Telmisartan increases systemic exposure to rosuvastatin after single and multiple doses, and in vitro studies show telmisartan inhibits ABCG2-mediated transport of rosuvastatin.

PURPOSE: The ATP-binding cassette transporter G2 (ABCG2) plays an important role in the disposition of rosuvastatin. Telmisartan, a selective angiotension-II type 1 (AT1) receptor blocker, inhibits the transport capacity of ABCG2, which may result in drug interactions. This study investigated the pharmacokinetic interaction between rosuvastatin and telmisartan and the potential mechanism. METHODS: In this two-phase fixed-order design study, healthy subjects received single doses of 10 mg rosuvastatin at baseline and after telmisartan 40 mg daily for 14 days. Patients with hyperlipidaemia who had been taking rosuvastatin 10 mg daily for at least 4 weeks were given telmisartan 40 mg daily for 14 days together with rosuvastatin. Plasma concentrations of rosuvastatin were measured over 24 h before and after telmisartan administration. In vitro experiments using a bidirectional transport assay were performed to investigate the involvement of ABCG2 in the interaction. RESULTS: Co-administration of telmisartan significantly increased the maximum plasma concentration (C max) and the area under the plasma concentration-time curve (AUC) of rosuvastatin by 71 and 26 %, respectively. The T max values were reduced after administration of telmisartan. There was no significant difference in the interaction of rosuvastatin with telmisartan between healthy volunteers and patients receiving long-term rosuvastatin therapy or among subjects with the different ABCG2 421 C>A genotypes. The in vitro experiment demonstrated that telmisartan inhibited ABCG2-mediated efflux of rosuvastatin. CONCLUSION: This study demonstrated that telmisartan significantly increased the systemic exposure to rosuvastatin after single and multiple doses.

Effect of common polymorphisms of the farnesoid X receptor and bile acid transporters on the pharmacokinetics of ursodeoxycholic acid.

Ursodeoxycholic acid (UDCA), a natural, dihydroxy bile acid, promotes gallstone dissolution and has been attributed with several other beneficial effects. The farnesoid X receptor (FXR) may influence the pharmacokinetics of UDCA by modulating the expression of bile acid transporters. This exploratory study examined whether common functional polymorphisms in FXR and in bile acid transporter genes affect the pharmacokinetics of exogenous UDCA. Polymorphisms in genes for transporters involved in bile acid transport, solute carrier organic anion 1B1 (SLCO1B1) 388A>G and 521T>C, solute carrier 10A1 (SLC10A1) 800 C>T and ATP-binding cassette B11 (ABCB11) 1331T>C, and the FXR -1G>T polymorphism were genotyped in 26 male Chinese subjects who ingested single oral 500-mg doses of UDCA. Plasma concentrations of UDCA and its major conjugate metabolite glycoursodeoxycholic acid (GUDCA) were determined. The mean systemic exposure of UDCA was higher in the five subjects with one copy of the FXR -1G>T variant allele than in those homozygous for the wild-type allele (n = 21) (AUC0-24 h : 38.5 ± 28.2 vs. 20.9 ± 8.0 µg h/mL, P = 0.021), but this difference appeared mainly due to one outlier with the -1GT genotype and elevated baseline and post-treatment UDCA concentrations. After excluding the outlier, body weight was the only factor associated with plasma concentrations of UDCA and there were no significant associations with the other polymorphisms examined. None of the polymorphisms affected the pharmacokinetics of GUDCA. This study showed that the common polymorphisms in bile acid transporters had no significant effect on the pharmacokinetics of exogenous UDCA but an effect of the FXR polymorphism cannot be excluded.

Pharmacokinetic interactions among major bioactive components in Radix Scutellariae via metabolic competition.

