Rhein inhibits ATP-triggered inflammatory responses in rheumatoid rat fibroblast-like synoviocytes

Rheumatoid arthritis (RA) is a chronic and systemic inflammatory disorder, which may lead to joint disabilities. So far the pathogenesis of RA remains largely undetermined, and there are still no potent drugs for clinical treatment. Rhein, a natural bioactive anthraquinone derivative, exhibited significant anti-inflammatory activities demonstrated by previous studies. Here we aimed to investigate the effects of rhein on ATP-induced inflammation responses in fibroblast-like synoviocytes isolated from a rat model of collagen induced arthritis (CIA). Our results showed that ATP triggered rapid cytosolic calcium concentration ([Ca2+](c)) increase depending on extracellular Ca2+ entry. Given the major P2 subtypes expressed in rat synoviocytes were P2X(4) and P2Y(2) receptors, ATP-elicited calcium entry should be mainly resulted from activating P2X(4). Interestingly, rhein could effectively block the ATP-induced [Ca2+](c) increases in a dose-dependent manner. Besides, rhein also suppressed the production of intracellular reactive oxygen species (ROS) induced by ATP in synoviocytes that was resulted from P2X(4) -mediated Ca2+ entry. Brilliant blue G (BBG), which can block P2X(4) receptor at high concentration, showed similar suppressive effects on above responses. Furthermore, in lipopolysaccharideprimed cells, application of ATP synergistically promoted the gene expression of cyclooxygenase-2, interleukin-6 and matrix metalloproteinase-9. Both rhein and BBG attenuated these inflammatory gene expressions enhanced by ATP. Above data together suggested a potential anti-arthritic role of rhein by inhibiting ATP-induced [Ca2+](c) increase, ROS production and inflammatory gene expression targeting P2X(4) in CIA rat synoviocytes, which will provide a novel insight in the therapy of RA.