Identification of a novel variant CYP2C9 allele in Chinese

APF2: an improved ensemble method for pharmacogenomic variant effect prediction

Lack of efficacy or adverse drug response are common phenomena in pharmacological therapy causing considerable morbidity and mortality. It is estimated that 20-30% of this variability in drug response stems from variations in genes encoding drug targets or factors involved in drug disposition. Leveraging such pharmacogenomic information for the preemptive identification of patients who would benefit from dose adjustments or alternative medications thus constitutes an important frontier of precision medicine. Computational methods can be used to predict the functional effects of variant of unknown significance. However, their performance on pharmacogenomic variant data has been lackluster. To overcome this limitation, we previously developed an ensemble classifier, termed APF, specifically designed for pharmacogenomic variant prediction. Here, we aimed to further improve predictions by leveraging recent key advances in the prediction of protein folding based on deep neural networks. Benchmarking of 28 variant effect predictors on 530 pharmacogenetic missense variants revealed that structural predictions using AlphaMissense were most specific, whereas APF exhibited the most balanced performance. We then developed a new tool, APF2, by optimizing algorithm parametrization of the top performing algorithms for pharmacogenomic variations and aggregating their predictions into a unified ensemble score. Importantly, APF2 provides quantitative variant effect estimates that correlate well with experimental results (R2 = 0.91, p = 0.003) and predicts the functional impact of pharmacogenomic variants with higher accuracy than previous methods, particularly for clinically relevant variations with actionable pharmacogenomic guidelines. We furthermore demonstrate better performance (92% accuracy) on an independent test set of 146 variants across 61 pharmacogenes not used for model training or validation. Application of APF2 to population-scale sequencing data from over 800,000 individuals revealed drastic ethnogeographic differences with important implications for pharmacotherapy. We thus think that APF2 holds the potential to improve the translation of genetic information into pharmacogenetic recommendations, thereby facilitating the use of Next-Generation Sequencing data for stratified medicine.

Optimisation of warfarin-dosing algorithms for Han Chinese patients with CYP2C9*13 variants

BACKGROUND

Existing pharmacogenetic algorithms cannot fully explain warfarin dose variability in all patients. CYP2C9*13 is an important allelic variant in the Han Chinese population. However, adjustment of warfarin dosing in CYP2C9*13 variant carriers remains unclear. To the best of our knowledge, this study is the first to assess the effects of adjusting warfarin dosages in Han Chinese patients harbouring CYP2C9*13 variants.

METHODS

In total, 971 warfarin-treated Han Chinese patients with atrial fibrillation were enrolled in this study. Clinical data were collected, and CYP2C9*2, *3, *13 and VKORC1-1639 G > A variants were genotyped. We quantitatively analysed the effect of CYP2C9*13 on warfarin maintenance dose and provided multiplicative adjustments for CYP2C9*13 using validated pharmacogenetic algorithms.

RESULTS

Approximately 0.6% of the Han Chinese population carried CYP2C9*13 variant, and the genotype frequency was between those of CYP2C9*2 and CYP2C9*3. The warfarin maintenance doses were significantly reduced in CYP2C9*13 carriers. When CYP2C9*13 variants were not considered, the pharmacogenetic algorithms overestimated warfarin maintenance doses by 1.03-1.16 mg/d on average. The actual warfarin dose in CYP2C9*13 variant carriers was approximately 40% lower than the algorithm-predicted dose. Adjusting the warfarin-dosing algorithm according to the CYP2C9*13 allele could reduce the dose prediction error.

CONCLUSION

Our study showed that the algorithm-predicted doses should be lowered for CYP2C9*13 carriers. Inclusion of the CYP2C9*13 variant in the warfarin-dosing algorithm tends to predict the warfarin maintenance dose more accurately and improves the efficacy and safety of warfarin administration in Han Chinese patients.

The impact of gene polymorphism and hepatic insufficiency on voriconazole dose adjustment in invasive fungal infection individuals

Voriconazole (VRZ) is a broad-spectrum antifungal medication widely used to treat invasive fungal infections (IFI). The administration dosage and blood concentration of VRZ are influenced by various factors, posing challenges for standardization and individualization of dose adjustments. On the one hand, VRZ is primarily metabolized by the liver, predominantly mediated by the cytochrome P450 (CYP) 2C19 enzyme. The genetic polymorphism of CYP2C19 significantly impacts the blood concentration of VRZ, particularly the trough concentration (Ctrough), thereby influencing the drug's efficacy and potentially causing adverse drug reactions (ADRs). Recent research has demonstrated that pharmacogenomics-based VRZ dose adjustments offer more accurate and individualized treatment strategies for individuals with hepatic insufficiency, with the possibility to enhance therapeutic outcomes and reduce ADRs. On the other hand, the security, pharmacokinetics, and dosing of VRZ in individuals with hepatic insufficiency remain unclear, making it challenging to attain optimal Ctrough in individuals with both hepatic insufficiency and IFI, resulting in suboptimal drug efficacy and severe ADRs. Therefore, when using VRZ to treat IFI, drug dosage adjustment based on individuals' genotypes and hepatic function is necessary. This review summarizes the research progress on the impact of genetic polymorphisms and hepatic insufficiency on VRZ dosage in IFI individuals, compares current international guidelines, elucidates the current application status of VRZ in individuals with hepatic insufficiency, and discusses the influence of CYP2C19, CYP3A4, CYP2C9, and ABCB1 genetic polymorphisms on VRZ dose adjustments and Ctrough at the pharmacogenomic level. Additionally, a comprehensive summary and analysis of existing studies' recommendations on VRZ dose adjustments based on CYP2C19 genetic polymorphisms and hepatic insufficiency are provided, offering a more comprehensive reference for dose selection and adjustments of VRZ in this patient population.

Clinical significance of the series of CYP2C9*non3 variants, an unignorable predictor of warfarin sensitivity in Chinese population

Backgrounds

Gene polymorphisms are critical for variations in warfarin dose. To date, more than 70 CYP2C9 alleles have been identified. This study was designed to clarify the clinical significance of CYP2C9*non-3 variants to warfarin sensitivity in Chinese Han patients.

Methods

The entire CYP2C9 gene region was sequenced in 1,993 individuals, and clinical data and VKORC1 genotypes were collected from 986 patients with atrial fibrillation treated with warfarin. The SKAT-O method was used to analyze the effects of CYP2C9*non-3 variants on warfarin sensitivity.

Results

A total of 20 CYP2C9 variants were identified, of which four were novel. Carriers with CYP2C9*non-3 variants may have lower warfarin dose requirements, and similar to CYP2C9*3, CYP2C9*non-3 variants are clearly relevant to warfarin-sensitive and highly sensitive responders.

Conclusion

Our results showed that, besides CYP2C9*3, the series of CYP2C9*non-3 variants is an unignorable predictor for warfarin sensitivity in Chinese population. From a safety consideration, people carried such variants may need a preferred choice of NOACs when they started anticoagulation therapy.

