Pharmacokinetic considerations related to therapeutic drug monitoring of tacrolimus in kidney transplant patients

The gut microbiome in solid organ transplantation

Despite ground-breaking advances in allogeneic transplantation, allograft rejection and immunosuppressant-specific complications remain a major challenge in transplant medicine. Growing evidence suggests the human gut microbiome as a potential contributor to transplant outcome and patient health. After breakthrough findings in haematopoietic stem cell transplantation (HSCT), the relevance of the microbiome in solid organ transplantation (SOT) is becoming increasingly clear. Here, we review the role of the microbiome in SOT focusing on its significance for transplant-associated complications such as allograft rejection and infections, and highlight its potential impact on immunosuppressive treatment. Moreover, we shed light on the emerging role of the microbiome as a diagnostic biomarker and therapeutic target and discuss current microbial intervention strategies. In addition, this review includes some practical considerations in designing clinical microbiome trials and offers some advice for the interpretation of the resulting data. Further investigation of the gut microbiome harbours countless clinical application possibilities and holds great promise of having a lasting impact on transplant medicine.

Effects of antifungal drugs on the plasma concentrations and dosage of tacrolimus in kidney transplant patients

OBJECTIVES

Tacrolimus is one of the three basic immunosuppressants used following kidney transplantation, and its plasma concentration is susceptible to antifungal drugs. Abnormal tacrolimus concentrations may lead to adverse outcomes for patients. Adjustment of the tacrolimus dose after administering antifungal drugs to patients with fungal infection after transplantations therefore has important clinical significance. Our objective is to measure the impact of antifungal drugs on the plasma concentration of tacrolimus in kidney transplant patients.

METHODS

A retrospective study was carried out in 109 kidney transplant recipients treated with a tacrolimus-based regimen and antifungal drugs simultaneously. Tacrolimus levels and dosage requirements were compared before and during antifungal therapy.

RESULTS

The plasma levels of tacrolimus were significantly increased after the combination with voriconazole and fluconazole (p<0.05). Consequently, the daily dose of tacrolimus was significantly reduced after the combination (p<0.05). However, although the tacrolimus concentration was significantly decreased after the administration of caspofungin (p<0.05), no apparent change in the daily dose of tacrolimus was found. Moreover, there were no significant changes in the tacrolimus levels and the daily dose after the combination with micafungin (p>0.05).

CONCLUSIONS

Our results suggest that there is considerable variability in the interaction between tacrolimus and different antifungal drugs. The dose of tacrolimus should be reduced by two-thirds and one-third before the combination with voriconazole and fluconazole, respectively. It is not recommended that the dose should be adjusted before combination with other antifungal drugs, and the dose should be adjusted under the guidance of therapeutic drug monitoring.

Effect of CYP3A5 on the Once-Daily Tacrolimus Conversion in Stable Liver Transplant Patients

Cytochrome P450 (CYP) 3A5 polymorphism influences tacrolimus metabolism, but its effect on the drug pharmacokinetics in liver transplant recipients switched to once-daily extended-release formulation remains unknown. The aim of this study is to analyze the effect of CYP3A5 polymorphism on liver function after once-daily tacrolimus conversion in liver transplant patients. A prospective open-label study included 60 stable liver transplant recipients who underwent 1:1 conversion from twice-daily tacrolimus to once-daily tacrolimus. All participants were genotyped for CYP3A5 polymorphism. The study was registered at ClinicalTrials.gov (NCT 02882113). Twenty-eight patients were enrolled in the CYP3A5 expressor group and 32 in the non-expressor group. Although there was no statistical difference, incidence of liver dysfunction was higher in the expressor group than in the non-expressor group when converted to once-daily extended-release tacrolimus (p = 0.088). No biopsy-proven acute rejection, graft failure, and mortality were observed in either group. The decrease in dose-adjusted trough level (−42.9% vs. −26.1%) and dose/kg-adjusted trough level of tacrolimus (−40.0% vs. −23.7%) was significantly greater in the expressor group than in the non-expressors after the conversion. A pharmacokinetic analysis was performed in 10 patients and tacrolimus absorption in the non-expressor group was slower than in the expressor group. In line with this observation, the area under the curve for once-daily tacrolimus correlated with trough level (Cmin) in the non-expressors and peak concentration (Cmax) in the expressors. CYP3A5 genotyping in liver transplant recipients leads to prediction of pharmacokinetics after switching from a twice-daily regimen to a once-daily dosage form, which makes it possible to establish an appropriate dose of tacrolimus.

Severe proteinuria during the administration of bevacizumab plus mFOLFOX6 in a colorectal cancer patient after kidney transplantation: a case report

Background

Bevacizumab (BEV) leads to proteinuria and renal damage. It is not clear whether the administration of immunosuppressive drugs after renal transplantation affects the safety of BEV administration. We report a case of severe proteinuria caused by BEV plus 5-fluorouracil, levofolinate, and oxaliplatin (mFOLFOX6) in a patient who had previously undergone kidney transplantation and the administration of tacrolimus.

Case presentation

The patient was a 67-year-old man with a history of diabetes and hypertension. He developed chronic renal failure 14 years earlier and underwent right kidney transplantation from a living donor followed by the administration of tacrolimus and mycophenolate mofetil for immunosuppression. After kidney transplantation, the patient was diagnosed with colorectal cancer with multiple lung and liver metastases and received BEV plus mFOLFOX6. After 5 cycles, proteinuria was observed, with a urinary protein concentration of > 300 mg/dL (urine protein creatinine ratio: 3.5), and after 16 cycles, the urinary protein concentration was > 1000 mg/dL (urine protein creatinine ratio: 7.1). Subsequently, BEV was discontinued, and only mFOLFOX6 administration was continued. Tacrolimus continued to be administered during chemotherapy. There was no association between serum tacrolimus concentration and proteinuria.

Conclusions

In this case, BEV administration caused severe proteinuria without affecting blood levels of tacrolimus. Patients with risk factors for renal impairment should be carefully evaluated for the risks and benefits of BEV administration.

