title: Impact of acellular hemoglobin-based oxygen carriers on brain apoptosis in rats.
abstract: BACKGROUND
  Extracellular hemoglobin (Hb)-based oxygen carriers (HBOCs) are under extensive consideration as oxygen therapeutics. Their effects on cellular mechanisms related to apoptosis are of particular interest, because the onset of proapoptotic pathways may give rise to tissue damage.
  
  
  METHODS
  The objective was to assess whether the properties of the Hb that replaces blood during an isovolemic hemodilution would modulate apoptotic-response mechanisms in rat brain and whether such signaling favors cytoprotection or damage. We exposed rats to exchange transfusion (ET; 50% blood volume and isovolemic replacement with Hextend [negative colloid control], MP4OX [PEGylated HBOC with high oxygen affinity], and ααHb [αα-cross-linked HBOC with low oxygen affinity; n=4-6/group]). Sham rats acted as control. Animals were euthanized at 2, 6, and 12 hours after ET; brain tissue was harvested and processed for analysis.
  
  
  RESULTS
  In MP4OX animals, the number of neurons that overexpressed the hypoxia-inducible factor (HIF)-1α was higher than in ααHb, particularly at the early time points. In addition, MP4OX was associated with greater phosphorylation of protein kinase B (Akt), a well-known cytoprotective factor. Indeed, the degree of apoptosis, measured as terminal deoxynucleotidyl transferase-positive neurons and caspase-3 cleavage, ranked in order of MP4OX < Hextend < ααHb.
  
  
  CONCLUSIONS
  Even though both HBOCs showed increased levels of HIF-1α compared to shams or Hextend-treated animals, differences in signaling events resulted in very different outcomes for the two HBOCs. ααHb-treated brain tissue showed significant neuronal damage, measured as apoptosis. This was in stark contrast to the protection seen with MP4OX, apparently due to recruitment of Akt and neuronal specific HIF-1α pathways.
authors.affiliation: Sangart, Inc., San Diego, California.
authors.forename: Kim D
authors.initials: KD
authors.lastname: Vandegriff
authors.forename: Ashok
authors.initials: A
authors.lastname: Malavalli
authors.forename: Jeff
authors.initials: J
authors.lastname: Lohman
authors.forename: Mark A
authors.initials: MA
authors.lastname: Young
authors.forename: Laura
authors.initials: L
authors.lastname: Terraneo
authors.forename: Eleonora
authors.initials: E
authors.lastname: Virgili
authors.forename: Paola
authors.initials: P
authors.lastname: Bianciardi
authors.forename: Anna
authors.initials: A
authors.lastname: Caretti
authors.forename: Michele
authors.initials: M
authors.lastname: Samaja
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001241:Aspirin / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D001802:Blood Substitutes / Q000494:pharmacology* / Q000627:therapeutic use; D001921:Brain / Q000187:drug effects* / Q000473:pathology; D015687:Cell Hypoxia / Q000187:drug effects; D004353:Drug Evaluation, Preclinical; D005078:Exchange Transfusion, Whole Blood; D006438:Hemodilution; D006454:Hemoglobins / Q000494:pharmacology* / Q000627:therapeutic use; D006470:Hemorrhage / Q000150:complications / Q000628:therapy*; D006895:Hydroxyethyl Starch Derivatives / Q000494:pharmacology* / Q000627:therapeutic use; D002534:Hypoxia, Brain / Q000209:etiology / Q000517:prevention & control*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis / Q000235:genetics; D008301:Maleimides / Q000494:pharmacology* / Q000627:therapeutic use; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000235:genetics; D009474:Neurons / Q000187:drug effects* / Q000473:pathology; D010100:Oxygen / Q000097:blood*; D011092:Polyethylene Glycols / Q000494:pharmacology* / Q000627:therapeutic use; D051057:Proto-Oncogene Proteins c-akt / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D001802:Blood Substitutes; D006454:Hemoglobins; C497444:Hif1a protein, rat; D006895:Hydroxyethyl Starch Derivatives; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008301:Maleimides; D009419:Nerve Tissue Proteins; C493836:maleimide-polyethylene glycol-modified hemoglobin, MP4; D011092:Polyethylene Glycols; D051057:Proto-Oncogene Proteins c-akt; C083478:diaspirin-cross-linked hemoglobin; D001241:Aspirin; D010100:Oxygen