On-tissue identification of insulin: in situ reduction coupled with mass spectrometry imaging

Proteomics Clin Appl. 2011 Aug;5(7-8):448-53. doi: 10.1002/prca.201000152. Epub 2011 Jun 8.


Purpose: The aim of this study was to use on-tissue reduction followed by MALDI-MS imaging (MSI) to identify an m/z 5812.85 peak, which is over-expressed in healthy human pancreatic tissue compared with type one Diabetes (T1D) tissue.

Experimental design: A major constraint of MALDI-MSI is identification of compounds with m/z ≥4000. On-tissue reduction using tris (2-carboxyethyl) phosphine (TCEP) breaks the inter-domain disulphide bonds generating low-molecular-weight peptides amenable to direct MS/MS analysis. Pancreatic tissues from healthy (n=4) and diabetic subjects (n=4) were profiled by MALDI-MSI with/without reduction.

Results: On-tissue reduction resulted in the loss of the over-expressed 5812.85 m/z peak and the simultaneous appearance of a 3430.664 m/z peak in healthy tissues. The latter peak presumably derived from the 5812.85 m/z peak was identified as the insulin B chain by MS/MS. MALDI-MSI images show that both the 5812.85 insulin peak before reduction and the 3430.664 peak after reduction co-localized with the healthy pancreatic islets.

Conclusion and clinical relevance: On-tissue reduction followed by MALDI-MSI resulted in the identification of insulin and localization of pancreatic islets of langerhans. The approach will be useful in the future identification of novel therapeutic molecular targets to β-cells lost during type one diabetes.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Case-Control Studies
  • Diabetes Mellitus, Type 1 / diagnosis*
  • Diabetes Mellitus, Type 1 / metabolism
  • Diabetes Mellitus, Type 1 / pathology
  • Humans
  • Insulin* / analysis
  • Insulin* / chemistry
  • Islets of Langerhans / anatomy & histology
  • Islets of Langerhans / metabolism*
  • Molecular Imaging / methods*
  • Oxidation-Reduction
  • Peptides / analysis*
  • Phosphines / chemistry
  • Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / methods*
  • Tandem Mass Spectrometry


  • Insulin
  • Peptides
  • Phosphines