Iron primes hepatic macrophages for NF-kappa B activation in alcoholic liver injury

NF-kappa B activation induced by lipopolysaccharide (LPS) in cultured hepat ic macrophages (HM) may be abrogated by pretreatment of cells with a lipoph ilic iron chelator, 1,2-dimethyl-3-hydraxypyrid-4-one (LI, deferiprone), su ggesting a role for iron in this molecular event [M. Lin, M., R. A. Rippe, O. Niemela, G. Brittenham, and H. Tsukamoto, Am. J. Physiol. 272 (Gastroint est. Liver Physiol. 35): G1355-G1364, 1997]. To ascertain the relevance in vivo of this hypothesis, HM from an experimental model of alcoholic liver i njury were examined for the relationship between nuclear factor (NF)-kappa B activation and iron storage. HM showed a significant increase in nonheme iron concentration (+70%), accompanied by enhanced generation of electron p aramagnetic resonance-detected radicals (+200%), NF-kappa B activation(+ 10 0%), and tumor necrosis factor-alpha (+150%) and macrophage inflammatory pr otein-1 (+280%) mRNA induction. Treatment of the cells ex vivo with L1 norm alized all these parameters. HM content of ferritin protein, ferritin L cha in mRNA, and hemeoxygenase-1 mRNA and splenic content of nonheme iron were increased, suggesting enhanced heme turnover as a cause of the increased ir on storage and NF-kappa B activation. To test this possibility, increased i ron content in HM was reproduced in vitro by phagocytosis of heat-treated r ed blood cells. Treatment caused a 40% increase in nonheme iron concentrati on and accentuated LPS-induced NF-kappa B activation twofold. Both effects could be abolished by pretreatment of cells with zinc protoporphyrin, a hem eoxygenase inhibitor. To extend this observation, animals were splenectomiz ed before 9-wk alcohol feeding. Splenectomy resulted in further increments in HM nonheme iron storage (+60%) and NF-kappa B activation (+90%) and mono nuclear cell infiltration (+450%), particularly around the iron-loaded HM i n alcohol-fed animals. These results support the pivotal role of heme-deriv ed iron in priming HM for NF-kappa B activation and expression of proinflam matory genes in alcoholic liver injury.