Identification of Human UDP-Glucuronosyltransferase 1A4 as the Major Isozyme Responsible for the Glucuronidation of 20(S)-Protopanaxadiol in Human Liver Microsomes

Progress in Identification of UDP-Glycosyltransferases for Ginsenoside Biosynthesis

Ginsenosides, the primary pharmacologically active constituents of the Panax genus, have demonstrated a variety of medicinal properties, including anticardiovascular disease, cytotoxic, antiaging, and antidiabetes effects. However, the low concentration of ginsenosides in plants and the challenges associated with their extraction impede the advancement and application of ginsenosides. Heterologous biosynthesis represents a promising strategy for the targeted production of these natural active compounds. As representative triterpenoids, the biosynthetic pathway of the aglycone skeletons of ginsenosides has been successfully decoded. While the sugar moiety is vital for the structural diversity and pharmacological activity of ginsenosides, the mining of uridine diphosphate-dependent glycosyltransferases (UGTs) involved in ginsenoside biosynthesis has attracted a lot of attention and made great progress in recent years. In this paper, we summarize the identification and functional study of UGTs responsible for ginsenoside synthesis in both plants, such as Panax ginseng and Gynostemma pentaphyllum, and microorganisms including Bacillus subtilis and Saccharomyces cerevisiae. The UGT-related microbial cell factories for large-scale ginsenoside production are also mentioned. Additionally, we delve into strategies for UGT mining, particularly potential rapid screening or identification methods, providing insights and prospects. This review provides insights into the study of other unknown glycosyltransferases as candidate genetic elements for the heterologous biosynthesis of rare ginsenosides.

Detection and identification of imperatorin metabolites in rat, dog, monkey, and human liver microsomes by ultra-high-performance liquid chromatography combined with high-resolution mass spectrometry and Compound Discoverer software

Imperatorin, a furanocoumarin that widely exists in many umbelliferous herbs, has been demonstrated to have a variety of pharmacological effects, including anti-inflammatory, antiosteoporosis, and antitumor activities. The purpose of this study was to investigate the metabolism of imperatorin using liver microsomes. The metabolites were generated by individually incubating imperatorin with rat, dog, monkey, and human liver microsomes. To trap the reactive metabolites during microsomal metabolism, glutathione (GSH) was included in the incubation. A LC technique coupled with benchtop orbitrap MS with full mass/data-dependent tandem mass spectrometry acquisition mode was used to detect and identify the generated metabolites. The possible structures of the metabolites were characterized according to their accurate masses and fragment ions. Under the current conditions, a total of 10 metabolites, including four GSH adducts, were identified. The results indicated that imperatorin underwent extensive metabolic reactions including hydroxylation, oxidation, glucuronidation, and GSH conjugation. This study provides essential data on the metabolism of imperatorin, which will be helpful for us to understand the safety and efficacy of this bioactive compound.

Identification of Human UDP-Glucuronosyltransferase Involved in Gypensapogenin C Glucuronidation and Species Differences

Gypensapogenin C (GPC) is one of the important aglycones of Gynostemma pentaphyllum (GP), which is structurally glucuronidated and is highly likely to bind to UGT enzymes in vivo. Due to the important role of glucuronidation in the metabolism of GPC, the UDP-glucuronosyltransferase metabolic pathway of GPC in human and other species' liver microsomes is investigated in this study. In the present study, metabolites were detected using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). The results show that GPC could generate a metabolite through glucuronidation in the human liver microsomes (HLMs). Additionally, chemical inhibitors combined with recombinant human UGT enzymes clarified that UGT1A4 is the primary metabolic enzyme for GPC glucuronidation in HLMs according to the kinetic analysis of the enzyme. Metabolic differential analysis in seven other species indicated that rats exhibited the most similar metabolic rate to that of humans. In conclusion, UGT1A4 is a major enzyme responsible for the glucuronidation of GPC in HLMs, and rats may be an appropriate animal model to evaluate the GPC metabolism.

Identification of human uridine diphosphate-glucuronosyltransferase isoforms responsible for the glucuronidation of 10,11-dihydro-10-hydroxy-carbazepine

OBJECTIVES

To determine the kinetics of the formation of 10,11-dihydro-10-hydroxy-carbazepine (MHD)-O-glucuronide in human liver microsomes (HLMs), human intestine microsomes (HIMs), human kidney microsomes (HKMs) and recombinant human UDP-glucuronosyltransferase (UGTs), and identify the primary UGT isoforms catalyzing the glucuronidation of MHD.

METHODS

The kinetics of the glucuronidation of MHD was determined in HLMs, HIMs as well as HKMs. Screening assays with 13 recombinant human UGTs, inhibition studies and correlation analysis were performed to identify the main UGTs involved in the glucuronidation of MHD.

