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.

Lipid peroxidation induced by carbon tetrachloride and its inhibition by antioxidant as evaluated by an oxidative stress marker, HODE.

We have recently proposed total hydroxyoctadecadienoic acid (HODE) as a biomarker for oxidative stress in vivo. The biological samples such as plasma, urine, and tissues were first reduced and then saponified to convert the oxidation products of linoleate to HODE. In the present study, this method was applied to measure the oxidative damage induced by the administration of carbon tetrachloride to mice and also to evaluate the capacity of antioxidant to inhibit the above damage. alpha-Tocopherol transfer protein knock out (alpha-TTP-/-) mice were used to evaluate antioxidant effect in the absence of alpha-tocopherol. The intraperitoneal administration of carbon tetrachloride to mice induced the increase in HODE in liver and plasma, which was followed by an increase in plasma glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT). F2-isoprostanes, another prevailing biomarker, were also increased similarly, but their concentration was approximately two to three orders of magnitude smaller than that of HODE. The lipophilic antioxidants such as gamma-tocopherol, gamma-tocotrienol and 2,3-dihydro-5-hydroxy-4,6-di-tert-butyl-2,2-dipentylbenzofuran (BO-653) were effective in suppressing the formation of HODE.