Subject(s)
Aromatase/genetics , Estradiol/blood , Hydroxysteroid Dehydrogenases/genetics , Polymorphism, Genetic , Steroid 17-alpha-Hydroxylase/genetics , Aged , Breast Neoplasms/etiology , Breast Neoplasms/genetics , England , Female , Genotype , Health Surveys , Humans , Middle Aged , Postmenopause , Risk FactorsSubject(s)
Mammography , Female , Humans , Mammography/adverse effects , Mammography/psychology , Pain/etiology , Patient ComplianceABSTRACT
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.
Subject(s)
Arylamine N-Acetyltransferase/genetics , Caffeine/pharmacokinetics , Diet , Uracil/analogs & derivatives , Acetylation , Administration, Oral , Adult , Arylamine N-Acetyltransferase/metabolism , Caffeine/administration & dosage , Caffeine/metabolism , Chromatography, High Pressure Liquid , Female , Genotype , Humans , Male , Middle Aged , Phenotype , Spectrometry, Mass, Electrospray Ionization , Time Factors , Uracil/chemistry , Uracil/urine , Uric Acid/analogs & derivatives , Uric Acid/chemistry , Uric Acid/urine , Xanthines/chemistry , Xanthines/urineABSTRACT
PURPOSE: The influence of biophysical factors (drug metabolism, transport proteins, and chemical stability) on the cellular accumulation of camptothecin (CPT) and SN-38 was examined. METHODS: Drug transporter RNA transcript levels were measured by real-time reverse transcriptase polymerase chain reaction (RT-PCR). Intracellular drug accumulation, metabolism, and drug stability studies were all performed by HPLC. RESULTS: A panel of three human cell lines exhibiting different drug resistant phenotypes was investigated. HT29 colon cells glucuronidated SN-38 but did not express P-gp or MRP1 or 2. HCT116 colon cells expressed P-gp and MRP2 but did not catalyse conjugation. A2780 ovarian cells neither catalysed drug metabolism nor contained these drug transporters. In all lines, SN-38 lactone was rapidly taken up achieving peak concentrations at the earliest time point studied (5 min, 3.3-4.1 ng/10(6) cells). Subsequently, a fall in intracellular lactone concentration occurred, stabilising after 4 h at 0.48-1.18 ng/10(6) cells. No significant differences in intracellular levels of lactone were observed between the three cell lines with one exception: a twofold increase in HCT116 cells at 24 h. Stability studies in culture medium revealed that SN-38 lactone concentrations disappeared at the same rate regardless of whether cells were present, initially falling to reach equilibrium with the hydroxy acid by 4 h. Indeed, changes in intracellular lactone concentrations followed closely chemical stability profiles in media. Similar patterns of cellular retention and chemical degradation were observed with CPT. CONCLUSION: The major determinant of drug accumulation in three diverse cell line phenotypes was lactone chemical stability in culture medium.
