Screening of six UGT enzyme activities in human liver microsomes using liquid chromatography/triple quadrupole mass spectrometry

Investigating the Contribution of Drug-Metabolizing Enzymes in Drug-Drug Interactions of Dapivirine and Miconazole

Dapivirine (DPV) is a potent NNRTI used to prevent the sexual transmission of HIV. In a phase 1 trial (IPM 028), the concomitant use of a DPV vaginal ring and an antifungal miconazole (MIC) vaginal capsule was found to increase the systemic exposure to DPV in women, suggesting a potential for drug-drug interactions. This study's objective was to investigate the mechanism of DPV-MIC interactions using drug-metabolizing enzymes (DMEs; CYPs and UGTs) that are locally expressed in the female reproductive tract (FRT). In vitro studies were performed to evaluate the metabolism of DPV and its inhibition and induction potential with DMEs. In addition, the impact of MIC on DPV metabolism and the inhibitory potential of DPV with DMEs were studied. Our findings suggest that DPV is a substrate of CYP1A1 and CYP3A4 enzymes and that MIC significantly decreased the DPV metabolism by inhibiting these two enzymes. DPV demonstrated potent inhibition of CYP1A1 and moderate/weak inhibition of the six CYP and eight UGT enzymes evaluated. MIC showed potent/moderate inhibition of seven CYP enzymes and weak/no inhibition of eight UGT enzymes. The combination of DPV and MIC showed potent inhibition of seven CYP enzymes (1A1, 1A2, 1B1, 2B6, 2C8, 2C19, and 3A4) and four UGT enzymes (1A3, 1A6, 1A9, and 2B7). DPV was not an inducer of CYP1A2, CYP2B6, and CYP3A4 enzymes in primary human hepatocytes. Therefore, the increased systemic concentrations of DPV observed in IPM 028 were likely due to the reduced metabolism of DPV because of CYP1A1 and CYP3A4 enzymes inhibition by MIC in the FRT.

Comprehensive Investigation of Stereoselective Food Drug Interaction Potential of Resveratrol on Nine P450 and Six UGT Isoforms in Human Liver Microsomes

The stereoselectivity of the food drug inhibition potential of resveratrol on cytochrome P450s and uridine 5'-diphosphoglucuronosyl transferases was investigated in human liver microsomes. Resveratrol enantiomers showed stereoselective inhibition of CYP2C9, CYP3A, and UGT1A1. The inhibitions of CYP1A2, CYP2B6, and CYP2C19 by resveratrol were stereo-nonselective. The estimated K_i values determined for CYP1A2 were 13.8 and 9.2 μM for trans- and cis-resveratrol, respectively. Trans-resveratrol noncompetitively inhibited CYP3A and UGT1A1 activities with K_i values of 23.8 and 27.4 μM, respectively. Trans-resveratrol inhibited CYP1A2, CYP2C19, CYP2E1, and CYP3A in a time-dependent manner with K_i shift values >2.0, while cis-resveratrol time-dependently inhibited CYP2C19 and CYP2E1. The time-dependent inhibition of trans-resveratrol against CYP3A4, CYP2E1, CYP2C19, and CYP1A2 was elucidated using glutathione as a trapping reagent. This information helped the prediction of food drug interaction potentials between resveratrol and co-administered drugs which are mainly metabolized by UGT1A1, CYP1A2, CYP2C19, CYP2E1, and CYP3A.

A novel ratiometric MALDI-MS quantitation strategy for alkaline phosphatase activity with a homogeneous reaction and a tunable dynamic range

A unique ratiometric MALDI-MS strategy is proposed for the convenient and reliable quantitation of alkaline phosphatase based on the homogeneous enzymatic cleavage of a coded phosphopeptide (CPP)-triggered double-signal output. The dynamic range can be tuned by simply adjusting the primary concentration of CPP. The proposed strategy is also capable of being challenged by real human serum, and thus it may offer a wonderful approach for the convenient identification and quantitation of various enzyme activities in clinical diagnosis.

In vitro modulatory effects of ginsenoside compound K, 20(S)-protopanaxadiol and 20(S)-protopanaxatriol on uridine 5'-diphospho-glucuronosyltransferase activity and expression

