Dendrimers as Antiamyloid Agents

Dendrimer-protein conjugates have significant prospects for biological applications. The complexation changes the biophysical behavior of both proteins and dendrimers. The dendrimers could influence the secondary structure of proteins, zeta-potential, distribution of charged regions on the surface, the protein-protein interactions, etc. These changes offer significant possibilities for the application of these features in nanotheranostics and biomedicine. Based on the dendrimer-protein interactions, several therapeutic applications of dendrimers have emerged. Thus, the formation of stable complexes retains the disordered proteins on the aggregation, which is especially important in neurodegenerative diseases. To clarify the origin of these properties and assess the efficiency of action, the mechanism of protein-dendrimer interaction and the nature and driving force of binding are considered in this review. The review outlines the antiamyloid activity of dendrimers and discusses the effect of dendrimer structures and external factors on their antiamyloid properties.

Antioxidant Berberine-Derivative Inhibits Multifaceted Amyloid Toxicity

Multiple lines of evidence indicate that amyloid beta (Aβ) peptide is responsible for the pathological devastation caused in Alzheimer's disease (AD). Aβ aggregation species predominantly contribute to multifaceted toxicity observed in neuronal cells including generation of reactive oxygen species (ROS), mitochondrial dysfunction, interfering with synaptic signaling, and activation of premature apoptosis. Herein, we report a natural product berberine-derived (Ber-D) multifunctional inhibitor to ameliorate in cellulo multifaceted toxicity of AD. The structural attributes of polyphenolic Ber-D have contributed to its efficient Cu chelation and arresting the redox cycle to prevent the generation of ROS and rescue biomacromolecules from oxidative damage. Ber-D inhibits metal-dependent and -independent Aβ aggregation, which is supported by in silico studies. Ber-D treatment averts mitochondrial dysfunction and corresponding neuronal toxicity contributing to premature apoptosis. These key multifunctional attributes make Ber-D a potential therapeutic candidate to ameliorate multifaceted Aβ toxicity in AD.

Remarkably Efficient Blood-Brain Barrier Crossing Polyfluorene-Chitosan Nanoparticle Selectively Tweaks Amyloid Oligomer in Cerebrospinal Fluid and Aβ1-40

Amyloid oligomers have emerged as a key neurotoxin in Alzheimer's dementia. Amyloid aggregation inhibitors and modulators have therefore offered potential applications in therapeutics and diagnosis. However, crossing the blood-brain barrier (BBB) and finding the toxic aggregates among aggregates of different sizes and shapes remain a challenge. The ability of identifying early aggregates can provide a new approach to find inhibitors of the initial nucleation events correlating presenile dementia. In this study, we have prepared polyfluorene nanoparticles using chitosan as an additive, which enables it to cross BBB efficiently and employed as a highly efficient amyloid oligomer modulator. The polymer conjugate, polyfluorene-chitosan (PC), shows no toxicity in MTT assay and precludes self-aggregation of Aβ1-40 and human cerebrospinal fluid oligomers to final fibril formation. This modulation strategy is supported by thioflavin T assay, circular dichroism studies, atomic force microscope images, and Fourier transform infrared analysis. The polymer-protein interface exhibits the presence of co-aggregates and responded with a stable optical response. The simple synthesis to get desired sizes and shapes with necessary photophysical behavior, biocompatibility, and most prominently BBB permeability makes this polymer conjugate very unique and highly attractive for modulation of amyloid oligomers selectively as well as for developing next generation nanotheranostic materials toward presenile dementia.

Modulation of Amyloid Aggregates into Nontoxic Coaggregates by Hydroxyquinoline Appended Polyfluorene

Inhibitory modulation toward de novo protein aggregation is likely to be a vital and promising therapeutic strategy for understanding the molecular etiology of amyloid related diseases such as Alzheimer's disease (AD). The building up of toxic oligomeric and fibrillar amyloid aggregates in the brain plays host to a downstream of events, causing damage to axons, dendrites, synapses, signaling, transmission, and finally cell death. Herein, we introduce a novel conjugated polymer (CP), hydroxyquinoline appended polyfluorene (PF-HQ), which has a typical "amyloid like" surface motif and exhibits inhibitory modulation effect on amyloid β (Aβ) aggregation. We delineate inhibitory effects of PF-HQ based on Thioflavin T (ThT) fluorescence, atomic force microscopy (AFM), circular dichroism (CD), and Fourier transform infrared (FTIR) studies. The amyloid-like PF-HQ forms nano coaggregates by templating with toxic amyloid intermediates and displays improved inhibitory impacts toward Aβ fibrillation and diminishes amyloid cytotoxicity. We have developed a CP based modulation strategy for the first time, which demonstrates beneficiary amyloid-like surface motif to interact efficiently with the protein, the pendant side groups to trap the toxic amyloid intermediates as well as optical signal to acquire the mechanistic insight.

