title: Modeling hemoglobin and hemoglobin:haptoglobin complex clearance in a non-rodent species-pharmacokinetic and therapeutic implications.
abstract: BACKGROUND
  Haptoglobin (Hp) prevents hemoglobin (Hb) extravasation and attenuates Hb induced tissue oxidation and vasoconstriction. Small animal models such as mouse, rat and guinea pig appear to demonstrate proof-of-concept for Hb neutralization by Hp in diverse pre-clinical conditions. However, these species differ significantly from humans in the clearance of Hb:Hp and demonstrate long persistence of circulating Hb:Hp complexes.
  
  
  OBJECTIVE
  The focus of this study is to understand Hb:Hp clearance in a non-rodent species. In contrast to rodents, dogs maintain high plasma Hp concentrations comparable to humans and demonstrate more rapid clearance of Hb:Hp when compared to rodent species, therefore dogs may represent a relevant species to evaluate Hb:Hp pharmacokinetics and cellular clearance.
  
  
  RESULTS
  In this study we show, that like human macrophages, dog peripheral blood monocyte derived macrophages express a glucocorticoid inducible endocytic clearance pathways with a high specificity for the Hb:Hp complex. Evaluating the Beagle dog as a non-rodent model species we provide the first pharmacokinetic parameter estimates of free Hb and Hb:Hp complexes. The data demonstrate a significantly reduced volume of distribution (Vc) for Hb:Hp compared to free Hb, increased maximum plasma concentrations and areas under plasma concentration time curves (Cmax and AUC). Significantly reduced total body clearance (CL) and a longer terminal half-life (t1/2) of approximately 12 h were also observed for the Hb:Hp complex. Distribution and clearance were identical for dimeric and multimeric Hb:Hp complexes. We found no significant effect of a high-dose glucocorticoid treatment protocol on Hb:Hp pharmacokinetic parameter estimates.
  
  
  CONCLUSIONS
  Collectively, our study supports the dog as a non-rodent animal model to study pharmacological and pharmacokinetic aspects of Hb clearance systems and apply the model to studying Hp as a therapeutic in diseases of hemolysis.
authors.affiliation: Division of Veterinary Internal Medicine, School of Veterinary Medicine, University of Zurich Zurich, Switzerland.
authors.forename: Felicitas S
authors.initials: FS
authors.lastname: Boretti
authors.affiliation: Laboratory of Biochemistry and Vascular Biology, FDA Center for Biologics Evaluation and Research Bethesda, MD, USA.
authors.forename: Jin Hyen
authors.initials: JH
authors.lastname: Baek
authors.affiliation: Chemical and Biomolecular Engineering, The Ohio State University Columbus, OH, USA.
authors.forename: Andre F
authors.initials: AF
authors.lastname: Palmer
authors.affiliation: Division of Internal Medicine, University of Zurich Hospital, University of Zurich Zurich, Switzerland.
authors.forename: Dominik J
authors.initials: DJ
authors.lastname: Schaer
authors.affiliation: Laboratory of Biochemistry and Vascular Biology, FDA Center for Biologics Evaluation and Research Bethesda, MD, USA.
authors.forename: Paul W
authors.initials: PW
authors.lastname: Buehler
keywords: haptoglobin; hemoglobin; macrophage uptake; non-rodent; pharmacokinetic modeling