Molecular determinants of Alzheimer’s disease Aβ peptide neurotoxicity

X-ray Absorption Spectroscopy Investigations of Copper(II) Coordination in the Human Amyloid β Peptide

Alzheimer's disease (AD) is the main cause of age-related dementia and currently affects approximately 5.7 million Americans. Major brain changes associated with AD pathology include accumulation of amyloid beta (Aβ) protein fragments and formation of extracellular amyloid plaques. Redox-active metals mediate oligomerization of Aβ, and the resultant metal-bound oligomers have been implicated in the putative formation of harmful, reactive species that could contribute to observed oxidative damage. In isolated plaque cores, Cu(II) is bound to Aβ via histidine residues. Despite numerous structural studies of Cu(II) binding to synthetic Aβ in vitro, there is still uncertainty surrounding Cu(II) coordination in Aβ. In this study, we used X-ray absorption spectroscopy (XAS) and high energy resolution fluorescence detected (HERFD) XAS to investigate Cu(II) coordination in Aβ(1-42) under various solution conditions. We found that the average coordination environment in Cu(II)Aβ(1-42) is sensitive to X-ray photoreduction, changes in buffer composition, peptide concentration, and solution pH. Fitting of the extended X-ray absorption fine structure (EXAFS) suggests Cu(II) is bound in a mixture of coordination environments in monomeric Aβ(1-42) under all conditions studied. However, it was evident that on average only a single histidine residue coordinates Cu(II) in monomeric Aβ(1-42) at pH 6.1, in addition to 3 other oxygen or nitrogen ligands. Cu(II) coordination in Aβ(1-42) at pH 7.4 is similarly 4-coordinate with oxygen and nitrogen ligands, although an average of 2 histidine residues appear to coordinate at this pH. At pH 9.0, the average Cu(II) coordination environment in Aβ(1-42) appears to be 5-coordinate with oxygen and nitrogen ligands, including two histidine residues.

Oxidative Stress in Alzheimer's Disease: Should We Keep Trying Antioxidant Therapies?

The risk of chronic diseases such as Alzheimer's disease is growing as a result of the continuous increasing average life span of the world population, a syndrome characterized by the presence of intraneural neurofibrillary tangles and senile plaques composed mainly by beta-amyloid protein, changes that may cause a number of progressive disorders in the elderly, causing, in its most advanced stage, difficulty in performing normal daily activities, among other manifestations. Therefore, it is important to understand the underlying pathogenic mechanisms of this syndrome. Nevertheless, despite intensive effort to access the physiopathological pathways of the disease, it remains poorly understood. In that context, some hypotheses have arisen, including the recent oxidative stress hypothesis, theory supported by the involvement of oxidative stress in aging, and the vulnerability of neurons to oxidative attack. In the present revision, oxidative changes and redox mechanisms in Alzheimer's disease will be further stressed, as well as the grounds for antioxidant supplementation as adjuvant therapy for the disease will be addressed.

Metal ions, Alzheimer's disease and chelation therapy

In the last few years, various studies have been providing evidence that metal ions are critically involved in the pathogenesis of major neurological diseases (Alzheimer, Parkinson). Metal ion chelators have been suggested as potential therapies for diseases involving metal ion imbalance. Neurodegeneration is an excellent target for exploiting the metal chelator approach to therapeutics. In contrast to the direct chelation approach in metal ion overload disorders, in neurodegeneration the goal seems to be a better and subtle modulation of metal ion homeostasis, aimed at restoring ionic balance. Thus, moderate chelators able to coordinate deleterious metals without disturbing metal homeostasis are needed. To date, several chelating agents have been investigated for their potential to treat neurodegeneration, and a series of 8-hydroxyquinoline analogues showed the greatest potential for the treatment of neurodegenerative diseases.

Metals in Alzheimer's and Parkinson's diseases

There has been steadily growing interest in the participation of metal ions (especially, zinc, copper, and iron) in neurobiological processes, such as the regulation of synaptic transmission. Recent descriptions of the release of zinc and copper in the cortical glutamatergic synapse, and influencing the response of the NMDA receptor underscore the relevance of understanding the inorganic milieu of the synapse to neuroscience. Additionally, major neurodegenerative disorders, including Alzheimer's disease and Parkinson's disease, are characterized by elevated tissue iron, and miscompartmentalization of copper and zinc (e.g. accumulation in amyloid). Increasingly sophisticated medicinal chemistry approaches, which correct these metal abnormalities without causing systemic disturbance of these essential minerals, are being tested. These small molecules show promise of being disease-modifying.

Platinum-based inhibitors of amyloid-beta as therapeutic agents for Alzheimer's disease

Amelyoid-beta peptide (Abeta) is a major causative agent responsible for Alzheimer's disease (AD). Abeta contains a high affinity metal binding site that modulates peptide aggregation and toxicity. Therefore, identifying molecules targeting this site represents a valid therapeutic strategy. To test this hypothesis, a range of L-PtCl(2) (L = 1,10-phenanthroline derivatives) complexes were examined and shown to bind to Abeta, inhibit neurotoxicity and rescue Abeta-induced synaptotoxicity in mouse hippocampal slices. Coordination of the complexes to Abeta altered the chemical properties of the peptide inhibiting amyloid formation and the generation of reactive oxygen species. In comparison, the classic anticancer drug cisplatin did not affect any of the biochemical and cellular effects of Abeta. This implies that the planar aromatic 1,10-phenanthroline ligands L confer some specificity for Abeta onto the platinum complexes. The potent effect of the L-PtCl(2) complexes identifies this class of compounds as therapeutic agents for AD.

Amyloid-beta-anti-amyloid-beta complex structure reveals an extended conformation in the immunodominant B-cell epitope

Alzheimer's disease (AD) is the most common form of dementia. Amyloid-beta (A beta) peptide, generated by proteolytic cleavage of the amyloid precursor protein, is central to AD pathogenesis. Most pharmaceutical activity in AD research has focused on A beta, its generation and clearance from the brain. In particular, there is much interest in immunotherapy approaches with a number of anti-A beta antibodies in clinical trials. We have developed a monoclonal antibody, called WO2, which recognises the A beta peptide. To this end, we have determined the three-dimensional structure, to near atomic resolution, of both the antibody and the complex with its antigen, the A beta peptide. The structures reveal the molecular basis for WO2 recognition and binding of A beta. The A beta peptide adopts an extended, coil-like conformation across its major immunodominant B-cell epitope between residues 2 and 8. We have also studied the antibody-bound A beta peptide in the presence of metals known to affect its aggregation state and show that WO2 inhibits these interactions. Thus, antibodies that target the N-terminal region of A beta, such as WO2, hold promise for therapeutic development.