title: Interaction of serum proteins with CYP isoforms in human liver microsomes: inhibitory effects of human and bovine albumin, alpha-globulins, alpha-1-acid glycoproteins and gamma-globulins on CYP2C19 and CYP2D6.
abstract: The effects of serum proteins on the in vitro hydroxylation pathways of mephenytoin (CYP2C19) and debrisoquine (CYP2D6) were studied to enhance the predictability of in vivo drug metabolism from in vitro assays. Both CYP substrates are known to be weakly bound to albumin and the applicability of the free drug hypothesis was further appraised. Since bovine serum albumin (BSA) is used widely in in vitro assays, a comparison between human and bovine proteins was made. Four major serum proteins were studied: albumin, alpha1-acid glycoprotein (AGP), alpha- and gamma-globulins. Human serum albumin (HSA) inhibited both CYP activities about 20% more than BSA. The addition of human alpha-globulins, but not the bovine protein, resulted in marked reduction of 86% and 41% in CYP2C19 and CYP2D6 activities, respectively. This reduction of activity was strikingly greater than the fraction bound (14 and 22%, respectively). The inhibition was of the competitive type and the Ki values of human alpha-globulins on CYP2C19 and CYP2D6 were found to be 0.45% (4.5 mg/ml) and 3.5% (35 mg/ml), respectively. The effect of both human and bovine gamma-globulins on CYP isoforms was negligible. The Ki values of human and bovine AGP for CYP2C19 were 1.84% (420 microM) and 0.93% (210 microM), respectively. For HSA, human alpha-globulins and human and bovine AGP, the strongly decreased CYP activities in vitro cannot be explained by the free drug hypothesis. A direct interaction of these serum proteins with CYP enzymes is postulated. Differential effects of bovine and human serum proteins and CYP specific inhibition were observed.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, University of Toronto, Canada M5S1A8.
authors.forename: Bang Qian
authors.initials: BQ
authors.lastname: Xu
authors.forename: Mikio
authors.initials: M
authors.lastname: Ishii
authors.forename: Li Rong
authors.initials: LR
authors.lastname: Ding
authors.forename: Nancy E
authors.initials: NE
authors.lastname: Fischer
authors.forename: Tadanobu
authors.initials: T
authors.lastname: Inaba
mesh_terms: D000510:Alpha-Globulins / Q000494:pharmacology; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors; D001798:Blood Proteins / Q000494:pharmacology*; D002417:Cattle; D002855:Chromatography, Thin Layer; D065731:Cytochrome P-450 CYP2C19; D065690:Cytochrome P-450 CYP2D6 Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D003647:Debrisoquin / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008617:Mephenytoin / Q000097:blood; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors; D009961:Orosomucoid / Q000494:pharmacology; D011485:Protein Binding; D012709:Serum Albumin / Q000494:pharmacology; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D005719:gamma-Globulins / Q000494:pharmacology
chemical_list: D000510:Alpha-Globulins; D001798:Blood Proteins; D065690:Cytochrome P-450 CYP2D6 Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D009961:Orosomucoid; D012709:Serum Albumin; D005719:gamma-Globulins; D012710:Serum Albumin, Bovine; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; D065731:Cytochrome P-450 CYP2C19; D008617:Mephenytoin; D003647:Debrisoquin