These projects explore the problems of adequate iron supply and the control of adverse effects of iron as well as the interaction between iron and inflammation.
Supplying extra iron goes along with risks and benefits. Their relationship is subject to gender- and age-specific differences in iron kinetics and to the impact of other food components, such as complex-forming ligands or competing metals. Moreover, they are influenced by mutual interactions between iron homoeostasis and inflammation that come to bearing in the context of infections, of atherosclerosis and of obesity. These complex interrelationships are subject to a number of HGF-supported projects.
Iron is an essential trace element. Its rare property to oscillate between the divalent and trivalent state is utilized in proteins and enzymes to transport oxygen and electrons, both of which is pivotal for energy metabolism and to degrade xenobiotics. However, these properties are also the basis for detrimental effects, such as catalysis of oxidative stress. Moreover, iron is essential for bacteria and parasites. Ample.iron-supply supports the expansion of pathogen populations which is, again, detrimental for the host organism. In order to supply enough iron to maintain the essential functions during periods of scarce supply on the one hand, and to avoid excess during situations of over-supply on the other, a complex system of mechanisms has evolved to maintain iron homoeostasis. This system encompasses adaptation of intestinal iron absorption to the demand as well as the regulation of intracellular iron stores to provide for situations of scarcity and, at the same time, to avoid damage by unbound iron. In the circulation, iron is bound to transferrin which is taken up by the cells via transferrin receptors according to their demand. This complex system can become dysfunctional in a number of hereditary diseases (e.g. hemochromatosis): it can be overwhelmed by oversupply and may not be able to cope with grave states of undersupply. Moreover, it may interact with inflammation of different origin, or with toxic trace metals such as lead or cadmium.
Click for complete referenceI51: Hfe and Hjv exhibit overlapping functions for iron signaling to hepcidin: Genetic evidence from single and double knockout mice I50: Mice are poor heme absorbers and do not require intestinal Hmox1 for dietary heme iron assimilation I49: 59Fe-distribution in conditional ferritin-H-deleted mice I48: Iron regulatory proteins control a mucosal block to intestinal iron absorption I47: Abnormal body iron distribution and erythropoiesis in a novel mouse model with inducible gain of iron regulatory protein (IRP)-1 function I41: Absorption of iron from ferritin is independent of heme iron and ferrous salts in women and rat intestinal segments I36: Does lead use the intestinal absorptive pathways of iron? Impact of iron status on murine 210Pb and 59Fe absorption in duodenum and ileum in vivo I35: Reproducibility and correspondence among different hepcidin forms in blood and urine and their relationships to iron status in healthy, male Guatemalan volunteers observed over 9 weeks I33: Intestinal ferritin H is required for an accurate control of iron absorption I31: Systems Analysis of Iron Metabolism: The Network of Iron Pools and Fluxes R20: Iron: Nutrition’s two-edged sword R19: Efficacy and safety of iron administration in juvenile populations R17: Iron deficiency R16: Acute iron intoxication R15: Hereditary hemochromatosis I27: Efficacy and safety of twice-weekly administration of three RDAs of iron and folic acid with and without complement of 14 essential micronutrients at one or two RDAs: a placebo-controlled intervention trial in anemic Cambodian infants 6 to 24 months of age
Genetically modified mice permit to investigate absorptive and metabolic pathways in vivo. Intestinal 59Fe-absorption can be determined in vivo in ligated intestinal loops and after gavage. HGF investigated the mechanisms of intestinal iron absorption and body iron distribution by the methods described under 1. in a number of genetically modified murine models in cooperation with those working groups who developed the models or had them at hand. These studies contribute to the understanding of the molecular and physiological bases of interactions between iron metabolism and inflammation (I33, I36, I37, I41, I47, I48, I49, I51), to testing the extent to which lead went piggyback on the iron absorption system (I36), and to what extent ferritin-bound iron enters the body by pathways that differ from those of Fe(II) (I41).
