Polymorphisms in CYP3A5, CYP3A4, and ABCB1 are not associated with cyclosporine pharmacokinetics nor with cyclosporine clinical end points after renal transplantation

Use of Pharmacogenetics to Optimize Immunosuppressant Therapy in Kidney-Transplanted Patients

Immunosuppressant drugs (ISDs) are routinely used in clinical practice to maintain organ transplant survival. However, these drugs are characterized by a restricted therapeutic index, a high inter- and intra-individual pharmacokinetic variability, and a series of severe adverse effects. In particular, genetic factors have been estimated to play a role in this variability because of polymorphisms regarding genes encoding for enzymes and transporters involved in the ISDs pharmacokinetic. Several studies showed important correlations between genetic polymorphisms and ISDs blood levels in transplanted patients; therefore, this review aims to summarize the pharmacogenetics of approved ISDs. We used PubMed database to search papers on pharmacogenetics of ISDs in adults or pediatric patients of any gender and ethnicity receiving immunosuppressive therapy after kidney transplantation. We utilized as search term: “cyclosporine or tacrolimus or mycophenolic acid or sirolimus or everolimus and polymorphism and transplant”. Our data showed that polymorphisms in CYP3A5, CYP3A4, ABCB1, and UGT1A9 genes could modify the pharmacokinetics of immunosuppressants, suggesting that patient genotyping could be a helpful strategy to select the ideal ISDs dose for each patient.

Frequency of ABCB1 C3435T and CYP3A5*3 Genetic Polymorphisms in the Lebanese Population

OBJECTIVES

CYP3A5 and ABCB1 are highly implicated in the pharmacokinetics and pharmacodynamics of immunosuppressive agents, such as calcineurin inhibitors and mammalian target of rapamycin inhibitors. The polymorphisms of their coding genes play important roles in the interindividual and intraindividual differences of bioavailability of these drugs. In this study, our objective was to investigate, in a Lebanese population,the frequency of ABCB1C3435T (rs1045642) and CYP3A5*3 (rs776746) polymorphisms and to compare the results to preexisting data from other populations.

MATERIALS AND METHODS

We determined the frequencies of the allelic variants of interest for 1824 Lebanese participants, and we compared these results with those from other major ethnic groups.

RESULTS

The allelic frequencies were 91.4% (C) and 8.6% (T) for CYP3A5*3 and 50.8% (T) and 49.2% (C) for ABCB1 C3435T. Our results were significantly different from most other world populations, except the European population.

CONCLUSIONS

The frequencies of gene variants of interest in our Lebanese population were similar to those found in European populations. Most of our study population were CYP3A5*3 carriers, and more than half may have a lower P-glycoprotein efflux pump. These characteristics might render Lebanese transplant recipients more prone to the development of drug toxicity and in need of lower drug doses.

Biomarkers for individualized dosage adjustments in immunosuppressive therapy using calcineurin inhibitors after organ transplantation

Calcineurin inhibitors (CNIs), such as cyclosporine A and tacrolimus, are widely used immunosuppressive agents for the prevention of post-transplantation rejection and have improved 1-year graft survival rates by up to 90%. However, CNIs can induce severe reactions, such as acute or chronic allograft nephropathy, hypertension, and neurotoxicity. Because CNIs have varied bioavailabilities, narrow therapeutic ranges, and individual propensities for toxic effects, therapeutic drug monitoring is necessary for all CNIs. Identifying the genetic polymorphisms in drug-metabolizing enzymes will help to determine personalized dosage regimens for CNIs, as CNIs are substrates for CYP3A5 and P-glycoprotein (P-gp, MDR1). CNIs are often concomitantly administered with voriconazole or proton pump inhibitors (PPIs), giving rise to drug interaction problems. Voriconazole and PPIs can increase the blood concentrations of CNIs, and both are primarily metabolized by CYP2C19. Thus, it is expected that interactions between CNIs and voriconazole or PPI would be affected by CYP2C19 and CYP3A5 polymorphisms. CNI-induced acute kidney injury (AKI) is a serious complication of transplantations. Neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule 1 (KIM-1) are noninvasive urinary biomarkers that are believed to be highly sensitive to CNI-induced AKI. In this article, we review the adverse events and pharmacokinetics of CNIs and the biomarkers related to CNIs, including CYP3A5, CYP2C19, MDR1, NGAL, and KIM-1. We hope that these data will help to identify the optimal biomarkers for monitoring CNI-based immunosuppressive therapy after organ transplantation.

