Superoxide mediates acute liver injury in irradiated mice lacking Sirtuin 3

Aims: This study determined whether acute radiation-induced liver injury seen in Sirtuin3^-/- mice after exposure to Cs-137 γ-rays was mediated by superoxide anion (O₂^•-). Results: Male wild-type (WT) and SIRT3^-/- mice were given 2×2 Gy whole-body radiation doses separated by 24 h and livers were harvested 20 h after the second dose. Ex vivo measurements in fresh frozen liver sections demonstrated 50% increases in dihydroethidium oxidation from SIRT3^-/- animals, relative to WT animals, before irradiation, but this increase was not detected 20 h after radiation exposure. In addition, irradiated livers from SIRT3 ^-/- animals showed significant hydropic degeneration, loss of MitoTracker Green FM staining, increased immunohistochemical staining for 3-nitrotyrosine, loss of Ki67 staining, and increased mitochondrial localization of p53. These parameters of radiation-induced injury were significantly attenuated by an intraperitoneal injection of 2 mg/kg of the highly specific superoxide dismutase mimic, GC4401, 30 min before each fraction. Innovation: Sirtuin 3 (SIRT3) is believed to regulate mitochondrial oxidative metabolism and antioxidant defenses in response to acute radiation-induced liver injury. This work provides strong evidence for the causal role of O₂ ^•- in the liver injury process initiated by whole-body irradiation in SIRT3^-/- mice. Conclusion: These results support the hypothesis that O₂^•- mediates acute liver injury in SIRT3^-/- animals exposed to whole-body γ-radiation and suggest that GC4401 could be used as a radio-protective compound in vivo. Antioxid.