Regulation of tissue iron homeostasis: the macrophage "ferrostat"

Influence of Sex and Strain on Hepatic and Adipose Tissue Trace Element Concentrations and Gene Expression in C57BL/6J and DBA/2J High Fat Diet Models

The objective of this study was to determine the influence of sex and strain on the dysregulation of trace element concentration and associative gene expression due to diet induced obesity in adipose tissue and the liver. Male and female C57BL/6J (B6J) and DBA/2J (D2J) were randomly assigned to a normal-fat diet (NFD) containing 10% kcal fat/g or a mineral-matched high-fat diet (HFD) containing 60% kcal fat/g for 16 weeks. Liver and adipose tissue were assessed for copper, iron, manganese, and zinc concentrations and related changes in gene expression. Notable findings include three-way interactions of diet, sex, and strain amongst adipose tissue iron concentrations (p = 0.005), adipose hepcidin expression (p = 0.007), and hepatic iron regulatory protein (IRP) expression (p = 0.012). Cd11c to Cd163 ratio was increased in adipose tissue due to HFD amongst all biological groups except B6J females, for which tissue iron concentrations were reduced due to HFD (p = 0.002). Liver divalent metal transporter 1 (DMT-1) expression was increased due to HFD amongst B6J males (p < 0.005) and females (p < 0.004), which coincides with the reduction in hepatic iron concentrations found in these biological groups (p < 0.001). Sex, strain, and diet affected trace element concentration, the expression of genes that regulate trace element homeostasis, and the expression of macrophages that contribute to tissue iron-handling in adipose tissue. These findings suggest that sex and strain may be key factors that influence the adaptive capacity of iron mismanagement in adipose tissue and its subsequent consequences, such as insulin resistance.

The role of iron in host-microbiota crosstalk and its effects on systemic glucose metabolism

Iron is critical for the appearance and maintenance of life on Earth. Almost all organisms compete or cooperate for iron acquisition, demonstrating the importance of this essential element for the biological and physiological processes that are key for the preservation of metabolic homeostasis. In humans and other mammals, the bidirectional interactions between the bacterial component of the gut microbiota and the host for iron acquisition shape both host and microbiota metabolism. Bacterial functions influence host iron absorption, whereas the intake of iron, iron deficiency and iron excess in the host affect bacterial biodiversity, taxonomy and function, resulting in changes in bacterial virulence. These consequences of the host-microbial crosstalk affect systemic levels of iron, its storage in different tissues and host glucose metabolism. At the interface between the host and the microbiota, alterations in the host innate immune system and in circulating soluble factors that regulate iron (that is, hepcidin, lipocalin 2 and lactoferrin) are associated with metabolic disease. In fact, patients with obesity-associated metabolic dysfunction and insulin resistance exhibit dysregulation in iron homeostasis and alterations in their gut microbiota profile. From an evolutionary point of view, the pursuit of two important nutrients - glucose and iron - has probably driven human evolution towards the most efficient pathways and genes for human survival and health.

Iron metabolism: pathways and proteins in homeostasis

Iron is essential to human survival. The biological role and trafficking of this trace essential inorganic element which is also a potential toxin is constantly being researched and unfolded. Vital for oxygen transport, DNA synthesis, electron transport, neurotransmitter biosynthesis and present in numerous other heme and non-heme enzymes the physiological roles are immense. Understanding the molecules and pathways that regulate this essential element at systemic and cellular levels are of importance in improving therapeutic strategies for iron related disorders. This review highlights the progress in understanding the metabolism and trafficking of iron along with the pathophysiology of iron related disorders.

Non-heme iron overload impairs monocyte to macrophage differentiation via mitochondrial oxidative stress

Iron is a key element for systemic oxygen delivery and cellular energy metabolism. Thus regulation of systemic and local iron metabolism is key for maintaining energy homeostasis. Significant changes in iron levels due to malnutrition or hemorrhage, have been associated with several diseases such as hemochromatosis, liver cirrhosis and COPD. Macrophages are key cells in regulating iron levels in tissues as they sequester excess iron. How iron overload affects macrophage differentiation and function remains a subject of debate. Here we used an in vitro model of monocyte-to-macrophage differentiation to study the effect of iron overload on macrophage function. We found that providing excess iron as soluble ferric ammonium citrate (FAC) rather than as heme-iron complexes derived from stressed red blood cells (sRBC) interferes with macrophage differentiation and phagocytosis. Impaired macrophage differentiation coincided with increased expression of oxidative stress-related genes. Addition of FAC also led to increased levels of cellular and mitochondrial reactive oxygen species (ROS) and interfered with mitochondrial function and ATP generation. The effects of iron overload were reproduced by the mitochondrial ROS-inducer rotenone while treatment with the ROS-scavenger N-Acetylcysteine partially reversed FAC-induced effects. Finally, we found that iron-induced oxidative stress interfered with upregulation of M-CSFR and MAFB, two crucial determinants of macrophage differentiation and function. In summary, our findings suggest that high levels of non-heme iron interfere with macrophage differentiation by inducing mitochondrial oxidative stress. These findings might be important to consider in the context of diseases like chronic obstructive pulmonary disease (COPD) where both iron overload and defective macrophage function have been suggested to play a role in disease pathogenesis.

Full spectrum cytometry improves the resolution of highly autofluorescent biological samples: Identification of myeloid cells in regenerating skeletal muscles

Autofluorescence (AF) is an intrinsic characteristic of cells caused by the presence of fluorescent biological compounds within the cell; these can include structural proteins (e.g., collagen and elastin), cellular organelles, and metabolites (e.g., aromatic amino acids). In flow cytometric studies, the presence of AF can lead to reduced antigen and population resolution, as well as the presence of artifacts due to false positive events. Here, we describe a methodology that uses the inherent ability of full spectrum cytometry to treat AF as a fluorochrome and to thereby separate it from the other fluorochromes of the assay. This method can be applied to complex inflamed tissues; for instance, in regenerating skeletal muscle we have developed a 16-color panel targeting highly autofluorescent myeloid cells. This represents a first step toward overcoming technological limitations in flow cytometry due to AF.

NCOA4 Regulates Iron Recycling and Responds to Hepcidin Activity and Lipopolysaccharide in Macrophages

Macrophages, via erythrophagocytosis, recycle iron from effete erythrocytes to newly developing red blood cells. Conversion of potentially cytotoxic levels of iron from its heme into nonheme form during iron recycling is safely accomplished via coordinated regulations of cellular iron transport and homeostasis. Herein, we demonstrate the roles and regulation of NCOA4 (nuclear receptor coactivator 4)-mediated ferritinophagy in macrophages after erythrophagocytosis using the mouse macrophage cell line J774 cells. Ferritin in J774 cells increased with the rise of nonheme iron by erythrocyte ingestion and declined when total cellular iron contents subsequently decreased. NCOA4, a selective autophagic cargo receptor for ferritin, was responsible for the control of cellular ferritin and total iron contents at the later stage of erythrophagocytosis. A hepcidin analog, which limits the flux of iron through iron-recycling by inhibiting iron export at the plasma membrane, repressed NCOA4 expression and led to accumulation of ferritin in the mouse macrophages. Transcriptome analyses revealed a functional association of immune response with NCOA4-dependent gene expressions, and we confirmed repression of Ncoa4 by lipopolysaccharide (LPS) in J774 cells and the spleen of mice. Collectively, our studies indicate that NCOA4 facilitates cellular ferritin turnover and the release of iron by macrophages after erythrophagocytosis and functions as a regulatory target for molecular signals of systemic iron overload and inflammation. These identify macrophage NCOA4 as a potential therapeutic target for disorders of systemic iron dysregulation, including anemia of inflammation and hemochromatosis.

