Vitamin E Biotransformation in Humans

Evaluation of Food Intake Biomarkers for Red Bell Peppers in Human Urine Based on HPLC-MS/MS Analysis

SCOPE

The validation of dietary biomarkers is essential for the use in objective and quantitative assessment of the human dietary intake. In this study, the urinary excretion of previously identified potential biomarkers after intake of red bell peppers is analyzed.

METHODS AND RESULTS

The urine samples obtained after a two-phase dietary intervention study in which 14 volunteers participated are quantitatively analyzed by high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS) after an extensive validation. In the first phase, the volunteers abstain completely from bell peppers and paprika products (control group) and in the second phase, the volunteers consume a defined amount of fresh red bell peppers (case group). After analysis, all potential biomarkers show high dispersions of their concentration, indicating interindividual differences. The glucuronidated apocarotenoid (compound 1), which probably resulted from the main carotenoids of red Capsicum fruits, shows a rapid urinary excretion. The other glucuronidated metabolites (compounds 2-8), described as potential derivatives of capsianosides from Capsicum, show a slightly delayed but longer urinary excretion.

CONCLUSIONS

A correlation between an intake of red bell pepper and the urinary excretion of recently described potential biomarkers is observed. Due to large interindividual differences, it is reasonable to assume that at least the qualitative detection of the consumption of bell peppers and possibly all Capsicum fruits is feasible.

Effect of γ-tocopherol supplementation on premenstrual symptoms and natriuresis: a randomized, double-blind, placebo-controlled study

BACKGROUND

This randomized, double-blind, placebo-controlled study aimed to investigate the effects of γ-tocopherol (Toc) supplementation on premenstrual symptoms and natriuresis.

METHODS

We enrolled 51 Japanese women with premenstrual symptoms, particularly those who showed increased symptoms induced by water retention during the luteal phase compared with the follicular phase. Premenstrual symptoms were recorded in the first cycle's postmenstrual follicular phase; physical measurements and urine collection were conducted during the 48-h run-in period. The test supplement, which contained 180 mg of γ-Toc or placebo, was orally administered twice a day for 7 days during the luteal phase of the first and second cycles in a crossover manner. The same evaluation was conducted during the luteal phase, beginning in the morning of the sixth day of supplement administration.

RESULTS

Compared with placebo intake, γ-Toc intake significantly reduced "fatigue" and "irritability/anger" symptoms. Furthermore, compared with placebo intake, γ-Toc intake significantly reduced the thigh circumference. Regarding the "swelling of the legs" and "heavy legs" symptoms and the thigh circumference, the biphasic trend of increasing and decreasing values in the daytime and morning, respectively, during the follicular phase was not observed at the luteal phase with placebo intake. Contrastingly, γ-Toc intake resulted in significantly lower values in the morning than placebo intake. The mean difference in 24-h urinary sodium excretion between γ-Toc and placebo intake was 10.6 mEq (95% confidence interval (CI): -0.1, 21.4, p = 0.05, power 55%). Plasma γ-Toc and its metabolite γ-carboxyethyl hydroxychroman (CEHC) levels were significantly higher with γ-Toc intake than with placebo intake. There were no significant between-supplement differences in serum electrolyte levels or cumulative urinary potassium excretion.

CONCLUSION

γ-Toc intake could effectively alleviate certain premenstrual syndrome symptoms, particularly those related to water retention during the luteal phase. Furthermore, the underlying mechanism may involve the diuretic effect of γ-CEHC, which is a γ-Toc metabolite.

TRIAL REGISTRATION

UMIN000047989; registration date: 10/06/2022, retrospectively registered.

The implications of Vitamin E acetate in E-cigarette, or vaping, product use-associated lung injury

In the summer of 2019, a cluster of cases were observed with users of battery-operated or superheating devices presenting with multiple symptoms, such as dyspnea, cough, fever, constitutional symptoms, gastrointestinal upset, and hemoptysis, that is now termed e-cigarette, or vaping, product use-associated lung injury (EVALI). The Centers for Disease Control and Prevention reported 2807 cases within the USA leading to at least 68 deaths as of February 18, 2020. The heterogeneous presentations of EVALI make diagnosis and treatment difficult; however, treatment focused on identifying and removal of the noxious substance and providing supportive care. Vitamin E acetate (VEA) is a likely cause of this lung injury, and others have reported other components to play a possible role, such as nicotine and vegetable glycerin/propylene glycol. EVALI is usually observed in adolescents, with a history of vaping product usage within 90 days typically containing tetrahydrocannabinol, and presenting on chest radiograph with pulmonary infiltrates or computed tomography scan with ground-glass opacities. Diagnosis requires a high degree of suspicion to diagnose and exclusion of other possible causes of lung disease. Here, we review the current literature to detail the major factors contributing to EVALI and primarily discuss the potential role of VEA in EVALI. We will also briefly discuss other constituents other than just VEA, as a small number of EVALI cases are reported without the detection of VEA, but with the same clinical diagnosis.

