Background: Catalpol, an iridoid glycoside, is one of the richest bioactive components present in
Rehmannia glutinosa. More and more metabolites of drugs have exhibited various pharmacological effects,
thus providing guidance for clinical application. However, few researches have paid attention to the
metabolism of catalpol.
Objective: This study aimed to establish a rapid and effective method to identify catalpol metabolites and evaluate
the biotransformation pathways of catalpol in rats.
Methods: In this study, catalpol metabolites in rat urine, plasma and faeces were analyzed by UHPLC-Q-Exactive
MS for the characterization of the metabolism of catalpol. Based on high-resolution extracted ion chromatograms
(HREICs) and parallel reaction monitoring mode (PRM), metabolites of catalpol were identified by comparing
the diagnostic product ions (DPIs), chromatographic retention times, neutral loss fragments (NLFs) and
accurate mass measurement with those of catalpol reference standard.
Results: A total of 29 catalpol metabolites were detected and identified in both negative and positive ion
modes. Nine metabolic reactions, including deglycosylation, hydroxylation, dihydroxylation, hydrogenation, dehydrogenation,
oxidation of methylene to ketone, glucuronidation, glycine conjugation and cysteine conjugation,
Conclusion: A rapid and effective method based on UHPLC-Q-Exactive MS was developed to mine the
metabolism information of catalpol. Results of metabolites and biotransformation pathways of catalpol suggested
that when orally administrated, catalpol was firstly metabolized into catalpol aglycone, after which phase I
and phase II reactions occurred. However, hydrophilic chromatography-mass spectrometry is still needed to further
find the polar metabolites of catalpol.