Reversible and Irreversible Inhibition of Cytochrome P450 Enzymes by Methylophiopogonanone A

Methylophiopogonanone A alleviates diabetic cardiomyopathy via inhibiting JNK1 signaling

OBJECTIVE

Diabetic cardiomyopathy (DCM) is a common complication of type 2 diabetes mellitus (T2DM). The effects of methylophiopogonanone A (MO-A), a natural homoisoflavonoid with anti-inflammatory effects, on DCM and its underlying mechanisms were investigated in this study.

METHODS

The T2DM mouse model was induced by intraperitoneal injection of 30 mg/kg streptozotocin for 7 consecutive days and fed with a high-fat diet for 12 weeks. T2DM mice received MO-A (2.5, 5, or 10 mg/kg) treatment for two weeks. Cardiac function, hypertrophy, fibrosis, and inflammation were evaluated. The binding energy between MO-A and JNK1 was analyzed using molecular docking. The underlying mechanism was further investigated in high glucose (HG)-induced H9C2 cells. The cytotoxic effects, cardiomyocyte hypertrophy, fibrosis, inflammation, and relevant signaling proteins were assessed.

RESULTS

MO-A treatment alleviated cardiac function and histopathological changes in DCM mice. Moreover, MO-A treatment significantly decreased COLI, TGF-β1, MYH7, and ANP expression levels in DCM mice. Furthermore, TNF-α, IL-6, and IL-1β expression levels were notably downregulated after treatment with MO-A in DCM mice. Similar results were also observed in vitro. Mechanistically, MO-A targets JNK1 and downregulates its phosphorylation levels in DCM mice. The protective properties of MO-A were reversed by JNK1 overexpression in HG-induced H9C2 cells.

CONCLUSION

Our results revealed that MO-A could alleviate cardiac function, hypertrophy, fibrosis, and inflammation in DCM via inhibiting JNK1 signaling.

In-depth understanding of the structure-based reactive metabolite formation of organic functional groups

Idiosyncratic drug-induced liver injury (DILI) is a leading cause of drug attrition and/or withdrawal. The formation of reactive metabolites is widely accepted as a key factor contributing to idiosyncratic DILI. Therefore, identifying reactive metabolites has become a critical focus during lead optimization, and a combination of GSH-/cyano-trapping and cytochrome P450 inactivation studies is recommended to identify compounds with the potential to generate reactive metabolites. Daily dose, clinical indication, detoxication pathways, administration route, and treatment duration are the most considerations when deprioritizing candidates that generate reactive metabolites. Removing the structural alerts is considered a pragmatic strategy for mitigating the risk associated with reactive metabolites, although this approach may sometimes exclude otherwise potent molecules. In this context, an in-depth insight into the structure-based reactive metabolite formation of organic functional groups can significantly aid in the rational design of drug candidates with improved safety profiles. The primary goal of this review is to delve into an analysis of the bioactivation mechanisms of organic functional groups and their potential detrimental effects with recent examples to assist medicinal chemists and metabolism scientists in designing safer drug candidates with a higher likelihood of success.

A Validated Liquid Chromatography-Tandem Mass Spectrometry Method for the Determination of Methylophiopogonanone A in Rat Plasma and Its Application to Pharmacokinetic Study

Methylophiopogonanone A (MOA) is one of the homoisoflavonoids isolated from Ophiopogon japonicus, which has been demonstrated to have extensive pharmacological activities. The aim of this study was to develop and validate a liquid chromatography-tandem mass spectrometry method for the measurement of MOA in rat plasma. Methylophiopogonanone B (MOB) was used as internal standard. After precipitation with acetonitrile, the samples were separated using a Waters ACQUITY HSS T3 column with 0.1% formic acid solution and acetonitrile as mobile phase. Mass detection was monitored using multiple reactions monitoring mode with precursor-to-product ion transition of m/z 343.2 > 135.1 for MOA and m/z 329.2 > 121.1 for internal standard. The assay showed good linearity over the concentration range of 1-1000 ng/mL, with correlation coefficient > 0.997. The lower limit of quantification (LLOQ) was 1 ng/mL. Acetonitrile-mediated precipitation showed high extraction efficiency (> 80%). The accuracy and precision were within the acceptable limits. MOA was demonstrated to be stable in rat plasma under the tested storage conditions. After validation, the proposed method was applied to the pharmacokinetic study of MOA in rat plasma, and the data revealed that MOA showed rapid absorption and elimination from rat plasma. The oral bioavailability of MOA in rat was 24.5%.

