Ultraeffective Inhibition of Amyloid Fibril Assembly by Nanobody–Gold Nanoparticle Conjugates

Inhibitors of amyloid fibril formation

Many diseases are caused by misfolded and denatured proteins, leading to neurodegenerative diseases. In recent decades researchers have developed a variety of compounds, including polymeric inhibitors and natural compounds, antibodies, and chaperones, to inhibit protein aggregation, decrease the toxic effects of amyloid fibrils, and facilitate refolding proteins. The causes and mechanisms of amyloid formation are still unclear, and there are no effective treatments for Amyloid diseases. This section describes research and achievements in the field of inhibiting amyloid accumulation and also discusses the importance of various strategies in facilitating the removal of aggregates species (refolding) in the treatment of neurological diseases such as chemical methods like as, small molecules, metal chelators, polymeric inhibitors, and nanomaterials, as well as the use of biomolecules (peptide and, protein, nucleic acid, and saccharide) as amyloid inhibitors, are also highlighted.

Targeting Amyloids with Coated Nanoparticles: A Review on Potential Combinations of Nanoparticles and Bio-Compatible Coatings

Amyloidosis is the major cause of many neurodegenerative diseases, such as, Alzheimer's and Parkinson's where the misfolding and deposition of a previously functional protein make it inept for carrying out its function. The genesis of amyloid fibril formation and the strategies to inhibit it have been studied extensively, although some parts of this puzzle still remain unfathomable to date. Many classes of molecules have been explored as potential drugs in vitro, but their inability to work in vivo by crossing the blood-brain-barrier has made them an inadequate treatment option. In this regard, nanoparticles (NPs) have turned out to be an exciting alternative because they could overcome many drawbacks of previously studied molecules and provide advantages, such as, greater bioavailability of molecules and target-specific delivery of drugs. In this paper, we present an overview on several coated NPs which have shown promising efficiency in inhibiting fibril formation. A hundred and thirty papers published in the past two decades have been comprehensively reviewed, which majorly encompass NPs comprising different materials like gold, silver, iron-oxide, poly(lactic-co-glycolic acid), polymeric NP, etc., which are coated with various molecules of predominantly natural origin, such as different types of amino acids, peptides, curcumin, drugs, catechin, etc. We hope that this review will shed light on the advancement of symbiotic amalgamation of NPs with molecules from natural sources and will inspire further research on the tremendous therapeutic potential of these combinations for many amyloid-related diseases.

Interfacial effect on the ability of peptide-modified gold nanoclusters to inhibit hIAPP fibrillation and cytotoxicity

Deposit of amyloid peptides in the cells is related to various amyloidosis diseases. A variety of nanomaterials have been developed to resist amyloid deposit. Most of the research on the inhibition of nanomaterials against amyloid aggregation are undertaken in solution, while the membranes that may mediate fibrillar aggregation and affect interaction of inhibitors with amyloid peptides in biotic environment are little taken into account. In this study, we synthesized three kinds of gold nanoclusters modified with cysteine (C@AuNCs), glutathione (GSH@AuNCs) and a peptide derived from the core region of hIAPP fibrillation (C-HL-8P@AuNCs), and investigated their inhibitory activities against hIAPP fibrillation in the absence and presence of lipid vesicles (POPC/POPG 4:1 LUVs) by the experiments of ThT fluorescence kinetics, AFM and CD. We also explored the inhibitions of hIAPP-induced membrane damage and cytotoxicity by peptide@AuNCs using fluorescent dye leakage and cell viability assays. Our study revealed that the inhibitory efficiency of these peptide@AuNCs against hIAPP fibrillation follows C-HL-8P@AuNCs≅GSH@AuNCs>C@AuNCs in lipid-free solution and C-HL-8P@AuNCs≫GSH@AuNCs>C@AuNCs in lipid membrane environment. Compared with the results obtained in lipid-free solution, the inhibitions of hIAPP fibrillation observed in lipid membrane environment were more associated with the inhibitions of hIAPP-induced damages of lipid vesicles and INS-1 cells (C-HL-8P@AuNCs≫GSH@AuNCs>C@AuNCs). An additional hydrophobic interaction with the homologous core region of hIAPP, which is only provided by C-HL-8P@AuNCs and largely suppressed in lipid-free solution, enhanced in the membrane environment and therefore made C-HL-8P@AuNCs much more powerful than GSH@AuNCs and C@AuNCs in the inhibitions of hIAPP fibrillation and cytotoxicity.

