Evaluation of UV-C Decontamination of Clinical Tissue Sections for Spatially Resolved Analysis by Mass Spectrometry Imaging (MSI)

Morphological and molecular preservation through universal preparation of fresh-frozen tissue samples for multimodal imaging workflows

The landscape of tissue-based imaging modalities is constantly and rapidly evolving. While formalin-fixed, paraffin-embedded material is still useful for histological imaging, the fixation process irreversibly changes the molecular composition of the sample. Therefore, many imaging approaches require fresh-frozen material to get meaningful results. This is particularly true for molecular imaging techniques such as mass spectrometry imaging, which are widely used to probe the spatial arrangement of the tissue metabolome. As high-quality fresh-frozen tissues are limited in their availability, any sample preparation workflow they are subjected to needs to ensure morphological and molecular preservation of the tissues and be compatible with as many of the established and emerging imaging techniques as possible to obtain the maximum possible insights from the tissues. Here we describe a universal sample preparation workflow, from the initial step of freezing the tissues to the cold embedding in a new hydroxypropyl methylcellulose/polyvinylpyrrolidone-enriched hydrogel and the generation of thin tissue sections for analysis. Moreover, we highlight the optimized storage conditions that limit molecular and morphological degradation of the sections. The protocol is compatible with human and plant tissues and can be easily adapted for the preparation of alternative sample formats (e.g., three-dimensional cell cultures). The integrated workflow is universally compatible with histological tissue analysis, mass spectrometry imaging and imaging mass cytometry, as well as spatial proteomic, genomic and transcriptomic tissue analysis. The protocol can be completed within 4 h and requires minimal prior experience in the preparation of tissue samples for multimodal imaging experiments.

Mass spectrometry imaging: new eyes on natural products for drug research and development

Natural products (NPs) and their structural analogs represent a major source of novel drug development for disease prevention and treatment. The development of new drugs from NPs includes two crucial aspects. One is the discovery of NPs from medicinal plants/microorganisms, and the other is the evaluation of the NPs in vivo at various physiological and pathological states. The heterogeneous spatial distribution of NPs in medicinal plants/microorganisms or in vivo can provide valuable information for drug development. However, few molecular imaging technologies can detect thousands of compounds simultaneously on a label-free basis. Over the last two decades, mass spectrometry imaging (MSI) methods have progressively improved and diversified, thereby allowing for the development of various applications of NPs in plants/microorganisms and in vivo NP research. Because MSI allows for the spatial mapping of the production and distribution of numerous molecules in situ without labeling, it provides a visualization tool for NP research. Therefore, we have focused this mini-review on summarizing the applications of MSI technology in discovering NPs from medicinal plants and evaluating NPs in preclinical studies from the perspective of new drug research and development (R&D). Additionally, we briefly reviewed the factors that should be carefully considered to obtain the desired MSI results. Finally, the future development of MSI in new drug R&D is proposed.

On-Slide Heat Sterilization Enables Mass Spectrometry Imaging of Tissue Infected with High-Threat Pathogens Outside of Biocontainment: A Study Directed at Mycobacterium tuberculosis

Mass spectrometry imaging investigations of tissues infected with agents that require high-security biocontainment, such as Mycobacterium tuberculosis, have been limited due to incompatible sterilization techniques. Here we describe an on-slide heat sterilization method that enables mass spectrometry imaging investigations of pharmaceuticals, lipids, and metabolites in infected tissue samples outside of biocontainment. An evaluation of different temperatures and incubation times determined that 100 °C for 1 h was essential to sterilize 5 times the bacterial burden observed in tuberculosis (TB) cavity sections. Laser-capture microdissection combined with liquid chromatography with tandem mass spectrometry quantitation, in addition to mass spectrometry imaging, showed that no degradation was observed following the on-slide heat sterilization protocol for a variety of drug classes covering a range of physicochemical properties. Utilizing the tissue mimetic model, we demonstrated that the detection of lipid and metabolite ions was not impacted by heat sterilization and that, for several metabolites, the on-slide heat sterilization method improved the sensitivity when compared to control samples. An application of the on-slide heat sterilization to M. tuberculosis infected tissue enabled the first detection and spatial distribution of lipids indicative of a lysosomal storage disease phenotype within TB granuloma macrophages, in addition to the differential distribution of metabolites central to the fatty acid oxidation pathway. These initial investigations detected a pronounced heterogeneity within the cellular regions and necrotic cores of individual TB granulomas and across different evolving granulomas. This study provides the framework for mass spectrometry imaging investigations of high-threat pathogens outside of biocontainment.