Direct and selective elimination of specific prions and amyloids by 4,5-dianilinophthalimide and analogs.

Mechanisms to safely eliminate amyloids and preamyloid oligomers associated with many devastating diseases are urgently needed. Biophysical principles dictate that small molecules are unlikely to perturb large intermolecular protein-protein interfaces, let alone extraordinarily stable amyloid interfaces. Yet 4,5-dianilinophthalimide (DAPH-1) reverses Abeta42 amyloidogenesis and neurotoxicity, which is associated with Alzheimer's disease. Here, we show that DAPH-1 and select derivatives are ineffective against several amyloidogenic proteins, including tau, alpha-synuclein, Ure2, and PrP, but antagonize the yeast prion protein, Sup35, in vitro and in vivo. This allowed us to exploit several powerful new tools created for studying the conformational transitions of Sup35 and decipher the mechanisms by which DAPH-1 and related compounds antagonize the prion state. During fibrillization, inhibitory DAPHs alter the folding of Sup35's amyloidogenic core, preventing amyloidogenic oligomerization and specific recognition events that nucleate prion assembly. Select DAPHs also are capable of attacking preformed amyloids. They remodel Sup35 prion-specific intermolecular interfaces to create morphologically altered aggregates with diminished infectivity and self-templating activity. Our studies provide mechanistic insights and reinvigorate hopes for small-molecule therapies that specifically disrupt intermolecular amyloid contacts.

Efficient reversal of Alzheimer's disease fibril formation and elimination of neurotoxicity by a small molecule.

The Abeta1-42 peptide that is overproduced in Alzheimer's disease (AD) from a large precursor protein has a normal amino acid sequence but, when liberated, misfolds at neutral pH to form "protofibrils" and fibrils that are rich in beta-sheets. We find that these protofibrils or fibrils are toxic to certain neuronal cells that carry Ca-permeant alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Disrupting the structure of the Abeta1-42 fibrils and protofibrils might lead to the discovery of molecules that would be very useful in the treatment of AD. A high-throughput screen of a library of >3,000 small molecules with known "biological activity" was set up to find compounds that efficiently decrease the beta-sheet content of aggregating Abeta1-42. Lead compounds were characterized by using thioflavin T (ThT) as a beta-sheet assay. The most effective of six compounds found was 4,5-dianilinophthalimide (DAPH) under the following conditions: DAPH at low micromolar concentrations abolishes or greatly reduces previously existing fully formed Abeta1-42 fibrils, producing instead amorphous materials without fibrils but apparently containing some protofibrils and smaller forms. Coincubation of the Abeta1-42 peptide with DAPH produces either amorphous materials or empty fields. Coincubation of DAPH and Abeta1-42 greatly reduces the beta-sheet content, as measured with ThT fluorescence, and produces a novel fluorescent complex with ThT. When the Abeta1-42 peptide was coincubated with DAPH at very low micromolar concentrations, the neuronal toxicity mentioned above (Ca(2+) influx) was eliminated. Clearly, DAPH is a promising candidate for AD therapy.

Mechanism of membrane depolarization caused by the Alzheimer Abeta1-42 peptide.

We report a novel observation that the neurotoxic Alzheimer peptide Abeta1-42, when pre-incubated, causes a dramatic and lasting membrane depolarization in differentiated human hNT neuronal cells and in rodent PC12 cells in a concentration-dependent manner. This phenomenon involves activation of the metabotropic glutamate receptor, mGluR(1). Abeta-induced membrane depolarization in PC12 cells is sensitive to mGluR(1) antagonists and to pertussis and cholera toxins, indicating the involvement of particular G-proteins. The effect is different from the known ability of aggregated Abeta1-42 to cause a calcium influx. Since mGluR(1) agonists mimic the Abeta effect, we deduce that in this cell system glutamate can control the membrane potential and thereby the excitability of its target neurons. We propose that Abeta-induced membrane depolarization described here leads in Alzheimer's disease to hyperexcitability of affected neurons and is a crucially important molecular mechanism for beta-amyloid toxicity and cognitive dysfunction in the disease.

Eliminating membrane depolarization caused by the Alzheimer peptide Abeta(1-42, aggr.).

A high-throughput screen found compounds that eliminate the dramatic membrane depolarization caused by the aggregated Alzheimer Abeta1-42 peptide, which activates mGluR1 receptors. The library was composed of known biologically active compounds; the cell-based assay measured the changes of membrane potential with a slow-acting voltage-sensitive dye. We found 10 potentially useful compounds, some of which reduce the Abeta-induced membrane depolarization up to 96%. Interestingly, the active compounds include specific tyrosine kinase inhibitors and inhibitors of certain chloride channels. We deduce that mGluR1 receptors, activated by Abeta1-42 or otherwise, can control the membrane potential via downstream activation of certain tyrosine kinases and certain ion channels. Dopaminergic and serotonergic agonists that emerged from the screen presumably compensate for the Abeta-induced membrane depolarization by themselves causing a hyperpolarization. The hit compounds, whose pharmacokinetics are known, show promise for the restoration of cognitive function in the treatment of early and mid-stage Alzheimer's disease.

Elimination of Amyloid beta Neurotoxicity.

Aggregation of the Alzheimer amyloid beta peptide (Abeta) Abeta1-42 forms neurotoxic fibrils. In contact with human neurons the fibrils cause rapid influx of external calcium through AMPA/kainate-channels. If this molecular mechanism reflects in vivo events, it could explain the pathogenesis of Alzheimer's disease; activation of AMPA/kainate channels is therefore a likely target for therapeutic intervention. Here we show that short antagonistic "decoy peptides", made of D-amino acids, eliminate this "calcium effect" of Ab1-42. Since chronically elevated calcium levels in the disease trigger activation of pathways that lead to neuron dysfunction and cell death, our decoy peptides are obvious candidates for drug development.