Amyloid-β peptides time-dependent structural modifications: AFM and voltammetric characterization

Extracts and Scirpusin B from Recycled Seeds and Rinds of Passion Fruits (Passiflora edulis var. Tainung No. 1) Exhibit Improved Functions in Scopolamine-Induced Impaired-Memory ICR Mice

In this paper, the seeds and rinds of passion fruit, which are the agricultural waste of juice processing, were recycled to investigate their biological activities for sustainable use. De-oiled seed powders (S) were successively extracted by refluxing 95% ethanol (95E), 50E, and hot water (HW), respectively, to obtain S-95EE, S-50EE, and S-HWE. Dried rind powders were successively extracted by refluxing HW and 95E to obtain rind-HWE and rind-95EE, respectively. S-50EE and S-95EE showed the most potent extracts, such as anti-amyloid-β1-42 aggregations and anti-acetylcholinesterase inhibitors, and they exhibited neuroprotective activities against amyloid-β25-35-treated or H2O2-treated SH-SY5Y cells. Scirpusin B and piceatannol were identified in S-95EE, S-50EE, and rind-HWE, and they showed anti-acetylcholinesterase activity at 50% inhibitory concentrations of 62.9 and 258.9 μM, respectively. Daily pretreatments of de-oiled seed powders and rind-HWE (600 mg/kg), S-95EE, and S-50EE (250 mg/kg) or scirpusin B (40 mg/kg) for 7 days resulted in improved learning behavior in passive avoidance tests and had significant differences (p < 0.05) compared with those of the control in scopolamine-induced ICR mice. The seeds and rinds of passion fruit will be recycled as materials for the development of functional foods, promoting neuroprotection and delaying the onset of cognitive dysfunctions.

13C- and 15N-labeling of amyloid-β and inhibitory peptides to study their interaction via nanoscale infrared spectroscopy

Interactions between molecules are fundamental in biology. They occur also between amyloidogenic peptides or proteins that are associated with different amyloid diseases, which makes it important to study the mutual influence of two polypeptides on each other's properties in mixed samples. However, addressing this research question with imaging techniques faces the challenge to distinguish different polypeptides without adding artificial probes for detection. Here, we show that nanoscale infrared spectroscopy in combination with 13C, 15N-labeling solves this problem. We studied aggregated amyloid-β peptide (Aβ) and its interaction with an inhibitory peptide (NCAM1-PrP) using scattering-type scanning near-field optical microscopy. Although having similar secondary structure, labeled and unlabeled peptides could be distinguished by comparing optical phase images taken at wavenumbers characteristic for either the labeled or the unlabeled peptide. NCAM1-PrP seems to be able to associate with or to dissolve existing Aβ fibrils because pure Aβ fibrils were not detected after mixing.

Inhibition of Acetylcholinesterase and Amyloid-β Aggregation by Piceatannol and Analogs: Assessing In Vitro and In Vivo Impact on a Murine Model of Scopolamine-Induced Memory Impairment

Currently, no drug is effective in delaying the cognitive impairment of Alzheimer's disease, which ranks as one of the top 10 causes of death worldwide. Hydroxylated stilbenes are active compounds that exist in fruit and herbal plants. Piceatannol (PIC) and gnetol (GNT), which have one extra hydroxyl group in comparison to resveratrol (RSV), and rhapontigenin (RHA) and isorhapontigenin (isoRHA), which were metabolized from PIC in vivo and contain the same number of hydroxyl groups as RSV, were evaluated for their effects on Alzheimer's disease-associated factors in vitro and in animal experiments. Among the five hydroxylated stilbenes, PIC was shown to be the most active in DPPH radical scavenging and in inhibitory activities against acetylcholinesterase and amyloid-β peptide aggregations, with concentrations for half-maximal inhibitions of 40.2, 271.74, and 0.48 μM. The different interactions of the five hydroxylated stilbenes with acetylcholinesterase or amyloid-β were obtained by molecular docking. The scopolamine-induced ICR mice fed with PIC (50 mg/kg) showed an improved learning behavior in the passive avoidance tests and had significant differences (p < 0.05) compared with those in the control group. The RHA and isoRHA at 10 μM were proven to stimulate neurite outgrowths in the SH-SY5Y cell models. These results reveal that nutraceuticals or functional foods containing PIC have the potential for use in the treatment of neurodegenerative disorders.

