Current Pharmaceutical Design - Volume 17, Issue 21, 2011

Tocotrienols are a form of vitamin E that have been under the shadow of the popular vitamin E form, α-tocopherol. There are eight forms of vitamin E: four tocopherols (alpha, beta, gamma, delta) and four tocotrienols (alpha, beta, gamma, delta). Tocorienol and tocopherol are similar in that both have the same head called chromanol nucleus, the site of antioxidant activities. Alpha-tocopherol (α-tocopherol) is the most common form in the diet, which is mainly available from many cereal, grains, and oils. Tocotrienols, on the other hand are only minor components present in plants Several sources with relatively high levels of tocotrienols include palm oil, rice bran oil and cereals. While the research on tocotrienols has been traditionally neglected, a number of the most recent studies have shown the potential of tocotrienols for the prevention of many human diseases. The studies also revealed the molecular targets of the tocotrienols and their roles in cancer, bone resorption, diabetes, cardiovascular diseases and neurological problems in both preclinical and clinical levels. Such multi-targeted role of tocotrienols in most degenerative diseases proves them to be ideal candidates for potential nutraceuticals/pharmaceutical agents. Eight reviews are carefully selected from the authorities of tocotrienol research. In one of the reviews, Professor Kailash Prasad from the University of Saskatchewan, Saskatoon, Canada, has discussed beneficial effects of tocotrienols in cardiovascular health. The review emphasis the effects of tocotrienols on the risk factors for atherosclerosis, plaque instability and thrombogenesis and compared these effects with those of tocopherol. The cardioprotective effects of tocotrienols on ischemic injury and its potential beneficial effects on the patients undergoing angioplasty, stent implantation and aorto-coronary bypass surgery are discussed. The authors recognized that although tocotrienols possess potential for cardiovascular health, long-term randomized clinical trials are needed to establish their efficacy in primary and secondary prevention of coronary heart disease. The second review by Professor Belma Turan of the Ankara University and Professor Guy Vassort of the INSERM U, Montpellier, France, deals with the antioxidant action of tocopherols and tocotrienols. This review has recognized the fact that tocotrienols possess antioxidative properties 1600 times more than tocopherols and only tocotrienols in nanomolar concentration can protect neuronal cells from glutamate-induced cell death. The authors have emphasized the use of optimal doses of tocopherol/tocotrienols because at high dosage of over 400 IU/day vitamin E may increase all-cause mortality and should be avoided. At higher doses only vitamin E does not show any health benefits, it is associated with an increase in total mortality, heart failure and hemorrhagic shock. The next review by Professor Vasanthi and Dr. Parameswai from Pondicherry University and Professor Dipak K Das from the University of Connecticut School of Medicine, USA have discussed the importance of tocotrienols in cardiovascular health based on their mechanisms of action. This review discusses how antagonizing the oxidation of low-density lipoproteins inhibition of platelet aggregation is secondary to inhibition of monocyte adhesion and prevention of smooth muscle proliferation. This review recognizes the importance of gamma tocotrienol in heart diseases. A multitude of cardiovascular diseases can be prevented with gamma tocotrienol including hypercholesterolemia, atherosclerosis, ischemic heart disease, hypertension, diabetes and obesity. The supplementation of gamma tocotrienol appears to be essential as dietary sources can provide very little amount of tocotrienol......

This review emphasizes the effects of tocotrienols on the risk factors for atherosclerosis, plaque instability and thrombogenesis, and compares these effects with tocopherol. Tocotrienols reduce serum lipids and raise serum HDL-C. Alpha-tocopherol, on the other hand, has no effect on serum lipids. Tocotrienols have greater antioxidant activity than tocopherols. Both reduce the serum levels of Creactive protein (CRP) and advanced glycation end products, and expression of cell adhesion molecules. The CRP-lowering effects of tocotrienols are greater than tocopherol. Tocotrienols reduce inflammatory mediators, δ-tocotrienol being more potent, followed by γ- and α-tocotrienol. Tocotrienols are antithrombotic and suppress the expression of matrix metalloproteinases. They suppress, regress and slow the progression of atherosclerosis, while tocopherol only suppresses, and has no effect on regression and slowing of progression of atherosclerosis. Tocotrienol reduces risk factors for destabilization of atherosclerotic plaques. There are no firm data to suggest that tocotrienols are effective in reducing the risk of cardiac events in established ischemic heart disease. Alpha-tocopherol is effective in primary prevention of coronary artery disease (CAD), but has no conclusive evidence that it has beneficial effects in patients with established ischemic heart disease. Tocotrienols are effective in reducing ischemia-reperfusion cardiac injury in experimental animals and has the potential to be used in patients undergoing angioplasty, stent implantation and aorto-coronary bypass surgery. In conclusion, experimental data suggest that tocotrienols have a potential for cardiovascular health, but long-term randomized clinical trials are needed to establish their efficacy in primary and secondary prevention of CAD.

