Role of Hepcidin In Anemia of Waldenström Macroglobulinemia

Waldenström macroglobulinemia (WM) is a B-cell lymphoproliferative disorder characterized by lymphoplasmacytic bone marrow infiltration, immunoglobulin M (IgM) monoclonal gammopathy and increased production of interleukin-6 (IL-6). Anemia occurs in a significant number of these patients and it is postulated that this occurs independently of tumor burden. Hepcidin is a hepatic peptide hormone that plays a central role in iron homeostasis and has been implicated in anemia of inflammation. Hepcidin binds to the cell-membrane iron exporter-ferroportin, causing its internalization and degradation, leading to iron deficiency anemia. The role of hepcidin in WM patients with anemia is not clearly understood. In this study we investigated the association between anemia, inflammation and hepcidin in WM patients with an eventual goal of providing improved treatment strategies for anemia in this complex set of patients.

Fifty-nine WM patients [Female N=25, Median Age 70 (49-89), Hemoglobin (Hg) 11.1gm/dl, IgM 3420mg/dl, Beta-2 Microglobulin (β2M) 3.105mcg/ml and Bone Marrow Involvement 30%] and fifteen healthy patients [Female N=6, Median Age 36 (18-51)] were analyzed. The patients were divided into anemics (Hg <12, N=38) and non-anemics (Hg >12, N=21). The serum level of IL-6 was measured using Human IL-6 ELISA Kit II (BD Biosciences) and hepcidin using Hepcidin ELISA (DRG Instruments GmbH, Germany) with protocols supplied by the manufacturers. Tumor cells from patients with WM were sorted by either CD19 or CD138 expression, RNA extracted and hybridized to Affymetrix U133A 2.0 expression arrays. Gene expression analysis was performed using Agilent Genespring GX 11.0 software. Gene expression data was summarized using GCRMA and median normalized per gene. Statistical analyses were performed by utilizing student t tests and One-way ANOVA using PRISM software.

WM patients with anemia had significantly higher levels of IgM (4121 vs. 2845mg/dl, p=0.021), beta-2 microglobulin (3.77 vs. 2.72mcg/ml, p=0.009) and bone marrow involvement (41.45 vs. 27.14%) as opposed to non-anemics. IL-6 levels were significantly higher in anemics when compared to non-anemics and controls (6.486 vs. 1.952 vs. 1.716 pg/ml, p=0.0433). Further, in WM patients with anemia serum hepcidin levels were significantly elevated when compared to non-anemics (13.03 vs. 6.08ng/ml, p=0.0123). An additional comparison was made with severe anemics (Hg <10g/dl) to non-anemics and higher mean hepcidin levels were noted in the former (16.21 vs. 6.08 gm/dl, p=0.0057).

Gene expression analysis was then performed on 12 patients identified as severe anemics (Hg < 10g/dl) or non-anemics (Hg > 12g/dl). Unsupervised clustering identified 2 major groups that separated anemics versus non-anemics. Further, unsupervised clustering segregated anemic patients with the largest IgM values, suggesting that the expression and subsequent clustering of genes was driven by the level of tumor burden in this patient cohort. Also, up-regulation of genes involved in the cell cycle and proliferation such as cyclin A2, cyclin B1, PCNA and BUB1B were identified in anemic WM patients.

A statistically significant increase in tumor burden (increased IgM, β2M and bone marrow involvement) was observed in WM patients with anemia as compared to patients without. A statistically significant increase in serum IL-6 was noted in WM patients with anemia. Interestingly, the WM patients with anemia were also noted to have higher serum hepcidin levels. Taken together, our data suggests that increased tumor burden may promote increased IL-6 and subsequently results in increased hepcidin, which correlates with anemia in WM patients. Additional studies are required to determine the specific role of hepcidin in anemia of WM. Anemia causes significant morbidity in WM patients; therefore, understanding the mechanism of anemia is important in providing superior patient care.

Fonseca:Amgen: Consultancy; Bristol-Myers Squibb: Consultancy; Celgene: Consultancy, Research Funding; Genzyme: Consultancy; Onyx: Research Funding; Otsuka: Consultancy; Medtronic: Consultancy.