We explored the inhibitory effect of ginsenoside compound K (CK), 20(S)-protopanaxadiol (PPD), and 20(S)-protopanaxatriol (PPT) on six uridine 5'-diphospho-glucuronosyltransferase (UGT) enzyme (UGT1A1, 1A3, 1A4, 1A6, 1A9, and 2B7) activities in human liver microsomes (HLMs) and 10 UGT enzyme (UGT1A1, 1A3, 1A4, 1A6, 1A9, 2B4, 2B7, 2B10, 2B15, and 2B17) activities in recombinant UGT isoforms.PPD was a potent inhibitor of UGT1A3 activity with half-maximal inhibitory concentration values of 5.62 and 3.38 μM in HLMs and recombinant UGT1A3, respectively. UGT1A3 inhibition by CK and PPD was competitive with inhibitory constant (K_i) values of 17.4 and 1.21 μM, respectively, and inhibition by PPT was non-competitive with a K_i value of 8.07 μM in HLMs. PPD exhibited more than 3.4-fold selectivity for UGT1A3 inhibition compared with other UGT isoforms inhibition, while CK and PPT showed more than 2.16- and 2.21-fold selectivity, respectively.PPD did not significantly increase the mRNA expression of UGT1A1, 1A3, 1A4, 1A9, and 2B7 in hepatocytes.Given the low plasma concentrations of PPD in healthy human subjects and the absence of induction potential on UGT isoforms, we conclude that PPD cause no pharmacokinetic interactions with other co-administered drugs metabolised by UGT1A3.

Inhibitory Effects of Schisandra Lignans on Cytochrome P450s and Uridine 5'-Diphospho-Glucuronosyl Transferases in Human Liver Microsomes

Schisandra chinensis has been widely used as a traditional herbal medicine to treat chronic coughs, fatigue, night sweats, and insomnia. Numerous bioactive components including lignans have been identified in this plant. Lignans with a dibenzocyclooctadiene moiety have been known to possess anti-cancer, anti-inflammatory, and hepatoprotective activity. Fragmentary studies have reported the ability of some lignans to modulate some cytochrome P450 (P450) enzymes. Herein, we investigated the drug interaction potential of six dibenzocyclooctadiene lignans (schisandrin, gomisin A, B, C, and N, and wuweizisu C) on nine P450 enzymes (CYP1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A) and six uridine 5'-diphosphoglucuronosyl transferase (UGT) enzymes (UGT1A1, 1A3, 1A4, 1A6, 1A9, and 2B7) using human liver microsomes. We found that lignans with one or two methylenedioxyphenyl groups inhibited CYP2B6, CYP2C8, CYP2C9, CYP2C19, and CYP2E1 activities in a time- and concentration-dependent like their CYP3A inhibition. In comparison, these lignans do not induce time-dependent inhibition of CYP1A2, CYP2A6, and CYP2D6. The time-dependent inhibition of gomisin A against CYP2C8, CYP2C19, and CYP3A4 was also elucidated using glutathione as a trapping reagent of reactive carbene metabolites given that gomisin A strongly inhibits these P450 enzymes in a time-dependent manner. A glutathione conjugate of gomisin A was generated in reactions with human recombinant CYP2C8, CYP2C19, and CYP3A4. This suggests that the time-dependent inhibition of gomisin A against CYP2C8, CYP2C9, and CYP3A4 is due to the production of carbene reactive metabolite. Six of the lignans we tested inhibited the activities of six UGT to a limited extent (IC₅₀ > 15 μM). This information may aid the prediction of possible drug interactions between Schisandra lignans and any co-administered drugs which are mainly metabolized by P450s.

Biotransformation of phytoestrogens from soy in enzymatically characterized liver microsomes and primary hepatocytes of Atlantic salmon

Efficient aquaculture is depending on sustainable protein sources. The shortage in marine raw materials has initiated a shift to "green aquafeeds" based on staple ingredients such as soy and wheat. Plant-based diets entail new challenges regarding fish health, product quality and consumer risks due to the possible presence of chemical contaminants, natural toxins and bioactive compounds like phytoestrogens. Daidzein (DAI), genistein (GEN) and glycitein (GLY) are major soy isoflavones with considerable estrogenic activities, potentially interfering with the piscine endocrine system and affecting consumers after carry-over. In this context, information on isoflavone biotransformation in fish is crucial for risk evaluation. We have therefore isolated hepatic fractions of Atlantic salmon (Salmo salar), the most important species in Norwegian aquaculture, and used them to study isoflavone elimination and metabolite formation. The salmon liver microsomes and primary hepatocytes were characterized with respect to phase I cytochrome P450 (CYP) and phase II uridine-diphosphate-glucuronosyltransferase (UGT) enzyme activities using specific probe substrates, which allowed comparison to results in other species. DAI, GEN and GLY were effectively cleared by UGT. Based on the measurement of exact masses, fragmentation patterns, and retention times in liquid chromatography high-resolution mass spectrometry, we preliminarily identified the 7-O-glucuronides as the main metabolites in salmon, possibly produced by UGT1A1 and UGT1A9-like activities. In contrast, the production of oxidative metabolites by CYP was insignificant. Under optimized assay conditions, only small amounts of mono-hydroxylated DAI were detectable. These findings suggested that bioaccumulation of phytoestrogens in farmed salmon and consumer risks from soy-containing aquafeeds are unlikely.

