Affinity for alpha-tocopherol transfer protein as a determinant of the biological activities of vitamin E analogs

Transporters in vitamin uptake and cellular metabolism: impacts on health and disease

Vitamins are vital nutrients essential for metabolism, functioning as coenzymes, antioxidants, and regulators of gene expression. Their absorption and metabolism rely on specialized transport proteins that ensure bioavailability and cellular utilization. Water-soluble vitamins, including B-complex and vitamin C, are transported by solute carrier (SLC) family proteins and ATP-binding cassette (ABC) transporters for efficient uptake and cellular distribution. Fat-soluble vitamins (A, D, E, and K) rely on lipid-mediated pathways through proteins like scavenger receptor class B type I (SR-BI), CD36, and Niemann-Pick C1-like 1 (NPC1L1), integrating their absorption with lipid metabolism. Defective vitamin transporters are associated with diverse metabolic disorders, including neurological, hematological, and mitochondrial diseases. Advances in structural and functional studies of vitamin transporters highlight their tissue-specific roles and regulatory mechanisms, shedding light on their impact on health and disease. This review emphasizes the significance of vitamin transporters and their potential as therapeutic targets for deficiencies and related chronic conditions.

Rab8a and Vps35 influence intracellular transport of vitamin E via α-Tocopherol transport protein in hepatocytes

Of all the forms of vitamin E, α-tocopherol is distinguished as the primary ligand for the α-tocopherol transport protein (α-TTP), a pivotal factor in its secretion into the bloodstream and subsequent systemic distribution. Nevertheless, the intricate molecular mechanisms governing the transport of α-tocopherol via α-TTP have yet to be fully elucidated. In this research, Co-Immunoprecipitation (Co-IP)/LC-MS and His-pull-down assays were utilized to identify proteins interacting with α-TTP. Immunofluorescence staining and Co-IP/Western blotting further confirmed these interactions. Meanwhile, RNA-seq was utilized to discover α-tocopherol-related genes. Genes knockdown was conducted to examine the influence of related genes on vitamin E transport. The concentrations of intracellular and extracellular vitamin E were quantified using LC-MS and specific assay kits. Immunofluorescence staining showed colocalization of Rab8a, SNX3, SNX5, SNX17, and SNX27 with α-TTP, whereas Co-IP/Western blot analysis indicated a specific interaction among Vps35, Rab8a and α-TTP. Notably, the knockdown of Rab8a, SNX5, SNX17, and SNX27 individually influenced the vitamin E content both intracellularly and extracellularly, whereas knockdown of SNX3 did not show such effects in hepatocytes. This research highlights the crucial roles of Rab8a and Vps35 in α-tocopherol's intracellular transport probably by direct interaction with α-TTP, and their association with Retromer-SNX27, Commander-SNX17, and ESCPE1 complexes.

Antioxidant-independent activities of alpha-tocopherol

Alpha-tocopherol (vitamin E) is a plant-derived dietary lipid that is essential for the health of most animals, including humans. Originally discovered as a fertility factor in rodents, the primary health-promoting properties of the vitamin in humans was shown to be protection of neuromuscular functions. Heritable vitamin E deficiency manifests in spinocerebellar ataxia that can be stabilized by timely supplementation with high-dose α-tocopherol. The molecular basis for α-tocopherol's biological activities has been attributed primarily to the vitamin's efficacy in preventing lipid peroxidation in membranes and lipoproteins, but the possibility that the vitamin possesses additional biological activities has been postulated and debated in the literature without conclusive resolution. We designed and synthesized a novel analog of α-tocopherol, 6-hydroxymethyl α-tocopherol (6-HMTC), which retains most of the vitamin's structural, physical, and biochemical properties, yet lacks measurable radical-trapping antioxidant activity. 6-HMTC bound to the tocopherol transfer protein with high (nanomolar) affinity, like that of the natural vitamin, attesting to the analog's preservation of structural integrity. Yet, 6-HMTC did not inhibit lipid peroxidation or associated ferroptotic cell death. Notably, 6-HMTC modulated the expression of some genes in a manner essentially identical to that exhibited by α-tocopherol. These findings support the notion that α-tocopherol modulates gene expression via an antioxidant-independent mechanism.

Molecular characterization of homogentisate phytyltransferase and methylphytylbenzoquinol methyltransferase genes from olive fruit with regard to the tocopherol content and the response to abiotic stresses

Two cDNA sequences, named OepHPT and OepMPBQ MT, encoding homogentisate phytyltransferase (HPT) and methylphytylbenzoquinol methyltransferase (MPBQ MT), respectively, have been cloned from olive (Olea europaea cv. Picual). Sequence analysis displayed the distinguishing characteristics typical of the HPT and MPBQ MT families and along with phylogenetic analysis indicated that they code for homogentisate phytyltransferase and methylphytylbenzoquinol methyltransferase enzymes, respectively. Transcriptional analysis in distinct olive tissues indicated that expression levels of HPT and MPBQ MT genes are spatially and temporally regulated in a cultivar-dependent manner and together with tocopherol analysis pointed out that both genes participate in the biosynthesis of the tocopherols present in olive mesocarp. These data also suggest that in olive mesocarp, HPT but not MPBQ MT could be implicated in the transcriptional regulation of the tocopherol biosynthetic pathway. In addition, HPT and MPBQ MT transcript levels are regulated by water status, temperature, light, and wounding in the olive fruit mesocarp, suggesting that both genes could be implicated in the abiotic stress response. Overall, this research constitutes a significant advance to elucidate the factors that regulate the tocopherol biosynthesis in olive fruit to obtain virgin olive oils with enhanced α-tocopherol content.

Development and Validation of Multiplex-PCR Assay for β-Carotene hydroxylase and γ-Tocopherol methyl transferase Genes Governing Enhanced Multivitamins in Maize for Its Application in Genomics-Assisted Breeding

Traditional maize possesses low concentrations of provitamin-A and vitamin-E, leading to various health concerns. Mutant alleles of crtRB1 and vte4 that enhance β-carotene (provitamin-A) and α-tocopherol (vitamin-E), respectively, in maize kernels have been explored in several biofortification programs. For genetic improvement of these target nutrients, uniplex-PCR assays are routinely used in marker-assisted selection. However, due to back-to-back breeding seasons, the time required for genotyping individually for each target gene in large backcross populations becomes a constraint for advancing the generations. Additionally, multiple PCR assays for various genes increase the required costs and resources. Here, we aimed to develop a multiplex-PCR assay to simultaneously identify different allelic forms of crtRB1 and vte4 genes and validate them in a backcross-based segregating population. The PCR assay was carried out using newly developed primers for crtRB1 and a gene-specific primer for vte4. The uniplex-PCR assay was standardized for selected primer pairs in the BC1F1 population segregating for crtRB1 and vte4 genes. Subsequently, a multiplex-PCR assay for crtRB1 and vte4 genes was developed and employed for genotyping in the BC1F1 population. The assay differentiated among four possible genotypic classes, namely crtRB1+crtRB1/vte4+vte4, crtRB1crtRB1/vte4+vte4, crtRB1+crtRB1/vte4+vte4+, and crtRB1crtRB1/vte4+vte4+. This newly developed multiplex-PCR assay saved 41.7% of the cost and 35.6% of the time compared to two individual uniplex-PCR assays. The developed assay could accelerate maize nutritional quality breeding programs through rapid and cost-effective genotyping for the target genes. This is the first report of a multiplex-PCR assay specific to crtRB1 and vte4 genes for its use in genomics-assisted breeding in maize.

