Inhibition mechanisms of four ellagitannins from terminalia chebula fruits on acetylcholinesterase by inhibition kinetics, spectroscopy and molecular docking analyses

Effect of polysaccharides on the inhibition and binding ability of hesperetin-copper(II) complex on α-glucosidase

The study aimed to investigate the inhibitory effect of hesperetin-copper (II) [Hsp-Cu(II)] on α-glucosidase in the presence of polysaccharides (xylan, β-glucan, low-, medium- and high-viscosity chitosan). The results showed that all the polysaccharides significantly reduced the inhibitory activity of α-glucosidase by Hsp-Cu(II), and the reduction effect of high-viscosity chitosan was the most significant. The polysaccharides significantly decreased the binding constant of Hsp-Cu(II)α-glucosidase, changed the binding sites of Hsp-Cu(II) to α-glucosidase and reduced the hydrogen bonds of Hsp-Cu(II) bound with α-glucosidase. Circular dichroism showed that the reduction of α-helix content in α-glucosidase caused by Hsp-Cu(II) was raised from 27.2 % to 29.5 %, 31.3 % and 32.7 % in the presence of xylan, β-glucan and high-viscosity chitosan, respectively, suggesting that the polysaccharides could restore the secondary structure of α-glucosidase. Fourier transforms infrared spectra showed that xylan and β-glucan formed hydrogen bonds with Hsp-Cu(II). The mechanism of the decreasing effect might be that the polysaccharides with the low viscosity compete with α-glucosidase to bind Hsp-Cu(II) through hydrogen bonds, restoring the catalytic center and active amino acid residues of Hsp-Cu(II) bound with α-glucosidase and the adsorption of high-viscosity chitosan decreases the binding affinity of Hsp-Cu(II) on α-glucosidase. The study may offer a reference for the development of Hsp-Cu(II)-based nutritional and healthy food for patients with hyperglycemia.

Molecular insight on conformational alterations and functional changes of acetylcholinesterase induced by an emerging environmental pollutant 6PPD-quinone

The emerging pollutant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-quinone) has attracted broad attention because of its widespread presence and harmful impacts, including hepatotoxicity and neurotoxicity. Acetylcholinesterase (AChE) is commonly used as a classical biomarker for assessing toxicity in the nervous system. Here, the interaction mechanism between AChE and 6PPD-quinone was investigated using a combination of multispectral and computational approaches, including enzyme activity assay, fluorescence thermodynamic titration, circular dichroism (CD) spectroscopy, molecular dynamics (MD) simulation, computational alanine scanning (CAS), and free energy landscape (FEL) analysis, among others. The result indicates that 6PPD-quinone spontaneously binds into the active site of AChE, thereby competitively inhibiting enzyme's activity. The interaction is primarily facilitated by hydrogen bonds and van der Waals forces, exhibiting a binding constant (Kb) of 1.044 × 104 M-1 at 298 K. The introduction of 6PPD-quinone causes a reduction in the α-helix content of AChE, making the structure less stable and more relaxed. Furthermore, the FEL analysis of AChE revealed that, with the presence of 6PPD-quinone, the number of global minima of AChE increased from 2 to 2-3. Additionally, Molecular docking outcomes exhibit that 6PPD-quinone interacted with tyrosine (TYR) 337, TYR124, tryptophan (TRP) 86, serine (SER) 203, glycine (GLY) 120 and other residues of AChE. CAS analysis shows binding free energy changes (ΔΔGbinding) of TRP86, TYR337 were 5.17 and 2.57 kcal mol-1, respectively, highlighting their key roles in the binding process of 6PPD-quinone with AChE. The interactions of 6PPD-quinone with the TRP86 and TYR337 may be the reason for the decrease in AChE activity.

The protective effects of geraniin against initial and intermediate carbonyl-induced glycoxidation stress in bovine serum albumin models

This study elucidates the multi-target anti-glycoxidation mechanisms of geraniin (G), a hydrolysable tannin, using bovine serum albumin (BSA) models incubated with glucose (BSA-G), glyoxal (BSA-GO), and methylglyoxal (BSA-MGO). Through comprehensive analysis employing multispectral analysis, molecular docking, and confocal microscopy, G demonstrated significant inhibitory capacity against advanced glycoxidation end-product (AGEs) formation across three stages. In the early stage, G competitively binds to specific lysine (Lys127-434) and arginine residues (Arg185-456) in BSA-subdomains, effectively reducing glucose-BSA covalent binding by 63 % (at 90 μM G; p < 0.05) and preserving 85 % of free lysine residues through steric hindrance mechanisms. During the intermediate stage, G efficiently traps reactive GO/MGO species, suppressing the formation of dityrosine and kynurenine by 60-70 %. In the advanced stage, G significantly inhibits AGEs crosslinking and amyloid-like aggregation, diminishing Thioflavin-T (β-sheet) and Nile red (hydrophobic) fluorescence by 55-70 %. Molecular dynamics simulations confirmed stable G-BSA binding (RMSD: 1.87 Å), while confocal microscopy visually demonstrated G's ability to prevent glycation-induced structural rearrangements in BSA. These findings position geraniin as potent natural anti-AGEs with efficacy comparable to aminoguanidine, while avoiding the toxicity risks associated with synthetic alternatives. The elucidated mechanisms provide valuable insights into protein-phytochemical interactions with potential applications in preventing glycoxidative damage to biological macromolecules.

