Iron transport

How are Trypanosoma brucei receptors protected from host antibody-mediated attack?

Trypanosoma brucei is the causal agent of African Trypanosomiasis in humans and other animals. It maintains a long-term infection through an antigenic variation based population survival strategy. To proliferate in a mammal, T. brucei acquires iron and haem through the receptor mediated uptake of host transferrin and haptoglobin-hemoglobin respectively. The receptors are exposed to host antibodies but this does not lead to clearance of the infection. Here we discuss how the trypanosome avoids this fate in the context of recent findings on the structure and cell biology of the receptors.

Examining the effect of iron (ferric) on physiological processes: Invertebrate models

Iron is a common and essential element for maintaining life in bacteria, plants and animals and is found in soil, fresh waters and marine waters; however, over exposure is toxic to organisms. Iron is used in electron transport complexes within mitochondria as well as a co-factor in many essential proteins. It is also established that iron accumulation in the central nervous system in mammals is associated with various neurological disorders. Ample studies have investigated the long-term effects of iron overload in the nervous system. However, its acute effects in nervous tissue and additional organ systems warrant further studies. This study investigates the effects of iron overload on development, behavior, survival, cardiac function, and glutamatergic synaptic transmission in the Drosophila melanogaster. Additionally, physiological responses in crayfish were examined following Fe3+ exposure. Fe3+ reduced neuronal excitability in proprioceptive neurons in a crayfish model. Thus, Fe3+ may block stretch activated channels (SACs) as well as voltage-gated Na+ channels. Exposure also rapidly reduces synaptic transmission but does not block ionotropic glutamatergic receptors, suggesting a blockage of pre-synaptic voltage-gated Ca2+ channels in both crustacean and Drosophila models. The effects are partly reversible with acute exposure, indicating the cells are not rapidly damaged. This study is relevant in demonstrating the effects of Fe3+ on various physiological functions in different organisms in order to further understand the acute and long-term consequences of overload.

Ferroptosis: a potential target for the treatment of atherosclerosis

Atherosclerosis (AS), the main contributor to acute cardiovascular events, such as myocardial infarction and ischemic stroke, is characterized by necrotic core formation and plaque instability induced by cell death. The mechanisms of cell death in AS have recently been identified and elucidated. Ferroptosis, a novel iron-dependent form of cell death, has been proven to participate in atherosclerotic progression by increasing endothelial reactive oxygen species (ROS) levels and lipid peroxidation. Furthermore, accumulated intracellular iron activates various signaling pathways or risk factors for AS, such as abnormal lipid metabolism, oxidative stress, and inflammation, which can eventually lead to the disordered function of macrophages, vascular smooth muscle cells, and vascular endothelial cells. However, the molecular pathways through which ferroptosis affects AS development and progression are not entirely understood. This review systematically summarizes the interactions between AS and ferroptosis and provides a feasible approach for inhibiting AS progression from the perspective of ferroptosis.

An invertebrate model in examining the effect of acute ferric iron exposure on proprioceptive neurons

Iron is an essential element for plant and animal life and is found in soil, fresh waters and marine waters. The Fe³⁺ ion is a vital prosthetic group and cofactor to mitochondrial electron transport complexes and numerous proteins involved in normal functioning. Despite its importance to life-sustaining processes, overexposure results in toxicity. For example, ferric iron (Fe³⁺) accumulation in the mammalian central nervous system is associated with various neurological disorders. Although current literature addresses the long-term effects of Fe³⁺ overload, fewer studies exist examining the effects of acute exposure. Using the blue crab (Callinectes sapidus), we investigate the effects of acute Fe³⁺ overload on proprioception within the propodite-dactylopodite (PD) nerve. For proprioceptive studies, 10- and 20-mM ferric chloride and ferric ammonium citrate solutions were used at 5- and 20- min exposure times. Exposure to 20 mM concentrations of ferric chloride and ferric ammonium citrate reduced excitability in proprioceptive neurons. Thus, Fe³⁺ likely blocks stretch-activated channels or voltage-gated Na⁺ channels. The depressive effects of Fe³⁺ are partly reversible following saline washout, indicating cells are not acutely damaged. Gadolinium (GdCl₃, 1 and 10 mM) was used to examine the effects of an additional trivalent ion comparator. Gd³⁺ depressed PD nerve compound action potential amplitude while increasing the compound action potential duration. This study is relevant in demonstrating the dose-dependent effects of acute Fe³⁺ and Gd³⁺ exposure on proprioception and provides a model system to further investigate the mechanisms by which metals act on the nervous system.

Identification of Transferrin Receptor 1 (TfR1) Overexpressed in Lung Cancer Cells, and Internalization of Magnetic Au-CoFe2O4 Core-Shell Nanoparticles Functionalized with Its Ligand in a Cellular Model of Small Cell Lung Cancer (SCLC)

Lung cancer is, currently, one of the main malignancies causing deaths worldwide. To date, early prognostic and diagnostic markers for small cell lung cancer (SCLC) have not been systematically and clearly identified, so most patients receive standard treatment. In the present study, we combine quantitative proteomics studies and the use of magnetic core-shell nanoparticles (mCSNP’s), first to identify a marker for lung cancer, and second to functionalize the nanoparticles and their possible application for early and timely diagnosis of this and other types of cancer. In the present study, we used label-free mass spectrometry in combination with an ion-mobility approach to identify 220 proteins with increased abundance in small cell lung cancer (SCLC) cell lines. Our attention was focused on cell receptors for their potential application as mCSNP’s targets; in this work, we report the overexpression of Transferrin Receptor (TfR1) protein, also known as Cluster of Differentiation 71 (CD71) up to a 30-fold increase with respect to the control cell. The kinetics of endocytosis, evaluated by a flow cytometry methodology based on fluorescence quantification, demonstrated that receptors were properly activated with the transferrin supported on the magnetic core-shell nanoparticles. Our results are important in obtaining essential information for monitoring the disease and/or choosing better treatments, and this finding will pave the way for future synthesis of nanoparticles including chemotherapeutic drugs for lung cancer treatments.

