Human macrophage hemoglobin-iron metabolism in vitro

Idiopathic Pulmonary Hemosiderosis: The Great Hemolytic Anemia Mimicker

Idiopathic pulmonary hemosiderosis (IPH) is a rare, potentially fatal disease characterized by recurrent diffuse alveolar hemorrhage. Presentation varies, and delay in diagnosis and treatment can result in respiratory complications and increased mortality. It is imperative to consider IPH in the differential of a patient presenting with transfusion-dependent microcytic anemia and concomitant pulmonary symptoms. This case series describes two pediatric patients with persistent severe microcytic anemia despite multiple blood transfusions. Both patients underwent extensive workup for their anemia, and ultimately, their respiratory symptoms led to their diagnosis of IPH. Both were then managed with long-term corticosteroids and had significant clinical improvement.

Recurrence of idiopathic pulmonary hemosiderosis in adults with childhood onset: A case report and literature review

We describe a rare case of a 20-year-old Japanese man with idiopathic pulmonary hemosiderosis (IPH) recurrence in adults with childhood onset (racIPH). IPH commonly occurs in children, and data regarding racIPH are lacking. A review of the literature showed that only five cases of racIPH have been reported (including the present case) and that racIPH shows features that are intermediate between childhood- and adult-onset IPH with respect to age and a lower frequency of smoking history. We also found that the degree of anemia was usually not severe, and a favorable response to corticosteroid therapy is expected in racIPH.

Differentiation of idiopathic pulmonary hemosiderosis from rheumatologic and autoimmune diseases causing diffuse alveolar hemorrhage: establishing a diagnostic approach

This narrative review provides an overview of diffuse alveolar hemorrhage (DAH) associated with rheumatologic and autoimmune diseases and their differentiation from idiopathic pulmonary hemosiderosis (IPH). Relevant immunologic diseases associated with DAH are discussed, and a diagnostic flowchart is proposed to establish a "definitive" diagnosis of IPH within the spectrum of DAH. IPH is a rare cause of recurrent DAH both in children and adults. In adults, a definitive diagnosis of IPH requires a lung biopsy and histopathologic examination demonstrating intraalveolar hemorrhage, hemosiderin-laden macrophages, and a variable degree of fibrosis in the absence of both capillaritis and cellular inflammation. The presence of small vessel vasculitis points towards immunologic, well-differentiated, or sometimes undifferentiated rheumatologic diseases. However, it is essential to recognize that many rheumatologic diseases may in the initial phase present with DAH without any evidence of capillaritis, thus mimicking IPH. Although not definitely established, it is likely that immunologic processes are involved in IPH, and we, therefore, suggest the consideration of a more suitable term for the disease, e.g., "Immune-mediated Pulmonary Hemosiderosis" to acknowledge the aberrancy in the immune parameters and a positive response to immunosuppressive therapy.

Quartz Disrupts Iron Homeostasis in Alveolar Macrophages To Impact a Pro-Inflammatory Effect

The biological response of bronchial epithelial cells to particles is associated with a sequestration of cell metal by the particle surface and a subsequent disruption in host iron homeostasis. The macrophage is the cell type resident in the respiratory tract that is most likely to make initial contact with inhaled particles. We tested the postulates that (1) silica, a prototypical particle, disrupts iron homeostasis in alveolar macrophages (AMs); and (2) the altered iron homeostasis results in both an oxidative stress and pro-inflammatory effects. Human AMs (1.0 × 10⁶/mL) demonstrated an increased import of iron following particle exposure with nonheme iron concentrations of 0.57 ± 0.03, 1.72 ± 0.09, 0.88 ± 0.09, and 3.21 ± 0.11 ppm in cells exposed for 4 h to media, 500 μM ferric ammonium citrate (FAC), 100 μg/mL silica, and both silica and FAC, respectively. Intracellular ferritin concentrations and iron release were similarly increased after AM exposure to FAC and silica. Silica increased oxidant generation by AMs measured using both dichlorofluorescein diacetate fluorescence and reduction of nitroblue tetrazolium salt. Concentrations of interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor-α in macrophage supernatant increased following 100 μg/mL silica exposure for 24 h. Treatment of AMs with 500 μM FAC decreased both oxidant generation and cytokine release associated with silica exposure, supporting a dependence of these effects on sequestration of cell metal by the particle surface. We conclude that (1) silica exposure disrupts iron homeostasis resulting in increased import, accumulation, and release of the metal; and (2) the altered iron homeostasis following silica exposure impacts oxidant generation and pro-inflammatory effects.

