Dafang Zhong

Fasiglifam (TAK-875) Inhibits Hepatobiliary Transporters: A Possible Factor Contributing to Fasiglifam-induced Liver Injury

Fasiglifam (TAK-875), a selective G-protein–coupled receptor 40 agonist, was developed for the treatment of type 2 diabetes mellitus; however, its development was terminated in phase III clinical trials because of liver safety concerns. Our preliminary study indicated that intravenous administration of 100 mg/kg of TAK-875 increased the serum total bile acid concentration by 3 to 4 times and total bilirubin levels by 1.5 to 2.6 times in rats. In the present study, we examined the inhibitory effects of TAK-875 on hepatobiliary transporters to explore the mechanisms underlying its hepatotoxicity. TAK-875 decreased the biliary excretion index and the in vitro biliary clearance of d8-taurocholic acid in sandwich-cultured rat hepatocytes, suggesting that TAK-875 impaired biliary excretion of bile acids, possibly by inhibiting bile salt export pump (Bsep). TAK-875 inhibited the efflux transporter multidrug resistance-associated protein 2 (Mrp2) in rat hepatocytes using 5 (and 6)-carboxy-2′,7′-dichlorofluorescein as a substrate. Inhibition of MRP2 was further confirmed by reduced transport of vinblastine in Madin-Darby canine kidney cells overexpressing MRP2 with IC50 values of 2.41 μM. TAK-875 also inhibited the major bile acid uptake transporter Na+/taurocholate cotransporting polypeptide (Ntcp), which transports d8-taurocholic acid into rat hepatocytes, with an IC50 value of 10.9 μM. TAK-875 significantly inhibited atorvastatin uptake in organic anion transporter protein (OATP) 1B1 and OATP1B3 cells with IC50 values of 2.28 and 3.98 μM, respectively. These results indicate that TAK-875 inhibited the efflux transporter MRP2/Mrp2 and uptake transporters Ntcp and OATP/Oatp, which may affect bile acid and bilirubin homeostasis, resulting in hyperbilirubinemia and cholestatic hepatotoxicity.

Bioactivation of 3-n-butylphthalide via sulfation of its major metabolite 3-hydroxy-NBP: mediated mainly by sulfotransferase 1A1.

3-n-Butylphthalide (NBP) [(±)-3-butyl-1(3H)-isobenzofuranone] is an anti-cerebral-ischemia drug. Moderate hepatotoxicity has been observed in clinical applications. One of the major metabolites, 3-N-acetylcysteine-NBP, has been detected in human urine, indicating the formation of a reactive metabolite. We elucidated the formation mechanism of the reactive metabolite and its association with the hepatotoxicity of NBP. The in vitro incubations revealed that 3-glutathione-NBP (3-GSH-NBP) was observed only in fresh rat liver homogenate rather than in liver microsomes, liver cytosol, or liver 9,000g supernatant supplemented with NADPH and GSH. We also detected 3-GSH-NBP when 3′-phosphoadenosine-5′-phosphosulfate was added in GSH-fortified human liver cytosol (HLC). The formation of 3-GSH-NBP was 39.3-fold higher using 3-hydroxy-NBP (3-OH-NBP) as the substrate than NBP. The sulfotransferase (SULT) inhibitors DCNP (2,6-dichloro-4-nitrophenol) and quercetin suppressed 3-GSH-NBP formation in HLC by 75 and 82%, respectively, suggesting that 3-OH-NBP sulfation was involved in 3-GSH-NBP formation. Further SULT phenotyping revealed that SULT1A1 is the major isoform responsible for the sulfation. Dose-dependent toxicity was observed in primary rat hepatocytes exposed to 3-OH-NBP, with an IC50 of approximately 168 μM. Addition of DCNP and quercetin significantly increased cell viability, whereas l-buthionine-sulfoximine (a GSH depleter) decreased cell viability. Overall, our study revealed the underlying mechanism for the bioactivation of NBP is as follows. NBP is first oxidized to 3-OH-NBP and further undergoes sulfation to form 3-OH-NBP sulfate. The sulfate spontaneously cleaves off, generating highly reactive electrophilic cations, which can bind either to GSH to detoxify or to hepatocellular proteins to cause undesirable side effects.

