白屈菜碱在大鼠肝微粒体中代谢的酶动力学及CYP450酶特异性抑制剂对其代谢的影响

目的研究白屈菜碱在大鼠肝微粒体中代谢的酶动力学及CYP450酶特异性抑制剂对其代谢的影响。方法将系列浓度的白屈菜碱与大鼠肝微粒体进行体外共孵育,采用HPLC法测定孵育液中剩余白屈菜碱的浓度,利用Graph Pad Prism 6.0软件进行数据拟合并计算酶动力学参数;分别将5种CYP450酶的特异性抑制剂与白屈菜碱进行共孵育,考察抑制剂对白屈菜碱代谢的影响,探讨参与其代谢的酶亚型。结果在大鼠肝微粒体中,白屈菜碱的Vmax为(3.52±0.18)mmol·min-1·kg-1;Km为(12.02±2.92)μmol·L-1;CLint为292.4 L·min-1·kg-1;CYP450酶特异性抑制剂酮康唑、α-萘黄酮、氟康唑和奎尼丁可以显著地抑制白屈菜碱的代谢,而噻氯匹定对白屈菜碱的代谢没有明显影响。结论白屈菜碱在大鼠肝微粒体中广泛代谢,CYP3A4、CYP1A2、CYP2D6、CYP2C9是参与其代谢的主要代谢酶。     

水黄皮素在大鼠肝微粒体中的代谢研究

目的 研究水黄皮素在大鼠肝微粒体中的代谢稳定性,确定水黄皮素的代谢酶表型.方法 将水黄皮素与大鼠肝微粒体于37℃孵育,应用UPLC-MS/MS法检测孵育液中水黄皮素的含量,考察水黄皮素的代谢稳定性.将水黄皮素与各细胞色素P450(CYP)酶中的各同工酶CYP2E1、2C19、1A2、2D6、2C9和3A4的特异性抑制剂共孵育,确定其代谢酶表型.结果 在大鼠肝微粒体中,水黄皮素的t1/2=1.97 h、Cl =0.70 mL·h-1 ·mg-1,CYP1 A2是其主要代谢酶.结论 水黄皮素在大鼠肝微粒体中是由多个CYP同工酶介导代谢的,其中,CYP1 A2酶的介导作用最强.     

Cocktail 探针药物法评价辣椒素对大鼠CYP450亚型的影响

目的：采用cocktail 探针药物法研究辣椒素在体外对大鼠肝微粒体CYP 450四种亚型的影响。方法：分为试验组和对照组,试验组采用大鼠肝微粒体孵育体系、探针药物和系列浓度的辣椒素（对照组仅加入缓冲液）共同孵育20 min,反应终止后用HPLC方法检测代谢产物的生成量以代表酶的活性。采用Graphpad prism 5.0计算辣椒素对各亚型的IC50值。将辣椒素与大鼠肝微粒体分别预孵育0,5,10,15,20,30 min,计算不同预孵育时间下各亚型的相对活性百分比。结果：辣椒素对大鼠肝微粒体CYP1A2、CYP2C11、CYP2E1和CYP3A2的IC50值分别为36.21,17.19,51.64,18.86μmol·L-1。预孵育没有增强辣椒素对CYP450的抑制作用。结论：辣椒素在体外对大鼠肝微粒CYP1A2、CYP2C11、CYP2E1和CYP3A2具有抑制作用,且未呈现出预孵育时间依赖性。     

诃子酸在不同种属肝微粒体中的代谢稳定性和代谢酶表型研究

目的 建立测定肝微粒体孵育体系中诃子酸浓度的方法,并比较其在人、犬、猴、小鼠、大鼠肝微粒体中的Ⅰ相、Ⅱ相代谢稳定性及种属差异,确定其在人肝微粒中的代谢表型。方法 将诃子酸与不同种属肝微粒体共同孵育,应用UPLCMS/MS检测孵育液中诃子酸的含量,考察其代谢稳定性及体外动力学参数。采用化学抑制剂法确定其在人肝微粒中的代谢表型。将诃子酸与各CYP450同工酶CYP1A2、CYP2A6、CYP2C9、CYP2C19、CYP2D6、CYP2E1和CYP3A4的特异性抑制剂（α-萘黄酮、香豆素、磺胺苯吡唑、噻氯匹定、奎尼丁、二乙基二硫代氨基甲酸钠、酮康唑）共同孵育,确定其代谢酶表型。结果 诃子酸在Ⅰ相、Ⅱ相孵育体系中均可代谢,在Ⅰ相代谢中,犬肝微粒体孵育与人最为相似,半衰期（t_1/2）分别为115.50 min和121.58 min;Ⅱ相代谢中5个种属代谢稳定性均中等,其中猴与人肝微粒体代谢趋势最为相近。诃子酸在人肝微粒中的代谢是由多种CYP酶共同介导的,其中CYP2C9、CYP2E1和CYP3A4是主要的同工酶。结论 建立的UPLCMS/MS方法简便、快速、专属性强、灵敏性高,可用于肝微粒体孵育体系中诃子酸浓度的测定及体外代谢的研究。诃子酸在人、犬、猴、小鼠、大鼠肝微粒体中代谢存在一定种属差异,且其代谢过程与多种CYP酶相关。     

