026: Differential Induction Effects of Prednisone & Prednisolone on Mycophenolic Acid Intrinsic Clearance

Statement of Purpose: Mycophenolic acid (MPA) is commonly prescribed for the prevention of graft rejection post-transplantation. MPA is frequently combined with prednisone/prednisolone (the latter in tapering regimens) for maintenance immunosuppression. Despite multiple reviews having suggested potential induction effects of corticosteroids on the metabolism of MPA, definitive evidence is still lacking (Rong and Kiang. Clin Pharmacokinet. 2023; 62:157-207). We hypothesized that prednisone/prednisolone can induce the metabolism of MPA (i.e., increasing the formation of the MPA-glucuronide [MPAG] metabolite) in a human hepatoma cell line.

Description of Methods & Materials: Metabolically competent HepaRG cells were maintained/differentiated per manufacture’s protocol (0.4 million/well in 24-well plates) and exposed to medium without hydrocortisone and dimethyl sulfoxide for 6 days prior to treatment. Initial time-course experiments to determine MPAG formation and MPA depletion were conducted by collecting supernatants from cells exposed to 0.4 µg/mL MPA (physiological concentration) for 0, 0.5, 1, 1.5, 3, 6 and 12 hours. Once linear conditions were determined, cells were pre-incubated with rifampicin (20 and 100 µM, positive control), prednisone (40, 80 and 400 µg/L), or prednisolone (200, 800 and 2,000 µg/L) for 3 or 6 days prior to MPA exposure. Concentrations of MPA and MPAG were quantified using a validated liquid‐chromatography tandem-mass spectrometry assay developed in our laboratory. One-way analysis of variance followed by Tukey or Kruskal-Wallis tests was used to determine statistical significance.

Data & Results: MPAG formation and MPA depletion were linear until 1.5 hours in cells exposed to 0.4 µg/mL MPA. The duration of inducer pre-incubation (i.e., 3-day vs 6-day) did not affect MPAG formation or MPA depletion. Rifampicin (20 µM and 100 µM, 6-day pre-incubation) increased MPAG formation by 55.9±17.6% (mean±standard deviation, p < 0.05) and 68.3±14.5%; while decreasing MPA concentrations by 41.2±6.1% and 43.9±5.4% compared to the control, respectively. Physiological concentrations of prednisone (40 and 80 µg/L) generated 5.7±13.7% and 9.8±17.3% increases in MPAG formation (6-day pre-incubation) and 10.7±1.8% and 14.9±4.9% reductions in MPA concentrations, respectively. Demonstrating a greater effect, cells treated with physiological concentrations of prednisolone (200 and 800 µg/L) exhibited 26.1±13.5% and 50.7±11.4% increases in MPAG formation (6-day pre-incubation) and 10.3±8.5% and 31.8±14.3% decreases in MPA concentrations, respectively. Supporting plateauing responses at the highest physiological concentrations, supra-physiological concentrations of prednisone (400 µg/L) and prednisolone (2,000 µg/L) did not lead to further increases (i.e., 14.5±22.4% and 54.2±9.6%) in MPAG production or decreases (i.e., 18.7±8.9% and 30.4±10.0%) in MPA concentrations, respectively.

Interpretation, Conclusion or Significance: To our knowledge, this is the first in vitro evidence supporting the induction effects of corticosteroids on the intrinsic clearance of MPA. Physiological concentrations of prednisolone generated greater effects compared to prednisone, suggesting the biological effects of prednisone are primarily mediated through its bioactive metabolite, prednisolone. Further in vitro experiments are being planned in our laboratory to characterize the contributing molecular mechanisms behind this drug interaction. Additional clinical studies are also ongoing to determine if MPA dosing should be tailored to corticosteroid tapering.

Disclosures: We acknowledge Christiane Guguen-Guillouzo, Philippe Gripon, Christian Trepo, and Biopredic International for supplying the undifferentiated cryopreserved HepaRG cells. This work was funded by a start‐up grant for Dr. Tony Kiang from the Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta. The authors declare no conflict of interests.