Expression of soluble, active, fluorescently tagged hephaestin in COS and CHO cell lines

Hephaestin (Hp) is a trans-membrane protein, which plays a critical role in intestinal iron absorption. Hp was originally identified as the gene responsible for the phenotype of sex-linked anaemia in the sla mouse. The mutation in the sla protein causes accumulation of dietary iron in duodenal cells, causing severe microcytic hypochromic anaemia. Although mucosal uptake of dietary iron is normal, export from the duodenum is inhibited. Hp is homologous to ceruloplasmin (Cp), a member of the family of multi copper ferroxidases (MCFs) and possesses ferroxidase activity that facilitates iron release from the duodenum and load onto the serum iron transport protein transferrin. In the present study, attempts were made to produce biologically active recombinant mouse hephaestin as a secretory form tagged with green fluorescent protein (GFP), Hpsec-GFP. Plasmid expressing Hpsec-GFP was constructed and transfected into COS and CHO cells. The GFP aided the monitoring expression in real time to select the best conditions to maximise expression and provided a tag for purifying and analysing Hpsec-GFP. The protein had detectable oxidase activity as shown by in-gel and solution-based assays. The methods described here can provide the basis for further work to probe the interaction of hephaestin with other proteins using complementary fluorescent tags on target proteins that would facilitate the fluorescence resonance energy transfer measurements, for example with transferrin or colocalisation studies, and help to discover more about hephaestin works at the molecular level.

Iron-oxide minerals in the human tissues

Iron is critically important and highly regulated trace metal in the human body. However, in its free ion form, it is known to be cytotoxic; therefore, it is bound to iron storing protein, ferritin. Ferritin is a key regulator of body iron homeostasis able to form various types of minerals depending on the tissue environment. Each mineral, e.g. magnetite, maghemite, goethite, akaganeite or hematite, present in the ferritin core carry different characteristics possibly affecting cells in the tissue. In specific cases, it can lead to disease development. Widely studied connection with neurodegenerative conditions is widely studied, including Alzheimer disease. Although the exact ferritin structure and its distribution throughout a human body are still not fully known, many studies have attempted to elucidate the mechanisms involved in its regulation and pathogenesis. In this review, we try to summarize the iron uptake into the body. Next, we discuss the known occurrence of ferritin in human tissues. Lastly, we also examine the formation of iron oxides and their involvement in brain functions.

Ceruloplasmin Plays a Neuroprotective Role in Cerebral Ischemia

Ceruloplasmin (Cp) is a ferroxidase that also plays a role in iron efflux from cells. It can thus help to regulate cellular iron homeostasis. In the CNS, Cp is expressed as a membrane-anchored form by astrocytes. Here, we assessed the role of Cp in permanent middle cerebral artery occlusion (pMCAO) comparing wildtype and Cp null mice. Our studies show that the lesion size is larger and functional recovery impaired in Cp null mice compared to wildtype mice. Expression of Cp increased ninefold at 72 h after pMCAO and remained elevated about twofold at day 14. We also assessed changes in mRNA and protein expression of molecules involved in iron homeostasis. As expected there was a reduction in ferroportin in Cp null mice at 72 h. There was also a remarkable increase in DMT1 protein in both genotypes at 72 h, being much higher in wildtype mice (19.5-fold), that then remained elevated about twofold at 14 days. No difference was seen in transferrin receptor 1 (TfR1) expression, except a small reduction in wildtype mice at 72 h, suggesting that the increase in DMT1 may underlie iron uptake independent of TfR1-endosomal uptake. There was also an increase of ferritin light chain in both genotypes. Iron histochemistry showed increased iron accumulation after pMCAO, initially along the lesion border and later throughout the lesion. Immunofluorescence labeling for ferritin (a surrogate marker for iron) and GFAP or CD11b showed increased ferritin in GFAP+ astrocytes along the lesion border in Cp null mice, while CD11b+ macrophages expressed ferritin equally in both genotypes. Increased lipid peroxidation assessed by 4HNE staining was increased threefold in Cp null mice at 72 h after pMCAO; and 3-nitrotyrosine labeling showed a similar trend. Three key pro-inflammatory cytokines (IL-1β, TNFα, and IL-6) were markedly increased at 24 h after pMCAO equally in both genotypes, and remained elevated at lower levels later, indicating that the lack of Cp does not alter key inflammatory cytokine expression after pMCAO. These data indicate that Cp expression is rapidly upregulated after pMCAO, and loss of Cp results in dysregulation of iron homeostasis, increased oxidative damage, greater lesion size and impaired recovery of function.