Switching Immunosuppression From Cyclosporine to Tacrolimus in Kidney Transplant Recipients Based on CYP3A5 Genotyping

BACKGROUND

Kidney transplant recipients on long-term cyclosporine (CsA) therapy may develop multiple adverse drug events, and immunosuppression conversion from CsA to tacrolimus (Tac) is an option. Genetic variations, especially cytochrome P450 (CYP) 3A5*3, affects Tac dosing. However, little information is available to guide the conversion with regards to patients' pharmacogenomics. We aimed to investigate whether CYP3A5, CYP3A4, and ABCB1 genotyping could contribute to a more precise and individualized initial dosing of Tac at the time of immunosuppressant conversion.

METHODS

Genotypes of 5 candidate genes (CYP3A5*3, CYP3A4*1G, ABCB1C1236T, ABCB1C3435T, and ABCB1G2677T/A) were investigated by polymerase chain reaction and restriction fragment-length polymorphism methods in 46 adult kidney transplant recipients requiring immunosuppressant conversion from CsA to TAC. Associations between these functional genetic polymorphisms and the dose-adjusted trough concentrations of CsA and Tac were evaluated, retrospectively.

RESULTS

Based on the linear regression analysis, CYP3A5 expressers (*1/*1 and *1/*3) had lower Tac dose-adjusted trough concentrations on days 7, 14, 21, and 28, and they required 1.40- to 1.75-fold higher daily dose to reach the target concentration compared with nonexpressers (*3/*3) on day 28 [0.07 (0.06-0.09) mg/kg/d versus 0.05 (0.02-0.06) mg/kg/d, P = 0.001]. CYP3A4*1G or ABCB1 genetic polymorphisms had no effect on the Tac dose-adjusted trough concentrations.

CONCLUSIONS

Our preliminary study supports the use of CYP3A5 genotyping to guide the initial dosing of Tac when converting the immunosuppression therapy from CsA to Tac.

Population Pharmacokinetics of Prednisolone in Relation to Clinical Outcome in Children With Nephrotic Syndrome

BACKGROUND

The relapse frequency in children with nephrotic syndrome (NS) is highly variable despite standardized prednisolone treatment regimens. Existing evidence on the relationship between prednisolone pharmacokinetics (PK) and clinical response in children with NS is scarce and limited. The aim of this study was to develop a pediatric popPK model for prednisolone based on our previous model based on healthy adults using salivary measurements in children with NS and to correlate clinical outcome with between-subject variability in prednisolone exposure.

METHODS

The pharmacokinetics of prednisolone in a well-defined, prospective cohort consisting of 104 children with NS while in remission was determined. Pharmacokinetic parameters were analyzed in relation to relapse patterns and side effects. Noninvasive salivary prednisolone measurements were performed using a sparse sampling strategy. A population pharmacokinetic approach was used to derive individual estimates of apparent clearance (CL/F) and apparent volume of distribution (V/F) from the salivary concentration-time curve, followed by calculation of the area under the curve (AUC) of free prednisolone. The individual free serum prednisolone exposure from prednisolone in saliva was derived from the salivary concentration-time curves. Genetic polymorphisms of CYP3A4, CYP3A5, ABCB1, NR1L2, and POR were explored in relation to between-subject variability of CL/F.

RESULTS

Moderate interindividual variability was found for CL/F (CV, 44.7%). Unexplained random between-subject variability (eta) of CL/F was lower in patients carrying 1 or 2 ABCB1 3435C>T alleles compared to wild type: median -0.04 (interquartile range, -0.17 to 0.21) and 0.00 (-0.11 to 0.16) versus 0.17 (-0.08 to 0.47), P = 0.046. Exposure to free prednisolone was not associated with frequent relapses or adverse effects.

CONCLUSIONS

This study provides evidence for the possibility of prednisolone drug monitoring through salivary measurements and this may be of particular usefulness in pediatric patients. However, the observed variability in prednisolone exposure, in the therapeutic dose range studied, is not considered to be a major determinant of clinical outcome in children with NS.

NFATC1 genotypes affect acute rejection and long-term graft function in cyclosporine-treated renal transplant recipients

AIM

To investigate the effects of SNPs in the cyclophilin A/calcineurin/nuclear factor of activated T-cells (NFATs) pathway genes (PPIA, PPP3CB, PPP3R1, NFATC1 and NFATC2) on cyclosporine (CsA) efficacy in renal transplant recipients.

MATERIALS & METHODS

Seventy-six tag SNPs were detected in 155 CsA-treated renal recipients with at least a 5-year follow-up. The associations of SNPs with acute rejection, nephrotoxicity, pneumonia and estimated glomerular filtration rate post transplant were explored.

RESULTS

NFATC1 rs3894049 GC was a risk factor for acute rejection compared with CC carriers (p = 0.0005). NFATC1 rs2280055 TT carriers had a more stable estimated glomerular filtration rate level than CC (p = 0.0004).

CONCLUSION

Detecting NFATC1 polymorphisms could help predict CsA efficacy in renal transplant patients.

