ROLE OF IRON IN NF-KAPPA-B ACTIVATION AND CYTOKINE GENE-EXPRESSION BYRAT HEPATIC MACROPHAGES

A redox-sensitive nuclear factor, NF-kappa B, induces transcription of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) in m acrophages. The present study has investigated the role of iron in NF- kappa B activation and TNF-alpha and IL-6 expression by rat hepatic ma crophages (HM). As an in vivo model, cholestatic liver injury was indu ced in rats by ligation of the common bile duct (BDL). During the firs t 2 wk after BDL, there was an increase in the hepatic level of thioba rbituric acid-reactive substances (TEARS) that was accompanied by the appearance of protein-malondialdehyde adducts in the periportal region . This increase was reduced after 3 wk. TNF-alpha and IL-B mRNA levels in HM from the BDL rats were increased at 1 and 2 wk and attenuated a t 3 wk. Gel mobility shift assay of HM nuclear extracts demonstrated t he similar temporal pattern of enhanced NF-kappa B binding activity. T reatment of the BDL animals with 1,2-dimethyl-3-hydroxypyrid-4-one (L- l), a lipophilic iron chelator, suppressed the increases in hepatic TE ARS by 64%, plasma alanine aminotransferase by 45%, and HM TNF-alpha a nd IL-6 mRNA by >84%. Concomitantly, the KM NF-kappa B binding activit y was reduced close to the level observed in sham-operated rats. Treat ment of cultured HM with L-l also blocked lipopolysaccharide-stimulate d NF-kappa B activation and TNF-alpha and IL-6 expression at mRNA and protein levels. These results demonstrate that the iron chelator effec tively blocks NF-kappa B activation and coordinate TNF-alpha and IL-6 gene upregulation by HM in cholestatic liver injury or under in vitro lipopolysaccharide stimulation. These findings support a pivotal role for iron in activation of NF-kappa B and cytokine gene expression by H M in vitro and in vivo.