Differential expression of genes related to calcineurin and mTOR signaling and regulatory miRNAs in peripheral blood from kidney recipients under tacrolimus-based therapy

Background

Genetic and epigenetics factors have been implicated in drug response, graft function and rejection in solid organ transplantation. Differential expression of genes involved in calcineurin and mTOR signaling pathway and regulatory miRNAs was analyzed in the peripheral blood of kidney recipient cohort (n=36) under tacrolimus-based therapy.

Methods

PPP3CA, PPP3CB, MTOR, FKBP1A, FKBP1B and FKBP5 mRNA expression and polymorphisms in PPP3CA and MTOR were analyzed by qPCR. Expression of miRNAs targeting PPP3CA (miR-30a, miR-145), PPP3CB (miR-10b), MTOR (miR-99a, miR-100), and FKBP1A (miR-103a) was measured by qPCR array.

Results

PPP3CA and MTOR mRNA levels were reduced in the first three months of treatment compared to pre-transplant (P<0.05). PPP3CB, FKBP1A, FKBP1B, and FKBP5 expression was not changed. In the 3^rd month of treatment, the expression of miR-99a, which targets MTOR, increased compared to pre-transplant (P<0.05). PPP3CA c.249G>A (GG genotype) and MTOR c.2997C>T (TT genotype) were associated with reduced expression of PPP3CA mRNA and MTOR, respectively. FKBP1B mRNA levels were higher in patients with acute rejection (P=0.026).

Conclusions

The expression of PPP3CA, MTOR and miR-99a in the peripheral blood of renal recipients is influenced by tacrolimus-based therapy and by PPP3CA and MTOR variants. These molecules can be potential biomarkers for pharmacotherapy monitoring.

Establishment of a Liquid Chromatography-Tandem Mass Spectrometry Method for the Determination of Immunosuppressant Levels in the Peripheral Blood Mononuclear Cells of Chinese Renal Transplant Recipients

BACKGROUND

Monitoring immunosuppressant levels, such as mycophenolic acid (MPA), cyclosporin A (CsA), and tacrolimus (TAC), in peripheral blood mononuclear cells (PBMCs) could be useful in organ transplant patients administered individualized therapy. The authors developed a liquid chromatography-tandem mass spectrometry assay technique to simultaneously determine immunosuppressant levels in PBMCs and assess their pharmacokinetics in Chinese renal allograft recipients.

METHODS

PBMCs were isolated from the whole blood of 27 Chinese renal transplant patients using Ficoll-Paque Plus solution, and cell number was determined; acetonitrile treatment for protein precipitation, and gradient elution was performed on an Agilent Eclipse XDB-C18 column (3.5 μm, 2.1 × 100 mm) with mobile phase: water and methanol (containing 2 mM ammonium formate); flow rate: 0.3 mL·min.

RESULTS

The calibration curves of MPA, CsA, and TAC had a linear range (ng·mL): 0.098-39.2 (r = 0.9987), 0.255-102 (r = 0.9969), and 0.028-11.2 (r = 0.9993), respectively. The extraction effects, matrix effects, and mean relative recovery of these immunosuppressants were 70.4%-93.2%, 72.7%-96.5%, and 90.1%-112.4%, respectively. The within-day and between-day coefficients of variation were <15%. The AUC0-12 of MPA in PBMCs correlated well with those in plasma. The level of MPA, CsA, and TAC in PBMCs might be more stable during dosing interval.

CONCLUSIONS

The derived liquid chromatography-tandem mass spectrometry assay is suitable for simultaneously monitoring different immunosuppressants in PBMCs. Pharmacokinetic of MPA, CsA, and TAC displayed considerable interindividual variability. Intracellular monitoring of immunosuppressants may facilitate individualized therapy for renal allograft recipients.

Torque teno virus for risk stratification of graft rejection and infection in kidney transplant recipients-A prospective observational trial

The nonpathogenic and ubiquitous torque teno virus (TTV) is associated with immunosuppression in solid organ transplant recipients. Studies in kidney transplant patients proposed TTV quantification for risk stratification of graft rejection and infection. In this prospective trial (DRKS00012335) 386 consecutive kidney transplant recipients were subjected to longitudinal per-protocol monitoring of plasma TTV load by polymerase chain reaction for 12 months posttransplant. TTV load peaked at the end of month 3 posttransplant and reached steady state thereafter. TTV load after the end of month 3 was analyzed in the context of subsequent rejection diagnosed by indication biopsy and infection within the first year posttransplant, respectively. Each log increase in TTV load decreased the odds for rejection by 22% (odds ratio [OR] 0.78, 95% confidence interval [CI] 0.62-0.97; P = .027) and increased the odds for infection by 11% (OR 1.11, 95% CI 1.06-1.15; P < .001). TTV was quantified at a median of 14 days before rejection was diagnosed and 27 days before onset of infection, respectively. We defined a TTV load between 1 × 10⁶ and 1 × 10⁸ copies/mL as optimal range to minimize the risk for rejection and infection. These data support the initiation of an interventional trial assessing the efficacy of TTV-guided immunosuppression to reduce infection and graft rejection in kidney transplant recipients.

Maintenance Immunosuppression in Solid Organ Transplantation: Integrating Novel Pharmacodynamic Biomarkers to Inform Calcineurin Inhibitor Dose Selection

Calcineurin inhibitors, the primary immunosuppressive therapy used to prevent alloreactivity of transplanted organs, have a narrow therapeutic index. Currently, treatment is individualized based on clinical assessment of the risk of rejection or toxicity guided by trough concentration monitoring. Advances in immune monitoring have identified potential markers that may have value in understanding calcineurin inhibitor pharmacodynamics. Integration of these markers has the potential to complement therapeutic drug monitoring. Existing pharmacokinetic-pharmacodynamic (PK-PD) data is largely limited to correlation between the biomarker and trough concentrations at single time points. Immune related gene expression currently has the most evidence supporting PK-PD integration. Novel biomarker-based approaches to pharmacodynamic monitoring including development of enhanced PK-PD models are proposed to realize the full clinical benefit.

