title: Inhibition of CYP3A4 and CYP3A5 catalyzed metabolism of alprazolam and quinine by ketoconazole as racemate and four different enantiomers.
abstract: OBJECTIVE
  The antifungal drug ketoconazole (KTZ) is known as an inhibitor of, especially, the CYP3A subfamily, which catalyzes the metabolism of a large variety of drugs. Interactions between KTZ and CYP3A substrates have been reported both in vivo and in vitro. Most of them, however, involved the KTZ racemate. KTZ racemate and the separate enantiomers, 2R,4R; 2R,4S; 2S,4S, and 2S,4R, were evaluated for their selectivity in inhibiting alprazolam and quinine metabolism.
  
  
  METHODS
  The inhibition of alprazolam and quinine metabolism was studied in an in vitro system of human liver microsomes (HLM), recombinant of CYP3A4 and CYP3A5. The concentrations of formed 3-hydroxyquinine and 4- and alpha-hydroxyalprazolam were measured by HPLC and LC-MS, respectively.
  
  
  RESULTS
  Quinine 3-hydroxylation was catalyzed to a similar extent by CYP3A4 and CYP3A5. The formation rate of 4-hydroxyalprazolam was higher than that of alpha-hydroxyalprazolam for each HLM, CYP3A4 and CYP3A5. KTZ racemate and enantiomers showed differential inhibitory effects of quinine and alprazolam metabolism. Quinine metabolism catalyzed by HLM, CYP3A4 and CYP3A5 was potently inhibited by the trans-enantiomer KTZ 2S,4S, with IC(50) value of 0.16 microM for HLM, 0.04 microM for CYP3A4 and 0.11 microM for CYP3A5. The same enantiomer showed the lowest IC(50) values of 0.11 microM for HLM and 0.04 microM for CYP3A5 with respect to alprazoalm 4-hydroxylation and also the same pattern for alprazolamalpha-hydroxylation, 0.13 microM for HLM and 0.05 microM for CYP3A5. Alprazolam metabolism (both alpha- and 4- hydroxylations) catalyzed by CYP3A4 was inhibited potently by the cis-enantiomer KTZ 2S,4R, with IC(50) values of 0.03 microM.
  
  
  CONCLUSIONS
  Alprazolam and quinine metabolism is catalyzed by both CYP3A4 and CYP3A5. The present study showed that different KTZ enantiomers inhibit CYP3A4 and CYP3A5 to different degrees, indicating that structural differences among the enantiomers would be related to their inhibitory potency on these two enzymes.
authors.affiliation: Karolinska Institutet, Department of Laboratory Medicine, Division of Clinical Pharmacology at Karolinska University Hospital, Huddinge, Stockholm, Sweden. annika.allqvist@ki.se
authors.forename: Annika
authors.initials: A
authors.lastname: Allqvist
authors.forename: Jun
authors.initials: J
authors.lastname: Miura
authors.forename: Leif
authors.initials: L
authors.lastname: Bertilsson
authors.forename: Rajaa A
authors.initials: RA
authors.lastname: Mirghani
mesh_terms: D000525:Alprazolam / Q000031:analogs & derivatives* / Q000378:metabolism; D014151:Anti-Anxiety Agents / Q000378:metabolism; D000935:Antifungal Agents / Q000494:pharmacology*; D000962:Antimalarials / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D002853:Chromatography, Liquid; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D006801:Humans; D020128:Inhibitory Concentration 50; D007654:Ketoconazole / Q000737:chemistry / Q000494:pharmacology*; D013058:Mass Spectrometry; D008862:Microsomes, Liver; D011802:Quinidine / Q000031:analogs & derivatives* / Q000378:metabolism; D013237:Stereoisomerism
chemical_list: D014151:Anti-Anxiety Agents; D000935:Antifungal Agents; D000962:Antimalarials; C013569:3-hydroxyquinidine; C032318:alpha-hydroxyalprazolam; D003577:Cytochrome P-450 Enzyme System; C510164:CYP3A5 protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D011802:Quinidine; D007654:Ketoconazole; C503150:4-hydroxyalprazolam; D000525:Alprazolam