Long-Term Dietary Supplementation with Pearl Oyster Shell-Derived Nacre Extract Improves Cognitive Performance and Attenuates Alzheimer's Disease-Like Pathology in APPNL-G-F/NL-G-F Knock-In Mice.

Abstract

Alzheimer's disease is characterized by cognitive decline, amyloid-β deposition, tau-related pathology, neuroinflammation, and oxidative stress. Pearl oyster shell-derived nacre extract is used in dietary supplement-related applications, but evidence from animal models should be interpreted cautiously and its effects on Alzheimer's disease-like pathology remain incompletely defined. To evaluate whether long-term oral dietary supplementation with nacre extract is associated with changes in cognitive performance and Alzheimer's disease-like pathological features in APPNL-G-F/NL-G-F knock-in mice. A controlled preclinical animal study was performed using male C57BL/6 wild-type mice and male APPNL-G-F/NL-G-F knock-in mice over a 6-month dietary supplementation period. Six mice were assigned to each group. APP knock-in mice received a standard diet with or without 0.5% (w/w) nacre extract, corresponding to an estimated intake of approximately 20 mg/mouse/day or approximately 600 mg/kg/day. Cognitive performance was assessed using the Y-maze and novel object recognition tests. Brain pathology and molecular responses were evaluated by histology, immunohistochemistry, RNA sequencing, qPCR, Western blotting, and oxidative stress-related assays. Nacre supplementation was associated with improved performance in the Y-maze and novel object recognition tests, reduced amyloid-β deposition and Congo red-positive plaque burden, lower phosphorylated tau immunoreactivity, and fewer histologically degenerated hippocampal neurons. Exploratory RNA sequencing of non-microdissected brain tissue excluding the cerebellum (n = 3/group) identified 53 genes meeting the criteria of an absolute fold change ≥ 1.5 and a valid non-zero FDR-adjusted p value < 0.05. A2M showed a 1.51-fold increase (FDR-adjusted p = 0.00091), and increased A2M abundance was confirmed at the protein level. Iba1 and GFAP immunoreactivity was reduced, and oxidative stress-related parameters were altered in the nacre-supplemented group. Long-term nacre supplementation was associated with improvements in behavioral performance and attenuation of several Alzheimer's disease-like pathological features in male APP knock-in mice. These findings represent an exploratory preclinical signal and do not establish a causal mechanism, dose-response relationship, comprehensive safety profile, or efficacy as a dietary supplement in humans.