A broad-spectrum matrix metalloproteinase inhibitor prevents hemorrhagic complications induced by tissue plasminogen activator in mice

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.

Guhong Injection Prevents Ischemic Stroke-Induced Neuro-Inflammation and Neuron Loss Through Regulation of C5ar1

C5ar1 (CD88) has been identified as an important potential therapeutic target for regulating inflammation in ischemic stroke. In this study, the neuroprotective effect of Guhong injection (GHI) on middle cerebral artery occlusion (MCAO)-induced reperfusion injury was assessed and the mechanism was explored by RNA-seq technology. GHI administered for 6 consecutive days significantly decreased body weight loss, infarction rate, neurological deficient scores, and neuron loss but improved rat survival percentage and regional cerebral blood flow after MCAO surgery. Furthermore, we identified inflammation as a vital process and C5AR1 as a vital target in GHI-mediated protection by using RNA-seq analysis. Further experiments confirmed that GHI decreased C5AR1, C5A, CASP3, 8-OHdG, and inflammatory factors such as IL-1β, TNF, IL6, ICAM-1, MMP9, and MCP-1, and enhanced the expression of TIMP1, JAM-A, and laminin. Furthermore, GHI and its major components hydroxysafflower yellow A (HSYA) and aceglutamide (AG) enhanced cell viability and reduced LDH level and C5AR1 expression in a C5A-induced Neuro-2a cell damage model. In general, this study elucidated the mechanism of GHI against ischemic stroke by inhibiting inflammation and highlighted the potential important role of C5AR1 in ischemic stroke. This research provided new insights into the mechanism of GHI in resisting ischemic stroke and benefits of its clinical application.

Changes to gut amino acid transporters and microbiome associated with increased E/I ratio in Chd8+/- mouse model of ASD-like behavior

Autism spectrum disorder (ASD), a group of neurodevelopmental disorders characterized by social communication deficits and stereotyped behaviors, may be associated with changes to the gut microbiota. However, how gut commensal bacteria modulate brain function in ASD remains unclear. Here, we used chromodomain helicase DNA-binding protein 8 (CHD8) haploinsufficient mice as a model of ASD to elucidate the pathways through which the host and gut microbiota interact with each other. We found that increased levels of amino acid transporters in the intestines of the mouse model of ASD contribute to the high level of serum glutamine and the increased excitation/inhibition (E/I) ratio in the brain. In addition, elevated α-defensin levels in the haploinsufficient mice resulted in dysregulation of the gut microbiota characterized by a reduced abundance of Bacteroides. Furthermore, supplementation with Bacteroides uniformis improved the ASD-like behaviors and restored the E/I ratio in the brain by decreasing intestinal amino acid transport and the serum glutamine levels. Our study demonstrates associations between changes in the gut microbiota and amino acid transporters, and ASD-like behavioral and electrophysiology phenotypes, in a mouse model.

The gut microbiota has been shown to modulate the neural function via the microbiota-gut-brain axis. Here, the authors show that Bacteroides uniformis, a gut commensal bacterium, restores the ASD-like phenotypes by reducing intestinal amino acid transport in an ASD mouse model.

CM-352 EFFICACY IN A MOUSE MODEL OF ANTICOAGULANT-ASSOCIATED INTRACRANIAL HAEMORRHAGE

BACKGROUND

Intracranial haemorrhage (ICH) is one of the major devastating complications of anticoagulation. Matrix metalloproteinases (MMPs) inhibition has been proposed as a novel pharmacological approach for ICH treatment.

OBJECTIVES

We evaluated the effects of CM-352 (MMPs-fibrinolysis inhibitor) in an experimental ICH model associated with oral anticoagulants as compared with clinically used prothrombin concentrate complex (PCC).

METHODS

ICH was induced by collagenase injection into the striatum of WT (C57BL/6J) anticoagulated mice (warfarin or rivaroxaban) and Mmp10 -/- mice. Hematoma volume and neurological deficits were measured 24h later by diaminobenzidine staining and different behavioural test. Circulating plasminogen activator inhibitor-1 (PAI-1) activity and interleukin-6 (IL-6) were measured in plasma samples and local inflammation was assessed by neutrophil infiltration. Finally, fibrinolytic effects of MMP-10 and rivaroxaban were evaluated by thromboelastometry and thrombin-activatable fibrinolysis inhibitor (TAFI) activation assays.

RESULTS

Only PCC reduced haemorrhage volume and improved functional outcome in warfarin-ICH, but both, PCC and CM-352 treatments, diminished haemorrhage volume (46%, p<0.01 and 64%, p<0.001, respectively) and ameliorated functional outcome in rivaroxaban-ICH. We further demonstrated that CM-352, but not PCC decreased neutrophil infiltration in the haemorrhage area at 24h. The effect of CM-352 could be related to MMP-10 inhibition since Mmp10-/- mice showed lower haemorrhage volume, better neurological score, reduced IL-6 levels and neutrophil infiltration, and increased PAI-1 after experimental ICH. Finally, we found that CM-352 reduced MMP-10 and rivaroxaban-related fibrinolytic effects in thromboelastometry and TAFI activation.

CONCLUSIONS

CM-352 treatment, by diminishing MMPs and rivaroxaban-associated fibrinolytic effects, might be a novel antihaemorrhagic strategy for rivaroxaban-associated ICH.

Modulation of gene expression on a transcriptome-wide level following human neural stem cell transplantation in aged mouse stroke brains

INTRODUCTION

Neural stem cell (NSC) transplantation offers great potential for treating ischemic stroke. Clinically, ischemia followed by reperfusion results in robust cerebrovascular injury that upregulates proinflammatory factors, disrupts neurovascular units, and causes brain cell death. NSCs possess multiple actions that can be exploited for reducing the severity of neurovascular injury. Our previous studies in young adult mice showed that human NSC transplantation during the subacute stage diminishes stroke pathophysiology and improves behavioral outcome.

METHODS

We employed a well-established and commonly used stroke model, middle cerebral artery occlusion with subsequent reperfusion (MCAO/R). Here, we assessed the outcomes of hNSC transplantation 48 h post-MCAO (24 h post-transplant) in aged mouse brains in response to stroke because aging is a crucial risk factor for cerebral ischemia. Next, we tested whether administration of the integrin α5β1 inhibitor, ATN-161, prior to hNSC transplantation further affects stoke outcome as compared with NSCs alone. RNA sequencing (RNA-seq) was used to assess the impact of hNSC transplantation on differentially expressed genes (DEGs) on a transcriptome-wide level.

RESULTS

Here, we report that hNSC-engrafted brains with or without ATN-161 showed significantly reduced infarct size, and attenuated the induction of proinflammatory factors and matrix metalloproteases. RNA-seq analysis revealed DEGs and molecular pathways by which hNSCs induce a beneficial post-stroke outcome in aged stroke brains. 811 genes were differentially expressed (651 downregulated and 160 upregulated) in hNSC-engrafted stroke brains. Functional pathway analysis identified enriched and depleted pathways in hNSC-engrafted aged mouse stroke brains. Depletion of pathways following hNSC-engraftment included signaling involving neuroinflammation, acute phase response, leukocyte extravasation, and phagosome formation. On the other hand, enrichment of pathways in hNSC-engrafted brains was associated with PPAR signaling, LXR/RXR activation, and inhibition of matrix metalloproteases. Hierarchical cluster analysis of DEGs in hNSC-engrafted brains indicate decreased expression of genes encoding TNF receptors, proinflammatory factors, apoptosis factors, adhesion and leukocyte extravasation, and Toll-like receptors.

CONCLUSIONS

Our study is the first to show global transcripts differentially expressed following hNSC transplantation in the subacute phase of stroke in aged mice. The outcome of our transcriptome study would be useful to develop new therapies ameliorating early-stage stroke injury.

Neural Stem Cells for Early Ischemic Stroke

Clinical treatments for ischemic stroke are limited. Neural stem cell (NSC) transplantation can be a promising therapy. Clinically, ischemia and subsequent reperfusion lead to extensive neurovascular injury that involves inflammation, disruption of the blood-brain barrier, and brain cell death. NSCs exhibit multiple potentially therapeutic actions against neurovascular injury. Currently, tissue plasminogen activator (tPA) is the only FDA-approved clot-dissolving agent. While tPA’s thrombolytic role within the vasculature is beneficial, tPA’s non-thrombolytic deleterious effects aggravates neurovascular injury, restricting the treatment time window (time-sensitive) and tPA eligibility. Thus, new strategies are needed to mitigate tPA’s detrimental effects and quickly mediate vascular repair after stroke. Up to date, clinical trials focus on the impact of stem cell therapy on neuro-restoration by delivering cells during the chronic stroke stage. Also, NSCs secrete factors that stimulate endogenous repair mechanisms for early-stage ischemic stroke. This review will present an integrated view of the preclinical perspectives of NSC transplantation as a promising treatment for neurovascular injury, with an emphasis on early-stage ischemic stroke. Further, this will highlight the impact of early sub-acute NSC delivery on improving short-term and long-term stroke outcomes.

