The amyloid beta protein induces oxidative damage of mitochondrial DNA

Multiple lines of evidence suggest involvement of oxidative stress in the pathogenesis of Alzheimer disease (AD). The finding that amyloid beta peptide (A beta) has neurotoxic properties and that such effects are mediated in part by free-radicals has provided an avenue to explore new therapeutic strategies. In this study, we showed that exposure of PC 12 cells to an A beta fragment induces oxidative damage of mitochondrial DNA. Cells were exposed for 24 h to 50 microM A beta (25-35) or to 50 microM of a control peptide with a scrambled sequence. Oxidative damage of mitochondrial DNA (mtDNA) was assessed using a Southern blot technique and an mtDNA-specific probe recognizing a 13.5-kilobase restriction fragment. Treatment of DNA with NaOH was used to reveal abasic sites and single strand breaks. Treatment with endonuclease III or FAPy glycosylase was used to detect pyrimidine or purine lesions, respectively. Cells exposed to A beta exhibited marked oxidative damage of mtDNA as evidenced by characteristic changes on Southern blots. Cells exposed to the scrambled peptide did not show such modifications. Simultaneous addition of the pineal hormone melatonin consistently prevented the A beta-induced oxidative damage to mtDNA. Mitochondrial dysfunction in AD has been demonstrated by several laboratories. This study provides experimental evidence supporting a causative role of A beta in mitochondrial lesions of AD.