Global antioxidant

By analogy, stratum comeum global antioxidant capacity was estimated from the anodic current recorded at around 0.9V/SCE or from the anodic charge recorded between 0 and around 0.9V/SCE, after... 

As classical analytical methods only give delayed results, no evolution of the global antioxidant capacity of these media with time can be examined. For the first time, owing to fast response of cyclic voltammetry, the presented direct electrochemical measurements give results in real time, thus allowing the monitoring of reaction kinetics. 

In this review, the concept of polyphenols as a global antioxidant is considered not appropriate to understand the potential health benefits of such molecules, as supported by recent updates of the concept of oxidative stress. Rather, polyphenols may modulate discreet redox pathways. In addition, I discuss the potential and acute biological impact of polyphenols (flavonoids and phenolic acids) as governed by their reduction potential and lipophilic properties, in connection with two notions ... 

The potential health benefits of plant polyphenols, such as the flavonoids, have been addressed over the years in the framework of the oxidative stress concept. Oxidative stress, as initially formulated by Sies (1985), refers to an imbalance in the dynamic equilibrium between oxidants and antioxidants that favors the formers, potentially leading to damage. As several diseases are supposed to mechanistically involve oxidative stress, such as atherosclerosis, ischemia-reperfusion injury, cancer, and neurodegenerative disorders (Halliwell Gutteridge, 1999), an impressive number of studies on the in vitro antioxidant activity of polyphenols have spotted these compounds as putatively useful to counteract the deleterious oxidant imbalance associated with disease. However, as will be discussed later, because of limited bioavailability and recent updated concept of oxidative stress, the putative activity of polyphenols as global antioxidants is a limited and simplistic view of polyphenol activity in vivo that can be scarcely supported by experimental data. 

Table 4.1 Effect of selected thiols, disulphides, amino acids and antioxidants on the time to the onset and the time to reach maximal ischaemic contracture in isolated perfused rat hearts. Hearts were perfused for a control period of 10 min at the end of which global low-flow (10% of control) ischaemia was initiated. The interventions described above were included in the perfusion fluid 5 min prior to the onset and throughout the ischaemic period. The data are shown as means standard errors of the means (n = 6)...

Carotenoids are one of the most abundant groups of pigments found in nature. Every year more than 100 million tonnes of them are being synthesized in the biosphere. Nearly 600 molecular species of carotenoids are currently identified (Del Campo et al., 2007). As powerful antioxidants, vitamin precursors, natural colorants, and odorants they became a serious global market commodity accounting for almost 1 billion dollars of the yearly trade (BCC research, 2007). 

Citric acid and its citrate compounds are widely used in hundreds of applications. Global production of citric acid in 2005 was 1.6 million tons, with China producing approximately 40% of the world supply. In the United States, approximately 65% of citric acid use is in the food and beverage industry. Citric acid is used as an acidulant to impart tartness, to control pH, as a preservative and antioxidant, as a metal chelator, and to stabilize color and taste. Citrate salts can be used as mineral and metal dietary supplement for example, calcium citrate... 

Reactions can be classified on the basis of their order, which is the sum of the powers to which the concentrations of the participating species are raised in the rate law. If a = p = 1 in equation 14, the reaction is first-order in A, first-order in B, and is globally of second order. Reactions 4 and 5 respond to this kind of second-order reaction rate law, and the k values have been established for the reactions between several oxidant species and antioxidants. 

Shutenko Z, Henry Y, Pinard E, Seylaz J, Potier P, Berthet F. 1999. Influence of the antioxidant quercetin in vivo on the level of nitric oxide determined by electron paramagnetic resonance in rat brain during global ischemia and reperfusion. Biochem Pharmacol 57 199-208. 

The new protocols presented here deal with the direct evaluation of antioxidant global capacity applied to skin and dermo-cosmetic creams. The analyses are performed directly in the medium without pre-treatment of the samples. This allows a simple and noninvasive measurement without introducing any possible interference. Moreover, cyclic voltammetry provides results in quasi-real time, allowing the direct monitoring of reaction kinetics. 

Comparison of cyclic voltammograms recorded in home-made creams without antioxidant (gel 1, gel 2 and emulsion 1) and commercial creams containing antioxidants illustrated the close relationship between the important anodic response and the antioxidant properties of the product (Fig. 8.5). Other results presented in Table 9.2 in Procedure 9 confirmed this relationship. Moreover, current and charge densities increase in the presence of antioxidant(s), proportionally with the antioxidant concentration (see Procedure 9). The overall anodic charge density was chosen as the indicator to estimate the antioxidant global capacity of the creams. 

Identification of the main electroactive antioxidants involved in the global anodic signal recorded on the stratum comeum or in the cream is difficult due to the wide diversity of components. Indeed, species can react according to a heterogeneous way directly at the electrode or according to a homogeneous coupled reaction. 

Evolution of the antioxidant global properties as a function of time... 

In this way, cyclic voltammograms were performed with platinum electrodes at regular time intervals of about 8 h. The antioxidant global capacity of creams changed as a function of the time when the product was exposed to fight or air (see Fig. 9.5 in Procedure 9). However, the... 

Cyclic voltammetry proved to be a convenient method to reveal the oxido-reduction properties of the skin and of dermo-cosmetic creams. On the one hand, using microelectrodes, it was for the first time possible to evaluate the antioxidant properties on the skin surface. This simple protocol allowed to study in real time the global oxido-reductive state and to determine several antioxidant species. On the other hand, results showed the effect of oxidative stress on the evolution of the antioxidant properties of dermo-cosmetic products in time. 

Shen W. H., Zhang C. Y., and Zhang G. Y. (2003). Antioxidants attenuate reperfusion injury after global brain ischemia through inhibiting nuclear factor-kappa B activity in rats. Acta Pharmacol. Sinica 24 1125-1130. 

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