Hepcidin regulation in a mouse model of acute hypoxia

Iron Metabolism and Inflammatory Mediators in Patients with Renal Dysfunction

Chronic kidney disease (CKD) affects around 850 million people worldwide, posing significant challenges in healthcare due to complications like renal anemia, end-stage kidney disease, and cardiovascular diseases. This review focuses on the intricate interplay between iron metabolism, inflammation, and renal dysfunction in CKD. Renal anemia, prevalent in CKD, arises primarily from diminished erythropoietin (EPO) production and iron dysregulation, which worsens with disease progression. Functional and absolute iron deficiencies due to impaired absorption and chronic inflammation are key factors exacerbating erythropoiesis. A notable aspect of CKD is the accumulation of uremic toxins, such as indoxyl sulfate (IS), which hinder iron metabolism and worsen anemia. These toxins directly affect renal EPO synthesis and contribute to renal hypoxia, thus playing a critical role in the pathophysiology of renal anemia. Inflammatory cytokines, especially TNF-α and IL-6, further exacerbate CKD progression and disrupt iron homeostasis, thereby influencing anemia severity. Treatment approaches have evolved to address both iron and EPO deficiencies, with emerging therapies targeting hepcidin and employing hypoxia-inducible factor (HIF) stabilizers showing potential. This review underscores the importance of integrated treatment strategies in CKD, focusing on the complex relationship between iron metabolism, inflammation, and renal dysfunction to improve patient outcomes.

Cardiac iron metabolism during aging - Role of inflammation and proteolysis

Iron is the most abundant trace element in the human body. Since iron can switch between its 2-valent and 3-valent form it is essential in various physiological processes such as energy production, proliferation or DNA synthesis. Especially high metabolic organs such as the heart rely on iron-associated iron-sulfur and heme proteins. However, due to switches in iron oxidation state, iron overload exhibits high toxicity through formation of reactive oxygen species, underlining the importance of balanced iron levels. Growing evidence demonstrates disturbance of this balance during aging. While age-associated cardiovascular diseases are often related to iron deficiency, in physiological aging cardiac iron accumulates. To understand these changes, we focused on inflammation and proteolysis, two hallmarks of aging, and their role in iron metabolism. Via the IL-6-hepcidin axis, inflammation and iron status are strongly connected often resulting in anemia accompanied by infiltration of macrophages. This tight connection between anemia and inflammation highlights the importance of the macrophage iron metabolism during inflammation. Age-related decrease in proteolytic activity additionally affects iron balance due to impaired degradation of iron metabolism proteins. Therefore, this review accentuates alterations in iron metabolism during aging with regards to inflammation and proteolysis to draw attention to their implications and associations.

Development of albumin monitoring system with hepatic hypoxia-on-a-chip

Hypoxia plays an essential role in the pathogenesis of various liver diseases, and albumin is one of the important biomarkers secreted by the liver. In this study, we developed an albumin monitoring system composed of hepatic hypoxia-on-a-chip and an albumin sensor to study liver function change due to hypoxia. In hepatic hypoxia-on-a-chip, we vertically stack an oxygen-scavenging channel on a liver on a chip with a thin gas-permeable membrane in the middle. This unique design of the hepatic hypoxia-on-a-chip can help to induce hypoxia quickly, attaining <5% within 10 min. An electrochemical albumin sensor was fabricated based on the covalent immobilization of antibodies on the Au electrode to monitor albumin secreting function on the hepatic hypoxia-on-a-chip. Standard albumin samples spiked in PBS, and culture media were measured by the electrochemical impedance spectroscopy using the fabricated immunosensor. The LOD was calculated to be 10 ag/mL in both cases. Using the electrochemical albumin sensor, we measured albumin secretion in normoxia and hypoxia in the chips. The albumin concentration decreased to 27% after 24 h in hypoxia compared to normoxia. This response was consistent with physiological studies. With technical refinements, the present albumin monitoring system can be a powerful tool in studying hepatic hypoxia with real-time liver function monitoring.

Distinctive modulation of hepcidin in cancer and its therapeutic relevance

Hepcidin, a short peptide synthesized primarily by hepatocytes in response to increased body iron and inflammation, is a crucial iron-regulating factor. Hepcidin regulates intestinal iron absorption and releases iron from macrophages into plasma through a negative iron feedback mechanism. The discovery of hepcidin inspired a torrent of research into iron metabolism and related problems, which have radically altered our understanding of human diseases caused by an excess of iron, an iron deficiency, or an iron disparity. It is critical to decipher how tumor cells manage hepcidin expression for their metabolic requirements because iron is necessary for cell survival, particularly for highly active cells like tumor cells. Studies show that tumor and non-tumor cells express and control hepcidin differently. These variations should be explored to produce potential novel cancer treatments. The ability to regulate hepcidin expression to deprive cancer cells of iron may be a new weapon against cancer cells.

