Effect of phytyl side chain of vitamin E on its antioxidant activity

Inhibition of the oxidation of methyl linoleate and soybean phosphatidylcholine in homogeneous solution and in aqueous dispersion by four chain-breaking antioxidants, vitamin E (alpha-tocopherol), 2,2,5,7,8-pentamethyl-6-chromanol, 2,6-di-tert-butyl-4-methylphenol, and stearyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, was studied to examine the effect of the phytyl side chain of vitamin E on its antioxidant activity. These four antioxidants exerted similar antioxidative activities. They were also effective as antioxidants in protecting the oxidation of soybean phosphatidylcholine liposomes in water dispersion. However, when they were incorporated into dimyristoyl phosphatidylcholine liposomes, only 2,2,5,7,8-pentamethyl-6-chromanol and 2,6-di-tert-butyl-4-methylphenol could suppress the oxidation of soybean phosphatidylcholine liposomes dispersed in the same aqueous system. It was concluded that the antioxidative properties of vitamin E and its model without the phytyl side chain are quite similar within micelles and liposomes as well as in homogeneous solution but that the phytyl side chain enhances the retainment of vitamin E in liposomes and suppresses the transfer of vitamin E between liposomal membranes.     

The mechanism of antioxidant activity of IRFI005 as a synthetic hydrophilic analogue of vitamin E

Developing a rational strategy to control intracellular reactive oxygen species (ROS) requires understanding the mechanism of antioxidant activity. In this investigation the properties of a novel synthetic analog of vitamin E (IRFI005) with potent antioxidant activity are described. A mechanism is proposed for its efficient radical-scavenging effects. Cellular antioxidant and antitoxicity assays showed IRFI005 to freely permeate across cellular membranes, enabling it to be an effective suppressor of intracellular ROS and to protect cells against toxicity induced by free radical generating compounds. The free radical-scavenging activity of IRFI005 examined by UV–Vis and electron spin resonance (ESR) techniques clearly confirmed a “two electrons and/or H-atom” donation mechanism for each molecule of IRFI005. Reducing power assay as well as semi-empirical calculations revealed that under physiological conditions (pH∼7) almost all IRFI005 molecules are in the anionic state (IRFI005⁻). Data indicated that the electron donating ability of IRFI005⁻ was dominant at physiological pH because of higher stability of quinine-IRFI005⁻ and less barrier energy of IRFI005⁻ than neutral IRFI005. Consequently, the efficient cellular protection of IRFI005 against toxic free radicals can be explained by a two electron-transfer process, because of reduced inter-frontier molecular orbital energy gap barrier at physiological pH. Our findings suggest that hydrophilic vitamin E-like antioxidants are good candidates in designing novel therapeutic strategies for inhibition of oxidative stress associated with different human diseases.     

Physiological levels of tea catechins increase cellular lipid antioxidant activity of vitamin C and vitamin E in human intestinal caco-2 cells

Oxidative stress has been linked to the development of various chronic diseases. Vegetables and fruits, which contain polyphenols, were shown to have protective effects. (-)-Epigallocatechin-3-gallate (EGCG), a polyphenol abundant in tea, has been shown to have antioxidant activities in cell-free conditions and this study focused on the effect of cellular EGCG. Using an intestinal cell model to examine the oxidative stress induced by hydroxyl radicals, we report here that physiological concentrations (0.1-1 microM) of EGCG have dose- and incubation duration-dependent cell-associated lipid antioxidant activity (measuring malondialdehyde production). Vitamin E and vitamin C at 10-40 microM also showed cell-associated lipid antioxidant activities under shorter incubation durations. When EGCG was included in the incubation with vitamin E or C, more antioxidant activities were consistently observed than when vitamins were added alone. Catechin (widely present in fruits and vegetables) at 1 microM also significantly increased the antioxidant activity of vitamins E and C. Previous studies examining cell-associated activity of EGCG mainly focused on the 10-100 microM concentration range. Our results suggest that although the physiological level (0.1-1 microM) of dietary catechins is much lower than that of vitamins, they further contribute to the total antioxidant capacity even in the presence of vitamins.     

