Combined neurothrombectomy or thrombolysis with adjunctive delivery of 3K3A-activated protein C in acute ischemic stroke

The Next Step in the Treatment of Stroke

Although many patients do not receive reperfusion therapy because of delayed presentation and/or severity and location of infarct, new reperfusion approaches are expanding the window of intervention. Novel application of neuroprotective agents in combination with the latest methods of reperfusion provide a path to improved stroke intervention outcomes. We examine why neuroprotective agents have failed to translate to the clinic and provide suggestions for new approaches. New developments in recanalization therapy in combination with therapeutics evaluated in parallel animal models of disease will allow for novel, intra-arterial deployment of therapeutic agents over a vastly expanded therapeutic time window and with greater likelihood success. Although the field of neuronal, endothelial, and glial protective therapies has seen numerous large trials, the application of therapies in the context of newly developed reperfusion strategies is still in its infancy. Given modern imaging developments, evaluation of the penumbra will likely play a larger role in the evolving management of stroke. Increasingly more patients will be screened with neuroimaging to identify patients with adequate collateral blood supply allowing for delayed rescue of the penumbra. These patients will be ideal candidates for therapies such as reperfusion dependent therapeutic agents that pair optimally with cutting-edge reperfusion techniques.

Stroke Treatment With PAR-1 Agents to Decrease Hemorrhagic Transformation

Ischemic stroke is the most widespread cause of disability and a leading cause of death in developed countries. To date, the most potent approved treatment for acute stroke is recanalization therapy with thrombolytic drugs such as tissue plasminogen activator (rt-PA or tPA) or endovascular mechanical thrombectomy. Although tPA and thrombectomy are widely available in the United States, it is currently estimated that only 10-20% of stroke patients get tPA treatment, in part due to restrictive selection criteria. Recently, however, tPA and thrombectomy selection criteria have loosened, potentially allowing more patients to qualify. The relatively low rate of treatment may also reflect the perceived risk of brain hemorrhage following treatment with tPA. In translational research and a single patient study, protease activated receptor 1 (PAR-1) targeted therapies given along with thrombolysis and thrombectomy appear to reduce hemorrhagic transformation after recanalization. Such adjuncts may likely enhance the availability of recanalization and encourage more physicians to use the recently expanded selection criteria for applying recanalization therapies. This narrative review discusses stroke therapies, the role of hemorrhagic transformation in producing poor outcomes, and presents the data suggesting that PAR-1 acting agents show promise for decreasing hemorrhagic transformation and improving outcomes.

Novel approaches for the delivery of therapeutics in ischemic stroke

Here, we review novel approaches to deliver neuroprotective drugs to salvageable penumbral brain areas of stroke injury with the goals of offsetting ischemic brain injury and enhancing recovery.

CNB-001, a pleiotropic drug is efficacious in embolized agyrencephalic New Zealand white rabbits and ischemic gyrencephalic cynomolgus monkeys

Ischemic stroke is an acute neurodegenerative disease that is extremely devastating to patients, their families and society. Stroke is inadequately treated even with endovascular procedures and reperfusion therapy. Using an extensive translational screening process, we have developed a pleiotropic cytoprotective agent with the potential to positively impact a large population of brain ischemia patients and revolutionize the process used for the development of new drugs to treat complex brain disorders. In this unique translational study article, we document that the novel curcumin-based compound, CNB-001, when administered as a single intravenous dose, has significant efficacy to attenuate clinically relevant behavioral deficits following ischemic events in agyrencephalic rabbits when administered 1 h post-embolization and reduces infarct growth in gyrencephalic non-human primates, when administered 5 min after initiation of middle cerebral artery occlusion. CNB-001 is safe and does not increase morbidity or mortality in either research species. Mechanistically, CNB-001 inhibits human 5- and 15-lipoxygenase in vitro, and can attenuate ischemia-induced inflammatory markers, and oxidative stress markers, while potentially promoting synaptic plasticity mediated by enhanced brain-derived neurotrophic factor (BDNF).

