Investigation of pilocarpine oxidative and hydrolytic metabolism in chimeric mice with humanized liver

Chimeric mice with humanized liver (humanized-liver mice) are an attractive alternative to conventional animals for predicting pharmacokinetics in humans. We aimed to investigate the role of CYP2A6 and PON1 on pilocarpine biotransformation in humanized-liver mice. Following a single oral dose of 10 mg/kg, higher plasma concentrations of pilocarpine and 3-hydroxypilocarpine were observed in humanized-liver mice than in non-humanized mice. The ratios of area under the curve (AUC) to total AUC for pilocarpine in humanized-liver mice were more similar to those observed in humans with extensive metabolizer phenotypes for CYP2A6 compared to those in non-humanized mice for both 3-hydroxypilocarpine and pilocarpic acid. Pilocarpine 3-hydroxylase activity in liver microsomes was higher in humanized-liver mice than in non-humanized mice, whereas the pilocarpine hydrolase activity in plasma was comparable between both groups. CYP2A6 levels and pilocarpine 3-hydroxylase activities in liver microsomes from humanized-liver mice were correlated (P = 0.04). Furthermore, both hepatic microsomal 3-hydroxylase and plasma hydrolase activities of pilocarpine in humanized-liver mice decreased in the presence of respective human CYP2A6 or PON1 inhibitors. The plasma metabolite profiles of pilocarpine in humanized-liver mice were similar to those in humans, highlighting the suitability of humanized-liver mice for investigating CYP2A6-and PON1-dependent drug biotransformation in humans.