Alpha-tocopheryl phosphate: a novel, natural form of vitamin E

We have detected alpha-tocopheryl phosphate in biological tissues including liver and adipose tissue, as well as in a variety of foods, suggesting a ubiquitous presence in animal and plant tissue. Alpha-tocopheryl phosphate is a water-soluble molecule that is resistant to both acid and alkaline hydrolysis, making it undetectable using standard assays for vitamin E. A new method was therefore developed to allow the extraction of both alpha-tocopheryl phosphate and alpha-tocopherol from a single specimen. We used ESMS to detect endogenous alpha-tocopheryl phosphate in biological samples that also contained alpha-tocopherol. Due to the significance of these findings, further proof was required to unequivocally demonstrate the presence of endogenous alpha-tocopheryl phosphate in biological samples. Four independent methods of analysis were examined: HPLC, LCMS, LCMS/MS, and GCMS. Alpha-tocopherol phosphate was identified in all instances by comparison between standard alpha-tocopheryl phosphate and extracts of biological tissues. The results show that alpha-tocopheryl phosphate is a natural form of vitamin E. The discovery of endogenous alpha-tocopheryl phosphate has implications for the expanding knowledge of the roles of alpha-tocopherol in biological systems.     

The relative contributions of vitamin E, urate, ascorbate and proteins to the total peroxyl radical-trapping antioxidant activity of human blood plasma

The Total (Peroxyl) Radical-trapping Antioxidant Parameter (TRAP) of six freshly prepared human plasma samples and 45 frozen plasma samples has been determined. It is shown that contributions from urate (35-65%), plasma proteins (10-50%), ascorbate (0-24%) and vitamin E (5-10%) to TRAP account for all of the peroxyl radical-trapping antioxidant activity in the majority of the samples. The changes in concentrations of the plasma antioxidants during peroxyl radical attack show that the first line of defense is provided by the plasma sulfhydryl groups, even urate being spared during the initial stages of the reaction. The modes of action of all of these plasma antioxidants and possible interactions between them are discussed, with particular emphasis on the abilities of the water-soluble antioxidants to regenerate or spare the only lipid-soluble antioxidant, vitamin E.     

The content of lipid peroxidation products and the activity of antioxidant enzymes in the myocardium and liver of rats with various vitamin E allowances

After 2 month of feeding vitamin E-supplemented diet (100.6 and 0 mg/kg; group I-control, II and III, respectively) the concentration of lipid peroxidation products (diene conjugates, malondialdehyde, Schiff's bases) and activity of antioxidant enzymes (superoxide dismutase, glutathione peroxidase) was estimated in rat heart and liver. Although the content of alpha-tocopherol in organs of group II was significantly decreased, the concentration of peroxidation products and enzyme activities was unchanged. Moreover, these parameters were constant in rat liver of group III. The heart was more sensitive because in group III to vitamin E deficiency (the alpha-tocopherol level was dropped fourfold) the concentration of diene conjugates and malondialdehyde was increased and superoxide dismutase activity was decreased. Thus insufficiency of vitamin E may result in selective alterations of myocardial functions. In addition, vitamin E may be useful instrument for correction of free radical oxidation and antioxidant system activity in the heart.     

The receptor binding domain of apolipoprotein E is responsible for its antioxidant activity

Apolipoprotein E (apoE) is a 34-kDa lipid-associated protein present in plasma and in the central nervous system. Previous studies have demonstrated that apoE has multiple functions, including the ability to transport lipids, regulate cell homeostasis, and inhibit lipid oxidation. The lipid binding domain of apoE has been localized to the carboxyl-terminal domain, whereas a cluster of basic amino acid residues within the N-terminal domain is responsible for its receptor binding activity. This study was undertaken to identify the domain in apoE responsible for its antioxidant activity. Results showed that apoE inhibits Cu(2+)-induced LDL oxidation by delaying conjugated diene formation in a concentration-dependent manner. Reductive methylation of lysine residues or cyclohexanedione modification of arginine residues in apoE abolished its ability to inhibit LDL oxidation. Additional studies showed that a 22-kDa peptide containing the N-terminal domain of apoE3 was more effective than a similar peptide with the apoE4 sequence in inhibiting Cu(2+)-induced LDL oxidation. In contrast, the 10-kDa peptide that contains the C-terminal domain of apoE was ineffective. Inhibition of Cu(2+)-induced LDL oxidation can also be accomplished with a peptide containing either a single sequence or a tandem repeat sequence of the receptor binding domain (residues 141-155) of apoE. Taken together, these results localized the antioxidant domain of apoE to its receptor binding domain and the basic amino acids in this domain are important for its antioxidant activity.     

