Free radical initiators as source of water- or lipid-soluble peroxyl radicals.
TL;DR: This chapter discusses the role of free radical initiators as source of water- or lipid-soluble peroxyl radicals and the damage induced by free radicals on biological and related molecules and membranes and the inhibition in model systems.
Abstract: Publisher Summary This chapter discusses the role of free radical initiators as source of water- or lipid-soluble peroxyl radicals. Free radicals can be generated in either an aqueous or the lipid phase as required by using water-soluble 2,2′-Azo-bis(2-amidinopropane) dihydrochloride (AAPH) or lipid-soluble 2,2′-azobis(2,4-dimethylvaleronitrile) (AMVN). Admittedly, such azo compounds are not present in biological systems, but they are useful tools for studying quantitatively (1) the damage induced by free radicals on biological and related molecules and membranes and (2) the inhibition in model systems. The advantages are that the radicals can be generated at a constant rate at a specific site and that the rate of radical flux can be measured and controlled. Obviously, the most important characteristic of the free radical reaction is that it proceeds by a chain mechanism—that is, the rate of the overall reaction or the extent of damage can be quite significant even if the rate of initial radical formation or the amount of attacking radical is very small. It is, therefore, quite important to know how long the kinetic chain lasts. The chain length can never be known without knowing the rate of chain initiation or the radical flux. In fact, in the in vitro experiment, the kinetic chain length is as long as 100 in the oxidation of erythrocyte membranes induced by AAPH. Another advantage in using azo compounds is that, unlike peroxides, they are not explosive and can be handled easily and safely.
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TL;DR: Methods available for the measurement of antioxidant capacity are reviewed, presenting the general chemistry underlying the assays, the types of molecules detected, and the most important advantages and shortcomings of each method.
Abstract: Methods available for the measurement of antioxidant capacity are reviewed, presenting the general chemistry underlying the assays, the types of molecules detected, and the most important advantages and shortcomings of each method. This overview provides a basis and rationale for developing standardized antioxidant capacity methods for the food, nutraceutical, and dietary supplement industries. From evaluation of data presented at the First International Congress on Antioxidant Methods in 2004 and in the literature, as well as consideration of potential end uses of antioxidants, it is proposed that procedures and applications for three assays be considered for standardization: the oxygen radical absorbance capacity (ORAC) assay, the Folin-Ciocalteu method, and possibly the Trolox equivalent antioxidant capacity (TEAC) assay. ORAC represent a hydrogen atom transfer (HAT) reaction mechanism, which is most relevant to human biology. The Folin-Ciocalteu method is an electron transfer (ET) based assay and gives reducing capacity, which has normally been expressed as phenolic contents. The TEAC assay represents a second ET-based method. Other assays may need to be considered in the future as more is learned about some of the other radical sources and their importance to human biology.
4,580 citations
2,083 citations
TL;DR: The most commonly methods used in vitro determination of antioxidant capacity of food constituents are reviewed and presented, and the general chemistry underlying the assays in the present paper was clarified.
Abstract: Recently, there has been growing interest in research into the role of plant-derived antioxidants in food and human health. The beneficial influence of many foodstuffs and beverages including fruits, vegetables, tea, coffee, and cacao on human health has been recently recognized to originate from their antioxidant activity. For this purpose, the most commonly methods used in vitro determination of antioxidant capacity of food constituents are reviewed and presented. Also, the general chemistry underlying the assays in the present paper was clarified. Hence, this overview provides a basis and rationale for developing standardized antioxidant capacity methods for the food, nutraceutical, and dietary supplement industries. In addition, the most important advantages and shortcomings of each method were detected and highlighted. The chemical principles of these methods are outlined and critically discussed. The chemical principles of methods of 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulphonate) radical (ABTS·+) scavenging, 1,1-diphenyl-2-picrylhydrazyl (DPPH·) radical scavenging, Fe3+–Fe2+ transformation assay, ferric reducing antioxidant power (FRAP) assay, cupric ions (Cu2+) reducing power assay (Cuprac), Folin-Ciocalteu reducing capacity (FCR assay), peroxyl radical scavenging, superoxide anion radical (O
2
·−
) scavenging, hydrogen peroxide (H2O2) scavenging, hydroxyl radical (OH·) scavenging, singlet oxygen (1O2) quenching assay and nitric oxide radical (NO·) scavenging assay are outlined and critically discussed. Also, the general antioxidant aspects of main food components were discussed by a number of methods which are currently used for detection of antioxidant properties food components. This review consists of two main sections. The first section is devoted to main components in the foodstuffs and beverages. The second general section is some definitions of the main antioxidant methods commonly used for determination of antioxidant activity of components in the foodstuffs and beverages. In addition, there are given some chemical and kinetic basis and technical details of the used methods.
