The gut in iron homeostasis: role of HIF-2 under normal and pathological conditions

Iron-Mediated Regulation in Adipose Tissue: A Comprehensive Review of Metabolism and Physiological Effects

PURPOSE OF REVIEW

Review the latest data regarding the intersection of adipose tissue (AT) and iron to meet the needs of AT metabolism and the progression of related diseases.

RECENT FINDINGS

Iron is involved in fundamental biological metabolic processes and is precisely fine-tuned within the body to maintain cellular, tissue and even systemic iron homeostasis. AT not only serves as an energy storage depot but also represents the largest endocrine organ in the human body, maintaining systemic metabolic homeostasis. It is involved in physiological processes such as energy storage, insulin sensitivity regulation and lipid metabolism. As a unique iron-sensing tissue, AT expresses related regulatory factors, including the classic hepcidin, ferroportin (FPN), iron regulatory protein/iron responsive element (IRP/IRE) and ferritin. Consequently, the interaction between AT and iron is intricately intertwined. Imbalance of iron homeostasis produces the potential risks of steatosis, impaired glucose tolerance and insulin resistance, leading to AT dysfunction diseases, including obesity, type 2 diabetes and metabolic dysfunction-associated steatotic liver disease (MASLD). Despite the role of AT iron has garnered increasing attention in recent years, a comprehensive review that systematically organizes the connection between iron and AT remains lacking. Given the necessity of iron homeostasis, emphasizing its potential impact on AT function and metabolism regulation provides valuable insights into physiological effects such as adipocyte differentiation and thermogenesis. Futhermore, regulators including adipokines, mitochondria and macrophages have been mentioned, along with analyzing the novel perspective of iron as a key mediator influencing the fat-gut crosstalk.

Could Hepcidin Be a New Biomarker in Patients with Idiopathic Pulmonary Fibrosis (IPF)?

Objectives: Hepcidin is a biomarker produced by hepatocytes in chronic disease anemia and is known to increase during chronic inflammation. This study compares the hepcidin levels in idiopathic pulmonary fibrosis (IPF) patients and controls, evaluating its relationship with anemia and systemic inflammation in IPF patients. Methods: This study included 82 IPF patients and 31 controls. Hepcidin levels were compared between the two groups. In the IPF group, the hepcidin and anemia parameters were compared between anemic and non-anemic patients. The significance between the hepcidin and systemic inflammation parameters such as Erythrocyte Sedimentation Rate, CRP (C-reactive protein) levels, ferritin levels, and the Systemic Immune-Inflammation Index (SII) was investigated. Erythrocyte Sedimentation Rate, C-reactive protein (CRP) levels, and ferritin levels were measured using automated analyzers. Hepcidin and erythropoietin (EPO) levels were determined using ELISA kits. Results: A significant difference in hepcidin levels was found between the IPF and control groups (37.13 ± 14.92 vs. 25.77 ± 11.25, p < 0.001). No significant difference in hepcidin levels was found between anemic and non-anemic IPF patients (38.25 ± 16.2 vs. 36.7 ± 14.6, p = 0.719). No significant correlation was found between hepcidin levels and anemia parameters (serum iron, ferritin, vitamin B12, serum transferrin, transferrin saturation, total iron-binding capacity, hemoglobin, folate, and erythropoietin) in IPF patients. Despite significant differences in the systemic inflammation parameters (ferritin and CRP) between patients and controls, no significant correlation was found between their hepcidin and systemic inflammation parameters. Conclusions: Our study demonstrates that the hepcidin levels in IPF patients are elevated independently of anemia and systemic inflammation. We propose that hepcidin could be a potential biomarker to be investigated in IPF patients.

Current iron therapy in the light of regulation, intestinal microbiome, and toxicity: are we prescribing too much iron?

Iron deficiency is a widespread global health concern with varying prevalence rates across different regions. In developing countries, scarcity of food and chronic infections contribute to iron deficiency, while in industrialized nations, reduced food intake and dietary preferences affect iron status. Other causes that can lead to iron deficiency are conditions and diseases that result in reduced intestinal iron absorption and blood loss. In addition, iron absorption and its bioavailability are influenced by the composition of the diet. Individuals with increased iron needs, including infants, adolescents, and athletes, are particularly vulnerable to deficiency. Severe iron deficiency can lead to anemia with performance intolerance or shortness of breath. In addition, even without anemia, iron deficiency leads to mental and physical fatigue, which points to the fundamental biological importance of iron, especially in mitochondrial function and the respiratory chain. Standard oral iron supplementation often results in gastrointestinal side effects and poor compliance. Low-dose iron therapy seems to be a valid and reasonable therapeutic option due to reduced hepatic hepcidin formation, facilitating efficient iron resorption, replenishment of iron storage, and causing significantly fewer side effects. Elevated iron levels influence gut microbiota composition, favoring pathogenic bacteria and potentially disrupting metabolic and immune functions. Protective bacteria, such as bifidobacteria and lactobacilli, are particularly susceptible to increased iron levels. Dysbiosis resulting from iron supplementation may contribute to gastrointestinal disorders, inflammatory bowel disease, and metabolic disturbances. Furthermore, gut microbiota alterations have been linked to mental health issues. Future iron therapy should consider low-dose supplementation to mitigate adverse effects and the impact on the gut microbiome. A comprehensive understanding of the interplay between iron intake, gut microbiota, and human health is crucial for optimizing therapeutic approaches and minimizing potential risks associated with iron supplementation.

Iron regulatory protein 1 is required for the propagation of inflammation in inflammatory bowel disease

Inflammatory bowel diseases (IBDs) are complex disorders. Iron accumulates in the inflamed tissue of IBD patients, yet neither a mechanism for the accumulation nor its implication on the course of inflammation is known. We hypothesized that the inflammation modifies iron homeostasis, affects tissue iron distribution, and that this in turn perpetuates the inflammation. This study analyzed human biopsies, animal models, and cellular systems to decipher the role of iron homeostasis in IBD. We found inflammation-mediated modifications of iron distribution, and iron-decoupled activation of the iron regulatory protein (IRP) 1. To understand the role of IRP1 in the course of this inflammation-associated iron pattern, a novel cellular coculture model was established, which replicated the iron-pattern observed in vivo, and supported involvement of nitric oxide in the activation of IRP1 and the typical iron pattern in inflammation. Importantly, deletion of IRP1 from an IBD mouse model completely abolished both, the misdistribution of iron and intestinal inflammation. These findings suggest that IRP1 plays a central role in the coordination of the inflammatory response in the intestinal mucosa and that it is a viable candidate for therapeutic intervention in IBD.

Roles of ghrelin, hepcidin and HIF-2α in iron metabolism in iron deficiency anemia

OBJECTIVES

This study investigates the roles of HIF-2α, hepcidin, and ghrelin in iron deficiency anemia (IDA), the most widespread nutritional disorder globally.

MATERIAL AND METHODS

Fifty IDA patients (18-50 years, BMI 19-25) and 40 healthy volunteers were studied. Hemoglobin, ferritin, hepcidin, HIF-2α, and ghrelin levels were analyzed.

RESULTS

IDA patients showed lower hemoglobin, ferritin, hepcidin, and ghrelin levels than the control group, but HIF-2α levels were similar. Positive correlations were observed in both groups between hepcidin and HIF-2α (p < 0.001), hepcidin and ghrelin (p < 0.001), and HIF-2α and ghrelin (p < 0.001). Hemoglobin was correlated positively with HIF-2α, and ferritin was correlated positively with HIF-2α in the patient group.

CONCLUSION

The study suggests that the low hepcidin levels in IDA patients enhance iron absorption. The lack of significant HIF-2α level differences may be due to the absence of chronic hypoxia in current hemoglobin levels of IDA patients. Moreover, the low ghrelin levels in patients and the correlations between ghrelin, hepcidin, and HIF-2α in both groups indicate their involvement in iron metabolism.

Deferasirox exerts anti-epileptic effects by improving brain iron homeostasis via regulation of ITPRIP

Epilepsy constitutes a global health concern, affecting millions of individuals and approximately one-third of patients exhibit drug resistance. Recent investigations have revealed alterations in cerebral iron content in both epilepsy patients and animal models. However, the extant literature lacks a comprehensive exploration into the ramifications of modulating iron homeostasis as an intervention in epilepsy. This study investigated the impact of deferasirox, a iron ion chelator, on epilepsy. This study unequivocally substantiated the antiepileptic efficacy of deferasirox in a kainic acid-induced epilepsy model. Furthermore, deferasirox administration mitigated seizure susceptibility in a pentylenetetrazol-induced kindling model. Conversely, the augmentation of iron levels through supplementation has emerged as a potential exacerbating factor in the precipitating onset of epilepsy. Intriguingly, our investigation revealed a hitherto unreported discovery: ITPRIP was identified as a pivotal modulator of excitatory synaptic transmission, regulating seizures in response to deferasirox treatment. In summary, our findings indicate that deferasirox exerts its antiepileptic effects through the precise targeting of ITPRIP and amelioration of cerebral iron homeostasis, suggesting that deferasirox is a promising and novel therapeutic avenue for interventions in epilepsy.

