Salidroside Protects Chondrocytes against IL-1β-Induced Injury and Alleviates Osteoarthritis Progression by Activating the Nrf2 Pathway

Background: Osteoarthritis (OA) is a common disease that causes pain to many older adults. Because the pathogenesis is not fully elucidated, effective drug therapies are currently lacking. This study aimed to determine how salidroside (Sal)-mediated reduction of osteoarthritis development in mice worked and to identify the underlying mechanism. Methods: Using in vitro experiments, ATDC5 cells were treated with various concentrations of Sal and interleukin (IL)-1β for 24 hours to mimic OA. An enzyme-linked immunosorbent assay (ELISA) was conducted to detect the production of pro-inflammatory cytokines and reactive oxygen species (ROS). Western blotting was performed to observe the nuclear factor-kappa B (NF-κB) and nuclear factor erythroid 2-related factor 2 (Nrf2) pathways. In in vivo experiments, pathological examination was used to assess the effects of Sal on alleviating OA progression in mice. Nrf2 signaling and its downstream proteins were further tested by immunofluorescence analysis. Results: The results showed that both pro-inflammatory cytokines and ROS were significantly reduced following Sal treatment in a concentration-dependent manner. Western blotting revealed that Sal could inhibit the expression of the NF-κB/hypoxia-inducible factor-2α pathway and activate the Nrf2/heme oxygenase-1 pathway. In vivo experiments showed that the cartilage surface in the saline-treated group eroded to a greater extent than the Sal-treated groups (p < 0.001). Immunohistochemistry analysis revealed that matrix metallopeptidase (MMP) 9, MMP13, and a disintegrin and metalloproteinase with thrombospondin motifs-5 (ADAMTS-5) decreased expression level. In contrast, collagen-II and aggrecan increased in the Sal-treated groups compared to the saline-treated group. Conclusions: Our findings indicate that Sal can alleviate OA progression by promoting anti-oxidant expression and inhibiting degradation enzyme expression. These findings suggest that Sal inhibits the NF-κB pathway and its downstream targets through up-regulating the Nrf2 pathway.