Linoleic acid peroxidation system

A series of substituted diaryselenides were examined in three lipid peroxidation model systems isolated rat liver microsomes treated with Fe(II)/(ADP)/ascorbate and isolated rat hepatocytes treated with two different initiators of oxidation. In rat hepatocytes, all of the tellurides performed more effectively than the selenides. Particularly for the rat liver microsome system, the substituent effects on lipid peroxidation were consistent with what would be expected Electron-donating groups give more active compounds, while electron-withdrawing groups give poorer antioxidants. The same trends were seen for substituted diaryItellurides in inhibition of linoleic acid peroxidation in a two-phase model, where the dimethylamino... 

B) TEARS Measurement in the Model Lipid Emulsion System. The TEARS generated in a model linoleic acid emulsion system containing Glu-Lys and Fru-Lys MRPs, in the absence of metal ions, is presented in Table 2 i.e., %AO). Unlike the oxygen depletion measurements which identified both the antioxidant or prooxidant activity of individual Glu-Lys and Fru-Lys model experiments, no potential prooxidant effect of MRPs was identified using the TBARs measurement. As such, all Glu-Lys and Fru-Lys MRPs derived from different experimental conditions, reduced lipid peroxidation in the lipid emulsion system. However, despite the finding that all experiments show antioxidant activity as assessed using TBARs endpoint measurements, many of the products derived from different Fru-Lys experiments exhibited relatively low e.g. below 5%) antioxidant activity. 

Dopamine, a strong water-soluble antioxidant, was identified in banana fruit (Musa cavendishii) by Kanazawa and Sakakibara (2000). Banana fruit contained high levels in the pulp and peel 2.5-10 mg/100 g and 80-560 mg/100 g, respectively. A banana water extract was reported to suppress the autoxidation of linoleic acid by 65-70% after a 5-day incubation in an emulsion system, as determined from peroxide value and thiobarbituric acid reactivity (Kanazawa and Sakakibara 2000). 

In contrast to numerous literature data, which indicate that protein oxidation, as a rule, precedes lipid peroxidation, Parinandi et al. [66] found that the modification of proteins in rat myocardial membranes exposed to prooxidants (ferrous ion/ascorbate, cupric ion/tert-butyl-hydroperoxide, linoleic acid hydroperoxide, and soybean lipoxygenase) accompanied lipid peroxidation initiated by these prooxidant systems. 

The effects of flavonoids on in vitro and in vivo lipid peroxidation have been thoroughly studied [123]. Torel et al. [124] found that the inhibitory effects of flavonoids on autoxidation of linoleic acid increased in the order fustin < catechin < quercetin < rutin = luteolin < kaempferol < morin. Robak and Gryglewski [109] determined /50 values for the inhibition of ascorbate-stimulated lipid peroxidation of boiled rat liver microsomes. All the flavonoids studied were very effective inhibitors of lipid peroxidation in model system, with I50 values changing from 1.4 pmol l-1 for myricetin to 71.9 pmol I 1 for rutin. However, as seen below, these /50 values differed significantly from those determined in other in vitro systems. Terao et al. [125] described the protective effect of epicatechin, epicatechin gallate, and quercetin on lipid peroxidation of phospholipid bilayers. 

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). 

Firstly, I will discuss recent evidence supporting the hypothesis that free radicals contribute to important chronic diseases in man and exert an important life-shortening effect. Secondly, I will review data on the toxicity of lipid hydroperoxides and their decomposition products, since lipid hydroperoxides can be a source of free radicals in vivo. And lastly, I will review a system under study in our laboratory in which quantitative data on lipid peroxidation and antioxidants is being obtained using linoleic acid in SDS micelles. 

Carcinogenic aminoazo dyes were previously found to increase the latent period of linoleate peroxidation and that DAB was a more effective antioxidant than MAB (13). Furthermore, as autoxidation of the linoleic acid proceeded, N-demethylation of DAB and MAB occurred. Demethylation of DAB also occurred in vitro when DAB is dissolved in cottonseed oil and mixed with ground brown rice (14). Our results clearly indicate that a linoleic acid hydroperoxide-hematin system readily N-demethylates DAB to MAB and MAB to AB. Previously, it was found that in this system, HCHO formation by N-demethylation of DAB was faster than that obtained with MAB (15). Similar results are now reported during the H202 peroxidase catalyzed oxidation of DAB and MAB. Peroxidase and H2O2 have previously been reported to catalyze the N-dealkylation of other arylamines (16, 17). 

A pre-emulsified linoleic acid system has been used to investigate the protective actions of phenolic compounds against lipid peroxidation. ... 

The antioxidant properties of naturally occurring anthraquinones and anthrones were evaluated using different model systems. For example, the antioxidant activity of these compounds was studied on the inhibition of peroxidation of linoleic acid. These results suggest that the antioxidant mechanism for two anthraquinones, emodin, Fig. (4) and aloe-emodin, Fig. (2), possibly depends on scavenging hydroxy radicals, while the pro-oxidant... 

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