Changes in the characteristics and distribution of ferritin in iron-loaded cell cultures

Induced eosinophilia and proliferation in Angiostrongylus cantonensis-infected mouse brain are associated with the induction of JAK/STAT1, IAP/NF-kappaB and MEKK1/JNK signals

Eosinophilic meningitis or meningoencephalitis caused by Angiostrongylus cantonensis is endemic to the Pacific area of Asia, especially Taiwan, Thailand, and Japan. Although eosinophilia is an important clinical manifestation of A. cantonensis infection, the role of eosinophils in the progress of the infection remains to be elucidated. In this experiment, we show that A. cantonensis-induced eosinophilia and inflammation might lead to the induction of IAP/NF-kappaB, JAK/STAT1 and MEKK1/JNK signals. The phosphorylation levels of JAK and JNK, STAT1, IAP, NF-kappaB and MEKK1 protein products were significantly increased after 12 days or 15 days of A. cantonensis infection. However, no significant differences in MAPKs such as Raf, MEK-1, ERK1/2 and p38 expression were found between control and infected mice. The activation potency of JAK/STAT1, IAP/NF-kappaB and MEKK1/JNK started increasing on day 3, with significant induction on day 12 or day 15 after A. cantonensis infection. Consistent results were noted in the pathological observations, including eosinophilia, leukocyte infiltration, granulomatous reactions, and time responses in the brain tissues of infected mice. These data suggest that the development of brain injury by eosinophilia of A. cantonensis infection is associated with activation of JAK/STAT1 signals by cytokines, and/or activation of MEKK1/JNK by oxidant stress, and/or activation of NF-kappaB by increasing IAP expression.

Development of brain injury in mice by Angiostrongylus cantonensis infection is associated with the induction of transcription factor NF-kappaB, nuclear protooncogenes, and protein tyrosine phosphorylation

Eosinophilic meningitis or meningoencephalitis caused by Angiostrongylus cantonensis is endemic to the Pacific area of Asia, especially Taiwan, Thailand, and Japan. Although eosinophilia is an important clinical manifestation of A. cantonensis infection, the role of eosinophils in the progress of the infection remains to be elucidated. In this experiment, we showed that A. cantonensis-caused eosinoplia and inflammation might lead to the induction of NF-kappaB and protooncogene expression via activation of the tyrosine phosphorylation signal pathway. After mice were infected daily with 30 third-stage larvae of A. cantonensis by oral adminstration for 6 weeks, no significant differences PKC-alpha, MEK-1, ERK-2, JNK, and p38 protein expression were found between the control and infected mice. However, the protein tyrosine phosphorylation levels, NF-kappaB, and iNOS protein products were significantly increased by 3.5-, 3.3-, and 6.3-fold, respectively, after 3 weeks of A. cantonensis infection. The same pattern was found for c-Myc, c-Jun, and c-Fos proteins, which were elevated by 3.2-, 2.3-, and 3.4-fold, respectively, compared to control animals after 3 weeks. The expression potency of these proteins started increasing in week 1, reaching maximal induction in week 3, and then declining in week 5 after A. cantonensis infection. Another consistent result was noted in the pathological observations, including eosinophilia, leukocyte infiltration, granulomatous reactions, and time responses in brain tissues of infected mice. These data suggest that the development of brain injury by eosinophlia of A. cantonensis infection is associated with NF-kappaB and/or nuclear protooncogenes expression, which is activated by the tyrosine phosphorylation pathway.

Ferritin: the role of aluminum in ferritin function

We previously showed that human brain ferritin (HBF) binds aluminum (Al) in vivo and in vitro and HBF isolated from Alzheimer's brain had more Al bound compared to aged matched controls (7). To further understand the role ferritin may play in Al neurotoxicity, we have studied in vitro the effect of Al on the function of human ferritin isolated from Alzheimer's (AD) and normal brain tissue, and compared the results with other mammalian ferritins. Al causes a concentration-dependent decrease in the initial rate of iron loading into apo-horse spleen and human brain ferritin and the rates were similar for ferritin isolated from both AD and normal brains. The rates of iron release of mammalian ferritins from different tissues were determined: horse spleen much greater than human liver greater than rat brain greater than human brain = rat liver ferritin. The rates of iron release of AD and normal human brain ferritin were similar and were unaffected by preloading with Al. Several mammalian ferritins were compared for their total iron uptake: horse spleen = human liver greater than human brain (normal) = human brain (AD) ferritin. In 20 mM HEPES (pH 6.0) buffer holoferritin is more resistant to precipitation by Al than apoferritin suggesting that holoferritin is a better chelator for nonferrous metal ions.

