淫羊藿苷对小鼠肝微粒体细胞色素P450酶及其亚型CYP2E1活性的影响

目的 研究淫羊藿苷对小鼠肝脏微粒体细胞色素P450(CYP)总酶含量及其亚型CYP2E1、CYP3A和CYP1A1活性的影响.方法 给予小鼠ig淫羊藿苷(50、100、200 mg·kg-1·d-1),3d后钙沉淀法制备肝细胞微粒体,UV法测定肝微粒体CYP的含量及其亚型CYP2E1与CYP3A的活性;荧光分光光度法测定肝微粒体CYP1A1的活性.结果 高剂量淫羊藿苷可降低小鼠肝脏微粒体CYP的含量(约54%)、抑制CYP2E1的活性(抑制率为53.1%),对CYP3A和CYP1A1的活性无影响.结论 大剂量淫羊藿苷可降低小鼠肝脏微粒体CYP的总含量,并抑制其亚型CYP2E1的活性.     

淫羊藿苷对不同月龄大鼠肝微粒体细胞色素P450的影响

目的 揭示淫羊藿苷(Ica)对大鼠肝微粒体细胞色素P450的含量及部分亚型的影响,并比较月龄的差异.方法 ig给予6月龄和18月龄的♂SD大鼠Ica( 60 mg· kg -1),4周后取肝脏,用钙沉淀法提取肝微粒体,BCA法测定微粒体蛋白浓度;用一氧化碳还原差示光谱法测定CYP450的含量;用ELISA法测定CYP1 A1、CYPb5的含量;用比色法测定苯胺羟化酶(反映CYP2E1活性)和红霉素-N-脱甲基酶(反映CYP3A活性)的活性;用real - time RT - PCR检测CYP1 A1、CYP2A3、CYP2E1、CYP3A1、CYP3A2和CYP4B1 mRNA的表达.结果 60 mg· kg-1 Ica明显增加了CYP450的总酶和CYP1 A1的含量、CYP3A的活性及CYP1 A1、CYP3A1、CYP3A2 mRNA的表达,降低了CYP2E1的活性及其mRNA的表达;但Ica对上述各指标的诱导或抑制作用在大鼠月龄方面差异不明显;Ica对CYPb5的含量及CYP2A3、CYP4B1 mRNA的表达未见明显影响.结论 Ica对大鼠肝微粒体CYP450总酶、CYPI A1和CYP3A具有诱导作用,对CYP2E1具有抑制作用,该作用未见明显月龄差异.     

酮康唑对大鼠肝脏CYP450酶系的影响*

目的:观察酮康唑对大鼠肝细胞色素P450及其主要亚型的影响。方法:Sprague-Dawley大鼠用140,280,420μmol.kg-1.d-1酮康唑连续灌胃7 d,测定肝脏微粒体中总CYP450含量和CYP1A1,1A2,1B1,2B1/2,2E1和3A亚型活性。结果:不同剂量酮康唑给药后大鼠肝脏脏器系数、CYP1A1和1B1亚型活性明显增高(P<0.05,P<0.01);总CYP450含量和CYP3A活性显著降低(P<0.01);低剂量的酮康唑抑制CYP1A2和CYP2B1/2亚型的活性,高剂量却出现了诱导作用(P<0.05,P<0.01)。各剂量组对CYP2E1均无明显影响。结论:酮康唑对大鼠肝脏CYP450及主要药物代谢亚型CYP1A1,1A2,1B1,2B1/2和3A有影响,临床长期用药或与经肝脏CYP450代谢的药物联合应用时要注意监测血药浓度和肝脏功能,防止药物代谢减缓出现蓄积中毒或药物代谢加快而降低药效。     

Z24对大鼠肝脏CYP450酶系的影响

目的:观察Z24对大鼠肝脏CYP450酶系的影响.方法:雌性Wistar大鼠,灌胃(ig)给予Z24(0,50,100,200 mg·kg-1·d-1),连续5 d,以0.9%氯化钠溶液作对照,末次给药后次日,处死大鼠,测定肝微粒体中CYP450总含量、细胞色素b5(Cyt-b5)含量、NADPH-CYP450还原酶活性以及1A2,181,2E1,3A4亚型活性.结果:与对照组相比,各剂量组CYP450总含量、NADPH-CYP450还原酶活性及CYPlB1、2El亚型活性均明显升高(P＜0.05);100和200 mg·kg-1组Cyt-b5含量升高(P＜0.05);200 mg·kg-1组CYPlA2和3A亚型活性升高(P＜0.05).结论:Z24对CYP450、NADPH-CYP450还原酶及CYPlB1、2El亚型有诱导作用,剂量达100和200 mg·kg-1时分别对cyt-b5和CYPlA2、3A亚型产生诱导作用.     

