Neurotoxicity In Rat Cortical Neurons Research Articles

Chitosan Oligosaccharides Inhibit/Disaggregate Fibrils and Attenuate Amyloid β-Mediated Neurotoxicity.

Alzheimer’s disease (AD) is characterized by a large number of amyloid-β (Aβ) deposits in the brain. Therefore, inhibiting Aβ aggregation or destabilizing preformed aggregates could be a promising therapeutic target for halting/slowing the progression of AD. Chitosan oligosaccharides (COS) have previously been reported to exhibit antioxidant and neuroprotective effects. Recent study shows that COS could markedly decrease oligomeric Aβ-induced neurotoxicity and oxidative stress in rat hippocampal neurons. However, the potential mechanism that COS reduce Aβ-mediated neurotoxicity remains unclear. In the present study, our findings from circular dichroism spectroscopy, transmission electron microscope and thioflavin T fluorescence assay suggested that COS act as an inhibitor of Aβ aggregation and this effect shows dose-dependency. Moreover, data from thioflavin T assay indicated that COS could significantly inhibit fibrils formation and disrupt preformed fibrils in a dose-dependent manner. Furthermore, the addition of COS attenuated Aβ1-42-induced neurotoxicity in rat cortical neurons. Taken together, our results demonstrated for the first time that COS could inhibit Aβ1-42 fibrils formation and disaggregate preformed fibrils, suggesting that COS may have anti-Aβ fibrillogenesis and fibril-destabilizing properties. These findings highlight the potential role of COS as novel therapeutic agents for the prevention and treatment of AD.

Telomerase activity-independent function of telomerase reverse transcriptase is involved in acrylamide-induced neuron damage

Polyacrylamide is used widely in industry, and its decomposition product, acrylamide (ACR), readily finds its way into commonly consumed cosmetics and baked and fried foods. ACR exerts potent neurotoxic effects in human and animal models. Telomerase reverse transcriptase (TERT), the catalytic subunit of telomerase, traditionally has been considered to play an important role in maintaining telomere length. Emerging evidence has shown, however, that TERT plays an important role in neuroprotection by inhibiting apoptosis and excitotoxicity, and by promoting angiogenesis, neuronal survival and neurogenesis, which are closely related to the telomere-independent functions of TERT. We investigated whether and how the TERT pathway is involved in ACR induced neurotoxicity in rat cortical neurons. We found that ACR 1) significantly reduced the viability of cortical neurons as measured by MTT assay, 2) induced neuron apoptosis as revealed by FITC-conjugated Annexin V/PI double staining and flow cytometry (FACS) analysis, 3) elevated expression of cleaved caspase-3, and 4) decreased bcl-2 expression of cortical neurons. ACR also increased intracellular ROS levels in cortical neurons, increased MDA levels and reduced GSH, SOD and GSH-Px levels in mitochondria in a dose-dependent manner. We found that TERT expression in mitochondria was increased by ACR at concentrations of 2.5 and 5.0 mM, but TERT expression was decreased by 10 mM ACR. Telomerase activity, however, was undetectable in rat cortical neurons. Our results suggest that the TERT pathway is involved in ACR induced apoptosis of cortical neurons. TERT also may exert its neuroprotective role in a telomerase activity-independent way, especially in mitochondria.

The Protective Effects of Jatrorrhizine on β-Amyloid (25-35)-Induced Neurotoxicity in Rat Cortical Neurons

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by selective neuronal loss, amyloid plaques and neurofibrillary tangles. Oxidative stress may play an important role in the pathogenesis of AD which is associated with the accumulation of β-amyloid (Aβ). Jatrorrhizine (JAT) is a novel tetrahydroisoquinoline alkaloid originally extracted from the Chinese herb coptidis rhizome. Our previous studies showed that JAT protected neuronallike cells against H₂O₂ -induced toxicity. In this study, we investigated the protective effects of JAT against Aβ₂₅₋₃₅- induced cell death in rat cortical neurons. When the cortical neurons were exposed to 25 μM Aβ₂₅₋₃₅ for 24h, there was a significant reduction in cell viability and activities of SOD and GSH-Px. It also increased the production of malondialdehyde (MDA) and ROS but reduced MMP. Pretreatment of the cortical neurons with various concentrations of JAT (1-10 μM) attenuated Aβ₂₅₋₃₅-induced neurotoxicity markedly. JAT was also showed to suppress the activation of caspase-3 induced by Aβ₂₅₋₃₅ and prevented the cytochrome c transporting into the cytosol. These results indicate that JAT demonstrates the neuroprotective effects against Aβ₂₅₋₃₅-induced injury via its antioxidative potential, which may provide a therapeutical potential to AD.

