Different Forms Of Tocopherols Research Articles

Functional Differentiation of BnVTE4 Gene Homologous Copies in α-Tocopherol Biosynthesis Revealed by CRISPR/Cas9 Editing.

Tocopherols are essential nutrients for human health known as vitamin E. Vitamin E deficiency can have a profound effect on human health, including the central nervous system and cardiovascular and immune protection. Multiple enzymatic steps are involved in the conversion between different forms of tocopherols. Among them, γ-tocopherol methyltransferase encoded by gene VTE4 catalyzes the conversion of γ- to α-tocopherol or δ- to β-tocopherol isoforms. However, the gene copies and their functional contribution of VTE4 homologs in Brassica napus were not elucidated. To this end, different mutation combinations of four putative BnVTE4 homologous copies were generated by using CRISPR/Cas9 genome editing technology. Editing of those BnVTE4 homologs led to a significant change of the α-tocopherol content and the ratio between α- and γ-tocopherol compared with wide-type control. Analysis of the different combinations of BnVTE4-edited homologs revealed that the contribution of the BnVTE4 individual gene displayed obvious functional differentiation in α-tocopherol biosynthesis. Their contribution could be in order of VTE4.C02-2 (BnaC02G0331100ZS) > VTE4.A02-1 (BnaA02G0247300ZS) > VTE4.A02-2 (BnaA02G0154300ZS). Moreover, the VTE4.A02-1 and VTE4.A02-2 copies might have severe functional redundancies in α-tocopherol biosynthesis. Overall, this study systemically studied the different effects of BnVTE4 homologs, which provided a theoretical basis for breeding high α-tocopherol content oilseed rape.

Cancer prevention by different forms of tocopherols

Low vitamin E nutritional status has been suggested to increase cancer risk. However, recent large-scale human trials with high doses of alpha-tocopherol (α-T) have produced disappointing results. This points out the need for a better understanding of the biological activities of different forms of tocopherols. Using a tocopherol mixture that is rich in γ-T (γ-TmT), we demonstrated the inhibition of colon carcinogenesis in mice, and the inhibition is associated with decreased levels of 8-isoprostane, nitrotyrosine, prostaglandin E2 and leukotriene B4. Dietary 0.3% γ-TmT also inhibited chemically induced lung tumorigenesis in the A/J mice as well as the growth of lung cancer cells in xenograft or allograft tumors; the inhibition was associated with a reduction of oxidative/nitrosative stress. δ-T was found to be more active than γ-T in the inhibition of cancer cell growth in culture and lung cancer xenograft tumors as well as in azoxymethane-induced colon aberrant crypt foci formation in rats, whereas α-T was ineffective. Analysis of the levels of tocopherols and their metabolites in blood and tissues suggests that metabolites of δ-T and γ-T contribute to their inhibitory activity. These studies demonstrate the broad cancer preventive activity of γ-TmT and higher activity of δ-T.

Vitamin E and cancer prevention: Studies with different forms of tocopherols and tocotrienols.

α-Tocopherol (α-T) is the major form of vitamin E (VE) in animals and has the highest activity in carrying out the essential antioxidant functions of VE. Because of the involvement of oxidative stress in carcinogenesis, the cancer prevention activity of α-T has been studied extensively. Lower VE intake or nutritional status has been shown to be associated with increased cancer risk, and supplementation of α-T to populations with VE insufficiency has shown beneficial effects in lowering the cancer risk in some intervention studies. However, several large intervention studies with α-T conducted in North America have not demonstrated a cancer prevention effect. More recent studies have centered on the γ- and δ-forms of tocopherols and tocotrienols (T3). In comparison with α-T, these forms have much lower systemic bioavailability but have shown stronger cancer-preventive activities in many studies in animal models and cell lines. γ-T3 and δ-T3 generally have even higher activities than γ-T and δ-T. In this article, we review recent results from human and laboratory studies on the cancer-preventive activities of different forms of tocopherols and tocotrienols, at nutritional and pharmacological levels. We aim to elucidate the possible mechanisms of the preventive actions and discuss the possible application of the available information for human cancer prevention by different VE forms.