Activated protein C inhibits lung injury induced by LPS via downregulating MAPK signaling

The aim of the present study was to investigate the effect and the underlying mechanism of activated protein C (APC) in lipopolysaccharide (LPS) induced lung injury, as well as the potential mechanism. According to the treatment, 50 rats were randomly divided into 5 groups: Control, model (LPS), low-dose group [LPS + 0.1 mg/kg recombined human activated protein C (rhAPC)], median-dose group (LPS + 0.3 mg/kg rhAPC) and high-dose group (LPS + 0.5 mg/kg rhAPC). Then, inflammation in the lung was assessed using hematoxylin and eosin (H&E) staining. Following the collection of bronchoalveolar lavage fluid (BALF), the number of leukocytes and neutrophils in BALF was counted, and superoxide dismutase (SOD) activity was assessed, as well as the expression levels of interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α using ELISA. Subsequently, the expression and phosphorylation of P-38, extracellular signal-regulated kinase (Erk)-1/2, and c-Jun N-terminal kinase (JNK) were estimated using western blotting. Based on H&E staining, rhAPC markedly suppressed inflammatory infiltration in the lung induced by LPS in a dose-dependent manner. In addition, rhAPC also significantly attenuated the accumulation of leptocytes and neutrophils, and the reduction of SOD in BALF induced by LPS in a dose-dependent manner. rhAPC also significantly attenuated the elevation of IL-1β, IL-6 and TNF-α in BALF induced by LPS in a dose-dependent manner. Further mechanistic analysis revealed that rhAPC treatment could evidently attenuate the phosphorylation levels of P-38, Erk1/2 and JNK in the lung induced by LPS in a dose-dependent manner. In conclusion, APC significantly alleviated the lung inflammation induced by LPS by downregulating the phosphorylation of P-38, ERK1/2 and JNK.

Salidroside improves brain ischemic injury by activating PI3K/Akt pathway and reduces complications induced by delayed tPA treatment

Cerebral ischemia causes blood-brain barrier (BBB) injury and thus increases the risk of complications secondary to thrombolysis, which limited its clinical application. This study aims to clarify the role and mechanism of salidroside (SALD) in alleviating brain ischemic injury and whether pretreatment of it could improve prognosis of delayed treatment of tissue plasminogen activator (t-PA). Rats were subjected to 3 h of middle cerebral artery occlusion (MCAO) and were intraperitoneally administered with 10, 20 or 40 mg/kg SALD before ischemia. 1.5% 5-triphenyl-2H-tetrazolium chloride (TTC) staining and neurological studies were performed to observe the effectiveness of SALD. The expressions and the distribution of phosphoinositide-3-kinase/protein kinase B (PI3K/Akt) signaling were analyzed. Experiments were further conducted in isolated microvessels and human brain microvascular endothelial cells (HBMECs) to explore the protective mechanism of SALD. Finally, rats were subjected to 6 h of MCAO and 24 h of reperfusion. tPA was given with or without the pretreatment of SALD. Various approaches including gelatin zymography, western blot and immunofluorescence were used to evaluate the effect of this combination therapy. SALD could reduce cerebral ischemic injury and enhance HBMECs viability subjected to OGD. In vivo and in vitro studies showed the mechanism might be related to the activation of PI3K/Akt signaling by phosphorylating Akt on Ser473. Pretreatment of SALD could alleviate BBB injury and improve the outcome of delayed treatment of tPA. These results provide evidence that SALD might be an effective adjuvant to reduce the complications induced by delayed tPA treatment for brain ischemia.

α2-Macroglobulin Is a Significant In Vivo Inhibitor of Activated Protein C and Low APC:α2M Levels Are Associated with Venous Thromboembolism

BACKGROUND

Activated protein C (APC) is a major regulator of thrombin formation. Two major plasma inhibitors form complexes with APC, protein C inhibitor (PCI) and α₁-antitrypsin (α₁AT), and these complexes have been quantified by specific enzyme-linked immunosorbent assays (ELISAs). Also, complexes of APC with α₂-macroglobulin (α₂M) have been observed by immunoblotting. Here, we report an ELISA for APC:α₂M complexes in plasma.

