Lower tacrolimus daily dose requirements and acute rejection rates in the CYP3A5 nonexpressers than expressers. Pharmacogenet Genomics. 2011;21:713-720. [PMID: 21886016 DOI: 10.1097/fpc.0b013e32834a48ca]

Customizing Tacrolimus Dosing in Kidney Transplantation: Focus on Pharmacogenetics

ABSTRACT

Different polymorphisms in genes encoding metabolizing enzymes and drug transporters have been associated with tacrolimus pharmacokinetics. In particular, studies on CYP3A4 and CYP3A5, and their combined cluster have demonstrated their significance in adjusting tacrolimus dosing to minimize under- and overexposure thereby increasing the proportion of patients who achieve tacrolimus therapeutic target. Many factors influence the pharmacokinetics of tacrolimus, contributing to inter-patient variability affecting individual dosing requirements. On the other hand, the growing use of population pharmacokinetic models in solid organ transplantation, including different tacrolimus formulations, has facilitated the integration of pharmacogenetic data and other variables into algorithms to easier implement the personalized dose adjustment in transplant centers. The future of personalized medicine in transplantation lies in implementing these models in clinical practice, with pharmacogenetics as a key factor to account for the high inter-patient variability in tacrolimus exposure. To date, three clinical trials have validated the clinical application of these approaches. The aim of this review is to provide an overview of the current studies regarding the different population pharmacokinetic including pharmacogenetics and those translated to the clinical practice for individualizing tacrolimus dose adjustment in kidney transplantation.

Effects of CYP3A4*22 polymorphism on trough concentration of tacrolimus in kidney transplantation: a systematic review and meta-analysis

Purpose: Tacrolimus (Tac) is a widely used immunosuppressive agent in kidney transplantation. Cytochrome P450 (CYP), especially CYP3A4 enzymes are responsible for the metabolism of drugs. However, the correlation between plasma Tac concentration and CYP3A4*22 gene variants is controversial. This meta-analysis aims to evaluate the association between CYP3A4*22 polymorphism and the dose-adjusted trough concentration (C0/D) of Tac in adult kidney transplant patients. Methods: We conducted a literature review for qualifying studies using the PubMed, Web of Science, and Embase databases until July 2023. For the continuous variables (C0/D and daily dose), mean difference (MD) and corresponding 95% confidence intervals (CIs) were calculated to evaluate the association between the CYP3A4 * 22 and Tac pharmacokinetics. We performed an additional analysis on the relationship of CYP3A5*3 with Tac PKs and analyzed the effects of CYP3A4*22 in CYP3A5 non-expressers. Results: Overall, eight eligible studies with 2,683 renal transplant recipients were included in this meta-analysis. The CYP3A4*22 allele was significantly associated with a higher C0/D (MD 0.57 ng/mL/mg (95% CI: 0.28 to 0.86; p = 0.0001) and lower mean daily dose requirement (MD -2.02 mg/day, 95% CI: -2.55 to -1.50; p < 0.00001). An additional meta-analysis demonstrated that carrying the CYP3A5*3 polymorphism greatly impacted Tac blood concentration. From the result with CYP3A5 non-expressers, CYP3A4*22 showed significant effects on the Tac C0/D and dose requirement even after adjusting the effect of CYP3A5*3. Conclusion: Patients with CYP3A4*22 allele showed significantly higher plasma C0/D of Tac and required lower daily dose to achieve the therapeutic trough level after kidney transplantation. These findings of our meta-analysis may provide further evidence for the effects of genetic polymorphism in CYP3A4 on the PKs of Tac, which will improve individualized treatment in a clinical setting.

CYP3A5 Polymorphism in Renal Transplantation: A Key to Personalized Immunosuppression

BACKGROUND

Tacrolimus is essential for the maintenance of immunosuppression after a kidney transplant. CYP3A5 is the gene that metabolizes tacrolimus, and polymorphism in this gene affects the metabolizing status.

AIM

To assess the genetic polymorphism status of patients undergoing kidney transplantation and determine its impact on graft function and complications in the post-transplant period.

METHODS

We retrospectively included the patients who had undergone a kidney transplant and had positive genetic polymorphism of the CYP3A5 gene. Based on loss of alleles, patients were categorized as non-expresser (loss of both alleles), intermediate expresser (loss of one allele), and expresser (no loss of allele) denoted by CYP3A5*3/*3, CYP3A5*1/*3, and CYP3A5*1/*1, respectively. Data were analyzed with descriptive statistics.

RESULTS

Of 25 patients, 60%, 32%, and 8% were non-expressers, intermediate-expressers, and expressers, respectively. The mean tacrolimus trough concentration to dose ratio after 6 months of the transplant was higher in non-expressers than intermediate-expressers and expressers (213 vs 85 and 46 ng/mL/mg/kg/d, respectively). The graft function was normal in all 3 groups except for graft rejection 1 patient in the expresser group. Compared with expressers, urinary tract infections (42.9% and 62.5%) and new-onset diabetes after transplantation (28.6% and 12.5%) were more frequent in non-expresser and intermediate expressers, respectively. The proportion of patients developing new-onset diabetes after transplantation was lower with the pre-transplant diagnosis of CYP3A5 polymorphism (16.7% vs 23.1%).

CONCLUSION

Genotype-based dosing of tacrolimus helps achieve the desired therapeutic concentrations that can help to optimize graft outcomes and reduce the tacrolimus-related adverse effects. Pre-transplant evaluation of CYP3A5 can be more helpful in planning treatment strategies for optimized outcomes after kidney transplantation.

Functional CYP3A variants affecting tacrolimus trough blood concentrations in Chinese renal transplant recipients

The aim of this study was to identify novel genetic variants affecting tacrolimus trough blood concentrations. We analyzed the association between 58 single nucleotide polymorphisms (SNPs) across the CYP3A gene cluster and the log-transformed tacrolimus concentration/dose ratio (log (C₀/D)) in 819 renal transplant recipients (Discovery cohort). Multivariate linear regression was used to test for associations between tacrolimus log (C₀/D) and clinical factors. Luciferase reporter gene assays were used to evaluate the functions of select SNPs. Associations of putative functional SNPs with log (C₀/D) were further tested in 631 renal transplant recipients (Replication cohort). Nine SNPs were significantly associated with tacrolimus log (C₀/D) after adjustment for CYP3A5*3 and clinical factors. Dual luciferase reporter assays indicated that the rs4646450 G allele and rs3823812 T allele were significantly associated with increased normalized luciferase activity ratios (p < 0.01). Moreover, CYP3A7*2 was associated with higher TAC log(C₀/D) in the group of CYP3A5 expressers. Age, serum creatinine and hematocrit were significantly associated with tacrolimus log (C₀/D). CYP3A7*2, rs4646450, and rs3823812 are proposed as functional SNPs affecting tacrolimus trough blood concentrations in Chinese renal transplant recipients. Clinical factors also significantly affect tacrolimus metabolism.