Differential Gene Regulation and Tumor-Inhibitory Activities of Alpha-, Delta-, and Gamma-Tocopherols in Estrogen-Mediated Mammary Carcinogenesis.

Despite experimental evidence elucidating the antitumor activities of tocopherols, clinical trials with α-tocopherol (α-T) have failed to demonstrate its beneficial effects in cancer prevention. This study compared the chemopreventive efficacy of individual tocopherols (α-, δ-, and γ-T) and a γ-T-rich tocopherol mixture (γ-TmT) in the August-Copenhagen Irish (ACI) rat model of estrogen-mediated mammary cancer. Female ACI rats receiving 17β-estradiol (E2) implants were administered with 0.2% α-T, δ-T, γ-T, or γ-TmT for 30 weeks. Although α-T had no significant effects on mammary tumor growth in ACI rats, δ-T, γ-T, and γ-TmT reduced mammary tumor volume by 51% (P < 0.05), 60% (P < 0.01), and 59% (P < 0.01), respectively. Immunohistochemical analysis revealed that δ-T, γ-T, and γ-TmT reduced levels of the cell proliferation marker, proliferating cell nuclear antigen, in the rat mammary tumors. To gain further insight into the biological functions of different forms of tocopherols, RNA-seq analysis of the tumors was performed. Treatment with γ-T induced robust gene expression changes in the mammary tumors of ACI rats. Ingenuity Pathway Analysis identified "Cancer" as a top disease pathway and "Tumor growth" and "Metastasis" as the top signaling pathways modulated by γ-T. Although the results need further functional validation, this study presents an unbiased attempt to understand the differences between biological activities of individual forms of tocopherols at the whole transcriptome level. In conclusion, δ-T and γ-T have superior cancer preventive properties compared to α-T in the prevention of estrogen-mediated mammary carcinogenesis. Cancer Prev Res; 10(12); 694-703. ©2017 AACR.

Abstract 5261: Tocopherols inhibit the estrogen-stimulated expansion of cancer stem cells via down-regulation of OCT4 and NFκB

Abstract Cancer stem cells have been suggested to play a role in tumor initiation, maintenance, resistance, and metastasis. Breast cancer stem cells are defined as CD44+/CD24- cell populations that have the properties of tumor-initiating ability, self-renewal and differentiation. Although the importance of estrogen in breast cancer is well established, the effects of estrogen on breast cancer stem cells are not fully understood. Vitamin E, which is consisted of different forms of tocopherols and tocotrienols, has anti-tumor effects in various cancers, including breast cancer. In the present study, we examined the effects of α-, γ-, and δ-tocopherol against estrogen-stimulated expansion of cancer stem cells. To determine the effects of tocopherols on breast cancer stem cells, the MCF-7 tumorsphere cell culture system, which enriches for mammary progenitor cells and putative breast cancer stem cells, was utilized. Treatment of MCF-7 tumorsphere with estrogen for four days resulted in an increase in CD44+/CD24- stem cell populations in tumorspheres as well as the number and size of tumorspheres. Tocopherols at 1 and 10 μM inhibited formation of estrogen-induced stem cell enriched tumorspheres, indicating that tocopherols reversed estrogen-induced expansion of breast cancer stem cells. Tocopherols decreased the expression of estrogen-related genes such as TFF/pS2, cathepsin D, progesterone receptor and SerpinA1 in estrogen-stimulated tumorspheres. In addition, the mRNA levels of stem cell markers, including OCT4, NFκB, SOX-2 and CD44, were upregulated by estrogen, which were downregulated by the treatment with tocopherols. Our results suggest that tocopherols repress the expansion of breast cancer stem cell population by regulating OCT4 and NFκB signaling. Tocopherols could be effective natural agents for the prevention and treatment of estrogen-induced breast cancer. (This work was supported in part by the National Institutes of Health grant R01 AT007036.) Citation Format: Min Ji Bak. Tocopherols inhibit the estrogen-stimulated expansion of cancer stem cells via down-regulation of OCT4 and NFκB [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5261. doi:10.1158/1538-7445.AM2017-5261

Inhibitory Effects of γ- and δ-Tocopherols on Estrogen-Stimulated Breast Cancer In Vitro and In Vivo.

