Biomedical subjects

Günter Weiss

Publications and source records attributed to Günter Weiss.

18 recordsLinked to original sources

PubMed2003

Nramp1 functionality increases inducible nitric oxide synthase transcription via stimulation of IFN regulatory factor 1 expression.

Natural-resistance associated macrophage protein 1 (Nramp1) encodes a transmembrane phagolysosomal protein exerting resistance toward infections with intracellular pathogens by a mechanism not fully elucidated so far. We used the murine macrophage cell line RAW264.7, stably transfected with functional (RAW-37) or nonfunctional (RAW-21) Nramp1, to study for differences in the expression of NO, a central antimicrobial effector molecule of macrophages. Following stimulation with IFN-gamma and LPS, Nramp1-expressing cells exhibit higher enzymatic activity of inducible NO synthase (iNOS) and increased cytoplasmic iNOS mRNA levels than RAW-21 cells. Time-course experiments showed that iNOS-mRNA levels remain increased in RAW-37 cells after prolonged cytokine stimulation while they decrease in RAW-21 cells. Reporter gene assays with iNOS-promoter luciferase constructs demonstrated an increased and prolonged promoter activity in Nramp1-resistant vs susceptible cells. This was paralleled by increased IFN regulatory factor 1 (IRF-1) expression and binding affinity to the iNOS promoter in RAW-37 cells, which may be related to enhanced STAT-1 binding affinity in these cells. A point mutation within the IRF-1 binding site of the iNOS promoter abolished the differences in iNOS transcription between RAW-21 and RAW-37 cells. Cells carrying functional Nramp1 express increased amounts of NO, which may be related to STAT-1-mediated stimulation of IRF-1 expression with subsequent prolonged activation of iNOS transcription. Enhanced NO expression may partly underlie the protection against infection with intracellular pathogens by Nramp1 functionality.

Animals↗

PubMed2003

Cytokine-mediated regulation of iron transport in human monocytic cells.

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-gamma (IFN-gamma) 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-gamma and LPS dose-dependently 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-gamma and LPS down-regulated 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-gamma 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.

Base Sequence↗

PubMed2003

Increase of haemoglobin levels by anti-retroviral therapy is associated with a decrease in immune activation.

DESIGN: We evaluated whether an increase in haemoglobin levels in the first 6 months of effective anti-retroviral therapy (ART) is associated with a decrease in immune activation. To reduce confounding factors only men (n = 35) and patients not receiving agents known to enhance haematopoiesis or patients without diseases that might suppress haematopoiesis were included. Simultaneously parameters of iron metabolism and cofactors for haematopoiesis were analysed. RESULTS: A median baseline haemoglobin level of 139 g L-1 increased to 149 g L-1 at month 6 of ART (P < 0.001). At baseline low haemoglobin levels were strongly associated with high neopterin concentrations (r = - 0.64, P < 0.001), and much less correlated to high HIV-1 RNA levels (r = - 0.41, P < 0.05) and to a lower CD4+ cell count (r = 0.33, P < 0.05). The change of neopterin levels during the study period correlated with the relative change in haemoglobin levels, r = - 0.35, P = 0.03, whereas no such correlations were found for the change of HIV-1 RNA levels and the CD4 cell count. A logistic regression analysis revealed that the change of neopterin and soluble transferrin receptors concentrations are independently associated with an increase of haemoglobin levels of more than 15 g L-1. CONCLUSION: Our study supports a cause-effect relationship between immune activation and anaemia in HIV-infected patients. Treatment of patients with ART decreases virus load, which may thereby result in silencing of immune effector activity thus ameliorating anaemia by reversing the anti-proliferative effects of cytokines towards erythroid progenitors and the iron withdrawal strategy of the immune system.

Adult↗

PubMed2003

Effect of iron treatment on circulating cytokine levels in ESRD patients receiving recombinant human erythropoietin.

