Screening of Plant Extracts for their Inhibitory Potential on Drug Efflux Transporter P-gp and Drug Metabolizing Enzymes Cytochrome P450 1A2, 2C19, 3A4 and 2D6

Drug efflux transporters and metabolizing enzymes play a major role in modulating the absorption, distribution, metabolism and excretion of a drug. Acting alone or in concert with each other they can alter the pharmacokinetics and pharmacodynamics of a drug. Pharmacokinetic drug interactions can occur via inhibition or induction of metabolic enzymes or efflux transporters by co-administered drugs. The purpose of this study is to identify potential P-gp and cytochrome P450 inhibitors from medicinal plants through an in vitro screening approach. Inhibition of P-gp was determined in a bidirectional transport assay across MDR1-MDCK monolayer using ³H-digoxin as a P-gp probe. Inhibition of CYP1A2, 2C19, 3A4 and 2D6 was determined by employing C-DNA baculovirus expressed enzymes and fluorescence substrates.

Plant extracts that inhibited P-gp activity by 30% or more at 50µg/mL were selected for further testing to determine their dose response effects. For the inhibition of CYP450 enzymes, plant extracts were initially screened at three concentrations and those showing an inhibition of >50% at the lowest concentration were further tested at lower concentrations to determine the IC₅₀ values. Several plant extracts were found to inhibit either CYP450, or P-gp, or both indicating a possibility of modulating the pharmacodynamics and pharmacokinetics of clinical drugs if co-administered with botanicals or alternative medicines that contain these plant extracts. Selected plant extracts that displayed P-gp mediated activity in the in vivo system will be further characterized for their potential to enhance the bioavailability of drugs using an in-situ intestinal perfusion assay with mesenteric vein blood collection. Acknowledgements: This research is supported in part by „Science Based Authentication of Dietary Supplements“ and „Botanical Dietary Supplement Research“ funded by the Food and Drug Administration grant numbers 5U01FD002071–09 and 1U01FD003871–01, and the United States Department of Agriculture, Agricultural Research Service, Specific Cooperative Agreement No. 58–6408–2-0009.