Early disruptions of the blood-brain barrier may contribute to exacerbated neuronal damage and prolonged functional recovery following stroke in aged rats

Senescence-associated microvascular endothelial dysfunction: A focus on the blood-brain and blood-retinal barriers

The blood-brain barrier (BBB) and blood-retinal barrier (BRB) constitute critical physiochemical interfaces, precisely orchestrating the bidirectional communication between the brain/retina and blood. Increased permeability or leakage of these barriers has been demonstrably linked to age-related vascular and parenchymal damage. While it has been suggested that the gradual aging process may coincide with disruptions in these barriers, this phenomenon is significantly exacerbated in individuals with age-related neurodegenerative disorders (ARND). This review focuses on the microvascular endothelium, a key constituent of BBB and BRB, highlighting the impact of endothelial senescence on barrier dysfunction and exploring recent discoveries regarding core pathways implicated in its breakdown. Subsequently, we address the "vascular senescence hypothesis" for ARND, with a particular emphasis on Alzheimer's disease and age-related macular degeneration, centered on endothelial senescence. Finally, we discuss potential senotherapeutic strategies targeting barrier dysfunction.

Biological and Procedural Predictors of Outcome in the Stroke Preclinical Assessment Network (SPAN) Trial

BACKGROUND

The SPAN trial (Stroke Preclinical Assessment Network) is the largest preclinical study testing acute stroke interventions in experimental focal cerebral ischemia using endovascular filament middle cerebral artery occlusion (MCAo). Besides testing interventions against controls, the prospective design captured numerous biological and procedural variables, highlighting the enormous heterogeneity introduced by the multicenter structure that might influence stroke outcomes. Here, we leveraged the unprecedented sample size achieved by the SPAN trial and the prospective design to identify the biological and procedural variables that affect experimental stroke outcomes in transient endovascular filament MCAo.

METHODS

The study cohort included all mice enrolled and randomized in the SPAN trial (N=1789). Mice were subjected to 60-minute MCAo and followed for a month. Thirteen biological and procedural independent variables and 4 functional (weight loss and 4-point neuroscore on days 1 and 2, corner test on days 7 and 28, and mortality) and 3 tissue (day 2, magnetic resonance imaging infarct volumes and swelling; day 30, magnetic resonance imaging tissue loss) outcome variables were prospectively captured. Multivariable regression with stepwise elimination was used to identify the predictors and their effect sizes.

RESULTS

Older age, active circadian stage at MCAo, and thinner and longer filament silicone tips predicted higher mortality. Older age, larger body weight, longer anesthesia duration, and longer filament tips predicted worse neuroscores, while high-fat diet and blood flow monitoring predicted milder neuroscores. Older age and a high-fat diet predicted worse corner test performance. While shorter filament tips predicted more ipsiversive turning, longer filament tips appeared to predict contraversive turning. Age, sex, and weight interacted when predicting the infarct volume. Older age was associated with smaller infarcts on day 2 magnetic resonance imaging, especially in animals with larger body weights; this association was most conspicuous in females. High-fat diet also predicted smaller infarcts. In contrast, the use of cerebral blood flow monitoring and more severe cerebral blood flow drop during MCAo, longer anesthesia, and longer filament tips all predicted larger infarcts. Bivariate analyses among the dependent variables highlighted a disconnect between tissue and functional outcomes.

CONCLUSIONS

Our analyses identified variables affecting endovascular filament MCAo outcome, an experimental stroke model used worldwide. Multiple regression refuted some commonly reported predictors and revealed previously unrecognized associations. Given the multicenter prospective design that represents a sampling of real-world conditions, the degree of heterogeneity mimicking clinical trials, the large number of predictors adjusted for in the multivariable model, and the large sample size, we think this is the most definitive analysis of the predictors of preclinical stroke outcome to date. Future multicenter experimental stroke trials should standardize or at least ensure a balanced representation of the biological and procedural variables identified herein as potential confounders.

Coenzyme Q10 and exercise training reinstate middle cerebral artery occlusion-induced behavioral deficits and hippocampal long-term potentiation suppression in aging rats

RATIONAL

Patients experience post-stroke cognitive impairment during aging. To date, no specific treatment solution has been reported for this disorder.

OBJECTIVE

The purpose of this study was to evaluate the effects of exercise training and coenzyme Q10 supplementation on middle cerebral artery occlusion (MCAO) induced behavioral impairment, long-term potentiation inhibition and cerebral infarction size in aging rats.

METHODS

Fifty aging male rats underwent MCAO surgery and were randomly distributed in to the following groups: 1-Sham, 2- control, 3- Coenzyme Q10, 4- Exercise training and 5- Exercise training with Q10 supplementation (Ex + Q10). Aerobic training groups were allowed to run on a treadmill for 12 weeks. Q10 (50 mg/kg) was administered intragastrically by gavage. Morris water maze, shuttle box and elevated plus maze tests were used to evaluate cognitive function. The population spike (PS) amplitude and slope of excitatory postsynaptic potentials (EPSP) in the dentate gyrus area were recorded as a result of perforant pathway electrical stimulation.

RESULTS

Our study showed that Q10 and aerobic training alone ameliorate spatial memory in the acquisition phase, but have no effect on spatial memory in the retention phase. Q10 and exercise training synergistically promoted spatial memory in the retention phase. Q10 and exercise training separately and simultaneously mitigated cerebral ischemia-induced passive avoidance memory impairment in acquisition and retention phases. The EPSP did not differ between the groups, but exercise training and Q10 ameliorate the PS amplitude in hippocampal responses to perforant path stimulation. Exercising and Q10 simultaneously reduced the cerebral infarction volume.

CONCLUSION

Collectively, the findings of the present study imply that 12 weeks of aerobic training and Q10 supplementation alone can simultaneously reverse cerebral ischemia induced neurobehavioral deficits via amelioration of synaptic plasticity and a reduction in cerebral infarction volume in senescent rats.

Pharmacological and stem cell therapy of stroke in animal models: Do they accurately reflect the response of humans?

Cerebrovascular diseases are the second leading cause of death worldwide. Despite significant research investment, the only available therapeutic options are mechanical thrombectomy and tissue plasminogen activator thrombolysis. None of the more than a thousand drugs tested on animal models have proven successful in human clinical trials. Several factors contribute to this poor translation of data from stroke-related animal models to human stroke patients. Firstly, our understanding of the molecular and cellular processes involved in recovering from an ischemic stroke is severely limited. Secondly, although the risk of stroke is particularly high among older patients with comorbidities, most drugs are tested on young, healthy animals in controlled laboratory conditions. Furthermore, in animal models, the tracking of post-stroke recovery typically spans only 3 to 28 days, with occasional extensions to 60 days, whereas human stroke recovery is a more extended and complex process. Thirdly, young animal models often exhibit a considerably higher rate of spontaneous recovery compared to humans following a stroke. Fourth, only a very limited number of animals are utilized for each condition, including control groups. Another contributing factor to the much smaller beneficial effects in humans is that positive outcomes from numerous animal studies are more readily accepted than results reported in human trials that do not show a clear benefit to the patient. Useful recommendations for conducting experiments in animal models, with increased chances of translatability to humans, have been issued by both the STEPS investigative team and the STAIR committee. However, largely, due to economic factors, these recommendations are largely ignored. Furthermore, one might attribute the overall failures in predicting and subsequently developing effective acute stroke therapies beyond thrombolysis to potential design deficiencies in clinical trials.

Treatment of stroke in aged male and female rats with Vepoloxamer and tPA reduces neurovascular damage

Stroke is a leading cause of death and disability worldwide, mainly affecting the elderly. Unfortunately, current treatments for acute ischemic stroke warrant improvement. To date, tissue plasminogen activator (tPA) is of limited use in stroke patients mainly due to its narrow therapeutic window and potential for hemorrhagic complication. The adjuvant treatment with Vepoloxamer, a purified amphipathic polymer has been shown to enhance the thrombolytic efficacy of tPA treatment in young adult male rats after embolic stroke. However, most stroke patients are aged; therefore, the current study investigated the therapeutic effect of the combined tPA and Vepoloxamer treatment in aged male and female rats subjected to embolic stroke.

Methods

Male and female Wistar rats at 18 months of age were subjected to embolic middle cerebral artery occlusion and treated either with monotherapy of tPA or Vepoloxamer, a combination of these two agents, or saline at 4 h after stroke onset. Neurological outcomes were evaluated with a battery of behavioral tests including adhesive removal, foot-fault, and modified neurological severity score tests at 1 and 7 days after stroke onset, followed by histopathological analysis of infarct volume. Residual clot size and vascular patency and integrity were analyzed.

