Study on mechanism of low bioavailability of black tea theaflavins by using Caco-2 cell monolayer.

This study aimed to clarify the bioavailability mechanism of theaflavins by using the Caco-2 monolayer in vitro model. Prior to the transport of theaflavin (TF), theaflavin-3-gallate (TF3G), theaflavin-3'-gallate (TF3'G), and theaflavin-3, 3'-digallate (TFDG), we found the cytotoxicity of theaflavins was in the order of TF3'G > TFDG > TF3G > TF, suggesting the galloyl moiety enhances the cytotoxicity of theaflavins. Meantime, the galloyl moiety made theaflavins unstable, with the stability in the order of TF > TFDG > TF3G/TF3'G. Four theaflavins showed poor bioavailability with the Papp values ranging from 0.44 × 10-7 to 3.64 × 10-7 cm/s in the absorptive transport. All the theaflavins showed an efflux ratio of over 1.24. And it is further confirmed that P-glycoprotein (P-gp), multidrug resistance associated proteins (MRPs) and breast cancer resistance protein (BCRP) were all shown to contribute to the efflux transport of four theaflavins, with P-gp playing the most important role, followed by MRPs and BCRP. Moreover, theaflavins increased the expression of P-gp, MRP1, MPR3, and BCRP while decreased the expression of MRP2 at the transcription and translation levels. Additionally, the gallated theaflavins were degraded into simple theaflavins and gallic acids when transported through Caco-2 monolayers. Overall, the structural instability, efflux transporters, and cell metabolism were all responsible for the low bioavailability of four theaflavins in Caco-2 monolayers.

Essential Oils, Pituranthos chloranthus and Teucrium ramosissimum, Chemosensitize Resistant Human Uterine Sarcoma MES-SA/Dx5 Cells to Doxorubicin by Inducing Apoptosis and Targeting P-Glycoprotein.

The multidrug resistance phenotype is a global phenomenon and causes chemotherapy failure in various cancers, such as in uterine sarcomas that have a high mortality rate. To overcome this phenotype, there is growing research interest in developing new treatment strategies. In this study, we highlight the potential of two essential oils from the Apiaceae family, Pituranthos chloranthus (PC) and Teucrium ramosissimum Desf. (TR), to act as chemopreventive and chemosensitizing agents against two uterine sarcoma cell lines, MES-SA and P-gp-overexpressing MES-SA/Dx5 cells. We found that PC and TR were able to inhibit the cell viability of sensitive MES-SA and resistant MES-SA/Dx5 cells by a slight modulation of the cell cycle and its regulators, but also through a significant induction of apoptosis. The molecular mechanism involved both caspase pathways associated with an overproduction of reactive oxygen species (ROS) and mitochondrial membrane depolarization. Very interestingly, the combination of doxorubicin with PC or TR induced a synergism to increase cell death in resistant MES-SA/Dx5 cells and, subsequently, had the benefit of decreasing the resistance index to doxorubicin. These synergistic effects were reinforced by a decrease in P-gp expression and its P-gp adenosine triphosphatase (ATPase) activity, which subsequently led to intracellular doxorubicin accumulation in resistant sarcoma cells.

Use of a Caco-2 permeability assay to evaluate the effects of several Kampo medicines on the drug transporter P-glycoprotein.

In modern medical care in which Kampo and Western drugs are often combined, it is extremely important to clarify drug-drug interaction (DDI) to ensure safety and efficacy. However, there is little evidence of DDI in Kampo medicines. Therefore, as part of our studies to clarify the DDI risk for Kampo medicines, we evaluated the effects of five Kampo medicines [yokukansan (YKS), rikkunshito (RKT), shakuyakukanzoto (SKT), hangeshashinto (HST), and goshajinkigan (GJG)] that are widely used in Japan, on drug transporter P-glycoprotein (P-gp) using a Caco-2 permeability assay. These Kampo medicines inhibited the P-gp transport of digoxin through a Caco-2 cell monolayer. The IC50 values were 1.94-10.80 mg/ml. Of the five Kampo medicines, YKS showed the strongest inhibition (IC50 = 1.94 mg/ml), which was attributed to Uncariae Uncis Cum Ramulus. Unfortunately, we could not find the active ingredients responsible for its action. Finally, the Igut/IC50 values for the five Kampo medicines were calculated, and the DDI risk was objectively evaluated according to the criteria in the DDI guidance issued by the Japanese Ministry of Health, Labor, and Welfare and the US Food and Drug Administration. The Igut/IC50 values for the five Kampo medicines were ≤3.4. As these values were <10, they were evaluated as having a weak P-gp inhibitory effect that does not require further verification in humans, suggesting that the DDI risk due to P-gp inhibition for these Kampo medicines is low. The results should provide useful clinical information on the safety and efficacy of the combined use of Kampo and Western medicines.

