Implications of cytochrome P450 genetic polymorphisms on the toxicity of antitumor agents

In the treatment of cancer, a narrow therapeutic window generally exists between toxicity and suboptimal therapy. In addition, interindividual variation in drug metabolism seriously complicates therapy. Genetic polymorphisms in phase 1 and phase 2 enzymes are present in the population and may explain part of the observed interindividual variation in drug pharmacokinetics. For the cytochrome P450 superfamily, information on variant alleles encoding enzymes with decreased activity is rapidly on the increase. The potential of applying pharmacogenetic screening before therapy in the treatment of cancer seems to be greatest for CYP2B6 (cyclophosphamide treatment), CYP2C8 (paclitaxel therapy), and CYP3A5; however, the drugs of interest still need to be identified for this latter enzyme.     

Coimmunoprecipitation of UDP-glucuronosyltransferase isoforms and cytochrome P450 3A4

Coimmunoprecipitation was used to investigate protein-protein interactions between several UDP-glucuronosyltransferase (UGT) isoforms and cytochrome P450 3A4. Solubilized human liver microsomes were incubated with specific antibodies to UGT2B7, UGT1A6, UGT1A1, and CYP3A4, and the immunoprecipitates were run on SDS-polyacrylamide gel electrophoresis. Western blots showed that UGT2B7, UGT1A6, UGT1A1, and CYP3A4 were successfully immunoprecipitated with the specific antibodies for each enzyme. Upon immunoprecipitating UGT2B7, the corresponding immunoblot showed that UGT1A6, UGT1A1, and CYP3A4 were immunoprecipitated. Similar studies found that different UGT isoforms or CYP3A4 immunoprecipitated along with the original immunoprecipitating enzyme. These data suggest that UGT isoforms may form complexes (dimers, tetramers, etc.) with each other in the endoplasmic reticulum and nuclear envelope. In addition, the UGT isoforms tested here may have interacted with CYP3A4 in the endoplasmic reticulum, suggesting that these enzymes may cooperate in the excretion of compounds in a multistep metabolic process.     

In vitro metabolism of eupatilin by multiple cytochrome P450 and UDP-glucuronosyltransferase enzymes

Eupatilin, a pharmacologically active flavone derived from Artemisia plants, is extensively metabolized to eupatilin glucuronide, 4-O-desmethyleupatilin and 4-O-desmethyleupatilin glucuronide in human liver microsomes. This study characterized the human liver cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) enzymes responsible for the metabolism of eupatilin. The specific CYPs responsible for O-demethylation of eupatilin to the major metabolite, 4-O-desmethyleupatilin were identified using a combination of correlation analysis, immuno-inhibition, chemical inhibition in human liver microsomes and metabolism by human cDNA-expressed CYP enzymes. UGT enzymes involved in the eupatilin glucuronidation were identified using pooled human liver microsomes and human cDNA-expressed UGT enzymes. Eupatilin was predominantly metabolized by CYP1A2 and, to a lesser extent, CYP2C8 mediated O-demethylation of eupatilin to 4-O-desmethyleupatilin. Eupatilin glucuronidation was catalysed by UGT1A1, UGT1A3, UGT1A7, UGT1A8, UGT1A9, and UGT1A10.     

In vitro metabolism of eupatilin by multiple cytochrome P450 and UDP-glucuronosyltransferase enzymes

Eupatilin, a pharmacologically active flavone derived from Artemisia plants, is extensively metabolized to eupatilin glucuronide, 4-O-desmethyleupatilin and 4-O-desmethyleupatilin glucuronide in human liver microsomes. This study characterized the human liver cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) enzymes responsible for the metabolism of eupatilin. The specific CYPs responsible for O-demethylation of eupatilin to the major metabolite, 4-O-desmethyleupatilin were identified using a combination of correlation analysis, immuno-inhibition, chemical inhibition in human liver microsomes and metabolism by human cDNA-expressed CYP enzymes. UGT enzymes involved in the eupatilin glucuronidation were identified using pooled human liver microsomes and human cDNA-expressed UGT enzymes. Eupatilin was predominantly metabolized by CYP1A2 and, to a lesser extent, CYP2C8 mediated O-demethylation of eupatilin to 4-O-desmethyleupatilin. Eupatilin glucuronidation was catalysed by UGT1A1, UGT1A3, UGT1A7, UGT1A8, UGT1A9, and UGT1A10.     