Results

The combination treatment with Vepoloxamer and tPA significantly reduced infarct volume and neurological deficits in male and female rats compared to rats treated with saline and the monotherapies of tPA and Vepoloxamer. While Vepoloxamer monotherapy moderately reduced neurological deficits, monotherapies with tPA and Vepoloxamer failed to reduce infarct volume compared to saline treatment. Furthermore, the combination treatment with tPA and Vepoloxamer accelerated thrombolysis, reduced ischemia and tPA-potentiated microvascular disruption, and concomitantly improved cerebrovascular integrity and perfusion in the male ischemic rats.

Conclusion

Combination treatment with tPA and Vepoloxamer at 4 h after stroke onset effectively reduces ischemic neurovascular damage by accelerating thrombolysis and reducing ischemia and tPA potentiated side effects in the aged rats. This funding suggests that the combination treatment with tPA and Vepoloxamer represents a promising strategy to potentially apply to the general population of stroke patients.

Stroke-induced damage on the blood-brain barrier

The blood-brain barrier (BBB) is a functional phenotype exhibited by the neurovascular unit (NVU). It is maintained and regulated by the interaction between cellular and non-cellular matrix components of the NVU. The BBB plays a vital role in maintaining the dynamic stability of the intracerebral microenvironment as a barrier layer at the critical interface between the blood and neural tissues. The large contact area (approximately 20 m2/1.3 kg brain) and short diffusion distance between neurons and capillaries allow endothelial cells to dominate the regulatory role. The NVU is a structural component of the BBB. Individual cells and components of the NVU work together to maintain BBB stability. One of the hallmarks of acute ischemic stroke is the disruption of the BBB, including impaired function of the tight junction and other molecules, as well as increased BBB permeability, leading to brain edema and a range of clinical symptoms. This review summarizes the cellular composition of the BBB and describes the protein composition of the barrier functional junction complex and the mechanisms regulating acute ischemic stroke-induced BBB disruption.

Biological agents and the aging brain: glial inflammation and neurotoxic signaling

Neuroinflammation is a universal characteristic of brain aging and neurological disorders, irrespective of the disease state. Glial inflammation mediates this signaling, through astrocyte and microglial polarization from neuroprotective to neurotoxic phenotypes. Glial reactivity results in the loss of homeostasis, as these cells no longer provide support to neurons, in addition to the production of chronically toxic pro-inflammatory mediators. These glial changes initiate an inflammatory brain state that injures the central nervous system (CNS) over time. As the brain ages, glia are altered, including increased glial cell numbers, morphological changes, and either a pre-disposition or inability to become reactive. These alterations induce age-related neuropathologies, ultimately leading to neuronal degradation and irreversible damage associated with disorders of the aged brain, including Alzheimer's Disease (AD) and other related diseases. While the complex interactions of these glial cells and the brain are well studied, the role additional stressors, such as infectious agents, play on age-related neuropathology has not been fully elucidated. Both biological agents in the periphery, such as bacterial infections, or in the CNS, including viral infections like SARS-CoV-2, push glia into neuroinflammatory phenotypes that can exacerbate pathology within the aging brain. These biological agents release pattern associated molecular patterns (PAMPs) that bind to pattern recognition receptors (PRRs) on glial cells, beginning an inflammatory cascade. In this review, we will summarize the evidence that biological agents induce reactive glia, which worsens age-related neuropathology.

Bystanders or not? Microglia and lymphocytes in aging and stroke

As the average age of the world population increases, more people will face debilitating aging-associated conditions, including dementia and stroke. Not only does the incidence of these conditions increase with age, but the recovery afterward is often worse in older patients. Researchers and health professionals must unveil and understand the factors behind age-associated diseases to develop a therapy for older patients. Aging causes profound changes in the immune system including the activation of microglia in the brain. Activated microglia promote T lymphocyte transmigration leading to an increase in neuroinflammation, white matter damage, and cognitive impairment in both older humans and rodents. The presence of T and B lymphocytes is observed in the aged brain and correlates with worse stroke outcomes. Preclinical strategies in stroke target either microglia or the lymphocytes or the communications between them to promote functional recovery in aged subjects. In this review, we examine the role of the microglia and T and B lymphocytes in aging and how they contribute to cognitive impairment. Additionally, we provide an important update on the contribution of these cells and their interactions in preclinical aged stroke.

Age-Associated Resilience Against Ischemic Injury in Mice Exposed to Transient Middle Cerebral Artery Occlusion

Ischemic stroke is the leading cause of death and disability. Although stroke mainly affects aged individuals, animal research is mostly one on young rodents. Here, we examined the development of ischemic injury in young (9-12-week-old) and adult (72-week-old) C57BL/6 and BALB/c mice exposed to 30 min of intraluminal middle cerebral artery occlusion (MCAo). Post-ischemic reperfusion did not differ between young and adult mice. Ischemic injury assessed by infarct area and blood-brain barrier (BBB) integrity assessed by IgG extravasation analysis was smaller in adult compared with young mice. Microvascular viability and neuronal survival assessed by CD31 and NeuN immunohistochemistry were higher in adult than young mice. Tissue protection was associated with stronger activation of cell survival pathways in adult than young mice. Microglial/macrophage accumulation and activation assessed by F4/80 immunohistochemistry were more restricted in adult than young mice, and pro- and anti-inflammatory cytokine and chemokine responses were reduced by aging. By means of liquid chromatography-mass spectrometry, we identified a hitherto unknown proteome profile comprising the upregulation of glycogen degradation-related pathways and the downregulation of mitochondrial dysfunction-related pathways, which distinguished post-ischemic responses of the aged compared with the young brain. Our study suggests that aging increases the brain's resilience against ischemic injury.

Increased NOX2 expression in astrocytes leads to eNOS uncoupling through dihydrofolate reductase in endothelial cells after subarachnoid hemorrhage

Introduction

Endothelial nitric oxide synthase (eNOS) uncoupling plays a significant role in acute vasoconstriction during early brain injury (EBI) after subarachnoid hemorrhage (SAH). Astrocytes in the neurovascular unit extend their foot processes around endothelia. In our study, we tested the hypothesis that increased nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2) expression in astrocytes after SAH leads to eNOS uncoupling.

Methods

We utilized laser speckle contrast imaging for monitoring cortical blood flow changes in mice, nitric oxide (NO) kits to measure the level of NO, and a co-culture system to study the effect of astrocytes on endothelial cells. Moreover, the protein levels were assessed by Western blot and immunofluorescence staining. We used CCK-8 to measure the viability of astrocytes and endothelial cells, and we used the H2O2 kit to measure the H2O2 released from astrocytes. We used GSK2795039 as an inhibitor of NOX2, whereas lentivirus and adeno-associated virus were used for dihydrofolate reductase (DHFR) knockdown in vivo and in vitro.

Results

The expression of NOX2 and the release of H2O2 in astrocytes are increased, which was accompanied by a decrease in endothelial DHFR 12 h after SAH. Moreover, the eNOS monomer/dimer ratio increased, leading to a decrease in NO and acute cerebral ischemia. All of the above were significantly alleviated after the administration of GSK2795039. However, after knocking down DHFR both in vivo and in vitro, the protective effect of GSK2795039 was greatly reversed.

Discussion

The increased level of NOX2 in astrocytes contributes to decreased DHFR in endothelial cells, thus aggravating eNOS uncoupling, which is an essential mechanism underlying acute vasoconstriction after SAH.

Hepatocyte growth factor-modified hair follicle stem cells ameliorate cerebral ischemia/reperfusion injury in rats

BACKGROUND

Hair follicle stem cells (HFSCs) are considered as a promising cell type in the stem cell transplantation treatment of neurological diseases because of their rich sources, easy access, and the same ectoderm source as the nervous system. Hepatocyte growth factor (HGF) is a pleiotropic cytokine that shows neuroprotective function in ischemic stroke. Here we assessed the therapeutic effects of HFSCs on ischemic stroke injury and the synthetic effect of HGF along with HFSCs.

METHODS

Rat HFSCs were intravenously transplanted into a middle cerebral artery ischemia/reperfusion (I/R) rat model. Neurological scoring and TTC staining were performed to assess the benefits of HFSC transplantation. Inflammatory cytokines, blood-brain barrier integrity and angiogenesis within penumbra were estimated by Western blot and immunohistochemistry. The differentiation of HFSCs was detected by immunofluorescence method 2 weeks after transplantation.