Hepcidin Signaling in Health and Disease: Ironing Out the Details

Hepcidin, a peptide hormone produced by hepatocytes, is the central regulator of systemic iron homeostasis through its interaction with ferroportin, the major cellular iron export protein. Hepcidin binding to ferroportin results in reduced iron export from macrophages and intestinal absorptive cells, leading to decreased serum iron levels. Hepcidin expression is influenced by several factors that include serum and liver iron stores, erythropoiesis, hypoxia, inflammation, and infection. Erythropoietic drive and hypoxia suppress hepcidin expression and promote red cell production. In contrast, inflammation and infection are associated with increased hepcidin production to sequester iron intracellularly as a means of depriving microorganisms of iron. Chronic inflammation may up-regulate hepcidin expression through the interleukin-6 (IL-6)-Janus kinase 2 (JAK2)-signal transducer and activator of transcription 3 (STAT3) pathway. The bone morphogenetic protein (BMP)-mothers against decapentaplegic homolog (SMAD) pathway is a major positive driver of hepcidin expression in response to either increased circulating iron in the form of transferrin or iron loading in organs. Hereditary hemochromatosis (HH) consists of several inherited disorders that cause inappropriately reduced hepcidin expression in response to body iron stores, leading to increased iron absorption from a normal diet. The most common form of HH is due to a mutation in the HFE gene, which causes a failure in the hepatocyte iron-sensing mechanism, leading to reduced hepcidin expression; the clinical manifestations of HFE-HH include increased serum transferrin-iron saturation and progressive iron loading in the liver and other tissues over time among patients who express the disease phenotype. In this article, we review the physiologic mechanisms and cellular pathways by which hepcidin expression is regulated, and the different forms of HH resulting from various mutations that cause hepcidin deficiency. We also review other drivers of hepcidin expression and the associated pathophysiologic consequences.

The Interplay between Drivers of Erythropoiesis and Iron Homeostasis in Rare Hereditary Anemias: Tipping the Balance

Rare hereditary anemias (RHA) represent a group of disorders characterized by either impaired production of erythrocytes or decreased survival (i.e., hemolysis). In RHA, the regulation of iron metabolism and erythropoiesis is often disturbed, leading to iron overload or worsening of chronic anemia due to unavailability of iron for erythropoiesis. Whereas iron overload generally is a well-recognized complication in patients requiring regular blood transfusions, it is also a significant problem in a large proportion of patients with RHA that are not transfusion dependent. This indicates that RHA share disease-specific defects in erythroid development that are linked to intrinsic defects in iron metabolism. In this review, we discuss the key regulators involved in the interplay between iron and erythropoiesis and their importance in the spectrum of RHA.

A Novel Choice to Correct Inflammation-Induced Anemia in CKD: Oral Hypoxia-Inducible Factor Prolyl Hydroxylase Inhibitor Roxadustat

Anemia is a complication of chronic kidney disease (CKD), primarily due to insufficient secretion of erythropoietin (EPO) by the kidney. Erythropoiesis-stimulating agents (ESAs) are used to treat anemia associated with chronic kidney disease. A poor response to ESAs has been associated with inflammation. Inflammation can affect erythrocytes and its production in many ways, but mainly through the inflammatory cytokine IL-6 to stimulate the synthesis of hepcidin in the liver. Hepcidin causes iron insufficiency, which causes erythrocytes to fail to mature normally. In addition, inhibition of bone marrow erythroid precursor cells by inflammatory cytokines such as IL-1 and TNF-α also affects bone marrow hematopoiesis. These cytokines are also important factors leading to EPO resistance. Roxadustat is a new drug for the treatment of renal anemia. In addition to promoting the production of EPO, clinical trials have shown that it can significantly reduce hepcidin and can potentially be used for the treatment of inflammation-induced anemia in CKD.

Hypoxia-induced hsa_circ_0000826 is linked to liver metastasis of colorectal cancer

Background

hsa_circ_0000826 has been previously linked to CRC through the competing endogenous RNA network; however, the upstream driver of hsa_circ_0000826 elevation remains unknown. In this study, we aim to elucidate the effect of hypoxia‐induced hsa_circ_0000826 on CRC tumorigenesis and metastasis.

