A sensitive on-tissue chemical derivatization-mass spectrometry imaging method for the quantitative visualization of helicid in mice

Abstract

Helicid (4-formylphenyl-O-β-d-allopyranoside) is an aromatic phenolic glucoside. It is one of the main active constituents from the seeds of the Chinese herb Helicia nilagirica. Helicid has been reported to exert sedative, analgesic, hypnotic and antidepressant effects, and is currently used clinically to treat neurasthenic syndrome, vascular headaches and trigeminal neuralgia. On-tissue chemical derivatization (OTCD) combined with matrix-assisted laser desorption ionization-mass spectrometry imaging (MALDI-MSI) was developed for the quantitative visualization of helicid in mice. The derivatization reagent, Girard’s reagent T (GT), was sprayed directly onto the tissue surface using an automated pneumatic TM-sprayer. The OTCD reaction was conducted in a closed container with 120 mL of 50% methanol with 0.4% TFA at 40 °C for 40 min. α-Cyano-4-hydroxycinnamic acid (2.22 μg/mm2) was used as the matrix, which was deposited onto the tissue surface. MALDI-MSI analysis was performed in the positive-ion mode with a spatial resolution of 200 μm. The sensitivity for the MALDI-MSI of helicid in tissue sections increased 1920 times after derivatization. The assay showed good linearity in the helicid concentration range of 0.32–32 ng/mm2. The method was used to investigate the spatiotemporal distribution of helicid in mice.