Role of Human Liver Microsomes in In Vitro Metabolism of Drugs—A Review

Comparison of Three Untargeted Data Processing Workflows for Evaluating LC-HRMS Metabolomics Data

The evaluation of liquid chromatography high-resolution mass spectrometry (LC-HRMS) raw data is a crucial step in untargeted metabolomics studies to minimize false positive findings. A variety of commercial or open source software solutions are available for such data processing. This study aims to compare three different data processing workflows (Compound Discoverer 3.1, XCMS Online combined with MetaboAnalyst 4.0, and a manually programmed tool using R) to investigate LC-HRMS data of an untargeted metabolomics study. Simple but highly standardized datasets for evaluation were prepared by incubating pHLM (pooled human liver microsomes) with the synthetic cannabinoid A-CHMINACA. LC-HRMS analysis was performed using normal- and reversed-phase chromatography followed by full scan MS in positive and negative mode. MS/MS spectra of significant features were subsequently recorded in a separate run. The outcome of each workflow was evaluated by its number of significant features, peak shape quality, and the results of the multivariate statistics. Compound Discoverer as an all-in-one solution is characterized by its ease of use and seems, therefore, suitable for simple and small metabolomic studies. The two open source solutions allowed extensive customization but particularly, in the case of R, made advanced programming skills necessary. Nevertheless, both provided high flexibility and may be suitable for more complex studies and questions.

Design, synthesis and anti-inflammatory study of novel N-heterocyclic substituted Aloe-emodin derivatives

A novel series of Aloe-emodin derivatives containing N-heterocyclic moieties was designed and synthesized. The structure-activity relationship studies (SARs) indicated that the replacement of hydroxyethyl and benzhydryl piperazine groups could improve efficacy. Compounds 12r and 14a-14c exhibited a higher inhibitory effect on LPS-induced nitric oxide (NO) production in RAW264.7 macrophages than Aloe-emodin did. Among them, 12r showed the most potent inhibition with an IC₅₀ value of 5.66 ± 0.47 μM. Further toxicity and pharmacokinetic studies were carried out and 12r was found to be the most active structure with low toxicity risk and good metabolic properties. It could also decrease the levels of IL-1β, TNF-α, PGE₂ and inhibit the activation of nuclear factor-κB signalling pathway. Importantly, 12r showed oral bioavailability of up to 55.16% and attenuated the inflammatory symptoms in an ulcerative colitis mouse model in vivo. These results indicate that 12r is suitable for development as an anti-inflammatory agent.

Integrated Array Chip for High-Throughput Screening of Species Differences in Metabolism

Species differences in metabolism may produce failure prediction of drug efficacy/toxicity in humans. Integration of metabolic competence and cellular effect assays in vitro can provide insight into the species differences in metabolism; however, a co-culture platform with features of high throughput, operational simplicity, low sample consumption, and independent layouts is required for potential usage in industrial test settings. Herein, we developed an integrated array chip (IAC) to evaluate the species differences in metabolism through metabolism-induced anticancer bioactivity as a case. The IAC consisted of two functional parts: a micropillar chip for immobilization of liver microsomes and a microwell chip for three-dimensional (3D) tumor cell culture. First, optimized parameters of the micropillar chip for microsomal encapsulation were obtained by cross-shaped protrusions and a 2.5 μL volume of 3D agarose spots. Next, we examined factors influencing metabolism-induced anticancer bioactivity. Feasibility of the IAC was validated by four model prodrugs using image-based bioactivity detection and mass spectrometry (MS)-based metabolite analysis. Finally, a species-specific IAC was used for selection of animal species that best resembles metabolism-induced drug response to humans at throughputs. Overall, the IAC provides a promising co-culture platform for identifying species differences in metabolism and selection of animal models to accelerate drug discovery.

In Vitro Metabolic Profile Elucidation of Synthetic Cannabinoid APP-CHMINACA (PX-3)

Indazole carboxamide synthetic cannabinoids remain the most prevalent subclass of new psychoactive substances (NPS) reported internationally. However, the metabolic and pharmacological properties of many of these compounds remain unknown. Elucidating these characteristics allows members of the clinical and forensic communities to identify causative agents in patient samples, as well as render conclusions regarding their toxic effects. This work presents a detailed report on the in vitro phase I metabolism of indazole carboxamide synthetic cannabinoid APP-CHMINACA (PX-3). Incubation of APP-CHMINACA with human liver microsomes, followed by analysis of extracts via high-resolution mass spectrometry, yielded 12 metabolites, encompassing 7 different metabolite classes. Characterization of the metabolites was achieved by evaluating the product ion spectra, accurate mass and chemical formula generated for each metabolite. The predominant biotransformations observed were hydrolysis of the distal amide group and hydroxylation of the cyclohexylmethyl (CHM) substituent. Nine metabolites were amide hydrolysis products, of which five were monohydroxylated, one dihydroxylated and two were ketone products. The metabolites in greatest abundance in the study were products of amide hydrolysis with no further biotransformation (M1), followed by amide hydrolysis with monohydroxylation (M2.1). Three APP-CHMINACA-specific metabolites were generated, all of which were hydroxylated on the CHM group; one mono-, di- and tri-hydroxylated metabolite each was produced, with dihydroxylation (M6) present in the greatest abundance. The authors propose that metabolites M1, M2.1 and M6 are the most appropriate markers to determine consumption of APP-CHMINACA. The methods used in the current study have broad applicability and have been used to determine the in vitro metabolic profiles of multiple synthetic cannabinoids and other classes of NPS. This research can be used to guide analytical scientists in method development, synthesis of reference material, pharmacological testing of proposed metabolites and prediction of metabolic processes of compounds yet to be studied.

In vitro and in vivo metabolism and detection of 3-HO-PCP, a synthetic phencyclidine, in human samples and pooled human hepatocytes using high resolution mass spectrometry

The new psychoactive substance (NPS) 3-HO-PCP, a phencyclidine (PCP) analog, was detected in a law enforcement seizure and in forensic samples in Denmark. Compared with PCP, 3-HO-PCP is known to be a more potent dissociative NPS, but no toxicokinetic investigations of 3-HO-PCP are yet available. Therefore, 3-HO-PCP was quantified in in vivo samples, and the following were investigated: plasma protein binding, in vitro and in vivo metabolites, and metabolic targets. All samples were separated by liquid chromatography and analyzed by mass spectrometry. The unbound fraction in plasma was determined as 0.72 ± 0.09. After in vitro incubation with pooled human hepatocytes, four metabolites were identified: a piperidine-hydroxyl-and piperidine ring opened N-dealkyl-COOH metabolite, and O-glucuronidated- and O-sulfate-conjugated metabolites. In vivo, depending on the sample and sample preparation, fewer metabolites were detected, as the O-sulfate-conjugated metabolite was not detected. The N-dealkylated-COOH metabolite was the main metabolite in the deconjugated urine sample. in vivo analytical targets in blood and brain samples were 3-HO-PCP and the O-glucuronidated metabolite, with 3-HO-PCP having the highest relative signal intensity. The drug levels of 3-HO-PCP quantified in blood were 0.013 and 0.095 mg/kg in a living and a deceased subject, respectively. The 3-HO-PCP concentrations in deconjugated urine in a sample from a living subject and in post-mortem brain were 7.8 and 0.16 mg/kg, respectively. The post mortem results showed a 1.5-fold higher concentration of 3-HO-PCP in the brain tissue than in the post mortem blood sample.

