Required Transient Dose Escalation of Tacrolimus in Living-Donor Liver Transplant Recipients with High Concentrations of a Minor Metabolite M-II in Bile

Revisiting the nature and pharmacodynamics of tacrolimus metabolites

The toxicity of tacrolimus metabolites and their potential pharmacodynamic (PD) interactions with tacrolimus might respectively explain the surprising combination of higher toxicity and lower efficacy of tacrolimus despite normal blood concentrations, described in extensive metabolizers. To evaluate such interactions, we produced tacrolimus metabolites in vitro and characterized them by high resolution mass spectrometry (HRMS, for all) and nuclear magnetic resonance (NMR, for the most abundant, M-I). We quantified tacrolimus metabolites and checked their structure in patient whole blood and peripheral blood mononuclear cells (PBMC). We explored the interactions of M-I with tacrolimus in silico, in vitro and ex vivo. In vitro metabolization produced isoforms of tacrolimus and of its metabolites M-I and M-III, whose HRMS fragmentation suggested an open-ring structure. M-I and M-III open-ring isomers were also observed in patient blood. By contrast, NMR could not detect these open-ring forms. Transplant patients expressing CYP3A5 exhibited higher M-I/TAC ratios in blood and PBMC than non-expressers. Molecular Dynamics simulations showed that: all possible tacrolimus metabolites and isomers bind FKPB12; and the hypothetical open-ring structures induce looser binding between FKBP12 and calcineurins, leading to lower CN inhibition. In vitro, tacrolimus bound FKPB12 with more affinity than purified M-I, and the pool of tacrolimus metabolites and purified M-I had only weak inhibitory activity on IL2 secretion and not at all on NFAT nuclear translocation. M-I showed no competitive effect with tacrolimus on either test. Finally, M-I or the metabolite pool did not significantly interact with tacrolimus MLR suppression, thus eliminating a pharmacodynamic interaction.

A simple and easy-to-perform liquid chromatography-mass spectrometry method for the quantification of tacrolimus and its metabolites in human whole blood. Application to the determination of metabolic ratios in kidney transplant patients

Tacrolimus is the cornerstone of immunosuppressive therapy in solid organ transplantation and its blood concentrations are routinely monitored. Tacrolimus is extensively metabolized into metabolites that are supposed to be nephrotoxic. Yet, few analytical methods have been described to simultaneously quantify tacrolimus and its main metabolites. We developed and validated a simple liquid chromatography-mass spectrometry method for the quantification of tacrolimus and its three desmethylated metabolites, 13-O, 15-O, and 31-O-desmethylated tacrolimus (M-I, M-III, and M-II respectively) in human whole blood. Protein precipitation of 50 µL of whole blood with 100 µL methanol and zinc sulfate was used as a single-extraction procedure. Tacrolimus and its metabolites were quantified using electrospray ionization-triple quadrupole mass spectrometry in combination with selected reaction monitoring detection in the positive ionization mode. The method was validated following FDA recommendations. This method was precise (intra- and inter-assay coefficients of variation: 2.88-7.81% and 3.96-12.10% for low and high levels of internal quality controls, respectively) and accurate (intra- and inter-assay biases: -1.67-10.30%, and -0.77--9.36%, respectively). In adult kidney transplant patients who were treated with tacrolimus prolonged release formulation, the median (10th-90th percentiles) trough concentrations (n = 16) of tacrolimus, M-I, and M-III were 5.85 (3.37-7.09), 0.100 (0.037-0.168), 0.051 (0.03-0.104), respectively. M-II was measured in only 2 trough samples. The metabolic ratios M-I/tacrolimus and M-III/tacrolimus were 0.017 (0.009-0.027) and 0.009 (0.006-0.015) when measured on trough concentration and 0.022 (0.011-0.037) and 0.008 (0.006-0.015) when measured on area under the curves 0-24 h. This method is a suitable and easy-to-perform tool for future pharmacokinetic-pharmacodynamics studies investigating the importance of tacrolimus and its metabolites blood exposure for solid organ graft survival.

