Structural stabilization in tetrameric or polymeric hemoglobin determines its interaction with endogenous antioxidant
Paul W Buehler1, Florence Vallelian, Malgorzata G Mikolajczyk
1Laboratory of Biochemistry and Vascular Biology, Division of Hematology, Center for Biologics Evaluation and Research (CBER), U.S. Food and Drug Administration (FDA), Rockville, Maryland, USA.
Antioxidants & Redox Signaling
|June 5, 2008
Summary
Chemically modified hemoglobin (Hb) toxicity is linked to heme
Area of Science:
- Biochemistry
- Pharmacology
- Toxicology
Background:
- Extracellular hemoglobin (Hb) and modified Hb therapeutics can cause toxicity due to heme's oxidant activity.
- Native Hb is cleared by haptoglobin (Hp) after dimerization, or by CD163 on monocytes/macrophages.
- Understanding Hb-scavenger interactions is crucial for developing safer Hb-based oxygen carriers (HBOCs).
Purpose of the Study:
- To investigate how chemical cross-linking patterns and molecular size affect Hb binding to Hp and CD163.
- To determine the impact of cross-linking on Hb clearance pathways.
- To guide the rational design of HBOCs with optimized safety profiles.
Main Methods:
- Evaluation of various chemically modified Hbs with different cross-linking strategies.
- Assessment of Hb binding affinity to haptoglobin (Hp).
- Analysis of Hb interaction with CD163 and cellular uptake in CD163-expressing cells, measuring HO-1 induction and ferritin accumulation.
Main Results:
- Beta-globin cross-linking increased Hp affinity, suggesting alpha-subunit accessibility is key for Hp binding without dimerization.
- Cross-linked tetramers/polymers showed strong polyvalent Hp binding, increased viscosity, and gel formation.
- CD163 interaction and cellular uptake decreased with increasing molecular size, regardless of cross-linking type.
Conclusions:
- Hb modifications influence interactions with endogenous clearance systems (Hp and CD163).
- Beta-globin cross-linking enhances Hp binding, while larger molecular size reduces CD163 uptake.
- These findings enable a systematic approach to designing safer and more effective HBOCs by optimizing Hb clearance and detoxification.
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