Cd18/ICAM-1-dependent oxidafive NF-κB activation leading to nitric oxide production in rat Kupffer cells cocultured with syngeneic hepatoma cells

Previous studies have indicated that nitric oxide (NO) released from Kupffer cells modulates biological viability of cocultured hepatoma cells. This study was designed to evaluate the mechanisms by which Kupffer cells synthesize and release NO in response to cocultured hepatoma cells. Kupffer cells isolated from male Wistar rats were cocultured with rat hepatoma cell line, AH70 cells. The sum of nitrite and nitrate levels increased in the culture medium of Kupffer cells with AH70 cells as compared with those of Kupffer cells or AH70 cells alone. Increased expressions of iNOS and iNOS mRNA in Kupffer cells cocultured with AH70 cells were detected by an immunofluorescence staining and a fluorescence in situ hybridization study, respectively. A fluorescence in situ DNA-protein binding assay revealed that NF-κB activation occurs in Kupffer cells and activated NF-κB moved into the nuclei preceding to an increased production of NO. Oxidative stress indicated by dichlorofluorescein fluorescence was observed in Kupffer cells cocultured with AH70 cells. An increased calcium mobilization indicated as increased fluo-3-associated fluorescence was also induced in Kupffer cells after coculture with AH70 cells. Monoclonal antibodies directed against rat CD18 and ICAM-1, as well as TMB-8, a calcium inhibitor, prevented the calcium mobilization, active oxygen production, and NF-κB activation in addition to the increased production of NO. Pyrrolidine dithiocarbamate, an inhibitor of oxidative NF-κB activation, diphenylene iodonium, an NADPH oxidase inhibitor, and quinacrine, a phospholipase A₂ inhibitor, significantly attenuated the increase in dichlorofluorescein fluorescence, NF-κB activation, and NO production. Therefore, this study suggests that CD18/ICAM- l-dependent cell-to-cell interaction with hepatoma cells causes calcium mobilization and oxidative activation of NF-κB, which may lead to the increased production of NO in Kupffer cells.