Coenzyme Q10 protects against amyloid beta-induced neuronal cell death by inhibiting oxidative stress and activating the P13K pathway

Oxidative stress plays critical roles in the pathogenic mechanisms of several neurodegenerative disorders including Alzheimer's disease (AD), thus much research effort has focused on antioxidants as potential treatment agents for AD. Coenzyme Q10 (CoQ10) is known to have powerful antioxidant effects. We investigated the neuroprotective effects of CoQ10 against Amyloid beta25–35 (Aβ25–35)-induced neurotoxicity in rat cortical neurons. To evaluate the neuroprotective effects of CoQ10 on Aβ25–35-injured neurons, primary cultured cortical neurons were treated with several concentrations of CoQ10 and/or Aβ25–35 for 48h. CoQ10 protected neuronal cells against Aβ25–35-induced neurotoxicity in a concentration-dependent manner. These neuroprotective effects of CoQ10 were blocked by LY294002 (10μM), a phosphatidylinositol 3-kinase (PI3K) inhibitor. Aβ25–35 concentration-dependent increased free radical levels in rat cortical neurons, while combined treatment with CoQ10 reduced these free radical levels in a dose-dependent manner. Meanwhile, CoQ10 treatment of Aβ25–35-injured primary cultured cortical neurons increased the expression levels of p85aPI3K, phosphorylated Akt, phosphorylated glycogen synthase kinase-3β, and heat shock transcription factor, which are proteins related to neuronal cell survival, and decreased the levels of cytosolic cytochrome c and cleaved caspase-3, which are associated with neuronal cell death. Together, these results suggest that the neuroprotective effects of CoQ10 on Aβ25–35 neurotoxicity are mediated by inhibition of oxidative stress together with activation of the PI3-K/Akt pathway.

The Protective Effect of Rho-Associated Kinase Inhibitor on Aluminum-Induced Neurotoxicity in Rat Cortical Neurons

Aluminum (Al) is a neurotoxicant and is implicated in several neurodegenerative diseases, including Alzheimer's disease (AD). In AD brains, one of the pathological hallmarks is the extracellular deposition of senile plaques, which are mainly composed of aggregated amyloid-beta (Abeta). Endoproteolysis of the amyloid-beta precursor protein (AbetaPP) by the beta-secretase and the gamma-secretase generates Abeta. AbetaPP can also be cleaved by the alpha-secretase within the Abeta region, which releases a soluble fragment sAPPalpha and precludes the formation of Abeta. Al has been reported to increase the level of Abeta, promote Abeta aggregation, and increase Abeta neurotoxicity. In contrast, small G protein Rho and its effector, Rho-associated kinase (ROCK), are known to negatively regulate the amount of Abeta. Inhibition of the Rho-ROCK pathway may underlie the ability of nonsteroidal anti-inflammatory drugs and statins to reduce Abeta production. Whether the Rho-ROCK pathway is involved in Al-induced elevation and aggregation of Abeta is unknown. In the present study, cultured rat cortical neurons were treated with Al(malt)(3) in the absence or presence of ROCK inhibitor Y-27632. After the treatment of Al(malt)(3), the cell viability and the level of sAPPalpha were reduced, whereas the amyloid fibrils in the conditioned media were increased. Treatment with Y-27632 prevented these adverse effects of Al(malt)(3) and thus maintained neuronal survival. These results reveal that the activation of the Rho-ROCK signaling pathway was involved in Al-induced effects in terms of the cell viability, the production of sAPPalpha, and the formation of amyloid fibril, which provides a novel mechanism underlying Al-induced neurotoxicity.