1,278 citations
Cites methods from "Free radical initiators as source o..."
...This method monitors the ability of antioxidant compounds to interfere with the reaction between ROO generated by AAPH and a target probe (Wayner et al. 1985; Niki 1990; Prior et al. 2005)....
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TL;DR: Investigation of adverse effects of single-wall carbon nanotubes using a cell culture of immortalized human epidermal keratinocytes indicates that dermal exposure to unrefined SWCNT may lead to dermal toxicity due to accelerated oxidative stress in the skin of exposed workers.
Abstract: Carbon nanotubes are new members of carbon allotropes similar to fullerenes and graphite. Because of their unique electrical, mechanical, and thermal properties, carbon nanotubes are important for novel applications in the electronics, aerospace, and computer industries. Exposure to graphite and carbon materials has been associated with increased incidence of skin diseases, such as carbon fiber dermatitis, hyperkeratosis, and naevi. We investigated adverse effects of single-wall carbon nanotubes (SWCNT) using a cell culture of immortalized human epidermal keratinocytes (HaCaT). After 18 h of exposure of HaCaT to SWCNT, oxidative stress and cellular toxicity were indicated by formation of free radicals, accumulation of peroxidative products, antioxidant depletion, and loss of cell viability. Exposure to SWCNT also resulted in ultrastructural and morphological changes in cultured skin cells. These data indicate that dermal exposure to unrefined SWCNT may lead to dermal toxicity due to accelerated oxidative stress in the skin of exposed workers.
1,202 citations
Cites methods from "Free radical initiators as source o..."
...A water-soluble azo-initiator, 2,2′-azobis(2-aminodinopropane) dihydrochloride (AAPH), was used to produce peroxyl radicals (Niki, 1990)....
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...A water-soluble azo-initiator, AAPH, was used to produce peroxyl radicals at a constant rate (Niki, 1990)....
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TL;DR: There is a great need to standardise antioxidant testing to minimise the present chaos in the methodologies used to evaluate antioxidants.
Abstract: The activity of antioxidants in foods and biological systems is dependent on a multitude of factors, including the colloidal properties of the substrates, the conditions and stages of oxidation and the localisation of antioxidants in different phases. When testing natural antioxidants in vitro, it is therefore important to consider the system composition, the type of oxidisable substrate, the mode of accelerating oxidation, the methods to assess oxidation and how to quantify antioxidant activity. Antioxidant effectiveness is also determined by the heterogeneity and heterophasic nature of the system, the type of lipid substrate, including its physicochemical state and degree of unsaturation, the types of initiators, notably transition metals, other components and their possible interaction. For this reason there cannot be a short-cut approach to determining antioxidant activity. Each evaluation should be carried out under various conditions of oxidation, using several methods to measure different products of oxidation. Because most natural antioxidants and phytochemicals are multifunctional, a reliable antioxidant protocol requires the measurement of more than one property relevant to either foods or biological systems. Several recent studies on natural phytochemical compounds produced conflicting results because non-specific one-dimensional methods were used to evaluate antioxidant activity. There is a great need to standardise antioxidant testing to minimise the present chaos in the methodologies used to evaluate antioxidants. Several methods that are more specific should be used to obtain chemical information that can be related directly to oxidative deterioration of food and biological systems.
1,096 citations
References
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TL;DR: The role of antioxidants in lipid peroxidation is reviewed and the rate and mechanism of inhibition by water-soluble and lipid-Soluble, chain-breaking antioxidants have been discussed.
705 citations
TL;DR: Thermally labile azo-initiators used to generate peroxyl radicals at a known, steady rate in an aqueous dispersion of dilinoleoylphosphatidylcholine multilamellar liposomes are used to study the antioxidant behaviour of asCorbate itself and ascorbate in combination with a water-soluble alpha-tocopherol analogue (TROLOX(-].
409 citations
TL;DR: This study clearly showed the damage of RBC membranes caused by oxygen radical attack from outside of the membranes, and suggested that membrane tocopherol even below a critically low level could suppress lipid oxidation but that it could not prevent protein oxidation and hemolysis.
358 citations
TL;DR: Efficacite de 18 antioxydants dans l'autooxydation de l'acide linoleique dans les micelles du titre.
Abstract: Efficacite de 18 antioxydants dans l'autooxydation de l'acide linoleique dans les micelles du titre
238 citations
TL;DR: In this paper, the rates and products of the oxidations of phosphatidylcholines (PCs) in organic homogeneous solutions and as multilamellar liposomes in an aqueous dispersion were studied at 50 degrees C initiated by oil-soluble and water soluble azo compounds and with the aim primarily of elucidating the effect of substrate and reaction medium.
215 citations