Hereditary hemochromatosis: genetic complexity and new diagnostic approaches

Cardiovascular Manifestations of Hemochromatosis: A Review of Pathophysiology, Mechanisms, and Treatment Options

Hemochromatosis is a genetic disorder characterized by excessive absorption and accumulation of iron in the body. It is one of the most common inherited disorders. The excess iron deposition can cause damage to various organs, including the liver, heart, pancreas, and joints. If left untreated, hemochromatosis can lead to serious complications such as cirrhosis, diabetes, heart failure, and increased risk of certain cancers. Iron overload in hemochromatosis significantly affects the cardiovascular system, leading to morbidity and mortality. This article reviews the current literature describing the pathogenesis and various cardiovascular manifestations of hemochromatosis, including dilated cardiomyopathy, conduction abnormalities, heart failure, cardiac fibrosis, myocardial infarction, and valvular heart disease. This article aims to provide a detailed understanding of the cardiovascular manifestations associated with hemochromatosis and their underlying mechanisms through a review of current literature in publicly available databases.

Therapeutic Implications of Ferroptosis in Renal Fibrosis

Renal fibrosis is a common feature of chronic kidney disease (CKD), and can lead to the destruction of normal renal structure and loss of kidney function. Little progress has been made in reversing fibrosis in recent years. Ferroptosis is more immunogenic than apoptosis due to the release and activation of damage-related molecular patterns (DAMPs) signals. In this paper, the relationship between renal fibrosis and ferroptosis was reviewed from the perspective of iron metabolism and lipid peroxidation, and some pharmaceuticals or chemicals associated with both ferroptosis and renal fibrosis were summarized. Other programmed cell death and ferroptosis in renal fibrosis were also firstly reviewed for comparison and further investigation.

Impact of HFE-2 and HAMP Gene Variations on Iron Overload in Pediatric Patients with Non-Transfusion Dependent Thalassemia: A Pilot Study

Patients with non-transfusion dependent thalassemia (NTDT) develop variable degrees of iron overload. Possible genes which may be implicated in causing iron overload are hepcidin (HAMP) and hemojuvelin (HFE). There is variable data assessing the role of c.-582Y A > G HAMP gene and H63D hotspot in HFE-1 gene in causing iron overload, while role of HFE-2 gene is undetermined. Twenty-five patients with NTDT (≥ 10 years) were assessed for iron overload. Genetic analysis for β-globin, α-globin, HAMP, HFE-2 and C282Y and H63D hotspots in HFE-1 genes was performed. T2*MRI demonstrated elevated LIC in 48% patients. No mutations were detected in HAMP gene or HFE-1 hotspots. Four single nucleotide variations (SNV) were detected in HFE-2 gene in 4 (20%) patients, including a novel SNV, p.Gln315Arg in 2 patients in heterozygous state. This is a likely pathogenic mutation; however, in heterozygous state, it did not lead to iron overload. HAMP and HFE-2 gene variations were infrequently seen in this pilot study, with no significant impact on iron overload. Presence of SNV p.Gln315Argin HFE-2 gene needs to be evaluated in larger sample sizes in our population to determine the incidence in homozygous state and its association with iron overload.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12288-021-01442-9.

Genetic Diagnosis in Hereditary Hemochromatosis: Discovering and Understanding the Biological Relevance of Variants

BACKGROUND

Hereditary hemochromatosis (HH) is a genetic disease, leading to iron accumulation and possible organ damage. Patients are usually homozygous for p. Cys282Tyr in the homeostatic iron regulator gene but may have mutations in other genes involved in the regulation of iron. Next-generation sequencing is increasingly being utilized for the diagnosis of patients, leading to the discovery of novel genetic variants. The clinical significance of these variants is often unknown.

CONTENT

Determining the pathogenicity of such variants of unknown significance is important for diagnostics and genetic counseling. Predictions can be made using in silico computational tools and population data, but additional evidence is required for a conclusive pathogenicity classification. Genetic disease models, such as in vitro models using cellular overexpression, induced pluripotent stem cells or organoids, and in vivo models using mice or zebrafish all have their own challenges and opportunities when used to model HH and other iron disorders. Recent developments in gene-editing technologies are transforming the field of genetic disease modeling.

SUMMARY

In summary, this review addresses methods and developments regarding the discovery and classification of genetic variants, from in silico tools to in vitro and in vivo models, and presents them in the context of HH. It also explores recent gene-editing developments and how they can be applied to the discussed models of genetic disease.

Pathogenesis, Diagnosis, and Clinical Implications of Hereditary Hemochromatosis-The Cardiological Point of View

Hereditary hemochromatosis (HH) is a genetic disease leading to excessive iron absorption, its accumulation, and oxidative stress induction causing different organ damage, including the heart. The process of cardiac involvement is slow and lasts for years. Cardiac pathology manifests as an impaired diastolic function and cardiac hypertrophy at first and as dilatative cardiomyopathy and heart failure with time. From the moment of heart failure appearance, the prognosis is poor. Therefore, it is crucial to prevent those lesions by upfront therapy at the preclinical phase of the disease. The most useful diagnostic tool for detecting cardiac involvement is echocardiography. However, during an early phase of the disease, when patients do not present severe abnormalities in serum iron parameters and severe symptoms of other organ involvement, heart damage may be overlooked due to the lack of evident signs of cardiac dysfunction. Considerable advancement in echocardiography, with particular attention to speckle tracking echocardiography, allows detecting discrete myocardial abnormalities and planning strategy for further clinical management before the occurrence of substantial heart damage. The review aims to present the current state of knowledge concerning cardiac involvement in HH. In addition, it could help cardiologists and other physicians in their everyday practice with HH patients.

The critical roles of iron during the journey from fetus to adolescent: Developmental aspects of iron homeostasis

Iron is indispensable for human life. However, it is also potentially toxic, since it catalyzes the formation of harmful oxidative radicals in unbound form and may facilitate pathogen growth. Therefore, iron homeostasis needs to be tightly regulated. Rapid growth and development require large amounts of iron, while (especially young) children are vulnerable to infections with iron-dependent pathogens due to an immature immune system. Moreover, unbalanced iron status early in life may have effects on the nervous system, immune system and gut microbiota that persist into adulthood. In this narrative review, we assess the critical roles of iron for growth and development and elaborate how the body adapts to physiologically high iron demands during the journey from fetus to adolescent. As a first step towards the development of clinical guidelines for the management of iron disorders in children, we summarize the unmet needs regarding the developmental aspects of iron homeostasis.

