Metabolism of Green Tea Catechins: An Overview

Abstract

Green tea is one of the most popular beverages worldwide. Its major components include (-)-epicatechin ((-)-EC), (-)-epicatechin-3-gallate (ECG) (-)-epigallocatechin (EGC) and (-)-epigallocatechin-3-gallate (EGCG). It has demonstrated strong antioxidative, anti-inflammatory and anti-cancerous properties and attracted a great deal of interest over last several years. However, there is some discrepancy between the results from human pidemiological studies and cultured cell and animal models. Two reasons for its limited in vivo activities have been considered: metabolism and bioavailability. Recent studies have demonstrated that green tea catechins undergo methylation, glucuronidation and sulfation in in vitro systems and in animals and in humans. It has been also found that efflux transporters Pgp, MRP1 and MRP2 play roles in the absorption and excretion of green tea catechins. Several processes including intestinal metabolism, microbial metabolism, hepatic metabolism and chemical degradation have been found to be involved in the fate of green tea, and to be responsible for its low availability in animals, and most likely also in humans. Pharmacokinetics, absorption, distribution, drug metabolism and excretion properties of green tea provide a better understanding for its in vivo activities. In this article, drug metabolism and microbial metabolism of green tea catechins in in vitro systems and in animals and in humans will be reviewed. It also covers the factors affecting their biotransformation and bioavailability: drug-drug inhibitory and inductive interactions of phase I and phase II enzymes, inhibition of non-drug-metabolizing enzymes, transporters, chemical instability, epimerization and interindividual variability.

Non-digestible stachyose promotes bioavailability of genistein through inhibiting intestinal degradation and first-pass metabolism of genistein in mice

“…P-gp, a well-known efflux pump responsible for multiple drug resistance, plays a major role in the cells to transport genistein from the intra-cell to the outside [23,24]. As represented in Figure 4(c), the small intestinal P-gp level in mice treated with stachyose alone showed a significant decrease ( p <0.05), but an independent treatment with genistein showed a significant increase ( p <0.05), relative to the intestinal P-gp expression in the untreated control group.…”

Green tea consumption and breast cancer risk or recurrence: a meta-analysis

“…EGCG has been shown to inhibit the growth and angiogenic spread of breast, bladder, prostate, and skin cancer cells [6][7][8]13]. A number of mechanisms of action have been adduced, ranging from inhibition of Wnt signaling [14], methylation [15], and matrix metalloproteinases [16] to interference with estrogen receptors [17]. Induction of apoptosis through proteasome inhibition [18] and induction of CDK inhibitor p27 [9] have also been described.…”

A Randomized Controlled Trial of Green Tea Beverages on the in vivo Radical Scavenging Activity in Human Skin

“…Green tea, being a very popular beverage, is a major source of antioxidant polyphenolic components, especially catechins and flavonols [12,13]. The most abundant and powerful antioxidant among the catechins, accounting for around 50% of total catechins in green tea, is epigallocatechin-3- O -gallate (EGCG) [14].…”

“…However, the results of in vitro and topical application may not be transferrable to orally administered substances, as green tea polyphenols undergo numerous biotransformation processes [12]. The knowledge of the underlying pharmacokinetics is crucial for the understanding of the biological effects of orally administered green tea polyphenols [26,27,28,29].…”

“…The knowledge of the underlying pharmacokinetics is crucial for the understanding of the biological effects of orally administered green tea polyphenols [26,27,28,29]. A large number of metabolites deriving from methylation, glucuronidation, and colonic ring fission have been described so far [12]. The impact of these biotransformation processes on the antioxidant potential, the pharmacological activity, and the cutaneous bioavailability of the metabolites is not yet clearly understood.…”