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PubMed2002

Reduction of iron by extracellular iron reductases: implications for microbial iron acquisition.

The extracellular enzymatic reduction of iron by microorganisms has not been appropriately considered. In this study the reduction and release of iron from ferrioxamine were examined using extracellular microbial iron reductases and compared to iron mobilization by chemical reductants, and to chelation by EDTA and desferrioxamine. A flavin semiquinone was formed during the enzymatic reduction of ferrioxamine, which was consistent with the 1 e(-) reduction of iron by an enzyme. The rates for the enzymatic reactions were substantially faster than both the 2 e(-) chemical reductions and the chelation reactions. The rapid rates of the enzymatic reduction reactions demonstrated that these enzymes are capable of accomplishing the extracellular mobilization of iron required by microorganisms. The data suggest that mechanistically there are two phases for the mobilization and transport of iron by those microorganisms that produce both extracellular iron reductases and siderophores, with reduction being the principle pathway.

Bacteria↗
PubMed1976

Iron deficiency in an Eskimo village. The value of serum ferritin in assessing iron nutrition before and after a three-month period of iron supplementation.

The serum ferritin concentration, a new means of assessing iron nutrition, was utilized in conjunction with the hematocrit value, serum iron concentration, and total iron binding capacity to determine the effect of a three-month period of iron supplementation in a group of 146 Eskimo children in Chevak, Alaska. Before treatment, 41% of the children had concentrations of serum ferritin below normal, 18% had a subnormal serum transferrin saturation, and 26% were anemic. After supplementation, only 6% had a subnormal serum ferritin concentration. Despite this evidence of improved iron stores in the group as a whole, the prevalence of low serum transferrin saturation and of anemia remained high, 15% and 17%, respectively. These results could be explained by a high incidence of infection, which, like iron deficiency, is associated with anemia and a low serum transferrin saturation. We conclude that the serum ferritin determination reflected an improvement in iron nutrition that was not as readily apparent by other measurements, and that factors other than iron deficiency also played an important role in the mild anemia that was prevalent in Chevak.

Adolescent↗
PubMed2003

Iron regulatory protein 2 as iron sensor. Iron-dependent oxidative modification of cysteine.

Iron regulatory protein 2 coordinates cellular regulation of iron metabolism by binding to iron responsive elements in mRNA. The protein is synthesized constitutively but is rapidly degraded when iron stores are replete. This iron-dependent degradation requires the presence of a 73-residue degradation domain, but its functions have not yet been established. We now show that the domain can act as an iron sensor, mediating its own covalent modification. The domain forms an iron-binding site with three cysteine residues located in the middle of the domain. It then reacts with molecular oxygen to generate a reactive oxidizing species at the iron-binding site. One cysteine residue is oxidized to dehydrocysteine and other products. This covalent modification may thus mark the protein molecule for degradation by the proteasome system.

Amino Acids↗
PubMed1977

Iron-poly (sorbitol-gluconic acid) complex and iron-dextran in the treatment of severe iron deficiency anaemia.

An investigation has been carried out to study the efficacy of iron-poly (sorbitol-gluconic acid) complex (Ferastral) in the treatment of iron deficiency anaemia. Ferastral was given by the intramuscular route every second or third day in a dose of 500 mg, divided in two injections. These were compared with the results of a group treated with iron-dextran given by Total Dose Infusion (TDI). A total of 38 patients were treated with either Ferastral or iron-dextran by TDI, respectively, given according to random allocation. The total dose of iron given in both groups was 1 500 mg of elemental iron. The parameters investigated were haematocrit and haemoglobin. Side-effects were also recorded. The results in the group treated with Ferastral where the mean initial haemoglobin value was 9.5 g/100 ml showed a mean haemoglobin increase to 13.2 g/100 ml after eight weeks. Initial haemoglobin values and haemoglobin increase for iron-dextran by TDI were quite similar. Three patients in the Ferastral group had transient discolouration at the site of injection and one patient in the iron-dextran TDI-group had a serious allergic reaction.

Anemia, Hypochromic↗
PubMed1993

Iron chelators may enhance erythropoiesis by increasing iron delivery to haematopoietic tissue and erythropoietin response in iron-loading anaemia.

Based on the mode of action of iron chelators, one might expect a decrease in bone marrow iron availability, resulting in worsening of the anaemia in certain types of iron-loading anaemia. However, improvement of anaemia or reduction in transfusion requirements during chelation treatment has been reported in various types of iron-loading anaemia. It is suggested that iron chelators act as mediators facilitating iron release from storage sites and its delivery to haematopoietic tissues. In addition, a reduction of iron stores may upregulate erythropoietin response and bring about a decrease of disease activity in inflammatory disorders, resulting in a haemoglobin rise. Large trials with (oral) iron chelators are required to verify these possible effects.