METHODS

Plasma samples were pre-treated with dithiothreitol and then with iodoacetamide. The detection range of the newly developed APC:α₂M assay was 0.031 to 8.0 ng/mL of complexed APC. Following infusions of APC in humans and baboons, complexes of APC with α₂M, PCI and α₁AT were quantified. These complexes as well as circulating APC were also measured in 121 patients with a history of venous thromboembolism (VTE) and 119 matched controls.

RESULTS

In all the in vivo experiments, α₂M was a significant APC inhibitor. The VTE case-control study showed that VTE patients had significantly lower APC:α₂M and APC levels than the controls (p < 0.001). Individuals in the lowest quartile of APC:α₂M or the lowest quartile of APC had approximately four times more VTE risk than those in the highest quartile of APC:α₂M or of APC. The risk increased for individuals with low levels of both parameters.

CONCLUSION

The APC:α₂M assay reported here may be useful to help monitor the in vivo fate of APC in plasma. In addition, our results show that a low APC:α₂M level is associated with increased VTE risk.

Thrombus Neutrophil Extracellular Traps Content Impair tPA-Induced Thrombolysis in Acute Ischemic Stroke

BACKGROUND AND PURPOSE

Neutrophil Extracellular Traps (NETs) are DNA extracellular networks decorated with histones and granular proteins produced by activated neutrophils. NETs have been identified as major triggers and structural factors of thrombosis. A recent study designated extracellular DNA threads from NETs as a potential therapeutic target for improving tissue-type plasminogen activator (tPA)-induced thrombolysis in acute coronary syndrome. The aim of this study was to assess the presence of NETs in thrombi retrieved during endovascular therapy in patients with acute ischemic stroke (AIS) and their impact on tPA-induced thrombolysis.

METHODS

We analyzed thrombi from 108 AIS patients treated with endovascular therapy. Thrombi were characterized by hematoxylin/eosin staining, immunostaining, and ex vivo enzymatic assay. Additionally, we assessed ex vivo the impact of deoxyribonuclease 1 (DNAse 1) on thrombolysis of AIS thrombi.

RESULTS

Histological analysis revealed that NETs contributed to the composition of all AIS thrombi especially in their outer layers. Quantitative measurement of thrombus NETs content was not associated with clinical outcome or AIS pathogenesis but correlated significantly with endovascular therapy procedure length and device number of passes. Ex vivo, recombinant DNAse 1 accelerated tPA-induced thrombolysis, whereas DNAse 1 alone was ineffective.

CONCLUSIONS

This study suggests that thrombus NETs content may be responsible for reperfusion resistance, including mechanical or pharmacological approaches with intravenous tPA, irrespectively of their etiology. The efficacy of a strategy involving an administration of DNAse 1 in addition to tPA should be explored in the setting of AIS.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT02907736.

Effect of recombinant human prourokinase on thrombolysis in a rabbit model of thromboembolic stroke

