A Recombinant Antibody Against ALK2 Promotes Tissue Iron Redistribution and Contributes to Anemia Resolution in a Mouse Model of Anemia of Inflammation

Abstract

Patients with chronic inflammation are burdened with anemia of inflammation (AI), where inflammatory cytokines inhibit erythropoiesis, impede erythropoietin production, and limit iron availability by inducing the iron regulator hepcidin. High hepcidin hinders iron absorption and recycling, thereby worsening the impaired erythropoiesis by restricting iron availability. AI management is important as anemia impacts quality of life and potentially affects morbidity and mortality. The bone morphogenetic protein (BMP)-SMAD pathway is crucial for hepcidin regulation. Here, we characterized a research antibody against BMP receptor ALK2, RKER-216, and investigated its mechanism in suppressing hepcidin and improving anemia in acute/chronic inflammation. Additive effects of RKER-216 and recombinant human erythropoietin (rhEPO) on erythropoiesis and iron utilization were also explored. We showed that RKER-216 neutralized ALK2 activity by competing with the binding of BMP6. RKER-216 reduced hepcidin transcription in Hep3B cells, and a subcutaneous dose of RKER-216 at 3 mg/kg suppressed serum hepcidin and increased circulating iron for 3–4 days in wildtype mice. Moreover, RKER-216 decreased hepcidin by inhibiting SMAD1/5/9 signaling in lipopolysaccharide-mediated inflammation and liberated iron from the recycling pathway to alleviate anemia in mice with adenine-induced chronic kidney disease (CKD), a mouse model of AI. Finally, RKER-216 reversed iron-restricted erythropoiesis in CKD mice and supplied the iron requirement for complete resolution of anemia when coupled with rhEPO in addressing AI. Our data support that ALK2 is a key hepcidin regulator and that a neutralizing ALK2 antibody has the potential to restore iron homeostasis as monotherapy or in combination with rhEPO to ameliorate AI.