Targeting hypoxia-inducible factors: therapeutic opportunities and challenges

Hypoxia-inducible factors (HIFs) are highly conserved transcription factors that are crucial for adaptation of metazoans to limited oxygen availability. Recently, HIF activation and inhibition have emerged as therapeutic targets in various human diseases. Pharmacologically desirable effects of HIF activation include erythropoiesis stimulation, cellular metabolism optimization during hypoxia and adaptive responses during ischaemia and inflammation. By contrast, HIF inhibition has been explored as a therapy for various cancers, retinal neovascularization and pulmonary hypertension. This Review discusses the biochemical mechanisms that control HIF stabilization and the molecular strategies that can be exploited pharmacologically to activate or inhibit HIFs. In addition, we examine medical conditions that benefit from targeting HIFs, the potential side effects of HIF activation or inhibition and future challenges in this field.

Gum Arabic-Derived Hydroxyproline-Rich Peptides Stimulate Intestinal Nonheme Iron Absorption via HIF2α-Dependent Upregulation of Iron Transport Proteins

The stimulation of host iron absorption is a promising antianemia strategy adjunctive/alternative to iron intervention. Here, gum arabic (GA) containing 3.14 ± 0.56% hydroxyproline-rich protein with repetitive X-(Pro/Hyp)n motifs was found to increase iron reduction, uptake, and transport to upregulate duodenal cytochrome b (Dcytb), divalent metal transporter 1 (DMT1), ferroportin, and hephaestin to inhibit hypoxia-inducible factor (HIF) prolyl hydroxylase (PHD) and to stabilize HIF2α in polarized Caco-2 cell monolayers in a dose-dependent manner, and this was dependent on its protein fraction, rather than the polysaccharide fraction. Three abundant GA-derived hydroxyproline-containing dipeptides of Hyp-Hyp, Pro-Hyp, and Ser-Hyp were detected by liquid chromatography-mass spectrometry in the lysates of polarized Caco-2 cell monolayers at the maximum levels of  0.167 ± 0.021, 0.134 ± 0.017, and 0.089 ± 0.015 μg/mg of protein, respectively, and showed desirable docking affinity energy values of -7.53, - 7.91, and -7.39 kcal/mol, respectively, against human PHD3. GA-derived peptides also acutely increased duodenal HIF2α stability and Dcytb, DMT1, ferroportin, and hephaestin transcription in rats (P < 0.05). Overall, GA-derived hydroxyproline-rich peptides stimulated intestinal iron absorption via PHD inhibition, HIF2α stabilization, and subsequent upregulation of iron transport proteins.

Human Gut Microbiota in Heart Failure: Trying to Unmask an Emerging Organ

There is a bidirectional relationship between the heart and the gut. The gut microbiota, the community of gut micro-organisms themselves, is an excellent gut-homeostasis keeper since it controls the growth of potentially harmful bacteria and protects the microbiota environment. There is evidence suggesting that a diet rich in fatty acids can be metabolized and converted by gut microbiota and hepatic enzymes to trimethyl-amine N-oxide (TMAO), a product that is associated with atherogenesis, platelet dysfunction, thrombotic events, coronary artery disease, stroke, heart failure (HF), and, ultimately, death. HF, by inducing gut ischemia, congestion, and, consequently, gut barrier dysfunction, promotes the intestinal leaking of micro-organisms and their products, facilitating their entrance into circulation and thus stimulating a low-grade inflammation associated with an immune response. Drugs used for HF may alter the gut microbiota, and, conversely, gut microbiota may modify the pharmacokinetic properties of the drugs. The modification of lifestyle based mainly on exercise and a Mediterranean diet, along with the use of pre- or probiotics, may be beneficial for the gut microbiota environment. The potential role of gut microbiota in HF development and progression is the subject of this review.

Iron Regulatory Protein 1 is Required for the Propagation of Inflammation in Inflammatory Bowel Disease

Objective

Inflammatory bowel diseases (IBD) are complex disorders. Iron accumulates in the inflamed tissue of IBD patients, yet neither a mechanism for the accumulation nor its implication on the course of inflammation are known. We hypothesized that the inflammation modifies iron homeostasis, affects tissue iron distribution and that this in turn perpetuates the inflammation.

Design

This study analyzed human biopsies, animal models and cellular systems to decipher the role of iron homeostasis in IBD.

Results

We found inflammation-mediated modifications of iron distribution, and iron-decoupled activation of the iron regulatory protein (IRP)1. To understand the role of IRP1 in the course of this inflammation-associated iron pattern, a novel cellular co-culture model was established, that replicated the iron-pattern observed in vivo, and supported involvement of nitric oxide in the activation of IRP1 and the typical iron pattern in inflammation. Importantly, deletion of IRP1 from an IBD mouse model completely abolished both, the misdistribution of iron and intestinal inflammation.

Conclusion

These findings suggest that IRP1 plays a central role in the coordination of the inflammatory response in the intestinal mucosa and that it is a viable candidate for therapeutic intervention in IBD.

HIF2α, Hepcidin and their crosstalk as tumour-promoting signalling

Not all aspects of the disruption of iron homeostasis in cancer have been fully elucidated. Iron accumulation in cancer cells is frequent for many solid tumours, and this is often accompanied by the contemporary rise of two key iron regulators, HIF2α and Hepcidin. This scenario is different from what happens under physiological conditions, where Hepcidin parallels systemic iron concentrations while HIF2α levels are inversely associated to Hepcidin. The present review highlights the increasing body of evidence for the pro-tumoral effect of HIF2α and Hepcidin, discusses the possible imbalance in HIF2α, Hepcidin and iron homeostasis during cancer, and explores therapeutic options relying on these pathways as anticancer strategies.

Roxadustat alleviates the inflammatory status in patients receiving maintenance hemodialysis with erythropoiesis-stimulating agent resistance by increasing the short-chain fatty acids producing gut bacteria

BACKGROUND

Hypoxia-inducible factor-prolyl hydroxylase inhibitors (HIF-PHIs) have improved the treatment of renal anemia, especially in patients resistant to erythropoiesis-stimulating agents (ESAs). HIF facilitates maintain gut microbiota homeostasis, which plays an important role in inflammation and iron metabolism, which are in turn key factors affecting ESA resistance. The current study aimed to investigate the effects of roxadustat on inflammation and iron metabolism and on the gut microbiota in patients with ESA resistance.

METHODS

We conducted a self-controlled, single-center study including 30 patients with ESA resistance undergoing maintenance hemodialysis. All patients received roxadustat without iron agents for renal anemia. Hemoglobin and inflammatory factors were monitored. Fecal samples were collected before and after 3 months' administration and the gut microbiota were analyzed by 16S ribosomal RNA gene sequencing.

RESULTS

Hemoglobin levels increased after treatment with roxadustat for 3 months (P < 0.05). Gut microbiota diversity and abundance also changed, with increases in short-chain fatty acid (SCFA)-producing bacteria (Acidaminococcaceae, Butyricicoccus, Ruminococcus bicirculans, Ruminococcus bromii, Bifidobacterium dentium, Eubacterium hallii) (P < 0.05). Serum SCFA levels also increased (P < 0.05). Inflammatory factors, including interleukin (IL)-1, IL-6, tumor necrosis factor (TNF)-α, interferon-γ, and endotoxin gradually decreased (P < 0.05). Serum hepcidin, ferritin, and total and unsaturated iron-binding capacities decreased (P < 0.05), while soluble transferrin receptor levels increased at each time point (P < 0.05). There were no significant differences in serum iron and transferrin saturation at each time point. The abundance of Alistipes shahii was significantly negatively correlated with IL-6 and TNF-α (P < 0.05).

CONCLUSIONS

Roxadustat alleviated renal anemia in patients with ESA resistance by decreasing inflammatory factors and hepcidin levels and improving iron utilization. These effects were at least partly mediated by improved diversity and abundance of SCFA-producing gut bacteria, probably via activation of HIF.

Interpreting Iron Homeostasis in Congenital and Acquired Disorders

Mammalian cells require iron to satisfy their metabolic needs and to accomplish specialized functions, such as hematopoiesis, mitochondrial biogenesis, energy metabolism, or oxygen transport. Iron homeostasis is balanced by the interplay of proteins responsible for iron import, storage, and export. A misbalance of iron homeostasis may cause either iron deficiencies or iron overload diseases. The clinical work-up of iron dysregulation is highly important, as severe symptoms and pathologies may arise. Treating iron overload or iron deficiency is important to avoid cellular damage and severe symptoms and improve patient outcomes. The impressive progress made in the past years in understanding mechanisms that maintain iron homeostasis has already changed clinical practice for treating iron-related diseases and is expected to improve patient management even further in the future.

