Influence of carboxylesterase 2 genetic polymorphisms on mycophenolic acid pharmacokinetics in Japanese renal transplant recipients

Mycophenolic acid (MPA), converted from the prodrug mycophenolate mofetil (MMF), is generated by intestinal and hepatic esterases. The role of carboxylesterase (CES) in MMF hydrolysis was examined in vitro using human liver microsomes. V(max) and K(m) values of MMF hydrolysis in pooled human liver microsomes were 1368 +/- 44 nmol min(-1) mg(-1) protein and 1030 +/- 65 microM, respectively. Hydrolytic activity was inhibited by the CES inhibitors phenylmethylsulfonylfluoride, bis-p-nitorophenylphosphate and diisopropylfluorophosphate, with IC(50) values of 77.1, 3.59 and 0.0312 microM, respectively. Eighty Japanese renal transplant recipients that received repeated-doses of MMF, tacrolimus and prednisolone,were evaluated for MPA pharmacokinetics 28 days after transplantation to investigate the relationship between MPA pharmacokinetics and CES2 genetic polymorphisms. No significant differences in MPA pharmacokinetics were observed between CES2 A4595G, C8721T orA-1548G genotype groups. CES2 allelic variants also did not appear to affect plasma MPA concentrations between individuals. In conclusion, the study demonstrated that while CES1 and/or CES2 are involved in the hydrolysis of MMF to MPA, CES2 allelic variants appeared to make only a minor contribution to inter-personal differences in MPA pharmacokinetics.