Modulation of Fibrillogenesis of Amyloid β(1−40) Peptide with Cationic Gemini Surfactant

Low-Temperature Layer-by-Layer Growth of Semiconducting Few-Layer γ-Graphyne to Exploit Robust Biocompatibility

The sp-hybridized carbon network in single- or few-layer γ-graphyne (γ-GY) has a polarized electron distribution, which can be crucial in overcoming biosafety issues. Here, we report the low-temperature synthesis, electronic properties, and amyloid fibril nanostructures of electrostatic few-layer γ-GY. ABC stacked γ-GY is synthesized by layer-by-layer growth on a catalytic copper surface, exhibiting intrinsic p-type semiconducting properties in few-layer γ-GY. Thickness-dependent electronic properties of γ-GY elucidate interlayer interactions by electron doping between electrostatic layers and layer stacking-involved modulation of the band gap. Electrostatic few-layer γ-GY induces high electronic sensitivity and intense interaction with amyloid beta (i.e., Aβ40) peptides assembling into elongated mature Aβ40 fibrils. Two-dimensional biocompatible nanostructures of Aβ40 fibrils/few-layer γ-GY enable excellent cell viability and high neuronal differentiation of living cells without external stimulation.

The Novel Role of Mitochondrial Citrate Synthase and Citrate in the Pathophysiology of Alzheimer's Disease

Citrate synthase is a key mitochondrial enzyme that utilizes acetyl-CoA and oxaloacetate to form citrate in the mitochondrial membrane, which participates in energy production in the TCA cycle and linked to the electron transport chain. Citrate transports through a citrate malate pump and synthesizes acetyl-CoA and acetylcholine (ACh) in neuronal cytoplasm. In a mature brain, acetyl-CoA is mainly utilized for ACh synthesis and is responsible for memory and cognition. Studies have shown low citrate synthase in different regions of brain in Alzheimer's disease (AD) patients, which reduces mitochondrial citrate, cellular bioenergetics, neurocytoplasmic citrate, acetyl-CoA, and ACh synthesis. Reduced citrate mediated low energy favors amyloid-β (Aβ) aggregation. Citrate inhibits Aβ25-35 and Aβ1-40 aggregation in vitro. Hence, citrate can be a better therapeutic option for AD by improving cellular energy and ACh synthesis, and inhibiting Aβ aggregation, which prevents tau hyperphosphorylation and glycogen synthase kinase-3 beta. Therefore, we need clinical studies if citrate reverses Aβ deposition by balancing mitochondrial energy pathway and neurocytoplasmic ACh production. Furthermore, in AD's silent phase pathophysiology, when neuronal cells are highly active, they shift ATP utilization from oxidative phosphorylation to glycolysis and prevent excessive generation of hydrogen peroxide and reactive oxygen species (oxidative stress) as neuroprotective action, which upregulates glucose transporter-3 (GLUT3) and pyruvate dehydrogenase kinase-3 (PDK3). PDK3 inhibits pyruvate dehydrogenase, which decreases mitochondrial-acetyl-CoA, citrate, and cellular bioenergetics, and decreases neurocytoplasmic citrate, acetyl-CoA, and ACh formation, thus initiating AD pathophysiology. Therefore, GLUT3 and PDK3 can be biomarkers for silent phase of AD.

Peptide-Modified Gemini Surfactants as Delivery System Building Blocks with Dual Functionalities for Glaucoma Treatment: Gene Carriers and Amyloid-Beta (Aβ) Self-Aggregation Inhibitors

