Bepridil decreases Aβ and calcium levels in the thalamus after middle cerebral artery occlusion in rats

Is Cerebral Amyloid-β Deposition Related to Post-stroke Cognitive Impairment?

Approximately two-thirds of ischemic stroke patients suffer from different levels of post-stroke cognitive impairment (PSCI), but the underlying mechanisms of PSCI remain unclear. Cerebral amyloid-β (Aβ) deposition, a pathological hallmark of Alzheimer's disease, has been discovered in the brains of stroke patients in some autopsy studies. However, less is known about the role of Aβ pathology in the development of PSCI. It is hypothesized that cerebral ischemic injury may lead to neurotoxic Aβ accumulation in the brain, which further induces secondary neurodegeneration and progressive cognitive decline after stroke onset. In this review, we summarized available evidence from pre-clinical and clinical studies relevant to the aforementioned hypothesis. We found inconsistency in the results obtained from studies in rodents, nonhuman primates, and stroke patients. Moreover, the causal relationship between post-stroke cerebral Aβ deposition and PSCI has been uncertain and controversial. Taken together, evidence supporting the hypothesis that brain ischemia induces cerebral Aβ deposition has been insufficient so far. And, there is still no consensus regarding the contribution of cerebral amyloid pathology to PSCI. Other non-amyloid neurodegenerative mechanisms might be involved and remain to be fully elucidated.

Neuroprotective Effects of Coffee Bioactive Compounds: A Review

Coffee is one of the most widely consumed beverages worldwide. It is usually identified as a stimulant because of a high content of caffeine. However, caffeine is not the only coffee bioactive component. The coffee beverage is in fact a mixture of a number of bioactive compounds such as polyphenols, especially chlorogenic acids (in green beans) and caffeic acid (in roasted coffee beans), alkaloids (caffeine and trigonelline), and the diterpenes (cafestol and kahweol). Extensive research shows that coffee consumption appears to have beneficial effects on human health. Regular coffee intake may protect from many chronic disorders, including cardiovascular disease, type 2 diabetes, obesity, and some types of cancer. Importantly, coffee consumption seems to be also correlated with a decreased risk of developing some neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease, and dementia. Regular coffee intake may also reduce the risk of stroke. The mechanism underlying these effects is, however, still poorly understood. This review summarizes the current knowledge on the neuroprotective potential of the main bioactive coffee components, i.e., caffeine, chlorogenic acid, caffeic acid, trigonelline, kahweol, and cafestol. Data from both in vitro and in vivo preclinical experiments, including their potential therapeutic applications, are reviewed and discussed. Epidemiological studies and clinical reports on this matter are also described. Moreover, potential molecular mechanism(s) by which coffee bioactive components may provide neuroprotection are reviewed.

Advances in Studies on Stroke-Induced Secondary Neurodegeneration (SND) and Its Treatment

Background:

The occurrence of secondary neurodegeneration has exclusively been observed after the first incidence of stroke. In humans and rodents, post-stroke secondary neurodegeneration (SND) is an inevitable event that can lead to progressive neuronal loss at a region distant to initial infarct. SND can lead to cognitive and motor function impairment, finally causing dementia. The exact pathophysiology of the event is yet to be explored. It is seen that the thalami, in particular, are susceptible to cause SND. The reason behind this is because the thalamus functioning as the relay center and is positioned as an interlocked structure with direct synaptic signaling connection with the cortex. As SND proceeds, accumulation of misfolded proteins and microglial activation are seen in the thalamus. This leads to increased neuronal loss and worsening of functional and cognitive impairment.

Objective:

There is a necessity of specific interventions to prevent post-stroke SND, which are not properly investigated to date owing to sparsely reproducible pre-clinical and clinical data. The basis of this review is to investigate about post-stroke SND and its updated treatment approaches carefully.

Methods:

Our article presents a detailed survey of advances in studies on stroke-induced secondary neurodegeneration (SND) and its treatment.

Results:

This article aims to put forward the pathophysiology of SND. We have also tabulated the latest treatment approaches along with different neuroimaging systems that will be helpful for future reference to explore.

Conclusion:

In this article, we have reviewed the available reports on SND pathophysiology, detection techniques, and possible treatment modalities that have not been attempted to date.

