Cytochrome P450 Specificity of Metabolism and Interactions of Oxybutynin in Human Liver Microsomes

Abstract: Oxybutynin has an extensive first pass metabolism after oral administration, the main active metabolite being N–desethyloxybutynin. The purpose of this study was to investigate the CYP isoform specificity of oxybutynin N–deethylation and possible interactions. Oxybutynin N–deethylation in human liver microsomes in vitro was potently inhibited by ketoconazole (IC₅₀ 4.5 uM), less and variably by itraconazole and not by quinidine or several other reference inhibitors, suggesting that CYP3A enzymes are predominant catalysts of the reaction. Recombinant CYP3A5 enzyme had higher activity in oxybutynin N–deethylation than recombinant CYP3A4. Ketoconazole inhibited oxybutynin N–deethylation by the recombinant CYP3A4 and CYP3A5 almost completely, whereas itraconazole inhibited the activity of CYP3A4 more potently than that of CYP3A5. Oxybutynin inhibited CYP3A4– and CYP2D6– associated activities (testosterone 6β–hydroxylase and dextromethorphan O– demethylase, respectively) in human liver microsomes. CYP1A1/2–, CYP2A6–, CYP2C9– and CYP2E1–associated activities were inhibited less potently or not at all by oxybutynin when compared with reference inhibitors. Although the reasons for the weak and variable inhibition by itraconazole remain to be studied, it seems that oxybutynin is predominantly metabolized by CYP3A4 and CYP3A5 but not by CYP2D6. However, it seems to have some affinity also to the latter enzyme.     

Inhibitory Effects of Trospium Chloride on Cytochrome P450 Enzymes in Human Liver Microsomes

Abstract Trospium chloride, an atropine derivative used for the treatment of urge incontinence, was tested for inhibitory effects on human cytochrome P-450 enzymes. Metabolic activities were determined in liver microsomes from two donors using the following selective substrates: dextromethorphan (CYP2D6), denitronifedipine (CYP3A4), caffeine (CYP1A2), chlorzoxazone (CYP2E1), S-(+)-mephenytoin (CYP2C19), S-(-)-warfarin (CYP2C9) and coumarin (CYP2A6). Incubations with each substrate were carried out without a possible inhibitor and in the presence of trospium chloride at varying concentrations (37–3000 μM) at 37° in 0.1 M KH₂PO₄ buffer containing up to 3% DMSO. Metabolite concentrations were determined by high-performance liquid chromatography (HPLC) in all cases except CYP2A6 where direct fluorescence spectroscopy was used. First, trospium chloride IC₅₀ values were determined for each substrate at respective K_M concentrations. Trospium chloride did not show relevant inhibitory effects on the metabolism of most substrates (IC₅₀ values considerably higher than 1 mM). The only clear inhibition was seen for the CYP2D6-dependent high-affinity O-demethylation of dextromethorphan, where IC₅₀ values of 27 μM and 44 μM were observed. Therefore, additional dextromethorphan concentrations (0.4–2000 μM) were tested. Trospium chloride was a competitive inhibitor of the reaction with K_i values of 20 and 51 μM, respectively. Thus, trospium chloride has negligible inhibitory effects on CYP3A4, CYP1A2, CYP2E1, CYP2C19, CYP2C9 and CYP2A6 activity but is a reasonably potent inhibitor of CYP2D6 in vitro. Compared to therapeutic trospium chloride peak plasma concentrations below 50 nM, the 1000-times higher competitive inhibition constant K_i however suggests that inhibition of CYP2D6 by trospium chloride is without any clinical relevance.     