Click for complete referenceI08: Jejunal transfer rates of 109cadmium chloride increase in rats in vitro and in vivo after oral pretreatment with cadmium or zinc chloride I02: Longitudinal pattern of enzymatic and absorptive functions in the small intestine of rats after short-term exposure to dietary cadmium chloride I01: Kinetic analysis of 59Fe movement across the intestinal wall in iron-deficient and iron-adequate duodenal rat segments ex vivo
The interaction between iron and malaria moved into focus of public health interests when a large intervention trial on Pemba Island, where malaria is hyper-endemic, was stopped at midterm. Evidence for more severe courses and higher mortality rates of malaria had become obvious in children without iron deficiency, who nevertheless received low-dose iron supplements. In consequence, the WHO stopped most iron supplementation programs in malaria endemic areas, leaving iron-deficiency in these areas untreated until date. This puts people living in malaria-endemic areas on the horns of a dilemma: either iron-deficient individuals receive no iron-supplements and suffer from deficiency symptoms (e.g. from impaired physical and intellectual capacity, cellular immune deficiency, increase rates of stillbirth and “small for gestational age” babies, or the population consumes iron-supplements which increases their risk for more severe courses of malaria and increased death rates (R23). Several ways to solve this dilemma were proposed: 1.) To target iron-supplements to iron-deficient individuals. 2.) To supplement iron-compounds that do not form non-transferrin-bound iron (= NTBI, a form of iron that is suspected to aggravate clinical malaria courses). 3.) To supply antimalarial drugs along with iron-supplements. HGF supported studies along the first two of these lanes.
Click for complete referenceR23: Can iron supplementation be reconciled with benefits and risks in areas hyperendemic for malaria? R20: Iron: Nutrition’s two-edged sword R19: Efficacy and safety of iron administration in juvenile populations R10: On risk and benefits of iron supplementation recommendations for iron intake revisited R09: Did the “iron age” end in Pemba?
Obesity goes along with inflammation. This increases circulating hepcidin concentrations which in turn reduces intestinal iron-absorption and promotes iron-sequestration into the stores. This disturbs hepcidin-medicated iron homoeostasis (R25, R26). Due to worldwide increases in obesity prevalence, particularly in developing countries, such interference between obesity and iron homoeostasis has considerable consequences. The same increments in body mass index (BMI), however, seem to affect iron homoeostasis to a different extent in different regions of the world. HGF plans to investigate this relationship in Guatemala.
According to current concepts hepcidin is a tissue hormone of largely hepatic origin. It regulates whole body iron availability by initiating ferroportin degradation which inhibits cellular iron export. Correspondingly, hepcidin expression increases in iron overload. This reduces intestinal iron absorption and sequesters iron in the reticuloendothelial system by blocking ferroportin-mediated iron export across the enterocytes’ basolateral membrane and out of leukocytes. Both reduces free iron concentration in the plasma. Hepcidin synthesis is also increased in inflammation in order to reduce iron availability to pathogens and to reduce oxidative stress as mediated by Fenton reaction.
However, in this respect literature reports are contradictory. Thus, reduced hepcidin concentrations were reported after injection of the pro-inflammatory cytokine TNF-α. Our foundation supported research on this issue in TNFΔARE/+- and IL10-/--mice, two murine models of inflammation. In contrast to expectation, hepcidin concentration was, indeed, reduced in inflammation which, again in contrast to expectation, was not accompanied by increased intestinal iron absorption (I53). Both models showed anemia and stimulated erythropoiesis to compensate for this, though compensation was more marked in TNFΔARE/+-mice. These results indicate interactions between competing regulatory mechanisms – such as inflammation and anemia, the first tending to reduce intestinal iron absorption, the second tending to increase it. The integrated effects of such mechanisms determine the impact on hepcidin synthesis and intestinal iron absorption (I53).
Click for complete referenceR26: Iron metabolism in obesity: How interaction between homoeostatic mechanisms can interfere with their original purpose. Part II: Epidemiological and historic aspects of the iron/obesity interaction R25: Iron metabolism in obesity: How interaction between homoeostatic mechanisms can interfere with their original purpose. Part I: Underlying homoeostatic mechanisms of energy storage and iron metabolisms and their interaction I53: Iron-homeostasis and obesity
Iron-deficient diets reduce the intensity of inflammation in a mouse model for colitis ulcerosa (I28). Intestinal iflammation remains low when the missing iron amounts were supplemented by parenteral injection (I37). These results help to understand the molecular mechanisms of inflammation and their contribution to oxidative stress and protein folding, as well as the effect of local inflammation on iron distribution (I29, I37). This opens perspectives for future therapeutic interventions.
