Genetic mechanisms and modifying factors in hereditary hemochromatosis

Variance quantitative trait loci reveal gene-gene interactions which alter blood traits

Gene-gene (GxG) interactions play an important role in human genetics, potentially explaining part of the "missing heritability" of polygenic traits and the variable expressivity of monogenic traits. Many GxG interactions have been identified in model organisms through experimental breeding studies, but they have been difficult to identify in human populations. To address this challenge, we applied two complementary variance QTL (vQTL)-based approaches to identify GxG interactions that contribute to human blood traits and blood-related disease risk. First, we used the previously validated genome-wide scale test for each trait in ~450,000 people in the UK Biobank and identified 4 vQTLs. Genome-wide GxG interaction testing of these vQTLs enabled discovery of novel interactions between (1) CCL24 and CCL26 for eosinophil count and plasma CCL24 and CCL26 protein levels and (2) HLA-DQA1 and HLA-DQB1 for lymphocyte count and risk of celiac disease, both of which replicated in ~140,000 NIH All of Us and ~70,000 Vanderbilt BioVU participants. Second, we used a biologically informed approach to search for vQTL in disease-relevant genes. This approach identified (1) a known interaction for hemoglobin between two pathogenic variants in HFE which cause hereditary hemochromatosis and alters risk of cirrhosis and (2) a novel interaction between the JAK2 46/1 haplotype and a variant on chromosome 14 which modifies platelet count, JAK2 V617F clonal hematopoiesis, and risk of polycythemia vera. This work identifies novel disease-relevant GxG interactions and demonstrates the utility of vQTL-based approaches in identifying GxG interactions relevant to human health at scale.

The Interactions between Maternal Iron Supplementation and Iron Metabolism-Related Genetic Polymorphisms on Birth Outcomes: A Prospective Study in Chinese

BACKGROUND

The effect of iron supplementation during pregnancy on birth outcomes may vary with maternal genetic background and needs more investigation.

OBJECTIVES

This prospective study aimed to evaluate the interactions between maternal iron supplementation and iron metabolism-related genetic polymorphisms on birth outcomes.

METHODS

This was a substudy from a community-based randomized control trial conducted in Northwest China, which included 860 women from the 2 micronutrient supplementation groups (folic acid [FA] and FA + iron group). Maternal peripheral blood, sociodemographic and health-related information, and neonatal birth outcomes were collected. Six single nucleotide polymorphisms in iron metabolism-related genes were genotyped. The alleles associated with decreased iron/hemoglobin status were used as the effect alleles. The genetic risk score (GRS) that reflected the genetic risk of low iron/hemoglobin status was estimated using the unweighted and weighted methods. Generalized estimating equations with small-sample corrections were applied to evaluate the interactions between iron supplementation and SNPs/GRS on birth outcomes.

RESULTS

There were significant interactions between maternal iron supplementation and rs7385804 (P = 0.009), rs149411 (P = 0.035), rs4820268 (P = 0.031), the unweighted GRS (P = 0.018), and the weighted GRS (P = 0.009) on birth weight. Compared with FA supplementation only, FA + iron supplementation significantly increased birth weight among women with more effect alleles in rs7385804 (β: 88.8 g, 95% CI: 9.2, 168.3) and the GRSs (the highest unweighted GRS, β: 135.5 g, 95% CI: 7.7, 263.4; the highest weighted GRS, β: 145.9 g, 95% CI: 43.4, 248.5); it had a trend of decreasing birth weight and increasing low birth weight risk among women with fewer effect alleles.

CONCLUSIONS

In our population, maternal genetic background related to iron metabolism plays a significant role in determining the efficacy of iron supplementation. Routine iron supplementation could be more beneficial to fetal weight growth among mothers with higher genetic risk for low iron/hemoglobin status.

1.5-T MR relaxometry in quantifying splenic and pancreatic iron: retrospective comparison of a commercial 3D-Dixon sequence and an established 2D multi-gradient echo sequence

OBJECTIVES

To compare the quantitative measurement of splenic and pancreatic iron content using a commercial 3D-Dixon sequence (qDixon) versus an established fat-saturated R2* relaxometry method (ME-GRE).

METHODS

We analyzed splenic and pancreatic iron levels in 143 MR examinations (1.5 T) using the qDixon and a ME-GRE sequence (108 patients: 65 males, 43 females, mean age 61.31 years). Splenic and pancreatic R2* values were compared between both methods using Bland-Altman plots, concordance correlation coefficients (CCC), and linear regression analyses. Iron overload (R2* > 50 1/s) was defined for both organs and compared using contingency tables, overall agreement, and Gwet's AC1 coefficient.

RESULTS

Of all analyzable examinations, the median splenic R2* using the qDixon sequence was 25.75 1/s (range: 5.6-433) and for the ME-GRE sequence 35.35 1/s (range: 10.9-400.8) respectively. Concerning the pancreas, a median R2* of 29.93 1/s (range: 14-111.45) for the qDixon and 31.25 1/s (range: 14-97) for the ME-GRE sequence was found. Bland-Altman analysis showed a mean R2* difference of 2.12 1/s with a CCC of 0.934 for the spleen and of 0.29 1/s with a CCC of 0.714 for the pancreas. Linear regression for the spleen/pancreas resulted in a correlation coefficient of 0.94 (p < 0.001)/0.725 (p < 0.001). Concerning iron overload, the proportion of overall agreement between the two methods was 91.43% for the spleen and 93.18% for the pancreas.

CONCLUSIONS

Our data show good concordance between R2* values obtained with a commercial qDixon sequence and a validated ME-GRE relaxometry method. The 3D-qDixon sequence, originally intended for liver assessment, seems to be a reliable tool for non-invasive evaluation of iron content also in the spleen and the pancreas.

KEY POINTS

• A 3D chemical shift imaging sequence and 2D multi-gradient echo sequence show good conformity quantifying splenic and pancreatic R2* values. • The 3D chemical shift imaging sequence allows a reliable analysis also of splenic and pancreatic iron status. • In addition to the liver, the analysis of the spleen and pancreas is often helpful for further differential diagnostic clarification and patient guidance regarding the iron status.

Left Ventricular Function and Iron Loading Status in a Tertiary Center Hemochromatosis Cohort-A Cardiac Magnetic Resonance Study

Background: Haemochromatosis (HCH), a common genetic disorder with variable penetrance, results in progressive but understudied iron overload. We prospectively evaluated organ iron loading and cardiac function in a tertiary center HCH cohort. Methods: 42 HCH patients (47 ± 14 years) and 36 controls underwent laboratory workup and cardiac magnetic resonance (CMR), including T1 and T2* mapping. Results: Myocardial T2* (myoT2*), myocardial T1 (myoT1) and liver T2* (livT2*) were lower in patients compared to controls (33 ± 4 ms vs. 36 ± 3 ms [p = 0.004], 964 ± 33 ms vs. 979 ± 25 ms [p = 0.028] and 21 ± 10 ms vs. 30 ± 5 ms [p < 0.001], respectively). MyoT2* did not reach the threshold of clinically significant iron overload (<20 ms), in any of the patients. In 22 (52.4%) patients, at least one of the tissue parameters was reduced. Reduced myocardial T2* and/or T1 were found in 10 (23.8%) patients, including 4 pts with normal livT2*. LivT2* was reduced in 18 (42.9%) patients. MyoT1 and livT2* inversely correlated with ferritin (rs = −0.351 [p = 0.028] and rs = −0.602 [p < 0.001], respectively). LivT2* by a dedicated sequence and livT2* by cardiac T2* mapping showed good agreement (ICC = 0.876 p < 0.001). Conclusions: In contemporary hemochromatosis, significant myocardial iron overload is rare. Low myocardial T2* and/or T1 values may warrant closer follow-up for accelerated myocardial iron overload even in patients without overt liver overload. Cardiac T2* mapping sequence allows for liver screening at the time of CMR.

