Pharmacogenetics of immunosuppressant drugs: A new aspect for individualized therapy

In recent years, pharmacogenetics has emerged as an important tool for choosing the right immunosuppressant drug and its appropriate dose. Indeed, pharmacogenetics may exert its action on immunosuppressant drugs at three levels. Pharmacogenetics identifies and studies the genes involved in encoding the proteins involved in drug pharmacokinetics and in encoding the enzymes involved in drug degradation. Pharmacogenetics is also relevant in encoding the enzymes and proteins involved in codifying the transmembrane proteins involved in transmembrane passage favoring the absorption and intracellular action of several immunosuppressants. Pharmacogenetics concern the variability of genes encoding the proteins involved as immunosuppressant triggers in the pharmacodynamic pathways. Of course, not all genes have been discovered and studied, but some of them have been clearly examined and their relevance together with other factors such as age and race has been defined. Other genes on the basis of relevant studies have been proposed as good candidates for future studies. Unfortunately, to date, clear conclusions may be drawn only for those drugs that are metabolized by CYP3A5 and its genotyping before kidney, heart and lung transplantation is recommended. The conclusions of the studies on the recommended candidate genes, together with the development of omics techniques could in the future allow us to choose the right dose of the right immunosuppressant for the right patient.     

传统抗精神病药物所致迟发性运动障碍的药理遗传学初步研究

目的：进一步探讨多巴胺D2、D3受体（dopamine D2,D3 receptor,DRD2,DRD3)功能基因多态性与迟发性运动障碍(tardive dyskinesia,TD）的相关性及各候选基因，同时包括五羟色胺2C受体（5－hydroxytryptamine 2C receptor,HTR2C）和锰超氧化物歧化酶（manganese superoxide dismutase,MnSOD）基因的相互作用对TD发生的影响。方法：使用异常不自主运动量表（abnormal involuntary movement scale,AIMS)评定精神分裂症（schizophrenia,CSH)患者有无TD及其严重程度，并采用简明精神病评定量表评定患者精神症状；应用聚合酶链反应－限制性片段长度多态性技术分析TD组和非TD组各候选基因等位基因和（或）基因型分布频率及其结合分布频率，并分析对AIMS总分值的影响。结果：各候选基因在SCH患者组以及TD和非TD组基因型分布均符合Hardy-Weinberg平衡定律；TD组HTR2C基因－697C（突变型）等位基因频率高于非TD组，差异有显著性（P＜0．05）；DRD2基因Taq I A1/A2、DRD3基因Ser9Gly和MnSOD基因Ala-9Val等位基因频率和基因型分布在TD组与非TD组之间差异均无显著性（P＞0．05）；仅DRD3突变型（Gly）和MnSOD野生型（Val）结合分布频率高于其它结合型，差异有显著性（P＜0．05）；但上述各候选基因不同等位基因和（或）基因型亚组间的临床学资料和AIMS总分值（TD值）差异均无显著性（P＞0．05）。结论：HTR2C基因启动区－697G→C单碱基置换可能是中国汉族男性SCH患者TD发生的易感因素；而SCH患者若同时携带DRD3基因9Gly突变型和MnSOD基因－9Val野生型等位基因可能增加了TD的易感性。     

Compound heterozygosity for two non-synonymous polymorphisms in NPC1L1 in a non-responder to ezetimibe

Ezetimibe reduces plasma low-density lipoprotein (LDL) cholesterol by blocking sterol absorption in enterocytes. The NPC1L1 gene product was recently identified as the molecular target for ezetimibe, although functional details are incomplete. We used the non-response phenotype of plasma LDL cholesterol to ezetimibe treatment to ascertain individuals who might have variant NPC1L1. We found that one non-responder to ezetimibe was a compound heterozygote for two rare non-synonymous polymorphisms in NPC1L1 that were absent in normal control subjects. We also characterized other NPC1L1 polymorphisms. While there are many explanations for non-response to medications, our data suggest a possible relationship between NPC1L1 variation and ezetimibe response and further indicate that a non-response phenotype might ascertain subjects with genomic DNA variants that could help define metabolic pathways.     