Nutrigenomics-Associated Impacts of Nutrients on Genes and Enzymes With Special Consideration of Aromatase

Interactions are occurring in the course of liberation, absorption, distribution, metabolism, and excretion of active ingredients, or at the target receptors. They are causing therapy failures and undesirable events. Forty-seven of fifty-seven human hepatic isoenzymes are specific and relevant in hormone and vitamin metabolism and biosynthesis. Aromatase (syn. CYP19A1) is one of the specific CYP450 isoenzymes so far not elucidated in detail. As aromatase-inhibiting phytochemicals are currently recommended for breast cancer prevention and as add-on accompanying aromatase-inhibitor pharmacotherapy, it was the aim of this literature review to assess whether a common interpretation on genetic and -omics basis could be found. Articles retrieved showed that traditional antioxidation diet is one of the most approved explanations of inhibition of aromatase by phytonutrients of flavonoid derivatives. Flavonoids compete for the oxygen provided by the heme moiety of aromatase in the course of aromatase-catalyzed conversion of steroid precursors to estrogens. Flavonoids are therefore promoted for breast cancer prevention. A further explanation of flavonoids' mechanism of action proposed was related to enzymatic histone deacetylation. By keeping DNA-structure wide through a high acetylation degree, acetylated histones favor transcription and replication. This mechanism corresponds to a procedure of switching genes on. Inhibiting acetylation and therefore switching genes off might be an important regulation of repressing cancer genes. Aromatase expression depends on the genotype and phenotype of a person. Aromatase itself depends on the expression of the heme moiety encoded in the genotype. Biosynthesis of porphyrins in turn depends on the substrates succinate and glycine, as well as on a series of further enzymes, with ALA synthetase as the rate-limiting step. The effect of the heme moiety as prosthetic group of aromatase further depends on the absorption of iron as a function of pH and redox state. To assess the function of aromatase precisely, multiple underlying biochemical pathways need to be evaluated. As a conclusion, the genetic regulation of metabolism is a complex procedure affecting multiple pathways. To understand a metabolic step, multiple underlying individually performing reactions need to be considered if personalized (nutritional) medicine should bring an advantage for a patient. Nutrition sciences need to consider the genome of an individual to truly find answers to nutrition-derived non-communicable diseases. With current GWAS (genome-wide association study) approaches, inherited errors of metabolism are identified and ideally treated effectively. It is much more difficult to get a precise genetic profile for non-communicable diseases stemming from multifactorial causes. Polygenic risks evaluation is feasible but diagnostic tools are not yet available in a desired extent. Neither flavonoid researchers nor providers of genetic testing kits are going into the details needed for a truly personalized nutritional medicine. The next step with profiling the exome and then the whole genome is on the threshold of becoming routine diagnosis and of bringing the desired details.

Electrochemical and in silico approaches for liver metabolic oxidation of antitumor-active triazoloacridinone C-1305

5-Dimethylaminopropylamino-8-hydroxytriazoloacridinone (C-1305) is a promising antitumor compound developed in our laboratory. A better understanding of its metabolic transformations is still needed to explain the multidirectional mechanism of pharmacological action of triazoloacridinone derivatives at all. Thus, the aim of the current work was to predict oxidative pathways of C-1305 that would reflect its phase I metabolism. The multi-tool analysis of C-1305 metabolism included electrochemical conversion and in silico sites of metabolism predictions in relation to liver microsomal model. In the framework of the first approach, an electrochemical cell was coupled on-line to an electrospray ionization mass spectrometer. The effluent of the electrochemical cell was also injected onto a liquid chromatography column for the separation of different products formed prior to mass spectrometry analysis. In silico studies were performed using MetaSite software. Standard microsomal incubation was employed as a reference procedure. We found that C-1305 underwent electrochemical oxidation primarily on the dialkylaminoalkylamino moiety. An unknown N-dealkylated and hydroxylated C-1305 products have been identified. The electrochemical system was also able to simulate oxygenation reactions. Similar pattern of C-1305 metabolism has been predicted using in silico approach. Both proposed strategies showed high agreement in relation to the generated metabolic products of C-1305. Thus, we conclude that they can be considered as simple alternatives to enzymatic assays, affording time and cost efficiency.

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Three different strategies for the investigation of C-1305 oxidative metabolism were presented.

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Phase I products of the antitumor agent were easily generated within a matrix-free environment.

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Products of C-1305 electrochemical oxidation were typical for P450-catalyzed reactions.

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We observed a good accordance between electrochemical, in silico, and enzymatic results.

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Electrochemical and in silico methods are fast alternatives for enzymatic assays.

Mimicking of Phase I Metabolism Reactions of Molindone by HLM and Photocatalytic Methods with the Use of UHPLC-MS/MS

Establishing the metabolism pathway of the drug undergoing the hepatic biotransformation pathway is one of the most important aspects in the preclinical discovery process since the presence of toxic or reactive metabolites may result in drug withdrawal from the market. In this study, we present the structural elucidation of six, not described yet, metabolites of an antipsychotic molecule: molindone. The elucidation of metabolites was supported with a novel photocatalytical approach with the use of WO3 and WS2 assisted photochemical reactions. An UHPLC-ESI-Q-TOF combined system was used for the registration of all obtained metabolite profiles as well as to record the high resolution fragmentation spectra of the observed transformation products. As a reference in the in vitro metabolism simulation method, the incubation with human liver microsomes was used. Chemometric comparison of the obtained profiles pointed out the use of the WO3 approach as being more convenient in the field of drug metabolism studies. Moreover, the photocatalysis was used in the direction of the main drug metabolite synthesis in order to further isolation and characterization.

