In vivo metabolic investigation of moxifloxacin using liquid chromatography/electrospray ionization tandem mass spectrometry in combination with online hydrogen/deuterium exchange experiments

Online Simultaneous Hydrogen/Deuterium Exchange of Multitarget Gas-Phase Molecules by Electrospray Ionization Mass Spectrometry Coupled with Gas Chromatography

In this study, a hydrogen/deuterium (H/D) exchange method using gas chromatography-electrospray ionization/mass spectrometry (GC-ESI/MS) was first investigated as a novel tool for online H/D exchange of multitarget analytes. The GC and ESI source were combined with a homemade heated column transfer line. GC-ESI/MS-based H/D exchange occurs in an atmospheric pressure ion source as a result of reacting the gas-phase analyte eluted from GC with charged droplets of deuterium oxide infused as the ESI spray solvent. The consumption of the deuterated solvent at a flow rate of 2 μL min^-1 was more economical than that in online H/D exchange methods reported to date. In-ESI-source H/D exchange by GC-ESI/MS was applied to 11 stimulants with secondary amino or hydroxyl groups. After H/D exchange, the spectra of the stimulants showed unexchanged, partially exchanged, and fully exchanged ions showing various degrees of exchange. The relative abundances corrected for naturally occurring isotopes of the fully exchanged ions of stimulants, except for etamivan, were in the range 24.3-85.5%. Methylephedrine and cyclazodone showed low H/D exchange efficiency under acidic, neutral, and basic spray solvent conditions and nonexchange for etamivan with an acidic phenolic OH group. The in-ESI-source H/D exchange efficiency by GC-ESI/MS was sufficient to determine the number of hydrogen by elucidation of fragmentation from the spectrum. Therefore, this online H/D exchange technique using GC-ESI/MS has potential as an alternative method for simultaneous H/D exchange of multitarget analytes.

In vivo metabolic investigation of silodosin using UHPLC-QTOF-MS/MS and in silico toxicological screening of its metabolites

Silodosin (SLD) is a novel α1-adrenoceptor antagonist which has shown promising clinical efficacy and safety in patients with benign prostatic hyperplasia (BPH). However, lack of information about metabolism of SLD prompted us to investigate metabolic fate of SLD in rats. To identify in vivo metabolites of SLD, urine, feces and plasma were collected from Sprague-Dawley rats after its oral administration. The samples were prepared using an optimized sample preparation approach involving protein precipitation followed by solid-phase extraction and then subjected to LC/HR-MS/MS analysis. A total of 13 phase I and six phase II metabolites of SLD have been identified in rat urine which includes hydroxylated, N-dealkylated, dehydrogenated, oxidative, glucosylated, glucuronide and N-sulphated metabolites, which are also observed in feces. In plasma, only dehydrogenated, N-dealkylated and unchanged SLD are observed. The structure elucidation of metabolites was done by fragmentation in MS/MS in combination with HRMS data. The potential toxicity profile of SLD and its metabolites were predicted using TOPKAT software and most of the metabolites were proposed to show a certain degree of skin sensitization and occular irritancy. Copyright © 2016 John Wiley & Sons, Ltd.

Investigation on fragmentation pathways of bisphenols by using electrospray ionization Orbitrap mass spectrometry

RATIONALE

Bisphenols, such as bisphenol A (BPA) and bisphenol S (BPS), are widely used in industrial products, although they have been demonstrated to be environmental contaminants with toxicity. However, few studies on the mass spectrometric fragmentation pathway of these compounds have been reported using high-resolution mass spectrometry (HRMS).

METHODS

The MS/MS fragmentations of nine bisphenols, together with several corresponding isotope-labeled compounds, were studied by Orbitrap MS using electrospray ionization (ESI) in negative ion mode and higher energy collisional-dissociation (HCD). The [M - H](-) ions of the compounds formed by ESI were selected as the precursor ions for MS/MS. The accurate m/z values for product ions were acquired to deduce the elemental compositions and fragmentation pathways.

