Absorption, distribution, elimination of tea polyphenols in rats

Tea polyphenols-including (-)-epigallocatechin-3-gallate (EGCG), (-)-epigallocatechin (EGC), and (-)-epicatechin (EC)-are believed to be responsible for the beneficial effects of tea. This study was conducted to investigate the absorption, distribution, and elimination of EGCG, EGC, and EC in rats after administration of decaffeinated green tea (DGT). For comparison, pure EGCG was also studied. The plasma and tissue levels of EGCG, EGC, and EC were quantified by HPLC, and the results were analyzed by the PCNONLIN program. Following intravenous injection of DGT (25 mg/kg), the plasma concentration-time curves of EGCG, EGC, and EC were fitted in a two-compartment model. The beta-elimination half-lives (t1/2beta) were 212, 45, and 41 min for EGCG, EGC, and EC, respectively; the clearances were 2.0, 7.0, and 13.9 ml x min/kg, and the apparent distribution volumes (V(d)) were 1.5, 2.1, and 3.6 dl/kg. When pure EGCG (10 mg/kg) was given, however, a shorter t1/2beta (135 min), a larger clearance (72.5 ml x min/kg), and a larger V(d) (22.5 dl/kg) for EGCG were observed, suggesting that other components in DGT could affect the plasma concentration and elimination of EGCG. After intragastric administration of DGT (200 mg/kg), approximately 13.7% of EGC and 31.2% of EC were shown in the plasma, but only 0.1% of EGCG was bioavailable as judged by the ratio of AUC(i.g.)/AUC(i.v.). After intravenous administration of DGT (25 mg/kg), the level of EGCG was found to be the highest in the intestine samples, and the intestinal EGCG level declined with a t1/2 of 173 min. The highest levels of EGC and EC were observed in the kidney, and the levels declined rapidly with t1/2 of 29 and 28 min, respectively. The AUC of EGCG in the intestine was 4-fold higher than that in the kidney, but the AUCs of EGC and EC in the intestine were similar to those in the kidney. The liver and lung levels of EGCG, EGC, and EC were generally lower than those in the intestine and the kidney. The distribution results suggest that EGCG is mainly excreted through bile, and that EGC and EC are excreted through both the bile and urine.