Antioxidants oxidation, resistance study

Interventions that block oxidative modification of LDL are currently under intensive study [1,3-5,10]. If oxidative modification of LDL results in enhanced uptake by macrophages, use of an appropriate antioxidant should protect LDL from oxidation, decrease the rate of LDL uptake by macrophage foam cells and slow the development of fatty streaks in the arterial wall. The role of antioxidants in preventing oxidative modification of LDL has been evaluated in a number of studies [1,5,8,10]. In our investigation we studied the influence of the vitamin E reach diet on the copper-mediated oxidizability of plasma LDL from patients with atherosclerosis. So far as LDL is the main transport form of natural antioxidant a-tocopherol we were surprised to find that during 3-months vitamin E supplementation in the daily dose 400 mg the oxidation resistance of LDL did not increase (Figure 14). 

Polyesters and polycarbonate polyols show improved resistance to oxidative attack, compared with that of the polyethers. Stress relation studies run at 130°C, comparing a urethane based on a poly(oxypropylene) polyol and a urethane based on poly(butane adipate) polyol show that, after 60 h, the urethane based on PPG lost most of its strength, while the polyester retained most of its strength [83], Urethanes made from poly(butadiene) polyols are also susceptible to oxidation, but they show good resistance to air-oven aging with antioxidants present (see p. 290 in [45],... 

The antioxidant activities of carotenoids and other phytochemicals in the human body can be measured, or at least estimated, by a variety of techniques, in vitro, in vivo or ex vivo (Krinsky, 2001). Many studies describe the use of ex vivo methods to measure the oxidisability of low-density lipoprotein (LDL) particles after dietary intervention with carotene-rich foods. However, the difficulty with this approach is that complex plant foods usually also contain other carotenoids, ascorbate, flavonoids, and other compounds that have antioxidant activity, and it is difficult to attribute the results to any particular class of compounds. One study, in which subjects were given additional fruits and vegetables, demonstrated an increase in the resistance of LDL to oxidation (Hininger et al., 1997), but two other showed no effect (Chopra et al, 1996 van het Hof et al., 1999). These differing outcomes may have been due to systematic differences in the experimental protocols or in the populations studied (Krinsky, 2001), but the results do indicate the complexity of the problem, and the hazards of generalising too readily about the putative benefits of dietary antioxidants. 

This method is also used to measure ex vivo low-density lipoprotein (LDL) oxidation. LDL is isolated fresh from blood samples, oxidation is initiated by Cu(II) or AAPH, and peroxidation of the lipid components is followed at 234 nm for conjugated dienes (Prior and others 2005). In this specific case the procedure can be used to assess the interaction of certain antioxidant compounds, such as vitamin E, carotenoids, and retinyl stearate, exerting a protective effect on LDL (Esterbauer and others 1989). Hence, Viana and others (1996) studied the in vitro antioxidative effects of an extract rich in flavonoids. Similarly, Pearson and others (1999) assessed the ability of compounds in apple juices and extracts from fresh apple to protect LDL. Wang and Goodman (1999) examined the antioxidant properties of 26 common dietary phenolic agents in an ex vivo LDL oxidation model. Salleh and others (2002) screened 12 edible plant extracts rich in polyphenols for their potential to inhibit oxidation of LDL in vitro. Gongalves and others (2004) observed that phenolic extracts from cherry inhibited LDL oxidation in vitro in a dose-dependent manner. Yildirin and others (2007) demonstrated that grapes inhibited oxidation of human LDL at a level comparable to wine. Coinu and others (2007) studied the antioxidant properties of extracts obtained from artichoke leaves and outer bracts measured on human oxidized LDL. Milde and others (2007) showed that many phenolics, as well as carotenoids, enhance resistance to LDL oxidation. 

The possible involvement of free radicals in the development of hypertension has been suspected for a long time. In 1988, Salonen et al. [73] demonstrated the marked elevation of blood pressure for persons with the lowest levels of plasma ascorbic acid and serum selenium concentrations. In subsequent studies these authors confirmed their first observations and showed that the supplementation with antioxidant combination of ascorbic acid, selenium, vitamin E, and carotene resulted in a significant decrease in diastonic blood pressure [74] and enhanced the resistance of atherogenic lipoproteins in human plasma to oxidative stress [75]. Kristal et al. [76] demonstrated that hypertention is accompanied by priming of PMNs although the enhancement of superoxide release was not correlated with the levels of blood pressure. Russo et al. [77] showed that essential hypertension patients are characterized by higher MDA levels and decreased SOD activities. 

In other applications the pattern of evolution of styrene, butadiene and acrylonitrile as a function of temperature has provided a unique way for classifying different types of ABS. The loss of the antioxidant butylated hydroxytoluene (BHT) was also detected by MS preceding EVA copolymer degradation [165] BHT was identified at a concentration level of 20 ppm. Lehrle and co-workers [52] have described a successful controlled release system for the stabilisation of rubber by encapsulating efficient but rather mobile antioxidants to prevent loss from the host polymer. The performance of the controlled-release of the antioxidant BHT from alginate matrix particles was studied by means of DSC, TG and TG-MS. Polyisoprene rubber is more resistant to oxidation when protected in this way than by the equivalent concentration of unencapsulated antioxidant. 

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