Lushan Yu

Identification of novel pregnane X receptor activators from traditional Chinese medicines

AIM OF THE STUDY To investigate the ability of traditional Chinese medicines (TCMs) and their bioactive compounds to activate pregnane X receptor (PXR) signalling pathway. MATERIALS AND METHODS We screened ethanol extracts of 28 commonly used TCMs for their capability to induce cytochrome P450 3A4 (CYP3A4) via PXR signalling pathway using a cell-based reporter gene assay combined with RT-PCR analysis. In addition, 34 bioactive components from these TCMs were examined for their potential to activate PXR. RESULTS Our observations showed that 22 ethanol extracts and 8 compounds could activate human PXR and induce CYP3A4 reporter construct in HepG2 cells. Among them, Ginkgo biloba, Ligusticum chuanxiong, Chinese angelica, prepared Rehmannia root, Epimedium brevicornum, Atractylodes macrocephala, Schisandra chinensis, Paeonia lactiflora, Ophiopogon japonicus, Polygonum multiflorum, Coptis chinensis, Artemisia scoparia, Trichosanthes kirilowii, Silybum marianum, Gardenia fruit and Lycium chinense could strongly trans-activate PXR. Moreover, ligustilide, schisantherin A, berberine hydrochloride and trans-resveratrol were identified for the first time as efficacious PXR agonists. CONCLUSIONS Twenty-two TCM ethanol extracts and eight bioactive compounds could activate PXR signalling pathway and induce CYP3A4 reporter gene. Therefore, caution should be taken when these PXR activators are used in combination with prescribed drugs metabolized by CYP3A4.

Stereoselective binding of chiral drugs to plasma proteins.

Chiral drugs show distinct biochemical and pharmacological behaviors in the human body. The binding of chiral drugs to plasma proteins usually exhibits stereoselectivity, which has a far-reaching influence on their pharmacological activities and pharmacokinetic profiles. In this review, the stereoselective binding of chiral drugs to human serum albumin (HSA), α1-acid glycoprotein (AGP) and lipoprotein, three most important proteins in human plasma, are detailed. Furthermore, the application of AGP variants and recombinant fragments of HSA for studying enantiomer binding properties is also discussed. Apart from the stereoselectivity of enantiomer-protein binding, enantiomer-enantiomer interactions that may induce allosteric effects are also described. Additionally, the techniques and methods used to determine drug-protein binding parameters are briefly reviewed.

Pharmacokinetic drug interaction profile of omeprazole with adverse consequences and clinical risk management.

Background Omeprazole, a proton pump inhibitor (PPI), is widely used for the treatment of dyspepsia, peptic ulcer, gastroesophageal reflux disease, and functional dyspepsia. Polypharmacy is common in patients receiving omeprazole. Drug toxicity and treatment failure resulting from inappropriate combination therapy with omeprazole have been reported sporadically. Systematic review has not been available to address the pharmacokinetic drug-drug interaction (DDI) profile of omeprazole with adverse consequences, the factors determining the degree of DDI between omeprazole and comedication, and the corresponding clinical risk management. Methods Literature was identified by performing a PubMed search covering the period from January 1988 to March 2013. The full text of each article was critically reviewed, and data interpretation was performed. Results Omeprazole has actual adverse influences on the pharmacokinetics of medications such as diazepam, carbamazepine, clozapine, indinavir, nelfinavir, atazanavir, rilpivirine, methotrexate, tacrolimus, mycophenolate mofetil, clopidogrel, digoxin, itraconazole, posaconazole, and oral iron supplementation. Meanwhile, low efficacy of omeprazole treatment would be anticipated, as omeprazole elimination could be significantly induced by comedicated efavirenz and herb medicines such as St John’s wort, Ginkgo biloba, and yin zhi huang. The mechanism for DDI involves induction or inhibition of cytochrome P450, inhibition of P-glycoprotein or breast cancer resistance protein-mediated drug transport, and inhibition of oral absorption by gastric acid suppression. Sometimes, DDIs of omeprazole do not exhibit a PPI class effect. Other suitable PPIs or histamine 2 antagonists may be therapeutic alternatives that can be used to avoid adverse consequences. The degree of DDIs associated with omeprazole and clinical outcomes depend on factors such as genotype status of CYP2C19 and CYP1A2, ethnicity, dose and treatment course of precipitant omeprazole, pharmaceutical formulation of object drug (eg, mycophenolate mofetil versus enteric-coated mycophenolate sodium), other concomitant medication (eg, omeprazole-indinavir versus omeprazole–indinavir–ritonavir), and administration schedule (eg, intensified dosing of mycophenolate mofetil versus standard dosing). Conclusion Despite the fact that omeprazole is one of the most widely prescribed drugs internationally, clinical professionals should enhance clinical risk management on adverse DDIs associated with omeprazole and ensure safe combination use of omeprazole by rationally prescribing alternatives, checking the appropriateness of physician orders before dispensing, and performing therapeutic drug monitoring.

