Under chronic inflammatory conditions cytokines induce a diversion of iron traffic, leading to hypoferremia and retention of the metal within the reticuloendothelial system. However, the regulatory pathways underlying these disturbances of iron homeostasis are poorly understood. We investigated transferrin receptor (TfR)-dependent and -independent iron transport mechanisms in cytokine-stimulated human monocytic cell lines THP-1 and U937. Combined treatment of cells with interferon-␥ (IFN-␥) and lipopolysaccharide (LPS) reduced TfR mRNA levels, surface expression, and iron uptake, and these effects were reversed by interleukin-10 (IL-10), thus stimulating TfR-mediated iron acquisition. IFN-␥ and LPS dosedependently increased the cellular expression of divalent metal transporter-1, a transmembrane transporter of ferrous iron, and stimulated the uptake of nontransferrin bound iron (NTBI) into cells. At the same time, IFN-␥ and LPS downregulated the expression of ferroportin mRNA, a putative iron exporter, and decreased iron release from monocytes. Preincubation with IL-10 partly counteracted these effects. Our results demonstrate that the proinflammatory stimuli IFN-␥ and LPS increase the uptake of NTBI via stimulation of divalent metal transporter-1 expression and cause retention of the metal within monocytes by down-regulating ferroportin synthesis. Opposite, the anti-inflammatory cytokine IL-10 stimulates TfR-mediated iron uptake into activated monocytes. The regulation of iron transport by cytokines is a key mechanism in the pathogenesis of anemia of chronic disease and a promising target for therapeutic intervention. IntroductionIron metabolism and immunity are closely interconnected. 1,2 This is due, on the one hand, to divergent regulatory effects of the metal on immune cell proliferation 3 and on the effectiveness of cellular immune effector pathways. [4][5][6] On the other hand, cytokines derived from T cells and monocytes regulate cellular iron homeostasis by affecting the expression of proteins involved in the uptake and storage of the metal. Proinflammatory cytokines such as tumor necrosis factor-␣ (TNF-␣), interleukin-1 (IL-1), or interleukin-6 (IL-6) directly stimulate the transcription and translation of the major iron storage protein ferritin, the latter by interfering with a so-called acute phase box. 7,8 Moreover, cytokines influence the posttranscriptional control of iron homeostasis by modulating the binding affinity of iron regulatory proteins (IRP-1 and IRP-2) to specific RNA stem loop structures, termed iron responsive elements (IREs), which are found within the 5Ј untranslated region of ferritin mRNA and within the 3Ј untranslated region of transferrin receptor (TfR) mRNA, the surface protein involved in the uptake of transferrinbound iron. Activation of IRP binding to IREs is controlled by intracellular iron availability, with IRP binding affinity being high when intracellular iron concentrations are low, thus resulting in stabilization of TfR mRNA while ferritin translation is reduced (fo...

SummaryIn being both, a modifier of cellular immune effector pathways and an essential nutrient for microbes, iron is a critical determinant in host-pathogen interaction. Here, we investigated the metabolic changes of macrophage iron homeostasis and immune function following the infection of RAW264.7 murine macrophages with Salmonella typhimurium. We observed an enhanced expression of the principal iron export protein, ferroportin 1, and a subsequent increase of iron efflux in Salmonella-infected phagocytes. In parallel, the expression of haem oxygenase 1 and of the siderophore-binding peptide lipocalin 2 was markedly enhanced following pathogen entry. Collectively, these modulations reduced both the cytoplasmatic labile iron and the ferritin storage iron pool within macrophages, thus restricting the acquisition of iron by intramacrophage Salmonella. Correspondingly, limitation of macrophage iron decreased microbial survival, whereas iron supplementation impaired immune response pathways in Salmonella-infected macrophages (nitric oxide formation and tumour necrosis factor-a production) and promoted intracellular bacterial proliferation. Our findings suggest that the enhancement of ferroportin 1-mediated iron efflux, the upregulation of the haem-degrading enzyme haem oxygenase 1 and the induction of lipocalin 2 following infection concordantly aim at withholding iron from intracellular S. typhimurium and to increase antimicrobial immune effector pathways thus limiting pathogen proliferation.

NOS2-derived nitric oxide drives ferroportin-1–mediated iron export in Salmonella-infected macrophages, thus limiting bacterial growth.

