Iron-dependent activation of NF-kappaB in Kupffer cells: a priming mechanism for alcoholic liver disease.

Alcoholic liver disease is associated with hepatic iron accumulation, and iron supplementation exacerbates alcoholic liver disease, suggesting the pathogenic role of iron in alcoholic liver disease. We have tested a hypothesis that iron plays a signaling role in activation of redox-sensitive nuclear factor-kappa B (NF-kappaB) and that increased iron content results in heightened expression of proinflammatory cytokines in Kupffer cells because of this signaling. In cultured Kupffer cells isolated from normal rats, treatment with a lipophilic iron chelator, 1,2-dimethyl-3-hydroxypyrid-4-one (L1), markedly reduced lipopolysaccharide (LPS)-induced NF-kappaB activation and expression of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6. Kupffer cells, isolated from rats with experimentally induced alcoholic liver disease, had significant increases in nonheme iron content, NF-kappaB binding, and mRNA expression for TNF-alpha and macrophage inflammatory protein-1. Ex vivo L1 treatment normalized all these parameters. Addition of ferrous iron to cultured normal rat Kupffer cells increased I-kappa B kinase (IKK) activity at 15 min and NF-kappaB binding at 30 min. L1 pretreatment completely abrogated both effects. Moreover, the iron treatment increased TNF-alpha release and TNF-alpha promoter activity in a NF-kappaB-dependent manner. Ferrous iron also transiently decreased cytoplasmic I-kappa B-alpha (IkappaB-alpha), with concomitant increases in nuclear p65 protein and DNA binding of p65/p50. Taken together, these results support the existence of iron-dependent signaling for activation of IKK/NF-kappaB in Kupffer cells, and this iron signaling serves as a target for a potential priming effect for the pathogenesis of experimental alcoholic liver disease.