BACKGROUND: Anemia in patients with end-stage renal disease (ESRD) is treated with recombinant human erythropoietin (rhEPO) often in combination with iron. However, iron catalyzes the formation of toxic radicals, which might promote vascular damage, is a nutrient for microorganisms, and negatively affects immune pathways, thus increasing the risk for severe infections. METHODS: We investigated 28 patients on chronic hemodialysis who were randomized to receive either rhEPO alone (N = 15) or rhEPO in combination with intravenous iron (N = 13) for a period of 12 weeks. We analyzed iron therapy associated changes in cytokine patterns and endogenous radical formation. RESULTS: Tumor necrosis factor-alpha (TNF-alpha) levels were increased in ESRD patients at study entry and then decreased significantly over time in subjects receiving additional iron, while they increased with rhEPO alone. In contrast, we found serum concentrations of the anti-inflammatory cytokine interleukin (IL)-4 to increase with iron therapy. A significant negative correlation between iron availability, as determined by transferrin saturation, and TNF-alpha levels (P = 0.008) and a positive one between transferring saturation and IL-4 (P = 0.02) pointed to the potential role of iron to induce immunologic changes. Interestingly, iron therapy resulted in a slight decrease in the amounts of endogenous peroxides, which may be referred to reduced TNF-alpha concentrations since peroxide concentrations were positively correlated to TNF-alpha levels (P = 0.046) and negatively to transferrin saturation (P = 0.02). CONCLUSION: Iron supplementation in ESRD patients down-regulates proinflammatory immune effector pathways and stimulates the expression of the anti-inflammatory cytokine IL-4. Such a condition is detrimental for host response toward invading pathogens. However, tissue damage by radicals such as endogenous peroxides may be reduced in this condition due to impaired TNF-alpha formation.

Aged↗

PubMed2003

[Antimicrobial combination therapy].

Anti-microbial combination therapy is a very frequently used therapeutic approach although clinical data from prospective randomized trials thus fulfilling the criteria of evidence based medicine are very rare. Rationales for the use of combination therapy are thus empirical treatment of polymicrobial infections, infections in critical ill or in immuno-compromised patients, prevention of the emerge of antibiotic resistances, utilization of a potential synergism of antibiotics directed against a certain bacterial strain, or simply despair. Prospective studies have demonstrated a superiority of combination therapy over single drug regimen in enterococcal endocarditis, and infections with gram negative rods including pseudomonas sp., but in the latter condition only if the patient is severely immuno-compromised. There is clinical indication that combination therapy may be beneficial in infections with staphylococci sp., however, well designed studies supporting this experience are largely absent. Nonetheless, antimicrobial combination therapy also harbors some risks for patients which can be referred to potential antagonism between antibiotics, accumulation of side effects, or stimulation of resistance pathways in bacteria by one drug leading to destabilization of the other one. Thus, the insightful use of combination therapy is warranted and well designed, prospective studies are urgently needed to evaluate the true benefit of combination therapy for the treatment of different infections and specific micro-organisms.

Anti-Bacterial Agents↗

PubMed2003

Unsuspected mesenteric vein thrombosis in a patient with a hereditary bleeding disorder.

We report on a female patient with hereditary hemorrhagic teleangiectasia complicated by subacute thrombosis of the superior mesenteric vein. Despite gastrointestinal bleeding, anticoagulation therapy with heparin had to be performed to prevent bowel infarction. In this case, local vascular lesions with altered blood flow in combination with hyperfibrinogenemia might have caused superior mesenteric vein thrombosis.

Blood Coagulation Disorders, Inherited↗

PubMed2003

Pathways for the regulation of interferon-gamma-inducible genes by iron in human monocytic cells.

To elucidate iron-regulated interferon-gamma (IFN-gamma) effector functions, we investigated three IFN-gamma-inducible genes [intercellular adhesion molecule-1 (ICAM-1), human leukocyte antigen (HLA)-DR, guanosine 5'-triphosphate-cyclohydrolase I (GTP-CH)] in primary human monocytes and the cell line THP-1. IFN-gamma increased the surface expression of ICAM-1 and HLA-DR and stimulated GTP-CH activity. Addition of iron before cytokine stimulation resulted in a dose-dependent reduction of these pathways, and iron restriction by desferrioxamine (DFO) enhanced ICAM-1, HLA-DR, and GTP-CH expression. Iron neither affected IFN-gamma binding to its receptor nor IFN-gamma receptor surface expression. IFN-gamma-inducible mRNA expression of ICAM-1, HLA-DR, and GTP-CH was reduced by iron and increased by DFO by a transcriptional mechanism. Moreover, ICAM-1 and to a lesser extent, GTP-CH and HLA-DR mRNA expression were regulated post-transcriptionally, as iron pretreatment resulted in shortening the mRNA half-life compared with cells treated with IFN-gamma alone. Thus, iron perturbations regulate IFN-gamma effector pathways by transcriptional and post-transcriptional mechanisms, indicating that iron rather interferes with IFN-gamma signal-transduction processes.