The aim of the present study was to investigate the efficacy of recombinant human prourokinase (rhPro-UK) on thromboembolic stroke in rabbits. A total of 210 rabbits were used in experiments. The 180 thromboembolic stroke rabbits were divided into three therapeutic time windows with six groups in each time window (n=10). The model group was administered saline, the reagent groups were administered rhPro-UK (2.5×, 5× and 10×10⁴ U/kg), and the positive control groups were administered 5×10⁴ urokinase (UK) U/kg and 4.5 mg/kg recombinant human tissue plasminogen activator via intravenous infusion at 3, 4.5 and 6 h after embolism. The remaining 30 rats (that had not undergone occlusion by autologous blood clots) served as a sham group and were administered saline. The radioactive intensity was detected using a medical gamma counter before and after the administration of the drug for 15, 30, 45, 60, 75, 90, 105 and 120 min. At 24 h after treatment, the brain samples were coronally sliced into 5 mm sections and hemorrhage was estimated used a semiquantitative method by counting the number of section faces with hemorrhaging. The plasma was collected for prothrombin time, activated partial thromboplastin time, fibrinogen and thrombin time tests using a solidification method with a blood coagulation factor analyzer. In addition, α₂-antiplasmin (α₂-AP) was evaluated using ELISA methods using a RT-6100 microplate reader. At the 3 h time point, the thrombolysis rate of rhPro-UK(2.5×, 5× and 10×10⁴ U/kg) was 21.5% (P<0.05), 36.8% (P<0.001) and 55.0% (P<0.001), respectively together with patency rates of 10% (P>0.05), 40% (P<0.05) and 70% (P<0.001). Furthermore, α₂-AP levels were reduced by 5.3% (P>0.05), 5.3% (P>0.05) and 18.1% (P<0.05). At the 4.5 h time point, the thrombolysis rate was 18.8% (P<0.05), 29.9% (P<0.01) and 49.0% (P<0.001) together with patency rates of 10% (P>0.05), 30% (P<0.05) and 50% (P<0.01), and α₂-AP levels were reduced by 2.4% (P>0.05), 6.5% (P>0.05) and 17.8% (P<0.05). At the 6 h time point, the thrombolysis rate was 14.7% (P<0.05), 24.1%(P<0.01) and 35.7% (P<0.001) together with patency rates of 20% (P>0.05), 30% (P<0.05) and 40% (P<0.01), and α₂-AP levels were reduced by 5.7% (P>0.05), 12.7% (P>0.05) and 22.2% (P<0.01). No significant differences (P>0.05) were identified between rhPro-UK (2.5×, 5× and 10×10⁴ U/kg) and the model group regarding hemorrhage type, size and blood coagulation factors at the different time points. Thus, rhPro-UK promoted thrombolysis and recanalization (patency rate), with reduced risk of cerebral hemorrhage, and thus exerted protective effects on cerebral ischemia rabbits.

Early administration of pyrrolidine dithiocarbamate extends the therapeutic time window of tissue plasminogen activator in a male rat model of embolic stroke

Tissue plasminogen activator (tPA) is used in fewer than 4% of patients after ischemic stroke because of its narrow therapeutic time window. We tested whether pyrrolidine dithiocarbamate (PDTC), a drug with multiple mechanisms to provide neuroprotection, can be used to extend the therapeutic time window of tPA. Three-month-old male Sprague-Dawley rats were subjected to embolic stroke in the area supplied by the right middle cerebral artery. tPA at 10 mg/kg was given intravenously 4 h after the onset of stroke. PDTC at 50 mg/kg was given via gastric gavage at 30 min or 4 h after the onset of stroke. Two days after the stroke, neurological outcome was evaluated and the right frontal cortex area 1 (Fr1), an ischemic penumbral region, was harvested for analysis. PDTC given at 30 min after the stroke reduced infarct volumes and improved neurological functions no matter whether the rats received tPA. PDTC also reduced tPA-increased hemorrhagic volumes. Consistent with these results, PDTC in the presence or absence of tPA treatment attenuated the increase of proinflammatory cytokines, oxidative stress and matrix metalloprotease 2 activity in the right Fr1. However, PDTC given at 4 h after the onset of stroke did not improve the neurological outcome of rats treated with or without tPA. Our results suggest that PDTC given at an early time point but not in a delayed phase provides neuroprotection against embolic stroke and may be used to extend the therapeutic time window of tPA.