Dimensionally Enhanced Antibacterial Library Screening

The emergence and spread of antimicrobial resistance is a major public health threat, and there is an urgent need to develop new strategies to address the issue. In this study, the possibility of enhancing a whole cell based antibacterial library screen by increasing the dimensionality of the screening effort is explored using methicillin-resistant Staphylococcus aureus (MRSA) as the target organism. One dimension involved generating and screening a human liver microsome metabolized FDA approved drug library. Comparative screening of the un-metabolized (UM) and pre-metabolized (PM) libraries allows identification of intrinsically active agents from the UM library screen and of agents with active metabolites from the PM library screen. To further enhance this screening effort, it was combined with a -/+ resistant to antibiotic screen (-/+ cefoxitin; Cef). This allows the identification of agents that can act synergistically with the resistant to antibiotic. This approach revealed five compounds with substantially improved activity after metabolism and four compounds with substantial synergistic activity with cefoxitin. Capecitabine in particular only had significant antibacterial activity after metabolism. Its metabolites were isolated, identified, and characterized for spectrum of activity along with several other anticancer drugs with anti-MRSA activity. Floxuridine, gemcitabine, novobiocin, and rifaximin were identified as having substantial synergy with cefoxitin from the -/+Cef screens. Checkerboard assays verified synergy for these agents. Floxuridine demonstrated a particularly high degree of synergy with cefoxitin (FIC = 0.14). This study demonstrates how a dimensionally enhanced comparative screening effort can identify new antibacterial agents and strategies for countering antibacterial agent resistance.

Comparative Proteomics Analysis of Human Liver Microsomes and S9 Fractions

Human liver microsomes (HLM) and human liver S9 fractions (HLS9) are commonly used to study drug metabolism in vitro. However, a quantitative comparison of HLM and HLS9 proteomes is lacking, resulting in the arbitrary selection of one hepatic preparation over another and in difficulties with data interpretation. In this study, we applied a label-free global absolute quantitative proteomics method to the analysis of HLS9 and the corresponding HLM prepared from 102 individual human livers. A total of 3137 proteins were absolutely quantified, and 3087 of those were determined in both HLM and HLS9. Protein concentrations were highly correlated between the two hepatic preparations (R = 0.87, P < 0.0001). We reported the concentrations of 98 drug-metabolizing enzymes (DMEs) and 51 transporters, and demonstrated significant differences between their abundances in HLM and HLS9. We also revealed the protein-protein correlations among these DMEs and transporters and the sex effect on the HLM and HLS9 proteomes. Additionally, HLM and HLS9 displayed distinct expression patterns for protein markers of cytosol and various cellular organelles. Moreover, we evaluated the interindividual variability of three housekeeping proteins, and identified five proteins with low variation across individuals that have the potential to serve as new internal controls for western blot experiments. In summary, these results will lead to better understanding of data obtained from HLM and HLS9 and assist in in vitro-in vivo extrapolations. Knowing the differences between HLM and HLS9 also allows us to make better-informed decisions when choosing between these two hepatic preparations for in vitro drug metabolism studies. SIGNIFICANCE STATEMENT: This investigation revealed significant differences in protein concentrations of drug-metabolizing enzymes and transporters between human liver microsomes and S9 fractions. We also determined the protein-protein correlations among the drug-metabolizing enzymes and transporters and the sex effect on the proteomes of these two hepatic preparations. The results will help interpret data obtained from these two preparations and allow us to make more informed decisions when choosing between human liver microsomes and S9 fractions for in vitro drug metabolism studies.

Simulation of phase I metabolism reactions of selected calcium channel blockers by human liver microsomes and photochemical methods with the use of Q-TOF LC/MS

The in vitro phase I metabolism of perhexiline and flunarizine, two calcium channel blockers was investigated during this study with the use of human liver microsomes (HLM) method compared with TiO₂, WO₃ and ZnO catalyzed photochemical reaction. In order to determine the structures of metabolites an quadrupole time-of-flight mass spectrometry combined with liquid chromatography (Q-TOF LC/MS) system was used. The obtained high resolution mass spectra enabled to identify thirteen products of metabolism of selected drugs including three not yet described metabolites of perhexiline and two new metabolites of flunarizine. The vast majority of metabolites were confirmed also with the participation of photocatalytic approach of the drug metabolism simulation. The comparison of all metabolic profiles made with the use of computational methods drew attention particularly to TiO₂ and WO₃ catalyzed photochemical reaction as similar to HLM incubation. Additionally, in silico toxicity assessment of the detected transformation products of the analyzed substances was also evaluated.

In vitro inhibition of human CYP2D6 by the chiral pesticide fipronil and its metabolite fipronil sulfone: Prediction of pesticide-drug interactions

Fipronil is a chiral insecticide employed worldwide in crops, control of public hygiene and control of veterinary pests. Humans can be exposed to fipronil through occupational, food, and environmental contamination. Therefore, the risk assessment of fipronil in humans is important to protect human health. Fipronil sulfone is the major metabolite formed during fipronil metabolism by humans. Since the CYP450 enzymes are the main ones involved in drug metabolism, the evaluation of their inhibition by fipronil and its main metabolite is important to predict drug-pesticide interactions. The aim of this work was to investigate the inhibition effects of rac-fipronil, S-fipronil, R-fipronil and fipronil sulfone on the main human CYP450 isoforms. The results showed that CYP2D6 is the only CYP450 isoform inhibited by these xenobiotics. In addition, no enantioselective differences were observed in the inhibition of CYP450 isoforms by fipronil and its individuals' enantiomers. Rac-fipronil, S-fipronil and R-fipronil are moderate CYP2D6 inhibitors showing a competitive inhibition profile. On the other hand, the metabolite fipronil sulfone showed to be a strong inhibitor of CYP2D6 also by competitive inhibition. These results highlight the importance of metabolite evaluation on pesticide safety since the metabolism of fipronil into fipronil sulfone increases the risk of pesticide-drug interactions for drugs metabolized by CYP2D6.

In vitro and in vivo Human Metabolism of (S)-[18F]Fluspidine - A Radioligand for Imaging σ1 Receptors With Positron Emission Tomography (PET)

(S)-[¹⁸F]fluspidine ((S)-[¹⁸F]1) has recently been explored for positron emission tomography (PET) imaging of sigma-1 receptors in humans. In the current report, we have used plasma samples of healthy volunteers to investigate the radiometabolites of (S)-[¹⁸F]1 and elucidate their structures with LC-MS/MS. For the latter purpose additional in vitro studies were conducted by incubation of (S)-[¹⁸F]1 and (S)-1 with human liver microsomes (HLM). In vitro metabolites were characterized by interpretation of MS/MS fragmentation patterns from collision-induced dissociation or by use of reference compounds. Thereby, structures of corresponding radio-HPLC-detected radiometabolites, both in vitro and in vivo (human), could be identified. By incubation with HLM, mainly debenzylation and hydroxylation occurred, beside further mono- and di-oxygenations. The product hydroxylated at the fluoroethyl side chain was glucuronidated. Plasma samples (10, 20, 30 min p.i., n = 5-6), obtained from human subjects receiving 250–300 MBq (S)-[¹⁸F]1 showed 97.2, 95.4, and 91.0% of unchanged radioligand, respectively. In urine samples (90 min p.i.) the fraction of unchanged radioligand was only 2.6% and three major radiometabolites were detected. The one with the highest percentage, also found in plasma, matched the glucuronide formed in vitro. Only a small amount of debenzylated metabolite was detected. In conclusion, our metabolic study, in particular the high fractions of unchanged radioligand in plasma, confirms the suitability of (S)-[¹⁸F]1 as PET radioligand for sigma-1 receptor imaging.

