Fruit Hydroxycinnamic Acids Inhibit Human Low-Density Lipoprotein Oxidation in Vitro

Abstract

Oxidative modification of low-density lipoprotein (LDL) is believed to play a crucial role in atherogenesis. The antioxidant activity of hydroxycinnamic acids typically present in fruits was investigated in vitro using a human LDL oxidation assay. The o-dihydroxy compounds caffeic, caftaric, chlorogenic, and neochlorogenic acids had highest antioxidant activities and inhibited LDL oxidation from 86 to 97% at 5 μM. Ferulic and fertaric acids had lower antioxidant activities, and p-coumaric and p-coutaric acids had the lowest. Differences in antioxidant activity were thus primarily related to the hydroxylation and methylation pattern. The esterification to tartaric acid slightly enhanced the antioxidant activity of p-coumaric and ferulic acids, but esterification of caffeic acid to quinic acid (as in chlorogenic and neochlorogenic acid) had no effect on or slightly decreased antioxidant activity. The observed differences in activities are discussed in terms of structural dissimilarities of the compounds. It is proposed that for the less active hydroxycinnamic acids, p-coumaric and ferulic acids, esterification to tartaric acid may enhance their ability to inhibit LDL oxidation by binding to apolipoprotein B in the LDL particle. Keywords: Antioxidant; LDL; p-coumaric, ferulic, caffeic, hydroxycinnamoyltartaric acids; hydroxycinnamoylquinic acids