斯皮诺素对人肝微粒体细胞色素P_(450)酶的体外抑制作用

目的:研究斯皮诺素对人肝微粒体细胞色素P_(450)(CYP_(450))酶7种亚型(CYP2B6、CYP2C8、CYP2C9、CYP2D6、CYP1A1、CYP2C19和CYP3A4)的体外抑制作用。方法:以200.00、100.00、50.00、25.00、12.50、6.25、3.13、1.56、0.78、0.39μmol/L的斯皮诺素与人肝微粒体共同孵育,分别以他克宁、安非他酮、盐酸阿莫地喹、双氯芬酸钠、美芬妥英、氢溴酸右美沙芬和咪达唑仑作为上述7种亚型CYP_(450)酶的特异性探针药物。采用超高效液相色谱-四级杆-飞行时间串联质谱法测定7种探针药物的代谢产物生成量,计算斯皮诺素对人肝微粒体中7种亚型CYP_(450)酶的半数抑制浓度(IC50)。结果:斯皮诺素对人肝微粒体7种亚型CYP_(450)酶的IC50分别为1 714、1 158、226.1、2 288、80.59、101.1、1 119μmol/L,均大于50μmol/L。结论:斯皮诺素对人肝微粒体CYP_(450)酶的上述7种亚型均无抑制作用,引发药物代谢性相互作用的可能性较小。     

Developmental Expression of Cytochrome P450 Enzymes in Human Liver

Abstract: Drug–metabolizing cytochrome P450 enzymes, the major phase I enzymes, are active in human liver already at very early stages of intrauterine development, although presumably at fairly low concentrations and in low numbers. During maturation, these enzymes go through various developmental programmes towards adulthood. The major increase both in abundance as well as in number of different enzymes takes place after birth, probably during the first year of life. Detailed information concerning these developmental changes is still limited. The major drug–metabolizing P450 enzymes appear to be primarily members of the CYP3A subfamily in all stages of development. The balance between different members of this subfamily, however, undergoes significant switches from the foetal predominant CYP3A7 to the major adult form CYP3A4. The ontogeny of the other cytochrome P450 enzymes is less well characterized, but the major switchon appears to occur mainly after birth. Developmental expression of P450 enzymes is one of the key factors determining the pharmacokinetic status of developing individuals both pre– and postnatally.     

Inhibitory Effects of Silibinin on Cytochrome P‐450 Enzymes in Human Liver Microsomes

Silibinin, the main constituent of silymarin, a flavonoid drug from silybum marianum used in liver disease, was tested for inhibition of human cytochrome P‐450 enzymes. Metabolic activities were determined in liver microsomes from two donors using selective substrates. With each substrate, incubations were carried out with and without silibinin (concentrations 3.7–300 μM) at 37° in 0.1 M KH₂PO₄ buffer containing up to 3% DMSO. Metabolite concentrations were determined by HPLC or direct spectroscopy. First, silibinin IC₅₀ values were determined for each substrate at respective K_M concentrations. Silibinin had little effect (IC₅₀>200 μM) on the metabolism of erythromycin (CYP3A4), chlorzoxazone (CYP2E1), S(+)‐mephenytoin (CYP2C19), caffeine (CYP1A2) or coumarin (CYP2A6). A moderate effect was observed for high affinity dextromethorphan metabolism (CYP2D6) in one of the microsomes samples tested only (IC₅₀=173 μM). Clear inhibition was found for denitronifedipine oxidation (CYP3A4; IC₅₀=29 μM and 46 μM) and S(?)‐warfarin 7‐hydroxylation (CYP2C9; IC₅₀=43 μM and 45 μM). When additional substrate concentrations were tested to assess enzyme kinetics, silibinin was a potent competitive inhibitor of dextromethorphan metabolism at the low affinity site, which is not CYP2D6 (K_i,c=2.3 μM and 2.4 μM). Inhibition was competitive for S(?)‐warfarin 7‐hydroxylation (K_i,c=18 μM and 19 μM) and mainly non‐competitive for denitronifedipine oxidation (K_i,n=9 μM and 12 μM). With therapeutic silibinin peak plasma concentrations of 0.6 μM and biliary concentrations up to 200 μM, metabolic interactions with xenobiotics metabolised by CYP3A4 or CYP2C9 cannot be excluded.     

