Gamma-Tocotrienol

Br J Pharmacol. 2011 May; 163(2): 283–298.

γ-Tocotrienol is a novel inhibitor of constitutive and inducible STAT3 signalling pathway in human hepatocellular carcinoma: potential role as an antiproliferative, pro-apoptotic and chemosensitizing agent[Pubmed: 21198544 ]

Activation of signal transducer and activator of transcription 3 (STAT3) play a critical role in the survival, proliferation, angiogenesis and chemoresistance of tumour cells. Thus, agents that suppress STAT3 phosphorylation have potential as cancer therapies. In the present study, we investigated whether the apoptotic, antiproliferative and chemosensitizing effects of Gamma-Tocotrienol are associated with its ability to suppress STAT3 activation in hepatocellular carcinoma (HCC).
METHODS AND RESULTS:
The effect of Gamma-Tocotrienol on STAT3 activation, associated protein kinases and phosphatase, STAT3-regulated gene products, cellular proliferation and apoptosis in HCC cells was investigated. Gamma-Tocotrienol inhibited both the constitutive and inducible activation of STAT3 with minimum effect on STAT5. Gamma-Tocotrienol also inhibited the activation of Src, JAK1 and JAK2 implicated in STAT3 activation. Pervanadate reversed the Gamma-Tocotrienol-induced down-regulation of STAT3, suggesting the involvement of a protein tyrosine phosphatase. Indeed, we found that Gamma-Tocotrienol induced the expression of the tyrosine phosphatase SHP-1 and deletion of the SHP-1 gene by small interfering RNA abolished the ability of Gamma-Tocotrienol to inhibit STAT3 activation. Gamma-Tocotrienol also down-regulated the expression of STAT3-regulated gene products, including cyclin D1, Bcl-2, Bcl-xL, survivin, Mcl-1 and vascular endothelial growth factor. Finally, Gamma-Tocotrienol inhibited proliferation, induced apoptosis and significantly potentiated the apoptotic effects of chemotherapeutic drugs (paclitaxel and doxorubicin) used for the treatment of HCC.
CONCLUSIONS:
Overall, these results suggest that Gamma-Tocotrienol is a novel blocker of the STAT3 activation pathway, with a potential role in future therapies for HCC and other cancers.

Toxicology. 2010 Jul-Aug;274(1-3):27-33.

gamma-Tocotrienol modulates the paracrine secretion of VEGF induced by cobalt(II) chloride via ERK signaling pathway in gastric adenocarcinoma SGC-7901 cell line.[Pubmed: 20452389 ]

Hypoxia is a common characteristic feature of solid tumors, and carcinoma cells are known to secrete many growth factors. These growth factors, such as vascular endothelial growth factor (VEGF), play a major role in the regulation of tumor angiogenesis and metastasis.
METHODS AND RESULTS:
In this study, the effect of Gamma-Tocotrienol, a natural product commonly found in palm oil and rice bran, on the accumulation of HIF-1alpha protein and the paracrine secretion of VEGF in human gastric adenocarcinoma SGC-7901 cell line induced by cobalt(II) chloride (as a hypoxia mimic) was investigated. These results showed that cobalt(II) chloride induced the high expression of VEGF in SGC-7901 cells at dose of 150 micromol/L for 24h. Both basal level and cobalt(II) chloride-induced HIF-1alpha protein accumulation and VEGF paracrine secretion were inhibited in SGC-7901 cells treated with Gamma-Tocotrienol at 60 micromol/L treatment for 24 h. U0126, a MEK1/2 inhibitor, decreased the expression of HIF-1alpha protein and the paracrine secretion of VEGF under normoxic and hypoxic conditions. In this study, Gamma-Tocotrienol also significantly inhibited the hypoxia-stimulated expression of phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2).
CONCLUSIONS:
The mechanism seems to involve in inhibiting hypoxia-mediated activation of p-ERK1/2, it leads to a marked decrease in hypoxia-induced HIF-1alpha protein accumulation and VEGF secretion. These data suggest that HIF-1alpha/VEGF could be a promising target for Gamma-Tocotrienol in an effective method of chemoprevention and chemotherapy in human gastric cancer.

