Does erythropoietin have a role in the treatment of β-hemoglobinopathies?

Genetic support of a causal relationship between iron status and atrial fibrillation: a Mendelian randomization study

Background

Atrial fibrillation is the most common arrhythmia disease. Animal and observational studies have found a link between iron status and atrial fibrillation. However, the causal relationship between iron status and AF remains unclear. The purpose of this investigation was to use Mendelian randomization (MR) analysis, which has been widely applied to estimate the causal effect, to reveal whether systemic iron status was causally related to atrial fibrillation.

Methods

Single nucleotide polymorphisms (SNPs) strongly associated (P < 5 × 10−8) with four biomarkers of systemic iron status were obtained from a genome-wide association study involving 48,972 subjects conducted by the Genetics of Iron Status consortium. Summary-level data for the genetic associations with atrial fibrillation were acquired from the AFGen (Atrial Fibrillation Genetics) consortium study (including 65,446 atrial fibrillation cases and 522,744 controls). We used a two-sample MR analysis to obtain a causal estimate and further verified credibility through sensitivity analysis.

Results

Genetically instrumented serum iron [OR 1.09; 95% confidence interval (CI) 1.02–1.16; p = 0.01], ferritin [OR 1.16; 95% CI 1.02–1.33; p = 0.02], and transferrin saturation [OR 1.05; 95% CI 1.01–1.11; p = 0.01] had positive effects on atrial fibrillation. Genetically instrumented transferrin levels [OR 0.90; 95% CI 0.86–0.97; p = 0.006] were inversely correlated with atrial fibrillation.

Conclusion

In conclusion, our results strongly elucidated a causal link between genetically determined higher iron status and increased risk of atrial fibrillation. This provided new ideas for the clinical prevention and treatment of atrial fibrillation.

Improving Ineffective Erythropoiesis in Thalassemia: A Hope on the Horizon

Beta-thalassemia is an inherited hemoglobinopathy characterized by the impaired synthesis of beta-globin chains of hemoglobin leading to chronic hemolytic anemia. The mainstay of treatment for most patients remains regular blood transfusions and iron chelation. This conventional therapy has many limitations and challenges. Allogeneic hematopoietic stem cell transplant (HSCT) is the only available curative treatment but the availability of a suitable donor, financial constraints, and a need for specialist physicians can be limiting factors. Gene therapy is an upcoming curative therapeutic modality. An increased understanding of the underlying pathophysiology and molecular mechanisms of thalassemia has paved the way for novel pharmacological agents targeting ineffective erythropoiesis. These drugs act by decreasing transfusion requirements and hence decrease transfusion-related complications. The present review intends to provide an insight into the recent advances in pharmacological agents targeting ineffective erythropoiesis. Literature was searched and relevant articles evaluating newer drugs in thalassemia were collected from databases, including Pubmed, Scopus, Prospero, Clinicaltrials.gov, Google Scholar, and the Google search engine. We used the following keywords: thalassemia, novel, treatment, drugs, and ineffective erythropoiesis during the initial search. Relevant titles and abstracts were screened to choose relevant articles. Further, the full-text articles were retrieved and relevant cross-references were scanned to collect information for the present review.

The EPO-FGF23 Signaling Pathway in Erythroid Progenitor Cells: Opening a New Area of Research

