Exploiting Kinetic Features of ORAC Assay for Evaluation of Radical Scavenging Capacity

The analysis and interpretation of data retrieved from Oxygen Radical Absorbance Capacity (ORAC) assays represent a challenging task. ORAC indexes originate from different mathematical approaches often lacking correct elucidation of kinetic features concerning radical scavenging reactions by antioxidant compounds. In this work, the expression of ORAC values as area under fluorescein (FL) decay curves (AUC) and lag time are critically compared. This multi-parametric analysis showed the extension of radical scavenging reactions beyond the lag time period for caffeic acid, gallic acid, reduced glutathione and quercetin, extending their antioxidant protection of FL. Ethanol delayed the reaction of both FL and antioxidant compounds with free radical species generated from 2,2'-azobis(2-amidinopropane) dihydrochloride thermolysis. Trolox equivalent values, commonly used to express ORAC values, were more affected by the differences in radical scavenging kinetics between the reference and the tested antioxidant compounds when calculated from AUC than from lag time. These findings stressed the importance of choosing calibrator compounds presenting ORAC kinetics similar to samples to prevent biased estimation of the antioxidant capacity. Additionally, the framework proposed here provides a sustainable analytical method for the evaluation of antioxidant capacity, with an AGREE score of 0.73.

Antioxidant action of fermented grain food supplement: Scavenging of peroxyl radicals and inhibition of plasma lipid oxidation induced by multiple oxidants

Unregulated oxidative modification of biological molecules induced by multiple oxidants in vivo has been implicated in the pathogenesis of various diseases. Accordingly, the role of antioxidants contained in foods in the maintenance of health and prevention of diseases has received much attention. The efficacy of antioxidants against oxidative stress depends on the nature of oxidants. In the present study, the antioxidant action of fermented grain food supplement, Antioxidant Biofactor (AOB), for scavenging peroxyl radical and inhibition of plasma lipid oxidation induced by multiple oxidants was measured. The antioxidant efficacy against lipid oxidation was assessed by the level of lipid hydroperoxides produced using diphenyl-1-pyrenylphosphine, which is not fluorescent per se but reacts with lipid hydroperoxides stoichiometrically to yield highly fluorescent diphenyl-1-pyrenylphosphine oxide. AOB acted as a potent peroxyl radical scavenger and suppressed lipid oxidation induced by peroxyl radical, peroxynitrite, hypochlorite, and singlet oxygen, but not by 15-lipoxygenase.

Antioxidant capacity of foods for scavenging reactive oxidants and inhibition of plasma lipid oxidation induced by multiple oxidants

Unregulated oxidation of biological molecules induced by multiple oxidants has been implicated in the pathogenesis of various diseases. Consequently, the effects of antioxidants contained in foods, beverages and supplements on the maintenance of health and prevention of diseases have attracted much attention of the public as well as scientists. However, recent human studies have shown inconsistent results and failed to demonstrate the beneficial effects of antioxidants. The mechanisms and dynamics of antioxidant action and assessment of antioxidant capacity have been the subject of extensive studies and arguments. In the present article, the antioxidant capacity has been reviewed focusing on two main issues: the capacity of antioxidants to scavenge multiple reactive oxidants and to inhibit plasma lipid oxidation induced by different biological oxidants. It is emphasized that the capacity of antioxidants to scavenge reactive oxidants does not always correlate linearly with the capacity to inhibit lipid oxidation and that it is necessary to specify the oxidant to assess the efficacy of antioxidants, since multiple oxidants contribute to oxidative damage in vivo and the effects of antioxidants depend on the nature of oxidants. A convenient and rapid method using a microplate reader is discussed for assessing the antioxidant capacity against plasma lipid oxidation induced by multiple oxidants including peroxyl radicals, peroxynitrite, hypochlorite, 15-lipoxygenase, and singlet oxygen.

Plasma lipid oxidation induced by peroxynitrite, hypochlorite, lipoxygenase and peroxyl radicals and its inhibition by antioxidants as assessed by diphenyl-1-pyrenylphosphine

Lipid oxidation has been implicated in the pathogenesis of many diseases. Lipids are oxidized in vivo by several different oxidants to give diverse products, in general lipid hydroperoxides as the major primary product. In the present study, the production of lipid hydroperoxides in the oxidation of mouse plasma induced by multiple oxidants was measured using diphenyl-1-pyrenylphosphine (DPPP) as a probe. DPPP itself is not fluorescent, but it reacts with lipid hydroperoxides stochiometrically to give highly fluorescent DPPP oxide and lipid hydroxides. The production of lipid hydroperoxides could be followed continuously in the oxidation of plasma induced by peroxynitrite, hypochlorite, 15-lipoxygenase, and peroxyl radicals with a microplate reader. A clear lag phase was observed in the plasma oxidation mediated by aqueous peroxyl radicals and peroxynitrite, but not in the oxidation induced by hypochlorite and lipoxygenase. The effects of several antioxidants against lipid oxidation induced by the above oxidants were assessed. The efficacy of antioxidants was dependent markedly on the type of oxidants. α-Tocopherol exerted potent antioxidant effects against peroxyl radical-mediated lipid peroxidation, but it did not inhibit lipid oxidation induced by peroxynitrite, hypochlorite, and 15-lipoxygenase efficiently, suggesting that multiple antioxidants with different selectivities are required for the inhibition of plasma lipid oxidation in vivo. This is a novel, simple and most high throughput method to follow plasma lipid oxidation induced by different oxidants and also to assess the antioxidant effects in biologically relevant settings.

Impact of Natural Juice Consumption on Plasma Antioxidant Status: A Systematic Review and Meta-Analysis

Background: Oxidative stress may lead to overproduction of reactive species and a decrease in antioxidant defenses, resulting in chronic diseases such as diabetes and cancer. The consumption of natural compounds with an antioxidant profile may be a preventive alternative. Therefore, we aimed to obtain evidence regarding the potential antioxidant activity of juices in human plasma. Methods: A systematic review and meta-analysis was performed, which included randomized controlled trials that compared the use of fruit or vegetable juices vs. placebo or other beverages. An electronic search was conducted in PubMed, Scopus, International Pharmaceutical Abstracts, and SciELO. The outcome measures extracted were related to antioxidant status, e.g., vitamin C, superoxide dismutase (SOD), and catalase (CAT) levels and reduction in malondialdehyde (MDA) and antioxidant capacity measured as TEAC. Results: Twenty-eight trials were identified (n = 1089), of which 16 were used for meta-analysis. No significant differences were observed between juices and placebo with regard to TEAC, SOD, and CAT. However, juices were superior to control in enhancing vitamin C and reducing MDA. Conclusions: Natural juices are possible candidates for the management of oxidative stress. The effects of juices should be further investigated by conducting larger and well-defined trials of longer duration.