Modulation of inflammatory signaling by vitamin E metabolites and its therapeutic implications

Naturally occurring vitamin E is a lipophilic plant-derived molecule corresponding to the 2 R forms of alpha-tocopherol. A series of natural analogs or tocochromanols are present in nature, including β-, γ- and δ-tocopherol (βT, γT, δT), the corresponding tocotrienols (αTE, βTE, γTE, δTE) and tocomonoenols. Differences between these analogs as lipophilic antioxidants and modulators of molecular processes suggest specific therapeutic properties against various disorders associated with acute and chronic inflammation. However, hepatic metabolism of these compounds via cytochrome P450-initiated side chain ω-oxidation involves the production of long-chain metabolites (LCMs) followed by intermediate (ICMs) and short-chain metabolites (SCMs), respectively. Despite the initial studies indicating these metabolites as catabolic-end products, recent findings identify their importance in providing biological functions. In this scope, LCMs, especially 13'-carboxychromanols (13'-COOHs), have been reported to hold stronger anti-inflammatory capacity than their unmetabolized precursors due to their ability to inhibit 5-lipoxygenase and cyclooxygenase-catalyzed eicosanoid formation, as well as their modulation of the pro-inflammatory transcriptional protein nuclear factor κB (NF-κB). Also, these LCMs have been reported to enhance detoxification and lipid metabolism pathways associated with cellular inflammation by modulating the nuclear receptors peroxisome proliferator-activated receptor-γ (PPARγ) and pregnane x receptor (PXR). These properties of LCMs will be described in this narrative review article focusing on recent information regarding their bioavailability, anti-inflammatory effects, and mechanisms of action in acute and chronic inflammatory disorders.

α-Tocopherol Long-Chain Metabolite α-T-13'-COOH Exhibits Biphasic Effects on Cell Viability, Induces ROS-Dependent DNA Damage, and Modulates Redox Status in Murine RAW264.7 Macrophages

SCOPE

The α-tocopherol long-chain metabolite α-tocopherol-13'-hydroxy-chromanol (α-T-13'-COOH) is a proposed regulatory intermediate of endogenous vitamin E metabolism. Effects of α-T-13'-COOH on cell viability and adaptive stress response are not well understood. The present study aims to investigate the concentration-dependent effects of α-T-13'-COOH on cellular redox homeostasis, genotoxicity, and cytotoxicity in murine RAW264.7 macrophages as a model system.

METHODS AND RESULTS

Murine RAW264.7 macrophages are exposed to various dosages of α-T-13'-COOH to determine its regulatory effects on reactive oxygen species (ROS) production, DNA damage, expression of stress-related markers, and the activity of ROS scavenging enzymes including superoxide dismutases, catalase, and glutathione-S-transferases. The impact on cell viability is assessed by analyzing cell proliferation, cell cycle arrest, and cell apoptosis.

CONCLUSION

α-T-13'-COOH influences ROS production and induces DNA damage in a dose-dependent manner. The metabolite modulates the activity of ROS-scavenging enzymes, with significant changes observed in the activities of antioxidant enzymes. A biphasic response affecting cell viability is noted: sub-micromolar doses of α-T-13'-COOH promote cell proliferation and enhance DNA synthesis, whereas supraphysiological doses lead to DNA damage and cytotoxicity. It hypothesizes an adaptive stress response, characterized by upregulation of ROS detoxification mechanisms, enhanced cell cycle arrest, and increased apoptosis, indicating a correlation with oxidative stress and subsequent cellular damage.

Interneurons in the CA1 stratum oriens expressing αTTP may play a role in the delayed-ageing Pol μ mouse model

Neurodegeneration associated with ageing is closely linked to oxidative stress (OS) and disrupted calcium homeostasis. Some areas of the brain, like the hippocampus - particularly the CA1 region - have shown a high susceptibility to age-related changes, displaying early signs of pathology and neuronal loss. Antioxidants such as α-tocopherol (αT) have been effective in mitigating the impact of OS during ageing. αT homeostasis is primarily regulated by the α-tocopherol transfer protein (αTTP), which is widely distributed throughout the brain - where it plays a crucial role in maintaining αT levels within neuronal cells. This study investigates the distribution of αTTP in the hippocampus of 4- and 24-month-old Pol μ knockout mice (Pol μ-/-), a delayed-ageing model, and the wild type (Pol μ+/+). We also examine the colocalisation in the stratum oriens (st.or) of CA1 region with the primary interneuron populations expressing calcium-binding proteins (CBPs) (calbindin (CB), parvalbumin (PV), and calretinin (CR)). Our findings reveal that αTTP immunoreactivity (-IR) in the st.or of Pol μ mice is significantly reduced. The density of PV-expressing interneurons (INs) increased in aged mice in both Pol μ genotypes (Pol μ-/- and Pol μ+/+), although the density of PV-positive INs was lower in the aged Pol μ-/- mice compared to wild-type mice. By contrast, CR- and CB-positive INs in Pol μ mice remained unchanged during ageing. Furthermore, double immunohistochemistry reveals the colocalisation of αTTP with CBPs in INs of the CA1 st.or. Our study also shows that the PV/αTTP-positive IN population remains unchanged in all groups. A significant decrease of CB/αTTP-positive INs in young Pol μ-/- mice has been detected, as well as a significant increase in CR/αTTP-IR in older Pol μ-/- animals. These results suggest that the differential expression of αTTP and CBPs could have a crucial effect in aiding the survival and maintenance of the different IN populations in the CA1 st.or, and their coexpression could contribute to the enhancement of their resistance to OS-related damage and neurodegeneration associated with ageing.

Associations between Brain Alpha-Tocopherol Stereoisomer Profile and Hallmarks of Brain Aging in Centenarians

Brain alpha-tocopherol (αT) concentration was previously reported to be inversely associated with neurofibrillary tangle (NFT) counts in specific brain structures from centenarians. However, the contribution of natural or synthetic αT stereoisomers to this relationship is unknown. In this study, αT stereoisomers were quantified in the temporal cortex (TC) of 47 centenarians in the Georgia Centenarian Study (age: 102.2 ± 2.5 years, BMI: 22.1 ± 3.9 kg/m2) and then correlated with amyloid plaques (diffuse and neuritic plaques; DPs, NPs) and NFTs in seven brain regions. The natural stereoisomer, RRR-αT, was the primary stereoisomer in all subjects, accounting for >50% of total αT in all but five subjects. %RRR was inversely correlated with DPs in the frontal cortex (FC) (ρ = -0.35, p = 0.032) and TC (ρ = -0.34, p = 0.038). %RSS (a synthetic αT stereoisomer) was positively correlated with DPs in the TC (ρ = 0.39, p = 0.017) and with NFTs in the FC (ρ = 0.37, p = 0.024), TC (ρ = 0.42, p = 0.009), and amygdala (ρ = 0.43, p = 0.008) after controlling for covariates. Neither RRR- nor RSS-αT were associated with premortem global cognition. Even with the narrow and normal range of BMIs, BMI was correlated with %RRR-αT (ρ = 0.34, p = 0.021) and %RSS-αT (ρ = -0.45, p = 0.002). These results providing the first characterization of TC αT stereoisomer profiles in centenarians suggest that DP and NFT counts, but not premortem global cognition, are influenced by the brain accumulation of specific αT stereoisomers. Further study is needed to confirm these findings and to determine the potential role of BMI in mediating this relationship.

Scientific opinion on the tolerable upper intake level for vitamin E

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver a scientific opinion on the revision of the tolerable upper intake level (UL) for vitamin E. As α-tocopherol is recognised as the only essential form of vitamin E, the Panel restricted its evaluation to α-tocopherol. Systematic reviews of the literature were conducted to assess evidence on priority adverse health effects of excess intake of vitamin E, namely risk of impaired coagulation and bleeding, cardiovascular disease and prostate cancer. The effect on blood clotting and associated increased risk of bleeding is considered as the critical effect to establish an UL for vitamin E. No new evidence has been published that could improve the characterisation of a dose-response. The ULs for vitamin E from all dietary sources, which were previously established by the Scientific Committee on Food, are retained for all population groups, i.e. 300 mg/day for adults, including pregnant and lactating women, 100 mg/day for children aged 1-3 years, 120 mg/day for 4-6 years, 160 mg/day for 7-10 years, 220 mg/day for 11-14 years and 260 mg/day for 15-17 years. A UL of 50 mg/day is established for infants aged 4-6 months and a UL of 60 mg/day for infants aged 7-11 months. ULs apply to all stereoisomeric forms of α-tocopherol. ULs do not apply to individuals receiving anticoagulant or antiplatelet medications (e.g. aspirin), to patients on secondary prevention for CVD or to patients with vitamin K malabsorption syndromes. It is unlikely that the ULs for vitamin E are exceeded in European populations, except for regular users of food supplements containing high doses of vitamin E.

