TY - JOUR T1 - Theophylline acetaldehyde as the initial product in Doxophylline metabolism in human liver JF - Drug Metabolism and Disposition JO - Drug Metab Dispos DO - 10.1124/dmd.119.089565 SP - dmd.119.089565 AU - Xiaohua Zhao AU - Hong Ma AU - Qiusha Pan AU - Haiyi Wang AU - Xingkai Qian AU - Peifang Song AU - Liwei Zou AU - Mingqing Mao AU - Shuyue Xia AU - Guangbo Ge AU - Ling Yang Y1 - 2020/01/01 UR - http://dmd.aspetjournals.org/content/early/2020/02/21/dmd.119.089565.abstract N2 - Abstract Doxophylline (DOXO) and theophylline are widely used as bronchodilators for treating asthma and chronic obstructive pulmonary disease, and DOXO has a better safety profile than theophylline. How DOXO metabolism and disposition affect its anti-asthmatic efficacy and safety remains to be explored. In this study, the metabolites of DOXO were characterized. A total of nine metabolites of DOXO were identified in vitro using liver microsomes from human and four other animal species. Among them, six metabolites were reported for the first time. The top three metabolites were theophylline acetaldehyde (M1), theophylline-7-acetic acid (M2) and etophylline (M4). A comparative analysis of DOXO metabolism in human using liver microsomes, S9 fraction, and plasma samples demonstrated that: (1) The metabolism of DOXO began with a CYP-mediated, rate-limiting step at the C ring and produced M1, the most abundant metabolite in human liver microsomes. However, in human plasma, the M1 production was rather low. (2) M1 was further converted to M2 and M4, the end products of DOXO metabolism in vivo, by non-CYP dismutase in the cytosol. This dismutation process also relied on the ratio of NADP+/NADPH in the cell. These findings for the first time elucidated the metabolic sites and routes of DOXO metabolism in human.SIGNIFICANCE STATEMENT We systematically characterized doxophylline metabolism using in vitro and in vivo assays. Our findings evolved the understandings of metabolic sites and pathways for methylxanthine derivatives with the aldehyde functional group. ER -