37. Vasoconstriction, Hypertension and Oxidative Toxicity are Regulated by Polymerized Hemoglobin Size

Hemoglobin (Hb)-based oxygen (O₂) carriers (HBOCs) are continuously being optimized as red blood cell (RBC) substitutes in order to overcome the well-known side-effects that are associated with transfusion of cell-free Hb (Alayash 1999, 2004). These side-effects include vasoconstriction, systemic hypertension and oxidative tissue toxicity (Alayash 1999, 2004). It is hypothesized that these side-effects are due to HBOC extravasation into the tissue space and the NO scavenging ability of cell-free Hb (Suaudeau et al. 1979; Nakai et al. 1998; Dull et al. 2004; Liu et al. 1998; Liao et al. 1999). Polymerized HBOCs (PolyHbs) were thus engineered with molecular sizes larger than that of cell-free Hb, with the goal of reducing extravasation of the HBOC from the vascular space into the tissue space (Alayash 2004; Palmer 2006). This approach should reduce the proximity of the HBOC to the endothelium, which in turn should reduce/eliminate the aforementioned side-effects (Alayash 2004; Palmer 2006). In order to address this need for large sized HBOCs compared to cell-free Hb, the following commercial PolyHbs were initially developed: Oxyglobin® (OPK Biotech LLC, Cambridge, MA), Hemopure® (OPK Biotech LLC, Cambridge, MA), PolyHeme® (Northfield Laboratories Inc., Evanston, IL) and Hemolink™ (Hemosol Inc., Toronto, Canada) (OPK Biotech 2012; Rentko et al. 2006; Day 2003; Adamson and Moore 1998). However, these commercial products still elicited the aforementioned side-effects and are coincidentally close together in molecular weight (MW) (Rentko et al. 2006; Day 2003; Adamson and Moore 1998; Tsai et al. 2006; Butt et al. 2010, 2011; Kasper et al. 1996; LaMuraglia et al. 2000; Jahr et al. 2008; Freilich et al. 2009; Yu et al. 2010; Handrigan et al. 2005; Cheng et al. 2004; Greenburg and Kim 2004; Hill et al. 2002; Lieberthal et al. 1999). In the case of Oxyglobin®, its’ side-effects were directly attributed to PolyHb extravasation from the blood vessel lumen into the tissue space Butt et al. (2010; 2011). Therefore, the ultrahigh MW HBOC Oxyvita™ (OXYVITA Inc., New Windsor, NY) was developed, which did not extravasate and induce significant vasoconstriction or hypertension (OXYVITA Inc. 2012; Matheson et al. 2002; Bucci et al. 2007; Jia and Alayash 2009). However, Oxyvita® has a high O₂ affinity so it is unclear how well it will deliver O₂ in vivo, despite its lack of vascular side-effects (Matheson et al. 2002; Jia and Alayash 2009). It is interesting to note that these commercial PolyHbs differ in MW by several orders of magnitude, and until recently there has been no systematic study of PolyHb MW on its’ in vivo safety profile (Rentko et al. 2006; Day 2003; Adamson and Moore 1998; Matheson et al. 2002; Bucci et al. 2007; Jia and Alayash 2009). To address this deficit in the literature, recent studies have shed light on the relationship between PolyHb molecular size and its’ in vivo safety profile (Cabrales et al. 2009; Cabrales et al. 2010; Baek et al. 2012). These studies demonstrate that increasing the molecular size of tense (T)-state bovine PolyHb reduces vasoconstriction, systemic hypertension, and oxidative tissue toxicity (Cabrales et al. 2009, 2010; Baek et al. 2012). Therefore, it is expected that further work in this area will lead to the optimization of PolyHb size in order to improve its in vivo safety profile for eventual human use.