Pharmacologic interaction between oxfendazole and triclabendazole: In vitro biotransformation and systemic exposure in sheep

The aim of the current work was to evaluate a potential pharmacokinetic interaction between the flukicide triclabendazole (TCBZ) and the broad-spectrum benzimidazole (BZD) anthelmintic oxfendazole (OFZ) in sheep. To this end, both an in vitro assay in microsomal fractions and an in vivo trial in lambs parasitized with Haemonchus contortus resistant to OFZ and its reduced derivative fenbendazole (FBZ) were carried out. Sheep microsomal fractions were incubated together with OFZ, FBZ, TCBZ, or a combination of either FBZ and TCBZ or OFZ and TCBZ. OFZ production was significantly diminished upon coincubation of FBZ and TCBZ, whereas neither FBZ nor OFZ affected the S-oxidation of TCBZ towards its sulfoxide and sulfone metabolites. For the in vivo trial, lambs were treated with OFZ (Vermox^® oral drench at a single dose of 5 mg/kg PO), TCBZ (Fasinex^® oral drench at a single dose of 12 mg/kg PO) or both compounds at a single dose of 5 (Vermox^®) and 12 mg/kg (Fasinex^®) PO. Blood samples were taken to quantify drug and metabolite concentrations, and pharmacokinetic parameters were calculated by means of non-compartmental analysis. Results showed that the pharmacokinetic parameters of active molecules and metabolites were not significantly altered upon coadministration. The sole exception was the increase in the mean residence time (MRT) of OFZ and FBZ sulfone upon coadministration, with no significant changes in the remaining pharmacokinetic parameters. This research is a further contribution to the study of metabolic drug-drug interactions that may affect anthelmintic efficacies in ruminants.

In vitro Phase I metabolism of indazole carboxamide synthetic cannabinoid MDMB-CHMINACA via human liver microsome incubation and high-resolution mass spectrometry

Synthetic cannabinoids have proliferated over the last decade and have become a major public health and analytical challenge, critically impacting the clinical and forensic communities. Indazole carboxamide class synthetic cannabinoids have been particularly rampant, and exhibit severe toxic effects upon consumption due to their high binding affinity and potency at the cannabinoid receptors (CB₁ and CB₂ ). MDMB-CHMINACA, methyl 2-[1-(cyclohexylmethyl)-1H-indazole-3-carboxamido]-3,3-dimethylbutanoate, a compound of this chemical class, has been identified in forensic casework and is structurally related to several other synthetic cannabinoids. This study presents the first extensive report on the Phase I metabolic profile of MDMB-CHMINACA, a potent synthetic cannabinoid. The in vitro metabolism of MDMB-CHMINACA was determined via incubation with human liver microsomes and high-resolution mass spectrometry. The accurate masses of precursor and fragments, mass error (ppm), and chemical formula were obtained for each metabolite. Twenty-seven metabolites were identified, encompassing twelve metabolite types. The major biotransformations observed were hydroxylation and ester hydrolysis. Hydroxylations were located predominantly on the cyclohexylmethyl (CHM) moiety. Ester hydrolysis was followed by additional biotransformations, including dehydrogenation; mono- and dihydroxylation and ketone formation, each with dehydrogenation. Minor metabolites were identified and reported. The authors propose that CHM-monohydroxylated metabolites specific to MDMB-CHMINACA are the most suitable candidates for implementation into bioanalytical assays to demonstrate consumption of this synthetic cannabinoid. Due to the structural similarity of MDMB-CHMINACA and currently trending synthetic cannabinoids whose metabolic profiles have not been reported, the results of this study can be used as a guide to predict their metabolic pathways.

In Vitro Metabolism and Hepatic Intrinsic Clearance of the Synthetic Cannabinoid Receptor Agonist JWH-122 and Its Four ω-Halogenated Analogues

The number of new psychoactive substances (NPS) emerging on the illicit drug market has increased over the last decade. Halogenation of existing illicit drugs is a particular trend, with the purpose of both circumventing the law and altering the toxicodynamic and toxicokinetic profiles of the compounds. This study investigates the in vitro impact of JWH-122 ω-halogenation (fluoro, chloro, bromo and iodo) on the metabolism, apparent intrinsic hepatic clearance and analytical targets for detecting drug consumption. Metabolite profiling was conducted with pooled human liver microsomes, suspended rat hepatocytes and pooled human hepatocytes. The in vitro half-life was also determined in pooled human hepatocytes. All samples were analysed by liquid chromatography/high-resolution mass spectrometry. All compounds, except for JWH-122, showed high formation rates of phase I metabolites, predominantly ω-COOH and methylnaphthyl hydroxylation metabolites. Phase II metabolites were ω-O-glucuronides, methylnaphthyl O-glucuronides and ω-glutathione conjugates. The relative ion intensity of the glutathione conjugates increased with the ω-halogen size, with I-JWH-122 having the highest intensity. Stability studies gave a low half-life and a high intrinsic hepatic clearance for JWH-122 (1305 mL/min/kg) and MAM-2201 (1408 mL/min/kg). Cl-, Br- and I-JWH-122 showed increasing half-life with increasing ω-halogen size, with intrinsic clearance values of 235-502 mL/min/kg. The recommended analytical targets for consumption of JWH-122 or ω-halogenated JWH-122 analogues are the ω-COOH metabolites for unspecific profiling and the methylnaphthyl hydroxylated metabolites to distinguish the compounds. Furthermore, ω-halogenation with larger halogens appears to increase the intrinsic hepatic stability, thereby prolonging exposure and possibly the duration of action.

P450 Monooxygenases Enable Rapid Late-Stage Diversification of Natural Products via C-H Bond Activation

The biological potency of natural products has been exploited for decades. Their inherent structural complexity and natural diversity might hold the key to efficiently address the urgent need for the development of novel pharmaceuticals. At the same time, it is that very complexity, which impedes necessary chemical modifications such as structural diversification, to improve the effectiveness of the drug. For this purpose, Cytochrome P450 enzymes, which possess unique abilities to activate inert sp3-hybridised C-H bonds in a late-stage fashion, offer an attractive synthetic tool. In this review the potential of cytochrome P450 enzymes in chemoenzymatic lead diversification is illustrated discussing studies reporting late-stage functionalisations of natural products and other high-value compounds. These enzymes were proven to extend the synthetic toolbox significantly by adding to the flexibility and efficacy of synthetic strategies of natural product chemists, and scientists of other related disciplines.

