RNAi-mediated reduction of hepatic Tmprss6 diminishes anemia and secondary iron overload in a splenectomized mouse model of β-thalassemia intermedia

Rational In Silico Design of Selective TMPRSS6 Peptidomimetic Inhibitors via Exploitation of the S2 Subpocket

TMPRSS6 is a potential therapeutic target for the treatment of iron overload due to its role in regulating levels of hepcidin. Although potent TMPRSS6 inhibitors have been previously developed, their lack of specificity requires optimization to avoid potential side effects before pursuing preclinical development with in vivo models. Here, using computer-aided drug design based on a TMPRSS6 homology model, we reveal that the S2 position of TMPRSS6 offers a potential avenue to achieve selectivity against other members of the TTSP family. Accordingly, we synthesized novel peptidomimetic molecules containing lipophilic amino acids at the P2 position to exploit this unexplored pocket. This enabled us to identify TMPRSS6-selective small molecules with low nanomolar affinity. Finally, pharmacokinetic parameters were determined, and a compound was found to be potent in cellulo toward its primary target while retaining TTSP-subtype selectivity and showing no signs of alteration in in vitro TEER experiments.

Is the Role of Hepcidin and Erythroferrone in the Pathogenesis of Beta Thalassemia the Key to Developing Novel Treatment Strategies?

Thalassemia is a disease of erythrocytes that varies largely on its genetic composition and associated clinical presentation. Though some patients may remain asymptomatic, those with a complicated course may experience severe anemia early in childhood, carrying into adulthood and requiring recurrent blood transfusions as a pillar of symptom management. Due to the consequences of ineffective erythropoiesis and frequent transfusions, patients with severe beta thalassemia may be subsequently susceptible to hemochromatosis. In light of the established role of hepcidin and erythroferrone in the pathogenesis of beta thalassemia, this review aims to discuss current clinical trials and studies in the field while presenting clinical implications of the HAMP gene polymorphisms and novel treatments. Research suggested incorporating erythroferrone and serum hepcidin testing as a part of routine workups for beta thalassemia, as they could be a predictive tool for early iron accumulation. Furthermore, ameliorating low hepcidin and high erythroferrone appeared to be crucial in treating beta thalassemia and its complications due to iron overload. Currently, hepcidin-like compounds, such as minihepcidins, LJPC-401, PTG-300, VIT-2763, and agents that promote hepcidin production by inhibiting TMPRSS6 expression or erythroferrone, were shown to be effective in restoring iron homeostasis in preliminary studies. Moreover, the natural bioactives astragalus polysaccharide and icariin have been recently recognized as hepcidin expression inductors.

Functionally impaired isoforms regulate TMPRSS6 proteolytic activity

TMPRSS6 is a type II transmembrane serine protease involved in iron homeostasis expressed as 4 isoforms in humans. TMPRSS6 isoform 2 downregulates hepcidin production by cleaving hemojuvelin and other surface proteins of hepatocytes. The functions of catalytically impaired isoforms 3 and 4 are still unknown. Here we demonstrate that TMPRSS6 isoforms 3 and 4 reduce the proteolytic activity of isoform 2 and uncover the ability of isoforms to interact. Moreover, we identified 49 potential protein partners common to TMPRSS6 isoforms, including TfR1, known to be involved in iron regulation. By co-expressing TMPRSS6 and TfR1, we show that TfR1 is cleaved and shed from the cell surface. Further, we demonstrate that TMPRSS6 isoforms 3 and 4 behave as dominant negative.