Signaling Integration of Hydrogen Sulfide and Iron on Cellular Functions

Significance: Hydrogen sulfide (H₂S) is an endogenous signaling molecule, regulating numerous physiological functions from vasorelaxation to neuromodulation. Iron is a well-known bioactive metal ion, being the central component of hemoglobin for oxygen transportation and participating in biomolecule degradation, redox balance, and enzymatic actions. The interplay between H₂S and iron metabolisms and functions impacts significantly on the fate and wellness of different types of cells. Recent Advances: Iron level in vivo affects the production of H₂S via nonenzymatic reactions. On the contrary, H₂S quenches excessive iron inside the cells and regulates the redox status of iron. Critical Issues: Abnormal metabolisms of both iron and H₂S are associated with various conditions and diseases such as iron overload, anemia, oxidative stress, and cardiovascular and neurodegenerative diseases. The molecular mechanisms for the interactions between H₂S and iron are unsettled yet. Here we review signaling links of the production, metabolism, and their respective and integrative functions of H₂S and iron in normalcy and diseases. Future Directions: Physiological and pathophysiological importance of H₂S and iron as well as their therapeutic applications should be evaluated jointly, not separately. Future investigation should expand from iron-rich cells and tissues to the others, in which H₂S and iron interaction has not received due attention. Antioxid. Redox Signal. 36, 275-293.

Genetic effects of iron levels on liver injury and risk of liver diseases: A two-sample Mendelian randomization analysis

Background and aims

Although iron homeostasis has been associated with liver function in many observational studies, the causality in this relationship remains unclear. By using Mendelian Randomization analyses, we aimed to evaluate the genetic effects of increased systemic iron levels on the risk of liver injury and various liver diseases. Moreover, in light of the sex-dependent iron regulation in human beings, we further estimated the sex-specific effect of iron levels in liver diseases.

Methods

Independent single nucleotide polymorphisms associated with systemic iron status (including four indicators) at the genome-wide significance level from the Genetics of Iron Status (GIS) Consortium were selected as instrumental variables. Summary data for six liver function biomarkers and five liver diseases were obtained from the UK Biobank, the Estonian Biobank, the eMERGE network, and FinnGen consortium. Mendelian Randomization assessment of the effect of iron on liver function and liver diseases was conducted.

Results

Genetically predicted iron levels were positively and significantly associated with an increased risk of different dimensions of liver injury. Furthermore, increased iron status posed hazardous effects on non-alcoholic fatty liver disease, alcoholic liver disease, and liver fibrosis/cirrhosis. Sex-stratified analyses indicated that the hepatoxic role of iron might exist in NAFLD and liver fibrosis/cirrhosis development among men. No significantly causal relationship was found between iron status and viral hepatitis.

Conclusion

Our study adds to current knowledge on the genetic role of iron in the risk of liver injury and related liver diseases, which provides clinical and public health implications for liver disease prevention as iron status can be modified.

Cell-specific expression of Hfe determines the outcome of Salmonella enterica serovar Typhimurium infection in mice

Mutations in HFE cause hereditary hemochromatosis type I hallmarked by increased iron absorption, iron accumulation in hepatocytes and iron deficiency in myeloid cells. HFE encodes an MHC-I like molecule, but its function in immune responses to infection remains incompletely understood. Here, we investigated putative roles of Hfe in myeloid cells and hepatocytes, separately, upon infection with Salmonella Typhimurium, an intracellular bacterium with iron-dependent virulence. We found that constitutive and macrophage-specific deletion of Hfe protected infected mice. The propagation of Salmonella in macrophages was reduced due to limited intramacrophage iron availability for bacterial growth and increased expression of the anti-microbial enzyme nitric oxide synthase-2. By contrast, mice with hepatocyte-specific deletion of Hfe succumbed earlier to Salmonella infection because of unrestricted extracellular bacterial replication associated with high iron availability in the serum and impaired expression of essential host defense molecules such as interleukin-6, interferon-γ and nitric oxide synthase-2. Wild-type mice subjected to dietary iron overload phenocopied hepatocyte-specific Hfe deficiency suggesting that increased iron availability in the serum is deleterious in Salmonella infection and underlies impaired host immune responses. Moreover, the macrophage-specific effect is dominant over hepatocyte-specific Hfe-depletion, as Hfe knock-out mice have increased survival despite the higher parenchymal iron load associated with systemic loss of Hfe. We conclude that cell-specific expression of Hfe in hepatocytes and macrophages differentially affects the course of infections with specific pathogens by determining bacterial iron access and the efficacy of anti-microbial immune effector pathways. This may explain the high frequency and evolutionary conservation of human HFE mutations.

Dietary Iron Overload and Hfe-/- Related Hemochromatosis Alter Hepatic Mitochondrial Function

Iron is an essential co-factor for many cellular metabolic processes, and mitochondria are main sites of utilization. Iron accumulation promotes production of reactive oxygen species (ROS) via the catalytic activity of iron species. Herein, we investigated the consequences of dietary and genetic iron overload on mitochondrial function. C57BL/6N wildtype and Hfe^-/- mice, the latter a genetic hemochromatosis model, received either normal diet (ND) or high iron diet (HI) for two weeks. Liver mitochondrial respiration was measured using high-resolution respirometry along with analysis of expression of specific proteins and ROS production. HI promoted tissue iron accumulation and slightly affected mitochondrial function in wildtype mice. Hepatic mitochondrial function was impaired in Hfe^-/- mice on ND and HI. Compared to wildtype mice, Hfe^-/- mice on ND showed increased mitochondrial respiratory capacity. Hfe^-/- mice on HI showed very high liver iron levels, decreased mitochondrial respiratory capacity and increased ROS production associated with reduced mitochondrial aconitase activity. Although Hfe^-/- resulted in increased mitochondrial iron loading, the concentration of metabolically reactive cytoplasmic iron and mitochondrial density remained unchanged. Our data show multiple effects of dietary and genetic iron loading on mitochondrial function and linked metabolic pathways, providing an explanation for fatigue in iron-overloaded hemochromatosis patients, and suggests iron reduction therapy for improvement of mitochondrial function.

Current Understanding of the Relationship between Blood Donor Variability and Blood Component Quality

While differences among donors has long challenged meeting quality standards for the production of blood components for transfusion, only recently has the molecular basis for many of these differences become understood. This review article will examine our current understanding of the molecular differences that impact the quality of red blood cells (RBC), platelets, and plasma components. Factors affecting RBC quality include cytoskeletal elements and membrane proteins associated with the oxidative response as well as known enzyme polymorphisms and hemoglobin variants. Donor age and health status may also be important. Platelet quality is impacted by variables that are less well understood, but that include platelet storage sensitive metabolic parameters, responsiveness to agonists accumulating in storage containers and factors affecting the maintenance of pH. An increased understanding of these variables can be used to improve the quality of blood components for transfusion by using donor management algorithms based on a donors individual molecular and genetic profile.

Revisiting hemochromatosis: genetic vs. phenotypic manifestations

Iron overload disorders represent an important class of human diseases. Of the primary iron overload conditions, by far the most common and best studied is HFE-related hemochromatosis, which results from homozygosity for a mutation leading to the C282Y substitution in the HFE protein. This disease is characterized by reduced expression of the iron-regulatory hormone hepcidin, leading to increased dietary iron absorption and iron deposition in multiple tissues including the liver, pancreas, joints, heart and pituitary. The phenotype of HFE-related hemochromatosis is quite variable, with some individuals showing little or no evidence of increased body iron, yet others showing severe iron loading, tissue damage and clinical sequelae. The majority of genetically predisposed individuals show at least some evidence of iron loading (increased transferrin saturation and serum ferritin), but a minority show clinical symptoms and severe consequences are rare. Thus, the disorder has a high biochemical penetrance, but a low clinical prevalence. Nevertheless, it is such a common condition in Caucasian populations (1:100–200) that it remains an important clinical entity. The phenotypic variability can largely be explained by a range of environmental, genetic and physiological factors. Men are far more likely to manifest significant disease than women, with the latter losing iron through menstrual blood loss and childbirth. Other forms of blood loss, immune system influences, the amount of bioavailable iron in the diet and lifestyle factors such as high alcohol intake can also contribute to iron loading and disease expression. Polymorphisms in a range of genes have been linked to variations in body iron levels, both in the general population and in hemochromatosis. Some of the genes identified play well known roles in iron homeostasis, yet others are novel. Other factors, including both co-morbidities and genetic polymorphisms, do not affect iron levels per se, but determine the propensity for tissue pathology.

