Erythropoietin regulates intestinal iron absorption in a rat model of chronic renal failure

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

OBJECTIVES

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSION

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

Managing Anemia: Point of Convergence for Heart Failure and Chronic Kidney Disease?

The pathologic triangle formed by chronic heart failure (HF), chronic kidney disease (CKD), and anemia carries high morbidity and mortality rates and decreases quality of life. Anemia represents a common condition in patients with advanced HF and CKD, with a total prevalence in cardiorenal syndrome (CRS) ranging from 5% to 55%. Searching for a pragmatic approach for these patients with guided and disease-specific recommendations beyond just targeted hemoglobin therapeutic behavior represents the core of research for ongoing clinical trials. It is well known that the prevalence of anemia increases with the advancement of CKD and HF. The physiopathological mechanisms of anemia, such as the reduction of endogenous erythropoietin and the decrease in oxygen transport, are leading to tissue hypoxia, peripheral vasodilation, stimulating neurohormonal activity, and maintenance of the progressive renal and cardiac dysfunction. Given the challenges with the treatment options for patients with cardiorenal anemia syndrome (CRSA), new therapeutic agents such as hypoxia-inducible factor-prolyl hydroxylase domain inhibitors (HIF-PH) or hepcidin antagonists are emerging in the light of recent research. This review summarizes the potential therapeutic tools for anemia therapy in the cardiorenal population.

C-FGF23 peptide alleviates hypoferremia during acute inflammation

Hypoferremia results as an acute phase response to infection and inflammation aiming to reduce iron availability to pathogens. Activation of toll-like receptors (TLR), the key sensors of the innate immune system, induces hypoferremia mainly through the rise of the iron hormone hepcidin. Conversely, stimulation of erythropoiesis suppresses hepcidin expression via induction of the erythropoietin-responsive hormone erythroferrone. Iron deficiency stimulates transcription of the osteocyte- secreted protein FGF23. Here we hypothesized that induction of FGF23 in response to TLR4 activation is a potent contributor to hypoferremia and, thus, impairment of its activity may alleviate hypoferremia induced by lipopolysaccharide (LPS), a TLR 4 agonist. We used the C-terminal tail of FGF23 to impair endogenous full-length FGF23 signaling in wildtype mice, and investigated its impact on hypoferremia. Our data show that FGF23 is induced as early as pro-inflammatory cytokines in response to LPS, followed by upregulation of hepcidin and downregulation of erythropoietin (Epo) expression in addition to decreased serum iron and transferrin saturation. Further, LPS-induced hepatic and circulating hepcidin were significantly reduced by FGF23 signaling disruption. Accordingly, iron sequestration in liver and spleen caused by TLR4 activation was completely abrogated by FGF23 signaling inhibition, resulting in alleviation of serum iron and transferrin saturation deficit. Taken together, our studies highlight for the first time that inhibition of FGF23 signaling alleviates LPS-induced acute hypoferremia.

Perinatal and early-life cobalt exposure impairs essential metal metabolism in immature ICR mice

The objective of the present study was to assess the impact of cobalt (Co) exposure on tissue distribution of iron (Fe), copper (Cu), manganese (Mn), and zinc (Zn), as well as serum hepcidin levels in immature mice (18, 25, 30 days). Pregnant mice were exposed to 75 mg/kg b.w. cobalt chloride (CoCl₂ × 6H2O) with drinking water starting from 3 days before delivery and during lactation. At weaning (day 25) the offspring were separated and housed in individual cages with subsequent exposure to 75 mg/kg b.w. CoCl₂ until 30 days postnatally. Evaluation of tissue metal levels was performed by an inductively coupled plasma-mass spectrometry (ICP-MS). Serum hepcidin level was assayed by enzyme linked immunosorbent assay (ELISA). Cobalt exposure resulted in a time- and tissue-dependent increase in Co levels in kidney, spleen, liver, muscle, erythrocytes, and serum on days 18, 25, and 30. In parallel with increasing Co levels, CoCl₂ exposure resulted in a significant accumulation of Cu, Fe, Mn, and Zn in the studied tissues, with the effect being most pronounced in 25-day-old mice. Cobalt exposure significantly increased serum hepcidin levels only in day18 mice. The obtained data demonstrate that Co exposure may alter essential metal metabolism in vivo.

