Association of CYP3A variants with kidney transplant outcomes

Effect of CYP3A4, CYP3A5, MDR1 and POR Genetic Polymorphisms in Immunosuppressive Treatment in Chilean Kidney Transplanted Patients

Cyclosporine (CsA) and tacrolimus (TAC) are immunosuppressant drugs characterized by a narrow therapeutic range and high pharmacokinetic variability. The effect of polymorphisms in genes related to the metabolism and transport of these drugs, namely CYP3A4, CYP3A5, MDR1 and POR genes, has been evaluated in diverse populations. However, the impact of these polymorphisms on drug disposition is not well established in Latin American populations. Using TaqMan® probes, we determined the allelic frequency of seven variants in CYP3A4, CYP3A5, MDR1 and POR in 139 Chilean renal transplant recipients, of which 89 were treated with CsA and 50 with TAC. We tested associations between variants and trough and/or 2-hour concentrations, normalized by dose (C₀/D and C₂/D) at specific time points post-transplant. We found that CYP3A5*3/*3 carriers required lower doses of TAC. In TAC treated patients, most CYP3A5*3/*3 carriers presented higher C₀/D and a high proportion of patients with C₀ levels outside the therapeutic range relative to other genotypes. These results reinforce the value of considering CYP3A5 genotypes alongside therapeutic drug monitoring for TAC treated Chilean kidney recipients.

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.

Incidence, risk factors and outcomes of malignancies after kidney transplantation in Singapore: a 12-year experience

INTRODUCTION

Data on malignancy after kidney transplantation (KTX) is limited in our region, leading to challenges in the care of renal allograft recipients. We aimed to examine the epidemiology, risk factors and outcomes of post-KTX patients.

METHODS

A retrospective cohort study was conducted of 491 patients who underwent KTX from 1 January 2000 to 31 December 2011. Data linkage analysis was done between our centre and the National Registry of Diseases Office to determine the standardised incidence ratio (SIR), standardised mortality ratio (SMR) and risk factors for malignancy after KTX.

RESULTS

31 patients (61.3% male) developed malignancy during this period, and their median age at diagnosis was 50 (range 18-65) years. Median time to malignancy diagnosis was 2.6 (range 0.3-7.9) years, with cumulative incidence of 1%, 4% and 10% at one, five and ten years, respectively. The commonest malignancy type was lymphoma, followed by kidney cancer, colorectal cancer and malignancy of the male genital organs. Multivariate analysis identified cyclosporine use as an independent risk factor for malignancy. Compared to the general population, KTX recipients had higher malignancy and mortality rates after malignancy diagnosis (SIR 3.36; SMR 9.45). Survival rates for KTX recipients with malignancy versus those without malignancy were 100%, 93% and 64% versus 97%, 93% and 83% at one, five and ten years, respectively.

CONCLUSION

KTX was associated with higher mortality and incidence of malignancy. Newer immunosuppressive agents and induction therapies were not found to be risk factors for malignancy, possibly due to our relatively small sample size.

The Pharmacogenetics of Immune-Modulating Therapy

Immunosuppressive drugs are a prerequisite in organ transplantation to prevent rejection and are also widely used in inflammatory diseases such as inflammatory bowel disease (IBD) or also in some hematologic malignancies-depending on the mode of action. For thiopurine analogs the polymorphic thiopurine S-methyltransferase (TPMT) was early detected to be associated with thiopurine-induced leukopenia; recent studies identified also NUDT15 to be related to this severe side effect. For drugs like methotrexate and mycophenolate mofetil a number of ADME genes like UDP-glucuronosyltransferases (UGTs) and ABC efflux transporters were investigated, however, with partly contradicting results. For calcineurin inhibitors like cyclosporine and in particular tacrolimus however, cytochrome P450 3A4 and 3A5 variants were found to significantly affect the pharmacokinetics. Genetic variants in genes encoding relevant pharmacodynamic proteins, however, lacked compelling evidence to affect the clinical outcome. This chapter reviews the current evidence on the association of pharmacogenetic traits to dose finding and clinical outcome of small-molecule immunosuppressants. Moreover this chapter critically summarizes suitability to apply pharmacogenetics in clinical practice in order to optimize immunosuppressant therapy.