Comparison of 4 Commercial Immunoassays Used in Measuring the Concentration of Tacrolimus in Blood and Their Cross-Reactivity to Its Metabolites

BACKGROUND

Therapeutic drug monitoring of tacrolimus is necessary for appropriate dose adjustment for a successful immunosuppressive therapy. Several commercial immunoassays are available for tacrolimus measurements. This study aimed at simultaneously evaluating the analytical performances of 4 such immunoassays, using liquid chromatography-tandem mass spectrometry (LC-MS/MS) as a standard. For the first time, cross-reactivity to tacrolimus metabolites was assessed at concentrations frequently observed in clinical settings, as opposed to the higher concentrations tested by assay manufacturers.

METHODS

An affinity column-mediated immunoassay (ACMIA), using upgraded flex reagents; released in 2015, a chemiluminescence immunoassay (CLIA), an electrochemiluminescence immunoassay (ECLIA), and a latex agglutination turbidimetric immunoassay (LTIA) were evaluated using frozen whole blood samples collected from transplantation patients. Cross-reactivities to 3 major tacrolimus metabolites (13-O-demethyl-tacrolimus [M-I], 31-O-demethyl-tacrolimus [M-II], and 15-O-demethyl-tacrolimus [M-III]) were evaluated.

RESULTS

Each immunoassay correlated well with LC-MS/MS, and the Pearson's correlation coefficients (R) were 0.974, 0.977, 0.978, and 0.902 for ACMIA, CLIA, ECLIA, and LTIA, respectively. Using Bland-Altman difference plots to compare the immunoassays with LC-MS/MS, the calculated average biases were -6.73%, 6.07%, 7.46%, and 12.27% for ACMIA, CLIA, ECLIA, and LTIA, respectively. The cross-reactivities of ACMIA to the tacrolimus metabolites M-II and M-III were 81% and 78%, respectively, when blood was spiked at 2 ng/mL, and 94% and 68%, respectively, when it was spiked at 5 ng/mL.

CONCLUSIONS

Each immunoassay was useful, but had its own characteristics. ACMIA cross-reactivities to M-II and M-III were much higher than the respective 18% and 15% reported on its package insert, suggesting that cross-reactivity should be examined at clinically relevant concentrations.

Relationship between In Vivo CYP3A4 Activity, CYP3A5 Genotype, and Systemic Tacrolimus Metabolite/Parent Drug Ratio in Renal Transplant Recipients and Healthy Volunteers

CYP3A5 genotype is a major determinant of tacrolimus clearance, and has been shown to affect systemic tacrolimus metabolite/parent ratios in healthy volunteers, which may have implications for efficacy and toxicity. In a cohort of 50 renal transplant recipients who underwent quantification of CYP3A4 activity using the oral midazolam drug probe, we confirmed that CYP3A5 genotype is the single most important determinant of tacrolimus metabolite/parent ratio [CYP3A5 expressors displayed 2.7- and 2-fold higher relative exposure to 13-desmethyltacrolimus (DMT) and 31-DMT, respectively; P < 0.001]. There was, however, no relationship between CYP3A4 activity and tacrolimus metabolite/parent ratios. Additional analyses in 16 healthy volunteers showed that dual pharmacological inhibition of CYP3A4 and P-glycoprotein using itraconazole resulted in increased tacrolimus metabolite/parent ratios (+65%, +112%, and 25% for 13-, 15-, and 31-DMT, respectively; P < 0.01). This finding was confirmed in a cohort of nine renal transplant recipients who underwent tacrolimus pharmacokinetic assessments before and during CYP3A4 inhibition (58% increase in overall metabolite/tacrolimus ratio; P = 0.017).

Long-Term Influence of CYP3A5 Gene Polymorphism on Pharmacokinetics of Tacrolimus and Patient Outcome After Living Donor Liver Transplantation

BACKGROUND

We investigated a long-term association between donor/recipient CYP3A5 polymorphisms, pharmacokinetics of tacrolimus, and recipient outcomes in settings of living donor liver transplantation (LDLT).

