Pharmacokinetics and safety of vitamin E δ-tocotrienol after single and multiple doses in healthy subjects with measurement of vitamin E metabolites

Different Roles of Tocopherols and Tocotrienols in Chemoprevention and Treatment of Prostate Cancer

The vitamin E family contains α-tocopherol (αT), βT, γT, and δT and α-tocotrienol (TE), βTE, γTE, and δTE. Research has revealed distinct roles of these vitamin E forms in prostate cancer (PCa). The ATBC trial showed that αT at a modest dose significantly decreased PCa mortality among heavy smokers. However, other randomized controlled trials including the Selenium and Vitamin E Cancer Prevention Trial (SELECT) indicate that supplementation of high-dose αT (≥400 IU) does not prevent PCa among nonsmokers. Preclinical cell and animal studies also do not support chemopreventive roles of high-dose αT and offer explanations for increased incidence of early-stage PCa reported in the SELECT. In contrast, accumulating animal studies have demonstrated that γT, δT, γTE, and δTE appear to be effective for preventing early-stage PCa from progression to adenocarcinoma in various PCa models. Existing evidence also support therapeutic roles of γTE and its related combinations against advanced PCa. Mechanistic and cell-based studies show that different forms of vitamin E display varied efficacy, that is, δTE ≥ γTE > δT ≥ γT >> αT, in inhibiting cancer hallmarks and enabling characteristics, including uncontrolled cell proliferation, angiogenesis, and inflammation possibly via blocking 5-lipoxygenase, nuclear factor κB, hypoxia-inducible factor-1α, modulating sphingolipids, and targeting PCa stem cells. Overall, existing evidence suggests that modest αT supplement may be beneficial to smokers and γT, δT, γTE, and δTE are promising agents for PCa prevention for modest-risk to relatively high-risk population. Despite encouraging preclinical evidence, clinical research testing γT, δT, γTE, and δTE for PCa prevention is sparse and should be considered.

Vitamin E in the management of pancreatic cancer: A scoping review

Pancreatic cancer is the leading cause of cancer mortality worldwide. Research investigating effective management strategies for pancreatic cancer is ongoing. Vitamin E, consisting of both tocopherol and tocotrienol, has demonstrated debatable effects on pancreatic cancer cells. Therefore, this scoping review aims to summarize the effects of vitamin E on pancreatic cancer. In October 2022, a literature search was conducted using PubMed and Scopus since their inception. Original studies on the effects of vitamin E on pancreatic cancer, including cell cultures, animal models and human clinical trials, were considered for this review. The literature search found 75 articles on this topic, but only 24 articles met the inclusion criteria. The available evidence showed that vitamin E modulated proliferation, cell death, angiogenesis, metastasis and inflammation in pancreatic cancer cells. However, the safety and bioavailability concerns remain to be answered with more extensive preclinical and clinical studies. More in-depth analysis is necessary to investigate further the role of vitamin E in the management of pancreatic cancers.

Potential “Therapeutic” Effects of Tocotrienol-Rich Fraction (TRF) and Carotene “Against” Bleomycin-Induced Pulmonary Fibrosis in Rats via TGF-β/Smad, PI3K/Akt/mTOR and NF-κB Signaling Pathways

Background: Pulmonary fibrosis (PF) is a chronic, progressive, and, ultimately, terminal interstitial disease caused by a variety of factors, ranging from genetics, bacterial, and viral infections, to drugs and other influences. Varying degrees of PF and its rapid progress have been widely reported in post-COVID-19 patients and there is consequently an urgent need to develop an appropriate, cost-effective approach for the prevention and management of PF. Aim: The potential “therapeutic” effect of the tocotrienol-rich fraction (TRF) and carotene against bleomycin (BLM)-induced lung fibrosis was investigated in rats via the modulation of TGF-β/Smad, PI3K/Akt/mTOR, and NF-κB signaling pathways. Design/Methods: Lung fibrosis was induced in Sprague-Dawley rats by a single intratracheal BLM (5 mg/kg) injection. These rats were subsequently treated with TRF (50, 100, and 200 mg/kg body wt/day), carotene (10 mg/kg body wt/day), or a combination of TRF (200 mg/kg body wt/day) and carotene (10 mg/kg body wt/day) for 28 days by gavage administration. A group of normal rats was provided with saline as a substitute for BLM as the control. Lung function and biochemical, histopathological, and molecular alterations were studied in the lung tissues. Results: Both the TRF and carotene treatments were found to significantly restore the BLM-induced alterations in anti-inflammatory and antioxidant functions. The treatments appeared to show pneumoprotective effects through the upregulation of antioxidant status, downregulation of MMP-7 and inflammatory cytokine expressions, and reduction in collagen accumulation (hydroxyproline). We demonstrated that TRF and carotene ameliorate BLM-induced lung injuries through the inhibition of apoptosis, the induction of TGF-β1/Smad, PI3K/Akt/mTOR, and NF-κB signaling pathways. Furthermore, the increased expression levels were shown to be significantly and dose-dependently downregulated by TRF (50, 100, and 200 mg/kg body wt/day) treatment in high probability. The histopathological findings further confirmed that the TRF and carotene treatments had significantly attenuated the BLM-induced lung injury in rats. Conclusion: The results of this study clearly indicate the ability of TRF and carotene to restore the antioxidant system and to inhibit proinflammatory cytokines. These findings, thus, revealed the potential of TRF and carotene as preventive candidates for the treatment of PF in the future.