Retinal ganglion cell (RGC) neurodegeneration in glaucoma has potential links with amyloid-β (Aβ) deposition. Targeting the Aβ pathway was shown to reduce RGC apoptosis and protect RGCs from degeneration. We report exploratory studies on the amyloid Aβ₄₀ aggregation inhibition properties of four cell adhesion peptide (CAP)-gemini surfactants that are intended as building blocks for gene carrier nanoparticles for glaucoma treatment. The CAP-gemini surfactants (18-7N(p_1-4)-18) were evaluated as potential Aβ40 peptide aggregation inhibitors by a fluorescence kinetic assay and for their binding interactions with Aβ40 dimers by molecular docking studies. In vitro Aβ40 peptide aggregation inhibition studies showed that the 18-7N(p₃)-18 and 18-7N(p₁)-18 ligands inhibit Aβ40 peptide aggregation and prevent the formation of higher order structures. CDOCKER energies and CDOCKER interaction energies demonstrated that the CAP-gemini surfactants formed more stable complexes in the Aβ40 dimer assembly and underwent both polar and nonpolar interactions compared to CAP peptides alone. Also, 18-7N(p₃)-18 showed a significantly lower CDOCKER energy compared to that of the unmodified gemini surfactant 18-7NH-18 (p < 0.0001) and 18-7N(p₄)-18 (p < 0.001), 18-7N(p₁)-18, and 18-7N(p₂)-18. Similarly, 18-7N(p₃)-18 showed a significantly lower CDOCKER interaction energy compared to that of 18-7NH-18, 18-7N(p₄)-18 (p < 0.0001), and 18-7N(p₂)-18 (p < 0.001), while 18-7N(p₃)-18 and 18-7N(p₁)-18 showed similar CDOCKER interaction energies. These studies suggest that a combination of both hydrophobic and electrostatic interactions contributes to the anti-Aβ40 aggregation activity of CAP-gemini surfactants. CAP-gemini surfactants showed 10-fold better Aβ40 peptide aggregation inhibition compared to previously reported values and could provide a new opportunity for glaucoma treatment as dual-functional gene carriers.

The unhappy chaperone

Chaperones protect other proteins against misfolding and aggregation, a key requirement for maintaining biological function. Experimental observations of changes in solubility of amyloid proteins in the presence of certain chaperones are discussed here in terms of thermodynamic driving forces. We outline how chaperones can enhance amyloid solubility through the formation of heteromolecular aggregates (co-aggregates) based on the second law of thermodynamics and the flux towards equal chemical potential of each compound in all phases of the system. Higher effective solubility of an amyloid peptide in the presence of chaperone implies that the chemical potential of the peptide is higher in the aggregates formed under these conditions compared to peptide-only aggregates. This must be compensated by a larger reduction in chemical potential of the chaperone in the presence of peptide compared to chaperone alone. The driving force thus relies on the chaperone being very unhappy on its own (high chemical potential), thus gaining more free energy than the amyloid peptide loses upon forming the co-aggregate. The formation of heteromolecular aggregates also involves the kinetic suppression of the formation of homomolecular aggregates. The unhappiness of the chaperone can explain the ability of chaperones to favour an increased population of monomeric client protein even in the absence of external energy input, and with broad client specificity. This perspective opens for a new direction of chaperone research and outlines a set of outstanding questions that aim to provide additional cues for therapeutic development in this area.

Contrastive Study of the Foaming Properties of N-Acyl Amino Acid Surfactants with Bovine Serum Albumin and Gelatin

A detailed study on the foamability, foam stability, foam liquid-carrying capacity, and foam morphology of two N-acyl amino acid surfactants with bovine serum albumin (BSA) and gelatin were performed by foam scanning. The results showed that the foamability of the mixed system increased gradually and then tended to be stable with increasing surfactant concentration. The foamability of the high-concentration BSA system was stronger than that of the low-concentration BSA system. The foamability and foam stability of sodium N-lauroyl phenylpropanoic acid (N-C₁₂P)/BSA were better than those of sodium N-lauroyl propylamino acid (N-C₁₂A)/BSA, and the foamability and foam stability of N-C₁₂A/gelatin was better than those of N-C₁₂P/gelatin. The liquid-carrying capacity of the foam initially increased and then decreased with increasing time, and the maximum liquid-carrying capacity increased with increasing surfactant concentration. When the concentration of the surfactant was 8 mM, the drainage rate of N-C₁₂A/protein was higher than that of N-C₁₂P/protein. The morphology of the bubble gradually changed from spherical to polyhedron and the number of bubbles gradually decreased with time increasing. Differences in surfactant structure and protein type had an important effect on the number and area of foam.