Hypoxia Pathway in Osteoporosis: Laboratory Data for Clinical Prospects

The hypoxia pathway not only regulates the organism to adapt to the special environment, such as short-term hypoxia in the plateau under normal physiological conditions, but also plays an important role in the occurrence and development of various diseases such as cancer, cardiovascular diseases, osteoporosis. Bone, as a special organ of the body, is in a relatively low oxygen environment, in which the expression of hypoxia-inducible factor (HIF)-related molecules maintains the necessary conditions for bone development. Osteoporosis disease with iron overload endangers individuals, families and society, and bone homeostasis disorder is linked to some extent with hypoxia pathway abnormality, so it is urgent to clarify the hypoxia pathway in osteoporosis to guide clinical medication efficiently. Based on this background, using the keywords "hypoxia/HIF, osteoporosis, osteoblasts, osteoclasts, osteocytes, iron/iron metabolism", a matching search was carried out through the Pubmed and Web Of Science databases, then the papers related to this review were screened, summarized and sorted. This review summarizes the relationship and regulation between the hypoxia pathway and osteoporosis (also including osteoblasts, osteoclasts, osteocytes) by arranging the references on the latest research progress, introduces briefly the application of hyperbaric oxygen therapy in osteoporosis symptoms (mechanical stimulation induces skeletal response to hypoxic signal activation), hypoxic-related drugs used in iron accumulation/osteoporosis model study, and also puts forward the prospects of future research.

Hypoxia and Intestinal Inflammation: Common Molecular Mechanisms and Signaling Pathways

The gastrointestinal tract (GI) has a unique oxygenation profile. It should be noted that the state of hypoxia can be characteristic of both normal and pathological conditions. Hypoxia-inducible factors (HIF) play a key role in mediating the response to hypoxia, and they are tightly regulated by a group of enzymes called HIF prolyl hydroxylases (PHD). In this review, we discuss the involvement of inflammation hypoxia and signaling pathways in the pathogenesis of inflammatory bowel disease (IBD) and elaborate in detail on the role of HIF in multiple immune reactions during intestinal inflammation. We emphasize the critical influence of tissue microenvironment and highlight the existence of overlapping functions and immune responses mediated by the same molecular mechanisms. Finally, we also provide an update on the development of corresponding therapeutic approaches that would be useful for treatment or prophylaxis of inflammatory bowel disease.

Mimicking Gene-Environment Interaction of Higher Altitude Dwellers by Intermittent Hypoxia Training: COVID-19 Preventive Strategies

Cyclooxygenase 2 (COX2) inhibitors have been demonstrated to protect against hypoxia pathogenesis in several investigations. It has also been utilized as an adjuvant therapy in the treatment of COVID-19. COX inhibitors, which have previously been shown to be effective in treating previous viral and malarial infections are strong candidates for improving the COVID-19 therapeutic doctrine. However, another COX inhibitor, ibuprofen, is linked to an increase in the angiotensin-converting enzyme 2 (ACE2), which could increase virus susceptibility. Hence, inhibiting COX2 via therapeutics might not always be protective and we need to investigate the downstream molecules that may be involved in hypoxia environment adaptation. Research has discovered that people who are accustomed to reduced oxygen levels at altitude may be protected against the harmful effects of COVID-19. It is important to highlight that the study's conclusions only applied to those who regularly lived at high altitudes; they did not apply to those who occasionally moved to higher altitudes but still lived at lower altitudes. COVID-19 appears to be more dangerous to individuals residing at lower altitudes. The downstream molecules in the (COX2) pathway have been shown to adapt in high-altitude dwellers, which may partially explain why these individuals have a lower prevalence of COVID-19 infection. More research is needed, however, to directly address COX2 expression in people living at higher altitudes. It is possible to mimic the gene-environment interaction of higher altitude people by intermittent hypoxia training. COX-2 adaptation resulting from hypoxic exposure at altitude or intermittent hypoxia exercise training (IHT) seems to have an important therapeutic function. Swimming, a type of IHT, was found to lower COX-2 protein production, a pro-inflammatory milieu transcription factor, while increasing the anti-inflammatory microenvironment. Furthermore, Intermittent Hypoxia Preconditioning (IHP) has been demonstrated in numerous clinical investigations to enhance patients' cardiopulmonary function, raise cardiorespiratory fitness, and increase tissues' and organs' tolerance to ischemia. Biochemical activities of IHP have also been reported as a feasible application strategy for IHP for the rehabilitation of COVID-19 patients. In this paper, we aim to highlight some of the most relevant shared genes implicated with COVID-19 pathogenesis and hypoxia. We hypothesize that COVID-19 pathogenesis and hypoxia share a similar mechanism that affects apoptosis, proliferation, the immune system, and metabolism. We also highlight the necessity of studying individuals who live at higher altitudes to emulate their gene-environment interactions and compare the findings with IHT. Finally, we propose COX2 as an upstream target for testing the effectiveness of IHT in preventing or minimizing the effects of COVID-19 and other oxygen-related pathological conditions in the future.

Beneficial effect of roxadustat on early posttransplant anemia and iron utilization in kidney transplant recipients: a retrospective comparative cohort study

Background

Although posttransplant anemia (PTA) is a common complication after kidney transplant, it has not been thoroughly evaluated for appropriate treatment. Roxadustat can stimulate erythropoiesis by increasing erythropoietin (EPO) production and improving the utilization of iron. However, there are currently a few case reports describing its effect on PTA in kidney transplant recipients (KTRs). Our purpose was to evaluate the efficacy and safety of roxadustat in KTRs with PTA.

Methods

In this retrospective study, KTRs with early PTA were divided into a roxadustat group, erythropoiesis-stimulating agent (ESA) group, and untreated group (neither roxadustat nor ESA) according to the treatment prescribed by their physicians. We compared the levels of hemoglobin (Hb), creatinine, lipids, hepcidin, intact fibroblast growth factor 23 (iFGF23) and iron-related indices, at baseline and different time points posttransplant. Outcome was assessed at both month 3 and month 12 posttransplant. Adverse events during the treatment course were also recorded.

Results

A total of 57 KTRs were included (n=22 roxadustat group, n=13 ESA group, n=22 untreated group). There was no difference in age, sex, body mass index, dialysis method and duration, donor type among three groups at baseline. The mean Hb levels at month 3 posttransplant (128.00±19.62 vs. 118.59±11.60 g/L, P=0.048) and the average change in Hb levels from week 2 to month 3 (48.05±22.53 vs. 31.45±12.96 g/L, P=0.005) in the roxadustat group were significantly higher than those in the untreated group. However, there was no significant difference in the above indices between the roxadustat and ESA groups. At month 3, the total iron binding capacity (TIBC) and levels of transferrin were significantly higher while levels of ferritin, hepcidin and iFGF23 were significantly lower in the roxadustat group than in other groups (P<0.05). No significant difference was found in creatinine or estimated glomerular filtration rate (eGFR) levels among the three groups at month 3. During the follow-up, no adverse events related to roxadustat were reported.

Conclusions

Administration of roxadustat in KTRs with early PTA could elevate Hb levels effectively and safely by enhancing endogenous EPO production and improving iron utilization. Further randomized studies with larger sample size are necessary to verify our results.

Hypoxia-Inducible Factor-Prolyl Hydroxyl Domain Inhibitors: From Theoretical Superiority to Clinical Noninferiority Compared with Current ESAs?

Anemia is a common complication of chronic kidney disease; it is mainly treated with erythropoiesis-stimulating agents (ESAs) and iron. Experimental studies extensively investigated the mechanisms involved in the body's response to hypoxia and led to the discovery of the hypoxia-inducible factor (HIF) pathway and the enzymes regulating its function. HIF-prolyl-hydroxyl domain (PHD) inhibitors are a new class of oral drugs developed to treat anemia in chronic kidney disease. By inhibiting the function of PHD enzymes, they mimic the exposure to moderate hypoxia and stimulate the production of endogenous erythropoietin and very likely increase iron availability. Some data also suggest that their efficacy and, consequently, dose needs are less influenced by inflammation than ESAs. Overall, data from phases 2 and 3 clinical development showed efficacy in anemia correction and maintenance for all of the class molecules compared with placebo (superiority) or erythropoiesis-stimulating agents (noninferiority). Three molecules, roxadustat, vadadustat, and daprodustat, underwent extensive clinical investigation to assess their safety on hard cardiovascular end points, mortality, and special interest events (including cancer and thrombosis). Aside from vadadustat in the nondialysis population, at the prespecified primary analyses, all three molecules met the noninferiority margin for the risk of major cardiovascular events compared with erythropoiesis-stimulating agents or placebo. The reason for this discrepancy is difficult to explain. Other safety signals came from secondary analyses of some of the other randomized clinical trials, including a higher incidence of thrombosis. A more extensive clinical experience with post-marketing data on hard safety issues is needed to define better when and how to use HIF-PHD inhibitors compared with already available ESAs.

