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.