Metabolism of natural forms of vitamin E and biological actions of vitamin E metabolites

Natural forms of vitamin E comprise four tocopherols and four tocotrienols. During the last twenty years, there have been breakthroughs in our understanding of vitamin E metabolism and biological activities of vitamin E metabolites. Research has established that tocopherols and tocotrienols are metabolized via ω-hydroxylase (CYP4F2)-initiated side chain oxidation to form 13'-hydroxychromanol and 13'-carobyxychromanol (13'-COOH). 13'-COOHs are further metabolized via β-oxidation and sulfation to intermediate carboxychromanols, terminal metabolite carboxyethyl-hydroxychroman (CEHC), and sulfated analogs. Animal and human studies show that γ-, δ-tocopherol and tocotrienols are more extensively metabolized than α-tocopherol (αT), as indicated by higher formation of CEHCs and 13'-COOHs from non-αT forms than those from αT. 13'-COOHs are shown to be inhibitors of cyclooxygenase-1/-2 and 5-lipoxygenase and much stronger than CEHCs for these activities. 13'-COOHs inhibit cancer cell growth, modulate cellular lipids and activate peroxisome proliferator-activated receptor-γ and pregnane X receptor. Consistent with mechanistic findings, αT-13'-COOH or δTE-13'-COOH, respective metabolites of αT or δ-tocotrienol, show anti-inflammatory and cancer-preventive effects, modulates the gut microbiota and prevents β-amyloid formation in mice. Therefore, 13'-COOHs are a new class of bioactive compounds with anti-inflammatory and anti-cancer activities and potentially capable of modulating lipid and drug metabolism. Based on the existing evidence, this author proposes that metabolites may contribute to disease-preventing effects of γ-, δ-tocopherol and tocotrienols. The role of metabolites in αT's actions may be somewhat limited considering controlled metabolism of αT because of its association with tocopherol-transport protein and less catabolism by CYP4F2 than other vitamin E forms.

Vitamin E: How much is enough, too much and why!

α-Tocopherol (α-T) is a required dietary nutrient for humans and thus is a vitamin. This narrative review focuses on vitamin E structures, functions, biological determinants and its deficiency symptoms in humans. The mechanisms for the preferential α-T tissue enrichment in the human body include the α-T transfer protein (TTPA) and the preferential metabolism of non-α-T forms. Potential new α-T biomarkers, pharmacokinetic data, and whether there are better approaches to evaluate and set the α-T dietary requirement are discussed. Finally, the possible role of α-T supplements in delay of chronic diseases and the evaluation of vitamin E safety are considered.

Dudrick Research Symposium: Expanding the boundaries of cancer care through nutrition support

The 2020 Dudrick Research Symposium, entitled "Expanding the Boundaries of Cancer Care Through Nutritional Support," was held on March 30, at the American Society for Parenteral and Enteral Nutrition (ASPEN), Nutrition Science & Practice Conference. It was scheduled to take place in Tampa, Florida, but had to be held virtually. The Dudrick Symposium honors the many pivotal and innovative contributions made by the late Dr Stanley J. Dudrick, physician scientist, academic leader, and a founding member of ASPEN. This year, in addition to honoring his legacy, we honored his life. As the 2019 recipient of the Dudrick Research Scholar Award, Dr Pimiento chaired the symposium. The presentations focused on discussing the history, the present and future frontiers in the overlapping fields of nutrition support and cancer care. The late Dr John Daly opened the presentation with a moving tribute to Dr Dudrick's life and then spoke about the impact of nutrition support on surgical care and outcomes for cancer patients. Dr Pimiento discussed the role of nutraceuticals for cancer chemoprevention, and the level 1 clinical evidence surrounding this topic. Dr Kraemer explored the role of exercise physiology for optimal nutrient utilization and the overlap between targeted physical activity and nutrition support to obtain better outcomes on the cancer population. The symposium was closed by Dr Stephen Hursting, who discussed the impact of obesity in the soaring cancer rates and its relationship with clinical outcomes. In this article, we cover the presentations by Drs Pimiento and Kraemer.

The medicinal chemistry of mitochondrial dysfunction: a critical overview of efforts to modulate mitochondrial health

Mitochondria are subcellular organelles that perform a variety of critical biological functions, including ATP production and acting as hubs of immune and apoptotic signalling. Mitochondrial dysfunction has been extensively linked to the pathology of multiple neurodegenerative disorders, resulting in significant investment from the drug discovery community. Despite extensive efforts, there remains no disease modifying therapies for neurodegenerative disorders. This manuscript aims to review the compounds historically used to modulate the mitochondrial network through the lens of modern medicinal chemistry, and to offer a perspective on the evidence that relevant exposure was achieved in a representative model and that exposure was likely to result in target binding and engagement of pharmacology. We hope this manuscript will aid the community in identifying those targets and mechanisms which have been convincingly (in)validated with high quality chemical matter, and those for which an opportunity exists to explore in greater depth.

Tocotrienols: Dietary Supplements for Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is one of the leading causes of death worldwide. Emphysema and chronic bronchitis are the two major phenotypes of COPD, which have many symptoms, such as dyspnea, chronic cough, and mucus overproduction. Emphysema is characterized by the destruction of the alveolar wall, while chronic bronchitis is characterized by limitations in expiratory airflow. Cigarette smoking is the most significant risk factor for the pathogenesis of COPD in the developed world. Chronic inflammation contributes to the onset and progression of the disease and furthers the risk of comorbidities. Current treatment options and prevention strategies for COPD are very limited. Tocotrienols are a group of vitamin E molecules with antioxidant and anti-inflammatory properties. Individual tocotrienols (α, γ, and δ) have shown their ability to attenuate inflammation specifically via suppressing nuclear factor-κB-mediated cytokine production. The δ- and γ-forms of tocotrienols have been indicated as the most effective in the prevention of macrophage infiltration, production of reactive oxygen species, and cytokine secretion. This review briefly discusses the pathogenesis of COPD and the role of inflammation therein. Furthermore, we summarize the in vitro and in vivo evidence for the anti-inflammatory activity of tocotrienols and their potential application to COPD management. Coupled with the bioavailability and safety profile of tocotrienols, the ability of these compounds to modulate COPD progression by targeting the inflammation pathways renders them potential candidates for novel therapeutic approaches in the treatment of COPD patients.

Concise Synthesis of (S)-δ-CEHC, a Metabolite of Vitamin E

Carboxyethyl hydroxychromans (CEHCs) are natural metabolites of vitamin E (VE). Their urinary levels can serve as useful biomarkers for the nutritional assessment of VE. Moreover, specific biological activities of CEHCs deserve further investigation. Here, we report a concise method to build up a chiral 6-hydroxychroman scaffold of VE and CEHCs. The first total synthesis of (S)-δ-CEHC was accomplished in 40% overall yield and 97% ee using a chiral synthon derived from naturally occurring (-)-linalool.

