Iron Phenotype Research Articles

Describing the effects of iron dyshomeostasis on cognitive function and dementia in UK Biobank

AbstractBackgroundIron dyshomeostasis is a feature of neurodegenerative disease. In circulating blood, changes in iron are associated with dementia disease phenotypes, while in brain tissue increased iron is associated with dementia progression. In UK Biobank, whole body imaging includes variables derived from the brain swMRI data which are indicative of iron in brain tissue. Complete blood counts per participant include hemoglobin concentration indicative of iron in oxygen transportation. Using the cognitive assessment and participants with all‐cause dementia we aimed to understand how measured changes in iron would affect dementia in a large UK‐based cohort.MethodUsing cross–sectional analysis at shared time points in UK Biobank data collection we compared both the iron phenotypes with cognitive measures. Firstly, the baseline values at the primary assessment centre visit where 478,082 participants were tested for cognitive function and red blood cell measures. Secondly, at Visit 2 (n = 5861), where brain imaging derived T2* measures and complete blood count (hemoglobin concentration) were captured alongside the repeated cognitive measures. Each linear regression model includes cognitive function (outcome) and iron measures (exposure) with correction for age and sex. Adjusted models include correction for education years, assessment centre and ethnicity.ResultWe found association between low hemoglobin and all‐cause dementia (beta = ‐0.125, p <0.001). This association was replicated with poorer cognitive function and low haemoglobin analysing cognitive function tests (including verbal and numerical reasoning and reaction time) and mean corpuscular hemoglobin, (p<0.05). Using quantile sets of hemoglobin concentration we found a non‐linear effect, whereby both high and low iron had a negative association on cognitive outcome (verbal reasoning ‐0.029,‐0.019, p’s = 0.002,0.049). Using MRI T2* we found associations between newer cognitive function tests, matrix pattern puzzles and symbol digit substitution (p <0.0001) as well as verbal reasoning (p = 0.015). These cognitive function measures were strongly associated with the T2* hippocampus region.ConclusionWe have shown an association between dementia and low hemoglobin concentration. We have demonstrated the complexities of this iron homeostasis relationship, showing how lower cognitive function is associated with both increased and reduced iron concentration in blood and how iron changes in brain effect different cognitive traits.

SIRT3 Regulates Clearance of Apoptotic Cardiomyocytes by Deacetylating Frataxin.

Efferocytosis is an activity of macrophages that is pivotal for the resolution of inflammation in hypertension. The precise mechanism by which macrophages coordinate efferocytosis and internalize apoptotic cardiomyocytes remains unknown. The aim of this study was to determine whether SIRT3 (sirtuin-3) is required for both apoptotic cardiomyocyte engulfment and anti-inflammatory responses during efferocytosis. We generated myeloid SIRT3 knockout mice and FXN (frataxin) knock-in mice carrying an acetylation-defective lysine to arginine K189R mutation (FXNK189R). The mice were given Ang II (angiotensin II) infusion for 7 days. We analyzed cardiac macrophages' mitochondrial iron levels, efferocytosis activity, and phenotype both in vivo and in vitro. We showed that SIRT3 deficiency exacerbated Ang II-induced downregulation of the efferocytosis receptor MerTK (c-Mer tyrosine kinase) and proinflammatory cytokine production, accompanied by disrupted mitochondrial iron homeostasis in cardiac macrophages. Quantitative acetylome analysis revealed that SIRT3 deacetylated FXN at lysine 189. Ang II attenuated SIRT3 activity and enhanced the acetylation level of FXNK189. Acetylated FXN further reduced the synthesis of ISCs (iron-sulfur clusters), resulting in mitochondrial iron accumulation. Phagocytic internalization of apoptotic cardiomyocytes increased myoglobin content, and derived iron ions promoted mitochondrial iron overload and lipid peroxidation. An iron chelator deferoxamine improved the levels of MerTK and efferocytosis, thereby attenuating proinflammatory macrophage activation. FXNK189R mice showed improved macrophage efferocytosis, reduced cardiac inflammation, and suppressed cardiac fibrosis. The SIRT3-FXN axis has the potential to resolve cardiac inflammation by increasing macrophage efferocytosis and anti-inflammatory activities.

Genetic Iron Overload Aggravates and Pharmacological Iron Restriction Improves MDS Pathophysiology in a Preclinical Mouse Model