Pharmacogenetics of common SNP affecting drug metabolizing enzymes: comparison of allele frequencies between European and Malaysian/Singaporean

Compared to Europe, data on genetic variation in genes transcribing drug metabolizing enzymes among Asian is limited due to ethnic diversity. Here we compare frequencies for clinically relevant single nucleotide polymorphism (SNP) commonly observed in drug metabolizing enzymes between European and Malaysian/Singaporean. Minor allele frequencies (MAF) for the indicated SNPs for European, South Asian and East Asian populations were obtained from the NCBI website (https://www.ncbi.nlm.nih.gov/snp). The SNP prevalence among Malaysian/Singaporean was characterized from gene association studies. Generally, some SNPs in CYP2D6 and CYP2C19 do not show good agreement between the two populations as to the MAF value obtained. CYP2D6*4 tends to be more common among European, whereas CYP2D6*10 is more common in Malays and Chinese among Singaporean. Regardless of different phenotype, MAF of CYP2D6*4 for Indians is similar to that seen by the European. Singaporeans show smaller MAF for CYP2C19*17 but higher CYP2C19*2 frequencies as opposed to European ones. Following growing attention to the contribution of CYP3A4/5, N-acetyltransferases (NAT2), thiopurine methyltransferase (TPMT) and uridine diphosphate glucuronosyltransferases (UGT)2B7 in predicting drug response across Europe, there are limited pharmacogenetics (PGx) studies examining the gene-drug interaction among Malaysian/Singaporean. To better understand the heterogeneity of the drug response, PGx studies for the abovementioned enzymes between ethnics in Malaysian/Singaporean should be identified.

Pharmacogenetics of common SNP affecting drug metabolizing enzymes: comparison of allele frequencies between European and Malaysian/Singaporean

Compared to Europe, data on genetic variation in genes transcribing drug metabolizing enzymes among Asian is limited due to ethnic diversity. Here we compare frequencies for clinically relevant single nucleotide polymorphism (SNP) commonly observed in drug metabolizing enzymes between European and Malaysian/Singaporean. Minor allele frequencies (MAF) for the indicated SNPs for European, South Asian and East Asian populations were obtained from the NCBI website (https://www.ncbi.nlm.nih.gov/snp). The SNP prevalence among Malaysian/Singaporean was characterized from gene association studies. Generally, some SNPs in CYP2D6 and CYP2C19 do not show good agreement between the two populations as to the MAF value obtained. CYP2D6*4 tends to be more common among European, whereas CYP2D6*10 is more common in Malays and Chinese among Singaporean. Regardless of different phenotype, MAF of CYP2D6*4 for Indians is similar to that seen by the European. Singaporeans show smaller MAF for CYP2C19*17 but higher CYP2C19*2 frequencies as opposed to European ones. Following growing attention to the contribution of CYP3A4/5, N-acetyltransferases (NAT2), thiopurine methyltransferase (TPMT) and uridine diphosphate glucuronosyltransferases (UGT)2B7 in predicting drug response across Europe, there are limited pharmacogenetics (PGx) studies examining the gene-drug interaction among Malaysian/Singaporean. To better understand the heterogeneity of the drug response, PGx studies for the abovementioned enzymes between ethnics in Malaysian/Singaporean should be identified.

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.

A Machine Learning-Based Identification of Genes Affecting the Pharmacokinetics of Tacrolimus Using the DMETTM Plus Platform

Tacrolimus is an immunosuppressive drug with a narrow therapeutic index and larger interindividual variability. We identified genetic variants to predict tacrolimus exposure in healthy Korean males using machine learning algorithms such as decision tree, random forest, and least absolute shrinkage and selection operator (LASSO) regression. rs776746 (CYP3A5) and rs1137115 (CYP2A6) are single nucleotide polymorphisms (SNPs) that can affect exposure to tacrolimus. A decision tree, when coupled with random forest analysis, is an efficient tool for predicting the exposure to tacrolimus based on genotype. These tools are helpful to determine an individualized dose of tacrolimus.

CYP3A5 gene polymorphisms and their impact on dosage and trough concentration of tacrolimus among kidney transplant patients: a systematic review and meta-analysis

Tacrolimus is an immunosuppressive drug widely used in kidney transplantation. Cytochrome P450 3A5 (CYP3A5) protein is involved in tacrolimus metabolism. Single nucleotide polymorphism in the CYP3A5 gene (6986A>G) results in alteration in metabolic activity of CYP3A5 protein which eventually affects the tacrolimus concentration. Patients with CYP3A5 expresser genotypes (A/A *1/*1 and A/G *1/*3) metabolize tacrolimus more rapidly than CYP3A5 nonexpressers (G/G *3/*3). We performed meta-analysis to estimate the effect of CYP3A5 polymorphism on the trough concentration-dose ratio (Co/D) and risk of renal allograft rejection with similar post-transplant periods and Asian vs. European populations. Our results showed that the tacrolimus Co/D ratio is significantly lower in CYP3A5 expresser group as compared with nonexpresser in Asian as well as in European populations at any post-transplant period (p < 0.00001). No significant association was found with renal allograft rejection episodes between expressers and nonexpressers in European populations (OR: 1.12; p = 0.47). Interestingly, Asian population (with expresser genotypes) and patients after 3 years post-transplantation (with expresser genotypes) have a higher risk of rejection (OR: 1.62; p < 0.05), (OR: 1.68; p < 0.05), respectively. This could be due to high prevalence of expresser genotypes in Asian population. Few tacrolimus-based studies are identified with long-term graft survival. There is a need to have more studies looking for long-term graft survival in expresser as well as no-expresser groups especially in Asian populations who have high frequency of CYP3A5 functional genotype.

