Neurovascular regulation in the ischemic brain

Assessment of MR blood-oxygen-level-dependent (BOLD) cerebrovascular reactivity under general anesthesia in children with moyamoya

BACKGROUND

Moyamoya is a progressive, non-atherosclerotic cerebral arteriopathy that may present in childhood and currently has no cure. Early diagnosis is critical to prevent a lifelong risk of neurological morbidity. Blood-oxygen-level-dependent (BOLD) MRI cerebrovascular reactivity (CVR) imaging provides a non-invasive, in vivo measure of autoregulatory capacity and cerebrovascular reserve. However, non-compliant or younger children require general anesthesia to achieve BOLD-CVR imaging.

OBJECTIVE

To determine the same-day repeatability of BOLD-CVR imaging under general anesthesia in children with moyamoya.

MATERIALS AND METHODS

Twenty-eight examination pairs were included (mean patient age = 7.3 ± 4.0 years). Positive and negatively reacting voxels were averaged over signals and counted over brain tissue and vascular territory. The intraclass correlation coefficient (ICC), Wilcoxon signed-rank test, and Bland-Altman plots were used to assess the variability between the scans.

RESULTS

There was excellent-to-good (≥ 0.59) within-day repeatability in 18 out of 28 paired studies (64.3%). Wilcoxon signed-rank tests demonstrated no significant difference in the grey and white matter CVR estimates, between repeat scans (all p-values > 0.05). Bland-Altman plots of differences in mean magnitude of positive and negative and fractional positive and negative CVR estimates illustrated a reasonable degree of agreement between repeat scans and no systematic bias.

CONCLUSION

BOLD-CVR imaging provides repeatable assessment of cerebrovascular reserve in children with moyamoya imaged under general anesthesia.

An-Gong-Niu-Huang-Wan (AGNHW) regulates cerebral blood flow by improving hypoperfusion, cerebrovascular reactivity and microcirculation disturbances after stroke

BACKGROUND

The restoration of cerebrovascular regulation and improvement of cerebral blood flow in ischaemic regions are crucial for improving the clinical prognosis after stroke. An-Gong-Niu-Huang-Wan (AGNHW) is a famous traditional compound Chinese medicine that has been used for over 220 years to treat acute ischaemic stroke; however, its role in the regulation of cerebral blood flow is still unclear. The aim of the present study was to investigate the regulatory effect of AGNHW on cerebral blood flow and microcirculation after ischaemic stroke and to elucidate the underlying mechanisms involved.

METHODS

Male C57BL/6 mice were subjected to distal middle cerebral artery occlusion (dMCAO) and randomly assigned to the sham, MCAO, or AGNHW groups. AGNHW was administered intragastrically 1 h after dMCAO. The rotarod test was utilized to evaluate behavioural function; TTC was used to determine the infarct volume; and ischaemic injury was assessed by detecting brain levels of SOD, MDA and NO. Then, cortical perfusion and acetazolamide-induced cerebrovascular reactivity were assessed using laser speckle contrast imaging, and the velocity and flux of red blood cells in cortical capillaries were detected using two-photon laser scanning microscopy. In addition, we employed RNA-Seq to identify variations in gene expression profiles and assessed endothelium-dependent changes in microcirculatory dysfunction by measuring vasoactive mediator levels.

RESULTS

AGNHW significantly increased cerebral blood flow, reduced the infarct volume, and promoted functional recovery after cerebral ischaemia. AGNHW increased the velocity and flux of red blood cells in capillaries and improved cerebrovascular reactivity in the ischaemic cortex. Furthermore, AGNHW regulated endothelium-dependent microcirculation, as evidenced by decreases in the expression of endothelins (Edn1, Edn3 and Ednrb) and the ratios of brain and serum TXB2/6-keto-PGF1α and ET-1/CGRP.

CONCLUSIONS

AGNHW improved cerebral hypoperfusion, regulated cerebrovascular reactivity and attenuated microcirculatory dysfunction within the ischaemic cortex after stroke. This outstanding effect was achieved by modulating the expression of genes related to vascular endothelial cell function and regulating endothelium-dependent vasoactive mediators.

Hypertension & dementia: Pathophysiology & potential utility of antihypertensives in reducing disease burden

Dementia is a common cause of disability and dependency among the elderly due to its progressive neurodegenerative nature. As there is currently no curative therapy, it is of major importance to identify new ways to reduce its prevalence. Hypertension is recognised as a modifiable risk factor for dementia, particularly for the two most common subtypes; vascular dementia (VaD) and Alzheimer's disease (AD). From the current literature, identified through a comprehensive literature search of PubMed and Cochrane Library, this review aims to establish the stage in adulthood when hypertension becomes a risk for cognitive decline and dementia, and whether antihypertensive treatment is effective as a preventative therapy. Observational studies generally found hypertension in mid-life (age 45-64) to be correlated with an increased risk of cognitive decline and dementia incidence, including both VaD and AD. Hypertension manifesting in late life (age ≥ 65) was demonstrated to be less of a risk, to the extent that incidences of high blood pressure (BP) in the very elderly (age ≥ 75) may even be related to reduced incidence of dementias. Despite the evidence linking hypertension to dementia, there were conflicting findings as to whether the use of antihypertensives was beneficial for its prevention and this conflicting evidence and inconsistent results could be due to the methodological differences between the reviewed observational and randomised controlled trials. Furthermore, dihydropyridine calcium channel blockers and potassium-sparing diuretics were proposed to have neuroprotective properties in addition to BP lowering. Overall, if antihypertensives are confirmed to be beneficial by larger-scale homogenous trials with longer follow-up durations, treatment of hypertension, particularly in mid-life, could be an effective strategy to considerably lower the prevalence of dementia. Furthermore, greater clarification of the neuroprotective properties that some antihypertensives possess will allow for better clinical practice guidance on the choice of antihypertensive class for both BP lowering and dementia prevention.

The effects of protein-rich extract from Rhizoma Gastrodiae against cerebral ischemia/reperfusion injury via regulating MAPK and PI3K/AKT signaling pathway

BACKGROUND

Rhizoma Gastrodiae is a highly valuable traditional Chinese medicine and functional health food that has been used in China to treat neurological disorders for thousands of years. Rhizoma Gastrodiae contains various of biological activities, such as antioxidative, neuroprotective, learning improvement, anxiolytic, and antidepressant effects. However, no studies have been conducted to explore the effects of the protein components in Rhizoma Gastrodiae (GEPS) and its potential protective effects against ischemic stroke.Our main goal was to investigate the effects of GEPS on ischemia/reperfusion (I/R) injury and its possible mechanisms.

METHODS

A middle cerebral artery occlusion (MCAO) induced focal cerebral ischemia mouse model and an oxygen-glucose deprivation (OGD/R) injury model in HT22 cells were established. A neurobehavioral test was performed 24 h after MCAO, and brain infarction was measured. A Morris water maze experiment was conducted on Day 14 after reperfusion in mice. Hematoxylin and eosin (HE) and TUNEL staining were performed to assess apoptotic neuronal death. Immunohistochemical analysis was used to detect BDNF and GAP43 expression. The content of SOD, MDA, GSH-PX and ROS were detected. The protein expression was analyzed using Western blotting. Cell viability was determined by MTT assay. Cell apoptosis was examined by flow cytometry.

RESULTS

GEPS reduced apoptosis, decreased cerebral infarction, improved neurological defects, and ameliorated oxidative stress in the ischemic penumbra. In addition, GEPS increased the expression of BDNF and GA43 in the penumbra. Mechanistically, GEPS counteracted MCAO-induced PI3K/AKT inhibition and activation of MAPK signaling pathways.

CONCLUSION

GEPS has a clear neuroprotective effect on I/R injury, and its mechanism may be linked to the PI3K/AKT and MAPK signaling pathways.

Mediator complex in neurological disease

Neurological diseases, including traumatic brain injuries, stroke (haemorrhagic and ischemic), and inherent neurodegenerative diseases cause acquired disability in humans, representing a leading cause of death worldwide. The Mediator complex (MED) is a large, evolutionarily conserved multiprotein that facilities the interaction between transcription factors and RNA Polymerase II in eukaryotes. Some MED subunits have been found altered in the brain, although their specific functions in neurodegenerative diseases are not fully understood. Mutations in MED subunits were associated with a wide range of genetic diseases for MED12, MED13, MED13L, MED20, MED23, MED25, and CDK8 genes. In addition, MED12 and MED23 were deregulated in the Alzheimer's Disease. Interestingly, most of the genomic mutations have been found in the subunits of the kinase module. To date, there is only one evidence on MED1 involvement in post-stroke cognitive deficits. Although the underlying neurodegenerative disorders may be different, we are confident that the signal cascades of the biological-cognitive mechanisms of brain adaptation, which begin after brain deterioration, may also differ. Here, we analysed relevant studies in English published up to June 2023. They were identified through a search of electronic databases including PubMed, Medline, EMBASE and Scopus, including search terms such as "Mediator complex", "neurological disease", "brains". Thematic content analysis was conducted to collect and summarize all studies demonstrating MED alteration to understand the role of this central transcriptional regulatory complex in the brain. Improved and deeper knowledge of the regulatory mechanisms in neurological diseases can increase the ability of physicians to predict onset and progression, thereby improving diagnostic care and providing appropriate treatment decisions.

