Metabolomics-assisted metabolite profiling of itraconazole in human liver preparations

Cyanide Trapping of Iminium Ion Reactive Metabolites: Implications for Clinical Hepatotoxicity

Reactive metabolite formation is a major mechanism of hepatotoxicity. Although reactive electrophiles can be soft or hard in nature, screening strategies have generally focused on the use of glutathione trapping assays to screen for soft electrophiles, with many data sets available to support their use. The use of a similar assay for hard electrophiles using cyanide as the trapping agent is far less common, and there is a lack of studies with sufficient supporting data. Using a set of 260 compounds with a defined hepatotoxicity status by the FDA, a comprehensive literature search yielded cyanide trapping data on an unbalanced set of 20 compounds that were all clinically hepatotoxic. Thus, a further set of 19 compounds was selected to generate cyanide trapping data, resulting in a more balanced data set of 39 compounds. Analysis of the data demonstrated that the cyanide trapping assay had high specificity (92%) and a positive predictive value (83%) such that hepatotoxic compounds would be confidently flagged. Structural analysis of the adducts formed revealed artifactual methylated cyanide adducts to also occur, highlighting the importance of full structural identification to confirm the nature of the adduct formed. The assay was demonstrated to add the most value for compounds containing typical structural alerts for hard electrophile formation: half of the severe hepatotoxins with these structural alerts formed cyanide adducts, while none of the severe hepatotoxins with no relevant structural alerts formed adducts. The assay conditions used included cytosolic enzymes (e.g., aldehyde oxidase) and an optimized cyanide concentration to minimize the inhibition of cytochrome P450 enzymes by cyanide. Based on the demonstrated added value of this assay, it is to be initiated for use at GSK as part of the integrated hepatotoxicity strategy, with its performance being reviewed periodically as more data is generated.

Untargeted metabolomics-assisted comparative cytochrome P450-dependent metabolism of fenbendazole in human and dog liver microsomes

Fenbendazole (FBZ), a benzimidazole carbamate anthelmintic, has attracted attention for its antitumor activity. This study examined the metabolic characteristics of FBZ in humans compared with those in dogs. The phase I metabolites were identified in liver microsomal incubates using liquid chromatography-mass spectrometry (MS)-based untargeted metabolomics approaches. Seven metabolites of FBZ were identified by principal component analysis and orthogonal partial least square-discriminant analysis based on the global ion variables of the FBZ incubation groups. The chemical structure of the FBZ metabolites was suggested by examining the MS/MS spectrum and isotope distribution pattern. Cytochrome P450 (CYP) 1A1, CYP2D6, and CYP2J2 were the major isozymes responsible for the FBZ metabolism. No differences in the types of metabolites produced by the two species were noted. Multivariate analysis of human and dog incubation groups showed that five metabolites were relatively abundant in humans and the other two were not. In summary, the phase I metabolic profile of FBZ and the comparative metabolism between humans and dogs were examined using an untargeted metabolomics approach. This study suggests a successful investigation of FBZ metabolism in humans for conducting safety assessments regarding drug repositioning.

Cytochrome P450 reaction phenotyping of itraconazole hydroxylation in the dog

Itraconazole (ITZ) is an important drug in the treatment of superficial and deep mycoses in dogs. Its primary metabolite is hydroxy-itraconazole, which has antifungal activity similar to the parent compound. The purpose of this study was to identify the cytochrome P450 enzyme (CYP) isoform(s) responsible for ITZ hydroxylation in canine liver. Reaction kinetics for ITZ hydroxylation were determined in a panel of canine recombinant CYPs and dog liver microsomes (DLMs). Findings were confirmed using CYP isoform-specific inhibitors in rCYPs and DLMs. In rCYP experiments, CYP2D15 and CYP3A12 had highest activity for ITZ hydroxylation. In inhibitor experiments, quinidine and erythromycin inhibited ITZ hydroxylation in CYP2D15 and CYP3A12, respectively, in an isoform-specific manner. In DLMs, quinidine and erythromycin combined inhibited ITZ hydroxylation more than erythromycin alone but not quinidine alone. However, this may be related to inhibitor potency rather than the contribution of the individual CYP isoforms to the reaction. These findings support a role for CYP2D15 and CYP3A12 in ITZ biotransformation in canine liver.