ISCA2 inhibition decreases HIF and induces ferroptosis in clear cell renal carcinoma

Clear cell renal cell carcinoma (ccRCC), the most common form of kidney cancer, is typically initiated by inactivation of the von Hippel Lindau (VHL) gene, which results in the constitutive activation of the hypoxia inducible factors, HIF-1α and HIF-2α. Using a high throughput screen, we identify novel compounds that decrease HIF-1/2α levels and induce ferroptosis by targeting Iron Sulfur Cluster Assembly 2 (ISCA2), a component of the late mitochondrial Iron Sulfur Cluster (L-ISC) assembly complex. ISCA2 inhibition either pharmacologically or using siRNA decreases HIF-2α protein levels by blocking iron-responsive element (IRE)-dependent translation, and at higher concentrations, also decreases HIF-1α translation through unknown mechanisms. Additionally, ISCA2 inhibition triggers the iron starvation response, resulting in iron/metals overload and death via ferroptosis. ISCA2 levels are decreased in ccRCC compared to normal kidney, and decreased ISCA2 levels are associated with pVHL loss and with sensitivity to ferroptosis induced by ISCA2 inhibition. Strikingly, pharmacological inhibition of ISCA2 using an orally available ISCA2 inhibitor significantly reduced ccRCC xenograft growth in vivo, decreased HIF-α levels and increased lipid peroxidation, suggesting increased ferroptosis in vivo. Thus, the targeting of ISCA2 may be a promising therapeutic strategy to inhibit HIF-1/2α and to induce ferroptosis in pVHL deficient cells.

The Dark Side of Iron: The Relationship between Iron, Inflammation and Gut Microbiota in Selected Diseases Associated with Iron Deficiency Anaemia—A Narrative Review

Iron is an indispensable nutrient for life. A lack of it leads to iron deficiency anaemia (IDA), which currently affects about 1.2 billion people worldwide. The primary means of IDA treatment is oral or parenteral iron supplementation. This can be burdened with numerous side effects such as oxidative stress, systemic and local-intestinal inflammation, dysbiosis, carcinogenic processes and gastrointestinal adverse events. Therefore, this review aimed to provide insight into the physiological mechanisms of iron management and investigate the state of knowledge of the relationship between iron supplementation, inflammatory status and changes in gut microbiota milieu in diseases typically complicated with IDA and considered as having an inflammatory background such as in inflammatory bowel disease, colorectal cancer or obesity. Understanding the precise mechanisms critical to iron metabolism and the awareness of serious adverse effects associated with iron supplementation may lead to the provision of better IDA treatment. Well-planned research, specific to each patient category and disease, is needed to find measures and methods to optimise iron treatment and reduce adverse effects.

Disordered Maternal and Fetal Iron Metabolism Occurs in Preterm Births in Human

Background. Increasing evidence reveals that iron deficiency during pregnancy causes adverse pregnancy outcomes. Thus far, the mechanisms underlying iron deficiency-associated preterm birth are mostly limited to animal studies. Whether the suggested mechanisms exist in human requires further investigation. The goal of this study was to characterize the iron metabolism in both the maternal side and fetal side in pregnant women with preterm birth. Methods. Serum and placenta samples were collected from 42 pregnant women divided into four groups according to the gestational week. Indicators of iron metabolism, including serum iron, serum hepcidin, placental tissue iron, ferroportin (FPN), transferrin receptor 1 (TfR1), and ferritin, were surveyed using enzyme-linked immunosorbent assays (Elisa), Western blots, and real-time quantitative polymerase chain reactions (qRT-PCR). Results. Significant reduction of maternal serum iron was observed in women with preterm birth relative to those with full-term birth, indicative of worsen iron deficiency in those mothers with preterm birth. Meanwhile, the maternal hepcidin levels were notably diminished in women with preterm birth, whereas the fetal hepcidin levels were comparable between the two groups. Moreover, the placental iron stores were remarkably reduced in the preterm group, associated with reduced concentration of TfR1 and increased FPN concentration relative to the normal controls. In other words, the ratio of placental FPN mass to TfR1 mass (PIDI index) was strikingly increased in the preterm group. Conclusions. Dysregulated iron homeostasis in both the maternal and fetal sides was implicated in preterm births, and disordered regulations in maintaining the placental iron equilibrium were also presumed to account for the compromised fetal iron supply.

Alcohol exposure increases manganese accumulation in the brain and exacerbates manganese-induced neurotoxicity in mice

Environmental and occupational exposure to heavy metals remains one of the major concerns in public health. Increased levels of manganese (Mn) pollution are associated with profound neurotoxic effects, including neurobehavioral deficits and disturbances resembling Parkinson's disease. While Mn absorption is in part mediated by iron transporters, recent studies have shown that the levels of iron transporters are modified by alcohol and that chronic alcohol consumption increases body iron stores. However, it is largely unexplored whether alcohol exposure influences the transport and neurotoxicity of Mn. To address this question, we exposed mice to ethanol (10%; v/v) by drinking water for 4 weeks, during which period MnCl₂ (5 mg/kg) or saline solutions were administered daily by intranasal instillation. Ethanol consumption in mice increased brain Mn levels in a dose-dependent manner after Mn instillation, determined by inductively-coupled plasma mass spectrometry, which was accompanied by up-regulation of iron transporters, as assessed by western blotting and qPCR. In addition, alcohol drinking increased hypoxic response and decreased hepcidin expression, providing the molecular mechanism of increased iron transporters and Mn uptake upon alcohol consumption. Moreover, brain dopamine levels, analyzed by HPLC, were decreased after intranasal Mn instillation, which was worsened by alcohol. Likewise, alcohol-Mn co-exposure synergistically altered dopaminergic protein expression. Finally, alcohol binge-drinking, which resembles alcohol drinking manner in humans, increased brain Mn content along with upregulation of iron transporters. Our study suggests that individuals who consume alcohol may have a higher risk of Mn neurotoxicity upon Mn exposure.

Role of Iron Metabolism-Related Genes in Prenatal Development: Insights from Mouse Transgenic Models

Iron is an essential nutrient during all stages of mammalian development. Studies carried out over the last 20 years have provided important insights into cellular and systemic iron metabolism in adult organisms and led to the deciphering of many molecular details of its regulation. However, our knowledge of iron handling in prenatal development has remained remarkably under-appreciated, even though it is critical for the health of both the embryo/fetus and its mother, and has a far-reaching impact in postnatal life. Prenatal development requires a continuous, albeit quantitatively matched with the stage of development, supply of iron to support rapid cell division during embryogenesis in order to meet iron needs for erythropoiesis and to build up hepatic iron stores, (which are the major source of this microelement for the neonate). Here, we provide a concise overview of current knowledge of the role of iron metabolism-related genes in the maintenance of iron homeostasis in pre- and post-implantation development based on studies on transgenic (mainly knock-out) mouse models. Most studies on mice with globally deleted genes do not conclude whether underlying in utero iron disorders or lethality is due to defective placental iron transport or iron misregulation in the embryo/fetus proper (or due to both). Therefore, there is a need of animal models with tissue specific targeted deletion of genes to advance the understanding of prenatal iron metabolism.

Advances in understanding the crosstalk between mother and fetus on iron utilization

A full-term pregnancy comes with significant demand for iron. Not meeting this demand has adverse effects on maternal health and on the intrauterine and postnatal development of the infant. In the infant, some of these adverse effects cannot be reversed by postnatal iron supplementation, highlighting the need to tackle iron deficiency in utero. Achieving this requires sound understanding of the pathways that govern iron transfer at the fetomaternal interface. Two pathways are emerging as key players in this context; the hepcidin/ferroportin axis pathway and the iron regulatory protein (IRPs) pathway. In late gestation, suppression of maternal hepcidin, by as yet unknown factors, is required for increasing iron availability to the growing fetus. In the placenta, the rate of iron uptake by transferrin receptor TfR1 at the apical/maternal side and of iron release by ferroportin FPN at the basal/fetal side is controlled by IRP1. In fetal hepatocytes, build up of fetal iron stores requires post-translational inhibition of FPN by the cell-autonomous action of hepcidin. In the fetal liver, FPN is also subject to additional control at the transcriptional level, possibly by the action of hypoxia-inducible factor HIF2α. The rates of apical iron uptake and basal iron release in the placenta are modulated according to iron availability in the maternal blood and the placenta's own needs. This placental modulation ensures that the amount of iron delivered to the fetal circulation is maintained within a normal range, even in the face of mild maternal iron deficiency or overload. However, when maternal iron deficiency or overload are extreme, placental modulation is not sufficient to maintain normal iron supply to the fetus, resulting in fetal iron deficiency and overload respectively. Thus, the rate of iron transfer at the fetomaternal interface is subject to several regulatory signals operating simultaneously in the maternal liver, the placenta and the fetal liver. These regulatory signals act in concert to maintain normal iron supply to the fetus within a wide range of maternal iron states, but fail to do so when maternal iron deficiency or overload are extreme. The limitations of existing experimental models must be overcome if we are to gain better understanding of the role of these regulatory signals in normal and complicated pregnancy. Ultimately, that understanding could help identify better markers of fetal iron demand and underpin novel iron replacement strategies to treat maternal and fetal iron deficiency.

