Finding of synergistic and cancel effects on the aroxyl radical-scavenging rate and suppression of prooxidant effect for coexistence of α-tocopherol with ß-, γ-, and δ-tocopherols (or -tocotrienols).

Measurements of aroxyl radical (ArO•)-scavenging rate constants (k(s)(AOH)) of antioxidants (AOHs) [α-, ß-, γ-, and δ-tocopherols (TocHs) and -tocotrienols (Toc-3Hs)] were performed in ethanol solution via stopped-flow spectrophotometry. k(s)(AOH) values of α-, ß-, γ-, and δ-Toc-3Hs showed good agreement with those of the corresponding α-, ß-, γ-, and δ- TocHs. k(s)(AOH) values were measured not only for each antioxidant but also for mixtures of two antioxidants: (i) α-TocH with ß-, γ-, or δ-TocH and (ii) α-TocH with α-, ß-, γ-, or δ-Toc-3H. A synergistic effect in which the k(s)(AOH) value increases by 12% for γ-TocH (or by 12% for γ-Toc-3H) was observed for solutions including α-TocH and γ-TocH (or γ-Toc-3H). On the other hand, a cancel effect in which the k(s)(AOH) value decreases (a) by 7% for ß-TocH (or 11% for ß-Toc-3H) and (b) by 24% for δ-TocH (or 25% for δ-Toc-3H) was observed for solutions including two kinds of antioxidants. However, only a synergistic effect may function in edible oils, because contents of ß- and δ-TocHs (and ß- and δ-Toc-3Hs) are much less than those of α- and γ-TocHs (and α- and γ-Toc-3Hs) in many edible oils. UV-vis absorption of α-Toc•, which was produced by reaction of α-TocH with ArO•, decreased remarkably for coexistence of α-TocH with ß-, γ-, or δ-TocH (or ß-, γ-, or δ-Toc-3H), indicating that the prooxidant effect of α-Toc• is suppressed by the coexistence of other TocHs and Toc-3Hs.

Inhibition of oxidative metabolism of tocopherols with omega-N-heterocyclic derivatives of vitamin E.

The oxidative metabolism of tocopherols and tocotrienols by monooxygenases is a key factor in the plasma and tissue clearance of forms of vitamin E other than alpha-tocopherol. It is well known that a commonly ingested form of vitamin E, gamma-tocopherol, has greatly reduced plasma half-life (faster clearance) than alpha-tocopherol. The tocotrienols are metabolized even faster than gamma-tocopherol. Both gamma-tocopherol and alpha- and delta-tocotrienol possess intriguing biological activities that are different from alpha-tocopherol, making them potentially of interest for therapeutic use. Unfortunately, the fast clearance of non-alpha-tocopherols from animal tissues is a significant hurdle to maximizing their effect(s) as dietary supplements. We report here the design and synthesis of N-heterocycle-containing analogues of alpha-tocopherol that act as inhibitors of Cyp4F2, the key monooxygenase responsible for omega-hydroxylation of the side chain of tocols. In particular, an omega-imidazole containing compound, 1, [(R)-2-(9-(1H-imidazol-1-yl)nonyl)-2,5,7,8-tetramethylchroman-6-ol] had an ED(50) for inhibition of gamma-CEHC production from gamma-tocopherol of approximately 1 nM when tested in HepG2 cells in culture. Furthermore, feeding of 1 to mice along with rapidly metabolized delta-tocopherol, resulted in a doubling of the delta-tocopherol/alpha-tocopherol ratio in liver (P<0.05). Thus, 1 may be a useful adjuvant to the therapeutic use of non-alpha-tocopherols.

In vivo and in vitro studies of anticancer actions of alpha-TEA for human prostate cancer cells.

BACKGROUND: Vitamin E analog, 2,5,7,8-tetramethyl-2R-(4R,8R, 12-trimethyltridecyl) chroman-6-yloxyacetic acid, referred to as alpha-TEA induces apoptosis in a variety of human cancer cells in cell culture and reduces tumor burden and metastases in preclinical animal models of breast and ovarian cancer. The goal of this study was to determine in vivo anticancer efficacy of alpha-TEA against human prostate cancer cells and identify mechanisms of action. METHODS: A PC-3-GFP xenograft model was used to assess the effects of alpha-TEA formulated in liposomes and administered orally on tumor burden and metastases. Tumor tissue was examined by immunohistochemical staining for percentage of cells undergoing apoptosis by TUNEL or cell proliferation by Ki-67. In vitro analyses of mechanisms employed western immunoblotting to examine effects of alpha-TEA-treatments in LNCaP and PC-3-GFP cells on levels of pro-survival and pro-death factors. Functional significance was determined using ectopically expressed constitutively active forms, inhibitors, or siRNA. RESULTS: alpha-TEA significantly reduced tumor burden and metastases, increased apoptosis and decreased proliferation of tumor cells (P < 0.05). alpha-TEA treatment of both LNCaP and PC-3-GFP cells in vitro reduced levels of pAkt1, pAkt2; FOXO1, c-FLIP(L) and survivin. Constitutively active Akt1, Akt2, c-FLIP or survivin reduced alpha-TEA-induced apoptosis. PI3K inhibitor enhanced apoptosis. Constitutively active FOXO1 enhanced alpha-TEA induced Fas ligand expression; whereas, FOXO1 siRNA reduced alpha-TEA induced Fas ligand expression. CONCLUSIONS: alpha-TEA is an effective anticancer agent for human prostate cancer cells. Downregulation of pro-survival and upregulation of pro-death factors play roles in alpha-TEA-induced apoptosis.

Amiodarone inhibits tocopherol-mediated human lipoprotein peroxidation.

It is unknown whether lipoprotein tocopherol-mediated peroxidation (TMP) is influenced by peculiar drug physicochemical properties such as hydrophobicity. Thus, we studied the effect of the extremely hydrophobic agent amiodarone on human non-HDL TMP. The drug, albeit devoid of specific radical-scavenging effects, inhibited TMP at therapeutic concentrations and with an efficiency similar to that of the physiological co-antioxidant ascorbic acid, showing indeed an IC(50) of 5microM. A comparable efficiency was observed with human LDL, and with a pure LDL-VLDL mixture. TMP was also inhibited by other hydrophobic cationic amphiphiles without radical-scavenging activity, namely desethylamiodarone, chlorpromazine, clomipramine, promethazine, promazine, verapamil, bromhexine, propranolol, mepivacaine, metoprolol, tramadol and ranitidine, whose anti-TMP potency was far lower than that of amiodarone and related to drug hydrophobicity degree. Further, TMP was strongly inhibited by butylhydroxytoluene, a lipophilic radical scavenger. Hydrophobic acidic (diclofenac, indomethacin, ibuprofen and ketoprofen) or neutral (n-hexane, anthracene, o-xylene and toluene) compounds could not instead inhibit TMP, indicating a stringent requirement for drug basicity in the pharmacological inhibition of TMP. Amiodarone effectiveness was lowered by lipoprotein alpha-tocopherol enrichment, suggesting some drug-alpha-tocopherol interaction and less lipid pharmacological protection at higher alpha-tocopheroxyl radical generation. Drug anti-TMP activity may so be related to electrostatic and hydrophobic interactions with lipoprotein alpha-tocopherol and lipid moiety, resulting in decreased radical phase transfer and lipid propensity to undergo radical-driven peroxidation. In conclusions, primarily drug basicity and then hydrophobicity are solely relevant to TMP inhibition. Amiodarone, at therapeutic concentrations, has anti-TMP properties, which could occur in the clinical setting.