Updates in the skeletal and joint protective effects of tocotrienol: a mini review

Osteoporosis and osteoarthritis continue to pose significant challenges to the aging population, with limited preventive options and pharmacological treatments often accompanied by side effects. Amidst ongoing efforts to discover new therapeutic agents, tocotrienols (TTs) have emerged as potential candidates. Derived from annatto bean and palm oil, TTs have demonstrated efficacy in improving skeletal and joint health in numerous animal models of bone loss and osteoarthritis. Mechanistic studies suggest that TTs exert their effects through antioxidant, anti-inflammatory, Wnt-suppressive, and mevalonate-modulating mechanisms in bone, as well as through self-repair mechanisms in chondrocytes. However, human clinical trials in this field remain scarce. In conclusion, TTs hold promise as agents for preventing osteoporosis and osteoarthritis, pending further evidence from human clinical trials.

Vitamin E: Not only a single stereoisomer

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

Vitamins as regulators of calcium-containing kidney stones - new perspectives on the role of the gut microbiome

Calcium-based kidney stone disease is a highly prevalent and morbid condition, with an often complicated and multifactorial aetiology. An abundance of research on the role of specific vitamins (B6, C and D) in stone formation exists, but no consensus has been reached on how these vitamins influence stone disease. As a consequence of emerging research on the role of the gut microbiota in urolithiasis, previous notions on the contribution of these vitamins to urolithiasis are being reconsidered in the field, and investigation into previously overlooked vitamins (A, E and K) was expanded. Understanding how the microbiota influences host vitamin regulation could help to determine the role of vitamins in stone disease.

Vitamin E discussion forum position paper on the revision of the nomenclature of vitamin E

This position paper opens a discussion forum of this Journal dedicated to a scientific debate on Vitamin E nomenclature. With this article we provide the scientific and medical communities with what we consider relevant information in favor of revising the nomenclature of vitamin E. To our knowledge, only RRR-α-tocopherol has been medically used to protect against a deficiency disease in humans, and therefore, it would be appropriate to restrict the term vitamin to this molecule. The direct demonstration of a vitamin function to other tocochromanols (including other tocopherols, tocotrienols and eventually tocomonoenols), has not yet been scientifically shown. In fact, the medical prescription of a molecule against the deficiency disease only because it has been included in the "Vitamin E family", but not tested as vitamin E, could lead to ineffective therapy and potentially dangerous consequences for patients. The idea of this revision launched during the recent 3rd Satellite Symposium on Vitamin E of the 2022 SFRR-Europe meeting, offers a open platform of discussion for the scientists involved in vitamin E research and scientific societies interested to this subject.

Evaluation of Vitamin E Isoforms in Placental Tissue and Their Relationship with Maternal Dietary Intake and Plasma Concentrations in Mother-Infant Dyads

α-tocopherol is a vitamin E isoform with potent antioxidant activity, while the γ-tocopherol isoform of vitamin E exerts more pro-inflammatory effects. In maternal-fetal environments, increased plasma α-tocopherol concentrations are associated with positive birth outcomes, while higher γ-tocopherol concentrations are linked with negative pregnancy outcomes. However, little is known about tocopherol concentrations in placental tissue and their role in modulating placental oxidative stress, a process that is implicated in many complications of pregnancy. The objectives of this research are to evaluate the concentrations of α- and γ-tocopherol in placental tissue and assess relationships with maternal and umbilical cord plasma concentrations. A total of 82 mother-infant dyads were enrolled at the time of delivery, and maternal and umbilical cord blood samples and placenta samples were collected. α- and γ-tocopherol concentrations in these samples were analyzed by high-performance liquid chromatography (HPLC). γ-tocopherol concentrations demonstrated significant, positive correlations among all sample types (p-values < 0.001). Placental tissue had a significantly lower ratio of α:γ-tocopherol concentrations when compared to maternal plasma and umbilical cord plasma (2.9 vs. 9.9 vs. 13.2, respectively; p < 0.001). Additional research should explore possible mechanisms for tocopherol storage and transfer in placental tissue and assess relationships between placental tocopherol concentrations and measures of maternal-fetal oxidative stress and clinical outcomes of pregnancy.

The Effects of Tocotrienol on Gut Microbiota: A Scoping Review

Gut dysbiosis has been associated with many chronic diseases, such as obesity, inflammatory bowel disease, and cancer. Gut dysbiosis triggers these diseases through the activation of the immune system by the endotoxins produced by gut microbiota, which leads to systemic inflammation. In addition to pre-/pro-/postbiotics, many natural products can restore healthy gut microbiota composition. Tocotrienol, which is a subfamily of vitamin E, has been demonstrated to have such effects. This scoping review presents an overview of the effects of tocotrienol on gut microbiota according to the existing scientific literature. A literature search to identify relevant studies was conducted using PubMed, Scopus, and Web of Science. Only original research articles which aligned with the review's objective were examined. Six relevant studies investigating the effects of tocotrienol on gut microbiota were included. All of the studies used animal models to demonstrate that tocotrienol altered the gut microbiota composition, but none demonstrated the mechanism by which this occurred. The studies induced diseases known to be associated with gut dysbiosis in rats. Tocotrienol partially restored the gut microbiota compositions of the diseased rats so that they resembled those of the healthy rats. Tocotrienol also demonstrated strong anti-inflammatory effects in these animals. In conclusion, tocotrienol could exert anti-inflammatory effects by suppressing inflammation directly or partially by altering the gut microbiota composition, thus achieving its therapeutic effects.

Effect of nano-delivery systems on the bioavailability and tissue biodistribution of vitamin E tocotrienols

Vitamin E is one of the most important essential vitamins to support the regulation of oxidative stress in human body. Tocotrienols are part of the vitamin E family. The potentials of tocotrienols as nutraceutical ingredient are largely understated due to low oral bioavailability, which is a common problem associated with fat-soluble bioactive compounds. Nanoencapsulation technology offers innovative solutions to enhance the delivery mechanisms of these compounds. In this study, the effect of nanoencapsulation on the oral bioavailability and tissue distribution of tocotrienols were investigated using two types of formulations, i.e. nanovesicles (NV-T3) and solid lipid nanoparticles (NP-T3). At least 5-fold increment in maximum plasma concentrations, evident with dual-peak pharmacokinetic profiles, were observed after oral administration of nano-encapsulated tocotrienols. Plasma tocotrienol composition showed a shift from α-tocotrienol dominant in control group (Control-T3) to γ-tocotrienol dominant after nanoencapsulation. Tissue distribution of tocotrienols was found to be strongly influenced by the type of nanoformulation. Both nanovesicles (NV-T3) and nanoparticles (NP-T3) showed elevated accumulation in the kidneys and liver (5-fold) compared to control group while selectivity for α-tocotrienol was evident for NP-T3. In brain and liver of rats given NP-T3, α-tocotrienol emerged as the dominant congener (>80%). Acute oral administration of nanoencapsulated tocotrienols did not show signs of toxicity. The study concluded enhanced bioavailability and selective tissue accumulation of tocotrienol congeners when delivered via nanoencapsulation.

α-Tocopherol in chloroplasts: Nothing more than an antioxidant?

