[Imaging of brain microgliosis by PET]

Area of Science:

• Neuroscience
• Immunology
• Radiochemistry

Background:

• Microglia, the brain's immune cells, are actively involved in immune surveillance, similar to peripheral macrophages.
• Morphological changes in microglia (ramified to ameboid) signal neuroinflammation, often triggered by neuronal damage or neurodegeneration.
• Microgliosis, the increase in microglia, is associated with various neurological conditions, including Alzheimer's disease.

Purpose of the Study:

• To discuss the application of peripheral benzodiazepine receptor (PBR) tracers for in vivo imaging of neuroinflammation.
• To highlight the utility of PBR tracers in assessing neuroinflammation in neurological and psychiatric diseases.
• To identify limitations of current PBR tracers and suggest future directions for improved neuroimaging agents.

Main Methods:

• Positron Emission Tomography (PET) imaging using the PBR tracer [11C] (R)-PK11195.
• In vivo detection of activated microglia based on increased PBR expression.
• Correlation of PBR tracer uptake with neuroinflammatory states in various diseases.

Main Results:

• PBR tracers, like [11C] (R)-PK11195, enable in vivo visualization of neuroinflammation by targeting increased PBR on activated microglia.
• PBR expression is elevated on the mitochondrial membrane of activated microglia.
• The PBR tracer allows for the assessment of overall neuroinflammation levels in vivo across numerous neurodegenerative conditions.

Conclusions:

• PBR tracers are valuable tools for imaging neuroinflammation in vivo across a spectrum of neurological and psychiatric disorders.
• A significant limitation of current PBR tracers is their inability to differentiate between protective and proinflammatory microglial phenotypes.
• Future research should focus on developing novel tracers capable of discriminating between distinct microglial states for more precise neuroinflammation assessment.