Characterization of intestinal and hepatic P450 enzymes in cynomolgus monkeys with typical substrates and inhibitors for human P450 enzymes

1. Cynomolgus monkeys are widely used to predict human pharmacokinetic and/or toxic profiles in the drug developmental stage. Characterization of cynomolgus monkey P450s such as the mRNA expression level, substrate specificity, and inhibitor selectivity were conducted to provide helpful information in designing monkey in vivo studies and monkey-to-human extrapolation.

2. The expression levels of 12 monkey P450 mRNAs, which are considered to be important P450 subfamilies in drug metabolism, were investigated in the liver, small intestine (duodenum, jejunum, and ileum), and colon of individual monkeys.

3. iIn vitro activities and intrinsic clearance values were determined in monkey intestinal and liver microsomes (MIM and MLM, respectively) using nine typical oxidative reactions for human P450s. Paclitaxel 6α-hydroxylation, diclofenac 4′-hydroxylation, and S-mephenytoin 4′-hydroxylation showed low activities in MIM and MLM.

4. IC₅₀ values of eight selective inhibitors of human P450s were determined in MIM and MLM. Inhibitory effects of furafylline and sulfaphenazole were weak in monkeys on phenacetin O-deethylation and diclofenac 4′-hydroxylation, respectively.

5. These results show profiles of monkey P450s in both the intestine and liver in detail and contribute to a better understanding of the species difference in substrate specificity and inhibitor selectivity between cynomolgus monkeys and humans.

     

细胞色素P450的基因多态性与药物代谢

细胞色素P450（cytochrome P450，CYP）是重要的药物代谢酶，参与催化多种内源和外源化合物，特别是多种临床药物的生物转化。CYP存在广泛的基因多态性和表型多态性，使其对于各种化合物的代谢存在统计学个体差异。核受体是配体依赖性转录因子超家族，与药物代谢过程中的基因表达调控密切相关，被外源物质活化后诱导或抑制CYP基因的表达。现综述CYP与药物代谢、CYP的基因多态性、CYP表达的诱导机制、核受体及其配体诱导CYP表达及近年研究CYP450的各种实验方法。     

细胞色素P450与药物代谢的研究现状

细胞色素P450(CYP)在众多中西药物代谢中起着非常重要的作用。本文综述了与药物代谢相关的CYP亚型、CYP与药物相互作用的关系及中药对CYP的影响，旨在合理解释和预测临床上药物间相互作用和药物不良反应等。同时选择适当的药物作为探针来评价CYP的活性，为实现临床个体化给药提供科学依据。     

介导候选药代谢的肝细胞色素P450酶表型鉴定的定性和定量方法

新药研发需要对候选药物的代谢途径、每个代谢途径对总清除率的贡献以及参与代谢的酶进行详细研究。候选药物经过肝细胞色素P450(CYP)酶代谢的比例(f_m)可以用放射性同位素标记的方法在人体水平测定,而肝中某酶亚型的代谢占总的CYP参与代谢的比例(f_CYPi)可以用体外酶表型鉴定的方法来测定,这两个参数的乘积f_m×f_CYPi即为某个CYP酶亚型代谢参与某候选药物体内清除的百分比,对研究体内药物-药物相互作用具有重要意义。本文从定性和定量两方面综述体外酶表型鉴定的研究方法。     

取代苯胺与细胞色素P450相互作用时的结构与活性关系

本研究用不同来源的鼠肝微粒体,测定了40余种取代苯胺生成细胞色素P450代谢中问体(MI)络合物的能力,其结构与活性间关系可归纳如下:(1)在氨基的对位或间位必须存在一个可提供孤对电子的取代基,当此取代基位于邻位时,化合物不能生成P450-MI络合物,(2)在对位取代基中除了可提供孤对电子的基团外,引入亲脂性结构有助于生成P450-MI络合物,(3)间氯或对-氯邻甲苯胺似仅选择性地络合苯巴比妥与Aroclor共诱导的P450亚族,(4)苯环上若无可提供孤对电子的基团,任何疏水性,亲水性或供电子取代基均无助于取代苯胺生成P450-MI络合物。(5)一组可形成P450-MI络合物的取代苯胺(取代对氨基二苯醚)延长小鼠戊巴比妥睡眠时间的能力与取代基的电性相关。     

六种大鼠肝微粒体细胞色素P450重组酶系对33种外来化合物的代谢

多氯联苯诱导的六种鼠肝微粒体细胞色素P450重组酶系A_1,A_2,B,C_1,C_2和D对33种外来化合物代谢的催化速率不同,其中以C_1酶系和C_2酶系催化活力最强,其次为A_1酶系,B酶系催化活力最弱,外来化合物的种类不同,经重组酶系催化的途径也不同,如卤代烷烃,卤代烯烃,苯及其同系物,亚硝胺类等化合物主要经P450C_1酶系代谢,而大多数有机磷酸酯,氨基甲酸酯类化合物及多环芳烃类致癌物则以P450 C_2酶系代谢为主。     

