Biological Evaluation of Liposome-Encapsulated Hemoglobin Surface-Modified With a Novel PEGylated Nonphospholipid Amphiphile

It is estimated that hemorrhage is responsible for 30–40% of trauma-associated mortality, and approximately half of these casualties occur before hospital care could be provided [1]. Lack of timely resuscitation, excessive bleeding, oxygen deficit in critical organs, and coagulopathy associated with hemorrhage and trauma are the major reasons of these trauma-related deaths. Massive transfusion of blood and/or crystalloids, together with fresh frozen plasma, is an instinctive approach of resuscitative intervention. However, adequate availability of safe blood remains a major world-wide concern in transfusion medicine. The issues related to inventory management, possibility of known and unknown infections, requirements of pre-transfusion processing and cross-matching of blood, and limited shelf-life are the factors that have provided thrust to the search for safe, shelf-stable, and efficacious oxygen carrying fluids. Moreover, an oxygen-carrying fluid mimicking safety and efficacy profile of natural red blood cells (RBCs) is the goal. Therefore, an ideal artificially-assembled oxygen carrier would be hemoglobin (Hb) in an encapsulated form, such as in liposome-encapsulated Hb (LEH) [2–7]. By mimicking the membrane enclosed cellular structure of red blood cells, LEH eliminates the toxicity associated with free, whether modified or unmodified, Hb [3, 6, 8]. One goal of LEH formulation is to enable its prolonged circulation after administration. Stealth technology based on the use of poly(ethylene) glycol (PEG)-linked phosphatidylethanolamine (PEs) is employed for this purpose [9]. PEG prolongs circulation persistence of LEH by evading the opsonization and subsequent elimination process through mononuclear phagocyte system (MPS) [10]. In a recent study, we have demonstrated that stealth liposomes formulated with novel synthetic hexadecylcarbamoylmethylhexadecanoate-conjugated PEG2000 (HDAS-PEG2K) maintained longer circulation and lowered complement activation better than the liposomes modified with commonly used stealth phospholipid distearoylphosphatidylethanolamine(DSPE)-PEG2K [11]. As a non-phospholipid alternative to PEG-PEs, HDAS-PEG2K does not contain phosphoryl domain which has been implicated in a few in vivo complications associated with phospholipids in general [12–15]. In case of LEH, the problems could be magnified many fold, because of the large amounts of product infused during resuscitation. In this article, we report immunologic evaluation and consequences of resuscitation with LEH constituted of HDAS-PEG2K as the stealth lipid in rodent models.