The pharmacogenetics of calcineurin inhibitor-related nephrotoxicity. Ther Drug Monit. 2010;32:387-393. [PMID: 20571464 DOI: 10.1097/ftd.0b013e3181e44244]

Impacts of dosing and drug withdrawal period on tacrolimus-based triple therapy in a non-human primate renal transplantation model

Non-human primate (NHP) renal transplantation models are widely used vivo models for researching new immunosuppressive therapies including allograft tolerance strategies. To enroll animals into a tolerance study, an immunosuppressive regimen that efficiently establishes stable renal function in NHPs is needed. Here, we assessed the effect of triple therapy comprising 2.0 mg/kg tacrolimus, mycophenolate mofetil and a steroid and its success rate for achieving stable renal function. In addition, to predict the pathophysiological consequences of withdrawing immunosuppressants, an indispensable process after induction of tolerance, we also assessed changes in the stable renal state maintained by triple therapy after drug withdrawal. Six cynomolgus monkeys were used. The median survival time was >176 days over the dosing period and 45 days after drug withdrawal. The triple therapy successfully induced stable graft function without calcineurin inhibitor nephrotoxicity in three of six recipients, although adopting trough-dependent tacrolimus dose adjustment rather than a preset dose regimen could improve on the present strategy. Further, drug withdrawal led to deterioration of renal function, de novo donor specific antibody production and increased the memory/naïve T cell ratio within two weeks post drug withdrawal. We expect that these findings contribute to establish one of the choices for animal model for evaluating future tolerance therapy for renal transplantation.

Tissue distribution and metabolic profiling of cyclosporine (CsA) in mouse and rat investigated by DESI and MALDI mass spectrometry imaging (MSI) of whole-body and single organ cryo-sections

Therapeutic peptides are a fast-growing class of pharmaceuticals. Like small molecules, the costs associated with their discovery and development are significant. In addition, since the preclinical data guides first-in-human studies, there is a need for analytical techniques that accelerate and improve our understanding of the absorption, distribution, metabolism, and excretion (ADME) characteristics of early drug candidates. Mass spectrometry imaging (MSI), which can be used to visualize drug distribution in intact tissue, has been extensively used to study small molecule drugs, but only applied to a limited extent to larger molecules, such as peptides, after dosing. Herein, we use MSI to obtain spatial information on the distribution and metabolism of a peptide drug. The immunosuppressant cyclosporine (CsA), a cyclic undecapeptide, was used as a-proof-of-concept peptide and investigated by desorption electrospray ionization (DESI) MSI. Calibration curves were made based on a spiked tissue homogenate model. Different washing protocols were tested to improve sensitivity, but CsA, being a quite lipophilic peptide, was found not to benefit from tissue washing. The distribution of CsA and its metabolites were mapped in whole-body mouse sections and within rat organs. Whole-body DESI-MSI studies in mice showed widespread distribution of CsA with highest abundance in organs like the pancreas and liver. After 24 h, hydroxy and dihydroxy metabolites of CsA were detected predominantly in the intestines, which were largely devoid of CsA. In addition to the DESI-MSI experiments, MALDI-MSI was also conducted on rat jejunum at higher spatial resolution, revealing the morphology of the jejenum at greater detail; however, DESI provided similar results for drug and metabolite distribution in rat jejunum at apparent slightly better sensitivity. Given its label-free nature, MSI could provide valuable ADME insight, especially for candidates in the early-stage pipeline before radiolabeling.

The Advantages of Polymeric Hydrogels in Calcineurin Inhibitor Delivery

In recent years, polymeric hydrogels (PolyHy) have been extensively explored for their applications in biomedicine as biosensors, in tissue engineering, diagnostic processes, and drug release. The physical and chemical properties of PolyHy indicate their potential use in regulating drug delivery. Calcineurin inhibitors, particularly cyclosporine (CsA) and tacrolimus (TAC), are two important immunosuppressor drugs prescribed upon solid organ transplants. Although these drugs have been used since the 1970s to significantly increase the survival of transplanted organs, there are concerns regarding their undesirable side effects, primarily due to their highly variable concentrations. In fact, calcineurin inhibitors lead to acute and chronic toxicities that primarily cause adverse effects such as hypertension and nephrotoxicity. It is suggested from the evidence that the encapsulation of calcineurin inhibitors into PolyHy based on polysaccharides, specifically alginate (Alg), offers effective drug delivery with a stable immunosuppressive response at the in vitro and in vivo levels. This not only may reduce the adverse effects but also would improve the adherence of the patients by the effective preservation of drug concentrations in the therapeutic ranges.

Proteomic Characterization of Urinary Extracellular Vesicles from Kidney-Transplanted Patients Treated with Calcineurin Inhibitors

Use of immunosuppressive drugs is still unavoidable in kidney-transplanted patients. Since their discovery, calcineurin inhibitors (CNI) have been considered the first-line immunosuppressive agents, in spite of their known nephrotoxicity. Chronic CNI toxicity (CNIT) may lead to kidney fibrosis, a threatening scenario for graft survival. However, there is still controversy regarding CNIT diagnosis, monitoring and therapeutic management, and their specific effects at the molecular level are not fully known. Aiming to better characterize CNIT patients, in the present study, we collected urine from kidney-transplanted patients treated with CNI who (i) had a normal kidney function, (ii) suffered CNIT, or (iii) presented interstitial fibrosis and tubular atrophy (IFTA). Urinary extracellular vesicles (uEV) were enriched and the proteome was analyzed to get insight into changes happening during CNI. Members of the uroplakin and plakin families were significantly upregulated in the CNIT group, suggesting an important role in CNIT processes. Although biomarkers cannot be asserted from this single pilot study, our results evidence the potential of uEV as a source of non-invasive protein biomarkers for a better detection and monitoring of this renal alteration in kidney-transplanted patients.