Pharmacogenetics of immunosuppressants: State of the art and clinical implementation - recommendations from the French National Network of Pharmacogenetics (RNPGx)

Therapeutic drug monitoring is already widely used for immunosuppressive drugs due to their narrow therapeutic index. This article summarizes evidence reported in the literature regarding the pharmacogenetics of (i) immunosuppressive drugs used in transplantation and (ii) azathioprine used in chronic inflammatory bowel disease. The conditions of use of currently available major pharmacogenetic tests are detailed and recommendations are provided based on a scale established by the RNPGx scoring tests as "essential", "advisable" and "potentially useful". Other applications for which the level of evidence is still debated are also discussed.

Barcelona Consensus on Biomarker-Based Immunosuppressive Drugs Management in Solid Organ Transplantation

With current treatment regimens, a relatively high proportion of transplant recipients experience underimmunosuppression or overimmunosuppression. Recently, several promising biomarkers have been identified for determining patient alloreactivity, which help in assessing the risk of rejection and personal response to the drug; others correlate with graft dysfunction and clinical outcome, offering a realistic opportunity for personalized immunosuppression. This consensus document aims to help tailor immunosuppression to the needs of the individual patient. It examines current knowledge on biomarkers associated with patient risk stratification and immunosuppression requirements that have been generally accepted as promising. It is based on a comprehensive review of the literature and the expert opinion of the Biomarker Working Group of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology. The quality of evidence was systematically weighted, and the strength of recommendations was rated according to the GRADE system. Three types of biomarkers are discussed: (1) those associated with the risk of rejection (alloreactivity/tolerance), (2) those reflecting individual response to immunosuppressants, and (3) those associated with graft dysfunction. Analytical aspects of biomarker measurement and novel pharmacokinetic-pharmacodynamic models accessible to the transplant community are also addressed. Conventional pharmacokinetic biomarkers may be used in combination with those discussed in this article to achieve better outcomes and improve long-term graft survival. Our group of experts has made recommendations for the most appropriate analysis of a proposed panel of preliminary biomarkers, most of which are currently under clinical evaluation in ongoing multicentre clinical trials. A section of Next Steps was also included, in which the Expert Committee is committed to sharing this knowledge with the Transplant Community in the form of triennial updates.

[Applied pharmacogenetic]

Pharmacokinetics is the link between genetic data and the use of treatments. It can be use on several relevant aspects in the clinic, including the treatment selection, efficacy or toxicity prediction and the choice of the dose. Pharmacogenetics has been applied in clinical nephrology since a long time by the genetic prediction of azathiorpine associated myelotoxicity. However, despite an extensive literature describing the links between genetics and metabolism and transport of drugs, genetic tests are little used in clinical practice. One reason for this poor implementation is the current lack of evidence of improved clinical outcomes with pharmacogenetic tests. In addition, with an effective therapeutic drug monitoring, it is possible to correct the effect of genotype on the pharmacokinetic differences, thus reducing the usefulness of the assay based on the genotype. The future of pharmacogenetics will be treatment models in which patient characteristics are combined with data on polymorphisms in multiple genes including pharmacodynamic parameters, drug transporter proteins, and predictors of toxicity.

Impact of Genetic Polymorphisms of ABCB1 (MDR1, P-Glycoprotein) on Drug Disposition and Potential Clinical Implications: Update of the Literature

ATP-binding cassette transporter B1 (ABCB1; P-glycoprotein; multidrug resistance protein 1) is an adenosine triphosphate (ATP)-dependent efflux transporter located in the plasma membrane of many different cell types. Numerous structurally unrelated compounds, including drugs and environmental toxins, have been identified as substrates. ABCB1 limits the absorption of xenobiotics from the gut lumen, protects sensitive tissues (e.g. the brain, fetus and testes) from xenobiotics and is involved in biliary and renal secretion of its substrates. In recent years, a large number of polymorphisms of the ABCB1 [ATP-binding cassette, sub-family B (MDR/TAP), member 1] gene have been described. The variants 1236C>T (rs1128503, p.G412G), 2677G>T/A (rs2032582, p.A893S/T) and 3435C>T (rs1045642, p.I1145I) occur at high allele frequencies and create a common haplotype; therefore, they have been most widely studied. This review provides an overview of clinical studies published between 2002 and March 2015. In summary, the effect of ABCB1 variation on P-glycoprotein expression (messenger RNA and protein expression) and/or activity in various tissues (e.g. the liver, gut and heart) appears to be small. Although polymorphisms and haplotypes of ABCB1 have been associated with alterations in drug disposition and drug response, including adverse events with various ABCB1 substrates in different ethnic populations, the results have been majorly conflicting, with limited clinical relevance. Future research activities are warranted, considering a deep-sequencing approach, as well as well-designed clinical studies with appropriate sample sizes to elucidate the impact of rare ABCB1 variants and their potential consequences for effect sizes.

