Limited Sampling Strategies to Estimate Exposure to the Green Tea Polyphenol, Epigallocatechin Gallate, in Fasting and Fed Conditions

Limited sampling estimates of epigallocatechin gallate exposures in cirrhotic and noncirrhotic patients with hepatitis C after single oral doses of green tea extract

BACKGROUND

Epigallocatechin-3-gallate (EGCG) has antiangiogenic, antioxidant, and antifibrotic properties that may have therapeutic potential for the treatment of cirrhosis induced by hepatitis C virus (HCV). However, cirrhosis might affect EGCG disposition and augment its reported dose-dependent hepatotoxic potential.

OBJECTIVE

The safety, tolerability, and disposition of a single oral dose of EGCG in cirrhotic patients with HCV were examined in an exploratory fashion.

METHODS

Eleven patients with hepatitis C and detectable viremia were enrolled. Four had Child-Pugh (CP) class A cirrhosis, 4 had Child-Pugh class B cirrhosis, and 3 were noncirrhotic. After a single oral dose of green tea extract 400 mg containing 94% pure EGCG, blood for EGCG levels and safety parameters was ascertained at 2, 4, and 10 hours.

RESULTS

C(max) and AUC to EGCG overlapped among the 3 groups, which suggests that the disposition of EGCG was not significantly altered in these patients with cirrhosis.

CONCLUSIONS

A single 400-mg oral dose of EGCG was safe and well tolerated by all of the patients in the study. These results provide guidance for the continued investigation of the long-term safety and antitumor potential of EGCG in cirrhotic patients with HCV.

Optimal sampling strategy development methodology using maximum a posteriori Bayesian estimation

Maximum a posteriori Bayesian (MAPB) pharmacokinetic parameter estimation is an accurate and flexible method of estimating individual pharmacokinetic parameters using individual blood concentrations and prior information. In the past decade, many studies have developed optimal sampling strategies to estimate pharmacokinetic parameters as accurately as possible using either multiple regression analysis or MAPB estimation. This has been done for many drugs, especially immunosuppressants and anticancer agents. Methods of development for optimal sampling strategies (OSS) are diverse and heterogeneous. This review provides a comprehensive overview of OSS development methodology using MAPB pharmacokinetic parameter estimation, determines the transferability of published OSSs, and compares sampling strategies determined by MAPB estimation and multiple regression analysis. OSS development has the following components: 1) prior distributions; 2) reference value determination; 3) optimal sampling time identification; and 4) validation of the OSS. Published OSSs often lack all data necessary for the OSS to be clinically transferable. MAPB estimation is similar to multiple regression analysis in terms of predictive performance but superior in flexibility.

Inhibitory effects of commonly used herbal extracts on UDP-glucuronosyltransferase 1A4, 1A6, and 1A9 enzyme activities

The aim of this study was to investigate the effect of commonly used botanicals on UDP-glucuronosyltransferase (UGT) 1A4, UGT1A6, and UGT1A9 activities in human liver microsomes. The extracts screened were black cohosh, cranberry, echinacea, garlic, ginkgo, ginseng, milk thistle, saw palmetto, and valerian in addition to the green tea catechin epigallocatechin gallate (EGCG). Formation of trifluoperazine glucuronide, serotonin glucuronide, and mycophenolic acid phenolic glucuronide was used as an index reaction for UGT1A4, UGT1A6, and UGT1A9 activities, respectively, in human liver microsomes. Inhibition potency was expressed as the concentration of the inhibitor at 50% activity (IC(50)) and the volume in which the dose could be diluted to generate an IC(50)-equivalent concentration [volume/dose index (VDI)]. Potential inhibitors were EGCG for UGT1A4, milk thistle for both UGT1A6 and UGT1A9, saw palmetto for UGT1A6, and cranberry for UGT1A9. EGCG inhibited UGT1A4 with an IC(50) value of (mean ± S.E.) 33.8 ± 3.1 μg/ml. Milk thistle inhibited both UGT1A6 and UGT1A9 with IC(50) values of 59.5 ± 3.6 and 33.6 ± 3.1 μg/ml, respectively. Saw palmetto and cranberry weakly inhibited UGT1A6 and UGT1A9, respectively, with IC(50) values >100 μg/ml. For each inhibition, VDI was calculated to determine the potential of achieving IC(50)-equivalent concentrations in vivo. VDI values for inhibitors indicate a potential for inhibition of first-pass glucuronidation of UGT1A4, UGT1A6, and UGT1A9 substrates. These results highlight the possibility of herb-drug interactions through modulation of UGT enzyme activities. Further clinical studies are warranted to investigate the in vivo extent of the observed interactions.

Epigallocatechin gallate (EGCG), a major component of green tea, is a dual phosphoinositide-3-kinase/mTOR inhibitor

The PI3K signaling pathway is activated in a broad spectrum of human cancers, either directly by genetic mutation or indirectly via activation of receptor tyrosine kinases or inactivation of the PTEN tumor suppressor. The key nodes of this pathway have emerged as important therapeutic targets for the treatment of cancer. In this study, we show that (-)-epigallocatechin-3-gallate (EGCG), a major component of green tea, is an ATP-competitive inhibitor of both phosphoinositide-3-kinase (PI3K) and mammalian target of rapamycin (mTOR) with K(i) values of 380 and 320nM respectively. The potency of EGCG against PI3K and mTOR is within physiologically relevant concentrations. In addition, EGCG inhibits cell proliferation and AKT phosphorylation at Ser473 in MDA-MB-231 and A549 cells. Molecular docking studies show that EGCG binds well to the PI3K kinase domain active site, agreeing with the finding that EGCG competes for ATP binding. Our results suggest another important molecular mechanism for the anticancer activities of EGCG.

Inhibitory effects of commonly used herbal extracts on UGT1A1 enzyme activity

Commonly used herbal supplements were screened for their potential to inhibit UGT1A1 activity using human liver microsomes. Extracts screened included ginseng, echinacea, black cohosh, milk thistle, garlic, valerian, saw palmetto, and green tea epigallocatechin gallate (EGCG). Estradiol-3-O-glucuronide (E-3-G) formation was used as the index of UGT1A1 activity. All herbal extracts except garlic showed inhibition of UGT1A1 activity at one or more of the three concentrations tested. A volume per dose index (VDI) was calculated to estimate the volume in which the daily dose should be diluted to obtain an IC(50)-equivalent concentration. EGCG, echinacea, saw palmetto, and milk thistle had VDI values >2.0 L per dose unit, suggesting a higher potential for interaction. Inhibition curves were constructed for EGCG, echinacea, saw palmetto, and milk thistle. IC(50) values were (mean ± SE) 7.8 ± 0.9, 211.7 ± 43.5, 55.2 ± 9.2, and 30.4 ± 6.9 µg/ml for EGCG, echinacea, saw palmetto, and milk thistle extracts, respectively. Based on our findings, inhibition of UGT1A1 by milk thistle and EGCG and to a lesser extent by echinacea and saw palmetto is plausible, particularly in the intestine where higher extract concentrations are anticipated. Further clinical studies are warranted.