Inhibitory Effects of Benzaldehyde, Vanillin, Muscone and Borneol on P-Glycoprotein in Caco-2 Cells and Everted Gut Sac.

AIMS: In clinical practice, herbal medicines have played an important role in the modulation of drug transporters through the combination of conventional prescription drugs, which necessitates the elucidation of herb-drug interactions. The present study was designed to investigate the inhibitory effects and mechanisms of benzaldehyde, vanillin, muscone, and borneol on P-glycoprotein (P-gp). METHODS: The effects of the 4 compounds on the intracellular accumulation of rhodamine-123 (Rho-123) in vinblastine-treated Caco-2 (VB-Caco-2) cells were studied by monitoring fluorescence intensity through a flow cytometry assay, and the effects of these compounds on Rho-123 transport through VB-Caco-2 monolayers and Rho-123 intestinal absorption in the rat everted gut sac were investigated by high-performance liquid chromatography. Moreover, P-gp expression in VB-Caco-2 cells was assessed using flow cytometry and Western blot analysis, and the relative ABCB1 mRNA level was determined by Real-time RT-PCR. KEY FINDINGS: The results showed that benzaldehyde, vanillin, muscone, and borneol significantly increased Rho-123 uptake in VB-Caco-2 cells, increased the absorption rate and apparent permeability coefficient of Rho-123 in rat jejunum and ileum, and decreased the efflux ratio of Rho-123 from 6.52 to less than 2 during transport across VB-Caco-2 cell monolayers. In addition, these compounds reduced the protein and ABCB1 mRNA levels of P-gp in VB-Caco-2 cells. CONCLUSIONS: These data indicate that benzaldehyde, vanillin, muscone and borneol could effectively reverse multidrug resistance via inhibiting the P-gp function and expression pathway. The data provide fodder for further investigation into the interaction between the 4 compounds and other drugs transported by P-gp.

Clerosterol from vinegar-baked radix bupleuri modifies drug transport.

Vinegar-baked Radix Bupleuri (VBRB) is reportedly used to treat liver cancer when combined with traditional chemotherapy and data show that this combination may modify drug transport. We isolated clerosterol from VBRB and studied its effect on drug transporters in normal or transporter-overexpressing cells. Transporter activity was assayed using cellular substrate concentration and transporter expression with Western blot and RT-qPCR. Clerosterol decreased cisplatin uptake in BRL cells mainly through increasing Mrp2 gene expression. Clerosterol also decreased the uptake of colchicine in HEK 293 cells by increasing both Pgp and Mrp1 activity; in detail, it could increase Pgp protein but had marginal effects on Mrp1 protein and gene expression. Further study showed clerosterol increased OCT2 activity in HEK293-Pgp cells by increasing OCT2 protein and mRNA. Clerosterol could suppress Pgp overexpression but not by regulating protein and gene expression. And clerosterol had marginal effects on Mrp2 and Mrp1 activity in Mrp2- and Mrp1-overexpressing HEK293 cells. Thus, Clerosterol may be an active constituent of VBRB and may work against cancer multidrug resistance by inhibiting Pgp activity.

Effect of Curcuma comosa extracts on the functions of peptide transporter and P-glycoprotein in intestinal epithelial cells.

