The mechanism underlying nitroxyl and nitric oxide formation from hydroxamic acids

Prior research has shown that hydroxamic acids (HXs) are known to release bioactive nitrogen species under oxidative stress. It was already known that these compounds can act as HNO or NO donors, but the exact oxidation pathways remain unclear. This gap motivated the need to better understand the mechanisms of HX oxidation. No prior work had resolved whether HX-derived HNO is primarily from direct oxidation or from decomposition of RC(O)NHO(·). Prior studies have focused on the biological effects of HXs, not their oxidation mechanisms. This uncertainty limits the ability to design HX-based drugs with predictable outcomes. Understanding the role of different oxidants is essential for drug development. This paper's contribution is to clarify the oxidation pathways under various conditions.

The aim of the study is to investigate the oxidation mechanisms of hydroxamic acids under oxidative stress. Specifically, the study focuses on how HXs generate HNO and NO under different oxidizing conditions. The researchers sought to determine whether HX oxidation leads to HNO or NO formation. The motivation stems from the need to improve the design of HX-based drugs. This work addresses the lack of clarity about the role of different oxidants in HX metabolism. The study also tests the influence of anoxia and normoxia on the oxidation products. It was already known that HXs can act as HNO or NO donors, but the mechanisms were not fully understood. This paper aims to clarify the conditions under which HXs release HNO or NO.

The study used acetohydroxamic and glycine-hydroxamic acids as model compounds. Oxidation was induced using radiolytically generated hydroxyl radicals or metmyoglobin and hydrogen peroxide systems. The experiments were conducted at pH 7.0 to mimic physiological conditions. Gas chromatography and spectroscopic methods were employed to detect N2O, N2, nitrite, and hydroxylamine. The researchers monitored the oxidation products under both anoxic and normoxic environments. The metmyoglobin/H2O2 system was used to generate compound I and II as oxidants. The study compared the effects of different oxidants on HX oxidation. These methods allowed the team to track the formation of HNO and NO intermediates.

Oxidation of HXs by hydroxyl radicals under anoxia produced N2O but not nitrite, N2, or hydroxylamine. The accumulation of RC(O)NHO(·) suggests that HNO is formed from this intermediate. The bimolecular decomposition of RC(O)NHO(·) competes with unimolecular processes like homolysis. When H2O2 was added to HX and metmyoglobin systems, nitrite and N2O were detected. Compound II oxidized HX, RC(O)NHO(·), HNO, and NO, with nitrite being the main product. The metmyoglobin/H2O2 system yielded more nitrite than N2O under both anoxia and normoxia. The study found that HNO oxidation is more efficient than its reaction with biological targets. These findings suggest that HXs can act as NO donors under certain conditions.

The authors propose that hydroxamic acids release HNO primarily through oxidation of the hydroxamate group. They suggest that RC(O)NHO(·) is a key intermediate in HNO formation. The study shows that HX oxidation under anoxia favors HNO over NO. The metmyoglobin/H2O2 system generates nitrite as the main product. The researchers propose that HXs can act as NO donors if HNO oxidation is efficient. The findings suggest that the oxidation mechanism depends on the type of oxidant used. The study highlights the importance of understanding HX oxidation under physiological conditions. These conclusions support the idea that HXs can be designed as targeted HNO or NO donors.