Iron Deposition and Ferroptosis in the Spleen in a Murine Model of Acute Radiation Syndrome

Total body irradiation (TBI) can result in death associated with hematopoietic insufficiency. Although radiation causes apoptosis of white blood cells, red blood cells (RBC) undergo hemolysis due to hemoglobin denaturation. RBC lysis post-irradiation results in the release of iron into the plasma, producing a secondary toxic event. We investigated radiation-induced iron in the spleens of mice following TBI and the effects of the radiation mitigator captopril. RBC and hematocrit were reduced ~7 days (nadir ~14 days) post-TBI. Prussian blue staining revealed increased splenic Fe3+ and altered expression of iron binding and transport proteins, determined by qPCR, western blotting, and immunohistochemistry. Captopril did not affect iron deposition in the spleen or modulate iron-binding proteins. Caspase-3 was activated after ~7–14 days, indicating apoptosis had occurred. We also identified markers of iron-dependent apoptosis known as ferroptosis. The p21/Waf1 accelerated senescence marker was not upregulated. Macrophage inflammation is an effect of TBI. We investigated the effects of radiation and Fe3+ on the J774A.1 murine macrophage cell line. Radiation induced p21/Waf1 and ferritin, but not caspase-3, after ~24 h. Radiation ± iron upregulated several markers of pro-inflammatory M1 polarization; radiation with iron also upregulated a marker of anti-inflammatory M2 polarization. Our data indicate that following TBI, iron accumulates in the spleen where it regulates iron-binding proteins and triggers apoptosis and possible ferroptosis.

Active transport nanochelators for the reduction of liver iron burden in iron overload

Liver dysfunction and failure account for a major portion of premature deaths in patients suffering from various iron associated pathogeneses, particularly primary and secondary iron overload disorders, despite intensive treatment. The liver is a central player in iron homeostasis and a major iron storage organ, and currently, there are no active approaches for the excretion of excess liver iron. Herein, we report a new method for the rapid reduction of iron burden in iron overload diseases by developing a new class of liver targeted nanochelators with favorable pharmacokinetics and biodistribution. The new nanochelators bypass the reticuloendothelial system and specifically target hepatocytes without non-specific accumulation in other organs. The targeted nanochelators bound and neutralized excess iron in the liver and from the vasculature and, eventually leading to rapid hepatobiliary excretion of labile iron. Further, these rapidly excreted nanochelators did not induce toxicity in the liver, were highly cytocompatible in both iron overload and non-loaded conditions, and were promising in mitigating iron triggered free radical oxidative damage. These studies provide key insights into the development of organ targeted nanochelating systems and the rapid reduction of iron burden in vivo. This methodology allows for further development of nanotherapeutics for specific iron overload diseases.

Ferroptosis: The Potential Target in Heart Failure with Preserved Ejection Fraction

Ferroptosis is a recently identified cell death characterized by an excessive accumulation of iron-dependent reactive oxygen species (ROS) and lipid peroxides. Intracellular iron overload can not only cause damage to macrophages, endothelial cells, and cardiomyocytes through responses such as lipid peroxidation, oxidative stress, and inflammation, but can also affect cardiomyocyte Ca²⁺ handling, impair excitation–contraction coupling, and play an important role in the pathological process of heart failure with preserved ejection fraction (HFpEF). However, the mechanisms through which ferroptosis initiates the development and progression of HFpEF have not been established. This review explains the possible correlations between HFpEF and ferroptosis and provides a reliable theoretical basis for future studies on its mechanism.

Computational Modeling of Macrophage Iron Sequestration during Host Defense against Aspergillus

Iron is essential to the virulence of Aspergillus species, and restricting iron availability is a critical mechanism of antimicrobial host defense. Macrophages recruited to the site of infection are at the crux of this process, employing multiple intersecting mechanisms to orchestrate iron sequestration from pathogens. To gain an integrated understanding of how this is achieved in aspergillosis, we generated a transcriptomic time series of the response of human monocyte-derived macrophages to Aspergillus and used this and the available literature to construct a mechanistic computational model of iron handling of macrophages during this infection. We found an overwhelming macrophage response beginning 2 to 4 h after exposure to the fungus, which included upregulated transcription of iron import proteins transferrin receptor-1, divalent metal transporter-1, and ZIP family transporters, and downregulated transcription of the iron exporter ferroportin. The computational model, based on a discrete dynamical systems framework, consisted of 21 3-state nodes, and was validated with additional experimental data that were not used in model generation. The model accurately captures the steady state and the trajectories of most of the quantitatively measured nodes. In the experimental data, we surprisingly found that transferrin receptor-1 upregulation preceded the induction of inflammatory cytokines, a feature that deviated from model predictions. Model simulations suggested that direct induction of transferrin receptor-1 (TfR1) after fungal recognition, independent of the iron regulatory protein-labile iron pool (IRP-LIP) system, explains this finding. We anticipate that this model will contribute to a quantitative understanding of iron regulation as a fundamental host defense mechanism during aspergillosis.

IMPORTANCE Invasive pulmonary aspergillosis is a major cause of death among immunosuppressed individuals despite the best available therapy. Depriving the pathogen of iron is an essential component of host defense in this infection, but the mechanisms by which the host achieves this are complex. To understand how recruited macrophages mediate iron deprivation during the infection, we developed and validated a mechanistic computational model that integrates the available information in the field. The insights provided by this approach can help in designing iron modulation therapies as anti-fungal treatments.

Novel insights into alcoholic liver disease: Iron overload, iron sensing and hemolysis

The liver is the major target organ of continued alcohol consumption at risk and resulting alcoholic liver disease (ALD) is the most common liver disease worldwide. The underlying molecular mechanisms are still poorly understood despite decades of scientific effort limiting our abilities to identify those individuals who are at risk to develop the disease, to develop appropriate screening strategies and, in addition, to develop targeted therapeutic approaches. ALD is predestined for the newly evolving translational medicine, as conventional clinical and health care structures seem to be constrained to fully appreciate this disease. This concept paper aims at summarizing the 15 years translational experience at the Center of Alcohol Research in Heidelberg, namely based on the long-term prospective and detailed characterization of heavy drinkers with mortality data. In addition, novel experimental findings will be presented. A special focus will be the long-known hepatic iron accumulation, the somewhat overlooked role of the hematopoietic system and novel insights into iron sensing and the role of hepcidin. Our preliminary work indicates that enhanced red blood cell (RBC) turnover is critical for survival in ALD patients. RBC turnover is not primarily due to vitamin deficiency but rather to ethanol toxicity directly targeted to erythrocytes but also to the bone marrow stem cell compartment. These novel insights also help to explain long-known aspects of ALD such as mean corpuscular volume of erythrocytes (MCV) and elevated aspartate transaminase (GOT/AST) levels. This work also aims at identifying future projects, naming unresolved observations, and presenting novel hypothetical concepts still requiring future validation.