Herpesvirus latent infection promotes stroke via activating the OTUD1/NF-κB signaling pathway

OBJECTIVE

Our study aimed to reveal the molecular mechanisms underlying the regulation of cerebral infarction by herpes virus latency infection via the OTUD1/NF-κB signaling pathway using evidence-based medicine Meta-analysis and bioinformatics analysis.

METHODS

We conducted a Meta-analysis by searching Pubmed, Embase, and Web of Science databases to evaluate the correlation between herpes virus infection and increased risk of cerebral infarction. We obtained wild-type or mutant herpes virus latent infection-related brain tissue datasets from the GEO database and performed differential analysis to identify differentially expressed genes (DEGs) in the brain tissue after herpes virus latent infection. We further conducted WGCNA co-expression analysis on the cerebral infarction-related datasets from the GEO database to obtain key module genes and intersect them with the DEGs. We used ROC curve analysis to identify the key gene OTUD1 for predicting the occurrence of cerebral infarction and combined correlation and pathway enrichment analyses to identify the downstream pathways regulated by OTUD1.

RESULTS

Our meta-analysis revealed that herpes virus infection is associated with an increased risk of cerebral infarction. By integrating the differential analysis and WGCNA co-expression analysis of GEO chip data, we identified three key genes mediating cerebral infarction after herpes virus latent infection. ROC curve analysis identified the key gene OTUD1, and the correlation and pathway enrichment analyses showed that OTUD1 regulates the NF-κB signaling pathway to mediate cerebral infarction.

CONCLUSION

Herpes virus latent infection promotes cerebral infarction by activating the OTUD1/NF-κB signaling pathway.

The Role of Nrf2 in Relieving Cerebral Ischemia-Reperfusion Injury

Ischemic stroke includes two related pathological damage processes: brain injury caused by primary ischemia and secondary ischemia reperfusion (I/R) injury. I/R injury has become a worldwide health problem. Unfortunately, there is still a lack of satisfactory drugs for ameliorating cerebral I/R damage. Nrf2 is a vital endogenous antioxidant protein, which combines with Keap1 to maintain a dormant state under physiological conditions. When pathological changes such as I/R occurs, Nrf2 dissociates from Keap1 and activates the expression of downstream antioxidant proteins to exert a protective effect. Recent research have shown that the activated Nrf2 not only effectively inhibits oxidative stress, but also performs the ability to repair the function of compromised mitochondria, alleviate endoplasmic reticulum stress, eliminate inflammatory response, reduce blood-brain barrier permeability, inhibit neuronal apoptosis, enhance the neural network remolding, thereby exerting significant protective effects in alleviating the injuries caused by cell oxygen-glucose deprivation, or animal cerebral I/R. However, no definite clinical application report demonstrated the efficacy of Nrf2 activators in the treatment of cerebral I/R. Therefore, further efforts are needed to elaborate the role of Nrf2 activators in the treatment of cerebral I/R. Here, we reviewed the possible mechanisms underlying its potential pharmacological benefits in alleviating cerebral I/R injury, so as to provide a theoretical basis for studying its mechanism and developing Nrf2 activators.

New insights into acupuncture techniques for poststroke spasticity

With the trend of aging population getting more obvious, stroke has already been a major public health problem worldwide. As a main disabling motor impairment after stroke, spasticity has unexpected negative impacts on the quality of life and social participation in patients. Moreover, it brings heavy economic burden to the family and society. Previous researches indicated that abnormality of neural modulation and muscle property corelates with the pathogenesis of poststroke spasticity (PSS). So far, there still lacks golden standardized treatment regimen for PSS; furthermore, certain potential adverse-events of the mainstream therapy, for example, drug-induced generalized muscle weakness or high risk related surgery somehow decrease patient preference and compliance, which brings challenges to disease treatment and follow-up care. As an essential non-pharmacological therapy, acupuncture has long been used for PSS in China and shows favorable effects on improvements of spastic hypertonia and motor function. Notably, previous studies focused mainly on the research of antispastic acupoints. In comparison, few studies lay special stress on the other significant factor impacting on acupuncture efficacy, that is acupuncture technique. Based on current evidences from the clinic and laboratory, we will discuss certain new insights into acupuncture technique, in particular the antispastic needling technique, for PSS management in light of its potential effects on central modulations as well as peripheral adjustments, and attempt to provide some suggestions for future studies with respect to the intervention timing and course, application of acupuncture techniques, acupoint selection, predictive and aggravating factors of PSS, aiming at optimization of antispastic acupuncture regimen and improvement of quality of life in stroke patients. More innovations including rigorous study design, valid objective assessments for spasticity, and related experimental studies are worthy to be expected in the years ahead.

ROS-responsive 18β-glycyrrhetic acid-conjugated polymeric nanoparticles mediate neuroprotection in ischemic stroke through HMGB1 inhibition and microglia polarization regulation

Ischemic stroke is an acute and serious cerebral vascular disease, which greatly affects people's health and brings huge economic burden to society. Microglia, as important innate immune components in central nervous system (CNS), are double-edged swords in the battle of nerve injury, considering their polarization between pro-inflammatory M1 or anti-inflammatory M2 phenotypes. High mobility group box 1 (HMGB1) is one of the potent pro-inflammatory mediators that promotes the M1 polarization of microglia. 18β-glycyrrhetinic acid (GA) is an effective intracellular inhibitor of HMGB1, but of poor water solubility and dose-dependent toxicity. To overcome the shortcomings of GA delivery and to improve the efficacy of cerebral ischemia therapy, herein, we designed reactive oxygen species (ROS) responsive polymer-drug conjugate nanoparticles (DGA) to manipulate microglia polarization by suppressing the translocation of nuclear HMGB1. DGA presented excellent therapeutic efficacy in stroke mice, as evidenced by the reduction of infarct volume, recovery of motor function, suppressed of M1 microglia activation and enhanced M2 activation, and induction of neurogenesis. Altogether, our work demonstrates a close association between HMGB1 and microglia polarization, suggesting potential strategies for coping with inflammatory microglia-related diseases.

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We synthesized GA-boronate ester-conjugated diethylaminoethylen-dextran polymer-drug conjugate nanoparticles.

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The DGA nanoparticles achieve ROS-responsive drug release.

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The DGA nanoparticles inhibit cytoplasmic translocation of nuclear HMGB1, thus modulate microglia to M2 phenotype.

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The DGA nanoparticles effectively alleviate the pathology of stroke, reduce infarct volume, and enhance neurogenesis.

Neutrophil dynamics and inflammaging in acute ischemic stroke: A transcriptomic review

Stroke is among the leading causes of death and disability worldwide. Restoring blood flow through recanalization is currently the only acute treatment for cerebral ischemia. Unfortunately, many patients that achieve a complete recanalization fail to regain functional independence. Recent studies indicate that activation of peripheral immune cells, particularly neutrophils, may contribute to microcirculatory failure and futile recanalization. Stroke primarily affects the elderly population, and mortality after endovascular therapies is associated with advanced age. Previous analyses of differential gene expression across injury status and age identify ischemic stroke as a complex age-related disease. It also suggests robust interactions between stroke injury, aging, and inflammation on a cellular and molecular level. Understanding such interactions is crucial in developing effective protective treatments. The global stroke burden will continue to increase with a rapidly aging human population. Unfortunately, the mechanisms of age-dependent vulnerability are poorly defined. In this review, we will discuss how neutrophil-specific gene expression patterns may contribute to poor treatment responses in stroke patients. We will also discuss age-related transcriptional changes that may contribute to poor clinical outcomes and greater susceptibility to cerebrovascular diseases.