Thwarting resistance: MgrA inhibition with methylophiopogonanone a unveils a new battlefront against S. aureus

Limitations in the clinical treatment of Staphylococcus aureus (S. aureus) infections have arisen due to the advent of antibiotic-resistant strains. Given the immense potential of therapeutic strategies targeting bacterial virulence, the role of MgrA as a pivotal virulence determinant in S. aureus-orchestrating resistance, adherence, and hundreds of virulence targets-becomes indispensable. In this investigation, leveraging advanced virtual screening and fluorescence anisotropy assays, we discerned methylophiopogonanone A (Mo-A), a flavonoid derivative, as a potent disruptor of the MgrA-DNA interaction nexus. Subsequent analysis revealed that Mo-A effectively inhibits the expression of virulence factors such as Hla and Pvl in S. aureus and markedly reduces its adhesion capability to fibrinogen. On a cellular landscape, Mo-A exerts a mitigating influence on the deleterious effects inflicted by S. aureus USA300 on A549 cells. Furthermore, our data indicate that Mo-A downregulates the transcription of genes associated with immune evasion, such as nucleases (nuc), Staphylococcal Chemotaxis Inhibitory Protein (chips), and Staphylococcal Complement Inhibitor (scin), thereby undermining immune escape and amplifying neutrophil chemotaxis. Upon application in an in vivo setting, Mo-A assumes a protective persona in a murine model of S. aureus USA300-induced pneumonia and demonstrates efficacy in the Galleria mellonella infection model. Of note, S. aureus displayed no swift acquisition of resistance to Mo-A, and the effect was synergistically enhanced when used in combination with vancomycin. Our findings add substantive weight to the expanding field of virulence-targeted therapeutic strategies and set the stage for more comprehensive exploration of Mo-A potential in combating antibiotic-resistant S. aureus.

Evidence for cytochrome P450 3A4-mediated metabolic activation of SCO-267

SCO-267 is a potent G-protein-coupled receptor 40 agonist that is undergoing clinical development for the treatment of type 2 diabetes mellitus. The current work was undertaken to investigate the bioactivation potential of SCO-267 in vitro and in vivo. Three SCO-267-derived glutathione (GSH) conjugates (M1-M3) were found both in rat and human liver microsomal incubations supplemented with GSH and nicotinamide adenine dinucleotide phosphate. Two GSH conjugates (M1-M2) together with two N-acetyl-cysteine conjugates (M4-M5) were detected in the bile of rats receiving SCO-267 at 10 mg/kg. The identified conjugates suggested the generation of quinone-imine and ortho-quinone intermediates. CYP3A4 was demonstrated to primarily catalyze the bioactivation of SCO-267. In addition, SCO-267 concentration-, time-, and NADPH-dependently inactivated CYP3A in human liver microsomes using testosterone as a probe substrate, along with KI and kinact values of 4.91 μM and 0.036 min-1 , respectively. Ketoconazole (a competitive inhibitor of CYP3A) displayed no significant protective effect on SCO-267-induced CYP3A inactivation. However, inclusion of GSH showed significant protection. These findings revealed that SCO-267 undergoes a facile CYP3A4-catalyzed bioactivation with the generation of quinone-imine and ortho-quinone intermediates, which were assumed to be involved in SCO-267 induced CYP3A inactivation. These findings provide further insight into the bioactivation pathways involved in the generation of reactive, potentially toxic metabolites of SCO-267. Further studies are needed to evaluate the influence of SCO-267 metabolism on the safety of this drug in vivo.

