Redistribution of accumulated cell iron: a modality of chelation with therapeutic implications

Abstract

Various pathologies are characterized by the accumulation of toxic iron in cell compartments. In anemia of chronic disease, iron is withheld by macrophages, leaving extracellular fluids iron-depleted. In Friedreich ataxia, iron levels rise in the mitochondria of excitable cells but decrease in the cytosol. We explored the possibility of using deferiprone, a membrane-permeant iron chelator in clinical use, to capture labile iron accumulated in specific organelles of cardiomyocytes and macrophages and convey it to other locations for physiologic reuse. Deferiprone's capacity for shuttling iron between cellular organelles was assessed with organelle-targeted fluorescent iron sensors in conjunction with time-lapse fluorescence microscopy imaging. Deferiprone facilitated transfer of iron from extracellular media into nuclei and mitochondria, from nuclei to mitochondria, from endosomes to nuclei, and from intracellular compartments to extracellular apotransferrin. Furthermore, it mobilized iron from iron-loaded cells and donated it to preerythroid cells for hemoglobin synthesis, both in the presence and in the absence of transferrin. These unique properties of deferiprone underlie mechanistically its capacity to alleviate iron accumulation in dentate nuclei of Friedreich ataxia patients and to donate tissuechelated iron to plasma transferrin in thalassemia intermedia patients. Deferiprone's shuttling properties could be exploited clinically for treating diseases involving regional iron accumulation. IntroductionThe pathologic effects of iron accumulation in tissue are recognized in diseases of systemic iron overload, in which the liver, heart, and endocrine glands are the principal affected organs. 1 At the cellular level, labile iron begins to rise once the intracellular capacity for iron storage is surpassed, leading to catalytic formation of reactive oxygen species (ROS) that ultimately overwhelm the cellular antioxidant defense mechanisms and lead to cell damage. 2 In recent years, several pathologies have been shown to be associated with specific defects in cellular iron metabolism that do not give rise to conspicuous systemic iron overload. 3 In the neuromuscular disorder Friedreich ataxia, the deficiency of the iron-chaperone protein frataxin is thought to lead to mitochondrial iron accumulation due to improper processing of iron for heme and iron-sulfur-cluster formation. 4 In the group of neuromuscular disorders termed NBIA (neurodegeneration with brain iron accumulation), a deficiency in pantothenate kinase (PKAN-2), a key enzyme in coenzyme A synthesis, 5 leads to iron deposition and ensuing brain damage by still-unresolved mechanisms. 6 In hereditary X-linked sideroblastic anemia, impaired heme synthesis causes mitochondrial iron accumulation and siderosis in erythroid cells. 3 However, an extreme example of systemic misdistribution of iron is encountered in anemia of chronic disease (ACD), where iron accumulates in reticuloendothelial cells responsible for recycling aged erythrocytes, presumably due to d...

The role of endocytic pathways in cellular uptake of plasma non-transferrin iron

“…Flow cytometric analysis was performed with an automated Eclipse instrument (iCyt, Champaign, IL, USA) on H9c2 cardiomyoblasts after trypsinization, as described elsewhere for other cells. [13][14][15] We also used cultured HL-1 cardiac muscle cells derived from the AT-1 mouse atrial cardiomyocyte tumor lineage that continuously divide and spontaneously contract while maintaining a differentiated cardiac phenotype (generously provided by Dr WC Claycomb, LSU, New Orleans, USA). 16 …”

“…13,14 RAW cells and H9c2 cultured cardiomyoblasts were grown as previously described. 13,14 Rat INS1 cells clone 832/13 (generously provided by Dr HE Hohmeier, Duke University, NC, USA) derived from rat pancreas were stably transfected with the human proinsulin gene. The cells were grown in RPMI containing 10% fetal bovine serum, 10 mM Hepes, 1mM Sodium Pyruvate and 50 μM β-Mercaptoethanol.…”

“…We predict that for macromolecular forms to gain access to cells, they would need to be initially transferred as fluid cargo or membrane adsorbed species that are taken up by endocytosis and subsequently by transmembrane mechanisms into the cytosol. In order to assess the initial steps of ingress of plasma NTBI into model cells, 13,14 we used as NTBI substrate the original sera from thalassemia major patients who had only undergone sporadic treatment with iron chelators, so that levels of Fe-chelates in circulation were negligible. As model NTBI forms, we used whole human serum or only its albumin (HSA) fraction supplemented with iron-citrate or other iron sources.…”

Facile transfer of [2Fe-2S] clusters from the diabetes drug target mitoNEET to an apo-acceptor protein

“…Disruption of FeS cluster biogenesis is deleterious to vital cell processes in humans, leading to diseases such as Friedreich's ataxia (18,19), X-linked sideroblastic anemia with ataxia (XLSA/A) (20), and a form of sideroblastic anemia associated with a deletion in the GLRX5 gene (21). The accumulation of iron in mitochondria, which leads to misdistribution of the metal (22) and mismanagement of cellular iron regulatory properties (23,24), is a hallmark of various diseases. These observations are consistent with the localization of the FeS cluster biogenesis machinery and key FeS protein metabolic functions in mitochondria (16,23).…”

NADPH Inhibits [2Fe-2S] Cluster Protein Transfer from Diabetes Drug Target MitoNEET to an Apo-acceptor Protein

“…Disruption of FeS cluster biogenesis is deleterious to vital cell processes in humans, leading to diseases such as Friedreich ataxia (4,5), X-linked sideroblastic anemia with ataxia (XLSA/A) (6), and a form of sideroblastic anemia associated with a deletion in the GLRX5 gene (7). The accumulation of iron in mitochondria, which leads to misdistribution of the metal (8) and mismanagement of cellular iron regulatory properties (9,10), is a hallmark of various diseases. These observations are consistent with the localization of the FeS cluster biogenesis machinery and key FeS protein metabolic functions in mitochondria (2,9).…”