New insights into the links between hypoxia and iron homeostasis

Purpose of review

This review outlines recent discoveries on the crosstalk between oxygen metabolism and iron homeostasis, focusing on the role of HIF-2 (hypoxia inducible factor-2) in the regulation of iron metabolism under physiopathological conditions.

Recent findings

The importance of the hepcidin/ferroportin axis in the modulation of intestinal HIF-2 to regulate iron absorption has been recently highlighted. Latest advances also reveal a direct titration of the bone morphogenetic proteins by the erythroferrone contributing to liver hepcidin suppression to increase iron availability. Iron is recycled thanks to erythrophagocytosis of senescent erythrocytes by macrophages. Hemolysis is frequent in sickle cell anemia, leading to increased erythrophagocytosis responsible of the macrophage polarization shift. New findings assessed the effects of hemolysis on macrophage polarization in the tumor microenvironment.

Summary

Hypoxia signaling links erythropoiesis with iron homeostasis. The use of HIF stabilizing or inhibiting drugs are promising therapeutic approaches in iron-associated diseases.

Anemia of Inflammation with An Emphasis on Chronic Kidney Disease

Iron is vital for a vast variety of cellular processes and its homeostasis is strictly controlled and regulated. Nevertheless, disorders of iron metabolism are diverse and can be caused by insufficiency, overload or iron mal-distribution in tissues. Iron deficiency (ID) progresses to iron-deficiency anemia (IDA) after iron stores are depleted. Inflammation is of diverse etiology in anemia of chronic disease (ACD). It results in serum hypoferremia and tissue hyperferritinemia, which are caused by elevated serum hepcidin levels, and this underlies the onset of functional iron-deficiency anemia. Inflammation is also inhibitory to erythropoietin function and may directly increase hepcidin level, which influences iron metabolism. Consequently, immune responses orchestrate iron metabolism, aggravate iron sequestration and, ultimately, impair the processes of erythropoiesis. Hence, functional iron-deficiency anemia is a risk factor for several ailments, disorders and diseases. Therefore, therapeutic strategies depend on the symptoms, severity, comorbidities and the associated risk factors of anemia. Oral iron supplements can be employed to treat ID and mild anemia particularly, when gastrointestinal intolerance is minimal. Intravenous (IV) iron is the option in moderate and severe anemic conditions, for patients with compromised intestinal integrity, or when oral iron is refractory. Erythropoietin (EPO) is used to treat functional iron deficiency, and blood transfusion is restricted to refractory patients or in life-threatening emergency situations. Despite these interventions, many patients remain anemic and do not respond to conventional treatment approaches. However, various novel therapies are being developed to treat persistent anemia in patients.

Erythropoietin inhalation enhances adult canine alveolar-capillary formation following pneumonectomy

Paracrine erythropoietin (EPO) signaling in the lung recruits endothelial progenitor cells, promotes cell maturation and angiogenesis, and is upregulated during canine postpneumonectomy (PNX) compensatory lung growth. To determine whether inhalational delivery of exogenous EPO augments endogenous post-PNX lung growth, adult canines underwent right PNX and received, via a permanent tracheal stoma, weekly nebulization of recombinant human EPO-containing nanoparticles or empty nanoparticles (control) for 16 wk. Lung function was assessed under anesthesia pre- and post-PNX. The remaining lobes were fixed for detailed morphometric analysis. Compared with control treatment, EPO delivery significantly increased serum EPO concentration without altering systemic hematocrit or hemoglobin concentration and abrogated post-PNX lipid oxidative stress damage. EPO delivery modestly increased post-PNX volume densities of the alveolar septum per unit of lung volume and type II epithelium and endothelium per unit of septal tissue volume in selected lobes. EPO delivery also augmented the post-PNX increase in alveolar double-capillary profiles, a marker of intussusceptive capillary formation, in all remaining lobes. EPO treatment did not significantly alter absolute resting lung volumes, lung and membrane diffusing capacities, alveolar-capillary blood volume, pulmonary blood flow, lung compliance, or extravascular alveolar tissue volumes or surface areas. Results established the feasibility of chronic inhalational delivery of growth-modifying biologics in a large animal model. Exogenous EPO selectively enhanced cytoprotection and alveolar angiogenesis in remaining lobes but not whole-lung extravascular tissue growth or resting function; the nonuniform response contributes to structure-function discrepancy, a major challenge for interventions aimed at amplifying the innate potential for compensatory lung growth.