Methods

RNA scope assay was used to evaluate the expression of hsa_circ_0000826 in CRC cells under hypoxia condition. The effects of hsa_circ_0000826 on phenotypes of CRC cells were evaluated through cell migration and invasion assay. The nude, AOM‐DSS model mice and APC^Min/+ mice were used to investigate the relationship between circ_0000826, hypoxia, and CRC in mice. A total of 100 CRC tissue samples, as well as the paired adjacent tissues, were collected, and qRT‐PCR assay was used to detect the expression of hsa_circ_0000826 in these samples.

Results

Hypoxia‐induced hsa_circ_0000826 overexpression can increase the malignant phenotypes, tumor formation, and metastasis capability of CRC cells in vitro. mmu_circ_0000826 levels were significantly increased in the CRC tissues from AOM‐DSS and APC mice model under hypoxia conditions. Further, the hypoxia‐induced upregulation of mmu_circ_0000826 can also promote CRC tumorigenesis and liver metastasis in vivo. The expression of hsa_circ_0000826 in serum was significantly increased in CRC tissues in 100‐pair of CRC and according to the adjacent normal tissues by qRT‐PCR assays. Moreover, the expression levels of hsa_circ_0000826 in serum of patient with liver metastasis were significantly increased than those without metastasis.

Conclusion

Our results suggested that hsa_circ_0000826 was induced by the hypoxia in CRC, which can be a potential biomarker of CRC liver metastasis.

High-Altitude Acclimatization Suppresses Hepcidin Expression During Severe Energy Deficit

Hennigar, Stephen R., Claire E. Berryman, Alyssa M. Kelley, Bradley J. Anderson, Andrew J. Young, James P. McClung, and Stefan M. Pasiakos. High-altitude acclimatization suppresses hepcidin expression during severe energy deficit. High Alt Med Biol. 21:232-236, 2020. Background: The erythropoietic cells in the bone marrow require iron to synthesize heme for incorporation into hemoglobin. Exposure to hypoxic conditions, such as extended sojourns to high altitude (HA), results in increased erythropoiesis and an increased physiological requirement for iron. In addition to increasing iron requirements, hypoxic conditions suppress appetite and often lead to decreased energy intake. The objective of this study was to determine the combined effects of severe energy deficit and hypoxia on hepcidin and measures of iron status in lowlanders sojourning to HA. Methods: Iron status indicators and hepcidin were determined in 17 healthy male volunteers (mean ± standard deviation, age 23 ± 6 years, body mass index 27 ± 4 kg/m²) fed a controlled diet (12 ± 1.2 mg iron/day) during a 20-day sojourn to 4300 m above sea level. Results: Chronic exposure to HA during severe energy deficit increased hematocrit by 12% (p < 0.01) and decreased serum hepcidin by 37% (p < 0.01) compared with baseline. Ferritin declined by 18% (p = 0.02) and transferrin saturation and soluble transferrin receptor increased by 55% and 83%, respectively (p < 0.01 for both) compared with baseline. Conclusions: HA acclimatization suppresses hepcidin expression to increase iron availability during severe energy deficit. Registered at ClinicalTrials.gov as NCT02731066.

Inherited iron overload disorders

Hereditary iron overload includes several disorders characterized by iron accumulation in tissues, organs, or even single cells or subcellular compartments. They are determined by mutations in genes directly involved in hepcidin regulation, cellular iron uptake, management and export, iron transport and storage. Systemic forms are characterized by increased serum ferritin with or without high transferrin saturation, and with or without functional iron deficient anemia. Hemochromatosis includes five different genetic forms all characterized by high transferrin saturation and serum ferritin, but with different penetrance and expression. Mutations in HFE, HFE2, HAMP and TFR2 lead to inadequate or severely reduced hepcidin synthesis that, in turn, induces increased intestinal iron absorption and macrophage iron release leading to tissue iron overload. The severity of hepcidin down-regulation defines the severity of iron overload and clinical complications. Hemochromatosis type 4 is caused by dominant gain-of-function mutations of ferroportin preventing hepcidin-ferroportin binding and leading to hepcidin resistance. Ferroportin disease is due to loss-of-function mutation of SLC40A1 that impairs the iron export efficiency of ferroportin, causes iron retention in reticuloendothelial cell and hyperferritinemia with normal transferrin saturation. Aceruloplasminemia is caused by defective iron release from storage and lead to mild microcytic anemia, low serum iron, and iron retention in several organs including the brain, causing severe neurological manifestations. Atransferrinemia and DMT1 deficiency are characterized by iron deficient erythropoiesis, severe microcytic anemia with high transferrin saturation and parenchymal iron overload due to secondary hepcidin suppression. Diagnosis of the different forms of hereditary iron overload disorders involves a sequential strategy that combines clinical, imaging, biochemical, and genetic data. Management of iron overload relies on two main therapies: blood removal and iron chelators. Specific therapeutic options are indicated in patients with atransferrinemia, DMT1 deficiency and aceruloplasminemia.