Effects of CYP2C19, CYP2C9 and CYP3A4 gene polymorphisms on plasma voriconazole levels in Chinese pediatric patients

OBJECTIVES

Voriconazole is the most commonly used antifungal agent in clinical application. Previous studies suggested that voriconazole was extensively metabolized by CYP450 enzyme system, including CYP2C19, CYP2C9 and CYP3A4, which contributed to the individual variability of the pharmacokinetic process of voriconazole. This study aimed to investigate the effects of CYP2C19, CYP2C9 and CYP3A4 gene polymorphisms on plasma voriconazole concentrations in Chinese pediatric patients.

METHODS

This study prospectively evaluated pediatric patients administrating voriconazole for the treatment or prophylaxis of invasive fungal infections from October 2018 to July 2020. Seven single-nucleotide polymorphisms in CYP2C19 (CYP2C19*2, CYP2C19*3, and CYP2C19*17), CYP2C9 (CYP2C9*3, CYP2C9*13) and CYP3A4 (CYP3A4*22, rs4646437) were detected by real-time fluorescent PCR with TaqMan probes. The voriconazole trough plasma concentration was determined by UPLC-MS/MS.

RESULTS

A total of 68 pediatric patients were enrolled in this study. Our results showed that voriconazole plasma concentrations of patients with CYP2C19*2 or CYP2C19*3 allele were significantly higher than that with wild-type carriers (P < 0.0001, P = 0.004, respectively). However, CYP2C9*3 and CYP3A4 rs4646437 were not significantly associated with voriconazole plasma levels. The CYP2C19*17, CYP2C9*13 and CYP3A4*22 alleles were not observed in our study. Additionally, multiple linear regression analysis indicated that CYP2C19*2 and CYP2C19*3 alleles remained predictors of voriconazole plasma concentration (r2 = 0.428; P < 0.0001). For CYP2C19 metabolizer phenotype, trough concentration of voriconazole was significantly lower in NM group compared with IM (P < 0.0001) and PM (P = 0.004) groups.

CONCLUSION

Voriconazole plasma levels in pediatric patients are mainly affected by CYP2C19 gene polymorphisms.

Effects of CYP2C9*3 and *13 alleles on the pharmacokinetics and pharmacodynamics of glipizide in healthy Korean subjects

Glipizide is a second-generation sulfonylurea antidiabetic drug. It is principally metabolized to inactive metabolites by genetically polymorphic CYP2C9 enzyme. In this study, we investigated the effects of CYP2C9*3 and *13 variant alleles on the pharmacokinetics and pharmacodynamics of glipizide. Twenty-four healthy Korean volunteers (11 subjects with CYP2C9*1/*1, 8 subjects with CYP2C9*1/*3, and 5 subjects with CYP2C9*1/*13) were recruited for this study. They were administered a single oral dose of glipizide 5 mg. The plasma concentration of glipizide was quantified for pharmacokinetic analysis and plasma glucose and insulin concentrations were measured as pharmacodynamic parameters. The results represented that CYP2C9*3 and *13 alleles significantly affected the pharmacokinetics of glipizide. In subjects with CYP2C9*1/*3 and CYP2C9*1/*13 genotypes, the mean AUC_0-∞ were increased by 44.8% and 58.2%, respectively (both P < 0.001), compared to those of subjects with CYP2C9*1/*1 genotype, while effects of glipizide on plasma glucose and insulin levels were not significantly different between CYP2C9 genotype groups. In conclusion, individuals carrying the defective CYP2C9*3 and CYP2C9*13 alleles have markedly elevated plasma concentrations of glipizide compared with CYP2C9*1/*1 wild-type.

Effect of CYP2C9 genetic polymorphism and breviscapine on losartan pharmacokinetics in healthy subjects

1. Breviscapine was an active ingredient of flavonoid glycosides. Our present study was conducted to evaluate the impact of breviscapine on the pharmacokinetics of losartan and its active metabolite E-3174, and that relationship with the gene polymorphism of CYP2C9 in healthy Chinese volunteers, to provide a basis for clinical rational drug use.2. The genotypes of 217 healthy Chinese subjects were determined using PCR-RFLP. Twelve healthy subjects were selected and were known CYP2C9 genotypes (six CYP2C9*1/*3 and six CYP2C9*1/*1) in a two-phase randomised crossover design study. These subjects were given daily doses of 120 mg (40 mg, three times a day) of breviscapine or a placebo for 14 days, followed by 50 mg losartan on day 15.3. Compared with individuals carrying the CYP2C9*1/*1 genotype, the CYP2C9*1/*3 genotype showed an increase in the AUC_(0-36) (833.6 ± 379.8 ng h ml^-1 vs. 526.1 ± 140.1 ng h ml^-1, p < 0.05) and a decrease in the MR (the metabolic ratio of losartan, AUC_E-3174/AUC_losartan) (2.67 ± 1.40 vs. 4.56 ± 0.83, p < 0.05) of losartan during the placebo treatment phase. Individuals with genotype CYP2C9*1/*3 showed a significant increase in AUC_(0-36) (2335 ± 851.8 ng h ml^-1 vs. 1927 ± 949.5 ng h ml^-1, p < 0.05) and AUC_(0-∞) (2363 ± 875.6 ng h ml^-1 vs. 1966 ± 966.1 ng h ml^-1, p < 0.05) of E-3174 after breviscapine treatment compared to the placebo group.4. In healthy subjects, breviscapine had no significant effect on the pharmacokinetics of losartan. The activity of CYP2C9 enzyme to losartan metabolism was more significant in subjects with CYP2C9*1/*3 than those with CYP2C9*1/*1 genotype.

Functional Measurement of CYP2C9 and CYP3A4 Allelic Polymorphism on Sildenafil Metabolism

Aim

We aimed to systematically examine the effects of enzymatic activity of 38 human CYP2C9 alleles and 21 human CYP3A4 alleles, including wild-type CYP2C9.1 and CYP3A4.1, which contain the 24 CYP2C9 novel alleles (*36–*60) and 6 CYP3A4 novel alleles (*28–*34) newly found in the Chinese population, on sildenafil metabolism through in vitro experiment.

Methods

The recombinant cytochrome P450 alleles protein of CYP2C9 and CYP3A4 expressed in insect baculovirus expression system were reacted with 10–500 µM sildenafil for 30 minutes at 37°C, and the reaction was terminated by cooling to −80°C immediately. Next, we used ultra-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) detection system to detect sildenafil and its active metabolite N-desmethyl sildenafil.

Results

The intrinsic clearance (Vmax/Km) values of most CYP2C9 variants were significantly altered when compared with the wild-type CYP2C9*1, with most of these variants exhibiting either reduced Vmax and/or increased Km values. Four alleles (CYP2C9*11, *14, *31, *49) exhibited no markedly decreased relative clearance (1-fold). The relative clearance of the remaining thirty-three variants exhibited decrease in different levels, ranging from 1.81% to 88.42%. For the CYP3A4 metabolic pathway, when compared with the wild-type CYP3A4*1, the relative clearance values of four variants (CYP3A4*3, *10, *14 and *I335T) showed significantly higher relative clearance (130.7–134.9%), while five variants (CYP3A4*2, *5, *24, *L22V and *F113I) exhibited sharply reduced relative clearance values (1.80–74.25%), and the remaining nine allelic variants showed no statistical difference. In addition, the kinetic parameters of two CYP3A4 variants (CYP3A4*17 and CYP3A4*30) could not be detected, due to the defect of the CYP3A4 gene.

