Therapeutic Strategies to Attenuate Hemorrhagic Transformation After Tissue Plasminogen Activator Treatment for Acute Ischemic Stroke

The effect of intravenous thrombolysis in stroke patients with unsuccessful thrombectomy

BACKGROUND

The benefit of intravenous thrombolysis (IVT) is well established. We aim to study the benefits of IVT in acute ischemic stroke (AIS) patients with large vessel occlusion (LVO) who underwent unsuccessful mechanical thrombectomy (MT).

METHODS

We included AIS patients who underwent MT for anterior circulation LVO with failed recanalization (modified treatment in cerebral ischemia [mTICI] score ≤ 2A). Patients who received IVT prior to MT were compared to those who received MT alone. Propensity score matching using demographic, clinical, radiographic and procedural variables was used to match patients with and without IVT. The primary outcome was favorable 90-day good functional outcome (defined as modified Rankin scale of 0-2), and secondary outcomes included intracranial hemorrhage (ICH), symptomatic ICH (sICH), and 90-day mortality.

RESULTS

Totally, 610 AIS patients with unsuccessful MT were included. After propensity matching, 219 patients were identified in each group. Median age was 70 years and 73 years in the IVT + MT and MT alone groups, respectively. In the IVT + MT group, final mTICI scores of 0, 1, and 2A were achieved in 92 (42.0%), 33 (15.1%), and 94 (42.9%) patients, respectively, versus 76 (34.7%), 29 (13.2%), and 114 (52.1%) in the MT alone group. The IVT + MT group had greater odds of 90-day good functional outcome (adjusted odds ratio 2.54, 95% confidence interval 1.53-4.32). There were no significant differences in secondary outcomes.

CONCLUSIONS

IVT is associated with improved functional outcomes in AIS patients with LVO despite unsuccessful MT.

Association between uric acid and the risk of hemorrhagic transformation in patients with acute ischemic stroke: a systematic review and meta-analysis

Background

The relationship between hemorrhagic transformation (HT) and uric acid (UA) remains controversial. This study aimed to investigate the relationship between UA concentrations and the risk of HT following acute ischemic stroke (AIS).

Methods

Electronic databases were searched for studies on HT and UA from inception to October 31, 2023. Two researchers independently reviewed the studies for inclusion. STATA Software 16.0 was used to compute the standardized mean difference (SMD) and 95% confidence interval (CI) for the pooled and post-outlier outcomes. Heterogeneity was evaluated using the I2 statistic and the Galbraith plot. Additionally, sensitivity analysis was performed. Lastly, Begg's funnel plot and Egger's test were used to assess publication bias.

Results

A total of 11 studies involving 4,608 patients were included in the meta-analysis. The pooled SMD forest plot (SMD = -0.313, 95% CI = -0.586--0.039, p = 0.025) displayed that low UA concentrations were linked to a higher risk of HT in post-AIS patients. However, heterogeneity (I2 = 89.8%, p < 0.001) was high among the studies. Six papers fell outside the Galbraith plot regression line, and there exclusive resulted in the absence of heterogeneity (I2 = 52.1%, p = 0.080). Meanwhile, repeated SMD analysis (SMD = -0.517, 95% CI = -0.748--0.285, p = 0.000) demonstrated that the HT group had lower UA concentrations. Finally, Begg's funnel plot and Egger's test indicated the absence of publication bias in our meta-analysis.

Conclusion

This meta-analysis illustrated a substantial connection between UA concentrations and HT, with lower UA concentrations independently linked with a higher risk of HT post-AIS. These results lay a theoretical reference for future studies.Systematic review registration:https://www.crd.york.ac.uk/PROSPERO/CRD42023485539.

Alleviating Recombinant Tissue Plasminogen Activator-induced Hemorrhagic Transformation in Ischemic Stroke via Targeted Delivery of a Ferroptosis Inhibitor

Intravenous thrombolysis with recombinant tissue plasminogen activator (rtPA) is the primary treatment for ischemic stroke. However, rtPA treatment can substantially increase blood-brain barrier (BBB) permeability and susceptibility to hemorrhagic transformation. Herein, the mechanism underlying the side effects of rtPA treatment is investigated and demonstrated that ferroptosis plays an important role. The ferroptosis inhibitor, liproxstatin-1 (Lip) is proposed to alleviate the side effects. A well-designed macrocyclic carrier, glucose-modified azocalix[4]arene (GluAC4A), is prepared to deliver Lip to the ischemic site. GluAC4A bound tightly to Lip and markedly improved its solubility. Glucose, modified at the upper rim of GluAC4A, imparts BBB targeting to the drug delivery system owing to the presence of glucose transporter 1 on the BBB surface. The responsiveness of GluAC4A to hypoxia due to the presence of azo groups enabled the targeted release of Lip at the ischemic site. GluAC4A successfully improved drug accumulation in the brain, and Lip@GluAC4A significantly reduced ferroptosis, BBB leakage, and neurological deficits induced by rtPA in vivo. These findings deepen the understanding of the side effects of rtPA treatment and provide a novel strategy for their effective mitigation, which is of great significance for the treatment and prognosis of patients with ischemic stroke.

Fibrinogen deposition promotes neuroinflammation and fibrin-derived γ377-395 peptide ameliorates neurological deficits after ischemic stroke

BACKGROUND

Fibrin(ogen) deposition in the central nervous system (CNS) contributes to neuropathological injury; however, its role in ischemic stroke is unknown. In this study, we identified fibrinogen as a novel proinflammatory regulator of post-stroke neuroinflammation and revealed the neuro-protection effect of fibrin-derived γ377-395peptide in stroke.

METHODS

Fibrinogen depletion and fibrinogen-derived γ377-395peptide treatment were performed 2 h after establishing a permanent middle cerebral artery occlusion (pMCAO) model. The infarction volume, neurological score, fibrin(ogen) deposition, and inflammatory response were evaluated 24 h after occlusion. Both in vivo and in vitro studies were conducted to assess the therapeutic potential of the γ377-395peptide in blocking the interactions between fibrin(ogen) and neutrophils.

RESULTS

Fibrin(ogen) deposited in the infarct core promoted post-stroke inflammation and exacerbated neurological deficits in the acute phase after stroke onset. Reducing fibrinogen deposition resulted in a decrease in infarction volume, improved neurological scores, and reduced inflammation in the brain. Additionally, the presence of neutrophil accumulation near fibrin(ogen) deposits was observed in ischemic lesions, and the engagement of fibrin(ogen) by integrin receptor αMβ2 promoted neutrophil activation and post-stroke inflammation. Finally, inhibiting fibrin(ogen)-mediated neutrophil activation using a fibrinogen-derived γ377-395peptide significantly attenuated neurological deficits.

CONCLUSIONS

Fibrin(ogen) is a crucial regulator of post-stroke inflammation and contributes to secondary brain injury. The inflammation induced by fibrin(ogen) is primarily driven by neutrophils during acute ischemic stroke and can be ameliorated using the fibrin-derived γ377-395peptide. Targeting the fibrin(ogen)-mediated neuropathological process represents a promising approach for neuroprotective therapy after stroke while preserving its beneficial coagulation function.

Angong Niuhuang Wan inhibit ferroptosis on ischemic and hemorrhagic stroke by activating PPARγ/AKT/GPX4 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Angong Niuhuang Wan (AGNHW) is a prescription from traditional Chinese medicine (TCM) that has been used for centuries to treat ischemic stroke (IS) and hemorrhagic stroke (HS). According to a recent study, targeting ferroptosis might be effective in the management of IS and HS. However, the ferroptosis-related effects and mechanisms of AGNHW have not yet been reported.

AIM OF THE STUDY

This research examines the anti-ferroptosis mechanisms of AGNHW in the treatment of IS and HS.

MATERIALS AND METHODS

A system pharmacological approach including in vivo experiment, UHPLC-Q-Orbitrap HRMS, network pharmacology, molecular docking, microscale thermophoresis, and in vitro experiment was utilized to study the anti-ferroptosis mechanisms of AGNHW against IS and HS.

RESULTS

In vivo experiments indicated that AGNHW enhanced nerve function, decreased cerebral infarct volume, ameliorated histological brain injuries, improved the structural integrity of the blood-brain barrier, ameliorated the mitochondrial dysfunction and morphology disruption, and inhibits ROS, LPO and Fe2+ accumulations in IS and HS rats. Using UHPLC-Q-Orbitrap HRMS, the key ingredients of AGNHW-containing serum were identified as bilirubin, berberine, baicalin, and wogonoside. According to the network pharmacology analyses, AGNHW could inhibit ferroptosis by modulating the PPAR and PI3K/AKT signaling pathways. The core targets are PPARγ, AKT, and GPX4. Molecular docking and microscale thermophoresis experiments further revealed that the key ingredients have strong interactions with ferroptosis-regulating core proteins. Moreover, in vitro experiment results showed that AGNHW alleviated ferroptosis injury induced by erastin in PC12 cells, increased cell viability, reduced the LPO and Fe2+ levels, and up-regulated mRNA expressions of PPARγ, AKT, and GPX4. AGNHW also up-regulated protein expressions of PPARγ, p-AKT/AKT, and GPX4 in IS and HS rats.

CONCLUSIONS

AGNHW attenuated ferroptosis in treating IS and HS by targeting the PPARγ/AKT/GPX4 pathway. This work reveals AGNHW's anti-ferroptosis mechanism against IS and HS, but it also develops an integrated approach to demonstrate the common characteristics of drugs in treating different diseases.

