Ginsenoside rb1 and rg3 attenuate glucocorticoid-induced neurotoxicity.

Glucocorticoid (GC) hormones, increased in response to stress, can cause neuronal loss. We tested the effect of GC hormone on cell viability of neural SHSY-5Y cells and protective effects of ginsenoside Rb1 and Rg3 on the action of GC. We treated SHSY-5Y cells with increasing concentrations of synthetic GC dexamethasone (DEX; 10, 25, 50, and 100 nM) for 24 and 48 h, and then determined cell viability by using MTT assay. We then treated SHSY-5Y cells with DEX (100 nM) with or without the ginsenosides to examine their preventive effects on the cytotoxicity. To explore the underlying molecular mechanisms, we measured mRNA expression of bax and bcl-2 by using reverse transcriptase real-time PCR. SHSY-5Y cells treated with DEX significantly reduced cell viability as compared with control cells. In the presence of Rb1 or Rg3, DEX-induced cytotoxicity was effectively blocked. DEX considerably increased pro-apoptotic bax mRNA expression as compared with control cells. However, Rb1 and Rg3 completely blocked DEX-mediated up-regulation of bax expression. DEX significantly increased neuronal death in organotypic hippocampal slice cultures of rat brain with enhanced generation of ROS, which was effectively inhibited by ginsenoside Rb1 and Rg3. This suggests a potential role of the ginsenosides to target GC action in the brain.

Mechanism of glucocorticoid-induced oxidative stress in rat hippocampal slice cultures.

Prolonged stress results in elevation of glucocorticoid (GC) hormones, which can have deleterious effects in the brain. The hippocampus, which has a high concentration of glucocorticoid receptors, is especially vulnerable to increasing levels of GCs. GCs have been suggested to endanger hippocampal neurons by exacerbating the excitotoxic glutamate-calcium-reactive oxygen species (ROS) cascade. In an effort to reveal the mechanisms underlying GC-mediated hippocampal neurotoxicity, we aimed to clarify the molecular pathway of GC-induced ROS increase by using organotypic hippocampal slice cultures. Assays for ROS, using 2',7'-dichlorodihydrofluorescein diacetate fluorescence, showed that treatment of synthetic GC, dexamethasone (DEX) significantly enhanced ROS levels. Time course and dose response analyses indicated that peak amount of ROS was generated at 4 h after treatment with 50 micromol/L DEX. By contrast, other steroid hormones, progesterone and estradiol did not influence ROS production. N-acetyl-L-cysteine completely suppressed ROS produced by DEX. Propidium iodide staining exhibited prominent cell death in the hippocampal layer after 96 h of DEX treatment. RU486, a GC receptor antagonist, almost completely blocked the effect of DEX on ROS production and cell death, indicating that DEX-induced ROS overproduction and hippocampal death are mediated via GC receptors. Real-time reverse transcriptase PCR analysis demonstrated that after DEX treatment the level of glutathione peroxidase mRNA was decreased whereas that of NADPH oxidase mRNA was significantly enhanced. These findings suggest that excess GCs cause hippocampal damage by regulating genes involved in ROS generation.