Vitamin A deficiency modulates iron metabolism independent of hemojuvelin (Hfe2) and bone morphogenetic protein 6 (Bmp6) transcript levels

BACKGROUND

Considering that vitamin A deficiency modulates hepcidin expression and consequently affects iron metabolism, we evaluated the effect of vitamin A deficiency in the expression of genes involved in the hemojuvelin (HJV)-bone morphogenetic protein 6 (BMP6)-small mothers against decapentaplegic protein (SMAD) signaling pathway.

METHODS

Male Wistar rats were treated: control AIN-93G diet (CT), vitamin A-deficient diet (VAD), iron-deficient diet (FeD), vitamin A- and iron-deficient diet (VAFeD), or 12 mg all-trans retinoic acid (atRA)/kg diet.

RESULTS

Vitamin A deficiency (VAD) increased hepatic Bmp6 and Hfe2 mRNA levels and down-regulated hepatic Hamp, Smad7, Rarα, and intestinal Fpn1 mRNA levels compared with the control. The FeD rats showed lower hepatic Hamp, Bmp6, and Smad7 mRNA levels compared with those of the control, while in the VAFeD rats only Hamp and Smad7 mRNA levels were lower than those of the control. The VAFeD diet up-regulated intestinal Dmt1 mRNA levels in relation to those of the control. The replacement of retinyl ester by atRA did not restore hepatic Hamp mRNA levels; however, the hepatic Hfe2, Bmp6, and Smad7 mRNA levels were similar to the control. The atRA rats showed an increase of hepatic Rarα mRNA levels and a reduction of intestinal Dmt1 mRNA and Fpn1 levels compared with those of the control.

CONCLUSIONS

The HJV-BMP6-SMAD signaling pathway that normally activates the expression of hepcidin in iron deficiency is impaired by vitamin A deficiency despite increased expression of liver Bmp6 and Hfe2 mRNA levels and decreased expression of Smad7 mRNA. This response may be associated to the systemic iron deficiency and spleen iron retention promoted by vitamin A deficiency.

Effects of developmental iron deficiency and post-weaning iron repletion on the levels of iron transporter proteins in rats

BACKGROUND/OBJECTIVES

Iron deficiency in early life is associated with developmental problems, which may persist until later in life. The question of whether iron repletion after developmental iron deficiency could restore iron homeostasis is not well characterized. In the present study, we investigated the changes of iron transporters after iron depletion during the gestational-neonatal period and iron repletion during the post-weaning period.

MATERIALS/METHODS

Pregnant rats were provided iron-deficient (< 6 ppm Fe) or control (36 ppm Fe) diets from gestational day 2. At weaning, pups from iron-deficient dams were fed either iron-deficient (ID group) or control (IDR group) diets for 4 week. Pups from control dams were continued to be fed with the control diet throughout the study period (CON).

RESULTS

Compared to the CON, ID rats had significantly lower hemoglobin and hematocrits in the blood and significantly lower tissue iron in the liver and spleen. Hepatic hepcidin and BMP6 mRNA levels were also strongly down-regulated in the ID group. Developmental iron deficiency significantly increased iron transporters divalent metal transporter 1 (DMT1) and ferroportin (FPN) in the duodenum, but decreased DMT1 in the liver. Dietary iron repletion restored the levels of hemoglobin and hematocrit to a normal range, but the tissue iron levels and hepatic hepcidin mRNA levels were significantly lower than those in the CON group. Both FPN and DMT1 protein levels in the liver and in the duodenum were not different between the IDR and the CON. By contrast, DMT1 in the spleen was significantly lower in the IDR, compared to the CON. The splenic FPN was also decreased in the IDR more than in the CON, although the difference did not reach statistical significance.

