In Vitro Studies on Accelerating the Degradation and Clearance of Amyloid-β Fibrils by an Antiamyloidogenic Peptide

Inhibition and Degradation of Amyloid Beta Fibrils by Peptide Inhibitors

Abnormal amyloid beta (Aβ) aggregation in the form of plaques and its deposition across the human nerve cells are a major hallmark of Alzheimer's disease. Aβ aggregation dynamics and, more importantly, various drugs' effects, either to inhibit the fibril aggregation or to degrade the mature fibrils, have been an area of active research. Large molecule (peptide-based) inhibitors, such as decapeptide (RYYAAFFARR) and pentapeptide (LPFFD), show inhibition/degradation effects on amyloid beta fibrils. Herein, a mathematical model has been proposed. The model simulates Aβ aggregation and inhibitory/degradative action of peptide inhibitors on Aβ fibrillation. Model parameters are tuned by curve fitting the experimental data. The tuned model is used to predict experimental data at different initial dose/fibril concentrations. Model predicted results are observed to be in good agreement with the reported experimental data, demonstrating model's applicability at the molecular level. Sensitivity analyses of the model parameters on the fibril concentration further establish the robustness of the proposed model.

Synthesis and evaluation of catecholamine derivatives as amyloid-beta aggregation inhibitors

Effectively inhibition of amyloid β (Aβ) aggregation is considered an important method for treatment of the Alzheimer's disease. Herein, inspired by the ability of trans-clovamide to effectively inhibit Aβ aggregation, we synthesized a series of structurally related catecholamine derivatives and tested them as Aβ aggregation inhibitors using the Thioflavin T assay. The results show that they demonstrated a higher inhibitory rate against Aβ aggregation. Furthermore, these compounds exhibited high water solubilities and low cytotoxicities. Additionally, transmission electron microscopy images and dynamic light scattering of their Aβ aggregations were observed. Docking simulations revealed that the catechol moiety of the synthesized compounds can form hydrogen bonds with the key regions of Aβ and thereby inhibit Aβ aggregation.

In vitro electrochemical detection of the degradation of amyloid-β oligomers

The clearance of overloaded amyloid β (Aβ) oligomers is thought to be an attractive and potential strategy for the therapy of Alzheimer's disease (AD). A variety of strategies have already been utilized to study Aβ degradation in vitro. Here, the electrochemical detection based on direct electrooxidation of specific Tyr residues within Aβ peptide has been developed as a simple and robust approach for monitoring the oligomers' degradation. C60 was employed for photodegrading Aβ oligomers due to the generated ROS under light irradiation. The oxidation current of Tyr residues by square wave voltammetry (SWV) increased upon the Aβ degradation, confirming that the structure variation of Aβ peptide indeed influenced the exposure of those redox species to the electrode surface and final signal output. Chronoamperometric assay also found the electrooxidation of Tyr undergone an irreversible process. Additionally, the direct electrochemistry was capable of detecting the aggregation with rapid test and better sensitivity in compared with dynamic light scattering (DLS), atomic force microscopy (AFM) and thioflavin T (ThT) based fluorescence assay. Thus, this work indicated the potential application of direct electrochemistry in the in vitro measurement of Aβ degradation and clearance, providing new insights and a complementary means into the AD theranostics.

The total synthesis of berberine and selected analogues, and their evaluation as amyloid beta aggregation inhibitors

The total synthesis of berberine and selected analogues. And their evaluation as amyloid β (Aβ) aggregation inhibitors is described. The key step in the synthesis, the assembly of the berberine framework, was accomplished using an intermolecular Heck reaction. Berberine analog 17 incorporating a tertiary amine moiety showed good anti Aβ aggregation activity, water solubility, and almost no toxicity to nerve cells.

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.

Mathematical aspects of the kinetics of formation and degradation of linear peptide or protein aggregates

In cells, peptides and proteins are sometimes prone to aggregation. In neurons, for example, amyloid β peptides form plaques related to Alzheimer's disease (AD). The corresponding kinetic models either ignore or do not pay attention to degradation of these species. Here, the author proposes a generic kinetic model describing formation and degradation of linear aggregates. The process is assumed to occur via reversible association of monomers and attachment of monomers to or detachment from terminal parts of aggregates. Degradation of monomers is described as a first-order process. Degradation of aggregates is considered to occur at their terminal and internal parts with different rates and these steps are described by first-order equations as well. Irrespective of the choice of the values of the rate constants, the model predicts that eventually the system reaches a stable steady state with the aggregate populations rapidly decreasing with increasing size at large sizes. The corresponding steady-state size distributions of aggregates are illustrated in detail. The transient kinetics are also shown. The observation of AD appears, however, to indicate that the peptide production becomes eventually unstable, i.e., the growth of the peptide population is not properly limited. This is expected to be related to the specifics of the genetic networks controlling the peptide production. Following this line, two likely general networks with, respectively, global negative and positive feedbacks in the peptide production are briefly discussed.

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.