振源胶囊对细胞色素P_(450)酶CYP1A2、CYP3A4、CYP2E1的影响

目的:研究振源胶囊对细胞色素P450酶CYP1A2、CYP3A4、CYP2E1的影响。方法:用Cocktail探针药物法,将Wistar大鼠随机分组,灌胃给予振源胶囊溶液,以生理盐水组为空白对照,诱导10d,于股动脉插管,注射给予3种探针药物咖啡因、氨苯砜、氯唑沙宗,通过高效液相色谱法检测各探针药物的代谢率来评价各组CYP1A2、CYP3A4、CYP2E1亚型酶的活性;药动学计算采用DAS2.0软件完成。结果:给予振源胶囊的大鼠,咖啡因代谢加快,半衰期缩短;氨苯砜代谢减慢,半衰期延长;氯唑沙宗半衰期与空白对照组比较无显著差异(P>0.05)。结论:振源胶囊对大鼠CYP1A2有诱导作用,对CYP3A4有抑制作用,对CYP2E1的作用不明显。     

乙烷硒啉对H-22荷瘤鼠CYP450酶系影响

[摘要]目的：观察新药乙烷硒啉（BBSKE）对肿瘤H-22引起的小鼠肝脏细胞色素P450含量及其主要亚型活性变化的影响。方法：H-22荷瘤小鼠,给予不同剂量的BBSKE 10d后,提取肝微粒体,Omura法测定CYP450的含量,分光光度法测定CYP1A,CYP3A和CYP2E1活性。结果：肿瘤H-22能引起CYP1A活性升高（P＜0.01）,CYP3A活性降低（P＜0.01）;BBSKE能明显下调荷瘤鼠CYP1A活性,上调CYP3A活性作用（P＜0.05）。肿瘤H-22和BBSKE对CYP450含量和CYP2E1均无明显影响。结论：BBSKE对荷瘤鼠CYP1A活性有下调作用;对CYP3A有诱导作用;对CYP2E1无明显影响。     

参麦注射液和注射用血塞通对大鼠肝脏及肠道药物代谢酶CYP450的影响

目的考察参麦注射液和注射用血塞通对大鼠药物代谢酶细胞色素P450(CYP450)的影响。方法连续给予大鼠试验药物后,制备肝及小肠微粒体;用CO还原差示光谱法,测定肝微粒体CYP450含量;用蛋白免疫印迹法,检测肝微粒体中CYP1A2、CYP2C11、CYP2E1、CYP3A和肠微粒体中CYP3A蛋白的表达量。结果参麦注射液和注射用血塞通组与空白对照组大鼠的肝脏总P450含量无显著性差异(P>0.05)。但参麦注射液可显著诱导肝脏CYP2E1表达,但抑制肠微粒体中CYP3A表达;肝CYP1A2、CYP2C11水平均有所上升。血塞通可显著诱导大鼠肝脏CYP1A2、CYP2E1、CYP2C11、CYP3A蛋白表达,肠CYP3A的表达水平显示出下降趋势。结论参麦注射液和注射用血塞通对大鼠肝脏P450酶总量无影响;但对特定亚型蛋白的表达量有影响,由此可能引发的药物相互作用不容忽视。     

丝裂霉素C在体外和体内对大鼠肝脏CYP2D1/2,CYP2C11和CYP1A2活性的影响

目的研究丝裂霉素C(MMC)在体外和体内对大鼠肝脏CYP2D1/2,CYP2C11和CYP1A2活性的影响。方法用诱导剂和抑制剂分别在体内和体外调节大鼠肝脏P450同工酶活性，并用HPLC检测3种同工酶各自底物的特定代谢产物，以计算同工酶活性。结果在体外, MMC可以使地塞米松诱导的大鼠肝脏微粒体CYP2D1/2,CYP2C11和CYP1A2活性分别抑制(19±6)%(P<0.05),(85±10)％(P<0.01)和(36±6)%(P<0.05)，并使β-萘黄酮诱导的CYP1A2活性降低(58±6)%(P<0.01)。在体内，以20% LD₅₀的剂量连续3 d或6 d腹腔注射MMC 对大鼠肝脏CYP2D1/2，CYP2C11和CYP1A2活性的影响无统计学差异。结论在体外MMC可以抑制大鼠肝微粒体CYP2D1/2，CYP2C11和CYP1A2的活性，但在体内对这3种细胞色素P450同工酶活性的影响无统计学差异。     

