Tocotrienols reduce 25-hydroxycholesterol-induced monocyte-endothelial cell interaction by inhibiting the surface expression of adhesion molecules

Synergic effects of α-tocopherol and β-carotene on tert-butylhydroperoxide-induced HepG2 cell injury

Oxidative stress produced by the dietary or chemical substrates is one of the major causes of liver cell injury. In this study, we compared the effects of two dietary antioxidants, α-tocopherol (α-T) and β-carotene (β-C) against tert-butyl hydroperxide (tBHP)-induced oxidative stress in human hepatoma HepG2 cells. Cell proliferation, lipid peroxidation (LPO), cellular lactate dehydrogenase (LDH), [3H]-aflatoxin B1(AFB1)-DNA adduct formation, and cytochrome P450 2E1 (CYP2E1) expression were determined after antioxidants were added to the tBHP-stressed cells. When compared to an ethanol-based control, all biomarkers for the cell damage were significantly increased by treatments. Treatments of β-C or the combination of two antioxidants at 50 ppm for 48 h enhanced cell proliferation ( P < 0.05) compared to tBHP control. The antioxidative and cytoprotective actions of α-T and β-C, alone or in combination, were associated with modulation of microsomal CYP2E1 expression, corresponding to the regulation of LPO production ( P < 0.0001). Our results indicate that α-T and β-C may contribute differently to protection of cellular membrane disruption in CYP2E1-expressing HepG2 cells. Moreover, the combination of α-T and β-C appears to impel the greater protection of pathogenic processes of oxidative stress in liver.

gamma-Tocotrienol ameliorates intestinal radiation injury and reduces vascular oxidative stress after total-body irradiation by an HMG-CoA reductase-dependent mechanism

Analogs of vitamin E (tocols) are under development as radioprophylactic agents because of their high efficacy and lack of toxicity. Gamma-tocotrienol (GT3) is of particular interest because, in addition to being an antioxidant, it also inhibits 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase and accumulates to greater extent in endothelial cells than other tocols. We addressed in vivo whether HMG-CoA reductase inhibition contributes to the radioprotection conferred by GT3. Groups of mice were treated with vehicle, mevalonate (the product of the reaction catalyzed by HMG-CoA reductase), GT3 alone or GT3 in combination with mevalonate. Lethality and standard parameters of injury to the hematopoietic, intestinal and vascular/endothelial systems were assessed after exposure to total-body irradiation. GT3 improved postirradiation survival and decreased radiation-induced vascular oxidative stress, an effect that was reversible by mevalonate. GT3 also enhanced hematopoietic recovery, reduced intestinal radiation injury, and accelerated the recovery of soluble markers of endothelial function. These parameters were not reversed by mevalonate co-administration. Our data confirm GT3's radioprophylactic properties against hematopoietic injury and, for the first time, demonstrate benefits in terms of protection against gastrointestinal and vascular injury. The radioprotective efficacy of GT3 against vascular injury is related to its properties as an HMG-CoA reductase inhibitor.

Vitamin E delta-tocotrienol levels in tumor and pancreatic tissue of mice after oral administration

Tocotrienols are natural vitamin E compounds that are known to have a neuroprotective effect at nanomolar concentration and anti-carcinogenic effect at micromolar concentration. In this report, we investigated the pharmacokinetics, tumor and pancreatic tissue levels, and toxicity of delta-tocotrienol in mice because of its anti-tumor activity against pancreatic cancer. Following a single oral administration of delta-tocotrienol at 100 mg/kg, the peak plasma concentration (C(max)) was 57 +/- 5 micromol/l, the time required to reach peak plasma concentration (T(max)) was 2 h and plasma half-life (t(1/2)) was 3.5 h. The delta-tocotrienol was cleared from plasma and liver within 24 h, but delayed from the pancreas. When mice were fed delta-tocotrienol for 6 weeks, the concentration in tumor tissue was 41 +/- 3.5 nmol/g. This concentration was observed with the oral dose (100 mg/kg) of delta-tocotrienol which inhibited tumor growth by 80% in our previous studies. Interestingly, delta-tocotrienol was 10-fold more concentrated in the pancreas than in the tumor. We observed no toxicity due to delta-tocotrienol as mice gained normal weight with no histopathological changes in tissues. Our data suggest that bioactive levels of delta-tocotrienol can be achieved in the pancreas following oral administration and supports its clinical investigation in pancreatic cancer.

