Academic literature on the topic 'Erythropoietin receptor, Thalassemia, Hemoglobin, Parkinson's disease'

Abstract Clinical data suggest that in beta-thalassemia-intermedia patients, higher levels of circulating fetal hemoglobin (HbF) are associated with greater disease severity at comparable degrees of anemia. We assessed the influence of the amount of circulating HbF on serum erythropoietin (s-Epo) levels and on serum transferrin receptor, a measure of erythropoiesis, in 30 beta-thalassemia-intermedia patients. Twenty-four showed more than 40% HbF (21 of whom with beta (0)-thalassemia) and 6 presented lower HbF levels (beta(+)-thalassemia). The two groups of patients did not differ in age (15.3 v 19 years, respectively) or degree of anemia (Hb = 8.8 g/dL in both groups). Log (s-Epo) was correlated inversely with Hb (r = -0.47; P < .01), and directly with HbF (r = .55; P < .001). Multivariate regression analysis showed that Hb and HbF were independently correlated with s-Epo levels. High-HbF patients had greater s-Epo values at the same Hb level than low-HbF patients. Considering that iron-deficiency anemia control patients represented the predicted physiologic response of s-Epo to anemia, the observed/predicted s-Epo ratio in low-HbF thalassemic patients was no different from controls, but was increased in the high-HbF group. High- HbF patients also showed an expansion of erythropoiesis as much as four to nine times the normal value at the same Hb level as low-HbF patients. We conclude that HbF exerts an independent regulatory effect on erythropoietin production and erythropoiesis that is detectable only when HbF levels exceed 40%.

Clinical data suggest that in beta-thalassemia-intermedia patients, higher levels of circulating fetal hemoglobin (HbF) are associated with greater disease severity at comparable degrees of anemia. We assessed the influence of the amount of circulating HbF on serum erythropoietin (s-Epo) levels and on serum transferrin receptor, a measure of erythropoiesis, in 30 beta-thalassemia-intermedia patients. Twenty-four showed more than 40% HbF (21 of whom with beta (0)-thalassemia) and 6 presented lower HbF levels (beta(+)-thalassemia). The two groups of patients did not differ in age (15.3 v 19 years, respectively) or degree of anemia (Hb = 8.8 g/dL in both groups). Log (s-Epo) was correlated inversely with Hb (r = -0.47; P < .01), and directly with HbF (r = .55; P < .001). Multivariate regression analysis showed that Hb and HbF were independently correlated with s-Epo levels. High-HbF patients had greater s-Epo values at the same Hb level than low-HbF patients. Considering that iron-deficiency anemia control patients represented the predicted physiologic response of s-Epo to anemia, the observed/predicted s-Epo ratio in low-HbF thalassemic patients was no different from controls, but was increased in the high-HbF group. High- HbF patients also showed an expansion of erythropoiesis as much as four to nine times the normal value at the same Hb level as low-HbF patients. We conclude that HbF exerts an independent regulatory effect on erythropoietin production and erythropoiesis that is detectable only when HbF levels exceed 40%.