Discovery of potent and specific inhibitors targeting the active site of MMP-9 from the engineered SPINK2 library

Matrix metalloproteinases (MMPs) contribute to many physiological and pathological phenomena via the proteolysis of extracellular matrix components. Specific blocking of the active site of each MMP sheds light on its particular role. However, it remains difficult to acquire an active-site inhibitor with high specificity for only the target MMP due to the highly conserved structure around the active site of MMPs. Recently, we reported that potent and specific inhibitors of serine proteases were obtained from our proprietary engineered serine protease inhibitor Kazal type 2 (SPINK2) library. In this research, using this library, we succeeded in obtaining potent and specific MMP-9 inhibitors. The obtained inhibitors bound to the active site of MMP-9 and inhibited MMP-9 with low nanomolar Ki values. The inhibitors did not cross-react with other MMPs that we tested. Further analysis using MMP-9 mutants demonstrated that the inhibitors recognize not only the residues around the conserved active site of MMP-9 but also different and unique residues in exosites that are distant from each other. This unique recognition manner, which can be achieved by the large interface provided by engineered SPINK2, may contribute to the generation of specific active-site inhibitors of MMPs.

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.

Roadmap for Stroke: Challenging the Role of the Neuronal Extracellular Matrix

Stroke is a major challenge in modern medicine and understanding the role of the neuronal extracellular matrix (NECM) in its pathophysiology is fundamental for promoting brain repair. Currently, stroke research is focused on the neurovascular unit (NVU). Impairment of the NVU leads to neuronal loss through post-ischemic and reperfusion injuries, as well as coagulatory and inflammatory processes. The ictal core is produced in a few minutes by the high metabolic demand of the central nervous system. Uncontrolled or prolonged inflammatory response is characterized by leukocyte infiltration of the injured site that is limited by astroglial reaction. The metabolic failure reshapes the NECM through matrix metalloproteinases (MMPs) and novel deposition of structural proteins continues within months of the acute event. These maladaptive reparative processes are responsible for the neurological clinical phenotype. In this review, we aim to provide a systems biology approach to stroke pathophysiology, relating the injury to the NVU with the pervasive metabolic failure, inflammatory response and modifications of the NECM. The available data will be used to build a protein–protein interaction (PPI) map starting with 38 proteins involved in stroke pathophysiology, taking into account the timeline of damage and the co-expression scores of their RNA patterns The application of the proposed network could lead to a more accurate design of translational experiments aiming at improving both the therapy and the rehabilitation processes.

The Combination of Astragalus membranaceus and Ligustrazine Protects Against Thrombolysis-Induced Hemorrhagic Transformation Through PKCδ/Marcks Pathway in Cerebral Ischemia Rats

Astragalus membranaceus (Ast) and ligustrazine (Lig) have a protective effect on lower hemorrhagic transformation induced by pharmaceutical thrombolysis. The cerebral ischemia rat model was induced with autologous blood clot injections. A combination of Ast and Lig, or a protein kinase C delta (PKCδ) inhibitor—rottlerin, or a combination of Ast, Lig, and rottlerin was administered immediately after recombinant tissue plasminogen activator injection. The cerebral infarct area, neurological deficits, cerebral hemorrhage status, neuronal damage and tight junctions’ changes in cerebral vessels, and the messenger RNA and protein levels of PKCδ, myristoylated alanine-rich C kinase substrate (Marcks), and matrix metallopeptidase 9 (MMP9) were determined after 3 h and 24 h of thrombolysis. The ultrastructure of the neuronal damage and tight junctions was examined under a transmission electron microscope. The expression levels of PKCδ, Marcks, and MMP9 were assessed by immunohistochemistry, western blot, and quantitative real-time polymerase chain reaction . Administration of Ast and Lig not only significantly decreased neurological deficit scores, infarct volumes, and cerebral hemorrhage but also inhibited the disruption due to neuronal dysfunction and the tight junction integrity in the cerebral vessel. Treatment with a combination of Ast and Lig effectively protected ischemia-induced microhemorrhage transformation through PKCδ/Marcks pathway suppression.

Human neural stem cells improve early stage stroke outcome in delayed tissue plasminogen activator-treated aged stroke brains

INTRODUCTION

Clinically, significant stroke injury results from ischemia-reperfusion (IR), which induces a deleterious biphasic opening of the blood-brain barrier (BBB). Tissue plasminogen activator (tPA) remains the sole pharmacological agent to treat ischemic stroke. However, major limitations of tPA treatment include a narrow effective therapeutic window of 4.5 h in most patients after initial stroke onset and off-target non-thrombolytic effects (e.g., the risk of increased IR injury). We hypothesized that ameliorating BBB damage with exogenous human neural stem cells (hNSCs) would improve stroke outcome to a greater extent than treatment with delayed tPA alone in aged stroke mice.

METHODS

We employed middle cerebral artery occlusion to produce focal ischemia with subsequent reperfusion (MCAO/R) in aged mice and administered tPA at a delayed time point (6 h post-stroke) via tail vein. We transplanted hNSCs intracranially in the subacute phase of stroke (24 h post-stroke). We assessed the outcomes of hNSC transplantation on pathophysiological markers of stroke 48 h post-stroke (24 h post-transplant).

RESULTS

Delayed tPA treatment resulted in more extensive BBB damage and inflammation relative to MCAO controls. Notably, transplantation of hNSCs ameliorated delayed tPA-induced escalated stroke damage; decreased expression of proinflammatory factors (tumor necrosis factor-alpha (TNF-α) and interleukin (IL)-6), decreased the level of matrix metalloprotease-9 (MMP-9), increased the level of brain-derived neurotrophic factor (BDNF), and reduced BBB damage.

CONCLUSIONS

Aged stroke mice that received delayed tPA treatment in combination with hNSC transplantation exhibited reduced stroke pathophysiology in comparison to non-transplanted stroke mice with delayed tPA. This suggests that hNSC transplantation may synergize with already existing stroke therapies to benefit a larger stroke patient population.

Evaluation of long-term rt-PA effects on bEnd.3 endothelial cells under ischemic conditions; changes in ZO-1 expression and glycosylation of the bradykinin B2 receptor

Recombinant tissue plasminogen activator (rt-PA) has proven effective in the treatment of acute ischemic stroke, despite the increased risk of hemorrhagic transformation (HT), its major associated complication. Although it is known that HT is related to blood brain barrier (BBB) disruption, the underlying mechanisms are not well established. We assessed time-dependent effects of rt-PA on the bEnd.3 murine brain endothelial cell line subjected either to normoxia or to 2.5 h of oxygen and glucose deprivation (OGD), evaluating a longer period than has previously been done, beyond 6 h post-reoxygenation. Parameters of cell viability, metabolic activity, ionic and transcellular permeability, as well as levels of claudin-5, zonula occludens-1 (ZO-1) and bradykinin B2 receptor (B2R) protein expression were analyzed at 24, 48 and 72 h post-reoxygenation with or without the administration of rt-PA. rt-PA treatment increased both the ionic and transcellular permeability until 72 h and did not modify cell viability or metabolic activity or the expression of claudin-5, ZO-1 and B2R under normoxia at any analyzed time. Under OGD conditions, rt-PA exacerbated OGD effects on metabolic activity from 48 to 72 h, increased transcellular permeability from 24 to 72 h, significantly decreased ZO-1 protein levels at the plasma membrane and increased B2R glycosylation at 72 h post-reoxygenation. Our findings suggest that a long-term analysis is necessary to elucidate time-dependent molecular mechanisms associated to BBB breakdown due to rt-PA administration under ischemia. Thus, protective BBB therapies after ischemic stroke and rt-PA treatment should be explored at least until 72 h after OGD and rt-PA administration.

Matrix metalloproteinases and ADAMs in stroke

Stroke is a leading cause of death and disability worldwide. However, after years of in-depth research, the pathophysiology of stroke is still not fully understood. Increasing evidence shows that matrix metalloproteinases (MMPs) and "a disintegrin and metalloproteinase" (ADAMs) participate in the neuro-inflammatory cascade that is triggered during stroke but also in recovery phases of the disease. This review covers the involvement of these proteins in brain injury following cerebral ischemia which has been widely studied in recent years, with efforts to modulate this group of proteins in neuroprotective therapies, together with their implication in neurorepair mechanisms. Moreover, the review also discusses the role of these proteins in specific forms of neurovascular disease, such as small vessel diseases and intracerebral hemorrhage. Finally, the potential use of MMPs and ADAMs as guiding biomarkers of brain injury and repair for decision-making in cases of stroke is also discussed.

tPA Helpers in the Treatment of Acute Ischemic Stroke: Are They Ready for Clinical Use?

