Single nucleotide polymorphisms of the pregnane x receptor gene in Han Chinese and a comparison with other ethnic populations

Effect of Pregnane X Receptor*1B genetic polymorphisms on postoperative analgesia with fentanyl in Chinese patients undergoing gynecological surgery

Background

The purpose of the study was to investigate the effects of the pregnane X receptor (PXR)*1B polymorphisms on CYP3A4 enzyme activity and postoperative fentanyl consumption in Chinese patients undergoing gynecological surgery.

Methods

A total of 287 females of Han ethnicity, aged 20 to 50 years old, ASA I or II, scheduled to abdominal total hysterectomy or myomectomy under general anesthesia were enrolled. The analgesic model used was fentanyl consumption via patient-controlled intravenous analgesia (PCIA) in the post-operative period. Additionally, pain was assessed using a visual analog score (VAS). Pain scores, occurrence of adverse reactions and consumption of fentanyl were recorded during the 24 h postoperative period. The enzyme activity of CYP3A4 was evaluated by measuring the plasma ratio of 1′-hydroxymidazolam to midazolam 1 h after intravenous administration of 0.1 mg/kg midazolam. PXR genotyping was performed by direct DNA sequencing and the PXR^*1B haplotype was analyzed via PHASE V.2.1 software.

Results

The polymorphism frequency of PXR11156A > C/11193 T > C and 8055C > T were 49.6 and 49.3%, and the rate of PXR^*1B haplotype was 48.8% in our study. None of the pain scores, consumption of fentanyl 24 h post-operatively or enzyme activity of CYP3A4, showed differences among different genotypes.

Conclusions

PXR11156A > C, PXR11193T > C, PXR8055C > T or the PXR^*1B haplotype do not appear to be important factors contributing to CYP3A4 activity and interindividual variations in postoperative fentanyl consumption in Han female patients undergoing gynecological surgery.

Trial registration

The DNA samples were obtained since 2007 to 2010 year in our hospital, there was no registration at that time. So this section is not applicable to our research.

Associations of CYP3A4, NR1I2, CYP2C19 and P2RY12 polymorphisms with clopidogrel resistance in Chinese patients with ischemic stroke

AIM

There is a high incidence of the antiplatelet drug clopidogrel resistance (CR) in Asian populations. Because clopidogrel is a prodrug, polymorphisms of genes encoding the enzymes involved in its biotransformation may be the primary influential factors. The goal of this study was to investigate the associations of polymorphisms of CYP3A4, NR1I2, CYP2C19 and P2RY12 genes with CR in Chinese patients with ischemic stroke.

METHODS

A total of 191 patients with ischemic stroke were enrolled. The patients were treated with clopidogrel for at least 5 days. Platelet function was measured by light transmission aggregometry. The SNPs NR1I2 (rs13059232), CYP3A4(*)1G (rs2242480), CYP2C19(*)2 (rs4244285) and P2RY12 (rs2046934) were genotyped.

RESULTS

The CR rate in this population was 36%. The CYP2C19(*)2 variant was a risk factor for CR ((*)2/(*)2+wt/(*)2 vs wt/wt, OR: 2.366, 95% CI: 1.180-4.741, P=0.014), whereas the CYP3A4(*)1G variant had a protective effect on CR ((*)1/(*)1 vs (*)1G/(*)1G+(*)1/(*)1G, OR: 2.360, 95% CI: 1.247-4.468, P=0.008). The NR1I2 (rs13059232) polymorphism was moderately associated with CR (CC vs TT+TC, OR: 0.533, 95% CI: 0.286-0.991, P=0.046). The C allele in P2RY12 (rs2046934) was predicted to be a protective factor for CR (CC+TC vs

TT, OR

0.407, 95% CI: 0.191-0.867, P=0.018). In addition, an association was found between hypertension and CR (P=0.022).

CONCLUSION

The individuals with both the CYP2C19(*)2 allele and hypertension are at high risk of CR during anti-thrombosis therapy. The CYP3A4(*)1G allele, P2RY12 (rs2046934) C allele and NR1I2 (rs13059232) CC genotype may be protective factors for CR. The associated SNPs studied may be useful to predict clopidogrel resistance in Chinese patients with ischemic stroke.

Genetic markers in CYP2C19 and CYP2B6 for prediction of cyclophosphamide's 4-hydroxylation, efficacy and side effects in Chinese patients with systemic lupus erythematosus

AIMS

The aim of the study was to investigate the combined impact of genetic polymorphisms in key pharmacokinetic genes on plasma concentrations and clinical outcomes of cyclophosphamide (CPA) in Chinese patients with systemic lupus erythematosus (SLE).