Fronto-Parietal and White Matter Haemodynamics Predict Cognitive Outcome in Children with Moyamoya Independent of Stroke

Moyamoya disease is a major arteriopathy characterised by progressive steno-occlusion of the arteries of the circle of Willis. Studies in adults with moyamoya suggest an association between abnormal fronto-parietal and white matter regional haemodynamics and cognitive impairments, even in the absence of focal infarction. However, these associations have not been investigated in children with moyamoya. We examined the relationship between regional haemodynamics and ratings of intellectual ability and executive function, using hypercapnic challenge blood oxygen level-dependent magnetic resonance imaging of cerebrovascular reactivity in a consecutive cohort of children with confirmed moyamoya. Thirty children were included in the final analysis (mean age: 12.55 ± 3.03 years, 17 females, 15 idiopathic moyamoya and 15 syndromic moyamoya). Frontal haemodynamics were abnormal in all regardless of stroke history and comorbidity, but occipital lobe haemodynamics were also abnormal in children with syndromic moyamoya. Executive function deficits were noted in both idiopathic and syndromic moyamoya, whereas intellectual ability was impaired in syndromic moyamoya, even in the absence of stroke. Analysis of the relative effect of regional abnormal haemodynamics on cognitive outcomes demonstrated that executive dysfunction was predominantly explained by right parietal and white matter haemodynamics independent of stroke and comorbidity, while posterior circulation haemodynamics predicted intellectual ability. These results suggest that parietal and posterior haemodynamics play a compensatory role in overcoming frontal vulnerability and cognitive impairment.

Novel Therapeutic Strategies for Ischemic Stroke: Recent Insights into Autophagy

Stroke is one of the leading causes of death and disability worldwide. Autophagy is a conserved cellular catabolic pathway that maintains cellular homeostasis by removal of damaged proteins and organelles, which is critical for the maintenance of energy and function homeostasis of cells. Accumulating evidence demonstrates that autophagy plays important roles in pathophysiological mechanisms under ischemic stroke. Previous investigations show that autophagy serves as a “double-edged sword” in ischemic stroke as it can either promote the survival of neuronal cells or induce cell death in special conditions. Following ischemic stroke, autophagy is activated or inhibited in several cell types in brain, including neurons, astrocytes, and microglia, as well as microvascular endothelial cells, which involves in inflammatory activation, modulation of microglial phenotypes, and blood-brain barrier permeability. However, the exact mechanisms of underlying the role of autophagy in ischemic stroke are not fully understood. This review focuses on the recent advances regarding potential molecular mechanisms of autophagy in different cell types. The focus is also on discussing the “double-edged sword” effect of autophagy in ischemic stroke and its possible underlying mechanisms. In addition, potential therapeutic strategies for ischemic stroke targeting autophagy are also reviewed.

Functional implications of microvascular heterogeneity for oxygen uptake and utilization

In the vascular system, an extensive network structure provides convective and diffusive transport of oxygen to tissue. In the microcirculation, parameters describing network structure, blood flow, and oxygen transport are highly heterogeneous. This heterogeneity can strongly affect oxygen supply and organ function, including reduced oxygen uptake in the lung and decreased oxygen delivery to tissue. The causes of heterogeneity can be classified as extrinsic or intrinsic. Extrinsic heterogeneity refers to variations in oxygen demand in the systemic circulation or oxygen supply in the lungs. Intrinsic heterogeneity refers to structural heterogeneity due to stochastic growth of blood vessels and variability in flow pathways due to geometric constraints, and resulting variations in blood flow and hematocrit. Mechanisms have evolved to compensate for heterogeneity and thereby improve oxygen uptake in the lung and delivery to tissue. These mechanisms, which involve long-term structural adaptation and short-term flow regulation, depend on upstream responses conducted along vessel walls, and work to redistribute flow and maintain blood and tissue oxygenation. Mathematically, the variance of a functional quantity such as oxygen delivery that depends on two or more heterogeneous variables can be reduced if one of the underlying variables is controlled by an appropriate compensatory mechanism. Ineffective regulatory mechanisms can result in poor oxygen delivery even in the presence of adequate overall tissue perfusion. Restoration of endothelial function, and specifically conducted responses, should be considered when addressing tissue hypoxemia and organ failure in clinical settings.

Activation of Glutamate Transport Increases Arteriole Diameter in v ivo: Implications for Neurovascular Coupling

In order to meet the energetic demands of cell-to-cell signaling, increases in local neuronal signaling are matched by a coordinated increase in local blood flow, termed neurovascular coupling. Multiple different signals from neurons, astrocytes, and pericytes contribute to this control of blood flow. Previously, several groups demonstrated that inhibition/ablation of glutamate transporters attenuates the neurovascular response. However, it was not determined if glutamate transporter activation was sufficient to increase blood flow. Here, we used multiphoton imaging to monitor the diameter of fluorescently labeled cortical arterioles in anesthetized C57/B6J mice. We delivered vehicle, glutamate transporter substrates, or a combination of a glutamate transporter substrate with various pharmacologic agents via a glass micropipette while simultaneously visualizing changes in arteriole diameter. We developed a novel image analysis method to automate the measurement of arteriole diameter in these time-lapse analyses. Using this workflow, we first conducted pilot experiments in which we focally applied L-glutamate, D-aspartate, or L-threo-hydroxyaspartate (L-THA) and measured arteriole responses as proof of concept. We subsequently applied the selective glutamate transport substrate L-THA (applied at concentrations that do not activate glutamate receptors). We found that L-THA evoked a significantly larger dilation than that observed with focal saline application. This response was blocked by co-application of the potent glutamate transport inhibitor, L-(2S,3S)-3-[3-[4-(trifluoromethyl)-benzoylamino]benzyloxy]-aspartate (TFB-TBOA). Conversely, we were unable to demonstrate a reduction of this effect through co-application of a cocktail of glutamate and GABA receptor antagonists. These studies provide the first direct evidence that activation of glutamate transport is sufficient to increase arteriole diameter. We explored potential downstream mechanisms mediating this transporter-mediated dilation by using a Ca2+ chelator or inhibitors of reversed-mode Na+/Ca2+ exchange, nitric oxide synthetase, or cyclo-oxygenase. The estimated effects and confidence intervals suggested some form of inhibition for a number of these inhibitors. Limitations to our study design prevented definitive conclusions with respect to these downstream inhibitors; these limitations are discussed along with possible next steps. Understanding the mechanisms that control blood flow are important because changes in blood flow/energy supply are implicated in several neurodegenerative disorders and are used as a surrogate measure of neuronal activity in widely used techniques such as functional magnetic resonance imaging (fMRI).

7,8-Dihydroxyflavone protects neurons against oxygen-glucose deprivation induced apoptosis and activates the TrkB/Akt pathway

BACKGROUND

7,8-dihydroxyflavone (7,8-DHF), a selective agonist of tropomyosin related kinase receptor B (TrkB), is known to exert protective effects in neurodegenerative diseases. However, the role of 7,8-DHF in TrkB signaling after ischemic stroke has remained elusive.

METHODS

In the vitro model of ischemic stroke, we investigated the neuroprotective effect of 7,8-DHF through activation of TrkB signaling. Neurons subjected to oxygen and glucose deprivation/reperfusion were treated with the protein kinase inhibitor K252a and a knockdown of TrkB. Cell counting kit-8 (CCK-8) assay, Flow Cytometric Analysis (FACS), TdT-mediated dUTP nick end labeling (TUNEL) assay were conducted for measuring cell viability and numbers of apoptotic cells. And apoptosis-associated proteins were analyzed by Western blotting.

RESULTS

Compared with the Control group, OGD/R group revealed lower cell viability by CCK-8 assay FACS and TUNEL assay showed increased rates of neuronal apoptosis. However, 7,8-DHF treatment increased cell viability and reduced neuronal apoptosis. Western blotting indicated upregulated Bax and cleaved caspase-3 and but downregulated Bcl-2 following OGD/R. Whereas 7,8-DHF treatment downregulated Bax and cleaved caspase-3 but upregulated Bcl-2. These changes were accompanied by a significant increase in the phosphorylation of TrkB and Akt following 7,8-DHF administration. However, the administration of K252a and knockdown of TrkB could alleviate those effects.

CONCLUSION

Our study demonstrates that activation of TrkB signaling by 7,8-DHF protects neurons against OGD/R injury via the TrkB/Akt pathway, which provides the evidence for the role of TrkB signaling in OGD-induced neuronal damage and may become a potential therapeutic target for ischemic stroke.