Conclusion

These findings were the first evaluation of all these infrequent CYP2C9 and CYP3A4 alleles for sildenafil metabolism; when treating people who carry these CYP2C9 and CYP3A4 variants, there should be more focus on the relation of dose intensity, side effects and therapeutic efficacy when administering sildenafil. The study will provide fundamental data on effect of CYP2C9 and CYP3A4 allelic variation on sildenafil metabolism for further clinical research.

Effects of rare CYP2C9 alleles on stable warfarin doses in Chinese Han patients with atrial fibrillation

Aim: Gene polymorphisms are critical in warfarin dosing variation. Here, the role of rare CYP2C9 alleles on warfarin doses in Chinese Han patients was investigated. Methods: A retrospective study recruited 681 warfarin treated atrial fibrillation patients. The genetic and clinical data were collected. Dose-related variables were selected by univariate analyses and the warfarin-dosing algorithm was derived by multivariate regression analysis. Results: Three rare CYP2C9 alleles (CYP2C9*13, *16 and *60) were associated with lower stable doses. Inclusion of the rare CYP2C9 alleles in the prediction model added an extra 3.7% warfarin dose predictive power. Conclusion: CYP2C9*13, *16 and *60 was associated with lower stable warfarin doses in Chinese patients. The algorithm including rare CYP2C9 alleles tends to more accurately predict stable warfarin doses.

Functional Characterization of Pharmcogenetic Variants of Human Cytochrome P450 2C9 in Korean Populations

Human cytochrome P450 2C9 is a highly polymorphic enzyme that is required for drug and xenobiotic metabolism. Here, we studied eleven P450 2C9 genetic variants—including three novel variants F69S, L310V, and Q324X—that were clinically identified in Korean patients. P450 2C9 variant enzymes were expressed in Escherichia coli and their bicistronic membrane fractions were prepared The CO-binding spectra were obtained for nine enzyme variants, indicating P450 holoenzymes, but not for the M02 (L90P) variant. The M11 (Q324X) variant could not be expressed due to an early nonsense mutation. LC-MS/MS analysis was performed to measure the catalytic activities of the P450 2C9 variants, using diclofenac as a substrate. Steady-state kinetic analysis revealed that the catalytic efficiency of all nine P450 2C9 variants was lower than that of the wild type P450 2C9 enzyme. The M05 (R150L) and M06 (P279T) variants showed high k_cat values; however, their K_m values were also high. As the M01 (F69S), M03 (R124Q), M04 (R125H), M08 (I359L), M09 (I359T), and M10 (A477T) variants exhibited higher K_m and lower k_cat values than that of the wild type enzyme, their catalytic efficiency decreased by approximately 50-fold compared to the wild type enzyme. Furthermore, the novel variant M07 (L310V) showed lower k_cat and K_m values than the wild type enzyme, which resulted in its decreased (80%) catalytic efficiency. The X-ray crystal structure of P450 2C9 revealed the presence of mutations in the residues surrounding the substrate-binding cavity. Functional characterization of these genetic variants can help understand the pharmacogenetic outcomes.

Effects of CYP2C9 genetic polymorphisms on the pharmacokinetics of celecoxib and its carboxylic acid metabolite

Celecoxib, a selective cyclooxygenase (COX)-2 inhibitor, is used for the treatment of rheumatoid arthritis and osteoarthritis. The predominant hepatic metabolism of celecoxib to celecoxib carboxylic acid (CCA) is mediated mainly by CYP2C9. We investigated the effects of the major CYP2C9 genetic variants in Asian populations, CYP2C9*3 and CYP2C9*13, on the pharmacokinetics of celecoxib and its carboxylic acid metabolite in healthy Korean subjects. A single 200-mg oral dose of celecoxib was given to 52 Korean subjects with different CYP2C9 genotypes: CYP2C9EM (n = 26; CYP2C9*1/*1), CYP2C9IM (n = 24; CYP2C9*1/*3 and *1/*13), and CYP2C9PM (n = 2; CYP2C9*3/*3). Celecoxib and CCA concentrations in plasma samples collected up to 48 or 96 h after drug intake were determined by HPLC-MS/MS. The mean area under the plasma concentration-time curve (AUC_0-∞) of celecoxib was increased 1.63-fold (P < 0.001), and the apparent oral clearance (CL/F) of celecoxib was decreased by 39.6% in the CYP2C9IM genotype group compared with that of CYP2C9EM (P < 0.001). The overall pharmacokinetic parameters for celecoxib in CYP2C9*1/*13 subjects were similar to those in CYP2C9*1/*3 subjects. Two subjects with CYP2C9PM genotype both showed markedly higher AUC_0-∞, prolonged half-life, and lower CL/F for celecoxib than did subjects with CYP2C9EM and IM genotypes. CYP2C9*3 and CYP2C9*13 variant alleles significantly affected the plasma concentration of celecoxib.

Effects of CYP2C9 genetic polymorphisms on the pharmacokinetics of zafirlukast

Zafirlukast, a cysteinyl leukotriene receptor antagonist, is indicated for the treatment of patients with mild to moderate asthma. Zafirlukast is metabolized mainly by CYP3A4 and CYP2C9. We investigated the effects of the major CYP2C9 variant alleles in Asian populations, CYP2C9*3 and CYP2C9*13, on the pharmacokinetics of zafirlukast in healthy Korean subjects. A single 20-mg oral dose of zafirlukast was given to 23 Korean male subjects divided into two genotype groups according to CYP2C9 genotypes, CYP2C9EM (n = 11; CYP2C9*1/*1) and CYP2C9IM (n = 12; 9 and 3 carriers of CYP2C9*1/*3 and *1/*13, respectively). Zafirlukast concentrations were determined using a validated HPLC-MS/MS analytical method in plasma samples collected after the drug intake. Compared with the CYP2C9EM group, the Cmax and AUCinf of zafirlukast in the CYP2C9IM group were 1.44- and 1.70-fold higher, respectively (p < 0.01 and p < 0.0001). The CL/F of zafirlukast was 42.8 % lower in the CYP2C9IM group compared with the CYP2C9EM group (p < 0.001). Slightly higher Cmax and AUC, and lower CL/F of zafirlukast were observed in subjects with the CYP2C9*1/*13 genotype compared with the CYP2C9*1/*3 genotype subjects. CYP2C9*3 and CYP2C9*13 alleles significantly affected the plasma concentrations of zafirlukast.