Tacrolimus: 20 years of use in adult kidney transplantation. What we should know about its nephrotoxicity

Tacrolimus (or FK506), a calcineurin inhibitor (CNI) introduced in field of transplantation in the 1990s, is the cornerstone of most immunosuppressive regimens in solid organ transplantation. Its use has revolutionized the future of kidney transplantation (KT) and has been associated with better graft survival, a lower incidence of rejection, and improved drug tolerance with fewer side effects compared to cyclosporine. However, its monitoring remains complicated and underexposure increases the risk of rejection, whereas overexposure increases the risk of adverse effects, primarily nephrotoxicity, neurotoxicity, infections, malignancies, diabetes, and gastrointestinal complaints. Tacrolimus nephrotoxicity can be nonreversible and can lead to kidney graft loss, and its diagnosis is therefore best made with reference to the clinical context and after exclusion of other causes of graft dysfunction. Many factors contribute to its development including: systemic levels of tacrolimus; local renal exposure to tacrolimus; exposure to metabolites of tacrolimus; local susceptibility factors for CNI nephrotoxicity independent of systemic or local tacrolimus levels, such as the age of a kidney; local renal P-glycoprotein, local intestinal and hepatic cytochrome P450A3, and renin angiotensin system activation. The aim of this review is to describe the pharmacokinetics, pharmacodynamics, and mechanisms of acute and chronic tacrolimus nephrotoxicity in adult KT.

Correlation between gene polymorphism and blood concentration of calcineurin inhibitors in renal transplant recipients: An overview of systematic reviews

BACKGROUND

To provide an overview of systematic reviews and meta-analyses (SRs/MAs) of the correlation between genetic polymorphisms and blood concentrations of calcineurin inhibitors (CNIs) in recipients of renal transplant.

METHODS

Databases including Medline, EMBase, The Cochrane Library (Issue 7, 2016), the Chinese Biomedical Literature Database, the China National Knowledge Infrastructure, the China Science and Technology Journal Database, and the Wan Fang Database were searched for SRs/MAs of the correlation between genetic polymorphisms and blood concentrations of CNIs in renal transplant recipients from inception to July 2016. Two reviewers independently screened the literatures and extracted data, then the AMSTAR measurement tool was used to assess the methodological quality of SRs/Mas included in the overview.

RESULTS

Fourteen SRs/MAs met the inclusion criteria. The most commonly reported genotype was CYP3A53/3, which was strongly associated with cyclosporine A (CsA) and tacrolimus (FK506). MDR1 C3435T CC was also associated with CNI use, especially with CsA therapy. Other less commonly reported genotypes such as CYP3A41B, MDR1 C1236T CC, and MDR1 G2677T/A GG also affected the blood concentrations of CNIs.

CONCLUSIONS

Our overview showed that polymorphisms influence the blood concentrations of CNIs, which suggests the necessity to monitor these concentrations in patients with genotypes that affect dose-adjusted trough concentrations (C0/D) or dose-adjusted peak concentrations (C2/D) to regulate the dosage for individual administration. Because of the limited number of included studies, these findings should be verified in more high-quality studies.

The Effects of CYP3A5 Genetic Polymorphisms on Serum Tacrolimus Dose-Adjusted Concentrations and Long-Term Prognosis in Chinese Heart Transplantation Recipients

BACKGROUND AND OBJECTIVES

Effective management of immunosuppressants is extemely important to improve prognosis of heart transplant recipients. We aim to investigate the effects of cytochrome P450 (CYP) 3A5 (rs776746) single nucleotide polymorphisms (SNPs) on serum tacrolimus concentrations/doses (C/Ds, ng/mL per mg/kg) and long-term prognosis in Chinese heart transplant recipients.

METHODS

We detected the CYP3A5 SNPs of 203 consecutive Chinese heart transplant recipients between August 2005 and July 2012, and 55 of them who received tacrolimus-based immunosuppressive therapy were enrolled in this study. The tacrolimus C/Ds at 1, 3, 6, 12, 24 and 36 months after transplantation were routinely calculated. X-ray-guided endomyocardial biopsies (EMBs) were performed at 1, 3 and 6 months after heart transplantion to evaluate acute rejection degrees. All participants were then followed up annually until May 2018. The designed primary endpoint was all-cause mortality.

RESULTS

In 55 heart transplant recipients (43 males and 12 females), CYP3A5 non-expressors (CYP3A5*3/*3, n = 40) had significantly higher tacrolimus C/Ds than expressors (CYP3A5*1/*3, n = 15) at all time points (P < 0.001). Chi-squared test showed no significant differences in EMB-proven acute rejections between the two groups within 6 months after heart transplantion. The median follow-up period was 94.7 months, and eight patients died. Kaplan-Meier analysis showed CYP3A5 expressors tend to have higher mortality than non-expressors (20% vs 12.5%, log-rank: P = 0.314).

CONCLUSIONS

CYP3A5 SNPs affect tacrolimus pharmacokinetics in Chinese heart transplant recipients, and non-expressors have higher tacrolimus C/Ds. In addition, expressors tend to have a worse long-term prognosis than non-expressors.

Recipient ABCB1, donor and recipient CYP3A5 genotypes influence tacrolimus pharmacokinetics in liver transplant cases

BACKGROUND

Effective immunosuppression through optimization of trough levels tacrolimus reduces post-transplant mortality rate in liver transplant cases.

METHODS

Meta-analysis was carried out to evaluate how donor/recipient CYP3A5 (n = 678) and recipient ABCB1 (n = 318) genotypes influence tacrolimus pharmacokinetics till one-month of transplantation.

RESULTS

The donor CYP3A5*3/*3 genotype exhibited higher concentration/dose (C/D) ratio of tacrolimus in week 1 (mean difference: 65.04, 95% CI: 15.30-114.79 ng/ml/mg/kg), week 2 (mean difference: 21.7, 95% CI: 12.6-30.9 ng/ml/mg/kg) and week 4 (mean difference: 43.28, 95% CI: 17.09 - 69.49 ng/ml/mg/kg) compared to *1/*1 and *1/*3 genotypes. The recipient CYP3A5 *3/*3 genotype did not showed significant difference in tacrolimus C/D ratio in week 1 compared to other two genotypes. However, week 2 (mean difference: 44.16, 95% CI: 3.68-84.65 ng/ml/mg/kg) and week 4 (mean difference: 43.74, 95% CI: 12.50-75.00 ng/ml/mg/kg) availability was higher in *3/*3 mutant recipients. However, the recipient ABCB1 3435 C > T polymorphism has no significant influence on tacrolimus pharmacokinetics till one month of transplant.

