Multitargeted therapy of cancer by tocotrienols

Preventative and therapeutic potential of tocotrienols on musculoskeletal diseases in ageing

Musculoskeletal health is paramount in an ageing population susceptible to conditions such as osteoporosis, arthritis and fractures. Age-related changes in bone, muscle, and joint function result in declining musculoskeletal health, reduced mobility, increased risk of falls, and persistent discomfort. Preserving musculoskeletal wellbeing is essential for maintaining independence and enhancing the overall quality of life for the elderly. The global burden of musculoskeletal disorders is significant, impacting 1.71 billion individuals worldwide, with age-related muscle atrophy being a well-established phenomenon. Tocotrienols, a unique type of vitamin E found in various sources, demonstrate exceptional antioxidant capabilities compared to tocopherols. This characteristic positions them as promising candidates for addressing musculoskeletal challenges, particularly in mitigating inflammation and oxidative stress underlying musculoskeletal disorders. This review paper comprehensively examines existing research into the preventive and therapeutic potential of tocotrienols in addressing age-related musculoskeletal issues. It sheds light on the promising role of tocotrienols in enhancing musculoskeletal health and overall wellbeing, emphasizing their significance within the broader context of age-related health concerns.

Development of gamma-tocotrienol as a radiation medical countermeasure for the acute radiation syndrome: current status and future perspectives

INTRODUCTION

The possibility of exposure to high doses of total- or partial-body ionizing radiation at a high dose rate due to radiological/nuclear accidents or terrorist attacks is increasing. Despite research and development during the last six decades, there is a shortage of nontoxic, safe, and effective radiation medical countermeasures (MCMs) for radiological and nuclear emergencies. To date, the US Food and Drug Administration (US FDA) has approved only four agents for the mitigation of hematopoietic acute radiation syndrome (H-ARS).

AREA COVERED

We present the current status of a promising radiation countermeasure, gamma-tocotrienol (GT3; a component of vitamin E) as a radiation MCM that has been investigated in murine and nonhuman primate models of H-ARS. There is significant work with this agent using various omic platforms during the last few years to identify its efficacy biomarkers.

EXPERT OPINION

GT3 is a newer type of radioprotector having significant injury-countering potential and is currently under advanced development for H-ARS. As a pre-exposure drug, it requires only single doses, lacks significant toxicity, and has minimal, ambient temperature storage requirements; thus, GT3 appears to be an ideal MCM for military and first responders as well as for storage in the Strategic National Stockpile.

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

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

Effects of Gamma-Tocotrienol on Partial-Body Irradiation-Induced Intestinal Injury in a Nonhuman Primate Model

Exposure to high doses of radiation, accidental or therapeutic, often results in gastrointestinal (GI) injury. To date, there are no therapies available to mitigate GI injury after radiation exposure. Gamma-tocotrienol (GT3) is a promising radioprotector under investigation in nonhuman primates (NHP). We have shown that GT3 has radioprotective function in intestinal epithelial and crypt cells in NHPs exposed to 12 Gy total-body irradiation (TBI). Here, we determined GT3 potential in accelerating the GI recovery in partial-body irradiated (PBI) NHPs using X-rays, sparing 5% bone marrow. Sixteen rhesus macaques were treated with either vehicle or GT3 24 h prior to 12 Gy PBI. Structural injuries and crypt survival were examined in proximal jejunum on days 4 and 7. Plasma citrulline was assessed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Crypt cell proliferation and apoptotic cell death were evaluated using Ki-67 and TUNEL staining. PBI significantly decreased mucosal surface area and reduced villous height. Interestingly, GT3 increased crypt survival and enhanced stem cell proliferation at day 4; however, the effects seemed to be minimized by day 7. GT3 did not ameliorate a radiation-induced decrease in citrulline levels. These data suggest that X-rays induce severe intestinal injury post-PBI and that GT3 has minimal radioprotective effect in this novel model.

Revisiting the therapeutic potential of tocotrienol

The therapeutic potential of the tocotrienol group stems from its nutraceutical properties as a dietary supplement. It is largely considered to be safe when consumed at low doses for attenuating pathophysiology as shown by animal models, in vitro assays, and ongoing human trials. Medical researchers and the allied sciences have experimented with tocotrienols for many decades, but its therapeutic potential was limited to adjuvant or concurrent treatment regimens. Recent studies have focused on targeted drug delivery by enhancing the bioavailability through carriers, self-sustained emulsions, nanoparticles, and ethosomes. Epigenetic modulation and computer remodeling are other means that will help increase chemosensitivity. This review will focus on the systemic intracellular anti-cancer, antioxidant, and anti-inflammatory mechanisms that are stimulated and/or regulated by tocotrienols while highlighting its potent therapeutic properties in a diverse group of clinical diseases.

Effects of Gamma-Tocotrienol on Intestinal Injury in a GI-Specific Acute Radiation Syndrome Model in Nonhuman Primate

The gastrointestinal (GI) system is highly susceptible to irradiation. Currently, there is no Food and Drug Administration (FDA)-approved medical countermeasures for GI radiation injury. The vitamin E analog gamma-tocotrienol (GT3) is a promising radioprotector in mice and nonhuman primates (NHP). We evaluated GT3-mediated GI recovery in total-body irradiated (TBI) NHPs. Sixteen rhesus macaques were divided into two groups; eight received vehicle and eight GT3 24 h prior to 12 Gy TBI. Proximal jejunum was assessed for structural injuries and crypt survival on day 4 and 7. Apoptotic cell death and crypt cell proliferation were assessed with TUNEL and Ki-67 immunostaining. Irradiation induced significant shortening of the villi and reduced mucosal surface area. GT3 induced an increase in crypt depth at day 7, suggesting that more stem cells survived and proliferated after irradiation. GT3 did not influence crypt survival after irradiation. GT3 treatment caused a significant decline in TUNEL-positive cells at both day 4 (p < 0.03) and 7 (p < 0.0003). Importantly, GT3 induced a significant increase in Ki-67-positive cells at day 7 (p < 0.05). These data suggest that GT3 has radioprotective function in intestinal epithelial and crypt cells. GT3 should be further explored as a prophylactic medical countermeasure for radiation-induced GI injury.

