Emodin inhibits ATP-induced IL-1 beta secretion, ROS production and phagocytosis attenuation in rat peritoneal macrophages via antagonizing P2X(7) receptor

Context: Previous in vitro studies have demonstrated that emodin (1,3,8-trihydroxy-6-methyl-anthraquinone), an anthraquinone derivative from the rhizome of Rheum palmatum L., can inhibit the activation of P2X(7) receptors (P2X(7)R) as a potential antagonist. However, the effects of emodin on P2X(7)R-related inflammatory processes remain unclear. Objective: This study aimed to investigate the effects of emodin on different inflammation responses of macrophages induced by ATP, the natural ligand of P2X(7)R. Materials and methods: Rat peritoneal macrophages were treated with millimolar ATP and emodin (0.1, 0.3, 1, 3, 10 mu M) or brilliant blue G (BBG, 0.1, 1, 10 mu M). Cytosolic Ca2+ concentration ([Ca2+](c)) was detected by fluorescent Ca2+ imaging. Interleukin-1 beta (IL-1 beta) release was measured by rat IL-1 beta ELISA kits. Reactive oxygen species (ROS) generation was examined by dihydroethidium (DHE) fluorescent staining. Phagocytic activity was tested by neutral red uptake assay. Results: We found that the [Ca2+](c) increase evoked by ATP (5 mM) was inhibited by emodin, in a dose-dependent manner with IC50 of 0.5 mu M. Furthermore, emodin reduced the IL-1 beta release induced by ATP (2 mM) in lipopolysaccharide (LPS)-activated macrophages, with an IC50 of 1.6 mu M. Emodin also strongly suppressed the ROS production and phagocytosis attenuation triggered by ATP (1 mM), with IC50 values of 1 mu M and 0.7 mu M, respectively. Besides, BBG, a specific antagonist of P2X(7)R, exhibited similar suppressive effects on these inflammation responses. Conclusion: These results showed the inhibitory effects of emodin on ATP-induced [Ca2+](c) increase, IL-1 beta release, ROS production and phagocytosis attenuation in rat peritoneal macrophages, by inhibiting the activation of P2X(7)R.