Li-Min Chen

Ginsenoside Rg1 attenuates dopamine-induced apoptosis in PC12 cells by suppressing oxidative stress

In Parkinsons disease, neuroprotective therapy to rescue dopamine neurons has been proposed. Ginsenoside Rg1, one of the biologically active ingredients of ginseng, may be a candidate neuroprotective drug. In the present study, the mechanism underlying the neuroprotection provided by ginsenosde Rg1 was studied against apoptosis induced by exogenous dopamine in PC12 cells. Pretreatment with ginsenoside Rg1 markedly reduced the generation of dopamine-induced reactive oxygen species and the release of mitochondrial cytochrome c into the cytosol, and subsequently inhibited the activation of caspase-3. In addition, Rg1 pretreatment also reduced inducible nitric oxide (NO) synthase protein level and NO production. These results suggested that ginsenoside Rg1 may attenuate dopamine-induced apoptotic cell death through suppression of intracellular oxidative stress, and that it may rescue or protect dopamine neurons in Parkinsons disease.

Ginsenoside Rg1 reduces MPTP-induced substantia nigra neuron loss by suppressing oxidative stress1

AbstractAim:To investigate the effect of ginsenoside Rg1, an effective ingredient from ginsenoside, on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced substantia nigra neuron lesion.Methods:C57-BL mice were given MPTP to prepare Parkinson disease mice model. Different doses of Rg1 (5, 10, and 20 mg·kg−1·d−1) or N-acetylcystein (NAC) (300 mg·kg−1·d−1) were given 3 d prior to MPTP in the pretreatment groups. Glutathione (GSH) level and total superoxide dismutase (T-SOD) activity in substantia nigra were determined by spectrophotometry. Nissl staining, tyrosine hydroxylase immunostaining, and TUNEL labeling were used to observe the damage and apoptosis of nigral neurons. Western blot analysis was used to detect the phospho-JNK and phospho-c-Jun levels in midbrain homogenates.Results:Pretreatments of C57-BL mice with different doses of Rg1 or NAC were found to protect against MPTP-induced substantia nigra neurons loss. Rg1 or NAC prevented GSH reduction and T-SOD activation in substantia nigra, and attenuated the phosphorylations of JNK and c-Jun following MPTP treatment.Conclusion:The antioxidant property of Rg1 along with the blocking of JNK signaling cascade might contribute to the neuroprotective effect of ginsenoside Rg1 against MPTP.

Tripchlorolide protects neuronal cells from microglia‐mediated β‐amyloid neurotoxicity through inhibiting NF‐κB and JNK signaling

Recent research has focused on soluble oligomeric assemblies of β‐amyloid peptides (Aβ) as the proximate cause of neuroinflammation, synaptic loss, and the eventual dementia associated with Alzheimers disease (AD). In this study, tripchlorolide (T4), an extract of Tripterygium wilfordii Hook. F (TWHF), was studied as a novel agent to suppress neuroinflammatory process in microglial cells and to protect neuronal cells against microglia‐mediated oligomeric Aβ toxicity. T4 significantly attenuated oligomeric Aβ(1‐42)‐induced release of inflammatory productions such as tumor necrosis factor‐α, interleukin‐1β, nitric oxide (NO), and prostaglandin E2. It also downregulated the protein levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase‐2 (COX‐2) in microglial cells. Further molecular mechanism study demonstrated that T4 inhibited the nuclear translocation of nuclear factor‐κB (NF‐κB) without affecting I‐κBα phosphorylation. It repressed Aβ‐induced JNK phosphorylation but not ERK or p38 MAPK. The inhibition of NF‐κB and JNK by T4 is correlated with the suppression of inflammatory mediators in Aβ‐stimulated microglial cells. These results suggest that T4 protects neuronal cells by blocking inflammatory responses of microglial cells to oligomeric Aβ(1‐42) and that T4 acts on the signaling of NF‐κB and JNK, which are involved in the modulation of inflammatory response. Therefore, T4 may be an effective agent in modulating neuroinflammatory process in AD.

Ginsenoside Rg1 Attenuates Amyloid-β Content, Regulates PKA/CREB Activity, and Improves Cognitive Performance in SAMP8 Mice