Blotting, Northern↗

PubMed2003

HMG-CoA reductase inhibitors are associated with decreased serum neopterin levels in stable coronary artery disease.

Neopterin, a marker of stimulated cellular immune response, is increased in unstable angina, acute myocardial infarction and possibly stable coronary artery disease. 3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) have anti-inflammatory properties, but their effect on neopterin is largely unknown. Neopterin was measured in 232 patients undergoing elective coronary angiography and compared to the degree of atherosclerosis, use of concomitant medications and demographics. Neopterin was lower in subjects using statins (n = 66) compared to those not taking statins (median (range): 6.65 (4.1-18.3) vs. 7.70 (3.6-29.1) nmol/l, p < 0.0001). This association was also found in the subgroup of patients with coronary artery disease (1-3-vessel disease, n = 164; 6.60 (4.1-18.3) vs. 7.80 (3.6-29.1) nmol/l, p = 0.0012), whereas only a slight tendency toward lower neopterin levels was found in the group without atherosclerosis (6.90 (5.1-16.0) vs. 7.60 (4.0-18.5) nmol/l, p = 0.17). In patients with coronary atherosclerosis, neopterin concentrations were lower in smokers (n = 105) compared to non-smokers (7.20 (3.6-29.1) vs. 7.90 (4.4-18.6) nmol/l, p < 0.02), confirming previous observations. However, use of statins was associated with lower neopterin levels in both non-smokers and smokers (6.70 (4.1-18.3) vs. 7.60 (3.6-29.1) nmol/l, p < 0.05, and 6.20 (5.2-16.0) vs. 7.80 (4.4-18.6) nmol/l, p < 0.05, respectively). Overall, similar serum neopterin concentrations were found in patients with coronary atherosclerosis and those without. In accordance with their anti-inflammatory effects, the use of statins is associated with lower neopterin levels in patients undergoing elective coronary angiography.

Adult↗

PubMed2002

Association between increased iron stores and impaired endothelial function in patients with hereditary hemochromatosis.

OBJECTIVES: We studied associations between iron status and early functional and structural vascular abnormalities in patients with hereditary hemochromatosis (HH). BACKGROUND: Iron may be involved in atherogenesis, and patients bearing a genetic mutation associated with HH are possibly at risk of developing coronary heart disease. METHODS: We studied the vascular properties of 41 HH patients who had homozygosity for the C282Y mutation, along with 51 age-matched control subjects, by determination of endothelium-dependent dilation (EDD) of the brachial artery and intima-media thickness (IMT) of the carotid artery. RESULTS: Male HH patients who were not receiving phlebotomy therapy showed a reduced EDD and increased IMT compared with controls and HH patients receiving therapy. In female HH patients, irrespective of treatment status, vascular parameters were not different from those of controls, and none of these patients had severe iron overload. In HH patients, increased iron load was significantly associated with reduced EDD and increased IMT. Moreover, we found a positive correlation between body iron stores and indicators of oxidative stress. When previously untreated male HH patients were re-investigated after intensive phlebotomy therapy, a significant improvement in EDD was observed (2.6 +/- 1.3% before vs. 5.5 +/- 2.1% after treatment, p = 0.0015). CONCLUSIONS: Impaired endothelial function and increased IMT are associated with iron overload, with subsequent induction of oxidative stress, and are not linked to a genetic disability in HH patients. Consequent iron-depletion therapy normalizes endothelial function and may thus reduce the increased risk of cardiovascular events. Female patients may be at a reduced risk, presumably due to continuous iron loss by menstruation.

Adult↗

PubMed2002

Role of IL-10 for induction of anemia during inflammation.