Predictive Role of Pre-Thrombolytic Neutrophil-Platelet Ratio on Hemorrhagic Transformation After Intravenous Thrombolysis in Acute Ischemic Stroke

To investigate the predictive role of the neutrophil-platelet ratio (NPR) before intravenous thrombolysis (IVT) on hemorrhagic transformation (HT) in patients with acute ischemic stroke (AIS). AIS patients treated with IVT without endovascular therapy between June 2019 and February 2023 were included. Patients were divided into high NPR (>35) and low NPR (≤35) groups according to the optimal threshold NPR value for identifying high-risk patients before IVT. The baseline data and the incidence of HT and symptomatic intracranial hemorrhage (sICH) were compared between the two groups. The predictive role of the NPR and other related factors on HT after IVT was analyzed by multivariate logistic regression. A total of 247 patients were included, with an average age of 67.5 ± 12.4 years. Post-thrombolytic HT was observed in 18.6% of the patients, and post-thrombolytic sICH was observed in 1.2% of the patients. There were 69 patients in the high NPR group and 178 patients in the low NPR group. The incidence of HT in the high NPR group was significantly higher than that in the low NPR group (30.4% vs 16.3%, P < .05). The incidence of sICH was significantly higher in the high NPR group than in the low NPR group (14.5% vs 1.7%, P < .001). Multivariate logistic regression analysis showed that NPR > 35 was positively correlated with HT (odds ratio (OR) = 3.236, 95% confidence interval (CI): 1.481-7.068, P = .003) and sICH (OR = 13.644, 95% CI: 2.392-77.833, P = .003). A high NPR (>35) before IVT may be a predictor of HT in AIS patients. This finding may help clinicians make clinical decisions before IVT in AIS patients.

Neurovascular Inflammation and Complications of Thrombolysis Therapy in Stroke

Intravenous thrombolysis via tPA (tissue-type plasminogen activator) is the only approved pharmacological treatment for acute ischemic stroke, but its benefits are limited by hemorrhagic transformation. Emerging evidence reveals that tPA swiftly mobilizes immune cells which extravasate into the brain parenchyma via the cerebral vasculature, augmenting neurovascular inflammation, and tissue injury. In this review, we summarize the pronounced alterations of immune cells induced by tPA in patients with stroke and experimental stroke models. We argue that neuroinflammation, triggered by ischemia-induced cell death and exacerbated by tPA, compromises neurovascular integrity and the microcirculation, leading to hemorrhagic transformation. Finally, we discuss current and future approaches to attenuate thrombolysis-associated hemorrhagic transformation via uncoupling immune cells from the neurovascular unit.

Development and validation of a machine learning-based prognostic risk stratification model for acute ischemic stroke

Acute ischemic stroke (AIS) is a most prevalent cause of serious long-term disability worldwide. Accurate prediction of stroke prognosis is highly valuable for effective intervention and treatment. As such, the present retrospective study aims to provide a reliable machine learning-based model for prognosis prediction in AIS patients. Data from AIS patients were collected retrospectively from the Second Affiliated Hospital of Xuzhou Medical University between August 2017 and July 2019. Independent prognostic factors were identified by univariate and multivariate logistic analysis and used to develop machine learning (ML) models. The ML model performance was assessed by area under the receiver operating characteristic curve (AUC) and radar plot. Shapley Additive explanations (SHAP) values were used to interpret the importance of all features included in the predictive model. A total of 677 AIS patients were included in the present study. Poor prognosis was observed in 209 patients (30.9%). Six variables, including neuron specific enolase (NSE), homocysteine (HCY), S-100β, dysphagia, C-reactive protein (CRP), and anticoagulation were included to establish ML models. Six different ML algorithms were tested, and Random Forest model was selected as the final predictive model with the greatest AUC of 0.908. Moreover, according to SHAP results, NSE impacted the predictive model the most, followed by HCY, S-100β, dysphagia, CRP and anticoagulation. Based on the RF model, an online tool was constructed to predict the prognosis of AIS patients and assist clinicians in optimizing patient treatment. The present study revealed that NSE, HCY, CRP, S-100β, anticoagulation, and dysphagia were important factors for poor prognosis in AIS patients. ML algorithms were used to develop predictive models for predicting the prognosis of AIS patients, with the RF model presenting the optimal performance.

The pleiotropic of GLP-1/GLP-1R axis in central nervous system diseases

Glucagon-like peptide-1(GLP-1) is a multifunctional polypeptide throughout the lifespan via activating Glucagon-like peptide-1 receptor (GLP-1R).GLP-1 can affect food ingestion, enhance the secretion of insulin from pancreatic islets induced by glucose and be utilized to treat type 2 diabetes mellitus(T2DM).But, accumulating evidences from the decades suggest that activation GLP-1R can not only regulate the blood glucose, but also sustain the homeostasis of intracellular environment and protect neuron from various damaged responses such as oxidative stress, inflammation, excitotoxicity, ischemia and so on. And more and more pre-clinical and clinical studies identified that GLP-1 and its analogues may play a significant role in improving multiple central nervous system (CNS) diseases including neurodegenerative diseases, epilepsy, mental disorders, ischemic stroke, hemorrhagic stroke, traumatic brain injury, spinal cord injury, chronic pain, addictive disorders, other diseases neurological complications and so on. In order to better reveal the relationship between GLP-1/GLP-1R axis and the growth, development and survival of neurons, herein, this review is aimed to summarize the multi-function of GLP-1/GLP-1R axis in CNS diseases.

Delayed revascularization in acute ischemic stroke patients

Stroke shares a significant burden of global mortality and disability. A significant decline in the quality of life is attributed to the so-called post-stroke cognitive impairment including mild to severe cognitive alterations, dementia, and functional disability. Currently, only two clinical interventions including pharmacological and mechanical thrombolysis are advised for successful revascularization of the occluded vessel. However, their therapeutic effect is limited to the acute phase of stroke onset only. This often results in the exclusion of a significant number of patients who are unable to reach within the therapeutic window. Advances in neuroimaging technologies have allowed better assessment of salvageable penumbra and occluded vessel status. Improvement in diagnostic tools and the advent of intravascular interventional devices such as stent retrievers have expanded the potential revascularization window. Clinical studies have demonstrated positive outcomes of delayed revascularization beyond the recommended therapeutic window. This review will discuss the current understanding of ischemic stroke, the latest revascularization doctrine, and evidence from clinical studies regarding effective delayed revascularization in ischemic stroke.

Can metformin use reduce the risk of stroke in diabetic patients? A systematic review and meta-analysis

BACKGROUND AND AIM

Stroke and cardiovascular diseases are major causes of death and disability, especially among diabetic patients. Some studies have shown that metformin has been effective in preventing cardiovascular diseases. In this study, we aim to evaluate the effect of metformin on stroke in type 2 diabetic patients.

METHODS

A comprehensive search was conducted in Medline, Embase, Scopus, and Web of Science databases from their inception till 1st July 2022. Randomized clinical trials (RCT) and cohort studies were included. Two independent researchers screened the records, extracted the data, and assessed the risk of bias and certainty of evidence. Findings were reported as risk ratio (RR) and 95% confidence interval (CI). All statistical analyses were performed using the STATA 17.0 software package.

RESULTS

Analysis of 21 included studies with 1,392,809 patients demonstrated that metformin monotherapy was effective in reducing stroke risk in both RCTs (RR = 0.66, 95% CI: 0.50, 0.87 p = 0.004) and cohort studies (RR = 0.67, 95% CI: 0.55, 0.81, p < 0.0001). However, combined administration of metformin with other antihyperglycemic agents had no significant effect on stroke risk reduction in either the RCTs (RR = 0.92, 95% CI: 0.69, 1.22 p = 0.558) or the cohort studies (RR = 0.79, 95% CI: 0.59, 1.06, p = 0.122).

CONCLUSION

Low to moderate level of evidence in RCTs showed that metformin monotherapy could reduce stroke risk in type 2 diabetic patients. However, the preventive effect of metformin in stroke was not observed in patients who received a combination of metformin plus other hypoglycemic agents.

Neutrophil extracellular traps: A novel target for the treatment of stroke

Stroke is a threatening cerebrovascular disease caused by thrombus with high morbidity and mortality rates. Neutrophils are the first to be recruited in the brain after stroke, which aggravate brain injury through multiple mechanisms. Neutrophil extracellular traps (NETs), as a novel regulatory mechanism of neutrophils, can trap bacteria and secret antimicrobial molecules, thereby degrading pathogenic factors and killing bacteria. However, NETs also exacerbate certain non-infectious diseases by activating autoimmune or inflammatory responses. NETs have been found to play important roles in the pathological process of stroke in recent years. In this review, the mechanisms of NETs formation, the physiological roles of NETs, and the dynamic changes of NETs after stroke are summarized. NETs participate in stroke through various mechanisms. NETs promote the coagulation cascade and interact with platelets to induce thrombosis. tPA induces the degranulation of neutrophils to form NETs, leading to hemorrhagic transformation and thrombolytic resistance. NETs aggravate stroke by mediating inflammation, atherosclerosis and vascular injury. In addition, the regulation of NETs in stroke, the potential of NETs as biomarker and the treatment of stroke targeting NETs are discussed. The increasing evidences suggest that NETs may be a potential target for stroke treatment. Inhibition of NETs formation or promotion of NETs degradation plays protective effects in stroke. However, how to avoid the adverse effects of NETs-targeted therapy deserves further study. In summary, this review provides a reference for the pathogenesis, drug targets, biomarkers and drug development of NETs in stroke.