Carbon Inks-Based Screen-Printed Electrodes for Qualitative Analysis of Amino Acids

Due to the great significance of amino acids, a substantial number of research studies has been directed toward the development of effective and reliable platforms for their evaluation, detection, and identification. In order to support these studies, a new electrochemical platform based on PANI/ZnO nanowires' modified carbon inks screen-printed electrodes was developed for qualitative analysis of electroactive amino acids, with emphasis on tyrosine (Tyr) and tryptophan (Trp). A comparative investigation of the carbon ink before and after modification with the PANI/ZnO was performed by scanning electron microscopy and by Raman spectroscopy, confirming the presence of PANI and ZnO nanowires. Electrochemical investigations by cyclic voltammetry and electrochemical impedance spectroscopy have shown a higher charge-transfer rate constant, which is reflected into lower charge-transfer resistance and higher capacitance values for the PANI/ZnO modified ink when compared to the simple carbon screen-printed electrode. In order to demonstrate the electrochemical performances of the PANI/ZnO nanowires' modified carbon inks screen-printed electrodes for amino acids analysis, differential pulse voltammograms were obtained in individual and mixed solutions of electroactive amino acids. It has been shown that the PANI/ZnO nanowires' modified carbon inks screen-printed electrodes allowed for tyrosine and tryptophan a peak separation of more than 100 mV, enabling their screening and identification in mixed solutions, which is essential for the electrochemical analysis of proteins within the proteomics research field.

Electrochemical Analysis in Studying β-Amyloid Aggregation

β-amyloid (Aβ) is comprised of a group of peptides formed as a result of cleavage of the amyloid precursor protein by secretases. Aβ aggregation is considered as a central event in pathogenesis of Alzheimer's disease, the most common human neurodegenerative disorder. Molecular mechanisms of Aβ aggregation have intensively being investigated using synthetic Aβ peptides by methods based on monitoring of aggregates, including determination of their size and structure. In this review, an orthogonal approach to the study of Aβ aggregation is considered, which relies on electrochemical registration of the loss of peptide monomers. Electrochemical analysis of Aβ (by voltammetry and amperometric flow injection analysis) is based on registration of the oxidation signal of electroactive amino acid residues of the peptide on an electrode surface. The Aβ oxidation signal disappears, when the peptide is included in the aggregate. The advantages and disadvantages of electrochemical analysis for the study of spontaneous and metal-induced aggregation of Aβ, comparative analysis of various peptide isoforms, and study of the process of complexation of metal ions with the metal-binding domain of Aβ are discussed. It is concluded that the combined use of the electrochemical method and the methods based on detection of Aβ aggregates makes it possible to obtain more complete information about the mechanisms of peptide 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.

Aβ1-40 Oligomers Trigger Neutrophil Extracellular Trap Formation through TLR4- and NADPH Oxidase-Dependent Pathways in Age-Related Macular Degeneration

Neutrophils participate in the advancement of the human innate immune system and respond to perceived endogenous and exogenous threats. As a response mechanism, neutrophil extracellular traps (NETs) form near pathogens and surrounding tissues during an immune response. Drusen is an important marker of Age-Related Macular Degeneration (AMD) and plays an important role in the course of AMD. Aβ1-40 is the main component of drusen. However, the relationship between NETs and AMD or Aβ1-40 is unclear. Here, we found elevated levels of NETs in the serum of AMD patients and elevated levels in the serum of mouse models. We also observed the accumulation of neutrophils in the mouse retina. In addition, the production of NETs was inhibited by PAD4 inhibitors, which can alleviate chronic inflammation. Moreover, we confirmed that Aβ1-40 can induce NETs formation via the Toll-like receptor 4 (TLR4) and neutrophil NADPH oxidase (NOX) pathways. Our study confirmed that the formation of NETs is induced by Aβ1–40, and the results suggest that NETs may play a vital role in AMD pathogenesis.