Dissecting the treatment-naive ecosystem of human melanoma brain metastasis

Melanoma brain metastasis (MBM) frequently occurs in patients with advanced melanoma; yet, our understanding of the underlying salient biology is rudimentary. Here, we performed single-cell/nucleus RNA-seq in 22 treatment-naive MBMs and 10 extracranial melanoma metastases (ECMs) and matched spatial single-cell transcriptomics and T cell receptor (TCR)-seq. Cancer cells from MBM were more chromosomally unstable, adopted a neuronal-like cell state, and enriched for spatially variably expressed metabolic pathways. Key observations were validated in independent patient cohorts, patient-derived MBM/ECM xenograft models, RNA/ATAC-seq, proteomics, and multiplexed imaging. Integrated spatial analyses revealed distinct geography of putative cancer immune evasion and evidence for more abundant intra-tumoral B to plasma cell differentiation in lymphoid aggregates in MBM. MBM harbored larger fractions of monocyte-derived macrophages and dysfunctional TOX+CD8+ T cells with distinct expression of immune checkpoints. This work provides comprehensive insights into MBM biology and serves as a foundational resource for further discovery and therapeutic exploration.

An Iron Refractory Phenotype in Obese Adipose Tissue Macrophages Leads to Adipocyte Iron Overload

Adipocyte iron overload is a maladaptation associated with obesity and insulin resistance. The objective of the current study was to determine whether and how adipose tissue macrophages (ATMs) regulate adipocyte iron concentrations and whether this is impacted by obesity. Using bone marrow-derived macrophages (BMDMs) polarized to M0, M1, M2, or metabolically activated (MMe) phenotypes, we showed that MMe BMDMs and ATMs from obese mice have reduced expression of several iron-related proteins. Furthermore, the bioenergetic response to iron in obese ATMs was hampered. ATMs from iron-injected lean mice increased their glycolytic and respiratory capacities, thus maintaining metabolic flexibility, while ATMs from obese mice did not. Using an isotope-based system, we found that iron exchange between BMDMs and adipocytes was regulated by macrophage phenotype. At the end of the co-culture, MMe macrophages transferred and received more iron from adipocytes than M0, M1, and M2 macrophages. This culminated in a decrease in total iron in MMe macrophages and an increase in total iron in adipocytes compared with M2 macrophages. Taken together, in the MMe condition, the redistribution of iron is biased toward macrophage iron deficiency and simultaneous adipocyte iron overload. These data suggest that obesity changes the communication of iron between adipocytes and macrophages and that rectifying this iron communication channel may be a novel therapeutic target to alleviate insulin resistance.

Ferroptosis and its role in cardiomyopathy

Heart disease is the leading cause of death worldwide. Cardiomyopathy is a disease characterized by the heart muscle damage, resulting heart in a structurally and functionally change, as well as heart failure and sudden cardiac death. The key pathogenic factor of cardiomyopathy is the loss of cardiomyocytes, but the related molecular mechanisms remain unclear. Ferroptosis is a newly discovered regulated form of cell death, characterized by iron accumulation and lipid peroxidation during cell death. Recent studies have shown that ferroptosis plays an important regulatory roles in the occurrence and development of many heart diseases such as myocardial ischemia/reperfusion injury, cardiomyopathy and heart failure. However, the systemic association of ferroptosis and cardiomyopathy remains largely unknown and needs to be elucidated. In this review, we provide an overview of the molecular mechanisms of ferroptosis and its role in individual cardiomyopathies, highlight that targeting ferroptosis maybe a potential therapeutic strategy for cardiomyopathy therapy in the future.

Potential role of selenium in alleviating obesity-related iron dyshomeostasis

Obesity is a serious health problem in modern life and increases the risk of many comorbidities including iron dyshomeostasis. In contrast to malnourished anemia, obesity-related iron dyshomeostasis is mainly caused by excessive fat accumulation, inflammation, and disordered gut microbiota. In obesity, iron dyshomeostasis also induces disorders associated with gut microbiota, neurodegenerative injury, oxidative damage, and fat accumulation in the liver. Selenium deficiency is often accompanied by obesity or iron deficiency, and selenium supplementation has been shown to alleviate obesity and overcome iron deficiency. Selenium inhibits fat accumulation and exhibits anti-inflammatory activity. It regulates gut microbiota, prevents neurodegenerative injury, alleviates oxidative damage to the body, and ameliorates hepatic fat accumulation. These effects theoretically meet the requirements for the inhibition of factors underlying obesity-related iron dyshomeostasis. Selenium supplementation may have a potential role in the alleviation of obesity-related iron dyshomeostasis. This review verifies this hypothesis in theory. All the currently reported causes and results of obesity-related iron dyshomeostasis are reviewed comprehensively, together with the effects of selenium. The challenges and strategies of selenium supplementation are also discussed. The findings demonstrate the possibility of selenium-containing drugs or functional foods in alleviating obesity-related iron dyshomeostasis.

Iron-Deficiency in Atopic Diseases: Innate Immune Priming by Allergens and Siderophores

Although iron is one of the most abundant elements on earth, about a third of the world's population are affected by iron deficiency. Main drivers of iron deficiency are beside the chronic lack of dietary iron, a hampered uptake machinery as a result of immune activation. Macrophages are the principal cells distributing iron in the human body with their iron restriction skewing these cells to a more pro-inflammatory state. Consequently, iron deficiency has a pronounced impact on immune cells, favoring Th2-cell survival, immunoglobulin class switching and primes mast cells for degranulation. Iron deficiency during pregnancy increases the risk of atopic diseases in children, while both children and adults with allergy are more likely to have anemia. In contrast, an improved iron status seems to protect against allergy development. Here, the most important interconnections between iron metabolism and allergies, the effect of iron deprivation on distinct immune cell types, as well as the pathophysiology in atopic diseases are summarized. Although the main focus will be humans, we also compare them with innate defense and iron sequestration strategies of microbes, given, particularly, attention to catechol-siderophores. Similarly, the defense and nutritional strategies in plants with their inducible systemic acquired resistance by salicylic acid, which further leads to synthesis of flavonoids as well as pathogenesis-related proteins, will be elaborated as both are very important for understanding the etiology of allergic diseases. Many allergens, such as lipocalins and the pathogenesis-related proteins, are able to bind iron and either deprive or supply iron to immune cells. Thus, a locally induced iron deficiency will result in immune activation and allergic sensitization. However, the same proteins such as the whey protein beta-lactoglobulin can also transport this precious micronutrient to the host immune cells (holoBLG) and hinder their activation, promoting tolerance and protecting against allergy. Since 2019, several clinical trials have also been conducted in allergic subjects using holoBLG as a food for special medical purposes, leading to a reduction in the allergic symptom burden. Supplementation with nutrient-carrying lipocalin proteins can circumvent the mucosal block and nourish selectively immune cells, therefore representing a new dietary and causative approach to compensate for functional iron deficiency in allergy sufferers.