The effects of diazinon on lipid peroxidation and antioxidant enzymes in rat heart and ameliorating role of vitamin E and vitamin C

Diazinon is one of the most widely used organophosphate insecticides (OPIs) in agriculture and public health programs. Reactive oxygen species (ROS) caused by OPIs may be involved in the toxicity of various pesticides. The aim of this study was to investigate how diazinon affects lipid peroxidation (LPO) and the antioxidant defense system in vivo and the possible ameliorating role of vitamins E and C. For this purpose, experiments were done to study the effects of DI on LPO and the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) in adult rat heart. Experimental groups were: (1) control group, (2) diazinon treated (DI) group, (3) DI+vitamins E and C-treated (DI+Vit) group. The levels of malondialdehyde (MDA) and the activities of SOD and CAT increased significantly in the DI group compared with the control group. The activity of SOD and the levels of MDA decreased significantly in the DI+Vit group compared with the DI group. The differences between the DI+Vit and control groups according to the MDA levels and the activities of both SOD and CAT were statistically significant. These results suggest that treating rats with a single dose of diazinon increases LPO and some antioxidant enzyme activities in the rat myocardium and, in addition, that single-dose treatment with a combination of vitamins E and C after the administration of diazinon can reduce LPO caused by diazinon, though this treatment was not sufficiently effective to reduce the values to those in control group.     

The role of ascorbate in antioxidant protection of biomembranes: Interaction with vitamin E and coenzyme Q

One of the vital roles of ascorbic acid (vitamin C) is to act as an antioxidant to protect cellular components from free radical damage. Ascorbic acid has been shown to scavenge free radicals directly in the aqueous phases of cells and the circulatory system. Ascorbic acid has also been proven to protect membrane and other hydrophobic compartments from such damage by regenerating the antioxidant form of vitamin E. In addition, reduced coenzyme Q, also a resident of hydrophobic compartments, interacts with vitamin E to regenerate its antioxidant form. The mechanism of vitamin C antioxidant function, the myriad of pathologies resulting from its clinical deficiency, and the many health benefits it provides, are reviewed.     

The antioxidant efficiency of vitamin C is concentration-dependent

The inhibition of autoxidation of plasma lipids by vitamin C (ascorbic acid) has been studied. The ascorbate stoichiometric factor, n, i.e., the number of peroxyl radicals trapped by each ascorbate molecule, decreases as the concentration of ascorbate increases. This is attributed to the fact that ascorbate not only acts as a radical-trapping antioxidant, but can also undergo autoxidation. The data indicate that n----2.0 as [ascorbate]----0 and that n----0 as [ascorbate]----infinity. This concentration-dependent behaviour accounts for the wide variation of n values reported in the literature. It is suggested that this autoxidative destruction of ascorbate may play a role regulating its concentration in blood plasma.     

Synthesis and antioxidative activity of structural analogs of vitamin E

Analogues of alpha-tocopherol with modified structure of side isoprenoid chain and chroman nucleus have been synthesised. The influence of chromanol structure on the dynamic of oxidation products formation have been investigated on models of induced and noninduced bulk-phase peroxidation of ethyl linoleate in presence of 2.3.10(-3)-1.2.10(-2) M alpha-tocopherol and the synthesised compounds.     

The antioxidant activity of cyclohistidylproline

A cyclohistidyl-proline, cyclopeptide possessing a hormonal and neurotrophic activity is shown to be an inhibitor of the (Fe + ascorbic acid)-induced peroxidation of membrane lipids, its effect being dependent on its concentration. Inhibition of the malondialdehyde formation by cyclohistidil-proline is accompanied by protection of the membrane bound Ca-pump. In the test of the free radical cumole oxidation antioxidative effect of cyclohistidyl-proline is 4 times higher than that of the hydrophilic antioxidant carnosine. After peritoneal injection of cyclohistidil-proline (15 mg/kg of body weight) to rats the stationary level of thiobarbituric acid reactive products in rat brain or serum is pronouncedly decreased, this effect being in progress up to 6 h after injection. Antioxidative action of cyclohistidyl-proline suggests to be on the basis of a variety of its biological effects.     

