Comparative effects of RRR-alpha- and RRR-gamma-tocopherol on proliferation and apoptosis in human colon cancer cell lines

The Role of Vitamin E Isoforms and Metabolites in Cancer Prevention: Mechanistic Insights into Sphingolipid Metabolism Modulation

Natural forms of vitamin E include four tocopherols and four tocotrienols (α, β, γ, and δ), which are essential as lipophilic antioxidants. Among these eight isoforms, α-tocopherol (αT), the predominant form of vitamin E found in tissues, has traditionally received the most attention in disease prevention research due to its robust antioxidant activity. However, recent studies suggest that other forms of vitamin E exhibit distinct and potentially more potent beneficial activities in disease prevention and treatment. These non-αT forms of vitamin E are metabolized in vivo, producing various metabolites, including 13'-carboxychromanol, though their biological roles remain largely unknown. Notably, sphingolipids, known for their significant roles in cancer biology, may be involved in the anticancer effects of vitamin E through the modulation of sphingolipid metabolism. This review focuses on the diverse biological activities of different vitamin E forms and their metabolites, particularly their anticancer effects, while highlighting the underlying mechanisms, including their novel impact on regulating sphingolipid pathways. By elucidating these interactions, we aim to provide a deeper understanding on the multifaceted roles of vitamin E in cancer prevention and therapy.

Exploring the potential of tocopherols: mechanisms of action and perspectives in the prevention and treatment of breast cancer

Currently, breast cancer is the most common cause of mortality caused by neoplasia in women worldwide. The unmet challenges of conventional cancer therapy are chemoresistance and lack of selectivity, which can lead to serious side effects in patients; therefore, new treatments based on natural compounds that serve as adjuvants in breast cancer therapy are urgently needed. Tocopherols are naturally occurring antioxidant compounds that have shown antitumor activity against several types of cancer, including breast cancer. This review summarizes the antitumoral activity of tocopherols, such as the antiproliferative, apoptotic, anti-invasive, and antioxidant effects of tocopherols, through different molecular mechanisms. According to the studies described, α-T, δ-T and γ-T are the most studied in breast tumor cells; however, α-T and γ-T show a more critical antitumor activity and significant potential as a complements to chemotherapeutic drugs against breast cancer, enhancing toxicity against tumor cells and preventing cytotoxicity in nontumor cells. However, the possible relationship between tocopherol intake, related to concentration, and the promotion of cancer in particular cases should not be ruled out, so additional studies are required to determine the correct dose to obtain the desired antitumor effect. Moreover, nanomicelles of D-α-tocopherol have promising potential as pharmaceutical excipients for drug delivery to improve the cytotoxicity and selectivity of first-line chemotherapeutics against breast cancer.

Chemopreventive effects of α-tocopherol and its long-chain metabolites α-13'-hydroxy- and α-13'-carboxychromanol in LT97 colon adenoma cells

Anticancer effects of vitamin E (tocopherols) have been studied extensively. While in vitro and animal studies showed promising results regarding anticancer effects of tocopherols, human intervention studies failed to reproduce these results. In vivo, α-tocopherol (α-TOH) is metabolized to the long-chain metabolites (LCM) 13'-hydroxychromanol (α-13'-OH) and 13'-carboxychromanol (α-13'-COOH), which likely reach the large intestine. The LCM showed antiproliferative effects in different colon cancer cell lines, but the exact mechanism of action remains unclear. To further clarify the chemopreventive action of the LCM, premalignant LT97 colon adenoma cells were treated with α-TOH, α-13'-OH and α-13'-COOH to study their impact on growth, apoptosis, antigenotoxicity, and ROS-scavenging capacity as well as expression of selected genes involved in detoxification and the cell cycle. Growth inhibitory potential was observed for α-13'-OH (IC50: 37.4 μM) and α-13'-COOH (IC50: 5.8 μM) but not for α-TOH in the tested concentrations. Levels of caspase-3 activity and expression of genes regulating the cell cycle and detoxification remained unchanged. However, α-TOH, α-13'-OH and α-13'-COOH exhibited antigenotoxic and partly ROS-scavenging capacity. The results indicate that the LCM exert chemopreventive effects via ROS-scavenging capacity, the protection against DNA damage and the induction of cell death via caspase-independent mechanisms in premalignant colon cells.

Vitamin E functions by association with a novel binding site on the 67 kDa laminin receptor activating diacylglycerol kinase

It is generally recognized that the main function of α-tocopherol (αToc), which is the most active form of vitamin E, is its antioxidant effect, while non-antioxidant effects have also been reported. We previously found that αToc ameliorates diabetic nephropathy via diacylglycerol kinase alpha (DGKα) activation in vivo, and the activation was not related to the antioxidant effect. However, the underlying mechanism of how αToc activates DGKα have been enigmatic. We report that the membrane-bound 67 kDa laminin receptor (67LR), which has previously been shown to serve as a receptor for epigallocatechin gallate (EGCG), also contains a novel binding site for vitamin E, and its association with Vitamin E mediates DGKα activation by αToc. We employed hydrogen-deuterium exchange mass spectrometry (HDX/MS) and molecular dynamics (MD) simulations to identify the specific binding site of αToc on the 67LR and discovered the conformation of the specific hydrophobic pocket that accommodates αToc. Also, HDX/MS and MD simulations demonstrated the detailed binding of EGCG to a water-exposed hydrophilic site on 67LR, while in contrast αToc binds to a distinct hydrophobic site. We demonstrated that 67LR triggers an important signaling pathway mediating non-antioxidant effects of αToc, such as DGKα activation. This is the first evidence demonstrating a membrane receptor for αToc and one of the underlying mechanisms of a non-antioxidant function for αToc.

Enriched Riceberry Bran Oil Exerts Chemopreventive Properties through Anti-Inflammation and Alteration of Gut Microbiota in Carcinogen-Induced Liver and Colon Carcinogenesis in Rats

Riceberry has recently been acknowledged for its beneficial pharmacological effects. Riceberry bran oil (RBBO) exhibited anti-proliferation activity in various cancer cell lines. However, animal studies of RBBO on anti-carcinogenicity and its molecular inhibitory mechanism have been limited. This study purposed to investigate the chemopreventive effects of RBBO on the carcinogen-induced liver and colorectal carcinogenesis in rats. Rats were injected with diethylnitrosamine (DEN) and 1,2-dimethylhydrazine (DMH) and further orally administered with RBBO equivalent to 100 mg/kg body weight of γ-oryzanol 5 days/week for 10 weeks. RBBO administration suppressed preneoplastic lesions including hepatic glutathione S-transferase placental form positive foci and colorectal aberrant crypt foci. Accordingly, RBBO induced hepatocellular and colorectal cell apoptosis and reduced pro-inflammatory cytokine expression. Interestingly, RBBO effectively promoted the alteration of gut microbiota in DEN- and DMH-induced rats, as has been shown in the elevated Firmicutes/Bacteroidetes ratio. This outcome was consistent with an increase in butyrate in the feces of carcinogen-induced rats. The increase in butyrate reflects the chemopreventive properties of RBBO through the mechanisms of its anti-inflammatory properties and cell apoptosis induction in preneoplastic cells. This would indicate that RBBO containing γ-oryzanol, phytosterols, and tocols holds significant potential in the prevention of cancer.