CONCLUSIONS

The donor and recipient CYP3A5*3 polymorphism influences tacrolimus pharmacokinetics in the first month post-transplantation, whereas the association with recipient ABCB1 3435 C > T is inconclusive.

Gene Variations of Sixth Complement Component Affecting Tacrolimus Metabolism in Patients with Liver Transplantation for Hepatocellular Carcinoma

BACKGROUND

Orthotopic liver transplantation (OLT) improves the prognosis of patients with hepatocellular carcinoma (HCC). Moreover, the complement system is a powerful immune effector that can affect liver function and process of liver cirrhosis. However, studies correlating the complement system with tacrolimus metabolism after OLT are scarce. In this study, the role of single nucleotide polymorphisms (SNPs) associated with the sixth complement component (C6) in tacrolimus metabolism was investigated during the early stages of liver transplantation.

METHODS

The study enrolled 135 adult patients treated with OLT for HCC between August 2011 and October 2013. Ten SNPs in C6 gene and rs776746 in cytochrome P450 3A5 (CYP3A5) gene were investigated. The tacrolimus levels were monitored daily during 4 weeks after transplantation.

RESULTS

Both donor and recipient CYP3A5 rs776746 allele A were correlated with decreased concentration/dose (C/D) ratios. Recipient C6 rs9200 allele G and donor C6 rs10052999 homozygotes were correlated with lower C/D ratios. Recipient CYP3A5 rs776746 allele A (yielded median tacrolimus C/D ratios of 225.90 at week 1 and 123.61 at week 2), C6 rs9200 allele G (exhibited median tacrolimus C/D ratios of 211.31 at week 1, 110.23 at week 2, and 99.88 at week 3), and donor CYP3A5 rs776746 allele A (exhibited median C/D ratios of 210.82 at week 1, 111.06 at week 2, 77.49 at week 3, and 85.60 at week 4) and C6 rs10052999 homozygote (exhibited median C/D ratios of 167.59 at week 2, 157.99 at week 3, and 155.36 at week 4) were associated with rapid tacrolimus metabolism. With increasing number of these alleles, patients were found to have lower tacrolimus C/D ratios at various time points during the 4 weeks after transplantation. In multiple linear regression analysis, recipient C6 rs9200 group (AA vs. GG/GA) was found to be related to tacrolimus metabolism at weeks 1, 2, and 3 (P = 0.005, P = 0.045, and P = 0.033, respectively), whereas donor C6 rs10052999 group (CC/TT vs. TC) was demonstrated to be correlated with tacrolimus metabolism only at week 4 (P = 0.001).

CONCLUSIONS

Recipient C6 gene rs9200 polymorphism and donor C6 gene rs10052999 polymorphism are new genetic loci that affect tacrolimus metabolism in patients with HCC after OLT.

Methods to analyze big data in pharmacogenomics research

The scale and scope of pharmacogenomics research continues to expand as the cost and efficiency of molecular data generation techniques advance. These new technologies give rise to enormous opportunity for the identification of important genetic and genomic factors important for drug treatment response. With this opportunity come significant challenges. Most of these can be categorized as 'big data' issues, facing not only pharmacogenomics, but other fields in the life sciences as well. In this review, we describe some of the analysis techniques and tools being implemented for genetic/genomic discovery in pharmacogenomics.

Influence of the CYP3A4/5 genetic score and ABCB1 polymorphisms on tacrolimus exposure and renal function in Brazilian kidney transplant patients

BACKGROUND

Polymorphisms in genes encoding transport proteins and metabolizing enzymes involved in tacrolimus (TAC) disposition may be important sources of individual variability during treatment.

OBJECTIVE

The aim of this study was to investigate the effect of combined CYP3A4 and CYP3A5 variants, using a CYP3A4/5 genetic score, and ABCB1 polymorphisms on therapeutic TAC monitoring and their relationship with clinical outcomes.

MATERIAL AND METHODS

Brazilian kidney transplant recipients (n=151), who received TAC over 3 months after transplantation, were genotyped for CYP3A4 rs2242480 (g.20230G>A), CYP3A5 rs15524 (g.31611C>T) and rs776746 (g.6986A>G), ABCB1 rs1128503 (c.1236C>T), rs1045642 (c.3435C>T), and rs2032582 (c.2677G>T/A) polymorphisms.

RESULTS

Frequencies of CYP3A4 g.20230A, CYP3A5 g.31611C, and g.6986A were 0.37, 0.26, and 0.28, respectively. These alleles were associated with TAC rapid metabolization and were used for CYP3A4/5 genetic score construction. A higher CYP3A4/5 genetic score was associated with higher TAC dose and lower concentrations for dose administered (Co/D, P<0.05). Ninety days after transplantation, the presence of two or more rapid metabolization alleles contributed toward 27.7% of Co/D variability and was associated with a lower estimated glomerular filtration rate values (P<0.05). For ABCB1, the frequencies of c.1236T, c.3435T, and c.2677T/A alleles were 0.42, 0.42, and 0.33/0.04. At 30 days after transplantation, patients carrying ABCB1 c.1236TT+c.3435TT+(c.2677TT+TA) genotypes had higher TAC Co/D than those with common or heterozygous genotypes (P<0.05).

CONCLUSION

The results show the impact of the CYP3A4/5 genetic score on TAC exposure and renal function in Brazilian patients. Furthermore, ABCB1 polymorphisms, in a combined analysis, influenced TAC Co/D at 30 days after transplantation.

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.

Risk factors for and management of ischemic-type biliary lesions following orthotopic liver transplantation: A single center experience

INTRODUCTION

Biliary complications can cause morbidity, graft loss, and mortality after liver transplantation. The most troublesome biliary complications are ischemic-type biliary lesions (ITBL), which occur since transplants can now be performed after the donor has undergone circulatory death. The exact origin of this type of biliary complication remains unknown.

MATERIAL AND METHODS

A total of 528 patients were retrospectively analyzed following liver transplantation after excluding 30 patients with primary sclerosing cholangitis and those lost to follow-up from January 2007 to January 2014. The incidence of and risk factors for ITBL were evaluated.

RESULTS

Cold ischemia time (CIT) (P = 0.042) and warm ischemia time (WIT) (P = 0.006) were found to be independent risk factors for the development of ITBL. Use of the cytochrome P450 (CYP) 3A5 genotype assay to guide individualization of immunosuppressive medications resulted in significantly fewer ITBL (P = 0.027. Autoimmune hepatitis might be a risk factor for ITBL, as determined using univariate analysis (P = 0.047).