In silico design and identification of new peptides for mitigating hIAPP aggregation in type 2 diabetes

The aberrant misfolding and self-aggregation of human islet amyloid polypeptide (hIAPP or amylin) into cytotoxic aggregates are implicated in the pathogenesis of type 2 diabetes (T2D). Among various inhibitors, short peptides derived from the amyloidogenic regions of hIAPP have been employed as hIAPP aggregation inhibitors due to their low immunogenicity, biocompatibility, and high chemical diversity. Recently, hIAPP fragment HSSNN18-22 was identified as an amyloidogenic sequence and displayed higher antiproliferative activity to RIN-5F cells. Various hIAPP aggregation inhibitors have been designed by chemical modifications of the highly amyloidogenic sequence (NFGAIL) of hIAPP. In this work, a library of pentapeptides based on fragment HSSNN18-22 was designed and assessed for their efficacy in blocking hIAPP aggregation using an integrated computational screening approach. The binding free energy calculations by molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) method identified HSSQN and HSSNQ that bind to hIAPP monomer with a binding affinity of -21.25 ± 4.90 and -19.73 ± 3.10 kcal/mol, respectively, which is notably higher as compared to HSSNN (-11.90 ± 4.12 kcal/mol). The sampling of the non aggregation-prone helical conformation was notably increased from 23.5 ± 3.0 in the hIAPP monomer to 38.1 ± 3.6, and 33.8 ± 3.0% on the incorporation of HSSQN, and HSSNQ, respectively, which indicate reduced aggregation propensity of hIAPP monomer. The pentapeptides, HSSQN and HSSNQ, identified as hIAPP aggregation inhibitors in this work can be further conjugated with various metal chelating peptides to yield more efficacious and clinically relevant multifunctional modulators for targeting various pathological hallmarks of T2D.

Multivalent Nanobody Conjugate with Rigid, Reactive Oxygen Species Scavenging Scaffold for Multi-Target Therapy of Alzheimer's Disease

Efficient therapeutic strategies that concurrently target both Aβ aggregation and oxidative stress in the Alzheimer's disease (AD) microenvironment emerge as a cutting-edge tool to combat the intricate pathogenesis of AD. Here, a multivalent nanobody conjugate with rigid, reactive oxygen species (ROS) scavenging scaffold is developed to achieve simultaneous Aβ amyloidogenesis mitigation, ROS elimination, and Aβ plaque clearance. Grafting Aβ segment (33-GLMVGGVVIA-42) into the third complementary-determining region of a parent nanobody generates an engineered nanobody NB that can recognize Aβ and inhibit its aggregation through homotypic interactions. NB is further genetically modified with a fragment of human interleukin-1β (163-VQGEESNDK-171), so that the obtained fusion nanobody NBIL can also facilitate the Aβ clearance by microglia. Linking NBIL covalently onto a rigid, ROS scavenging scaffold poly(deca-4,6-diynedioic acid) (PDDA) creates the multivalent nanobody conjugate PNBIL, which not only boosts the binding affinity between NBIL and Aβ aggregates for nearly 100 times but also possesses a long-term capability of oxidative stress alleviation, inflammation reduction, and neuron protection. PNBIL has significantly attenuated symptoms on two AD mouse models through amyloidogenesis inhibition and AD microenvironment modulation, validating that the multivalent nanobody conjugate design based on combinatory nanobody and molecular engineering is a promising approach of multi-target therapeutic strategies.

