Oral Absorption and Bioavailability of Tea Catechins

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Abstract
The absorption characteristics and oral bioavailability of three tea catechins, namely (-)-epicatechin (EC), (-)-epicatechin gallate (ECG), and (-)-epigallocatechin gallate (EGCG), were assessed in this study. Male Sprague Dawley rats (210 - 230 g) received either an intravenous (i.v. 50 mg/kg) or oral (5000 mg/kg) dose of decaffeinated catechin-fraction containing EC (5 %), EGCG (50 %), and ECG (13 %). Concentrations of the compounds in plasma, urine, and feces were measured using HPLC. A non-compartmental approach was employed for pharmacokinetic analysis. Results indicated that maximum plasma concentrations for the catechins (15 - 112 μg/ml) were achieved at 2 h post-oral dosing and the apparent volume of distribution (Vd/F) ranged from 30 to 63 l/kg. Absolute bioavailability (F) of EC, EGCG, and ECG was assessed to be 0.39, 0.14, and 0.06, respectively. Estimates of terminal elimination half-life (t1/2,λz) of the catechins after oral dosing were 451 - 479 min and were 1.4 - 10 fold longer than those observed for the i.v. dosing. The discrepancy in terminal elimination and low rate and extent of absorption indicated the possibility of flip-flop kinetics. Respective urinary recoveries were 0.17 - 4.72 % and 2.11 - 14.2 % after oral and i.v. dosing. In conclusion, the low systemic availability of tea catechins observed could be a result of slow absorption, high first pass effect, and wide tissue distribution.

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