Calcineurin Inhibitor–Induced Nephrotoxicity and Renal Expression of P-glycoprotein

Tacrolimus dose, blood concentrations and acute nephrotoxicity, but not CYP3A5/ABCB1 genetics, are associated with allograft tacrolimus concentrations in renal transplant recipients

AIMS

Long-term use of the immunosuppressant tacrolimus is limited by nephrotoxicity. Following renal transplantation, the risk of nephrotoxicity may be determined more by allograft than by blood tacrolimus concentrations, and thus may be affected by donor CYP3A5 and ABCB1 genetics. Little is known regarding factors that determine tacrolimus intrarenal exposure.

METHODS

This study investigated the relationship between trough blood (C_0Blood ) and allograft (C_Graft ) tacrolimus concentrations and tacrolimus dose, haematocrit, genetics, acute nephrotoxicity, rejection status, delayed graft function, and time post-transplant. C_0Blood and C_Graft were quantified in 132 renal transplant recipients together with recipient and donor CYP3A5 (rs776746) and ABCB1 3435 (rs1045642) genotypes.

RESULTS

C_0Blood ranged from 2.6 to 52.3 ng/mL and C_Graft from 33 to 828 pg/mg tissue. Adjusting for dose, recipients who were CYP3A5 expressors had lower C_0Blood compared to nonexpressors, whilst delayed graft function was associated with higher C_0Blood . Linear regression showed that the significant predictors of C_Graft were C_0Blood (point-wise P = 7 × 10^-10 ), dose (P = .004) acute nephrotoxicity (P = .002) and an interaction between C_0Blood and acute tacrolimus nephrotoxicity (P = .0002), with an adjusted r²  = 0.35 and no contribution from donor or recipient CYP3A5 or ABCB1 genotype. The association between C_Graft and acute nephrotoxicity depended on one very high C_Graft (828 pg/mg tissue).

CONCLUSIONS

Recipient and donor CYP3A5 and ABCB1 3435C>T genotypes are not determinants of allograft tacrolimus exposure in kidney transplant recipients. However, tacrolimus dose and C_0Blood were significant predictors of C_Graft , and the relationship between C_0Blood and C_Graft appeared to differ in the presence or absence of acute nephrotoxicity.

Identification of Novel Biomarkers for Predicting Kidney Injury Due to Drugs Using "Omic" Strategies

Drug-induced kidney injury accounts for 20% of community- and hospital-acquired cases of acute kidney injury (AKI). The incidence is higher among older individuals, who often have co-existing morbidities and are exposed to more diagnostic procedures and therapies. While demographic and clinical components have been identified as risk factors, the proposed cellular mechanisms of drug-induced kidney injury are numerous and complicated. There are also limitations recognized in the use of traditional biomarkers, such as serum creatinine and blood urea nitrogen, to provide high sensitivity, specificity, and timeliness to identification of drug-induced kidney injury. Therefore, novel biomarkers are currently being investigated, identified, developed, and validated for their performance over the traditional biomarkers. This review will provide an overview of drug-induced kidney injury and will discuss what is known regarding "omic" (proteomic, genomic, transcriptomic, and metabolomic) biomarker strategies for drugs known to induce nephrotoxicity.

Repeated dose multi-drug testing using a microfluidic chip-based coculture of human liver and kidney proximal tubules equivalents

A microfluidic multi-organ chip emulates the tissue culture microenvironment, enables interconnection of organ equivalents and overcomes interspecies differences, making this technology a promising and powerful tool for preclinical drug screening. In this study, we established a microfluidic chip-based model that enabled non-contact cocultivation of liver spheroids and renal proximal tubule barriers in a connecting media circuit over 16 days. Meanwhile, a 14-day repeated-dose systemic administration of cyclosporine A (CsA) alone or in combination with rifampicin was performed. Toxicity profiles of the two different doses of CsA on different target organs could be discriminated and that concomitant treatment with rifampicin from day6 onwards decreased the CsA concentration and attenuated the toxicity compared with that after treatment with CsA for 14 consecutive days. The latter is manifested with the changes in cytotoxicity, cell viability and apoptosis, gene expression of metabolic enzymes and transporters, and noninvasive toxicity biomarkers. The on chip coculture of the liver and the proximal tubulus equivalents showed its potential as an effective and translational tool for repeated dose multi-drug toxicity screening in the preclinical stage of drug development.