去氢厄弗酚在小鼠肝微粒体中代谢产物及CYP450酶亚型的鉴定

目的建立去氢厄弗酚(DHE)小鼠体外肝微粒体孵育方法,鉴定DHE在小鼠肝微粒体中的代谢产物及参与DHE代谢的CYP450酶亚型。方法采用UPLC-Q-TOF-MS/MS分析鉴定DHE在体外肝微粒体共温孵后的代谢产物,筛选7种CYP450酶亚型,并通过特异性化学抑制剂法,鉴别参与DHE代谢的主要CYP450酶亚型。结果在体外肝微粒体共温孵后,检测到4个代谢产物;所筛选的7种CYP450酶亚型中,CYP1A2、CYP2C8和CYP2D2对DHE体外肝微粒体代谢的参与度较高。结论在肝脏中,有多种代谢酶亚型参与DHE的代谢,表明DHE在临床上不易与其他药物产生相互作用。     

补骨脂酚在大鼠和人肝微粒体中细胞色素P450酶和尿苷二磷酸葡萄糖醛酸转移酶代谢稳定性及性别差异

目的探究补骨脂酚在大鼠和人肝微粒体中细胞色素P450酶(CYP酶)和尿苷二磷酸葡萄糖醛酸转移酶(UGT酶)的代谢稳定性及性别差异。方法补骨脂酚分别与雄、雌性SD大鼠和男、女性人肝微粒体在37℃与不同辅酶因子孵育,应用高效液相色谱(HPLC)法测定补骨脂酚的剩余浓度,采用底物消除法观察补骨脂酚的代谢稳定性。结果补骨脂酚在雄、雌性SD大鼠肝微粒体中,CYP酶介导的Ⅰ相代谢固有清除率(Clint)分别是326.6±15.4和(77.2±4.8)mL·min~(-1)·kg~(-1),雄性代谢显著快于雌性(P<0.01);UGT酶介导的Ⅱ相代谢Clint分别是164.5±8.4和(419.1±24.1)mL·min~(-1)·kg~(-1),雌性代谢显著快于雄性(P<0.01);CYP酶和UGT酶共同代谢的Clint分别是1063.1±27.2和(781.2±16.5)mL·min~(-1)·kg~(-1),雄性代谢显著快于雌性(P<0.01)。在男、女性人肝微粒体中,CYP酶介导的Ⅰ相代谢Clint分别是24.8±2.1和(17.6±1.0)mL·min~(-1)·kg~(-1),男性代谢显著快于女性(P<0.01);UGT酶介导的Ⅱ相代谢Clint分别是176.4±26.5和(165.9±8.6)mL·min~(-1)·kg~(-1),代谢无显著性别差异;CYP酶和UGT酶共同代谢的Clint分别是262.5±20.9和(236.2±10.5)mL·min~(-1)·kg~(-1),代谢无显著性别差异。结论补骨脂酚在SD大鼠和人肝微粒体中,均发生CYP酶介导的Ⅰ相代谢和UGT酶介导的Ⅱ相代谢反应,且代谢稳定性具有一定的种属和性别差异。     

