Sharon Campbell

Gamma (γ) tocopherol upregulates peroxisome proliferator activated receptor (PPAR) gamma (γ) expression in SW 480 human colon cancer cell lines

BackgroundTocopherols are lipid soluble antioxidants that exist as eight structurally different isoforms. The intake of γ-tocopherol is higher than α-tocopherol in the average US diet. The clinical results of the effects of vitamin E as a cancer preventive agent have been inconsistent. All published clinical trials with vitamin E have used α-tocopherol. Recent epidemiological, experimental and molecular studies suggest that γ-tocopherol may be a more potent chemopreventive form of vitamin E compared to the more-studied α-tocopherol. γ-Tocopherol exhibits differences in its ability to detoxify nitrogen dioxide, growth inhibitory effects on selected cancer cell lines, inhibition of neoplastic transformation in embryonic fibroblasts, and inhibition of cyclooxygenase-2 (COX-2) activity in macrophages and epithelial cells. Peroxisome proliferator activator receptor γ (PPARγ) is a promising molecular target for colon cancer prevention. Upregulation of PPARγ activity is anticarcinogenic through its effects on downstream genes that affect cellular proliferation and apoptosis. The thiazolidine class of drugs are powerful PPARγ ligands. Vitamin E has structural similarity to the thiazolidine, troglitazone. In this investigation, we tested the effects of both α and γ tocopherol on the expression of PPARγ mRNA and protein in SW 480 colon cancer cell lines. We also measured the intracellular concentrations of vitamin E in SW 480 colon cancer cell lines.ResultsWe have discovered that the α and γ isoforms of vitamin E upregulate PPARγ mRNA and protein expression in the SW480 colon cancer cell lines. γ-Tocopherol is a better modulator of PPARγ expression than α-tocopherol at the concentrations tested. Intracellular concentrations increased as the vitamin E concentration added to the media was increased. Further, γ-tocopherol-treated cells have higher intracellular tocopherol concentrations than those treated with the same concentrations of α-tocopherol.ConclusionOur data suggest that both α and γ tocopherol can upregulate the expression of PPARγ which is considered an important molecular target for colon cancer chemoprevention. We show that the expression of PPARγ mRNA and protein are increased and these effects are more pronounced with γ-tocopherol. γ-Tocopherols ability to upregulate PPARγ expression and achieve higher intracellular concentrations in the colonic tissue may be relevant to colon cancer prevention. We also show that the intracellular concentrations of γ-tocopherol are several fold higher than α-tocopherol. Further work on other colon cancer cell lines are required to quantitate differences in the ability of these forms of vitamin E to induce apoptosis, suppress cell proliferation and act as PPAR ligands as well as determine their effects in conjunction with other chemopreventive agents. Upregulation of PPARγ by the tocopherols and in particular by γ-tocopherol may have relevance not only to cancer prevention but also to the management of inflammatory and cardiovascular disorders.

Tocopherols and the treatment of colon cancer

Abstract: Colorectal cancer is the second most common cause of cancer deaths in the United States. Vitamin E (VE) and other antioxidants may help prevent colon cancer by decreasing the formation of mutagens arising from the free radical oxidation of fecal lipids or by “non‐antioxidant” mechanisms. VE is not a single molecule, but refers to at least eight different molecules, that is, four tocopherols and four tocotrienols. Methods: Both animal models and human colon cancer cell lines were used to evaluate the chemopreventive potential of different forms of VE. Rats were fed diets deficient in tocopherols or supplemented with either α‐tocopherol or γ‐tocopherol. Half the rats in each of these groups received normal levels of dietary Fe and the other half Fe at eight times the normal level. In our cell experiments, we looked at the role of γ‐tocopherol in upregulating peroxisome proliferator‐activated receptor‐γ (PPAR‐γ) in the SW 480 human cell line. Results: Rats fed the diets supplemented with α‐tocopherol had higher levels of VE in feces, colonocytes, plasma, and liver than did rats fed diets supplemented with γ‐tocopherol. Dietary Fe levels did not influence tocopherol levels in plasma, liver, or feces. For colonocytes, high dietary Fe decreased tocopherol levels. Rats fed the γ‐tocopherol‐supplemented diets had lower levels of fecal lipid hydroperoxides than rats fed the α‐tocopherol‐supplemented diets. Ras‐p21 levels were significantly lower in rats fed the γ‐tocopherol‐supplemented diets compared with rats fed the α‐tocopherol‐supplemented diets. High levels of dietary Fe were found to promote oxidative stress in feces and colonocytes. Our data with the SW480 cells suggest that both α‐ and γ‐tocopherol upregulate PPAR‐γ mRNA and protein expression. γ‐tocopherol was, however, found to be a better enhancer of PPAR‐γ expression than α‐tocopherol at the concentrations tested.