Relationship between allograft cyclosporin concentrations and P-glycoprotein expression in the 1st month following renal transplantation

The immunosuppressant cyclosporin is a P-glycoprotein (P-gp) substrate whose impaired function has been associated with an increased risk of cyclosporin-induced nephrotoxicity following renal transplantation. This study investigated the relationship between blood and allograft cyclosporin concentration, and the effect of P-gp expression. Fifty biopsy samples were obtained from 39 renal transplant recipients who received cyclosporin as part of maintenance immunosuppression. Blood cyclosporin concentrations (2 hours postdose) were obtained from clinical records, matching allograft cyclosporin concentrations were measured in frozen biopsy tissue by liquid chromatography-tandem mass spectrometry, and allograft P-gp expression was assessed by immunohistochemistry. Blood and allograft cyclosporin concentrations in the 1st month post-transplantation ranged from 505-2005 μg/L and 0.01-16.7 ng/mg tissue, respectively. Dose was the only significant predictor of allograft cyclosporin concentrations (adjusted R²  = .24, F-statistic = 11.52, P = .0019), with no effect of P-gp expression or blood cyclosporin concentrations. P-gp expression is not the major determinant of allograft cyclosporin concentrations.

Pharmacokinetics, Pharmacodynamics and Pharmacogenetics of Tacrolimus in Kidney Transplantation

Background:

Tacrolimus (Tac, or FK506), a calcineurin inhibitor (CNI), is the first-line immu-nosuppressant which consists of the footstone as immunosuppressive regimens in kidney transplantation. However, the drug toxicity and the significant differences of pharmacokinetics (PK) and pharmacodynam-ics (PD) among individuals are hidden troubles for clinical application. Recently, emerging evidences of Tac pharmacogenetics (PG) regarding drug absorption, metabolism, disposition, excretion and response are discovered for better understanding of this drug.

Method:

We reviewed the published articles regarding the Tac PG and its effects on PK and PD in kidney transplantation. In addition, we summarized information on polygenic algorithms.

Results:

The polymorphism of genes encoding metabolic enzymes and transporters related to Tac were largely investigated, but the results were inconsistent. In addition to CYP3A4, CYP3A5 and P-gp (also known as ABCB1), single nucleotide polymorphisms (SNPs) might also affect the PK and PD parameters of Tac.

Conclusion:

The correlation between Tac PK, PD and PG is very complex. Although many factors need to be verified, it is envisaged that thorough understanding of PG may assist clinicians to predict the optimal starting dosage, help adjust the maintenance regimen, as well as identify high risk patients for adverse ef-fects or drug inefficacy

Impact of CYP3A5 genomic variances on clinical outcomes among African American kidney transplant recipients

Little is known about the impact of CYP3A5 polymorphisms on transplantation outcomes among African American (AA) kidney transplant recipients (KTRs). To assess this issue, clinical outcomes were compared between AA CYP3A5*1 expressers and nonexpressers. This retrospective cohort study analyzed AA KTRs. Biopsy-proven acute rejection (BPAR), delayed graft function (DGF), glomerular filtration rate (GFR), infections, and tacrolimus dosing requirements were examined in 106 immunologically high-risk AA kidney transplant patients over a 2-year follow-up period. In CYP3A5*1 expressers compared to nonexpressers, the incidence of BPAR was significantly higher in the first 6 months (13% vs 0%; P = .016) compared to 24 months (13% vs 7%; P = .521). Tacrolimus total daily dose at first therapeutic level was significantly higher in CYP3A5*1 expressers (12 mg/day) compared to nonexpressers (8 mg/day; P < .001). Compared to CYP3A5*1 nonexpressers, DGF incidence was significantly higher among CYP3A5*1 expressers (27.6% vs 6.7%; P = .006). By contrast, median GFR was significantly higher in CYP3A5*1 expressers compared to nonexpressers (54.5 mL/min vs 50.0 mL/min; P = .003) at 24 months. The findings from this retrospective study suggest that AAs with CYP3A5*1 expression require 50% more tacrolimus and have an increased incidence of DGF and acute rejection.

Kidney Fibrosis: Origins and Interventions

All causes of renal allograft injury, when severe and/or sustained, can result in chronic histological damage of which interstitial fibrosis and tubular atrophy are dominant features. Unless a specific disease process can be identified, what drives interstitial fibrosis and tubular atrophy progression in individual patients is often unclear. In general, clinicopathological factors known to predict and drive allograft fibrosis include graft quality, inflammation (whether "nonspecific" or related to a specific diagnosis), infections, such as polyomavirus-associated nephropathy, calcineurin inhibitors (CNI), and genetic factors. The incidence and severity of chronic histological damage have decreased substantially over the last 3 decades, but it is difficult to disentangle what effects individual innovations (eg, better matching and preservation techniques, lower CNI dosing, BK viremia screening) may have had. There is little evidence that CNI-sparing/minimization strategies, steroid minimization or renin-angiotensin-aldosterone system blockade result in better preservation of intermediate-term histology. Treatment of subclinical rejections has only proven beneficial to histological and functional outcome in studies in which the rate of subclinical rejection in the first 3 months was greater than 10% to 15%. Potential novel antifibrotic strategies include antagonists of transforming growth factor-β, connective tissue growth factor, several tyrosine kinase ligands (epidermal growth factor, platelet-derived growth factor, vascular endothelial growth factor), endothelin and inhibitors of chemotaxis. Although many of these drugs are mainly being developed and marketed for oncological indications and diseases, such as idiopathic pulmonary fibrosis, a number may hold promise in the treatment of diabetic nephropathy, which could eventually lead to applications in renal transplantation.