细胞色素P4503A5~*3基因多态性与环孢素所致肝损伤相关性的评价

目的系统评价细胞色素P450 3A5*3(CYP3A5*3)基因多态性与环孢素所致的肝损伤的相关性。方法系统检索Pub Med、MedLine、EMbase、Cochrane图书馆、维普数据库、中国知网和万方数据库,查找CYP3A5*3基因多态性与环孢素致患者肝损伤相关性的研究,检索时间自各数据库建库至2016年3月。试验组为环孢素致肝损伤患者,对照组为无肝损伤患者或其他原因致肝损伤患者。用Rev Man 5. 2. 0软件进行Meta分析。结果共纳入病例对照研究3篇(包括英文1篇和中文2篇),患者807名。患者的基因型分布均符合Hardy-Weinberg平衡定律。试验组和对照组CYP3A5*3AA型的分布率分别为21. 70%(87例/401例)和22. 36%(91例/407例),差异有统计学意义(P <0. 01)。试验组和对照组中携带等位基因A的分布率分别为21. 20%和32. 89%,携带等位基因G的分布率分别为78. 80%和67. 11%,差异均无统计学意义(均P> 0. 05)。结论 CYP3A5*3基因多态性与环孢素致患者肝损伤相关,其中携带CYP3A5*3AA基因型的患者服用环孢素所致肝损伤的发生率较低,而此发生率与等位基因A和G的分布无关。     

Genetic polymorphisms of cytochrome P450 enzymes and antidepressant metabolism

INTRODUCTION: The cytochrome P450 (CYP) enzymes are the major enzymes responsible for Phase I reactions in the metabolism of several substances, including antidepressant medications. Thus, it has been hypothesized that variants in the CYP network may influence antidepressant efficacy and safety. Nonetheless, data on this field are still contradictory. The authors aim to give an overview of the published studies analyzing the influence of CYP highly polymorphic loci on antidepressant treatment in order to translate the acquired knowledge to a clinical level. AREAS COVERED: The authors collected and compared experimental works and reviews published from the 1980s to the present and included in the Medline database. The included studies pertain to the effects of CYP gene polymorphisms on antidepressant pharmacokinetic parameters and clinical outcomes (response and drug-related adverse effects), with a focus on applications in clinical practice. The authors focused mainly on in vivo studies in humans (patients or healthy volunteers). EXPERT OPINION: Great variability in antidepressant metabolism among individuals has been demonstrated. Thus, with the current interest in individualized medicine, several genetic tests to detect CYP variants have been produced. They provide a potentially useful way to anticipate some clinical outcomes of antidepressant treatment, although they will only be extensively used in clinical practice if precise and specific treatment options and guidelines based on genetic tests can be provided.     

中国汉族健康人群细胞色素P450 2S1的基因多态性研究

目的探索中国汉族健康人群细胞色素P4502S1(CYP2S1)基因多态性及其单倍型的分布。方法用基质辅助激光解吸电离飞行时间质谱技术(MALDI-TOF-MS)对204例无直接血缘关系的中国汉族健康受试者进行CYP2S1基因多态性检测,并用Phase 2.1软件分析单倍型的分布频率。结果 rs184623、rs338583、rs338598、rs338600在中国汉族健康人群的分布频率分别为21.3%,21.2%,55.5%,23.0%;TTGA、TTTA、CCTA、TTTG单倍型的分布频率分别为37.3%,26.1%,10.2%,8.8%。结论 rs184623、rs338583、rs338598、rs338600在中国汉族健康人群中的分布频率较高,TTGA单倍型分布频率最高。     

Pyrosequencing-based screening for genetic polymorphisms in cytochrome P450 2B6 of potential clinical relevance

