ABCB1 genotypes predict cyclosporine-related adverse events and kidney allograft outcome

Racial Disparities in Hospitalization Rates During Long-Term Follow-Up After Deceased-Donor Kidney Transplantation

OBJECTIVE

To compare hospitalization rates between African American (AA) and European American (EA) deceased-donor (DD) kidney transplant (KT) recipients during over a10-year period.

METHOD

Data from the Scientific Registry of Transplant Recipients and social determinants of health (SDoH), measured by the Social Deprivation Index, were used. Hospitalization rates were estimated for kidney recipients from AA and EA DDs who had one kidney transplanted into an AA and one into an EA, leading to four donor/recipient pairs (DRPs): AA/AA, AA/EA, EA/AA, and EA/EA. Poisson-Gamma models were fitted to assess post-transplant hospitalizations.

RESULT

Unadjusted hospitalization rates (95% confidence interval) were higher among all DRP involving AA, 131.1 (122.5, 140.3), 134.8 (126.3, 143.8), and 102.4 (98.9, 106.0) for AA/AA, AA/EA, and EA/AA, respectively, compared to 97.1 (93.7, 100.6) per 1000 post-transplant person-years for EA/EA pairs. Multivariable analysis showed u-shaped relationships across SDoH levels within each DRP, but findings varied depending on recipients' race, i.e., AA recipients in areas with the worst SDoH had higher hospitalization rates. However, EA recipients in areas with the best SDoH had higher hospitalization rates than their counterparts.

CONCLUSIONS

Relationship between healthcare utilization and SDoH depends on DRP, with higher hospitalization rates among AA recipients living in areas with the worst SDoH and among EA recipients in areas with the best SDoH profiles. SDoH plays an important role in driving disparities in hospitalizations after kidney transplantation.

Employment status at transplant influences ethnic disparities in outcomes after deceased donor kidney transplantation

Background

African American (AA) recipients of deceased-donor (DD) kidney transplants (KT) have shorter allograft survival than recipients of other ethnic groups. Reasons for this disparity encompass complex interactions between donors and recipients characteristics.

Methods

Outcomes from 3872 AA and 19,719 European American (EA) DDs who had one kidney transplanted in an AA recipient and one in an EA recipient were analyzed. Four donor/recipient pair groups (DRP) were studied, AA/AA, AA/EA, EA/AA, and EA/EA. Survival random forests and Cox proportional hazard models were fitted to rank and evaluate modifying effects of DRP on variables associated with allograft survival. These analyses sought to identify factors contributing to the observed disparities in transplant outcomes among AA and EA DDKT recipients.

Results

Transplant era, discharge serum creatinine, delayed graft function, and DRP were among the top predictors of allograft survival and mortality among DDKT recipients. Interaction effects between DRP with the kidney donor risk index and transplant era showed significant improvement in allograft survival over time in EA recipients. However, AA recipients appeared to have similar or poorer outcomes for DDKT performed after 2010 versus before 2001; allograft survival hazard ratios (95% CI) were 1.15 (0.74, 1.76) and 1.07 (0.8, 1.45) for AA/AA and EA/AA, compared to 0.62 (0.54, 0.71) and 0.5 (0.41, 0.62) for EA/EA and AA/EA DRP, respectively. Recipient mortality improved over time among all DRP, except unemployed AA/AAs. Relative to DDKT performed pre-2001, employed AA/AAs had HR = 0.37 (0.2, 0.69) versus 0.59 (0.31, 1.11) for unemployed AA/AA after 2010.

Conclusion

Relative to DDKT performed before 2001, similar or worse overall DCAS was observed among AA/AAs, while EA/EAs experienced considerable improvement regardless of employment status, KDRI, and EPTS. AA recipients of an AA DDKT, especially if unemployed, had worse allograft survival and mortality and did not appear to benefit from advances in care over the past 20 years.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02631-4.

TCF7L2 rs7903146 Is Associated With Increased Risk of New-Onset Diabetes After Transplant: A Meta-analysis of Literature

BACKGROUND

Single nucleotide polymorphisms may influence the risk of development of new-onset diabetes after transplant (NODAT), a post-transplant clinical complication that is often implicated in allograft rejection and mortality. We performed a meta-analysis of association between transcription factor 7-like-2 (TCF7L2) rs7903146 and risk of NODAT.

METHODS

A systematic search was conducted using PubMed and ScienceDirect electronic databases for studies published between January 2001 and January 2021. Case-control or cohort studies reporting association between NODAT (diagnosis based on American Diabetes Association criteria) and TCF7L2 rs7903146 were included. MetaGenyo was used for meta-analysis (random-effects model). Pooled odds ratios with 95% confidence intervals were reported to evaluate the strength of association.

RESULTS

Two reviewers independently screened for articles. A total of 6 case-control studies were included for full-text review and quantitative analysis after screening for eligibility. Genotypic distributions were in Hardy-Weinberg equilibrium for included studies. All articles reported statistically significant association of TCF7L2 rs7903146 for risk of NODAT except for 1 study. There was moderate heterogeneity among studies (I² = 60.6%). Pooled analysis revealed 51% odds of developing NODAT with TCF7L2 rs7903146 T allele (allele contrast model: odds ratio, 1.51; 95% confidence interval, 1.13-2.02; P = .005).