Vascular Dementia and Crosstalk Between the Complement and Coagulation Systems

Vascular Dementia (VaD) is a neurocognitive disorder caused by reduced blood flow to the brain tissue, resulting in infarction, and is the second most common type of dementia. The complement and coagulation systems are evolutionary host defence mechanisms activated by acute tissue injury to induce inflammation, clot formation and lysis; recent studies have revealed that these systems are closely interlinked. Overactivation of these systems has been recognised to play a key role in the pathogenesis of neurological disorders such as Alzheimer's disease and multiple sclerosis, however their role in VaD has not yet been extensively reviewed. This review aims to bridge the gap in knowledge by collating current understanding of VaD to enable identification of complement and coagulation components involved in the pathogenesis of this disorder that may have their effects amplified or supressed by crosstalk. Exploration of these mechanisms may unveil novel therapeutic targets or biomarkers that would improve current treatment strategies for VaD.

The Relationship Between ADAMTS13 Activity and Overall Cerebral Small Vessel Disease Burden: A Cross-Sectional Study Based on CSVD

Objectives: This study aimed to investigate the association between plasma von Willebrand factor (VWF) level, ADAMTS13 activity, and neuroimaging features of cerebral small vessel disease (CSVD), including the CSVD neuroimaging markers and the overall CSVD burden.

Methods: CSVD patients admitted to our hospital from 2016 to 2020 were recruited. Plasma VWF level and ADAMTS13 activity were measured. The overall effect of CSVD on the brain was described as a validated CSVD score. We evaluated the association between VWF levels, ADAMTS13 activity, and the increasing severity of CSVD score by the logistic regression model.

Results: We enrolled 296 patients into this study. The mean age of the sample was 69.0 years (SD 7.0). The mean VWF level was 1.31 IU/mL, and the ADAMTS13 activity was 88.01 (SD 10.57). In multivariate regression analysis, lower ADAMTS13 activity and higher VWF level was related to white matter hyperintensity (WMH) [β = −7.31; 95% confidence interval (CI) (−9.40, −4.93); p<0.01; β = 0.17; 95% confidence interval (0.11, 0.23); p<0.01], subcortical infarction (SI) [(β = −9.22; 95% CI (−11.37, −7.06); p<0.01); β = 0.21; 95% confidence interval (0.15, 0.27); p<0.01] independently, but not cerebral microbleed (CMB) [(β = −2.3; 95% CI (−4.95, 0.05); p = 0.22); β = 0.02; 95% confidence interval (−0.05, 0.08); p = 0.63]. Furthermore, ADAMTS13 activity was independently negatively correlated with the overall CSVD burden (odd ratio = 21.33; 95% CI (17.46, 54.60); p < 0.01) after adjustment for age, history of hypertension, and current smoking.

Conclusions: Reducing ADAMTS13 activity change is related to white matter hyperintensity, subcortical infarction, but not with cerebral microhemorrhage. In addition, ADAMTS13 may have played an essential role in the progression of CSVD.

Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation

Brain function critically depends on a close matching between metabolic demands, appropriate delivery of oxygen and nutrients, and removal of cellular waste. This matching requires continuous regulation of cerebral blood flow (CBF), which can be categorized into four broad topics: 1) autoregulation, which describes the response of the cerebrovasculature to changes in perfusion pressure; 2) vascular reactivity to vasoactive stimuli [including carbon dioxide (CO2)]; 3) neurovascular coupling (NVC), i.e., the CBF response to local changes in neural activity (often standardized cognitive stimuli in humans); and 4) endothelium-dependent responses. This review focuses primarily on autoregulation and its clinical implications. To place autoregulation in a more precise context, and to better understand integrated approaches in the cerebral circulation, we also briefly address reactivity to CO2 and NVC. In addition to our focus on effects of perfusion pressure (or blood pressure), we describe the impact of select stimuli on regulation of CBF (i.e., arterial blood gases, cerebral metabolism, neural mechanisms, and specific vascular cells), the interrelationships between these stimuli, and implications for regulation of CBF at the level of large arteries and the microcirculation. We review clinical implications of autoregulation in aging, hypertension, stroke, mild cognitive impairment, anesthesia, and dementias. Finally, we discuss autoregulation in the context of common daily physiological challenges, including changes in posture (e.g., orthostatic hypotension, syncope) and physical activity.

Artificial neurovascular network (ANVN) to study the accuracy vs. efficiency trade-off in an energy dependent neural network

Artificial feedforward neural networks perform a wide variety of classification and function approximation tasks with high accuracy. Unlike their artificial counterparts, biological neural networks require a supply of adequate energy delivered to single neurons by a network of cerebral microvessels. Since energy is a limited resource, a natural question is whether the cerebrovascular network is capable of ensuring maximum performance of the neural network while consuming minimum energy? Should the cerebrovascular network also be trained, along with the neural network, to achieve such an optimum? In order to answer the above questions in a simplified modeling setting, we constructed an Artificial Neurovascular Network (ANVN) comprising a multilayered perceptron (MLP) connected to a vascular tree structure. The root node of the vascular tree structure is connected to an energy source, and the terminal nodes of the vascular tree supply energy to the hidden neurons of the MLP. The energy delivered by the terminal vascular nodes to the hidden neurons determines the biases of the hidden neurons. The "weights" on the branches of the vascular tree depict the energy distribution from the parent node to the child nodes. The vascular weights are updated by a kind of "backpropagation" of the energy demand error generated by the hidden neurons. We observed that higher performance was achieved at lower energy levels when the vascular network was also trained along with the neural network. This indicates that the vascular network needs to be trained to ensure efficient neural performance. We observed that below a certain network size, the energetic dynamics of the network in the per capita energy consumption vs. classification accuracy space approaches a fixed-point attractor for various initial conditions. Once the number of hidden neurons increases beyond a threshold, the fixed point appears to vanish, giving place to a line of attractors. The model also showed that when there is a limited resource, the energy consumption of neurons is strongly correlated to their individual contribution to the network's performance.

N,N-Dimethyltryptamine attenuates spreading depolarization and restrains neurodegeneration by sigma-1 receptor activation in the ischemic rat brain

Dimethyltryptamine (DMT), an endogenous ligand of sigma-1 receptors (Sig-1Rs), acts against systemic hypoxia, but whether DMT may prevent cerebral ischemic injury is unexplored. Here global forebrain ischemia was created in anesthetized rats and aggravated with the induction of spreading depolarizations (SDs) and subsequent short hypoxia before reperfusion. Drugs (DMT, the selective Sig-1R agonist PRE-084, the Sig-1R antagonist NE-100, or the serotonin receptor antagonist asenapine) were administered intravenously alone or in combination while physiological variables and local field potential from the cerebral cortex was recorded. Neuroprotection and the cellular localization of Sig-1R were evaluated with immunocytochemistry. Plasma and brain DMT content was measured by 2D-LC-HRMS/MS. The affinity of drugs for cerebral Sig-1R was evaluated with a radioligand binding assay. Both DMT and PRE-084 mitigated SDs, counteracted with NE-100. Further, DMT attenuated SD when co-administered with asenapine, compared to asenapine alone. DMT reduced the number of apoptotic and ferroptotic cells and supported astrocyte survival. The binding affinity of DMT to Sig-1R matched previously reported values. Sig-1Rs were associated with the perinuclear cytoplasm of neurons, astrocytes and microglia, and with glial processes. According to these data, DMT may be considered as adjuvant pharmacological therapy in the management of acute cerebral ischemia.

Spatiotemporal monitoring of changes in oxy/deoxy-hemoglobin concentration and blood pulsation on human skin using smartphone-enabled remote multispectral photoplethysmography

We propose a smartphone-enabled remote multispectral photoplethysmography (SP-rmPPG) system and method to realize spatiotemporal monitoring of perfusion changes and pulsations of the oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) information of the effective blood volume within light interrogated skin tissue beds. The system is implemented on an unmodified smartphone utilizing its built-in camera and flashlight to acquire videos of the skin reflectance. The SP-rmPPG method converts the RGB video into multispectral cubes, upon which to decouple the dynamic changes in HbO2 and Hb information using a modified Beer-Lambert law and the selective wavelength bands of 500 nm and 650 nm. Blood pulsation amplitudes are then obtained by applying a window-based lock-in amplification on the derived spatiotemporal changes in HbO2 or Hb signals. To demonstrate the feasibility of proposed method, we conduct two experiments on the skin tissue beds that are conditioned by occlusive maneuver of supplying arteries: one using the popular blood cuff pressure maneuver on the upper arm, and another artificially inducing a transient ischemic condition on the facial skin tissue beds by finger pressing on the supplying external carotid artery. The cuff experiment shows that the measured dynamic information of HbO2 and Hb in the downstream agrees well with the parallel measurements of oxygenation saturation given by the standard pulse oximeter. We also observe the expected imbalance of spatiotemporal changes in the HbO2 and Hb between the right and left cheeks when the transient ischemic condition is induced in the one side of facial skin tissue beds. The results from the two experiments sufficiently demonstrate the feasibility of the proposed method to monitor the spatiotemporal changes in the skin hemodynamics, including blood oxygenation and pulsation amplitudes. Considering the ever-growing accessibility and affordability of the smartphone to the general public, the proposed strategy promises the early screening of vascular diseases and improving general public health particularly in rural areas with low resource settings.

