Ferritin Formation Research Articles

Dissociation-association properties of apoferritin in the milligram and microgram range

Concentration dependent association of the 17 S unit of horse spleen apoferritin leads to dimer formation at c ∼ 0.1 mg/ml; at c > 0.4 mg/ml trimers and higher aggregates are formed. Dissociation into subunits is not detectable at concentrations as low as 10 −2 or 10 −4 mg/ml using sedimentation velocity or gel chromatography, respectively. In accordance with iron incorporation into the preformed protein shell as the basic mechanism of ferritin formation, the results suggest the quaternary structure of apoferritin to be stable under quasi physiological conditions.

The subcellular distribution of 59 Fe in small intestinal mucosa: studies with normal, iron deficient and iron overloaded rats.

SummaryIron deficient and iron loaded rats were given 59Fe by stomach tube and the subcellular distribution of 59Fe in the intestinal mucosa was investigated. There was considerable concentration of 59Fe in the soluble fraction shortly after administration of the dose but concentration in the mitochondria at 12 and 18 hr. Concentration in the mitochondria was particularly marked in the iron deficient rats. After intravenous injection of 59Fe normal, iron deficient and iron loaded rats all showed the greatest concentration of the isotope in the mitochondrial fraction. The incorporation of 59Fe into ferritin was not greater in the iron loaded rats than in normal rats, although the absorption of 59Fe was only one third of the normal level. In iron deficiency very little radioiron was incorporated into ferritin. These results support the suggestion that ferritin formation may not be a major controlling factor in iron absorption and demonstrate the need to consider the role of mitochondria in iron transport within the intestinal epithelial cell.

The formation of ferritin from apoferritin. Kinetics and mechanism of iron uptake.

Ferritin has a high capacity as an iron store, incorporating some 4500 iron atoms as a microcrystalline ferric oxide hydrate. Starting from apoferritin, or ferritin of low iron content, Fe(2+) and an oxidizing agent, the uptake of iron can be recorded spectrophotometrically. Progress curves were obtained and the reconstituted ferritin was shown by several physical methods to be similar to natural ferritin. The progress curves of iron uptake by apoferritin are sigmoidal; those for ferritins of low iron content are hyperbolic. The rate of iron uptake is dependent on the amount of iron already present in the molecule. The distribution of iron contents among reconstituted ferritin molecules is inhomogeneous. These findings are interpreted in terms of a crystal growth model. The surface area of the crystallites forming inside the protein increases until the molecule is half full, and then declines. This surface controls the rate at which new material is deposited. The experimental results can best be accounted for by a two-stage mechanism, an initial slow ;nucleation' stage, which is apparently zero order with respect to [Fe(2+)], followed by a more rapid ;growth' stage. The rate of Fe(2+) oxidation is increased in the presence of apoferritin as compared with controls. Ferritin can therefore be regarded as an enzyme to which the product remains firmly attached. The protein appears to increase the rate of ;nucleation'. The apparent zero order of this stage suggests the presence of binding sites on the protein, which are saturated with respect to Fe(2+). These sites are presumed also to be oxidation sites. The oxidation and subsequent formation of the ferric oxide hydrate may proceed according to one of three alternative models.

The anaemia of rheumatoid arthritis: the significance of iron deposits in the synovial membrane.

SummaryHistological examination of synovial membrane removed from 100 joints in 81 patients with rheumatoid arthritis has shown iron deposits, often of an extensive nature in 96 joints. Electron microscopic examination revealed ferritin within synovial cell cytoplasm and concentrated into lysosomes in 16 of 20 biopsies. It is suggested that the iron deposits arise from continued oozing of blood from the vascular granulation tissue into the synovial cavity. The sequence from erythrophagocytosis to ferritin formation can be followed with the electron microscope. It is also likely that some of the iron given as parenteral therapy finds its way into synovial macrophages.In 28 patients a highly significant relationship was found between the presence of anaemia due to rheumatoid arthritis and the histological estimate of the extent of iron deposits. There was also a relationship between the duration of disease in the joint, the grade of x‐ray change and the iron deposits.The synovial membrane appears to be an important source of iron sequestration. A delay in release of iron from this and the reticuloendothelial storage sites could explain many of the features of the anaemia of rheumatoid arthritis.

Studies on iron-chondroitinsulfate colloid for intravenous injection. IV. Distribution of 59Fe in the mice followed by the injection of 59 fe labeled iron-chondroitinsulfate colloid. 2. Dose dependence of the distribution and the fractionation of 59Fe in organs

In order to examine the course of intravenously injected iron chondroitinsulfate phagocytized in the reticuloendothelial system and the iron in it utilized as hemoglobin iron, iron chondroitinsulfate labeled with 59Fe was injected intravenously in normal mice, in three different doses, and examinations were made on its systemic distribution, separation of 59Fe into hemin iron and non-hemin iron in liver and spleen, and periodical changes in non-hemin 59Fe in the fraction separated by the Yoneyama -Konno method from the liver and small intestine, and the following points were revealed. 1) Disappearance of 59Fe from blood immediately after intravenous injection of iron (59Fe) chondroitinsulfate, its incorporation into the liver, followed by its disappearance from the liver, and incorporation of 59Fe into erythrocytes all become rapid with decreased amount administered. 2). Introduction of 59Fe into hemin iron is not observed in the liver but the peak of 59Fe in the spleen during 8-96 hours after the intravenous injection is clearly due to the incorporation of 59Fe into hemin iron. 3) Formation of ferritin in the liver requires a certain time lag and there is a good correspondence between that and incorporation of 59Fe into erythrocytes. 4) 59Fe that has collected in the small intestine is partly excreted and its excretion rate is dependend on the dose administered but follows the first-order formula.