CONCLUSIONS

The present meta-analysis demonstrated association between TCF7L2 variant rs7903146 and risk of developing NODAT. This finding suggest clinical implications for individuals undergoing kidney transplant.

Genetic variants associated with cytomegalovirus infection after allogeneic hematopoietic cell transplantation

Human cytomegalovirus (CMV) reactivation is a frequent complication of allogeneic hematopoietic cell transplantation (HCT). Despite routine screening for CMV reactivation and early antiviral treatment, the rates of CMV-related complications after HCT remain high. Genetic variants in both the donor and recipient have been associated with the risk of CMV reactivation and disease after HCT, but these associations have not been validated, and their clinical importance remains unclear. In this study, we assessed 117 candidate variants previously associated with CMV-related phenotypes for association with CMV reactivation and disease in a cohort of 2169 CMV-seropositive HCT recipients. We also carried out a genome-wide association study (GWAS) for CMV reactivation and disease in the same cohort. Both analyses used a prespecified discovery and replication approach to control the risk of false-positive results. Among the 117 candidate variants, our analysis implicates only the donor ABCB1 rs1045642 genotype as a risk factor for CMV reactivation. This synonymous variant in P-glycoprotein may influence the risk of CMV reactivation by altering the efflux of cyclosporine and tacrolimus from donor lymphocytes. In the GWAS analysis, the donor CDC42EP3 rs11686168 genotype approached the significance threshold for association with CMV reactivation, although we could not identify a mechanism to explain this association. The results of this study suggest that most genomic variants previously associated with CMV phenotypes do not significantly alter the risk for CMV reactivation or disease after HCT.

Diabetes and Cardiovascular Risk in Renal Transplant Patients

End-stage kidney disease (ESKD) is a main public health problem, the prevalence of which is continuously increasing worldwide. Due to adverse effects of renal replacement therapies, kidney transplantation seems to be the optimal form of therapy with significantly improved survival, quality of life and diminished overall costs compared with dialysis. However, post-transplant patients frequently suffer from post-transplant diabetes mellitus (PTDM) which an important risk factor for cardiovascular and cardiovascular-related deaths after transplantation. The management of post-transplant diabetes resembles that of diabetes in the general population as it is based on strict glycemic control as well as screening and treatment of common complications. Lifestyle interventions accompanied by the tailoring of immunosuppressive regimen may be of key importance to mitigate PTDM-associated complications in kidney transplant patients. More transplant-specific approach can include the exchange of tacrolimus with an alternative immunosuppressant (cyclosporine or mammalian target of rapamycin (mTOR) inhibitor), the decrease or cessation of corticosteroid therapy and caution in the prescribing of diuretics since they are independently connected with post-transplant diabetes. Early identification of high-risk patients for cardiovascular diseases enables timely introduction of appropriate therapeutic strategy and results in higher survival rates for patients with a transplanted kidney.

Beyond Single Nucleotide Polymorphisms: CYP3A5∗3∗6∗7 Composite and ABCB1 Haplotype Associations to Tacrolimus Pharmacokinetics in Black and White Renal Transplant Recipients

Interpatient variability in tacrolimus pharmacokinetics is attributed to metabolism by cytochrome P-450 3A5 (CYP3A5) isoenzymes and membrane transport by P-glycoprotein. Interpatient pharmacokinetic variability has been associated with genotypic variants for both CYP3A5 or ABCB1. Tacrolimus pharmacokinetics was investigated in 65 stable Black and Caucasian post-renal transplant patients by assessing the effects of multiple alleles in both CYP3A5 and ABCB1. A metabolic composite based upon the CYP3A5 polymorphisms: ^∗3(rs776746), ^∗6(10264272), and ^∗7(41303343), each independently responsible for loss of protein expression was used to classify patients as extensive, intermediate and poor metabolizers. In addition, the role of ABCB1 on tacrolimus pharmacokinetics was assessed using haplotype analysis encompassing the single nucleotide polymorphisms: 1236C > T (rs1128503), 2677G > T/A(rs2032582), and 3435C > T(rs1045642). Finally, a combined analysis using both CYP3A5 and ABCB1 polymorphisms was developed to assess their inter-related influence on tacrolimus pharmacokinetics. Extensive metabolizers identified as homozygous wild type at all three CYP3A5 loci were found in 7 Blacks and required twice the tacrolimus dose (5.6 ± 1.6 mg) compared to Poor metabolizers [2.5 ± 1.1 mg (P < 0.001)]; who were primarily Whites. These extensive metabolizers had 2-fold faster clearance (P < 0.001) with 50% lower AUC^∗ (P < 0.001) than Poor metabolizers. No differences in C_{12 h} were found due to therapeutic drug monitoring. The majority of blacks (81%) were classified as either Extensive or Intermediate Metabolizers requiring higher tacrolimus doses to accommodate the more rapid clearance. Blacks who were homozygous for one or more loss of function SNPS were associated with lower tacrolimus doses and slower clearance. These values are comparable to Whites, 82% of who were in the Poor metabolic composite group. The ABCB1 haplotype analysis detected significant associations of the wildtype 1236T-2677T-3435T haplotype to tacrolimus dose (P = 0.03), CL (P = 0.023), CL/LBW (P = 0.022), and AUC^∗ (P = 0.078). Finally, analysis combining CYP3A5 and ABCB1 genotypes indicated that the presence of the ABCB1 3435 T allele significantly reduced tacrolimus clearance for all three CPY3A5 metabolic composite groups. Genotypic associations of tacrolimus pharmacokinetics can be improved by using the novel composite CYP3A5^∗3^∗4^∗5 and ABCB1 haplotypes. Consideration of multiple alleles using CYP3A5 metabolic composites and drug transporter ABCB1 haplotypes provides a more comprehensive appraisal of genetic factors contributing to interpatient variability in tacrolimus pharmacokinetics among Whites and Blacks.