丹红注射液对大鼠肝微粒体5种CYP亚型酶活性的影响

摘要目的研究丹红注射液对5种细胞色素P450亚型酶活性的影响,为临床合理用药提供参考。方法采用大鼠体外肝微粒体孵育法,分别以非那西丁、甲苯磺丁脲、右美沙芬、氯唑沙宗、睾酮为CYP1A2、CYP2C9、CYP2D6、CYP2E1、CYP3A4的探针药物,在大鼠肝微粒体孵育体系中孵育,用高效液相色谱（HPLC）法测定相应的代谢产物,比较空白对照组和丹红注射液低、中、高剂量组之间探针药物代谢率的差异,评价丹红注射液对各亚型酶活性的影响。结果在体外肝微粒体孵育体系中,丹红注射液低剂量组中CYP1A2 和CYP2C9活性与空白对照组相比,差异无统计学意义（P＞0.05）;中和高剂量组中CYP1A2和CYP2C9活性与空白对照组相比降低,差异有统计学意义（P＜0.05或P＜0.01）;丹红注射液低、中、高剂量组中CYP2D6、CYP2E1、CYP3A4的活性与空白对照组相比,差异无统计学意义（P＞0.05）。丹红注射液对大鼠肝微粒体CYP1A2酶活性的半数抑制浓度（IC50）和抑制常数（Ki）分别为0.54%和0.226%。结论丹红注射液对大鼠肝微粒体CYP1A2酶活性有抑制作用,且为混合型抑制;对CYP2C9有弱抑制作用;对CYP2D6、CYP2E1、CYP3A4酶活性无明显影响。     

Stereo‐Selective Metabolism of Methadone by Human Liver Microsomes and cDNA‐Expressed Cytochrome P450s: A Reconciliation

Abstract: In vitro metabolism of methadone was investigated in cytochrome P450 (CYP) supersomes and phenotyped human liver microsomes (HLMs) to reconcile past findings on CYP involvement in stereo‐selective metabolism of methadone. Racaemic methadone was used for incubations; (R)‐ and (S)‐methadone turnover and (R)‐ and (S)‐EDDP formation were determined using chiral liquid chromatography–tandem mass spectrometry. CYP supersome activity for methadone use and EDDP formation ranked CYP2B6 > 3A4 > 2C19 > 2D6 > 2C18, 3A7 > 2C8, 2C9, 3A5. After abundance scaling, CYP3A4, 2B6 and 2C19 accounted for 63–74, 12–32 and 1. 4–14% of respective activity. CYP2B6, 2D6 and 2C18 demonstrated a preference for (S)‐EDDP formation; CYP2C19, 3A7 and 2C8 for (R)‐EDDP; 3A4 none. Correlation analysis with 15 HLMs supported the involvement of CYP2B6 and 3A. The significant correlation of S/R ratio with CYP2B6 activity confirmed its stereo‐selectivity. CYP2C19 and 2D6 inhibitors and monoclonal antibody (mAb) did not inhibit EDDP formation in HLM. Chemical and mAb inhibition of CYP3A in high 3A activity HLM reduced EDDP formation by 60–85%; inhibition of CYP2B6 in 2B6 high‐activity HLM reduced (S)‐EDDP formation by 80% and (R)‐EDDP formation by 55%. Inhibition changed methadone metabolism in a stereo‐selective manner. When CYP3A was inhibited, 2B6 mediated (S)‐EDDP formation predominated; S/R stereo‐selectivity increased. When 2B6 was inhibited (S)‐EDDP formation fell and stereo‐selectivity decreased. The results confirmed the primary roles of CYPs 3A4 and 2B6 in methadone metabolism; CYP2C8 and 2C9 did not appear involved; 2C19 and 2D6 have minimal roles. CYP2B6 is the primary determinant of stereo‐selective metabolism; stereo‐selective inhibition might play a role in varied plasma concentrations of the two enantiomers.     