Curcuma comosa has been widely used as a herbal medicine in Thailand; however, it remains unclear whether C. comosa influences the absorption of drugs that are substrates for the transporters in the small intestine. In this study, we investigated the effect of C. comosa extracts on the functioning of peptide transporter 1 (PEPT1), an influx transporter, and P-glycoprotein (P-gp), an efflux transporter, in Caco-2 cells and rat intestine. In Caco-2 cells, the ethanolic extract of C. comosa (CCE) lowered the uptake of glycylsarcosine (Gly-Sar), a PEPT1 substrate, while it enhanced the uptake of rhodamine 123 (Rho123), a P-gp substrate, in a concentrationdependent manner. In addition, CCE inhibited apical-to-basal transport of Gly-Sar and basal-to-apical transport of Rho123. Furthermore, the absorption of cephalexin, another PEPT1 substrate, and the exsorption of Rho123 across the rat intestine were inhibited by CCE. Conversely, CCW, the hot water extract of C. comosa, suppresses the function of PEPT1 but not of P-gp in Caco-2 cells. These results suggest that C. comosa used as a herbal medicine in Thailand may affect the intestinal absorption of certain drugs.

Diterpenoid constituents of Euphorbia macrorrhiza.

Ten diterpenoids, named macrorilone A-B, macroripremyrsinone A, macrorilathyrone A-B, macrorieuphorone A-B and macroricasbalone A-C, together with ten known diterpenoids, jatrophalone, sikkimenoids A-D, jatrophodione A, latilagascenes F, jolkinol B, 15ß-O-benzoyl-5α-hydroxyisolathyrol and jatrophalactone were isolated from the whole plant of Euphorbia macrorrhiza C.A. Mey. These diterpenoids belong to six skeleton-types, including jatropholane, premyrsinane, lathyrane, euphoractin, casbene and rhamnofolane diterpenoids. Their structures were elucidated by extensive analysis of 1D, 2D NMR and HRESIMS spectroscopic data. The absolute configurations of macrorilone B, macroripremyrsinone A and macrorilathyrone A were established by comparing their experimental and calculated electronic circular dichroism (ECD) spectra. Several of the isolated compounds exhibited weak cytotoxicity against the KB and KBv200 cell lines with IC50 values ranging from 21.19 to 47.87µM. Some also showed multidrug resistance (MDR) reversal activity, among which macrorilathyrone B exhibited a remarkable inhibitory effect on P-gp-mediated drug exclusion.

Natural Products based P-glycoprotein Activators for Improved ß-amyloid Clearance in Alzheimer's Disease: An in silico Approach.

Alzheimer's disease is an age related disorder and is defined to be progressive, irreversible neurodegenerative disease. The potential targets which are associated with the Alzheimer's disease are cholinesterases, N-methyl-D-aspartate receptor, Beta secretase 1, Pregnane X receptor (PXR) and P-glycoprotein (Pgp). P-glycoprotein is a member of the ATP binding cassette (ABC) transporter family, which is an important integral of the blood-brain, blood-cerebrospinal fluid and the blood-testis barrier. Reports from the literature provide evidences that the up-regulation of the efflux pump is liable for a decrease in ß -amyloid intracellular accumulation and is an important hallmark in Alzheimer's disease (AD). Thus, targeting ß-amyloid clearance by stimulating Pgp could be a useful strategy to prevent Alzheimer's advancement. Currently available drugs provide limited effectiveness and do not assure to cure Alzheimer's disease completely. On the other hand, the current research is now directed towards the development of synthetic or natural based therapeutics which can delay the onset or progression of Alzheimer's disease. Since ancient time medicinal plants such as Withania somnifera, Bacopa monieri, Nerium indicum have been used to prevent neurological disorders including Alzheimer's disease. Till today around 125 Indian medicinal plants have been screened on the basis of ethnopharmacology for their activity against neurological disorders. In this paper, we report bioactives from natural sources which show binding affinity towards the Pgp receptor using ligand based pharmacophore development, virtual screening, molecular docking and molecular dynamics simulation studies for the bioactives possessing acceptable ADME properties. These bioactives can thus be useful to treat Alzheimer's disease.

Modulation of P-glycoprotein function and multidrug resistance in cancer cells by Thai plant extracts.