Formulation and In Vivo Evaluation of a Solid Self-Emulsifying Drug Delivery System Using Oily Liquid Tocotrienols as Model Active Substance

Self-emulsifying drug delivery systems (SEDDS) can improve the oral bioavailability of poorly water-soluble drugs. Solid self-emulsifying drug delivery systems (s-SEDDS) offer several advantages including improved drug stability, ease of administration, and production. Most compounds employed in developing s-SEDDS are solid in nature, with a high amount of surfactants added. The aim of this study was to develop an s-SEDDS using a tocotrienol-rich fraction (TRF) as the model liquid active substance via a simple adsorption method. The solid formulation was developed using magnesium aluminosilicate as the carrier with 70% TRF and 30% surfactants (poloxamer and Labrasol^®). The formulation showed good self-emulsification efficiency with stable emulsion formed, excellent powder flowability, and small emulsion droplet size of 210–277 nm. The s-SEDDS with combined surfactants (poloxamer and Labrasol^®) showed a faster absorption rate compared to preparations with only a single surfactant and enhanced oral bioavailability (3.4–3.8 times higher) compared to the non-self-emulsifying oily preparation when administered at a fasted state in rats. In conclusion, an s-SEDDS containing a high amount of TRF was successfully developed. It may serve as a useful alternative to a liquid product with enhanced oral bioavailability and the added advantage of being a solid dosage form.

Challenges and Opportunities of Nanotechnology as Delivery Platform for Tocotrienols in Cancer Therapy

Plant-derived phytonutrients have emerged as health enhancers. Tocotrienols from the vitamin E family gained high attention in recent years due to their multi-targeted biological properties, including lipid-lowering, neuroprotection, anti-inflammatory, antioxidant, and anticancer effects. Despite well-defined mechanism of action as an anti-cancer agent, their clinical use is hampered by poor pharmacokinetic profile and low oral bioavailability. Delivery systems based on nanotechnology were proven to be advantageous in elevating the delivery of tocotrienols to tumor sites for enhanced efficacy. To date, preclinical development of nanocarriers for tocotrienols include niosomes, lipid nanoemulsions, nanostructured lipid carriers (NLCs) and polymeric nanoparticles. Active targeting was explored via the use of transferrin as targeting ligand in niosomes. In vitro, nanocarriers were shown to enhance the anti-proliferative efficacy and cellular uptake of tocotrienols in cancer cells. In vivo, improved bioavailability of tocotrienols were reported with NLCs while marked tumor regression was observed with transferrin-targeted niosomes. In this review, the advantages and limitations of each nanocarriers were critically analyzed. Furthermore, a number of key challenges were identified including scale-up production, biological barriers, and toxicity profiles. To overcome these challenges, three research opportunities were highlighted based on rapid advancements in the field of nanomedicine. This review aims to provide a wholesome perspective for tocotrienol nanoformulations in cancer therapy directed toward effective clinical translation.

Anti-inflammatory Activity of Tocotrienols in Age-related Pathologies: A SASPected Involvement of Cellular Senescence

Tocotrienols (T3) have been shown to represent a very important part of the vitamin E family since they have opened new opportunities to prevent or treat a multitude of age-related chronic diseases. The beneficial effects of T3 include the amelioration of lipid profile, the promotion of Nrf2 mediated cytoprotective activity and the suppression of inflammation. All these effects may be the consequence of the ability of T3 to target multiple pathways. We here propose that these effects may be the result of a single target of T3, namely senescent cells. Indeed, T3 may act by a direct suppression of the senescence-associated secretory phenotype (SASP) produced by senescent cells, mediated by inhibition of NF-kB and mTOR, or may potentially remove the origin of the SASP trough senolysis (selective death of senescent cells). Further studies addressed to investigate the impact of T3 on cellular senescence “in vitro” as well as in experimental models of age-related diseases “in vivo” are clearly encouraged.

Vitamin E and its anticancer effects

Vitamin E is a lipid soluble vitamin comprising of eight natural isoforms, namely, α, β, δ, γ isoforms of tocopherol and α, β, δ, γ isoforms of tocotrienol. Many studies have been performed to elucidate its role in cancer. Until last decade, major focus was on alpha tocopherol and its anticancer effects. However, major clinical trials using alpha-tocopherol like SELECT trial and ATBC trial did not yield meaningful results. Hence there was a shift of focus to gamma-tocopherol, delta-tocopherol and tocotrienol. Unlike alpha-tocopherol, gamma-tocopherol and delta-tocopherol can scavenge reactive nitrogen species in addition to reactive oxygen species. Antiangiogenic effect, inhibition of HMG CoA reductase enzyme and inhibition of NF-κB pathway make the anti-cancer effects of tocotrienols unique compared to other vitamin E isoforms. Preclinical research on non-alpha tocopherol isoforms of vitamin E showed promising data on their anticancer effects. In this review, we deal with the current understanding on the potential mechanisms involved in the anticancer effects of vitamin E and the controversies in this field over last three decades. We also highlight the need to conduct further research on the anticancer effects of non-alpha-tocopherol isoforms in larger population and clinical setting.