Tissue plasminogen activator (tPA) is the only therapeutic agent approved to treat patients with acute ischemic stroke. The clinical benefits of tPA manifest when the agent is administered within 4.5 hours of stroke onset. However, tPA administration, especially delayed administration, is associated with increased intracranial hemorrhage (ICH), hemorrhagic transformation (HT), and mortality. In the ischemic brain, vascular remodeling factors are upregulated and microvascular structures are destabilized. These factors disrupt the blood brain barrier (BBB). Delayed recanalization of the vessels in the presence of relatively matured infarction appears to damage the BBB, resulting in HT or ICH, also known as reperfusion injury. Moreover, tPA itself activates matrix metalloproteases, further aggravating BBB disruption. Therefore, attenuation of edema, HT, or ICH after tPA treatment is an important therapeutic strategy that may enable clinicians to extend therapeutic time and increase the probability of excellent outcomes. Recently, numerous agents with various mechanisms have been developed to interfere with various steps of ischemia/ reperfusion injuries or BBB destabilization. These agents successfully reduce infarct volume and decrease the incidence of ICH and HT after delayed tPA treatment in various animal stroke models. However, only some have entered into clinical trials; the results have been intriguing yet unsatisfactory. In this narrative review, I describe such drugs and discuss the problems and future directions. These “tPA helpers” may be clinically used in the future to increase the efficacy of tPA in patients with acute ischemic stroke.

Visualizing the Distribution of Matrix Metalloproteinases in Ischemic Brain Using In Vivo 19F-Magnetic Resonance Spectroscopic Imaging

Matrix metalloproteinases (MMPs) damage the neurovascular unit, promote the blood-brain barrier (BBB) disruption following ischemic stroke, and play essential roles in hemorrhagic transformation (HT), which is one of the most severe side effects of thrombolytic therapy. However, no biomarkers have presently been identified that can be used to track changes in the distribution of MMPs in the brain. Here, we developed a new ¹⁹F-molecular ligand, TGF-019, for visualizing the distribution of MMPs in vivo using ¹⁹F-magnetic resonance spectroscopic imaging (¹⁹F-MRSI). We demonstrated TGF-019 has sufficient sensitivity for the specific MMPs suspected in evoking HT during ischemic stroke, i.e., MMP2, MMP9, and MMP3. We then utilized it to assess those MMPs at 22 to 24 hours after experimental focal cerebral ischemia on MMP2-null mice, as well as wild-type mice with and without the systemic administration of the recombinant tissue plasminogen activator (rt-PA). The ¹⁹F-MRSI of TGN-019-administered mice showed high signal intensity within ischemic lesions that correlated with total MMP2 and MMP9 activity, which was confirmed by zymographic analysis of ischemic tissues. Based on the results of this study, ¹⁹F-MRSI following TGN-019 administration can be used to assess potential therapeutic strategies for ischemic stroke.

Tissue plasminogen activator and neuropathy open the blood-nerve barrier with upregulation of microRNA-155-5p in male rats

The blood-nerve barrier (BNB) consisting of the perineurium and endoneurial vessels is sealed by tight junction proteins. BNB alterations are a crucial factor in the pathogenesis of peripheral neuropathies. However, barrier opening, e.g. by tissue plasminogen activator (tPA), can also facilitate topical application of analgesics. Here, we examined tPA both in the pathophysiology of neuropathy-induced BNB opening or via exogenous application and its effect on the cytoplasmatic tight junction protein anchoring protein, zona occludens-1 (ZO-1), the adherens molecule JAM-C and microRNA(miR)-155-5p. Specifically, we investigated whether tPA alone and barrier opening lead to pain behavioral changes, i.e. hyperalgesia, or whether these effects require further factors. Male Wistar rats underwent chronic constriction injury (CCI) or were treated by a single perisciatic application of recombinant (r)tPA. CCI elicited mechanical allodynia, tPA mRNA upregulation, macrophage invasion, BNB leakage for large molecule tracers, downregulation of ZO-1 and JAM-C mRNA/protein, and a loss of immunoreactivity of both in perineurium and endoneurial cells. Similarly, after perisciatic rtPA injection, ZO-1 and JAM-C mRNA as well as cytosolic/membrane protein and ZO-1 immunoreactivity were downregulated, and the BNB was opened. Neither mechanical hypersensitivity nor macrophage infiltration was observed after rtPA in contrast to CCI. Mechanistically, miR-155-5p, which is known to destabilize barriers and tight junction proteins like claudin-1 and ZO-1, was increased in CCI and to lesser extent after rtPA application. In summary, tPA transiently opens the BNB possibly via miR-155-5p. However, tPA does not provoke allodynia in the absence of a neuropathic stimulus like a ligation or inflammation.

Basement membrane and stroke

Located at the interface of the circulation system and the CNS, the basement membrane (BM) is well positioned to regulate blood-brain barrier (BBB) integrity. Given the important roles of BBB in the development and progression of various neurological disorders, the BM has been hypothesized to contribute to the pathogenesis of these diseases. After stroke, a cerebrovascular disease caused by rupture (hemorrhagic) or occlusion (ischemic) of cerebral blood vessels, the BM undergoes constant remodeling to modulate disease progression. Although an association between BM dissolution and stroke is observed, how each individual BM component changes after stroke and how these components contribute to stroke pathogenesis are mostly unclear. In this review, I first briefly introduce the composition of the BM in the brain. Next, the functions of the BM and its major components in BBB maintenance under homeostatic conditions are summarized. Furthermore, the roles of the BM and its major components in the pathogenesis of hemorrhagic and ischemic stroke are discussed. Last, unsolved questions and potential future directions are described. This review aims to provide a comprehensive reference for future studies, stimulate the formation of new ideas, and promote the generation of new genetic tools in the field of BM/stroke research.

Combination therapy for ischemic stroke: Novel approaches to lengthen therapeutic window of tissue plasminogen activator

Tissue plasminogen activator (tPA) thrombolysis continues to be the gold standard therapy for ischemic stroke. Due to the time-limited treatment window, within 4.5 h of stroke onset, and a variety of potentially deadly complications related to delayed administration, particularly hemorrhagic transformation (HT), clinical use of tPA is limited. Combination therapies with other interventions, drug or nondrug, have been hypothesized as a logical approach to enhancing tPA effectiveness. Here, we discuss various potential pharmacological and nondrug treatments to minimize adverse effects, primarily HT, associated with delayed tPA administration. Pharmacological interventions include many that support the integrity of the blood–brain barrier (i.e., atorvastatin, batimastat, candesartan, cilostazol, fasudil, and minocycline), promote vascularization and preserve cerebrovasculature (i.e., coumarin derivative IMM-H004 and granulocyte-colony stimulating factor), employing other mechanisms of action (i.e., oxygen transporters and ascorbic acid). Nondrug treatments are comprised of stem cell transplantation and gas therapies with multi-faceted approaches. Combination therapy with tPA and the aforementioned treatments demonstrated promise for mitigating the adverse complications associated with delayed tPA treatment and rescuing stroke-induced behavioral deficits. Therefore, the conjunctive therapy method is a novel therapeutic approach that can attempt to minimize the limitations of tPA treatment and possibly increase the therapeutic window for ischemic stroke treatment.

Rosuvastatin Reduces Neuroinflammation in the Hemorrhagic Transformation After rt-PA Treatment in a Mouse Model of Experimental Stroke

Hemorrhagic transformation (HT) is a serious complication that stimulates inflammation during reperfusion therapy after acute ischemic stroke. Rosuvastatin, a 3-hydroxymethyl-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, might improve the outcome of HT by inhibiting neuroinflammation. This study aimed to explore the protective effects of rosuvastatin against HT after recombinant tissue plasminogen activator (rt-PA) treatment in mice with experimental stroke via the attenuation of inflammation. A total of one hundred sixty-nine male BALB/c mice were used in the experiment. HT was successfully established in 70 mice that were subjected to 3 h of middle cerebral artery occlusion (MCAO) followed by a 10 mg/kg rt-PA injection over 10 min and reperfusion for 24 h. The mice were then administered rosuvastatin (1 mg/kg, 5 mg/kg) or saline (vehicle). The brain water content and neurological deficits (wire hang and adhesive removal somatosensory tests) were assessed at 24 h after rt-PA reperfusion following MCAO surgery. The morphology, blood-brain barrier (BBB) permeability and number of astrocytes and microglia were assessed by immunohistochemistry, electron microscopy and western blotting at 24 h after rt-PA reperfusion following MCAO surgery. Rosuvastatin protected against impaired neurological function and reversed the BBB leakage observed in the HT group. The increased activation of astrocytes and microglia and secretion of inflammatory factors caused by HT damage were significantly attenuated by high-dose rosuvastatin treatment vs. normal-dose rosuvastatin treatment. Related inflammatory pathways, such as the nuclear factor kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) pathways, were downregulated in the rosuvastatin-treated groups compared with the HT group. In conclusion, our results indicate that rosuvastatin is a promising therapeutic agent for HT after rt-PA reperfusion following MCAO surgery in mice, as it attenuates neuroinflammation. Additionally, high-dose rosuvastatin treatment could have a greater anti-inflammatory effect on HT than normal-dose rosuvastatin treatment.