Baicalein (B), wogonin (W) and oroxylin A (OA) are major components in Radix Scutellariae with similar pharmacokinetic properties. Due to the co-presence of these three flavones in herbal formulations for Radix Scutellariae, they are likely consumed together. The aim of this study is to investigate whether the pharmacokinetics of individual flavones is influenced by each other and the underlying mechanism of the interaction. Various systems were utilized in the current study including a rat in vivo study, a Caco-2 cell monolayer model and a rat in situ single-pass intestinal perfusion as well as in vitro enzymatic kinetics studies. The B, W and OA given singly as well as in a mixture were administered and the corresponding pharmacokinetic parameters were calculated and compared. After co-administration of the three flavones to rats, OA absorption increased significantly in comparison with when OA was administered alone. Mechanistic studies on the Caco-2 cell monolayer and rat in situ single-pass intestinal perfusion models revealed that co-administration of B, W and OA could significantly enhance their absorption and decrease the extent of phase II metabolism. Further in vitro enzymatic study and a transport study in transfected MDCK cells revealed that metabolic competition rather than membrane transporters might contribute to the pharmacokinetic interactions. The co-presence of multiple active components would result in metabolic interactions, which may induce further changes in pharmacodynamics.

Population pharmacokinetics and IVIVC for mesalazine enteric-coated tablets.

Although in-vivo bioequivalence (BE) study serves as a golden standard for establishing interchangeability of oral dosage forms, it remains challenging for products with high inter-subject variability such as mesalazine enteric-coated tablet to fulfil the BE criteria set by regulatory authorities. Mesalazine, as a BCS class IV drug, targets to be delivered to distal ileum or colon with a pH-sensitive polymer coating for the remission of ulcerative colitis. Through population pharmacokinetic (PK) analysis and in-vitro in-vivo correlation (IVIVC) modeling on the dissolution and BE data of a generic enteric-coated product (EM) and its reference Salofalk® 250 mg tablet (SM), we for the first time revealed the underlying mechanism of the high inter-subject variability for such delayed-release formulation. It was also noted that the in-vivo start time of absorption (Ts) for EM and SM was positively correlated with their in-vitro lag time (Tlag) under the USP three-stage dissolution condition and reversely correlated with their in-vivo bioavailability. The varied oral bioavailability of mesalazine enteric-coated tablet was mainly due to the varied N-acetyltransferase activities along GI tract. Although such extensive intestinal first-pass metabolism with large individual differences led to a significant variation of mesalazine Cmax (coefficient of variation: 60-63.5%) and AUC0-t (coefficient of variation: 37.5-46.9%), the corresponding variations in the total absorbed mesalazine (mesalazine and its metabolite N-acetyl mesalazine) were significantly reduced by 12 to 45%. Since the BE purpose for mesalazine enteric-coated tablet focused on their comparable safety profiles, total absorbed mesalazine was recommended to be adopted for the development of the IVIVC model and BE evaluation for EM. All in all, our model-based approach has not only successfully identified the key factors that affect the BE of EM to guide its further formulation optimization, but also demonstrated the indispensable role of modeling in the development of generic pharmaceutical product at its early stages.

Nitrile assisted, Brønsted acid catalyzed regio and stereoselective diarylphosphonylation of allyl silyl ethers.

We have discovered a mild, catalytic protocol for the regio- and stereoselective synthesis of trisubstituted allyl diarylphosphonates from the corresponding disubstituted allyl silyl ethers, circumventing the challenges related to the preparation and availability of stereodefined trisubstituted olefins. A closely related arylation reaction was also discovered during the methodology development. By simply switching the reaction medium, high phosphonylation/arylation ratios and vice versa can be achieved. This may not be a direct result of changing solvent polarity. The allyl diarylphosphonates were evaluated as carboxylesterase inhibitors, and the screening results revealed that the inhibitory efficiency is highly related to the choice of alkenes and aryl substituents.

Pharmacokinetics and brain dispositions of tacrine and its major bioactive monohydroxylated metabolites in rats.