Low Serum Vitamin D Status Is Associated with Incident Alzheimer's Dementia in the Oldest Old

Background. Vitamins A, D and E and beta-carotene may have a protective function for cognitive health, due to their antioxidant capacities. Methods. We analyzed data from 1334 non-demented participants (mean age 84 years) from the AgeCoDe study, a prospective multicenter-cohort of elderly general-practitioner patients in Germany, of whom n = 250 developed all-cause dementia and n = 209 developed Alzheimer’s dementia (AD) during 7 years of follow-up. We examined whether concentrations of vitamins A (retinol), D (25-hydroxycholecalciferol) and E (alpha-tocopherol) and beta-carotene, would be associated with incident (AD) dementia. Results. In our sample, 33.7% had optimum vitamin D concentrations (≥50 nmol/L). Higher concentrations of vitamin D were associated with lower incidence of all-cause dementia and AD (HR 0.99 (95%CI 0.98; 0.99); HR0.99 (95%CI 0.98; 0.99), respectively). In particular, subjects with vitamin D deficiency (25.3%, <25 nmol/L) were at increased risk for all-cause dementia and AD (HR1.91 (95%CI 1.30; 2.81); HR2.28 (95%CI 1.47; 3.53), respectively). Vitamins A and E and beta-carotene were unrelated to (AD) dementia. Conclusions. Vitamin D deficiency increased the risk to develop (AD) dementia. Our study supports the advice for monitoring vitamin D status in the elderly and vitamin D supplementation in those with vitamin D deficiency. We observed no relationships between the other vitamins with incident (AD) dementia, which is in line with previous observational studies.

Wheat germ oil vitamin E cytoprotective effect and its nutrigenomics signature in human hepatocyte lipotoxicity

Wheat germ oil (WGO) is rich in α-tocopherol (vitamin E, VE), a vitamin that has long been suggested to exert hepatoprotective effects. In this study, this function of WGO-VE and its transcriptomics fingerprint were investigated in comparison with RRR-α-tocopherol and all-rac-α-tocopherol (nVE and sVE, respectively), in human liver cells treated with oleic acid (OA) to develop steatosis and lipotoxicity. Used in chemoprevention mode, all the VE formulations afforded significant reduction of the OA-induced steatosis and its consequent impact on lipotoxicity indicators, including ROS production and efflux (as H₂O₂), and apoptotic and necrotic cell death. A trend toward a better control of lipotoxicity was observed for WGO-VE and nVE compared to sVE. Gene microarray data demonstrated that these effects of VE formulations were associated with significantly different responses of the cellular transcriptome to compensate for the modifications of OA treatment, including the downregulation of cellular homeostasis genes and the induction of genes associated with defects of liver cell metabolism, fibrosis and inflammation, liver disease and cancer. Ingenuity Pathway Analysis data showed that WGO-VE modulated genes associated with liver carcinogenesis and steatosis, whereas nVE modulated genes involved in liver cell metabolism and viability biofunctions; sVE did not significantly modulate any gene dataset relevant to such biofunctions. In conclusion, WGO-VE prevents lipotoxicity in human liver cells modulating genes that differ from those affected by the natural or synthetic forms of pure VE. These differences can be captured by precision nutrition tools, reflecting the molecular complexity of this VE-rich extract and its potential in preventing specific cues of hepatocellular lipotoxicity.

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.