CONCLUSIONS

Our findings demonstrate that iron transporter proteins in the duodenum, liver and spleen are differentially regulated during developmental iron deficiency. Also, post-weaning iron repletion efficiently restores iron transporters in the duodenum and the liver but not in the spleen, which suggests that early-life iron deficiency may cause long term abnormalities in iron recycling from the spleen.

[Use of intravenous iron supplementation in chronic kidney disease: Interests, limits, and recommendations for a better practice]

Iron deficiency is an important clinical concern in chronic kidney disease (CKD), giving rise to iron-deficiency anaemia, and various impaired cellular functions. Oral supplementation, in particular with ferrous salts, is associated with a high rate of gastro-intestinal side effects and is poorly absorbed, a problem that is avoided with intravenous (IV) irons. Recently, with the approval of the European Medicines Agency's Committee for Medicinal Products for Human Use, the French Agence nationale de sécurité du médicament et des produits de santé (ANSM) took adequate measures to minimize the risk of allergic reactions, by correction on the summary of intravenous iron products characteristics. All IV iron products should be prescribed, administered and injected, inside public or private hospitals exclusively, and a clinical follow-up after the infusion for at least 30 minutes is mandatory. The most stable intravenous iron complexes (low molecular weight iron dextran, ferric carboxymaltose, and iron isomaltoside 1000 [under agreement]) can be given in higher single doses and more rapidly than less recent preparations such as iron sucrose (originator or similars). Test doses are advisable for conventional low molecular weight iron dextrans, but are no more mandatory. Iron supplementation is recommended for all CKD patients with iron-deficiency anaemia and those who receive erythropoiesis-stimulating agents, whether or not they require dialysis. Intravenous iron is the preferred route of administration in haemodialysis patients, with randomized trials showing a significantly greater increase in haemoglobin levels for intravenous versus oral iron and a low rate of treatment-related adverse events during these trials. According ANSM, physicians should apply the product's label recommendations especially the posology. In the non-dialysis CKD population, the erythropoietic response is also significantly higher using intravenous versus oral iron, and tolerability is at least as good. Moreover in some non-dialysis patients, intravenous iron supplementation might avoid or at least delay the need for erythropoiesis-stimulating agents. Following the new ANSM's recommendations, we now have the ability to achieve iron stores replenishment correctly and conveniently in dialysis dependent and non-dialysis dependent CKD patients without compromising safety using the various pharmaceutical forms of iron products especially intravenous compounds.

Iron and oxygen sensing: a tale of 2 interacting elements?

Iron and oxygen metabolism are intimately linked with one another.

Effect of erythropoietin on hepatic cytochrome P450 expression and function in an adenine-fed rat model of chronic kidney disease

BACKGROUND AND PURPOSE

Erythropoietin (EPO) is used to treat anaemia associated with chronic kidney disease (CKD). Hypoxia is associated with anaemia and is known to cause a decrease in cytochrome P450 (P450) expression. As EPO production is regulated by hypoxia, we investigated the role of EPO on P450 expression and function.

EXPERIMENTAL APPROACH

Male Wistar rats were subjected to a 0.7% adenine diet for 4 weeks to induce CKD. The diet continued for an additional 2 weeks while rats received EPO by i.p. injection every other day. Following euthanasia, hepatic P450 mRNA and protein expression were determined. Hepatic enzyme activity of selected P450s was determined and chromatin immunoprecipitation was used to characterize binding of nuclear receptors involved in the transcriptional regulation of CYP2C and CYP3A.

KEY RESULTS

EPO administration decreased hepatic mRNA and protein expression of CYP3A2 (P < 0.05), but not CYP2C11. Similarly, EPO administration decreased CYP3A2 protein expression by 81% (P < 0.001). A 32% decrease (P < 0.05) in hepatic CYP3A enzymatic activity (Vmax ) was observed for the formation of 6βOH-testosterone in the EPO-treated group. Decreases in RNA pol II recruitment (P < 0.01), hepatocyte nuclear factor 4α binding (P < 0.05) and pregnane X receptor binding (P < 0.01) to the promoter region of CYP3A were also observed in EPO-treated rats.

