Martine De Meyer

The effect of CYP3A5 and MDR1 (ABCB1) polymorphisms on cyclosporine and tacrolimus dose requirements and trough blood levels in stable renal transplant patients.

Cyclosporine and tacrolimus are immunosuppressive drugs largely used in renal transplantation. They are characterized by a wide inter-individual variability in their pharmacokinetics with a potential impact on their therapeutic efficacy or induced toxicity. CYP3A5 and P-glycoprotein appear as important determinants of the metabolism of these drugs. The objective of this study was to investigate the effect of CYP3A5 and MDR1 (ABCB1) polymorphisms on cyclosporine and tacrolimus dose requirements and trough blood concentrations in stable transplant patients. Stable renal transplant recipients receiving cyclosporine (n = 50) or tacrolimus (n = 50) were genotyped for CYP3A5*3 and *6, and MDR1 C1236T, G2677T/A and C3435T. Dose-adjusted trough blood levels (ng/ml per mg/kg body weight) as well as doses (mg/kg body weight) required to achieve target blood concentrations were compared among patients according to allelic status for CYP3A5 and MDR1. Dose-adjusted trough concentrations were three-fold and 1.6-fold higher in CYP3A5*3/*3 patients than in CYP3A5*1/*3 patients for tacrolimus and cyclosporine, respectively. In the case of tacrolimus, the difference was even more striking when considering CYP3A5*1/*1 patients showing dose-adjusted trough concentrations 5.8-fold lower than CYP3A5*3/*3 patients. For both drugs, no association was found between trough blood concentrations or dose requirement and MDR1 genotype. Multiple regression analyses showed that CYP3A5*1/*3 polymorphism explained up to 45% of the variability in dose requirement in relation to tacrolimus use. Given the importance of rapidly achieving target blood concentrations after transplantation, further prospective studies should consider the immediate post-graft period and assess the influence of this specific polymorphism. Beside non-genetic factors (e.g. steroids dosing, drugs interactions), CYP3A5 pharmacogenetic testing performed just before transplantation could contribute to a better individualization of immunosuppressive therapy.

Effect of a new functional CYP3A4 polymorphism on calcineurin inhibitors’ dose requirements and trough blood levels in stable renal transplant patients

AIMS CYP3A4 is involved in the oxidative metabolism of many drugs and xenobiotics including the immunosuppressants tacrolimus (Tac) and cyclosporine (CsA). The objective of the study was to assess the potential influence of a new functional SNP in CYP3A4 on the pharmacokinetic parameters assessed by dose requirements and trough blood levels of both calcineurin inhibitors (CNI) in stable renal transplant patients. PATIENTS & METHODS A total of 99 stable renal transplant patients receiving either Tac (n = 49) or CsA (n = 50) were genotyped for the CYP3A4 intron 6 C>T (rs35599367) and CYP3A5*3 SNPs. Trough blood levels ([Tac](0) or [CsA](0) in ng/ml), dose-adjusted [Tac](0) or [CsA](0) (ng/ml per mg/kg bodyweight) as well as doses (mg/kg bodyweight) required to achieve target concentrations were compared among patients according to allelic status for CYP3A4 and CYP3A5. RESULTS Dose-adjusted concentrations were 2.0- and 1.6-fold higher in T-variant allele carriers for the CYP3A4 intron 6 C>T SNP compared with homozygous CC for Tac and CsA, respectively. When CYP3A4/CYP3A5 genotypes were combined, the difference was even more striking as the so-defined CYP3A poor metabolizer group presented dose-adjusted concentration 1.6- and 4.1-fold higher for Tac, and 1.5- and 2.2-fold higher for CsA than the intermediate metabolizer and extensive metabolizer groups, respectively. Multiple linear regression analysis revealed that, taken together, both CYP3A4 intron 6 and CYP3A5*3 SNPs explained more than 60 and 20% of the variability observed in dose-adjusted [Tac](0) and [CsA](0), respectively. CONCLUSION The CYP3A4 intron 6 C>T polymorphism is associated with altered Tac and CsA metabolism. CYP3A4 intron 6 C>T along with CYP3A5*3 (especially for Tac) pharmacogenetic testing performed just before transplantation may help identifying patients at risk of CNI overexposure and contribute to limit CNI-related nephrotoxicity by refining the starting dose according to their genotype. Original submitted 5 May 2011; Revision submitted 29 June 2011.

