MS imaging enabling visualization of lipid C=C positional isomers in biological tissues using Oxygen Attachment Dissociation (OAD)

Significance of the Topic

Lipids are key biomolecules that support membrane structure energy storage and signaling functions. Conventional CID MS/MS fails to localize double bond positions in unsaturated lipids which are critical for biological activity. Oxygen Attachment Dissociation based imaging integrates radical dissociation chemistry with MS imaging enabling in situ mapping of positional isomers.

Objectives and Study Overview

This work demonstrates the integration of Oxygen Attachment Dissociation (OAD) into MALDI MS imaging. It aims to selectively fragment C=C bonds in lipid ions to distinguish positional isomers directly in tissue sections. A mouse cerebellum model is used to validate spatial distribution of PC 16:0_18:1 n-7 and n-9 isomers and sulfatides.

Instrumentation Used

• Shimadzu LCMS™-9050 Q-TOF mass spectrometer equipped with an OAD cell
• Microwave-driven radical source generating atomic oxygen and hydroxyl radicals
• MALDI matrix sublimation apparatus and iMLayer for uniform DHB coating

Methodology

OAD is achieved by exposing lipid ions to neutral atomic oxygen radicals in the Q2 collision cell of a Q-TOF. Radical attachment selectively cleaves carbon–carbon bonds adjacent to C=C sites producing diagnostic fragment ions. Both positive and negative ion modes are applied. MS imaging acquisitions collect OAD MS/MS spectra at each raster point on tissue sections coated with DHB.

Main Results and Discussion

• OAD MS/MS of model lipids yields characteristic fragment pairs that precisely locate C=C bonds in PC and sulfatide standards.
• MS images distinguish PC 16:0_18:1(n-7) and (n-9) isomers, revealing distinct localization in cerebellar white matter and granule cell layers.
• Negative-ion mode OAD permits mapping of sulfatide 24:1 isomers with clear separation based on unique diagnostic ions.

Benefits and Practical Applications

OAD-MS imaging provides direct in situ structural characterization of lipid isomers, enhancing molecular specificity of imaging experiments. It is compatible with existing MALDI-MS platforms and can be applied in both ion modes. Potential applications include spatial lipidomics research, biomarker discovery in disease models, quality control in pharmaceutical development, and industrial lipid analysis.

Future Trends and Possibilities

• Integration of OAD with ion mobility separation for superior isomer resolution.
• Extension of the approach to diverse lipid classes and complex biological tissues.
• Coupling with high-resolution laser optics and AI-based data analysis pipelines.
• Development of compact radical sources for ambient and real-time imaging workflows.

Conclusion

The incorporation of Oxygen Attachment Dissociation into MS imaging workflows offers a robust strategy to localize double bond positions in lipids directly within tissue sections. This advance significantly extends the structural insights obtainable by MSI and supports comprehensive spatial lipidomics studies.

References

1. Takahashi H et al Anal Chem 2018 90(12) 7230-7238
2. Takahashi H et al Mass Spectrometry 2019 S0080
3. Uchino H et al Commun Chem 2022 5 162
4. Peggi M et al Anal Chem 2012 84(3) 1557-1564