Abstract Erythropoietin (EPO), a hormone produced on hypoxia mainly in the kidneys, enhances red blood cell (RBC) production (erythropoiesis) by stimulating the proliferation of erythroid progenitors and precursors in the bone marrow. This effect is mediated by the homodimeric EPO receptor, a class 1 cytokine receptor. Recombinant human EPO is widely used for the treatment of anemia, e.g., in patients on dialysis, patients with myelodysplastic syndrome and oncology patients undergoing chemotherapy. Treatment with EPO was also tried experimentally in patients with thalassemia. In these patients, in spite the state of chronic anemia, the levels of EPO is usually low relative to the degree of anemia. Administration of EPO to thalassemic patients have been shown to increase erythropoiesis and in some cases to elevate fetal hemoglobin production. In addition, EPO has been suggested to have cardio- and neuro-protecting effects and to increase RBC survival in dialysis patients. We have previously shown that RBC and platelets derived from patients with beta-thalassemia and sickle cell disease are under oxidative stress; they have elevated potential to generate reactive oxygen species (ROS) and membrane lipid peroxides, and have lower content of reduced glutathione (GSH) than normal RBC. This oxidative stress resulted in high exposure of phosphatidylserine (PS) that is considered a major factor in shortening the life span of thalassemic RBC, and in the tendency of platelets to undergo activation and thus contributes to the high incidence of thromboembolic complications in thalassemia. In the present study, we investigated the in vitro and in vivo effects of EPO as an antioxidant on RBC and platelets from beta-thalassemic patients and mice. Using flow-cytometry methodology, we showed that in vitro treatment of blood cells from beta-thalassemic patients with 1–4 U/ml of EPO for 2 hours increased the GSH content of RBC (2.1-fold) and platelets (1.7-fold) and reduced their ROS (1.5-fold), membrane lipid peroxidation and externalization of PS. Intraperitoneal injection of EPO to heterozygotes (Hbbth3/+) beta-thalassemic mice (3,000U/kg) significantly reduced ROS and increased GSH in their RBC within 3 hours. The in vitro effects of EPO on oxidative stress resulted in reduced sensitivity of thalassemic RBC to undergo hemolysis and phagocytosis by macrophages, and reduced tendency of platelets to undergo activation, as reflected by fewer platelets carrying external PS. Our results suggest that in addition to its effect on erythropoiesis and fetal hemoglobin production, EPO might alleviate symptoms in thalassemia and other hemolytic anemias as a potent antioxidant.

Abstract Background: β-thalassemia (BT) is a hereditary hemolytic anemia. The imbalance between α- and β-globin chain synthesis results in ineffective erythropoiesis, severe microcytic hypochromic anemia and iron overload. Although regular transfusions and iron-chelation therapy markedly improve the survival and quality of life of BT patients, they have also led to the emergence of previously unrecognized complications. Patients with thalassemia major often present with endocrine abnormalities due to dysfunction of the hypothalamic-pituitary axis (Poggi, 2016), and are frequently underweight with abnormally low body-fat percentage (Fung, 2010). Adipose tissue stores lipids, but it also has an endocrine function through the production of leptin, an adipocyte-derived hormone that regulates food intake, metabolic and endocrine functions by activating its receptor in the central nervous system. Leptin plays a regulatory role in immunity and inflammation, and also seems to act synergistically with erythropoietin on mammalian hematopoiesis (Bennett, 1996). For example, a stimulatory effect of leptin on erythropoiesis among patients with end-stage renal disease was observed (Axelsson 2005). Previous studies on leptin in BT patients have shown lower levels than in healthy controls, and a negative correlation with the level of soluble transferrin receptor in transfused patients (Dedoussis, 2002). The reduced leptin levels were explained by a possible toxic effect of iron on adipocytes (Chaliasos, 2010). Study aims: In this study, we investigated the correlation between leptin level and anthropometric parameters in BT patients compared to heathy controls. We also explored the relationship between leptin and hematological and erythropoietic parameters, as well as iron-overload status in BT patients. Patients and methods: Transfusion-dependent BT patients (n = 33; 16 females, 17 males, mean age 23.5 ± 8.6 [range 8-41] years), treated at the Pediatric Hematology Unit of Emek Medical Center, and 11 healthy controls (6 females, 5 males, mean age 26.4 ± 10.4 [range 8-39] years) were studied. Patients were treated by regular blood transfusions and iron-chelation therapy. Anthropometric assessments included height, weight, fat percentage and BMI calculation. Blood samples were obtained at fasting and before blood transfusion. Serum leptin, complete blood count, hemoglobin and reticulocyte counts and serum erythropoietin were analyzed. These studies were performed twice, 3 months apart, and the mean values were utilized for the statistical analysis. Serum leptin levels were analyzed by radioimmunoassay, and leptin-normalized values were calculated (ng/dL leptin per % body fat). Results: BT patients were found to have lower leptin levels than healthy controls (5.4 ± 5.9 vs. 13 ± 10.1 ng/dL; p= 0.0006). Leptin levels were higher in females than in males (mean leptin 7.2 ± 6.5 vs. 3.7 ± 4.7 ng/dL; p= 0.01), and increased with age (r= 0.4635, p= 0.0066). A negative correlation was found between leptin and erythropoietin (r= -0.43473, p= 0.0115), and a positive correlation between leptin and hemoglobin, as well as the mean pre-transfusion hemoglobin levels in the previous 5 years (r= 0.66884, p &lt; 0.001; r= 0.40261, p= 0.0202, respectively). No correlation was observed between leptin levels and anthropometric parameters (weight, height, BMI), iron-overload parameters or reticulocyte count. Fasting and normalized leptin showed similar patterns. Conclusions: This study confirms that BT patients are unable to maintain adequate leptin production, suggesting that adipose tissue dysfunction may be related to the chronic anemia. Our results correlate well with previous studies of lower leptin levels in BT patients. The positive correlation of leptin level with hemoglobin, together with the inverse correlation with erythropoietin provide further evidence of the effect of leptin on erythropoiesis. Additional studies are needed to examine the intricate interplay between adipose tissue, leptin and erythropoiesis in the environment of chronic anemia and iron overload present in BT patients. Disclosures No relevant conflicts of interest to declare.