Whole-body iron transport and metabolism: Mechanistic, multi-scale model to improve treatment of anemia in chronic kidney disease

Iron plays vital roles in the human body including enzymatic processes, oxygen-transport via hemoglobin and immune response. Iron metabolism is characterized by ~95% recycling and minor replenishment through diet. Anemia of chronic kidney disease (CKD) is characterized by a lack of synthesis of erythropoietin leading to reduced red blood cell (RBC) formation and aberrant iron recycling. Treatment of CKD anemia aims to normalize RBC count and serum hemoglobin. Clinically, the various fluxes of iron transport and accumulation are not measured so that changes during disease (e.g., CKD) and treatment are unknown. Unwanted iron accumulation in patients is known to lead to adverse effects. Current whole-body models lack the mechanistic details of iron transport related to RBC maturation, transferrin (Tf and TfR) dynamics and assume passive iron efflux from macrophages. Hence, they are not predictive of whole-body iron dynamics and cannot be used to design individualized patient treatment. For prediction, we developed a mechanistic, multi-scale computational model of whole-body iron metabolism incorporating four compartments containing major pools of iron and RBC generation process. The model accounts for multiple forms of iron in vivo, mechanisms involved in iron uptake and release and their regulation. Furthermore, the model is interfaced with drug pharmacokinetics to allow simulation of treatment dynamics. We calibrated our model with experimental and clinical data from peer-reviewed literature to reliably simulate CKD anemia and the effects of current treatment involving combination of epoietin-alpha and iron dextran. This in silico whole-body model of iron metabolism predicts that a year of treatment can potentially lead to 90% downregulation of ferroportin (FPN) levels, 15-fold increase in iron stores with only a 20% increase in iron flux from the reticulo-endothelial system (RES). Model simulations quantified unmeasured iron fluxes, previously unknown effects of treatment on FPN-level and iron stores in the RES. This mechanistic whole-body model can be the basis for future studies that incorporate iron metabolism together with related clinical experiments. Such an approach could pave the way for development of effective personalized treatment of CKD anemia.

Determination of Mineral Constituents, Phytochemicals and Antioxidant Qualities of Cleome gynandra, Compared to Brassica oleracea and Beta vulgaris

The study compared mineral, chemical and antioxidant qualities of Cleome gynandra, a wild leafy vegetable, with two widely consumed commercial vegetables, Brassica oleracea and Beta vulgaris. Mineral nutrients were quantified with inductively coupled plasma mass spectrometry (ICP-MS), phenolic compounds using ultra-high performance liquid chromatography coupled to a mass spectrometer (UHPLC-MS) and β-carotene and vitamin C using high performance liquid chromatography with a photodiode array detector (HPLC-PDA). The antioxidant potential was evaluated using 2,2-diphenyl-1-picryl hydrazyl (DPPH) and oxygen radical absorbance capacity (ORAC) assays. Cleome gynandra had highest concentrations of phosphorus, potassium, calcium, iron, zinc, ascorbic acid, total phenolics, and flavonoids; whereas sodium, magnesium, manganese, copper and β-carotene were higher for B. vulgaris. The significantly higher antioxidant activity (P ≤ 0.05) exhibited by C. gynandra in comparison to the two commercial vegetables may be due to its significantly high levels of vitamin C and phenolic acids. These findings on the mineral, chemical and antioxidant properties of C. gynandra provide compelling scientific evidence of its potential in adding diversity to the diet and contributing toward the daily nutritional requirements of millions of people for food and nutritional security.

Safety and efficacy of iron dextran as a feed additive for piglets

The additive, 'Iron dextran 10%', is a liquid preparation containing iron dextran (25%, of which 10% is total iron), sodium chloride (1.5%), phenol (0.4%) and water (73.1%). Iron dextran 10% is considered safe for suckling piglets when given at an oral dose of 1 mL/kg body weight (bw) once in each of the first 2 weeks of life; this dose corresponds to 100 mg Fe/kg bw. The administration of iron dextran 10% to piglets deficient in vitamin E and/or selenium is considered a risk. The oral use of iron dextran 10% in suckling piglets does not pose any safety concerns to consumers, provided that the conditions identified as safe for the target animal are respected. Iron dextran 10% is considered a respiratory sensitiser and may be harmful if inhaled; however, exposure by inhalation is not expected; therefore, the risk is considered to be negligible. Iron dextran 10% is an irritant to skin and eyes; a risk by skin sensitisation cannot be excluded. The presence of phenol in the additive should be considered to pose a hazard for users. The use of the additive for suckling piglets at the proposed level does not pose a safety concern to the environment. The available studies with orally administered iron dextran indicate that the additive is a bioavailable source of iron for suckling piglets; however, the efficacy of the additive when given to newborn pigs as proposed via water for drinking (voluntary intake) has not been demonstrated. The Panel proposed some recommendations regarding the dextran used in the manufacture of the additive and the procedure for administering the additive to piglets.

Iron acquisition in Leishmania and its crucial role in infection

Iron is an essential cofactor for many basic metabolic pathways in pathogenic microbes and their hosts. It is also dangerous as it can catalyse the production of reactive free radicals. This dual character makes the host can either limit iron availability to invading microbes or exploit iron to induce toxicity to pathogens. Successful pathogens, including Leishmania species, must possess mechanisms to circumvent host's iron limitation and iron-induced toxicity in order to survive. In this review, we discuss the regulation of iron metabolism in the setting of infection and delineate the iron acquisition strategies used by Leishmania parasites and their subversions to host iron metabolism to overcome host's iron-related defences.

Pathophysiology of the Belgrade rat

The Belgrade rat is an animal model of divalent metal transporter 1 (DMT1) deficiency. This strain originates from an X-irradiation experiment first reported in 1966. Since then, the Belgrade rat’s pathophysiology has helped to reveal the importance of iron balance and the role of DMT1. This review discusses our current understanding of iron transport homeostasis and summarizes molecular details of DMT1 function. We describe how studies of the Belgrade rat have revealed key roles for DMT1 in iron distribution to red blood cells as well as duodenal iron absorption. The Belgrade rat’s pathology has extended our knowledge of hepatic iron handling, pulmonary and olfactory iron transport as well as brain iron uptake and renal iron handling. For example, relationships between iron and manganese metabolism have been discerned since both are essential metals transported by DMT1. Pathophysiologic features of the Belgrade rat provide us with a unique and interesting animal model to understand iron homeostasis.

