PI3K-ERK1/2 activation contributes to extracellular H2O2 generation in amyloid β toxicity

A Ru3+-functionalized-NMOF nanozyme as an inhibitor and disaggregator of β-amyloid aggregates

Alzheimer's disease (AD) heavily impacts human lives and is becoming serious as societies age. Inhibiting and disaggregating β-amyloid aggregates is a possible solution for AD therapy. In this study, a novel type of nanozyme based on Ru3+-chelated nanoscale metal organic frameworks (Ru3+-NMOFs), displaying strong peroxidase-like activity, was proposed as an inhibitor and disaggregator of β-amyloid aggregates. As a high concentration of hydrogen peroxide is present at the sites of β-amyloid aggregates, Ru3+-NMOFs could catalyze the conversion of hydrogen peroxide to hydroxyl radicals. Thus, these hydroxyl radicals would attack the β-amyloid chain, oxidizing it to enhance its hydrophilicity, which results in a decreased hydrophobic interaction and reduced degree of aggregation. Ru3+-NMOFs could effectively inhibit as well as disaggregate β-amyloid fibrils both in vitro and in vivo. Additionally, the reduction of the β-amyloid aggregates and the attenuation of reactive oxygen species transfer led to lower levels of inflammatory factors, which could be beneficial in alleviating AD symptoms. In a typical treatment, Ru3+-NMOFs could mitigate the paralysis of C. elegans CL2120 and elevate survival rates. This study opens a new avenue for MOF-based nanozymes as potential treatment agents for AD therapy.

Upregulation of NADPH-oxidase, inducible nitric oxide synthase and apoptosis in the hippocampus following impaired insulin signaling in the rats: Development of sporadic Alzheimer's disease

NADPH-oxidase (NOX) is a multi-subunit enzyme complex. The upregulation of NOX causes massive production of superoxide (O2¯), which avidly reacts with nitric oxide (NO) and increases cellular reactive oxygen/nitrogen species (ROS/RNS). Increased ROS/RNS plays pivotal role in the sporadic Alzheimer's disease (sAD) development and brain damage following impaired insulin signaling. Hence, this study aimed to examine early-time course of changes in NOX and NOS expression, and apoptotic proteins in the rats hippocampi following insulin signaling impairment [induced by STZ injection; intraperitoneal (IP) or in cerebral ventricles (ICV)]. Early effects (1, 3, or 6 weeks) on the NOX activity, translocation of NOX subunits from cytosol to the membrane, NO-synthases [neuronal-, inducible- and endothelial-NOS; nNOS, iNOS and eNOS], The Rac-1 protein expression, levels of NO and O2¯, cytochrome c release, caspase-3 and 9 activations (cleavage) were studied. STZ injection (in both models) increased NOX activity, O2¯ production, and enhanced cytosolic subunits translocation into membrane. The iNOS but not nNOS and eNOS expression and NO levels were increased in STZ treated rats. Finally, STZ injection increased cytochrome c release, caspase-3 and 9 activations in a manner that was significantly associated with levels of O2¯ and NO in the hippocampus. ICV-STZ administration resulted in significant profound changes over the IP route. In conclusion, impairment in insulin function induces early changes in ROS/RNS contents through NOX and iNOS upregulation and neuronal apoptosis in the hippocampus. Our results could mechanistically explain the role of impaired insulin function in the development of sAD.

Streptozotocin Induces Alzheimer's Disease-Like Pathology in Hippocampal Neuronal Cells via CDK5/Drp1-Mediated Mitochondrial Fragmentation