Iron overload cardiomyopathy: Using the latest evidence to inform future applications

Iron overload can be the result of either dysregulated iron metabolism in the case of hereditary hemochromatosis or repeated blood transfusions in the case of secondary hemochromatosis (e.g. in β-thalassemia and sickle cell anemia patients). Under iron overload conditions, transferrin (Tf) saturation leads to an increase in non-Tf bound iron which can result in the generation of reactive oxygen species (ROS). These excess ROS can damage cellular components, resulting in the dysfunction of vital organs including iron overload cardiomyopathy (IOC). Multiple studies have demonstrated that L-type and T-type calcium channels are the main routes for iron uptake in the heart, and that calcium channel blockers, given either individually or in combination with standard iron chelators, confer cardioprotective effects under iron overload conditions. Treatment with antioxidants may also provide therapeutic benefits. Interestingly, recent studies have suggested that mitochondrial dynamics and regulated cell death (RCD) pathways are potential targets for pharmacological interventions against iron-induced cardiomyocyte injury. In this review, the potential therapeutic roles of iron chelators, antioxidants, iron uptake/metabolism modulators, mitochondrial dynamics modulators, and inhibitors of RCD pathways in IOC are summarized and discussed.

Novel Therapeutic Advances in β-Thalassemia

Simple Summary

Beta-thalassemia (β-thalassemia) is an autosomal recessive inherited disorder that causes decreased production of hemoglobin. Ineffective erythropoiesis and excess iron deposition are the most significant pathophysiological problems. Chronic red blood cell transfusions along with control of iron overload are the main principles of treatment. Yet, the patients have a problematic quality of life. Recently, novel therapies have emerged based on better knowledge of the pathophysiology of the disease. Aiming at ineffective erythropoiesis through the TGF-β ligand traps, such as luspatercept, has been shown to reduce the transfusion burden. Therapeutic approaches aiming at the iron metabolism mechanisms as well as the pathway of the production of erythroid cyclic guanosine monophosphate are being used in clinical trials with encouraging results. Significant improvements in the technique of hemopoietic stem cell transplantation have been accomplished, with a focus on the improvement of the conditioning regimen and the donor selection. Gene therapy has exhibited remarkable advances using lentiviral β-globin gene insertion techniques or gene editing platforms that target the suppression of γ-globin repressors. All these approaches will have a positive result in the quality of life of thalassemia patients.

Abstract

The main characteristic of the pathophysiology of β-thalassemia is reduced β-globin chain production. The inevitable imbalance in the α/β-globin ratio and α-globin accumulation lead to oxidative stress in the erythroid lineage, apoptosis, and ineffective erythropoiesis. The result is compensatory hematopoietic expansion and impaired hepcidin production that causes increased intestinal iron absorption and progressive iron overload. Chronic hemolysis and red blood cell transfusions also contribute to iron tissue deposition. A better understanding of the underlying mechanisms led to the detection of new curative or “disease-modifying” therapeutic options. Substantial evolvement has been made in allogeneic hematopoietic stem cell transplantation with current clinical trials investigating new condition regimens as well as different donors and stem cell source options. Gene therapy has also moved forward, and phase 2 clinical trials with the use of β-globin insertion techniques have recently been successfully completed leading to approval for use in transfusion-dependent patients. Genetic and epigenetic manipulation of the γ- or β-globin gene have entered the clinical trial setting. Agents such as TGF-β ligand traps and pyruvate kinase activators, which reduce the ineffective erythropoiesis, have been tested in clinical trials with favorable results. One TGF-β ligand trap, luspatercept, has been approved for use in adults with transfusion-dependent β-thalassemia. The induction of HbF with the phosphodiesterase 9 inhibitor IMR-687, which increase cyclic guanosine monophosphate, is currently being tested. Another therapeutic approach is to target the dysregulation of iron homeostasis, using, for example, hepcidin agonists (inhibitors of TMPRSS6 and minihepcidins) or ferroportin inhibitors (VIT-2763). This review provides an update on the novel therapeutic options that are presently in development at the clinical level in β-thalassemia.

