Iron Shuttle Chelation Therapy: A Novel Approach To Treating Hemoglobinopathies

I. Mustafa, N. Rossi, J. N. Kizhakkedathu and M.D. Scott
Canadian Blood Services and the Centre for Blood Research and the Department of Pathology and Laboratory Medicine at the University of British Columbia, Vancouver, BC, Canada

Background: Thalassemias arise from deficiency of the globin subunits of adult hemoglobin (HbA) and results in ineffective erythropoiesis and the rapid destruction of RBC in the periphery. These iron-driven events give rise to anemia. While transfusion therapy corrects the anemia, it give rise to secondary iron overload. Thus, both the primary and secondary pathology of thalassemia arise from “misplaced” iron. Our previous studies suggest that chelation of bioreactive iron within the thalassemic/sickle RBC may be an effective therapeutic intervention. Our research is focused on a novel iron-shuttle chelation therapy utilizing both low (shuttle) and high (docking) molecular weight iron chelators.
Methods: The effect of shuttle and docking chelators on ferric iron (Fe3+) – driven Hb and lipid oxidation was assessed singularly and in combination. Experiments were conducted in vitro using HbA exposed to Fe3+ (0-175µM). HbA oxidation was quantitated spectrophotometrically. Shuttle chelators included DFO, L1, HBED and ICL-670.The docking chelators consisted of S-DFO (a starch conjugate of DFO) and P-DFO (a novel poly(ethylene glycol)-acrylate based copolymer of DFO).Lipid peroxidation was measured by thiobabutaric acid reactive substances (TBARS) formation
Results: In the absence of Fe3+ no HbA oxidation was noted. Addition of 175µM Fe3+ resulted in rapid methemoglobin formation. Importantly, inclusion of any of our chelators inhibited HbA oxidation in a dose-dependent manner. For example,175 or 200 µM DFO , P-DFO or S-DFO respectively, inhibited >90% HbA oxidation induced by 175 µM Fe3+. Similarly, lipid peroxidation was inhibited in a chelator dose dependent manner: 400 µM DFO or P-DFO equivalents resulted in a 58 or 70% reduction TBARS formation (respectively).
Conclusions: As shown, both shuttle and docking chelators can effectively bind and remove free and complexed iron /heme from aqueous and lipid environments and prevent redox-driven damage. These data suggest that a two component iron shuttle chelation system may effectively slow/prevent iron-driven damage and improve both effective erythropoiesis and the viability of abnormal RBC within the periphery. Thus this iron shuttle system may have therapeutic importance in the treatment of hemoglobinopathies.

Note: This abstract was published on AABB Transfusion journal 2008 special edition for the anual conference in Montreal.

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