Background: Patients with myelodysplastic syndromes (MDS) are prone to develop iron overload as a consequence of ineffective erythropoiesis and chronic transfusion therapy. Although iron overload is a common feature in MDS, it remains unclear whether and how iron excess is detrimental for MDS pathophysiology. Aims: This study aimed at characterizing altered iron homeostasis in a preclinical MDS mouse model, understanding the molecular mechanisms underlying iron toxicity and unraveling the potential therapeutic value of pharmacologic iron restriction in this disease condition. Methods: To this end, we took advantage of complementary approaches and analyzed the effect of iron overload obtained through genetic activation of the iron exporter ferroportin (FPNC326S), and iron restriction achieved through the administration of the FPN inhibitor vamifeport in NUP98-HOXD13 MDS mice, starting at 3 or 5 months of age. Results: At steady-state MDS mice develop an iron overload phenotype, hallmarked by low hepcidin levels, elevated serum iron and transferrin saturation, non-transferrin-bound iron (NTBI) formation and tissue iron deposition. This is associated with anemia and low WBCs in the peripheral blood. FPNC326S MDS mice show an aggravated iron phenotype, with further elevated NTBI and tissue iron accumulation and still inappropriately low hepcidin levels. Vamifeport administration in MDS mice reduced serum iron (194.8 vs 141.8 mg/dl; P<0.05) and NTBI formation (0.62 vs 0 μM; P<0.05) and prevented tissue iron loading. While iron excess in FPNC326S MDS mice did not improve erythropoiesis and hematologic parameters in the peripheral blood, iron restriction by vamifeport significantly ameliorated anemia (Hb 9.5 vs 11.4 g/dl; RBC 5.4 vs 6.9x106 cells/ml; P<0.05) and maturation of bone marrow as well as splenic RBCs in MDS mice. The improved ineffective erythropoiesis was associated with reduced oxidative stress and apoptosis in erythroid progenitors. Importantly, we observed a major role of the iron status in myeloid expansion in MDS. The number of immature myeloid blasts and myeloid progenitors in the bone marrow of MDS mice were aggravated by iron overload in FPNC326S MDS mice and attenuated by iron restriction in vamifeport-treated MDS mice compared to control MDS animals. Myeloid bias, monitored as percentage bone marrow myeloid cells, was exacerbated by iron overload (54.3 vs 43.1% bone marrow mononuclear cells - BMNCs) and alleviated by iron restriction (67.5 vs 74.8% BMNCs; P<0.05). This was associated with increased and reduced inflammatory activation of bone marrow macrophages in FPNC326S MDS and vamifeport-treated MDS mice, respectively. This observation demonstrates a role for NTBI in driving the reported pro-inflammatory activation of MDS monocytes/macrophages (Fuster JJ et al, Science 2017; Jaiswal S et al, NEJM 2017; Cull AH et al, Exp Hematol 2017) and suggests that this iron-driven mechanism contributes to myeloid expansion. Overall, these alterations translated into a faster and delayed transition to AML in iron-overloaded and iron-restricted MDS mice, respectively. Finally, iron overload aggravated and iron restriction alleviated ROS formation, DNA damage and pyroptotic cell death in HSPCs. By reducing the intracellular labile iron pool, vamifeport improved HSPC quality and survival, partially rescuing the stem cell pool size (0.16 vs 0.38% Lin-BMNCs; P<0.05) in MDS mice. The ameliorated HSPC pool, reduced myeloid bias and inflammation, and attenuated ineffective erythropoiesis resulted in improved hematologic parameters for more than 3 months, and a significant survival increment in iron-restricted compared to control MDS mice (>45 days; P=0.037). We further demonstrate that a subgroup of mice can benefit from late iron restriction by vamifeport administration at 5 months of age, resulting in improved anemia and prolonged survival. Conclusion: Our results show for the first time in a preclinical mouse model of MDS that iron excess driven by ineffective erythropoiesis has pathological implication in transfusion-independent MDS. These effects are likely aggravated by transfusions causing additional iron overload. Finally, iron restriction achieved through pharmacologic FPN inhibition by the oral FPN inhibitor vamifeport significantly improves MDS pathophysiology, uncovering the therapeutic potential of early prevention of NTBI formation in MDS.

Regulation of iron homeostasis by hepatocyte TfR1 requires HFE and contributes to hepcidin suppression in β-thalassemia

AbstractTransferrin receptor 1 (TfR1) performs a critical role in cellular iron uptake. Hepatocyte TfR1 is also proposed to influence systemic iron homeostasis by interacting with the hemochromatosis protein HFE to regulate hepcidin production. Here, we generated hepatocyte Tfrc knockout mice (Tfrcfl/fl;Alb-Cre+), either alone or together with Hfe knockout or β-thalassemia, to investigate the extent to which hepatocyte TfR1 function depends on HFE, whether hepatocyte TfR1 impacts hepcidin regulation by serum iron and erythropoietic signals, and its contribution to hepcidin suppression and iron overload in β-thalassemia. Compared with Tfrcfl/fl;Alb-Cre− controls, Tfrcfl/fl;Alb-Cre+ mice displayed reduced serum and liver iron; mildly reduced hematocrit, mean cell hemoglobin, and mean cell volume; increased erythropoietin and erythroferrone; and unchanged hepcidin levels that were inappropriately high relative to serum iron, liver iron, and erythroferrone levels. However, ablation of hepatocyte Tfrc had no impact on iron phenotype in Hfe knockout mice. Tfrcfl/fl;Alb-Cre+ mice also displayed a greater induction of hepcidin by serum iron compared with Tfrcfl/fl;Alb-Cre− controls. Finally, although acute erythropoietin injection similarly reduced hepcidin in Tfrcfl/fl;Alb-Cre+ and Tfrcfl/fl;Alb-Cre− mice, ablation of hepatocyte Tfrc in a mouse model of β-thalassemia intermedia ameliorated hepcidin deficiency and liver iron loading. Together, our data suggest that the major nonredundant function of hepatocyte TfR1 in iron homeostasis is to interact with HFE to regulate hepcidin. This regulatory pathway is modulated by serum iron and contributes to hepcidin suppression and iron overload in murine β-thalassemia.

Functional role of endothelial transferrin receptor 1 in iron sensing and homeostasis.