Sacha inchi (Plukenetia volubilis L.): An emerging source of nutrients, omega-3 fatty acid and phytochemicals

Sacha inchi (Plukenetia volubilis) (SI) is an oleaginous plant producing oil and protein-rich seeds. It has been cultivated for centuries and is native to the tropical rainforest of the Amazon region of South America including parts of Peru and northwestern Brazil. At present, SI seeds are emerging as a potential source of macro- and micronutrients, α-linolenic acid and phytochemicals. This review attempts to elucidate the nutrients, phytonutrients, safety, toxicity, health benefits and food applications of SI seed. Recent scientific studies have associated the consumption of SI seed/oil with reduced risk of chronic inflammatory diseases. However, lack of awareness and in-depth understanding has resulted in it being neglected both at the consumer and industrial level. In all, SI is an underutilized and undervalued oleaginous crop which not only has the potential to mitigate food and nutritional insecurity but also offers humongous opportunities for the development of novel value-added food products.

Utilization of redox modulating small molecules that selectively act as pro-oxidants in cancer cells to open a therapeutic window for improving cancer therapy

There is a rapidly growing body of literature supporting the notion that differential oxidative metabolism in cancer versus normal cells represents a metabolic frailty that can be exploited to open a therapeutic window into cancer therapy. These cancer cell-specific metabolic frailties may be amenable to manipulation with non-toxic small molecule redox active compounds traditionally thought to be antioxidants. In this review we describe the potential mechanisms and clinical applicability in cancer therapy of four small molecule redox active agents: melatonin, vitamin E, selenium, and vitamin C. Each has shown the potential to have pro-oxidant effects in cancer cells while retaining antioxidant activity in normal cells. This dichotomy can be exploited to improve responses to radiation and chemotherapy by opening a therapeutic window based on a testable biochemical rationale amenable to confirmation with biomarker studies during clinical trials. Thus, the unique pro-oxidant/antioxidant properties of melatonin, vitamin E, selenium, and vitamin C have the potential to act as effective adjuvants to traditional cancer therapies, thereby improving cancer patient outcomes.

Extract of Pogostemon cablin Possesses Potent Anticancer Activity against Colorectal Cancer Cells In Vitro and In Vivo

Pogostemon cablin (PCa), an herb used in traditional Chinese medicine, is routinely used in the amelioration of different types of gastrointestinal discomfort. However, the mechanisms underlying the cancer suppression activity of PCa in colorectal cancer (CRC) cells have yet to be clarified. The aim of this study was to investigate the anticancer effects of PCa, specifically the induction of apoptosis in CRC cells. The growth inhibition curve of CRC cells following exposure to PCa was detected by an MTT assay. Moreover, PCa combined with 5-FU revealed a synergic effect of decreased cell viability. PCa inhibited cell proliferation and induced cell cycle arrest at the G₀/G₁ phase and cell apoptosis through regulation of associated protein expression. An in vivo study showed that PCa suppressed the growth of CRC via induction of cell apoptosis with no significant change in body weight or organ histology. Our results demonstrated that PCa inhibits the growth of CRC cells and induces apoptosis in vitro and in vivo, which suggests the potential applicability of PCa as an anticancer agent.

Comparative Effects of Alpha- and Gamma-Tocopherol on Mitochondrial Functions in Alzheimer's Disease In Vitro Model

Vitamin E acts as an antioxidant and reduces the level of reactive oxygen species (ROS) in Alzheimer's disease (AD). Alpha-tocopherol (ATF) is the most widely studied form of vitamin E besides gamma-tocopherol (GTF) which also shows beneficial effects in AD. The levels of amyloid-beta (Aβ) and amyloid precursor protein (APP) increased in the brains of AD patients, and mutations in the APP gene are known to enhance the production of Aβ. Mitochondrial function was shown to be affected by the increased level of Aβ and may induce cell death. Here, we aimed to compare the effects of ATF and GTF on their ability to reduce Aβ level, modulate mitochondrial function and reduce the apoptosis marker in SH-SY5Y cells stably transfected with the wild-type or mutant form of the APP gene. The Aβ level was measured by ELISA, the mitochondrial ROS and ATP level were quantified by fluorescence and luciferase assay respectively whereas the complex V enzyme activity was measured by spectrophotometry. The expressions of genes involved in the regulation of mitochondrial membrane permeability such as voltage dependent anion channel (VDAC1), adenine nucleotide translocase (ANT), and cyclophilin D (CYPD) were determined by quantitative real-time polymerase chain reaction (qRT-PCR), while the expressions of cyclophilin D (CypD), cytochrome c, Bcl2 associated X (BAX), B cell lymphoma-2 (Bcl-2), and pro-caspase-3 were determined by western blot. Our results showed that mitochondrial ROS level was elevated accompanied by decreased ATP level and complex V enzyme activity in SH-SY5Y cells expressing the mutant APP gene (p < 0.05). Treatment with both ATF and GTF reduced the mitochondrial ROS level with maximum reduction was observed in the cells treated with high concentrations of ATF and GTF (p < 0.05). However, only GTF at 80 µM significantly increase the ATP level and complex V enzyme activity (p < 0.05). VDAC1 and CYPD were downregulated and CypD protein was significantly overexpressed in cells transfected with the wild-type (WT) and mutant APP gene (p < 0.05). Cytochrome c release, the ratio of BAX/Bcl-2, and pro-caspase-3 expression increased in cells expressing mutated APP gene (p < 0.05). The expression of CypD and pro-caspase 3 protein, and the ratio of BAX/Bcl-2 were increased in the following order; SH-SY5Y-APP-WT < SH-SY5Y-APP Swe Collapse

Key Words

• preclinical research
• translational research

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MESH Headings

• Alzheimer Disease/drug therapy
• Alzheimer Disease/metabolism
• Amyloid beta-Peptides/metabolism
• Amyloid beta-Protein Precursor/drug effects
• Amyloid beta-Protein Precursor/metabolism
• Apoptosis/drug effects
• Caspase 3/metabolism
• Cell Line, Tumor
• Cytochromes c/metabolism
• Humans
• Mitochondria/drug effects
• Proto-Oncogene Proteins c-bcl-2/metabolism
• Reactive Oxygen Species/metabolism
• Tocopherols/pharmacology
• alpha-Tocopherol/pharmacology
• gamma-Tocopherol/pharmacology

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Grants

• Universiti Kebangsaan Malaysia DIP/2013/003 Universiti Kebangsaan Malaysia FF-2015-025

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Affiliation(s)