Gamma-tocotrienol-induced apoptosis in human gastric cancer SGC-7901 cells is associated with a suppression in mitogen-activated protein kinase signalling

Tocotrienols have been shown to inhibit proliferation and induce apoptosis in cancer cells. However, the molecular mechanisms involved in tocotrienol-induced apoptosis are still unclear. In the present study, gamma-tocotrienol induced apoptosis in human gastric adenocarcinoma SGC-7901 cell line through down regulation of the extracellular signal-regulated kinase (ERK) signalling pathway. Furthermore, gamma-tocotrienol-induced apoptosis was accompanied by down regulation of Bcl-2, up regulation of Bax, activation of caspase-3, and subsequent poly (ADP-ribose) polymerase cleavage. These results indicated that up or down regulation of Bcl-2 family proteins play a major role in the initiation of gamma-tocotrienol-induced apoptosis as an activator of caspase-3. Gamma-tocotrienol also down regulated the activation of the Raf-ERK signalling pathway, and down regulated c-Myc by decreasing the expressions of Raf-1 and p-ERK1/2 proteins. The results suggest that key regulators in tocotrienol-induced apoptosis may be Bcl-2 families and caspase-3 in SGC-7901 cells through down regulation of the Raf-ERK signalling pathway.

Cellular, molecular and clinical aspects of vitamin E on atherosclerosis prevention

Randomised clinical trials and epidemiologic studies addressing the preventive effects of vitamin E supplementation against cardiovascular disease reported both positive and negative effects, and recent meta-analyses of the clinical studies were rather disappointing. In contrast to that, many animal studies clearly show a preventive action of vitamin E in several experimental settings, which can be explained by the molecular and cellular effects of vitamin E observed in cell cultures. This review is focusing on the molecular effects of vitamin E on the cells playing a role during atherosclerosis, in particular on the endothelial cells, vascular smooth muscle cells, monocytes/macrophages, T cells, and mast cells. Vitamin E may act by normalizing aberrant signal transduction and gene expression in antioxidant and non-antioxidant manners; in particular, over-expression of scavenger receptors and consequent foam cell formation can be prevented by vitamin E. In addition to that, the cellular effects of alpha-tocopheryl phosphate and of EPC-K1, a composite molecule between alpha-tocopheryl phosphate and l-ascorbic acid, are summarized.

Bioavailability of a novel, water-soluble vitamin E formulation in malabsorbing patients

In cystic fibrosis (CF), pancreatic insufficiency and a diminished bile acid pool cause malabsorption of important nutrients and dietary components leading to deficiency, poor nutritional status, and oxidative stress. Of particular significance is the malabsorption of fat-soluble nutrients and antioxidants, which are important for normal immune and neurologic function. Patients with CF often are deficient in these compounds despite supplementation with the current standard of care therapy. The objective was to compare the pharmacokinetic profile of this water-soluble vitamin E formulation (Aqua-E) with an oil-based softgel formulation in a malabsorbing patient population. Patients with CF who had documented malabsorption were recruited for participation in this pharmacokinetic study. Patients who met inclusion and exclusion criteria discontinued vitamin E supplementation, except for that in a multivitamin, for 7 to 21 days before the day of dosing. Patients were randomized to a single dose of 20 ml of Aqua-E or three oil-based softgels, which contained equivalent amounts of tocopherols. Blood was drawn from patients at time 0, 2, 4, 8, 24, 48, and 168 hr and analyzed for tocopherols. Eight patients were enrolled in the study and randomized to Aqua-E or softgels. The primary outcome, the absorption of gamma-tocopherol in Aqua-E (AUC=115 micro g/ml(*)hr), was significantly greater than that of oil-based softgels (AUC=25.3 micro g/ml(*)hr; P=0.013). Total-tocopherols (alpha+gamma+delta) in Aqua-E (AUC=294 micro g/ml(*)hr) showed a strong trend toward increased absorption compared with that of oil-based softgels (AUC=117 micro g/ml(*)hr; P=0.09). In conclusion, this novel, water-soluble formulation showed a marked and statistically significant increase in absorption of gamma-tocopherol in malabsorbing patients with CF compared with an oil-based formulation.