A Dynamic Model for Estimating the Interaction of ROS–PUFA–Antioxidants in Rabbit

Defining optimal nutrition in animals and humans remains a main scientific challenge. The objective of the work was to develop a dynamic model of reactive oxygen species (ROS)–polyunsaturated fatty acid (PUFA)–antioxidant homeostasis using the rabbit as a model. The problem entity was to evaluate the main metabolites generated from interactions between traits included in the conceptual model and identified by three main sub–models: (i) ROS generation, (ii) PUFA oxidation and (iii) antioxidant defence. A mathematical model (VENSIM software) that consisted of molecular stocks (INPUTs, OUTPUTs), exchange flows (intermediate OUTPUTs) and process rates was developed. The calibration was performed by using standard experimental data (Experiment 1), whereas the validation was carried out in Experiments 2 and 3 by using supra–nutritional dietary inputs (VIT E+ and PUFA+). The accuracy of the models was measured using 95% confidence intervals. Analytical OUTPUTs (ROS, PUFA, Vit E, Ascorbic acid, Iso–/NeuroProstanes, Aldehydes) were well described by the standard model. There was also good accuracy for the VIT E+ scenario, whereas some compensatory rates (Kc1–Kc4) were added to assess body compensation when high levels of dietary PUFA were administered (Experiment 3). In conclusion, the model can be very useful for predicting the effects of dietary treatments on the redox homeostasis of rabbits.

Vitamin E in foodstuff: Nutritional, analytical, and food technology aspects

Vitamin E is a group of isoprenoid chromanols with different biological activities. It comprises eight oil-soluble compounds: four tocopherols, namely, α-, β-, γ-, and δ-tocopherols; and four tocotrienols, namely, α-, β-, γ, and δ-tocotrienols. Vitamin E isomers are well-known for their antioxidant activity, gene-regulation effects, and anti-inflammatory and nephroprotective properties. Considering that vitamin E is exclusively synthesized by photosynthetic organisms, animals can only acquire it through their diet. Plant-based food is the primary source of vitamin E; hence, oils, nuts, fruits, and vegetables with high contents of vitamin E are mostly consumed after processing, including industrial processes and home-cooking, which involve vitamin E profile and content alteration during their preparation. Accordingly, it is essential to identify the vitamin E content and profile in foodstuff to match daily intake requirements. This review summarizes recent advances in vitamin E chemistry, metabolism and metabolites, current knowledge on their contents and profiles in raw and processed plant foods, and finally, their modern developments in analytical methods.

Increased α-tocopherol metabolism in horses with equine neuroaxonal dystrophy

Background

Equine neuroaxonal dystrophy/equine degenerative myeloencephalopathy (eNAD/EDM) is an inherited neurodegenerative disorder associated with a vitamin E deficiency within the first year of life. Vitamin E consists of 8 isoforms metabolized by the CYP4F2 enzyme. No antemortem diagnostic test currently exists for eNAD/EDM.

Hypothesis/Objectives

Based on the association of α‐tocopherol deficiency with the development of eNAD/EDM, we hypothesized that the rate of α‐tocopherol, but not γ‐tocopherol or tocotrienol metabolism, would be increased in eNAD/EDM‐affected horses.

Animals

Vitamin E metabolism: Proof of concept (POC) study; eNAD/EDM‐affected (n = 5) and control (n = 6) horses. Validation study: eNAD/EDM‐affected Quarter Horses (QHs; n = 6), cervical vertebral compressive myelopathy affected (n = 6) horses and control (n = 29) horses. CYP4F2 expression and copy number: eNAD/EDM‐affected (n = 12) and age‐ and sex‐matched control (n = 11‐12) horses.

Methods

The rates of α‐tocopherol/tocotrienol and γ‐tocopherol/tocotrienol metabolism were assessed in equine serum (POC and validation) and urine (POC only) using liquid chromatography tandem mass spectrometry (LC‐MS/MS). Quantitative reverse‐transcriptase PCR (qRT‐PCR) and droplet digital (dd)‐PCR were used to assay expression and genomic copy number of a CYP4F2 equine ortholog.

Results

Metabolic rate of α‐tocopherol was increased in eNAD/EDM horses (POC,P < .0001; validation, P = .03), with no difference in the metabolic rate of γ‐tocopherol. Horses with eNAD/EDM had increased expression of the CYP4F2 equine orthologue (P = .02) but no differences in copy number.

Conclusions and Clinical Importance

Increased α‐tocopherol metabolism in eNAD/EDM‐affected QHs provides novel insight into alterations in vitamin E processing in eNAD/EDM and highlights the need for high‐dose supplementation to prevent the clinical phenotype in genetically susceptible horses.

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.