Effects of impaired microvascular flow regulation on metabolism-perfusion matching and organ function

Impaired tissue oxygen delivery is a major cause of organ damage and failure in critically ill patients, which can occur even when systemic parameters, including cardiac output and arterial hemoglobin saturation, are close to normal. This review addresses oxygen transport mechanisms at the microcirculatory scale, and how hypoxia may occur in spite of adequate convective oxygen supply. The structure of the microcirculation is intrinsically heterogeneous, with wide variations in vessel diameters and flow pathway lengths, and consequently also in blood flow rates and oxygen levels. The dynamic processes of structural adaptation and flow regulation continually adjust microvessel diameters to compensate for heterogeneity, redistributing flow according to metabolic needs to ensure adequate tissue oxygenation. A key role in flow regulation is played by conducted responses, which are generated and propagated by endothelial cells and signal upstream arterioles to dilate in response to local hypoxia. Several pathophysiological conditions can impair local flow regulation, causing hypoxia and tissue damage leading to organ failure. Therapeutic measures targeted to systemic parameters may not address or may even worsen tissue oxygenation at the microvascular level. Restoration of tissue oxygenation in critically ill patients may depend on restoration of endothelial cell function, including conducted responses.

The Role of Resolvins: EPA and DHA Derivatives Can Be Useful in the Prevention and Treatment of Ischemic Stroke

INTRODUCTION

Most ischemic strokes develop as a result of atherosclerosis, in which inflammation plays a key role. The synthesis cascade of proinflammatory mediators participates in the process induced in the vascular endothelium and platelets. Resolvins are anti-inflammatory mediators originating from eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which may improve the prognosis related to atherosclerosis by inhibiting the production of proinflammatory cytokines, limiting neutrophil migration, or positively influencing phagocytosis. Although clinical trials with resolvin in humans after stroke have not been realized, they may soon find application.

AIM

The aim of the study was to review the available literature on the scope of the possibilities of the prevention and treatment of stroke with the use of resolvins, EPA and DHA derivatives.

MATERIALS AND METHODS

The review features articles published until 31 January 2020. The search for adequate literature was conducted using the keywords: stroke and resolvins. Over 150 articles were found. Studies not written in English, letters to the editor, conference abstracts, and duplicate information were excluded.

RESULTS

In several studies using the animal model, the supplementation of resolvin D2 decreased brain damage caused by myocardial infarction, and it reversed the neurological dysfunction of the brain. A decrease in the concentration of proinflammatory cytokines, such as TNF-α, Il-6, and Il-1β, was also observed, as well as a decrease in the scope of brain damage. In the context of stroke in animals, the treatment with resolvin D2 (RvD2) (injection) has a better effect than supplementation with DHA.

CONCLUSIONS

Resolvins are characterised by strong anti-inflammatory properties. Resolvins improve prognosis and decrease the risk of developing cardiovascular disease, consequently lowering the risk of stroke, and may find application in the treatment of stroke.

Association of White Matter Hyperintensities and Cardiovascular Disease

Cardiac and cerebrovascular diseases are currently the leading causes of mortality and disability worldwide. Both the heart and brain display similar vascular anatomy, with large conduit arteries running on the surface of the organ providing tissue perfusion through an intricate network of penetrating small vessels. Both organs rely on fine tuning of local blood flow to match metabolic demand. Blood flow regulation requires adequate functioning of the microcirculation in both organs, with loss of microvascular function, termed small vessel disease (SVD) underlying different potential clinical manifestations. SVD in the heart, known as coronary microvascular dysfunction, can cause chronic or acute myocardial ischemia and may lead to development of heart failure. In the brain, cerebral SVD can cause an acute stroke syndrome known as lacunar stroke or more subtle pathological alterations of the brain parenchyma, which may eventually lead to neurological deficits or cognitive decline in the long term. Coronary microcirculation cannot be visualized in vivo in humans, and functional information can be deduced by measuring the coronary flow reserve. The diagnosis of cerebral SVD is largely based on brain magnetic resonance imaging, with white matter hyperintensities, microbleeds, and brain atrophy reflecting key structural changes. There is evidence that such structural changes reflect underlying cerebral SVD. Here, we review interactions between SVD and cardiovascular risk factors, and we discuss the evidence linking cerebral SVD with large vessel atheroma, atrial fibrillation, heart failure, and heart valve disease.

Melatonin receptor agonist ramelteon attenuates mouse acute and chronic ischemic brain injury

Melatonin receptors (MTs) are potential drug targets for stroke therapy. Ramelteon is a selective melatonin receptor agonist used to treat insomnia. In this study we investigated whether ramelteon could attenuate cerebral ischemia in mice. Acute focal cerebral ischemia was induced in mice via middle cerebral artery occlusion (MCAO). We found oral administration of ramelteon (3.0 mg/kg) significantly attenuated ischemic injury even when it was given 4 h after the onset of ischemia. We showed that administration of ramelteon (3.0 mg/kg) displayed comparable protective efficacy and length of effective time window as administration of edaravone (10 mg/kg, i.p.), which was used in clinic to treat ischemic stroke. Chronic ischemic brain injury was induced in mice using photothrombosis. Oral administration of ramelteon (3.0 mg · kg^-1 · d^-1) for 7 days after ischemia significantly attenuated functional deficits for at least 15 days. The neuroprotection of ramelteon was blocked by 4-P-PDOT, a specific MT antagonist. We further revealed that ramelteon significantly inhibited autophagy in the peri-infarct cortex in both the mouse ischemia models via regulating AMPK/mTOR signaling pathway. Intracerebroventricular injection of rapamycin, an autophagy activator, compromised the neuroprotection of ramelteon, suggesting ramelteon might attenuate ischemic injury by counteracting autophagic cell death. These data demonstrate for the first time the potential benefits of ramelteon in the treatment of both acute and chronic ischemic brain injury and provide the rationale for the application of ramelteon in stroke therapy.

Cathodal tDCS exerts neuroprotective effect in rat brain after acute ischemic stroke

BACKGROUND

Transcranial direct current stimulation (tDCS) is a non-invasive brain modulation technique that has been proved to exert beneficial effects in the acute phase of stroke. To explore the underlying mechanism, we investigated the neuroprotective effects of cathodal tDCS on brain injury caused by middle cerebral artery occlusion (MCAO).

RESULTS

We established the MCAO model and sham MCAO model with an epicranial electrode implanted adult male Sprague-Dawley rats, and then they were randomly divided into four groups (MCAO + tDCS, MCAO + sham tDCS (Sham), Control + tDCS and Control + Sham group). In this study, the severity degree of neurological deficit, the morphology of brain damage, the apoptosis, the level of neuron-specific enolase and inflammatory factors, the activation of glial cells was detected. The results showed that cathodal tDCS significantly improved the level of neurological deficit and the brain morphology, reduced the brain damage area and apoptotic index, and increased the number of Nissl body in MCAO rats, compared with MCAO + Sham group. Meanwhile, the high level of NSE, inflammatory factors, Caspase 3 and Bax/Bcl2 ratio in MCAO rats was reduced by cathodal tDCS. Additionally, cathodal tDCS inhibited the activation of astrocyte and microglia induced by MCAO. No difference was found in two Control groups.

CONCLUSION

Our results suggested that cathodal tDCS could accelerate the recovery of neurologic deficit and brain damage caused by MCAO. The inhibition of neuroinflammation and apoptosis resulted from cathodal tDCS may be involved in the neuroprotective process.

Time for a Systems Biological Approach to Cognitive Aging?-A Critical Review

The underlying premise of current theories of cognitive decline with age tend to be primarily cognitive or biological explanations, with relatively few theories adequately integrating both aspects. Though literature has also emphasized the importance of several factors that contribute to cognitive aging including: (a) decline in sensory abilities; (b) the effect of motor speed on paper-pencil measures of cognitive speed; (c) the impact of level of education and physical activity; and (d) molecular biological changes that occur with age, these factors have seldom been implicated into any single theoretical model of cognitive aging. Indeed, such an integrated bio-cognitive model of aging has the potential to provide a more comprehensive understanding of attention, perception, learning, and memory across the lifespan. Thus, the aim of this review was to critically evaluate common theories of age-related cognitive decline and highlight the need for a more comprehensive systems neuroscience approach to cognitive aging.