The POR rs1057868-rs2868177 GC-GT diplotype is associated with high tacrolimus concentrations in early post-renal transplant recipients

AIM

Cytochrome P450 oxidoreductase (POR) is the only flavoprotein that donates electrons to all microsomal P450 enzymes (CYP), and several POR SNPs have been shown to be important contributors to altered CYP activity or CYP-mediated drug metabolism. In this study we examined the association between 6 POR SNPs and tacrolimus concentrations in Chinese renal transplant recipients.

METHODS

A total of 154 renal transplant recipients were enrolled. Genotyping of CYP3A5*3 and 6 POR SNPs was performed. All patients received a triple immunosuppressive regimen comprising tacrolimus, mycophenolate mofetil and prednisone. Dose-adjusted tacrolimus trough concentrations were obtained on d 7 (C0D7/D) after transplantation when steady-state concentration of tacrolimus was achieved (dosage had been unchanged for more than 3 d).

RESULTS

Tacrolimus C0D7/D in CYP3A5*3/*3/ POR rs1057868-rs2868177 GC-GT diplotype carriers was 1.62- and 2.72-fold higher than those in CYP3A5*3/*3/ POR rs1057868-rs2868177 GC-GT diplotype non-carriers and CYP3A5*1 carriers (220.17±48.09 vs 135.69±6.86 and 80.84±5.27 ng/mL/mg/kg, respectively, P<0.0001). Of CYP3A5*3/*3/ POR rs1057868-rs2868177GC-GT diplotype carriers, 85.71% exceeded the upper limit of the target range (8 ng/mL), which was also significantly higher compared with the latter two groups (14.29% and 0.00%, respectively, P<0.0001). The CYP3A5*3 and POR rs1057868-rs2868177 GC-GT diplotype explained 31.7% and 5.7%, respectively, of the inter-individual variability of tacrolimus C0D7/D, whereas the POR rs1057868-rs2868177 GC-GT diplotype could explain 10.9% of the inter-individual variability of tacrolimus C0D7/D in CYP3A5 non-expressers.

CONCLUSION

The CYP3A5*3 and POR rs1057868-rs2868177 GC-GT diplotype accounted for the inter-individual variation of tacrolimus C0D7/D. Genotyping of POR rs1057868-rs2868177 diplotypes would help to differentiate initial tacrolimus dose requirements and to achieve early target C0 ranges in Chinese renal transplant recipients.

Role of Pharmacogenomics in Kidney Disease and Injury

There has been considerable excitement in the kidney community surrounding the research findings on the genetic contributions to kidney diseases. However, positive outcomes of personalized therapeutic interventions can be circumvented by unpredictable pharmacokinetics of prescribed drugs. Furthermore, unpredictable drug disposition can result in toxicities such as kidney injury. Patient covariates, disease covariates, and pharmacogenetics all contribute to variability in drug disposition. Further treatment personalization and avoidance of drug- and biologic- induced kidney injury will require extensive knowledge and expertise in renal clinical pharmacology. The current review will focus on the pharmacogenetics of drugs and biologics used in the treatment of glomerular kidney diseases and drugs implicated in inducing kidney injury phenotypes.

Deceased donor multidrug resistance protein 1 and caveolin 1 gene variants may influence allograft survival in kidney transplantation

Variants in donor multidrug resistance protein 1 (ABCB1) and caveolin 1 (CAV1) genes are associated with renal allograft failure after transplantation in Europeans. Here we assessed transplantation outcomes of kidneys from 368 African American (AA) and 314 European American (EA) deceased donors based on 38 single nucleotide polymorphisms (SNPs) spanning ABCB1 and 16 SNPs spanning CAV1, including previously associated index and haplotype-tagging SNPs. Tests for association with time to allograft failure were performed for the 1,233 resultant kidney transplantations, adjusting for recipient age, sex, ethnicity, cold ischemia time, PRA, HLA match, expanded-criteria donation, and APOL1- nephropathy variants in AA donors. Interaction analyses between APOL1 with ABCB1 and CAV1 were performed. In a meta-analysis of all transplantations, ABCB1 index SNP rs1045642 was associated with time to allograft failure and other ABCB1 SNPs were nominally associated, but not CAV1 SNPs. ABCB1 SNP rs1045642 showed consistent effects with the 558 transplantations from EA donors, but not with the 675 transplantations from AA donors. ABCB1 SNP rs956825 and CAV1 SNP rs6466583 interacted with APOL1 in transplants from AA donors. Thus, the T allele at ABCB1 rs1045642 is associated with shorter renal allograft survival for kidneys from American donors. Interactions between ABCB1 and CAV1 with APOL1 may influence allograft failure for transplanted kidneys from AA donors.

