Forum: therapeutic applications of reactive oxygen and nitrogen species in human diseasePyridoxalated hemoglobin polyoxyethylene: a nitric oxide scavenger with antioxidant activity for the treatment of nitric oxide-induced shock
Introduction
Hemoglobin-based therapeutics are currently under development for a wide range of applications. These include oxygen-carrying fluids intended for blood replacement during surgery and hemorrhagic shock, enhancers of radiation and chemotherapy, and scavengers of nitric oxide [1], [2], [3]. Hemoglobin-based therapeutics are produced by modification of ultrapurified or stroma-free hemoglobin using a variety of intermolecular or intramolecular reactions. The class of hemoglobin molecules can be characterized by the type of modification and can be grouped into one of the following categories: cross-linked, conjugated, or polymerized [4], [5], [6]. In addition, liposomal encapsulation of unmodified or modified hemoglobin is under development as a hemoglobin-based oxygen carrier [3]. These modifications are generally designed to stabilize the protein and modulate oxygen binding (P50) to acceptable physiological levels, as well as to decrease renal toxicity. Due to the presence of both the heme and iron moieties, potential toxicities have been postulated with in vivo use of these products [7], [8]. These toxicities include rapid autoxidation of cell-free hemoglobin following free radical interactions, hemoglobin-mediated vasoconstriction, and reactions of hemoglobins with cellular oxidants such as hydrogen peroxide, resulting in production of both methemoglobin (Fe3+) and ferrylhemoglobin (Fe4+), a strong oxidant reported to cross-link proteins and peroxidize lipids. In addition, the complex interplay of reactive species including superoxide, nitric oxide, and peroxynitrite, whose levels will be influenced by reaction with hemoglobin, can potentially perturb the balance between pro- and antioxidant processes normally present in the vasculature [9].
Pyridoxalated hemoglobin polyoxyethylene conjugate (PHP) is a chemically modified, human-derived hemoglobin currently in clinical trials as a nitric oxide (NO) scavenger for the treatment of shock associated with systemic inflammatory response syndrome (SIRS), a subset of NO-induced shock [10]. NO-induced shock occurs in proinflammatory states that can be the result of infection or other etiologies such as burns, pancreatitis, hemodialysis, and cytokine therapies. These proinflammatory disorders are collectively referred to as systemic inflammatory response syndrome (SIRS) [11]. NO-induced shock is characterized by clinical hypotension (acute low blood pressure) and contributes to significant morbidity (multiple organ failure) and high mortality [12]. The role of NO in various forms of shock [13] and sepsis [14] has been the subject of recent reviews. In addition to overproduction of NO, patients with septic shock, a subset of NO-induced shock, have decreased antioxidant status [15], increased lipid peroxidation [15], and increased xanthine oxidase activity [16], suggesting a role for oxidative stress in shock and multiple organ failure.
These findings, in conjunction with concerns regarding hemoglobin-mediated production of or participation in oxygen radical-mediated events, suggest that a hemoglobin-based NO scavenger with antioxidant activity would be a candidate for treatment of the hypotension associated with NO-induced shock. In this regard, the chemical modification described below results in a surface-decorated hemoglobin, PHP, which contains endogenous catalase-superoxide dismutase (SOD) activities [17], [18], [19], [20], [21]. PHP, in several in vitro models, has been demonstrated to display decreased reactivity toward hydrogen peroxide (H2O2)-mediated oxidations when compared to unmodified HbA or αα-crosslinked hemoglobin [17], [18], [19], [20]. These results indicate that the redox reactivity of hemoglobin preparations can be manipulated and, in addition, suggest that modified hemoglobins containing endogenous antioxidants may reduce the pro-oxidant potential of hemoglobin.
Section snippets
Chemical characterization
PHP was initially developed in the 1980s as an oxygen carrier [22], [23]. PHP is produced from erythrocyte lysate obtained from outdated human red blood cells. The purification method used for production provides for separation of the hemoglobin from red cell stroma and potential adventitious agents, but not from several of the enzymes normally associated with hemoglobin in red blood cells [21]. The purified hemoglobin is then subjected to pyridoxalation in order to reduce the oxygen affinity.
Conclusion
The pro-oxidant potential of modified hemoglobins is currently the focus of intense interest as these products are being evaluated in clinical trials as hemoglobin-based oxygen carriers and nitric oxide scavengers. One such product, PHP, is a human-derived and chemically modified hemoglobin preparation currently in clinical trials as a NO scavenger for the treatment of shock associated with SIRS. This new mechanism-based therapy has yielded promising results in Phase II clinical trials. PHP, in
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Cited by (62)
Hemoglobin-based blood substitutes - progress and challenges
2019, Comprehensive BiotechnologyHemoglobin-Based Blood Substitutes - Preparation Technologies and Challenges
2011, Comprehensive Biotechnology, Second EditionSetbacks in Blood Substitutes Research and Development: A Biochemical Perspective
2010, Clinics in Laboratory MedicineCitation Excerpt :The manufacturing methods currently employed by industry invariably generate heterogeneous mixtures of polymeric/conjugated species with variable sites of chemical modification making product characterization and structure-function relationships difficult to predict.4 The starting material is usually a stroma free-Hb (SFH), or stroma poor Hb, obtained after red cells lysis followed by filtration and chromatographic procedures, which will invariably result in a mixture of Hb and other red cell proteins in solution before chemical modifications.5 Anionic and cationic chromatographic procedures have been used to produce, in some cases, an extremely purified human Hb known as HbA0 that has demonstrated purity of approximately 99%.
Nitric oxide dioxygenase. an ancient enzymic function of hemoglobin
2008, The Smallest Biomolecules: Diatomics and their Interactions with Heme ProteinsNitric oxide in shock
2007, Kidney InternationalCitation Excerpt :Some of these compounds have been proposed as efficient NO scavengers in various animal models of sepsis, reducing hypotension, organ dysfunction, bacterial translocation, and mortality.69–73 Some NO scavengers have even entered clinical trials, such as the chemically modified human-derived hemoglobin conjugate pyridoxalated hemoglobin polyoxyethylene (PHP), which demonstrated its potential to increase systemic blood pressure and reduce vasopressor and ventilation needs without adverse effects on cardiac output, organ damage, or survival.74,75 Based on these promising results, a phase III trial has recently been conducted, but was not yet published.
Electrochemical investigation of immobilized hemoglobin: Redox chemistry and enzymatic catalysis
2006, Journal of Biochemical and Biophysical Methods
- 1
Christopher T. Privalle obtained his Ph.D. in Pharmacology from the University of Wisconsin, Madison. Following a postdoctoral fellowship in the laboratory of Irwin Fridovich, he became a research assistant professor in the Department of Biochemistry at Duke University. He joined Apex Bioscience, Inc. in 1993 and is currently the Director of Research, Biochemistry.
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Todd Talarico is the Director of Product Development at Apex Bioscience, Inc. He received his Ph.D. in Microbiology from North Carolina State University. Following postdoctoral work at Burroughs-Wellcome Company (now part of Glaxo-Wellcome), he joined Apex Bioscience, Inc. in 1993.
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Teresa Keng received her Ph.D. in Biology from the Massachusetts Institute of Technology where she was also a postdoctoral fellow. She became an assistant professor in the Department of Microbiology and Immunology at McGill University in Montreal, Canada. She joined Apex Bioscience, Inc. in 1993 where she is now the Director of Research, Molecular Biology.
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Joseph DeAngelo is the Chief Scientific Officer and Vice President of Research at Apex Bioscience, Inc. He received both undergraduate and graduate training at the Massachusetts Institute of Technology.