Pharmacokinetic drug interactions with clopidogrel: updated review and risk management in combination therapy.

Background Coprescribing of clopidogrel and other drugs is common. Available reviews have addressed the drug–drug interactions (DDIs) when clopidogrel is as an object drug, or focused on combination use of clopidogrel and a special class of drugs. Clinicians may still be ignorant of those DDIs when clopidogrel is a precipitant drug, the factors determining the degree of DDIs, and corresponding risk management. Methods A literature search was performed using PubMed, MEDLINE, Web of Science, and the Cochrane Library to analyze the pharmacokinetic DDIs of clopidogrel and new P2Y12 receptor inhibitors. Results Clopidogrel affects the pharmacokinetics of cerivastatin, repaglinide, ferulic acid, sibutramine, efavirenz, and omeprazole. Low efficacy of clopidogrel is anticipated in the presence of omeprazole, esomeprazole, morphine, grapefruit juice, scutellarin, fluoxetine, azole antifungals, calcium channel blockers, sulfonylureas, and ritonavir. Augmented antiplatelet effects are anticipated when clopidogrel is coprescribed with aspirin, curcumin, cyclosporin, St John’s wort, rifampicin, and angiotensin-converting enzyme inhibitors. The factors determining the degree of DDIs with clopidogrel include genetic status (eg, cytochrome P540 [CYP]2B6*6, CYP2C19 polymorphism, CYP3A5*3, CYP3A4*1G, and CYP1A2-163C.A), species differences, and dose strength. The DDI risk does not exhibit a class effect, eg, the effects of clopidogrel on cerivastatin versus other statins, the effects of proton pump inhibitors on clopidogrel (omeprazole, esomeprazole versus pantoprazole, rabeprazole), the effects of rifampicin on clopidogrel versus ticagrelor and prasugrel, and the effects of calcium channel blockers on clopidogrel (amlodipine versus P-glycoprotein-inhibiting calcium channel blockers). The mechanism of the DDIs with clopidogrel involves modulating CYP enzymes (eg, CYP2B6, CYP2C8, CYP2C19, and CYP3A4), paraoxonase-1, hepatic carboxylesterase 1, P-glycoprotein, and organic anion transporter family member 1B1. Conclusion Effective and safe clopidogrel combination therapy can be achieved by increasing the awareness of potential changes in efficacy and toxicity, rationally selecting alternatives, tailoring drug therapy based on genotype, checking the appropriateness of physician orders, and performing therapeutic monitoring.

Stereoselectivity of chiral drug transport: a focus on enantiomer-transporter interaction.

Abstract Drug transporters and drug metabolism enzymes govern drug absorption, distribution, metabolism and elimination. Many literature works presenting important aspects related to stereochemistry of drug metabolism are available. However, there is very little literature on stereoselectivity of chiral drug transport and enantiomer–transporter interaction. In recent years, the experimental research within this field showed good momentum. Herein, an up-to-date review on this topic was presented. Breast Cancer Resistance Protein (BCRP), Multidrug Resistance Proteins (MRP), P-glycoprotein (P-gp), Organic Anion Transporters (OATs), Organic Anion Transporting Polypeptides (OATPs), Organic Cation Transporters (OCTs), Peptide Transport Proteins (PepTs), Human Proton-Coupled Folate Transporter (PCFT) and Multidrug and Toxic Extrusion Proteins (MATEs), have been reported to exhibit either positive or negative enantio-selective substrate recognition. The approaches utilized to study chirality in enantiomer–transporter interaction include inhibition experiments of specific transporters in cell models (e.g. Caco-2 cells), transport study using drug resistance cell lines or transgenic cell lines expressing transporters in wild type or variant, the use of transporter knockout mice, pharmacokinetics association of single nucleotide polymorphism in transporters, pharmacokinetic interaction study of racemate in the presence of specific transporter inhibitor or inducer, molecule cellular membrane affinity chromatography and pharmacophore modeling. Enantiomer–enantiomer interactions exist in chiral transport. The strength and/or enantiomeric preference of stereoselectivity may be species or tissue-specific, concentration-dependent and transporter family member-dependent. Modulation of specific drug transporter by pure enantiomers might exhibit opposite stereoselectivity. Further studies with integrated approaches will open up new horizons in stereochemistry of pharmacokinetics.