Aslina Pahrudin Arrozi Department of Biochemistry, Level 17, Preclinical Building, Universiti Kebangsaan Malaysia Medical Centre, Jalan Yaacob Latif, Bandar Tun Razak, Cheras, 56000, Kuala Lumpur, Malaysia
Siti Nur Syazwani Shukri Department of Biochemistry, Level 17, Preclinical Building, Universiti Kebangsaan Malaysia Medical Centre, Jalan Yaacob Latif, Bandar Tun Razak, Cheras, 56000, Kuala Lumpur, Malaysia
Wan Zurinah Wan Ngah Department of Biochemistry, Level 17, Preclinical Building, Universiti Kebangsaan Malaysia Medical Centre, Jalan Yaacob Latif, Bandar Tun Razak, Cheras, 56000, Kuala Lumpur, Malaysia
Yasmin Anum Mohd Yusof Department of Biochemistry, Level 17, Preclinical Building, Universiti Kebangsaan Malaysia Medical Centre, Jalan Yaacob Latif, Bandar Tun Razak, Cheras, 56000, Kuala Lumpur, Malaysia
Mohd Hanafi Ahmad Damanhuri Department of Biochemistry, Level 17, Preclinical Building, Universiti Kebangsaan Malaysia Medical Centre, Jalan Yaacob Latif, Bandar Tun Razak, Cheras, 56000, Kuala Lumpur, Malaysia
Faizul Jaafar Department of Biochemistry, Level 17, Preclinical Building, Universiti Kebangsaan Malaysia Medical Centre, Jalan Yaacob Latif, Bandar Tun Razak, Cheras, 56000, Kuala Lumpur, Malaysia
Suzana Makpol Department of Biochemistry, Level 17, Preclinical Building, Universiti Kebangsaan Malaysia Medical Centre, Jalan Yaacob Latif, Bandar Tun Razak, Cheras, 56000, Kuala Lumpur, Malaysia.

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Diversity of Chromanol and Chromenol Structures and Functions: An Emerging Class of Anti-Inflammatory and Anti-Carcinogenic Agents

Natural chromanols and chromenols comprise a family of molecules with enormous structural diversity and biological activities of pharmacological interest. A recently published systematic review described more than 230 structures that are derived from a chromanol ortpd chromenol core. For many of these compounds structure-activity relationships have been described with mostly anti-inflammatory as well as anti-carcinogenic activities. To extend the knowledge on the biological activity and the therapeutic potential of these promising class of natural compounds, we here present a report on selected chromanols and chromenols based on the availability of data on signaling pathways involved in inflammation, apoptosis, cell proliferation, and carcinogenesis. The chromanol and chromenol derivatives seem to bind or to interfere with several molecular targets and pathways, including 5-lipoxygenase, nuclear receptors, and the nuclear-factor "kappa-light-chain-enhancer" of activated B-cells (NFκB) pathway. Interestingly, available data suggest that the chromanols and chromenols are promiscuitively acting molecules that inhibit enzyme activities, bind to cellular receptors, and modulate mitochondrial function as well as gene expression. It is also noteworthy that the molecular modes of actions by which the chromanols and chromenols exert their effects strongly depend on the concentrations of the compounds. Thereby, low- and high-affinity molecular targets can be classified. This review summarizes the available knowledge on the biological activity of selected chromanols and chromenols which may represent interesting lead structures for the development of therapeutic anti-inflammatory and chemopreventive approaches.

γ-Tocotrienol and α-Tocopherol Ether Acetate Enhance Docetaxel Activity in Drug-Resistant Prostate Cancer Cells

Prostate cancer is the second most commonly diagnosed cancer in men, and metastatic prostate cancer is currently incurable. Prostate cancer frequently becomes resistant to standard of care treatments, and the administration of chemotherapeutic drugs is often accompanied by toxic side effects. Combination therapy is one tool that can be used to combat therapeutic resistance and drug toxicity. Vitamin E (VE) compounds and analogs have been proposed as potential non-toxic chemotherapeutics. Here we modeled combination therapy using mixture design response surface methodology (MDRSM), a statistical technique designed to optimize mixture compositions, to determine whether combinations of three chemotherapeutic agents: γ-tocotrienol (γ-T3), α-tocopherol ether acetate (α-TEA), and docetaxel (DOC), would prove more effective than docetaxel alone in the treatment of human prostate cancer cells. Response surfaces were generated for cell viability, and the optimal treatment combination for reducing cell viability was calculated. We found that a combination of 20 µM γ-T3, 30 µM α-TEA, and 25 nm DOC was most effective in the treatment of PC-3 cells. We also found that the combination of γ-T3 and α-TEA with DOC decreased the amount of DOC required to reduce cell viability in PC-3 cells and ameliorated therapeutic resistance in DOC-resistant PC-3 cells.

Adjuvant therapy with γ-tocopherol-induce apoptosis in HT-29 colon cancer via cyclin-dependent cell cycle arrest mechanism

Resistance to chemotherapy with 5-fluorouracil (5-FU) in patients with colorectal cancer (CRC) is the major obstacle to reach the maximum efficiency of CRC treatment. Combination therapy has emerged as a novel anticancer strategy. The present study evaluates the cotreatment of γ-tocopherol and 5-FU in enhancing the efficacy of chemotherapy against HT-29 colon cancer cells. Cytotoxic effect of this combination was examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and a synergistic effect was evaluated by a combination index technique. Nuclear morphology was studied via 4',6-diamidino-2-phenylindole staining and flow cytometric assays were conducted to identify molecular mechanisms of apoptosis and cell cycle progression. We investigated the expression of Cyclin D1, Cyclin E, Bax, and Bcl-2 by a quantitative real-time polymerase chain reaction. The IC₅₀ values for 5-FU and γ-tocopherol were 21.8  ± 2.5 and 14.4 ± 2.6 μM, respectively, and also this combination therapeutic increased the percentage of apoptotic cells from 35% ± 2% to 40% ±  4% (P  <  .05). Furthermore, incubation HT-29 colon cells with combined concentrations of two drugs caused significant accumulation of cells in the subGsubG1 phase. Our results presented the combination therapy with 5-FU and γ-tocopherol as a novel therapeutic approach, which can enhance the efficacy of chemotherapy.

Co-carcinogenic effects of vitamin E in prostate

A large number of basic researches and observational studies suggested the cancer preventive activity of vitamin E, but large-scale human intervention trials have yielded disappointing results and actually showed a higher incidence of prostate cancer although the mechanisms underlying the increased risk remain largely unknown. Here we show through in vitro and in vivo studies that vitamin E produces a marked inductive effect on carcinogen-bioactivating enzymes and a pro-oxidant status promoting both DNA damage and cell transformation frequency. First, we found that vitamin E in the human prostate epithelial RWPE-1 cell line has the remarkable ability to upregulate the expression of various phase-I activating cytochrome P450 (CYP) enzymes, including activators of polycyclic aromatic hydrocarbons (PAHs), giving rise to supraphysiological levels of reactive oxygen species. Furthermore, our rat model confirmed that vitamin E in the prostate has a powerful booster effect on CYP enzymes associated with the generation of oxidative stress, thereby favoring lipid-derived electrophile spread that covalently modifies proteins. We show that vitamin E not only causes DNA damage but also promotes cell transformation frequency induced by the PAH-prototype benzo[a]pyrene. Our findings might explain why dietary supplementation with vitamin E increases the prostate cancer risk among healthy men.