Pharmacogenetics and drug-induced nephrotoxicity in renal transplant recipients

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

Associations of HSD11B1 polymorphisms with tacrolimus concentrations in Chinese renal transplant recipients with prednisone combined therapy

Tacrolimus requires close therapeutic drug monitoring because of its narrow therapeutic index and marked interindividual pharmacokinetic variation. In this study, we investigated the associations of polymorphisms in the gene encoding 11β-hydroxysteroid dehydrogenase type 1 (HSD11B1) with tacrolimus concentrations in Chinese renal transplant recipients during the early posttransplantation stage. A total of 258 renal transplant recipients receiving tacrolimus with prednisone (30 mg) combined therapy were genotyped for HSD11B1 rs846908, rs846910, rs4844880, and CYP3A5*3 polymorphisms. Tacrolimus trough concentrations were determined on days 6-9 after transplantation, measured by a chemiluminescent microparticle immunoassay. Among the CYP3A5 expressers, the dose-adjusted trough concentration (C0/D) of tacrolimus in HSD11B1 rs846908 AA homozygous individuals was considerably lower than found in GG+GA carriers [56.2 (23.9-86.6) versus 76.7 (12.6-220.0) (ng/ml)/(mg/kg), P = 0.0204]; HSD11B1 rs846910 AA homozygotes had a lower tacrolimus C0/D compared with GG+GA carriers [51.2 (23.9-86.6) versus 76.3 (12.6-220.0) (ng/ml)/(mg/kg), P = 0.0367]; carriers with the HSD11B1 rs4844880 AA genotype had a significantly lower tacrolimus C0/D with respect to carriers of TT+TA genotypes [61.3 (23.9-97.5) versus 77.2 (12.6-220.0) (ng/ml)/(mg/kg), P = 0.0002]; the HSD11B1 AA-AA-AA haplotype carriers had a lower tacrolimus C0/D than noncarriers [51.2 (23.9-86.6) versus 76.3 (12.6-220.0) (ng/ml)/(mg/kg), P = 0.0367]. These findings illustrate that the HSD11B1 genotypes are closely correlated with tacrolimus trough concentrations, suggesting that these polymorphisms may be useful for safer dosing of tacrolimus.

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.

Phosphodiesterase type 5 inhibition attenuates cyclosporine A induced nephrotoxicity in mice

We investigated the renal protective effects of phophodiesterase type 5 (PDE5) inhibitors in mice with cyclosporine A (CyA; a calcineurin phosphatase inhibitor) induced nephrotoxicity. Fifty male mice were divided into five groups of 10. Group 1 received no treatment, group 2 received only saline orally, group 3 received 30 mg/kg/day CyA by subcutaneous injection, group 4 received only 30 mg/kg/day vardenafil orally, and group 5 received 30 mg/kg/day CyA by subcutaneous injection and 30 mg/kg/day vardenafil orally. At 28 days, platelet-derived growth factor A (PDGF-A) and C (PDGF-C), transforming growth factor-beta 1 (TGF-β1), cyclo-oxygenase 1 and 2 (COX-1 and COX-2), and P glycoprotein (Pgp) expression levels were measured in the renal tissues. In addition, expressions of COX-1 and COX-2 genes were determined using real-time PCR. PDE5 inhibitor administration ameliorated decreased PDGF-A and C, TGF-β1, COX-1 and -2, and Pgp expression levels by modulation of cyclic guanosine monophosphate (cGMP) activity in kidneys. The relative expressions of COX-1 and COX-2 genes to GAPDH revealed that the maximum increase was obtained in the group treated with CyA and vardenafil for both COX-1 and COX-2 genes. Our study revealed that long term oral treatment with vardenafil protects kidneys from CyA induced nephrotoxicity. We showed that long term oral treatment with PDE5 prevents pathological kidney changes caused by CyA induced nephrotoxicity.

Calcineurin inhibitors: 40 years later, can't live without

Calcineurin inhibitors (CNIs) revolutionized the field of organ transplantation and remain the standard of care 40 years after the discovery of cyclosporine. The early impressive results of cyclosporine in kidney transplant recipients led to its subsequent use in other organ transplant recipients and for treatment of a variety of autoimmune diseases as well. In this review, we examine the discovery of CNIs, their mechanism of action, preclinical and clinical studies with CNIs, and the usage of CNIs in nontransplant recipients. We review the mechanisms of renal toxicity associated with CNIs and the recent efforts to avoid or reduce usage of these drugs. Although minimization strategies are possible, safe, and of potential long-term benefit, complete avoidance of CNIs has proven to be more challenging than initially thought.

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.

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.