OBJECTIVES: Three exonic single nucleotide polymorphisms (SNPs) in the cytochrome P450 2B6 (CYP2B6) gene, 516G>T, 785A>G and 1459C>T, have been described to be associated with functional changes in the CYP2B6 catalytic activity or protein expression. They are therefore of potential clinical importance for drug efficacy and safety of CYP2B6 substrates, in particular of antiretroviral therapy regimes that include efavirenz. Therefore, we aimed at providing genetic screening assays for these three SNPs. METHODS: Simplex Pyrosequencing assays were developed for the selected CYP2B6 SNPs. A total of 273 DNA samples from healthy volunteers of Caucasian ethnicity were genotyped. RESULTS: The presently developed Pyrosequencing assays afford an accurate determination of the three SNPs in the 273 DNA samples. The assays were verified by routine implementation of control samples obtained by conventional sequencing. The frequencies for the variant alleles 516T, 785G and 1459T were 0.22, 0.24 and 0.13, respectively. All genotype frequencies were in agreement with the Hardy-Weinberg equilibrium. CYP2B6 alleles CYP2B6*5A (1459T), CYP2B6*6 (516T/785G) and *7B (516T/785G/1459T) were found at allelic frequencies of 0.12, 0.20 and 0.01. CONCLUSION: The present reliable and quick Pyrosequencing assays afford facilitating future research on the importance of CYP2B6 pharmacogenetics for personalized drug therapy with CYP2B6 substrates.     

Involvement of multiple cytochrome P450 and UDP-glucuronosyltransferase enzymes in the in vitro metabolism of muraglitazar.

Muraglitazar (Pargluva), a dual alpha/gamma peroxisome proliferator-activated receptor activator, has both glucose- and lipid-lowering effects in animal models and in patients with diabetes. The human major primary metabolic pathways of muraglitazar include acylglucuronidation, aliphatic/aryl hydroxylation, and O-demethylation. This study describes the identification of human cytochrome P450 (P450) and UDP-glucuronosyltransferase (UGT) enzymes involved in the in vitro metabolism of muraglitazar. [(14)C]Muraglitazar was metabolized by cDNA-expressed CYP2C8, 2C9, 2C19, 2D6, and 3A4, but to a very minimal extent by CYP1A2, 2A6, 2B6, 2C18, 2E1, and 3A5. Inhibition of the in vitro metabolism of muraglitazar in human liver microsomes, at a clinically efficacious concentration, by chemical inhibitors and monoclonal antibodies further supported involvement of CYP2C8, 2C9, 2C19, 2D6, and 3A4 in its oxidation. A combination of intrinsic clearance (V(max)/K(m)) and relative concentrations of each P450 enzyme in the human liver was used to predict the contribution of CYP2C8, 2C9, 2C19, 2D6, and 3A4 to the formation of each primary oxidative metabolite and to the overall oxidative metabolism of muraglitazar. Glucuronidation of [(14)C]muraglitazar was catalyzed by cDNA-expressed UGT1A1, 1A3, and 1A9, but not by UGT1A6, 1A8, 1A10, 2B4, 2B7, and 2B15. The K(m) values for muraglitazar glucuronidation by the three active UGT enzymes were similar (2-4 muM). In summary, muraglitazar was metabolized by multiple P450 and UGT enzymes to form multiple metabolites. This characteristic predicts a low potential for the alteration of the pharmacokinetic parameters of muraglitazar via polymorphic drug metabolism enzymes responsible for clearance of the compound or by coadministration of drugs that inhibit or induce relevant metabolic enzymes.     

Human drug metabolising cytochrome P450 enzymes: properties and polymorphisms

The cytochrome P450s are responsible for about 75% of phase I dependent drug metabolism and for the metabolism of a huge amount of dietary constituents and endogenous chemicals. The human has 59 active genes, and 6 of those encode important drug metabolising enzymes. About 40% of cytochrome P450 dependent drug metabolism is catalysed by polymorphic enzymes and such drug P450 interactions are frequently seen in adverse drug reaction reports. In this contribution an update of human cytochrome P450 enzymology and pharmacogenetics is given with particular emphasis on CYP1B1, CYP2B6, CYP2E1 and CYP3As.     

Inhibition of human drug-metabolising cytochrome P450 and UDP-glucuronosyltransferase enzyme activities in vitro by uremic toxins

Objective

To investigate the potential inhibitory effects of uremic toxins on the major human hepatic drug-metabolising cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) enzymes in vitro.