The current study aims to investigate the pharmacokinetics and brain disposition of tacrine and its three major bioactive monohydroxylated metabolites (1-hydroxytacrine, 2-hydroxytacrine and 4-hydroxytacrine). An assay for simultaneous quantification of tacrine and three above metabolites in rat plasma and brain tissue was developed. Four analytes together with internal standard were extracted from rat plasma or brain tissue homogenate by liquid-liquid extraction using ethyl acetate. Baseline separation of the four studied compounds was achieved by a Thermo Hypersil BDS C(18) column with gradient elution using acetonitrile and ammonium formate-triethylamine (pH 4.0) under fluorescence detection. Extraction recoveries of all analytes ranged from 82.1% to 93.2% in both rat plasma and brain tissue. The intra- and inter-day precision and accuracy of each analyte at lower limit of quantification (LLOQ) and three quality control (QC) concentrations (low, middle and high) was within 12% RSD and within 11% bias in both biological matrices. The LLOQ for tacrine, 1-hydroxytacrine, 2-hydroxytacrine and 4-hydroxytacrine were found to be 2.5, 6.7, 2.1 and 2.1 ng/ml in plasma, and 12.3, 33.5, 10.6 and 10.5 ng/g in brain tissue, respectively. All four analytes were stable during analysis. The developed method provides a simple, sensitive and reproducible procedure for pharmacokinetics and brain disposition study of tacrine and its three major metabolites in rats after oral administration of tacrine. Pharmacokinetic study demonstrated that tacrine could be quickly absorbed and extensively metabolized to its monohydroxylated metabolites in vivo. In addition, rat brain disposition study showed that tacrine and its monohydroxylated metabolites were evenly distributed in different brain regions except for a slight lower concentration of tacrine in olfactory region. Moreover, tacrine and 4-hydroxytacrine exhibited a much higher brain-to-plasma ratio than that of 1-hydroxytacrine and 2-hydroxytacrine.

Investigation of the disposition of loxapine, amoxapine and their hydroxylated metabolites in different brain regions, CSF and plasma of rat by LC-MS/MS.

Loxapine represents an interesting example of old "new" drug and is recently drawing attention for its novel inhalation formulation for the treatment of both psychiatric and non-psychiatric disorders. It is extensively metabolized to several active metabolites with diverging pharmacological properties. To further pursue the contribution of metabolites to the overall outcome after loxapine administration, quantification of both loxapine and its active metabolites is essential. The current study developed a rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the simultaneous quantification of loxapine and its five metabolites (amoxapine, 7-hydroxy-loxapine, 8-hydroxy-loxapine, 7-hydroxy-amoxapine and 8-hydroxy-amoxapine) in rat brain tissues, plasma and cerebrospinal fluid (CSF). By evaluating the effects of perchloric acid and methanol on analyte recovery, the extraction methods were optimized and only small amounts of sample (100 µl for plasma and less than 100mg for brain tissue) were required. The lower limits of quantification (LLOQs) in brain tissue were 3 ng/g for loxapine and amoxapine and 5 ng/g for the four hydroxylated metabolites of loxapine. The LLOQs were 1 ng/ml for loxapine and amoxapine and 2 ng/ml for the four hydroxylated metabolites in plasma, and 10 ng/ml for all analytes in CSF. The developed method was applied to a pharmacokinetic study on rats treated with a low-dose loxapine by oral administration. Four hours after loxapine dosing, high levels of 7-hydroxy-loxapine were found throughout the ten brain regions examined (68-124 ng/g), while only trace amount of loxapine was measured in brain (<5 ng/g) and plasma (<3 ng/ml). The method provides a useful tool for both preclinical and clinical investigations on the dispositions of loxapine and its metabolites, which would help to elucidate their roles in neurotherapeutics.

Comparison of intestinal absorption and disposition of structurally similar bioactive flavones in Radix Scutellariae.

