Molecular insights into the interactions of theaflavin and epicatechin with different lipid bilayer membranes by molecular dynamics simulation.

At present, consumers increasingly favored the natural food preservatives with fewer side-effects on health. The green tea catechins and black tea theaflavins attracted considerable interest, and their antibacterial effects were extensively reported in the literature. Epicatechin (EC), a green tea catechin without a gallate moiety, showed no bactericidal activity, whereas the theaflavin (TF), also lacking a gallate moiety, exhibited potent bactericidal activity, and the antibacterial effects of green tea catechins and black tea theaflavins were closely correlated with their abilities to disrupt the bacterial cell membrane. In our present study, the mechanisms of membrane interaction modes and behaviors of TF and EC were explored by molecular dynamics simulations. It was demonstrated that TF exhibited markedly stronger affinity for the POPG bilayer compared to EC. Additionally, the hydrophobic interactions of tropolone/catechol rings with the acyl chain part could significantly contribute to the penetration of TF into the POPG bilayer. It was also found that the resorcinol/pyran rings were the key functional groups in TF for forming hydrogen bonds with the POPG bilayer. We believed that the findings from our current study could offer useful insights to better understand the stronger antibacterial effects of TF compared to EC.

Molecular insights into the structure destabilization effects of ECG and EC on the Aß protofilament: An all-atom molecular dynamics simulation study.

The formation of Aß into amyloid fibrils was closely connected to AD, therefore, the Aß aggregates were the primary therapeutic targets against AD. Previous studies demonstrated that epicatechin-3-gallate (ECG), which possessed a gallate moiety, exhibited a greater ability to disrupt the preformed Aß amyloid fibrils than epicatechin (EC), indicating that the gallate moiety was crucial. In the present study, the molecular mechanisms were investigated. Our results demonstrated that ECG had more potent disruptive impacts on the ß-sheet structure and K28-A42 salt bridges than EC. We found that ECG significantly interfered the interactions between Peptide-4 and Peptide-5. However, EC could not. The disruption of K28-A42 salt bridges by ECG was mainly due to the interactions between ECG and the hydrophobic residues located at C-terminus. Interestingly, EC disrupted the K28-A42 salt bridges by the interactions with C-terminal hydrophobic residues and the cation-π interactions with K28. Moreover, our results indicated that hydrophobic interactions, H-bonds, π-π interactions and cation-π interactions between ECG and the bend of L-shaped region caused the disaggregation of interactions between Peptide-4 and Peptide-5. Significantly, gallate moiety in ECG had contributed tremendously to the disaggregation. We believed that our findings could be useful for designing prospective drug candidates targeting AD.

Interactions of chlorogenic acid and isochlorogenic acid A with model lipid bilayer membranes: Insights from molecular dynamics simulations.

Because of the negative side-effects of synthetic preservatives, the naturally-occurring polyphenols aroused intense interest of researchers. It has been suggested that chlorogenic acid (CA) and isochlorogenic acid A (iso-CAA) were good candidates to replace the synthetic preservatives. Moreover, the bactericidal activity of iso-CAA was stronger than CA, and the anti-bacterial activities of iso-CAA and CA were highly membrane-dependent. However, the mechanisms were still unclear. Therefore, in the present study, we investigated the mechanisms of the interactions between the two polyphenols and lipid bilayers through molecular dynamics simulations. The results revealed that iso-CAA could be inserted much deeper into POPG lipid bilayer than CA. We also found that hydrophobic interactions and hydrogen bonds both contributed to the insertion of iso-CAA into the POPG lipid bilayer, and the quinic acid moiety was the key structure in iso-CAA to form hydrogen bonds with POPG lipid bilayer. We believed that these findings would provide more useful information to explain the stronger bactericidal activity of iso-CAA than CA at the atomic level.

Influence of the gallate moiety on the interactions between green tea polyphenols and lipid membranes elucidated by molecular dynamics simulations.