J Nutr Biochem. 2009 Apr;20(4):276-84.

gamma-Tocotrienol induces mitochondria-mediated apoptosis in human gastric adenocarcinoma SGC-7901 cells.[Pubmed: 18602811 ]

Tocotrienols are naturally occurring isoprenoid compounds highly enriched in palm oil, rice bran, oat, wheat germ, barley and rye. Tocotrienols have antioxidant properties as well as potent anticancer properties.
METHODS AND RESULTS:
In this study, the mechanisms underlying the apoptosis of Gamma-Tocotrienol on human gastric adenocarcinoma SGC-7901 cells were further studied, especially in correlation with the involvement of the apoptotic pathway. Gamma-Tocotrienol inhibited SGC-7901 cell growth in a concentration- and time-dependent manner. The inhibitory effects of SGC-7901 cells were correlated with the DNA damage and arresting cell cycle at G(0)/G(1) phase in a time-dependent manner at 60 mumol/L concentration of Gamma-Tocotrienol. Gamma-Tocotrienol induced activation of caspase-3 and increased the cleavage of the downstream substrate poly(ADP-ribose) polymerase. Furthermore, Gamma-Tocotrienol-induced apoptosis on SGC-7901 cells was mediated by activation of caspase-9.
CONCLUSIONS:
The data in this study suggested that Gamma-Tocotrienol could induce the apoptosis on human gastric cancer SGC-7901 cells via mitochondria-dependent apoptosis pathway. Thus, our findings revealed Gamma-Tocotrienol as a potential, new chemopreventive agent for human gastric cancer.

Lipids. 1993 Dec;28(12):1113-8.

gamma-Tocotrienol as a hypocholesterolemic and antioxidant agent in rats fed atherogenic diets.[Pubmed: 8121254]

This study was designed to determine whether incorporation of Gamma-Tocotrienol or alpha-tocopherol in an atherogenic diet would reduce the concentration of plasma cholesterol, triglycerides and fatty acid peroxides, and attenuate platelet aggregability in rats.
METHODS AND RESULTS:
For six weeks, male Wistar rats (n = 90) were fed AIN76A semisynthetic test diets containing cholesterol (2% by weight), providing fat as partially hydrogenated soybean oil (20% by weight), menhaden oil (20%) or corn oil (2%). Feeding the ration with menhaden oil resulted in the highest concentrations of plasma cholesterol, low and very low density lipoprotein cholesterol, triglycerides, thiobarbituric acid reactive substances and fatty acid hydroperoxides. Consumption of the ration containing Gamma-Tocotrienol (50 mg/kg) and alpha-tocopherol (500 mg/kg) for six weeks led to decreased plasma lipid concentrations. Plasma cholesterol, low and very low density lipoprotein cholesterol, and triglycerides each decreased significantly (P < 0.001). Plasma thiobarbituric acid reactive substances decreased significantly (P < 0.01), as did the fatty acid hydroperoxides (P < 0.05), when the diet contained both chromanols. Supplementation with Gamma-Tocotrienol resulted in similar, though quantitatively smaller, decrements in these plasma values. Plasma alpha-tocopherol concentrations were lowest in rats fed menhaden oil without either chromanol.
CONCLUSIONS:
Though plasma alpha-tocopherol did not rise with Gamma-Tocotrienol supplementation at 50 mg/kg, Gamma-Tocotrienol at 100 mg/kg of ration spared plasma alpha-tocopherol, which rose from 0.60 +/- 0.2 to 1.34 +/- 0.4 mg/dL (P < 0.05). The highest concentration of alpha-tocopherol was measured in plasma of animals fed a ration supplemented with alpha-tocopherol at 500 mg/kg.