, many antioxidants also have prooxidant effects. Thus, clinically relevant animal models of antioxidant function are essential for improving our understanding of the role of antioxidants in the pathogenesis of complex diseases as well as evaluating the therapeutic potential and risks of their supplementation. Recent progress in gene knockout mice and virus-based gene expression has potentiated these areas of study. Here, we review the current genetically modified animal models of dietary antioxidant function and their clinical relevance in chronic diseases. This review focuses on the 3 major antioxidants in the human body: vitamin C, vitamin E, and uric acid. We examine genetic models of vitamin C synthesis (guinea pig, Osteogenic Disorder Shionogi rat, Gulo(-/-) and SMP30(-/-) mouse mutants) and transport (Slc23a1(-/-) and Slc23a2(-/-) mouse mutants), vitamin E transport (Ttpa(-/-) mouse mutant), and uric acid synthesis (Uox(-/-) mouse mutant). The application of these models to current research goals is also discussed.

Altered vitamin E status in Niemann-Pick type C disease

Vitamin E (α-tocopherol) is the major lipid-soluble antioxidant in many species. Niemann-Pick type C (NPC) disease is a lysosomal storage disorder caused by mutations in the NPC1 or NPC2 gene, which regulates lipid transport through the endocytic pathway. NPC disease is characterized by massive intracellular accumulation of unesterified cholesterol and other lipids in lysosomal vesicles. We examined the roles that NPC1/2 proteins play in the intracellular trafficking of tocopherol. Reduction of NPC1 or NPC2 expression or function in cultured cells caused a marked lysosomal accumulation of vitamin E in cultured cells. In vivo, tocopherol significantly accumulated in murine Npc1-null and Npc2-null livers, Npc2-null cerebella, and Npc1-null cerebral cortices. Plasma tocopherol levels were within the normal range in Npc1-null and Npc2-null mice, and in plasma samples from human NPC patients. The binding affinity of tocopherol to the purified sterol-binding domain of NPC1 and to purified NPC2 was significantly weaker than that of cholesterol (measurements kindly performed by R. Infante, University of Texas Southwestern Medical Center, Dallas, TX). Taken together, our observations indicate that functionality of NPC1/2 proteins is necessary for proper bioavailability of vitamin E and that the NPC pathology might involve tissue-specific perturbations of vitamin E status.