Modeling Mixed Vascular and Alzheimer's Dementia Using Focal Subcortical Ischemic Stroke in Human ApoE4-TR:5XFAD Transgenic Mice

Subcortical white matter ischemic lesions are increasingly recognized to have pathologic overlap in individuals with Alzheimer's disease (AD). The interaction of white matter ischemic lesions with amyloid pathology seen in AD is poorly characterized. We designed a novel mouse model of subcortical white matter ischemic stroke and AD that can inform our understanding of the cellular and molecular mechanisms of mixed vascular and AD dementia. Subcortical white matter ischemic stroke underlying forelimb motor cortex was induced by local stereotactic injection of an irreversible eNOS inhibitor. Subcortical white matter ischemic stroke or sham procedures were performed on human ApoE4-targeted-replacement (TR):5XFAD mice at 8 weeks of age. Behavioral tests were done at 7, 10, 15, and 20 weeks. A subset of animals underwent ¹⁸FDG-PET/CT. At 20 weeks of age, brain tissue was examined for amyloid plaque accumulation and cellular changes. Compared with sham E4-TR:5XFAD mice, those with an early subcortical ischemic stroke showed a significant reduction in amyloid plaque burden in the region of cortex overlying the subcortical stroke. Cognitive performance was improved in E4-TR:5XFAD mice with stroke compared with sham E4-TR:5XFAD animals. Iba-1+ microglial cells in the region of cortex overlying the subcortical stroke were increased in number and morphologic complexity compared with sham E4-TR:5XFAD mice, suggesting that amyloid clearance may be promoted by an interaction between activated microglia and cortical neurons in response to subcortical stroke. This novel approach to modeling mixed vascular and AD dementia provides a valuable tool for dissecting the molecular interactions between these two common pathologies.

Interactions of Aromatase and Seladin-1: A Neurosteroidogenic and Gender Perspective

Aromatase and seladin-1 are enzymes that have major roles in estrogen synthesis and are important in both brain physiology and pathology. Aromatase is the key enzyme that catalyzes estrogen biosynthesis from androgen precursors and regulates the brain’s neurosteroidogenic activity. Seladin-1 is the enzyme that catalyzes the last step in the biosynthesis of cholesterol, the precursor of all hormones, from desmosterol. Studies indicated that seladin-1 is a downstream mediator of the neuroprotective activity of estrogen. Recently, we also showed that there is an interaction between aromatase and seladin-1 in the brain. Therefore, the expression of local brain aromatase and seladin-1 is important, as they produce neuroactive steroids in the brain for the protection of neuronal damage. Increasing steroid biosynthesis specifically in the central nervous system (CNS) without affecting peripheral hormone levels may be possible by manipulating brain-specific promoters of steroidogenic enzymes. This review emphasizes that local estrogen, rather than plasma estrogen, may be responsible for estrogens’ protective effects in the brain. Therefore, the roles of aromatase and seladin-1 and their interactions in neurodegenerative events such as Alzheimer’s disease (AD), ischemia/reperfusion injury (stroke), and epilepsy are also discussed in this review.

Neuronal loss without amyloid-β deposits in the thalamus and hippocampus in the late period after middle cerebral artery occlusion in cynomolgus monkeys

Conflicting evidence exists regarding whether focal cerebral infarction contributes to cerebral amyloid-β (Aβ) deposition, as observed in Alzheimer's disease. In this study, we aimed to evaluate the presence of Aβ deposits in the ipsilateral thalamus and hippocampus 12 months post-stroke in non-human primates, whose brains are structurally and functionally similar to that of humans. Four young male cynomolgus monkeys were subjected to unilateral permanent middle cerebral artery occlusion (MCAO), and another four sham-operated monkeys served as controls. All monkeys underwent magnetic resonance imaging examination on post-operative day 7 to assess the location and size of the infarction. The numbers of neurons, astrocytes, microglia and the Aβ load in the non-affected thalamus and hippocampus ipsilaterally remote from infarct foci were examined immunohistochemically at sacrifice 12 months after operation. Thioflavin S and Congo Red stainings were used to identify amyloid deposits. Multiple Aβ antibodies recognizing both the N-terminal and C-terminal epitopes of Aβ peptides were used to avoid antibody cross-reactivity. Aβ levels in cerebrospinal fluid (CSF) and plasma were examined using enzyme-linked immunosorbent assay. The initial infarct was restricted to the left temporal, parietal, insular cortex and the subcortical white matter, while the thalamus and hippocampus remained intact. Of note, there were fewer neurons and more glia in the ipsilateral thalamus and hippocampus in the MCAO group at 12 months post-stroke compared to the control group (all P < 0.05). However, there was no sign of extracellular Aβ plaques in the thalamus or hippocampus. No statistically significant difference was found in CSF or plasma levels of Aβ₄₀ , Aβ₄₂ or the Aβ₄₀ /Aβ₄₂ ratio between the two groups (P > 0.05). These results suggest that significant secondary neuronal loss and reactive gliosis occur in the non-affected thalamus and hippocampus without Aβ deposits in the late period after MCAO in non-human primates.