Among the eight forms of vitamin E, only tocopherols are essential compounds that are distributed throughout the entire plant kingdom, with α-tocopherol being the most predominant form in photosynthetic tissues. At the cellular level, α-tocopherol is of special relevance inside the chloroplast, where it eliminates singlet oxygen and modulates lipid peroxidation. This is of utmost relevance since tocopherols are the only antioxidants that counteract lipid peroxidation. Moreover, at the whole-plant level, α-tocopherol appears to modulate several physiological processes from germination to senescence. The antioxidant role of α-tocopherol at the cellular level can have profound effects at the whole-plant level, including the modulation of physiological processes that are apparently not related to redox processes and could be considered non-antioxidant functions. Here, we discuss whether non-antioxidant functions of α-tocopherol at the whole-plant level are mediated by its antioxidant role in chloroplasts and the regulation of redox processes at the cellular level.

The Role of Tocotrienol in Arthritis Management-A Scoping Review of Literature

Arthritis is a cluster of diseases impacting joint health and causing immobility and morbidity in the elderly. Among the various forms of arthritis, osteoarthritis (OA) and rheumatoid arthritis (RA) are the most common. Currently, satisfying disease-modifying agents for arthritis are not available. Given the pro-inflammatory and oxidative stress components in the pathogenesis of arthritis, tocotrienol, a family of vitamin E with both anti-inflammatory and antioxidant properties, could be joint-protective agents. This scoping review aims to provide an overview of the effects of tocotrienol on arthritis derived from the existing scientific literature. A literature search using PubMed, Scopus and Web of Science databases was conducted to identify relevant studies. Only cell culture, animal and clinical studies with primary data that align with the objective of this review were considered. The literature search uncovered eight studies investigating the effects of tocotrienol on OA (n = 4) and RA (n = 4). Most of the studies were preclinical and revealed the positive effects of tocotrienol in preserving joint structure (cartilage and bone) in models of arthritis. In particular, tocotrienol activates the self-repair mechanism of chondrocytes exposed to assaults and attenuates osteoclastogenesis associated with RA. Tocotrienol also demonstrated strong anti-inflammatory effects in RA models. The single clinical trial available in the literature showcases that palm tocotrienol could improve joint function among patients with OA. In conclusion, tocotrienol could be a potential anti-arthritic agent pending more results from clinical studies.

Chemopreventive and anti-tumor potential of vitamin E in preclinical breast cancer studies: A systematic review

BACKGROUND

Vitamin E has been investigated for its antitumor potential, including the ability to change cancer gene pathways as well as promote antioxidant and pro-oxidant activity.

OBJECTIVE

Therefore, this systematic review aimed to evaluate antitumor and chemopreventive activity of different vitamin E isoforms (tocopherols and tocotrienols) through in vitro and in vivo studies.

METHOD

The systematic review was registered in PROSPERO (No. CRD4202126207) and the search was carried out in four electronic databases (PubMed, Science Direct, Scopus and Web of Science) in June 2021 by three independent reviewers. The search equation used was: "Supplementation" AND ("Vitamin E" OR Tocopherol OR Tocotrienol) AND "breast cancer" AND (chemotherapy OR therapy OR prevention). In vitro studies and animal models of breast cancer supplemented with tocopherol or tocotrienol vitamers, alone or in combination, were included.

RESULTS

The results revealed 8546 relevant studies that were initially identified in our search. After analysis, a total of 12 studies were eligible for this systematic review. All studies included animal models, and 5 of them also performed in vitro experiments on cancer cell lines. The studies performed supplementation with tocopherols, mixtures (tocopherols and tocotrienols) and synthetic vitamin E forms. There was an significant association of estradiol, dendritic cells and pterostilbene in combined therapy with vitamin E. Vitamin E delayed tumor development, reduced tumor size, proliferation, viability, expression of anti-apoptotic and cell proliferation genes, and upregulated pro-apoptotic genes, tumor suppressor genes and increased immune response. The effects on oxidative stress markers and antioxidant activity were conflicting among studies. Only one study with synthetic vitamin E reported cardiotoxicity, but it did not show vitamin E genotoxicity.

CONCLUSION

In conclusion, vitamin E isoforms, isolated or associated, showed antitumor and chemopreventive activity. However, due to studies heterogeneity, there is a need for further analysis to establish dose, form, supplementation time and breast cancer stage.

Oxidants and Antioxidants in the Redox Biochemistry of Human Red Blood Cells

Red blood cells (RBCs) are exposed to both external and internal sources of oxidants that challenge their integrity and compromise their physiological function and supply of oxygen to tissues. Autoxidation of oxyhemoglobin is the main source of endogenous RBC oxidant production, yielding superoxide radical and then hydrogen peroxide. In addition, potent oxidants from other blood cells and the surrounding endothelium can reach the RBCs. Abundant and efficient enzymatic systems and low molecular weight antioxidants prevent most of the damage to the RBCs and also position the RBCs as a sink of vascular oxidants that allow the body to maintain a healthy circulatory system. Among the antioxidant enzymes, the thiol-dependent peroxidase peroxiredoxin 2, highly abundant in RBCs, is essential to keep the redox balance. A great part of the RBC antioxidant activity is supported by an active glucose metabolism that provides reducing power in the form of NADPH via the pentose phosphate pathway. There are several RBC defects and situations that generate oxidative stress conditions where the defense mechanisms are overwhelmed, and these include glucose-6-phosphate dehydrogenase deficiencies (favism), hemoglobinopathies like sickle cell disease and thalassemia, as well as packed RBCs for transfusion that suffer from storage lesions. These oxidative stress-associated pathologies of the RBCs underline the relevance of redox balance in these anucleated cells that lack a mechanism of DNA-inducible antioxidant response and rely on a complex and robust network of antioxidant systems.

Vitamin E functions by association with a novel binding site on the 67 kDa laminin receptor activating diacylglycerol kinase

It is generally recognized that the main function of α-tocopherol (αToc), which is the most active form of vitamin E, is its antioxidant effect, while non-antioxidant effects have also been reported. We previously found that αToc ameliorates diabetic nephropathy via diacylglycerol kinase alpha (DGKα) activation in vivo, and the activation was not related to the antioxidant effect. However, the underlying mechanism of how αToc activates DGKα have been enigmatic. We report that the membrane-bound 67 kDa laminin receptor (67LR), which has previously been shown to serve as a receptor for epigallocatechin gallate (EGCG), also contains a novel binding site for vitamin E, and its association with Vitamin E mediates DGKα activation by αToc. We employed hydrogen-deuterium exchange mass spectrometry (HDX/MS) and molecular dynamics (MD) simulations to identify the specific binding site of αToc on the 67LR and discovered the conformation of the specific hydrophobic pocket that accommodates αToc. Also, HDX/MS and MD simulations demonstrated the detailed binding of EGCG to a water-exposed hydrophilic site on 67LR, while in contrast αToc binds to a distinct hydrophobic site. We demonstrated that 67LR triggers an important signaling pathway mediating non-antioxidant effects of αToc, such as DGKα activation. This is the first evidence demonstrating a membrane receptor for αToc and one of the underlying mechanisms of a non-antioxidant function for αToc.

