The primary goal of this study is to determine the role of each component of whole blood (hemoglobin, stroma, hemoglobin + stroma) in the hypertension observed during hemolysis and then evaluate the therapeutic value of Angeli's salt (Na2N2O32-) in a canine model of acute intravascular hemolysis. Nitric oxide (NO) is a vasodilator which is constantly produced by the vascular endothelium. The amount of NO available in the circulation is, in part, regulated by the binding of NO to hemoglobin. Hemoglobin is normally contained within the red blood cell and reacts with nitric oxide at a relatively slow rate. However, the destruction of red blood cells within the circulation (intravascular hemolysis) causes the release of hemoglobin (cell-free hemoglobinh) from the red blood cell into the circulation. The cell-free hemoglobin released into the circulation during hemolysis binds to NO at a much faster rate than hemoglobin within the red blood cell. This binding of NO by cell-free hemoglobin disrupts the normal balance of NO available within the circulation resulting in vasoconstriction that decreases blood flow and leads to organ injury. Though it is not clear what role stroma (the contents of the red cell + the red cell membrane) has during hemolysis. This study will determine this role. In addition, Angeli's salt is known to react rapidly with hemoglobin to form, nitrosyl hemoglobin Fe(II)NO which does not bind NO.? ? N2O3- (Angeli's Salt) NO2- + NO? ? NO + Fe(II)-O2 (oxyhemoglobin in plasma) Fe(III) (methemoglobin) + ? ? Fe(III) + NO- Fe(II)-NO (iron-nitrosyl-hemoglobin)? ? If the Angeli's salt can prevent the cell-free hemoglobin from binding NO, it may prevent the vasoconstriction and resulting organ injury that occurs during hemolysis. This study will test the ability of Angeli's salt to prevent cell-free hemoglobin binding of NO during hemolysis using the canine model of intravascular hemolysis that we successfully developed and used in two previous protocols. Our model uses a free water infusion to create intravascular hemolysis which mimics the physiologic and biochemical characteristics of acute intravascular hemolysis in the human. This model disrupts the red cell membrane within the circulation leading to the release of hemoglobin into circulation of the animal. In our model, acute intravascular hemolysis leads to changes in hemodynamics and organ function, i.e., increases in mean arterial pressure and systemic vascular resistance and decreases in heart and kidney function as measured by cardiac index and creatinine clearance respectively. ? ? Previous studies in our laboratory showed that elevated levels of cell-free hemoglobin consume NO, and therapy with inhaled nitric oxide or intravenous nitrite can limit the deleterious effects of intravascular hemolysis. Despite the demonstrated benefits, these two therapies have limitations. Inhaled nitric oxide is expensive, requires a specialized delivery system and is not readily available. Intravenous nitrite, although inexpensive and easy to administer, reacts slowly with cell free hemoglobin. Both therapies produce methemoglobin which: (1) promotes inflammation, (2) is associated with atherosclerosis and (3) can potentially undergo reduction and be recycled to free hemoglobin. Angeli's salt, on the other hand, has been shown to rapidly react with hemoglobin to produce nitrosyl hemoglobin. Unlike methemoglobin, (the product of nitrite or NO reacting with hemoglobin), nitrosyl hemoglobin is relatively stable and with no known toxicities. Angeli's salt also has the advantage of being inexpensive and can be administered intravenously. Thus, the chemical profile of Angeli's salt suggests that it should irreversibly react with cell free hemoglobin thereby preventing the consumption of NO, possibly reverse the adverse effects of intravascular hemolysis and have fewer side effects than either nitric oxide or nitrite therapy.
| Solomon, Steven B; Bellavia, Landon; Sweeney, Daniel et al. (2012) Angeli's salt counteracts the vasoactive effects of elevated plasma hemoglobin. Free Radic Biol Med 53:2229-39 |
