Fukinolic acid facilitates toxic amyloid-β oligomerization and exacerbates synaptic dysfunction.

Alzheimer's disease (AD) is characterized by the accumulation of amyloid-β (Aβ) aggregates that induce synaptic dysfunction and neuronal loss. Among the various Aβ species, soluble oligomers are considered the most neurotoxic forms and play a critical role in AD progression. Fukinolic acid (FA), a polyphenolic compound isolated from medicinal plants, has been reported to possess antioxidant and anti-inflammatory activities; however, its effects on Aβ aggregation have not been investigated. In the present study, we investigated whether FA modulates Aβ aggregation and synaptic dysfunction. Molecular docking analysis suggested that FA directly interacts with Aβ monomers at aggregation-prone regions. Consistent with this prediction, FA facilitated the formation of toxic Aβ oligomers and enhanced Aβ-induced neuronal cytotoxicity. The potentiation of Aβ toxicity by FA was abolished by an N-methyl-D-aspartate (NMDA) receptor antagonist, indicating the involvement of NMDA receptor-dependent signaling. Electrophysiological recordings showed that FA exacerbated Aβ-induced long-term potentiation (LTP) impairment in hippocampal slices without affecting basal synaptic transmission. In addition, FA administration increased Aβ deposition and reduced neuronal viability in the hippocampus of 5XFAD mice. FA treatment showed non-significant trends toward reduced hippocampal LTP and spontaneous alternation in the Y-maze test, indicating that further studies are required to determine whether FA affects synaptic and cognitive function in vivo. These findings suggest that FA promotes toxic Aβ oligomer formation and may aggravate Aβ-associated synaptic impairment through NMDA receptor-dependent mechanisms, highlighting the importance of evaluating the effects of natural compounds on Aβ pathology in AD.