Anticancer properties of tocotrienols: A review of cellular mechanisms and molecular targets

Vitamin E is composed of two groups of compounds: α-, β-, γ-, and δ-tocopherols (TPs), and the corresponding unsaturated tocotrienols (TTs). TTs are found in natural sources such as red palm oil, annatto seeds, and rice bran. In the last decades, TTs (specifically, γ-TT and δ-TT) have gained interest due to their health benefits in chronic diseases, based on their antioxidant, neuroprotective, cholesterol-lowering, anti-inflammatory activities. Several in vitro and in vivo studies pointed out that TTs also exert a significant antitumor activity in a wide range of cancer cells. Specifically, TTs were shown to exert antiproliferative/proapoptotic effects and to reduce the metastatic or angiogenic properties of different cancer cells; moreover, these compounds were reported to specifically target the subpopulation of cancer stem cells, known to be deeply involved in the development of resistance to standard therapies. Interestingly, recent studies pointed out that TTs exert a synergistic antitumor effect on cancer cells when given in combination with either standard antitumor agents (i.e., chemotherapeutics, statins, "targeted" therapies) or natural compounds with anticancer activity (i.e., sesamin, epigallocatechin gallate (EGCG), resveratrol, ferulic acid). Based on these observations, different TT synthetic derivatives and formulations were recently developed and demonstrated to improve TT water solubility and to reduce TT metabolism in cancer cells, thus increasing their biological activity. These promising results, together with the safety of TT administration in healthy subjects, suggest that these compounds might represent a new chemopreventive or anticancer treatment (i.e., in combination with standard therapies) strategy. Clinical trials aimed at confirming this antitumor activity of TTs are needed.

Cebpd Is Essential for Gamma-Tocotrienol Mediated Protection against Radiation-Induced Hematopoietic and Intestinal Injury

Gamma-tocotrienol (GT3) confers protection against ionizing radiation (IR)-induced injury. However, the molecular targets that underlie the protective functions of GT3 are not yet known. We have reported that mice lacking CCAAT enhancer binding protein delta (Cebpd^−/−) display increased mortality to IR due to injury to the hematopoietic and intestinal tissues and that Cebpd protects from IR-induced oxidative stress and cell death. The purpose of this study was to investigate whether Cebpd mediates the radio protective functions of GT3. We found that GT3-treated Cebpd^−/− mice showed partial recovery of white blood cells compared to GT3-treated Cebpd^+/+ mice at 2 weeks post-IR. GT3-treated Cebpd^−/− mice showed an increased loss of intestinal crypt colonies, which correlated with increased expression of inflammatory cytokines and chemokines, increased levels of oxidized glutathione (GSSG), S-nitrosoglutathione (GSNO) and 3-nitrotyrosine (3-NT) after exposure to IR compared to GT3-treated Cebpd^+/+ mice. Cebpd is induced by IR as well as a combination of IR and GT3 in the intestine. Studies have shown that granulocyte-colony stimulating factor (G-CSF), mediates the radioprotective functions of GT3. Interestingly, we found that IR alone as well as the combination of IR and GT3 caused robust augmentation of plasma G-CSF in both Cebpd^+/+ and Cebpd^−/− mice. These results identify a novel role for Cebpd in GT3-mediated protection against IR-induced injury, in part via modulation of IR-induced inflammation and oxidative/nitrosative stress, which is independent of G-CSF.

Drug repurposing in malignant pleural mesothelioma: a breath of fresh air?

Drug repurposing is the use of known drugs for new indications. Malignant pleural mesothelioma (MPM) is a rare cancer with a poor prognosis. So far, few treatments have been approved in this disease. However, its incidence is expected to increase significantly, particularly in developing countries. Consequently, drug repurposing appears as an attractive strategy for drug development in MPM, since the known pharmacology and safety profile based on previous approvals of repurposed drugs allows for faster time-to-market for patients and lower treatment cost. This is critical in low- and middle-income countries where access to expensive drugs is limited. This review assesses the published preclinical and clinical data about drug repurposing in MPM.In this review, we identified 11 therapeutic classes that could be repositioned in mesothelioma. Most of these treatments have been evaluated in vitro, half have been evaluated in vivo in animal models of MPM and only three (i.e. valproate, thalidomide and zoledronic acid) have been investigated in clinical trials, with limited benefits so far. Efforts could be coordinated to pursue further investigations and test promising drugs identified in preclinical experiments in appropriately designed clinical trials.

Tumor regression after intravenous administration of targeted vesicles entrapping the vitamin E α-tocotrienol

The therapeutic potential of tocotrienol, a member of the vitamin E family of compounds with potent in vitro anti-cancer properties, is limited by its inability to specifically reach tumors following intravenous administration. The purpose of this study is to determine whether a novel tumor-targeted vesicular formulation of tocotrienol would suppress the growth of A431 epidermoid carcinoma and B16-F10 melanoma in vitro and in vivo. In this work, we demonstrated that novel transferrin-bearing multilamellar vesicles entrapping α-T3 resulted in a dramatically improved (by at least 52-fold) therapeutic efficacy in vitro on A431 cell line, compared to the free drug. In addition, the intravenous administration of tocotrienol entrapped in transferrin-bearing vesicles resulted in tumor suppression for 30% of A431 and 60% of B16-F10 tumors, without visible toxicity. Mouse survival was enhanced by >13days compared to controls administered with the drug solution only. This tumor-targeted, tocotrienol-based nanomedicine therefore significantly improved the therapeutic response in cancer treatment.

Progenitor Cell Mobilization by Gamma-tocotrienol: A Promising Radiation Countermeasure

This article reviews studies of progenitor mobilization with gamma-tocotrienol (GT3), a tocol under advanced development as a radiation countermeasure for acute radiation syndrome (ARS). GT3 protects mice against high doses of ionizing radiation and induces high levels of granulocyte colony-stimulating factor (G-CSF). GT3-induced G-CSF in conjunction with AMD3100 (a chemokine receptor antagonist clinically used to improve the yield of mobilized progenitors) mobilizes progenitors; these mobilized progenitors mitigate injury when infused to mice exposed to acute, high-dose ionizing radiation. The administration of a G-CSF antibody to GT3-injected donor mice abrogated the radiomitigative efficacy of blood or peripheral blood mononuclear cells (PBMC) in irradiated recipient mice. The efficacy of GT3-injected donor mice blood or PBMC was comparable to a recently published article involving blood or mononuclear cells obtained from mice injected with G-CSF. The injected progenitors were found to localize in various tissues of irradiated hosts. The authors demonstrate the efficacy of a bridging therapy in a preclinical animal model that allows the lymphohematopoietic system of severely immunocompromised mice to recover. This suggests that GT3 is a highly effective agent for radioprotection and mobilizing progenitors with significant therapeutic potential. Therefore, GT3 may be considered for further translational development and ultimately for use in humans.