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.

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.

Genetic Variants Associated With Immunosuppressant Pharmacokinetics and Adverse Effects in the DeKAF Genomics Genome-wide Association Studies

BACKGROUND

The immunosuppressants tacrolimus and mycophenolate are important components to the success of organ transplantation, but are also associated with adverse effects, such as nephrotoxicity, anemia, leukopenia, and new-onset diabetes after transplantation. In this report, we attempted to identify genetic variants which are associated with these adverse outcomes.

METHODS

We performed a genome-wide association study, using a genotyping array tailored specifically for transplantation outcomes containing 722 147 single nucleotide polymorphisms, and 2 cohorts of kidney allograft recipients-a discovery cohort and a confirmation cohort-to identify and then confirm genetic variants associated with immunosuppressant pharmacokinetics and adverse outcomes.

RESULTS

Several genetic variants were found to be associated with tacrolimus trough concentrations. We did not confirm variants associated with the other phenotypes tested although several suggestive variants were identified.

CONCLUSIONS

These results show that adverse effects associated with tacrolimus and mycophenolate are complex, and recipient risk is not determined by a few genetic variants with large effects with but most likely are due to many variants, each with small effect sizes, and clinical factors.

Effect of combined sublethal X-ray irradiation and cyclosporine A treatment in NOD scid gamma (NSG) mice

Cyclosporine A (CsA) is used in hematopoietic stem cell transplantations (HSCT) to prevent graft-versus-host disease (GvHD). GvHD is the most severe side effect of allogeneic HSCT and efficient therapies are lacking. Mouse models are an essential tool for assessing potential new therapeutic strategies. Our aim is to mimic a clinical setting as close as possible using CsA treatment after sublethal irradiation in NSG mice and thereby evaluate the feasibility of this mouse model for GvHD studies. The effect of CsA (7.5 mg/kg body weight) on sublethally X-ray irradiated (2 Gy) and non-irradiated NSG mice was tested. CsA was administered orally every twelve hours for nine days. Animals irradiated and treated with CsA showed a shorter survival (n=3/10) than irradiated animals treated with NaCl (n=10/10). Furthermore, combined therapy resulted in severe weight loss (82 ± 6% of initial weight, n=7, day 8), with weight recovery after the CsA application was ceased. A high number of apoptotic events in the liver was observed in these mice (0.431 ± 0.371 apoptotic cells/cm², n=2, compared to 0.027 ± 0.034 apoptotic cells/cm², n=5, in the non-irradiated group). Other adverse effects, including a decrease in white blood cell counts were non-CsA-specific manifestations of irradiation. The combination of CsA treatment with irradiation has a hepatotoxic and lethal effect on NSG mice, whereas the treatment without irradiation is tolerated. Therefore, when using in vivo models of GvHD in NSG mice, a combined treatment with CsA and X-ray irradiation should be avoided or carefully evaluated.

Association of CYP3A5, CYP2C8, and ABCB1 Polymorphisms With Early Renal Injury in Chinese Liver Transplant Recipients Receiving Tacrolimus

BACKGROUND

The purpose of this study is to explore the association of CYP3A5, ABCB1, and CYP2C8 polymorphisms with the risk of developing early kidney impairment in Chinese liver transplant recipients receiving tacrolimus.

METHODS

CYP3A5, ABCB1, and CYP2C8 polymorphisms were genotyped in the Chinese liver transplant recipients in the study receiving tacrolimus for at least 2 years by polymerase chain reaction and high-resolution melting method. Serum cystatin C and urine microprotein (α1-microglobulin, microalbumin, transferrin, and immunoglobulin) of liver transplant recipients were used to determine both the status of early renal injury and the lesion part.

RESULTS

We documented 3 genotypes of CYP3A5 and ABCB1 and only 2 genotypes of CYP2C8 in our cohort. The levels of cystatin C and all 4 indicators of the urine microprotein in the recipient group were significantly higher than those in the control group (P < .05). The concentrations of transferrin differed significantly in each CYP3A5 genotype group (P < .05). Based on diverse CYP2C8 genotypes, we divided all the recipients into 2 groups: CYP2C8*1*1 group and CYP2C8*3*1 group. The concentrations of α1-microglobulin and cystatin C differed significantly between the 2 groups (P < .05). For CYP2C8*3, the positive predictive value is 68.5% and negative predictive value is 70.2%. For CYP3A5*3, the positive predictive value is 55.3% and negative predictive value is 60.4%.

CONCLUSIONS

CYP2C8*3 and CYP3A5*3 appear to be predictive of risk of tacrolimus-induced early renal impairment. CYP3A5*3 was associated with the risk of early renal glomerular lesion, while CYP2C8*3 was associated with the risk of the tubulointerstitial injury. ABCB1 polymorphisms (both C3435T and C1236T) were not associated with the early renal injury in liver transplant recipients.

Influence of CYP3A and ABCB1 polymorphisms on cyclosporine concentrations in renal transplant recipients

Aim: Cyclosporine is a substrate of CYP3A and ABCB1. This study examined the role of CYP3A and ABCB1 polymorphisms on cyclosporine pharmacokinetics in renal transplant recipients. Patients & methods: CYP3A and ABCB1 SNPs were detected in 521 recipients. The relationships of dose-adjusted concentrations with corresponding genotypes were investigated at the different terms. Results: CYP3A5 rs776746 and CYP3A7 rs10211 genotype affect C0/D at the short-term, medium-term and long-term after transplantation (p < 0.05). CYP3A7 rs2257401 genotype affects C2/D at the medium-term (p < 0.05). CYP3A4 rs4646437, CYP3A5 rs776746 and CYP3A7 rs2257401 genotype affect C2/D at the long-term (p < 0.05). There are no relationships between ABCB1 polymorphism and cyclosporine C/D. Conclusion: CYP3A genetic factors (rs776746, rs4646437, rs2257401 and rs10211) were varied in different stages after transplantation. The role of CYP3A7 in cyclosporine metabolism requires further study.

