Potential of measured relative shifts in collision cross section values for biotransformation studies.

Ion mobility spectrometry-mass spectrometry (IMS-MS) separates gas phase ions due to differences in drift time from which reproducible and analyte-specific collision cross section (CCS) values can be derived. Internally conducted in vitro and in vivo metabolism (biotransformation) studies indicated repetitive shifts in measured CCS values (CCSmeas) between parent drugs and their metabolites. Hence, the purpose of the present article was (i) to investigate if such relative shifts in CCSmeas were biotransformation-specific and (ii) to highlight their potential benefits for biotransformation studies. First, mean CCSmeas values of 165 compounds were determined (up to n = 3) using a travelling wave IMS-MS device with nitrogen as drift gas (TWCCSN2, meas). Further comparison with their predicted values (TWCCSN2, pred, Waters CCSonDemand) resulted in a mean absolute error of 5.1%. Second, a reduced data set (n = 139) was utilized to create compound pairs (n = 86) covering eight common types of phase I and II biotransformations. Constant, discriminative, and almost non-overlapping relative shifts in mean TWCCSN2, meas were obtained for demethylation (- 6.5 ± 2.1 Å2), oxygenation (hydroxylation + 3.8 ± 1.4 Å2, N-oxidation + 3.4 ± 3.3 Å2), acetylation (+ 13.5 ± 1.9 Å2), sulfation (+ 17.9 ± 4.4 Å2), glucuronidation (N-linked: + 41.7 ± 7.5 Å2, O-linked: + 38.1 ± 8.9 Å2), and glutathione conjugation (+ 49.2 ± 13.2 Å2). Consequently, we propose to consider such relative shifts in TWCCSN2, meas (rather than absolute values) as well for metabolite assignment/confirmation complementing the conventional approach to associate changes in mass-to-charge (m/z) values between a parent drug and its metabolite(s). Moreover, the comparison of relative shifts in TWCCSN2, meas significantly simplifies the mapping of metabolites into metabolic pathways as demonstrated.

Absorption and Metabolism of the Natural Sweeteners Erythritol and Xylitol in Humans: A Dose-Ranging Study.

The natural sweeteners erythritol and xylitol might be helpful to reduce sugar consumption and therefore prevent obesity and diabetes. The aim of the present study was to determine the absorption and metabolization into erythronate of different concentrations of erythritol and xylitol. Seventeen healthy lean participants received intragastric solutions of 10, 25, or 50 g erythritol or 7, 17, or 35 g xylitol on three study days in a randomized order. The study was double blinded with respect to the doses administered. We assessed plasma concentrations of erythritol, xylitol, and erythronate at fixed time intervals after administration with gas chromatography-mass spectrometry. We found: (i) a dose-dependent and saturable absorption of erythritol, (ii) a very low absorption of xylitol, (iii) a dose-dependent metabolization of erythritol into erythronate, and (iv) no metabolization of xylitol into erythronate. The implications of the metabolization of erythritol into erythronate for human health remain to be determined and more research in this area is needed.

Analytical Platforms at Swiss Universities of Applied Sciences.

Numerous projects and industrial and academic collaborations benefit from state-of-the-art facilities and expertise in analytical chemistry available at the Swiss Universities of Applied Sciences. This review summarizes areas of expertise in analytical sciences at the University of Applied Sciences and Arts Northwestern Switzerland (FHNW), the University of Applied Sciences and Arts Western Switzerland (HES-SO), and the Zurich University of Applied Sciences (ZHAW). We briefly discuss selected projects in different fields of analytical sciences.

Caco-2 Permeability Studies and In Vitro hERG Liability Assessment of Tryptanthrin and Indolinone.