Iron considerations for the athlete: a narrative review

Iron plays a significant role in the body, and is specifically important to athletes, since it is a dominant feature in processes such as oxygen transport and energy metabolism. Despite its importance, athlete populations, especially females and endurance athletes, are commonly diagnosed with iron deficiency, suggesting an association between sport performance and iron regulation. Although iron deficiency is most common in female athletes (~ 15-35% athlete cohorts deficient), approximately 5-11% of male athlete cohorts also present with this issue. Furthermore, interest has grown in the mechanisms that influence iron absorption in athletes over the last decade, with the link between iron regulation and exercise becoming a research focus. Specifically, exercise-induced increases in the master iron regulatory hormone, hepcidin, has been highlighted as a contributing factor towards altered iron metabolism in athletes. To date, a plethora of research has been conducted, including investigation into the impact that sex hormones, diet (e.g. macronutrient manipulation), training and environmental stress (e.g. hypoxia due to altitude training) have on an athlete's iron status, with numerous recommendations proposed for consideration. This review summarises the current state of research with respect to the aforementioned factors, drawing conclusions and recommendations for future work.

Deciphering the Iron Side of Stroke: Neurodegeneration at the Crossroads Between Iron Dyshomeostasis, Excitotoxicity, and Ferroptosis

In general, iron represents a double-edged sword in metabolism in most tissues, especially in the brain. Although the high metabolic demands of brain cells require iron as a redox-active metal for ATP-producing enzymes, the brain is highly vulnerable to the devastating consequences of excessive iron-induced oxidative stress and, as recently found, to ferroptosis as well. The blood-brain barrier (BBB) protects the brain from fluctuations in systemic iron. Under pathological conditions, especially in acute brain pathologies such as stroke, the BBB is disrupted, and iron pools from the blood gain sudden access to the brain parenchyma, which is crucial in mediating stroke-induced neurodegeneration. Each brain cell type reacts with changes in their expression of proteins involved in iron uptake, efflux, storage, and mobilization to preserve its internal iron homeostasis, with specific organelles such as mitochondria showing specialized responses. However, during ischemia, neurons are challenged with excess extracellular glutamate in the presence of high levels of extracellular iron; this causes glutamate receptor overactivation that boosts neuronal iron uptake and a subsequent overproduction of membrane peroxides. This glutamate-driven neuronal death can be attenuated by iron-chelating compounds or free radical scavenger molecules. Moreover, vascular wall rupture in hemorrhagic stroke results in the accumulation and lysis of iron-rich red blood cells at the brain parenchyma and the subsequent presence of hemoglobin and heme iron at the extracellular milieu, thereby contributing to iron-induced lipid peroxidation and cell death. This review summarizes recent progresses made in understanding the ferroptosis component underlying both ischemic and hemorrhagic stroke subtypes.

Iron metabolism under conditions of ineffective erythropoiesis in β-thalassemia

β-Thalassemia (BT) is an inherited genetic disorder that is characterized by ineffective erythropoiesis (IE), leading to anemia and abnormal iron metabolism. IE is an abnormal expansion of the number of erythroid progenitor cells with unproductive synthesis of enucleated erythrocytes, leading to anemia and hypoxia. Anemic patients affected by BT suffer from iron overload, even in the absence of chronic blood transfusion, suggesting the presence of ≥1 erythroid factor with the ability to modulate iron metabolism and dietary iron absorption. Recent studies suggest that decreased erythroid cell differentiation and survival also contribute to IE, aggravating the anemia in BT. Furthermore, hypoxia can also affect and increase iron absorption. Understanding the relationship between iron metabolism and IE could provide important insights into the BT condition and help to develop novel treatments. In fact, genetic or pharmacological manipulations of iron metabolism or erythroid cell differentiation and survival have been shown to improve IE, iron overload, and anemia in animal models of BT. Based on those findings, new therapeutic approaches and drugs have been proposed; clinical trials are underway that have the potential to improve erythrocyte production, as well as to reduce the iron overload and organ toxicity in BT and in other disorders characterized by IE.