Transferrin synthesis in the rat: a study using the fluorescent antibody technique.

The fluorescent antibody technique has been used to investigate transferrin synthesis in rats. The alteration in hepatic transferrin content has been noted in rats suffering from acute blood loss, chronic iron deficiency before and after treatment with iron, iron loading and localized hepatic sepsis. Marked changes in the transferrin content in the rat liver can be correlated with changes in erythropoietic rate, plasma transferrin concentration and the associated variation in catabolic rate of transferrin in these different situations. Rapid increases in hepatic transferrin content are considered to represent a synthetic response and are associated with elevation of plasma transferrin concentration. The synthesis response follows an extreme reduction in liver transferrin content; after acute blood loss and treatment of chronic iron deficiency anaemia with iron, a transferrin synthesis response coincides with the onset of erythropoiesis. The injection of iron‐dextran into normal rats appears to be associated with a suppression of transferrin synthesis during the period of peak hepatic ferritin formation. It is thought that iron influences transferrin synthesis through its regulatory effect on erythropoietic rate.

Biosynthesis of ferritin molecules.

IN the News and Views section of Nature of May 18, 1968 (ref. 1), attention is directed to a recent paper by Pape, Multani, Stitt and Saltman2, in which a new model for ferritin synthesis is proposed. The authors suggested that ferritin formation occurs by way of aggregation of apoferritin subunits around a preformed polynuclear iron micelle and that their mechanism accounts for the apparent induction of ferritin synthesis by iron. While welcoming this new hypothesis, we would like to indicate that results obtained by several other groups of workers support the alternative view that apoferritin molecules are formed first and that these then accumulate iron in their interior to give ferritin.

Ferritin formation by synovial cells exposed to haemoglobin in vitro.

Ferritin formation by synovial cells exposed to haemoglobin in vitro.

ON THE FORMATION OF HAEMOSIDERIN AND ITS RELATION TO FERRITIN. II. A RADIOISOTOPIC STUDY.

In vivo biochemical studies on rabbits have shown that, with the intravenous injection of iron dextran, the rate of liver ferritin formation limits the uptake of iron by this organ. When ferritin production reaches 25‐30 mg. Fe per day, increased rates of iron dextran injection result only in increased serum concentrations of the compound. Regardless of the rate of injection, haemosiderin (insoluble iron) forms at a rate of approximately one‐tenth that of ferritin (soluble iron) until the total liver ferritin iron reaches 150‐200 mg. Therefore, when iron dextran is injected, the rate of haemosiderin formation is limited by the liver ferritin concentration. When this concentration reaches the ‘critical’level of 150‐200 mg. of iron and loading is continued, a process begins whereby ferritin production gradually decreases until the ferritin content of the liver reaches a maximum. Simultaneously the rate of haemosiderin production increases until all subsequent iron deposition is reflected in increased haemosiderin content (Shoden and Sturgeon, 1962a).Histochemical studies have shown that there is no appreciable deposition of stainable iron in the Kupffer cells of the liver when iron dextran is administered intravenously. When saccharated iron oxide is given, however, there is immediate and marked deposition of stainable iron in the Kupffer cells, even when relatively small amounts of iron are injected at slow rates. In contrast to the Kupffer cell insoluble iron, deposition of histochemically demonstrable iron in the parenchymal cells does not begin until the total liver ferritin iron reaches approximately the 150‐200 mg. level. At this level, regardless of the type of iron compound given, faint bluish areas or vacuoles, some of which may contain discrete blue granules, appear in the parenchymal cells. As the iron load is increased beyond this point, the number and size of the parenchymal cell granules increase. When iron dextran is given, the appearance of the blue granules is paralleled by a marked increase in the water‐insoluble iron fraction. Extraction with normal saline of small liver cubes, preceding the fixation and staining, shows that ferritin is removed, but not the haemosiderin granules (Shoden and Sturgeon, 1962b).From the above observations, the hypothesis was advanced that liver ferritin is a precursor of the haemosiderin granules found in the parenchymal liver cells (Shoden and Sturgeon, 1961). The present study was designed to test this hypothesis. It was planned to establish in the two iron storage ‘compartments’(ferritin and parenchymal haemosiderin) known specific activities (concentrations) of radioactive iron. Then, to study the pathway taken by new iron, non‐radioactive iron in form of iron dextran was administered. The sequence in the dilution of radioactive iron in the two compartments, and the shift of radioactivity between them,

