Neuroprotective effects of ginsenoside Rg₃ against 24-OH-cholesterol-induced cytotoxicity in cortical neurons

Ginsenoside Rg₃ (Rg₃), one of the active ingredients in Panax ginseng, attenuates NMDA receptor-mediated currents in vitro and antagonizes NMDA receptors through a glycine modulatory site in rat cultured hippocampal neurons. In the present study, we examined the neuroprotective effects of Rg₃ on 24-hydroxycholesterol (24-OH-chol)-induced cytotoxicity in vitro. The results showed that Rg₃ treatment significantly and dose-dependently inhibited 24-OH-chol-induced cell death in rat cultured cortical neurons, with an IC₅₀ value of 28.7 ± 7.5 μm. Furthermore, the Rg₃ treatment not only significantly reduced DNA damage, but also dose-dependently attenuated 24-OH-chol-induced caspase-3 activity. To study the mechanisms underlying the in vitro neuroprotective effects of Rg₃ against 25-OH-chol-induced cytotoxicity, we also examined the effect of Rg₃ on intracellular Ca²⁺ elevations in cultured neurons and found that Rg₃ treatment dose-dependently inhibited increases in intracellular Ca²⁺, with an IC₅₀ value of 40.37 ± 12.88 μm. Additionally, Rg₃ treatment dose-dependently inhibited apoptosis with an IC ₅₀ of 47.3 ± 14.2 μm. Finally, after confirming the protective effect of Rg₃ using a terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay, we found that Rg₃ is an active component in ginseng-mediated neuroprotection. These results collectively indicate that Rg₃induced neuroprotection against 24-OH-chol in rat cortical neurons might be achieved via inhibition of a 24-OH-chol-mediated Ca²⁺ channel. This is the first report to employ cortical neurons to study the neuroprotective effects of Rg₃ against 24-OH-chol. In conclusion, Rg₃ was effective for protecting cells against 24-OH-chol-induced cytotoxicity in rat cortical neurons. This protective ability makes Rg₃ a promising agent in pathologies implicating neurodegeneration such as apoptosis or neuronal cell death.