Sappanwood-derived polyphenolic antidote of amyloidal toxins achieved detoxification via inhibition/reversion of amyloidal fibrillation

The formidable virulence of methicillin-resistant staphylococcus aureus (MRSA) have thrown great challenges to biomedicine, which mainly derives from their autocrine phenol-soluble modulins (PSMs) toxins, especially the most toxic member termed phenol-soluble modulins α3 (PSMα3). PSMα3 cytotoxicity is attributed to its amyloidal fibrillation and subsequent formation of cross-α sheet fibrils. Inspired by the multiple biological activity of Sappanwood, herein, we adopted brazilin, a natural polyphenolic compound originated from Caesalpinia sappan, as a potential antidote of PSMα3 toxins, and attempted to prove that the regulation of PSMα3 fibrillation was an effective alexipharmic way for MRSA infections. In vitro results revealed that brazilin suppressed PSMα3 fibrillation and disassembled preformed amyloidal fibrils in a dose-dependent manner, in which molar ratio (brazilin: PSMα3) of efficient inhibition and disassembly were both 1:1. These desired regulations dominated by brazilin benefited from its bonding to core fibrils-forming residues of PSMα3 monomers urged by hydrogen bonding and pi-pi stacking, and such binding modes facilitated brazilin-mediated inhibition or disruption of interactions between neighboring PSMα3 monomers. In this context, these inhibited and disassembled PSMα3 assemblies could not easily insert into cell membrane and subsequent penetration, and thus alleviating the membrane disruption, cytoplasmic leakage, and reactive oxygen species (ROS) generation in normal cells. As such, brazilin dramatically decreased the cytotoxicity borne by toxic PSMα3 fibrils. In addition, in vivo experiments affirmed that brazilin relieved the toxicity of PSMα3 toxins and thus promoted the skin wound healing of mice. This study provides a new antidote of PSMα3 toxins, and also confirms the feasibility of the assembly-regulation strategy in development of antidotes against supramolecular fibrillation-dependent toxins.

Human islet amyloid polypeptide: A therapeutic target for the management of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) and other metabolic disorders are often silent and go unnoticed in patients because of the lack of suitable prognostic and diagnostic markers. The current therapeutic regimens available for managing T2DM do not reverse diabetes; instead, they delay the progression of diabetes. Their efficacy (in principle) may be significantly improved if implemented at earlier stages. The misfolding and aggregation of human islet amyloid polypeptide (hIAPP) or amylin has been associated with a gradual decrease in pancreatic β-cell function and mass in patients with T2DM. Hence, hIAPP has been recognized as a therapeutic target for managing T2DM. This review summarizes hIAPP's role in mediating dysfunction and apoptosis in pancreatic β-cells via induction of endoplasmic reticulum stress, oxidative stress, mitochondrial dysfunction, inflammatory cytokine secretion, autophagy blockade, etc. Furthermore, it explores the possibility of using intermediates of the hIAPP aggregation pathway as potential drug targets for T2DM management. Finally, the effects of common antidiabetic molecules and repurposed drugs; other hIAPP mimetics and peptides; small organic molecules and natural compounds; nanoparticles, nanobodies, and quantum dots; metals and metal complexes; and chaperones that have demonstrated potential to inhibit and/or reverse hIAPP aggregation and can, therefore, be further developed for managing T2DM have been discussed.

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Misfolded species of hIAPP form toxic oligomers in pancreatic β-cells.

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hIAPP amyloids has been detected in the pancreas of about 90% subjects with T2DM.

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Inhibitors of hIAPP aggregation can help manage T2DM.

Conformation-reconstructed multivalent antibody mimic for amplified mitigation of human islet amyloid polypeptide amyloidogenesis

The misfolding and aggregation of human islet amyloid polypeptide (IAPP) into β-sheet-enriched amyloid fibrils is linked to type 2 diabetes. Antibodies are potent inhibitors of IAPP amyloidogenesis, but their preparation is usually complicated and expensive. Here we have created a multivalent antibody mimic SPEPS@Au through conformational engineering of the complementary-determining regions (CDRs) of antibodies on gold nanoparticles (AuNPs). By immobilizing both terminals of an IAPP-recognizing CDR loop (PEP) on the surface of AuNPs, the active conformation of PEP can simply recur on the gold-based antibody mimic, significantly enhancing the binding affinity between PEP and IAPP. SPEPS@Au mitigated amyloidogenesis of IAPP at low sub-stoichiometric concentrations, even after IAPP started aggregating, and dramatically reduced the amyloidogenesis-induced toxicity and ROS production both in vitro and in vivo. The conformation-reconstructed multivalent antibody mimic not only renders a facile strategy to approach potent amyloidogenesis inhibitors, but also provides new perspectives to exploit NP-based substitutes for antibodies in various applications.

