Quinine metabolism in man : emphasis on the 3-hydroxylation as a biomarker reaction for the activity of CYP3A4

<p>Quinine is one of the cinchona alkaloids and used in the treatment of severe forms of malaria. Formation of 3-hydroxyquinine is catalysed by cytochrome P-450 3A4 (CYP3A4), which is the enzyme involved in the metabolism of about 50% of all drugs in clinical use.</p><p>In this thesis I investigated the relative importance of four metabolites of quinine in its metabolism in vitro and in vivo and studied the usefulness of the metabolic ratio (MR) of quinine (quinine/3-hydroxyquinine) as a measure of the activity of CYP3A4 in vivo.</p><p>High performance liquid chromatographic methods for determination of quinine and four of its metabolites in plasma and urine samples were developed. In healthy subjects co-administration of quinine with ketoconazole (inhibits CYP3A4) decreased the mean apparent oral clearance of quinine and mean area under the plasma concentration time curve (AUC) of 3-hydroxyquinine significantly. The mean total urinary recovery of quinine plus its 3hydroxy metabolite was 28±8 %.</p><p>The role of CYP3A4 in the metabolism of quinine to 2'-quininone, (1OS)- and (1OR)-11-dihydroxydihydroquinine in vitro and the relative importance of these metabolites compared to 3-hydroxyquinine in the metabolism of quinine were studied in human liver microsomes. 3-hydroxyquinine had the highest rate of formation and intrinsic clearance in all five human livers used. Incubations with human recombinant CYP3A4 resulted mainly in the formation of 3-hydroxyquinine and to a minor extent 2'-quininone. Formation of these two metabolites but not that of (10R)-11-dihydroxydihydroquinine was completely inhibited by inhibitors of CYP3A4 (ketoconazole and troleandomycin). Formation of (1 OS)-11-dihydroxydihydroquinine was only partly inhibited.</p><p>The effects of ketoconazole and fluvoxamine (inhibitor of CY1P1A2) on the formation of 2'-quininone, (1OR)- and (10S)-11-dihydroxydihydroquinine and the relative importance of these metabolites for the elimination of quinine in vivo were investigated. Co-administration with ketoconazole significantly increased the mean AUC of 2'-quininone and (1OR)-11-dihydroxydihydroquinine, but not that of (10S)-11-dihydroxydihydroquinine. The mean total recovery of quinine plus its four metabolites after hydrolysis of conjugates in urine was 56±16%. We investigated the usefulness of the 3-hydroxylation of quinine as a biomarker reaction for the activity of CYP3A4 in man and the intraindividual variation in the metabolic ratio (MR) of quinine. There was no significant difference (p=0.36) between the mean MRs in plasma or urine collected 16h after a single oral dose of 250 mg of quinine hydrochloride on two different occasions. There was a significant correlation between the MR of quinine and omeprazole sulphone formation (r=0.52, p=0.009), but not to the MRs of probe drugs for the other enzymes.</p><p>Our results strongly suggest that 3-hydroxyquinine is the major metabolite of quinine both in vitro and in vivo and that CYP3A4 is the major enzyme involved in the 3-hydroxylation of quinine. The metabolic ratio of quinine may serve as a stable measure of the activity of CYP3A4.</p><h3>List of scientific papers</h3><p>I. Mirghani RA, Ericsson O, Gustafsson LL (1998). High-performance liquid chromatographic method for the determination of the major quinine metabolite, 3-hydroxyquinine, in plasma and urine. J Chromatogr B. 708(1-2): 209-16. <br><a href="https://pubmed.ncbi.nlm.nih.gov/9653964">https://pubmed.ncbi.nlm.nih.gov/9653964</a><br><br></p><p>II. Mirghani RA, Hellgren U, Westerberg PA, Ericsson O, Bertilsson L, Gustafsson LL (1999). The roles of cytochrome P450 3A4 and 1A2 in the 3-hydroxylation of quinine in vivo. Clin Pharmacol Ther. 66(5): 454-60. <br><a href="https://pubmed.ncbi.nlm.nih.gov/10579472">https://pubmed.ncbi.nlm.nih.gov/10579472</a><br><br></p><p>III. Mirghani RA, Ericsson O, Cook J, Yu P, Gustafsson LL (2001). Simultaneous determination of quinine and four metabolites in plasma and urine by high-performance liquid chromatography. J Chromatogr B. 754(1): 57-64. <br><a href="https://pubmed.ncbi.nlm.nih.gov/11318427">https://pubmed.ncbi.nlm.nih.gov/11318427</a><br><br></p><p>IV. Mirghani RA, Yasar U, Zheng T, Cook JM, Gustafsson LL, Tybring G, Ericsson O (2002). Enzyme kinetics for the formation of four metabolites of quinine in vitro; 3-hydroxylation by CYP3A4 is the major metabolic pathway. [Manuscript]</p><p>V. Mirghani RA, Hellgren U, Bertilsson L, Gustafsson LL, Ericsson O (2002). Formation of four metabolites of quinine; 3-hydroxylation is the major metabolic pathway for the elimination in vivo. [Submitted]</p><p>VI. Mirghani RA, Ericsson O, Tybring G, Gustafsson LL, Bertilsson L (2002). Quinine 3-hydroxylation as a biomarker reaction for the activity of CYP3A4 in man. [Submitted]</p>