Donor ABCB1 variant associates with increased risk for kidney allograft failure

The impact of variation within genes responsible for the disposition and metabolism of calcineurin inhibitors (CNIs) on clinical outcomes in kidney transplantation is not well understood. Furthermore, the potential influence of donor, rather than recipient, genotypes on clinical endpoints is unknown. Here, we investigated the associations between donor and recipient gene variants with outcome among 4471 white, CNI-treated kidney transplant recipients. We tested for 52 single-nucleotide polymorphisms (SNPs) across five genes: CYP3A4, CYP3A5, ABCB1 (MDR1; encoding P-glycoprotein), NR1I2 (encoding the pregnane X receptor), and PPIA (encoding cyclophilin). In a discovery cohort of 811 patients from Birmingham, United Kingdom, kidney donor CC genotype at C3435T (rs1045642) within ABCB1, a variant known to alter protein expression, was associated with an increased risk for long-term graft failure compared with non-CC genotype (hazard ratio [HR], 1.69; 95% confidence interval [CI], 1.20-2.40; P=0.003). No other donor or recipient SNPs were associated with graft survival or mortality. We validated this association in 675 donors from Belfast, United Kingdom (HR, 1.68; 95% CI, 1.21-2.32; P=0.002), and in 2985 donors from the Collaborative Transplant Study (HR, 1.84; 95% CI, 1.08-3.13; P=0.006). In conclusion, these data suggest that an ABCB1 variant known to alter protein expression represents an attractive candidate for future study and risk stratification in kidney transplantation.

The role of genetics in drug dosing

Renal transplantation is the optimal form of renal replacement therapy (RRT) for the majority of patients. Both short- and long-term graft rejection are well recognized complications following transplantation, and optimal immunosuppression is often difficult to achieve. Pharmacodynamics (PD) and pharmacokinetics (PK) are hard to predict in all patients, and best practice involves the use of standard dosing based on weight and therapeutic drug monitoring (TDM). Pharmacogenetics (PG) is the use of genetic screening to predict metabolic responses to different immunosuppressive drugs and enables more accurate predictions of PD and PK to be made. This has the potential to improve graft outcome by reducing both short- and long-term graft rejection.

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.

Expression of CYP3A5 and P-glycoprotein in renal allografts with histological signs of calcineurin inhibitor nephrotoxicity

BACKGROUND

Susceptibility to calcineurin inhibitor nephrotoxicity (CNIT) after solid organ transplantation could be related to an interindividual variability in renal expression and function of the metabolizing cytochrome P450 3A5 (CYP3A5) isoenzyme and of the multidrug efflux transporter P-glycoprotein (P-gp, ABCB1).

METHODS

We compared renal expression of CYP3A5 and P-gp, measured by immunohistochemistry, in 32 renal allograft biopsies with de novo arteriolar hyalinosis as a sign of CNIT with a control group, consisting of normal protocol allograft biopsies (n=50) and protocol biopsies demonstrating alloimmune injury (n=21). In addition, we studied the association between renal expression and donor and recipient single-nucleotide polymorphisms CYP3A5 A6986G (rs776746), ABCB1 C3435T (rs1045642), and G2677T (rs2032582).

RESULTS

CYP3A5 positivity at the brushborder of the proximal tubules was present in 47% of CNIT and 14% of control biopsies (P<0.01). In contrast, brushborder staining for CYP3A5 in distal tubules was present in 10% of CNIT and 39% of control biopsies (P<0.01). No significant association between tubular cell P-gp expression and CNIT was detected. The presence of genetic polymorphisms CYP3A5 A6986G and ABCB1 C3435T and G2677T in donors and recipients was not predictive of the renal expression profile of these molecules.

CONCLUSIONS

Based on retrospectively collected data of 103 renal transplant recipients receiving tacrolimus in combination with mycophenolate mofetil and corticosteroids, we found that renal expression and localization of CYP3A5 but not P-gp is associated with the occurrence of CNIT. Common genetic polymorphisms in these proteins did not influence their expression profile as measured by immunohistochemistry.

The pharmacogenetics of calcineurin inhibitor-related nephrotoxicity

Chronic calcineurin inhibitor (CNI)-induced nephrotoxicity is associated with prolonged use of cyclosporine and tacrolimus and has been observed after all types of transplantation, as well as during treatment of autoimmune disease. Extensive alterations in the renal architecture including glomerular sclerosis, tubular atrophy and interstitial fibrosis may lead to end-stage renal failure. Increasing evidence shows that pharmacogenetic factors explain part of the between-patient differences in susceptibility to developing CNI-induced nephrotoxicity. In this paper this evidence is reviewed, with special emphasis on the role of genetic factors influencing metabolism and transportation of CNIs in both acceptor and donor.

Tacrolimus dose requirements and CYP3A5 genotype and the development of calcineurin inhibitor-associated nephrotoxicity in renal allograft recipients

OBJECTIVES

Prolonged calcineurin inhibitor maintenance therapy in kidney allograft recipients is complicated by the development of chronic irreversible drug-induced nephrotoxicity (CNIT).