Radix Scutellariae is a commonly used herbal medicine. Baicalein, wogonin, and oroxylin A are three major bioactive flavones in Radix Scutellariae and share similar chemical structures. The intestinal absorption and disposition of baicalein have been systematically investigated by our group before. In this study, the intestinal absorption and disposition of wogonin and oroxylin A were further explored and compared with the profiles of baicalein to find potential structure-activity relationship. Absorptive models including Caco-2 cell monolayer model and rat in situ single-pass intestinal perfusion model as well as in vitro enzymatic kinetic study were employed in the current study. The absorption of baicalein, wogonin, and oroxylin A were favorable with wogonin showing the highest permeability based on two absorptive models. However, three flavones underwent a fast and extensive phase II metabolism. The intestinal metabolism of three flavones exhibited species difference between human and rat. Oroxylin A demonstrated the highest intrinsic clearance of glucuronidation among three flavones. The multidrug resistance proteins might be involved in the efflux of their intracellularly formed conjugated metabolites. The pathway of intestinal absorption and disposition of B, W, and OA was similar. However, the extent of permeability and metabolism was different among three flavones which might be due to the number and position of the hydroxyl group.

In vitro and in situ evaluation of herb-drug interactions during intestinal metabolism and absorption of baicalein.

ETHNOPHARMACOLOGICAL RELEVANCE: Baicalein (B), a bioactive flavone isolated from the root of a traditional Chinese medicinal herb Scutellaria baicalensis Georgi, was found to undergo extensive intestinal Phase II metabolism during its absorption process. Compounds sharing the same metabolic pathways with B or being inhibitors of enzymes UGT and SULT are expected to interfere with the metabolism of B leading to alteration of the absorption of B. The present study aims to identify potential intestinal absorption and metabolism interactions between B and four selected compounds, namely acetaminophen (APAP), (-)-epicatechin (EC), piperine (PIP) and curcumin (CUR) using in vitro and in situ models. MATERIALS AND METHODS: Three in vitro and one in situ methods were employed to investigate the effect of selected compounds on the metabolism and absorption on B. Incubation studies using rat intestinal s9 and Caco-2 cell lysate were used to study the effect of selected compounds on glucuronidation and sulfation of B. Sigmoidal dose-response curves were plotted and IC(50) values were estimated. Apical to basolateral absorption study using Caco-2 cell monolayer model was also employed to study the effect of selected compounds on absorption of B. The most potent inhibitor identified was selected to further investigate its potential herb-drug interaction with B using in situ rat intestinal perfusion model. LC/MS/MS was used for the analysis of B and its metabolites in collected samples. RESULTS: It was found that all the four selected compounds could produce a dose-dependent inhibition on the glucuronidation and sulfation of B. Moreover, the presence of CUR and high-dose EC demonstrated a subsequent increase in the absorption of B. In general, the order of potency on glucuronidation inhibition is: CUR>PIP>EC>APAP; while the potency order on sulfation inhibition is: CUR>EC>PIP>APAP. CUR was selected to further study its in vivo effect on B using in situ rat intestinal perfusion model. It was found that CUR could significantly increase the absorption of B via the inhibition on formation of its metabolites. CONCLUSIONS: Our findings indicated that the intestinal metabolism of B could be inhibited by all the selected compounds with CUR being the most potent inhibitor, which could result in subsequent increase of absorption of B. The current study had significant implications for further investigation on the in vivo evaluations of the herb-drug and herb-herb interactions between B and selected compounds, especially CUR.

Simultaneous measurement of S-warfarin, R-warfarin, S-7-hydroxywarfarin and R-7-hydroxywarfarin in human plasma by liquid chromatography-tandem mass spectrometry.

