Abstract
BackgroundFolate receptor-β (FR-β) is a cell surface receptor that is significantly upregulated on activated macrophages during inflammation and provides a potential target for folate-based therapeutic and diagnostic agents. FR-β expression in central nervous system inflammation remains relatively unexplored. Therefore, we used focally induced acute and chronic phases of experimental autoimmune encephalomyelitis (EAE) to study patterns of FR-β expression and evaluated its potential as an in vivo imaging target.MethodsFocal EAE was induced in rats using heat-killed Bacillus Calmette-Guérin followed by activation with complete Freund’s adjuvant supplemented with Mycobacterium tuberculosis. The rats were assessed with magnetic resonance imaging and positron emission tomography/computed tomography (PET/CT) at acute (14 days) and chronic (90 days) phases of inflammation. The animals were finally sacrificed for ex vivo autoradiography of their brains. PET studies were performed using FR-β-targeting aluminum [18F]fluoride-labeled 1,4,7-triazacyclononane-1,4,7-triacetic acid conjugated folate ([18F]AlF-NOTA-folate, 18F-FOL) and 18 kDa translocator protein (TSPO)-targeting N-acetyl-N-(2-[11C]methoxybenzyl)-2-phenoxy-5-pyridinamine (11C-PBR28). Post-mortem immunohistochemistry was performed using anti-FR-β, anti-cluster of differentiation 68 (anti-CD68), anti-inducible nitric oxide synthase (anti-iNOS), and anti-mannose receptor C-type 1 (anti-MRC-1) antibodies. The specificity of 18F-FOL binding was verified using in vitro brain sections with folate glucosamine used as a blocking agent.ResultsImmunohistochemical evaluation of focal EAE lesions demonstrated anti-FR-β positive cells at the lesion border in both acute and chronic phases of inflammation. We found that anti-FR-β correlated with anti-CD68 and anti-MRC-1 immunohistochemistry; for MRC-1, the correlation was most prominent in the chronic phase of inflammation. Both 18F-FOL and 11C-PBR28 radiotracers bound to the EAE lesions. Autoradiography studies verified that this binding took place in areas of anti-FR-β positivity. A blocking assay using folate glucosamine further verified the tracer’s specificity. In the chronic phase of EAE, the lesion-to-background ratio of 18F-FOL was significantly higher than that of 11C-PBR28 (P = 0.016).ConclusionOur EAE results imply that FR-β may be a useful target for in vivo imaging of multiple sclerosis-related immunopathology. FR-β-targeted PET imaging with 18F-FOL may facilitate the monitoring of lesion development and complement the information obtained from TSPO imaging by bringing more specificity to the PET imaging armamentarium for neuroinflammation.
Highlights
Folate receptor-β (FR-β) is a cell surface receptor that is significantly upregulated on activated macrophages during inflammation and provides a potential target for folate-based therapeutic and diagnostic agents
We investigated the application of 18FFOL for evaluation and monitoring of the progression of neuroinflammatory lesions in a rat model of Multiple sclerosis (MS) and endeavored to determine whether FR-β expression correlates with disease progression and neuroinflammation during the time course of DTH lesions in focal EAE
In vivo positron emission tomography/computed tomography (PET/computed tomography (CT)) imaging with 18F-FOL and 11CPBR28 showed focal uptake in the induced brain hemisphere, which was co-localized with the magnetic resonance imaging (MRI)-depicted lesion
Summary
Folate receptor-β (FR-β) is a cell surface receptor that is significantly upregulated on activated macrophages during inflammation and provides a potential target for folate-based therapeutic and diagnostic agents. We used focally induced acute and chronic phases of experimental autoimmune encephalomyelitis (EAE) to study patterns of FR-β expression and evaluated its potential as an in vivo imaging target. With the progression of the disease into the secondary progressive phase (SPMS), the pathology is altered and is characterized by microglial activation and widespread damage in areas of cortical gray matter, white matter, and NAWM [6,7,8]. In this secondary phase, the disease is no longer treatable using the anti-inflammatory treatments that are effective during the RRMS phase [6]. DTH lesions resemble those occurring in the progressive phase of MS when they advance to the chronic phase of inflammation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