Standardized serum hepcidin values in Dutch children: Set point relative to body iron changes during childhood

BACKGROUND

Use of serum hepcidin measurements in pediatrics would benefit from standardized age- and sex-specific reference ranges in children, in order to enable the establishment of clinical decision limits that are universally applicable.

PROCEDURE

We measured serum hepcidin-25 levels in 266 healthy Dutch children aged 0.3-17 years, using an isotope dilution mass spectrometry assay, standardized with our commutable secondary reference material (RM), assigned by a candidate primary RM.

RESULTS

We constructed age- and sex-specific values for serum hepcidin and its ratio with ferritin and transferrin saturation (TSAT). Serum hepcidin levels and hepcidin/ferritin and TSAT/hepcidin ratios were similar for both sexes. Serum hepcidin and hepcidin/ferritin ratio substantially declined after the age of 12 years and TSAT/hepcidin ratio gradually increased with increasing age. Serum hepcidin values for Dutch children <12 years (n = 170) and >12 years (n = 96) were 1.9 nmol/L (median); 0.1-13.1 nmol/L (p2.5-p97.5) and 0.9 nmol/L; 0.0-9.1 nmol/L, respectively. Serum ferritin was the most significant correlate of serum hepcidin in our study population, explaining 15.1% and 7.9% of variance in males and females, respectively. Multivariable linear regression analysis including age, blood sampling time, iron parameters, ALT, CRP, and body mass index as independent variables showed a statistically significant negative association between age as a dichotomous variable (≤12 vs >12 years) and log-transformed serum hepcidin levels in both sexes.

CONCLUSIONS

We demonstrate that serum hepcidin relative to indicators of body iron is age dependent in children, suggesting that the set point of serum hepcidin relative to stored and circulating iron changes during childhood.

- 174 G>C IL-6 polymorphism and primary iron overload in male patients

Primary iron overload (IO) is commonly associated with mutations in the hereditary hemochromatosis gene (HFE). Nonetheless, other genetic variants may influence the development of IO beyond HFE mutations. There is a single nucleotide polymorphism (SNP) at - 174 G>C of the interleukin (IL)-6 gene which might be associated with primary IO. Our aim was to study the association between the SNP - 174 G>C gene promoter of IL-6 and primary IO in middle-aged male patients. We studied 37 men with primary IO diagnosed by liver histology. Controls were age-matched male volunteers (n = 37). HFE mutations and the SNP - 174 G>C gene promoter of IL-6 were evaluated by PCR-RFLP. Logistic regression was used to evaluate the association between primary IO and SNP - 174 G>C gene promoter of IL-6. Patients and control subjects were in Hardy-Weinberg equilibrium for the SNP - 174 G>C gene promoter of IL-6 (p = 0.17). Significantly different genotype frequencies were observed between patients (43% CC, 43% CG, and 14% GG) and control subjects (10% CC, 41% CG, and 49% GG) (OR = 4.09, 95% CI = 2.06-8.13; p < 0.0001). The multiple logistic regression analysis showed that IO was significantly associated with CC homozygosis in the SNP - 174 G>C gene promoter of IL-6 (OR = 6.3, 95% CI = 1.9-21.4; p < 0.005) in a model adjusted by age and body mass index. In conclusion, CC homozygosis in the SNP - 174 G>C gene promoter of IL-6 can be proposed as one of the gene variants influencing iron accumulation in male adults with HFE mutations. Studies in larger cohorts are warranted.

[Assessment and management of post-transplant iron overload: Guidelines of the Francophone Society of Marrow Transplantation and Cellular Therapy (SFGM-TC)]

To harmonize clinical practice in hematopoietic stem cell transplantation, the Francophone Society of Bone Marrow Transplantation and Cell Therapy (SFGM-TC) set up the sixth annual series of workshops which brought together practitioners from all member centers and took place in September 2015 in Lille. The main aim of this session was to describe the impact, evaluation and treatment of post-transplant iron overload.

Meta-GWAS and Meta-Analysis of Exome Array Studies Do Not Reveal Genetic Determinants of Serum Hepcidin

Serum hepcidin concentration is regulated by iron status, inflammation, erythropoiesis and numerous other factors, but underlying processes are incompletely understood. We studied the association of common and rare single nucleotide variants (SNVs) with serum hepcidin in one Italian study and two large Dutch population-based studies. We genotyped common SNVs with genome-wide association study (GWAS) arrays and subsequently performed imputation using the 1000 Genomes reference panel. Cohort-specific GWAS were performed for log-transformed serum hepcidin, adjusted for age and gender, and results were combined in a fixed-effects meta-analysis (total N 6,096). Six top SNVs (p<5x10-6) were genotyped in 3,821 additional samples, but associations were not replicated. Furthermore, we meta-analyzed cohort-specific exome array association results of rare SNVs with serum hepcidin that were available for two of the three cohorts (total N 3,226), but no exome-wide significant signal (p<1.4x10-6) was identified. Gene-based meta-analyses revealed 19 genes that showed significant association with hepcidin. Our results suggest the absence of common SNVs and rare exonic SNVs explaining a large proportion of phenotypic variation in serum hepcidin. We recommend extension of our study once additional substantial cohorts with hepcidin measurements, GWAS and/or exome array data become available in order to increase power to identify variants that explain a smaller proportion of hepcidin variation. In addition, we encourage follow-up of the potentially interesting genes that resulted from the gene-based analysis of low-frequency and rare variants.

High maternal iron status, dietary iron intake and iron supplement use in pregnancy and risk of gestational diabetes mellitus: a prospective study and systematic review

AIM

High iron measured using dietary intake and biomarkers is associated with Type 2 diabetes. It is uncertain whether a similar association exists for gestational diabetes mellitus. The aim of this systematic review was to conduct a cohort study examining first trimester body iron stores and subsequent risk of gestational diabetes, and to include these findings in a systematic review of all studies examining the association between maternal iron status, iron intake (dietary and supplemental) and the risk of gestational diabetes.

METHODS

Serum samples from women with first trimester screening were linked to birth and hospital records for data on maternal characteristics and gestational diabetes diagnosis. Blood was analysed for ferritin, soluble transferrin receptor and C-reactive protein. Associations between iron biomarkers and gestational diabetes were assessed using multivariate logistic regression. A systematic review and meta-analysis, registered with PROSPERO (CRD42014013663) included studies of all designs published in English from January 1995 to July 2015 that examined the association between iron and gestational diabetes and included an appropriate comparison group.