Renal function in HIV/HBV co‐infected and HBV mono‐infected patients on a long‐term treatment with tenofovir in real life setting

The human immunodeficiency virus (HIV)/hepatitis B virus (HBV) co‐infection is likely to be associated with an increased risk of kidney disease, due to the additional factors that may affect renal function in the HIV population. We aimed to evaluate renal toxicity in HIV/HBV and HBV mono‐infected patients on long‐term therapy with tenofovir (TDF) and to explore the association of polymorphisms in ATP‐binding cassette (ABCC)2, ABCC4, ABCC10 with the development of renal dysfunction. From September 2006 to November 2014, 44 HIV/HBV co‐infected and 34 HBV mono‐infected patients were commenced on TDF. Data of renal safety were retrospectively collected and analyzed. ABCC2, ABCC4 and ABCC10 genotypes were identified by real‐time PCR. Over 60 months of observation, there was a significant increase in mean creatinine levels from baseline (P<.01) that was not significantly different between the two study groups. Moreover, a significant decline in estimated glomerular filtration rate (eGFR) was observed from baseline (P<.01), and it was significantly greater in HBV mono‐infected than co‐infected patients (P=.03). The distribution of ABCC2, ABCC4 and ABCC10 genotypes among a subgroup of 34 patients did not show significant association with eGFR decline <90 mL/min per 1.73 m². Although our findings showed a statistically significant decrease in eGFR with long‐term use of TDF, its clinical impact seems to be modest. The role of genetic factors to identify patients at greater risk for developing tenofovir‐induced renal toxicity needs to be further investigated.     

The ABCG2 C421A polymorphism does not affect oral nitrofurantoin pharmacokinetics in healthy Chinese male subjects

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• An increasing number of drugs on the market or under development have been identified as substrates of the ATP-binding cassette drug efflux transporter breast cancer resistance protein (BCRP; ABCG2), which can affect the pharmacokinetics of drugs by reducing absorption and/or increasing biliary elimination.
• ABCG2 C421A, a single nucleotide polymorphism associated with decreased protein expression/transport activity in vitro and higher anti-cancer drug concentrations in carriers of the C421A polymorphism, may contribute to the intersubject pharmacokinetic variability of BCRP substrates.
• Predicting the potential influence of BCRP on drug disposition or drug interactions is challenging because of the lack of a well-characterized, BCRP-selective clinical probe substrate.
• Nitrofurantoin is potentially a suitable clinical BCRP probe substrate based on preclinical and clinical information available (e.g. in vitro transport studies, Bcrp knockout mouse studies, inhibition studies in rats, and milk secretion studies in rats and humans).

WHAT THIS STUDY ADDS

• The ABCG2 C421A SNP had no effect on oral nitrofurantoin plasma and urine pharmacokinetic parameters in healthy male Chinese subjects.
• Nitrofurantoin does not appear to be a useful clinical BCRP probe.

AIMS

A number of drugs are substrates or inhibitors of the efflux transporter breast cancer resistance protein (BCRP; ABCG2), which can limit systemic exposure by reducing absorption and/or increasing biliary elimination. The identification of a BCRP-selective clinical probe drug would provide a useful tool to understand the effect of genetic polymorphisms and transporter-based drug interactions on drug pharmacokinetics. The aim of this study was to assess the utility of nitrofurantoin as a clinical probe substrate for BCRP activity by evaluating the impact of genetic variation on nitrofurantoin pharmacokinetics.

METHODS

Nitrofurantoin pharmacokinetics were studied in an open-label, single-oral dose (100 mg) study in 36 male Chinese subjects who were pre-screened for ABCG2 421 CC, CA and AA genotypes (n = 12 each). Plasma and urine concentrations of nitrofurantoin were determined by LC/MS/MS and LC/UV respectively. anova was used to compare pharmacokinetic parameters among genotypes.

