Bioavailability of the green tea polyphenol, (-)-epigallocatechin-3-gallate (EGCG), in mice: Dose-dependence and improvement via peracetylation

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Epigallocatechin-3-gallate (EGCG) has been shown to undergo extensive biotransformation to yield methylated and glucuronidated metabolites in mice, rats, and humans. In the present study, we determined the concentration-dependent uptake of EGCG (20 - 600 μM) by HT-29 human colon cancer cells and the dose-dependence of EGCG plasma and tissue levels following a single dose of EGCG (50 - 2000 mg/kg, i.g.) to male CF-1 mice. The cytosolic levels of EGCG were linear with respect to extracellular concentration of EGCG following treatment of HT-29 cells for 2 h (915.3 - 6851.6 μg/g). In vivo EGCG exhibited a linear dose-relationship in the plasma (0.03 - 4.17 μg/mL), prostate (0.01 - 0.91 μg/g), and liver (0.09 - 18.3 μg/g). In the small intestine and colon, however, the levels of EGCG plateaued between 500 and 2000 mg/kg, i.g. The levels of 4“-O-methylEGCG and 4’,4”-di-O-methylEGCG parallel those of EGCG with respect to dose. As a means of improving the stability and bioavailability of EGCG, we have also prepared a peracetylated EGCG (AcEGCG) derivative. AcEGCG exhibited enhanced growth inhibitory activity relative to EGCG in both KYSE150 human esophageal squamous cell carcinoma (IC₅₀ = 10 vs. 20 μM) and HCT116 human colon adenocarcinoma cells (IC₅₀ = 32 vs. 45 μM). AcEGCG was rapidly converted to EGCG by HCT116 cells, and treatment of cells with AcEGCG resulted in a 2.8 - 30-fold greater intracellular concentration of EGCG as compared to treatment with EGCG. AcEGCG was also more potent than EGCG at inhibiting nitric oxide-production (4.4-fold) and arachidonic acid-release (2.0-fold) from lipopolysaccharide-stimulated RAW264.7 murine macrophages. Intragastric administration of AcEGCG to CF-1 mice resulted in improved bioavailability compared to administration of equimolar doses of EGCG. The plasma AUC_0→∞ of total EGCG was 3.29x10⁵ and 1.26x10⁵ ((ng/mL)^.min) for AcEGCG and EGCG, respectively. The t_1/2 of EGCG was also increased following administration of AcEGCG compared to EGCG (310.4 vs. 135.2 min). The AUC_0→∞ and t_1/2 were also increased in the small intestine (18.5- and 3.3-fold, respectively) and the colon (4.0 and 4.4-fold, respectively). The present study provides information with respect to what concentrations of EGCG are achieveable in mice. Our results suggest that absorption of EGCG from the small intestine is largely via passive diffusion, however, at high concentrations, the small intestinal and colonic tissues become saturated. Acetylation represents a means of increasing the biological potency in vitro, increasing the bioavailability of EGCG in vivo, and may result in improved cancer preventive activity (Supported by NIH grant CA88961).