Determination of tissue-specific interaction between vitamin C and vitamin E in vivo using senescence marker protein-30 knockout mice as a vitamin C synthesis deficiency model

Vitamin E (α-tocopherol; VE) is known to be regenerated from VE radicals by vitamin C (L-ascorbic acid; VC) in vitro. However, their in vivo interaction in various tissues is still unclear. Therefore, we alternatively examined the in vivo interaction of VC and VE by measurement of their concentrations in various tissues of senescence marker protein-30 (SMP30) knockout (KO) mice as a VC synthesis deficiency model. Male SMP30-KO mice were divided into four groups (VC+/VE+, VC+/VE-, VC-/VE+ and VC-/VE-), fed diets with or without 500 mg/kg VE and given water with or without 1·5 g/l VC ad libitum. Then, VC and VE concentrations in the plasma and various tissues were determined. Further, gene expression levels of transporters associated with VC and VE, such as α-tocopherol transfer protein (α-TTP) and sodium-dependent vitamin C transporters (SVCTs), were examined. These results showed that the VE levels in the VC-depleted (VC-/VE+) group were significantly lower than those in the VC+/VE+ group in the liver and heart; the VC levels in the VE-depleted (VC+/VE-) group were significantly lower than those in the VC+/VE+ group in the kidneys. The α-TTP gene expression in the liver and kidneys was decreased by VC and/or VE depletion. Moreover, SVCT1 gene expression in the liver was decreased by both VC and VE depletion. In conclusion, these results indicate that VC spares VE mainly in the liver and heart and that VE spares VC in the kidneys of SMP30-KO mice. Thus, interaction between VC and VE is likely to be tissue specific.

Electrochemical and Spectroscopic Characterization of Oxidized Intermediate Forms of Vitamin E

Vitamin E, a collection of lipophilic phenolic compounds based on chroman-6-ol, has a rich and fascinating oxidative chemistry involving a range of intermediate forms, some of which are proposed to be important in its biological functions. In this review, the available electrochemical and spectroscopic data on these oxidized intermediates are summarized, along with a discussion on how their lifetimes and chemical stability are either typical of similar phenolic and chroman-6-ol derived compounds, or atypical and unique to the specific oxidized isomeric form of vitamin E. The overall electrochemical oxidation mechanism for vitamin E can be summarized as involving the loss of two-electrons and one-proton, although the electron transfer and chemical steps can be controlled to progress along different pathways to prolong the lifetimes of discreet intermediates by modifying the experimental conditions (applied electrochemical potential, aqueous or non-aqueous solvent, and pH). Depending on the environment, the electrochemical reactions can involve single electron transfer (SET), proton-coupled electron transfer (PCET), as well as homogeneous disproportionation and comproportionation steps. The intermediate species produced via chemical or electrochemical oxidation include phenolates, phenol cation radicals, phenoxyl neutral radicals, dications, diamagnetic cations (phenoxeniums) and para-quinone methides. The cation radicals of all the tocopherols are atypically long-lived compared to the cation radicals of other phenols, due to their relatively weak acidity. The diamagnetic cation derived from α-tocopherol is exceptionally long-lived compared to the diamagnetic cations from the other β-, γ- and δ-isomers of vitamin E and compared with other phenoxenium cations derived from phenolic compounds. In contrast, the lifetime of the phenoxyl radical derived from α-tocopherol, which is considered to be critical in biological reactions, is typical for what is expected for a compound with its structural features. Over longer times via hydrolysis reactions, hydroxy para-quinone hemiketals and quinones can be formed from the oxidized intermediates, which can themselves undergo reduction processes to form intermediate anion radicals and dianions. Methods for generating the oxidized intermediates by chemical, photochemical and electrochemical methods are discussed, along with a summary of how the final products vary depending on the method used for oxidation. Since the intermediates mainly only survive in solution, they are most often monitored using UV-vis spectroscopy, FTIR or Raman spectroscopies, and EPR spectroscopy, with the spectroscopic techniques sometimes combined with fast photoinitiated excitation and time-resolved spectroscopy for detection of short-lived species.

Vitamin E and Metabolic Health: Relevance of Interactions with Other Micronutrients

A hundred years have passed since vitamin E was identified as an essential micronutrient for mammals. Since then, many biological functions of vitamin E have been unraveled in both cell and animal models, including antioxidant and anti-inflammatory properties, as well as regulatory activities on cell signaling and gene expression. However, the bioavailability and physiological functions of vitamin E have been considerably shown to depend on lifestyle, genetic factors, and individual health conditions. Another important facet that has been considered less so far is the endogenous interaction with other nutrients. Accumulating evidence indicates that the interaction between vitamin E and other nutrients, especially those that are enriched by supplementation in humans, may explain at least some of the discrepancies observed in clinical trials. Meanwhile, increasing evidence suggests that the different forms of vitamin E metabolites and derivates also exhibit physiological activities, which are more potent and mediated via different pathways compared to the respective vitamin E precursors. In this review, possible molecular mechanisms between vitamin E and other nutritional factors are discussed and their potential impact on physiological and pathophysiological processes is evaluated using published co-supplementation studies.

[Physiological Function and Congenital Deficiency of α-TTP, a Determinant of Vitamin E Transport in the Body -One Portion of the Research for Which the Pharmaceutical Society of Japan Award Was Given]

This review summarizes one portion of the research for which the author received the Pharmaceutical Society of Japan Award. The complete title of the awarded research is "Pharmacological Studies on Metabolism and Functions of Biomembrane Lipids". Because the awarded research is a very broad study, this review describes the discovery, physiological functions, and congenital defects of α-tocopherol transfer protein (α-TTP), a critical factor in determining the transport of vitamin E in the body, which has been the focus of the author's work throughout his research career.

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.

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.

Tocotrienol in Pre-Eclampsia Prevention: A Mechanistic Analysis in Relation to the Pathophysiological Framework

The pathophysiology of pre-eclampsia involves two major pathways, namely systemic oxidative stress and subsequent generalised inflammatory response, which eventually culminates in endothelial cell injury and the syndrome of pre-eclampsia with multi-organ dysfunction. Aspirin has been used to reduce the risk of pre-eclampsia, but it only possesses anti-inflammatory properties without any antioxidant effect. Hence, it can only partially alleviate the problem. Tocotrienols are a unique form of vitamin E with strong antioxidant and anti-inflammatory properties that can be exploited as a preventive agent for pre-eclampsia. Many preclinical models showed that tocotrienol can also prevent hypertension and ischaemic/reperfusion injury, which are the two main features in pre-eclampsia. This review explores the mechanism of action of tocotrienol in relation to the pathophysiology of pre-eclampsia. In conclusion, the study provides sufficient justification for the establishment of a large clinical trial to thoroughly assess the capability of tocotrienol in preventing pre-eclampsia.

Differential Mechanisms of Action and Efficacy of Vitamin E Components in Antioxidant Cytoprotection of Human Retinal Pigment Epithelium

The purpose of this study was to determine if different vitamin E components exhibit similar efficacy and mechanism of action in protecting Retinal pigment epithelium (RPE) cells from oxidative damage. We hypothesized that α-tocopherol (αT) is unique among vitamin E components in its cytoprotective mechanism of action against oxidative stress in RPE cells and that it requires protein synthesis for optimal antioxidant effect. We used cell viability assays, fluorescent chemical labeling of DNA and actin and immuno-labeling of the antioxidant proteins Nrf2 and Sod2 and of the tight junction protein, ZO-1, and confocal microscopy to determine the effects of αT and γT against oxidative stress in immortalized human RPE cells (hTERT-RPE). Using the four main vitamin E components, αT, γT, δ-tocopherol (δT) and α-tocotrienol (αTr), we ascertained that they exhibit similar, but not identical, antioxidant activity as αT when used at equimolar concentrations. In addition, we determined that the exposure time of RPE cells to α-tocopherol is critical for its ability to protect against oxidative damage. Lastly, we determined that αT, but not γT, partially requires the synthesis of new proteins within a 24-h period and prior to exposure to tBHP for optimal cytoprotection. We conclude that, unlike γT and δT, αT appears to be unique in its requirement for transport and/or signaling for it to be an effective antioxidant. As a result, more focus should be paid to which vitamin E components are used for antioxidant interventions.