Estrogens have been implicated as complete carcinogens for breast and other tissues through mechanisms involving increased cell proliferation, oxidative stress, and DNA damage. Because of their potent antioxidant activity and other effects, tocopherols have been shown to exert antitumor activities in various cancers. However, limited information is available on the effect of different forms of tocopherols in estrogen-mediated breast cancer. To address this, we examined the effects of α-, γ-, and δ-tocopherols as well as a natural γ-tocopherol-rich mixture of tocopherols, γ-TmT, on estrogen-stimulated MCF-7 cells in vitro and in vivo For the in vivo studies, MCF-7 cells were injected into the mammary fat pad of immunodeficient mice previously implanted with estrogen pellets. Mice were then administered diets containing 0.2% α-, γ-, δ-tocopherol, or γ-TmT for 5 weeks. Treatment with α-, γ-, δ-tocopherols, and γ-TmT reduced tumor volumes by 29% (P < 0.05), 45% (P < 0.05), 41% (P < 0.05), and 58% (P < 0.01), as well as tumor weights by 20%, 37% (P < 0.05), 39% (P < 0.05), and 52% (P < 0.05), respectively. γ- and δ-tocopherols and γ-TmT inhibited the expression of cell proliferation-related genes such as cyclin D1 and c-Myc, and estrogen-related genes such as TFF/pS2, cathepsin D, and progesterone receptor in estrogen-stimulated MCF-7 cells in vitro Further, γ- and δ-tocopherols decreased the levels of estrogen-induced oxidative stress and nitrosative stress markers, 8-hydroxy-2'-deoxyguanosine and nitrotyrosine, as well as the DNA damage marker, γ-H2AX. Our results suggest that γ- and δ-tocopherols and the γ-tocopherol-rich mixture are effective natural agents for the prevention and treatment of estrogen-mediated breast cancer. Cancer Prev Res; 10(3); 188-97. ©2017 AACR.

Abstract 5237: Protection of tocopherols against estrogen-induced breast cancer via mechanisms targeting cancer stem cells

Abstract Estrogens have been implicated to be complete carcinogens through mechanisms involving increased proliferation, oxidative stress and DNA damage. Although the importance of estrogen in breast cancer is well established, the effects of estrogen on breast cancer stem cells are not fully understood. Due to the role of breast cancer stem cells in tumor initiation, maintenance, and progression, targeting cancer stem cells has become important for understanding estrogen-mediated breast carcinogenesis. The vitamin E family, which is consisted of four different forms of tocopherols and tocotrienols, has been shown to exert anti-tumor effects in animal models of various cancers. In the present study, we examined the protective effects of α-, γ-, δ-tocopherol as well as a natural γ-tocopherol rich mixture of tocopherols (γ-TmT) against estrogen-induced expansion of cancer stem-like cells and estrogen-mediated tumor growth. To determine the effects of tocopherols on breast cancer stem cells, the MCF-7 mammosphere cell culture system, which enriches for mammary progenitor cells and putative breast cancer stem cells, was utilized. Treatment of MCF-7 mammosphere with estrogen for six days resulted in an increase in CD44+/CD24- stem-like cell populations as well as the number and size of mammosphere. α-, γ-, δ-Tocopherol, and most significantly γ-TmT, inhibited estrogen-induced mammosphere formation, indicating that tocopherols reverse estrogen-induced expansion of breast cancer stem cells. In MCF-7 xenograft tumor study, MCF-7 cells (5 × 106 cells/mouse) were injected into the mammary fat pad in immunodeficient mice after subcutaneous implantation with 0.72 mg of estrogen pellet. Mice were then administered with diets containing 0.2% α-, γ-, δ-tocopherol and γ-TmT for 5 weeks. Treatment of α-, γ-, δ-tocopherol or γ-TmT reduced the tumor volume by 71% (p&amp;lt;0.05), 55% (p&amp;lt;0.05), 59% (p&amp;lt;0.05) and 42% (p&amp;lt;0.01) as well as tumor weight by 80%, 63% (p&amp;lt;0.05), 61% (p&amp;lt;0.05) and 48% (p&amp;lt;0.05), respectively. Our results suggest that tocopherols significantly repress the expansion of breast cancer stem cell-like population and tumor development. Tocopherols, in particular a naturally occurring tocopherol mixture rich in γ and δ-tocopherols, could thus be effective natural agents for the prevention and treatment of estrogen-induced breast cancer.(This work was supported by NIH R01 AT007036) Citation Format: Min Ji Bak, Soumyasri Das Gupta, Joseph Wahler, Mao-Jung Lee, Yong Lin, Weichung Joe Shih, Chung S Yang, Nanjoo Suh. Protection of tocopherols against estrogen-induced breast cancer via mechanisms targeting cancer stem cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5237.