We provide an overview of the evidence for an erythropoietin-fibroblast growth factor 23 (FGF23) signaling pathway directly influencing erythroid cells in the bone marrow. We outline its importance for red blood cell production, which might add, among others, to the understanding of bone marrow responses to endogenous erythropoietin in rare hereditary anemias. FGF23 is a hormone that is mainly known as the core regulator of phosphate and vitamin D metabolism and it has been recognized as an important regulator of bone mineralization. Osseous tissue has been regarded as the major source of FGF23. Interestingly, erythroid progenitor cells highly express FGF23 protein and carry the FGF receptor. This implies that erythroid progenitor cells could be a prime target in FGF23 biology. FGF23 is formed as an intact, biologically active protein (iFGF23) and proteolytic cleavage results in the formation of the presumed inactive C-terminal tail of FGF23 (cFGF23). FGF23-knockout or injection of an iFGF23 blocking peptide in mice results in increased erythropoiesis, reduced erythroid cell apoptosis and elevated renal and bone marrow erythropoietin mRNA expression with increased levels of circulating erythropoietin. By competitive inhibition, a relative increase in cFGF23 compared to iFGF23 results in reduced FGF23 receptor signaling and mimics the positive effects of FGF23-knockout or iFGF23 blocking peptide. Injection of recombinant erythropoietin increases FGF23 mRNA expression in the bone marrow with a concomitant increase in circulating FGF23 protein. However, erythropoietin also augments iFGF23 cleavage, thereby decreasing the iFGF23 to cFGF23 ratio. Therefore, the net result of erythropoietin is a reduction of iFGF23 to cFGF23 ratio, which inhibits the effects of iFGF23 on erythropoiesis and erythropoietin production. Elucidation of the EPO-FGF23 signaling pathway and its downstream signaling in hereditary anemias with chronic hemolysis or ineffective erythropoiesis adds to the understanding of the pathophysiology of these diseases and its complications; in addition, it provides promising new targets for treatment downstream of erythropoietin in the signaling cascade.

Recombinant erythropoietin as alternative to red cell transfusion in sickle cell disease

Disturbances in the physiological regulation of erythropoietin (EPO) in patients with sickle cell disease (SCD) may contribute to worsening anaemia and increased transfusion requirements, but the use of recombinant EPO in this group of patients is controversial. The objective of this study was to evaluate the use of this drug in adult patients with SCD and its effects on haemoglobin levels and transfusion requirements. We conducted a retrospective analysis at the University of Campinas, with nineteen adults with a diagnosis of SCD (HbSS and HbS/β⁺ thalassaemia), who had received at least 1 year of EPO therapy between 2007 and 2014. Haemoglobin concentrations and trends of variation in transfused RBC volumes were compared before and after EPO administration. We observed that seven patients had a good response to treatment (Hb increment higher than 1·5 g/dl) and nine had a partial response (0·5-1·5 g/dl increment) and there was a significant decrease in the need for transfusion amongst those who usually required regular transfusions. There were no increases in the rates of vaso-occlusive crisis or venous thromboembolism in comparison to the year before the onset of the therapy. Erythropoietin therapy led to a marked increase in haemoglobin concentration with a concomitant decrease in the demand for transfusion. Considering all complications related to allogeneic transfusion, we believe that EPO therapy represents an important therapeutic tool in sickle cell anaemia.

Luspatercept improves hemoglobin levels and blood transfusion requirements in a study of patients with β-thalassemia

β-thalassemia is a hereditary disorder with limited approved treatment options; patients experience anemia and its complications, including iron overload. The study aim was to determine whether luspatercept could improve anemia and disease complications in patients with β-thalassemia. This open-label, nonrandomized, uncontrolled study consisted of a 24-week dose-finding and expansion stage (initial stage) and a 5-year extension stage, currently ongoing. Sixty-four patients were enrolled; 33 were non-transfusion dependent (mean hemoglobin, <10.0 g/dL; <4 red blood cell [RBC] units transfused per 8 weeks), and 31 were transfusion dependent (≥4 RBC units per 8 weeks). Patients received 0.2 to 1.25 mg/kg luspatercept subcutaneously every 21 days for ≥5 cycles (dose-finding stage) and 0.8 to 1.25 mg/kg (expansion cohort and 5-year extension). The primary end point was erythroid response, defined as hemoglobin increase of ≥1.5 g/dL from baseline for ≥14 consecutive days (without RBC transfusions) for non-transfusion-dependent patients or RBC transfusion burden reduction ≥20% over a 12-week period vs the 12 weeks before treatment for transfusion-dependent patients. Eighteen non-transfusion-dependent patients (58%) receiving higher dose levels of luspatercept (0.6-1.25 mg/kg) achieved mean hemoglobin increase ≥1.5 g/dL over ≥14 days vs baseline. Twenty-six (81%) transfusion-dependent patients achieved ≥20% reduction in RBC transfusion burden. The most common grade 1 to 2 adverse events were bone pain, headache, and myalgia. As of the cutoff, 33 patients remain on study. In this study, a high percentage of β-thalassemia patients receiving luspatercept had hemoglobin or transfusion burden improvements. These findings support a randomized clinical trial to assess efficacy and safety. This study was registered at www.clinicaltrials.gov as #NCT01749540 and #NCT02268409.