The antioxidant activity of regularly consumed fruit and vegetables reflects their phenolic and vitamin C composition

Recent studies are emphasising the importance and putative modes of action of specific flavonoids as bioactive components of the diet in in vivo and in vitro models. Thus, it is important to have a clear idea of the major phenolic families of which fruit and vegetables are comprised and the levels contained therein. Regularly consumed fruit and vegetables of mixed varieties available on the UK market were analysed for the composition of the major individual phenolic components. The total phenolic content (applying the Folin assay) and the vitamin C levels were also determined. The antioxidant capacities of aqueous/methanolic extracts were comparatively assessed using the TEAC (Trolox Equivalent Antioxidant Capacity), the FRAP (Ferric Reducing Ability of Plasma) and ORAC (Oxygen Radical Absorbance Capacity) assays, which comprise contributions from polyphenols, simple phenols and the ascorbate component. The results were calculated in terms of 100 g fresh weight (FW) uncooked portion sizes. Fruit and vegetables rich in anthocyanins (e.g. strawberry, raspberry and red plum) demonstrated the highest antioxidant activities, followed by those rich in flavanones (e.g. orange and grapefruit) and flavonols (e.g. onion, leek, spinach and green cabbage), while the hydroxycinnamate-rich fruit (e.g. apple, tomato, pear and peach) consistently elicited the lower antioxidant activities. The TEAC, FRAP and ORAC values for each extract were relatively similar and well-correlated with the total phenolic and vitamin C contents. The antioxidant activities (TEAC) in terms of 100 g FW uncooked portion size were in the order: strawberry> raspberry = red plum > red cabbage >grapefruit = orange > spinach > broccoli > green grape approximately/= onion > green cabbage > pea > apple > cauliflower tomato approximately/= peach=leek > banana approximately/= lettuce.     

Effects of beta-carotene,vitamin C and E on antioxidant status in hyperlipidemic smokers

Smoking can accelerate the consumption of the stored antioxidant vitamins and increase the oxidative stress in the hyperlipidemic patients. The study investigated the effects of combined beta-carotene, vitamin C, and vitamin E on plasma antioxidant levels, erythrocyte antioxidative enzyme activities, and LDL lipid peroxides. Male hyperlipidemic smokers (35-78 years old) were randomly divided into two antioxidant supplemented groups: intervention 1 (I1, n = 22) (15 mg beta-carotene/day, 500 mg vitamin C/day, and 400 mg alpha-tocopherol equivalent/day) and intervention 2 (I2, n = 20) (30 mg beta-carotene/day, 1000 mg vitamin C/day, and 800 mg alpha-tocopherol equivalent/day). After 6-week supplementation, plasma beta-carotene, vitamin C, vitamin E, and erythrocyte glutathione levels increased significantly by 200%, 98%, 129%, and 39%, respectively, in the I1 group, and by 209%, 216%, 197%, and 32%, respectively, in the I2 group. Plasma Fe(+2) concentrations and Fe(+2)/Fe(+3) decreased significantly in both groups. Except erythrocyte glutathione peroxidase activity in the I1 group, erythrocyte catalase, glutathione peroxidase, and superoxide dismutase activities increased significantly in both groups. Lipid peroxides in LDL decreased significantly by 56% and 72% in the I1 and I2 groups, respectively. However, the levels of plasma iron, erythrocyte glutathione, and LDL lipid peroxides, and the activities of erythrocyte antioxidative enzymes did not differ between two groups. In conclusion, combined antioxidant supplements increased plasma antioxidant levels and antioxidative enzyme activities, and lowered LDL lipid peroxides in male hyperlipidemic smokers. Higher dosage of the supplements did not have an additive effect.     

Radiosensitive antioxidant membrane-bound factors in rat liver microsomes: I. The roles of glutathione and vitamin E

In vitro lipid peroxidation initiated by NADPH/ADP/Fe3+ reveals an alteration of rat liver microsomal antioxidant factors at day D+4 after whole-body gamma irradiation (8Gy). This alteration is partly reversed by GSH, and more efficiently by Trolox C, a water-soluble analog of vitamin E. This reversion by Trolox C, together with the observed 50% decrease in vitamin E content in microsomes of irradiated rats as compared to those of control animals, indicate that Trolox C acts as a free-radical scavenger like and in place of vitamin E. The antioxidant action of Trolox C is not improved in the presence of GSH, which suggests that the former acts earlier than the latter on the autoxidative free-radical chain reactions. Neither GSH, nor Trolox C, nor both antioxidants totally inhibit in vitro lipid peroxidation, which appeals attention on the possible role of extra-microsomal antioxidant factors, especially cytosolic ones.