Neuroprotective effects of donepezil through inhibition of GSK‐3 activity in amyloid‐β‐induced neuronal cell death

Acetylcholinesterase inhibitors (AChE-inhibitors) are used for the treatment of Alzheimer's disease. Recently, the AChE-inhibitor donepezil was found to have neuroprotective effects. However, the protective mechanisms of donepezil have not yet been clearly identified. We investigated the neuroprotective effects of donepezil and other AChE-inhibitors against amyloid-beta1-42 (Abeta42)-induced neurotoxicity in rat cortical neurons. To evaluate the neuroprotective effects of AChE-inhibitors, primary cultured cortical neurons were pre-treated with several concentrations of AChE-inhibitors for 24 h and then treated with 20 microM Abeta42 for 6 h. In addition to donepezil, other AChE-inhibitors (galantamine and huperizine A) also showed increased neuronal cell viability against Abeta42 toxicity in a concentration-dependent manner. However, we demonstrated that donepezil has a more potent effect in inhibiting glycogen synthase kinase-3 (GSK-3) activity compared with other AChE-inhibitors. The neuroprotective effects of donepezil were blocked by LY294002 (10 microM), a phosphoinositide 3 kinase inhibitor, but only partially by mecamylamine (10 microM), a blocker of nicotinic acetylcholine receptors. Additionally, donepezil's neuroprotective mechanism was related to the enhanced phosphorylation of Akt and GSK-3beta and reduced phosphorylation of tau and glycogen synthase. These results suggest that donepezil prevents Abeta42-induced neurotoxicity through the activation of phosphoinositide 3 kinase/Akt and inhibition of GSK-3, as well as through the activation of nicotinic acetylcholine receptors.

Mechanisms of Neuroprotective Effects of Therapeutic Acetylcholinesterase Inhibitors Used in Treatment of Alzheimer′s Disease

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Mechanisms of Neuroprotective Effects of Therapeutic Acetylcholinesterase Inhibitors Used in Treatment of Alzheimer's Disease

Donepezil, galanthamine, and tacrine are therapeutic acetylcholinesterase (AChE) inhibitors used for the treatment of Alzheimer's disease. The aim of this paper is to review recent findings on their neuroprotective properties and the mechanisms of neuroprotection against glutamate neurotoxicity in rat cortical neurons. First, the hallmark of neurotoxicity induced by two different glutamate treatment conditions was examined, revealing that acute glutamate treatment (1 mM, 10 min) induces necrotic neuronal death and that moderate glutamate treatment (100 microM, 24 hr) induces apoptotic neuronal death. Next, we showed that therapeutic AChE inhibitors protect cortical neurons from glutamate neurotoxicity in a time- and concentration-dependent manner. We examined the mechanism of this neuroprotective effect and found that the neuroprotective effects against both acute and moderate glutamate treatments are mediated through nicotinic acetylcholine receptors (nAChRs), or more specifically, the effects of donepezil and galanthamine are mediated through alpha4- and alpha7-nAChR. We also showed that donepezil and galanthamine protect cortical neurons against acute glutamate treatment-induced neurotoxicity at steps before, and that tacrine protects at steps after, nitric oxide radical formation. On the other hand, the neuroprotective effects of donepezil and galanthamine, but not of tacrine, against neurotoxicity induced by moderate glutamate treatment were mediated through the phosphatidylinositol 3-kinase-Akt pathway. These findings unveiled the hitherto unknown neuroprotective effects of therapeutic AChE inhibitors and provided valuable insights into its neuroprotective mechanisms. They may very likely form the basis for a novel treatment strategy against Alzheimer's disease.

Molecular mechanisms of cannabinoid-induced neurotoxicity in rat cortical neurons

Molecular mechanisms of cannabinoid-induced neurotoxicity in rat cortical neurons

Stepholidine protects against H 2O 2 neurotoxicity in rat cortical neurons by activation of Akt

The fundamental pathological process(es) associated with schizophrenia (SZ) remain(s) uncertain, but multiple lines of evidence suggest that this condition is associated with excessive stimulation of striatal dopamine (DA) D 2 receptors, deficient stimulation of medial prefrontal cortex (mPFC) D 1 receptors as well as neuronal apoptosis. Unlike typical antipsychotics, stepholidine (SPD), which is isolated from the Chinese herb stephania, has D 1 and D 2 dual properties and regulates neuronal cell differentiation and proliferation. It is unknown, however, whether it possesses a neuroprotective property. Here, we report that SPD prevented neuronal cell death from H 2O 2 exposure and increased the levels of phosphorylated Akt (pAkt), a serine/threonine protein kinase. The SPD-induced neuroprotection and activation of Akt were blocked by LY294002, a PI3-K inhibitor, suggesting that the anti-apoptotic action of SPD is mediated via the PI3-K/Akt signaling pathway. Thus, as a survival or anti-apoptotic factor for neuronal cells, SPD may contribute to the therapeutic action of SPD in SZ treatment.