Alzheimer's disease: A case study involving EEG-based fE/I ratio and pTau-181 protein analysis through nasal administration of Saraswata Ghrita

Background

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that impairs memory, language, and cognitive functions and currently has no definitive cure. Saraswata Ghrita (SG), a traditional Ayurvedic remedy administered nasally, offers a holistic approach and is believed to directly affect brain functions through its unique delivery route.

Objective

This study aimed to evaluate the effectiveness of SG in improving cognitive function and neurochemical biomarkers in a patient with AD. Key outcomes included electroencephalography-based excitation/inhibition (fE/I) ratio, and levels of phosphorylated Tau-181 (pTau-181), serotonin, dopamine, acetylcholine, and dehydroepiandrosterone (DHEA).

Methods

A 90-day proof-of-concept clinical trial was conducted with one AD patient. Nasal administration of SG was performed twice daily. Measurements included EEG spectral power analysis across 1-48 Hz, cognitive function assessed by Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog), Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA), and Quality of Life in Alzheimer's Disease (QoL-AD) scales, and biochemical analyses of pTau-181, serotonin, dopamine, acetylcholine, and DHEA.

Results

Notable improvements were observed: ADAS-Cog score decreased from 40 to 36, QoL-AD score increased from 23 to 31, MMSE score improved from 13 to 18, and MoCA score increased from 8 to 13. Biochemical markers showed a decrease in pTau-181 (12.50 pg/ml to 6.28 pg/ml), an increase in acetylcholine (13.73 pg/ml to 31.83 pg/ml), while serotonin and DHEA levels rose, and dopamine levels decreased (39.14 pg/ml to 36.21 pg/ml).

Conclusions

SG demonstrated potential in enhancing cognitive functions and neurochemical markers in AD, with the nasal route proving safe and effective. These findings suggest the value of traditional Ayurvedic treatments in contemporary AD management.

Interactions between forsythoside E and two cholinesterases at the different conditions: fluorescence sections

Forsythoside E is one secondary metabolite ofForsythia suspensa(Thunb.) Vahl. In the study, the interactions between forsythoside E and two types of cholinesterases, acetylcholinesterase and butyrylcholinesterase were investigated in the different conditions. Forsythoside E increased the fluorescence intensity of acetylcholinesterase but quenched the fluorescence of butyrylcholinesterase. Aβ25-35used in the study may not form complexes with cholinesterases, and did not affect the interaction between forsythoside E and cholinesterases. The charged quaternary group of AsCh interacted with the 'anionic' subsite in acetylcholinesterase, which did not affect the interaction between forsythoside E and acetylcholinesterase. The enhancement rate of forsythoside E to acetylcholinesterase fluorescence from high to low was acid solution (pH 6.4), neutral solution (pH 7.4) and alkaline solution (pH 8.0), while the reduction rate of forsythoside E to butyrylcholinesterase fluorescence was in reverse order. Metal ions may interact with cholinesterases, and increased the effects of forsythoside E to cholinesterases fluorescence, in order that Fe3+was the highest, followed by Cu2+, and Mg2+. A forsythoside E-butyrylcholinesterase complex at stoichiometric ratio of 1:1 was spontaneously formed, and the static quenching was the main quenching mode in the process of forsythoside E binding with butyrylcholinesterase. TheKvalues of two complexes were pretty much the same, suggesting that the interaction between cholinesterases and forsythoside E was almost unaffected by acid-base environment and metal ions. Thennumbers of two cholinesterases approximately equaled to one, indicating that there was only one site on each cholinesterase applicable for forsythoside E to bind to.

In vitro inhibitory effect of five natural sweeteners on α-glucosidase and α-amylase

A promising and efficacious approach to manage diabetes is inhibiting α-glucosidase and α-amylase activity. Therefore, the inhibitory activities of five natural sweeteners (mogrosides (Mog), stevioside (Ste), glycyrrhizinic acid (GA), crude trilobatin (CT), and crude rubusoside (CR)) against α-glucosidase and α-amylase and their interactions were evaluated in vitro using enzyme kinetics, fluorescence spectroscopy, Fourier infrared spectroscopy, and molecular docking. The inhibitor sequence was CT > GA > Ste, as GA competitively inhibited α-glycosidase activity while CT and Ste exhibited mixed inhibitory effects. Compared to a positive control acarbose, the inhibitory activity of CT was higher. For α-amylase, the mixed inhibitors CT, CR, and Mog and the competitive inhibitor Ste effectively inhibited the enzyme, with the following order: CT > CR > Ste > Mog; nevertheless, the inhibitors were slightly inferior to acarbose. Three-dimensional fluorescence spectra depicted that GA, CT, and CR bound to the hydrophobic cavity of α-glucosidase or α-amylase and changed the polarity of the hydrophobic amino acid-based microenvironment and structure of the polypeptide chain backbone. Infrared spectroscopy revealed that GA, CT, and CR could disrupt the secondary structure of α-glucosidase or α-amylase, which decreased enzyme activity. GA, trilobatin and rubusoside bound to amino acid residues through hydrogen bonds and hydrophobic interactions, changing the conformation of enzyme molecules to decrease the enzymatic activity. Thus, CT, CR and GA exhibit promising inhibitory effects against α-glucosidase and α-amylase.