PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 11393735

Extractionless method for the simultaneous high-performance liquid chromatographic determination of urinary caffeine metabolites for N-acetyltransferase 2, cytochrome P450 1A2 and xanthine oxidase activity assessment.

A Nyéki·J Biollaz·U W Kesselring·L A Décosterd
View original source ↗Export metadata ↓

Abstract

Urinary metabolic ratios of caffeine are used in humans to assess the enzymatic activities of cytochrome P450 isoenzyme 1A2 (CYP1A2), xanthine oxidase (XO) and for phenotyping individuals for the bimodal N-acetyltransferase 2 (NAT2), all of them involved in the activation or detoxification of various xenobiotic compounds. Most reported analytical procedures for the measurement of the urinary metabolites of caffeine include a liquid-liquid extraction of urine samples prior to their analysis by reversed-phase HPLC. At neutral to basic pH however, 5-acetylamino-6-formylamino-3-methyluracil (AFMU), a metabolite of caffeine, spontaneously decomposes to 5-acetylamino-6-amino-3-methyluracil (AAMU). Since AAMU is not extracted in most organic solvents, the extent of AFMU decomposition cannot be precisely assessed. Although the decomposition reaction can be minimized by immediate acidification of the urine, accurate results can only be obtained when both AAMU and AFMU are monitored, or alternatively, if AAMU is measured after complete transformation of AFMU into AAMU in basic conditions. We report a liquid chromatographic method for the simultaneous quantitative analysis of the five urinary metabolites of caffeine used for the CYP1A2, XO and NAT2 phenotyping studies: AAMU, AFMU, 1-methylxanthine, 1-methyluric acid and 1,7-dimethyluric acid. These metabolites are satisfactory separated from all other known caffeine metabolites as well as endogenous urinary constituents. Sample treatment does not require any liquid-liquid extraction procedure. Urine samples are diluted and centrifuged before being injected (10 microl) onto a YMC-Pack Polyamine II (250x4.6 mm) column. A step-wise gradient elution program is applied using acetonitrile-0.75% (v/v) formic acid: (91:9) at 0 min-->(75:25) at 25 min-->(65:35) at 35 min-->(65:35) at 45 min, followed by a re-equilibration step to the initial solvent composition. The flow-rate is 1.0 ml/min and the separations are monitored by UV absorbance at 260 and 280 nm. The procedure described here represents a substantial improvement over previous methods: a single analysis and a minimal urine sample treatment enables the simultaneous quantitation of five caffeine metabolites, notably AFMU and AAMU, used for the determination of CYP450 1A2, XO and NAT2 enzyme activity. Importantly enough, phenotyping individuals for the bimodal NAT2 is made possible without the uncertainty associated with the deformylation of AFMU, which is likely to happen at all steps prior to the analysis, during sample storage and even in the bladder of the subjects.

Explore related subjects

Arylamine N-AcetyltransferaseCaffeineChromatography, High Pressure LiquidCytochrome P-450 CYP1A2HumansModels, ChemicalReproducibility of ResultsUracilXanthine OxidaseJournal Article

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

A Nyéki, J Biollaz, U W Kesselring, L A Décosterd. 2001-05-05. Extractionless method for the simultaneous high-performance liquid chromatographic determination of urinary caffeine metabolites for N-acetyltransferase 2, cytochrome P450 1A2 and xanthine oxidase activity assessment.. https://doi.org/10.1016/s0378-4347(00)00616-2

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2026

Clinical Function Assignment of NAT2 Alleles by the Clinical Pharmacogenetics Implementation Consortium Pharmacogene Curation Expert Panel.