Vitamin E: inflammation and atherosclerosis

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in the western world with its incidence increasing lately in developing countries. Several lines of evidence support a role for inflammation in atherogenesis. Hence, dietary micronutrients having antiinflammatory properties may have a potential beneficial effect with regard to CVD. Vitamin E is a potent antioxidant with antiinflammatory properties. It comprises eight different isoforms: four tocopherols (T) (alpha, beta, gamma, and delta) and four tocotrienols (T3) (alpha, beta, gamma, and delta). A wealth of data is available for the preventive efficacy of alpha-T. alpha-T supplementation in human subjects and animal models has been shown to be antioxidant and antiinflammatory in terms of decreasing C-reactive protein (CRP) and release of proinflammatory cytokines, the chemokine IL-8 and PAI-1 levels especially at high doses. gamma-T is effective in decreasing reactive nitrogen species and also appears to have antiinflammatory properties; however, there are scanty data examining pure gamma-T preparations. Furthermore, tocotrienols (alpha and gamma) also have implications for prevention of CVD; however, there are conflicting and insufficient data in the literature with regards to their potency. In this chapter, we have gathered recent emerging data on alpha-T specifically and also have given a composite view of gamma-T and tocotrienols especially with regards to their effect on inflammation as it relates to CVD.

Tocotrienols: the emerging face of natural vitamin E

Natural vitamin E includes eight chemically distinct molecules: alpha-, beta-, gamma-, and delta-tocopherols and alpha-, beta-, gamma-, and delta-tocotrienols. More than 95% of all studies on vitamin E are directed toward the specific study of alpha-tocopherol. The other forms of natural vitamin E remain poorly understood. The abundance of alpha-tocopherol in the human body and the comparable efficiency of all vitamin E molecules as antioxidants led biologists to neglect the non-tocopherol vitamin E molecules as topics for basic and clinical research. Recent developments warrant a serious reconsideration of this conventional wisdom. The tocotrienol subfamily of natural vitamin E possesses powerful neuroprotective, anticancer, and cholesterol-lowering properties that are often not exhibited by tocopherols. Current developments in vitamin E research clearly indicate that members of the vitamin E family are not redundant with respect to their biological functions. alpha-Tocotrienol, gamma-tocopherol, and delta-tocotrienol have emerged as vitamin E molecules with functions in health and disease that are clearly distinct from that of alpha-tocopherol. At nanomolar concentration, alpha-tocotrienol, not alpha-tocopherol, prevents neurodegeneration. On a concentration basis, this finding represents the most potent of all biological functions exhibited by any natural vitamin E molecule. Recently, it has been suggested that the safe dose of various tocotrienols for human consumption is 200-1000/day. A rapidly expanding body of evidence supports that members of the vitamin E family are functionally unique. In recognition of this fact, title claims in publications should be limited to the specific form of vitamin E studied. For example, evidence for toxicity of a specific form of tocopherol in excess may not be used to conclude that high-dosage "vitamin E" supplementation may increase all-cause mortality. Such conclusion incorrectly implies that tocotrienols are toxic as well under conditions where tocotrienols were not even considered. The current state of knowledge warrants strategic investment into the lesser known forms of vitamin E. This will enable prudent selection of the appropriate vitamin E molecule for studies addressing a specific health need.

γ-Tocotrienol Inhibits Nuclear Factor-κB Signaling Pathway through Inhibition of Receptor-interacting Protein and TAK1 Leading to Suppression of Antiapoptotic Gene Products and Potentiation of Apoptosis