γ-Tocotrienol as a Promising Countermeasure for Acute Radiation Syndrome: Current Status

The hazard of ionizing radiation exposure due to nuclear accidents or terrorist attacks is ever increasing. Despite decades of research, still, there is a shortage of non-toxic, safe and effective medical countermeasures for radiological and nuclear emergency. To date, the U.S. Food and Drug Administration (U.S. FDA) has approved only two growth factors, Neupogen (granulocyte colony-stimulating factor (G-CSF), filgrastim) and Neulasta (PEGylated G-CSF, pegfilgrastim) for the treatment of hematopoietic acute radiation syndrome (H-ARS) following the Animal Efficacy Rule. Promising radioprotective efficacy results of γ-tocotrienol (GT3; a member of the vitamin E family) in the mouse model encouraged its further evaluation in the nonhuman primate (NHP) model. These studies demonstrated that GT3 significantly aided the recovery of radiation-induced neutropenia and thrombocytopenia compared to the vehicle controls; these results particularly significant after exposure to 5.8 or 6.5 Gray (Gy) whole body γ-irradiation. The stimulatory effect of GT3 on neutrophils and thrombocytes (platelets) was directly and positively correlated with dose; a 75 mg/kg dose was more effective compared to 37.5 mg/kg. GT3 was also effective against 6.5 Gy whole body γ-irradiation for improving neutrophils and thrombocytes. Moreover, a single administration of GT3 without any supportive care was equivalent, in terms of improving hematopoietic recovery, to multiple doses of Neupogen and two doses of Neulasta with full supportive care (including blood products) in the NHP model. GT3 may serve as an ultimate radioprotector for use in humans, particularly for military personnel and first responders. In brief, GT3 is a promising radiation countermeasure that ought to be further developed for U.S. FDA approval for the ARS indication.

Potential of tocotrienols in the prevention and therapy of Alzheimer's disease

Currently there is no cure for Alzheimer's disease (AD); clinical trials are underway to reduce amyloid generation and deposition, a neuropathological hallmark in brains of AD patients. While genetic factors and neuroinflammation contribute significantly to AD pathogenesis, whether increased cholesterol level is a causative factor or a result of AD is equivocal. Prenylation of proteins regulating neuronal functions requires mevalonate-derived farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP). The observation that the levels of FPP and GGPP, but not that of cholesterol, are elevated in AD patients is consistent with the finding that statins, competitive inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, reduce FPP and GGPP levels and amyloid β protein production in preclinical studies. Retrospective studies show inverse correlations between incidence of AD and the intake and serum levels of the HMG CoA reductase-suppressive tocotrienols; tocopherols show mixed results. Tocotrienols, but not tocopherols, block the processing and nuclear localization of sterol regulatory element binding protein-2, the transcriptional factor for HMG CoA reductase and FPP synthase, and enhance the degradation of HMG CoA reductase. Consequently, tocotrienols deplete the pool of FPP and GGPP and potentially blunt prenylation-dependent AD pathogenesis. The antiinflammatory activity of tocotrienols further contributes to their protection against AD. The mevalonate- and inflammation-suppressive activities of tocotrienols may represent those of an estimated 23,000 mevalonate-derived plant secondary metabolites called isoprenoids, many of which are neuroprotective. Tocotrienol-containing plant foods and tocotrienol derivatives and formulations with enhanced bioavailability may offer a novel approach in AD prevention and treatment.

Validation of a HPLC/FLD Method for Quantification of Tocotrienols in Human Plasma

Quantification of tocotrienols in human plasma is critical when the attention towards tocotrienols on its distinctive properties is arising. We aim to develop a simple and practical normal-phase high performance liquid chromatography method to quantify the amount of four tocotrienol homologues in human plasma. Using both the external and internal standards, tocotrienol homologues were quantified via a normal-phase high performance liquid chromatography with fluorescence detector maintained at the excitation wavelength of 295 nm and the emission wavelength of 325 nm. The four tocotrienol homologues were well separated within 30 minutes. A large interindividual variation between subjects was observed as the absorption of tocotrienols is dependent on food matrix and gut lipolysis. The accuracies of lower and upper limit of quantification ranged between 92% and 109% for intraday assays and 90% and 112% for interday assays. This method was successfully applied to quantify the total amount of four tocotrienol homologues in human plasma.

A new formulation of Gamma Delta Tocotrienol has superior bioavailability compared to existing Tocotrienol-Rich Fraction in healthy human subjects

Gamma and delta tocotrienols are isomers of Vitamin E with established potency in pre-clinical anti-cancer research. This single-dose, randomized, crossover study aimed to compare the safety and bioavailability of a new formulation of Gamma Delta Tocotrienol (GDT) in comparison with the existing Tocotrienol-rich Fraction (TRF) in terms of gamma and delta isomers in healthy volunteers. Subjects were given either two 300 mg GDT (450 mg γ-T3 and 150 mg δ-T3) capsules or four 200 mg TRF (451.2 mg γ-T3 & 102.72 mg δ-T3) capsules and blood samples were taken at several time points over 24 hours. Plasma tocotrienol concentrations were determined using HPLC method. The 90% CI for gamma and delta tocotrienols for the ratio of log-transformation of GDT/TRF for C_max and AUC_0–∞ (values were anti-logged and expressed as a percentage) were beyond the bioequivalence limits (106.21–195.46, 154.11–195.93 and 52.35–99.66, 74.82–89.44 respectively). The Wilcoxon Signed Rank Test for T_max did not show any significant difference between GDT and TRF for both isomers (p > 0.05). No adverse events were reported during the entire period of study. GDT was found not bioequivalent to TRF, in terms of AUC and C_max. Gamma tocotrienol in GDT showed superior bioavailability whilst delta tocotrienol showed less bioavailability compared to TRF.

