Verapamil hepatic clearance in four preclinical rat models: towards activity-based scaling

• Published in: Biopharmaceutics & drug disposition Vol. 36; no. 7; pp. 462 - 480
• Main Authors: Nicolaï, J., De Bruyn, T., Van Veldhoven, P. P., Keemink, J., Augustijns, P., Annaert, P.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.10.2015; Wiley Subscription Services, Inc
• Subjects: Animals; Cells, Cultured; Drug Evaluation, Preclinical - methods; hepatic clearance; Hepatocytes - drug effects; Hepatocytes - metabolism; isolated perfused liver; Kpu; Kpu,u; Liver - drug effects; Liver - metabolism; liver microsomes; Male; Metabolic Clearance Rate - drug effects; Metabolic Clearance Rate - physiology; Microsomes, Liver - drug effects; Microsomes, Liver - metabolism; Models, Animal; Rats; scaling factors; suspended hepatocytes; verapamil; Verapamil - metabolism; Verapamil - pharmacology; isolated perfused liver; verapamil; scaling factors; hepatic clearance; Kpu,u; suspended hepatocytes; liver microsomes
• ISSN: 0142-2782; 1099-081X
• DOI: 10.1002/bdd.1959

The current study was designed to cross‐validate rat liver microsomes (RLM), suspended rat hepatocytes (SRH) and the isolated perfused rat liver (IPRL) model against in vivo pharmacokinetic data, using verapamil as a model drug. Michaelis‐Menten constants (Km), for the metabolic disappearance kinetics of verapamil in RLM and SRH (freshly isolated and cryopreserved), were determined and corrected for non‐specific binding. The ‘unbound’ Km determined with RLM (2.8 µ m) was divided by the ‘unbound’ Km determined with fresh and cryopreserved SRH (3.9 µ m and 2.1 µ m, respectively) to calculate the ratio of intracellular to extracellular unbound concentration (Kpu,u). Kpu,u was significantly different between freshly isolated (0.71) and cryopreserved (1.31) SRH, but intracellular capacity for verapamil metabolism was maintained after cryopreservation (200 vs. 191 µl/min/million cells). Direct comparison of intrinsic clearance values (Clint) in RLM versus SRH, yielded an activity‐based scaling factor (SF) of 0.28–0.30 mg microsomal protein/million cells (MPPMC). Merging the IPRL‐derived Clint with the MPPMC and SRH data, resulted in scaling factors for MPPGL (80 and 43 mg microsomal protein/g liver) and HPGL (269 and 153 million cells/g liver), respectively. Likewise, the hepatic blood flow (61 ml/min/kg b.wt) was calculated using IPRL Clint and the in vivo Cl. The scaling factors determined here are consistent with previously reported CYP450‐content based scaling factors. Overall, the results show that integrated interpretation of data obtained with multiple preclinical tools (i.e. RLM, SRH, IPRL) can contribute to more reliable estimates for scaling factors and ultimately to improved in vivo clearance predictions based on in vitro experimentation. Copyright © 2015 John Wiley & Sons, Ltd.