Drug metabolism letters最新文献

Background: Nitroproston is a novel prostaglandin-based compound modified by NOdonating groups with potential application in obstructive respiratory diseases such as asthma and obstructive bronchitis. Nitroproston has been extensively studied using various pharmacological models. Its biological stability is still uncertain.

Objective: The aim of the present study was to evaluate Nitroproston stability in vitro, as well as to identify and characterize its major biodegradation products.

Methods: The principal biodegradation products of Nitroproston were identified in vitro using liquid chromatography/ion trap - time-of-flight mass-spectrometry. The postulated structure of metabolites was confirmed using authentic reference standards. Rat, rabbit and human plasma and human whole blood samples were used for comparative in vitro degradation study. Nitroproston and its biodegradation products in biological samples were measured by liquid chromatography/triple -stage quadrupole mass spectrometry.

Results: Nitroproston is rapidly hydrolyzed in rat plasma to generate glycerol-1,3-dinitrate and prostaglandin E2. The latter can undergo conversion to cyclopentenone prostaglandins A2 and B2. Thereby less than 5% of the parent compound was observed in rat plasma at the first moment of incubation. A similar pattern was observed for rabbit plasma where half-life (T1/2) of Nitroproston was about 2.0 minutes. Nitroproston biodegradation rate for human plasma was the slowest (T1/2 = 2.1 h) among tested species, occurred more rapidly in whole blood (T1/2 = 14.8 min).

Conclusion: It was found that Nitroproston is rapidly hydrolyzed in rodent compared to human plasma incubations. Whereas Nitroproston is relatively stable in human plasma an enhanced hydrolytic activity was observed in whole human blood incubations. Extensive metabolism of Nitroproston in human whole blood was mainly associated with red blood cells. The observed interspecies variability highlights the need of suitable animal model selection for Nitroproston follow-up PK/PD studies.

Background: The HepaRG cells have key drug metabolism functionalities comparable to those of primary human hepatocytes. Many studies have reported that this cell line can be used as a reliable in vitro model for human drug metabolism studies, including the assessment of cytochrome P450 (CYP) induction.

Objectives: The objective of this study is to determine whether CYP mRNA level measurement is superior to the CYP enzyme activity measurement as a convenient high-throughput method for evaluating CYP induction potential using HepaRG cells.

Methods: QuantiGene Plex 2.0 Assay and LC/MS/MS. mRNA expression levels and enzyme activities of CYP1A2, CYP2B6, and CYP3A in HepaRG cells treated with prototypical inducers of each CYP isoform [omeprazole (OME) for CYP1A2, phenobarbital (PB) for CYP2B6, and rifampicin (RIF) for CYP3A] were evaluated.

Results: Although the activities of CYP2B6 and CYP3A were induced by treatment with PB and RIF, we found that the activity of phenacetin O-deethylase (PHOD), which is known as a marker of the activity of CYP1A2, was also enhanced by treatment with these non-CYP1A2 inducers in HepaRG cells. Based on previously published reports, we hypothesized that the expression ratio of CYP3A to CYP1A2 is much higher in HepaRG cells than in human hepatocytes; this may result in a nonnegligible contribution of CYP3A to the PHOD reaction in HepaRG cells. Studies using CYP3A inhibitor and pregnane X receptor-knockout HepaRG cells supported this hypothesis.

Conclusion: The measurement of mRNA serves as a higher reliable indicator for the evaluation of CYP induction potential when using HepaRG cells.

Background: There is a continued need for improvements in the efficiency of metabolite structure elucidation.

Objective: We propose to take LC Retention Time (RT) into consideration during the process of structure determination.

Methods: Herein, we develop a simple methodology that employs a Chromatographic Hydrophobicity Index (CHI) framework for standardizing LC conditions and introduce and utilize the concept of a predictable CHI change upon Phase 1 biotransformation (CHIbt). Through the analysis of literature examples, we offer a Quantitative Structure-Retention Relationship (QSRR) for several types of biotransformation (especially hydroxylation) using physicochemical properties (clogP, hydrogen bonding).

Results: The CHI system for retention indexing is shown to be practical and simple to implement. A database of CHIbt values has been created from re-incubation of 3 compounds and from analysis of an additional 17 datasets from the literature. Application of this database is illustrated.

Conclusion: In our experience, this simple methodology allows complementing the discovery efforts that saves resources for in-depth characterization using NMR.

