PUFAs

Figure 45-6. Interaction and synergism between antioxidant systems operating in the lipid phase (membranes) of the cell and the aqueous phase (cytosol). (R-,free radical PUFA-00-, peroxyl free radical of polyunsaturated fatty acid in membrane phospholipid PUFA-OOH, hydroperoxy polyunsaturated fatty acid in membrane phospholipid released as hydroperoxy free fatty acid into cytosol by the action of phospholipase Aj PUFA-OH, hydroxy polyunsaturated fatty acid TocOH, vitamin E (a-tocopherol) TocO, free radical of a-tocopherol Se, selenium GSH, reduced glutathione GS-SG, oxidized glutathione, which is returned to the reduced state after reaction with NADPH catalyzed by glutathione reductase PUFA-H, polyunsaturated fatty acid.)...

The detection and quantification of one or more of the above lipid peroxidation produas (primary and/or secondary) in appropriate biofluids and tissue samples serves to provide indices of lipid peroxidation both in ntro and in vivo. However, it must be stressed that it is absolutely essential to ensure that the products monitored do not arise artifactually, a very difiScult task since parameters such as the availability of catalytic trace metal ions and O2, temperature and exposure to light are all capable of promoting the oxidative deterioration of PUFAs. Indeed, one sensible precaution involves the treatment of samples for analysis with sufficient levels of a chainbreaking antioxidant [for example, butylated hydroxy-toluene (BHT)] immediately after collection to retard or prevent peroxidation occurring during periods of storage or preparation. 

The simple spectrophotometric thiobarbituric acid (TBA) test has been frequently used for many years as an indicator of the peroxidation of PUFAs present in biological matrices. This test involves the reaction of aldehydes in the sample with TBA at c. 100°C under acidic conditions (Equation 1.13) to produce a pink-coloured chromogen, which absorbs light strongly at a wavelength of 532 nm (Nair and Turner, 1984). 

Second-derivative spectrophotometry has been used to monitor the time-dependent production of cis,tmns-(Xmax 242 nm) and trans, tram- (Xmax 232 nm) diene conjugates of microsomal PUFAs following the exposure of rats to carbon tetrachloride (CCU) (Corongui et al., 1986). These signals have been postulated to be derived from mixtures of peroxidized substrates. Previous studies using chemical model systems have established that autoxidation of linolenic or arachidonic acid results in the production of cis, trans- and tmns, trawr-conjugated diene... 

The concentrations of PUFA-derived conjugated hydroperoxydienes and oxodienes in biological samples can also be determined by a modification of a spec-trophotometric method originally developed by Fishwick and Swoboda (1977). This assay system involves (1) reduction of conjugated hydroperoxydienes and oxodienes to their corresponding hydroxydienes with... 

Studies conducted by Barenghi eta.1. (1990) and Lodge etal. (1993) independently have demonstrated the facile, multicomponent analysis of a wide range of PUFA-derived peroxidation products (e.g. conjugated dienes, epoxides and oxysterols) in samples of oxidized LDL by high-field H-NMR spectroscopy. Figure 1.9 shows the applications of this technique to the detection of cholesterol oxidation products (7-ketocholesterol and the 5a, 6a and 5/3,60-epoxides) in isolated samples of plasma LDL pretreated with added coppcr(Il) or an admixture of this metal ion with H2O2, an experiment conducted in the authors laboratories. 

The identification and quantification of potentially cytotoxic carbonyl compounds (e.g. aldehydes such as pentanal, hexanal, traw-2-octenal and 4-hydroxy-/mAW-2-nonenal, and ketones such as propan- and hexan-2-ones) also serves as a useful marker of the oxidative deterioration of PUFAs in isolated biological samples and chemical model systems. One method developed utilizes HPLC coupled with spectrophotometric detection and involves precolumn derivatization of peroxidized PUFA-derived aldehydes and alternative carbonyl compounds with 2,4-DNPH followed by separation of the resulting chromophoric 2,4-dinitrophenylhydrazones on a reversed-phase column and spectrophotometric detection at a wavelength of378 nm. This method has a relatively high level of sensitivity, and has been successfully applied to the analysis of such products in rat hepatocytes and rat liver microsomal suspensions stimulated with carbon tetrachloride or ADP-iron complexes (Poli etui., 1985). 

High-resolution H-NMR analysis has recently been employed to ascertain the nature and levels of aldehydes arising from the peroxidation of PUFAs. Indeed, chemical shifts, coupling patterns and coupling constants of the aldehydic (-CHO) and, for a,0-unsaturated... 

Selley et al. (1992) have recently employed gas chromatography combined with mass spectrometric detection to determine levels of the cytotoxic monounsaturated aldehyde 4-hydroxy-/7 t-2-nonenal in the blood plasma of healthy human subjects, and patients with rheumatoid and osteoarthritis. Intriguingly, this lipid peroxidation end-product is present at a concentration ofc. lx 10 mol/dm in healthy and osteoarthritic human plasma samples (but significantly elevated in those collected from rheumatoid arthritis patients). Although at least some of this could originate from the oxidative degradation of PUFAs invm, there may be a relationship existing between these levels and the frequency of thermally/... 

Lipid peroxidation is a radical-mediated chain reaction resulting in the degradation of polyunsaturated fatty acids (PUFAs) that contain more than two covalent carbon-carbon double bonds (reviewed by Esterbauer et al., 1992). One of the major carriers of plasma lipids is LDL, a spherical molecule with a molecular weight of 2.5x10 . A single LDL particle contains 1300 PUFA molecules (2700 total fatty-acid molecules) and is... 

Haemoglobin-derived haem iron has multiple pro-inflammatory effects resulting from its ability to initiate decomposition of lipid hydroperoxides from PUFAs. In... 

It is now widely appreciated that polyunsaturated fatty acids (PUFAs) are highly susceptible to oxidative damage. Indeed, the process of lipid peroxidation was broadly defined as the oxidative deterioration of polyunsaturated lipids by Tappel (1979). The presence of a double... 

PT Pertussis toxin PTCA Percutaneous transluminal coronary angioplasty PTCR Percutaneous transluminal coronary recanalization Pte-H Tetrahydropteridine PUFA Polyunsaturated fatty acid PUMP-1 Punctuated metalloproteinase also known as matrilysin... 

As mentioned earlier, both MCTs and LCTs are used in tube feeding products. Corn, soy, and safflower oils have been the mainstay sources of fat in these products, providing mainly co-6 polyunsaturated fatty acids (PUFAs). On the other hand, some newer EN products contain higher quantities of co-3 PUFAs from sources such as fish oil [i.e., docosahexenoic acid (DHA) and eicosapentenoic acid or (EPA)]. Still other formulas contain higher quantities of monounsaturated fatty acids from canola oil and high-oleic safflower or sunflower oils. The essential fatty acid (EFA) content (mainly linoleic acid) of EN... 

DMS Dimethylsulfide DMSP Dimethylsulfoniopropionate DSP Diarrhetic shellfish poisoning PSP Paralytic shellfish poisoning PUFA Polyunsaturated fatty acid... 

Interestingly, the release of PUFAs without subsequent action of a lipoxygenase can act as a wound-activated defense diatom in rich fresh water biofilms. This reaction could be directly associated with a chemical defense against the grazer Thamnocephalus platyurus [78]. 

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