Genetic polymorphisms of the drug-metabolizing enzyme CYP2C19 in the Uyghur population in northwest China

1.?CYP2C19 is a clinically important enzyme and is involved in the metabolism of approximately 10% of drugs used in daily clinical practice. Previous studies mainly focused on Chinese Han populations or other ethnic groups, little is known about Uyghur populations.

2.?The present study was designed to determine the genetic basis of CYP2C19 polymorphisms.

3.?We used direct sequencing to investigate the promoter, exons and surrounding introns, and 3′-untranslated region of the CYP2C19 gene in 96 unrelated healthy Uyghur individuals.

4.?A total of 31 different CYP2C19 polymorphisms were identified in the Uyghur population, three of which were novel, including two nonsynonymous variants (57807A?>?M, Gln279Pro and 19257G?>?R, Asp262Asn) and one synonymous variants in exon 5 (19184T?>?Y, Leu237Leu). In addition, CYP2C19*1, *2 and *3 alleles showed frequencies of 83.34%, 14.06% and 2.08%, respectively.

5.?This is the first study that systematically screened the polymorphisms of the whole CYP2C19 gene in Uyghur population. Hence, our results provided important information on CYP2C19 polymorphisms in Uyghur population and could be helpful for future personalized medicine studies in Uyghur population generally.     

Genetic polymorphisms of the drug-metabolizing enzyme cytochrome P450 3A5 in a Uyghur Chinese population

1. Detection of CYP3A5 variant alleles, and knowledge about their allelic frequency in Uyghur ethnic groups, is important to establish the clinical relevance of screening for these polymorphisms to optimize pharmacotherapy.

2.?We used DNA sequencing to investigate the promoter, exons and surrounding introns, and 3′-untranslated region of the CYP3A5 gene in 96 unrelated healthy Uyghur individuals. We also used SIFT and PolyPhen-2 to predict the protein function of the novel non-synonymous mutation in CYP3A5 coding regions.

3.?We found 24 different CYP3A5 polymorphisms in the Uyghur population, three of which were novel: the synonymous mutation 43C?>?T in exon 1, two mutations 32120C?>?G and 32245T?>?C in 3′-untranslated region, and we detected the allele frequencies of CYP3A5*1 and *3 as 64.58% and 35.42%, respectively. While no subjects with CYP3A5*6 were identified. Other identified genotypes included the heterozygous genotype 1A/3A (59.38%) and 1A/3E (11.46%), which lead to decreased enzyme activity. In addition, the frequency of haplotype “TTAGGT” was the most prevalent with 0.781.

4.?Our data provide new information regarding CYP3A5 genetic polymorphisms in Uyghur individuals, which may help to improve individualization of drug therapy and offer a preliminary basis for more rational use of drugs.     

Genotype and allele frequencies of polymorphic <Emphasis Type="Italic">CYP2E1</Emphasis> in the Turkish population

Cytochrome P4502E1 (CYP2E1) gene shows genetic polymorphisms that vary markedly in frequency among different ethnic and racial groups. We studied the genotype distributions and allele frequencies of three CYP2E1 polymorphisms: CYP2E1*5B (RsaI/PstI RFLP, C-1053T/G-1293C SNP, rs2031920 /rs3813867), CYP2E1*6 (DraI RFLP, T7632A SNP, rs6413432), and CYP2E1*7B (DdeI RFLP, G-71T SNP, rs6413420) by PCR/RFLP technique in a sample of 206 healthy subjects representing Turkish population. CYP2E1*5B polymorphism analysis yielded the genotype distribution as 96.12% for *1A/*1A (c1/c1), and 3.88% for *1A/*5B (c1/c2). The genotype frequencies for CYP2E1*6 polymorphism were found as 83.98% for *1A/*1A (T/T), 15.53% for *1A/*6 (T/A) and 0.49% for *6/*6 (A/A). For CYP2E1*7B (G-71T) polymorphism, the genotype frequencies were determined to be 86.89% for *1A/*1A (G/G), 12.62% for *1A/*7B (G/T) and 0.49% for *7B/*7B (T/T). Accordingly, the allele frequencies for *5B, *6 and *7B were 1.94, 8.25, and 6.80%, respectively. The genotype distributions of CYP2E1*5B and *6 in Turkish population were similar to those in other Caucasian populations, while differed significantly from East Asian populations. Recently, a novel and functionally important CYP2E1*7B polymorphism was identified in the promoter region. There have been few studies and limited data on CYP2E1*7B polymorphism frequency in the world and, so far, no information has been available for Turkish population. The genotype frequencies of CYP2E1*7B in Turkish population were found to be similar to those of other Caucasian populations. Population studies like this could be useful in assessing the susceptibility of different populations to chemical-induced diseases, including several types of cancer. An account of this work has been presented at the 31st Federation of European Biochemical Societies (FEBS) Congress, in Istanbul, Turkey, on June 24–29, 2006.     