Visual discrimination impairment after experimental stroke is associated with disturbances in the polarization of the astrocytic aquaporin-4 and increased accumulation of neurotoxic proteins

Numerous clinical studies have documented the high incidence of cognitive impairment after stroke. However, there is only limited knowledge about the underlying mechanisms. Interestingly, there is emerging evidence suggesting that cognitive function after stroke may be affected due to reduced waste clearance and subsequent accumulation of neurotoxic proteins. To further explore this potential association, we utilised a model of experimental stroke in mice. Specifically, a photothrombotic vascular occlusion targeting motor and sensory parts of the cerebral cortex was induced in young adult mice, and changes in cognition were assessed using a touchscreen platform for pairwise visual discrimination. The results showed that the execution of the visual discrimination task was impaired in mice 10 to 14 days post-stroke compared to sham. Stroke also induced significant neuronal loss within the peri-infarct, thalamus and the CA1 sub-region of the hippocampus. Further, immunohistochemical and protein analyses of the selected brain regions revealed an increased accumulation and aggregation of both amyloid-β and α-synuclein. These alterations were associated with significant disturbances in the aquaporin-4 protein expression and polarization at the astrocytic end-feet. The results suggest a link between the increased accumulation of neurotoxic proteins and the stroke-induced cognitive impairment. Given that the neurotoxic protein accumulation appeared alongside changes in astrocytic aquaporin-4 distribution, we suggest that the function of the waste clearance pathways in the brain post-stroke may represent a therapeutic target to improve brain recovery.

Identification of Novel Inhibitors of Auxin-Induced Ca2+ Signaling via a Plant-Based Chemical Screen

Many signal perception mechanisms are connected to Ca2+-based second messenger signaling to modulate specific cellular responses. The well-characterized plant hormone auxin elicits a very rapid Ca2+ signal. However, the cellular targets of auxin-induced Ca2+ are largely unknown. Here, we screened a biologically annotated chemical library for inhibitors of auxin-induced Ca2+ entry in plant cell suspensions to better understand the molecular mechanism of auxin-induced Ca2+ and to explore the physiological relevance of Ca2+ in auxin signal transduction. Using this approach, we defined a set of diverse, small molecules that interfere with auxin-induced Ca2+ entry. Based on annotated biological activities of the hit molecules, we found that auxin-induced Ca2+ signaling is, among others, highly sensitive to disruption of membrane proton gradients and the mammalian Ca2+ channel inhibitor bepridil. Whereas protonophores nonselectively inhibited auxin-induced and osmotic stress-induced Ca2+ signals, bepridil specifically inhibited auxin-induced Ca2+ We found evidence that bepridil severely alters vacuolar morphology and antagonized auxin-induced vacuolar remodeling. Further exploration of this plant-tailored collection of inhibitors will lead to a better understanding of auxin-induced Ca2+ entry and its relevance for auxin responses.

MicroRNA‑497 attenuates cerebral infarction in patients via the TLR4 and CREB signaling pathways

The aim of the present study was to investigate the function and mechanism of microRNA‑497 (miRNA/miR‑149) in the regulation of cerebral infarction. In patients with cerebral infarction, the serum of microRNA‑497 expression was upregulated compared with that in healthy controls. In N2A cells, overexpression of miR‑497 induced cell proliferation, decreased apoptosis and caspase‑3 and caspase‑9 activities, and suppressed Bax protein expression compared with that in the negative control group. Overexpression of miR‑497 reduced inflammation factors, and suppressed the Toll‑like receptor 4 (TLR4), myeloid differentiation primary response protein MyD88 (MyD88) and nuclear factor‑κB (NF‑κB) protein expression of the N2A cells. Next, miR‑497 overexpression suppressed the protein expression of interleukin‑1 receptor associated kinase (IRAK1) and phosphorylated cyclic AMP response element binding protein (p-CREB) in the N2A cells. Following miR‑497 overexpression, TLR4 inhibitor was found to suppress the inflammation factors, suppress the TLR4, MyD88 and NF‑κB protein expression, and reduce the IRAK1 and p‑CREB protein expression of the N2A cells. Lastly, CREB inhibitor also suppressed p‑CREB protein expression, induced cell proliferation, decreased apoptosis and caspase‑3 and caspase‑9 activities, and suppressed Bax protein expression in the N2A cells following miR‑497 overexpression. Taken together, these data demonstrated that miR‑497 attenuated cerebral infarction in patients by regulating the TLR4 and CREB signaling pathways.