Iron Metabolism in the Bone Marrow as Seen by Electron Microscopy: A Critical Review

Abstract High resolution electron microscopy has made possible the visualization of transport and storage iron in the form of ferritin, both in dispersed form and in aggregates and in the form of "iron micelles" in mitochondria. Hemosiderin was found to consist either of pure ferritin in crystalline clusters or, more frequently, of ferritin associated with other substances, including a lipid component in the form of myelinic figures and PAS positive material. In the following paragraphs we have summarized the new morphologic findings and what appears to us the most likely interpretation in the light of known biochemical and isotopic studies. Alternative interpretations have been discussed in the body of the paper. Electron microscopy has established the erythroblastic island as a morphologic and functional unit of the bone marrow. A central reticular "nurse cell" appears to impart nutrients to surrounding rows of erythroblasts by the process of rhopheocytosis. Transfer of ferritin by this process is probably a passive phenomenon, since the amount transferred parallels the amount of iron present in the central reticular cell. Ferritin is increased both in the reticular cell and in erythroblasts in hemochromatosis. It is absent in iron deficiency, although rhopheocytosis remains prominent. Normally all erythroblasts (proerythroblasts and normoblasts) and reticulocytes contain ferritin. Only the larger aggregates can be visualized by the Prussian blue reaction in sideroblasts and siderocytes. Ferritin generally disappears when reticulocytes mature, even in hemochromatosis and infections, two conditions in which there is an excess of ferritin in erythroblasts. Interestingly, the increase in infections is entirely in form of dispersed ferritin and cannot be visualized by the Prussian blue reaction; i.e., sideroblasts are absent, in contrast to hemochromatosis where they are normal or increased. It appears most likely that ferritin disappears from normal maturing reticulocytes because it is utilized for hemoglobin formation. It persists in mature red cells in Cooley’s anemia, hypersideremia, hypochromic anemia and lead poisoning where hemoglobin formation is disturbed. The origin of the ferritin in the nurse cells and the extent to which ferritin rather than siderophilin contributes to hemoglobin synthesis are unsolved problems. Isotopic studies indicate that almost all of the iron used for hemoglobin synthesis is derived from siderophilin and hemoglobin synthesis can proceed without any visible ferritin, as in iron deficiency anemia. These facts must be reconciled with the electron microscopic observations which suggest that normally some iron reutilization within the marrow proceeds by way of erythrophagocytosis, fragmentation, intracellular hemolysis of red cells, formation of ferritin and ropheocytosis. Iron derived from erythrophagocytosis elsewhere in the body probably reaches the marrow bound to siderophilin. Such iron can be incorporated into ferritin of reticular cells as may be seen in hyperferremia and following injection of iron compounds. The process of rhopheocytosis would then lead to utilization of at least part of this ferritin iron for hemoglobin synthesis. In certain pathologic states, accumulation of ferritin and related visible dispersed or conglomerated iron micelles may point to the sites where hemoglobin synthesis or iron transport is blocked. In Cooley’s anemia and the hypersideremic hypochromic (non-thalassemic) anemias, iron accumulates in the mitochondria, which are known to be involved in hemoglobin synthesis. In lead poisoning, the mitochondria are markedly abnormal, and probably correspond to the areas of punctate basophilia. However, the iron accumulates in other areas of the cell, suggesting a different type of block.

The reticulo-endothelial system (RES), its function in phagocytosis and iron metabolism.

The authors observed the disappearance rate of iron from serum, and the ferritin, and hemoglobin formation or incorporation of iron into red cells after the intravenous injection of colloidal iron. It has been elucidated that the phagocytosis function and iron assimilation function of RES can be estimated concomitantly. Observations by changing the quantity of the injected iron proved that the smaller the quantity of iron injected the more rapid and efficient is the incorporation of iron into red cells. In the animals whose RES is blocked by Evans blne injection, a marked delay is observed both in the disappearance of iron from serum, phagocytosis by RES, and in the incorporation of iron into red cells. But in the animals treated with E. Coli suspension the disappearance of iron from the serum is as rapid as in normal control animals and a marked delay in the incorporation of iron into red cells, is found with the inhibition of the ferritin formation. The data show that the test on the ability of phagocytosis of RES does not always give information of the function of RES for iron ssimilation.

Renal pathology in paroxysmal nocturnal hemoglobinuria: An electron microscopic illustration of the formation and disposition of ferritin in the nephron

The pathologic changes seen on light and electron microscopy of the kidney in paroxysmal nocturnal hemoglobinuria are described in two cases, one at autopsy and the other at biopsy. Intense hemosiderosis of the kidney is the most characteristic pathologic change in paroxysmal nocturnal hemoglobinuria although not specific for this disease. There is no apparent structural or functional reaction to the hemosiderosis. The intensity of ferritin accumulation at various points in the nephron is correlated with current concepts of hemoglobinuria, hemoglobin and ferritin metabolism and large molecule transport.

The Presence of Ferritin in the Duodenal Mucosa and Liver in Hemochromatosis

ConclusionThe cause of hemochromatosis does not appear to be a defect in the formation of ferritin in the duodenal mucosa or the liver.