Vitamin E Analogs as Radiation Response Modifiers

The potentially life-threatening effects of total body ionizing radiation exposure have been known for more than a century. Despite considerable advances in our understanding of the effects of radiation over the past six decades, efforts to identify effective radiation countermeasures for use in case of a radiological/nuclear emergency have been largely unsuccessful. Vitamin E is known to have antioxidant properties capable of scavenging free radicals, which have critical roles in radiation injuries. Tocopherols and tocotrienols, vitamin E analogs together known as tocols, have shown promise as radioprotectors. Although the pivotal mechanisms of action of tocols have long been thought to be their antioxidant properties and free radical scavenging activities, other alternative mechanisms have been proposed to drive their activity as radioprotectors. Here we provide a brief overview of the effects of ionizing radiation, the mechanistic mediators of radiation-induced damage, and the need for radiation countermeasures. We further outline the role for, efficacy of, and mechanisms of action of tocols as radioprotectors, and we compare and contrast their efficacy and mode of action with that of another well-studied chemical radioprotector, amifostine.

Delta-tocotrienol suppresses radiation-induced microRNA-30 and protects mice and human CD34+ cells from radiation injury

We reported that microRNA-30c (miR-30c) plays a key role in radiation-induced human cell damage through an apoptotic pathway. Herein we further evaluated radiation-induced miR-30 expression and mechanisms of delta-tocotrienol (DT3), a radiation countermeasure candidate, for regulating miR-30 in a mouse model and human hematopoietic CD34+ cells. CD2F1 mice were exposed to 0 (control) or 7–12.5 Gy total-body gamma-radiation, and CD34+ cells were irradiated with 0, 2 or 4 Gy of radiation. Single doses of DT3 (75 mg/kg, subcutaneous injection for mice or 2 μM for CD34+ cell culture) were administrated 24 h before irradiation and animal survival was monitored for 30 days. Mouse bone marrow (BM), jejunum, kidney, liver and serum as well as CD34+ cells were collected at 1, 4, 8, 24, 48 or 72 h after irradiation to determine apoptotic markers, pro-inflammatory cytokines interleukin (IL)-1β and IL-6, miR-30, and stress response protein expression. Our results showed that radiation-induced IL-1β release and cell damage are pathological states that lead to an early expression and secretion of miR-30b and miR-30c in mouse tissues and serum and in human CD34+ cells. DT3 suppressed IL-1β and miR-30 expression, protected against radiation-induced apoptosis in mouse and human cells, and increased survival of irradiated mice. Furthermore, an anti-IL-1β antibody downregulated radiation-induced NFκBp65 phosphorylation, inhibited miR-30 expression and protected CD34+ cells from radiation exposure. Knockdown of NFκBp65 by small interfering RNA (siRNA) significantly suppressed radiation-induced miR-30 expression in CD34+ cells. Our data suggest that DT3 protects human and mouse cells from radiation damage may through suppression of IL-1β-induced NFκB/miR-30 signaling.

Effect of vitamin E on lead exposure-induced learning and memory impairment in rats

Chronic lead (Pb(2+)) exposure has been associated with learning and memory impairments, whereas vitamin E improves cognitive deficits. In this study, using a passive avoidance learning model in rats, we investigated the effects of vitamin E on Pb(2+) exposure-induced learning and memory impairments in rats. In the present study, 56 Wistar male rats (weighting 230-250g) were divided into eight groups (n=7). The Pb(2+) exposure involved gavages of lead acetate solution using three different doses (0.05%, 0.1%, and 0.2%) and the vitamin E consisted of three different doses (10, 25, 50μg/rat) for 30days. After the 30-day period, the rats were tested using a passive avoidance task (acquisition test). In a retrieval test conducted 48h after the training, step through latency (STL) and time in the dark compartment (TDC) were recorded. The statistical analysis of data was performed using ANOVA followed by Tukey's post hoc analysis. In all cases, differences were considered significant if p<0.05. The results of the present study showed that chronic exposure to high doses of Pb(2+) significantly increased both the number of trails required for learning and the TDC, whereas it decreased the STL in the passive avoidance test. Administration of vitamin E ameliorated the effects of Pb(2+) on animal behavior in the passive avoidance learning and memory task. Our results indicate that impairments of learning and memory in Pb(2+)-exposed rats are dose dependent and can be inhibited by antioxidants such as vitamin E.

Progenitors mobilized by gamma-tocotrienol as an effective radiation countermeasure

The purpose of this study was to elucidate the role of gamma-tocotrienol (GT3)-mobilized progenitors in mitigating damage to mice exposed to a supralethal dose of cobalt-60 gamma-radiation. CD2F1 mice were transfused 24 h post-irradiation with whole blood or isolated peripheral blood mononuclear cells (PBMC) from donors that had received GT3 72 h prior to blood collection and recipient mice were monitored for 30 days. To understand the role of GT3-induced granulocyte colony-stimulating factor (G-CSF) in mobilizing progenitors, donor mice were administered a neutralizing antibody specific to G-CSF or its isotype before blood collection. Bacterial translocation from gut to heart, spleen and liver of irradiated recipient mice was evaluated by bacterial culture on enriched and selective agar media. Endotoxin in serum samples also was measured. We also analyzed the colony-forming units in the spleens of irradiated mice. Our results demonstrate that whole blood or PBMC from GT3-administered mice mitigated radiation injury when administered 24 h post-irradiation. Furthermore, administration of a G-CSF antibody to GT3-injected mice abrogated the efficacy of blood or PBMC obtained from such donors. Additionally, GT3-mobilized PBMC inhibited the translocation of intestinal bacteria to the heart, spleen, and liver, and increased colony forming unit-spleen (CFU-S) numbers in irradiated mice. Our data suggests that GT3 induces G-CSF, which mobilizes progenitors and these progenitors mitigate radiation injury in recipient mice. This approach using mobilized progenitor cells from GT3-injected donors could be a potential treatment for humans exposed to high doses of radiation.