The haemochromatosis gene Hfe and Kupffer cells control LDL cholesterol homeostasis and impact on atherosclerosis development

AIMS

Imbalances of iron metabolism have been linked to the development of atherosclerosis. However, subjects with hereditary haemochromatosis have a lower prevalence of cardiovascular disease. The aim of our study was to understand the underlying mechanisms by combining data from genome-wide association study analyses in humans, CRISPR/Cas9 genome editing, and loss-of-function studies in mice.

METHODS AND RESULTS

Our analysis of the Global Lipids Genetics Consortium (GLGC) dataset revealed that single nucleotide polymorphisms (SNPs) in the haemochromatosis gene HFE associate with reduced low-density lipoprotein cholesterol (LDL-C) in human plasma. The LDL-C lowering effect could be phenocopied in dyslipidaemic ApoE-/- mice lacking Hfe, which translated into reduced atherosclerosis burden. Mechanistically, we identified HFE as a negative regulator of LDL receptor expression in hepatocytes. Moreover, we uncovered liver-resident Kupffer cells (KCs) as central players in cholesterol homeostasis as they were found to acquire and transfer LDL-derived cholesterol to hepatocytes in an Abca1-dependent fashion, which is controlled by iron availability.

CONCLUSION

Our results disentangle novel regulatory interactions between iron metabolism, KC biology and cholesterol homeostasis which are promising targets for treating dyslipidaemia but also provide a mechanistic explanation for reduced cardiovascular morbidity in subjects with haemochromatosis.

The effect of hepcidin on components of metabolic syndrome in chronic kidney disease: a cross-sectional study

BACKGROUND

Hepcidin is an important regulator of iron homeostasis.

OBJECTIVES

This cross-sectional study was conducted to evaluate the association between hepcidin and components of metabolic syndrome in patients with chronic kidney disease (CKD).

DESIGN AND SETTING

103 CKD patients and 59 healthy volunteers were included in the study from the University Hospital.

METHODS

Serum hepcidin levels were measured by enyzme-linked immunosorbent assay (ELISA) test. As for the study parameters, age, sex, body mass index, renal diseases, serum biochemistry, complete blood count, iron and total iron-binding capacity, ferritin, high-sensitive C-reactive protein (hsCRP), C- reactive protein (CRP), and erythrocyte sedimentation rate (ESR) were evaluated.

RESULTS

The mean age of the patients was 58.63 ± 11.8 years. Hepcidin level was significantly associated with hypertension and higher uric acid levels (P < 0.05). There was a positive correlation between hepcidin and urea, uric acid, creatinine, ferritin, CRP, ESR, phosphorus, triglyceride, low-density lipoprotein (LDL), proteinuria and albuminuria in 24-hour urine collection. A negative correlation was found between hepcidin and estimated glomerular filtration rate (eGFR), hemoglobin, hematocrit, calcium, 25 OH vitamin D, pH, and bicarbonate levels.

CONCLUSION

Hepcidin, a well-known hormone regulator of iron metabolism, may play an important role in the pathogenesis of metabolic syndrome in patients with CKD, and further studies might delineate in-depth its potential as a promising early marker in these patients.

The Proteomics Study of Compounded HFE/TF/TfR2/HJV Genetic Variations in a Thai Family with Iron Overload, Chronic Anemia, and Motor Neuron Disorder

The mutation of the homeostatic iron regulatory genes (HFE) impaired the hepatic hepcidin transcription leading to the chronic excess of the iron pool, with the adverse consequences of free radical oxidative damages. We herein reported the findings of Thai family members who had the compound of uncommon HFE rs2794719, together with transferrin (TF) rs1867504, transferrin receptor 2 (TfR2) rs7385804, and hemojuvelin (HJV) rs16827043 genetic variants involved in the hepcidin transcriptional pathway. These compounded genetic variants could produce the spectrum of clinical phenotypes that spanned from mild to moderate symptoms of chronic anemia to an established motor neuron disorder. The feasible pathophysiologies were the impairment of the transferrin receptor functions, which affected the endocytic uptake of halo-transferrin into the erythroblast precursors. Such a defect left the erythropoiesis depleted of their iron supply. These alterations also promoted the TfR-independent uptake of iron into other target tissues and left the TrF2/BMP-dependent-hepcidin activation pathway unattended. We used the predicted molecular interactive proteomes to support our speculated dysregulated iron metabolism. During the early stage of an elevated ferritin level, there was no inhibition of ferroportin activities from hepcidin. These pathophysiological processes went on to the point of an iron overload threshold. After that, the hepcidin transcription started to kick in with the resulting decreased serum iron levels and deterioration of clinical symptoms.

Gnpat does not play an essential role in systemic iron homeostasis in murine model

The GNPAT variant rs11558492 (p.D519G) was identified as a novel genetic factor that modifies the iron‐overload phenotype in homozygous carriers of the HFE p.C282Y variant. However, the reported effects of the GNPAT p.D519G variant vary among study populations. Here, we investigated the role of GNPAT in iron metabolism using Gnpat‐knockout (Gnpat^−/−), Gnpat/Hfe double‐knockout (Gnpat^−/−Hfe^−/− or DKO) mice and hepatocyte‐specific Gnpat‐knockout mice (Gnpat^fl/fl;Alb‐Cre). Our analysis revealed no significant difference between wild‐type (Gnpat^+/+) and Gnpat^−/− mice, between Hfe^−/− and DKO mice, or between Gnpat^fl/fl and Gnpat^fl/fl;Alb‐Cre with respect to serum iron and tissue iron. In addition, the expression of hepcidin was not affected by deleting Gnpat expression in the presence or absence of Hfe. Feeding Gnpat^−/− and DKO mice a high‐iron diet had no effect on tissue iron levels compared with wild‐type and Hfe^−/− mice, respectively. Gnpat knockdown in primary hepatocytes from wild‐type or Hfe^−/− mice did not alter hepcidin expression, but it repressed BMP6‐induced hepcidin expression. Taken together, these results support the hypothesis that deleting Gnpat expression has no effect on either systemic iron metabolism or the iron‐overload phenotype that develops in Hfe^−/− mice, suggesting that GNPAT does not directly mediate iron homeostasis under normal or high‐iron dietary conditions.

The Role of Iron Regulation in Immunometabolism and Immune-Related Disease

Immunometabolism explores how the intracellular metabolic pathways in immune cells can regulate their function under different micro-environmental and (patho-)-physiological conditions (Pearce, 2010; Buck et al., 2015; O'Neill and Pearce, 2016). In the last decade great advances have been made in studying and manipulating metabolic programs in immune cells. Immunometabolism has primarily focused on glycolysis, the TCA cycle and oxidative phosphorylation (OXPHOS) as well as free fatty acid synthesis and oxidation. These pathways are important for providing the energy needs of cell growth, membrane rigidity, cytokine production and proliferation. In this review, we will however, highlight the specific role of iron metabolism at the cellular and organismal level, as well as how the bioavailability of this metal orchestrates complex metabolic programs in immune cell homeostasis and inflammation. We will also discuss how dysregulation of iron metabolism contributes to alterations in the immune system and how these novel insights into iron regulation can be targeted to metabolically manipulate immune cell function under pathophysiological conditions, providing new therapeutic opportunities for autoimmunity and cancer.

Metabolic Signature of Dietary Iron Overload in a Mouse Model

Iron is an essential co-factor for several metabolic processes, including the Krebs cycle and mitochondrial oxidative phosphorylation. Therefore, maintaining an appropriate iron balance is essential to ensure sufficient energy production and to avoid excessive reactive oxygen species formation. Iron overload impairs mitochondrial fitness; however, little is known about the associated metabolic changes. Here we aimed to characterize the metabolic signature triggered by dietary iron overload over time in a mouse model, where mice received either a standard or a high-iron diet. Metabolic profiling was assessed in blood, plasma and liver tissue. Peripheral blood was collected by means of volumetric absorptive microsampling (VAMS). Extracted blood and tissue metabolites were analyzed by liquid chromatography combined to high resolution mass spectrometry. Upon dietary iron loading we found increased glucose, aspartic acid and 2-/3-hydroxybutyric acid levels but low lactate and malate levels in peripheral blood and plasma, pointing to a re-programming of glucose homeostasis and the Krebs cycle. Further, iron loading resulted in the stimulation of the urea cycle in the liver. In addition, oxidative stress was enhanced in circulation and coincided with increased liver glutathione and systemic cysteine synthesis. Overall, iron supplementation affected several central metabolic circuits over time. Hence, in vivo investigation of metabolic signatures represents a novel and useful tool for getting deeper insights into iron-dependent regulatory circuits and for monitoring of patients with primary and secondary iron overload, and those ones receiving iron supplementation therapy.

