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  • Title: Phenotyping of N-acetyltransferase type 2 by caffeine from uncontrolled dietary exposure.
    Author: Jetter A, Kinzig-Schippers M, Illauer M, Hermann R, Erb K, Borlak J, Wolf H, Smith G, Cascorbi I, Sörgel F, Fuhr U.
    Journal: Eur J Clin Pharmacol; 2004 Mar; 60(1):17-21. PubMed ID: 14747882.
    Abstract:
    BACKGROUND AND OBJECTIVE: The standard approach for phenotyping of the human arylamine N-acetyltransferase 2 (NAT2) uses urinary caffeine metabolite ratios after a caffeine test dose taken in after methylxanthine abstinence. We tested whether these standardization measures were still needed when a more sensitive quantification technique was used. METHODS: A new liquid chromatography/tandem mass spectrometry (LC-MS/MS) method for the quantification of the caffeine metabolites 5-acetylamino-6-formylamino-3-methyluracil (AFMU), 5-acetylamino-6-amino-3-methyluracil (AAMU), 1-methylxanthine (1X), and 1-methylurate (1U) was developed. Urine samples from 77 healthy volunteers collected before and 5-6 h after oral intake of 150-200 mg caffeine were analyzed. The lower limits of quantification were 0.1 microg/ml for caffeine, 1X, 1U, and AFMU, and 0.2 microg/ml for AAMU. RESULTS: The urinary NAT2 ratios (AFMU+AAMU) / (AFMU+AAMU+1X+1U) before and after caffeine intake correlated well in 65 volunteers (r(2)=0.827; P< 0.0001). In 12 participants (16%), metabolite concentrations in urine before caffeine intake were below the quantification limit. NAT2 genotyping, done in 41 volunteers for four SNPs, corroborated the phenotyping results. CONCLUSION: NAT2 activity can be determined from a spontaneous urine probe in most subjects by quantification of caffeine metabolites arising from non-standardized dietary caffeine exposure using LC-MS/MS. This may facilitate the phenotyping procedure.
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