Fucoxanthin enhances AMPK/mTOR-dependent autophagic flux and attenuates ferroptosis in Alzheimer's disease models

Alzheimer's disease (AD) is characterized by Amyloid-β (Aβ) accumulation, impaired proteostatic clearance, and oxidative damage, all of which contribute to neuronal dysfunction and disease progression. Fucoxanthin (FX), a marine-derived carotenoid abundant in brown algae, has shown antioxidant and neuroprotective potential. However, its role in autophagy-lysosome dysfunction and ferroptosis-associated oxidative injury under amyloidogenic conditions remains unclear. In this study, the effects of FX were investigated in APP Swedish mutant-expressing Neuro2a (SweAPP N2a) cells treated with 0.1-5 μM FX and in 5XFAD transgenic mice orally administered FX at 200 mg kg^-1. FX treatment increased LC3-II expression and reduced p62 accumulation in SweAPP N2a cells, indicating enhanced autophagic degradation. FX also increased the expression of the lysosomal markers LAMP1 and Cathepsin D (CTSD), suggesting enhanced lysosome-associated degradative capacity. These responses were accompanied by AMPK activation and suppression of mTOR signaling, together with increased autophagic flux as confirmed by bafilomycin A1-based analysis. Moreover, FX significantly reduced intracellular ROS levels and lipid peroxidation marker 4-hydroxynonenal (4-HNE), while modulating ferroptosis-associated proteins, including GPX4 and FTH1. Consistent with the cellular findings, FX administration in 5XFAD mice modulated autophagy-lysosome-related and ferroptosis-associated proteins in the brain and significantly reduced ThS-positive amyloid plaque burden. Collectively, these findings demonstrate that FX enhances autophagy-lysosome-associated proteostatic regulation through AMPK/mTOR signaling and attenuates ferroptosis-linked oxidative injury under amyloidogenic conditions. These results provide mechanistic evidence supporting the role of FX as a marine-derived bioactive compound for modulating AD-related pathological processes.