Akiko Ohno

Alzheimer’s disease (AD) is driven primarily by the self-assembly of amyloid-β (Aβ) peptides, a process stabilized by intermolecular π–π stacking interactions involving Phe19 and Phe20 residues of adjacent Aβ molecules. To competitively disrupt these interactions, we designed novel peptide inhibitors derived from the Aβ recognition motif KLVFFA (Aβ_16–21), in which phenylalanine residues were replaced with L-3,4-dihydroxyphenylalanine (DOPA), featuring a catechol moiety capable of enhanced aromatic stacking and hydrogen bonding. The DOPA-substituted peptides effectively inhibited Aβ_1–42 (Aβ42) aggregation, as demonstrated via Thioflavin T fluorescence assays, circular dichroism spectroscopy, and transmission electron microscopy. These complementary analyses collectively revealed substantial suppression of β-sheet formation and fibril elongation. Notably, the anti-aggregation potency was dependent on the substitution position, with the Phe19-substituted analog (KDF) exhibiting stronger inhibitory activity than the Phe20-substituted analog (KFD). The dual-substituted analog (KDD) displayed the greatest overall anti-aggregation activity. Molecular simulations further supported the superior activity of KDF over KFD, revealing a more favorable binding free energy for KDF compared to the parent peptide. Furthermore, the DOPA peptides potently mitigated Aβ42-induced neurotoxicity in SH−SY5Y cells, with the dual-substituted analog (KDD) providing the highest level of cytoprotection. Collectively, these findings validate that targeted modulation of aromatic interactions through DOPA substitution represents a powerful molecular strategy for controlling Aβ42 self-assembly, positioning these peptides as promising therapeutic tools for the treatment of AD.

Alzheimer’s disease (AD) pathology is primarily driven by the self-assembly of amyloid-β (Aβ) peptides, a process significantly stabilized through π-π stacking interactions between the aromatic residues Phe19 and Phe20. To competitively disrupt this crucial interaction, we designed novel peptide inhibitors derived from the Aβ recognition motif KLVFFA (Aβ16−21), in which phenylalanine residues were replaced with L-3,4-dihydroxyphenylalanine (DOPA), a residue featuring an enhanced π-stacking and hydrogen-bonding catechol moiety. The DOPA-substituted peptides effectively inhibited Aβ1−42 (Aβ42) aggregation, as demonstrated by Thioflavin T fluorescence assays, circular dichroism spectroscopy, and transmission electron microscopy. These complementary analyses collectively exhibited substantial suppression of β-sheet formation and fibril elongation. Notably, the anti-aggregation potency was dependent on the substitution position, with the Phe19-substituted analogue (KDF) exhibiting stronger inhibitory activity than the Phe20-substituted analogue (KFD). The dual-substituted analogue (KDD) displayed the greatest overall anti-aggregation activity. Molecular simulations further supported the superior activity of KDF over KFD, revealing a more favorable binding free energy for KDF compared to the parent peptide. Furthermore, the DOPA-peptides potently mitigated Aβ42-induced neurotoxicity in SH−SY5Y cells, with the dual-substituted analogue (KDD) providing the highest level of cytoprotection. Collectively, these findings validate that targeted modulation of aromatic interactions through DOPA substitution represents a powerful molecular strategy for controlling Aβ42 self-assembly, presenting these peptides as promising therapeutic leads for AD.

Oxidative stress is a major driver of chronic disease, making natural polyphenols attractive scaffolds for modulating inflammation, proteostasis, and cell fate. However, green-tea catechins possess a twisted, conformationally flexible flavan-3-ol framework that limits π-conjugation, phenoxyl-radical stabilization, and productive interactions with biological targets. This review presents a structure-based framework in which conformational planarization serves as a strategy for functional amplification. Preorganization of the A/C–B inter-ring bond into a nearly coplanar arrangement reduces the conformational entropy penalty (−TΔS) upon binding or reaction while extending conjugation, strengthening π–π interactions, and facilitating redox reactions. This review highlights planarized catechin (PCat) architectures, including PCat–DTPA (a lesion-activated metal-responsive antioxidant), PCat–TrOH (a self-regenerating antioxidant network), procyanidin B3–PCat hybrids, and a planar silybin analog, illustrating how planarization and multivalent recognition enhance ROS regulation, inhibit amyloid-β aggregation and neurotoxicity, and suppress cancer cell phenotypes. Collectively, these studies establish PCat as a modular platform for the mechanism-informed design of disease-tailored phenolic antioxidants.

