Neuroprotection Against MPP+-Induced Cytotoxicity Through the Activation of PI3-K/Akt/GSK3β/MEF2D Signaling Pathway by Rhynchophylline, the Major Tetracyclic Oxindole Alkaloid Isolated From Uncaria rhynchophylla

Rhynchophylline is a major tetracyclic oxindole alkaloid in Uncaria rhynchophylla, which has been extensively used as traditional herb medicine for the prevention of convulsions and hypertension. However, there is still little evidence about the neuroprotective effects of rhynchophylline for Parkinson’s disease (PD), a neurodegenerative condition currently without any effective cure. In this present study, the neuroprotective molecular mechanisms of rhynchophylline were investigated in a cellular model associated with PD. It is shown that rhynchophylline (10–50 μM) greatly prevented neurotoxicity caused by 1-methyl-4-phenylpyridinium ion (MPP+) in primary cerebellar granule neurons, as evidenced by the promotion of cell viability as well as the reversal of dysregulated protein expression of Bax/Bcl-2 ratio. Very encouragingly, we found that rhynchophylline markedly enhanced the activity of the transcription factor myocyte enhancer factor 2D (MEF2D) at both basal and pathological conditions using luciferase reporter gene assay, and reversed the inhibition of MEF2D caused by MPP+. Additionally, pharmacological inhibition of PI3-Kinase or short hairpin RNA-mediated gene down-regulation of MEF2D abrogated the protection provided by rhynchophylline. Furthermore, Western blot analysis revealed that rhynchophylline could potentiate PI3-K/Akt to attenuate GSK3β (the MEF2D inhibitor) in response to MPP+ insult. In conclusion, rhynchophylline inhibits MPP+-triggered neurotoxicity by stimulating MEF2D via activating PI3-K/Akt/GSK3β cascade. Rhynchophylline is served as a novel MEF2D enhancer and might be a potential candidate for further preclinical study in the prevention of PD

A Novel Tetramethylpyrazine Derivative Prophylactically Protects against Glutamate-Induced Excitotoxicity in Primary Neurons through the Blockage of N-Methyl-D-aspartate Receptor

The over-activation of NMDA receptor via the excessive glutamate is believed to one of the most causal factors associated with Alzheimer’s disease (AD), a progressive neurodegenerative brain disorder. Molecules that could protect against glutamate-induced neurotoxicity may hold therapeutic values for treating AD. Herein, the neuroprotective mechanisms of dimeric DT-010, a novel derivative of naturally occurring danshensu and tetramethylpyrazine, were investigated using primary rat cerebellar granule neurons (CGNs) and hippocampal neurons. It was found that DT-010 (3–30 μM) markedly prevented excitotoxicity of CGNs caused by glutamate, as evidenced by the promotion of neuronal viability as well as the reversal of abnormal morphological changes. While its parent molecules did not show any protective effects even when their concentration reached 50 μM. Additionally, DT-010 almost fully blocked intracellular accumulation of reactive oxygen species caused by glutamate and exogenous oxidative stimulus. Moreover, Western blot results demonstrated that DT-010 remarkably attenuated the inhibition of pro-survival PI3K/Akt/GSK3β pathway caused by glutamate. Ca2+ imaging with Fluo-4 fluorescence analysis further revealed that DT-010 greatly declined glutamate-induced increase in intracellular Ca2+. Most importantly, with the use of whole-cell patch clamp electrophysiology, DT-010 directly inhibited NMDA-activated whole-cell currents in primary hippocampal neurons. Molecular docking simulation analysis further revealed a possible binding mode that inhibited NMDA receptor at the ion channel, showing that DT-010 favorably binds to Asn602 of NMDA receptor via arene hydrogen bond. These results suggest that DT-010 could be served as a novel NMDA receptor antagonist and protect against glutamate-induced excitotoxicity from blocking the upstream NMDA receptors to the subsequent Ca2+ influx and to the downstream GSK3β cascade

Synergistic Inhibition on Acetylcholinesterase by the Combination of Berberine and Palmatine Originally Isolated from Chinese Medicinal Herbs

Alzheimer's disease is a multi-factorial neurodegenerative disorder devastatingly affecting the aged population worldwide. Previous studies have shown that medicinal herbs used in traditional Chinese medicine might be benefit to Alzheimer's disease patients. Berberine and palmatine, two isoquinoline alkaloids found in several medicinal herbs, were used for memory enhancement in China. In this study, the inhibitory effects of combined berberine and palmatine on acetylcholinesteras were evaluated using recombinant human acetylcholinesterase. Our results showed that the combination of berberine and palmatine inhibited acetylcholinesterase in a mixed competitive pattern. By the median-effect principle, the calculated combination index of the combination was less than 1, suggesting that berberine and plamatine inhibited acetylcholinesterase synergistically. Furthermore, the drug-reducing index of berberine and palmatine were 2.98 and 2.66, respectively. Taken together, the results showed that the combination of the two alkaloids might potentially be developed as a more effective therapeutic strategy for Alzheimer's disease patients

Preventing H(2)O(2)-induced apoptosis in cerebellar granule neurons by regulating the VEGFR-2/Akt signaling pathway using a novel dimeric antiacetylcholinesterase bis(12)-hupyridone