Anemia is frequently observed in patients suffering from chronic inflammatory disorders. Recent in vitro data suggest that Th2 cytokines, such as IL-10, could be involved in its pathogenesis. We analyzed 1) changes in hemoglobin values in 329 patients with chronic active Crohn's disease receiving the anti-inflammatory cytokine IL-10 as part of a randomized, double-blind, placebo-controlled study, 2) serum iron parameters in a subgroup of these patients (n = 54), and 3) the in vitro effects of IL-10 on ferritin transcription and translation in human monocytic cells (THP-1) by means of Northern blot and immunoprecipitation after metabolic labeling. Patients receiving higher doses of IL-10 developed anemia and presented with a dose-dependent increase of ferritin and soluble transferrin receptor levels, an indicator of iron restriction to erythroid progenitor cells. According to our in vitro data, hyperferritinemia may result from direct stimulation of ferritin translation by IL-10 in activated monocytic cells, most likely by cytokine-mediated reduction of the binding affinity of translational repressors, iron-regulatory proteins, to the 5'-untranslated region of ferritin mRNA. In patients, all observed changes were most pronounced at the end of therapy (day +29), and thereafter hemoglobin levels and serum iron parameters returned to baseline levels within 4 wk of follow-up. Our data demonstrate that IL-10 causes anemia in patients with inflammatory bowel disease which may be referred to the induction of imbalances in iron homeostasis by the cytokine, leading to hyperferritinemia and limited iron availability to erythroid progenitor cells, a condition typically seen in the anemia of chronic inflammation.

Adolescent↗

PubMed2002

[Iron, infection and anemia--a classical triad].

Iron plays an essential role in immunosurveillance, because of its growth promoting and differentiation inducing properties for immune cells and its interference with cell mediated immune effector pathways and cytokine activities. At the same time, iron is crucial for the proliferation of tumour cells and micro-organisms, due to its role in mitochondrial respiration and DNA synthesis. Thus, gaining control over iron homeostasis is of vital importance for the course of an infection or a tumour disease, since increased iron availability or iron overload of the immune system are associated with an unfavourable course of many of these diseases. The most frequent clinical condition demonstrating this interaction of iron and immunity is anaemia of chronic disease (ACD). ACD develops in patients with chronic activation of cellular immunity such as subjects suffering from malignancies, auto-immune disorders or infections. ACD may be seen as an immune driven disease since cytokines and their products cause (i) a diversion of iron traffic into the reticuloendothelial systems, thus limiting the availability of the metal to erythroid progenitor cells for haem biosynthesis, (ii) an inhibition of erythroid progenitor cell proliferation and (iii) blunted production and activity of erythropoietin (EPO). However, ACD may also hold some benefit by reducing iron availability to invading pathogens, thus limiting their growth, and by stimulating cell mediated immune function. The latter can be referred to the correction of an inhibitory effect of iron towards IFN-gamma induced immune effector pathways in macrophages. Whereas ACD can be easily diagnosed based on the characteristic changes of iron homeostasis, therapy of ACD is much more controversial. Where a cure of the underlying disease is impossible, transfusions for rapid correction of haemoglobin levels and human recombinant EPO can be used with varying success. The sole application of iron should be strictly avoided due to promotion of pathogen growth and impairment of immune function.

Anemia, Hypochromic↗

PubMed2002

Erythroid 5-aminolevulinate synthase, ferrochelatase and DMT1 expression in erythroid progenitors: differential pathways for erythropoietin and iron-dependent regulation.

To determine whether erythropoietin (EPO) affects haem biosynthesis and iron transport, we studied the effects of EPO on the expression of erythroid 5-aminolevulinate synthase (eALAS), ferrochelatase and divalent metal transporter 1 (DMT-1) in human erythroid progenitor cells, and in the murine and human erythroid cell lines MEL and K562. Cytoplasmic e-ALAS mRNA levels were significantly increased after incubation of cells with EPO for at least 24 h, which could be the result of a transcriptional mechanism. In contrast, ferrochelatase or DMT-1 mRNA expression were not affected. Moreover, EPO also increased e-ALAS enzyme activity after only 4 h of stimulation, when mRNA levels were unchanged. The underlying mechanism was an effect of EPO on e-ALAS mRNA translation, which was under the control of iron regulatory proteins (IRP) 1 and 2. Thereby, EPO weakened the binding affinity of IRP-2 to the iron responsive element (IRE) within e-ALAS mRNA which resulted in the increased expression of e-ALAS IRE-controlled reporter gene constructs, following EPO stimulation. Our results show that EPO directly affected haem biosynthesis by stimulating the transcriptional and post-transcriptional expression of the key enzyme e-ALAS. These data provide new insights into the complex biochemical interaction between iron metabolism, haem biosynthesis and EPO biology.