Methods

Benzyl alcohol, p-cresol, indoxyl sulfate, hippuric acid and a combination of the four uremic toxins were co-incubated with human liver microsomes and selective probe substrates for the major human drug-metabolising CYP and UGT enzymes. The percentage of enzyme inhibition was calculated by measuring the rates of probe metabolite formation in the absence and presence of the uremic toxins. Kinetics studies were conducted to evaluate the K _i values and mechanism(s) of the inhibition of CYP2E1, CYP3A4, UGT1A1 and UGT1A9 by p-cresol.

Results

The individual uremic toxins inhibited CYP and UGT enzymes to a variable extent. p-Cresol was the most potent individual inhibitor, producing >50 % inhibition of CYP2E1, CYP3A4, UGT1A1, UGT1A9 and UGT2B7 at a concentration of 100 μM. The greatest inhibition was observed with UGT1A9. p-Cresol was shown to be an uncompetitive inhibitor of UGT1A9, with unbound K _i values of 9.1 and 2.5 μM in the absence and presence of bovine serum albumin (BSA), respectively. K _i values for p-cresol inhibition of human liver microsomal CYP2E1, CYP3A4 and UGT1A1 ranged from 43 to 89 μM. A combination of the four uremic toxins produced >50 % decreases in the activities of CYP1A2, CYP2C9, CYP2E1, CYP3A4, UGT1A1, UGT1A9 and UGT2B7.

Conclusions

Uremic toxins may contribute to decreases in drug hepatic clearance in individuals with kidney disease by inhibition of hepatic drug-metabolising enzymes.     

The role of the cytochrome P450 polymorphisms in clopidogrel efficacy and clinical utility

Clopidogrel, an antiplatelet agent, prevents platelet aggregation by inhibiting the adenosine disphosphate (ADP) P2Y12 receptor, which is located on the platelet surface. Although dual antiplatelet therapy appears to be efficient, a considerable number of patients continue to experience adverse cardiovascular events, such as stent thrombosis. The percentage of low response to antiplatelet therapy varies from 4% to 30% of patients depending on the cut-off values. In addition, several factors such as poor absorption, drug-to-drug interactions, inadequate dosing, elevated body mass index, insulin resistance and the nature of acute coronary syndromes have been implicated in low clopidogrel response. Recently, studies have focused on the role of genetic polymorphisms encoding enzymes that participate in clopidogrel hepatic metabolism or receptors involved in intestinal absorption and ADP induced platelet aggregation, which may affect the percentage of platelet inhibition after clopidogrel administration. The management of clopidogrel resistance remains a controversial issue and additional studies are required to evaluate the safety and efficacy of increased loading of clopidogrel or replacement with other new antiplatelet agents such as prasugrel.     

Effect of cytochrome P450 enzyme polymorphisms on pharmacokinetics of venlafaxine

This study examines the relationship between blood concentrations of venlafaxine and its active metabolite, O-desmethyl venlafaxine (ODV), and genetic variants of the cytochrome P450 enzymes CYP2D6 and CYP2C19 in human subjects. Trough blood concentrations were measured at steady state in patients treated with venlafaxine extended release in a clinical practice setting. CYP2D6 and CYP2C19 genotypes were converted to activity scores based on known activity levels of the two alleles comprising a genotype. After adjusting for drug dose and gender effects, higher CYP2D6 and CYP2C19 activity scores were significantly associated with lower venlafaxine concentrations (P < 0.001 for each). Only CYP2D6 was associated with the concentration of ODV (P < 0.001), in which genotypes with more active alleles were associated with higher ODV concentrations. The sum of venlafaxine plus ODV concentration showed the same pattern as venlafaxine concentrations with CYP2D6 and CYP2C19 genotypes with higher activity scores being associated with a lower venlafaxine plus ODV concentration (2D6 P = 0.01; 2C19 P < 0.001). Because allelic variants in both CYP2D6 and CYP2C19 influence the total concentration of the active compounds venlafaxine and ODV, both CYP2D6 and CYP2C19 genotypes should be considered when using pharmacogenomic information for venlafaxine dose alterations.