No abstract

Plasma non-transferrin-bound-iron (NTBI) is believed to be responsible for catalyzing the formation of reactive radicals in the circulation of iron overloaded subjects, resulting in accumulation of oxidation products. We assessed the redox active component of NTBI in the plasma of healthy and ␤-thalassemic patients. The labile plasma iron (LPI) was determined with the fluorogenic dihydrorhodamine 123 by monitoring the generation of reactive radicals prompted by ascorbate but blocked by iron chelators. The assay was LPI specific since it was generated by physiologic concentrations of ascorbate, involved no sample manipulation, and was blocked by iron chelators that bind iron selectively. LPI, essentially absent from sera of healthy individuals, was present in those of ␤-thalassemia patients at levels (1-16 M) that correlated significantly with those of NTBI measured as mobilizer-dependent chelatable iron or desferrioxamine chelatable iron. Oral treatment of patients with deferiprone (L1) raised plasma NTBI due to iron mobilization but did not lead to LPI appearance, indicating that L1-chelated iron in plasma was not redox active. Moreover, oral L1 treatment eliminated LPI in patients. The approach enabled the assessment of LPI susceptibility to in vivo or in vitro chelation and the potential of LPI to cause tissue damage, as found in iron overload conditions. (Blood. 2003;102: 2670-2677)

Progressive iron overload is the most salient and ultimately fatal complication of ␤-thalassemia. However, little is known about the relationship among ineffective erythropoiesis (IE), the role of iron-regulatory genes, and tissue iron distribution in ␤-thalassemia. We analyzed tissue iron content and iron-regulatory gene expression in the liver, duodenum, spleen, bone marrow, kidney, and heart of mice up to 1 year old that exhibit levels of iron overload and anemia consistent with both ␤-thalassemia intermedia (th3/؉) and major (th3/th3). Here we show, for the first time, that tissue and cellular iron distribution are abnormal and different in th3/؉ and th3/th3 mice, and that transfusion therapy can rescue mice affected by ␤-thalassemia major and modify both the absorption and distribution of iron. Our study reveals that the degree of IE dictates tissue iron distribution and that IE and iron content regulate hepcidin (Hamp1) and other iron-regulatory genes such as Hfe and Cebpa. In young th3/؉ and th3/th3 mice, low Hamp1 levels are responsible for increased iron absorption. However, in 1-year-old th3/؉ animals, Hamp1 levels rise and it is rather the increase of ferroportin (Fpn1) that sustains iron accumulation, thus revealing a fundamental role of this iron transporter in the iron overload of ␤-thalasse- Introduction␤-Thalassemia is the most common congenital hemolytic anemia due to partial or complete lack of synthesis of ␤-globin chains. Cooley anemia, 1 also known as ␤-thalassemia major, is the most severe form of ␤-thalassemia, which is characterized by profound ineffective erythropoiesis (IE) requiring regular red blood cell (RBC) transfusions to sustain life. Transfusion therapy leads to excess iron accumulation in many organs resulting in tissue damage. Therefore, iron chelation is essential in the management of this otherwise fatal disease. 2 In ␤-thalassemia intermedia, in which a larger amount of ␤-globin chains are synthesized, the clinical picture is milder and the patients do not require frequent transfusions. However, progressive iron overload still occurs due to increased gastrointestinal (GI) iron absorption. [3][4][5] Studies in thalassemic patients showed that the rate of iron uptake from the GI tract is approximately 3 to 4 times greater than normal. 6 Ferrokinetic studies revealed that 75% to 90% of the iron in donor serum, labeled with 59 Fe and injected into healthy subjects, appeared in circulating red cells within 7 to 10 days. In some thalassemic patients, however, only 15% of the 59 Fe was incorporated into circulating erythrocytes. 7 This discrepancy was attributed to the fact that iron would be sequestered in those organs in which premature destruction of erythroid precursors occurs. In ␤-thalassemia, it has been suggested that 60% to 80% of erythroid precursors die in the marrow and extramedullary sites. [8][9][10] Therefore, in ␤-thalassemia erythropoietic organs such as the bone marrow (BM) in humans and the BM and spleen in mice would be expected to show the highest iron concen...