Impacts of High Intra- and Inter-Individual Variability in Tacrolimus Pharmacokinetics and Fast Tacrolimus Metabolism on Outcomes of Solid Organ Transplant Recipients

Tacrolimus is a first-line calcineurin inhibitor (CNI) and an integral part of the immunosuppressive strategy in solid organ transplantation. Being a dose-critical drug, tacrolimus has a narrow therapeutic index that necessitates periodic monitoring to maintain the drug’s efficacy and reduce the consequences of overexposure. Tacrolimus is characterized by substantial intra- and inter-individual pharmacokinetic variability. At steady state, the tacrolimus blood concentration to daily dose ratio (C/D ratio) has been described as a surrogate for the estimation of the individual metabolism rate, where a low C/D ratio reflects a higher rate of metabolism. Fast tacrolimus metabolism (low C/D ratio) is associated with the risk of poor outcomes after transplantation, including reduced allograft function and survival, higher allograft rejection, CNI nephrotoxicity, a faster decline in kidney function, reduced death-censored graft survival (DCGS), post-transplant lymphoproliferative disorders, dyslipidemia, hypertension, and cardiovascular events. In this article, we discuss the potential role of the C/D ratio in a noninvasive monitoring strategy for identifying patients at risk for potential adverse events post-transplant.

Successful Treatment of Hepatitis C Virus Infection Using Direct-Acting Antiviral Agents (DAAs) in Adolescents with Kidney Transplantation: A Case Series

INTRODUCTION

Hepatitis C virus (HCV) infection is common among end-stage renal disease patients undergoing hemodialysis. The standard treatment for HCV infection has been interferon-ribavirin combination prior to renal transplantation. However, compared to direct-acting antiviral agents (DAAs), the risk of graft rejection is higher with interferon therapy. Many recent studies have investigated the efficacy and safety of DAAs for treating HCV infection in kidney disease in adults; however, it has not been established in pediatric patients. To the best of our knowledge, this is the first report describing successful treatment using the DAAs sofosbuvir/daclatasvir in two pediatric kidney transplant recipients who had HCV genotype 1a infection without liver fibrosis.

CASE PRESENTATION

Case 1 describes a 13-year-old Indonesian boy who had undergone hemodialysis since 2014 after being diagnosed with end-stage renal disease (ESRD) secondary to bilateral renal hypoplasia. Later, he had HCV infection and was treated with interferon-based therapy with ribavirin prior to living-related renal transplantation (LRRT). The HCV was undetected and his liver function normalized six months after treatment initiation. However, 10 months after treatment initiation, he had HCV virological breakthrough, leading to cessation of interferon therapy. Plans for LRRT were continued and HCV treatment using DAAs was set up to be given post LRRT. Case 2 describes a 14-year-old Indonesian girl who also had hemodialysis prior to LRRT after she was diagnosed with ESRD secondary to nephrotic syndrome. Later, she had HCV infection and was treated with interferon and ribavirin prior to the live-unrelated renal transplantation. HCV infection did not resolve, in addition, she experienced thrombocytopenia-which is a side effect of interferon-resulting in termination of interferon treatment. Both cases were treated with DAAs one year following renal transplantation after reaching stable graft function, leading to achievement of sustained virological response at 24 weeks.

CONCLUSION

Post-transplantation treatment of chronic HCV is preferred in KTRs. The sofosbuvir/daclatasvir regimen as an interferon-free therapy is a safe, effective option for HCV infection in pediatric KTRs, who can tolerate sofosbuvir/daclatasvir well and respond favorably without significant adverse events.

Predictive engines based on pharmacokinetics modelling for tacrolimus personalized dosage in paediatric renal transplant patients

The development of predictive engines based on pharmacokinetic-physiological mathematical models for personalised dosage recommendations is an immature field. Nevertheless, these models are extensively applied during the design of new drugs. This study presents new advances in this subject, through a stable population of patients who underwent kidney transplantation and were prescribed tacrolimus. We developed 2 new population pharmacokinetic models based on a compartmental approach, with one following the physiologically based pharmacokinetic approach and both including circadian modulation of absorption and clearance variables. One of the major findings was an improved predictive capability for both models thanks to the consideration of circadian rhythms, both in estimating the population and in Bayesian individual customisation. This outcome confirms a plausible mechanism suggested by other authors to explain circadian patterns of tacrolimus concentrations. We also discovered significant intrapatient variability in tacrolimus levels a week after the conversion from a fast-release (Prograf) to a sustained-release formulation (Advagraf) using adaptive optimisation techniques, despite high adherence and controlled conditions. We calculated the intrapatient variability through parametric intrapatient variations, which provides a method for quantifying the mechanisms involved. We present a first application for the analysis of bioavailability changes in formulation conversion. The 2 pharmacokinetic models have demonstrated their capability as predictive engines for personalised dosage recommendations, although the physiologically based pharmacokinetic model showed better predictive behaviour.

Donor CYP3A5 Gene Polymorphism Alone Cannot Predict Tacrolimus Intrarenal Concentration in Renal Transplant Recipients

CYP3A5 gene polymorphism in recipients plays an important role in tacrolimus blood pharmacokinetics after renal transplantation. Even though CYP3A5 protein is expressed in renal tubular cells, little is known about the influence on the tacrolimus intrarenal exposure and hence graft outcome. The aim of our study was to investigate how the tacrolimus intrarenal concentration (C_tissue) could be predicted based on donor CYP3A5 gene polymorphism in renal transplant recipients. A total of 52 Japanese renal transplant patients receiving tacrolimus were enrolled in this study. Seventy-four renal biopsy specimens were obtained at 3 months and 1 year after transplantation to determine the donor CYP3A5 polymorphism and measure the C_tissue by liquid chromatography-tandem mass spectrometry (LC-MS-MS). The tacrolimus C_tissue ranged from 52 to 399 pg/mg tissue (n = 74) and was weak but significantly correlated with tacrolimus trough concentration (C₀) at 3 months after transplantation (Spearman, r = 0.3560, p = 0.0096). No significant relationship was observed between the donor CYP3A5 gene polymorphism and C_tissue or C_tissue/C₀. These data showed that the tacrolimus systemic level has an impact on tacrolimus renal accumulation after renal transplantation. However, donor CYP3A5 gene polymorphism alone cannot be used to predict tacrolimus intrarenal exposure_. This study may be valuable for exploring tacrolimus renal metabolism and toxicology mechanism in renal transplant recipients.

