Vitamin E and neurological function

Restoration of tryptophan hydroxylase functions and serotonin content in the Atlantic croaker hypothalamus by antioxidant treatment during hypoxic stress

Antioxidants are prototypical scavengers of oxygen-free radicals and have been shown to prevent neuroendocrine dysfunction in vertebrates during oxidative stress. In the present study, we investigated whether antioxidant treatment can reverse hypoxia-induced down-regulation of hypothalamic tryptophan hydroxylase (TPH) and serotonergic functions in Atlantic croaker. Hypothalamic neuronal contents of TPH-1 and TPH-2 proteins, serotonin (5-hydroxytryptamine, 5-HT) and its precursor, 5-hydroxytryptophan (5-HTP) as well as hypothalamic TPH-1 and TPH-2 mRNA expression and TPH activity were measured in croaker after exposure to hypoxia and treatment with pharmacological agents. Multiple injections of N-ethylmaleimide, a sulfhydryl alkylating agent, caused comparable decreases in hypothalamic TPHs functions and 5-HT contents to that induced by hypoxia exposure (dissolved oxygen: 1.7 mg/L for 4 weeks) which were partially restored by repeated injections with a nitric oxide synthase (NOS)-inhibitor and/or vitamin E. Double-labeled immunohistochemical results showed that TPHs and 5-HT neurons were co-expressed with neuronal NOS (nNOS, a neuroenzyme) that catalyzes the production of nitric oxide, a free radical, in hypothalamic neurons. These results suggest that hypoxia-induced impairment of TPH and serotonergic functions are mediated by nNOS and involve the generation of free radicals and a decrease in the antioxidant status. This study provides, to our knowledge, the first evidence of a protective role for an antioxidant in maintaining neural TPHs functions and 5-HT regulation in an aquatic vertebrate during hypoxic stress.

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.

Nutritional neuropathies

Neuropathies due to nutritional problems can affect certain patient populations and have a varied presentation because of multiple coexistent nutritional deficiencies. Clinicians should consider nutritional neuropathies in patients presenting with neuropathies. Clinicians should be alert for signs and symptoms of neuropathy in patients who have had bariatric surgery.

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.

Engineering tocopherol selectivity in α-TTP: a combined in vitro/in silico study

We present a combined in vitro/in silico study to determine the molecular origin of the selectivity of [Formula: see text]-tocopherol transfer protein ([Formula: see text]-TTP) towards [Formula: see text]-tocopherol. Molecular dynamics simulations combined to free energy perturbation calculations predict a binding free energy for [Formula: see text]-tocopherol to [Formula: see text]-TTP 8.26[Formula: see text]2.13 kcal mol[Formula: see text] lower than that of [Formula: see text]-tocopherol. Our calculations show that [Formula: see text]-tocopherol binds to [Formula: see text]-TTP in a significantly distorted geometry as compared to that of the natural ligand. Variations in the hydration of the binding pocket and in the protein structure are found as well. We propose a mutation, A156L, which significantly modifies the selectivity properties of [Formula: see text]-TTP towards the two tocopherols. In particular, our simulations predict that A156L binds preferentially to [Formula: see text]-tocopherol, with striking structural similarities to the wild-type-[Formula: see text]-tocopherol complex. The affinity properties are confirmed by differential scanning fluorimetry as well as in vitro competitive binding assays. Our data indicate that residue A156 is at a critical position for determination of the selectivity of [Formula: see text]-TTP. The engineering of TTP mutants with modulating binding properties can have potential impact at industrial level for easier purification of single tocopherols from vitamin E mixtures coming from natural oils or synthetic processes. Moreover, the identification of a [Formula: see text]-tocopherol selective TTP offers the possibility to challenge the hypotheses for the evolutionary development of a mechanism for [Formula: see text]-tocopherol selection in omnivorous animals.

Dissecting tocopherols content in maize (Zea mays L.), using two segregating populations and high-density single nucleotide polymorphism markers

BACKGROUND

Tocopherols, which are vitamin E compounds, play an important role in maintaining human health. Compared with other staple foods, maize grains contain high level of tocopherols.

RESULTS

Two F(2) populations (K22/CI7 and K22/Dan340, referred to as POP-1 and POP-2, respectively), which share a common parent (K22), were developed and genotyped using a GoldenGate assay containing 1,536 single nucleotide polymorphism (SNP) markers. An integrated genetic linkage map was constructed using 619 SNP markers, spanning a total of 1649.03 cM of the maize genome with an average interval of 2.67 cM. Seventeen quantitative trait loci (QTLs) for all the traits were detected in the first map and 13 in the second. In these two maps, QTLs for different traits were localized to the same genomic regions and some were co-located with candidate genes in the tocopherol biosynthesis pathway. Single QTL was responsible for 3.03% to 52.75% of the phenotypic variation and the QTLs in sum explained 23.4% to 66.52% of the total phenotypic variation. A major QTL (qc5-1/qd5-1) affecting α-tocopherol (αT) was identified on chromosome 5 between the PZA03161.1 and PZA02068.1 in the POP-2. The QTL region was narrowed down from 18.7 Mb to 5.4 Mb by estimating the recombination using high-density markers of the QTL region. This allowed the identification of the candidate gene VTE4 which encodes γ-tocopherol methyltransferase, an enzyme that transforms γ-tocopherol (γT)to αT.

CONCLUSIONS

These results demonstrate that a few QTLs with major effects and several QTLs with medium to minor effects might contribute to the natural variation of tocopherols in maize grain. The high-density markers will help to fine map and identify the QTLs with major effects even in the preliminary segregating populations. Furthermore, this study provides a simple guide line for the breeders to improve traits that minimize the risk of malnutrition, especially in developing countries.

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.