Unlike the tocopherols, the tocotrienols, also members of the vitamin E family, have an unsaturated isoprenoid side chain. In contrast to extensive studies on tocopherol, very little is known about tocotrienol. Because the nuclear factor-kappaB (NF-kappaB) pathway has a central role in tumorigenesis, we investigated the effect of gamma-tocotrienol on the NF-kappaB pathway. Although gamma-tocotrienol completely abolished tumor necrosis factor alpha (TNF)-induced NF-kappaB activation, a similar dose of gamma-tocopherol had no effect. Besides TNF, gamma-tocotrienol also abolished NF-kappaB activation induced by phorbol myristate acetate, okadaic acid, lipopolysaccharide, cigarette smoke, interleukin-1beta, and epidermal growth factor. Constitutive NF-kappaB activation expressed by certain tumor cells was also abrogated by gamma-tocotrienol. Reducing agent had no effect on the gamma-tocotrienol-induced down-regulation of NF-kappaB. Mevalonate reversed the NF-kappaB inhibitory effect of gamma-tocotrienol, indicating the role of hydroxymethylglutaryl-CoA reductase. Gamma-tocotrienol blocked TNF-induced phosphorylation and degradation of IkappaBalpha through the inhibition of IkappaBalpha kinase activation, thus leading to the suppression of the phosphorylation and nuclear translocation of p65. gamma-Tocotrienol also suppressed NF-kappaB-dependent reporter gene transcription induced by TNF, TNFR1, TRADD, TRAF2, TAK1, receptor-interacting protein, NIK, and IkappaBalpha kinase but not that activated by p65. Additionally, the expressions of NF-kappaB-regulated gene products associated with antiapoptosis (IAP1, IAP2, Bcl-xL, Bcl-2, cFLIP, XIAP, Bfl-1/A1, TRAF1, and Survivin), proliferation (cyclin D1, COX2, and c-Myc), invasion (MMP-9 and ICAM-1), and angiogenesis (vascular endothelial growth factor) were down-regulated by gamma-tocotrienol. This correlated with potentiation of apoptosis induced by TNF, paclitaxel, and doxorubicin. Overall, our results demonstrate that gamma-tocotrienol inhibited the NF-kappaB activation pathway, leading to down-regulation of various gene products and potentiation of apoptosis.

Short-term high glucose exposure induces monocyte-endothelial cells adhesion and transmigration by increasing VCAM-1 and MCP-1 expression in human aortic endothelial cells

Acute, short-term hyperglycemia is becoming recognized as an important risk factor for several diseases. In the present study, using human aortic endothelial cells (HAECs), we investigated whether short-term high glucose exposure, either on the scale of hours, could enhance the monocyte adhesion and migration to the subendothelium via increasing expression of adhesion molecules and release of chemotactic factors. HAECs stimulated with 25mM d(+)glucose (HG) for not more than 12h, exhibited rapid up-regulation of vascular cell adhesion molecule-1 (VCAM-1) and monocyte chemoattractant protein-1 (MCP-1) mRNA and protein. Although intercellular adhesion molecule-1 (ICAM-1) is considered as a marker of the activation of the atherogenic process, early up-regulation was not observed, and VCAM-1 and MCP-1 protein enhance was sufficient to increase the adhesiveness of human monocytes U-937 to HAECs and their transmigration into the subendothelial space after 4h HG stimulation; both effects were prevented by interfering with monoclonal antibodies against VCAM-1, CD11b, and MCP-1. An increased intracellular oxidative stress, a translocation of NF-kappaB to the nucleus and a prevention of adhesion and transmigration of U-937 by interfering with NF-kappaB inhibitors was also observed after a short HG treatment. Taken together, these results suggest that either acute hyperglycemic spikes could exert an influence on the onset of diabetic complications and on the development of the atherogenic profile on diabetic and non-diabetic subjects.

Azelnidipine, a new calcium channel blocker, inhibits endothelial inflammatory response by reducing intracellular levels of reactive oxygen species

Oxidized low-density lipoprotein (ox-LDL) plays an important in the development of atherosclerosis by stimulating the production of reactive oxygen species in endothelial cells, and thereby up-regulating vascular cell adhesion molecule-1 (VCAM-1). The objectives of the present study were to determine the effects of azelnidipine, a new calcium channel blocker, on the expression of VCAM-1 induced by 7-ketocholesterol, components of ox-LDL, and tumor necrosis factor-alpha (TNF-alpha). The scavenging activities of azelnidipine against superoxide, hydroxyl, and carbon-centered radicals were determined by electron spin resonance assay. The levels of intracellular reactive oxygen species were determined fluorometrically with the use of dichlorodihydrofluorescein diacetate (H(2)DCF-DA). Human aortic endothelial cells and U937 were used as endothelial cells and monocytic cells, respectively. The surface expression and mRNA levels of VCAM-1 were determined by enzyme immunoassay and RT-PCR performed on endothelial cell monolayers stimulated with 7-ketocholesterol or TNF-alpha. The numbers of monocytic cells adhering on the stimulated endothelial cells were counted in the microscopic fields. Translocation of p65 protein to the nucleus was estimated by fluorescence microscopy. Azelnidipine, but not nifedipine, reduced the signal intensity of 1,1-diphenyl-2-picrylhydrazyl radicals. Azelnidipine scavenged hydroxyl radicals, but not superoxide radicals. Intracellular levels of reactive oxygen species and RelA (p65) nuclear translocation in stimulated endothelial cells were reduced by azelnidipine. Azelnidipine significantly inhibited the expression of protein and mRNA of VCAM-1, and prevented the U937 cell adhesion to endothelial cells treated with 7-ketocholesterol or TNF-alpha. These results suggest that azelnidipine works as an anti-atherogenic agent by inhibiting the reactive oxygen species-dependent expression of VCAM-1 induced by 7-ketocholesterol and TNF-alpha.