Beta-thalassemia is a hereditary iron-independent anemia, caused by a reduction of β-globin, affecting millions of people globally. Current treatments such as blood transfusions and iron chelation show significant toxicities and add to organ damage. Luspatercept (Acvr2b(L79D)-Fc) is a novel treatment for transfusion-dependent β-thalassemia patients that improves erythropoiesis independent of erythropoietin. The exact mechanism of action remains unknown, and it is controversially discussed if growth differentiation factor 11 (GDF11) is the main target of this drug. Genetic models raised doubts that GDF11 is the target of Acvr2b(L79D)-Fc. Here we tested if a GDF11 specific blocking antibody improves β-thalassemia intermedia in mice. Our findings support the genetic data that GDF11 does not play a role in the ineffective erythropoiesis in β-thalassemia. Anti-GDF11 treatment did not change hematocrit, hemoglobin and red blood cell number and it did not improve erythropoiesis. Ex vivo treatment of erythroblasts with recombinant GDF11 did not inhibit red blood cell maturation. Lastly, we identified that inhibiting GDF8 in β-thalassemia mice has a small effect on erythropoiesis and increased hemoglobin levels without being as effective as Acvr2b(L79D)-Fc. Of note, wild-type animals treated with anti-GDF8 did not show changes in any hematology parameters and therefore the small effect we observed might be due to the disease phenotype, but not due to a physiological mechanism involved in erythropoiesis. Taken together, GDF11 is not involved in erythropoiesis but GDF8 may have a minor role in the regulation of ineffective erythropoiesis. Given the small effect of anti-GDF8 on erythropoiesis compared to Acvr2b(L79D)-Fc, we conclude that either there is another target or several targets of Acvr2b(L79D)-Fc driving ineffective erythropoiesis, or that Acvr2b(L79D)-Fc efficacy is due to it altering the overall BMP/GDF/Activin ligand and receptor balance. Disclosures Lob: Regeneron Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Kravets:Regeneron Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Miloscio:Regeneron Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Mastaitis:Regeneron Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Economides:Regeneron Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Hatsell:Regeneron Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company.

