Neuroprotective effects of ginsenoside Rb1 on hippocampal neuronal injury and neurite outgrowth

Ginsenoside Rb1 has been reported to exert anti-aging and anti-neurodegenerative effects. In the present study, we investigate whether ginsenoside Rb1 is involved in neurite outgrowth and neuroprotection against damage induced by amyloid beta（25–35） in cultured hippocampal neurons, and explore the underlying mechanisms. Ginsenoside Rb1 significantly increased neurite outgrowth in hippocampal neurons, and increased the expression of phosphorylated-Akt and phosphorylated extracellular signal-regulated kinase 1/2. These effects were abrogated by API-2 and PD98059, inhibitors of the signaling proteins Akt and MEK. Additionally, cultured hippocampal neurons were exposed to amyloid beta（25–35） for 30 minutes; ginsenoside Rb1 prevented apoptosis induced by amyloid beta（25–35）, and this effect was blocked by API-2 and PD98059. Furthermore, ginsenoside Rb1 significantly reversed the reduction in phosphorylated-Akt and phosphorylated extracellular signal-regulated kinase 1/2 levels induced by amyloid beta（25–35）, and API-2 neutralized the effect of ginsenoside Rb1. The present results indicate that ginsenoside Rb1 enhances neurite outgrowth and protects against neurotoxicity induced by amyloid beta（25–35） via a mechanism involving Akt and extracellular signal-regulated kinase 1/2 signaling.

Ginsenoside Rg1 protects against neurodegeneration by inducing neurite outgrowth in cultured hippocampal neurons

Ginsenoside Rg1（Rg1） has anti-aging and anti-neurodegenerative effects. However, the mechanisms underlying these actions remain unclear. The aim of the present study was to determine whether Rg1 affects hippocampal survival and neurite outgrowth in vitro after exposure to amyloid-beta peptide fragment 25–35（Aβ_（25–35））, and to explore whether the extracellular signal-regulated kinase（ERK） and Akt signaling pathways are involved in these biological processes. We cultured hippocampal neurons from newborn rats for 24 hours, then added Rg1 to the medium for another 24 hours, with or without pharmacological inhibitors of the mitogen-activated protein kinase（MAPK） family or Akt signaling pathways for a further 24 hours. We then immunostained the neurons for growth associated protein-43, and measured neurite length. In a separate experiment, we exposed cultured hippocampal neurons to Aβ_（25–35） for 30 minutes, before adding Rg1 for 48 hours, with or without Akt or MAPK inhibitors, and assessed neuronal survival using Hoechst 33258 staining, and phosphorylation of ERK1/2 and Akt by western blot analysis. Rg1 induced neurite outgrowth, and this effect was blocked by API-2（Akt inhibitor） and PD98059（MAPK/ERK kinase inhibitor）, but not by SP600125 or SB203580（inhibitors of c-Jun N-terminal kinase and p38 MAPK, respectively）. Consistent with this effect, Rg1 upregulated the phosphorylation of Akt and ERK1/2; these effects were reversed by API-2 and PD98059, respectively. In addition, Rg1 significantly reversed Aβ_（25–35）-induced apoptosis; this effect was blocked by API-2 and PD98059, but not by SP600125 or SB203580. Finally, Rg1 significantly reversed the Aβ_（25–35）-induced decrease in Akt and ERK1/2 phosphorylation, but API-2 prevented this reversal. Our results indicate that Rg1 enhances neurite outgrowth and protects against Aβ_（25–35）-induced damage, and that its mechanism may involve the activation of Akt and ERK1/2 signaling.