Biotransformation of indomethacin by the fungus Cunninghamella blakesleeana

AbstractAim:To investigate the biotransformation of indomethacin, the first of the newer nonsteroidal anti-inflammatory drugs, by filamentous fungus and to compare the similarities between microbial transformation and mammalian metabolism of indomethacin.Methods:Five strains of Cunninghamella (C elegans AS 3.156, C elegans AS 3.2028, C blakesleeana AS 3.153, C blakesleeana AS 3.910 and C echinulata AS 3.2004) were screened for their ability to catalyze the biotransformation of indomethacin. Indomethacin was partially metabolized by five strains of Cunninghamella, and C blakesleeana AS 3.910 was selected for further investigation. Three metabolites produced by C blakesleeana AS 3.910 were isolated using semi-preparative HPLC, and their structures were identified by a combination analysis of LC/MSn and NMR spectra. These three metabolites were separated and quantitatively assayed by liquid chromatography-ion trap mass spectrometry.Results:After 120 h of incubation with C blakesleeana AS 3.910, approximately 87.4% of indomethacin was metabolized to three metabolites: O-desmethylindomethacin (DMI, M1, 67.2%), N-deschlorobenzoylindomethacin (DBI, M2, 13.3%) and O-desmethyl-N-deschlorobenzoylindomethacin (DMBI, M3, 6.9%). Three phase I metabolites of indomethacin produced by C blakesleeana AS 3.910 were identical to those obtained in humans.Conclusion:C blakesleeana could be a useful tool for generating the mammalian phase I metabolites of indomethacin.

Trimethylsilyldiazomethane derivatization coupled with solid-phase extraction for the determination of alendronate in human plasma by LC-MS/MS

AbstractAlendronate is an important representative of bisphosphonates, strongly polar compounds that lack chromophores. With rare exceptions, derivatization of the analytes is necessary for bioanalysis. In this study, a rapid liquid chromatography–tandem mass spectrometry method employing pre-column derivatization was developed and validated for the determination of alendronate concentrations in human plasma. The procedure was based on derivatization with trimethylsilyldiazomethane during solid-phase extraction on a weak anion-exchange solid-phase cartridge, which integrated sample purification and derivatization into one step. The alendronate derivative was eluted with methanol. Chromatographic separation was performed on a Capcell PAK-C18 column. The total run time was 6.5xa0min. The calibration curve was linear in the range 1.00–1,000xa0ng/mL using d6-alendronate as the internal standard. The lower limit of quantification was 1.00xa0ng/mL. The intra- and inter-assay precision (in RSD) calculated from quality control samples was less than 15%, and the accuracy was between 98.1% and 100.2%. The validated method was successfully applied to characterize the pharmacokinetic profiles of alendronate following the intravenous infusion of 5 or 10xa0mg alendronate sodium to healthy volunteers.n FigureDerivatization and determination procedures of alendronate in human plasma

High-throughput salting-out-assisted liquid–liquid extraction for the simultaneous determination of atorvastatin, ortho-hydroxyatorvastatin, and para-hydroxyatorvastatin in human plasma using ultrafast liquid chromatography with tandem mass spectrometry

A high-throughput, specific, and rapid liquid chromatography withxa0tandem mass spectrometry method was established and validated for the simultaneous determination of atorvastatin and its two major metabolites, ortho-hydroxyatorvastatin and para-hydroxyatorvastatin, in human plasma. A simple salting-out-assisted liquid-liquid extraction using acetonitrile and a mass-spectrometry-friendly salt, ammonium acetate, was employed to extract the analytes from human plasma. A recovery of more than 81% for all analytes was achieved in 1 min extraction time. Chromatographic separation was performed on a Kinetex XB C18 column utilizing a gradient elution starting with a 60% of water solution (1% formic acid), followed by increasing percentages of acetonitrile. Analytes were detected on a tandem mass spectrometer equipped with an electrospray ionization source that was operated in the positive mode, using the transitions of m/z 559.3 → m/z 440.2 for atorvastatin, and m/z 575.3 → m/z 440.2 for both ortho- and para-hydroxyatorvastatin. Deuterium-labeled compounds were used as the internal standards. The method was validated over the concentration ranges of 0.0200-15.0 ng/mL for atorvastatin and ortho-hydroxyatorvastatin, and 0.0100-2.00 ng/mL for para-hydroxyatorvastatin with acceptable accuracy and precision. It was then successfully applied in a bioequivalence study of atorvastatin.