The Role of Vitamin E in Breast Cancer Treatment and Prevention: Current Perspectives

Background:

Regarding the multifactorial etiology of breast cancer, food choices, as well as dietary intake, are the main modified factors in cancer prevention. In this sense, understanding molecular pathways involved in breast cancer proliferation can help determine the mechanisms of action of organic compounds such as antioxidant vitamins that are known to protect against cancer.

Objective:

Assess the mechanism of action of vitamin E in breast cancer modulation, with emphasis on important markers of tumor development.

Methods:

It is a systematic review carried out in PubMed and Web of Science databases, from the last 5 years, in Portuguese, English and Spanish. The following terms were selected according to The Medical Subject Headings (MeSH): “breast cancer” OR “breast neoplasms”, “tocopherol” OR “tocotrienols” OR “vitamin E”, as equated terms.

Results:

A total of 595 articles were found and 25 were selected according to inclusion criteria. Vitamin E has been related to suppression/overexpression of important tumorigenic pathways, mainly associated with proliferation, energy metabolism, chemosensitivity and invasion/metastasis. Clinical studies of vitamin E supplementation are needed to assess the dose/response effect on breast cancer patients.

Conclusion:

The safety of vitamin E supplementation is still controversial due to current studies design available. However, when vitamin E is supplemented, the dose and therapeutic regimen must be carefully decided, including the route of administration and breast cancer subtypes to enhance desired effects and minimize unwanted side effects.

Role of Palm Oil Vitamin E in Preventing Pre-eclampsia: A Secondary Analysis of a Randomized Clinical Trial Following ISSHP Reclassification

Background: Preeclampsia is a significant cause of maternal and perinatal mortality worldwide. Oxidative stress plays a key role in its pathophysiology, hence antioxidants such as tocotrienol may be preventive against preeclampsia. In 2018, the ISSHP revised the definition of preeclampsia. In accordance with the new definition, we report a secondary data analysis from a clinical trial comparing palm oil vitamin E in the form of tocotrienol-rich fraction (TRF) against placebo, in preventing preeclampsia.

Method: A randomized double-blind controlled trial was conducted in 2002–2005 to assess the benefits of TRF in preeclampsia prevention. A total of 299 primigravidae were recruited. The intervention group was supplemented with TRF 100 mg daily in super-olein capsules, whereas the placebo group was prescribed super-olein capsules without TRF, beginning from 12 to 16 gestational weeks until delivery. The primary outcome measure was incidence of preeclampsia.

Results: The total incidence of pregnancy induced hypertension (PIH) was 5%, whereas the incidence of preeclampsia was 2.3%. The odds of developing PIH (adjusted OR 0.254; 95% CI: 0.07–0.93; p–value 0.038) and preeclampsia (adjusted OR 0.030; 95% CI: 0.001–0.65; p-value 0.025) were significantly lower in the TRF arm compared to the placebo arm.

Conclusion: Antenatal supplementation with palm oil vitamin E in the form of TRF is associated with significant reductions in the incidence of preeclampsia and PIH in a single urban tertiary hospital. Palm oil vitamin E deserves further scrutiny as a potential public health preventive measure against preeclampsia and PIH.

Pharmacology and Pharmacokinetics of Vitamin E: Nanoformulations to Enhance Bioavailability

Vitamin E belongs to the family of lipid-soluble vitamins and can be divided into two groups, tocopherols and tocotrienols, with four isomers (alpha, beta, gamma and delta). Although vitamin E is widely known as a potent antioxidant, studies have also revealed that vitamin E possesses anti-inflammatory properties. These crucial properties of vitamin E are beneficial in various aspects of health, especially in neuroprotection and cardiovascular, skin and bone health. However, the poor bioavailability of vitamin E, especially tocotrienols, remains a great limitation for clinical applications. Recently, nanoformulations that include nanovesicles, solid-lipid nanoparticles, nanostructured lipid carriers, nanoemulsions, and polymeric nanoparticles have shown promising outcomes in improving the efficacy and bioavailability of vitamin E. This review focuses on the pharmacological properties and pharmacokinetics of vitamin E and current advances in vitamin E nanoformulations for future clinical applications. The limitations and future recommendations are also discussed in this review.

Synthesis of [18F]F-γ-T-3, a Redox-Silent γ-Tocotrienol (γ-T-3) Vitamin E Analogue for Image-Based In Vivo Studies of Vitamin E Biodistribution and Dynamics

Vitamin E, a natural antioxidant, is of interest to scientists, health care pundits and faddists; its nutritional and biomedical attributes may be validated, anecdotal or fantasy. Vitamin E is a mixture of tocopherols (TPs) and tocotrienols (T-3s), each class having four substitutional isomers (α-, β-, γ-, δ-). Vitamin E analogues attain only low concentrations in most tissues, necessitating exacting invasive techniques for analytical research. Quantitative positron emission tomography (PET) with an F-18-labeled molecular probe would expedite access to Vitamin E’s biodistributions and pharmacokinetics via non-invasive temporal imaging. (R)-6-(3-[¹⁸F]Fluoropropoxy)-2,7,8-trimethyl-2-(4,8,12-trimethyltrideca-3,7,11-trien-1-yl)-chromane ([¹⁸F]F-γ-T-3) was prepared for this purpose. [¹⁸F]F-γ-T-3 was synthesized from γ-T-3 in two steps: (i) 1,3-di-O-tosylpropane was introduced at C6-O to form TsO-γ-T-3, and (ii) reaction of this tosylate with [¹⁸F]fluoride in DMF/K₂₂₂. Non-radioactive F-γ-T-3 was synthesized by reaction of γ-T-3 with 3-fluoropropyl methanesulfonate. [¹⁸F]F-γ-T-3 biodistribution in a murine tumor model was imaged using a small-animal PET scanner. F-γ-T-3 was prepared in 61% chemical yield. [¹⁸F]F-γ-T-3 was synthesized in acceptable radiochemical yield (RCY 12%) with high radiochemical purity (>99% RCP) in 45 min. Preliminary F-18 PET images in mice showed upper abdominal accumulation with evidence of renal clearance, only low concentrations in the thorax (lung/heart) and head, and rapid clearance from blood. [¹⁸F]F-γ-T-3 shows promise as an F-18 PET tracer for detailed in vivo studies of Vitamin E. The labeling procedure provides acceptable RCY, high RCP and pertinence to all eight Vitamin E analogues.

