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Intravenous iron as adjuvant therapy: a two-edged sword?

The importance of iron in the manufacture of erythrocytes is self-evident. In recent years, the treatment of anaemia of end-stage renal disease with recombinant human erythropoietin (epoetin) has been optimized by adequate iron supply. Intravenous therapy with dextran-free iron compounds has become the ideal and necessary companion of epoetin therapy. Anxiety has been expressed by clinicians and researchers over the impact of excess levels of iron following i.v. administration. Their concerns have included the potential for short-term side effects such as anaphylactic reactions and response to 'free iron'. Long-term concerns have included the possibility of increased infection, oxidative stress and cardiovascular disease with higher levels of iron. The literature also implies that i.v. iron could be a 'two-edged sword', i.e. on the one hand, it optimizes epoetin therapy, while on the other, it puts the patient at greater risk of other complications. This review assesses the evidence for these concerns and concludes that i.v. therapy with dextran-free iron compounds, such as iron sucrose, optimizes epoetin therapy with no direct evidence of any short-term or long-term complications.

Anemia↗

The usefulness of elemental iron for cereal flour fortification: a SUSTAIN Task Force report. Sharing United States Technology to Aid in the Improvement of Nutrition.

Fortification of cereal flours may be a useful public health strategy to combat iron deficiency. Cereal flours that are used shortly after production (e.g., baking flour) can be fortified with soluble iron compounds, such as ferrous sulfate, whereas the majority of flours stored for longer periods is usually fortified with elemental iron powders to avoid unacceptable sensory changes. Elemental iron powders are less well absorbed than soluble iron compounds and they vary widely in their absorption depending on manufacturing method and physicochemical characteristics. Costs vary with powder type, but elemental iron powders are generally less expensive than ferrous sulfate. This review evaluates the usefulness of the different elemental iron powders based on results from in vitro studies, rat assays, human bioavailability studies, and efficacy studies monitoring iron status in human subjects. It concludes that, at the present time, only electrolytic iron powder can be recommended as an iron fortificant. Because it is only approximately half as well absorbed as ferrous sulfate, it should be added to provide double the amount of iron.

Anemia, Iron-Deficiency↗

Myxochelin A, a new iron-chelating compound from Angiococcus disciformis (Myxobacterales). Production, isolation, physico-chemical and biological properties.

Myxochelin A, a new catechole siderophore, was isolated from the culture broth of the myxobacterium, Angiococcus disciformis strain An d30. As is the case with other iron-chelating compounds the production of myxochelin A could be markedly increased up to 44 mg/liter by fermentation at low iron concentrations (10(-7) M FeCl3). The new substance showed weak activity against some bacteria.

Chemical Phenomena↗

Primordial carbonylated iron-sulfur compounds and the synthesis of pyruvate.

Experiments exploring the potential catalytic role of iron sulfide at 250 degrees C and elevated pressures (50, 100, and 200 megapascals) revealed a facile, pressure-enhanced synthesis of organometallic phases formed through the reaction of alkyl thiols and carbon monoxide with iron sulfide. A suite of organometallic compounds were characterized with ultraviolet-visible and Raman spectroscopy. The natural synthesis of such compounds is anticipated in present-day and ancient environments wherever reduced hydrothermal fluids pass through iron sulfide-containing crust. Here, pyruvic acid was synthesized in the presence of such organometallic phases. These compounds could have provided the prebiotic Earth with critical biochemical functionality.

Carbon Monoxide↗

Use of Mishell-Dutton culture for the detection of the immunosuppressive effect of iron-containing compounds.

Mishell-Dutton culture, known as an in vitro model for the evaluation of the humoral immune response of mice spleen cells to sheep red blood cells (SRBC), was used to study the immunosuppressive effect of iron-containing compounds. This response was indicated by the number of antibody forming cell (AFC) per million nucleated cells. Ferrous sulfate and ferric citrate (0.1 mM), when continuously present in Mishell-Dutton culture, significantly decreased the SRBC AFC response by approximately 63% and 86% of the control values, respectively. Ferric citrate, preincubated (24 h) with spleen cells and followed by lavage, significantly decreased the SRBC AFC response by approximately 54% of the control values. Primary and iron-treated coal, in concentrations ranging from 40 micrograms.ml-1 to 120 micrograms.ml-1, significantly decreased the SRBC AFC response when continuously present in Mishell-Dutton culture. Iron-treated coal, suppressed this response, in dose-dependent amounts, to a greater extent than did the primary coal:73% versus 54% at 120 micrograms.ml-1. We concluded that Mishell-Dutton culture is suitable for studying the immunotoxicity of iron and these results may contribute to explain a decrease of host resistance against parasitic and bacterial infection in workers exposed to iron.