RESULTS

HFSC transplantation could significantly inhibit the activation of microglia, improve the integrity of blood-brain barrier and reduce brain edema. Moreover, the number of surviving neurons and microvessels density in the penumbra were upregulated by HFSC transplantation, leading to better neurological score. The combination of HFSCs and HGF could significantly improve the therapeutic benefit.

CONCLUSION

Our results indicate for the first time that HGF modified HFSCs can reduce I/R injury and promote the neurological recovery by inhibiting inflammatory response, protecting blood-brain barrier and promoting angiogenesis.

VCAM1 Drives Vascular Inflammation Leading to Continuous Cortical Neuronal Loss Following Chronic Cerebral Hypoperfusion

BACKGROUND

Chronic cerebral hypoperfusion (CCH) is associated with neuronal loss and blood-brain barrier (BBB) impairment in vascular dementia (VaD). However, the relationship and the molecular mechanisms between BBB dysfunction and neuronal loss remain elusive.

OBJECTIVE

We explored the reasons for neuron loss following CCH.

METHODS

Using permanent bilateral common carotid artery occlusion (2VO) rat model, we observed the pathological changes of cortical neurons and BBB in the sham group as well as rats 3d, 7d, 14d and 28d post 2VO. In order to further explore the factors influencing neuron loss following CCH with regard to cortical blood vessels, we extracted cortical brain microvessels at five time points for transcriptome sequencing. Finally, integrin receptor a4β1 (VLA-4) inhibitor was injected into the tail vein, and cortical neuron loss was detected again.

RESULTS

We found that cortical neuron loss following CCH is a continuous process, but damage to the BBB is acute and transient. Results of cortical microvessel transcriptome analysis showed that biological processes related to vascular inflammation mainly occurred in the chronic phase. Meanwhile, cell adhesion molecules, cytokine-cytokine receptor interaction were significantly changed at this phase. Among them, the adhesion molecule VCAM1 plays an important role. Using VLA-4 inhibitor to block VCAM1-VLA-4 interaction, cortical neuron damage was ameliorated at 14d post 2VO.

CONCLUSION

Injury of the BBB may not be the main reason for persistent loss of cortical neurons following CCH. The continuous inflammatory response within blood vessels maybe an important factor in the continuous loss of cortical neurons following CCH.

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.

Novel mitoNEET ligand NL-1 improves therapeutic outcomes in an aged rat model of cerebral ischemia/reperfusion injury

Cerebral ischemic stroke is a leading cause of mortality and disability worldwide. Currently, there are a lack of drugs capable of reducing neuronal cell loss due to ischemia/reperfusion-injury after stroke. Previously, we identified mitoNEET, a [2Fe-2S] redox mitochondrial protein, as a putative drug target for ischemic stroke. In this study, we tested NL-1, a novel mitoNEET ligand, in a preclinical model of ischemic stroke with reperfusion using aged female rats. Using a transient middle cerebral artery occlusion (tMCAO), we induced a 2 h ischemic injury and then evaluated the effects of NL-1 treatment on ischemic/reperfusion brain injury at 24 and 72 h. Test compounds were administered at time of reperfusion via intravenous dosing. Results of the study demonstrated that NL-1 (10 mg/kg) treatment markedly improved survival and reduced infarct volume and hemispheric swelling in the brain as compared aged rats treated with vehicle or a lower dose of NL-1 (0.25 mg/kg). Interestingly, the protective effect of NL-1 was significantly improved when encapsulated in PLGA nanoparticles, where a 40-fold lesser dose (0.25 mg/kg) of NL-1 produced an equivalent effect as the 10 mg/kg dose. Evaluation of changes in blood-brain barrier permeability and lipid peroxidation corroborated the protective actions of NL-1 (10 mg/kg) or NL-1 NP treatment demonstrated a reduced accumulation of parenchymal IgG, decreased levels of 4-hydroxynonenal (4-HNE) and a decreased TUNEL positive cells in the brains of aged female rats at 72 h after tMCAO with reperfusion. Our studies indicate that targeting mitoNEET following ischemia/reperfusion-injury is a novel drug target pathway that warrants further investigation.

The ATX-LPA Axis Regulates Vascular Permeability during Cerebral Ischemic-Reperfusion

Endothelial permeability is a major complication that must be addressed during stroke treatment. Study of the mechanisms underlying blood−brain barrier (BBB) disruption and management of the hypoxic stress-induced permeability of the endothelium following reperfusion are both urgently needed for stroke management. Lysophosphatidic acid (LPA), a bioactive lipid essential for basic cellular functions, causes unfavorable outcomes during stroke progression. LPA-producing enzyme autotaxin (ATX) is regulated in ischemic stroke. We used an electrical cell-substrate impedance sensor (ECIS) to measure endothelial permeability. Mitochondrial bioenergetics were obtained using a Seahorse analyzer. AR-2 probe fluorescence assay was used to measure ATX activity. LPA increased endothelial permeability and reduced junctional protein expression in mouse brain microvascular endothelial cells (MBMEC). LPA receptor inhibitors Ki16425 and AM095 attenuated the LPA-induced changes in the endothelial permeability and junctional proteins. LPA significantly diminished mitochondrial function in MBMEC. ATX was upregulated (p < 0.05) in brain microvascular endothelial cells under hypoxic reperfusion. ATX activity and permeability were attenuated with the use of an ATX inhibitor in a mouse stroke model. The upregulation of ATX with hypoxic reperfusion leads to LPA production in brain endothelial cells favoring permeability. Inhibition of the ATX−LPA−LPAR axis could be therapeutically targeted in stroke to achieve better outcomes.

Blood-Brain Barrier Transporters: Opportunities for Therapeutic Development in Ischemic Stroke

Globally, stroke is a leading cause of death and long-term disability. Over the past decades, several efforts have attempted to discover new drugs or repurpose existing therapeutics to promote post-stroke neurological recovery. Preclinical stroke studies have reported successes in identifying novel neuroprotective agents; however, none of these compounds have advanced beyond a phase III clinical trial. One reason for these failures is the lack of consideration of blood-brain barrier (BBB) transport mechanisms that can enable these drugs to achieve efficacious concentrations in ischemic brain tissue. Despite the knowledge that drugs with neuroprotective properties (i.e., statins, memantine, metformin) are substrates for endogenous BBB transporters, preclinical stroke research has not extensively studied the role of transporters in central nervous system (CNS) drug delivery. Here, we review current knowledge on specific BBB uptake transporters (i.e., organic anion transporting polypeptides (OATPs in humans; Oatps in rodents); organic cation transporters (OCTs in humans; Octs in rodents) that can be targeted for improved neuroprotective drug delivery. Additionally, we provide state-of-the-art perspectives on how transporter pharmacology can be integrated into preclinical stroke research. Specifically, we discuss the utility of in vivo stroke models to transporter studies and considerations (i.e., species selection, co-morbid conditions) that will optimize the translational success of stroke pharmacotherapeutic experiments.

Association of Multiple Passes during Mechanical Thrombectomy with Incomplete Reperfusion and Lesion Growth

INTRODUCTION

Despite complete recanalization by mechanical thrombectomy, abnormal perfusion can be detected on MRI obtained post-endovascular therapy (EVT). The presence of residual perfusion abnormalities post-EVT may be associated with blood-brain barrier breakdown in response to mechanical disruption of the endothelium from multiple-pass thrombectomy. We hypothesize that multiple-pass versus single-pass thrombectomy is associated with a higher rate of residual hypoperfusion and increased lesion growth at 24 h.

MATERIALS AND METHODS

For this analysis, we included patients presenting to one of two stroke centers between January 2015 and February 2018 with an acute ischemic stroke within 12 h from symptom onset if they had a large vessel occlusion of the anterior circulation documented on magnetic resonance angiography or CTA, baseline MRI pre-EVT with imaging evidence of hypoperfusion, underwent EVT, and had a post-EVT MRI with qualitatively interpretable perfusion-weighted imaging data at 24 h. MRI Tmax maps using a time delay threshold of >6 s were used to quantitate hypoperfusion volumes. Residual hypoperfusion at 24 h was solely defined as Tmax volume >10 mL with >6 s delay. Complete recanalization was defined as modified treatment in cerebral infarction visualized on angiography at EVT completion. Hyperintense acute reperfusion injury marker was assessed on post-EVT pre-contrast fluid-attenuated inversion recovery at 24 h. Major early neurological improvement was defined as a reduction of the admission National Institutes of Health Stroke Scale by ≥8 points or a score of 0-1 at 24 h. Good functional outcome was defined as 0-2 on the modified Rankin Scale on day 30 or 90.