Tryptanthrin and (E,Z)-3-(4-hydroxy-3,5-dimethoxybenzylidene)indolinone (indolinone) were recently isolated from Isatis tinctoria as potent anti-inflammatory and antiallergic alkaloids, and shown to inhibit COX-2, 5-LOX catalyzed leukotriene synthesis, and mast cell degranulation at low µM to nM concentrations. To assess their suitability for oral administration, we screened the compounds in an in vitro intestinal permeability assay using human colonic adenocarcinoma cells. For exact quantification of the compounds, validated UPLC-MS/MS methods were used. Tryptanthrin displayed high permeability (apparent permeability coefficient > 32.0 × 10(-6) cm/s) across the cell monolayer. The efflux ratio below 2 (< 1.12) and unchanged apparent permeability coefficient values in the presence of the P-glycoprotein inhibitor verapamil (50 µM) indicated that tryptanthrin was not involved in P-glycoprotein interactions. For indolinone, a low recovery was found in the human colon adenocarcinoma cell assay. High-resolution mass spectrometry pointed to extensive phase II metabolism of indolinone (sulfation and glucuronidation). Possible cardiotoxic liability of the compounds was assessed in vitro by measurement of an inhibitory effect on human ether-a-go-go-related gene tail currents in stably transfected HEK 293 cells using the patch clamp technique. Low human ether-a-go-go-related gene inhibition was found for tryptanthrin (IC50 > 10 µM) and indolinone (IC50 of 24.96 µM). The analysis of compounds using various in silico methods confirmed favorable pharmacokinetic properties, as well as a slight inhibition of the human ether-a-go-go-related gene potassium channel at micromolar concentrations.

Novel Analytical Workflow for Comprehensive Non-targeted Phytochemical Metabolic Profiling.

The understanding and interpretation of pharmacological properties on a molecular level is of great importance for many different fields of research. Our study provides a novel model work-flow for comprehensive metabolic profiling by structural identification of relevant metabolites not limited to phytochemistry applications. High resolution liquid chromatography mass spectrometry LC-MS/MS data can be directly correlated with pharmacological test results on a molecular level. Thus the understanding and interpretation of pharmacological properties is supported by structural and chemical information.

Development, validation, and application of a novel LC-MS/MS trace analysis method for the simultaneous quantification of seven iodinated X-ray contrast media and three artificial sweeteners in surface, ground, and drinking water.

A new method for the simultaneous determination of iodated X-ray contrast media (ICM) and artificial sweeteners (AS) by liquid chromatography-tandem mass spectrometry (LC-MS/MS) operated in positive and negative ionization switching mode was developed. The method was validated for surface, ground, and drinking water samples. In order to gain higher sensitivities, a 10-fold sample enrichment step using a Genevac EZ-2 plus centrifugal vacuum evaporator that provided excellent recoveries (90 ± 6 %) was selected for sample preparation. Limits of quantification below 10 ng/L were obtained for all compounds. Furthermore, sample preparation recoveries and matrix effects were investigated thoroughly for all matrix types. Considerable matrix effects were observed in surface water and could be compensated by the use of four stable isotope-labeled internal standards. Due to their persistence, fractions of diatrizoic acid, iopamidol, and acesulfame could pass the whole drinking water production process and were observed also in drinking water. To monitor the fate and occurrence of these compounds, the validated method was applied to samples from different stages of the drinking water production process of the Industrial Works of Basel (IWB). Diatrizoic acid was found as the most persistent compound which was eliminated by just 40 % during the whole drinking water treatment process, followed by iopamidol (80 % elimination) and acesulfame (85 % elimination). All other compounds were completely restrained and/or degraded by the soil and thus were not detected in groundwater. Additionally, a direct injection method without sample preparation achieving 3-20 ng/L limits of quantification was compared to the developed method.

Laser diode thermal desorption atmospheric pressure chemical ionization tandem mass spectrometry applied for the ultra-fast quantitative analysis of BKM120 in human plasma.

