Pharmacogenetics in immunosuppressants: impact on dose requirement of calcineurin inhibitors in renal and liver pediatric transplant recipients

P450 oxidoreductase *28 (POR*28) and tacrolimus disposition in pediatric kidney transplant recipients--a pilot study

BACKGROUND

Both age and CYP3A5 genotype are important determinants of tacrolimus disposition in pediatric kidney transplant recipients. In a recent study in adults, POR*28 was associated with increased dosing requirements early after transplant of CYP3A5-expressing kidney transplant recipients. The authors aimed to evaluate the additional contribution of POR*28 to early tacrolimus disposition in pediatric kidney transplant recipients.

METHODS

Retrospective data of 43 pediatric kidney transplant recipients up to 14 days posttransplant were evaluated on tacrolimus dose and tacrolimus predose blood concentrations. Recipient POR*28 and CYP3A5 genotype were determined.

RESULTS

CYP3A5 expressers carrying at least 1 POR*28 allele had on average 18.3% lower tacrolimus predose concentrations and 20.2% lower concentration/dose ratios compared with CYP3A5 expressers with POR*1/*1 genotype (P = 0.002 and P = 0.001, respectively). In CYP3A5 nonexpressers, tacrolimus disposition did not significantly differ between POR genotypes.

CONCLUSIONS

In this small cohort of pediatric kidney transplant recipients, POR*28 genotype seems to explain part of the variability found in tacrolimus disposition, in addition to age and CYP3A5 genotype. This finding should be validated in a larger population, and it would be worthwhile to evaluate the clinical impact of this genotype.

Tacrolimus dose requirement in pediatric liver transplantation: influence of CYP3A5 gene polymorphism

AIM

Little information is available regarding the influence of CYP3A5 genetic polymorphisms on tacrolimus dose requirement in pediatric liver transplantation.

PATIENTS & METHODS

We performed a retrospective study among 179 pediatric liver recipients grafted between 2002 and 2009 in order to determine the influence of donor CYP3A5 genotype along with clinical variables on tacrolimus daily dose requirement during the first weeks following transplantation.

RESULTS

Mean stable tacrolimus daily dose requirement was higher among children who received a liver expressing CYP3A5 (carrying the CYPA3A5*1 allele) compared with those with a liver that did not express CYP3A5 (CYP3A5*3/*3 genotype): 0.29 ± 0.20 vs 0.18 ± 0.13 mg.kg(-1).d(-1), p = 0.005, respectively. A younger recipient age and fluconazole prescription were also significantly associated with tacrolimus daily dose requirement. Time to reach stable tacrolimus therapeutic trough concentrations was prolonged among patients with a CYP3A5-expressing graft (26 vs 21 days, p = 0.04).

CONCLUSION

Donor CYP3A5 genotype partially explains tacrolimus dose requirement. Original submitted 30 January 2013; Revision submitted 2 May 2013.

Pharmacogenomics and pharmacoepigenomics in pediatric medicine

In the past several years, human genetics studies have progressed from monogenic to complex and common diseases because of the advancement in technologies. There is increased knowledge of the pharmacokinetics and pharmacogenomics of the drugs in adults as well as in children. These technological developments provided new diagnostic, prognostic, and therapeutic opportunities. We are now in a position to address many additional ambitious questions. For instance, in clinical medicine, interindividual variation in drug response is a major problem. Some of the heterogeneity of drug safety and efficacy among individuals can be explained by pharmacogenomics. It has also the potential to improve the treatment in both adults and children. In pediatrics however, there is ontogeny and metabolic capacity in children is different compared to adults. Several specific developmental changes may underlie some of the variability in drug response seen in children. They may also be responsible for adverse drug reactions (ADRs). Therefore, much of the diversity in drug effects cannot be explained by studying the genomic diversity alone. It is necessary to include the effect of growth (involves variations in gene expression) along with genetic differences when explaining the variability in treatment response. In this respect epigenomics may expand the scope of pharmacogenomics towards optimization of drug therapy. Future studies must focus on periods of maturation of the drug-metabolizing enzymes and polymorphisms in their genes by using candidate gene approach, gene expression analysis, genome-wide haplotype mapping, and proteomics. The integration of genetic data and clinical phenotypes along with the role of other factors is necessary to evaluate both efficacy and ADRs of any drug. It may require extensive genetic epidemiological studies spanning over many years.

