title: 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.
authors.affiliation: Research Team for Mechanism of Aging, Tokyo Metropolitan Institute of Gerontology, Tokyo, Japan. tsasaki@center.tmig.or.jp
authors.forename: Toru
authors.initials: T
authors.lastname: Sasaki
authors.forename: Takahiko
authors.initials: T
authors.lastname: Shimizu
authors.forename: Tomoko
authors.initials: T
authors.lastname: Koyama
authors.forename: Masanobu
authors.initials: M
authors.lastname: Sakai
authors.forename: Satoshi
authors.initials: S
authors.lastname: Uchiyama
authors.forename: Satoru
authors.initials: S
authors.lastname: Kawakami
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Noda
authors.forename: Takuji
authors.initials: T
authors.lastname: Shirasawa
authors.forename: Shuji
authors.initials: S
authors.lastname: Kojima
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D002534:Hypoxia, Brain / Q000378:metabolism; D049449:Luminescence; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008928:Mitochondria / Q000378:metabolism*; D009924:Organ Culture Techniques; D015427:Reperfusion Injury / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism*
chemical_list: D013481:Superoxides; D013482:Superoxide Dismutase