EFFECTS OF GREEN TEA, BLACK TEA AND DIETARY LIPOPHILIC ANTIOXIDANTS ON LDL OXIDIZABILITY AND ATHEROSCLEROSIS IN HYPERCHOLESTEROLEMIC RABBITS

The hypothesis that tea or dietary lipid-soluble antioxidants reduce a therogenesis by lowering the oxidizability of low-density lipoprotein (LDL) was investigated. Five groups of 20 female New Zealand white rab bits were fed a restricted amount of a high-fat (30 en%) semipurified diet supplemented with cholesterol (0.15%, w/w) for 21 weeks. The vita min E content of the control diet was 40 mg/kg diet. The animals recei ved either green tea or black tea in their drinking water or vitamin E (200 mg/kg diet) or P-carotene (20 mg/kg). The serum cholesterol conc entrations (in the order of 18-23 mmol/l) were not significantly diffe rent between the groups. Vitamin E was substantially increased as comp ared to controls in vitamin E supplemented animals (3-fold within 8 we eks in plasma and LDL; P < 0.01) and weakly (1.2-fold) by green and bl ack tea (P < 0.05). Green tea consumption tended to reduce aortic lesi on formation by 31% (24 +/- 3.2% versus 35 +/- 5.7% for control animal s, P = 0.11), while black tea, vitamin E and beta-carotene had no effe ct. This was in contrast to the resistance of isolated LDL to oxidatio n induced at high copper concentration. Green and black tea induced a 13% and 15% (P < 0.05) prolongation of the lag phase, respectively, wi th a correspondingly lower oxidation rate, while vitamin E increased t he lag phase by 63% (P < 0.01) with a concomitant diminution of the ox idation rate and p-carotene had no effect. Regression analysis showed that there was no relationship between the extent of atherosclerosis a nd LDL oxidizability or plasma malondialdehyde as marker of in vivo li pid peroxidation. The results of the present study raise the question whether LDL oxidizability (al least when tested at high induction rate ex vivo) is a primary causal mechanism in atherosclerosis in the chol esterol-fed rabbit. The suitability of the cholesterol-fed rabbit with extreme hypercholesterolaemia as a model to study antiatherosclerotic properties of dietary antioxidants, such as the tested polyphenols, i s discussed. (C) 1997 Elsevier Science Ireland Ltd.