Aberrant brain insulin signaling plays a critical role in the pathology of Alzheimer’s disease (AD). Mitochondrial dysfunction plays a role in the progression of AD, with excessive mitochondrial fission in the hippocampus being one of the pathological mechanisms of AD. However, the molecular mechanisms underlying the progression of AD and mitochondrial fragmentation induced by aberrant brain insulin signaling in the hippocampal neurons are poorly understood. Therefore, we investigated the molecular mechanistic signaling associated with mitochondrial dynamics using streptozotocin (STZ), a diabetogenic compound, in the hippocampus cell line, HT-22 cells. In this metabolic dysfunctional cellular model, hallmarks of AD such as neuronal apoptosis, synaptic loss, and tau hyper-phosphorylation are induced by STZ. We found that in the mitochondrial fission protein Drp1, phosphorylation is increased in STZ-treated HT-22 cells. We also determined that inhibition of mitochondrial fragmentation suppresses STZ-induced AD-like pathology. Furthermore, we found that phosphorylation of Drp1 was induced by CDK5, and inhibition of CDK5 suppresses STZ-induced mitochondrial fragmentation and AD-like pathology. Therefore, these findings indicate that mitochondrial morphology and functional regulation may be a strategy of potential therapeutic for treating abnormal metabolic functions associated with the pathogenesis of AD.

Pelargonidin exhibits restoring effects against amyloid β-induced deficits in the hippocampus of male rats

Background: Alzheimer's disease (AD) is characterized by amyloid-beta plaques, neuronal loss, and cognitive dysfunction. Oxidative stress plays a key role in the pathophysiology of AD, and it has been suggested that antioxidants may slow the progress of the disease. In this study, the possible protective effects of pelargonidin (a natural flavonoid) against amyloid β (Aβ)-induced behavioral deficits was investigated in rats.

Methods: Adult Wistar male rats were treated with intrahippocampal injections of the Aβ (aa 25-35) and intraperitoneal injection of pelargonidin. Learning and spatial memory were tested using the Morris water maze (MWM) task. The antioxidant activity was evaluated using the ferric reducing/antioxidant power assay (FRAP assay). Data were analyzed using SPSS 20, and value of p≤0.05 was considered significant.

Results: The results of this study showed that Aβ significantly increased escape latency and the distance traveled in the MWM, and pelargonidin attenuated these behavioral changes. Aβ induced a significant decrease in the total thiol content of hippocampus, and pelargonidin restored the hippocampal antioxidant capacity.

Conclusion: The results of this study suggest that pelargonidin can improve Aβ-induced behavioral changes in rats.

Autophagy-ERK1/2-Involved Disinhibition of Hippocampal Neurons Contributes to the Pre-Synaptic Toxicity Induced by Aβ42 Exposure

Alzheimer's disease (AD) is a progressive neurodegenerative disease and the most frequent cause of progressive cognitive decline in the elderly population. To date, there is still no effective treatment for AD, requiring more underlying mechanisms. In the present study, we investigated the effects of Aβ42 on the inhibitory synaptic transmission in the cultured hippocampal neurons, and explored the possible mechanism. The frequency, but not amplitude, of miniature inhibitory post-synaptic currents was significantly suppressed by Aβ42, indicating that Aβ42 played its role in inhibitory transmitter release at the pre-synaptic sites. Aβ42 had no effect on miniature excitatory post-synaptic currents, suggesting GABAergic synapses are more susceptible to Aβ42 exposure. However, the number of GABAergic neurons or synapses was not influenced, suggesting the corresponding stage may be a preclinical one. The effect of Aβ42 can be mimicked by PD98059 (an inhibitor of ERK1/2) and blocked by curcumin (an activator of MEK), which reveals Aβ-involved influence is via the decreased phosphorylation of MAPK-ERK1/2. In addition, synaptophysin is confirmed to be a downstream protein of MAPK-ERK1/2 at the pre-synaptic site. At the same time, suppressed autophagy was observed after Aβ42 exposure, and the activation of autophagy increased pERK1/2 level and salvaged the disinhibition of hippocampal neurons. These data suggest that diminished GABAergic tone likely starts from the preclinical stage of AD, so some GABAergic stress test may be effective for identifying cognitively normal elder adults. Strategies against the dysfunction of autophagy should be adopted in the early stage of AD because of its initial effects.

Antioxidant activity against H2O2-induced cytotoxicity of the ethanol extract and compounds from Pyrola decorate leaves

CONTEXT

The leaves of Pyrola decorate H. Andr (Pyrolaceae), known as Luxiancao, have long been used for treating kidney deficiency, gastric haemorrhage and rheumatic arthritic diseases in traditional Chinese medicine.

