The MDR1/ABCB1 Gene, a High-Impact Risk Factor for Cardiac Transplant Rejection

Advancement of Heart Transplantation in Thai Recipients: Survival Trends and Pharmacogenetic Insights

Since 1987, King Chulalongkorn Memorial Hospital (KCMH) has performed a substantial number of heart transplants as a specific therapy for advanced-stage heart failure. This descriptive study aimed to analyze post-transplant survival in the recent era compared to earlier periods and examine the pharmacogenetics of related immunosuppressants. Data from all recipients who underwent heart transplants from 1987 to 2021 were retrospectively retrieved from the electronic medical record. The genotypes of relevant pharmacogenes were analyzed in recipients who were alive during the enrollment period. Kaplan-Meier analysis revealed improved overall survival rates in the recent era compared to the past. Dilated cardiomyopathy was identified as the most common pretransplant diagnosis, while infection remained the leading cause of mortality. In conclusion, the findings demonstrate significant advancements in the quality of heart transplantation in Thailand. Future studies are warranted to explore the correlation between pharmacogenetic variations identified in this study and subsequent clinical outcomes, with a focus on genetic-guided treatment to optimize patient care.

Cannabis Pharmacogenomics: A Path to Personalized Medicine

Cannabis and related compounds have created significant research interest as a promising therapy in many disorders. However, the individual therapeutic effects of cannabinoids and the incidence of side effects are still difficult to determine. Pharmacogenomics may provide the answers to many questions and concerns regarding the cannabis/cannabinoid treatment and help us to understand the variability in individual responses and associated risks. Pharmacogenomics research has made meaningful progress in identifying genetic variations that play a critical role in interpatient variability in response to cannabis. This review classifies the current knowledge of pharmacogenomics associated with medical marijuana and related compounds and can assist in improving the outcomes of cannabinoid therapy and to minimize the adverse effects of cannabis use. Specific examples of pharmacogenomics informing pharmacotherapy as a path to personalized medicine are discussed.

Pharmacogenetic Study of the Impact of ABCB1 Single Nucleotide Polymorphisms on the Response to Cyclosporine in Psoriasis Patients

Psoriasis is a chronic, T cell-mediated skin disease affecting 2-3% of the Caucasian population. Cyclosporine A is a calcineurin inhibitor that acts selectively on T cells. The cyclosporine A treatment response has been suggested to be modulated by single-nucleotide polymorphisms (SNPs) in the ABCB1 gene. The aim of this research was to evaluate the effect of ABCB1 genetic variants that could affect the response to a cyclosporine treatment in Russian psoriasis patients with the ABCB1 genotype status. The ABCB1 T-129C, G1199A, C1236T, G2677T/A and C3435T SNPs in the 168 patients with psoriasis were genotyped by PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism) and TaqMan SNP genotyping assays. The ABCB1 C1236T, G2677T/A and C3435T SNPs were significantly associated with a negative response to cyclosporine therapy. A very strong association was evident for the C3435T SNP in the ABCB1 gene in the allele, dominant and recessive models (OR = 2.58, OR = 4.01, OR = 2.50, respectively). ABCB1 C1236T and G2677T/A polymorphisms were significantly associated with a negative response to the cyclosporine therapy in the codominant, dominant and recessive models (p ˂ 0.05). Additionally, the haplotype analysis identified that the TGC haplotype is significantly associated with a negative response to cyclosporine therapy in psoriasis patients (p ˂ 0.05). The current study to the best of our knowledge is the first of its kind to be performed in the Russian population. In conclusion, the present results suggest an association between the ABCB1 genetic variants and unresponsiveness to cyclosporine in the Russian population. Further, larger studies are necessary to confirm our findings and replicate them in various ethnic populations before its implementation in the clinical practice.

Non-HLA Genetic Factors and Their Influence on Heart Transplant Outcomes: A Systematic Review

Supplemental digital content is available in the text.

