Competitive advantage of diferric transferrin in delivering iron to reticulocytes.

Huebers, Helmut A.; Csiba, Eva; Huebers, Eiko; Finch, Clement A.

doi:10.1073/pnas.80.1.300

Cited by 57 publications

(25 citation statements)

References 15 publications

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“…66 Each molecule of monoferric-Tf delivers less iron to erythroid precursors than holo-Tf. 65 This enables a greater number of erythroid precursors to receive a smaller portion of the iron pool to offset developing anemia and is consistent with a low mean cellular volume and mean corpuscular Hb (MCH). What controls this apportioning of iron to erythroid precursors is not completely understood, but the relation between decreased Tf concentration and the regulation of hepcidin expression has recently been further elucidated.…”

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confidence: 67%

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β-thalassemia: a model for elucidating the dynamic regulation of ineffective erythropoiesis and iron metabolism

Ginzburg

Rivella

2011

Blood

181

207

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␤-thalassemia is a disease characterized by anemia and is associated with ineffective erythropoiesis and iron dysregulation resulting in iron overload. The peptide hormone hepcidin regulates iron metabolism, and insufficient hepcidin synthesis is responsible for iron overload in minimally transfused patients with this disease. Understanding the crosstalk between erythropoiesis and iron metabolism is an area of active investigation in which patients with and models of ␤-thalassemia have provided significant insight. The dependence of erythropoiesis on iron presupposes that iron demand for hemoglobin synthesis is involved in the regulation of iron metabolism. Major advances have been made in understanding iron availability for erythropoiesis and its dysregulation in ␤-thalassemia. In this review, we describe the clinical characteristics and current therapeutic standard in ␤-thalassemia, explore the definition of ineffective erythropoiesis, and discuss its role in hepcidin regulation. In preclinical experiments using interventions such as transferrin, hepcidin agonists, and JAK2 inhibitors, we provide evidence of potential new treatment alternatives that elucidate mechanisms by which expanded or ineffective erythropoiesis may regulate iron supply, distribution, and utilization in diseases such as ␤-thalassemia. IntroductionErythroid cells are highly dependent on iron for survival. In light of this dependence, mutual regulation of erythropoiesis and iron metabolism has been proposed. However, how iron demand for erythropoiesis is communicated to the iron regulatory machinery is incompletely understood. In the past few decades, significant progress has been made to advance our understanding of iron metabolism and its regulation. Furthermore, several diseases, ␤-thalassemia in particular, have provided glimpses of the crosstalk between iron regulation and erythropoiesis. By exploring ineffective erythropoiesis (IE) and its associated dysfunctional iron regulation, this disease may lay the foundation for more completely understanding, diagnosing, and treating patients with different forms of ␤-thalassemia as well as other anemias or iron overloadrelated disorders. In this review, we focus on the current state of knowledge on the regulation of iron metabolism and attempt to elucidate the interface between iron regulation and erythropoiesis with the use of evidence in part derived from animal models of ␤-thalassemia; despite being all nonhuman models of disease, their utility as in vivo tools for experimentation is worthy of note. We discuss potential ways in which this new knowledge can be translated into clinical application for patients with ␤-thalassemia. ␤-thalassemia Clinical characteristics␤-thalassemias are caused by mutations in the ␤-globin gene or its promoter, resulting in reduced or absent ␤-globin synthesis. 1 Patients either homozygous or compound heterozygous for mutation in the ␤-globin gene present with a broad range of clinical severity; the disease course can be associated with severe transfusion dep...

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confidence: 67%

“…However, this greater affinity wanes as the iron supply is diminished. 65 Monoferric-Tf is the predominant form of Tf in circulation when Tf saturation is lowered. 66 Each molecule of monoferric-Tf delivers less iron to erythroid precursors than holo-Tf.…”

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confidence: 99%

β-thalassemia: a model for elucidating the dynamic regulation of ineffective erythropoiesis and iron metabolism

Ginzburg

Rivella

2011

Blood

181

207

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“…In addition, iron release from any form of transferrin to erythroid cells was found to be an "all or none" phenomenon, generating only apotransferrin (5)(6)(7)(8)(9)(10)(11). The most important feature is a competitive advantage of diferric over monoferric transferrin in delivering iron to reticulocytes (13). In the human system, this amounts to a 7-fold advantage, but similar competitive advantages were observed in other homologous systems, including the rabbit and the rat (4,22).…”

Section: Resultsmentioning

confidence: 99%

“…Recent studies failed to reveal functional differences in iron release between the two sites (3)(4)(5)(6)(7)(8)(9)(10)(11)(12). Instead, a competitive advantage of difemc transferrin over the two monoferric forms in delivering iron was apparent (13,14). Were there a process which could adjust the generation of diferric vs. monoferric transferrin, it would have major implications for the regulation of internal iron exchange.…”

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confidence: 99%

Occupancy of the iron binding sites of human transferrin.