Electrochemical simulation of metabolism for antitumor-active imidazoacridinone C-1311 and in silico prediction of drug metabolic reactions

The metabolism of antitumor-active 5-diethylaminoethylamino-8-hydroxyimidazoacridinone (C-1311) has been investigated widely over the last decade but some aspects of molecular mechanisms of its metabolic transformation are still not explained. In the current work, we have reported a direct and rapid analytical tool for better prediction of C-1311 metabolism which is based on electrochemistry (EC) coupled on-line with electrospray ionization mass spectrometry (ESI-MS). Simulation of the oxidative phase I metabolism of the compound was achieved in a simple electrochemical thin-layer cell consisting of three electrodes (ROXY^™, Antec Leyden, the Netherlands). We demonstrated that the formation of the products of N-dealkylation reactions can be easily simulated using purely instrumental approach. Newly reported products of oxidative transformations like hydroxylated or oxygenated derivatives become accessible. Structures of the electrochemically generated metabolites were elucidated on the basis of accurate mass ion data and tandem mass spectrometry experiments. In silico prediction of main sites of C-1311 metabolism was performed using MetaSite software. The compound was evaluated for cytochrome P450 1A2-, 3A4-, and 2D6-mediated reactions. The results obtained by EC were also compared and correlated with those of reported earlier for conventional in vitro enzymatic studies in the presence of liver microsomes and in the model peroxidase system. The in vitro experimental approach and the in silico metabolism findings showed a quite good agreement with the data from EC/ESI-MS analysis. Thus, we conclude here that the electrochemical technique provides the promising platform for the simple evaluation of drug metabolism and the reaction mechanism studies, giving first clues to the metabolic transformation of pharmaceuticals in the human body.

Quantitative MALDI Imaging of Spatial Distributions and Dynamic Changes of Tetrandrine in Multiple Organs of Rats

Detailed spatio-temporal information on drug distribution in organs is of paramount importance to assess drug clinically-relevant properties and potential side-effects. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) as a label-free and sensitive imaging modality provides an additional means of accurately visualizing drug and its metabolites distributions in tissue sections. However, technical limitations, complex physiochemical environment of surface and low abundance of target drugs make quantitative MALDI imaging of drug and its metabolites quite challenging.

Methods: In this study, an internal standard correction strategy was applied for quantitative MALDI imaging of tetrandrine in multiple organs of rats including lung, liver, kidney, spleen, and heart. The feasibility and reliability of the developed quantitative MSI method were validated by conventional liquid chromatography-tandem MS (LC-MS/MS) analysis, and the two methods showed a significant correlation.

Results: The quantitative MALDI imaging method met the requirements of specificity, sensitivity and linearity. Tissue-specific spatio-temporal distribution patterns of tetrandrine in different organs were revealed after intravenous administration in the rat. Moreover, demethylated metabolite was detected in liver tissues.

Conclusions: The current work illustrates that quantitative MALDI imaging provides an alternative means of accurately addressing the problem of drug and its metabolites distribution in tissues, complementary to traditional LC-MS/MS of tissue homogenates and whole-body autoradiography (WBA). Quantitative spatio-chemical information obtained here can improve our understanding of pharmacokinetics (PK), pharmacodynamics (PD), and potential transient toxicities of tetrandrine in organs, and possibly direct further optimization of drug properties to reduce drug-induced organ toxicity.

Use of high-throughput enzyme-based assay with xenobiotic metabolic capability to evaluate the inhibition of acetylcholinesterase activity by organophosphorous pesticides

The inhibition of acetylcholinesterase (AChE) has pharmaceutical applications as well as potential neurotoxic effects. The in vivo metabolites of some chemicals including organophosphorus pesticides can become more potent AChE inhibitors compared to their parental compounds. To account for the effects of biotransformation, we have developed and characterized a high-throughput screening method for identifying AChE inhibitors that become active or more potent following xenobiotic metabolism. In this study, an enzyme-based assay was developed in 1536-well plates using recombinant human AChE combined with human or rat liver microsomes. The AChE activity was measured by two methods with different readouts: colorimetric and fluorescent. The assay exhibited exceptional performance characteristics including large assay signal window, low well-to-well variability and high reproducibility. The performance of the assays with microsomes was characterized by testing a group of known AChE inhibitors including parent compounds and their metabolites. Large potency differences between the parent compounds and the metabolites were observed in the assay with microsome addition. Both assay readouts were required for maximal sensitivity. These results demonstrate that this platform is a promising method to profile large numbers of chemicals that require metabolic activation for inhibiting AChE activity.

Antibiotics may increase triazine herbicide exposure risk via disturbing gut microbiota

BACKGROUND

Antibiotics are commonly used worldwide, and pesticide is a kind of xenobiotic to which humans are frequently exposed. The interactive impact of antibiotics on pesticides has rarely been studied. We aim to investigate the effects of antibiotics on the pesticide exposure risk and whether gut microbiota altered by antibiotics has an influence on pesticide bioavailability. Furthermore, we explored the mechanisms of gut microbiota affecting the fate of pesticides in the host.

RESULTS

The oral bioavailability of triazine herbicides significantly increased in the rats treated with ampicillin or antibiotic cocktails. The antibiotic-altered gut microbiota directly influenced the increased pesticide bioavailability through downregulating hepatic metabolic enzyme gene expression and upregulating intestinal absorption-related proteins.

CONCLUSIONS

Antibiotics could increase the pesticide bioavailability and thereby may increase the pesticide exposure risk. The antibiotic-altered gut microbiota that could alter the hepatic metabolic enzyme gene expression and intestinal absorption-related proteome was a critical cause of the increased bioavailability. This study revealed an undiscovered potential health impact of antibiotics and reminded people to consider the co-exposed xenobiotics when taking antibiotics.

Synthesis, antituberculosis studies and biological evaluation of new quinoline derivatives carrying 1,2,4-oxadiazole moiety

Tuberculosis is the infectious disease caused by mycobacterium tuberculosis (Mtb), responsible for the utmost number of deaths annually across the world. Herein, twenty-one new substituted 1,2,4-oxadiazol-3-ylmethyl-piperazin-1-yl-quinoline derivatives were designed and synthesized through multistep synthesis followed by in vitro evaluation of their antitubercular potential against Mtb WT H37Rv. The compound QD-18 was found to be promising with MIC value of 0.5 µg/ml and QD-19 to QD-21 were also remarkable with MIC value of 0.25 µg/ml. Additionally, we have carried out experiments to confirm the metabolic stability, cytotoxicity and pharmacokinetics of these compounds along with kill kinetics of QD-18. These compounds were found to be orally bioavailable and highly effective. Altogether, these results indicate that QD-18, QD-19, QD-20 and QD-21 are promising lead compounds for the development of a novel chemical class of antitubercular drugs.