Crosstalk between Heme Oxygenase-1 and Iron Metabolism in Macrophages: Implications for the Modulation of Inflammation and Immunity

Heme oxygenase-1 (HO-1) is an enzyme that catalyzes the degradation of heme, releasing equimolar amounts of carbon monoxide (CO), biliverdin (BV), and iron. The anti-inflammatory and antioxidant properties of HO-1 activity are conferred in part by the release of CO and BV and are extensively characterized. However, iron constitutes an important product of HO-1 activity involved in the regulation of several cellular biological processes. The macrophage-mediated recycling of heme molecules, in particular those contained in hemoglobin, constitutes the major mechanism through which living organisms acquire iron. This process is finely regulated by the activities of HO-1 and of the iron exporter protein ferroportin. The expression of both proteins can be induced or suppressed in response to pro- and anti-inflammatory stimuli in macrophages from different tissues, which alters the intracellular iron concentrations of these cells. As we discuss in this review article, changes in intracellular iron levels play important roles in the regulation of cellular oxidation reactions as well as in the transcriptional and translational regulation of the expression of proteins related to inflammation and immune responses, and therefore, iron metabolism represents a potential target for the development of novel therapeutic strategies focused on the modulation of immunity and inflammation.

Iron imbalance in cancer: Intersection of deficiency and overload

Iron, an essential trace element, plays a complex role in tumour biology. While iron causes cancer clearance through toxic free radical generation, iron‐induced free radical flux also acts as a cancer promoter. These fates majorly guided through cellular response towards pro‐oxidant and antioxidant settings in a tumour microenvironment, designate iron‐induced oxidative stress as a common yet paradoxical factor in pro‐tumorigenesis as well as anti‐tumorigenesis, posing a challenge to laying down iron thresholds favouring tumour clearance. Additionally, complexity of iron's association with carcinogenesis has been extended to iron‐induced ROS's involvement in states of both iron deficiency and overload, conditions identified as comparable, inevitable and significant coexisting contributors as well as outcomes in chronic infections and tumorigenesis. Besides, iron overload may also develop as an unwanted outcome in certain cancer patients, as a result of symptomatic anaemia treatment owed to irrational iron‐restoration therapies without a prior knowledge of body's iron status with both conditions synergistically acting towards tumour aggravation. The co‐play of iron deficiency and overload along with iron's pro‐tumour and antitumour roles with intersecting mechanisms, thus presents an unpredictable regulatory response loop in a state of malignancy. The relevance of iron's thresholds beyond which it proves to be beneficial against tumorigenesis hence becomes questionable. These factors pose a challenge, over establishing if iron chelation or iron flooding acts as a better approach towards antitumour therapies. This review presents a critical picture of multiple contrasting features of iron's behaviour in cancer, leading towards two conditions lying at opposite ends of a spectrum: iron deficiency and overload in chronic disease conditions including cancer, hence, validating the critical significance of diagnosis of patients' iron status prior to opting for subsequent therapies.

NOD1 splenic activation confers ferroptosis protection and reduces macrophage recruitment under pro-atherogenic conditions

The bioavailability and regulation of iron is essential for central biological functions in mammals. The role of this element in ferroptosis and the dysregulation of its metabolism contribute to diseases, ranging from anemia to infections, alterations in the immune system, inflammation and atherosclerosis. In this sense, monocytes and macrophages modulate iron metabolism and splenic function, while at the same time they can worsen the atherosclerotic process in pathological conditions. Since the nucleotide-binding oligomerization domain 1 (NOD1) has been linked to numerous disorders, including inflammatory and cardiovascular diseases, we investigated its role in iron homeostasis. The iron content was measured in various tissues of Apoe^-/- and Apoe^-/-Nod1^-/- mice fed a high-fat diet (HFD) for 4 weeks, under normal or reduced splenic function after ligation of the splenic artery. In the absence of NOD1 the iron levels decreased in spleen, heart and liver regardless the splenic function. This iron decrease was accompanied by an increase in the recruitment of F4/80⁺-macrophages in the spleen through a CXCR2-dependent signaling, as deduced by the reduced recruitment after administration of a CXCR2 inhibitor. CXCR2 mediates monocyte/macrophage chemotaxis to areas of inflammation and accumulation of leukocytes in the atherosclerotic plaque. Moreover, in the absence of NOD1, inhibition of CXCR2 enhanced atheroma progression. NOD1 activation increased the levels of GPX4 and other iron and ferroptosis regulatory proteins in macrophages. Our findings highlight the preeminent role of NOD1 in iron homeostasis and ferroptosis. These results suggest promising avenues of investigation for the diagnosis and treatment of iron-related diseases directed by NOD1.

Metabolism of tissue macrophages in homeostasis and pathology

Cellular metabolism orchestrates the intricate use of tissue fuels for catabolism and anabolism to generate cellular energy and structural components. The emerging field of immunometabolism highlights the importance of cellular metabolism for the maintenance and activities of immune cells. Macrophages are embryo- or adult bone marrow-derived leukocytes that are key for healthy tissue homeostasis but can also contribute to pathologies such as metabolic syndrome, atherosclerosis, fibrosis or cancer. Macrophage metabolism has largely been studied in vitro. However, different organs contain diverse macrophage populations that specialize in distinct and often tissue-specific functions. This context specificity creates diverging metabolic challenges for tissue macrophage populations to fulfill their homeostatic roles in their particular microenvironment and conditions their response in pathological conditions. Here, we outline current knowledge on the metabolic requirements and adaptations of macrophages located in tissues during homeostasis and selected diseases.

The role of ferroptosis in acute lung injury

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a common disease with high morbidity and mortality, and its pathogenesis is believed to be related to oxidative stress, apoptosis, inflammation, and hypoxia. Ferroptosis is a type of nonapoptotic cell death characterized by iron-dependent lipid peroxide accumulation and is involved in many cellular physiological processes. Recent studies have confirmed that ferroptosis may be involved in the development of ALI. This review summarizes the most recent discoveries on the role of ferroptosis in ALI to provide new strategies for its prevention and treatment.

Erythrophagocytosis by Microglia/Macrophage in Intracerebral Hemorrhage: From Mechanisms to Translation

Intracerebral hemorrhage (ICH) is a devastating condition characterized by hematoma related mass effect. Microglia/macrophage (M φ) are rapidly recruited in order to remove the red blood cells through erythrophagocytosis. Efficient erythrophagocytosis can detoxify hemolytic products and facilitate neurological recovery after ICH. The underlying mechanisms include modulation of inflammatory response and oxidative stress, among others. It is a dynamic process mediated by a cascade of signal transduction, including “find-me” signals, “eat-me” signals and a set of phagocytotic receptors-ligand pairs that may be exploited as therapeutic targets. This review summarizes mechanistic signaling pathways of erythrophagocytosis and highlights the potential of harnessing M φ-mediated phagocytosis for ICH treatment.

Macrophages, Metabolism and Heterophagy in the Heart

The heart is a never-stopping engine that relies on a formidable pool of mitochondria to generate energy and propel pumping. Because dying cardiomyocytes cannot be replaced, this high metabolic rate creates the challenge of preserving organelle fitness and cell function for life. Here, we provide an immunologist's perspective on how the heart solves this challenge, which is in part by incorporating macrophages as an integral component of the myocardium. Cardiac macrophages surround cardiomyocytes and capture dysfunctional mitochondria that these cells eject to the milieu, effectively establishing a client cell-support cell interaction. We refer to this heterologous partnership as heterophagy. Notably, this process shares analogies with other biological systems, is essential for proteostasis and metabolic fitness of cardiomyocytes, and unveils a remarkable degree of dependence of the healthy heart on immune cells for everyday function.

