TARGETED DESI IMAGING MS OF DRUG DISTRIBUTION AND DRUG- INDUCED LIVER INJURY (DILI) METABOLITES FROM METHAPYRILENE IN THE MALE WISTAR RAT

Significance of the Topic

Understanding the spatial distribution of drug molecules and lipid biomarkers within tissue is critical for elucidating mechanisms of drug-induced liver injury (DILI). Targeted desorption electrospray ionization (DESI) imaging mass spectrometry extends conventional lipidomics by preserving spatial context, enabling researchers to correlate histological changes with molecular alterations.

Study Objectives and Overview

The study aimed to apply targeted DESI imaging MS to map the localization of methapyrilene, its metabolites, and key lipid classes in male Wistar rat liver tissue. Using two dose levels (50 and 150 mg/kg) administered orally over five days, the researchers compared treated and control samples at day six to identify dose-dependent molecular changes associated with toxicity.

Methods and Instrumentation

• Sample Preparation
  10 μm fresh-frozen liver sections were cryosectioned and thaw-mounted on glass slides without embedding.
• DESI Imaging Conditions
  Solvent: 98:2 methanol:water with 0.01% formic acid at 2 μL/min; nebulizing gas: 0.9 bar N₂; sprayer voltage: 0.7 kV; cone voltage: 10–50 V; source temperature: 120 °C; pixel sizes: 20 and 50 μm.
• Instrumentation
  Waters DESI XS source with High-Performance Sprayer and heated transfer line; Xevo TQ-Absolute tandem quadrupole mass spectrometer performing multiple reaction monitoring (MRM) with unit mass resolution from m/z 20 to 2000.
• Data Processing
  Acquisition and processing were performed in MassLynx 4.2 with DESI Method Editor and HDI v1.7 for image assembly and visualization.

Main Results and Discussion

• Detection Sensitivity
  Targeted MRM imaging achieved over tenfold lower limits of detection (~1 fmol/pixel) compared to full-scan and MS/MS on a QTOF high-resolution instrument.
• Lipid Distribution Changes
  Dose-dependent alterations were observed in several lipid classes. Negative ion mode revealed pronounced changes in bile acids, phosphatidylinositols (PI), phosphatidylglycerols (PG), and phosphatidylethanolamines (PE). Positive ion mode showed modest variations in sphingomyelins (SM) and phosphatidylcholines (PC).
• Spatial Correlation
  Overlay images at 20 μm pixel resolution highlighted distinct localization patterns of drug metabolites and lipid biomarkers, linking molecular distributions to regions of altered morphology in injured tissue.

Benefits and Practical Applications

• Enhanced Specificity and Sensitivity
  Targeted DESI imaging on a tandem quadrupole enables selective mapping of known metabolites and lipids with minimal background.
• Complementary Spatial Insights
  Provides critical spatial context missing from bulk LC-MS workflows, supporting mechanistic toxicology and biomarker discovery.
• High-Throughput Compatibility
  Ambient ionization and minimal sample preparation allow rapid analysis of multiple sections from the same tissue block.

Future Trends and Potential Applications

• Integration with Multi-Omics
  Combining DESI imaging with transcriptomic or proteomic maps to build comprehensive spatial omics atlases.
• High-Resolution Protocols
  Advancements in pixel size and ion mobility separation to resolve subcellular distributions of small molecules.
• Broader Drug Screening
  Adapting targeted imaging methods to a wider range of pharmaceuticals and toxicological models.

Conclusion

Targeted DESI imaging mass spectrometry on a tandem quadrupole platform effectively maps the spatial distribution of methapyrilene, its metabolites, and lipid biomarkers in liver tissue. By combining high sensitivity and specificity with spatial resolution, this approach enhances our understanding of DILI mechanisms and supports biomarker-driven investigations.

References

1. Graichen ME, Neptun DA, Dent JG, Popp JA, Leonard TB. Effects of methapyrilene on rat hepatic xenobiotic metabolizing enzymes and liver morphology. Fundam Appl Toxicol. 1985;5(2):165–174.
2. EVOTEC (France) SAS. Dosing animal study and tissue preparation for methapyrilene investigation. Toulouse, France.