Analytical strategies to assess the functional metabolome of vitamin E

Vitamin E and Non-Communicable Diseases: A Review

Vitamin E, a nutrient found in several foods, comprises eight lipophilic vitamers, the α-, β-, γ- and δ-tocopherols and the α-, β-, γ- and δ-tocotrienols. This vitamin is capable of exerting antioxidant and anti-inflammatory activities, and acting as immunomodulators. Despite these well-known biological activities, the findings regarding the ability of vitamin E and its serum metabolites to prevent and/or control chronic disease are often conflicting and inconsistent. In this review, we have described the metabolism of vitamin E and its interaction with the gut microbiota, considering that these factors may be partially responsible for the divergent results obtained. In addition, we focused on the correlations between vitamin E serum levels, dietary intake and/or supplementation, and the main non-communicable diseases, including diabetes mellitus, asthma, cardiovascular diseases, and the four most common cancers (breast cancer, lung cancer, colorectal cancer, and prostate cancer) with the intention of providing an overview of its health effects in the non-communicable-diseases prevention.

Vitamin E (Alpha-Tocopherol) Metabolism and Nutrition in Chronic Kidney Disease

Vitamin E (alpha-tocopherol) is an essential micronutrient and fat-soluble antioxidant with proposed role in protecting tissues from uncontrolled lipid peroxidation. This vitamin has also important protein function and gene modulation effects. The metabolism of vitamin E depends on hepatic binding proteins that selectively retain food alpha-tocopherol for incorporation into nascent VLDL and tissue distribution together with esterified cholesterol and triglycerides. Chronic kidney disease (CKD) is a condition of oxidative stress and increased lipid peroxidation, that are associated with alterations of alpha-tocopherol metabolism and function. Specific changes have been reported for the levels of its enzymatic metabolites, including both short-chain and long-chain metabolites, the latter being endowed with regulatory functions on enzymatic and gene expression processes important for the metabolism of lipids and xenobiotics detoxification, as well as for the control of immune and inflammatory processes. Vitamin E therapy has been investigated in CKD using both oral vitamin E protocols and vitamin E-coated hemodialyzers, showing promising results in the secondary prevention of cardiovascular disease, as well as of immune and hematological complications. These therapeutic approaches are reviewed in the present article, together with a narrative excursus on the main findings indicating CKD as a condition of relative deficiency and impaired metabolism of vitamin E.

Pre-analytical monitoring and protection of oxidizable lipids in human plasma (vitamin E and ω-3 and ω-6 fatty acids): An update for redox-lipidomics methods

Sample manipulation for storage and storage itself, interfere with the stability of labile lipids in human plasma, including vitamin E (α-tocopherol), polyunsaturated fatty acids (PUFAs), and their enzymatic and free radical-derived oxidation metabolites. This remains a main limit of lipidomics studies that often lack of sufficient standardization and validation at the pre-analytical level. In order to characterize the stability of these lipids in human plasma and to develop a standardized pre-analytical protocol for lipidomics methods, the oxidation metabolites of α-tocopherol, the free form of ω3 and ω6 PUFAs, and some arachidonic acid (AA)-derived eicosanoids were investigated in human plasma during storage at different freezing temperatures. The effect of a protection/defense cocktail of antioxidants and lipoxygenase inhibitors (PD solution) on these lipid parameters was also evaluated. The temperature of storage markedly affected the formation of α-tocopheryl quinone (α-TQ), the main lipoperoxyl radical-derived oxidation metabolite of vitamin E, with the lowest production rate observed in samples stored at -80 °C or in liquid nitrogen. A similar effect of the storage temperature was observed for the free form of the ω-3 species eicosapentaenoic and docosahexaenoic acid, and for the ω-6 AA. Freezing samples at -20 °C resulted in a time-dependent formation of the pro-inflammatory eicosanoid LTB4. The PD solution prevents non-specific alterations of these lipid parameters in samples that are processed for direct analysis and protects from the temperature-dependent modifications of free PUFAs. Combining PD solution and preservation at -80 °C or in liquid nitrogen, resulted in levels of α-TQ and PUFAs that remained stable over 1 month and up to 8 months of storage, respectively. This method paper provides indications for the optimal processing and storage of human plasma utilized in lipidomics studies.

