Antioxidant effect of naturally occurring furan fatty acids on oxidation of linoleic acid in aqueous dispersion

trans-10,cis-12-conjugated linoleic acid isomer exhibits stronger oxyradical scavenging capacity than cis-9,trans-11-conjugated linoleic acid isomer

Although studies have been performed to test whether conjugated linoleic acid (CLA) acts as an antioxidant, the results were not conclusive. In addition, the CLA widely used in previous research contains 43% cis-9,trans-11 isomer, 45% trans-10,cis-12 isomer, and 10 other minor isomers. The objective of this study was to investigate the antioxidant activity of cis-9,trans-11- and trans-10, cis-12-CLA isomers using high-purity CLA isomers (>98%) by total oxyradical scavenging capacity assay (Winston, G. W.; Regoli, F.; Dugas, Jr., A. J.; Fong, J. H.; Blanchard, K. A. Free Radical Biol. Med. 1998, 24, 480-493). At all concentrations (2-200 microM), t10, c12-CLA performed as an antioxidant with a 15-min lag phase, which was more effective than c9,t11-CLA and alpha-tocopherol at lower concentrations (2 and 20 microM). On the other hand, c9,t11-CLA possessed weak antioxidant activity at 2 and 20 microM, whereas at 200 microM it acted as a strong pro-oxidant, which suggests that discrepancies of the results of the previous studies on the antioxidant properties of CLA may be due to the balance of the antioxidant properties of t10,c12-CLA and the pro-oxidant properties of c9,t11-CLA in different oxidation conditions.

Determination of furan fatty acids in extra virgin olive oil

The presence of 4 different furan fatty acids (F-acids) was detected in 18 samples of transmethylated monovarietal extra virgin olive oil: methyl 10,13-epoxy-11,12-dimethyloctadeca-10,12-dienoate [diMeF(9,5)], methyl 12,15-epoxy-13,14-dimethyleicosa-12,14-dienoate [diMeF(11,5)] and both olefinic derivatives of diMeF(11,5) with one unsaturation on the side chains conjugated with the furan ring. Transmethylated oils were analyzed by normal phase high-performance liquid chromatography coupled on-line with capillary gas chromatography. After the gas chromatographic separation step, a more selective detection of F-acids was achieved by using a photoionization detector mounted in series with a flame ionization detector. The concentration of F-acids ranged between 50 ppb (detection limit of the method) and 2.1 ppm in the oil. The olefinic derivatives of diMeF(11,5) acids detected were not artifacts created during the sample preparation or during the chromatographic analysis.

Linoleic acid peroxidation--the dominant lipid peroxidation process in low density lipoprotein--and its relationship to chronic diseases

Modern separation and identification methods enable detailed insight in lipid peroxidation (LPO) processes. The following deductions can be made: (1) Cell injury activates enzymes: lipoxygenases generate lipid hydroperoxides (LOOHs), proteases liberate Fe ions--these two processes are prerequisites to produce radicals. (2) Radicals attack any activated CH2-group of polyunsaturated fatty acids (PUFAs) with about a similar probability. Since linoleic acid (LA) is the most abundant PUFA in mammals, its LPO products dominate. (3) LOOHs are easily reduced in biological surroundings to corresponding hydroxy acids (LOHs). LOHs derived from LA, hydroxyoctadecadienoic acids (HODEs), surmount other markers of LPO. HODEs are of high physiological relevance. (4) In some diseases characterized by inflammation or cell injury HODEs are present in low density lipoproteins (LDL) at 10-100 higher concentration, compared to LDL from healthy individuals.

The influence of fatty acid micelles on the assays for SOD activity

The influence of fatty acid (FA) micelles on cytochrome c(cyt.c) reduction and nitroblue tetrazolium (NBT) reduction assays for SOD activity, which continue to be widely used, has been studied. In the presence of FA micelles, the use of cyt.c reduction assay was found to overestimate the real activity of SOD. This effect is attributed to the following reasons. 1. The FA micelles lead to the denaturation of cyt.c, which gives rise to suppression of the reactivity of ferricyt.c(cyt.c(ox)) towards O2-. Furthermore, this denaturation increases the reoxidation rate of ferrocyt.c, and consequently the reoxidation causes a decreased rate of cyt.c(ox) reduction. 2. Positively charged cyt.c(ox) interacts with negatively charged FA micelles, and so cyt.c(ox) on the surface of FA micelles reacts less with negatively charged O2- because of electrostatic repulsion. Also in NBT reduction assay using a positively charged probe molecule, FA micelles cause the appearance of enhancement of SOD activity, due to suppression of the reactivity of NBT towards O2- by electrostatic repulsion. However, in both chemiluminescence assay using the uncharged probe molecule and LDH-NADH assay using the negatively charged probe molecule, FA micelles cannot influence the assays of the SOD activity, because the micelles do not interact electrostatically with probe molecules.

Effects of soybean lipoxygenase-1 on phosphatidylcholines containing furan fatty acids

Naturally occurring tetraalkylsubstituted furan fatty acids (F-acids) were tested as potential substrates for soybean lipoxygenase-1. For this purpose, F-acid methyl ester and phosphatidylcholines containing F-acids at the sn-2 position of the glycerol residue were incubated with the enzyme. Oxidation of F-acids only occurs in the presence of linoleic acid as co-substrate. Linoleic acid is converted by lipoxygenase to the corresponding hydroperoxide that oxidizes the F-acid, probably in a radical reaction, to form an unstable dioxoene compound. This intermediate then forms, dependent on pH, unsaturated furanoid acids or isomers with cyclopentenolone structure that can be detected by gas chromatography/mass spectrometry (GC/MS). F-acids located at the sn-2 position of a synthetic phosphatidylcholine (PC), containing linoleic acid in the sn-1 position, are co-oxidized to a greater extent by incubation with soybean lipoxygenase-1 than are F-acids bound to PC with myristic acid in the sn-1 position when subjected to the enzyme in the presence of a great excess of linoleic acid. The results suggest that F-acids may play a strategic role in antioxidative processes in plant cells.

Oxidation of furan fatty acids by soybean lipoxygenase-1 in the presence of linoleic acid

The interaction of furan fatty acids (F-acids) with lipoxygenase was investigated by incubation experiments of a synthetic dialkyl-substituted F-acid with soybean lipoxygenase-1. Originally the oxidation of furan fatty acids was assumed to be directly effected by lipoxygenase. It is now demonstrated that this reaction is a two-step process that requires the presence of lipoxygenase substrates, e.g. linoleic acid. In the first step linoleic acid is converted by the enzyme to the corresponding hydroperoxide. This attacks, probably in a radical reaction, the furan fatty acid to produce a dioxoene compound that can be detected unequivocally by gas chromatography-mass spectrometry.