雷公藤甲素在大鼠肝微粒体中代谢及酶促反应动力学研究

目的:研究雷公藤甲素在大鼠肝微粒体中代谢及酶促反应动力学。方法:将雷公藤甲素与5种不同诱导剂(地塞米松(DEX)、苯巴比妥(PB)、β-萘黄酮(β-NF)、吡啶(PD))诱导的大鼠肝微粒体进行体外共孵育;并与8种选择性CYP酶抑制剂(酮康唑、醋竹桃霉素、磺胺苯吡唑、二乙基二硫代氨基甲酸酯(盐)、奎尼丁、呋拉茶碱、毛果芸香碱、奥芬那君)在空白肝微粒体中共孵育。采用液相色谱-质谱联用技术测定孵育后剩余雷公藤甲素的含量。结果:酮康唑和醋竹桃霉素能明显抑制雷公藤甲素的代谢;磺胺苯吡唑和奥芬那君对其代谢也有一定抑制作用,但不及酮康唑和醋竹桃霉素。结论:雷公藤甲素在大鼠肝微粒体中代谢主要由CYP3A介导,其次由CYP2C和CYP2B介导。     

氟他胺在大鼠肝微粒体经细胞色素P450 1A2代谢的性别差异

目的体外研究大鼠肝微粒体细胞色素P450 1A2(CYP1A2)对氟他胺(flutamide Flu)代谢的性别差异影响。方法制备正常♀♂大鼠肝微粒体,用CYP1A2抗体与氟他胺(2 mg·L^-1)共同温孵,测定氟他胺主要代谢产物2-羟基氟他胺(2-hydroxyflutamide, HF)和原药的浓度比(HF/Flu),评价氟他胺在大鼠肝微粒体代谢的性别差异。结果在CYP1A2抗体浓度为1∶400,孵育时间为30 min条件下,氟他胺在♂大鼠肝微粒体中的HF/Flu为(1.5±0.6),而♀动物为(0.9±0.4)。不同性别大鼠肝微粒体对氟他胺的代谢存在性别差异(P<0.01)。结论Flu在♂大鼠肝微粒体中代谢快,而在♀大鼠肝微粒体中代谢较慢。♂大鼠体内的CYP1A2酶活性高于♀大鼠。     

新型抗慢性肾功能不全药硝克柳胺在大鼠肝微粒体和胞浆的代谢

目的：研究硝克柳胺在大鼠肝微粒体和胞浆中的代谢动力学及参与硝克柳胺体外代谢的药物代谢酶鉴定。方法：硝克柳胺分别与大鼠肝微粒体和胞浆温孵一定时间后，应用HPLC方法测定硝克柳胺含量，计算体外代谢速率和动力学参数（Kin，Vmax）。在微粒体或胞浆中加入选择性CYP抑制剂、硝基还原酶抑制剂，鉴定参与硝克柳胺代谢的药酶类型。结果：硝克柳胺在肝微粒体代谢是依赖NADPH／NADH的酶促反应，缺氧代谢高于有氧代谢，微粒体代谢明显快于胞浆。CYP2C6特异性抑制剂西米替丁、NADPH-细胞色素C还原酶特异性抑制剂2‘-单磷酸腺苷（2’-AMP）和细胞色素b5还原酶特异性抑制剂6-丙基-2-硫脲嘧啶（PTU）可明显抑制肝微粒体中硝克柳胺的代谢，其它CYP特异性抑制剂对硝克柳胺的代谢无明显影响。NAD（P）H脱氢酶特异性抑制剂双香豆素和黄嘌呤氧化酶特异性抑制剂别嘌呤醇也可显著抑制肝胞浆中硝克柳胺的代谢。结论：硝克柳胺的体外代谢是依赖多个药物代谢酶参与的酶促反应，包括微粒体NADPH-细胞色素C还原酶、细胞色素b5还原酶和CYP2C6以及胞浆NAD（P）H脱氢酶和黄嘌呤氧化酶。     

羟基喜树碱的代谢与CYP450的相关性研究

目的：研究羟基喜树碱（HCPT）在体外小鼠肝微粒体中对 CYP450活性的影响,为临床合理联合用药提供参考。方法：在小鼠体外肝微粒体中分别加入六种亚型酶的探针药物对乙酰氨基酚、非那西丁、双氯芬酸钠、睾酮、酒石酸美托洛尔、奥美拉唑和羟基喜树碱溶液,在优化的孵育体系下温孵。用 HPLC 法测定各空白对照组和羟基喜树碱溶液中各探针药物代谢产物的浓度并比较代谢率的差异,以评价羟基喜树碱对各亚型酶活性的影响。结果：在代谢反应过程中,在50~200μmol·L-1内,羟基喜树碱的浓度与孵育体系中 CYP3A4的特异性底物睾酮、CYP2E1的特异性底物对乙酰氨基酚的剩余药量呈正比例关系,且具显著性差异（P＜0.05）,与其他四种探针药物的剩余药量无明显的浓度依存关系（P＞0.05）。结论：HCPT 在肝微粒体的代谢反应过程中受代谢酶 CYP3A4和 CYP2E1的作用,竞争性地抑制了睾酮和对乙酰氨基酚在肝微粒体中的代谢。     

