Identification of Potent Inhibitors of β-Amyloid Production and Aggregation from the Aerial Parts of Humulus japonicus

초록

Alzheimer's disease (AD) is characterized by the excessive production and aggregation of beta-amyloid (A beta), which serves as key pathological features of disease progression. Although Humulus japonicus Siebold & Zucc. is a traditional medicinal plant rich in flavonoids and phenolic compounds, its specific anti-amyloidogenic constituents remain to be fully elucidated. This study evaluated the effects of the aerial parts of H. japonicus on A beta production and aggregation, and identified its active constituents through bioassay-guided isolation. The 80% ethanolic extract of H. japonicus aerial parts significantly reduced soluble amyloid precursor protein beta (sAPP beta) levels and BACE1 protein expression in Chinese Hamster Ovary cells stably expressing amyloid precursor protein (APP-CHO cells). Furthermore, it inhibited A beta aggregation and promoted fibril disaggregation in Thioflavin T assays. Among the solvent-partitioned fractions, the ethyl acetate fraction exhibited the most potent anti-amyloidogenic activity and was subjected to chromatographic isolation, leading to the characterization of fourteen compounds (7 flavonoids, 2 phenolic acids, 2 sesquiterpenoids, and 3 phenylpropanoids). Specifically, luteolin 7-O-beta-d-glucopyranoside (2), orientin (3), vitexin (5), vomifoliol (8), abscisic acid (9), and p-hydroxyphenylethyl-p-coumarate (12) significantly decreased sAPP beta levels, as well as BACE1 and Presenilin-1 protein expression. Meanwhile, luteolin 7-O-beta-d-glucopyranoside (2), orientin (3), vitexin (5), and quercetin 7-O-beta-d-glucopyranoside trimer (7) effectively reduced A beta aggregation and enhanced the disaggregation of pre-formed A beta aggregates. Collectively, luteolin 7-O-beta-d-glucopyranoside (2), orientin (3), and vitexin (5) exhibited the most consistent dual inhibitory effects on both A beta production and aggregation, supporting their selection as key marker compounds. Among the extracts prepared with varying ethanol concentrations, the 100% ethanol extract yielded the highest levels of these flavonoid glycosides and exhibited the strongest anti-amyloidogenic activity. These findings suggest that the aerial parts of H. japonicus and its constituent flavonoid glycosides represent promising natural resources for modulating amyloidogenic APP processing and A beta aggregation in AD.

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