Saikosaponins (SSs) are a class of naturally occurring oleanane-type triterpenoid saponins found in Radix bupleuri that has been widely used in traditional Chinese medicine. As the main active principals of Radix bupleuri, SSs have been shown to suppress mouse motor activity, impair learning and memory, and decrease hippocampal neurogenesis. In the present study, we investigated the effect of five SSs (SSa, SSb1, SSb2, SSc, and SSd) on neuronal viability and the underlying mechanisms in cultured murine neocortical neurons. We demonstrate that SSa, SSb1 and SSd produce concentration-dependent apoptotic neuronal death and induce robust increase in intracellular Ca2+ concentration ([Ca2+]i) at low micromolar concentrations with a rank order of SSd > SSa > SSb1, whereas SSb2 and SSc have no detectable effect on both neuronal survival and [Ca2+]i. Mechanistically, SSd-induced elevation in [Ca2+]i is the primary result of enhanced extracellular Ca2+ influx, which likely triggers Ca2+-induced Ca2+ release through ryanodine receptor activation, but not SERCA inhibition. SSd-induced Ca2+ entry occurs through a non-selective mechanism since blockers of major neuronal Ca2+ entry pathways, including L-type Ca2+ channel, NMDA receptor, AMPA receptor, Na+-Ca2+ exchanger, and TRPV1, all failed to attenuate the Ca2+ response to SSd. Further studies demonstrate that SSd increases calcein efflux and induces an inward current in neocortical neurons. Together, these data demonstrate that SSd elevates [Ca2+]i due to its ability to increase membrane permeability, likely by forming pores in the surface of membrane, which leads to massive Ca2+ influx and apoptotic neuronal death in neocortical neurons.

中文翻译：

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Saikosaponin d 通过增加膜通透性和提高细胞内 Ca2+ 浓度导致培养的新皮层神经元凋亡。

柴胡皂苷 (SSs) 是一类天然存在的齐墩果烷型三萜皂苷，存在于柴胡中，已广泛用于中药。作为柴胡的主要活性成分，SSs 已被证明可以抑制小鼠运动活动，损害学习和记忆，并减少海马神经发生。在本研究中，我们研究了五种 SS（SSa、SSb1、SSb2、SSc 和 SSd）对神经元活力的影响以及培养的小鼠新皮层神经元的潜在机制。我们证明 SSa、SSb1 和 SSd 会产生浓度依赖性凋亡神经元死亡，并在低微摩尔浓度下诱导细胞内 Ca2+ 浓度 ([Ca2+]i) 的强劲增加，排列顺序为 SSd > SSa > SSb1，而 SSb2 和 SSc 没有对神经元存活和 [Ca2+]i 的可检测影响。从机制上讲，SSd 诱导的 [Ca2+]i 升高是细胞外 Ca2+ 流入增强的主要结果，这可能通过兰尼碱受体激活而非 SERCA 抑制触发 Ca2+ 诱导的 Ca2+ 释放。SSd 诱导的 Ca2+ 进入是通过非选择性机制发生的，因为主要神经元 Ca2+ 进入途径的阻断剂，包括 L 型 Ca2+ 通道、NMDA 受体、AMPA 受体、Na+-Ca2+ 交换剂和 TRPV1，都未能减弱 Ca2+ 对固态硬盘。进一步的研究表明，SSd 增加钙黄绿素流出并在新皮层神经元中诱导内向电流。总之，这些数据表明，SSd 提高了 [Ca2+]i，因为它具有增加膜通透性的能力，可能是通过在膜表面形成孔隙，导致新皮质神经元中大量 Ca2+ 流入和细胞凋亡性神经元死亡。