Simultaneous Quantification of Mycophenolic Acid and Its Glucuronide Metabolite in PBMCs from Kidney Transplant Recipients by LC-MS/MS.

BACKGROUND

Mycophenolic acid (MPA), administered as mycophenolate mofetil (MMF) or enteric-coated mycophenolate sodium (EC-MPS), is the first-line immunosuppressant for kidney transplant patients. Traditional plasma-based therapeutic drug monitoring (TDM) for MPA fails to accurately reflect intracellular drug exposure at the pharmacological action site.

PURPOSE: This study aimed to establish and validate a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous quantification of MPA and its glucuronide metabolite, MPAG, in peripheral blood mononuclear cells (PBMCs) to support cellular pharmacokinetic (PK) assessment.

METHODS

Chromatographic separation was performed on a BEH C18 column using methanol-water containing 0.1% formic acid and 5 mmol/L ammonium acetate. A total of 139 PBMC samples from 40 kidney transplant recipients (n=19 receiving EC-MPS; n=21 receiving MMF) were analyzed to evaluate the plasma-PBMC PK correlations and gender-related differences.

RESULTS

The method exhibited excellent linearity over the concentration range of 0.2-500 ng/mL (R2 > 0.998), along with acceptable precision, accuracy and matrix effect. The analytes remained stable under various experimental conditions. Significant inter-individual variability in intracellular MPA and MPAG concentrations was observed among patients. Spearman correlation analysis demonstrated a weak-to-moderate positive correlation between plasma and intracellular PBMC concentrations of MPA (EC-MPS, Rs=0.396; MMF, Rs=0.480). Additionally, the concentration-time profiles of MPA and MPAG in PBMCs of kidney transplant recipients after administration of EC-MPS or MMF exhibited different characteristics. No significant gender-based differences in plasma and PBMCs were observed.

CONCLUSION

We established and validated an LC-MS/MS method for simultaneous quantification of intracellular MPA and MPAG. The observed weak-to-moderate correlation between plasma and PBMC exposure highlights the inherent limitations of conventional plasma-based TDM for MPA. Collectively, our study provides a feasible approach for monitoring intracellular drug levels and facilitates the optimization of individualized immunosuppressive dosing regimens for renal transplant recipients.