Iron overload-induced oxidative stress in myelodysplastic syndromes and its cellular sequelae

The myelodysplastic syndromes (MDS) are clonal hematopoietic stem cell disorders. MDS patients often require red blood cell transfusions, resulting in iron overload (IOL). IOL increases production of reactive oxygen species (ROS), oxygen free radicals. We review and illustrate how IOL-induced ROS influence cellular activities relevant to MDS pathophysiology. ROS damage lipids, nucleic acids in mitochondrial and nuclear DNA, structural proteins, transcription factors and enzymes. Cellular consequences include decreased metabolism and tissue and organ dysfunction. In hematopoietic stem cells (HSC), consequences of ROS include decreased glycolysis, shifting the cell from anaerobic to aerobic metabolism and causing HSC to exit the quiescent state, leading to HSC exhaustion or senescence. ROS oxidizes DNA bases, resulting in accumulation of mutations. Membrane oxidation alters fluidity and permeability. In summary, evidence indicates that IOL-induced ROS alters cellular signaling pathways resulting in toxicity to organs and hematopoietic cells, in keeping with adverse clinical outcomes in MDS.

SLN124, a GalNac-siRNA targeting transmembrane serine protease 6, in combination with deferiprone therapy reduces ineffective erythropoiesis and hepatic iron-overload in a mouse model of β-thalassaemia

Beta‐thalassaemia is an inherited blood disorder characterised by ineffective erythropoiesis and anaemia. Consequently, hepcidin expression is reduced resulting in increased iron absorption and primary iron overload. Hepcidin is under the negative control of transmembrane serine protease 6 (TMPRSS6) via cleavage of haemojuvelin (HJV), a co‐receptor for the bone morphogenetic protein (BMP)‐mothers against decapentaplegic homologue (SMAD) signalling pathway. Considering the central role of the TMPRSS6/HJV/hepcidin axis in iron homeostasis, the inhibition of TMPRSS6 expression represents a promising therapeutic strategy to increase hepcidin production and ameliorate anaemia and iron overload in β‐thalassaemia. In the present study, we investigated a small interfering RNA (siRNA) conjugate optimised for hepatic targeting of Tmprss6 (SLN124) in β‐thalassaemia mice (Hbb^th3/+). Two subcutaneous injections of SLN124 (3 mg/kg) were sufficient to normalise hepcidin expression and reduce anaemia. We also observed a significant improvement in erythroid maturation, which was associated with a significant reduction in splenomegaly. Treatment with the iron chelator, deferiprone (DFP), did not impact any of the erythroid parameters. However, the combination of SLN124 with DFP was more effective in reducing hepatic iron overload than either treatment alone. Collectively, we show that the combination therapy can ameliorate several disease symptoms associated with chronic anaemia and iron overload, and therefore represents a promising pharmacological modality for the treatment of β‐thalassaemia and related disorders.

NCOA4 is regulated by HIF and mediates mobilization of murine hepatic iron stores after blood loss

The mechanisms by which phlebotomy promotes the mobilization of hepatic iron stores are not well understood. NCOA4 (nuclear receptor coactivator 4) is a widely expressed intracellular protein previously shown to mediate the autophagic degradation of ferritin. Here, we investigate a local requirement for NCOA4 in the regulation of hepatic iron stores and examine mechanisms of NCOA4 regulation. Hepatocyte-targeted Ncoa4 knockdown in nonphlebotomized mice had only modest effects on hepatic ferritin subunit levels and nonheme iron concentration. After phlebotomy, mice with hepatocyte-targeted Ncoa4 knockdown exhibited anemia and hypoferremia similar to control mice with intact Ncoa4 regulation but showed a markedly impaired ability to lower hepatic ferritin subunit levels and hepatic nonheme iron concentration. This impaired hepatic response was observed even when dietary iron was limited. In both human and murine hepatoma cell lines, treatment with chemicals that stabilize hypoxia inducible factor (HIF), including desferrioxamine, cobalt chloride, and dimethyloxalylglycine, raised NCOA4 messenger RNA. This NCOA4 messenger RNA induction occurred within 3 hours, preceded a rise in NCOA4 protein, and was attenuated in the setting of dual HIF-1α and HIF-2α knockdown. In summary, we show for the first time that NCOA4 plays a local role in facilitating iron mobilization from the liver after blood loss and that HIF regulates NCOA4 expression in cells of hepatic origin. Because the prolyl hydroxylases that regulate HIF stability are oxygen- and iron-dependent enzymes, our findings suggest a novel mechanism by which hypoxia and iron deficiency may modulate NCOA4 expression to impact iron homeostasis.