Expression of isoferritins in peripheral blood lymphocytes: effect of phytohaemagglutinin and iron

This study shows that incubation of lymphocytes in phytohaemagglutinin medium together with iron supplementation leads to an increase of ferritin synthesis concomitant with increased intracellular ferritin concentration especially of heart-type ferritin. Increasing levels of iron do not increase heart-type ferritin concentration further; in contrast, spleen-type ferritin is gradually increased with increasing iron levels. The preferential increase in spleen-type ferritin on growth in iron-enriched medium may be explained by two distinct roles in the metabolism of these two isoferritins. Heart-type isoferritin appears to be involved in more active iron metabolism in lymphocytes whilst the spleen-type isoferritin may function as an intracellular depot of excess iron that is not immediately utilised for metabolic activity.

Siderosomal ferritin. The missing link between ferritin and haemosiderin?

A minor electrophoretically fast component was found in ferritin from iron-loaded rat liver in addition to a major electrophoretically slow ferritin similar to that observed in control rats. The electrophoretically fast ferritin showed immunological identity with the slow component, but on electrophoresis in SDS it gave a peptide of 17.3 kDa, in contrast with the electrophoretically slow ferritin, which gave a major band corresponding to the L-subunit (20.7 kDa). Thus the electrophoretically fast ferritin resembles that reported by Massover [(1985) Biochim. Biophys. Acta 829, 377-386] in livers of mice with short-term parenteral iron overload. The electrophoretically fast ferritin had a lower iron content (2000 Fe atoms/molecule) than the electrophoretically slow ferritin (3000 Fe atoms/molecule). Removal and re-incorporation of iron was possible without effect on the electrophoretic mobility of either ferritin species. On subcellular fractionation the electrophoretically fast ferritin was enriched in pellet fractions and was the sole soluble ferritin isolated from iron-laden secondary lysosomes (siderosomes). The amount and relative proportion of the electrophoretically fast species increased with iron loading. Haemosiderin isolated from siderosomes was found to contain a peptide reactive to anti-ferritin serum and corresponding to the 17.3 kDa peptide of the electrophoretically fast ferritin species. Unlike the electrophoretically slow ferritin, the electrophoretically fast ferritin did not become significantly radioactive in a 1 h biosynthetic labelling experiment. We conclude that the minor ferritin is not, as has been suggested for mouse liver ferritin, 'a completely new species of smaller holoferritin that represents a shift in the ferritin phenotype' in response to siderosis, but a precursor of haemosiderin, in agreement with the proposal by Richter [(1984) Lab. Invest. 50, 26-35] concerning siderosomal ferritin.

Macrophage ferritin and iron deposition in the rat air pouch model of inflammatory synovitis

Using a rat air pouch model of red cell promoted allergic inflammation, we have investigated the relation between ferritin synthesis and iron deposition in pouch wall lining cells. These cells have structural and immunohistochemical similarities to human synovial intimal cells and studies of them are pertinent to the clinical situation. In control air pouch wall tissue after single or double antigenic challenge the (apo)ferritin containing macrophages are most numerous seven days after antigenic challenge when there is active connective tissue proliferation and a generalised mononuclear cell response in the pouch wall, suggesting that (apo)ferritin is produced in macrophages as part of the tissue inflammatory response. In contrast with control tissue, where there is a steady decrease in positive cells over the ensuing weeks, injection of blood into both single and double challenge air pouches produces a significant (p less than 0.001) and continuing rise in the numbers of ferritin containing macrophages after day 7. Also, after 14 days Perls' positive ferric iron is detectable in increasing numbers of ferritin containing macrophages, a trend which is more marked in double challenge, blood injected air pouches. The histological data clearly show that there is a close relation between the presence of Perls' iron and proliferation of vascular and connective tissue elements in the pouch wall. We propose that this proinflammatory role of iron is the result of its ability to promote oxidative damage in tissues, and discuss ways in which this may take place.

Iron-induced changes in rat liver isoferritins

The effects of single and of multiple iron injection on the distribution of isoferritins was studied in rat liver with the aid of 14C-labelling either after or before iron treatment. Several effects of iron can be seen. Analysis of protein and labelling patterns show that it not only produces a disproportionate increase in the more-basic isoferritins, but may, in sufficient dose, actually lead to a decrease in the more-acidic isoferritins. Use of iron injection after radioactivity shows that it must give rise to post-assembly changes causing acidic isoferritins to become more basic. With a moderate iron dose this change is relatively slow, taking several hours, and seems to occur in addition to a differential stimulation of the synthesis of the more-basic isoferritins. With higher iron dosage the post-assembly changes may be so rapid that it is difficult to distinguish them from a switch in the pattern of synthesis.

