Dimethyl fumarate mitigates osteoarthritis progression through Nrf2 activation-mediated suppression of oxidative stress and subchondral osteoclastogenesis.

Osteoarthritis (OA) is a degenerative joint disease associated with imbalanced subchondral bone remodeling, and there is currently no curative treatment available. In OA, excessive osteoclast activity leads to bone loss and inflammatory responses. Dimethyl fumarate (DMF), an Nrf2 activator already used in treating psoriasis and multiple sclerosis, may alleviate OA by suppressing oxidative stress and osteoclastogenesis. This study investigates the effects of DMF on osteoclasts, subchondral bone, articular cartilage, and the mechanisms underlying OA progression. The research employed bone marrow-derived macrophages (BMDMs, 93 % purity) from C57BL/6 mice to establish an in vitro OA model, with DMF's safe concentration determined via CCK-8 assay. Techniques such as TRAP staining, RT-PCR, ROS probes, immunofluorescence, and computational molecular docking were used to assess osteoclast differentiation, oxidative stress, and the Nrf2 signaling pathway. For in vivo experiments, OA was induced via destabilization of the medial meniscus (DMM) surgery, with mice divided into sham, DMM, and DMF-treated (50 mg/kg/day) groups. Evaluations at 2, 4, and 8 weeks included Micro-CT, gait analysis, TRAP/H&E/Safranin-O staining, and immunohistochemistry (Nrf2, CTSK, Netrin-1) to examine subchondral bone microstructure, cartilage integrity, pain-related behavior, and molecular changes. In vitro experiments demonstrated that DMF inhibited RANKL-induced osteoclast formation, reduced ROS levels, and promoted Nrf2 nuclear translocation. TRAP staining and RT-PCR confirmed its suppression of osteoclast markers such as CTSK, while immunofluorescence revealed restored Nrf2 expression. In vivo, DMF-treated mice exhibited reduced subchondral bone remodeling (as shown by Micro-CT), decreased TRAP+ osteoclast numbers, and better-preserved cartilage structure (lower OARSI scores compared to the DMM group). Safranin-O staining indicated mitigated cartilage degradation, and immunohistochemistry showed upregulated Nrf2 alongside downregulated CTSK and Netrin-1 in the DMF group. Gait analysis confirmed improved motor function and pain relief. DMF alleviates OA progression by activating Nrf2 to suppress oxidative stress and osteoclastogenesis. In vitro experiments show it inhibits ROS and osteoclast differentiation; in vivo experiments indicate it protects subchondral bone structure, reduces cartilage damage, and alleviates pain. These findings suggest DMF as a potential therapeutic agent for early OA, offering a novel strategy to delay disease progression by targeting oxidative stress and subchondral remodeling. CLINICAL PERSPECTIVES: Osteoarthritis (OA) is a degenerative joint disease associated with imbalanced subchondral bone remodeling, and there is currently no curative treatment available. In OA, excessive osteoclast activity leads to bone loss and inflammatory responses. Dimethyl fumarate (DMF), an Nrf2 activator already used in treating psoriasis and multiple sclerosis, may alleviate OA by suppressing oxidative stress and osteoclastogenesis. This study demonstrates that DMF activates Nrf2 to reduce ROS accumulation, thereby inhibiting osteoclastogenesis in early OA, protecting subchondral bone microstructure, alleviating articular cartilage damage, and ultimately mitigating OA progression. Concurrently, DMF reduces joint pain by suppressing osteoclast-mediated aberrant sensory innervation in subchondral bone. Our findings highlight DMF as a promising candidate for OA prevention and treatment.