Ferroportin and erythroid cells: an update

Iron metabolism and its contribution to cancer (Review)

Iron is an essential element for biological processes. Iron homeostasis is regulated through several mechanisms, from absorption by enterocytes to recycling by macrophages and storage in hepatocytes. Iron has dual properties, which may facilitate tumor growth or cell death. Cancer cells exhibit an increased dependence on iron compared with normal cells. Macrophages potentially deliver iron to cancer cells, resulting in tumor promotion. Mitochondria utilize cellular iron to synthesize cofactors, including heme and iron sulfur clusters. The latter is composed of essential enzymes involved in DNA synthesis and repair, oxidation‑reduction reactions, and other cellular processes. However, highly increased iron concentrations result in cell death through membrane lipid peroxidation, termed ferroptosis. Ferroptosis, an emerging pathway for cancer treatment, is similar to pyroptosis, apoptosis and necroptosis. In the present review, previous studies on the physiology of iron metabolism and its role in cancer are summarized. Additionally, the significance of iron regulation, and the association between iron homeostasis and carcinogenic mechanisms are discussed.

Using a multi-biomarker approach to assess the effects of pollution on sand flathead (Platycephalus bassensis) from Port Phillip Bay, Victoria, Australia

Hepatic gene expression and liver histology were examined in sand flathead (Platycephalus bassensis) from six locations in Port Phillip Bay, Victoria, Australia. Four sets of genes including thyroid-related genes (D1, D2, TTR, TRα and TRβ), metal metabolism-related genes (MT, MTF1, TF, Ferritin and FPN1), apoptosis-related genes (Diablo/SMAC1, Diablo/SMAC2 and CYP1A) and an endoplasmic reticulum stress biomarker gene (GRP78) were examined in female flathead using qRT-PCR. TRβ and Diablo/SMAC1 gene expression was significantly up-regulated in fish from all polluted sites compared to those from a reference site. The transcripts of TRα and FPN1 were significantly higher in flathead from Corio Bay, while the hepatic mRNA of TTR and GRP78 were significantly lower in those fish. Positive correlations were observed between Diablo/SMAC1 and CYP1A, D2 and TRβ, TRα and TRβ. This study demonstrates that application of pathway-based biomarker genes and histopathology can provide comprehensive information on the impact of environmental pollutants on fish.

Iron toxicity and its possible association with treatment of Cancer: lessons from hemoglobinopathies and rare, transfusion-dependent anemias

Exposure to elevated levels of iron causes tissue damage and organ failure, and increases the risk of cancer. The toxicity of iron is mediated through generation of oxidants. There is also solid evidence indicating that oxidant stress plays a significant role in a variety of human disease states, including malignant transformation. Iron toxicity is the main focus when managing thalassemia. However, the short- and long-term toxicities of iron have not been extensively considered in children and adults treated for malignancy, and only recently have begun to draw oncologists' attention. The treatment of malignancy can markedly increase exposure of patients to elevated toxic iron species without the need for excess iron input from transfusion. This under-recognized exposure likely enhances organ toxicity and may contribute to long-term development of secondary malignancy and organ failure. This review discusses the current understanding of iron metabolism, the mechanisms of production of toxic free iron species in humans, and the relation of the clinical marker, transferrin saturation (TS), to the presence of toxic free iron. We will present epidemiological data showing that high TS is associated with poor outcomes and development of cancer, and that lowering free iron may improve outcomes. Finally, we will discuss the possible relation between some late complications seen in survivors of cancer and those due to iron toxicity.

Physiology and pathophysiology of iron in hemoglobin-associated diseases

Iron overload and iron toxicity, whether because of increased absorption or iron loading from repeated transfusions, can be major causes of morbidity and mortality in a number of chronic anemias. Significant advances have been made in our understanding of iron homeostasis over the past decade. At the same time, advances in magnetic resonance imaging have allowed clinicians to monitor and quantify iron concentrations noninvasively in specific organs. Furthermore, effective iron chelators are now available, including preparations that can be taken orally. This has resulted in substantial improvement in mortality and morbidity for patients with severe chronic iron overload. This paper reviews the key points of iron homeostasis and attempts to place clinical observations in patients with transfusional iron overload in context with the current understanding of iron homeostasis in humans.

The cardiorenal syndrome in heart failure: cardiac? renal? syndrome?

There has been increasing interest on the so-called cardiorenal syndrome (CRS), defined as a complex pathophysiological disorder of the heart and kidneys whereby acute or chronic dysfunction in one organ may induce acute or chronic dysfunction in the other. In this review, we contend that there is lack of evidence warranting the adoption of a specific clinical construct such as the CRS within the heart failure (HF) syndrome by demonstrating that: (a) the approaches and tools regarding the definition of kidney involvement in HF are suboptimal; (b) development of renal failure in HF is often confounded by age, hypertension, and diabetes; (c) worsening of renal function (WRF) in HF may be largely independent of alterations in cardiac function; (d) the bidirectional association between HF and renal failure is not unique and represents one of the several such associations encountered in HF; and (e) inflammation is a common denominator for HF and associated noncardiac morbidities. Based on these arguments, we believe that dissecting one of the multiple bidirectional associations in HF and constructing the so-called cardiorenal syndrome is not justified pathophysiologically. Fully understanding of all morbid associations and not only the cardiorenal is of great significance for the clinician who is caring for the patient with HF.

Physiological focus on the erythropoietin-hepcidin-ferroportin axis

To analyze the interconnection between erythropoiesis and iron metabolism, one of the issues raised in this study was to know iron bioavailability under physiopathological conditions. Our aim was to understand the functional axis response composed of erythropoietin (Epo)-hepcidin-ferroportin (FPN), when 2 dysfunctional states coexist, using an animal model of iron overload followed by hypoxia. FPN and prohepcidin were assessed by immunohistochemistry using rabbit anti-mouse FPN polyclonal and prohepcidin monoclonal antibodies. Goat-labeled polymer - horseradish peroxidase anti-rabbit EnVision + System (DAB) was used as the secondary antibody. Epo levels were measured by ELISA. Tissue iron was studied by Prussian blue iron staining. Erythropoietic response was assessed using conventional hematological tests. Iron overload increased prohepcidin that remained high in hypoxia, coexisting with high levels of Epo in hypoxia, with or without iron overload. In hypoxia, FPN was clearly evident in reticuloendothelial macrophages, more than in hypoxia with iron overload. Interestingly, duodenal FPN was clearly identified on the basolateral membrane in hypoxia, with or without iron overload. Our data indicate that 2 signals could induce the cell-specific response as follows: (i) iron signal, induced prohepcidin, which reduced reticuloendothelial FPN and reduced iron availability; and (ii) hypoxia signal, stimulated Epo, which affected iron absorption by stabilizing duodenal FPN and allowed iron supply to erythropoiesis independently of store size.