A detrimental role of NLRP6 in host iron metabolism during Salmonella infection

Maintaining host iron homeostasis is an essential component of nutritional immunity responsible for sequestrating iron from pathogens and controlling infection. Nucleotide-oligomerization domain-like receptors (NLRs) contribute to cytoplasmic sensing and antimicrobial response orchestration. However, it remains unknown whether and how NLRs may regulate host iron metabolism, an important component of nutritional immunity. Here, we demonstrated that NLRP6, a member of the NLR family, has an unconventional role in regulating host iron metabolism that perturbs host resistance to bacterial infection. NLRP6 deficiency is advantageous for maintaining cellular iron homeostasis in both macrophages and enterocytes through increasing the unique iron exporter ferroportin-mediated iron efflux in a nuclear factor erythroid-derived 2–related factor 2 (NRF2)-dependent manner. Additional studies uncovered a novel mechanism underlying NRF2 regulation and operating through NLRP6/AKT interaction and that causes a decrease in AKT phosphorylation, which in turn reduces NRF2 nuclear translocation. In the absence of NLRP6, increased AKT activation promotes NRF2/KEAP1 dissociation via increasing mTOR-mediated p62 phosphorylation and downregulates KEAP1 transcription by promoting FOXO3A phosphorylation. Together, our observations provide new insights into the mechanism of nutritional immunity by revealing a novel function of NLRP6 in regulating iron metabolism, and suggest NLRP6 as a therapeutic target for limiting bacterial iron acquisition.

Macrophages expressing uncoupling protein 1 increase in adipose tissue in response to cold in humans

Acute cold induces beige adipocyte protein marker expression in human subcutaneous white adipose tissue (SC WAT) from both the cold treated and contralateral leg, and the immune system regulates SC WAT beiging in mice. Cold treatment significantly increased the gene expression of the macrophage markers CD68 and 86 in SC WAT. Therefore, we comprehensively investigated the involvement of macrophages in SC WAT beiging in lean and obese humans by immunohistochemistry. Cold treatment significantly increased CD163/CD68 macrophages in SC WAT from the cold treated and contralateral legs of lean and obese subjects, and had similar effects on CD206/CD68 macrophages, whereas the effects on CD86/CD68 macrophages were inconsistent between lean and obese. However, linear regression analysis did not find significant relationships between the change in macrophage numbers and the change in UCP1 protein abundance. A high percentage of CD163 macrophages in SC WAT expressed UCP1, and these UCP1 expressing CD163 macrophages were significantly increased by cold treatment in SC WAT of lean subjects. In conclusion, our results suggest that CD163 macrophages are involved in some aspect of the tissue remodeling that occurs during SC WAT beiging in humans after cold treatment, but they are likely not direct mediators of the beiging process.

Immunotherapy for cancer: effects of iron oxide nanoparticles on polarization of tumor-associated macrophages

Cancer immunotherapy is the most promising trend in oncology, focusing on helping or activating the patient's immune system to identify and fight against cancer. In the last decade, interest in metabolic reprogramming of tumor-associated macrophages from M2-like phenotype (promoting tumor progression) to M1-like phenotypes (suppressing tumor growth) as a therapeutic strategy against cancer has increased considerably. Iron metabolism has been standing out as a target for the reprogramming of tumor-associated macrophages to M1-like phenotype with therapeutic purposes against cancer. Due to the importance of the iron levels in macrophage polarization states, iron oxide nanoparticles can be used to change the activation state of tumor-associated macrophages for a tumor suppressor phenotype and as an anti-tumor strategy.

Iron Deficiency Caused by Intestinal Iron Loss-Novel Candidate Genes for Severe Anemia

The adult human body contains about 4 g of iron. About 1-2 mg of iron is absorbed every day, and in healthy individuals, the same amount is excreted. We describe a patient who presents with severe iron deficiency anemia with hemoglobin levels below 6 g/dL and ferritin levels below 30 ng/mL. Although red blood cell concentrates and intravenous iron have been substituted every month for years, body iron stores remain depleted. Diagnostics have included several esophago-gastro-duodenoscopies, colonoscopies, MRI of the liver, repetitive bone marrow biopsies, psychological analysis, application of radioactive iron to determine intact erythropoiesis, and measurement of iron excretion in urine and feces. Typically, gastrointestinal bleeding is a major cause of iron loss. Surprisingly, intestinal iron excretion in stool in the patient was repetitively increased, without gastrointestinal bleeding. Furthermore, whole exome sequencing was performed in the patient and additional family members to identify potential causative genetic variants that may cause intestinal iron loss. Under different inheritance models, several rare mutations were identified, two of which (in CISD1 and KRI1) are likely to be functionally relevant. Intestinal iron loss in the current form has not yet been described and is, with high probability, the cause of the severe iron deficiency anemia in this patient.

Increased Lipid Peroxidation May Be Linked to Ferritin Levels Elevation in Adult-Onset Still's Disease

Lipid peroxidation (LPO) and hyper-ferritinemia are involved in inflammatory responses. Although hyper-ferritinemia is a characteristic of AOSD, its link to LPO remains unclear. We investigated the association between LPO and ferritin expression, and evaluated the relationship between LPO-related metabolites and inflammatory parameters. Mean fluorescence intensity (MFI) of LPO (C11-Biodipy^581/591)-expressing PBMCs/monocytes in AOSD patients and healthy control (HC) subjects was determined by flow-cytometry analysis. Expression of ferritin and cytokines on PBMCs/macrophages was examined by immunoblotting. Plasma levels of LPO-related metabolites and cytokines were determined by ELISA and the MULTIPLEX platform, respectively. LPO MFI on PBMCs/monocytes were significantly higher in patients (median 4456 and 9091, respectively) compared with HC (1900, p < 0.05, and 4551, p < 0.01, respectively). Patients had higher ferritin expression on PBMCs (mean fold, 1.02) than HC (0.55, p < 0.05). Their ferritin expression levels on PBMCs stimulated with LPO inducers erastin or RSL3 (2.47 or 1.61, respectively) were higher than HC (0.84, p < 0.05, or 0.74, p < 0.01). Ferritin expression on erastin-treated/IL-1β-treated macrophages from patients were higher than those from HC (p < 0.001). The elevated levels of LPO-related metabolites, including malondialdehyde and 4-hydroxyalkenals, were positively correlated with disease activity scores, suggesting LPO involvement in AOSD pathogenesis. Increased ferritin expression on PBMCs/macrophages stimulated with LPO inducers indicates a link between LPO and elevated ferritin.

Leptin Receptor-Deficient db/db Mice Show Significant Heterogeneity in Response to High Non-heme Iron Diet

Recent studies have shown an association between iron homeostasis, obesity and diabetes. In this work, we investigated the differences in the metabolic status and inflammation in liver, pancreas and visceral adipose tissue of leptin receptor-deficient db/db mice dependent on high iron concentration diet. 3-month-old male BKS-Leprdb/db/JOrlRj (db/db) mice were divided into two groups, which were fed with different diets containing high iron (29 g/kg, n = 57) or standard iron (0.178 g/kg; n = 42) concentrations for 4 months. As anticipated, standard iron-fed db/db mice developed obesity and diabetes. However, high iron-fed mice exhibited a wide heterogeneity. By dividing into two subgroups at the diabetes level, non-diabetic subgroup 1 (<13.5 mmol/l, n = 30) significantly differed from diabetic subgroup two (>13.5 mmol/l, n = 27). Blood glucose concentration, HbA1c value, inflammation markers interleukin six and tumor necrosis factor α and heme oxygenase one in visceral adipose tissue were reduced in subgroup one compared to subgroup two. In contrast, body weight, C-peptide, serum insulin and serum iron concentrations, pancreatic islet and signal ratio as well as cholesterol, LDL and HDL levels were enhanced in subgroup one. While these significant differences require further studies and explanation, our results might also explain the often-contradictory results of the metabolic studies with db/db mice.