Tocopherols in cancer: An update.

Tocopherols exist in four forms designated as α, β, δ, and γ. Due to their strong antioxidant properties, tocopherols have been suggested to reduce the risk of cancer. Cancer prevention studies with tocopherols have mostly utilized α-tocopherol. Large-scale clinical trials with α-tocopherol provided inconsistent results regarding the cancer-preventive activities of tocopherols. This review summarizes our current understanding of the anticancer activities of different forms of tocopherols based on follow-up of the clinical trials, recent epidemiological evidences, and experimental studies using in vitro and in vivo models. The experimental data provide strong evidence in support of the anticancer activities of δ-tocopherol, γ-tocopherol, and the natural tocopherol mixture rich in γ-tocopherol, γ-TmT, over α-tocopherol. Such outcomes emphasize the need for detailed investigation into the cancer-preventive activities of different forms of tocopherols to provide a strong rationale for intervention studies in the future.

δ-Tocopherol inhibits receptor tyrosine kinase-induced AKT activation in prostate cancer cells.

The cancer preventive activity of vitamin E is suggested by epidemiological studies and supported by animal studies with vitamin E forms, γ-tocopherol and δ-tocopherol (δ-T). Several recent large-scale cancer prevention trials with high dose of α-tocopherol, however, yielded disappointing results. Whether vitamin E prevents or promotes cancer is a serious concern. A better understanding of the molecular mechanisms of action of the different forms of tocopherols would enhance our understanding of this topic. In this study, we demonstrated that δ-T was the most effective tocopherol form in inhibiting prostate cancer cell growth, by inducing cell cycle arrest and apoptosis. By profiling the effects of δ-T on the cell signaling using the phospho-kinase array, we found that the most inhibited target was the phosphorylation of AKT on T308. Further study on the activation of AKT by EGFR and IGFR revealed that δ-T attenuated the EGF/IGF-induced activation of AKT (via the phosphorylation of AKT on T308 induced by the activation of PIK3). Expression of dominant active PIK3 and AKT in prostate cancer cell line DU145 in which PIK3, AKT, and PTEN are wild type caused the cells to be reflectory to the inhibition of δ-T, supporting that δ-T inhibits the PIK3-mediated activation of AKT. Our data also suggest that δ-T interferes with the EGF-induced EGFR internalization, which leads to the inhibition of the receptor tyrosine kinase-dependent activation of AKT. In summary, our results revealed a novel mechanism of δ-T in inhibiting prostate cancer cell growth, supporting the cancer preventive activity δ-T. © 2015 Wiley Periodicals, Inc.