Previous studies suggested that naturally occurring EGCG primarily acted on the bacterial cell membrane then damaged the membrane and the gallate moiety in EGCG was very important to its anti-bacterial activity. However, the detailed mechanisms were still poorly understood. In this paper, EGCG and EGC were selected to study the great contribution of gallate moiety on the anti-bacterial activities of polyphenols. The results indicated that EGCG could penetrate deeper into the POPG lipid bilayer and possess more potent structure-perturbing potency on the POPG lipid bilayer than EGC. We also found that EGCG had the ability to form hydrogen bonds with the deeper inside oxygen atoms in the POPG lipid bilayer and the gallate moiety was the key functional group for EGCG forming hydrogen bonds with the POPG lipid bilayer. Moreover, results from the binding free energy analysis demonstrated that the gallate moiety made great contribution to the high affinity between EGCG and the POPG lipid bilayer. We believed that these findings could yield useful insights into the influence mechanisms of gallate moiety on the anti-bacterial activities of polyphenols.

Molecular insights into the inhibitory mechanisms of gallate moiety on the Aß1-40 amyloid aggregation: A molecular dynamics simulation study.

Alzheimer's disease is the most common form of neurodegenerative disease and the formation of Aß amyloid aggregates has been widely demonstrated to be the principal cause of Alzheimer's disease. Our previous study and other studies suggested that the gallate moiety played an obligatory role in the inhibition process of naturally occurring polyphenols on Aß amyloid fibrils formation. However, the detailed mechanisms were still unknown. Thus, in the present study, the gallic acid (GA) was specially selected and the molecular recognition mechanisms between GA molecules and Aß1-40 monomer were examined and analyzed by molecular dynamics simulation. The in silico experiments revealed that GA significantly prevented the conformational changes of Aß1-40 monomer with no ß-sheet structure during the whole 100 ns. By analyzing the binding sites of GA molecules to Aß1-40 monomer, we found that both hydrophilic and hydrophobic amino acid residues were participated in the binding of GA molecules to Aß1-40 monomer. Moreover, results from the binding free energy analysis further demonstrated that the strength of polar interactions was significantly stronger than that of nonpolar interactions. We believed that our results could help to elucidate the underlying mechanisms of gallate moiety on the anti-amyloidogenic effects of polyphenols at the atomic level.

Comparison of disaggregative effect of A-type EGCG dimer and EGCG monomer on the preformed bovine insulin amyloid fibrils.

In the present study, the disruptive effects of epigallocatechin-3-gallate (EGCG) and A-type dimeric epigallocatechin-3-gallate (A-type EGCG dimer) on the preformed bovine insulin amyloid fibrils were studied by several biophysical methods including thioflavin-T (ThT) fluorescence assay, 1-anilinonaphthalene-8-sulfonic (ANS) fluorescence assay, Congo red (CR) binding assay, dynamic light scattering (DLS), transmission electron microscopy (TEM), Gel electrophoresis (SDS-PAGE) and Bradford assay. Our results demonstrated that A-type EGCG dimer showed significantly more potential disaggregative effects on the bovine insulin amyloid fibrils than EGCG. A-type EGCG dimer could not only dramatically promote the disaggregation of the preformed bovine insulin amyloid fibrils, but also restructure the amyloid fibrils into amorphous aggregates. While, EGCG could only shorten and thin the fibrils, but induce no small amorphous aggregates. Our present results provided additional evidence for the more potent disaggregation effects of dimeric polyphenols than monomeric polyphenols and suggested that A-type EGCG dimer seems to have potential application as an excellent anti-amyloidogenic agent.

A-type dimeric epigallocatechin-3-gallate (EGCG) is a more potent inhibitor against the formation of insulin amyloid fibril than EGCG monomer.

Because fibrillary protein aggregates is regarded to be closely associated with many diseases such as Alzheimer's disease, diabetes, and Parkinson's disease, growing interest and researches have been focused on finding potential fibrillation inhibitors. In the present study, the inhibitory effects of epigallocatechin-3-gallate (EGCG) and A-type dimeric epigallocatechin-3-gallate (A-type EGCG dimer) on the formation of insulin fibrillation were compared by multi-dimensional approaches including thioflavin-T (ThT) fluorescence assay, 1-anilinonaphthalene-8-sulfonic (ANS) fluorescence assay, dynamic light scattering (DLS), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and circular dichroism (CD) spectroscopy. Our results confirmed that A-type EGCG dimer is a more potent inhibitor against the formation of bovine insulin amyloid fibril than EGCG. In addition, A-type EGCG dimer could not only inhibit insulin amyloid fibril formation, but also change the aggregation pathway and induce bovine insulin into amorphous aggregates. The results of the present study may provide a new guide on finding novel anti-amyloidogenic agents.