Dietary iron loading negatively affects liver mitochondrial function

Iron is an essential co-factor for several metabolic processes, including mitochondrial respiration, and mitochondria are the major sites of iron-utilization. Cellular iron homeostasis must be tightly regulated, as intracellular iron deficiency can lead to insufficient energy production, whereas iron overload triggers ROS (reactive oxygen species) formation via the Fenton reaction. So far little is known on how iron imbalances affect mitochondrial function in vivo and the impact of the genotype on that, we studied the effects of dietary iron loading on mitochondrial respiratory capacity in liver by comparing two genetically divergent mouse strains, namely C57BL/6N and FVB mice. Both mouse strains differed in their basal iron levels and their metabolic responses to iron loading as determined by expression of iron trafficking proteins (ferritin was increased in livers of animals receiving high iron diet) as well as tissue iron content (2-fold increase, FVB p = 0.0013; C57BL/6N p = 0.0022). Dietary iron exposure caused a significant impairment of mitochondrial oxidative phosphorylation, especially regarding OXPHOS capacity (FVB p = 0.0006; C57BL/6N p = 0.0087) and S-ETS capacity (FVB p = 0.0281; C57BL/6N p = 0.0159). These effects were more pronounced in C57BL/6N than in FVB mice and were paralleled by an iron mediated induction of oxidative stress in mitochondria. The increased susceptibility of C57BL6/N mice to iron loading may be due to reduced expression of anti-oxidant defense mechanisms and altered iron trafficking upon dietary challenge pointing to a role of genetic modifiers for cellular and mitochondrial iron trafficking. Finally, iron-mediated induction of mitochondrial oxidative stress and reduction of oxidative phosphorylation may underlie fatigue in subjects with iron loading diseases.

Genetic and Dietary Iron Overload Differentially Affect the Course of Salmonella Typhimurium Infection

Genetic and dietary forms of iron overload have distinctive clinical and pathophysiological features. HFE-associated hereditary hemochromatosis is characterized by overwhelming intestinal iron absorption, parenchymal iron deposition, and macrophage iron depletion. In contrast, excessive dietary iron intake results in iron deposition in macrophages. However, the functional consequences of genetic and dietary iron overload for the control of microbes are incompletely understood. Using Hfe^+/+ and Hfe^-/- mice in combination with oral iron overload in a model of Salmonella enterica serovar Typhimurium infection, we found animals of either genotype to induce hepcidin antimicrobial peptide expression and hypoferremia following systemic infection in an Hfe-independent manner. As predicted, Hfe^-/- mice, a model of hereditary hemochromatosis, displayed reduced spleen iron content, which translated into improved control of Salmonella replication. Salmonella adapted to the iron-poor microenvironment in the spleens of Hfe^-/- mice by inducing the expression of its siderophore iron-uptake machinery. Dietary iron loading resulted in higher bacterial numbers in both WT and Hfe^-/- mice, although Hfe deficiency still resulted in better pathogen control and improved survival. This suggests that Hfe deficiency may exert protective effects in addition to the control of iron availability for intracellular bacteria. Our data show that a dynamic adaptation of iron metabolism in both immune cells and microbes shapes the host-pathogen interaction in the setting of systemic Salmonella infection. Moreover, Hfe-associated iron overload and dietary iron excess result in different outcomes in infection, indicating that tissue and cellular iron distribution determines the susceptibility to infection with specific pathogens.

"Pumping iron"-how macrophages handle iron at the systemic, microenvironmental, and cellular levels

Macrophages reside in virtually every organ. First arising during embryogenesis, macrophages replenish themselves in the adult through a combination of self-renewal and influx of bone marrow-derived monocytes. As large phagocytic cells, macrophages participate in innate immunity while contributing to tissue-specific homeostatic functions. Among the key metabolic tasks are senescent red blood cell recycling, free heme detoxification, and provision of iron for de novo hemoglobin synthesis. While this systemic mechanism involves the shuttling of iron between spleen, liver, and bone marrow through the concerted function of defined macrophage populations, similar circuits appear to exist within the microenvironment of other organs. The high turnover of iron is the prerequisite for continuous erythropoiesis and tissue integrity but challenges macrophages’ ability to maintain cellular iron homeostasis and immune function.

This review provides a brief overview of systemic, microenvironmental, and cellular aspects of macrophage iron handling with a focus on exciting and unresolved questions in the field.

Disposal of iron by a mutant form of lipocalin 2

Iron overload damages many organs. Unfortunately, therapeutic iron chelators also have undesired toxicity and may deliver iron to microbes. Here we show that a mutant form (K3Cys) of endogenous lipocalin 2 (LCN2) is filtered by the kidney but can bypass sites of megalin-dependent recapture, resulting in urinary excretion. Because K3Cys maintains recognition of its cognate ligand, the iron siderophore enterochelin, this protein can capture and transport iron even in the acidic conditions of urine. Mutant LCN2 strips iron from transferrin and citrate, and delivers it into the urine. In addition, it removes iron from iron overloaded mice, including models of acquired (iron-dextran or stored red blood cells) and primary (Hfe^−/−) iron overload. In each case, the mutants reduce redox activity typical of non-transferrin-bound iron. In summary, we present a non-toxic strategy for iron chelation and urinary elimination, based on manipulating an endogenous protein:siderophore:iron clearance pathway.

Iron overload can be either hereditary or acquired via transfusions, and current treatments include the use of iron chelators that have adverse effects in some patients. Here the authors modify siderocalin to enhance iron excretion in urine, and demonstrate therapeutic efficacy in iron overload mouse models.

Iron Together with Lipid Downregulates Protein Levels of Ceruloplasmin in Macrophages Associated with Rapid Foam Cell Formation

AIM

Iron accumulation in foam cells was previously shown to be involved in atherogenesis. However, the mechanism for iron accumulation was not clarified. Ceruloplasmin (Cp) is an important factor in cellular iron efflux and was found to be downregulated in atherosclerotic plaques in our previous study. The current study is to investigate the role of Cp in atherosclerosis.

METHODS

We used RAW264.7 cells, a well-accepted cell model of atherosclerosis, which were treated with lipopolysaccharides (LPS), ferric ammonium citrate (FAC) or deferoxamine, and oxidized low density lipoprotein (ox-LDL) to detect the regulation of Cp and its influence in iron efflux and lipid accumulation using biochemical and histological assays.

RESULTS

Our results showed that the Cp protein level increased after 200-μM FAC treatment in LPS-activated RAW264.7 cells. Ox-LDL treatment (50 μg/ml) moderately reduced both mRNA and protein levels and ferroxidase activity of Cp (p＜0.05). No significant difference was observed in the expression of ferritin and ferroportin, two important iron-related proteins for iron storage and efflux, respectively, after ox-LDL treatment. However, co-treatment with ox-LDL and FAC drastically reduced the expression of Cp. Accordingly, the ferroxidase activities simultaneously decreased, whereas the protein levels of Ft and Fpn1 significantly increased, indicating further iron accumulation. Moreover, co-treatment with FAC and ox-LDL enhanced the accumulation of cholesterol compared with ox-LDL-only treatment to trigger apoptosis.

CONCLUSION

Our findings suggest that physiological interaction of iron and lipid obstructs iron efflux and accelerates the lipid accumulation in macrophages during foam cell formation, which implicates the role of iron in the pathology of atherosclerosis.

Associations between Common Variants in Iron-Related Genes with Haematological Traits in Populations of African Ancestry

BACKGROUND

Large genome-wide association (GWA) studies of European ancestry individuals have identified multiple genetic variants influencing iron status. Studies on the generalizability of these associations to African ancestry populations have been limited. These studies are important given interethnic differences in iron status and the disproportionate burden of iron deficiency among African ancestry populations.