RESULTS

Fifty-five patients were included with median age 67 years, 58% female, 45% Black/African American, 36% White/Caucasian, median admission National Institutes of Health Stroke Scale 19, large vessel occlusion locations: 71% M1, 14.5% iICA, 14.5% M2, 69% treated with intravenous recombinant tissue plasminogen activator. Of these, 58% had multiple-pass thrombectomy, 39% had residual perfusion abnormalities at 24 h, and 64% had severe hyperintense acute reperfusion injury marker at 24 h. After adjusting for complete recanalization, only multiple-pass thrombectomy (odds ratio, 4.3 95% CI, 1.07-17.2; p = 0.04) was an independent predictor of residual hypoperfusion at 24 h. Patients with residual hypoperfusion had larger lesion growth on diffusion-weighted imaging (59 mL vs. 8 mL, p < 0.001), lower rate of major early neurological improvement (24% vs. 70%, p = 0.002) at 24 h, and worse long-term outcome based on the modified Rankin Scale at 30 or 90 days, 5 versus 2 (p < 0.001).

CONCLUSIONS

Our findings suggest that incomplete reperfusion on post-EVT MRI is present even in some patients with successful recanalization at the time of EVT and is associated with multiple-pass thrombectomy, lesion growth, and worse outcome. Future studies are needed to investigate whether patients with residual hypoperfusion may benefit from immediate adjunctive therapy to limit lesion growth and improve clinical outcome.

TNF-α antagonism rescues the effect of ageing on stroke: Perspectives for targeting inflamm-ageing

AIMS

Epidemiologic evidence links ischemic stroke to age, yet the mechanisms that underlie the specific and independent effects of age on stroke remain elusive, impeding the development of targeted treatments. This study tested the hypothesis that age directly aggravates stroke outcomes and proposes inflamm-aging as a mediator and potential therapeutic target.

METHODS

3 months- (young) and 18-20 months-old (old) mice underwent transient middle cerebral artery occlusion (tMCAO) for 30 minutes followed by 48 hours of reperfusion. Old animals received weekly treatment with the TNF-α neutralizing antibody adalimumab over 4 weeks before tMCAO in a separate set of experiments. Plasma levels of TNF- α were assessed in patients with ischemic stroke and correlated with age and outcome.

RESULTS

Old mice displayed larger stroke size than young ones with increased neuromotor deficit. Immunohistochemical analysis revealed impairment of the blood-brain barrier in old mice, i.e. increased post-stroke degradation of endothelial tight junctions and expression of tight junctions-digesting and neurotoxic matrix metalloproteinases. At baseline, old animals showed a broad modulation of several circulating inflammatory mediators. TNF-α displayed the highest increase in old animals and its inhibition restored the volume of stroke, neuromotor performance, and survival rates of old mice to the levels observed in young ones. Patients with ischemic stroke showed increased TNF-α plasma levels which correlated with worsened short-term neurological outcome as well as with age.

CONCLUSIONS

This study identifies TNF-α as a causative contributor to the deleterious effect of aging on stroke and points to inflamm-aging as a mechanism of age-related worsening of stroke outcomes and potential therapeutic target in this context. Thus, this work provides a basis for tailoring novel stroke therapies for the particularly vulnerable elderly population.

Adjunctive cytoprotective therapies in acute ischemic stroke: a systematic review

With the introduction of endovascular thrombectomy (EVT), a new era for treatment of acute ischemic stroke (AIS) has arrived. However, despite the much larger recanalization rate as compared to thrombolysis alone, final outcome remains far from ideal. This raises the question if some of the previously tested neuroprotective drugs warrant re-evaluation, since these compounds were all tested in studies where large-vessel recanalization was rarely achieved in the acute phase. This review provides an overview of compounds tested in clinical AIS trials and gives insight into which of these drugs warrant a re-evaluation as an add-on therapy for AIS in the era of EVT. A literature search was performed using the search terms "ischemic stroke brain" in title/abstract, and additional filters. After exclusion of papers using pre-defined selection criteria, a total of 89 trials were eligible for review which reported on 56 unique compounds. Trial compounds were divided into 6 categories based on their perceived mode of action: systemic haemodynamics, excitotoxicity, neuro-inflammation, blood-brain barrier and vasogenic edema, oxidative and nitrosative stress, neurogenesis/-regeneration and -recovery. Main trial outcomes and safety issues are summarized and promising compounds for re-evaluation are highlighted. Looking at group effect, drugs intervening with oxidative and nitrosative stress and neurogenesis/-regeneration and -recovery appear to have a favourable safety profile and show the most promising results regarding efficacy. Finally, possible theories behind individual and group effects are discussed and recommendation for promising treatment strategies are described.

Leukoaraiosis and acute ischemic stroke

Ischaemic stroke is characterized by high morbidity, high disability rate, high mortality and high recurrence rate, which can have a grave impact on the quality of life of the patients and consequently becomes an economic burden on their families and society. With the developments in imaging technology in recent years, patients with acute cerebral infarction are predominantly more likely to be diagnosed with leukoaraiosis (LA). LA is a common degenerative disease of the nervous system, which is related to cognitive decline, depression, abnormal gait, ischaemic stroke and atherosclerosis. The aetiology of LA is not clear and there is no gold standard for imaging assessment. Related studies have shown that LA has an adverse effect on the prognosis of cerebral infarction, but some experts have contrary beliefs. Hence, we undertook the present review of the literature on the mechanism and the effect of LA on the prognosis of patients with acute ischaemic stroke.

Molecular and cellular pathways contributing to brain aging

Aging is the leading risk factor for several age-associated diseases such as neurodegenerative diseases. Understanding the biology of aging mechanisms is essential to the pursuit of brain health. In this regard, brain aging is defined by a gradual decrease in neurophysiological functions, impaired adaptive neuroplasticity, dysregulation of neuronal Ca2+ homeostasis, neuroinflammation, and oxidatively modified molecules and organelles. Numerous pathways lead to brain aging, including increased oxidative stress, inflammation, disturbances in energy metabolism such as deregulated autophagy, mitochondrial dysfunction, and IGF-1, mTOR, ROS, AMPK, SIRTs, and p53 as central modulators of the metabolic control, connecting aging to the pathways, which lead to neurodegenerative disorders. Also, calorie restriction (CR), physical exercise, and mental activities can extend lifespan and increase nervous system resistance to age-associated neurodegenerative diseases. The neuroprotective effect of CR involves increased protection against ROS generation, maintenance of cellular Ca2+ homeostasis, and inhibition of apoptosis. The recent evidence about the modem molecular and cellular methods in neurobiology to brain aging is exhibiting a significant potential in brain cells for adaptation to aging and resistance to neurodegenerative disorders.

Decoding the Transcriptional Response to Ischemic Stroke in Young and Aged Mouse Brain

Ischemic stroke is a well-recognized disease of aging, yet it is unclear how the age-dependent vulnerability occurs and what are the underlying mechanisms. To address these issues, we perform a comprehensive RNA-seq analysis of aging, ischemic stroke, and their interaction in 3- and 18-month-old mice. We assess differential gene expression across injury status and age, estimate cell type proportion changes, assay the results against a range of transcriptional signatures from the literature, and perform unsupervised co-expression analysis, identifying modules of genes with varying response to injury. We uncover downregulation of axonal and synaptic maintenance genetic program, and increased activation of type I interferon (IFN-I) signaling following stroke in aged mice. Together, these results paint a picture of ischemic stroke as a complex age-related disease and provide insights into interaction of aging and stroke on cellular and molecular level.

Mesenchymal Stem Cell Derived Extracellular Vesicles for Repairing the Neurovascular Unit after Ischemic Stroke

Ischemic stroke is a debilitating disease and one of the leading causes of long-term disability. During the early phase after ischemic stroke, the blood-brain barrier (BBB) exhibits increased permeability and disruption, leading to an influx of immune cells and inflammatory molecules that exacerbate the damage to the brain tissue. Mesenchymal stem cells have been investigated as a promising therapy to improve the recovery after ischemic stroke. The therapeutic effects imparted by MSCs are mostly paracrine. Recently, the role of extracellular vesicles released by these MSCs have been studied as possible carriers of information to the brain. This review focuses on the potential of MSC derived EVs to repair the components of the neurovascular unit (NVU) controlling the BBB, in order to promote overall recovery from stroke. Here, we review the techniques for increasing the effectiveness of MSC-based therapeutics, such as improved homing capabilities, bioengineering protein expression, modified culture conditions, and customizing the contents of EVs. Combining multiple techniques targeting NVU repair may provide the basis for improved future stroke treatment paradigms.