Reflections on a century of vitamin E research: Looking at the past with an eye on the future

The name vitamin E, was given by Barnett and Sure who suggested that the factor proposed by Evans and Bishop as substance "X," be termed vitamin "E" as the next vitamin after the A, B, C and D vitamins had been already described. The identification of vitamin E with a-tocopherol was made in 1936 by Evans' group. One year later β-tocopherol and 11 years later δ-tocopherol were isolated. Tocotrienol (named zetatocopherol) was first described in 1957 and later isolated in 1961. The antioxidant property of tocopherols was reported by Olcott and Emerson in 1937. Inherited vitamin E deficiency, AVED, characterized by a form of neuromyopathy was first described in 1981. The disease, was localized to chromosome 8q and found to be caused by a mutation of the a-TTP gene. The subsequent paragraphs are not a comprehensive review but only critical reflections on some important aspects of vitamin E research.

Simultaneous quantification of vitamin E and vitamin E metabolites in equine plasma and serum using LC-MS/MS

Vitamin E deficiencies can impact normal growth and development in humans and animals, and assessment of circulating levels of vitamin E and its metabolites may be an important endpoint for evaluation. Development of a sensitive method to detect and quantify low concentrations of vitamin E and metabolites in biological specimens allows for a proper diagnosis for patients and animals that are deficient. We developed a method to simultaneously extract, detect, and quantify the vitamin E compounds alpha-tocopherol (α-TP), gamma-tocopherol (γ-TP), alpha-tocotrienol (α-TT), and gamma-tocotrienol (γ-TT), and the corresponding metabolites formed after β-oxidation of α-TP and γ-TP, alpha-carboxymethylbutyl hydroxychroman (α-CMBHC) and alpha- or gamma-carboxyethyl hydroxychroman (α- or γ-CEHC), respectively, from equine plasma and serum. Quantification was achieved through liquid chromatography-tandem mass spectrometry. We applied a 96-well high-throughput format using a Phenomenex Phree plate to analyze plasma and serum. Compounds were separated by using a Waters ACQUITY UPLC BEH C18 column with a reverse-phase gradient. The limits of detection for the metabolites and vitamin E compounds were 8-330 pg/mL. To validate the method, intra-day and inter-day accuracy and precision were evaluated along with limits of detection and quantification. The method was then applied to determine concentrations of these analytes in plasma and serum of horses. Alpha-TP levels were 3-6 µg/mL of matrix; the metabolites were found at much lower levels, 0.2-1.0 ng/mL of matrix.

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.

Antioxidant action of vitamin E in vivo as assessed from its reaction products with multiple biological oxidants

Vitamin E acts as essential antioxidant against detrimental oxidation of biological molecules induced by multiple reactive species. To gain more insight into the physiological role of vitamin E, the levels of its oxidation products in humans under normal and pathological conditions were compared. α-Tocopherol quinone (α-TQ) and 5-nitro-γ-tocopherol (5-NgT) were focused. α-TQ is produced by multiple oxidants including oxygen radicals, peroxynitrite, hypochlorite, singlet oxygen, and ozone, while 5-NgT is produced by nitrogen dioxide radical derived from peroxynitrite and the reaction of nitrite and hypochlorite. The reported concentrations of α-TQ and 5-NgT in healthy human plasma are highly variable ranging from 15 to 360 and 4 to 170 nM, respectively. In general, the molar ratio 5-NgT/γ-tocopherol was higher than the ratio α-TQ/α-tocopherol. Both absolute concentrations of α-TQ and 5-NgT and the molar ratios to the parent tocopherols were elevated significantly in the plasma of patients with various diseases compared with healthy subjects except neurological diseases. The molar ratios of the products to the respective parent compounds decreased in the order of 5-NgT/γ-tocopherol > α-TQ/α-tocopherol > hydroxyoctadecadienoate/linoleate > 3-nitrotyrosine/tyrosine > isoprostane/arachidonate. The molar ratios of nitrated products to the respective parent compounds in human plasma are approximately 10^-2 for 5-NgT and 10^-5 for 3-nitrotyrosine, nitro-oleic acid, and 8-nitroguaine. These data indicate that vitamin E acts as an important physiological antioxidant and that α-TQ and 5-NgT represent biomarker for oxidative stress and nitrative stress respectively.

Metabolism and biological activity of α-tocopherol derived from vitamin E-enriched transgenic maize in broilers

BACKGROUND

The aim of this study was to investigate the metabolism of α-tocopherol derived from vitamin E-enriched transgenic maize (VER) and its effects on antioxidant and immune functions in broilers aged 1-42 days. A total of 360 1-day-old male broilers were randomly divided into three groups containing six replicates with 20 broilers per replicate. The negative control (NC) group and the positive control (PC) group were given non-GM maize and non-GM maize plus exogenous vitamin E (VE), respectively, and the VER group was given VER, replacing the non-GM maize given to the NC group. Between days 1 and 21 and days 22 and 42, VE levels were 4.38 and 4.63 mg kg^-1 in the NC group, and 14.11 and 14.91 mg kg^-1 in the PC and VER group, respectively.