Huebers¹,

Josephson²,

Huebers³

et al. 1984

Proc. Natl. Acad. Sci. U.S.A.

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The in vivo distribution of iron between the binding sites of transferrin was examined. Plasma was obtained from normal subjects under basal conditions and after in vitro and in vivo iron loading. Independent methods, including measurement of the transferrin profile after isoelectric focusing and cross immunoelectrophoresis, and determination of the iron content in the separated fractions were in agreement that there was a random distribution of iron on binding sites. This held true with in vitro loading, when iron was increased by intestinal absorption and with loading from the reticuloendothelial system. The MATERIALS AND METHODSFresh heparinized plasma samples were obtained from normal adults after an overnight fast. Loading of plasma with iron above basal levels was achieved in vitro by adding ferrous sulfate (4, 6) and in vivo either through intestinal absorption after oral ingestion of 100 mg of iron as ferrous ascorbate (molar ratio Fe/ascorbate = 1:5) or from the reticuloendothelial system through hemolysis induced by oral ingestion of 300 mg of niacin (15, 16). In both in vivo loading studies, plasma samples were obtained at basal levels of saturation and at 20-min intervals for up to 6 hr after drug ingestion. These plasma samples were trace-labeled by the addition of 125I-labeled apotransferrin or with 59Fe.Labeling of transferrin with 1251 was carried out by the iodine monochloride procedure of McFarlane (17) with modifications as described (5, 6). To 4 ml of the plasma to be analyzed was added 0.2 ,uCi (1 Ci = 37 GBq) of 125I-apotransferrmn (specific activity, 0.4 mCi/mg of protein). The 59Fe was added as ferrous sulfate (0.1 ,uCi in 0.1 ml of 0.01 M HCl (specific activity, 10 ,uCi/,tg of Fe), to the same 4 ml of plasma. The mixture was incubated for 10 min at 370C and thereafter stored at 40C.Electrophoresis in the presence of 6 M urea was based on the separation principle described by Makey and Seal (18), and crossed immunoelectrophoresis was based on the procedures described by Weeke and Soderholm et al. (19,20). The replacement of polyacrylamide by Sea Kem LE agarose (FMC, Marine Colloid Division, Rockland, ME) gave better separation and required less manipulation than did the system described by Leibman and Aisen (21). This particular type of agarose will gel even in the presence of 6 M urea. Reagents were prepared with deionized water and further treated with a chelating resin (Chelex 100, Bio-Rad) to remove any residual contaminating iron (22). The 10 M urea stock solution was mixed for 5 hr with bed resin (50 g/liter; AG501-X8, Bio-Rad), filtered, and stored at 40C. The barbital buffer (0.1 M, pH 8.6) was mixed (5 g/liter) with Chelex 100 and then filtered. In the actual procedure, a mixture of 45 ml of 10 M urea, 35 ml of 0.1 M barbital buffer, and 0.75 g of Sea Kem LE agarose was heated to boiling. We poured the gel in a cold room (2°C) using a precooled leveling table in a humidity chamber. A volume of 16.5 ml of gel per 110 x 102.5 mm sheet of agarose gel support medium (Gel B...

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“…Supply is rep-resented by the amount of transferrin iron reaching the tissue per unit time and by the degree of saturation of transferrin with iron (1). Previous studies have emphasized the importance of the amount of diferric transferrin present, since this complex is capable of delivering much more iron than monoferric transferrin (2,3). The total number of iron-containing transferrin molecules vs. membrane receptor number is also important, since iron uptake will be decreased if the number of iron-loaded transferrin molecules is insufficient to saturate receptors.…”

Section: Introductionmentioning

confidence: 99%