Mesenchymal stem cell-derived extracellular vesicles attenuate tPA-induced blood-brain barrier disruption in murine ischemic stroke models

Intracerebral hemorrhage following blood-brain barrier (BBB) disruption resulting from thrombolysis of ischemic stroke with tissue plasminogen activator (tPA) remains a critical clinical problem. Mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) are promising nanotherapeutic agents that have the potential to repair the BBB after ischemic stroke; however, whether they can attenuate BBB disruption and hemorrhagic transformation after tPA thrombolysis is largely unknown. Here, we observed that MSC-EVs efficiently passed through the BBB and selectively accumulated in injured brain regions in ischemic stroke model mice in real time using aggregation-induced emission luminogens (AIEgens), which exhibit better tracking ability than the commercially available tracer DiR. Moreover, tPA administration promoted the homing of MSC-EVs to the ischemic brain and increased the uptake of MSC-EVs by astrocytes. Furthermore, the accumulated MSC-EVs attenuated the tPA-induced disruption of BBB integrity and alleviated hemorrhage by inhibiting astrocyte activation and inflammation. Mechanistically, miR-125b-5p delivered by MSC-EVs played an indispensable role in maintaining BBB integrity by targeting Toll-like receptor 4 (TLR4) and inhibiting nuclear transcription factor-kappaB (NF-κB) signaling in astrocytes. This study provides a noninvasive method for real-time tracking of MSC-EVs in the ischemic brain after tPA treatment and highlights the potential of MSC-EVs as thrombolytic adjuvants for ischemic stroke. STATEMENT OF SIGNIFICANCE: Although tPA thrombolysis is the most effective pharmaceutical strategy for acute ischemic stroke, its clinical application and therapeutic efficacy are challenged by tPA-induced BBB disruption and hemorrhagic transformation. Our study demonstrated that MSC-EVs can act as an attractive thrombolytic adjuvant to repair the BBB and improve thrombolysis in a mouse ischemic stroke model. Notably, by labeling MSC-EVs with AIEgens, we achieved accurate real-time imaging of MSC-EVs in the ischemic brain and therapeutic visualization. MSC-EVs inhibit astrocyte activation and associated inflammation through miR-125b-5p/TLR4/NF-κB pathway. Consequently, we revealed that MSC-EVs combined with tPA thrombolysis may be a promising approach for the treatment of ischemic stroke in clinical setting.

Association of Red Blood Cell Distribution Width with Stroke Prognosis Among Patients with Small Artery Occlusion: A Hospital-Based Prospective Follow-Up Study

Objective

Stroke is the leading cause of mortality and disability worldwide. However, there is no study on the relationship between red blood cell distribution width and the prognosis of small artery occlusion, which is a stroke subtype. This study aimed to assess the association of red blood cell distribution width at admission with outcomes among patients with small artery occlusion.

Methods

In this hospital-based follow-up study, all included patients were diagnosed with small artery occlusion. Outcomes included death, recurrence, and dependency at 3, 12, and 36 months after stroke onset. Multivariate analysis was performed to explore the association of red blood cell distribution width with stroke outcomes.

Results

This study included 1576 patients with small artery occlusion who were followed up at 3, 12, and 36 months. For every unit increase in red blood cell distribution width, the risk of stroke recurrence and dependency increased by 5.1% (95% CI 1.002–1.102, P=0.039) at 3 months after stroke onset. At the 12-month follow-up, for every unit increase in red blood cell distribution width, the risk of stroke recurrence increased by 3.4% (95% CI 1.000–1.069, P=0.047). However, the relationship between red blood cell distribution width and mortality rate was not significant at 36 months after stroke onset after adjustment of covariates.

Conclusion

Red blood cell distribution width is an important hematological index of small artery occlusion. It may be used to predict the recurrence of acute ischemic stroke in small artery occlusion. Therefore, patients with higher baseline values of red blood cell distribution width may need more risk factor control to reduce recurrence and dependency.

Cerebral edema after ischemic stroke: Pathophysiology and underlying mechanisms

Ischemic stroke is associated with increasing morbidity and has become the main cause of death and disability worldwide. Cerebral edema is a serious complication arising from ischemic stroke. It causes an increase in intracranial pressure, rapid deterioration of neurological symptoms, and formation of cerebral hernia, and is an important risk factor for adverse outcomes after stroke. To date, the detailed mechanism of cerebral edema after stroke remains unclear. This limits advances in prevention and treatment strategies as well as drug development. This review discusses the classification and pathological characteristics of cerebral edema, the possible relationship of the development of cerebral edema after ischemic stroke with aquaporin 4, the SUR1-TRPM4 channel, matrix metalloproteinase 9, microRNA, cerebral venous reflux, inflammatory reactions, and cerebral ischemia/reperfusion injury. It also summarizes research on new therapeutic drugs for post-stroke cerebral edema. Thus, this review provides a reference for further studies and for clinical treatment of cerebral edema after ischemic stroke.

Macrophage Infiltration Reduces Neurodegeneration and Improves Stroke Recovery after Delayed Recanalization in Rats

Background

Recent cerebrovascular recanalization therapy clinical trials have validated delayed recanalization in patients outside of the conventional window. However, a paucity of information on the pathophysiology of delayed recanalization and favorable outcomes remains. Since macrophages are extensively studied in tissue repair, we anticipate that they may play a critical role in delayed recanalization after ischemic stroke.

Methods

In adult male Sprague-Dawley rats, two ischemic stroke groups were used: permanent middle cerebral artery occlusion (pMCAO) and delayed recanalization at 3 days following middle cerebral artery occlusion (rMCAO). To evaluate outcome, brain morphology, neurological function, macrophage infiltration, angiogenesis, and neurodegeneration were reported. Confirming the role of macrophages, after their depletion, we assessed angiogenesis and neurodegeneration after delayed recanalization.

Results

No significant difference was observed in the rate of hemorrhage or animal mortality among pMCAO and rMCAO groups. Delayed recanalization increased angiogenesis, reduced infarct volumes and neurodegeneration, and improved neurological outcomes compared to nonrecanalized groups. In rMCAO groups, macrophage infiltration contributed to increased angiogenesis, which was characterized by increased vascular endothelial growth factor A and platelet-derived growth factor B. Confirming these links, macrophage depletion reduced angiogenesis, inflammation, neuronal survival in the peri-infarct region, and favorable outcome following delayed recanalization.

Conclusion

If properly selected, delayed recanalization at day 3 postinfarct can significantly improve the neurological outcome after ischemic stroke. The sanguineous exposure of the infarct/peri-infarct to macrophages was essential for favorable outcomes after delayed recanalization at 3 days following ischemic stroke.

Clonidine ameliorates cerebral ischemia-reperfusion injury by up-regulating the GluN3 subunits of NMDA receptor

This study aimed to investigate the protective effects of the alpha-2 adrenergic receptor (α2-AR) agonist, clonidine, on the cerebral ischemia-reperfusion (I/R) injury and elaborate the underlying mechanisms. Cerebral I/R model was established by middle cerebral artery occlusion (MCAO) for 2 h followed by reperfusion for 4 h in adult male SD rats. Saline, clonidine and yohimbine (an α2-AR antagonist) were intraperitoneally administered each day for one week before surgery. Neurological deficit was evaluated just before decapitation. TTC staining was applied for correlation of cerebral infarction volume. HE staining was performed to observe the neuron morphology. Immunohistochemical staining was performed to detect the localization and expression of GluN3 proteins. Western blot analysis also was used to detect the expression levels of GluN3 proteins. Our data showed that clonidine ameliorated neurological deficit and reduced the cerebral infarction volume of the rats with cerebral I/R. It is worth noting that treatment with clonidine up-regulated the protein expression of GluN3 in the rats with the cerebral I/R, especially in the cell membrane. Moreover, clonidine also up-regulated the transposition from cytoplasm to cell membrane of GluN3 after cerebral I/R. In addition, yohimbine abolished the neuroprotective effects of clonidine. The results indicated that clonidine played a protective role in cerebral I/R injury through regulation of the protein expression of GluN3 subunits of N-methyl-D-aspartate (NMDA) receptor.

Angong Niuhuang Wan reduces hemorrhagic transformation and mortality in ischemic stroke rats with delayed thrombolysis: involvement of peroxynitrite-mediated MMP-9 activation

Background

Hemorrhagic transformation (HT) is a common complication of delayed tissue plasminogen activator (t-PA) treatment for ischemic stroke. Peroxynitrite plays an important role in the breakdown of blood–brain barrier (BBB) and the development of HT. We tested the hypothesis that Angong Niuhuang Wan (AGNHW), a traditional Chinese medicinal formula, could be used in conjunction with t-PA to protect the BBB, minimize HT, and improve neurological function by suppressing peroxynitrite-mediated matrix metalloproteinase-9 (MMP-9) activation.

Methods

We first performed quality control study and chemical identification of AGNHW by using UPLC. In animal experiments, male Sprague–Dawley rats were subjected to 5 h of middle cerebral artery occlusion (MCAO) followed by 19 h of reperfusion plus t-PA infusion (10 mg/kg) at 5 h of cerebral ischemia. AGNHW (257 mg/kg) was given orally at 2 h after MCAO. Hemorrhagic transformation was measured using hemorrhagic scores and hemoglobin levels in ischemic brains. Evans blue leakage was utilized to assess the severity of the blood–brain barrier (BBB) damage. The modified neurologic severity score (mNSS) test was used to assess neurological functions. Peroxynitrite and superoxide was detected by using fluorescent probes. MMP-9 activity and expression were examined by gelatin zymography and immunostaining. The antioxidant effects were also studied by using brain microvascular endothelial b.End3 cells exposed to 5 h of oxygen and glucose deprivation (OGD) plus 5 h of reoxygenation with t-PA treatment (20 µg/ml).