CONCLUSIONS

Efforts should be taken to minimize risk factors associated with ITBL, such as CIT and WIT. The CYP3A5 genotype assay should be used to guide selection of immunosuppressive therapy in an effort to reduce the occurrence of ITBL.

Liver Transplant Patient Carriers of Polymorphism Cyp3a5*1 Donors May Need More Doses of Tacrolimus From the First Month After Transplantation

BACKGROUND

The aim of this work was to evaluate the CYP3A5:CYP3A5*1/CYP3A5*3 (6986A>G) polymorphism related to the pharmacokinetic characteristics of tacrolimus during the first 3 months after transplantation, analyzing both donor and recipient genotype, in liver transplant patients.

METHODS

This retrospective, single-center, cohort study included patients who had been treated with tacrolimus monotherapy with or without corticoids (n = 67). Donors and recipients were genotyped for the CYP3A5*3 allele polymorphism (6986A>G) by use of a TaqMan polymerase chain reaction technique. The presence or absence of the *1 allele ("minor-allele") was analyzed for correlation with the tacrolimus dose-normalized ratio during the 3 months after transplantation.

RESULTS

The following observations were obtained in the population studied: (1) Frequency of the minor allele*1 was much lower both in recipients (11.9% versus 88.1%) and donors (19.4% versus 80.6%), with no statistically significant differences between both distributions. (2) Recipient genotype for CYP3A5*1/*3-polymorphism had no influence in tacrolimus pharmacokinetics, with no differences between carriers and non-carriers of the minor-allele*1. (3) However, from the first month after transplantation, patients with grafts from donor carriers of minor allele*1 had lower concentration-dose ratios compared with patients with grafts from donor non-carriers of that allele (71.1 versus 119.3 and 90.5 versus 126.3, for 30 and 90 days after transplantation, respectively; P < .05).

CONCLUSIONS

The presence of the CYP3A5-6986A>G-polymorphism in the donor affects tacrolimus pharmacokinetics in the recipient, although the difference was statistically significant only for the first month after transplantation. This means that in liver transplant patients receiving grafts from donors carrying the CYP3A5*1-polymorphism, a larger dose of tacrolimus from the first month after transplantation would be needed. The evidence provided in this study showed no effect of the recipient genotype.

Influence of combined CYP3A4 and CYP3A5 single-nucleotide polymorphisms on tacrolimus exposure in kidney transplant recipients: a study according to the post-transplant phase

AIM

The present study investigated in Tunisian renal transplant patients, genetic polymorphisms of CYP3A4 -392A>G and CYP3A5 6986A>G and their influence on tacrolimus (Tac) pharmacokinetics during early and late post-transplant (PT) phases and established customized ranges of Tac doses matching the C0 target levels according to CYP3A4 and CYP3A5 genotype combination and the PT phase.

PATIENTS & METHODS

We included adult Tunisian patients having received Tac for de novo kidney grafts and undergone a therapeutic drug monitoring of Tac by morning C0 monitoring during early (1 to 90 days) and late (over 90 days) PT phases. The genomic DNA was extracted from peripheral blood mononuclear cells using a salting-out procedure. CYP3A4 promoter (rs2740574; -392A>G) and CYP3A5 (rs776746; 6986A>G) SNP genotyping was analyzed using PCR-RFLP.

RESULTS

Fifty-two patients were enrolled in the study. During the early PT phase, the CYP3A5 polymorphism but not that of CYP3A4, correlates significantly with Tac dose-normalized C0 (C0/D ratio). During the late PT phase, the effect of CYP3A4 polymorphism becomes significant and that of CYP3A5 becomes nonsignificant on Tac C0/D Tac. The mean daily doses (mg/kg) matching therapeutic C0, regardless of the CYP3A genotypes, were 0.16 ± 0.05 and 0.10 ± 0.05 during early and late PT phase, respectively. Carriers of the CYP3A4*1B allele require higher doses to maintain the C0 in the therapeutic range during the two PT phases. However, patients carrying the CYP3A5*1 require significant higher Tac doses, only during the early phase.

CONCLUSION

Our data support a critical role of the CYP3A5 6986A>G and CYP3A4 -392A>G polymorphisms on the variation of Tac exposure during the early and the late PT phase, respectively. The establishment of customized Tac doses, according to CYP3A4/CYP3A5 genotype combination and the PT time, may allow preventing graft rejection and improving the safety profile of this drug. Further studies are needed to investigate this issue.

A Simple Novel Technique to Estimate Tacrolimus Dosages During the Early Post Kidney Transplantation Period

BACKGROUND

Tacrolimus pharmacokinetics prediction by CYP3A5 genotyping is not available in many Asian resource-limited settings. Therefore, an alternative technique is needed to estimate the dose of tacrolimus perioperatively. The 12-hour level after the first dose (C12-0) is an alternative technique for estimating the dose of tacrolimus. This simple and inexpensive calculation technique can be used by any transplantation center.

METHODS

A prospective study on a cohort of 57 incident post-kidney transplant recipients was conducted. The whole-blood tacrolimus trough level (C12-0) was measured at 12 hours after the first dose (0.1 mg/kg) of orally administered tacrolimus during transplantation. Concomitant medications with CYP3A5 inhibitors/inducers were not allowed. Genotyping for CYP3A5 expression was carried out by reverse transcription polymerase chain reaction. The dosages and trough levels of tacrolimus at postoperative day 7 and postoperative months 1 to 3 were measured and analyzed for the dose requirements for therapeutic levels (mg/kg/d).

RESULTS

The doses of tacrolimus were widely diverse, ranging from 0.049 to 0.260 mg/kg/d and 0.031 to 0.298 mg/kg/d at day 7 and months 1 to 3, respectively. There were 9, 28, and 20 patients (15.8%, 49.1%, and 35.1%) with CYP3A5 *1/*1, *1/*3, and *3/*3, respectively. The CYP3A5 genotypes were significantly correlated with the target tacrolimus dose at day 7 (r(2) = 0.307) and the stable dose at months 1 to 3 (r(2) = 0.337). The C12-0 level also was significantly correlated with the dose of tacrolimus at day 7 (r(2) = 0.546) and the stable dose at months 1 to 3 (r(2) = 0.406).

CONCLUSIONS

There were strong correlations between the C12-0 level and the tacrolimus doses during the perioperative period at day 7 and the stable period at 1 to 3 months. Countries with limited resources for genotype testing can use the C12-0 level as an alternative to estimate the tacrolimus dose.

