Optimization and application of an HPLC method for quantification of inosine-5′-monophosphate dehydrogenase activity as a pharmacodynamic biomarker of mycophenolic acid in Chinese renal transplant patients

Background The immunosuppressive agent mycophenolic acid (MPA) is a non-competitive, reversible inhibitor of inosine-5′-monophosphate dehydrogenase (IMPDH). Thus, IMPDH activity can serve as a potential pharmacodynamic biomarker to optimize dosing of MPA. Methods Peripheral blood mononuclear cells were isolated from 2 mL blood samples and an in vitro enzymatic reaction was subsequently performed for 120 min. To determine IMPDH activity in Chinese healthy volunteers and renal transplant patients, a high performance liquid chromatography assay was established and validated by subtracting adenosine monophosphate (AMP) from blank samples for eliminating exogenous AMP interference. Results The accuracy of our method ranged between −0.8% and 12.5%, and the precision ranged between 0.7% and 6.3%. The mean value of IMPDH activity across 11 healthy volunteers was 46.60 ± 14.28 μmol/s/mol AMP. A negative relationship between MPA concentration and IMPDH activity was observed in four renal transplant patients treated with MPA 13 days post-transplantation, while the inhibitory rate of IMPDH activity ranged from 24% to 42%. Conclusion A bioanalytical assay for IMPDH quantification was optimized and evaluated. The differences in the pharmacodynamics of MPA between Asians and Caucasians may provide some evidence for dosing differences among ethnicities.