Recurrent idiopathic pulmonary hemosiderosis after long-term remission presented with Sjogren's syndrome: Idiopathic no more?

We report a case of recurrent idiopathic pulmonary hemosiderosis after a long-term remission presented with Sjögren's syndrome. The patient was diagnosed with IPH due to repeated pneumonia and blood sputum in his childhood. He was admitted to our hospital due to exertional dyspnea and dry cough with bilateral ground-glass opacity in chest computed tomography at the age of 32. Video-assisted thoracoscopic surgery was performed and the specimens showed nonspecific interstitial pneumonia pattern with diffuse, chronic alveolar hemorrhage, suggesting recurrence of IPH. He was also diagnosed with Sjögren's syndrome. Further immunological studies will reveal the pathogenesis of IPH.

Iron delocalisation in the pathogenesis of malarial anaemia

There is consensus that the pathophysiology of malaria-associated anaemia is multifactorial, but the precise mechanisms behind many of the haematological changes during malaria remain unclear. In this review, we attempt to build a composite picture of the pathophysiology of malarial anaemia using evidence from experimental, human and animal studies. We propose that cytokine- and hepcidin-mediated iron delocalisation, a principal mechanism in the anaemia of inflammation, plays an important role in the aetiology of malarial anaemia, and can explain some of the clinical and laboratory findings. These mechanisms interact with other aetiological determinants, such as dietary iron and micronutrient supply, helminth load, other infections and genetic variation, in determining the severity and associated features of anaemia. We suggest that iron delocalisation as a mechanism for malarial anaemia could be exploited for the development of alternative therapeutic strategies for post-malaria anaemia.

Ferritin subunits in CSF are decreased in restless legs syndrome

Restless legs syndrome (RLS) is a neurological disorder that may be related to iron misregulation at the level of the central nervous system. Evidence that iron is involved in RLS comes from magnetic resonance imaging data, autopsy studies, analyses of cerebrospinal fluid (CSF), and correlations of symptoms with serum ferritin. To further examine the possibility that brain iron status is insufficient in RLS, we determined ferritin levels in the CSF. Specifically, we differentiated between the H- and L-subunits of ferritin, because these peptides are expressed from different chromosomes and have different functions. We measured H- and L-ferritin subunit levels in control and RLS human CSF using immunoblot analysis and found that both H- and L-ferritin are significantly decreased in early but not late-onset RLS. Additionally, we quantified total protein in each CSF sample to establish that the decrease in ferritin subunits in RLS did not reflect a decrease in total protein in CSF. Furthermore, we used equal amounts of total CSF protein in the immunoblot analyses, in contrast to previously published studies that provided only volumetric data, to determine which approach was more accurate for quantifying the amount of ferritin relative to other proteins in CSF. Our results establish a protein standard in RLS, provide a comparative analysis of protein-controlled versus volumetric immunoblot techniques, and argue for a profound loss of iron storage capacity in the brain in RLS, specifically in the early onset RLS phenotype. These data suggest that CSF ferritin levels may provide a biomarker for assisting in the diagnosis of RLS.

Heme-oxygenase-mediated iron accumulation in the liver

Heme oxygenase (HO) isozymes, HO-1 and HO-2, catalyze the conversion of heme to iron, carbon monoxide, and biliverdin. The present study was aimed at elucidating the role of the HO system in iron accumulation and oxidative stress in the liver. We have also studied the regulation of an iron exporter, ferroportin-1 (FPN-1), as an adaptive response mechanism to increased iron levels. Sprague-Dawley rats were treated with HO inducer hemin or HO inhibitor tin-protoporphyrin IX (SnPPIX) for 1 month. A portion of liver tissues was subjected to RT-PCR for HO-1, HO-2, and FPN-1 gene expression as well as an HO activity assay. Paraffin-embedded tissues were stained for iron with Prussian blue. Hepatic iron concentration was measured by High Resolution-Inductively Coupled Plasma-Mass Spectrometry. 8-hydroxy-2'-deoxyguanosine (8-OHdG) stain, a sensitive and specific marker of oxidative DNA damage, was performed to assess oxidative stress. Hemin treatment led to augmented HO expression and activity in association with increased iron accumulation and oxidative stress. FPN-1 expression was also found to be upregulated. SnPPIX treatment reduced HO activity, intracellular iron levels, and oxidative stress as compared to controls. Our data provides evidence of increased HO activity as an important pro-oxidant mechanism leading to iron accumulation in the liver.

