A possible role for secreted ferritin in tissue iron distribution.
ABSTRACT Ferritin is known as a well-conserved iron detoxification and storage protein that is found in the cytosol of many prokaryotic and eukaryotic organisms. In insects and worms, ferritin has evolved into a classically secreted protein that transports iron systemically. Mammalian ferritins are found intracellularly in the cytosol, as well as in the nucleus, the endo-lysosomal compartment and the mitochondria. Extracellular ferritin is found in fluids such as serum and synovial and cerebrospinal fluids. We recently characterized the biophysical properties, secretion mechanism and cellular origin of mouse serum ferritin, which is actively secreted by a non-classical pathway involving lysosomal processing. Here, we review the data to support a hypothesis that intracellular and extracellular ferritin may play a role in intra- and intercellular redistribution of iron.
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ABSTRACT: The current study aimed to investigate radiation-induced regulation of iron proteins including ferritin subunits in rats. Rat livers were selectively irradiated in vivo at 25 Gy. This dose can be used to model radiation effects to the liver without inducing overt radiation-induced liver disease. Sham-irradiated rats served as controls. Isolated hepatocytes were irradiated at 8 Gy. Ferritin light polypeptide (FTL) was detectable in the serum of sham-irradiated rats with an increase after irradiation. Liver irradiation increased hepatic protein expression of both ferritin subunits. A rather early increase (3 h) was observed for hepatic TfR1 and Fpn-1 followed by a decrease at 12 h. The increase in TfR2 persisted over the observed time. Parallel to the elevation of AST levels, a significant increase (24 h) in hepatic iron content was measured. Complete blood count analysis showed a significant decrease in leukocyte number with an early increase in neutrophil granulocytes and a decrease in lymphocytes. In vitro, a significant increase in ferritin subunits at mRNA level was detected after irradiation which was further induced with a combination treatment of irradiation and acute phase cytokine. Irradiation can directly alter the expression of ferritin subunits and this response can be strongly influenced by radiation-induced proinflammatory cytokines. FTL can be used as a serum marker for early phase radiation-induced liver damage.
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ABSTRACT: Ferritin, an iron storage protein, is present in the serum and cerebrospinal fluid, has receptors on the cell surface, able to penetrate the brain-blood barrier, can be secreted from the cells, and leaks from destroyed cell in insult and brain trauma. The effect of exogenous ferritin on the key characteristic of glutamatergic neurotransmission was assessed in rat brain nerve terminals (synaptosomes). Exogenous ferritin (80μg/ml, iron content 0.7 %) significantly increased the ambient level of L-[(14)C]glutamate (0.200±0.015 versus 0.368±0.016nmol/mg of protein) and endogenous glutamate (fluorimetric glutamate dehydrogenase assay) in the nerve terminals. This increase was not a result of augmentation of tonic release because the velocity of tonic release of L-[(14)C]glutamate was not changed significantly in ferritin-treated synaptosomes as compared to the control. Ferritin caused a decrease in synaptic vesicle acidification that was shown using fluorescent dye acridine orange. Iron-dependence of the effects of ferritin was analyzed with apoferritin (0.0025 % residual iron). Apoferritin weakly affected the proton electrochemical gradient of synaptic vesicles but increased the ambient level and decreased the initial velocity of uptake of L-[(14)C]glutamate by synaptosomes, nevertheless these effects were ~30 % lesser than those caused by ferritin. Exogenous ferritin can provoke the development of excitotoxicity increasing the ambient level of glutamate and lowering synaptic vesicle acidification and glutamate uptake in the nerve terminals, however these effects are not completely iron-dependent. Thus, in the CNS exogenous ferritin can act as modulator of glutamate homeostasis in iron-dependent and iron-independent manner.Molecular and Cellular Neuroscience 12/2013; · 3.84 Impact Factor
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ABSTRACT: A markedly elevated serum ferritin level has been associated with inflammatory conditions such as adult-onset Still's disease, systemic juvenile idiopathic arthritis, and hemophagocytic lymphohistiocytosis/macrophage activation syndrome. Hyperferritinemia, however, can also be caused by a wide variety of disparate conditions, often with impressively high serum levels. The objective of this analysis was to investigate the underlying etiology of markedly elevated ferritin levels in a large group of patients treated as outpatients and inpatients in a tertiary-care medical center. Data of all adult patients from 2008 through 2010 with at least 1 serum ferritin level greater than 1000 μg/L were reviewed. If a patient had multiple qualifying levels, the highest one was used. For each case, the most likely cause of the elevated ferritin was assessed based on the available clinical data using a simple algorithmic approach. Six hundred twenty-seven patients were found. The average serum ferritin level was 2647 μg/L. The most frequent condition was malignancy (153/627), with iron-overload syndromes the second most common (136/627). There were 6 cases of adult-onset Still's disease, systemic juvenile idiopathic arthritis, or hemophagocytic lymphohistiocytosis/macrophage activation syndrome. The average ferritin level in these syndromes was 14242 μg/L. Seven patients appeared to have anemia of chronic inflammation, and in 5 patients, there was no clearly definable cause for hyperferritinemia. Although extremely elevated ferritin levels may be associated with rheumatologic diseases, more often they are found in patients with other conditions such as malignancy or infection. In addition, extremely high ferritin levels can be found in patients with seemingly indolent disease or levels of chronic inflammation.Journal of clinical rheumatology: practical reports on rheumatic & musculoskeletal diseases 08/2013; · 1.19 Impact Factor