Animals↗

Cytotoxin (leukotoxin) production by Pasteurella haemolytica: requirement for an iron-containing compound.

In studies of Pasteurella haemolytica type 1 cytotoxin, filter-sterilized culture supernatants from organisms grown in RPMI-1640 tissue culture medium generally have been used. Supplementation of the medium with 7% bovine fetal serum was shown to be necessary for maximal cytotoxin production, as measured by percentage of bovine peripheral blood leukocytes that were killed. The serum-induced increase in cytotoxicity could not be explained simply by a greater percentage of increase in the number of viable organisms produced in the enriched medium. There also was no correlation between encapsulation of the organisms and cytotoxin production. Several natural iron-containing proteins including transferrin, lactoferrin, conalbumin, and hemoglobin stimulated cytotoxin production in lieu of bovine fetal serum, leading to the conclusion that one function of serum supplementation may be to increase the medium's iron concentration. A number of additional iron-containing and iron-chelating compounds were tested, with the conclusion that the iron concentration of the growth medium, as well as the presence of a suitable carrier molecule, may be critical for efficient cytotoxin production by P haemolytica.

Cytotoxins↗

Sodium iron NaFeEDTA as an iron fortification compound in Central America. Absorption studies.

Studies were performed in seven children and 98 adults to compare the proportion of iron absorbed when administered as ferric sulfate (Fe2(SO4)3), NaFeEDTA, hemoglobin (Hb), and ferrous ascorbate. Studies in children (mostly iron deficient) showed that when the compounds were given with a milk-rice-sugar formula totalling 5 mg Fe, iron from hemoglobin was absorbed best, followed by NaFeEDTA and by Fe2(SO4)3 (mean percent absorption +/-SD = 34.5 +/- 1.5, 8.6 +/- 1.9 and 3.3 +/- 1.5, respectively). Studies in normal or iron deficient adults also demonstrated a better absorption of iron from NaFeEDTA than from Fe2(SO4)3 whether these compounds were given in an aqueous solution (5 mg Fe) or with a standard meal consisting of beans, tortillas, bread, and coffee providing also a total of 5 mg Fe. Hb iron under the same conditions was absorbed in the same proportion to the reference iron ascorbate, always being higher than iron absorbed from the other compounds. Fe2(SO4)3 and NaFeEDTA mixed in the same meal were absorbed in the same proportion as when NaFeEDTA alone was added to the meal and 2 to 3 times better than when Fe2(SO4)3 alone was added to the meal. Addition of desferrioxamine depressed iron absorption from Fe2(SO4)3 and NaFeEDTA, the latter being less affected. Addition of ascorbic acid increased absorption from both. When the compounds were added to the meal to provide 50 mg of iron, percent absorption was depressed in relation to the smaller iron dose in the case of Fe2(SO4)3 and Hb but remained unaltered in the case of NaFeEDTA. Addition of 45 mg Fe as Fe2(SO4)3 or NaFeEDTA to 0.4 mg Fe from the Hb in the meal did not change Hb iron absorption. Addition of 45 mg Fe as Hb or NaFeEDTA to 0.4 mg Fe from Fe2(SO4)3 in the meal enhanced iron absorption from the latter in the same proportions. Addition of 45 mg Fe as Fe2(SO4)3 and Hb to 0.4 mg Fe as NaFeEDTA in the meal respectively depressed and enhanced iron absorption from NaFeEDTA. These studies indicate that NaFeEDTA, Fe2(SO4)3 and nonheme food iron from a common pool different from the heme pool but which is changed in its characteristics by the presence of NaFeEDTA, resulting in a better absorption of iron.

Absorption↗

Biosynthesis of the iron-transport compound enterochelin: mutants of Escherichia coli unable to synthesize 2,3-dihydroxybenzoate.

Mutants of Escherichia coli K-12 blocked in each of the three enzymatic reactions between chorismate and 2,3-dihydroxybenzoate, in the pathway leading to the iron-sequestering compound enterochelin, have been isolated and biochemically characterized. The three genes concerned (designated entA, entB and entC) have been shown to be clustered on the chromosome between purE and gal and to be located near minute 14 by cotransduction with the purE, lip, and fep genes. entA, entB, and entC were shown to be the structural genes for 2,3-dihydro-2,3-dihydroxybenzoate dehydrogenase, 2,3-dihydro-2,3-dihydroxybenzoate synthetase, and isochorismate synthetase, respectively.

Benzoates↗

Phosphate compounds as iron chelators in animal cell cultures.

