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Published on: October 20, 2013
Imaging of activated macrophages in experimental osteoarthritis using folate-targeted animal single-photon-emission
Tom M Piscaer1, Cristina Müller, Thomas L Mindt
1Erasmus University Medical Center, Rotterdam, The Netherlands. t.piscaer@erasmusmc.nl
Objective:
Evaluation of macrophage activation may provide essential information about the etiology and progression rate of osteoarthritis (OA). Activated macrophages abundantly express folate receptor β (FRβ), which can be targeted using radioactive-labeled folic acid. This study was undertaken to investigate whether macrophage activation can be monitored in small animal models of OA using a folate radiotracer and to determine whether macrophage activation differs in different models of OA with different OA progression.
Methods:
Two rat models of OA were used: the mono-iodoacetate (MIA) model, which is a fast-progressing biochemically induced model, and the anterior cruciate ligament transection (ACLT) model, which induces OA at a slower pace. Images were obtained using high-resolution small animal single-photon-emission computed tomography/computed tomography. The specificity of the technique was tested by eradicating macrophages using clodronate-laden liposomes and blockade of FRβ by cold folic acid.
Results:
The MIA model had high initial macrophage activation, with a peak after 2 weeks which disappeared after 8 weeks. The ACLT model showed less activation but was still active 12 weeks after induction. The technique allowed monitoring of the disease process over time, in which late stages of the disease showed less macrophage activation than early stages, especially in the fast-progressing MIA model of OA.
Conclusion:
Our findings indicate that macrophage activation in experimental OA can clearly be demonstrated and monitored by the folate radiotracer. The high resolution, high sensitivity, and high specificity of the technique allow clear localization of macrophage activity in a disease model that is not known for abundant macrophage involvement.
Insights
A novel folate radiotracer effectively monitors macrophage activation in osteoarthritis (OA) animal models. This imaging technique tracks disease progression by visualizing macrophage activity over time.
Area of Science:
- Biomedical imaging
- Radiochemistry
- Immunology
Background:
- Macrophage activation is crucial for understanding osteoarthritis (OA) etiology and progression.
- Folate receptor beta (FRβ) is highly expressed on activated macrophages and can be targeted with folate-based tracers.
- Non-invasive monitoring of macrophage activation in OA models is needed.
Purpose of the Study:
- To evaluate a folate radiotracer for monitoring macrophage activation in rat models of OA.
- To compare macrophage activation patterns in different OA models with varying progression rates.
- To assess the feasibility of using this technique for OA research.
Main Methods:
- Utilized two rat OA models: mono-iodoacetate (MIA) and anterior cruciate ligament transection (ACLT).
- Employed high-resolution small animal single-photon-emission computed tomography/computed tomography (SPECT/CT) for imaging.
- Validated technique specificity through macrophage depletion and FRβ blockade.
Main Results:
- The MIA model exhibited rapid, transient macrophage activation, peaking at 2 weeks and subsiding by 8 weeks.
- The ACLT model showed sustained, lower-level macrophage activation up to 12 weeks.
- The folate radiotracer successfully monitored disease progression, revealing decreased macrophage activity in later OA stages.
Conclusions:
- Folate radiotracer imaging reliably demonstrates and monitors macrophage activation in experimental OA.
- The high-resolution, sensitive, and specific technique allows precise localization of macrophage activity.
- This method is valuable for studying OA, even in models with less prominent macrophage involvement.
