Reinvestigation of the antioxidant properties of conjugated linoleic acid
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Despite repeated suggestions that antioxidant activity of conjugated linoleic acid (CLA), a collective of conjugated dienoic isomers of linoleic acid, underlies its reported anticarcinogenic and antiatherosclerotic effects, the antioxidant properties of CLA remain ill-defined. Therefore, this study was undertaken to gain more insight into the mechanism of potential CLA antioxidant activity. It was tested whether CLA could protect membranes composed of 1-palmitoyl-2-linoleoyl phosphatidylcholine (PLPC) from oxidative modification under conditions of metal ion-dependent or-independent oxidative stress. Progress of oxidation was determined by direct spectrophotometric measurement of conjugated diene formation and by gas chromatographic/mass spectrometric analysis of fatty acids. The oxidative susceptibility of CLA was higher than that of linoleic acid, and comparable to arachidonic acid. When oxidation of PLPC (1.0 mM) was initiated using the lipid-soluble 2,2′-azobis(2,4-dimethylvaleronitrile) or the water-soluble 2,2′-azobis(2-amidinopropane) hydrochloride, the radical scavengers vitamin E and butylated hydroxytoluene (BHT) at 0.75 μM efficiently inhibited PLPC oxidation, as evident from a clear lagphase. In contrast, 0.75 μM CLA did not have any significant effect on PLPC oxidation. Inhibition of PLPC oxidation by higher concentrations of CLA appeared due to competition, not to an antioxidant effect. When oxidation of PLPC was initiated by hydrogen peroxide/Fe2+ (500 μM/0.05–20 μM), both vitamin E (1 μM) and ethylene glycol-bis(aminoethyl ether) tetraacetic acid (50 μM) efficiently inhibited PLPC oxidation. However, CLA (1–50 μM) did not show a clear protective effect under any of the conditions tested. We conclude that CLA, under these test conditions, does not act as an efficient radical scavenger in any way comparable to vitamin E or BHT. CLA also does not appear to be converted into a metal chelator under metal-ion dependent oxidative stress, as had previously been suggested. On the basis of our observations, a role for CLA as an antioxidant does not seem plausible.
conjugated linoleic acid
gas chromatography/mass spectrometry
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- 3.Harrison, K., Cawood, P., Iversen, A., and Dormandy, T. (1985) Diene Conjugation Patterns in Normal Human Serum,Life Chem. Rep. 3, 41–44.Google Scholar
- 12.Pariza, M.W. (1991) CLA, A New Cancer Inhibitor in Dairy Products,Bull. Int. Dairy Fed. 257, 29–30.Google Scholar
- 17.Pariza, M.W., Ha, Y.L., Benjamin, H., Sword, J.T., Grüter, A., Chin, S.F., Storkson, J., Faith, N., and Albright, K. (1991) Formation and Action of Anticarcinogenic Fatty Acids, inNutritional and Toxicological Consequences of Food Processing (Friedman M., ed.) pp. 269–272, Plenum Press, New York.Google Scholar
- 23.Tribble, D.L., van den Berg, J.J.M., Motchnik, P.A., Ames, B.N., Lewis, D.M., Chait, A., and Krauss, R.M. (1994) Oxidative Susceptibility of Low Density Lipoprotein Subfractions Is Related to Their Ubiquinol-10 and α-Tocopherol Content,Proc. Natl. Acad. Sci. USA 91, 1183–1187.PubMedCrossRefGoogle Scholar
- 24.van den Berg, J.J.M. (1994) Effects of Oxidants and Antioxidants Evaluated Using Parinaric Acid as a Sensitive Probe for Oxidative Stress,Redox Rep. 1, 11–21.Google Scholar