Systemic-onset juvenile chronic arthritis (SoJCA) is associated with high levels of circulating interleukin-6 (IL-6) and is frequently complicated by severe microcytic anemia whose pathogenesis is unclear. Therefore, we studied 20 consecutive SoJCA patients with hemoglobin (Hb) levels <12 g/dL, evaluating erythroid progenitor proliferation, endogenous erythropoietin production, body iron status, and iron supply for erythropoiesis. Hb concentrations ranged from 6.5 to 11.9 g/dL. Hb level was directly related to mean corpuscular volume (r = .82, P < .001) and inversely related to circulating transferrin receptor (r = - .81, P < .001) suggesting that the severity of anemia was directly proportional to the degree of iron-deficient erythropoiesis. Serum ferritin ranged from 18 to 1,660 microgram/L and was unrelated to Hb level. Bone marrow iron stores wore markedly reduced in the three children investigated, and they also showed increased serum transferrin receptor and normal-to-high serum ferritin. All 20 patients had elevated IL-6 levels and normal in vitro growth of erythroid progenitors. Endogenous erythropoietin (epo) production was appropriate for the degree of anemia as judged by both the observed to predicted log (serum epo) ratio 10.95 +/- 0.12) and a comparison of the serum epo- Hb regression found in these subjects with that of thalassemia patients. Multiple regression analysis showed that serum transferrin receptor was the parameter most closely related to hemoglobin concentration: variation in circulating transferrin receptor explained 61% of the variation in Hb level (P < .001). In 10 severely anemic patients, amelioration of anemia following intravenous iron administration resulted in normalization of serum transferrin receptor. Defective iron supply to the erythron rather than blunted epo production is the major cause of the microcytic anemia associated with SoJCA. A true body-iron deficiency caused by decreased iron absorption likely complicates long-lasting inflammation in the most anemic children, and this can be recognized by high serum transferrin receptor levels. Although oral iron is of no benefit, intravenous iron saccharate is a safe and effective means for improving iron availability for erythropoiesis and correcting this anemia. Thus, while chronically high endogenous IL-6 levels do not appear to blunt epo production, they are probably responsible for the observed abnormalities in iron metabolism. Anemia of chronic disease encompasses a variety of anemic conditions whose peculiar features may specifically correlate with the type of cytokine(s) predominantly released.

Abstract Abstract 3187 ß-Thalassemia and sickle cell disease (SCD) are the most common genetic red blood cell (RBC) disorders characterized respectively by limited production of aberrant ß-globin chains. In both cases, chronic transfusions and iron chelation are required to treat the anemia and/or formation of abnormal RBC. In ß-thalassemia, anemia stimulates erythropoietin (Epo) synthesis, which in turn leads to increased erythropoiesis and development of hepatosplenomegaly, often resulting in the need for splenectomy. Recently, we demonstrated that erythroid cells from ß-thalassemic mice have a hyper-activation of Jak2, a kinase that mediates the signaling triggered by the binding of Epo to the Epo receptor. This led us to hypothesize that Jak2 inhibitors could be utilized to minimize erythroid expansion in this disorder, limiting splenomegaly. A Jak2 inhibitor (Tg101209 or Tg) was first tested in mice affected by ß-thalassemia intermedia (th3/+). Two doses of Tg (150 and 100 mg/Kg/day) were given orally for 10 days. Tg administration induced a mild decrease of hemoglobin levels (8.8±0.2, 8±0.2 and 7.8±0.2g/dL for placebo, Tg 100 mg/Kg and Tg 150 mg/Kg treated mice, respectively. p<0.05) and in the number of reticulocytes (approximately 75% of the levels seen in controls, p<0.05). Splenomegaly was also reduced in Tg-treated mice (up to 60%; p<0.05), the extent of this effect correlating with the dosage used. Reduction of splenomegaly was associated with a decrease in the number of erythroid progenitors in this organ (p<0.05) and trend toward normalization of the splenic architecture. These data support our hypothesis that, in ß-thalassemia, splenomegaly is associated with increased erythroid proliferation and it can be alleviated by administration of Jak2 inhibitors, with only a mild increase in anemia. We further tested the effect of Tg in other anemias associated with extramedulary hematopoiesis (EMH) and splenomegaly, including SCD. Administration of the drug to mice affected by SCD led to a significant worsening of anemia (more pronounced than that seen in th3/+ mice) and a proportional reduction of splenomegaly and EMH. We then evaluated the outcome of combining Tg with blood transfusion, a common therapy in b-thalassemia and SCD. In b-thalassemia, massively enlarged spleens are believed to sequester a significant proportion of circulating RBC, thereby limiting their lifespan and the efficacy of transfusion regimens. We hypothesize that decreasing splenomegaly by administration of Jak2 inhibitors could increase the efficacy of transfusion. This was first tested in th3/+ animals. In