Impact of CYP2C8*3 polymorphism on in vitro metabolism of imatinib to N-desmethyl imatinib

Abstract

1.?Imatinib is metabolized to N-desmethyl imatinib by CYPs 3A4 and 2C8. The effect of CYP2C8*3 genotype on N-desmethyl imatinib formation was unknown.

2.?We examined imatinib N-demethylation in human liver microsomes (HLMs) genotyped for CYP2C8*3, in CYP2C8*3/*3 pooled HLMs and in recombinant CYP2C8 and CYP3A4 enzymes. Effects of CYP-selective inhibitors on N-demethylation were also determined.

3.?A single-enzyme Michaelis–Menten model with autoinhibition best fitted CYP2C8*1/*1 HLM (n?=?5) and recombinant CYP2C8 kinetic data (median?±?SD K_i?=?139?±?61?µM and 149?µM, respectively). Recombinant CYP3A4 showed two-site enzyme kinetics with no autoinhibition. Three of four CYP2C8*1/*3 HLMs showed single-enzyme kinetics with no autoinhibition. Binding affinity was higher in CYP2C8*1/*3 than CYP2C8*1/*1 HLM (median?±?SD K_m?=?6?±?2 versus 11?±?2?µM, P=0.04). CYP2C8*3/*3 (pooled HLM) also showed high binding affinity (K_m?=?4?µM) and single-enzyme weak autoinhibition (K_i?=?449?µM) kinetics. CYP2C8 inhibitors reduced HLM N-demethylation by 47–75%, compared to 0–30% for CYP3A4 inhibitors.

4.?In conclusion, CYP2C8*3 is a gain-of-function polymorphism for imatinib N-demethylation, which appears to be mainly mediated by CYP2C8 and not CYP3A4 in vitro in HLM.     

Bisphenol-A glucuronidation in human liver and breast: identification of UDP-glucuronosyltransferases (UGTs) and influence of genetic polymorphisms

1.?Bisphenol-A is a ubiquitous environmental contaminant that is primarily metabolized by glucuronidation and associated with various human diseases including breast cancer. Here we identified UDP-glucuronosyltransferases (UGTs) and genetic polymorphisms responsible for interindividual variability in bisphenol-A glucuronidation in human liver and breast.

2.?Hepatic UGTs showing the highest bisphenol-A glucuronidation activity included UGT2B15 and UGT1A9. Relative activity factor normalization indicated that UGT2B15 contributes?>80% of activity at bisphenol-A concentrations under 5?μM, while UGT1A9 contributes up to 50% of activity at higher concentrations.

3.?Bisphenol-A glucuronidation by liver microsomes (46 donors) ranged from 0.25 to 4.3 nmoles/min/mg protein. Two-fold higher glucuronidation (p?=?0.018) was observed in UGT1A9 *22/*22 livers compared with *1/*1 and *1/*22 livers. However, no associations were observed for UGT2B15*2 or UGT1A1*28 genotypes.

4.?Bisphenol-A glucuronidation by breast microsomes (15 donors) ranged from <0.2 to 56 fmoles/min/mg protein. Breast mRNA expression of UGTs capable of glucuronidating bisphenol-A was highest for UGT1A1, followed by UGT2B4, UGT1A9, UGT1A10, UGT2B7 and UGT2B15. Bisphenol-A glucuronidation was over 10-fold lower in breast tissues with the UGT1A1*28 allele compared with tissues without this allele (p?=?0.006).

5.?UGT2B15 and UGT1A9 contribute to glucuronidation variability in liver, while UGT1A1 is important in breast.     

CYP2C19 polymorphism affects single-dose pharmacokinetics of oral pantoprazole in healthy volunteers

Objectives

Pantoprazole is metabolized by cytochrome P450 2?C19, which shows genetic polymorphism. The effect of CYP2C19 polymorphism on single-dose pharmacokinetics of oral pantoprazole in healthy volunteers was evaluated.

Methods

Pantoprazole pharmacokinetics was determined in 32 healthy volunteers after a 40-mg single oral dose of the drug.