Systemic iron homeostasis is regulated by the hepatic hormone hepcidin to balance meeting iron requirements while limiting toxicity from iron excess. Iron-mediated induction of bone morphogenetic protein (BMP) 6 is a central mechanism for regulating hepcidin production. Liver endothelial cells (LECs) are the main source of endogenous BMP6, but how they sense iron to modulate BMP6 transcription and thereby hepcidin is uncertain. Here, we investigate the role of endothelial cell transferrin receptor 1 (TFR1) in iron uptake, BMP6 regulation, and systemic iron homeostasis using primary LEC cultures and endothelial Tfrc (encoding TFR1) knockout mice. We show that intracellular iron regulates Bmp6 expression in a cell-autonomous manner, and TFR1 mediates iron uptake and Bmp6 expression by holo-transferrin in primary LEC cultures. In addition, endothelial Tfrc knockout mice exhibit altered iron homeostasis compared with littermate controls when fed a limited iron diet, as evidenced by increased liver iron and inappropriately low Bmp6 and hepcidin expression relative to liver iron. However, endothelial Tfrc knockout mice have a similar iron phenotype compared to littermate controls when fed an iron-rich standard diet. Finally, ferritin and non-transferrin bound iron (NTBI) are additional sources of iron that mediate Bmp6 induction in primary LEC cultures via TFR1-independent mechanisms. Together, our data demonstrate a minor functional role for endothelial cell TFR1 in iron uptake, BMP6 regulation, and hepatocyte hepcidin regulation under iron limiting conditions, and suggest that ferritin and/or NTBI uptake by other transporters have a dominant role when iron availability is high.

A154 COMPARING RESPONSE TO INTRAVENOUS IRON INFUSION IN CROHN’S DISEASE AND ULCERATIVE COLITIS

BackgroundIron deficiency anemia (IDA) is common in persons with inflammatory bowel disease (IBD). Current evidence-based guidelines suggest iron replacement therapy in IBD patients with IDA. Intravenous (IV) iron has been demonstrated to be more effective than oral iron replacement in the IBD population, and this is thought to be related to oral iron being poorly tolerated, absorbed, and possibly having an adverse impact on the gut microbiome. Studies have not directly compared the response of IV iron between persons with ulcerative colitis (UC) and Crohn’s disease (CD).Aims(1) To compare the increase in serum hemoglobin and ferritin following IV iron therapy between persons with UC and CD. (2) To determine factors associated with response to IV iron (other than disease type), including age, sex, IBD therapies, abdominal surgeries, and IBD phenotype.MethodsIn a retrospective chart review, we evaluated 536 IV iron infusions (iron sucrose) prescribed to 117 IBD patients by a single gastroenterologist between 2012–2020, and collected data on IBD type, age, sex, medications (IBD therapies, NSAIDs, ASA, oral iron), abdominal surgeries, and IBD phenotype. Statistical analysis was performed using SPSS version 26.ResultsMost IV iron infusions were given to patients with CD (77% of infusions, 68% of persons). The majority of infusions were given as a series of multiple iron infusions (84%) over a mean of 27 weeks, rather than a single infusion. Persons with UC had a greater increase in serum ferritin than those with CD (mean difference ± SE of 13.2 ± 5.6 µg/L, p = 0.02). There was no significant difference in the increase in serum hemoglobin between UC and CD (UC= 6.5 ± 1.0 g/L; CD 4.9 ± 2.1 g/L; p = 0.62).ConclusionsPersons with UC had a better ferritin response to IV iron therapy than persons with CD. Patients with UC were prescribed less IV iron than those with CD. In summary, persons with CD may require greater dosing of IV iron therapy than patients with UC. Further studies are needed to discern if this difference is secondary to CD being associated with a greater extent of mucosal disease burden, impaired iron absorption, or a greater intolerance to oral iron.Funding AgenciesFellowship Funding from Pfizer Canada

Association of GNPAT p.D519G with Higher Iron Phenotypes in Women with HFE p.C282Y Homozygosity

The severity of iron overload among HFE p.C282Y homozygotes varies due to heritable and acquired factors but remains incompletely explained. Using exome sequencing, we previously demonstrated that the GNPAT p.D519G variant is associated with extreme iron loading among HFE p.C282Y homozygous males who did not report excessive alcohol consumption or other known risk factors for severe iron loading (Hepatology 2015;62:429-439). Demonstrating an effect of GNPAT p.D519G across a wider range of iron phenotypes has yielded mixed results in several study cohorts.The current investigation was undertaken to examine the question whether the association previously observed between iron stores and p.D519G in p.C282Y homozygous men also exists in p.C282Y homozygous women. We used an extreme phenotypes design comprising 11 high- and 57 low-expressing HFE p.C282Y homozygous females. Criteria for high expressers were age >18 and either (a) mobilized body iron >10 g by quantitative phlebotomy or (b) hepatic iron concentration >236 µmol/g dry weight (reference range 0-36 µmol/g). Criteria for low expressers included age >50 y and serum ferritin <200 µg/L or <3.0 g iron removed by phlebotomy to achieve serum ferritin <50 µg/L. Linear regression was applied with GNPAT p.D519G allele count as the independent variable and either of two continuous phenotype measurements as the dependent variable. We tested for associations between GNPAT p.D519G allele count and (a) serum ferritin level at presentation and (b) total iron removed by phlebotomy to achieve iron depletion among women for whom complete genotype and alcohol consumption data were available (N=68). We adjusted for age, alcohol consumption reports, and body mass index at presentation.Serum ferritin at presentation was associated with alternate allele count for rs11558492 (corresponding to GNPAT p.D519G). We observed an increase in serum ferritin of 430 µg/L for each increase in the number of variant alleles in GNPAT p.D519G (p=0.025, 95% CI=[19.9, 840]). Total iron removed was also associated with genotype. We observed an increase of 1.9 g iron removed for each increase in the number of variant alleles in GNPAT p.D519G (p=0.019, 95% CI=[0.34, 3.4]).In women with HFE p.C282Y homozygosity, GNPAT p.D519G is significantly associated with serum ferritin phenotypes at presentation and with iron removed by phlebotomy in an extreme phenotypes model. Some women with GNPAT p.D519G do not have high iron phenotypes at presentation. This suggests that some women with HFE p.C282Y homozygosity and GNPAT p.D519G also have genetic or environmental factors that decrease iron absorption. DisclosuresNo relevant conflicts of interest to declare.