Can adjunctive therapies augment the efficacy of endovascular thrombolysis? A potential role for activated protein C

In the management of acute ischemic stroke, vessel recanalization correlates with functional status, mortality, cost, and other outcome measures. Thrombolysis with intravenous tissue plasminogen activator has many limitations that restrict its applicability, but recent advances in the development of mechanical thrombectomy devices as well as improved systems of stroke care have resulted in greater likelihood of vessel revascularization. Nonetheless, there remains substantial discrepancy between rates of recanalization and rates of favorable outcome. The poor neurological recovery among some stroke patients despite successful recanalization confirms the need for adjuvant pharmacological therapy for neuroprotection and/or neurorestoration. Prior clinical trials of such drugs may have failed due to the inability of the agent to access the ischemic tissue beyond the occluded artery. A protocol that couples revascularization with concurrent delivery of a neuroprotectant drug offers the potential to enhance the benefit of thrombolysis. Analogs of activated protein C (APC) exert pleiotropic anti-inflammatory, anti-apoptotic, antithrombotic, cytoprotective, and neuroregenerative effects in ischemic stroke and thus appear to be promising candidates for this novel approach. A multicenter, prospective, double-blinded, dose-escalation Phase 2 randomized clinical trial has enrolled 110 patients to assess the safety, pharmacokinetics, and efficacy of human recombinant 3K3A-APC following endovascular thrombolysis. This article is part of the Special Issue entitled 'Cerebral Ischemia'.

Anti-Inflammatory Targets for the Treatment of Reperfusion Injury in Stroke

While the mainstay of acute stroke treatment includes revascularization via recombinant tissue plasminogen activator or mechanical thrombectomy, only a minority of stroke patients are eligible for treatment, as delayed treatment can lead to worsened outcome. This worsened outcome at the experimental level has been attributed to an entity known as reperfusion injury (R/I). R/I is occurred when revascularization is delayed after critical brain and vascular injury has occurred, so that when oxygenated blood is restored, ischemic damage is increased, rather than decreased. R/I can increase lesion size and also worsen blood barrier breakdown and lead to brain edema and hemorrhage. A major mechanism underlying R/I is that of poststroke inflammation. The poststroke immune response consists of the aberrant activation of glial cell, infiltration of peripheral leukocytes, and the release of damage-associated molecular pattern (DAMP) molecules elaborated by ischemic cells of the brain. Inflammatory mediators involved in this response include cytokines, chemokines, adhesion molecules, and several immune molecule effectors such as matrix metalloproteinases-9, inducible nitric oxide synthase, nitric oxide, and reactive oxygen species. Several experimental studies over the years have characterized these molecules and have shown that their inhibition improves neurological outcome. Yet, numerous clinical studies failed to demonstrate any positive outcomes in stroke patients. However, many of these clinical trials were carried out before the routine use of revascularization therapies. In this review, we cover mechanisms of inflammation involved in R/I, therapeutic targets, and relevant experimental and clinical studies, which might stimulate renewed interest in designing clinical trials to specifically target R/I. We propose that by targeting anti-inflammatory targets in R/I as a combined therapy, it may be possible to further improve outcomes from pharmacological thrombolysis or mechanical thrombectomy.

Recent advances in targeted delivery of tissue plasminogen activator for enhanced thrombolysis in ischaemic stroke

Tissue plasminogen activator (tPA) is the only FDA approved medical treatment for the ischaemic stroke. However, it associates with some inevitable limitations, including: short therapeutic window, extremely short half-life and low penetration in large clots. Systemic administration may lead to complications such as haemorrhagic conversion in the brain and relapse in the form of re-occlusion. Furthermore, ultrasound has been utilised in combination with contrast agents, echogenic liposome, microspheres or nanoparticles (NPs) carrying tPA for improving thrombolysis - an approach that has resulted in slight improvement of tPA delivery and facilitated thrombolysis. Most of these delivery systems are able to extend the circulating half-life and clot penetration of tPA. Various technologies employed for ameliorated thrombolytic therapy are in different phases, some are in final steps for clinical applications while some others are under investigations for their safety and efficacy in human cases. Here, recent progresses on the thrombolytic therapy using novel nano- and micro-systems incorporating tPA are articulated. Of these, liposomes and microspheres, polymeric NPs and magnetic nanoparticles (MNPs) are discussed. Key technologies implemented for efficient delivery of tPA and advanced thrombolytic therapy and their advantages/disadvantages are further expressed.