The effects of ethanol extracts from Thai plants belonging to the families of Annonaceae, Rutaceae, and Zingiberaceae on P-glycoprotein (P-gp) function and multidrug resistance were examined in paclitaxel-resistant HepG2 (PR-HepG2) cells. All the extracts tested, significantly increased the accumulation of [3H]paclitaxel, a P-gp substrate, in the cells. Among nine extracts, Z01 and Z02, extracts from Curcuma comosa and Kaempferia marginata (Zingiberaceae family), respectively, potently increased the accumulation. In addition, Z01 and Z02 increased the accumulation of other P-gp substrates, rhodamine 123 and doxorubicin, in PR-HepG2 cells in a concentration-dependent manner. Increased accumulation of rhodamine 123 and doxorubicin by Z01 and Z02 was also confirmed by confocal laser scanning microscopy. The effect of Z01 and Z02 pretreatment on the expression of MDR1 mRNA was also examined. The expression of MDR1 mRNA was not affected by the treatment of PR-HepG2 cells with these extracts for 48 hours. Cytotoxicity of paclitaxel was examined by XTT and protein assays in the absence and presence of Z02. Z02 potentiated the cytotoxicity of paclitaxel in PR-HepG2 cells. These results suggest that Curcuma comosa and Kaempferia marginata belonging to Zingiberaceae are useful sources to search for new P-gp modulator(s) that can be used to overcome multidrug resistance of cancer cells.

Chemogenomics approaches to rationalizing the mode-of-action of traditional Chinese and Ayurvedic medicines.

Traditional Chinese medicine (TCM) and Ayurveda have been used in humans for thousands of years. While the link to a particular indication has been established in man, the mode-of-action (MOA) of the formulations often remains unknown. In this study, we aim to understand the MOA of formulations used in traditional medicine using an in silico target prediction algorithm, which aims to predict protein targets (and hence MOAs), given the chemical structure of a compound. Following this approach we were able to establish several links between suggested MOAs and experimental evidence. In particular, compounds from the 'tonifying and replenishing medicinal' class from TCM exhibit a hypoglycemic effect which can be related to activity of the ingredients against the Sodium-Glucose Transporters (SGLT) 1 and 2 as well as Protein Tyrosine Phosphatase (PTP). Similar results were obtained for Ayurvedic anticancer drugs. Here, both primary anticancer targets (those directly involved in cancer pathogenesis) such as steroid-5-alpha-reductase 1 and 2 were predicted as well as targets which act synergistically with the primary target, such as the efflux pump P-glycoprotein (P-gp). In addition, we were able to elucidate some targets which may point us to novel MOAs as well as explain side effects. Most notably, GPBAR1, which was predicted as a target for both 'tonifying and replenishing medicinal' and anticancer classes, suggests an influence of the compounds on metabolism. Understanding the MOA of these compounds is beneficial as it provides a resource for NMEs with possibly higher efficacy in the clinic than those identified by single-target biochemical assays.

Clinical evidence of herbal drugs as perpetrators of pharmacokinetic drug interactions.

The use of herbal/botanical products, also referred to as complementary and alternative medicines (CAM), worldwide enjoys increasing popularity. It appears in particular highly prevalent in patient populations already exposed to complex treatment algorithms and polypharmacotherapy, frequently involving narrow therapeutic index drugs. Accordingly, the potential clinical dimension and relevance of herb-drug interactions has received considerable attention over the last years. However, review of pertinent literature indicates that the available clinical evidence in this regard is still limited and sometimes inconclusive. Also, communication of herb-drug interaction data in the biopharmaceutical/medical literature is often complex and confusing, not always unbiased, and in many cases appears not to strive for clear-cut and useful guidance in terms of the clinical relevance of such findings.This systematic review summarizes and interprets the published evidence on clinical herb-drug interaction studies which examined the potential of six popular herbal drugs (Echinacea, garlic, gingko, ginseng, goldenseal, and milk thistle) as perpetrators of pharmacokinetic (PK) drug interactions. Reported effect sizes were systematically categorized according to FDA drug interaction guideline criteria. A total of 66 clinical PK interaction studies, meeting the scope of the present review, were identified. The clinical evidence was found to be most robust and informative for Gingko biloba (GB; 21 studies) and milk thistle/silymarin (MT; 13), and appears still limited for ginseng (9), goldenseal/berberine (GS; 8), garlic (8), and Echinacea (7). Collectively, the available evidence indicates that, at commonly recommended doses, none of these herbs act as potent or moderate inhibitors or inducers of cytochrome P450 (CYP) enzymes or P-glycoprotein (ABCB1). Weak effects in terms of either induction or inhibition were found for GB (presystemic/hepatic CYP3A4 induction/inhibition, CYP2C19 induction at high doses), milk thistle/silymarin (CYP2C9 inhibition), GS/berberine (CYP3A4 and CYP2D6 inhibition), Echinacea (presystemic/hepatic CYP3A4 inhibition/induction, CYP1A2 and CYP2C9 inhibition at high doses). Information was found not always complete for the major drug metabolizing CYP enzymes in the less well-studied herbs and is largely limited to P-glycoprotein (ABCB1) when effects on drug transporters have been investigated.

