The Identification of Bioactive Compounds in the Aerial Parts of Agrimonia pilosa and Their Inhibitory Effects on Beta-Amyloid Production and Aggregation

Abstract

Alzheimer’s disease (AD) is a progressive neurodegenerative condition characterized by memory and cognitive decline in older individuals. Beta-amyloid (Aβ), a significant component of senile plaques, is recognized as a primary contributor to AD pathology. Hence, substances that can inhibit Aβ production and/or accumulation are crucial for AD prevention and treatment. Agrimonia pilosa LEDEB. (A. pilosa) (Rosaceae), specifically its aerial parts, was identified in our previous screening study as a promising candidate with inhibitory effects on Aβ production. Therefore, in this study, A. pilosa extract was investigated for its anti-amyloidogenic effects, and its bioactive principles were isolated and identified. The ethanol extract of A. pilosa reduced the levels of sAPPβ and β-secretase by approximately 3% and 40%, respectively, compared to the DMSO-treated control group in APP-CHO cells (a cell line expressing amyloid precursor protein), which were similar to those in the positive control group. In addition, the ethanol extract of A. pilosa also hindered Aβ’s aggregation into fibrils and facilitated the disaggregation of Aβ aggregates, as confirmed by a Thioflavin T (Th T) assay. Subsequently, the active constituents were isolated using a bioassay-guided isolation method involving diverse column chromatography. Eleven compounds were identified—epi-catechin (1), catechin (2), (2S, 3S)-dihydrokaempferol 3-O-β-D-glucopyranoside (3), (-)-epiafzelechin 5-O-β-D-glucopyranoside (4), kaempferol 3-O-β-D-glucopyranoside (5), apigenin 7-O-β-D-glucopyranoside (6), dihydrokaempferol 7-O-β-D-glucopyranoside (7), quercetin 3-O-β-D-glucopyranoside (8), (2S, 3S)-taxifolin 3-O-β-D-glucopyranoside (9), luteolin 7-O-β-D-glucopyranoside (10), and apigenin 7-O-β-D-methylglucuronate (11)—identified through 1D and 2D NMR analysis and comparison with data from the literature. These compounds significantly decreased Aβ production by reducing β- and γ-secretase levels. Moreover, none of the compounds affected the expression levels of sAPPα or α-secretase. Further, compounds 1, 2, 4, 8, and 10 demonstrated a dose-dependent reduction in Aβ aggregation and promoted the disaggregation of pre-formed Aβ aggregates. Notably, compound 8 inhibited the aggregation of Aβ into fibrils by about 43% and facilitated the disassembly of Aβ aggregates by 41% compared to the control group containing only Aβ. These findings underscore the potential of A. pilosa extract and its constituents to mitigate a crucial pathological aspect of AD. Therefore, A. pilosa extract and its active constituents hold promise for development as therapeutics and preventatives of AD.