Epigenetic activation of the drug transporter OCT2 sensitizes renal cell carcinoma to oxaliplatin

The expression of drug transporter OCT2 is suppressed in renal cell carcinoma, and targeting this pathway sensitizes the tumor to oxaliplatin. Opening a door into cancer cells Renal cell carcinoma is a common cancer that is often resistant to chemotherapy. To address this, Liu et al. investigated the role of OCT2, a protein that normally transports oxaliplatin, a common chemotherapy drug, into cells. The authors found that OCT2 was epigenetically silenced in renal cancer and figured out the underlying mechanism, then designed a combination therapy with decitabine, a drug that reverses epigenetic silencing of OCT2, followed by oxaliplatin, and demonstrated its effectiveness in mouse models. The researchers also found that MATE-2K, another transporter that normally pumps oxaliplatin out of renal cells into the urine, is repressed in cancer cells regardless of decitabine treatment, so oxaliplatin accumulates in treated cancer cells, but not in the surrounding normal tissues. Renal cell carcinoma (RCC) is known for its multidrug resistance. Using data obtained from the cancer transcriptome database Oncomine and the proteome database The Human Protein Atlas, we identified the repression of organic cation transporter OCT2 as a potential factor contributing to oxaliplatin resistance in RCC. By analyzing OCT2 expression in collected patient tissues and commercial tissue microarray specimens, we demonstrated OCT2 repression in RCC at both transcription and protein levels. Epigenetic analysis revealed that the repressed OCT2 promoter in RCC is characterized by hypermethylated CpG islands and the absence of H3K4 methylation. Further mechanistic studies showed that DNA hypermethylation blocked MYC activation of OCT2 by disrupting its interaction with the E-Box motif, which prevented MYC from recruiting MLL1 to catalyze H3K4me3 at the OCT2 promoter and resulted in repressed OCT2 transcription. Targeting this mechanism, we designed a sequential combination therapy and demonstrated that epigenetic activation of OCT2 by decitabine sensitizes RCC cells to oxaliplatin both in vitro and in xenografts. Our study highlights the potential of translating “omics” data into the development of targeted therapies.

Interaction of five anthraquinones from rhubarb with human organic anion transporter 1 (SLC22A6) and 3 (SLC22A8) and drug–drug interaction in rats

ETHNOPHARMACOLOGICAL RELEVANCE Rhubarb is a well-known traditional Chinese medicine and has been used in China for thousands of years. Anthraquinone derivatives including rhein, emodin, aloe-emodin, chrysophanol and physcion are the important components in rhubarb. MATERIALS AND METHODS Here we studied the interaction of five anthraquinone derivatives with human renal organic anion transporter 1 (hOAT1) and hOAT3 stably expressed in cells, and interaction of rhein or rhubarb extract (RE) with furosemide (FS, substrate of OATs) in rats. RESULTS Uptake of 6-carboxyl fluorescein via hOAT1 and fluorescein via hOAT3 were markedly inhibited by rhein, emodin and aloe-emodin, and slightly inhibited by chrysophanol and physcion. The estimated IC₅₀ values for rhein, emodin, aloe-emodin and probenecid (typical inhibitor of hOAT1 and hOAT3) were 0.23, 0.61, 2.29 and 18.34 μM for hOAT1, and 0.08, 1.22, 5.37 and 5.83 μM for hOAT3, respectively. Furthermore, the data from the cellular accumulation assay indicated that these five compounds were not substrates of hOAT1 or hOAT3. Pharmacokinetic interaction between rhein and FS in rats showed that area under the curve (AUC₀-t) for FS was increased by 65% when coadministrated with rhein. RE was also used to interact with FS in rats and results showed that AUC₀-t of FS was increased by 32% and by 52% when coadministrated with single-dose or multiple-dose of RE, respectively. CONCLUSIONS These findings suggested that five anthraquinones inhibited hOAT1 and hOAT3, but these compounds were not transported by hOAT1 or hOAT3. Furthermore, rhein or RE, might cause drug-drug interaction when coadministrated with substrates of OAT1 or OAT3 in vivo.