Targeting vascular inflammation in ischemic stroke: Recent developments on novel immunomodulatory approaches

Ischemic stroke is a devastating and debilitating medical condition with limited therapeutic options. However, accumulating evidence indicates a central role of inflammation in all aspects of stroke including its initiation, the progression of injury, and recovery or wound healing. A central target of inflammation is disruption of the blood brain barrier or neurovascular unit. Here we discuss recent developments in identifying potential molecular targets and immunomodulatory approaches to preserve or protect barrier function and limit infarct damage and functional impairment. These include blocking harmful inflammatory signaling in endothelial cells, microglia/macrophages, or Th17/γδ T cells with biologics, third generation epoxyeicosatrienoic acid (EET) analogs with extended half-life, and miRNA antagomirs. Complementary beneficial pathways may be enhanced by miRNA mimetics or hyperbaric oxygenation. These immunomodulatory approaches could be used to greatly expand the therapeutic window for thrombolytic treatment with tissue plasminogen activator (t-PA). Moreover, nanoparticle technology allows for the selective targeting of endothelial cells for delivery of DNA/RNA oligonucleotides and neuroprotective drugs. In addition, although likely detrimental to the progression of ischemic stroke by inducing inflammation, oxidative stress, and neuronal cell death, 20-HETE may also reduce susceptibility of onset of ischemic stroke by maintaining autoregulation of cerebral blood flow. Although the interaction between inflammation and stroke is multifaceted, a better understanding of the mechanisms behind the pro-inflammatory state at all stages will hopefully help in developing novel immunomodulatory approaches to improve mortality and functional outcome of those inflicted with ischemic stroke.

Early Abrogation of Gelatinase Activity Extends the Time Window for tPA Thrombolysis after Embolic Focal Cerebral Ischemia in Mice

Acute ischemic stroke (AIS) is caused by clotting in the cerebral arteries, leading to brain oxygen deprivation and cerebral infarction. Recombinant human tissue plasminogen activator (tPA) is currently the only Food and Drug Administration-approved drug for ischemic stroke. However, tPA has to be administered within 4.5 h from the disease onset and delayed treatment of tPA can increase the risk of neurovascular impairment, including neuronal cell death, blood-brain barrier (BBB) disruption, and hemorrhagic transformation. A key contributing factor for tPA-induced neurovascular impairment is activation of matrix metalloproteinase-9 (MMP-9). We used a clinically-relevant mouse embolic model of focal-cerebral ischemia by insertion of a single embolus of blood clot to block the right middle cerebral artery. We showed that administration of the potent and highly selective gelatinase inhibitor SB-3CT extends the time window for administration of tPA, attenuating infarct volume, mitigating BBB disruption, and antagonizing the increase in cerebral hemorrhage induced by tPA treatment. We demonstrated that SB-3CT attenuates tPA-induced expression of vascular MMP-9, prevents gelatinase-mediated cleavage of extracellular laminin, rescues endothelial cells, and reduces caveolae-mediated transcytosis of endothelial cells. These results suggest that abrogation of MMP-9 activity mitigates the detrimental effects of tPA treatment, thus the combination treatment holds great promise for extending the therapeutic window for tPA thrombolysis, which opens the opportunity for clinical recourse to a greater number of patients.

Improved Reperfusion and Vasculoprotection by the Poly(ADP-Ribose)Polymerase Inhibitor PJ34 After Stroke and Thrombolysis in Mice

Benefits from thrombolysis with recombinant tissue plasminogen activator (rt-PA) after ischemic stroke remain limited due to a narrow therapeutic window, low reperfusion rates, and increased risk of hemorrhagic transformations (HT). Experimental data showed that rt-PA enhances the post-ischemic activation of poly(ADP-ribose)polymerase (PARP) which in turn contributes to blood-brain barrier injury. The aim of the present study was to evaluate whether PJ34, a potent PARP inhibitor, improves poor reperfusion induced by delayed rt-PA administration, exerts vasculoprotective effects, and finally increases the therapeutic window of rt-PA. Stroke was induced by thrombin injection (0.75 UI in 1 μl) in the left middle cerebral artery (MCA) of male Swiss mice. Administration of rt-PA (0.9 mg kg^-1) or saline was delayed for 4 h after ischemia onset. Saline or PJ34 (3 mg kg^-1) was given intraperitoneally twice, just after thrombin injection and 3 h later, or once, 3 h after ischemia onset. Reperfusion was evaluated by laser Doppler, vascular inflammation by immunohistochemistry of vascular cell adhesion molecule-1 (VCAM-1) expression, and vasospasm by morphometric measurement of the MCA. Edema, cortical lesion, and sensorimotor deficit were evaluated. Treatment with PJ34 improved rt-PA-induced reperfusion and promoted vascular protection including reduction in vascular inflammation (decrease in VCAM-1 expression), HT, and MCA vasospasm. Additionally, the combined treatment significantly reduced brain edema, cortical lesion, and sensorimotor deficit. In conclusion, the combination of the PARP inhibitor PJ34 with rt-PA after cerebral ischemia may be of particular interest in order to improve thrombolysis with an extended therapeutic window.

Adjunctive Therapy Approaches for Ischemic Stroke: Innovations to Expand Time Window of Treatment

Tissue plasminogen activator (tPA) thrombolysis remains the gold standard treatment for ischemic stroke. A time-constrained therapeutic window, with the drug to be given within 4.5 h after stroke onset, and lethal side effects associated with delayed treatment, most notably hemorrhagic transformation (HT), limit the clinical use of tPA. Co-administering tPA with other agents, including drug or non-drug interventions, has been proposed as a practical strategy to address the limitations of tPA. Here, we discuss the pharmacological and non-drug approaches that were examined to mitigate the complications-especially HT-associated with delayed tPA treatment. The pharmacological treatments include those that preserve the blood-brain barrier (e.g., atovarstatin, batimastat, candesartan, cilostazol, fasudil, minocycline, etc.), enhance vascularization and protect the cerebrovasculature (e.g., coumarin derivate IMM-H004 and granulocyte-colony stimulating factor (G-CSF)), and exert their effects through other modes of action (e.g., oxygen transporters, ascorbic acid, etc.). The non-drug approaches include stem cell treatments and gas therapy with multi-pronged biological effects. Co-administering tPA with the abovementioned therapies showed promise in attenuating delayed tPA-induced side effects and stroke-induced neurological and behavioral deficits. Thus, adjunctive treatment approach is an innovative therapeutic modality that can address the limitations of tPA treatment and potentially expand the time window for ischemic stroke therapy.

Inhibition of tPA-induced hemorrhagic transformation involves adenosine A2b receptor activation after cerebral ischemia

Tissue plasminogen activator (tPA) is administered after ischemic stroke to dissolve intravascular clots, but its use can lead to hemorrhagic transformation (HT). Therapeutic strategies to reduce hemorrhagic complications of tPA might be of benefit for stroke patients. Adenosine A2b receptor (A2bR) plays pivotal roles in regulating vascular protection in peripheral organs. This study explored whether A2bR agonist BAY 60-6583 reduces hemorrhage risk after tPA usage. Using a rat transient middle cerebral artery occlusion model, we showed that mRNA and protein expression of A2bR increased to a greater extent after ischemia-reperfusion than did expression of the other three adenosine receptors (A1, A2a, and A3). tPA administration reduced A2bR expression in ischemic brain microvessels. Post-treatment with BAY 60-6583 (1mg/kg) at the start of reperfusion reduced lesion volume in the absence or presence of tPA (10mg/kg) and attenuated brain swelling, blood-brain barrier disruption, and tPA-exacerbated HT at 24h. Additionally, BAY 60-6583 mitigated sensorimotor deficits in the presence of tPA. BAY 60-6583 inhibited tPA-enhanced matrix metalloprotease-9 activation, probably through elevation of tissue inhibitor of matrix metalloproteinases-1 expression, and thereby reduced degradation of tight junction proteins. These effects would likely protect cerebrovascular integrity. A2bR agonists as an adjuvant to tPA could be a promising strategy for decreasing the risk of HT during treatment for ischemic stroke.