Background

Improvement of immunosuppressive therapies and surgical techniques has increased the survival rate after heart transplantation. Nevertheless, a large number of patients still experience complications, such as allograft rejection, vasculopathy, kidney dysfunction, and diabetes in response to immunosuppressive therapy. Variants in HLA genes have been extensively studied for their role in clinical outcomes after transplantation, whereas the knowledge about non-HLA genetic variants in this setting is still limited. Non-HLA polymorphisms are involved in the metabolism of major immunosuppressive therapeutics and may play a role in clinical outcomes after cardiac transplantation. This systematic review summarizes the existing knowledge of associations between non-HLA genetic variation and heart transplant outcomes.

Methods

The current evidence available on genetic polymorphisms associated with outcomes after heart transplantation was identified by a systematic search in PubMed and Embase. Studies reporting on polymorphisms significantly associated with clinical outcomes after cardiac transplantation were included.

Results

A total of 56 studies were included, all were candidate gene studies. These studies identified 58 polymorphisms in 36 genes that were associated with outcomes after cardiac transplantation. Variants in TGFB1, CYP3A5, and ABCB1 are consistently replicated across multiple studies for various transplant outcomes.

Conclusions

The research currently available supports the hypothesis that non-HLA polymorphisms are associated with clinical outcomes after heart transplantation. However, many genetic variants were only identified in a single study, questioning their true effect on the clinical outcomes tested. Further research in larger cohorts with well-defined phenotypes is warranted.

High intra-individual variability of cyclosporine pharmacokinetics in lung transplant recipients without cystic fibrosis

BACKGROUND

There has been little study on the variability of CsA pharmacokinetics in stable lung transplant (LT) recipients without cystic fibrosis. This study was conducted to determine the prevalence of high intra-individual variability of CsA in LT recipients and its implications in CsA monitoring.

METHODS

Twenty-nine pharmacokinetic curves were performed in 10 consecutive stable patients from a single center. The intra-individual coefficient of variation (CV) of the AUC₀₋₁₂ h was calculated in each case. Patients were grouped according to whether their CV was high (≥20%) or low (<20%). Correlations between cyclosporine CsA concentration at each time point, AUC₀₋₄ h , and AUC₀₋₁₂ h were also calculated.

RESULTS

Six (60%) patients presented low CVs and four (40%) high CVs. In patients with low CVs, the best correlation of AUC₀₋₁₂ h was with CsA concentration at two h post-dose (C₂) (r = 0.674, p = 0.002), whereas in those with high CV, the best correlation was with C5 (r = 0.800, p = 0.003). In the latter group, the correlation with C₂ was low (r = 0.327, p = 0.32), whereas the correlation with C₀ was high (r = 0.709, p < 0.05).

CONCLUSIONS

Intra-individual variability of CsA pharmacokinetics may be high in many LT recipients. In patients with high CV, the use of C₀ levels may be more appropriate for CsA monitoring than C₂ levels.

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.

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.

Renal function in the long term after pediatric liver transplantation: is there a need for protocol kidney biopsies?

PURPOSE OF REVIEW

With improving survival rates following solid organ transplantation, assessment of its success has broadened with a focus on long-term outcomes, including nongraft-related medical outcomes and family and patient perceptions of quality of life. Posttransplant renal dysfunction contributes to long-term morbidity and mortality following pediatric liver transplantation. In this review, we provide an overview of our understanding and approach to managing posttransplant renal dysfunction and highlight the existing gaps in knowledge in this area.

RECENT FINDINGS

The literature regarding renal dysfunction following liver transplant primarily focuses on the experience in the adult population. Studies on children are limited by small numbers and varying definitions of outcomes. Thus, lessons in the current literature must be closely examined before they can be extrapolated and applied to children.

SUMMARY

The current literature validates that posttransplant renal dysfunction is a frequent and important outcome for adults and children. Although the characteristics of children at high risk are less clear, calcineurin inhibitor minimization is considered a viable strategy for preserving renal function. The risk-benefit ratio of kidney biopsy in children and the possibility of renal preservation via immunosuppression withdrawal are intriguing concepts that remain to be defined.

