title: Metabolism of pimobendan in long-term human hepatocyte culture: in vivo-in vitro comparison.
abstract: The aim of this study was to investigate further the potential of a new hepatocyte culture based on the hypothesis that liver cells in an appropriate in vitro environment (immobilizing gel technique) maintain high metabolic activity comparable with that in vivo. Pimobendan (UD-CG 115), a pyridazinone derivative, is a cardiotonic vasodilator that increases myocardial contractility through calcium sensitization and relaxation of vascular smooth muscle, probably due to phosphodiesterase inhibition. In man, pimobendan is O-demethylated to UD-CG 212. This latter is metabolized to O- and N-glucuronides. Pimobendan itself is also glucuronidated to a N-glucuronide. Human hepatocytes immobilized in collagen gel were incubated with pimobendan to investigate their metabolic activity in the long-term and to compare the results to the data from clinical trials. 14C-labelled pimobendan was incubated at two concentrations (10 and 100 microM) at day 3, 11 and 22 of culture, and samples were analysed after 4, 24 and 48-h incubation. Metabolic patterns were evaluated by hplc with radioactivity-, diode array-, and mass spectral-detection. In vitro, pimobendan was O-demethylated and subsequently O-glucuronidated. The rate of metabolism of pimobendan could be maintained in this culture system for > 3 weeks. However, the relative amount of a putative N-glucuronide under in vitro conditions was lower than in vivo.
authors.affiliation: Chirurgische Klinik, Klinikum Grosshadern, Ludwig-Maximilians-Universitaet Muenchen, Germany.
authors.forename: S A
authors.initials: SA
authors.lastname: Pahernik
authors.forename: J
authors.initials: J
authors.lastname: Schmid
authors.forename: T
authors.initials: T
authors.lastname: Sauter
authors.forename: F W
authors.initials: FW
authors.lastname: Schildberg
authors.forename: H G
authors.initials: HG
authors.lastname: Koebe
mesh_terms: D001711:Biotransformation; D002316:Cardiotonic Agents / Q000378:metabolism* / Q000493:pharmacokinetics; D002478:Cells, Cultured; D018914:Cells, Immobilized; D002851:Chromatography, High Pressure Liquid; D003094:Collagen; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D005965:Glucuronates / Q000378:metabolism; D020723:Glucuronic Acid; D006801:Humans; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D013058:Mass Spectrometry; D015394:Molecular Structure; D010726:Phosphodiesterase Inhibitors / Q000378:metabolism / Q000493:pharmacokinetics; D011724:Pyridazines / Q000378:metabolism* / Q000493:pharmacokinetics; D014665:Vasodilator Agents / Q000378:metabolism / Q000493:pharmacokinetics
chemical_list: D002316:Cardiotonic Agents; D005965:Glucuronates; D010726:Phosphodiesterase Inhibitors; D011724:Pyridazines; D014665:Vasodilator Agents; C041648:pimobendan; D020723:Glucuronic Acid; D003094:Collagen; D003577:Cytochrome P-450 Enzyme System