Protective effects of swimming exercise on experimental rheumatoid arthritis in rats through modulation of leptin receptor expression and inflammation

Objectives: This study aims to investigate the effects of swimming exercise on arthritis severity, radiological joint damage, and leptinrelated molecular changes in experimental rheumatoid arthritis (RA) in rats. Materials and methods: A total of 30 male Wistar rats were randomly assigned to three groups (n=10 per group): Control, Arthritis, and Exercise + Arthritis. Experimental arthritis was induced by a single intradermal injection of Complete Freund's Adjuvant (CFA). The Exercise + Arthritis group underwent a six-week swimming protocol (1 h/day, five days/week), beginning two weeks before arthritis induction and continuing thereafter. Arthritis severity was assessed by visual scoring, radiological analysis, and histopathological evaluation. Plasma concentrations of leptin and matrix metalloproteinases (MMP-1, MMP-3, MMP-8, MMP-13) were measured using enzyme-linked immunosorbent assay (ELISA), and leptin receptor expression in paw tissues was analyzed immunohistochemically. Results: The Exercise + Arthritis group exhibited significantly lower visual arthritis scores (p=0.002), reduced ankle swelling (p<0.001), and decreased cartilage and bone damage radiologically (p=0.045) compared to the Arthritis group. Histopathological evaluation revealed that swimming exercise markedly attenuated inflammatory cell infiltration, pannus formation, and bone resorption. Although plasma leptin and MMP levels did not differ between the groups (p>0.05), leptin receptor expression, considered to be associated with joint damage, was found to be significantly lower in the Exercise + Arthritis group (p=0.009). Swimming exercise reduced arthritis severity and joint damage. Conclusion: Moderate-intensity swimming exerts protective, anti-inflammatory effects in experimental RA by reducing inflammation and preserving joint structure in rats, possibly through modulating leptin receptor expression and inflammatory pathways. Although regular swimming may serve as a useful adjunct to slow disease progression and joint damage in RA in rats, the translational relevance of these results remains uncertain in humans.