Subject Antioxidant activity

The effect substitution on the phenolic ring has on activity has been the subject of several studies (11—13). Hindering the phenolic hydroxyl group with at least one bulky alkyl group ia the ortho position appears necessary for high antioxidant activity. Neatly all commercial antioxidants are hindered ia this manner. Steric hindrance decreases the ability of a phenoxyl radical to abstract a hydrogen atom from the substrate and thus produces an alkyl radical (14) capable of initiating oxidation (eq. 18). 

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. 

Many reviews have been written about the antioxidant activities of carotenoids. Some also describe prooxidant activities. - In consequence, only selected points about this very broad subject will be presented in the first part of this chapter. Linked to these properties and important for food nutritional value is the stability of caro-... 

Experimental evidence in humans is based upon intervention studies with diets enriched in carotenoids or carotenoid-contaiifing foods. Oxidative stress biomarkers are measured in plasma or urine. The inhibition of low density lipoprotein (LDL) oxidation has been posmlated as one mechanism by which antioxidants may prevent the development of atherosclerosis. Since carotenoids are transported mainly via LDL in blood, testing the susceptibility of carotenoid-loaded LDL to oxidation is a common method of evaluating the antioxidant activities of carotenoids in vivo. This type of smdy is more precisely of the ex vivo type because LDLs are extracted from plasma in order to be tested in vitro for oxidative sensitivity after the subjects are given a special diet. 

Gerli, G., Locatelli, G.F., Mongiat, R., Zenoni, L., Agostoni, A., Moschini, G., Zafiropoulos, D., Bruno, S., Rossi, S., Vignati, A. Tarolo, G. and Podda, M. (1992). Erythrocyte antioxidant activity, serum caeruloplasmin, and trace element levels in subjects with alcoholic liver disease. Am. J. Clin. Pathol. 97, 614-618. 

Antioxidant activity was also tested in a liver microsome system. In this study, mice were treated by oral intubation (2 times/wk) with 0.2 ml olive oil alone or containing CLA (0.1 ml), linoleic acid (0.1 ml), or dl-a-tocopherol (lOmg). Four weeks after the first treatment, liver microsomes were prepared and subsequently subjected to oxidative stress using a non-enzymatic iron-dependent lipid peroxidation system. Microsomal lipid peroxidation was measured as thiobarbituric acid-reactive substance (TBARS) production using malondialdehyde as the standard. It was found that pretreatment of mice with CLA or dl-a-tocopherol significantly decreased TBARS formation in mouse liver microsomes (p < 0.05) (Sword, J. T. and M. W. Pariza, University of Wisconsin, unpublished data). 

In vivo studies were also conducted by several researchers. Anraku et al. (2009) examined the antioxidant effects of water-soluble chitosan in normal subjects by measuring the reduction of indices of oxidative stress. Treatment with chitosan for 4weeks produced a significant decrease in levels of plasma glucose and the atherogenic index, and led to an increase in high-density lipoprotein cholesterol (HDL-C). Chitosan treatment also lowered the ratio of oxidized to reduced albumin and increased total plasma antioxidant activity. Further, Anraku et al. (2011) proved the antioxidant effects of high MW chitosan in normal volunteers, and the obtained results were consistent with previous results observed by Anraku et al. (2009). 

Particular attention is given to the D-Roms test (14), which is very simple and has been used also to evaluate the antioxidant activity of some products in patients and healthy subjects. The test is based on the determination of hydroperoxides that are derivatives of oxidized lipids and consequently indicate the OS at cellular level. The test is used for the epidemiological study on metabolic syndrome, in Italy by the European Society of Biological Nutrition. 

The evidence that a 24-hour fasting and tranquillity have both the ability for a strong antioxidant activity and may create some complexity in the definition of antioxidants. In many instances, subjects suffering from some diseases (hypertension, infection, inflammation) or under particular conditions such as menopause may also have OS, which can be considered as an epiphenomenon of that given condition. Once the disease (or the symptom and/or the condition) is controlled by a therapy, the OS may disappear. This means that a product can be considered as an antioxidant indirectly." These aspects may further complicate the definition of an antioxidant. 

Tressl et all6 11 have isolated some of the oligomers formed in their model systems, based mainly on pyrroles (/V-methyl and A-methyl-2-formyl), and have subjected them to tests for antioxidant activity (DPPH and Fe3+ thiocyanate). Although activity was found, its occurrence seemed somewhat haphazard. 

Iwli et al [97] have reports based on the evaluation of plant-extract of D. multiradiata for antileishmanial activity using a mechanism-based radiorespirometric micro-technique. Extracts were found to be active at concentrations of 50 pg/ml or less against a visceral leishmania isolate. A number of Dorstenia species used traditionally as anti-snake venom were subjected to a pharmacological screening process and were found to possess analgesic and anti-inflammatory activities [98]. Many of the flavonoids isolated from African Dorstenia show moderate to good antioxidant activities [Croft, unpublished results]. The cytotoxic properties of... 

We observed a small but significant inaease in plasma hydrophilic and lipophilic antioxidant capacity following the consumption of a single meal of 189 g of blueberries (10 mg anthocyanins/kg). Others " reported an increase in plasma antioxidant capacity (acetone fraction) after the consumption of approximately 1.2 g of anthocyanins (15 mg anthocyanins/kg) from blueberry. Matsumoto et al." observed a rapid inaease in plasma antioxidant activity, as indicated by monitoring chemiluminescence intensity, after oral administration of black currant anthocyanins (0.573 mg/kg). A small iuCTease in antioxidant activity in plasma was observed in elderly subjects who consumed 1 cup of blueberries per day for a period of 30 days. What is not known is if anthocyanins are accumulated in tissues when consumed over an extended period of time. 

Plaza et al. (2006b) studied the stability of carotenoids and the antioxidant activity of Mediterranean vegetable soup (gazpacho) subjected to high-pressure treatment (up to 300 MPa, 60°C) and stored at 4°C during 40 days. The results indicated that a treatment at ISOMPa led to better preservation of both properties as compared to a treatment at 300MPa. 

Delfino RJ, Staimer N, Tjoa T et al (2008) Circulating biomarkers of inflammation, antioxidant activity, and platelet activation are associated with primary combustion aerosols in subjects with coronary artery disease. Environ Health Perspect 116 898-906 Delfino RJ, Staimer N, Tjoa T et al (2009) Air pollution exposures and circulating biomarkers of effect in a susceptible population clues to potential causal component mixtures and mechanisms. Environ Health Perspect 117 1232-1238 Dockery DW, Pope CA, Xu X et al (1993) An association between air pollution and mortality in six US cities. N Engl J Med 329 1753-1759... 

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