Tocols induce G-CSF and mobilise progenitors that mitigate radiation injury

Tocols induce high levels of granulocyte-colony-stimulating factor (G-CSF). G-CSF mobilises progenitors that allow mice that have been severely immunocompromised by exposure to acute, high-dose ionising irradiation to recover and to survive. The neutralisation of G-CSF abrogates the radioprotective efficacy of tocols. This article reviews studies in which CD2F1 mice were irradiated with sufficiently high doses to cause acute radiation syndrome symptoms and then administered (iv) progenitor-enriched whole blood or peripheral blood mononuclear cells from tocol- and AMD3100-injected donor mice (AMD3100 is a chemokine receptor antagonist used to improve the yield of mobilised progenitors). In some experiments, G-CSF was neutralised completely. Irradiated recipient mice were observed for 30 d post-irradiation for survival, a primary endpoint used for determining therapeutic effectiveness. Additionally, potential tocol-induced biomarkers (cytokines, chemokines and growth factors) were quantified. The authors suggest that tocols are highly effective agents for mobilising progenitors with significant therapeutic potential.

Bioavailability of tocotrienols: evidence in human studies

As a minor component of vitamin E, tocotrienols were evident in exhibiting biological activities such as neuroprotection, radio-protection, anti-cancer, anti-inflammatory and lipid lowering properties which are not shared by tocopherols. However, available data on the therapeutic window of tocotrienols remains controversial. It is important to understand the absorption and bioavailability mechanisms before conducting in-depth investigations into the therapeutic efficacy of tocotrienols in humans. In this review, we updated current evidence on the bioavailability of tocotrienols from human studies. Available data from five studies suggested that tocotrienols may reach its target destination through an alternative pathway despite its low affinity for α-tocopherol transfer protein. This was evident when studies reported considerable amount of tocotrienols detected in HDL particles and adipose tissues after oral consumption. Besides, plasma concentrations of tocotrienols were shown to be higher when administered with food while self-emulsifying preparation of tocotrienols was shown to enhance the absorption of tocotrienols. Nevertheless, mixed results were observed based on the outcome from 24 clinical studies, focusing on the dosages, study populations and formulations used. This may be due to the variation of compositions and dosages of tocotrienols used, suggesting a need to understand the formulation of tocotrienols in the study design. Essentially, implementation of a control diet such as AHA Step 1 diet may influence the study outcomes, especially in hypercholesterolemic subjects when lipid profile might be modified due to synergistic interaction between tocotrienols and control diet. We also found that the bioavailability of tocotrienols were inconsistent in different target populations, from healthy subjects to smokers and diseased patients. In this review, the effect of dosage, composition and formulation of tocotrienols as well as study populations on the bioavailability of tocotrienols will be discussed.

Vitamin E: tocopherols and tocotrienols as potential radiation countermeasures

Despite the potential devastating health consequences of intense total-body irradiation, and the decades of research, there still remains a dearth of safe and effective radiation countermeasures for emergency, radiological/nuclear contingencies that have been fully approved and sanctioned for use by the US FDA. Vitamin E is a well-known antioxidant, effective in scavenging free radicals generated by radiation exposure. Vitamin E analogs, collectively known as tocols, have been subject to active investigation for a long time as radioprotectors in patients undergoing radiotherapy and in the context of possible radiation accidents or terrorism scenarios. Eight major isoforms comprise the tocol group: four tocopherols and four tocotrienols. A number of these agents and their derivatives are being investigated actively as radiation countermeasures using animal models, and several appear promising. Although the tocols are well recognized as potent antioxidants and are generally thought to mediate radioprotection through 'free radical quenching', recent studies have suggested several alternative mechanisms: most notably, an 'indirect effect' of tocols in eliciting specific species of radioprotective growth factors/cytokines such as granulocyte colony-stimulating factor (G-CSF). The radioprotective efficacy of at least two tocols has been abrogated using a neutralizing antibody of G-CSF. Based on encouraging results of radioprotective efficacy, laboratory testing of γ-tocotrienol has moved from a small rodent model to a large nonhuman primate model for preclinical evaluation. In this brief review we identify and discuss selected tocols and their derivatives currently under development as radiation countermeasures, and attempt to describe in some detail their in vivo efficacy.

Tocopherols and tocotrienols plasma levels are associated with cognitive impairment

Vitamin E includes 8 natural compounds (4 tocopherols, 4 tocotrienols) with potential neuroprotective activity. α-Tocopherol has mainly been investigated in relation to cognitive impairment. We examined the relation of all plasma vitamin E forms and markers of vitamin E damage (α-tocopherylquinone, 5-nitro-γ-tocopherol) to mild cognitive impairment (MCI) and Alzheimer's disease (AD). Within the AddNeuroMed-Project, plasma tocopherols, tocotrienols, α-tocopherylquinone, and 5-nitro-γ-tocopherol were assessed in 168 AD cases, 166 MCI, and 187 cognitively normal (CN) people. Compared with cognitively normal subjects, AD and MCI had lower levels of total tocopherols, total tocotrienols, and total vitamin E. In multivariable-polytomous-logistic regression analysis, both MCI and AD cases had 85% lower odds to be in the highest tertile of total tocopherols and total vitamin E, and they were, respectively, 92% and 94% less likely to be in the highest tertile of total tocotrienols than the lowest tertile. Further, both disorders were associated with increased vitamin E damage. Low plasma tocopherols and tocotrienols levels are associated with increased odds of MCI and AD.