CYP3A5*3 and POR*28 genetic variants influence the required dose of tacrolimus in heart transplant recipients

BACKGROUND

After heart transplantation (HTx), the interindividual pharmacokinetic variability of immunosuppressive drugs represents a major therapeutic challenge due to the narrow therapeutic window between over-immunosuppression causing toxicity and under-immunosuppression leading to graft rejection. Although genetic polymorphisms have been shown to influence pharmacokinetics of immunosuppressants, data in the context of HTx are scarce. We thus assessed the role of genetic variation in CYP3A4, CYP3A5, POR, NR1I2, and ABCB1 acting jointly in immunosuppressive drug pathways in tacrolimus (TAC) and ciclosporin (CSA) dose requirement in HTx recipients.

METHODS

Associations between 7 functional genetic variants and blood dose-adjusted trough (C0) concentrations of TAC and CSA at 1, 3, 6, and 12 months after HTx were evaluated in cohorts of 52 and 45 patients, respectively.

RESULTS

Compared with CYP3A5 nonexpressors (*3/*3 genotype), CYP3A5 expressors (*1/*3 or *1/*1 genotype) required around 2.2- to 2.6-fold higher daily TAC doses to reach the targeted C0 concentration at all studied time points (P ≤ 0.003). Additionally, the POR*28 variant carriers showed higher dose-adjusted TAC-C0 concentrations at all time points resulting in significant differences at 3 (P = 0.025) and 6 months (P = 0.047) after HTx. No significant associations were observed between the genetic variants and the CSA dose requirement.

CONCLUSIONS

The CYP3A5*3 variant has a major influence on the required TAC dose in HTx recipients, whereas the POR*28 may additionally contribute to the observed variability. These results support the importance of genetic markers in TAC dose optimization after HTx.

Effects of the CYP3A4*1B Genetic Polymorphism on the Pharmacokinetics of Tacrolimus in Adult Renal Transplant Recipients: A Meta-Analysis

BACKGROUND AND OBJECTIVE

The association between the CYP3A4*1B single nucleotide polymorphism (SNP) and tacrolimus pharmacokinetics in different studies is controversial. Therefore, a meta-analysis was employed to evaluate the correlation between the CYP3A4*1B genetic polymorphism and tacrolimus pharmacokinetics at different post-transplantation times in adult renal transplant recipients.

METHODS

Studies evaluating the CYP3A4*1B genetic polymorphism and tacrolimus pharmacokinetics were retrieved through a systematical search of Embase, PubMed, the Cochrane Library, ClinicalTrials.gov and three Chinese literature databases (up to Sept. 2014). The pharmacokinetic parameters (weight-adjusted tacrolimus daily dose and tacrolimus trough concentration/weight-adjusted tacrolimus daily dose ratio) were extracted, and the meta-analysis was performed using Stata 12.1.

RESULTS

Seven studies (involving 1182 adult renal transplant recipients) were included in this meta-analysis. For the weight-adjusted tacrolimus daily dose, in all included renal transplant recipients (European & Indian populations), CYP3A4*1/*1 recipients required a significantly lower weight-adjusted tacrolimus daily dose than did CYP3A4*1B carriers at 7 days (WMD -0.048; 95% CI -0.083 ~ -0.014), 6 months (WMD -0.058; 95% CI -0.081 ~ -0.036) and 12 months (WMD - 0.061; 95% CI -0.096 ~ -0.027) post-transplantation. In light of the heterogeneity, the analysis was repeated after removing the only study in an Indian population, and CYP3A4*1/*1 European recipients (mostly Caucasian) required a lower weight-adjusted tacrolimus daily dose within the first year post-transplantation. The tacrolimus trough concentration/weight-adjusted tacrolimus daily dose ratio (C0/Dose ratio) was significantly higher in CYP3A4*1/*1 recipients than in CYP3A4*1B carriers at 6 months (WMD 52.588; 95% CI 22.387 ~ 82.789) and 12 months (WMD 62.219; 95% CI 14.218 ~ 110.221) post-transplantation. When the only study in an Indian population was removed to examine European recipients (mostly Caucasian), the significant difference persisted at 1 month, 6 months and 12 months post-transplantation.

CONCLUSION

Based on our meta-analysis, the CYP3A4*1B genetic polymorphism affects tacrolimus dose requirements and tacrolimus trough concentration/weight-adjusted tacrolimus daily dose ratio within the first year post-transplantation in adult renal transplant recipients, especially in European recipients (mostly Caucasian).

Parsing interindividual drug variability: an emerging role for systems pharmacology

There is notable interindividual heterogeneity in drug response, affecting both drug efficacy and toxicity, resulting in patient harm and the inefficient utilization of limited healthcare resources. Pharmacogenomics is at the forefront of research to understand interindividual drug response variability, but although many genotype-drug response associations have been identified, translation of pharmacogenomic associations into clinical practice has been hampered by inconsistent findings and inadequate predictive values. These limitations are in part due to the complex interplay between drug-specific, human body and environmental factors influencing drug response and therefore pharmacogenomics, whilst intrinsically necessary, is by itself unlikely to adequately parse drug variability. The emergent, interdisciplinary and rapidly developing field of systems pharmacology, which incorporates but goes beyond pharmacogenomics, holds significant potential to further parse interindividual drug variability. Systems pharmacology broadly encompasses two distinct research efforts, pharmacologically-orientated systems biology and pharmacometrics. Pharmacologically-orientated systems biology utilizes high throughput omics technologies, including next-generation sequencing, transcriptomics and proteomics, to identify factors associated with differential drug response within the different levels of biological organization in the hierarchical human body. Increasingly complex pharmacometric models are being developed that quantitatively integrate factors associated with drug response. Although distinct, these research areas complement one another and continual development can be facilitated by iterating between dynamic experimental and computational findings. Ultimately, quantitative data-derived models of sufficient detail will be required to help realize the goal of precision medicine.

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.

Clinical implementation of pharmacogenetics in kidney transplantation: calcineurin inhibitors in the starting blocks

Pharmacogenetics has generated many expectations for its potential to individualize therapy proactively and improve medical care. However, despite the huge amount of reported genetic associations with either pharmacokinetics or pharmacodynamics of drugs, the translation into patient care is still slow. In fact, strong evidence for a substantial clinical benefit of pharmacogenetic testing is still limited, with a few exceptions. In kidney transplantation, established pharmacogenetic discoveries are being investigated for application in the clinic to improve efficacy and to limit toxicity associated with the use of immunosuppressive drugs, especially the frequently used calcineurin inhibitors (CNIs) tacrolimus and ciclosporin. The purpose of the present review is to picture the current status of CNI pharmacogenetics and to discuss the most promising leads that have been followed so far.

