A quantitative approach to the free radical interaction between alpha-tocopherol and the coantioxidants eugenol, resveratrol or ascorbate.
نویسندگان
چکیده
The regeneration of alpha-tocopherol (vitamin E; VE) by coantioxidants such as phenolics and ascorbate has been studied in homogeneous hydrocarbon solution and in biological systems. However, VE phenoxyl radicals (VE*) may be sufficiently reactive to cooxidize phenolic compounds and ascorbates. The coantioxidant behavior of some relevant phenols such as eugenol (EUG), isoeugenol (IsoEUG), 2,6-di-tert-butyl-4-methoxyphenol (DTBMP), trans-resveratrol (RES) and L-ascorbyl-2,6-dibutyrate (ASDB; an ascorbate derivative) with the antioxidant VE at a molar ratio of 1:1 was investigated by the induction period (IP) method in the kinetics of polymerization of methyl methacrylate (MMA) initiated by the thermal decomposition of 2,2'-azobis(isobutyronitrile) (AIBN; a source of alkyl radicals, R*) or benzoyl peroxide (BPO; a source of peroxy radicals, PhCOO*) under nearly anaerobic conditions. Synergism, implying regeneration of VE by the coantioxidant, was observed with only two of these combinations, VE/EUG with PhCOO* and VE/DTBMP with R*. For other mixtures of VE with a phenolic coantioxidant, VE was able to cooxidize the phenolic. Regeneration can only be observed if the bond dissociation energy (BDE) of the coantioxidant is lower than, or at least close to, that of VE. The driving force for regeneration of VE by EUG may be removal of the semiquinone radical of EUG by VE, leading to the formation of VE and EUG-quinonemethide, even though the BDE value of EUG is greater by 5.8 kcal/mol than that of VE. Further evidence for this mechanism of regeneration is provided by the value of approximately 2 for the stoichiometric factor (n) of EUG induced by PhCOO*, but not by R*, again implying the formation of EUG-quinonemethide. The regeneration of VE by DTBMP in the R* system may result from their much smaller difference in BDE (0.1-1.3 kcal/mol). Since VE is rapidly oxidized by PhCOO*, regeneration of VE by DTBMP was not found in this system. The observed IP for the VE/ASDB mixture in the R* system was much lower than that for VE alone, whereas the IP for VE/ASDB in the PhCOO* system was similar to that of VE. In the R* system, VE* was sufficiently reactive to cooxidize ASDB and, in addition, the prooxidation of VE may be promoted by the catalytic action of the ascorbate derivative. The present system, under nearly anaerobic conditions, is relatively biomimetic, since oxygen in living cells is sparse. Such studies could help to explain the mechanism of regeneration of VE by coantioxidants such as phenolic compounds and vitamin C in vivo.
منابع مشابه
A quantitative approach to the free radical interaction between alpha-tocopherol or ascorbate and flavonoids.
Despite numerous previous studies, the mechanism of the free radical interaction between alpha-tocopherol (VE), or ascorbate and flavonoids, as coantioxidants remains unclear. The synergistic antioxidant effects of VE or L-ascorbyl 2,6-dibutyrate (ASDB, an ascorbate derivative) with the flavonoids (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG) and (-)-epigalloca...
متن کاملFree radical interaction between vitamin E (alpha-, beta-, gamma- and delta-tocopherol), ascorbate and flavonoids.
Despite a large number of previous studies, the mechanism of free radical interaction between vitamin E (VE) (alpha-, beta-, gamma- and delta-tocopherol) and ascorbate or flavonoids as coantioxidants remains unclear. VE, particularly alpha-tocopherol, shows less antioxidant activity against peroxyl radicals, suggesting that VE possesses functions that are independent of its antioxidant/radical-...
متن کاملPeroxynitrite-mediated alpha-tocopherol oxidation in low-density lipoprotein: a mechanistic approach.
Previous reports proposed that peroxynitrite (ONOO-) oxidizes alpha-tocopherol (alpha-TOH) through a two-electron concerted mechanism. In contrast, ONOO- oxidizes phenols via free radicals arising from peroxo bond homolysis. To understand the kinetics and mechanism of alpha-TOH and gamma-tocopherol (gamma-TOH) oxidation in low-density lipoprotein (LDL) (direct vs. radical), we exposed LDL to ON...
متن کاملSynergistic interaction between the probucol phenoxyl radical and ascorbic acid in inhibiting the oxidation of low density lipoprotein.
Chain-breaking antioxidants such as butylated hydroxytoluene, alpha-tocopherol, and probucol have been shown to decrease markedly the oxidative modification of low density lipoprotein (LDL). Their mechanism of action appears to involve scavenging of LDL-lipid peroxyl radicals. The purpose of this study was to investigate the occurrence of radical reactions produced during oxidation of LDL and L...
متن کاملAntioxidant activity of eugenol and related monomeric and dimeric compounds.
Since the inhibitory effect of eugenol (a), which was isolated as an antioxidative component from plant, Caryopylli flos, on lipid peroxidation was less than that of alpha-tocopherol, we synthesized the eugenol-related compounds dieugenol (b), tetrahydrodieugenol (c), and dihydroeugenol (d), to find new strong antioxidants and assessed them for their inhibitory effect on lipid peroxidation and ...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید
ثبت ناماگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید
ورودعنوان ژورنال:
- In vivo
دوره 20 1 شماره
صفحات -
تاریخ انتشار 2006