In vitro metabolism of phenytoin in 36 CYP2C9 variants found in the Chinese population

Cytochrome P450 2C9 (CYP2C9) is an important member of the cytochrome P450 enzyme superfamily, with 57 CYP2C9 allelic variants being previously reported. Recently, we identified 22 novel alleles (*36 -*56 and N418T) in the Han Chinese population. This study aims to assess the catalytic activities of wild-type (CYP2C9*1) and 36 CYP2C9 allelic variants found in the Chinese population toward phenytoin (PHT) in vitro. Insect microsomes expressing CYP2C9*1 and 36 CYP2C9 variants were incubated with 1-200 μM phenytoin for 30 min at 37 °C. Then, these products were extracted and the signal detection was performed by HPLC-MS/MS. The intrinsic clearance (Vmax/Km) values of all variants, with the exception of CYP2C9*2, CYP2C9*11, CYP2C9*23, CYP2C9*29, CYP2C9*34, CYP2C9*38, CYP2C9*44, CYP2C9*46 and CYP2C9*48, were significantly different from CYP2C9*1. CYP2C9*27, *40, *41, *47, *49, *51, *53, *54, *56 and N418T variant exhibited markedly larger values than CYP2C9*1 (>152.8%), whereas 17 variants exhibited smaller values (from 48.6% to 99.9%) due to larger Km and/or smaller Vmax values than CYP2C9*1. The findings suggest that more attention should be paid on subjects carrying these infrequent CYP2C9 alleles when administering phenytoin in clinic.

Genetic Polymorphism of Cytochrome p450 (2C9) Enzyme in Iranian Baluch Ethnic Group

The aim of the present study is to assess and compare the frequencies of the cytochrome P450 CYP2C9 variations in the Baluch ethnic group (n=110) with other ethnic groups. The allele frequencies of CYP2C9*1, CYP2C9*2 and CYP2C9*3 were 80.90%, 11.82% and 7.27%, respectively. 70.90%, 11.82%, 8.18%, 4.55%, 2.73% and 1.82% of subjects were with CYP2C9*1/*1, CYP2C9*1/*2, CYP2C9*1/*3, CYP2C9*2/*2, CYP2C9*2/*3 and CYP2C9*3/*3 genotypes, respectively. Different mutants may effect on prediction of drug dose requirements in different ethnic groups. Thus, CYP2C9 variants to be determined for findings high risk groups use optimal dosage of drugs metabolized by this polymorphic enzyme.

Influence of genetic polymorphisms on the pharmacokinetics of celecoxib and its two main metabolites in healthy Chinese subjects

Celecoxib is a selective cyclooxygenase-2 inhibitor used extensively for the treatment of rheumatism and osteoarthritis. The aim of this study was to evaluate the influence of the genetic polymorphisms of CYP2C9, CYP2D6 and CYP3A4 on the pharmacokinetics (PK) of celecoxib and its two main metabolites, hydroxyl-celecoxib and carboxy-celecoxib, in healthy Chinese subjects, based on a bioequivalence study of celecoxib. This study was an open-label, two-period, crossover study. 52 healthy Chinese male subjects were recruited and were genotyped for CYP2C9*3, CYP2C9*13, CYP2D6*10 and CYP3A4*18 by using polymerase chain reactions (PCR). They were randomly divided into two groups and each group received either 200mg test formulation followed by reference formulation or vice versa with a one-week washout period. Safety and tolerability were monitored throughout the study and no severe adverse events were observed. Genotyping using PCR revealed that none of the subjects carried the CYP3A4*18 and CYP2C9*13. Therefore, the influence of the CYP2C9*3 and CYP2D6*10 on the PK of celecoxib and its metabolites in Chinese was studied. Compared with CYP2C9*1/*1 group, pharmacokinetic parameters of celecoxib such as AUC0-48 and Cmax was increased by 90.6% and 45.8%, the t1/2 was extended by 21.8% and the CL/F was decreased by 51.1% in CYP2C9*1/*3 group. In terms of hydroxy-celecoxib, compared with CYP2C9*1/*1 group, the Cmax was decreased by 17.2%, the t1/2 prolonged 42.1% in CYP2C9*1/*3 group. In terms of carboxy-celecoxib, the AUC0-48 was increased by 25.2%, the t1/2 prolonged 16.1% and the CL/F was decreased by 21.2% in CYP2C9*1/*3 group. Except for the t1/2 of hydroxy-celecoxib, no statistically significant difference was observed in other pharmacokinetic parameters of hydroxy-celecoxib and carboxy-celecoxib between the two CYP2C9 genotypic groups. This study revealed that there was no significant influence of CYP2D6*10 on the metabolism of celecoxib, and the expression of CYP2C9*3 led to increased drug exposure and slowed drug disposition in healthy Chinese male subjects.

In vitro and in vivo characterization of 13 CYP2C9 allelic variants found in Chinese Han population

Our previous study detected totally 35 CYP2C9 allelic variants in 2127 Chinese subjects, of whom 21 novel alleles were reported for the first time in Chinese populations. The aim of the present study was to characterize the 13 CYP2C9 allelic variants both in vitro and in vivo. Different types of CYP2C9 variants were highly expressed in COS-7 cells, and 50 μM tolbutamide was added as the probing substrate to evaluate their metabolic abilities in vitro. Subsequently, the concentrations of tolbutamide and its metabolite in the plasma and urine within individuals with different types of genotypes were determined by HPLC to evaluate the catalytic activity of the 13 mutant CYP2C9 proteins in vivo. Our results showed that compared with *1/*1 wild-type subjects, subjects with *1/*40 genotype showed increased oral clearance (CL/F), whereas individuals with *1/*3, *1/*13, *3/*3, *3/*13, *1/*16, *1/*19, *1/*34, *1/*42, *1/*45, *1/*46, and *1/*48 genotype exhibited significantly decreased CL/F, and those with *1/*27, *1/*29, *1/*40, and *1/*41 genotype presented similar CL/F value. When expressed in COS-7 cells, the CYP2C9 variants showed similar pattern to the results in clinical study. The study suggests that, besides two typical defective alleles, *3 and *13, seven CYP2C9 allelic variants (*16, *19, *34, *42, *45, *46, and *48) cause defective effects on the enzymatic activities both in vitro and in vivo. In clinic, patients with these defective alleles should be paid close attention to.

The role of CYP2C9 genetic polymorphism in carvedilol O-desmethylation in vitro

We aimed at investigating the role of CYP2C9 in carvedilol O-desmethylation and identifying the effect of 35 CYP2C9 allelic variants we found in Chinese Han population on the in vitro metabolism of carvedilol. Recombinant CYP2C9 and CYP2D6 microsomes of the wild type were used to test and verify the enzymes involved in carvedilol O-desmethylation. Recombinant CYP2C9 microsomes of distinguished genotypes were used to characterize the corresponding enzyme activity toward carvedilol. 2-100 μM carvedilol was incubated for 30 min at 37 °C. The products were detected using high-performance liquid chromatography. CYP2C9 plays a certain role in carvedilol metabolism. Compared with wild-type CYP2C9*1, the intrinsic clearance (V max/K m) values of all variants toward carvedilol O-desmethylation were significantly altered. The variants exhibited significantly decreased values (from 30 to 99.8 %) due to increased K m and/or decreased V max values. We conclude that recombinant system could be used to investigate the enzymes involved in drug metabolism and these findings complement the database where CYP2C9 polymorphism interacts with biotransformation of exogenous substances like drugs and toxins.