The nature of iron deposits in haemophilic synovitis. An immunohistochemical, ultrastructural and X-ray microanalytical study

Using a computerized electron-probe X-ray microanalytical technique to measure phosphorus/iron ratios we have defined the iron saturation of ferritin in vitro from prepared ferritin standards of known iron loading. This technique has been applied to the study of 5 haemophilic synovial membranes. At light microscope level the distribution and relationship of iron/ferritin were defined using Perls' reaction and an immunoperoxidase technique respectively. The synovia from all cases contained intra and extra-cellular deposits of Perls' positive material which were granular in nature in the most superficial synovial cells. There were increasing numbers of pheomorphic (1-12 micron diameter ovate bodies in the deeper synovial layers. Immunoperoxidase ferritin staining produced a strongly positive reaction in the granular material but the ovate bodies were negative with the exception of some peripheral staining. X-ray microanalysis showed the granular material to be highly iron saturated ferritin and the ovate bodies to be almost pure iron. We suggest that iron saturated ferritin in the synovial membrane could increase/perpetuate inflammation by promoting lipid peroxidation.

Accumulation and release of isoferritins during incubation in vitro of human peripheral blood mononuclear cells

Ferritin concentration has been measured in peripheral blood mononuclear cells and in the incubation medium following in vitro culture. Antibodies to both heart and spleen ferritin were used. Mononuclear cells cultured in medium containing about 12 mumol Fe/l accumulate ferritin rapidly with an increase in the heart:spleen ferritin ratio from 3:1 to about 10:1. Higher concentrations of iron (100 mumol/l) produce an even greater effect. The accumulation of ferritin is prevented by the addition of desferrioxamine (2 mmol/l) to the incubation medium. Accumulation of ferritin appears to take place largely in monocytes. Phagocytosis of red blood cells also causes rapid accumulation of ferritin but without any change in the heart:spleen ratio. Small amounts of both spleen and heart type ferritin are released during incubation in an iron containing medium and following phagocytosis of red blood cells. Some concanavalin A binding ferritin is also released suggesting that phagocytic cells may be a source of the concanavalin A binding ferritin found in normal plasma.

Iron overload disorders: natural history, pathogenesis, diagnosis, and therapy

Hemochromatosis is a syndrome which, when fully expressed, is manifested by melanoderma , diabetes mellitus, and liver cirrhosis, with iron overload involving parenchymal and reticuloendothelial cells in many organ systems. This clinical presentation may arise as a consequence of either hereditary or acquired abnormalities of iron overload, although the mechanisms are quite different. In hereditary hemochromatosis (also known as primary, or idiopathic, hemochromatosis), increased intestinal iron absorption leads to excessive accumulations of iron, throughout the body, particularly in parenchymal cells. In secondary forms of iron overload including transfusional hemosiderosis, alcoholic cirrhosis, thalassemia, sideroblastic anemia, and porphyria cutanea tarda, iron accumulates in the reticuloendothelial system initially, but with increasing amounts of total body iron, excessive iron deposits eventually accumulate in parenchymal cells throughout the body producing a picture indistinguishable from hereditary hemochromatosis. In this article, the course, prognosis, and therapy of iron overload will be reviewed in detail. Clinical and experimental data concerning the pathogenesis of the different forms of iron overload will be examined critically. In particular, information relating to possible abnormalities of reticuloendothelial function, intestinal mucosal iron transport, and alterations in serum and tissue isoferritin patterns in hereditary hemochromatosis will be analyzed, and possible directions for future research will be suggested. The mode of inheritance and linkage with the major histocompatibility (HLA) complex will be discussed. Theories on the pathogenesis of tissue damage by excess iron will be evaluated. Methods for measuring the extent of iron overload in clinical practice will be described, including measurements of serum iron, serum ferritin, iron absorption, cobalt excretion, desferrioxamine excretion, liver biopsy and tissue iron determinations, and HLA typing. Finally, unresolved problems in the understanding of the disease process, diagnosis, and therapy will be delineated.

Ferritin polymers and the formation of haemosiderin

When ferritin is isolated from Chang liver cells in culture iron loading is found to be associated with changes in the surface of the protein shell characterized by a change in immunoreactivity to anti "heart' and anti"spleen' antibodies at each specific pI and an overall shift in isoferritins to a lower pI range (Hoy & Jacobs, 1981). Ferritin polymers have been isolated from human tissues and their biochemical properties assessed in terms of these surface changes and the iron/protein ratio of the molecules. The results suggest that changes in the surface of ferritin molecules are associated with the formation of stable polymers. These are precursors of clumps of ferritin and eventually haemosiderin. Changes in the surface of the molecule may provide a signal for polymerization and incorporation of the protein within the lysosomes.