Highly sensitive determination of new metabolite in rat plasma after oral administration of swertiamarin by liquid chromatography/time of flight mass spectrometry following picolinoyl derivatization

The metabolism of swertiamarin (STM) in vivo was studied by LC/MS following picolinoyl derivatization. Incubation of erythrocentaurin (ECR), one of the main in vitro metabolites of STM by intestinal bacteria, with liver microsome indicated that STM may be metabolized to the final metabolite 3,4-dihydro-5-(hydroxymethyl) isochroman-1-one (HMIO) in vivo. After hydrolyzation with sulfatase, HMIO was successfully detected in rat plasma after oral administration of STM by LC/MS following picolinoyl derivatization. 4-Methoxyphenyl methanol was used as the internal standard to quantify HMIO in rat plasma. The full metabolic pathway of STM in rats is proposed. STM is first hydrolyzed by bacterial β-glucusidase to give aglycone, which is readily converted to ECR and nitrogen-containing metabolite. ECR is further reduced to HMIO by both liver and intestinal bacteria and HMIO is finally converted to the new sulfate conjugate metabolite. The monoterpene compound STM was found to be metabolized to dihydroisocoumarin and alkaloid compounds in vivo, which may be responsible for the pharmacological effect of STM. The results may shed light on clinical efficacy of STM and the new analytical method developed may assist in studies of the metabolism of other natural iridoids and secoiridoids in vivo.