Oxidative stress in the intestinal gut content participates in the pathogenesis of inflammatory bowel diseases and of colonic tumors. HGF supported the development of a method to determine the extent of oxidative stress in stool samples (I30). Oral iron supplementation at dosages recommended by WHO increases oxidative stress in the gut lumen significantly. This can be balanced by simultaneous consumption of antioxidative food components, such as palm oil (I30).
Click for complete referenceR23: Can iron supplementation be reconciled with benefits and risks in areas hyperendemic for malaria? I46: Differences in circulating non-transferrin-bound iron after oral administration of ferrous sulfate, sodium iron EDTA, or iron polymaltose in women with marginal iron stores I43: Equivalent effects on fecal reactive oxygen species generation with oral supplementation of three iron compounds: ferrous sulfate, sodium iron EDTA and iron polymaltose I42: Studies on variation in fecal reactive oxidative species generation in free-living populations in Guatemala I40: Oral administration of ferrous sulfate, but not of iron polymaltose or sodium iron ethylenediaminetetraacetic acid (NaFeEDTA), results in a substantial increase of non-transferrin-bound iron in healthy iron-adequate men I38: Impact of iron status and oral iron challenges on circulating non-transferrin-bound iron (NTBI) in healthy Guatemalan males I37: Depletion of luminal iron alters the gut microbiota and prevents Crohn’s disease-like ileitis I30: Antioxidant-rich Oral Supplements Attenuate the Effects of Oral Iron on In Situ Oxidation Susceptibility of Human Feces I29: Iron absorption and distribution in TNFΔARE/+ mice, a model of chronic inflammation I28: Intestinal epithelial cell proteome from wild-type and TNFΔARE/WT mice: effect of iron on the development of chronic ileitis
Investigation of interactions between iron-ingestion, non-transferrin-bound iron and oxidative stress
M Orozco, NW Solomons
Guatemala City, Guatemala
Project finished and published
Iron supplements aggravate the clinical course of Plasmodium falciparum-induced malaria tropica, if they are not explicitly targeted to iron-deficient individuals. On the one hand, these findings point out the problem of untargeted iron-supplementation in malaria-endemic areas, as they lead to more severe clinical courses and increased death rates. Without iron intervention programs, on the other hand, iron-deficiency leading to impaired physical and mental development and increased numbers of still births and abortions are the consequence (R10). HGF analyzed this dilemma (R23) and supports the quest for its solution. A possible way-out is to develop or adapt inexpensive and robust methods for the determination of the hematological status, inflammatory- and iron-status. These methods should preferably be non-invasive to prevent dissemination of AIDS and hepatitis through blood sampling. HGF supported field-testing of devices for non-invasive, transcutaneous hemoglobin determination (I44, I32). To differ between anemia of iron-deficiency and anemia of inflammation, and to help with the decision whether to administer iron or not, we tested non-invasive parameters, e.g. the use of urinary 25-hepcidin (I35).
In spite of some initially promising results, a breakthrough has not been reached and a reliable method for non-invasive hemoglobin determination could not be picked. The correlation with invasive standard methods remained poor for all tested methods of transcutaneous photometry.
Click for complete referenceR23: Can iron supplementation be reconciled with benefits and risks in areas hyperendemic for malaria? I45: Targeted provision of oral iron: The evolution of a practical screening option I44: Validity and correspondence of non-invasively determined hemoglobin concentrations by two trans-cutaneous digital measuring devices I32: Correspondence of a non-invasive, cutaneous-contact method to determine hemoglobin values with conventional whole blood samples within a Guatemalan field setting R20: Iron: Nutrition’s two-edged sword R19: Efficacy and safety of iron administration in juvenile populations R10: On risk and benefits of iron supplementation recommendations for iron intake revisited R09: Did the “iron age” end in Pemba?
Testing of devices for non-invasive measurement of iron-deficiency
C Crowley, J Casimiro de Almeida, C Luzón, NW Solomons
Data collection completed, project finished and published