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.

TAM-ing the CIA-Tumor-Associated Macrophages and Their Potential Role in Unintended Side Effects of Therapeutics for Cancer-Induced Anemia.

Cancer-induced anemia (CIA) is a common consequence of neoplasia and has a multifactorial pathophysiology. The immune response and tumor treatment, both intended to primarily target malignant cells, also affect erythropoiesis in the bone marrow. In parallel, immune activation inevitably induces the iron-regulatory hormone hepcidin to direct iron fluxes away from erythroid progenitors and into compartments of the mononuclear phagocyte system. Moreover, many inflammatory mediators inhibit the synthesis of erythropoietin, which is essential for stimulation and differentiation of erythroid progenitor cells to mature cells ready for release into the blood stream. These pathophysiological hallmarks of CIA imply that the bone marrow is not only deprived of iron as nutrient but also of erythropoietin as central growth factor for erythropoiesis. Tumor-associated macrophages (TAM) are present in the tumor microenvironment and display altered immune and iron phenotypes. On the one hand, their functions are altered by adjacent tumor cells so that they promote rather than inhibit the growth of malignant cells. As consequences, TAM may deliver iron to tumor cells and produce reduced amounts of cytotoxic mediators. Furthermore, their ability to stimulate adaptive anti-tumor immune responses is severely compromised. On the other hand, TAM are potential off-targets of therapeutic interventions against CIA. Red blood cell transfusions, intravenous iron preparations, erythropoiesis-stimulating agents and novel treatment options for CIA may interfere with TAM function and thus exhibit secondary effects on the underlying malignancy. In this Hypothesis and Theory, we summarize the pathophysiological hallmarks, clinical implications and treatment strategies for CIA. Focusing on TAM, we speculate on the potential intended and unintended effects that therapeutic options for CIA may have on the innate immune response and, consequently, on the course of the underlying malignancy.

HIF1A: A Putative Modifier of Hemochromatosis.

HFE-related hereditary hemochromatosis (HH) is characterized by marked phenotypic heterogeneity. Homozygosity for p.C282Y is a low penetrance genotype suggesting that the HFE-HH is a multifactorial disease resulting from a complex interaction involving a major gene defect, genetic background and environmental factors. We performed a targeted NGS-based gene panel to identify new candidate modifiers by using an extreme phenotype sampling study based on serum ferritin and iron removed/age ratio. We found an increased prevalence of the HIF1A p.Phe582Ser and p.Ala588Thr variants in patients with a severe iron and clinical phenotype. Accordingly, Huh-7 cells transfected with both variants showed significantly lower HAMP promoter activity by luciferase assay. The qRT-PCR assays showed a downregulation of hepcidin and an upregulation of the HIF1A target genes (VEGF, HMOX, FUR, TMPRSS6) in cells transfected with the HIF1A-P582S vector. We identified mutations in other genes (e.g., Serpina1) that might have some relevance in single cases in aggravating or mitigating disease manifestation. In conclusion, the present study identified HIF1A as a possible modifier of the HFE-HH phenotype cooperating with the genetic defect in downregulating hepcidin synthesis. In addition, this study highlights that an NGS-based approach could broaden our knowledge and help in characterizing the genetic complexity of HFE-HH patients with a severe phenotype expression.

Mitochondrial Dysfunction, Oxidative Stress and Neuroinflammation in Neurodegeneration with Brain Iron Accumulation (NBIA).

The syndromes of neurodegeneration with brain iron accumulation (NBIA) encompass a group of invalidating and progressive rare diseases that share the abnormal accumulation of iron in the basal ganglia. The onset of NBIA disorders ranges from infancy to adulthood. Main clinical signs are related to extrapyramidal features (dystonia, parkinsonism and choreoathetosis), and neuropsychiatric abnormalities. Ten NBIA forms are widely accepted to be caused by mutations in the genes PANK2, PLA2G6, WDR45, C19ORF12, FA2H, ATP13A2, COASY, FTL1, CP, and DCAF17. Nonetheless, many patients remain without a conclusive genetic diagnosis, which shows that there must be additional as yet undiscovered NBIA genes. In line with this, isolated cases of known monogenic disorders, and also, new genetic diseases, which present with abnormal brain iron phenotypes compatible with NBIA, have been described. Several pathways are involved in NBIA syndromes: iron and lipid metabolism, mitochondrial dynamics, and autophagy. However, many neurodegenerative conditions share features such as mitochondrial dysfunction and oxidative stress, given the bioenergetics requirements of neurons. This review aims to describe the existing link between the classical ten NBIA forms by examining their connection with mitochondrial impairment as well as oxidative stress and neuroinflammation.