Unexpected complication in a rat stroke model: exacerbation of secondary pathology in the thalamus by subacute intraarterial administration of human bone marrow-derived mesenchymal stem cells

This study examined whether human bone marrow mesenchymal stromal/stem cells (BMMSCs) could alleviate the secondary pathology in the thalamus after middle cerebral artery occlusion (MCAO) in rats. Atypical accumulation of both amyloid-β (Aβ) and calcium in the thalamus was significantly higher in rats receiving the BMMSCs infusion 48 hours after MCAO as compared with the vehicle MCAO group. The elevated Aβ/calcium accumulation correlated with the level of impaired sensorimotor function. Although secondary pathology in the thalamus seems to be rodent specific, it needs to be taken into account because it may impair long-term behavioral recovery and negate therapeutic treatment effects.

Lack of secondary pathology in the thalamus after focal cerebral ischemia in nonhuman primates

Remote regions such as the thalamus undergo secondary degeneration after cerebral ischemia. In rodents, the pathology in the thalamus is characterized by a robust inflammatory reaction, β-amyloid (Aβ) accumulation and calcification. Here we studied whether nonhuman primates subjected to middle cerebral artery occlusion (MCAO) display a similar pathology. Common marmosets (n=4) were subjected to transient MCAO for 3 h. Two sham-operated animals served as controls. All animals underwent MRI examination (T2) on postoperative day 7 to assess the location of the infarct. After a 45-day follow-up period, the animals were perfused for histology to evaluate β-amyloid and calcium load in the peri-infarct regions and the thalamus. There was no Aβ or calcium staining in the sham-operated marmosets. The contralateral hemisphere was devoid of Aβ and calcium staining in MCAO animals, except calcium staining in one animal. In the ipsilateral cortex, patchy groups of Aβ-positive cells were observed. Occasional calcium staining was observed in the peri-infarct regions, lesion core, and remote regions such as the substantia nigra. The most important, the thalamus was devoid of any sign of Aβ and calcium aggregation in MCAO animals. Staining for glial fibrillary acidic protein (GFAP) showed marked astrogliosis in the ipsilateral cortex and thalamus. In conclusion, our preliminary study in marmosets did not identify Aβ and calcium pathology in the thalamus following cerebral ischemia as shown in rodents.

Non-selective calcium channel blocker bepridil decreases secondary pathology in mice after photothrombotic cortical lesion

Experimental studies have identified a complex link between neurodegeneration, β-amyloid (Aβ) and calcium homeostasis. Here we asked whether early phase β-amyloid pathology in transgenic hAPP_SL mice exaggerates the ischemic lesion and remote secondary pathology in the thalamus, and whether a non-selective calcium channel blocker reduces these pathologies. Transgenic hAPP_SL (n = 33) and non-transgenic (n = 30) male mice (4–5 months) were subjected to unilateral cortical photothrombosis and treated with the non-selective calcium channel blocker bepridil (50 mg/kg, p.o., once a day) or vehicle for 28 days, starting administration 2 days after the operation. Animals were then perfused for histological analysis of infarct size, Aβ and calcium accumulation in the thalamus. Cortical photothrombosis resulted in a small infarct, which was associated with atypical Aβ and calcium accumulation in the ipsilateral thalamus. Transgenic mice had significantly smaller infarct volumes than non-transgenic littermates (P<0.05) and ischemia-induced rodent Aβ accumulation in the thalamus was lower in transgenic mice compared to non-transgenic mice (P<0.01). Bepridil decreased calcium load in the thalamus (P<0.01). The present data suggest less pronounced primary and secondary pathology in hAPP_SL transgenic mice after ischemic cortical injury. Bepridil particularly decreased calcium pathology in the thalamus following ischemia.