Synergistic Impact of Xanthorrhizol and d-δ-Tocotrienol on the Proliferation of Murine B16 Melanoma Cells and Human DU145 Prostate Carcinoma Cells

Isoprenoids suppress the mevalonate pathway that provides prenyl groups for the posttranslational modification of growth-regulating proteins. We hypothesize that xanthorrhizol and d-δ-tocotrienol synergistically suppress the growth of murine B16 melanoma and human DU145 prostate carcinoma cells. Xanthorrhizol (0-200 µmol/L; half maximal inhibitory concentration [IC₅₀] = 65 µmol/L) and d-δ-tocotrienol (0-40 µmol/L; IC₅₀ = 20 µmol/L) each induced a concentration-dependent suppression of the proliferation of B16 cells and concurrent cell cycle arrest at the G1 phase. A blend of 16.25 µmol/L xanthorrhizol and 10 µmol/L d-δ-tocotrienol suppressed B16 cell proliferation by 69%, an impact greater than the sum of those induced by xanthorrhizol (15%) and d-δ-tocotrienol (12%) individually. The blend cumulatively reduced the levels of cyclin-dependent kinase four and cyclin D1, key regulators of cell cycle progression at the G1 phase. The expression of RAS and extracellular signal-regulated kinase (ERK1/2) in the proliferation-stimulating RAS-RAF-MEK-ERK pathway was downregulated by the blend. Xanthorrhizol also induced a concentration-dependent suppression of the proliferation of DU145 cells with concomitant morphological changes. Isobologram confirmed the synergistic effect of xanthorrhizol and d-δ-tocotrienol on DU145 cell proliferation with combination index values ranging 0.61-0.94. Novel combinations of isoprenoids with synergistic actions may offer effective approaches in cancer prevention and therapy.

Delta-tocotrienol supplementation improves biochemical markers of hepatocellular injury and steatosis in patients with nonalcoholic fatty liver disease: A randomized, placebo-controlled trial

OBJECTIVE

The aim of this study was to examine the effects of delta-tocotrienol (δ-tocotrienol) supplementation on biochemical markers of hepatocellular injury and steatosis in patients with nonalcoholic fatty liver disease (NAFLD).

DESIGN

The study design was a two-group, randomized, double-blind, placebo-controlled trial. The patients with NAFLD were randomly assigned to receive δ-tocotrienol 300 mg twice daily or placebo for 24 weeks.

ENDPOINTS

The primary endpoints were change from baseline in fatty liver index (FLI) and homeostasis model of insulin resistance (HOMA-IR) after 24 weeks. Secondary endpoints included change from baseline in high sensitivity C-reactive protein (hs-CRP), malondialdehyde (MDA), alanine transaminase (ALT), aspartate transaminase (AST) and grading of hepatic steatosis on ultrasound. Between-group differences were tested for significance using ANCOVA. Mean differences (MD) with 95 % CIs are reported.

RESULTS

A total of 71 patients (tocotrienol=35, placebo=36) were randomized and included in the intention to treat analysis. Compared with placebo, δ-tocotrienol significantly reduced (MD [95 % CI]) FLI (-8.52 [-10.7, -6.3]; p < 0.001); HOMA-IR (-0.37 [-0.53, -0.21]; p < 0.001), hs-CRP (-0.61[-0.81, -0.42]; p < 0.001), MDA (-0.91 [-1.20, -0.63]; p < 0.001), ALT (-8.86 [-11.5, -6.2]; p < 0.001) and AST (-6.6 [-10.0, -3.08]; p < 0.001). Hepatic steatosis was also reduced by a significantly greater extent with tocotrienol than with placebo (p =0.047). No adverse events were reported.

CONCLUSION

δ-tocotrienol effectively improved biochemical markers of hepatocellular injury and steatosis in patients with NAFLD. δ-tocotrienol supplementation might be considered as a therapeutic option in the management of patients with NAFLD.

TRIAL REGISTRATION

Sri Lankan Clinical Trials Registry (SLCTR/2015/023, 2015-10-03).

Actions of annatto-extracted tocotrienol supplementation on obese postmenopausal women: study protocol for a double-blinded, placebo-controlled, randomised trial

INTRODUCTION

Obesity is a major health concern in postmenopausal women, and chronic low-grade inflammation contributes to the development of obesity. Cellular studies and high-fat-diet-induced obese mouse model mimicking obesity show the antiobesity effect of annatto-extracted tocotrienols (TT) with antioxidant capability. We aim to assess the safety and efficacy of TT consumption for lipid-related parameters in obese postmenopausal women.

METHODS AND ANALYSIS

Eligible obese postmenopausal women will be randomly assigned to placebo group (430 mg olive oil) and TT group (DeltaGold Tocotrienol 70%) for 24 weeks. In the present study, the primary outcome is total/regional fat mass and visceral adipose tissue. The secondary outcomes include lipid profile in serum, mRNA expression of fatty acid synthase and carnitine palmitoyltransferase 1A in fat tissue, oxylipins and endocannabinoids in plasma and adipose tissue, abundance and composition of intestinal microbiome in faeces, high-sensitivity C-reactive protein (hs-CRP) in serum and leptin in serum. Every participant will be evaluated at 0 (prior to starting intervention) and 24 weeks of intervention, except for serum lipid profile and hs-CRP at 0, 12 and 24 weeks. 'Intent-to-treat' principle is employed for data analysis. Hierarchical linear modelling is used to estimate the effects of dietary TT supplementation while properly accounting for dependency of data and identified covariates. To our knowledge, this is the first randomised, placebo-controlled, double-blinded study to determine dietary TT supplementation on an obese population. If successful, this study will guide the future efficacy TT interventions and TT can be implemented as an alternative for obese population in antiobesity management.