Vitamin E acetate as linactant in the pathophysiology of EVALI

The recent identification of Vitamin E acetate as one of the causal agents for the e-cigarette, or vaping, product use associated lung injury (EVALI) is a major milestone. In membrane biophysics, Vitamin E is a linactant and a potent modulator of lateral phase separation that effectively reduces the line tension at the two-dimensional phase boundaries and thereby exponentially increases the surface viscosity of the pulmonary surfactant. Disrupted dynamics of respiratory compression-expansion cycling may result in an extensive hypoxemia, leading to an acute respiratory distress entailing the formation of intraalveolar lipid-laden macrophages. Supplementation of pulmonary surfactants which retain moderate level of cholesterol and controlled hypothermia for patients are recommended when the hypothesis that the line-active property of the vitamin derivative drives the pathogenesis of EVALI holds.

Metabolic and functional interplay between gut microbiota and fat-soluble vitamins

Gut microbiota is a complex ecosystem seen as an extension of human genome. It represents a major metabolic interface of interaction with food components and xenobiotics in the gastrointestinal (GI) environment. In this context, the advent of modern bacterial genome sequencing technology has enabled the identification of dietary nutrients as key determinants of gut microbial ecosystem able to modulate the host-microbiome symbiotic relationship and its effects on human health. This article provides a literature review on functional and molecular interactions between a specific group of lipids and essential nutrients, e.g., fat-soluble vitamins (FSVs), and the gut microbiota. A two-way relationship appears to emerge from the available literature with important effects on human metabolism, nutrition, GI physiology and immune function. First, FSV directly or indirectly modify the microbial composition involving for example immune system-mediated and/or metabolic mechanisms of bacterial growth or inhibition. Second, the gut microbiota influences at different levels the synthesis, metabolism and transport of FSV including their bioactive metabolites that are either introduced with the diet or released in the gut via entero-hepatic circulation. A better understanding of these interactions, and of their impact on intestinal and metabolic homeostasis, will be pivotal to design new and more efficient strategies of disease prevention and therapy, and personalized nutrition.

Garcinoic Acid Is a Natural and Selective Agonist of Pregnane X Receptor

Pregnane X receptor (PXR) is a master xenobiotic-sensing transcription factor and a validated target for immune and inflammatory diseases. The identification of chemical probes to investigate the therapeutic relevance of the receptor is still highly desired. In fact, currently available PXR ligands are not highly selective and can exhibit toxicity and/or potential off-target effects. In this study, we have identified garcinoic acid as a selective and efficient PXR agonist. The properties of this natural molecule as a specific PXR agonist were demonstrated by the screening on a panel of nuclear receptors, the assessment of the physical and thermodynamic binding affinity, and the determination of the PXR-garcinoic acid complex crystal structure. Cytotoxicity, transcriptional, and functional properties were investigated in human liver cells, and compound activity and target engagement were confirmed in vivo in mouse liver and gut tissue. In conclusion, garcinoic acid is a selective natural agonist of PXR and a promising lead compound toward the development of new PXR-regulating modulators.

Lipidomic biomarkers and mechanisms of lipotoxicity in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) represents the most common form of chronic liver disease worldwide (about 25% of the general population) and 3-5% of patients develop non-alcoholic steatohepatitis (NASH), characterized by hepatocytes damage, inflammation and fibrosis, which increase the risk of developing liver failure, cirrhosis and hepatocellular carcinoma. The pathogenesis of NAFLD, particularly the mechanisms whereby a minority of patients develop a more severe phenotype, is still incompletely understood. In this review we examine the available literature on initial mechanisms of hepatocellular damage and inflammation, deriving from toxic effects of excess lipids. Accumulating data indicate that the total amount of triglycerides stored in the liver cells is not the main determinant of lipotoxicity and that specific lipid classes act as damaging agents. These lipotoxic species affect the cell behavior via multiple mechanisms, including activation of death receptors, endoplasmic reticulum stress, modification of mitochondrial function and oxidative stress. The gut microbiota, which provides signals through the intestine to the liver, is also reported to play a key role in lipotoxicity. Finally, we summarize the most recent lipidomic strategies utilized to explore the liver lipidome and its modifications in the course of NALFD. These include measures of lipid profiles in blood plasma and erythrocyte membranes that can surrogate to some extent lipid investigation in the liver.