Predictability of Capillary Blood Spot Toward Venous Whole Blood Sampling for Therapeutic Drug Monitoring of Tacrolimus in Solid Organ Transplant Recipients

Therapeutic drug monitoring (TDM) of tacrolimus in whole blood obtained from venipuncture is routinely practiced. Dried blood spotting (DBS) may act as a suitable alternative for tacrolimus TDM due to relative ease of sampling and processing. The objective of this literature review was to provide a critical evaluation on the feasibility (i.e., accuracy and precision) of DBS for predicting tacrolimus whole blood concentrations in solid organ transplant recipients. A comprehensive systematic literature search using PubMed, Scopus, EMBASE, and Google Scholar was conducted. The primary objective was to extract the bias and precision data from the identified papers. In addition, the collection, storage, and analysis protocols were also summarized. Both adult and pediatric data were included. The reported bias data (primarily based on individual concentrations) in the majority of studies were within acceptable limits (< 15%). However, the precision data were not consistently reported. The area under the concentration-time curve of tacrolimus derived from DBS appeared to be a better predictor of whole blood compared to single concentrations based on a limited number of studies. No apparent differences in prediction were observed between pediatric and adult patients. Small sample sizes and the lack of complete description of the study population were common limitations. DBS is a promising approach for tacrolimus TDM. However, in order for DBS to become a useful substitute for tacrolimus whole blood monitoring in solid organ transplant patients, further systematic studies with sufficient power and comprehensive prediction error analyses are required.

Relationship between 2-Hour Tacrolimus Concentrations and Clinical Outcomes in Long Term Kidney Transplantation

Background: Tacrolimus is routinely monitored using trough concentrations, however, recent data have suggested that area under the curve (AUC) provides better correlation with toxicity and efficacy. Area under the curve is cumbersome to measure, but studies have demonstrated that surrogate time points such as 2-hour concentrations are well correlated with AUC. Methods: This is a single center, retrospective study of adult kidney transplant recipients with 2-hour tacrolimus concentrations measured over three years post-transplant. The primary outcome was to determine the difference in serum creatinine (Scr) in those with 2-hour tacrolimus concentrations greater than 20 ng/mL versus those less than or equal to 20 ng/mL. Results: A total of 150 kidney transplant recipients were included. The mean Scr and glomerular filtration rate were 1.49 ± 1.01 mg/dL and 59 ± 23.2 mL/min/1.73 m2, respectively, for the entire cohort. The rate of donor specific antibody formation was 2% and 8% experienced biopsy-proven rejection. The rate of cytomegalovirus viremia was 2% and BK viremia was 13%. There was no significant difference in kidney function over 36 months for the groups specified a priori. Conclusions: Long-term outcomes of maintaining tacrolimus 2-hour concentrations over 20 ng/mL is favorable with minimal opportunistic infections.

Torque Teno Virus for Risk Stratification of Acute Biopsy-Proven Alloreactivity in Kidney Transplant Recipients

Background

Drug-induced immunosuppression in kidney transplant recipients is crucial to prevent allograft rejection, but increases risk for infectious disease. Immunologic monitoring to tailor immunosuppressive drugs might prevent alloreactivity and adverse effects simultaneously. The apathogenic torque teno virus (TTV) reflects the immunocompetence of its host and might act as a potential candidate for a holistic monitoring.

Methods

We screened all 1010 consecutive patients from the prospective Vienna Kidney Transplant Cohort Study for availability of allograft biopsies and adequately stored sera for TTV quantification by polymerase chain reaction.

Results

Patients with acute biopsy-proven alloreactivity according to the Banff classification (n = 33) showed lower levels of TTV in the peripheral blood compared to patients without rejection (n = 80) at a median of 43 days before the biopsy. The risk for alloreactivity decreased by 10% per log level of TTV copies/mL (risk ratio, .90 [95% confidence interval, .84–.97]; P = .005). TTV levels >1 × 10⁶ copies/mL exclude rejection with a sensitivity of 94%. Multivariable generalized linear modeling suggests an independent association between TTV level and alloreactivity.

Conclusions

TTV is a prospective biomarker for risk stratification of acute biopsy-proven alloreactivity in kidney transplant recipients and might be a potential tool to tailor immunosuppressive drug therapy.

Tacrolimus treatment in childhood refractory nephrotic syndrome: A retrospective study on efficacy, therapeutic drug monitoring, and contributing factors to variable blood tacrolimus levels

Tacrolimus, an immunosuppressive drug, was recommended by the 2012 KDIGO guidelines to treat nephrotic syndrome (NS) in children and adults. However, it has high interpatient pharmacokinetic variability and exposure levels should be monitored, although there are no specified target concentrations. This retrospective study aimed to review efficacy and safety after concomitant treatment with tacrolimus and prednisone, and to identify factors that contribute to the variable blood-trough-concentration-to-dose (C₀/Dose) ratio in children with refractory NS (RNS). A 6-month therapy induced complete or partial remission in 95% of patients. One-year follow-up indicated a high remission rate and low nephrotoxicity. Under maintenance dosages, approximately 95% of the C₀ values were 2-7 ng/mL. Body weight (BW), age, CYP3A5 polymorphisms were the factors affecting the C₀/Dose ratio. The C₀/Dose ratio in patients with a BW of <20 kg was 1.5-fold than that in patients with BW of ≥40 kg. Moreover, the C₀/Dose ratio in patients aged 1-≤6 and 6-≤12 years was significantly lower than that in patients aged 12-≤18 years, by 25% and 48%, respectively. There were no significant association between CYP3A5 genotyping and C₀/Dose ratio in younger children (1-≤6 years), rather than older children (6-≤18 years). In conclusion, routine CYP3A5 genotyping should be considered in children aged over 6 years and exposure levels (C₀) of 2-7 ng/mL may be feasible when tacrolimus is combined with low-dose prednisone to treat childhood RNS.

