细胞色素P450 2A6与2B6基因多态性影响丙戊酸血药浓度的系统评价

目的 评价细胞色素P450 2A6、2B6(CYP2A6、CYP2B6)基因多态性对癫痫患者丙戊酸浓度剂量比(C/D)的影响。方法 检索Pub Med、EMBase、中国知网、维普与万方数据库,系统评价CYP2A6、CYP2B6基因多态性对癫痫患者丙戊酸C/D影响的临床研究。结果 共纳入5篇文献,CYP2A6*1/*1基因型患者的丙戊酸C/D显著低于*1/*4+*4/*4基因型患者(P<0.05);CYP2B6*1/*1基因型患者的丙戊酸C/D显著低于*1/*6+*6/*6基因型患者(P<0.05)。结论 CYP2A6*4与CYP2B6*6基因多态性对丙戊酸的血药浓度预测具有一定的临床指导价值。     

一个新的人细胞色素P450 2B6 cDNA 序列

本实验室于 1 995年克隆了人细胞色素 P450 2 B6c DNA并建立了稳定表达 CYP2 B6的转基因细胞 (吴健敏 ,等 .中国药理学与毒理学杂志 ,1 996,1 0 ( 2 ) :1 31 - 1 35) .其表达产物具有 7-乙氧基 - 4-三氟甲基香豆素去乙基酶活性 ,建立的转基因细胞有代谢活化甲基亚硝胺吡啶酮 ,黄曲霉素 B1 ,环磷酰胺 ,二乙基亚硝胺和吗啉亚硝胺的能力 .限于当时条件 ,仅用 T7引物测得 CYP2 B63′端 1 90 bp序列 (吴健敏 ,等 .癌变·畸变·突变 ,1 995,7( 1 ) :1 - 6) ,与 Yamano等报道的序列相同 ( Yamano S,etal. Biochemistry,1 989;2 8:7340 - 73…     

药物代谢酶细胞色素P450 2C9研究进展

P450 2C9是人体中重要的药物代谢酶。P450 2C9基因编码区的多态性造成氨基酸序列的变化。主要包括P450 2C9*2和P450 2C9*3两种突变体，变异纯合子对P450 2C9底物的代谢能力明显降低。P450 2C9的底物包括甲苯磺丁脲、苯妥英、S-法华令、氟西汀、洛沙坦等。P450 2C9可被利福平诱导，被胺碘酮和氟康唑等多种药物抑制。     

草鱼肝脏细胞色素P450酶系生物转化酪胺生成章鱼胺的研究

目的以草鱼肝脏S-9部位为酶源,以酪胺为原料生物转化生成章鱼胺。方法制备草鱼肝的S-9部位,测定细胞色素P450酶的含量并作生物转化试验。以维生素C为氢载体,异烟肼为单胺氧化酶抑制剂。结果反应1h产生的章鱼胺为879.7μg/4.5mL反应液,章鱼胺的生物合成率为21.4%,酪胺代谢率为90.0%。结论以草鱼肝脏S-9部位为酶源生物转化生成章鱼胺是可行的,但由于P450酶系的非专一性,章鱼胺的生物合成率较低,有待进一步改进。     

细胞色素P450酶系在药物代谢中的作用

该文从细胞色素P450概述、参与药物代谢的人类细胞色素P450亚型、细胞色素P450与药物的相互作用、细胞色素P450多态性在药物不良反应中的作用及细胞色素P450酶系产生药物不良反应的机制等方面综述细胞色素P450酶系对药物代谢的影响，为指导临床合理用药，避免药物不良反应及个体化用药提供参考。     

细胞色素P450基因突变及其效应的研究进展

细胞色素P450(CYP450)作为一组重要的氧化酶在人体药物代谢中发挥着重要作用，随着基因组学的发展，其基因多态性逐步得到深入研究。近年来，对于CYP450的研究重点也逐渐由基因定位和单纯的突变位点发现，转移到等位基因功能多态性和基因突变导致的酶学改变这些基因与蛋白的效应关系上来。本文综述了CYP450新的单核苷酸多态性的出现及相应功能的研究进展。     

药物代谢中的肝细胞色素P450

肝细胞色素Ｐ４５０参与许多外源性物质（包括药物）的生物转化。本文从肝细胞色素Ｐ４５０在体内的分布及命名,被诱导和抑制的机制,对映体代谢的选择性与代谢差异遗传多态性以及国内外关于Ｐ４５０的研究方法等方面介绍了该领域研究的新进展。     

细胞色素氧化酶P450 2C19的研究进展

细胞色素氧化酶P450 2C19（CYP2C19）是细胞色素氧化酶家族中的一种很重要的酶,它在药物代谢中的具有重要作用。本文综述CYP2C19的结构特点、基因、底物、探针药物、影响其活性的主要因素和多态性及 其分子生物学机制。     

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.     

