Department of Internal Medicine, Chung-Shan Medical University Hospital, Taichung, Taiwan.
Institute of Medicine, Chung-Shan Medical University, Taichung, Taiwan.
BMC Complement Med Ther. 2020 Dec 2;20(1):370. doi: 10.1186/s12906-020-03163-4.
Insulin resistance could be associated with the development of Alzheimer disease (AD). The neuropathological hallmarks of AD are beta amyloid (Aβ) produced from sequential cleavage initiated by β-secretase and degraded by insulin degradation enzyme (IDE), as well as hyperphosphorylation of tau (p-tau). Insulin action involves the cascades of insulin receptor substrates (IRS) and phosphatidylinositol 3-kinase (PI3K), while phosphorylation of IRS-1 at ser307 (p-IRS-1) hinders the response. Our previous report suggested dipeptidyl peptidase-4 (DPP-4) is crucial to insulin resistance, and the subfractions of Abelmoschus esculentus (AE), F1 and F2, attenuate the signaling. Here we aim to investigate whether AE works to reduce Aβ generation via regulating DPP4 and insulin resistance.
The subfractions F1 and F2 were prepared according to a succession of procedures. F1 was composed by quercetin glycosides and triterpene ester, and F2 contained a large amount of polysaccharides. The in vitro insulin resistance model was established by SK-N-MC cell line treated with palmitate. MTT was used to define the dose range, and thereby Western blot, ELISA, and the activity assay were used to detect the putative markers. One-way ANOVA was performed for the statistical analysis.
Treatment of palmitate induced the level of p-IRS-1. Both F1 and F2 effectively decrease p-IRS-1, and recover the expression of p-PI3K. However, the expression of total IRS plunged with 25 μg/mL of F1, while descended steadily with 5 μg/mL of F2. As palmitate increased the levels of Aβ40 and Aβ42, both AE subfractions were effective to reduce Aβ generation of and β-secretase activity, but IDE was not altered in any treatment conditions. The expression of DPP4 was also accompanied with insulin resistance signals. Inhibition of DPP4 attenuated the activity of β-secretase and production of Aβ. Moreover, the present data revealed that both AE subfractions significantly decrease the level of p-Tau.
In conclusion, we demonstrated that AE would be a potential adjuvant to prevent insulin resistance and the associated pathogenesis of AD, and F2 seems more feasible to be developed.
胰岛素抵抗可能与阿尔茨海默病（AD）的发展有关。AD 的神经病理学特征是β淀粉样蛋白（Aβ），它由β-分泌酶起始的连续切割产生，并被胰岛素降解酶（IDE）降解，以及tau 的过度磷酸化（p-tau）。胰岛素作用涉及胰岛素受体底物（IRS）和磷脂酰肌醇 3-激酶（PI3K）的级联反应，而 IRS-1 丝氨酸 307 位的磷酸化（p-IRS-1）会阻碍反应。我们之前的报告表明二肽基肽酶 4（DPP-4）对胰岛素抵抗至关重要，而黄蜀葵（AE）的亚组分 F1 和 F2 可减轻这种信号。在这里，我们旨在研究 AE 是否通过调节 DPP4 和胰岛素抵抗来减少 Aβ的产生。
根据一系列程序制备亚组分 F1 和 F2。F1 由槲皮素糖苷和三萜酯组成，F2 含有大量多糖。用棕榈酸处理 SK-N-MC 细胞系建立体外胰岛素抵抗模型。MTT 用于确定剂量范围，然后使用 Western blot、ELISA 和活性测定来检测假定的标记物。进行单因素方差分析进行统计分析。
棕榈酸处理诱导了 p-IRS-1 的水平。F1 和 F2 均可有效降低 p-IRS-1，并恢复 p-PI3K 的表达。然而，用 25μg/mL 的 F1 处理时，总 IRS 的表达下降，而用 5μg/mL 的 F2 处理时则持续下降。随着棕榈酸增加 Aβ40 和 Aβ42 的水平，AE 的两个亚组分都能有效减少 Aβ的产生和β-分泌酶的活性，但在任何处理条件下 IDE 都没有改变。DPP4 的表达也伴随着胰岛素抵抗信号。抑制 DPP4 可减弱β-分泌酶的活性和 Aβ的产生。此外，本研究数据表明，AE 的两个亚组分均可显著降低 p-Tau 的水平。
综上所述，我们证明 AE 可能是预防胰岛素抵抗和 AD 相关发病机制的潜在辅助剂，F2 似乎更适合开发。