Results

Carriers of CYP2C19*2/*2 (n?=?2) were characterized by higher, starting from 3.5?h post dose, plasma concentrations of pantoprazole in comparison to wild-type (CYP2C19*1/*1, n?=?6) volunteers. In subjects with CYP2C19*17/*17 genotype (n?=?6) significantly lower plasma concentrations of the drug vs CYP2C19*1/*1 carriers, were observed from 3.0?h after oral pantoprazole administration. Carriers of CYP2C19*1/*17 (n?=?6) and CYP2C19*2/*17 (n?=?6) displayed concentration–time profiles comparable to wild-type subjects. CYP2C19*2/*2 volunteers showed a decrease in terminal elimination rate constant (λ_z) by 83.3%, prolongation of terminal half-life (t_?) by 572%, a rise in area under the concentration–time curve (AUC) and mean residence time (MRT) by 506% and 259% respectively. Heterozygotes, i.e.. CYP2C19*1/*2 vs CYP2C19*1/*1 were characterized by higher AUC (4.38?±?1.00?mg?h/L vs 3.00?±?1.02 mg?h/L, p?max (2.13?±?0.42?mg/L vs 1.61?±?0.35?mg/L, p?p?CYP2C19*17/*17 vs CYP2C19*1/*1 genotypes was observed. Population modeling confirmed the influence of *1/*2, *2/*2, and *17/*17 genotypes on the pharmacokinetics of pantoprazole. The lowest population oral clearance was assessed in the carriers of genotype *2/*2 (3.68?L/h) and the highest value in subjects with genotype *17/*17 (31.13?L/h).

Conclusion

These data suggest that CYP2C19 polymorphism is an important determinant of pantoprazole pharmacokinetics.     

Role of pharmacodiagnostic of CYP2C9 variants in the optimization of warfarin therapy in Malaysia: A 6-month follow-up study

1.?A retrospective study was conducted to explore the importance of CYP2C9 genotyping for the initiation and maintenance therapy of warfarin in clinical practice. A total of 191 patients on warfarin therapy in a local hospital were recruited after written informed consent. Their medical records were reviewed and no intervention of warfarin dose was performed.

2.?A total of 5 ml of blood were taken from each subject for DNA extraction and identification of *1, *2, *3 and *4 CYP2C9 alleles, using a nested-allele-specific-multiplex-polymerase chain reaction (PCR). Half the patients were Malays and the remaining were Chinese.

3.?Two genotypes were detected; 93.2% had CYP2C9*1/*1 and 6.8% were CYP2C9*1/* 3. Warfarin doses were higher in patients with CYP2C9*1/*1. Patients with the *1/* 3 genotype experienced a higher rate of serious and life-threatening bleeding; 15.4 versus 6.2 per 100 patients per 6 months.

4.?The observation clearly highlights the inadequacy of the current dosing regimens and the need to move toward a more individualized approach to warfarin therapy. Prospective clinical studies are now being conducted to assess dosing algorithms that incorporate the contribution of the genotype to allow the individualization of warfarin dose.     

Identification of CYP2D6 impaired functional alleles in Mexican Americans

Objectives To extend the genotyping analysis of the CYP2D6 gene and further explain variability of CYP2D6 activity in Mexican Americans by genetic factors. Methods CYP2D6 gene sequence variations associated with *6, *7, *8, *9, *11, *14, *29, *41, *45, and *46 alleles as well as the 2988G>A SNP were examined in 264 Mexican Americans; 236 had previously been phenotyped with dextromethorphan. All subjects were previously genotyped for CYP2D6*2, *3, *4, *5, *10, *17, and the presence of a gene duplication. Associations between genotype and CYP2D6 activity were determined. Results Mexican Americans revealed a high frequency of functional alleles (CYP2D6*1 and *2; 73.1%), followed by CYP2D6*4 (non-functional, 10.0%) and the reduced-function allele *41 (9.5%). The frequencies of CYP2D6*5, *6, *9, *10, duplication, and 2988A were 1.7%, 0.4%, 1.1%, 2.8%, 0.8%, and 5.7%, respectively. CYP2D6*3, *17, and *29 were found only in one individual (CYP2D6*2/*3, *1/*17, and *4/*29), while CYP2D6*7, *8, *11, *14, *45, and *46 were absent in this study population. Decreased CYP2D6 activity was more accurately predicted by the presence *41[−1584C] compared to *41[2988A]. One genotype/phenotype discordant subject was resolved by the presence of a CYP2D6*6 allele (*4/*6), while two other cases remained discordant (*41/*41 and *1/*1). Conclusions The CYP2D6*4, *5, and *6 null alleles along the reduced function alleles *9, *10, and *41 are the major cause for diminished dextromethorphan oxidative capacity in Mexican Americans. These findings may have implications for the safety and efficacy of CYP2D6 substrates taken by Mexican Americans.     

Effect of glycyrrhizin on CYP2C19 and CYP3A4 activity in healthy volunteers with different CYP2C19 genotypes

1. The objective of this study was to investigate the interaction between glycyrrhizin and omeprazole and observe the effects of glycyrrhizin on CYP2C19 and CYP3A4 activities in healthy Chinese male volunteers with different CYP2C19 genotypes.