RESULTS

Of 3776 women, 3.4% subsequently developed gestational diabetes. Adjusted analyses found increased odds of gestational diabetes for ferritin (OR 1.41; 95% CI 1.11, 1.78), but not for soluble transferrin receptor (OR 1.00; 95% CI 0.97, 1.03) per unit increase of the biomarker. Two trials of iron supplementation found no association with gestational diabetes. Increased risk of gestational diabetes was associated with higher levels of ferritin and serum iron and dietary haem iron intakes.

CONCLUSIONS

Increased risk of gestational diabetes among women with high serum ferritin and iron levels and dietary haem iron intakes warrants further investigation.

Course of iron parameters in HFE-hemochromatosis patients during initial treatment with erythrocytapheresis compared to phlebotomy

Current treatment for newly diagnosed patients with hereditary hemochromatosis (HH) and iron overload consist of weekly phlebotomy or less frequent and more personalized erythrocytapheresis. Previous observations during phlebotomy suggest an increase in intestinal iron uptake caused by lowering of hepcidin as a result of intensive bloodletting. It is not known whether such an effect is present or even more pronounced using erythrocytapheresis since a larger amount of iron is extracted per procedure. In this study we aimed to assess the effect of erythrocytapheresis on the course of iron parameters, with special focus on serum hepcidin. We performed a retrospective proof-of-principle observational study, comparing serum iron parameters in 12 males during the depletion phase using either phlebotomy (n = 6) or erythrocytapheresis (n = 6). Decreases in serum ferritin over time were similar for both treatments but more pronounced using erythrocytapheresis when expressed per treatment procedure. Hemoglobin did not change during erythrocytapheresis, whereas during phlebotomy decreased with 10%. Increase of erythropoietin and soluble transferrin receptor and decrease in transferrin saturation were similar for both treatments. Reduction in serum hepcidin was higher (50% versus 25% of initial value) and occurred more early using phlebotomy (10 versus 20 weeks after start). In aggregate, compared to phlebotomy, the less frequent and more personalized erythrocytapheresis leads to a more pronounced decrease in serum ferritin per treatment procedure, without a larger decrease in serum hepcidin. This may be clinically relevant and may prevent an increase in intestinal iron uptake and an ensuing vicious circle of more frequent treatment procedures. J. Clin. Apheresis 31:564-570, 2016. © 2015 Wiley Periodicals, Inc.

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.

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.

Diagnosis and treatment of hereditary hemochromatosis: an update

Hereditary hemochromatosis is an inherited iron overload disorder caused by inappropriately low hepcidin secretion leading to increased duodenal absorption of dietary iron, most commonly in C282Y homozygous individuals. This can result in elevated serum ferritin, iron deposition in various organs and ultimately end-organ damage, although there is incomplete biochemical and clinical penetrance and variable phenotypic expression of the HFE mutation in hereditary hemochromatosis. An elevated SF >1000 mg/l [corrected] is associated with an increased risk of cirrhosis and mortality in C282Y homozygotes.Conversely, a SF <1000 µg/l is associated with a very low likelihood of cirrhosis, making liver biopsy unnecessary among C282Y homozygotes in the absence of concomitant risk factors for liver disease. Phlebotomy remains the mainstay of treatment and new treatments being studied include erythrocytapheresis and 'mini-hepcidins'. Iron overload is being recognized to play a carcinogenic role in hepatocellular carcinoma and other cancers, possibly supporting iron depletion in these patients.

Biomarkers of hypochromia: the contemporary assessment of iron status and erythropoiesis

Iron status is the result of the balance between the rate of erythropoiesis and the amount of the iron stores. Direct consequence of an imbalance between the erythroid marrow iron requirements and the actual supply is a reduction of red cell hemoglobin content, which causes hypochromic mature red cells and reticulocytes. The diagnosis of iron deficiency is particularly challenging in patients with acute or chronic inflammatory conditions because most of the biochemical markers for iron metabolism (serum ferritin and transferrin ) are affected by acute phase reaction. For these reasons, interest has been generated in the use of erythrocyte and reticulocyte parameters, available on the modern hematology analyzers. Reported during blood analysis routinely performed on the instrument, these parameters can assist in early detection of clinical conditions (iron deficiency, absolute, or functional; ineffective erythropoiesis, including iron restricted or thalassemia), without additional cost. Technological progress has meant that in recent years modern analyzers report new parameters that provide further information from the traditional count. Nevertheless these new parameters are exclusive of each manufacturer, and they are patented. This is an update of these new laboratory test biomarkers of hypochromia reported by different manufactures, their meaning, and clinical utility on daily practice.

Reference measurement procedures for the iron saturation in human transferrin based on IDMS and Raman scattering

Two reference measurement procedures are presented here that allow the determination of the iron saturation in human transferrin, based on different molecular properties. The results, directly derived from the number of ions bound to the protein molecule, are traceable to the SI. Up to now, the iron saturation has only been deduced indirectly from the amount-of-substance ratio of serum iron to transferrin in serum. Interlaboratory tests have shown the need for more accurate methods, as the results from many participant test samples for both parameters do not lie within the acceptable range of deviation given by relevant guidelines when different methods or kits are applied. Using isotope dilution, an HPLC ICP-MS procedure was developed in compliance with the requirements of a primary reference measurement procedure. In this manner, the iron saturation was measured with an associated relative expanded measurement uncertainty of 4%. Based on the results, a straightforward Raman procedure was evolved, which allows the determination of the iron saturation in transferrin with an associated relative expanded uncertainty of 7%.

Non-HFE hemochromatosis

Hereditary hemochromatosis (HH) is an autosomal recessive disorder classically related to HFE mutations. However, since 1996, it is known that HFE mutations explain about 80% of HH cases, with the remaining around 20% denominated non-HFE hemochromatosis. Nowadays, four main genes are implicated in the pathophysiology of clinical syndromes classified as non-HFE hemochromatosis: hemojuvelin (HJV, type 2Ajuvenile HH), hepcidin (HAMP, type 2B juvenile HH), transferrin receptor 2 (TFR2, type 3 HH) and ferroportin (SLC40A1, type 4 HH). The aim of this review is to explore molecular, clinical and management aspects of non-HFE hemochromatosis.