METHODS

In 304 de novo renal graft recipients, the association among tacrolimus exposure indices (dose, C(0), AUC(0-12h)), CYP3A5, CYP3A4 and ABCB1 polymorphisms, clinical covariables and de novo arteriolar hyalinization as a histologic sign of CNIT was examined.

RESULTS

Tacrolimus C(0) and AUC(0-12h) at 3 and 12 months posttransplantation did not differ between patients with and without CNIT. Patients who developed CNIT more often carried the CYP3A5*1 allele (32.4% versus 15.2%, P = 0.01). Twenty-five percent of recipients with tacrolimus dose requirements exceeding 0.2 mg/kg per day at 3 months posttransplantation developed CNIT, whereas 16.2% of patients with dose requirements between 0.10 and 0.20 mg/kg per day and 4.5% of patients who needed less than 0.10 mg/kg per day developed CNIT (P < 0.0001). These early differences in tacrolimus dose requirements between recipients with and without CNIT persisted during subsequent follow-up. In a Cox proportional hazards analysis, the CYP3A5*1 allele (hazard ratio: 2.38; 95% confidence interval: 1.15-4.92) or tacrolimus dose range (hazard ratio: 2.06; 95% confidence interval: 1.30-3.27) and continued corticosteroid therapy (hazard ratio: 4.75; 95% confidence interval: 1.13-19.98) were independently associated with CNIT. A Kaplan-Meier survival curve demonstrated a significant difference in CNIT-free survival (93.5% versus 81.8% versus 66.9%; log-rank test: P = 0.0006) between patients with, respectively, tacrolimus dose requirements less than 0.1, 0.1 or greater, less than 0.2, and 0.2 mg/kg per day or greater. More patients with CNIT sustained graft loss during follow-up (32.3% versus13.7%, P = 0.004).

CONCLUSIONS

High early tacrolimus dose requirements, predominantly but not exclusively encountered in CYP3A5*1 expressers, are associated with the development of calcineurin inhibitor-related nephrotoxicity, especially in recipients who continue corticosteroid therapy.

Impact of ATP-binding cassette, subfamily B, member 1 pharmacogenetics on tacrolimus-associated nephrotoxicity and dosage requirements in paediatric patients with liver transplant

IMPORTANCE OF THE FIELD

Tacrolimus is the most commonly used immunosuppressive agent following solid-organ transplantation in children. Its clinical use, however, is complicated by side effects (mainly nephrotoxicity), narrow therapeutic index and pharmacokinetic variability which can result in an increased risk of treatment failure or toxicity. Studies examining interindividual differences in the expression of the ABCB1 (ATP-binding cassette, subfamily B, member 1) gene (which encodes the drug transporter, P-gp) and its genetic polymorphisms have attempted to elucidate variations in tacrolimus response and disposition in children.

AREAS COVERED IN THIS REVIEW

This review explores pharmacogenetic knowledge developed over the last decade regarding the impact of ABCB1 polymorphisms on tacrolimus toxicity and dosage requirements in children.

WHAT THE READER WILL GAIN

A better understanding of the role of ABCB1 genetic polymorphisms (and corresponding haplotypes) and ABCB1 expression levels in various tissues and organs on tacrolimus outcomes in children with liver transplant.

TAKE HOME MESSAGE

Pharmacogenetics offers significant potential for optimising tacrolimus use. ABCB1 donor genotypes and ABCB1 expression level in the intestine and leukocytes may be useful in dosage selection. Large prospective studies are, however, required to further explore the potential of genetic testing in identifying children who are at risk of toxicity and to better individualise tacrolimus therapy.

Effect of CYP3A and ABCB1 single nucleotide polymorphisms on the pharmacokinetics and pharmacodynamics of calcineurin inhibitors: Part II