Global loss of Tfr2 with concomitant induced iron deficiency greatly ameliorates the phenotype of a murine thalassemia intermedia model

β-thalassemias result from mutations in β-globin, causing ineffective erythropoiesis and secondary iron overload due to inappropriately low levels of the iron regulatory hormone hepcidin. Mutations in transferrin receptor 2 (TFR2) lead to hereditary hemochromatosis (HH) as a result of inappropriately increased iron uptake from the diet, also due to improperly regulated hepcidin. TFR2 is also thought to be required for efficient erythropoiesis through its interaction with the erythropoietin receptor in erythroid progenitors. Transmembrane serine protease 6 (TMPRSS6), a membrane serine protease expressed selectively in the liver, participates in regulating hepcidin production in response to iron stores by cleaving hemojuvelin (HJV). We have previously demonstrated that inhibiting TMPRSS6 expression with a hepatocyte-specific siRNA formulation, induces hepcidin, mitigates anemia, and reduces iron overload in murine models of β-thalassemia intermedia and HH. Here, we demonstrate that Tmprss6 siRNA treatment of double mutant Tfr2^Y245X/Y245X HH Hbb^th3/+ thalassemic mice induces hepcidin and diminishes tissue and serum iron levels. Importantly, treated double mutant animals produce more mature red blood cells and have a nearly 50% increase in hemoglobin compared to untreated β-thalassemic mice. Furthermore, we also show that treatment of Tfr2^Y245X/Y245X HH mice leads to increased hepcidin expression and reduced total body iron burden. These data indicate that siRNA suppression of Tmprss6, in conjunction with the targeting of TFR2, may be superior to inhibiting Tmprss6 alone in the treatment of the anemia and secondary iron loading in β-thalassemia intermedia and may be useful as a method of suppressing the primary iron overload in TFR2-related (type 3) hereditary hemochromatosis.

Diagnostic Relevance of Ferrokinetic Laboratory Markers in Anemic Pregnant Women

OBJECTIVES

Different forms of anemia are considered as the most frequent complication of the gestational period. By its etiology, pathogenesis, and clinical hematology, it is not a single disease. Among all forms of anemia occurring during pregnancy, iron deficiency anemia (IDA) is the most common, accounting for 80-95% of all cases.

DESIGN

The article describes a theoretical basis for the diagnosis of the anemic syndrome among pregnant women, the determining factors of its development, and the diagnostic methods at different gestational periods. Participants/Materials, Setting, and Methods: Diagnostic and prognostic values of iron balance indicators in the body were established for IDA during pregnancy to improve the outcome of childbirth. A total of 140 anemic patients were examined. The control group consisted of 50 pregnant women without anemia and other significant health problems, 48 IDA pregnant women, and 42 pregnant women with anemia caused by various chronic diseases, including rheumatoid arthritis. All patients of the main and control groups were registered on clinical records at the Family Planning Center in Aktobe city, Kazakhstan.

RESULTS

Ferrokinetic indicators were suggested for diagnosing IDA and anemia of chronic diseases. It was established that IDA is characterized by low ferritin levels during gestation, while increased ferritin and C-reactive protein are typical for anemia of chronic diseases.

LIMITATIONS

Differential diagnostics was applied for pregnant women with IDA and anemia of chronic diseases to observe the dynamics of serum ferritin and C-reactive protein (CRP) levels at different gestational periods. The article presents the results of a study on ferrokinetics in pregnant women with IDA and anemia caused by inflammation or chronic diseases. Other causes of anemia leading to a decrease in hemoglobin (Hb) levels to <90 g/L include hemoglobinopathies, which were not considered in this study.

