Current Drug Metabolism - Volume 22, Issue 3, 2021

Background: The roots of Polygonum multiflorum (PM) are a well-known traditional Chinese medicine, widely used to treat a variety of conditions in Southeast Asia, South Korea, Japan and other countries. It is known that Polygoni Multiflori Radix Praeparata (PMRP) may enhance the efficacy and reduce the toxicity of PM. However, reports of adverse reactions, such as hepatotoxicity, caused by PM or PMRP, have continuously appeared around the world, which increased the known risks of the medication and gradually gained the extensive attention of many researchers. The chemical constituents of PM that cause hepatotoxicity have not been distinctly elucidated using the traditional phytochemical screening. Recently, with the rapid development of metabolomics, there has been a growing need to explore the potential hepatotoxic components and mechanisms of PM. Methods: The metabolites and metabolomics of PM were searched by the Web of Science, PubMed, Google scholar and some Chinese literature databases. Results: A brief description of metabolites and metabolomics of PM is followed by a discussion on the metabolite- induced toxicity in this review. More than 100 metabolites were tentatively identified and this will contribute to further understanding of the potential hepatotoxic components of PM. Meanwhile, some toxic compounds were identified and could be used as potential toxic markers of PM. Conclusion: This review mainly outlines the metabolites and metabolomics of PM that have been identified in recent years. This study could help to clarify the potential hepatotoxic components and metabolic mechanisms of PM and provide a scientific reference for its safe clinical use in the future.

Background: Catalpol, an iridoid glycoside, is one of the richest bioactive components present in Rehmannia glutinosa. More and more metabolites of drugs have exhibited various pharmacological effects, thus providing guidance for clinical application. However, few researches have paid attention to the metabolism of catalpol. Objective: This study aimed to establish a rapid and effective method to identify catalpol metabolites and evaluate the biotransformation pathways of catalpol in rats. Methods: In this study, catalpol metabolites in rat urine, plasma and faeces were analyzed by UHPLC-Q-Exactive MS for the characterization of the metabolism of catalpol. Based on high-resolution extracted ion chromatograms (HREICs) and parallel reaction monitoring mode (PRM), metabolites of catalpol were identified by comparing the diagnostic product ions (DPIs), chromatographic retention times, neutral loss fragments (NLFs) and accurate mass measurement with those of catalpol reference standard. Results: A total of 29 catalpol metabolites were detected and identified in both negative and positive ion modes. Nine metabolic reactions, including deglycosylation, hydroxylation, dihydroxylation, hydrogenation, dehydrogenation, oxidation of methylene to ketone, glucuronidation, glycine conjugation and cysteine conjugation, were proposed. Conclusion: A rapid and effective method based on UHPLC-Q-Exactive MS was developed to mine the metabolism information of catalpol. Results of metabolites and biotransformation pathways of catalpol suggested that when orally administrated, catalpol was firstly metabolized into catalpol aglycone, after which phase I and phase II reactions occurred. However, hydrophilic chromatography-mass spectrometry is still needed to further find the polar metabolites of catalpol.

Background: Vitexin is a natural flavonoid compound with multiple pharmacological activities and is extracted from the leaves and seeds of Vitex negundo L. var. cannabifolia (Sieb. et Zucc.) Hand.-Mazz. However, the metabolite characterization of this component remains insufficient. Objective: To establish a rapid profiling and identification method for vitexin metabolites in rat urine, plasma and faeces after oral administration using a UHPLC-Q-Exactive orbitrap mass spectrometer were coupled with multiple data-mining methods. Methods: In this study a simple and rapid systematic strategy for the detection and identification of constituents was proposed based on UHPLC-Q-Exactive Orbitrap mass spectrometry in parallel reaction monitoring mode combining diagnostic fragment ion filtering techniques. Results: A total of 49 metabolites were fully or partially characterized based on their accurate mass, characteristic fragment ions, retention times, corresponding ClogP values, and so on. It is obvious that C-glycosyl flavonoids often display an [M+H-120]⁺ ion that represents the loss of C4H8O4. As a result, these metabolites were presumed to be generated through glucuronidation, sulfation, deglucosylation, dehydrogenation, methylation, hydrogenation, hydroxylation, ring cleavage and their composite reactions. Moreover, the characteristic fragmentation pathways of flavonoids, chalcones and dihydrochalcones were summarized for the subsequent metabolite identification. Conclusion: The current study provided an overall metabolic profile of vitexin which will be of great help in predicting the in vivo pharmacokinetic profiles and understanding the action mechanism of this active ingredient.