It is well established that the presence of soluble amyloid-beta protein (Abeta) correlates with the severity of dementia in Alzheimers disease (AD). Several lines of evidence indicate that cyclic AMP responsive element binding protein (CREB) and protein kinase A (PKA) are involved in soluble Abeta-trigged disruption of synaptic plasticity in early AD. Previously we demonstrated the beneficial effects of ginsenoside Rg1 on Abeta-induced neuronal insult. Therefore, in the present study, we examined the effects of long-term consumption of Rg1 on the cerebral Abeta content and PKA/CREB signaling molecules, as well as cognitive performance in senescence-accelerated mouse prone 8 (SAMP8). Notably, a significant dose-dependent reduction of soluble Abeta(1-40) was shown in the hippocampus of SAMP8 mice after administration with ginsenoside Rg1 for 3 months. Furthermore, Rg1 treatment resulted in a significant decrease of hippocampal PKA RIIalpha level (isoform IIalpha of the regulatory subunit of PKA). In contrast, phospho-CREB and brain derived neurotrophic factor (BDNF) levels were dramatically increased in the hippocampus of SAMP8 treated with Rg1. Additionally, administration of ginsenoside Rg1 consequently improved learning and memory outcomes in SAMP8 mice. These data suggest that long-term consumption of ginsenoside Rg1 may delay cognitive decline, associated with significant effects on Abeta generation, PKA/CREB activity, as well as BDNF content in the brain. These data provide further support for the therapeutic or intervention potency of ginsenoside Rg1 in the early stage of AD.

Ginsenoside Rg1 attenuates β-amyloid generation via suppressing PPARγ-regulated BACE1 activity in N2a-APP695 cells

The level of β-site APP-cleaving enzyme 1 (BACE1) has been documented to increase in the brains of patients with Alzheimers disease, which has resulted in elevation of β-amyloid (Aβ) peptides. As a transcription factor binding site of the BACE1 promoter, peroxisome proliferator-activated receptor-γ (PPARγ) response element regulates the activity of the BACE1 promoter activity, indicating that PPARγ may become a potential target for Alzheimers disease treatment. Recent studies have demonstrated that ginsenoside Rg1 which is an effective component of extracts of ginseng can prevent memory loss and improve cognitive function in a variety of animal models. However, the underlying mechanism remains unclear. In the present study, we found that Rg1 decreased the levels of Aβ₁₋₄₀ and Aβ₁₋₄₂ secreted in N2a-APP695 cells. The expression levels of both BACE1 mRNA and protein as well as β-CTFs, a cleavaged C-terminal fragment of APP by BACE1, were reduced in cells treated with Rg1. Moreover, Rg1 treatment led to a translocation of PPARγ from cytoplasm to nuclear. Intriguingly, Rg1, like pioglitazone (a PPARγ agonist), suppressed BACE1 activity in N2a-APP695 cells, while its effect on BACE1 activity was attenuated by GW9662 (a PPARγ antagonist). These results indicate that Rg1 may be a PPARγ agonist to enhance the binding of nuclear PPARγ to the BACE1 promoter, which may in turn inhibit the transcription and translation of BACE1, suppress the activity of BACE1, and ultimately attenuate Aβ generation. Therefore, ginsenoside Rg1 may serve as a promising agent in modulating Aβ-related pathology in Alzheimers disease.

Neuroprotective role of tripchlorolide on inflammatory neurotoxicity induced by lipopolysaccharide-activated microglia

A large body of evidence has suggested a strong association between neuroinflammation and the pathogenesis of many neurodegenerative diseases. Therefore, it is a good target for therapeutic treatment. So far, studies have proven anti-inflammatory herbal medicine and its constituents to be effective in slowing down the neurodegenerative process. The present study tested tripchlorolide, an extract of Tripterygium wilfordii Hook F (TWHF), as a novel agent to suppress inflammatory process in microglia. It showed this novel agent to be cytotoxic at a dose of 20-40 nM to primary microglia and BV-2 microglial cells but not to primary cortical neurons and Neuro-2A cells in vitro. Moreover, tripchlorolide protected primary cortical neurons and Neuro-2A cells from neuroinflammatory toxicity induced by the conditioned media from lipopolysaccharide (LPS)-stimulated microglia, which resulted in a significant decrease in their cell survival. The changes of the inflammatory mediators in this process were further investigated. In the LPS-stimulated microglia, the production of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), nitric oxide (NO), prostaglandin E(2) (PGE(2)), and intracellular superoxide anion (SOA) was markedly attenuated by tripchlorolide at a dose of 1.25-10 nM in a dose-dependent manner. Furthermore, the production of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) was also significantly inhibited by tripchlorolide in both mRNA and protein levels. These results suggest that tripchlorolide can protect neuronal cells via a mechanism involving inhibition of inflammatory responses of microglia to pathological stimulations. Therefore, it is potentially a highly effective therapeutic agent in treating neuroninflammatory diseases.

Protective effect of ginsenoside Rg1 on MPP+-induced apoptosis in SHSY5Y cells.