Sample-to-SNP kit: a reliable, easy and fast tool for the detection of HFE p.H63D and p.C282Y variations associated to hereditary hemochromatosis

Classical hereditary hemochromatosis involves the HFE-gene and diagnostic analysis of the DNA variants HFE p.C282Y (c.845G>A; rs1800562) and HFE p.H63D (c.187C>G; rs1799945). The affected protein alters the iron homeostasis resulting in iron overload in various tissues. The aim of this study was to validate the TaqMan-based Sample-to-SNP protocol for the analysis of the HFE-p.C282Y and p.H63D variants with regard to accuracy, usefulness and reproducibility compared to an existing SNP protocol. The Sample-to-SNP protocol uses an approach where the DNA template is made accessible from a cell lysate followed by TaqMan analysis. Besides the HFE-SNPs other eight SNPs were used as well. These SNPs were: Coagulation factor II-gene F2 c.20210G>A, Coagulation factor V-gene F5 p.R506Q (c.1517G>A; rs121917732), Mitochondria SNP: mt7028 G>A, Mitochondria SNP: mt12308 A>G, Proprotein convertase subtilisin/kexin type 9-gene PCSK9 p.R46L (c.137G>T), Plutathione S-transferase pi 1-gene GSTP1 p.I105V (c313A>G; rs1695), LXR g.-171 A>G, ZNF202 g.-118 G>T. In conclusion the Sample-to-SNP kit proved to be an accurate, reliable, robust, easy to use and rapid TaqMan-based SNP detection protocol, which could be quickly implemented in a routine diagnostic or research facility.

Acute acetaminophen intoxication leads to hepatic iron loading by decreased hepcidin synthesis

Acetaminophen (APAP), a major cause of acute liver injury in the Western world, is mediated by metabolism and oxidative stress. Recent studies have suggested a role for iron in potentiating APAP-induced liver injury although its regulatory mechanism is not completely understood. The current study was designed to unravel the iron-regulating pathways in mice after APAP-induced hepatotoxicity. Mice with severe injury showed a significant increase in liver iron concentration and oxidative stress. Concurrently, the plasma concentration of hepcidin, the key regulator in iron metabolism, and hepatic hepcidin antimicrobial peptide (Hamp) mRNA expression levels were significantly reduced. We showed that hepcidin transcription was inhibited via several hepcidin-regulating factors, including the bone morphogenetic protein/small mother against decapentaplegic (BMP/SMAD) pathway, CCAAT/enhancer-binding protein α (C/EBPα), and possibly also via erythropoietin (EPO). Downregulation of the BMP/SMAD signaling pathway was most likely caused by hypoxia-inducible factor 1α (HIF-1α), which was increased in mice with severe APAP-induced liver injury. HIF-1α stimulates cleaving of hemojuvelin, the cofactor of the BMP receptor, thereby blocking BMP-induced signaling. In addition, gene expression levels of C/ebpα were significantly reduced, and Epo mRNA expression levels were significantly increased after APAP intoxication. These factors are regulated through HIF-1α during oxidative stress and suggest that HIF-1α is a key modulator in reduced hepcidin transcription after APAP-induced hepatotoxicity. In conclusion, acute APAP-induced liver injury leads to activation of HIF-1α, which results in a downregulation in hepcidin expression through a BMP/SMAD signaling pathway and through C/EBPα inhibition. Eventually, this leads to hepatic iron loading associated with APAP cytotoxicity.

Molecular diagnostic and pathogenesis of hereditary hemochromatosis

Hereditary hemochromatosis (HH) is an autosomal recessive disorder characterized by enhanced intestinal absorption of dietary iron. Without therapeutic intervention, iron overload leads to multiple organ damage such as liver cirrhosis, cardiomyopathy, diabetes, arthritis, hypogonadism and skin pigmentation. Most HH patients carry HFE mutant genotypes: homozygosity for p.Cys282Tyr or p.Cys282Tyr/p.His63Asp compound heterozygosity. In addition to HFE gene, mutations in the genes that encode hemojuvelin (HJV), hepcidin (HAMP), transferrin receptor 2 (TFR2) and ferroportin (SLC40A1) have been associated with regulation of iron homeostasis and development of HH. The aim of this review was to identify the main gene mutations involved in the pathogenesis of type 1, 2, 3 and 4 HH and their genetic testing indication. HFE testing for the two main mutations (p.Cys282Tyr and p.His63Asp) should be performed in all patients with primary iron overload and unexplained increased transferrin saturation and/or serum ferritin values. The evaluation of the HJV p.Gly320Val mutation must be the molecular test of choice in suspected patients with juvenile hemochromatosis with less than 30 years and cardiac or endocrine manifestations. In conclusion, HH is an example that genetic testing can, in addition to performing the differential diagnostic with secondary iron overload, lead to more adequate and faster treatment.

Hepcidin in human iron disorders: diagnostic implications

BACKGROUND

The peptide hormone hepcidin plays a central role in regulating dietary iron absorption and body iron distribution. Many human diseases are associated with alterations in hepcidin concentrations. The measurement of hepcidin in biological fluids is therefore a promising tool in the diagnosis and management of medical conditions in which iron metabolism is affected.

CONTENT

We describe hepcidin structure, kinetics, function, and regulation. We moreover explore the therapeutic potential for modulating hepcidin expression and the diagnostic potential for hepcidin measurements in clinical practice.

SUMMARY

Cell-culture, animal, and human studies have shown that hepcidin is predominantly synthesized by hepatocytes, where its expression is regulated by body iron status, erythropoietic activity, oxygen tension, and inflammatory cytokines. Hepcidin lowers serum iron concentrations by counteracting the function of ferroportin, a major cellular iron exporter present in the membrane of macrophages, hepatocytes, and the basolateral site of enterocytes. Hepcidin is detected in biologic fluids as a 25 amino acid isoform, hepcidin-25, and 2 smaller forms, i.e., hepcidin-22 and -20; however, only hepcidin-25 has been shown to participate in the regulation of iron metabolism. Reliable assays to measure hepcidin in blood and urine by use of immunochemical and mass spectrometry methods have been developed. Results of proof-of-principle studies have highlighted hepcidin as a promising diagnostic tool and therapeutic target for iron disorders. However, before hepcidin measurements can be used in routine clinical practice, efforts will be required to assess the relevance of hepcidin isoform measurements, to harmonize the different assays, to define clinical decision limits, and to increase assay availability for clinical laboratories.

Four variants in transferrin and HFE genes as potential markers of iron deficiency anaemia risk: an association study in menstruating women

BACKGROUND

Iron deficiency anaemia is a worldwide health problem in which environmental, physiologic and genetic factors play important roles. The associations between iron status biomarkers and single nucleotide polymorphisms (SNPs) known to be related to iron metabolism were studied in menstruating women.