We have studied the capacity of a number of phosphate compounds to act in the double role as a phosphate source and a detoxifier of ferric chloride hydroxo compounds, i.e. as Fe(III) chelators. The tested compounds were: orthophosphate, trimetaphosphate, alpha-glycerophosphate, beta-glycerophosphate, phytic acid, and phosphorylcholine; the test organism the ciliate protozoon Tetrahymena thermophila, an animal cell; and the nutrient medium was synthetic, consisting solely of low-molecular-weight compounds. We assessed growth rates of cells in two experimental series. First, phosphate-starved cells were exposed to the tested phosphate compound as the only phosphate source and the ferric chloride concentrations were varied stepwise from 0 to 1000 microM. Second, we offered the cells orthophosphate as a phosphate source and selected phosphate compounds as chelators. The cell growth results allow the following conclusions: orthophosphate, trimetaphosphate, alpha-glycerophosphate, and beta-glycerophosphate are excellent phosphate sources; trimetaphosphate, alpha-glycerophosphate, beta-glycerophosphate, and phytic acid are excellent Fe(III) chelators; of the tested compounds trimetaphosphate, alpha-glycerophosphate, and beta-glycerophosphate are excellent in the double role as a phosphate source and a ferric chloride hydroxo detoxifier, i.e. as a Fe(III) chelator.

Animals↗

Use of heme compounds as iron sources by pathogenic neisseriae requires the product of the hemO gene.

Heme compounds are an important source of iron for neisseriae. We have identified a neisserial gene, hemO, that is essential for heme, hemoglobin (Hb), and haptoglobin-Hb utilization. The hemO gene is located 178 bp upstream of the hmbR Hb receptor gene in Neisseria meningitidis isolates. The product of the hemO gene is homologous to enzymes that degrade heme; 21% of its amino acid residues are identical, and 44% are similar, to those of the human heme oxygenase-1. DNA sequences homologous to hemO were ubiquitous in commensal and pathogenic neisseriae. HemO genetic knockout strains of Neisseria gonorrhoeae and N. meningitidis were unable to use any heme source, while the assimilation of transferrin-iron and iron-citrate complexes was unaffected. A phenotypic characterization of a conditional hemO mutant, constructed by inserting an isopropyl-beta-D-thiogalactopyranoside (IPTG)-regulated promoter upstream of the ribosomal binding site of hemO, confirmed the indispensability of the HemO protein in heme utilization. The expression of HemO also protected N. meningitidis cells against heme toxicity. hemO mutants were still able to transport heme into the cell, since both heme and Hb could complement an N. meningitidis hemA hemO double mutant for growth. The expression of the HmbR receptor was reduced significantly by the inactivation of the hemO gene, suggesting that hemO and hmbR are transcriptionally linked. The expression of the unlinked Hb receptor, HpuAB, was not altered. Comparison of the polypeptide patterns of the wild type and the hemO mutant led to detection of six protein spots with an altered expression pattern, suggesting a more general role of HemO in the regulation of gene expression in Neisseriae.

Amino Acid Sequence↗

Differential protein expression during growth of Acidithiobacillus ferrooxidans on ferrous iron, sulfur compounds, or metal sulfides.

A set of proteins that changed their levels of synthesis during growth of Acidithiobacillus ferrooxidans ATCC 19859 on metal sulfides, thiosulfate, elemental sulfur, and ferrous iron was characterized by using two-dimensional polyacrylamide gel electrophoresis. N-terminal amino acid sequencing and mass spectrometry analysis of these proteins allowed their identification and the localization of the corresponding genes in the available genomic sequence of A. ferrooxidans ATCC 23270. The genomic context around several of these genes suggests their involvement in the energetic metabolism of A. ferrooxidans. Two groups of proteins could be distinguished. The first consisted of proteins highly upregulated by growth on sulfur compounds (and downregulated by growth on ferrous iron): a 44-kDa outer membrane protein, an exported 21-kDa putative thiosulfate sulfur transferase protein, a 33-kDa putative thiosulfate/sulfate binding protein, a 45-kDa putative capsule polysaccharide export protein, and a putative 16-kDa protein of unknown function. The second group of proteins comprised those downregulated by growth on sulfur (and upregulated by growth on ferrous iron): rusticyanin, a cytochrome c(552), a putative phosphate binding protein (PstS), the small and large subunits of ribulose biphosphate carboxylase, and a 30-kDa putative CbbQ protein, among others. The results suggest in general a separation of the iron and sulfur utilization pathways. Rusticyanin, in addition to being highly expressed on ferrous iron, was also newly synthesized, as determined by metabolic labeling, although at lower levels, during growth on sulfur compounds and iron-free metal sulfides. During growth on metal sulfides containing iron, such as pyrite and chalcopyrite, both proteins upregulated on ferrous iron and those upregulated on sulfur compounds were synthesized, indicating that the two energy-generating pathways are induced simultaneously depending on the kind and concentration of oxidizable substrates available.