Summary. The neuroprotective mechanism of Rg1 was studied in this paper by means of its obvious anti-apoptotic effect on human SHSY5Y cells. SHSY5Y cells were treated with MPP+ (1-methyl-4-phenyl-pyridinium) for 72 hours to induce apoptosis. During the apoptosis, production of reactive oxygen species (ROS), activation of c-Jun N-terminal kinase (JNK) and activation of caspase-3 were observed. The results showed that the signal transduction pathway of MPP+-induced apoptosis might be ROS to JNK, then to caspase-3. MPP+-induced apoptosis in SHSY5Y cells was obviously inhibited in both NAC (N-acetylcysteine) pretreated groups and Rg1 pretreated groups. Meanwhile, compared to that of the controls, our results showed decreased level of ROS, less JNK activity and lower expression of cleaved caspase-3 in pretreated NAC groups and in Rg1 pretreated groups. The protection by Rg1 might be mediated by removing of ROS. The removal of ROS might inhibit the activity of JNK and the expression of cleaved caspase-3. These results suggest that ginsenoside Rg1 may take effect through its anti-apoptotic activity in neurodegenerative diseases.

Involvement of calpain and p25 of CDK5 pathway in ginsenoside Rb1's attenuation of β-amyloid peptide25-35-induced tau hyperphosphorylation in cortical neurons

Increasing evidence have shown that beta-amyloid (Abeta) induced hyperphosphorylation of tau, which eventually resulted in the disruption of microtubule (MT) integrity. Cyclin-dependent kinase 5 (CDK5) and its activator p35 are required for neurite outgrowth. The cleavage of p35 to p25, mediated by calpain and calcium, caused CDK5 dislocation and subsequently p25/CDK5-induced tau hyperphosphorylation, which disrupted the cytoskeleton and resulted in neuronal death. In the present study we investigated the effects of ginsenoside Rb1 on fibrillar Abeta(25-35)-induced tau hyperphosphorylation in primary cultured cortical neurons and also the potential involvement of Ca(2+)-calpain-CDK5 signal pathway. The present study suggests that Ca(2+), calpain, and p25 in CDK5 pathway may play important roles in Abeta(25-35)-induced tau hyperphosphorylation.

Ginsenoside Rb1 selectively inhibits the activity of L-type voltage-gated calcium channels in cultured rat hippocampal neurons.

Aim:To investigate the effect of ginsenoside Rb1 on voltage-gated calcium currents in cultured rat hippocampal neurons and the modulatory mechanism.Methods:Cultured hippocampal neurons were prepared from Sprague Dawley rat embryos. Whole-cell configuration of the patch-clamp technique was used to record the voltage-gated calcium currents (VGCCs) from the hippocampal neurons,and the effect of Rb1 was examined.Results:Rb1 (2–100 μmol/L) inhibited VGCCs in a concentration-dependent manner, and the current was mostly recovered upon wash-out. The specific L-type Ca2+ channel inhibitor nifedipine (10 μmol/L) occluded Rb1-induced inhibition on VGCCs. Neither the selective N-type Ca2+ channel blocker ω-conotoxin-GVIA (1 μmol/L), nor the selective P/Q-type Ca2+ channel blocker ω-agatoxin IVA (30 nmol/L) diminished Rb1-sensitive VGCCs. Rb1 induced a leftward shift of the steady-state inactivation curve of ICa to a negative potential without affecting its activation kinetics or reversal potential in the I–V curve. The inhibitory effect of Rb1 was neither abolished by the adenylyl cyclase activator forskolin (10 μmol/L), nor by the PKA inhibitor H-89 (10 μmol/L).Conclusion:Ginsenoside Rb1 selectively inhibits the activity of L-type voltage-gated calcium channels, without affecting the N-type or P/Q-type Ca2+ channels in hippocampal neurons. cAMP-PKA signaling pathway is not involved in this effect.

Ginsenoside Rg1 Attenuates Oligomeric Aβ1-42-Induced Mitochondrial Dysfunction

Mitochondrial dysfunction is one of the major pathological changes seen in Alzheimers disease (AD). Amyloid beta-peptide (Aβ), a neurotoxic peptide, accumulates in the brain of AD subjects and mediates mitochondrial and neuronal stress. Therefore, protecting mitochondrion from Aβ-induced toxicity holds potential benefits for halting and treating and perhaps preventing AD. Here, we report that administration of ginsenoside Rg1, a known neuroprotective drug, to primary cultured cortical neurons, rescues Aβ-mediated mitochondrial dysfunction as shown by increases in mitochondrial membrane potential, ATP levels, activity of cytochrome c oxidase (a key enzyme associated with mitochondrial respiratory function), and decreases in cytochrome c release. The protective effects of Rg1 on mitochondrial dysfunction correlate to neuronal injury in the presence of Aβ. This finding suggests that ginsenoside Rg1 may attenuate Aβ-induced neuronal death through the suppression of intracellular mitochondrial oxidative stress and may rescue neurons in AD.