Superoxide dismutase deficiency enhances superoxide levels in brain tissues during oxygenation and hypoxia‐reoxygenation

Abstract

To determine whether the mitochondria or cytoplasm produces superoxide during ischemia-reperfusion of the brain, we analyzed lucigenine-enhanced chemiluminescence emission in slices of brain tissue prepared from manganese-superoxide dismutase (Mn-SOD)-deficient (Sod2-deficient) and copper and zinc-superoxide dismutase (Cu,Zn-SOD)-deficient (Sod1-deficient) mice during oxygenation and hypoxia-reoxygenation. The steady-state level of chemiluminescence under oxygenated conditions was significantly enhanced by a lack of either Sod. We hypothesize that the enhanced chemiluminescence produced by Sod2 and Sod1 deficiency reflects in situ superoxide generation in the mitochondria and cytoplasm, respectively. Based on this hypothesis, the major site of intracellular superoxide generation was assumed to be the cytoplasm. However, mitochondria occupy less cellular space than the cytoplasm. In terms of volume, the superoxide concentration is assumed to be higher in mitochondria than in the cytoplasm. Mn-SOD activity was 18% of the Cu,Zn-SOD activity observed in the wild-type mouse brain. However, when mitochondrial SOD activity was expressed as per volume, it was assumed to be equal to that observed in the cytoplasm. This imbalance between superoxide and SOD activity is expected to cause mitochondrial oxidative damage. The chemiluminescence intensity increased significantly during reoxygenation and was enhanced by Sod2 deficiency but was not significantly affected by Sod1 deficiency. The superoxide concentration in the reoxygenated brain would be higher in the mitochondria than in the cytoplasm. The present study indicated that the major site of intracellular superoxide generation in the brain during oxygenation is the cytoplasm, whereas it is the mitochondria during reoxygenation.

SOD1 (Copper/Zinc Superoxide Dismutase) Deficiency Drives Amyloid β Protein Oligomerization and Memory Loss in Mouse Model of Alzheimer Disease

“…Alternatively, 6 -8-month aging might be a transient period of oxidative damaging against proteins or DNA. Recently, Sasaki et al (68) reported that the superoxide-dependent chemiluminescence levels triggered by ischemia-reperfusion were significantly increased in 3-week-old Sod1 Ϫ/Ϫ . Given the recent report by Ansari and Scheff (43) that total SOD activity was not decreased in the postmitochondrial supernatant of mild cognitive impairment cases, early down-regulation of cytoplasmic SOD1 may predict the onset of dementia.…”

Increased Levels of Reactive Oxygen Species in Brain Slices after Transient Hypoxia Induced By a Reduced Oxygen Supply

“…We previously demonstrated that ROSdependent chemiluminescence in the brain increased during reoxygenation after hypoxia caused by the deprivation of an adequate oxygen supply using a photonic imaging method with lucigen, a chemilumigenic probe [15][16][17][18][19]. Due to its high sensitivity, lucigenin has been frequently used to detect superoxide anion radicals produced by enzymatic and cellular systems in tissue and isolated heart slices [20][21][22][23][24][25][26].…”

“…Our findings suggested that ROS generation does not directly depend on the energy metabolic rate; it may be related to a transient decrease in tissue pO 2 levels and a shift in the tissue redox balance towards reduction. We also reported that ROSdependent chemiluminescence in the brain increased during reoxygenation after hypoxia caused by the deprivation of an adequate oxygen supply [15][16][17][18][19]. However, the relationships among ROS generation, tissue pO 2 levels, and the redox balance during the restoration of hypoxia caused by a decreased oxygen supply have not yet been investigated.…”

“…Previously, we analyzed lucigenineenhanced chemiluminescence emission in slices of brain tissue prepared from Mn-SOD (located in mitochondria) and Cu, Zn-SOD (located in cytoplasm)-deficient mice to estimate the superoxide levels in mitochondria and cytoplasm. The enhanced chemiluminescence with Mn-SOD and Cu,Zn-SOD deficiency indicated that superoxide level in mitochondria was lower than that in cytoplasm, however the superoxide concentration was assumed to be higher in mitochondrial than the cytoplasm [18]. We also demonstrated that complexes I, III, and IV of the mitochondrial electron transfer chain are major sites for the generation of Research Toru Sasaki superoxide during the reoxygenation of hypoxia induced by a decreased oxygen supply, because the chemiluminescence in brain tissues was transiently enhanced by complex I inhibition by rotenone, complex III inhibition by antimycin A, and complex IV inhibition by cyanide.…”

Revisiting an age-old question regarding oxidative stress

“…In contrast, some Cre-lox mediated tissue-specific mice have been shown to have dramatic effects on survival. Sod2 knockout in the brain (Nestin promoter) or peripheral nervous system (Nestin promoter) cause peri-natal death before approximately 4 weeks of age (116, 117). Heart- and skeletal musclespecific knockout of Sod2 (MCK promoter) causes severe cardiac abnormalities and survive only until ~150 days (118).…”