Postprandial levels of the natural vitamin E tocotrienol in human circulation

Compared to tocopherols, tocotrienols are poorly understood. The postabsorptive fate of tocotrienol isomers and their association with lipoprotein subfractions was examined. Normocholesterolemic women were subjected to an oral fat challenge supplemented with vitamin E (capsule containing 77 mg alpha-tocotrienol, 96 mg alpha-tocotrienol, 3 mg gamma-tocotrienol, 62 mg alpha-tocopherol, and 96 mg gamma-tocopherol). Plasma samples were collected at every 2 h intervals for up to 8 h following a one-time supplementation. Lipoproteins were measured by NMR spectroscopy, and subfractions of lipoproteins were isolated by density gradient ultracentrifugation. The maximal alpha-tocotrienol concentrations in supplemented individuals averaged approximately 3 microM in blood plasma, 1.7 microM in LDL, 0.9 microM in triglyceride-rich lipoprotein, and 0.5 microM in HDL. The peak plasma level corresponded to 12- to 30-fold more than the concentration of alpha-tocotrienol required to completely prevent stroke-related neurodegeneration. Tocotrienols were detected in the blood plasma and all lipoprotein subfractions studied postprandially.

Tumor suppressive effects of tocotrienol in vivo and in vitro

Tocotrienols have been reported to have higher biological activities than tocopherols. We investigated the antitumor effect of tocotrienols both in vivo and in vitro. Oral administration of tocotrienols resulted in significant suppression of liver and lung carcinogenesis in mice. In human hepatocellular carcinoma HepG2 cells, delta-tocotrienol exerted more significant antiproliferative effect than alpha-, beta-, and gamma-tocotrienols. delta-Tocotrienol induced apoptosis, and also tended to induce S phase arrest. On the other hand, gene expression analysis showed that delta-tocotrienol increased CYP1A1 gene, a phase I enzyme. Although further study will be necessary to investigate possible adverse effect, the data obtained in present study suggest that tocotrienols could be promising agents for cancer prevention.

Vitamin E composition of walnuts (Juglans regia L.): a 3-year comparative study of different cultivars

The tocopherol and tocotrienol composition of walnuts (Juglans regia L.) was determined for nine cultivars (cvs. Arco, Franquette, Hartley, Lara, Marbot, Mayette, Mellanaise, Parisienne, and Rego). Walnuts were harvested over three consecutive years from two different geographical origins (Bragança and Coimbra, Portugal), for a total of 26 samples. The methodology employed was a normal-phase high-performance liquid chromatography coupled to a series arrangement of a diode array detector followed by a fluorescence detector, allowing the simultaneous analysis of all tocopherols and tocotrienols. The analyses showed that all samples presented a similar qualitative profile composed of five compounds: alpha-tocopherol, beta-tocopherol, gamma-tocopherol, delta-tocopherol, and gamma-tocotrienol. gamma-Tocopherol was the major compound in all samples, ranging from 172.6 to 262.0 mg/kg, followed by alpha- and delta-tocopherols, ranging from 8.7 to 16.6 mg/kg and from 8.2 to 16.9 mg/kg, respectively. Multivariate analysis of the data obtained showed the existence of significant differences in composition among cultivars. These differences were also significant when cultivars were grouped by year of production, showing that besides genetic factors, the vitamin E composition was influenced by environmental factors.