Development of a19F-n.m.r. method for studies on the invivoandin vitrometabolism of 2-fluoroaniline

Abstract

1. A ¹⁹F-n.m.r. method has been developed for study of the metabolism of 2-fluoroaniline both after in vivo exposure of rats and in in vitro model systems. 2. From the ¹⁹F-n.m.r. spectrum of the 24 h urine it was calculated that over 90% of the dose was excreted within 24 h. The metabolic pattern showed that 85% of the metabolites were para-hydroxylated, 72% sulphated, 13% glucuronidated and 29% N-acetylated, 4-amino-3-fluorophenyl sulphate being the main urinary metabolite (53%). 3. In vitro studies of phase I metabolism of 2-fluoroaniline with rat liver microsomes was representative for the in vivo metabolism as hydroxylation in both systems was observed only at the para-position. 4. Phase I + II metabolism was studied in vitro in either isolated rat hepatocytes in suspension or in a 1 h recirculating liver perfusion system. In both these in vitro systems para-hydroxylation, N-acetylation, sulphation and glucuronidation of 2-fluoroaniline were observed. The ratio between glucuronidation and sulphation was dependent on sulphate availability 5. Of the in vitro systems tested, hepatocytes in Krebs Ringer (sulphate limited) medium was the best model for in vivo metabolism. 6. The detection limit for fluoro-containing metabolites in this ¹⁹F-n.m.r. method was 1 μM for an overnight run using a Bruker CXP 300 spectrometer. From this it can be concluded that ¹⁹F-n.m.r. urine analysis is a useful tool in biomonitoring studies. For 2-fluoroaniline the method appears to be more sensitive than currently available h.p.l.c./t.l.c. methods. In addition, concentration of urine samples can result in either lower detection limits, or in shorter times needed for n.m.r. data acquisition. 7. N-acetylation is known to show genetic polymorphism. Therefore, the ¹⁹F-n.m.r. method, detecting all 2-fluoroaniline metabolites, has the additional advantage of eliminating the risk of obtaining false negatives for fast acetylators.