An update on the ability of St. John's wort to affect the metabolism of other drugs.

INTRODUCTION: Hypericum perforatum (HP), more commonly known as St. John's wort, is a popular medicinal herb used for the treatment of depression. HP affects the pharmacokinetics of many drugs by inducing cytochrome P450 (CYP) isozymes, such as CYP3A4, CYP2C19, CYP2C9, and the P-glycoprotein (P-gp) transporter. AREAS COVERED: This review focuses on drugs that are metabolized by CYP3A4, CYP2C19, CYP2C9 and P-gp as their plasma concentrations show the effects of concomitant use of HP. For the purpose of this review, all electronic databases such as PubMed, Scopus, Google Scholar and Cochrane library were searched to identify in vitro, in vivo or human studies about the effects of HP on the metabolism of drugs. Data collected were published between 1966 and January 2012. EXPERT OPINION: There are a number of drugs whose metabolism is reduced by HP. The authors point out that metabolic interactions between HP and drugs are not always unfavorable and sometimes have benefits (e.g., reduction of irinotecan toxicity and increase in clopidogrel responsiveness). HP does not have a significant influence on the kinetics of drugs such as carbamazepine, ibuprofen and theophylline. The use of HP preparations is not recommended in people who are taking immunosuppressants or cardiovascular drugs. With other medications, it is recommended that practitioners should only use HP preparations with a low hyperforin content and under careful monitoring. It is also recommended that because of the reduction in the bioavailability of oral contraceptives administered concurrently with HP, women who use HP preparations should use additional preventive methods to avoid unintended pregnancy.

Utilizing mobile networks for the detection of clinically relevant interactions between chemotherapy regimens and complementary and alternative medicines.

OBJECTIVES: Patients with cancer who use complementary and alternative medicines (CAMs) in conjunction with chemotherapy treatment are at risk of manifesting anticancer drug-CAM interactions (DCIs), which may lead to negative therapeutic outcomes. This article describes a novel iPhone application developed for the Mobile Internet, called OncoRx-MI, which identifies DCIs of single-agent and multiple-agent chemotherapy regimen (CReg) prescriptions. METHODS: Drug-, CAM-, and DCI-related information was compiled from various hardcopy and softcopy sources, and published literature from PubMed. Overall management plans for the CRegs were then developed. The iPhone Web documents were constructed using Adobe software and programming scripts, and mounted onto a third-party server. DCI searches are based on CReg acronyms, and OncoRx-MI is designed to fit the iPhone screen configuration for improved usability. A small usability study was also carried out and the user feedback presented. RESULTS: OncoRx-MI is able to detect over 2700 interactions between 256 CRegs and 166 CAMs, making up a total of over 4400 DCI pairs. The CAMs are classified into seven categories based on their uses in supportive care, and non-cancer-related CAMs are also included. The majority of the DCIs are pharmacokinetic in nature (79%), involving the induction and inhibition of the cytochrome P450 isozymes and p-glycoprotein. Pharmacodynamic DCIs include hepatotoxicity (39%), altered corticosteroid efficacies (30%), and increased risks of hypoglycemia (4%), hypertensive crisis (2%), bleeding, and serotonin syndrome (1% each). CONCLUSIONS: OncoRx-MI is the first mobile application of its kind that allows searching of DCIs for CRegs through 3G networks, and is intended to improve pharmaceutical care of patients with cancer by assisting health care practitioners in managing CReg interactions in their clinical practices.