Treadmill exercise promotes neurogenesis and myelin repair via upregulating Wnt/β‑catenin signaling pathways in the juvenile brain following focal cerebral ischemia/reperfusion

Physical exercise has a neuroprotective effect and is an important treatment after ischemic stroke. Promoting neurogenesis and myelin repair in the penumbra is an important method for the treatment of ischemic stroke. However, the role and potential mechanism of exercise in neurogenesis and myelin repair still needs to be clarified. The goal of the present study was to ascertain the possible effect of treadmill training on the neuroprotective signaling pathway in juvenile rats after ischemic stroke. The model of middle cerebral artery occlusion (MCAO) in juvenile rats was established and then the rats were randomly divided into 9 groups. XAV939 (an inhibitor of the Wnt/β‑catenin pathway) was used to confirm the effects of the Wnt/β‑catenin signaling pathway on exercise‑mediated neurogenesis and myelin repair. Neurological deficits were detected by modified neurological severity score, the injury of brain tissue and the morphology of neurons was detected by hematoxylin‑eosin staining and Nissl staining, and the infarct volume was detected by 2,3,5‑triphenyl tetrazolium chloride staining. The changes in myelin were observed by Luxol fast blue staining. The neuron ultrastructure was observed by transmission electron microscopy. Immunofluorescence and western blots analyzed the molecular mechanisms. The results showed that treadmill exercise improved neurogenesis, enhanced myelin repair, promoted neurological function recovery and reduced infarct volume. These were the results of the upregulation of Wnt3a and nucleus β‑catenin, brain‑derived neurotrophic factor (BDNF) and myelin basic protein (MBP). In addition, XAV939 inhibited treadmill exercise‑induced neurogenesis and myelin repair, which was consistent with the downregulation of Wnt3a, nucleus β‑catenin, BDNF and MBP expression, and the deterioration of neurological function. In summary, treadmill exercise promotes neurogenesis and myelin repair by upregulating the Wnt/β‑catenin signaling pathway, to improve the neurological deficit caused by focal cerebral ischemia/reperfusion.

Small Vessel Disease-Related Dementia: An Invalid Neurovascular Coupling?

The arteriosclerosis-dependent alteration of brain perfusion is one of the major determinants in small vessel disease, since small vessels have a pivotal role in the brain's autoregulation. Nevertheless, as far as we know, endothelium distress can potentiate the flow dysregulation and lead to subcortical vascular dementia that is related to small vessel disease (SVD), also being defined as subcortical vascular dementia (sVAD), as well as microglia activation, chronic hypoxia and hypoperfusion, vessel-tone dysregulation, altered astrocytes, and pericytes functioning blood-brain barrier disruption. The molecular basis of this pathology remains controversial. The apparent consequence (or a first event, too) is the macroscopic alteration of the neurovascular coupling. Here, we examined the possible mechanisms that lead a healthy aging process towards subcortical dementia. We remarked that SVD and white matter abnormalities related to age could be accelerated and potentiated by different vascular risk factors. Vascular function changes can be heavily influenced by genetic and epigenetic factors, which are, to the best of our knowledge, mostly unknown. Metabolic demands, active neurovascular coupling, correct glymphatic process, and adequate oxidative and inflammatory responses could be bulwarks in defense of the correct aging process; their impairments lead to a potentially catastrophic and non-reversible condition.

Targeting the NF-κB pathway for therapy of ischemic stroke

Ischemic strokes occur when a major cerebral artery or its branches are occluded, resulting in activation of inflammatory processes that cause secondary tissue injury, breakdown of the blood–brain barrier, edema or hemorrhage. Treatments that inhibit inflammatory processes may thus be highly beneficial. A key regulator of the inflammatory process is the nuclear factor kappa B (NF-κB) pathway. In its active form, NF-κB regulates expression of proinflammatory and proapoptotic genes. The molecules that interact with NF-κB, and the subunits that compose NF-κB itself, represent therapeutic targets that can be modulated to decrease inflammation. This review focuses on our current understanding of the NF-κB pathway and the potential benefits of inhibiting NF-κB in ischemia-reperfusion injury of the brain.

Therapeutic Relevance of Elevated Blood Pressure After Ischemic Stroke in the Hypertensive Rats

Over 80% of patients exhibit an acute increase in blood pressure (BP) following stroke. Current clinical guidelines make no distinction in BP management between patients with or without prior hypertension. Spontaneously hypertensive (SH) rats were preinstrumented with telemeters to record BP, intracranial pressure, and brain tissue oxygen in the predicted ischemic penumbra for 3 days before and 10 days after transient middle cerebral artery occlusion (n=8 per group) or sham (n=5). Before stroke, BP was either left untreated or chronically treated to a normotensive level (enalapril 10 mg/kg per day). Poststroke elevations in BP were either left uncontrolled, controlled (to the prestroke baseline level), or overcontrolled (to a normotensive level) via subcutaneous infusion of labetalol. Baseline values of intracranial pressure and brain tissue oxygen were similar between all groups, whereas BP was lower in treated SH rats (144±3 versus 115±5 mm Hg; P<0.001). Following middle cerebral artery occlusion, a similar rise in BP was observed in untreated (+16±2 mm Hg; P=0.005) and treated SH rats (+13±5 mm Hg; P=0.021). Intervening to prevent BP from increasing after stroke did not worsen outcome. However, reducing BP below prestroke baseline levels was associated with higher intracranial pressure (days 1-3; P<0.001), reduced cerebral perfusion pressure (days 2-4; P<0.001), higher mortality, slower functional recovery and larger infarct volumes. Although treating to maintain BP at the prestroke baseline level was not detrimental, our results suggest that when setting BP targets after stroke, consideration must be given to the potential negative impact of inadvertent excessive BP lowering in subjects with undiagnosed or poorly controlled hypertension.

Cigarette smoke extract exacerbates hyperpermeability of cerebral endothelial cells after oxygen glucose deprivation and reoxygenation

Cigarette smoking is a risk factor for stroke and is linked to stroke severity. Previous studies have shown that cigarette smoke extract (CSE) triggers endothelial dysfunction in vitro by initiating oxidative stress and/or an inflammatory response. In addition, cerebral endothelial dysfunction (particularly at the level of the blood-brain barrier [BBB]) contributes to stroke pathogenesis. Therefore, we hypothesized that cigarette smoking may influence stroke, at least in part, by exacerbating ischaemia-induced BBB disruption. To test this, we examined the effect of CSE on the permeability of cerebral endothelial cells exposed to oxygen glucose deprivation and reoxygenation (OGD + RO). We found that the loss of BBB integrity following ischaemic/reperfusion-like conditions was significantly worsened by CSE. Despite this being associated with increased mRNA expression of Nox catalytic subunits, reactive oxygen species (ROS) levels were however markedly lower. Furthermore, this occurred in association with elevated expression of antioxidant enzymes (SOD1, SOD2, and Gpx-1), suggesting an antioxidant defence response. Lastly, we found that CSE significantly upregulated mRNA expression of cytokines (IL-6 and TGF-β). Collectively, these results show that acute exposure to CSE worsens BBB disruption caused by OGD + RO, however, this is not linked to elevated ROS levels but may involve inflammatory mechanisms.

Baicalein administered in the subacute phase ameliorates ischemia-reperfusion-induced brain injury by reducing neuroinflammation and neuronal damage

Ischemic stroke is a cerebrovascular disease with high morbidity, high mortality, and high disability, representing a serious threat to human life and health. Clinically, the extensive injury caused by ischemic stroke results from ischemia-reperfusion (I/R) injury thrombolytic treatment. However, there are few reports on the use of medications in the subacute stage of cerebral I/R. Baicalein (5,6,7-trihydroxyflavone) is a biologically active ingredient extracted from the root of Scutellaria baicalensis Georgi. In the present study, we investigated the therapeutic effect of baicalein administered in the subacute phase of cerebral I/R injury in a rat model of ischemia induced by occlusion of the middle cerebral artery (MCA). Rats were treated daily with baicalein (200 mg/kg, i.g.) in the subacute phase (24 h after reperfusion) for 7 days. The results showed that baicalein significantly reduced neurobehavioral deficits and decreased brain infarct volume from 18.99% to 7.41%. Immunofluorescence analysis of the ischemic penumbra showed that baicalein significantly reduced expression of the M1 marker, cluster of differentiation (CD) 16 and CD86, and increased expression of the M2 marker, CD 163 and CD206, indicating that baicalein inhibited M1 transformation and promoted M2 transformation of microglia/macrophage to inhibit neuroinflammation. Moreover, baicalein suppressed NF-κB signaling by reducing IκBα phosphorylation and nuclear translocation of NF-κB/p65, which decreased the release of the pro-inflammatory factors IL-6, IL-18, and TNF-α. In addition, baicalein reduced phosphorylation of JNK, ERK and p38, which are involved modulation of microglia/macrophage M1/M2 polarization. Western blot analysis of apoptosis- and autophagy-related proteins showed that baicalein increased the Bcl-2/Bax ratio and reduced caspase-3 expression to decrease neuronal apoptosis and ameliorate neuronal loss. Baicalein also decreased the LC3-II/LC3-I ratio and promoted phosphorylation of the PI3K/Akt/mTOR signaling pathway which implied inhibition of autophagy. These observations suggest that baicalein exerts neuroprotective effects by reducing neuroinflammation, apoptosis and autophagy, and protects against cerebral I/R injury in the subacute phase in vivo.