RESULTS

The results showed that α-tocopherol from both VER and additives increased α-tocopherol transfer protein and cytochrome P450 concentrations. Serum α-tocopherol and α-tocopherylquinone levels of broilers in the PC and VER groups were also significantly higher than those in the NC group (P < 0.05). Compared with the NC group, broilers in both groups that received α-tocopherol had reduced NF-κB p65 concentrations, significantly decreased serum prostaglandin E₂ , interleukin-6, malondialdehyde, and hydrogen peroxide levels (P < 0.05), and significantly increased glutathione, glutathione peroxidase, and total antioxidant capacity (P < 0.05).

CONCLUSION

In summary, both VER and non-GM maize fortified with exogenous VE showed similar effects on broilers, indicating that the α-tocopherol in VER has sufficient biological activity. © 2020 Society of Chemical Industry.

Serum level and clinical significance of vitamin E in children with allergic rhinitis

BACKGROUND

Allergic rhinitis (AR) is one of the most prevalent allergic diseases in children. This study aimed to investigate the association between serum concentrations of vitamin E and AR to determine if the vitamin E level is correlated with the occurrence and severity of AR.

METHODS

A total of 113 children were enrolled in this cross-sectional study. Sixty-five children in the outpatient group were diagnosed with AR, and 48 healthy children were recruited as controls. All subjects underwent serum vitamin E (adjusted for total cholesterol and triglycerides) measurements. Serum to total IgE (tIgE), the five most common allergen-specific IgE (sIgE) levels and skin prick test (SPT) were measured in children with AR. The severity of AR was assessed with the nasal symptoms score, and the situation of exposure to passive smoking were inquired.

RESULTS

Serum vitamin E levels were significantly lower in the AR group than in the normal children (P < 0.001). A significant negative correlation was observed between serum vitamin E levels and sIgE as well as the SPT grade. Serum vitamin E levels were also inversely related to the nasal symptoms score; however, statistical significance was not found.

CONCLUSIONS

A significantly lower vitamin E level was found in children with AR. Lower serum vitamin E levels may have correlation with the occurrence of AR in children. However, serum vitamin E levels were not statistically correlated with the severity of AR.

Roles of vitamins in stem cells

Stem cells can differentiate to diverse cell types in our body, and they hold great promises in both basic research and clinical therapies. For specific stem cell types, distinctive nutritional and signaling components are required to maintain the proliferation capacity and differentiation potential in cell culture. Various vitamins play essential roles in stem cell culture to modulate cell survival, proliferation and differentiation. Besides their common nutritional functions, specific vitamins are recently shown to modulate signal transduction and epigenetics. In this article, we will first review classical vitamin functions in both somatic and stem cell cultures. We will then focus on how stem cells could be modulated by vitamins beyond their nutritional roles. We believe that a better understanding of vitamin functions will significantly benefit stem cell research, and help realize their potentials in regenerative medicine.

PTML Model of ChEMBL Compounds Assays for Vitamin Derivatives

Determining the biological activity of vitamin derivatives is needed given that organic synthesis of analogs of vitamins is an active field of interest for medicinal chemistry, pharmaceuticals, and food additives. Accordingly, scientists from different disciplines perform preclinical assays (n_ij) with a considerable combination of assay conditions (c_j). Indeed, the ChEMBL platform contains a database that includes results from 36 220 different biological activity bioassays of 21 240 different vitamins and vitamin derivatives. These assays present are heterogeneous in terms of assay combinations of c_j. They are focused on >500 different biological activity parameters (c₀), >340 different targets (c₁), >6200 types of cell (c₂), >120 organisms of assay (c₃), and >60 assay strains (c₄). It includes a total of >1850 niacin assays, >1580 tretinoin assays, >1580 retinol assays, 857 ascorbic acid assays, etc. Given the complexity of this combinatorial data in terms of being assimilated by researchers, we propose to build a model by combining perturbation theory (PT) and machine learning (ML). Through this study, we propose a PTML (PT + ML) combinatorial model for ChEMBL results on biological activity of vitamins and vitamins derivatives. The linear discriminant analysis (LDA) model presented the following results for training subset a: specificity (%) = 90.38, sensitivity (%) = 87.51, and accuracy (%) = 89.89. The model showed the following results for the external validation subset: specificity (%) = 90.58, sensitivity (%) = 87.72, and accuracy (%) = 90.09. Different types of linear and nonlinear PTML models, such as logistic regression (LR), classification tree (CT), näive Bayes (NB), and random Forest (RF), were applied to contrast the capacity of prediction. The PTML-LDA model predicts with more accuracy by applying combinatorial descriptors. In addition, a PCA experiment with chemical structure descriptors allowed us to characterize the high structural diversity of the chemical space studied. In any case, PTML models using chemical structure descriptors do not improve the performance of the PTML-LDA model based on ALOGP and PSA. We can conclude that the three variable PTML-LDA model is a simplified and adaptable tool for the prediction, for different experiment combinations, the biological activity of derivative vitamins.