Systemic cyclosporine and corneal transplantation

Corneal transplantation is the most commonly performed tissue transplant boasting over a century of history, science, and tradition. While favorable outcomes have been reported after penetrating keratoplasty, rejection remains a major cause of graft failure. The long-term survival rates of this relatively immunologically privileged tissue are only just comparable to those of vascularized organs. While corticosteroids treatment remains the gold standard for postoperative immunomodulation, other agents have been utilized in an ongoing effort to improve graft survival and patient outcomes. One of the most promising immunomodulatory substances whose immunosuppressive effect has revolutionized solid organ transplantation is cyclosporine (CsA). A calcineurin inhibitor, cyclosporine has been used as an immunosuppressive agent in corneal transplantation since the 1980's. Although some studies have shown beneficial effects of cyclosporine in both low- and high-risk corneal transplant patients the use of cyclosporine in rejection prophylaxis and treatment remain controversial and disputable. We herein present a literature review on the role of systemic cyclosporine in corneal transplantation.

Pharmacogenetic-based strategy using de novo tacrolimus once daily after kidney transplantation: prospective pilot study

Aim: The once daily tacrolimus formulation (Tac-OD) has been associated with better patient adherence and low variability in exposure. Patients carrying the CYP3A5*1 allele show accelerated clearance of Tac. Authors prospectively evaluate a simplified strategy for Tac-OD administration. Patients & methods: After grafting, 151 patients were divided into four groups and received a daily dose calculated according to CYP3A5 genotypes and unchanged for the first 3 days: CYP3A5*3/*3: 0.20 mg/kg/day, CYP3A5*3/*3: 0.25 mg/kg/day, CYP3A5*1/*3: 0.30 mg/kg/day and CYP3A5*1/*1: 0.35 mg/kg/day. The dose was adaptated on day 4 and remained unchanged a further three days and so on. Results: On day 3, median Cmin fell within the therapeutic range in all study groups. CYP3A5 expressors require significantly higher Tac-OD throughout the follow-up period to achieve a comparable Cmin. Conclusion: This simplified strategy does not hamper treatment efficacy.

[MicroRNAs in kidney fibrosis]

Renal fibrosis represents the final stage of most chronic kidney diseases and contributes to the progressive and irreversible decline in kidney function with accumulation of extracellular matrix components in the renal parenchyma. The molecular mechanisms governing the renal fibrosis process are complex and remain poorly understood. Recently, the profibrotic role of several microRNAs (miRNAs) has been described in kidney fibrosis. MiRNAs are a new class of, small non-coding RNAs of about 20 nucleotides that act as gene expression negative regulators at the post-transcriptional level. Seminal studies have highlighted the potential importance of miRNA as new therapeutic targets and innovative diagnostic and/or prognostic biomarkers. This review summarizes recent scientific advances on the role played by miRNAs in kidney fibrogenesis and discusses potential clinical applications as well as future research directions.

Genetic variance in ABCB1 and CYP3A5 does not contribute toward the development of chronic kidney disease after liver transplantation

INTRODUCTION

Chronic kidney disease (CKD) after liver transplantation (LT) is a major clinical problem that appears to be associated with nongenetic as well as genetic determinants. Calcineurin inhibitor (CNI) use is considered to play a major role in the development of CKD after LT. We studied the influence of single-nucleotide polymorphisms (SNPs) in the genes of the donor and recipient CNI-metabolizing enzyme CYP3A5 and the CNI-transporting ABCB1 on the development of CKD after LT.

MATERIALS AND METHODS

Tacrolimus (Tac) predose concentrations at different time-points after transplantation and the CYP3A5 6986A>G and ABCB1 3435C>T SNPs were determined in 125 LT recipients and their respective donors to study the influence of Tac predose levels and genetics on the development of CKD.

RESULTS

After a median follow-up of 5.7±2.9 years, CKD developed in 47 patients (36%). The Tac predose levels were not correlated with the development of CKD. Neither did we find a correlation between the investigated SNPs in either donor or recipient ABCB1 and CYP3A5 genes (or combinations thereof) and the development of CKD. These genetic variations did not relate to Tac predose blood concentrations in our study.

CONCLUSION

An individual's risk of developing CKD after LT is not associated with genetic variation in either recipient or donor CYP3A5 or ABCB1 genotype status.

Kidney transplant recipients carrying the CYP3A4*22 allelic variant have reduced tacrolimus clearance and often reach supratherapeutic tacrolimus concentrations

CYP3A4*22 is an allelic variant of the cytochrome P450 3A4 associated with a decreased activity. Carriers of this polymorphism may require reduced tacrolimus (Tac) doses to reach the target residual concentrations (Co). We tested this hypothesis in a population of kidney transplant recipients extracted from a multicenter, prospective and randomized study. Among the 186 kidney transplant recipients included, 9.3% (18 patients) were heterozygous for the CYP3A4*22 genotype and none were homozygous (allele frequency of 4.8%). Ten days after transplantation (3 days after starting treatment with Tac), 11% of the CYP3A4*22 carriers were within the target range of Tac Co (10-15 ng/mL), whereas among the CYP3A4*1/*1 carriers, 40% were within the target range (p = 0.02, OR = 0.19 [0.03; 0.69]). The mean Tac Co at day 10 in the CYP3A4*1/*22 group was 23.5 ng/mL (16.6-30.9) compared with 15.1 ng/mL (14-16.3) in the CYP3A4*1/*1 group, p < 0.001. The Tac Co/dose significantly depended on the CYP3A4 genotype during the follow-up (random effects model, p < 0.001) with the corresponding equivalent dose for patients heterozygous for CYP3A4*22 being 0.67 [0.54; 0.84] times the dose for CYP3A4*1/*1 carriers. In conclusion, the CYP3A4*22 allelic variant is associated with a significantly altered Tac metabolism and carriers of this polymorphism often reach supratherapeutic concentrations.