Association between interleukin-18 promoter variants and tacrolimus pharmacokinetics in Chinese renal transplant patients

PURPOSE

Interleukin 18 (IL-18) is a potent proinflammatory cytokine thought to down-regulate cytochrome P450 (CYP) enzyme activities. This study aimed to assess the potential influence of two functional single nucleotide polymorphisms (SNPs) in the IL-18 promoter region on the tacrolimus pharmacokinetics in Chinese renal transplant patients.

METHODS

We enrolled 96 renal allograft recipients receiving tacrolimus-based immunosuppressive regiments. Two functional SNPs in the IL-18 gene promoter region at the positions -137G/C (rs187283) and -607A/C (rs1946518) and one SNP (rs776746) of CYP3A5 were genotyped using a Mass ARRAY platform. Tacrolimus daily doses (mg/day) and trough tacrolimus concentration (ng/ml) were continuously recorded for 1 month after transplantation.

RESULTS

The tacrolimus C/D ratio was significantly associated with the IL-18 rs1946518 gene polymorphism in the first month after transplantation (P = 0.0225). We studied the influence of its polymorphism on tacrolimus C/D ratios in subjects with different CYP3A5 genotype backgrounds, and among patients with CYP3A5 expressers, the difference among the three genotypes was even more striking (P < 0.001). We did not find significant differences in tacrolimus C/D ratios between the IL-18 rs187238 genotypes, either nominally or according to the CYP3A5 genotype. In a simple linear regression model, age, hemoglobin (Hb), CYP3A5 gene polymorphisms, and IL-18 A-607C gene polymorphisms were associated with log-transformed tacrolimus C/D ratios (P < 0.05). In the final multiple linear regression model, CYP3A5 polymorphisms were the most important variant, accounting for 19.5 % of total variation involved in tacrolimus pharmacokinetics.

CONCLUSION

Our findings suggest that a combined analysis of CYP3A5 and IL-18 promoter polymorphisms may help clinicians develop individualized tacrolimus treatment, which is based on determining CYP3A5 genotype.

Pharmacogenetics and immunosuppressive drugs

Several candidate genes have been proposed as potential biomarkers for altered pharmacodynamics or pharmacokinetics of immunosuppressive drugs. However, there is usually only limited clinical evidence substantiating the implementation of biomarkers into clinical practice. Testing for thiopurine-S-methyltransferase polymorphisms has been put into routine clinical use quite widely, while the other pharmacogenetic tests are much less frequently used. Relatively good evidence appeared for tacrolimus-related biomarkers; thus, their utilization may be envisaged in the near future. Although the biomarkers related to mycophenolate, sirolimus or other drugs in the therapeutic class may be promising, further research is necessary to provide more robust evidence. The present review focuses on immunosuppressive drugs, excluding biological treatment.

Long-term outcome of ketoconazole and tacrolimus co-administration in kidney transplant patients

AIM: To study the long-term outcome of ketoconazole and tacrolimus combination in kidney transplant recipients.

METHODS: From 2006 to 2010, ketoconazole was given in 199 patients and was continued for at least 1 year or until graft failure (Group 1), while 149 patients did not receive any ketoconazole (Group 2). A combination of tacrolimus, mycophenolate and steroid was used as maintenance therapy. High risk patients received basiliximab induction.

RESULTS: Basic demographic data was similar between the 2 groups. The 5-year cumulative incidence of biopsy-confirmed and clinically-treated acute rejection was significantly higher in Group 1 than in Group 2 (34% vs 18%, P = 0.01). The 5-year Kaplan-Meier estimated graft survival (74.3% vs 76.4%, P = 0.58) and patient survival (87.8% vs 87.5%, P = 0.93) were not different between the 2 groups. Multivariable analyses identified ketoconazole usage as an independent risk of acute rejection (HR = 2.33, 95%CI: 1.33-4.07; P = 0.003) while tacrolimus dose in the 2^nd month was protective (HR = 0.89, 95%CI: 0.75-0.96; P = 0.041).

CONCLUSION: Co-administration of ketoconazole and tacrolimus is associated with significantly higher incidence of acute rejection in kidney transplant recipients.

Conversion from twice- to once-daily tacrolimus in pediatric kidney recipients: a pharmacokinetic and bioequivalence study

BACKGROUND

The objectives of this study were to investigate pharmacokinetic and pharmacogenetic parameters during the conversion on a 1:1 (mg:mg) basis from a twice-daily (Prograf) to once-daily (Advagraf) tacrolimus formulation in pediatric kidney transplant recipients.

METHODS

Twenty-four-hour pharmacokinetic profiles were analyzed before and after conversion in 19 stable renal transplant recipients (age 7-19 years). Tacrolimus pharmacokinetic parameters [area under the concentration-time curve (AUC0-24), minimum whole-blood concentration (Cmin), maximum whole-blood concentration (Cmax), and time to achieve maximum whole-blood concentration (tmax)] were compared between Tac formulations and between CYP3A5 and MDR1 genotypes after dose normalization.

RESULTS

Both AUC0-24 and Cmin decreased after conversion (223.3 to 197.5 ng.h/ml and 6.5 to 5.6 ng/ml; p = 0.03 and 0.01, respectively). However, the ratio of the least square means (LSM) for AUC0-24 was 90.8 %, with 90 % CI limits of 85.3 to 96.7 %, falling within bioequivalence limits. The CYP3A5 genotype influences the dose-normalized Cmin with the twice-daily formulation only.

CONCLUSIONS

Both tacrolimus formulations are bioequivalent in pediatric renal recipients. However, we observed a decrease in AUC0-24 and Cmin after the conversion, requiring close pharmacokinetic monitoring during the conversion period.

The effect of ABCB1 C3435T polymorphism on pharmacokinetics of tacrolimus in liver transplantation: a meta-analysis

OBJECTIVES

The effect of ABCB1 C3435T SNP on the pharmacokinetics of immunosuppressive drug tacrolimus in different studies was conflicting. So a meta-analysis was employed to study the correlation of ABCB1 C3435T SNP and the pharmacokinetics of tacrolimus at different post-transplantation times.