Emerging Roles for Lymphatics in Chronic Liver Disease

Chronic liver disease (CLD) is a global health epidemic causing ∼2 million deaths annually worldwide. As the incidence of CLD is expected to rise over the next decade, understanding the cellular and molecular mediators of CLD is critical for developing novel therapeutics. Common characteristics of CLD include steatosis, inflammation, and cholesterol accumulation in the liver. While the lymphatic system in the liver has largely been overlooked, the liver lymphatics, as in other organs, are thought to play a critical role in maintaining normal hepatic function by assisting in the removal of protein, cholesterol, and immune infiltrate. Lymphatic growth, permeability, and/or hyperplasia in non-liver organs has been demonstrated to be caused by obesity or hypercholesterolemia in humans and animal models. While it is still unclear if changes in permeability occur in liver lymphatics, the lymphatics do expand in number and size in all disease etiologies tested. This is consistent with the lymphatic endothelial cells (LEC) upregulating proliferation specific genes, however, other transcriptional changes occur in liver LECs that are dependent on the inflammatory mediators that are specific to the disease etiology. Whether these changes induce lymphatic dysfunction or if they impact liver function has yet to be directly addressed. Here, we will review what is known about liver lymphatics in health and disease, what can be learned from recent work on the influence of obesity and hypercholesterolemia on the lymphatics in other organs, changes that occur in LECs in the liver during disease and outstanding questions in the field.

Association of Genetic Variants in CYP3A4, CYP3A5, CYP2C8, and CYP2C19 with Tacrolimus Pharmacokinetics in Renal Transplant Recipients

BACKGROUND

Our study aimed to investigate the pharmacogenetics of cytochrome P3A4 (CYP3A4), CYP3A5, CYP2C8, and CYP2C19 and their influence on TAC Pharmacokinetics (PKs) in short-term renal transplant recipients.

METHODS

A total of 105 renal transplant recipients were enrolled. Target Sequencing (TS) based on next-generation sequencing technology was used to detect all exons, exon/intron boundaries, and flanking regions of CYP3A4, CYP3A5, CYP2C8, and CYP2C19. After adjustment of Minor Allele Frequencies (MAF) and Hardy-Weinberg Equilibrium (HWE) analysis, tagger Single-nucleotide Polymorphisms (SNPs) and haplotypes were identified. Influence of tagger SNPs on TAC concentrations was analyzed.

RESULTS

A total of 94 SNPs were identified in TS analysis. Nine tagger SNPs were selected, and two SNPs (rs15524 and rs4646453) were noted to be significantly associated with TAC PKs in short-term post-transplant follow-up. Measurement time points of TAC, body mass index (BMI), usage of sirolimus, and incidence of Delayed Graft Function (DGF) were observed to be significantly associated with TAC PKs. Three haplotypes were identified, and rs15524-rs4646453 was found to remarkably contribute to TAC PKs. Recipients carrying H2/H2 (GG-AA) haplotype also showed significantly high weight- and dose-adjusted TAC concentrations in posttransplant periods of 7, 14, and 30 days and 3 and 6 months.

CONCLUSIONS

Two tagger SNPs, namely, rs15524 and rs4646453, are significantly related to the variability of TAC disposition, and TAC measurement time points, BMI, usage of sirolimus, and incidence of DGF contribute to this influence. Recipients carrying H2/H2 (GG-AA) haplotype in rs15524-rs4646453 may require a low dosage of TAC during 1-year follow-up posttransplant.

Tacrolimus- and sirolimus-induced human β cell dysfunction is reversible and preventable

Posttransplantation diabetes mellitus (PTDM) is a common and significant complication related to immunosuppressive agents required to prevent organ or cell transplant rejection. To elucidate the effects of 2 commonly used agents, the calcineurin inhibitor tacrolimus (TAC) and the mTOR inhibitor sirolimus (SIR), on islet function and test whether these effects could be reversed or prevented, we investigated human islets transplanted into immunodeficient mice treated with TAC or SIR at clinically relevant levels. Both TAC and SIR impaired insulin secretion in fasted and/or stimulated conditions. Treatment with TAC or SIR increased amyloid deposition and islet macrophages, disrupted insulin granule formation, and induced broad transcriptional dysregulation related to peptide processing, ion/calcium flux, and the extracellular matrix; however, it did not affect regulation of β cell mass. Interestingly, these β cell abnormalities reversed after withdrawal of drug treatment. Furthermore, cotreatment with a GLP-1 receptor agonist completely prevented TAC-induced β cell dysfunction and partially prevented SIR-induced β cell dysfunction. These results highlight the importance of both calcineurin and mTOR signaling in normal human β cell function in vivo and suggest that modulation of these pathways may prevent or ameliorate PTDM.

Optimization of tacrolimus in kidney transplantation: New pharmacokinetic perspectives

Tacrolimus is the cornerstone of immunosuppressive therapy after kidney transplantation (KT), but its use is complicated by a narrow therapeutic index and high inter- and intra-patient pharmacokinetic variability. There are three available oral formulations of tacrolimus: immediate-release tacrolimus (IR-Tac), extended-release tacrolimus (ER-Tac) and a MeltDose® (LCPT) formulation, the latter favoring a prolonged drug release and increased bioavailability. The time-concentration curves of these formulations are different. Compared with IR-Tac and ER-Tac, LCPT has a relatively flat pharmacokinetic profile with less fluctuation between trough and peak exposures, and a delayed peak concentration. This translates to a more stable delivery of tacrolimus and may alleviate the risk of underexposure and allograft rejection or overexposure and toxicity. The once-daily formulation of both ER-TAC and LCPT may also offer a potential advantage on patient adherence. Fast metabolizers of tacrolimus, the elderly, and human leukocyte antigen-sensitized patients are at risk of poorer outcomes after KT, possibly associated with a different exhibited pharmacokinetics of tacrolimus or different requirements in terms of exposure. Simple, practical strategies are needed to identify patients at risk of suboptimal KT outcomes and those who would benefit from a more proactively personalized approach to tacrolimus treatment. This review aims to increase awareness of the link between the pharmacokinetics of oral tacrolimus formulations and the clinical needs of patients after KT, particularly among those who have clinically significant pharmacokinetic variation of tacrolimus.