Tóth O, Török Z, Varga DP, Menyhárt Á, Frank R, Hantosi D, Hunya Á, Bari F, Horváth I, Vigh L, Farkas E. The impact of dihydropyridine derivatives on the cerebral blood flow response to somatosensory stimulation and spreading depolarization

BACKGROUND AND PURPOSE

A new class of dihydropyridine derivatives, which act as co-inducers of heat shock protein but are devoid of calcium channel antagonist and vasodilator effects, has recently been developed with the purpose of selectively targeting neurodegeneration. Here, we evaluated the action of one of these novel compounds LA1011 on neurovascular coupling in the ischaemic rat cerebral cortex. As a reference, we applied nimodipine, a vasodilator dihydropyridine and well-known calcium channel antagonist.

EXPERIMENTAL APPROACH

Rats were treated with LA1011 or nimodipine, either by chronic, systemic (LA1011), or acute, local administration (LA1011 and nimodipine). In the latter treatment group, global forebrain ischaemia was induced in half of the animals by bilateral common carotid artery occlusion under isoflurane anaesthesia. Functional hyperaemia in the somatosensory cortex was created by mechanical stimulation of the contralateral whisker pad under α-chloralose anaesthesia. Spreading depolarization (SD) events were elicited subsequently by 1 M KCl. Local field potential and cerebral blood flow (CBF) in the parietal somatosensory cortex were monitored by electrophysiology and laser Doppler flowmetry.

KEY RESULTS

LA1011 did not alter CBF, but intensified SD, presumably indicating the co-induction of heat shock proteins, and, perhaps an anti-inflammatory effect. Nimodipine attenuated evoked potentials and SD. In addition to the elevation of baseline CBF, nimodipine augmented hyperaemia in response to both somatosensory stimulation and SD, particularly under ischaemia.

CONCLUSIONS AND IMPLICATIONS

In contrast to the CBF improvement achieved with nimodipine, LA1011 seems not to have discernible cerebrovascular effects but may up-regulate the stress response.

Rapamycin in ischemic stroke: Old drug, new tricks?

The significant morbidity that accompanies stroke makes it one of the world's most devastating neurological disorders. Currently, proven effective therapies have been limited to thrombolysis and thrombectomy. The window for the administration of these therapies is narrow, hampered by the necessity of rapidly imaging patients. A therapy that could extend this window by protecting neurons may improve outcome. Endogenous neuroprotection has been shown to be, in part, due to changes in mTOR signalling pathways and the instigation of productive autophagy. Inducing this effect pharmacologically could improve clinical outcomes. One such therapy already in use in transplant medicine is the mTOR inhibitor rapamycin. Recent evidence suggests that rapamycin is neuroprotective, not only via neuronal autophagy but also through its broader effects on other cells of the neurovascular unit. This review highlights the potential use of rapamycin as a multimodal therapy, acting on the blood-brain barrier, cerebral blood flow and inflammation, as well as directly on neurons. There is significant potential in applying this old drug in new ways to improve functional outcomes for patients after stroke.

The modular architecture and neurochemical patterns in the cerebellar cortex

The review deals with topical issues of the neuronal arrangement underlying basic cerebellar functions. The cerebellum and its auxiliary structures contain several hundreds of modules (so called "microzones"). Each module receives the corticopetal input specific for the lobule it belongs to and forms the topographic projection. The precision of the major input-output signal flow in the cerebellar cortex is provided by a pronounced stratification of its synaptic zones of a various origin and regular topography of its afferent connections, interneurons, and efferent neurons. There is a nice match between the anatomical and functional coordinates of the modules, whose spatial boundaries are determined by the spread of afferent excitation and local interneuron connections. The dynamic characteristics of the modules are analyzed by the example of the formation of the nitrergic neuron ensembles and cerebellar projections of corticopetal fibers. The authors discuss the cerebellar blood flow and its relation to the activity of NO/GABAergic Lugaro cells and other interneurons in the cerebellar cortex. A generalized scheme of intra- and intermodular communication is proposed.

Oxidative stress in cerebral small vessel disease. Role of reactive species

Cerebral small vessel disease (CSVD) is a wide term describing the condition affecting perforating arterial branches as well as arterioles, venules, and capillaries. Cerebral vascular net is one of the main targets of localised oxidative stress processes causing damage to vasculature, changes in the blood flow and blood-brain barrier and, in consequence, promoting neurodegenerative alterations in the brain tissue. Numerous studies report the fact of oxidation to proteins, sugars, lipids and nucleic acids, occurring in most neurodegenerative diseases mainly in the earliest stages and correlations with the development of cognitive and motor disturbances. The dysfunction of endothelium can be caused by oxidative stress and inflammatory mechanisms as a result of reactions and processes generating extensive reactive oxygen species (ROS) production such as high blood pressure, oxidised low density lipoproteins (oxLDL), very low density lipoproteins (vLDL), diabetes, homocysteinaemia, smoking, and infections. Several animal studies show positive aspects of ROS, especially within cerebral vasculature.

NRG-1β exerts neuroprotective effects against ischemia reperfusion-induced injury in rats through the JNK signaling pathway

BACKGROUND

Neuregulin-1β (NRG-1β) has great potential to be developed into therapeutics for neuroprotection. The aim of the current study was to analyze the effects and possible signaling pathway of NRG-1β on brain tissues in a rat model of middle cerebral artery occlusion/reperfusion (MCAO/R).

METHODS

In order to observe the protective effect of NRG-1β on MCAO/R, the neurological deficit and infarct volume were measured using a modified neurological severity score (mNSS) test and by triphenyl tetrazolium chloride (TTC) staining. In order to detect the antagonistic effect of NRG-1β on nerve cells and the blood-brain barrier (BBB), the morphology and structure of cortical brain tissues were observed by Evans Blue (EB) staining, hematoxylin-eosin (H&E) and Nissl staining, in situ cell death detection kit, and transmission electron microscopy (TEM). In order to investigate whether NRG-1β exhibited a significant neuroprotective effect via the JNK signaling pathway, the activity of JNK and the levels of phospho-MKK4, phospho-JNK, pan-JNK and phospho-c-Jun were tested using a JNK activity screening kit, immunofluorescent labeling, and western blot analysis, respectively.

RESULTS

In the NRG-1β treatment group, accompanied with a decrease in JNK activity, the protein levels of phospho-JNK, phospho-MKK4 and phospho-c-Jun decreased, the ischemia-induced apoptosis decreased, the abnormal morphological structures of nerve cells were ameliorated, the integrity of the BBB was restored, and infarct volume was reduced. At the same time, neurological function was significantly recovered.

CONCLUSION

NRG-1β exerts a neuroprotective effect through the JNK signaling pathway in MCAO/R rats.

