Pro-oxidant effects

Transformation products of stabilizers formed during melt processing may exert either or both anti- and/ or pro-oxidant effects. For example, in the case of BHT, peroxydienones, PxD (reactions 9b, b") lead to pro-oxidant effects, due to the presence of the labile peroxide bonds, whereas quinonoid oxidation products, BQ, SQ, and G- (reaction 9 b, c, d) are antioxidants and are more effective than BHT as melt stabilizers for PP [29], The quinones are effective CB—A antioxidants and those which are stable in their oxidized and reduced forms (e.g., galvinoxyl, G-, and its reduced form, hydrogalvi-noxyl, HG) may deactivate both alkyl (CB—A mecha-... 

Green tea Tea catechins (300 ppm is typically required) Raw minced beef, pork, poultry and fish Cooked red meat, poultry and fish Frozen chicken meat Effect up to four times that of a-tocopherol Inhibits pro-oxidative effect of added NaCl Protection of a-tocopherol in muscles when added to chicken feed Tang et al., 2001c Tang et al., 2001b Tang et al., 2002... 

Palozza, R, Evidence for pro-oxidant effects of carotenoids in vitro and in vivo implications in health and disease, in Carotenoids in Health and Disease, Krinsky, S.T.M. and Sies, H., Eds., Marcel Dekker, New York, 2004, 127. 

It has been shown in many studies that protective effects of carotenoids can be observed only at small carotenoid concentrations, whereas at high concentrations carotenoids exert pro-oxidant effects via propagation of free radical damage (Chucair et al., 2007 Lowe et al., 1999 Palozza, 1998, 2001 Young and Lowe, 2001). For example, supplementation of rat retinal photoreceptors with small concentrations of lutein and zeaxanthin reduces apoptosis in photoreceptors, preserves mitochondrial potential, and prevents cytochrome c release from mitochondria subjected to oxidative stress induced by paraquat or hydrogen peroxide (Chucair et al., 2007). However, this protective effect has been observed only at low concentrations of xanthophylls, of 0.14 and 0.17 pM for lutein and zeaxanthin, respectively. Higher concentrations of carotenoids have led to deleterious effects (Chucair et al., 2007). 

As mentioned previously, in the AMD retina iron metabolism is compromised (He et al., 2007 Wong et al., 2007). Thus, it is of interest to determine the effects of potential antioxidants in the presence of iron. In an in vitro study of ARPE-19 cells, addition of a lipophilic iron complex led to about a ninefold increase in the photosensitized yield of 7a,(3-cholesterol hydroperoxides (Wrona et al., 2004). In the presence of the iron, ascorbate exerted pro-oxidant effects, while the effects of a-tocopherol, zeaxanthin, or their combination were still protective (Wrona et al., 2004). Thus, it appears that the effects of potential antioxidants are strongly dependent on the sources of oxidative damage. The same antioxidant may be protective under certain conditions and exert deleterious effects when the conditions are changed. Therefore a detailed understanding of the sources of the oxidative damage is required in order to design an adequate antioxidant mixture. 

Rozanowski, B, Burke, J, Sarna, T, and Rozanowska, M, 2008a. The pro-oxidant effects of interactions of ascorbate with photoexcited melanin fade away with aging of the retina. Photochem Photobiol 84, 658-670. 

In summary, unoxidized lycopene can act as a lipid and a DNA antioxidant at physiological concentrations but oxidized lycopene or high concentrations of lycopene, and depending upon the oxidizing conditions, may increase lipid peroxidation and oxidative DNA damage. Furthermore, the pro-oxidant effects may result in an increased apoptosis and a decreased cell viability, which should be kept in mind as studies on proliferation and apoptosis are reviewed. 

Although the cellular concentrations of lycopene or its oxidation products may be too low to have a general antioxidant or pro-oxidant effect on cells, there is sufficient evidence of its in vivo effect on the classical measures of oxidative stress to indicate that its participation in the redox state... 

Yeh, SL, and ML Hu. 2000. Antioxidant and pro-oxidant effects of lycopene in comparison with beta-carotene on oxidant-induced damage in Hs68 cells. J Nutr Biochem 11 548-554. 

The concurrent slow homolytic reaction gives rise to free radicals [14]. The occurrence of the homolytic reaction can be revealed by the consumption of free radical acceptors [8,15], CL [16], or NMR spectroscopy [17,18]. The introduction of phosphite into the hydroperoxide-containing cumene causes an initiation, pro-oxidative effect related to the formation of free radicals [6]. The yield of radicals from aliphatic phosphites is much lower (0.01-0.02%) than that from aromatic phosphites (up to 5%) [17]. The homolytic reaction of phosphites with hydroperoxide has a higher activation energy than the heterolytic reaction, which results in the predominance of the former reaction at elevated temperatures. 

These reactions produce free radicals, as follows from the fact of consumption of free radical acceptor [42]. The oxidation of ethylbenzene in the presence of thiophenol is accompanied by CL induced by peroxyl radicals of ethylbenzene [43]. Dilauryl dithiopropionate induces the pro-oxidative effect in the oxidation of cumene in the presence of cumyl hydroperoxide [44] provided that the latter is added at a sufficiently high proportion ([sulfide]/[ROOH] > 2). By analogy with similar systems, it can be suggested that sulfide should react with ROOH both heterolytically (the major reaction) and homolytically producing free radicals. When dilauryl dithiopropionate reacts with cumyl hydroperoxide in chlorobenzene, the rate constants of these reactions (molecular m and homolytic i) in chlorobenzene are [42]... 

Fig. 7.1 Pro-oxidant effect of C60/pol y vi nyI pyrrol idone (C6Q/PVP) complex (1 - in the darkness, 2 - illumination with visible light 15 min, 3 - illumination with visible light 30 min). Test method - fluorescence of 2, 7 -dichlorofluorescein...

Pro-oxidant effects. The antioxidant effect described above occurs when NO concentrations are low. If the concentration of NO rises, rather than reducing the damaging effects of 02" the two may combine to form an even more powerful oxidant called peroxynitrite (ONOO ) ... 

Bowry, V. W., and Stocker, R. (1993),Tocopherol-mediated peroxidation.The pro-oxidant effect of Vitamin E on the radical-initiated oxidation of human low-density lipoprotein, J. Am. Chem. Soc., 115, 6029-6040. 

Milk contains trace amounts of SOD which has been isolated and characterized it appears to be identical to the bovine erythrocyte enzyme. SOD inhibits lipid oxidation in model systems. The level of SOD in milk parallels that of XO (but at a lower level), suggesting that SOD may be excreted in milk in an attempt to offset the pro-oxidant effect of XO. However, the level of SOD in milk is probably insufficient to explain observed differences in the oxidative stability of milk. The possibility of using exogenous SOD to retard or inhibit lipid oxidation in dairy products has been considered. 

Liu and Ng (2000) studied the antioxidative and superoxide- and hydroxyl-radical-scavenging activities and pro-oxidant effect of 12 selected medicinal herbs. The aqueous extracts of Coplis... 

The dimension of standard error is such that many subjects are not reaching the Recommended Dietary Daily Allowance (RDA) and consequently they need to increase the vitamins, intake either with food or supplements. On the other hand, many subjects take a very high amount of vitamins with the food. In these last cases a further intake through supplements could generate the condition of a pro-oxidant effect. 

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