Inflammation Imaging Biomarkers

Inflammation plays a central role in numerous pathological conditions, including autoimmune diseases, infections, cancer, and neurodegenerative disorders. The ability to visualise and quantify inflammation in vivo has significantly advanced with the development of molecular imaging techniques. Inflammation imaging biomarkers serve as crucial tools for diagnosing diseases, monitoring disease progression, and evaluating treatment efficacy.

Types of Inflammation Imaging Biomarkers

Several biomarkers have been identified for imaging inflammation, each targeting specific cellular or molecular mechanisms involved in the inflammatory response. These include:

  1. Translocator Protein (TSPO): TSPO is a mitochondrial protein expressed in activated microglia and macrophages, making it a valuable biomarker for neuroinflammation. Radiolabelled TSPO ligands, such as [¹¹C]PK11195 and [¹⁸F]DPA-714, are widely used in positron emission tomography (PET) imaging of neuroinflammatory diseases like multiple sclerosis, Alzheimer’s disease, and traumatic brain injury.
  2. Fluorodeoxyglucose (FDG): [¹⁸F]FDG PET is a widely used imaging technique that measures glucose metabolism. Activated immune cells, particularly macrophages and neutrophils, exhibit increased glucose uptake, making FDG a useful, albeit non-specific, biomarker for inflammation in conditions such as vasculitis, rheumatoid arthritis, and infection.
  3. Matrix Metalloproteinases (MMPs): MMPs play a role in extracellular matrix remodelling during inflammation and tumour progression. Radiolabelled MMP inhibitors have been explored for PET imaging to assess inflammatory tissue damage.
  4. C-X-C Motif Chemokine Receptor 4 (CXCR4): CXCR4 is overexpressed on immune cells during inflammation and is involved in cell migration. PET tracers such as [¹⁸F]Pentixafor enable imaging of CXCR4 expression in inflammatory diseases, including atherosclerosis and certain cancers.
  5. Myeloperoxidase (MPO): MPO is an enzyme secreted by activated neutrophils and is a marker of acute inflammation. Imaging MPO activity using radiolabelled tracers or optical probes has been explored in cardiovascular diseases and pulmonary inflammation.

Applications of Inflammation Imaging

Inflammation imaging biomarkers have found applications across multiple medical fields:

  • Neurology: In neuroinflammatory disorders, TSPO imaging aids in understanding disease pathology and assessing therapeutic responses in conditions such as multiple sclerosis and Parkinson’s disease.
  • Cardiology: Inflammation is a key component of atherosclerosis, and imaging macrophage activity in arterial plaques can help predict cardiovascular events.
  • Oncology: Tumour-associated inflammation can be assessed using FDG PET and other targeted biomarkers, providing insights into tumour progression and response to immunotherapy.
  • Infectious Diseases: Imaging techniques help distinguish between sterile inflammation and infection, aiding in the diagnosis of conditions such as osteomyelitis and tuberculosis.

Advancements in imaging technology, combined with novel biomarker discovery, continue to improve the specificity and sensitivity of inflammation imaging, enhancing diagnostic capabilities and personalised treatment strategies.

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