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Comparison of CYP2A6 catalytic activity on coumarin 7-hydroxylation in human and monkey liver microsomes

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Summary

Comparison of 7-hydroxylation of coumarin, a CYP2A6 substrate, in human and African green and cynomolgus monkey liver microsomes was made by means of an HPLC assay with UV detection. In human liver microsomes, the Km and Vmax values for the metabolic conversion were 2.1 μM and 0.79 nmol/mg/min, respectively. While African green monkey showed Km and Vmax values of 2.7 μM and 0.52 nmol/mg/min, which were similar to human, higher Km and Vmax values were found in cynomolgus monkey. Coumarin 7-hydroxylation in human and African green monkey was selectively inhibited by methoxsalen and pilocarpine (CYP2A6 inhibitors) but not by other inhibitors, i.e. α-naphthoflavone (CYP1A1), orphenadrine (CYP2B6), sulfaphenazole (CYP2C9), quinidine (CYP2D6) and ketoconazole (CYP3A4). Immunoinhibition results supported CYP2A6 involvement in human and its homolog in monkey in coumarin 7-hydroxylation, as only anti-CYP2A6, but not CYP2B1, CYP2C13, CYP2D6, CYP2E1 or CYP3A antibodies, inhibited this conversion. African green monkey was found to be similar to human in catalytic activity of coumarin 7-hydroxylation and response to CYP2A6 inhibitors or antibody inhibition. However, the monkey CYP2A6 is not identical to the human in that Ki values were different, and differences were observed with some CYP2A6 inhibitors, such as nicotine and methoxsalen, suggesting that, under some circumstances, studies of nicotine kinetics and drug taking behavior in monkey may not be comparable to human.

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Authors and Affiliations

  1. Department of Medicine and Psychiatry, University of Toronto, Toronto, Ontario, Canada

    Yan Li, Ning-Yuan Li & Edward M. Sellers

  2. Department of Psychopharmacology and Dependence Research Unit, Center for Research in Women’s Health, Women’s College Hospital, Toronto, Ontario, Canada

    Yan Li, Ning-Yuan Li & Edward M. Sellers

  3. Addiction Research Foundation, Toronto, Ontario, Canada

    Yan Li, Ning-Yuan Li & Edward M. Sellers

  4. Department of Pharmacology, Room 4334, Medical Sciences Building, University of Toronto, 1 King’s College Circle, M5S 1A8, Toronto, Ontario, Canada

    Yan Li, Ning-Yuan Li & Edward M. Sellers

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  1. Yan Li
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Li, Y., Li, NY. & Sellers, E.M. Comparison of CYP2A6 catalytic activity on coumarin 7-hydroxylation in human and monkey liver microsomes. Eur. J. Drug Metab. Pharmacokinet. 22, 295–304 (1997). https://doi.org/10.1007/BF03190960

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