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. We have also observed that nitrite induces regional vasodialtion in healthy human subjects. 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). We began enrolling patients in January 2005. Forearm blood flow studies have been completed on fourteen patients to date and Part A has completed enrollment. These patients have been infused with SNP, L-NMMA and Nitrite at the three designated doses, and there have been no significant side effects. The average increase in forearm blood flow over baseline with the SNP doses of 0.8mg/min, 1.6mg/min, and 3.2mg/min were +27%, +12%, and +32% respectively. The average drop in forearm blood flow after the L-NMMA infusions of 4mmol/min and 8mmol/min were -17% and -20% respectively. As hypothesized the forearm blood flow did increase after each successive dose of nitrite. The average increase in forearm flow after the 0.4mM, 4mM and 40mM infusions was +8%, +25%, and +77% respectively. The post nitrite SNP forearm blood flow responses were as predicted, greater than the pre-nitrite forearm flows. There was no statistically significant difference in the pre-nitrite SNP forearm blood flow response and the post-nitrite SNP forearm blood flow response in our 14 patients with sickle cell disease who participated in the study. At this time we do not intend to pursue part B of the study that was to be performed in subjects during vaso-occlusive crisis.
| Mack, A Kyle; McGowan Ii, Vicki R; Tremonti, Carole K et al. (2008) Sodium nitrite promotes regional blood flow in patients with sickle cell disease: a phase I/II study. Br J Haematol 142:971-8 |