Marmoset cytochrome P450 2B6, a propofol hydroxylase expressed in liver

1. The common marmoset (Callithrix jacchus) is a useful experimental animal to evaluate the pharmacokinetics of drug candidates. Cytochrome P450 (P450) 2B enzyme in marmoset livers has been identified; however, only limited information on the enzymatic properties and distribution has been available.

2. Marmoset P450 2B6 amino acids showed high sequence identities (>86%) with those of primates including humans and cynomolgus monkeys. Phylogenetic analysis using amino acid sequences indicated that marmoset P450 2B6 was closer to human and cynomolgus monkey P450 2B6 than to P450 2B orthologs of other species, including pigs, dogs, rabbits and rodents.

3. Quantitative polymerase chain reaction analysis using specific primers showed P450 2B6 mRNA predominantly expressed in livers among the five marmoset tissues, similar to those of humans and cynomolgus monkeys.

4. Marmoset P450 2B6 heterologously expressed in Escherichia coli membranes oxidized 7-ethoxycoumarin, pentoxyresorufin, propofol and testosterone, at roughly similar rates to those of humans and/or cynomolgus monkeys. A high capacity of marmoset P450 2B6 with propofol 4-hydroxylation (at low ionic strength conditions) with a low K_m value was relatively comparable to that for marmoset livers.

5. These results collectively indicated a high propofol 4-hydroxylation activity of P450 2B6 expressed in marmoset livers.

     

Site-specific oxidation of flavanone and flavone by cytochrome P450 2A6 in human liver microsomes

1. The roles of human cytochrome P450 (P450 or CYP) 2A6 in the oxidation of flavanone [(2R)- and (2S)-enantiomers] and flavone were studied in human liver microsomes and recombinant human P450 enzymes.

2. CYP2A6 was highly active in oxidizing flavanone to form flavone, 2′-hydroxy-, 4′-, and 6-hydroxyflavanones and in oxidizing flavone to form mono- and di-hydroxylated products, such as mono-hydroxy flavones M6, M7, and M11 and di-hydroxy flavones M3, M4, and M5.

3. Liver microsomes prepared from human sample HH2, defective in coumarin 7-hydroxylation activity, were very inefficient in forming 2′-hydroxyflavanone from flavanone and a mono-hydroxylated product, M6, from flavone. Coumarin and anti-CYP2A6 antibodies strongly inhibited the formation of these metabolites in microsomes prepared from liver samples HH47 and 54, which were active in coumarin oxidation activities.

4. Molecular docking analysis showed that the C2′-position of (2R)-flavanone (3.8 Å) was closer to the iron center of CYP2A6 than the C6-position (10 Å), while distances from C2′ and C6 of (2S)-flavanone to the CYP2A6 were 6.91 Å and 5.42 Å, respectively.

5. These results suggest that CYP2A6 catalyzes site-specific oxidation of (racemic) flavanone and also flavone in human liver microsomes. CYP1A2 and CYP2B6 were also found to play significant roles in some of the oxidations of these flavonoids by human liver microsomes.

     

Intra- and Inter-ethnic Differences in the Allele Frequencies of Cytochrome P450 2B6 Gene in Chinese

Abstract This study aimed to investigate the allele frequencies of CYP2B6 gene in 193 Han Chinese and compared with 91 Uygur Chinese. Five single nucleotide polymorphisms of CYP2B6, 64C>T, 516G>T, 777C>A, 785A>G and 1459C>T, were tested using the polymerase chain reaction–restriction fragment length polymorphism method. The allele frequencies for CYP2B6*2, CYP2B6*3, CYP2B6*4, CYP2B6*5, CYP2B6*6, CYP2B6*7 and CYP2B6*9 in Han and Uygur Chinese were 0.034 and 0.027, 0 and 0.011, 0.091 and 0.033, 0.003 and 0.049, 0.184 and 0.214, 0 and 0.022, and 0.018 and 0.044, respectively, with CYP2B6*4, CYP2B6*5, and CYP2B6*7 being significantly different between these two races (P<0.05). CYP2B6*6 was the most prevalent allele among all detected variants in Han and Uygur Chinese. The most frequent genotypes were CYP2B6*1/CYP2B6*1 (50.8%), CYP2B6*1/CYP2B6*6 (24.4%), and CYP2B6*1/CYP2B6*4 (7.3%) in Han subjects, whereas the most frequent genotypes in Uygur subjects were CYP2B6*1/CYP2B6*1 (36.3%), CYP2B6*1/CYP2B6*6 (25.3%), CYP2B6*1/CYP2B6*5 (5.5%) and CYP2B6*6/CYP2B6*6 (5.5%). The frequencies of 64C>T mutation in Han and Uygur Chinese were significantly lower than that in American Caucasian (P<0.05). These results indicate that there were marked ethnic differences in the mutant frequencies of CYP2B6 between Chinese and other ethnic groups. Further studies are warranted to explore the clinical impact of such ethnic differences.     