The calcineurin inhibitors ciclosporin (cyclosporine) and tacrolimus are immunosuppressant drugs used for the prevention of organ rejection following transplantation. Both agents are metabolic substrates for cytochrome P450 (CYP) 3A enzymes - in particular, CYP3A4 and CYP3A5 - and are transported out of cells via P-glycoprotein (ABCB1). Several single nucleotide polymorphisms (SNPs) have been identified in the genes encoding for CYP3A4, CYP3A5 and P-glycoprotein, including CYP3A4 -392A>G (rs2740574), CYP3A5 6986A>G (rs776746), ABCB1 3435C>T (rs1045642), ABCB1 1236C>T (rs1128503) and ABCB1 2677G>T/A (rs2032582). The aim of this review is to provide the clinician with an extensive overview of the recent literature on the known effects of these SNPs on the pharmacodynamics of ciclosporin and tacrolimus in solid-organ transplant recipients. Literature searches were performed and all relevant primary research articles were critiqued and summarized. There is no evidence that the CYP3A4 -392A>G SNP has an effect on the pharmacodynamics of either ciclosporin or tacrolimus; however, studies have been limited. For patients prescribed ciclosporin, the CYP3A5 6986A>G SNP may influence long-term survival, possibly because of a different metabolite pattern over time. This SNP has no clear association with acute rejection during ciclosporin therapy. Despite a strong association between the CYP3A5 6986A>G SNP and tacrolimus pharmacokinetics, there is no consistent evidence of organ rejection as a result of genotype-related under-immunosuppression. This is likely to be explained by the practice of performing tacrolimus dose adjustments in the early phase after transplantation. The effect of the CYP3A5 6986A>G SNP on ciclosporin- and tacrolimus-related nephrotoxicity and development of hypertension is unclear. Similarly, the ABCB1 SNPs exert no clear influence on either ciclosporin or tacrolimus pharmacodynamics, with studies showing conflicting results in regard to the main parameters of acute rejection and nephrotoxicity. In kidney transplant patients, consideration of the donor kidney genotype rather than the recipient genotype may be more important when assessing development of nephrotoxicity. Studies with low patient numbers may account for many inconsistent results to date. The majority of studies have only evaluated the effects of individual SNPs; however, multiple polymorphisms may interact to produce a combined effect. Further haplotype analyses are likely to be useful, particularly ones that consider both donor and recipient genotype. The effects of polymorphisms associated with the pregnane X receptor, organic anion transporting polypeptides, calcineurin inhibitor target sites and immune response pathways need to be further investigated. A large standardized clinical trial is now required to evaluate the relationship between the pharmacokinetics and pharmacodynamics of CYP3A5-mediated tacrolimus metabolism, particularly in regard to the outcomes of acute rejection and nephrotoxicity. It is not yet clear whether pharmacogenetic profiling of calcineurin inhibitors will be a useful clinical tool for personalizing immunosuppressant therapy.

Donor P-gp polymorphisms strongly influence renal function and graft loss in a cohort of renal transplant recipients on cyclosporine therapy in a long-term follow-up

Cyclosporin A (CsA) is a substrate for cytochrome P450 3A and the efflux transporter P-glycoprotein (P-gp; ABCB1), both abundantly expressed in the kidney. In a long-term follow-up of a cohort of patients who had received kidney transplants between the years 1990 and 2005, we retrospectively investigated the effect of CYP3A4, CYP3A5, and ABCB1 polymorphisms in kidney graft donors on recipients' renal function and risk of subsequent graft loss. DNA samples from 227 donors and clinical data from the 259 respective recipients were analyzed. Graft loss was significantly associated with the presence of the ABCB1 variant haplotype 1236T/2677T/3435T in the donor (1236T/2677T/3435T vs. other haplotypes: hazard ratio = 9.346; 95% confidence interval (CI) (2.278-38.461); P = 0.0019) and with previous episodes of acute organ rejection (hazard ratio = 3.077; 95% CI (1.213-7.812); P = 0.0178). The variant haplotype was also associated with a greater decrease in renal function (homozygotes for TTT -3.047 mlxmin(-1)/year; heterozygotes for TTT -4.435 mlxmin(-1)/year; others -2.186 mlxmin(-1)/year; P = 0.0240). The study showed that the presence of ABCB1 polymorphisms in donors influences long-term graft outcome adversely with decrease in renal function and graft loss in transplant recipients receiving CsA.

Donor age and renal P-glycoprotein expression associate with chronic histological damage in renal allografts

The contributions of donor kidney quality (partially determined by donor age), allograft rejection, and calcineurin inhibitor nephrotoxicity on the progression of histologic damage of renal allografts are not completely defined. Moreover, the determinants of individual susceptibility to calcineurin inhibitor nephrotoxicity are not known but may include variability in drug transport and metabolism. In a prospective cohort of 252 adult renal allograft recipients treated with a combination of tacrolimus, mycophenolate mofetil, and corticosteroids, we studied 744 renal allograft biopsies obtained regularly from time of transplantation for 3 yr. We assessed determinants of histologic evolution, including tacrolimus exposure, renal P-glycoprotein (ABCB1) expression, and polymorphisms in the CYP3A4, CYP3A5, and ABCB1 genes. Within the first 3 yr after transplantation, we noted a progressive increase in interstitial fibrosis, tubular atrophy, glomerulosclerosis, and vascular intimal thickening. Older donor age, absence of P-glycoprotein expression at the apical membrane of tubular epithelial cells, and combined donor-recipient homozygosity for the C3435T variant in ABCB1 significantly associated with increased susceptibility to chronic allograft damage independent of graft quality at implantation. Changes in graft function over time reflected these associations with donor age and ABCB1 polymorphisms, but it was acute T cell-mediated and antibody-mediated rejection that determined early graft survival. In conclusion, the effects of older donor age reach beyond the quality of the allograft at implantation and continue to be important for histologic evolution in the posttransplantation period. In addition, ABCB1 genotype and expression of P-glycoprotein in renal tubular epithelial cells determine susceptibility to chronic tubulointerstitial damage of transplanted kidneys.