Hereditary hemochromatosis and transfusional iron overload are frequent clinical conditions associated with progressive iron accumulation in parenchymal tissues, leading to eventual organ failure. We have discovered a new mechanism to reverse iron overload-pharmacological modulation of the divalent metal transporter-1 (DMT-1). DMT-1 mediates intracellular iron transport during the transferrin cycle and apical iron absorption in the duodenum. Its additional functions in iron handling in the kidney and liver are less well understood. We show that the L-type calcium channel blocker nifedipine increases DMT-1-mediated cellular iron transport 10- to 100-fold at concentrations between 1 and 100 microM. Mechanistically, nifedipine causes this effect by prolonging the iron-transporting activity of DMT-1. We show that nifedipine mobilizes iron from the liver of mice with primary and secondary iron overload and enhances urinary iron excretion. Modulation of DMT-1 function by L-type calcium channel blockers emerges as a new pharmacological therapy for the treatment of iron overload disorders.

Imatinib exerts potent antileukemic effects in vitro and in vivo.Despite its well known antitumor activity, the potential of imatinib for the treatment of inflammatory diseases remains elusive so far. Our current report provides strong evidence that imatinib has potent antiinflammatory effects. It potently inhibits LPS-and Con A-induced TNF-␣ production by human myeloid cells in vitro (peripheral blood mononuclear cells, CD14-selected monocytes, and monocyte-derived macrophages). Of note, the production of the antiinflammatory cytokine IL-10 was not significantly regulated by imatinib. In line with this observation, phosphorylation of I B and subsequent DNA binding of NF-B, which is critically involved in TNF-␣, but not IL-10 expression, was reduced by imatinib. Using several murine models of acute hepatitis, we could corroborate our in vitro findings, as imatinib prevented macrophage-and TNF-␣-dependent inflammatory damage of the liver induced by injection of either Con A or D-galactosamine͞LPS by inhibition of hepatic TNF-␣ production. Of note, D-galactosamine͞TNF-induced hepatitis was not affected, showing that imatinib does not directly inhibit TNF-␣-induced hepatocellular cell death. These findings suggest a potent antiinflammatory role of imatinib by modulation of TNF-␣ production in monocytes͞macrophages. This observation might be of therapeutic value for the treatment of TNF-mediated diseases.cytokines ͉ monocytes͞macrophages ͉ immunosuppression

HFE affects the interaction of transferrin bound iron with transferrin receptors (TfR) thereby modulating iron uptake. To study genetically determined differences in HFE expression we examined individual HFE levels in C57BL/Sv129 mice and assessed their relationship to the regulation of iron homeostasis in the duodenum and the liver, and their regulation by diet. We found an up to 14-fold variation in inter-individual expression of HFE mRNA in the duodenum. Mice with high duodenal HFE mRNA expression presented with significantly higher levels of TfR and DMT-1 mRNAs and an increased IRP-1 binding affinity as compared to mice with low HFE levels. Duodenal HFE expression was positively associated with serum iron and liver HFE levels. Dietary iron supplementation decreased HFE in the duodenum but not in the liver. This was paralleled by reduced amounts of DMT-1 and FP-1 in the duodenum while the expression of DMT-1, FP-1, and hepcidin in the liver were increased with dietary iron overload. Duodenal and liver HFE levels are regulated by divergent penetration of as yet unelucidated modifier genes and to a much lesser extent by dietary iron. These measures control duodenal iron transport and liver iron homeostasis by modulating HFE expression either directly or via stimulation of iron sensitive regulatory molecules, such as hepcidin, which then exert their effects on body iron homeostasis.

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Although the recent identification of several genes has extended our knowledge on the maintenance of body iron homeostasis, their tissue specific expression patterns and the underlying regulatory networks are poorly understood. We studied C57black/Sv129 mice and HFE knockout (HFE À/À) variants thereof as a model for hemochromatosis, and investigated the expression of iron metabolism genes in the duodenum, liver, and kidney as a function of dietary iron challenge. In HFE þ/þ mice dietary iron supplementation increased hepatic expression of hepcidin which was paralleled by decreased iron regulatory protein (IRP) activity, and reduced expression of divalent metal transporter-1 (DMT-1) and duodenal cytochrome b (Dcytb) in the enterocyte. In HFE À/À mice hepcidin formation was diminished upon iron challenge which was associated with decreased hepatic transferrin receptor (TfR)-2 levels. Accordingly, HFE À/À mice presented with high duodenal Dcytb and DMT-1 levels, and increased IRP and TfR expression, suggesting iron deficiency in the enterocyte and increased iron absorption. In parallel, HFE À/À resulted in reduced renal expression of Dcytb and DMT-1. Our data suggest that the feed back regulation of duodenal iron absorption by hepcidin is impaired in HFE À/À mice, a model for genetic hemochromatosis. This change may be linked to inappropriate iron sensing by the liver based on decreased TfR-2 expression, resulting in reduced circulating hepcidin levels and an inappropriate up-regulation of Dcytb and DMT-1 driven iron absorption. In addition, iron excretion/reabsorption by the kidneys may be altered, which may aggravate progressive iron overload.