5-Aminolevulinate Synthetase↗

PubMed2002

Iron and immunity: a double-edged sword.

Iron is a crucial element for many central metabolic pathways of the body. Lack of iron leads to growth arrest and anaemia while increased accumulation of this metal, as it occurs in highly frequent inherited diseases such as hereditary haemochromatosis and thalassaemia, is associated with toxic radical formation and progressive tissue damage. As shown by several groups, iron also modulates immune effector mechanisms, such as cytokine activities (IFN-gamma effector pathways towards macrophages), nitric oxide (NO) formation or immune cell proliferation, and thus host immune surveillance. Therefore, gaining control over iron homeostasis is one of the central battlefields in deciding the fate of an infection with intracellular pathogens or a malignant disease. Thus, the reticulo-endothelial system has evoked sophisticated strategies to control iron metabolism in general and especially the handling of the metal within immune cells.

Cytokines↗

PubMed2002

Pathogenesis and treatment of anaemia of chronic disease.

Anaemia of chronic disease (ACD), the most frequent anaemia among hospitalized patients, develops under chronic inflammatory disorders such as chronic infections, cancer or autoimmune diseases. A number of different pathways contribute to ACD, such as diversion of iron traffic, a diminished erythropoiesis, a blunted response to erythropoietin, erythrophagocytosis and bone marrow invasion by tumour cells and pathogens. Nevertheless, ACD is a reflection of an activated immune system and possibly results from an innovative defence strategy of the body in order to withdraw the essential growth factor iron from invading pathogens and to increase the efficacy of cell-mediated immunity. Diagnosis of ACD can be assessed by examination of chances in serum iron parameters with low to normal serum iron, transferrin saturation and transferrin concentrations on the one hand and normal to increased ferritin, zinc protoporphyrin IX and cytokine levels on the other side. Therapy of ACD includes the cure of the underlying the disease. Apart from this transfusions for rapid correction of haemoglobin levels, and human recombinant erythropoietin for prolonged therapy are used. However, response rates to recombinant erythropoietin are sometimes low. Iron alone should be strictly avoided due to its growth-promoting effect towards micro-organisms and tumour cells and because of it capacity to inhibit T-cell-mediated immune effector pathways. We urgently need prospective clinical trials to gain knowledge about the effects of anaemia correction and/or the use of erythropoietin towards the course of the underlying disease, to find out if a combination therapy with erythropoietin and iron may be beneficial in ACD and to define therapeutic end-points.

Anemia↗

PubMed2002

Effects of synthetic siderophores on proliferation of Plasmodium falciparum in infected human erythrocytes.

Because iron is essential for Plasmodium falciparum, we investigated the in vitro potential of various synthetic siderophores to kill P. falciparum in infected human erythrocytes. The substances with the most promising profile, i.e., low 50% lethal doses for plasmodia and minimum toxicity towards mammalian cells, were siderophores with an acylated monocatecholate or a triscatecholate as substituent.

Animals↗

PubMed2000

Clinical Consequences of New Insights in the Pathophysiology of Disorders of Iron and Heme Metabolism.