Iron release from macrophages after erythrophagocytosis is up-regulated by ferroportin 1 overexpression and down-regulated by hepcidin

Ferroportin 1 (FPN1) is transmembrane protein involved in iron homeostasis. In the duodenum, FPN1 localizes to the basolateral surface of enterocytes where it appears to export iron out of the cell and into the portal circulation. FPN1 is also abundantly expressed in reticuloendothelial macrophages of the liver, spleen, and bone marrow, suggesting that this protein serves as an iron exporter in cells that recycle iron from senescent red blood cells. To directly test the hypothesis that FPN1 functions in the export of iron after erythrophagocytosis, FPN1 was stably expressed in J774 mouse macrophages by using retroviral transduction, and release of 59Fe after phagocytosis of 59Fe-labeled rat erythrocytes was measured. J774 cells overexpressing FPN1 released 70% more 59Fe after erythrophagocytosis than control cells, consistent with a role in the recycling of iron from senescent red cells. Treatment of cells with the peptide hormone hepcidin, a systemic regulator of iron metabolism, dramatically decreased FPN1 protein levels and significantly reduced the efflux of 59Fe after erythrophagocytosis. Subsequent fractionation of the total released 59Fe into heme and nonheme compounds revealed that hepcidin treatment reduced the release of nonheme 59Fe by 50% and 25% from control and FPN1-overexpressing cells, respectively, but did not diminish efflux of 59Fe-heme. We conclude that FPN1 is directly involved in the export of iron during erythrocyte-iron recycling by macrophages.

Imaging of macrophage-related lung diseases

Macrophage-related pulmonary diseases are a heterogeneous group of disorders characterized by macrophage accumulation, activation or dysfunction. These conditions include smoking-related interstitial lung diseases, metabolic disorders such as Niemann-Pick or Gaucher disease, and rare primary lung tumors. High-resolution computed tomography abnormalities include pulmonary ground-glass opacification secondary to infiltration by macrophages, centrilobular nodules or interlobular septal thickening reflecting peribronchiolar or septal macrophage accumulation, respectively, emphysema caused by macrophage dysfunction, and honeycombing following macrophage-related lung matrix remodeling.

Iron metabolism in the reticuloendothelial system

Comprised mainly of monocytes and tissue macrophages, the reticuloendothelial system (RES) plays two major roles in iron metabolism: it recycles iron from senescent red blood cells and it serves as a large storage depot for excess iron. Although iron recycling by the RES represents the largest pathway of iron efflux in the body, the precise mechanisms involved have remained elusive. However, studies characterizing the function and regulation of Nramp1, DMT1, HFE, FPN1, CD163, and hepcidin are rapidly expanding our knowledge of the molecular aspects of RE iron handling. This review summarizes fundamental physiological and biochemical aspects of iron metabolism in the RES and focuses on how recent studies have advanced our understanding of these areas. Also discussed are novel insights into the molecular mechanisms contributing to the abnormal RE iron metabolism characteristic of hereditary hemochromatosis and the anemia of chronic disease.

Haptoglobin reduces lung injury associated with exposure to blood

The biological functions of the acute- phase protein haptoglobin (Hp) may be related to its ability to bind hemoglobin (Hb) or to modulate immune response. Hp is expressed at a high level in lung cells, yet its protective role(s) in the lung is not known. With the use of transgenic mice overexpressing Hp in alveolar macrophages, we demonstrated that Hp diminished Hb-induced lung injury when the lung was exposed to whole blood. In transgenic mouse lungs, Hb was more efficiently removed, and the induction of stress- responsive heme oxygenase-1 gene was significantly lower when compared with wild-type mice. At 24 h after blood treatment, the ferritin level that serves as an index for intracellular iron content was also lower in alveolar macrophages in transgenic mice than in wild-type mice. We propose that an Hp-mediated Hb catabolism process exists in alveolar macrophages. This process is likely coupled to an iron mobilization pathway and may be an efficient mechanism to reduce oxidative damage associated with hemolysis.

