Regeneration of α-Tocopherol in Human Low-Density Lipoprotein by Green Tea Catechin

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Abstract
Oxidative modification of low-density lipoproteins (LDL) may play an important role in the development of atherosclerosis. α-Tocopherol functions as a major antioxidant in human LDL. The present study was to test whether green tea catechins (GTC) would protect or regenerate α-tocopherol in human LDL. The oxidation of LDL incubated in sodium phosphate buffer (pH 7.4, 10 mM) was initiated by addition of 1.0 mM of 2,2‘-azobis(2-amidinopropane) dihydrochloride at 40 °C. It was found that α-tocopherol was completely depleted within 1 h. Under the same experimental conditions, the longjing GTC extracts demonstrated a dose-dependent protective activity to α-tocopherol in LDL at concentrations ranging from 2 to 20 μM. Four pure epicatechin derivatives showed varying protective activity against depletion of α-tocopherol in LDL with (−)-epigallocatechin (EGC) and (−)-epigallocatechin gallate (EGCG) being less effective than (−)-epicatechin (EC) and (−)-epicatechin gallate (ECG). The results showed that addition of longjing GTC extracts, EC, ECG, and EGCG at 5, 10, and 15 min to the incubation mixture demonstrated a gradual regeneration of α-tocopherol in human LDL. Keywords: Epicatechin; epicatechin gallate; epigallocatechin; epigallocatechin gallate; α-tocopherol