Rate of Free-Radical Oxidation of C₁₈ Diene and Triene Fatty Acids in Aqueous Micellar Solutions and Effectiveness of beta-Carotene as an Inhibitor of Their Oxidation

L. G. Nagler^1*, V. Z. Lankin², A. I. Kozachenko¹, and S. M. Gurevich¹

¹Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 119991 Russia; E-mail: nagler@sky.chph.ras.ru

²Russian Cardiology Research and Production Association, Ministry of Public Health of the Russian Federation, 3-ya Cherepkovskaya ul. 15a, Moscow, 121552 Russia; E-mail: lankin@cardio.ru

^* To whom correspondence should be addressed.

Received January 15, 2002; Revision received November 5, 2002

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The rate of accumulation of conjugated dienes of polyunsaturated fatty acids was measured during free-radical oxidation of linoleic acid (18:2n-6, LA), alpha-linolenic acid (18:3n-3, alpha-LNA), and gamma-linolenic acid (18:3n-6, gamma-LNA) initiated by 2,2´-azo-bis-(2-amidinopropane) hydrochloride in aqueous micellar solutions of sodium dodecyl sulfate and sodium cholate. It was shown that, unlike homogeneous solutions, the oxidative stability of PUFAs in aqueous dispersions increased with an increase in the extent of unsaturation. The rate of LA oxidation was more than tenfold greater than that of alpha- and gamma-LNA. The antioxidant activity of beta-carotene, in contrast to homogeneous solutions, in both micellar systems studied depended on the degree of PUFA unsaturation. We found that 5 µM beta-carotene effectively inhibited the LA oxidation (almost by 90%), whereas the oxidation of alpha-LNA and gamma-LNA was not inhibited by beta-carotene even at much greater concentration (30 µM). The paradoxical discrepancy between the extent of unsaturation and the PUFA oxidation rate, as well as a decrease in the efficiency of beta-carotene-dependent inhibition of oxidation of more polyunsaturated fatty acids in reactions conducted in aqueous dispersions is consistent with the model according to which the peroxyl radicals of LA and fatty acids with the double-bond number greater than two exhibit different polarity.

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KEY WORDS: linoleic acid, linolenic acid, beta-carotene, conjugated dienes, lipoperoxides, antioxidants, free-radical oxidation, micelle

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