METHODS

We tested the associations of 20 previously identified iron status-associated single nucleotide polymorphisms (SNPs) in 628 Kenyans, 609 Tanzanians, 608 South Africans and 228 African Americans. In each study, we examined the associations present between 20 SNPs with ferritin and haemoglobin, adjusting for age, sex and CRP levels.

RESULTS

In the meta analysis including all 4 African ancestry cohorts, we replicated previously reported associations with lowered haemoglobin concentrations for rs2413450 (β = -0.19, P = 0.02) and rs4820268 (β = -0.16, P = 0.04) in TMPRSS6. An association with increased ferritin concentrations was also confirmed for rs1867504 in TF (β = 1.04, P = <0.0001) in the meta analysis including the African cohorts only.

CONCLUSIONS

In all meta analyses, we only replicated 4 of the 20 single nucleotide polymorphisms reported to be associated with iron status in large GWA studies of European ancestry individuals. While there is now evidence for the associations of a number of genetic variants with iron status in both European and African ancestry populations, the considerable lack of concordance highlights the importance of continued ancestry-specific studies to elucidate the genetic underpinnings of iron status in ethnically diverse populations.

Inadequate hepcidin serum concentrations predict incident type 2 diabetes mellitus

BACKGROUND

Type 2 diabetes mellitus (T2DM) is closely associated with elevated body iron stores. The hormone hepcidin is the key regulator of iron homeostasis. Inadequately low hepcidin levels were recently reported in subjects with manifest T2DM. We investigated whether alterations of hepcidin levels precede the manifestation of T2DM and predict T2DM development independently of established risk conditions.

METHODS

This prospective population-based study included 675 subjects aged 50-89 years, 51.9% of whom were female. Hepcidin levels were measured by gold standard tandem mass spectrometry. Diabetes was diagnosed according to American Diabetes Association criteria, and incident diabetes was recorded between baseline in 2000 and 2010.

RESULTS

The baseline hepcidin-to-ferritin ratio in subjects that subsequently developed diabetes during follow-up was reduced on average by 29.8% as compared with subjects with normal glucose tolerance (95% confidence interval, -50.7% to -0.2%; p = 0.049). After adjustment for age, sex, and serum ferritin, higher hepcidin levels were associated with reduced risk of incident diabetes (hazard ratio per 1-unit higher log2 hepcidin, 0.80; 95% confidence interval, 0.64-0.98; p = 0.035; 33 events). Additional adjustment for established diabetes risk factors and determinants of hepcidin concentration did not appreciably change these results (HR, 0.81; 95% CI, 0.66-0.99). Likewise, inadequately low hepcidin levels were also detected in subjects with prevalent T2DM (n = 76).

CONCLUSIONS

Hepcidin levels that are inadequately low in relation to body iron stores are an independent predictor for incident T2DM and may contribute to diabetes-related tissue iron overload. Copyright © 2015 John Wiley & Sons, Ltd.

Impaired hepcidin expression in alpha-1-antitrypsin deficiency associated with iron overload and progressive liver disease

Liver disease due to alpha-1-antitrypsin deficiency (A1ATD) is associated with hepatic iron overload in a subgroup of patients. The underlying cause for this association is unknown. The aim of the present study was to define the genetics of this correlation and the effect of alpha-1-antitrypsin (A1AT) on the expression of the iron hormone hepcidin. Full exome and candidate gene sequencing were carried out in a family with A1ATD and hepatic iron overload. Regulation of hepcidin expression by A1AT was studied in primary murine hepatocytes. Cells co-transfected with hemojuvelin (HJV) and matriptase-2 (MT-2) were used as a model to investigate the molecular mechanism of this regulation. Observed familial clustering of hepatic iron overload with A1ATD suggests a genetic cause, but genotypes known to be associated with hemochromatosis were absent. Individuals homozygous for the A1AT Z-allele with environmental or genetic risk factors such as steatosis or heterozygosity for the HAMP non-sense mutation p.Arg59* presented with severe hepatic siderosis. In hepatocytes, A1AT induced hepcidin mRNA expression in a dose-dependent manner. Experiments in overexpressing cells show that A1AT reduces cleavage of the hepcidin inducing bone morphogenetic protein co-receptor HJV via inhibition of the membrane-bound serine protease MT-2. The acute-phase protein A1AT is an inducer of hepcidin expression. Through this mechanism, A1ATD could be a trigger of hepatic iron overload in genetically predisposed individuals or patients with environmental risk factors for hepatic siderosis.

Elevated serum transaminase activities were associated with increased serum levels of iron regulatory hormone hepcidin and hyperferritinemia risk

Iron imbalance is a feature of liver damage. However, the biological correlation of serum hepcidin, a key regulator of iron homeostasis, with liver malfunction is undefined. To this end, we piloted the Chinese population studies to address whether hepcidin is linked to liver functionality. The serum hepcidin, ferritin, alanine transaminase, aspartate transaminase, gamma-glutamyltransferase and bilirubin were examined in two independent Chinese cohorts consisted of 3455 individuals. After adjustment for sex, age, body mass index, smoking habits, drinking categories and diabetic status, a positive association between hepcidin and alanine transaminase (ALT) (beta = 0.18 ± 0.01, P < 0.0001) was discovered using linear regression in a cohort consisting of 1813 individuals. This association was then validated in the second independent cohort of 1642 individuals (beta = 0.08 ± 0.02, P < 0.0001). Furthermore, consistent with cohort study, by applying both CCl4 and lipopolysaccharide induced mouse liver injury models, at least 2-fold elevations in hepcidin expression, serum ALT and inflammatory cytokine IL-6 were discovered during the initiation stage of liver injury. Our findings suggest that increased serum hepcidin may reflect a protective response to the iron status and elevated serum cytokines during liver injury. Additional studies are warranted to validate these findings and test their potential clinical relevance in patients.

Dysregulation of iron and copper homeostasis in nonalcoholic fatty liver

Elevated iron stores as indicated by hyperferritinemia with normal or mildly elevated transferrin saturation and mostly mild hepatic iron deposition are a characteristic finding in subjects with non-alcoholic fatty liver disease (NAFLD). Excess iron is observed in approximately one third of NAFLD patients and is commonly referred to as the “dysmetabolic iron overload syndrome”. Clinical evidence suggests that elevated body iron stores aggravate the clinical course of NAFLD with regard to liver-related and extrahepatic disease complications which relates to the fact that excess iron catalyses the formation of toxic hydroxyl-radicals subsequently resulting in cellular damage. Iron removal improves insulin sensitivity, delays the onset of type 2 diabetes mellitus, improves pathologic liver function tests and likewise ameliorates NAFLD histology. Several mechanisms contribute to pathologic iron accumulation in NAFLD. These include impaired iron export from hepatocytes and mesenchymal Kupffer cells as a consequence of imbalances in the concentrations of iron regulatory factors, such as hepcidin, cytokines, copper or other dietary factors. This review summarizes the knowledge about iron homeostasis in NAFLD and the rationale for its therapeutic implications.

The liver in haemochromatosis

The review deals with genetic, regulatory and clinical aspects of iron homeostasis and hereditary haemochromatosis. Haemochromatosis was first described in the second half of the 19th century as a clinical entity characterized by excessive iron overload in the liver. Later, increased absorption of iron from the diet was identified as the pathophysiological hallmark. In the 1970s genetic evidence emerged supporting the apparent inheritable feature of the disease. And finally in 1996 a new "haemochromatosis gene" called HFE was described which was mutated in about 85% of the patients. From the year 2000 onward remarkable progress was made in revealing the complex molecular regulation of iron trafficking in the human body and its disturbance in haemochromatosis. The discovery of hepcidin and ferroportin and their interaction in regulating the release of iron from enterocytes and macrophages to plasma were important milestones. The discovery of new, rare variants of non-HFE-haemochromatosis was explained by mutations in the multicomponent signal transduction pathway controlling hepcidin transcription. Inhibited transcription induced by the altered function of mutated gene products, results in low plasma levels of hepcidin which facilitate entry of iron from enterocytes into plasma. In time this leads to progressive accumulation of iron and subsequently development of disease in the liver and other parenchymatous organs. Being the major site of excess iron storage and hepcidin synthesis the liver is a cornerstone in maintaining normal systemic iron homeostasis. Its central pathophysiological role in HFE-haemochromatosis with downgraded hepcidin synthesis, was recently shown by the finding that liver transplantation normalized the hepcidin levels in plasma and there was no sign of iron accumulation in the new liver.