Results

AGNHW significantly reduced the BBB damage, brain edema, reduced hemorrhagic transformation, enhanced neurological function, and reduced mortality rate in the ischemic stroke rats with t-PA treatment. AGNHW reduced peroxynitrite and superoxide in vivo and in vitro and six active chemical compounds were identified from AGNHW with peroxynitrite scavenging activity. Furthermore, AGNHW inhibited MMP-9 activity, and preserved tight junction protein claudin-5 and collagen IV in the ischemic brains.

Conclusion

AGNHW could be a potential adjuvant therapy with t-PA to protect the BBB integrity, reduce HT, and improve therapeutic outcome in ischemic stroke treatment via inhibiting peroxynitrite-mediated MMP-9 activation.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13020-022-00595-7.

Optimized mouse model of embolic MCAO: From cerebral blood flow to neurological outcomes

The embolic middle cerebral artery occlusion (eMCAO) model mimics ischemic stroke due to large vessel occlusion in humans and is amenable to thrombolytic therapy with rtPA. However, two major obstacles, the difficulty of the eMCAO surgery and unpredictable occurrence of clot autolysis, had impeded its application in mice. In this study, we modified catheters to produce suitable fibrin-rich embolus and optimized the eMCAO model using cerebral blood flow (CBF) monitored by both laser Doppler flowmetry (LDF) and 2D laser speckle contrast imaging (LSCI) to confirm occlusion of MCA. The results showed that longer embolus resulted in higher mortality. There was a compensatory increase in MCA territory perfusion after eMCAO associated with decreased infarct volume; however, this was only partly dependent on recanalization as clot autolysis was only observed in ∼30% of mice. Cortical CBF monitoring with LSCI showed that the size of peri-core area at 3 h displayed the best correlation with infarct volume that is attributed to compensatory collateral blood flow. The peri-core area best predicted functional outcome after eMCAO. In summary, we developed a reliable eMCAO mouse model that better mimics embolic ischemic stroke in humans, which will increase the potential for successful translation of stroke neuroprotective therapies.

The Quinazoline Otaplimastat (SP-8203) Reduces the Hemorrhagic Transformation and Mortality Aggravated after Delayed rtPA-Induced Thrombolysis in Cerebral Ischemia

Acute ischemic stroke is the leading cause of morbidity and mortality worldwide. Recombinant tissue plasminogen activator (rtPA) is the only agent clinically approved by FDA for patients with acute ischemic stroke. However, delayed treatment of rtPA (e.g., more than 3 h after stroke onset) exacerbates ischemic brain damage by causing intracerebral hemorrhage and increasing neurotoxicity. In the present study, we investigated whether the neuroprotant otaplimastat reduced delayed rtPA treatment-evoked neurotoxicity in male Sprague Dawley rats subjected to embolic middle cerebral artery occlusion (eMCAO). Otaplimastat reduced cerebral infarct size and edema and improved neurobehavioral deficits. In particular, otaplimastat markedly reduced intracerebral hemorrhagic transformation and mortality triggered by delayed rtPA treatment, consequently extending the therapeutic time window of rtPA. We further found that ischemia-evoked extracellular matrix metalloproteases (MMPs) expression was closely correlated with cerebral hemorrhagic transformation and brain damage. In ischemic conditions, delayed rtPA treatment further increased brain injury via synergistic expression of MMPs in vascular endothelial cells. In oxygen-glucose-deprived endothelial cells, otaplimastat suppressed the activity rather than protein expression of MMPs by restoring the level of tissue inhibitor of metalloproteinase (TIMP) suppressed in ischemia, and consequently reduced vascular permeation. This paper shows that otaplimastat under clinical trials is a new drug which can inhibit stroke on its own and extend the therapeutic time window of rtPA, especially when administered in combination with rtPA.

Post-stroke treatment with argon preserved neurons and attenuated microglia/macrophage activation long-termly in a rat model of transient middle cerebral artery occlusion (tMCAO)

In a previous study from our group, argon has shown to significantly attenuate brain injury, reduce brain inflammation and enhance M₂ microglia/macrophage polarization until 7 days after ischemic stroke. However, the long-term effects of argon have not been reported thus far. In the present study, we analyzed the underlying neuroprotective effects and potential mechanisms of argon, up to 30 days after ischemic stroke. Argon administration with a 3 h delay after stroke onset and 1 h after reperfusion demonstrated long-term neuroprotective effect by preserving the neurons at the ischemic boundary zone 30 days after stroke. Furthermore, the excessive microglia/macrophage activation in rat brain was reduced by argon treatment 30 days after ischemic insult. However, long-lasting neurological improvement was not detectable. More sensorimotor functional measures, age- and disease-related models, as well as further histological and molecular biological analyses will be needed to extend the understanding of argon’s neuroprotective effects and mechanism of action after ischemic stroke.

Impact of systemic inflammatory response syndrome on acute ischemic stroke patients treated with mechanical thrombectomy

AIM

Systemic inflammatory response syndrome (SIRS) has been associated with poor outcomes after acute ischemic stroke (AIS). The primary goal of this study was to determine whether SIRS status on admission correlated with functional outcomes in AIS treated with mechanical thrombectomy (MT).

METHODS

Consecutive patients from September 2015 to April 2019 were retrospectively reviewed for SIRS on admission. SIRS was defined as the presence of ≥2 of the following: temperature < 36 °C or > 38 °C, heart rate > 90, respiratory rate > 20, and white blood cell count <4000/mm or > 12,000 mm.

RESULTS

Of 202 patients, 188 met inclusion criteria. 49 patients (26%) had evidence of SIRS. Neither basic patient demographics nor standard stroke risk factors predicted the development of SIRS. However, presentation with SIRS was correlated with higher rates of death (odds ratio [OR], 2.6; 95% confidence interval [CI], 1.2-5.5) as well as lower rates of favorable functional outcomes at discharge (OR, 0.09; 95% CI, 0.02-0.40) and 3-month follow up (OR 0.12; 95% CI 0.03-0.43). These results remained significant even after adjustment for age, sex, baseline NIHSS, recanalization status, and prior co-morbidities.

CONCLUSION

In our sample population, SIRS was associated with worse outcomes and higher rates of mortality in AIS patients treated with MT. Recognition of key risk factors can provide better prognostication and possible future therapeutic targets.

Nanoparticles-mediated emerging approaches for effective treatment of ischemic stroke

Ischemic stroke leads to high disability and mortality. The limited delivery efficiency of most therapeutic substances is a major challenge for effective treatment of ischemic stroke. Inspired by the prominent merit of nanoscale particles in brain targeting and blood-brain barrier (BBB) penetration, various functional nanoparticles have been designed as promising drug delivery platforms that are expected to improve the therapeutic effect of ischemic stroke. Based on the complex pathological mechanisms of ischemic stroke, this review outline and summarize the rationally designed nanoparticles-mediated emerging approaches for effective treatment of ischemic stroke, including recanalization therapy, neuroprotection therapy, and combination therapy. On this bases, the potentials and challenges of nanoparticles in the treatment of ischemic stroke are revealed, and new thoughts and perspectives are proposed for the design of feasible nanoparticles for effective treatment of ischemic stroke.

High red blood cell distribution width levels could increase the risk of hemorrhagic transformation after intravenous thrombolysis in acute ischemic stroke patients

The association between the red blood cell distribution width (RDW) and hemorrhagic transformation (HT) after thrombolysis in acute ischemic stroke patients remains inconclusive. Our study aimed to assess whether high RDW levels are associated with the occurrence of HT after thrombolysis. Data were consecutively collected and retrospectively analyzed for stroke patients treated with thrombolysis between 1 January 2017 and 31 December 2019. The primary outcomes were the occurrence of HT and symptomatic HT. Among the 286 patients enrolled, 36 (12.6%) developed HT and15 (5.2%) were classified as symptomatic HT. Patients with high RDW levels were associated with a higher percentage of HT and symptomatic HT (P<0.05). The RDW levels in the HT and symptomatic HT groups were also greater compared with the no-HT group (P<0.001). Multivariable logistic regression analysis revealed that high RDW levels were independently associated with an increased risk of HT (adjusted odds ratio 2.5, 95 % CI, 1.74–3.83 P < 0.001). In conclusion, we found that high RDW levels may be an independent predictor of HT in stroke patients after thrombolysis.

Inflammatory Biomarkers and Intracranial Hemorrhage after Endovascular Thrombectomy

BACKGROUND

Intracranial hemorrhage after endovascular thrombectomy is associated with poorer prognosis compared with those who do not develop the complication. Our study aims to determine predictors of post-EVT hemorrhage - more specifically, inflammatory biomarkers present in baseline serology.

METHODS

We performed a retrospective review of consecutive patients treated with EVT for acute large vessel ischemic stroke. The primary outcome of the study is the presence of ICH on the post-EVT scan. We used four definitions: the SITS-MOST criteria, the NINDS criteria, asymptomatic hemorrhage, and overall hemorrhage. We identified nonredundant predictors of outcome using backward elimination based on Akaike Information Criteria. We then assessed prediction accuracy using area under the receiver operating curve. Then we implemented variable importance ranking from logistic regression models using the drop in Naegelkerke R2 with the exclusion of each predictor.

RESULTS

Our study demonstrates a 6.3% SITS (16/252) and 10.0% NINDS (25/252) sICH rate, as well as a 19.4% asymptomatic (49/252) and 29.4% (74/252) overall hemorrhage rate. Serologic markers that demonstrated association with post-EVT hemorrhage were: low lymphocyte count (SITS), high neutrophil count (NINDS, overall hemorrhage), low platelet to lymphocyte ratio (NINDS), and low total WBC (NINDS, asymptomatic hemorrhage).