Genetic Polymorphisms in Cytochrome P450 Enzymes

Adverse drug reactions are common; they are responsible for a number of debilitating side effects and are a significant cause of death following drug therapy. It is now clear that a significant proportion of these adverse drug reactions, as well as therapeutic failures, are caused by genetic polymorphism, genetically based interindividual differences in drug absorption, disposition, metabolism, or excretion. HMG-CoA reductase inhibitors are generally very well tolerated and easy to administer with good patient acceptance. There are only two uncommon but potentially serious adverse effects related to HMG-CoA reductase inhibitor therapy: hepatotoxicity and myopathy. The occurrence of lethal rhabdomyolysis in patients treated with cerivastatin has prompted concern on the part of physicians and patients regarding the tolerability of HMG-CoA reductase inhibitors. Apart from pravastatin and rosuvastatin, HMG-CoA reductase inhibitors are metabolized by the phase I cytochrome P450 (CYP) superfamily of drug metabolizing enzymes. The best-characterized pharmacogenetic polymorphisms are those within this enzyme family. One of these enzymes, CYP2D6, plays an important role in the metabolism of simvastatin. It has been shown that the cholesterol-lowering effect as well as the efficacy and tolerability of simvastatin is influenced by CYP2D6 genetic polymorphism. Because the different HMG-CoA reductase inhibitors differ, with respect to the degree of metabolism by the different CYP enzymes, genotyping may help to select the appropriate HMG-CoA reductase inhibitor and the optimal dosage during the start of the treatment and will allow for more efficient individual therapy. A detailed knowledge of the genetic basis of individual drug response is potentially of major clinical and economic importance.     

葛根素对人肝微粒体中细胞色素P450酶活性的影响

目的:研究葛根素对人肝微粒体中细胞色素P450 1A2(CYP1A2)、CYP3A4、CYP2C9、CYP2C19、CYP2D6、CYP2E1酶活性的影响.方法:分别以咖啡因、咪达唑仑、甲苯磺丁脲、氯唑沙宗、美托洛尔、美芬妥因为探针药,利用HPLC方法测定探针药与相应代谢产物的浓度,研究葛根素在人肝微粒体孵化体系中对CYP1A2、CYP3A4、CYP2C9、CYP2E1、CYP2D6、CYP2C19酶活性的影响.结果:在人肝微粒体反应体系中,0.1,0.2,0.4,0.8mmol·L-1葛根素使咖啡因的代谢产物的生成分别降低了(31±15)%(P＜0.01),(43±8)%(P＜0.05),(48±6)%(P＜0.05),(49±4)%(P＜0.05),0.05,0.1,0.2,0.4,0.8mmol·L-1葛根素使美托洛尔的代谢产物生成分别降低了(25±7)%(P＜0.01),(33±4)%(P＜0.05),(40±9)%(P＜0.01),(46±5)%(P<0.01),(72±9)%(P＜0.01);而对甲苯磺丁脲、美芬妥因、咪达唑仑和氯唑沙宗的代谢产物没有明显影响.结论:在人肝微粒体反应体系中,葛根素(0.1 mmol·L-1)对CYP1A2和CYP2D6酶活性有较明显的抑制作用;且随着葛根素浓度的增高,对这两种酶活性的抑制作用也随之增强,而对CYP2C9、CYP2C19、CYP3A4和CYP2E1酶活性没有影响.     

Enantioselective N-Demethylation and Hydroxylation of Sibutramine in Human Liver Microsomes and Recombinant Cytochrome P-450 Isoforms

The enantioselective metabolism of sibutramine was examined using human liver microsomes (HLM) and recombinant cytochrome P-450 (CYP) isoforms. This drug is metabolized to N-mono-desmethyl- (M1) and N,N-di-desmethylsibutramine (M2), and subsequent hydroxylation results in hydroxyl M1 (HM1) and hydroxyl M2 (HM2). No significant difference was noted in formation of M1from sibutramine between R- and S-sibutramine in HLM. However, S-enantiomers of M1 and M2 were preferentially metabolized to M2, HM1, and HM2compared to R-enantiomers in HLM, and intrinsic clearance (Cl_int) ratios of S-enantiomers/R-enantiomers were 1.97, 4.83, and 9.94 for M2, HM1, and HM2, respectively. CYP3A4 and CYP3A5 were only involved in the formation of M1, whereas CYP2B6 and CYP2C19 were responsible for all metabolic reactions of sibutramine. CYP2C19 and CYP3A5 displayed catalytic preference for S-sibutramine to S-M1, whereas CYP2B6 and CYP3A4 showed little or no stereoselectivity in metabolism of sibutramine to M1. In the case of M2 formation, CYP2B6 metabolized S-M1 more rapidly than R-M1 with a Cl_int ratio of 2.14. However, CYP2C19 catalyzed less S-M1 than R-M1 and the Cl_int ratio of S-M1 to R-M1 was 0.65. The most significant enantioselectivity was observed in formation of HM1 from M1, and HM2 from M2. CYP2B6 and CYP2C19 exhibited preferential catalysis of formation of hydroxyl metabolites from S-enantiomers rather than R-enantiomers. These results indicate that S-sibutramine was more rapidly metabolized by CYP isoforms than R-sibutramine, and that enantioselective metabolism needs to be considered in drug interactions involving sibutramine and co-administered drugs.     

