Abstract
Hepcidin is a key regulator of body iron homeostasis and its increase in synthesis is implicated in anemia of inflammation (AI), which is commonly observed in patients with chronic inflammatory disorders such as MCD and RA. Inflammatory cytokines, mainly interleukin-6 (IL-6), play a central role in hepcidin induction during inflammation. However, tumor necrosis factor-a (TNF-a) does not induce but rather inhibits hepcidin expression in vitro and in vivo. The bone morphogenetic proteins (BMP) and erythropoietin (EPO) are the known positive and negative regulators of hepcidin expression. Our preliminary data has showed that MCD patients have more severe anemia and higher serum hepcidin-25 concentration than did RA patients. To clarify the mechanisms resulting in this difference, the activated patterns of hepcidin-regulating cytokines and their associations with serum hepcidin-25 levels and severity of anemia were analyzed in MCD and RA patients.
42 patients with AI (14 with MCD and 28 with RA) treated with tocilizumab (an anti-IL-6 receptor antibody) were enrolled in this study. Major iron-related parameters including serum hepcidin-25, and serum levels of cytokines including IL-6, TNF-a, BMP and EPO were measured and correlations with hepcidin-25 as well as Hb were evaluated. Effects of cytokines on IL-6-induced hepcidin expression were analyzed in hepatoma cells by quantitative real-time PCR.
The mean levels of hepcidin-25 at baseline was significantly higher (44.6 ng/ml), and Hb was significantly lower (9.2 g/dL) in MCD, than those in RA (28.6 ng/ml for hepcidin-25, 11.2 g/dL for Hb). There were significant and positive correlations of serum hepcidin-25 levels with serum ferritin and CRP in both groups (r=0.67 and 0.68 for ferritin, and r=0.41 and 0.36 for CRP, p< 0.001 respectively for both). In contrast, serum hepcidin-25 levels did not show any significant correlation with the levels of serum IL-6 or BMP or TNF-a (p > 0.05, respectively for both groups). The mean values of IL-6, TNF-a, BMP2, BMP4 and hepcidin-25 at baseline were elevated in two groups as compared to healthy control. Of note, we found that MCD patients showed significantly lower serum TNF-a (mean 195 pg/ml) and higher serum BMP4 (mean 193 pg/ml) concentrations than did RA patients (TNF-a= 241 pg/ml, BMP4= 92 pg/ml), although the two patient groups showed comparably elevated values for IL-6, BMP2 and EPO (p> 0.05, respectively). Significant improvements in anemia and systemic symptoms, and reductions in serum hepcidin-25 levels were observed within 2 weeks in both groups after tocilizumab treatment. In in vitro experiments, IL-6-induced hepcidin mRNA expression in hepatocytes was completely inhibited with tocilizumab and partially with TNF-a, but enhanced by BMP4 as well as MCD patient's serum. These results suggest that the negative effect of TNF-a on the IL-6-induced hepcidin was more pronounced in the RA than in MCD, in contrast, the positive effect of BMP was stronger in MCD than in RA. In addition, the finding that IL-6-induced hepcidin in hepatocytes was enhanced only by adding MCD patients’ serum but not RA patients’ serum, indicating the activated pattern of serum hepcidin-regulating factors in the MCD different from it in RA.
Our results suggest that the difference between MCD and RA in serum hepcidin-25 levels is partially due to the different activated patterns of positive and negative regulators of hepcidin expression. By the evidence that treatment with tocilizumab can reduce serum hepcidin and improve AI in patients with MCD and RA, we believe that IL-6 plays an essential role in the induction of hepcidin which leads to AI in MCD and RA, although multiple factors affect hepcidin levels.
No relevant conflicts of interest to declare.
Author notes
Asterisk with author names denotes non-ASH members.