CD44 promotes multi-drug resistance by protecting P-glycoprotein from FBXO21-mediated ubiquitination

Here we demonstrate that a ubiquitin E3-ligase, FBXO21, targets the multidrug resistance transporter, ABCB1, also known as P-glycoprotein (P-gp), for proteasomal degradation. We also show that the Ser291-phosphorylated form of the multifunctional protein and stem cell marker, CD44, inhibits FBXO21-directed degradation of P-gp. Thus, CD44 increases P-gp mediated drug resistance and represents a potential therapeutic target in P-gp-positive cells.

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.

Personalization of the immunosuppressive treatment in renal transplant recipients: the great challenge in "omics" medicine

Renal transplantation represents the most favorable treatment for patients with advanced renal failure and it is followed, in most cases, by a significant enhancement in patients’ quality of life. Significant improvements in one-year renal allograft and patients’ survival rates have been achieved over the last 10 years primarily as a result of newer immunosuppressive regimens. Despite these notable achievements in the short-term outcome, long-term graft function and survival rates remain less than optimal. Death with a functioning graft and chronic allograft dysfunction result in an annual rate of 3%–5%. In this context, drug toxicity and long-term chronic adverse effects of immunosuppressive medications have a pivotal role. Unfortunately, at the moment, except for the evaluation of trough drug levels, no clinically useful tools are available to correctly manage immunosuppressive therapy. The proper use of these drugs could potentiate therapeutic effects minimizing adverse drug reactions. For this purpose, in the future, “omics” techniques could represent powerful tools that may be employed in clinical practice to routinely aid the personalization of drug treatment according to each patient’s genetic makeup. However, it is unquestionable that additional studies and technological advances are needed to standardize and simplify these methodologies.

Genotype and allele frequencies of drug-metabolizing enzymes and drug transporter genes affecting immunosuppressants in the Spanish white population

Interpatient variability in drug response can be widely explained by genetically determined differences in metabolizing enzymes, drug transporters, and drug targets, leading to different pharmacokinetic and/or pharmacodynamic behaviors of drugs. Genetic variations affect or do not affect drug responses depending on their influence on protein activity and the relevance of such proteins in the pathway of the drug. Also, the frequency of such genetic variations differs among populations, so the clinical relevance of a specific variation is not the same in all of them. In this study, a panel of 33 single nucleotide polymorphisms in 14 different genes (ABCB1, ABCC2, ABCG2, CYP2B6, CYP2C19, CYP2C9, CYP3A4, CYP3A5, MTHFR, NOD2/CARD15, SLCO1A2, SLCO1B1, TPMT, and UGT1A9), encoding for the most relevant metabolizing enzymes and drug transporters relating to immunosuppressant agents, was analyzed to determine the genotype profile and allele frequencies in comparison with HapMap data. A total of 570 Spanish white recipients and donors of solid organ transplants were included. In 24 single nucleotide polymorphisms, statistically significant differences in allele frequency were observed. The largest differences (>100%) occurred in ABCB1 rs2229109, ABCG2 rs2231137, CYP3A5 rs776746, NOD2/CARD15 rs2066844, TPMT rs1800462, and UGT1A9 rs72551330. In conclusion, differences were recorded between the Spanish and other white populations in terms of allele frequency and genotypic distribution. Such differences may have implications in relation to dose requirements and drug-induced toxicity. These data are important for further research to help explain interindividual pharmacokinetic and pharmacodynamic variability in response to drug therapy.

Pharmacogenetics and immunosuppressive drugs in solid organ transplantation

The transplantation literature includes numerous papers that report associations between polymorphisms in genes encoding metabolizing enzymes and drug transporters, and pharmacokinetic data on immunosuppressive drugs. Most of these studies are retrospective in design, and although a substantial number report significant associations, pharmacogenetic tests are hardly used in clinical practice. One of the reasons for this poor implementation is the current lack of evidence of improved clinical outcome with pharmacogenetic testing. Furthermore, with efficient therapeutic drug monitoring it is possible to rapidly correct for the effect of genotypic deviations on pharmacokinetics, thereby decreasing the utility of genotype-based dosing. The future of pharmacogenetics will be in treatment models in which patient characteristics are combined with data on polymorphisms in multiple genes. These models should focus on pharmacodynamic parameters, variations in the expression of drug transporter proteins, and predictors of toxicity. Such models will provide more information than the relatively small candidate gene studies performed so far. For implementation of these models into clinical practice, linkage of genotype data to medication prescription systems within electronic health records will be crucial.

Multidrug-resistance 1 gene single-nucleotide polymorphisms do not influence long-term graft survival after kidney transplantation

BACKGROUND

The single-nucleotide polymorphisms (SNPs) of the Multidrug resistance 1 (MDR1) gene have been associated with changes in the pharmacokinetics of cyclosporine (CsA) and tacrolimus (FK506). Our aim was investigate the influence of MDR1 SNPs on long-term graft survival in a population of kidney transplant recipients.

