Sample preparation strategy for the detection of steroid-like compounds using MALDI mass spectrometry imaging: pulmonary distribution of budesonide as a case study

Abstract

Corticosteroids as budesonide can be effective in reducing topic inflammation processes in different organs. Therapeutic use of budesonide in respiratory diseases, like asthma, chronic obstructive pulmonary disease, and allergic rhinitis is well known. However, the pulmonary distribution of budesonide is not well understood, mainly due to the difficulties in tracing the molecule in lung samples without the addition of a label. In this paper, we present a matrix-assisted laser desorption/ionization mass spectrometry imaging protocol that can be used to visualize the pulmonary distribution of budesonide administered to a surfactant-depleted adult rabbit. Considering that budesonide is not easily ionized by MALDI, we developed an on-tissue derivatization method with Girard's reagent P followed by ferulic acid deposition as MALDI matrix. Interestingly, this sample preparation protocol results as a very effective strategy to raise the sensitivity towards not only budesonide but also other corticosteroids, allowing us to track its distribution and quantify the drug inside lung samples.

Keywords: Budesonide; Ferulic acid; Girard reagent; Mass spectrometry imaging; On-tissue derivatization; Pulmonary drug distribution.

Fig. 1

Comparison of in-solution derivatized corticosteroids. MALDI-FT full scan mass spectra of six Girard’s P derivatized corticosteroids. Compound mixture was then spotted onto MALDI plate and analyzed with 2,5-dihydroxybenzoic acid (DHB) or ferulic acid (FA). Testosterone (TS), prednisone (PR), cortisone (CO), budesonide (BUD), and triamcinolone acetonide (TA)

Fig. 2

MSI analysis with different matrices. Comparison of the response of the budesonide ion (m/z 564.308) on consecutive lung sections when FA and HCCA are used as MALDI matrix in MSI experiments

Fig. 3

Investigation of linearity and reproducibility of the on-tissue calibration curves. a Linearity of the response of dilution series of budesonide spotted on normal control homogenate tissue slices in the presence of a different amount of poractant alfa. b Reproducibility of the response on tissue homogenates spiked either with BUD alone or with surfBUD combination

Fig. 4

MSI analysis on rabbit lung sections. Bottom panels represent the distribution maps of budesonide ion (m/z 564.308) on a frontal lung section on treated (left) and control rabbits (right). Corresponding H&E-stained tissue section optical scans are represented in top panels