Hepcidin Overproduction Mediates the Anemia of Multiple Myeloma.

Hepcidin is a liver-produced protein that has been implicated in the anemia of chronic inflammatory/infectious disease. Hepcidin expression is stimulated during infection/inflammation and, by downregulating the iron exporter ferroportin, hepcidin prevents release of iron from macrophages and enterocytes. This results in a decrease in delivery of iron to maturing erythrocytes and significant anemia. Since IL-6 is the major cytokine upregulating hepcidin expression during inflammation/infection and, since high levels of IL-6 are often present in multiple myeloma (MM), we initiated the current study examining a role of hepcidin in the anemia of MM. Pretreatment urinary hepcidin levels were determined in 44 patients with stage III MM. The mean level of hepcidin (191ng/mg of creatinine) was significantly higher than normal controls (64.5ng/mg of creatinine). In contrast, patients with MGUS did not demonstrate elevated hepcidin levels. In the subset of MM patients without renal insufficiency (n=27) a marked inverse correlation was seen between hemoglobin level at diagnosis and hepcidin level (r= −0.46, p=0.014). This correlation is even more impressive because anemia in general (when not due to hepcidin overexpression) results in a decrease in hepcidin levels. These data strongly supported hepcidin upregulation as a major cause of anemia of MM. The hepcidin level also correlated with serum ferritin levels (n=28, r=0.37, p=0.048). A role for IL-6 in hepcidin upregulation was suggested by a significant correlation between hepcidin levels and C-reactive protein, an IL-6 targeted gene (n=28, r= 0.57, p=0.0012). However a correlation between hepcidin and serum IL-6 levels just missed significance (n=27, r= 0.36, p= 0.0599). Furthermore, real time PCR in vitro studies also suggested that IL-6 played a role but could not completely account for all cases of hepcidin upregulation. As compared to normal serum, sera from six MM patients (with known elevated hepcidin levels) significantly induced hepcidin RNA in a liver cell line, Hep3B. In the patients with co-existing high IL-6 levels, the serum-induced hepcidin RNA was prevented by anti-IL-6 and anti-IL6 receptor antibodies. However, in the patients with lower IL-6 levels, these blocking antibodies were unable to prevent sera-induced hepcidin RNA. Additional studies on myeloma cells isolated from marrow of a patient with high hepcidin level demonstrated an absence of hepcidin RNA in the resting or IL-6 stimulated state, indicating that the MM cells themselves do not participate in the increased production of hepcidin. These data strongly support the notion that enhanced expression of hepcidin is an important cause of the anemia of MM and suggest a role of IL-6 and other, yet to be identified, serum factors in the hepcidin upregulation.