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.

Molecular and clinical aspects of drug-induced gingival overgrowth

Drug-induced gingival overgrowth is a tissue-specific condition and is estimated to affect approximately one million North Americans. Lesions occur principally as side-effects from phenytoin, nifedipine, or ciclosporin therapy in approximately half of the people who take these agents. Due to new indications for these drugs, their use continues to grow. Here, we review the molecular and cellular characteristics of human gingival overgrowth lesions and highlight how they differ considerably as a function of the causative drug. Analyses of molecular signaling pathways in cultured human gingival fibroblasts have provided evidence for their unique aspects compared with fibroblasts from the lung and kidney. These findings provide insights into both the basis for tissue specificity and into possible therapeutic opportunities which are reviewed here. Although ciclosporin-induced gingival overgrowth lesions exhibit principally the presence of inflammation and little fibrosis, nifedipine- and especially phenytoin-induced lesions are highly fibrotic. The increased expression of markers of gingival fibrosis, particularly CCN2 [also known as connective tissue growth factor (CTGF)], markers of epithelial to mesenchymal transition, and more recently periostin and members of the lysyl oxidase family of enzymes have been documented in phenytoin or nifedipine lesions. Some oral fibrotic conditions such as leukoplakia and oral submucous fibrosis, after subsequent additional genetic damage, can develop into oral cancer. Since many pathways are shared, the study of gingival fibrosis and comparisons with characteristics and molecular drivers of oral cancer would likely enhance understandings and functional roles of molecular drivers of these oral pathologies.

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.

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.

Pharmacogenetics and immunosuppressive drugs in solid organ transplantation

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

Conversion to sirolimus ameliorates cyclosporine-induced nephropathy in the rat: focus on serum, urine, gene, and protein renal expression biomarkers

Protocols of conversion from cyclosporin A (CsA) to sirolimus (SRL) have been widely used in immunotherapy after transplantation to prevent CsA-induced nephropathy, but the molecular mechanisms underlying these protocols remain nuclear. This study aimed to identify the molecular pathways and putative biomarkers of CsA-to-SRL conversion in a rat model. Four animal groups (n = 6) were tested during 9 weeks: control, CsA, SRL, and conversion (CsA for 3 weeks followed by SRL for 6 weeks). Classical and emergent serum, urinary, and kidney tissue (gene and protein expression) markers were assessed. Renal lesions were analyzed in hematoxylin and eosin, periodic acid-Schiff, and Masson's trichrome stains. SRL-treated rats presented proteinuria and NGAL (serum and urinary) as the best markers of renal impairment. Short CsA treatment presented slight or even absent kidney lesions and TGF-β, NF-κβ, mTOR, PCNA, TP53, KIM-1, and CTGF as relevant gene and protein changes. Prolonged CsA exposure aggravated renal damage, without clear changes on the traditional markers, but with changes in serums TGF-β and IL-7, TBARs clearance, and kidney TGF-β and mTOR. Conversion to SRL prevented CsA-induced renal damage evolution (absent/mild grade lesions), while NGAL (serum versus urine) seems to be a feasible biomarker of CsA replacement to SRL.

Genes and beans: pharmacogenomics of renal transplant

Advances in the management of patients after solid organ transplantation have led to dramatic decreases in rates of acute rejection, but long-term graft and patient survival have remained unchanged. Individualized therapy after transplant will ideally provide adequate immunosuppression while limiting the adverse effects of drug therapy that significantly impact graft survival. Therapeutic drug monitoring represents the best approximation of individualized drug therapy in transplant at this time; however, obtaining pharmacogenomic data in transplant patients has the potential to enhance our current practice. Polymorphisms of target genes that impact pharmacokinetics have been identified for most immunosuppressants, including tacrolimus, cyclosporine, mycophenolate, azathioprine and sirolimus. In the future, pre-emptive assessment of a patient's genetic profile may inform drug selection and provide information on specific doses that will improve efficacy and limit toxicity.

Calcineurin inhibitor nephrotoxicity: a review and perspective of the evidence

BACKGROUND

There is no doubt that acute calcineurin inhibitor (CNI) nephrotoxicity exists; however, chronic CNI nephrotoxicity is questionable at best.

METHODS

We reviewed the literature to identify original articles related to the use of CNIs in renal and nonrenal solid organ transplantation in order to examine the available evidence about their chronic nephrotoxicity and contribution to graft failure.

RESULTS

Early clinical experience and animal studies support the evidence of CNI nephrotoxicity. These findings evolved into the dogma that CNI nephrotoxicity is the major cause of late renal allograft failure. However, in transplanted kidneys the specific role of chronic CNI nephrotoxicity has been questioned. The emerging literature clearly highlights the lack of solid evidence for the role of CNIs as the sole and major injurious agents that cause chronic renal dysfunction and subsequent graft failure. Most of the evidence available to date is against complete CNI avoidance, and minimization appears to be a more viable strategy. It is becoming increasingly clear that the typical pathological lesions linked to chronic CNI use are highly nonspecific, and most of the chronic changes that have been attributed to chronic CNI nephrotoxicity are the consequences of previously unrecognized immunologic injuries. One needs to keep in mind that the potential risk of side effects of CNI use should be balanced against the risk of rejection.

CONCLUSIONS

More research should focus on addressing the true causes of chronic graft dysfunction rather than focusing on the overexaggerated contribution of CNIs to late graft loss.

