EFFECT OF TEA FLAVONOID SUPPLEMENTATION ON THE SUSCEPTIBILITY OF LOW-DENSITY-LIPOPROTEIN TO OXIDATIVE MODIFICATION

Dietary flavonoid intake has been reported to be inversely associated with the incidence of coronary artery disease. To clarify the possible role of tea flavonoids in the prevention of atherosclerosis, we inves tigated the effects of tea flavonoids on the susceptibility of low-den sity lipoprotein (LDL) to oxidative modification. In an in vitro study , catechins or theaflavins (25-400 mu mol/L) were added to plasma and incubated for 3 h at 37 degrees C. Then, the LDL fraction was separate d by ultracentrifugation. The oxidizability of LDL was estimated by me asuring conjugated diene, thiobarbituric acid-reactive substances (TEA RS), and lipid peroxides after cupric sulfate was added. TEARS and lip id peroxides in the supernates were also measured after incubation wit h macrophages. Catechins significantly (P < 0.01 by ANOVA) and dose-de pendently prolonged the lag time before initiation of oxidation. Among the catechins, epigallocatechin gallate exerted the most marked effec t, prolonging the oxidation lag time more than vitamin E at the same m olar concentration. Theaflavins exerted stronger inhibitory effects th an catechins. Macrophage-mediated LDL oxidation was also inhibited by adding these tea flavonoids to the plasma samples. In an in vivo study , 14 healthy volunteers consumed 750 mt black tea/d for 4 wk. After th e subjects had consumed tea for 4 wk, the lag time before LDL oxidatio n was significantly (P < 0.01) prolonged from 54 to 62 min. This minor prolongation occurred despite much lower plasma flavonoids than were used in vitro. No significant change was observed in eight control vol unteers. LDL exposed to tea flavonoids in vitro or in vivo reduced oxi dizability. We speculate that tea flavonoids may have a role in amelio rating atherosclerosis.