Abstract: (1) Background: No consensus has been reached on indicators and protocols for monitoring drug concentrations in organ transplant recipients for the immunosuppressant mycophenolic acid (MPA) in clinical therapy.In this study, we propose to establish a Ultra Performance Liquid Chromatography–Tandem Mass Spectrometry (UPLC-MS/MS) for quantitative determination of MPA and its metabolites ( mycophenolic acid carboxybutoxyether, MPAG and mycophenolic acid carboxyglucuronide, AcMPAG) concentrations in peripheral blood mononuclear cells (PBMCs) and to assess the clinical application of PBMCs concentration detection of MPA and its metabolites in infection prediction in Chinese kidney transplant recipients(KTRs); (2) Methods: PBMCs were isolated with Ficoll-Paque solution, and cells were counted. Acetonitrile precipitated proteins to extract the target compounds.Waters ACQUITY UPLC BEH C18 column of 1.7μm (2.1 mm*50 mm) and an ACQUITY-Xevo TQ-S UPLC-MS/MS system were used for the detection with mobile phases: water and methanol (containing 2 mmol/L NH4Ac + 0.1% formic acid); flow rate: 0.3 mL/min. After gradient elution, the samples were positively ionized by an electrospray positive ion source (ESI) and then quantitatively analyzed by a triple quadrupole tandem mass spectrometer in multiple reaction monitoring (MRM) mode. The performance of the established method was evaluated through a series of validation experiments according to the requirements of the relevant guidelines. We enrolled 7 KTRs with stable conditions and 8 KTRs with infection from August to November 2022, who were treated at the West China Hospital of Sichuan University.Their peripheral blood samples were collected and detected MPA, MPAG, and AcMPAG concentrations in PBMCs using the methods mentioned above and evaluated for their clinical application in the prediction and monitoring of infections in KTRs; (3) Results: After validation of the methodology, the UPLC-MS/MS method established in this study for the determination of MPA, MPAG, and AcMPAG concentrations in PBMCs showed good linearity in the quantitative ranges of 0.0625-50 ng/ml, 0.5-50 ng/ml and 0.1-20 ng/ml, and the selectivity, specificity, matrix effect, carry-over contamination, reproducibility, precision and accuracy all satisfied the requirements.AcMPAG in PBMCs was poorly stabilized and showed significant degradation after -80°C storage for 24 h or 3 cycles of freeze-thaw.There was a large variability in MPA and MPAG concentrations in PBMCs of KTRs and it correlated poorly with plasma MPA concentrations (rs=0.206,p=0.117).Subgroup analysis showed that the correlation between MPA in plasma and PBMCs was still poor in the infected group(rs=0.201,p=0.116), but significant correlation in the stable group (rs=0.643,p=0.001). A significantly higher level of MPA in PBMCs was observed in the infected group than those in the stable group at 2h and 4h after drug dosing (p<0.05).AcMPAG concentrations in PBMCs of KTRs were extremely low and virtually undetectable.ROC curve analysis (area under the curve, AUC) was performed for infection after renal transplantation with indicators of significant difference showed that the area AUC for PBMCs-MPA-C4 was 0.928 ,for PBMCs-MPA-C2 was 0.875,and for Plasma-MPA-C4 was 0.803; (4) Conclusions: In this study, a method based on UPLC-MS/MS was developed and validated for the simultaneous determination of MPA, MPAG, and AcMPAG concentrations in PBMCs.With easy operability and good stability, this method provides a reliable analytical method for the clinical implementation of the detection of MPA, MPAG, and AcMPAG concentrations in PBMCs.The concentrations of MPA and MPAG in PBMCs from KTRs were highly variable and were closely associated with the development of infections after renal transplantation.Monitoring MPA and MPAG in PBMCs may be useful indicators for mycophenolic acid therapeutic drug concentration monitoring (TDM) in KTRs.