Age or ischemia uncouples the blood flow response, tissue acidosis, and direct current potential signature of spreading depolarization in the rat brain

Spreading depolarization (SD) events contribute to lesion maturation in the acutely injured human brain. Neurodegeneration related to SD is thought to be caused by the insufficiency of the cerebral blood flow (CBF) response; yet the mediators of the CBF response, or their deficiency in the aged or ischemic cerebral cortex, remain the target of intensive research. Here, we postulated that tissue pH effectively modulates the magnitude of hyperemia in response to SD, the coupling of which is prone to be dysfunctional in the aged or ischemic cerebral cortex. To test this hypothesis, we conducted systematic correlation analysis between the direct current (DC) potential signature of SD, SD-associated tissue acidosis, and hyperemic element of the CBF response in the isoflurane-anesthetized, young or old, and intact or ischemic rat cerebral cortex. The data demonstrate that the amplitude of the SD-related DC potential shift, tissue acidosis, and hyperemia are tightly coupled in the young intact cortex; ischemia and old age uncouples the amplitude of hyperemia from the amplitude of the DC potential shift and acidosis; the duration of the DC potential shift, hyperemia and acidosis positively correlate under ischemia alone; and old age disproportionally elongates the duration of acidosis with respect to the DC potential shift and hyperemia under ischemia. The coincidence of the variables supports the view that local CBF regulation with SD must have an effective metabolic component, which becomes dysfunctional with age or under ischemia. Finally, the known age-related acceleration of ischemic neurodegeneration may be promoted by exaggerated tissue acidosis.

NEW & NOTEWORTHY The hyperemic element of the cerebral blood flow response to spreading depolarization is effectively modulated by tissue pH in the young intact rat cerebral cortex. This coupling becomes dysfunctional with age or under ischemia, and tissue acidosis lasts disproportionally longer in the aged cortex, making the tissue increasingly more vulnerable.

Extracellular matrix inflammation in vascular cognitive impairment and dementia

Vascular cognitive impairment and dementia (VCID) include a wide spectrum of chronic manifestations of vascular disease related to large vessel strokes and small vessel disease (SVD). Lacunar strokes and white matter (WM) injury are consequences of SVD. The main vascular risk factor for SVD is brain hypoperfusion from cerebral blood vessel narrowing due to chronic hypertension. The hypoperfusion leads to activation and degeneration of astrocytes with the resulting fibrosis of the extracellular matrix (ECM). Elasticity is lost in fibrotic cerebral vessels, reducing the response of stiffened blood vessels in times of increased metabolic need. Intermittent hypoxia/ischaemia activates a molecular injury cascade, producing an incomplete infarction that is most damaging to the deep WM, which is a watershed region for cerebral blood flow. Neuroinflammation caused by hypoxia activates microglia/macrophages to release proteases and free radicals that perpetuate the damage over time to molecules in the ECM and the neurovascular unit (NVU). Matrix metalloproteinases (MMPs) secreted in an attempt to remodel the blood vessel wall have the undesired consequences of opening the blood-brain barrier (BBB) and attacking myelinated fibres. This dual effect of the MMPs causes vasogenic oedema in WM and vascular demyelination, which are the hallmarks of the subcortical ischaemic vascular disease (SIVD), which is the SVD form of VCID also called Binswanger's disease (BD). Unravelling the complex pathophysiology of the WM injury-related inflammation in the small vessel form of VCID could lead to novel therapeutic strategies to reduce damage to the ECM, preventing the progressive damage to the WM.

Multi-modal assessment of neurovascular coupling during cerebral ischaemia and reperfusion using remote middle cerebral artery occlusion

Hyperacute changes in cerebral blood flow during cerebral ischaemia and reperfusion are important determinants of injury. Cerebral blood flow is regulated by neurovascular coupling, and disruption of neurovascular coupling contributes to brain plasticity and repair problems. However, it is unknown how neurovascular coupling is affected hyperacutely during cerebral ischaemia and reperfusion. We have developed a remote middle cerebral artery occlusion model in the rat, which enables multi-modal assessment of neurovascular coupling immediately prior to, during and immediately following reperfusion. Male Wistar rats were subjected to remote middle cerebral artery occlusion, where a long filament was advanced intraluminally through a guide cannula in the common carotid artery. Transcallosal stimulation evoked increases in blood flow, tissue oxygenation and neuronal activity, which were diminished by middle cerebral artery occlusion and partially restored during reperfusion. These evoked responses were not affected by administration of the thrombolytic alteplase at clinically used doses. Evoked cerebral blood flow responses were fully restored at 24 h post-middle cerebral artery occlusion indicating that neurovascular dysfunction was not sustained. These data show for the first time that the rat remote middle cerebral artery occlusion model coupled with transcallosal stimulation provides a novel method for continuous assessment of hyperacute neurovascular coupling changes during ischaemia and reperfusion, and offers unique insight into hyperacute ischaemic pathophysiology.

Correlation between serum S100β protein levels and cognitive dysfunction in patients with cerebral small vessel disease: a case-control study

The present study was designed to explore the correlation between serum S100β levels and cognitive dysfunction in patients with cerebral small vessel disease (SVD). A total of 172 SVD patients participated in the study, and they were assigned to patients with no cognitive impairment (NCI group) and those with vascular cognitive impairment no dementia (VCIND group). In total, 105 people were recruited into the normal control group. Serum S100β protein level was detected by ELISA. A receiver operating characteristic (ROC) curve was employed for the predictive value of serum S100β in diagnosing SVD with cognitive dysfunction. Pearson correlation analysis was used to examine the association of S100β level with mini-mental state examination (MMSE) and Montreal cognitive assessment (MoCA) and the association of S100β levels with hypertension. Logistic regression analysis was used to analyze risk factors of SVD. The serum S100β levels in the VCIND group were higher than those in the NCI and normal control groups. Logistic regression analysis revealed that a high serum S100β protein level, hypertension, and high low density lipoprotein-cholesterol (LDL-C) level were the independent risk factors for SVD. In addition, hypertension patients showed higher S100β levels than those with normal blood pressure and the normal control group, and there was a positive correlation between S100β level and blood pressure. The concentration of serum S100β level was related to impairment of cognition function of VCIND patients, therefore, early detection of serum S100β was of great value for diagnosis of SVD.

Early Changes in Glutamate Metabolism and Perfusion in Basal Ganglia following Hypoxia-Ischemia in Neonatal Piglets: A Multi-Sequence 3.0T MR Study

The excitotoxicity of glutamate metabolism as well as hemodynamic disorders of the brain are both risk factors for neonatal hypoxic–ischemic brain damage (HIBD). In the present study, changes in glutamate metabolism in the basal ganglia were detected by proton magnetic resonance spectroscopy (¹H-MRS) at 0–6, 8–12, 24–30, and 48–60 h after the induction of hypoxia-ischemia (HI) in newborn piglets. Meanwhile, correlation analysis was performed by combining the microcirculatory perfusion informations acquired by intravoxel incoherent motion (IVIM) scan to explore their possible interaction mechanism. The results suggested that Glu level in the basal ganglia underwent a “two-phase” change after HI; perfusion fraction f, an IVIM-derived perfusion parameter, was clearly decreased in the early stage after HI, then demonstrated a transient and slight recovery process, and thereafter continued to decrease. The changes in f and Glu level were in a significant negative correlation (r = −0.643, P = 0.001). Our study results revealed that Glu level is closely associated with the microcirculatory perfusion changes in the acute stage of HIBD.

Pathogenic mechanisms following ischemic stroke

Stroke is the second most common cause of death and the leading cause of disability worldwide. Brain injury following stroke results from a complex series of pathophysiological events including excitotoxicity, oxidative and nitrative stress, inflammation, and apoptosis. Moreover, there is a mechanistic link between brain ischemia, innate and adaptive immune cells, intracranial atherosclerosis, and also the gut microbiota in modifying the cerebral responses to ischemic insult. There are very few treatments for stroke injuries, partly owing to an incomplete understanding of the diverse cellular and molecular changes that occur following ischemic stroke and that are responsible for neuronal death. Experimental discoveries have begun to define the cellular and molecular mechanisms involved in stroke injury, leading to the development of numerous agents that target various injury pathways. In the present article, we review the underlying pathophysiology of ischemic stroke and reveal the intertwined pathways that are promising therapeutic targets.

COPD and stroke: are systemic inflammation and oxidative stress the missing links?

Chronic obstructive pulmonary disease (COPD) is characterized by progressive airflow limitation and loss of lung function, and is currently the third largest cause of death in the world. It is now well established that cardiovascular-related comorbidities such as stroke contribute to morbidity and mortality in COPD. The mechanisms linking COPD and stroke remain to be fully defined but are likely to be interconnected. The association between COPD and stroke may be largely dependent on shared risk factors such as aging and smoking, or the association of COPD with traditional stroke risk factors. In addition, we propose that COPD-related systemic inflammation and oxidative stress may play important roles by promoting cerebral vascular dysfunction and platelet hyperactivity. In this review, we briefly discuss the pathogenesis of COPD, acute exacerbations of COPD (AECOPD) and cardiovascular comorbidities associated with COPD, in particular stroke. We also highlight and discuss the potential mechanisms underpinning the link between COPD and stroke, with a particular focus on the roles of systemic inflammation and oxidative stress.