Background: Neuropathic pain (NP) is an egregious problem worldwide. Due to the side-effects of oral drugs, drugs delivered directly to the affected area of pain are preferred. Objective: Capsaicin, a chemical compound isolated from chili peppers, is used as an analgesic in topical ointments and dermal patches to alleviate pain. Objective of the study is to review the application and functionality of topical capsaicin in treatment of neuropathic pain. Data sources: To systematically review capsaicin’s functions on NP, we retrieved articles from the PubMed database published in the last ten years. Study eligibility criteria: The inclusion criteria were capsaicin and the use of capsaicin for the treatment of NP; on the other hand, articles were excluded according to the mentioned criteria such as abstracts, articles written in any language other than English, incomplete articles, and conference papers. Participants and interventions: Out of 265 articles, 108 articles were selected after filtering through the inclusion and exclusion criteria. The data and knowledge currently existing for capsaicin treatment in NP are summarized. Results: This review indicates that capsaicin effectively improves NP treatment without affecting the motor and large nerve fibres involved in sensory function. Transient receptor potential channel vanilloid type 1 (TRPV1) is the capsaicin receptor expressed in central and peripheral terminals of a sensitive primary nerve cell. Conclusions and implications of key findings: Topical capsaicin has a sensible safety profile and is effective in reducing NP. Therefore, studies over the last decade suggest that capsaicin might be a potential drug for NP treatment.

Aims: Base dissociation constants of 30 model chemicals were investigated to constitute potential determinant factors predicting the contributions of flavin-containing monooxygenases (FMOs). Background: The contributions of FMOs to the metabolic elimination of new drug candidates could be underestimated under certain experimental conditions during drug development. Objective: A method for predicting metabolic sites and the contributions of FMOs to N-oxygenations is proposed using a molecular descriptor, the base dissociation constant (pKa base), which can be estimated in silico using commonly available chemoinformatic prediction systems. Methods: Model drugs and their oxidative pathways were surveyed in the literature to investigate the roles of FMOs in their N-oxygenations. The acid and base dissociation constants of the nitrogen moieties of 30 model substrates were estimated using well-established chemoinformatic software. Results: The base dissociation constants of 30 model chemicals were classified into two groups based on the reported optimal in vitro pH of 8.4 for FMO enzymes as a key determinant factor. Among 18 substrates (e.g., trimethylamine, benzydamine, and itopride) with pKa (base) values in the range of 8.4-9.8, all N-oxygenated metabolites were reported to be predominantly catalyzed by FMOs. Except for three cases (xanomeline; L-775,606; and tozasertib), the nine substrates with pKa (base) values in the range 2.7-7.9 were only moderately or minorly N-oxygenated by FMOs in addition to their major metabolic pathway of oxidation mediated by cytochrome P450s. N-Oxygenation of T-1032 (with a pKa of 4.8) is mediated predominantly by P450 3A5, but not by FMO1/3. Conclusion: The predicted contributions of FMOs to the N-oxygenation of drug candidates can be simply estimated using classic base dissociation constants.

Background: Pharmacokinetic and pharmacodynamic assessment of ester-containing drugs can be impacted by hydrolysis of the drugs in plasma samples post blood collection. The impact is different in the plasma of different species. Objective: This study evaluated the stability of a prodrug, ketoprofen methylester (KME), in commercially purchased and freshly collected plasma of mouse, rat, dog, cat, pig, sheep, cattle and horse. Methods: KME hydrolysis was determined following its incubation in commercially purchased and freshly collected plasma of those species. Different esterase inhibitors were evaluated for prevention of the hydrolysis in rat, dog and pig plasma. Results: KME was rapidly hydrolyzed in both commercially purchased and freshly collected plasma of mouse, rat, and horse. The hydrolysis was initially quick and then limited in cat plasma. KME hydrolysis was minimum in commercially purchased plasma of dog, pig, sheep and cattle but substantial in freshly collected plasma of those species. Different esterase inhibitors showed different effects on the stability of KME in rat, dog and pig plasma. Conclusion: These results indicate that plasma of different species has different hydrolytic activities to estercontaining drugs. The activities in commercially purchased and freshly collected plasma may be different and species-dependent. Esterase inhibitors have different effects on preventing hydrolysis of the ester-containing drugs in the plasma of different species.

