Tomas Ganz

Hepcidin, a liver-derived hormone, is the central regulator of systemic iron homeostasis. Elevated hepcidin levels contribute to iron-refractory iron-deficiency anemia and anemia of inflammation, both characterized by restricted iron availability. Current treatments, such as parenteral iron infusions, are often ineffective and pose risks of adverse reactions, underscoring the need for alternative therapeutic strategies targeting hepcidin. We previously identified a novel hepcidin regulatory pathway involving liver heparan sulfate (HS) proteoglycans (HSPGs), which modulate receptor-ligand interactions through their sulfated HS chains. Recently, we found that halofuginone (HF) impairs HS biosynthesis and considered whether it could be used as a hepcidin modulator. Here, we demonstrate that in human hepatoma (Hep3B) cells, HF inhibits both basal and bone morphogenetic protein 6–induced hepcidin expression and SMAD1 phosphorylation signaling in a dose- and time-dependent manner. Consistently, Hep3B cells lacking HS (EXT1−/−) show no hepcidin suppression in response to HF. In vivo administration of HF reduces hepcidin expression in an iron-overload mouse model (8.3 g/kg carbonyl iron). This effect was absent in mice with impaired liver HS sulfation (Ndst1f/fAlbCre+), confirming that HF suppresses hepcidin via HSPG-mediated mechanisms. Additionally, HF decreased hepcidin expression in mice subjected to acute inflammation. These findings establish HF as a potential therapeutic for mitigating hepcidin-driven iron restriction in anemic disorders.

Non-transfusion dependent β-thalassemia (NTDT) is characterized by ineffective erythropoiesis, suppression of hepcidin, and iron overload, which is a major cause of morbidity and mortality. Hepatic protease Tmprss6 regulates hepcidin by modulating BMP/Smad signaling. Suppression of Tmprss6 in the mouse model of NTDT (Th3 mice), increased hepcidin and improved disease outcomes, but similar benefits have not been reported in human trials. We hypothesized that the resistance to the effects of anti-TMPRSS6 treatment in patients with NTDT may be caused by high erythroferrone (ERFE) concentrations and more severe iron overload, both known to modulate BMP/Smad signaling in hepatocytes. We therefore examined how ERFE and iron overload modulate the effects of Tmprss6 antisense oligonucleotides (ASO) in mouse models.We treated ERFE-overexpressing Th3 mice (T-E(M)) and their littermates (wild-type, Th3, and Erfe-overexpressing E(M) mice) with Tmprss6 ASO or non-targeting ASO for 4 weeks. Tmprss6 ASO increased phospho-Smad1/5/8 and hepcidin levels, decreased splenomegaly, reduced extramedullary erythropoiesis and improved iron parameters in Th3 mice but not in T-E(M) mice, despite similar Tmprss6 decrease. To determine whether iron overload alone blunted the effects of Tmprss6 ASO, we assessed the responses of C57BL/6 mice after 10 mg of iron dextran or 5000 ppm high iron diet. Unlike iron-adequate mice, iron-overloaded mice already had high phospho-Smad and hepcidin, with no further increase after Tmprss6 ASO treatment, and no effect on erythroid or iron parameters.Higher ERFE concentrations and more severe iron overload may be responsible for diminished benefits of Tmprss6 ASO in human NTDT.

Anemia is a common and disabling complication of chronic kidney disease (CKD). Current therapies can be burdensome, and full correction of anemia is limited by their cardiovascular side effects. New approaches that may offer additional therapeutic options are needed. We explored the antianemic effects of erythroferrone, an erythroid hormone that induces iron mobilization by suppressing the master iron-regulatory hormone hepcidin. In a preclinical murine model of adenine-induced CKD, transgenic augmentation of erythroferrone mobilized iron, increased hemoglobin concentrations by approximately 2 g/dL, and modestly improved renal function without affecting systemic or renal inflammation, fibrosis, or markers of mineral metabolism. This study supports the concept that therapeutic augmentation of erythroferrone is a promising approach for alleviating CKD-associated anemia.

Iron, a versatile electron donor and acceptor, is essential for life as a component of enzymes and oxygen transporters but also has the potential to cause toxicity when in excess. Its dietary absorption as well as plasma and tissue concentrations are subject to close regulation, systemically coordinated by the interaction of the hepatic peptide hormone hepcidin and its cellular receptor, the iron exporter ferroportin. Ferroportin mediates the delivery of iron to plasma from absorptive enterocytes, from macrophages that digest senescent erythrocytes, and from iron-storing hepatocytes. Hepcidin inhibits the transport of iron into plasma by occluding ferroportin and inducing its endocytosis and proteolysis. The production of hepcidin is feedback-regulated by the concentration of extracellular iron, as well as by the amount of iron in hepatic storage. Hepcidin production is also modulated by erythroid regulators (e.g., erythroferrone) that act to match the supply of iron to the fluctuating requirements of hemoglobin synthesis and erythropoiesis. During infections, hepcidin is induced by IL6 and restricts the growth of invading microorganisms by limiting the production of non-transferrin-bound iron. Although many of the underlying molecular and cellular mechanisms have been elucidated through the study of human diseases and their laboratory models, substantial gaps remain to be filled by further investigations.