A sensitive and ultra-fast method utilizing the laser diode thermal desorption ion source using atmospheric pressure chemical ionization coupled to tandem mass spectrometry (LDTD-APCI-MS/MS) was developed for the quantitative analysis of BKM120, an investigational anticancer drug in human plasma. Samples originating from protein precipitation (PP) followed by salting-out assisted liquid-liquid extraction (SALLE) were spotted onto the LazWell™ plate prior to their thermal desorption and detection by tandem mass spectrometry in positive mode. The validated method described in this paper presents a high absolute extraction recovery (>90 %) for BKM120 and its internal standard (ISTD) [D8]BKM120, with precision and accuracy meeting the acceptance criteria. Standard curves were linear over the range of 5.00 to 2000 ng mL(-1) with a coefficient of determination (R (2)) >0.995. The method specificity was demonstrated in six different batches of human plasma. Intra- and inter-run precision as well as accuracy within ±20 % at the lower limit of quantification (LLOQ) and ±15 % (other levels) were achieved during a three-run validation for quality control (QC) samples. The post-preparative stability on the LazWell™ plate at room temperature was 72 h and a 200-fold dilution of spiked samples was demonstrated. The method was applied successfully to three clinical studies (n = 847) and cross-checked with the validated LC-ESI-MS/MS reference method. The sample analysis run time was 10 s as compared to 4.5 min for the current validated LC-ESI-MS/MS method. The resultant data were in agreement with the results obtained using the validated reference LC-ESI-MS/MS assay and the same pharmacokinetic (PK) parameters were calculated for both analytical assays. This work demonstrates that LDTD-APCI-MS/MS is a reliable method for the ultra-fast quantitative analysis of BKM120 which can be used to speed-up and support its bioanalysis in the frame of the clinical trials.

In vitro anti-inflammatory and wound-healing potential of a Phyllostachys edulis leaf extract--identification of isoorientin as an active compound.

Extracts prepared from the leaves of Phyllostachys edulis (bamboo) have received attention in pharmacological research due to their potent antitumor, anti-inflammatory, antimicrobial, and anti-ulcerogenic activities. In this study, anti-inflammatory effects of a bamboo leaf extract on tumor necrosis factor alpha-induced overproduction of interleukin 8, vascular endothelial growth factor, and interleukin 6 in immortalized human keratinocytes were investigated for the first time. In addition, wound-healing effects were evaluated in 3T3-swiss albino mouse fibroblasts. Bamboo leaf extract and isoorientin inhibited the tumor necrosis factor alpha-induced release of interleukin 8 and vascular endothelial growth factor. Furthermore, isoorientin dose-dependently reduced levels of interleukin 6 in tumor necrosis factor alpha-α-treated immortalized human keratinocytes cells. Wound healing was evaluated using a modification of the classical scratch assay. For evaluation of the wound gap, a new computerized method based on time-lapse microscopy was developed. It was shown that bamboo leaf extract (10 µg/mL) improved wound closure by 28 % (12 h) and 54 % (24 h), respectively. In concentrations of 50 µg/mL and above, bamboo leaf extract inhibited cell migration without affecting cell viability. Isoorientin (10 µM) improved wound closure by 29 % (12 h) and 56 % (24 h), respectively. Comparable to bamboo leaf extract, higher concentrations of isoorientin prevented cell migration. It is suggested that bamboo leaf extract as well as isoorientin have a dual activity - in higher doses, they show anti-inflammatory effects, and in lower concentrations, they exert anti-angiogenic activities.

Single and few cell analysis for correlative light microscopy, metabolomics, and targeted proteomics.