ETHICS AND DISSEMINATION

This study has been approved by the Bioethics Committee of the Texas Tech University Health Sciences Center, Lubbock. An informed consent form will be signed by a participant before enrolling in the study. The results from this trial will be actively disseminated through academic conference presentation and peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT03705845.

Vitamin E and cancer prevention: Studies with different forms of tocopherols and tocotrienols

α-Tocopherol (α-T) is the major form of vitamin E (VE) in animals and has the highest activity in carrying out the essential antioxidant functions of VE. Because of the involvement of oxidative stress in carcinogenesis, the cancer prevention activity of α-T has been studied extensively. Lower VE intake or nutritional status has been shown to be associated with increased cancer risk, and supplementation of α-T to populations with VE insufficiency has shown beneficial effects in lowering the cancer risk in some intervention studies. However, several large intervention studies with α-T conducted in North America have not demonstrated a cancer prevention effect. More recent studies have centered on the γ- and δ-forms of tocopherols and tocotrienols (T3). In comparison with α-T, these forms have much lower systemic bioavailability but have shown stronger cancer-preventive activities in many studies in animal models and cell lines. γ-T3 and δ-T3 generally have even higher activities than γ-T and δ-T. In this article, we review recent results from human and laboratory studies on the cancer-preventive activities of different forms of tocopherols and tocotrienols, at nutritional and pharmacological levels. We aim to elucidate the possible mechanisms of the preventive actions and discuss the possible application of the available information for human cancer prevention by different VE forms.

Tocopherols and Tocotrienols Are Bioavailable in Rats and Primarily Excreted in Feces as the Intact Forms and 13'-Carboxychromanol Metabolites

BACKGROUND

Vitamin E α-, γ-, or δ-tocopherol (αT, γT, δT) and γ- or δ-tocotrienol (γTE, δTE) are metabolized to hydroxychromanols and carboxychromanols including 13'-carboxychromanol (13'-COOH), 11'-COOH, and carboxyethyl hydroxychroman (CEHC), some of which have unique bioactivities compared with the vitamers. However, the bioavailability of these metabolites has not been well characterized.

OBJECTIVE

We investigated the pharmacokinetics (PK) of vitamin E forms and metabolites in rats.

METHODS

Six-week-old male Wistar rats received 1-time gavage of γT-rich tocopherols (50 mg/kg) containing γT/δT/αT (57.7%, 21.9%, and 10.9%, respectively) or δTE-rich tocotrienols (35 mg/kg) containing δTE/γTE (8:1). We quantified the time course of vitamin E forms and metabolites in the plasma and their 24-h excretion to the urine and feces. The general linear model repeated measure was used for analyses of the PK data.

RESULTS

In the rats' plasma, Cmax of γT or δTE was 25.6 ± 9.1 μM (Tmax = 4 h) or 16.0 ± 2.3 μM (Tmax = 2 h), respectively, and sulfated CEHCs and sulfated 11'-COOHs were the predominant metabolites with Cmax of 0.4-0.5 μM (Tmax ∼5-7 h) or ∼0.3 μM (Tmax at 4.7 h), respectively. In 24-h urine, 2.7% of γT and 0.7% of δTE were excreted as conjugated CEHCs. In the feces, 17-45% of supplemented vitamers were excreted as unmetabolized forms and 4.9-9.2% as unconjugated carboxychromanols, among which 13'-COOHs constituted ∼50% of total metabolites and the amount of δTE-derived 13'-COOHs was double that of 13'-COOH derived from γT.

CONCLUSIONS

PK data of vitamin E forms in rats reveal that γT, δT, γTE, and δTE are bioavailable in the plasma and are mainly excreted as unmetabolized forms and long-chain metabolites including 13'-COOHs in feces, with more metabolites from tocotrienols than from tocopherols.

Beneficial effects of δ-tocotrienol against oxidative stress in osteoblastic cells: studies on the mechanisms of action

Purpose

Natural antioxidants are considered as promising compounds in the prevention/treatment of osteoporosis. We studied the ability of purified δ-tocotrienol (δ-TT) isolated from a commercial palm oil (Elaeis guineensis) fraction to protect osteoblast MC3T3-E1 and osteocyte MLO-Y4 cells against tert-butyl hydroperoxide (t-BHP)-induced oxidative damage and the mechanisms involved in its protective action in MC3T3-E1.

Methods

MC3T3-E1 and MLO-Y4 cells were treated with δ-TT (1.25–20 µg/ml for 2 h) followed by t-BHP at 250 µM or 125 µM for 3 h, respectively. MTT test was used to measure cell viability. Apoptotic cells were stained with Hoechst-33258 dye. Intracellular ROS levels were measured by dichlorofluorescein CM-DCFA. The OPT fluorimetric assay was used to detect the reduced glutathione to oxidized glutathione ratio (GSH/GSSG) contents.

Results

δ-TT significantly prevented the effects of t-BHP on cell viability and apoptosis reaching a maximum protective activity at 10 and 5 µg/ml in MC3T3-E1 and MLO-Y4 cells, respectively. This protective effect was due to a reduction of intracellular ROS levels and an increase in the defense systems shown by the increase in the GSH/GSSG. GSH loss induced by an inhibitor of GSH synthesis significantly reduced the δ-TT-positive effect on ROS levels. δ-TT prevention of oxidative damage was completely removed by combined treatment with the specific inhibitors of PI3K/AKT (LY294002) and Nrf2 (ML385).

Conclusions

The δ-TT protective effect against oxidative damage in MC3T3-E1 cells is due to a reduction of intracellular ROS levels and an increase of the GSH/GSSG ratio, and involves an interaction between the PI3K/Akt–Nrf2 signaling pathways.