The Association of Suppressed Hypoxia-Inducible Factor-1 Transactivation of Angiogenesis With Defective Recovery From Cerebral Ischemic Injury in Aged Rats

Elderly patients suffer more brain damage in comparison with young patients from the same ischemic stroke. The present study was undertaken to test the hypothesis that suppressed hypoxia-inducible factor-1 (HIF-1) transcription activity is responsible for defective recovery after ischemic stroke in the elders. Aged and young rats underwent 1-h transient middle cerebral artery occlusion (MCAO) to produce cerebral ischemic injury. The initial cerebral infarct volume in the young gradually declined as time elapsed, but in the aged rats remained the same. The defective recovery in the aged was associated with depressed angiogenesis and retarded neurorestoration. There was no difference in HIF-1α accumulation in the brain between the two age groups, but the expression of HIF-1 regulated genes involved in cerebral recovery was suppressed in the aged. In confirmation, inhibition of HIF-1 transactivation of gene expression in the young suppressed cerebral recovery from MCAO as the same as that observed in the aged rats. Furthermore, a copper metabolism MURR domain 1 (COMMD1) was significantly elevated after MCAO only in the brain of aged rats, and suppression of COMMD1 by siRNA targeting COMMD1 restored HIF-1 transactivation and improved recovery from MCAO-induced damage in the aged brain. These results demonstrate that impaired HIF-1 transcription activity, due at least partially to overexpression of COMMD1, is associated with the defective cerebral recovery from ischemic stroke in the aged rats.

Sex differences in stroke outcome correspond to rapid and severe changes in gut permeability in adult Sprague-Dawley rats

BACKGROUND

Sex differences in experimental stroke outcomes are well documented, such that adult males have a greater infarct volume, increased stroke-induced mortality, and more severe sensory-motor impairment. Based on recent evidence that the gut is an early responder to stroke, the present study tested the hypothesis that sex differences in stroke severity will be accompanied by rapid and greater permeability of the gut-blood barrier and gut dysbiosis in males as compared to females.

METHOD

Male and female Sprague-Dawley rats (5-7 months of age) were subject to endothelin (ET)-1-induced middle cerebral artery occlusion (MCAo). Sensory-motor tests were conducted pre- and 2 days after MCAo. Gut permeability was assessed in serum samples using biomarkers of gut permeability as well as functional assays using size-graded dextrans. Histological analysis of the gut was performed with H&E staining, periodic acid-Schiff for mucus, and immunohistochemistry for the tight junction protein, ZO-1. Fecal samples obtained pre- and post-stroke were analyzed for bacterial taxa and short-chain fatty acids (SCFAs).

RESULTS

After stroke, males displayed greater mortality, worse sensory-motor deficit, and higher serum levels of proinflammatory cytokines IL-17A, MCP-1, and IL-5 as compared to females. MCAo-induced gut permeability was rapid and severe in males as indicated by dextran extravasation from the gut to the blood in the hyperacute (< 2 h) and early acute (2 days) phase of stroke. This was accompanied by dysmorphology of the gut villi and dysregulation of the tight junction protein ZO-1 in the acute phase. Fecal 16s sequencing showed no differences in bacterial diversity in the acute phase of stroke. Predictive modeling indicated that markers of gut permeability were associated with acute sensory-motor impairment and infarct volume.

CONCLUSIONS

These data show that extensive leakiness of the gut barrier is associated with severe post-stroke disability and suggest that reinforcing this barrier may improve stroke outcomes.

Impact of aging and comorbidities on ischemic stroke outcomes in preclinical animal models: A translational perspective

Ischemic stroke is a highly complex and devastating neurological disease. The sudden loss of blood flow to a brain region due to an ischemic insult leads to severe damage to that area resulting in the formation of an infarcted tissue, also known as the ischemic core. This is surrounded by the peri-infarct region or penumbra that denotes the functionally impaired but potentially salvageable tissue. Thus, the penumbral tissue is the main target for the development of neuroprotective strategies to minimize the extent of ischemic brain damage by timely therapeutic intervention. Given the limitations of reperfusion therapies with recombinant tissue plasminogen activator or mechanical thrombectomy, there is high enthusiasm to combine reperfusion therapy with neuroprotective strategies to further reduce the progression of ischemic brain injury. Till date, a large number of candidate neuroprotective drugs have been identified as potential therapies based on highly promising results from studies in rodent ischemic stroke models. However, none of these interventions have shown therapeutic benefits in stroke patients in clinical trials. In this review article, we discussed the urgent need to utilize preclinical models of ischemic stroke that more accurately mimic the clinical conditions in stroke patients by incorporating aged animals and animal stroke models with comorbidities. We also outlined the recent findings that highlight the significant differences in stroke outcome between young and aged animals, and how major comorbid conditions such as hypertension, diabetes, obesity and hyperlipidemia dramatically increase the vulnerability of the brain to ischemic damage that eventually results in worse functional outcomes. It is evident from these earlier studies that including animal models of aging and comorbidities during the early stages of drug development could facilitate the identification of neuroprotective strategies with high likelihood of success in stroke clinical trials.

CNS and peripheral immunity in cerebral ischemia: partition and interaction

Stroke elicits excessive immune activation in the injured brain tissue. This well-recognized neural inflammation in the brain is not just an intrinsic organ response but also a result of additional intricate interactions between infiltrating peripheral immune cells and the resident immune cells in the affected areas. Given that there is a finite number of immune cells in the organism at the time of stroke, the partitioned immune systems of the central nervous system (CNS) and periphery must appropriately distribute the limited pool of immune cells between the two domains, mounting a necessary post-stroke inflammatory response by supplying a sufficient number of immune cells into the brain while maintaining peripheral immunity. Stroke pathophysiology has mainly been neurocentric in focus, but understanding the distinct roles of the CNS and peripheral immunity in their concerted action against ischemic insults is crucial. This review will discuss stroke-induced influences of the peripheral immune system on CNS injury/repair and of neural inflammation on peripheral immunity, and how comorbidity influences each.

Ischemic lesion water homeostasis after thrombectomy for large vessel occlusion stroke within the anterior circulation: The impact of age

The effect of age on lesion pathophysiology in the context of thrombectomy has been poorly investigated. We aimed to investigate the impact of age on ischemic lesion water homeostasis measured with net water uptake (NWU) within a multicenter cohort of patients receiving thrombectomy for anterior circulation large vessel occlusion (LVO) stroke. Lesion-NWU was quantified in multimodal CT on admission and 24 h for calculating Δ-NWU as their difference. The impact of age and procedural parameters on Δ-NWU was analyzed. Multivariable regression analysis was performed to identify significant predictors for Δ-NWU. Two hundred and four patients with anterior circulation stroke were included in the retrospective analysis. Comparison of younger and elderly patients showed no significant differences in NWU on admission but significantly higher Δ-NWU (p = 0.005) on follow-up CT in younger patients. In multivariable regression analysis, higher age was independently associated with lowered Δ-NWU (95% confidence interval: -0.59 to -0.16, p < 0.001). Although successful recanalization (TICI ≥ 2b) significantly reduced Δ-NWU progression by 6.4% (p < 0.001), younger age was still independently associated with higher Δ-NWU (p < 0.001). Younger age is significantly associated with increased brain edema formation after thrombectomy for LVO stroke. Younger patients might be particularly receptive targets for future adjuvant neuroprotective drugs that influence ischemic edema formation.

Emerging neuroprotective strategies for the treatment of ischemic stroke: An overview of clinical and preclinical studies

Stroke is the leading cause of disability and thesecond leading cause of death worldwide. With the global population aged 65 and over growing faster than all other age groups, the incidence of stroke is also increasing. In addition, there is a shift in the overall stroke burden towards younger age groups, particularly in low and middle-income countries. Stroke in most cases is caused due to an abrupt blockage of an artery (ischemic stroke), but in some instances stroke may be caused due to bleeding into brain tissue when a blood vessel ruptures (hemorrhagic stroke). Although treatment options for stroke are still limited, with the advancement in recanalization therapy using both pharmacological and mechanical thrombolysis some progress has been made in helping patients recover from ischemic stroke. However, there is still a substantial need for the development of therapeutic agents for neuroprotection in acute ischemic stroke to protect the brain from damage prior to and during recanalization, extend the therapeutic time window for intervention and further improve functional outcome. The current review has assessed the past challenges in developing neuroprotective strategies, evaluated the recent advances in clinical trials, discussed the recent initiative by the National Institute of Neurological Disorders and Stroke in USA for the search of novel neuroprotectants (Stroke Preclinical Assessment Network, SPAN) and identified emerging neuroprotectants being currently evaluated in preclinical studies. The underlying molecular mechanism of each of the neuroprotective strategies have also been summarized, which could assist in the development of future strategies for combinational therapy in stroke treatment.