Aggregation induced emission enhancement and growth of naphthalimide nanoribbons via J-aggregation: insight into disaggregation induced unfolding and detection of ferritin at the nanomolar level

A core substituted naphthalimide AIEEgen displays unusual nanoribbon growth in aqueous media with ultra-sensitivity towards non-heme protein ferritin at physiological conditions.

Multiple function fluorescein probe performs metal chelation, disaggregation, and modulation of aggregated Aβ and Aβ-Cu complex

An exceptional probe comprising indole-3-carboxaldehyde fluorescein hydrazone (FI) performs multiple tasks, namely, disaggregating amyloid β (Aβ) aggregates in different biomarker environments such as cerebrospinal fluid (CSF), Aβ1-40 fibrils, β-amyloid lysozyme aggregates (LA), and U87 MG human astrocyte cells. Additionally, the probe FI binds with Cu(2+) ions selectively, disrupts the Aβ aggregates that vary from few nanometers to micrometers, and prevents their reaggregation, thereby performing disaggregation and modulation of amyloid-β in the presence as well as absence of Cu(2+) ion. The excellent selectivity of probe FI for Cu(2+) was effectively utilized to modulate the assembly of metal-induced Aβ aggregates by metal chelation with the "turn-on" fluorescence via spirolactam ring opening of FI as well as the metal-free Aβ fibrils by noncovalent interactions. These results confirm that FI has exceptional ability to perform multifaceted tasks such as metal chelation in intracellular conditions using Aβ lysozyme aggregates in cellular environments by the disruption of β-sheet rich Aβ fibrils into disaggregated forms. Subsequently, it was confirmed that FI had the ability to cross the blood-brain barrier and it also modulated the metal induced Aβ fibrils in cellular environments by "turn-on" fluorescence, which are the most vital properties of a probe or a therapeutic agent. Furthermore, the morphology changes were examined by atomic force microscopy (AFM), polarizable optical microscopy (POM), fluorescence microscopy, and dynamic light scattering (DLS) studies. These results provide very valuable clues on the Aβ (CSF Aβ fibrils, Aβ1-40 fibrils, β-amyloid lysozyme aggregates) disaggregation behavior via in vitro studies, which constitute the first insights into intracellular disaggregation of Aβ by "turn-on" method thereby influencing amyloidogenesis.

Modulation of Amyloid-β Fibrils into Mature Microrod-Shaped Structure by Histidine Functionalized Water-Soluble Perylene Diimide

Alzheimer's disease (AD) is associated with different types of amyloid peptide aggregates including senile plaques, fibrils, protofibrils, and oligomers. Due to these difficulties, a powerful strategy is needed for the disaggregation of amyloid aggregates by modulating their self-aggregation behavior. Herein, we report a unique approach toward transforming the aggregated amyloidogenic peptides using an amino acid functionalized perylene diimide as a molecular modulator, which is a different nondestructive approach as compared to inhibiting the aggregation of peptides. The histidine functionalized perylenediimide (PDI-HIS) molecule could coassemble with amyloid β (Aβ) peptides via hydrogen bonding that leads to the enhancement in the π-π interactions between Aβ and PDI-HIS moieties. The Thioflavin T (ThT) assay and various spectroscopic and microscopic techniques establish that the PDI-HIS molecules accelerate the Aβ1-40 and the amyloid aggregates in CSF into micro size coassembled structures. These results give rise to a new and unique complementary approach for modulating the biological effects of the aggregates in amyloidogenic peptides.

Monodispersed nanoparticles of conjugated polyelectrolyte brush with high charge density for rapid, specific and label-free detection of tumor marker

Rapid and label-free detection of human α-fetoprotein (AFP) based on selective superquenching of monodispersed nanoparticles of conjugated polyelectrolyte.