High-throughput assay to simultaneously evaluate activation of CYP3A and the direct and time-dependent inhibition of CYP3A, CYP2C9, and CYP2D6 using liquid chromatography-tandem mass spectrometry

In the early stages of drug discovery, adequate evaluation of the potential drug-drug interactions (DDIs) of drug candidates is important. Several CYP3A activators are known to lead to underestimation of DDIs. These compounds affect midazolam 1'-hydroxylation but not midazolam 4-hydroxylation.We used both metabolic reactions of midazolam to evaluate the activation and inhibition of CYP3A activators simultaneously. For our CYP inhibition assay using cocktail probe substrates, simultaneous liquid chromatography-tandem mass spectrometry monitoring of 1'-hydroxymidazolam and 4-hydroxymidazolam for CYP3A was established in addition to monitoring of 4-hydroxydiclofenac and 1'-hydroxybufuralol for CYP2C9 and CYP2D6.The results of our cocktail inhibition assay were well correlated with those of a single inhibition assay, as were the estimated inhibition parameters for typical CYP3A inhibitors. In our assay, a proprietary compound that activated midazolam 1'-hydroxylation and tended to inhibit 4-hydroxylation was evaluated along with known CYP3A activators. All compounds were well characterised by comparison of the results of midazolam 1'- and 4-hydroxylation.In conclusion, our CYP cocktail inhibition assay can detect CYP3A activation and assess the direct and time-dependent inhibition potentials for CYP3A, CYP2C9, and CYP2D6. This method is expected to be very efficient in the early stages of drug discovery.

CYP1A inhibitors: Recent progress, current challenges, and future perspectives

Mammalian cytochrome P450 1A (CYP1A) are key phase I xenobiotic-metabolizing enzymes that play a distinctive role in metabolic activation or metabolic clearance of a variety of procarcinogens, drugs, and endogenous substances. Human CYP1A subfamily contains two members (hCYP1A1 and hCYP1A2), which are known to catalyze the oxidative activation of some environmental procarcinogens into carcinogenic species. Increasing evidence has demonstrated that CYP1A inhibitor therapies are promising strategies for cancer chemoprevention or overcoming CYP1A-associated drug toxicity and resistance. Herein, we reviewed recent advances in the discovery and characterization of hCYP1A inhibitors, from the discovery approaches to structural features and biomedical applications of hCYP1A inhibitors. The inhibition potentials, inhibition modes, and inhibition constants of all reported hCYP1A inhibitors are comprehensively summarized. Meanwhile, the structural features and structure-activity relationships of different classes of hCYP1A1 and hCYP1A2 inhibitors are analyzed and discussed in depth. Furthermore, the major challenges and future directions for this field are presented and highlighted. Collectively, the information and knowledge presented here will strongly facilitate the researchers to discover and develop more efficacious CYP1A inhibitors for specific purposes, such as chemo-preventive agents or as tool molecules in hCYP1A-related fundamental studies.

Unraveling a Combined Inactivation Mechanism of Cytochrome P450s by Genipin, the Major Reactive Aglycone Derived from Gardeniae Fructus

