Simultaneous Spatial Mapping and Identification of C-Peptides Alongside Lipids in Mouse Pancreatic Tissues with Nano-DESI Mass Spectrometry Imaging.

Peptides secreted by pancreatic islet cells regulate glucose homeostasis. Their dysregulation may contribute to metabolic disorders such as diabetes and pancreatic disease. Here, we use nanospray desorption electrospray ionization mass spectrometry imaging (nano-DESI MSI) to identify and map intact and truncated C-peptides in mouse pancreatic tissue. Alongside commonly observed lipids and metabolites, we detected 36 multiply-charged acidic peptides that preferentially ionize in negative ion mode. On-tissue tandem mass spectrometry (MS/MS) was used to identify them as intact C-peptide isoforms and multiple truncated variants, including several previously unreported peptides. Molecular networking of MS/MS data assigned some unidentified species to C-peptide families based on shared fragmentation patterns. Ion images revealed distinct distributions of truncated peptides, with chemical gradients extending from β-cells into peri-insular acinar cells, suggesting their potential roles in endocrine-exocrine communication. These findings demonstrate the power of nano-DESI MSI to identify and spatially map novel peptides, which is critical for understanding their roles in pancreatic tissues.