Strong and Selective Inhibitory Effects of the Biflavonoid Selamariscina A against CYP2C8 and CYP2C9 Enzyme Activities in Human Liver Microsomes

Like flavonoids, biflavonoids, dimeric flavonoids, and polyphenolic plant secondary metabolites have antioxidant, antibacterial, antiviral, anti-inflammatory, and anti-cancer properties. However, there is limited data on their effects on cytochrome P450 (P450) and uridine 5'-diphosphoglucuronosyl transferase (UGT) enzyme activities. In this study we evaluate the inhibitory potential of five biflavonoids against nine P450 activities (P450s1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A) in human liver microsomes (HLMs) using cocktail incubation and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The most strongly inhibited P450 activity was CYP2C8-mediated amodiaquine N-dealkylation with IC50 ranges of 0.019~0.123 μM. In addition, the biflavonoids-selamariscina A, amentoflavone, robustaflavone, cupressuflavone, and taiwaniaflavone-noncompetitively inhibited CYP2C8 activity with respective K_i values of 0.018, 0.083, 0.084, 0.103, and 0.142 μM. As selamariscina A showed the strongest effects, we then evaluated it against six UGT isoforms, where it showed weaker inhibition (UGTs1A1, 1A3, 1A4, 1A6, 1A9, and 2B7, IC50 1.7 μM). Returning to the P450 activities, selamariscina A inhibited CYP2C9-mediated diclofenac hydroxylation and tolbutamide hydroxylation with respective K_i values of 0.032 and 0.065 μM in a competitive and noncompetitive manner. However, it only weakly inhibited CYP1A2, CYP2B6, and CYP3A with respective K_i values of 3.1, 7.9, and 4.5 μM. We conclude that selamariscina A has selective and strong inhibitory effects on the CYP2C8 and CYP2C9 isoforms. This information might be useful in predicting herb-drug interaction potential between biflavonoids and co-administered drugs mainly metabolized by CYP2C8 and CYP2C9. In addition, selamariscina A might be used as a strong CYP2C8 and CYP2C9 inhibitor in P450 reaction-phenotyping studies to identify drug-metabolizing enzymes responsible for the metabolism of new chemicals.

The Ontogeny of UDP-glucuronosyltransferase Enzymes, Recommendations for Future Profiling Studies and Application Through Physiologically Based Pharmacokinetic Modelling

Limited understanding of drug pharmacokinetics in children is one of the major challenges in paediatric drug development. This is most critical in neonates and infants owing to rapid changes in physiological functions, especially in the activity of drug-metabolising enzymes. Paediatric physiologically based pharmacokinetic models that integrate ontogeny functions for cytochrome P450 enzymes have aided our understanding of drug exposure in children, including those under the age of 2 years. Paediatric physiologically based pharmacokinetic models have consequently been recognised by the European Medicines Agency and the US Food and Drug Administration as innovative tools in paediatric drug development and regulatory decision making. However, little is currently known about age-related changes in UDP-glucuronosyltransferase-mediated metabolism, which represents the most important conjugation reaction for xenobiotics. Therefore, the objective of the review was to conduct a thorough literature survey to summarise our current understanding of age-related changes in UDP-glucuronosyltransferases as well as associated clinical and experimental sources of variance. Our findings indicate that there are distinct differences in UDP-glucuronosyltransferase expression and activity between isoforms for different age groups. In addition, there is substantial variability between individuals and laboratories reported for human liver microsomes, which results in part from a lack of standardised experimental conditions. Therefore, we provide a number of best practice recommendations for experimental conditions, which ultimately may help improve the quality of data used for quantitative clinical pharmacology approaches, and thus for safe and effective pharmacotherapy in children.

Screening of ten cytochrome P450 enzyme activities with 12 probe substrates in human liver microsomes using cocktail incubation and liquid chromatography-tandem mass spectrometry