METHODS

A group of 270 Caucasian menstruating women, a population group at risk of iron deficiency anaemia, participated in the study. Haematological and biochemical parameters were analysed and 10 selected SNPs were genotyped by minisequencing assay. The associations between genetic and biochemical data were analysed by Bayesian Model Averaging (BMA) test and decision trees. Dietary intake of a representative subgroup of these volunteers (n = 141) was assessed, and the relationship between nutrients and iron biomarkers was also determined by linear regression.

RESULTS

Four variants, two in the transferrin gene (rs3811647, rs1799852) and two in the HFE gene (C282Y, H63D), explain 35% of the genetic variation or heritability of serum transferrin in menstruating women. The minor allele of rs3811647 was associated with higher serum transferrin levels and lower transferrin saturation, while the minor alleles of rs1799852 and the C282Y and H63D mutations of HFE were associated with lower serum transferrin levels. No association between nutrient intake and iron biomarkers was found.

CONCLUSIONS

In contrast to dietary intake, these four SNPs are strongly associated with serum transferrin. Carriers of the minor allele of rs3811647 present a reduction in iron transport to tissues, which might indicate higher iron deficiency anaemia risk, although the simultaneous presence of the minor allele of rs1799852 and HFE mutations appear to have compensatory effects. Therefore, it is suggested that these genetic variants might potentially be used as markers of iron deficiency anaemia risk.

Effects of a single dose of oral iron on hepcidin concentrations in human urine and serum analyzed by a robust LC-MS/MS method

BACKGROUND

The measurement of serum hepcidin, a peptide hormone that regulates iron metabolism, is clinically important to the understanding of iron homeostasis in health and disease. To date, the quantification of serum hepcidin levels by conventional immunological detection methods has proven problematic due to challenges in obtaining high quality antibodies which demonstrate good reproducibility. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) has been employed recently for more sensitive quantification of hepcidin; however, this method has high background levels and therefore less than optimal specificity.

METHODS

In order to increase the specificity of the mass spectrometry based assay, we developed a robust, ultra-performance liquid-chromatography-tandem mass spectrometry (UPLC-MS/MS) protocol using multiple selected reaction monitoring (mSRM) for quantification of hepcidin levels in urine and serum of human subjects. With this assay, we assessed levels of hepcidin before and for up to 8 h after oral ingestion of ferrous sulfate in ten adult human subjects without known disease.

RESULTS

The linear response of hepcidin quantitation on each instrument was measured, and the correlation coefficients of these calibrations were r(2)=0.9512±0.0202 (n=5) for urine and r(2)=0.9709±0.0291 (n=5) for serum [r(2)=mean±SD]. Compared to baseline, the levels of urinary hepcidin between 2-4 h and 4-8 h of both women and men showed significant increases with p<0.05 and p<0.001, respectively. The levels of serum hepcidin between 4 h and 8 h in both women and men showed significant increases, compared with baseline values, with both p<0.01. Interestingly, we also observed some degree of oscillation of levels, occurring at later time points.

CONCLUSIONS

We have developed and validated a new method for measuring hepcidin concentrations in human serum and urine and used it to demonstrate early increases with iron supplement in both urinary and serum levels of hepcidin, which return to baseline levels, except in urine samples from men.

Treatment with iron of patients with heart failure with and without anemia

Iron deficiency is a common cause of anemia in otherwise healthy individuals and plays an important role in the development of anemia within the heart failure patient population. Iron-deficient heart failure patients experience worse symptoms and are less exercise tolerant than those without iron deficiency. These symptoms may occur even before clinical anemia is evident. This article reviews studies of the benefits of the use of intravenous iron to treat iron deficiency in anemic and nonanemic heart failure patients and an overview of the physiology and pathophysiology of iron metabolism in chronic heart failure.

Treatment of anemia in heart failure: potential risks and benefits of intravenous iron therapy in cardiovascular disease

Iron-deficiency anemia is common in patients with heart failure (HF), but the optimum diagnostic tests to detect iron deficiency and the treatment options to replete iron have not been fully characterized. Recent studies in patients with HF indicate that intravenous iron can rapidly replenish iron stores in patients having iron-deficiency anemia, with resultant increased hemoglobin levels and improved functional capacity. Preliminary data from a subgroup analysis also suggest that supplemental intravenous iron therapy can improve functional capacity even in those subjects without anemia. The mechanisms responsible for this observation are not fully characterized, but may be related to beneficial effects of iron supplementation on mitochondrial respiration in skeletal muscle. The long-term safety of using intravenous iron supplementation in HF populations is not known. Iron is a known pro-oxidant factor that can inhibit nitric oxide signaling and irreversibly injury cells. Increased iron stores are associated with vascular endothelial dysfunction and increased risk of coronary heart disease events. Additional clinical trials are needed to more fully characterize the therapeutic potential and safety of intravenous iron in HF patients.

Serum hepcidin: reference ranges and biochemical correlates in the general population

To date, concentrations of the promising biomarker hepcidin have only been assessed in serum of relatively small series of healthy volunteers and patients. We assessed age- and sex-stratified reference ranges of serum hepcidin concentration in a selected reference set and performed regression analyses to study associations between hepcidin and (biochemical) variables in a large, well-phenotyped sample of the general population (n = 2998). All participants filled out a questionnaire on lifestyle, health status, and medical history. Serum measurements of iron parameters, liver enzyme alanine aminotransferase, creatinine and C-reactive protein were available. Serum hepcidin concentrations were lower for premenopausal than for postmenopausal women (median, 4.1 nM vs 8.5 nM, respectively). Hepcidin concentrations in men were constant over age (median, 7.8 nM). Serum hepcidin was strongly associated with serum ferritin in men and women: β-coefficient of log-transformed variables (95% confidence interval): 0.78 (0.74-0.82) and 0.83 (0.78-0.88), respectively. Additional significant, though less strong, associations were observed for C-reactive protein and total iron binding capacity in men and for total iron binding capacity, alanine aminotransferase, and glomerular filtration rate in women. Our study provides age- and sex-specific reference ranges of serum hepcidin concentration and indicates ferritin as the primary correlate of serum hepcidin concentration.

