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 b eta peptide (A beta) has neurotoxic properties and that such effects a re mediated in part by free-radicals has provided an avenue to explore new therapeutic strategies. In this study, we showed that exposure of PC12 cells to an A beta fragment induces oxidative damage of mitochon drial DNA. Cells were exposed for 24 h to 50 mu M A beta (25-35) or to 50 mu M of a control peptide with a scrambled sequence. Oxidative dam age of mitochondrial DNA (mtDNA) was assessed using a Southern blot te chnique and an mtDNA-specific probe recognizing a 13.5-kilobase restri ction fragment. Treatment of DNA with NaOH was used to reveal abasic s ites and single strand breaks. Treatment with endonuclease III or FAPy glycosylase was used to detect pyrimidine or purine lesions, respecti vely. Cells exposed to A beta exhibited marked oxidative damage of mtD NA as evidenced by characteristic changes on Southern blots. Cells exp osed to the scrambled peptide did not show such modifications. Simulta neous addition of the pineal hormone melatonin consistently prevented the A beta-induced oxidative damage to mtDNA. Mitochondrial dysfunctio n in AD has been demonstrated by several laboratories. This study prov ides experimental evidence supporting a causative role of A beta in mi tochondrial lesions of AD.