Identification of α-Tocopherol and Its Oxidation Products by Ultra-Performance Liquid Chromatography Coupled with Quadrupole Time-of-Flight Mass Spectrometry

This study aimed to determine α-tocopherol (α-T) and its thermal oxidation products simultaneously. A novel method based on an ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) was developed. This approach was achieved by means of a BEH C18 analytical column under gradient elution conditions with eluents of acetonitrile/isopropanol (1:9, v/v) and acetonitrile/water (4:6, v/v). Compounds were elucidated through exact molecular mass and fragmentation ions obtained from the Q-TOF-MS detector. Two oxidation products, α-tocopheryl quinone and 5-formyl-γ-tocopherol, were identified, and one new compound was determined. This approach offered a simple, precise, and reliable method to determine oxidation products of α-T, which may give a way to understand the mechanism of the thermal oxidative process of α-T.

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.

Machine Learning as a Proposal for a Better Application of Food Nanotechnology Regulation in the European Union

AIMS

Given the current gaps of scientific knowledge and the need of efficient application of food law, this paper makes an analysis of principles of European food law for the appropriateness of applying biological activity Machine Learning prediction models to guarantee public safety.

BACKGROUND

Cheminformatic methods are able to design and create predictive models with high rate of accuracy saving time, costs and animal sacrifice. It has been applied on different disciplines including nanotechnology.

OBJECTIVE

Given the current gaps of scientific knowledge and the need of efficient application of food law, this paper makes an analysis of principles of European food law for the appropriateness of applying biological activity Machine Learning prediction models to guarantee public safety.

METHODS

A systematic study of the regulation and the incorporation of predictive models of biological activity of nanomaterials was carried out through the analysis of the express nanotechnology regulation on foods, applicable in European Union.

RESULTS

It is concluded Machine Learning could improve the application of nanotechnology food regulation, especially methods such as Perturbation Theory Machine Learning (PTML), given that it is aligned with principles promoted by the standards of Organization for Economic Co-operation and Development, European Union regulations and European Food Safety Authority.

CONCLUSION

To our best knowledge this is the first study focused on nanotechnology food regulation and it can help to support technical European Food Safety Authority Opinions for complementary information.

Effects of antibiotics on degradation and bioavailability of different vitamin E forms in mice

Tocopherols (T) and tocotrienols (T3), all existing in α, β, γ, and δ-forms, are the eight forms of vitamin E (VE). In this study, we investigated the effects of gut microbiota on the degradation and tissue levels of different VE forms by treating mice with antibiotics in drinking water for 12 days. The mice also received an intragastric (i.g.) dose of VE mixture (mVE; α-T, γ-T, δ-T, γ-T3, and δ-T3, each at a dose of 75 mg/kg) every morning. Antibiotic treatment significantly increased the blood levels of all VE forms in mice that received an i.g. dose of mVE in the morning, 3 h before sacrifice. Without this morning dose, the blood levels of α-T were at the normal physiological levels, but those of the other VE forms were much lower; and the levels of all VE forms were not significantly affected by antibiotics. The liver levels of these VE forms were generally higher and followed the same pattern as the serum. On the contrary, the levels of most side-chain degradation metabolites of VE forms in the serum, liver, kidney, urine, and fecal samples were significantly decreased by antibiotics. The increased bioavailability of VE by antibiotics is probably due to increased absorption of VE or its decreased degradation by gut microbes. The results demonstrate the important roles of gut microbiota in the degradation of VE and in decreasing the bioavailabilities of VE forms. © 2019 BioFactors, 45(3):450-462, 2019.