Genipin (GP) is the reactive aglycone of geniposide, the main component of traditional Chinese medicine Gardeniae Fructus (GF). The covalent binding of GP to cellular proteins is suspected to be responsible for GF-induced hepatotoxicity and inhibits drug-metabolizing enzyme activity, although the mechanisms remain to be clarified. In this study, the mechanisms of GP-induced human hepatic P450 inactivation were systemically investigated. Results showed that GP inhibited all tested P450 isoforms via distinct mechanisms. CYP2C19 was directly and irreversibly inactivated without time dependency. CYP1A2, CYP2C9, CYP2D6, and CYP3A4 T (testosterone as substrate) showed time-dependent and mixed-type inactivation, while CYP2B6, CYP2C8, and CYP3A4 M (midazolam as substrate) showed time-dependent and irreversible inactivation. For CYP3A4 inactivation, the kinact/KI values in the presence or absence of NADPH were 0.26 or 0.16 min-1 mM-1 for the M site and 0.62 or 0.27 min-1 mM-1 for the T site. Ketoconazole and glutathione (GSH) both attenuated CYP3A4 inactivation, suggesting an active site occupation- and reactive metabolite-mediated inactivation mechanism. Moreover, the in vitro and in vivo formation of a P450-dependent GP-S-GSH conjugate indicated the involvement of metabolic activation and thiol residues binding in GP-induced enzyme inactivation. Lastly, molecular docking analysis simulated potential binding sites and modes of GP association with CYP2C19 and CYP3A4. We propose that direct covalent binding and metabolic activation mediate GP-induced P450 inactivation and alert readers to potential risk factors for GP-related clinical drug-drug interactions.

Mechanistic Study of Icaritin-Induced Inactivation of Cytochrome P450 2C9

Icaritin (ICT) is a prenylflavonoid derivative that has been approved by National Medical Products Administration for the treatment of hepatocellular carcinoma. This study aims to evaluate the potential inhibitory effect of ICT against cytochrome P450 (CYP) enzymes and to elucidate the inactivation mechanisms. Results showed that ICT inactivated CYP2C9 in a time-, concentration-, and NADPH-dependent manner with Ki = 1.896 μM, Kinact = 0.02298 minutes-1, and Kinact/Ki = 12 minutes-1 mM-1, whereas the activities of other CYP isozymes was minimally affected. Additionally, the presence of CYP2C9 competitive inhibitor, sulfaphenazole, superoxide dismutase/catalase system, and GSH all protected CYP2C9 from ICT-induced activity loss. Moreover, the activity loss was neither recovered by washing the ICT-CYP2C9 preincubation mixture nor the addition of potassium ferricyanide. These results, collectively, implied the underlying inactivation mechanism involved the covalent binding of ICT to the apoprotein and/or the prosthetic heme of CYP2C9. Furthermore, an ICT-quinone methide (QM)-derived GSH adduct was identified, and human glutathione S-transferases (GST) isozymes GSTA1-1, GSTM1-1, and GSTP1-1 were shown to be substantially involved in the detoxification of ICT-QM. Interestingly, our systematic molecular modeling work predicted that ICT-QM was covalently bound to C216, a cysteine residue located in the F-G loop downstream of substrate recognition site (SRS) 2 in CYP2C9. The sequential molecular dynamics simulation confirmed the binding to C216 induced a conformational change in the active catalytic center of CYP2C9. Lastly, the potential risks of clinical drug-drug interactions triggered by ICT as a perpetrator were extrapolated. In summary, this work confirmed that ICT was an inactivator of CYP2C9. SIGNIFICANCE STATEMENT: This study is the first to report the time-dependent inhibition of CYP2C9 by icaritin (ICT) and the intrinsic molecular mechanism behind it. Experimental data indicated that the inactivation was via irreversible covalent binding of ICT-quinone methide to CYP2C9, while molecular modeling analysis provided additional evidence by predicting C216 as the key binding site which influenced the structural confirmation of CYP2C9's catalytic center. These findings suggest the potential of drug-drug interactions when ICT is co-administered with CYP2C9 substrates clinically.