Genetics and genomics in human lung transplantation

Lung transplantation is the only effective treatment for many advanced lung diseases. However, long-term survival after transplantation remains relatively poor, thus limiting the application of lung transplantation to patients with end-stage disease only. Acute and chronic rejection is the main reason for allograft failure. Attempts to treat or prevent rejection have been stymied by our incomplete understanding of the mechanisms leading to this devastating complication and the lack of representative animal models. A systems-biology approach to lung transplantation with the use of genomics and gene expression profiling has led to new insights into the pathogenesis of rejection, by elucidating the mechanisms of T-cell activation and uncovering the role of B cells and innate immunity. Systems-biology approaches, such as genetics and genomics, may allow minimally invasive diagnosis of rejection and permit individually tailored immunosuppressive regimens. Herein we review the emerging application of genomics and genetics to human lung transplantation and highlight the tremendous potential for these approaches to enhance clinical practice and augment our understanding of basic transplant biology.

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.

Update on the clinical pharmacogenomics of organ transplantation

Organ transplantation suffers from a static graft and patient survival rate, and a high incidence of serious adverse drug effects. The pharmacogenomics of organ transplantation has emerged only recently and is complementary to the immunogenetic information that has accumulated over the past decade. Gene polymorphism studies have focused on the genes that interact across the group of immunosuppressants, including ciclosporin, tacrolimus, sirolimus and corticosteroids. The polymorphisms that hold the most potential for use in a drug selection algorithm are in genes CYP3A5, ABCB1, IMPDH1 and IMPDH2, and cytokines and growth factors. Gene-expression arrays have led to gene-expression testing, such as the use of AlloMap((R)) with heart transplant patients. The expanded use of gene-expression assays, proteomics and drug selection algorithms in organ transplantation will progress slowly and may be outpaced by drug test co-development programs for new transplant drugs. In the future, clinical pharmacogenomics will be a routine part of patient care for organ transplant patients.

New insights into the pharmacokinetics and pharmacodynamics of the calcineurin inhibitors and mycophenolic acid: possible consequences for therapeutic drug monitoring in solid organ transplantation

Although therapeutic drug monitoring (TDM) of immunosuppressive drugs has been an integral part of routine clinical practice in solid organ transplantation for many years, ongoing research in the field of immunosuppressive drug metabolism, pharmacokinetics, pharmacogenetics, pharmacodynamics, and clinical TDM keeps yielding new insights that might have future clinical implications. In this review, the authors will highlight some of these new insights for the calcineurin inhibitors (CNIs) cyclosporine and tacrolimus and the antimetabolite mycophenolic acid (MPA) and will discuss the possible consequences. For CNIs, important relevant lessons for TDM can be learned from the results of 2 recently published large CNI minimization trials. Furthermore, because acute rejection and drug-related adverse events do occur despite routine application of CNI TDM, alternative approaches to better predict the dose-concentration-response relationship in the individual patient are being explored. Monitoring of CNI concentrations in lymphocytes and other tissues, determination of CNI metabolites, and CNI pharmacogenetics and pharmacodynamics are in their infancy but have the potential to become useful additions to conventional CNI TDM. Although MPA is usually administered at a fixed dose, there is a rationale for MPA TDM, and this is substantiated by the increasing knowledge of the many nongenetic and genetic factors contributing to the interindividual and intraindividual variability in MPA pharmacokinetics. However, recent, large, randomized clinical trials investigating the clinical utility of MPA TDM have reported conflicting data. Therefore, alternative pharmacokinetic (ie, MPA free fraction and metabolites) and pharmacodynamic approaches to better predict drug efficacy and toxicity are being explored. Finally, for MPA and tacrolimus, novel formulations have become available. For MPA, the differences in pharmacokinetic behavior between the old and the novel formulation will have implications for TDM, whereas for tacrolimus, this probably will not to be the case.