The scope of this review is to summarize the important roles of vitamin E family members as protective agents in cardiovascular pathologies of different types of disease states and particularly in diabetes, including some of our research results, to illustrate how this recent knowledge is helping to better understand the roles of the vitamin E family in biology, in animals and humans specifically. Cardiovascular disease, a general name for a wide variety of diseases, disorders and conditions, is caused by disorders of the heart and blood vessels. Cardiovascular disease is the world's largest killer, claiming 17.1 million lives a year. Cardiovascular complications result from multiple parameters including glucotoxicity, lipotoxicity, fibrosis. Obesity and diabetes mellitus are also often linked to cardiovascular disease. In fact, cardiovascular disease is the most life-threatening of the diabetic complications and diabetics are 2- to 4-fold more likely to die of cardiovascular-related causes than non-diabetics. In order to prevent the tendency of cardiovascular disease, primary prevention is needed by modifying risk factors. Several recent studies, besides earlier ones, have reported beneficial effects of therapy with antioxidant agents, including trace elements, vitamins (E and/or C), other antioxidants, against the cardiovascular dysfunction. Hence, the use of peroxisome proliferator-activated receptor-α (PPARα) agonists to reduce fatty acid oxidation, of trace elements such as selenium as antioxidant and other antioxidants such as vitamins E and C, contributes to the prevention of these dysfunctions. Moreover, therapy with antioxidants and the above vitamins to prevent or delay the onset and development of cardiovascular complications in diabetic patients and animal models has been investigated although these studies showed inconsistent results.

The worldwide cardiovascular disease (CVD) burden has resulted in an intense interest in pharmaceutical approaches to combat this multifactorial disease. Vitamins are high-flying among natural or endogenous compounds, considered to be beneficial to human health and have become attractive targets for research. Of all the vitamins, tocopherols and tocotrienols, parent congeners in the vitamin E family, are found to be effective in decreasing mortality due to CVD. As understanding of the antioxidant effect of this vitamin evolved, tocotrienols gained eminence in recent years and researchers begun to further study the biological effects of it. Tocotrienols have several cardioprotective effects; including antagonizing the oxidation of low density lipoproteins, anti atherosclerotic, inhibiting platelet aggregation and monocyte adhesion, preventing smooth muscle proliferation and various other cardiovascular disorders. Recent studies have also revealed the molecular targets of the tocotrienols and their roles in cancer, bone resorption, diabetes and neurological diseases at both preclinical and clinical levels. The multitargeted role of tocotrienols in most degenerative diseases proves it to be an ideal candidate as a nutraceutical/pharmaceutical agent for useful exploitation.

Tocotrienols are members of vitamin E family and possess broad biological activities including antioxidant, anti-inflammatory and antitumor effects. In the present study, we examine the potential of α-tocotrienol (AT) and γ-tocotrienol (GT) in inhibiting the proliferation of human T cell lymphoma Jurkat cells and elucidate the pathways involved in anti tumor effects of GT. GT but not AT inhibited proliferation and induced apoptosis in Jurkat cells in a dose dependent manner. GT treatment resulted in elevated mitochondrial ROS production, activation of JNK and suppression of ERK and p38 MAPK. GT also induced calcium release, loss of mitochondrial membrane potential and cytochrome c release from the mitochondria. These changes were accompanied by increase in Bax expression with a concomitant decrease in Bcl-xl expression suggesting activation of mitochondrial apoptotic pathway. GT induced increase in mitochondrial ROS was abrogated by catalase. Besides, GT also up-regulated surface expression of Fas and FasL on Jurkat cells. Further, caspase activation and PARP degradation were also seen in cells treated with GT. Inhibitors of caspase-8 and caspase-9 significantly abrogated GT mediated apoptosis. In contrast GT was not toxic to normal human peripheral blood mononuclear cells suggesting differential cytotoxicity towards normal lymphocytes and transformed lymphoma cells. Cellular uptake studies with tocotrienols showed higher intracellular accumulation of GT as compared to AT which may be responsible for its better antitumor activity. Our results show antitumor effects of GT in human lymphoma cells via increased mitochondrial ROS generation and activation of both intrinsic and extrinsic apoptotic pathways.