In vitro assessment of 36 CYP2C9 allelic isoforms found in the Chinese population on the metabolism of glimepiride

Of the 57 reported CYP2C9 alleles, to date, 36 of them have been identified in the Chinese population. The aim of this study was to assess the catalytic characteristics of these allelic isoforms and their effects on the metabolism of glimepiride in vitro. Baculovirus-mediated expressing system was used to highly express wild-type and the 35 CYP2C9 allelic variants in insect cell microsomes. Then, the enzymatic characteristics of each variant were evaluated using glimepiride as the substrate. Reactions were performed at 37°C with the insect microsomes and 0.125-10 μM glimepiride for 40 min. After termination, the products were extracted and used for signal collection by LC-MS/MS. Of the 36 tested CYP2C9 allelic isoforms, only four variants (CYP2C9.40, CYP2C9.47, CYP2C9.51 and CYP2C9.54) exhibited similar relative clearance values to that of wild-type CYP2C9.1. In addition, one variant (CYP2C9.36) showed a higher intrinsic clearance value than the wild-type protein, while the remaining 30 CYP2C9 allelic isoforms exhibited significantly decreased clearance values (from 0.1% to 87.2%) compared to CYP2C9.1. This study provided the most comprehensive data on the enzymatic activities of all reported CYP2C9 variants in the Chinese population with regard to the commonly used antidiabetic drug, glimepiride. Our results indicate that most of the tested rare alleles significantly decrease the catalytic activity of CYP2C9 variants towards glimepiride hydroxylation in vitro.

In vitro functional characterization of 37 CYP2C9 allelic isoforms found in Chinese Han population

AIM

Cytochrome P450 2C9 (CYP2C9) is a polymorphic enzyme that is responsible for the metabolism of approximately 15% of clinically important drugs. The aim of this study was to assess the catalytic characteristics of 37 CYP2C9 allelic isoforms found in Chinese Han population on the metabolism of tolbutamide in vitro.

METHODS

The wild-type and 36 CYP2C9 variants were expressed in sf21 insect cells using a baculovirus-mediated expression system. Then the insect microsomes were prepared for assessing the metabolic characteristics of each variant toward the CYP2C9-specific drug substrate tolbutamide.

RESULTS

Of 36 allelic variants tested, the intrinsic clearance values of 2 allelic isoforms (CYP2C9.36 and CYP2C9.51) were much higher than the wild-type CYP2C9.1 protein, 3 allelic isoforms (CYP2C9.11, CYP2C9.56 and N418T) exhibited similar intrinsic clearance values as the wild-type enzyme, whereas the other 31 variants showed significantly reduced intrinsic clearance values, ranging from 0.08% to 66.88%, for tolbutamide.

CONCLUSION

Our study provides the most comprehensive data concerning the enzymatic activity of the CYP2C9 variants that are present in the Chinese Han population, and our data suggest that most of the carriers of these alleles might be paid more attention when using CYP2C9 mediated drugs clinically.

Advances in molecular modeling of human cytochrome P450 polymorphism

Cytochrome P450 (CYP) is a supergene family of metabolizing enzymes involved in the phase I metabolism of drugs and endogenous compounds. CYP oxidation often leads to inactive drug metabolites or to highly toxic or carcinogenic metabolites involved in adverse drug reactions (ADR). During the last decade, the impact of CYP polymorphism in various drug responses and ADR has been demonstrated. Of the drugs involved in ADR, 56% are metabolized by polymorphic phase I metabolizing enzymes, 86% among them being CYP. Here, we review the major CYP polymorphic forms, their impact for drug response and current advances in molecular modeling of CYP polymorphism. We focus on recent studies exploring CYP polymorphism performed by the use of sequence-based and/or protein-structure-based computational approaches. The importance of understanding the molecular mechanisms related to CYP polymorphism and drug response at the atomic level is outlined.

Optimal dosing of warfarin and other coumarin anticoagulants: the role of genetic polymorphisms

Coumarin anticoagulants, which include warfarin, acenocoumarol and phenprocoumon, are among the most widely prescribed drugs worldwide. There is now a large body of published data showing that genotype for certain common polymorphisms in the genes encoding the target vitamin K epoxide reductase (G-1639A/C1173T) and the main metabolizing enzyme CYP2C9 (CYP2C9*2 and *3 alleles) are important determinants of the individual coumarin anticoagulant dose requirement. Additional less common polymorphisms in these genes together with polymorphisms in other genes relevant to blood coagulation such as the cytochrome P450 CYP4F2, gamma-glutamyl carboxylase, calumenin and cytochrome P450 oxidoreductase may also be significant predictors of dose, especially in ethnic groups such as Africans where there have been fewer genetic studies compared with European populations. Using relevant genotypes to calculate starting dose may improve safety during the initiation period. Various algorithms for dose calculation, which also take patient age and other characteristics into consideration, have been developed for all three widely used coumarin anticoagulants and are now being tested in ongoing large randomised clinical trials. One recently completed study has provided encouraging results suggesting that calculation of warfarin dose on the basis of individual patient genotype leads to few adverse events and a higher proportion of time within the therapeutic coagulation rate window, but these findings still need confirmation.

Distribution of CYP2C9*13 allele in the Chinese Han and the long-range haplotype containing CYP2C9*13 and CYP2C19*2

Cytochrome P450 2C9 (CYP2C9) and CYP2C19, located in tandem on chromosome 10q23-24, are known as genetically polymorphic. CYP2C9*13 is an important CYP2C9 variant in Asian populations, and is correlated with the reduced plasma clearance of some clinically important drugs. In this research, the allele frequency of CYP2C9*13 was determined to be 0.42% (95% CI of 0.17% to 0.86%) in 839 Chinese Han, male subjects. All detected subjects with CYP2C9*13 carry the CYP2C19*2 allele, too. Sequencing results infer the CYP2C9*13 haplotype, which contains eight linked SNPs, originates from the CYP2C9*1B haplotype group. CYP2C9*1B has been reported to be linked with CYP2C19*2. These indicate a long-range haplotype containing the CYP2C9*13 and CYP2C19*2 mutation, which means most CYP2C9*13 carriers will carry the CYP2C19*2 allele and the six SNPs of the CYP2C9*1B haplotype group, and may have more reduced intrinsic clearance of drugs such as phenytoin, tolbutamide and chlorpropamide that are metabolized by both CYP2C9 and CYP2C19.

Distal effect of amino acid substitutions in CYP2C9 polymorphic variants causes differences in interatomic interactions against (S)-warfarin

Cytochrome P450 2C9 (CYP2C9) is crucial in excretion of commonly prescribed drugs. However, changes in metabolic activity caused by CYP2C9 polymorphisms inevitably result in adverse drug effects. CYP2C9*2 and *3 are prevalent in Caucasian populations whereas CYP2C9*13 is remarkable in Asian populations. Single amino acid substitutions caused by these mutations are located outside catalytic cavity but affect kinetic activities of mutants compared to wild-type enzyme. To relate distal effects of these mutations and defective drug metabolisms, simulations of CYP2C9 binding to anti-coagulant (S)-warfarin were performed as a system model. Representative (S)-warfarin-bound forms of wild-type and mutants were sorted and assessed through knowledge-based scoring function. Interatomic interactions towards (S)-warfarin were predicted to be less favorable in mutant structures in correlation with larger distance between hydroxylation site of (S)-warfarin and reactive oxyferryl heme than wild-type structure. Using computational approach could delineate complication of CYP polymorphism in management of drug therapy.