Impact of donor and recipient CYP3A5 and ABCB1 genetic polymorphisms on tacrolimus dosage requirements and rejection in Caucasian Spanish liver transplant patients

Studies of liver transplant (LT) patients, mainly in Asians, have evaluated the influence of the CYP3A5*1 allele and P-glycoprotein gene ABCB1 on tacrolimus pharmacokinetics or biopsy-proven acute rejection (BPAR) incidence, with no conclusive results. To investigate these issues, 98 Caucasian Spanish LT patients with tacrolimus, mycophenolate mofetil and steroids and 88 cadaveric donors were genotyped for the SNPs CYP3A5 6986G>A, ABCB1 1236C>T, ABCB1 2677G>A/T and ABCB1 3435C>T;. On day 7 post-LT, patients with a native CYP3A5*1 allele had significantly lower tacrolimus trough concentrations C0 (P = .03) and dose-adjusted concentrations C0 /D (P = .02) than CYP3A5 *3/*3 homozygotes. Three months post-LT, patients carrying a liver with CYP3A5*1 had significantly lower C0 /D (P = .03) and took significantly higher tacrolimus doses (P = .03) than the corresponding *3/*3 homozygotes. ABCB1 SNPs showed no significant association with tacrolimus variables. The 3-month incidence of BPAR was 10.2%, with no statistically significant differences related to CYP3A5 (14.3% in expresser vs. 9.5% in non-expresser) or ABCB1 genotype of either patient or donor. We conclude that in Caucasian Spanish LT patients, a native or graft-borne CYP3A5*1 allele tends to lower tacrolimus concentrations and increase dosage needs, but has no significant impact on the incidence of BPAR.

Immune function assay (ImmuKnow) as a predictor of allograft rejection and infection in kidney transplantation

BACKGROUND

The Cylex ImmuKnow (IK) assay provides a rapid and quantitative assessment of T-cell-mediated immune function. Studies have shown correlations between ImmuKnow assay and adverse events, such as immunosuppression and low or high calcineurin inhibitor trough levels. We investigated the correlation between IK changes and rejection or infection in kidney transplant patients and studied the potential application of the IK assays in optimizing individual immunosuppressive therapy.

METHODS

ImmuKnow assay was used to determine dynamic intracellular ATP changes in CD4 cells in 193 samples from 42 kidney transplant patients and 25 healthy subjects. Patients were categorized into rejection, infection, and event-free groups. The IK values were assayed and analyzed between kidney transplant patients and healthy controls.

RESULTS

Most IK values fell between 200 and 599 ng/mL from pre-transplantation to 30 months post-transplantation. The mean IK values continuously increased throughout 30 months. Incidental allograft rejection patients had significantly higher IK values compared with the event-free patients and controls. However, infection patients had significantly lower IK values. Seven days after treatment, IK values in rejection/infection patients were different compared with the values in autograft patients, and there was a significant correlation between calcineurin inhibitor (FK506) trough levels and IK values in rejection/infection patients. Serum creatinine levels in the rejection patients were significantly higher than those in the event-free patients, and C-reactive protein levels were significantly higher in the infection patients compared with the event-free patients.

CONCLUSIONS

The IK assay combined with other biomarkers can be used to identify kidney transplant patients at high risk of rejection and infection.

Serologic vaccination response after solid organ transplantation: a systematic review

BACKGROUND

Infectious diseases after solid organ transplantation (SOT) are one of the major complications in transplantation medicine. Vaccination-based prevention is desirable, but data on the response to active vaccination after SOT are conflicting.

METHODS

In this systematic review, we identify the serologic response rate of SOT recipients to post-transplantation vaccination against tetanus, diphtheria, polio, hepatitis A and B, influenza, Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitides, tick-borne encephalitis, rabies, varicella, mumps, measles, and rubella.

RESULTS

Of the 2478 papers initially identified, 72 were included in the final review. The most important findings are that (1) most clinical trials conducted and published over more than 30 years have all been small and highly heterogeneous regarding trial design, patient cohorts selected, patient inclusion criteria, dosing and vaccination schemes, follow up periods and outcomes assessed, (2) the individual vaccines investigated have been studied predominately only in one group of SOT recipients, i.e. tetanus, diphtheria and polio in RTX recipients, hepatitis A exclusively in adult LTX recipients and mumps, measles and rubella in paediatric LTX recipients, (3) SOT recipients mount an immune response which is for most vaccines lower than in healthy controls. The degree to which this response is impaired varies with the type of vaccine, age and organ transplanted and (4) for some vaccines antibodies decline rapidly.

CONCLUSION

Vaccine-based prevention of infectious diseases is far from satisfactory in SOT recipients. Despite the large number of vaccination studies preformed over the past decades, knowledge on vaccination response is still limited. Even though the protection, which can be achieved in SOT recipients through vaccination, appears encouraging on the basis of available data, current vaccination guidelines and recommendations for post-SOT recipients remain poorly supported by evidence. There is an urgent need to conduct appropriately powered vaccination trials in well-defined SOT recipient cohorts.