Regulation of DMT1 on Bone Microstructure in Type 2 Diabetes

Diabetic osteoporosis is gradually attracted people's attention. However, the process of bone microstructure changes in diabetic patients, and the exact mechanism of osteoblast iron overload are unclear. Therefore, the present study aimed to explore the function of DMT1 in the pathological process of diabetic osteoporosis. We build the type two diabetes osteoporosis models with SD rats and Belgrade rats, respectively. Difference expression of DMT1 was detected by using the method of immunohistochemistry and western blotting. Detection of bone microstructure and biomechanics and iron content for each group of samples. We found that DMT1 expression in type 2 diabetic rats was higher than that in normal rats. The bone biomechanical indices and bone microstructure in the rat model deficient in DMT1 was significantly better than that in the normal diabetic model. The loss of DMT1 can reduce the content of iron in bone. These findings indicate that DMT1 expression was enhanced in the bone tissue of type 2 diabetic rats, and plays an important role in the pathological process of diabetic osteoporosis. Moreover, DMT1 may be a potential therapeutic target for diabetic osteoporosis.

Novel loci affecting iron homeostasis and their effects in individuals at risk for hemochromatosis

Variation in body iron is associated with or causes diseases, including anaemia and iron overload. Here, we analyse genetic association data on biochemical markers of iron status from 11 European-population studies, with replication in eight additional cohorts (total up to 48,972 subjects). We find 11 genome-wide-significant (P<5 × 10(-8)) loci, some including known iron-related genes (HFE, SLC40A1, TF, TFR2, TFRC, TMPRSS6) and others novel (ABO, ARNTL, FADS2, NAT2, TEX14). SNPs at ARNTL, TF, and TFR2 affect iron markers in HFE C282Y homozygotes at risk for hemochromatosis. There is substantial overlap between our iron loci and loci affecting erythrocyte and lipid phenotypes. These results will facilitate investigation of the roles of iron in disease.

'Ride on the ferrous wheel'--the cycle of iron in macrophages in health and disease

Iron homeostasis and macrophage biology are closely interconnected. On the one hand, iron exerts multiple effects on macrophage polarization and functionality. On the other hand, macrophages are central for mammalian iron homeostasis. The phagocytosis of senescent erythrocytes and their degradation by macrophages enable efficient recycling of iron and the maintenance of systemic iron balance. Macrophages express multiple molecules and proteins for the acquisition and utilization of iron and many of these pathways are affected by inflammatory signals. Of note, iron availability within macrophages has significant effects on immune effector functions and metabolic pathways within these cells. This review summarizes the physiological and pathophysiological aspects of macrophage iron metabolism and highlights its relevant consequences on immune function and in common diseases such as infection and atherosclerosis.

Computational modeling and analysis of iron release from macrophages

A major process of iron homeostasis in whole-body iron metabolism is the release of iron from the macrophages of the reticuloendothelial system. Macrophages recognize and phagocytose senescent or damaged erythrocytes. Then, they process the heme iron, which is returned to the circulation for reutilization by red blood cell precursors during erythropoiesis. The amount of iron released, compared to the amount shunted for storage as ferritin, is greater during iron deficiency. A currently accepted model of iron release assumes a passive-gradient with free diffusion of intracellular labile iron (Fe2+) through ferroportin (FPN), the transporter on the plasma membrane. Outside the cell, a multi-copper ferroxidase, ceruloplasmin (Cp), oxidizes ferrous to ferric ion. Apo-transferrin (Tf), the primary carrier of soluble iron in the plasma, binds ferric ion to form mono-ferric and di-ferric transferrin. According to the passive-gradient model, the removal of ferrous ion from the site of release sustains the gradient that maintains the iron release. Subcellular localization of FPN, however, indicates that the role of FPN may be more complex. By experiments and mathematical modeling, we have investigated the detailed mechanism of iron release from macrophages focusing on the roles of the Cp, FPN and apo-Tf. The passive-gradient model is quantitatively analyzed using a mathematical model for the first time. A comparison of experimental data with model simulations shows that the passive-gradient model cannot explain macrophage iron release. However, a facilitated-transport model associated with FPN can explain the iron release mechanism. According to the facilitated-transport model, intracellular FPN carries labile iron to the macrophage membrane. Extracellular Cp accelerates the oxidation of ferrous ion bound to FPN. Apo-Tf in the extracellular environment binds to the oxidized ferrous ion, completing the release process. Facilitated-transport model can correctly predict cellular iron efflux and is essential for physiologically relevant whole-body model of iron metabolism.

Iron metabolism regulates p53 signaling through direct heme-p53 interaction and modulation of p53 localization, stability, and function

Iron excess is closely associated with tumorigenesis in multiple types of human cancers, with underlying mechanisms yet unclear. Recently, iron deprivation has emerged as a major strategy for chemotherapy, but it exerts tumor suppression only on select human malignancies. Here, we report that the tumor suppressor protein p53 is downregulated during iron excess. Strikingly, the iron polyporphyrin heme binds to p53 protein, interferes with p53-DNA interactions, and triggers both nuclear export and cytosolic degradation of p53. Moreover, in a tumorigenicity assay, iron deprivation suppressed wild-type p53-dependent tumor growth, suggesting that upregulation of wild-type p53 signaling underlies the selective efficacy of iron deprivation. Our findings thus identify a direct link between iron/heme homeostasis and the regulation of p53 signaling, which not only provides mechanistic insights into iron-excess-associated tumorigenesis but may also help predict and improve outcomes in iron-deprivation-based chemotherapy.

Profound morphological changes in the erythrocytes and fibrin networks of patients with hemochromatosis or with hyperferritinemia, and their normalization by iron chelators and other agents

It is well-known that individuals with increased iron levels are more prone to thrombotic diseases, mainly due to the presence of unliganded iron, and thereby the increased production of hydroxyl radicals. It is also known that erythrocytes (RBCs) may play an important role during thrombotic events. Therefore the purpose of the current study was to assess whether RBCs had an altered morphology in individuals with hereditary hemochromatosis (HH), as well as some who displayed hyperferritinemia (HF). Using scanning electron microscopy, we also assessed means by which the RBC and fibrin morphology might be normalized. An important objective was to test the hypothesis that the altered RBC morphology was due to the presence of excess unliganded iron by removing it through chelation. Very striking differences were observed, in that the erythrocytes from HH and HF individuals were distorted and had a much greater axial ratio compared to that accompanying the discoid appearance seen in the normal samples. The response to thrombin, and the appearance of a platelet-rich plasma smear, were also markedly different. These differences could largely be reversed by the iron chelator desferal and to some degree by the iron chelator clioquinol, or by the free radical trapping agents salicylate or selenite (that may themselves also be iron chelators). These findings are consistent with the view that the aberrant morphology of the HH and HF erythrocytes is caused, at least in part, by unliganded (‘free’) iron, whether derived directly via raised ferritin levels or otherwise, and that lowering it or affecting the consequences of its action may be of therapeutic benefit. The findings also bear on the question of the extent to which accepting blood donations from HH individuals may be desirable or otherwise.

Age-dependent ferritin elevations and HFE C282Y mutation as risk factors for symptomatic knee osteoarthritis in males: a longitudinal cohort study

Background

Age, gender and genetic predisposition are major intrinsic risk factors for osteoarthritis (OA). Iron increases are associated with age and gene mutation. In the present study, we examined whether serum ferritin, an indicator of total body iron stores, correlates with clinical features in patients with OA, and whether the hemochromatosis Fe (HFE) gene mutation plays a role.

Methods

In a 2-year longitudinal observational study, 127 patients with knee OA and 20 healthy individuals (controls) were enrolled. All patients underwent standardized weight-bearing fixed-flexion posteroanterior knee radiographs. Peripheral blood samples were analyzed for serum ferritin, and genotyped for HFE using allelic discrimination methods.

