Intra-articular Injection of Baicalein Inhibits Cartilage Catabolism and NLRP3 Inflammasome Signaling in a Posttraumatic OA Model

Abstract

Baicalein has been shown to have chondroprotective potential in vitro. However, its effect on disease modification in osteoarthritis (OA) is largely unknown. The present study is aimed at determining whether baicalein could slow the progression of OA and inhibit OA-related inflammation in a rat model of destabilization of the medial meniscus (DMM) and the underlying mechanisms. The rats subjected to DMM surgery were treated with baicalein (0.8, 1.6, and 3.2 μg/L, 50 μL, once a week) by intra-articular injection for 6 weeks. Dexamethasone (0.4 mg/mL, 50 μL, once a week) was used as a positive control. Histologic grading of cartilage degeneration was performed using the Osteoarthritis Research Society International (OARSI) recommended grading system (on a scale of 0-6). The expression levels of molecules associated with cartilage homeostasis and inflammatory cytokines were analyzed; moreover, the NLRP3 inflammasome activation and cartilage oxidative stress-associated molecules were determined. Baicalein treatment reduced the OARSI score and slowed OA disease progression in a dose-dependent manner within a certain range. Compared with DMM rats, intra-articular injection of baicalein led to (1) reduced levels of inflammatory mediates such as IL-1β and TNF-α, (2) reduced immunochemical staining of MMP-13 and ADAMTS-5, (3) suppressed immunochemical staining loss of type II collagen, (4) reduced expression of cartilage degradation markers including CTX-II and COMP in urine, and (5) inhibited NLRP3 inflammasome activation rather than regulated expression of SOD, GSH, and MDA. In contrast to the administration of baicalein, dexamethasone injection showed similar effects to slow OA progression, while dexamethasone inhibited NLRP3 inflammasome partly through decreasing levels of SOD, GSH, and MDA. This study indicated that baicalein may have the potential for OA prevention and exerts anti-inflammatory effects partly via suppressing NLRP3 inflammasome activation without affecting oxidative stress-associated molecules, and inhibition of cartilage catabolism enzymes in an OA rat model.