Dietary Iron Deficiency Modulates Adipocyte Iron Homeostasis, Adaptive Thermogenesis, and Obesity in C57BL/6 Mice

BACKGROUND

Adaptive thermogenesis is an iron-demanding pathway, significantly contributing to whole-body energy expenditure. However, the effects of iron-deficient diets on adaptive thermogenesis and obesity remain unknown.

OBJECTIVES

We aimed to determine the impact of dietary iron deficiency on iron homeostasis in adipocytes, adaptive thermogenic capacity, and metabolic consequences in obesity.

METHODS

C57BL/6 male mice were assigned to either the iron-adequate (IA, 35 ppm) or the iron-deficient group (ID, 3 ppm) at weaning. Upon 8 wk of age, both IA and ID groups received an isocaloric high-fat diet (45% kcal from fat) for 10 wk, maintaining the same iron content. Mice (n = 8) were used to determine the iron status at the systemic and tissue levels and lipid metabolism and inflammatory signaling in adipose tissue. The same mice were used to evaluate cold tolerance (4°C) for 3 h. For assessing adaptive thermogenesis, mice (n = 5) received an intraperitoneal injection of β3-adrenoceptor agonist CL316243 (CL) for 5 d.

RESULTS

Compared with the IA group, the ID group had nonanemic iron deficiency, lower serum ferritin (42.8%, P < 0.01), and greater weight gain (8.67%, P < 0.05) and insulin resistance (159%, P < 0.01), partly due to reduced AMP-activated protein kinase activation (61.0%, P < 0.05). Upon cold exposure, the ID group maintained a core body temperature 2°C lower than the IA group. The ID group had lower iron content (47.0%, P < 0.01) in the inguinal adipose tissue (iWAT) than the IA group, which was associated with impaired adaptive thermogenesis. In response to CL, ID mice showed decreased heat production (P < 0.01) and defective upregulation of beige adipocyte-specific markers, including uncoupling protein 1 (41.1%, P < 0.001), transferrin receptor 1 (47.5%, P < 0.001), and mitochondrial respiratory chain complexes (P < 0.05) compared with IA mice.

CONCLUSIONS

Dietary iron deficiency deregulates iron balance in the iWAT and impairs adaptive thermogenesis, thereby escalating the diet-induced weight gain in C57BL/6 mice.

Macrophages form erythropoietic niches and regulate iron homeostasis to adapt erythropoiesis in response to infections and inflammation

It has recently emerged that tissue-resident macrophages are key regulators of several stem cell niches orchestrating tissue formation during development, as well as postnatally, when they also organize the repair and regeneration of many tissues including the hemopoietic tissue. The fact that macrophages are also master regulators and effectors of innate immunity and inflammation allows them to coordinate hematopoietic response to infections, injuries, and inflammation. After recently reviewing the roles of phagocytes and macrophages in regulating normal and pathologic hematopoietic stem cell niches, we now focus on the key roles of macrophages in regulating erythropoiesis and iron homeostasis. We review herein the recent advances in understanding how macrophages at the center of erythroblastic islands form an erythropoietic niche that controls the terminal differentiation and maturation of erythroblasts into reticulocytes; how red pulp macrophages in the spleen control iron recycling and homeostasis; how these macrophages coordinate emergency erythropoiesis in response to blood loss, infections, and inflammation; and how persistent infections or inflammation can lead to anemia of inflammation via macrophages. Finally, we discuss the technical challenges associated with the molecular characterization of erythroid island macrophages and red pulp macrophages.

Myeloid-specific deletion of ferroportin impairs macrophage bioenergetics but is disconnected from systemic insulin action in adult mice

Tissue iron overload is associated with insulin resistance and mitochondrial dysfunction in rodents and humans; however, the mechanisms or cell types that mediate this phenotype are not completely understood. Macrophages (Mɸs) are known to contribute to iron handling; thus, we hypothesized that perturbed iron handling by Mɸs impairs mitochondrial energetics and evokes systemic insulin resistance in mice. Male and female mice with myeloid-targeted (LysMCre) deletion of the canonical iron exporter, ferroportin (Fpn, encoded by Slc40a1), floxed littermates, and C57BL/6J wild-type mice were used to test our hypotheses. Myeloid-targeted deletion of Fpn evoked multitissue iron accumulation and reduced mitochondrial respiration in bone marrow-derived Mɸs, liver leukocytes, and Mɸ-enriched populations from adipose tissue (AT). In addition, a single bolus of exogenous iron administered to C57BL/6J mice phenocopied the loss of Fpn, resulting in a reduction in maximal and mitochondrial reserve capacity in Mɸ-enriched cellular fractions from liver and AT. In vivo exogenous iron chelation restored mitochondrial reserve capacity in liver leukocytes from Fpn LysMCre mice, but had no effect in AT myeloid populations. However, despite the impairments in mitochondrial respiration, neither loss of myeloid-specific Fpn nor exogenous iron overload perturbed glucose homeostasis or systemic insulin action in lean or obese mice, whereas aging coupled with lifelong loss of Fpn unmasked glucose intolerance. Together these data demonstrate that iron handling is critical for the maintenance of macrophage mitochondrial function, but perturbing myeloid iron flux via the loss of Fpn action is not sufficient to evoke systemic insulin resistance in young adult mice. These findings also suggest that if Mɸs are capable of storing iron properly, they have a pronounced ability to withstand iron excess without evoking overt collateral damage and associated insulin resistance that may be age dependent.NEW & NOTEWORTHY We used myeloid-specific knockout of ferroportin to determine whether macrophage iron enrichment alters systemic metabolism. We found that macrophages in several tissues showed mitochondrial defects such as a reduction in mitochondrial reserve capacity. However, insulin action in the mice was preserved. These findings also suggest that Mɸs have a pronounced ability to withstand iron excess without evoking overt collateral damage and associated insulin resistance, which appears to be age dependent.

Ferroptosis: Biological Rust of Lipid Membranes

Significance: Iron is an essential element required for growth and proper functioning of the body. However, an excess of labile ferrous iron increases the risk of oxidative stress-induced injury due to the high reactivity of the unpaired reactive electrons of both ferrous iron and oxygen. This high reactivity can be exemplified in the outside world by one of its consequences, rust formation. In cells, this redox-active iron is involved in the formation of lipid radicals. Recent Advances: Defect or insufficient membrane-protective mechanisms can result in iron-catalyzed excessive lipid peroxidation and subsequent cell death, now conceptualized as ferroptosis. Growing reports propose the detrimental role of iron and ferroptosis in many experimental disease models such as ischemia-reperfusion, acute and chronic organ injuries. Critical Issues: This review first provides a snapshot of iron metabolism, followed by a brief introduction of the molecular mechanisms of ferroptosis, as an iron-dependent lipid peroxidation-driven mode of cell death. Upon describing how iron dysbiosis affects ferroptosis induction, we elaborate on the detrimental role of the iron-ferroptosis axis in several diseases. Future Directions: Despite compelling findings suggesting a role of ferroptosis in experimental animal models, the exact contribution of ferroptosis in human contexts still needs further investigation. Development of reliable ferroptosis biomarkers will be an important step in characterizing ferroptosis in human disease. This can provide therapeutic opportunities aiming at targeting ferroptosis in human diseases. Antioxid. Redox Signal. 35, 487-509.