In Vitro Cytotoxic Activity of Clinacanthus nutans Leaf Extracts Against HeLa Cells

Objective:

This study was conducted to investigate the antiproliferative activity of extracts of Clinacanthus nutans leaves against human cervical cancer (HeLa) cells.

Methods:

C. nutans leaves were subjected to extraction using 80% methanol or water. The methanol extract was further extracted to obtain hexane, dichloromethane (DCM), and aqueous fractions. The antiproliferative activity of the extracts against HeLa cells was determined. The most cytotoxic extract was furthered analyzed by apoptosis and cell cycle assays, and the phytochemical constituents were screened by gas chromatography-mass spectrometry (GC-MS).

Results:

All of the extracts were antiproliferative against HeLa cells, and the DCM fraction had the lowest IC₅₀ value of 70 µg/mL at 48 h. Microscopic studies showed that HeLa cells exposed to the DCM fraction exhibited marked morphological features of apoptosis. The flow cytometry study also confirmed that the DCM fraction induced apoptosis in HeLa cells, with cell cycle arrest at the S phase. GC-MS analysis revealed the presence of at least 28 compounds in the DCM fraction, most of which were fatty acids.

Conclusion:

The DCM fraction obtained using the extraction method described herein had a lower IC₅₀ value than those reported in previous studies that characterized the anticancer activity of C. nutans against HeLa cells.

Effect of Chemotherapeutics and Tocopherols on MCF-7 Breast Adenocarcinoma and KGN Ovarian Carcinoma Cell Lines In Vitro

The combination of doxorubicin and cyclophosphamide commonly used to treat breast cancer can cause premature ovarian failure and infertility. α-Tocopherol is a potent antioxidant whereas γ-tocopherol causes apoptosis in a variety of cancer models in vitro including breast cancer. We hypothesised that the combination of doxorubicin (Dox) and 4-hydroperoxycyclophosphamide (4-Cyc) would be more cytotoxic in vitro than each agent alone, and that α-tocopherol would reduce and γ-tocopherol would augment the cytotoxicity of the combined chemotherapeutics. Human MCF-7 breast cancer and KGN ovarian cells were exposed to Dox, 4-Cyc, combined Dox and 4-Cyc, α-tocopherol, γ-tocopherol, or a combination of Dox and 4-Cyc with α-tocopherol or γ–tocopherol. Cell viability was assessed using a crystal violet assay according to four schedules: 24h exposure, 24h exposure + 24h culture in medium, 24h exposure + 48h culture in medium, or 72h continuous exposure. Supernatants from each separate KGN culture experiment (n=3) were examined using an estradiol ELISA. Dox was cytotoxic to both MCF-7 and KGN cells, but 4-Cyc only killed MCF-7 cells. γ-Tocopherol significantly decreased MCF-7 but not KGN cell viability. The combined chemotherapeutics and γ-tocopherol were more cytotoxic to MCF-7 than KGN cells, and α-tocopherol reduced the cytotoxicity of the combined chemotherapeutics towards KGN ovarian cells, but not MCF-7 cells. The addition of both γ-tocopherol and α-tocopherol to the chemotherapeutic combination of Dox and cyclophosphamide has the potential to increase in vitro chemotherapeutic efficacy against breast cancer cells whilst decreasing cytotoxicity towards ovarian granulosa cells.

Natural 6-hydroxy-chromanols and -chromenols: structural diversity, biosynthetic pathways and health implications

We present the first comprehensive and systematic review on the structurally diverse toco-chromanols and -chromenols found in photosynthetic organisms, including marine organisms, and as metabolic intermediates in animals. The focus of this work is on the structural diversity of chromanols and chromenols that result from various side chain modifications. We describe more than 230 structures that derive from a 6-hydroxy-chromanol- and 6-hydroxy-chromenol core, respectively, and comprise di-, sesqui-, mono- and hemiterpenes. We assort the compounds into a structure-activity relationship with special emphasis on anti-inflammatory and anti-carcinogenic activities of the congeners. This review covers the literature published from 1970 to 2017.

Natural Forms of Vitamin E as Effective Agents for Cancer Prevention and Therapy

Initial research on vitamin E and cancer has focused on α-tocopherol (αT), but recent clinical studies on cancer-preventive effects of αT supplementation have shown disappointing results, which has led to doubts about the role of vitamin E, including different vitamin E forms, in cancer prevention. However, accumulating mechanistic and preclinical animal studies show that other forms of vitamin E, such as γ-tocopherol (γT), δ-tocopherol (δT), γ-tocotrienol (γTE), and δ-tocotrienol (δTE), have far superior cancer-preventive activities than does αT. These vitamin E forms are much stronger than αT in inhibiting multiple cancer-promoting pathways, including cyclo-oxygenase (COX)- and 5-lipoxygenase (5-LOX)-catalyzed eicosanoids, and transcription factors such as nuclear transcription factor κB (NF-κB) and signal transducer and activator of transcription factor 3 (STAT3). These vitamin E forms, but not αT, cause pro-death or antiproliferation effects in cancer cells via modulating various signaling pathways, including sphingolipid metabolism. Unlike αT, these vitamin E forms are quickly metabolized to various carboxychromanols including 13'-carboxychromanols, which have even stronger anti-inflammatory and anticancer effects than some vitamin precursors. Consistent with mechanistic findings, γT, δT, γTE, and δTE, but not αT, have been shown to be effective for preventing the progression of various types of cancer in preclinical animal models. This review focuses on cancer-preventive effects and mechanisms of γT, δT, γTE, and δTE in cells and preclinical models and discusses current progress in clinical trials. The existing evidence strongly indicates that these lesser-known vitamin E forms are effective agents for cancer prevention or as adjuvants for improving prevention, therapy, and control of cancer.

The diverse effects of α- and γ-tocopherol on chicken liver transcriptome

α-Tocopherol is the form of vitamin E with the highest biological value and is almost exclusively considered as vitamin E in feed and feed supplements. Because γ-tocopherol, the predominant form of vitamin E naturally present in chicken feed, is not considered as a source of vitamin E, its re-evaluation with newer methods might be important.Despite γ-tocopherol's lower estimated biological value, it has been shown to be effective in reducing reactive nitrogen species, regulating immune and inflammatory processes, and diminishing the risk of metabolic perturbations and associated diseases. A 30-day nutritional trial in broiler chickens (Ross 308) was conducted to investigate how specific forms of vitamin E (α- and γ-tocopherol) and their combination impact liver gene expression when oxidative susceptibility of the organism is induced by high n-3 polyunsaturated fatty acids (PUFA) intake (linseed oil). Thirty-six one-day-old male broilers were fed a diet enriched with 5% linseed oil. A control group (Cont; N = 10) was used as a reference group, Tα (N = 10) was supplemented with 67 mg/kg RRR-α-tocopherol, Tγ (N = 8) with 67 mg/kg RRR-γ-tocopherol, and Tαγ (N = 8) with a combination of 33.5 mg/kg of each tocopherol. Beside oxidative stress indicators, whole chicken genome microarray analysis was performed on liver RNA and selected differentially expressed genes were confirmed by real time quantitative PCR. α-Tocopherol alone and in combination with γ-tocopherol was able to prevent lipid oxidation, which was also supported by transcriptome analysis. The effect of γ-tocopherol was evident in the expression of genes involved in inflammatory processes and immune response, while α-tocopherol affected genes involved in lipid and cholesterol metabolism. Both isomers of vitamin E influenced the transcription of genes, which are related to improved fat oxidation and enhanced glucose sparing.