OBJECTIVE

The phytochemicals and antioxidant capacities in vitro of P. decorate leaves were investigated.

MATERIALS AND METHODS

Ethanol, petroleum ether, acetidin, n-butyl alcohol and aqueous extracts of Pyrola decorate leaves were prepared by solvent sequential process, and then isolated and purified to obtain phytochemicals. Cell viability was measured by MTT assay. PC12 cells were pretreated for 24 h with different extractions of P. decorate leaves at concentrations of 0.1, 0.5, 1, 5 and 10 mg/mL, then H2O2 of 0.4 mM was added in all samples for an additional 2 h. The antioxidant capacities of betulin, ursolic acid and monotropein were determined in PC12 cells against H2O2 induced cytotoxicity in vitro as well.

RESULTS

Nine compounds (1-9) were isolated and structurally determined by spectroscopic methods, especially 2D NMR analyses. Ethanol extract treated groups showed inhibitory activity with IC50 value of 10.83 mg/mL. Betulin, ursolic acid and monotropein were isolated from P. decorate, and demonstrated with IC50 values of 6.88, 6.15 and 6.13 μg/mL, respectively.

DISCUSSION AND CONCLUSIONS

In conclusion, Pyrola decorate is a potential antioxidative natural plant and worth testing for further pharmacological investigation in the treatment of oxidative stress related neurological disease.

Pre-treatment with amitriptyline causes epigenetic up-regulation of neuroprotection-associated genes and has anti-apoptotic effects in mouse neuronal cells

Antidepressants, such as imipramine and fluoxetine, are known to alter gene expression patterns by inducing changes in the epigenetic status of neuronal cells. There is also some evidence for the anti-apoptotic effect of various groups of antidepressants; however, this effect is complicated and cell-type dependent. Antidepressants of the tricyclic group, in particular amitriptyline, have been suggested to be beneficial in the treatment of neurodegenerative disorders. We examined whether amitriptyline exerts an anti-apoptotic effect via epigenetic mechanisms. Using DNA microarray, we analyzed global gene expression in mouse primary cultured neocortical neurons after treatment with amitriptyline and imipramine. The neuroprotection-associated genes, activating transcription factor 3 (Atf3) and heme oxygenase 1 (Hmox1), were up-regulated at both mRNA and protein levels by treatment with amitriptyline. Quantitative chromatin immunoprecipitation assay revealed that amitriptyline increased enrichments of trimethylation of histone H3 lysine 4 in the promoter regions of Atf3 and Hmox1 and acetylation of histone H3 lysine 9 in the promoter regions of Atf3, which indicate an active epigenetic status. Amitriptyline pre-treatment attenuated 1-methyl-4-phenylpyridinium ion (MPP⁺)- or amyloid β peptide 1-42 (Aβ_1-42)-induced neuronal cell death and inhibited the activation of extracellular signal-regulated kinase 1 and 2 (ERK1/2). We found that Atf3 and Hmox1 were also up-regulated after Aβ_1-42 treatment, and were further increased when pre-treated with amitriptyline. Interestingly, the highest up-regulation of Atf3 and Hmox1, at least at mRNA level, was observed after co-treatment with Aβ_1-42 and amitriptyline, together with the loss of the neuroprotective effect. These findings suggest preconditioning and neuroprotective effects of amitriptyline; however, further investigations are needed for clarifying the contribution of epigenetic up-regulation of Atf3 and Hmox1 genes.

An integrative genome-wide transcriptome reveals that candesartan is neuroprotective and a candidate therapeutic for Alzheimer's disease

BACKGROUND

Alzheimer's disease is the most frequent age-related dementia, and is currently without treatment. To identify possible targets for early therapeutic intervention we focused on glutamate excitotoxicity, a major early pathogenic factor, and the effects of candesartan, an angiotensin receptor blocker of neuroprotective efficacy in cell cultures and rodent models of Alzheimer's disease. The overall goal of the study was to determine whether gene analysis of drug effects in a primary neuronal culture correlate with alterations in gene expression in Alzheimer's disease, thus providing further preclinical evidence of beneficial therapeutic effects.