Ageing as a risk factor for cerebral ischemia: Underlying mechanisms and therapy in animal models and in the clinic

Age is the only one non-modifiable risk of cerebral ischemia. Advances in stroke medicine and behavioral adaptation to stroke risk factors and comorbidities was successful in decreasing stroke incidence and increasing the number of stroke survivors in western societies. Comorbidities aggravates the outcome after cerebral ischemia. However, due to the increased in number of elderly, the incidence of stroke has increased again paralleled by an increase in the number of stroke survivors, many with severe disabilities, that has led to an increased economic and social burden in society. Animal models of stroke often ignore age and comorbidities frequently associated with senescence. This might explain why drugs working nicely in animal models fail to show efficacy in stroke survivors. Since stroke afflicts mostly the elderly comorbid patients, it is highly desirable to test the efficacy of stroke therapies in an appropriate animal stroke model. Therefore, in this review, we make parallels between animal models of stroke und clinical data and summarize the impact of ageing and age-related comorbidities on stroke outcome.

Cerebrovascular and Neurological Dysfunction under the Threat of COVID-19: Is There a Comorbid Role for Smoking and Vaping?

The recently discovered novel coronavirus, SARS-CoV-2 (COVID-19 virus), has brought the whole world to standstill with critical challenges, affecting both health and economic sectors worldwide. Although initially, this pandemic was associated with causing severe pulmonary and respiratory disorders, recent case studies reported the association of cerebrovascular-neurological dysfunction in COVID-19 patients, which is also life-threatening. Several SARS-CoV-2 positive case studies have been reported where there are mild or no symptoms of this virus. However, a selection of patients are suffering from large artery ischemic strokes. Although the pathophysiology of the SARS-CoV-2 virus affecting the cerebrovascular system has not been elucidated yet, researchers have identified several pathogenic mechanisms, including a role for the ACE2 receptor. Therefore, it is extremely crucial to identify the risk factors related to the progression and adverse outcome of cerebrovascular-neurological dysfunction in COVID-19 patients. Since many articles have reported the effect of smoking (tobacco and cannabis) and vaping in cerebrovascular and neurological systems, and considering that smokers are more prone to viral and bacterial infection compared to non-smokers, it is high time to explore the probable correlation of smoking in COVID-19 patients. Herein, we have reviewed the possible role of smoking and vaping on cerebrovascular and neurological dysfunction in COVID-19 patients, along with potential pathogenic mechanisms associated with it.

Transporter-Mediated Delivery of Small Molecule Drugs to the Brain: A Critical Mechanism That Can Advance Therapeutic Development for Ischemic Stroke

Ischemic stroke is the 5th leading cause of death in the United States. Despite significant improvements in reperfusion therapies, stroke patients still suffer from debilitating neurocognitive deficits. This indicates an essential need to develop novel stroke treatment paradigms. Endogenous uptake transporters expressed at the blood-brain barrier (BBB) provide an excellent opportunity to advance stroke therapy via optimization of small molecule neuroprotective drug delivery to the brain. Examples of such uptake transporters include organic anion transporting polypeptides (OATPs in humans; Oatps in rodents) and organic cation transporters (OCTs in humans; Octs in rodents). Of particular note, small molecule drugs that have neuroprotective properties are known substrates for these transporters and include 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (i.e., statins) for OATPs/Oatps and 1-amino-3,5-dimethyladamantane (i.e., memantine) for OCTs/Octs. Here, we review current knowledge on specific BBB transporters that can be targeted for improvement of ischemic stroke treatment and provide state-of-the-art perspectives on the rationale for considering BBB transport properties during discovery/development of stroke therapeutics.

Aging exacerbates neutrophil pathogenicity in ischemic stroke

Ischemic stroke is major cause of disability and mortality worldwide, and aging is strong risk factor for poor post-stroke outcome. Neutrophils traffic rapidly to the brain following ischemic stroke, and recent evidence has suggested that aging may alter neutrophil function after tissue injury. In this study, we hypothesize that aging enhances the pro-inflammatory function of neutrophils, directly contributing to the poorer outcomes seen in aging patients. We utilized demographic data and biological specimens from ischemic stroke patients and an experimental mouse model to determine the correlation between age, neutrophil function and stroke outcomes. In ischemic stroke patients, age was associated with increased mortality and morbidity and higher levels of neutrophil-activating cytokines. In mice, aged animals had higher stroke mortality and morbidity, higher levels of neutrophil-activating cytokines and enhanced generation of neutrophil reactive oxygen species compared to young mice. Finally, depletion of neutrophils via a specific monoclonal antibody after ischemic stroke led to long-term benefits in functional outcome in aged male and female animals, with no benefit observed in young. These results demonstrate that aging is associated with augmented neutrophil pathogenicity in ischemic stroke, and that neutrophil-targeted therapies may confer greater benefit in aged subjects.

The need to incorporate aged animals into the preclinical modeling of neurological conditions

Neurological conditions such as traumatic brain injury, stroke, Parkinson's disease, epilepsy, multiple sclerosis, and Alzheimer's disease are serious clinical problems that affect millions of people worldwide. The majority of clinical trials for these common conditions have failed, and there is a critical need to understand why treatments in preclinical animal models do not translate to patients. Many patients with these conditions are middle-aged or older, however, the majority of preclinical studies have used only young-adult animals. Considering that aging involves biological changes that are relevant to the pathobiology of neurological diseases, the lack of aged subjects in preclinical research could contribute to translational failures. This paper details how aging affects biological processes involved in neurological conditions, and reviews aging research in the context of traumatic brain injury, stroke, Parkinson's disease, epilepsy, multiple sclerosis, and Alzheimer's disease. We conclude that aging is an important, but often overlooked, factor that influences biology and outcomes in neurological conditions, and provide suggestions to improve our understanding and treatment of these diseases in aged patients.

Insulin-Like Growth Factor-1 Is Neuroprotective in Aged Rats With Ischemic Stroke

Post-stroke systemic injections of insulin-like growth factor-1 (IGF-1) exert neuroprotective effects in rats. In the current study, we aimed to test the efficacy of IGF-1 neuroprotection in aged rats (24–25 months old) and to compare the results with adult rats (6–7 months old). Furthermore, we addressed putative differences in microglial responses to IGF-1 in adult and aged rats. Rats were subjected to ischemic stroke while they were conscious by infusing endothelin-1 (Et-1) through a guide cannula that was implemented in the vicinity of the middle cerebral artery (MCA). Rats were given subcutaneous injections of IGF-1 (1 mg/kg) at 30 min and 120 min after the insult. Post-stroke IGF-1 treatment reduced the infarct size by 34% and 38% in aged and adult rats, respectively. The IGF-1 treated adult rats also showed significant improvement in sensorimotor function following stroke, while this function was not significantly affected in aged rats. Furthermore, aged rats displayed exaggerated activation of microglia in the ischemic hemisphere. Significant reduction of microglial activation by IGF-1 was only detected at specific regions in the ipsilateral hemisphere of adult rats. We show that IGF-1 reduced infarct size in aged rats with an ischemic stroke. It remains to be established, however, whether the age-related changes in microglial function affect the improvement in behavioral outcomes.

Age and sex differences in the pathophysiology of acute CNS injury

Despite the immeasurable burden on patients and families, no effective therapies to protect the CNS after an acute injury are available yet. Furthermore, the underlying mechanisms that promote neuronal death and functional deficits after injury remain to be poorly understood. The prevalence, age of onset, pathophysiology, and symptomatology of many CNS insults differ significantly between males and females. In the case of stroke, younger males tend to show a higher risk than younger females, while this trend reverses with age. Accumulating evidence from preclinical studies have shown that sex hormones play a crucial role in providing neuroprotection following ischemic stroke and other acute CNS injuries. Estrogen, in particular, exerts a neuroprotective effect by modulating the immune responses after injury. In addition, there exists a sexual dimorphism in cell death pathways between males and females that are independent of hormones. Meanwhile, recent studies suggest that microRNAs are critically involved in the sex-specific mechanisms of cell death. This review discusses the current knowledge on the contribution of sex and age to outcome after stroke. Implication of the interplay between these two factors on other CNS injuries (spinal cord injury and traumatic brain injury) from the experimental evidence were also discussed.