Conversion from tacrolimus to belatacept improves renal function in kidney transplant patients with chronic vascular lesions in allograft biopsy

Background

Conversion from tacrolimus to belatacept has been shown to be beneficial for an increasing number of kidney transplant (KT) patients. Predicting factors for favorable outcomes are still unknown. We aimed to investigate whether histological vascular lesions at the time of conversion might correlate with greater improvement in renal function post-conversion.

Methods

The study was conducted on a retrospective cohort of 34 KT patients converted from tacrolimus to belatacept. All patients underwent an allograft biopsy prior to conversion. We analyzed the evolution of the estimated glomerular filtration rate (eGFR) at 3 and 12 months after conversion.

Results

Median time to conversion was 6 (2–37.2) months post-transplant. About 52.9% of patients had moderate-to-severe chronic vascular lesions (cv2–3). We observed an increase in eGFR in the whole cohort from 35.4 to 41 mL/min/1.73 m² at 3 months (P = 0.032) and 43.7 at 12 months (P = 0.013). Nine patients experienced acute rejection post-conversion, with one graft loss observed beyond the first year after conversion. Patients with cv2–3 had significant improvement in eGFR at 12 months (+8.6 mL/min/1.73 m²; 31.6 to 40.2 mL/min/1.73 m²; P = 0.047) compared with those without these lesions (+6.8 mL/min/1.73 m²; 40.9 to 47.7 mL/min/1.73 m²; P = 0.148).

Conclusions

Conversion from tacrolimus to belatacept has a beneficial effect in terms of renal function in KT patients. This benefit might be more significant in patients with cv in the biopsy.

The Expanding Role of APOL1 Risk in Chronic Kidney Disease and Cardiovascular Disease

Variants of the APOL1 gene, found primarily in individuals of African descent, are associated with various forms of kidney disease and kidney disease progression. Recent studies evaluating the association of APOL1 with cardiovascular disease have yielded conflicting results, and the potential role in cardiovascular disease remains unclear. In this review, we summarize the observational studies linking the APOL1 risk variants with chronic kidney and cardiovascular disease among persons of African descent.

Risk factors for calcineurin inhibitor nephrotoxicity after renal transplantation: a systematic review and meta-analysis

Background

Nephrotoxicity of calcineurin inhibitors (CNIs) is the major concern for long-term allograft survival despite its predominant role in current immunosuppressive regime after renal transplantation. CNI nephrotoxicity is multifactorial with demographic, environmental, and pharmacogenetic flexibility, whereas studies indicating risk factors for CNI nephrotoxicity obtained incomplete or conflicting results.

Methods

A systematic review and meta-analysis of risk factors for CNI nephrotoxicity was performed on all retrieved studies through a comprehensive research of network database. Data were analyzed by Review Manager 5.2 with heterogeneity assessed using the Cochrane Q and I² tests. CNI nephrotoxicity was primarily indicated with protocol biopsy or index-based clinical diagnosis, and the secondary outcome was defined as delayed graft function.

Results

Twelve observational studies containing a total of 2,849 cases were identified. Donor age (odds ratio [OR], 1.01; 95% CI, 1.01-1.03; p=0.02), recipient zero-time arteriosclerosis (OR, 1.44; 95% CI, 1.04-1.99; p=0.03), and CYP3A5*3/*3 genotype (OR, 2.80; 95% CI, 2.63-2.98; p=0.00) were confirmed as risk factors for CNI nephrotoxicity. Subgroup and sensitivity analysis claimed donor age as a significant contributor in Asian and Caucasian areas.

Conclusion

Older donor age, recipient zero-time arteriosclerosis, and CYP3A5*3/*3 genotype might add up the risk for CNI nephrotoxicity, which could be interpreted into a robust biomarker system.

Genetic predictors of long-term graft function in kidney and pancreas transplant patients

Kidney and pancreas transplantation have helped transform the lives of people with end-stage renal failure and individuals with type 1 diabetes who have poor glycaemic control/severe secondary complications, respectively. Despite an improvement in immunosuppressive regimes, operative techniques and decreased initial rejection rates, there has been little improvement in long-term graft survival rates over the past decade. Whilst limited progress has been made in establishing clinical markers of graft function, several genetic markers of long-term graft function have been identified. These genetic markers have the potential to (i) assist in selecting marginal donor organs for transplantation, (ii) provide better understanding of the mechanisms behind graft loss enabling identification of new, or repurposing, current treatments to extend graft function and (iii) provide a window of opportunity to identify and treat individuals before graft failure has occurred. This review will discuss the different genetic variants screened for a role in predicting transplant longevity, examine their findings and limitations and introduce where the future of genetic research within the transplantation field lies.

