Nitric oxide converts fatty acid alkoxyl radicals into fatty acid allyl radicals

Nitric oxide (NO) is thought to react with fatty acid alkoxyl radical, which is generated from fatty acid hydroperoxide via one-electron reduction. However, detail in the reaction remains obscure. In the present study, we examined the reaction of nitric oxide with fatty acid alkoxyl radical generated in the lipoxygenase/linoleate/13-hydroperoxyoctadecadienoate (13-HpODE) system under anaerobic conditions via HPLC equipped with mass spectrometry and photodiode array detections. In this reaction system, nitric oxide can scavenge linoleate alkoxyl radical, producing 13-ONO-9Z,11E-ODE. However, instead of 13-ONO-9Z,11E-ODE, 13-NO-9E,11E-ODE and 9-NO-10E,12E-ODE were alternatively detected in the reaction solution. To explain this contradiction, we proposed a mechanism as follows: (1) 13-ONO-9E/11Z-ODE undergoes homolytic cleavage at >CHONO bond into the linoleate allyl radical and nitrogen dioxide, (2) the allyl radical undergoes resonance stabilization into the E/E-form, and (3) nitric oxide scavenges the E/E-pentadiene radical at C9 or C13 position. Consequently, we concluded that nitric oxide immediately converts fatty acid alkoxyl radical into allyl radical.

► A model system for fatty acid alkoxyl radical generation was established. ► NO scavenges lipid alkoxyl radical through radical–radical combination. ► Fatty acid alkoxyl radical-nitric oxide adduct dissociates into allyl radical. ► NO should consequently prevent β-elimination of fatty acid alkoxyl radical.