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酶系介导的甾体羟化反应及其在分子水平上的研究进展

细胞色素P450单加氧酶系(cytochrome P450 monooxygenases,P450s)是主要位于某些细胞的内质网上的一个氧化酶系.P450酶系介导羟化反应是微生物甾体化合物转化反应中最重要的反应.本文概述了微生物细胞色素P450酶系,并注重综述了细胞色素P450酶系基因在转录水平调控、克隆表达以及在甾体转化应用、药物代谢等分子水平方面的研究进展.     

异源细胞色素P450全细胞活性的高通量筛选

细胞色素P450是一类单加氧酶的超家族，催化许多具有立体和区域特异性的氧化反应，因此具有潜在的生物转化价值。特别是相对于哺乳动物，植物P450通常具有更高的底物特异性。由于大多数真核生物P450是膜结合蛋白，需要辅因子NAD（P）H和细胞色素P450还原酶（CPR），因此最好以全细胞系统应用于生物合成。     

炎症过程中细胞色素P450酶活性降低及其机制的研究进展

机体在感染或炎症状态下,肝脏细胞色素P450药物代谢酶mRNA表达和蛋白含量显著降低,酶的催化活性降低。这种变化对人体内药物代谢过程乃至相关药物临床治疗安全性具有显著影响。细胞色素P450异构酶活性降低具有不同的变化过程与模式,反映细胞色素P450酶系具有多种活性调节机制。现有研究表明,细胞色素P450酶活性降低主要发生在基因表达环节,由多种炎症细胞因子介导。阐明炎症对细胞色素P450活性的影响有助于明确细胞色素P450酶活性的调控机制,对指导临床安全合理用药具有重要意义。     

中成药对细胞色素P450酶的影响

通过参阅大量近年来国内外有关中成药对药物代谢酶细胞色素P450酶影响的文献,对中成药对细胞色素P450酶的研究的文献进行整理和分析.发现一些中成药对细胞色素P450酶确实存在不同程度的抑制或诱导作用.因此深入研究中成药对细胞色素P450酶活性的影响,既有助于指导中成药在临床上的合理使用以避免因药物相互作用导致的不良反应...     

探讨细胞色素P450酶系和药物的代谢情况

在药物代谢过程中细胞色素P450酶系具有十分重要的作用。此类酶主要存在于肝微粒当中,在生物转化过程承担了十分重要的功能。其活性与药物代谢速率具有密切的关联性,甚至可对药物清除产生直接作用。基于上述特点学术界将其作药物代谢过程中的第一相酶。本文对细胞色素P450酶系和药物的代谢进行了分析并对细胞色素P450酶系的作用进行了综合性阐述,提出了相应的观点,供以参考。     

细胞色素P450靶向抗肿瘤药物研发进展

细胞色素P450酶能催化各种内源性及外源性化合物的代谢,与多种肿瘤的发生发展有着密切关系,因此细胞色素P450酶靶向药物的研制已成为肿瘤治疗的新的研究方向之一,其中肿瘤特异性表达细胞色素P450酶成为研究热点。综述细胞色素P450酶靶向抗肿瘤药物研发进展,并介绍细胞色素P450 2W1及其靶向药物的研究近况。     

复方丹参滴丸对大鼠肝微粒体细胞色素P450含量的影响

目的探讨复方丹参滴丸对大鼠肝微粒体细胞色素P450含量的影响。方法利用细胞色素P450在铁蛋白的铁原子被还原与一氧化碳形成复合物时出现一特异性吸收峰，在波长大约450nm处呈现最大吸收，450-490nm波长的消光系数经精确测定为91nm^-1cm^-1，可定量测定细胞色素P450。结果复方丹参滴丸能诱导大鼠肝微粒体细胞色素P450的活性，且其作用随给药时间的延长而增强。结论复方丹参滴丸虽然作为OCT药品，但在长期服用或配伍应用时亦应当慎重。     

细胞因子与细胞色素P450

随着生物技术的发展,细胞因子的生物工程产品已越来越多地应用于临床治疗。本文通过对近年国外文献分析总结,综述了细胞因子对细胞色素P450的活性及其使RNA的表达影响,从中可以了解细胞因子对细胞色素P450的调节作用,对细胞因子在临床上的合理应用的重要意义。     

