FOLATE RECEPTOR POSITIVE MACROPHAGES IN ANIMAL MODELS FOR OSTEOARTHRITIS AND EFFECTS OF TRIAMCINOLONE

Summary: Folate-based SPECT and PET scans are emerging as interesting tools for macrophage imaging. However, it remains unclear which macrophage subtypes express the folate receptor (FR-β). In this study we investigated macrophage activation and FR-β expression both in vitro and in two animal models for knee osteoarthritis. Human peripheral blood monocytes were differentiated to macrophages in vitro using GM-CSF and M-CSF and stimulated with cytokines and treated with TA. FACS and gene expression analysis showed higher FR-β expression in M2 anti-inflammatory macrophages and significant upregulation of FR-β expression by treatment with TA. Osteoarthritis was induced in the knees of Wistar rats with either papaine or MIA. Rats were treated intra-articularly with triamcinolone acetonide (TA) and folate-SPECT scans were performed. Higher folate uptake was seen in OA knees compared to controls and in knees treated with TA. Together, these results suggest folate-based imaging mainly visualizes anti-inflammatory macrophages and corticosteroid treatment needs to be taken into account when applying this imaging tool in a clinical setting.