Validation and evaluation of four sample preparation methods for the quantification of intracellular tacrolimus in peripheral blood mononuclear cells by UHPLC-MS/MS

Rejection and toxicity occur despite monitoring of tacrolimus blood levels during clinical routine. The intracellular concentration in lymphocytes could be a better reflection of the tacrolimus exposure. Four extraction methods for tacrolimus in peripheral blood mononuclear cells were validated and evaluated with UHPLC-MS/MS. Methods based on protein precipitation (method 1), solid phase extraction (method 2), phospholipids and proteins removal (method 3) and liquid-liquid extraction (method 4) were evaluated on linearity, lower limit of quantification (LLOQ), imprecision and bias. Validation was completed for the methods within these requirements, adding matrix effect and recovery. Linearity was 0.126 (LLOQ)-15 µg/L, 0.504 (LLOQ)-15 µg/L and 0.298 (LLOQ)-15 µg/L with method 1, 2 and 3, respectively. With method 4 non-linearity and a LLOQ higher than 0.504 µg/L were observed. Inter-day imprecision and bias were ≤4.6%, ≤10.9%; ≤6.8%, ≤-11.2%; ≤9.4%, ≤10.3% and ≤44.6%, ≤23.1%, respectively, with methods 1, 2, 3 and 4. Validation was completed for method 1 and 3 adding matrix effect (7.6%; 15.0%) and recovery (8.9%; 10.8%), respectively. The most suitable UHPLC-MS/MS method for quantification of intracellular tacrolimus was protein precipitation due to the best performance characteristics and the least time-consuming rate and complexity.

Impact of low tacrolimus exposure and high tacrolimus intra-patient variability on the development of de novo anti-HLA donor-specific antibodies in kidney transplant recipients

Introduction: De novo donor-specific antibodies (dnDSA) directed against HLA are a major contributing factor to the chronic deterioration of renal allograft function. Several factors, including the degree of HLA matching, younger recipient age, and past sensitization events have been shown to increase the risk for the development of dnDSA. The development of dnDSA is also strongly associated with modifications in the immunosuppressive regimen, non-adherence, and under-immunosuppression.Areas covered: Tacrolimus is widely used after solid organ transplantation (SOT) and in recent years, both a high intra-patient variability in tacrolimus exposure and low tacrolimus exposure have been found to be associated with a higher risk of dnDSA development in kidney transplant recipients. This article provides an overview of current findings published in the recent 5 years regarding the relationship between tacrolimus exposure and variation therein and the development of dnDSA.Expert opinion: In this review, we describe how combining data on tacrolimus intra-patient variability and mean pre-dose concentration may be an effective tool to identify kidney transplant recipients who are at higher risk of developing dnDSA.

Population Pharmacokinetic Analysis of Immediate-Release Oral Tacrolimus Co-administered with Mycophenolate Mofetil in Corticosteroid-Free Adult Kidney Transplant Recipients

BACKGROUND AND OBJECTIVE

Tacrolimus is the mainstay calcineurin inhibitor frequently administered with mycophenolic acid with or without corticosteroids to prevent graft rejection in adult kidney transplant recipients. The primary objective of this study was to develop and evaluate a population pharmacokinetic model characterizing immediate-release oral tacrolimus co-administered with mycophenolate mofetil (a pro-drug of mycophenolic acid) in adult kidney transplant recipients on corticosteroid-free regimens. The secondary objective was to investigate the effects of clinical covariates on the pharmacokinetics of tacrolimus, emphasizing the interacting effects of mycophenolic acid.

METHODS

Population modeling and evaluation were conducted with Monolix (Suite-2018R1) using the stochastic approximation expectation-maximization algorithm in 49 adult subjects (a total of 320 tacrolimus whole-blood concentrations). Effects of clinical variables on tacrolimus pharmacokinetics were determined by population covariate modeling, regression modeling, and categorical analyses.

RESULTS

A two-compartment, first-order absorption with a lag-time, linear elimination, and constant error model best represented the population pharmacokinetics of tacrolimus. The apparent clearance value for tacrolimus was 17.9 l/h (6.95% relative standard error) in our model, which is lower compared with similar subjects on corticosteroid-based therapy. The glomerular filtration rate had significant effects on the apparent clearance and central compartment volume of distribution. Conversely, mycophenolic acid did not affect the apparent clearance of tacrolimus.

CONCLUSION

We have developed and internally evaluated a novel population pharmacokinetic model for tacrolimus co-administered with mycophenolate mofetil in corticosteroid-free adult kidney transplant patients. These findings are clinically important and provide further reasons for conducting therapeutic drug monitoring in this specific population.

Effect of a Smart Pill Bottle and Pharmacist Intervention on Medication Adherence in Patients with Multiple Myeloma New to Lenalidomide Therapy

BACKGROUND

U.S. specialty drug spend is expected to reach $400 billion by 2020, with significant growth in oncology. New oral oncology approvals have allowed for more convenient outpatient administration compared with physician-administered chemotherapies; however, patients may encounter challenges with adherence when taking medications at home. Emerging medication adherence technology (MAT) attempts to provide at-home adherence support, and while one such technology, smart pill bottles (SPB), claims to improve medication adherence, few studies have formally assessed their effects.

OBJECTIVES

To assess the effect of an SPB with pharmacist intervention on medication adherence in adult patients with multiple myeloma (MM) new to lenalidomide therapy (≤ 5 cycle dispenses). Secondary objectives were to evaluate treatment cycles completed, evaluate the significance of real-time pharmacist engagement (intervention group only), determine the incremental cost-effectiveness ratio (ICER), and evaluate patient satisfaction and likelihood to use an SPB.

METHODS

This prospective, random assignment, single-site, and single-blinded study recruited 40 adult patients diagnosed with MM new to lenalidomide at a specialty pharmacy. Recruitment was completed January-February 2016, and the length of study was 6 months. Participants were randomized 1:1 between the intervention and control groups. The intervention group received lenalidomide in activated SPBs with light, chimes, text message reminders, and pharmacist follow-up if weekly SPB adherence rates dropped below 80%. The control group received lenalidomide in identical SPBs with all alerts deactivated. SBPs contained cellular capabilities, enabling around-the-clock data transmission and captured data upon bottle-uncapping events. Patient adherence was calculated by dividing the number of bottle-uncapping events by the total number of doses supplied for each dosing cycle. Lenalidomide cycles completed and pharmacist outreach to the same patient were counted to determine pharmacist intervention. The ICER was calculated to determine SPB cost-effectiveness, and a Likert scale survey was given to the intervention group to evaluate patient satisfaction with the full-service SPB.