METHODS

Primary neuronal cultures were treated with candesartan at neuroprotective concentrations followed by excitotoxic glutamate amounts. We performed genome-wide expression profile analysis and data evaluation by ingenuity pathway analysis and gene set enrichment analysis, compared with alterations in gene expression from two independent published datasets identified by microarray analysis of postmortem hippocampus from Alzheimer's disease patients. Preferential expression in cerebrovascular endothelial cells or neurons was analyzed by comparison to published gene expression in these cells isolated from human cortex by laser capture microdissection.

RESULTS

Candesartan prevented glutamate upregulation or downregulation of several hundred genes in our cultures. Ingenuity pathway analysis and gene set enrichment analysis revealed that inflammation, cardiovascular disease and diabetes signal transduction pathways and amyloid β metabolism were major components of the neuronal response to glutamate excitotoxicity. Further analysis showed associations of glutamate-induced changes in the expression of several hundred genes, normalized by candesartan, with similar alterations observed in hippocampus from Alzheimer's disease patients. Gene analysis of neurons and cerebrovascular endothelial cells obtained by laser capture microdissection revealed that genes up- and downregulated by glutamate were preferentially expressed in endothelial cells and neurons, respectively.

CONCLUSIONS

Our data may be interpreted as evidence of direct candesartan neuroprotection beyond its effects on blood pressure, revealing common and novel disease mechanisms that may underlie the in vitro gene alterations reported here and glutamate-induced cell injury in Alzheimer's disease. Our observations provide novel evidence for candesartan neuroprotection through early molecular mechanisms of injury in Alzheimer's disease, supporting testing this compound in controlled clinical studies in the early stages of the illness.

Peroxiredoxin 5 prevents amyloid-beta oligomer-induced neuronal cell death by inhibiting ERK-Drp1-mediated mitochondrial fragmentation

Alzheimer's disease (AD), a neurodegenerative disorder, is caused by amyloid-beta oligomers (AβOs). AβOs induce cell death by triggering oxidative stress and mitochondrial dysfunction. A recent study showed that AβO-induced oxidative stress is associated with extracellular signal-regulated kinase (ERK)-dynamin related protein 1 (Drp1)-mediated mitochondrial fission. Reactive oxygen species (ROS) are regulated by antioxidant enzymes, especially peroxiredoxins (Prxs) that scavenge H2O2. These enzymes inhibit neuronal cell death induced by various neurotoxic reagents. However, it is unclear whether Prx5, which is specifically expressed in neuronal cells, protects these cells from AβO-induced damage. In this study, we found that Prx5 expression was upregulated by AβO-induced oxidative stress and that Prx5 decreased ERK-Drp1-mediated mitochondrial fragmentation and apoptosis of HT-22 neuronal cells. Prx5 expression was affected by AβO, and amelioration of oxidative stress by N-acetyl-L-cysteine decreased AβO-induced Prx5 expression. Prx5 overexpression reduced ROS as well as RNS and apoptotic cell death but Prx5 knockdown did not. In addition, Prx5 overexpression ameliorated ERK-Drp1-mediated mitochondrial fragmentation but Prx5 knockdown did not. These results indicated that inducible Prx5 expression by AβO plays a key role in inhibiting both ERK-Drp1-induced mitochondrial fragmentation and neuronal cell death by regulating oxidative stress. Thus, Prx5 may be a new therapeutic agent for treating AD.