METHODS

We retrospectively analyzed 154 patients; they were genotyped for the SNPs C1236T, G2677T/A, and C3435T and evaluated for the influence of those 3 SNPs on CsA or FK506 pharmacokinetics and on long-term graft survival.

RESULTS

Thirty-one patients were wild-type for C1236T, G2677T/A, and C3435T polymorphisms (group A), 76 patients had ≥1 heterozygous mutations (group B), and 47 patients had ≥1 homozygous mutations (group C). CsA-receiving patients in group C needed a significantly higher oral dose than patients in groups B and A (P=.02). No differences in FK506 trough level nor in oral dose taken were observed in FK506-receiving patients. Kaplan-Meier analysis did not show survival differences in the 3 groups, and Cox proportional hazards model confirmed that the MDR1 SNPs did not represent a risk for graft loss.

CONCLUSIONS

Pretransplantation determination of MDR1 SNPs may be helpful to optimize the starting dose of CsA but can not predict long-term graft survival.

The impact of APOL1, CAV1, and ABCB1 gene variants on outcomes in kidney transplantation: donor and recipient effects

Dramatic improvements have been seen in short-term kidney allograft survival over recent decades with introduction of more potent immunosuppressant medications and regimens. Unfortunately, improvements in long-term graft survival have lagged behind. The genomics revolution is providing new insights regarding the potential impact of kidney donor genotypes on long-term graft survival. Variation in the donor apolipoprotein L1 (APOL1), caveolin 1 (CAV1), and multi-drug resistance 1 encoding P-glycoprotein genes (ABCB1) are all associated with graft survival after kidney transplantation. Although the precise mechanisms whereby these donor gene variants confer risk for graft loss have yet to be determined, these findings provide novel opportunities for modifying interactive environmental factors and optimizing kidney allocation with the ultimate goal of improving long-term graft survival rates.

Impact of POR*28 on the pharmacokinetics of tacrolimus and cyclosporine A in renal transplant patients

BACKGROUND

The P450 oxidoreductase (POR)*28 variant allele has been associated with altered cytochrome P450 3A enzyme activities. Both CYP3A5 and CYP3A4 are involved in the metabolism of calcineurin inhibitors and recent data show that POR*28 may explain part of the variability observed in tacrolimus (Tac) pharmacokinetics. The aim of this study was to investigate the impact of the POR*28 allele on Tac and cyclosporine A (CsA) immunosuppressive therapies.

METHODS

Kidney transplant recipients receiving either Tac (n = 184) or CsA (n = 174), participating in a prospective multicenter trial, were genotyped for POR*28, CYP3A4*22, and CYP3A5*3.

RESULTS

CYP3A5 expressers that were carriers of at least 1 POR*28 allele had a 16.9% decrease in dose-adjusted predose concentrations when compared CYP3A5 expressers that carried the POR*1/*1 genotype (P = 0.03), indicating an increased CYP3A5 activity for POR*28 carriers. In CYP3A5, nonexpressers carrying 2 POR*28 alleles, a 24.1% (confidence interval95% = -39.4% to -4.9%; P = 0.02) decrease in dose-adjusted predose concentrations was observed for Tac, suggesting higher CYP3A4 activity. For CsA, POR*28/*28 patients not expressing CYP3A5 and not carrying the CYP3A4*22 decrease-of-function allele showed 15% lower CsA dose-adjusted predose concentrations (P = 0.01), indicating also increased CYP3A4 activity. In both cohorts (ie, Tac and CsA), the POR*28 allele was neither associated with the incidence of delayed graft function nor with biopsy-proven acute rejection. These results were further confirmed in 2 independent cohorts.

CONCLUSIONS

Our results show that the POR*28 allele is associated with increased in vivo CYP3A5 activity for Tac in CYP3A5 expressers, whereas POR*28 homozygosity was associated with a significant higher CYP3A4 activity in CYP3A5 nonexpressers for both Tac and CsA.

A functional common polymorphism of the ABCB1 gene is associated with chronic kidney disease and hypertension in Chinese

BACKGROUND

Permeability glycoprotein is encoded by the ATP-binding cassette B1 gene (ABCB1) and is an extruder of toxic metabolites in the kidney. A functional common polymorphism (C3435T, rs1045642) in the human ABCB1 gene has been found to be associated with allograft outcome in kidney transplant patients. In this study, we investigated the association of the C3435T polymorphism with renal function and blood pressure (BP) in 2 Chinese populations.

METHODS

The discovery and replication populations were recruited from a mountainous area (Zhejiang Province) and a newly urbanized suburban area (Shanghai), respectively. We genotyped all subjects using the ABI SNapShot method. Chronic kidney disease (CKD) was defined as an estimated glomerular filtration rate <60 ml/min × 1.73 m(2) or 24-hour urinary albumin excretion ≥30 mg.

