The role of CYP3A5 polymorphism and dose adjustments following conversion of twice-daily to once-daily tacrolimus in renal transplant recipients

Inhibitory effects of traditional Chinese medicine colquhounia root tablet on the pharmacokinetics of tacrolimus in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Tacrolimus (TAC) was widely used in various renal diseases while high recurrence rate and high expense restricted its applications. Traditional herbal medicine has become increasingly popular as an adjuvant therapy to minimize the adverse effects of TAC. Colquhounia root tablet (CRT), a prescribed drug prepared from the water extract of the peeled root of Tripterygium hypoglaucum (H. Lév.) Hutch., showed excellent anti-inflammatory, analgesic and immunosuppressive pharmacological properties. TAC used in combination with CRT was substantially more efficacious and safer than the monotherapy for the treatment of nephrotic syndrome. However, studies on their herb-drug interaction were scanty.

AIM OF THE STUDY

The study was proposed to examine the effect of CRT on the pharmacokinetics of TAC in rats and identify the key natural constituents in CRT that affected the metabolism of TAC.

MATERIALS AND METHODS

TAC was orally and intravenously administered to rats alone or in combination with CRT and the pharmacokinetic parameters of TAC were compared. After pretreatment with CRT for 15 d, the expressions of the drug-metabolizing enzymes (DMEs), drug transporters (DTs) and nuclear receptors (NRs) were determined by polymerase chain reaction and western blotting and compared with the control group. The hepatic microsomal incubation system was employed to confirm the inhibitory effects of CRT and its major components on rat cytochrome P450 (CYP) 3A2. The roles of the primary components in the regulation of human CYP3A4 and mouse P-gp activities were evaluated by using docking analysis.

RESULTS

The blood concentrations of TAC were significantly increased in a dose- and pretreatment time-dependent manner after combined administration of CRT. The maximal effect was found at 300 mg/kg (43.70 ± 8.77 ng/mL and 141.45 ± 21.58 h·ng/mL) in a single dose run and the pharmacokinetic parameters gradually returned to the normal levels at 24 h interval of long-term CRT pretreatment. In contrast, CRT had no effect on the pharmacokinetics of intravenous TAC. Further study indicated that the mRNA and protein expressions of DMEs and DTs, such as CYP3A1, CYP3A2, P-glycoprotein (P-gp) and multidrug resistance-associated protein 2 in rat intestine and liver were down-regulated, whereas the expressions of NRs like constitutive androstane receptor and pregnane X receptor were up-regulated after multiple oral doses of CRT. Molecular docking showed the binding potency of five CRT major constituents with both human CYP3A4 and mouse P-gp. Celastrol, wilforgine and wilforine were the strongest inhibitors towards midazolam metabolism in rat liver microsomes, with the 50% inhibition concentrations being at 8.33 μM, 22.18 μM and 22.22 μM, respectively.

CONCLUSIONS

Our results revealed that co-dosing of CRT could lead to a significant increase in blood concentration of TAC and this effect could be ascribed to the resultant co-regulation of DMEs, DTs and NRs. Our study provided an experimental basis for the combination use of CRT and TAC in clinical practice.

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.

Screening for CYP3A4 inhibition and induction coupled to parallel artificial membrane permeability assay (PAMPA) for prediction of botanical-drug interactions: The case of açaí and maca

BACKGROUND

The consumption of botanical dietary supplements (BDS) is a common practice among the US population. However, the potential for botanical-drug interactions exists, and their mechanisms have not been thoroughly studied. CYP3A4 is an important enzyme that contributes to the metabolism of about 60% of clinically used drugs.

PURPOSE

To investigate the potential for botanical-drug interactions of Lepidium meyenii Walpers (maca) root and Euterpe oleracea Mart. (açaí) berries, two commonly used BDS, when co-administered with CYP3A4-metabolized drugs.

METHODS

In an attempt to decrease the general discrepancy between in vivo and in vitro studies, the absorption profiles, particularly for passive diffusion, of plant extracts were investigated. Specifically, the parallel artificial membrane permeability assay (PAMPA) model was utilized to simulate intestinal filtration of passively diffused constituents of açaí and maca extracts. These were subsequently screened for in vitro liver CYP3A4 inhibition and induction. In the inhibition assay, midazolam was used as the probe substrate on genotyped human liver microsomes (CYP3A5 null), and the production of its 1'-substituted metabolite when co-cultured with extract treatments was monitored. In the induction assay, extract treatments were applied to human primary hepatocytes, and quantitative PCR analysis was performed to determine CYP3A4 mRNA expression.

RESULTS

Passively diffused constituents of the methanol açaí extract (IC₅₀ of 28.03 µg/µl) demonstrated the highest inhibition potential, and, at 1.5 µg/µl, induced significant changes in CYP3A4 gene expression. The composition of this extract was further investigated using the chemometric tool Mass Profiler Professional (MPP) on liquid chromatography-mass spectroscopy (LC-MS) data. Subsequently, five compounds of interest characterized by high abundance or high permeability were extracted for further study. This included efforts in effective passive permeability determination and structural elucidation by tandem mass spectrometry (MS/MS).

CONCLUSION

The passively absorbable portion of a methanol açaí extract exhibited inhibition and induction effects on CYP3A4 suggesting the potential to produce botanical-drug interactions.

