Neuronal NOS‐mediated nitration and inactivation of manganese superoxide dismutase in brain after experimental and human brain injury

Abstract

Manganese superoxide dismutase (MnSOD) provides the first line of defense against superoxide generated in mitochondria. SOD competes with nitric oxide for reaction with superoxide and prevents generation of peroxynitrite, a potent oxidant that can modify proteins to form 3-nitrotyrosine. Thus, sufficient amounts of catalytically competent MnSOD are required to prevent mitochondrial damage. Increased nitrotyrosine immunoreactivity has been reported after traumatic brain injury (TBI); however, the specific protein targets containing modified tyrosine residues and functional consequence of this modification have not been identified. In this study, we show that MnSOD is a target of tyrosine nitration that is associated with a decrease in its enzymatic activity after TBI in mice. Similar findings were obtained in temporal lobe cortical samples obtained from TBI cases versus control patients who died of causes not related to CNS trauma. Increased nitrotyrosine immunoreactivity was detected at 2 h and 24 h versus 72 h after experimental TBI and co-localized with the neuronal marker NeuN. Inhibition and/or genetic deficiency of neuronal nitric oxide synthase (nNOS) but not endothelial nitric oxide synthase (eNOS) attenuated MnSOD nitration after TBI. At 24 h after TBI, there was predominantly polymorphonuclear leukocytes accumulation in mouse brain whereas macrophages were the predominant inflammatory cell type at 72 h after injury. However, a selective inhibitor or genetic deficiency of inducible nitric oxide synthase (iNOS) failed to affect MnSOD nitration. Nitration of MnSOD is a likely consequence of peroxynitrite within the intracellular milieu of neurons after TBI. Nitration and inactivation of MnSOD could lead to selfamplification of oxidative stress in the brain progressively enhancing peroxynitrite production and secondary damage.

Oxidative stress and modification of synaptic proteins in hippocampus after traumatic brain injury

“…Because GPx and CAT both control H 2 O 2 , they represent the major defense against ROS [14]. Decreased activity of Mn-SOD is a likely consequence of peroxynitrite after TBI, and could lead to further oxidative stress and progressively enhance peroxynitrite production as part of the secondary damage cascade [10]. Decreased activity of Cu/Zn-SOD in ipsilateral hippocampus of young animals post injury compromises defense capacities against oxidative stress [39].…”

“…Enhanced production of reactive oxygen/nitrogen species (ROS/RNS) cause oxidative/ nitrosative stress [5,6] leading to damage in lipids, proteins and nucleic acids [7,8]. Oxidative stress-related cascades resulting from TBI have been implicated in cytoskeletal damage, mitochondrial dysfunction [9] and altered signal transduction [10,11].…”

Protective effect of aminoguanidine against oxidative stress and bladder injury in cyclophosphamide‐induced hemorrhagic cystitis in rat

“…SOD is a target of tyrosine nitration and nitration inactivates the enzyme. 34 Nitration and inactivation of SOD could lead to self-amplification of oxidative stress in the tissues progressively enhancing peroxynitrite production and secondary damage. It has been already demonstrated that CP-induced bladder damage involves peroxynitrite formation and protein nitration.…”

Redox Proteomics in Selected Neurodegenerative Disorders: From Its Infancy to Future Applications

“…In other reactions involving oxidation of the Met 35 formation of methionine sulfoxide (MetO) occurs, which can be reduced back to methionine by MetO reductase. The activity of MetO reductase is reduced in AD brain (161).…”

“…The recovery rate of 3-NT-containing peptides was *55% as measured with UV-Vis detection. Recovery rate was increased by varying incubation time on the column and incorporating more washes (35). Immunopurification strategies have been recently employed for the characterization of 3-NT-modified proteins in CSF of human patients to better understand HIV-associated neurocognitive disorders (37).…”