This review examines the clinical consequences for the practicing hematologist of remarkable new insights into the pathophysiology of disorders of iron and heme metabolism. The familiar proteins of iron transport and storage-transferrin, transferrin receptor, and ferritin-have recently been joined by a host of newly identified proteins that play critical roles in the molecular management of iron homeostasis. These include the iron-regulatory proteins (IRP-1 and -2), HFE (the product of the HFE gene that is mutated in most patients with hereditary hemochromatosis), the divalent metal transporter (DMT1), transferrin receptor 2, ceruloplasmin, hephaestin, the "Stimulator of Fe Transport" (SFT), frataxin, ferroportin 1 and others. The growing appreciation of the roles of these newly identified proteins has fundamental implications for the clinical understanding and laboratory evaluation of iron metabolism and its alterations with iron deficiency, iron overload, infection, and inflammation. In Section I, Dr. Brittenham summarizes current concepts of body and cellular iron supply and storage and reviews new means of evaluating the full range of body iron stores including genetic testing for mutations in the HFE gene, measurement of serum ferritin iron, transferrin receptor, reticulocyte hemoglobin content and measurement of tissue iron by computed tomography, magnetic resonance imaging and magnetic susceptometry using superconducting quantum interference device (SQUID) instrumentation. In Section II, Dr. Weiss discusses the improved understanding of the molecular mechanisms underlying alterations in iron metabolism due to chronic inflammatory disorders. The anemia of chronic disorders remains the most common form of anemia found in hospitalized patients. The network of interactions that link iron metabolism with cellular immune effector functions involving pro- and anti-inflammatory cytokines, acute phase proteins and oxidative stress is described, with an emphasis on the implications for clinical practice. In Section III, Dr. Brissot and colleagues discuss how the diagnosis and management of hereditary hemochromatosis has changed following the identification of the gene, HFE, that is mutated in most patients with hereditary hemochromatosis, and the subsequent development of a genotypic test. The current understanding of the molecular effects of HFE mutations, the usefulness of genotypic and phenotypic approaches to screening and diagnosis and recommendations for management are summarized.

Journal Article↗

PubMedDate not supplied

Hemochromatosis protein (HFE) and tumor necrosis factor receptor 2 (TNFR2) influence tissue iron levels: elements of a common gut pathway?

Quantitative genetic analysis of hepatic and splenic iron levels in recombinant inbred mice yielded a quantitative trait locus that was found to coincide with the genomic locale encompassing the tumor necrosis factor receptor 2 gene (Tnfr2). When fed an iron-enriched diet, mice nullizygous with respect to Tnfr2, but not the Tnfr1 gene, showed a significant increase in splenic non-heme iron levels. This result contrasted with mice deficient in the hemochromatosis protein, HFE, which demonstrated a significant increase in normally high hepatic iron levels, but no change in splenic iron, when fed an iron-enriched chow. Both Tnfr2 knockout and HFE knockout mice fed an iron-enriched diet failed to demonstrate intestinal epithelial cell iron following the application of the Perls' stain, as compared to both Tnfr1 knockout and normal control mice. Moreover, intestinal intraepithelial lymphocytes (IELs) isolated from HFE knockout mice did not show an increase in TNF expression following challenge with the iron-enriched diet, in contrast to normal controls. These results suggest that HFE and TNFR2 are both involved in regulating iron deposition in tissues and that the regulation occurs at the level of the intestine through IEL-orchestrated production of TNF following the binding to TNFR2. These data suggest that HFE and TNFR2 may contribute to a common pathway of the iron stores regulator insuring the controlled efflux of gut iron.

Animals↗

PubMedDate not supplied

Mechanisms of iron mediated regulation of the duodenal iron transporters divalent metal transporter 1 and ferroportin 1.

Intestinal iron absorption is regulated by the body's demands for iron. Identification of divalent metal transporter 1 (DMT1) and ferroportin 1 (FPN1) has improved our understanding of iron transport across the intestinal epithelium. Although DMT1 and FPN1 mRNA bear an iron responsive element (IRE) within its untranslated regions which should cause susceptibility to iron mediated posttranscriptional regulation the latter has not been shown so far. The effects of iron perturbations on DMT1 and FPN1 expression were investigated in CaCo2 cells and in primary tissue cultures of human duodenal biopsies by means of Northern Blot, Western Blot, RNA-bandshift and Nuclear Run off analysis. Both DMT1 and FPN1 mRNA levels were increased upon treatment of CaCo2 cells with desferrioxamine, whereas iron treatment resulted in the opposite effect. These changes were paralleled by the respective alterations in DMT1 and FPN1 protein expression. Although desferrioxamine treatment increased the binding affinity of iron regulatory protein-1 to DMT1- and FPN1-IRE, the mRNA half life of DMT1 mRNA remained unchanged. Nuclear run-off analysis then demonstrated that the effects of iron and desferrioxamine on DMT1 and FPN1 mRNA expression are rather due to modulation of transcription of these genes. Our results demonstrate that iron unidirectionally regulates the expression of the two ferrous ion transporters DMT1 and FPN1 by affecting their transcription. This provides evidence for a negative feed-back loop between intracellular iron availability and transmembrane iron transport.

Caco-2 Cells↗