Inhibition of β-Amyloid-Induced Neurotoxicity by Imidazopyridoindoles Derived from a Synthetic Combinatorial Library
ABSTRACT Alzheimer's disease is a progressive neurodegenerative disorder characterized by the deposit of amyloid fibrils in the brain that result from the self-aggregative polymerization of the β-amyloid peptide (Aβ). Evidence of a direct correlation between the ability of Aβ to form stable aggregates in aqueous solution and its neurotoxicity has been reported. The cytotoxic effects of Aβ have been attributed to the aggregation properties of a domain corresponding to the peptide fragment Aβ25–35. In an effort to generate novel inhibitors of Aβ neurotoxicity and/or aggregation, a mixture-based synthetic combinatorial library composed of 23 375 imidazopyridoindoles was generated and screened for inhibition of Aβ25–35 neurotoxicity toward the rat pheochromocytoma PC-12 cell line. The effect of the identified lead compounds on Aβ25–35 aggregation was then evaluated by means of circular dichroism (CD) and thioflavin-T fluorescence spectroscopy. Their activity against Aβ1–42 neurotoxicity toward the PC-12 cell line was also determined. The most active imidazopyridoindoles inhibited both Aβ25–35 and Aβ1–42 neurotoxicity in the low- to mid-micromolar range. Furthermore, inhibition of the random coil to β-sheet transition and self-aggregation of Aβ25–35 was observed by CD and fluorescence spectroscopy, supporting the relationship between inhibition of the Aβ aggregation process and neurotoxicity.
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ABSTRACT: An in vitro tissue culture cell model system for investigating the biochemical mechanisms involved in the neurodegenerative actions of beta-amyloid has been established. Using rat pheochromocytoma PC12 cells, it was found that an early, specific response of cells to the beta-amyloid protein or the beta-amyloid fragment 25-35 was a potent inhibition of cellular redox activity, as measured by 3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide (MTT) reduction. This inhibitory response was rapid and occurred at nanomolar concentrations of peptide, concentrations at which no equivalent decreases in cell proliferation or cell survival were observed. The inhibition of PC12 cell MTT reduction was initially reversible upon removal of the peptide; if sustained for several days, however, by repeated peptide application, it became associated with a dramatic reduction in cell survival. Inhibition of MTT reduction may, therefore, be an early indicator of the mechanism of beta-amyloid-mediated cell death.Proceedings of the National Academy of Sciences 03/1994; 91(4):1470-4. · 9.74 Impact Factor
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ABSTRACT: The neurodegeneration of Alzheimer's disease has been theorized to be mediated, at least in part, by insoluble aggregates of β-amyloid protein that are widely distributed in the form of plaques throughout brain regions affected by the disease. Previous studies by our laboratory and others have demonstrated that the neurotoxicity of β-amyloid in vitro is dependent upon its spontaneous adoption of an aggregated structure. In this study, we report extensive structure-activity analyses of a series of peptides derived from both the proposed active fragment of β-amyloid, β25–35, and the full-length protein, β1–42. We examine the effects of amino acid residue deletions and substitutions on the ability of β-amyloid peptides to both form sedimentable aggregates and induce toxicity in cultured hippocampal neurons. We observe that significant levels of peptide aggregation are always associated with significant β-amyloid-induced neurotoxicity. Further, both N- and C-terminal regions of β25–35 appear to contribute to these processes. In particular, significant disruption of peptide aggregation and toxicity result from alterations in the β33–35 region. In β1–42 peptides, aggregation disruption is evidenced by changes in both electrophoresis profiles and fibril morphology visualized at the light and electron microscope levels. Using circular dichroism analysis in a subset of peptides, we observed classic features of β-sheet secondary structure in aggregating, toxic β-amyloid peptides but not in nonaggregating, nontoxic β-amyloid peptides. Together, these data further define the primary and secondary structures of β-amyloid that are involved in its in vitro assembly into neurotoxic peptide aggregates and may underlie both its pathological deposition and subsequent degenerative effects in Alzheimer's disease.Journal of Neurochemistry 11/2002; 64(1):253 - 265. · 3.97 Impact Factor
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ABSTRACT: Deposition of the beta-amyloid protein in senile plaques is a pathologic hallmark of Alzheimer disease (AD). Focal deposition of beta amyloid in the adult rat cerebral cortex caused profound neurodegenerative changes, including neuronal loss and degenerating neurons and neurites. Chronic induction of the Alz-50 antigen appeared in neurons around focal cortical deposits of beta amyloid. Immunoblot analysis showed that beta amyloid induced Alz-50-immunoreactive proteins in rat cerebral cortex that were very similar to the proteins induced in human cerebral cortex from patients with AD. The neuropeptide substance P prevented beta-amyloid-induced neuronal loss and expression of Alz-50 proteins when coadministered into the cerebral cortex. Systemic administration of substance P also provided protection against the effects of intracerebral beta amyloid. Thus, beta amyloid is a potent neurotoxin in the adult brain in vivo, and its effects can be blocked by substance P.Proceedings of the National Academy of Sciences 09/1991; 88(16):7247-51. · 9.74 Impact Factor