CYP450氧化还原酶的遗传多态对药物代谢的影响

CYP450氧化还原酶(cytochrome P450 oxidoreductase,POR)是所有肝微粒体的细胞色素P450氧化酶(cytochrome P450 monooxygenases,CYP)的唯一电子供体,其中一些CYP是I相药物代谢酶,负责临床上超过80%药物的氧化代谢。另外,POR直接介导了一些抗肿瘤前体药物的代谢。因此,POR的遗传多态引起其活性的改变,对临床药物代谢具有非常重要的临床意义。该文总结了近年来POR的遗传多态影响药物代谢的最新研究进展。     

Human plasma concentrations of cytochrome P450 probes extrapolated from pharmacokinetics in cynomolgus monkeys using physiologically based pharmacokinetic modeling

Abstract

1.?Cynomolgus monkeys are widely used in preclinical studies as non-human primate species. Pharmacokinetics of human cytochrome P450 probes determined in cynomolgus monkeys after single oral or intravenous administrations were extrapolated to give human plasma concentrations.

2.?Plasma concentrations of slowly eliminated caffeine and R-/S-warfarin and rapidly eliminated omeprazole and midazolam previously observed in cynomolgus monkeys were scaled to human oral biomonitoring equivalents using known species allometric scaling factors and in vitro metabolic clearance data with a simple physiologically based pharmacokinetic (PBPK) model. Results of the simplified human PBPK models were consistent with reported experimental PK data in humans or with values simulated by a fully constructed population-based simulator (Simcyp).

3.?Oral administrations of metoprolol and dextromethorphan (human P450 2D probes) in monkeys reportedly yielded plasma concentrations similar to their quantitative detection limits. Consequently, ratios of in vitro hepatic intrinsic clearances of metoprolol and dextromethorphan determined in monkeys and humans were used with simplified PBPK models to extrapolate intravenous PK in monkeys to oral PK in humans.

4.?These results suggest that cynomolgus monkeys, despite their rapid clearance of some human P450 substrates, could be a suitable model for humans, especially when used in conjunction with simple PBPK models.     

新型抗抑郁药的代谢与细胞色素P450介导的药物相互作用

新型抗抑郁药(选择性5-羟色胺再摄取抑制剂,SSRI)疗效肯定,耐受性好,已得到广泛应用。SSRI剂既是P 450酶的底物又是P 450酶的抑制剂,其重要特征是对P 450酶的抑制。当SSRI剂与P 450酶的其他底物合用时,可能发生明显的具有临床意义的药物相互作用。     

消草磷同类物使P450失活的能力与其理化性质间的定量关系(英文)

十四种消草磷结构类似物与经苯巴比妥预处理大鼠肝匀浆S9悬液一起温育,在有NADPH存在时,可不同程度地使P450失活.若温育10 min后P450丢失量用Y表示,化合物的疏水性和电性分别用P_(gc)和μ_(gc)表示,可建立如下相关性: logY=4.106logP_(gc)-0.575(logP_(gc))~2-5.822 (n=14,r=0.954,s=0.054);logY=3.678 logP_(gc)-0.520(logP_(gc))~2-0.037μ_(gc)-4.877 (n=14,r=0.965,S=0.049) 上述两方程表明,消草磷同类物体外使P450失活的能力与其疏水性呈良好的抛物线型相关,化合物的电性对此能力也有影响,但贡献较小.     

皮肤细胞色素P450酶的研究进展

皮肤是肝外药物代谢的主要器官之一，有多种代谢酶表达。细胞色素P450酶（CYP）是一组含亚铁血红素的超家族基因编码的同工酶，皮肤CYP参与了多种内源性物质和外源性物质的代谢，在维持皮肤的正常生理功能和保护内环境稳定方面发挥重要作用。对皮肤CYP的研究有助于了解它在药物代谢和皮肤疾病中的作用，对提高药物疗效、开发经皮给药新制剂、防止药物和毒性物质对皮肤的侵害等，具有重要意义。     

细胞色素氧化酶CYP 1A2基因多态性与物质代谢和癌症发生相关性的研究进展

细胞色素氧化酶CYP 1A2亚家族是近年来药物代谢研究领域较受关注的热点之一。该酶具有高度的个体间差异,并参与多种临床药物以及环境致癌物质的代谢,与癌症、炎症、心肌梗塞等疾病的发病易感性相关。CYP 1A2具有抗氧化作用;CYP 1A2基因多态性和表型差异的研究,可用于评价临床药物治疗效果;探针药物的应用是研究CYP 1A2活性的主要方法;人源化CYP 1A2转基因动物模型,是癌症发生研究中、新的研究手段。     