Haplotypic structure of ABCB1/MDR1 gene modifies the risk of the acute allograft rejection in renal transplant recipients

BACKGROUND

Bioavailability of tacrolimus (Tac) and cyclosporine is determined by cytochrome P450IIIA and by P-glycoprotein encoded by the CYP3A4/CYP3A5 and ABCB1 genes. Polymorphisms in these genes have been suggested to influence acute rejection and pharmacokinetics in renal transplantation. We aimed to validate these findings in a haplotype analysis.

METHODS

A total of 832 renal transplant recipients were genotyped for the CYP3A4 -288A>G, CYP3A5 +6986G>A, ABCB1 +1236C>T, +2677G>T>A, and +3435C>T polymorphisms. Their association with acute rejection and with pharmacokinetic parameters was analyzed in haplotype models.

RESULTS

Apart from human leukocyte antigen-DR mismatches, delayed graft function and age at renal transplantation, acute rejection was also predicted by the [ABCB1 +1236C; +2677G; +3435T] haplotype. Allograft survival was determined by donor age, age at renal transplantation, delayed graft function, cold ischemia, and history of more than two acute rejections. Homozygotes for the [CYP3A4 -288A; CYP3A5 +6986G] haplotype achieved earlier therapeutic concentrations of Tac and a higher concentration to dose ratio at week 1. ABCB1 haplotypes did not influence pharmacokinetic parameters.

CONCLUSIONS

ABCB1 haplotypes modify the risk of acute rejection, suggesting that ABCB1 allelic arrangement is a stronger regulator of P-glycoprotein activity than single polymorphisms. The risk of acute rejection determined by ABCB1 is independent of pharmacokinetic parameters. CYP3A haplotypes control the bioavailability of Tac, but do not modify the risk of acute rejection.

Pharmacogenetics of immunosuppressants: progress, pitfalls and promises

Most of the immunosuppressants used in organ transplantation are characterized by a narrow therapeutic index, whereby underdosing is associated with increased risk of rejection episodes and overdosing may exacerbate drug-related toxicity. Pharmacogenetics--complementary to pharmacokinetics--holds the potential to allow individualized dosing of immunosuppressive agents to optimize their therapeutic actions while minimizing adverse effects. Most of the studies have focused on polymorphisms of genes involved in drug metabolism and distribution, but as of now, only thiopurine-S-methyltransferase and cytochrome P 450 3A5 genotypes appear to have sufficiently large influence to have potentialities in guiding drug dosing. This may reflect the fact that available information from other polymorphisms derives almost exclusively from retrospective observations or from studies with important methodological biases. Active investigations aimed at identifying allelic variants of gene encoding for the pharmacologic targets are now ongoing. Recent studies have demonstrated that also donor genotype may play a significant role in immunosuppressive drug pharmacokinetics and pharmacodynamics. As one of the main future tasks, it is mandatory to develop mathematical models able to incorporate multiple gene polymorphisms with pharmacokinetic data and other critical information, providing algorithms able to individualize the best immunosuppressive therapy for each patient before transplantation.

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

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

Influence of ABCB1 genetic polymorphisms on cyclosporine intracellular concentration in transplant recipients

OBJECTIVE

The expression on lymphocytes of P-glycoprotein, an efflux transporter encoded by the ABCB1 gene, might influence cyclosporine intracellular concentration.

METHODS

ABCB1 genotypes, cyclosporine intracellular and blood concentrations were determined in 64 stable renal, liver or lung transplant recipients.

RESULTS

Cyclosporine intracellular concentration correlated moderately with blood concentration (r=0.30, P<0.00005). The ABCB1 1199A carriers presented a 1.8-fold decreased cyclosporine intracellular concentration (P=0.04), whereas the 3435T carriers presented a 1.7-fold increase (P=0.02) as well as a 1.2-fold increased blood concentration (P=0.04). In contrast, ABCB1 61A>G, 1236C>T and 2677G>T polymorphisms did not influence cyclosporine intracellular and blood concentrations.

CONCLUSION

This is the first report demonstrating that ABCB1 polymorphisms influence cyclosporine intracellular concentration. Interestingly, its influence on intracellular concentration is significantly higher than on blood concentration (P<0.002). This may therefore modulate cyclosporine immunosuppressive activity.