Littérature scientifique sur le sujet « Antiamyloidogenic »

Transmissible spongiform encephalopathies (TSEs) are fatal neurodegenerative diseases caused by misfolding and aggregation of prion protein (PrP). Previous studies have demonstrated that quercetin can disaggregate some amyloid fibrils, such as amyloid β peptide (Aβ) and α-synuclein. However, the disaggregating ability is unclear in PrP fibrils. In this study, we examined the amyloid fibril-disaggregating activity of quercetin on mouse prion protein (moPrP) and characterized quercetin-bound moPrP fibrils by imaging, proteinase resistance, hemolysis assay, cell viability, and cellular oxidative stress measurements. The results showed that quercetin treatment can disaggregate moPrP fibrils and lead to the formation of the proteinase-sensitive amorphous aggregates. Furthermore, quercetin-bound fibrils can reduce the membrane disruption of erythrocytes. Consequently, quercetin-bound fibrils cause less oxidative stress, and are less cytotoxic to neuroblastoma cells. The role of quercetin is distinct from the typical function of antiamyloidogenic drugs that inhibit the formation of amyloid fibrils. This study provides a solution for the development of antiamyloidogenic therapy.

Alzheimer’s disease is increased in diabetic patients. A defective insulin activity on the brain has been hypothesized to contribute to the neuronal cell dysregulation leading to AD, but the mechanism is not clear. We analyzed the effect of insulin on several molecular steps of amyloid precursor protein (APP) processing and β-amyloid (Aβ) intracellular accumulation in a panel of human neuronal cells and in human embryonic kidney 293 cells overexpressing APP-695. The data indicate that insulin, via its own receptor and the phosphatidylinositol-3-kinase/AKT pathway, influences APP phosphorylation at different sites. This rapid-onset, dose-dependent effect lasts many hours and mainly concerns dephosphorylation at the APP-T668 site. This effect of insulin was confirmed also in a human cortical neuronal cell line and in rat primary neurons. Cell fractionation and immunofluorescence studies indicated that insulin-induced APP-T668 dephosphorylation prevents the translocation of the APP intracellular domain fragment into the nucleus. As a consequence, insulin increases the transcription of antiamyloidogenic proteins such as the insulin-degrading enzyme, involved in Aβ degradation, and α-secretase. In contrast, the transcripts of pro-amyloidogenic proteins such as APP, β-secretase, and glycogen synthase kinase (Gsk)-3β are decreased. Moreover, cell exposure to insulin favors the nonamyloidogenic, α-secretase-dependent APP-processing pathway and reduces Aβ40 and Aβ42 intracellular accumulation, promoting their release in the extracellular compartment. The latter effects of insulin are independent of both Gsk-3β phosphorylation and APP-T668 dephosphorylation, as indicated by experiments with Gsk-3β inhibitors and with cells transfected with the nonphosphorylatable mutated APP-T668A analog. In human neuronal cells, therefore, insulin may prevent Aβ formation and accumulation by multiple mechanisms, both Gsk-3β dependent and independent.

Nonsteroidal anti-inflammatory drugs (NSAIDs) constitute an important pharmacotherapeutic class that, over the past decade, have expanded in application to a panoply of medical conditions. They have been tested for neurodegenerative diseases such as Alzheimer’s to reduce inflammation and also in the attempt to abrogate amyloid deposition. However, the use of NSAIDs as aggregation inhibitors has not been extensively studied in pancreatic amyloid deposition. Pancreatic amyloidosis involves the misfolding of islet amyloid polypeptide (IAPP) and contributes to the progression of type-2 diabetes in humans and felines. To ascertain their antiamyloidogenic activity, several NSAIDs were tested using fluorometric thioflavin-T assays, circular dichroism, photo-induced cross-linking assays, and cell culture. Celecoxib, diclofenac, indomethacin, meloxicam, niflumic acid, nimesulide, phenylbutazone, piroxicam, sulindac, and tenoxicam reduced fibrillization at a molar ratio of 1:10. The circular dichroism spectra of diclofenac, piroxicam, and sulindac showed characteristic spectral signatures found in predominantly α-helical structures. The oligomerization of human IAPP was abrogated with diclofenac and sulindac at a molar ratio of 1:5. The cytotoxic effects of pre-incubated human IAPP on cultured INS-1 cells were noticeably reduced in the presence of diclofenac, meloxicam, phenylbutazone, sulindac, and tenoxicam at a molar ratio of 1:10. Our results demonstrate that NSAIDs can provide chemical scaffolds to generate new and promising antiamyloidogenic agents that can be used alone or as a coadjuvant therapy.

