Molecular Imaging Provides Insights into Rheumatoid Arthritis

A recent study utilized positron emission tomography (PET) and single photon emission tomography (SPECT) systems and their respective imaging agents to help identify the cause of inflammation involved in the ongoing pathology of osteoarthritis.

Rheumatoid arthritis causes chronic pain for almost half of adults by the time they retire, but a new molecular imaging technique can visualize inflammation in the joints, giving doctors a clear read on chronic pain and possible joint destruction, according to researchers, who presented their findings at the Society of Nuclear Medicine and Molecular Imaging’s (SNMMI) 2014 annual meeting, held June 7–11, 2014, in St. Louis (MO, USA).

To image arthritis inside the joints, researchers employed multiple molecular imaging systems, PET and SPECT, both of which image physiologic processes with the aid of dedicated detectors that capture signals from injected radionuclide imaging agents. In this instance, researchers evaluated anti-fibroblast activation protein (FAP) antibodies involved in the inflammation associated with rheumatoid arthritis. This was made possible with radiotracers that combine the molecular compound 28H1, which can bind to FAP in the body, with the radionuclides In-111, used in conjunction with SPECT imaging systems, and Zr-89, used with PET systems.

“This research is novel because radiolabeled anti-FAP antibodies have never been used before in molecular imaging for rheumatoid arthritis,” remarked Peter Laverman, PhD, assistant professor of nuclear medicine from the department of radiology and nuclear medicine at Radboud University Medical Center (Nijmegen, The Netherlands). “These antibodies are used for cancer imaging, but can also be used to image FAP expressed on activated fibroblasts in arthritic joints. We found a high accumulation of radiolabeled anti-FAP antibodies in arthritic joints using SPECT and PET imaging.”

This was a preclinical study using small animal scanners. The research findings revealed that both In-111 28H1 and Zr-89 28H1 showed significantly increased imaging agent uptake, or engagement, in inflamed joints. In fact, that uptake was three to four times higher with these agents than another antibody agent evaluated as a control. Researchers also evaluated a very commonly used imaging agent, fluorodeoxyglucose (FDG), to image the inflammation, but uptake of this agent was not associated with the severity of inflammation. This research model validated that 28H1 tagged with either In-111 or Zr-89 is a better way to image arthritis.

“To the best of our knowledge, high-contrast images of this kind were unheard of until now,” said Dr. Laverman. He projected that it may take two or more years to accumulate enough research to get the agents approved for arthritis imaging in mainstream clinical practice.

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Radboud University Medical Center