The interactions of proteins, membranes, nucleic acid, and metabolites shape a cell's phenotype. These interactions are stochastic, and each cell develops differently, making it difficult to synchronize cell populations. Consequently, studying biological processes at the single- or few-cell level is often necessary to avoid signal dilution below the detection limit or averaging over many cells. We have developed a method to study metabolites and proteins from a small number of or even a single adherent eukaryotic cell. Initially, cells are lysed by short electroporation and aspirated with a microcapillary under a fluorescent microscope. The lysate is placed on a carrier slide for further analysis using liquid-chromatography mass spectrometry (LC-MS) and/or reverse-phase protein (RPPA) approach. This method allows for a correlative measurement of (i) cellular structures and metabolites and (ii) cellular structures and proteins on the single-cell level. The correlative measurement of cellular structure by light-microscopy, metabolites by LC-MS, and targeted protein detection by RPPA was possible on the few-cell level. We discuss the method, potential applications, limitations, and future improvements.

Detection of N-desethyl etonitazene in a drug checking sample: Chemical analysis and pharmacological characterization of a recent member of the 2-benzylbenzimidazole "nitazene" class.

The emergence of 2-benzylbenzimidazole "nitazene" opioids is stirring up the recreational synthetic opioid market. Many nitazene analogues act as potent agonists at the µ­opioid receptor (MOR), as demonstrated in various in vitro and in vivo studies. Severe intoxication and overdose deaths associated with nitazene analogues are increasingly being reported. Nitazene opioids are classified as a public health threat, stressing the need for close monitoring of new developments on the recreational drug market. This study reports on the detection of N-desethyl etonitazene in a sample handed in by a recreational drug user at a Swiss drug checking service in August 2023. The person bought the sample through an internet source where it was stated to contain isotonitazene. Chemical analyses were conducted to characterize the sample, i.e. nuclear magnetic resonance (NMR), capillary electrophoresis (CE), and high-resolution mass spectrometry (HRMS). The sample was additionally investigated using two different in vitro MOR activation assays. NMR and high-performance liquid chromatography (HPLC) coupled to HRMS confirmed the presence of N-desethyl etonitazene at a high purity and in the absence of isotonitazene and etonitazene. N-Desethyl nitazene analogues have been detected before as metabolites of isotonitazene and etonitazene. However, as first seen with N-desethyl isotonitazene, they are now emerging as standalone drugs. The applied bioassays demonstrated increased efficacy and approximately 6-9-fold higher potency of N-desethyl etonitazene at MOR compared to fentanyl. N-Desethyl etonitazene showed EC50 values of 3.35 nM and 0.500 nM in the ß-arrestin 2 recruitment and Aequoscreen® assays, respectively. The opioid activity present in the collected sample was additionally evaluated using the bioassays and showed good overlap with the reference standard, in line with the analytical purity assessment. This demonstrates the potential of these bioassays to provide a rapid opioid activity assessment of authentic samples. The emergence of other N-desethyl nitazene analogues must be considered during forensic and clinical toxicology casework, to avoid misclassification of intake of such analogues as metabolites. Finally, drug checking services enable the close monitoring of market developments and trends and are of great value for early warning and harm reduction purposes.

Combination of bioautography with HPTLC-MS/NMR: a fast identification of acetylcholinesterase inhibitors from galbanum(†).