Cationic gemini surfactant stimulates amyloid fibril formation in bovine liver catalase at physiological pH. A biophysical study

Surfactant molecules stimulate amyloid fibrillation and conformational switching in proteins but the mechanisms by which they accomplish these effects are unclear. A cationic gemini surfactant, C₁₆C₄C₁₆Br₂, with two positively charged heads and two-16C hydrophobic tails induces the amyloid fibrillation of bovine liver catalase (BLC) in vitro at physiological pH. The BLC transformed into amyloid aggregates in the presence of low concentrations (2–150 μM) of C₁₆C₄C₁₆Br₂ at pH 7.4, as confirmed by the use of several biophysical techniques (Rayleigh light scattering (RLS), intrinsic fluorescence, thioflavin T fluorescence (ThT), far-UV circular dichroism, and transmission electron microscopy). The secondary structure of BLC also changed according to the concentration of C₁₆C₄C₁₆Br₂: the α-helical structure of BLC decreased in the presence of 2–100 μM of C₁₆C₄C₁₆Br₂ but at concentrations above 200 μM BLC regained a α-helical structure very similar to the native BLC. In silico molecular docking between BLC and C₁₆C₄C₁₆Br₂ suggest that the positively charged heads of the surfactant interact with Asp127 through attractive electrostatic interactions. Moreover, a Pi-cation electrostatic interaction and hydrophobic interactions also take place between the tails of the surfactant and BLC. The stability of the BLC–C₁₆C₄C₁₆Br₂ complex was confirmed by performing a molecular dynamics simulation and evaluating parameters such as root mean square deviation (RMSD), root mean square fluctuation (RMSF), radius of gyration (R_g), and solvent accessible surface area (SASA). Apart from its aggregation inducing properties, the gemini surfactant itself causes toxicity to the cancerous cell (A549): which is confirmed by MTT assay. This work delivers new insight into the effect of cationic gemini surfactants in amyloid aggregation and paves the way to the rational design of new anti-amyloidogenic agents.

Surfactant molecules stimulate amyloid fibrillation and conformational switching in proteins but the mechanisms by which they accomplish these effects are unclear.

Effects of Gold Nanospheres and Nanocubes on Amyloid-β Peptide Fibrillation

Direct exposure or intake of engineered nanoparticles (ENPs) to the human body will trigger a series of complicated biological consequences. Especially, ENPs could either up- or downregulate peptide fibrillation, which is associated with various degenerative diseases like Alzheimer's and Parkinson's diseases. This work reports the effects of gold nanoparticles (AuNPs) with different shapes on the aggregation of an amyloid-β peptide (Aβ(1-40)) involved in Alzheimer's disease. Two kinds of AuNPs were investigated, i.e., gold nanospheres (AuNSs, ∼20 nm in diameter) and gold nanocubes (AuNCs, ∼20 nm in edge length). It was found that AuNPs play a catalytic role in peptide nucleation through interfacial adsorption of Aβ(1-40). AuNSs with hybrid facets have higher affinity to Aβ(1-40) because of the higher degree of surface atomic unsaturation than the {100}-faceted AuNCs. Therefore, AuNSs exert a more significant acceleration effect on the fibrillation process of Aβ(1-40) than AuNCs. Besides, a shape-dependent secondary structure transformation of Aβ(1-40) with different AuNPs was observed using Fourier transform infrared spectroscopy. The variation of peptide-NP and peptide-peptide interactions caused by the shape alteration of AuNPs influences the equilibrium of inter- and intramolecular hydrogen bonds, which is believed to be responsible for the shape-dependent secondary structure transformation. The study offers further understanding on the complicated NP-mediated Aβ aggregation and also facilitates further development on designing and synthesizing task-specific AuNPs for amyloid disease diagnosis and therapy.