Incorporation of57Fe-isotopically enriched in apoferritin: formation and characterization of isotopically enriched Fe nanoparticles for metabolic studies

The use of⁵⁷Fe-isotopically enriched ferritin for the accurate measurement of Fe : ferritin ratios is proposed for metabolic studies.

Pharmacology of iron transport

Elucidating the molecular basis for the regulation of iron uptake, storage, and distribution is necessary to understand iron homeostasis. Pharmacological tools are emerging to identify and distinguish among different iron transport pathways. Stimulatory or inhibitory small molecules with effects on iron uptake can help characterize the mechanistic elements of iron transport and the roles of the transporters involved in these processes. In particular, iron chelators can serve as potential pharmacological tools to alleviate diseases of iron overload. This review focuses on the pharmacology of iron transport, introducing iron transport membrane proteins and known inhibitors.

Heme carrier protein 1 transports heme and is involved in heme-Fe metabolism

Heme-Fe is an important source of dietary iron in humans; however, the mechanism for heme-Fe uptake by enterocytes is poorly understood. Heme carrier protein 1 (HCP1) was originally identified as mediating heme-Fe transport although it later emerged that it was a folate transporter. We asked what happened to heme-Fe and folate uptake and the relative abundance of hcp1 and ho1 mRNA in Caco-2 cells after knockdown by transfection with HCP1-directed short hairpin (sh)RNA. Control Caco-2 cells were cultured in bicameral chambers with 0–80 μM heme-Fe for selected times. Intracellular Fe and heme concentration increased in Caco-2 cells reflecting higher external heme-Fe concentrations. Maximum Fe, heme, and heme oxygenase 1 (HO1) expression and activity were observed between 12 and 24 h of incubation. Quantitative RT-PCR for hcp1 revealed that its mRNA decreased at 20 μM heme-Fe while ho1 mRNA and activity increased. When shRNA knocked down hcp1 mRNA, heme-55Fe uptake and [3H]folate transport mirrored the mRNA decrease, ho1 mRNA increased, and flvcr mRNA was unchanged. These data argue that HCP1 is involved in low-affinity heme-Fe uptake not just in folate transport.

Pre-pregnancy iron reserves, iron supplementation during pregnancy, and birth weight

BACKGROUND

Early iron supplementation in women with sufficient reserves could provoke iron excess resulting in haemoconcentration and low infant birth weight (IBW).

AIM

To clarify the influence of early iron supplementation on maternal iron status and the IBW, taking into account pre-pregnancy iron deposits.

STUDY DESIGN

Longitudinal, prospective study.

SUBJECTS

Healthy women volunteers (n=82) intending to become pregnant.

OUTCOME MEASURES

Women were grouped as a function of their pre-pregnancy (low or present) iron stores (serum ferritin (SF)<or≥20μg/L) and time of commencement of iron supplementation during pregnancy; "early" (<20weeks) or "late" (≥20weeks). Obstetric and clinical history, smoking habit, dietary intake and iron biochemical parameters were obtained at pre-pregnancy as well as at 1st, 2nd and 3rd trimesters. Haemoglobin, MCV, SF and transferrin saturation (TS) were measured.

RESULTS

Overall, 36% of the women had low iron stores at pre-pregnancy. The mean early supplementation with iron was 140.7mg/d and the mean of late supplementation was 99.01mg/d. Early supplementation improves the biochemical status of the mother and does not provoke a significant increase in haemoconcentration relative to late supplementation independently of the pre-pregnancy iron levels. Supplemental iron had a positive effect on birth weight among women with pre-pregnancy low iron stores (β=4.37; SE=1.8; p=0.038) and did not affect birth weight among women with present iron stores (β=-0.008; SE=3.03; p=0.998).

CONCLUSION

Early iron supplementation with doses ~100mg/d improves the biochemical status of the mother independently of her pre-pregnancy iron status. Supplementation with iron improves newborn birth weight in those women who start pregnancy with iron deficiency, and makes no significant difference to those women who are not iron deficient.

An iron-dependent and transferrin-mediated cellular uptake pathway for plutonium

Plutonium is a toxic synthetic element with no natural biological function, but it is strongly retained by humans when ingested. Using small-angle X-ray scattering, receptor binding assays and synchrotron X-ray fluorescence microscopy, we find that rat adrenal gland (PC12) cells can acquire plutonium in vitro through the major iron acquisition pathway--receptor-mediated endocytosis of the iron transport protein serum transferrin; however, only one form of the plutonium-transferrin complex is active. Low-resolution solution models of plutonium-loaded transferrins derived from small-angle scattering show that only transferrin with plutonium bound in the protein's C-terminal lobe (C-lobe) and iron bound in the N-terminal lobe (N-lobe) (Pu(C)Fe(N)Tf) adopts the proper conformation for recognition by the transferrin receptor protein. Although the metal-binding site in each lobe contains the same donors in the same configuration and both lobes are similar, the differences between transferrin's two lobes act to restrict, but not eliminate, cellular Pu uptake.

