Characterization of limonin glucoside metabolites from human prostate cell culture medium using high-performance liquid chromatography/electrospray ionization mass spectrometry and tandem mass spectrometry

The metabolism of limonin 17-beta-D-glucopyranoside (LG) by non-cancerous (RWPE-1) and cancerous (PC-3) human prostate epithelial cells was investigated using high-performance liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) with in-source fragmentation and tandem mass spectrometry (MS/MS). During positive ion LC/ESI-MS, LG formed an abundant sodiated species (M+Na]+) while the protonated molecule was barely observable. M+Na]+ further fragmented into the less abundant LARL+H]+ and a predominantly protonated aglycone molecule (limonin) due to in-source fragmentation. The major metabolite, limonin A-ring lactone (LARL), formed an abundant protonated molecule that was fragmented into a protonated molecule of limonin by loss of one molecule of water. In MS/MS by collisionally activated dissociation (CAD), LG produced the sodiated aglycone, aglycone+Na]+, while LARL fragmented into M+H]+ of limonin and fragment ions resulted by further loss of water, carbon monoxide and carbon dioxide, indicating the presence of oxygenated-ring structures. The limits of detection of LG were 0.4 and 20 fmol in selected-ion monitoring (SIM) and selected-reaction monitoring (SRM) detection, respectively.