The anemia of chronic disease (ACD) is one of the most common clinical syndromes encountered in the practice of medicine. This disorder typically manifests itself as a hypoproliferative anemia accompanied by a low serum iron concentration despite adequate reticuloendothelial iron stores. ACD has generally been considered to result from a combination of pathologic processes which can be linked to the cytokine mediators of inflammation. However, the diagnostic importance of altered iron metabolism in ACD has led many investigators to consider that this feature denotes the dominant pathophysiologic mechanism of this syndrome. Hepcidin is an antibacterial protein which is produced in the liver, circulates in the blood, and is excreted in the urine. It is a type II acute phase protein, the expression of which is induced by interleukin (IL)-6, and down-regulated by tumor necrosis factor (TNF). The specific iron regulatory functions of hepcidin, as well as the anemia syndromes observed in patients and transgenic animals with abnormalities of hepcidin gene expression (discussed below), have led many to consider that it is the key to unlocking """"""""the mysteries of ACD """""""". Three major processes are involved in the pathogenesis of ACD. A slight shortening of red cell survival creates a demand for a small increase in red cell production by the bone marrow. The marrow cannot respond adequately to this demand due to impaired erythropoiesis and impaired mobilization of reticuloendothelial system iron stores. A potential role for hepcidin in the iron anomalies of ACD is strongly supported by available data. However, iron changes are not the sole abnormality characteristic of ACD. If hepcidin is the major factor responsible for ACD, then it should also contribute to the impaired erythropoiesis observed in this syndrome. The hypothesis that hepcidin contributes to impaired erythropoiesis in ACD will be addressed through the following specific aims: 1. Determination of hepcidin effects on erythroid colony formation, and investigation of the mechanisms involved. This will include A., whether the effects of hepcidin on erythropoiesis are direct-acting, or require an accessory cell;B., the role of Epo concentration in hepcidin effects on erythropoiesis;C., the role of apoptosis/anti-proliferation in inhibitory effects of hepcidin on erythropoiesis;D., the effects of cytokines on the hepcidin/erythropoiesis relationship;E., the contributions of iron to hepcidin effects on CFU-E colony formation;F., the role of ferroportin (FPN) and variant FPN in hepcidin effects on CFU-E;and G., effects of Epo and inflammatory cytokines on FPN variant expression in erythroid cells. 2. Determination of the interactions of hepcidin and cytokines in bone marrow macrophage iron transport. Hepcidin inhibits egress of iron from bone marrow macrophages by downregulation of the iron export protein FPN. The ability of inflammatory cytokines to enhance or diminish this effect will be determined, as well as any effects on the expression of variant FPN.3. Determination of hepcidin effects on induced Epo production in vitro, and delineation of involved mechanisms. This will include A., determination and quantification of the effects of hepcidin on the induction of Epo protein in hepatic and renal models, and of the time-course of these effects;and B., determination of the roles of inflammatory cytokines in modulating these effects;C., the role of iron availability in these effects;and D., determination of the effects of hepcidin on Epo transcription, and the mechanism involved in these effects. 4. Effects of rhEpo on hepcidin production in vitro. In this Aim, we will determine A., the effects of Epo on hepcidin production by HepG2, as well as B., the extent to which these effects are modulated by TNF, IL-1, and IL-6. Relevance to VA mission: The proposed studies can potentially lead to an enhanced understanding of the mechanisms of ACD, and lead to more effective therapy.
Anemia is a major contributor to morbidity and mortality in chronically ill patients, and the anemia of chronic disease (ACD) is the major etiology of this anemia. This disorder typically manifests itself as a hypoproliferative anemia accompanied by a low serum iron concentration despite adequate reticuloendothelial iron stores. ACD is highly prevalent in the VA population. In ACD, a slight shortening of red cell survival creates a demand for a small increase in red cell production by the bone marrow. The marrow cannot respond adequately to this demand due to impaired erythropoiesis and impaired mobilization of reticuloendothelial system iron stores. A potential role for hepcidin in the iron anomalies of ACD is strongly supported by available data. If hepcidin is the major factor responsible for ACD, then it should also contribute to the impaired erythropoiesis observed in this syndrome. The proposed studies can potentially lead to an enhanced understanding of the mechanisms of ACD, and therefore to more effective therapy.
