α-Tocopherol (Vitamin E) and Its Relationship to Tumor Induction and Development

Newmark, Harold L.; Mergens, William J.

doi:10.1007/978-1-4615-9218-1_5

Cited by 28 publications

(13 citation statements)

References 86 publications

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“…2), with yT reducing NO2 to NO at a significantly greater rate than did a-T. It has been postulated that the ability of a-T to react with nitrosating agents to produce NO accounts for its ability to prevent nitrosation reactions (43,44). While limited NO formation by a-T under our reaction conditions was observed, yT was superior in this regard.…”

Section: Materials and Methods Chemicals Morpholine A-t And -T-t Smentioning

confidence: 37%

“…Two major sources of y-T, soybeans and corn, are known to produce nitrogen oxides (24,25 the nitrite ester of a-tocopherylquinone. Organic nitrite esters are potent nitrosating agents (39)(40)(41) and are not inhibited by a-T (42), although a-T is reported to block nitrosation by nitrous acid and nitrogen oxides (43,44). In contrast, it has been suggested that y-T may catalyze nitrosation reactions through formation of a C-nitroso intermediate (43,44), although this has not been verified experimentally.…”

mentioning

confidence: 95%

“…Organic nitrite esters are potent nitrosating agents (39)(40)(41) and are not inhibited by a-T (42), although a-T is reported to block nitrosation by nitrous acid and nitrogen oxides (43,44). In contrast, it has been suggested that y-T may catalyze nitrosation reactions through formation of a C-nitroso intermediate (43,44), although this has not been verified experimentally. In light of the occurrence of yT in plants and seeds, known to produce nitrogen oxides, and the demonstrated ability of a-T to form a nitrite ester, we sought to identify the relative reactivities of these tocopherol homologues with NO2 and the products formed in order to assess their role in nitrosation.…”

mentioning

confidence: 95%

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Gamma-tocopherol detoxification of nitrogen dioxide: superiority to alpha-tocopherol.

Cooney

Franke

Harwood

et al. 1993

Proc. Natl. Acad. Sci. U.S.A.

310

180

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In the vitamin E group, a-tocopherol is generally considered to be the most potent antioxidant with the highest vitamin bioactivity, yet y-tocopherol is produced in greater amounts by many plants and Is the principal tocopherol in the United States diet. This report describes a fundamental difference in the chemical reactivities of a-tocopherol and y-tocopherol with nitrogen dioxide (NO2), which leads to the formation of a nitrosating agent from a-tocopherol, but not from y-tocopherol. Nitric oxide (NO) is a major product of the reaction of --tocopherol with NO2, while a-tocopherol reacts with NO2 to form an intermediate tocopheroxide analogue. The biological sgnificance of y-tocopherol is s d by m epidemiological data as well as the observation that it is a more potent inhibitor than a-tocopherol of neoplastic transformation during the postinitiation phase in 3-methylcholanthrenetreated C3H/10T½ murine fibroblasts. This latter property suggests the superiority of y-tocopherol in a mammalian biologcal assay and a role for endogenous NO production in promotion of neoplasic ransformation.

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Section: Materials and Methods Chemicals Morpholine A-t And -T-t Smentioning

confidence: 37%

mentioning

confidence: 95%

mentioning

confidence: 95%

See 1 more Smart Citation

Gamma-tocopherol detoxification of nitrogen dioxide: superiority to alpha-tocopherol.

Cooney

Franke

Harwood

et al. 1993

Proc. Natl. Acad. Sci. U.S.A.

310

180

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“…20). This may explain the dual role of ␣T in inhibiting and catalyzing nitrosation reactions (46,47). It remains to be determined if the superior activity of ␥T in our experiments was due to more efficient trapping of oxidants formed during the peroxidation process (such as NO 2 ⅐), or if the products formed from ␥T themselves possess antioxidant activity (47).…”

Section: Discussionmentioning

confidence: 84%

“…This capacity of ␥T to trap electrophilic species like NO x clearly extends to other dietary phenolic ''antioxidants'' (e.g., flavonoids, tea, and wine polyphenolics). It may therefore be important to test antioxidants not only for their ability to inhibit oxidation reactions but also their ability to trap electrophiles (46). For example, the addition of sesamin to a diet rich in tocopherols markedly increases ␥T levels in plasma and other tissues but has no effect on ␣T levels.…”