Increased frequency of GNPAT p.D519G in compound HFE p.C282Y/p.H63D heterozygotes with elevated serum ferritin levels

Glyceronephosphate O-acyltransferase (GNPAT) p.D519G (rs11558492) was identified as a genetic modifier correlated with more severe iron overload in hemochromatosis through whole-exome sequencing of HFE p.C282Y homozygotes with extreme iron phenotypes. We studied the prevalence of p.D519G in HFE p.C282Y/p.H63D compound heterozygotes, a genotype associated with iron overload in some patients. Cases were Australian participants with elevated serum ferritin (SF) levels ≥300μg/L (males) and ≥200μg/L (females); subjects whose SF levels were below these cut-offs were designated as controls. Samples were genotyped for GNPAT p.D519G. We compared the allele frequency of the present subjects, with/without elevated SF, to p.D519G frequency in public datasets. GNPAT p.D519G was more prevalent in our cohort of p.C282Y/p.H63D compound heterozygotes with elevated SF (37%) than European public datasets: 1000G 21%, gnomAD 20% and ESP 21%. We conclude that GNPAT p.D519G is associated with elevated SF in Australian HFE p.C282Y/p.H63D compound heterozygotes.

The Disturbed Iron Phenotype of Tumor Cells and Macrophages in Renal Cell Carcinoma Influences Tumor Growth.

Accumulating evidence suggests that iron homeostasis is disturbed in tumors. We aimed at clarifying the distribution of iron in renal cell carcinoma (RCC). Considering the pivotal role of macrophages for iron homeostasis and their association with poor clinical outcome, we investigated the role of macrophage-secreted iron for tumor progression by applying a novel chelation approach. We applied flow cytometry and multiplex-immunohistochemistry to detect iron-dependent markers and analyzed iron distribution with atomic absorption spectrometry in patients diagnosed with RCC. We further analyzed the functional significance of iron by applying a novel extracellular chelator using RCC cell lines as well as patient-derived primary cells. The expression of iron-regulated genes was significantly elevated in tumors compared to adjacent healthy tissue. Iron retention was detected in tumor cells, whereas tumor-associated macrophages showed an iron-release phenotype accompanied by enhanced expression of ferroportin. We found increased iron amounts in extracellular fluids, which in turn stimulated tumor cell proliferation and migration. In vitro, macrophage-derived iron showed pro-tumor functions, whereas application of an extracellular chelator blocked these effects. Our study provides new insights in iron distribution and iron-handling in RCC. Chelators that specifically scavenge iron in the extracellular space confirmed the importance of macrophage-secreted iron in promoting tumor growth.

Iron in the Tumor Microenvironment.

Cancer metabolism is a well-known target of cancer therapeutics. Classically, cancer metabolism has been studied in terms of the dependence of cancer cells on crucial metabolites, such as glucose and glutamine. But, the accumulating data show that iron metabolism in tumor microenvironment is also an important factor in preserving the survival of cancer cells. Cancer cells have a distinct phenotype of iron metabolism, which secures the much-needed iron for these metabolically active cells. In order to use this iron efficiently, cancer cells need to increase their iron supply and decrease iron loss. As recent research suggests, this is not only done by modifying the expression of iron-related proteins in cancer cells, but also by interaction of cancer cells with other cells from the tumor milieu. Tumor microenvironment is a dynamic environment characterized with intricate relationship between cancer cells, tumor-associated macrophages, fibroblasts, and other cells. Some of the mechanistic aspects of this relationship have been elucidated, while others are yet to be identified. In any case, identifying the details of the iron phenotype of the cells in tumor microenvironment presents with a new therapeutic opportunity to treat this deadly disease.

Increased Allele Frequency of GNPAT p.D519G in Compound HFE p.C282Y/p.H63D Heterozygotes with Elevated Serum Ferritin Levels