Matrix-metalloproteinases as targets for controlled delivery in cancer: An analysis of upregulation and expression

While commonly known for degradation of the extracellular matrix, matrix metalloproteinases (MMPs) exhibit broad potential for use in targeting of bioactive and imaging agents in cancer treatment. MMPs are upregulated at all stages of expression in cancers. A comprehensive analysis of published literature on expression of all MMP subtypes at the genetic, protein, and activity levels in normal and diseased tissues indicate targeting applicability in a variety of cancers. This expression significantly increases at advanced cancer stages, providing an improved opportunity for controlled release in higher-stage patients. Since MMPs are integral at every stage of metastasis, MMP roles in cancer are discussed with a focus on MMP distribution and mobility within cells and tumors for cancer targeting applications. Several strategies for MMP utilization in targeting - such as matrix degradation, MMP cleavage, MMP binding, and MMP-induced environmental changes - are addressed.

Strategies to Extend Thrombolytic Time Window for Ischemic Stroke Treatment: An Unmet Clinical Need

To date, reperfusion with tissue plasminogen activator (tPA) remains the gold standard treatment for ischemic stroke. However, when tPA is given beyond 4.5 hours of stroke onset, deleterious effects of the drug ensue, especially, hemorrhagic transformation (HT), which causes the most significant morbidity and mortality in stroke patients. An important clinical problem at hand is to develop strategies that will enhance the therapeutic time window for tPA therapy and reduce the adverse effects (especially HT) of delayed tPA treatment. We reviewed the pharmacological agents which reduced the risk of HT associated with delayed (beyond 4.5 hours post-stroke) tPA treatment in preclinical studies, which we classified into those that putatively preserve the blood-brain barrier (e.g., minocycline, cilostazol, fasudil, candesartan, and bryostatin) and/or enhance vascularization and protect the cerebrovasculature (e.g., coumarin derivate IMM-H004 and granulocyte colony-stimulating factor). Recently, other new therapeutic modalities (e.g., oxygen transporters) have been reported which improved delayed tPA-associated outcomes by acting through other mechanisms. While the above-mentioned interventions unequivocally reduced delayed tPA-induced HT in stroke models, the long-term efficacy of these drugs are not yet established. Further optimization is required to expedite their future clinical application. The findings from this review indicate the need to explore the most ideal adjunctive interventions that will not only reduce delayed tPA–induced HT, but also preserve neurovascular functions. While waiting for the next breakthrough drug in acute stroke treatment, it is equally important to allocate considerable effort to find approaches to address the limitations of the only FDA-approved stroke therapy.

Plasma kallikrein mediates brain hemorrhage and edema caused by tissue plasminogen activator therapy in mice after stroke

Thrombolytic therapy using tissue plasminogen activator (tPA) in acute stroke is associated with increased risks of cerebral hemorrhagic transformation and angioedema. Although plasma kallikrein (PKal) has been implicated in contributing to both hematoma expansion and thrombosis in stroke, its role in the complications associated with the therapeutic use of tPA in stroke is not yet available. We investigated the effects of tPA on plasma prekallikrein (PPK) activation and the role of PKal on cerebral outcomes in a murine thrombotic stroke model treated with tPA. We show that tPA increases PKal activity in vitro in both murine and human plasma, via a factor XII (FXII)-dependent mechanism. Intravenous administration of tPA increased circulating PKal activity in mice. In mice with thrombotic occlusion of the middle cerebral artery, tPA administration increased brain hemorrhage transformation, infarct volume, and edema. These adverse effects of tPA were ameliorated in PPK (Klkb1)-deficient and FXII-deficient mice and in wild-type (WT) mice pretreated with a PKal inhibitor prior to tPA. tPA-induced brain hemisphere reperfusion after photothrombolic middle cerebral artery occlusion was increased in Klkb1^-/- mice compared with WT mice. In addition, PKal inhibition reduced matrix metalloproteinase-9 activity in brain following stroke and tPA therapy. These data demonstrate that tPA activates PPK in plasma and PKal inhibition reduces cerebral complications associated with tPA-mediated thrombolysis in stroke.

One-Compound-Multi-Target: Combination Prospect of Natural Compounds with Thrombolytic Therapy in Acute Ischemic Stroke

Tissue plasminogen activator (t-PA) is the only FDA-approved drug for acute ischemic stroke treatment, but its clinical use is limited due to the narrow therapeutic time window and severe adverse effects, including hemorrhagic transformation (HT) and neurotoxicity. One of the potential resolutions is to use adjunct therapies to reduce the side effects and extend t-PA&#039;s therapeutic time window. However, therapies modulating single target seem not to be satisfied, and a multitarget strategy is warranted to resolve such complex disease. Recently, large amount of efforts have been made to explore the active compounds from herbal supplements to treat ischemic stroke. Some natural compounds revealed both neuro- and bloodbrain- barrier (BBB)-protective effects by concurrently targeting multiple cellular signaling pathways in cerebral ischemia-reperfusion injury. Thus, those compounds are potential to be one-drug-multi-target agents as combined therapy with t-PA for ischemic stroke. In this review article, we summarize current progress about molecular targets involving in t-PA-mediated HT and neurotoxicity in ischemic brain injury. Based on these targets, we select 23 promising compounds from currently available literature with the bioactivities simultaneously targeting several important molecular targets. We propose that those compounds merit further investigation as combined therapy with t-PA. Finally, we discuss the potential drawbacks of the natural compounds&#039; studies and raise several important issues to be addressed in the future for the development of natural compound as an adjunct therapy.

Matrix Metalloproteinase in Blood-Brain Barrier Breakdown in Dementia

The neurovascular unit, which consists of astrocytic end-feet, neurons, pericytes, and endothelial cells, plays a key role in maintaining brain homeostasis by forming the blood-brain barrier and carefully controlling local cerebral blood flow. When the blood-brain barrier is disrupted, blood components can leak into the brain, damage the surrounding tissue and lead to cognitive impairment. This disruption in the blood-brain barrier and subsequent impairment in cognition are common after stroke and during cerebral amyloid angiopathy and Alzheimer's disease. Matrix metalloproteinases are proteases that degrade the extracellular matrix as well as tight junctions between endothelial cells and have been implicated in blood-brain barrier breakdown in neurodegenerative diseases. This review will focus on the roles of MMP2 and MMP9 in dementia, primarily post-stroke events that lead to dementia, cerebral amyloid angiopathy, and Alzheimer's disease.

Increased Plasma Matrix Metalloproteinase-9 Levels Contribute to Intracerebral Hemorrhage during Thrombolysis after Concomitant Stroke and Influenza Infection

BACKGROUND

Thrombolysis is the only approved therapy for acute stroke. However, life-threatening complications such as intracerebral hemorrhage (ICH) can develop after intravenous administration of tissue plasminogen activator (tPA). Both infection and thrombolysis during cerebral ischemia disrupt the blood-brain barrier (BBB). tPA can induce matrix metalloproteinase-9 (MMP-9), which is known to be involved in BBB disruption. However, it has still not been investigated whether preexisting influenza virus infection during thrombolysis after acute stroke affects systemic levels of MMP-9 and its inhibitor TIMP-1 and whether increased systemic MMP-9 levels affect ICH. This study aimed to investigate the influence of influenza virus infection on plasma levels of MMP-9 and TIMP-1 after thrombolysis in acute stroke, and to determine whether the infection correlates with intracerebral bleeding.

METHODS

C57BL/6 mice were infected by administering 1 × 105 plaque-forming units of human influenza (H1N1) virus intranasally. After 3 days of infection the middle cerebral artery was occluded for 45 min and then reperfused. Intravenous tPA (10 mg/kg) treatment was started 10 min after stroke onset. Twenty-four hours after stroke onset, mice were deeply anesthetized with ketamine, venous blood was drawn from the caval vein and centrifuged at 2,000 rpm, and the supernatant was collected and frozen at -80°C. Plasma levels of MMP-9 and TIMP-1 were quantified by using ELISA.

RESULTS

After stroke, plasma MMP-9 was significantly increased in mice with a concomitant influenza infection that were treated with tPA (9.99 ± 0.62 ng/ml, n = 7) as compared to noninfected control mice that were treated with tPA (4.74 ± 0.48 ng/ml, n = 8). Moreover, plasma levels of TIMP-1, an inhibitor of MMP-9, were also significantly increased in mice treated with tPA after concomitant infection and stroke (42.17 ± 7.02 ng/ml, n = 7) as compared to noninfected control mice that were treated with tPA after stroke (20.22 ± 2.12 ng/ml, n = 8). MMP-9 values significantly correlated with intracerebral hemoglobin levels in animals treated with tPA after stroke (p = 0.028, r = 0.76, n = 8) and after concomitant stroke and infection (p = 0.039, r = 0.78, n = 7).

CONCLUSION

Preexisting influenza A virus infection led to increased plasma MMP-9 and TIMP-1 levels in mice undergoing thrombolysis after induced stroke. MMP-9 levels closely correlated with intracerebral bleeding after thrombolysis during concomitant infection and stroke. Thus, our data indicate that thrombolysis may be dangerous during influenza infection. MMP-9 inhibitors might be considered to reduce the side effects of thrombolysis during concomitant infection and stroke.