Sirolimus and tacrolimus trough concentrations and dose requirements after kidney transplantation in relation to CYP3A5 and MDR1 polymorphisms and steroids

Background. CYP3A5 and MDR1 polymorphisms have been shown to influence tacrolimus blood concentrations and dose requirements. The aim is to determine whether these polymorphisms also affect sirolimus trough concentrations and dose requirements after kidney transplantation. Methods. Eighty-five renal transplant recipients receiving sirolimus were included. Twenty-four were treated with a combined sirolimus-tacrolimus regimen. Eighty-one patients received steroids. Sirolimus and tacrolimus were adjusted to a target therapeutic window. CYP3A5 (intron 3) and MDR1 (exons 12, 21, 26) genotypes were correlated to the adjusted trough concentrations and dose requirements for both sirolimus and tacrolimus. Results. There were no significant correlation between adjusted sirolimus trough concentrations or dose requirements and genetic polymorphisms. In a multiple regression model, adjusted-prednisone dose was involved with a positive or negative effect when considering sirolimus dose requirements or adjusted concentrations, respectively. In the subgroup of patients treated by tacrolimus and sirolimus, adjusted tacrolimus doses were higher in patients carrying at least one CYP3A5 *1 allele (median 0.083 vs. 0.035 mg/kg for CYP3A5*3/*3 patients, P<0.05). Adjusted-prednisolone dose and CYP3A5 polymorphism explained up to 61% of the variability in tacrolimus dose requirements. Conclusions. Unlike tacrolimus, sirolimus adjusted trough concentrations and dose requirements seem not affected by CYP3A5 and MDR1 polymorphisms. Adjusted-prednisone dose has a significant impact on tacrolimus and sirolimus dose requirements.

The place of liver transplantation in Caroli's disease and syndrome

Carolis disease (CD) or syndrome (CS) are rare inherited disorders which may cause severe, life‐threatening, cholangitis or which may lead to hepatobiliary degeneration. The typical cystic biliary anomalies are often associated to congenital hepatic fibrosis (CHF) and, less frequently, to cystic renal disease especially autosomic recessive polycystic kidney disease (ARPKD). The place of liver transplantation (LT) in the treatment of CD or CS is evaluated based on our own experience of three successfully transplanted patients, the literature review of 19 patients and the European experience with 110 patients collected in the European Liver Transplant Registry. LT should be proposed as a definitive therapeutic option once severe cholangitis or (suspicion of) malignant transformation is present. The frequently used radiological, endoscopical or surgical biliary drainage procedures carry a high morbidity and mortality rate. In case of concomitant symptomatic CHF and renal failure, combined or sequential hepatorenal transplantation should be carried out, dependant on the evolution of the hepatic and renal disease. In case of associated ARPKD, renal transplantation is often indicated early on because of the more rapid progression of the renal component of the disease.

CYP3A5 and ABCB1 polymorphisms influence tacrolimus concentrations in peripheral blood mononuclear cells after renal transplantation.

AIMS This prospective study investigated the effect of genetic polymorphisms in a biotransformation enzyme (CYP3A5) and a transporter protein (ABCB1) on tacrolimus (Tac) whole blood concentrations in renal transplantation, and more specifically on peripheral blood mononuclear cell (PBMC) drug concentrations, after renal transplantation. MATERIALS & METHODS A total of 96 renal transplant recipients were genotyped for the exon 11 (1199G>A), 21 (3435C>T) and 26 (2677G>T/A) polymorphisms in the ABCB1 gene and for the intron 3 polymorphism in the CYP3A5 gene. Tac blood and PBMC concentrations were determined at day 7 after transplantation and at steady state, and then compared with recipient genotypes. RESULTS & CONCLUSION The ABCB1 1199G>A, 3435C>T and 2677G>T/A SNPs, appeared to reduce the activity of P-glycoprotein towards Tac, increasing Tac PBMC concentrations. The impact of ABCB1 genetic polymorphisms on Tac blood concentrations was negligible. As increased Tac intracellular concentrations might in turn enhance immunosuppressive status and prevention or rejection, ABCB1 recipient genotyping might be useful to better individualize the Tac immunosuppressive therapy in renal transplantation.

The influence of genetic polymorphisms of cytochrome P450 3A5 and ABCB1 on starting dose- and weight-standardized tacrolimus trough concentrations after kidney transplantation in relation to renal function.

Abstract Background: Cytochrome P450 3A5 (CYP3A5) and ABCB1 polymorphisms have been shown to influence tacrolimus (Tc) blood concentrations in the stable phase after organ transplantation. We hypothesized that Tc pharmacokinetics may be affected by genetic mutations subsequent to starting doses. Methods: We retrospectively analyzed data from a cohort of 59 kidney transplant recipients, in whom CYP3A5 (intron 3) and ABCB1 (exons 12, 21 and 26) genotypes were correlated to dose- and weight-standardized Tc trough concentrations obtained after initial Tc doses. Renal function, expressed as glomerular filtration rate (GFR) (MDRD equation), on days 7 and 14 after transplantation was evaluated and its relationship with Tc concentrations was analyzed. Results: Dose- and weight-standardized Tc trough concentrations were lower in patients carrying the CYP3A5 *1 allele (p<0.01). There was no statistically significant association with ABCB1 polymorphisms. In a multivariate analysis, both the presence of at least one CYP3A5 *1 allele (p=0.006) and age at the time of transplantation (p=0.010) were significant independent variables affecting Tc trough blood concentrations standardized to the first dosages (model r2=0.23). GFR was not affected by Tc concentrations. Conclusions: Prospective trials are needed to prove that a genetic approach to Tc pharmacokinetics and its related side effects during the early period after grafting may improve patient outcome. Clin Chem Lab Med 2006;44:1192–8.

