Isolation of Neuroprotective Constituents from Dryopteris crassirhizoma Rhizomes Inhibiting Beta-Amyloid Production and BACE1 Activity

Alzheimer’s disease (AD) is a prevalent neurodegenerative condition that progressively impairs cognitive processes, particularly learning and memory. A key pathological feature of AD involves senile plaques mainly composed of β-amyloid (Aβ) peptides, generated via the amyloidogenic pathway from amyloid precursor protein (APP) through sequential β-secretase (BACE1) and γ-secretase cleavage, positioning BACE1 inhibition as a prime therapeutic target. In this study, we applied bioassay-guided fractionation of the butanol-soluble fraction from Dryopteris crassirhizoma rhizomes, previously reported to inhibit Aβ production, to isolate and characterize Aβ-lowering constituents. Through successive chromatographic steps, nine compounds were isolated and structurally classified into flavonoids, chromones, and phloroglucinols, including epicatechin (1), β-carboxymethyl-(-)-epicatechin (2), 7-methoxy-isobiflorin (3), biflorin (4), eriodictyol (5), noreugenin (6), phloroglucinols (butyrylphloroglucinol (7), 2-propionyl-4-methylphloroglucinol (8), and 2-butyryl-4-methylphloroglucinol (9) by comprehensive spectroscopic analysis (NMR, MS, UV, IR). These compounds were assessed for effects on sAPPβ and BACE1 (β-secretase) levels by Western blot, with Aβ production quantified via ELISA in a cellular AD model (APP-CHO cells). Compounds 5–9 significantly reduced sAPPβ and BACE1 expression while potently suppressing Aβ generation. These results demonstrate that diverse constituents from D. crassirhizoma rhizomes inhibited Aβ production through BACE1 suppression, highlighting their potential as natural lead compounds for AD prevention or therapy.