The ongoing challenge of novel psychoactive drugs of abuse. Part I. Synthetic cannabinoids (IUPAC Technical Report)

In the past decade, the world has experienced a large increase in the number of novel compounds appearing on the illicit drug market for recreational purposes. Such substances are designed to circumvent governmental regulations; the illegal drug manufacturers take a known psychoactive compound reported in the scientific literature and slightly modify its chemical structure in order to produce analogues that will mimic the pharmacological activity of the original substance. Many of these novel substances are sold via the Internet. Among the various chemical classes, synthetic cannabinoid receptor modulators, commonly referred to as “synthetic cannabinoids” have been at the forefront, as demonstrated by the frequency of drug seizures, numerous severe toxic effects, and fatalities associated with some of these substances. This review presents the chemical structures of relevant synthetic cannabinoids and describes their mechanism of action, pharmacological features, metabolic pathways, and structure-activity relationships. It illustrates the approaches used in forensic testing, both for bulk analysis (drug seizures) and for analytical toxicology (biological matrices) and discusses aspects of regulation surrounding this drug class. This report is intended to provide pertinent information for the purposes of informing scientific, medical, social, and governmental bodies about this ever-evolving recreational drug class and the challenges it poses worldwide.

High-throughput metabolism-induced toxicity assays demonstrated on a 384-pillar plate

The US Environmental Protection Agency (EPA) launched the Transform Tox Testing Challenge in 2016 with the goal of developing practical methods that can be integrated into conventional high-throughput screening (HTS) assays to better predict the toxicity of parent compounds and their metabolites in vivo. In response to this need and to retrofit existing HTS assays for assessing metabolism-induced toxicity of compounds, we have developed a 384-pillar plate that is complementary to traditional 384-well plates and ideally suited for culturing human cells in three dimensions at a microscale. Briefly, human embryonic kidney (HEK) 293 cells in a mixture of alginate and Matrigel were printed on the 384-pillar plates using a microarray spotter, which were coupled with 384-well plates containing nine model compounds provided by the EPA, five representative Phase I and II drug metabolizing enzymes (DMEs), and one no enzyme control. Viability and membrane integrity of HEK 293 cells were measured with the calcein AM and CellTiter-Glo^® kit to determine the IC₅₀ values of the nine parent compounds and DME-generated metabolites. The Z' factors and the coefficient of variation measured were above 0.6 and below 14%, respectively, indicating that the assays established on the 384-pillar plate are robust and reproducible. Out of nine compounds tested, six compounds showed augmented toxicity with DMEs and one compound showed detoxification with a Phase II DME. This result indicates that the 384-pillar plate platform can be used to measure metabolism-induced toxicity of compounds in high-throughput with individual DMEs. As xenobiotics metabolism is a complex process with a variety of DMEs involved, the predictivity of our approach could be further improved with mixtures of DMEs.

Study of the in vitro and in vivo metabolism of 4-HO-MET

4-Hydroxy-N-methyl-N-ethyltryptamine (4-HO-MET) is a new psychoactive substance (NPS) of the chemical class of tryptamines. It shows structural similarities to the endogenous neurotransmitter serotonin, and is a serotonergic hallucinogen, affecting emotional, motoric, and cognitive functions. The knowledge about its biotransformation is mandatory to confirm the abuse of the substance by urine analysis in forensic cases. Therefore, phase I metabolites were generated by the use of the pooled human liver microsomes (pHLM) in vitro model and analyzed by high-performance liquid chromatography high-resolution tandem mass spectrometry with information-dependent acquisition (HPLC-IDA-HR-MS/MS). Furthermore, three authentic urine samples was analyzed and results were compared: 12 different in vitro and 4 in vivo metabolites were found. The predominant biotransformation steps observed in vitro were mono- or dihydroxylation of 4-HO-MET, besides demethylation, demethylation in combination with monohydroxylation, formation of a carboxylic acid, deethylation, and oxidative deamination. In vivo, monohydroxylation, and glucuronidation were detected. A metabolic pathway based on these results was proposed. For the analysis of urine samples in forensic cases, the N-oxide metabolite and the HO-alkyl metabolite are recommended as target compounds, besides the glucuronides of 4-HO-MET and the parent compound 4-HO-MET itself.

Characterization of in vitro and in vivo metabolism of leelamine using liquid chromatography-tandem mass spectrometry

Leelamine is a diterpene compound found in the bark of pine trees and has garnered considerable interest owing to its potent anticancer properties. The aim of the present study was to investigate the metabolic profile of leelamine in human liver microsomes (HLMs) and mice using liquid chromatography-tandem mass spectrometry (LC-MS/MS). We found that leelamine undergoes only Phase I metabolism, which generates one metabolite that is mono-hydroxylated at the C9 carbon of the octahydrophenanthrene ring (M1) both in vitro and in vivo. The structure and metabolic pathway of M1 were determined from the MSⁿ fragmentation obtained by collision-induced dissociation using LC-MS/MS in HLMs. Cytochrome p450 (CYP) 2D6 was found to be the dominant CYP enzyme involved in the biotransformation of leelamine to its hydroxylated metabolite, whereas CYP2C19, CYP1A1, and CYP3A4 contributed to some extent. Moreover, we identified only one metabolite M1, in the urine, but none in the feces. In conclusion, leelamine was metabolized to a mono-hydroxyl metabolite by CYP2D6 and mainly excreted in the urine.

Exploring the Metabolism of (+)-[18F]Flubatine in Vitro and in Vivo: LC-MS/MS Aided Identification of Radiometabolites in a Clinical PET Study

Both (+)-[¹⁸F]flubatine and its enantiomer (−)-[¹⁸F]flubatine are radioligands for the neuroimaging of α4β2 nicotinic acetylcholine receptors (nAChRs) by positron emission tomography (PET). In a clinical study in patients with early Alzheimer’s disease, (+)-[¹⁸F]flubatine ((+)-[¹⁸F]1) was examined regarding its metabolic fate, in particular by identification of degradation products detected in plasma and urine. The investigations included an in vivo study of (+)-flubatine ((+)-1) in pigs and structural elucidation of formed metabolites by LC-MS/MS. Incubations of (+)-1 and (+)-[¹⁸F]1 with human liver microsomes were performed to generate in vitro metabolites, as well as radiometabolites, which enabled an assignment of their structures by comparison of LC-MS/MS and radio-HPLC data. Plasma and urine samples taken after administration of (+)-[¹⁸F]1 in humans were examined by radio-HPLC and, on the basis of results obtained in vitro and in vivo, formed radiometabolites were identified. In pigs, (+)-1 was monohydroxylated at different sites of the azabicyclic ring system of the molecule. Additionally, one intermediate metabolite underwent glucuronidation, as also demonstrated in vitro. In humans, a fraction of 95.9 ± 1.9% (n = 10) of unchanged tracer remained in plasma, 30 min after injection. However, despite the low metabolic degradation, both radiometabolites formed in humans could be characterized as (i) a product of C-hydroxylation at the azabicyclic ring system, and (ii) a glucuronide conjugate of the precedingly-formed N8-hydroxylated (+)-[¹⁸F]1.