Biochemical mechanism of modulation of human P-glycoprotein by stemofoline.

The resistance to chemotherapeutic drugs by cancer cells is considered to be one of the major obstacles for success in the treatment of cancer. A major mechanism underlying this multidrug resistance is the overexpression of P-glycoprotein (P-gp), resulting in insufficient drug delivery to the tumor sites. A previous study has shown that stemofoline, an alkaloid isolated from Stemona burkillii, could enhance the sensitivity of chemotherapeutics in a synergistic fashion. In the present study, we have focused on the effect of stemofoline on the modulation of P-gp function in a multidrug resistant human cervical carcinoma cell line (KB-V1). The effects of stemofoline on a radiolabeled drug, [(3)H]-vinblastine, and fluorescent P-gp substrates, rhodamine 123 and calcein-AM accumulation or retention were investigated to confirm this finding. Stemofoline could increase the accumulation or retention of radiolabeled drugs or fluorescent P-gp substrates in a dose-dependent manner. For additional studies on drug-P-gp binding, P-gp ATPase activity was stimulated by stemofoline in a concentration-dependent manner. More evidence was offered that stemofoline inhibits the effect on photoaffinity labeling of P-gp with [(125)I]-iodoarylazidoprazosin in a concentration-dependent manner. These data indicate that stemofoline may interact directly with P-gp and inhibit P-gp activity, whereas stemofoline has no effect on P-gp expression. Taken together, the results exhibit that stemofoline possesses an effective MDR modulator, and may be used in combination with conventional chemotherapeutic drugs to reverse MDR in cancer cells.

Danshen extract does not alter pharmacokinetics of docetaxel and clopidogrel, reflecting its negligible potential in P-glycoprotein- and cytochrome P4503A-mediated herb-drug interactions.

Danshen (Salvia miltiorrhiza) contains tanshinones, which inhibit P-glycoprotein (P-gp) and the cytochrome P450 (CYP) system. In the present study, we evaluated the possible pharmacokinetic interactions of Danshen extract with docetaxel and clopidogrel in rats. Docetaxel (5 mg/kg intravenously and 40 mg/kg orally) or clopidogrel (30 mg/kg orally) was administered to rats with or without oral co-administration of Danshen (400 mg/kg). Co-administration of Danshen did not affect the plasma concentration profiles and pharmacokinetic parameters of docetaxel and clopidogrel, whereas cyclosporine A, a P-gp and CYP3A inhibitor, significantly influenced the pharmacokinetics of co-administered docetaxel and clopidogrel. Orally administered Danshen had no substantial effect on the pharmacokinetics of docetaxel and clopidogrel, suggesting the negligible safety concern of Danshen in P-gp- and CYP3A-mediated interactions in vivo.

Oxymatrine inhibits development of morphine-induced tolerance associated with decreased expression of P-glycoprotein in rats.

The effect of oxymatrine on the development of tolerance to the antinociceptive effects of morphine was investigated in rats. The degree of tolerance was assessed using the tail-flick test before and after 6 days of twice daily administration of oxymatrine premorphine (10/20/30 mg/kg). High doses of oxymatrine inhibited the development of morphine tolerance (resembling the effect of 7.5 mg/kg of the NMDA receptor antagonist memantine) while also increasing the antinociceptive effects. A high dose of oxymatrine (30 mg/kg) also significantly inhibited the dramatic increase in expression of morphine-induced P-glycoprotein (P-gp), an ATP-dependent efflux pump acting at the blood-brain barrier, by Western blot analysis. Furthermore, these studies suggest that P-gp modulates the development of morphine tolerance while not affecting the magnitude of the analgesic effect of morphine. These results imply that oxymatrine prevention of the development of tolerance of morphine may be related to a considerable inhibition of P-gp expression. In contrast, the authors' data suggest that the mechanism of oxymatrine enhancement of morphine's analgesic effects is not associated with increase in the level of expression of P-gp. However, they believe that their findings can be used by researchers to develop therapies that will allow patients to take morphine without becoming tolerant of its benefits.

The enhancement of vincristine cytotoxicity by combination with feselol.