Cytotoxicity, cellular uptake, and metabolism to short-chain metabolites of 11'-α-tocomonoenol is similar to RRR-α-tocopherol in HepG2 cells

Contrary to the major vitamin E congener α-tocopherol, which carries a saturated sidechain, and α-tocotrienol, with a threefold unsaturated sidechain, little is known about the intracellular fate of α-tocomonoenol, a minor vitamin E derivative with a single double bond in C11'-position of the sidechain. We hypothesized that, due to structural similarities, the uptake and metabolism of α-tocomonoenol will resemble that of α-tocopherol. Cytotoxicity, cellular uptake of α-tocomonoenol, α-tocopherol and α-tocotrienol and conversion into the short-chain metabolites αCEHC and αCMBHC were studied in HepG2 cells. α-Tocomonoenol did not show significant effects on cell viability and its uptake was similar to that observed for α-tocopherol and significantly lower than for α-tocotrienol. α-Tocomonoenol was mainly metabolized to αCMBHC in liver cells, but to a lower extent than α-tocotrienol, while α-tocopherol was not metabolized in quantifiable amounts at all. In summary, the similarities in the cytotoxicity, uptake and metabolism of α-tocomonoenol and α-tocopherol suggest that this minor vitamin E congener deserves more attention in future research with regard to its potential vitamin E activity.

Absorption, transportation, and distribution of vitamin E homologs

Vitamin E has eight different naturally occurring forms: four tocopherols and four tocotrienols. Because α-tocopherol has three asymmetric carbons, both natural α-tocopherol (RRR-α-tocopherol) and synthetic α-tocopherol (all-rac-α-tocopherol) are utilized in both pharmaceutical products and food additives. Therefore, determining the distribution of vitamin E in the body is very important. With regard to absorption, and transportation of vitamin E, it is suggested that the pathways mediated by three proteins (CD36, SR-BI, and NPC1L1) as well as passive diffusion affect absorption of vitamin E. Vitamin E homologs are mainly transported by very low-density lipoprotein (VLDL) with the α-tocopherol being recognized by the α-tocopherol transfer protein in liver. However, it is also suggested that chylomicrons (CMs) and high-density lipoprotein (HDL) are involved in transportation of vitamin E homologs from the small intestine to each section of peripheral tissue. In particular, it is speculated that vitamin E homologs transportation by CMs and HDL from enterocytes to peripheral tissues such as adipose tissue greatly affects the distribution of vitamin E homologs, excluding α-tocopherol. However, how lipoprotein lipase affects the incorporation of vitamin E homologs containing lipoprotein into peripheral tissues is unclear. Whether there is biodiscrimination when vitamin E homologs are incorporated into peripheral tissues from lipoprotein is an interesting question. It is likely that future research will reveal how individual vitamin E homologs are incorporated into peripheral tissue, especially the brain, adipose tissue, and skin.

α-Tocopherol transfer protein (α-TTP)

α-Tocopherol transfer protein (α-TTP) is so far the only known protein that specifically recognizes α-tocopherol (α-Toc), the most abundant and most biologically active form of vitamin E, in higher animals. α-TTP is highly expressed in the liver where α-TTP selects α-Toc among vitamin E forms taken up via plasma lipoproteins and promotes its secretion to circulating lipoproteins. Thus, α-TTP is a major determinant of plasma α-Toc concentrations. Familial vitamin E deficiency, also called Ataxia with vitamin E deficiency, is caused by mutations in the α-TTP gene. More than 20 different mutations have been found in the α-TTP gene worldwide, among which some missense mutations provided valuable clues to elucidate the molecular mechanisms underlying intracellular α-Toc transport. In hepatocytes, α-TTP catalyzes the vectorial transport of α-Toc from the endocytotic compartment to the plasma membrane (PM) by targeting phosphatidylinositol phosphates (PIPs) such as PI(4,5)P₂. By binding PIPs at the PM, α-TTP opens the lid covering the hydrophobic pocket, thus facilitating the release of bound α-Toc to the PM.

Deleterious side effects of nutritional supplements

Vitamin and mineral supplement consumption is widespread. They are taken for a variety of conditions, including dermatologic disorders. Although consumers often assume these supplements are safe, excessive consumption of supplements may have deleterious effects. Such vitamin supplements include vitamin A, niacin, biotin, vitamin D, and vitamin E, and specific mineral supplements include zinc, copper, and iron. These supplements may have a number of potential adverse effects.

Diverse cytoprotective actions of vitamin E isoforms- role as peroxyl radical scavengers and complementary functions with selenoproteins

Vitamin E, a generic term for tocopherol (T) and tocotrienol (T3), is one of the most potent lipid-soluble antioxidants in the body. It is classified into T and T3 based on the difference in the side chain structure. T and T3 have four isoforms: α-, β-, γ-, and δ, which have different chroman rings. Both T and T3 exhibit a similar ability to scavenge free radicals, and the extent of this ability depends on the difference in the chroman structure. However, they display unique cytoprotective activities in cultured cells depending on the difference in the side chain structure. The cytoprotective effects of vitamin E have received much attention in the prevention of ferroptosis, which is a distinct form of cell death involving iron-dependent lipid peroxidation. This review focuses on the cytoprotective actions of vitamin E isoforms against oxidative stress, particularly the difference between T and T3 and its relation to cellular uptake and distribution. Moreover, the molecular mechanism for cytoprotection of vitamin E oxidation products is explained, and the complementary role of vitamin E and selenoproteins to prevent lipid peroxidation and ferroptosis is described. Furthermore, the evaluation of vitamin E's radical scavenging activity in vivo using oxidative stress markers is discussed, particularly based on kinetic data and the physiological molar ratio of vitamin E to substrates, and the limited role of vitamin E as a peroxyl radical scavenger is described. The future directions and unresolved issues related to vitamin E and lipid peroxidation are also discussed.

Stress-activated leukocyte 12/15-lipoxygenase metabolite enhances struggle behaviour and tocotrienols relieve stress-induced behaviour alteration

Stress induces emotional arousal causing anxiety, irritability, exaggerated startle behaviour, and hypervigilance observed in patients with trauma and stress-related mental disorders, including acute stress disorder and post-traumatic stress disorder. Central norepinephrine release promotes stress-induced emotional arousal. However, the regulator of emotional arousal remains unknown. Here, we show that the arachidonate-derived metabolite produced by stress-activated leukocyte 12/15-lipoxygenase is remarkably elevated in the plasma and upregulates the central norepinephrine release, resulting in the enhancement of the struggle behaviour (= escape behaviour) in the tail suspension test. Struggle behaviour is mimicking a symptom of emotional arousal. This stress-induced struggle behaviour was absent in 12/15-lipoxygenase deficient mice; however, intravenous administration of a 12/15-lipoxygenase metabolite to these mice after stress exposure rekindled the struggle behaviour. Furthermore, tocotrienols and geranylgeraniol reduced stress-induced 12/15-lipoxygenase metabolite production and suppressed the struggle behaviour. Our findings indicate that arachidonate-derived 12/15-lipoxygenase metabolite is involved in the regulation of stress-enhanced central norepinephrine release and struggle behaviour. In addition, we propose 12/15-lipoxygenase as a potential therapeutic target for the treatment of emotional arousal observed in stress-related mental disorders.

Gene Expression of CRAL_TRIO Family Proteins modulated by Vitamin E Deficiency in Zebrafish (Danio Rerio)

An evaluation of the impact of vitamin E deficiency on expression of the alpha-tocopherol transfer protein (α-TTP) and related CRAL_TRIO genes was undertaken using livers from adult zebrafish based on the hypothesis that increased lipid peroxidation would modulate gene expression. Zebrafish were fed either a vitamin E sufficient (E+) or deficient (E-) diet for 9 months, then fish were euthanized, and livers were harvested. Livers from the E+ relative to E- fish contained 40-times more α-tocopherol (P <0.0001) and one fourth the malondialdehyde (P = 0.0153). RNA was extracted from E+ and E- livers, then subject to evaluation of gene expression of ttpa and other genes of the CRAL_TRIO family, genes of antioxidant markers, and genes related to lipid metabolism. Ttpa expression was not altered by vitamin E status. However, one member of the CRAL_TRIO family, tyrosine-protein phosphatase non-receptor type 9 gene (ptpn9a), showed a 2.4-fold increase (P = 0.029) in E- relative to E+ livers. Further, we identified that the gene for choline kinase alpha (chka) showed a 3.0-fold increase (P = 0.010) in E- livers. These outcomes are consistent with our previous findings that show vitamin E deficiency increased lipid peroxidation causing increases in phospholipid turnover.

