The highly malignant +SA mouse mammary epithelial cells were used as the model cell line over the years to establish the anticancer activity of tocotrienols. Tocotrienols, however, have poor oral bioavailability and were therefore entrapped into parenteral nanoemulsions for parenteral administration. The objective of this work was to test whether the activity of tocotrienols in lipid nanoemulsions against the +SA cells was retained. A secondary objective was to test whether stabilizing the nanoemulsions with poloxamer or sodium oleate would affect their activity. Nanoemulsions were found to be significantly more potent than tocotrienol/albumin conjugate. The IC50 values of the poloxamer and sodium oleate nanoemulsions were 3 and 6 microM, respectively, whereas the IC50 value of the conjugate was 10 microM. The antiproliferative activity of the nanoemulsions was also found to inversely correlate with particle size. No activity was observed with nanoemulsions loaded with alpha-tocopherol or vehicle, which confirmed the cytotoxic activity of tocotrienols and the potential use of nanoemulsions in cancer therapy.
Previous findings showed that the anticancer effects of combined γ -tocotrienol and peroxisome proliferator activated receptor γ (PPAR γ ) antagonist treatment caused a large reduction in PPAR γ expression. However, other studies suggest that the antiproliferative effects of γ -tocotrienol and/or PPAR γ antagonists are mediated, at least in part, through PPAR γ -independent mechanism(s). Studies were conducted to characterize the role of PPAR γ in mediating the effects of combined treatment of γ -tocotrienol with PPAR γ agonists or antagonists on the growth of PPAR γ negative +SA mammary cells and PPAR γ -positive and PPAR γ -silenced MCF-7 and MDA-MB-231 breast cancer cells. Combined treatment of γ -tocotrienol with PPAR γ antagonist decreased, while combined treatment of γ -tocotrienol with PPAR γ agonist increased, growth of all cancer cells. However, treatment with high doses of 15d-PGJ2, an endogenous natural ligand for PPAR γ , had no effect on cancer cell growth. Western blot and qRT-PCR studies showed that the growth inhibitory effects of combined γ -tocotrienol and PPAR γ antagonist treatment decreased cyclooxygenase (COX-2), prostaglandin synthase (PGDS), and prostaglandin D2 (PGD2) synthesis. In conclusion, the anticancer effects of combined γ -tocotrienol and PPAR γ antagonists treatment in PPAR γ negative/silenced breast cancer cells are mediated through PPAR γ -independent mechanisms that are associated with a downregulation in COX-2, PGDS, and PGD2 synthesis.
The Vitamin E family consists of four tocopherols and four tocotrienols. α-Tocopherol (αT) is the predominant form of vitamin E in tissues and its deficiency leads to ataxia in humans. However, results from many clinical studies do not support protective roles of αT in disease prevention in people with adequate nutrient status. On the other hand, recent mechanistic studies indicate that other forms of vitamin E such as γ-tocopherol (γT), δ-tocopherol (δT) and γ-tocotrienol (γTE) have unique antioxidant and anti-inflammatory properties that are superior to αT in prevention and therapy against chronic diseases. These vitamin E forms scavenge reactive nitrogen species, inhibit cyclooxygenase- and 5-lipoxygenase-catalyzed eicosanoids and suppress pro-inflammatory signaling such as NF-κB and STAT3/6. Unlike αT, other vitamin E forms are significantly metabolized to carboxychromanols via cytochrome P-450 (CYP4F2)-initiated side-chain ω-oxidation. Long-chain carboxychromanols, esp.13′-carboxychromanols, are shown to have stronger anti-inflammatory effects than un-metabolized vitamins and may therefore contribute to beneficial effects of vitamin E forms in vivo. Consistent with mechanistic findings, animal and human studies show that γT and tocotrienols may be useful against inflammation-associated diseases. This review focuses on non-αT forms of vitamin E with respect to their metabolism, anti-inflammatory effects and mechanisms and in vivo efficacy in preclinical models as well as human clinical intervention studies.
gamma-tocotrienol (GT3), an analogue of vitamin E, has gained increasing scientific interest recently as it provides significant health benefits. It has been shown that emulsified GT3, after subcutaneous administration, has long-term biological effects. However, whether the effects are due to the increase of GT3 level in the early phase following administration or the persistent functions after accumulation in tissues is unknown. This study was conducted to determine the levels of GT3 in different tissues by high performance liquid chromatography (HPLC) with a fluorescence detector after a single-dose of GT3 with polyethylene glycol (PEG-400) emulsion via subcutaneous injection. Previous studies have explored that GT3 has favorable effects on bone and can inhibit osteoclast formation. To confirm the persistent biological activity of accumulated GT3 in tissues, receptor activator of NF-kappaB ligand (RANKL) and osteoprotegerin (OPG) gene expressions, which have an important role in regulating osteoclast formation, were also evaluated in bone tissue on day 1, 3, 7 and 14 after a signal subcutaneous injection of GT3.
C57BL/6 female mice were administrated GT3 (100mg/kg body weight) with PEG-400 emulsion by subcutaneous injection. GT3 levels in different tissues were determined by HPLC with a fluorescence detector. Gene expressions were measured by real-time PCR.
GT3 predominantly accumulated in adipose and heart tissue, and was maintained at a relatively stable level in bone tissues after a single-dose administration. Accumulated GT3 in bone tissues significantly inhibited the increase in RANKL expression and the decrease in OPG expression induced by db-cAMP.
We investigated the tissue distribution of GT3 with PEG emulsion by subcutaneous administration, which has never been reported so far. Our results suggest that GT3 with PEG emulsion accumulated in tissues is able to carry out a long-term biological effect and has therapeutic value for treating and preventing osteoporosis.
