Imaging Demyelinated Axons After Spinal Cord Injuries with PET Tracer [¹⁸F]3F4AP.

Area of Science:

• Neuroscience
• Radiochemistry
• Medical Imaging

Background:

• Spinal cord injuries (SCIs) can cause lifelong disability, with demyelination exacerbating functional loss in incomplete injuries.
• Current imaging methods struggle to accurately assess and monitor demyelination after SCI.
• 4-aminopyridine (4AP) shows potential for restoring conduction in demyelinated axons by targeting K+ channels.

Purpose of the Study:

• To introduce and evaluate a novel PET tracer, 3-[18F]fluoro-4-aminopyridine ([18F]3F4AP), for imaging demyelination in SCIs.
• To assess the tracer's ability to detect and monitor demyelination in animal models and human subjects.

Main Methods:

• Rats with incomplete contusion injuries underwent [18F]3F4AP PET imaging up to 1 month post-injury.
• PET results were validated using autoradiography and immunohistochemistry.
• A proof-of-concept study included 2 human subjects with incomplete SCIs.

Main Results:

• [18F]3F4AP PET in rats showed a >2-fold increase in tracer binding localized to the injury site, confirming sensitivity and temporal detection capabilities.
• Histological analyses validated [18F]3F4AP's specific targeting of demyelinated axons.
• [18F]3F4AP successfully differentiated between severe and recovered incomplete SCIs in humans, indicating axonal loss and demyelination, respectively.

Conclusions:

• [18F]3F4AP PET is effective for detecting incomplete SCIs in both animal models and humans.
• The tracer's ability to monitor demyelination and treatment response highlights its utility in advancing SCI understanding and management.