In Vitro Metabolism Study of Seongsanamide A in Human Liver Microsomes Using Non-Targeted Metabolomics and Feature-Based Molecular Networking

Seongsanamide A is a bicyclic peptide with an isodityrosine residue discovered in Bacillus safensis KCTC 12796BP which exhibits anti-allergic activity in vitro and in vivo without significant cytotoxicity. The purpose of this study was to elucidate the in vitro metabolic pathway and potential for drug interactions of seongsanamide A in human liver microsomes using non-targeted metabolomics and feature-based molecular networking (FBMN) techniques. We identified four metabolites, and their structures were elucidated by interpretation of high-resolution tandem mass spectra. The primary metabolic pathway associated with seongsanamide A metabolism was hydroxylation and oxidative hydrolysis. A reaction phenotyping study was also performed using recombinant cytochrome P450 isoforms. CYP3A4 and CYP3A5 were identified as the major metabolic enzymes responsible for metabolite formation. Seongsanamide A did not inhibit the cytochrome P450 isoforms commonly involved in drug metabolism (IC₅₀ > 10 µM). These results will contribute to further understanding the metabolism and drug interaction potential of various bicyclic peptides.

In Vitro Metabolism of Donepezil in Liver Microsomes Using Non-Targeted Metabolomics

Donepezil is a reversible acetylcholinesterase inhibitor that is currently the most commonly prescribed drug for the treatment of Alzheimer’s disease. In general, donepezil is known as a safe and well-tolerated drug, and it was not associated with liver abnormalities in several clinical trials. However, rare cases of drug-related liver toxicity have been reported since it has become commercially available. Few studies have investigated the metabolic profile of donepezil, and the mechanism of liver damage caused by donepezil has not been elucidated. In this study, the in vitro metabolism of donepezil was investigated using liquid chromatography–tandem mass spectrometry based on a non-targeted metabolomics approach. To identify metabolites, the data were subjected to multivariate data analysis and molecular networking. A total of 21 donepezil metabolites (17 in human liver microsomes, 21 in mice liver microsomes, and 17 in rat liver microsomes) were detected including 14 newly identified metabolites. One potential reactive metabolite was identified in rat liver microsomal incubation samples. Metabolites were formed through four major metabolic pathways: (1) O-demethylation, (2) hydroxylation, (3) N-oxidation, and (4) N-debenzylation. This study indicates that a non-targeted metabolomics approach combined with molecular networking is a reliable tool to identify and detect unknown drug metabolites.

Nontargeted Metabolomics by High-Resolution Mass Spectrometry to Study the In Vitro Metabolism of a Dual Inverse Agonist of Estrogen-Related Receptors β and γ, DN203368

DN203368 ((E)-3-[1-(4-[4-isopropylpiperazine-1-yl]phenyl) 3-methyl-2-phenylbut-1-en-1-yl] phenol) is a 4-hydroxy tamoxifen analog that is a dual inverse agonist of estrogen-related receptor β/γ (ERRβ/γ). ERRγ is an orphan nuclear receptor that plays an important role in development and homeostasis and holds potential as a novel therapeutic target in metabolic diseases such as diabetes mellitus, obesity, and cancer. ERRβ is also one of the orphan nuclear receptors critical for many biological processes, such as development. We investigated the in vitro metabolism of DN203368 by conventional and metabolomic approaches using high-resolution mass spectrometry. The compound (100 μM) was incubated with rat and human liver microsomes in the presence of NADPH. In the metabolomic approach, the m/z value and retention time information obtained from the sample and heat-inactivated control group were statistically evaluated using principal component analysis and orthogonal partial least-squares discriminant analysis. Significant features responsible for group separation were then identified using tandem mass spectra. Seven metabolites of DN203368 were identified in rat liver microsomes and the metabolic pathways include hydroxylation (M1-3), N-oxidation (M4), N-deisopropylation (M5), N,N-dealkylation (M6), and oxidation and dehydrogenation (M7). Only five metabolites (M2, M3, and M5-M7) were detected in human liver microsomes. In the conventional approach using extracted ion monitoring for values of mass increase or decrease by known metabolic reactions, only five metabolites (M1-M5) were found in rat liver microsomes, whereas three metabolites (M2, M3, and M5) were found in human liver microsomes. This study revealed that nontargeted metabolomics combined with high-resolution mass spectrometry and multivariate analysis could be a more efficient tool for drug metabolite identification than the conventional approach. These results might also be useful for understanding the pharmacokinetics and metabolism of DN203368 in animals and humans.

