Direct molecular analysis of whole-body animal tissue sections by MALDI imaging mass spectrometry

Abstract

The determination of the localization of various compounds in a whole animal is valuable for many applications, including pharmaceutical absorption, distribution, metabolism, and excretion (ADME) studies and biomarker discovery. Imaging mass spectrometry is a powerful tool for localizing compounds of biological interest with molecular specificity and relatively high resolution. Utilizing imaging mass spectrometry for whole-body animal sections offers considerable analytical advantages compared to traditional methods, such as whole-body autoradiography, but the experiment is not straightforward. This chapter addresses the advantages and unique challenges that the application of imaging mass spectrometry to whole-body animal sections entails, including discussions of sample preparation, matrix application, signal normalization, and image generation. Lipid and protein images obtained from whole-body tissue sections of mouse pups are presented along with detailed protocols for the experiments.

Fig. 17.1.

Generation of whole-body tissue sections from fresh frozen mouse pups. Photomicrographs of (a, c) a 3-day-old pup frozen in a block of ice from which 15-μm thick sections were cut using a whole-body cryostat and mounted on conductive glass slides using the CryoJane system; (b, d) a 1-day-old pup held into position using OCT from which 12-μm thick sections were cut in a biological specimen cryostat and directly thaw-mounted on conductive glass slides. See text for details.

Fig. 17.2.

Olanzapine (oral administration, 8 mg/kg) and metabolite distribution at 2 h post-dose in a whole-rat sagittal tissue section monitored by imaging MS. Organs are outlined in red on the photomicrograph of the section (a). MS/MS ion images of olanzapine (b) and its N-desmethyl (c) and 2-hydroxymethyl (d) metabolites are displayed. (Adapted from Ref. (2) with permission.)

Fig. 17.3.

Whole-body imaging MS of proteins from a 1-day-old mouse pup. (a) H&E stained section from which numerous organs are clearly visible. (b) Serial section used for imaging MS on which matrix (sinapinic acid) has been automatically deposited in an array manner with a final center-to-center spacing of 200 μm. (c) Overlay of 12 individual organ or tissue-specific protein images, each presented with a different color. See text for details.

Fig. 17.4.

Whole-body imaging MS of lipids from a 1-day-old mouse pup. (a) H&E stained section from which numerous organs are clearly visible. (b) Serial section used for imaging MS on which matrix (DHB) has been homogeneously applied using the dry deposition approach. (c) Overlay of six individual organ or tissue-specific lipid images, each presented with a different color. See text for details.