Ex vivo Lung Perfusion Tissue Analysis by Desorption Electrospray Ionization (DESI) Imaging in Clinical Research

Importance of the Topic

The integration of ex vivo lung perfusion (EVLP) with desorption electrospray ionization (DESI) mass spectrometry imaging (MSI) offers a minimally invasive approach to map the spatial distribution of metabolites, lipids, and small biomolecules in donor lung tissue. This capability is critical for evaluating organ quality, identifying biochemical markers of injury or repair, and advancing translational research in organ transplantation and pulmonary diseases.

Objectives and Study Overview

This study demonstrates the application of DESI-MSI on human lung allograft sections following EVLP. The primary goals are to establish a streamlined workflow, evaluate analytical performance on the Xevo G2-XS QTof mass spectrometer, and correlate molecular images with histopathology for potential diagnostic utility.

Methodology and Instrumentation

Samples from donor lungs were stored at −80°C and cryosectioned into 10µm slices. Sections were thaw-mounted on glass slides for direct DESI analysis. Key parameters:

• SOLVENT: 95:5 methanol:water at 1.5µL/min
• DESI GAS: Nitrogen at 7 bar
• SPATIAL RESOLUTION: 100µm pixels, 1 scan/s
• MASS SPECTROMETER: Waters Xevo G2-XS QTof with DESI source (also compatible with SYNAPT G2-Si)
• SOFTWARE: Waters High Definition Imaging (HDI) version 1.4

After DESI acquisition, slides underwent standard H&E staining and were digitally scanned (NanoZoomer S210) to align optical and molecular images.

Key Results and Discussion

Both negative and positive ion modes yielded spatially resolved ion images corresponding to distinct tissue compartments:

• Negative mode: detection of dichlorohydroxyphenylpyruvate (m/z 246.95), phosphatidylglycerols (e.g., PG(36:2) m/z 773.53) and other diagnostic lipids.
• Positive mode: visualization of potassium-adducted phosphatidylcholines (e.g., PC(34:1)-K at m/z 798.54) and low-mass biomarkers (e.g., C21H37N at m/z 304.30).
• Overlay analyses highlighted complementary distributions of lipid species, matching histological structures.

The non-destructive workflow preserved tissue integrity, enabling sequential histological staining and molecular imaging correlations.

Benefits and Practical Applications

DESI-MSI of EVLP-treated lungs offers:

• Minimal sample preparation and rapid analysis under ambient conditions.
• High sensitivity to low-molecular-weight compounds and tissue-specific lipids.
• Compatibility with downstream histology on the same section.
• Potential for identifying spatial biomarkers of organ viability and disease processes.

Future Trends and Applications

Advances may include integration with real-time EVLP monitoring, development of automated biomarker classifiers for transplant decision-making, and expansion to other organ systems. Combining DESI-MSI with machine learning could enable predictive mapping of tissue function and pathology.

Conclusion

The study validates a robust, high-resolution DESI-MSI workflow for ex vivo perfused human lung tissue. The approach bridges molecular profiling and histopathology, unlocking new insights into transplant biology and precision diagnostics.