慢性间断性低氧对大鼠肝脏CYP3A_2和CYP2E_1的影响

目的:观察慢性间断性低氧对大鼠肝脏CYP3A2和CYP2E1的影响。方法:♂SD大鼠随机分为对照组和实验组,实验组分别低氧3、7、14、28d。采用酶法测定血清丙氨酸氨基转移酶(ALT)和天冬氨酸氨基转移酶(AST)活性,分光光度法测定大鼠肝微粒体红霉素N-脱甲基酶(ERD)、苯胺羟化酶(ANH)活性,半定量逆转录聚合酶链式反应(RT-PCR)检测大鼠肝脏细胞色素P4503A2、2E1的mRNA表达水平。结果:慢性间断性低氧对血清ALT和AST活性无明显影响;低氧7d后,大鼠肘脏ERD和ANH活性明显升高,28d时诱导率分别为155.5%和42.2%;同时CYP3A2和CYP2E1mRNA的表达水平也分别增加了220.5%和102.8%。结论:慢性间断性低氧能显著增加大鼠肝脏ERD(CYP4503A2)和ANH(CYP2E1)活性,其机制可能与其在转录水平上提高肝脏CYP4503A2和CYP2E1的基因表达水平有关。     

Cocktail法研究脉络宁注射液对大鼠CYP1A2、CYP2E1和CYP3A4活性的影响

目的：研究脉络宁注射液对大鼠CYP1A2、CYP2E1和CYP3A4活性的影响。方法：14只大鼠随机均分成临床等效剂量组和高剂量组,连续2周静脉给予脉络宁注射液（临床等效剂量纽,2mL／kg;高剂量组,4mL／kg）前后,均同时灌胃给予3个探针底物（茶碱,30mg／kg;氯唑沙宗,50rag／kg;氨苯砜,20mg/kg）,进行采血试验。用HPLC法同时测定大鼠体内各探针的血药浓度,DAS1．0软件计算药动学参数,并以配对t检验对各组大鼠前后两轮主要药动学参数进行差异性比较。结果：在1个给药疗程（14d）内,临床等效剂量组大鼠用药前后,3个探针的药动学参数均无显著性变化（P〉0．05）;高剂量组大鼠用药后,与用药前相比,茶碱的药动学参数没有显著变化（P〉0．05）;氨苯砜和氯唑沙宗的AUC0-24h均有升高趋势（P〈0．05）,给药后分别是给药前的1．44倍和1．28倍,同时氯唑沙宗的CL显著降低（P〈0．05）。结论：临床等效剂量脉络宁对大鼠CYP1A2、CYP2E1和CYP3A4活性均无显著影响,而高剂量脉络宁对大鼠CYP2E1和CYP3A4均有弱抑制作用。     

Bupropion hydroxylation as a selective marker of rat CYP2B1 catalytic activity

Benzyloxyresorufin-O-dealkylation (BROD) is usually used as a marker of cytochrome P450 (P450) 2B1 in rat. However, some reports show that CYP1A2 is also highly implicated. The purpose of the present study was to establish bupropion (BUP) hydroxylation, but not BROD, as a selective in vitro marker of CYP2B1 catalytic activity. IC(50) for BROD and BUP hydroxylation were equivalent (40.8 ± 4.6 and 41.8 ± 3.4 μM, respectively) when using liver microsomes from β-naphthoflavone-pretreated rats in the presence of metyrapone (CYP2B1 inhibitor). When using the same microsomes in the presence of CYP1A1/2-selective inhibitor α-naphthoflavone, we found an IC(50) of 2.5 × 10(-3) ± 0.8 × 10(-3) μM for BROD and >100 μM for BUP hydroxylation. These results suggest that CYP2B1 is similarly involved in both activities, whereas CYP1A2 is involved in BROD activity but not in BUP hydroxylation. BUP hydroxylation was assessed in microsomes from baculovirus-infected insect cells coexpressing NADPH-P450 oxidoreductase, and 14 rat P450s and kinetic parameters (K(m) and V(max)) were determined. BUP hydroxylation was predominantly catalyzed by CYP2B1 (75% of total hydroxybupropion formation), low activity was detected with CYP2E1 and CYP2C11 (10.9 and 8.7% of total hydroxybupropion, respectively), and activity was almost undetectable with the other P450 isoforms at saturating substrate concentrations (2500 μM), thereby validating the use of BUP as a diagnostic in vitro marker of CYP2B1 catalytic activity in rat.     