Vitamin E and cancer: an update on the emerging role of γ and δ tocotrienols

Despite significant advances in the diagnosis and treatment of cancer, the latter still remains a fatal disease due to the lack of prevention, early diagnosis, and effective drugs. Radiotherapy, chemotherapy, and surgery are not only expensive but produce a number of side effects that are detrimental to the patients' quality of life. Therefore, there is a great need to discover anti-cancer therapies that are specific to cancer cells and affordable, safe, and well tolerated by the patients. Vitamin E is a potential candidate due to its safety. Accumulating evidence on the anti-cancer potency of vitamin E has shifted the focus from tocopherols (TOCs) to tocotrienols (TTs). γ-TT and δ-TT have the highest anti-cancer activities and target common molecular pathways involved in the inhibition of the cell cycle, the induction of apoptosis and autophagy, and the inhibition of invasion, metastasis, and angiogenesis. Future directions should focus on further investigating how γ-TT and δ-TT (solely or in combination) induce anti-cancer molecular pathways when used in the presence of conventional chemotherapeutic drugs. These studies should be carried out in vitro, and promising results and combinations should then be assessed in in vivo experiments and finally in clinical trials. Finally, future research should focus on further evaluating the roles of γ-TT and δ-TT in the chemoprevention of cancer.

Delta-Tocotrienol Modulates Glutamine Dependence by Inhibiting ASCT2 and LAT1 Transporters in Non-Small Cell Lung Cancer (NSCLC) Cells: A Metabolomic Approach

The growth and development of non-small cell lung cancer (NSCLC) primarily depends on glutamine. Both glutamine and essential amino acids (EAAs) have been reported to upregulate mTOR in NSCLC, which is a bioenergetics sensor involved in the regulation of cell growth, cell survival, and protein synthesis. Seen as novel concepts in cancer development, ASCT2 and LAT transporters allow glutamine and EAAs to enter proliferating tumors as well as send a regulatory signal to mTOR. Blocking or downregulating these glutamine transporters in order to inhibit glutamine uptake would be an excellent therapeutic target for treatment of NSCLC. This study aimed to validate the metabolic dysregulation of glutamine and its derivatives in NSCLC using cellular 1H-NMR metabolomic approach while exploring the mechanism of delta-tocotrienol (δT) on glutamine transporters, and mTOR pathway. Cellular metabolomics analysis showed significant inhibition in the uptake of glutamine, its derivatives glutamate and glutathione, and some EAAs in both cell lines with δT treatment. Inhibition of glutamine transporters (ASCT2 and LAT1) and mTOR pathway proteins (P-mTOR and p-4EBP1) was evident in Western blot analysis in a dose-dependent manner. Our findings suggest that δT inhibits glutamine transporters, thus inhibiting glutamine uptake into proliferating cells, which results in the inhibition of cell proliferation and induction of apoptosis via downregulation of the mTOR pathway.

Utilization of Vitamin E Analogs to Protect Normal Tissues While Enhancing Antitumor Effects

Despite advances in radiation delivery techniques, side effects of radiation therapy due to radiation exposure of normal tissues are common and can limit the deliverable dose to tumors. Significant interests lie in pharmacologic modifiers that may protect against normal tissue toxicity from cancer treatment while simultaneously enhancing the tumor response to therapy. While no such treatments are available in the clinic, this is an area of active preclinical and clinical research. This review summarizes research studies that provide evidence to indicate that tocotrienols, natural forms of vitamin E, are potent radiation protectors and may also have antitumor effects. Hence, several current clinical trials test tocotrienols as concomitant treatment in cancer therapies.

gRASping the redox lever to modulate cancer cell fate signaling

RAS proteins are critical regulators of signaling networks controlling diverse cellular functions such as cell proliferation and survival and its mutation are among the most powerful oncogenic drivers in human cancers. Despite intense efforts, direct RAS-targeting strategies remain elusive due to its "undruggable" nature. To that end, bulk of the research efforts has been directed towards targeting upstream and/or downstream of RAS signaling. However, the therapeutic efficacies of these treatments are limited in the long run due to the acquired drug resistance in RAS-driven cancers. Interestingly, recent studies have uncovered a potential role of RAS in redox-regulation as well as the interplay between ROS and RAS-associated signaling networks during process of cancer initiation and progression. More specifically, these studies provide ample evidence to implicate RAS as a redox-rheostat, manipulating ROS levels to provide a redox-milieu conducive for carcinogenesis. Importantly, the understanding of RAS-ROS interplay could provide us with novel targetable vulnerabilities for designing therapeutic strategies. In this review, we provide a brief summary of the advances in the field to illustrate the dual role of RAS in redox-regulation and its implications in RAS signaling outcomes and also emerging redox-based strategies to target RAS-driven cancers.

Natural forms of vitamin E and metabolites-regulation of cancer cell death and underlying mechanisms

The disappointing results from large clinical studies of α-tocopherol (αT), the major form of vitamin E in tissues, for prevention of chronic diseases including cancer have cast doubt on not only αT but also other forms of vitamin E regarding their role in preventing carcinogenesis. However, basic research has shown that specific forms of vitamin E such as γ-tocopherol (γT), δ-tocopherol (δT), γ-tocotrienol (γTE) and δ-tocotrienol (δTE) can inhibit the growth and induce death of many types of cancer cells, and are capable of suppressing cancer development in preclinical cancer models. For these activities, these vitamin E forms are much stronger than αT. Further, recent research revealed novel anti-inflammatory and anticancer effects of vitamin E metabolites including 13'-carboxychromanols. This review focuses on anti-proliferation and induction of death in cancer cells by vitamin E forms and metabolites, and discuss mechanisms underlying these anticancer activities. The existing in vitro and in vivo evidence indicates that γT, δT, tocotrienols and 13'-carboxychromanols have anti-cancer activities via modulating key signaling or mediators that regulate cell death and tumor progression, such as eicosanoids, NF-κB, STAT3, PI3K, and sphingolipid metabolism. These results provide useful scientific rationales and mechanistic understanding for further translation of basic discoveries to the clinic with respect to potential use of these vitamin E forms and metabolites for cancer prevention and therapy. © 2018 IUBMB Life, 71(4):495-506, 2019.

