Effect of ethyl esterification of phenolic acids on low-density lipoprotein oxidation

Inhibition of copper-induced low-density lipoprotein (LDL) oxidation by phe nolic acids and their ethyl esters was investigated. LDL oxidation was eval uated by the hydroperoxide concentration and the chromatographic pattern of apoprotein fractions after fast protein liquid chromatography (FPLC). Anti radical properties against 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical an d 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH) were also investigate d, and lipophilicity determined by thin-layer chromatography. Caffeic acid at 5 muM and sinapic acid at 10 muM protected LDL against oxidation, inhibi ting both hydroperoxide formation and the increase of apoprotein negative c harge. Ferulic, gallic and p-hydroxy cinnamic acids were ineffective. Ethyl esterification increased the lipophilicity of the five acids, and enhanced the antioxidant properties of caffeic, sinapic and ferulic acids. Ethyl ca ffeate was protective at 1 muM. In contrast, garlic and p-hydroxy cinnamic ethyl esters were ineffective. Our results indicate that ethyl esterificati on of phenolic acids increases lipophilicity of their ethyl esters and may enable a better incorporation into the lipid layer of the LDL particle and the exertion of their antioxidant effect in the true site of lipoperoxidati on. However, increasing lipophilicity is not the only mechanism able to pot entiate preexisting antioxidant properties of molecules, and probably other mechanisms are implicated. (C) 2001 Editions scientifiques et medicales El sevier SAS.