The double-edged sword role of copper in rheumatoid arthritis: Mechanisms, therapeutics, and challenges

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease with an unclear etiology, in which abnormal copper homeostasis has been shown in the blood and synovial fluid of the joints of patients. As an essential trace element in the human body, copper plays a critical role in various biological processes, including antioxidant defense, angiogenesis, and bone maintenance. However, the accumulation of excessive copper ions has been shown to be positively correlated with disease activity and the degree of inflammation in RA. While copper-bound ceruloplasmin may exert anti-inflammatory effects, excess "free" copper acts as a potent pro-oxidant, driving oxidative stress, cartilage and bone destruction, inflammatory responses, as well as pannus formation. The recently discovered copper-dependent cell death pathway, named cuproptosis, further adds to the complexity of its role in RA. This review integrates current research advances on the double-edged role of copper in the pathogenesis of RA, systematically examines copper-related therapeutic strategies, and finally analyzes their potential applications and challenges. The aim is to harness the physiological functions of copper while mitigating its pathological effects, thereby opening new avenues for the diagnosis and precision treatment of RA.