Complex Interactions in Regulation of Haematopoiesis-An Unexplored Iron Mine

Iron is one of the most abundant metals on earth and is vital for the growth and survival of life forms. It is crucial for the functioning of plants and animals as it is an integral component of the photosynthetic apparatus and innumerable proteins and enzymes. It plays a pivotal role in haematopoiesis and affects the development and differentiation of different haematopoietic lineages, apart from its obvious necessity in erythropoiesis. A large amount of iron stores in humans is diverted towards the latter process, as iron is an indispensable component of haemoglobin. This review summarises the important players of iron metabolism and homeostasis that have been discovered in recent years and highlights the overall significance of iron in haematopoiesis. Its role in maintenance of haematopoietic stem cells, influence on differentiation of varied haematopoietic lineages and consequences of iron deficiency/overloading on development and maturation of different groups of haematopoietic cells have been discussed.

Leishmaniasis: the act of transmission

The contribution of vector transmission to pathogen establishment is largely underrated. For Leishmania, transmission by sand flies is critical to early survival involving an irreproducible myriad of parasite, vector, and host molecules acting in concert to promote infection at the bite site. Here, we review recent breakthroughs that provide consequential insights into how vector transmission of Leishmania unfolds. We focus on recent work pertaining to the effect of gut microbiota, sand fly immunity, and changes in metacyclogenesis upon multiple blood meals, on Leishmania development and transmission. We also explore how sand fly saliva, egested parasite molecules and vector gut microbiota, and bleeding have been implicated in modulating the early innate host response to Leishmania, affecting the phenotype of neutrophils and monocytes arriving at the bite site.

The Macrophage Iron Signature in Health and Disease

Throughout life, macrophages are located in every tissue of the body, where their main roles are to phagocytose cellular debris and recycle aging red blood cells. In the tissue niche, they promote homeostasis through trophic, regulatory, and repair functions by responding to internal and external stimuli. This in turn polarizes macrophages into a broad spectrum of functional activation states, also reflected in their iron-regulated gene profile. The fast adaptation to the environment in which they are located helps to maintain tissue homeostasis under physiological conditions.

Ironing Out the Details: How Iron Orchestrates Macrophage Polarization

Iron fine-tunes innate immune responses, including macrophage inflammation. In this review, we summarize the current understanding about the iron in dictating macrophage polarization. Mechanistically, iron orchestrates macrophage polarization through several aspects, including cellular signaling, cellular metabolism, and epigenetic regulation. Therefore, iron modulates the development and progression of multiple macrophage-associated diseases, such as cancer, atherosclerosis, and liver diseases. Collectively, this review highlights the crucial role of iron for macrophage polarization, and indicates the potential application of iron supplementation as an adjuvant therapy in different inflammatory disorders relative to the balance of macrophage polarization.

Nutritional immunity: the impact of metals on lung immune cells and the airway microbiome during chronic respiratory disease

Nutritional immunity is the sequestration of bioavailable trace metals such as iron, zinc and copper by the host to limit pathogenicity by invading microorganisms. As one of the most conserved activities of the innate immune system, limiting the availability of free trace metals by cells of the immune system serves not only to conceal these vital nutrients from invading bacteria but also operates to tightly regulate host immune cell responses and function. In the setting of chronic lung disease, the regulation of trace metals by the host is often disrupted, leading to the altered availability of these nutrients to commensal and invading opportunistic pathogenic microbes. Similarly, alterations in the uptake, secretion, turnover and redox activity of these vitally important metals has significant repercussions for immune cell function including the response to and resolution of infection. This review will discuss the intricate role of nutritional immunity in host immune cells of the lung and how changes in this fundamental process as a result of chronic lung disease may alter the airway microbiome, disease progression and the response to infection.

Counter Regulation of Spic by NF-κB and STAT Signaling Controls Inflammation and Iron Metabolism in Macrophages

Activated macrophages must carefully calibrate their inflammatory responses to balance efficient pathogen control with inflammation-mediated tissue damage, but the molecular underpinnings of this "balancing act" remain unclear. Using genetically engineered mouse models and primary macrophage cultures, we show that Toll-like receptor (TLR) signaling induces the expression of the transcription factor Spic selectively in patrolling monocytes and tissue macrophages by a nuclear factor κB (NF-κB)-dependent mechanism. Functionally, Spic downregulates pro-inflammatory cytokines and promotes iron efflux by regulating ferroportin expression in activated macrophages. Notably, interferon-gamma blocks Spic expression in a STAT1-dependent manner. High levels of interferon-gamma are indicative of ongoing infection, and in its absence, activated macrophages appear to engage a "default" Spic-dependent anti-inflammatory pathway. We also provide evidence for the engagement of this pathway in sterile inflammation. Taken together, our findings uncover a pathway wherein counter-regulation of Spic by NF-κB and STATs attune inflammatory responses and iron metabolism in macrophages.

On Iron Metabolism and Its Regulation

Iron is a critical metal for several vital biological processes. Most of the body’s iron is bound to hemoglobin in erythrocytes. Iron from senescent red blood cells is recycled by macrophages in the spleen, liver and bone marrow. Dietary iron is taken up by the divalent metal transporter 1 (DMT1) in enterocytes and transported to portal blood via ferroportin (FPN), where it is bound to transferrin and taken up by hepatocytes, macrophages and bone marrow cells via transferrin receptor 1 (TfR1). While most of the physiologically active iron is bound hemoglobin, the major storage of most iron occurs in the liver in a ferritin-bound fashion. In response to an increased iron load, hepatocytes secrete the peptide hormone hepcidin, which binds to and induces internalization and degradation of the iron transporter FPN, thus controlling the amount of iron released from the cells into the blood. This review summarizes the key mechanisms and players involved in cellular and systemic iron regulation.

The Iron Curtain: Macrophages at the Interface of Systemic and Microenvironmental Iron Metabolism and Immune Response in Cancer

Macrophages fulfill central functions in systemic iron metabolism and immune response. Infiltration and polarization of macrophages in the tumor microenvironment is associated with differential cancer prognosis. Distinct metabolic iron and immune phenotypes in tumor associated macrophages have been observed in most cancers. While this prompts the hypothesis that macroenvironmental manifestations of dysfunctional iron metabolism have direct associations with microenvironmental tumor immune response, these functional connections are still emerging. We review our current understanding of the role of macrophages in systemic and microenvironmental immune response and iron metabolism and discuss these functions in the context of cancer and immunometabolic precision therapy approaches. Accumulation of tumor associated macrophages with distinct iron pathologies at the invasive tumor front suggests an "Iron Curtain" presenting as an innate functional interface between systemic and microenvironmental iron metabolism and immune response that can be harnessed therapeutically to further our goal of treating and eliminating cancer.

