Since cell-free hemoglobin (Hb) scavenges nitric oxide (NO) more effectively than that encapsulated in the red blood cell (RBC), hemolysis reduces NO bioavailability with pathological consequences in sickle cell disease and other hemolytic anemias, paroxysmal nocturnal hemoglobinuria, thalassemia intermedia, malaria, and cardiopulomonary bypass. The ability of the cell-free Hb to scavenge NO is reduced when the Hb is converted from its oxygenated form (HbO2) to its oxidized form, methemoglobin (MetHb). We show that Angeli’s salt (AS) can convert two OxyHb to two MetHb molecules through its release of nitroxyl (HNO). AS also further converts the MetHb to less potentially oxidative forms: nitrite bound MetHb and iron-nitrosyl hemoglobin. We also show that, due to the fast reactivity of HNO with Hb (like NO), AS preferentially reacts with cell-free rather than RBC encapsulated Hb. In conditions simulating sickle cell crisis, within six minutes, AS converted 45 ± 12% of cell-free Hb to non-NO scavenging forms (MetHb and iron-nitrosyl Hb) and only converted 0.4 ± 0.3% of RBC encapsulated Hb (n=3). Similar preferential reactivity was observed under other physiologically relevant conditions. We conclude that, as AS preferentially reacts with cell-free Hb compared to RBC encapsulated Hb, converting it to species that do not effectively scavenge NO, it is has promise as a treatment for increasing NO biavailability in conditions associated with hemolysis.

Author notes

Disclosure:Research Funding: Grant Support from the NHLBI of the NIH.