Testing for potential drug interactions of new chemical entities is essential when developing a novel drug. In this study, an assay was designed to evaluate drug interactions with 10 major human cytochrome P450 (P450) enzymes incubated in liver microsomes, involving 12 probe substrates with two cocktail incubation sets used in a single liquid chromatography-tandem mass spectrometry (LC-MS/MS) run. The P450 substrate composition in each cocktail set was optimized to minimize solvent effects and mutual drug interactions among substrates as follows: cocktail A was composed of phenacetin for CYP1A2, bupropion for CYP2B6, amodiaquine for CYP2C8, diclofenac for CYP2C9, S-mephenytoin for CYP2C19, and dextromethorphan for CYP2D6; cocktail B was composed of coumarin for CYP2A6, chlorzoxazone for CYP2E1, astemizole for CYP2J2, and midazolam, nifedipine, and testosterone for CYP3A. Multiple probe substrates were used for CYP3A owing to the multiple substrate-binding sites and substrate-dependent inhibition. After incubation in human liver microsomes, each incubation mixture was pooled and all probe metabolites were simultaneously analysed in a single LC-MS/MS run. Polarity switching was used to acquire the negative-ion mode for hydroxychlorzoxazone and positive-ion mode for the remaining analytes. The method was validated by comparing the inhibition data obtained from incubation of each individual probe substrate alone and with the substrate cocktails. The half-maximal inhibitory concentration values obtained from the cocktail and individual incubations were well correlated and in agreement with previously reported values. This new method will be useful in assessing the drug interaction potential of new chemical entities during new drug development.

Optimization of Experimental Conditions of Automated Glucuronidation Assays in Human Liver Microsomes Using a Cocktail Approach and Ultra-High Performance Liquid Chromatography-Tandem Mass Spectrometry

UDP-glucuronosyltransferase (UGT)-mediated metabolism is possibly the most important conjugation reaction for marketed drugs. However, there are currently no generally accepted standard incubation conditions for UGT microsomal assays, and substantial differences in experimental design and methodology between laboratories hinder cross-study comparison of in vitro activities. This study aimed to define optimal experimental conditions to determine glucuronidation activity of multiple UGT isoforms simultaneously using human liver microsomes. Hepatic glucuronidation activities of UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B4, UGT2B7, UGT2B10, UGT2B15, and UGT2B17 were determined using cocktail incubations of 10 UGT probe substrates. Buffer components and cosubstrates were assessed over a range of concentrations including magnesium chloride (MgCl₂; 0-10 mM) and uridine 5'-diphosphoglucuronic acid (UDPGA; 1-25 mM) with either Tris-HCl or potassium phosphate buffer (100 mM, pH 7.4). Greater microsomal glucuronidation activity by different hepatic UGT isoforms was obtained using 10 mM MgCl₂ and 5 mM UDPGA with 100 mM Tris-HCl buffer. The influence of bovine serum albumin (BSA; 0.1%-2% w/v) on glucuronidation activity was also assessed. Enzyme- and substrate-dependent effects of BSA were observed, resulting in decreased total activity of UGT1A1, UGT1A3, and UGT2B17 and increased total UGT1A9 and UGT2B7 activity. The inclusion of BSA did not significantly reduce the between-subject variability of UGT activity. Future in vitro UGT profiling studies under the proposed optimized experimental conditions would allow high-quality positive control data to be generated across laboratories, with effective control of a high degree of between-donor variability for UGT activity and for chemical optimization toward lower-clearance drug molecules in a pharmaceutical drug discovery setting.

LC-MS/MS method for the simultaneous quantification of intestinal CYP and UGT activity

Many orally administered drugs are subject to first-pass metabolism by cytochrome P450 (CYP) enzymes and uridine 5'-diphospho-glucuronosyltransferases (UGT). While their hepatic activity is well characterized, respective information about the intestine are very scare due to limited availability of tissue, very low microsomal protein content and the heterogeneity of the individual segments. As a consequence, determination of enzyme kinetic parameters is challenging. It was therefore the aim of this study to develop a sensitive liquid chromatography tandem mass spectrometry method for the simultaneous quantification of CYP and UGT metabolites formed by clinically relevant intestinal biotransformation enzymes: 4-hydroxydiclofenac (CYP2C9), 5-hydroxyomeprazole (CYP2C19), dextrorphan (CYP2D6), 1-hydroxymidazolam (CYP3A), ezetimibe glucuronide (UGT1A) and naloxone glucuronide (UGT2B7). After precipitation of microsomal protein with acetonitrile, analytes were chromatographically separated on a C18 column with gradient elution using acetonitrile and water, both containing 0.1% formic acid and detected with a tandem mass spectrometer operating in positive mode with electron spray ionization. The assay was validated according to current bioanalytical guidelines regarding linearity, accuracy, precision, stability, recovery and matrix effects spanning an analytical range from 1 to 200 nmol/L for each analyte. The developed method was successfully applied to a proof of concept experiment using pooled human jejunal microsomes (50 μg protein/mL) in order to determine enzyme kinetic parameters. Formation of all monitored metabolites followed Michaelis-Menten kinetics and allowed calculation of K_M and V_max values. The developed method may be useful for characterization of enzymatic activity in the human intestine which may allow more precise insights into the intestinal contribution to first pass metabolism of drugs.