Tocotrienols as an Anti-Breast Cancer Agent

In the past few years, breast cancer has become the most prevalent type of cancer. The majority of patients receive combinatorial chemotherapy treatments, which may result in increased risk of developing drug resistance, a reduced quality of life, and substantial side effects. Treatment modalities that could lessen the physical toll of standard treatments or act in synergy with chemotherapeutic treatments would benefit women worldwide. Research into tocotrienols has thus far demonstrated their potential to be such an agent, with tocotrienols surpassing the pharmacological potential of tocopherols. Further research using in vitro and preclinical breast cancer models to support clinical trials is needed. This review uses bibliometric analysis to highlight this gap in research and summarizes the current and future landscape of tocotrienols as an anti-breast cancer agent.

Spatiotemporal biodistribution of α-tocopherol is impacted by the source of 13C-labeled α-tocopherol in mice following a single oral dose

Natural (RRR-) α-tocopherol (αT) is more bioactive than synthetic (all racemic, all rac-) αT, but not enough is known about the tissue kinetics of the 2 αT sources. We examined the time-course bioaccumulation of natural versus synthetic αT in tissues of young, marginally vitamin E-deficient mice using ¹³C-RRR-αT or ¹³C-all rac-αT tracers. In experiment 1, 3-week old male wild-type mice were fed a vitamin E-deficient diet for 0, 1, 2, or 3 weeks (n = 5/time point). Tissue αT levels were analyzed by HPLC-PDA. Feeding a vitamin E-deficient diet for up to 3 weeks decreased total αT concentrations in all analyzed tissues except the brain, which maintained its αT level. In experiment 2, a 2-week αT-depletion period was followed by administration of a single oral dose of 0.5 mg of ¹³C-RRR-αT or ¹³C-all rac-αT. At 12 hr, 1, 2, and 4 days post-dose, serum and multiple tissues were collected (n = 3/time point). αT was quantified by HPLC-PDA, and ¹³C-αT enrichment was determined by LC-MS. Both sources of ¹³C-αT reached maximum serum levels at 12 hr post-dose. ¹³C-RRR-αT levels were significantly higher than ¹³C-all rac-αT in serum at 1 d post-dose, and in heart, lungs, and kidney at 2d post-dose. In brain, ¹³C-RRR-αT concentrations were significantly higher than ¹³C-all rac-αT at 2 and 4 d post-dose. At 4 d post-dose, ¹³C-αT levels were similar between the 2 sources in examined tissues except for brain and adipose tissue where ¹³C-RRR-αT was higher. In conclusion, αT bioaccumulation over time varied substantially depending on αT source and tissue type.

Effect of δ-Tocopherol on Mice Adipose Tissues and Mice Adipocytes Induced Inflammation

The study aim was to evaluate the potential anti-inflammatory effects of vitamin E analogs, especially α-tocopherol and δ-tocopherol. We used male C57BL/6JJcl mice, which were divided into four groups: the control (C), high-fat and high-sucrose diet (H), high-fat and high-sucrose diet+α-tocopherol (Ha) and high-fat and high-sucrose diet+δ-tocopherol (Hd) groups. The mice were fed for 16 weeks. To the high-fat and high-sucrose diet, 800 mg/kg of α-tocopherol or δ-tocopherol was added more. The final body weight was significantly higher in the H group than in the C group. On the other hand, the final body weight was drastically lower in the Ha group and Hd group than in the H group. However, the energy intake was not significantly different among all groups. Therefore, we assumed that α-tocopherol and δ-tocopherol have potential anti-obesity effect. Besides, inflammatory cytokine gene expression was significantly higher in the epididymal fat of the H group than in the C group. These results showed that inflammation was induced by epididymal fat of mice fed a high-fat and high-sucrose diet for 16 weeks. Unfortunately, addition of α-tocopherol or δ-tocopherol to the diet did not restrain inflammation of epididymal fat. Investigation of the anti-inflammatory effects of α-tocopherol or δ-tocopherol in co-cultured 3T3-L1 cells and RAW264.7 cells showed that δ-tocopherol inhibited increased gene expression of the inflammatory cytokines, IL-1β, IL-6, and iNOS. These results suggest that an anti-inflammatory effect in the δ-tocopherol is stronger than that in the α-tocopherol in vitro. We intend to perform an experiment by in vivo sequentially in the future.

Water-soluble tocopherol derivatives inhibit SARS-CoV-2 RNA-dependent RNA polymerase

The recent emergence of a novel coronavirus, SARS-CoV-2, has led to the global pandemic of the severe disease COVID-19 in humans. While efforts to quickly identify effective antiviral therapies have focused largely on repurposing existing drugs ^1-4 , the current standard of care, remdesivir, remains the only authorized antiviral intervention of COVID-19 and provides only modest clinical benefits ⁵ . Here we show that water-soluble derivatives of α-tocopherol have potent antiviral activity and synergize with remdesivir as inhibitors of the SARS-CoV-2 RNA-dependent RNA polymerase (RdRp). Through an artificial-intelligence-driven in silico screen and in vitro viral inhibition assay, we identified D-α-tocopherol polyethylene glycol succinate (TPGS) as an effective antiviral against SARS-CoV-2 and β-coronaviruses more broadly that also displays strong synergy with remdesivir. We subsequently determined that TPGS and other water-soluble derivatives of α-tocopherol inhibit the transcriptional activity of purified SARS-CoV-2 RdRp and identified affinity binding sites for these compounds within a conserved, hydrophobic interface between SARS-CoV-2 nonstructural protein 7 and nonstructural protein 8 that is functionally implicated in the assembly of the SARS-CoV-2 RdRp ⁶ . In summary, we conclude that solubilizing modifications to α-tocopherol allow it to interact with the SARS-CoV-2 RdRp, making it an effective antiviral molecule alone and even more so in combination with remdesivir. These findings are significant given that many tocopherol derivatives, including TPGS, are considered safe for humans, orally bioavailable, and dramatically enhance the activity of the only approved antiviral for SARS-CoV-2 infection ^7-9 .

A Review on Vitamin E Natural Analogues and on the Design of Synthetic Vitamin E Derivatives as Cytoprotective Agents

Vitamin E, essential for human health, is widely used worldwide for therapeutic or dietary reasons. The differences in the metabolism and excretion of the multiple vitamin E forms are presented in this review. The important steps that influence the kinetics of each form and the distribution and processing of vitamin E forms by the liver are considered. The antioxidant as well as non-antioxidant properties of vitamin E forms are discussed. Finally, synthetic tocopherol and trolox derivatives, based on the design of multitarget directed compounds, are reviewed. It is demonstrated that selected derivatization of vitamin E or trolox structures can produce improved antioxidants, agents against cancer, cardiovascular and neurodegenerative disorders.

Tocopherols and Tocotrienols-Bioactive Dietary Compounds; What Is Certain, What Is Doubt?

Tocopherols and tocotrienols are natural compounds of plant origin, available in the nature. They are supplied in various amounts in a diet, mainly from vegetable oils, some oilseeds, and nuts. The main forms in the diet are α- and γ-tocopherol, due to the highest content in food products. Nevertheless, α-tocopherol is the main form of vitamin E with the highest tissue concentration. The α- forms of both tocopherols and tocotrienols are considered as the most metabolically active. Currently, research results indicate also a greater antioxidant potential of tocotrienols than tocopherols. Moreover, the biological role of vitamin E metabolites have received increasing interest. The aim of this review is to update the knowledge of tocopherol and tocotrienol bioactivity, with a particular focus on their bioavailability, distribution, and metabolism determinants in humans. Almost one hundred years after the start of research on α-tocopherol, its biological properties are still under investigation. For several decades, researchers' interest in the biological importance of other forms of vitamin E has also been growing. Some of the functions, for instance the antioxidant functions of α- and γ-tocopherols, have been confirmed in humans, while others, such as the relationship with metabolic disorders, are still under investigation. Some studies, which analyzed the biological role and mechanisms of tocopherols and tocotrienols over the past few years described new and even unexpected cellular and molecular properties that will be the subject of future research.