Application of a liquid chromatography-tandem mass spectrometry method to the pharmacokinetics, tissue distribution and excretion studies of Dactylicapnos scandens in rats

The herbal ingredients of isocorydine and protopine were isolated from Dactylicapnos scandens. This study was aimed at developing a liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method to quantify isocorydine and protopine in rat plasma and tissues for pharmacokinetic, tissue distribution and excretion studies. Biological samples were processed with ethyl acetate extraction, and corydaline was chosen as the internal standard (IS). The analytes were separated by a C(18) column and detected with a triple quadrupole mass spectrometer using positive ion ESI in the multiple reaction monitoring (MRM) mode. The MS/MS ion transitions monitored were m/z 342.0→278.9 for isocorydine, 354.1→188.0 for protopine and 370.0→192.0 for IS, respectively. Excellent linearity was observed over the concentration range between 10 and 3000 ng/mL for isocorydine and 10-300 ng/mL for protopine. The lower limit of quantification (LLOQ) was 10 ng/mL for both isocorydine and protopine. This novel method was rapid, accurate, high sensitive and high selective. It was successfully applied to the pharmacokinetic, tissue distribution and excretion studies of D. scandens. These preclinical data of D. scandens would be useful for the clinical reference.

Oestrogen sulfotransferase ablation sensitizes mice to sepsis

Sepsis is the hosts deleterious systemic inflammatory response to microbial infections. Here we report an essential role for the estrogen sulfotransferase (EST or SULT1E1), a conjugating enzyme that sulfonates and deactivates estrogens, in sepsis response. Both the cecal ligation and puncture (CLP) and lipopolysacharide (LPS) models of sepsis induce the expression of EST and compromise the activity of estrogen, an anti-inflammatory hormone. Surprisingly, EST ablation sensitizes mice to sepsis-induced death. Mechanistically, EST ablation attenuates sepsis-induced inflammatory responses due to compromised estrogen deactivation, leading to increased sepsis lethality. In contrast, transgenic overexpression of EST promotes estrogen deactivation and sensitizes mice to CLP-induced inflammatory response. The induction of EST by sepsis is NF-κB dependent and EST is a NF-κB target gene. The reciprocal regulation of inflammation and EST may represent a yet to be explored mechanism of endocrine regulation of inflammation, which has an impact on the clinical outcome of sepsis.

Cyclosporin A affects the bioavailability of ginkgolic acids via inhibition of P-gp and BCRP.

Ginkgolic acids (GAs) in natural product Ginkgobiloba L. are the pharmacological active but also toxic components. Two compounds, GA (C15:1) and GA (C17:1) are the most abundant GAs. In this study, several in vitro and in vivo models were applied to investigate transport mechanism of GAs. A rapid and sensitive LC-MS/MS method for the simultaneous determination of GA (C15:1) and GA (C17:1) was applied to analyze the biological specimens. The Papp(AP→BL) values of GA (C15:1) and GA (C17:1) were 1.66-2.13×10(-)(6)cm/s and 1.34-1.85×10(-)(6)cm/s determined using MDCK and MDCK-MDR1 cell monolayers, respectively. The Papp(BL→AP) were remarkably greater in the MDCK-MDR1 cell line, which were 6.77-11.2×10(-)(6)cm/s for GA (C15:1) and 4.73-5.15×10(-)(6)cm/s for GA (C17:1). Similar results were obtained in LLC-PK1 and LLC-PK1-BCRP cell monolayers. The net efflux ratio of GA (C15:1) and GA (C17:1) in both cell models was greater than 2 and markedly reduced by the presence of Cyclosporin A (CsA) or GF120918, inhibitors of P-gp and BCRP, suggesting that GAs are P-gp and BCRP substrates. The results from a rat bioavailability study also showed that co-administrating CsA intravenously (20mg/kg) could significantly increase GA (C15:1) and GA (C17:1) AUC0-t by 1.46-fold and 1.53-fold and brain concentration levels of 1.43-fold and 1.51-fold, respectively, due to the inhibition of P-gp and BCRP efflux transporters by CsA.