<i>Fraxinus excelsior</i> L. Hydromethanolic Extract Modulates Rheumatoid Arthritis Induced by Complete Freund’s Adjuvant in Rats Emphasizing Inflammatory and Antioxidant Pathways

Background: Rheumatoid arthritis (RA) is a persistent inflammatory condition characterized by an imbalance in oxidative stress and chronic inflammation of joint tissues. Objectives: Fraxinus excelsior L., commonly known as ash, has demonstrated anti-inflammatory, antioxidant, immunomodulatory, and neuroprotective properties. The present study aims to evaluate the therapeutic effects of F. excelsior L. bark hydromethanolic extract (FEE) in the management of RA. Methods: Thirty male rats were randomly divided into six groups: Normal control, RA, three dosages of FEE (20, 40, 80 mg/kg/day, orally), and prednisolone (10 mg/kg/day, orally). These doses were selected to evaluate the potential dose-dependent effects of FEE. The hot plate test, serum glutathione (GSH), malondialdehyde (MDA), and histopathological investigations were assessed. The activity of matrix metalloproteinases (MMP-2 and MMP-9) was measured using zymography. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis previously confirmed the presence of coumarins in FEE. Results: The FEE significantly reduced pain perception in the hot plate test (P < 0.001). Malondialdehyde levels were significantly elevated in RA rats (P < 0.001) but were reduced following FEE and prednisolone treatment (P < 0.01). Similarly, GSH levels were significantly decreased in RA rats (P < 0.001) but were restored in FEE-treated groups (P < 0.01, P < 0.001 for higher doses). The FEE also significantly decreased MMP-2 and MMP-9 activity (P < 0.001), confirming its anti-inflammatory potential. Histopathological analyses corroborated these findings, demonstrating reduced synovial hyperplasia and inflammatory cell infiltration in FEE-treated groups. Coumarins in FEE are known to modulate inflammation through inhibition of MMP-2 and MMP-9 activity and regulate oxidative stress by enhancing antioxidant defenses, including increasing GSH levels and reducing MDA accumulation. Conclusions: Given the improvements in behavioral, biochemical, and histopathological parameters alongside modulation of inflammation (MMP-2, MMP-9) and oxidative stress (MDA, GSH), our results suggest that FEE, rich in coumarins, could be a promising candidate for RA management.