A Novel In Vitro Experimental System for the Evaluation of Drug Metabolism: Cofactor-Supplemented Permeabilized Cryopreserved Human Hepatocytes (MetMax Cryopreserved Human Hepatocytes)

We report here a novel experimental system, cryopreserved MetMax human hepatocytes (MMHHs), for in vitro drug metabolism studies. MMHHs consist of cofactor-supplemented permeabilized cryopreserved human hepatocytes. The use procedures for MMHHs are significantly simplified from that for conventional cryopreserved human hepatocytes (CCHHs): 1) storage at -80°C instead of in liquid nitrogen and 2) usage directly after thawing without centrifugation and microscopic evaluation of cell density and viability and cell density adjustment. In this study, we compared MMHHs and CCHHs in CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2D6, CYP2E1, CYP3A4, CYP2J2, monoamine oxidase A, aldehyde oxidase, flavin-containing monooxygenase, UDP-glucuronyl transferase, SULT, N-acetyltransferase 1, and acetaminophen glutathione (GSH) conjugation activities based on liquid chromatography-tandem mass spectrometry quantification of substrate metabolism. MMHHs were prepared from CCHHs consisting of hepatocytes pooled from 10 individual donors. The drug metabolizing enzyme activities of both CCHHs and MMHHs were cell concentration and time dependent, with specific activities of MMHHs ranging from 27.2% (carboxylesterase 2) to 234.2% (acetaminophen GSH conjugation) of that for CCHHs. As observed in CCHHs, sequential oxidation and conjugation was observed in MMHHs for coumarin, 7-ethoxycoumarin, and acetaminophen. 7-Hydroxycoumarin conjugation results showed that metabolic pathways in MMHHs could be selected via the choice of cofactors, with glucuronidation but not sulfation observed in the presence of UDP-glucuronic acid and not 3-phosphoadenosine-5-phosphosulfate, and vice versa. Results with noncytotoxic and cytotoxic concentrations of acetaminophen showed that drug metabolism was compromised in CCHHs but not in MMHHs. Our results suggest that the MMHHs system represents a convenient and robust in vitro experimental system for the evaluation of drug metabolism.

Direct comparison of UDP-glucuronosyltransferase and cytochrome P450 activities in human liver microsomes, plated and suspended primary human hepatocytes from five liver donors

UDP-glucuronosyltransferases (UGTs) and cytochrome P450s (CYPs) are the major enzymes involved in hepatic metabolism of drugs. Hepatic drug metabolism is commonly investigated using human liver microsomes (HLM) or primary human hepatocytes (PHH). We describe the development of a sensitive assay to phenotype activities of six major hepatic UGT isoforms (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9 and UGT2B7) in intact PHH by analysis of glucuronidation of selective probe substrates. The non-selective, general substrate 7-hydroxycoumarin was included for comparison. For each liver donor preparation (five donors) UGT activities in cryopreserved suspended and plated PHH were compared to HLM prepared from the same donors. Standard CYP reaction phenotyping of seven major isoforms was performed in parallel. For all donors, CYP- and UGT-isoforms activity profiles were comparable in PHH and HLM, indicating that reaction phenotyping with selective probe substrates in intact cells primarily reflects respective CYP or UGT activity. System-dependent effects on UGT and CYP isoform activity were still found. While UGT activity of UGT1A1 was equivalent in plated and suspended PHH, UGT1A3, UGT1A6 and UGT2B7 activity was higher in suspended PHH and UGT1A9 and UGT1A4 activity was higher in plated PHH. The well-known decrease in activity of most CYP isoforms in plated compared to suspended PHH was confirmed. Importantly, we found a significant loss in CYP2C19 and CYP2B6 in HLM, activity being lower than in intact cells. Taken together, these findings implicate that, dependent on the UGT or CYP isoforms involved in the metabolism of a given compound, the outcome of metabolic assays is strongly dependent on the choice of the in vitro system. The currently described UGT- and CYP- activity profiling method can be used as a standard assay in intact cells and can especially aid in reaction phenotyping of in vitro systems for which a limited number of cells are available.

Inhibitory Effect of Selaginellins from Selaginella tamariscina (Beauv.) Spring against Cytochrome P450 and Uridine 5'-Diphosphoglucuronosyltransferase Isoforms on Human Liver Microsomes