RESULTS

Sixteen participants in each arm completed the study; 4 patients in each arm were lost to follow-up. Median adherence was improved for the intervention group compared with the control group (median = 100% vs. 87.4%; P = 0.001). The ICER per patient percentage adherence increase was found to be $96.03. Sixty percent of patients in the intervention group who responded to the post-satisfaction survey rated the full SPB service very positively.

CONCLUSIONS

In this study, SPB interventions were associated with increased medication adherence and patient satisfaction. This pilot also provides empirical data on the cost-effectiveness of adherence technology used in a specialty pharmacy oncology setting.

DISCLOSURES

This study was supported by Avella Specialty Pharmacy and AdhereTech. All authors are employees of Avella; Eric Sredzinski was an option holder of Avella; and none of the Avella authors had a financial interest in AdhereTech. AdhereTech provided the SPBs and data services for the duration of this study. The authors report no other potential conflicts of interest. Interim study data were presented at the 2016 Southwestern States Residency Conference (SSRC) on June 20, 2016, in Phoenix, AZ.

Nanosensors for therapeutic drug monitoring: implications for transplantation

The number of patients requiring organ transplantations is exponentially increasing. New organs are either provided by healthy or deceased donors, or are grown in laboratories by tissue engineers. Post-surgical follow-up is vital for preventing any complications that can cause organ rejection. Physiological monitoring of a patient who receives newly transplanted organs is crucial. Many efforts are being made to enhance follow-up technologies for monitoring organ recipients, and point-of-care devices are beginning to emerge. Here, we describe the role of biosensors and nanosensors in improving organ transplantation efficiency, managing post-surgical follow-up and reducing overall costs. We provide an overview of the state-of-the-art biosensing technologies and offer some perspectives related to their further development.

Immunomonitoring of Tacrolimus in Healthy Volunteers: The First Step from PK- to PD-Based Therapeutic Drug Monitoring?

Therapeutic drug monitoring is routinely performed to maintain optimal tacrolimus concentrations in kidney transplant recipients. Nonetheless, toxicity and rejection still occur within an acceptable concentration-range. To have a better understanding of the relationship between tacrolimus dose, tacrolimus concentration, and its effect on the target cell, we developed functional immune tests for the quantification of the tacrolimus effect. Twelve healthy volunteers received a single dose of tacrolimus, after which intracellular and whole blood tacrolimus concentrations were measured and were related to T cell functionality. A significant correlation was found between tacrolimus concentrations in T cells and whole blood concentrations (r = 0.71, p = 0.009), while no correlation was found between tacrolimus concentrations in peripheral blood mononuclear cells (PBMCs) and whole blood (r = 0.35, p = 0.27). Phytohemagglutinin (PHA) induced the production of IL-2 and IFNγ, as well as the inhibition of CD71 and CD154 expression on T cells at 1.5 h post-dose, when maximum tacrolimus levels were observed. Moreover, the in vitro tacrolimus effect of the mentioned markers corresponded with the ex vivo effect after dosing. In conclusion, our results showed that intracellular tacrolimus concentrations mimic whole blood concentrations, and that PHA-induced cytokine production (IL-2 and IFNγ) and activation marker expression (CD71 and CD154) are suitable readout measures to measure the immunosuppressive effect of tacrolimus on the T cell.

Quantification of Torque Teno Virus Viremia as a Prospective Biomarker for Infectious Disease in Kidney Allograft Recipients

Background

Drug-induced immunosuppression following kidney transplantation is crucial to prevent allograft rejection, but increases risk for infectious disease. Tailoring of drug dosing to prevent both rejection and infection is greatly desirable. The apathogenic and ubiquitous torque teno virus (TTV) reflects immunocompetence of the host and might be a potential candidate for immunologic monitoring.

Methods

To assess TTV as an infection biomarker, virus load was prospectively quantified in peripheral blood of 169 consecutive renal allograft recipients at the Medical University Vienna.

Results

Patients with infection showed higher TTV levels compared to patients without infection (4.2 × 10⁸ copies/mL [interquartile range, IQR, 2.7 × 10⁷–1.9 × 10⁹] vs 2.9 × 10⁷ [IQR 1.0 × 10⁶–7.2 × 10⁸]; P = .006). Differences in TTV load became evident almost 3 months before infection (median 77 days, IQR 19–98). Each log level of TTV copies/mL increased the odds ratio for infection by 23% (95% confidence interval 1.04–1.45; P = .014). TTV >3.1 × 10⁹ copies/mL corresponded to 90% sensitivity to predict infections. Logistic regression demonstrated independent association between TTV levels and infection.

Conclusions

TTV quantification predicts infection after kidney transplantation and might be a potential tool to tailor immunosuppressive drug therapy.

Comparison of Tacrolimus Starting Doses Based on CYP3A5 Phenotype or Genotype in Kidney Transplant Recipients

BACKGROUND

Selection of expected phenotypes (ie, expressers/non-expressers) is currently used in CYP3A5*3 genotype-based tacrolimus dosing. The authors assessed whether a dosing regimen based on the 3 CYP3A5 genotypes may reduce the occurrence of inadequate exposure.

METHODS

Tacrolimus whole blood trough levels (C ₀) were retrieved from a retrospective cohort of 100 kidney transplant recipients treated with a starting dose of 0.15 (non-expressers) or 0.30 (expressers) mg/kg/d. The authors evaluated the occurrence of overexposures (12 < C ₀ < 20 ng/mL) or toxic concentrations (C ₀ ≥ 20 ng/mL). These results were used to set up a new strategy based on the 3 distinct CYP3A5 genotypes, which relevance was evaluated in a prospective cohort of 107 patients.

RESULTS

In the retrospective cohort, non-expressers exhibited frequent overexposure (63.6%) or toxic C ₀ (20.8%). Among expressers, none of the homozygous *1 carriers exhibited overexposure contrary to 25% of the heterozygotes. Based on these results, new tacrolimus starting doses were set at 0.10, 0.20, and 0.30 mg/kg/d for CYP3A5*3/*3, CYP3A5*1/*3, and CYP3A5*1/*1 genotypes, respectively. Tacrolimus overexposure was reduced in the CYP3A5*3/*3 group (63.6% vs 40%, P = .0038). None of the heterozygous patients exhibited toxic tacrolimus C ₀. Clinical outcomes were not different between the 2 periods, whatever the genotype. Our results indicate that the best tacrolimus exposure was obtained for doses of 0.10, 0.20, and 0.20 mg/kg/d for CYP3A5*3/3, CYP3A5*1/*3, and CYP3A5*1/*1, respectively.