METHODS

From February 2002 to November 2009, 67 couples of donor/recipients with tacrolimus administration, who could be genotyped for CYP3A5*3 and *1, were eligible in this study. We compared the dose-adjusted trough levels (C/D ratio) and dose/weight ratio of tacrolimus at 1 to 36 months postoperatively and recipient prognosis according to donor/recipient CYP3A5 polymorphisms; *1*1 in 7, *1*3 in 15, and *3*3 in 45, based on recipient genotype, and *1*1 in 1, *1*3 in 28, and *3*3 in 38, based on donor genotype.

RESULTS

On the basis of the data from C/D ratio and dose/weight ratio of tacrolimus, the recipients who had *1 allele and/or whose donor had *1allele required significantly high doses of tacrolimus with, compared with those without, all through 3 years after transplantation. These data allowed us to show the importance of not only recipient CYP3A5 polymorphisms but also donor polymorphisms to obtain the target tacrolimus blood concentration. The overall survival rates of the recipients with *1*1 (5-year survival rate: 28.6%) were significantly unfavorable, which might have been caused by over-immunosuppression, compared with those with *1*3 (5-year survival rate: 78.8%) and *3*3 genotype (5-year survival rate: 84.3%).

CONCLUSIONS

Immune suppressive therapy with the use of tacrolimus should be tailored on the basis of CYP3A5 genotype, which may reduce the adverse effects and improve graft outcome.

Assessment of four methodologies (microparticle enzyme immunoassay, chemiluminescent enzyme immunoassay, affinity column-mediated immunoassay, and flow injection assay-tandem mass spectrometry) for measuring tacrolimus blood concentration in Japanese liver transplant recipients

Therapeutic drug monitoring (TDM) and subsequent dosage adjustment for individual patients in the treatment with tacrolimus are required after liver transplantation to prevent rejection and over-immunosuppression, which leads to severe infection and adverse reactions including nephrotoxicity. The purpose of this study was to evaluate the analytical performance among commercially available immunoassay methods, which were microparticle enzyme immunoassay (MEIA), chemiluminescent enzyme immunoassay (CLIA), and affinity column-mediated immunoassay (ACMIA), compared with an assay using liquid chromatography-tandem mass spectrometry (LC-MS/MS). In addition, the flow injection assay (FIA-MS/MS) was also evaluated to determine whether it could be available as a new method of analysis in tacrolimus therapy. The blood tacrolimus concentrations in samples from liver transplant recipients (n = 102) were measured using MEIA, CLIA, ACMIA, and LC-MS/MS. Additional blood samples from liver transplant recipients (n = 54) were analyzed using both FIA-MS/MS and LC-MS/MS. Because the assay performance and characteristics of MEIA, CLIA, ACMIA, and FIA-MS/MS are relatively different, the measured data should be carefully considered depending on the methodology.

Association between CYP3A5 genotypes in graft liver and increase in tacrolimus biotransformation from steroid treatment in living-donor liver transplant patients

  We retrospectively examined whether cytochrome P450 (CYP) 3A5 genotypes are associated with high-dose steroid pulse treatment-induced functional gain of tacrolimus biotransformation in living-donor liver transplant patients. Concentrations of tacrolimus and its 3 primary metabolites, 13-O-demethyl tacrolimus (M-I), 31-O-demethyl tacrolimus (M-II), and 15-O-demethyl tacrolimus (M-III), were measured in trough blood samples from 18 liver transplant patients, by liquid chromatography-tandem mass spectrometry/mass spectrometry (LC-MS/MS). In patients engrafted with a CYP3A5*1-carrying liver but not with a CYP3A5*3/*3-carrying liver, the concentration/dose ratio of tacrolimus significantly fell after therapy, while ratios of M-I/tacrolimus, M-II/tacrolimus, and M-III/tacrolimus were significantly higher after therapy than before (p = 0.032, p = 0.023, and p = 0.0078, respectively). After steroid pulse therapy, the concentration of tacrolimus measured by immunoassay was significantly higher than that measured by LC-MS/MS in patients engrafted with a CYP3A5*1-carrying liver, but not those engrafted with a CYP3A5*3/*3-carrying liver. This suggests that the increased ratio of tacrolimus metabolites/tacrolimus can be explained by induction of CYP3A5 via high-dose steroid pulse therapy. Further, the concentrations of tacrolimus measured by the immunoassays were overestimated, partly because of cross-reactivity of the monoclonal antibody they incorporated to detect tacrolimus, with the increased metabolites in patients with a CYP3A5*1-carrying graft liver.