γ-Tocotrienol induces growth arrest through a novel pathway with TGFβ2 in prostate cancer

Regions along the Mediterranean and in southern Asia have lower prostate cancer incidence compared to the rest of the world. It has been hypothesized that one of the potential contributing factors for this low incidence includes a higher intake of tocotrienols. Here we examine the potential of γ-tocotrienol (GT3) to reduce prostate cancer proliferation and focus on elucidating pathways by which GT3 could exert a growth-inhibitory effect on prostate cancer cells. We find that the γ and δ isoforms of tocotrienol are more effective at inhibiting the growth of prostate cancer cell lines (PC-3 and LNCaP) compared with the γ and δ forms of tocopherol. Knockout of PPAR-γ and GT3 treatment show inhibition of prostate cancer cell growth, through a partially PPAR-γ-dependent mechanism. GT3 treatment increases the levels of the 15-lipoxygenase-2 enzyme, which is responsible for the conversion of arachidonic acid to the PPAR-γ-activating ligand 15-S-hydroxyeicosatrienoic acid. In addition, the latent precursor and the mature forms of TGFβ2 are down-regulated after treatment with GT3, with concomitant disruptions in TGFβ receptor I, SMAD-2, p38, and NF-κB signaling.

Gamma tocopherol upregulates the expression of 15-S-HETE and induces growth arrest through a PPAR gamma-dependent mechanism in PC-3 human prostate cancer cells.

Chronic inflammation and dietary fat consumption correlates with an increase in prostate cancer. Our previous studies in the colon have demonstrated that γ-tocopherol treatment could upregulate the expression of peroxisome proliferator-activated preceptors (PPAR) γ, a nuclear receptor involved in fatty acid metabolism as well modulation of cell proliferation and differentiation. In this study, we explored the possibility that γ-tocopherol could induce growth arrest in PC-3 prostate cancer cells through the regulation of fatty acid metabolism. Growth arrest (40%) and PPAR γ mRNA and protein upregulation was achieved with γ-tocopherol within 6 h. γ-Tocopherol-mediated growth arrest was demonstrated to be PPAR γ dependent using the agonist GW9662 and a PPAR γ dominant negative vector. γ-tocopherol was shown not to be a direct PPAR γ ligand, but rather 15-S-HETE (an endogenous PPAR γ ligand) was upregulated by γ-tocopherol treatment. 15-Lipoxygenase-2, a tumor suppressor and the enzyme that converts arachidonic acid to 15-S-HETE, was upregulated at 3 h following γ-tocopherol treatment. Expression of proteins downstream of the PPAR γ pathway were examined. Cyclin D1, cyclin D3, bcl-2, and NFκ B proteins were found to be downregulated following γ-tocopherol treatment. These data demonstrate that the growth arrest mediated by γ-tocopherol follows a PPAR-γ-dependent mechanism.

The Role of Vitamin E in Prostate Cancer

This chapter reviews the current literature linking vitamin E to prostate cancer with the overall goal of providing a rationale for the design of potential future large-scale clinical chemoprevention studies. Vitamin E is not a single organic compound and refers to at least four tocopherols (alpha, beta, gamma, and delta) and four corresponding tocotrienols. Much of the literature linking vitamin E with cancer does not distinguish between these various isoforms and has primarily focused on alpha-tocopherol which is the primary vitamin E isoform found in plasma from fasting individuals and in most dietary supplements. Considerable evidence now supports the view that the various isoforms of vitamin E (and their chemical derivatives) have distinct biochemical properties and distinct abilities to modulate oxidative stress, signal transduction pathways, and pathophysiological processes important in carcinogenesis (e.g., apoptosis and angiogenesis). This chapter reviews the recent clinical trials as well as the in vitro and in vivo evidence connecting the various isoforms of vitamin E with prostate cancer. Particular emphasis is placed on gamma-tocopherol, the primary dietary isoform of vitamin E. A major conclusion is that some non-alpha-tocopherol forms of vitamin E hold considerable promise for both the chemoprevention and chemotherapy of prostate cancer.