CONCLUSIONS AND IMPLICATIONS

Our data show that EPO decreases the expression and function of CYP3A, but not CYP2C in rat liver.

Iron as the key modulator of hepcidin expression in erythroid antibody-mediated hypoplasia

Erythroid hypoplasia (EH) is a rare complication associated with recombinant human erythropoietin (rHuEPO) therapies, due to development of anti-rHuEPO antibodies; however, the underlying mechanisms remain poorly clarified. Our aim was to manage a rat model of antibody-mediated EH induced by rHuEPO and study the impact on iron metabolism and erythropoiesis. Wistar rats treated during 9 weeks with a high rHuEPO dose (200 IU) developed EH, as shown by anemia, reduced erythroblasts, reticulocytopenia, and plasmatic anti-rHuEPO antibodies. Serum iron was increased and associated with mRNA overexpression of hepatic hepcidin and other iron regulatory mediators and downregulation of matriptase-2; overexpression of divalent metal transporter 1 and ferroportin was observed in duodenum and liver. Decreased EPO expression was observed in kidney and liver, while EPO receptor was overexpressed in liver. Endogenous EPO levels were normal, suggesting that anti-rHuEPO antibodies blunted EPO function. Our results suggest that anti-rHuEPO antibodies inhibit erythropoiesis causing anemia. This leads to a serum iron increase, which seems to stimulate hepcidin expression despite no evidence of inflammation, thus suggesting iron as the key modulator of hepcidin synthesis. These findings might contribute to improving new therapeutic strategies against rHuEPO resistance and/or development of antibody-mediated EH in patients under rHuEPO therapy.

Anemia in Adenine-Induced Chronic Renal Failure and the Influence of Treatment With Gum Acacia Thereon

Anemia frequently complicates chronic kidney disease (CKD). We investigated here the effect of adenine-induced CKD in rats on erythrocyte count (EC), hematocrit (PCV) and hemoglobin (Hb) concentration, as well as on the activity of L-γ-glutamyl transferase (GGT) and the concentrations of iron (Fe), transferrin (Tf), ferritin (F), total iron binding capacity (TIBC) / unsaturated iron binding capacity (UIBC) and hepcidin (Hp) in serum and erythropoietin (Epo) in renal tissue. Renal damage was assessed histopathologically, and also by measuring the serum concentrations of the uremic toxin indoxyl sulfate (IS), creatinine, and urea, and by creatinine clearance. We also assessed the influence of concomitant treatment with gum acacia (GA) on the above analytes. Adenine feeding induced CKD, accompanied by significant decreases (P<0.05) in EC, PCV, and Hb, and in the serum concentrations of Fe, Tf, TIBC, UIBC and Epo. It also increased Hp and F levels. GA significantly ameliorated these changes in rats with CKD. A general improvement in the renal status of rats with CKD after GA is shown due to its anti-inflammatory and anti-oxidant actions, and reduction of the uremic toxin IS, which is known to suppress Epo production, and this may be a reason for its ameliorative actions on the indices of anemia studied.

Modulation of intestinal folate absorption by erythropoietin in vitro

Besides the direct stimulation of erythropoiesis, erythropoietin (EPO) therapy in renal anemia may also play a regulatory role in maintaining the homeostasis of hematopoietic nutrients. It has been reported that EPO can stimulate intestinal iron absorption. However, the involvement of EPO in intestinal folate absorption remains elusive. The objective of this study was to investigate the effect of EPO on intestinal transport of folate in vitro and to elucidate the possible mechanism(s) involved in this regulation. Transport assays of folic acid were performed in Caco-2 monolayers treated with EPO. The effect of EPO on the expression of transporters involved in the folate absorption was investigated. The possible involvement of three main EPO signaling pathways, the janus protein tyrosine kinase 2 (JAK-2) pathway, extracellular signal regulated kinases (ERK) pathway, and phosphatidylinositol 3 kinase/Akt (PI3K/Akt) pathway, in the transporter regulation was explored. The absorptive flux (apical to basolateral) of folic acid was enhanced by EPO treatment in a dose-dependent manner, which was companied with the significant up-regulation of reduced folate carrier (RFC) and apical proton coupled folate transporter (PCFT). The efflux (basolaterial to apical) of folic acid was enhanced only by the high dose of EPO treatment, which was associated with the significant up-regulation of apical multidrug resistance-associated protein 2 (MRP2). The expression levels of all of these transporters were up-regulated by EPO treatment in a dose- and time-dependent manner. Transporter expression in response to blocking EPO induced activation of JAK-2, ERK, and PI3K/Akt was changed to a different extent. As a conclusion, intestinal folate absorption was enhanced by EPO treatment in vitro. Our findings provided direct evidence to establish the correlation between EPO and folate homeostasis.