Sotatercept, a novel transforming growth factor β ligand trap, improves anemia in β-thalassemia: a phase II, open-label, dose-finding study

β-thalassemia, a hereditary blood disorder caused by defective synthesis of hemoglobin β globin chains, leads to ineffective erythropoiesis and chronic anemia that may require blood transfusions. Sotatercept (ACE-011) acts as a ligand trap to inhibit negative regulators of late-stage erythropoiesis in the transforming growth factor β superfamily, correcting ineffective erythropoiesis. In this phase II, open-label, dose-finding study, 16 patients with transfusion-dependent β -thalassemia and 30 patients with non-transfusion-dependent β-thalassemia were enrolled at seven centers in four countries between November 2012 and November 2014. Patients were treated with sotatercept at doses of 0.1, 0.3, 0.5, 0.75, or 1.0 mg/kg to determine a safe and effective dose. Doses were administered by subcutaneous injection every 3 weeks. Patients were treated for ≤22 months. Response was assessed as a ≥20% reduction in transfusion burden sustained for 24 weeks in transfusion-dependent β-thalassemia patients, and an increase in hemoglobin level of ≥1.0 g/dL sustained for 12 weeks in non-transfusion-dependent β-thalassemia patients. Sotatercept was well tolerated. After a median treatment duration of 14.4 months (range 0.6-35.9), no severe life-threatening adverse events were observed. Thirteen percent of patients reported serious but manageable adverse events. The active dose of sotatercept was ≥0.3 mg/kg for patients with non-transfusion-dependent β-thalassemia and ≥0.5 mg/kg for those with transfusion-dependent β-thalassemia. Of 30 non-transfusion-dependent β-thalassemia patients treated with ≥0.1 mg/kg sotatercept, 18 (60%) achieved a mean hemoglobin increase ≥1.0 g/dL, and 11 (37%) an increase ≥1.5 g/dL, sustained for ≥12 weeks. Four (100%) transfusion-dependent β-thalassemia patients treated with 1.0 mg/kg sotatercept achieved a transfusion-burden reduction of ≥20%. Sotatercept was effective and well tolerated in patients with β-thalassemia. Most patients with non-transfusion-dependent β-thalassemia treated with higher doses achieved sustained increases in hemoglobin level. Transfusion-dependent β-thalassemia patients treated with higher doses of sotatercept achieved notable reductions in transfusion requirements. This trial was registered at ClinicalTrials.gov with the number NCT01571635.

Inheritance of the Bantu/Benin haplotype causes less severe hemolytic and oxidative stress in sickle cell anemia patients treated with hydroxycarbamide

Beta S-globin gene cluster haplotypes (β(S)-haplotypes) can modulate the response to hydroxycarbamide (HC) treatment in sickle cell anemia (SCA) patients. In Brazil, the most common haplotypes are Bantu and Benin, and both confer a poor prognosis for patients when untreated with HC. We evaluated oxidative and hemolytic biomarkers in 48 SCA patients undergoing HC treatment separated in three subgroups: Bantu/Bantu, Bantu/Benin and Benin/Benin haplotype. On the basis of reduced haptoglobin (HP) levels, patients with Bantu/Bantu haplotypes had 3.0% higher hemolysis degree when compared with those with Bantu/Benin haplotypes (P=0.01). The Benin/Benin patients had 53.6% greater lipid peroxidation index than the Bantu/Bantu patients (P=0.01) because of evaluated thiobarbituric acid reactive species levels. The Bantu/Benin subgroup had intermediate levels of hemolytic and oxidative stress markers compared with the homozygous subgroups. Through strict inclusion criteria adopted, as well as consolidated and well-described hemolytic and the oxidative parameters evaluated, we suggest a haplotype-interaction response to HC treatment mediated by a 'balance' between the genetic factors of each haplotype studied.