Islet amyloid toxicity: From genesis to counteracting mechanisms

Islet amyloid polypeptide (IAPP or amylin) is a hormone co-secreted with insulin by pancreatic β-cells and is the major component of islet amyloid. Islet amyloid is found in the pancreas of patients with type 2 diabetes (T2D) and may be involved in β-cell dysfunction and death, observed in this disease. Thus, investigating the aspects related to amyloid formation is relevant to the development of strategies towards β-cell protection. In this sense, IAPP misprocessing, IAPP overproduction, and disturbances in intra- and extracellular environments seem to be decisive for IAPP to form islet amyloid. Islet amyloid toxicity in β-cells may be triggered in intra- and/or extracellular sites by membrane damage, endoplasmic reticulum stress, autophagy disruption, mitochondrial dysfunction, inflammation, and apoptosis. Importantly, different approaches have been suggested to prevent islet amyloid cytotoxicity, from inhibition of IAPP aggregation to attenuation of cell death mechanisms. Such approaches have improved β-cell function and prevented the development of hyperglycemia in animals. Therefore, counteracting islet amyloid may be a promising therapy for T2D treatment.

Hierarchical Vitalization of Oligotyrosine in Mitigating Islet Amyloid Polypeptide Amyloidogenesis through Multivalent Macromolecules with Conformation-Restrained Nanobody Ligands

The development of inhibitors that can effectively mitigate the amyloidogenesis of human islet amyloid polypeptide (hIAPP), which is linked to type II diabetes, remains a great challenge. Oligotyrosines are intriguing candidates in that they can block the hIAPP aggregation through multiplex phenol-hIAPP interactions. However, oligotyrosines containing too many tyrosine units (larger than three) may fail to inhibit amyloidogenesis due to their increased hydrophobicity and strong self-aggregation propensity. In this work, we developed a strategy to hierarchically vitalize oligotyrosines in mitigating hIAPP amyloidogenesis. Tetratyrosine YYYY (4Y) was grafted into the third complementary-determining region (CDR3) of a parent nanobody to construct a sequence-programmed nanobody N4Y, in which the conformation of the grafted 4Y fragment was constrained for a significantly enhanced binding affinity with hIAPP. We next conjugated N4Y to a polymer to approach a secondary vitalization of 4Y through a multivalent effect. The in vitro and in vivo experiments validated that the resulting PDN4Y could completely inhibit the hIAPP amyloidogenesis at low stoichiometric concentrations and effectively suppress the generation of toxic reactive oxygen species and alleviate amyloidogenesis-mediated damage to INS-1 cells and zebrafish (Danio rerio) embryos. The hierarchical vitalization of 4Y via a synergistic conformation restraint and multivalent effect represents a strategic prototype of boosting the efficacy of peptide-based amyloidogenesis inhibitors, especially those with a high hydrophobicity and strong aggregation tendency, which holds great promise for future translational studies.

Boosting the Photodynamic Degradation of Islet Amyloid Polypeptide Aggregates Via a "Bait-Hook-Devastate" Strategy

Photosensitizers that can generate reactive oxygen species (ROS) upon irradiation have emerged as promising agents for photodynamic degradation of toxic amyloid aggregates that are linked to many amyloidogenic diseases. However, due to the ultrastable β-sheet structure in amyloid aggregates and inefficient utilization of the generated ROS, it usually requires high stoichiometric concentration of the photosensitizer and/or intensive light irradiation to fully dissociate aggregates. In this work, we have developed a "bait-hook-devastate" strategy to boost the efficiency of the photodynamic degradation of amyloid aggregates. This strategy employs anionic polyacrylic acid as a bait to accumulate cationic human islet amyloid polypeptide (IAPP) aggregates and positively charged photosensitizer TPCI in a confined area through electronic interactions. Multiple characterization studies proved that the utilization rate of ROS generated by TPCI was remarkably improved via this strategy, which amplified the ability of TPCI to dissociate IAPP aggregates. Rapid and complete degradation of IAPP aggregates could be achieved by irradiating the system under very mild conditions for less than 30 min, and the IAPP-mediated cytotoxicity was also largely alleviated, providing a new paradigm to accelerate photodynamic degradation of amyloid aggregates for further practical applications.