Impact of genetic polymorphisms in CYP2C9 and CYP2C19 on the pharmacokinetics of clinically used drugs

Human cytochrome P450 (CYP) is a superfamily of hemoproteins which oxidize a number of endogenous compounds and xenobiotics. The human CYP2C subfamily consists of four members: CYP2C8, CYP2C9, CYP2C18 and CYP2C19. CYP2C9 and CYP2C19 are important drug-metabolizing enzymes and together metabolize approximately 20% of therapeutically used drugs. Forty-two allelic variants for CYP2C9 and 34 for CYP2C19 have been reported. The frequencies of these variants show marked inter-ethnic variation. The functional consequences of genetic polymorphisms have been examined, and many studies have shown the clinical importance of these polymorphisms. Current evidence suggests that taking the genetically determined metabolic capacity of CYP2C9 and CYP2C19 into account has the potential to improve individual risk/benefit relationships. However, more prospective studies with clinical endpoints are needed before the paradigm of "personalized medicine" based on the variants can be established. This review summarizes the currently available important information on this topic.

Interethnic and Intraethnic Variability of CYP2C8 and CYP2C9 Polymorphisms in Healthy Individuals

Cytochrome P450 (CYP) superfamily members CYP2C8 and CYP2C9 are polymorphically expressed enzymes that are involved in the metabolic inactivation of several drugs, including, among others, antiepileptics, NSAIDs, oral hypoglycemics, and anticoagulants. Many of these drugs have a narrow therapeutic index, and growing evidence indicates a prominent role of CYP2C8 and CYP2C9 polymorphisms in the therapeutic efficacy and in the development of adverse effects among patients treated with drugs that are CYP2C8 or CYP2C9 substrates. In this review, we summarize present knowledge on human variability in the frequency of variant CYP2C8 and CYP2C9 alleles. Besides an expected interethnic variability in allele frequencies, a large intraethnic variability exists. Among Asian subjects, for example, statistically significant differences (p < 0.0001) in CYP2C9*3 allele frequencies between Chinese and Japanese individuals have been reported. In addition, individuals from East Asia present different allele frequencies for CYP2C9*2 and CYP2C9*3 compared with South Asian subjects (p < 0.0001). Among Caucasian Europeans, statistically significant differences for the frequency of CYP2C8*3, CYP2C9*2, and CYP2C9*3 exist (p < 0.0001). This indicates that Asian individuals or Caucasian European individuals cannot be considered as homogeneous groups regarding CYP2C8 or CYP2C9 allele frequencies. Caucasian American subjects also show a large variability in allele frequencies, which is likely to be related to ethnic ancestry. A higher frequency of variant CYP2C8 and CYP2C9 alleles is expected among Caucasian Americans with South European ancestry than in individuals with North European ancestry. The findings summarized in this review suggest that among individuals with Asian or European ancestry, intraethnic differences in the risk of developing adverse effects with drugs that are CYP2C8 or CYP2C9 substrates are to be expected. In addition, the observed intraethnic variability reinforces the need for proper selection of control subjects and points against the use of surrogate control groups for studies involving association of CYP2C8 or CYP2C9 alleles with adverse drug reactions or spontaneous diseases.

Polymorphic metabolism by functional alterations of human cytochrome P450 enzymes

The study of cytochrome P450 pharmacogenomics is of particular interest because of its promise in the development of rational means to optimize drug therapy with respect to patient's genotype to ensure maximum efficacy with minimal adverse effects. Drug metabolizing P450 enzymes are polymorphic and are the main phase I enzymes responsible for the metabolism of clinical drugs. Therefore, polymorphisms in the P450s have the most impact on the fate of clinical drugs in phase I metabolism since almost 80% of drugs in use today are metabolized by these enzymes. Predictive genotyping for P450 enzymes for a more effective therapy will be routine for specific drugs in the future. In this review, we discuss the current knowledge of polymorphic metabolism by functional alterations in nonsynonymous SNPs of P450 1A2, 2A6, 2C8, 2C9, 2C19, 2D6, and 3A4 enzymes.

Frequency of CYP2C9 alleles in Koreans and their effects on losartan pharmacokinetics

AIM

CYP2C9 enzyme metabolizes numerous clinically important drugs. The aim of this study is to investigate the frequencies of CYP2C9 genotypes and the effects of selected alleles on losartan pharmacokinetics in a large sample of the Korean population.

METHODS

The CYP2C9 gene was genotyped in 1796 healthy Korean subjects. CYP2C9 alleles (CYP2C9*1, *2, *3 and *13 alleles) were measured using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay and direct sequencing assay. The enzymatic activity of each CYP2C9 genotype was evaluated using losartan as the substrate.

RESULTS

The frequencies of CYP2C9*1, *3 and *13 allele were 0.952 (95% confidence interval 0.945-0.959), 0.044 (95% CI 0.037-0.051) and 0.005 (95% CI 0.003-0.007), respectively. The frequencies of the CYP2C9*1/*1, *1/*3, *1/*13 and *3/*3 genotypes were 0.904 (95% CI 0.890-0.918), 0.085 (95% CI 0.072-0.098), 0.009 (95% CI 0.005-0.013) and 0.001 (95% CI 0.000-0.002), respectively. In the pharmacokinetics studies, the AUC(0-∞) of losartan in CYP2C9*3/*3 subjects was 1.42-fold larger than that in CYP2C9*1/*1 subjects, and the AUC(0-∞) of E-3174, a more active metabolite of losartan, in CYP2C9*3/*3 subjects was only 12% of that in CYP2C9*1/*1 subjects.

CONCLUSION

The results confirmed the frequencies of CYP2C9 genotypes in a large cohort of Koreans, and detected the CYP2C9*3/*3 genotype. CYP2C9*3/*3 subjects metabolized much less losartan into E-3174 than CYP2C9*1/*1 subjects.

Low dose requirement for warfarin treatment in a patient with CYP2C9*3/*13 genotype

BACKGROUND

Cytochrome P450 2C9 (CYP2C9) is the major isoform of the CYP2C subfamily, and is involved in the metabolism of many clinically important therapeutic agents. Here we describe a patient who was intolerant of warfarin treatment because of impaired drug metabolism related to the CYP2C9*3/*13 genotype and high warfarin sensitivity associated with the VKORC1 1173TT genotype.

CASE

A 64-year-old Korean man had taken warfarin for treatment of an occluded left subclavian artery and atrial fibrillation. Although the warfarin doses prescribed were not high (14 mg/week) during the induction of anticoagulation, the prothrombin time (PT) was elevated to over 120 s after two weeks of warfarin therapy. For this patient, a very low dose of warfarin (4 mg/week) was required in order to achieve target INR values.

