RT Journal Article
SR Electronic
T1 Flavin-Containing Monooxygenase Activity in Hepatocytes and Microsomes: In Vitro Characterization and In Vivo Scaling of Benzydamine Clearance
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 1087
OP 1093
DO 10.1124/dmd.30.10.1087
VO 30
IS 10
A1 Michael B. Fisher
A1 Kwansik Yoon
A1 Marcie L. Vaughn
A1 Timothy J. Strelevitz
A1 Robert S. Foti
YR 2002
UL http://dmd.aspetjournals.org/content/30/10/1087.abstract
AB Liver microsomes, and more recently cryopreserved hepatocytes, are commonly used in the in vitro characterization of the metabolism of new xenobiotics. The flavin-containing monooxygenases (FMO) are a major nonP450 oxidase present in liver microsomes and hepatocytes. Since FMO is known to be thermally labile, and this enzyme may be involved in the metabolic clearance of some drugs, we sought to more completely characterize the metabolic competency of this enzyme in cryopreserved hepatocytes and in liver microsomes preincubated under various conditions using benzydamine as an in vitro and in vivo probe. The metabolism of benzydamine to its major metabolite, theN-oxide, is mediated by FMO3 in humans. We found that the in vitro microsomal t1/2 was 70% longer when incubations were prewarmed at 37°C in the absence of NADPH compared with prewarming in the presence of an NADPH-regenerating system, and N-oxide formation was inhibited >99%. Interestingly, the in vivo clearance predicted from these incubations and from human hepatocytes overpredicted the observed clearance of benzydamine in humans (>10.5 versus 2.4 ml/min/kg). In contrast, rat hepatocytes successfully predicted rat in vivo benzydamine clearance to within ∼30% (>68 versus 48 ml/min/kg). BenzydamineN-oxidation in liver microsomes from all common preclinical species demonstrated heat sensitivity. This information should be considered when extrapolating metabolism data of xenobiotics from these in vitro systems. The American Society for Pharmacology and Experimental Therapeutics