Rationally Engineered CYP3A4 Fluorogenic Substrates for Functional Imaging Analysis and Drug-Drug Interaction Studies

Cytochrome P450 3A4 (CYP3A4) is a key xenobiotic-metabolizing enzyme-mediated drug metabolism and drug-drug interaction (DDI). Herein, an effective strategy was used to rationally construct a practical two-photon fluorogenic substrate for hCYP3A4. Following two-round structure-based substrate discovery and optimization, we have successfully constructed a hCYP3A4 fluorogenic substrate (F8) with desirable features, including high binding affinity, rapid response, excellent isoform specificity, and low cytotoxicity. Under physiological conditions, F8 is readily metabolized by hCYP3A4 to form a brightly fluorescent product (4-OH F8) that can be easily detected by various fluorescence devices. The practicality of F8 for real-time sensing and functional imaging of hCYP3A4 has been examined in tissue preparations, living cells, and organ slices. F8 also demonstrates good performance for high-throughput screening of hCYP3A4 inhibitors and assessing DDI potentials in vivo. Collectively, this study develops an advanced molecular tool for sensing CYP3A4 activities in biological systems, which strongly facilitates CYP3A4-associated fundamental and applied research studies.

A high-resolution mass spectrometry-based methodology for characterization and identification of methylophiopogonanone B metabolites from cryopreserved hepatocytes and liver microsomes

Methylophiopogonanone B (MOB), one of the homoisoflavonoids isolated from Ophiopogon japonicus, has been demonstrated to possess antioxidative and antitumor activities. The aim of this work was to investigate the metabolism of MOB using liver microsomes and hepatocytes. MOB was individually incubated with rat, monkey, and human hepatocytes to generate the metabolites. To investigate the bioactivation pathways, MOB was incubated with liver microsomes in the presence of glutathione (GSH). All the metabolites were detected and identified using LC with a quadrupole Orbitrap mass spectrometer. Under the current conditions, nine metabolites were identified in hepatocyte incubations. Of these metabolites, M7 derived from hydroxylation was identified as the most abundant metabolite in hepatocyte incubation. MOB was metabolized via demethylation, hydroxylation, and glucuronidation. In liver microsomes, five GSH conjugates were detected and identified. MOB was subjected to bioactivation through demethylation yielding M9, which further formed quinone-methide and ortho-quinone intermediates, followed by GSH conjugation. This work is the first to study the metabolism of MOB, which will help us understand its disposition and efficacy.

The Chinese herb Styrax triggers pharmacokinetic herb-drug interactions via inhibiting intestinal CYP3A

Human cytochrome P450 3A4 (hCYP3A4) is a predominant enzyme to trigger clinically relevant drug/herb-drug interactions (DDIs or HDIs). Although a number of herbal medicines have been found with strong anti-hCYP3A4 effects in vitro, the in vivo modulatory effects of herbal medicines on hCYP3A4 and their potential risks to trigger HDIs are rarely investigated. Herein, we demonstrate a case study to efficiently find the herbal medicine(s) with potent hCYP3A4 inhibition in vitro and to accurately assess the potential HDIs risk in vivo. Following screening over 100 herbal medicines, the Chinese herb Styrax was found with the most potent hCYP3A4 inhibition in HLMs. In vitro assays demonstrated that Styrax could potently inhibit mammalian CYP3A in liver and intestinal microsomes from both humans and rats. In vivo pharmacokinetic assays showed that Styrax (i.g., 100 mg/kg) significantly elevated the plasma exposure of two CYP3A-substrate drugs (midazolam and felodipine) when midazolam or felodipine was administered orally. By contrast, the plasma exposure of either midazolam or felodipine was hardly affected by Styrax (i.g.) when the victim drug was administered intravenously. Further investigations demonstrated that seven pentacyclic triterpenoid acids (PTAs) in Styrax were key substances responsible for CYP3A inhibition, while these PTAs could be exposed to intestinal tract at relatively high exposure levels but their exposure levels in rat plasma and liver were extremely low. These findings well explained why Styrax (i.g.) could elevate the plasma exposure of victim drugs only when these agents were orally administrated. Collectively, our findings demonstrate that Styrax can modulate the pharmacokinetic behavior of CYP3A-substrate drugs via inhibiting intestinal CYP3A, which is very helpful for the clinical pharmacologists to better assess the HDIs triggered by Styrax or Styrax-related herbal products.