Gastrins, iron homeostasis and colorectal cancer

The peptide hormone gastrin has been identified as a major regulator of acid secretion and a potent mitogen for normal and malignant gastrointestinal cells. The importance of gastric acid in the absorption of dietary iron first became evident 50 years ago when iron deficiency anemia was recognized as a long-term consequence of partial gastrectomy. This review summarizes the connections between circulating gastrins, iron status and colorectal cancer. Gastrins bind two ferric ions with micromolar affinity and, in the case of non-amidated forms of the hormone, iron binding is essential for biological activity in vitro and in vivo. The demonstration of an interaction between gastrin and transferrin by biochemical techniques led to the proposal that gastrins catalyze the loading of transferrin with iron. Several lines of evidence, including the facts that the concentrations of circulating gastrins are increased in mice and humans with the iron overload disease hemochromatosis and that transferrin saturation positively correlates with circulating gastrin concentration, suggest the potential involvement of gastrins in iron homeostasis. Conversely, recognition that ferric ions play an unexpected role in the biological activity of gastrins may assist in the development of useful therapies for colorectal carcinoma and other disorders of mucosal proliferation in the gastrointestinal tract. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.

Synthesis and characterization of a triazine dendrimer that sequesters iron(III) using 12 desferrioxamine B groups

The synthesis of a third generation triazine dendrimer, 1, containing multiple, iron-sequestering desferrioxamine B (DFO) groups is described. Benzoylation of the hydroxamic acid groups of DFO and formation of a reactive dichlorotriazine provide the intermediate for reaction with the second generation dendrimer displaying twelve amines. This strategy further generalizes the 'functional monomer' approach to generate biologically active triazine dendrimers. Dendrimer 1 is prepared in seven steps in 35% overall yield and displays 12 DFO groups making it 56% drug by weight. Spectrophotometric titrations (UV-vis) show that 1 sequesters iron(III) atoms with neither cooperativity nor significant interference from the dendrimer backbone. Evidence from NMR spectroscopy and mass spectrometry reveals a limitation to this functional monomer approach: trace amounts of O-to-N acyl migration from the protected hydroxamic acids to the amine-terminated dendrimer occurs during the coupling step leading to N-benzoylated dendrimers displaying fewer than 12 DFO groups.

Mineral metabolism in a black-necked swan (Cygnus melanocoryphus) population from southern Chile

A population of black-necked swans (Cygnus melanocoryphus) residing in a perturbed habitat revealed a low body mass, malnutrition, and hyperferremia during 2005; the swans main dietary item, Egeria densa, was lost during an environmental crisis which occurred in 2004. The objective of this study was to monitor the diet and nutritional status of this population during 2006, as well as to verify how the consumption of sediment, as part of their new diet, may explain the mineral disorders observed in these birds. Results revealed that swans increased their body mass and had an adequate protein, lipid, and iron metabolism, in spite of the fact that they maintained the same new diet (sediment and roots) during 2005-2006. In addition, transferrine saturation was indicative of the high endogenous iron load in birds which agrees with the high iron load of their environment. On the other hand, the consumption of the Cayumapu River sediment in the diet (25%) did not affect the body mass nor the nutritional and hepatic function in domestic geese over a 45-day period.

Effect of malnutrition on iron homeostasis in black-necked swans (Cygnus melanocoryphus)

The Cayumapu River black-necked swan (Cygnus melanocoryphus) population in southern Chile suffered a syndrome of malnutrition and hyperferremia in 2005. The iron metabolic imbalance could not be explained on the basis of the quality of their diet. Hence, the primary objective of this study was to determine the relationship between malnutrition and iron homeostasis in black-necked swans. It was proposed that catabolic processes could increase serum iron levels due to the release of endogenous iron from tissues. A free-living swan population undergoing natural nutritional imbalance due to molting was studied. In addition, swans captured were subjected to a diet restriction until they became emaciated. The results revealed that neither lipolytic activity nor emaciation affected serum iron concentrations. The increment of total iron binding capacity observed was in agreement with the reduction of endogenous iron stored, with the increase of erythropoeitic demand, or with both. Future studies are needed to determine the effect of incremental erythropoietic activity on iron homeostasis in anemic, malnourished birds.

Iron acquisition within host cells and the pathogenicity of Leishmania

Iron is an essential cofactor for several enzymes and metabolic pathways, in both microbes and in their eukaryotic hosts. To avoid toxicity, iron acquisition is tightly regulated. This represents a particular challenge for pathogens that reside within the endocytic pathway of mammalian cells, because endosomes and lysosomes are gradually depleted in iron by host transporters. An important player in this process is Nramp1 (Slc11a1), a proton efflux pump that translocates Fe(2+) and Mn(2+) ions from macrophage lysosomes/phagolysosomes into the cytosol. Mutations in Nramp1 cause susceptibility to infection with the bacteria Salmonella and Mycobacteria and the protozoan Leishmania, indicating that an available pool of intraphagosomal iron is critical for the intracellular survival and replication of these pathogens. Salmonella and Mycobacteria are known to express iron transporter systems that effectively compete with host transporters for iron. Until recently, however, very little was known about the molecular strategy used by Leishmania for survival in the iron-poor environment of macrophage phagolysosomes. It is now clear that intracellular residence induces Leishmania amazonensis to express LIT1, a ZIP family membrane Fe(2+) transporter that is required for intracellular growth and virulence.

