Neferine, a bisbenzylisoquinoline alkaloid of Nelumbo nucifera, inhibits glutamate release in rat cerebrocortical nerve terminals through 5-HT1A receptors.

Neferine, a bisbenzylisoquinoline alkaloid present in Nelumbo nucifera, has been reported to exhibit neuroprotective effects. Because reduced glutamatergic transmission through inhibition of glutamate release has been proposed as a mechanism of neuroprotection, we investigated whether and how neferine inhibits glutamate release in the nerve terminals of the cerebral cortex of rats. The results demonstrated that neferine inhibits the glutamate release that is evoked by the potassium channel blocker 4-aminopyridine, doing so in a dose-dependent manner. This effect was prevented by removing extracellular calcium and blocking vesicular transporters or N- and P/Q-type calcium channels but not by blocking glutamate transporters. Neferine decreased the 4-aminopyridine-stimulated elevation in intrasynaptosomal calcium concentration; however, it had no effect on the synaptosomal membrane potential. The inhibition of glutamate release by neferine was also eliminated by the selective 5-hydroxytryptamine 1A (5HT1A) receptor antagonist WAY100635, Gi/o protein inhibitor pertussis toxin, adenylyl cyclase inhibitor MDL12330A, and protein kinase A inhibitor H89. Moreover, immunocytochemical analysis revealed the presence of 5-HT1A receptor proteins in the vesicular transporter of glutamate type 1 positive synaptosomes. The molecular docking study also demonstrated that neferine exhibited the highest binding affinity with 5-HT1A receptors (Autodock scores for 5-HA1A = -11.4 kcal/mol). Collectively, these results suggested that neferine activates 5-HT1A receptors in cortical synaptosomes, which decreases calcium influx and glutamate release through the activation of Gi/o protein and the inhibition of adenylyl cyclase/cAMP/protein kinase A cascade.

Aquilariae Lignum extract attenuates glutamate-induced neuroexcitotoxicity in HT22 hippocampal cells.

An imbalance between excitatory and inhibitory neurotransmitters is known to induce neuronal excitotoxicity which is a major cause of neurodegenerative disorders. Excessive glutamate concentration leads to the neuronal death by increasing oxidative stress and affecting the apoptotic signaling pathway. We investigated the anti-excitotoxic effects and associated working mechanisms of 30% ethanol extract of Aquilariae Lignum (ALE) against hippocampal neuronal death by glutamate. HT22 cells were treated with glutamate (20 mM) for 24 h following pretreatment with ALE (5, 10, 25 µg/mL). Cell viability, biochemical analysis, flow chemistry, and Western blotting assays were performed. Glutamate treatment substantially increased the intracellular level of reactive oxygen species (ROS) and Ca2+ influx into the cell, which were followed by apoptosis. ALE pretreatment, however, significantly attenuated these excitotoxicity-related features according to the results of Annexin V analysis and the lactate dehydrogenase assay, in which the calpain pathway (in a caspase 3-independent manner) may be involved. ALE pretreatment also significantly attenuated the glutamate-induced activation of both inflammation-associated molecules (extracellular signal-regulated kinase, c-Jun N-terminal kinases and p38) and death-related molecules (p53, apoptosis-inducing factor). The inactivation of brain-derived neurotrophic factor (BDNF) was restored by ALE pretreatment. Our results verified that A. Lignum has potential neuroprotective effects on glutamate-induced excitotoxicity in hippocampal neuron cells, and its underlying mechanism may involve the regulation of ROS-mediated cell death pathways.

Water extract from the leaves of Withania somnifera protect RA differentiated C6 and IMR-32 cells against glutamate-induced excitotoxicity.

Glutamate neurotoxicity has been implicated in stroke, head trauma, multiple sclerosis and neurodegenerative disorders. Search for herbal remedies that may possibly act as therapeutic agents is an active area of research to combat these diseases. The present study was designed to investigate the neuroprotective role of Withania somnifera (Ashwagandha), also known as Indian ginseng, against glutamate induced toxicity in the retinoic acid differentiated rat glioma (C6) and human neuroblastoma (IMR-32) cells. The neuroprotective activity of the Ashwagandha leaves derived water extract (ASH-WEX) was evaluated. Cell viability and the expression of glial and neuronal cell differentiation markers was examined in glutamate challenged differentiated cells with and without the presence of ASH-WEX. We demonstrate that RA-differentiated C6 and IMR-32 cells, when exposed to glutamate, undergo loss of neural network and cell death that was accompanied by increase in the stress protein HSP70. ASH-WEX pre-treatment inhibited glutamate-induced cell death and was able to revert glutamate-induced changes in HSP70 to a large extent. Furthermore, the analysis on the neuronal plasticity marker NCAM (Neural cell adhesion molecule) and its polysialylated form, PSA-NCAM revealed that ASH-WEX has therapeutic potential for prevention of neurodegeneration associated with glutamate-induced excitotoxicty.