Tizanidine is mainly metabolized by cytochrome p450 1A2 in vitro

AIMS: To identify the cytochrome p450 (CYP) enzyme(s) that catalyze the metabolism of tizanidine in vitro. METHODS: The effect of CYP isoform inhibitors on the elimination of tizanidine was studied using pooled human liver microsomes. The metabolism of the drug by a range of human recombinant CYP isoforms was then investigated. RESULTS: Incubation of tizanidine (80 nm) with human liver microsomes resulted in time- and NADPH-dependent substrate consumption with a half-life of 50 min, initial reaction velocity of 1.1 pmol x min-1 x mg-1 protein and intrinsic clearance of 17 ml x min-1 x kg-1. The predicted in vivo hepatic clearance (CLh) of tizanidine using the well-stirred and parallel-tube model was close (68% and 82%, respectively) to its estimated in vivo CLh. Fluvoxamine and furafylline strongly inhibited tizanidine metabolism. Inhibitors specific to isoforms other than CYP1A2 had no substantial effect. Recombinant CYP1A2 metabolized tizanidine to a substantial degree (35% in 45 min), but other recombinant CYPs had little metabolic capacity for the drug. CONCLUSIONS: CYP1A2 is primarily responsible for the metabolism of tizanidine. CYP1A2 inhibitors may inhibit its metabolism also in vivo.     

阿帕替尼对大鼠肝微粒体细胞色素P_(450)3A1酶活性的影响研究

目的:研究阿帕替尼对大鼠肝微粒体细胞色素P450(CYP)3A1酶活性的影响。方法:取SD大鼠随机分为空白对照组、地塞米松组(100mg·kg-1)和阿帕替尼高、中、低剂量组(100、50、25mg·kg-1),每组5只,灌胃给予相应药物,每日1次,除地塞米松组连续给药3d外,其余各组连续给药14d,采用高效液相色谱-紫外检测法,以睾酮为探针,测定睾酮经大鼠肝微粒体温孵后转化的代谢产物6β-羟基睾酮(6β-OHT)的生成速率,以评价各组CYP3A1酶活性。结果:空白对照组、地塞米松组和阿帕替尼高、中、低剂量组6β-OHT的生成速率分别为(3.41±0.39)、(23.36±1.76)、(4.25±0.48)、(3.82±0.40)、(3.48±0.74)nmo·lmg-1·min-1,与地塞米松组比较,阿帕替尼各剂量组6β-OHT的生成速率均明显降低(P<0.01)。结论:阿帕替尼对大鼠肝细胞CYP3A1酶活性无诱导作用。     

非那西丁探针法动态观测非酒精性脂肪肝大鼠发病进程中的CYP1A2活性

目的:建立探针法动态观测非酒精性脂肪肝大鼠发病进程中细胞色素(CY)P450酶系的活性。方法:制备非酒精性脂肪肝大鼠模型,分别于造模后第0、7、9、11、13、15、17周给予探针药物非那西丁并收集尿液,检测其中非那西丁代谢产物对乙酰氨基酚的各代谢指标以考察CYP1A2的活性变化情况,同时设立正常大鼠组为对照。含量检测采用高效液相色谱法,色谱柱为HypersilODS,流动相为甲醇-水(12.5∶87.5),流速为1.0 mL.min-1,检测波长为254 nm。结果:对乙酰氨基酚的单位体重代谢量在第9周时达到最高,明显高于第0周和正常组((15.02±3.12)、(10.03±3.60)、(9.96±4.00)mg.kg-1),随后又逐渐降低,即CYP1A2的活性先升高后降低。结论:建立的探针法简便可靠,适用于大鼠尿中对乙酰氨基酚的测定以及CYP1A2活性的研究。     

Involvement of CYP2B6 in the biotransformation of propofol by human liver microsomes

