Intra-Articular Cyclo(His-Pro) Attenuates Monosodium Iodoacetate-Induced Osteoarthritis by Suppressing COX-2/PGE₂...

Osteoarthritis (OA) remains an alarming therapeutic challenge, as conventional intra-articular interventions primarily address symptomatic relief without halting progressive cartilage and bone degeneration. In this study, we investigated the disease-modifying potential of Cyclo(His-Pro) (CHP) in a monosodium iodoacetate (MIA)-induced OA rat model. Intra-articular CHP yielded significant clinical improvements, reducing joint edema and reversing OA-induced mechanical and thermal hypersensitivity, as evidenced by lifting behavior, rotarod performance, and hot plate tests. Beyond analgesia, micro-computed tomography (micro-CT) analysis showed that CHP preserved subchondral bone architecture, restoring trabecular volume and thickness and reducing serum C-terminal telopeptide of type II collagen (CTX-2), indicative of suppressed cartilage degradation. At the molecular level, CHP reprogrammed the joint microenvironment by suppressing Cox2, Adamts5, Mmp13, Mmp1, Mmp2, and Timp2 expression and decreasing systemic prostaglandin E2 (PGE₂) levels. Moreover, CHP showed efficacy comparable to Conjuran, a polynucleotide-based mechanical supportive agent, while additionally targeting COX-2/PGE₂-driven inflammatory cascades and cartilage catabolic pathways. Collectively, these findings indicate that intra-articular CHP confers combined analgesic, chondroprotective, and osteoprotective effects, supporting its potential as a promising disease-modifying osteoarthritis drug candidate.