2. Eighteen healthy subjects (six CYP2C19*1/*1, five CYP2C19*1/*2, one CYP2C19*1/*3, five CYP2C19*2/*2 and one CYP2C19*2/*3) were enrolled in a two-phase randomized crossover trial. In each phase, all subjects received placebo or glycyrrhizin salt tablet 150?mg twice daily for 14 consecutive days. The pharmacokinetics of omeprazole (20?mg orally on day 15) was determined for up to 12?h following administration by high-performance liquid chromatography.

3. After 14-day treatment of glycyrrhizin, plasma omeprazole significantly decreased, and those of omeprazole sulfone significantly increased. However, plasma concenetrations of 5-hydroxyomeprazole did not significantly change. The ratio of AUC_0–∞ of omeprazole to omeprazole sulfone decreased by 43.93% ± 13.56% (p?=?0.009) in CYP2C19*1/*1, 44.85% ± 14.84% (p?=?0.002) in CYP2C19*1/*2 or *3 and 36.16% ± 7.52% (p?<?0.001) in CYP2C19*2/*2 or *3 while those of omeprazole to 5-hydroxyomeprazole did not change significantly in all three genotypes. No significant differences in glycyrrhizin response were found among CYP2C19 genotypes.

4. Glycyrrhizin induces CYP3A4-catalyzed sulfoxidation of omeprazole and leads to decreased omeprazole plasma concentrations, but has no significant impact on CYP2C19-dependent hydroxylation of omeprazole.

     

Responsiveness to low-dose warfarin associated with genetic variants of VKORC1, CYP2C9, CYP2C19, and CYP4F2 in an Indonesian population

Purpose

The aim of this study was to assess the pharmacokinetics and pharmacodynamics of warfarin associated with genetic polymorphisms in VKORC1, CYP2C9, CYP2C19, and CYP4F2 in Indonesian patients treated with low-dose warfarin.

Methods

Genotyping of VKORC1, CYP2C9, CYP2C19, and CYP4F2 was carried out in 103 patients treated with a daily dose of 1–2 mg warfarin, 89 of whom were treated with a fixed daily dose of warfarin (1 mg). The plasma concentrations of S- and R-warfarin and S- and R-7-hydroxywarfarin were used as pharmacokinetic indices, while prothrombin time expressed as the international normalized ratio (PT-INR) was used as a pharmacodynamic index.

Results

In patients treated with a fixed daily dose of warfarin (1 mg), a higher PT-INR was associated with VKORC1-1639 AA [median 1.35; interquartile range (IQR)?1.21–1.50] than with the GA (1.18; IQR?1.12–1.32; p?<?0.01) and GG (1.02; IQR?=?1.02–1.06; p?<?0.01) polymorphisms, and with CYP2C9*1/*3 (1.63; IQR?1.45–1.85) compared to *1/*1 (1.23; IQR??1.13–1.43; p?<?0.05). The S-warfarin concentration was significantly higher in patients with CYP2C9*1/*3 than in those with *1/*1 (p?<?0.05). With low-dose warfarin administration, there was no significant difference in the concentrations of warfarin metabolites among any of the genotype variants. The genotype variations of CYP2C19 and CYP4F2 were not significantly associated with the PT-INR.

Conclusion

For low-dose warfarin treatment, the VKORC1-1639 G?>?A and CYP2C9 genotype variations affected the pharmacokinetics and pharmacodynamics of warfarin, while we could not find significant effects of CYP4F2 or CYP2C19 genotype variations on warfarin (metabolite) concentrations or PT-INR.     

Influence of CYP3A5 Genetic Polymorphism on Tacrolimus Daily Dose Requirements and Acute Rejection in Renal Graft Recipients

Abstract: Tacrolimus is a widely used immunosuppressive drug in organ transplantation. Its oral bioavailability varies greatly between individuals, and it is a substrate of cytochrome P450 3A (CYP3A) and P‐glycoprotein. Our objective was to determine the influence of CYP3A5 and ABCB1 genetic polymorphisms on tacrolimus daily requirements and on transplantation outcome. One hundred and thirty‐six renal graft recipients treated with tacrolimus were genotyped for CYP3A5 (6986A>G), ABCB1 exon26 (3435C>T) and exon21 (2677G>T/A) single nucleotide polymorphisms. Genotypes were correlated to tacrolimus daily dose at 1‐week, 1‐, 6‐ and 12‐month post‐transplantation and with transplantation outcome. At 1‐month post‐transplantation, tacrolimus daily dose was higher for patients with CYP3A5*1/*1 genotype compared to CYP3A5*3/*3 genotype (0.26 ± 0.03 versus 0.16 ± 0.01 mg/kg/day, respectively, P < 0.0001). Similar results were obtained at 6‐ and 12‐month post‐transplantation. Furthermore, CYP3A5*1 homozygotes were associated with increased risk of acute rejection episodes compared to patients with CYP3A5*1/*3 and CYP3A5*3/*3 genotypes (38% versus 10% and 9%, respectively, P = 0.01). CYP3A5 genetic polymorphism was not associated with tacrolimus‐related nephrotoxicity. ABCB1 polymorphisms were not related with transplantation outcome. CYP3A5 genetic polymorphism appeared in our study to affect tacrolimus daily dose requirements and transplantation outcome. Screening for this single nucleotide polymorphism before the transplantation might be helpful for the selection of adequate initial daily dose and to achieve the desired immunosuppression.     