Pulmonary-renal syndromes in the intensive care unit

Renal disease associated with pulmonary hemorrhage is seen in a variety of clinical disorders and is a common cause of admission to intensive care units. Recent advances in the understanding of the pathogenesis of these disorders have improved the therapeutic options significantly and have favorably influenced the course of many of these disorders. This article discusses rheumatologic diseases that involve both the kidney and lungs, with emphasis on pathogenesis and therapeutic options. Common pulmonary-renal syndromes including anti-glomerular basement membrane disease and anti-neutrophil cytoplasmic autoantibodies-associated vasculitis.

Pathogenesis and treatment of anaemia of chronic disease

Anaemia of chronic disease (ACD), the most frequent anaemia among hospitalized patients, develops under chronic inflammatory disorders such as chronic infections, cancer or autoimmune diseases. A number of different pathways contribute to ACD, such as diversion of iron traffic, a diminished erythropoiesis, a blunted response to erythropoietin, erythrophagocytosis and bone marrow invasion by tumour cells and pathogens. Nevertheless, ACD is a reflection of an activated immune system and possibly results from an innovative defence strategy of the body in order to withdraw the essential growth factor iron from invading pathogens and to increase the efficacy of cell-mediated immunity. Diagnosis of ACD can be assessed by examination of chances in serum iron parameters with low to normal serum iron, transferrin saturation and transferrin concentrations on the one hand and normal to increased ferritin, zinc protoporphyrin IX and cytokine levels on the other side. Therapy of ACD includes the cure of the underlying the disease. Apart from this transfusions for rapid correction of haemoglobin levels, and human recombinant erythropoietin for prolonged therapy are used. However, response rates to recombinant erythropoietin are sometimes low. Iron alone should be strictly avoided due to its growth-promoting effect towards micro-organisms and tumour cells and because of it capacity to inhibit T-cell-mediated immune effector pathways. We urgently need prospective clinical trials to gain knowledge about the effects of anaemia correction and/or the use of erythropoietin towards the course of the underlying disease, to find out if a combination therapy with erythropoietin and iron may be beneficial in ACD and to define therapeutic end-points.

Time course of hemosiderin production by alveolar macrophages in a murine model

STUDY OBJECTIVES

The diagnosis of alveolar hemorrhage is assisted by the presence of hemosiderin-laden macrophages (HLMs) in the BAL fluid or lung tissue. Despite the importance of this diagnostic method in clinical settings, limited information is available on the formation and clearance of HLMs as a function of time. The objectives of this study are to determine the time course of HLMs within the BAL and lung tissue, and to evaluate the effect of a single blood aspiration on the recruitment of inflammatory cells within the BAL.

DESIGN

Under light anesthesia, Balb/c mice received a single intranasal instillation of species-specific blood (50 microL). Control animals received heparinized sterile saline solution in a similar manner. At several time points after blood aspiration, BAL was recovered for cell differentials and determination of HLMs. The time course for HLMs was also established in the lung tissue.

RESULTS

Hemosiderin staining within alveolar macrophages was first detected in the BAL and lung tissue at day 3, peaked at day 7, and persisted through 2 months. The analysis of the BAL revealed an increased number of total cells, with an acute inflammatory reaction that resolved within 2 weeks.

CONCLUSIONS

Our findings demonstrate the validity of this model for the study of HLM production after blood aspiration. Additional work using animal models of lung hemorrhage is needed to further characterize the cellular events leading to clearance of erythrocytes within the lung.

Iron transport

Iron homeostasis is maintained by regulating its absorption: Under conditions of deficiency, assimilation is enhanced but iron uptake is otherwise limited to prevent toxicity due to overload. Iron deficiency remains the most important micronutrient deficiency worldwide, but increasing awareness of the genetic basis for iron-loading diseases points to iron overload as a major public health issue as well. Recent identification of mutant alleles causing iron uptake disorders in mice and humans provides new insights into the mechanisms involved in iron transport and its regulation. This article summarizes these discoveries and discusses their impact on our current understanding of iron transport and its regulation.