Tocotrienols: the unsaturated sidekick shifting new paradigms in vitamin E therapeutics

Vitamin E family members: tocotrienols and tocopherols are widely known for their health benefits. Decades of research on tocotrienols have shown they have diverse biological activities such as antioxidant, anti-inflammatory, anticancer, neuroprotective and skin protection benefits, as well as improved cognition, bone health, longevity and reduction of cholesterol levels in plasma. Tocotrienols also modulate several intracellular molecular targets and, most importantly, have been shown to improve lipid profiles, reduce total cholesterol and reduce the volume of white matter lesions in human clinical trials. This review provides a comprehensive update on the little-known therapeutic potentials of tocotrienols, which tocopherols lack in a variety of inflammation-driven diseases.

α-Tocopheryl Succinate Affects Malignant Cell Viability, Proliferation, and Differentiation

The widespread occurrence of malignant tumors motivates great attention to finding and investigating effective new antitumor preparations. Such preparations include compounds of the vitamin E family. Among them, α-tocopheryl succinate (vitamin E succinate (VES)) has the most pronounced antitumor properties. In this review, various targets and mechanisms of the antitumor effect of vitamin E succinate are characterized. It has been shown that VES has multiple intracellular targets and effects, and as a result VES is able to induce apoptosis in tumor cells, inhibit their proliferation, induce differentiation, prevent metastasizing, and inhibit angiogenesis. However, VES has minimal effects on normal cells and tissues. Due to the variety of targets and selectivity of action, VES is a promising agent against malignant neoplasms. More detailed studies in this area can contribute to development of effective and safe chemotherapeutic preparations.

Tocopherols and Tocotrienols in Common and Emerging Dietary Sources: Occurrence, Applications, and Health Benefits

Edible oils are the major natural dietary sources of tocopherols and tocotrienols, collectively known as tocols. Plant foods with low lipid content usually have negligible quantities of tocols. However, seeds and other plant food processing by-products may serve as alternative sources of edible oils with considerable contents of tocopherols and tocotrienols. Tocopherols are among the most important lipid-soluble antioxidants in food as well as in human and animal tissues. Tocopherols are found in lipid-rich regions of cells (e.g., mitochondrial membranes), fat depots, and lipoproteins such as low-density lipoprotein cholesterol. Their health benefits may also be explained by regulation of gene expression, signal transduction, and modulation of cell functions. Potential health benefits of tocols include prevention of certain types of cancer, heart disease, and other chronic ailments. Although deficiencies of tocopherol are uncommon, a continuous intake from common and novel dietary sources of tocopherols and tocotrienols is advantageous. Thus, this contribution will focus on the relevant literature on common and emerging edible oils as a source of tocols. Potential application and health effects as well as the impact of new cultivars as sources of edible oils and their processing discards are presented. Future trends and drawbacks are also briefly covered.

The role of antioxidants and pro-oxidants in colon cancer

This review focuses on the roles antioxidants and pro-oxidants in colorectal cancer (CRC). Considerable evidence suggests that environmental factors play key roles in the incidence of sporadic CRC. If pro-oxidant factors play an etiological role in CRC it is reasonable to expect causal interconnections between the well-characterized risk factors for CRC, oxidative stress and genotoxicity. Cigarette smoking, a high dietary consumption of n-6 polyunsaturated fatty acids and alcohol intake are all associated with increased CRC risk. These risk factors are all pro-oxidant stressors and their connections to oxidative stress, the intestinal microbiome, intestinal microfold cells, cyclooxygenase-2 and CRC are detailed in this review. While a strong case can be made for pro-oxidant stressors in causing CRC, the role of food antioxidants in preventing CRC is less certain. It is clear that not every micronutrient with antioxidant activity can prevent CRC. It is plausible, however, that the optimal food antioxidants for preventing CRC have not yet been critically evaluated. Increasing evidence suggests that RRR-gamma-tocopherol (the primary dietary form of vitamin E) or other “non-alpha-tocopherol” forms of vitamin E (e.g., tocotrienols) might be effective. Aspirin is an antioxidant and its consumption is linked to a decreased risk of CRC.

Gamma-tocopherol attenuates moderate but not severe colitis and suppresses moderate colitis-promoted colon tumorigenesis in mice

Inflammation can promote colon cancer. Mechanistic studies indicate that γ-tocopherol (γT), a major form of vitamin E in diets, has anti-inflammatory and anticancer properties. Here we investigated the effectiveness of γT and a mixture of tocopherols against colitis and colitis-promoted colon tumorigenesis in male BALB/c mice. γT or mixed tocopherols (at 0.1% diet) did not show any effect on colon tumorigenesis induced by azoxymethane (AOM, 10mg/kg) with three cycles of dextran sodium sulfate (DSS at 1.5-2.5%). γT failed to exhibit protection of severe colitis caused by three cycles of DSS at 2.5%. In contrast, when AOM-initiated carcinogenesis was promoted by relatively mild colitis induced by one-cycle DSS (1.5%), γT, but not mixed tocopherols, suppressed total multiplicity of macroscopic adenomas (P=0.06) and large adenomatous polyps (>2mm(2), P<0.05) by 60 and 85%, respectively. γT also significantly decreased tumor multiplicity (>2mm(2)) induced by AOM with two cycles of 1.5% DSS even when dietary supplementation was started after AOM injection. Consistently, γT but not mixed tocopherols attenuated DSS (1.5%)-induced colon inflammation and damage as well as formation of atypical glandular hyperplasia. Mice supplemented with tocopherols had high fecal excretion of 13'-carboxychromanol, a long-chain vitamin E metabolite shown to have potent anti-inflammatory activities. Our study demonstrates that γT is able to alleviate moderate but not severe colitis and its promoted tumorigenesis, and indicates that inflammation severity should be considered in evaluating anticancer effectiveness of chemoprevention agents.

