Synergistic defense: Quercetin and chondroitin sulfate combat bacterial trigger of rheumatoid arthritis, Proteus mirabilis through in-vitro and in-vivo mechanisms

Rheumatoid arthritis, a chronic autoimmune disorder characterized by joint inflammation, is thought to be exacerbated by bacterial infections, notably Proteus mirabilis. This study explores the combined effects of quercetin, a potent antioxidant and anti-inflammatory flavonoid, and chondroitin sulfate, known for its cartilage-protective properties, as a potential therapeutic approach. Molecular docking analyses revealed favourable interactions between these compounds and key pro-inflammatory cytokines IL-6 and TNF-α, suggesting their potential to disrupt inflammation-related signaling pathways. In vitro assays demonstrated that the quercetin- chondroitin sulfate combination (1:1 ratio) significantly inhibited oxidative stress and hemolysis, highlighting its enhanced anti-inflammatory and membrane-protective effects. The free radical scavenging assays further confirmed the antioxidant potential of this combination, which demonstrated strong radical scavenging activity. Antimicrobial assays showed notable antibacterial effects, with an increased inhibition zone against P. mirabilis when quercetin and chondroitin sulfate were combined, suggesting a synergistic antimicrobial action. In vivo, zebrafish subjected to bacterial stress showed improved survival rates with the quercetin and chondroitin sulfate combination treatment, along with enhanced mineralization and significant modulation of alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) activities, indicating its protective role in maintaining joint health. Furthermore, gene expression analysis revealed a substantial reduction in pro-inflammatory markers, including TNF-α and IL-6, demonstrating the quercetin and chondroitin sulfate combination's ability to mitigate inflammation. Together, these findings suggest that the quercetin and chondroitin sulfate combination hold significant therapeutic potential in reducing oxidative stress, inflammation, and microbial-induced RA exacerbations.