Effect of Etomidate on N-methyl-D-aspartate Induced Neurotoxicity in Rat Cortical Neurons

Background: The present investigation was undertaken to evaluate the neuroprotective effect of etomidate against N-methyl-Daspartate (NMDA) induced neurotoxicity in rat cortical neurons by measuring lactate dehydrogenase (LDH). Methods: The cerebral cortical neurons of fetal rat were grown for 12 days in dissociated cell culture. They were divided into four groups: first group acted as control with no drug administration and other groups treated with either NMDA 100 or Etomidate (ET) 10 + NMDA 100 or ET 100 + NMDA 100. After 24 hrs, cell death was assessed by morphology under the light microscope and quantified by measuring the LDH in the culture media. Results: In the light microscopic findings, the intact cortical neurons were increased in the ET groups. NMDA-induced LDH production also significantly suppressed in ET group (P ＜ 0.05). There were no significant difference between the ET 10 and 100 groups. Conclusions: These results suggest that the etomidate has protective effect on the cultured rat cortical neurons against NMDA-induced neurotoxicity.

Nicotinic acetylcholine receptor-mediated neuroprotection by donepezil against glutamate neurotoxicity in rat cortical neurons.

Donepezil is a potent and selective acetylcholinesterase (AChE) inhibitor developed for the treatment of Alzheimer's disease. To elucidate whether donepezil shows neuroprotective action in addition to amelioration of cognitive deficits, we examined the effects of donepezil on glutamate-induced neurotoxicity using primary cultures of rat cortical neurons. A 10-min exposure of cultures to glutamate followed by a 1-h incubation with glutamate-free medium caused a marked loss of viability, as determined by Trypan blue exclusion. Glutamate neurotoxicity was prevented by 24-h pretreatment of donepezil in a concentration-dependent manner. Among AChE inhibitors examined, donepezil and certain AChE inhibitors such as tacrine and galanthamine showed potent neuroprotective action, although physostigmine did not affect glutamate neurotoxicity. Neuroprotective action of donepezil was antagonized by mecamylamine, a nicotinic acetylcholine receptor (nAChR) antagonist, but not by scopolamine, a muscarinic acetylcholine receptor antagonist. Furthermore, both dihydro-beta-erythroidine, an alpha4beta2-neuronal nAChR antagonist, and methyllycaconitine, an alpha7-nAChR antagonist, each also significantly antagonized the effect of donepezil. Next, we examined the effects of donepezil on glutamate-induced apoptosis. Exposure of 100 microM glutamate to cortical neurons for 24 h induced apoptotic neuronal death and nuclear fragmentation. Donepezil for 24 h before and 24 h during glutamate exposure prevented nuclear fragmentation and glutamate-induced apoptosis. These results suggest that donepezil not only protects cortical neurons against glutamate neurotoxicity via alpha4beta2- and alpha7-nAChRs but also prevents apoptotic neuronal death.

Serum-dependence of LPS-induced neurotoxicity in rat cortical neurons.

Previous studies have shown that the bacterial endotoxin, lipopolysaccharide (LPS), is neurotoxic both in vitro and in vivo. The rate of binding of LPS to a target cell is greatly enhanced by serum in general and by LPS binding protein (LBP) in particular. The purpose of the study described in this paper was to determine if microglia activation and LPS-induced neurotoxicity is serum or LBP dependent. A murine microglial cell line, BV2, was used to assess the serum dependence of nitric oxide production and tumor necrosis factor a release in microglia. Embryonic rat cortical neuron/glia mixed cultures were used to determine the serum dependence of LPS-induced neurotoxicity. Our results from both cell culture systems show that LPS-induced inflammatory responses are serum dependent at lower doses of LPS and progressively become serum independent above 10 ng/ml. Purified human recombinant LBP reconstitutes the lost LPS-induced inflammatory responses in primary and immortalized cell cultures treated with heat-denatured serum and appears to account for the serum dependence. These data suggest that the cell surface signaling receptor for LPS at the low and high concentrations are likely to differ, consistent with the existence of a variety of LPS receptors.