Self-Assembly and Functions of Star-Shaped Oligomeric Surfactants

Oligomeric surfactants consist of three or more amphiphilic moieties which are connected by spacer groups covalently at the level of headgroups. It provides a possible route to bridge the gap from conventional single-chain surfactants to polymeric surfactants and leads to many profound improvements in the properties of surfactants in aqueous solution and at the air/water and water/solid interfaces. Generally, oligomeric surfactants are categorized into linear, ring-like, and star-shaped on the basis of the topological structures of their spacer groups, and their aggregation behavior strongly depends on the resultant topological structures. In recent years, we studied trimeric, tetrameric, and hexameric surfactants with a star-shaped spacer which spreads from a central site of elemental nitrogen or carbon, and their charged headgroups connect with each other through the spacers. It has been found that both the nature of spacer groups and the degree of oligomerization show important influences on the self-assembly of oligomeric surfactants and provide great possibilities in fabricating various surfactant aggregate morphologies by adjusting the molecule conformations. The unique self-assembly behavior endows them with superior physicochemical properties and potential applications. This feature article summarizes the development of star-shaped oligomeric surfactants, including self-assembly at the air/water and water/solid interfaces, self-assembly in aqueous solution, and their functions. We expect that this review could provide a comprehensive understanding of the structure-property relationship and various potential applications of star-shaped oligomeric surfactants and offer additional motivation for their future research.

Pharmacodynamics in Alzheimer's disease model rats of a bifunctional peptide with the potential to accelerate the degradation and reduce the toxicity of amyloid β-Cu fibrils

The accumulation of the extracellular β-amyloid (Aβ) aggregates with metal ions in conjunction with reactive oxygen species (ROS) is closely related to the pathogenesis of Alzheimer's disease (AD). Accounting on Cu ions chelating of our previously designed bifunctional peptide GGHRYYAAFFARR (GR) as well as Aβ-Cu fibrils (fAβ-Cu) dissociation potentials, we report herein an efficient route to synthetically minimize ROS toxicity and degrade fAβ-Cu. It is worth mentioning that GR combines the metal chelating agent GGH and β-sheet breaker RYYAAFFARR (RR). The in vitro results have showed that GR disassociates fAβ-Cu into smaller fragments (sAβ-Cu, 150-200 nm), easily assimilated by PC12 cell and subsequently degraded in the lysosomes; GR can also suppress the ROS generated by fAβ-Cu. The viability of PC12 cell treated with fAβ-Cu has increased, from 38% to about 70% after administration of GR, overwhelming the GGH chelator (46%) and single functional peptide RR (48%). The in vivo results indicated that GR has efficiently reduced Aβ deposition, ameliorated neurologic changes and rescued memory loss, thus, enhancing the cognitive and spatial memory in a AD rat model. This study confirms the superior effect of GR and paves the way toward its future employment in large scale AD treatment.

STATEMENT OF SIGNIFICANCE

We have focused on accelerating the degradation of fAβ-Cu as well as synthetically reducing the ROS toxicity by GR, and, consequently, its benefits in vivo. The bifunctional peptide GR can not only disaggregate fAβ-Cu into smaller fragments to facilitate uptake and degradation by PC12 cell, but also suppresses the ROS generated by fAβ-Cu. Thus, the viability of PC12 cell treated with fAβ-Cu has increased from 38% to 70% after GR administration, overwhelming GGH (46%) and RR (48%). The in vivo studies have revealed that GR improves the spatial memory ability and reduce the amount of senile plaques within brain of AD model rats. Thus, we suppose the bifunctional inhibitor GR has good application prospects in the treatment of AD treatment.

Study of a Bifunctional Aβ Aggregation Inhibitor with the Abilities of Antiamyloid-β and Copper Chelation

In this study, a bifunctional Aβ aggregation inhibitor peptide, GGHRYYAAFFARR (GR), with the abilities to bind copper and antiamyloid was designed to inhibit the neurotoxicity of the Aβ-Cu(II) complex. The thioflavin T (ThT) assay, turbidimetric analysis, transmission electron microscopy (TEM), and (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) (MTT) assay were used to study its potential inhibitory effect on Aβ aggregation. Our findings indicate that GGH was the specific chelating sequence and that the RYYAAFFARR (RR) component acted as an aggregation inhibitor. More importantly, GR significantly decreased the cytotoxicity of the Aβ-Cu(II) complex. The cell viability improved to 88%, which was higher than with the single functional peptide GGH and RR by 39% and 20%, respectively. Moreover, the qualitative effect of Cu(II) on the Aβ-Cu(II) complex was also studied. Our results indicate that Cu(II) induces the formation of the β-sheet structure with a subequimolar Cu(II):Aβ molar ratio (0.25:1) but led to increased ROS production at a supra-equimolar ratio.

Electrical impedance monitoring of protein unfolding

We have applied electrical impedance spectroscopy (EIS) to investigate how the dielectric characteristics of protein aqueous solutions respond to varying amounts of a co-dissolved surfactant.