Iron depletion induced by bloodletting and followed by rhEPO administration as a therapeutic strategy in progressive multiple sclerosis: a pilot, open-label study with neurophysiological measurements

OBJECTIVES

To evaluate the concept that iron depletion (ID) induced by bloodletting and followed by recombinant human erythropoietin (rhEPO) administration could be a therapeutic strategy in progressive multiple sclerosis (PMS) and that it could be assessed by neurophysiological measurements.

PATIENTS AND METHODS

In four patients with PMS, bloodletting was performed until ID was induced, and then rhEPO was administered (300 UI/kg/week). The changes induced by the treatment were assessed by clinical scores, biological tests, and neurophysiological study of cortical excitability using transcranial magnetic stimulation techniques.

RESULTS

The treatment was well tolerated except for muscle cramps and one popliteal vein thrombosis in a patient confined to chair. ID was obtained within 28 weeks and was associated with endogenous production of EPO. No bloodletting was further required during a six-month period after introduction of rhEPO. At the end of the follow-up (up to one year), fatigue and walking capacities tended to improve in two patients. Neurophysiological changes were characterized by an increased cortical excitability, including a decrease of motor thresholds and an enhancement of intracortical facilitation and cerebellothalamocortical inhibition.

CONCLUSIONS

The combined ID-rhEPO therapy could authorize a prolonged administration of rhEPO in PMS patients, able to modify cortical excitability of the glutamatergic and gabaergic circuits. These preliminary data are encouraging to design a larger, controlled therapeutical trial to assess the value of such a strategy to improve functional symptoms in PMS patients, and maybe to prevent axonal degeneration. Neurophysiological measurements based on cortical excitability studies could provide sensitive parameters to evaluate treatment-induced changes in this context.

Iron absorption in Drosophila melanogaster

The way in which Drosophila melanogaster acquires iron from the diet remains poorly understood despite iron absorption being of vital significance for larval growth. To describe the process of organismal iron absorption, consideration needs to be given to cellular iron import, storage, export and how intestinal epithelial cells sense and respond to iron availability. Here we review studies on the Divalent Metal Transporter-1 homolog Malvolio (iron import), the recent discovery that Multicopper Oxidase-1 has ferroxidase activity (iron export) and the role of ferritin in the process of iron acquisition (iron storage). We also describe what is known about iron regulation in insect cells. We then draw upon knowledge from mammalian iron homeostasis to identify candidate genes in flies. Questions arise from the lack of conservation in Drosophila for key mammalian players, such as ferroportin, hepcidin and all the components of the hemochromatosis-related pathway. Drosophila and other insects also lack erythropoiesis. Thus, systemic iron regulation is likely to be conveyed by different signaling pathways and tissue requirements. The significance of regulating intestinal iron uptake is inferred from reports linking Drosophila developmental, immune, heat-shock and behavioral responses to iron sequestration.

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

Although earlier, seminal studies demonstrated that the gut per se has the intrinsic ability to regulate the rates of iron absorption, the spotlight in the past decade has been placed on the systemic regulation of iron homeostasis by the hepatic hormone hepcidin and the molecular mechanisms that regulate its expression. Recently, however, attention has returned to the gut based on the finding that hypoxia inducible factor-2 (HIF-2α) regulates the expression of key genes that contribute to iron absorption. Here we review the current understanding of the molecular mechanisms that regulate iron homeostasis in the gut by focusing on the role of HIF-2 under physiological steady-state conditions and in the pathogenesis of iron-related diseases. We also discuss implications for adapting HIF-2-based therapeutic strategies in iron-related pathological conditions.