Nutritional and lipidomics biomarkers of docosahexaenoic acid-based multivitamin therapy in pediatric NASH

Two recent randomized controlled trials demonstrated improved radiographic, histological and hepatometabolic cues of non-alcoholic steatohepatitis (NASH) in pediatric patients treated with the ω-3 fatty acid docosahexaenoic acid (DHA) in combination with vitamin D (VD) or with choline (CHO) and vitamin E (VE), the DHA-VD and DHA-CHO-VE trials, respectively). In the present study we verified the nutritional compliance to these DHA-based multivitamin treatments; lipidomics biomarkers of the reported outcome on NASH indicators were also investigated. Samples were obtained from 30 biopsy-proven pediatric NASH patients of the DHA-CHO-VE trial randomized in multivitamin treatment group and placebo group (n = 15 each), and from 12 patients of the treatment group of the DHA-VD trial. All patients underwent 6-month therapy plus 6 months of follow-up. Plasma samples and clinical data were obtained at baseline and at the end of the study (12 months). Selected biomarkers included the free form of DHA and other ω-3 fatty acid arachidonic acid (AA), indices of the vitamin E status, and some hepatic metabolites of these lipids. Radiographic and histological improvements of treated patients were associated with increased concentrations of DHA, α-linolenic acid and α-tocopherol (i.e. VE), and with decreased AA that was also investigated in complex lipids by untargetd lipidomics. As a result a significantly lowered AA/DHA ratio was observed to represent the main indicator of the response to the DHA-based therapy. Furthermore, baseline levels of AA/DHA showed strong association with NAS and US improvement. A stable correction of DHA AA metabolism interaction is associated with the curative effect of this therapy and may represent a key nutritional endpoint in the clinical management of pediatric NASH.

Increased plasma levels of the lipoperoxyl radical-derived vitamin E metabolite α-tocopheryl quinone are an early indicator of lipotoxicity in fatty liver subjects

Lipid peroxidation is one of the earliest pathogenic events of non-alcoholic fatty liver disease (NAFLD). In this context, an increased oxidation of the lipoperoxyl radical scavenger α-tocopherol (α-TOH) should occur already in the subclinical phases of the disease to compensate for the increase oxidation of the lipid excess of liver and possibly of other tissues. However, this assumption remains unsupported by direct analytical evidence. In this study, GC-MS/MS and LC-MS/MS procedures have been developed and applied for the first time to measure the vitamin E oxidation metabolite α-tocopheryl quinone (α-TQ) in plasma of fatty liver (FL) subjects that were compared in a pilot cross-sectional study with healthy controls. The protein adducts of 4-hydroxynonenal (4-HNE) and the free form of polyunsaturated free fatty acids (PUFA) were measured as surrogate indicators of lipid peroxidation. α-TQ formation was also investigated in human liver cells after supplementation with α-TOH and/or fatty acids (to induce steatosis). Compared with controls, FL subjects showed increased (absolute and α-TOH-corrected) levels of plasma α-TQ and 4-HNE, and decreased concentrations of PUFA. α-TQ levels positively correlated with indices of liver damage and metabolic dysfunction, such as alanine aminotransferase, bilirubin and triglycerides, and negatively correlated with HDL cholesterol. Fatty acid supplementation in human hepatocytes stimulated the generation of cellular oxidants and α-TOH uptake leading to increased α-TQ formation and secretion in the extracellular medium - both were markedly stimulated by α-TOH supplementation. In conclusion, plasma α-TQ represents an early biomarker of the lipoperoxyl radical-induced oxidation of vitamin E and lipotoxicity of the fatty liver.

Excitotoxicity, neuroinflammation and oxidant stress as molecular bases of epileptogenesis and epilepsy-derived neurodegeneration: The role of vitamin E

Glutamate-mediated excitotoxicity, neuroinflammation, and oxidative stress are common underlying events in neurodegeneration. This pathogenic "triad" characterizes the neurobiology of epilepsy, leading to seizure-induced cell death, increased susceptibility to neuronal synchronization and network alterations. Along with other maladaptive changes, these events pave the way to spontaneous recurrent seizures and progressive degeneration of the interested brain areas. In vivo models of epilepsy are available to explore such epileptogenic mechanisms, also assessing the efficacy of chemoprevention and therapy strategies at the pre-clinical level. The kainic acid model of pharmacological excitotoxicity and epileptogenesis is one of the most investigated mimicking the chronicization profile of temporal lobe epilepsy in humans. Its pathogenic cues include inflammatory and neuronal death pathway activation, mitochondrial disturbances and lipid peroxidation of several regions of the brain, the most vulnerable being the hippocampus. The importance of neuroinflammation and lipid peroxidation as underlying molecular events of brain damage was demonstrated in this model by the possibility to counteract the related maladaptive morphological and functional changes of this organ with vitamin E, the main fat-soluble cellular antioxidant and "conditional" co-factor of enzymatic pathways involved in polyunsaturated lipid metabolism and inflammatory signaling. The present review paper provides an overview of the literature supporting the potential for a timely intervention with vitamin E therapy in clinical management of seizures and epileptogenic processes associated with excitotoxicity, neuroinflammation and lipid peroxidation, i.e. the pathogenic "triad".