Hereditary hemochromatosis: laboratory evaluation

The condition of hereditary hemochromatosis (HH) is caused by gene-dependent protein abnormalities involved in iron absorption, storage, or modulation of iron; these abnormalities result in iron overload. The clinical laboratory plays a significant role in case finding, diagnostic validation, and monitoring HH therapy. Elevated serum iron, transferrin saturation, and ferritin suggest HH, but results can also indicate other forms of hepatocyte injury such as alcoholic or viral hepatitis, or other inflammatory disorders involving the liver. In the context of elevated serum iron, transferrin saturation, and ferritin, and after ruling out secondary causes of iron overload, HFE gene evaluation is the preferred test to confirm the diagnosis of HH. However, 5% to 15% of patients with phenotypic HH do not have HFE gene mutations. In these cases, MRI evaluation or liver biopsy with iron quantification is indicated. The clinical role of hepcidin, the iron modulating protein, is undetermined at this time. Because hepcidin also plays a key role in antimicrobial and inflammatory activities, interpretation of hepcidin serum or urine concentration will require thorough understanding of its complex role in iron regulation.

Mass spectrometry analysis of hepcidin peptides in experimental mouse models

The mouse is a valuable model for unravelling the role of hepcidin in iron homeostasis, however, such studies still report hepcidin mRNA levels as a surrogate marker for bioactive hepcidin in its pivotal function to block ferroportin-mediated iron transport. Here, we aimed to assess bioactive mouse Hepcidin-1 (Hep-1) and its paralogue Hepcidin-2 (Hep-2) at the peptide level. To this purpose, fourier transform ion cyclotron resonance (FTICR) and tandem-MS was used for hepcidin identification, after which a time-of-flight (TOF) MS-based methodology was exploited to routinely determine Hep-1 and -2 levels in mouse serum and urine. This method was biologically validated by hepcidin assessment in: i) 3 mouse strains (C57Bl/6; DBA/2 and BABL/c) upon stimulation with intravenous iron and LPS, ii) homozygous Hfe knock out, homozygous transferrin receptor 2 (Y245X) mutated mice and double affected mice, and iii) mice treated with a sublethal hepatotoxic dose of paracetamol. The results showed that detection of Hep-1 was restricted to serum, whereas Hep-2 and its presumed isoforms were predominantly present in urine. Elevations in serum Hep-1 and urine Hep-2 upon intravenous iron or LPS were only moderate and varied considerably between mouse strains. Serum Hep-1 was decreased in all three hemochromatosis models, being lowest in the double affected mice. Serum Hep-1 levels correlated with liver hepcidin-1 gene expression, while acute liver damage by paracetamol depleted Hep-1 from serum. Furthermore, serum Hep-1 appeared to be an excellent indicator of splenic iron accumulation. In conclusion, Hep-1 and Hep-2 peptide responses in experimental mouse agree with the known biology of hepcidin mRNA regulators, and their measurement can now be implemented in experimental mouse models to provide novel insights in post-transcriptional regulation, hepcidin function, and kinetics.

Hepcidin: a novel peptide hormone regulating iron metabolism

BACKGROUND

Hepcidin is a low-molecular weight hepatic peptide regulating iron homeostasis. Hepcidin inhibits the cellular efflux of iron by binding to, and inducing the internalization and degradation of, ferroportin, the exclusive iron exporter in iron-transporting cells. It has been recently recognized as a main hormone behind anemia of chronic disease.

METHOD

A comprehensive literature search was conducted from the websites of Pubmed Central, the US National Library of Medicine's digital archive of life sciences literature (http://www.pubmedcentral.nih.gov/) and the National Library of Medicine (http://www.ncbl.nlm.nih.gov). The data was also assessed from journals and books that published relevant articles in this field.

RESULT

Hepcidin regulates iron uptake constantly on a daily basis, to maintain sufficient iron stores for erythropoiesis. Hepcidin, by its iron regulatory action on iron metabolism may be expected to have an important role in immune regulation, inflammatory diseases and malignancies. Hepcidin is the underlying cause of anemia in these clinical settings.

CONCLUSION

Hepcidin analysis may prove to be a novel tool for differential diagnosis and monitoring of disorders of iron metabolism, and establishment of therapeutic measures in various disease conditions like hereditary hemochromatosis, anemia associated with chronic kidney disease, rheumatoid arthritis and cancers.

Design and Rationale for the Study of Changes in Iron and Atherosclerosis Risk in Perimenopause

This study seeks to investigate changes in iron homeostasis and carotid arteries in women at risk of atherosclerosis, addressing a relatively unexplored hypothesis explaining why women have a 5-10 year lag in initial atherosclerotic events. Recent evidence points to hepcidin, the key regulator of macrophage iron uptake and release, as a potential mediator of risk. Furthermore, iron catalyzes the generation of free radicals that oxidize cholesterol stimulating atheroma formation. Magnetic resonance imaging (MRI) is ideally suited to study iron because of iron's local effects on magnetic susceptibility that can be quantified using a relaxation parameter called T2* ('T2-star'), as well as the ability to noninvasively characterize and quantify atherosclerotic plaque with MRI. This work outlines the rationale and study design to provide critical evidence related to the iron hypothesis, such that novel diagnostics and therapeutics to attenuate risk may be derived from a better understanding of iron's role in atherosclerosis.

Ferritin concentrations in synovial fluid are higher in osteoarthritis patients with HFE gene mutations (C282Y or H63D)

OBJECTIVES

In view of the clinical similarities between polyarticular osteoarthritis (POA) with metacarpophalangeal (MCP) joint involvement and the arthropathy that occurs in hereditary haemochromatosis (HH), it was hypothesized that osteochondral damage in both disorders may be due to localized iron overload. Accordingly, it was predicted that the concentration of ferritin in synovial fluid (SF) would be higher in OA patients with HFE gene mutations than in HFE wild-type (wt) OA patients. The aim of this study was to test this proposition.

METHODS

Sequential patients with physician-diagnosed OA and, for comparison, diverse inflammatory diseases of the joints, who required diagnostic or therapeutic arthrocentesis, were studied. Participants underwent HFE genotyping. SF samples were assayed for ferritin and also for selected cytokines and matrix metalloproteinases (MMPs).

RESULTS

Seventy-three patients with diverse rheumatic disorders were recruited. Of the 29 patients who had knee OA, 15 were wt and 14 were heterozygous for HFE mutations (C282Y or H63D). Mean SF ferritin concentrations in the wt and heterozygous OA groups were 273 and 655 ng/mL, respectively (p = 0.0146).

CONCLUSIONS

A predicted difference in SF ferritin concentrations in patients with knee OA was confirmed. Concentrations of ferritin in the SF were found to be two- to threefold higher in knee OA patients with HFE gene mutations compared to wt patients. This finding is consistent with the possibility that, in OA patients with HFE gene mutations, localized iron overload may contribute either directly or indirectly to osteochondral damage, possibly in a similar way to that which occurs in the arthropathy that complicates HH.