this case, transfusion alone was sufficient to increase the hemoglobin (Hb) levels approximately 3 g/dL and reduce the spleen size to 65% of that seen in non-transfused controls. In this model, the combined effect of transfusion and administration of Tg was more effective, the spleen size been 50% of non-transfused controls (p<0.05). We further tested this approach in mice affected by ß-thalassemia-major (th3/th3), for which transfusion is required for survival and massive splenomegaly develops rapidly. Administration of Tg together with transfusion led to a greater increase in Hb levels compared to transfusion alone (9.3±0.4 vs 7.3±0.5g/dL, p<0.05). This was likely a consequence of reduced splenomegaly and decreased sequestration of RBCs in Tg/transfused mice. Lastly, we tested combination therapy in a mouse model of SCD. Mice treated with Tg and transfusion exhibited slightly lower levels of Hb than transfused controls (Hb=9.7±0.2g/dL versus Hb=10.9±0.2g/dL). However, compared to the control, mice receiving combination therapy exhibited a larger percentage of donor RBCs, while endogenous erythropoiesis was markedly suppressed along with the production of sickle RBCs (1.3±0.3×106 RBC/ul compared to transfused-controls exhibiting 2.7±0.3×106 RBC/ul). In summary, administration of Jak2 inhibitors might reduce the production of pathological cells that, together with preservation of the splenic architecture, could minimize the propensity of patients to thrombotic events. Furthermore, suppression of endogenous erythropoiesis and reduction of the transfusion regimen would be expected to also reduce iron accumulation, making it easier to prevent its toxic effects through chelation therapy. Disclosures: No relevant conflicts of interest to declare.

Abstract Abstract 3179 Ineffective erythropoiesis in congenital dyserythropoietic anemia type I (CDA I) is characterized by increased iron absorption mediated by down-regulation of hepcidin. It has been suggested that growth differentiation factor 15 (GDF15) contributes to the inappropriate suppression of hepcidin. Hemojuvelin (HJV), an important regulator of hepcidin production, is highly expressed in skeletal muscle and the liver. Mutations in the gene encoding HJV lead to severe hepcidin deficiency and juvenile hemochromatosis. Membrane-bound HJV (m-HJV) acts as a co-receptor for bone morphogenetic proteins (BMPs). HJV also exists in a soluble form (s-HJV) which competitively down-regulates hepcidin by interfering with BMP signaling. At least two proteases, furin and matriptase-2, cleave m-HJV into s-HJV. Recently, Brasse-Lagnel et al. (Heamtologica 95:2031–7, 2010) reported a new assay for measuring both the furin- and the matriptase-2-cleaved forms of s-HJV. The aim of the present study was to evaluate the possible role of s-HJV in the development of iron overload in CDA I. The study group included eight (8) Israeli Bedouins with CDA I who were homozygous for the founder mutation, c.3124C>T. All were young adults of mean age 27 years. One patient had undergone splenectomy and is currently transfusion-dependent; 3 female patients required occasional blood transfusion during intercurrent infection, pregnancy, and delivery. Nine healthy volunteers served as the comparative group. Laboratory data, including levels of serum hepcidin, ferritin, erythropoietin, soluble transferrin receptor (sTfR), and GDF 15, were previously collected in both groups (Tamary et al. Blood 112:5241–4, 2008). Serum levels of s-HJV were measured in stored frozen samples using a competitive ELISA assay based on an anti-HJV polyclonal antibody (Brasse-Lagnel et al. Heamtologica 95:2031–7, 2010). Compared to the healthy volunteers, the patient group was characterized by significantly higher levels of s-HJV (1.99±0.98mg/L vs 0.36±0.25mg/L; p=0.001), significantly lower level of hemoglobin, and significantly higher levels of serum ferritin, erythropoietin, GDF 15, and sTfR. Serum hepcidin levels were similar in the CDA I patients and the healthy volunteers, but the hepcidin-to-ferritin ratio was significantly lower in the patient group, suggesting that serum hepcidin concentrations were inappropriately low. Levels of s-HJV negatively correlated with hemoglobin levels (R= −0.69 p=0.002) and positively correlated with the iron loading parameter, serum ferritin (R=0.73 p=0.000), and parameters of erythropoiesis, such as serum erythropoietin (R=0.63 p= 0.006) and sTfR (R=0.66 p= 0.008). Additionally, GDF 15 level was positively correlated with s-HJV level (R= 0.64 p=0.006), whereas the hepcidin-to-ferritin ratio (R=−0.797 p=0.000) was negatively correlated with s-HJV level. In summary, our study suggests that s-HJV is overexpressed in patients with CDA I and probably contributes to the down-regulation of hepcidin and the iron-loading pathology. To our knowledge, this is the first study to analyze s-HJV levels in a disease characterized by ineffective erythropoiesis. The main limitation of our study is the small number of patients. Larger studies including patients with CDA and thalassemia are indicated. The source of serum s-HJV and the trigger for its overexpression in CDA I still need to be established. Disclosures: No relevant conflicts of interest to declare.

