Silica induces macrophage cytokines through phosphatidylcholine-specific phospholipase C with hydrogen peroxide

Silica particle-associated inflammation is implicated in the genesis of several pulmonary diseases, including silicosis and lung cancer. In this study we investigated the role of phosphaticlylcholine-specific phospholipase C (PC-PLC) in silica-stimulated induction of TNF-alpha and IL-1 beta and how PC-PLC activity is regulated by silica in a rat alveolar macrophage model. We demonstrated that inhibition of PC-PLC, which was achieved with tricychodecan-9-yl-xanthate (D609), blocked the silica-stimulated induction of TNF-alpha and IL-1 beta in alveolar macrophage, suggesting that PC-PLC is involved in the silica-associated inflammatory response. PC-PLC activity was increased significantly by silica exposure, and this could be inhibited by MnTBAP, which catalyzes both the dismutation of O-2 to O-2 and H2O2 and the dismutation of H2O2 to O-2 and H2O, revealing that PC-PLC activity is regulated in a redox-dependent manner. This is further confirmed by the finding that PC-PLC activity was increased by exogenous H2O2. The intracellular calcium chelator BAPTA blocked the H2O2-increased PC-PLC activity, while the calcium iono-phore, A23187, enhanced PC-PLC activity. The data indicate that PC-PLC plays critical roles in the silicai-associated inflammatory response and that PC-PLC is regulated through redox- and calcium dependent manners in alveolar macrophages.