加替沙星和环丙沙星对大鼠肝细胞色素P450酶系的影响

目的 研究加替沙星和环丙沙星对大鼠肝微粒体细胞色素P450酶系的影响。方法 加替沙星和环丙沙星400 mg.kg-1灌胃给药大鼠,qd,7天后,用差速离心法制备大鼠肝微粒体,用Lowry法测定蛋白浓度,用分光光度计法检测6种肝微粒体细胞色素P450酶含量及活性,并用单因素方差分析进行统计。结果 加替沙星组的6种细胞色素P450酶的活性与空白对照组相比差异无统计学意义;而环丙沙星能抑制6种细胞色素P450酶中的b5、NADPH-CytC还原酶、氨基比林N-脱甲基酶、红霉素N-脱甲基酶和7-乙氧基香豆素脱烃酶的活性,对CYP450酶系有选择性抑制作用。结论 加替沙星对大鼠肝微粒体CYP450酶系无显著性影响,而环丙沙星对CYP450酶系有选择性抑制作用。     

Cytochrome P450 reductase dependent inhibition of cytochrome P450 2B1 activity: Implications for gene directed enzyme prodrug therapy

Cytochrome P450 (P450) enzymes are often used in suicide gene cancer therapy strategies to convert an inactive prodrug into its therapeutic active metabolites. However, P450 activity is dependent on electrons supplied by cytochrome P450 reductase (CPR). Since endogenous CPR activity may not be sufficient for optimal P450 activity, the overexpression of additional CPR has been considered to be a valuable approach in gene directed enzyme prodrug therapy (GDEPT). We have analysed a set of cell lines for the effects of CPR on cytochrome P450 isoform 2B1 (CYP2B1) activity. CPR transfected human embryonic kidney 293 (HEK293) cells showed both strong CPR expression in Western blot analysis and 30-fold higher activity in cytochrome c assays as compared to parental HEK293 cells. In contrast, resorufin and 4-hydroxy-ifosfamide assays revealed that CYP2B1 activity was up to 10-fold reduced in CPR/CYP2B1 cotransfected HEK293 cells as compared to cells transfected with the CYP2B1 expression plasmid alone. Determination of ifosfamide-mediated effects on cell viability allowed independent confirmation of the reduction in CYP2B1 activity upon CPR coexpression. Inhibition of CYP2B1 activity by CPR was also observed in CYP2B1/CPR transfected or infected pancreatic tumour cell lines Panc-1 and Pan02, the human breast tumour cell line T47D and the murine embryo fibroblast cell line NIH3T3. A CPR mediated increase in CYP2B1 activity was only observed in the human breast tumour cell line Hs578T. Thus, our data reveal an effect of CPR on CYP2B1 activity dependent on the cell type used and therefore demand a careful evaluation of the therapeutic benefit of combining cytochrome P450 and CPR in respective in vivo models in each individual target tissue to be treated.     

The role of renal proximal tubule P450 enzymes in chloroform-induced nephrotoxicity: Utility of renal specific P450 reductase knockout mouse models

The kidney is a primary target for numerous toxic compounds. Cytochrome P450 enzymes (P450) are responsible for the metabolic activation of various chemical compounds, and in the kidney are predominantly expressed in proximal tubules. The aim of this study was to test the hypothesis that renal proximal tubular P450s are critical for nephrotoxicity caused by chemicals such as chloroform. We developed two new mouse models, one having proximal tubule-specific deletion of the cytochrome P450 reductase (Cpr) gene (the enzyme required for all microsomal P450 activities), designated proximal tubule-Cpr-null (PTCN), and the other having proximal tubule-specific rescue of CPR activity with the global suppression of CPR activity in all extra-proximal tubular tissues, designated extra-proximal tubule-Cpr-low (XPT-CL). The PTCN, XPT-CL, Cpr-low (CL), and wild-type (WT) mice were treated with a single oral dose of chloroform at 200 mg/kg. Blood, liver and kidney samples were obtained at 24 h after the treatment. Renal toxicity was assessed by measuring BUN and creatinine levels, and by pathological examination. The blood and tissue levels of chloroform were determined. The severity of toxicity was less in PTCN and CL mice, compared with that of WT and XPT-CL mice. There were no significant differences in chloroform levels in the blood, liver, or kidney, between PTCN and WT mice, or between XPT-CL and CL mice. These findings indicate that local P450-dependent activities play an important role in the nephrotoxicity induced by chloroform. Our results also demonstrate the usefulness of these novel mouse models for studies of chemical-induced kidney toxicity.     

Inhibition of Cytochromes P450: Existing and New Promising Therapeutic Targets

Mammalian cytochromes P450 have been shown to play highly important roles in the metabolism of drugs and xenobiotics as well as in the biosynthesis of a variety of endogenous compounds, many of them displaying hormonal function. The role of P450s as therapeutic targets is still inadequately recognized although several P450 inhibitors became efficient drugs that even reached blockbuster status. Here, we try to give a comprehensive overview on cytochromes P450s, which are already well-established targets – particularly focussing on the treatment of infectious diseases, metabolic disorders and cancer – and on those, which have a high potential to become successful targets. In addition, the design of inhibitors of cytochromes P450 will be discussed.     