Effects of Ganoderma lucidum polysaccharide on CYP2E1, CYP1A2 and CYP3A activities in BCG-immune hepatic injury in rats

The purpose of the present study was to investigate the effect of Ganoderma lucidum polysaccharide (GLPS), a major active component in Chinese medicinal fungus, on cytochrome P450 metabolic activity in Bacillus Calmette Guérin (BCG)-induced immune hepatic injury in rats. The enzyme kinetics of the probes including chlorzoxazone (CYP2E1), phenacetin (CYP1A2) and nifedipine (CYP3A) were evaluated by HPLC. The results showed that BCG-pretreatment (125 mg/kg) significantly increased serum levels of alanine transaminase (ALT), nitrite and malondialdehyde (MDA), inhibited activities of superoxide dismutase (SOD) and decreased P450 total content in microsomes (p<0.05). Administration of GLPS (50 and 200 mg/kg) reversed above hepatic injury stimulated by BCG in vivo. Moreover, GLPS dose-dependently inhibited activities of CYP2E1, CYP1A2 and CYP3A in hepatic microsomes in vitro, suggesting that inhibition of GLPS on P450 oxidative metabolism might participate in the hepatoprotective mechanism, and also suggested that pharmacokinetics might be changed by drug-herb interaction.     

Induction of CYP1A1 and CYP2E1 in rat liver by histamine: binding and kinetic studies

Histamine (HA) may bind to cytochrome P450 (CYP450) in rat liver microsomes. The CYP450-HA complex seems to regulate some cellular processes such as proliferation. In the present work, it is shown that HA increases the activity and protein level of CYP1A1 and CYP2E1, in vivo. CYP1A1 is associated with polycyclic aromatic hydrocarbon-mediated carcinogenesis and CYP2E1 with liver damage by oxidative stress. Studies of enzyme kinetics and binding with rat liver microsomes and supersomes were carried out to determine whether HA is a substrate of CYP1A1 and/or CYP2E1. The lack of NADPH oxidation in the presence of HA showed that it is not a substrate for CYP1A1. Activity measurements using the O-dealkylation of ethoxyresorufin indicated that HA is a mixed-type inhibitor of CYP1A1 in both microsomes and supersomes. On the other hand, HA induced a significant NADPH oxidation catalyzed by CYP2E1 supersomes, strongly suggesting that HA is a substrate for this isoform. Furthermore, HA is consumed in the presence of CYP2E1-induced microsomes and supersomes, as determined by o-phtalaldehyde complexes with HA by HPLC. The present findings may contribute to understand better the physiological function of CYP450 in relation with inflammation and other physiological processes in which HA may have a relevant role.     

In vitro biotransformation of sildenafil (Viagra) in the male rat: the role of CYP2C11.

To assess the suitability of the male rat model for human studies on sildenafil metabolism, we examined the biotransformation of sildenafil in male rat liver microsomes and identified the role of specific cytochrome P450s (P450) using inhibitory antibodies and cDNA-expressed P450s. Rates of formation of the major circulating metabolite of sildenafil, UK-103,320, were 11-fold greater in the male rat than in human liver microsomes at 36 microM sildenafil, whereas substrate concentration corresponding to 50% V(max) (K(m) values) were 2.9-fold lower in the male rat. Although sildenafil is largely metabolized by CYP3A isoforms in humans, coincubation of rat liver microsomes with immunoinhibitory antibodies (CYP1A1/2, 2B1/2, 2C11, 2E1, and 3A1/2) revealed that metabolite formation was inhibited only by an antirat CYP2C11 antibody. Incubation of sildenafil with a cDNA-expressed CYP2C11 produced 10-fold higher levels of UK-103,320 than other P450s (CYP1A1, 1A2, 2B1, 2C6, 2C12, 2C13, 2E1, 3A1, and 3A2). Thus CYP2C11 contributes in a major way to the metabolism of sildenafil in the male rat. P450 isoforms mediating sildenafil biotransformation differ substantially between humans and the male rat, thereby limiting the applicability of this species as a model for sildenafil metabolism and drug interactions in humans.     