Association of CYP3A4*18B polymorphisms with the pharmacokinetics of cyclosporine in healthy subjects

The aim of this study is to evaluate the association of the CYP3A4*18B genotype with the cyclosporine metabolism in healthy subjects. We employed PCR–RFLP assays for analysis of the CYP3A4*18B genotype. Each of 26 subjects, comprising 12 CYP3A4*1/*1, 12 CYP3A4*1/*18B and 2 CYP3A4*18B/*18B, was given a single oral dose of cyclosporine (4?mg?kg^?1). The plasma concentrations of cyclosporine were measured for up to 24?h post dose by high-performance liquid chromatography–electrospray mass spectrometry. We found that the mean C_max (95% confidence intervals) of cyclosporine were 2237 (2905, 1859) (*1/*1), 2247 (2916, 1869) (*1/*18B), and 905 (1192, 506) ng?ml^?1 (*18B/*18B) (p?=?0.037) and the mean AUC0-4 were 5026 (6181, 4372) (*1/*1), 4434 (5481, 3841) (*1/*18B) and 2561 (3155, 1736) ng ml-1?h (*18B/*18B) (p?=?0.021). The CL in the *18B/*18B group was significantly higher than in the *1/*1 group. However, T_max exhibited no difference among the three genotypes. *18B/*18B group showed 50% reduction in concentration at 2?h post dose compared with *1/*18B (p?=?0.062) or *1/*1 (p?=?0.047), but no statistical significance was detected between*1/*1 and *1/*18B groups (p?>?0.05). The data suggest that the CYP3A4*18B genotype affects cyclosporine pharmacokinetics probably resulting from a higher enzymatic activity of this mutation in healthy subjects.     

Effects of cytochrome P450 3A4 and non-genetic factors on initial voriconazole serum trough concentrations in hematological patients with different cytochrome P450 2C19 genotypes

1.?Polymorphisms of cytochrome P450 2C19 (CYP2C19) is an important factor contributing to variability of voriconazole pharmacokinetics. Polymorphisms of CYP3A4, CYP3A5, CYP2C9 and non-genetic factors such as age, gender, body mass index (BMI), transaminase levels, concomitant medications might also affect voriconazole initial steady serum trough concentration (VIC_min) in haematological patients, but the effects were not clear.

2.?Eighteen single-nucleotide polymorphisms in CYP2C19, CYP3A4, CYP3A5, CYP2C9 were genotyped. Patients were stratified into two groups according to CYP2C19 genotype. Group 1 were patients with CYP2C19*2 or CYP2C19*3, and Group 2 were homozygous extensive metabolizers. The effects were studied in different groups. VIC_min was adjusted on daily dose (VIC_min/D) for overcoming effect of dose.

3.?A total of 106 blood samples from 86 patients were included. In final optimal scaling regression models, polymorphisms of rs4646437 (CYP3A4), age, BMI was identified to be factors of VIC_min/D in Group 1 (R^2?=^?.255, p?<?.001). Only age was confirmed as a factor of VIC_min/D in Group 2 (R^2?=^?0.144, p?=?.021).

4.?Besides polymorphisms of CYP2C19, in individualized medication of voriconazole in haematological patients, polymorphisms of CYP3A4, and non-genetic factors as BMI, age should also be taken into account, especially for individuals with CYP2C19*2 or CYP2C19*3.     

Impact of CYP3A5 polymorphism on platelet reactivity at percutaneous coronary intervention and after 9 months of aspirin and clopidogrel therapy in Japanese patients with coronary artery disease

Background

High residual platelet reactivity in patients receiving clopidogrel is associated with an increased risk of a cardiovascular event after coronary stenting. The aim of our study was to evaluate the impact of the cytochrome P450 (CYP) 3A5 and CYP2C19 polymorphisms on platelet reactivity during dual antiplatelet therapy.