Analysis of the Interactions of Cytochrome b5 with Flavocytochrome P450 BM3 and its Domains

Interactions between a soluble form of microsomal cytochrome b₅ (b₅) from Musca domestica (housefly) and Bacillus megaterium flavocytochrome P450 BM3 and its component reductase (CPR), heme (P450) and FAD/NADPH-binding (FAD) domains were analyzed by a combination of steady-state and stopped-flow kinetics methods, and optical spectroscopy techniques. The high affinity binding of b₅ to P450 BM3 induced a low-spin to high-spin transition in the P450 heme iron (K_d for b₅ binding?=?0.44 μM and 0.72 μM for the heme domain and intact flavocytochrome, respectively). The b₅ had modest inhibitory effects on steady-state turnover of P450 BM3 with fatty acids, and the ferrous-carbon monoxy P450 complex was substantially stabilized on binding b₅. Single turnover reduction of b₅ by BM3 using stopped-flow absorption spectroscopy (k_lim?=?116 s^?1) was substantially faster than steady-state reduction of b₅ by P450 BM3 (or its CPR and FAD domains), indicating rate-limiting step(s) other than BM3 flavin-to-b₅ heme electron transfer in the steady-state reaction. Steady-state b₅ reduction by P450 BM3 was considerably accelerated at high ionic strength. Pre-reduction of P450 BM3 by NADPH decreased the k_lim for b₅ reduction ～10-fold, and also resulted in a lag phase in steady-state b₅ reduction that was likely due to BM3 conformational perturbations sensitive to the reduction state of the flavocytochrome. Ferrous b₅ could not reduce the ferric P450 BM3 heme domain under anaerobic conditions, consistent with heme iron reduction potentials of the two proteins. However, rapid oxidation of both hemoproteins occurred on aeration of the ferrous protein mixture (and despite the much slower autoxidation rate of b₅ in isolation), consistent with electron transfer occurring from b₅ to the oxyferrous P450 BM3 in the complex. The results demonstrate that strong interactions occur between a eukaryotic b₅ and a model prokaryotic P450. Binding of b₅ perturbs BM3 heme iron spin-state equilibrium, as is seen in many physiologically relevant b₅ interactions with eukaryotic P450s. These results are consistent with the conservation of structure of P450s (particularly at the heme proximal face) between prokaryotes and eukaryotes, and may point to as yet undiscovered roles for b₅-like proteins in the control of activities of certain prokaryotic P450s.     

Novel Properties of P450s in Streptomyces coelicolor

In the process of investigating the function of the 18 P450s that make up the CYPome in the soil bacterium Streptomyces coelicolor, we have discovered new and novel biochemical features of some of these monooxygenases. This article which is dedicated to Ron Estabrook summarizes these discoveries with emphasis on their novelty. It is concluded from this work that there are many interesting features of P450 enzymes waiting to be discovered. Since there are more than 6500 P450 gene sequences known today, we can expect that many new biochemical aspects of P450s will be discovered as these individual monooxygenases are investigated.     

CYP450氧化还原酶遗传多态性对CYP酶影响的研究进展

细胞色素P450氧化还原酶(Cytochrome P450 0xidoreductase,POR)是将电子从NADPH转运至所有肝微粒体的细胞色素P450氧化酶(Cytochrome P450 monooxygenases,CYP)中的唯一供体.药物、类固醇激素等物质的代谢和转化需要CYP参与.POR基因具有遗传多态性,遗传变异可以改变CYP活性,引起P450氧化还原酶缺陷(P450 0xidoreductase deficiency,PORD)、临床药物代谢和反应差异.本文将从POR的结构功能、基因突变引起的疾病及其对酶活性影响三个方面进行论述,总结近年来POR遗传多态性对CYP酶影响的最新研究进展.     

Significantly reduced cytochrome P450 3A4 expression and activity in liver from humans with diabetes mellitus

BACKGROUND AND PURPOSE

Patients with diabetes mellitus require pharmacotherapy with numerous medications. However, the effect of diabetes on drug biotransformation is not well understood. Our goal was to investigate the effect of diabetes on liver cytochrome P450 3As, the most abundant phase I drug-metabolizing enzymes in humans.

EXPERIMENTAL APPROACH

Human liver microsomal fractions (HLMs) were prepared from diabetic (n = 12) and demographically matched nondiabetic (n = 12) donors, genotyped for CYP3A4*1B and CYP3A5*3 polymorphisms. Cytochrome P450 3A4, 3A5 and 2E1 mRNA expression, protein level and enzymatic activity were compared between the two groups.