Glutathione sulfotransferase inhibition activity of a self-fermented beverage, Kanji

CONTEXT

Kanji, a liquid preparation of roots of Daucus carota L. ssp. sativus (Hoffm.) Arcang. var. vavilovii Mazk. (Apiaceae), may inhibit glutathione sulfotransferase (GST) activity due to ferulic acid content.

OBJECTIVES

GST inhibition activity and characterization of Kanji and methanol extract of D. carota roots, and oral absorption pattern of ferulic acid from Kanji in rats.

MATERIALS AND METHODS

GST inhibition activity of Kanji and methanol extract of D. carota roots in concentration range 0.001-100.00 mg/mL was determined using Sprague Dawley rat liver cytosolic fraction. Methanol extract upon column chromatography gave ferulic acid, which was used to characterize Kanji and determine its oral absorption pattern in Wistar rats.

RESULTS

The GST inhibition activity of Kanji (100.00 μg/mL), methanol extract of D. carota roots (100.00 μg/mL) and tannic acid (10.00 μg/mL, positive control) was found to be 0.162 ± 0.016, 0.106 ± 0.013 and 0.073 ± 0.004 μM/min/mg, respectively. Different Kanji samples and methanol extract contained ferulic acid (0.222-0.316 mg/g) and 0.77 mg/g, respectively. Ferulic acid did not appear in plasma after oral administration of Kanji.

DISCUSSION

Kanji having solid contents 80.0 μg/mL, equivalent to 0.0025 μg/mL ferulic acid, does not inhibit the activity of GST. The oral administration of Kanji, in human equivalent dose (528 mg/kg, 16.67 μg ferulic acid), to rats indicated poor absorption of ferulic acid.

CONCLUSION

Kanji having solid contents 14-36 mg/mL does not inhibit GST activity, hence may not interfere with drugs that are the substrates of GST, if taken concomitantly.

Inhibition of HIV-1 infection in humanized mice and metabolic stability of protein phosphatase-1-targeting small molecule 1E7-03

We recently identified the protein phosphatase-1 - targeting compound, 1E7-03 which inhibited HIV-1 in vitro. Here, we investigated the effect of 1E7-03 on HIV-1 infection in vivo by analyzing its metabolic stability and antiviral activity of 1E7-03 and its metabolites in HIV-1 infected NSG-humanized mice. 1E7-03 was degraded in serum and formed two major degradation products, DP1 and DP3, which bound protein phosphatase-1 in vitro. However, their anti-viral activities were significantly reduced due to inefficient cell permeability. In cultured cells, 1E7-03 reduced expression of several protein phosphatase-1 regulatory subunits including Sds22 as determined by a label free quantitative proteomics analysis. In HIV-1-infected humanized mice, 1E7-03 significantly reduced plasma HIV-1 RNA levels, similar to the previously described HIV-1 transcription inhibitor F07#13. We synthesized a DP1 analog, DP1-07 with a truncated side chain, which showed improved cell permeability and longer pharmacokinetic retention in mice. But DP1-07 was less efficient than 1E7-03 as a HIV-1 inhibitor both in vitro and in vivo, indicating that the full side chain of 1E7-03 was essential for its anti-HIV activity. Analysis of 1E7-03 stability in plasma and liver microsomes showed that the compound was stable in human, primate and ferret plasma but not in rodent plasma. However, 1E7-03 was not stable in human liver microsomes. Our findings suggest that 1E7-03 is a good candidate for future development of HIV-1 transcription inhibitors. Further structural modification and advanced formulations are needed to improve its metabolic stability and enhance its antiviral activity in non-human primate animals and humans.

In Vitro Biotransformation, Safety, and Chemopreventive Action of Novel 8-Methoxy-Purine-2,6-Dione Derivatives

Metabolic stability, mutagenicity, antimutagenicity, and the ability to scavenge free radicals of four novel 8-methoxy-purine-2,6-dione derivatives (compounds 1–4) demonstrating analgesic and anti-inflammatory properties were determined. Metabolic stability was evaluated in Cunninghamella and microsomal models, mutagenic and antimutagenic properties were assessed using the Ames and the Vibrio harveyi tests, and free radical scavenging activity was evaluated with 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay. In the Cunninghamella model, compound 2 did not undergo any biotransformation; whereas 3 and 4 showed less metabolic stability: 1–9 and 53–88% of the parental compound, respectively, underwent biotransformation reactions in different Cunninghamella strains. The metabolites detected after the biotransformation of 3 and 4 were aromatic hydroxylation and N-dealkylation products. On the other hand, the N-dealkylation product was the only metabolite formed in microsome assay. Additionally, these derivatives do not possess mutagenic potential in microbiological models (Vibrio harveyi and Salmonella typhimurium) considered. Moreover, all compounds showed a strong chemopreventive activity in the modified Vibrio harveyi strains BB7X and BB7M. However, radical scavenging activity was not the mechanism which explained the observed chemopreventive activity.

Study on the pharmacokinetics of deoxyschizandrin and schizandrin in combination with epigallocatechin gallate, a component of green tea, in rats

1. Green tea is commonly used worldwide due to its potential positive health benefits. We have examined the effects of epigallocatechin gallate (EGCG), the most abundant catechin in green tea, on the pharmacokinetics of deoxyschizandrin (DSD) and schizandrin (SD), which are the representative lignans in popular traditional Chinese medicines Fructus schisandrae, in rats. 2. The effects on the transport in Caco-2 cells and metabolism in human liver microsomes (HLMs) of DSD and SD by EGCG were determined to analyze their interactions thoroughly. 3. In pharmacokinetic studies, rats were divided into four groups. Each group was orally treated with DSD alone (Group 1), DSD combined with EGCG (Group 2), SD alone (Group 3) and SD combined with EGCG (Group 4). The pharmacokinetic parameters of DSD and SD in rats were determined by UPLC-MS/MS. 4. The in vivo results indicated that EGCG had no significant influence on the pharmacokinetic behaviors of DSD or SD in rats, which were in accordance with the in vitro transport and metabolism studies. However, there were marked differences between male and female rats among C_max, AUC_0-t, AUC_0-∞ of DSD and SD. This disparity suggested that gender differences might exist in the pharmacokinetic processes of DSD or SD in rats.