Abstract 2814: Inhibition of PhIP/DSS-induced colon carcinogenesis by different forms of tocopherols in CYP1A-humanized mice

Abstract Tocopherols (T), which exist as α-, β-, γ-, and δ-T are important dietary antioxidants. Our previous studies have demonstrated that a mixture of tocopherols (γ-TmT), δ-T, and γ-T effectively inhibited colon carcinogenesis in AOM/DSS-treated mice or AOM-treated rats. However, the effects of different forms of tocopherols on carcinogenesis in animal models and in humans remain controversial. In the present study, we investigated the inhibitory effects of α-T, γ-T, and δ-T on colon carcinogenesis induced by a dietary carcinogen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), and promoted by dextran sodium sulfate (DSS) in CYP1A-humanized (hCYP1A) mice. At 5-6 weeks age, male hCYP1A mice were fed the AIN93M diet or diet supplemented with 0.2% α-T, γ-T, or δ-T for 1 week before PhIP treatment (2x 100mg/kg b.w., 3 days apart), which was followed by DSS (1.5% in drinking water for 4 days) treatment. The mice were sacrificed 10 weeks after the first dose of PhIP. Significant inhibition of colon tumor incidences was caused by dietary δ-T and γ-T, but not by α-T. In addition, oxidative and nitrosative stress markers (i.e., 8-oxo-dG and nitrotyrosine) as well as pro-inflammatory stress markers (i.e., PGE2, LTB4, NFκB and p-STAT3) were significantly reduced by δ-T. Dietary treatment with δ-T and γ-T significantly increased the δ-T and γ-T levels, respectively, in the blood and tissues, but their levels were still lower than the levels of α-T. However, the levels of their side-chain degradation metabolites (δ-T and γ-T forms of carboxyethyl hydroxychroman and carboxymethylbutyl hydroxychroman) were much higher than their parent tocopherols in blood and tissues. Altogether, we demonstrated the inhibitory effects of δ-T and γ-T in a dietary carcinogen-induced colon carcinogenesis model. The inhibition is possibly due to the antioxidative, reactive nitrogen species-trapping, and anti-inflammatory activities δ-T and γ-T. (Supported by NIH grants F31CA168333, RO1CA120915 and RO1AT007036 as well as shared facilities funded by CA72720 and ES05022) Citation Format: Chung S. Yang, Jayson X. Chen, Anna B. Liu, Hong Wang, Marlon Lee, Siyuan Yu, Chunfang Zhao, Ying-Yi Kuo, Eric Chi, Nanjoo Suh. Inhibition of PhIP/DSS-induced colon carcinogenesis by different forms of tocopherols in CYP1A-humanized mice. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2814. doi:10.1158/1538-7445.AM2015-2814

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.

Abstract 961: Higher activity of δ-tocopherol (δ-T) than γ-tocopherol and α-tocopherol in the inhibition of lung cancer H1299 xenograft tumors in mice

Abstract Our previous study showed that γ-TmT (a tocopherol mixture containing 57% γ-T, 24% δ-T, 13% α-T and 1.5% β-T) effectively inhibited colon and lung carcinogenesis as well as the growth of transplanted human lung cancer in mice. This study aims to determine the more active constituents in this mixture in a xenograft model. After injection of human lung cancer H1299 cells into NCr nu/nu nude mice, the mice were maintained on a standard AIN93M diet or diet enriched with α-T, γ-T, δ-T or γ-TmT (each at 0.3% and 0.17%) for 50 days. Dietary δ-T showed the strongest inhibition based on final tumor weight (35.6% and 57.6% reduction from the control by 0.17% and 0.3% δ-T, respectively). Dietary 0.3% γ-T and γ-TmT also showed significant inhibition (37.4% and 46% reduction from control, respectively). However, an inhibitory effect was not observed with dietary α-T group. Consistent with the animal study, the growth of H1299 cells was inhibited by tocopherols with their effectiveness following the order of δ-T &amp;gt; γ-TmT &amp;gt; γ-T, but α-T was not effective. We also found that dietary α-T, γ-T and δ-T treatment respectively increased serum α-T, γ-T and δ-T levels (up to 45, 9.7 and 1.2μM, respectively). However, the serum α-T level was decreased by dietary γ-T and δ-T; for example, at 0.3% they decreased α-T levels by 50% and 42% from the control group, respectively. The results suggest a competition among different forms of tocopherols. Dietary treatment with each form of tocopherol also increased the corresponding side-chain degradation metabolites: carboxyethyl hydroxychromans (CEHC) and carboxymethylbutyl hydroxychromans (CMBHC). With 0.3% α-, γ- and δ-T in the diet, the mean serum levels of α-, γ- and δ-CEHC were 0.08, 0.7 and 3.0μM, respectively; and α-, γ- and δ-CMBHC were 0.14, 0.83 and 4.0μM, respectively. These metabolites retain the intact chromanol ring and, similar to their parent tocopherols, could trap reactive oxygen and nitrogen species. δ-CEHC and δ-CMBHC, which are present at rather high concentrations, may play an important role in inhibiting xenograph and tumor growth. The present results show that δ-T and γ-T effectively inhibited human lung cancer xenograft tumors and the inhibition may be due to the apoptosis-inducing, antioxidative, and reactive nitrogen species-trapping activities of these tocopherols and their metabolites (Supported by NIH grants CA120915, CA122474, and CA133021). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 961.

