Green tea polyphenols (flavan 3-ols) prevent oxidative modification of lowdensity lipoproteins: An ex vivo study in humans

Oxidation of low density lipoprotein (LDL) plays crucial roles in atherogen esis. We previously reported that green tea polyphenols (flavan 3-ols), esp ecially epigallocatechingallate (EGCg) and epicatechingallate, exerted pote nt inhibitory effects on LDL oxidation in vitro. To examine whether intake of green tea polyphenols renders LDL resistant to ex vivo oxidation in huma ns, 22 male volunteers aged between 22 and 32 years were recruited and assi gned the same dietary regimen for 2 weeks. After a 1-week baseline period, they were equally divided into two groups: control and tea. The tea group i ngested 300 mg of green tea polyphenol extract twice daily for 1 week. Plas ma EGCg concentration at the end of the experiment was 56 nmol/L on average (56% in free form) in the tea group; no EGCg was detected before the exper iment. Plasma concentrations of lipids, ascorbate, alpha-tocopherol, and li pid peroxides did not change before and after the experiment in either grou p, but beta-carotene was higher in the tea group (P < 0.01) by paired Stude nt's t-test). LDL (0.1 mg/mL) was incubated with 5 mu M Cu2+ and the oxidat ion was measured by absorbance at 234 nm. The lag time was significantly pr olonged by 13.7 min in the tea group (P < 0.05 by paired Student's t-test, before versus after), whereas such a change was not observed in the control group. These results suggest that daily consumption of seven to eight cups (approximately 100 mL each cup) of green tea may increase resistance of LD L to in vivo oxidation, leading to reduction in the risk of cardiovascular diseases. (C) Elsevier Science Inc. 2000. All rights reserved.