RESULTS

In the discovery population of 1,987 subjects, after adjustment for covariables, TT homozygosity (n = 217) was associated with a higher risk of CKD (n = 369; odds ratio (OR) = 1.73; P = 0.003) and with higher systolic BP (+3.1 mm Hg; P = 0.03) and pulse pressure (+3.4 mm Hg; P = 0.001). These associations were dependent on age (Pint ≤ 0.05). In subjects aged ≥60 years (n = 374), the corresponding OR or difference was 2.40 for CKD, 15.1 mm Hg for systolic BP, and 12.4 mm Hg for pulse pressure (P < 0.001). In similar adjusted analyses in the replication population of 2,427 elderly (≥60 years) subjects, TT homozygosity was also associated with a higher risk of CKD (OR = 1.39; P = 0.02) and an enhanced association of hypertension with CKD (OR = 1.50; P = 0.04).

CONCLUSIONS

The ABCB1 C3435T polymorphism might predict CKD, especially in the elderly.

From gut to kidney: transporting and metabolizing calcineurin-inhibitors in solid organ transplantation

Since their introduction circa 35 years ago, calcineurin-inhibitors (CNI) have become the cornerstone of immunosuppressive therapy in solid organ transplantation. However, CNI's possess a narrow therapeutic index with potential severe consequences of drug under- or overexposure. This demands a meticulous policy of Therapeutic Drug Monitoring (TDM) to optimize outcome. In clinical practice optimal dosing is difficult to achieve due to important inter- and intraindividual variation in CNI pharmacokinetics. A complex and often interdependent set of factors appears relevant in determining drug exposure. These include recipient characteristics such as age, race, body composition, organ function, and food intake, but also graft-related characteristics such as: size, donor-age, and time after transplantation can be important. Fundamental (in vitro) and clinical studies have pointed out the intrinsic relation between the aforementioned variables and the functional capacity of enzymes and transporters involved in CNI metabolism, primarily located in intestine, liver and kidney. Commonly occurring polymorphisms in genes responsible for CNI metabolism (CYP3A4, CYP3A5, CYP3A7, PXR, POR, ABCB1 (P-gp) and possibly UGT) are able to explain an important part of interindividual variability. In particular, a highly prevalent SNP in CYP3A5 has proven to be an important determinant of CNI dose requirements and drug-dose-interactions. In addition, a discrepancy in genotype between graft and receptor has to be taken into account. Furthermore, common phenomena in solid organ transplantation such as inflammation, ischemia- reperfusion injury, graft function, co-medication, altered food intake and intestinal motility can have a differential effect on the expression enzymes and transporters involved in CNI metabolism. Notwithstanding the built-up knowledge, predicting individual CNI pharmacokinetics and dose requirements on the basis of current clinical and experimental data remains a challenge.

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.

CYP2C8*3 polymorphism and donor age are associated with allograft dysfunction in kidney transplant recipients treated with calcineurin inhibitors

Epoxieicosatrienoic acids (EETs) play a protective role against damaging processes in the kidney. We have assessed the effect of polymorphisms in EETs-producing enzymes (CYP2C8 and CYP2J2) and other proteins involved in calcineurin inhibitors (CNIs) disposition (CYP3A4, CYP3A5, and ABCB1) on graft function and clinical outcome in 166 renal transplant recipients treated with CNIs. Both CYP2C8*3 and donor age greater than 48 years were associated to a higher incidence of delayed graft function (DGF) [OR = 2.01 (1.1-4.1), P = .04 and 5.14 (2.4-10.9), P < .0001; respectively] and worse creatinine clearance 1 year after grafting (P < .05 and P < .001, respectively). In addition, carrying 4-6 variants in the 3 ABCB1 loci and older donor age were individually associated to higher incidence of calcineurin-inhibitor-induced nephrotoxicity [OR = 2.38 (1.1-5.4), P = .03 and OR = 1.03 (1.01-1.06), P = .038]. Regression analyses confirmed the relevant effect of both CYP2C8*3 and donor age on graft dysfunction. Carrying the 2C8*3 allele and having a donor older than 48 years was defined as a high-risk status and observed to be highly related to DGF [OR = 3.91 (1.46-10.48), P < .01] and worse creatinine clearance (P = .033). Our results show that genetic and clinical parameters can be combined to identify risk factors for allograft dysfunction in renal transplant recipients.

Association of CYP3A polymorphisms with the pharmacokinetics of cyclosporine A in early post-renal transplant recipients in China

AIM

To evaluate retrospectively the association of cytochrome P450 3A (CYP3A) and ATP-binding cassette sub-family B member 1 (ABCB1) gene polymorphisms with the pharmacokinetics of cyclosporine A (CsA) in Chinese renal transplant patients.