RESULTS

The elemental compositions of the ions were calculated from the accurate mass data. Common MS/MS product ions and characteristic neutral losses were summarized. Six bisphenols formed the common product ion at m/z 93 (C6 H5 O). The [M - H](-) ions of five bisphenols were found to lose a phenol group (C6 H5 OH). Four bisphenols formed the [M - H - CH4 ](-) ion. The proposed fragmentation pathways of representative compounds of BPA and BPS were verified from the analysis of isotope-labeled compounds.

CONCLUSIONS

The MS/MS fragmentation pathways of nine bisphenols were, for the first time, systematically investigated with HRMS. The obtained data could be valuable for the identification of a variety of bisphenols in environmental and biological samples.

Absence of ethnic differences in the pharmacokinetics of moxifloxacin, simvastatin, and meloxicam among three East Asian populations and Caucasians

Aim

To examine whether strict control of clinical trial conditions could reduce apparent differences of pharmacokinetic (PK) parameters among ethnic groups.

Methods

Open‐label, single dose PK studies of moxifloxacin, simvastatin and meloxicam were conducted in healthy male subjects from three East Asian populations (Japanese, Chinese and Koreans) and one Caucasian population as a control. These three drugs were selected because differences in PK parameters have been reported, even though the backgrounds of these East Asian populations are similar. Moxifloxacin (400 mg) was administered orally to 20 subjects, and plasma and urine levels of moxifloxacin and its metabolite (M2) were measured. Simvastatin (20 mg) was given to 40 subjects, and plasma levels of simvastatin and simvastatin acid were measured. Meloxicam (7.5 mg) was given to 30 subjects and its plasma concentration was determined. Intrinsic factors (polymorphism of UGT1A1 for moxifloxacin, SLCO1B1 for simvastatin, and CYP2C9 for meloxicam) were also examined.

Results

AUC_inf values for moxifloxacin, simvastatin and meloxicam showed no significant differences among the East Asian groups. C_max values of moxifloxacin and simvastatin, but not meloxicam, showed significant differences. There were no significant differences of data for M2 or simvastatin acid. Genetic analysis identified significant differences in the frequencies of relevant polymorphisms, but these differences did not affect the PK parameters observed.

Conclusions

Although there were some differences in PK parameters among the three East Asian groups, the present study performed under strictly controlled conditions did not reproduce the major ethnic differences observed in previous studies.

Structural identification of neopanaxadiol metabolites in rats by ultraperformance liquid chromatography/quadrupole-time-of-flight mass spectrometry

RATIONALE

Neopanaxadiol (NPD) is one of the major ginsenosides in Panax ginseng C. A. Meyer (Araliaceae) that has been suggested to be a drug candidate against Alzheimer's disease. However, few data are available regarding its metabolism in rats.

METHODS

In this study, a method of ultraperformance liquid chromatography/quadrupole-time-of-flight mass spectrometry (UPLC/QTOFMS) was developed to identify major metabolites of NPD in the stomach, intestine, urine and feces of rats, with the aim of determining the main metabolic pathways of NPD in rats after oral administration.

RESULTS

UPLC/QTOFMS revealed two metabolites in the stomach of rats, one metabolite in the intestine and two metabolites in feces. One metabolite, named M2, was isolated and purified from rats feces, which was identified as (20S,22S)-dammar-22,25-epoxy-3β,12β,20-triol based on extensive NMR spectroscopy and mass spectrometry data. The main metabolites of NPD in rats were the products of epoxidation, dehydrogenation and hydroxylation. NPD was predominantly metabolized by 20,22-double-bond epoxidation and rearrangement to yield an expoxidation product (M2).

CONCLUSIONS

Based on the profiles of the metabolites, possible metabolic pathways of NPD in rats were proposed for the first time. This study provides new and available information on the metabolism of NPD, which is indispensable for further research on metabolic pathways of dammarane ginsengenins in vivo.