Amyloid-β42 oligomeric forms: AFM nanoscale structural characterization and impact on long-term memory of young and aged zebrafish

The contribution of amyloid-β (Aβ) soluble forms to Alzheimer's Disease (AD) is undergoing revision and the characterization of monomeric, oligomeric and protofibrillar Aβ forms used in vivo to model AD is a critical step to ensure data interpretation. Atomic force microscopy (AFM) was used to characterize the nanoscale morphology of different Aβ₄₂ forms also used for cerebroventricular injection (cvi) in young (6mo) and aged (36mo) adult zebrafish behavioral and cognitive tests. On the AFM, monomeric solution deposited onto mica resulted mostly in thin filamentous structures and shorter monomeric agglomerates with heights around or below 1.5 nm, as expected for single Aβ₄₂. The oligomeric form was dominated by particles with globular morphology and a few short aggregates around 1 nm high and 8-12 nm long. The protofibrillar form had micrometer-long twisted fibrils of varying diameters (4.5 to 10nm) and large entangled clusters with sizes of up to several tens of micrometers. On the Open Tank used to test exploratory parameters, no differences were observed between injected animals and their age-matched controls, except for a reduced distance travelled by aged individuals that received the Aβ₄₂ oligomeric form. Long-term memory (LTM) for the inhibitory avoidance task was not influenced by monomers cvi, whilst oligomeric and fibrillar Aβ₄₂ hindered LTM formation in young and aged groups. Our findings support current views of deleterious effects of Aβ₄₂ soluble forms on cognition and ensures that preparations were structurally unique and within expected morphologies and dimensions.

Gabapentin Inhibits Multiple Steps in the Amyloid Beta Toxicity Cascade

Oligomeric β-amyloid peptide (Aβ) is one of the main neurotoxic agents of Alzheimer's disease (AD). Oligomers associate to neuronal membranes, forming "pore-like" structures that cause intracellular calcium and neurotransmitter dyshomeostasis, leading to synaptic failure and death. Through molecular screening targeting the C terminal region of Aβ, a region involved in the toxic properties of the peptide, we detected an FDA approved compound, gabapentin (GBP), with neuroprotective effects against Aβ toxicity. At micromolar concentrations, GBP antagonized peptide aggregation over time and reduced the Aβ absorbance plateau to 28% of control. In addition, GBP decreased Aβ association to membranes by almost half, and the effects of Aβ on intracellular calcium in hippocampal neurons were antagonized without causing effects on its own. Finally, we found that GBP was able to block the synaptotoxicity induced by Aβ in hippocampal neurons, increasing post-synaptic currents from 1.7 ± 0.9 to 4.2 ± 0.7 fC and mean relative fluorescence intensity values of SV2, a synaptic protein, from 0.7 ± 0.09 to 1.00 ± 0.08. The results show that GBP can interfere with Aβ-induced toxicity by blocking multiple steps, resulting in neuroprotection, which justifies advancing toward additional animal and human studies.

Differential Proliferation Effect of the Newly Synthesized Valine, Tyrosine and Tryptophan-Naphthoquinones in Immortal and Tumorigenic Cervical Cell Lines

We previously showed that microwave assisted synthesis is the best method for the synthesis of naphthoquinone amino acid and chloride-naphthoquinone amino acid derivatives by a complete evaluation of reaction conditions such as stoichiometry, bases, and pH influence. Following the same strategy, we synthesized chloride and non-chloride tyrosine, valine, and tryptophan-naphthoquinones achieving 85–95%, 80–92%, and 91–95% yields, respectively. The cyclic voltammetry profiles showed that both series of naphthoquinone amino acid derivatives mainly display one redox reaction process. Overall, chloride naphthoquinone amino acid derivatives exhibited redox potential values (E_1/2) more positive than non-chloride compounds. The six newly synthesized compounds were tested in HPV positive and negative as well as in immortal and tumorigenic cell lines to observe the effects in different cellular context simulating precancerous and cancerous status. A dose-response was achieved to determine the IC50 of six newly synthesized compounds in SiHa (Tumorigenic and HPV16 positive), CaLo (Tumorigenic and HPV18 positive), C33-A (Tumorigenic and HPV negative) and HaCaT (Keratinocytes immortal HPV negative) cell lines. Non-chloride tryptophan-naphthoquinone (3c) and chloride tyrosine-naphthoquine (4a) effects were more potent in tumorigenic SiHa, CaLo, and C33-A cells with respect to non-tumorigenic HaCaT cells. Interestingly, there seems to be a differential effect in non-chloride and chloride naphthoquinone amino acid derivatives in tumorigenic versus non tumorigenic cells. Considering all naphthoquinone amino acid derivatives that our group synthesized, it seems that hydrophobic and aromatic amino acids have the greatest effect on cell proliferation inhibition. These results show promising compounds for cervical cancer treatment.