Tocotrienol as a potential anticancer agent

Vitamin E is composed of two structurally similar compounds: tocopherols (TPs) and tocotrienols (T3). Despite being overshadowed by TP over the past few decades, T3 is now considered to be a promising anticancer agent due to its potent effects against a wide range of cancers. A growing body of evidence suggests that in addition to its antioxidative and pro-apoptotic functions, T3 possesses a number of anticancer properties that make it superior to TP. These include the inhibition of epithelial-to-mesenchymal transitions, the suppression of vascular endothelial growth factor tumor angiogenic pathway and the induction of antitumor immunity. More recently, T3, but not TP, has been shown to have chemosensitization and anti-cancer stem cell effects, further demonstrating the potential of T3 as an effective anticancer therapeutic agent. With most of the previous clinical studies on TP producing disappointing results, research has now focused on testing T3 as the next generation vitamin E for chemoprevention and cancer treatment. This review will summarize recent developments in the understanding of the anticancer effects of T3. We will also discuss current progress in clinical trials involving T3 as an adjuvant to conventional cancer therapy.

Research Spotlight: Delivery of the vitamin E compound tocotrienol to cancer cells

Tocotrienol, a member of the vitamin E family of compounds, is currently receiving increased attention owing to its highly promising anticancer effects. However, its potential in cancer therapy is limited by its poor bioavailability and its inability to specifically reach tumors at therapeutic concentrations after intravenous administration. In order to address these problems, various delivery strategies have been proposed, such as the inclusion of tocotrienol in γ-cyclodextrins, prodrugs and emulsions, and entrapment in lipid nanoparticles and vesicles. Among these approaches, we have demonstrated that the entrapment of tocotrienol within vesicles bearing transferrin, whose receptors are overexpressed on numerous cancer cells, significantly improved the uptake by cancer cells overexpressing transferrin receptors. Consequently, the intravenous administration of tocotrienol entrapped in transferrin-bearing vesicles led to tumor regression and even complete tumor suppression in some cases in a murine tumor model, as well as improvement of animal survival. Transferrin-bearing vesicles are therefore highly promising for the delivery of tocotrienol to cancer cells in vitro and in vivo, and should be further investigated to optimize the anticancer therapeutic effect of tocotrienol.

Assessment of the protective effects of oral tocotrienols in arginine chronic-like pancreatitis

Tocotrienols exhibit anti-inflammatory properties over macrophages and promote cytotoxicity in activated pancreatic stellate cells, suggesting that they may limit chronic pancreatitis progression. We aimed to quantitate the effect of oral tocotrienols on a rat model of chronic pancreatic injury. Chronic-like pancreatitis was induced by repeated arginine pancreatitis. Palm oil tocotrienol-rich fraction (TRF) was given by gavage before and after pancreatitis inductions. Amylase and hydroxyproline were determined in pancreatic homogenates; collagen, fibronectin, α-smooth muscle actin (SMA), glial fibrillary acidic protein (GFAP), and phosphorylated Smad3 were assessed by Western blotting. Transforming growth factor (TGF)-β1 was measured in plasma. Morphological assessment included light microscopy, fibrosis area fraction, and collagen network fractal analysis. Arginine pancreatitis induced pancreatic atrophy and increased hydroxyproline that ameliorated after TRF. Arginine increased TGF-β1 (185 ± 40 vs. 15 ± 2 ng/ml; P <0.01) that was blunted by TRF (53 ± 19; P < 0.01). TRF reduced protease and Smad3 activation, collagen, and fibronectin. α-SMA increased and GFAP diminished in arginine pancreatitis, consistent with long-term stellate cell activation, and TRF reverted these changes to basal. Arginine pancreatitis increased fibrosis area fraction (4.5 ± 0.3% vs. 0.2 ± 0.2%), collagen network complexity (fractal dimension 1.52 ± 0.03 vs. 1.42 ± 0.01; P < 0.001), and inhomogeneity (lacunarity 0.63 ± 0.03 vs. 0.40 ± 0.02; P < 0.001), which were all reduced by TRF (1.3 ± 0.4%, 1.43 ± 0.02%, and 0.51 ± 0.03%, respectively; P < 0.01). Best correlation coefficients were obtained when comparing fibrosis area fraction with lacunarity (r = 0.88) and both parameters with pancreatic weight (r = -0.91 and -0.79, respectively). TRF administered only before pancreatitis best, but not fully, recapitulated the beneficial effects of TRF. Tocotrienols improve quantitative measures of chronic pancreatic damage. They may be of benefit in human chronic pancreatitis.

Tocotrienols: inflammation and cancer

Inflammation is an organism's response to environmental assaults. It can be classified as acute inflammation that leads to therapeutic recovery or chronic inflammation, which may lead to the development of cancer and other ailments. Genetic changes that occur within cancer cells themselves are responsible for many aspects of cancer development but are dependent on ancillary processes for tumor promotion and progression. Inflammation has long been associated with the development of cancer. The distinct characteristics of cancer cells to proliferate, metastasize, evade apoptotic signals, and develop chemoresistance have been linked to the inflammatory response. Due to the involvement of multiple genes and various pathways, current drugs that target single genes have not been effective in providing a therapeutic cure. On the other hand, natural products target multiple genes and therefore have better success compared to drugs. Tocotrienols, the potent isoforms of vitamin E, are such a natural product. This review will discuss the relationship between cancer and inflammation with particular focus on the roles played by NF-κB, STAT3, and COX-2.

Tocotrienols and breast cancer: the evidence to date

Breast cancer is the second most frequent cancer affecting women worldwide after lung cancer. The toxicity factor associated with synthetic drugs has turned the attention toward natural compounds as the primary focus of interest as anticancer agents. Vitamin E derivatives consisting of the well-established tocopherols and their analogs namely tocotrienols have been extensively studied due to their remarkable biological properties. While tocopherols have failed to offer protection, tocotrienols, in particular, α-, δ-, and γ-tocotrienols alone and in combination have demonstrated anticancer properties. The discovery of the antiangiogenic, antiproliferative, and apoptotic effects of tocotrienols, as well as their role as an inducer of immunological functions, not only reveals a new horizon as a potent antitumor agent but also reinforces the notion that tocotrienols are indeed more than antioxidants. On the basis of a transcriptomic platform, we have recently demonstrated a novel mechanism for tocotrienol activity that involves estrogen receptor (ER) signaling. In silico simulations and in vitro binding analyses indicate a high affinity of specific forms of tocotrienols for ERβ, but not for ERα. Moreover, we have demonstrated that specific tocotrienols increase ERβ translocation into the nucleus which, in turn, activates the expression of estrogen-responsive genes (MIC-1, EGR-1 and Cathepsin D) in breast cancer cells only expressing ERβ cells (MDA-MB-231) and in cells expressing both ER isoforms (MCF-7). The binding of specific tocotrienol forms to ERβ is associated with the alteration of cell morphology, caspase-3 activation, DNA fragmentation, and apoptosis. Furthermore, a recently concluded clinical trial seems to suggest that tocotrienols in combination with tamoxifen may have the potential to extend breast cancer-specific survival.