Methods

We determined the CYP2C19 and CYP3A5 genotypes of 101 angina patients (65 male patients, mean age 64 years) receiving dual antiplatelet therapy with aspirin and clopidogrel and evaluated the effect of these polymorphism on platelet reactivity at the early and late phases of treatment using a conventional light transmission aggregometry. Early and late phases were defined as 24 h after the loading dose and after 9 months on a maintenance dose of 75 mg daily, respectively.

Results

The distribution of the CYP2C19 genotype was 30 % in extensive metabolizers (EM; CYP2C19*1/*1), 46 % in intermediate metabolizers (IM; *1/*2, *1/*3), and 25 % in poor metabolizers (PM; *2/*2, *2/*3, *3/*3). Platelet reactivity levels in during the early and late phases were 3,793?±?1,476 and 2,960?±?1,410, respectively, in EM, 4,706?±?1,417 and 3,239?±?1,479, respectively, in IM, and 5,402?±?776 and 4,736?±?1,356 aggregation units (AU)?min, respectively in EM. The distribution of the CYP3A5 genotype was 33 % in patients carrying the wild-type or one loss-of-function allele (Expressor phenotype; *1/*1 and *1/*3, respectively) and 67 % in those carrying two loss-of-function alleles (Non-expressor; *3/*3). In total, eight patients were EM+Expressor, 22 were EM+Non-expressor, 18 were IM+Expressor, 28 were IM+Non-expressor, eight were PM+Expressor, and 17 were PM+Non-expressor. In the late phase of PM with the CYP2C19 polymorphism, the levels of platelet reactivity according to CYP3A5 genotype were 3,963?±?1,436 and 5,100?±?1,190 AU?min in Expressor and Non-expressor, respectively (P?<?0.05), however, there was no difference in platelet reactivity between Expressor and Non-expressor in EM and IM.

Conclusions

Our results suggest that antiplatelet response to clopidogrel in the late phase depends on the CYP3A5 polymorphism in PM with CYP2C19.     

The impact of CYP2D6 polymorphisms on the pharmacokinetics of codeine and its metabolites in Mongolian Chinese subjects

Purpose

Codeine is an analgesic drug acting on μ-opioid receptors predominantly via its metabolite morphine formed almost exclusively by CYP2D6. Genetic polymorphisms in CYP2D6 are associated with diminished pain relief and/or severe opioid side effects. In Chinese individuals, CYP2D6*10 is the most common allele with reduced enzyme activity. In this study, we investigated the effect of this allele on the pharmacokinetics of codeine and its metabolites.

Method

A blood sample was collected from healthy Mongolian volunteers for CYP2D6 genotyping using a PCR-RFLP assay. A pharmacokinetic study was then carried out in three groups with CYP2D6*1/*1 (n?=?10), CYP2D6*1/*10 (n?=?10) and CYP2D6*10/*10 (n?=?9) genotypes by collecting serial blood samples for determination of plasma levels of codeine and its metabolites, morphine, morphine 3-glucuronide (M3G) and morphine 6-glucuronide (M6G) before and after a single 30-mg oral dose of codeine phosphate. Codeine and its metabolites were measured by LC-MS/MS.

Results

No significant differences were observed in the pharmacokinetic parameters of codeine in the three genotype groups. However, the C _max and AUC_0-∞ of morphine, M3G and M6G were significantly different between the study groups (P?<?0.05). Compared with the *1/*1 group, the AUC_0-∞ for morphine in the *1/*10 and *10/*10 groups decreased by ratios (95 % CI) of 0.93 (0.26–1.59) and 0.494 (0.135–0.853) respectively. Corresponding ratios for M3G were 0.791 (0.294–1.288) and 0.615 (0.412–0.818) and for M6G were 0.643 (0.39–0.957) and 0.423 (0.267–0.579).

Conclusion

This study demonstrates that the CYP2D6*10 allele plays an important role in the pharmacokinetics of the O-demethylated metabolites of codeine after oral administration.     

Influence of clinical and genetic factors on warfarin dose requirements among Japanese patients

Objective

The aim of this study was to investigate the influence of clinical and genetic factors on warfarin dose requirements in the Japanese population.

Methods

We enrolled 125 patients on stable warfarin anticoagulant therapy with an international normalized ratio maintained between 1.5 and 3.0. PCR-based methods were performed to analyze genetic polymorphisms in the genes pharmacokinetically and pharmacodynamically related to warfarin reactions, including cytochrome P450 (CYP) 2C9, vitamin K epoxide reductase complex subunit 1 (VKORC1), gamma-glutamyl carboxylase (GGCX) and factor VII (FVII).