Simultaneous Absolute Quantification of 11 Cytochrome P450 Isoforms in Human Liver Microsomes by Liquid Chromatography Tandem Mass Spectrometry with In Silico Target Peptide Selection

Cytochrome P450 (CYP) proteins are involved in the biological oxidation and reduction of xenobiotics, affecting the pharmacological efficiency of drugs. This study aimed to establish a method to simultaneously quantify 11 CYP isoforms by multiplexed-multiple reaction monitoring analysis with liquid chromatography tandem mass spectrometry and in silico peptide selection to clarify CYP isoform expression profiles in human liver tissue. CYP1A2, 2A6, and 2D6 target peptides were identified by shot-gun proteomic analysis, and those of other isoforms were selected by in silico peptide selection criteria. The established quantification method detected target peptides at 10 fmol, and the dynamic range of calibration curves was at least 500-fold. The quantification value of CYP1A2 in Supersomes was not significantly different between the established method and quantitative immunoblot analysis. The absolute protein expression levels of 11 CYP isoforms were determined from one pooled and 10 individual human liver microsomes. In the individual microsomes, CYP2C9 showed the highest protein expression level, and CYP1A2, 2A6, 2C19, and 3A4 protein expression exhibited more than a 20-fold difference among individuals. This highly sensitive and selective quantification method is a useful tool for the analysis of highly homologous CYP isoforms and the contribution made by each CYP isoform to drug metabolism.     

Stereoselective Metabolism of Bupropion by Cytochrome P4502B6 (CYP2B6) and Human Liver Microsomes

Purpose Hydroxylation of the antidepressant and smoking deterrent drug bupropion is a clinically important bioactivation and elimination pathway. Bupropion hydroxylation is catalyzed selectively by cytochrome P4502B6 (CYP2B6). CYP2B6-catalyzed bupropion hydroxylation has been used as an in vitro and in vivo phenotypic probe for CYP2B6 activity and CYP2B6 drug interactions. Bupropion is chiral, used clinically as a racemate, and disposition is stereoselective. Nevertheless, it is unknown whether CYP2B6-catalyzed bupropion hydroxylation is stereoselective. Methods Hydroxylation of racemic bupropion by recombinant CYP2B6 and human liver microsomes was evaluated using a stereoselective assay. Results At therapeutic concentrations, hydroxylation of (S)-bupropion was threefold and 1.5-greater than (R)-bupropion, respectively, by recombinant CYP2B6 and human liver microsomes. In vitro intrinsic clearances were likewise different for bupropion enantiomers. Conclusions Stereoselective bupropion hydroxylation may have implications for the therapeutic efficacy of bupropion as an antidepressant or smoking cessation therapy, and for the use of bupropion as an in vivo phenotypic probe for CYP2B6 activity.     

