Analysis of anisodine and identification of twenty of its metabolites in rat urine by liquid chromatography-tandem mass spectrometry

A simple and rapid high-performance liquid chromatographic-electrospray ionization (ESI) tandem mass spectrometric method has been developed for elucidation of the structures of the metabolites of anisodine in rat urine after administration of a single dose (20 mg). Different extraction techniques (free fraction, acid hydrolysis, and enzyme hydrolysis) were compared for investigation of the metabolism of anisodine. After extraction the pretreated samples were injected into a reversed-phase C-18 column with 60:40 (v/v) methanol-0.01% triethylamine solution (2 mM, adjusted to pH 3.5 with formic acid) as mobile phase. Detection was by on-line MS-MS. Identification of the metabolites and elucidation of their structure were performed by comparing changes in molecular masses (Delta M), retention-times, and spectral patterns of product ions with those of the parent drug. At least twenty metabolites (norscopine, scopine, alpha-hydroxytropic acid, aponoranisodine, apoanisodine, noranisodine, anisodine N-oxide, hydroxyanisodine, hydroxyanisodine N- oxide, methoxyanisodine, hydroxymethoxyanisodine, trihydroxyanisodine, dihydroxymethoxyanisodine, hydroxydimethoxyanisodine, glucuronide conjugates, and sulfate conjugates of noranisodine, hydroxyanisodine and the parent drug) and the parent drug were found in the urine after ingestion of 20 mg anisodine by healthy rats. Anisodine N-oxide, hydroxyanisodine, and the parent drug were detected in rat urine for up 120 h after ingestion of the drug.