Identification of the metabolite of ophiopogonanone A by liquid chromatography/quadrupole time-of-flight mass spectrometry

RATIONALE

Ophiopogonanone A (OPA) is one of the representative homoisoflavonoids isolated from Ophiopogonis Radix. The aim of this study was to identify and characterize the metabolites of OPA generated in the liver microsomes and hepatocytes of rats and humans.

METHODS

The metabolites were generated by incubating OPA (5 μM) with liver microsomes or hepatocytes at 37°C. To trap the reactive metabolites, glutathione (GSH, 5mM) was added into microsomal incubations. The metabolite identification and profiling were performed using ultra-high-performance liquid chromatography combined with photo-diode array detector and quadrupole time-of-flight tandem mass spectrometry (LC-Q/TOF-MS). The acquired mass data were processed by MetaboLynx software. The structures of the metabolites were tentatively characterized in terms of their accurate masses, product ions, and retention times.

RESULTS

Under the present conditions, a total of nine metabolites were detected and their structures were tentatively identified. Among these metabolites, M8 (OPA catechol) was the most abundant metabolite both in rat and human liver microsomes. M7 (glucuronidation product of M8) was the major metabolite both in rat and human hepatocytes. The metabolic pathways of OPA include demethylenation, dehydrogenation, hydroxylation, methylation and glucuronidation and GSH conjugation.

CONCLUSION

Our results provided valuable information regarding the in vitro metabolism of OPA, which would help us understand the mechanism of the elimination of OPA and in turn the effectiveness and potential toxicity.

Identification of the metabolites of methylophiopogonanone A by ultra-high-performance liquid chromatography combined with high-resolution mass spectrometry

RATIONALE

Methylophiopogonanone A (MOA) is a naturally occurring homoisoflavonoid from the Chinese herb Ophiopogon japonicus, which has been demonstrated to attenuate myocardial apoptosis. However, the metabolism of MOA remains unknown. The goal of the present work was to investigate the in vitro metabolism of MOA using liver microsomes and hepatocytes.

METHODS

The metabolites were generated by incubating MOA with rat, monkey and human liver microsomes or hepatocytes. The resulting samples were analyzed by using a quadrupole-orbitrap high-resolution mass spectrometer. The metabolites were identified through the measurements of the exact mass, elemental composition and product ions.

RESULTS

A total of 15 metabolites were detected and identified. Among these metabolites, M7 (demethylenation) was the most abundant metabolite in liver microsomes, while M6 (hydroxylation) was the predominant metabolite in hepatocytes, and glucuronidation metabolites (M9 and M10) were also the main metabolites in hepatocytes. The metabolic pathways of MOA included hydroxylation, demethylenation, glucuronidation, methylation, sulfation and glutathione conjugation.

CONCLUSIONS

This study for the first time provides valuable data on the metabolites of MOA, which will be of great importance for a better understanding of its disposition and to predict human pharmacokinetics.

Characterization and identification of the metabolites of dihydromethysticin by ultra-high-performance liquid chromatography orbitrap high-resolution mass spectrometry