Acidithiobacillus↗

Melano-macrophage centres and endocytic cells in kidney and spleen of pearl gouramy and platyfish (Anabantidae, Poeciliidae: Teleostei).

The structure and putative cellular content of melano-macrophage centres (MMCs) and single macrophages in kidney and spleen of two teleosts, pearl gouramy Trichogaster leeri (Bleeker) and platyfish Xiphophorus maculatus (Günther), are described and compared. The MMCs were confined to the haemopoetic tissue in both species, and were markedly more prominent in pearl gouramy than in platyfish. They were rich in iron-compounds, probably haemosiderin, in the former species, whereas they contained mainly iron-free pigments, probably lipofuscin, in the latter species. We suggest that the kidney and spleen MMCs are involved in the regular storage, relocation and recycling of iron-compounds of effete or damaged red blood cells in healthy pearl gouramies, whereas they function more or less as a deposit for undegradable and potentially harmful iron-free cell debris in the corresponding organs in healthy platies. Numerous single macrophages took up much intraperitoneally injected horse ferritin in the kidney and spleen haemopoetic tissue in platies, whereas these cells contain much iron-containing pigment, probably haemosiderin, in the control pearl gouramies. We suggest that these cells are able to play a role in cleansing the circulation of foreign macromolecules and particles in platies, whereas they are mainly involved in the regular uptake of scavenger iron-containing compounds in pearl gouramies.

Animals↗

Halide Ion Addition to Bismuth-Containing Iron Carbonyl Compounds: Synthesis and Characterization of the Two Bridged-Butterfly Cluster Compounds [Et(4)N][(&mgr;-H)Fe(2)(CO)(6)Bi(2){&mgr;-Fe(CO)(4)}] and [{PhCH(2)NMe(3)}{(&mgr;-H)Fe(2)(CO)(6)Bi(2)(&mgr;-Cl)(2)}](infinity) and Stabilization of Reduced-Hypervalent Bismuth Centers by Coordination to a Metal Center in [PhCH(2)NMe(3)](3)[Bi(3)Cl(4)(&mgr;-Cl)(4){Fe(CO)(3)}].

The reaction of [Q](2)[Bi(4)Fe(4)(CO)(13)] ([Q](2)[1]; [Q] = [Et(4)N](+), [PhCH(2)NMe(3)](+)) with MePCl(2) in MeCN is a complicated reaction which gives different results depending upon the stoichiometry of the reaction. At a ratio of 1:1.33 (cluster:phosphine), the reaction yields a mixture of the new bismuth-iron carbonyl compounds [Q][(&mgr;-H)Fe(2)(CO)(6)Bi(2){Fe(CO)(4)}] ([Q][2]), which has a tetrahedral Fe(2)Bi(2) core edge-bridged across the bismuth centers by an [Fe(CO)(4)](2)(-) fragment, and [Q](3)[Bi(3)Cl(4)(&mgr;-Cl)(4){Fe(CO)(3)}] ([Q](3)[3]), containing a reduced complex ion [Bi(3)Cl(8)](-) stabilized by coordination to an iron tricarbonyl fragment. Extended Hückel molecular orbital calculations on this unusual anion are consistent with each bismuth atom possessing the same reduced oxidation state of +2.33. The compound [Et(4)N][2] crystallizes in the triclinic space group P&onemacr; (No. 2) with a = 10.246(2) Å, b = 11.859(2) Å, c = 12.474(2) Å, alpha = 71.11(3) degrees, beta = 79.60(3) degrees, gamma = 76.37(3) degrees, V = 1384.7(4) Å(3), and Z = 2, while [PhCH(2)NMe(3)](3)[3].0.87Et(2)O was characterized in the orthorhombic space group Pbca (No. 61) with a = 20.801(4) Å, b = 19.937(4) Å, c = 25.480(5) Å, V = 10566.8(36) Å(3), and Z = 8. When the reaction is carried out at a ratio of 1:2, the novel hydride [{Q}{(&mgr;-H)Fe(2)(CO)(6)Bi(2){&mgr;-Cl}(2)}](infinity) ([{Q}{4}](infinity)) is isolated. This cluster also has a "tetrahedral" core, with the Bi-Bi vector bridged by a chloride ligand and the molecules joined into infinite polymeric chains in the solid state by the second intermolecularly-bridging chloride ligand. [{PhCH(2)NMe(3)}{4}](infinity) crystallizes in the monoclinic space group P2(1)/n (No. 14) with a = 7.864(2) Å, b = 22.465(4) Å, c = 13.797(3) Å, beta = 105.96(3) degrees, V = 2343.5(9) Å(3), and Z = 4. The metal framework of [4](-) is similar to that of [2](-) with the notable exception that the Bi-Bi bond present in [2](-) is missing in [4](-) because of the additional electrons provided by the chloride ions. At stoichiometries greater than 2:1, the previously reported [Fe(CO)(4)Bi(2)Cl(6)](2)(-) ion is formed.

