10�C12 Evidence has shown that SiO2 NPs induce cytotoxicity in hepatocytes13,14 Z-VAD-FMK and lead to liver injury, including particle accumulation,11 disturbances in metabolism,15 and fibrogenesis.16 However, in addition to the direct hepatotoxicity of SiO2 NPs, are there other factors that mediate hepatic injury induced by SiO2 NPs? Kupffer cells (KCs), the resident macrophages in the liver, play an important role in the normal physiology and homeostasis of the liver as well as participate in the acute and chronic responses of the liver to toxic compounds.17�C20 Thus, it will be valuable to determine whether KCs mediate SiO2 NP-induced hepatic injury. KCs are phagocytic and ingest substances to provide the first line of defense against invading particles.

21 We previously found that SiO2 NPs were taken up mainly by KCs in the liver after intravenous injection.22 In addition to phagocytosis of particles, KCs are reported to contribute to the formation of silicotic nodules in the liver.23 These studies indicate that KCs may play a certain role in hepatic injury induced by SiO2 NPs, but the mechanism is still unclear. However, KCs are located in the hepatic sinusoids and lie in between or on top of endothelial cells, so how do they affect hepatocytes? The pathogenesis of hepatic injury resulting from acetaminophen/lipopolysaccharide treatment provides us with some insight into this question. A study has demonstrated that acetaminophen activates KCs to form reactive oxygen species (ROS) and nitric oxide (NO), which contribute to hepatotoxicity.

24 Furthermore, a previous study has shown that KCs participate in monocrotaline/ lipopolysaccharide-induced liver injury through the release of inflammatory cytokines, such as tumor necrosis factor (TNF)-��.25 These studies suggest that KCs are activated by foreign stimuli and release a variety of bioactive mediators, which fulfill a crucial function in the response to liver injury. Drug_discovery However, there have been few relevant reports addressing whether KCs can be activated to release these bioactive substances and mediate hepatic injury after phagocytosis of SiO2 NPs, which is essential to understanding the mechanism underlying hepatotoxicity induced by SiO2 NPs. To explore the role of KCs in hepatic injury induced by SiO2 NPs, we first analyzed the release of ROS, NO, and TNF-�� by SiO2 NP-stimulated KCs to investigate whether SiO2 NPs can activate these cells. To demonstrate KC-mediated hepatotoxicity and to determine the underlying preliminary mechanism, we established a noncontact coculture model by treating Buffalo rat liver (BRL) cells with particle free supernatants of SiO2 NP-stimulated KCs. An in vivo study was then carried out to examine the response of KCs after exposure to SiO2 NPs.