A multimodal characterization of early monoarthritis in rats using an MBSA/CFA-induced model

Abstract A detailed characterization of the initial inflammatory events in arthritis is essential to improve experimental models and accelerate translational research. In this study, we comprehensively established and characterized a monoarthritis model in male Wistar rats, induced by intra-articular injection of methylated bovine serum albumin (mBSA) combined with Freund’s complete adjuvant (CFA). Animals were allocated into a control group and two groups with arthritis, evaluated at early (8 days) and late acute phase (13 days). Arthritis induction resulted in pronounced synovial inflammation, characterized by increased cellular infiltration composed predominantly of CD68 + macrophages, extracellular matrix remodeling with elevated collagen I and V deposition, and increased intra-articular glucose metabolism, assessed by PET/CT with [18F]FDG. Biochemical analysis revealed significantly elevated levels of prostaglandin E 2 in the synovial lavage fluid of arthritic joints. These pathological changes were accompanied by transient clinical and behavioral changes, including reduced limb-use impairment, decreased body weight gain, and increased pain scores, which were attenuated by tramadol administration. Taken together, these findings demonstrate that a single mBSA/CFA challenge followed by an mBSA booster is sufficient to induce consistent monoarthritis with measurable pathological, metabolic, clinical, and behavioral correlations. This model provides a robust platform for investigating early inflammatory mechanisms and evaluating diagnostic and therapeutic strategies targeting joint inflammation.“