The effects of dihydroxyphenyl lactic acid on alleviating blood-brain barrier injury following subarachnoid hemorrhage in rats

BACKGROUND

In this study, the protective effects of 3,4-dihydroxyphenyl lactic acid (DLA) on blood-brain barrier (BBB) injury following subarachnoid hemorrhage (SAH) has been explored.

METHODS

Male Sprague-Dawley rats (weight 300-350 g) were used to establish the SAH model using the endovascular perforation method. The animals were randomly divided into four groups: sham (n = 40), SAH (n = 46), SAH + vehicle (n = 44), and SAH + DLA (n = 40) treatment groups. At 1 h after SAH, either DLA (10 mg/kg) or normal saline (vehicle) was administered by femoral vein injection. The effects of DLA on mortality, neurological function, brain water content, and BBB were observed. Additionally, immunohistochemistry and western blot techniques were applied to investigate the mechanism of action of DLA.

RESULTS

We found that the administration of DLA (10 mg/kg) following SAH could improve neurological functions, reduce brain water content, and maintain BBB integrity. The expression of pro-inflammatory and pro-apoptotic factors such as toll-like receptor 4 (TLR4), NF-κB (p-p65), tumor necrosis factor-α, p-p38 MAPK, p-p53, and caspase-3 were significantly increased after SAH. These same factors were markedly attenuated following treatment with DLA.

CONCLUSIONS

These findings showed that DLA can alleviate BBB injury following SAH through its anti-inflammatory and anti-apoptotic effects via suppression of TLR4 and its downstream NF-κB and p38 MAPK pathways.

TRIM9-Mediated Resolution of Neuroinflammation Confers Neuroprotection upon Ischemic Stroke in Mice

Excessive and unresolved neuroinflammation is a key component of the pathological cascade in brain injuries such as ischemic stroke. Here, we report that TRIM9, a brain-specific tripartite motif (TRIM) protein, was highly expressed in the peri-infarct areas shortly after ischemic insults in mice, but expression was decreased in aged mice, which are known to have increased neuroinflammation after stroke. Mechanistically, TRIM9 sequestered β-transducin repeat-containing protein (β-TrCP) from the Skp-Cullin-F-box ubiquitin ligase complex, blocking IκBα degradation and thereby dampening nuclear factor κB (NF-κB)-dependent proinflammatory mediator production and immune cell infiltration to limit neuroinflammation. Consequently, Trim9-deficient mice were highly vulnerable to ischemia, manifesting uncontrolled neuroinflammation and exacerbated neuropathological outcomes. Systemic administration of a recombinant TRIM9 adeno-associated virus that drove brain-wide TRIM9 expression effectively resolved neuroinflammation and alleviated neuronal death, especially in aged mice. These findings reveal that TRIM9 is essential for resolving NF-κB-dependent neuroinflammation to promote recovery and repair after brain injury and may represent an attractive therapeutic target.

Sex Differences in Ischemia/Reperfusion Injury: The Role of Mitochondrial Permeability Transition

Brain and heart ischemia are among the leading causes of death and disability in both men and women, but there are significant sex differences in the incidence and severity of these diseases. Ca²⁺ dysregulation in response to ischemia/reperfusion injury (I/RI) is a well-recognized pathogenic mechanism leading to the death of affected cells. Excess intracellular Ca²⁺ causes mitochondrial matrix Ca²⁺ overload that can result in mitochondrial permeability transition (MPT), which can have severe consequences for mitochondrial function and trigger cell death. Recent findings indicate that estrogens and their related receptors are involved in the regulation of MPT, suggesting that sex differences in I/RI could be linked to estrogen-dependent modulation of mitochondrial Ca²⁺. Here, we review the evidence supporting sex differences in I/RI and the role of estrogen and estrogen receptors in producing these differences, the involvement of mitochondrial Ca²⁺ overload in disease pathogenesis, and the estrogen-dependent modulation of MPT that may contribute to sex differences.

High-fructose diet during adolescent development increases neuroinflammation and depressive-like behavior without exacerbating outcomes after stroke

Diseases, disorders, and insults of aging are frequently studied in otherwise healthy animal models despite rampant co-morbidities and exposures among the human population. Stressor exposures can increase neuroinflammation and augment the inflammatory response following a challenge. The impact of dietary exposure on baseline neural function and behavior has gained attention; in particular, a diet high in fructose can increase activation of the hypothalamic-pituitary-adrenal axis and alter behavior. The current study considers the implications of a diet high in fructose for neuroinflammation and outcomes following the cerebrovascular challenge of stroke. Ischemic injury may come as a "second hit" to pre-existing metabolic pathology, exacerbating inflammatory and behavioral sequelae. This study assesses the neuroinflammatory consequences of a peri-adolescent high-fructose diet model and assesses the impact of diet-induced metabolic dysfunction on behavioral and neuropathological outcomes after middle cerebral artery occlusion. We demonstrate that consumption of a high-fructose diet initiated during adolescent development increases brain complement expression, elevates plasma TNFα and serum corticosterone, and promotes depressive-like behavior. Despite these adverse effects of diet exposure, peri-adolescent fructose consumption did not exacerbate neurological behaviors or lesion volume after middle cerebral artery occlusion.

Insulin-like Growth Factor (IGF)-1 treatment stabilizes the microvascular cytoskeleton under ischemic conditions

Our previous studies showed that Insulin-like Growth Factor (IGF)-1 reduced blood brain barrier permeability and decreased infarct volume caused by middle cerebral artery occlusion (MCAo) in middle aged female rats. Similarly, cultures of primary brain microvessel endothelial cells from middle-aged female rats and exposed to stroke-like conditions (oxygen glucose deprivation; OGD) confirmed that IGF-1 reduced dye transfer across this cell monolayer. Surprisingly, IGF-1 did not attenuate endothelial cell death caused by OGD. To reconcile these findings, the present study tested the hypothesis that, at the earliest phase of ischemia, IGF-1 promotes barrier function by increasing anchorage and stabilizing cell geometry of surviving endothelial cells. Cultures of human brain microvessel endothelial cells were subject to oxygen-glucose deprivation (OGD) in the presence of IGF-1, IGF-1 + JB-1 (IGFR inhibitor) or vehicle. OGD disrupted the cell monolayer and reduced cell-cell interactions, which was preserved in IGF-1-treated cultures and reversed by concurrent treatment with JB-1. IGF-1-mediated preservation of the endothelial monolayer was reversed with LY294002 treatment, but not by Rapamycin, indicating that IGF-1 s actions on cell-cell contacts are likely mediated via the PI3K pathway. In vivo, microvessel morphology was evaluated in middle-aged female rats that were subjected to ischemia by MCAo, and treated ICV with IGFI, IGF-1 + JB-1, or artificial CSF (aCSF; vehicle) after reperfusion. Compared to vehicle controls, IGF-1 treated animals displayed larger microvessel diameters in the peri-infarct area and increased staining density for vinculin, an anchorage protein. Both these measures were reversed by concurrent IGF-1 + JB-1 treatment. Moreover these effects were restricted to 24 h after ischemia-reperfusion and no treatment effects were seen at 5d post stroke. Collectively, these data suggest that in the earliest hours during ischemia, IGF-1 promotes receptor-mediated anchorage of endothelial cells, and its actions may be accurately characterized as vasculoprotective.

Oophorectomy Reduces Estradiol Levels and Long-Term Spontaneous Neurovascular Recovery in a Female Rat Model of Focal Ischemic Stroke

Although epidemiological evidence suggests significant sex and gender-based differences in stroke risk and recovery, females have been widely under-represented in preclinical stroke research. The neurovascular sequelae of brain ischemia in females, in particular, are largely uncertain. We set out to address this gap by a multimodal in vivo study of neurovascular recovery from endothelin-1 model of cortical focal-stroke in sham vs. ovariectomized female rats. Three weeks post ischemic insult, sham operated females recapitulated the phenotype previously reported in male rats in this model, of normalized resting perfusion but sustained peri-lesional cerebrovascular hyperreactivity. In contrast, ovariectomized (Ovx) females showed reduced peri-lesional resting blood flow, and elevated cerebrovascular responsivity to hypercapnia in the peri-lesional and contra-lateral cortices. Electrophysiological recordings showed an attenuation of theta to low-gamma phase-amplitude coupling in the peri-lesional tissue of Ovx animals, despite relative preservation of neuronal power. Further, this chronic stage neuronal network dysfunction was inversely correlated with serum estradiol concentration. Our pioneering data demonstrate dramatic differences in spontaneous recovery in the neurovascular unit between Ovx and Sham females in the chronic stage of stroke, underscoring the importance of considering hormonal-dependent aspects of the ischemic sequelae in the development of novel therapeutic approaches and patient recruitment in clinical trials.

