Analysis of common polymorphisms within NR1I2 and NR1I3 genes and tacrolimus dose-adjusted concentration in stable kidney transplant recipients

Why We Need to Take a Closer Look at Genetic Contributions to CYP3A Activity

Cytochrome P450 3A (CYP3A) subfamily enzymes are involved in the metabolism of 40% of drugs in clinical use. Twin studies have indicated that 66% of the variability in CYP3A4 activity is hereditary. Yet, the complexity of the CYP3A locus and the lack of distinct drug metabolizer phenotypes has limited the identification and clinical application of CYP3A genetic variants compared to other Cytochrome P450 enzymes. In recent years evidence has emerged indicating that a substantial part of the missing heritability is caused by low frequency genetic variation. In this review, we outline the current pharmacogenomics knowledge of CYP3A activity and discuss potential future directions to improve our genetic knowledge and ability to explain CYP3A variability.

CYP and SXR gene polymorphisms influence in opposite ways acute rejection rate in pediatric patients with renal transplant

Background

We evaluated the role of CYP3A5, ABCB1 and SXR gene polymorphisms in the occurrence of acute kidney rejection in a cohort of pediatric renal transplant recipients.

Methods

Forty-nine patients were genotyped for CYP3A5, ABCB1 and SXR polymorphisms and evaluated with tacrolimus through levels in a retrospective monocenter study.

Results

Patients with the A allele of CYP3A5 treated with tacrolimus had a higher risk of acute rejection than those without the A allele, while patients carrying the homozygous GG variant for SXR A7635GG did not show any episode of acute rejection.

Conclusion

Genetic analysis of polymorphisms implicated in drug metabolism and tacrolimus trough levels may help to forecast the risk of acute rejection and individualize drug dosage in children undergoing renal transplantation.

Pharmacogenetics and tacrolimus administration in stem cell transplantation

Tacrolimus is the gold standard immunosuppressant administered in solid organ and stem cell transplantation to avoid graft rejection post-transplant. Despite its widespread use, there is a large variation in response to therapy, likely due to high inter-individual pharmacokinetic variability. Therapeutic drug monitoring is employed to improve clinical response and reduce toxicity. There is substantial evidence that pharmacogenetics influences drug exposure and response. CYP3A5 genotype significantly impacts oral tacrolimus concentrations and response after solid organ transplantation. There are fewer studies in stem cell transplantation and with intravenous tacrolimus dosing. This report highlights recent evidence suggesting genes such as CYP3A4 and ABCB1 play a larger role after intravenous dosing compared with CYP3A5, and the role for novel genes on tacrolimus outcomes.

PXR haplotype clusters will affect the pharmacokinetics of ciclosporin in Chinese renal transplant recipients

OBJECTIVE

PXR was reported to be the key nuclear receptor regulating the expression of metabolizing enzymes and transporters. The aim of this study was to evaluate the influence of PXR haplotype clusters on ciclosporin concentration in Chinese renal transplant recipients during the early stage after transplantation.

METHODS

A total of 98 recipients receiving ciclosporin were genotyped by PCR-RFLP, and the ciclosporin concentration was determined by EMIT.

KEY FINDINGS

The frequency of IVS2+55A>G, IVS2+78A>G, IVS6-17C>T, 1792A>G, 1944T>C and 2654T>C variant alleles was 0.343, 0.332, 0.378, 0.515, 0.520 and 0.393, which fitted Hardy-Weinberg equilibrium. Only the IVS6-17C>T and 2654T>C were significantly associated with the ciclosporin C₂ /D during the end of the first month. The mean ciclosporin C₂ /D level of the PXR*1B haplotype clusters was 1.3-fold and 1.2-fold higher compared with the *1A and *1C. No significant difference was observed in CsA C₂ /D between the PXR*1A and PXR*1C. We found no difference in C₀ /D among the six genotypes or the three haplotype clusters.

CONCLUSIONS

The PXR*1B in Chinese renal transplant patients was associated with ciclosporin concentration. Genetic polymorphisms and specific haplotype clusters in PXR could have significant contributory roles in affecting interethnic variations in drug disposition in the Chinese population.