KEY RESULTS

Midazolam 1′- or 4-hydroxylation and testosterone 6β-hydroxylation, catalyzed by P450 3A, were markedly reduced in diabetic HLMs, irrespective of genotype. Significantly lower P450 3A4 protein and comparable mRNA levels were observed in diabetic HLMs. In contrast, neither P450 3A5 protein level nor mRNA expression differed significantly between the two groups. Concurrently, we have observed increased P450 2E1 protein level and higher chlorzoxazone 6-hydroxylation activity in diabetic HLMs.

CONCLUSIONS AND IMPLICATIONS

These studies indicate that diabetes is associated with a significant decrease in hepatic P450 3A4 enzymatic activity and protein level. This finding could be clinically relevant for diabetic patients who have additional comorbidities and are receiving multiple medications. To further characterize the effect of diabetes on P450 3A4 activity, a well-controlled clinical study in diabetic patients is warranted.     

黄芩苷对小鼠肝细胞色素P450的选择性诱导

目的　观察黄芩苷对小鼠肝细胞色素P450及其亚家族的影响。方法　用紫外分光光度法分别测定小鼠肝微粒体细胞色素P450与b5含量及氨基比林N-脱甲基酶(ADM)、7-乙氧基香豆素O-脱乙基酶(ECD)、苯并芘羟化酶(AHH)活性。用蛋白印迹杂交技术鉴定细胞色素P450同功酶。结果　黄芩苷可使小鼠肝微粒体细胞色素P450含量显著增加,并使ADM,ECD及AHH 3种酶活力显著增强。对6种P450同功酶的鉴定结果显示,黄芩苷可选择性诱导1A1,2B1及2C11 3种同功酶,对细胞色素b5含量及3A2,2D1和2E1 3种同功酶无诱导作用。结论　黄芩苷对小鼠肝细胞色素P450有选择性诱导作用。     

Terfenadine metabolism of human cytochrome P450 2J2 containing genetic variations (G312R,P351L and P115L)

The human cytochrome P450 2J2 is involved in several metabolic reactions, including the oxidation of important therapeutics and epoxidation of endogenous arachidonic acid. At least ten genetic variations of P450 2J2 have been identified, but their effects on enzymatic activity have not been clearly characterized. Here, we evaluated the functional effects of three genetic variations of P450 2J2 (G312R, P351L, and P115L). Recombinant enzymes of wild-type and three variant P450 2J2 were heterologously expressed in Escherichia coli and purified. P450 expression levels in the wild-type and two variants (P351L and P115L) were 142–231 nmol per liter culture, while the G312R variant showed no holoenzyme peak in the CO-binding spectra. Substrate binding titrations to terfenadine showed that the wild-type and two variants displayed K_d values of 0.90–2.2 μM, indicating tight substrate binding affinities. Steady-state kinetic analysis for t-butyl methyl hydroxylation of terfenadine indicated that two variant enzymes had similar k_cat and K_m values to wild-type P450 2J2. The locations of mutations in three-dimensional structural models indicated that the G312R is located in the I-helix region near the formal active site in P450 2J2 and its amino acid change affected the structural stability of the P450 heme environment.     

Effects of transient overexpression or knockdown of cytochrome P450 reductase on reactive oxygen species generation and hypoxia reoxygenation injury in liver cells

1. Literature data suggest that the electron-donating enzyme, cytochrome P450 reductase (CPR), might act as a source of reactive oxygen species (ROS). However, the role of CPR in pathophysiological conditions associated with oxidative stress is unknown. The aim of the present study was to study the role of CPR in the generation of ROS and cellular injury under basal conditions, and after simulated in vitro ischaemia-reperfusion (IR). 2. Plasmid DNA or siRNA approaches were used to transiently overexpress or knockdown the human CPR gene in rat liver epithelial (WB-F344) or human hepatoblastoma (HepG2) cells, respectively. The generation of ROS and/or cellular injury was then studied under the basal conditions and after simulated IR (4 h of ischaemia plus 30 min of reoxygenation). 3. Under the basal conditions, transient overexpression of CPR protein in WB-F344 cells caused a 90% increase in the CPR activity, which was associated with a 100% increase in the ROS production. In contrast, after simulated IR, a 2.5-fold higher CPR activity did not significantly affect the magnitude of ROS generation or cell death. Similarly, although the knockdown of CPR protein resulted in a significant reduction (～30%) in the CPR activity, the ROS production was not substantially altered after simulated IR in HepG2 cells. 4. Our data suggest that CPR plays a major role in the ROS generation by liver cells under the basal conditions. However, the role of CPR in the ROS generation during simulated in vitro IR injury in these cells is minimal, if any.