Targeted Delivery of Gaseous Ligands (CO and NO) for the Treatment of Ischemia Reperfusion Injury

Hemorrhagic shock is sudden loss of intravascular blood volume which induces tissue ischemia, characterized by limited oxygen (O2) transport to tissues coupled with an accumulation of tissue excretory products eventually leading to cell death. Clinicians normally stop the bleeding and transfuse the patient with either red blood cells (RBCs) or plasma expanders in order to restore the lost blood volume. Re-establishment of blood flow and restoration of tissue oxygenation is known as reperfusion. This abrupt change in tissue oxygenation can paradoxically induce cell apoptosis, tissue inflammation, infarct formation and has been shown to elicit multiple organ dysfunctions by activating cytotoxic injury processes such as reactive O2 species (ROS) generation, neutrophil-endothelium interactions, and hypercontracture. These collective set of side-effects that occur during the ischemic and reperfusion phases is classified as ischemia reperfusion injury (IRI) and is a major obstacle towards successful treatment of hemorrhagic shock. Therefore, it is vital to develop novel therapeutics to protect the cardiovascular system during acute ischemic and post-ischemic phases that occur during resuscitation from hemorrhagic shock. Neutrophils, activated by elevated ROS levels post reperfusion, infiltrate into the extravascular compartment and damage the endothelium by secreting cytotoxic molecules such as ROS and cytokines. The damaged endothelium may further aggravate tissue injury by the suppression of vasoactive molecules such as nitric oxide (NO), adenosine, and endothelin; which can disrupt homeostasis of coronary vasculature and lead to reduced tissue perfusion. In light of the anti-apoptotic, anti-inflammatory and vasoactive properties of carbon monoxide (CO) and NO, their presence in the systemic circulation could inhibit the release of cytotoxic molecules during reperfusion.;Previously, inhalation-based delivery of NO to ischemic tissues has been successful in treating IRI. However, this increases methemoglobin (metHb) levels in the blood and delivers NO systemically throughout the body. Another treatment strategy involves transfusion of CO saturated RBCs to prevent sudden oxygenation of ischemic tissues. Therefore, RBCs seem like a logical carrier for in vivo delivery of NO and CO. However, in order to circumvent potential issues associated with RBC transfusion (i.e. short storage shelf life and limited supply), hemoglobin (Hb)-based O2 carriers (HBOCs) have been used to deliver exogenous CO to ischemic tissues in rats. Properties of HBOCs such as low viscosity and smaller size are expected to improve microcirculation upon reperfusion.;In this study, we hypothesize that HBOCs can be used to deliver potent gaseous ligands such as CO and NO to ischemic tissues in order to treat IRIs encountered during resuscitation from hemorrhagic shock. Initially, ligand loaded HBOCs are expected to supply beneficial gaseous molecules to ischemic tissues in order to mitigate IRI. Transfusion of these particles will also help in restoring blood volume and shear stress, thereby promoting increased endothelial NO synthesis. After the beneficial gaseous ligands dissociate from the ligand carriers, the particles are expected to store and transport O2. Thus, the HBOCs will perform multiple functions at different stages of the proposed treatment. The novel therapeutic proposed in this study can be an economical alternative for current IRI treatment strategies.