Increased expression of host iron-binding proteins precedes iron accumulation and calcification of primary lung lesions in experimental tuberculosis in the guinea pig

The growth and virulence of Mycobacterium tuberculosis depends on its ability to scavenge host iron, an essential and limited micronutrient in vivo. In this study, we show that ferric iron accumulates both intra- and extra-cellularly in the primary lung lesions of guinea pigs aerosol-infected with the H37Rv strain of M. tuberculosis. Iron accumulated within macrophages at the periphery of the primary granulomatous lesions while extra-cellular ferric iron was concentrated in areas of lesion necrosis. Accumulation of iron within primary lesions was preceded by an increase in expression of heavy chain (H) ferritin, lactoferrin and receptors for transferrin, primarily by macrophages and granulocytes. The increased expression of intra-cellular H ferritin and extra-cellular lactoferrin, more so than transferrin receptor, paralleled the development of necrosis within primary lesions. The deposition of extra-cellular ferric iron within necrotic foci coincided with the accumulation of calcium and phosphorus and other cations in the form of dystrophic calcification. Primary lung lesions from guinea pigs vaccinated with Mycobactrium bovis BCG prior to experimental infection, had reduced iron accumulation as well as H ferritin, lactoferrin and transferrin receptor expression. The amelioration of primary lesion necrosis and dystrophic calcification by BCG vaccination was coincident with the lack of extra-cellular ferric iron and lactoferrin accumulation. These data demonstrate that BCG vaccination ameliorates primary lesion necrosis, dystrophic mineralization and iron accumulation, in part by down-regulating the expression of macrophage H ferritin, lactoferrin and transferrin receptors, in vivo.

Site-directed mutagenesis investigation of coupling properties of metal ion transport by DCT1

DCT1 (NRAMP2, DMT1, slc11a2) is a member of the NRAMP family and functions as general metal ion transporter in mammals; defective DCT1 causes anemia. The driving force for metal ion transport is protonmotive force, where protons are transported in the same direction as metal ions. The stoichiometry between metal ion and proton varies under different conditions due to mechanistic proton slip. To better understand this phenomenon, we performed site-directed mutagenesis of DCT1 and analyzed the mutants by measurement of metal ion uptake activity and electrophysiology in Xenopus laevis oocytes. A single reciprocal mutation, I144F, between DCT1 and the homologous yeast transporter Smf1p located in putative transmembrane domain 2 abolished the metal ion transport activity of DCT1, significantly increased the slip currents, and generated sodium slip currents. A double mutation adding F227I in transmembrane domain 4 to I144F in transmembrane domain 2 restored the uptake activity of DCT1 and reduced the slip currents. These results demonstrate the importance of these regions in coupling of metal ions and protons as well as the possible proximity of I144 and F227 in the folded structure of DCT1.

Electrolytic iron or ferrous sulfate increase body iron in women with moderate to low iron stores

Commercial elemental iron powders (electrolytic and reduced iron), as well as heme iron supplements, were tested for efficacy in improving the iron status of women. In a randomized, double-blind trial, 51 women with moderate to low iron stores received daily for 12 wk: 1) placebo, 2) 5 mg iron as heme iron or 50 mg iron as 3) electrolytic iron, 4) reduced iron, or 5) FeSO(4). Treatments were provided in 2 capsules (heme carrier) and 3 wheat rolls (other iron sources). Differences in iron status, food nonheme iron absorption, and fecal properties were evaluated. Body iron, assessed from the serum transferrin receptor:ferritin ratio, increased significantly more in subjects administered FeSO(4) (127 +/- 29 mg; mean +/- SEM) and electrolytic (115 +/- 37 mg), but not the reduced (74 +/- 32 mg) or heme (65 +/- 26 mg) iron forms, compared with those given placebo (2 +/- 19 mg). Based on body iron determinations, retention of the added iron was estimated as 3.0, 2.7, 1.8, and 15.5%, in the 4 iron-treated groups, respectively. Iron treatments did not affect food iron absorption. The 50 mg/d iron treatments increased fecal iron and free radical-generating capacity in vitro, but did not affect fecal water cytotoxicity. In subjects administered FeSO(4), fecal water content was increased slightly but significantly more than in the placebo group. In conclusion, electrolytic iron was approximately 86% as efficacious as FeSO(4) for improving body iron, but the power of this study was insufficient to detect any efficacy of the reduced or heme iron within 12 wk. With modification, this methodology of testing higher levels of food fortification for several weeks in healthy women with low iron stores has the potential for economically assessing the efficiency of iron compounds to improve iron status.

Iron bioavailability: UK Food Standards Agency workshop report

The UK Food Standards Agency convened a group of expert scientists to review current research investigating factors affecting iron status and the bioavailability of dietary iron. Results presented at the workshop show menstrual blood loss to be the major determinant of body iron stores in premenopausal women. In the presence of abundant and varied food supplies, the health consequences of lower iron bioavailability are unclear and require further investigation.

Biosynthesis of heme in mammals

Most iron in mammalian systems is routed to mitochondria to serve as a substrate for ferrochelatase. Ferrochelatase inserts iron into protoporphyrin IX to form heme which is incorporated into hemoglobin and cytochromes, the dominant hemoproteins in mammals. Tissue-specific regulatory features characterize the heme biosynthetic pathway. In erythroid cells, regulation is mediated by erythroid-specific transcription factors and the availability of iron as Fe/S clusters. In non-erythroid cells the pathway is regulated by heme-mediated feedback inhibition. All of the enzymes in the heme biosynthetic pathway have been crystallized and the crystal structures have permitted detailed analyses of enzyme mechanisms. All of the genes encoding the heme biosynthetic enzymes have been cloned and mutations of these genes are responsible for a group of human disorders designated the porphyrias and for X-linked sideroblastic anemia. The biochemistry, structural biology and the mechanisms of tissue-specific regulation are presented in this review along with the key features of the porphyric disorders.