RESULTS

There were no significant differences in nitrofurantoin pharmacokinetics among the genotypic cohorts. The geometric mean nitrofurantoin plasma AUC_(0-∞) (95% confidence interval) values were 2.21 (2.00, 2.45), 2.42 (2.11, 2.78) and 2.32 (1.99, 2.70) µg h ml⁻¹ and half-life values were 0.79 (0.59, 1.0), 0.76 (0.64, 0.89) and 0.72 (0.62, 0.84) h for ABCG2 421 genotypes CC, CA and AA, respectively. The percentage of dose excreted unchanged in the urine was 43, 44 and 39%, respectively.

CONCLUSIONS

The ABCG2 C421A polymorphism had no effect on nitrofurantoin plasma and urine pharmacokinetic parameters in healthy Chinese subjects. These results indicate that nitrofurantoin is not a suitable clinical probe substrate for assessing BCRP activity.     

Interaction between variants in the CYP2C9 and POR genes and the risk of sulfonylurea‐induced hypoglycaemia: A GoDARTS Study

Data on the association of CYP2C9 genetic polymorphisms with sulfonylurea (SU)‐induced hypoglycaemia (SH) are inconsistent. Recent studies showed that variants in the P450 oxidoreductase (POR) gene could affect CYP2C9 activity. In this study, we explored the effects of POR*28 and combined CYP2C9*2 and CYP2C9*3 genotypes on SH and the efficacy of SU treatment in type 2 diabetes. A total of 1770 patients were included in the analysis of SU efficacy, assessed as the combined outcome of the HbA1c reduction and the prescribed SU daily dose. Sixty‐nine patients with severe SH were compared with 311 control patients. The number of CYP2C9 deficient alleles was associated with nearly three‐fold higher odds of hypoglycaemia (OR, 2.81; 95% CI, 1.30‐6.09; P = .009) and better response to SU treatment (β, ?0.218; SE, 0.074; P = .003) only in patients carrying the POR*1/*1 genotype. Our results indicate that interaction between CYP2C9 and POR genes may be an important determinant of efficacy and severe adverse effects of SU treatment.     

Genetic study of neuregulin 1 and receptor tyrosine-protein kinase erbB-4 in tardive dyskinesia

Objectives: Tardive dyskinesia (TD) is a movement disorder that may develop as a side effect of antipsychotic medication. The aetiology underlying TD is unclear, but a number of mechanisms have been proposed.

Methods: We investigated single-nucleotide polymorphisms (SNPs) in the genes coding for neuregulin-1 and erbB-4 receptor in our sample of 153 European schizophrenia patients for possible association with TD.

Results: We found the ERBB4 rs839523?CC genotype to be associated with risk for TD occurrence and increased severity as measured by the Abnormal Involuntary Movement Scale (AIMS) (P?=?.003).

Conclusions: This study supports a role for the neuregulin signalling pathway in TD, although independent replications are warranted.     

Statin-associated muscle symptoms in coronary patients: design of a randomized study

Objectives. Estimate the effect of atorvastatin on muscular symptom intensity in coronary patients with subjective statin-associated muscle symptoms (SAMS) and to determine the association with blood levels of atorvastatin and its metabolites, to obtain an objective marker for true SAMS. Design. A randomized, double-blinded, cross-over study will include 80 coronary patients with subjectively reported SAMS during ongoing atorvastatin therapy or previous muscle symptoms that led to discontinuation of atorvastatin. Patients will be randomized to 7-weeks treatment with atorvastatin 40?mg/day in the first period and matched placebo in the second 7-weeks period, or placebo in the first period and atorvastatin in the second period. Each period is preceded by 1-week wash-out. A control group (n?=?40) without muscle symptoms will have 7 weeks open treatment with atorvastatin 40?mg/day. Blood samples will be collected at baseline and at the end of each treatment period, and muscular symptoms will be rated by the patients weekly using a Visual Analogue Scale (VAS). The primary outcome is the difference in aggregated mean VAS scores between the last three weeks of atorvastatin treatment and of placebo treatment. The main purpose is to develop an objective marker for true SAMS, by comparing SAMS associated with blinded atorvastatin treatment with blood concentrations of atorvastatin and its metabolites. Diagnostic and discrimination performance will be determined. Conclusions. The study provides new knowledge on SAMS in coronary patients and may contribute to more personalized statin treatment and monitoring, fewer side-effects and consequently improved adherence and lipid management in future practice.