Abstract Introduction Anemia and bone disease are hallmarks of multiple myeloma (MM). Sotatercept (ACE-011) is a novel, first-in-class activin type IIA receptor fusion protein that binds with high affinity to activin A and GDF11, and it acts during late-stage erythropoiesis to increase the production of mature erythrocytes through a mechanism independent of erythropoietin. Sotatercept has shown promising activity in clinical trials for anemia in myelodysplastic syndromes (Komrokji et al., ASH 2014) and in thalassemia (Cappellini et al., EHA 2015). Additionally, we have shown that targeting activin A through an analog of sotatercept reverses osteoblast inhibition and improves MM bone disease in a mouse model (Vallet et al., PNAS 2010). Lenalidomide increases activin A secretion with consequent inhibition of osteoblastogeneis, and this can be abrogated by treatment with an activin A neutralizing antibody (Scullen et al., Leukemia 2013). Sotatercept has been previously studied with melphalan, prednisolone, and thalidomide in MM (Abdulkadyrov et al., Br J Haematol 2014). Based on these findings, we evaluated sotatercept in combination with lenalidomide and dexamethasone in MM (NCT01562405). Methods Patient with relapsed and/or refractory MM with at least one prior line of therapy, anemia with hemoglobin <13 g/dL, lytic bone disease, and otherwise adequate organ function were eligible to participate. Sotatercept 10, 15, 30, or 45 mg was given s.c. q28 days along with lenalidomide and weekly dexamethasone on a standard 28 day schedule, with dose escalation following a 3 + 3 design. Sotatercept was held for hemoglobin ≥13 g/dL or for ≥ grade 3 hypertension. Bone mineral density by DEXA was assessed after four cycles. Bisphosphonates were not permitted during the study; prior bisphosphonate therapy was allowed. Results Thirteen patients with a median age of 62 years (range 49-77) and a median of 2 prior lines (range 1-5) of therapy have been enrolled to date (July 31, 2015). Median duration of treatment is 8.1 months (range 0.5, 27 months); five patients continue on study. The MTD has not been reached, and the current dosing level is sotatercept 45 mg with lenalidomide 25 mg. Grade 3-4 adverse events included anemia (38%), diarrhea (15%), fatigue (15%), hypophosphatemia (15%), and thrombocytopenia (38%). Grade 3 hypertension occurred in one patient receiving sotatercept 15 mg (hemoglobin at the time, 11.5 g/dL). There was one death on study that was unrelated to treatment. In patients who completed at least two cycles of treatment, there was a significant mean increase in hemoglobin on study of 0.94 g/dL (N = 10, p = 0.0048) from a mean starting hemoglobin 10.27 g/dL (range 8.6, 12.2). Mean maximal increase in hemoglobin was 2.11 g/dL (range 1.1, 4). Bone density by DEXA was assessed after four cycles. In patients who received a cumulative dose of sotatercept over 45 mg (N = 6), total lumbar spine BMD increased by a mean of 2.0% after four cycles; 83% had increase in BMD. ORR for this combination was 60% (CR = 1, VGPR = 1, PR = 4, SD = 4) in patients evaluable for response. Conclusion Sotatercept in combination with lenalidomide and dexamethasone is well tolerated with expected toxicities related to lenalidomide in MM. Preliminary data from this ongoing study suggest that sotatercept leads to early increases in both hemoglobin and bone mineral density, and it is the first agent that may address both of these significant causes of morbidity in MM. Disclosures Laubach: Novartis: Research Funding; Onyx: Research Funding; Celgene: Research Funding; Millennium: Research Funding. Nooka:Onyx Pharmaceuticals: Consultancy; Spectrum Pharmaceuticals: Consultancy. O'Donnell:Millennium: Consultancy. Puccio-Pick:Celgene Corp.: Employment. Laadem:Celgene Corporation: Employment. Sherman:Acceleron Pharma: Employment. Raje:Acetylon: Research Funding; AstraZeneca: Research Funding; Onyx: Consultancy; Takeda: Consultancy; Eli Lilly: Research Funding; Millenium: Consultancy; Novartis: Consultancy; Amgen: Consultancy; BMS: Consultancy; Celgene Corporation: Consultancy.