Deactivation of anti-cancer drug letrozole to a carbinol metabolite by polymorphic cytochrome P450 2A6 in human liver microsomes

1. Cytochromes P450 (P450) involved in letrozole metabolism were investigated. Among 13 recombinant P450 forms examined, only P450 2A6 and 3A4 showed activities in transforming letrozole to its carbinol metabolite with small K_m and high V_max values yielding apparent V_max/K_m values of 0.48 and 0.24 nl min^?1 nmol^?1 P450, respectively.

2. The metabolic activities of individual human liver microsomes showed a significant correlation with coumarin 7-hydroxylase activities (P450 2A6 marker) at a letrozole concentration of 0.5 μM, while a good correlation was also seen with testosterone 6β-hydroxylase activities (P450 3A4 marker) at 5 μM substrate concentration with different inhibition by 8-methoxypsolaren.

3. Significantly low carbinol-forming activities were seen in human liver microsomes from individuals possessing CYP2A6*4/*4 (whole CYP2A6 gene deletion) at a letrozole concentration of 0.5 μM. A V_max/K_m value measured for CYP2A6.7 (amino acid substitution type) in human liver microsomes, in the presence of anti-P450 3A4 antibodies, was approximately seven-fold smaller than that for CYP2A6.1 (wild-type).

4. These results demonstrate that P450 2A6 and 3A4 catalyse the conversion of letrozole to its carbinol metabolite in vitro at low and high concentrations of letrozole. Polymorphic variation of CYP2A6 is considered to be relevant to inter-subject variation in therapeutic exposure of letrozole.

     

Roles of CYP2A6 and CYP2B6 in nicotine C-oxidation by human liver microsomes

Nicotine C-oxidation by recombinant human cytochrome P450 (P450 or CYP) enzymes and by human liver microsomes was investigated using a convenient high-performance liquid chromatographic method. Experiments with recombinant human P450 enzymes in baculovirus systems, which co-express human nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH)-P450 reductase, revealed that CYP2A6 had the highest nicotine C-oxidation activities followed by CYP2B6 and CYP2D6; the K _m values by these three P450 enzymes were determined to be 11.0, 105, and 132 μM, respectively, and the V _max values to be 11.0, 8.2, and 8.6 nmol/min per nmol P450, respectively. CYP2E1, 2C19, 1A2, 2C8, 3A4, 2C9, and 1A1 catalysed nicotine C-oxidation only at high (500 μM) substrate concentration. CYP1B1, 2C18, 3A5, and 4A11 had no measurable activities even at 500 μM nicotine. In liver microsomes of 16 human samples, nicotine C-oxidation activities were correlated with CYP2A6 contents at 10 μM substrate concentration, whereas such correlation coefficients were decreased when the substrate concentration was increased to 500 μM. Contribution of CYP2B6 (as well as CYP2A6) was demonstrated by experiments with the effects of orphenadrine (and also coumarin and anti-CYP2A6) on the nicotine C-oxidation activities by human liver microsomes at 500 μM nicotine. CYP2D6 was found to have minor roles since quinidine did not inhibit microsomal nicotine C-oxidation at both 10 and 500 μM substrate concentrations. These results support the view that CYP2A6 has major roles for nicotine C-oxidation at lower substrate concentration and both CYP2A6 and 2B6 play roles at higher substrate concentrations in human liver microsomes. Received: 27 October 1998 / Accepted: 11 January 1999     

Regioselective hydroxylation of an antiarrhythmic drug,propafenone, mediated by rat liver cytochrome P450 2D2 differs from that catalyzed by human P450 2D6

1. Propafenone, an antiarrhythmic drug, is a typical human cytochrome P450 (P450) 2D6 substrate used in preclinical studies. Here, propafenone oxidation by mammalian liver microsomes was investigated in vitro.

2. Liver microsomes from humans and marmosets preferentially mediated propafenone 5-hydroxylation, minipig, rat and mouse livers primarily mediated 4′-hydroxylation, but cynomolgus monkey and dog liver microsomes differently mediated N-despropylation.

