Hydroxyurea represents a new treatment for sickle cell disease, a condition that affects 1 in 600 Americans of African descent. While the molecular mechanisms of how hydroxyurea beneficially affects sickle cell disease patients remain unknown, recent evidence indicates a role for nitric oxide (NO) in both the pathophysiology and treatment of sickle cell disease. The long-term goal of the proposed research is to thoroughly and clearly understand how the NO producing reactions of hydroxyurea contribute to the beneficial effects of hydroxyurea therapy. This goal is based upon the hypothesis that hydroxyurea-derived NO mediates the beneficial effects of hydroxyurea therapy in sickle cell disease. Product analysis, kinetic and spectroscopic studies will determine the mechanism of in vitro NO production from hydroxyurea, which should provide relevant information to the in vivo reaction. Similar studies applied to the incubation of hydroxyurea with various tissues and purified enzymes will reveal both the mechanism and site of in vivo NO formation from hydroxyurea. Specifically, these results will distinguish between hydrolytic and oxidative mechanisms of both in vitro and in vivo NO formation from hydroxyurea. In addition, the extent of the reaction of hydroxyurea-derived NO with the identified target proteins, soluble guanylate cyclase and cell-free hemoglobin, will be demonstrated by determining the extent of enzyme activation and the ultimate reaction products and kinetics of these reactions using spectroscopic methods and product analysis. These results will indicate the ability of hydroxyurea or hydroxyurea derived-NO to influence or react with these target proteins and provide evidence for a mechanism for the beneficial effects of hydroxyurea treatment. Unique hydroxyurea-based NO delivery systems and water-soluble nitroxyl donors will be prepared through chemical synthesis. The ability of these compounds to release NO will be determined using spectroscopic and cyclic voltammetric studies and these results will reveal the ability of these new systems to act as NO or nitroxyl donors. These new compounds will also be evaluated for their ability to stimulate soluble guanylate cyclase and react with cell free hemoglobin. Together, these results will provide important information regarding the mechanism of action of hydroxyurea that can be applied to the further development of superior sickle cell treatments. [unreadable] [unreadable]