Tissue kallikrein protects against ischemic stroke by suppressing TLR4/NF-κB and activating Nrf2 signaling pathway in rats

Brain damage following cerebral ischemia-reperfusion (I/R) is a complicated pathophysiological course, in which inflammation and oxidative stress have been suggested to serve an important role. Toll-like receptor 4 (TLR4) has been suggested to be involved in secondary inflammatory process in cerebral ischemia. Nuclear factor erythroid 2-related factor 2 (Nrf2), an important regulator of the antioxidant host defense, maintains the cellular redox homeostasis. Tissue kallikrein (TK) has been proven to elicit a variety of biological effects in ischemic stroke through its anti-inflammatory and anti-oxidant properties. However, the mechanisms underlying its beneficial effects remain poorly defined. The present study examined the hypothesis that TK attenuates ischemic cerebral injury via the TLR4/nuclear factor-κB (NF-κB) and Nrf2 signaling pathways. Using a transient rat middle cerebral artery occlusion (MCAO) model, the effects of immediate and delayed TK treatment subsequent to reperfusion were investigated. The neurological deficits, infarct size, and the expression of TLR4/NF-κB and Nrf2 pathway in ischemic brain tissues were measured at 24 following MCAO. The results indicated that TK immediate treatment significantly improved neurological deficits and reduced the infarct size, accompanied by the inhibition of TLR4 and NF-κB levels, and the activation of Nrf2 pathway. Furthermore, TK delayed treatment also exerted neuroprotection against I/R injury. However, the neuroprotective effect of TK immediate treatment was better compared with that of TK delayed treatment. In conclusion, the results indicated that TK protected the brain against ischemic injury in rats after MCAO through its anti-oxidative and anti-inflammatory effects. Suppression of TLR4/NF-κB and activation of the Nrf2 pathway contributed to the neuroprotective effects induced by TK in cerebral ischemia. Therefore, TK may provide an effective intervention with a wider therapeutic window for ischemic stroke.

Activated protein C promotes neuroprotection: mechanisms and translation to the clinic

Activated protein C (APC) is a plasma serine protease that is capable of antithrombotic, anti-inflammatory, anti-apoptotic, and cell-signaling activities. Animal injury studies show that recombinant APC and some of its mutants are remarkably therapeutic for a wide range of injuries. In particular, for neurologic injuries, APC reduces damage caused by ischemia/reperfusion in the brain, by acute brain trauma, and by chronic neurodegenerative conditions. For these neuroprotective effects, APC requires endothelial cell protein C receptor. APC activates cell signaling networks with alterations in gene expression profiles by activating protease activated receptors 1 and 3. To minimize APC-induced bleeding risk, APC variants were engineered to lack > 90% anticoagulant activity but retain normal cell signaling. The neuroprotective APC mutant, 3K3A-APC which has Lys191-193 mutated to Ala191-193, is very neuroprotective and it is currently in clinical trials for ischemic stroke.

2016 Scientific Sessions Sol Sherry Distinguished Lecturer in Thrombosis: Thrombotic Stroke: Neuroprotective Therapy by Recombinant-Activated Protein C

APC (activated protein C), derived from the plasma protease zymogen, is antithrombotic and anti-inflammatory. In preclinical injury models, recombinant APC provides neuroprotection for multiple injuries, including ischemic stroke. APC acts directly on brain endothelial cells and neurons by initiating cell signaling that requires multiple receptors. Two or more major APC receptors mediate APC's neuroprotective cell signaling. When bound to endothelial cell protein C receptor, APC can cleave protease-activated receptor 1, causing biased cytoprotective signaling that reduces ischemia-induced injury. Pharmacological APC alleviates bleeding induced by tissue-type plasminogen activator in murine ischemic stroke studies. Remarkably, APC's signaling promotes neurogenesis. The signaling-selective recombinant variant of APC, 3K3A-APC, was engineered to lack most of the APC's anticoagulant activity but retain APC's cell signaling actions. Recombinant 3K3A-APC is in ongoing National Institutes of Health (NIH)-funded clinical trials for ischemic stroke.