Simultaneous determination of itraconazole and its CYP3A4-mediated metabolites including N-desalkyl itraconazole in human plasma using liquid chromatography-tandem mass spectrometry and its clinical application

Background

Itraconazole (ITZ), a triazole antifungal agent, is metabolized to hydroxy-ITZ (OH-ITZ), keto-ITZ (KT-ITZ), and N-desalkyl ITZ (ND-ITZ) by cytochrome P450 3A4. The pharmacokinetics of ND-ITZ remain largely unknown due to the lack of an accurate and reliable determination method. This study aimed to develop a simultaneous determination method for ITZ and its three major metabolites including ND-ITZ in human plasma using isocratic liquid chromatography coupled to tandem mass spectrometry and then apply the method in a clinical setting.

Methods

Plasma specimens were pretreated by protein precipitation with acetonitrile. The supernatant was separated on a 3-μm particle octadecyl silane column (75 × 2.0 mm I.D.) in an isocratic elution of acetonitrile and 5 mM ammonium acetate (pH 6.0) (57:43, v/v). The method was applied to 10 patients treated with oral ITZ.

Results

The calibration curves of ITZ, OH-ITZ, KT-ITZ, and ND-ITZ were linear over the concentration ranges of 15–1500, 15–1500, 1–100, and 1–100 ng/mL, respectively. The pretreatment recoveries and matrix factors were 90.1–102.2% and 99.1–102.7%. Their intra- and inter-assay accuracies and imprecisions were 94.1–106.7% and 0.3–4.4%. The plasma concentrations of ITZ, OH-ITZ, KT-ITZ, and ND-ITZ 12 h after dosing ranged from 32.5–1127.1, 19.0–1166.7, 1.1–5.4, and 3.5–28.3 ng/mL, respectively, in immunocompromised patients.

Conclusions

This study developed a simultaneous determination method for concentrations of ITZ and its three metabolites including ND-ITZ in a clinical setting.

Metabolite identification and profile of endosulfan sulfate in three human liver preparations using liquid chromatography-high resolution mass spectrometry

In this study, we performed the metabolism of endosulfan sulfate in human liver preparations (human liver microsomes, S9 fractions and hepatocytes) to identify new metabolites using liquid chromatography-high resolution mass spectrometry (LC-HRMS). Endosulfan sulfate is a major oxidized metabolite of the organochlorine insecticide endosulfan, and it exhibits a similar toxicity to endosulfan. Six metabolites, including 5 novel metabolites of endosulfan sulfate, were identified in the three different human liver reaction mixtures and metabolic pathways of endosulfan sulfate were proposed. The phase I metabolites M1 and M2 were observed in human liver microsomes, S9 fractions and hepatocytes. M1 was suggested to be an endosulfan diol monosulfate and M2 was identified as (1,4,5,6,7,7-hexachloro-3-formylbicyclo[2,2,1]hept-5-en-2-yl)methyl hydrogen sulfate through the interpretation of the HRMS spectrum. The phase II metabolite M3 was produced as an endosulfan sulfate-GSH conjugate in those three liver preparations and transformed to M5 (dipeptide) in S9 fractions and hepatocytes. M3 was the most predominant metabolite identified in the three liver preparations. M4 was only detected in microsomes as an M2-GSH conjugate and was metabolized to M6 (monopeptide) in hepatocytes. These results are different from the metabolic pathway of endosulfan and suggest the possible detoxification metabolic reaction of endosulfan sulfate in living organisms.