Vitamin E: Regulatory role of metabolites

Vitamin E plays an important role as a lipophilic antioxidant in cellular redox homeostasis. Besides this function, numerous non-antioxidant properties of this vitamin have been discovered in the past. DNA microarray technology revealed a complex regulatory network influenced by the different vitamin E forms (Rimbach et al., Molecules, 15, 1746 (2010); Galli et al., Free Radic. Biol. Med., 102, 16 (2017)); however, little is known about the biological activity of vitamin E metabolites. A new chapter of vitamin E research was been opened when endogenous long-chain tocopherol metabolites were identified and their high biological activity in vitro and in vivo was recognized (Schmölz et al., World J. Biol. Chem., 7, 14 (2016); Torquato et al., J. Pharm. Biomed. Anal., 124, 399 (2016)). Just recently, it was shown that an endogenous metabolite of vitamin E inhibits 5-lipoxygenase at nanomolar concentrations, thereby limiting inflammation (Pein et al., Nat. Commun., 9, 3834 (2018)). Furthermore, long-chain vitamin E metabolites (LCM) exhibit hormone-like activities similar to the lipid soluble vitamins A and D (Galli et al., Free Radic. Biol. Med., 102, 16 (2017); Schubert et al., Antioxidants, 7 (2018)). This review aims at summarizing recent findings on the regulatory activities of vitamin E metabolites, especially of LCMs. © 2018 IUBMB Life, 71(4):479-486, 2019.

Vitamin E - The Next 100 Years

α-Tocopherol is the only tocopherol that has been shown to prevent the human deficiency disease Ataxia with Isolated Vitamin E Deficiency (AVED), and thus it is the only one that, for humans, can be called vitamin E. Vitamin E in addition to preventing AVED has documented immune boosting properties and an activity against nonalcoholic hepatosteatosis and low-grade inflammation. Epidemiological studies indicating that vitamin E could prevent cardiovascular events, neurodegenerative disease, macular degeneration, and cancer were in general not confirmed by clinical intervention studies. Vitamin E and some of its metabolites modulate cell signaling and gene transcription. Future research is needed to achieve a better understanding of the molecular events leading to gene regulation by vitamin E, especially in its phosphorylated form. Isolation and characterization of the vitamin E kinase and vitamin E phosphate phosphatase will help in the understanding of cell regulation processes modulated by vitamin E. A clarification of the pathogenesis of AVED remains an important goal to be achieved. © 2018 IUBMB Life, 71(4):411-415, 2019.

A Metabolomic Serum Signature from Nonhuman Primates Treated with a Radiation Countermeasure, Gamma-tocotrienol, and Exposed to Ionizing Radiation

The search for and development of radiation countermeasures to treat acute lethal radiation injury has been underway for the past six decades, resulting in the identification of multiple classes of radiation countermeasures. However, to date only granulocyte colony-stimulating factor (Neupogen) and PEGylated granulocyte colony-stimulating factor (Neulasta) have been approved by the U.S. Food and Drug Administration for the treatment of hematopoietic acute radiation syndrome. Gamma-tocotrienol has demonstrated radioprotective efficacy in murine and nonhuman primate models. Currently, this agent is under advanced development as a radioprotector, and the authors are trying to identify its efficacy biomarkers. In this study, global metabolomic changes were analyzed using ultraperformance liquid chromatography quadrupole time-of-flight mass spectrometry. The pilot study using 16 nonhuman primates (8 nonhuman primates each in gamma-tocotrienol- and vehicle-treated groups), with samples obtained from gamma-tocotrienol-treated and irradiated nonhuman primates, demonstrates several metabolites that are altered after irradiation, including compounds involved in fatty acid beta-oxidation, purine catabolism, and amino acid metabolism. The machine-learning algorithm, Random Forest, separated control, irradiated gamma-tocotrienol-treated, and irradiated vehicle-treated nonhuman primates at 12 h and 24 h as evident in a multidimensional scaling plot. Primary metabolites validated included carnitine/acylcarnitines, amino acids, creatine, and xanthine. Overall, gamma-tocotrienol administration reduced high fluctuations in serum metabolite levels, suggesting an overall beneficial effect on animals exposed to radiation. This initial assessment also highlights the utility of metabolomics in determining underlying physiological mechanisms responsible for the radioprotective efficacy of gamma-tocotrienol.

Ionization of tocopherols and tocotrienols in atmospheric pressure chemical ionization

RATIONALE

Tocopherols and tocotrienols are chemical compounds insusceptible to the ionization process under atmospheric pressure conditions. Therefore, the selection of the optimal ion source settings for their quantification requires special attention. The aim of this study was to analyse the influence of the APCI source parameters on the response of tocochromanols and two related compounds.

