Characterization of β-secretase inhibitory extracts from sea cucumber (Stichopus japonicus) hydrolysis with their cellular level mechanism in SH-SY5Y cells.

Alzheimer's disease (AD) is the main type of dementia found in the elderly population. The prevention of β-amyloid (Aβ) production by inhibiting β-secretase, which is required for Aβ generation, is the major focus of research in AD therapeutics. In this study, enzymatic extracts obtained from sea cucumber (Stichopus japonicus) hydrolysis were investigated for β-secretase inhibitory activities. Sea cucumber hydrolysates were prepared using various enzymes (Alcalase, α-chymotrypsin, Neutrase, papain, pepsin, and trypsin). Trypsin hydrolysate (IC50, 93.59 ± 0.68 μg/ml) with the highest β-secretase inhibitory activity was separated into crude polysaccharide (TCP) and protein (TP) by ethanol precipitation. TCP (IC50, 16.13 ± 1.15 μg/ml) exhibited higher β-secretase inhibitory activity than trypsin hydrolysate and TP (IC50, 563.50 ± 25.18 μg/ml). Total sugar content in TCP was 11.58 ± 0.32 g/100 g. Major monosaccharides present in S. japonicus were arabinose, fucose, galactose, mannose and ramnose at 1.76 mg/g, 11.98 mg/g, 1.33 mg/g and 0.1 mg/g, respectively. Sulfate and uronic acid contents were 5.69 ± 0.15 g/100 g and 0.49 ± 0.01 g/100 g. Cytotoxicity of TCP different concentrations were tested in SH-SY5Y cells using MTT assay. Treated concentrations at 1, 5, 10, 30, 50, and 100 µg/ml concentrations were not toxic at cellular level. Further, quantitative protein expression reduction of BACE, sAPPβ, β-amyloid, p-JNK, and p-p38 in SH-SY5Y cells were confirmed by Western blot analysis. Therefore, results of this study suggest the potential application of S. japonicus in food and biomedicine industries. [ABSTRACT FROM AUTHOR]