Selaginella tamariscina (Beauv.) has been used for traditional herbal medicine for treatment of cancer, hepatitis, and diabetes in the Orient. Numerous bioactive compounds including alkaloids, flavonoids, lignans, and selaginellins have been identified in this medicinal plant. Among them, selaginellins having a quinone methide unit and an alkylphenol moiety have been known to possess anticancer, antidiabetic, and neuroprotective activity. Although there have been studies on the biological activities of selaginellins, their modulatory potential of cytochrome P450 (P450) and uridine 5'-diphosphoglucuronosyltransferase (UGT) activities have not been previously evaluated. In this study, we investigated the drug interaction potential of two selaginellins on ten P450 isoforms (CYP1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 2J2 and 3A) and six UGT isoforms (UGT1A1, 1A3, 1A4, 1A6, 1A9 and 2B7) using human liver microsomes and liquid chromatography-tandem mass spectrometry. Selaginellin and selaginellin M had high inhibitory potential for CYP2C8-mediated amodiaquine O-demethylation with IC₅₀ values of 0.5 and 0.9 μM, respectively. Selaginellin and selaginellin M also showed medium inhibitory potential against CYP2C9, CYP2J2, UGT1A1, and UGT1A3 (1 μM < IC₅₀ < 5 μM). These two selaginellins had low inhibitory potential against CYP1A2, CYP2A6, CYP2E1, and UGT1A6 (IC₅₀ > 25 μM). This information might be helpful to predict possible drug interaction potential of between selaginellins and co-administered drugs.

Profiles and Gender-Specifics of UDP-Glucuronosyltransferases and Sulfotransferases Expressions in the Major Metabolic Organs of Wild-Type and Efflux Transporter Knockout FVB Mice

Hepatic and extrahepatic tissues participate in xenobiotic detoxication, carcinogen activation, prodrug processing, and estrogen regulation through UDP-glucuronosyltransferases (UGTs/Ugts) and sulfotransferases (SULTs/Sults). Wild-type (WT) and efflux transporter knockout (KO) FVB mice have been commonly used to perform the studies of pharmacokinetics, metabolism, and toxicity. We employed the developed UHPLC-MS/MS approach to gain systematic insight on gender-specific of Ugts and Sults in major metabolic organs. Results showed that the liver was the most abundant with Ugts/Sults, followed by the small intestine and the kidney. In the liver, Ugt2b5, Ugt2b1, Ugt1a6a, Ugt1a1, Sult1a1, and Sult1d1 were the major isoforms. The protein amounts of Ugt1a9 were significantly higher in male efflux transporter KO mice than in WT mice, whereas Ugt1a5 and Sult1a1 severely decreased in female efflux transporter KO mice. In WT and efflux transporter KO mice, the expression levels of Ugt1a1, Ugt1a5, Sult1a1, Sult1d1, and Sult3a1 were female-specific, whereas those of Ugt2b1, Ugt2b5, and Ugt2b36 were male-specific. In the small intestine, Ugt1a1, Sult1b1, and Sult2b1 were the major isoforms. The protein levels and gender differences of Ugts/Sults were obviously affected when KO of Mdr1a, and Bcrp1, Mrp1, Mrp2, and Mdr1a, respectively. The KO of efflux transporter affected the protein amounts of Ugts/Sults in the kidney, heart, and spleen. Therefore, a better understanding of the expression profiles and gender-specific of Ugts and Sults in major metabolic organs of WT and efflux transporter KO mice is useful for the evaluation of potential efficacy, and toxicity of corresponding substrates.

Single-shot multi-reaction monitoring of intact marker conjugates for quantitative profiling of human major microsomal glucuronidations and its utility to screen inhibitors from medicinal herbs

UDP-glucuronosyltransferase (UGT) is a polymorphic family of conjugating enzymes responsible for the elimination of a myriad of xenobiotics and endogenous compounds. The precise reaction phenotyping of this multi-isoform superfamily is hampered by a lack of fast generic methods for directly measuring the diverse glucuronoconjugate metabolites for comprehensive profiling of UGT isoform-specific glucuronidations. We report here a single-shot liquid chromatography-tandem mass spectrometry (LC-MS/MS) method enabling the simultaneous direct measurement of nine intact glucuronides from hepatic microsomal glucuronidations mediated by a battery of isoforms (1A1, 1A3, 1A4, 1A6, 1A9, 2B7, 2B10, 2B15, and 2B17), which represent the majority of human UGTs in drug metabolism. This new method is based on post-incubation pooling of the individual probe reaction samples for nine-in-one cassette analysis with polarity switching multiple reaction monitoring (MRM) of all the marker glucuronides within a single LC-MS/MS injection. The pooled sample strategy overcomes the cross-interferences among the cocktail substrates and also increases the throughput. The periodic polarity switching of the LC-MRM acquisition expands the glucuronide profiling coverage using a generic single-run analysis. The source-induced dissociation of the glucuronoconjugates was evaluated as a generic alternative for their quantitation as their free aglycones, but a significant bias occurs against the traditional assumption that the parent substrates could be used as the surrogates for quantifying their glucuronide metabolites without authentic standards. After collective validations for analyte quantitation and enzyme kinetics, this single-shot cassette quantitative profiling approach may prove useful in large-scale phenotyping of human glucuronidations and rapid screening for UGT inhibitors in natural products. Graphical abstract Multi-reaction monitoring of intact conjugate metabolites for quantitative profiling of human major glucuronidations.