Pharmacogenetics of drugs used in the treatment of ocular inflammatory diseases

INTRODUCTION

Ocular inflammatory diseases comprise uveitis, scleritis, and inflammation of adjacent structures of the eye. Therapy may be challenging and often involves corticosteroids and immunomodulatory agents.

AREAS COVERED

This review describes the genes involved in noninfectious ocular inflammatory diseases and focuses on pharmacogenetic studies regarding different classes of anti-inflammatory drugs used in the management of uveitis, including corticosteroids, antimetabolites, calcineurin inhibitors, alkylating agents, and biological agents.

EXPERT OPINION

Pharmacogenetics holds the promise of a personalized medicine with potential to customize treatment that can achieve the best clinical response and avoid toxicity. Several polymorphisms in various genes involved in the metabolism of drugs commonly utilized in the treatment of ocular inflammatory diseases have been described. Most promising is the polymorphism in thiopurinemethyltransferase gene for which a genotype analysis can reveal slow metabolizers of azathioprine and help avoid serious drug toxicity. Although pharmacogenetic studies with specific focus on ocular inflammatory diseases are lacking, knowledge from studies in rheumatologic diseases and transplant medicine can provide a platform for future research. Prospective clinical studies are needed to determine the clinical significance of such polymorphisms and their true effect on drug metabolism and side effects.

Allopurinol safely and effectively optimises thiopurine metabolites in patients with autoimmune hepatitis

BACKGROUND

Ten percent of patients with autoimmune hepatitis (AIH) are nonresponsive or intolerant to thiopurine therapy. A skewed metabolism, leading to the preferential generation of (hepato)toxic thiopurine metabolites (6-MMPs) instead of the metabolic active 6-tioguanine (thioguanine) nucleotides (6-TGNs), may explain this unfavourable outcome. Co-administration of allopurinol to low-dose thiopurine therapy may effectively revert this deviant metabolism, as has been shown in inflammatory bowel disease.

AIM

To describe the effect of adding allopurinol to low-dose thiopurine therapy in patients with AIH with intolerance or nonresponse to normal thiopurine dosages due to a skewed metabolism.

METHODS

We describe the clinical efficacy and tolerability of allopurinol-thiopurine combination therapy with allopurinol 100 mg and low-dose thiopurine (25-33% of the original dosage) in eight AIH patients with a skewed thiopurine metabolism. Patients were switched because of dose-limiting intolerance (n = 3), nonresponse (n = 3) or loss of response (n = 2) to conventional thiopurine treatment.

RESULTS

All eight patients showed biochemical improvement with a reduction in median alanine aminotransferase (ALT) levels of 62 U/L at start to 35 U/L at 1 month (P = 0.03). This clinical benefit was sustained in seven patients. Allopurinol-thiopurine combination therapy effectively bypassed thiopurine side effects in four of five patients. Median 6-tioguanine nucleotides levels increased from 100 to 200 pmol/8 × 10(8) red blood cells (RBC) at 3 months (P = 0.04). Median 6-MMP levels decreased in all patients from 6090 to 175 pmol/8 × 10(8) RBC (P = 0.01).

CONCLUSION

Allopurinol safely and effectively optimises thiopurine therapy in patients with autoimmune hepatitis with intolerance and/or nonresponse due to an unfavourable thiopurine metabolism.

Increased circulating miR-21 levels are associated with kidney fibrosis

MicroRNAs (miRNAs) are a class of noncoding RNA acting at a post-transcriptional level to control the expression of large sets of target mRNAs. While there is evidence that miRNAs deregulation plays a causative role in various complex disorders, their role in fibrotic kidney diseases is largely unexplored. Here, we found a strong up-regulation of miR-21 in the kidneys of mice with unilateral ureteral obstruction and also in the kidneys of patients with severe kidney fibrosis. In addition, mouse primary fibroblasts derived from fibrotic kidneys exhibited higher miR-21 expression level compared to those derived from normal kidneys. Expression of miR-21 in normal primary kidney fibroblasts was induced upon TGFβ exposure, a key growth factor involved in fibrogenesis. Finally, ectopic expression of miR-21 in primary kidney fibroblasts was sufficient to promote myofibroblast differentiation. As circulating miRNAs have been suggested as promising non-invasive biomarkers, we further assess whether circulating miR-21 levels are associated with renal fibrosis using sera from 42 renal transplant recipients, categorized according to their renal fibrosis severity, evaluated on allograft biopsies (Interstitial Fibrosis/Tubular Atrophy (IF/TA). Circulating miR-21 levels are significantly increased in patients with severe IF/TA grade (IF/TA grade 3: 3.0±1.0 vs lower grade of fibrosis: 1.5±1.2; p = 0.001). By contrast, circulating miR-21 levels were not correlated with other renal histological lesions. In a multivariate linear regression model including IF/TA grade and estimated GFR, independent associations were found between circulating miR-21 levels and IF/TA score (ß = 0.307, p = 0.03), and between miR-21 levels and aMDRD (ß = −0.398, p = 0.006). Altogether, these data suggest miR-21 has a key pathogenic role in kidney fibrosis and may represent a novel, predictive and reliable blood marker of kidney fibrosis.

Anti-apoptotic and anti-oxidant effects of grape seed proanthocyanidin extract in preventing cyclosporine A-induced nephropathy

AIM

Although the pathogenesis of cyclosporine (CsA) nephropathy is not completely understood, it is attributed to oxidative damage and apoptosis. Grape seed proanthocyanidin extract (GSPE) is a molecule with anti-oxidant and anti-apoptotic properties. Our aim was to demonstrate the effects of GSPE in preventing CsA nephropathy.