NFATC1 genotypes affect acute rejection and long-term graft function in cyclosporine-treated renal transplant recipients

AIM

To investigate the effects of SNPs in the cyclophilin A/calcineurin/nuclear factor of activated T-cells (NFATs) pathway genes (PPIA, PPP3CB, PPP3R1, NFATC1 and NFATC2) on cyclosporine (CsA) efficacy in renal transplant recipients.

MATERIALS & METHODS

Seventy-six tag SNPs were detected in 155 CsA-treated renal recipients with at least a 5-year follow-up. The associations of SNPs with acute rejection, nephrotoxicity, pneumonia and estimated glomerular filtration rate post transplant were explored.

RESULTS

NFATC1 rs3894049 GC was a risk factor for acute rejection compared with CC carriers (p = 0.0005). NFATC1 rs2280055 TT carriers had a more stable estimated glomerular filtration rate level than CC (p = 0.0004).

CONCLUSION

Detecting NFATC1 polymorphisms could help predict CsA efficacy in renal transplant patients.

The evolving science of apolipoprotein-L1 and kidney disease

PURPOSE OF REVIEW

There are evolving epidemiological and biological data to support an association between the gene encoding apolipoprotein-L1 (APOL1) and progressive chronic kidney disease (CKD) among African-Americans.

RECENT FINDINGS

Individuals with two APOL1 risk alleles are at greater risk of incident albuminuria, CKD, and progression to end-stage renal disease despite optimal blood pressure management and use of angiotensin-converting enzyme inhibitors. These variants also appear to influence outcomes in donor and recipients in kidney transplantation. Recent studies have also variably shown a potential role of APOL1 variants in cardiovascular disease. A number of studies have addressed genetic and environmental factors such as HIV but most do not modify the course of APOL1-related kidney disease. Although the exact mechanism remains unclear, functional studies have demonstrated the effect of APOL1 and related protein on innate immunity and cytotoxicity.

SUMMARY

APOL1 is an important genetic risk factor for kidney disease among African-Americans. With approximately one in 10 African-Americans at risk, further studies are warranted to identify underlying biological mechanisms and other potential modifiers leading to CKD. Moreover, studies that clarify the association of APOL1 variants with cardiovascular disease, independent of CKD, are also needed.

Barcelona Consensus on Biomarker-Based Immunosuppressive Drugs Management in Solid Organ Transplantation

With current treatment regimens, a relatively high proportion of transplant recipients experience underimmunosuppression or overimmunosuppression. Recently, several promising biomarkers have been identified for determining patient alloreactivity, which help in assessing the risk of rejection and personal response to the drug; others correlate with graft dysfunction and clinical outcome, offering a realistic opportunity for personalized immunosuppression. This consensus document aims to help tailor immunosuppression to the needs of the individual patient. It examines current knowledge on biomarkers associated with patient risk stratification and immunosuppression requirements that have been generally accepted as promising. It is based on a comprehensive review of the literature and the expert opinion of the Biomarker Working Group of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology. The quality of evidence was systematically weighted, and the strength of recommendations was rated according to the GRADE system. Three types of biomarkers are discussed: (1) those associated with the risk of rejection (alloreactivity/tolerance), (2) those reflecting individual response to immunosuppressants, and (3) those associated with graft dysfunction. Analytical aspects of biomarker measurement and novel pharmacokinetic-pharmacodynamic models accessible to the transplant community are also addressed. Conventional pharmacokinetic biomarkers may be used in combination with those discussed in this article to achieve better outcomes and improve long-term graft survival. Our group of experts has made recommendations for the most appropriate analysis of a proposed panel of preliminary biomarkers, most of which are currently under clinical evaluation in ongoing multicentre clinical trials. A section of Next Steps was also included, in which the Expert Committee is committed to sharing this knowledge with the Transplant Community in the form of triennial updates.

Effect of an Early Switch to Belatacept Among Calcineurin Inhibitor-Intolerant Graft Recipients of Kidneys From Extended-Criteria Donors

Transplant recipients receiving a kidney from an extended-criteria donor (ECD) are exposed to calcineurin inhibitor (CNI) nephrotoxicity, as demonstrated by severe delayed graft function and/or a low GFR. Belatacept is a nonnephrotoxic drug that is indicated as an alternative to CNIs. We reported 25 cases of conversion from a CNI to belatacept due to CNI intolerance within the first 6 mo after transplantation. The mean age of the recipients was 59 years, and 24 of 25 patients received ECD kidneys. At the date of the medication switch, 12 of 25 patients displayed a calculated GFR (cGFR) <15 mL/min, six patients remained on dialysis, and the biopsies showed evidence of acute tubular damage associated with severe vascular or tubulointerstitial chronic lesions. Three patients did not recover renal function, and three patients died during the follow-up period. Among the remaining patients, renal function improved: The cGFR was 18.28 ± 12.3 mL/min before the medication switch compared with 34.9 ± 14.5 mL/min at 1 year after conversion to belatacept (p = 0.002). Tolerance of and compliance with belatacept were good, and only one patient experienced acute rejection. Belatacept is an effective therapy that preserves renal function in kidney transplant patients who are intolerant of CNIs.