Oxidative stress is a major driver of chronic disease, making natural polyphenols attractive scaffolds for modulating inflammation, proteostasis, and cell fate. However, green-tea catechins possess a twisted, conformationally flexible flavan-3-ol framework that limits π-conjugation, phenoxyl-radical stabilization, and productive interactions with biological targets. This review presents a structure-based framework in which conformational planarization serves as a strategy for functional amplification. Preorganization of the A/C–B inter-ring bond into a nearly coplanar arrangement reduces the conformational entropy penalty (−TΔS) upon binding or reaction while extending conjugation, strengthening π–π interactions, and facilitating redox reaction. This review highlights planarized catechin (PCat) architectures, including PCat–DTPA (a lesion-activated metal-responsive antioxidant), PCat–TrOH (a self-regenerating antioxidant network), procyanidin B3–PCat hybrids, and a planar silybin analogue, illustrating how planarization and multivalent recognition enhances ROS regulation, inhibits amyloid-β aggregation and neurotoxicity, and suppresses cancer-cell phenotypes. Collectively, these studies establish PCat as a modular platform for the mechanism-informed design of disease-tailored phenolic antioxidants.

In diseases related to oxidative stress, accumulation of metal ions at the site of pathogenesis results in the generation of reactive oxygen species (ROS) through the reductive activation of oxygen molecules catalyzed by the metal ions. If these metals can be removed and the generated ROS can be strongly scavenged, such diseases can be prevented and treated. Planar catechins exhibit stronger radical scavenging activity than natural catechins and can efficiently scavenge hydroxyl radicals generated by the Fenton reaction without showing pro-oxidant effects, even in the presence of iron ions. Hence, in the current study, we designed a compound in which diethylenetriaminepentaacetic acid (DTPA), a metal chelator, was bound to a planar catechin with enhanced radical scavenging activity by immobilizing the steric structure of a natural catechin to be planar. This compound showed almost no radical scavenging activity due to intramolecular hydrogen bonding of DTPA with the planar catechins; however, when coordinated with Fe³⁺, it showed more potent radical scavenging activity than planar catechins. Owing to its potent antioxidant activity triggered by metal coordination and its inhibition of ROS generation by trapping metal ions, this compound might exert excellent preventive and therapeutic effects against oxidative stress-related diseases.

Most of the active components of polypeptides have a complex molecular structure, large molecular size. Such components may also be structurally heterogeneous. Therefore, development of a method that can confirm the consistency of polypeptides amino-acid sequences for product characterization is desirable. In general, it is extremely difficult to distinguish differences of a few amino acid residues in the ¹H-NMR spectrum of polypeptides with molecular weights greater than several thousand. However, we have been able to distinguish between three insulin species differing in one to three amino acid residues using a combination of multivariate statistics and ¹H-NMR spectra. These results demonstrate that this methodology could be useful for characterization of polypeptides.

The taste of black tea differs according to the different areas in which the tea is grown, even for the same species of tea. A combination of ¹H NMR spectroscopy and partial least-squares discriminate analysis (PLS-DA) was used to assess the quality differences of tea leaves from four cultivation areas with different elevations, RAN > 1800 m, UDA = 1200 m, MEDA = 600 m, and YATA < 300 m, in Sri Lanka. As a result of a statistical analysis, PLS-DA showed a separation between high- and low-quality black teas derived from the four different tea cultivation areas. RAN from the highest elevation showed characteristic trends in the levels of theaflavin and theaflavin 3,3′-digallate that were found only in RAN, and the levels of theanine and caffeine were higher, and the levels of thearubigins, especially thearubigin 3,3′-digallate, were lower in RAN than in UDA, MEDA, and YATA. The structures of these components were determined by 1D and 2D NMR analyses. These results demonstrate that this method can be used to evaluate black tea quality according to the chemical composition or metabolites, which are characteristic of the tea leaves cultivated in four regions with different elevations in Sri Lanka.