The Inhibitory Effects of Tea Polyphenols (Flavan-3-ol Derivatives) on Cu2+ Mediated Oxidative Modification of Low Density Lipoprotein.

Abstract

Tea polyphenols (flavan-3-ol derivatives) suppressed the oxidative modification of low density lipoprotein (LDL) which is assumed to be an important step in the pathogenesis of atherosclerosis lesions. Inhibitory experiments on the oxidative impairment of porcine serum LDL by flavan-3-ols were carried out by incubating them at 37 degrees C in the presence of 5 microM Cu2+. The oxidation of LDL was monitored either by an absorption increase at 234 nm due to the conjugated diene formation, or the formation of hydroperoxides and thiobarbituric acid reactive substances (TBARS). It was found that the oxidation was strongly inhibited by various flavan-3-ols, and a lag time over 100 min appeared, depending on the types of flavan-3-ols used. The activities based on the prolongation of the lag time were in the order of (-)-epigallocatechin (EGC) < (+)-catechin (C) < (-)-epicatechin (EC) < (-)-epicatechingallate (ECG) < (-)-epigallocatechingallate (EGCG). IC50 of flavan-3-ols on Cu2+ mediated hydroperoxides and TBARS formation of LDL were 0.90, 0.95 microM for ECG and 2.38, 2.74 microM for EGC, respectively. It was found that the Cu2+ mediated cholesterol ester degradation in LDL was almost completely inhibited by 5.0 microM C or EGCG. Cu2+ mediated apolipoprotein B-100 fragmentation was also inhibited (up to 60%) in the presence of C or EGCG.