Exploring genetic and non-genetic risk factors for delayed graft function, acute and subclinical rejection in renal transplant recipients

AIMS

This study aimed at identifying pharmacological factors such as pharmacogenetics and drug exposure as new predictive biomarkers for delayed graft function (DGF), acute rejection (AR) and/or subclinical rejection (SCR).

METHODS

Adult renal transplant recipients (n = 361) on cyclosporine-based immunosuppression were followed for the first 6 months after transplantation. The incidence of DGF and AR were documented as well as the prevalence of SCR at 6 months in surveillance biopsies. Demographic, transplant-related factors, pharmacological and pharmacogenetic factors (ABCB1, CYP3A5, CYP3A4, CYP2C8, NR1I2, PPP3CA and PPP3CB) were analysed in a combined approach in relation to the occurrence of DGF, AR and prevalence of SCR at month 6 using a proportional odds model and time to event model.

RESULTS

Fourteen per cent of the patients experienced at least one clinical rejection episode and only DGF showed a significant effect on the time to AR. The incidence of DGF correlated with a deceased donor kidney transplant (27% vs. 0.6% of living donors). Pharmacogenetic factors were not associated with risk for DGF, AR or SCR. A deceased donor kidney and acute rejection history were the most important determinants for SCR, resulting in a 52% risk of SCR at 6 months (vs. 11% average). In a sub-analysis of the patients with AR, those treated with rejection treatment including ATG, significantly less frequent SCR was found in the 6-month biopsy (13% vs. 50%).

CONCLUSIONS

Transplant-related factors remain the most important determinants of DGF, AR and SCR. Furthermore, rejection treatment with depleting antibodies effectively prevented SCR in 6-month surveillance biopsies.

[Applied pharmacogenetic]

Pharmacokinetics is the link between genetic data and the use of treatments. It can be use on several relevant aspects in the clinic, including the treatment selection, efficacy or toxicity prediction and the choice of the dose. Pharmacogenetics has been applied in clinical nephrology since a long time by the genetic prediction of azathiorpine associated myelotoxicity. However, despite an extensive literature describing the links between genetics and metabolism and transport of drugs, genetic tests are little used in clinical practice. One reason for this poor implementation is the current lack of evidence of improved clinical outcomes with pharmacogenetic tests. In addition, with an effective therapeutic drug monitoring, it is possible to correct the effect of genotype on the pharmacokinetic differences, thus reducing the usefulness of the assay based on the genotype. The future of pharmacogenetics will be treatment models in which patient characteristics are combined with data on polymorphisms in multiple genes including pharmacodynamic parameters, drug transporter proteins, and predictors of toxicity.

Impact of Genetic Polymorphisms of ABCB1 (MDR1, P-Glycoprotein) on Drug Disposition and Potential Clinical Implications: Update of the Literature

ATP-binding cassette transporter B1 (ABCB1; P-glycoprotein; multidrug resistance protein 1) is an adenosine triphosphate (ATP)-dependent efflux transporter located in the plasma membrane of many different cell types. Numerous structurally unrelated compounds, including drugs and environmental toxins, have been identified as substrates. ABCB1 limits the absorption of xenobiotics from the gut lumen, protects sensitive tissues (e.g. the brain, fetus and testes) from xenobiotics and is involved in biliary and renal secretion of its substrates. In recent years, a large number of polymorphisms of the ABCB1 [ATP-binding cassette, sub-family B (MDR/TAP), member 1] gene have been described. The variants 1236C>T (rs1128503, p.G412G), 2677G>T/A (rs2032582, p.A893S/T) and 3435C>T (rs1045642, p.I1145I) occur at high allele frequencies and create a common haplotype; therefore, they have been most widely studied. This review provides an overview of clinical studies published between 2002 and March 2015. In summary, the effect of ABCB1 variation on P-glycoprotein expression (messenger RNA and protein expression) and/or activity in various tissues (e.g. the liver, gut and heart) appears to be small. Although polymorphisms and haplotypes of ABCB1 have been associated with alterations in drug disposition and drug response, including adverse events with various ABCB1 substrates in different ethnic populations, the results have been majorly conflicting, with limited clinical relevance. Future research activities are warranted, considering a deep-sequencing approach, as well as well-designed clinical studies with appropriate sample sizes to elucidate the impact of rare ABCB1 variants and their potential consequences for effect sizes.

