Macrophage Targeting Agent Aids RA Diagnosis

A novel positron emission tomography (PET) tracer can visualize joint inflammation and could provide early diagnosis of rheumatoid arthritis (RA), according to a new study.

Researchers at Ewha Women’s University (Seoul, Korea), Seoul National University College of Medicine (SNU; South Korea), and other institutions conducted a study in mice to examine if Fluorine-18 (18F)-FEDAC, a radiolabeled ligand that targets the 18-kDa translocator protein (TSPO), which is abundant in activated macrophages, could be used to detect and monitor RA development. The mouse model studied both 18F-FEDAC and 18F-FDG PET imaging, with microscopic examinations of tissue performed to evaluate macrophages and TSPO expression.

The results revealed increased TSPO mRNA and protein expression in the activated macrophages, with uptake of 18F-FEDAC in activated macrophages higher than in non-activated cells. In addition, 18F-FEDAC uptake by arthritic joints increased early on, whereas uptake of 18F-FDG uptake did not; on the other hand, 18F-FDG uptake by arthritic joints increased at later stages to a higher level than 18F-FEDAC uptake. Histologic sections of arthritic joints demonstrated an influx of macrophages, as compared with that in normal joints. The study was published in the May 2015 issue of The Journal of Nuclear Medicine.

“We observed that 18F-FEDAC uptake increased in paws of murine rheumatoid arthritis models in association with TSPO expression of activated macrophages, even before the onset of clinical symptoms of arthritis,” said senior author Gi Jeong Cheon, MD, PhD, of SNU. “18F-FEDAC can help us to find which patients will actually progress to clinically significant rheumatoid arthritis and need treatment. These findings are expected to contribute to the improvement of personalized therapeutic outcomes by expanding the scope of molecular imaging and nuclear medicine.”

18F is a fluorine radioisotope that decays by positron emission 97% of the time, and electron capture 3% of the time; both modes of decay yield stable oxygen-18 (18O). 18F is an important radioisotope as a result of both its short half-life and the emission of positrons when decaying. It is primarily synthesized into fluorodeoxyglucose (FDG) for use in PET scans for cancer detection.

Related Links:
Ewha Women’s University
Seoul National University College of Medicine