Urinary bladder cancer is one of the most common cancers worldwide. Human transitional cell carcinoma (TCC) cells are epithelial-like adherent cells originally established from a primary bladder carcinoma. Studies have shown that TCC cells are resistant to some chemotherapeutic agents such as vincristine (VCR). In the present study, the effect of feselol, a sesquiterpene coumarin isolated from the fruits of Ferula badrakema, was investigated on VCR effectiveness. Our results demonstrated that feselol itself did not have any cytotoxic effect on TCC cells. In order to check its combinatorial effects, TCC cells were exposed to various combined concentrations of feselol and VCR. Then, morphological changes were monitored and cytotoxicity was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay for three consequent days. Results showed that the combination of 40 microg/ml VCR with 16 microg/ml feselol increased the cytotoxicity of VCR by 28.32% after 48 h. This effect might be due to inhibition of P-glycoprotein in TCC cells by feselol.

Effect of Thai plant extracts on P-glycoprotein function and viability in paclitaxel-resistant HepG2 cells.

The effects of ethanol extracts from Thai plants on P-glycoprotein (P-gp) function and cell viability were examined using paclitaxel-resistant HepG2 (PR-HepG2) cells. KP018 from Ellipeiopsis cherrevensis and AT80 from Ancistrocladus tectorius increased both rhodamine 123, a typical P-gp substrate, and [(3)H]paclitaxel uptake in PR-HepG2 cells. However, some extracts such as MT80 from Microcos tomentosa increased rhodamine 123, but not [(3)H]paclitaxel, uptake, while MM80 from Micromelum minutum increased only [(3)H]paclitaxel uptake. Thus, the effects of extracts of Thai plants on rhodamine 123 uptake were not necessarily the same as those on [(3)H]paclitaxel uptake. Purified compounds such as bergapten did not affect the uptake of either substrate. KP018, AT80, and MM80 increased [(3)H]paclitaxel uptake and decreased the cell viability in a concentration-dependent manner. Among these extracts, KP018 showed the most potent cytotoxicity. The cytotoxic potency of KP018 on PR-HepG2 cells was similar to that on wild-type HepG2 cells, and was not potentiated by verapamil. At concentrations resulting in no cytotoxicity, AT80 and MM80 potentiated paclitaxel-induced cytotoxicity in PR-HepG2 cells. These results indicate that K018 may be a useful source to search for a new anticancer drug, while AT80 and MM80 may be useful as modulators of P-gp-mediated multidrug resistance in cancer cells.

Effects of Acanthopanax senticosus HARMS extract on drug transport in human intestinal cell line Caco-2.

Acanthopanax senticosus HARMS (AS) is used as a Chinese herbal medicine and as a health supplement in Japan. However, little is known about the interaction between AS and other drugs. In this study, we investigated the effect of AS extract on intestinal drug transporter (P-glycoprotein, or P-gp) and peptide transporter activities in Caco-2 cells. Caco-2 cells were cultured on a culture dish and a permeable membrane for 1-3 weeks. The apical-to-basolateral (A-to-B) transport of digoxin, a P-gp substrate, was significantly increased by the addition of AS extract in a concentration-dependent manner. In contrast, the A-to-B transport of cephalexin, a peptide transporter substrate, was significantly decreased by the addition of AS extract in the same manner. The effects of AS extract addition on the kinetics of the uptake of rhodamine 123, a P-gp substrate, and Gly-Sar, a peptide transporter substrate, were investigated. V (max) for rhodamine 123 uptake was significantly increased by AS extract addition compared with the control, whereas that for Gly-Sar uptake was significantly decreased. On the other hand, K (m) and K (d) for rhodamine 123 and Gly-Sar uptake were not affected. We conducted further investigations to clarify the effect of AS extract addition on P-gp activity. When AS extract was added to the apical side, B-to-A transport of rhodamine 123 was significantly decreased compared with the control. Furthermore, the amount of intracellular rhodamine 123 was increased by AS extract addition compared with the control. These results suggest that P-gp and peptide transporter activities are suppressed by AS extract addition in a non-competitive manner.

Modulation of P-glycoprotein ATPase activity by some phytoconstituents.

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 determining their role in several key pharmacodynamic events.