It is well known that vitamin E functions as an antioxidant, and it is expected to exert an antioxidant effect when taken as a supplement. However, a number of cohort studies have shown that vitamin E does not alleviate oxidative stress and could even worsen it. Recently, Wang et al. investigated whether vitamin E intake was associated with amyotrophic lateral sclerosis (ALS) based on data from 5 cohort studies with 1,055,546 participants, of which 805 of them had developed ALS. They concluded in this large pooled prospective study, in which long-term vitamin E supplementation was associated with lower ALS rates, and therefore, a possible protective effect of vitamin E deserves further consideration. Performing further large cohort studies may reveal similar findings for other oxidative stressrelated diseases. It is still controversial if antioxidants such as vitamin E provide a clinical therapeutic effect against oxidative stressrelated diseases. If effective, the dose at which they should be administered and the duration of supplement exposure should be of interest. Vitamin E reduces production of reactive oxygen species by mitochondria and elicits further reactions in cells. It should be noted that mitochondria are important targets for vitamin E and its homologues. Therefore, a proper usage of vitamin E in subjects under high oxidative stress, due to its individually targeting property, will arise its importance in healthy life.

Vitamin E family constitutes of tocopherol and tocotrienol. Each form has several isomers: alpha,beta, gamma, delta, desmo and didesmo. Although tocopherol is known much earlier, tocotrienol has been discovered more recently.Tocotrienol has higher antioxidant potential than tocopherol. Research shows that tocotrienol can inhibit the induced oxidative damage to lipids and proteins. Cholesterol biosynthesis pathway requires HMG Co A reductase. Tocotrienol degrades HMG Co A reductase protein and in turn lowers cholesterol synthesis. Tocotrienol can reverse ischemia-reperfusion which mediates cardiac dysfunction and induces c-Src protein expression. Tocotrienol prevents oxytosis and offers protection against Alzheimer's disease, Parkinson's disease, Hungtington's disease. Tocotrienol exerts anticancer property through cell cycle arrest, induction of apoptosis, inhibition of angiogenesis; antitumor activity. Tocotrienol also possesses anti-inflammatory, antidiabetic, antiadipogenic and antiatherogenic effect.

Metabolic syndrome is defined as a set of health risk factors that are associated with an increased chance of cardiovascular diseases and type 2 diabetes. These include abdominal obesity, hyperglycemia, impaired glucose tolerance, dyslipidemia, and hypertension. Interventions in metabolic syndrome include lifestyle interventions such as a healthy diet using functional foods together with increased physical activity to induce weight loss as the first aim of treatment. Nutraceuticals such as tocotrienols and tocopherols as members of the vitamin E family may be more targeted interventions. This review evaluates the effects of tocotrienols on the risk factors of metabolic syndrome using data from human, animal and in vitro studies. Tocotrienols improved lipid profiles and reduced atherosclerotic lesions, decreased blood glucose and glycated hemoglobin concentrations, normalized blood pressure, and inhibited adipogenesis. The differences in responses between tocopherols and tocotrienols in preventing obesity, diabetes, hypertension, artherosclerosis, ischemia, and inflammation suggest that different receptors or signaling mechanisms may be involved.

Tocotrienols, components belonging to vitamin E members, are used as potent therapeutics in the treatment of several diseases. Recent studies suggested tocotrienol to have better activity in many situations compared to tocopherols. Tocotrienols have been shown to lower the atherogenic apolipoprotein B and lipoprotein plasma levels. Additionally, tocotrienols with their anti-tumor effect together with anti-angiogenic and anti-thrombotic effects may serve as effective agents in cancer therapy. Besides these effects, some properties such as water insolubility and low stability limit the usage of tocotrienols in the clinic. However recent studies tried to increase the bioavailability with esterification and combination use. These efforts for the clinical usage of tocotrienols which may help them to take a wide place in the clinic and additional studies are needed to identify their therapeutical mechanisms.

Human pancreatic cancer remains a highly malignant disease with almost similar incidence and mortality despite extensive research. Many targeted therapies are under development. However, clinical investigation showed that single targeted therapies and most combined therapies were not able to improve the prognosis of this disease, even though some of these therapies had excellent anti-tumor effects in pre-clinical models. Cross-talk between cell proliferation signaling pathways may be an important phenomenon in pancreatic cancer, which may result in cancer cell survival even though some pathways are blocked by targeted therapy. Pancreatic cancer may possess different characteristics and targets in different stages of pathogenesis, maintenance and metastasis. Sensitivity to therapy may also vary for cancer cells at different stages. The unique pancreatic cancer structure with abundant stroma creates a tumor microenvironment with hypoxia and low blood perfusion rate, which prevents drug delivery to cancer cells. In this review, the most commonly investigated targeted therapies in pancreatic cancer treatment are discussed. However, how to combine these targeted therapies and/or combine them with chemotherapy to improve the survival rate of pancreatic cancer is still a challenge. Genomic and proteomic studies using pancreatic cancer samples obtained from either biopsy or surgery are recommended to individualize tumor characters and to perform drug sensitivity study in order to design a tailored therapy with minimal side effects. These studies may help to further investigate tumor pathogenesis, maintenance and metastasis to create cellular expression profiles at different stages. Integration of the information obtained needs to be performed from multiple levels and dimensions in order to develop a successful targeted therapy.