In hemochromatosis, iron overload is due to increased intestinal iron absorption attributable to mutations in several genes involved in the regulation of iron absorption and metabolism. The most common type of hemochromatosis is caused by mutations in the HFE gene, and homozygosity for the HFE p.C282Y mutation is associated with a risk of iron overload. Approximately 1:200 people of Caucasian origin are homozygous for p.C282Y, but only a minority of p.C282Y homozygotes develop significant iron overload. This is attributed in part to the presence of putative genetic modifiers of iron absorption. Recently, we identified GNPAT, encoding glyceronephosphate O-acyltransferase, as a potential modifier of HFE hemochromatosis in a whole-exome sequencing study of p.C282Y homozygotes with extreme iron overload phenotypes. A GNPAT polymorphism (p.D519G, rs11558492) was associated with severe iron overload among p.C282Y homozygous men (Hepatology 2015;62:429-39). Other studies have either substantiated or contradicted the importance of GNPAT p.D519G as a genetic modifier of iron phenotypes in HFE p.C282Y homozygotes. p.D519G is also a risk factor for familial (but not sporadic) porphyria cutanea tarda (Plos One 2016;11:e0163322). Some patients with hemochromatosis phenotypes are heterozygous for p.C282Y and a different HFE polymorphism, p.H63D (which is also common but usually not itself associated with clinically significant iron overload). Many p.C282Y/p.H63D compound heterozygotes have milder iron overload phenotypes than p.C282Y homozygotes. Herein, we report studies of the prevalence of p.D519G in a cohort of compound heterozygous p.C282Y/p.H63D Australian patients, with or without elevated serum ferritin (SF) levels. We also compared p.D519G allele frequency of the present p.C282Y/p.H63D compound heterozygotes with those of large population cohorts. We identified 72 HFE p.C282Y/p.H63D compound heterozygotes with DNA available for analysis. Of these, 9 had missing SF data and were excluded. GNPAT p.D519G was assessed in the remaining 63 subjects. Compound heterozygotes with elevated SF levels ≥300 µg/mL (males) and ≥200 µg/mL (females) were selected as cases (n=28), and participants with SF levels below these cut-offs were classified as controls (n=35). The mean age at the time of testing was 31 y (males 31, females 31) in the control group and 48 y (males 47, females 51) in subjects with elevated SF levels. Among cases, mean SF was 612 µg/L (median 557 µg/L, IQR 361- 821 µg/L). Mean SF in the control group was 85 µg/L (median 58 µg/L, IQR 38 - 121 µg/L). All samples were genotyped for GNPAT p.D519G. We compared the p.D519G allele frequency of the present subjects, with and without elevated SF, to the p.D519G frequency in publically available datasets. p.D519G allele frequency was greater in the elevated SF group (37.5%) than the control group (24.3%), but this difference was not significant (p=0.1285). p.D519G was more prevalent in our cohort of p.C282Y/p.H63D compound heterozygotes with elevated SF (37.5%) than in European populations reported in public datasets: ExAC 19.7%, 1000G 21.3%, gnomAD 20.4%, and ESP 20.6%. There was a significant association between allele count and case/control status among men (type 3 analysis of effects; p = 0.049) but not women. For a male case, the odds of having either 1 or 2 alleles versus having 0 alleles was 5.08 (95% CI, 1.01, 25.66) times higher than that of a male control. In conclusion, our results demonstrate that GNPAT p.D519G is associated with elevated SF levels in Australian HFE p.C282Y/p.H63D compound heterozygotes and that the p.D519G allele frequency is greater in p.C282Y/p.H63D compound heterozygotes with elevated SF than in several large European population cohorts. We found a statistically significant association between the allele count and the case/control status among men. The small number of subjects with elevated SF in our study may have limited our ability to demonstrate significant differences in some comparisons. Some subjects with p.D519G do not have elevated SF, suggesting that there are other factors, genetic or environmental, which also affect iron absorption in p.C282Y/p.H63D compound heterozygotes. Disclosures No relevant conflicts of interest to declare.

Hepcidin and Anemia: A Tight Relationship

Hepcidin, the master regulator of systemic iron homeostasis, tightly influences erythrocyte production. High hepcidin levels block intestinal iron absorption and macrophage iron recycling, causing iron restricted erythropoiesis and anemia. Low hepcidin levels favor bone marrow iron supply for hemoglobin synthesis and red blood cells production. Expanded erythropoiesis, as after hemorrhage or erythropoietin treatment, blocks hepcidin through an acute reduction of transferrin saturation and the release of the erythroblast hormone and hepcidin inhibitor erythroferrone. Quantitatively reduced erythropoiesis, limiting iron consumption, increases transferrin saturation and stimulates hepcidin transcription. Deregulation of hepcidin synthesis is associated with anemia in three conditions: iron refractory iron deficiency anemia (IRIDA), the common anemia of acute and chronic inflammatory disorders, and the extremely rare hepcidin-producing adenomas that may develop in the liver of children with an inborn error of glucose metabolism. Inappropriately high levels of hepcidin cause iron-restricted or even iron-deficient erythropoiesis in all these conditions. Patients with IRIDA or anemia of inflammation do not respond to oral iron supplementation and show a delayed or partial response to intravenous iron. In hepcidin-producing adenomas, anemia is reverted by surgery. Other hepcidin-related anemias are the “iron loading anemias” characterized by ineffective erythropoiesis and hepcidin suppression. This group of anemias includes thalassemia syndromes, congenital dyserythropoietic anemias, congenital sideroblastic anemias, and some forms of hemolytic anemias as pyruvate kinase deficiency. The paradigm is non-transfusion-dependent thalassemia where the release of erythroferrone from the expanded pool of immature erythroid cells results in hepcidin suppression and secondary iron overload that in turn worsens ineffective erythropoiesis and anemia. In thalassemia murine models, approaches that induce iron restriction ameliorate both anemia and the iron phenotype. Manipulations of hepcidin might benefit all the above-described anemias. Compounds that antagonize hepcidin or its effect may be useful in inflammation and IRIDA, while hepcidin agonists may improve ineffective erythropoiesis. Correcting ineffective erythropoiesis in animal models ameliorates not only anemia but also iron homeostasis by reducing hepcidin inhibition. Some targeted approaches are now in clinical trials: hopefully they will result in novel treatments for a variety of anemias.

Ablation of Hepatocyte Smad1, Smad5, and Smad8 Causes Severe Tissue Iron Loading and Liver Fibrosis in Mice.