Correlation of the L-Arginine Pathway with Thrombo-Inflammation May Contribute to the Outcome of Acute Ischemic Stroke

BACKGROUND

Immune responses contribute to secondary injury after acute ischemic stroke (AIS), and metabolites of the L-arginine pathway are associated with stroke outcome. Here, we analyzed the relationship of the L-arginine pathway with thrombo-inflammatory biomarkers in AIS and their additive and independent associations to outcome.

METHODS

Serial changes in P-selectin, tPA, MCP-1, sCD40L, IL-6, IL-8, L-arginine, and asymmetric and symmetric dimethylarginine (ADMA, SDMA) were investigated in 55 patients with AIS and without infection within 6 and 72 hours after stroke onset. Outcomes were assessed as National Institutes of Health Stroke Scale (NIHSS) worsening by 24 hours, poststroke infection, and death by 1 month.

RESULTS

Serum levels of L-arginine showed negative correlation, whereas ADMA and SDMA showed positive correlation with thrombo-inflammatory biomarkers in the hyperacute phase. Most of these correlations disappeared by 72 poststroke hours. Correlation of MCP-1 with both ADMA and SDMA levels at 6 hours was associated with both NIHSS worsening and poststroke infections, respectively; sCD40L and SDMA correlation at 6 hours was also associated with NIHSS worsening. Negative correlation between P-selectin and L-arginine concentrations in the hyperacute phase was associated with NIHSS worsening. Strong negative correlation was found between IL-6 and L-arginine levels in the hyperacute phase in patients with poststroke infection. Only L-arginine and SDMA at 72 hours were independently associated with poststroke infection respectively.

CONCLUSIONS

Concentration of L-arginine and ADMA/SDMA differentially correlates with thrombo-inflammation in the hyperacute phase of ischemic stroke. Such correlations are independently associated with poststroke infection but not with other outcomes.

Tissue inhibitor of metalloproteinases 3-dependent microvascular endothelial cell barrier function is disrupted under septic conditions

Sepsis is associated with dysfunction of microvascular endothelial cells (MVEC) leading to tissue edema and multiple organ dysfunction. Metalloproteinases can regulate MVEC function through processing of cell surface proteins, and tissue inhibitor of metalloproteinases 3 (TIMP3) regulates metalloproteinase activity in the lung following injury. We hypothesize that TIMP3 promotes normal pulmonary MVEC barrier function through inhibition of metalloproteinase activity. Naive Timp3(-/-) mice had significantly higher basal pulmonary microvascular Evans blue (EB) dye-labeled albumin leak vs. wild-type (WT) mice. Additionally, cecal-ligation/perforation (CLP)-induced sepsis significantly increased pulmonary microvascular EB-labeled albumin leak in WT but not Timp3(-/-) mice. Similarly, PBS-treated isolated MVEC monolayers from Timp3(-/-) mice displayed permeability barrier dysfunction vs. WT MVEC, evidenced by lower transendothelial electrical resistance and greater trans-MVEC flux of fluorescein-dextran and EB-albumin. Cytomix (equimolar interferon γ, tumor necrosis factor α, and interleukin 1β) treatment of WT MVEC induced significant barrier dysfunction (by all three methods), and was associated with a time-dependent decrease in TIMP3 mRNA and protein levels. Additionally, basal Timp3(-/-) MVEC barrier dysfunction was associated with disrupted MVEC surface VE-cadherin localization, and both barrier dysfunction and VE-cadherin localization were rescued by treatment with GM6001, a synthetic metalloproteinase inhibitor. TIMP3 promotes normal MVEC barrier function, at least partially, through inhibition of metalloproteinase-dependent disruption of adherens junctions, and septic downregulation of TIMP3 may contribute to septic MVEC barrier dysfunction.

A Review of the Mechanisms of Blood-Brain Barrier Permeability by Tissue-Type Plasminogen Activator Treatment for Cerebral Ischemia

Cerebrovascular homeostasis is maintained by the blood-brain barrier (BBB), which forms a mechanical and functional barrier between systemic circulation and the central nervous system (CNS). In patients with ischemic stroke, the recombinant tissue-type plasminogen activator (rt-PA) is used to accelerate recanalization of the occluded vessels. However, rt-PA is associated with a risk of increasing intracranial bleeding (ICB). This effect is thought to be caused by the increase in cerebrovascular permeability though various factors such as ischemic reperfusion injury and the activation of matrix metalloproteinases (MMPs), but the detailed mechanisms are unknown. It was recently found that rt-PA treatment enhances BBB permeability not by disrupting the BBB, but by activating the vascular endothelial growth factor (VEGF) system. The VEGF regulates both the dissociation of endothelial cell (EC) junctions and endothelial endocytosis, and causes a subsequent increase in vessel permeability through the VEGF receptor-2 (VEGFR-2) activation in ECs. Here, we review the possibility that rt-PA increases the penetration of toxic molecules derived from the bloodstream including rt-PA itself, without disrupting the BBB, and contributes to these detrimental processes in the cerebral parenchyma.

Nitric Oxide Interacts with Caveolin-1 to Facilitate Autophagy-Lysosome-Mediated Claudin-5 Degradation in Oxygen-Glucose Deprivation-Treated Endothelial Cells

Using in vitro oxygen-glucose deprivation (OGD) model, we have previously demonstrated that 2-h OGD induces rapid, caveolin-1-mediated dissociation of claudin-5 from the cellular cytoskeletal framework and quick endothelial barrier disruption. In this study, we further investigated the fate of translocated claudin-5 and the mechanisms by which OGD promotes caveolin-1 translocation. Exposure of bEND3 cells to 4-h OGD, but not 2-h OGD plus 2-h reoxygenation, resulted in claudin-5 degradation. Inhibition of autophagy or the fusion of autophagosome with lysosome, but not proteasome, blocked OGD-induced claudin-5 degradation. Moreover, knockdown of caveolin-1 with siRNA blocked OGD-induced claudin-5 degradation. Western blot analysis showed a transient colocalization of caveolin-1, claudin-5, and LC3B in autolysosome or lipid raft fractions at 2-h OGD. Of note, inhibiting autophagosome and lysosome fusion sustained the colocalization of caveolin-1, claudin-5, and LC3B throughout the 4-h OGD exposure. EPR spin trapping showed increased nitric oxide (NO) generation in 2-h OGD-treated cells, and inhibiting NO with its scavenger C-PTIO or inducible nitric oxide synthase (iNOS) inhibitor 1400W prevented OGD-induced caveolin-1 translocation and claudin-5 degradation. Taken together, our data provide a novel mechanism underlying endothelial barrier disruption under prolonged ischemic conditions, in which NO promotes caveolin-1-mediated delivery of claudin-5 to the autophagosome for autophagy-lysosome-dependent degradation.

Effects of Kaixinjieyu, a Chinese herbal medicine preparation, on neurovascular unit dysfunction in rats with vascular depression

BACKGROUND

Kaixinjieyu (KJ), derived from Kaixin and Sini powder, is an effective Chinese herbal medicine preparation used in the treatment of vascular depression (VD). We hypothesize that broad antidepressant effect of KJ results from the improved neurovascular unit (NVU) function via neurogenesis, permeability of blood-brain barrier (BBB) and balance of the fibrinolytic system.

METHODS

A VD model of rat was established by chronic unpredictable mild stress and separation after ligation of the bilateral common carotid arteries. The rats were treated with KJ and fluoxetine hydrochloride (FLU) for 21 days, respectively. The behavior and cerebral perfusion were investigated and then NVU functions including neurogenesis, permeability of BBB and balance of the fibrinolytic system were studied using a number of biomarkers and TUNEL assay.

RESULTS

KJ significantly increased sucrose preference, moving distance, number of rearing and cortical blood flow. NVU functions measured by brain-derived neurotrophic factor (BDNF), tropomyosin receptor kinase B (TrkB) and tissue plasminogen activator (t-PA) proteins and mRNA, zona occludens protein-1 (ZO-1), occludin and claudin-5 proteins increased significantly, whereas, plasminogen activator inhibitor-1 (PAI-1), matrix metalloproteinase-2 (MMP-2) proteins, mRNA and apoptotic rates of neurons decreased significantly with treatment of KJ. FLU has a function similar to KJ in behavior, regulation of BDNF, TrkB, MMP-2, occludin and apoptotic rates of cells.

CONCLUSIONS

KJ has function of reducing depression-like behavior and improving cerebral hypoperfusion, which might be mediated by the up-regulation of neurogenesis and tight junction of BBB, and balance of the fibrinolytic system. The results imply that KJ is better than FLU in improving cerebral hypoperfusion and the fibrinolytic system.