From gut to kidney: transporting and metabolizing calcineurin-inhibitors in solid organ transplantation

Since their introduction circa 35 years ago, calcineurin-inhibitors (CNI) have become the cornerstone of immunosuppressive therapy in solid organ transplantation. However, CNI's possess a narrow therapeutic index with potential severe consequences of drug under- or overexposure. This demands a meticulous policy of Therapeutic Drug Monitoring (TDM) to optimize outcome. In clinical practice optimal dosing is difficult to achieve due to important inter- and intraindividual variation in CNI pharmacokinetics. A complex and often interdependent set of factors appears relevant in determining drug exposure. These include recipient characteristics such as age, race, body composition, organ function, and food intake, but also graft-related characteristics such as: size, donor-age, and time after transplantation can be important. Fundamental (in vitro) and clinical studies have pointed out the intrinsic relation between the aforementioned variables and the functional capacity of enzymes and transporters involved in CNI metabolism, primarily located in intestine, liver and kidney. Commonly occurring polymorphisms in genes responsible for CNI metabolism (CYP3A4, CYP3A5, CYP3A7, PXR, POR, ABCB1 (P-gp) and possibly UGT) are able to explain an important part of interindividual variability. In particular, a highly prevalent SNP in CYP3A5 has proven to be an important determinant of CNI dose requirements and drug-dose-interactions. In addition, a discrepancy in genotype between graft and receptor has to be taken into account. Furthermore, common phenomena in solid organ transplantation such as inflammation, ischemia- reperfusion injury, graft function, co-medication, altered food intake and intestinal motility can have a differential effect on the expression enzymes and transporters involved in CNI metabolism. Notwithstanding the built-up knowledge, predicting individual CNI pharmacokinetics and dose requirements on the basis of current clinical and experimental data remains a challenge.

[Factors affecting the pharmacokinetics after living donor liver transplant]

Fifty-five thousand organ transplants are performed each year around the world. It is now estimated that over 300,000 organ transplant recipients are alive worldwide. Most of these transplant recipients will remain on immunosuppressive drugs for the remainder of their lives to prevent rejection episodes. Doses of these medications must be judiciously managed to optimize patient outcomes. Subtherapeutic drug concentrations may lead to graft rejection and subsequent graft loss. Supratherapeutic drug concentrations increase the likelihood of drug toxicities and increase the likelihood of opportunistic infections. In this review, the latest reports concerning the factors affecting the pharmacokinetics of tacrolimus and micafungin after living donor liver transplant (LDLT) are summarized. Our experimental results demonstrate that preoperative assessment of cytochrome P450 3A5 (CYP3A5) genotypes in both recipients and donors and an immune cell function assay would be useful not only for predicting tacrolimus pharmacokinetics but also for defining groups at high-risk of infectious complications after LDLT. Finally, monitoring plasma trough micafungin concentrations allows safe and effective dose titration of micafungin in LDLT-recipients with total bilirubin concentrations greater than 5 mg/dL.

Impact of CYP3A5 genetic polymorphism on cross-reactivity in tacrolimus chemiluminescent immunoassay in kidney transplant recipients

BACKGROUND

Tacrolimus immunoassays possess cross-reactivity with metabolites in the blood. The aim of this study was to evaluate the cross-reactivity in tacrolimus chemiluminescent immunoassay (CLIA) in kidney transplant recipients and to characterize the cross-reactivity according to CYP3A5 genetic polymorphism.

METHODS

The subjects were 50 kidney transplant recipients receiving low-dose tacrolimus. Blood levels of tacrolimus at 12h (C(12)) measured by CLIA were compared with that by LC-MS/MS using Bland-Altman analysis. The influence of CYP3A5 genotypes on the cross-reactivity in tacrolimus CLIA was evaluated by interaction plots.

