(?? < 0.01). 3.5. to diseases such as malignancy, neurodegeneration, and cardiovascular diseases. Persistent and long-term action of ROS in cells can result in a permanent damage despite the low ROS production under physiological conditions . Proteins are one of the major targets of oxidative stress, which also can have detrimental effects on other cellular components (i.e., nucleic acids and lipids). For example, the mitochondrial genome is usually in close proximity to the ROS production site in the mitochondria (i.e., the respiratory chain) and is less guarded by stabilizing proteins and therefore is highly susceptible to oxidative damage which accumulates with aging of, for example, the human brain  and leads to alterations expressed in Alzheimer's disease (AD) too [3, 4]. Age is a major risk for pronounced oxidative Top1 inhibitor 1 damage of the organism as well as for AD. The disease was described more than hundred years ago  and is still incurable due to its complexity and lack of understanding of its cause(s) despite modern technology and tremendous scientific efforts. Although a growing amount of evidence has pointed out the inconsistency of the amyloid cascade hypothesis  as reviewed by Herrup , amyloid beta Top1 inhibitor 1 (Apeptides aggregate in the form Top1 inhibitor 1 of extracellular plaques in the brain and represent a clinical hallmark of AD, Apeptide was found within neurons of AD human brains as well . Aoligomers are toxic forms of the peptide as reviewed by Stefani . Amonomers and small oligomers interact with model lipid membranes, by deep penetration into the membrane [12, 13] and by induction of channels . Mitochondria of SH-SY5Y cells as well as those of neurons of human brain import Apeptide through TOM (translocase of the outer membrane) complex . Mitochondrial dysfunction as a result of mtDNA damage, changes in the number of oxidative phosphorylation subunits, and abnormalities of fission and fusion processes of the organelle as well as disruption of protein maturation and import into mitochondria are discussed as early events in AD [16C18]. Very high level of oxidative stress affects Apeptide trafficking with the increase of intralysosomal Acontent through activation of macroautophagy . Furthermore, amylospheroids (ASPD) made up of Apeptide oligomers interact with the peptide-induced alterations are still obscure. On the list of other possible causative brokers and factors for the development of AD is ionizing radiation (IR), particularly dental X-rays and related IR capable of destroying dividing microglial cells that support neurons , by damaging microglia telomeres causing premature death as proposed by Rodgers . Furthermore, mitochondria are very important targets of ionizing radiation  and their direct damage leads to further nuclear DNA damage . Accumulation of a common deletion in mtDNA (-mtDNA4977) occurs after mitochondrial degeneration in diseases and aging and is induced by ionizing radiation as well [25, 26]. Since oxygen in the cell culture modulates cellular response to stress , we studied effects of ionizing radiation or Apeptide and ionizing radiation on cellular parameters and survival were investigated. We observed the accumulation of Apeptide treatment and irradiation led to decreased level of cell death even below the level of death in control cells, particularly ENOX1 at 5% O2. Our data reveal complex interplay of ionizing radiation and amyloid beta peptide depending on.