KEY FINDINGS

MHD-O-glucuronide was formed in HLMs, HIMs as well as HKMs, HLMs showed the highest intrinsic clearance of MHD. Among 13 recombinant human UGTs, UGT2B7 and UGT1A9 were identified to be the principal UGT isoforms mediating the glucuronidation of MHD, while UGT1A4 played a partial role. In addition, inhibition studies and correlation analysis further confirmed that UGT2B7 and UGT1A9 participated in the formation of MHD-O-glucuronide.

CONCLUSIONS

MHD could be metabolized by UGTs in the liver, intestine and kidney, and the hepatic glucuronidation was the critical metabolic pathway. UGT2B7 and UGT1A9 were the primary UGT isoforms mediating the formation of MHD-O-glucuronide in the liver.

Human variability in isoform-specific UDP-glucuronosyltransferases: markers of acute and chronic exposure, polymorphisms and uncertainty factors

UDP-glucuronosyltransferases (UGTs) are involved in phase II conjugation reactions of xenobiotics and differences in their isoform activities result in interindividual kinetic differences of UGT probe substrates. Here, extensive literature searches were performed to identify probe substrates (14) for various UGT isoforms (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B7 and UGT2B15) and frequencies of human polymorphisms. Chemical-specific pharmacokinetic data were collected in a database to quantify interindividual differences in markers of acute (Cmax) and chronic (area under the curve, clearance) exposure. Using this database, UGT-related uncertainty factors were derived and compared to the default factor (i.e. 3.16) allowing for interindividual differences in kinetics. Overall, results show that pharmacokinetic data are predominantly available for Caucasian populations and scarce for other populations of different geographical ancestry. Furthermore, the relationships between UGT polymorphisms and pharmacokinetic parameters are rarely addressed in the included studies. The data show that UGT-related uncertainty factors were mostly below the default toxicokinetic uncertainty factor of 3.16, with the exception of five probe substrates (1-OH-midazolam, ezetimibe, raltegravir, SN38 and trifluoperazine), with three of these substrates being metabolised by the polymorphic isoform 1A1. Data gaps and future work to integrate UGT-related variability distributions with in vitro data to develop quantitative in vitro-in vivo extrapolations in chemical risk assessment are discussed.

Dose-dependent exposure profile and metabolic characterization of notoginsenoside R1 in rat plasma by ultra-fast liquid chromatography-electrospray ionization-tandem mass spectrometry

Notoginsenoside R₁ (NGR₁ ), a diagnostic protopanaxatriol-type (ppt-type) saponin in Panax notoginseng, possesses potent biological activities including antithrombotic, anti-inflammatory, neuron protection and improvement of microcirculation, yet its pharmacokinetics and metabolic characterization as an individual compound remain unclear. The aim of this study was to investigate the exposure profile of NGR₁ in rats after oral and intravenous administration and to explore the metabolic characterization of NGR₁ . A simple and sensitive ultra-fast liquid chromatographic-tandem mass spectrometric method was developed and validated for the quantitative determination of NGR₁ and its major metabolites, and for characterization of its metabolic profile in rat plasma. The blood samples were precipitated with methanol, quantified in a negative multiple reaction monitoring mode and analyzed within 6.0 min. Validation parameters (linearity, precision and accuracy, recovery and matrix effect, stability) were within acceptable ranges. After oral administration, NGR₁ exhibited dose-independent exposure behaviors with t_1/2 over 8.0 h and oral bioavailability of 0.25-0.29%. A total of seven metabolites were characterized, including two pairs of epimers, 20(R)-notoginsenoside R₂ /20(S)-notoginsenoside R₂ and 20(R)-ginsenoside Rh₁ /20(S)-ginsenoside Rh₁ , with the 20(R) form of saponins identified for the first time in rat plasma. Five deglycometabolites were quantitatively determined, among which 20(S)-notoginsenoside R₂ , ginsenoside Rg₁ , ginsenoside F₁ and protopanaxatriol displayed relatively high exploration, which may partly explain the pharmacodynamic diversity of ginsenosides after oral dose.

Characterization of ginsenoside compound K metabolites in rat urine and feces by ultra-performance liquid chromatography with electrospray ionization quadrupole time-of-flight tandem mass spectrometry

Ginsenoside compound K (CK) is an active metabolite of ginsenoside and has been shown to have ameliorative property in various diseases. However, the detailed in vivo metabolism of this compound has rarely been reported. In the present study, a method using liquid chromatography quadrupole time-of-flight tandem mass spectrometry together with multiple data processing techniques, including extracted ion chromatogram, multiple mass defect filter and MS/MS scanning, was developed to detect and characterize the metabolites of CK in rat urine and feces. After oral administration of CK at a dose of 50 mg/kg, urine and feces were collected for a period of time and subjected to a series of pretreatment. A total of 12 metabolites were tentatively or conclusively identified, comprising 11 phase I metabolites and a phase II metabolite. Metabolic pathways of CK has been proposed, including oxidation, deglycosylation, deglycosylation with sequential oxidation and dehydrogenation and deglycosylation with sequential glucuronidation. Relative quantitative analyses suggested that deglycosylation was the main metabolic pathway. The result could offer insights for better understanding of the mechanism of its pharmacological activities.