Bystander Effect Fuels Human Induced Pluripotent Stem Cell-Derived Neural Stem Cells to Quickly Attenuate Early Stage Neurological Deficits After Stroke

: Present therapies for stroke rest with tissue plasminogen activator (tPA), the sole licensed antithrombotic on the market; however, tPA's effectiveness is limited in that the drug not only must be administered less than 3-5 hours after stroke but often exacerbates blood-brain barrier (BBB) leakage and increases hemorrhagic incidence. A potentially promising therapy for stroke is transplantation of human induced pluripotent stem cell-derived neural stem cells (hiPSC-NSCs). To date, the effects of iPSCs on injuries that take place during early stage ischemic stroke have not been well studied. Consequently, we engrafted iPSC-NSCs into the ipsilesional hippocampus, a natural niche of NSCs, at 24 hours after stroke (prior to secondary BBB opening and when inflammatory signature is abundant). At 48 hours after stroke (24 hours after transplant), hiPSC-NSCs had migrated to the stroke lesion and quickly improved neurological function. Transplanted mice showed reduced expression of proinflammatory factors (tumor necrosis factor-α, interleukin 6 [IL-6], IL-1β, monocyte chemotactic protein 1, macrophage inflammatory protein 1α), microglial activation, and adhesion molecules (intercellular adhesion molecule 1, vascular cell adhesion molecule 1) and attenuated BBB damage. We are the first to report that engrafted hiPSC-NSCs rapidly improved neurological function (less than 24 hours after transplant). Rapid hiPSC-NSC therapeutic activity is mainly due to a bystander effect that elicits reduced inflammation and BBB damage.

SIGNIFICANCE

Clinically, cerebral vessel occlusion is rarely permanent because of spontaneous or thrombolytic therapy-mediated reperfusion. These results have clinical implications indicating a much extended therapeutic window for transplantation of human induced pluripotent stem cell-derived neural stem cells (hiPSC-NSCs; 24 hours after stroke as opposed to the 5-hour window with tissue plasminogen activator [tPA]). In addition, there is potential for a synergistic effect by combining hiPSC-NSC transplantation with tPA to attenuate stroke's adverse effects.

Measuring direct current trans-epithelial electrical resistance in organ-on-a-chip microsystems

Trans-epithelial electrical resistance (TEER) measurements are widely used as real-time, non-destructive, and label-free measurements of epithelial and endothelial barrier function. TEER measurements are ideal for characterizing tissue barrier function in organs-on-chip studies for drug testing and investigation of human disease models; however, published reports using this technique have reported highly conflicting results even with identical cell lines and experimental setups. The differences are even more dramatic when comparing measurements in conventional Transwell systems with those obtained in microfluidic systems. Our goal in this work was therefore to enhance the fidelity of TEER measurements in microfluidic organs-on-chips, specifically using direct current (DC) measurements of TEER, as this is the most widely used method reported in the literature. Here we present a mathematical model that accounts for differences measured in TEER between microfluidic chips and Transwell systems, which arise from differences in device geometry. The model is validated by comparing TEER measurements obtained in a microfluidic gut-on-a-chip device versus in a Transwell culture system. Moreover, we show that even small gaps in cell coverage (e.g., 0.4%) are sufficient to cause a significant (~80%) drop in TEER. Importantly, these findings demonstrate that TEER measurements obtained in microfluidic systems, such as organs-on-chips, require special consideration, specifically when results are to be compared with measurements obtained from Transwell systems.

Human neural stem cells rapidly ameliorate symptomatic inflammation in early-stage ischemic-reperfusion cerebral injury

Introduction

Clinically, a good deal of injury from stroke results from ischemic-reperfusion. There is a loss of cerebral parenchyma and its associated cells, disruption of neuronal connections, compromise of the blood-brain barrier, and inflammation. We tested whether exogenously engrafted human neural stem cells could migrate rapidly and extensively to damaged regions, following transplantation into a neurogenic site where migration cues are already underway during stroke onset, then counteract a number of these pathological processes.

Methods

One day post-injury, we injected human neural stem cells (hNSCs) into the ipsilesional hippocampus of a mouse model of stroke with middle cerebral artery occlusion to induce focal ischemia followed by reperfusion (MCAO/R). The time frame for hNSC transplantation corresponded to upregulation of endogenous proinflammatory cytokines. We examined the effect of hNSC transplantation on pathological processes and behavioral dysfunction 48 hours post-injury.

Results

Twenty-four hours after transplantation, engrafted hNSCs had migrated extensively to the lesion, and infarct volume was reduced relative to MCAO/R controls. The behavioral deficits seen in MCAO/R controls were also significantly improved. Given this rapid response, we hypothesized that the mechanisms underlying therapeutic activity were anti-inflammatory rather than due to cell replacement. In support of this idea, in hNSC-transplanted mice we observed reduced microglial activation, decreased expression of proinflammatory factors (tumor necrosis factor-α, interleukin (IL)-6, IL-1β, monocyte chemotactic protein-1, macrophage inflammatory protein-1α) and adhesion molecules (intercellular adhesion molecule-1, vascular cell adhesion molecule-1), and amelioration of blood-brain barrier damage.

Conclusions

While long-term effects of engrafted hNSCs on the amelioration of ischemic stroke-induced behavioral dysfunction in a rodent model have been reported, our study is the first to show rapid, beneficial impacts on behavioral function (within 24 hours) upon early delivery of hNSCs into the hippocampus.

Electronic supplementary material

The online version of this article (doi:10.1186/scrt519) contains supplementary material, which is available to authorized users.

Relationship of gelatinases-tight junction proteins and blood-brain barrier permeability in the early stage of cerebral ischemia and reperfusion

Gelatinases matrix metalloproteinase-2 and matrix metalloproteinase-9 have been shown to mediate claudin-5 and occludin degradation, and play an important regulatory role in blood-brain barrier permeability. This study established a rat model of 1.5-hour middle cerebral artery occlusion with reperfusion. Protein expression levels of claudin-5 and occludin gradually decreased in the early stage of reperfusion, which corresponded to the increase of the gelatinolytic activity of matrix metalloproteinase-2 and matrix metalloproteinase-9. In addition, rats that received treatment with matrix metalloproteinase inhibitor N-[(2R)-2-(hydroxamidocarbonylmethyl)-4-methylpenthanoyl]-L-tryptophan methylamide (GM6001) showed a significant reduction in Evans blue leakage and an inhibition of claudin-5 and occludin protein degradation in striatal tissue. These data indicate that matrix metalloproteinase-2 and matrix metalloproteinase-9-mediated claudin-5 and occludin degradation is an important reason for blood-brain barrier leakage in the early stage of reperfusion. The leakage of the blood-brain barrier was present due to gelatinases-mediated degradation of claudin-5 and occludin proteins. We hypothesized that the timely closure of the structural component of the blood-brain barrier (tight junction proteins) is of importance.

Effects of edaravone, a free radical scavenger, on circulating levels of MMP-9 and hemorrhagic transformation in patients with intravenous thrombolysis using low-dose alteplase

BACKGROUND

Matrix metalloproteinase-9 (MMP-9) plays a key role for the blood-brain barrier disruption and intravenous tissue plasminogen activator (iv-tPA) therapy increases MMP-9. Edaravone, a free radical scavenger, reduces MMP-9-related blood-brain barrier disruption. We aimed to investigate whether edaravone would suppress the MMP-9 increase after iv-tPA using low-dose alteplase (0.6 mg/kg).

SUBJECTS

Patients hospitalized within 12 hours after ischemic stroke onset between April 2008 and June 2013 were retrospectively examined. Patients with slight deficits (National Institutes of Health Stroke Scale score ≤ 4), stroke caused by arterial dissection, severe inflammatory disease or autoimmune disease, or regular use of steroid were excluded. Serum concentrations of high-sensitivity C-reactive protein, interleukin-6, MMP-2, and MMP-9 were serially measured at admission, after 24 hours, day 7, and day 14. General linear models were used to compare changes in concentrations of these biomarkers over time.

RESULTS

A total of 63 patients (38 men, aged 74.48 ± 13.8 years) were studied. Patients were divided into 2 groups according to the iv-tPA therapy, that is, tPA group (n = 32) and non-tPA group (n = 31). Edaravone was administered routinely except for contraindication (90.6% in the tPA group and 87.1% in the non-tPA group). Significant interaction of group × time factor was observed only in MMP-9 concentrations by repeated-measure analysis of variance (P = .004). Association between iv-tPA therapy and subsequent hemorrhagic transformation was highly significant, but MMP-9 concentrations at any point did not predictive of subsequent hemorrhagic transformation (area under the receiver operating characteristic curve, .681).

CONCLUSIONS

Low-dose iv-tPA increases MMP-9 concentration even in combination with Edaravone. The effect of higher dosage of Edaravone on circulating MMP-9 concentration and subsequent hemorrhagic transformation should be investigated.