Blood-brain barrier dysfunction in ischemic stroke: targeting tight junctions and transporters for vascular protection

The blood-brain barrier (BBB) is a physical and biochemical barrier that precisely controls cerebral homeostasis. It also plays a central role in the regulation of blood-to-brain flux of endogenous and exogenous xenobiotics and associated metabolites. This is accomplished by molecular characteristics of brain microvessel endothelial cells such as tight junction protein complexes and functional expression of influx and efflux transporters. One of the pathophysiological features of ischemic stroke is disruption of the BBB, which significantly contributes to development of brain injury and subsequent neurological impairment. Biochemical characteristics of BBB damage include decreased expression and altered organization of tight junction constituent proteins as well as modulation of functional expression of endogenous BBB transporters. Therefore, there is a critical need for development of novel therapeutic strategies that can protect against BBB dysfunction (i.e., vascular protection) in the setting of ischemic stroke. Such strategies include targeting tight junctions to ensure that they maintain their correct structure or targeting transporters to control flux of physiological substrates for protection of endothelial homeostasis. In this review, we will describe the pathophysiological mechanisms in cerebral microvascular endothelial cells that lead to BBB dysfunction following onset of stroke. Additionally, we will utilize this state-of-the-art knowledge to provide insights on novel pharmacological strategies that can be developed to confer BBB protection in the setting of ischemic stroke.

Aging- and vascular-related pathologies

Our aging population is set to grow considerably in the coming decades. In fact, the number of individuals older than 65 years will double by 2050. This projected increase in people living with extended life expectancy represents an inevitable upsurge in the presentation of age-related pathologies. However, our current understanding of the impact of aging on a number of biological processes is unfortunately inadequate. Cardiovascular, cerebrovascular, and neurodegenerative diseases are particularly prevalent in the elderly population. Intriguingly, these pathologies are all associated with vascular dysfunction, suggesting that the process of aging can induce structural and functional impairments in vascular networks. Together with elevated cell senescence, pre-existing comorbidities, and the emerging concept of age-associated inflammatory imbalance, impaired vascular functions can significantly increase one's risk in acquiring age-related diseases. In this short review, we highlight some current clinical and experimental evidence of how biological aging contributes to three vascular-associated pathologies: atherosclerosis, stroke, and Alzheimer's disease.

Early Blood-Brain Barrier Disruption after Mechanical Thrombectomy in Acute Ischemic Stroke

BACKGROUND AND PURPOSE

The impact of blood-brain barrier (BBB) disruption can be detected by intraparenchymal hyperdense lesion on the computed tomography (CT) scan after endovascular stroke therapy. The purpose of this study was to determine whether early BBB disruption predicts intracranial hemorrhage and poor outcome in patients with acute ischemic stroke treated with mechanical thrombectomy.

METHODS

We analyzed patients with anterior circulation stroke treated with mechanical thrombectomy and identified BBB disruption on the noncontrast CT images immediately after endovascular treatment. Follow-up CT or magnetic resonance imaging scan was performed at 24 hours to assess intracranial hemorrhage. We dichotomized patients into those with moderate BBB disruption versus those with minor BBB disruption and no BBB disruption. We evaluated the association of moderate BBB disruption after mechanical thrombectomy with intracranial hemorrhage and clinical outcomes.

RESULTS

Moderate BBB disruption after mechanical thrombectomy was found in 56 of 210 patients (26.7%). Moderate BBB disruption was independently associated with higher rates of hemorrhagic transformation (OR 25.33; 95% CI 9.93-64.65; P < .001), parenchymal hematoma (OR 20.57; 95% CI 5.64-74.99; P < .001), and poor outcome at discharge (OR 2.35; 95% CI 1.09-5.07; P = .03). The association of BBB disruption with intracranial hemorrhage remained in patients with successful reperfusion after mechanical thrombectomy. The location of BBB disruption was not associated with intracranial hemorrhage and poor outcome.

CONCLUSIONS

Moderate BBB disruption is common after mechanical thrombectomy in a quarter of patients with acute ischemic stroke and increases the risk of intracranial hemorrhage and poor outcome.

Present Status and Future Challenges of New Therapeutic Targets in Preclinical Models of Stroke in Aged Animals with/without Comorbidities

The aging process, comorbidities, and age-associated diseases are closely dependent on each other. Cerebral ischemia impacts a wide range of systems in an age-dependent manner. However, the aging process has many facets which are influenced by the genetic background and epigenetic or environmental factors, which can explain why some people age differently than others. Therefore, there is an urgent need to identify age-related changes in body functions or structures that increase the risk for stroke and which are associated with a poor outcome. Multimodal imaging, electrophysiology, cell biology, proteomics, and transcriptomics, offer a useful approach to link structural and functional changes in the aging brain, with or without comorbidities, to post-stroke rehabilitation. This can help us to improve our knowledge about senescence firstly, and in this context, aids in elucidating the pathophysiology of age-related diseases that allows us to develop therapeutic strategies or prevent diseases. These processes, including potential therapeutical interventions, need to be studied first in relevant preclinical models using aged animals, with and without comorbidities. Therefore, preclinical research on ischemic stroke should consider age as the most important risk factor for cerebral ischemia. Furthermore, the identification of effective therapeutic strategies, corroborated with successful translational studies, will have a dramatic impact on the lives of millions of people with cerebrovascular diseases.

Protective Effect of Klotho against Ischemic Brain Injury Is Associated with Inhibition of RIG-I/NF-κB Signaling

Aging is the greatest independent risk factor for the occurrence of stroke and poor outcomes, at least partially through progressive increases in oxidative stress and inflammation with advanced age. Klotho is an antiaging gene, the expression of which declines with age. Klotho may protect against neuronal oxidative damage that is induced by glutamate. The present study investigated the effects of Klotho overexpression and knockdown by an intracerebroventricular injection of a lentiviral vector that encoded murine Klotho (LV-KL) or rat Klotho short-hairpin RNA (LV-KL shRNA) on cerebral ischemia injury and the underlying anti-neuroinflammatory mechanism. The overexpression of Klotho induced by LV-KL significantly improved neurobehavioral deficits and increased the number of live neurons in the hippocampal CA1 and caudate putamen subregions 72 h after cerebral hypoperfusion that was induced by transient bilateral common carotid artery occlusion (2VO) in mice. The overexpression of Klotho significantly decreased the immunoreactivity of glial fibrillary acidic protein and ionized calcium binding adaptor molecule-1, the expression of retinoic-acid-inducible gene-I, the nuclear translocation of nuclear factor-κB, and the production of proinflammatory cytokines (tumor necrosis factor α and interleukin-6) in 2VO mice. The knockdown of Klotho mediated by LV-KL shRNA in the brain exacerbated neurological dysfunction and cerebral infarct after 22 h of reperfusion following 2 h middle cerebral artery occlusion in rats. These findings suggest that Klotho itself or enhancers of Klotho may compensate for its aging-related decline, thus providing a promising therapeutic approach for acute ischemic stroke during advanced age.

Tau-mediated iron export prevents ferroptotic damage after ischemic stroke

Functional failure of tau contributes to age-dependent, iron-mediated neurotoxicity, and as iron accumulates in ischemic stroke tissue, we hypothesized that tau failure may exaggerate ischemia-reperfusion-related toxicity. Indeed, unilateral, transient middle cerebral artery occlusion (MCAO) suppressed hemispheric tau and increased iron levels in young (3-month-old) mice and rats. Wild-type mice were protected by iron-targeted interventions: ceruloplasmin and amyloid precursor protein ectodomain, as well as ferroptosis inhibitors. At this age, tau-knockout mice did not express elevated brain iron and were protected against hemispheric reperfusion injury following MCAO, indicating that tau suppression may prevent ferroptosis. However, the accelerated age-dependent brain iron accumulation that occurs in tau-knockout mice at 12 months of age negated the protective benefit of tau suppression against MCAO-induced focal cerebral ischemia-reperfusion injury. The protective benefit of tau knockout was revived in older mice by iron-targeting interventions. These findings introduce tau-iron interaction as a pleiotropic modulator of ferroptosis and ischemic stroke outcome.