Journal Article↗

Isolation and structure of nocobactin NA, a lipid-soluble iron-binding compound from Nocardia asteroides.

Nocobactin NA, a lipid-soluble iron-chelating product with an unusual and characteristic u.v.-absorption spectrum, was isolated from Nocardia asteroides grown under conditions of iron deficiency. Its structure was determined by physical methods and by synthesis of one of its degradation products. Nocobactin NA was obtained as a homologous mixture of compounds with side chains of differing length, and resembles mycobactin M in structure except that it has an oxazole ring in place of an oxazoline ring, and the side chains in the cobactin fragment are considerably shorter.

Chemical Phenomena↗

Helicobacter pylori infection, iron absorption, and gastric acid secretion in Bangladeshi children.

BACKGROUND: Nonheme-iron absorption requires an acidic milieu. Reduced gastric acid output as a consequence of Helicobacter pylori infection could be an important limiting factor for iron absorption. OBJECTIVE: We measured gastric acid output and iron absorption from a non-water-soluble iron compound (ferrous fumarate) and a water-soluble iron compound (ferrous sulfate) in children with and without H. pylori infection. DESIGN: Gastric acid output was quantified before (basal acid output, or BAO) and after pentagastrin stimulation (stimulated acid output, or SAO) in 2-5-y-old children with iron deficiency anemia who were (n = 13) or were not (n = 12) infected with H. pylori. Iron absorption was measured by using a double-stable-isotope technique. H. pylori-infected children were studied before and after eradication therapy. RESULTS: BAO and SAO were significantly lower in the H. pylori-infected children (0.2 +/- 0.2 and 1.6 +/- 0.9 mmol/h, respectively) than in the uninfected children (0.9 +/- 0.7 and 3.1 +/- 0.9 mmol/h, respectively; P = 0.01 and P < 0.005). BAO and SAO improved to 0.8 +/- 1.3 and 3.3 +/- 2.4 mmol/h, respectively, after therapy. Iron absorption from ferrous sulfate was significantly greater than that from ferrous fumarate both before (geometric : 19.7% compared with 5.3%; P < 0.0001) and after (22.5% compared with 6.4%; P < 0.0001) treatment in H. pylori-infected children. Corresponding values for uninfected children were 15.6% and 5.4%, respectively (P < 0.001; n = 12). CONCLUSIONS: Iron absorption from ferrous fumarate was significantly lower than that from ferrous sulfate in both H. pylori-infected and uninfected Bangladeshi children. Treatment of H. pylori infection improved gastric acid output but did not significantly influence iron absorption. The efficacy of ferrous fumarate in iron fortification programs to prevent iron deficiency in young children should be evaluated.

Anemia, Iron-Deficiency↗

Liver iron quantification: studies in aqueous iron solutions, iron overloaded rats, and patients with hereditary hemochromatosis.

For the noninvasive liver iron quantification by MRI in human iron overload diseases, fundamental proton relaxation mechanisms were studied in aqueous solutions with ferritin and other iron compounds, in experimentally iron overloaded rats, and in patients with iron overload diseases. MR-relaxation rates as a function of iron concentrations in the range of 0-7.5 mg Fe/g aqueous iron solutions, 0-5.4 mg Fe/g rat liver in vivo, and 0.16-4.9 mg Fe/g human liver in vivo were determined from multi- and sets of single-spin echo sequences (1.5 T imager). As predicted by theory, transverse relaxation rates (1/T2) in aqueous iron solutions, in liver tissue of rats, and in human liver tissue increased linearly with the iron concentration. A preliminary calibration for the liver iron quantification by MRI was performed from in vivo measurements of liver 1/T2-relaxation rates and liver iron quantification by atomic absorption spectroscopy in biopsies from 13 patients. With the single spin-echo method, precise in vivo liver iron quantification in humans also above 2.0 mg Fe/g liver tissue (T2 < 15 ms) should be accomplished on any imager with shortest spin-echo time available, at least TE < 20 ms.

Adult↗