METHOD

Several studies about ABCB1 C3435T polymorphism and the pharmacokinetics of tacrolimus were collected through the search on PubMed and the Cochrane Library. After the extraction of pharmacokinetic parameters from these studies, a meta-analysis was performed on the software STATA version 11.0.

RESULTS

A total of 9 studies were adopted including 558 liver transplant recipients. For the dose of tacrolimus, the subjects with wild-type CC had a significantly higher tacrolimus dose than homozygous mutated genotype TT within 1 week (WMD=0.01 (0.00, 0.02), P=0.014) and the similar result in recipients with heterozygous CT compared with TT after transplantation for 1 month (WMD=0.01 (0.00, 0.02), P=0.002). For the tacrolimus concentration/dose ratio, subjects with CT had higher C/D ratio than those with CC and TT at different post-transplantation times. A subgroup analysis based on different ethnic populations was also carried out. Donors' genotypes were also considered in this meta-analysis.

CONCLUSION

Through this meta-analysis for the including studies about the pharmacokinetics of tacrolimus and ABCB1 C3435T SNP, several significant associations were obtained. Particularly, the Caucasians showed more significant associations between the C/D ratio and ABCB1 C3435T polymorphism; however, the correlations were not steady at different post-transplantation times.

A taste of individualized medicine: physicians' reactions to automated genetic interpretations

The potential of pharmacogenomics is well documented, and functionality exploiting this knowledge is about to be introduced into electronic medical records. To explore physicians' reactions to automatic interpretations of genetic tests, we built a prototype with a simple interpretive algorithm. The algorithm was adapted to the needs of physicians handling immunosuppressive treatment during organ transplantation. Nine physicians were observed expressing their thoughts while using the prototype for two patient scenarios. The computer screen and audio were recorded, and the qualitative results triangulated with responses to a survey instrument. The physicians' reactions to the prototype were very positive; they clearly trusted the results and the theory behind them. The explanation of the algorithm was prominently placed in the user interface for transparency, although this design led to considerable confusion. Background information and references should be available, but considerably less prominent than the result and recommendation.

Novel single nucleotide polymorphisms in interleukin 6 affect tacrolimus metabolism in liver transplant patients

BACKGROUND

Tacrolimus is the first-line immunosuppressant after organ transplantation. It is mainly metabolized by cytochrome P450, family 3, subfamily A (CYP3A) enzymes, but there are large individual differences in metabolism. Interleukin 6 (IL6) has been shown to cause a pan-suppression of mRNA levels of ten major CYP enzymes in human hepatocyte cultures. IL6 has been shown to provide hepatoprotection in various models of liver injury. Rs1800796 is a locus in the IL6 gene promoter region which regulates cytokine production. We speculated that IL6 rs1800796 polymorphisms may lead to individual differences in tacrolimus metabolism by affecting CYP3A enzymes levels and liver function after liver transplantation.

METHODOLOGY/PRINCIPAL FINDINGS

Ninety-six liver transplant patients receiving tacrolimus were enrolled in the study. Two single nucleotide polymorphisms (SNP), CYP3A5 rs776746 and IL6 rs1800796, were genotyped in both donors and recipients. The effects of SNPs on tacrolimus concentration/dose (C/D ratio) at four weeks after transplantation were studied, as well as the effects of donor IL6 rs1800796 polymorphisms on liver function. Both donor and recipient CYP3A5 rs776746 allele A showed association with lower C/D ratios, while donor IL6 rs1800796 allele G showed an association with higher C/D ratios. Donor CYP3A5 rs776746 allele A, IL6 rs1800796 allele C, and recipient CYP3A5 rs776746 allele A were associated with fast tacrolimus metabolism. With increasing numbers of these alleles, patients were found to have increasingly lower tacrolimus C/D ratios at time points after transplantation. Donor IL6 rs1800796 allele G carriers showed an association with higher glutamic-pyruvic transaminase (GPT) levels.

CONCLUSIONS

Combined analysis of donor CYP3A5 rs776746, IL6 rs1800796, and recipient CYP3A5 rs776746 polymorphisms may distinguish tacrolimus metabolism better than CYP3A5 rs776746 alone. IL6 may lead to individual differences in tacrolimus metabolism mainly by affecting liver function.

Pharmacogenomics and heart failure in congenital heart disease

Congenital heart disease (CHD) constitutes a lifelong challenge in heart failure management. Current therapy is based mainly on physiologic principles extrapolated from the management of left ventricular failure in adult populations with either ischemic or nonischemic cardiomyopathy. However, there is good evidence of genomic variability in the origin and progression of CHD that suggests the need for a individualized approach to treatment. The developing science of pharmacogenomics presents an opportunity for CHD management broadly, and especially in the context of heart failure. There is growing evidence that individualizing drug therapy for these patients might be beneficial, and that prediction of response to therapy might be possible by incorporating genomic data into the treatment algorithm for individual patients.

Severe acute nephrotoxicity in a kidney transplant patient despite low tacrolimus levels: a possible interaction between donor and recipient genetic polymorphisms

WHAT IS KNOWN AND OBJECTIVE

Tacrolimus has a narrow therapeutic index and shows large interindividual variations in pharmacokinetics, which may be partly explained by genetic variability in metabolic enzymes of the cytochrome P450 (mainly CYP3A4 and CYP3A5) and transport P-glycoprotein (encoded by the ABCB1 gene). Genetic variability in the expression of biotransformation enzymes and drug transporters may also predispose individuals to tacrolimus-induced nephrotoxicity.

CASE SUMMARY

We report a case of severe biopsy-proven Tacrolimus (TAC) nephrotoxicity that occurred 1 month after renal transplantation despite persistently low TAC levels. The donor genotype was CYP3A5*3/*3 (loss-of-function genotype), whereas that of the recipient was CYP3A5*1/*3. The donor and recipient genotypes did not differ with respect to either CYP3A4 rs35599367C>T (both were CC homozygotes) or ABCB1 gene polymorphisms (both TT homozygotes for the 1236C>T polymorphism and CT heterozygotes for the 3435C>T polymorphism).

WHAT IS NEW AND CONCLUSION

This case study suggests that donor/recipient genetic mismatch in metabolic enzymes may have an important role in modulating tacrolimus nephrotoxicity. It provides a possible explanation for the intriguing observation that for a subset of patients, cumulative TAC doses appear to correlate better with nephrotoxicity than trough levels.