Involvement of reactive oxygen species and nitric oxide radicals in activation and proliferation of rat hepatic stellate cells

Background/Aims: Reactive oxygen species (ROS) induce HSCs activation, prol iferation and collagen gene expression in vitro. Nitric oxide (NO) represen ts a reactive molecule that reacts with ROS, yielding peroxynitrite. We thu s verified the effect of NO on ROS-induced HSCs proliferation in vitro and correlated iNOS expression and ROS formation to HSCs activation in the earl y phase of liver injury leading to hepatic fibrosis in vivo. Methods/Result s: HSCs were incubated with iron ascorbate (FeAsc) in vitro, which induced ROS production, ERK1/2 phosphorylation and increased cell proliferation. Th is effect was significantly reduced by the presence of the NO donor S-nitro so-N-acetylpenicillamine. Liver injury was induced in vivo in rats by dimet hylnitrosamine administration. HSCs activation started 6 h after DMN admini stration and peaked at 1 week. ROS generation and neutrophil infiltration w ere evident for at least 48 h after DMN treatment, showing an identical dis tribution pattern. Only a few inflammatory cells expressed iNOS 6 h after D MN administration. Conclusions: we have shown that NO acts as a ROS scaveng er in vitro, thus inhibiting HSCs proliferation. ROS production by infiltra ting neutrophils occurs in the early phase of liver fibrosis and can repres ent a stimulus to HSCs activation in vivo. The reduced iNOS expression may account for the low NO levels and the inability to prevent the ROS-induced HSC activation in vivo.