Reduction in Cell Viability and in Homeobox Protein Levels Following in Vitro Exposure to δ-tocopherol in Acute Myeloid Leukemia

ABSTRACT δ-Tocopherol (δ-T), the least prevalent tocopherol in our diet, was described to have a more potent anticancer activity in solid tumors compared to the other tocopherols. δ-T induces tumor cell death through peroxisome proliferator-activated receptor γ (PPAR-γ) induction, cyclin-D1 inhibition, and modulation of redox balance. Nevertheless, the role of δ-T in preventing or treating hematologic malignancies has not been studied. In this study, we screened the efficacy of δ-T against six cell lines representing a wide spectrum of hematologic malignancies: Jurkat (acute T-cell leukemia), K-562 (chronic myeloid leukemia), KG-1 [acute myeloid leukemia (AML)], THP-1 (acute monocytic leukemia), TOM-1 (acute lymphoblastic leukemia), and UMCL01-101 (AIDS-associated diffuse large B-cell lymphoma). Interestingly, the AML cell line KG-1 was the only one to be significantly affected at concentrations of δ-T as low as 20 µM. The antileukemic activity of δ-T in AML was verified in a set of primary cells collected from patients newly diagnosed with AML. Apoptotic induction and cell cycle arrest explained the efficacy of δ-T against KG-1 cells. The mechanism of cell growth inhibition of δ-T was through downregulation of cyclin-D1 and a set of homeobox proteins (HOXA9, PBX1, and Cdx2) that have a well-documented role in the pathobiology of AML.

Abstract 4490: Tocotrienols inhibit PI3/Akt and ERK pathways to induce growth arrest in pancreatic cancer cell lines by downregulation of Her-2/ErbB2 receptors

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Abstract: Pancreatic cancer is the fifth leading cause of cancer death in the United States. Alternate strategies to treat and prevent this cancer are urgently required. In this regard, novel therapeutic agents that can inhibit signaling pathways implicated in the proliferation and survival of pancreatic cancer cells are of immense interest. Tocotrienols are members of the Vitamin E family but, unlike tocopherols, possess an unsaturated isoprenoid side-chain that confers superior anti-cancer properties. The ability of tocotrienols to selectively inhibit the HMG CoA reductase pathway through post-translational degradation of HMG CoA reductase and to suppress the activity of transcription factor NFκβ could be the basis for some of these properties. Data: Our studies indicate that γ- and Δ-tocotrienol have potent anti-proliferative activity in pancreatic cancer cells (Panc-28, MIA-PACA-2 and BXPC-3). Indeed both tocotrienols induced cell death (> 50%) by the MTT cell viability assay in all three pancreatic cancer cell lines. We also examined the effects of the tocotrienols on the Akt and the Ras/Raf/MEK/ERK signaling pathways by Western blotting analysis. γ- and Δ-Tocotrienol treatment of cells reduced the activation of ERK MAP kinase and that of its downstream mediator RSK (ribosomal protein S6k) in addition to suppressing the activation of protein kinase, Akt. Suppression of activation of Akt by gamma-tocotrienol led to downstream upregulation of Fox-03 and GSK-3b. These effects were mediated by the downregulation of Her2/ErbB2 at the messenger level. Tocotrienols but not tocopherols were able to induce the observed effects. Conclusion: Our results suggest that the tocotrienol isoforms of vitamin E can induce apoptosis in pancreatic cancer cells through the suppression of vital cell survival and proliferative signaling pathways such as those mediated by the PI3/Akt and ERK/MAP kinases via downregulation of Her2/ErbB2 expression. The molecular components for this mechanism are not completely elucidated and needs further investigation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4490. doi:10.1158/1538-7445.AM2011-4490