Effectiveness of tocotrienol-rich fraction combined with tamoxifen in the management of women with early breast cancer: a pilot clinical trial

Introduction

Basic research has indicated that tocotrienols have potent antiproliferative and proapoptotic effects that would be expected to reduce the effect of breast cancer.

Methods

We conducted a double-blinded, placebo-controlled pilot trial to test the effectiveness of adjuvant tocotrienol therapy in combination with tamoxifen for 5 years in women with early breast cancer. Two-hundred-forty women, aged between 40 and 60 years, with either tumor node metastases (TNM) Stage I or II breast cancer and estrogen receptor (ER)-positive tumors were nonrandomly assigned to two groups. The intervention group received tocotrienol-rich fraction (TRF) plus tamoxifen, whereas the control group received placebo plus tamoxifen, for 5 years.

Results

During the 5 years of the study, eight patients died of breast cancer, whereas in 36 patients, a local or systemic recurrence developed. Five-year breast cancer-specific survival was 98.3% (95% confidence interval (CI), 95.9% to 100%) in the intervention group and 95% (95% CI, 91.1% to 98.9%) in the control group, whereas the 5-year disease-free survival was 86.7% (95% CI, 80.6% to 92.8%) and 83.3% (95% CI, 76.6% to 90.0%), respectively. Risk of mortality due to breast cancer was 60% (HR, 0.40; 95% CI, 0.08 to 2.05) lower in the intervention group versus the controls after adjustment for age, ethnicity, stage, and lymph node status, but this was not statistically significant. Adjuvant TRF therapy was not associated with breast cancer recurrence (HR, 0.84; 95% CI, 0.43 to 1.65).

Conclusions

From the current study, no association seems to exist between adjuvant tocotrienol therapy and breast cancer-specific survival in women with early breast cancer.

Trial registration

ClinicalTrials.gov Identifier: NCT01157026.

Delta-tocotrienol protects mouse and human hematopoietic progenitors from gamma-irradiation through extracellular signal-regulated kinase/mammalian target of rapamycin signaling

BACKGROUND

Exposure to γ-radiation causes rapid hematopoietic cell apoptosis and bone marrow suppression. However, there are no approved radiation countermeasures for the acute radiation syndrome. In this study, we demonstrated that natural δ-tocotrienol, one of the isomers of vitamin E, significantly enhanced survival in total body lethally irradiated mice. We explored the effects and mechanisms of δ-tocotrienol on hematopoietic progenitor cell survival after γ-irradiation in both in vivo and in vitro experiments.

DESIGN AND METHODS

CD2F1 mice and human hematopoietic progenitor CD34(+) cells were treated with δ-tocotrienol or vehicle control 24 h before or 6 h after γ-irradiation. Effects of δ-tocotrienol on hematopoietic progenitor cell survival and regeneration were evaluated by clonogenicity studies, flow cytometry, and bone marrow histochemical staining. δ-tocotrienol and γ-irradiation-induced signal regulatory activities were assessed by immunofluorescence staining, immunoblotting and short-interfering RNA assay.

RESULTS

δ-tocotrienol displayed significant radioprotective effects. A single injection of δ-tocotrienol protected 100% of CD2F1 mice from total body irradiation-induced death as measured by 30-day post-irradiation survival. δ-tocotrienol increased cell survival, and regeneration of hematopoietic microfoci and lineage(-)/Sca-1(+)/ckit(+) stem and progenitor cells in irradiated mouse bone marrow, and protected human CD34(+) cells from radiation-induced damage. δ-tocotrienol activated extracellular signal-related kinase 1/2 phosphorylation and significantly inhibited formation of DNA-damage marker γ-H2AX foci. In addition, δ-tocotrienol up-regulated mammalian target of rapamycin and phosphorylation of its downstream effector 4EBP-1. These alterations were associated with activation of mRNA translation regulator eIF4E and ribosomal protein S6, which is responsible for cell survival and growth. Inhibition of extracellular signal-related kinase 1/2 expression by short interfering RNA abrogated δ-tocotrienol-induced mammalian target of rapamycin phosphorylation and clonogenicity, and increased γ-H2AX foci formation in irradiated CD34(+) cells.

CONCLUSIONS

Our data indicate that δ-tocotrienol protects mouse bone marrow and human CD34(+) cells from radiation-induced damage through extracellular signal-related kinase activation-associated mammalian target of rapamycin survival pathways.

An update on vitamin E, tocopherol and tocotrienol-perspectives

Vitamin E, like tocotrienols and tocopherols, is constituted of compounds essential for animal cells. Vitamin E is exclusively synthesized by photosynthetic eukaryotes and other oxygenic photosynthetic organisms such as cyanobacteria. In order to prevent lipid oxidation, the plants mainly accumulate tocochromanols in oily seeds and fruits or in young tissues undergoing active cell divisions. From a health point of view, at the moment there is a great interest in the natural forms of tocochromanols, because they are considered promising compounds able to maintain a healthy cardiovascular system and satisfactory blood cholesterol levels. Some evidence suggests that the potency of the antioxidant effects may differ between natural or synthetic source of tocochromanols (vitamin E).