METHODS

Standard solutions of target compounds were injected on the high-performance liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry (HPLC/APCI-MS/MS) system separately and analysed with 30 randomly selected ion source settings. The obtained responses were modelled by multivariate linear regression with least absolute shrinkage and selection operator. The developed models were used to choose the best APCI conditions.

RESULTS

Multivariate linear models were built for eight tocochromanols, trolox and BHT. The APCI settings derived from the models did not increase the peak areas obtained for T and T3 during the ionization process. Ionization conditions based on models for trolox and BHT improved analytical responses by 12-36% and 4-32%, respectively. The application of the ion source settings optimal for trolox and BHT to tocochromanols did not result in better analytical responses.

CONCLUSIONS

The ionization pattern of tocochromanols in the APCI source is problematic and should be further investigated. Modelling methodology for response improvement presented in this study can be applied in similar studies.

Long-Chain Metabolites of Vitamin E: Metabolic Activation as a General Concept for Lipid-Soluble Vitamins?

Vitamins E, A, D and K comprise the class of lipid-soluble vitamins. For vitamins A and D, a metabolic conversion of precursors to active metabolites has already been described. During the metabolism of vitamin E, the long-chain metabolites (LCMs) 13'-hydroxychromanol (13'-OH) and 13'-carboxychromanol (13'-COOH) are formed by oxidative modification of the side-chain. The occurrence of these metabolites in human serum indicates a physiological relevance. Indeed, effects of the LCMs on lipid metabolism, apoptosis, proliferation and inflammatory actions as well as tocopherol and xenobiotic metabolism have been shown. Interestingly, there are several parallels between the actions of the LCMs of vitamin E and the active metabolites of vitamin A and D. The recent findings that the LCMs exert effects different from that of their precursors support their putative role as regulatory metabolites. Hence, it could be proposed that the mode of action of the LCMs might be mediated by a mechanism similar to vitamin A and D metabolites. If the physiological relevance and this concept of action of the LCMs can be confirmed, a general concept of activation of lipid-soluble vitamins via their metabolites might be deduced.

Nonalcoholic fatty liver disease impairs the cytochrome P-450-dependent metabolism of α-tocopherol (vitamin E)

This study aims to investigate in in vivo and in vitro models of nonalcoholic fatty liver disease (NAFLD) the enzymatic metabolism of α-tocopherol (vitamin E) and its relationship to vitamin E-responsive genes with key role in the lipid metabolism and detoxification of the liver. The experimental models included mice fed a high-fat diet combined or not with fructose (HFD+F) and HepG2 human hepatocarcinoma cells treated with the lipogenic agents palmitate, oleate or fructose. CYP4F2 protein, a cytochrome P-450 isoform with proposed α-tocopherol ω-hydroxylase activity, decreased in HFD and even more in HFD+F mice liver; this finding was associated with increased hepatic levels of α-tocopherol and decreased formation of the corresponding long-chain metabolites α-13-hydroxy and α-13-carboxy chromanols. A decreased expression was also observed for PPAR-γ and SREBP-1 proteins, two vitamin E-responsive genes with key role in lipid metabolism and CYP4F2 gene regulation. A transient activation of CYP4F2 gene followed by a repression response was observed in HepG2 cells during the exposure to increasing levels of the lipogenic and cytotoxic agent palmitic acid; such gene repression effect was further exacerbated by the co-treatment with oleic acid and α-tocopherol and was also observed for PPAR-γ and the SREBP isoforms 1 and 2. Such gene response was associated with increased uptake and ω-hydroxylation of α-tocopherol, which suggests a minor role of CYP4F2 in the enzymatic metabolism of vitamin E in HepG2 cells. In conclusion, the liver metabolism and gene response of α-tocopherol are impaired in experimental NAFLD.

Semi-preparative HPLC purification of δ-tocotrienol (δ-T3) from Elaeis guineensis Jacq. and Bixa orellana L. and evaluation of its in vitro anticancer activity in human A375 melanoma cells

In this work, we report a rapid and convenient HPLC-UV-DAD method for the isolation of δ-T3 on semi-preparative scale from two different vitamin E rich processed, commercially available products obtained from the fruits of Elaeis guineensis Jacq. (oil palm) and from the seeds of Bixa orellana L. (achiote tree). Chromatography was run using reverse phase (RP) C-18 columns and HPLC-grade acetonitrile as mobile phase. The purity of the isolated δ-T3, assessed by GC-MS and ¹H NMR was above 98%. The δ-T3 cytotoxic activity found in vitro against the proliferation of human A375 melanoma cells compared to that of the other δ-T3 free tocols mixture suggest its primary role in the experimental anticancer activity observed for palm oil derived products. Taken altogether, the results of this study highlight the importance of the application of suitable purification systems for the preparations of tocotrienols prior to their experimental or clinical testing.

