An in vitro Evaluation of Cytochrome P450 Inhibition and P-Glycoprotein Interaction with Goldenseal, Ginkgo biloba, Grape Seed, Milk Thistle, and Ginseng Extracts and Their Constituents

Abstract

Drug-herb interactions can result from the modulation of the activities of cytochrome P450 (P450) and/or drug transporters. The effect of extracts and individual constituents of goldenseal, Ginkgo biloba (and its hydrolyzate), grape seed, milk thistle, and ginseng on the activities of cytochrome P450 enzymes CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 in human liver microsomes were determined using enzyme-selective probe substrates, and their effect on human P-glycoprotein (Pgp) was determined using a baculovirus expression system by measuring the verapamil-stimulated, vanadate-sensitive ATPase activity. Extracts were analyzed by HPLC to standardize their concentration(s) of constituents associated with the pharmacological activity, and to allow comparison of their effects on P450 and Pgp with literature values. Many of the extracts/constituents exerted > or = 50 % inhibition of P450 activity. These include those from goldenseal (normalized to alkaloid content) inhibiting CYP2C8, CYP2D6, and CYP3A4 at 20 microM, ginkgo inhibiting CYP2C8 at 10 microM, grape seed inhibiting CYP2C9 and CYP3A4 at 10 microM, milk thistle inhibiting CYP2C8 at 10 microM, and ginsenosides F1 and Rh1 (but not ginseng extract) inhibiting CYP3A4 at 10 microM. Goldenseal extracts/constituents (20 microM, particularly hydrastine) and ginsenoside Rh1 stimulated ATPase at about half of the activity of the model substrate, verapamil (20 microM). The data suggest that the clearance of a variety of drugs may be diminished by concomitant use of these herbs via inhibition of P450 enzymes, but less so by Pgp-mediated effects.

Microsomal Cytochrome P450-Mediated Metabolism of Protopanaxatriol Ginsenosides: Metabolite Profile, Reaction Phenotyping, and Structure-Metabolism Relationship

“…PPT and Rh1, characterized with K m values at 15.0 and 14.2 M, respectively, can possibly serve as new probe substrates for CYP3A4 in vitro, considering that CYP3A4 has been found to be the predominant, if not the sole, P450 isoform involved in microsomal-mediated metabolism. Findings from this study also provide novel explanations for the previously reported ginseng-drug interactions (Coon and Ernst, 2002;Bressler, 2005) and for the reason that only PPT and Rh1 but not their precursors exhibit competitive inhibition on CYP3A4 activity (Liu et al, 2004(Liu et al, , 2006aEtheridge et al, 2007;Hao et al, 2008b). However, it should be noted that although Re and Rg1 are not direct substrates of CYP3A4, they can be transformed to the CYP3A4 substrates Rh1 and PPT by gastric acid and intestinal bacteria and thus may also exert competitive inhibition of other CYP3A4 substrates.…”

“…Oxygenated metabolites had been also identified for Rg3 (Qian et al, 2005b), Rh2 (Qian et al, 2005a), and Rd in rats and for PPT in rat hepatic microsomes (Kasai et al, 2000). Moreover, some previous reports demonstrated that various ginsenosides and especially their degradation products were capable of modulating cytochrome P450 enzyme activities (Liu et al, 2006a,b;Etheridge et al, 2007;. Such evidence strongly suggests that the microsomal cytochrome P450 enzymes may play an important role in the systematic disposition of ginsenosides that finally reach the systemic circulation after oral ingestion.…”

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“…Etheridge et al [65] found G-Rh1 ranging from 1 to 10 µM did not affect the activities of CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and testosterone 6β-hydroxylase. At the concentration of 10 µM, G-Rh1 suppressed midazolam 1-hydroxylase activity by 54 % and increased P-glycoprotein ATPase activity to 17.2 nmol P i / mg protein/min, but it exerted negligible effects on these at the low concentration of 1 µM.…”

Drug—Botanical Interactions: A Review of the Laboratory, Animal, and Human Data for 8 Common Botanicals

“…Other studies conducted in either Caco-2 cells, human liver microsomes, or baculovirus expression system demonstrate that milk thistle inhibits CYP3A4 or -2C8 but does not inhibit Pgp. 73,98,171 …”