Detection of Dietary Chalcone and Flavonoid Metabolites in Mice Using UPLC-MS/MS and Their Modulatory Effects on Amyloid ß Aggregation.

Amyloid ß-protein (Aß42) aggregates have been demonstrated to induce cognitive decline and neurodegeneration in Alzheimer's disease (AD). Thus, functional food ingredients that inhibit Aß42 aggregation are valuable for AD prevention. Although several food ingredients have been studied for their anti-aggregation activity, information on their bioavailability in the brain, incorporated forms, and relevance to AD etiology is limited. Here, we first detected the sulfate- and glucuronic-acid-conjugated forms of green perilla-derived chalcone (1) and taxifolin (2), which inhibit Aß42 aggregation, in the brain, small intestine, and plasma of mice (1 and 2 were administered orally) using ultra-performance liquid chromatography-tandem mass spectrometry. We observed that the conjugated metabolites (sulfate (4) and glucuronide (5)) of 1 prevented the fibrillization and oligomerization of Aß42. These findings imply that the conjugated metabolites of 1 can prove beneficial for AD treatment.

Lysine-targeting inhibition of amyloid ß oligomerization by a green perilla-derived metastable chalcone in vitro and in vivo.

Oligomers of amyloid ß (Aß) represent an early aggregative form that causes neurotoxicity in the pathogenesis of Alzheimer's disease (AD). Thus, preventing Aß aggregation is important for preventing AD. Despite intensive studies on dietary compounds with anti-aggregation properties, some identified compounds are susceptible to autoxidation and/or hydration upon incubation in water, leaving unanswered issues regarding which active structures in metastable compounds are actually responsible for the inhibition of Aß aggregation. In this study, we observed the site-specific inhibition of 42-mer Aß (Aß42) oligomerization by the green perilla-derived chalcone 2',3'-dihydroxy-4',6'-dimethoxychalcone (DDC), which was converted to its decomposed flavonoids (dDDC, 1-3) via nucleophilic aromatic substitution with water molecules. DDC suppressed Aß42 fibrillization and slowed the transformation of the ß-sheet structure, which is rich in Aß42 aggregates. To validate the contribution of dDDC to the inhibitory effects of DDC on Aß42 aggregation, we synthesized 1-3 and identified 3, a catechol-type flavonoid, as one of the active forms of DDC. 1H-15N SOFAST-HMQC NMR revealed that 1-3 as well as DDC could interact with residues between His13 and Leu17, which were near the intermolecular ß-sheet (Gln15-Ala21). The nucleation in Aß42 aggregates involves the rate-limiting formation of low-molecular-weight oligomers. The formation of a Schiff base with dDDC at Lys16 and Lys28 in the dimer through autoxidation of dDDC was associated with the suppression of Aß42 nucleation. Of note, in two AD mouse models using immunoaffinity purification-mass spectrometry, adduct formation between dDDC and brain Aß was observed in a similar manner as reported in vitro. The present findings unraveled the lysine-targeting inhibitory mechanism of metastable dietary ingredients regarding Aß oligomerization.