INTRODUCTION: In the search for new natural compounds with acetylcholinesterase (AChE) inhibitory activity this study focused on galbanum, the oleo gum-resin from Ferula gummosa Boiss., which had shown AChE inhibitory activity in a screening. OBJECTIVE: The isolation of bioactive compounds from plant extracts usually is laborious and time consuming. In an approach to accelerate the characterisation of compounds with AChE inhibitory activity, the potential of a combination of HPTLC bioautography with HPTLC-MS/NMR for the fast identification of active compounds in galbanum was studied. METHOD: Pre-fractionation of the dichloromethane extract was performed by vacuum liquid chromatography. The resulting fractions were separated by HPTLC and active zones determined by bioautography. A TLC-MS interface was used to elute the single zones from the plates directly into a mass spectrometer. The interface was also used to extract the two major active zones from HPTLC plates for off-line one- and two-dimensional NMR and quadrupole time of flight (QTOF) MS. RESULTS: The isolated compounds were identified as 7-{[(2E)-3,7-dimethylocta-2,6-dien-1-yl]oxy}-2H-chromen-2-one (auraptene) and 7-{[(1R,4aR,6S,8aS)-6-hydroxy-5,5,8a-trimethyl-2-methylenedecahydronaphthalen-1-yl]methoxy}-2H-chromen-2-one (farnesiferol A). This is the first report of these substances in F. gummosa. Their median inhibitory concentration (IC50 ) values for AChE inhibition were determined as 47 and 17 µg/mL in comparison with physostigmine as a positive control (IC50 : 0.8 µg/mL) and their concentrations in galbanum were quantified by HPLC as 3.5% and 7.9%, respectively. CONCLUSION: The study showed that HPTLC-MS/NMR can be considered as a fast and high-confidence method for dereplication of natural compounds. From the correlation of the concentration of the elucidated compounds and their IC50 values for AChE inhibition it can be concluded that auraptene and farnesiferol A are contributing to this activity of galbanum.

Thin-layer chromatography-nuclear magnetic resonance spectroscopy - a versatile tool for pharmaceutical and natural products analysisa.

Thin-layer chromatography (TLC) is a mature and very established technique, frequently used in many fields of applications ranging from natural product analysis to chemical or pharmaceutical applications. The introduction of a commercially available TLC-MS interface was a major step complementing the ease of use of TLC with structural elucidation power of mass spectrometry (MS). The TLC-MS interface simplifies the workflow dramatically to gain structural information directly from TLC separations. This article describes the potential of TLC-nuclear magnetic resonance spectroscopy (NMR) utilizing the TLC-MS interface to straightforwardly characterize zones of interest by NMR spectroscopy with a focus on quantification of active pharmaceutical ingredients (API) in formulations and identification of active principles in plant extracts.

Metabolomic Abnormalities in Serum from Untreated and Treated Dogs with Hyper- and Hypoadrenocorticism.

The adrenal glands play a major role in metabolic processes, and both excess and insufficient serum cortisol concentrations can lead to serious metabolic consequences. Hyper- and hypoadrenocorticism represent a diagnostic and therapeutic challenge. Serum samples from dogs with untreated hyperadrenocorticism (n = 27), hyperadrenocorticism undergoing treatment (n = 28), as well as with untreated (n = 35) and treated hypoadrenocorticism (n = 23) were analyzed and compared to apparently healthy dogs (n = 40). A validated targeted proton nuclear magnetic resonance (1H NMR) platform was used to quantify 123 parameters. Principal component analysis separated the untreated endocrinopathies. The serum samples of dogs with untreated endocrinopathies showed various metabolic abnormalities with often contrasting results particularly in serum concentrations of fatty acids, and high- and low-density lipoproteins and their constituents, which were predominantly increased in hyperadrenocorticism and decreased in hypoadrenocorticism, while amino acid concentrations changed in various directions. Many observed serum metabolic abnormalities tended to normalize with medical treatment, but normalization was incomplete when compared to levels in apparently healthy dogs. Application of machine learning models based on the metabolomics data showed good classification, with misclassifications primarily observed in treated groups. Characterization of metabolic changes enhances our understanding of these endocrinopathies. Further assessment of the recognized incomplete reversal of metabolic alterations during medical treatment may improve disease management.

Metabolomic serum abnormalities in dogs with hepatopathies.