Alpha-tocopherol acetate and alpha lipoic acid may mitigate the development of wooden breast myopathy in broilers at an early age

1. The objective of this study was to identify the effects of the antioxidant alpha-tocopherol acetate (ATA) and alpha lipoic acid (ALA) which have anti-inflammatory effects on developmental onset, severity and the progression of wooden breast (WB) based on Pectoralis major (P. major) muscle morphology and expression of genes associated with WB during the first three weeks post-hatch.2. A total of 160 newly hatched Ross 708 broiler chicks were randomly assigned in a replicated trial to either a control group or three dietary treatments (ATA 160 mg/kg feed, ALA 500 mg/kg feed or in combination).3. Microscopic changes associated with WB began at one week of age in all groups. The ATA acetate and ALA fed in combination decreased WB severity at two weeks of age (P = 0.05) and ATA alone or in combination reduced severity at three weeks of age compared to the control group (P = 0.05). Expression of myogenic determination factor 1 and peroxisome proliferator-activated receptor gamma was reduced in all dietary treatments compared to the control at three weeks of age (P ≤ 0.05), which suggested reduced muscle degeneration and lipid deposition.4. ATA and ALA fed both independently and in combination had a positive effect on mitigating WB severity microscopically as early as two weeks of age.

Adherence to Nutritional Supplementation Determines Postoperative Vitamin D Status, but Not Levels of Bone Resorption Marker, in Sleeve-Gastrectomy Patients

BACKGROUND

Taking advantage of isomeric form of vitamin E in the supplement, adherence to supplement could be evaluated by changes in circulating α- and γ-tocopherol concentrations. Accordingly, effects of supplementation on postoperative nutrition and bone metabolism were studied in terms of adherence.

METHODS

Thirty-eight SG patients were all prescribed a postoperative nutritional supplement containing a low dose of vitamin D (600 IU) and calcium (200 mg). Blood samples were collected prior to (M0) and 6 months after (M6) surgery and concentrations of nutrients and C-terminal telopeptide of type I collage (CTX), a marker of bone resorption, were measured. Adherence and non-adherence were stratified according to change (△, M6-M0) in serum α-tocopherol concentrations (> 0 vs. ≤ 0, respectively).

RESULTS

When M0 and M6 were compared, there were significant increases in serum concentrations of 25(OH)D, α-tocopherol and selenium, whereas there were reductions in parathyroid hormone, ferritin, and γ-tocopherol. At M6, the prevalence of vitamin D insufficiency (25(OH)D < 30 ng/mL) and high CTX were 72 and 26%, respectively. When comparison was made between adherence and non-adherence, only △25(OH)D concentrations, but no other nutrients nor postoperative CTX differed. Multiple linear regression demonstrated that postoperative vitamin D status was independently associated with its preoperative concentrations (β = 0.85, p < 0.001) and adherence (β = 0.52, p < 0.05).

CONCLUSION

SG patients' adherence to supplementation, even with a low dose of vitamin D and calcium, determined vitamin D status but not bone resorption marker concentrations, at least within 6 months after surgery.

Vitamin E analogs limit in vitro oxidant damage to bovine mammary endothelial cells

Diseases that occur during the transition period are exacerbated when cows are unable to cope with an increased pro-oxidant load that results in oxidative stress. Dairy cattle are routinely supplemented with the vitamin E analog α-tocopherol to mitigate the severity of oxidative stress. Nonetheless, oxidative stress remains a disease predisposing condition for many dairy cattle. A better method of optimizing the antioxidant functions of vitamin E is needed. α-Tocopherol is only 1 of 8 analogs of vitamin E, all of which have varying antioxidant properties in other mammals, albeit a shorter physiological half-life compared with α-tocopherol. A primary bovine mammary endothelial cell oxidant challenge model was used to determine functions of certain vitamin E analogs. The aim of this study was to determine if other analogs, namely γ-tocopherol or γ-tocotrienol, have antioxidative functions in bovine cells and if these functions may protect cellular viability and endothelial function from oxidant damage. Physiological (10 μM) and supraphysiological (50 μM) concentrations of γ-tocopherol and γ-tocotrienol had a greater capacity to reduce accumulated reactive oxygen species derived from a nitric oxide donating pro-oxidant antagonist, when compared with α-tocopherol, after 30 min to 6 h of treatment. Further, γ-tocotrienol (10 μM) decreased cell cytotoxicity to a greater amount than other analogs at like concentrations, whereas γ-tocopherol (10 μM) reduced lipid peroxidation and apoptosis more effectively than other analogs. Last, α-tocopherol (5 and 10 μM) and γ-tocopherol (5 and 10 μM) significantly slowed pro-oxidant induced loss of endothelial cell barrier integrity over a 48-h period using an electrical cell-substrate impedance sensing system. Concerningly, γ-tocotrienol drastically reduced the endothelial barrier integrity at only 5 μM despite no apparent effect on cellular viability at like concentrations. γ-Tocotrienol, however, was also the only analog to show significant cytotoxicity and reductions in viability at supraphysiological doses (25 and 50 μM). Our results suggest that γ-tocopherol has antioxidant activities that reduces cellular damage and loss of function due to oxidant challenge as effectively as α-tocopherol. These data set the foundation for further investigation into the antioxidant properties of vitamin E analogs in other bovine cells types or whole animal models.

Antioxidant-Based Therapies in Male Infertility: Do We Have Sufficient Evidence Supporting Their Effectiveness?

Under physiological conditions, reactive oxygen species (ROS) play pivotal roles in various processes of human spermatozoa. Indeed, semen requires the intervention of ROS to accomplish different stages of its maturation. However, ROS overproduction is a well-documented phenomenon occurring in the semen of infertile males, potentially causing permanent oxidative damages to a vast number of biological molecules (proteins, nucleic acids, polyunsaturated fatty acids of biological membrane lipids), negatively affecting the functionality and vitality of spermatozoa. ROS overproduction may concomitantly occur to the excess generation of reactive nitrogen species (RNS), leading to oxidative/nitrosative stress and frequently encountered in various human pathologies. Under different conditions of male infertility, very frequently accompanied by morpho-functional anomalies in the sperm analysis, several studies have provided evidence for clear biochemical signs of damages to biomolecules caused by oxidative/nitrosative stress. In the last decades, various studies aimed to verify whether antioxidant-based therapies may be beneficial to treat male infertility have been carried out. This review analyzed the results of the studies published during the last ten years on the administration of low-molecular-weight antioxidants to treat male infertility in order to establish whether there is a sufficient number of data to justify antioxidant administration to infertile males. An analysis of the literature showed that only 30 clinical studies tested the effects of the administration of low-molecular-weight antioxidants (administered as a single antioxidant or as a combination of different antioxidants with the addition of vitamins and/or micronutrients) to infertile males. Of these studies, only 33.3% included pregnancy and/or live birth rates as an outcome measure to determine the effects of the therapy. Of these studies, only 4 were case–control studies, and only 2 of them found improvement of the pregnancy rate in the group of antioxidant-treated patients. Additionally, of the 30 studies considered in this review, only 43.3% were case–control studies, 66.7% enrolled a number of patients higher than 40, and 40% carried out the administration of a single antioxidant. Therefore, it appears that further studies are needed to clearly define the usefulness of antioxidant-based therapies to treat male infertility.