P26: Nitrite induced oxidation of oxygenated hemoglobin is accelerated by nitroxyl (HNO)

Abstract

Angeli’s salt decomposes into nitrite and nitroxyl (HNO), compounds of physiological and therapeutic interest for their impact on biological signaling through both nitric oxide dependent and independent pathways. Both nitrite and nitroxyl oxidize oxygenated hemoglobin (oxyHb) to methemoglobin (metHb), though the nitroxyl reaction rate is approximately seven orders of magnitude larger, and the nitroxyl reaction is thus often considered independent of the nitrite reaction. Earlier work has shown that nitroxyl catalyzes the reduction of nitrite by deoxygenated hemoglobin. However, this research represents the first known report showing nitroxyl accelerates the nitrite reaction with oxyHb. We have demonstrated this nitroxyl mediated acceleration of the nitrite/oxyHb reaction with oxyHb in excess to nitroxyl and nitrite (as would be found under physiological conditions) by monitoring the formation of metHb in the presence of Angeli’s salt with and without added nitrite. In addition, this acceleration has been demonstrated using the nitroxyl donor 4-nitrosotetrahydro-2H-pyran-4-yl pivalate, a water-soluble acyloxy nitroso compound that does not release significant amounts of nitrite but does generate nitroxyl in the presence of esterase. This nitroxyl donor was used both with and without nitrite and acceleration of the nitrite induced formation of methemoglobin was observed. We found that the acceleration was not significantly affected by catalase, superoxide dismutase, or IHP, suggesting that it is not due to formation of peroxide, or superoxide, or to modulation of allosteric properties. In addition, we found that the acceleration is not likely to be related to nitroxyl binding to free reduced hemoglobin. We suggest that the mechanism of acceleration involves local propagation of autocatalysis in the nitrite/oxyHb reaction. This acceleration of the nitrite/oxyHb reaction could affect studies aimed at understanding physiological roles of nitroxyl and nitrite and the use of these agents in therapeutics for conditions such as hypertension, hemolytic anemia, heart failure, and ischemia reperfusion injury. Disclosure Supported by HL098032.