SHORT COMMUNICATION Modulation of P-glycoprotein ATPase Activity by Some Phytoconstituents I. A. Najar, 1 B. S. Sachin, 1 S. C. Sharma, 1 N. K. Satti, 2 K. A. Suri 2 and R. K. Johri 1 * 1 Division of Pharmacology, Indian Institute of Integrative Medicine, (Formerly Regional Research Laboratory), CSIR, Jammu 180 001, India 2 Division of Natural Products Chemistry, Indian Institute of Integrative Medicine, (Formerly Regional Research Laboratory), CSIR, Jammu 180 001, India In the present investigation 16 phytoconstituents, which are active moieties found in several medicinal herbs, have been evaluated for their P-glycoprotein (P-gp) stimulation/inhibition profiles using a P-gp-dependent ATPase assay in rat jejunal membrane (in vitro). Acteoside, agnuside, catechin, chlorogenic acid, picroside -II and santonin showed an inhibitory effect. Negundoside, picroside -I and oleanolic acid caused a stimulatory effect. Andrographolide, apocyanin, berberine, glycyrrhizin, magniferin and piperine produced a biphasic response (stimulation at low concentration and inhibition at high concentration). The results suggested that a possible interaction of these phytoconstituents at the level of P-gp, could be an important parameter in deter- mining their role in several key pharmacodynamic events. Copyright © 2009 John Wiley & Sons, Ltd. Keywords: P-glycoprotein; ATPase activity; phytoconstituents. INTRODUCTION P-glycoprotein (P-gp) is a membrane-located protein of the ABC superfamily found primarily in drug- eliminating organs. It is recognized as an important host defense mechanism mitigating the cellular burden of exogenous and endogenous substrates. P-gp is a poly- specific efflux transporter that can pump out a very broad range of substrates. In addition, the role of this protein in the regulation of oral bioavailability of several clinically important drugs, and in potential drug–drug interactions has also drawn considerable attention (Marchetti et al., 2007). In recent times an enormous increase in the consump- tion of herbal remedies along with prescription drugs has been witnessed. Most of such remedies are derived from a variety of medicinal plants. The majority of such herbal medicinal products contain a wide array of bioac- tive compounds which have been shown to modulate P-gp function (Deferme and Augustijns, 2003; Brand et al., 2006). This has brought into focus a substantial impact of P-gp on herb–drug interactions of wide clini- cal relevance (Izzo, 2004). P-gp is an unusual ATP-driven transporter, in that it has a low affinity for ATP and exhibits a high level of constitutive or basal ATPase activity. This protein has 12 transmembrane domains contained in two homolo- gous halves and two ATP-binding cassette domains in each half that catalyse ATP hydrolysis (Kokubu et al., 1997). One characteristic of this protein is that it couples binding and hydrolysis of ATP at the two nucleotide- binding domains to drug export by transmembrane domains (Tombline et al., 2008). Therefore ATP hydro- lysis happens to be an inherent property of P-gp. However, no evaluation of the effect of most herbal moieties on P-gp ATPase activity had been undertaken prior to a current investigation of which the results on some phytoconstituents presented herein are a part. MATERIALS AND METHODS Chemicals. ATP, dithiotreitol (DTT), ethylene-bis (oxyethylenenitrilo) tetracetic acid (EGTA), Hepes, ouabain octahydrate, sodium ortho-vanadate, Tris-HCl were purchased from Sigma Chemical Co. (St Louis, MO, USA). All other chemicals and reagents were of high purity analytical grade. Animals. Healthy Wistar rats (150–175 g body weight) of both sexes were maintained in regulated environ- mental conditions (well-ventilated with >10 air changes/h; 12 h light/dark photoperiod; temperature 28 ± 2 ºC; relative humidity, 60 ± 10%), according to CPCSEA guidelines. Animal experiments were approved by the Institutional Animal Ethics Committee and were performed as per the Guidelines for Animal Care as recommended by the Indian National Academy, New Delhi (1992). Animals were fed with standard pelleted diet (Ashirwad Industries, Chandigarh, India) and water was provided ad libitum. Seven days after acclimatization, the animals were used. * Correspondence to: Dr R. K. Johri, Division of Pharmacology, Indian Institute of Integrative Medicine, (Formerly Regional Research Labora- tory), CSIR, Jammu 180 001, India. E-mail: rakeshkjohri@rediffmail.com; rkjohri@iiim.res.in Received 20 May 2009 Revised 27 May 2009 Copyright © 2009 John Wiley & Sons, Ltd. Accepted 28 May 2009 PHYTOTHERAPY RESEARCH Phytother. Res. 24: 454–458 (2010) Published online 3 August 2009 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/ptr.2951