Implication of reactive oxygen species in the antibacterial activity against Salmonella typhimurium of hepatocyte cell lines

We recently described the antibacterial activity of a murine hepatocyte cel l line stimulated with interferon-gamma (IFN-gamma), interleukin-1 (IL-1), and lipopolysaccharide (LPS) against intracellular Salmonella organisms. He re we show for the first time the existence of basal antibacterial activity in cultured hepatocyte cell lines. Thus treatment of resting and stimulate d hepatocytes with catalase or superoxide dismutase increased bacterial num ber recovered per monolayer, which suggests that the mechanism involved wit h antibacterial activity of hepatocytes is mediated by reactive oxygen spec ies (ROS). Also, the capacity of these cell lines to generate intracellular peroxides under resting and stimulated conditions was investigated This re vealed that IL-1 and LPS did not induce any increase in the amount of intra cellular peroxides by themselves, but they primed IFN-gamma for maximal ind uction of peroxides. The intracellular amount of peroxides was highly incre ased on stimulation with IFN-gamma, IL-1, and LPS, and it was strongly inhi bited by catalase. This explains that the mechanism whereby this enzyme inh ibits antibacterial activity takes place by decreasing the intracellular po ol of peroxides. In turn, experiments performed in the presence of several inhibitors of metabolic pathways involved in ROS generation suggested that cyclo-oxygenase are a source of these species in hepatocyte cell lines. The se results attribute a prominent role to the generation of peroxides as eff ector molecules of antibacterial activity in hepatocyte cell lines. Thus th ese cells displayed a moderate basal level, which increased on stimulation with proinflammatory cytokines such as IFN-gamma IL-1, and bacterial produc ts such as LPS. Finally, it has been also shown for the first time that IFN -gamma stimulation induces production of peroxides in human and murine hepa tocyte cell lines. (C) 1999 Elsevier Science Inc.