CONCLUSIONS

To the best of our knowledge, this is the first report of a patient with CYP2C9*3/*13 and VKORC1 1173TT genotypes who had slower than normal warfarin metabolism, resulting in the need to administer an extremely low dose of warfarin in order to achieve the target INR value. Our report reinforces the relevance of pharmacogenetic testing to explain warfarin dose variability and to enable individualized dosage adjustments for improved warfarin treatment outcomes.

Effects of CYP2C9*1/*13 on the pharmacokinetics and pharmacodynamics of meloxicam

AIMS

To determine the effects of the CYP2C9*1/*13 genotype on the pharmacokinetics and pharmacodynamics of meloxicam in Korean subjects.

METHODS

Meloxicam (15 mg) was orally administered to 21 healthy Korean volunteers with either the CYP2C9*1/*1 or the CYP2C9*1/*13 genotype. Plasma meloxicam concentrations were analysed by HPLC-UV for 72 h after drug administration. The pharmacodynamic effects of meloxicam were determined by measuring TXB(2) generated in blood.

RESULTS

The AUC(0,∞) and C(max) of meloxicam were 2.43- and 1.46-fold higher in the CYP2C9*1/*13 group than in the CYP2C9*1/*1 group, respectively. The oral clearance of meloxicam was significantly lower in the CYP2C9*1/*13 group (37.9% of wild type) than in the CYP2C9*1/*1 group. The t(1/2) of meloxicam was 1.84-fold longer in the CYP2C9*1/*13 group than in the CYP2C9*1/*1 group. The rate of TXB(2) production was significantly lower in the CYP2C9*1/*13 group than in the CYP2C9*1/*1 group.

CONCLUSIONS

The CYP2C9*1/*13 genotype is associated with decreased metabolism and increased pharmacodynamic effects of meloxicam.

Genetic factors associated with patient-specific warfarin dose in ethnic Indonesians

Background

CYP2C9 and VKORC1 are two major genetic factors associated with inter-individual variability in warfarin dose. Additionally, genes in the warfarin metabolism pathway have also been associated with dose variance. We analyzed Single Nucleotide Polymorphisms (SNPs) in these genes to identify genetic factors that might confer warfarin sensitivity in Indonesian patients.

Methods

Direct sequencing method was used to identify SNPs in CYP2C9, VKORC1, CYP4F2, EPHX1, PROC and GGCX genes in warfarin-treated patients. Multiple linear regressions were performed to model the relationship warfarin daily dose requirement with genetic and non-genetic variables measured and used to develop a novel algorithm for warfarin dosing.

Results

From the 40 SNPs analyzed, CYP2C9 rs17847036 and VKORC1 rs9923231 showed significant association with warfarin sensitivity. In our study population, no significant correlation could be detected between CYP2C9*3, CYP2C9C-65 (rs9332127), CYP4F2 rs2108622, GGCX rs12714145, EPHX1 rs4653436 and PROC rs1799809 with warfarin sensitivity.

Conclusions

VKORC1 rs9923231 AA and CYP2C9 rs17847036 GG genotypes were associated with low dosage requirements of most patients (2.05 ± 0.77 mg/day and 2.09 ± 0.70 mg/day, respectively). CYP2C9 and VKORC1 genetic variants as well as non-genetic factors such as age, body weight and body height account for 15.4% of variance in warfarin dose among our study population. Additional analysis of this combination could allow for personalized warfarin treatment in ethnic Indonesians.

Frequency of CYP2C9 variant alleles, including CYP2C9*13 in a Korean population and effect on glimepiride pharmacokinetics

WHAT IS KNOWN AND OBJECTIVE

Cytochrome P450 (CYP) 2C9 is a clinically important enzyme involved in the metabolism of many drugs commonly used in humans. Of several allelic variants known to affect the catalytic activity of the CYP2C9 enzyme, the frequencies of the CYP2C9*3 and CYP2C9*13 alleles in the Korean population have been reported as 1·1% and 0·6%, respectively. Our objective was to re-evaluate the frequencies of CYP2C9 allelic variants in the Korean population, including the CYP2C9*13 allele by pyrosequencing, and to investigate the pharmacokinetics of glimepiride in relation to CYP2C9 genotypes, including CYP2C9*3/*3.

METHODS

295 subjects were genotyped for CYP2C9*2 and CYP2C9*3 using the TaqMan procedure, and for CYP2C9*13 using pyrosequencing. These data were combined with our previously reported data to assess the CYP2C9 allele and genotype frequencies in 869 Korean subjects. Data from 24 of the 295 genotyped subjects (22 CYP2C9*1/*1 homozygotes, one CYP2C9*1/*3 heterozygote and one CYP2C9*3/*3 homozygote) who had participated in a bioequivalence study were analysed retrospectively to examine the effects of CYP2C9 genotype on glimepiride pharmacokinetics.

RESULTS

The frequencies of the CYP2C9*1/*3, *3/*3, and *1/*13 genotypes in the study population (n = 295) were 0·081 (n = 24), 0·010 (n = 3) and 0·003 (n = 1), respectively. In the 869 subjects from the combined studies, allele frequencies for CYP2C9*3 and CYP2C9*13 were 0·025 (95% CI: 0·018, 0·033) and 0·002 (95% CI: 0·000, 0·010), respectively. Relative to CYP2C9*1 homozygotes, the one CYP2C9*3 homozygous subject was found to have a higher AUC(0-∞) value (490% of the reference value) and a lower oral clearance rate (18% of the reference).

WHAT IS NEW AND CONCLUSION

This study is the first examination of CYP2C9*3 homozygotes in the Korean population. Our data on the one subject with this genotype suggest that CYP2C9*3/*3 momozygotes have lower clearance of glimepiride and are exposed to higher levels of the drug than wild-type homozygotes. Although we identified a subject with the CYP2C9*13 allele using a new pyrosequencing assay, we were unfortunately unable to investigate its effects on glimepiride pharmacokinetics.

Combined CYP2C9, VKORC1 and CYP4F2 frequencies among racial and ethnic groups

AIMS

CYP4F2*3 (p.V433M) has been associated with higher warfarin dose requirements; however, its frequency, like other CYP2C9 and VKORC1 variants, has not been systematically assessed in major racial/ethnic populations. Thus, we determined the individual and combined frequencies of important CYP2C9, VKORC1 and CYP4F2 variants in several racial/ethnic groups.

MATERIALS & METHODS

Healthy African-American, Asian, Caucasian, Hispanic and Ashkenazi Jewish (AJ) blood donors were genotyped for CYP2C9 (*2, *3, *4, *5, *6, *8, *11 and *13), VKORC1 (g.-1639G>A) and CYP4F2 (*3 [p.V433M] and rs2189784).