Surfactant-induced assembly of enzymatically-stable peptide hydrogels

The secondary structure of peptides in the presence of interacting additives is an important topic of study, having implications in the application of peptide science to a broad range of modern technologies. Surfactants constitute a class of biologically relevant compounds that are known to influence both peptide conformation and aggregation or assembly. We have characterized the secondary structure of a linear nonapeptide composed of a hydrophobic alanine/phenylalanine core flanked by hydrophilic acid/amine units. We show that the anionic surfactant sodium dodecyl sulfate (SDS) induces the formation of β-sheets and macroscopic gelation in this otherwise unstructured peptide. Through comparison to related additives, we propose that SDS-induced secondary structure formation is the result of amphiphilicity created by electrostatic binding of SDS to the peptide. In addition, we demonstrate a novel utility of surfactants in manipulating and stabilizing peptide nanostructures. SDS is used to simultaneously induce secondary structure in a peptide and to inhibit the activity of a model enzyme, resulting in a peptide hydrogel that is impervious to enzymatic degradation. These results complement our understanding of the behavior of peptides in the presence of interacting secondary molecules and provide new potential pathways for programmable organization of peptides by the addition of such components.

Modulation of bovine serum albumin fibrillation by ester bonded and conventional gemini surfactants

Modulation of bovine serum albumin fibrillation by gemini surfactants.

Interaction of bovine serum albumin (BSA) with novel gemini surfactants studied by synchrotron radiation scattering (SR-SAXS), circular dichroism (CD), and nuclear magnetic resonance (NMR)

The interaction of three dicationic (gemini) surfactants-3,3'-[1,6-(2,5-dioxahexane)]bis(1-dodecylimidazolium) chloride (oxyC2), 3,3'-[1,16-(2,15-dioxahexadecane)]bis(1-dodecylimidazolium) chloride (oxyC12), and 1,4-bis(butane)imidazole-1-yl-3-dodecylimidazolium chloride (C4)--with bovine serum albumin (BSA) has been studied by the use of small-angle X-ray scattering (SAXS), circular dichroism (CD), and (1)H nuclear magnetic resonance diffusometry. The results of CD studies show that the conformation of BSA was changed dramatically in the presence of all studied surfactants. The greater decrease (from 56 to 24%) in the α-helical structure of BSA was observed for oxyC2 surfactant. The radii of gyration estimated from SAXS data varied between 3 and 26 nm for the BSA/oxyC2 and BSA/oxyC12 systems. The hydrodynamic radius of the BSA/surfactant system estimated from NMR diffusometry varies between 5 and 11 nm for BSA/oxyC2 and 5 and 8 nm for BSA/oxyC12.

Charged surfactants induce a non-fibrillar aggregation pathway of amyloid-beta peptide

The amyloid β-peptide with a sequence of 42 amino acids is the major constituent of extracellular amyloid deposits in Alzheimer's disease plaques. The control of the peptide self-assembly is difficult to achieve because the process is fast and is affected by many variables. In this paper, we describe the effect of different charged and non-charged surfactants on Aβ(₁₋₄₂) fibrillation to define common alternate aggregation pathways. The characterization of the peptide-surfactant interactions by ultra-structural analysis, thioflavin T assay and secondary structure analysis, suggested that charged surfactants interact with Aβ(₁₋₄₂) through electrostatic interactions. Charged micelles slow down the aggregation process and stabilize the peptide in the oligomeric state, whereas non-charged surfactants promote the Aβ(₁₋₄₂) fibril formation.

Disassembly of amyloid fibrils by premicellar and micellar aggregates of a tetrameric cationic surfactant in aqueous solution

We report a finding that not only the micelles but also the premicellar aggregates of a star-like tetrameric quaternary ammonium surfactant PATC can disassemble and clear mature β-amyloid Aβ(1-40) fibrils in aqueous solution. Different from other surfactants, PATC self-assembles into network-like aggregates below its critical micelle concentration (CMC). The strong self-assembly ability of PATC even below its CMC enables PATC to disaggregate the Aβ(1-40) fibrils far below the charge neutralization point of the Aβ(1-40) with PATC. There may be two key features of the fibril disassembly induced by the surfactant. First, the positively charged surfactant molecules bind with the negatively charged Aβ(1-40) fibrils through electrostatic interaction. Second, the self-assembly of the surfactant molecules bound onto the Aβ(1-40) fibrils disaggregate the fibrils, and the surfactant molecules form mixed aggregates with the Aβ(1-40) molecules. The result reveals a structural approach of constructing efficient disassembly agents to mature β-amyloid fibrils.