Dihydromethysticin, a natural component from Piper methysticum Forst, has been reported to display pharmacological effects in mental disorders and some malignant tumors. However, the metabolism of this component remained unknown. The goal of this work was conducted to discover the metabolic profiles of dihydromethysticin. The in vitro incubation was performed by incubating dihydromethysticin with rat, monkey, and human liver microsomes and hepatocytes. An analytical assay of ultra-high performance liquid chromatography combined with Orbitrap high-resolution mass spectrometry was utilized to detect and identify the metabolites. With high resolution mass spectrometric determination, the accurate mass, elemental composition, and product ions of the metabolites were determined, which enabled structural characterization to become easy. Under the present conditions, four phase-I metabolites, as well as six phase-II metabolites, were detected and their tentative structures were characterized by mass spectra. M4 was found as the most abundant metabolite both in liver microsomes and hepatocytes. Cytochrome P450 1A2, 2C9, and 3A4 contributed to the formation of this metabolite by using human recombinant P450 enzymes. M4 can be oxidized into reactive ortho-quinone intermediate followed by conjugating with glutathione. M4 was also subject to glucuronidation (M1 and M2) and methylation (M5). Demethylenation, oxidation, hydroxylation, glucuronidation, glutathionylation, and methylation were the primary metabolic pathways of dihydromethysticin. This study provides in vitro metabolism data of dihydromethysticin, which is indispensable for understanding the disposition of this compound.

Methysticin Acts as a Mechanism-Based Inactivator of Cytochrome P450 2C9

Methysticin is one of the naturally occurring bioactive constituents extracted from Piper methysticum Forst. In the present study, we intended to investigate the inhibitory effect of methysticin on cytochrome P450 (P450) enzymes. Methysticin exhibited time-, concentration-, and NADPH-dependent inhibition on CYP2C9 using diclofenac as a probe substrate. Approximately 85% of CYP2C9 activity was inhibited by methysticin at 50 μM after a 30 min preincubation with human liver microsomes in the presence of NADPH. The kinetic parameters K_I, k_inact, and t_1/2,inact were 13.32 ± 1.35 μM, 0.054 ± 0.005 min^-1, and 12.83 ± 3.23 min, respectively. Sulfaphenazole (competitive inhibitor of CYP2C9) displayed a significant protective effect on methysticin-induced CYP2C9 inactivation. However, the inclusion of catalase/superoxide dismutase or glutathione (GSH) showed no such protection. A carbene intermediate was postulated to be involved in methysticin-induced CYP2C9 inactivation as K₃Fe(CN)₆ recovered 14.96% of CYP2C9 activity. A methysticin-derived ortho-quinone intermediate dependent on NADPH was trapped by GSH, and this intermediate was believed to be involved in CYP2C9 inactivation. CYP1A2, 2C9, and 3A4 were the major enzymes responsible for methysticin bioactivation. Taken together, the present work demonstrated that methysticin was a mechanism-based inactivator of CYP2C9. Both ortho-quinone and carbene intermediates appeared to be involved in the inactivation of CYP2C9 induced by methysticin.

Methylophiopogonanone A is a naturally occurring broad-spectrum inhibitor against human UDP-glucuronosyltransferases: Inhibition behaviours and implication in herb-drug interactions

Methylophiopogonanone A (MOA) is an abundant homoisoflavonoid in the Chinese herb Ophiopogonis Radix. Recent investigations revealed that MOA inhibited several human cytochrome P450 enzymes (CYPs) and stimulated OATP1B1. However, the inhibitory effects of MOA on phase II drug-metabolizing enzymes, such as human UDP-glucuronosyltransferases (hUGTs), have not been well investigated. Herein, the inhibition potentials of MOA on hUGTs were assessed. The results clearly demonstrated that MOA dose-dependently inhibited all tested hUGTs including UGT1A1 (IC₅₀  = 1.23 μM), one of the most important detoxification enzymes in humans. Further investigations showed that MOA strongly inhibited UGT1A1-catalysed NHPH-O-glucuronidation in a range of biological settings including hUGT1A1, human liver microsomes (HLM) and HeLa cells overexpressing UGT1A1. Inhibition kinetic analyses demonstrated that MOA competitively inhibited UGT1A1-catalysed NHPH-O-glucuronidation in both hUGT1A1 and HLM, with K_i values of 0.52 and 1.22 μM, respectively. Collectively, our findings expanded knowledge of the interactions between MOA and human drug-metabolizing enzymes, which would be very helpful for guiding the use of MOA-related herbal products in clinical settings.