Focal cerebral ischemia induces Alzheimer’s disease-like pathological change in rats

Neuroprotective effect of Potentilla reptans L. root in the rat brain global ischemia/reperfusion model

Stroke is the most common cause of death among neurological diseases. The protective effects of Potentilla reptans L. include antioxidative, anti-inflammatory, and antiapoptotic effects. In this study, the brain protection and beta-amyloid effects of P. reptans root extract were investigated in the rat brain ischemia/reperfusion (IR) model. Forty male Wistar rats were randomly divided into five groups (n = 8), including IR, sham, and three groups receiving P. reptans with concentrations of 0.025, 0.05, and 0.1 (g/kg/b.w.), which were injected daily for 7 days. For the IR model, the common carotid artery was occluded bilaterally for 8 min. All injections were intraperitoneal (IP). The shuttle box test was used to measure passive avoidance memory. Then the brain tissue was extracted for the histological examination of neuron counts and β-amyloid plaques using a morphometric technique, and finally, Statistical Package for the Social Sciences software was used for statistical analysis of the data. Pretreatment with P. reptans improved memory impairment. Also, by examining the tissues of the CA1, CA3, and dentate gyrus areas of the hippocampus, it was observed that the number of plaques in the groups receiving P. reptans extract was reduced compared to the IR group, especially at the concentration of 0.05 g/kg/b.w. Also, P. reptans improved the number of neurons at all concentrations, in which the concentration of 0.05 g/kg/b.w. showed more effective therapeutic results. Taken together, we found that P. reptans root extract has beneficial effects on memory impairment, neuronal loss, and β-amyloid accumulation.

Regulation of Tau protein phosphorylation by glucosamine-induced O-GlcNAcylation as a neuroprotective mechanism in a brain ischemia-reperfusion model

Purpose:Tau hyperphosphorylation is a modification frequently observed after brain ischemia which has been related to the aggregation of this protein, with subsequent cytoskeletal damage, and cellular toxicity. The present study tests the hypothesis of using glucosamine, an agent that increases protein O-GlcNAcylation, to decrease the levels of phosphorylation in Tau during ischemia-reperfusion.Material and methods: Transient focal ischemia was artificially induced in male Wistar rats by occlusion of the middle cerebral artery (MCAO) with an intraluminal monofilament. A single dose of intraperitoneal glucosamine of 200 mg/kg diluted in normal saline (SSN) was administered 60 min before ischemia. Histological brain sections were processed using indirect immunofluorescence with primary antibodies (anti-O-GlcNAc and anti pTau-ser 396). The Image J software was used to calculate the immunofluorescence signal intensity.Results: The phosphorylation of Tau at the serine residue 396 had a significant decrease with the administration of glucosamine during ischemia-reperfusion compared with the administration of placebo.Conclusions: These results show that glucosamine can reduce the phosphorylation levels of Tau in rodents subjected to ischemia and cerebral reperfusion, which implies a neuroprotective role of glucosamine.

Association between T-tau protein and Aβ42 in plasma neuronal-derived exosomes and cognitive impairment in patients with permanent atrial fibrillation and the role of anticoagulant therapy and inflammatory mechanisms

BACKGROUND

This study explores whether the differences in cognitive performance among individuals with permanent atrial fibrillation (AF) are attributable to the duration of AF and anticoagulant therapy and explores the possible inflammatory mechanism of cognitive dysfunction related to AF.

METHODS

A total of 260 patients aged 50-75 years without previous cerebrovascular events were enrolled in this study. These 260 patients had been divided into the AF group (140 patients) and sinus rhythm group (120 patients). In the AF group, we divided participants into cognitive impairment (CI) group (90 patients) and cognitive normal (CN) group (50 patients). In the sinus rhythm group, we also divided participants into CI group (61 patients) and CN group (59 patients). The Mini-Mental State Examination (MMSE) was used to assess the cognitive function of all participants. Neuronal-derived exosomes were enriched in peripheral blood by immunoprecipitation and were confirmed by a transmission electron microscope, nanoparticle tracking analysis, and western blot. Alzheimer's disease-pathogenic exosomal proteins and inflammatory cytokines were quantified. The association between AF and cognitive function was estimated by logistic regression analysis. ANOVA or Welch's t-test compared the difference in protein concentrations between groups.

RESULTS

Non-anticoagulant therapy in patients with AF was significantly associated with CI (OR = 13.99, 95% CI: 2.67-73.36, p < .01). The incidence of dementia in patients with AF > 3 years was significantly higher than in patients with AF ≤ 3 years, but there was no significant difference in total cognitive dysfunction (mild cognitive impairment [MCI] + dementia) (p = .126). The adjusted exosome concentrations of T-tau and amyloid-β protein 42 (Aβ42) in the CI group were significantly higher than in the CN group (p < .001). The serum concentrations of IL-6 and matrix metalloproteinase-9 (MMP-9) in patients with AF were higher than those in patients with sinus rhythm (p <  .001).

