Ginsenosides Rb1 and Rg1 effects on mesencephalic dopaminergic cells stressed with glutamate

Ginseng, the root of Panax ginseng C.A. Meyer (Araliaceae), is a well known and popular herbal medicine used worldwide. Among more than 30 ginsenosides, the active ingredients of ginseng, ginsenosides Rb1 and Rg1 are regarded as the main compounds responsible for many pharmaceutical actions of ginseng. In our study, primary cultures from embryonic mouse mesencephala were exposed to neurotoxic glutamate concentration and potential protective effects of these two ginsenosides on survival and neuritic growth of dopaminergic cells were tested. Treatment of primary mesencephalic culture with 500 microM glutamate for 15 min on the 10th day in vitro (DIV) increased the release of lactate dehydrogenase (LDH) into the culture medium, the propidium iodide (PI) uptake by cultured cells and the total number of nuclei with condensed and fragmented chromatin (apoptotic features) as evaluated with Hoechst 33342. Moreover, it extensively decreased the number of tyrosine hydroxylase immunopositive (TH+) cells and adversely affected the length and number of their neuronal processes. The toxic effect of glutamate was primarily mediated by over-activation of N-methyl-D-aspartate receptor (NMDA) as treatment of cultured cells with (+)-MK 801, an NMDA receptor antagonist, nearly abolished dopaminergic cells loss and LDH release induced by glutamate. When either ginsenoside was added alone for six consecutive days (at final concentrations 0.1, 1, 10, 20 microM), ginsenoside Rb1 (at 10 microM) significantly enhanced the survival of dopaminergic neurons compared to untreated controls. In these cultures, neurite lengths and numbers were not affected by both ginsenosides. Against glutamate exposure, ginsenosides Rb1 and Rg1 could not prevent cell death. However when pre-treating for 4 days or post-treating for 2 days following glutamate exposure, they significantly increased the numbers and lengths of neurites of surviving dopaminergic cells. Thus our study indicates that ginsenosides Rb1 and Rg1 have a partial neurotrophic and neuroprotective role in dopaminergic cell culture.