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

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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°C in the presence of 5 μM Cu²⁺. The oxidation of LDL was monitored either by an absorption increase at 234nm 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, 0.95μM for ECG and 2.38, 2.74μM for EGC, respectively. It was found that the Cu²⁺ mediated cholesterol ester degradation in LDL was almost completely inhibited by 5.0μM C or EGCG. Cu²⁺ mediated apolipoprotein B-100 fragmentation was also inhibited (up to 60%) in the presence of C or EGCG.