Hypoplastic anemia in cartilage-hair hypoplasia-balancing between iron overload and chelation

OBJECTIVE

To evaluate the severity of iron overload and the success of iron chelation therapy in patients with cartilage-hair hypoplasia (CHH) and hypoplastic anemia, with particular focus on adverse effects of iron chelators.

STUDY DESIGN

Four of the 23 presently surviving Finnish patients with CHH under 18 years of age are dependent on regular red blood cell transfusions. Their hospital records were reviewed for history of anemia and chelation therapy. Cumulative iron load from transfusions was calculated. Efficacy of the chelation therapy was evaluated biochemically and by liver iron content assessments.

RESULTS

At the introduction of iron chelation, the patients had received on average 99 (37-151) transfusions; the mean cumulative iron overload was 4640 (800-8200) mg, the annual iron accumulation rate 0.35 (0.25-0.41) mg/kg/d, and the mean plasma ferritin was 2896 (1217-6240) μg/L. Liver iron content, determined by biopsy in 3 patients, was on average 20.0 (6.6-30.0) mg/g liver dry weight. All patients, except 1 with Hirschsprung disease, tolerated deferoxamine, deferiprone, and deferasirox therapy well, showing only mild adverse effects typical for the agents. Plasma ferritin levels and liver magnetic resonance imaging T2* of iron overload showed successful chelation.

CONCLUSION

Iron chelation is well tolerated in patients with CHH, with possible exception of patients with Hirschsprung disease. Successful chelation will prepare for hematopoietic stem cell transplantation in patients with CHH with persistent transfusion dependency.

Comparative Efficacy of Three Brands of Gum Acacia on Adenine-Induced Chronic Renal Failure in Rats

Gum acacia (GA) is used in pharmaceutical, cosmetic and food industries as an emulsifier and stabilizer, and in some countries in the traditional treatment of patients with chronic kidney disease (CKD). We have previously found that GA ameliorates adenine -induced chronic renal failure (CRF) in rats. Different brands of GA are commercially available, but their comparative efficacy against adenine-induced CKD is unknown. Here, we explored the effects of three different brands of GA (Sudanese GA, SupergumTM and GA from BDH) on some physiological, biochemical, and histological effects of adenine-induced CRF in rats. Adenine (0.75 %, w/w in feed, four weeks) reduced body weight, and increased urine output. It also induced significant increases in blood pressure, and in creatinine, urea, several inflammatory cytokines in plasma, and indices of oxidative stress, and caused histological damage in kidneys. Treatment of rats concomitantly with any of the three GA brands, significantly, and to a broadly similar extent, mitigated all the signs of CRF. The results suggested equivalent efficacy of these brands in antagonizing the CRF in this animal model. However, to enable standardization of different brands between laboratories, the use of the chemically well-characterized GA preparation (such as SupergumTM) is recommended.

Iron deficiency and heart failure: diagnostic dilemmas and therapeutic perspectives

Iron is a micronutrient essential for cellular energy and metabolism, necessary for maintaining body homoeostasis. Iron deficiency is an important co-morbidity in patients with heart failure (HF). A major factor in the pathogenesis of anaemia, it is also a separate condition with serious clinical consequences (e.g. impaired exercise capacity) and poor prognosis in HF patients. Experimental evidence suggests that iron therapy in iron-deficient animals may activate molecular pathways that can be cardio-protective. Clinical studies have demonstrated favourable effects of i.v. iron on the functional status, quality of life, and exercise capacity in HF patients. It is hypothesized that i.v. iron supplementation may become a novel therapy in HF patients with iron deficiency.

Timing and determinants of erythropoietin deficiency in chronic kidney disease

BACKGROUND AND OBJECTIVES

Anemia in patients with CKD is highly related to impaired erythropoietin (EPO) response, the timing and determinants of which remain unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study measured EPO levels and studied their relation to GFR measured by 51Cr-EDTA renal clearance (mGFR) in 336 all-stage CKD patients not receiving any erythropoiesis-stimulating agent.