Endotoxin depresses hepatic cytochrome P450-mediated drug metabolism in women

Aims In men, the inflammatory response to intravenous endotoxin depresses apparent oral clearances of antipyrine, hexobarbitone, and theophylline. The aim of this study was to investigate whether there might be gender differences in the regulation of hepatic cytochromes P450.
Methods Experiments were carried out in seven healthy women volunteers (ages 19–51, median 22 years). Each woman received a cocktail of the three drugs on two occassions, once after a saline injection and again after endotoxin.
Results Endotoxin injections, but not saline, caused the expected physiologic responses of inflammation including fever and increases in circulating tumor necrosis factor-α, interleukin-6, and C-reactive protein. When compared with the saline control studies, endotoxin significantly decreased clearances of all probes: antipyrine, 31% (95%CI 21%–41%); hexobarbitone, 20% (95%CI 10–31%); and theophylline, 20% (95%CI 10%–30%). The decreases were comparable with those found in the men previously studied (35%, 27%, and 22%, respectively).
Conclusions These data show that endotoxin-induced inflammation decreases hepatic cytochrome P450-mediated metabolism of selected probe drugs in women as it does in men.     

Mechanisms underlying the inhibition of the cytochrome P450 system by copper ions

Copper toxicity has been associated to the capacity of free copper ions to catalyze the production of superoxide anion and hydroxyl radical, reactive species that modify the structure and/or function of biomolecules. In addition, nonspecific Cu²⁺‐binding to thiol enzymes, which modifies their catalytic activities, has been reported. Cytochrome P450 (CYP450) monooxygenase is a thiol protein that binds substrates in the first and limiting step of CYP450 system catalytic cycle, necessary for the metabolism of lipophilic xenobiotics. Therefore, copper ions have the potential to oxidize and bind to cysteinyl residues of this monooxygenase, altering the CYP450 system activity. To test this postulate, we studied the effect of Cu²⁺ alone and Cu²⁺/ascorbate in rat liver microsomes, to independently evaluate its nonspecific binding and its pro‐oxidant effects, respectively. We assessed these effects on the absorbance spectrum of the monooxygenase, as a measure of structural damage, and p‐nitroanisole O‐demethylating activity of CYP450 system, as a marker of functional impairment. Data obtained indicate that Cu²⁺ could both oxidize and bind to some amino acid residues of the CYP450 monooxygenase but not to its heme group. The differences observed between the effects of Cu²⁺ and Cu²⁺/ascorbate show that both mechanisms are involved in the catalytic activity inhibition of CYP450 system by copper ions. The significance of these findings on the pharmacokinetics and pharmacodynamics of drugs is discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

mRNA levels of drug-metabolizing enzymes in 11 brain regions of cynomolgus macaques

The cynomolgus macaque is an important nonhuman primate species in drug metabolism studies, in part because of its evolutionary closeness to humans. Cytochromes P450 (P450s) have been investigated in the major drug-metabolizing organs, i.e., the liver and small intestine, but have not been fully investigated in the brain. However, recent investigations have indicated possible important roles for P450s in the brain. In this study, by using the quantitative polymerase chain reaction, we measured the mRNA levels of 38 cynomolgus drug-metabolizing enzymes, including 19 P450s, 10 UDP-glycosyltransferases, and 9 other enzymes, in 11 brain regions. Among these drug-metabolizing enzymes, expression of 32 enzyme mRNAs were detected in one or more brain regions, indicating their possible roles in the brain. Further investigation of metabolic activities would facilitate better understanding of the importance of these enzymes in the brain.     

甘草次酸在人细胞色素CYP450中体外代谢研究(英)

甘草根是中医临床常用解毒草药, 其活性成分甘草次酸主要是通过肝脏代谢。本文研究了人肝微粒体以及人源性CYP450s对甘草次酸的体外代谢影响, 以及甘草次酸对几种CYP450酶活性的影响。实验结果表明, 甘草次酸体外主要代谢酶为CYP3A4。体外药代动力学参数K_m, V_max和CL_int分别为18.6 μmol·L⁻¹, 4.4 nmol·mg⁻¹(protein)·min⁻¹和0.237 mL·mg⁻¹(protein)·min⁻¹。体外抑制试验显示, 50 μmol·L⁻¹甘草次酸可以抑制CYP2C19、CYP2C9、CYP3A4酶的活性, 其抑制率可高达50%以上。     

细胞色素P450氧化还原酶的研究进展

细胞色素P450氧化还原酶(Cytochrom e P450 Reduc-tase,CPR)是细胞色素P450药物代谢酶系中为细胞色素P450提供电子的膜蛋白,本文从电子传递、底物作用及其基因调控三方面的特性对其进行了论述,并探讨了CPR领域一些待研究的问题。     

丹参活性成分或制剂对CYP450活性的影响及药物相互作用研究进展

丹参是一种传统医疗的草本植物,临床上广泛应用于心脑血管疾病的辅助治疗。丹参活性成分复杂,部分成分可影响肝脏中细胞色素P450酶（CYP450）的活性,可能导致药物相互作用的发生。探讨丹参对CYP450活性的影响及药物相互作用机制,对指导临床合理联用丹参与其他药物具有重要的意义。