METHODS

Twenty-four Sprague-Dawley rats were divided into four groups. The control, GSPE, CsA and CsA+GSPE groups were given 1 mL olive oil, 100 mg/kg GSPE, 25 mg/kg CsA and 100 mg/kg GSPE+25 mg/kg CsA, respectively. On day 21, blood samples were taken for blood urea nitrogen (BUN), creatinine and CsA levels, and renal tissue was used for total oxidant system (TOS), total anti-oxidant system (TAS), oxidative stress index (OSI) and malondialdehyde (MDA) measurements. In addition to renal histopathology, apoptosis staining was performed on renal tissue.

RESULTS

The BUN, creatinine, TOS, OSI, MDA, histopathological score, and apoptotic index exhibited increases in the CsA group. In the CsA+GSPE group, however, BUN, creatinine, OSI, MDA, renal histopathological score and apoptotic index (AI) decreased and TAS levels increased. In addition, there was no difference between the CsA and CsA+GSPE groups with regard to CsA levels.

CONCLUSION

We demonstrated that GSPE prevents CsA nephropathy and that this effect is achieved by anti-apoptotic and anti-oxidant activity. We also achieved a significant recovery in kidney functions without affecting CsA plasma levels.

Long-term therapeutic effects and safety of tacrolimus added to methotrexate in patients with rheumatoid arthritis

To assess the long-term safety and efficacy of tacrolimus (TAC) used in combination with oral methotrexate (MTX) in patients with rheumatoid arthritis (RA) whose disease remains active despite treatment with MTX alone. The clinical courses of 24 RA patients who received TAC added to MTX from a single center were analyzed retrospectively. The disease activity was evaluated by the DAS28-ESR(3) every 12 months after the addition of TAC, and side effects were evaluated for 3 years. At 3 years after starting the treatment, TAC was still being used by 19 patients (79 %). The causes of discontinuation were an inadequate response (3 cases), oral ulcers and elevation of creatinine (1 case), and worsening of interstitial pneumonia (1 case). No death was registered. The DAS28-ESR(3) was decreased from 4.81 to 3.41 after 3 years of treatment. The doses of prednisolone were decreased from 5.1 mg/day to 3.2 mg/day after 3 years. In patients whose active RA persists despite treatment with MTX, TAC in combination with MTX is safe and well tolerated and provided clinical benefit for a long time in this single-center retrospective study. Further studies are required to confirm the safety and efficacy of this combination therapy.

Mycophenolate mofetil inhibits macrophage infiltration and kidney fibrosis in long-term ischemia-reperfusion injury

Immunosuppressants have been widely used in renal transplantation, in which ischemia-reperfusion injury is inevitable. Mycophenolate mofetil (MMF) is a relative novel immunosuppressant and also attenuates ischemia-reperfusion injury in the acute phase, but its long-term effects are still obscure. Unilateral renal ischemia-reperfusion injury model was established in Sprague-Dawley rats and 30 mg/kg/day MMF or natural saline was administered a day before the surgery. Renal function was monitored, and histological changes and fibrosis in the kidney were evaluated in both short and long terms. TGF-β1 secretion and MCP-1 expression were determined by immunohistochemistry and real-time PCR respectively. The infiltration of macrophages in renal tissues was also assessed by fluorescence activated cell sorting (FACS). MMF treatment significantly improved renal function in ischemia-reperfusion injury rats in the short and long-term and also effectively prevented interstitial fibrosis. TGF-β1 secretion and MCP-1 expression in the renal tissue of MMF-treated rats were much lower than those in natural saline-treated rats, with much less macrophage infiltration as well. MMF treatment effectively prevented the deterioration of renal function and interstitial fibrosis in ischemia-reperfusion injury rats, which may be associated with decreased TGF-β1, MCP-1 and macrophages. These results provide evidence for the choice of MMF in the renal transplant patients not only for acute renal injury but also for long-term survival of renal allograft.

Genetic and clinical determinants of early, acute calcineurin inhibitor-related nephrotoxicity: results from a kidney transplant consortium

BACKGROUND

Calcineurin inhibitor (CNI)-related acute nephrotoxicity is a common complication of transplantation. Clinical factors and elevated CNI levels are associated with nephrotoxicity; however, they do not fully explain the risk. Genetic factors may also predispose individuals to nephrotoxicity.

METHODS

We enrolled 945 kidney recipients into a multicenter, prospective study. DNA was genotyped for 2724 single-nucleotide polymorphisms (SNPs) using a customized chip. Cox models, unadjusted and adjusted for clinical factors, examined the association between SNPs and time to early CNI-related acute nephrotoxicity in the first 6 months posttransplant.

RESULTS

Cyclosporine was associated with a 1.49 hazard (95% confidence interval, 1.04-2.14) of acute nephrotoxicity relative to tacrolimus. Acute nephrotoxicity occurred in 22.6% of cyclosporine and 19.8% of tacrolimus recipients. The median (interquartile range) daily dose and trough concentration at time of nephrotoxicity were 400 mg (400-500 mg) and 228 ng/mL (190-272 ng/mL) in the cyclosporine group, and 6 mg (4-8 mg) and 12.6 ng/mL (10.2-15.9 ng/mL) in the tacrolimus group, respectively. In single-SNP adjusted analysis, nine SNPs in the XPC, CYP2C9, PAX4, MTRR, and GAN genes were associated with cyclosporine nephrotoxicity. In a multi-SNP analysis, SNPs from the same genes remained significant after adjusting for the clinical factors, showing that the SNPs are jointly and independently predictive of cyclosporine nephrotoxicity. No SNPs were associated with tacrolimus nephrotoxicity.

CONCLUSION

We identified SNPs that were potentially associated with early, acute cyclosporine-related nephrotoxicity. Identifying risk SNPs before transplantation provides an opportunity for personalization of immunosuppression by identifying those who may benefit from CNI-avoidance or minimization, or assist in selecting CNI type. These SNPs require independent validation.