METHODS

One hundred and twenty-six renal transplant patients were recruited. Blood samples were collected, and corresponding clinical indices were recorded on the seventh day after the procedure. The patients were genotyped for CYP3A4*1G, CYP3A5*3C, ABCB1 1236 C>T, ABCB1 2677 G>T/A, and ABCB1 3435 C>T polymorphisms. Whole blood trough concentrations of CsA at time zero (C(0)) were measured before the drug administration. A multiple regression model was developed to analyze the effects of genetic factors on the CsA dose-adjusted C(0) (C(0)/dose) based on several clinical indices.

RESULTS

The CYP3A5*3C polymorphism influenced the C(0) and C(0)/dose of CsA, which were significantly higher in patients with the GG genotype than in patients with the AA or GA genotypes. No significant differences were detected for other SNPs (CYP3A4*1G, ABCB1 1236 C>T, ABCB1 2677 G>T/A, and ABCB1 3435 C>T). In a univariate analysis using Pearson's correlation test, age, hemoglobin, blood urea nitrogen and blood creatinine levels were significantly correlated with the log-transformed CsA C(0)/dose. In the multiple regression model, CYP3A5*3C, age, hemoglobin and blood creatinine level were associated with the log-transformed CsA C(0)/dose.

CONCLUSION

CYP3A5*3C correlates with the C(0)/dose of CsA on the seventh day after renal transplantation. The allele is a putative indicator for the optimal CsA dosage in the early phase of renal transplantation in the Chinese population.

The potential of steroids and xenobiotic receptor polymorphisms in forecasting cyclosporine pharmacokinetic variability in young kidney transplant recipients

The steroids and xenobiotics receptor (SXR) up-regulates the expression and the synthesis of key enzymes in CyA metabolism. In this study, we examined the possible interactions between CyA exposure and SXR polymorphisms during the first year after renal transplantation. The study involved 66 pediatric renal transplant recipients (25 women and 41 men, mean age 13.9 ± 7.4 yr). All patients were genotyped for two sequence variations in the NR1I2 gene: g.-205_-200delGAGAAG and 7635 A>G. CyA trough levels and CyA weight-adjusted daily dose were recorded at 30, 90, 180, and 360 days after transplantation and compared between the different genotypes. A third newly discovered SXR polymorphism was characterized and also included in the study. CyA trough levels and CyA weight-adjusted daily dose were comparable on four time points throughout the first year post-transplant in all three groups. GEE showed a significant reduction in weight-adjusted CyA daily dose in patients carrying the deletion of 6 bp in SXR with a significant group-by-time effect that persisted also when analysis was corrected for age, prednisone dose, and acute rejection episodes. In our group of patients, only the g.-205_-200delGAGAAG SXR polymorphism was able to influence the metabolism of CyA continuously, during the first year after transplantation.

ABCB1 polymorphisms are associated with cyclosporine-induced nephrotoxicity and gingival hyperplasia in renal transplant recipients

PURPOSE

There is a great deal of controversy regarding the clinical impact of genetic variants in patients receiving cyclosporine (CsA) as immunosuppressant therapy. We have investigated the effect of polymorphisms in the CYP3A and ABCB1 genes on CsA pharmacokinetics, acute rejection incidence and drug-related side effects in renal transplant recipients

METHODS

The presence of CYP3A5*3, CYP3A4*1B and ABCB1 C1236T, G2677T/A and C3435T polymorphisms was assessed in 68 patients and retrospectively associated with pharmacokinetic and clinical parameters at 1 week and 1, 5 and 12 months after transplantation.

RESULTS

Only minor associations were found between the tested polymorphisms and CsA pharmacokinetics. Most notably, CYP3A5 expressers showed lower blood trough levels than non-expressers in the first week after grafting (32.5 ± 14.7 vs. 55.1 ± 3.8 ng/ml per mg/day per kilogram). In terms of CsA-induced adverse effects, the incidence of nephrotoxicity was higher in carriers of the ABCB1 3435TT genotype and in those patients carrying four to six variants in the three ABCB1 loci [odds ratio (OR) 4.2, 95 % confidence interval (CI) 1.3-13.9, p = 0.02 and OR 3.6, 95 % CI 1.1-11.8, p = 0.05, respectively]. These subjects with four to six ABCB1 variants were also at higher risk for gingival hyperplasia (OR 3.29, 95 % CI 1.1-10.3, p = 0.04). Renal function and the incidence of neurotoxicity and of acute rejection did not vary across the different genotypes.

CONCLUSIONS

ABCB1 polymorphisms may be helpful in predicting certain CsA-related side effects in renal transplant recipients. Our results also suggest that the mechanisms underlying these genetic associations are most likely independent of the drug's trough blood concentrations.