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 hydroquinone is an endogenous regulator of ferroptosis via redox control of 15-lipoxygenase

Ferroptosis is a form of programmed cell death associated with inflammation, neurodegeneration, and ischemia. Vitamin E (alpha-tocopherol) has been reported to prevent ferroptosis, but the mechanism by which this occurs is controversial. To elucidate the biochemical mechanism of vitamin E activity, we systematically investigated the effects of its major vitamers and metabolites on lipid oxidation and ferroptosis in a striatal cell model. We found that a specific endogenous metabolite of vitamin E, alpha-tocopherol hydroquinone, was a dramatically more potent inhibitor of ferroptosis than its parent compound, and inhibits 15-lipoxygenase via reduction of the enzyme's non-heme iron from its active Fe3+ state to an inactive Fe2+ state. Furthermore, a non-metabolizable isosteric analog of vitamin E which retains antioxidant activity neither inhibited 15-lipoxygenase nor prevented ferroptosis. These results call into question the prevailing model that vitamin E acts predominantly as a non-specific lipophilic antioxidant. We propose that, similar to the other lipophilic vitamins A, D and K, vitamin E is instead a pro-vitamin, with its quinone/hydroquinone metabolites responsible for its anti-ferroptotic cytoprotective activity.

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.

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.

Human serum determination and in vitro anti-inflammatory activity of the vitamin E metabolite α-(13'-hydroxy)-6-hydroxychroman

Cytochrome P450-derived long-chain metabolites are gaining increasing interest as bioactive intermediates of vitamin E. In this study we first report on the HPLC-ECD and GC-MS analysis in human serum of the earliest metabolite of this vitamin, namely α-(13'-hydroxy)-6-hydroxychroman (α-13'-OH). The two chromatographic procedure are sensitive enough (LOQ of 10nM) to measure α-13'-OH after hexane extraction of 1 ml of sample obtained from healthy volunteers supplemented for 1-week with 1000 IU/d (671 mg/d) RRR-α-tocopherol. The observed concentrations ranged between 15 and 50 nM, with minor differences between fasting and 4-hr post-meal state. Baseline (non-supplemented state) levels of 7.2 ± 1.6 nM were observed extracting higher volumes of serum. Biological effects of α-13'-OH investigated for the first time in RAW264.7 murine macrophages involved transcriptional control of inflammatory cytokines, and transcriptional and functional regulation of COX2 and iNOS enzymes in response to lipopolysaccharides. In conclusion, here we present the first quantitative evaluation of serum α-13'-OH also providing early evidence of the anti-inflammatory potential of this metabolite that is worth of further investigation in the area of functional and nutraceutical implications of vitamin E metabolism.

Tocotrienamines and tocopheramines: reactions with radicals and metal ions

The antioxidant activity of vitamin E (VE) homologs α, γ and δ-tocotrienamines (4b-6b), never studied before, and α, γ and δ-tocopheramines (4a-7a) was investigated by means of different total antioxidant capacity (TAC) tests. In all the test model systems, compounds 4a-7a and 4b-6b showed similar or higher TAC values than the parental vitamin E forms and their physiological metabolites. α-Homologs of VE amines showed markedly higher activity than the VE congeners in the TEAC test, which is tailored for liposoluble antioxidants, while γ-homologs of the amine analogs showed higher activity in the FRAP tests. Kinetics analysis of the reaction with DPPH(·) showed higher second order rate k for 4a than for α-tocopherol (1a). α-Tocopherolquinone 1f was the common main oxidation product for both 1a and α-tocopheramine (4a) exposed to ferric ions or DPPH(·), and the implied oxidative deamination of 4a was accompanied by a nitration reaction of phenolic substrates that were added to the reaction medium. Possible mechanisms of these reactions were studied.

Why tocotrienols work better: insights into the in vitro anti-cancer mechanism of vitamin E

The selective constraint of liver uptake and the sustained metabolism of tocotrienols (T3) demonstrate the need for a prompt detoxification of this class of lipophilic vitamers, and thus the potential for cytotoxic effects in hepatic and extra-hepatic tissues. Hypomethylated (γ and δ) forms of T3 show the highest in vitro and in vivo metabolism and are also the most potent natural xenobiotics of the entire vitamin E family of compounds. These stimulate a stress response with the induction of detoxification and antioxidant genes. Depending on the intensity of this response, these genes may confer cell protection or alternatively they stimulate a senescence-like phenotype with cell cycle inhibition or even mitochondrial toxicity and apoptosis. In cancer cells, the uptake rate and thus the cell content of these vitamers is again higher for the hypomethylated forms, and it is the critical factor that drives the dichotomy between protection and toxicity responses to different T3 forms and doses. These aspects suggest the potential for marked biological activity of hypomethylated "highly metabolized" T3 that may result in cytoprotection and cancer prevention or even chemotherapeutic effects. Cytotoxicity and metabolism of hypomethylated T3 have been extensively investigated in vitro using different cell model systems that will be discussed in this review paper as regard molecular mechanisms and possible relevance in cancer therapy.