Angiogenesis is one of the key hallmarks of cancer. In this study, we investigated whether γ-tocotrienol can abrogate angiogenesis-mediated tumor growth in hepatocellular carcinoma (HCC) and if so, through what molecular mechanisms. We observed that γ-tocotrienol inhibited vascular endothelial growth factor (VEGF)-induced migration, invasion, tube formation and viability of HUVECs in vitro. Moreover, γ-tocotrienol reduced the number of capillary sprouts from matrigel embedded rat thoracic aortic ring in a dose-dependent manner. Also, in chick chorioallantoic membrane assay, γ-tocotrienol significantly reduced the blood vessels formation. We further noticed that γ-tocotrienol blocked angiogenesis in an in vivo matrigel plug assay. Furthermore, γ-tocotrienol inhibited VEGF-induced autophosphorylation of VEGFR2 in HUVECs and also suppressed the constitutive activation of AKT/mammalian target of rapamycin (mTOR) signal transduction cascades in HUVECs as well as in HCC cells. Interestingly, γ-tocotrienol was also found to significantly reduce the tumor growth in an orthotopic HCC mouse model and inhibit tumor-induced angiogenesis in HCC patient xenografts through the suppression of various biomarkers of proliferation and angiogenesis. Taken together, our findings strongly suggest that γ-tocotrienol might be a promising anti-angiogenic drug with significant antitumor activity in HCC.
Tocotrienols are known to possess potent antioxidant, anticancer, and cholesterol lowering activities. Being able to rapidly penetrate the skin, these vitamin E isoforms have been explored for potential treatment against melanoma. This study aimed to elucidate the mechanism involved in the anti-melanogenic effects of δ-tocotrienol (δT3) in B16 melanoma cells. Results showed that at 20μM of δT3 significantly inhibited melanin formation and ROS generation. Treatment with δT3 also effectively suppressed the expression of melanogenesis-related proteins, including MC1R, MITF, TYRP-1, and TYRP-2. More importantly, we observed that the mitogen-activated protein kinase (MAPK) pathway was involved in mediating δT3’s inhibitory effect against melanin production. Specifically, δT3 treatment markedly induced the activation of extracellular signal-regulated kinases (ERK). The use of ERK activation inhibitor (PD98059) abrogated the δT3-mediated downregulation expression melanogenesis-related proteins and restored melanin production. Furthermore, siRNA targeting ERK effectively blocked the δT3-induced repression of tyrosinase and TYRP-1 expression. These results suggest that δT3’s inhibitory effect against melanogenesis is mediated by the activation of ERK signaling, thereby resulting in downstream repression of melanogenesis-related proteins and the subsequent melanin production. These data provide insight to δT3’s effect and the targeting of ERK signaling for treatment against melanogenesis.
BACKGROUND AND PURPOSE:
Previous cell-based and animal studies showed mixed tocotrienols are neuroprotective, but the effect is yet to be proven in humans. Thus, the present study aimed to evaluate the protective activity of mixed tocotrienols in humans with white matter lesions (WMLs). WMLs are regarded as manifestations of cerebral small vessel disease, reflecting varying degrees of neurodegeneration and tissue damage with potential as a surrogate end point in clinical trials.
A total of 121 volunteers aged ≥35 years with cardiovascular risk factors and MRI-confirmed WMLs were randomized to receive 200 mg mixed tocotrienols or placebo twice a day for 2 years. The WML volumes were measured from MRI images taken at baseline, 1 year, and 2 years using a validated software and were compared. Fasting blood samples were collected for full blood chemistry investigation.
According to per-protocol (88 volunteers) and intention-to-treat (121 volunteers) analyses, the mean WML volume of the placebo group increased after 2 years, whereas that of the tocotrienol-supplemented group remained essentially unchanged. The mean WML volume change between the 2 groups was not significantly different (P=0.150) at the end of 1 year but was significant at the end of 2 years for both per-protocol and intention-to-treat analyses (P=0.019 and P=0.018). No significant difference was observed in the blood chemistry parameters between the 2 groups.
Mixed tocotrienols were found to attenuate the progression of WMLs.
CLINICAL TRIAL REGISTRATION: URL:
http://www.clinicaltrials.gov. Unique identifier: NCT00753532.
This study investigated the mechanistic details by which gamma-tocotrienol (γ-T3) manipulates adipocyte differentiation in human adipose derived stem cells (hASCs).
METHODS AND RESULTS:
γ-T3 specifically inhibited the early stage of adipocyte differentiation by acting on downstream of C/EBP-β but upstream of C/EBP-α in hASCs. In searching a potential mechanism, we identified that γ-T3 promoted two catabolic signaling pathways: (i) AMP kinase (AMPK), and (ii) enhanced autophagy, as assessed by autophagic flux and cytosolic autophagosome (LC3II) accumulation. In addition, chronic exposure of γ-T3 induced caspase3-mediated apoptotic cell death. The blockage of AMPK by a dominant negative mutant of AMPK was insufficient to normalize γ-T3-mediated autophagy, suggesting that enhanced autophagic activity of γ-T3 is independent of AMPK activation. Intriguingly, AMPK inhibition significantly restored PPAR-γ activation, but marginally rescued lipid-loaded adipocyte morphology due to, at least partly, a lack of lipid droplet-coating protein. These data suggest that γ-T3 activates AMPK and autophagy signaling, which synergistically contributes to the suppression of adipogenic conversion of hASCs into adipocytes.
These results provide a novel insight into the molecular mechanism involved in anti-adipogenic action of γ-T3 in humans via AMPK and autophagy activation. Thus, γ-T3 may constitute a new dietary avenue to attenuate hyperplastic obesity in humans.