Different tocopherol isoforms vary in capacity to scavenge free radicals, prevent inflammatory response, and induce apoptosis in both adult- and fetal-derived intestinal epithelial cells

Gamma-tocopherol (γ-Toc) and δ-Toc are two vitamin E isoforms for which biological activities are not well established, yet these isoforms are present in many different sources of vegetable oils and, therefore, contribute significantly to the total dietary intake of vitamin E. Infant formula also contains relatively high amounts of γ-Toc and δ-Toc, compared with that found in human milk. The efficacy of γ-Toc and δ-Toc to modulate cellular events that include oxidative stress, inflammatory response, and apoptosis-mediated cytotoxicity, relative to α-Toc, was determined using differentiated Caco-2 and primary FHs 74 Int cells intestinal epithelial cell lines. Antioxidant capacity of Toc-isoforms followed the order of δ-Toc > γ-Toc > α-Toc against peroxyl radical-induced membrane oxidation in both Caco-2 and FHs 74 Int cells, respectively. The different Toc-isoforms suppressed inflammatory response in interferon (IFN) γ/phorbol myristate acetate (PMA)-induced Caco-2 adult-derived intestinal epithelial cells, but exacerbated both IL8 and PGE2 secretion in fetal-derived FHs 74 Int intestinal epithelial cells. Lastly, Toc exhibited an isoform-dependent apoptosis-mediated cytotoxicity, whereby δ-Toc elicited the greatest apoptosis followed by γ-Toc, whereas α-Toc was not cytotoxic. Cellular uptake of non-α-Toc isoforms were greater (P < 0.05) than that observed for α-Toc in both intestinal epithelial cell lines which in part explains the superior bioactive function observed for both γ-Toc and δ-Toc, compared with α-Toc. We conclude that the non-α-Toc isoforms of vitamin E have distinct roles that influence oxidative stress and inflammatory responses in both adult and fetal-derived intestinal epithelial cell lines.

Inhibitory effects of different forms of tocopherols, tocopherol phosphates, and tocopherol quinones on growth of colon cancer cells

Tocopherols are the major source of dietary vitamin E. In this study, the growth inhibitory effects of different forms of tocopherols (T), tocopheryl phosphates (TP), and tocopherol quinones (TQ) on human colon cancer HCT116 and HT29 cells were investigated. δ-T was more active than γ-T in inhibiting colon cancer cell growth, decreasing cancer cell colony formation, and inducing apoptosis; however, α-T was rather ineffective. Similarly, the rate of cellular uptake also followed the ranking order δ-T > γ-T ≫ α-T. TP and TQ generally had higher inhibitory activities than their parent compounds. Interestingly, the γ forms of TP and TQ were more active than the δ forms in inhibiting cancer cell growth, whereas the α forms were the least effective. The potencies of γ-TQ and δ-TQ (showing IC50 values of ∼0.8 and ∼2 μM on HCT116 cells after a 72 h incubation, respectively) were greater than 100-fold and greater than 20-fold higher, respectively, than those of their parent tocopherols. Induction of cancer cell apoptosis by δ-T, γ-TP, and γ-TQ was characterized by the cleavage of caspase 3 and PARP1 and DNA fragmentation. These studies demonstrated the higher growth inhibitory activity of δ-T than γ-T, the even higher activities of the γ forms of TP and TQ, and the ineffectiveness of the α forms of tocopherol and their metabolites against colon cancer cells.

Effects of vitamin E supplementation on cellular α-tocopherol concentrations of neutrophils in Holstein calves

The effects of vitamin E supplementation on cellular α-tocopherol concentrations of neutrophils from Holstein calves and the mechanism of scavenger receptor class B type I (SR-BI)-mediated uptake of α-tocopherol were examined. Cellular α-tocopherol concentrations in vitamin E-treated calves increased from 3.5 ± 0.38 to 7.2 ± 0.84 μg/10(7) cells, respectively, within 14 d after vitamin E supplementation; these concentrations were significantly higher than those of control calves (P < 0.01). The expression indices of SR-BI [a major receptor that recognizes high-density lipoprotein (HDL)] mRNA in neutrophils were two to five times higher (P < 0.01) in neutrophils obtained from vitamin E-supplemented calves compared with those from control calves, and anti-SR-B1 antibody, ranging from 0.1 to 1.0 μg/mL, significantly (P < 0.01) decreased cellular α-tocopherol concentrations of neutrophils. Cytochalasin D and latrunculin B, major inhibitors of actin polymerization of neutrophils, significantly decreased cellular α-tocopherol concentrations of neutrophils (P < 0.01). Our results demonstrated that in vitamin E-supplemented calves: 1) α-tocopherol is mainly distributed with HDL, 2) α-tocopherol within HDL is recognized by SR-BI on the surface of neutrophils, and 3) rearrangement of the actin cytoskeleton is a crucial step for the uptake of α-tocopherol by neutrophils.

Engineering tocopherol selectivity in α-TTP: a combined in vitro/in silico study

We present a combined in vitro/in silico study to determine the molecular origin of the selectivity of [Formula: see text]-tocopherol transfer protein ([Formula: see text]-TTP) towards [Formula: see text]-tocopherol. Molecular dynamics simulations combined to free energy perturbation calculations predict a binding free energy for [Formula: see text]-tocopherol to [Formula: see text]-TTP 8.26[Formula: see text]2.13 kcal mol[Formula: see text] lower than that of [Formula: see text]-tocopherol. Our calculations show that [Formula: see text]-tocopherol binds to [Formula: see text]-TTP in a significantly distorted geometry as compared to that of the natural ligand. Variations in the hydration of the binding pocket and in the protein structure are found as well. We propose a mutation, A156L, which significantly modifies the selectivity properties of [Formula: see text]-TTP towards the two tocopherols. In particular, our simulations predict that A156L binds preferentially to [Formula: see text]-tocopherol, with striking structural similarities to the wild-type-[Formula: see text]-tocopherol complex. The affinity properties are confirmed by differential scanning fluorimetry as well as in vitro competitive binding assays. Our data indicate that residue A156 is at a critical position for determination of the selectivity of [Formula: see text]-TTP. The engineering of TTP mutants with modulating binding properties can have potential impact at industrial level for easier purification of single tocopherols from vitamin E mixtures coming from natural oils or synthetic processes. Moreover, the identification of a [Formula: see text]-tocopherol selective TTP offers the possibility to challenge the hypotheses for the evolutionary development of a mechanism for [Formula: see text]-tocopherol selection in omnivorous animals.

Phenolic content, antioxidant effect and cytotoxic activity of Leea indica leaves

BACKGROUND

The leaves of Leea indica (Vitaceae), commonly known as 'Huo Tong Shu' in Malaysia, have been traditionally used as natural remedy in folk medicine by the locals. The current study reports the outcome of antioxidant and cytotoxic investigation of L. indica leaves. To the best of our knowledge, this is the first report of L. indica leaf crude ethanol and its fractionated extracts (hexane, ethyl acetate and water) for evaluation of total phenolic content, antioxidant effect and cytotoxic activity against colon cancer cell lines.

METHODS

In the present study, L. indica leaf crude ethanol and its fractionated extracts (hexane, ethyl acetate and water) were firstly prepared prior to phenolic content, antioxidant effect and cytotoxic activity assessment. Folin-Ciocalteau's method was used for the measurement of total phenolic content of the extracts. The antioxidant activity was measured by employing three different established testing systems, such as scavenging activity on DPPH (1,1-diphenyl-2-picrylhydrazyl) radicals, reducing power assay and SOD (superoxide dismutase) activity assay. The cytotoxic activity of the extracts were evaluated against three colon cancer cell lines with varying molecular characteristics (HT-29, HCT-15 and HCT-116) by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay.

