title: Evaluation of hepatic disposition of paroxetine using sandwich-cultured rat and human hepatocytes.
abstract: Paroxetine, a selective serotonin reuptake inhibitor, is metabolized in the liver and excreted into bile and urine as metabolites, but species differences have been observed in hepatic disposition between rats and humans. A major metabolite in rats is M1-glucuronide, whereas M1-glucuronide and M1-sulfate are found in humans. The primary excretion route of paroxetine-derived radioactivity in rats and humans is bile and urine, respectively. The aim of this study was to examine the usefulness of sandwich-cultured hepatocytes (SCH) to evaluate in vivo species differences of the hepatic disposition of paroxetine between rats and humans. The metabolite profile of [(3)H]paroxetine in SCH was similar to that in hepatocytes in suspension, and the in vitro metabolite profiles were similar to the published in vivo metabolic pathways for both species. Furthermore, the biliary excretion index (BEI) of formed M1-glucuronide in rat SCH (25.8-50.9%) was higher than that in human SCH (15.1-16.7%). The BEI of formed M1-sulfate (16.4-29.1%) was comparable to that of M1-glucuronide in human SCH, whereas the BEIs of paroxetine were negligible in SCH of both species. Moreover, M1-glucuronide was demonstrated to be a multidrug resistance-associated protein 2 substrate in both species, as determined by its uptake into ATP-binding cassette transporter-expressing membrane vesicles. SCH should prove to be useful to evaluate the processes of hepatic uptake and metabolism of parent drugs and the simultaneous examination of the biliary excretion of both parent drug and liver-derived metabolites.
authors.affiliation: Department of Membrane Transport and Biopharmaceutics, Faculty of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan.
authors.forename: Norikazu
authors.initials: N
authors.lastname: Matsunaga
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Nunoya
authors.forename: Masahiro
authors.initials: M
authors.lastname: Okada
authors.forename: Mikio
authors.initials: M
authors.lastname: Ogawa
authors.forename: Ikumi
authors.initials: I
authors.lastname: Tamai
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000818:Animals; D001646:Bile / Q000378:metabolism; D018929:Cell Culture Techniques / Q000379:methods*; D022781:Hepatocytes / Q000166:cytology* / Q000378:metabolism*; D006801:Humans; D008297:Male; D017374:Paroxetine / Q000493:pharmacokinetics*; D051381:Rats; D017367:Selective Serotonin Reuptake Inhibitors / Q000493:pharmacokinetics*; D013045:Species Specificity; D014018:Tissue Distribution; D022161:Transport Vesicles / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D017374:Paroxetine; D017367:Selective Serotonin Reuptake Inhibitors