Iron disequilibrium in the rat lung after instilled blood

STUDY OBJECTIVES

The extravasation of erythrocytes into the human lung occurs in a myriad of pulmonary disorders. Metal that is initially included in hemoglobin has been postulated to precipitate a disequilibrium in iron metabolism, to present an oxidative stress, and to contribute to tissue injury in several lung diseases. The objective of this study is to test the hypothesis that the tracheal instillation of blood in an animal model would have significant effects on iron equilibrium and would be associated with an injury to the lower respiratory tract.

DESIGN

Rats were intratracheally instilled with either 1.0 mL saline solution (n = 36) or 1.0 mL blood (n = 36). Biochemical end points and histochemistry were obtained at times between 20 min and 14 days after the exposure to saline solution or blood.

RESULTS

Total and nonheme iron concentrations in tracheal lavage fluid increased after the instillation of the blood. The percentage of neutrophils in the lavage fluid was elevated 1 day after the instillation of blood and remained at that level for at least 4 days following exposure, while protein concentrations were significantly increased at 1 day and 2 days only. Erythrocytes in the lung tissue were stained for hemoglobin immediately after exposure, but by 4 days after exposure, there was none. Ferritin was elevated between 1 day and 4 days after exposure, but by 7 days after exposure, the expression of this storage protein had returned to baseline values.

CONCLUSIONS

We conclude that intratracheal instillation of whole blood in the rat can induce a neutrophilic lung injury that is associated with a disruption of normal iron metabolism. This disruption of the iron equilibrium is made evident by quantifying iron and staining for hemoglobin and ferritin. All indexes of biological effect had corrected by 7 days after exposure.

A novel mammalian iron-regulated protein involved in intracellular iron metabolism

We have isolated and characterized a novel iron-regulated gene that is homologous to the divalent metal transporter 1 family of metal transporters. This gene, termed metal transporter protein (mtp1), is expressed in tissues involved in body iron homeostasis including the developing and mature reticuloendothelial system, the duodenum, and the pregnant uterus. MTP1 is also expressed in muscle and central nervous system cells in the embryo. At the subcellular level, MTP1 is localized to the basolateral membrane of the duodenal epithelial cell and a cytoplasmic compartment of reticuloendothelial system cells. Overexpression of MTP1 in tissue culture cells results in intracellular iron depletion. In the adult mouse, MTP1 expression in the liver and duodenum are reciprocally regulated. Iron deficiency induces MTP1 expression in the duodenum but down-regulates expression in the liver. These data indicate that MTP1 is an iron-regulated membrane-spanning protein that is involved in intracellular iron metabolism.

Iron Release From Human Monocytes After Erythrophagocytosis In Vitro: An Investigation in Normal Subjects and Hereditary Hemochromatosis Patients

This study investigated the release of erythrocyte-derived iron from purified human monocytes obtained from healthy volunteers and hereditary hemochromatosis (HH) patients. After erythrophagocytosis of59Fe-labeled erythrocytes, a complete transfer of iron from hemoglobin (Hb) to ferritin was observed within 24 hours in both control and HH monocytes. The iron was released from the monocytes in the form of ferritin, Hb, and as nonprotein bound low molecular weight iron (LMW-Fe). During the initial rapid phase (<1.5 hours), iron release mostly consisted of Hb and LMW-Fe, while in the later phase (>1.5 hours), it was composed of ferritin and LMW-Fe. The kinetics of iron release were identical for HH monocytes. A high percentage of the total amount of iron was released as Hb both by viable normal and HH monocytes, suggesting that iron release as Hb is a physiologic process, which may occur whenever the erythrocyte-processing capacity of macrophages is exceeded. Most remarkably, HH monocytes released twice as much iron in a LMW form as control cells. Iron released in the form of LMW-Fe readily binds to plasma transferrin and may contribute to the high transferrin saturation and the occurrence of circulating nontransferrin-bound iron observed in HH patients.

