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Reinvestigation of the antioxidant properties of conjugated linoleic acid

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Lipids

Abstract

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.

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Abbreviations

AAPH:

2,2′-azobis(2-amidinopropane) hydrochloride

AMVN:

2,2′-azobis(2,4-dimethylvaleronitrile)

BHT:

butylated hydroxytoluene

CLA:

conjugated linoleic acid

GC/MS:

gas chromatography/mass spectrometry

LA:

linoleic acid

LDL:

low-density lipoproteins

PLPC:

1-palmitoyl-2-linoleoyl phosphatidylcholine

POPC:

1-palmitoyl-2-oleoyl phosphatidylcholine

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Authors and Affiliations

  1. Children's Hospital Oakland Research Institute, 94609, Oakland, California

    Jeroen J. M. van den Berg & Nancy E. Cook

  2. Department of Molecular and Nuclear Medicine, Lawrence Berkeley Laboratory, University of California, 94720, Berkeley, California

    Diane L. Tribble

Authors
  1. Jeroen J. M. van den Berg
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  2. Nancy E. Cook
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  3. Diane L. Tribble
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van den Berg, J.J.M., Cook, N.E. & Tribble, D.L. Reinvestigation of the antioxidant properties of conjugated linoleic acid. Lipids 30, 599–605 (1995). https://doi.org/10.1007/BF02536996

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  • DOI: https://doi.org/10.1007/BF02536996

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