Role of Iron in the Molecular Pathogenesis of Diseases and Therapeutic Opportunities

Iron is an essential mineral that serves as a prosthetic group for a variety of proteins involved in vital cellular processes. The iron economy within humans is highly conserved in that there is no proper iron excretion pathway. Therefore, iron homeostasis is highly evolved to coordinate iron acquisition, storage, transport, and recycling efficiently. A disturbance in this state can result in excess iron burden in which an ensuing iron-mediated generation of reactive oxygen species imparts widespread oxidative damage to proteins, lipids, and DNA. On the contrary, problems in iron deficiency either due to genetic or nutritional causes can lead to a number of iron deficiency disorders. Iron chelation strategies have been in the works since the early 1900s, and they still remain the most viable therapeutic approach to mitigate the toxic side effects of excess iron. Intense investigations on improving the efficacy of chelation strategies while being well tolerated and accepted by patients have been a particular focus for many researchers over the past 30 years. Moreover, recent advances in our understanding on the role of iron in the pathogenesis of different diseases (both in iron overload and iron deficiency conditions) motivate the need to develop new therapeutics. We summarized recent investigations into the role of iron in health and disease conditions, iron chelation, and iron delivery strategies. Information regarding small molecule as well as macromolecular approaches and how they are employed within different disease pathogenesis such as primary and secondary iron overload diseases, cancer, diabetes, neurodegenerative diseases, infections, and in iron deficiency is provided.

Mendelian inheritance of anemia due to disturbed iron homeostasis

Genetic disorders that affect proteins involved in maintaining iron balance may lead to Mendelian anemias. They may be classified as defects of intestinal iron absorption, iron transport in the circulation, iron uptake and utilization by maturing erythroid cells, iron recycling by macrophages and systemic regulation of iron homeostasis. All these Mendelian anemias are rare disorders, prevalently recessive, characterized by microcytic and hypochromic red blood cells. Advances in our knowledge of iron metabolism and its systemic regulation on one side have facilitated the identification of novel iron related anemias, while on the other the study of the affected patients and of the corresponding animal models have contributed to our understanding of iron trafficking and regulation.

Marginally reduced maternal hepatic and splenic ferroportin under severe nutritional iron deficiency in pregnancy maintains systemic iron supply

The demand for iron is high in pregnancy to meet the increased requirements for erythropoiesis. Even pregnant females with initially iron‐replete stores develop iron‐deficiency anemia, due to inadequate iron absorption. In anemic females, the maternal iron supply is dedicated to maintaining iron metabolism in the fetus and placenta. Here, using a mouse model of iron deficiency in pregnancy, we show that iron recycled from senescent erythrocytes becomes a predominant source of this microelement that can be transferred to the placenta in females with depleted iron stores. Ferroportin is a key protein in the molecular machinery of cellular iron egress. We demonstrate that under iron deficiency in pregnancy, levels of ferroportin are greatly reduced in the duodenum, placenta and fetal liver, but not in maternal liver macrophages and in the spleen. Although low expression of both maternal and fetal hepcidin predicted ferroportin up‐regulation in examined locations, its final expression level was very likely correlated with tissue iron status. Our results argue that iron released into the circulation of anemic females is taken up by the placenta, as evidenced by high expression of iron importers on syncytiotrophoblasts. Then, a substantial decrease in levels of ferroportin on the basolateral side of syncytiotrophoblasts, may be responsible for the reduced transfer of iron to the fetus. As attested by the lowest decrease in iron content among analyzed tissues, some part is retained in the placenta. These findings confirm the key role played by ferroportin in tuning iron turnover in iron‐deficient pregnant mouse females and their fetuses.

Effect of 8-Day Fasting on Leukocytes Expression of Genes and Proteins Involved in Iron Metabolism in Healthy Men

The popularity of fasting and restricted food intake is increasing. While the body's adaptability to dietary insufficiency is crucial for health, molecular mechanisms of adaptive changes are not well understood. Here, we compared the effects of fasting and exercise on the expression of leukocyte genes and proteins involved in the storage, export, and acquisition of iron, an essential element with physiological roles. Healthy men participated in the study (age, 30-70 years; body weight, 60-100 kg; body mass index, 20-29.9 kg/m²). The participants performed an exercise test with a gradually increasing intensity until the individual maximum exercise capacity was reached, before and after 8-d fast. Blood samples were collected before, immediately after, and 3 h after exercise. Gene expression was analyzed by reverse-transcription quantitative polymerase chain reaction and protein levels were analyzed by immunobloting. Eight days of total starvation diet affected the body composition and decreased exercise capacity. Further, fasting decreased the expression of genes associated with iron storage and export, and increased the expression of genes involved in iron acquisition. Conversely, only PCBP2 protein increased after fasting; however, an upward trend was apparent for all proteins. In conclusion, the body adapts to starvation by adjusting iron economy.

Hypoxia-inducible factor (HIF): The link between obesity and COVID-19

The COVID-19 death toll has involved to date more than 1 million confirmed deaths. The death rate is even higher in the obese COVID-19 patients, as a result of hypoxia, due to the interplay between adipose tissue hypoxia and obstructive sleep apnea. The discrepancy of manifestations seen in COVID-19 seems to be mediated by a differential immune response rather than a differential viral load. One of the key players of the immune response is HIF. HIF-1β is a stable constitutively expressed protein in the nucleus; and under hypoxic changes, its activity is unaffected, whereas the HIF-α subunit has a short half-life and because of its degradation by an enzyme known as propyl hydroxylase; under hypoxic conditions, propyl hydroxylase gets deactivated thus leading to the stabilization of HIF-1α. As mentioned before, HIF-1α expression is triggered by hypoxic states, this crippling condition will aggravate the pro-inflammatory characteristics of HIF-1α. The vast majority of decompensated COVID19 cases manifest with drastic lung injury and severe viral pneumonia, the infection-induced hypoxia will the existing hypoxia in obesity. This will additionally augment HIF-1α levels that will provoke the already existing cytokines' storm to fulminant. Consequently, this will directly correlate the effect of a hypoxic environment with the increase of HIF-1α level. HIFɑ exists in two main isoforms HIF-1α and HIF-2α. HIF-1α and HIF-2α act in distinct ways in how they work on different target genes. For example, HIF-2α may act on hemopoietin genes (heme-regulating genes); while HIF-1α acts on EPO. HIF-1α release seems to be markedly augmented in obesity due to adipose tissue hypoxia and obstructive sleep apnea resulting in cyclic hypoxia. HIF-1α can also be secreted by direct viral proteolytic effects. Whereas, HIF-2α is stimulated by chronic hypoxia. HIF-1α exerts detrimental effects on the immune system, characterized by unopposed pro-inflammation at the macrophages, dendritic cells, T cells, and complement levels resulting in cytokines' storm, which is linked to the poor outcomes of COVID-19. On the other hand, HIF-2α role is regulatory and largely opposes the actions mediated by HIF-1α. In view of this, inhibiting HIF-1α release or switching its production to HIF-2α by natural products such as resveratrol or by synthetic drugs, offer a good therapeutic strategy that can prevent COVID-19 worst outcome in infected patients. The approach of breaking the vicious circle between lung damage-induced hypoxia and HIF-1α pro-inflammatory stimulant through drugs is considered to be extremely promising as a therapeutic manner to combat further deterioration of COVID19 cases.

Iron and Chronic Kidney Disease: Still a Challenge

Anemia is a clinical feature of chronic kidney disease (CKD). Most common causes are iron and erythropoietin deficiency. The last two decades have yielded significant advances in understanding iron balance's physiology, including iron trafficking and the crosstalk between iron, oxygen, and erythropoiesis. This knowledge sheds new light on the regulation and disturbance of iron homeostasis in CKD and holds the promise for developing new diagnostic and therapeutic tools to improve the management of iron disorders. Hepcidin-ferroportin axis has a central role in regulating body iron balance and coordinating communication between tissues and cells that acquire, store, and utilize iron. Recent research has revealed a bidirectional relationship between fibroblast growth factor 23 (FGF23) and iron status, anemia, and inflammation, as well as the role of erythroferrone (ERFE) in iron homeostasis. However, ERFE concentrations and actions are not well-characterized in CKD patients. Studies on ERFE in CKD are limited with slightly conflicting results. Despite general interest in iron metabolism in kidney diseases, studies on the less prevalent renal replacement therapy mode, such as peritoneal dialysis or hemodiafiltration, are scarce. Slightly more was published on hemodialysis. There are several novel options on the horizon; however, clinical data are limited. One should be aware of the potential risks and benefits of the novel, sophisticated therapies. An inhibition of hepcidin on the different pathways might be also a viable adjunctive therapeutic option in other clinical situations.