Iron Release From Human Monocytes After Erythrophagocytosis In Vitro: An Investigation in Normal Subjects and Hereditary Hemochromatosis Patients

This study investigated the release of erythrocyte-derived iron from purified human monocytes obtained from healthy volunteers and hereditary hemochromatosis (HH) patients. After erythrophagocytosis of59Fe-labeled erythrocytes, a complete transfer of iron from hemoglobin (Hb) to ferritin was observed within 24 hours in both control and HH monocytes. The iron was released from the monocytes in the form of ferritin, Hb, and as nonprotein bound low molecular weight iron (LMW-Fe). During the initial rapid phase (<1.5 hours), iron release mostly consisted of Hb and LMW-Fe, while in the later phase (>1.5 hours), it was composed of ferritin and LMW-Fe. The kinetics of iron release were identical for HH monocytes. A high percentage of the total amount of iron was released as Hb both by viable normal and HH monocytes, suggesting that iron release as Hb is a physiologic process, which may occur whenever the erythrocyte-processing capacity of macrophages is exceeded. Most remarkably, HH monocytes released twice as much iron in a LMW form as control cells. Iron released in the form of LMW-Fe readily binds to plasma transferrin and may contribute to the high transferrin saturation and the occurrence of circulating nontransferrin-bound iron observed in HH patients.

Idiopathic pulmonary haemosiderosis. Epidemiology, pathogenic aspects and diagnosis

Idiopathic pulmonary haemosiderosis (IPH) is a rare clinical entity characterized by recurrent episodes of diffuse alveolar haemorrhage, often presenting with haemoptysis. Many patients have iron deficiency anaemia due to deposition of haemosiderin iron in the alveoli, and eventually develop moderate pulmonary fibrosis. Typically, intensive search for an aetiology ends up negative. There is no evidence of pulmonary vasculitis or capillaritis. The aetiology is obscure, but may be an immunological or toxic mechanism causing a defect in the basement membrane of the pulmonary capillary. IPH affects both children and adults. During an acute episode, a chest X-ray demonstrates bilateral, alveolar infiltrates. Sputum examination discloses haemosiderin-laden alveolar macrophages. Diagnosis is established by lung biopsy (fiber-optic or thoracoscopic), showing large numbers of haemosiderin-laden macrophages in the alveoli and without evidence of capillaritis or deposition of immunoglobulins. Corticosteroids and/or immunosuppressive drugs may be effective during an acute bleeding episode, and may in some patients improve symptoms and prognosis on the long-term, but the response to treatment displays great interindividual variation.

Iron compounds after erythrophagocytosis: chemical characterization and immunomodulatory effects

In humans, the lymphomyeloid system has a fundamental role on iron metabolism promoting its recycling due to a continuous removal of effete red blood cells. Additionally, one of the most intriguing aspects of metalloporphyrins in biology is their effect on the immune system. However, the process of erythrocyte catabolism is still poorly understood and needs further research. In the present study, we attempt to investigate the nature and the possible physiologic role of Fe compounds released after erythrophagocytosis during the removal of red blood cells. Monocyte erythrophagocytosis in vitro experiments were done to characterize chemically the Fe compounds present inside the cells and in the culture supernatants. We tested the probable immunomodulatory functions of erythrophagocytosis products over lymphocyte cultures activated in vitro with T mitogens (alpha-CD3). Data obtained from atomic absorption spectroscopy confirmed the presence of Fe in the culture supernatants of monocyte cultures after erythrophagocytosis. Also, high-spin haem complexes derived from erythrocyte catabolism were detected by electron paramagnetic electronic resonance. Finally, in vitro activated lymphocyte proliferation experiments indicate the co-mitogenic properties of monocyte culture supernatants after red blood cells phagocytosis. Thus, the results of the present work provide evidence that culture monocyte supernatants after in vitro erythrophagocytosis contain Fe (III) high-spin haem complexes and show lymphocyte proliferation co-stimulatory properties.

Lysosomotropic agents ameliorate macrophage dysfunction following the phagocytosis of IgG-coated erythrocytes: a role for lipid peroxidation

Phagocytosis of IgG-coated erythrocytes (EIgG) can depress several macrophage functions. Our previous studies have suggested that this macrophage dysfunction may be due to an oxidative stress caused by the interaction of hemoglobin-derived iron with superoxide and/or hydrogen peroxide. Since lysosomotropic agents are capable of altering iron handling by macrophages, the present study evaluated the ability of these agents to prevent the macrophage dysfunction and lipid peroxidation caused by a phagocytic challenge with EIgG. Elicited rat peritoneal macrophages showed a depression of PMA-stimulated hydrogen peroxide production, calcium ionophore-stimulated arachidonate release and Fc receptor-mediated phagocytosis. The lysosomotropic agents; chloroquine, quinacrine, ammonium chloride and methylamine all prevented the depression of hydrogen peroxide production and arachidonate release but did not alter the depression of phagocytic function. These agents also prevented the increase in lipid peroxidation products caused by a phagocytic challenge with EIgG. These results suggest that the ability of lysosomotropic agents to prevent some aspects of macrophage dysfunction after a phagocytic challenge may be due to their ability to block the oxidative stress caused by the challenge.

