In vivo Overhauser-enhanced MRI of proteolytic activity

Area of Science:

• Biomedical Imaging
• Molecular Imaging
• Magnetic Resonance Imaging

Background:

• Developing in vivo imaging strategies for proteolytic activity is crucial.
• Overhauser-enhanced MRI (OMRI) detects proteolysis by monitoring changes in nitroxide moiety rotational correlation time.
• Nitroxide-labeled macromolecules show a sharp decrease in rotational correlation time upon cleavage.

Purpose of the Study:

• To demonstrate in vivo Overhauser-enhanced MRI (OMRI) for sensing proteolytic activity.
• To illustrate the concept using orally administered nitroxide-labeled elastin in mice.
• To evaluate the potential of OMRI for disease modeling and drug testing.

Main Methods:

• In vitro and in vivo Overhauser-enhanced MRI (OMRI) at 0.2 T.
• Oral administration of nitroxide-labeled elastin in mice.
• Three-dimensional OMRI acquisition using a keyhole fully balanced steady-state free precession sequence (20 s at 0.125 mm(3) resolution).

Main Results:

• In vitro, elastin derivative showed high Overhauser enhancements (19-fold) upon proteolysis by pancreatic porcine elastase.
• In vivo, proteolysis was detected in the duodenum approximately 30 min after oral administration (Overhauser enhancements of 7.2 ± 2.4).
• No proteolysis was observed in the stomach; free nitroxides or pre-digested elastin were detected in the stomach.

Conclusions:

• Overhauser-enhanced MRI (OMRI) successfully visualizes in vivo proteolysis.
• The technique allows for spatial and temporal detection of enzymatic activity in specific organs.
• OMRI holds promise for evaluating proteolytic activities in disease models and for drug screening.