A 12-week evaluation of annatto tocotrienol supplementation for postmenopausal women: safety, quality of life, body composition, physical activity, and nutrient intake

BACKGROUND

Evidence suggests that tocotrienols may benefit bone health in osteopenic women. However, their safety in this population has never been investigated. This study was to evaluate the safety of a 12-week supplementation of annato tocotrienol in postmenopausal osteopenic women, along with effects of the supplementation on quality of life, body composition, physical activity, and nutrient intake in this population.

METHODS

Eighty nine postmenopausal osteopenic women were randomly assigned to 3 treatment arms: (1) Placebo (430 mg olive oil/day), (2) Low tocotrientol (Low TT) (430 mg tocotrienol/day from DeltaGold 70 containing 300 mg tocotrienol) and (3) High tocotrienol (High TT) (860 mg tocotrienol/day from DeltaGold 70 containing 600 mg tocotrienol) for 12 weeks. DeltaGold 70 is an extract from annatto seed with 70% tocotrienol consisting of 90% delta-tocotrienol and 10% gamma-tocotrienol. Safety was examined by assessing liver enzymes (aspartate aminotransferase, alanine aminotransferase), alkaline phosphatase, bilirubin, kidney function (blood urea nitrogen and creatinine), electrolytes, glucose, protein, albumin, and globulin at 0, 6, and 12 weeks. Serum tocotrienol and tocopherol concentrations were assessed and pills counted at 0, 6, and 12 weeks. Quality of life, body composition, physical activity, and dietary macro- and micro-nutrient intake were evaluated at 0 and 12 weeks. A mixed model of repeated measures ANOVA was applied for analysis.

RESULTS

Eighty seven subjects completed the study. Tocotrienol supplementation did not affect liver or kidney function parameters throughout the study. No adverse event due to treatments was reported by the participants. Tocotrienol supplementation for 6 weeks significantly increased serum delta-tocotrienol level and this high concentration was sustained to the end of study. There was no difference in serum delta-tocotrienol levels between the Low TT and the High TT groups. No effects of tocotrienol supplementation were observed on quality of life, body composition, physical activity, and nutrient intake.

CONCLUSIONS

Annatto-derived tocotrienol up to 600 mg per day for 12 weeks appeared to be safe in postmenopausal osteopenic women, particularly in terms of liver and kidney functions. Tocotrienol supplementation for 12 weeks did not affect body composition, physical activity, quality of life, or intake of macro- and micro-nutrients in these subjects.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02058420 .

TITLE

Tocotrienols and bone health of postmenopausal women.

δ-Tocotrienol, a natural form of vitamin E, inhibits pancreatic cancer stem-like cells and prevents pancreatic cancer metastasis

The growth, metastasis, and chemotherapy resistance of pancreatic ductal adenocarcinoma (PDAC) is characterized by the activation and growth of tumor-initiating cells in distant organs that have stem-like properties. Thus, inhibiting growth of these cells may prevent PDAC growth and metastases. We have demonstrated that δ-tocotrienol, a natural form of vitamin E (VEDT), is bioactive against cancer, delays progression, and prevents metastases in transgenic mouse models of PDAC. In this report, we provide the first evidence that VEDT selectively inhibits PDAC stem-like cells. VEDT inhibited the viability, survival, self-renewal, and expression of Oct4 and Sox2 transcription factors in 3 models of PDAC stem-like cells. In addition, VEDT inhibited the migration, invasion, and several biomarkers of epithelial-to-mesenchymal transition and angiogenesis in PDAC cells and tumors. These processes are critical for tumor metastases. Furthermore, in the L3.6pl orthotopic model of PDAC metastases, VEDT significantly inhibited growth and metastases of these cells. Finally, in an orthotopic xenograft model of human PDAC stem-like cells, we showed that VEDT significantly retarded the growth and metastases of gemcitabine-resistant PDAC human stem-like cells. Because VEDT has been shown to be safe and to reach bioactive levels in humans, this work supports investigating VEDT for chemoprevention of PDAC metastases.

Targeting melanoma stem cells with the Vitamin E derivative δ-tocotrienol

The prognosis of metastatic melanoma is very poor, due to the development of drug resistance. Cancer stem cells (CSCs) may play a crucial role in this mechanism, contributing to disease relapse. We first characterized CSCs in melanoma cell lines. We observed that A375 (but not BLM) cells are able to form melanospheres and show CSCs traits: expression of the pluripotency markers SOX2 and KLF4, higher invasiveness and tumor formation capability in vivo with respect to parental adherent cells. We also showed that a subpopulation of autofluorescent cells expressing the ABCG2 stem cell marker is present in the A375 spheroid culture. Based on these data, we investigated whether δ-TT might target melanoma CSCs. We demonstrated that melanoma cells escaping the antitumor activity of δ-TT are completely devoid of the ability to form melanospheres. In contrast, cells that escaped vemurafenib treatment show a higher ability to form melanospheres than control cells. δ-TT also induced disaggregation of A375 melanospheres and reduced the spheroidogenic ability of sphere-derived cells, reducing the expression of the ABCG2 marker. These data demonstrate that δ-TT exerts its antitumor activity by targeting the CSC subpopulation of A375 melanoma cells and might represent a novel chemopreventive/therapeutic strategy against melanoma.