Clinically used anticoagulant warfarin is usually available as a racemic mixture of S- and R-warfarin that are both metabolized mainly by cytochrome P450 isoenzymes. Determination of warfarin enantiomers and their enantiomeric 7-hydroxywarfarin (7-OH-warfarin) metabolites in the human plasma sample allows probing of cytochrome P450 isoenzyme activities and detection of ingestion of warfarin-containing products for the investigation of unexplained bleeding. The present study aims to develop a sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous detection of S-warfarin, R-warfarin, S-7-OH-warfarin and R-7-OH-warfarin in human plasma. Plasma samples were extracted with mixed-mode cation-exchange (MCX) cartridge with recoveries of greater than 87.0% for all four analytes. The selectivity of 7-OH-warfarin from other monohydroxylated warfarin metabolites such as 4'-, 6-, 8- and 10-hydroxywarfarins using a Chirobiotic V chiral column and multiple reaction monitoring (MRM) was addressed. The developed LC-MS/MS method is simple, specific and has been fully validated with satisfactory accuracy and adequate reproducibility with limit of quantification (LOQ) of 5 ng/ml for all four analytes. The method was successfully applied to analyze the steady state plasma concentrations of the four analytes in 30 patients.

Simultaneous quantification of active components in the herbs and products of Si-Wu-Tang by high performance liquid chromatography-mass spectrometry.

Si-Wu-Tang (SWT), comprising Paeoniae, Angelicae, Chuanxiong and Rehmanniae, is one of the most popular Traditional Chinese Medicine (TCM) formulae for woman's health. Data mining from the available Chinese and English literatures indicated that the major bioactive components of SWT consist of paeoniflorin, paeonol, gallic acid, ferulic acid, Z-ligustilide, ligustrazine, butylphthalide, senkyunolide A and catalpol. Since content determination of the marker compounds is generally considered as an initial step for quality control of TCM product, a high performance liquid chromatography-mass spectrometric method employing both positive and negative electrospray ionization was developed for the simultaneous determination of the nine identified compounds in the raw herbs and products of SWT. The LOQ of the developed assay method for the tested components was 10ng/ml for ligustrazine, 200ng/ml for catalpol, and 100ng/ml for the other seven compounds. The intra-day and inter-day variations of the current assay were within 17.5%. Paeoniflorin, ferulic acid, gallic acid, Z-ligustilide and senkyunolide A were found in all SWT products investigated. Variations in the contents of the studied compounds were observed among batches of raw herbs and SWT products. The currently developed method provides a sensitive and rapid quantification approach that can be useful in the quality control of raw herbs and products of SWT.

Analytical application of acetate anion in negative electrospray ionization mass spectrometry for the analysis of triterpenoid saponins--ginsenosides.

Ginsenosides containing different numbers of glycosyl groups can be easily differentiated based on the formation of characteristic ginsenoside-acetate adduct anions and deprotonated ginsenosides generated by electrospray ionization (ESI) of methanolic solutions of ginsenosides (M) and ammonium acetate (NH4OAc). Ginsenosides containing two glycosyl groups gave a characteristic mass spectral pattern consisting of [M+2OAc]2-, [M-H+OAc]2- and [M-2H]2- ions with m/z values differing by 30 Th, while this mass spectral pattern was not observed for ginsenosides containing one glycosyl group. Formation of [M+2OAc]2- was influenced by the chain length of glycosyl groups and was used to differentiate the ginsenosides containing different combinations of monosaccharide and disaccharide units in the glycosyl groups. Under identical collisional activation conditions, [M+OAc]-, [M-H+OAc]2- and [M+2OAc]2- underwent proton abstractions predominantly to generate [M-H]-, [M-2H]2- and [M-H+OAc]2- ions, respectively. The ion intensity ratios, I[M-H](-/I) [M+OAc]-, I[M-2H](2-/I) [M-H+2OAc]2- and I[M-H+OAc](2-/I) [M+OAc]2-, being sensitive to the structural differences of ginsenosides, could differentiate the isomeric ginsenosides, including (i) Rf, F11 and Rg1, (ii) Rd and Re, and (iii) Rb2 and Rc. Additionally, NH4OAc was found to enhance the sensitivity of detection of ginsenosides in the form of [M-H]- down to the femtomole level.