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.

EPAS1 and VEGFA gene variants are related to the symptoms of acute mountain sickness in Chinese Han population: a cross-sectional study

BACKGROUND

More people ascend to high altitude (HA) for various activities, and some individuals are susceptible to HA illness after rapidly ascending from plains. Acute mountain sickness (AMS) is a general complaint that affects activities of daily living at HA. Although genomic association analyses suggest that single nucleotide polymorphisms (SNPs) are involved in the genesis of AMS, no major gene variants associated with AMS-related symptoms have been identified.

METHODS

In this cross-sectional study, 604 young, healthy Chinese Han men were recruited in June and July of 2012 in Chengdu, and rapidly taken to above 3700 m by plane. Basic demographic parameters were collected at sea level, and heart rate, pulse oxygen saturation (SpO₂), systolic and diastolic blood pressure and AMS-related symptoms were determined within 18-24 h after arriving in Lhasa. AMS patients were identified according to the latest Lake Louise scoring system (LLSS). Potential associations between variant genotypes and AMS/AMS-related symptoms were identified by logistic regression after adjusting for potential confounders (age, body mass index and smoking status).

RESULTS

In total, 320 subjects (53.0%) were diagnosed with AMS, with no cases of high-altitude pulmonary edema or high-altitude cerebral edema. SpO₂ was significantly lower in the AMS group than that in the non-AMS group (P = 0.003). Four SNPs in hypoxia-inducible factor-related genes were found to be associated with AMS before multiple hypothesis testing correction. The rs6756667 (EPAS1) was associated with mild gastrointestinal symptoms (P = 0.013), while rs3025039 (VEGFA) was related to mild headache (P = 0.0007). The combination of rs6756667 GG and rs3025039 CT/TT further increased the risk of developing AMS (OR = 2.70, P < 0.001).

CONCLUSIONS

Under the latest LLSS, we find that EPAS1 and VEGFA gene variants are related to AMS susceptibility through different AMS-related symptoms in the Chinese Han population; this tool might be useful for screening susceptible populations and predicting clinical symptoms leading to AMS before an individual reaches HA.

TRIAL REGISTRATION

Chinese Clinical Trial Registration, ChiCTR-RCS-12002232 . Registered 31 May 2012.

Oral iron supplementation in iron-deficient women: How much and how often?

Iron deficiency and iron deficiency anemia (IDA) are major public health problems worldwide, especially in young women. Oral iron supplementation can be an effective strategy to treat and prevent IDA, but guidelines vary. Some experts recommend doses of 150-200 mg elemental iron per day, with the dose split through the day. However, recent studies suggest this may not be an optimal regimen. The fraction of iron absorbed from high doses of oral iron is low, and unabsorbed iron can cause gut irritation, inflammation and dysbiosis, and these reduce compliance. In recent studies using serum hepcidin profiles and stable iron isotopes to quantify iron absorption in young women, we have shown that: (a) oral iron doses ≥60 mg in iron-deficient women, and doses ≥100 mg in women with IDA, stimulate an acute increase in hepcidin that persists 24 h after the dose, but subsides by 48 h; (b) therefore, to maximize fractional iron absorption, oral doses ≥60 mg should be given on alternate days; (c) the circadian increase in plasma hepcidin is augmented by a morning iron dose; therefore, iron doses should not be given in the afternoon or evening after a morning dose. If rate of Hb response is important, a pooled analysis of our data done for this review indicates that total iron absorption is also higher if twice the target daily iron dose is given on alternate days. In summary, these studies suggest changing from daily to alternate-day schedules and from divided to morning single doses increases iron absorption and may reduce side effects. Thus, providing morning doses of 60-120 mg iron as a ferrous salt given with ascorbic acid on alternate days may be an optimal oral dosing regimen for women with iron-deficiency and mild IDA.

Anemia of Chronic Diseases: Wider Diagnostics-Better Treatment?

Anemia of chronic diseases is a condition that accompanies a specific underlying disease, in which there is a decrease in hemoglobin, hematocrit and erythrocyte counts due to a complex process, usually initiated by cellular immunity mechanisms and pro-inflammatory cytokines and hepcidin. This is the second most common type of anemia after iron deficiency anemia in the world. Its severity generally correlates with the severity of the underlying disease. This disease most often coexists with chronic inflammation, autoimmune diseases, cancer, and kidney failure. Before starting treatment, one should undertake in-depth diagnostics, which includes not only assessment of complete blood count and biochemical parameters, but also severity of the underlying disease. The differential diagnosis of anemia of chronic diseases is primarily based on the exclusion of other types of anemia, in particular iron deficiency. The main features of anemia of chronic diseases include mild to moderate lowering of hemoglobin level, decreased percentage of reticulocyte count, low iron and transferrin concentration, but increased ferritin. Due to the increasingly better knowledge of the pathomechanism of chronic diseases and cancer biology, the diagnosis of this anemia is constantly expanding with new biochemical indicators. These include: the concentration of other hematopoietic factors (folic acid, vitamin B₁₂), hepcidin, creatinine and erythropoietin. The basic form of treatment of anemia of chronic diseases remains supplementation with iron, folic acid and vitamin B₁₂ as well as a diet rich in the above-mentioned hematopoietic factors. The route of administration (oral, intramuscular or intravenous) requires careful consideration of the benefits and possible side effects, and assessment of the patient’s clinical status. New methods of treating both the underlying disease and anemia are raising hopes. The novel methods are associated not only with supplementing deficiencies, but also with the administration of drugs molecularly targeted to specific proteins or receptors involved in the development of anemia of chronic diseases.

Iron homeostasis is dysregulated, but the iron-hepcidin axis is functional, in chronic liver disease

BACKGROUND

Perturbations in iron homeostasis have been reported to be associated with irreversible liver injury in chronic liver disease (CLD). However, it is not clear whether liver dysfunction per se underlies such dysregulation or whether other factors also contribute to it. This study attempted to examine the issues involved.

METHODS

Patients diagnosed to have chronic liver disease (n = 63), who underwent a medically-indicated upper gastrointestinal endoscopy, were the subjects of this study. Patients with dyspepsia, who underwent such a procedure, and were found to have no endoscopic abnormalities, were used as control subjects (n = 49). Duodenal mucosal samples were obtained to study mRNA and protein levels of duodenal proteins involved in iron absorption. A blood sample was also obtained for estimation of hematological, iron-related, inflammatory and liver function-related parameters.

RESULTS

Patients with CLD had impaired liver function, anemia of inflammation and lower serum levels of hepcidin than control subjects. Gene (mRNA) expression levels of duodenal ferroportin and duodenal cytochrome b (proteins involved in iron absorption) were decreased, while that of divalent metal transporter-1 (DMT-1) was unchanged. Protein expression of DMT-1 was, however, decreased while that of ferroportin was unchanged. In the CLD group, serum hepcidin was predicted independently by serum ferritin and hemoglobin, but not by C-reactive protein (a marker of inflammation). CLD patients with serum ferritin greater than 300 μg/dL had significantly greater liver dysfunction (as indicated by significantly higher serum concentrations of bilirubin, AST and ALT, and MELD scores), higher serum concentrations of CRP and hepcidin, and higher ferroportin protein expression, than those with serum ferritin ≤ 300 μg/dL.

CONCLUSIONS

In patients with CLD, anemia of inflammation and low serum hepcidin levels were found to paradoxically co-exist. Expression of duodenal proteins involved in iron absorption were either decreased or unaltered in these patients. The hepcidin response to higher body iron levels and/or inflammation appeared to be functional in these patients, despite the presence of liver disease.

Iron deficiency anaemia revisited

Iron deficiency anaemia is a global health concern affecting children, women and the elderly, whilst also being a common comorbidity in multiple medical conditions. The aetiology is variable and attributed to several risk factors decreasing iron intake and absorption or increasing demand and loss, with multiple aetiologies often coexisting in an individual patient. Although presenting symptoms may be nonspecific, there is emerging evidence on the detrimental effects of iron deficiency anaemia on clinical outcomes across several medical conditions. Increased awareness about the consequences and prevalence of iron deficiency anaemia can aid early detection and management. Diagnosis can be easily made by measurement of haemoglobin and serum ferritin levels, whilst in chronic inflammatory conditions, diagnosis may be more challenging and necessitates consideration of higher serum ferritin thresholds and evaluation of transferrin saturation. Oral and intravenous formulations of iron supplementation are available, and several patient and disease-related factors need to be considered before management decisions are made. This review provides recent updates and guidance on the diagnosis and management of iron deficiency anaemia in multiple clinical settings.