Aggregation behavior of gemini surfactants and their interaction with macromolecules in aqueous solution

Gemini surfactants are constructed by two hydrophobic chains and two polar/ionic head groups covalently connected by a spacer group at the level of the head groups. Gemini surfactants possess unique structural variations and display special aggregate transitions. Their aggregation ability and aggregate structures can be more effectively adjusted through changing their molecular structures compared with the corresponding monomeric surfactants. Moreover, gemini surfactants exhibit special and useful properties while interacting with polymers and biomacromolecules. Their strong self-aggregation ability can be applied to effectively influence the aggregation behavior of both polymers and biomacromolecules. This short review is focused on the performances of gemini surfactants in aqueous solutions investigated in the last few years, and summarizes the effects of molecular structures on aggregation behavior of gemini surfactants in aqueous solution as well as the interaction of gemini surfactants with polymers and biomacromolecules respectively.

Inhibition of phosphodiesterase-4 reverses memory deficits produced by Aβ25-35 or Aβ1-40 peptide in rats

RATIONALE

Cyclic AMP signaling plays an important role in memory loss associated with Alzheimer's disease (AD). However, little is known about whether inhibition of phosphodiesterase-4 (PDE4), which increases intracellular cAMP, reverses β-amyloid peptide (Aβ)-induced memory deficits.

OBJECTIVE

Experiments were performed to demonstrate the effect of the PDE4 inhibitor rolipram on memory impairment produced by Aβ1-40 (Aβ40) or its core fragment Aβ25-35.

METHODS

We tested memory using Morris water-maze and passive avoidance tasks and examined expression of phosphorylated cAMP response-element binding protein (pCREB) in the hippocampus in rats treated with Aβ25-35 or Aβ40 into bilateral CA1 subregions, with or without rolipram administration.

RESULTS

Aβ25-35 (10 μg/side) increased escape latency during acquisition training and decreased swimming time and distance in the target quadrant in the water-maze probe trial; it also decreased 24-h retention in the passive avoidance paradigm. All these were reversed by chronic administration of rolipram (0.5 mg/kg). Similarly, Aβ40 (4 μg/side) produced memory impairment, as demonstrated by decreased retention in passive avoidance; this was also reversed by repeated treatment with rolipram. In addition, rolipram blocked extinction of memory during the 32-day testing period in the passive avoidance test. Further, Aβ40 decreased pCREB expression in the hippocampus, which was also reversed by rolipram; the changes in pCREB were highly correlated with those in memory.

CONCLUSIONS

These results suggest that the PDE4 inhibitor rolipram reverses cognitive deficits associated with AD most likely via increased cAMP/CREB signaling in the hippocampus; PDE4 could be a target for drugs that improve cognition in AD.

Investigating the effects of sodium dodecyl sulfate on the aggregative behavior of hen egg-white lysozyme at acidic pH

The research presented here is aimed at examining the effects of sodium dodecyl sulfate on the aggregative behavior of hen egg-white lysozyme at pH 2.0. Through various spectroscopic techniques, dynamic light scattering, and electron microscopy, we first demonstrated that SDS exhibited a biphasic effect on lysozyme fibrillation. The presence of SDS at higher concentrations (e.g., 0.25, 5.00, or 20.00 mM SDS) was found to suppress fibril formation of lysozyme whereas fibrillogenic lysozyme-SDS ensemble containing beta-sheet-rich conformation was observed upon the addition of lower concentrations of SDS (e.g., 0.00, 0.06, or 0.1mM SDS). Next, our equilibrium urea-unfolding data revealed that lysozyme samples with higher SDS concentrations showed superior thermodynamic stabilities over the ones with no or lower levels of SDS. Finally, the correlation between SDS concentration and lysozyme aggregative/fibrillogenic propensity and the underlying interacting mechanism were further explored using surface tensiometry and isothermal titration calorimetry. We believe the outcome from this work may not only help decipher the molecular mechanism of amyloid fibrillation, but also shed light on a rational design of potential therapeutic strategies for amyloid pathology.