Contribution of CYP3A4, CYP2B6, and CYP2C9 isoforms to N-demethylation of ketamine in human liver microsomes.

Ketamine is a widely used drug for its anesthetic and analgesic properties; it is also considered as a drug of abuse, as many cases of ketamine illegal consumption were reported. Ketamine is N-demethylated by liver microsomal cytochrome P450 into norketamine. The identification of the enzymes responsible for ketamine metabolism is of great importance in clinical practice. In the present study, we investigated the metabolism of ketamine in human liver microsomes at clinically relevant concentrations. Liver to plasma concentration ratio of ketamine was taken into consideration. Pooled human liver microsomes and human lymphoblast-expressed P450 isoforms were used. N-demethylation of ketamine was correlated with nifedipine oxidase activity (CYP3A4-specific marker reaction), and it was also correlated with S-mephenytoin N-demethylase activity (CYP2B6-specific marker reaction). Orphenadrine, a specific inhibitor to CYP2B6, and ketoconazole, a specific inhibitor to CYP3A4, inhibited the N-demethylation of ketamine in human liver microsomes. In human lymphoblast-expressed P450, the activities of CYP2B6 were higher than those of CYP3A4 and CYP2C9 at three concentrations of ketamine, 0.005, 0.05, and 0.5 mM. When these results were extrapolated using the average relative content of these P450 isoforms in human liver, CYP3A4 was the major enzyme involved in ketamine N-demethylation. The present study demonstrates that CYP3A4 is the principal enzyme responsible for ketamine N-demethylation in human liver microsomes and that CYP2B6 and CYP2C9 have a minor contribution to ketamine N-demethylation at therapeutic concentrations of the drug.     

Predicting the contribution of rat cytochrome P-450 3A1, 3A2 and human cytochrome P-450 3A4, 3A5 to territrem a 4beta-C hydroxylation using the relative activity factor

The relative activity factor (RAF) was used to predict the contribution of different cytochrome P-450 (CYP) 3A isoforms (3A1 and 3A2 in rat liver microsomes and 3A4 and 3A5 in human liver microsomes) to 4beta-C hydroxylation of territrem A (TRA). Seven recombinant rat and eight recombinant human CYP450 isoforms, five rat liver microsomes, and seven human liver microsomes were assessed. In liver microsomes from five male Wistar rats, TRA 4beta-C hydroxylation activity significantly correlated with CYP3A1/2 activity, while, in liver microsomes from seven humans, there was marked correlation with CYP3A4 activity. Immunoinhibition confirmed that CYP3A2 and CYP3A4 were responsible for the hepatic metabolism of TRA 4beta-C hydroxylation. Using RAF, the percent contributions of CYP3A1 and CYP3A2 to 4beta-C hydroxylation of TRA in rat liver microsomes were estimated as 5 to 6 and 94 to 96, respectively, and those of CYP3A4 and CYP3A5 in human liver microsomes as 70 to 72 and 28 to 30%, respectively. These results suggest that CYP3A2 and CYP3A4 are the main form involved in the 4beta-C hydroxylation of TRA in rat and 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.     

The involvement of CYP3A4 and CYP2C9 in the metabolism of 17 alpha-ethinylestradiol.