Progesterone attenuates hemorrhagic transformation after delayed tPA treatment in an experimental model of stroke in rats: involvement of the VEGF-MMP pathway

Tissue plasminogen activator (tPA) is the only FDA-approved treatment for acute stroke, but its use remains limited. Progesterone (PROG) has shown neuroprotection in ischemia, but before clinical testing, we must determine how it affects hemorrhagic transformation in tPA-treated ischemic rats. Male Sprague-Dawley rats underwent middle cerebral artery occlusion with reperfusion at 4.5 hours and tPA treatment at 4.5 hours, or PROG treatment intraperitoneally at 2 hours followed by subcutaneous injection at 6 hours post occlusion. Rats were killed at 24 hours and brains evaluated for cerebral hemorrhage, swelling, blood-brain barrier (BBB) permeability, and levels of matrix metalloproteinase-9 (MMP-9), vascular endothelial growth factor level (VEGF), and tight junction (TJ) proteins. We also evaluated PROG's efficacy in preventing tPA-induced impairment of transendothelial electrical resistance (TEER) and TJ proteins under hypoxia/reoxygenation in the endothelial cells. Delayed tPA treatment induced significant hemorrhagic conversion and brain swelling. Treatment with PROG plus tPA ameliorated hemorrhage, hemispheric swelling, BBB permeability, MMP-9 induction, and VEGF levels compared with controls. Progesterone treatment significantly prevented tPA-induced decrease in TEER and expression of occludin and claudin-5, and attenuated VEGF levels in culture media subjected to hypoxia. The study concluded that PROG may extend the time window for tPA administration in ischemic stroke and reduce hemorrhagic conversion.

Involvement of Mincle and Syk in the changes to innate immunity after ischemic stroke

Accumulating evidence shows that post-ischemic inflammation originated by Toll-like receptors (TLR) plays critical roles in ischemic stroke. However, the functions of other innate immune receptors are poorly understood in cerebral ischemia. Macrophage-inducible C-type lectin, Mincle, is one of the innate immune receptor C-type lectin-like receptor (CLR) to response against dying cells. In the present study, we showed that Mincle, its ligand SAP130, and its downstream phospho-Syk/Syk were upregulated after ischemia, and that Mincle is expressed in immune and non-immune cells in the ischemic brains of mice and human. We treated mice with piceatannol, a Syk inhibitor, and consequently the infarct volume and swelling were suppressed by piceatannol. The levels of phospho-Syk, MMP9 and ICAM-1 were downregulated, and the level of Claudin5 was uplegurated in piceatannol-treated groups. These data indicate that innate immune system, such as Mincle and Syk plays a pivotal role in the pathogenesis after the ischemia and reperfusion.

MMP9 variation after thrombolysis is associated with hemorrhagic transformation of lesion and death

BACKGROUND AND PURPOSE

Experimentally, matrix metalloproteinases (MMPs) play a detrimental role related to hemorrhagic transformation and severity of an ischemic brain lesion. Tissue-type plasminogen activator (tPA) enhances such effects. This study aimed to expand clinical evidence in this connection.

METHODS

We measured MMPs 1, 2, 3, 7, 8, 9, and tissue inhibitors of metalloproteinases 1, 2, 4 circulating level in blood taken before and 24 hours after tPA from 327 patients (mean age, 68.9±12.1 years; median National Institutes of Health Stroke Scale, 11) with acute ischemic stroke. Delta median values ([24 hours post tPA-pre tPA]/pre tPA) of each MMP or tissue inhibitors of metalloproteinase were analyzed across subgroups of patients undergoing symptomatic intracerebral hemorrhage, 3-month death, or 3-month modified Rankin Scale score 3 to 6.

RESULTS

Adjusting for major clinical determinants, only matrix metalloproteinase-9 variation proved independently associated with death (odds ratio [95% confidence interval], 1.58 [1.11-2.26]; P=0.045) or symptomatic intracerebral hemorrhage (odds ratio [95% confidence interval], 1.40 [1.02-1.92]; P=0.049). Both matrix metalloproteinase-9 and tissue inhibitors of metalloproteinase-4 changes were correlated with baseline, 24 hours, and 7 days National Institutes of Health Stroke Scale (Spearman P from <0.001 to 0.040).

CONCLUSIONS

Our clinical evidence corroborates the detrimental role of matrix metalloproteinase-9 during ischemic stroke treated with thrombolysis, and prompts clinical trials testing agents antagonizing its effects.

Metabolic regulatory clues from the naked mole rat: toward brain regulatory functions during stroke

Resistance to tissue hypoxia is a robust fundamental adaptation to low oxygen supply, and represents a novel neuroscience problem with significance to mammalian physiology as well as human health. With the underlying mechanisms strongly conserved in evolution, the ability to resist tissue hypoxia in natural systems has recently emerged as an interesting model in mammalian physiology research to understand mechanisms that can be manipulated for the clinical management of stroke. The extraordinary ability to resist tissue hypoxia by the naked mole rat (NMR) indicates the presence of a unique mechanism that underlies the remarkable healthy life span and exceptional hypoxia resistance. This opens an interesting line of research into understanding the mechanisms employed by the naked mole rat (Heterocephalus glaber) to protect the brain during hypoxia. In a series of studies, we first examined the presence of neuroprotection in the brain cells of naked mole rats (NMRs) subjected to hypoxic insults, and then characterized the expression of such neuroprotection in a wide range of time intervals. We used oxygen nutrient deprivation (OND), an in vitro model of resistance to tissue hypoxia to determine whether there is evidence of neuronal survival in the hippocampal (CA1) slices of NMRs that are subjected to chronic hypoxia. Hippocampus neurons of NMRs that were kept in hypoxic condition consistently tolerated OND right from the onset time of 5h. This tolerance was maintained for 24h. This finding indicates that there is evidence of resistance to tissue hypoxia by CA1 neurons of NMRs. We further examined the effect of hypoxia on metabolic rate in the NMR. Repeated measurement of metabolic rates during exposure of naked mole rats to hypoxia over a constant ambient temperature indicates that hypoxia significantly decreased metabolic rates in the NMR, suggesting that the observed decline in metabolic rate during hypoxia may contribute to the adaptive mechanism used by the NMR to resist tissue hypoxia. This work is aimed to contribute to the understanding of mechanisms of resistance to tissue hypoxia in the NMR as an important life-sustaining process, which can be translated into therapeutic interventions during stroke.

Prevention of rt-PA induced blood-brain barrier component degradation by the poly(ADP-ribose)polymerase inhibitor PJ34 after ischemic stroke in mice

Recombinant tissue plasminogen activator (rt-PA) is the only pharmacological treatment approved for thrombolysis in patients suffering from ischemic stroke, but its administration aggravates the risk of hemorrhagic transformations. Experimental data demonstrated that rt-PA increases the activity of poly(ADP-ribose)polymerase (PARP). The aim of the present study was to investigate whether PJ34, a potent (PARP) inhibitor, protects the blood-brain barrier components from rt-PA toxicity. In our mouse model of cerebral ischemia, administration of rt-PA (10 mg/kg, i.v.) 6h after ischemia aggravated the post-ischemic degradation of ZO-1, claudin-5 and VE-cadherin, increased the hemorrhagic transformations (assessed by brain hemoglobin content and magnetic resonance imaging). Furthermore, rt-PA also aggravated ischemia-induced functional deficits. Combining PJ34 with rt-PA preserved the expression of ZO-1, claudin-5 and VE-cadherin, reduced the hemorrhagic transformations and improved the sensorimotor performances. In vitro studies also demonstrated that PJ34 crosses the blood-brain barrier and may thus exert its protective effect by acting on endothelial and/or parenchymal cells. Thus, co-treatment with a PARP inhibitor seems to be a promising strategy to reduce rt-PA-induced vascular toxicity after stroke.

Matrix metalloproteinases and blood-brain barrier disruption in acute ischemic stroke

Ischemic stroke continues to be one of the most challenging diseases in translational neurology. Tissue plasminogen activator (tPA) remains the only approved treatment for acute ischemic stroke, but its use is limited to the first hours after stroke onset due to an increased risk of hemorrhagic transformation over time resulting in enhanced brain injury. In this review we discuss the role of matrix metalloproteinases (MMPs) in blood-brain barrier (BBB) disruption as a consequence of ischemic stroke. MMP-9 in particular appears to play an important role in tPA-associated hemorrhagic complications. Reactive oxygen species can enhance the effects of tPA on MMP activation through the loss of caveolin-1 (cav-1), a protein encoded in the cav-1 gene that serves as a critical determinant of BBB permeability. This review provides an overview of MMPs' role in BBB breakdown during acute ischemic stroke. The possible role of MMPs in combination treatment of acute ischemic stroke is also examined.