Anemia↗
PubMed1993

Non-transferrin-bound-iron in serum and low-molecular-weight-iron in the liver of dietary iron-loaded rats.

1. The feeding of 0.5% (3,5,5-trimethylhexanoyl)ferrocene (TMH-ferrocene) in rats resulted in a severe and progressive liver siderosis (total liver iron, 30 mg/g liver wet weight, after 30 weeks). 2. High concentrations of an iron-rich ferritin (up to 250 mg/l) were detected in serum of heavily iron-loaded rats forming a large fraction of non-transferrin-bound-iron (5000 micrograms/dl in maximum). 3. Ferritin and not haemosiderin was the major iron storage protein in the liver. 4. The total liver iron concentration (from 0.4 to > 30 mg Fe/g wet wt) but not the cytosolic low-molecular-weight-iron fraction (from 0.5 to 2.5 microM) was extremely increased during iron-loading.

Animals↗
PubMed1986

Structural variations in soluble iron complexes of models for ferritin: an x-ray absorption and Mössbauer spectroscopy comparison of horse spleen ferritin to Blutal (iron-chondroitin sulfate) and Imferon (iron-dextran).

Variations in the turnover of storage iron have been attributed to differences in apoferritin and in the cytoplasm but rarely to differences in the structure of the iron core (except size). To explore the idea that the iron environment in soluble iron complexes could vary, we compared horse spleen ferritin to pharmaceutically important model complexes of hydrous ferric oxide formed from FeCl3 and dextran (Imferon) or chondroitin sulfate (Blutal), using x-ray absorption (EXAFS) and Mössbauer spectroscopy. The results show that the iron in the chondroitin sulfate complex was more ordered than in either horse spleen ferritin or the dextran complex (EXAFS), with two magnetic environments (Mössbauer), one (80%-85%) like Fe2O3 X nH2O (ferritinlike) and one (15%-20%) like Fe2O3 (hematite); since sulfate promotes the formation of inorganic hematite, the sulfate in the chondroitin sulfate most likely nucleated Fe2O3 and hydroxyl/carboxyls, which are ligands common to chondroitin sulfate, ferritin and dextran most likely nucleated Fe2O3 X nH2O. Differences in the structure of the iron complexed with chondroitin sulfate or dextran coincide with altered rates of iron release in vivo and in vitro and provide the first example relating function to local iron structure. Differences might also occur among ferritins in vivo, depending on the apoferritin (variations in anion-binding sites) or the cytoplasm (anion concentration).

Animals↗
PubMed1986

The relationship between iron release, ferritin synthesis and intracellular iron distribution in mouse peritoneal macrophages. Evidence for a reduced level of metabolically available iron in elicited macrophages.

The rate of iron release from thioglycollate-elicited mouse peritoneal macrophages pulsed with 59Fe-labelled transferrin-antitransferrin immune complexes was lower than that from resident or Corynebacterium parvum-activated macrophages. Anaerobic conditions increased the rate of iron release by thioglycollate-elicited macrophages but had no effect on resident or C. parvum-activated macrophages. Thioglycollate-elicited macrophages also contained less ferritin and were deficient in their ability to synthesis ferritin. Incubation of these cells in medium containing 100 microM iron caused some increase in ferritin synthesis, but the response to iron was much less pronounced than that by resident or C. parvum-activated macrophages. In the thioglycollate-elicited macrophages, relatively less iron was incorporated into ferritin, and more into other soluble macromolecules and insoluble haemosiderin-like compounds than in the other types of macrophages. It is proposed that thioglycollate-elicited macrophages tend to divert iron to a relatively inert intracellular pool, and that this could account for their reduced ability to release iron. Such a mechanism might help to explain the reduced release of iron by liver and spleen macrophages occurring during inflammation.

Anaerobiosis↗
PubMed1991

Effects of calcium on hepatocyte iron uptake from transferrin, iron-pyrophosphate and iron-ascorbate.

Calcium stimulates hepatocyte iron uptake from transferrin, ferric-iron-pyrophosphate and ferrous-iron-ascorbate. Maximal stimulation of iron uptake is observed at 1-1.5 mM of extra-cellular calcium and the effect is reversible and immediate. Neither the receptor affinity for transferrin, nor the total amounts of transferrin associated with the cells or the rate of transferrin endocytosis are significantly affected by calcium. In the presence of calcium the rate of iron uptake of non-transferrin bound iron increases abruptly at approximate 17 degrees C and 27 degrees C and as assessed by Arrhenius plots, the activation energy is reduced in a calcium dependent manner at approx. 27 degrees C. At a similar temperature, i.e., between 25 degrees C and 28 degrees C, calcium increases the rates of cellular iron uptake from transferrin in a way that is not reflected in the rate of transferrin endocytosis. By the results of this study it is concluded that calcium increases iron transport across the plasma membrane by a mechanism dependent on membrane fluidity.

