## 4 Discussion  
We previously reported that sulfated polysaccharides in nacre extract mitigate memory impairment induced by a single administration of scopolamine [31]. In this study, we further demonstrated that sulfated polysaccharides alleviate memory impairment following the chronic administration of scopolamine. [PERSON] et al. suggested that chronic administration of scopolamine to rats causes A\(\beta\) deposition via increased expression of BACE1, which produces A\(\beta\) from APP [22]. Here, we showed that chronic administration of scopolamine increased the expression levels of BACE1 and promoted A\(\beta\) deposition in the brain. Although sulfated polysaccharides did not decrease BACE1 expression, it suppressed A\(\beta\) deposition. Accumulation of A\(\beta\) induces tau phosphorylation, increases expression of inflammatory cytokines, and promotes neuronal degeneration [6]. Chronic administration of scopolamine  
Figure 6: Effect of sulfated polysaccharide (PS) on insulin signaling in chronic scopolamine-induced mice. (**a**) Expression levels of insulin, phosphorylated protein kinase B (p-Akt), and nuclear factor (NF)-kB in the hippocampus CA2 region determined via immunostaining in the hippocampus in the control group, scopolamine group, and scopolamine + PS group. Stained areas are indicated by arrows. Scale bar: 10 \(\upmu\)m. (**b**) At least five areas per mouse (\(n=2\) mice) were randomly selected and analyzed, and the results are represented as the mean \(\pm\) SD (right panel). \({}^{*}\)\(p<0.05\) vs. scopolamine group. increases the p-tau, inflammatory cytokine, and GFAP levels in hippocampal neurons. However, sulfated polysaccharides suppressed these effects. These results suggest that sulfated polysaccharides inhibit A\(\beta\) deposition. In this study, sulfated polysaccharides increased the IDE expression levels in a chronic scopolamine administration model. This increase in IDE expression may contribute to the suppression of A\(\beta\) deposition. Activation of insulin signaling significantly upregulates IDE expression [18,19]. Conversely, inhibition of insulin signaling pathways delays A\(\beta\) degradation by altering NEP and IDE levels in vitro [18]. The expression of p-Akt, which is increased by insulin signaling activation, was decreased, whereas NF-kB expression, which inhibits insulin signaling, was increased in the hippocampal region of chronic scopolamine-treated mice. These observations suggest that the chronic administration of scopolamine suppresses insulin signaling. This finding is consistent with other reports that scopolamine administration decreases p-Akt expression in the brain [38,39]. In contrast, sulfated polysaccharides suppressed the downregulation in p-Akt expression and enhanced expression of NF-kB. Brain-derived insulin synthesis and functions remain controversial [40,41]. [PERSON] et al. showed that exertion-4 improves cognitive function in diabetic mice by augmenting brain insulin synthesis; moreover, a decrease in brain insulin levels leads to increased phosphorylated tau levels [42]. Here, administration of sulfated polysaccharides increased these levels in the hippocampus. These results suggest that sulfated polysaccharides restore insulin signaling by increasing brain-derived insulin expression, leading to high IDE expression. Administration of sulfated polysaccharide altered gene expression and inhibited A\(\beta\) deposition. Polysaccharides typically cannot cross the blood-brain barrier. Recent studies have reported exosome-mediated signal transduction in the brain [43,44]. Exo-somes secreted after polysaccharide administration may transmit information to the brain. Polysaccharide metabolites may be also involved in brain signal transduction. However, further studies are necessary to determine the effects of exosomes and metabolites. A\(\beta\) and p-tau are produced by different mechanisms in different types of AD model mice [45]. We previously demonstrated that the nacre extract improves memory impairment in several AD mouse models [25,26,29,31].