Urea in phenol red-free cell differentiation medium was quantified using a colorimetric Urea Assay Kit III (MAK471, MilliporeSigma, St. Louis, MO, USA). Phenol red-free differentiation medium was composed of HepaRG differentiation medium supplement with antibiotics (ADD711C, Biopredic International) in phenol red-free Williams E medium (A1217601, Thermo Fisher, Pittsburgh, PA, USA) and GlutaMAX 100X supplement (35050061, Thermo Fisher, Pittsburgh, PA, USA) diluted to 1X final concentration. An aliquot of 0.75 mL of 24-hr culture medium was collected for urea quantification following the assay kit's manual.