Finding of remarkable synergistic effect on the aroxyl‐radical‐scavenging rates under the coexistence of α‐tocopherol and catechins

Abstract

Measurements of aroxyl radical (ArO•)‐scavenging rate constants (ks AOH ) of antioxidants (AOHs) (α‐tocopherol (α‐TocH) and three catechins (CatHs) (ie, epicatechin (EC), epigallocatechin (EGC), and epigallocatechin gallate (EGCG)) were performed in ethanol solution, using stopped‐flow spectrophotometry. ks AOH values were measured not only for each AOH, but also for the mixtures of two AOHs (α‐TocH and CatH). A notable synergistic effect that the ksαnormal- TocH value of α‐TocH increases 1.29, 1.84, and 1.65 times under the coexistence of constant concentrations of EC, EGC, and EGCG, respectively, was observed for the solutions including α‐TocH and CatH. Similarly, ks CatH values of CatHs (EC, EGC, and EGCG) increased 1.72, 2.25, and 2.34 times under the coexistence of constant concentrations of α‐TocH, respectively. UV‐Vis absorption of α‐tocopheroxyl radical (α‐Toc•) (λmax = 428 nm), which had been produced by reaction of α‐TocH with ArO•, decreased remarkably under the coexistence of α‐TocH and CatHs due to the fast α‐TocH‐regeneration reaction by CatHs. The result suggests that the prooxidant reaction due to α‐Toc• is suppressed by the coexistence of CatHs. By analyzing the formation and decay curves of α‐Toc•, it has been ascertained that one molecule of EGCG having three OH groups at B‐ring may rapidly regenerate three molecules of α‐Toc• to α‐TocH.

Zeaxanthin and Lutein: Photoprotectors, Anti-Inflammatories, and Brain Food

“…The antioxidant effect of zeaxanthin and vitamin E (tocopherol) in biological membranes are synergistic (i.e., multiplicative rather than additive; [56,57]; see also [58]). In addition, both zeaxanthin and vitamin E can be recycled by water-soluble antioxidants at the membrane-cytosol interface; the oxidized forms of zeaxanthin and vitamin E can both be re-reduced by water-soluble vitamin C [57] or water-soluble plant phenolics [59][60][61]. Oxidized vitamin C and other water-soluble antioxidant metabolites can, in turn, be re-reduced by antioxidant enzymes.…”

Finding of Remarkable Synergistic Effect on the Aroxyl-Radical-Scavenging Rates (<i>k</i>_s) under the Coexistence of Vitamin E Homologues (or Vegetable Oils) and Ubiquinol-10: Proposal of A New Mechanism to Explain An Increase of <i>k</i>_s Value

“…A notable synergistic effect that is, an increase of k s AOH value was observed for mixtures of two AOHs. In addition, measurement was performed for the mixture of α-TocH and CatHs EC, EGC, and EGCG in ethanol solution 34 , and a similar synergistic effect was observed. However, examples are very limited, and mechanism of synergistic effect has not been clarified.…”

“…The scavenging rate k obsd of ArO was measured by following the decrease in absorbance at 376 or 580 nm of the ArO radical Fig. 1 As listed in Table 1, the k s AOH alone value increases in Figure 1 C closed circle shows the k obsd versus α-TocH plot 34,43 .…”

“…TocH alone values In such a case, we can expect that the k obsd value depends on Eq. 11 , if the interaction between TocH and UQ 10 H 2 is negligible 34,43 . M for β-TocH, 2.37 10 4 M for γ-TocH, and 2.32 10 4 M for δ-TocH used for measurements Table 1 into Eq.…”

Flow Chemistry in Contemporary Chemical Sciences: A Real Variety of Its Applications

“…In a very early example of such works, the kinetics of unstable compounds in a biochemical reaction (e.g., the formation of catalase-hydrogen peroxide complex) was reported with spectrophotometric detection in a time span from milliseconds to several minutes [62]. Then, a very recent example was the examination of the kinetics of aroxyl-radical scavenging rates by important lipid-soluble antioxidant α-tocopherol and catechins [63]. An example of some recent stopped-flow kinetic investigations with the use of fluorimetric detection was a study on the binding of biotin and biocytin to avidin and streptavidin, which is broadly used in biotechnology and bioanalysis [64].…”