CYP3A5 polymorphisms in renal transplant recipients: influence on tacrolimus treatment

Tacrolimus is a commonly used immunosuppressant after kidney transplantation. It has a narrow therapeutic range and demonstrates wide interindividual variability in pharmacokinetics, leading to potential underimmunosuppression or toxicity. Genetic polymorphism in CYP3A5 enzyme expression contributes to differences in tacrolimus bioavailability between individuals. Individuals carrying one or more copies of the wild-type allele *1 express CYP3A5, which increases tacrolimus clearance. CYP3A5 expressers require 1.5 to 2-fold higher tacrolimus doses compared to usual dosing to achieve therapeutic blood concentrations. Individuals with homozygous *3/*3 genotype are CYP3A5 nonexpressers. CYP3A5 nonexpression is the most frequent phenotype in most ethnic populations, except blacks. Differences between CYP3A5 genotypes in tacrolimus disposition have not translated into differences in clinical outcomes, such as acute rejection and graft survival. Therefore, although genotype-based dosing may improve achievement of therapeutic drug concentrations with empiric dosing, its role in clinical practice is unclear. CYP3A5 genotype may predict differences in absorption of extended-release and immediate-release oral formulations of tacrolimus. Two studies found that CYP3A5 expressers require higher doses of tacrolimus in the extended-release formulation compared to immediate release. CYP3A5 genotype plays a role in determining the impact of interacting drugs, such as fluconazole, on tacrolimus pharmacokinetics. Evidence conflicts regarding the impact of CYP3A5 genotype on risk of nephrotoxicity associated with tacrolimus. Further study is required.

Comparative clinical trial of the variability factors of the exposure indices used for the drug monitoring of two tacrolimus formulations in kidney transplant recipients

BACKGROUND

Several studies found differences in tacrolimus whole blood trough levels (C0) or area-under-the curve (AUC) between the twice-daily (Tac-BID) and once-daily (Tac-OD) formulations given to kidney transplant recipients at equal doses. As C0 is widely used as a surrogate of the AUC for individual dose adjustment, this study investigated the correlation and proportionality between C0 and the 24h-AUC, depending on the formulation, time post-transplantation, pharmacogenetics traits and other individual characteristics.

METHODS

45 adult kidney transplant recipients were randomized to receive either Tac OD or Tac BID. On days 8±1 (D8) and 90±3 (month 3, M3), blood samples were collected over 24h in both groups. Tacrolimus concentrations were determined using HPLC-MS/MS and common CYP3A5, CYP3A4 and ABCB1 genotypes characterized using allelic discrimination assays. Tacrolimus population pharmacokinetics was studied in the two patient groups using the Iterative Two Stage (ITS) technique, considering a one-compartment model with two gamma laws to describe the absorption phase. Bayesian estimation based on the C0, C1h and C3h concentrations was employed to estimate individual Tac AUC_0-12h and AUC_12-24h (for Tac BID), or AUC_0-24h (for Tac OD). Multiple linear regression was used to evaluate the influence of Tac formulation, post-transplantation period, recipient gender, existing glucose metabolism disorders, and CYP3A5, CYP3A4 and ABCB1 genotypes on C0, AUC_0-24h and the AUC-to-trough concentration ratios.

RESULTS

The Full Analysis Set comprised 22 patients on Tac OD and 20 on Tac BID. Tac exposure indices as well as their time evolution were similar in the two groups. Multi-linear modeling analysis showed that the Tac dose was higher with Tac-OD than Tac-BID, on D8 than at M3 and in CYP3A5 expressors (p<0.0001 for all). No such influence was found on C0 or C24h, while the AUC_0-24h was significantly higher on D8 than at M3. The AUC_0-24h/C0 ratio was not affected by the drug formulation and the polymorphisms studied, but it was significantly lower on D8 than at M3 (p=7.8×10^-5). In contrast, both the post-transplantation period (p=1.53×10^-4), and CYP3A5 expression (p=0.003) had a significant influence on the AUC_0-24h/C24h ratio, explaining 19% and 12% of its variability, respectively. Consistently, for both Tac formulations, the AUC_0-24h was better correlated with C24h than C0, and for Tac-BID the AUC_0-12h was better correlated with C12h than C0.

CONCLUSIONS

This study confirms that the precisely timed 12h- or 24h-post-dose blood concentration (as opposed to the vaguely defined 'trough level') is a convenient surrogate of the 24h-AUC of tacrolimus for the two TAC formulations over the first 3 months post-transplantation. Still, for a given C24h value, AUC_0-24h was higher on D8 and in CYP3A5 expressors. Bayesian estimation of AUC_0-12h for TAC BID and AUC_0-24h for TAC OD is feasible using only 3 time points within the first 3h, thus giving access to the actual overall exposure.

Pharmacokinetics of prolonged-release tacrolimus and implications for use in solid organ transplant recipients

Prolonged-release tacrolimus was developed as a once-daily formulation with ethylcellulose as the excipient, resulting in slower release and reduction in peak concentration (Cmax ) for a given dose compared with immediate-release tacrolimus, which is administered twice daily. This manuscript reviews pharmacokinetic information on prolonged-release tacrolimus in healthy subjects, in transplant recipients converted from immediate-release tacrolimus, and in de novo kidney and liver transplant recipients. As with the immediate-release formulation, prolonged-release tacrolimus shows a strong correlation between trough concentration (Cmin ) and area under the 24-hour time-concentration curve (AUC24 ), indicating that trough whole blood concentrations provide an accurate measure of drug exposure. We present the pharmacokinetic similarities and differences between the two formulations, so that prescribing physicians will have a better understanding of therapeutic drug monitoring in patients receiving prolonged-release tacrolimus.