Facile disassembly of amyloid fibrils using gemini surfactant micelles

The accumulation of a peptide of 38-43 amino acids, in the form of fibrillar plaques, was one of the essential reasons for Alzheimer's disease (AD). Discovering an agent that is able to disassemble and clear disease-associated Abeta peptide fibrils from the brains of AD patients would have critical implications not only in understanding the dynamic process of peptide aggregation but also in the development of therapeutic strategies for AD. This study reported a new finding that cationic gemini surfactant C(12)C(6)C(12)Br(2) micelles can effectively disassemble the Abeta(1-40) fibrils in vitro. Systematic comparisons with other surfactants using ThT fluorescence, AFM, and FTIR techniques suggested that the disassembly effectiveness of gemini surfactant micelles arises from their special molecular structure (i.e., positively bicharged head and twin hydrophobic chains). To track the disassembly process, systematic cryoTEM characterization was also done, which suggested a three-stage disassembly process: (i) Spherical micelles are first absorbed onto the Abeta fibrils because of attractive electrostatic interaction. (ii) Elongated fibrils then disintegrate into short pieces and form nanoscopic aggregates via synergistic hydrophobic and electrostatic interactions. (iii) Finally, complete disaggregation of fibrils and dynamic reassembly result in the formation of peptide/surfactant complexes.

Inhibition of beta-amyloid(1-40) Peptide Aggregation and Neurotoxicity by Citrate

The accumulation of beta-amyloid (Abeta) aggregates is a characteristic of Alzheimer's disease (AD). Furthermore, these aggregates have neurotoxic effects on cells, and thus, molecules that inhibit Abeta aggregate formation could be valuable therapeutics for AD. It is well known that aggregation of Abeta depends on its hydrophobicity, and thus, in order to increase the hydrophilicity of Abeta, we considered using citrate, an anionic surfactant with three carboxylic acid groups. We hypothesized that citrate could reduce hydrophobicity and increase hydrophilicity of Abeta(1-40) molecules via hydrophilic/electrostatic interactions. We found that citrate significantly inhibited Abeta(1-40) aggregation and significantly protected SH-SY5Y cell line against Abeta(1-40) aggregates-induced neurotoxicity. In details, we examined the effects of citrate on Abeta(1-40) aggregation and on Abeta(1-40) aggregates-induced cytotoxicity, cell viability, and apoptosis. Th-T assays showed that citrate significantly inhibited Abeta(1-40) aggregation in a concentration-dependent manner (Th-T intensity: from 91.3% in 0.01 mM citrate to 82.1% in 1.0 mM citrate vs. 100.0% in Abeta(1-40) alone). In cytotoxicity and viability assays, citrate reduced the toxicity of Abeta(1-40) in a concentration-dependent manner, in which the cytotoxicity decreased from 107.5 to 102.3% as compared with Abeta(1-40) aggregates alone treated cells (127.3%) and the cell viability increased from 84.6 to 93.8% as compared with the Abeta(1-40) aggregates alone treated cells (65.3%). Furthermore, Hoechst 33342 staining showed that citrate (1.0 mM) suppressed Abeta(1-40) aggregates-induced apoptosis in the cells. This study suggests that citrate can inhibit Abeta(1-40) aggregation and protect neurons from the apoptotic effects of Abeta(1-40) aggregates. Accordingly, our findings suggest that citrate administration should be viewed as a novel neuroprotective strategy for AD.

Inhibition of Alzheimer amyloid β aggregation by polyvalent trehalose

A glycopolymer carrying trehalose was found to suppress the formation of amyloid fibrils from the amyloid β peptide (1-42) (Aβ), as evaluated by thioflavin T assay and atomic force microscopy. Glycopolymers carrying sugar alcohols also changed the aggregation properties of Aβ, and the inhibitory effect depended on the type of sugar and alkyl side chain. Neutralization activity was confirmed by in vitro assay using HeLa cells. The glycopolymer carrying trehalose strongly inhibited amyloid formation and neutralized cytotoxicity.