3. Quinine, ketoconazole or anti-P450 2D antibodies suppressed propafenone 4′/5-hydroxylation in human and rat liver microsomes. Pretreatments with β-naphthoflavone or dexamethasone increased N-despropylation in rat livers.

4. Recombinant rat P450 2D2 efficiently catalysed propafenone 4′-hydroxylation in a substrate inhibition manner, comparable to rat liver microsomes, while human P450 2D6 displayed propafenone 5-hydroxylation. Human and rat P450 1A, 2C and 3A enzymes mediated propafenone N-despropylation with high capacities.

5. Carbon-4′ of propafenone docked favourably into the active site of P450 2D2 based on an in silico model; in contrast, carbon-5 of propafenone docked into human P450 2D6.

6. These results suggest that the major roles of individual P450 2D enzymes in regioselective hydroxylations of propafenone differ between human and rat livers, while the minor roles of P450 1A, 2C and 3A enzymes for propafenone N-despropylation are similar in livers of both species.     

细胞色素P4502D6的研究进展

ＣＹＰ２Ｄ６在临床重要药代谢中具有重要作用。本文综述了ＣＹＰ２Ｄ６的结构特点,底物,探针药物,影响其活性的因素,基因多态性以及它与疾病的关系。     

Inhibitory effects of antiparasitic drugs on cytochrome P450 2D6

The interaction of antiparasitic drugs with the polymorphic cytochrome P450 2D6 was studied in human liver microsomes.Of ten different drugs tested, three quinolines, oxamniquine, primaquine and chloroquine inhibited microsomal CYP2D6-catalysed formation of 1hydroxybufuralol at concentrations that might have clinical consequences in drug use. These drugs inhibited competitively bufuralol metabolism with K _i values of 22, 23 and 15 M, respectively, indicative of high affinity for the CYP2D6-active site. The results imply that oxamniquine, primaquine and chloroquine could be substrates of cytochrome P4502 D6 or that they are potent non-substrate inhibitors of the enzyme similar to quinidine.In either case, the inhibition of CYP2D6 by these agents could lead to interference with in vivo population-phenotyping procedures in the tropical regions where treatment with the drugs is common.     

The influence of CYP2B6, CYP2C9 and CYP2D6 genotypes on the formation of the potent antioestrogen Z-4-hydroxy-tamoxifen in human liver

AIMS: To investigate in a large panel of 50 human liver samples the contribution of CYP2C9, CYP2D6, and CYP3A4 to the overall formation of the potent antioestrogen Z-4-hydroxy-tamoxifen, and how various genotypes affect its formation from tamoxifen. METHODS: The formation of Z-4-hydroxy-tamoxifen from 10 microm tamoxifen was studied in human liver microsomes (n=50), characterized for CYP2B6, CYP2C9, CYP2D6 and CYP3A4 expression, and CYP2B6, CYP2C9 and CYP2D6 genotype. The effect of chemical and monoclonal antibody inhibitors, and the formation in supersomes expressing recombinant CYP isoforms was also investigated. Z-4-hydroxy-tamoxifen was quantified using LC-MS analysis. RESULTS: Z-4-hydroxy-tamoxifen was formed by supersomes expressing CYP2B6, CYP2C9, CYP2C19 and CYP2D6, but not CYP3A4. In agreement with these data, the mean formation of Z-4-hydroxy-tamoxifen was inhibited 49% by sulphaphenazole (P=0.001), 38% by quinidine (P<0.05) and 13% by monoclonal antibody against CYP2B6 (MAB-2B6, P<0.05). Furthermore, Z-4-hydroxy-tamoxifen formation significantly correlated with both CYP2C9 expression (r(s)=0.256, P<0.05) and CYP2D6 expression (r(s)=0.309, P<0.05). Genotypes of CYP2D6, CYP2B6 and CYP2C9 had an effect on metabolite formation in such a way that samples with two nonfunctional CYP2D6, or two variant CYP2C9 or CYP2B6 alleles, showed lower enzyme activity compared with those with two functional or wild-type alleles, (5.0 vs 9.9 pmol mg(-1) protein min(-1), P=0.046, 5.1 vs 9.9 pmol mg(-1) protein min(-1), P=0.053, and 6.8 vs 9.4 pmol mg(-1) protein min(-1), P=0.054, respectively). CYP2D6 and CYP2C9 contribute on average 45 and 46%, respectively, to the overall formation of Z-4-hydroxy-tamoxifen. CONCLUSIONS: CYP2B6, CYP2C9 and CYP2D6 genotypes all affected Z-4-hydroxy-tamoxifen formation and can predict individual ability to catalyse this reaction.