Results

Higher levels of serum ferritin were found in patients older than 56 years (P =0.0186) and males (P =0.0006), with a trend toward higher ferritin in patients with OA. HFE gene mutation carriers were more prevalent among patients with OA than among healthy controls. When stratified further by gender, we found that male patients with OA had higher levels of serum ferritin than male control subjects [odds ratio = 4.18 (limits of 95% confidence interval: 0.86–27.69, P = 0.048)]. Analyses of radiographic data indicated that higher ferritin was associated with narrower joint space width at baseline (P = 0.032) in male patients. Additionally, among men, risk prediction of radiographic severity [Kellgren-Lawrence (KL) grade >2)] in the higher ferritin group was almost five times that of the lower ferritin group (odds ratio = 4.74, P = 0.023).

Conclusion

Our data suggest that increased ferritin levels are associated with symptomatic knee OA in males. This finding needs to be validated in a larger cohort of patients.

The complex interplay of iron metabolism, reactive oxygen species, and reactive nitrogen species: insights into the potential of various iron therapies to induce oxidative and nitrosative stress

Production of minute concentrations of superoxide (O2(*-)) and nitrogen monoxide (nitric oxide, NO*) plays important roles in several aspects of cellular signaling and metabolic regulation. However, in an inflammatory environment, the concentrations of these radicals can drastically increase and the antioxidant defenses may become overwhelmed. Thus, biological damage may occur owing to redox imbalance-a condition called oxidative and/or nitrosative stress. A complex interplay exists between iron metabolism, O2(*-), hydrogen peroxide (H2O2), and NO*. Iron is involved in both the formation and the scavenging of these species. Iron deficiency (anemia) (ID(A)) is associated with oxidative stress, but its role in the induction of nitrosative stress is largely unclear. Moreover, oral as well as intravenous (iv) iron preparations used for the treatment of ID(A) may also induce oxidative and/or nitrosative stress. Oral administration of ferrous salts may lead to high transferrin saturation levels and, thus, formation of non-transferrin-bound iron, a potentially toxic form of iron with a propensity to induce oxidative stress. One of the factors that determine the likelihood of oxidative and nitrosative stress induced upon administration of an iv iron complex is the amount of labile (or weakly-bound) iron present in the complex. Stable dextran-based iron complexes used for iv therapy, although they contain only negligible amounts of labile iron, can induce oxidative and/or nitrosative stress through so far unknown mechanisms. In this review, after summarizing the main features of iron metabolism and its complex interplay with O2(*-), H2O2, NO*, and other more reactive compounds derived from these species, the potential of various iron therapies to induce oxidative and nitrosative stress is discussed and possible underlying mechanisms are proposed. Understanding the mechanisms, by which various iron formulations may induce oxidative and nitrosative stress, will help us develop better tolerated and more efficient therapies for various dysfunctions of iron metabolism.

Where genotype is not predictive of phenotype: towards an understanding of the molecular basis of reduced penetrance in human inherited disease

Some individuals with a particular disease-causing mutation or genotype fail to express most if not all features of the disease in question, a phenomenon that is known as 'reduced (or incomplete) penetrance'. Reduced penetrance is not uncommon; indeed, there are many known examples of 'disease-causing mutations' that fail to cause disease in at least a proportion of the individuals who carry them. Reduced penetrance may therefore explain not only why genetic diseases are occasionally transmitted through unaffected parents, but also why healthy individuals can harbour quite large numbers of potentially disadvantageous variants in their genomes without suffering any obvious ill effects. Reduced penetrance can be a function of the specific mutation(s) involved or of allele dosage. It may also result from differential allelic expression, copy number variation or the modulating influence of additional genetic variants in cis or in trans. The penetrance of some pathogenic genotypes is known to be age- and/or sex-dependent. Variable penetrance may also reflect the action of unlinked modifier genes, epigenetic changes or environmental factors. At least in some cases, complete penetrance appears to require the presence of one or more genetic variants at other loci. In this review, we summarize the evidence for reduced penetrance being a widespread phenomenon in human genetics and explore some of the molecular mechanisms that may help to explain this enigmatic characteristic of human inherited disease.

Relevance of dietary iron intake and bioavailability in the management of HFE hemochromatosis: a systematic review

BACKGROUND

Hereditary hemochromatosis (HH) leads to iron loading because of a disturbance in the negative-feedback mechanism between dietary iron absorption and iron status. The management of HH is achieved by repeated phlebotomies.

OBJECTIVE

We investigated whether HH patients would benefit from a diet with low iron intake and bioavailability.

DESIGN

We performed a systematic review of studies that linked iron bioavailability and status with dietary factors in subjects with diagnosed HH. Studies on heterozygotes for the HFE mutation were excluded.

RESULTS

No prospective, randomized study was reported. Nine studies that directly measured iron bioavailability from test meals in HH patients have been described as well as 3 small, prospective, longitudinal studies in HH patients. Eight cross-sectional studies were identified that investigated the effect of dietary composition on iron status. Calculations of iron bioavailability in HH were made by extrapolating data on hepcidin concentrations and their association with iron bioavailability. The potential reduction in the yearly amount of blood to be phlebotomized when restricting dietary iron absorbed was estimated in the 3 longitudinal studies and ranged between 0.5 and 1.5 L. This amount would be dependent on individual disease penetrance as well as the dietary intervention.

CONCLUSIONS

Despite the limited quantitative evidence and the lack of randomized, prospective trials, dietary interventions that modify iron intake and bioavailability may affect iron accumulation in HH patients. Although this measure may be welcome in patients willing to contribute to their disease management, limited data exist on the clinical and quality-of-life benefit.

Screening identifies the Chinese medicinal plant Caulis Spatholobi as an effective HAMP expression inhibitor

Hepcidin, the pivotal regulator of iron metabolism, plays a critical role in multiple diseases including anemia of chronic disease and hemochromatosis. Recent studies have focused on identifying antagonists of hepcidin. We hypothesized that bioactive extracts from Chinese medicinal plants may be efficacious in the inhibition of expression of the hepcidin-encoding gene (HAMP) product, hepcidin. To test this, we measured the level of hepcidin expression in cultured cells treated with 16 different medicinal plant extracts, all of which are used to treat anemia-related disorders in traditional Chinese medicine. Among the extracts tested, that of Caulis Spatholobi (CS; also called Jixueteng, the stem of Spatholobus suberectus Dunn) showed the most potent inhibitory effect on HAMP expression in the Huh7 cell line and was therefore selected for further mechanistic study. In cells treated with 400 μg/mL of extract, phosphorylated mothers against decapentaplegic homolog proteins 1/5/8 levels were 80% less than those of controls (P < 0.001), and the inhibitory effect on interleukin-6-induced HAMP expression (65% inhibition) was weaker than the strong inhibition on bone morphogenetic protein 6-induced HAMP expression (97% inhibition). Seven-week-old C57BL/6 female mice were fed an AIN-76A diet containing 10.8% dried CS and then analyzed on d 0, 5, 10, or 15. On d 5, there was a 60% decrease in hepatic HAMP expression (P < 0.05), an 18% decrease in hepatic iron concentration, and a 100% increase in serum iron concentration (P < 0.05) compared with the d 0 group. In conclusion, we identify the extract of CS as a novel, potent HAMP expression inhibitor, which may be further modified and optimized to become a dietary supplement or a therapeutic option for the amelioration of hepcidin-overexpression-related diseases, including iron deficiency anemia.

Worldwide policies on haemochromatosis and blood donation: a survey among blood services

BACKGROUND AND OBJECTIVES

Haemochromatosis (HC) is a disorder of iron metabolism, requiring frequent phlebotomy to normalize high serum iron levels. There is currently no consensus relating to the eligibility of these patients to donate blood for transfusion. To gain a better understanding of the policies worldwide, a survey amongst blood services was performed.

MATERIALS AND METHODS

A web-based questionnaire was developed and distributed among 44 blood services in 41 countries to identify the different policies relating to patients with HC and blood donation.