Iron metabolism and iron disorders revisited in the hepcidin era

Iron is biologically essential, but also potentially toxic; as such it is tightly controlled at cell and systemic levels to prevent both deficiency and overload. Iron regulatory proteins post-transcriptionally control genes encoding proteins that modulate iron uptake, recycling and storage and are themselves regulated by iron. The master regulator of systemic iron homeostasis is the liver peptide hepcidin, which controls serum iron through degradation of ferroportin in iron-absorptive enterocytes and iron-recycling macrophages. This review emphasizes the most recent findings in iron biology, deregulation of the hepcidin-ferroportin axis in iron disorders and how research results have an impact on clinical disorders. Insufficient hepcidin production is central to iron overload while hepcidin excess leads to iron restriction. Mutations of hemochro-matosis genes result in iron excess by downregulating the liver BMP-SMAD signaling pathway or by causing hepcidin-resistance. In iron-loading anemias, such as β-thalassemia, enhanced albeit ineffective ery-thropoiesis releases erythroferrone, which sequesters BMP receptor ligands, thereby inhibiting hepcidin. In iron-refractory, iron-deficiency ane-mia mutations of the hepcidin inhibitor TMPRSS6 upregulate the BMP-SMAD pathway. Interleukin-6 in acute and chronic inflammation increases hepcidin levels, causing iron-restricted erythropoiesis and ane-mia of inflammation in the presence of iron-replete macrophages. Our improved understanding of iron homeostasis and its regulation is having an impact on the established schedules of oral iron treatment and the choice of oral versus intravenous iron in the management of iron deficiency. Moreover it is leading to the development of targeted therapies for iron overload and inflammation, mainly centered on the manipulation of the hepcidin-ferroportin axis.

Management of iron deficiency

Iron deficiency (ID) affects billions of people worldwide and remains the leading cause of anemia with significant negative impacts on health. Our approach to ID and iron deficiency anemia (IDA) involves three steps (I3): (1) identification of ID/IDA, (2) investigation of and management of the underlying etiology of ID, and (3) iron repletion. Iron repletion options include oral and intravenous (IV) iron formulations. Oral iron remains a therapeutic option for the treatment of ID in stable patients, but there are many populations for whom IV iron is more effective. Therefore, IV iron should be considered when there are no contraindications, when poor response to oral iron is anticipated, when rapid hematologic responses are desired, and/or when there is availability of and accessibility to the product. Judicious use of red cell blood transfusion is recommended and should be considered only for severe, symptomatic IDA with hemodynamic instability. Identification and management of ID and IDA is a central pillar in patient blood management.

Iron and Vitamin D/Calcium Deficiency after Gastric Bypass: Mechanisms Involved and Strategies to Improve Oral Supplement Disposition

Background:

Nutritional deficiencies are common following Roux-en-Y Gastric Bypass (RYGB). Aetiology is diverse; including non-compliance, altered diet, unresolved preoperative deficiency and differential degrees of post-operative malabsorption occurring as function of length of bypassed intestine. Iron and calcium/vitamin D deficiency occur in up to 50% of patients following RYGB. Currently, treatment strategies recommend the prescription of oral supplements for those who become deficient. Meanwhile, debate exists regarding the absorption capacity of these post-operatively and their efficacy in treating deficiency.

Objective:

To examine the disposition of oral iron and calcium/vitamin D supplementation following RYGB. Methods: A literature review was carried out using PubMed and Embase. Data from the key interventional studies investigating iron and calcium/vitamin D oral supplement absorption and efficacy following RYGB was summarized.

Results:

Absorption of both iron and vitamin D/calcium is adversely affected following RYGB. Distribution and metabolism may be altered by the predominance of paracellular absorption pathways which promote unregulated influx into the circulatory system. Overall, studies indicate that current supplementation strategies are efficacious to a degree in treating deficiency following RYGB, generally restoration of optimal status is not achieved.

Conclusion:

Oral supplement disposition is altered following RYGB. As a result, patients are required to take regimens of oral supplementation indefinitely. The dosage which confers optimum health benefit while avoiding potential toxicity and tolerability issues remains unknown. Novel preparations with improved disposition could help limit the extent of post-RYGB nutritional deficiencies.

An intimate crosstalk between iron homeostasis and oxygen metabolism regulated by the hypoxia-inducible factors (HIFs)

Oxygen and iron are among the most abundant elements and have significant roles in human biology. Iron is essential for oxygen transport and is a component of molecular O₂-carrying proteins, such as hemoglobin and myoglobin. Iron is also a constituent of redox enzymes and can occupy multiple oxidation states. An elaborate system has evolved to stringently regulate the concentrations of both, free iron and oxygen, in various sites of the body. The final destination for iron and oxygen in the cells is the mitochondria. The mitochondria require substantial amounts of iron for heme synthesis and maturation of iron-sulfur clusters, and oxygen, as the electron acceptor in oxidative phosphorylation. Therefore, the balance between the control of iron availability and the physiology of hypoxic responses is critical for maintaining cell homeostasis. Several lines of study have clearly demonstrated that the transcription factors, hypoxia-inducible factors (HIFs), play a central role in cellular adaptation to critically low oxygen levels in both normal and compromised tissues. It has also been shown that several target genes of HIFs are involved in iron homeostasis, reflecting the molecular links between oxygen homeostasis and iron metabolism. Furthermore, HIF activation is modulated by intracellular iron, through regulation of hydroxylase activity, which requires iron as a cofactor. In addition, HIF-2α translation is controlled by iron regulatory protein (IRP) activity, providing another level of interdependence between iron and oxygen homeostasis.

Iron deficiency

Iron deficiency anemia affects >1.2 billions individuals worldwide, and iron deficiency in the absence of anemia is even more frequent. Total-body (absolute) iron deficiency is caused by physiologically increased iron requirements in children, adolescents, young and pregnant women, by reduced iron intake, or by pathological defective absorption or chronic blood loss. Adaptation to iron deficiency at the tissue level is controlled by iron regulatory proteins to increase iron uptake and retention; at the systemic level, suppression of the iron hormone hepcidin increases iron release to plasma by absorptive enterocytes and recycling macrophages. The diagnosis of absolute iron deficiency is easy unless the condition is masked by inflammatory conditions. All cases of iron deficiency should be assessed for treatment and underlying cause. Special attention is needed in areas endemic for malaria and other infections to avoid worsening of infection by iron treatment. Ongoing efforts aim at optimizing iron salts-based therapy by protocols of administration based on the physiology of hepcidin control and reducing the common adverse effects of oral iron. IV iron, especially last-generation compounds administered at high doses in single infusions, is becoming an effective alternative in an increasing number of conditions because of a more rapid and persistent hematological response and acceptable safety profile. Risks/benefits of the different treatments should be weighed in a personalized therapeutic approach to iron deficiency.

An intensified training schedule in recreational male runners is associated with increases in erythropoiesis and inflammation and a net reduction in plasma hepcidin

Background

Iron status is a determinant of physical performance, but training may induce both low-grade inflammation and erythropoiesis, exerting opposing influences on hepcidin and iron metabolism. To our knowledge, the combined effects on iron absorption and utilization during training have not been examined directly in humans.

Objective

We hypothesized that 3 wk of exercise training in recreational male runners would decrease oral iron bioavailability by increasing inflammation and hepcidin concentrations.

Design

In a prospective intervention, nonanemic, iron-sufficient men (n = 10) completed a 34-d study consisting of a 16-d control phase and a 22-d exercise-training phase of 8 km running every second day. We measured oral iron absorption and erythroid iron utilization using oral 57Fe and intravenous 58Fe tracers administered before and during training. We measured hemoglobin mass (mHb) and total red blood cell volume (RCV) by carbon monoxide rebreathing. Iron status, interleukin-6 (IL-6), plasma hepcidin (PHep), erythropoietin (EPO), and erythroferrone were measured before, during, and after training.

Results

Exercise training induced inflammation, as indicated by an increased mean ± SD IL-6 (0.87 ± 1.1 to 5.17 ± 2.2 pg/mL; P < 0.01), while also enhancing erythropoiesis, as indicated by an increase in mean EPO (0.66 ± 0.42 to 2.06 ± 1.6 IU/L), mHb (10.5 ± 1.6 to 10.8 ± 1.8 g/kg body weight), and mean RCV (30.7 ± 4.3 to 32.7 ± 4.6 mL/kg) (all P < 0.05). Training tended to increase geometric mean iron absorption by 24% (P = 0.083), consistent with a decreased mean ± SD PHep (7.25 ± 2.14 to 5.17 ± 2.24 nM; P < 0.05). The increase in mHb and erythroid iron utilization were associated with the decrease in PHep (P < 0.05). Compartmental modeling indicated that iron for the increase in mHb was obtained predominantly (>80%) from stores mobilization rather than from increased dietary absorption.