CONCLUSION

Aβ42 and T-tau in peripheral blood neuronal-derived exosomes maybe be associated with the early diagnosis of CI in patients with permanent AF. However, the value of Aβ42 and T-tau for CI in patients with permanent AF still needs to be confirmed in future randomized control trials.

Covert strokes prior to Alzheimer's disease onset accelerate peri-lesional pathology but not cognitive deficits in an inducible APP mouse model

It is estimated that up to 1 in 3 healthy middle-aged adults will have had a covert stroke during their lifetime. Furthermore, post-stroke, survivors are more than twice as likely to develop dementia. In the present study, we aimed to model the impact of focal subclinical ischemia prior to the onset of AD pathogenesis in a preclinical model. We utilized endothelin-1 to induce ischemia in an iducible transgenic mouse model of Alzheimer's disease, APPsi:tTA, allowing for temporal control of APP gene expression. We induced the focal subclinical ischemic events in the absence of APP expression, thus prior to AD onset. T2 structural magnetic resonance imaging confirmed the volume and location of focal subclinical ischemic lesions to the medial prefrontal cortex. Following recovery from surgery and 7 weeks of APP expression, we found that two subclinical ischemic lesions resulted in a significant localized increase in amyloid load and in microglial activation proximal to the lesion. However, no differences were found in astrogliosis. A battery of behaviour tests was conducted, in which no significant differences were detected in activities of daily living and cognitive function between stroked and sham cohorts. Overall, our results demonstrated that APP expression was the sole driving force behind behavioural deficits. In conclusion, our results suggest that a history of two subclinical strokes prior to AD onset does not worsen early disease trajectory in a mouse model.

Atrial Fibrillation and Cognitive Impairment: New Insights and Future Directions

INTRODUCTION

Atrial fibrillation (AF) has been recognised as the most prevalent sustained arrhythmia. Recently, a growing body of evidence has suggested that AF might be involved in the progression of cognitive impairment (CIM), potentially extending into types of dementia. Accordingly, the purpose of the present study was to summarise the findings of investigations examining association between AF and cognitive function as well as highlighting the possible causes of discrepancy between the findings and reviewing the probable mechanisms of CIM in patients affected with AF.

METHODS

A systematic search in the literature was conducted in the databases of PubMed, Scopus, Cochrane Library, and Google Scholar with no language restrictions, using specified search terms to identify studies published between 1 January 1990 and 1 April 2018. Then, study designs, participant information, diagnostic approaches used for cognitive assessments, and incidence/prevalence rates of CIM and/or dementia were assessed.

RESULTS

Out of the initial 2,364 articles retrieved, a total number of 40 studies were selected for data collection. Most studies had suggested a significant relationship between AF and CIM. In this regard, cerebral hypo-perfusion, altered cerebral blood flow, cerebral micro-bleeds, micro-emboli, vascular inflammation, cerebral small vessel diseases, vascular inflammation, and genetic factors were considered as the possible mechanisms of CIM in patients suffering from AF. It seemed that differences in study settings and designs, variations of diagnostic tools for CIM and AF, as well as underlying conditions such as age groups, concurrent chronic diseases, and therapeutic interventions for AF might be amongst probable factors justifying the diversity of findings across the selected articles.

CONCLUSION

Although evidence is much more directed towards an association between AF and CIM, the role of AF in CIM needs to be confirmed in-depth via longer prospective and cohort studies at larger scales using accurate neuropsychological and cognitive function assessments. Moreover, the mechanisms involved in the relationship between AF and Alzheimer's disease (AD) require further studies. To conclude, the effect of different therapeutic strategies of AF on CIM should be investigated in more clinical trials.

Dental pulp stem cells promote regeneration of damaged neuron cells on the cellular model of Alzheimer's disease

Alzheimer's disease (AD) is an incurable neurodegenerative disease and many types of stem cells have been used in AD therapy with some favorable effects. In this study, we investigated the potential therapeutical effects of human dental pulp stem cells (hDPSCs) on AD cellular model which established by okadaic acid (OA)-induced damage to human neuroblastoma cell line, SH-SY5Y, in vitro for 24 h. After confirmed the AD cellular model, the cells were co-culture with hDPSCs by transwell co-culture system till 24 h for treatment. Then the cytomorphology of the hDPSCs-treated cells were found to restore gradually with re-elongation of retracted dendrites. Meanwhile, Cell Counting Kit-8 assay and Hoechst 33258 staining showed that hDPSCs caused significant increase in the viability and decrease in apoptosis of the model cells, respectively. Observation of DiI labeling also exhibited the prolongation dendrites in hDPSCs-treated cells which were obviously different from the retraction dendrites in AD model cells. Furthermore, specific staining of α-tubulin and F-actin demonstrated that the hDPSCs-treated cells had the morphology of restored neurons, with elongated dendrites, densely arranged microfilaments, and thickened microtubular fibrils. In addition, results from western blotting revealed that phosphorylation at Ser 396 of Tau protein was significantly suppressed by adding of hDPSCs. These results indicate that hDPSCs may promote regeneration of damaged neuron cells in vitro model of AD and may serve as a useful cell source for treatment of AD.