RESULTS

No significant difference was observed in tacrolimus C(12) between the CYP3A5*1/*3 and CYP3A5*3/*3 genotypes. The dose-normalized C(12) of tacrolimus was significantly higher in the CYP3A5*3/*3 genotype than in the CYP3A5*1/*3 genotype. The C(12) ratio of 13-O-demethylate to tacrolimus was significantly lower in the CYP3A5*3/*3 genotype than in the CYP3A5*1/*3 genotype. Tacrolimus C(12) measured by CLIA was 35% higher than that by LC-MS/MS. A higher cross-reactivity was observed in the patients with a tacrolimus C(12) of less than 3 μg/l and CYP3A5*1/*3 genotype.

CONCLUSION

This study confirmed the cross-reactivity in CLIA in kidney transplant recipients receiving low-dose tacrolimus. High metabolic capacity associated with the CYP3A5*1 genotype affected the cross-reactivity in patients with low tacrolimus levels.

Significance of trough monitoring for tacrolimus blood concentration and calcineurin activity in adult patients undergoing primary living-donor liver transplantation

PURPOSE

Tacrolimus pharmacokinetics and calcineurin activity in peripheral blood mononuclear cells (PBMCs) were investigated in adult patients undergoing primary living-donor liver transplantation (LDLT) in order to clarify the significance of monitoring the tacrolimus blood trough concentration during the early post-transplantation period.

METHODS

Fourteen patients were enrolled in this study, and time-course data following the oral administration of a conventional tacrolimus formulation twice daily were obtained at 1 and 3 weeks post-transplantation. The concentration of tacrolimus in whole blood and calcineurin activity in PBMCs were measured.

RESULTS

The apparent clearance of tacrolimus significantly increased at 3 weeks versus 1 week post-transplantation, although the trough concentration did not significantly differ at these time points. The concentration at each sampling time, except at 1 h post-dose, correlated well with the area under the concentration-time curve from 0 to 12 h (AUC(0-12)). Neither the concentration at the trough time point nor AUC(0-12) was correlated with the area under the calcineurin activity-time curve from 0 to 12 h; however, calcineurin activity at the trough time point was strongly correlated with the latter (r (2) > 0.92).

CONCLUSIONS

Based on these results, trough concentration monitoring can be considered an appropriate procedure for routine tacrolimus dosage adjustment in adult LDLT patients. Monitoring of calcineurin activity at the trough time point was also found to be potentially useful for predicting the immunological status of the patient during the tacrolimus dosing interval.

Impact of intestinal CYP2C19 genotypes on the interaction between tacrolimus and omeprazole, but not lansoprazole, in adult living-donor liver transplant patients

To assess the effects of intestinal cytochrome P450 2C19 on the interaction between tacrolimus and proton pump inhibitors, we examined the concentration/dose ratio [(ng/ml)/(mg/day)] of tacrolimus coadministered with omeprazole (20 mg) or lansoprazole (30 mg) to 89 adult living-donor liver transplant patients on postoperative days 22 to 28, considering the CYP2C19 genotypes of the native intestine and the graft liver, separately. The concentration/dose ratio of tacrolimus coadministered with omeprazole was significantly higher in patients with two variants (*2 or *3) for intestinal CYP2C19 (median, 6.38; range, 1.55-22.9) than intestinal wild-type homozygotes (median, 2.11; range, 1.04-2.54) and heterozygotes (median, 2.11; range, 0.52-4.33) (P = 0.010), but the extent of the increase was attenuated by carrying the wild-type allele in the graft liver even when patients were CYP3A5*1 noncarriers. Conversely, the CYP2C19 polymorphisms both in the native intestine and in the graft liver little influenced the interaction between tacrolimus and lansoprazole, but CYP3A5*1 noncarriers showed higher tacrolimus concentration/dose ratio than CYP3A5*1 carriers. Furthermore, our experiments in vitro revealed that lansoprazole had a stronger inhibitory effect on the CYP3A5-mediated metabolism of tacrolimus than omeprazole, although not significantly (IC(50) = 19.9 +/- 13.8 microM for lansoprazole, 53.7 +/- 6.1 microM for omeprazole). Our findings suggest that intestinal and graft liver CYP2C19 plays a relatively greater role in the metabolism of omeprazole than it does for lansoprazole, so that the effects of CYP3A5 on the metabolism of tacrolimus might be masked by the interaction with omeprazole associated with the CYP2C19 genotype.