Ameliorating Effect of Akebia quinata Fruit Extracts on Skin Aging Induced by Advanced Glycation End Products

The accumulation of free radicals and advanced glycation end products (AGEs) in the skin plays a very important role in skin aging. Both are known to interact with each other. Therefore, natural compounds or extracts that possess both antioxidant and antiglycation activities might have great antiageing potential. Akebia quinata fruit extract (AQFE) has been used to treat urinary tract inflammatory disease in traditional Korean and Chinese medicines. In the present study, AQFE was demonstrated to possess antioxidant and antiglycation activity. AQFE protects human dermal fibroblasts (HDFs) from oxidative stress and inhibits cellular senescence induced by oxidative stress. We also found that AQFE inhibits glycation reaction between BSA and glucose. The antiglycation activity of AQFE was dose-dependent. In addition, the antiglycation activity of AQFE was confirmed in a human skin explant model. AQFE reduced CML expression and stimulated fibrillin-1 expression in comparison to the methyglyoxal treatment. In addition, the possibility of the extract as an anti-skin aging agent has also been clinically validated. Our analysis of the crow’s feet wrinkle showed that there was a decrease in the depth of deep furrows in RI treated with AQFE cream over an eight-week period. The overall results suggest that AQFE may work as an anti-skin aging agent by preventing oxidative stress and other complications associated with AGEs formation.

Cytosolic phospholipase A2α upregulation mediates apoptotic neuronal death induced by aggregated amyloid-β peptide1-42

Increased cytosolic phospholipase A2α (cPLA2α) immunoreactivity and transcript were observed in Alzheimer's disease (AD) brain associated with amyloid deposits. Thus, the present study examined whether cPLA2α upregulation participate in cortical neuron damage induced by aggregated Aβ1-42 and determined its role in the signaling events leading to damage, using an antisense technology. Exposure of primary cortical neurons to 1μM aggregated Aβ1-42 for 24h induced up-regulation and activation of cPLA2α and apoptotic cell death of about 30% as detected by: cell count, MTT reduction, caspases-3 and -8 activation, DAPI and TUNEL staining, that were prevented by inhibition of cPLA2α up-regulation and activity in the presence of antisense against cPLA2α (AS). cPLA2α was rapidly activated upon addition of aggregated Aβ1-42, as determined by its phosphorylated form on serine 505, and this activity was dependent on NADPH oxidase activity. NOX2- and NOX4-NADPH oxidase upregulation at 24h of aggregated Aβ1-42 exposure was not affected by the presence of AS, but superoxide production was reduced, probably due to NOX2 inhibition. cPLA2α upregulation led to activation of neutral sphingomyelinase (N-SMase) as its activity was inhibited in the presence of AS, and could be restored by addition of arachidonic acid. Addition of ceramide analog induced caspase-8 activation leading to caspase-3 activation and apoptotic neuronal death. In conclusion, our results suggest that cPLA2α activity plays a crucial role in the signaling cascade leading to apoptotic neuronal death by aggregated Aβ1-42 probably via activation of N-SMase, ceramide production and caspases-3 and -8.

Melatonin protects against amyloid-β-induced impairments of hippocampal LTP and spatial learning in rats

Alzheimer's disease (AD), the most prevalent neurodegenerative disease in the elderly, leads to progressive loss of memory and cognitive deficits. Amyloid-β protein (Aβ) in the brain is thought to be the main cause of memory loss in AD. Melatonin, an indole hormone secreted by the pineal gland, has been reported to produce neuroprotective effects. We examined whether melatonin could protect Aβ-induced impairments of hippocampal synaptic plasticity, neuronal cooperative activity, and learning and memory. Rats received bilateral intrahippocampal injection of Aβ1-42 or Aβ31-35 followed by intraperitoneal application of melatonin for 10 days, and the effects of chronic melatonin treatment on in vivo hippocampal long-term potentiation (LTP) and theta rhythm and Morris water maze performance were examined. We showed that intrahippocampal injection of Aβ1-42 or Aβ31-35 impaired hippocampal LTP in vivo, while chronic melatonin treatment reversed Aβ1-42- or Aβ31-35-induced impairments in LTP induction. Intrahippocampal injection of Aβ31-35 impaired spatial learning and decreased the power of theta rhythm in the CA1 region induced by tail pinch, and these synaptic, circuit, and learning deficits were rescued by chronic melatonin treatment. These results provide evidence for the neuroprotective action of melatonin against Aβ insults and suggest a strategy for alleviating cognition deficits of AD.