Glucuronidation assays were performed using 12.5 μg HLM protein and 300 μM OLZ, and incubated at 37°C for 2 h with 4 mM UDP-glucuronic acid prior to analysis by UPLC as described in the Materials and Methods. Panel A, HLM + vehicle (1% DMSO); panel B, UGT-null HEK 293 cell homogenates + OLZ; panel C, HLM + OLZ; panel D, HLM + OLZ and 1,000 U of β-glucuronidase . Panel E, mass spectra of UPLC peaks 1 and 2; panel F, mass spectra of peak 3; Peak 1, OLZ-10-N-glucuronide isomer 1; peak 2, OLZ-10-N-glucuronide isomer 2; peak 3, OLZ-4’-N-glucuronide; peak 4, OLZ; peak 5, UDP-glucuronic acid. AU, absorbance.