Ferritin expression after in vitro exposures of human alveolar macrophages to silica is iron-dependent

The increased availability of catalytically active iron after silica exposure can present an oxidative injury to a living system. Sequestration of reactive iron would, therefore, confer a protective effect. The intracellular storage of iron by ferritin within macrophages can limit the potential for radical generation and cellular injury resulting from exposure to a metal chelate. We tested the hypothesis that in vitro exposure of human alveolar macrophages to silica increases the expression of ferritin through a posttranscriptional mechanism. Exposure of 1.0 x 10(6) macrophages to 100 microg/ml silica for 4 h increased light-subunit (L)-ferritin protein concentrations in both cell supernatants and lysates. Inclusion of 1.0 mM deferoxamine in the reaction mixtures inhibited increases in ferritin after silica. To test for a posttranscriptional regulation of ferritin protein expression, cells were incubated with acid-washed particles, silica with complexed zinc cation, and silica with complexed iron cation. L-ferritin protein concentrations were increased in both cell supernatants and lysates after 4 h of exposure to silica with complexed iron cation. There were no increases in L-ferritin after incubations with acid-washed particles or silica with complexed zinc cation. There were no significant differences in levels of L-ferritin cDNA between any of the exposures, suggesting a posttranscriptional control of ferritin expression.

Tracing iron and transferrin in the macrophage by visual means

The purpose of the study was to investigate the movement of iron and transferrin in the macrophage using light and electron microscopy. First, depicted here are the phagocytosis of antibody sensitized murine red cells by the murine bone marrow derived macrophage and the formation of red cell phagosomes. Second, we show the fusion of the lysosomes with the red cell phagosome to form a lysophagosome and the lysis of the red cell using acid phosphatase as a lysosome marker. Third by autoradiography, the presence of 55Fe silver grains in the phagocytosed red cells and its delivery to the organelles of the macrophage are demonstrated. Fourth a transferrin species is shown in red cells of all ages, in the phagocytosed as well as the non-phagocytosed, and in the phagocytosed as well as the non-phagocytosed, and in the macrophage itself. Transferrin was detected using immunogold and fluorescence labelling. These studies suggest that iron, using vesicles as means of transport, moves from the effete red cells inside the macrophage to the outside possibly bound to transferrin.

Red cell destruction by human monocytes--changes in intracellular ferritin concentration and phenotype

Mononuclear cells from 5 normal men and 5 patients homozygous for hereditary haemochromatosis (HFE) have been incubated for 18 h with or without the addition of sheep red blood cells coated with antibody (SRBC). In the absence of SRBC mean H type ferritin concentrations were greater than L type (normals: mean L type 11.6 ng/10(6) cells, H type 15.5; patients, L type 23.5 ng/10(6) cells, H type 41.6). In the presence of SRBC, monocyte L type ferritin concentrations increased considerably (76 ng/10(6) cells in normals and 141 ng/10(6) cells in patients) but H type ferritin concentrations were the same or decreased compared with incubation in medium only. Incubation with additional iron (ferric ammonium citrate, 2.5 micrograms Fe/ml) increased both H and L type ferritin concentrations. Erythrophagocytosis thus appears to cause differential regulation of H and L ferritin subunit synthesis or breakdown. Normal subjects and patients do not differ in this response to erythrophagocytosis.