Extensive neovascularization is a hallmark of glioblastoma (GBM). In addition to supplying oxygen and nutrients, vascular endothelial cells provide trophic support to GBM cells via paracrine signaling. Here we report that Endocan (ESM1), an endothelial-secreted proteoglycan, confers enhanced proliferative, migratory, and angiogenic properties to GBM cells and regulates their spatial identity. Mechanistically, Endocan exerts at least part of its functions via direct binding and activation of the PDGFRA receptor. Subsequent downstream signaling enhances chromatin accessibility of the Myc promoter and upregulates Myc expression inducing stable phenotypic changes in GBM cells. Furthermore, Endocan confers radioprotection on GBM cells in vitro and in vivo. Inhibition of Endocan-PDGFRA signaling with ponatinib increases survival in the Esm1 wild-type but not in the Esm1 knock-out mouse GBM model. Our findings identify Endocan and its downstream signaling axis as a potential target to subdue GBM recurrence and highlight the importance of vascular-tumor interactions for GBM development.

Anemia is a common and disabling complication of chronic kidney disease (CKD). Current therapies can be burdensome, and full correction of anemia is limited by cardiovascular side effects. New approaches that may offer additional therapeutic options are needed. We explored the anti-anemic effects of erythroferrone, an erythroid hormone that induces iron mobilization by suppressing the master iron-regulatory hormone hepcidin. In a preclinical murine model of adenine-induced CKD, transgenic augmentation of erythroferrone mobilized iron, increased hemoglobin concentrations by approximately 2 g/dl, and modestly improved renal function without affecting systemic or renal inflammation, fibrosis, or markers of mineral metabolism. This study supports the concept that therapeutic augmentation of erythroferrone is a promising approach for alleviating CKD-associated anemia.

Vadadustat is an oral hypoxia‐inducible factor prolyl hydroxylase inhibitor for treating anemia in chronic kidney disease (CKD). Single ascending dose (SAD) and multiple ascending dose (MAD) studies assessed pharmacokinetics (PK), pharmacodynamics (PD), and safety of vadadustat in healthy volunteers. A single‐dose, open‐label study was conducted in patients with CKD stages 3 and 4 not on dialysis. In the SAD study, 48 healthy adult men (n = 8/cohort) received single doses of vadadustat (80–1,200 mg) or placebo. In the MAD study, 34 healthy adult men (n = 8–9/cohort) received daily vadadustat (500–900 mg) or placebo for 10 days. In the single‐dose CKD study, 22 male and female patients with CKD (stage 3: n = 10; stage 4: n = 12) received single doses of vadadustat (500 mg). PK parameters included plasma vadadustat; PD biomarkers were measured, including erythropoietin (EPO) levels, reticulocytes, and others. Plasma vadadustat peaked 3–4 hours after single or multiple dosing in healthy volunteers, with a mean t _1/2 of approximately 4.5 hours. In patients with CKD, plasma vadadustat peaked at 5–6 hours, with a mean t _1/2 of 7.2 (stage 3) and 8.5 (stage 4) hours. Vadadustat AUC_∞ and C _max increased dose proportionally in SAD and MAD trials. In all trials, EPO concentrations increased in a dose‐related manner and returned approximately to baseline by 24 hours. Adverse events were mild and considered not study drug related. The PK and PD results of these studies were utilized for further clinical development of vadadustat for treatment of anemia in CKD patients.

Key Points: Serum ferritin was the strongest independent correlate of greater marrow iron stores in children with kidney failure supported by dialysis. Compared with current clinical guideline-based cutoffs for iron deficiency, ferritin outperforms these cut points for stainable marrow iron stores. Background: Iron deficiency is common in children with kidney failure, but current guidelines are based on biomarkers of iron stores that may be influenced by inflammation. This is the first study that examined which serum iron indices were associated with stainable marrow iron stores (the gold standard) in this population with kidney failure who underwent bone biopsies. Methods: This cross-sectional study enrolled 71 clinically stable children and young adults receiving dialysis who underwent bone biopsy for CKD-mineral bone disorder between 2007 and 2011. Bone biopsies were stained with Perls Prussian blue and independently interpreted by a pathologist blinded to participants' iron parameters and clinical status. Marrow staining was scored absent versus present to facilitate receiver operator curve (ROC) analysis. In ROC analysis, the ability of serum ferritin to detect stainable marrow iron stores was compared with that of transferrin saturation (TSAT), serum hepcidin, and clinical guideline-based iron deficiency cutoffs for serum iron, TSAT, and their combinations. Results: The mean age was 17.2±4.4 years (range 2–28), and 30% of patients were female. Median dialysis vintage was 1.2 (interquartile range, 0.7–2.0) years, and 56% were supported by peritoneal dialysis. Mean hemoglobin was 12.4±1.7 g/dl, and 35% were receiving iron supplementation at the time of biopsy. On the basis of the gold standard of depleted marrow iron stores, 46.5% of patients were iron deficient. As an indicator of marrow iron staining, serum ferritin provided a larger area under the ROC curve than serum hepcidin, TSAT, or clinical guideline-based evaluation of TSAT+ferritin. Conclusions: In this cohort of children and young adults with kidney failure, serum ferritin provided the best indication of stainable marrow iron stores, followed by TSAT. Podcast: This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2024_08_01_CJASNJuly197812024.mp3