Intraparenchymal injection of bone marrow mesenchymal stem cells reduces kidney fibrosis after ischemia-reperfusion in cyclosporine-immunosuppressed rats

Ischemia-reperfusion and immunosuppressive therapy are a major cause of progressive renal failure after kidney transplantation. Recent studies have shown that administration of bone marrow mesenchymal stem cells (MSCs) improves kidney functional recovery in the acute phase of post ischemia-reperfusion injury. In the present study, we used an original model of renal ischemia-reperfusion in immunosuppressed rats (NIRC) to investigate the effects of bone marrow MSCs on progression of chronic renal failure and the mechanisms potentially involved. Left renal ischemia-reperfusion (IR) was induced in unilateral nephrectomized Lewis rats. After IR, rats were treated daily with cyclosporine (10 mg/kg SC) for 28 days. MSCs were injected into the kidney at day 7 after IR. At day 28 after IR, kidneys were removed for histomorphological, biochemical, and gene expression analysis. The effect of conditioned media from MSCs on epithelial-mesenchymal transition was studied in vitro on HK2 cells. Our results show that, as compared to untreated NIRC rats, rats treated by intrarenal injection of MSCs 7 days after IR displayed improvement in renal function, reduction of interstitial fibrosis, and decrease in chronic tubule injury. These effects were associated with a decrease in interstitial α-SMA accumulation and MMP2 activity, markers of fibroblast/fibroblast-like cell activation, and renal remodeling, respectively. Finally, experiments in vitro showed that MSC-conditioned medium prevented epithelial-mesenchymal transition induced by TGF-β in HK2 cells. In conclusion, our results show that, in immunosuppressed animals, a single intrarenal administration of MSCs reduced renal fibrosis and promoted the recovery of renal function.

Low-dose cyclosporine mediates donor hyporesponsiveness in a fully mismatched rat kidney transplant model

Tolerance induction protocols have been successfully tested in animal models, yet their compatibility with immunosuppressive drugs remains to be fully elucidated. Our own previous data have indicated that cyclosporine A (CsA) affects the balance of effector and regulatory mechanisms with low-dose CsA doses promoting hyporesponsiveness. Here, we present a fully mismatched rat kidney model in which low-dose CsA treatment induces donor hyporesponsiveness to secondary renal allografts. Lewis recipients of DA kidney grafts received low, medium or high doses of CsA × 10 days. By 30 days, the primary transplant was removed and a second transplant of donor origin was engrafted. Following low-dose CsA, but not high-dose CsA treatment of the primary recipient, secondary transplants were accepted long-term in the absence of immunosuppression. Regulatory T-cell function was unimpaired and independent of the CyA dosage. Of note, low-dose CsA significantly reduced alloantibody titers in primary recipients. Adoptive transfer of graft infiltrating cells or splenocytes from hyporesponsive recipients supported long-term acceptance of donor kidney allografts. These results demonstrate a dose-dependent and transferable "pro-tolerogenic" effect of low-dose CsA treatment. This model is of clinical relevance to test the interference of CsA with tolerance induction in the absence of additional immunosuppression.

Impact of genetic polymorphisms on tacrolimus pharmacokinetics and the clinical outcome of renal transplantation

We retrospectively examined the association of polymorphisms in the CYP3A, CYP2J2, CYP2C8, and ABCB1 genes with pharmacokinetic (PKs) and pharmacodynamic (PDs) parameters of tacrolimus in 103 renal transplant recipients for a period of 1 year. CYP3A5 expressers had lower predose concentrations (C(0) )/dose and higher dose requirements than nonexpressers throughout the study. Among CYP3A5*1 carriers, those also carrying the CYP3A4*1B allele showed the lowest C(0) /dose, as compared with CYP3A4*1/CYP3A5*3 carriers (54.28±26.45, 59.12±24.00, 62.43±41.12, and 57.01±17.34 vs. 112.37± 76.60, 123.21±59.57, 163.34±76.23, and 183.07±107.82 at 1 week, 1 month, 5 months, and 1 year after transplantation). In addition, CYP3A4*1B/CYP3A5*1 carriers showed significantly lower dose-corrected exposure than CYP3A4*1/CYP3A5*1 carriers 1 year after transplantation (57.01±17.34 vs. 100.09±24.78; P=0.016). Only the ABCB1 TGC (3435-2677-1236) haplotype showed a consistent association with PDs (nephrotoxicity; OR=4.73; CI: 1.3-16.7; P=0.02). Our findings indicate that the CYP3A4*1B-CYP3A5*1 haplotype may have a more profound impact in tacrolimus PKs than the CYP3A5*1 allele. This study does not support a critical role of the CYP450 or ABCB1 single nucleotide polymorphisms in the occurrence of toxicity or acute rejection in renal transplant recipients treated with tacrolimus.

Cyclosporine: a review

The discovery and use of cyclosporine since its inception into clinical use in the late 1970s has played a major role in the advancement of transplant medicine. While it has improved rates of acute rejection and early graft survival, data on long-term survival of renal allografts is less convincing. The finding of acute reversible nephrotoxicity and nephrotoxicity in nonrenal transplants has since led to the widely accepted view that there is a chronic more irreversible component to this agent as well. Since that time, there has been intense interest in finding protocols which seek to minimize and even avoid the use of calcineurin inhibitors altogether. We seek to review cyclosporine in terms of its mechanism of action, pathophysiologic, and histologic features associated with acute and chronic nephrotoxicity and recent studies looking to avoid its toxic side effects.