Section: Discussionmentioning

confidence: 99%

γ-Tocopherol traps mutagenic electrophiles such as NO _x and complements α-tocopherol: Physiological implications

Christen

Woodall

Shigenaga

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

502

274

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Peroxynitrite, a powerful mutagenic oxidant and nitrating species, is formed by the near diffusion-limited reaction of ⅐NO and O 2 . during activation of phagocytes.Chronic inf lammation induced by phagocytes is a major contributor to cancer and other degenerative diseases. We examined how ␥-tocopherol (␥T), the principal form of vitamin E in the United States diet, and ␣-tocopherol (␣T), the major form in supplements, protect against peroxynitriteinduced lipid oxidation. Lipid hydroperoxide formation in liposomes (but not isolated low-density lipoprotein) exposed to peroxynitrite or the ⅐NO and O 2 . generator SIN-1 (3-morpholinosydnonimine) was inhibited more effectively by ␥T than ␣T. More importantly, nitration of ␥T at the nucleophilic 5-position, which proceeded in both liposomes and human low density lipoprotein at yields of Ϸ50% and Ϸ75%, respectively, was not affected by the presence of ␣T. These results suggest that despite ␣T's action as an antioxidant ␥T is required to effectively remove the peroxynitrite-derived nitrating species. We postulate that ␥T acts in vivo as a trap for membranesoluble electrophilic nitrogen oxides and other electrophilic mutagens, forming stable carbon-centered adducts through the nucleophilic 5-position, which is blocked in ␣T. Because large doses of dietary ␣T displace ␥T in plasma and other tissues, the current wisdom of vitamin E supplementation with primarily ␣T should be reconsidered.

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Effects of vitamins C and E on N‐nitroso compound formation, carcinogenesis, and cancer

Mirvish

1986

Cancer

227

106

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The properties of N-nitroso compounds (NNC) and of vitamins C and E are briefly described. The author reviews the ability of vitamins C and E to inhibit NNC formation in chemical systems, in nitrite-preserved meat, in experimental animals and in humans. Dietary vitamins C and E both produced 30% to 60% inhibitions in most carcinogenesis experiments employing preformed carcinogens. Vitamin C reversed transformation in an in vitro system. Carcinogenicity tests of the vitamins are reviewed (vitamin C can promote bladder carcinogenesis). Intake of fresh fruits and vegetables (which contain vitamin C) is negatively correlated with cancer of the stomach, esophagus, larynx, mouth and cervix. For gastric and esophageal cancer, there is evidence that this association is due to an inhibition of in vivo NNC formation. Vitamin C is apparently not a useful treatment for cancer. The author supports the recommendation that fresh fruit and vegetable intake be increased to lower the risk of cancer.

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α-Tocopherol (Vitamin E) and Its Relationship to Tumor Induction and Development

Cited by 28 publications

References 86 publications

Gamma-tocopherol detoxification of nitrogen dioxide: superiority to alpha-tocopherol.

Gamma-tocopherol detoxification of nitrogen dioxide: superiority to alpha-tocopherol.

γ-Tocopherol traps mutagenic electrophiles such as NO _x and complements α-tocopherol: Physiological implications

Effects of vitamins C and E on N‐nitroso compound formation, carcinogenesis, and cancer

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α-Tocopherol (Vitamin E) and Its Relationship to Tumor Induction and Development

Cited by 28 publications

References 86 publications

Gamma-tocopherol detoxification of nitrogen dioxide: superiority to alpha-tocopherol.

Gamma-tocopherol detoxification of nitrogen dioxide: superiority to alpha-tocopherol.

γ-Tocopherol traps mutagenic electrophiles such as NO x and complements α-tocopherol: Physiological implications

Effects of vitamins C and E on N‐nitroso compound formation, carcinogenesis, and cancer

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γ-Tocopherol traps mutagenic electrophiles such as NO _x and complements α-tocopherol: Physiological implications