Alternative matrices for therapeutic drug monitoring of immunosuppressive agents using LC-MS/MS

Immunosuppressive drugs used in solid organ transplants typically have narrow therapeutic windows and high intra- and intersubject variability. To ensure satisfactory exposure, therapeutic drug monitoring (TDM) plays a pivotal role in any successful posttransplant maintenance therapy. Currently, recommendations for optimum immunosuppressant concentrations are based on blood/plasma measurements. However, they introduce many disadvantages, including poor prediction of allograft survival and toxicity, a weak correlation with drug concentrations at the site of action and the invasive nature of the sample collection. Thus, alternative matrices have been investigated. This paper reviews tandem-mass spectrometry (LC-MS/MS) methods used for the quantification of immunosuppressant drugs utilizing nonconventional matrices, namely oral fluids, fingerprick blood and intracellular and intratissue sampling. The advantages, disadvantages and clinical application of such alternative mediums are discussed. Additionally, sample extraction techniques and basic chromatography information regarding these methods are presented in tabulated form.

A HuGE Review and Meta-Analyses of Genetic Associations in New Onset Diabetes after Kidney Transplantation

PURPOSE

New onset diabetes after transplantation (NODAT) is a serious complication following solid organ transplantation. There is a genetic contribution to NODAT and we have conducted comprehensive meta-analysis of available genetic data in kidney transplant populations.

METHODS

Relevant articles investigating the association between genetic markers and NODAT were identified by searching PubMed, Web of Science and Google Scholar. SNPs described in a minimum of three studies were included for analysis using a random effects model. The association between identified variants and NODAT was calculated at the per-study level to generate overall significance values and effect sizes.

RESULTS

Searching the literature returned 4,147 citations. Within the 36 eligible articles identified, 18 genetic variants from 12 genes were considered for analysis. Of these, three were significantly associated with NODAT by meta-analysis at the 5% level of significance; CDKAL1 rs10946398 p = 0.006 OR = 1.43, 95% CI = 1.11-1.85 (n = 696 individuals), KCNQ1 rs2237892 p = 0.007 OR = 1.43, 95% CI = 1.10-1.86 (n = 1,270 individuals), and TCF7L2 rs7903146 p = 0.01 OR = 1.41, 95% CI = 1.07-1.85 (n = 2,967 individuals).

CONCLUSION

Evaluating cumulative evidence for SNPs associated with NODAT in kidney transplant recipients has revealed three SNPs associated with NODAT. An adequately powered, dense genome-wide association study will provide more information using a carefully defined NODAT phenotype.

Genetics and nonmelanoma skin cancer in kidney transplant recipients

Kidney transplant recipients (KTRs) have a 65- to 250-fold greater risk than the general population of developing nonmelanoma skin cancer. Immunosuppressive drugs combined with traditional risk factors such as UV radiation exposure are the main modifiable risk factors for skin cancer development in transplant recipients. Genetic variation affecting immunosuppressive drug pharmacokinetics and pharmacodynamics has been associated with other transplant complications and may contribute to differences in skin cancer rates between KTRs. Genetic polymorphisms in genes encoding the prednisolone receptor, GST enzyme, MC1R, MTHFR enzyme and COX-2 enzyme have been shown to increase the risk of nonmelanoma skin cancer in KTRs. Genetic association studies may improve our understanding of how genetic variation affects skin cancer risk and potentially guide immunosuppressive treatment and skin cancer screening in at risk individuals.

Association of Extrarenal Adverse Effects of Posttransplant Immunosuppression With Sex and ABCB1 Haplotypes

Extrarenal adverse effects (AEs) associated with calcineurin inhibitor (CNI) and mycophenolic acid (MPA) occur frequently but are unpredictable posttransplant complications. AEs may result from intracellular CNI accumulation and low activity of P-glycoprotein, encoded by the ABCB1 gene. Since ABCB1 single nucleotide polymorphisms (SNPs) and sex influence P-glycoprotein, we investigated haplotypes and extrarenal AEs. A prospective, cross-sectional study evaluated 149 patients receiving tacrolimus and enteric coated mycophenolate sodium or cyclosporine and mycophenolate mofetil. Immunosuppressive AE assessment determined individual and composite gastrointestinal, neurologic, aesthetic, and cumulative AEs. Lipids were quantitated after 12-hour fast. ABCB1 SNPs: c.1236C>T (rs1128503), c.2677G>T/A (rs2032582), and c.3435C>T (rs1045642) were determined with haplotype associations computed using the THESIAS program, and evaluated by immunosuppression, sex and race using multivariate general linear models. Tacrolimus patients exhibited more frequent and higher gastrointestinal AE scores compared with cyclosporine with association to CTT (P = 0.018) and sex (P = 0.01). Aesthetic AE score was 3 times greater for cyclosporine with TTC haplotype (P = 0.005). Females had higher gastrointestinal (P = 0.022), aesthetic (P < 0.001), neurologic (P = 0.022), and cumulative AE ratios (P < 0.001). Total cholesterol (TCHOL), low-density lipoproteins (LDL), and triglycerides were higher with cyclosporine. The TTC haplotype had higher TCHOL (P < 0.001) and LDL (P = 0.005). Higher triglyceride (P = 0.034) and lower high-density lipoproteins (P = 0.057) were associated with TTT with sex-adjusted analysis. ABCB1 haplotypes and sex were associated with extrarenal AEs. Using haplotypes, certain female patients manifested more AEs regardless of CNI. Haplotype testing may identify patients with greater susceptibility to AEs and facilitate CNI individualization.