HFE gene mutations in patients with primary iron overload: is there a significant improvement in molecular diagnosis yield with HFE sequencing?

Rare HFE variants have been shown to be associated with hereditary hemochromatosis (HH), an iron overload disease. The low frequency of the HFE p.C282Y mutation in HH-affected Brazilian patients may suggest that other HFE-related mutations may also be implicated in the pathogenesis of HH in this population. The main aim was to screen for new HFE mutations in Brazilian individuals with primary iron overload and to investigate their relationship with HH. Fifty Brazilian patients with primary iron overload (transferrin saturation>50% in females and 60% in males) were selected. Subsequent bidirectional sequencing for each HFE exon was performed. The effect of HFE mutations on protein structure were analyzed by molecular dynamics simulation and free binding energy calculations. p.C282Y in homozygosis or in heterozygosis with p.H63D were the most frequent genotypic combinations associated with HH in our sample population (present in 17 individuals, 34%). Thirty-six (72.0%) out of the 50 individuals presented at least one HFE mutation. The most frequent genotype associated with HH was the homozygous p.C282Y mutation (n=11, 22.0%). One novel mutation (p.V256I) was indentified in heterozygosis with the p.H63D mutation. In silico modeling analysis of protein behavior indicated that the p.V256I mutation does not reduce the binding affinity between HFE and β2-microglobulin (β2M) in the same way the p.C282Y mutation does compared with the native HFE protein. In conclusion, screening of HFE through direct sequencing, as compared to p.C282Y/p.H63D genotyping, was not able to increase the molecular diagnosis yield of HH. The novel p.V256I mutation could not be implicated in the molecular basis of the HH phenotype, although its role cannot be completely excluded in HH-phenotype development. Our molecular modeling analysis can help in the analysis of novel, previously undescribed, HFE mutations.

The C282Y polymorphism of the hereditary hemochromatosis gene is associated with increased sex hormone-binding globulin and normal testosterone levels in men

BACKGROUND

Hereditary hemochromatosis resulting either from homozygosity for the C282Y polymorphism of the HFE gene, or compound heterozygosity for C282Y and H63D, manifests with liver disease and hypogonadism. However, it is unclear whether men who are heterozygotes for C282Y or H63D exhibit subtle abnormalities of sex hormone status.

AIMS

To evaluate whether heterozygosity for either of the HFE gene polymorphisms C282Y or H63D is associated with circulating testosterone and SHBG in men.

SUBJECTS AND METHODS

We performed a cross-sectional analysis of 388 community-dwelling men. Men were genotyped for C282Y and H63D. Sera were analysed for testosterone and SHBG, and insulin resistance was estimated using a homeostatic model (HOMA2-IR).

RESULTS

Mean age of men in the cohort was 56.9 yr. Men who were heterozygous for the C282Y polymorphism in the HFE gene had higher SHBG levels than men who did not carry this polymorphism (mean ± SE, 38.2 ± 1.64 vs 32.8 ± 0.71 nmol/l, p=0.006). Total and free testosterone levels did not differ in the two groups. In multivariate analysis adjusting for potential confounders including age, waist circumference, testosterone, and HOMA2-IR, C282Y heterozygosity remained associated with SHBG levels (p<0.001).

CONCLUSION

The C282Y polymorphism is associated with SHBG levels in men who do not manifest iron overload. Further studies are needed to clarify potential mechanisms and determine the clinical relevance of this finding.

Hemochromatosis in Italy in the last 30 years: role of genetic and acquired factors

The clinical presentation of hereditary hemochromatosis has changed markedly in recent years. The aim of this study was to analyze a large series of consecutive Italian patients with hemochromatosis diagnosed between 1976 and 2007 to determine whether the genetic background and the presence of acquired risk factors influenced the severity of iron overload and the natural history of the disease. A cohort of 452 Italian patients with iron overload-338 HFE-related (C282Y homozygotes or compound C82Y/H63D heterozygotes) and 114 non-HFE-related-were followed prospectively for a median of 112 months. Alcohol intake, smoking habits, and iron removed to depletion were similar in patients with and without HFE-related iron overload. Hepatitis B virus (4% and 9%; P = 0.04) and hepatitis C virus (6% and 19%; P = 0.002) infections were more frequent in patients with non-HFE-related iron overload. Seventy-three percent of patients with HFE and 61% of patients with non-HFE-related disease had no acquired risk factor. Cirrhosis was significantly more frequent in non-HFE patients independent of the presence of acquired risk factors (P = 0.02). Sex, alcohol intake, prevalence of smoking, hepatitis C virus infection, glucose, lipids, iron-related parameters, and prevalence of C282Y/H63D differed significantly over the years. At enrollment, cirrhosis was present in 145 cases and was significantly more frequent in the first decade (80%, 47%, and 13%; P = 0.001). Survival did not differ across the decades in cirrhotic patients; hepatocellular carcinoma occurred similarly in HFE and non-HFE patients.

CONCLUSION

Patients with HFE and non-HFE-related iron overload have comparable iron overload and similar clinical history. Patients who were diagnosed during the last 10 years and were not identified as cirrhotic at enrollment have less severe disease and lower prevalence of acquired risk factors, independent of genetic background.

Neogenin inhibits HJV secretion and regulates BMP-induced hepcidin expression and iron homeostasis

Neogenin, a deleted in colorectal cancer (DCC) family member, has been identified as a receptor for the neuronal axon guidance cues netrins and repulsive guidance molecules repulsive guidance molecules (RGM). RGMc, also called hemojuvelin (HJV), is essential for iron homeostasis. Here we provide evidence that neogenin plays a critical role in iron homeostasis by regulation of HJV secretion and bone morphogenetic protein (BMP) signaling. Livers of neogenin mutant mice exhibit iron overload, low levels of hepcidin, and reduced BMP signaling. Mutant hepatocytes in vitro show impaired BMP2 induction of Smad1/5/8 phosphorylation and hepcidin expression. Neogenin is expressed in liver cells in a reciprocal pattern to that of hepcidin, suggesting that neogenin functions in a cell nonautonomous manner. Further studies demonstrate that neogenin may stabilize HJV, a glycosylphosphatidylinositol-anchored protein that interacts with neogenin and suppresses its secretion. Taken together, our results lead the hypothesis that neogenin regulates iron homeostasis via inhibiting secretion of HJV, an inhibitor of BMP signaling, to enhance BMP signaling and hepcidin expression. These results reveal a novel mechanism underlying neogenin regulation of HJV-BMP signaling.

