Aβ Oligomers Induce Neuronal Oxidative Stress through an N-Methyl-D-aspartate Receptor-dependent Mechanism That Is Blocked by the Alzheimer Drug Memantine

Abstract

Oxidative stress is a major aspect of Alzheimer disease (AD) pathology. We have investigated the relationship between oxidative stress and neuronal binding of A␤ oligomers (also known as ADDLs). ADDLs are known to accumulate in brain tissue of AD patients and are considered centrally related to pathogenesis. Using hippocampal neuronal cultures, we found that ADDLs stimulated excessive formation of reactive oxygen species (ROS) through a mechanism requiring N-methyl-D-aspartate receptor (NMDA-R) activation. ADDL binding to neurons was reduced and ROS formation was completely blocked by an antibody to the extracellular domain of the NR1 subunit of NMDA-Rs. In harmony with a steric inhibition of ADDL binding by NR1 antibodies, ADDLs that were bound to detergent-extracted synaptosomal membranes co-immunoprecipitated with NMDA-R subunits. The NR1 antibody did not affect ROS formation induced by NMDA, showing that NMDA-Rs themselves remained functional. Memantine, an open channel NMDA-R antagonist prescribed as a memory-preserving drug for AD patients, completely protected against ADDL-induced ROS formation, as did other NMDA-R antagonists. Memantine and the anti-NR1 antibody also attenuated a rapid ADDL-induced increase in intraneuronal calcium, which was essential for stimulated ROS formation. These results show that ADDLs bind to or in close proximity to NMDA-Rs, triggering neuronal damage through NMDA-R-dependent calcium flux. This response provides a pathologically specific mechanism for the therapeutic action of memantine, indicates a role for ROS dysregulation in ADDL-induced cognitive impairment, and supports the unifying hypothesis that ADDLs play a central role in AD pathogenesis. Reactive oxygen species (ROS)4 are minor cytotoxic products of normal mitochondrial metabolism. Approximately 1-2% of the oxygen molecules consumed in electron transport generate species, such as superoxide and hydrogen peroxide (1, 2), mainly through side reactions catalyzed by respiratory complexes I (3) and III (1, 3-5). However, imbalance between mitochondrial ROS production and the intracellular levels of antioxidant defenses leads to oxidative stress, a condition that has been associated with apoptosis (6, 7), inflammation (8), ischemia-reperfusion injury (9, 10), and neurodegenerative diseases (11-15). Several cellular features of the brain suggest that it is highly sensitive to oxidative stress (reviewed in Ref. 16). The brain possesses the highest oxygen metabolic rate of any organ in the body (16), consuming approximately 20% of the total amount of oxygen in the body (17). This enhanced metabolic rate leads to an increased probability that excessive levels of ROS will be produced.In some circumstances, particularly in the brain, even small imbalances can be deleterious. Transient production of ROS plays a role in synaptic signaling, with ROS acting as messenger molecules in the process of long term potentiation (LTP), a well known model for synaptic plasticity and learning (18). On the other hand, abnormally elevated ROS ...

Molecular mechanisms of excitotoxicity and their relevance to pathogenesis of neurodegenerative diseases

“…Researchers have investigated the relationship between oxidative stress and neuronal binding of Aβ, which is known to accumulate in the brain tissue of AD patients. Using hippocampal neuronal cultures,investigator found that Aβ stimulated excessive formation of ROS through a mechanism requiring NMDAR activation [85] . Therefore, the dysregulation of NMDAR activity and oxidative stress may have dual deleterious roles in AD.…”

Transformation of amyloid β(1–40) oligomers into fibrils is characterized by a major change in secondary structure

“…However, many publications over the last decade rather blamed oligomers. They were indeed shown to be responsible for the formation of tau protein tangles [11], neuronal oxidative stress [12], prolonged long-term depression [13] and inhibition of long-term potentiation [14]. Other groups linked oligomers to abnormal dendritic spine morphology, spine loss, change in synaptic receptor composition [15] and finally cell death.…”

Calpain inhibition prevents amyloid-β-induced neurodegeneration and associated behavioral dysfunction in rats

“…However, a greater understanding of the underlying process of amyloid toxicity is pressing in order to develop medication that specifically interferes with the Ab-induced disease cascade. A number of authors reporting in vitro studies have suggested that the pathological effect of Ab oligomers is mediated by the NMDA receptor (Shankar et al, 2007;Kelly and Ferreira, 2006;De Felice et al, 2007), and that over activation of the NMDA receptor should be considered as a common principle for some major neurological diseases, including AD (Lipton and Rosenberg, 1994; Harkany et al, 2000; Mattson, 2004). Stimulation of the NMDA receptor leads to excessive entry of calcium into the cell, which activates proteases that are involved in cell death signaling.…”