Iron Metabolism and Erythropoietic Stress in Myelodysplastic Syndromes.
Authors: Santini Valeria , Sanna Alessandro , Duca Lorena , Gozzini Antonella , Girelli Domenico , Cortelezzi Agostino , Reda Gianluigi , Campostrini Natascia , Cappellini Maria Domenica 
Published: October 2019

Abstract
Abstract 1752
Poster Board I-778
Iron overload (IO) occurs in a large proportion of patients affected by myelodysplastic syndromes; however data on the mechanisms responsible for IO and on the consequences on organ damages are scanty. IO in MDS may result both from ineffective erythropoiesis and from reiterative transfusions. The role of iron chelation therapy in MDS is deduced from thalassemia experience. We evaluated parameters of iron metabolism and erythropoiesis in 171 consecutive chelation naïve MDS patients. Patients were classified according WHO criteria, and prognostic scores evaluated according IPSS and WPSS criteria. CMML patients (n= 7) were also included in the analysis. Serum ferritin, iron, transferrin, transferrin saturation and non-transferrin-bound iron (NTBI) were measured. Growth-differentiation factor-15 (GDF-15) and hepcidin-25 were also determined, parallel to hemoglobin, endogenous erythropoietin (EPO) and LDH. All the parameters studied were highly variable within the analyzed cohort, as expected due to the great heterogeneity of MDS. As already observed, ferritin levels were higher than normal range in MDS patients (1091 ± 1135 ng/ml) and significantly increased in transfused ones (1890,55 ± 1833 ng/ml). EPO production was stimulated in all MDS patients (215, 40; range 85-1011 U/L), respect to normal range, and physiologically inversely correlated with hemoglobin levels (p<0.001). Serum EPO was lower in IPSS low risk patients than in IPSS high risk ones. Analysis of variance among different WHO subtypes indicated that RAEB-2 patients had the highest levels of EPO, 5q- patients had significantly increased levels of EPO (313; 67,7-836 U/L), while RARS and RA patients did not show significantly higher EPO than other WHO MDS subtypes. NTBI was found elevated in all MDS patients (0,35 ± 1,73 microM) respect to normal subjects (-0,72 ± 0,39 microM). NTBI levels did not correlate with disease duration, nor with patient age. NTBI was significantly elevated in RARS patients (2,37; -0,8-9,3 microM) compared to other WHO subtypes (0,123; -2,3 - 4,5 microM). An increasing trend was observed in MDS patients with high and very high WPSS score. Consistently, toxic iron was significantly increased in transfused MDS patients (1,214; -1,38-9,26 microM) vs non transfused ones (-0,052; -2,23 - 5,84 microM). GDF-15, a marker of erythropoietic stress, was significantly increased in MDS patients (9429; 302-87758 pg/ml) compared to normal subjects (450 ± 50 pg/ml). Transfused patients had higher GDF-15 values vs non-transfused patients (12458,0; 838-74717 pg/ml vs 6623,15; 302-43816 pg/ml respectively). GDF-15 levels did not correlate with disease duration, age, WHO subtypes, or IPSS and WPSS prognostic scores. A correlation between NTBI and: ferritin (p< 0.001), GDF-15 (p= 0.048) and transferrin saturation (p<0.001) was observed. Serum hepcidin-25, measured by mass spectrometry, was significantly elevated in IPSS low risk MDS patients (9,48; 1,06-38,35 nM) respect to normal (4,62 3.01–7.02 nM), with the exception of RARS patients, where hepcidin-25 was significantly lower (3,71 ± 1,33 nM) than normal, with high GDF-15 (8027,82 ± 7086,32 pg/ml). Hepcidin was found significantly increased in CMML, RAEB-1 and unclassifiable MDS patients (19,1 nM), while patients with RCMD had less high levels (8,27 ± 6,63 nM). Hepcidin levels did not show linear correlation with GDF-15, NTBI, and ferritin. LDH was not correlated with NTBI, GDF-15, hepcidin, EPO and ferritin. These observations indicate that in MDS patients iron homeostasis is altered although the clear relationship among the different players (hepcidin, GDF-15, EPO) is not yet fully understood. Many factors may be involved, including the intervention of pro-inflammatory cytokines as stimulators of hepcidin production in MDS, counterbalancing GDF-15 effect. The “ferrostat“ mechanism seemed to be maintained only in RARS patients who had the highest levels of NTBI and elevated GDF-15, with consequent repression of hepcidin production. Our results suggest that the regulation of iron absorption in MDS may be altered by the concomitant effect of several parameters acting at different rates in the various subtypes of dysplasia: GDF-15, induced by the expanded erythroid dysplastic compartment, but also EPO, hypoxia, generation of ROS and production of cytokines. The significance of each of these molecules needs to be further investigated.

Disclosures
No relevant conflicts of interest to declare.