The role of specific cytochrome P450 (P450) isoforms in the metabolism of ethinylestradiol (EE) was evaluated. The recombinant human P450 isozymes CYP1A1, CYP1A2, CYP2C9, CYP2C19, and CYP3A4 were found to be capable of catalyzing the metabolism of EE (1 microM). Without exception, the major metabolite was 2-hydroxy-EE. The highest catalytic efficiency (Vmax/Km) was observed with rCYP1A1, followed by rCYP3A4, rCYP2C9, and rCYP1A2. The P450 isoforms 3A4 and 2C9 were shown to play a significant role in the formation of 2-hydroxy-EE in a pool of human liver microsomes by using isoform-specific monoclonal antibodies, in which the inhibition of formation was approximately 54 and 24%, respectively. The involvement of CYP3A4 and CYP2C9 was further confirmed by using selective chemical inhibitors (i.e., ketoconazole and sulfaphenazole). The relative contribution of each P450 isoform to the 2-hydroxylation pathway was obtained from the catalytic efficiency of each isoform normalized by its relative abundance in the same pool of human liver microsomes, as determined by quantitative Western blot analysis. Collectively, these results suggested that multiple P450 isoforms were involved in the oxidative metabolism of EE in human liver microsomes, with CYP3A4 and CYP2C9 as the major contributing enzymes.     

The role of CYP2A and CYP2E1 in the metabolism of 3-methylindole in primary cultured porcine hepatocytes.

The accumulation of 3-methylindole (3MI) in uncastrated male pigs (boars) is a major cause of boar taint, which negatively affects the quality of meat from the animal. Previously, CYP2E1 and CYP2A have been identified as cytochrome P450 (P450) isoforms involved in the metabolism of 3MI using porcine liver microsomes. This study further examines the role of these isoforms in the metabolism of 3MI using a primary porcine hepatocyte model by examining metabolic profiles of 3MI after incubation with P450 inhibitors. Incubation of hepatocytes with 4-methylpyrazole resulted in a selective inhibition of CYP2E1 activity as determined by p-nitrophenol hydroxylase activity and an associated significant decrease in the production of the 3MI metabolites 3-hydroxy-3-methyloxindole and 3-methyloxindole. Furthermore, inhibition of CYP2A, as assayed by coumarin 7-hydroxylase activity, using 8-methoxypsoralen and diethyldithiocarbamate was not associated with any further significant inhibition of the production of 3MI metabolites. Treatment with general P450 inhibitors resulted in further decreases in CYP2E1 activity and a more dramatic decrease in the production of 3MI metabolites, suggesting that additional P450s may be involved in the phase 1 metabolism of 3-methylindole. In conclusion, CYP2E1 activity levels are more important than CYP2A activity levels for the metabolism of 3-methylindole in isolated pig hepatocytes.     

Substrate specificity for rat cytochrome P450 (CYP) isoforms: screening with cDNA-expressed systems of the rat

In this study, we performed a screening of the specificities of rat cytochrome P450 (CYP) isoforms for metabolic reactions known as the specific probes of human CYP isoforms, using 13 rat CYP isoforms expressed in baculovirus-infected insect cells or B-lymphoblastoid cells. Among the metabolic reactions studied, diclofenac 4-hydroxylation (DFH), dextromethorphan O-demethylation (DMOD) and midazolam 4-hydroxylation were specifically catalyzed by CYP2C6, CYP2D2 and CYP3A1/3A2, respectively. These results suggest that diclofenac 4-hydroxylation, dextromethorphan O-demethylation and midazolam 4-hydroxylation are useful as catalytic markers of CYP2C6, CYP2D2 and CYP3A1/3A2, respectively. On the other hand, phenacetin O-deethylation and 7-ethoxyresorufin O-deethylation were catalyzed both by CYP1A2 and by CYP2C6. Benzyloxyresorufin O-dealkylation and pentoxyresorufin O-dealkylation were also catalyzed by CYP1A2 in addition to CYP2B1. Bufuralol 1'-hydroxylation was extensively catalyzed by CYP2D2 but also by CYP2C6 and CYP2C11. p-Nitrophenol 2-hydroxylation and chlorzoxazone 6-hydroxylation were extensively catalyzed by CYP2E1 but also by CYP1A2 and CYP3A1. Therefore, it is necessary to conduct further study to clarify whether these activities in rat liver microsomes are useful as probes of rat CYP isoforms. In contrast, coumarin 7-hydroxylation and S- and R-mephenytoin 4'-hydroxylation did not show selectivity toward any isoforms of rat CYP studied. Therefore, activities of coumarin 7-hydroxylation and S- and R-mephenytoin 4'-hydroxylation are not able to be used as catalytic probes of CYP isoforms in rat liver microsomes. These results may provide useful information regarding catalytic probes of rat CYPs for studies using rat liver microsomal samples.