Abstract
Caffeine is commonly taken via the daily dietary consumption of caffeine-containing foods. The absorbed caffeine is metabolized to yield various metabolites by drug-metabolizing enzymes, and measuring the levels of each caffeine metabolite can provide useful information for evaluating the phenotypes of those enzymes. In this study, the urinary concentrations of caffeine and its 13 metabolites were determined, and the phenotypes of drug metabolic enzymes were investigated based on the caffeine metabolite ratios. Human urine samples were pretreated using solid phase extraction, and caffeine and its metabolites were analyzed using liquid chromatography-tandem mass spectrometry. Based on the urinary caffeine metabolite concentrations, the caffeine metabolite ratios were calculated for six human subjects at specified time points after caffeine intake. Variations in urinary metabolite levels among individuals and time points were reported. In addition, the resultant enzyme activities showed different patterns, depending on the metabolite ratio equations applied. However, some data presented a constant metabolite ratio range, irrespective of time points, even at pre-dose. This suggests the possibility of urinary caffeine metabolite analysis for routine clinical examination. These findings show that urinary caffeine and the metabolite analysis would be useful in evaluating metabolic phenotypes for personalized medicine.
Highlights
Caffeine, an alkaloid of the methylxanthine class, is the world’s most widely consumed psychoactive substance
The cytochrome P450—particularly 1A2 (CYP1A2) activity of Subject #6 appeared to be higher than that of the urine was diluted in post-dose samples, as the urine was frequently collected after other subjects, but plot F (Figure 2f) did not exhibit this tendency. These findings suggest that caffeine intake; at pre-dose, the caffeine metabolites, which resulted from usual dietary
Caffeine is popularly present in a wide variety of foods and beverages, and is extensively consumed via the daily diet
Summary
An alkaloid of the methylxanthine class, is the world’s most widely consumed psychoactive substance. As a naturally occurring substance, caffeine is found in the leaves, fruits, or seeds of more than 60 plant species. Caffeine is popularly and extensively taken via the daily dietary consumption of caffeine-containing beverages or foods [1,2]. Caffeine is subjected to a series of metabolic reactions to yield a mixture of. N-methylated xanthines, uric acids, and an acetylated uracil, as its metabolites [3]. There are various metabolic enzymes involved in each caffeine metabolic pathway (Figure 1). These enzymes include N-acetyltransferase 2 (NAT2), xanthine oxidase (XO), and cytochrome P450— 1A2
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