Conclusions

In iron-sufficient men, mild intensification of exercise intensity increases both inflammation and erythropoiesis. The net effect is to decrease hepcidin concentrations and to tend to increase oral iron absorption. This trial was registered at clinicaltrials.gov as NCT01730521.

Iron Supplementation in Suckling Piglets: An Ostensibly Easy Therapy of Neonatal Iron Deficiency Anemia

In pigs, iron deficiency anemia (IDA) is the most prevalent deficiency disorder during the early postnatal period, frequently developing into a serious illness. On the other hand, in humans, only low-birth-weight infants, including premature infants, are especially susceptible to developing IDA. In both human and pig neonates, the initial cause of IDA is low birth iron stores. In piglets this shortage of stored iron results mainly from genetic selection over the past few decades for large litter sizes and high birth weights. As a consequence, pregnant sows cannot provide a sufficient amount of iron to the increasing number of developing fetuses. Supplementation with iron is a common practice for the treatment of IDA in piglets. For decades, the preferred procedure for delivering iron supplements during early life stages has been through the intramuscular injection of a large amount of iron dextran. However, this relatively simple therapy, which in general, efficiently corrects IDA, may generate toxic effects, and by inducing hepcidin expression, may decrease bioavailability of supplemental iron. New iron supplements are considered herein with the aim to combine the improvement of hematological status, blunting of hepcidin expression, and minimizing the toxicity of the administered iron. We propose that iron-deficient piglets constitute a convenient animal model for performing pre-clinical studies with iron supplements.

Hypoxia-inducible transcription factors in fish: expression, function and interconnection with the circadian clock

The hypoxia-inducible transcription factors are key regulators for the physiological response to low oxygen availability. In vertebrates, typically three Hif-α isoforms, Hif-1α, Hif-2α and Hif-3α, are expressed, each of which, together with Hif-1β, may form a functional heterodimer under hypoxic conditions, controlling expression of hundreds of genes. A teleost-specific whole-genome duplication complicates the analysis of isoform-specific functions in fish, but recent studies suggest that the existence of paralogues of a specific isoform opens up the possibility for a subfunctionalization. In contrast to during development inside the uterus, fish eggs are freely accessible and studies analyzing Hif expression in fish embryos during development have revealed that Hif proteins are not only controlling the hypoxic response, but are also crucial for proper development and organ differentiation. Significant advances have been made in our knowledge about tissue-specific functions of Hif proteins, especially with respect to gill or gonadal tissue. The hypoxia signalling pathway is known to be tightly and mutually intertwined with the circadian clock in zebrafish and mammals. Recently, a mechanistic explanation for the hypoxia-induced dampening of the transcriptional clock was detected in zebrafish, including also metabolically induced alterations of cellular redox signalling. In turn, MAP kinase-mediated H2O2 signalling modulates the temporal expression of Hif-1α protein, similar to the redox regulation of the circadian clock itself. Once again, the zebrafish has emerged as an excellent model organism with which to explore these specific functional aspects of basic eukaryotic cell biology.

Advances in understanding iron metabolism and its crosstalk with erythropoiesis

Recent years have witnessed impressive advances in our understanding of iron metabolism. A number of studies of iron disorders and of their animal models have provided landmark insights into the mechanisms of iron trafficking, distribution and homeostatic regulation, the latter essential to prevent both iron deficiency and iron excess. Our perception of iron metabolism has been completely changed by an improved definition of cellular and systemic iron homeostasis, of the molecular pathogenesis of iron disorders, the fine tuning of the iron hormone hepcidin by activators and inhibitors and the dissection of the components of the hepcidin regulatory pathway. Important for haematology, the crosstalk of erythropoiesis, the most important iron consumer, and the hepcidin pathway has been at least partially clarified. Novel potential biomarkers are available and novel therapeutic targets for iron-related disorders have been tested in murine models. These preclinical studies provided proofs of principle and are laying the ground for clinical trials. Understanding iron control in tissues other than erythropoiesis remains a challenge for the future.

Intracellular iron and heme trafficking and metabolism in developing erythroblasts

Vertebrate red blood cells (RBCs) arise from erythroblasts in the human bone marrow through a process known as erythropoiesis. Iron uptake is a crucial hallmark, essential for heme biosynthesis in the differentiating erythroblasts, which are dedicated to producing hemoglobin. Erythropoiesis is facilitated by a network of intracellular transport proteins, chaperones, and circulating hormones. Intracellular iron is targeted to the mitochondria for incorporation into a porphyrin ring to form heme and cytosolic iron-sulfur proteins, including Iron Regulatory Protein 1 (IRP1). These processes are tightly regulated to prevent both excess and insufficient levels of iron and heme precursors. Crosstalk between the heme and iron-sulfur synthesizing pathways has been demonstrated to serve as a regulatory feedback mechanism. The activity of δ-aminolevulinic acid synthase (ALAS), the first and rate-limiting enzyme of heme biosynthesis, is a fundamental node of this regulation. Recently, the mitochondrial unfoldase, ClpX, has received attention as a novel key player that modulates this step in heme biogenesis, implicating a role in the pathophysiology of anemic diseases. This chapter reviews the canonical pathways in intracellular iron and heme trafficking and recent findings of iron and heme metabolism in vertebrate red cells. A discussion of the molecular approaches to studying iron and heme transport is provided to highlight opportunities for revealing therapeutic targets.

The hypoxia inducible factor/erythropoietin (EPO)/EPO receptor pathway is disturbed in a rat model of chronic kidney disease related anemia

Objectives

Anemia is a known driver for hypoxia inducible factor (HIF) which leads to increased renal erythropoietin (EPO) synthesis. Bone marrow (BM) EPO receptor (EPOR) signals are transduced through a JAK2-STAT5 pathway. The origins of anemia of chronic kidney disease (CKD) are multifactorial, including impairment of both renal EPO synthesis as well as intestinal iron absorption. We investigated the HIF- EPO- EPOR axis in kidney, BM and proximal tibia in anemic juvenile CKD rats.

Methods

CKD was induced by 5/6 nephrectomy in young (20 days old) male Sprague-Dawley rats while C group was sham operated. Rats were sacrificed 4 weeks after CKD induction and 5 minutes after a single bolus of IV recombinant human EPO. An additional control anemic (C-A) group was daily bled for 7 days.

Results

Hemoglobin levels were similarly reduced in CKD and C-A (11.4 ± 0.3 and 10.8±0.2 Vs 13.5±0.3 g/dL in C, p<0.0001). Liver hepcidin mRNA was decreased in CA but increased in CKD. Serum iron was unchanged while transferrin levels were mildly decreased in CKD. Kidney HIF2α protein was elevated in C-A but unchanged in CKD. Kidney EPO protein and mRNA levels were unchanged between groups. However, BM EPO protein (which reflects circulating EPO) was increased in C-A but remained unchanged in CKD. BM and proximal tibia EPOR were unchanged in C-A but decreased in CKD. Proximal tibial phospho-STAT5 increased after the EPO bolus in C but not in CKD.

Conclusions

Compared to blood loss, anemia in young CKD rats is associated with inappropriate responses in the HIF-EPO-EPO-R axis: kidney HIF2α and renal EPO are not increased, BM and bone EPOR levels, as well as bone pSTAT5 response to EPO are reduced. Thus, anemia of CKD may be treated with additional therapeutic avenues beyond iron and EPO supplementation.

Ferric citrate and ferric EDTA but not ferrous sulfate drive amphiregulin-mediated activation of the MAP kinase ERK in gut epithelial cancer cells

Ferric chelates may be used as oral iron supplements or phosphate binders but both ferric citrate and ferric EDTA have been shown to promote tumor burden in murine models of colon cancer. Here we studied their effects on cancer cell growth, at typical supplemental iron levels encountered in the gastrointestinal tract (0.01-0.2 mM). Caco-2 and/or Hutu-80 cells were exposed to these forms of chelated iron or to ferrous sulfate and outcomes were assessed using cell proliferation assays, proteome profiler arrays, western blot, and ELISA. Ferric EDTA and ferric citrate increased cellular levels of the onco-protein amphiregulin and its receptor (EGFr) which in turn stimulated the activation of the MAP kinase ERK. Simultaneously, the expression of the negative Wnt regulator, DKK-1, increased suggesting that cell proliferation through the Wnt pathway may be less pronounced in the presence of ferric EDTA and ferric citrate, unlike for ferrous sulfate. Moreover, ferrous sulfate did not increase levels of cellular amphiregulin or EGFr. We conclude that specific iron compounds affect cell signaling differently and some may increase the risk of colon cancer advancement in an amphiregulin-dependent fashion. Further scrutiny of safe oral iron use is merited.