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Abstract
Caffeine metabolism via the 3-demethylation pathway is sequentially catalyzed by the enzymes cytochrome P4501A2 (CYP1A2), xanthine oxidase (XO) and N-acetyltransferase (NAT2). The activities of the three enzymes can be estimated from urinary metabolic ratios of five caffeine metabolites, 5-acetylamino-6-formylamino-3-methyluracil (AFMU), 1-methylxanthine (1MX), 1-methyluric acid (1MU), 1,7-dimethylxanthine (1,7DMX), and 1,7-dimethyluric acid (17DMU), after the ingestion of caffeine. A HPLC method for simultaneous determination of the five metabolites in human urine was developed, with all the thirteen metabolites of caffeine having good separation. The recoveries of the five metabolites were all above 87.5%, and the interday and intraday coefficients of variation were less than 3%. The method was employed successfully in a population study of 120 healthy volunteers for the assessment of CYP1A2, NAT2, and XO enzymes.
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