Icariside II (ICS II), a phosphodiesterase 5 inhibitor (PDE 5-I), is a major ingredient of Epimedium brevicornum, with wide spectrum of neuroprotective properties. However, little is known about the potential beneficial effect of ICS II on neuronal cell proliferation, and its possible underlying mechanism remains still unclear. We hypothesized that the beneficial effect of ICS II on neuron-like highly differentiated rat pheochromocytoma (PC12) cell proliferation is correlated with the nitric oxide (NO) signaling pathway and its upstream of PI3K/AKT pathway. PC12 cells were treated with ICS II alone or together with L-NMMA, H89, KT-5823, and/or LY294002 (the inhibitor of NOS, PKA, PKG, PI3K, respectively). It was found that ICS II concentration-dependently promoted PC12 cells proliferation, and cell cycle analysis showed that the proportion of ICS II-treated PC12 cells in S phase was higher than that of control. Moreover, ICS II at the appropriate concentration (100 μM) not only increased nNOS expression, NO production, but also enhanced cGMP content and PKG activity. The addition of L-NMMA and KT-5 823 significantly inhibited the effects of ICS II on nNOS expression, NO production and PKG activity. Furthermore, LY294002 significantly decreased p-AKT level, NOS activity, NO production and nNOS expression, but it did not affect iNOS expression. These findings demonstrate that the beneficial effect of ICS II on neuronal cell proliferation, and its possible underlying mechanisms are, at least partly, through activating AKT/nNOS/NO/cGMP/PKG signaling pathway.

淫羊藿次苷II（ICS II），磷酸二酯酶5抑制剂（PDE 5-I），是一个主要的成分淫羊藿，具有广泛的神经保护特性。但是，关于ICS II对神经元细胞增殖的潜在有益作用知之甚少，其可能的潜在机制仍不清楚。我们假设ICS II对神经元样高分化大鼠嗜铬细胞瘤（PC12）细胞增殖的有益作用与一氧化氮（NO）信号通路及其PI3K / AKT通路上游有关。PC12细胞单独用ICS II或与L-NMMA，H89，KT-5823和/或LY294002（分别为NOS，PKA，PKG，PI3K的抑制剂）一起处理。发现ICS II浓度依赖性地促进PC12细胞增殖，并且细胞周期分析显示，在S期中，用ICS II处理的PC12细胞的比例高于对照。而且，适当浓度（100μM）的ICS II不仅增加了nNOS的表达，NO的产生，而且还提高了cGMP含量和PKG活性。L-NMMA和KT-5 823的加入显着抑制了ICS II对nNOS表达，NO产生和PKG活性的影响。此外，LY294002明显降低p -AKT水平，NOS活性，NO产生和nNOS表达，但不影响iNOS表达。这些发现表明，ICS II对神经元细胞增殖的有益作用及其可能的潜在机制至少部分是通过激活AKT / nNOS / NO / cGMP / PKG信号通路来实现的。