South African plants used in traditional medicine to treat epilepsy have an antagonistic effect on NMDA receptor currents.

ETHNOPHARMACOLOGICAL RELEVANCE: Several Searsia species (Anacardiaceae), including Searsia dentata and Searsia pyroides, are used in South Africa traditional medicine to treat epilepsy. Ethanol leaf extracts of these plants have been shown to act as possible antagonists of N-methyl-d-aspartate (NMDA)-type glutamate receptors. MATERIALS AND METHODS: Leaf material of three Searsia species were collected from the Botanical Garden at the University of KwaZulu-Natal, Pietermaritzburg; dried and extracted with ethanol in an ultrasound bath. Filtered and dried extracts were resuspended in DMSO (100mg/ml) and diluted in the recording solution. The effect of Searsia dentata, Searsia pyroides and Searsia glauca extracts was investigated in dissociated cerebellar granule cells (CGCs) from 8-day-old rats and in transiently transfected HEK (human embryonic kidney) 293 cells (HEK), expressing either NR1a/NR2A or NR1a/NR2B receptors. In both systems we measured whole-cell currents elicited by 0.5mM NMDA (CGCs) or 50 µM glutamic acid (HEK) at -60 mV in 0Mg and 30 µM glycine and NMDA driven Ca influx in Fura2-loaded CGC. RESULTS: Searsia dentata and Searsia pyroides ethanol extracts caused a dose-dependent decrease of NR current with ED(50) close to 0.03 mg/ml in CGC and a similar inhibition (80% with 1mg/ml) in HEK cells, while Searsia glauca was much less effective. The inhibition was dependent on time of incubation and slightly favored by opening of the NR channel. It was hardly reversible during the recording time, but was not caused by accelerated run-down or by interaction with the modulatory redox site. Searsia pyroides ethanol extract also depressed the NMDA stimulated increase in intracellular Ca. CONCLUSIONS: The data confirm the specificity of Searsia dentata and Searsia pyroides and justify their use in traditional medicine. These plants may combine one or more γ-aminobutyric acid (GABA)(A) agonists with one or more NMDA antagonists, thus representing an efficient treatment for epilepsy.

Neuroprotective effect of Alpinia oxyphylla Miq. fruits against glutamate-induced apoptosis in cortical neurons.

The protective effect of ethanol extract from the fruits of Alpinia oxyphylla on glutamate-induced neuronal apoptosis was examined in primary cultured mouse cortical neurons. After exposure of cortical neurons to 30 microM glutamate for 24 h, cortical neurons exhibited remarkable apoptotic-like death as evidenced by multi-indices including morphological features, cell viability assay, DNA fragmentation on agarose gel and flow cytometric analysis. Co-treatment of the neurons with A. oxyphylla fruits extract (AFEx) (80-200 microg/ml) in the presence of glutamate significantly elevated cell viability, reduced the number of apoptotic cells and decreased the intensity of glutamate-induced DNA fragmentation. These results suggest the neuroprotective potential of A. oxyphylla fruits against glutamate-induced neuronal apoptosis.

N-methyl-D-aspartate receptor antagonist activity in traditional Chinese stroke medicines.

Traditional Chinese medicine (TCM) has a long history in stroke therapy and its therapeutic efficacy has been confirmed by clinical studies. The molecular basis of the neuroprotective effects is unknown. We wondered whether or not the neuroprotective effect of TCMs might be due to their N-methyl-D-aspartate (NMDA) receptor (NMDAR) antagonist properties. We used the patch-clamp technique to screen 22 TCM stroke drugs for NMDAR antagonist activity in cultured cortical neurons. The drugs were also screened for their ability to abate NMDA-induced neurotoxicity. Aqueous extracts of Scutellaria baicalensis, Stephania tetrandra, and Salvia miltiorrhiza blocked currents induced by NMDA (200 microM, 10 microM glycine, 0 Mg2+) at a holding potential of -80 mV by 83.45+/-4.34, 38.65+/-7.50, and 52.97+/-1.78%, respectively. The block of the NMDA-evoked currents was voltage-dependent and showed a negative slope conductance reminiscent of Mg2+. Atomic absorption spectrophotometry revealed the presence of 12.5, 2, and 8.7 mM Mg2+ in the extracts of S. baicalensis,S. tetrandra, and S. miltiorrhiza, respectively. None of these extracts blocked NMDA-induced neuronal death. The Uncaria rhynchophylla extract blocked NMDA-evoked currents by 54.98+/-8.61% even at +60 mV and reduced NMDA-induced neuronal death by 59.13+/-3.52%. NMDAR antagonist activity may underlie the neuroprotective effects of this TCM. Some TCM drugs may exert therapeutic effects due to their Mg2+ content.