Abstract Abstract 1018 β-Thalassemia intermedia (TI), an inherited hemoglobinopathy caused by partial loss of β-globin synthesis, is characterized by anemia, extramedullary hematopoiesis and ineffective erythropoiesis as well as secondary iron overload. Hereditary hemochromatosis (HH) is most frequently caused by mutations in HFE and is marked by excess uptake of dietary iron with concomitant tissue iron overload. In both diseases, increased iron absorption is due to inappropriately low levels of the liver hormone, hepcidin (encoded by Hamp1). The membrane serine protease Matriptase-2 (encoded by Tmprss6) attenuates BMP-mediated Hamp1 induction by cleaving the BMP co-receptor, hemojuvelin. Previously, it has been shown that elevating Hamp1 expression by genetic inactivation of Tmprss6 reduces disease severity in the Hbbth3/+ mouse model of TI and prevents iron overload in Hfe−/− mice. Therefore, a therapeutic approach comprising specific inhibition of Tmprss6 could prove efficacious in TI and HH. Here we show that systemic administration of a potent lipid nanoparticle (LNP) formulated siRNA directed against Tmprss6 leads to >80% inhibition of Tmprss6 mRNA in the livers of Hbbth3/+ and Hfe−/− mice with concomitant >2-fold elevation in Hamp1 expression. In the TI model, Tmprss6 silencing leads to ∼30% reductions in serum iron and non-heme liver iron. In Hfe−/− mice, serum iron and non-heme liver iron are similarly reduced, and Perls staining of peri-portal iron is diminished. Remarkably, the partial iron restriction induced by Tmprss6 inhibition in Hbbth3/+ mice leads to dramatic improvements in the hematological aspects of the disease phenotype: the severity of the anemia is decreased as evidenced by an approximately 1 g/dL increase in total hemoglobin and a 50% decrease in circulating erythropoietin levels. As in the human disease, Hbbth3/+ mice exhibit the hallmarks of ineffective erythropoiesis including splenomegaly, decreased erythrocyte survival and marked reticulocytosis. Treatment with LNP formulated Tmprss6 siRNA leads to a dramatic 2–3 fold decrease in spleen size, a 3–4 fold decrease in reticulocyte counts and a >7-day increase in RBC half-life. Histological analysis of spleens from Tmprss6 siRNA treated animals demonstrates restoration of normal splenic architecture, as well as a reduction in the number of Tfr1-positive erythrocyte precursors in the spleen. Furthermore, as evidenced by the near normalization of blood smears, the overall quality of erythropoiesis in treated animals is vastly improved. Taken together, these data demonstrate that RNAi-mediated silencing of liver Tmprss6 elevates Hamp1 expression and reduces iron overload in both TI and HH model mice. More significantly, Tmprss6 siRNA treatment ameliorates all aspects of the disease phenotype in the TI mouse model. These results support the development of an RNAi therapeutic targeting TMPRSS6 for the treatment of TI, HH and potentially other disorders characterized by excess iron absorption due to physiologically inappropriately low levels of hepcidin. Disclosures: Racie: Alnylam Pharmaceuticals: Employment. Butler:Alnylam Pharmaceuticals, Inc.: Employment, Equity Ownership. Bumcrot:Alnylam Pharmaceuticals, Inc.: Employment, Equity Ownership.