A failure of iron to appropriately regulate liver hepcidin production is central to the pathogenesis of hereditary hemochromatosis. SMAD1/5 transcription factors, activated by bone morphogenetic protein (BMP) signaling, are major regulators of hepcidin production in response to iron; however, the role of SMAD8 and the contribution of SMADs to hepcidin production by other systemic cues remain uncertain. Here, we generated hepatocyte Smad8 single (Smad8fl/fl ;Alb-Cre+ ), Smad1/5/8 triple (Smad158;Alb-Cre+ ), and littermate Smad1/5 double (Smad15;Alb-Cre+ ) knockout mice to investigate the role of SMAD8 in hepcidin and iron homeostasis regulation and liver injury. We found that Smad8;Alb-Cre+ mice exhibited no iron phenotype, whereas Smad158;Alb-Cre+ mice had greater iron overload than Smad15;Alb-Cre+ mice. In contrast to the sexual dimorphism reported for wild-type mice and other hemochromatosis models, hepcidin deficiency and extrahepatic iron loading were similarly severe in Smad15;Alb-Cre+ and Smad158;Alb-Cre+ female compared with male mice. Moreover, epidermal growth factor (EGF) failed to suppress hepcidin in Smad15;Alb-Cre+ hepatocytes. Conversely, hepcidin was still increased by lipopolysaccharide in Smad158;Alb-Cre+ mice, although lower basal hepcidin resulted in lower maximal hepcidin. Finally, unlike most mouse hemochromatosis models, Smad158;Alb-Cre+ developed liver injury and fibrosis at 8weeks. Liver injury and fibrosis were prevented in Smad158;Alb-Cre+ mice by a low-iron diet and were minimal in iron-loaded Cre- mice. Conclusion: Hepatocyte Smad1/5/8 knockout mice are a model of hemochromatosis that encompasses liver injury and fibrosis seen in human disease. These mice reveal the redundant but critical role of SMAD8 in hepcidin and iron homeostasis regulation, establish a requirement for SMAD1/5/8 in hepcidin regulation by testosterone and EGF but not inflammation, and suggest a pathogenic role for both iron loading and SMAD1/5/8 deficiency in liver injury and fibrosis.

Transfusion-Induced Impairment of Macrophage Responses Is Partially Restored By the Iron Chelator Deferasirox

Iron overload is common in MDS, as a consequence of chronic red blood cell (RBC) transfusions and to a lesser extent, increased intestinal iron absorption to support erythropoiesis. Clinical evidence suggests that patients with transfusional iron overload show an enhanced susceptibility to infections, which represent one of the most common causes of morbidity and mortality in low risk MDS patients. Iron overload may increase the risk of infections by supporting bacterial growth and altering the immune response.We asked whether transfusions impair macrophage effector functions. Therefore we investigated the impact of transfusions on the phenotypic plasticity of monocytes and macrophages and their functional responses to infectious cues. We applied a mouse model of repeated transfusions of allogeneic RBCs in wild-type and NUP98-HOXD13 MDS mice. Monocytes as well as hepatic and splenic macrophages were analyzed in transfused and non-transfused mice, subjected or not to LPS challenge.Under steady-state condition, MDS mice displayed a mild but significant iron phenotype, hallmarked by elevated systemic and hepatic iron levels, due to inappropriately low hepcidin levels. Repeated transfusions increased serum iron levels and transferrin saturation and promoted iron deposition and oxidative damage in tissues.Transfusions caused macrophage iron loading, monocyte recruitment to the liver and spleen and massive splenic macrophage cell death. Macrophages from transfused mice developed an M2-like anti-inflammatory phenotype, hallmarked by elevated expression of M2 markers (CD206, Arg-1, Ym1) and reduced expression of M1 markers (MHCII, CD86). Accordingly, circulating pro-inflammatory cytokines (IL-6, TNFα, INFγ, IL-1β) were reduced, and anti-inflammatory cytokines (IL-10) increased. Consistently, after LPS challenge macrophages show a markedly reduced expression of M1 markers and inflammatory cytokines, and increased expression of M2 markers in transfused compared to non-transfused mice. Similar results were obtained both in wild-type and MDS mice. All together these observations indicate that transfusion-induced erythrophagocytosis dampens the inflammatory response to infectious cues.In an attempt to relieve macrophages from iron overload, transfused mice have been administered the iron chelator deferasirox during the transfusion period, up to 1 week after the last transfusion. Deferasirox significantly reduced iron levels in liver and spleen. Interestingly, chelation therapy partially restored the phenotype of macrophages by rescuing the expression of M1 markers, including MHCII and CD86, and M2 markers, such as CD206. Similar results have been obtained in the setting of transfusion with and without LPS stimulation.Our results show that transfusions lead to iron-overload mediated toxicity in macrophages blunting their inflammatory response to infectious stimuli by affecting cell plasticity. Our data support a role for transfusions in triggering a phenotypic switching of macrophages towards an anti-inflammatory phenotype, with reduced ability to counteract infections. By restoring cell polarization, iron chelation likely improves the functional response of macrophages to invading microorganisms. Combined with marked cytopenias, the weak pro-inflammatory activation of macrophages might explain the increased propensity of transfused MDS patients to develop infections. Transfusion practice might therefore increase the risk of infections not solely through increased iron availability to microorganisms, but also through the impairment of macrophage functions. Our results suggest that transfused MDS patients might benefit from chelation therapy by both restricting iron from pathogens and improving the innate immune response. DisclosuresVinchi:Novartis: Research Funding. Platzbecker:Celgene: Research Funding. Muckenthaler:Novartis: Research Funding.

