Site-specific cross-linking of human and bovine hemoglobins differentially alters oxygen binding and redox side reactions producing rhombic heme and heme degradation

Nagababu Enika, Somasundaram Ramasamy, Joseph Moses Rifkind, Yiping Jia, Abdu I. Alayash

Research output: Contribution to journalArticle

Abstract

Chemically modified human or bovine hemoglobins (Hb) have been developed as oxygen-carrying therapeutics and are currently under clinical evaluation. Oxidative processes, which are in many cases enhanced when modifications are introduced that lower the oxygen affinity, can limit the safety of these proteins. We have carried out a systematic evaluation of two modified human Hbs (O-R-polyHbA0 and DBBF-Hb) and one bovine Hb (polyHbBv). We have both measured the oxidative products present in the Hb preparations and followed the oxidative reactions during 37 °C incubations. Autoxidation, the primary oxidative reaction which initiates the oxidative cascade, is highly correlated with P50 (R = 0.987; p <0.002). However, when the results for the other oxidative processes are compared, two different classes of oxidative reactions are identified. The formation of oxyferrylHb, like the rate of autoxidation, increases for all modified Hbs. However, the subsequent reactions, which lead to heme damage and eventually heme degradation, are enhanced for the modified human Hbs but are actually suppressed for bovine-modified Hbs. The rhombic heme measured by electron paramagnetic resonance, which is the initial step that causes irreversible damage to the heme, is found to be a reliable measure of the stability of ferrylHb and has the tendency to produce degradation products, DBBF-Hb, a Hb-based oxygen carrier (HBOC) for which toxic side effects have been well documented, has the highest level of rhombic heme (41-fold greater than for HbA0), even though its rate of autoxidation is relatively low. These findings establish the importance of these secondary oxidative reactions over autoxidation in evaluating the toxicity of HBOCs.

Original languageEnglish (US)
Pages (from-to)7407-7415
Number of pages9
JournalBiochemistry®
Volume41
Issue number23
DOIs
StatePublished - Jun 11 2002
Externally publishedYes

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Heme
Oxidation-Reduction
Hemoglobins
Oxygen
Degradation
Poisons
Electron Spin Resonance Spectroscopy
Paramagnetic resonance
Toxicity
Safety
Proteins

ASJC Scopus subject areas

  • Biochemistry

Cite this

Site-specific cross-linking of human and bovine hemoglobins differentially alters oxygen binding and redox side reactions producing rhombic heme and heme degradation. / Enika, Nagababu; Ramasamy, Somasundaram; Rifkind, Joseph Moses; Jia, Yiping; Alayash, Abdu I.

In: Biochemistry®, Vol. 41, No. 23, 11.06.2002, p. 7407-7415.

Research output: Contribution to journalArticle

Enika, Nagababu ; Ramasamy, Somasundaram ; Rifkind, Joseph Moses ; Jia, Yiping ; Alayash, Abdu I. / Site-specific cross-linking of human and bovine hemoglobins differentially alters oxygen binding and redox side reactions producing rhombic heme and heme degradation. In: Biochemistry®. 2002 ; Vol. 41, No. 23. pp. 7407-7415.
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AB - Chemically modified human or bovine hemoglobins (Hb) have been developed as oxygen-carrying therapeutics and are currently under clinical evaluation. Oxidative processes, which are in many cases enhanced when modifications are introduced that lower the oxygen affinity, can limit the safety of these proteins. We have carried out a systematic evaluation of two modified human Hbs (O-R-polyHbA0 and DBBF-Hb) and one bovine Hb (polyHbBv). We have both measured the oxidative products present in the Hb preparations and followed the oxidative reactions during 37 °C incubations. Autoxidation, the primary oxidative reaction which initiates the oxidative cascade, is highly correlated with P50 (R = 0.987; p <0.002). However, when the results for the other oxidative processes are compared, two different classes of oxidative reactions are identified. The formation of oxyferrylHb, like the rate of autoxidation, increases for all modified Hbs. However, the subsequent reactions, which lead to heme damage and eventually heme degradation, are enhanced for the modified human Hbs but are actually suppressed for bovine-modified Hbs. The rhombic heme measured by electron paramagnetic resonance, which is the initial step that causes irreversible damage to the heme, is found to be a reliable measure of the stability of ferrylHb and has the tendency to produce degradation products, DBBF-Hb, a Hb-based oxygen carrier (HBOC) for which toxic side effects have been well documented, has the highest level of rhombic heme (41-fold greater than for HbA0), even though its rate of autoxidation is relatively low. These findings establish the importance of these secondary oxidative reactions over autoxidation in evaluating the toxicity of HBOCs.

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