Simultaneous determination of 20(S)-protopanaxadiol and its three metabolites in rat plasma by LC-MS/MS: application to their pharmacokinetic studies

The aim of this study was to develop an LC-MS/MS method for simultaneous determination of 20(S) protopanaxadiol (PPD) and its three metabolites, PPD-glucuronide (M1), (20S,24S)-epoxy-dammarane-3,12,25-triol (M2) and (20S,24R)-epoxydammarane-3,12,25-triol (M3), in rat plasma. Precipitation with acetonitrile was employed for sample preparation and chromatographic separations were achieved on a C₁₈ column. The sample was detected using triple quadrupole tandem mass spectrometer with selected reaction monitoring mode. The monitored precursor-to-product ion transitions were m/z 459.4 → 375.3 for PPD, m/z 635.4 → 113.0 for M1, m/z 477.4 → 441.4 for M2 and M3 and m/z 475.4 → 391.3 for IS. The developed assay was validated according to the guidelines of the US Food and Drug Administration. The calibration curves showed good linearity over the tested concentration ranges (r > 0.9993), with the LLOQ being 1 ng/mL for all analytes. The intra- and inter-day precisions (RSD) were < 9.51% while the accuracy (RE) ranged from -8.91 to 12.84%. The extraction recovery was >80% and no obvious matrix effect was detected. The analytes were stable in rat plasma with the RE ranging from -12.34 to 9.77%. The validated assay has been successfully applied to the pharmacokinetic study of PPD as well as its metabolites in rat plasma. According to the pharmacokinetic parameters, the in vivo exposures of M1, M2 and M3 were 11.91, 47.95 and 22.62% of that of PPD, respectively.

In Vitro Glucuronidation of Wushanicaritin by Liver Microsomes, Intestine Microsomes and Expressed Human UDP-Glucuronosyltransferase Enzymes

Wushanicaritin, a natural polyphenol compound, exerts many biological activities. This study aimed to characterize wushanicaritin glucuronidation by pooled human liver microsomes (HLM), human intestine microsomes and individual uridine diphosphate-glucuronosyltransferase (UGT) enzyme. Glucuronidation rates were determined by incubating wushanicaritin with uridine diphosphoglucuronic acid-supplemented microsomes. Kinetic parameters were derived by appropriate model fitting. Reaction phenotyping, the relative activity factor (RAF) and activity correlation analysis were performed to identify the main UGT isoforms. Wushanicaritin glucuronidation in HLM was efficient with a high CL_int (intrinsic clearance) value of 1.25 and 0.69 mL/min/mg for G1 and G2, respectively. UGT1A1 and 1A7 showed the highest activities with the intrinsic clearance (CL_int) values of 1.16 and 0.38 mL/min/mg for G1 and G2, respectively. In addition, G1 was significantly correlated with β-estradiol glucuronidation (r = 0.847; p = 0.0005), while G2 was also correlated with chenodeoxycholic acid glucuronidation (r = 0.638, p = 0.026) in a bank of individual HLMs (n = 12). Based on the RAF approach, UGT1A1 contributed 51.2% for G1, and UGT1A3 contributed 26.0% for G2 in HLM. Moreover, glucuronidation of wushanicaritin by liver microsomes showed marked species difference. Taken together, UGT1A1, 1A3, 1A7, 1A8, 1A9 and 2B7 were identified as the main UGT contributors responsible for wushanicaritin glucuronidation.

A Network-Based Pharmacology Study of the Herb-Induced Liver Injury Potential of Traditional Hepatoprotective Chinese Herbal Medicines

Herbal medicines are widely used for treating liver diseases and generally regarded as safe due to their extensive use in Traditional Chinese Medicine practice for thousands of years. However, in recent years, there have been increased concerns regarding the long-term risk of Herb-Induced Liver Injury (HILI) in patients with liver dysfunction. Herein, two representative Chinese herbal medicines: one—Xiao-Chai-Hu-Tang (XCHT)—a composite formula, and the other—Radix Polygoni Multiflori (Heshouwu)—a single herb, were analyzed by network pharmacology study. Based on the network pharmacology framework, we exploited the potential HILI effects of XCHT and Heshouwu by predicting the molecular mechanisms of HILI and identified the potential hepatotoxic ingredients in XCHT and Heshouwu. According to our network results, kaempferol and thymol in XCHT and rhein in Heshouwu exhibit the largest number of liver injury target connections, whereby CASP3, PPARG and MCL1 may be potential liver injury targets for these herbal medicines. This network pharmacology assay might serve as a useful tool to explore the underlying molecular mechanism of HILI. Based on the theoretical predictions, further experimental verification should be performed to validate the accuracy of the predicted interactions between herbal ingredients and protein targets in the future.