Therapeutic Application of Intravascular Nitrite for Sickle Cell Disease

Sickle cell disease is an autosomal recessive disorder and the most common genetic disease affecting African-Americans. Approximately 0.15% of African-Americans are homozygous for sickle cell disease, and 8% have sickle cell trait. Hemoglobin S polymerization leads to red cell rigidity, microvascular obstruction, inflammation, and end-organ ischemia-reperfusion injury and infarction. Our published data indicate that up to 50% of sickle cell patients have endothelial dysfunction due to impaired bioavailability of endogenous nitric oxide due in large part to scavenging of nitric oxide by cell-free plasma hemoglobin. These data suggest that therapies directed at restoring NO bioavailability might prove beneficial. We have recently discovered that the nitrite anion, available currently for human use as a component of the cyanide antidote kit, is a vasodilator in vivo by generating nitric oxide (NO) in tissues with lower oxygen tension and pH. The mechanism involves a novel physiological function of human hemoglobin as an oxygen- and pH dependent nitrite reductase. To date we have observed that nitrite infusions in animal models significantly reduce liver and cardiac ischemia-reperfusion injury and infarction in mouse models, prevent cerebral vasospasm after subarachnoid hemorrhage in primates, and decrease pulmonary hypertension in newborn hypoxic sheep. The current protocol is designed as a phase I/II trial to address the hypothesis that nitrite infusions will vasodilate the circulation in patients with sickle cell disease at rest and during vaso-occlusive pain crisis, inactivate circulating cell-free plasma hemoglobin, reduce pulmonary artery pressures and reduce ischemia-reperfusion injury (measured by circulating markers of oxidant stress).