Determination of tocopherols and their metabolites by liquid-chromatography coupled with tandem mass spectrometry in human plasma and serum

Several studies are increasingly underlying the biological role of vitamin E metabolites as bioactive compounds with anti-inflammatory, anti-proliferative and anti-atherogenic activity. A quantitative method for the simultaneous determination in human plasma and serum of vitamin E (α-tocopherol, α-T and γ-tocopherol, γ-T) and its cytochrome P-450 metabolites: 13'-hydroxychromanol (α-13'-OH), 13'-carboxychromanol (α-13'-COOH) and carboxyethyl hydroxychromanols (α-CEHC and γ-CEHC), was developed and validated. After enzymatic hydrolysis and deproteinization, the metabolites were extracted with a mixture of hexane/ methyl tertiary butyl ether (2/1, v/v). The separation was achieved by reversed phase chromatography and the analytes detected by a triple quadrupole mass analyser using electrospray ionization in positive mode (LC-MS/MS). α-T and γ-T were extracted separately without enzymatic hydrolysis. The analytes were quantified with the isotopic dilution method. After an extensive validation study (three levels in three different occasions for a total of 54 experiments), the procedure was successfully applied to the analysis of sera of healthy volunteers (before and after supplementation with α-T) and plasma of patients affected by chronic kidney disease. Finally, the structures of three unknown compounds found in blood and related to the long chain metabolites (α-13'-OH and α-13'-COOH) were further investigated using liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS).

Nutrigenomics of extra-virgin olive oil: A review

Nutrigenomics data on the functional components of olive oil are still sparse, but rapidly increasing. Olive oil is the main source of fat and health-promoting component of the Mediterranean diet. Positive effects have been observed on genes involved in the pathobiology of most prevalent age- and lifestyle-related human conditions, such as cancer, cardiovascular disease and neurodegeneration. Other effects on health-promoting genes have been identified for bioactive components of olives and olive leafs. Omics technologies are offering unique opportunities to identify nutritional and health biomarkers associated with these gene responses, the use of which in personalized and even predictive protocols of investigation, is a main breakthrough in modern medicine and nutrition. Gene regulation properties of the functional components of olive oil, such as oleic acid, biophenols and vitamin E, point to a role for these molecules as natural homeostatic and even hormetic factors with applications as prevention agents in conditions of premature and pathologic aging. Therapeutic applications can be foreseen in conditions of chronic inflammation, and particularly in cancer, which will be discussed in detail in this review paper as major clinical target of nutritional interventions with olive oil and its functional components. © 2016 BioFactors, 43(1):17-41, 2017.

Vitamin E: Emerging aspects and new directions

The discovery of vitamin E will have its 100th anniversary in 2022, but we still have more questions than answers regarding the biological functions and the essentiality of vitamin E for human health. Discovered as a factor essential for rat fertility and soon after characterized for its properties of fat-soluble antioxidant, vitamin E was identified to have signaling and gene regulation effects in the 1980s. In the same years the cytochrome P-450 dependent metabolism of vitamin E was characterized and a first series of studies on short-chain carboxyethyl metabolites in the 1990s paved the way to the hypothesis of a biological role for this metabolism alternative to vitamin E catabolism. In the last decade other physiological metabolites of vitamin E have been identified, such as α-tocopheryl phosphate and the long-chain metabolites formed by the ω-hydroxylase activity of cytochrome P-450. Recent findings are consistent with gene regulation and homeostatic roles of these metabolites in different experimental models, such as inflammatory, neuronal and hepatic cells, and in vivo in animal models of acute inflammation. Molecular mechanisms underlying these responses are under investigation in several laboratories and side-glances to research on other fat soluble vitamins may help to move faster in this direction. Other emerging aspects presented in this review paper include novel insights on the mechanisms of reduction of the cardiovascular risk, immunomodulation and antiallergic effects, neuroprotection properties in models of glutamate excitotoxicity and spino-cerebellar damage, hepatoprotection and prevention of liver toxicity by different causes and even therapeutic applications in non-alcoholic steatohepatitis. We here discuss these topics with the aim of stimulating the interest of the scientific community and further research activities that may help to celebrate this anniversary of vitamin E with an in-depth knowledge of its action as vitamin.