ABSTRACT
We previously demonstrated that ginsenoside Rg(3) (Rg(3)), one of the active ingredients in Panax ginseng, attenuates NMDA receptor-mediated currents and NMDA-induced neurotoxicity (Kim, S., Kim, T., Ahn, K., Park, W.K., Nah, S.Y., Rhim, H., 2004. Ginsenoside Rg(3) antagonizes NMDA receptors through a glycine modulatory site in rat cultured hippocampal neurons. Biochem. Biophys. Res. Commun. 323, 416-424). Accumulating evidence suggests that homocysteine (HC), a metabolite of methionine, exerts its excitotoxicity through NMDA receptor activation. In the present study, we examined the neuroprotective effects of Rg(3) on HC-induced hippocampal excitotoxicity in vitro and in vivo. Our in vitro studies using rat cultured hippocampal neurons revealed that Rg(3) treatment significantly and dose-dependently inhibited HC-induced hippocampal cell death, with an EC(50) value of 28.7+/-7.5 muM. Rg(3) treatment not only significantly reduced HC-induced DNA damage, but also dose-dependently attenuated HC-induced caspase-3 activity in vitro. Our in vivo studies revealed that intracerebroventricular (i.c.v.) pre-administration of Rg(3) significantly and dose-dependently reduced i.c.v. HC-induced hippocampal damage in rats. To examine the mechanisms underlying the in vitro and in vivo neuroprotective effects of Rg(3) against HC-induced hippocampal excitotoxicity, we examined the effect of Rg(3) on HC-induced intracellular Ca(2+) elevations in cultured hippocampal cells and found that Rg(3) treatment dose-dependently inhibited HC-induced intracellular Ca(2+) elevation, with an IC(50) value of 41.5+/-17.5 muM. In addition, Rg(3) treatment dose-dependently inhibited HC-induced currents in Xenopus oocytes expressing the NMDA receptor, with an IC(50) of 47.3+/-14.2 muM. These results collectively indicate that Rg(3)-induced neuroprotection against HC in rat hippocampus might be achieved via inhibition of HC-mediated NMDA receptor activation.
Subject(s)
Ginsenosides/pharmacology , Hippocampus/cytology , Homocysteine/toxicity , Neurons/drug effects , Neuroprotective Agents/pharmacology , Neurotoxins/toxicity , Animals , Calcium/metabolism , Caspase 3/metabolism , Cell Death/drug effects , Cells, Cultured , Dose-Response Relationship, Drug , Embryo, Mammalian , Embryo, Nonmammalian , In Situ Nick-End Labeling , Male , Membrane Potentials/drug effects , Membrane Potentials/physiology , Membrane Potentials/radiation effects , Oocytes , Patch-Clamp Techniques , Rats , Rats, Sprague-Dawley , Receptors, N-Methyl-D-Aspartate/metabolism , Xenopus laevisABSTRACT
Recent studies have shown that Panax ginseng has a variety of beneficial effects on the cardiovascular systems. Homocysteine (Hcy), which is derived from L-methionine (Met), has been closely associated with the increased risk of cardiovascular diseases. In the present study, we examined whether in vivo long-term administration of ginseng saponins (GS), active ingredients of Panax ginseng, attenuate adverse vascular effects associated with chronic Met-induced hyperhomocysteinemia (H-Hcy). We found that plasma Hcy level, which was measured after 30 and 60 d, in GS (100 mg/kg)+Met co-administration group was significantly reduced when it was compared with Met alone treatment group. We could also observe the alleviation of endothelial damages of aortic artery vessels in GS (100 mg/kg)+Met co-administration group compared with Met alone treatment group. We compared aortic vasocontractile and vasodilatory responses between Met alone and GS (100 mg/kg)+Met co-treatment groups. We found that norepinephrine-induced vasocontractile responses were greatly decreased in GS (100 mg/kg)+Met co-treatment group and that carbachol-induced dilatory responses were greatly enhanced in GS (100 mg/kg)+Met co-administration groups as compared with Met alone treatment group. The present results indicate that in vivo long-term administration of GS attenuates adverse vascular effects associated with chronic Met-induced H-Hcy in rats.