Novel Insights Into Systemic Iron Regulation

Iron, an essential element in mammals, is absorbed by duodenal enterocytes, enters the circulation through the iron exporter ferroportin, (FPN), circulates bound to transferrin and is uptaken through Transferrin Receptor 1. If in excess, iron is stored in macrophages and hepatocytes and released when needed. To maintain systemic iron homeostasis and to avoid the formation of “non transferrin bound iron” (NTBI), a highly reactive form which causes organ damage, the liver synthetizes hepcidin that, binding FPN, blocks iron export to the circulation. Hepcidin integrates signals from body iron, erythropoiesis and inflammatory cytokines. Defective hepcidin production causes iron overload and organ failure in Hereditary Hemochromatosis and Thalassemia; hepcidin excess leads to anemia in Iron Refractory iron Deficiency Anemia (IRIDA) and Anemia of Inflammation (AI).In hepatocytes hepcidin is under the control of the BMP-SMAD pathway, which is activated in a paracrine manner by BMP2 and BMP6 produced by liver sinusoidal endothelial cells. BMP2 maintains hepcidin basal levels, while BMP6 controls its expression in response to iron. The two ligands have different affinity for BMP type I receptors ALK2 and ALK3, suggesting two distinct branches of the hepcidin activation pathway. This possibility is consistent with the non-redundant function of BMP2 and BMP6, the different iron phenotype of hepatocyte-conditional ALK2 and ALK3 KO mice and the residual ability of BMP6 to activate hepcidin in hemochromatosis mice. Moreover ALK2, but not ALK3, is inhibited by the immunophilin FKBP12 in the absence of ligands. The BMP pathway activation depends upon the coreceptor hemojuvelin (HJV), the MHC class I protein HFE and the second transferrin receptor (TFR2). Mutations of all these proteins lead to decreased hepcidin expression in hemochromatosis.Hepcidin expression is inhibited in iron deficiency, hypoxia and when erythropoiesis is increased. Inhibitors are the liver transmembrane serine protease TMPRSS6, whose genetic inactivation causes IRIDA, and the erythroid hormone erythroferrone (ERFE), which is released by erythropoietin-stimulated erythroblasts. The mechanism of hepcidin inhibition by ERFE is unclear; still to allow ERFE function the BMP-SMAD pathway has not to be hyperactive. Intriguingly, both iron deficiency and erythropoiesis require epigenetic modifications at the hepcidin locus with HDAC3-dependent reversible loss of H3K9ac and H3K4me3.Hepcidin also acts as an antimicrobial peptide since its expression, increased by proinflammatory cytokines, such as IL6 through JAK2-STAT3 signaling, restricts iron availability for microbial growth. This first-line of defense against infections negatively influences erythropoiesis since chronic hepcidin activation causes AI. Despite persistent JAK2-STAT3 activation, inhibition of the BMP-SMAD pathway reduces hepcidin activation in AI experimental rodent models, suggesting that hepcidin activation in inflammation requires a functional BMP-SMAD pathway. Independently from hepcidin, inflammation also reduces FPN mRNA levels, favoring macrophage iron sequestration.The identification of hepcidin-ferroportin axis molecular players has translational implications. In primary and secondary iron overload hepcidin agonists (hepcidin peptides or mimics, agents that inhibit the hepcidin inhibitor TMPRSS6 and likely the ALK2-inhibitor FKBP12) and ferroportin inhibitors are potentially useful to prevent iron overload and/or to favor iron redistribution to macrophages. In case of AI, hepcidin antagonists (including anti-hepcidin, anti-HJV and anti-BMP6 monoclonal antibodies, L-enantiomeric oligonucleotides targeting hepcidin, siRNA against hepcidin, non-anticoagulant heparins, the ALK2 inhibitor momelotinib) might improve erythropoiesis increasing iron availability.The effect of some agents that have now entered the clinical phase will become apparent in the coming years. DisclosuresCamaschella:vifor Pharma: Honoraria, Membership on an entity's Board of Directors or advisory committees.

A potential role for hepcidin in obesity-driven colorectal tumourigenesis.

The obesity epidemic is associated with increases in the incidence of several types of cancer, including colorectal cancer, and is associated with poor outcomes for patients. Adipose tissue is considered biologically active and represents a plausible link between cancer and obesity due to the many factors that it secretes. In the present study, human adipose tissue was cultured invitro and predifferentiated adipocyte secretome[preadipocyte (PAS)] and differentiated adipocyte secretome(DAS) were collected. Quantification of interleukin-6(IL-6), leptin and hepcidin in the DAS medium was compared to the PAS medium. Fold change levels of hepcidin, leptin and IL-6 in DAS (2.88±0.28, 12.34±0.95 and 31.29±1.89 fold increases) were significantly higher compared to these in PAS (p=0.05). The SW480 colorectal cancer cells were co-cultured with DAS in the presence or absence of leptin, IL-6 or hepcidin inhibitors and cellular viability and proliferation assays were performed. The culture of SW480 with DAS increased the cell proliferation and viability by 30and15% (p=0.02 and p=0.03) respectively, which was reversed in the presence of inhibitors. Challenging the SW480 cells with IL-6 or hepcidin significantly elevated colonocyte‑secreted leptin(p=0.05). Challenging the SW480 cells with leptin or hepcidin resulted in elevated levels of colonocyte-secreted IL-6(p=0.05). Similarly, challenging cells with either IL-6 or leptin markedly elevated the level of secreted hepcidin(p=0.05) and this was associated with an induction in colonocyte iron levels in both cases. Collectively, these data revealed that adipocyte-secreted factors can ultimately modulate colonocyte iron levels and phenotype.