CONCLUSION

Higher neutrophil counts, low WBC counts, low lymphocyte counts, and low platelet to lymphoycyte ratio were baseline serology biomarkers that were associated with post-EVT hemorrhage. Our findings, particularly the association of diabetes mellitus and high neutrophil, support experimental data on the role of thromboinflammation in hemorrhagic transformation of large vessel occlusions.

Pinocembrin attenuates hemorrhagic transformation after delayed t-PA treatment in thromboembolic stroke rats by regulating endogenous metabolites

Hemorrhagic transformation (HT) is a common serious complication of stroke after thrombolysis treatment, which limits the clinical use of tissue plasminogen activator (t-PA). Since early diagnosis and treatment for HT is important to improve the prognosis of stroke patients, it is urgent to discover the potential biomarkers and therapeutic drugs. Recent evidence shows that pinocembrin, a natural flavonoid compound, exerts anti-cerebral ischemia effect and expands the time window of t-PA. In this study, we investigated the effect of pinocembrin on t-PA-induced HT and the potential biomarkers for HT after t-PA thrombolysis, thereby improving the prognosis of stroke. Electrocoagulation-induced thrombotic focal ischemic rats received intravenous infusion of t-PA (10 mg/kg) 6 h after ischemia. Administration of pinocembrin (10 mg/kg, iv) prior t-PA infusion significantly decreased the infarct volume, ameliorated t-PA-induced HT, and protected blood-brain barrier. Metabolomics analysis revealed that 5 differential metabolites in the cerebral cortex and 16 differential metabolites in serum involved in amino acid metabolism and energy metabolism were significantly changed after t-PA thrombolysis, whereas pinocembrin administration exerted significant intervention effects on these metabolites. Linear regression analysis showed that lactic acid was highly correlated to the occurrence of HT. Further experiments confirmed that t-PA treatment significantly increased the content of lactic acid and the activity of lactate dehydrogenase in the cerebral cortex and serum, and the expression of monocarboxylate transporter 1 (MCT 1) in the cerebral cortex; pinocembrin reversed these changes, which was consistent with the result of metabolomics. These results demonstrate that pinocembrin attenuates HT after t-PA thrombolysis, which may be associated with the regulation of endogenous metabolites. Lactic acid may be a potential biomarker for HT prediction and treatment.

Interferon-β alleviates delayed tPA-induced adverse effects via modulation of MMP3/9 production in ischemic stroke

Tissue plasminogen activator (tPA) is the only US Food and Drug Administration (FDA)-approved drug for ischemic stroke. However, delayed tPA administration is associated with increased risk of blood-brain barrier (BBB) disruption and hemorrhagic transformation (HT). Interferon-β (IFNβ), an FDA-approved drug for the treatment of multiple sclerosis, is a cytokine with immunomodulatory properties. Previous studies, including ours, demonstrated that IFNβ or type I IFN receptor signaling conferred protection against ischemic stroke in preclinical models, suggesting IFNβ might have translational therapeutic potential for the treatment of ischemic stroke. Currently, whether IFNβ could be coadministered with tPA to alleviate delayed tPA-induced adverse effects remains unknown. To elucidate that, IFNβ was coadministered with delayed tPA to ischemic stroke animals, and the severity and pathology of ischemic brain injury were assessed. We found delayed tPA treatment exacerbated ischemic brain injury, manifested by aggravated BBB disruption and HT. Notably, IFNβ ameliorated delayed tPA-exacerbated brain injury and alleviated adverse effects. Mechanistic studies revealed IFNβ suppressed tPA-enhanced neuroinflammation and MMP3/9 production in the ischemic brain. Furthermore, we identified IFNβ suppressed MMP9 production in microglia and attenuated tight junction protein degradation in brain endothelial cells. Moreover, we observed that peripheral immune cells may participate to a lesser extent in delayed tPA-exacerbated brain injury during the early phase of ischemic stroke. In conclusion, we provide the first evidence that IFNβ can be coadministered with tPA to mitigate delayed tPA-induced adverse effects of BBB disruption and HT that could potentially extend the tPA therapeutic window for the treatment of ischemic stroke.

Xiao-Xu-Ming decoction prevented hemorrhagic transformation induced by acute hyperglycemia through inhibiting AGE-RAGE-mediated neuroinflammation

Stroke is one of the leading causes of death worldwide. Hemorrhagic transformation (HT) is a common serious complication of ischemic stroke (IS) and is related to poor prognosis. Hyperglycemia after stroke is associated with the occurrence of HT and seriously affects the clinical treatment of stroke. Our previous experiments demonstrated that the Xiao-Xu-Ming decoction effective components group (XXMD), which is a Chinese medicine formula reconstituted by active ingredients, has multiple pharmacological effects in the treatment of IS. However, the effects of XXMD on HT after IS remain unclear. Thus, we investigated the preventive effects of XXMD on hyperglycemia-induced HT and further explored the underlying mechanism. Acute hyperglycemia combined with the electrocoagulation cerebral ischemia model was used to establish the HT model. XXMD (37.5, 75, 150 mg/kg/d) was given by gavage for 5 days. Network pharmacology was used to predict potential targets and pathways of XXMD in HT occurrence, and further studies confirmed the related targets. The results showed that hyperglycemia aggravated neurological deficits and blood-brain barrier (BBB) disruption, leading to intracerebral hemorrhage. Pretreatment with XXMD improved neurological function and BBB integrity and inhibited HT occurrence. Network pharmacology revealed that AGE-RAGE-mediated neuroinflammation may be associated with hyperglycemia-induced HT. Further studies confirmed that hyperglycemia activated the AGE-RAGE signaling pathway, increased the expression of HMGB1, TLR4 and p-p65, and induced the release of inflammatory factors and neutrophil infiltration, leading to HT. XXMD could inhibit AGE-RAGE-mediated neuroinflammation. These findings indicated that pretreatment with XXMD alleviated hyperglycemia-induced HT, which may be associated with the inhibition of AGE-RAGE-mediated neuroinflammation. Therefore, XXMD may be a potential therapeutic drug for HT.

Inhibition of hypoxia inducible factor 1 by YC-1 attenuates tissue plasminogen activator induced hemorrhagic transformation by suppressing HMGB1/TLR4/NF-κB mediated neutrophil infiltration in thromboembolic stroke rats

Hemorrhagic transformation (HT) is a frequent complication of ischemic stroke after thrombolytic therapy and seriously affects the prognosis of stroke. Due to the limited therapeutic window and hemorrhagic complications, tissue plasminogen activator (t-PA) is underutilized in acute ischemic stroke. Currently, there are no clinically effective drugs to decrease the incidence of t-PA-induced HT. Hypoxia-inducible factor 1 (HIF-1) is an important transcription factor that maintains oxygen homeostasis and mediates neuroinflammation under hypoxia. However, the effect of HIF-1 on t-PA-induced HT is not clear. The aim of this study was to investigate the role of HIF-1 in t-PA-induced HT by applying YC-1, an inhibitor of HIF-1. In the present study, we found that HIF-1 expression was significantly increased in ischemic brain tissue after delayed t-PA treatment and was mainly localized in neurons and endothelial cells. Inhibition of HIF-1 by YC-1 improved infarct volume and neurological deficits. YC-1 inhibited matrix metalloproteinase protein expression, increased tight junction protein expression, and ameliorated BBB disruption and the occurrence of HT. Furthermore, YC-1 suppressed the release of inflammatory factors, neutrophil infiltration and the activation of the HMGB1/TLR4/NF-κB signaling pathway. These results demonstrated that inhibition of HIF-1 could protect BBB integrity by suppressing HMGB1/TLR4/NF-κB-mediated neutrophil infiltration, thereby reducing the risk of t-PA-induced HT. Thus, HIF-1 may be a potential therapeutic target for t-PA-induced HT.

Strategies to prevent hemorrhagic transformation after reperfusion therapies for acute ischemic stroke: A literature review

BACKGROUND

Reperfusion therapies by tissue plasminogen activator (tPA) and mechanical thrombectomy (MT) have ushered in a new era in the treatment of acute ischemic stroke (AIS). However, reperfusion therapy-related HT remains an enigma.

AIM

To provide a comprehensive review focused on emerging concepts of stroke and therapeutic strategies, including the use of protective agents to prevent HT after reperfusion therapies for AIS.

METHODS

A literature review was performed using PubMed and the ClinicalTrials.gov database.

RESULTS

Risk of HT increases with delayed initiation of tPA treatment, higher baseline glucose level, age, stroke severity, episode of transient ischemic attack within 7 days of stroke onset, and hypertension. At a molecular level, HT that develops after thrombolysis is thought to be caused by reactive oxygen species, inflammation, remodeling factor-mediated effects, and tPA toxicity. Modulation of these pathophysiological mechanisms could be a therapeutic strategy to prevent HT after tPA treatment. Clinical mechanisms underlying HT after MT are thought to involve smoking, a low Alberta Stroke Program Early CT Score, use of general anesthesia, unfavorable collaterals, and thromboembolic migration. However, the molecular mechanisms are yet to be fully investigated. Clinical trials with MT and protective agents have also been planned and good outcomes are expected.

CONCLUSION

To fully utilize the easily accessible drug-tPA-and the high recanalization rate of MT, it is important to reduce bleeding complications after recanalization. A future study direction could be to investigate the recovery of neurological function by combining reperfusion therapies with cell therapies and/or use of pleiotropic protective agents.