Background: Shenqi Jiangtang Granule (SJG), a classical prescription of traditional Chinese medicine, is widely used to treat diabetes and its complications. Although, the clinical efficacy of SJG, is sufficient, the pharmacokinetic behavior of various substances in the plasma of SJG is unknown. Objective: The aim of this study was to investigate the plasma pharmacokinetics during absorption of SJG after oral administration in rats. Methods: A rapid and accurate ultra-high performance liquid chromatography/tandem mass spectrometry (UPLC- MS/MS) method was developed for the simultaneous determination of eight analytes in SJG, including gomisin D, schisandrin A, schisandrin B, schizandrol A, schizandrol B, ginsenoside Rd, ginsenoside Re and notoginsenoside Ft1. The analysis was carried out on a BEH C18 column (2.1 mm × 50 mm, 1.7 μm) with gradient elution at a flow rate of 0.2 mL/min in a mobile phase consisting of 0.1% formic acid water and acetonitrile. In addition, lignans and saponins were detected in positive ion mode and negative ion mode, respectively. Results: Eight analytes in SJG, including gomisin D, schisandrin A, schisandrin B, schizandrol A, schizandrol B, ginsenoside Rd, ginsenoside Re and notoginsenoside Ft1, showed good linearity (R2 in the range of 0.9955 ~ 0.9999). The lower limit of quantification (LLOQ) was 5, 0.8, 0.8, 8, 0.8, 5, 0.6 and 10 ng/mL. The accuracy and precision of all analytes were at ±15%. Matrix effect and average extraction recovery were > 85%. All analytes performed well under four storage conditions. Conclusion: The results showed that in vivo absorption and exposure of gomisin D and ginsenoside Rd were better than other analytes, while schizandrol B and notoginsenoside Ft1 were poorly absorbed. This approach could be applied to study the pharmacokinetic characteristics of various analytes in plasma after oral administration of SJG in rats.

Background: Praziquantel (PZQ), which possesses an asymmetric center, is classified as a pyrazinoisoquinoline and has been the mainstay in the treatment of schistosomiasis since 1980. PZQ undergoes a pronounced first-pass metabolism in the liver through the CYP450 system which could be mediated by nuclear receptors. Objective: The purpose of this study was to investigate the possible different induction effects of CYP3A4 by PZQ racemate and enantiomers via the pregnane X receptor (PXR) and the effect of PXR polymorphism on the induction potency of PZQs. Methods: The dual-luciferase reporter gene systems constructed in HepG2 cells were used to measure the abilities of PZQs to induce CYP3A4 expression mediated by PXR. The mRNA and protein levels of CYP3A4 were evaluated by polymerase chain reaction (PCR) and western blotting, respectively. Results: In HepG2 cells transfected with PXRwt, PXR158, PXR163, PXR370 or PXR403 expression plasmids, PZQ racemate and its enantiomers up-regulated the luciferase activity in a concentration-dependent manner, while reaching saturation after transfected with PXR379 expression plasmids. The mRNA and protein expression of CYP3A4 was effectively activated in PXR-transfected HepG2 cells. The induction ability of CYP3A4 mediated by PXR activation by PZQ racemate and its enantiomers were statistically different between the same PXR group and different PXR groups. Conclusion: The enantioselective induction effects of PZQs on CYP3A4 were related to the enantioselective activations of PXR by PZQs and were influenced by the PXR gene polymorphism. These findings provide a basis for further understanding the enantiomeric metabolism and the variable efficacy of PZQs.

Aims: To study the effects of blood glucose regulating compounds on human and rat sulfotransferases (SULTs) expressions. Background: Phase-II enzymes, sulfotransferases catalyze the sulfuryl-group-transfer to endogenous/exogenous compounds. The alteration of expressions of SULTs may have influence on the sulfation of its substrate and other biomolecules. Objectives: The influence of the altered biotransformation might alter different biochemical events, drug-drug interactions and bioaccumulation or excretion pattern of certain drug. Methods: In this brief study, diabetes-inducing drug streptozotocin (STZ; 10 or 50 mg/kg to male Sprague Dawley rat for 2 weeks) or hyperglycemia controlling drug tolbutamide (TLB 0.1 or 10μM to human hepato-carcinoma cells, HepG2 for 10 days) was applied and the SULTs expressions were verified. Extensive protein-protein (STa, SULT2A1/DHEAST) interactions were studied by the STRING (Search-Tool-for-the-Retrieval-of-Interacting Genes/Proteins) Bioinformatics-software. Results: Present result suggests that while STZ increased the STa (in rat) (dehydroepiandrosterone catalyzing SULT; DHEAST in human HepG2), tolbutamide decreased PPST (phenol catalyzing SULT) and DHEAST activity in human HepG2 cells. Moderate decreases of MPST (monoamine catalyzing SULT) and EST (estrogen catalyzing) activities are noticed in this case. STa/DHEAST was found to be highly interactive to SHBG/- sex-hormone-binding-globulin; PPARα/lipid-metabolism-regulator; FABP1/fatty-acid-binding-protein. Conclusion: Streptozotocin and tolbutamide, these two glycaemia-modifying drugs demonstrated regulation of rat and human SULTs activities. The reciprocal nature of these two drugs on SULTs expression may be associated with their contrasting abilities in influencing glucose-homeostasis. Possible association of certain SULT-isoform with hepatic fat-regulations may indicate an unfocused link between calorie-metabolism and the glycemic-state of an individual. Explorations of this work may uncover the role of sulfation metabolism of specific biomolecule on cellular glycemic regulation.