Characterization of oxycodone in vitro metabolism by human cytochromes P450 and UDP-glucuronosyltransferases

The hepatic metabolism of oxycodone by cytochromes P450 (CYP) and the UDP-glucuronosyltransferases (UGT), the main metabolic enzymes of phase I and phase II, respectively, was assessed in vitro. The N-demethylation by CYP3A4/5 and the O-demethylation by CYP2D6 in human liver microsomes (HLM) followed Michaelis-Menten kinetics, with intrinsic clearances of 1.46μL/min/mg and 0.35μL/min/mg, respectively. Although noroxycodone and oxymorphone mainly contribute to the elimination of oxycodone, the simulated total in vivo clearance using in vitro phase I metabolism was underestimated. For the first time, metabolism of oxycodone by UGT was deeply investigated using HLM, recombinant enzymes and selective inhibitors. Oxycodone-glucuronide was mainly produced by UGT2B7 (K_m=762±153μM, V_max=344±20 peak area/min/mg) and to a lesser extent by UGT2B4 (K_m=2454±497μM, V_max=201±19 peak area/min/mg). Finally, the kinetics of the drug-drug interactions were assessed using two CYP and UGT cocktail approaches. Incubations of HLM with phase I and phase II drug probes showed that oxycodone mainly decreased the in vitro activities of CYP2D6, CYP3A4/5, UGT1A3, UGT1A6 and UGT2B subfamily with an important impact on UGT2B7.

Inhibitory Effects of Aschantin on Cytochrome P450 and Uridine 5'-diphospho-glucuronosyltransferase Enzyme Activities in Human Liver Microsomes

Aschantin is a bioactive neolignan found in Magnolia flos with antiplasmodial, Ca²⁺-antagonistic, platelet activating factor-antagonistic, and chemopreventive activities. We investigated its inhibitory effects on the activities of eight major human cytochrome P450 (CYP) and uridine 5′-diphospho-glucuronosyltransferase (UGT) enzymes of human liver microsomes to determine if mechanistic aschantin–enzyme interactions were evident. Aschantin potently inhibited CYP2C8-mediated amodiaquine N-de-ethylation, CYP2C9-mediated diclofenac 4′-hydroxylation, CYP2C19-mediated [S]-mephenytoin 4′-hydroxylation, and CYP3A4-mediated midazolam 1′-hydroxylation, with K_i values of 10.2, 3.7, 5.8, and 12.6 µM, respectively. Aschantin at 100 µM negligibly inhibited CYP1A2-mediated phenacetin O-de-ethylation, CYP2A6-mediated coumarin 7-hydroxylation, CYP2B6-mediated bupropion hydroxylation, and CYP2D6-mediated bufuralol 1′-hydroxylation. At 200 µM, it weakly inhibited UGT1A1-catalyzed SN-38 glucuronidation, UGT1A6-catalyzed N-acetylserotonin glucuronidation, and UGT1A9-catalyzed mycophenolic acid glucuronidation, with IC₅₀ values of 131.7, 144.1, and 71.0 µM, respectively, but did not show inhibition against UGT1A3, UGT1A4, or UGT2B7 up to 200 µM. These in vitro results indicate that aschantin should be examined in terms of potential interactions with pharmacokinetic drugs in vivo. It exhibited potent mechanism-based inhibition of CYP2C8, CYP2C9, CYP2C19, and CYP3A4.

MALDI-MS Patterning of Caspase Activities and Its Application in the Assessment of Drug Resistance

Mass spectrometry (MS) has been widely used for enzyme activity assays. Herein, we propose a MALDI-MS patterning strategy for the convenient visual presentation of multiple enzyme activities with an easy-to-prepare chip. The array-based caspase-activity patterned chip (Casp-PC) is fabricated by hydrophobically assembling different phospholipid-tagged peptide substrates on a modified ITO slide. The advantages of amphipathic phospholipids lead to high-quality mass spectra for imaging analysis. Upon the respective cleavage of these substrates by different caspases, such as caspase-1, -2, -3, and -8, to produce a mass shift, the enzyme activities can be directly evaluated by MALDI-MS patterning by m/z-dependent imaging of the cleavage products. The ability to identify drug-sensitive/resistant cancer cells and assess the curative effects of anticancer drugs is demonstrated, indicating the applicability of the method and the designed chip.