Calcineurin inhibitor nephrotoxicity

The use of the calcineurin inhibitors cyclosporine and tacrolimus led to major advances in the field of transplantation, with excellent short-term outcome. However, the chronic nephrotoxicity of these drugs is the Achilles' heel of current immunosuppressive regimens. In this review, the authors summarize the clinical features and histologic appearance of both acute and chronic calcineurin inhibitor nephrotoxicity in renal and nonrenal transplantation, together with the pitfalls in its diagnosis. The authors also review the available literature on the physiologic and molecular mechanisms underlying acute and chronic calcineurin inhibitor nephrotoxicity, and demonstrate that its development is related to both reversible alterations and irreversible damage to all compartments of the kidneys, including glomeruli, arterioles, and tubulo-interstitium. The main question--whether nephrotoxicity is secondary to the actions of cyclosporine and tacrolimus on the calcineurin-NFAT pathway--remains largely unanswered. The authors critically review the current evidence relating systemic blood levels of cyclosporine and tacrolimus to calcineurin inhibitor nephrotoxicity, and summarize the data suggesting that local exposure to cyclosporine or tacrolimus could be more important than systemic exposure. Finally, other local susceptibility factors for calcineurin inhibitor nephrotoxicity are reviewed, including variability in P-glycoprotein and CYP3A4/5 expression or activity, older kidney age, salt depletion, the use of nonsteroidal anti-inflammatory drugs, and genetic polymorphisms in genes like TGF-beta and ACE. Better insight into the mechanisms underlying calcineurin inhibitor nephrotoxicity might pave the way toward more targeted therapy or prevention of calcineurin inhibitor nephrotoxicity.

Individualizing Therapy in Patients With Chronic Kidney Disease

Patients with chronic kidney diseases have multiple clinical abnormalities that may affect disposition of drugs, including alterations in glomerular filtration rate, excretion of plasma proteins, reductions in serum albumin, and reductions in drug metabolizing enzyme activity. Inflammation may also influence the previous factors. Concomitant drug therapies can lead to drug— drug interactions that may affect the pharmacokinetics of administered drugs. Pharmacogenomics has begun to be evaluated for effects of genotype and haplotype of drug metabolizing enzymes and transporters on drug disposition. Because of the multiple potential etiologies for alterations in drug disposition in patients with chronic kidney diseases, they require appropriate evaluation for implementation of individualized strategies in therapies to enhance efficacy and reduce toxicities. This review will highlight the disease- and patient-specific variables that are targets for patient-centered approaches to therapeutic interventions. The field of pharmacogenomics will be reviewed with reference to common therapies for transplantation and glomerular diseases.

Pharmacogenetics of immunosuppressive drugs: prospect of individual therapy for transplant patients

The immunosuppressive drugs used in solid-organ transplantation are potent and toxic agents with narrow therapeutic ranges. Underdosing is associated with immunological rejection of the transplanted organ, whereas overdosing results in infections, malignancy and direct toxicity to a number of organs. Pharmacokinetic heterogeneity makes initial dose determination difficult, as there is a poor correlation between dose and blood concentration. Therapeutic drug monitoring is available but the pharmacokinetic–pharmacodynamic association is imperfect and it does not help in achieving target blood concentrations during the critical early 2–3 days after transplantation. Genetic polymorphisms in drug targets, drug-metabolizing enzymes and drug efflux pumps have been identified as potential targets for developing a pharmacogenetic strategy to individualize initial drug choice and dose. To date, use of the CYP3A5 genotype to predict the appropriate initial dose of tacrolimus is the most promising option for individualization of drug therapy in organ transplantation.

Pharmacogenetics as a tool for optimising drug therapy in solid-organ transplantation

Existing immunosuppressive therapies used for solid-organ transplantation have narrow therapeutic indices, whereby underdosing is associated with acute immunological rejection of the transplanted organ and overdosing is associated with infections and malignancy, as well as organ-specific toxicities. There is significant inter-individual variation in the pharmacokinetics and pharmacodynamics of these drugs, an issue that has been addressed, in part, by therapeutic drug monitoring. Genetic polymorphisms in drug metabolising enzymes, drug efflux pumps and drug targets which may underly this heterogeneity have been identified and may provide a tool to guide prescribing. There are a number of associations between genotype and pharmacology, but as of now, only thiopurine-S-methyltransferase and cytochrome P450 3A5 have a sufficiently large influence to have potential in guiding therapy. Recent studies have also identified that donor genotype may play a significant role in immunosuppressive drug pharmacokinetics and pharmacodynamics.