CONCLUSIONS

Determination of iron deficiency in pregnant women at different gestational periods will allow for identifying the risk group of anemic patients and deciding on the treatment. IDA (Hb <100 g/L) can be effectively measured by ferritin level <15 ng/mL, iron level of <11.5 μmol/L, and transferrin level >2.6 mg/L at p < 0.001. Anemia due to chronic diseases (Hb <100 g/L) can be effectively diagnosed with ferritin above 15 μg/L and CRP above 10 mg/L at p < 0.001.

Mild iron deficiency does not ameliorate the phenotype of a murine erythropoietic protoporphyria model

Reduced ferrochelatase activity in erythropoietic protoporphyria (EPP) causes the accumulation of protoporphyrin IX (PPIX) leading to acute cutaneous photosensitivity and liver injury. Many EPP patients also have a mild hypochromic, microcytic anemia and iron deficiency. Iron deficiency can lead to decreased PPIX accumulation in another erythropoietic porphyria, congenital erythropoietic porphyria (CEP). Expression of the iron regulatory peptide hepcidin is negatively regulated by the serine protease TMPRSS6. Hepcidin induction by siRNA-mediated inhibition of TMPRSS6 expression reduces iron availability and induces iron deficiency. To interrogate the therapeutic potential of iron deficiency to modify EPP, we treated an ethylnitrosourea-induced mouse model of EPP, Fech ^m1Pas , with a GalNAc-conjugated Tmprss6 siRNA and PPIX levels, anemia and iron parameters were monitored. The GalNAc-RNAi therapeutic reduces Tmprss6 expression and induces mild iron deficiency in Fech ^m1Pas animals. However, decreases in erythrocyte PPIX levels and liver PPIX accumulation were not seen. These results indicate short-term induction of iron deficiency, at least in a murine model of EPP, does not lead to decreased PPIX production.

Therapeutic Advances in Regulating the Hepcidin/Ferroportin Axis

The interaction between hepcidin and ferroportin is the key mechanism involved in regulation of systemic iron homeostasis. This axis can be affected by multiple stimuli including plasma iron levels, inflammation and erythropoietic demand. Genetic defects or prolonged inflammatory stimuli results in dysregulation of this axis, which can lead to several disorders including hereditary hemochromatosis and anaemia of chronic disease. An imbalance in iron homeostasis is increasingly being associated with worse disease outcomes in many clinical conditions including multiple cancers and neurological disorders. Currently, there are limited treatment options for regulating iron levels in patients and thus significant efforts are being made to uncover approaches to regulate hepcidin and ferroportin expression. These approaches either target these molecules directly or regulatory steps which mediate hepcidin or ferroportin expression. This review examines the current status of hepcidin and ferroportin agonists and antagonists, as well as inducers and inhibitors of these proteins and their regulatory pathways.

Hepcidin Therapeutics

Hepcidin is a key hormonal regulator of systemic iron homeostasis and its expression is induced by iron or inflammatory stimuli. Genetic defects in iron signaling to hepcidin lead to “hepcidinopathies” ranging from hereditary hemochromatosis to iron-refractory iron deficiency anemia, which are disorders caused by hepcidin deficiency or excess, respectively. Moreover, dysregulation of hepcidin is a pathogenic cofactor in iron-loading anemias with ineffective erythropoiesis and in anemia of inflammation. Experiments with preclinical animal models provided evidence that restoration of appropriate hepcidin levels can be used for the treatment of these conditions. This fueled the rapidly growing field of hepcidin therapeutics. Several hepcidin agonists and antagonists, as well as inducers and inhibitors of hepcidin expression have been identified to date. Some of them were further developed and are currently being evaluated in clinical trials. This review summarizes the state of the art.