RESULTS

The combined frequencies of variant CYP2C9 alleles were 0.133, 0.078, 0.212, 0.178 and 0.212 among African-American, Asian, Caucasian, Hispanic and AJ individuals, respectively. CYP4F2*3 frequencies were prevalent (0.233-0.342) among Asian, Caucasian, Hispanic and AJ individuals, while significantly less frequent among African-Americans (0.117; p < 0.0001). In addition, CYP4F2*3 was in linkage disequilibrium with rs2189784, an allele recently associated with time-to-therapeutic international normalized ratio, among all studied populations. Importantly, 87-95% of Asian, Caucasian, Hispanic and AJ individuals had a variant CYP2C9, VKORC1 and/or CYP4F2*3 allele, compared with only 53% of African-Americans (p < 0.0001).

CONCLUSIONS

Compared with other racial/ethnic populations studied, only approximately one in 80 African-Americans were CYP4F2*3 homozygous, indicating that this population would benefit less from dosing algorithms that include this variant. In addition, the unique allele frequency profiles identified among the different populations partly explain why genotype-guided warfarin dosing algorithms perform less well for African-Americans and suggest that other unidentified genetic and/or nongenetic factors that influence warfarin dosage may exist in this population.

Pharmacogenetics of cytochrome P450 (CYP) in the elderly

The genetics of cytochrome P450 (CYP) is a very active area of multidisciplinary research, overlapping the interest of medicine, biology and pharmacology, being the CYP enzyme system responsible for the metabolism of more than 80% of the commercially available drugs. Variations in CYP encoding genes are responsible for inter-individual differences in CYP production or function, with severe clinical consequences as therapeutic failures (TFs) and adverse drug reactions (ADRs), being ADRs worldwide primary causes of morbidity and mortality in elderly people. In fact, the prevalence of both TFs and ADRs strongly increased in the presence of multiple pharmacological treatments, a common status in subjects aging 65 years and over. The present article explored some basic concepts of human genetics that have important implications in the genetics of CYP. An attempted to transfer these basic concepts to the genetic data reported by the Home Page of The Human Cytochrome P450 (CYP) Allele Nomenclature Committee was also made, focusing on the current knowledge of CYP genetics. The status of what we know and what we need to know is the base for the clinical applications of pharmacogenetics, in which personalized drug treatments constituted the main aim, in particular in patients attending a geriatric ward.

CYP2C9*8 is prevalent among African-Americans: implications for pharmacogenetic dosing

AIMS

Although the frequencies of pharmacogenetic variants differ among racial groups, most pharmacogenetic algorithms for genotype-guided warfarin dosing only include two CYP2C9 alleles (*2 and *3) and a single VKORC1 allele (g.-1639G>A or g.1173C>T) commonly found among Caucasians. Therefore, this study sought to identify other CYP2C9 and VKORC1 alleles important in warfarin dose variability and to determine their frequencies in different racial and ethnic groups.

MATERIALS & METHODS

The CYP2C9 and VKORC1 genes were sequenced in selected sensitive (< 21 mg/week) and resistant (> 49 mg/week) individuals with discrepant therapeutic and algorithm-predicted warfarin doses based on prior CYP2C9 and VKORC1 genotyping. The CYP2C9 and VKORC1 allele frequencies were determined in healthy, racially self-identified blood donors.

RESULTS

Sequencing identified an African-American male with a lower than predicted therapeutic warfarin dose (14.4 mg/week), previously genotyped as CYP2C9*1/*1, who was homozygous for CYP2C9*8 (c.449G>A; p.R150H). Genotyping 600 African-American alleles identified CYP2C9*8 as their most frequent variant CYP2C9 allele (0.047), and the combined allele frequency of CYP2C9*2, *3, *5, *6, *8 and *11 was 0.133. Given most warfarin pharmacogenetic dosing algorithms only include CYP2C9*2 and *3, the inclusion of CYP2C9*8 alone could reclassify the predicted metabolic phenotypes of almost 10% of African-Americans, or when combined with CYP2C9*5, *6 and *11, more than 15%. In addition, the African-American VKORC1 g.-1639A allele frequency was 0.108 and three g.1331G>A (p.V66M) carriers were identified.

CONCLUSIONS

CYP2C9*8 is prevalent among African-Americans ( approximately 1 in 11 individuals). Thus, in this racial group, the incorporation of CYP2C9*8 into genotyping panels may improve dose prediction of CYP2C9-metabolized drugs, including warfarin.

ARMS test for diagnosis of CYP2C9 and VKORC1 mutation in patients with pulmonary embolism in Han Chinese

Aims: VKORC1 and CYP2C9 are important genetic factors affecting warfarin dose requirement. Our aim is to establish a simple, rapid and economical method to detect SNPs in the two genes. Materials & methods: Primer Premier 5 was used and a normal primer, a mutational primer and a common primer have been designed using the amplification refractory mutation system for VKORC1 c.-1639G>A (rs9923231), CYP2C9*3 c.1075A>C (rs1057910) and CYP2C9*13 c.269T>C substitutions. The amplification refractory mutation system (ARMS) assay was validated by the restriction enzyme cleavage method of reference or direct sequencing. Results: The ARMS primers designed can distinguish between heterozygotes and homozygotes successfully. In the Han Chinese population, patients with pulmonary embolism allele frequencies of CYP2C9*3 c.1075A>C (rs1057910), *13 c.269T>C and VKORC1 -1639G>A (rs9923231) are 4.3, 0.7 and 8.6%, respectively. Conclusion: The ARMS-PCR method is a simple, economical method that can be used for the rapid detection of SNPs in VKORC1 and CYP2C9.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Polymorphisms of human cytochrome P450 2C9 and the functional relevance

Human cytochrome P450 2C9 (CYP2C9) accounts for ∼20% of hepatic total CYP content and metabolizes ~15% clinical drugs such as phenytoin, S-warfarin, tolbutamide, losartan, and many nonsteroidal anti-inflammatory agents (NSAIDs). CYP2C9 is highly polymorphic, with at least 33 variants of CYP2C9 (*1B through *34) being identified so far. CYP2C9*2 is frequent among Caucasians with ~1% of the population being homozygous carriers and 22% are heterozygous. The corresponding figures for the CYP2C9*3 allele are 0.4% and 15%, respectively. There are a number of clinical studies addressing the impact of CYP2C9 polymorphisms on the clearance and/or therapeutic response of therapeutic drugs. These studies have highlighted the importance of the CYP2C9*2 and *3 alleles as a determining factor for drug clearance and drug response. The CYP2C9 polymorphisms are relevant for the efficacy and adverse effects of numerous NSAIDs, sulfonylurea antidiabetic drugs and, most critically, oral anticoagulants belonging to the class of vitamin K epoxide reductase inhibitors. Warfarin has served as a practical example of how pharmacogenetics can be utilized to achieve maximum efficacy and minimum toxicity. For many of these drugs, a clear gene-dose and gene-effect relationship has been observed in patients. In this regard, CYP2C9 alleles can be considered as a useful biomarker in monitoring drug response and adverse effects. Genetic testing of CYP2C9 is expected to play a role in predicting drug clearance and conducting individualized pharmacotherapy. However, prospective clinical studies with large samples are warranted to establish gene-dose and gene-effect relationships for CYP2C9 and its substrate drugs.