Effective inhibition of Cbf-14 against Cryptococcus neoformans infection in mice and its related anti-inflammatory activity

Cbf-14 (RLLRKFFRKLKKSV), a designed peptide derived from cathelicidin family AMP, has proven to be potent against drug-resistant bacteria. In the present study, we investigated the anti-cryptococcal activity of Cbf-14 in vitro and in a pulmonary infection mouse model. Sensitivity test indicated that Cbf-14 possessed effective antifungal activity against Cryptococcus neoformans with an MIC of 4-16 µg/ml, and killing experiments showed that fungicidal activity was achieved after only 4 h treatment with Cbf-14 at 4× MIC concentrations in vitro. Meanwhile, Cbf-14 was effective at prolonging the survival of infected mice when compared with controls, and significantly inhibited the secretion of pro-inflammatory cytokines TNF-α, IL-1β and IL-6, suggesting its anti-inflammatory activity against fungal infections. As a positively charged peptide, Cbf-14 was proven to neutralize the negative zeta potential of the fungal cell surface, disrupt the capsule polysaccharide of fungi, and further damage cell membrane integrity. These results were confirmed by flow cytometry analysis of the fluorescence intensity after PI staining, while cell membrane damage could be clearly observed by transmission electron microscopy after Cbf-14 (4× MIC) treatment for 1 h. In addition, Cbf-14 increased the IL-10 levels in cultured RAW 264.7 cells, which were stimulated by C. neoformans infection. The obtained data demonstrated that Cbf-14 could rapidly kill C. neoformans cells in vitro, effectively inhibit C. neoformans induced-infection in mice, and inhibit inflammation in vitro / vivo. Therefore, Cbf-14 could potentially be used for the treatment of fungal infections clinically.

Natural Forms of Vitamin E as Effective Agents for Cancer Prevention and Therapy

Initial research on vitamin E and cancer has focused on α-tocopherol (αT), but recent clinical studies on cancer-preventive effects of αT supplementation have shown disappointing results, which has led to doubts about the role of vitamin E, including different vitamin E forms, in cancer prevention. However, accumulating mechanistic and preclinical animal studies show that other forms of vitamin E, such as γ-tocopherol (γT), δ-tocopherol (δT), γ-tocotrienol (γTE), and δ-tocotrienol (δTE), have far superior cancer-preventive activities than does αT. These vitamin E forms are much stronger than αT in inhibiting multiple cancer-promoting pathways, including cyclo-oxygenase (COX)- and 5-lipoxygenase (5-LOX)-catalyzed eicosanoids, and transcription factors such as nuclear transcription factor κB (NF-κB) and signal transducer and activator of transcription factor 3 (STAT3). These vitamin E forms, but not αT, cause pro-death or antiproliferation effects in cancer cells via modulating various signaling pathways, including sphingolipid metabolism. Unlike αT, these vitamin E forms are quickly metabolized to various carboxychromanols including 13'-carboxychromanols, which have even stronger anti-inflammatory and anticancer effects than some vitamin precursors. Consistent with mechanistic findings, γT, δT, γTE, and δTE, but not αT, have been shown to be effective for preventing the progression of various types of cancer in preclinical animal models. This review focuses on cancer-preventive effects and mechanisms of γT, δT, γTE, and δTE in cells and preclinical models and discusses current progress in clinical trials. The existing evidence strongly indicates that these lesser-known vitamin E forms are effective agents for cancer prevention or as adjuvants for improving prevention, therapy, and control of cancer.

Tocotrienols for bone health: a translational approach

Osteoporosis, a degenerative bone disease, is characterized by low bone mass and microstructural deterioration of bone tissue resulting in aggravated bone fragility and susceptibility to fractures. The trend of extended life expectancy is accompanied by a rise in the prevalence of osteoporosis and concomitant complications in the elderly population. Epidemiological evidence has shown an association between vitamin E consumption and the prevention of age-related bone loss in elderly women and men. Animal studies show that ingestion of vitamin E, especially tocotrienols, may benefit bone health in terms of maintaining higher bone mineral density and improving bone microstructure and quality. The beneficial effects of tocotrienols on bone health appear to be mediated via antioxidant/anti-inflammatory pathways and/or 3-hydroxy-3-methylglutaryl coenzyme A mechanisms. We discuss (1) an overview of the prevalence and etiology of osteoporosis, (2) types of vitamin E (tocopherols versus tocotrienols), (3) findings of tocotrienols and bone health from published in vitro and animal studies, (4) possible mechanisms involved in bone protection, and (5) challenges and future direction for research.

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

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

Safety and efficacy of tocotrienol supplementation for bone health in postmenopausal women: protocol for a dose-response double-blinded placebo-controlled randomised trial

INTRODUCTION

Osteoporosis is a major health concern in postmenopausal women, and oxidative stress contributes to the development of bone loss. Cellular studies and ovariectomised rat model mimicking bone loss in postmenopausal women show the bone-protective effect of tocotrienols (TTs) with antioxidant capability. We aim to access the safety and efficacy of TT consumption for bone health in postmenopausal women.

METHODS AND ANALYSIS

In this 12-week randomised double-blinded placebo-controlled trial for the effects of dietary TT supplementation in postmenopausal women, postmenopausal women aged 45 years and older with at least 1 year after menopause and bone mineral density T-score at the spine and/or hip 2.5 or more below the reference values will be randomly assigned to 3 daily supplements: (1) placebo group receiving 860 mg olive oil, (2) low TT group receiving 430 mg of 70% pure TTs (containing 300 mg TT) and (3) high TT group receiving 860 mg of 70% pure TTs (600 mg TT). The primary outcome measure will be urinary N-terminal telopeptide. The secondary outcome measures will be serum bone-specific alkaline phosphatase, receptor activator of nuclear factor-κB ligand, osteoprotegerin, urinary 8-hydroxy-2'-deoxyguanosine and quality of life. At 0, 6 and 12 weeks, the following will be assessed: (1) primary and secondary outcome measures; (2) serum TT and tocopherol concentrations; (3) physical activity and food frequency questionnaires. Liver function will be monitored every 6 weeks for safety. 'Intent-to-treat' principle will be employed for data analysis. A model of repeated measurements with random effect error terms will be applied. Analysis of covariance, χ² analysis and regression will be used for comparisons.

ETHICS AND DISSEMINATION

This study was approved by the Bioethics Committee of the Texas Tech University Health Sciences Center. The findings of this trial will be submitted to a peer-reviewed journal in the areas of bone or nutrition and international conferences.

TRIAL REGISTRATION NUMBER

NCT02058420; results.