Hepatocyte injury by activated neutrophils in vitro is mediated by proteases

Objective: This study determined the mechanism used by neutrophils (PMNs) to induce hepatocellular injury. Summary Background Data: Neutrophils have been shown to be potent mediators of cell and tissue injury and have been hypothesized to contribute to the hepatic injury that occurs after trauma and infection. Oxygen radical scavengers protect the liver in vivo from inflammatory injury and it has been suggested that PMNs are the source of these toxic oxygen radicals. The specific mechanism used by PMNs to produce hepatocellular damage, however, has not been determined. Methods: Neutrophils were cultured in vitro with hepatocytes (HCs) and stimulated with phorbol 12-myristate 13-acetate (PMA) to induce HC injury in the presence of oxygen radical scavengers and protease inhibitors. Results: PMA induced a PMN-mediated HC injury that was dependent on the number of PMNs present and the concentration of PMA. Protease inhibitors reduced the extent of HC injury, while oxygen radical scavengers had no effect. Hydrogen peroxide, directly applied, was able to injure HCs, but only at concentrations greater than those that could be produced by PMA-stimulated PMNs. Conclusions: PMNs are cytotoxic to cultured HCs, predominantly due to the release of proteolytic enzymes, while HCs appear relatively resistant to oxidative injury. Involvement of neutrophil toxic oxygen radicals in hepatic damage in vivo may require impairment of HC antioxidant defenses or may involve injury to nonparenchymal liver cells with secondary effects on HCs.