Biotransformation and metabolic profile of catalpol with human intestinal microflora by ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry

• Metabolic pathways of catalpol produced by human bacteria were firstly investigated.
• 4 metabolites were identified based on the characteristics of their protonated ions.
• UPLC–Q–TOF/MS was applied for analysis of the metabolites of catalpol.

Traditional Chinese medicine (TCM) has been used in clinical practice for thousands of years. Catalpol, an iridoid glucoside, abundantly found in the root of the common used herb medicine Rehmannia glutinosa Libosch, has been reported to show various biological effects and pharmacological activities. After oral administration, the active ingredient might have interactions with the intestinal bacteria, which could help unravel how the medicine was processed in vivo. In this work, different pure bacteria from healthy human feces were isolated and used to bioconvert catalpol. Ultra performance liquid chromatography/quadrupole-time-of-flight mass spectrometry (UPLC–Q–TOF/MS) technique combined with Metabolynx™ software was applied to analyze catalpol metabolites. Compared with blank samples, parent compound (M0) and four metabolites (M1–M4) were detected and tentatively identified based on the characteristics of their protonated ions. The metabolites were likely to be: catalpol aglycone (M1), acetylated catalpol (M2), dimethylated and hydroxylated catalpol aglycone (M3), nitrogen-containing catalpol aglycone (M4). M1 and M4 were generated in the majority of the samples like Bacteroides sp. 45. M3 was obtained in several bacterial samples like Enterococcus sp. 8-2 and M2 was detected only in the sample of Enterococcus sp. 43-1. To our knowledge, the metabolic routes and metabolites of catalpol produced by human intestinal bacteria were all firstly reported.