METHODS

One hundred and eighty nine Chinese SLE patients treated with CPA induction therapy (200 mg, every other day) were recruited and adverse reactions were recorded. After 4 weeks induction therapy, 128 lupus nephritis (LN) patients continued to CPA maintenance therapy (200-600 mg week(-1)) for 6 months, and their clinical outcomes were recorded. Blood samples were collected for CYP2C19, CYP2B6, GST and PXR polymorphism analysis, as well as CPA and its active metabolite (4-hydroxycyclophosphamide (4-OH-CPA)) plasma concentration determination.

RESULTS

Multiple linear regression analysis revealed that CYP2B6 -750 T > C (P < 0.001), -2320 T > C (P < 0.001), 15582C > T (P = 0.017), CYP2C19*2 (P < 0.001) and PXR 66034 T > C (P = 0.028) accounted for 47% of the variation in 4-OH-CPA plasma concentration. Among these variants, CYP2B6 -750 T > C and CYP2C19*2 were selected as the combination genetic marker because these two SNPs contributed the most to the inter-individual variability in 4-OH-CPA concentration, accounting for 23.6% and 21.5% of the variation, respectively. Extensive metabolizers (EMs) (CYP2B6 -750TT, CYP2C19*1*1) had significantly higher median 4-OH-CPA plasma concentrations (34.8, 11.0 and 6.6 ng ml(-1) for EMs, intermediate metabolizers (IMs) and poor metabolizers (PMs), P < 0.0001), higher risks of leukocytopenia (OR = 7.538, 95% CI 2.951, 19.256, P < 0.0001) and gastrointestinal toxicity (OR = 7.579, 95% CI 2.934, 19.578, P < 0.0001), as well as shorter median time to achieve complete remission (13.2, 18.3 and 23.3 weeks for EMs, IMs and PMs, respectively, P = 0.026) in LN patients than PMs (CYP2B6 -750CC, CYP2C19*2*2) and IMs.

CONCLUSIONS

Our findings have indicated that genetic markers of drug metabolizing enzymes could predict the 4-hydroxylation, adverse reactions and clinical efficacy of CPA. This is a necessary first step towards building clinical tools that will help assess clinical benefit and risk before undergoing CPA treatment in Chinese SLE patients.

Interactive effects of CYP3A4, CYP3A5, MDR1 and NR1I2 polymorphisms on tracrolimus trough concentrations in early postrenal transplant recipients

Aims: To evaluate the influences of CYP3A4, CYP3A5, MDR1 and NR1I2 polymorphisms on tacrolimus concentration in early postrenal transplant recipients. Patients & methods: A total of 159 patients were included, dose-adjusted tacrolimus trough concentration on day 7 after transplantation (C0D7/D) was calculated and 10 SNPs in four genes were genotyped. Results: CYP3A5*3 explained 32.8% of variability of tacrolimus C0D7/D. CYP3A4*1G, MDR1 1236–2677–3435 diplotype and NR1I2 -25385C > T explained 21.4% of variability of tacrolimus C0D7/D in CYP3A5 nonexpressers. Conclusion: CYP3A5*3 was the predominant determinant affecting tacrolimus concentration. Genotyping of CYP3A4/MDR1/NR1I2 polymorphisms may be helpful for better guiding tacrolimus dosing in CYP3A5 nonexpressers.

Pharmacogenomics and personalized medicine: a review focused on their application in the Chinese population

The field of pharmacogenomics was initiated in the 1950s and began to thrive after the completion of the human genome project 10 years ago. Thus far, more than 100 drug labels and clinical guidelines referring to pharmacogenomic biomarkers have been published, and several key pharmacogenomic markers for either drug safety or efficacy have been identified and subsequently adopted in clinical practice as pre-treatment genetic tests. However, a tremendous variation of genetic backgrounds exists between different ethnic groups. The application of pharmacogenomics in the Chinese population is still a long way off, since the published guidelines issued by the organizations such as US Food and Drug Administration require further confirmation in the Chinese population. This review highlights important pharmacogenomic discoveries in the Chinese population and compares the Chinese population with other nations regarding the pharmacogenomics of five most commonly used drugs, ie, tacrolimus, cyclosporine A, warfarin, cyclophosphamide and azathioprine.

Population pharmacokinetics of nevirapine in Thai HIV-infected patients

BACKGROUND

Nevirapine-based antiretroviral therapy is widely used as a first-line treatment for HIV-infected patients in resource-limited settings. Nevirapine plasma concentration has been shown to be associated with virological response and treatment failure. Therefore, identifying sources of the variability of nevirapine pharmacokinetics is important for dose optimization. The purpose of the current study was to determine the population mean pharmacokinetic parameters and identify factors that influence pharmacokinetic parameters of nevirapine in Thai HIV-infected patients.

METHODS

The model was developed by a non-linear mixed-effects modelling approach using NONMEM. Model validation was performed using bootstrap analysis and external validation. Additionally, nevirapine plasma concentrations of 200 mg twice daily (NVPBID) and 400 mg once daily (NVPOD) were simulated using the final model to investigate the impact of the covariates and different dosage regimens on nevirapine steady state concentrations.