CONCLUSIONS

Our results confirm that selecting tacrolimus dosing regimen according to the expected phenotype is appropriate, but that lower than currently recommended doses may be preferable.

Pharmacology and pharmacogenetics of prednisone and prednisolone in patients with nephrotic syndrome

Nephrotic syndrome is one of the most common glomerular disorders in childhood. Glucocorticoids have been the cornerstone of the treatment of childhood nephrotic syndrome for several decades, as the majority of children achieves complete remission after prednisone or prednisolone treatment. Currently, treatment guidelines for the first manifestation and relapse of nephrotic syndrome are mostly standardized, while large inter-individual variation is present in the clinical course of disease and side effects of glucocorticoid treatment. This review describes the mechanisms of glucocorticoid action and clinical pharmacokinetics and pharmacodynamics of prednisone and prednisolone in nephrotic syndrome patients. However, these mechanisms do not account for the large inter-individual variability in the response to glucocorticoid treatment. Previous research has shown that genetic factors can have a major influence on the pharmacokinetic and dynamic profile of the individual patient. Therefore, pharmacogenetics may have a promising role in personalized medicine for patients with nephrotic syndrome. Currently, little is known about the impact of genetic polymorphisms on glucocorticoid response and steroid-related toxicities in children with nephrotic syndrome. Although the evidence is limited, the data summarized in this study do suggest a role for pharmacogenetics to improve individualization of glucocorticoid therapy. Therefore, studies in larger cohorts with nephrotic syndrome patients are necessary to draw final conclusions about the influence of genetic polymorphisms on the glucocorticoid response and steroid-related toxicities to ultimately implement pharmacogenetics in clinical practice.

Conversion from Twice-Daily Prograf® to Once-Daily Advagraf® in Multi-ethnic Asian Adult Renal Transplant Recipients With or Without Concomitant Use of Diltiazem: Impact of CYP3A5 and MDR1 Genetic Polymorphisms on Tacrolimus Exposure

BACKGROUND AND OBJECTIVES

Tacrolimus is the mainstay of immunosuppression in renal transplantation. Given that once-daily administration improves patient compliance, 1:1 dose conversion from twice-daily Prograf^® to once-daily Advagraf^® is recommended. Although cytochrome P450 (CYP) 3A5 and multi-drug resistance 1 (MDR1) polymorphisms influence tacrolimus concentrations, it is unknown if these impact on conversion. This study investigated the change in the pharmacokinetics of tacrolimus after conversion from Prograf^® to Advagraf^® and examined the impact of CYP3A5 and MDR1 C3435T polymorphisms on those pharmacokinetics.

METHODS

A prospective open-label pharmacokinetic study of 1:1 conversion from Prograf^® to Advagraf^® with or without diltiazem was conducted on 26 stable renal transplant recipients. Blood samples were collected over 24 h during each phase, tacrolimus concentrations were assayed, and noncompartmental pharmacokinetic analysis was performed. All participants were genotyped for CYP3A5*3 and MDR1 C3435T.

RESULTS

After conversion, without diltiazem, the area under the concentration-time curve at steady state from 0 to 24 h after dose administration (AUC_{ss, 0-24}) was significantly reduced [median 224 (range 172-366) vs. 184 (104-347) ng·h/mL, p = 0.006, n = 26]. A decrease in tacrolimus exposure (median 21%) was only evident among CYP3A5 expressors [227 (172-366) vs. 180 (104-347) ng·h/mL, p = 0.014, n = 18], not among non-expressors [215 (197-290) vs. 217 (129-281) ng·h/mL, p = 0.263, n = 8]. In contrast, among CYP3A5 expressors receiving diltiazem, AUC_{ss, 0-24} did not change significantly upon conversion [229 (170-296) vs. 221 (123-342) ng·h/mL, p = 0.575, n = 10]. An independent effect was not evident for MDR1 C3435T polymorphism.

CONCLUSION

The high prevalence of CYP3A5 polymorphism among Asians may lead to a significant reduction in tacrolimus exposure with 1:1 dose conversion of Prograf^® to Advagraf^®. These results advocate for CYP3A5 determination prior to conversion, and suggest that 1:1.25 conversion should be used for CYP3A5 expressors and 1:1 conversion for other patients.

Analysis of NFATc1 amplification in T cells for pharmacodynamic monitoring of tacrolimus in kidney transplant recipients

Background

Therapeutic drug monitoring (TDM) of tacrolimus, based on blood concentrations, shows an imperfect correlation with the occurrence of rejection. Here, we tested whether measuring NFATc1 amplification, a member of the calcineurin pathway, is suitable for TDM of tacrolimus.

Materials and methods

NFATc1 amplification was monitored in T cells of kidney transplant recipients who received either tacrolimus- (n = 11) or belatacept-based (n = 10) therapy. Individual drug effects on NFATc1 amplification were studied in vitro, after spiking blood samples of healthy volunteers with either tacrolimus, belatacept or mycophenolate mofetil.

Results

At day 30 after transplantation, in tacrolimus-treated patients, NFATc1 amplification was inhibited in CD4⁺ T cells expressing the co-stimulation receptor CD28 (mean inhibition 37%; p = 0.01) and in CD8⁺CD28⁺ T cells (29% inhibition; p = 0.02), while this was not observed in CD8⁺CD28^- T cells or belatacept-treated patients. Tacrolimus pre-dose concentrations of these patients correlated inversely with NFATc1 amplification in CD28⁺ T cells (r_s = -0.46; p < 0.01). In vitro experiments revealed that 50 ng/ml tacrolimus affected NFATc1 amplification by 58% (mean; p = 0.02).

Conclusion

In conclusion, measuring NFATc1 amplification is a direct tool for monitoring biological effects of tacrolimus on T cells in whole blood samples of kidney transplant recipients. This technique has potential that requires further development before it can be applied in daily practice.