Rat Kupffer cell-derived nitric oxide suppresses proliferation and induces apoptosis of syngeneic hepatoma cells

Background and Aims: Evidence increasingly indicates that nitric oxide plays an important role in antitumor mechanisms. The aim of this study was to investigate the role of NO in the mechanisms regulating the proliferation and death of hepatoma cells cocultured with Kupffer cells. Methods: Kupffer cells were isolated from male Wistar rats and cocultured with rat hepatoma AH70 cells. Proliferation was determined by calculating the number of total and 5- bromodeoxyuridine-positive AH70 cells. Apoptosis was assessed by electron- microscopic and fluorescence-microscopic observations and in situ nick end labeling method. Immunofluorescence and in situ hybridization studies were performed to investigate the induction of inducible NO synthase (iNOS). Results: Kupffer cells reduced proliferation and induced apoptosis of AH70 cells, which were attenuated by the NO synthesis inhibitors N(G)monomethyl- L-arginine and aminoguanidine. Increased inductions of iNOS messenger RNA and iNOS were observed in Kupffer cells cocultured with AH70 cells. Addition of monoclonal antibody directed against either rat CD18 or intercellular adhesion molecule 1 also attenuated the increased NO production of Kupffer cells and the alterations of AH70 cells. Conclusions: Kupffer cell-derived NO suppresses proliferation and induces apoptosis of hepatoma cells. The CD18 intercellular adhesion molecule 1-dependent adhesive interaction with hepatoma cells triggers NO production by Kupffer cells.