Targeting the neurotoxic species in Alzheimer's disease: inhibitors of Abeta oligomerization

The Cure of One of the Most Frequent Types of Dementia: A Historical Parallel

The year 2005 marks the centenary of the discovery of Treponema pallidum by Schaudinn and Hoffmann, an important milestone in a long process that culminated in the cure of general paralysis of the insane, probably the most frequent type of dementia up to the first half of the 20th century. Reflections on the process that achieved the virtual eradication of general paralysis of the insane may be important in developing approaches to manage Alzheimer disease, today's most prevalent type of dementia. Both for general paralysis of the insane and Alzheimer disease, it took time for them to be recognized as frequent causes of dementia. The hypothesis of the syphilitic origin of general paralysis of the insane instigated heated debates during the 19th century, even surpassing those between proponents of the amyloid cascade versus the tau protein hypotheses for Alzheimer disease. The results of the management of general paralysis of the insane warrant special reflection. Penicillin therapy arrests the disease, but many patients did not regain their previous cognitive performance. The treatment, to be completely efficient, must be accomplished in the phase of early syphilis or in the latent period, thereby preventing the evolution to general paralysis of the insane. The same probably will be true for Alzheimer disease-to be completely successful, treatment should be given before the disease has begun to damage the brain.

The influence of phospholipid membranes on bovine calcitonin secondary structure and amyloid formation

Calcitonin, a peptide hormone associated with medullary carcinoma of the thyroid, has the potential to form amyloid fibrils and may be a valuable model for investigating the role of peptide-membrane interactions in beta-sheet and amyloid formation. Via a new model peptide system, bovine calcitonin, we found that the exposure of peptide to phospholipid membranes altered its structure relative to the structures formed in aqueous solutions. Of particular relevance to the amyloidoses, incubation of calcitonin with cholesterol-rich and ganglioside-containing membranes resulted in significant enrichment in the beta-sheet and amyloid content of the peptide. The formation of amyloid was also accelerated in these systems. A correlation between the phospholipid-induced structural alterations and calcitonin binding affinities to phospholipid membranes was evident. Bovine calcitonin has considerably higher binding affinity for the phospholipid systems that enhanced its beta-sheet and amyloid structure. Electrostatic forces were not the governing forces behind the observed behavior, as supported by the fact that the ionic strength did not affect the peptide structures or binding affinities. A Van't Hoff analysis of the temperature-dependent peptide binding affinities indicated that binding led to an increase in enthalpy and possibly an increase in entropy of the peptide-membrane systems. Experiments with other amyloid-forming peptides such as beta-amyloid of Alzheimer's disease have also shown similar results and may indicate the need to manipulate peptide-membrane interactions in order to control amyloid formation and its associated disease.

Neurovascular pathways and Alzheimer amyloid beta-peptide

According to the prevailing amyloid cascade hypothesis, the onset and progression of a chronic neurodegenerative condition in Alzheimer disease (AD) is initiated by the amyloid beta-peptide (Abeta) accumulation in brain and consequent neuronal toxicity. Recent emphasis on co-morbidity of AD and cerebrovascular disease and the recognition that cerebrovascular dysregulation is an important feature of AD, has shed new light on neurovascular dysfunction as a possible contributor to cognitive decline and Alzheimer neurodegeneration. In the same time, this association has raised a question as to whether there is a causal relationship between cerebrovascular dysregulation and Abeta-initiated pathology, and whether influencing targets in the neurovasculature may prevent different forms of Abeta brain accumulation and/or lower pre-existing accumulates in a later stage of the disease. Pathogenic cascades which operate to dissociate normal transport exchanges between central and peripheral pools of Abeta, and decreased vascular competence leading to brain hypoperfusion and impaired Abeta clearance are discussed. We suggest that there is a link between neurovascular dysfunction and elevated brain Abeta which provides a new scenario for therapeutic interventions to control Alzheimer mental deterioration.