Hepatopathies can cause major metabolic abnormalities in humans and animals. This study examined differences in serum metabolomic parameters and patterns in left-over serum samples from dogs with either congenital portosystemic shunts (cPSS, n = 24) or high serum liver enzyme activities (HLEA, n = 25) compared to control dogs (n = 64). A validated targeted proton nuclear magnetic resonance spectroscopy platform was used to assess 123 parameters. Principal component analysis of the serum metabolome demonstrated distinct clustering among individuals in each group, with the cluster of HLEA being broader compared to the other groups, presumably due to the wider spectrum of hepatic diseases represented in these samples. While younger and older adult control dogs had very similar metabolomic patterns and clusters, there were changes in many metabolites in the hepatopathy groups. Higher phenylalanine and tyrosine concentrations, lower branched-chained amino acids (BCAAs) concentrations, and altered fatty acid parameters were seen in cPSS dogs compared to controls. In contrast, dogs with HLEA had increased concentrations of BCAAs, phenylalanine, and various lipoproteins. Machine learning based solely on the metabolomics data showed excellent group classification, potentially identifying a novel tool to differentiate hepatopathies. The observed changes in metabolic parameters could provide invaluable insight into the pathophysiology, diagnosis, and prognosis of hepatopathies.

Effect of a Chronic Intake of the Natural Sweeteners Xylitol and Erythritol on Glucose Absorption in Humans with Obesity.

In patients with obesity, accelerated nutrients absorption is observed. Xylitol and erythritol are of interest as alternative sweeteners, and it has been shown in rodent models that their acute ingestion reduces intestinal glucose absorption. This study aims to investigate whether a chronic intake of xylitol and erythritol impacts glucose absorption in humans with obesity. Forty-six participants were randomized to take either 8 g of xylitol or 12 g of erythritol three times a day for five to seven weeks, or to be part of the control group (no substance). Before and after the intervention, intestinal glucose absorption was assessed during an oral glucose tolerance test with 3-Ortho-methyl-glucose (3-OMG). The effect of xylitol or erythritol intake on the area under the curve for 3-OMG concentration was not significant. Neither the time (pre or post intervention), nor the group (control, xylitol, or erythritol), nor the time-by-group interaction effects were significant (p = 0.829, p = 0.821, and p = 0.572, respectively). Therefore, our results show that a chronic intake of the natural sweeteners xylitol and erythritol does not affect intestinal glucose absorption in humans with obesity.

Automated chiral method screening - Evaluation of generated chromatographic data sets to further optimize screening efficiency.

We set up an automated screening process to routinely test 10 chiral supercritical fluid chromatography (SFC) methods - five columns combined with two co-solvents - as part of a chiral separation lab workflow. Proprietary software tools enabled automated method screening of racemates, parallel evaluation of the resulting chromatograms for enantiomer separation and report generation. This process is largely automated and resulted in an efficient and reliable lab process with a minimum requirement for human intervention. Screenings were conducted on a test set of 756 racemates that were selected with focus on structural variation and on 2667 proprietary samples from lab routines. Statistical analysis revealed that up to 92% of the tested racemic mixtures could be successfully separated with at least one of the tested conditions of the screening. Process efficiency was further increased by identification of optimal method screening sequence, re-definition of the optimal column set and project-specific adaptations considering reduced structural variation of the analytes. This study illustrates the usefulness of consistent chromatographic data sets to accelerate and facilitate the identification of chiral methods to separate enantiomers by automated processing and statistical analysis.

Whole-genome sequence-informed MALDI-TOF MS diagnostics reveal importance of Klebsiella oxytoca group in invasive infections: a retrospective clinical study.

