High Resolution Imaging of Adrenal Glands by DESI-MS (ASMS)

Importance of the Topic

The adrenal glands are key lipid‐rich endocrine organs that generate glucocorticoids, mineralocorticoids and androgens essential for metabolic regulation, cardiovascular function and fertility.
Spatial variations in lipid distribution reflect functional zones and can reveal early indicators of adrenal disorders such as congenital adrenal hyperplasia, Cushing’s syndrome and Addison’s disease.

Study Objectives and Overview

This feasibility study aimed to evaluate desorption electrospray ionization mass spectrometry imaging (DESI‐MSI) for mapping lipid distributions in murine adrenal tissue.
Comparative analyses were performed on a conventional quadrupole time‐of‐flight (QToF) instrument and a high‐resolution multi‐reflecting time‐of‐flight (MRT) mass spectrometer to assess spatial resolution, mass accuracy and molecular identification capabilities.

Methodology and Instrumentation

Sample Preparation:

• Cryo‐sectioning of healthy wild‐type mouse adrenal glands at 15 µm thickness onto glass slides.
• Non‐destructive DESI spray deposition of solvent (95:5 methanol:water) at 5 bar and 0.7 kV onto tissue sections.

Imaging Acquisition:

• Conventional QToF (SYNAPT G2-XS) at 25 µm pixel size, 2 scans/s.
• MRT QToF (SELECT SERIES MRT) at 50 µm pixel size, 2 scans/s, achieving >200,000 FWHM mass resolution.

Data Processing and Software:

• HDI (High Definition Imaging) for ROI selection, peak picking and initial visualization.
• MassLynx for centroiding, elemental composition prediction and database searching (LIPID MAPS).
• MetaboAnalyst for statistical analysis (unsupervised PCA, Pareto scaling).
• Lipostar MSI for advanced visualization, composite RGB overlays and annotation.

Main Results and Discussion

Regional Lipid Profiles:

• PCA analysis clearly separated medulla, cortex and capsule regions based on scored m/z features.
• Key markers included phenylalanine (m/z 166.08615) in the medulla, cholesterol fragment (m/z 369.35159) in the capsule and a sterol derivative (m/z 461.28796) in the cortex.

High‐Resolution Benefits:

• MRT instrument resolved a single m/z 806.55 peak from QToF into three distinct species (806.51038, 806.55902, 806.56897), each showing differential localization.
• Improved mass accuracy (<300 ppb) narrowed elemental composition candidates and enhanced confidence in putative identifications.

MS/MS Confirmation:

• Targeted fragmentation (m/z 166.06) confirmed phenylalanine assignment via characteristic fragment ions.

Benefits and Practical Applications

DESI‐MSI offers rapid, label‐free mapping of lipid distributions without damaging tissue architecture, enabling subsequent histological analysis.
High‐resolution MRT imaging uncovers subtle molecular differences unresolved by conventional instruments, supporting biomarker discovery in adrenal pathology.
Integration with statistical and imaging software provides a comprehensive pipeline from data acquisition to compound annotation.

Future Trends and Opportunities

The non‐destructive nature of DESI allows multiplexed analyses on the same tissue, combining MSI with histology and targeted MS/MS.
Further developments may include higher spatial resolution, integration with ion mobility separation and machine learning for automated feature recognition.
Extending DESI‐MSI studies to diseased adrenal models will advance understanding of lipid alterations in endocrine disorders.

Conclusion

This study demonstrates that DESI‐MSI, particularly when coupled with high‐resolution MRT mass spectrometry, provides detailed spatial lipidomics of adrenal tissue.
The approach delivers robust molecular maps, high mass accuracy and actionable tissue biomarkers, paving the way for advanced studies of adrenal health and disease.

References

1. US Department of Health Sciences, NIH National Institute of Child Health and Human Development. Adrenal Gland Disorders. 2022.