Identification of Novel Metabolites of Colchicine in Rat Bile Facilitated by Enhanced Online Radiometric Detection

Abstract

Three novel conjugation metabolites of colchicine were identified in rat bile facilitated by enhanced on-line liquid chromatography-accurate radioisotope counting. The known 2- and 3-demethylcolchicines (DMCs) underwent O-sulfate conjugation in addition to the previously described O-glucuronidation. 2-DMC was preferably O-glucuronidated, whereas 3-DMC predominantly yielded O-sulfation conjugates, indicating phase II conjugation regiopreferences. Moreover, M1 was identified as a novel glutathione conjugate and a possible biotransformation pathway for its formation was proposed. The known 2-DMC (M6), 3-DMC (M7), 2-DMC glucuronide (M4), and novel 3-DMC sulfate (M3) were confirmed as the major metabolites. Radiometric data were acquired by the XFlow liquid chromatography-accurate radioisotope counting (XFlow LC-ARC) system, a novel technology for dynamic control of both on-column and postcolumn high-performance liquid chromatography flow rates to maximize sensitivity and resolution of radiochromatograms. A comparative evaluation was also performed between the XFlow LC-ARC system and a conventional flow radiometric detection system using bile samples from an in vivo disposition study of colchicine in male Sprague-Dawley rats. Results demonstrated a 20-fold sensitivity improvement of the XFlow LC-ARC system in comparison with radioactivity detection by conventional flow scintillation analyzers. The dynamic flow mode also provided the best chromatographic resolution. Unambiguous metabolite identification was performed by high-resolution mass spectrometry and nuclear magnetic resonance analysis.