<Emphasis Type="Italic">In Vitro</Emphasis> Metabolism of a New Neuroprotective Agent,KR-31543 in the Human Liver Microsomes: Identification of Human Cytochrome P450

KR-31543, (2S,3R,4S)-6-amino-4-[N-(4-chlorophenyl)-N-(2-methyl-2H-tetrazol-5-ylmethyl)amino]-3,4-dihydro-2-dimethoxymethyl-3-hydroxy-2-methyl-2H-1-benzopyran, is a new neuroprotective agent for preventing ischemia-reperfusion damage. This study was performed to identify the metabolic pathway of KR-31543 in human liver microsomes and to characterize cytochrome P450 (CYP) enzymes that are involved in the metabolism of KR-31543. Human liver microsomal incubation of KR-31543 in the presence of NADPH resulted in the formation of two metabolites, M1 and M2. M1 was identified as N-(4-chlorophenyl)-N-(2-methyl-2H-tetrazol-5-ylmethyl)amine on the basis of LC/MS/MS analysis with a synthesized authentic standard, and M2 was suggested to be hydroxy-KR-31543. Correlation analysis between the known CYP enzyme activities and the rates of the formation of M1 and M2 in the 12 human liver microsomes have showed significant correlations with testosterone 6beta-hydroxylase activity (a marker of CYP3A4). Ketoconazole, a selective inhibitor of CYP3A4, and anti-CYP3A4 monoclonal antibodies potently inhibited both N-hydrolysis and hydroxylation of KR-31543 in human liver microsomes. These results provide evidence that CYP3A4 is the major isozyme responsible for the metabolism of KR-31543 to M1 and M2.     

Human Cytochrome P450 Family 4 Enzymes: Function,Genetic Variation and Regulation

The microsomal cytochrome P450 (CYP) family 4 monooxygenases are the major fatty acid ω-hydroxylases. These enzymes remove excess free fatty acids to prevent lipotoxicity, catabolize leukotrienes and prostanoids, and also produce bioactive metabolites from arachidonic acid ω-hydroxylation. In addition to endogenous substrates, recent evidence indicates that CYP4 monooxygenases can also metabolize xenobiotics, including therapeutic drugs. This review focuses on human CYP4 enzymes and updates current knowledge concerning catalytic activity profiles, genetic variation and regulation of expression. Comparative differences between the human and rodent CYP4 enzymes regarding catalytic function and conditional expression are also discussed.     

细胞色素P450酶的表观遗传学调控及研究进展

细胞色素P450（CYPs）家族是体内重要的药物代谢酶,其功能主要是代谢临床药物及外源性物质。长期以来,CYP450酶的个体间功能活性差异往往被认为是由基因多态性所导致。然而随着研究的日益深入,人们发现基因序列的改变并不能完全解释CYP450酶的个体间活性差异。表观遗传学作为研究DNA序列未发生变化而基因表达发生可遗传变异的学科,可作为重要研究手段进一步解释CYP450酶的个体差异。该学科主要研究内容包括DNA甲基化、组蛋白翻译后修饰和RNA编辑等。本文就各主要CYP450酶的表观遗传学调控研究进行综述并讨论其在药物代谢和临床应用中的意义。     

细胞色素P450酶系体外药物代谢研究方法进展

目的 综述细胞色素P450 (CYP 450)酶影响药物代谢的体外研究方法.方法 参考国内外文献,对与药物代谢相关的CYP酶亚型、CYP酶种属差异、CYP酶体外反应体系、药物主要代谢酶的确认方法及体外CYP酶的抑制和诱导,进行分类、归纳和整理.结果与结论 CYP 450在药物代谢中具有重要作用,药物代谢研究是新药评价体系中重要的一部分.     

人类细胞色素P450与免疫：对药物代谢、疾病的影响

人类细胞色素P450有三十多种,肝脏中富含CYP1,2,3家族的成员,主要参与外源性物质的代谢。CYP17、CYP21等及分布于血管内皮的CYP2J2则参与内源性物质的合成和代谢。除物质代谢外,近年来研究发现人类细胞色素P450还与免疫有关;细胞因子可抑制或诱导CYP的表达和CYP的代谢活性,已在淋巴细胞上发现有CYP表达,CYP可影响细胞黏附分子的作用。参与自身免疫性疾病的免疫损伤等,本文就人类细胞色素P450与细胞因子、黏附分子及自身免疫反应的关系。对药物代谢,疾病的影响及免疫抑制剂的开发进展作一介绍。