Background: A recent advancement in isolation and cryopreservation has resulted in commercially available primary human enterocytes that express various drug metabolizing enzymes (DMEs) and transporters. The main objective of this study was to further evaluate the utility of pooled cryopreserved enterocytes, specifically MetMax™ cryopreserved human enterocytes (In vitro ADMET Laboratories), as an in vitro model for assessing intestinal clearance in comparison to hepatocytes.

Methods: It was found that, for CYP3A4/5 substrates such as midazolam, amprenavir and loperamide, in vitro metabolic clearance is generally lower in enterocytes compared to that of hepatocytes, which is consistent with the relative abundance of the enzyme between the intestine and liver. In contrast, raloxifene, a surrogate UGT activity substrate, showed 3-fold greater turnover in enterocytes than hepatocytes, which is likely attributed to the differential expression of individual UGTs in human liver and intestine. For procaine, a known CES2 substrate, the measured apparent clearance was higher in hepatocytes, but formation of 4-aminobenzoic acid, a CE2-specific metabolite, was more pronounced in enterocytes, suggesting that CE2 is more active in enterocytes. Salbutamol, a SULT1A3 substrate, showed little turnover in both enterocytes and hepatocytes, and more abundant sulfate conjugate was detected in enterocytes, indicating higher SULT activity in enterocytes than hepatocytes. As expected, ketoconazole inhibited CYP3A4/5-mediated metabolite formation in enterocytes for midazolam, amprenavir and loperamide, suggesting that cryopreserved enterocytes may be useful in determining intestinal CYP3A inhibition parameters. Interestingly, elacridar, a P-gp inhibitor, suppressed metabolite formation in enterocytes for loperamide, a substrate of CYP3A4 and P-gp, suggesting that enterocytes in suspension do not have active P-gp efflux functions, and the suppression of metabolism in enterocytes is probably caused by inhibition of CYP3A4/5 by elacridar.

Results: Our results suggest that pooled cryopreserved human enterocytes, specifically the MetMax™ cryopreserved human enterocytes, represent a valuable in vitro model for assessing first-pass clearance and potential drug interactions in human intestine.

Background: The high levels of blood alcohol achieved with chronic plus binge alcohol exposures are somewhat reduced by co-administration of tobacco-specific Nicotine-Derived Nitrosamine Ketone (NNK) suggesting that NNK may alter alcohol metabolism.

Objective: We examined ethanol and acetaldehyde-metabolizing enzyme activities and malondialdehyde adduct formation in rats exposed to ethanol (chronic + binge), NNK, or both.

Methods: 4-week old Long Evans rats were fed liquid diets containing 0% or 26% caloric ethanol for 8 weeks. Ethanol-fed rats were binge-administered ethanol (2 g/kg; on Mondays, Wednesdays, and Fridays) by intraperitoneal (i.p.) injection, while control group administered saline in weeks 7 and 8 (n=12/group). Six rats from each group were administered i.p. injections of NNK (2 mg/kg) or saline on Tuesdays, Thursdays, and Saturdays of weeks 3 through 8. Alcohol dehydrogenase, catalase, and aldehyde dehydrogenase activities were measured using commercial assays. Cytochrome P450 mRNA levels (17 isoforms) were measured by quantitative reverse transcription-polymerase chain reaction. Malondialdehyde immunoreactivity was measured by enzyme-linked immunosorbent assay.

Results: Dual exposures to ethanol and NNK significantly increased frontal lobe ADH activity relative to control (P=0.01) and ethanol only (P=0.04) treatments, and ALDH relative to control (P=0.02). In contrast, malondialdehyde-protein expression was not significantly altered by ethanol+NNK. Ethanol decreased CYP1A1 mRNA expression relative to control (P=0.02), and combined ethanol+NNK exposures decreased the expression of CYP1A1 (P=0.01) and CYP2C6 (P=0.03).

Conclusion: Dual exposures to ethanol and NNK increase brain ethanol metabolism and inhibit the expression of CYP450s that regulate xenobiotic metabolism.

Background: Recently, it has been an increasing concern on the bioactivation and adverse reactions associated with consumption of herbal and nature products. 7-Ethoxycoumarin is one of coumarin family compounds, but little information is available regarding its potential reactive metabolites.

Method: 7-ethoxylcoumarin was incubated individually with human, monkey, dog and rat hepatocytes for 2 hr, metabolites were detected, identified and characterized using high resolution liquid chromagraphy - tandem mass spectrometry.