Increased vitamin E intake is associated with higher alpha-tocopherol concentration in the maternal circulation but higher alpha-carboxyethyl hydroxychroman concentration in the fetal circulation

BACKGROUND

The transfer of vitamin E across the placenta is limited, but no data exist on the concentrations of vitamin E metabolites carboxyethyl hydroxychromans (α- and γ-CEHCs) in the fetal circulation.

OBJECTIVE

We measured α- and γ-CEHC concentrations in maternal and umbilical cord blood pairs and examined their relations to circulating vitamin E (α- and γ-tocopherol) and maternal dietary vitamin E intake.

DESIGN

Healthy, pregnant women were enrolled from Oregon Health and Science University's obstetric clinic (<22 wk gestation), and at least one fasting blood sample and a previous day's 24-h diet recall were collected during their pregnancy (n = 19). Umbilical cord blood samples were obtained at the time of delivery and were analyzed for α- and γ-tocopherol, α- and γ-CEHC, and total lipid concentrations.

RESULTS

Mean (±SD) concentrations of umbilical cord blood α-CEHC (30.2 ± 28.9 nmol/L) and γ-CEHC (104.5 ± 61.3 nmol/L) were not significantly different from maternal concentrations (P = 0.07 and 0.08, respectively), but metabolite:tocopherol ratios were significantly higher in cord blood (P < 0.01 and 0.001, respectively). Maternal α-tocopherol:total lipids ratios were correlated with cord blood α-CEHCs (r = 0.67, P = 0.004), and higher vitamin E intakes were associated with higher cord blood α-CEHC concentrations (r = 0.75, P < 0.003).

CONCLUSION

Higher maternal intake of vitamin E during pregnancy may result in increased metabolite concentrations in the fetal circulation, suggesting increased maternal or fetal liver metabolism of vitamin E. This trial was registered at clinicaltrials.gov as NCT00632476.

Tocopheryl quinones and mitochondria

In the past, the role of tocopherols and tocopheryl hydroquinones as antioxidants in mitochondria has been examined. However, structural properties of tocopherols and tocopheryl quinones (arrangement of polar/apolar moieties) have also been recognized as being crucial for the selective transport of RRR-alpha-congeners compared with other tocopherols in the cell, suggesting that these properties might be generally important for the binding of vitamin E-related compounds to proteins and enzymes in mitochondria. Therefore, direct modulation of mitochondrial activities, such as bioenergetics, production of reactive oxygen species and apoptosis, not exclusively related to the redox activity of these compounds is increasingly studied. This overview focuses on the influence of alpha-/gamma-tocopheryl quinones and their parent alpha-/gamma-tocopherols on mitochondrial functions, including formation of tocopheryl quinones, their analytical aspects, their potential as alternative substrates and their inhibitory activity for some mitochondrial functions. It is shown that the understanding of how tocopheryl quinones and tocopherols interfere with mitochondrial functions on the molecular level is still incomplete and that a better comprehension requires further research activities.

Present trends in vitamin E research

Nearly after one century of research and thousands of publications, the physiological function(s) of vitamin E remain unclear. Available evidence suggests a role in cell homeostasis that occurs through the modulation of specific signaling pathways and genes involved in proliferative, metabolic, inflammatory, and antioxidant pathways. Vitamin E presence in the human body is under close metabolic control so that only alpha-tocopherol and, to a lower extent, gamma-tocopherol are retained and delivered to tissues. Other vitamin E forms that are not retained in the body in significant amounts, exhibit responses in vitro that are different form those of alpha-tocopherol and may include tumor cell specific toxicity and apoptosis. These responses provide a therapeutic potential for these minor forms, either as such or metabolically modified, to produce bioactive metabolites. These cellular effects go beyond the properties of lipophilic antioxidant attributed to alpha-tocopherol particularly investigated for its alleged protective role in atherosclerosis or other oxidative stress conditions. Understanding signaling and gene expression effects of vitamin E could help assign a physiological role to this vitamin, which will be discussed in this review. Besides vitamin E signaling, attention will be given to tocotrienols as one of the emerging topics in vitamin E research and a critical re-examination of the most recent clinical trials will be provided together with the potential use of vitamin E in disease prevention and therapy.