Metabolic profiling of five flavonoids from Dragon's Blood in human liver microsomes using high-performance liquid chromatography coupled with high resolution mass spectrometry

Although much is known about the pharmacological activities of Dragon's Blood (DB, a traditional Chinese herb), its metabolism in human liver microsomes (HLMs) and the cytochrome P450 (CYP) enzymes has not been studied. This study aims to identify the metabolic profile of five flavonoids (loureirin A, loureirin B, loureirin C, 7,4'-dihydroxyflavone and 5,7,4'-trihydroxyflavanone) from DB in HLMs as well as the CYP enzymes that are involved in the metabolism of them. High-resolution mass spectrometry was used to characterize the structures of their metabolites and 10 cDNA-expressed CYP enzymes (CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4 and CYP3A5) were used to verify which isozymes mediate in the metabolism of the metabolites. Totally, 29 metabolites including 10 metabolites of loureirin A, 10 metabolites of loureirin B, 4 metabolites of loureirin C, 2 metabolites of 7,4'-dihydroxyflavone and 3 metabolites of 5,7,4'-trihydroxyflavanone were elucidated and identified on the basis of the high-resolution MSⁿ data. The metabolic profile of the five flavonoids in HLMs involved hydroxylation, oxidation and demethylation. Among them, hydroxylation was the predominant biotransformation of the five flavonoids in HLMs, occurring in combination with other metabolic reactions. Assay with recombinant P450s revealed that CYP2C9 and CYP2C19 played an important role in the hydroxylation of flavonoids in HLMs. To the best of our knowledge, this is the first in vitro evaluation of the metabolic profile of loureirin A, loureirin B, loureirin C, 7,4'-dihydroxyflavone and 5,7,4'-trihydroxyflavanone in HLMs.

Large-scale multiplex absolute protein quantification of drug-metabolizing enzymes and transporters in human intestine, liver, and kidney microsomes by SWATH-MS: Comparison with MRM/SRM and HR-MRM/PRM

The purpose of the present study was to examine simultaneously the absolute protein amounts of 152 membrane and membrane-associated proteins, including 30 metabolizing enzymes and 107 transporters, in pooled microsomal fractions of human liver, kidney, and intestine by means of SWATH-MS with stable isotope-labeled internal standard peptides, and to compare the results with those obtained by MRM/SRM and high resolution (HR)-MRM/PRM. The protein expression levels of 27 metabolizing enzymes, 54 transporters, and six other membrane proteins were quantitated by SWATH-MS; other targets were below the lower limits of quantitation. Most of the values determined by SWATH-MS differed by less than 50% from those obtained by MRM/SRM or HR-MRM/PRM. Various metabolizing enzymes were expressed in liver microsomes more abundantly than in other microsomes. Ten, 13, and eight transporters listed as important for drugs by International Transporter Consortium were quantified in liver, kidney, and intestinal microsomes, respectively. Our results indicate that SWATH-MS enables large-scale multiplex absolute protein quantification while retaining similar quantitative capability to MRM/SRM or HR-MRM/PRM. SWATH-MS is expected to be useful methodology in the context of drug development for elucidating the molecular mechanisms of drug absorption, metabolism, and excretion in the human body based on protein profile information.

Comparative metabolism of four limonoids in human liver microsomes using ultra-high-performance liquid chromatography coupled with high-resolution LTQ-Orbitrap mass spectrometry

RATIONALE

Limonoids, characterized by a triterpenoid skeleton with a furan ring, are unique secondary metabolites widely distributed in the families of Rutaceae, particularly in Citrus species and Meliaceae. Studies on health benefits have demonstrated that limonoids have a range of biological activities. Dietary intake of citrus limonoids may provide a protective effect against the onset of various cancers and other xenobiotic related diseases. However, few studies about the metabolic profiles of limonoids have been carried out.

METHODS

The objectives of this study were to investigate the metabolic profiles of four limonoids (limonin, obacunone, nominin and gedunin) in human liver microsomes (HLMs) using ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry (UHPLC/HRMS) and to identify the cytochrome P450 (CYP) enzymes involved in the formation of their metabolites by recombinant human CYP enzymes.

RESULTS

Based on the accurate HR-MS/MS spectra and the proposed MS/MS fragmentation pathways, four metabolites of limonin (M1-1, M1-2, M1-3 and M1-4), eight metabolites ofobacunone (M2-1, M2-2, M2-3, M2-4, M2-5, M2-6, M2-7 and M2-8), six metabolites of nominin (M3-1, M3-2, M3-3, M3-4, M3-5 and M3-6) and three metabolites of gedunin (M4-1, M4-2 and M4-3) in HLMs were tentatively identified and the involved CYPs were investigated.

CONCLUSIONS

The results demonstrated that reduction at C-7 and C-16, hydroxylation and reaction of glycine with reduction limonoids were the major metabolic pathways of limonoids in HLMs. Among them, glycination with reduction was the unique metabolic process of limonoids observed for the first time. CYP2D6 and CYP3A4 played an important role in the isomerization and glycination of limonoids in HLMs, whereas other CYP isoforms were considerably less active. The results might help to understand the metabolic process of limonoids in vitro such as the unidentified metabolites of limonin glucoside observed in the medium of microbes and the biotransformation of limonin in juices. Moreover, it would be beneficial for us to further study the pharmacokinetic behavior of limonoids in vivo systematically.

Comparative metabolism of tussilagone in rat and human liver microsomes using ultra-high-performance liquid chromatography coupled with high-resolution LTQ-Orbitrap mass spectrometry

RATIONALE

Tussilagone is a major component in Tussilago farfara that has been widely used as an anti-tussive herbal medicine for the treatment of bronchitis, cough and asthmatic disorders in the clinic. However, its metabolism has been poorly investigated. In order to clarify its in vitro metabolism, a comparative analysis of its metabolic profile in rat liver microsomes (RLMs) and human liver microsomes (HLMs) was carried out. Further, the cytochrome P450 isoforms (CYPs) involved in the metabolism were investigated.

METHODS

In this work, the biotransformation of tussilagone in RLMs and HLMs was compared using ultra-high-performance liquid chromatography coupled with high-resolution LTQ-Orbitrap mass spectrometry (UHPLC/HRMS) and the CYPs involved in the metabolism were further investigated by recombinant human CYP enzymes.

RESULTS

Totally, nine metabolites of tussilagone were identified in RLMs and HLMs based on the proposed MS/MS fragmentation pathways of tussilagone and the accurate MS/MS spectra. Among them, one metabolite (M9) was detected in both RLMs and HLMs while the other eight metabolites were only detected in HLMs. Three hydroxylation metabolites (M6, M7 and M8) were detected in the assay with individual recombinant P450s incubation. M6 was detected in all CYPs except CYP2A6 while M7 and M8 were only observed in CYP3A4.

CONCLUSIONS

The HR-ESI-MS/MS fragmentation behavior of tussilagone and its metabolic profile in RLMs and HLMs were investigated for the first time. The results demonstrated that the biotransformation of tussilagone involved hydrolysis of ester bonds at C-14 and hydroxylation in the side chains at C-12, C-5' or C-6'. Among the CYPs, CYP3A4 played an important role in the hydroxylation reaction of tussilagone in vitro. Furthermore, the results indicated a species-related difference in the metabolism of tussilagone between RLMs and HLMs. This work provided basic information for the metabolism of tussilagone in RLMs and HLMs, which would help to better understand the pharmacological activities of tussilagone.