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.

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.

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.

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.

A functional common polymorphism of the ABCB1 gene is associated with chronic kidney disease and hypertension in Chinese

BACKGROUND

Permeability glycoprotein is encoded by the ATP-binding cassette B1 gene (ABCB1) and is an extruder of toxic metabolites in the kidney. A functional common polymorphism (C3435T, rs1045642) in the human ABCB1 gene has been found to be associated with allograft outcome in kidney transplant patients. In this study, we investigated the association of the C3435T polymorphism with renal function and blood pressure (BP) in 2 Chinese populations.

METHODS

The discovery and replication populations were recruited from a mountainous area (Zhejiang Province) and a newly urbanized suburban area (Shanghai), respectively. We genotyped all subjects using the ABI SNapShot method. Chronic kidney disease (CKD) was defined as an estimated glomerular filtration rate <60 ml/min × 1.73 m(2) or 24-hour urinary albumin excretion ≥30 mg.

RESULTS

In the discovery population of 1,987 subjects, after adjustment for covariables, TT homozygosity (n = 217) was associated with a higher risk of CKD (n = 369; odds ratio (OR) = 1.73; P = 0.003) and with higher systolic BP (+3.1 mm Hg; P = 0.03) and pulse pressure (+3.4 mm Hg; P = 0.001). These associations were dependent on age (Pint ≤ 0.05). In subjects aged ≥60 years (n = 374), the corresponding OR or difference was 2.40 for CKD, 15.1 mm Hg for systolic BP, and 12.4 mm Hg for pulse pressure (P < 0.001). In similar adjusted analyses in the replication population of 2,427 elderly (≥60 years) subjects, TT homozygosity was also associated with a higher risk of CKD (OR = 1.39; P = 0.02) and an enhanced association of hypertension with CKD (OR = 1.50; P = 0.04).

CONCLUSIONS

The ABCB1 C3435T polymorphism might predict CKD, especially in the elderly.

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.

CYP2C8*3 polymorphism and donor age are associated with allograft dysfunction in kidney transplant recipients treated with calcineurin inhibitors

Epoxieicosatrienoic acids (EETs) play a protective role against damaging processes in the kidney. We have assessed the effect of polymorphisms in EETs-producing enzymes (CYP2C8 and CYP2J2) and other proteins involved in calcineurin inhibitors (CNIs) disposition (CYP3A4, CYP3A5, and ABCB1) on graft function and clinical outcome in 166 renal transplant recipients treated with CNIs. Both CYP2C8*3 and donor age greater than 48 years were associated to a higher incidence of delayed graft function (DGF) [OR = 2.01 (1.1-4.1), P = .04 and 5.14 (2.4-10.9), P < .0001; respectively] and worse creatinine clearance 1 year after grafting (P < .05 and P < .001, respectively). In addition, carrying 4-6 variants in the 3 ABCB1 loci and older donor age were individually associated to higher incidence of calcineurin-inhibitor-induced nephrotoxicity [OR = 2.38 (1.1-5.4), P = .03 and OR = 1.03 (1.01-1.06), P = .038]. Regression analyses confirmed the relevant effect of both CYP2C8*3 and donor age on graft dysfunction. Carrying the 2C8*3 allele and having a donor older than 48 years was defined as a high-risk status and observed to be highly related to DGF [OR = 3.91 (1.46-10.48), P < .01] and worse creatinine clearance (P = .033). Our results show that genetic and clinical parameters can be combined to identify risk factors for allograft dysfunction in renal transplant recipients.

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.

Acute kidney injury in a preterm infant homozygous for the C3435T polymorphism in the ABCB1 gene given oral morphine

A 34-week infant born from a mother with a history of drug abuse developed neonatal abstinence syndrome (NAS) in the first hours of life. Urine drug screening was positive for cocaine and heroin. The infant developed acute kidney injury and bilateral hydronephrosis while receiving oral morphine for control of NAS. Cessation of morphine therapy and urinary catheterization resulted in a rapid and complete resolution of the symptoms. Our patient was homozygous for the C3435T polymorphism in the ABCB1 gene, a polymorphism previously associated with impaired P-glycoprotein activity. We hypothesize that acute renal toxicity was related to accumulation of morphine within urothelial cells due to genetically determined impaired P-glycoprotein activity.

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.

The new CYP3A4 intron 6 C>T polymorphism (CYP3A4*22) is associated with an increased risk of delayed graft function and worse renal function in cyclosporine-treated kidney transplant patients

OBJECTIVE

Cyclosporine A (CsA) is a substrate of cytochrome P450 3A4 (CYP3A4). Recently, a newly discovered intron 6 single-nucleotide polymorphism in CYP3A4 (rs35599367 C>T), defining the CYP3A4*22 allele, has been linked to reduced hepatic expression and activity of CYP3A4. In the present study, the clinical impact of this single-nucleotide polymorphism was investigated in a cohort of patients receiving a CsA-based immunosuppressive regimen.