Amyloidoses are protein misfolding diseases caused by deposition of fibrillar proteins in target organs. Nowadays, most of them are still incurable and their relevance to public health system is growing, especially as a consequence of population aging. Spinocerebellar ataxia type 3 is a member of this group of pathologies and its causative agent is ataxin-3 (ATX3). This is consists of a globular N-terminal (JD), followed by a flexible tail carrying a poly-glutamine (polyQ) tract. An expanded polyQ tract triggers the aggregation. In this work, I have investigated the capability of tetracycline (Tetra), epigallocatechin-gallate (EGCG), epigallocatechin (EGC), gallic acid (GA) and trifluoroethanol (TFE) to interfere with ATX3 amyloid deposition. Tetra is an antibiotic recently re-evaluated as anti- amyloidogenic compound. EGCG, EGC and GA, which are natural polyphenols, are already known in literature for their anti-amyloidogenic effect; finally, TFE is an osmolyte that stabilizes secondary structure, preferentially α-helix. Data obtained by aggregation assay, spectroscopic analyses (NMR, FTIR) and morphologic characterisation clearly demonstrated Tetra capability of increasing ATX3 aggregates solubility, without a substantial remodelling of the internal structure. Nevertheless, this antibiotic reduced the toxicity of the oligomeric species and ameliorated ataxic C. elegans phenotype. On the contrary, the analysed polyphenols were capable to interfere with ATX3 aggregation but, instead of preventing, they accelerated the aggregation rate redirecting the process towards the formation of soluble, not toxic, off-pathway aggregates. All compounds were also active against the JD in isolation, but only the polyphenols were capable to bind the monomeric form. In particular, they overlapped specific aggregation-prone regions directly involved in the fibrillation. This could explain their capability of redirecting the aggregation pathway and the different mode of action with respect to Tetra. These polyphenols showed a remarkable reduction of ATX3-mediated cytotoxicity and mitigation of ataxic phenotype in C. elegans and E. coli models. However, the compounds displayed a different efficacy, whereby EGCG was the most and GA the least effective. All data strongly support the idea that GA is the minimal functional unit of EGCG. TFE did not show the capability of preventing aggregation; in fact, even at very low concentration it promotes a faster amyloid-like aggregation. Biophysical characterization of its effect on JD aggregation, instead, provided evidence that ATX3 aggregation proceeds along a new identified pathway by which protein misfolding follows protein aggregation. In fact, TFE induces the formation of a native-like state almost indistinguishable from fully native protein, but more aggregation prone.
Amyloidoses are protein misfolding diseases caused by deposition of fibrillar proteins in target organs. Nowadays, most of them are still incurable and their relevance to public health system is growing, especially as a consequence of population aging. Spinocerebellar ataxia type 3 is a member of this group of pathologies and its causative agent is ataxin-3 (ATX3). This is consists of a globular N-terminal (JD), followed by a flexible tail carrying a poly-glutamine (polyQ) tract. An expanded polyQ tract triggers the aggregation. In this work, I have investigated the capability of tetracycline (Tetra), epigallocatechin-gallate (EGCG), epigallocatechin (EGC), gallic acid (GA) and trifluoroethanol (TFE) to interfere with ATX3 amyloid deposition. Tetra is an antibiotic recently re-evaluated as anti- amyloidogenic compound. EGCG, EGC and GA, which are natural polyphenols, are already known in literature for their anti-amyloidogenic effect; finally, TFE is an osmolyte that stabilizes secondary structure, preferentially α-helix. Data obtained by aggregation assay, spectroscopic analyses (NMR, FTIR) and morphologic characterisation clearly demonstrated Tetra capability of increasing ATX3 aggregates solubility, without a substantial remodelling of the internal structure. Nevertheless, this antibiotic reduced the toxicity of the oligomeric species and ameliorated ataxic C. elegans phenotype. On the contrary, the analysed polyphenols were capable to interfere with ATX3 aggregation but, instead of preventing, they accelerated the aggregation rate redirecting the process towards the formation of soluble, not toxic, off-pathway aggregates. All compounds were also active against the JD in isolation, but only the polyphenols were capable to bind the monomeric form. In particular, they overlapped specific aggregation-prone regions directly involved in the fibrillation. This could explain their capability of redirecting the aggregation pathway and the different mode of action with respect to Tetra. These polyphenols showed a remarkable reduction of ATX3-mediated cytotoxicity and mitigation of ataxic phenotype in C. elegans and E. coli models. However, the compounds displayed a different efficacy, whereby EGCG was the most and GA the least effective. All data strongly support the idea that GA is the minimal functional unit of EGCG. TFE did not show the capability of preventing aggregation; in fact, even at very low concentration it promotes a faster amyloid-like aggregation. Biophysical characterization of its effect on JD aggregation, instead, provided evidence that ATX3 aggregation proceeds along a new identified pathway by which protein misfolding follows protein aggregation. In fact, TFE induces the formation of a native-like state almost indistinguishable from fully native protein, but more aggregation prone.