Results

The presence of CYP2C9*3 and VKORC1-1639G>A had a significant impact on the mean maintenance dose of warfarin (CYP2C9*1/*1 2.74?±?1.24 mg/day vs. *1/*3 and *3/*3 1.56?±?0.85 mg/day, P?=?0.009; VKORC1-1639AA 2.42?±?0.95 mg/day vs. GA 3.71?±?1.43 mg/day vs. GG 7.25?±?0.35 mg/day, P?<?0.001). In the multiple linear regression model, the combination of age, body surface area, and genotypes of CYP2C9*3 and VKORC1-1639G>A explained 54.8% of the variance in warfarin dose requirements.

Conclusions

The influences of CYP2C9*3 and VKORC1-1639G>A on the maintenance dose of warfarin were well-defined in Japanese patients, while polymorphisms of GGCX and FVII did not affect it. The model established in this study might provide us most likely individual maintenance dose based on clinical and genetic backgrounds.

     

Comparisons of <Emphasis Type="Italic">CYP1A2</Emphasis> genetic polymorphisms,enzyme activity and the genotype-phenotype relationship in Swedes and Koreans

Objectives To investigate the CYP1A2 genotype-phenotype relationship and to compare CYP1A2 genetic polymorphisms and enzyme activity in terms of the effect of smoking and oral contraceptive (OC) use in Swedes and Koreans. Methods CYP1A2 enzyme activity was determined in 194 and 150 healthy Swedish and Korean subjects, respectively, on the basis of the 4-h plasma paraxanthine/caffeine (17X/137X) ratio determined using high-performance liquid chromatography. Genotyping for the −3860G>A, −2467delT, −739 T>G, −729 C>T, −163C>A and −3113A>G polymorphisms was performed by PCR-restriction fragment length polymorphism analysis. Results The mean 17X/137X ratio was 1.54-fold higher in Swedes than in Koreans (mean difference: 0.16; 95% CI of the mean difference: 0.12, 0.20; p < 0.0001). Smokers had a significantly higher 17X/137X ratio (higher CYP1A2 activity) than non-smokers, while Swedish OC users had a significantly lower 17X/137X ratio than non-users (mean difference: 0.31, 95% CI of the mean difference: 0.23, 0.39; p < 0.0001). No effect of gender differences on enzyme activity was observed. Four known (CYP1A2*1A, *1D, *1F, and *1L) and two novel haplotypes (CYP1A2*1V and CYP1A2*1W) were found. CYP1A2*1K was rare in Swedes and absent in Koreans. No significant genotype-phenotype relationship was observed, with the exception of CYP1A2*1F in Swedish smokers, where it was associated with higher enzyme inducibility (p = 0.02). Koreans displayed a significantly lower mean 17X/137X ratio than Swedes having the same CYP1A2 genotype, smoking habit and OC use. Conclusions We found significant differences in CYP1A2 enzyme activity between Swedes and Koreans that could not be explained by environmental factors or the CYP1A2 haplotypes examined, despite differences in allele frequencies. None of the investigated CYP1A2 haplotypes are critical in inducing variations in enzyme activity, with the exception of CYP1A2*1F.     

The impact of the CYP2D6 and CYP2C19 genotypes on venlafaxine pharmacokinetics in a Japanese population

Objective: The cytochrome P ₄₅₀ isozymes CYP2D6 and CYP2C19 exhibit genetic polymorphism in human, including a marked interethnic difference. As the functional status of the isozymes CYP2D6 and CYP2C19 have an impact on the pharmacokinetics of some antidepressants, we investigated whether the disposition of venlafaxine was affected by the CYP2D6 and CYP2C19 genotypes. Methods: Twenty-eight adult Japanese men in good health participated in this study. Genomic DNA was isolated from peripheral lymphocytes, and the CYP2D6 genotype was determined using polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP) analysis and XbaI-RFLP analysis. Subjects were categorized into the following four groups: group 1 CYP2D6*10/*10; group 2 CYP2D6*1/*10 and *2/*10; group 3 CYP2D6*1/*1, *1/*2 and *2/*2; and group 4 the other genotypes. Two defective CYP2C19 alleles (CYP2C19*2 and CYP2C19*3) were identified by means of PCR-RFLP analysis. Venlafaxine was administered orally following an overnight fast. Plasma concentrations of venlafaxine and O-desmethylvenlafaxine were monitored using high-performance liquid chromatography up to 24 h. Results: The peak plasma concentration and values of area under the concentration–time curve up to 24 h for venlafaxine were 298% and 453% higher for group 1 than group 3, and 91% and 120% higher for group 2 than for group 3, respectively. The homozygote for two defective alleles of CYP2C19 showed a higher concentration of venlafaxine within group 1 and group 2. Conclusion: The CYP2D6*10 allele and two CYP2C19 defective alleles, common in an Asian population, are the most likely genetic factors to use in determining interindividual differences in the pharmacokinetics of venlafaxine, although the results with respect to CYP2C19 are preliminary because of the few subjects used. Received: 6 July 1999 / Accepted in revised form 11 January 2000     

