The Growth Differentiation Factor-15 Levels Are Increased in Patients with Compound Heterozygous Sickle Cell and Beta-Thalassemia, Correlate with Hepcidin-25/Ferritin Molar Ratio and with Markers of Hemolysis, Endothelial Dysfunction and Angiogenesis

Background: The clinical manifestations of Sickle Cell Disease (SCD) include episodes of vascular occlusion, chronic hemolytic anemia and frequent infections. SCD is also characterized by the presence of chronic inflammation manifested by leukocytosis and monocytosis and increased circulating levels of pro-inflammatory cytokines and chemokines. Growth Differentiation Factor-15 (GDF-15), also known as macrophage inhibitory cytokine 1 (MIC-1) or non-steroidal anti-inflammatory drug-activated gene (NAG-1) is a member of the transforming growth factor- superfamily. Expression of the GDF-15 gene in cardiomyocytes, vascular smooth muscle cells, and endothelial cells is strongly upregulated in response to oxidative stress, inflammation and tissue injury. Recently, GDF-15 and Twisted Gastrulation Protein (TWSG1) have been proposed to be erythroblast-derived factors, although not erythroblast specific, that mediate Hepcidin-25 suppression under conditions of increased erythropoietic activity. High levels of GDF15 associate with ineffective erythropoiesis and may reflect a certain type of bone marrow stress or erythroblast apoptosis. However, the role of GDF15 in Hepcidin-25 regulation under physiologic conditions and in other disorders is unclear and has been debated.

Aims: The aim of this study was to evaluate the GDF-15 levels in patients with compound heterozygous HbS and beta-thalassemia (HbS/β^thal) and to explore possible associations with disease features, such as Hepcidin-25 production, hemolysis, inflammation, endothelial dysfunction and angiogenesis.

Methods: Seventy-five adult Caucasian patients with HbS/β^thal were included in the study, while 20 healthy individuals served as controls. Patients with HbS/β^thal divided in two groups: group A included 36 patients under hydroxycarbamide (HC+) treatment and group B included 39 patients without hydroxycarbamide (HC-) treatment. Along with hematology and blood chemistry parameters determination, measurements of circulating levels of GDF-15, hepcidin-25, hs-CRP, vWF-antigen, hs-TnT and Placental Growth Factor (PlGF) were performed in both patients with HbS/β^thaland controls using immunoenzymatic techniques.

Results: The main results of the study included: GDF-15 levels were elevated in patients with HbS/β^thal compared to controls ((1,980.7±159.8 vs 665.4±50.9 pg/mL, p<0.001). Regarding hydroxycarbamide treatment, GDF-15 levels were elevated in (HC+) patients compared to (HC-) patients (p=0.002), or 30/36 vs 21/39 patients had elevated GDF-15 levels (p=0.002). In contrast, Hepcidin-25 levels were significantly lower in patients with HbS/β^thal compared to controls (57.2±12.3 vs 67.3±9.1 ng/mL, p<0.01). The reduction of Hepcidin-25 levels was more pronounced in (HC-) patients compared to (HC+) patients (p=0.005). In addition, a markedly low Hepcidin-25/Ferritin molar ratio was obsereved in patients with HbS/β^thal compared to controls (p<0.001). Whilst, no direct correlation was found between GDF-15 and hepcidin-25 levels, a significant negative correlation between GDF-15 levels and Hepcidin-25/Ferritin molar ratio was detected in patients with HbS/β^thal(p=0.002). GDF-15 levels also correlated significantly with markers of erythropoiesis, such as Hb, HbF, ferritin and reticulocytes (p<0.05), with markers of hemolysis, such as LDH and uric acid (p<0.01), and with markers of endothelial dysfunction and angiogenesis such as vWF-antigen and PlGF (p<0.01). Surprisingly, no correlation was found between GDF-15 and hs-CRP levels.

Conclusions: These findings demonstrate a multifactorial role of GDF-15 in patients with HbS/β^thal as it correlates with erythropoiesis, hemolysis, endothelial dysfunction and angiogenesis. However, we found no direct specific function, despite the negative correlation with Hepcidin-25/Ferritin molar ratio. Interestingly, the higher GDF-15 levels measured in patients treated with hydroxycarbamide may reflect possible drug induced sub-clinical cardiotoxicity, although this has not been described to-date. To this end, our knowledge is restricted only to doxorubicin-induced cardiotoxicity, where GDF-15 up-regulation seems to be more sensitive than that of hs-TnT, LDH and NT-proBNP. Further studies will reveal the role of GDF-15 in the biology of HbS/β^thal.