Objective To determine whether the cytochrome P4502B6(CYP2B6)is involved in the oxidation of propofol by human liver microsomes.Methods The change of propofol concentration in an incubation mixture with human liver microsomes was monitored by the high performance liquid chromatography(HPLC),in order to calculate the rate constants of metabolism of propofol.The correlation between the rate constants and the rate of metabolism of CYP2B6 selective substrate bupropion,and the effect of two different CYP2B6 specific inhibitors on the propofol metabolism were examined.Results The mean rate constant of propofol metabolism by liver microsomes obtained from twelve individuals was 3.9(95% confidence intervals 3.3,4.5)nmol·min-1·mg-1 protein.The rate constants of propofol metabolism by liver microsomes were significantly correlated with bupropion hydroxylation(r=0.888,P<0.001).Both selective chemical inhibitors of CYP2B6,orphenadrine and N,N',N″-triethylenethiophosphoramide(thioTEPA),reduced the rate constants of propofol metabolism by 37.5%(P<0.001)and 42.7%(P<0.001)in liver microsomes,respectively.Conclusions CYP2B6 is predominantly involved in the oxidation of propofol by human liver microsomes.     

Roles of human CYP2A6 and rat CYP2B1 in the oxidation of (+)-fenchol by liver microsomes

The metabolism of (+)-fenchol was investigated in vitro using liver microsomes of rats and humans and recombinant cytochrome P450 (P450 or CYP) enzymes in insect cells in which human/rat P450 and NADPH-P450 reductase cDNAs had been introduced. The biotransformation of (+)-fenchol was investigated by gas chromatography-mass spectrometry (GC-MS). (+)-Fenchol was oxidized to fenchone by human liver microsomal P450 enzymes. The formation of metabolites was determined by the relative abundance of mass fragments and retention times on GC. Several lines of evidence suggested that CYP2A6 is a major enzyme involved in the oxidation of (+)-fenchol by human liver microsomes. (+)-Fenchol oxidation activities by liver microsomes were very significantly inhibited by (+)-menthofuran, a CYP2A6 inhibitor, and anti-CYP2A6. There was a good correlation between CYP2A6 contents and (+)-fenchol oxidation activities in liver microsomes of ten human samples. Kinetic analysis showed that the Vmax/Km values for (+)-fenchol catalysed by liver microsomes of human sample HG03 were 7.25 nM-1 min-1. Human recombinant CYP2A6-catalyzed (+)-fenchol oxidation with a Vmax value of 6.96 nmol min-1 nmol-1 P450 and apparent Km value of 0.09 mM. In contrast, rat CYP2A1 did not catalyse (+)-fenchol oxidation. In the rat (+)-fenchol was oxidized to fenchone, 6-exo-hydroxyfenchol and 10-hydroxyfenchol by liver microsomes of phenobarbital-treated rats. Recombinant rat CYP2B1 catalysed (+)-fenchol oxidation. Kinetic analysis showed that the Km values for the formation of fenchone, 6-exo- hydroxyfenchol and 10-hydroxyfenchol in rats treated with phenobarbital were 0.06, 0.03 and 0.03 mM, and Vmax values were 2.94, 6.1 and 13.8 nmol min-1 nmol-1 P450, respectively. Taken collectively, the results suggest that human CYP2A6 and rat CYP2B1 are the major enzymes involved in the metabolism of (+)-fenchol by liver microsomes and that there are species-related differences in the human and rat CYP2A enzymes.     

多索茶碱对大鼠肝CYP2D6酶的影响

目的:通过体内、体外实验观察多索茶碱对大鼠肝CYP2D6酶的影响。方法:取16只大鼠随机均分为对照Ⅰ组和实验组,分别灌胃给予生理盐水1mL和多索茶碱50mg·kg-1·d-1,连续1周,第8天时均灌胃给予探针药物右美沙芬(6mg·kg-1),收集8h尿液后处死大鼠,测定大鼠尿样及肝微粒体中右美沙芬浓度并计算其代谢率;实验组肝微粒体再分为对照Ⅱ组、多索茶碱组和CYP2D6特异性抑制剂西咪替丁组,分别加入相应药物孵育后测定并计算右美沙芬的代谢率;将体内、体外实验得到的右美沙芬的代谢率进行相关性分析。结果:以右美沙芬的代谢率为指标,体内实验中2组比较无明显差别(P>0.05);体外试验中,与对照Ⅱ组比较,多索茶碱组未见明显降低(P>0.05),西咪替丁组明显降低(P<0.01);体内和体外实验数据具有很好的相关性(r=0.9537)。结论:多索茶碱对大鼠肝CYP2D6酶无诱导或抑制作用。     