Impact of CYP2D6*10 on mexiletine pharmacokinetics in healthy adult volunteers

Objective In vitro studies with human liver microsomes have suggested that the oxidative conversion of mexiletine (MX) to its metabolites is catalyzed by CYP2D6 and is significantly impaired in microsomes with the CYP2D6*10/*10 genotype. Therefore, we examined the influence of the CYP2D6*10 allele on MX pharmacokinetics in Japanese subjects.Methods Subjects with CYP2D6*1/*1 (group*1/*1; n=5), CYP2D6*10/*10 (group*10/*10; n=6) and CYP2D6*5/*10 (group*5/*10; n=4) genotypes received a single 200-mg dose of MX. Plasma and urinary levels of MX and its metabolites (p-hydroxymexiletine (PHM), hydroxymethylmexiletine (HMM) and N-hydroxymexiletine (NHM)) were determined by means of high-performance liquid chromatography.Results Mean area under the concentration–time curve (AUC) and t_1/2 of MX were significantly (P<0.05) higher in the CYP2D6*10/*5 group (AUC 11.23±3.05 µg·h/ml; t_1/2 15.5±3.2 h) than in the CYP2D6*1/*1 (AUC 5.53±1.01 µg·h/ml; t_1/2 8.1±1.6 h) and CYP2D6*10/*10 (AUC 7.32±2.36 µg·h/ml; t_1/2 10.8±2.8 h) groups, but there was no significant difference between the CYP2D6*1/*1 and CYP2D6*10/*10 groups. The maximum plasma concentration of MX was not significantly different among the three groups. The values of urinary excretion of PHM and HMM in the CYP2D6*1/*1 group were significantly (P<0.05) higher than those in the CYP2D6*10/*10 and CYP2D6*5/*10 groups, but there was no significant difference in that of NHM among the three groups. Clearance of MX in the CYP2D6*5/*10 subjects was comparable to that in the poor metabolizers described previously.Conclusion The present findings demonstrated that carriers of the CYP2D6*10 allele showed a decreased clearance of MX. Subjects with CYP2D6*5/*10 showed significantly (P<0.05) increased plasma levels of MX, and homozygotes for CYP2D6*10 also showed an increase, although to a lesser extent. Thus, the CYP2D6*10 allele plays an important role in MX pharmacokinetics.     

Effect of CYP2C9, VKORC1, CYP4F2 and GGCX genetic variants on warfarin maintenance dose and explicating a new pharmacogenetic algorithm in South Indian population

Objective

To determine the influence of genetic polymorphisms on warfarin maintenance dose and to explicate an algorithm using the pharmacogenetic and clinical factors to determine the maintenance and/or starting dose of warfarin in South Indian patients receiving warfarin therapy.

Methods

Patients receiving stabilized warfarin therapy (n?=?257) were included in the study. Single nucleotide polymorphisms (SNPs) of CYP2C9 (rs1799853 and rs1057910), VKORC1 (rs9923231, rs7196161, rs2884737, rs9934438, rs8050894, rs2359612 and rs7294), CYP4F2 (rs2108622) and GGCX (rs11676382) were genotyped by the quantitative real time-PCR method.

Results

The mean daily maintenance dose of warfarin was found to be 4.7?±?2.1 mg/day. Patients with the CYP2C9*1/*2, *1/*3 and *2/*3 variant genotypes required a 51.0 (2.8 mg), 60.9 (2.3 mg) and 62.2 % (2.2 mg) lower daily maintenance dose of warfarin, respectively, than those patients with the CYP2C9*1/*1 wild-type genotype (5.2 mg) (p?<?0.0001). The genetic variants of CYP2C9, VKORC1 and GGCX were associated with decreased warfarin dose, except for rs7196161, rs7294 and rs2108622 which were associated with an increased warfarin dose. Genetic variations of CYP2C9 (*2 and *3), VKORC1 (rs9923231, rs7294, rs9934438 and rs2359612), CYP4F2, GGCX and non-genetic factors such as age, body weight, clinical status (post mechanical valve replacement) could explain up to 62.1 % of the overall variation (adjusted r ² 60.2 %, p?<?0.0001) in warfarin maintenance dose.

Conclusion

Genetic polymorphisms of CYP2C9, VKORC1, CYP4F2 and GGCX are important predictive factors of warfarin maintenance dose, and the developed algorithm will be useful to predict the required maintenance and/or starting warfarin dose in South Indian populations.