Evaluating the effect of aminoglycosides on the interaction between bovine serum albumins by atomic force microscopy

Characterization and determination of protein-protein interactions (PPIs) plays an important role in molecular biological science. In this study, the effect of aminoglycosides (AGs: streptomycin, gentamycin, lincomycin and clindamycin) on interactions between bovine serum albumin (BSA) was evaluated employing imaging and probing adhesion event by AFM. Multi-spectroscopy and molecular docking were supplementary to investigate the acting forces of the effect. AFM measurements revealed the aggregation of BSA grains and changes of adhesion forces at single molecule level. With adhesion forces between BSA pairs decomposed by Poisson method, specific forces in streptomycin, gentamycin, lincomycin and climdamycin were obviously decreased with the rate of 33.1%, 26.4%, 32.3% and 31.3% while non-specific forces slightly decreased with 5.5%, 3.3%, 4.0% and 7.7%. Combined with results of multi-spectroscopy as well as molecular docking, the whole determination showed AGs affected PPIs by multiple forces, where the hydrogen bonding and hydration effect were the main reasons. The binding of drugs and proteins acted by hydrogen bonding affected the interaction forces between BSA. Consequently, AFM was proposed to be an effective and precise tool in application including evaluating the effects of exogenous compounds on biomacromolecular interactions and rapid screening of drug candidates to avoid potential damages in disease treatment.

Role of the cell membrane interface in modulating production and uptake of Alzheimer's beta amyloid protein

The beta amyloid protein (Aβ) plays a central role in Alzheimer's disease (AD) pathogenesis and its interaction with cell membranes in known to promote mutually disruptive structural perturbations that contribute to amyloid deposition and neurodegeneration in the brain. In addition to protein aggregation at the membrane interface and disruption of membrane integrity, growing reports demonstrate an important role for the membrane in modulating Aβ production and uptake into cells. The aim of this review is to highlight and summarize recent literature that have contributed insight into the implications of altered membrane composition on amyloid precursor protein (APP) proteolysis, production of Aβ, its internalization in to cells via permeabilization and receptor mediated uptake. Here, we also review the various membrane model systems and experimental tools used for probing Aβ-membrane interactions to investigate the key mechanistic aspects underlying the accumulation and toxicity of Aβ in AD.

Insights into the Molecular Mechanisms of Alzheimer's and Parkinson's Diseases with Molecular Simulations: Understanding the Roles of Artificial and Pathological Missense Mutations in Intrinsically Disordered Proteins Related to Pathology

Amyloid-β and α-synuclein are intrinsically disordered proteins (IDPs), which are at the center of Alzheimer's and Parkinson's disease pathologies, respectively. These IDPs are extremely flexible and do not adopt stable structures. Furthermore, both amyloid-β and α-synuclein can form toxic oligomers, amyloid fibrils and other type of aggregates in Alzheimer's and Parkinson's diseases. Experimentalists face challenges in investigating the structures and thermodynamic properties of these IDPs in their monomeric and oligomeric forms due to the rapid conformational changes, fast aggregation processes and strong solvent effects. Classical molecular dynamics simulations complement experiments and provide structural information at the atomic level with dynamics without facing the same experimental limitations. Artificial missense mutations are employed experimentally and computationally for providing insights into the structure-function relationships of amyloid-β and α-synuclein in relation to the pathologies of Alzheimer's and Parkinson's diseases. Furthermore, there are several natural genetic variations that play a role in the pathogenesis of familial cases of Alzheimer's and Parkinson's diseases, which are related to specific genetic defects inherited in dominant or recessive patterns. The present review summarizes the current understanding of monomeric and oligomeric forms of amyloid-β and α-synuclein, as well as the impacts of artificial and pathological missense mutations on the structural ensembles of these IDPs using molecular dynamics simulations. We also emphasize the recent investigations on residual secondary structure formation in dynamic conformational ensembles of amyloid-β and α-synuclein, such as β-structure linked to the oligomerization and fibrillation mechanisms related to the pathologies of Alzheimer's and Parkinson's diseases. This information represents an important foundation for the successful and efficient drug design studies.

