Cytokine Expression in Hepatocytes: Role of Oxidant Stress

Abstract

Inflammatory mediators, including cytokines and chemokines, are associated with the pathology of chronic liver disease. Interleukin-8 (IL-8) in humans and macrophage inflammatory protein-2 (MIP-2) in rodents, both members of the C-X-C family of chemokines, are particularly potent neutrophil attractants and have been implicated in chronic liver diseases. In the liver, cytokine secretion is usually associated with nonparenchymal cells, particularly Kupffer cells. In the present studies, chemokine gene expression and secretion were investigated in hepatocytes treated with various stimulators. Using human Hep G2 cells, it was demonstrated that, in contrast to lipopolysaccharides (LPS), both tumor necrosis factor-α (TNF-α) and H₂O₂ are potent inducers of IL-8, presumably acting via protein kinase C (PKC)-dependent pathways. MIP-2 expression occurred in freshly isolated rat hepatocytes following treatment with TNF-α, LPS, and to a lesser degree, H₂0₂. Both IL-8 and MIP-2 secretion were inhibited, although to varying degrees, by such antioxidants as TMTU, DMSO, catalase, and N-acetylcysteine. Furthermore, in vitro TNF-α neutralization experiments and transfection of Hep G2 cells with an IL-8 construct confirmed that TNF-α and H₂0₂ directly stimulate IL-8 secretion. RT-PCR analyses indicated that chemokine secretion induced by these agents operates via increased gene expression. Furthermore, a variety of cytokine genes were found to be expressed by hepatocytes, including MCP-1, cytokine-induced neutrophil chemoattractant (CINC), and IL-6. Taken together, these studies indicate that hepatocytes respond to biologically relevant levels of common activators, including H₂0₂, to produce cytokines and chemokines that contribute to pathophysiologic and repair processes in the liver.