Efficacy and safety of changing from cyclosporine C0 to C2 monitoring in stable recipients following renal transplantation: a prospective cohort study

Cyclosporine doses can be adjusted individually to decrease the occurrence of rejection and nephrotoxic episodes using concentrations at 2 hours postdosing (C2). However, some transplantation centers still use trough concentrations (C0) to adjust cyclosporine doses among stable renal transplant recipients. We analyzed the efficacy and safety of changing from monitoring C0 to C2 among stable recipients following living relative donor renal transplantation. We enrolled 65 stable renal transplant recipients whose cyclosporine (Neoral) dosages were adjusted by C0, recording their cyclosporine C2 values. They were divided into low (<500 ng/mL, n=25), target (500-600 ng/mL, n=23), or high (>600 ng/mL, n=17) C2 groups. The cyclosporine dose was prospectively modified in the low and high C2 groups; all patients were followed for 12 months. We compared the incidences of complications among their transplanted kidneys and other organs. Among patients in the high C2 group, the C2 target value was achieved by reducing the cyclosporine dose by up to 575.0 mg (mean=33.8 mg/patient); 88.2% of patients showed stable levels of creatinine (Cr) and urea nitrogen (BUN) during the follow-up with decreased blood cholesterol and uric acid levels in some patients, while two subjects suffered acute rejection episodes. Among the low C2 group, the target value was achieved by increasing the cyclosporine dose by up to 755.0 mg (mean=30.2 mg/patient); during the follow-up with 84.0% of subjects displaying stable levels of Cr and BUN, four suffered increasing Cr and BUN values. Although most of stable recipients in this study benefited from C2 monitoring, some patients suffered rejection or nephrotoxicity episodes. One must be cautious to change from monitoring C0 to C2 in stable recipients following renal transplantation.

Top Three Pharmacogenomics and Personalized Medicine Applications at the Nexus of Renal Pathophysiology and Cardiovascular Medicine

Pharmacogenomics is a field with origins in the study of monogenic variations in drug metabolism in the 1950s. Perhaps because of these historical underpinnings, there has been an intensive investigation of 'hepatic pharmacogenes' such as CYP450s and liver drug metabolism using pharmacogenomics approaches over the past five decades. Surprisingly, kidney pathophysiology, attendant diseases and treatment outcomes have been vastly under-studied and under-theorized despite their central importance in maintenance of health, susceptibility to disease and rational personalized therapeutics. Indeed, chronic kidney disease (CKD) represents an increasing public health burden worldwide, both in developed and developing countries. Patients with CKD suffer from high cardiovascular morbidity and mortality, which is mainly attributable to cardiovascular events before reaching end-stage renal disease. In this paper, we focus our analyses on renal function before end-stage renal disease, as seen through the lens of pharmacogenomics and human genomic variation. We herein synthesize the recent evidence linking selected Very Important Pharmacogenes (VIP) to renal function, blood pressure and salt-sensitivity in humans, and ways in which these insights might inform rational personalized therapeutics. Notably, we highlight and present the rationale for three applications that we consider as important and actionable therapeutic and preventive focus areas in renal pharmacogenomics: 1) ACE inhibitors, as a confirmed application, 2) VDR agonists, as a promising application, and 3) moderate dietary salt intake, as a suggested novel application. Additionally, we emphasize the putative contributions of gene-environment interactions, discuss the implications of these findings to treat and prevent hypertension and CKD. Finally, we conclude with a strategic agenda and vision required to accelerate advances in this under-studied field of renal pharmacogenomics with vast significance for global public health.

Pharmacogenetic biomarkers: cytochrome P450 3A5

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

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

BACKGROUND

The association of CYP3A5, CYP3A4, and ABCB1 single nucleotide polymorphisms (SNPs) with cyclosporine (CsA) pharmacokinetics is controversial. The authors studied the influence of these SNPs on CsA pharmacokinetics as well as on the incidence of biopsy-proven acute rejection (BPAR) and renal function after kidney transplantation.

METHOD

One hundred seventy-one patients participating in an international, randomized controlled trial were genotyped for CYP3A5*3, CYP3A4*1B and the ABCB1 1236 C>T, 2677 G>T/A, and 3435 C>T SNPs. The patients were treated with CsA, mycophenolate mofetil, and glucocorticoids. CsA was dosed to reach predose concentrations (C0) or two hours postdose concentrations (C2). Pharmacokinetic parameters were measured on Days 3 and 10 and Months 1, 3, 6, and 12 after transplantation. Renal function was assessed by measuring serum creatinine and calculating the creatinine clearance. The incidence of BPAR and delayed-graft function was recorded.

RESULTS

CYP3A5, CYP3A4, and ABCB1 genotype were not associated with dose-adjusted CsA C0 or C2. The incidence of BPAR in this cohort was 16% and was comparable between the different ABCB1 genotype groups. No significant difference in the incidence of BPAR was found between CYP3A5 expressers (10%) and nonexpressers (18%) (P = 0.24) nor was there a difference in the incidence of BPAR between CYP3A4*1 homozygotes (5%) versus CYP3A4*1B carriers (18%) (P = 0.13). There were no differences with regard to creatinine clearance between the different CYP3A and ABCB1 genotype groups.

CONCLUSION

According to the results, determination of CYP3A and ABCB1 SNPs pretransplantation is not helpful in determining the CsA starting dose and does not aid in predicting the risk of BPAR or worse renal function in an individual patient.

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.

Conventional and novel approaches to immunosuppression

Immunosuppressive therapy has contributed significantly to improved survival after solid organ transplantation. Nevertheless, treatment-related adverse events and persistently high risk of chronic graft rejection remain major obstacles to long-term survival after lung transplantation. The development of new agents, refinements in techniques to monitor immunosuppression, and enhanced understanding of transplant immunobiology are essential for further improvements in outcome. In this article, conventional immunosuppressive regimens, novel approaches to preventing graft rejection, and investigational agents for solid organ transplantation are reviewed.