NAT2 encodes arylamine N-acetyltransferase 2, a key enzyme in the phase II metabolism of arylamines and arylhydrazines. NAT2 is highly polymorphic, resulting in variable distributions of rapid and poor metabolizers across global populations. Here, we detail the process undertaken by the Clinical Pharmacogenetics Implementation Consortium (CPIC) NAT2 Pharmacogene Curation Expert Panel (PCEP) to assign clinical function to NAT2 star (*) alleles using CPIC's standard terminology. Given the observed impact of NAT2 genetic variability on drug response, CPIC convened the NAT2-PCEP to standardize clinical allele function assignments. The NAT2-PCEP is comprised of multidisciplinary and international members, including researchers, clinicians, and implementers with expertise in pharmacogenomics and NAT2 molecular biology. Extensive in vitro and clinical literature was curated from PubMed and other sources to assess NAT2 genotype-to-phenotype concordance as well as the biochemical function of NAT2 star alleles. The NAT2-PCEP assigned allele clinical function using CPIC's standard terminology (increased, decreased, uncertain, and unknown function) to 59 star alleles cataloged by the Pharmacogene Variation Consortium (PharmVar). Two alleles, NAT2*1 and NAT2*4, were assigned increased function (historically known as rapid), 40 alleles were assigned decreased function (historically known as slow), 10 alleles were assigned uncertain function, and seven alleles were assigned unknown function. Rigorous evidence review and in-depth PCEP discussion were crucial in determining these function assignments. The findings reported here underscore the importance of standardized allele functional terms and diplotype-to-phenotype assignments to further the clinical implementation of NAT2 pharmacogenetic test results.

Arylamine N-Acetyltransferase↗
PubMed2007

Induction of human arylamine N-acetyltransferase type I by androgens in human prostate cancer cells.

Human arylamine N-acetyltransferases (NAT) bioactivate arylamine and heterocyclic amine carcinogens present in red meat and tobacco products. As a result, factors that regulate expression of NATs have the potential to modulate cancer risk in individuals exposed to these classes of carcinogens. Because epidemiologic studies have implicated well-done meat consumption as a risk factor for prostate cancer, we have investigated the effects of androgens on the expression of arylamine N-acetyltransferase type I (NAT1). We show that NAT1 activity is induced by R1881 in androgen receptor (AR)-positive prostate lines 22Rv1 and LNCaP, but not in the AR-negative PC-3, HK-293, or HeLa cells. The effect of R1881 was dose dependent, with an EC(50) for R1881 of 1.6 nmol/L. Androgen up-regulation of NAT1 was prevented by the AR antagonist flutamide. Real-time PCR showed a significant increase in NAT1 mRNA levels for R1881-treated cells (6.60 +/- 0.80) compared with vehicle-treated controls (1.53 +/- 0.17), which was not due to a change in mRNA stability. The increase in NAT1 mRNA was attenuated by concurrent cycloheximide treatment, suggesting that the effect of R1881 may not be by direct transcriptional activation of NAT1. The dominant NAT1 transcript present following androgen treatment was type IIA, indicating transcriptional activation from the major NAT1 promoter P1. A series of luciferase reporter deletions mapped the androgen responsive motifs to a 157-bp region of P1 located 745 bases upstream of the first exon. These results show that human NAT1 is induced by androgens, which may have implications for cancer risk in individuals.

Arylamine N-Acetyltransferase↗
PubMed2006

Bayesian synthesis of epidemiological evidence with different combinations of exposure groups: application to a gene-gene-environment interaction.

Meta-analysis to investigate the joint effect of multiple factors in the aetiology of a disease is of increasing importance in epidemiology. This task is often challenging in practice, because studies typically concentrate on studying the effect of only one exposure, sometimes may report the interaction between two exposures, but rarely address more complex interactions that involve more than two exposures. In this paper, we develop a meta-analysis framework that combines estimates from studies of multiple exposures. A key development is an approach to combining results from studies that report information on any subset or combination of the full set of exposures. The model requires assumptions to be made about the prevalence of the specific exposures. We discuss several possible model specifications and prior distributions, including information internal and external to the meta-analysis data set, and using fixed-effect and random-effects meta-analysis assumptions. The methodology is implemented in an original meta-analysis of studies relating the risk of bladder cancer to two N-acetyltransferase genes, NAT1 and NAT2, and smoking status.

Arylamine N-Acetyltransferase↗