五味子醇甲在大鼠肝微粒体内的代谢动力学和性别差异

体外研究五味子醇甲(schizandrin，SZ)在大鼠肝微粒体内的代谢动力学和性别差异。制备正常雌、雄大鼠肝微粒体，与SZ共同温孵，以高效液相色谱法测定SZ及其代谢产物。SZ在雄鼠肝微粒体内代谢反应的最大速率V_max、米氏常数K_m和清除率Cl_int分别为(21.88±2.30) μmol·L^-1·min^-1·mg^-1(protein)，(389.00±46.26) μmol·L^-1和(0.056 3±0.000 7) min·mg^-1(protein)；在雌鼠肝微粒体内代谢反应的最大速率V_max、米氏常数K_m和清除率Clint_{分别为(0.61±0.07) μmol·L^-1·min^-1·mg^-1(protein)，(72.64±13.61) μmol·L^-1和(0.008 4±0.000 8) min·mg^-1(protein)，雌、雄鼠肝微粒体内SZ的主要代谢物不同，分别为7,8-顺二羟基五味子醇甲(M1)和7,8-顺二羟基-2-去甲基五味子醇甲(M2b)。酮康唑、奎尼丁和奥芬得林对SZ的在雌、雄大鼠肝微粒体内代谢均有不同程度的抑制作用，西咪替丁对其在雄鼠肝微粒体内的代谢也有一定的抑制作用。SZ在雌、雄大鼠肝微粒体中代谢动力学及代谢产物存在明显的性别差异，这种差异可能主要是由CYP3A和CYP2C11在大鼠肝微粒体内的性别差异引起的。}     

淫羊藿总黄酮对大鼠肝微粒体CYP1A2、CYP3A4和CYP2E1活性的影响

评估淫羊藿总黄酮对大鼠肝细胞色素P450及其主要亚型活性的潜在影响。淫羊藿总黄酮以300mg／kg／d的剂量对SD大鼠进行连续灌胃处理15天，测定肝微粒体中cYP450含量与CYP1A2、CYP3A4和CYP2E1亚型活性，观察淫羊藿总黄酮的效应。CYP1A2的活性用荧光比色法进行测定，CYP3A4和CYP2E1的活性用紫外可见分光光度法测定。淫羊藿总黄酮处理后的大鼠肝脏CYP450含量及CYP1A2、CYP3A4和CYP2E1亚型活性均明显增高，其中CYP1A2和CYP2E1活性升高显著（P〈0．01）。淫羊藿总黄酮对大鼠肝脏CYP450及主要亚型CYP1A2、CYP3A4和CYP2E1活性均有诱导效应。     

Involvement of human liver cytochrome P4502B6 in the metabolism of propofol

AIMS: To determine the cytochrome P450 (CYP) isoforms involved in the oxidation of propofol by human liver microsomes. METHODS: The rate constant calculated from the disappearance of propofol in an incubation mixture with human liver microsomes and recombinant human CYP isoforms was used as a measure of the rate of metabolism of propofol. The correlation of these rate constants with rates of metabolism of CYP isoform-selective substrates by liver microsomes, the effect of CYP isoform-selective chemical inhibitors and monoclonal antibodies on propofol metabolism by liver microsomes, and its metabolism by recombinant human CYP isoforms were examined. RESULTS: The mean rate constant of propofol metabolism by liver microsomes obtained from six individuals was 4.2 (95% confidence intervals 2.7, 5.7) nmol min(-1) mg(-1) protein. The rate constants of propofol by microsomes were significantly correlated with S-mephenytoin N-demethylation, a marker of CYP2B6 (r = 0.93, P < 0.0001), but not with the metabolic activities of other CYP isoform-selective substrates. Of the chemical inhibitors of CYP isoforms tested, orphenadrine, a CYP2B6 inhibitor, reduced the rate constant of propofol by liver microsomes by 38% (P < 0.05), while other CYP isoform-selective inhibitors had no effects. Of the recombinant CYP isoforms screened, CYP2B6 produced the highest rate constant for propofol metabolism (197 nmol min-1 nmol P450-1). An antibody against CYP2B6 inhibited the disappearance of propofol in liver microsomes by 74%. Antibodies raised against other CYP isoforms had no effect on the metabolism of propofol. CONCLUSIONS: CYP2B6 is predominantly involved in the oxidation of propofol by human liver microsomes.