RESULTS

The total phenolic content and antioxidant capabilities differed significantly among the L. indica leaf extracts. A strong correlation between total phenolic content and antioxidant properties was found, indicating that phenolic compounds are the major contributor to the antioxidant properties of these extracts. Among the crude ethanol and its fractionated extracts, fractionated water extract showed significantly the highest total phenolic content and strongest antioxidant effect in all the antioxidant testing systems employed in this study. All the four extracts exert no damage to the selected colon cancer cells.

CONCLUSIONS

The data obtained in these testing systems clearly establish the antioxidant potency of the fractionated water extract of L. indica leaves. Additional studies should be carried out to isolate and identify the bioactive compounds in the fractionated water extract, in order to provide more convincing evidence.

Colon cancer cell chemosensitisation by fish oil emulsion involves apoptotic mitochondria pathway

Adjuvant use of safe compounds with anti-tumour properties has been proposed to improve cancer chemotherapy outcome. We aimed to investigate the effects of fish oil emulsion (FOE) rich in n-3 PUFA with the standard chemotherapeutic agents 5-fluorouracil (5-FU), oxaliplatin (OX) or irinotecan (IRI) on two human colorectal adenocarcinoma cells with different genetic backgrounds. The HT-29 (Bax+/+) and LS174T (Bax-/-) cells were co-treated for 24-72 h with 1 μm-5-FU, 1 μm-OX or 10 μm-IRI and/or FOE dilution corresponding to 24 μm-EPA and 20·5 μm-DHA. Soyabean oil emulsion (SOE) was used as isoenergetic and isolipid control. Cell viability, apoptosis and nuclear morphological changes were evaluated by cytotoxic colorimetric assay, flow cytometry analysis with annexin V and 4',6'-diamidino-2-phenylindole staining, respectively. A cationic fluorescent probe was used to evaluate mitochondrial dysfunction, and protein expression involved in mitochondrial apoptosis was determined by Western blot. In contrast to SOE, co-treatment with FOE enhanced significantly the pro-apoptotic and cytotoxic effects of 5-FU, OX or IRI in HT-29 but not in LS174T cells (two-way ANOVA, P <0.01). These results were confirmed by the formation of apoptotic bodies in HT-29 cells. A significant increase in mitochondrial membrane depolarisation was observed after the combination of 5-FU or IRI with FOE in HT-29 but not in LS174T cells (P <0.05). Co-administration of FOE with the standard agents, 5-FU, OX and IRI, could be a good alternative to increase the efficacy of chemotherapeutic protocols through a Bax-dependent mitochondrial pathway.

A Summary of the Prostate Cancer Prevention Trials With a Focus on the Role of Vitamin E

Prostate cancer is the most common noncutaneous malignancy in men. It is an excellent target for primary prevention. Vitamin E trials conducted for prevention of prostate cancer have had conflicting results with a lower incidence of prostate cancer in the ATBC trial and a higher incidence in the vitamin E arm of the SELECT trial. Most of the clinical trials with vitamin E have been limited to the alpha-tocopherol isoform alone. An increasing body of evidence suggests, however, that the gamma- and delta-isoforms of tocopherol and tocotrienols are more promising with regard to cancer prevention. This review tries to justify our assertion that the gamma- and delta-isoforms of tocopherol and tocotrienol might be superior as prostate cancer preventers.

Induction of DNA damage and caspase-independent programmed cell death by vitamin E

Vitamin E comprises 8 functionally unique isoforms and may be a suitable candidate for the adjuvant treatment of prostate cancer. In this study, we examined the ability of 2 vitamin E isoforms [α-tocotrienol (γ-TT) and δ-tocotrienol (δ-TT)] and 4 synthetic derivatives [γ- and δ-tocotrienol succinate (γ-TS, δ-TS), α-tocopheryl polyethylene glycol succinate (TPGS), and α-tocopheryl polyethylene glycol ether (TPGS-e)] of vitamin E to induce cell death in AR- (DU145 and PC-3) and AR+ (LNCaP) prostate cancer cell lines. Our results show that δ-TT and TPGS-e are the most effective isoform and synthetic derivative, respectively, of all compounds examined. Overall, the results of our study suggest that isoforms and synthetic derivatives of vitamin E have the potency to trigger both caspase-dependent and -independent DNA damage and dominant caspase-independent programmed cell death. The capacity of vitamin E to trigger caspase-independent programmed cell death suggests that it may be useful in the chemotherapy of prostate cancer since it may prevent the tumor resistance commonly associated with the use of classical chemotherapeutic agents that trigger caspase-dependent programmed cell death.

Chemopreventive activity of vitamin E in breast cancer: a focus on γ- and δ-tocopherol

Vitamin E consists of eight different variants: α-, β-, γ-, and δ-tocopherols (saturated phytyl tail) and α-, β-, γ-, and δ-tocotrienols (unsaturated phytyl tail). Cancer prevention studies with vitamin E have primarily utilized the variant α-tocopherol. To no avail, a majority of these studies focused on variant α-tocopherol with inconsistent results. However, γ-tocopherol, and more recently δ-tocopherol, have shown greater ability to reduce inflammation, cell proliferation, and tumor burden. Recent results have shown that γ-enriched mixed tocopherols inhibit the development of mammary hyperplasia and tumorigenesis in animal models. In this review, we discuss the possible differences between the variant forms, molecular targets, and cancer-preventive effects of tocopherols. We recommend that a γ-enriched mixture, γ- and δ-tocopherol, but not α-tocopherol, are promising agents for breast cancer prevention and warrant further investigation.

C. Inhibitory Effect of a γ-Tocopherol-Rich Mixture of Tocopherols on the Formation and Growth of LNCaP Prostate Tumors in Immunodeficient Mice

In the present study, we determined the effects of a γ-tocopherol-rich mixture of tocopherols (γ-TmT) on the growth and apoptosis of cultured human prostate cancer LNCaP cells. We also determined the effects of dietary γ-TmT on the formation and growth of LNCaP tumors in immunodeficient mice. In the in vitro study, we found that the activity of γ-TmT was stronger than α-tocopherol for inhibiting the growth and stimulating apoptosis in LNCaP cells. In the animal study, treatment of severe combined immunodeficient (SCID) mice with dietary γ-TmT inhibited the formation and growth of LNCaP xenograft tumors in a dose-dependent manner. Mechanistic studies showed that γ-TmT administration inhibited proliferation as reflected by decreased mitosis and stimulated apoptosis as reflected by increased caspase-3 (active form) expression in LNCaP tumors. In addition, dietary administration of γ-TmT increased the levels of α-, γ- and δ- tocopherol in plasma, and increased levels of γ- and δ- tocopherol were also observed in the prostate and in tumors. The present study demonstrated that γ-TmT had strong anticancer activity both in vitro and in vivo. Additional studies are needed to determine the potential preventive effect of γ-TmT for prostate cancer in humans.