RESULTS

In patients with anemia defined by World Health Organization criteria (hemoglobin [Hb] <13 g/dl in men and 12 g/dl in women), EPO response to Hb level varied by mGFR level. EPO and Hb levels were negatively correlated (r=-0.22, P=0.04) when mGFR was >30 ml/min per 1.73 m(2), whereas they were not correlated when mGFR was <30 (r=0.09, P=0.3; P for interaction=0.01). In patients with anemia, the ratio of observed EPO to the level predicted by the equation for their Hb level decreased from 0.72 (interquartile range, 0.57-0.95) for mGFR ≥60 ml/min per 1.73 m(2) to 0.36 (interquartile range, 0.16-0.69) for mGFR <15. Obesity, diabetes with nephropathy other than diabetic glomerulopathy, absolute iron deficiency, and high C-reactive protein concentrations were associated with increased EPO levels, independent of Hb and mGFR.

CONCLUSIONS

Anemia in CKD is marked by an early relative EPO deficiency, but several factors besides Hb may persistently stimulate EPO synthesis. Although EPO deficiency is likely the main determinant of anemia in patients with advanced CKD, the presence of anemia in those with mGFR >30 ml/min per 1.73 m(2) calls for other explanatory factors.

Renal anemia of inflammation: the name is self-explanatory

BACKGROUND

Anemia is inevitable as chronic kidney disease (CKD) advances. With the advent of erythropoietin-stimulating agents (ESAs), considerable improvement has been achieved in the management of anemia. However, some patients show a reduced response to ESAs.

METHODS

Many factors affect the response to ESA treatment. CKD is now considered as an inflammatory disorder and this understanding led to the recognition of the central role of inflammation in ESA resistance. Inflammation is related to untoward outcomes, including atherosclerosis and anemia, in the CKD population. Furthermore, recognition of deleterious effects of proinflammatory markers at different levels of erythropoiesis led to a change in the name of 'anemia of chronic disease' to anemia of inflammation.

RESULTS

The discovery of hepcidin as the major controller of iron metabolism in anemia of inflammation answered many questions regarding the interaction of erythropoietin, iron and bone marrow. Hepcidin production in the liver is driven by three major factors: inflammation, iron overload and anemia/hypoxia. Hepcidin levels are increased in patients with CKD due to the interaction of many factors; a comprehensive understanding of these pathways is thus critical in the effort to alleviate anemia of inflammation and ESA resistance.

CONCLUSION

In this review, we discussed the epidemiology, determinants and consequences of anemia of inflammation in CKD patients with special emphasis on the central role of hepcidin along with molecular pathways driving its production.

Increased hepcidin-25 and erythropoietin responsiveness in patients with cardio–renal anemia syndrome

Evaluation of: van der Putten K, Jie KE, van den Broek D et al.: Hepcidin-25 is a marker of the response rather than resistance to exogenous erythropoietin in chronic kidney disease/chronic heart failure patients. Eur. J. Heart Fail. 12(9), 943–950 (2010). Hepcidin is a key regulator controlling iron intestinal absorption and distribution through the body. The article by van der Putten et al. examined the association between hepcidin-25 and erythropoietin responsiveness and inflammation in erythropoietin-naive, iron-replete patients with chronic heart failure and chronic kidney disease. A cross-sectional observation revealed that serum hepcidin-25 was elevated almost twofold when compared with levels in healthy subjects. Hepcidin-25 was inversely correlated with hemoglobin (r2 = 0.18; p < 0.02), and positively with ferritin (r2 = 0.51; p < 0.01) and transferrin saturation (r2 = 0.14; p < 0.03), while it did not correlate with levels of IL-6 and highly sensitive C-reactive protein. They found that 2-week erythropoietin therapy (50 IU/kg/week) significantly decreased hepcidin-25 levels. The magnitude of the decrease in hepcidin-25 levels correlated with the increase in reticulocytes (r2 = 0.23; p < 0.03) and soluble transferrin receptor (r2 = 0.23; p = 0.03), but not with inflammatory markers. A decline in hepcidin-25 correlated with the increment of hemoglobin after 6 months (r2 = 0.49; p < 0.01). The findings convincingly suggest that hepcidin-25 may be useful in predicting erythropoietin responsiveness in stable chronic heart failure patients. However, further studies will be needed to establish clinically available methods to reliably measure hepcidin-25 level.