Oral administration of lactoferrin increases hemoglobin and total serum iron in pregnant womenThis paper is one of a selection of papers published in this Special Issue, entitled 7th International Conference on Lactoferrin: Structure, Function, and Applications, and has undergone the Journal's usual peer review process

Iron deficiency anemia (IDA) during pregnancy continues to be of world-wide concern. IDA is a risk factor for preterm delivery and subsequent low birth weight, and possibly for poor neonatal health. Iron supplementation in pregnancy is a widely recommended practice, yet intervention programs have met with many controversies. In our study, 300 women at different trimesters of pregnancy were enrolled in a trial of oral administration of ferrous sulfate (520 mg once a day) or 30% iron-saturated bovine lactoferrin (bLf) (100 mg twice a day). Pregnant women refusing treatment represented the control group. In this group hemoglobin and total serum iron values measured after 30 d without treatment decreased significantly, especially in women at 18–31 weeks of pregnancy. In contrast, after 30 d of oral administration of bLf, hemoglobin and total serum iron values increased and to a greater extent than those observed in women treated orally for 30 d with ferrous sulfate, independently of the trimester of pregnancy. Unlike ferrous sulfate, bLf did not result in any side effects. These findings lead us to hypothesize that lactoferrin could influence iron homeostasis directly or through other proteins involved in iron transport out of the intestinal cells into the blood.

The NRAMP family of metal-ion transporters

The family of NRAMP metal ion transporters functions in diverse organisms from bacteria to human. NRAMP1 functions in metal transport across the phagosomal membrane of macrophages, and defective NRAMP1 causes sensitivity to several intracellular pathogens. DCT1 (NRAMP2) transport metal ions at the plasma membrane of cells of both the duodenum and in peripheral tissues, and defective DCT1 cause anemia. The driving force for the metal-ion transport is proton gradient (protonmotive force). In DCT1 the stoichiometry between metal ion and proton varied at different conditions due to a mechanistic proton slip. Though the metal ion transport by Smf1p, the yeast homolog of DCT1, is also a protonmotive force, a slippage of sodium ions was observed. The mechanism of the above phenomena could be explained by a combination between transporter and channel mechanisms.

Single-cell FRET imaging of transferrin receptor trafficking dynamics by Sfp-catalyzed, site-specific protein labeling

Fluorescence imaging of living cells depends on an efficient and specific method for labeling the target cellular protein with fluorophores. Here we show that Sfp phosphopantetheinyl transferase-catalyzed protein labeling is suitable for fluorescence imaging of membrane proteins that spend at least part of their membrane trafficking cycle at the cell surface. In this study, transferrin receptor 1 (TfR1) was fused to peptide carrier protein (PCP), and the TfR1-PCP fusion protein was specifically labeled with fluorophore Alexa 488 by Sfp. The trafficking of transferrin-TfR1-PCP complex during the process of transferrin-mediated iron uptake was imaged by fluorescence resonance energy transfer between the fluorescently labeled transferrin ligand and TfR1 receptor. We thus demonstrated that Sfp-catalyzed small molecule labeling of the PCP tag represents a practical and efficient tool for molecular imaging studies in living cells.

The acute phase response alters cationic amino acid transporter expression in growing chickens (Gallus gallus domesticus)

The effect of an acute phase response (APR) on cationic amino acid transporter (CAT1-3) mRNA expression in liver, muscle, bursa and thymus was determined in broiler strain chickens. The APR was initiated by injecting Salmonella typhimurium lipopolysaccharide subcutaneously (LPS; 1 mg/kg bw). In Experiment 1, CAT1-3 mRNA expression was determined at multiple time points following LPS administration. LPS increased bursa and liver total and high affinity CAT mRNA expression (P<0.05) and transiently increased pectoralis total CAT mRNA expression (P<0.05). Total CAT mRNA expression in the thymus decreased 7.7-fold from 0 to 8 h after LPS injection (P<0.05). In Experiment 2, fasted chicks were uninjected or LPS-injected. LPS increased total and high affinity CAT mRNA 2-fold in both the bursa and liver (P<0.05) and did not change thymus total and high affinity CAT mRNA expression (P>0.05). LPS increased liver weight only (P<0.05) and did not alter the plasma lysine and arginine concentration (P>0.05). In Experiments 3 and 4, thymocyte proliferation and total protein content were dependent upon the media lysine concentration (P<0.001). The inability of the thymus to compete for lysine and arginine during the APR may limit the ability of thymocytes to develop during infections.

Iron bioavailability in prenatal multivitamin supplements with separated and combined iron and calcium

OBJECTIVE

To compare iron absorption of a prenatal multivitamin supplement containing both iron and calcium (HICA) to that of another multivitamin containing a lower iron dose and no calcium (LI).

METHODS

In a crossover study, serum iron was measured in 12 healthy women administered HICA and LI separately on 2 different occasions. Blood samples were taken at 0, 1, 2, 3, 4, 6, and 8 hours after administration of each supplement.

RESULTS

The values of the area under the concentration-time curve (AUC) were not significantly different between LI (79.1 +/- 36.0 micro M*h) and HICA (91.4 +/- 50.4 micro M*h) (P =.37). After standardizing the AUC for dose, the relative absorption over the 8-hour time period was significantly higher for LI (2.3 +/-.0 micro M*h/mg) than for HICA (1.5 +/- 0.8 micro M*h/mg) (P =.021).

CONCLUSION

The absorption of iron from a low-iron-containing supplement was similar to that from a supplement with almost twice the amount of iron, due possibly to the exclusion of calcium in the LI product. Thus, while offering similar amounts of iron, the LI supplement may be better tolerated by women who are sensitive to iron-induced adverse effects.