Results: Twenty-eight metabolites (M1 - M28) were detected and identified. O-deethylation, glucuronidation, sulfation, oxygenation, oxidative ring-opening, hydrogenation, glutathionation, dehydrogenation, cysteination, glucosidation, methylation, and hydrolysis were observed. At least sixteen metabolites not reported previously, were newly identified. M1 (O-deethylation, mono-oxygenation and glucuronidation), M3 (O-deethylation and glucuronidation), M5 (hydrolysis and mono-oxygenation), M14 (O-deethylation), M16 (hydrolysis), M22 (oxidative ring-opening and oxygenation) and M27 (monooxygenation) exhibited high mass spectrometric responses in human hepatocytes. M3, M5, M8, M13 (mono-oxygenation), M14, M16, M18 (O-deethylation and sulfation), M22 and M27 exhibited high mass spectrometric responses in monkey hepatocytes. M14, M16, M18, M20 (glutathionation and dehydrogenation) and M27 exhibited high mass spectrometric responses in dog hepatocytes. M1 (Odeethylation, mono-oxygenation and glucuronidation), M3, M5, M13, M14, M16, M17 (cysteination), M18, M20, and M22 exhibited high mass spectrometric responses in rat hepatocytes.

Conclusion: Most of new metabolites via oxidative ring-opening and glutathionation were identified. Species differences in metabolism of 7-ethoxylcoumarin in hepatocytes were observed. The analysis of metabolites suggests that 7-ethoxylcoumarin may undergo 3,4-epoxidation responsible for formation of glutathione and its derived cysteine conjugates, carboxylic acid and its glucuronides, glucosides and sulfate.

Background: We report here an evaluation of a novel experimental system- cofactorsupplemented permeabilized cryopreserved human enterocytes (MetMax™ cryopreserved human enterocytes (MMHE), patent pending) for applications in the evaluation of enteric drug metabolism. A major advantage of MMHE over Conventional Cryopreserved Human Enterocytes (CCHE) is the simplification of the use procedures including storage at -80°C instead of in liquid nitrogen, and use of the cells immediately after thawing without a need for centrifugation and microscopic evaluation of cell density and viability and cell density adjustment.

Methods: In this study, we compared MMHE and CCHE in key phase 1 oxidation and phase 2 conjugation Drug Metabolism Enzyme (DME) activities that we recently reported for cryopreserved human enterocytes: CYP2C9 (diclofenac 4'- hydroxylation), CYP2C19 (s-mephenytoin hydroxylation), CYP3A4 (midazolam 1'-hydroxylation), CYP2J2 (astemizole O-demethylation), uridine 5'-diphosphoglucuronosyltransferase (UGT; 7-hydroxycoumarin glucuronidation), sulfotransferase (SULT; 7- hydroxycoumarin sulfation), N-acetyl transferase-1 (NAT-1; p-benzoic acid N-acetylation), and carboxyesterase- 2 (CES-2; hydrolysis of irinotecan to SN38). Both CCHE and MMHE were active in all the DME pathways evaluated, with specific activities of MMHE ranged from 142% (CYP2C9) to 1713% (UGT) of that for CCHE. β-hydroxylation and testosterone 6.

Result and conclusion: Our results suggest that the MMHE system represents a convenient and robust in vitro experimental system for the evaluation of enteric drug metabolism.

Background: Age has a significant impact on activities of hepatic metabolizing enzymes in humans and animals. Flavin-containing Monooxygenase (FMO) and Aldehyde Oxidase (AO) are two important hepatic enzymes. Understanding of the impact of age on these two enzymes is still limited in pigs.

Objective: The aim of this work was to assess hepatic FMO and AO activities of male domestic pigs at five different ages of 1 day, 2, 5, 10 and 20 weeks.

Methods: Porcine liver microsomes and cytosol were prepared from the livers of male domestic pigs at ages of 1 day, 2, 5, 10 and 20 weeks. FMO activity was assessed using N-oxidation of benzydamine in porcine liver microsomes and AO activity was evaluated using oxidation of O6-benzylguanine in the porcine liver cytosol.

Results: Porcine hepatic FMO activity was substantial at the age of 1 day, rapidly increased in 2 weeks, and remained high afterwards. Porcine hepatic AO activity was minimal at the age of 1 day and gradually increased to the maximum in 5 weeks and remained relatively constant to the age of 20 weeks. Porcine hepatic FMO activity is higher than other species, including humans. Age-dependent FMO developmental pattern in porcine liver is different from porcine hepatic CYP450 and human hepatic FMO. Porcine hepatic AO activity is much lower than humans although their developmental patterns are similar.

Conclusion: Age impact on hepatic activities of both FMO and AO is obvious in domestic male pigs although age patterns of both enzymes are different.