MATERIALS AND METHODS

A total of 172 de-novo kidney transplant recipients, receiving CsA/mycophenolate mofetil as immunosuppressive therapy and participating in the Fixed-Dose Concentration Controlled study, were genotyped for the new CYP3A4*22 allele. CsA C(0) and/or C(2) levels were measured on days 3 and 10 and in months 1, 3, 6, and 12 after transplantation. Plasma creatinine concentrations, delayed graft function (DGF), and biopsy-proven acute rejection were recorded.

RESULTS

The CYP3A4*22 allele was significantly associated with a higher risk of DGF compared with the CYP3A4*1/*1 patients after adjustment for known risk factors [odds ratio (OR)=6.34, confidence interval (CI(95%): 1.38-29.3), P=0.015]. Mixed-model analysis demonstrated that the overall creatinine clearance was 20% lower in CYP3A4*22 allele carriers compared with CYP3A4*1/*1 patients [CI(95%) (-33.1 to -7.2%), P=0.002]. For ABCB1 3435C>T, T-variant carriers had a decreased risk of developing DGF compared with CC patients [CT: OR=0.30, CI(95%) (0.11-0.77), P=0.011; TT: OR=0.18, CI(95%) (0.05-0.67), P=0.011].

CONCLUSION

CYP3A4*22 constitutes a risk factor for DGF and worse creatinine clearance in patients receiving CsA-based immunosuppressive therapy. Therefore, pretransplant genotyping for the CYP3A4*22 allele might help clinicians to identify patients at risk of DGF and poor renal function when treated with CsA.

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.

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.

The genetics of kidney transplantation

Over the last decade, the search for gene variants with the potential to influence transplant outcomes or predispose individuals to host-recipient-related phenotypes has generated a considerable number of studies with conflicting results. Thousands of genotypes have been associated with complex traits related to transplant medicine, including acute rejection, immunosuppressive drug metabolism and side effects, infections, long-term outcomes, and cardiovascular complications. However, these efforts have given disappointing results, both in terms of gaining understanding of the biological basis of disease and in patient management. The methodological weaknesses that constitute the major limitations of most of these studies have been discussed widely. A new generation of approaches is needed to understand the relationship between gene variants and complex kidney transplantation traits. These approaches should be global, to generate original pathophysiological hypotheses, and should rely on advanced genomic tools, including Genome Wide Association studies and Whole Genome Sequencing technologies. Such enterprises will only be successful with the creation of international consortiums that connect partners in clinical, industrial, and academic transplant medicine.

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.

Deciphering calcineurin inhibitor nephrotoxicity: a pharmacological approach

The calcineurin inhibitors ciclosporin and tacrolimus are used to prevent acute rejection of solid organs after transplantation. Their use can lead to chronic renal damage characterized by progressive and irreversible deterioration of renal function associated with interstitial fibrosis, tubular atrophy, arteriolar hyalinosis and glomerulosclerosis. Many approaches to better understand the mechanisms of this toxicity are in use. The aim of these approaches is to find biomarkers of early kidney injury and potential therapeutic targets. Despite these efforts, the biological processes leading to calcineurin inhibitor nephrotoxicity remain poorly understood. Furthermore, the diagnosis of chronic renal damage remains inaccurate without definitive diagnostic tools, no effective prevention exists and a therapy to treat the damage has yet to be developed. In this article, theories of pharmacodynamics, pharmacokinetics, therapeutic drug monitoring and pharmacogenetics are synthesized in ways that may improve the understanding of mechanisms leading to calcineurin inhibitor toxicity. The importance of global approaches such as toxicogenomics is emphasized to characterize early cellular responses implicated in calcineurin inhibitor nephrotoxicity.

Do drug transporter (ABCB1) SNPs influence cyclosporine and tacrolimus dose requirements and renal allograft outcome in the posttransplantation period?

Polymorphisms in the drug transporter gene (ABCB1) may play a significant role in individualizing cyclosporine (CsA) and tacrolimus (Tac) dosage and subsequently the allograft outcome in renal transplant recipients. In total, 225 recipients on CsA and 75 on Tac-based immunosuppression regimen were recruited, and 6 common polymorphic sites in the ABCB1 gene were analyzed for association with dose-adjusted levels of CsA/Tac. Furthermore, association of ABCB1 single-nucleotide polymorphisms (SNPs) with allograft outcome was examined. GG and CC genotype patients at ABCB1 2677G>T and ABCB1 3435C>T were associated with lower dose-adjusted levels of CsA and Tac at 1 month (P = .057, P = .034), 3 months (P = .001, P = .015), and 6 months (P = .043) posttransplantation. Wild-type patients at 1236C>T (log P = .025) and 2677G>T (log P = .002) in CsA and 2677G>T (log P = .008) and 3435C>T (log P = .015) in Tac therapy patients demonstrated lower mean time to allograft rejection. No influence of ABCB1 haplotypes on CsA/Tac dose-adjusted levels was observed. Wild-type patients at ABCB1 2677G>T and 3435C>T were associated with lower dose-adjusted levels and thereby were at increased risk of allograft rejection because of under-immunosuppression in the early part of posttransplantation. Thus, genetic evaluation may be helpful to identify patients at risk for allograft rejection and also to individualize immunosuppressant dosing.

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.