Animals↗
PubMed1977

Iron absorption in infants: high bioavailability of breast milk iron as indicated by the extrinsic tag method of iron absorption and by the concentration of serum ferritin.

Breast feeding is thought to result in a lower incidence of iron deficiency than does the use of unfortified cow milk forumalas, but there is scant documentation for this belief. The relationship of breast and cow milk feeding to absorption of iron and to iron status was investigated in a total of 45 term infants at about six months of age. Iron absorption was measured by total body counting. Laboratory assessment of iron status was based on the serum ferritin, hemoglobin, mean corpuscular volume, and transferrin saturation. The results indicated that infants fed breast milk during the entire first six to seven months of life attained greater iron stores than did those fed a cow milk formula. Breast-fed infants absorbed an average of 49% of a trace dose of extrinsic iron administered during a breast feeding in contrast to about 10% reported to be absorbed from cow milk under similar conditions. The data indicate that term infants who are breast fed may not require routine administration of supplemental iron.

Animals↗
PubMed1976

Absorption from different types of iron tablets - correlation between serum iron increase in total absorption of iron.

The absorption of iron from three different iron tablets - rapidly-disintegrating ferrous sulphate and ferrous carbonate tablets and slow-release ferrous sulphate tablets - was studied in healthy subjects with a serum iron technique and by whole-body counter measurements. A solution of ferrous sulphate was used as a reference. There were no differences in the absorption from the ferrous sulphate preparations, but the ferrous carbonate tablets were less well absorbed. Good correlation was found between the maximal serum iron response and the total absorption of iron and it was concluded that serum iron studies may be used for semiquantitative measurements of iron absorption in comparative studies on different iron preparations.

Adult↗
PubMed1979

Transferrin binding and iron transport in iron-deficient and iron-replete rat reticulocytes.

Three aspects of iron metabolism were studies in reticulocytes from iron-deficient, phlebotomized, and phenylhydrazine-treated rats: (1) the number of transferrin binding sites; (2) the uptake of 59Fe-transferrin; and (3) the ability of cytosol to mobilize 59Fe from 59Fe-labeled reticulocyte plasma membrane. The number of transferrin binding sites, assayed by measuring the binding of 125I-labeled transferrin to reticulocytes, were similar in iron-deficient and phlebotomy-induced reticulocytes, 66,000 and 75,000 binding sites/cell, respectively, but were about doubled, 120,000 binding sites/cell, in phenylhydrazine-induced reticulocytes. Uptake of 59Fe into iron-deficient reticulocytes was about one-half that for phlebotomy-induced reticulocytes and one-quarter that for phenylhydrazine-induced reticulocytes, the rates of uptake being measured as 21,540, 41,233, and 79,600 molecules of 59Fe per minute per cell, respectively. The mobilizing activity of cytosol free iron-deficient reticulocytes was also about one-half that of cytosol from phlebotomy-induced reticulocytes and about one-quarter that of cytosol from phenylhydrazine-induced reticulocytes. These results indicate that instead of a compensatory increase in these aspects of iron metabolism, the iron-deficient reticulocyte had a decreased ability to transport iron.

Anemia, Hypochromic↗
PubMed1983

Relationship among plasma iron, plasma iron turnover, and reticuloendothelial iron release.

A circadian rhythm was demonstrated in 10 males and 10 females with respective mean decreases in plasma iron concentration at 18 hr of 62% and 47% of morning values. Ferrokinetic studies performed on 5 normal males and 5 normal females showed a more rapid disappearance rate and lower plasma iron turnover in the evening. Parallel studies were done on 6 normal males in the morning and 4 normal males in the evening of the release of reticuloendothelial iron at 8 and 18 hr after intravenous injection of 59Fe chondroitin ferrous sulfate. The 6-hr release in the morning was 54.1% and in the evening 25.9%. Composite data from morning and evening showed a correlation between plasma iron level and plasma iron turnover (r = 0.76, p less than 0.001). A similar correlation existed between the plasma iron level and the percent of radioiron released from the reticuloendothelial system (r = 0.67, 0.02 less than p less than 0.05). These data are consistent with a fluctuating iron release from the reticuloendothelial cell in normal subjects, which would account for the diurnal variation in plasma iron.

Chondroitin Sulfates↗
PubMed1998

Comparative study of tolerability and efficacy of iron protein succinylate versus iron hydroxide polymaltose complex in the treatment of iron deficiency in children.

