Joon-Hee Lee

Neuroprotective effects of ginsenoside Rg3 against homocysteine-induced excitotoxicity in rat hippocampus.

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.

Identification of ginsenoside interaction sites in 5-HT3A receptors.

We previously demonstrated that 20(S)-ginsenoside Rg(3) (Rg(3)), one of the active components of Panax ginseng, non-competitively inhibits 5-HT(3A) receptor channel activity on extracellular side of the cell. Here, we sought to elucidate the molecular mechanisms underlying Rg(3)-induced 5-HT(3A) receptor regulation. We used the two-microelectrode voltage-clamp technique to investigate the effect of Rg(3) on 5-HT-mediated ion currents (I(5-HT)) in Xenopus oocytes expressing wild-type or 5-HT(3A) receptors harboring mutations in the gating pore region of transmembrane domain 2 (TM2). In oocytes expressing wild-type 5-HT(3A) receptors, Rg(3) dose-dependently inhibited peak I(5-HT) with an IC(50) of 27.6+/-4.3microM. Mutations V291A, F292A, and I295A in TM2 greatly attenuated or abolished the Rg(3)-induced inhibition of peak I(5-HT). Mutation V291A but not F292A and I295A induced constitutively active ion currents with decrease of current decay rate. Rg(3) accelerated the rate of current decay with dose-dependent manner in the presence of 5-HT. Rg(3) and TMB-8, an open channel blocker, dose-dependently inhibited constitutively active ion currents. The IC(50) values of constitutively active ion currents in V291A mutant receptor were 72.4+/-23.1 and 6.5+/-0.7microM for Rg(3) and TMB-8, respectively. Diltiazem did not prevent Rg(3)-induced inhibition of constitutively active ion currents in occlusion experiments. These results indicate that Rg(3) inhibits 5-HT(3A) receptor channel activity through interactions with residues V291, F292, and I295 in the channel gating region of TM2 and further demonstrate that Rg(3) regulates 5-HT(3A) receptor channel activity in the open state at different site(s) from those of TMB-8 and diltiazem.

Effects of Korean red ginseng extract on cisplatin-induced nausea and vomiting

Ginseng, the root ofPanax ginseng C. A. Meyer, is well known as a tonic medicine for restoring and enhancing human health. In traditional medicine, ginseng is utilized for the alleviation of emesis, which includes nausea and vomiting. However, it has not yet been demonstrated whether ginseng exhibitsin vivo anti-nausea and anti-vomiting properties. In this study, we examined the anti-emetic effect of Korean red ginseng total extract (KRGE) on cisplatin-induced nausea and vomiting using ferrets. Intraperitoneal administration (i.p.) of cisplatin (7.5 mg/kg) induced both nausea and vomiting with one-hour latency. The episodes of nausea and vomiting reached a peak after 1.5 h and persisted for 3 h. Treatment with KRGEvia oral route significantly reduced the cisplatin-induced nausea and vomiting in a dose-dependent manner. The anti-emetic effect was 12.7±8.6, 31.8±6.9, and 67.6±4.0% with doses of 0.3, 1.0, and 3.0 g/kg of KRGE, respectively. Pretreatment with KRGEvia oral route 1 and 2 h before cisplatin administration also significantly attenuated the cisplatin-induced nausea and vomiting. However this did not occur with a pretreatment 4 h before cisplatin administration. These results are supportive of KRGE being utilized as an anti-emetic agent against nausea and vomiting caused by chemotherapy (i.e. cisplatin).

Effects of Minor Ginsenosides, Ginsenoside Metabolites, and Ginsenoside Epimers on the Growth of Caenorhabditis elegans

In the previous report, we have demonstrated that ginsenoside Rc, one of major ginsenosides, is a major component for the restoration for normal growth of worms in cholesterol-deprived medium. In the present study, we further investigated the roles of minor ginsenosides, such as ginsenoside Rh1 and Rh2, ginsenoside metabolites such as compound K (CK), protopanaxadiol (PPD), and protopanaxatriol (PPT) and ginsenoside epimers such as 20(R)- and 20(S)-ginsenoside Rg3 in cholesterol-deprived medium. We found that ginsenoside Rh1 almost restored normal growth of worms in cholesterol-deprived medium in F1 generation. However, supplement of ginsenoside Rh2 caused a suppression of worm growths in cholesterol-deprived medium. In addition, CK and PPD also slightly restored normal growth of worms in cholesterol-deprived medium but PPT not. In experiments using ginsenoside epimers, supplement of 20(S)- but not 20(R)-ginsenoside Rg3 in cholesterol-deprived medium also almost restored worm growth. These results indicate that the absence or presence of carbohydrate component at backbone of ginsenoside, the number of carbohydrate attached at carbon-3, and the position of hydroxyl group at carbon-20 of ginsenoside might plays important roles in restoration of worm growth in cholesterol-deprived medium.

Human glycine α1 receptor inhibition by quercetin is abolished or inversed by α267 mutations in transmembrane domain 2

Quercetin, one of the flavonoids, is a compound of low molecular weight found in fruits and vegetables. Besides its antioxidative effect, quercetin also shows a wide range of diverse neuropharmacological actions. However, the cellular mechanisms of quercetins actions, especially on ligand-gated ion channels and synaptic transmissions, are not well studied. We investigated the effect of quercetin on the human glycine alpha1 receptor channel expressed in Xenopus oocytes using a two-electrode voltage clamp technique. Application of quercetin reversibly inhibited glycine-induced current (I(Gly)). Quercetins inhibition depends on its dose, with an IC(50) of 21.5+/-.2 microM. The inhibition was sensitive to membrane voltages. Site-directed mutations of S267 to S267Y but not S267A, S267F, S267G, S267K, S267L and S267T at transmembrane domain 2 (TM2) nearly abolished quercetin-induced inhibition of I(Gly). In contrast, in site-directed mutant receptors such as S267 to S267I, S267R and S267V, quercetin enhanced I(Gly) compared to the wild-type receptor. The EC(50) was 22.6+/-1.4, 25.5+/-4.2, and 14.5+/-3.1 microM for S267I, S267R and S267V, respectively. These results indicate that quercetin might regulate the human glycine alpha(1) receptor via interaction with amino acid residue alpha267 and that alpha267 plays a key role in determining the regulatory consequences of the human glycine alpha1 receptor by quercetin.

Study on life span extension efficacy by Korean Red Ginseng

The backbone structure of ginsenosides, active ingredients of Panax ginseng, is similar with that of sterol, especially cholesterol. Caenorhabditis elegans (C. elegans) is one of free living nematodes and is well-established animal model for biochemical and genetic studies. C. elegans cannot synthesize de novo cholesterol, although cholesterol is essential requirement for its growth and development. In the present study, we investigated the effects of Korean red ginseng total extract (KRGE), ginseng total saponins (GTS) on life span of C. elegans in cholesterol-deprived and -fed medium. Cholesterol deprivation caused damages on life span of worms throughout F1 to F3 generations. KRGE or GTS supplement to cholesterol-deprived medium restored the life span of worms as much as cholesterol alone-fed medium. In study to identify which ginsenosides are responsible for life span restoring effects of KRGE, we found that ginsenoside Rc supplement not only restored life span of worms grown in cholesterol-deprived medium but also prolonged life span of worms grown in cholesterol-fed medium. These results show a possibility that ginsenosides could be utilized by C. elegans as a sterol substitute and further indicate that ginsenoside Rc is the effective component of Korean red ginseng that prolongs the life span of C. elegans.