Genetic Polymorphisms and Adverse Events on Unbound Imatinib and Its Active Metabolite Concentration in Patients With Gastrointestinal Stromal Tumors

Imatinib is a first-line drug for the treatment of gastrointestinal stromal tumors (GIST). This study aims to investigate the influence of different kinds of protein concentrations and genetic polymorphisms of metabolizing enzymes and drug transporters on unbound imatinib and its active metabolite N-desmethyl-imatinib concentration, as well as the relationship between adverse drug reactions (ADRs) and drug concentration. A total of 62 Chinese patients with GIST were genotyped for five single nucleotide polymorphisms (SNPs). Total and unbound 3h and trough concentration of imatinib and N-desmethyl-imatinib in GIST patients were determined by an LC-MS/MS method combined with an equilibrium dialysis. Single-Use Red Plate with inserts was used to separate the unbound drug. When the protein concentration became higher, the unbound imatinib and N-desmethyl-imatinib plasma concentration got higher (p < 0.05). Patients with GA genotype in rs755828176 had significantly higher unbound N-desmethyl-imatinib dose-adjusted trough plasma concentrations (p = 0.012). Patients with CC genotype in rs3814055 had significantly higher unbound imatinib dose-adjusted trough plasma concentrations (p = 0.040). The mean total imatinib C_3h of patients with ADRs (3.10 ± 0.96 µg/ml) was significantly higher than that of patients without ADRs (p = 0.023). The mean total N-desmethyl-imatinib C_3h of patients (0.64 ± 0.21 µg/ml) with ADRs was significantly higher than that of patients without ADRs (p = 0.004). The mean unbound N-desmethyl-imatinib C_3h of patients with ADRs (6.49 ± 2.53 ng/ml) was significantly higher than that of patients without ADRs (p = 0.042). The total and unbound C_3h of imatinib and N-desmethyl-imatinib in patients with ADRs was significantly higher than that in patients without ADRs (p < 0.05). Protein concentrations have great influence on the unbound imatinib and N-desmethyl-imatinib concentrations. The genetic polymorphisms of CYP3A4 rs755828176 and NR1I2 rs3814055 were significantly associated with unbound imatinib and N-desmethyl-imatinib dose-adjusted trough plasma levels. The total and unbound imatinib or N-desmethyl-imatinib concentration in patients with GIST was also significantly correlated with ADRs.

Genetic analysis of pharmacogenomic VIP variants in the Blang population from Yunnan Province of China

Background

Genetic polymorphisms in numerous pharmacogenetics studies were regarded as the essential factors involved in the response to or metabolism of drugs. These genetic variants called very important pharmacogenetic (VIP) variants played a role in drugs metabolism, which have been summarized in the PharmGKB database. In this study, we genotyped 80 VIP variants from the PharmGKB in 100 members of Blang volunteers from Yunnan province.

Methods

Based on the PharmGKB database, we genotyped 80 VIP variants loci located in 47 genes. We used χ² tests to evaluate the significant loci between Blang and the other populations, including ASW, CEU, CHB, CHD, GIH, JPT, LWK, MEX, MKK, TSI, and YRI. The global variation distribution of the significant variants was observed from the ALlele FREquency Database. And then, we used F‐statistics (Fst), genetic structure, and phylogenetic tree analyses to ascertain the genetic affinity among 12 populations.

Results

Comparing the Blang with the other 11 populations from the HapMap Project, the statistical results revealed that rs3814055 (NC_000003.12:g.119781188C>T) of nuclear receptor subfamily 1 group I member 2 (NR1I2, OMIM# 603,065) was the most significant variant, followed by rs1540339 (NC_000012.12:g.47863543C>T) of vitamin D receptor (VDR, OMIM#601,769). Furthermore, we found that genotype frequency of rs3814055 in the Blang was closer to the populations distributed in Miao. And genetic structure and F‐statistics indicated that the Blangs had a relatively closer affinity with CHD, CHB, and JPT populations. In addition, the Han nationality in Shaanxi was closer to it.

Conclusions

Our results will complement the pharmacogenomics information of the Blang ethnic group and provide a theoretical basis for safer drug administration for Blang.