Evaluation of the anti-inflammatory effect of ectoine–leflunomide combination in adjuvant-induced arthritis in rats, and its colonic protective action against leflunomide-induced gastrointestinal injury

Rheumatoid arthritis (RA) is an autoimmune disease with an intriguing pathophysiological mechanism that primarily affects the joints and leads to extra-articular manifestations. Leflunomide is one of the most effective disease-modifying anti-rheumatic drugs (DMARDs), utilized in RA treatment, but its use comes with frequent gastrointestinal adverse effects, which might necessitate therapy discontinuation. The current work aimed to explore the antirheumatic and gastroprotective effects of ectoine, a compatible solute found in nature, on adjuvant-induced arthritis (AIA) in rats, and to compare its efficacy with that of leflunomide. In this study, animals were divided into five groups: Normal control rats, Untreated adjuvant arthritis (AA) rats, Leflunomide group treated with 10 mg/kg/day, Ectoine group treated with 100 mg/kg/ day, and AA rats treated orally with the combination of ectoine and leflunomide daily with the same dosses. Ectoine administration significantly abolished both articular and extraarticular inflammatory responses in AA rats. Serum levels of nitric oxide (NOx), Interleukin-1β (IL-1β), and anti-cyclic citrullinated peptide (anti-CCP) were significantly reduced, with a significant increase in IL-10. It dramatically suppressed tibiotarsal tissue expression of tumor necrosis factor-α (TNF-α), nuclear factor-kappa B-p65 (NF-κB-p65), receptor activator of NF-κB ligand (RANKL), and matrix metalloproteinase-9 (MMP-9). Colonic examination also showed lower expression levels of TNF-α, NF-κB-p65, intracellular adhesion molecule-1 (ICAM-1), and MMP-9, in addition to a significant antioxidant effect by enhancing reduced glutathione synthesis (GSH) and reduction of myeloperoxidase (MPO) and malondialdehyde (MDA) levels. Our results demonstrate that ectoine has a strong potential for being an efficient anti-inflammatory and anti-rheumatic agent.