A nutrient approach to prostate cancer prevention: The Selenium and Vitamin E Cancer Prevention Trial (SELECT)

The Selenium and Vitamin E Cancer Prevention Trial (SELECT) randomized 35,533 healthy men, >55 yr old (>50 yr if African American), with normal digital rectal exams and prostate specific antigens <4 ng/ml to 1) 200 μg/day l-selenomethionine, 2) 400 IU/day all-rac-alpha-tocopheryl acetate (vitamin E), 3) both supplements, or 4) placebo for 7 to 12 yr. The hypotheses underlying SELECT, that selenium and vitamin E individually and together decrease prostate cancer incidence, derived from epidemiologic and laboratory evidence and significant secondary endpoints in the Nutritional Prevention of Cancer (selenium) and Alpha-Tocopherol Beta-Carotene (vitamin E) trials. In SELECT, prostate cancer incidence did not differ among the 4 arms: hazard ratios [99% confidence intervals (CIs)] for prostate cancer were 1.13 (99% CI = 0.95-1.35, P = 0.06; n = 473) for vitamin E, 1.04 (99% CI = 0.87-1.24, P = 0.62; n = 432) for selenium, and 1.05 (99% CI = 0.88-1.25, P = 0.52; n = 437) for selenium + vitamin E vs. 1.00 (n = 416) for placebo. Statistically nonsignificant increased risks of prostate cancer with vitamin E alone [relative risk (RR) = 1.13, P = 0.06) and newly diagnosed Type 2 diabetes mellitus with selenium alone (RR = 1.07, P = 0.16) were observed. SELECT data show that neither selenium nor vitamin E, alone or together, in the doses and formulations used, prevented prostate cancer in this heterogeneous population of healthy men.

Synergic effect of α-tocopherol and naringenin in transglutaminase-induced differentiation of human prostate cancer cells

Prostate cancer is the second most common cancer in men worldwide. Its prevention and treatment remain a challenge to clinicians. Thus, there is an urgent need to discover novel, less toxic, and more effective therapies for patients. Many vitamins and related chemicals, including vitamin E, (tocopherols) have shown their anti-cancer activities as anti-oxidants, activators of transcription factors or factors influencing epigenetic events. Although laboratory tests including the use of animal models showed that this vitamin may have anticancer properties, whether it can effectively prevent the development and/or progression of prostate cancer in humans remains to be intensively studied. This review provides up-to-date information regarding the recent outcomes of laboratory, epidemiology and/or clinical trials on the effects of tocopherols on prostate cancer development, along with our last observations on a combined treatment of a prostate cancer cell line (PC-3) with two natural antineoplastic compounds, naringenin (NG) and α-tocopherol (α-TOC). We report the synergic effect of α-TOC and NG in transglutaminase-induced differentiation of human PC-3 prostate cancer cells. While our results are based on one histological class of tumor, the most significant implication of this observation is that establishes a new way in the screening for detecting new differentiative antineoplastic agents.

Induction of caspase-independent programmed cell death by vitamin E natural homologs and synthetic derivatives

Current observations in the literature suggest that vitamin E may be a suitable candidate for cancer chemotherapy. To investigate this further, we examined the ability of the vitamin E natural homologs [alpha-, beta-, gamma-, delta-tocopherols (alpha-TOC, beta-TOC, gamma-TOC, delta-TOC) and alpha-, beta-, gamma-, delta-tocotrienols (alpha-TT, beta-TT, gamma-TT, delta-TT)] and their corresponding succinate synthetic derivatives [alpha-, beta-, gamma-, delta-tocopheryl succinates and alpha-, beta-, gamma-, delta-tocotrienyl succinates (alpha-TS, beta-TS, gamma-TS, delta-TS)] to induce cell death in AR- (DU145 and PC3) and AR+ (LNCaP) prostate cancer cell lines. The most effective of all the natural homologs of vitamin E was determined to be delta-TT, whereas delta-TS was the most potent of all the natural and synthetic compounds of vitamin E examined. Both gamma-TT and delta-TT induced caspase activity selectively in AR+ LNCaP cells, suggesting a possible role for AR for the activation of caspase-dependent programmed cell death (CD-PCD). More important, however, gamma-TT, delta-TT, gamma-TS, and delta-TS activated dominant caspase-independent programmed cell death (CI-PCD) in all prostate cancer cell lines examined. Thus, vitamin E homologs and synthetic derivatives may find applications in the treatment of prostate tumors that are resistant to caspase-activating therapeutic agents.

Cancer-preventive activities of tocopherols and tocotrienols

The cancer-preventive activity of vitamin E has been studied. Whereas some epidemiological studies have suggested a protective effect of vitamin E against cancer formation, many large-scale intervention studies with alpha-tocopherol (usually large doses) have not demonstrated a cancer-preventive effect. Studies on alpha-tocopherol in animal models also have not demonstrated robust cancer prevention effects. One possible explanation for the lack of demonstrable cancer-preventive effects is that high doses of alpha-tocopherol decrease the blood and tissue levels of delta-tocopherols. It has been suggested that gamma-tocopherol, due to its strong anti-inflammatory and other activities, may be the more effective form of vitamin E in cancer prevention. Our recent results have demonstrated that a gamma-tocopherol-rich mixture of tocopherols inhibits colon, prostate, mammary and lung tumorigenesis in animal models, suggesting that this mixture may have a high potential for applications in the prevention of human cancer. In this review, we discuss biochemical properties of tocopherols, results of possible cancer-preventive effects in humans and animal models and possible mechanisms involved in the inhibition of carcinogenesis. Based on this information, we propose that a gamma-tocopherol-rich mixture of tocopherols is a very promising cancer-preventive agent and warrants extensive future research.

The effect of three lipid emulsions differing in fatty acid composition on growth, apoptosis and cell cycle arrest in the HT-29 colorectal cancer cell line

BACKGROUND & AIMS

An in vitro study showed that a lipid emulsion containing fish oil (FO) slows the growth of colon cancer cells and enhances their sensitivity to 5-fluorouracil (FU). The aim was to confirm this finding and to compare such an emulsion with an alternative to lowered n-6 fatty acid exposure.

METHODS

We determined the number of viable cells, apoptosis and cell cycle distribution of HT-29 cells after exposure to one of three lipid emulsions. Cell cycle distribution was also assessed after treatment with lipid emulsions and FU.

RESULTS

The lipid emulsion containing FO induced a significant growth inhibitory effect without changing the percentage of apoptotic cells. Exposure to the other lipid emulsions had no effect on growth and decreased apoptosis. Each lipid emulsion potentiated the S phase-halting effect of 1 and 10microM FU. This effect also occurred at 0.1microM FU when the cells were exposed to the FO containing lipid emulsion.

CONCLUSIONS

A lipid emulsion containing FO has a growth inhibitory effect on a human colon adenocarcinoma cell line, an effect not due to the induction of apoptosis, and potentiated the S phase-halting effect of FU. Thus, an FO lipid emulsion may be of benefit in colorectal cancer.