Non-Transferrin-Bound Iron and Oxidative Stress Are Related to the Degree of Erythropoiesis in Patients with Thalassemia Intermedia.

There is strong evidence that reactive oxygen species (ROS) are involved in the pathogenesis of thalassaemias. It has been shown that ROS are generated in increased amounts in thalassemic erythrocytes following the precipitation of excess unmatched globin chains and the deposition of non-heme iron and hemichromes. Continuous ROS production in thalassemic individuals may alter their overall redox status and cause tissue damage. Reduction in the levels of vitamin C, vitamin E, and carotenoids has been reported in beta-thalassemic patients receiving transfusion therapy. In this study we investigated the oxidative stress in relation to the degree of erythropoiesis in patients with beta-thalassemia Intermedia (TI). Forty patients with TI were included in the study. Sixteen patients had mild anemia and mild clinical phenotype. The remaining 24 patients had more severe phenotype, but rare transfusions had been used in only 8 of them. Non-transferrin-bound iron (NTBI) levels were determined using graphite furnace atomic absorption spectrometry. Lipid peroxidation expressed as malonyldialdehyde (MDA) concentration was measured by reverse-phase HPLC with fluorimetric detection. The erythroid marrow activity was estimated by measuring soluble transferrin receptors (sTfR) levels with a turbidimetric technique. The main results of the study showed thatNTBI and MDA levels were increased (normal controls <0.05micromol/L and <0.65 micromol/L respectively) in 32/40 patients, while sTfR was found 4- to 20-fold higher than normal in all patients,NTBI, MDA and sTFR levels were significantly higher in patients with the more severe phenotype compared with patients with the milder phenotype (p<0.01),NTBI correlated positively: with MDA (rho=0.502, p<0.003), with sTfR (rho=0.371, p<0.02) and Hb F (rho=0.464, p<0.005), while no correlation was found between NTBI and Hb levels (p>0.278) andMDA was correlated significantly with Hb F (rho=0.464, p<0.005), while the correlation with sTfR levels was poor (rho=0.313, p<0.05). Patients with thalassemia intermedia have increased MDA levels, suggestive of imbalanced oxidant/antioxidant equilibrium. This phenomenon seems to be related to altered iron homoestasis, especially with the increased levels of NTBI. NTBI induces ROS production mainly through the Fenton reaction. NTBI levels are affected by the severity of tissue hypoxia, as these were expressed by their positive correlations with levels of sTfR, MDA and Hb F. The following hypothesis may be explain our findings; increased Hb F leads to tissue hypoxia, which induces further erythropoetic activity, as this is expressed by increased sTfR levels. Increased erythropoetic activity, possibly through a negative effect on hepcidin production (Kattamis et al, Haematologica91: 809–12, 2006) results in increased NTBI levels, which lead to increased ROS production and MDA levels. Further studies are required to validate this hypothesis that altered iron cycle contributes to the oxidant/antioxidant imbalance observed in thalassemia intermedia.