Comparison of the glycopattern alterations of mitochondrial proteins in cerebral cortex between rat Alzheimer's disease and the cerebral ischemia model

Alzheimer’s disease (AD) and ischemic brain injury are two major neurodegenerative diseases. Mitochondrial dysfunction commonly occurs in AD and ischemic brain injury. Currently, little attention has been paid to the glycans on mitochondrial glycoproteins, which may play vital roles during the process of mitochondrial dysfunction. The aim of this study was to illustrate and compare the glycopattern alterations of mitochondrial glycoproteins extracted from the cerebral cortex of the rat models of these two diseases using High-throughput lectin microarrays. The results shown that the number of lectins with significant differences compared to normal brains was nine for the rat sporadic Alzheimer’s disease (SAD) model and eighteen for the rat middle cerebral artery occlusion (MCAO) model. Interestingly, five lectins showed opposite expression patterns between the SAD and MCAO rat models. We conclude that glycopattern alterations of mitochondrial glycoproteins in the cerebral cortex may provide vital information to help understand mitochondrial dysfunction in AD and ischemic brain injury. In addition, glycans recognized by diverse lectins with opposite expression patterns between these two diseases hints at the different pathomechanisms of mitochondrial dysfunction in AD and ischemic brain injury.

Amyloid beta-peptide worsens cognitive impairment following cerebral ischemia-reperfusion injury

Amyloid β-peptide, a major component of senile plaques in Alzheimer's disease, has been implicated in neuronal cell death and cognitive impairment. Recently, studies have shown that the pathogenesis of cerebral ischemia is closely linked with Alzheimer's disease. In this study, a rat model of global cerebral ischemia-reperfusion injury was established via occlusion of four arteries; meanwhile, fibrillar amyloid β-peptide was injected into the rat lateral ventricle. The Morris water maze test and histological staining revealed that administration of amyloid β-peptide could further aggravate impairments to learning and memory and neuronal cell death in the hippocampus of rats subjected to cerebral ischemia-reperfusion injury. Western blot showed that phosphorylation of tau protein and the activity of glycogen synthase kinase 3β were significantly stronger in cerebral ischemia-reperfusion injury rats subjected to amyloid β-peptide administration than those under-going cerebral ischemia-reperfusion or amyloid β-peptide administration alone. Conversely, the activity of protein phosphatase 2A was remarkably reduced in rats with cerebral ischemia-reperfusion injury following amyloid β-peptide administration. These findings suggest that amyloid β-peptide can potentiate tau phosphorylation induced by cerebral ischemia-reperfusion and thereby aggravate cognitive impairment.

Tau and caspase 3 as targets for neuroprotection

The peptide drug candidate NAP (davunetide) has demonstrated protective effects in various in vivo and in vitro models of neurodegeneration. NAP was shown to reduce tau hyperphosphorylation as well as to prevent caspase-3 activation and cytochrome-3 release from mitochondria, both characteristic of apoptotic cell death. Recent studies suggest that caspases may play a role in tau pathology. The purpose of this study was to evaluate the effect of NAP on tau hyperphosphorylation and caspase activity in the same biological system. Our experimental setup used primary neuronal cultures subjected to oxygen-glucose deprivation (OGD), with and without NAP or caspase inhibitor. Cell viability was assessed by measuring mitochondrial activity (MTS assay), and immunoblots were used for analyzing protein level. It was shown that apoptosis was responsible for all cell death occurring following ischemia, and NAP treatment showed a concentration-dependent protection from cell death. Ischemia caused an increase in the levels of active caspase-3 and hyperphosphorylated tau, both of which were prevented by either NAP or caspase-inhibitor treatment. Our data suggest that, in this model system, caspase activation may be an upstream event to tau hyperphosphorylation, although additional studies will be required to fully elucidate the cascade of events.

A meta-analysis of mood stabilizers for Alzheimer's disease

The objective of this study was to assess the clinical evidence for or against mood stabilizers as a treatment for Alzheimer's disease (AD). We searched 5 databases from their inception to January 2010. Five randomized clinical trials of mood stabilizers to treat human patients suffering from AD were included. These trials assessed the effectiveness of mood stabilizers as an adjunct treatment to conventional anti-dementia drugs on behavioral and psychological symptoms, especially on agitation. Methodological quality was assessed using the Jadad score. The results suggested a significant effect in favor of placebo on the Mini-Mental Status Examination [n=270, weight mean difference (WMD), -0.89; 95% confidence intervals (CIs) -1.69 to -0.09, P=0.03] and on the Neuropsychiatric Inventory total (NPI total) (n=51, WMD, 3.71; 95% CIs 0.15 to 7.26, P=0.04). There were no significant differences in change scores on total Brief Psychiatric Rating Scale (BPRS total), NPI/BPRS agitation, Cohen-Mansfield Agitation Inventory total and Physical Self Maintenance Scale between mood stabilizers and placebo. Only one of these studies was free of methodological limitations (Jadad score=5). In conclusion, based on the existing evidence, mood stabilizers are ineffective or even harmful as a treatment for AD.