The long and successful journey of electrochemically active amino acids. From fundamental adsorption studies to potential surface engineering tools

Proteins have been the subject of electrochemical studies. It is possible to apply electrochemical techniques to obtain information about their structure due to the presence of five electroactive amino acids that can be oriented to the outside of the peptidic chain. These amino acids are L-Tryptophan (L-Trp), L-Tyrosine (L-Tyr), L-Histidine (L-His), L-Methionine (L-Met) and L-Cysteine (L-Cys); their electrochemical behavior being subject of extensive research, but it is still controversial. No spectroscopic investigations have been reported on L-Trp, and due to the short life time of the intermediates, ex situ techniques cannot be employed, leading to a never-ending discussion about possible intermediates. In the L-Tyr and L-His cases, spectroelectrochemical studies were performed and different intermediates were observed, suggesting that some intermediates may be observed under specific conditions, as proposed for L-Cys. This amino acid is the most interesting among the electroactive ones because of the presence of a thiol moiety at its side chain, leading to a wide range of oxidation states. It can adsorb onto surfaces of different crystallographic orientation in stereoselective conformation, modifying the surface for different applications.as a surface engineering tool since it plays the role of as an anchor for the growing of nanocrystals inside proteic templates.

Amyloid Beta Peptide VHHQ, KLVFF, and IIGLMVGGVV Domains Involved in Fibrilization: AFM and Electrochemical Characterization

The time-dependent structural modifications and oxidation behavior of specifically chosen five short amyloid beta (Aβ) peptides, Aβ_1-16, Aβ_1-28, Aβ_10-20, Aβ_12-28, and Aβ_17-42, fragments of the complete human Aβ_1-40 peptide, were investigated by atomic force microscopy (AFM) and voltammetry. The objective was to determine the influence of different Aβ domains (VHHQ that contains electroactive histidine H residues, KLVFF that is the peptide hydrophobic aggregation core, and IIGLMVGGVV that is the C-terminus hydrophobic region), and of Aβ peptide hydrophobicity, in the fibrilization mechanism. The short Aβ peptides absence of aggregation or the time-dependent aggregation mechanisms, at room temperature, in free chloride media, within the time window from 0 to 48 h, were established by AFM via changes in their adsorption morphology, and by differential pulse voltammetry, via modifications of the amino acid residues oxidation peak currents. The first oxidation peak was of tyrosine Y residue and the second peak was of histidine H and methionine M residues oxidation. A correlation between the presence of an intact highly hydrophobic KLVFF aggregation core and the time-dependent changes on the Aβ peptides aggregation was found. The hydrophobic C-terminal domain IIGLMVGGVV, present in the Aβ_1-40 peptide, also contributed to accelerate the formation of Aβ_1-40 peptide aggregates and fibrils.

Peptide-based electrochemical biosensor for juvenile idiopathic arthritis detection

Juvenile idiopathic arthritis (JIA) is a wide group of diseases, characterized by synovial inflammation and joint tissue damage. Due to the delay in the implementation of biomarkers into clinical practice and the association with severe sequels, there is an imperative need for new JIA diagnosis strategies. Electrochemical biosensors based on screen-printed electrodes and peptides are promising alternatives for molecular diagnosis. In this work, a novel biosensor for detecting juvenile idiopathic arthritis (JIA) was developed based on the immobilization of the PRF+1 mimetic peptide, as recognition biological element, on the surface of screen-printed carbon electrode. This biosensor was able to discriminate the JIA positive and negative serum samples from different individuals using differential pulse voltammetry, presenting limits of detection and quantification in diluted samples of 1:784 (v/v) and 1:235 (v/v), respectively. Evaluation by electrochemical impedance spectroscopy showed R_CT 3 times higher for JIA positive sample than for a pool of human serum samples from healthy individuals. Surface analysis of the biosensor by atomic force microscopy, after contact with JIA positive serum, presented great globular clusters irregularly distributed. The long-term stability of the biosensor was evaluated, remaining functional for over 40 days of storage (after storage at 8°C). Therefore, a simple, miniaturized and selective biosensor was developed, being the first one based on mimetic peptide and screen-printed carbon electrode, aiming at the diagnosis of the juvenile idiopathic arthritis in real serum samples.