A facile colorimetric method for the quantification of labile iron pool and total iron in cells and tissue specimens

Quantification of iron is an important step to assess the iron burden in patients suffering from iron overload diseases, as well as tremendous value in understanding the underlying role of iron in the pathophysiology of these diseases. Current iron determination of total or labile iron, requires extensive sample handling and specialized instruments, whilst being time consuming and laborious. Moreover, there is minimal to no overlap between total iron and labile iron quantification methodologies-i.e. requiring entirely separate protocols, techniques and instruments. Herein, we report a unified-ferene (u-ferene) assay that enables a 2-in-1 quantification of both labile and total iron from the same preparation of a biological specimen. We demonstrate that labile iron concentrations determined from the u-ferene assay is in agreement with confocal laser scanning microscopy techniques employed within the literature. Further, this assay offers the same sensitivity as the current gold standard, inductively coupled plasma mass spectrometry (ICP-MS), for total iron measurements. The new u-ferene assay will have tremendous value for the wider scientific community as it offers an economic and readily accessible method for convenient 2-in-1 measurement of total and labile iron from biological samples, whilst maintaining the precision and sensitivity, as compared to ICP-MS.

Iron Availability in Tissue Microenvironment: The Key Role of Ferroportin

Body iron levels are regulated by hepcidin, a liver-derived peptide that exerts its function by controlling the presence of ferroportin (FPN), the sole cellular iron exporter, on the cell surface. Hepcidin binding leads to FPN internalization and degradation, thereby inhibiting iron release, in particular from iron-absorbing duodenal cells and macrophages involved in iron recycling. Disruption in this regulatory mechanism results in a variety of disorders associated with iron-deficiency or overload. In recent years, increasing evidence has emerged to indicate that, in addition to its role in systemic iron metabolism, FPN may play an important function in local iron control, such that its dysregulation may lead to tissue damage despite unaltered systemic iron homeostasis. In this review, we focus on recent discoveries to discuss the role of FPN-mediated iron export in the microenvironment under both physiological and pathological conditions.

"Iron"ing out hemophagocytosis through PIEZO1

In this issue of Cell, Ma et al. reveal a mechanistic role for PIEZO1 in iron homeostasis through molecular genetic mouse studies. They also demonstrate implications for human iron overload and deficiency syndromes, susceptibility to malarial infection, and red blood cell turnover in persons of African ancestries.

Schistosome and intestinal helminth modulation of macrophage immunometabolism

Macrophages are fundamental to sustain physiological equilibrium and to regulate the pathogenesis of parasitic and metabolic processes. The functional heterogeneity and immune responses of macrophages are shaped by cellular metabolism in response to the host's intrinsic factors, environmental cues and other stimuli during disease. Parasite infections induce a complex cascade of cytokines and metabolites that profoundly remodel the metabolic status of macrophages. In particular, helminths polarize macrophages to an M2 state and induce a metabolic shift towards reliance on oxidative phosphorylation, lipid oxidation and amino acid metabolism. Accumulating data indicate that helminth-induced activation and metabolic reprogramming of macrophages underlie improvement in overall whole-body metabolism, denoted by improved insulin sensitivity, body mass in response to high-fat diet and atherogenic index in mammals. This review aims to highlight the metabolic changes that occur in human and murine-derived macrophages in response to helminth infections and helminth products, with particular interest in schistosomiasis and soil-transmitted helminths.

Quantitative laser-induced breakdown spectroscopy for discriminating neoplastic tissues from non-neoplastic ones

In this paper, we present a method to distinguish neoplastic tissues from non-neoplastic ones using calibration-free laser-induced breakdown spectroscopy (CF-LIBS). For this propose, plasma emission was collected from neoplastic and non-neoplastic tissues taken from the ovarian cancer mice models. Results were obtained by utilizing the characteristic plasma emission lines of different elements that have been confirmed in the investigated samples. From the temporal evolution of plasma emission, the optimum temporal-observation-windows are identified for LIBS investigation. The concentrations of the detected elements in tissues were measured by a calibration-free approach based on data process of plasma parameters at the local thermodynamic equilibrium. The neoplastic specimens provided more energetic plasma than non-neoplastic ones that resulting in higher peaks intensities, electron density and electron temperature especially in the early windows (between 0.1 µs to 0.8 µs). Results demonstrated higher concentrations of major and trace elements such as Mg, Fe, Ca, Na, and K in the neoplastic tissues. Finally, the results using CF-LIBS method were found to be in good agreement with that of Inductive coupled plasma-optical emission spectroscopy (ICP-OES).

The versatile biochemistry of iron in macrophage effector functions

Macrophages are mononuclear phagocytes with remarkable polarization ability that allow them to have tissue-specific functions during development, homeostasis, inflammatory and infectious disease. One particular trophic factor in the tissue environment is iron, which is intimately linked to macrophage effector functions. Macrophages have a well-described role in the control of systemic iron levels, but their activation state is also depending on iron-containing proteins/enzymes. Haemoproteins, dioxygenases and iron-sulphur (Fe-S) enzymes are iron-binding proteins that have bactericidal, metabolic and epigenetic-related functions, essential to shape the context-dependent macrophage polarization. In this review, I describe mainly pro-inflammatory macrophage polarization focussing on the role of iron biochemistry in selected haemoproteins and Fe-S enzymes. I show how iron, as part of haem or Fe-S clusters, participates in the cellular control of pro-inflammatory redox reactions in parallel with its role as enzymatic cofactor. I highlight a possible coordinated regulation of haemoproteins and Fe-S enzymes during classical macrophage activation. Finally, I describe tryptophan and α-ketoglutarate metabolism as two essential effector pathways in macrophages that use diverse iron biochemistry at different enzymatic steps. Through these pathways, I show how iron participates in the regulation of essential metabolites that shape macrophage function.

Can diet-induced weight loss improve iron homoeostasis in patients with obesity: A systematic review and meta-analysis

Despite the increasing worldwide prevalence of obesity and iron deficiency (ID), there are still no guidelines on how to treat and manage obesity-related ID. The aim of this systematic review and meta-analysis was to investigate whether weight loss can re-establish iron homoeostasis among subjects with unhealthy weight (overweight [OW] or obesity). PubMed, Medline, Embase, Web of Science, and the Cochrane Library were systemically searched for studies that compared the iron status before and after a weight-loss intervention. A random-effects model was used to calculate the pooled and subgroup weighted mean differences (WMDs) of iron biomarkers. In total, 879 subjects were pooled across 14 studies. Improved haemoglobin was found in longitudinal studies (WMD = 2.50 g/dl, 95% confidence interval [CI]: 0.88, 4.12 g/dl, I² = 14%) but not in randomized controlled trials or after being stratified by dietary programmes. Significantly increased transferrin saturation was observed in pooled (WMD = 1.68%, 95% CI: 0.97%, 2.39%, I² = 44%) and subgroup analyses. A meta-regression showed that changes in the iron status were positively correlated with changes in the body mass index (BMI) and the intervention duration but negatively correlated with the baseline body weight/BMI, age, gender and a standard hypocaloric diet. Our data suggested that in spite of energy restrictions, weight loss may help re-establish iron homoeostasis in people who are OW or obese.