RESULTS

The apparent clearance (CL/F) of nevirapine estimated from this population was 2.51 l/h which is lower than the values previously reported in other populations. The concomitant use of rifampicin increased CL/F by 20%. Simulated nevirapine plasma concentrations from NVPBID were superior to the NVPOD regimen.

CONCLUSIONS

This population-based pharmacokinetic model can be used for optimizing nevirapine dosage regimens for individual patients to improve efficacy and safety of nevirapine therapy in this population.

Associations of ABCB1, NFKB1, CYP3A, and NR1I2 polymorphisms with cyclosporine trough concentrations in Chinese renal transplant recipients

AIM

Cyclosporine requires close therapeutic drug monitoring because of its narrow therapeutic index and marked inter-individual pharmacokinetic variation. In this study, we investigated the associations of CYP3A4, CYP3A5, ABCB1, NFKB1, and NR1I2 polymorphisms with cyclosporine concentrations in Chinese renal transplant recipients in the early period after renal transplantation.

METHODS

A total of 101 renal transplant recipients receiving cyclosporine were genotyped for CYP3A4(*)1G, CYP3A5(*)3, ABCB1 C1236T, G2677T/A, C3435T, NFKB1 -94 ins/del ATTG, and NR1I2 polymorphisms. Cyclosporine whole blood levels were measured by a fluorescence polarization immunoassay. Trough concentrations of cyclosporine were determined for days 7-18 following transplantation.

RESULTS

The dose-adjusted trough concentration (C0) of cyclosporine in ABCB1 2677 TT carriers was significantly higher than that in GG carriers together with GT carriers [90.4±24.5 vs 67.8±26.8 (ng/mL)/(mg/kg), P=0.001]. ABCB1 3435 TT carriers had a significantly higher dose-adjusted C0 of cyclosporine than CC carriers together with CT carriers [92.0±24.0 vs 68.4±26.5 (ng/mL)/(mg/kg), P=0.002]. Carriers of the ABCB1 1236TT-2677TT-3435TT haplotype had a considerably higher CsA C0/D than carriers of other genotypes [97.2±21.8 vs 68.7±26.9 (ng/mL)/(mg/kg), P=0.001]. Among non-carriers of the ABCB1 2677 TT and 3435 TT genotypes, patients with the NFKB1 -94 ATTG ins/ins genotype had a significantly higher dose-adjusted C0 than those with the -94 ATTG del/del genotype [75.9±32.9 vs 55.1±15.1 (ng/mL)/(mg/kg), P=0.026].

CONCLUSION

These results illustrate that the ABCB1 and NFKB1 genotypes are closely correlated with cyclosporine trough concentrations, suggesting that these SNPs are useful for determining the appropriate dose of cyclosporine.

PXR variants and artemisinin use in Vietnamese subjects: frequency distribution and impact on the interindividual variability of CYP3A induction by artemisinin

Artemisinins induce drug metabolism through the activation of the pregnane X receptor (PXR) in vitro. Here, we report the resequencing and genotyping of PXR variants in 75 Vietnamese individuals previously characterized for CYP3A enzyme activity after artemisinin exposure. We identified a total of 31 PXR variants, including 5 novel single nucleotide polymorphisms (SNPs), and we identified significantly different allele frequencies relative to other ethnic groups. A trend of significance was observed between the level of CYP3A4 induction by artemisinin and two PXR variants, the 8118C→T (Y328Y) and 10719A→G variants.

Frequency of genetic polymorphisms of PXR gene in the Brazilian population

INTRODUCTION

PXR polymorphisms have been implicated in modulating CYP3A4 and PXR expression, potentially accounting for interindividual differences in drug metabolism. The prevalence of PXR polymorphisms varies among ethnic groups and data on the allelic distribution in the highly mixed Brazilian population is lacking. The aim of this study was to analyze genetic variations in the PXR gene in Brazilians and to compare the results to other ethnic groups.

METHODS

DNA samples from 117 healthy Brazilians underwent PCR amplification and sequencing.

RESULTS

Eleven polymorphisms were identified, 3 of which are highly associated with differences in CYP3A4 expression. We also identified 1 new synonymous variant in 1.3% of the alleles. Among the functional polymorphisms, -25913 C>T and -6994T>C occurred at a higher frequency comparedtothe Africanalleles (p < 0.05) but at a lower frequency compared to Caucasian alleles. The 8055 C>T allele was found at a similar frequency to those described in Caucasians and Africans (p > 0.05).

CONCLUSION

We observed that functional variants of the PXR were frequent in our sample of the Brazilian population. Our results suggest that PXR gene variants may be of interest in pharmacogenetic studies involving Brazilians.