BACKGROUND: Klebsiella spp. are opportunistic pathogens which can cause severe infections, are often multi-drug resistant and are a common cause of hospital-acquired infections. Multiple new Klebsiella species have recently been described, yet their clinical impact and antibiotic resistance profiles are largely unknown. We aimed to explore Klebsiella group- and species-specific clinical impact, antimicrobial resistance (AMR) and virulence. METHODS: We analysed whole-genome sequence data of a diverse selection of Klebsiella spp. isolates and identified resistance and virulence factors. Using the genomes of 3594 Klebsiella isolates, we predicted the masses of 56 ribosomal subunit proteins and identified species-specific marker masses. We then re-analysed over 22,000 Matrix-Assisted Laser Desorption Ionization - Time Of Flight (MALDI-TOF) mass spectra routinely acquired at eight healthcare institutions in four countries looking for these species-specific markers. Analyses of clinical and microbiological endpoints from a subset of 957 patients with infections from Klebsiella species were performed using generalized linear mixed-effects models. RESULTS: Our comparative genomic analysis shows group- and species-specific trends in accessory genome composition. With the identified species-specific marker masses, eight Klebsiella species can be distinguished using MALDI-TOF MS. We identified K. pneumoniae (71.2%; n = 12,523), K. quasipneumoniae (3.3%; n = 575), K. variicola (9.8%; n = 1717), "K. quasivariicola" (0.3%; n = 52), K. oxytoca (8.2%; n = 1445), K. michiganensis (4.8%; n = 836), K. grimontii (2.4%; n = 425) and K. huaxensis (0.1%; n = 12). Isolates belonging to the K. oxytoca group, which includes the species K. oxytoca, K. michiganensis and K. grimontii, were less often resistant to 4th-generation cephalosporins than isolates of the K. pneumoniae group, which includes the species K. pneumoniae, K. quasipneumoniae, K. variicola and "K. quasivariicola" (odds ratio = 0.17, p < 0.001, 95% confidence interval [0.09,0.28]). Within the K. pneumoniae group, isolates identified as K. pneumoniae were more often resistant to 4th-generation cephalosporins than K. variicola isolates (odds ratio = 2.61, p = 0.003, 95% confidence interval [1.38,5.06]). K. oxytoca group isolates were found to be more likely associated with invasive infection to primary sterile sites than K. pneumoniae group isolates (odds ratio = 2.39, p = 0.0044, 95% confidence interval [1.05,5.53]). CONCLUSIONS: Currently misdiagnosed Klebsiella spp. can be distinguished using a ribosomal marker-based approach for MALDI-TOF MS. Klebsiella groups and species differed in AMR profiles, and in their association with invasive infection, highlighting the importance for species identification to enable effective treatment options.

Extended and Fully Automated Newborn Screening Method for Mass Spectrometry Detection.

A new and fully automated newborn screening method for mass spectrometry was introduced in this paper. Pathological relevant amino acids, acylcarnitines, and certain steroids are detected within 4 min per sample. Each sample is treated in an automated and standardized workflow, where a mixture of deuterated internal standards is sprayed onto the sample before extraction. All compounds showed good linearity, and intra- and inter-day variation lies within the acceptance criteria (except for aspartic acid). The described workflow decreases analysis cost and labor while improving the sample traceability towards good laboratory practice.

GABAA receptor activity modulating piperine analogs: In vitro metabolic stability, metabolite identification, CYP450 reaction phenotyping, and protein binding.

In a screening of natural products for allosteric modulators of GABAA receptors (γ-aminobutyric acid type A receptor), piperine was identified as a compound targeting a benzodiazepine-independent binding site. Given that piperine is also an activator of TRPV1 (transient receptor potential vanilloid type 1) receptors involved in pain signaling and thermoregulation, a series of piperine analogs were prepared in several cycles of structural optimization, with the aim of separating GABAA and TRPV1 activating properties. We here investigated the metabolism of piperine and selected analogs in view of further cycles of lead optimization. Metabolic stability of the compounds was evaluated by incubation with pooled human liver microsomes, and metabolites were analyzed by UHPLC-Q-TOF-MS. CYP450 isoenzymes involved in metabolism of compounds were identified by reaction phenotyping with Silensomes™. Unbound fraction in whole blood was determined by rapid equilibrium dialysis. Piperine was the metabolically most stable compound. Aliphatic hydroxylation, and N- and O-dealkylation were the major routes of oxidative metabolism. Piperine was exclusively metabolized by CYP1A2, whereas CYP2C9 contributed significantly in the oxidative metabolism of all analogs. Extensive binding to blood constituents was observed for all compounds.