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

Progressive histological damage in renal allografts is associated with expression of innate and adaptive immunity genes

The degree of progressive chronic histological damage is associated with long-term renal allograft survival. In order to identify promising molecular targets for timely intervention, we examined renal allograft protocol and indication biopsies from 120 low-risk pediatric and adolescent recipients by whole-genome microarray expression profiling. In data-driven analysis, we found a highly regulated pattern of adaptive and innate immune gene expression that correlated with established or ongoing histological chronic injury, and also with development of future chronic histological damage, even in histologically pristine kidneys. Hence, histologically unrecognized immunological injury at a molecular level sets the stage for the development of chronic tissue injury, while the same molecular response is accentuated during established and worsening chronic allograft damage. Irrespective of the hypothesized immune or nonimmune trigger for chronic allograft injury, a highly orchestrated regulation of innate and adaptive immune responses was found in the graft at the molecular level. This occurred months before histologic lesions appear, and quantitatively below the diagnostic threshold of classic T-cell or antibody-mediated rejection. Thus, measurement of specific immune gene expression in protocol biopsies may be warranted to predict the development of subsequent chronic injury in histologically quiescent grafts and as a means to titrate immunosuppressive therapy.

Senile nephrosclerosis--does it explain the decline in glomerular filtration rate with aging?

Nephrosclerosis can be defined by the presence of glomerulosclerosis, tubular atrophy, interstitial fibrosis, and arteriosclerosis on renal biopsy. Chronic kidney disease is identified clinically by a reduction in glomerular filtration rate (GFR) and has been characterized histologically by nephrosclerosis. Many relatively healthy older adults have been diagnosed with chronic kidney disease because of a decline in GFR with normal aging. Recent data show that in healthy adults (living kidney donors), nephrosclerosis on renal biopsy does not associate with GFR independent of age. This may be explained by the decline in GFR and nephrosclerosis being universal with aging (i.e. senescence), by structural changes in the kidney other than nephrosclerosis impacting GFR, or by extrarenal factors affecting GFR decline with age. However, the argument that the age-related decline in GFR can be fully explained by the development of nephrosclerosis in a subset of older adults is not supported by existing data.

Pharmacogenetics of tacrolimus: ready for clinical translation?

Tacrolimus (Tac) exhibits an interindividual pharmacokinetic variability that affects the dose required to reach the target concentration in blood. Tac is metabolized by two enzymes of the cytochrome P450 family, CYP3A5 and CYP3A4. The effect of the CYP3A5 genotype on Tac bioavailability has been demonstrated, and the main determinant of this pharmacogenetic effect is a single-nucleotide polymorphism (SNP) in intron 3 of CYP3A5 (6986 A>G; SNP rs776746; also known as CYP3A5*3). The mean dose-adjusted blood Tac concentration was significantly higher among CYP3A5*3 homozygotes than that of carriers of the wild-type allele (CYP3A5*1). In a recent prospective study, a group of kidney transplant patients received a Tac dose either according to the CYP3A5 genotype (the adapted group) or according to the standard regimen (the control group). All patients received induction therapy with mycophenolate mofetil, corticosteroids, and either basiliximab or intravenous anti-thymocyte globulin. Patients in the adapted-dose group required 3–8 days (median 6 days) to reach the target range compared with 3–25 days (median 7 days) in the control group (P=0.001). The total number of dose modifications was also lower in the adapted-dose group. This study also suggested that the CYP3A5 genotype might contribute minimally to the reduction of early acute rejection. However, additional studies are necessary to determine whether the pharmacogenetic approach could help reduce the necessity for induction therapy and co-immunosuppressors.

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.

CYP3A5 and ABCB1 polymorphisms in donor and recipient: impact on Tacrolimus dose requirements and clinical outcome after renal transplantation

BACKGROUND

The effect of potentially relevant genetic polymorphisms, CYP3A5 6986A>G and ABCB1 3435C>T, on Tacrolimus pharmacokinetics and graft clinical outcome was investigated in donor and recipient DNA samples from 209 kidney transplant patients.

METHODOLOGY/PRINCIPAL FINDINGS

The mean follow-up was 21.8 ± 9 months. The Tacrolimus dose, trough blood concentrations (C0) and C0/dose ratio were only statistically correlated with the recipient CYP3A5 genotype. CYP3A5 and ABCB1 genotypes appeared to have no influence on the incidence of Biopsy Proven Acute Rejection and Delayed Graft Function. Renal function was not affected by CYP3A5 and ABCB1 genotypes. Histological evaluation of biopsies revealed also no significant association between Tacrolimus toxicity features and donor or recipient CYP3A5 and ABCB1 polymorphisms. Tacrolimus sparing appeared to be independent of CYP3A5 and ABCB1 genotypes.