Impact of CYP3A4*22 allele on tacrolimus pharmacokinetics in early period after renal transplantation: toward updated genotype-based dosage guidelines

Background: Tacrolimus (Tac) metabolism is mainly mediated by the cytochrome P450 3A (CYP3A) subfamily. Recently, it has been reported that kidney transplant recipients carrying the CYP3A4*22 decrease-of-function allele require lower Tac doses and are more at risk of Tac overexposure than CYP3A4*1/*1 patients. This effect was shown to be independent of the CYP3A5*3 allelic status. However, the pharmacokinetic (PK) parameters assessed in previous studies were limited on single time point whole blood trough concentrations (C0) during routine follow-up of the patient after transplantation. Methods: Our study investigates the impact of the CYP3A4*22 allele on Tac PK [C0, area under the time vs concentration curve (AUC0–12h), apparent clearance (Cl/F), Cmax, and dose requirement], time to achieve target C0, and creatinine clearance (CrCl) in 96 kidney transplant recipients considering the 2 first weeks after the graft. All patients were genotyped for both the CYP3A4*22 and the CYP3A5*3 polymorphisms. Results: CYP3A4*22 carriers had higher Tac C0 during the first week with significant longer exposures to C0 > 15 ng/mL. These patients showed reduced Tac Cl/F but higher dose-adjusted AUC0–12h and Cmax and were at increased risk of C0 > 20 ng/mL. These effects were independent from CYP3A5*3 genotype: clustering patients according to both CYP3A4*22 and CYP3A5*3 allelic status did increase the predictive value of the genotype to explain interindividual differences in Tac PK. During the second week after transplantation, CrCl was on average 9.5 mL/min higher for CYP3A4*22 carriers compared with CYP3A4*1/*1 patients (P = 0.007), suggesting that Tac overexposure in CYP3A4*22 carriers might provide a renal function benefit. Conclusions: Our study confirms the decreased CYP3A4 activity toward Tac for CYP3A4*22 carriers early after transplantation and provides evidence for refining genotype-based dosage by adding the CYP3A4*22 genotype information to the CYP3A5*3 allelic status.

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.

Biotransformation enzymes and drug transporters pharmacogenetics in relation to immunosuppressive drugs: impact on pharmacokinetics and clinical outcome

Immunosuppressive drugs commonly used after organ transplantation to prevent acute rejection including tacrolimus, cyclosporine, sirolimus, and mycophenolic acid are characterized by a narrow therapeutic index and broad interindividual variability in their pharmacokinetics. Adequate immunosuppression aims to reach an optimal benefit–risk ratio. Therapeutic drug monitoring represents a crucial step in routine practice to maintain blood concentrations within the target window, because the bioavailability of these drugs depends on their absorption, distribution, biotransformation, and elimination. Single nucleotide polymorphisms (SNPs) in genes encoding biotransformation enzymes (CYP3A) and drug transporters (ABCB1) have opened up a promising way for the selection of individual dosages. The relationship of these SNPs with immunosuppressive drug pharmacokinetics was extensively studied after kidney, liver, heart, and lung transplantations. Patient susceptibility to nephrotoxicity in the long term was also reported in relation to some SNPs, which could allow effective assessment of individual risk and selection of treatment according to patient parameters. Further studies are needed to provide evidence that a genetic analysis combined with therapeutic drug monitoring has the potential to optimize drug use after transplantation.

Therapeutic monitoring of mycophenolate mofetil in organ transplant recipients: is it necessary?

Adequate immunosuppression minimising the risk of organ rejection with acceptable tolerability of the used drugs is a crucial step in organ transplantation. The primary goal is to maintain a consistent time-dependent target concentration by tailoring individual dosage leading to the best efficacy and tolerability combination. The use of therapeutic drug monitoring (TDM) to optimise immunosuppressive therapy is routinely employed for maintenance drugs such as cyclosporin and tacrolimus. The question whether therapeutic monitoring of mycophenolic acid (MPA) in organ transplant recipients treated with mycophenolate mofetil is necessary is not definitely answered. The correlation of mycophenolic acid pharmacokinetic parameters with efficacy and toxicity makes the therapeutic monitoring of this drug promising. However, further studies are mandatory to draw the best guidelines in order to achieve higher levels of evidence that MPA-TDM may improve patient outcome.