Acceleration of α-synuclein fibril formation and associated cytotoxicity stimulated by silica nanoparticles as a model of neurodegenerative diseases

A wide range of biophysical and theoretical analysis were employed to explore the formation of (α-syn) amyloid fibril formation as a model of Parkinson's disease in the presence of silica oxide nanoparticles (SiO₂ NPs). Also, different cellular and molecular assays such as MTT, LDH, caspase, ROS, and qPCR were performed to reveal the α-syn amyloid fibrils-associated cytotoxicity against SH-SY5Y cells. Fluorescence measurements showed that SiO₂ NPs accelerate the α-syn aggregation and exposure of hydrophobic moieties. Congo red absorbance, circular dichroism (CD), and transmission electron microscopy (TEM) analysis depicted the SiO₂ NPs accelerated the formation of α-syn amyloid fibrils. Molecular docking study showed that SiO₂ clusters preferably bind to the N-terminal of α-syn as the helix folding site. We also realized that SiO₂ NPs increase the cytotoxicity of α-syn amyloid fibrils through a significant decrease in cell viability, increase in membrane leakage, activation of caspase-9 and -3, elevation of ROS, and increase in the ratio of Bax/Bcl2 mRNA. The cellular assay indicated that α-syn amyloid fibrils formed in the presence of SiO₂ NPs induce their cytotoxic effects through the mitochondrial-mediated intrinsic apoptosis pathway. We concluded that these data may reveal some adverse effects of NPs on the progression of Parkinson's disease.

Targeting Human Islet Amyloid Polypeptide Aggregation and Toxicity in Type 2 Diabetes: An Overview of Peptide-Based Inhibitors

Type 2 diabetes (T2D) is a chronic metabolic disease characterized by insulin resistance and a progressive loss of pancreatic islet β-cell mass, which leads to insufficient secretion of insulin and hyperglycemia. Emerging evidence suggests that toxic oligomers and fibrils of human islet amyloid polypeptide (hIAPP) contribute to the death of β-cells and lead to T2D pathogenesis. These observations have opened new avenues for the development of islet amyloid therapies for the treatment of T2D. The peptide-based inhibitors are of great value as therapeutic agents against hIAPP aggregation in T2D owing to their biocompatibility, feasibility of synthesis and modification, high specificity, low toxicity, proteolytic stability (modified peptides), and weak immunogenicity as well as the large size of involved interfaces during self-aggregation of hIAPP. An understanding of what has been done and achieved will provide key insights into T2D pathology and assist in the discovery of more potent drug candidates for the treatment of T2D. In this article, we review various peptide-based inhibitors of hIAPP aggregation, including those derived from the hIAPP sequence and those not based on the sequence, consisting of both natural as well as unnatural amino acids and their derivatives. The present review will be beneficial in advancing the field of peptide medicine for the treatment of T2D.

Nanomaterial synthesis, an enabler of amyloidosis inhibition against human diseases

Amyloid diseases are global epidemics with no cure currently available. In the past decade, the use of engineered nanomaterials as inhibitors or probes against the pathogenic aggregation of amyloid peptides and proteins has emerged as a new frontier in nanomedicine. In this Minireview, we summarize for the first time the pivotal role of chemical synthesis in enabling the development of this multidisciplinary field.

Monomer-targeting affinity peptide inhibitors of amyloid with no self-fibrillation and low cytotoxicity

A monomer-targeting strategy based on solution-phase biopanning to obtain peptide inhibitors increases the suppression efficiency and reduces the cytotoxicity of amylin.