Comparative performance of oral midazolam clearance and plasma 4β-hydroxycholesterol to explain interindividual variability in tacrolimus clearance

Abstract

Aims: We compared the CYP3A4 metrics weight-corrected midazolam apparent oral clearance (MDZ Cl/F/W) and plasma 4β-hydroxycholesterol/cholesterol (4β-OHC/C) as they relate to tacrolimus (TAC) Cl/F/W in renal transplant recipients.

Methods: For a cohort of 147 patients, 8 h area under the curve (AUC) values for TAC and oral MDZ were calculated besides measurement of 4β-OHC/C. A subgroup of 70 patients additionally underwent intravenous erythromycin breath test (EBT) and were administered the intravenous MDZ probe. All patients were genotyped for common polymorphisms in CYP3A4, CYP3A5 and P450 oxidoreductase, among others.

Results: MDZ Cl/F/W, 4β-OHC/C/W, EBT and TAC Cl/F/W were all moderately correlated (r = 0.262-0.505). Neither MDZ Cl/F/W nor 4β-OHC/C/W explained variability in TAC Cl/F/W in CYP3A5 expressors (n = 29). For CYP3A5 non-expressors (n = 118), factors explaining variability in TAC Cl/F/W in a MDZ-based model were MDZ Cl/F/W (R² = 0.201), haematocrit (R² = 0.139), TAC formulation (R² = 0.107) and age (R² = 0.032; total R² = 0.479). In the 4β-OHC/C/W-based model, predictors were 4β-OHC/C/W (R² = 0.196), haematocrit (R² = 0.059) and age (R² = 0.057; total R² = 0.312). When genotype information was ignored, predictors of TAC Cl/F/W in the whole cohort were 4β-OHC/C/W (R² = 0.167), MDZ Cl/F/W (R² = 0.045); Tac QD formulation (R² = 0.036), and haematocrit (R² = 0.032; total R² = 0.315). 4β-OHC/C/W, but not MDZ Cl/F/W, was higher in CYP3A5 expressors because it was higher in CYP3A4*1b carriers, which were almost all CYP3A5 expressors.

Conclusions: A MDZ-based model explained more variability in TAC clearance in CYP3A5 non-expressors. However, 4β-OHC/C/W was superior in a model in which no genotype information was available, likely because 4β-OHC/C/W was influenced by the CYP3A4*1b polymorphism.

Keywords: 4β-hydroxycholesterol; CYP3A4; CYP3A5; kidney transplantation; midazolam; tacrolimus.

Figure 1

Correlation between TAC Cl/F/W and MDZ Cl/F/W (A) or 4β‐OHC/C/W (B). CYP3A4*22 carriers were all CYP3A4*1/*22. There were two CYP3A4*1b carriers in the CYP3A5*3/*3 group and 12 CYP3A4*1b carriers in the CYP3A5*1 carrier group

Figure 2

4β‐OHC/C/W according to recipient CYP3A4 genotype. The CYP3A4*1 group includes 16 CYP3A5 expressors; the CYP3A4*1b group includes 12 CYP3A5 expressors. CYP3A5 genotype was not predictive of 4β‐OHC/C/W concentration after correction for CYP3A4 genotype (see text). 4β‐OHC/C/W, weight‐corrected 4β‐hydroxycholesterol/cholesterol

Figure 3

TAC clearance, MDZ clearance, 4β‐OHC and EBT according to recipient genotype. CYP3A4*22 and CYP3A5*1 had a clear effect on TAC clearance, whereas MDZ Cl/F/W was only influenced by CYP3A4*22. 4β‐OHC/C/W was affected by CYP3A4*22 and CYP3A4*1b, which was in strong linkage disequilibrium with CYP3A5 (all CYP3A4*1b carriers were also CYP3A5 expressors, apart from two CYP3A4*1b/CYP3A5*3 patients who are not shown). The CYP3A5*1/CYP3A4*1 group includes one homozygous CYP3A5*1/5*1 patient and one CYP3A4*22/CYP3A5*1 patient. 4β‐OHC/C/W, weight‐corrected 4β‐hydroxycholesterol/cholesterol; C ₀/D, dose‐corrected trough level; EBT C60, erythromycin breath test recovery after 60 min; MDZ, midazolam; TAC, tacrolimus; Cl/F/W, weight‐corrected apparent oral clearance