Pathophysiology of Blood-Brain Barrier Permeability Throughout the Different Stages of Ischemic Stroke and Its Implication on Hemorrhagic Transformation and Recovery

The blood-brain barrier (BBB) is a dynamic interface responsible for maintaining the central nervous system homeostasis. Its unique characteristics allow protecting the brain from unwanted compounds, but its impairment is involved in a vast number of pathological conditions. Disruption of the BBB and increase in its permeability are key in the development of several neurological diseases and have been extensively studied in stroke. Ischemic stroke is the most prevalent type of stroke and is characterized by a myriad of pathological events triggered by an arterial occlusion that can eventually lead to fatal outcomes such as hemorrhagic transformation (HT). BBB permeability seems to follow a multiphasic pattern throughout the different stroke stages that have been associated with distinct biological substrates. In the hyperacute stage, sudden hypoxia damages the BBB, leading to cytotoxic edema and increased permeability; in the acute stage, the neuroinflammatory response aggravates the BBB injury, leading to higher permeability and a consequent risk of HT that can be motivated by reperfusion therapy; in the subacute stage (1-3 weeks), repair mechanisms take place, especially neoangiogenesis. Immature vessels show leaky BBB, but this permeability has been associated with improved clinical recovery. In the chronic stage (>6 weeks), an increase of BBB restoration factors leads the barrier to start decreasing its permeability. Nonetheless, permeability will persist to some degree several weeks after injury. Understanding the mechanisms behind BBB dysregulation and HT pathophysiology could potentially help guide acute stroke care decisions and the development of new therapeutic targets; however, effective translation into clinical practice is still lacking. In this review, we will address the different pathological and physiological repair mechanisms involved in BBB permeability through the different stages of ischemic stroke and their role in the development of HT and stroke recovery.

Neuroinflammation in hemorrhagic transformation after tissue plasminogen activator thrombolysis: Potential mechanisms, targets, therapeutic drugs and biomarkers

Hemorrhagic transformation (HT) is a common and serious complication following ischemic stroke, especially after tissue plasminogen activator (t-PA) thrombolysis, which is associated with increased mortality and disability. Due to the unknown mechanisms and targets of HT, there are no effective therapeutic drugs to decrease the incidence of HT. In recent years, many studies have found that neuroinflammation is closely related to the occurrence and development of HT after t-PA thrombolysis, including glial cell activation in the brain, peripheral inflammatory cell infiltration and the release of inflammatory factors, involving inflammation-related targets such as NF-κB, MAPK, HMGB1, TLR4 and NLRP3. Some drugs with anti-inflammatory activity have been shown to protect the BBB and reduce the risk of HT in preclinical experiments and clinical trials, including minocycline, fingolimod, tacrolimus, statins and some natural products. In addition, the changes in MMP-9, VAP-1, NLR, sICAM-1 and other inflammatory factors are closely related to the occurrence of HT, which may be potential biomarkers for the diagnosis and prognosis of HT. In this review, we summarize the potential inflammation-related mechanisms, targets, therapeutic drugs, and biomarkers associated with HT after t-PA thrombolysis and discuss the relationship between neuroinflammation and HT, which provides a reference for research on the mechanisms, prevention and treatment drugs, diagnosis and prognosis of HT.

Early Electroacupuncture Extends the rtPA Time Window to 6 h in a Male Rat Model of Embolic Stroke via the ERK1/2-MMP9 Pathway

Background. Recombinant tissue plasminogen activator (rtPA) is the only recommended pharmacological treatment for acute ischemic stroke, but it has a restricted therapeutic time window. When administered at time points greater than 4.5 h after stroke onset, rtPA disrupts the blood-brain barrier (BBB), which leads to serious brain edema and hemorrhagic transformation. Electroacupuncture (EA) exerts a neuroprotective effect on cerebral ischemia; however, researchers have not clearly determined whether EA increases the safety of thrombolysis and extends the therapeutic time window of rtPA administration following ischemic stroke. Objective. The present study was conducted to test the hypothesis that EA extends the therapeutic time window of rtPA for ischemic stroke in a male rat model of embolic stroke. Methods. SD rats were randomly divided into the sham operation group, model group, rtPA group, EA+rtPA group, and rtPA+MEK1/2 inhibitor group. An injection of rtPA was administered 6 h after ischemia. Rats were treated with EA at the Shuigou (GV26) and Neiguan (PC6) acupoints at 2 h after ischemia. Neurological function, infarct volume, BBB permeability, brain edema, and hemorrhagic transformation were assessed at 24 h after ischemia. Western blotting and immunofluorescence staining were performed to detect the levels of proteins involved in the ERK1/2 signaling pathway (MEK1/2 and ERK1/2), tight junction proteins (Claudin5 and ZO-1), and MMP9 in the ischemic penumbra at 24 h after stroke. Results. Delayed rtPA treatment aggravated hemorrhagic transformation and brain edema. However, treatment with EA plus rtPA significantly improved neurological function and reduced the infarct volume, hemorrhagic transformation, brain edema, and EB leakage in rats compared with rtPA alone. EA increased the levels of tight junction proteins, inhibited the activation of the ERK1/2 signaling pathway, and reduced MMP9 overexpression induced by delayed rtPA thrombolysis. Conclusions. EA potentially represents an effective adjunct method to increase the safety of thrombolytic therapy and extend the therapeutic time window of rtPA administration following ischemic stroke. This neuroprotective effect may be mediated by the inhibition of the ERK1/2-MMP9 pathway and alleviation of the destruction of the BBB.

Diabetes Mellitus/Poststroke Hyperglycemia: a Detrimental Factor for tPA Thrombolytic Stroke Therapy

Intravenous administration of tissue-type plasminogen activator (IV tPA) therapy has long been considered a mainstay in ischemic stroke management. However, patients respond to IV tPA therapy unequally with some subsets of patients having worsened outcomes after treatment. In particular, diabetes mellitus (DM) is recognized as a clinically important vascular comorbidity that leads to lower recanalization rates and increased risks of hemorrhagic transformation (HT). In this short-review, we summarize the recent advances in understanding of the underlying mechanisms involved in post-IV tPA worsening of outcome in diabetic stroke. Potential pathologic factors that are related to the suboptimal tPA recanalization in diabetic stroke include higher plasma plasminogen activator inhibitor (PAI)-1 level, diabetic atherogenic vascular damage, glycation of the tPA receptor annexin A2, and alterations in fibrin clot density. While factors contributing to the exacerbation of HT in diabetic stroke include hyperglycemia, vascular oxidative stress, and inflammation, tPA neurovascular toxicity and imbalance in extracellular proteolysis are discussed. Besides, impaired collaterals in DM also compromise the efficacy of IV tPA therapy. Additionally, several tPA combination approaches developed from experimental studies that may help to optimize IV tPA therapy are also briefly summarized. In summary, more research efforts are needed to improve the safety and efficacy of IV tPA therapy in ischemic stroke patients with DM/poststroke hyperglycemia.

Exosomes Derived From CircAkap7-Modified Adipose-Derived Mesenchymal Stem Cells Protect Against Cerebral Ischemic Injury

Background

Cerebral ischemic injury is a complicated pathological process. Adipose-derived stromal cells (ADSCs) have been used as a therapeutic strategy, with their therapeutic effects chiefly attributed to paracrine action rather than trans-differentiation. Studies have shown that circAkap7 was found to be downregulated in a mouse model of transient middle cerebral artery occlusion (tMCAO).

Methods

To explore whether exosomes derived from circAkap7-modified ADSCs (exo-circAkap7) have therapeutic effects on cerebral ischemic injury, a mouse model of tMCAO, as well as an in vitro model of oxygen and glucose deprivation-reoxygenation (OGD-R) in primary astrocytes, were used.

Results

Results showed that treatment with exo-circAkap7 protected against tMCAO in mice, and in vitro experiments confirmed that co-culture with exo-circAkap7 attenuated OGD-R-induced cellular injury by absorbing miR-155-5p, promoting ATG12-mediated autophagy, and inhibiting NRF2-mediated oxidative stress.

Conclusion

We demonstrate here that exo-circAkap7 protected against cerebral ischemic injury by promoting autophagy and ameliorating oxidative stress.

Cell Therapies under Clinical Trials and Polarized Cell Therapies in Pre-Clinical Studies to Treat Ischemic Stroke and Neurological Diseases: A Literature Review

Stroke remains a major cause of serious disability because the brain has a limited capacity to regenerate. In the last two decades, therapies for stroke have dramatically changed. However, half of the patients cannot achieve functional independence after treatment. Presently, cell-based therapies are being investigated to improve functional outcomes. This review aims to describe conventional cell therapies under clinical trial and outline the novel concept of polarized cell therapies based on protective cell phenotypes, which are currently in pre-clinical studies, to facilitate functional recovery after post-reperfusion treatment in patients with ischemic stroke. In particular, non-neuronal stem cells, such as bone marrow-derived mesenchymal stem/stromal cells and mononuclear cells, confer no risk of tumorigenesis and are safe because they do not induce rejection and allergy; they also pose no ethical issues. Therefore, recent studies have focused on them as a cell source for cell therapies. Some clinical trials have shown beneficial therapeutic effects of bone marrow-derived cells in this regard, whereas others have shown no such effects. Therefore, more clinical trials must be performed to reach a conclusion. Polarized microglia or peripheral blood mononuclear cells might provide promising therapeutic strategies after stroke because they have pleiotropic effects. In traumatic injuries and neurodegenerative diseases, astrocytes, neutrophils, and T cells were polarized to the protective phenotype in pre-clinical studies. As such, they might be useful therapeutic targets. Polarized cell therapies are gaining attention in the treatment of stroke and neurological diseases.