Decay mechanisms of protonated 4-quinolone antibiotics after electrospray ionization and ion activation

This study presents a detailed experimental investigation of charge isomers of protonated 4-quinolone antibiotics molecules formed during electrospray ionization (ESI) with proposed dissociation mechanisms after collisional activation. Piperazinyl quinolones have been previously shown to exhibit erratic behavior during tandem MS analyses of biological samples, which originated from varying ratios of two isomeric variants formed during ESI. Here, a combination of ESI-collision-induced dissociation (CID), differential ion mobility spectrometry (DMS), high resolution MS, and density functional theory (DFT) was used to investigate the underlying mechanisms of isomer formation and their individual dissociation behaviors. The study focused on ciprofloxacin; major findings were confirmed using structurally related 4-quinolones. DFT calculations showed a reversal of basicity for piperazinyl quinolones between liquid and gas phase. We provide an experimental comparison and theoretical treatment of factors influencing the formation ratio of the charge isomers during ESI, including solvent pH, protic/aprotic nature of solvent, and structural effects such as pK a and proton affinity. The actual dissociation mechanisms of the isomers of the protonated molecules were studied by separating the individual isomers via DMS-MS, which allowed type-specific CID spectra to be recorded. Both primary CID reactions of the two charge isomers originated from the same carboxyl group by charge-remote (CO(2) loss) and charge-mediated (H(2)O loss) fragmentation of the piperazinyl quinolones, depending on whether the proton resides on the more basic keto or the piperazinyl group, followed by a number of secondary dissociation reactions. The proposed mechanisms were supported by calculated energies of precursors, transition states, and products for competing pathways.

Moxifloxacin hydrochloride

A comprehensive profile of moxifloxacin HCl with 198 references is reported. A full description including nomenclature, formulae, elemental analysis, and appearance is included. Methods of preparation for moxifloxacin HCl, its intermediates, and derivatives are fully described. In addition, the physical properties, analytical methods, stability, uses and applications, and pharmacology of moxifloxacin HCl are also discussed.

Metabolite identification of a new tyrosine kinase inhibitor, HM781-36B, and a pharmacokinetic study by liquid chromatography/tandem mass spectrometry

RATIONALE

HM781-36B (1-[4-[4-(3,4-dichloro-2-fluorophenylamino)-7-methoxyquinazolin-6-yloxy]-piperidin-1-yl]prop-2-en-1-one hydrochloride) is a new anticancer drug to treat advanced solid tumors in clinical trial. In order to understand the behavior of HM781-36B in vitro and in vivo we validated an analytical method for HM781-36B and its major metabolites in plasma.

METHODS

In vivo and in vitro metabolism of HM781-36B was studied in dog plasma, urine and feces as well as using human and dog liver microsomes with extraction by ethyl acetate or methyl tert-butyl ether, respectively, and successfully separated by high-performance liquid chromatography diode-array detection mass spectrometry (HPLC-DAD/MS). Ten metabolites were identified by LC/ESI-ion trap mass spectrometry (MS, MS(2) , MS(3) and MRM) and LC/Q-TOF-MS/MS for exact mass measurement. For accurate characterization of the major metabolites, authentic standards (M1, M2, M4, and M10) were synthesized.

RESULTS

Ten metabolites of HM781-36B in an in vitro mixture were separated and identified by LC/ESI-MS(n) . The MS/MS spectral patterns of the parent drug and metabolites exhibited two characteristic ions (A- and B-type ions) attributed to the cleavage of the ether bond between the piperidine ring and the quinazoline ring, providing important information on the site of chemical conversion during the metabolism. Six hydroxylated derivatives including dehalogenation and demethylation, two N-oxide forms, a demethylated form and de-acryloylpiperideine metabolites were observed.

CONCLUSIONS

The LC/ESI-ion trap MS(n) technique was effective in obtaining structural information and yielded diagnostic ions for the identification of diverse metabolites. The multiple metabolic pathways of HM781-36B were suggested in in vitro and in vivo samples and the dihydroxylation (M1) and demethylation (M2) appeared to be the major metabolites.