Elucidation of a CGP7930 in vitro metabolite by liquid chromatography/electrospray ionization quadrupole time-of-flight tandem mass spectrometry

RATIONALE

γ-Aminobutyric acid-B (GABAB ) receptors are widely expressed in the nervous system and have been implicated as targets for various neurological and psychiatric disorders. CGP7930 is a positive allosteric modulator of GABAB receptors. It has been demonstrated to reduce drug self-administration and has gained increased research as a potential psychotropic treatment.

METHODS

An in vitro metabolic system with liver microsomes of SD rats has been conducted and evaluated by probe drugs. The predominant in vitro metabolite of CGP7930 was identified and elucidated using liquid chromatography/electrospray ionization quadrupole time-of-flight tandem mass spectrometry (LC/ESI-QTOF-MS/MS). Its structure was determined by comparing the characteristic ions of CGP7930 and those of the metabolite, based on the accurate mass measurement by MS and the fragmentation pattern obtained by MS/MS.

RESULTS

We found that the main metabolic pathway of CGP7930 was via a monohydroxylation reaction and the hydroxylation site located at the terminal butyl-carbon. The collision-induced dissociation (CID) fragmentation of the hydroxylated metabolite underwent McLafferty rearrangement and α-cleavage.

CONCLUSIONS

This work provides an understanding of the in vitro metabolism of CGP7930, which is helpful for the further study of the development of potential drug candidates targeting GABAB receptors, for the treatment of depression. The work also demonstrates that the LC/ESI-QTOF-MS/MS method has the advantage of possibly determining the structures of drug metabolites without the use of standards.

Characterization of in vitro metabolites of cudratricusxanthone A in human liver microsomes

Cudratricusxanthone A (CTXA), isolated from the roots of Cudrania tricuspidata, exhibits several biological activities; however, metabolic biotransformation was not investigated. Therefore, metabolites of CTXA were investigated and the major metabolic enzymes engaged in human liver microsomes (HLMs) were characterized using liquid chromatography-tandem mass spectrometry (LC-MS/MS). CTXA was incubated with HLMs or human recombinant CYPs and UGTs, and analysed by an LC-MS/MS equipped electrospray ionization (ESI) to qualify and quantify its metabolites. In total, eight metabolites were identified: M1-M4 were identified as mono-hydroxylated metabolites during Phase I, and M5-M8 were identified as O-glucuronidated metabolites during Phase II in HLMs. Moreover, these metabolite structures and a metabolic pathway were identified by elucidation of MS(n) fragments and formation by human recombinant enzymes. M1 was formed by CYP2D6, and M2-M4 were generated by CYP1A2 and CYP3A4. M5-M8 were mainly formed by UGT1A1, respectively. While investigating the biotransformation of CTXA, eight metabolites of CTXA were identified by CYPs and UGTs; these data will be valuable for understanding the in vivo metabolism of CTXA.

Simultaneous Screening of Activities of Five Cytochrome P450 and Four Uridine 5'-Diphospho-glucuronosyltransferase Enzymes in Human Liver Microsomes Using Cocktail Incubation and Liquid Chromatography-Tandem Mass Spectrometry

Cytochrome P450 (P450) and uridine 5'-diphospho-glucuronosyltransferase (UGT) are major metabolizing enzymes in the biotransformation of most drugs. Altered P450 and UGT activities are a potential cause of adverse drug-drug interaction. A method for the simultaneous evaluation of the activities of five P450s (CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A) and four UGTs (UGT1A1, UGT1A4, UGT1A9, and UGT2B7) was developed using in vitro cocktail incubation and tandem mass spectrometry. The nine probe substrates used in this assay were phenacetin (CYP1A2), diclofenac (CYP2C9), S-mephenytoin (CYP2C19), dextromethorphan (CYP2D6), midazolam (CYP3A), 7-ethyl-10-hydroxy-camptothecin (SN-38) (UGT1A1), trifluoperazine (UGT1A4), mycophenolic acid (UGT1A9), and naloxone (UGT2B7). This new method involves incubation of two cocktail doses and single cassette analysis. The two cocktail doses and the concentration of each probe substrate in vitro were determined to minimize mutual drug interactions among substrates. Cocktail A comprised phenacetin, diclofenac, S-mephenytoin, dextromethorphan, and midazolam, whereas cocktail B comprised SN-38, trifluoperazine, mycophenolic acid, and naloxone. In the incubation study of these cocktails, the reaction mixtures were pooled and simultaneously analyzed using liquid chromatography-tandem mass spectrometry. The method was validated by comparing inhibition data obtained from the incubation of each probe substrate alone with data from the cocktail method. The IC50 values obtained in both cocktail and individual incubations were in agreement with values previously reported in the literature. This cocktail method offers a rapid and robust way to simultaneously evaluate phase I and II enzyme inhibition profiles of many new chemical entities. This new method will also be useful in the drug discovery process and for advancing the mechanistic understanding of drug interactions.