Fibrinolytic tissue plasminogen activator installed redox-active nanoparticles (t-PA@iRNP) for cancer therapy

Favorable blood flow within solid tumors has become the principal strategy for drug delivery. The use of thrombolytic drugs, such as tissue plasminogen activator (t-PA), in combination with other drugs or drug carriers may increase their therapeutic effect by increasing drug delivery near the solid tumor through fibrin degradation and blood flow restoration. We, therefore, designed t-PA-installed redox-active nanoparticles (t-PA@iRNP) to improve the perfusion of antioxidant nanoparticles in tumors, via fibrin degradation to decompress tumor vessels. Additionally, antioxidant iRNP was developed for tumor inhibition by reduction of critically elevated levels of reactive oxygen species (ROS) in tumors. The t-PA@iRNP, when administered to a colon cancer model, degraded the deposited fibrin and improved the iRNP and immune cells penetration in tumor tissues via the restored blood flow, thus more effectively inhibited tumor growth. The anti-tumor effect of iRNP was attributed to ROS-reduction mediated downregulation of crucial a transcriptional factor, NF-κB. Conclusively, this study provides a new strategy to enhance the delivery of nanotherapeutics into solid tumors.

Reperfusion Into Severely Damaged Brain Tissue Is Associated With Occurrence of Parenchymal Hemorrhage for Acute Ischemic Stroke

Background and Purpose: This study aims to quantify the reperfusion status within severely damaged brain tissue and to evaluate its relationship with high grade of hemorrhagic transformation (HT).

Methods: Pseudo-continuous ASL was performed along with DWI in 102 patients within 24 h post-treatments. The infarction core was identified using ADC values <550 × 10⁻⁶ mm²/s. CBF within the infarction core and its contralateral counterpart were acquired. CBF at the 25th, median, and 75th percentiles of the contralateral counterpart were used as thresholds and the ASL reperfusion volume above the threshold was labeled as vol-25, -50, and -75, respectively. Recanalization was defined according to Thrombolysis in Myocardial Infarction (TIMI) criteria.

Results: Quantified reperfusion within the infarction core differed significantly in patients with complete and incomplete recanalization. In the ROC analysis for the prediction of parenchymal hematoma (PH), ASL reperfusion vol-25 had the highest area under the curve (AUC) when compared with ASL vol-50 and ASL vol-75. ASL reperfusion vol-25 had significantly higher AUC compared with ADC threshold volume in the prediction of PH (0.783 vs. 0.685, P = 0.0036) and PH-2 (0.844 vs. 0.754, P = 0.0035). In stepwise multivariate logistic regression analysis, only ASL reperfusion vol-25 emerged as an independent predictor of PH (OR = 3.51, 95% CI: 1.65–7.45, P < 0.001) and PH-2 (OR = 2.32, 95% CI: 1.13–4.76, P = 0.022).

Conclusions: Increased reperfusion volume within severely damaged brain tissue is associated with the occurrence of higher grade of HT.

Effects of β-Adrenergic Blockade on Metabolic and Inflammatory Responses in a Rat Model of Ischemic Stroke

Ischemic stroke provokes an inflammatory response concurrent with both sympathetic nervous system activation and hyperglycemia. Currently, their crosstalk and consequences in stroke outcomes are of clinical attraction. We have provided experimental evidence showing the suppressive effects of the nonselective β-adrenoreceptor antagonist propranolol on hyperglycemia, inflammation, and brain injury in a rat model experiencing cerebral ischemia. Pretreatment with propranolol protected against postischemic brain infarction, edema, and apoptosis. The neuroprotection caused by propranolol was accompanied by a reduction in fasting glucose, fasting insulin, glucose tolerance impairment, plasma C-reactive protein, plasma free fatty acids, plasma corticosterone, brain oxidative stress, and brain inflammation. Pretreatment with insulin alleviated-while glucose augmented-postischemic brain injury and inflammation. Additionally, the impairment of insulin signaling in the gastrocnemius muscles was noted in rats with cerebral ischemia, with propranolol improving the impairment by reducing oxidative stress and tumor necrosis factor-α signaling. The anti-inflammatory effects of propranolol were further demonstrated in isoproterenol-stimulated BV2 and RAW264.7 cells through its ability to decrease cytokine production. Despite their potential benefits, stroke-associated hyperglycemia and inflammation are commonly linked with harmful consequences. Our findings provide new insight into the anti-inflammatory, neuroprotective, and hypoglycemic mechanisms of propranolol in combating neurodegenerative diseases, such as stroke.

Tissue Plasminogen Activator Promotes TXNIP-NLRP3 Inflammasome Activation after Hyperglycemic Stroke in Mice

Hyperglycemia has been shown to counterbalance the beneficial effects of tissue plasminogen activator (tPA) and increase the risk of intracerebral hemorrhage in ischemic stroke. Thioredoxin interacting protein (TXNIP) mediates hyperglycemia-induced oxidative damage and inflammation in the brain and reduces cerebral glucose uptake/utilization. We have recently reported that TXNIP-induced NLRP3 (NOD-like receptor pyrin domain-containing-3) inflammasome activation contributes to neuronal damage after ischemic stroke. Here, we tested the hypothesis that tPA induces TXNIP-NLRP3 inflammasome activation after ischemic stroke, in hyperglycemic mice. Acute hyperglycemia was induced in mice by intraperitoneal (IP) administration of a 20% glucose solution. This was followed by transient middle cerebral artery occlusion (t-MCAO), with or without intravenous (IV) tPA administered at reperfusion. The IV-tPA exacerbated hyperglycemia-induced neurological deficits, ipsilateral edema and hemorrhagic transformation, and accentuated peroxisome proliferator activated receptor-γ (PPAR-γ) upregulation and TXNIP/NLRP3 inflammasome activation after ischemic stroke. Higher expression of TXNIP in hyperglycemic t-MCAO animals augmented glucose transporter 1 (GLUT-1) downregulation and increased vascular endothelial growth factor-A (VEGF-A) expression/matrix metallopeptidase 9 (MMP-9) signaling, all of which result in blood brain barrier (BBB) disruption and increased permeability to endogenous immunoglobulin G (IgG). It was also associated with a discernible buildup of nitrotyrosine and accumulation of dysfunctional tight junction proteins: zonula occludens-1 (ZO-1), occludin and claudin-5. Moreover, tPA administration triggered activation of high mobility group box protein 1 (HMGB-1), nuclear factor kappa B (NF-κB), and tumor necrosis factor-α (TNF-α) expression in the ischemic penumbra of hyperglycemic animals. All of these observations suggest a powerful role for TXNIP-NLRP3 inflammasome activation in the tPA-induced toxicity seen with hyperglycemic stroke.

Glycyrrhizin Prevents Hemorrhagic Transformation and Improves Neurological Outcome in Ischemic Stroke with Delayed Thrombolysis Through Targeting Peroxynitrite-Mediated HMGB1 Signaling

Peroxynitrite (ONOO^-) and high mobility group box 1 protein (HMGB1) are important cytotoxic factors contributing to cerebral ischemia-reperfusion injury. However, the roles of ONOO^- in mediating HMGB1 expression and its impacts on hemorrhagic transformation (HT) in ischemic brain injury with delayed t-PA treatment remain unclear. In the present study, we tested the hypothesis that ONOO^- could directly mediate the activation and release of HMGB1 in ischemic brains with delayed t-PA treatment. With clinical studies, we found that plasma nitrotyrosine (NT, a surrogate marker of ONOO^-) was positively correlated with HMGB1 level in acute ischemic stroke patients. Hemorrhagic transformation and t-PA-treated ischemic stroke patients had increased levels of nitrotyrosine and HMGB1 in plasma. In animal experiments, we found that FeTmPyP, a representative ONOO^- decomposition catalyst (PDC), significantly reduced the expression of HMGB1 and its receptor TLR2, and inhibited MMP-9 activation, preserved collagen IV and tight junction claudin-5 in ischemic rat brains with delayed t-PA treatment. ONOO^- donor SIN-1 directly induced expression of HMGB1 and its receptor TLR2 in naive rat brains in vivo and induced HMGB1 in brain microvascular endothelial b.End3 cells in vitro. Those results suggest that ONOO^- could activate HMGB1/TLR2/MMP-9 signaling. We then addressed whether glycyrrhizin, a natural HMGB1 inhibitor, could inhibit ONOO^- production and the antioxidant properties of glycyrrhizin contribute to the inhibition of HMGB1 and the neuroprotective effects on attenuating hemorrhagic transformation in ischemic stroke with delayed t-PA treatment. Glycyrrhizin treatment downregulated the expressions of NADPH oxidase p47 phox and p67 phox and iNOS, inhibited superoxide and ONOO^- production, reduced the expression of HMGB1, TLR2, MMP-9, preserved type IV collagen and claudin-5 in ischemic brains. Furthermore, glycyrrhizin significantly decreased the mortality rate, attenuated hemorrhagic transformation, brain swelling, blood-brain barrier damage, neuronal apoptosis, and improved neurological outcomes in the ischemic stroke rat model with delayed t-PA treatment. In conclusion, peroxynitrite-mediated HMGB1/TLR2 signaling contributes to hemorrhagic transformation, and glycyrrhizin could be a potential adjuvant therapy to attenuate hemorrhagic transformation, possibly through inhibiting the ONOO^-/HMGB1/TLR2 signaling cascades.