A novel monoclonal antibody against the N-terminus of Aβ1-42 reduces plaques and improves cognition in a mouse model of Alzheimer's disease

Senile plaques consisting of Amyloid-beta (Aβ) peptides, in particular Aβ1-42, are the hallmark of Alzheimer's disease (AD) and have been the primary therapeutic targets. Passive immunotherapy with monoclonal antibodies (mAbs) has shown initial success in mouse models of AD. However, the existing Aβ-directed mAbs mostly were tested on animal models or patients with advanced disease. The effects and mechanisms of mAbs on animals or human trial participants in the prodromal phase of AD are not fully clarified. In the current study, a novel mAb (3F5) directed against the 1-11 amino acids of Aβ1-42 was generated by immunizing mice with an emulsion of full length human Aβ1-42. The mAb (3F5) showed the ability to disrupt Aβ1-42 aggregation and prevent Aβ-mediated neurotoxicity in vitro. In a mouse model of AD, administration with 3F5 for 3 months in 6 months-old mice demonstrated that the mAb specifically bound with Aβ1-42 to promote the depolymerization of Aβ fibrils, facilitated endocytosis of Aβ1-42 by microglia, and attenuated the death and apoptosis of neuronal cells, accompanied by neurite outgrowth. APP/PS1 double-transgenic mice treated with 3F5 mAb showed reduced memory loss, cognitive decline, and decreased levels of amyloid deposits in the brain. Aβ1-42 levels in cerebral tissues were also significantly reduced, whereas serum Aβ1-42 was markedly increased. Interestingly, the concentration of 3F5 in peripheral circulation is much higher than that in the brain. These results indicate that 3F5 is able to cross the blood-brain barrier (BBB) to bind Aβ and initiates the phagocytosis of antibody/Aβ complexes by microglia in the amyloid depositing mice. 3F5 also promotes Aβ efflux from the brain. As a consequence, the antibody reduces plaques in the AD mouse brain, in association with reduction in the pathology of AD.

Alzheimer's disease amyloid beta peptides in vitro electrochemical oxidation

The oxidative behaviour of the human amyloid beta (Aβ_1-40 and Aβ_1-42) peptides and a group of similar peptides: control inverse (Aβ_40-1 and Aβ_42-1), mutants (Aβ_1-40Phe¹⁰ and Aβ_1-40Nle³⁵), rat Aβ_1-40Rat, and fragments (Aβ_1-28, Aβ_1-16, Aβ_10-20, Aβ_12-28, and Aβ_17-42), in solution or adsorbed, at a glassy carbon electrode, by cyclic and differential pulse voltammetry, were investigated and compared. Structurally the Aβ_1-40 and Aβ_1-42 sequences contain five electroactive amino acid residues, one tyrosine (Tyr¹⁰), three histidines (His⁶, His¹³ and His¹⁴) and one methionine (Met³⁵). The Aβ peptide 3D structure influenced the exposure of the redox residues to the electrode surface and their oxidation peak currents. Depending on the amino acid sequence length and content, the Aβ peptides gave one or two oxidation peaks. The first electron transfer reaction corresponded to the tyrosine amino acid residue oxidation, and the second to both histidines and methionine amino acid residues. The highest contribution to the second oxidation peak current was from His¹³, followed by His¹⁴ and His⁶ residues, and Met³⁵ residue had the lowest contribution. The Aβ peptides electron transfer depended on peptide hydrophobicity and 3D structure, the redox residues position in the sequence, the redox residues close to N-termini giving the highest oxidation peak currents.