Isomer-selective distribution of 3-n-butylphthalide （NBP） hydroxylated metabolites, 3-hydroxy-NBP and 10-hydroxy-NBP, across the rat blood-brain barrier

Aim:To investigate the mechanisms underlying the isomer-selective distribution of 3-n-butylphthalide (NBP) hydroxylated metabolites, 3-hydroxy-NBP (3-OH-NBP) and 10-hydroxy-NBP (10-OH-NBP), across the blood brain barrier (BBB).Methods:After oral administration of NBP (20 mg/kg) to rats, the pharmacokinetics of two major hydroxylated metabolites, 3-OH-NBP and 10-OH-NBP, in plasma and brains were investigated. Plasma and brain protein binding of 3-OH-NBP and 10-OH-NBP was also assessed. To evaluate the influences of major efflux transporters, rats were pretreated with the P-gp inhibitor tariquidar (10 mg/kg, iv) and BCRP inhibitor pantoprazole (40 mg/kg, iv), then received 3-OH-NBP (12 mg/kg, iv) or 10-OH-NBP (3 mg/kg, iv). The metabolic profile of NBP was investigated in rat brain homogenate.Results:After NBP administration, the plasma exposure of 3-OH-NBP was 4.64 times that of 10-OH-NBP, whereas the brain exposure of 3-OH-NBP was only 11.8% of 10-OH-NBP. In the rat plasma, 60%±5.2% of 10-OH-NBP was unbound to proteins versus only 22%±2.3% of 3-OH-NBP being unbound, whereas in the rat brain, free fractions of 3-OH-NBP and 10-OH-NBP were 100%±9.7% and 49.9%±14.1%, respectively. In the rats pretreated with tariquidar and pantoprazole, the unbound partition coefficient Kp,uu of 3-OH-NBP was significantly increased, while that of 10-OH-NBP showed a slight but not statistically significant increase. Incubation of rat brain homogenate with NBP yielded 3-OH-NBP but not 10-OH-NBP.Conclusion:The isomer-selective distribution of 10-OH-NBP and 3-OH-NBP across the BBB of rats is mainly attributed to the differences in plasma and brain protein binding and the efflux transport of 3-OH-NBP. The abundant 10-OH-NBP is not generated in rat brains.

Effects of Renal Impairment on the Pharmacokinetics of Morinidazole: Uptake Transporter-Mediated Renal Clearance of the Conjugated Metabolites

ABSTRACT Morinidazole is a novel 5-nitroimidazole antimicrobial drug that undergoes extensive metabolism in humans via N+-glucuronidation (N+-glucuronide of S-morinidazole [M8-1] and N+-glucuronide of R-morinidazole [M8-2]) and sulfation (sulfate conjugate of morinidazole [M7]). Our objectives were to assess the effects of renal impairment on the pharmacokinetics (PK) of morinidazole and to elucidate the potential mechanisms. In this parallel-group study, healthy subjects and patients with severe renal impairment received an intravenous infusion of 500 mg of morinidazole. Plasma and urine samples were collected and analyzed. The areas under the plasma concentration-time curves (AUC) for M7, M8-1, and M8-2 were 15.1, 20.4, and 17.4 times higher, respectively, in patients with severe renal impairment than in healthy subjects, while the AUC for morinidazole was 1.5 times higher. The urinary recovery of the major metabolites was not significantly different between the two groups over 0 to 48 h, but the renal clearances of M7, M8-1, and M8-2 in patients were 85.3%, 92.5%, and 92.2% lower, respectively. In vitro transporter studies revealed that M7 is a substrate for organic anion transporter 1 (OAT1) and OAT3 (Km = 28.6 and 54.0 μM, respectively). Only OAT3 transported M8-1 and M8-2. Morinidazole was not a substrate for the transporter-transfected cells examined. These results revealed that the function or activity of renal uptake transporters might be impaired in patients with severe renal impairment, which accounted for dramatically increased plasma exposure and reduced renal clearance of the conjugated metabolites of morinidazole, the substrates of renal transporters in patients. It will help clinicians to adjust the dose in patients with severe renal impairment and to predict possible transporter-based drug-drug interactions.