Intravenous thrombolysis with 0.9 mg/kg alteplase for acute ischaemic stroke: a network meta-analysis of treatment delay

OBJECTIVES

The aim of this study was to evaluate the effect of alteplase in intravenous thrombolysis of acute ischaemic stroke (AIS) regarding the different time windows of treatment (<3 hours, 3-4.5 hours, >4.5 hours).

METHODS

A systematic literature search was conducted from PubMed, Cochrane Library and Embase. 12 clinical randomised controlled trials with 3402 patients with AIS met the inclusion criteria. The primary, secondary and tertiary outcomes were modified Rankin Scale (mRS) scores 0-1, mortality at 90th day after treatment and symptomatic intracerebral haemorrhage within 36 hours, respectively. Network meta-analysis and conventional meta-analysis were carried out for calculating odds ratio (OR), the surface under cumulative ranking curve (SUCRA) and the probabilities of being the best.

RESULTS

For mRS, alteplase regardless of time delay was significantly more effective than placebo (OR 1.33-2.17). However, alteplase used within 3 hours after AIS occurrence (SUCRA=98.3%) was significantly more effective (OR=1.64) than that at 3-4.5 hours (SUCRA=43%) and showed the trend of priority (OR=1.47) compared with that beyond 4.5 hours (SUCRA=58%). For the mortality, compared with placebo (SUCRA=64.7%), alteplase within 3 hours was similar to that of 3-4.5 hours whereas alteplase beyond 4.5 hours (SUCRA=7.3%) showed the trend of significantly increasing 85% mortality. For the tertiary outcome, alteplase within 3 hours (SUCRA=19.0%) was comparable with placebo (SUCRA=99.9%) whereas alteplase beyond 3 hours significantly increased (OR 5.89-6.67) the symptomatic intracerebral haemorrhage.

CONCLUSIONS

Alteplase within 3 hours should be recommended as the best treatment delay for its best efficacy among all the intervention and equivalent safety compared with placebo. Alteplase beyond 3 hours was less effective compared with that within 3 hours and increased the risk of mortality on 3 months as well as symptomatic intracerebral haemorrhage at 36 hours. More head-to-head clinical trials are needed to confirm those findings.

Safety and Efficacy of Otaplimastat in Patients with Acute Ischemic Stroke Requiring tPA (SAFE-TPA): A Multicenter, Randomized, Double-Blind, Placebo-Controlled Phase 2 Study

Objective

Otaplimastat is a neuroprotectant that inhibits matrix metalloprotease pathway, and reduces edema and intracerebral hemorrhage induced by recombinant tissue plasminogen activator (rtPA) in animal stroke models. We aimed to assess the safety and efficacy of otaplimastat in patients receiving rtPA.

Methods

This was a phase 2, 2‐part, multicenter trial in stroke patients (19–80 years old) receiving rtPA. Intravenous otaplimastat was administered <30 minutes after rtPA. Stage 1 was a single‐arm, open‐label safety study in 11 patients. Otaplimastat 80 mg was administered twice daily for 3 days. Stage 2 was a randomized, double‐blind, placebo‐controlled study involving 69 patients, assigned (1:1:1) to otaplimastat 40 mg, otaplimastat 80 mg, or a placebo. The primary endpoint was the occurrence of parenchymal hematoma (PH) on day 1. Secondary endpoints included serious adverse events (SAEs), mortality, and modified Rankin scale (mRS) distribution at 90 days (http://clinicaltrials.gov identifier: NCT02787278).

Results

No safety issues were encountered in stage 1. The incidence of PH during stage 2 was comparable: 0 of 22 with the placebo, 0 of 22 with otaplimastat 40 mg, and 1 of 21 with the 80 mg dose. No differences in SAEs (13%, 17%, 14%) or death (8.3%, 4.2%, 4.8%) were observed among the 3 groups. Three adverse events (chills, muscle rigidity, hepatotoxicity) were judged to be related to otaplimastat.

Interpretation

Intravenous otaplimastat adjunctive therapy in patients receiving rtPA is feasible and generally safe. The functional efficacy of otaplimastat needs to be investigated with further large trials. ANN NEUROL 2020;87:233–245

[VEGF-A therapeutic target against hemorrhagic transformation after t-PA treatment]

Tissue plasminogen activator (t-PA) treatment is beneficial for patients with ischemic stroke within 4.5 h of stroke onset, because the risk of intracerebral hemorrhagic transformation (HT) increases with delayed t-PA treatment. The benefits of t-PA thrombolysis are heavily dependent on time to treatment. Development of vasoprotective drugs that attenuate HT after delayed t-PA treatment might improve the prognosis of stroke patients and extend the therapeutic time window of t-PA and endovascular thrombolysis. An angiogenic factor, vascular endothelial growth factor (VEGF), might be associated with the blood-brain barrier (BBB) disruption after focal cerebral ischemia. By using a rat thromboembolic model, delayed t-PA treatment at 4 h after ischemia promoted expression of VEGF in BBB, matrix metalloproteinase-9 (MMP-9) activation, degradation of BBB components, and HT. We demonstrated that HT was inhibited by intravenous administration of an anti-VEGF neutralizing antibody/VEGF receptor antagonist. In addition, for clinical application, reverse translation studies, a path from bedside to bench, are necessary.

Influencing neuroplasticity in stroke treatment with advanced biomaterials-based approaches

Since the early 1990s, we have known that the adult brain is not static and has the capacity to repair itself. The delivery of various therapeutic factors and cells have resulted in some exciting pre-clinical and clinical outcomes in stroke models by targeting post-injury plasticity to enhance recovery. Developing a deeper understanding of the pathways that modulate plasticity will enable us to optimize delivery strategies for therapeutics and achieve more robust effects. Biomaterials are a key tool for the optimization of these potential treatments, owing to their biocompatibility and tunability. In this review, we identify factors and targets that impact plastic processes known to contribute to recovery, discuss the role of biomaterials in enhancing the efficacy of treatment strategies, and suggest combinatorial approaches based on the stage of injury progression.

Structural Biology and Protein Engineering of Thrombolytics

Myocardial infarction and ischemic stroke are the most frequent causes of death or disability worldwide. Due to their ability to dissolve blood clots, the thrombolytics are frequently used for their treatment. Improving the effectiveness of thrombolytics for clinical uses is of great interest. The knowledge of the multiple roles of the endogenous thrombolytics and the fibrinolytic system grows continuously. The effects of thrombolytics on the alteration of the nervous system and the regulation of the cell migration offer promising novel uses for treating neurodegenerative disorders or targeting cancer metastasis. However, secondary activities of thrombolytics may lead to life-threatening side-effects such as intracranial bleeding and neurotoxicity. Here we provide a structural biology perspective on various thrombolytic enzymes and their key properties: (i) effectiveness of clot lysis, (ii) affinity and specificity towards fibrin, (iii) biological half-life, (iv) mechanisms of activation/inhibition, and (v) risks of side effects. This information needs to be carefully considered while establishing protein engineering strategies aiming at the development of novel thrombolytics. Current trends and perspectives are discussed, including the screening for novel enzymes and small molecules, the enhancement of fibrin specificity by protein engineering, the suppression of interactions with native receptors, liposomal encapsulation and targeted release, the application of adjuvants, and the development of improved production systems.

Post-stroke treatment with argon attenuated brain injury, reduced brain inflammation and enhanced M2 microglia/macrophage polarization: a randomized controlled animal study

BACKGROUND

In recent years, argon has been shown to exert neuroprotective effects in an array of models. However, the mechanisms by which argon exerts its neuroprotective characteristics remain unclear. Accumulating evidence imply that argon may exert neuroprotective effects via modulating the activation and polarization of microglia/macrophages after ischemic stroke. In the present study, we analyzed the underlying neuroprotective effects of delayed argon application until 7 days after reperfusion and explored the potential mechanisms.

METHODS

Twenty-one male Wistar rats underwent transient middle cerebral artery occlusion or sham surgery randomly for 2 h using the endoluminal thread model. Three hours after transient middle cerebral artery occlusion induction and 1 h after reperfusion, animals received either 50% vol Argon/50% vol O2 or 50% vol N2/50% vol O2 for 1 h. The primary outcome was the 6-point neuroscore from 24 h to d7 after reperfusion. Histological analyses including infarct volume, survival of neurons (NeuN) at the ischemic boundary zone, white matter integrity (Luxol Fast Blue), microglia/macrophage activation (Iba1), and polarization (Iba1/Arginase1 double staining) on d7 were conducted as well. Sample size calculation was performed using nQuery Advisor + nTerim 4.0. Independent t test, one-way ANOVA and repeated measures ANOVA were performed, respectively, for statistical analysis (SPSS 23.0).

RESULTS

The 6-point neuroscore from 24 h to d7 after reperfusion showed that tMCAO Ar group displayed significantly improved neurological performance compared to tMCAO N2 group (p = 0.026). The relative numbers of NeuN-positive cells in the ROIs of tMCAO Ar group significantly increased compared to tMCAO N2 group (p = 0.010 for cortex and p = 0.011 for subcortex). Argon significantly suppressed the microglia/macrophage activation as revealed by Iba1 staining (p = 0.0076) and promoted the M2 microglia/macrophage polarization as revealed by Iba1/Arginase 1 double staining (p = 0.000095).

CONCLUSIONS

Argon administration with a 3 h delay after stroke onset and 1 h after reperfusion significantly alleviated neurological deficit within the first week and preserved the neurons at the ischemic boundary zone 7 days after stroke. Moreover, argon reduced the excessive microglia/macrophage activation and promoted the switch of microglia/macrophage polarization towards the anti-inflammatory M2 phenotype. Studies making efforts to further elucidate the protective mechanisms and to benefit the translational application are of great value.