Oxidative stress signalling in Alzheimer's disease.

Multiple lines of evidence demonstrate that oxidative stress is an early event in Alzheimer's disease (AD), occurring prior to cytopathology, and therefore may play a key pathogenic role in the disease. Indeed, that oxidative mechanisms are involved in the cell loss and other neuropathology associated with AD is evidenced by the large number of metabolic signs of oxidative stress as well as by markers of oxidative damage. However, what is intriguing is that oxidative damage decreases with disease progression, such that levels of markers of rapidly formed oxidative damage, which are initially elevated, decrease as the disease progresses to advanced AD. This finding, along with the compensatory upregulation of antioxidant enzymes found in vulnerable neurons in AD, indicates that reactive oxygen species (ROS) not only cause damage to cellular structures but also provoke cellular responses. Mammalian cells respond to extracellular stimuli by transmitting intracellular instructions by signal transduction cascades to coordinate appropriate responses. Therefore, not surprisingly stress-activated protein kinase (SAPK) pathways, pathways that are activated by oxidative stress, are extensively activated during AD. In this paper, we review the evidence of oxidative stress and compensatory responses that occur in AD with a particular focus on the roles and mechanism of activation of SAPK pathways.