Traditional Chinese Medicine College, Shandong University of Traditional Chinese Medicine, Jinan, China.
Department of Endocrinology, Hospital Affiliated to Shandong Traditional Chinese Medicine University, Jinan, China.
Endocrinol Diabetes Nutr (Engl Ed). 2021 May;68(5):329-337. doi: 10.1016/j.endien.2021.08.004.
Saponins are the main bioactive substances with anti-hyperglycemic activities of Momordica charantia. This study aimed to verify the effects of M. charantia saponins on insulin secretion and explore the potential underlying mechanisms in INS-1 pancreatic β-cells. We injured INS-1 cells with 33.3mM glucose and then treated them with saponins. Saponins improved cell morphology and viability as demonstrated by inverted microscopy and CCK8 detection and significantly increased insulin secretion in a concentration-dependent manner as shown by ELISA. Thus, we obtained the optimal concentration for the subsequent experiments. Potential mechanisms were explored by immunofluorescence, western blotting, and RT-qPCR techniques. First, saponins increased the mRNA and protein levels of IRS-2 but decreased the serine 731 phosphorylation level of IRS-2. Moreover, saponins increased the phosphorylation of Akt protein and decreased the protein level of FoxO1, which were both reversed by the PI3K inhibitor ly294002. Furthermore, saponins increased the protein level of the downstream molecule and insulin initiating factor PDX-1, which was also reversed by ly294002. Saponins also increased Akt and PDX-1 mRNA and decreased FoxO1 mRNA, which were both reversed by ly294002. Saponins increased glucose-stimulated insulin secretion (GSIS) and intracellular insulin content, which were reversed by ly294002, as determined by ELISA. The immunofluorescence results also confirmed this tendency. In conclusion, our findings improve our understanding of the function of saponins in INS-1 pancreatic β-cells and suggest that saponins may increase insulin secretion via the PI3K/Akt/FoxO1 signaling pathway.
苦瓜中的主要生物活性物质皂甙具有降血糖活性。本研究旨在验证苦瓜皂甙对胰岛素分泌的影响，并探讨其在 INS-1 胰岛 β 细胞中的潜在作用机制。我们用 33.3mM 葡萄糖损伤 INS-1 细胞，然后用皂甙处理。倒置显微镜和 CCK8 检测结果表明，皂甙改善了细胞形态和活力，并通过 ELISA 显示以浓度依赖的方式显著增加胰岛素分泌。因此，我们获得了后续实验的最佳浓度。通过免疫荧光、Western blot 和 RT-qPCR 技术探讨潜在机制。首先，皂甙增加了 IRS-2 的 mRNA 和蛋白水平，但降低了 IRS-2 的丝氨酸 731 磷酸化水平。此外，皂甙增加了 Akt 蛋白的磷酸化，降低了 FoxO1 蛋白水平，这两者均被 PI3K 抑制剂 ly294002 逆转。此外，皂甙增加了下游分子胰岛素启动因子 PDX-1 的蛋白水平，这也被 ly294002 逆转。皂甙还增加了 Akt 和 PDX-1 的 mRNA 水平，降低了 FoxO1 的 mRNA 水平，这两者均被 ly294002 逆转。ELISA 结果还表明，皂甙增加了葡萄糖刺激的胰岛素分泌 (GSIS) 和细胞内胰岛素含量，这一作用被 ly294002 逆转。免疫荧光结果也证实了这一趋势。总之，我们的研究结果提高了我们对皂甙在 INS-1 胰岛 β 细胞中功能的认识，并表明皂甙可能通过 PI3K/Akt/FoxO1 信号通路增加胰岛素分泌。