CONCLUSIONS/SIGNIFICANCE

Recipient CYP3A5 6986A>G polymorphism explains part of the interindividual variability of the pharmacokinetics of Tacrolimus. The clinical outcome at 2-year follow-up does not appear to be related to the donor or recipient CYP3A5 6986A>G and/or ABCB1 3435C>T polymorphisms.

The influence of pharmacogenetics and cofactors on clinical outcomes in kidney transplantation

INTRODUCTION

Immunosuppressive drugs have a narrow therapeutic range and large inter-individual response variability. This has prompted pharmacogenetic studies, mostly with regard to their dose-concentration relationships, but also about proteins involved in their pharmacodynamics. Some polymorphisms of genes involved in their disposition pathways were shown to affect their dose-concentration relationships. The impact of pharmacogenetics on tissue distribution and the resulting clinical effects have less often been studied. More importantly, a few single nucleotide polymorphisms seem to have a significant impact on the incidence of acute rejection or the adverse effects of immunosuppressants. Environmental factors often interact with such genotype-phenotype relationships.

AREAS COVERED

This article reviews the impact of genetic polymorphisms of the metabolic enzymes, membrane transporters and target proteins of mycophenolic acid, calcineurin inhibitors and mammalian target of rapamycin inhibitors on clinical outcomes in kidney transplantation.

EXPERT OPINION

The current level of evidence is not yet high enough to recommend pharmacogenetic personalization of immunosuppressive regimens in transplant recipients. The prevention of cellular toxicity associated with local metabolism or transport, which cannot be addressed by routine monitoring, is worth investigating further.

Assessment of kidney organ quality and prediction of outcome at time of transplantation

The critical importance of donor organ quality, i.e., number of surviving nephrons, ability to withstand injury, and capacity for repair in determining short- and long-term outcomes is becoming increasingly clear. This review provides an overview of studies to assess donor kidney quality and subsequent transplant outcomes based on clinical pathology and transcriptome-based variables available at time of transplantation. Prediction scores using clinical variables function when applied to large data sets but perform poorly for the individual patient. Histopathology findings in pre-implantation or post-reperfusion biopsies help to assess structural integrity of the donor kidney, provide information on pre-existing donor disease, and can serve as a baseline for tracking changes over time. However, more validated approaches of analysis and prospective studies are needed to reduce the number of discarded organs, improve allocation, and allow prediction of outcomes. Molecular profiling detects changes not seen by morphology or captured by clinical markers. In particular, molecular profiles provide a quantitative measurement of inflammatory burden or immune activation and reflect coordinated changes in pathways associated with injury and repair. However, description of transcriptome patterns is not an end in itself. The identification of predictive gene sets and the application to an individualized patient management needs the integration of clinical and pathology-based variables, as well as more objective reference markers of transplant function, post-transplant events, and long-term outcomes.

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.

Molecular diagnostics in transplantation

The past few decades are characterized by an explosive evolution of genetics and molecular cell biology. Advances in chemistry and engineering have enabled increased data throughput, permitting the study of complete sets of molecules with increasing speed and accuracy using techniques such as genomics, transcriptomics, proteomics, and metabolomics. Prediction of long-term outcomes in transplantation is hampered by the absence of sufficiently robust biomarkers and a lack of adequate insight into the mechanisms of acute and chronic alloimmune injury and the adaptive mechanisms of immunological quiescence that may support transplantation tolerance. Here, we discuss some of the great opportunities that molecular diagnostic tools have to offer both basic scientists and translational researchers for bench-to-bedside clinical application in transplantation medicine, with special focus on genomics and genome-wide association studies, epigenetics (DNA methylation and histone modifications), gene expression studies and transcriptomics (including microRNA and small interfering RNA studies), proteomics and peptidomics, antibodyomics, metabolomics, chemical genomics and functional imaging with nanoparticles. We address the challenges and opportunities associated with the newer high-throughput sequencing technologies, especially in the field of bioinformatics and biostatistics, and demonstrate the importance of integrative approaches. Although this Review focuses on transplantation research and clinical transplantation, the concepts addressed are valid for all translational research.

Dosing tacrolimus based on CYP3A5 genotype: will it improve clinical outcome?

Tacrolimus, widely used to prevent acute rejection following solid-organ transplantation, has become the cornerstone of immunosuppressive therapy after kidney transplantation. More than 70% of all renal transplant recipients receive this remarkably effective agent.(1) But tacrolimus is also highly toxic, and there is great between-patient variability in its pharmacokinetics. This, combined with a low therapeutic index, mandates routine therapeutic drug monitoring in clinical practice.(2) Typically, predose concentrations are monitored and the dose is adjusted to aim for target values that depend on immunological risk, comedication, and time since transplantation.(2).

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.