RESULTS

Respondents from 35 blood services (80%) of 33 countries completed the questionnaire. In 24 blood services among them (69%), individuals with genetic susceptibility for HC and/or patients with HC are accepted as blood donors. In approximately one-third of these blood centres (33%), genetic carriers/patients are allowed to donate blood more frequently than regular donors. Prescription from/approval by the patient's treating physician and/or a donor physician is required in the majority of the blood services (87%). Similar policies were identified in a few countries; however, in general, the policies regarding blood donation from patients with HC remain widely variable.

CONCLUSION

The results of our survey demonstrate large differences in the blood donation policies regarding carriers/patients with HC illustrating the need for uniform evidence-based and cost-effective policies which could benefit both HC patients and the blood supply around the world.

On myocardial siderosis and left ventricular dysfunction in hemochromatosis

BACKGROUND

Chronically increased intestinal iron uptake in genetic hemochromatosis (HC) may cause organ failure. Whilst iron loading from blood transfusions may cause dilated cardiomyopathy in conditions such as thalassemia, the in-vivo prevalence of myocardial siderosis in HC is unclear, and its relation to left ventricular (LV) dysfunction is controversial. Most previous data on myocardial siderosis in HC has come from post-mortem studies.

METHODS

Cardiovascular magnetic resonance (CMR) was performed at first presentation of 41 HC patients (58.9 ± 14.1 years) to measure myocardial iron and left ventricular (LV) ejection fraction (EF).

RESULTS

In 31 patients (genetically confirmed HFE-HC), the HFE genotype was C282Y/C282Y (n = 30) and C282Y/H63D (n = 1). Patients with other genotypes (n = 10) were labeled genetically unconfirmed HC. Of the genetically confirmed HFE-HC patients, 6 (19%) had myocardial siderosis (T2* <20 ms). Of these, 5 (83%) had heart failure and reduced LVEF which was correlated to the severity of siderosis (R2 0.57, p = 0.049). Two patients had follow-up scans and both had marked improvements in T2* and LVEF following venesection. Myocardial siderosis was present in 6/18 (33%) of patients with presenting ferritin ≥ 1000 μg/L at diagnosis but in 0/13 (0%) patients with ferritin <1000 μg/L (p = 0.028). Overall however, the relation between myocardial siderosis and ferritin was weak (R2 0.20, p = 0.011). In the 10 genetically unconfirmed HC patients, 1 patient had mild myocardial siderosis but normal EF. Of all 31 patients, 4 had low LVEF from other identifiable causes without myocardial siderosis.

CONCLUSION

Myocardial siderosis was present in 33% of newly presenting genetically confirmed HFE-HC patients with ferritin >1000 μg/L, and was the commonest cause of reduced LVEF. Heart failure due to myocardial siderosis was only found in these HFE-HC patients, and was reversible with venesection. Myocardial iron was normal in patients with other causes of LV dysfunction.

Paraoxonase-1 status in patients with hereditary hemochromatosis

Hereditary hemochromatosis (HH) is characterized by accumulation of iron, oxidative stress, inflammation, and fibrogenesis in liver tissue. In this setting, research on the protection afforded by intracellular antioxidants is of clinical relevance. Paraoxonase-1 (PON1) is an enzyme that degrades lipid peroxides. This study investigates the alterations in serum PON1 status, PON1 gene polymorphisms, and PON1 hepatic expression in patients with HH. We performed a case-control study in 77 patients with HH (80.5% men, 22-70 years of age) and 408 healthy individuals (43.1% men, 26-74 years of age). Serum PON1 activities against different substrates and PON1192 and PON155 polymorphisms were analyzed. PON1 protein expression was investigated in 20 liver biopsies. HH patients had significantly lower serum PON1 activity, which was inversely correlated with ferritin (marker of iron stores) and serum 8-isoprostane concentrations (index of oxidative stress). PON1 protein expression in liver tissue was higher in patients and showed stronger staining in hepatocytes surrounding the areas of inflammation. Our study provides preliminary evidence that PON1 may play a role in protecting against iron-induced oxidative stress in hereditary hemochromatosis.

Deleterious- and disease-allele prevalence in healthy individuals: insights from current predictions, mutation databases, and population-scale resequencing

We have assessed the numbers of potentially deleterious variants in the genomes of apparently healthy humans by using (1) low-coverage whole-genome sequence data from 179 individuals in the 1000 Genomes Pilot Project and (2) current predictions and databases of deleterious variants. Each individual carried 281-515 missense substitutions, 40-85 of which were homozygous, predicted to be highly damaging. They also carried 40-110 variants classified by the Human Gene Mutation Database (HGMD) as disease-causing mutations (DMs), 3-24 variants in the homozygous state, and many polymorphisms putatively associated with disease. Whereas many of these DMs are likely to represent disease-allele-annotation errors, between 0 and 8 DMs (0-1 homozygous) per individual are predicted to be highly damaging, and some of them provide information of medical relevance. These analyses emphasize the need for improved annotation of disease alleles both in mutation databases and in the primary literature; some HGMD mutation data have been recategorized on the basis of the present findings, an iterative process that is both necessary and ongoing. Our estimates of deleterious-allele numbers are likely to be subject to both overcounting and undercounting. However, our current best mean estimates of ~400 damaging variants and ~2 bona fide disease mutations per individual are likely to increase rather than decrease as sequencing studies ascertain rare variants more effectively and as additional disease alleles are discovered.

Anaemia in inflammatory rheumatic diseases

Anaemia is frequently observed in patients with inflammatory rheumatic diseases. Depending on its severity, anaemia negatively affects cardiovascular performance, physical activity and the quality of life of patients. However, anaemia is considered to be a symptom of the underlying inflammatory disease and, thus, neglected as a complex medical condition that warrants specific diagnosis and treatment. Although inflammation-induced alterations in iron homeostasis and erythropoiesis have a dominant role in the pathogenesis of this type of anaemia, multiple other factors such as chronic blood loss, haemolysis, disease and treatment-associated adverse effects or vitamin deficiencies can also take part in the development of anaemia. Accordingly, the prevalence of anaemia is positively associated with the severity of the underlying disease. This Review will summarize epidemiological data on anaemia in inflammatory rheumatic diseases, along with a detailed description of underlying pathophysiological pathways, available diagnostic tools and practical diagnostic strategies. Discussion of established and newly emerging treatment regimens, as well as the need for further research in this clinically relevant field, will also be included.

Glucose acts as a regulator of serum iron by increasing serum hepcidin concentrations

Mutual clinical and molecular interactions between iron and glucose metabolism have been reported. We aimed to investigate a potential effect of glucose on iron homeostasis. We found that serum iron concentrations gradually decreased over 180 min after the administration of 75 g of glucose from 109.8 ± 45.4 mg/L to 94.4 ± 40.4 mg/L (P<.001; N=40) but remained unchanged in control subjects receiving tap water (N=21). Serum hepcidin, the key iron regulatory hormone which is mainly derived from hepatocytes but also expressed in pancreatic β-cells, increased within 120 min after glucose ingestion from 19.7 ± 9.9 nmol/L to 31.4 ± 21.0 nmol/L (P<.001). In cell culture, glucose induced the secretion of hepcidin and insulin into the supernatant of INS-1E cultures, but did not change the amount of hepcidin detectable in the hepatocyte cell culture HepG2. We additionally confirmed the expression of hepcidin in a human islet cell preparation. These results suggest that glucose acts as a regulator of serum iron concentrations, most likely by triggering the release of hepcidin from β-cells.

Penetrance of biallelic SMARCAL1 mutations is associated with environmental and genetic disturbances of gene expression

Biallelic mutations of the DNA annealing helicase SMARCAL1 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a-like 1) cause Schimke immuno-osseous dysplasia (SIOD, MIM 242900), an incompletely penetrant autosomal recessive disorder. Using human, Drosophila and mouse models, we show that the proteins encoded by SMARCAL1 orthologs localize to transcriptionally active chromatin and modulate gene expression. We also show that, as found in SIOD patients, deficiency of the SMARCAL1 orthologs alone is insufficient to cause disease in fruit flies and mice, although such deficiency causes modest diffuse alterations in gene expression. Rather, disease manifests when SMARCAL1 deficiency interacts with genetic and environmental factors that further alter gene expression. We conclude that the SMARCAL1 annealing helicase buffers fluctuations in gene expression and that alterations in gene expression contribute to the penetrance of SIOD.