Assessment of variation in antioxidative defense system in salt-treated pea ( Pisum sativum) cultivars and its putative use as salinity tolerance markers

The present work describes whether the changes in the activities of antioxidant enzymes and the levels of some non-enzymatic antioxidants could be used as markers of salt tolerance in nine genetically diverse pea (Pisum sativum) cultivars. All cultivars were exposed to four levels of NaCl i.e., 0, 40, 80 and 120mM in sand culture. Plant fresh biomass, total phenolics, total soluble proteins, hydrogen peroxide (H(2)O(2)), malondialdehyde (MDA), superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in leaves while different forms of tocopherols (alpha-, gamma- and Delta-tocopherol) in fresh seed of salt-stressed and non-stressed plants were analyzed. On the basis of percent inhibition in shoot biomass at the highest salt level (120mM) cultivars 2001-35, 2001-55 and Climax were ranked as tolerant (percent inhibition less than 60%), 2001-20, 9800-5 and 9800-10 moderately tolerant (percent inhibition 60-70%), and 2001-40, 9200 and Tere 2 salt sensitive (percent inhibition more than 70%). Salt stress markedly enhanced the activities of SOD and POD, levels of total phenolics and gamma- and Delta-tocopherols, and decreased the total soluble proteins and CAT activity, while the internal levels of H(2)O(2) remained unaffected in all pea cultivars. Although salt-induced oxidative stress occurred in all pea cultivars, the response of salt-tolerant and salt-sensitive cultivars with respect to the generation of enzymatic and non-enzymatic metabolites measured in the present study was not consistent. Of different antioxidant enzymes and metabolites analyzed, only CAT activity was found to be a reliable marker of salt tolerance in the set of pea cultivars examined.

Cyclodextrin-modified microemulsion electrokinetic chromatography for separation of α-, γ-, δ-tocopherol and α-tocopherol acetate

Different forms of tocopherols, together with tocotrienols, are collectively named as vitamin E, and each possesses different degree of medical, biological and physiochemical significance. The main difficulty of separating different forms of tocopherols lay in their highly structural similarities and hydrophobicities. Microemulsion electrokinetic chromatography (MEEKC), claimed to attain high peak efficiency with great solubilization power, has not previously been applied to the separation of tocopherols. The effects that various parameters, such as buffer system, type and concentration of cyclodextrins, temperature, and sample matrix, have on the separation of tocopherols by MEEKC have been investigated. By using a buffer mixture of 4% (w/w) sodium dodecyl sulfate (SDS), 6.6% (w/w) 1-butanol, 0.8% (w/w) n-octane, 20% (w/w) 2-propanol, 68.6% (w/w) phosphate (25 mM, pH 2.5), and 25 mM heptakis(2,6-di- O-methyl)-β-cyclodextrin (DM-β-CD), the separation of α-, γ-, and δ-tocopherol, α-tocopherol acetate, as well as the antioxidant butylated hydroxytoluene (BHT) at −26 kV, 25 °C was completed within 35 min. The practical potential of the present approach has been further validated by the determination of tocopherols in a vitamin E preparation, with the result of 132.63 (RSD 1.25%), 176.51 (RSD 0.29%), and 64.32 mg (RSD 3.34%) per 500 mg capsule for α-, γ- and δ-tocopherol, respectively.