Nitroxyl accelerates the oxidation of oxyhemoglobin by nitrite

The role of nitroxyl (HNO) in hemoglobin oxidation remains unclear. Prior research has shown that HNO and nitrite (NO₂⁻) both oxidize oxygenated hemoglobin to methemoglobin. However, the interaction between HNO and nitrite in this process has not been fully explored. Some studies suggest HNO may influence nitrite activity through unknown mechanisms. This uncertainty drives the need for more detailed investigations. Researchers have examined how HNO affects the rate of methemoglobin formation. The impact of HNO on nitrite-induced oxidation is not well established. This gap motivated the current study to explore the relationship between HNO and nitrite. Understanding this interaction could clarify the physiological and therapeutic implications of HNO.

This study aimed to determine whether HNO accelerates the oxidation of oxygenated hemoglobin by nitrite. The researchers wanted to clarify the mechanism of this potential acceleration. They examined the role of HNO in the nitrite-hemoglobin reaction under physiological conditions. The study focused on the formation of methemoglobin in the presence of HNO and nitrite. The researchers used Angeli's salt as a source of HNO and NO₂⁻. They also tested a water-soluble HNO donor that does not release NO₂⁻. The goal was to isolate the effect of HNO from that of nitrite. This approach allowed for a more precise analysis of HNO's role in the reaction.

The researchers used Angeli's salt to generate HNO and NO₂⁻ in solution. They monitored the oxidation of oxygenated hemoglobin to methemoglobin using spectrophotometric methods. The experiments were conducted under conditions where hemoglobin was in excess. They repeated the experiments with a different HNO donor, 4-nitrosotetrahydro-2H-pyran-4-yl pivalate. This donor releases HNO but not NO₂⁻, allowing for a controlled comparison. The researchers added and omitted NO₂⁻ to assess the effect of HNO alone. They tested the influence of catalase, superoxide dismutase, c-PTIO, and IHP. These agents were used to rule out alternative mechanisms such as peroxide or NO₂ formation.

The study found that HNO significantly accelerated the oxidation of oxygenated hemoglobin by NO₂⁻. This acceleration was observed even when hemoglobin was in excess. The effect was confirmed using a second HNO donor that does not release NO₂⁻. The researchers observed a similar acceleration when NO₂⁻ was added. The acceleration was not affected by catalase or superoxide dismutase. This suggests that peroxide or superoxide radicals were not involved. The effect was also not influenced by c-PTIO or IHP. These findings indicate that the acceleration is not due to extramolecular peroxide or NO₂ formation.

The researchers concluded that HNO accelerates the oxidation of oxygenated hemoglobin by nitrite. This effect appears to be independent of peroxide or NO₂ formation. The mechanism may involve local propagation of autocatalysis in the nitrite-hemoglobin reaction. The study found that HNO binding to reduced hemoglobin was weaker than previously proposed. This suggests that the acceleration is not due to HNO binding to free hemoglobin. The findings support a model where HNO enhances the nitrite-hemoglobin reaction. The researchers propose that this mechanism could influence physiological studies of HNO. This acceleration may also affect the use of HNO and nitrite in therapeutic applications.