Oxidative stress-induced apoptosis plays a critical role in the pathogenesis of various neurodegenerative disorders. In this study, the neuroprotective properties of bis(12)-hupyridone (B12H), a novel dimeric acetylcholinesterase (AChE) inhibitor modified from a naturally occurring monomeric analogue, huperzine A, on H(2)O(2)-induced neurotoxicity were investigated in cerebellar granule neurons (CGNs). Exposure of CGNs to H(2)O(2) resulted in apoptosis which could be attenuated by the pre-treatment of B12H (0.3-5 nM) in a concentration-dependent manner. Moreover, tacrine and neostigmine failed to prevent neurotoxicity, indicating that the neuroprotection of B12H might not be due to its inhibitory property of AChE enzymatic activity. Increased activation of extracellular signal-regulated kinase (ERK) and decreased activation of glycogen synthase kinase (GSK) 3 beta, were observed after H(2)O(2) exposure, and B12H reversed the altered activation of GSK3 beta, but not that of ERK. Furthermore, using vascular endothelial growth factor (VEGF), phospho-VEGF receptor-2 (VEGFR-2) antibody, a specific VEGFR-2 inhibitor (PTK787/ZK222584) and specific phosphoinositide 3-kinase inhibitors (LY294002 and wortmannin), it was found that VEGF prevented H(2)O(2)-induced neuronal loss from activating the VEGF/VEGFR-2 system and that the observed B12H neuroprotective effects might share the same signaling pathway. These findings strongly suggest that B12H prevents H(2)O(2)-induced neuronal apoptosis independent of inhibiting AChE, but through regulating VEGFR-2/Akt/GSK3 beta signaling pathway. (C) 2011 Elsevier B.V. All rights reserved

Bis(12)-hupyridone, a novel acetylcholinesterase inhibitor, protects against glutamate-induced neuronal excitotoxicity via activating alpha 7 nicotinic acetylcholine receptor/phosphoinositide 3-kinase/Akt cascade

Bis(12)-hupyridone (B12H), derived from the Chinese medicinal component huperzine A, was originally designed as a novel acetylcholinesterase (AChE) inhibitor. In this paper, we report that B12H (24-h pretreatment) effectively blocked glutamate-induced neuronal excitotoxicity in cerebellar granule neurons (CGNs). However, the huge discrepancy between the EC50 value and IC50 value of B12H, to protect against neuronal toxicity (0.09 mu M) and to block the NMDA receptor (21.8 mu M) respectively, suggests that the neuroprotection of B12H might be not primarily due to the blockade of the NMDA receptor. Pretreatment by specific antagonists of alpha7-nicotinic acetylcholine receptor (alpha 7nAChR), but not muscarinic acetylcholine receptor (mAChR) or alpha 4 beta 2nAChR, decreased the neuroprotection of B12H. The neuroprotection of B12H could also be abolished by the pretreatment of specific PI3-K inhibitors. Furthermore, B12H restored the suppressed activation of the Akt pathway caused by glutamate as evidenced by the decreased expressions of pSer473-Akt and pSer9-GSK3 beta. All these results suggest that B12H substantially protected CGNs against glutamate-induced neuronal excitotoxicity via activating alpha 7nAChR/PI3-K/Akt cascade. (C) 2012 Elsevier Ireland Ltd. All rights reserved

SU5416 prevents MPP⁺-induced apoptosis in a concentration-dependent manner.

<p>(A) SU5416, but not VRI, prevented MPP⁺-induced cell death in a concentration-dependent manner. CGNs were treated with SU5416, VRI, EPTU, 7-nitroindazole (7-NI), 1400 W or DMSO (vehicle control) at the indicated concentrations for 2 hours and then exposed to 35 µM MPP⁺. Cell viability was measured by MTT assay at 24 hours after MPP⁺ challenge. (B) SU5416 blocked neuronal loss induced by MPP⁺. CGNs were pre-incubated with or without 20 µM SU5416 and exposed to 35 µM MPP⁺2 hours later. At 24 hour after MPP⁺ challenge, CGNs were assayed with FDA/PI double staining. (C) SU5416 reversed the morphological alteration induced by MPP⁺. CGNs were pre-incubated with or without 20 µM SU5416 and exposed to 35 µM MPP⁺2 hours later. At 24 hour after MPP⁺ challenge, CGNs were assayed with nNOS and Hoechst double staining. (D) The number of apoptotic nuclei with condensed chromatin was counted from representative Hoechst staining photomicrographs and represented as a percentage of the total number of nuclei counted. Data, expressed as percentage of control, were the mean ± SEM of three separate experiments; *<i>p</i><0.05 and **<i>p</i><0.01 <i>versus</i> MPP⁺ group in (A) or <i>versus</i> control in (D); ^##<i>p</i><0.01 <i>versus</i> MPP⁺ group in (D) (Turkey’s test).</p

SU5416 reduces the expression of nNOS protein elevated by MPP+ in CGNs.

<p>(A) CGNs were pre-treated with 20 µM SU5416 or DMSO (vehicle control) for 2 hours, and then treated with 35 µM MPP⁺ for various durations as indicated. The total proteins were extracted for Western blot analysis with specific iNOS, nNOS and β-actin antibodies. (B) Statistical analysis of nNOS expression in each treatment group. Data are expressed as the ratio to OD values of the corresponding controls. Data, expressed as percentage of control, were the mean ± SEM of five separate experiments; *<i>p</i><0.05 <i>versus</i> MPP⁺ group at the same time (Turkey’s test).</p

SU5416 increases the number of dopaminergic neurons in MPTP-treated zebrafish larval.

<p>One dpf zebrafish embryos were co-incubated with 200 µM MPTP and 1 µM SU5416 or 0.3% DMSO (vehicle control) for 2 days. After treatment, zebrafish were collected to perform paraffin-embedding, sectioning and immunostaining. (A) Representative picture of immunostaining of zebrafish section. (B) Statistical analysis of the number of TH-positive neurons in each treatment group (n = 12 fish/group). *<i>p</i><0.05 <i>versus</i> MPTP group (Turkey’s test).</p