Hereditary hemochromatosis is reflected in the iron isotope composition of blood

It has recently been shown that the iron isotopic composition of blood differs between individuals and sexes, which is supposed to reflect individual differences in iron metabolism. We hypothesized that patients suffering from hereditary hemochromatosis would demonstrate alterations in the iron isotopic composition of blood due to persistent up-regulation of intestinal iron absorption. Blood from 30 patients with homozygous C282Y hemochromatosis was analyzed for iron isotopic composition by a newly developed technique using multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). Blood of patients with hemochromatosis is characterized by a higher 56Fe/54Fe isotope ratio than blood of healthy individuals, which are either members of an age-matched control group (n = 10; P &lt; .001) or young adults (n = 36; P &lt; .001). In patients with hereditary hemochromatosis, the 56Fe/54Fe isotope ratio of blood significantly correlates with total-body iron accumulation, severity of clinical disease, and the need for regular phlebotomies to prevent iron reaccumulation. We conclude that blood of patients with hereditary hemochromatosis contains more of the heavier iron isotopes than blood of healthy individuals. The primary determinant of the iron isotopic composition of blood appears to be isotope-sensitive iron absorption in the intestine and the efficiency of this process.

Calorimetric studies of melanotransferrin (p97) and its interaction with iron

The mammalian molecule melanotransferrin (mTf), also called p97, is a member of the transferrin family of molecules. It exists in both secreted and glycosylphosphatidylinositol-anchored forms and is thought to play a role in angiogenesis and in transporting iron across the blood brain barrier. The binding affinity of iron to this molecule has not been formally established. Here, the binding of ferric ion (chelated with a 2-fold molar ratio of nitrilotriacetate) to mTf has been studied using isothermal titration calorimetry and differential scanning calorimetry. One iron-binding site was determined for mTf with similar binding characteristics to other transferrins. In the absence of bicarbonate, binding occurs quickly with an apparent association constant of 2.6 x 10(7) M(-1) at 25 degrees C. The presence of bicarbonate introduces kinetic effects that prevent direct determination of the apparent binding constant by isothermal titration calorimetry. Differential scanning calorimetry thermograms of mTf unfolding in the presence and absence of iron were therefore used to determine the apparent binding constant in the bicarbonate-containing system; at pH 7.5 and 25 degrees C, iron binding occurs in a 1:1 ratio with a K(app) of 4.4 x 10(17) M(-1). This affinity is intermediate between the high and low affinity lobes of transferrin and suggests that mTf is likely to play a significant role in iron transport where the high affinity lobe of transferrin is occupied or where transferrin is in proportionally low concentrations.

Identification of dietary copper- and iron-regulated genes in rat intestine

Copper and iron act at different levels on gene expression. Due to their chemical reactivity, both metals could play a role in the regulation of the protein machinery involved in their metabolism, and/or of the metabolic function they are involved in. Experimental and clinical evidences raise also the hypothesis of the existence of genes commonly regulated by both metals. Purpose of this work was to find genes modulated by copper and iron in the rat intestine. A panel of 24 animals was randomly divided into three nutritional treatments including a control, a copper-deficient and an iron-deficient diet. The positive regulation of iron responsive element (IRE)-DMT1 gene was found, with different extent, in both experimental groups. A differential display reverse transcription (DDRT)-polymerase chain reaction (PCR) analysis carried out on the rat intestinal mRNAs demonstrated the differential expression of five cDNA fragments. Among these, the Cytochrome c oxidase (COX) subunit II mitochondrial gene resulted to be regulated by both metals, the Serum and Glucocorticoids-regulated Kinase (SGK) gene mainly by iron, and an Ebnerin-like 2 kb mRNA dramatically down-regulated by copper. Two residual clones showed low identity scores with sequences present in data bank. Finally, we observed that both iron and copper are able to modulate the expression of the three characterized genes in some tissues, other than intestine.

Identification of small molecule inhibitors that distinguish between non-transferrin bound iron uptake and transferrin-mediated iron transport

Chemical genetics is an emerging field that takes advantage of combinatorial chemical and small molecule libraries to dissect complex biological processes. Here we establish a fluorescence-based assay to screen for inhibitors of iron uptake by mammalian cells. Using this approach, we screened the National Cancer Institute's Diversity Set library for inhibitors of non-transferrin bound iron uptake. This screen identified 10 novel small molecule inhibitors of iron transport with IC(50) values that ranged from 5 to 30 microM. Of these ten compounds, only two blocked uptake of iron mediated by transferrin. Thus, this study characterizes the first small molecule inhibitors that distinguish between different pathways of iron transport.

Iron, ferritin, and nutrition

Ferritin, a major form of endogenous iron in food legumes such as soybeans, is a novel and natural alternative for iron supplementation strategies where effectiveness is limited by acceptability, cost, or undesirable side effects. A member of the nonheme iron group of dietary iron sources, ferritin is a complex with Fe3+ iron in a mineral (thousands of iron atoms inside a protein cage) protected from complexation. Ferritin illustrates the wide range of chemical and biological properties among nonheme iron sources. The wide range of nonheme iron receptors matched to the structure of the iron complexes that occurs in microorganisms may, by analogy, exist in humans. An understanding of the chemistry and biology of each type of dietary iron source (ferritin, heme, Fe2+ ion, etc.), and of the interactions dependent on food sources, genes, and gender, is required to design diets that will eradicate global iron deficiency in the twenty-first century.