The new CYP3A4 intron 6 C>T polymorphism (CYP3A4*22) is associated with an increased risk of delayed graft function and worse renal function in cyclosporine-treated kidney transplant patients

OBJECTIVE

Cyclosporine A (CsA) is a substrate of cytochrome P450 3A4 (CYP3A4). Recently, a newly discovered intron 6 single-nucleotide polymorphism in CYP3A4 (rs35599367 C>T), defining the CYP3A4*22 allele, has been linked to reduced hepatic expression and activity of CYP3A4. In the present study, the clinical impact of this single-nucleotide polymorphism was investigated in a cohort of patients receiving a CsA-based immunosuppressive regimen.

MATERIALS AND METHODS

A total of 172 de-novo kidney transplant recipients, receiving CsA/mycophenolate mofetil as immunosuppressive therapy and participating in the Fixed-Dose Concentration Controlled study, were genotyped for the new CYP3A4*22 allele. CsA C(0) and/or C(2) levels were measured on days 3 and 10 and in months 1, 3, 6, and 12 after transplantation. Plasma creatinine concentrations, delayed graft function (DGF), and biopsy-proven acute rejection were recorded.

RESULTS

The CYP3A4*22 allele was significantly associated with a higher risk of DGF compared with the CYP3A4*1/*1 patients after adjustment for known risk factors [odds ratio (OR)=6.34, confidence interval (CI(95%): 1.38-29.3), P=0.015]. Mixed-model analysis demonstrated that the overall creatinine clearance was 20% lower in CYP3A4*22 allele carriers compared with CYP3A4*1/*1 patients [CI(95%) (-33.1 to -7.2%), P=0.002]. For ABCB1 3435C>T, T-variant carriers had a decreased risk of developing DGF compared with CC patients [CT: OR=0.30, CI(95%) (0.11-0.77), P=0.011; TT: OR=0.18, CI(95%) (0.05-0.67), P=0.011].

CONCLUSION

CYP3A4*22 constitutes a risk factor for DGF and worse creatinine clearance in patients receiving CsA-based immunosuppressive therapy. Therefore, pretransplant genotyping for the CYP3A4*22 allele might help clinicians to identify patients at risk of DGF and poor renal function when treated with CsA.

Pharmacogenetic biomarkers: cytochrome P450 3A5

The immunosuppressive drugs used for solid organ transplantation all have a narrow therapeutic index with wide variation between individuals in the blood concentration achieved by a given dose. Therapeutic drug monitoring is employed routinely but may not allow optimisation of drug exposure during the critical period two to three days following transplantation. A key factor in the inter-individual variability for tacrolimus, and probably sirolimus, is whether an individual is genetically predicted to express the drug metabolising enzyme cytochrome P450 3A5 (CYP3A5). Individuals predicted to express CYP3A5 by possession of at least one wild-type CYP3A5*1 allele require 1.5-2 times higher doses of tacrolimus to achieve target blood concentrations than individuals homozygous for the CYP3A5*3 allele who are functional non-expressers of CYP3A5. Planning the initial tacrolimus dose based on the CYP3A5 genotype has been shown to allow more rapid achievement of target blood concentrations after transplantation than a standard dose given to all patients. However, it remains to be demonstrated that use of this approach as an adjunct to therapeutic drug monitoring can reduce either efficacy failure (transplant rejection) or toxicity. Use of a pharmacogenetic approach to dosing sirolimus awaits testing and it is unlikely to be useful for ciclosporin or everolimus.

ATP-binding cassette transporters as pharmacogenetic biomarkers for kidney transplantation

Immunosuppressive drugs used in organ transplantation are highly effective in preventing acute rejection. However, the clinical use of these drugs is complicated by the fact that they display highly variable pharmacokinetics and pharmacodynamics between individual patients. The influence of genetic variation on the interindividual variability in immunosuppressive drug disposition, efficacy, and toxicity has been explored in recent years. The polymorphically-expressed ATP-binding cassette (ABC) transporter proteins, in particular ABCB1 and ABCC2, have been investigated extensively because they play an important role in the absorption, distribution and elimination of many immunosuppressive drugs in use today. From these studies it can be concluded that polymorphisms in ABCB1 and ABCC2 have no consistent effect on immunosuppressant pharmacokinetics and toxicity although polymorphisms in ABCB1 appear to be related to the risk of developing calcineurin inhibitor-related nephrotoxicity. However, the latter needs to be replicated before an individual's ABCB1 genotype can become a useful marker that is applied in clinical practice. Future studies evaluating the influence of ABC transporter gene polymorphisms should explore the relationship with intracellular rather than systemic drug concentrations further in well-designed clinical studies. Until then, single-nucleotide polymorphisms in ABC transporter genes are not suitable to act as biomarkers for solid organ transplantation.