Interactions between isolated hepatocytes and Kupffer cells in iron metabolism: a possible role for ferritin as an iron carrier protein

Like the rat peritoneal macrophage, the isolated Kupffer cell is capable of processing and releasing iron acquired by phagocytosis of immunosensitized homologous red blood cells. When erythrophagocytosis is restrained to levels which do not affect cell viability, about one red cell per macrophage, close to 50% of iron acquired from red cells is released within 24 hr in the form of ferritin. Immunoradiometric assay of the extracellular medium indicates that 160 ng ferritin are released by 10(6) Kupffer cells after 24-hr incubation at 37 degrees C. Iron release is temperature-dependent, the rate at 37 degrees C being nearly 5-fold greater than at 4 degrees C. As estimated by sucrose-gradient ultracentrifugation, ferritin released by the erythrophagocytosing Kupffer cell averages 2,400 iron atoms per molecule. When reincubated with isolated hepatocytes, this released ferritin is rapidly taken up by the cells. Via this process, hepatocytes may accumulate more than 160,000 iron atoms per cell per min. Such accumulation is not impeded by the presence of iron-loaded transferrin in the culture medium, but is markedly depressed by rat liver ferritin. In contrast to the conservation of transferrin during its interaction with hepatocytes, the protein shell of the ferritin molecule is rapidly degraded into trichloroacetic acid-soluble fragments. Ferritin-mediated transfer of iron from Kupffer cells to hepatocytes may help explain the resistance of the liver to iron deficiency as well as the liver's susceptibility to iron overload.

Ferritin synthesis by monocyte-derived macrophages in thalassemic patients with intrinsic iron overload

Macrophage ferritin content was determined following culture of peripheral blood monocytes for a period of 8 d in 40% autologous plasma to render them mature macrophages. Ferritin content was measured prior to and following culture using the radioimmunoassay. The normal range of values was established in a group of 22 healthy volunteer blood donors. A significant increase in the ratio of macrophage/monocyte ferritin was observed in every donor studied (range 1.2 - 1.8, p less than 0.001). Also, a further significant increase was observed when these macrophages were additionally incubated for 6 h with heterologous antibody-coated sheep red blood cells (range 1.2 - 1.57, p less than 0.001). Finally, the same studies were performed on a group of thalassemic patients with and without intrinsic iron overload. Again there were significant increases in monocyte ferritin content following culture as well as ingestion of heterologous sheep red cells, with magnitudes similar to those obtained with normal donor monocytes. Therefore we could not demonstrate the presence of a cellular ferritin synthesis defect in macrophages of thalassemic patients with intrinsic iron overload to explain the uncontrolled absorption of dietary iron from their gut.

Interaction of transferrin with iron-loaded rat peritoneal macrophages

Rat peritoneal macrophages are capable, in vitro, of processing and releasing iron derived from phagocytosed, immunosensitized red cells. From 20% to 60% of the red cell iron can be returned to the culture medium in 24 h, with resident macrophages more active than inflammatory, peptone-induced macrophages. When apotransferrin is present in the culture medium, from 39% to 72% of iron released from macrophages is bound to the protein, with most of the remainder in a ferritin-like form. No distinct preference of released iron for either site of transferrin could be observed. The absence of apotransferrin depresses iron release only slightly, with much of the iron then released in a form readily available to the protein in vitro. Pronase treatment of macrophages, which abolishes their ability to bind transferrin, depresses iron release no more than 10-15%. It appears, therefore, that binding of apotransferrin to macrophages may not be essential for iron excretion by the cells.

[Blood destruction in pulmonary alveoli: signs of vitality and determination of survival time]

Lungs from 26 cases were examined in which blood was present as a result of a gunshot wound, a stab wound, or aspiration. Signs of vitality and of a time-dependent reaction sequence were evaluated to determine survival time. Only those morphologic criteria were considered that could be obtained on paraffin sections. In addition to H & E staining, siderin was identified with the Prussian blue reaction and the activities were determined of tartrate-resistant acid phosphatase, as macrophage marker, and naphthol AS-D chloracetate esterase, as granulocyte marker. The following criteria were evaluated: granulocyte emigration, erythrocyte adherence to the surface of macrophages, macrophage ingestion of erythrocytes, and determination of siderin as indicator of intracellular erythrocyte digestion. Adherence was also observed in those cases that did not survive. The initial sign of vitality was granulocyte emigration, which was observed for the first time after a survival time of 5 min. Erythrophages were found after a survival time of 30 min at least, siderophages after 17 h at the earliest. Literature dealing with vitality and age determination, as well as the pathogenesis of the reaction sequence, is discussed.