Pharmacologic inhibition of hepcidin expression reverses anemia of chronic inflammation in rats

Abstract

Anemia of chronic inflammation (ACI) is the most frequent anemia in hospitalized patients and is associated with significant morbidity. A major underlying mechanism of ACI is the retention of iron within cells of the reticuloendothelial system (RES), thus making the metal unavailable for efficient erythropoiesis. This reticuloendothelial iron sequestration is primarily mediated by excess levels of the iron regulatory peptide hepcidin downregulating the functional expression of the only known cellular iron export protein ferroportin resulting in blockade of iron egress from these cells. Using a well-established rat model of ACI, we herein provide novel evidence for effective treatment of ACI by blocking endogenous hepcidin production using the small molecule dorsomorphin derivative LDN-193189 IntroductionAnemia of chronic inflammation (ACI), also termed anemia of chronic disease, is the most frequent anemia in hospitalized patients and develops in subjects suffering from diseases with associated immune activation, such as infections, autoimmune disorders, cancer and end stage renal disease. 1,2 A major cornerstone in the pathophysiology of ACI is iron limited erythropoiesis, caused by iron retention within macrophages. 1,[3][4][5][6] Cytokines and most importantly the acute phase protein hepcidin promote macrophage iron retention by increasing erythrophagocytosis and cellular iron uptake and by blocking iron egress from these cells. 5,[7][8][9][10] The primarily liver derived peptide, hepcidin, exerts regulatory effects on iron homeostasis by binding to ferroportin, the only known iron export protein, thereby leading to ferroportin degradation and subsequently to inhibition of duodenal iron absorption and macrophage iron release. 5,6,11,12 The crucial role of hepcidin for the development of macrophage iron retention, hypoferremia and ACI is underscored by the observations that mice overexpressing hepcidin develop severe anemia, 7,13 that macrophage iron retention and hyperferritinemia are positively associated with hepcidin formation 5,14 and that injection of LPS into healthy volunteers results in hepcidin production and hypoferremia. 15 The expression of hepcidin in hepatocytes is regulated by multiple signals. 16 Iron overload induces the formation of bone morphogenetic proteins (BMPs) 17 and activates phosphorylation of Smad1/5/8 phosphorylation, 17-20 which forms a transcriptional activator complex with Smad4 to stimulate hepcidin transcription. [21][22][23] In mice, BMP6 appears to play a major role in hepcidin regulation, as BMP6 knock out mice have hepcidin deficiency resulting in systemic iron overload. 24,25 Hemojuvelin (HJV) or HFE2, a membrane bound GPI-anchored protein 26,27 acts as a BMP coreceptor and promotes hepcidin transcription. 21 In contrast, a soluble form of HJV (sHJV) blocks BMP6 and inhibits hepcidin expression. 28 The inflammation mediated activation of hepcidin is mainly transmitted via the IL6-inducible transcription factor Stat3. [29][30][31] In addition, Stat3 signaling is influe...

Manipulation of the hepcidin pathway for therapeutic purposes

“…This regimen decreased hepcidin, increased serum iron and effectively reversed anemia. 74 Similarly, in a chronic turpentine model of anemia of inflammation in mice, daily injections of LDN-193189 administered concurrently with turpentine injections 77 prevented the development of anemia. LDN-193189 improved hemoglobin even when administered to mice after the turpentine-induced anemia was already established.…”

“…72,73 sHJV.Fc was also shown to ameliorate anemia of inflammation in a rat model. 74 Rats were injected with Group A Streptococcal Peptidoglycan-Polysaccharide (PG-APS), and three weeks later they were injected with sHJV.Fc (20 mg/kg) twice a week for an additional four weeks. sHJV.Fc treatment resulted in higher hemoglobin, increased ferroportin levels in the spleen and higher serum iron, although by this point hepcidin mRNA was not significantly decreased.…”

Mechanisms of Anemia in CKD

“…Several strategies under investigation include antagonizing hepcidin directly, inhibiting hepcidin production, interfering with the hepcidin/ferroportin interaction, or stabilizing ferroportin. [38][39][40][41] Initial small studies suggest that targeting this pathway can increase iron mobilization and hemoglobin in animal models of anemia of chronic disease. [39][40][41] The side effect profiles and whether these strategies will prove effective for treating anemia of CKD in humans remain unknown.…”

BMPS and Liver: More Questions than Answers

“…In spite of their potential effects on other kinases different from the BMP pathways, these inhibitors are potentially effective for some clinical disorders. Dorsomorphin was proved to inhibit BMP-induced expression of hepcidin in vitro and maintained iron-hepcidin homeostasis in vivo [98] LDN-193189 attenuates anemia associated with inflammation due to its capacity to inhibit hepcidin expression [101,163] The use of biological compounds, such as antibodies or soluble extracellular inhibitors (traps) might allow for more specific inhibition of ALK1 activity, although caution must be taken to minimize crosstalk between different signaling pathways. The development of different biological ALK1 inhibitors for use in vivo has been reported [153].…”