One-hundred children, 48 males and 52 females, mean age +/- SD 39.9 +/- 28.2 months (range 12 to 113) with sideropenia or sideropenic anemia were randomly divided into 2 groups of 50 patients each (groups A and B) and were treated with iron protein succinylate (group A) or iron hydroxide polymaltose complex (group B). Patients of both groups received 4 mg/kg elemental iron, maximally 80 mg daily, for 2 months. Side-effects of therapy and laboratory values (RBC, hematocrit, hemoglobin, MCV, serum iron, total iron binding capacity, and ferritin) were registered before treatment, 30 days after the beginning of therapy as well as after 60 days in order to evaluate tolerability and efficacy of the drugs. Both drugs were well tolerated and showed only few adverse reactions, which were comparable in severity and frequency. Iron protein succinylate led not only to a faster increase of hemoglobin, hematocrit, MCV, serum iron, and ferritin than iron hydroxide polymaltose complex, but the laboratory values remained higher in group A than in B even after 2 months of treatment.

Abdominal Pain↗
PubMed1977

Iron metabolism in Trypanosoma lewisi infection: serum iron and serum iron-binding capacity.

Progressive changes in iron levels, total iron binding capacity and hematocrit values in sera of rats infected with Trypanosoma lewisi are described. The host dietary group were: (1) complete or full complement; (2) iron-deficient, and (3) pair-fed or calorically restricted. The hematocrit values of T. lewisi-infected rats given the various diets were not significantly different from those of the controls. The decrease in total iron binding capacity (TIBC) of rats inoculated with T. lewisi and fed complete and pair-fed diets ranged up to 15% over uninfected controls. TIBC levels in rats fed an iron-deficient diet and inoculated with T. lewisi ranged up to 32% over uninfected controls. TIBC levels of deficient infected rats were significantly different from the controls from day 90 to infection to the end of the observation period. Serum iron (SI) values of non-infected rats regardless of dietary regimen showed significantly higher values than T. lewisi-infected animals between days 95 and 120. The average SI value, for this period, in adequately fed control rats was 204 +/- 7 microgram/100 ml as compared to 172 +/- 5 microgram/100 for trypanosome-infected rats. SI levels of rats on a pair-fed diet and infected with T. lewisi decreased to 17% over uninfected controls. SI levels of animals on an iron-deficient diet and infected with T. lewisi decreased up to 76% over uninfected controls.

Animals↗
PubMed2000

Regulation of intracellular iron levels in iron-acceptor and iron-donor cells.

In recent years many new genes and proteins were identified with crucial functions in iron metabolism. This gave an explosion of our knowledge and understanding of iron related disorders. Mutations have been found that are responsible for disturbances in iron transport, leading to either iron overload or iron deficiency. For experts in the field, these new findings clarify the sky and open new routes for exploring hitherto hidden fields of research. For the physician, however, iron metabolism may become even more complicated. In this review, we have tried to assemble all new iron related genes into the context of pathophysiology. Important results from animal experiments, mainly derived from knockout mouse models, are included in this review as they often explain the phenotype of human disease.

Animals↗
PubMed2006

De novo design of synthetic di-iron(I) complexes as structural models of the reduced form of iron-iron hydrogenase.

Simple synthetic di-iron dithiolate complexes provide good models of the composition of the active site of the iron-iron hydrogenase enzymes. However, the formally Fe(I)Fe(I) complexes synthesized to date fail to reproduce the precise orientation of the diatomic ligands about the iron centers that is observed in the molecular structure of the reduced form of the enzyme active site. This structural difference is often used to explain the fact that the synthetic di-iron complexes are generally poor catalysts when compared to the enzyme. Herein, density functional theory computations are used for the rational design of synthetic complexes as structural models of the reduced form of the enzyme active site. These computations suggest several possible synthetic targets. The synthesis of complexes containing five-atom S-to-S linkers of the form S(CH2)2X(CH2)2S (X = CH2, NH, or O) or pendant functionalities attached to the three-carbon framework is one method. Another approach is the synthesis of asymmetrically substituted complexes, in which one iron center has strongly electron donating ligands and the adjacent iron center has strongly electron accepting ligands. The combination of a sterically demanding S-to-S linker and asymmetric substitution of the CO ligands is predicted to be a particularly effective synthetic target.

Hydrogenase↗
PubMed1979

Normal serum iron and elevated total iron-binding capacity in iron-deficiency states.

Five nonanemic patients with normal erythrocytic indexes were found to have normal serum iron, elevated total iron-binding capacity, normal percentage of saturation of transferrin, and depleted bone marrow iron stores. These findings suggest that during the development of iron deficiency, an elevation of total iron-binding capacity occurs before the decrease of the serum iron. This may represent a compensatory mechanism to mobilize all traces of tissue iron to maintain normal erythropoiesis.

Adult↗