Iron deficiency and frequency of HFE C282Y gene mutation in Brazilian blood donors

Limited data are available about iron deficiency (ID) in Brazilian blood donors. This study evaluated the frequencies of ID and iron-deficiency anaemia (IDA) separately and according to frequency of blood donations. The protective effect of the heterozygous genotype for HFE C282Y mutation against ID and IDA in female blood donors was also determined. Five hundred and eight blood donors were recruited at the Blood Bank of Santa Casa in Sao Paulo, Brazil. Haemoglobin and serum ferritin concentrations were measured. The genotype for HFE C282Y mutation was determined by polymerase chain reaction followed by restriction fragment length polymorphism analysis. The ID was found in 21.1% of the women and 2.6% of the men whereas the IDA was found in 6.8 and 0.3%, respectively. The ID was found in 11.9% of the women in group 1 (first-time blood donors) and the frequency increased to 38.9% in women of the group 3 (blood donors donating once or more times in the last 12 months). No ID was found in men from group 1; however the ID frequency increased to 0.9% in group 2 (who had donated blood before but not in the last 12 months) and 5.0% in group 3. In summary, the heterozygous genotype was not associated with reduction of ID or IDA frequencies in both genders, but in male blood donors it was associated with a trend to elevated ferritin levels (P = 0.060). ID is most frequent in Brazilian women but was also found in men of group 3.

HFE gene mutations and iron status of Brazilian blood donors

Mutations of the HFE and TFR2 genes have been associated with iron overload. HFE and TFR2 mutations were assessed in blood donors, and the relationship with iron status was evaluated. Subjects (N = 542) were recruited at the Hemocentro da Santa Casa de São Paulo, São Paulo, Brazil. Iron status was not influenced by HFE mutations in women and was independent of blood donation frequency. In contrast, men carrying the HFE 282CY genotype had lower total iron-binding capacity (TIBC) than HFE 282CC genotype carriers. Men who donated blood for the first time and were carriers of the HFE 282CY genotype had higher transferrin saturation values and lower TIBC concentrations than those with the homozygous wild genotype for the HFE C282Y mutation. Moreover, in this group of blood donors, carriers of HFE 63DD plus 63HD genotypes had higher serum ferritin values than those with the homozygous wild genotype for HFE H63D mutation. Multiple linear regression analysis showed that HFE 282CY leads to a 17.21% increase (P = 0.018) and a 83.65% decrease (P = 0.007) in transferrin saturation and TIBC, respectively. In addition, serum ferritin is influenced by age (3.91%, P = 0.001) and the HFE 63HD plus DD genotype (55.84%, P = 0.021). In conclusion, the HFE 282Y and 65C alleles were rare, while the HFE 63D allele was frequent in Brazilian blood donors. The HFE C282Y and H63D mutations were associated with alterations in iron status in blood donors in a gender-dependent manner.

Hepcidin suppression and defective iron recycling account for dysregulation of iron homeostasis in heme oxygenase-1 deficiency

Heme oxygenase-1 (HO-1) contribution to iron homeostasis has been postulated, because it facilitates iron recycling by liberating iron mostly from heme catabolism. This enzyme also appears to be responsible for the resolution of inflammatory conditions. In a patient with HO-1 deficiency, inflammation and dysregulation of body iron homeostasis, including anemia and liver and kidney hemosiderosis, are evidenced. Here we postulated that HO-1 is critical in the regulation of ferroportin, the major cellular iron exporter, and hepcidin, the key regulator of iron homeostasis central in the pathogenesis of anemia of inflammation. Our current experiments in human THP-1 monocytic cells indicate a HO-1-induced iron-mediated surface-ferroportin expression, consistent with the role of HO-1 in iron recycling. Surprisingly, we observed low hepcidin levels in the HO-1-deficient patient, despite the presence of inflammation and hemosiderosis, both inducers of hepcidin. Instead, we observed highly increased soluble transferrin receptor levels. This suggests that the decreased hepcidin levels in HO-1 deficiency reflect the increased need for iron in the bone marrow due to the anaemia. Using human hepatoma cells, we demonstrate that HO-activity did not have a direct modulating effect on expression of HAMP, the gene that encodes for hepcidin. Therefore, we argue that the decreased iron recycling may, in part, have contributed to the low hepcidin levels. These findings indicate that dysregulation of iron homeostasis in HO-1 deficiency is the result of both defective iron recycling and erythroid activity-associated inhibition of hepcidin expression. This study therefore shows a crucial role for HO-1 in maintaining body iron balance.

Hepcidin assay in serum by SELDI-TOF-MS and other approaches

Hepcidin, a liver peptide hormone, is the central regulator of iron homeostasis. Hepcidin synthesis is modulated by iron stores, so that iron repletion increases its levels to prevent pathological overload, while iron deficiency strongly inhibits hepcidin to allow an increase in iron absorption from duodenal cells. The emerging pivotal role of hepcidin in iron homeostasis, along with its important links with basic pathways like inflammation, makes the availability of an accurate hepcidin assay as a potentially powerful investigative tool to improve our understanding as well as our diagnostic/prognostic capabilities in many human diseases. There has been a great interest worldwide in developing a reliable and widely applicable assay of the hormone in biological fluids. Being optimal for low-molecular-weight biomarkers, SELDI-TOF-MS has emerged as a valid tool for hepcidin assay. Here we review recent results obtained with this technique, as well as with other Mass Spectrometry-based and immunological methods.

Time-course analysis of serum hepcidin, iron and cytokines in a C282Y homozygous patient with Schnitzler's syndrome treated with IL-1 receptor antagonist

It is currently unknown if the increase of the hepatic iron regulatory hormone hepcidin during inflammation in man depends on an intact HFE-protein. Here we describe the temporal relationship of serum hepcidin, serum iron and cytokines in a patient with HFE-related (C282Y homozygous) hereditary hemochromatosis who was treated for an auto-inflammatory condition, i.e. variant Schnitzler's syndrome, with the potent anti-inflammatory cytokine inter-leukin-1 receptor antagonist (IL-1ra, anakinra). The patient had bouts of fever with peaking serum IL-6 concentrations followed by peaking serum hepcidin levels, while serum iron was low. Upon treatment, these peaks disappeared and hepcidin levels became non-detectable, consistent with HFE deficiency. In conclusion, this in vivo human model: i) supports the importance of an HFE-independent IL-6-hepcidin axis in the development of hypoferremia and anemia of inflammation; and ii) suggests that chronic inflammation protects patients with HFE-related hereditary hemochromatosis from iron accumulation.