Analysis of diacylglycerols by ultra performance liquid chromatography-quadrupole time-of-flight mass spectrometry: Double bond location and isomers separation

Diacylglycerols (DAGs) are important lipid intermediates and have been implicated in human diseases. Isomerism complicates their mass spectrometric analysis; in particular, it is difficult to identify fatty acid substituents and locate the double bond positions in unsaturated DAGs. We have developed an analytical strategy using ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF MS) in conjunction with dimethyl disulfide (DMDS) derivatization and collision cross-section (CCS) measurement to characterize DAGs in biological samples. The method employs non-aqueous reversed-phase chromatographic separation and profile collision energy (CE) mode for MS(E) and MS/MS analyses. Three types of fragment ions were produced simultaneously. Hydrocarbon ions (m/z 50-200) obtained at high CE helped to distinguish unsaturated and saturated DAGs rapidly. Neutral loss ions and acylium ions (m/z 300-400) produced at low CE were used to identify fatty acid substituents. Informative methyl thioalkane fragment ions were used to locate the double bonds of unsaturated DAGs. Mono-methylthio derivatives were formed mainly by the reaction of DAGs with DMDS, where methyl thiol underwent addition to the first double bond farthest from the ester terminus of unsaturated fatty acid chains. The addition of CCS values maximized the separation of isomeric DAG species and improved the confidence of DAG identification. Fourteen DAGs were identified in mouse myotube cells based on accurate masses, characteristic fragment ions, DMDS derivatization, and CCS values.

Chemical and Enzymatic Transformations of Nimesulide to GSH Conjugates through Reductive and Oxidative Mechanisms

Nimesulide (NIM) is a nonsteroidal anti-inflammatory drug, and clinical treatment with NIM has been associated with severe hepatotoxicity. The bioactivation of nitro-reduced NIM (NIM-NH2), a major NIM metabolite, has been thought to be responsible for the hepatotoxicity of NIM. However, we found that NIM-NH2 did not induce toxic effects in primary rat hepatocytes. This study aimed to investigate other bioactivation pathways of NIM and evaluate their association with hepatotoxicity. After incubating NIM with NADPH- and GSH-supplemented human or rat liver microsomes, we identified two types of GSH conjugates: one was derived from the attachment of GSH to NIM-NH2 (NIM-NH2-GSH) and the other one was derived from a quinone-imine intermediate (NIM-OH-GSH). NIM-NH2-GSH was generated not only by the oxidative activation of NIM-NH2 but also from the reductive activation of NIM. Both NADPH and GSH could act as reducing agents. Moreover, aldehyde oxidase also participated in the reductive activation of NIM. NIM-OH-GSH was generated mainly from NIM via epoxidation with CYP1A2 as the main catalyzing enzyme. NIM was toxic to both primary human and rat hepatocytes, with IC50 values of 213 and 40 μM, respectively. Inhibition of the oxidative and reductive activation of NIM by the nonspecific CYP inhibitor 1-aminobenzotriazole and selective aldehyde oxidase inhibitor estradiol did not protect the cells from NIM-mediated toxicity. Moreover, pretreating cells with l-buthionine-sulfoximine (a GSH depletor) did not affect the cytotoxicity of NIM. These results suggested that oxidative and reductive activation of NIM did not cause the hepatotoxicity and that the parent drug concentration was associated with the cytotoxicity.

A chiral high-performance liquid chromatography-tandem mass spectrometry method for the stereospecific determination of morinidazole in human plasma.

Morinidazole is a novel 5-nitroimidazole derivative used for the treatment of amoebiasis, trichomoniasis, and anaerobic bacterial infections. Morinidazole possesses a chiral carbon and is clinically administered as a racemate. In the present study, an enantioselective and sensitive liquid chromatography-tandem mass spectrometry method of determining morinidazole enantiomers in human plasma was developed and validated to characterize the stereoselective pharmacokinetics. Plasma samples were processed by liquid-liquid extraction using tert-butyl methyl ether. Chiral separation was optimized within 8.5min on a cellulose column using an isocratic mobile phase of methanol/water (80:20, v/v). Detection was using mass spectrometry in multiple reaction monitoring mode, using the transitions of m/z 271→144 for morinidazole enantiomers, and m/z 275→148 for d4-morinidazole (internal standard). The calibration curves were linear over 5.00-6000ng/mL for each enantiomer. The lower limit of quantification for each enantiomer was established at 5.00ng/mL. Intra- and inter-day precisions were less than 6.4% for each enantiomer in terms of relative standard deviation, and accuracies were between -2.5% and 6.4% in terms of relative error for each enantiomer. No chiral inversion was observed during sample storage, preparation procedure and analysis. Major glucuronide and sulfate conjugates were not observed to interfere with the determination of morinidazole enantiomers. The method was applied to study the stereoselective pharmacokinetics of morinidazole in humans. Moderate stereoselectivity was observed in healthy subjects and patients with severe renal impairment.