Intracellular ATP production in CD4+ T cells as a predictor for infection and allograft rejection in trough-level guided pediatric liver transplant recipients under calcineurin-inhibitor therapy

BACKGROUND

The assessment of cell-mediated immune responses through the measurement of intracellular adenosine-tri-phosphate (iATP) production (Cylex ImmuKnow) as a pharmacodynamic biomarker of immune function represents a potential tool to optimize individual immunosuppressive therapy independent of drug dosage or trough levels. This study aims to investigate the correlations between iATP and adverse events, immunosuppression, calcineurin-inhibitor-trough levels, and age.

METHODS

In this prospective trial, 31 nontransplant pediatric subjects and 50 consecutive children were included after they underwent liver transplantation (LTX). During the study period, 4 allograft rejections and 3 acute infections occurred. The patients were treated with cyclosporine, tacrolimus, mycophenolate mofetil, and everolimus either as monotherapy or in combinations. The reactivity of the immune system was measured as iATP concentration in CD4+ T-cells after in vitro stimulation by phytohemagglutinin.

RESULTS

The iATP concentrations in patients with intercurrent, clinically significant infections were in the low immune response range (median iATP 181 versus 251 ng/mL, P = 0.308), whereas the patients with incidental allograft rejection had significantly higher iATP concentrations as compared with the event-free group (median iATP 444 versus 251 ng/mL, P = 0.017). However, there was a wide range of iATP concentrations in both nontransplant and LTX patient groups, and no clear iATP cut-off values for an increased risk of infection or rejection could be defined. Post LTX, stable-phase patients showed a significantly lower iATP compared with respective controls (median iATP 297 versus 384 ng/mL, P = 0.013). No significant correlation between calcineurin-inhibitor-trough concentrations and iATP was found. iATP was not correlated with age, but was inversely correlated with time after transplantation.

CONCLUSIONS

The observed correlation between clinical events and iATP concentrations is similar to the findings previously reported in adult patients who underwent transplantation. The lack of correlation of iATP with trough drug concentrations suggests that the ImmuKnow assay provides independent information that may be useful to guide immunosuppressive therapy in pediatric (liver) transplant patients. However, the wide range of iATP levels in event-free patients suggests that serial iATP measurements will be necessary to assess and guide the individual immunosuppressive therapy. Further investigations are needed to evaluate and extend these findings.

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.

The interactions of age, genetics, and disease severity on tacrolimus dosing requirements after pediatric kidney and liver transplantation

Purpose

In children, data on the combined impact of age, genotype, and disease severity on tacrolimus (TAC) disposition are scarce. The aim of this study was to evaluate the effect of these covariates on tacrolimus dose requirements in the immediate post-transplant period in pediatric kidney and liver recipients.

Methods

Data were retrospectively collected describing tacrolimus disposition, age, CYP3A5 and ABCB1 genotype, and pediatric risk of mortality (PRISM) scores for up to 14 days post-transplant in children receiving liver and renal transplants. Initial TAC dosing was equal in all patients and adjusted using therapeutic drug monitoring. We determined the relationship between covariates and tacrolimus disposition.

Results

Forty-eight kidney and 42 liver transplant recipients (median ages 11.5 and 1.5 years, ranges 1.5–17.7 and 0.05–14.8 years, respectively) received TAC post-transplant. In both transplant groups, younger children (<5 years) needed higher TAC doses than older children [kidney: 0.15 (0.07–0.35) vs. 0.09 (0.02–0.20) mg/kg/12h, p = 0.046, liver: 0.12 (0.04–0.32) vs. 0.09 (0.01–0.18) mg/kg/12h, p = 0.038]. In kidney but not liver transplants, CYP3A5 expressors needed significantly higher TAC doses than nonexpressors [0.15 (0.07–0.20) vs. 0.09 (0.02–0.35) mg/kg/12h, P = 0.001]. In these patients, age and CYP3A5 genotype were independently associated with TAC dosing requirement. In liver, but not kidney transplant patients, homozygous ABCB1 T-T-T haplotype carriers needed higher TAC doses than noncarriers [0.26 (0.15–0.32) vs. 0.11 (0.01–0.25) mg/kg/12h, p = 0.013].

Conclusion

CYP3A5 genotype may explain variation in tacrolimus disposition early after transplant in pediatric kidney recipients, independent of age-related variation. In contrast, in pediatric liver recipients, variation in tacrolimus disposition appears related to age and ABCB1 genotype. These findings illustrate the importance of the interplay among age, genotype, and transplant organ on tacrolimus disposition.