Genetic Variations Associated with Anti-Tuberculosis Drug-Induced Liver Injury

Purpose of this Review

In order to combat the development of drug resistance, the clinical treatment of tuberculosis requires the combined use of several anti-tuberculosis (anti-TB) drugs, including isoniazid and rifampicin. Combinational treatment approaches are suggested by the World Health Organization (WHO) and are widely accepted throughout the world. Unfortunately, a major side effect of the treatment is the development of anti-tuberculosis drug-induced liver injury (AT-DILI). Many factors contribute to isoniazid- and rifampicin-mediated AT-DILI and genetic variations are among the most common factors. The purpose of this review is to provide information on genetic variations associated with isoniazid- and rifampicin-mediated AT-DILI.

Recent Findings

The genetic variations associated with AT-DILI have been identified in the genomic regions within or near genes encoding proteins in the following pathways: drug metabolizing enzymes (NAT2, CYP2E1, and GSTs), accumulation of bile acids, lipids, and heme metabolites (CYP7A1, BSEP, UGTs, and PXR), immune adaptation (HLAs and TNF-α), and oxidant challenge (TXNRD1, SOD1, BACH1, and MAFK).

Summary

The information summarized in this review considers the genetic bases of risk factors contributing to AT-DILI and provides information that may help for future studies. Some of the implicated genetic variations can be used in the design of genetic tests and serve as biomarkers for the prediction of isoniazid- and rifampicin-mediated AT-DILI risk in personalized medicine.

Genetic predictors of long-term graft function in kidney and pancreas transplant patients

Kidney and pancreas transplantation have helped transform the lives of people with end-stage renal failure and individuals with type 1 diabetes who have poor glycaemic control/severe secondary complications, respectively. Despite an improvement in immunosuppressive regimes, operative techniques and decreased initial rejection rates, there has been little improvement in long-term graft survival rates over the past decade. Whilst limited progress has been made in establishing clinical markers of graft function, several genetic markers of long-term graft function have been identified. These genetic markers have the potential to (i) assist in selecting marginal donor organs for transplantation, (ii) provide better understanding of the mechanisms behind graft loss enabling identification of new, or repurposing, current treatments to extend graft function and (iii) provide a window of opportunity to identify and treat individuals before graft failure has occurred. This review will discuss the different genetic variants screened for a role in predicting transplant longevity, examine their findings and limitations and introduce where the future of genetic research within the transplantation field lies.

Pharmacogenetics and drug-induced nephrotoxicity in renal transplant recipients

INTRODUCTION

The advent of calcineurin inhibitors (CNIs), as the leading immunosuppressive agents, not only has revolutionized the transplant medicine but also made it a better therapeutic intervention that guarantees the graft outcome and improves the survival rate of patients. However, genetic polymorphism(s) in the CNIs metabolic substrates genes (CYP3A4, CYP3A5) and their transporter such as P-glycoprotein (P-gp) can influence the CNIs metabolism and elicit some possible systemic and intra-renal exposures to drugs and/or metabolites with differential risk of nephrotoxicity, jeopardizing the transplantation.

METHODS

In the current study, we review the recent literatures to evaluate the effects of genetic polymorphisms of the genes involved in development of chronic calcineurin nephrotoxicity and progression of chronic allograft dysfunction (CAD) providing an extensive overview on their clinical impacts.

RESULTS

Identifying the inherited genetic basis for the inter-individual differences in terms of drug responses and determining the risk of calcineurin-mediated nephrotoxicity and CAD allow optimized personalized administration of these agents whith minimal adverse effects.

CONCLUSION

Pharmacogenetics characteristics of CYP isoforms (CYP3A) and efflux transporters (P-gp and MRP), involved in metabolism and extracellular transportation of the immunosuppressive CNIs, can be of pivotal information in the pharmacotherapy of the renal-transplant recipients. Such information can be used for the successes clinical interventions to attain an improved drug administration strategy with reduced rates of rejection and toxicity.