Genistein alleviates the mitochondria-targeted DNA damage induced by β-amyloid peptides 25-35 in C6 glioma cells

Reactive oxygen species (ROS) are mainly produced by mitochondria which can cause oxidative stress. It has been considered that mitochondrial damage induced by oxidative stress is related to Alzheimer's disease (AD). Besides, mitochondrial DNA (mtDNA) is more vulnerable to oxidative damage than other biomacromolecules, causing serious dysfunction to mitochondria. beta-amyloid peptides (A beta) is a main factor responsible for the occurence and development of AD. Astrocytes is an important target cell for A beta' toxicity and can be activated to neglect their normal fountain in the central nervous system. Genistein (Gen), a main active ingredient of soybean isoflavone, has been shown to have neuroprotective effects by antagonizing oxidative damage induced by A beta. Thus, in the present study, we evaluated A beta 25-35 induced mitochondrial DNA (mtDNA) damage and the protective effect of Gen in C6 glioma cells (C6 cells). The study design was consisted of four groups: control group (vehicle), A beta group treated with A beta 25-35, Gen + A beta group treated with Gen + A beta 25-35 and Gen group treated with Gen only. C6 cells were pre-incubated with or without Gen (50 mu M) for 2 h followed by the incubation with A beta 25-35 (25 mu M) for another 24 h. Then the cells were harvested and processed to perform the analysis according to protocols. The mitochondrial ROS in C6 cells were measured by fluorescence spectrometer. Enzyme-linked immunosorbent assay (ELISA) was used to detect the mitochondrial reduced glutathione (GSH) and oxidized glutathione (GSSG) in C6 cells, then the ratio of GSH and GSSG was calculated. The levels of 8-hydroxydeoxyguanosine (8-OHdG) in C6 cells was also detected by ELISA. In addition, mtDNA deletion was detected by polymerase chain reaction (PCR). The mRNA and protein expression of 8-oxoguanine DNA glycosylase (OGG1) in both C6 cells and its mitochondria, and manganese superoxide dismutase (MnSOD) in mitochondria were detected by using reverse transcription-PCR and Western blot. The results showed that the increased mitochondrial ROS accumulation in C6 cells induced by A beta was profoundly reversed by pre-treaded with Gen (p < 0.05). The ratio of GSH and GSSG in mitochondria was significantly increased in both Gen + A beta group and Gen group compared with A beta group (p < 0.05). The levels of 8-OHdG in C6 cells and mtDNA deletion were decreased after pre-treated with Gen (p < 0.05). Gen could also up-regulate the mRNA and protein expression of OGG1 in both C6 cells and its mitochondria and mitochondrial MnSOD compared with the A beta group (p < 0.05). These results confirmed that Gen could alleviate the mitochondria-targeted oxidative damage induced by beta-amyloid 25-35 in C6 cells which might be useful for the treatment of neurodegenerative diseases.