Direct thrombin inhibitor argatroban reduces stroke damage in 2 different models

Before, during, and after: An Argument for Safety and Improved Outcome of Thrombolysis in Acute Ischemic Stroke with Direct Oral Anticoagulant Treatment

Direct oral anticoagulants are the primary stroke prevention option in patients with atrial fibrillation. Anticoagulant use before stroke, however, might inhibit clinician comfort with thrombolysis if a stroke does occur. Resuming anticoagulants after ischemic stroke is also problematic for fear of hemorrhage. We describe extensive literature showing that thrombolysis is safe after stroke with direct anticoagulant use. Early reinstitution of direct anticoagulant treatment is associated with lower risk of embolic recurrence and lower hemorrhage risk. The use of direct anticoagulants before, during, and after thrombolysis appears to be safe and is likely to promote improved outcomes after ischemic stroke. ANN NEUROL 2024.

Rescue therapy of early neurological deterioration in lacunar stroke

BACKGROUND

Early neurological deterioration (END) occurs in many patients with acute ischemic stroke due to a variety of causes. Although pharmacologically induced hypertension (PIH) and anticoagulants have been investigated in several clinical trials for the treatment of END, the efficacy and safety of these treatments remain unclear. Here, we investigated whether PIH or anticoagulation is better as a rescue therapy for the progression of END in patients with lacunar stroke.

METHODS

This study included patients with lacunar stroke who received rescue therapy with END within 3 days of symptom onset between April 2014 and August 2021. In the PIH group, phenylephrine was administered intravenously for 24 h and slowly tapered when symptoms improved or after 5 days of PIH. In the anticoagulation group, argatroban was administered continuously intravenously for 2 days and twice daily for next 5 days. We compared END recovery, defined as improvement in NIHSS from baseline, excellent outcomes (0 or 1 mRS at 3 months), and safety profile.

RESULTS

Among the 4818 patients with the lacunar stroke, END occurred in 147 patients. Seventy-nine patients with END received PIH (46.9%) and 68 patients (46.3%) received anticoagulation therapy. There was no significant difference in age (P = 0.82) and sex (P = 0.87) between the two groups. Compared to the anticoagulation group, the PIH group had a higher incidence of END recovery (77.2% vs. 51.5%, P < 0.01) and excellent outcomes (34.2% vs. 16.2%, P = 0.04). PIH was associated with END (HR 2.49; 95% CI 1.06-5.81, P = 0.04). PIH remained associated with END recovery (adjusted HR 3.91; 95% CI 1.19-12.90, P = 0.02). Safety outcomes, like hemorrhagic conversion and mortality, were not significantly different between the two groups.

CONCLUSIONS

As a rescue therapy for the progression of END in lacunar stroke patients, PIH with phenylephrine was more effective with similar safety compared to anticoagulation with argatroban.

Thrombin in Pregnancy and Preeclampsia: Expression, Localization, and Vasoactivity in Brain and Microvessels From Rats

ABSTRACT

Thrombin is a coagulation factor increased in pregnancy and further increased in preeclampsia (PE), a hypertensive disorder. Thrombin is also expressed in the brain and may have a nonhemostatic role. We characterized thrombin expression and vasoactivity in brain cerebral parenchymal arterioles (PAs) in rat models of pregnancy and PE. PAs were isolated and pressurized from nonpregnant (NP) and late-pregnant (LP) rats and rats with experimental preeclampsia (ePE). Reactivity to thrombin (1-50 U/mL) was measured in the absence and presence of inhibition of cyclooxygenase and nitric oxide synthase. Plasma levels of prothrombin, thrombin-antithrombin (TAT), tissue plasminogen activator, and plasminogen activator inhibitor-1 (PAI-1) and cerebrospinal fluid levels of TAT were compared using enzyme-linked immunosorbent assay. Expression of protease-activated receptor types 1 and 2 in PAs were measured by Western blot and immunohistochemistry. Neuronal thrombin expression was quantified in brains from all groups by immunohistochemistry. Prothrombin and TAT were elevated in ePE plasma compared with NP and LP. TAT was detected in cerebrospinal fluid from all groups and significantly elevated in LP (NP: 0.137 ± 0.014 ng/mL, LP: 0.241 ± 0.015 ng/mL, ePE: 0.192 ± 0.028 ng/mL; P < 0.05). Thrombin caused modest vasoconstriction in PAs from all groups regardless of cyclooxygenase or nitric oxide synthase inhibition. PAR1 and PAR2 were found in PAs from all groups colocalized to smooth muscle. Thrombin expression in central neurons was decreased in both LP and ePE groups compared with NP. These findings suggest a role for thrombin and other hemostatic changes during pregnancy and PE beyond coagulation.

Differential Vulnerability and Response to Injury among Brain Cell Types Comprising the Neurovascular Unit

The neurovascular unit (NVU) includes multiple different cell types, including neurons, astrocytes, endothelial cells, and pericytes, which respond to insults on very different time or dose scales. We defined differential vulnerability among these cell types, using response to two different insults: oxygen-glucose deprivation (OGD) and thrombin-mediated cytotoxicity. We found that neurons are most vulnerable, followed by endothelial cells and astrocytes. After temporary focal cerebral ischemia in male rats, we found significantly more injured neurons, compared with astrocytes in the ischemic area, consistent with differential vulnerability in vivo. We sought to illustrate different and shared mechanisms across all cell types during response to insult. We found that gene expression profiles in response to OGD differed among the cell types, with a paucity of gene responses shared by all types. All cell types activated genes relating to autophagy, apoptosis, and necroptosis, but the specific genes differed. Astrocytes and endothelial cells also activated pathways connected to DNA repair and antiapoptosis. Taken together, the data support the concept of differential vulnerability in the NVU and suggest that different elements of the unit will evolve from salvageable to irretrievable on different time scales while residing in the same brain region and receiving the same (ischemic) blood flow. Future work will focus on the mechanisms of these differences. These data suggest future stroke therapy development should target different elements of the NVU differently.

Argatroban in Patients With Acute Ischemic Stroke With Early Neurological Deterioration: A Randomized Clinical Trial

Importance

The effect of argatroban in patients with acute ischemic stroke (AIS) and early neurological deterioration (END) is unknown.

Objective

To assess the efficacy of argatroban for END in AIS.

Design, Setting, and Participants

This open-label, blinded-end point, randomized clinical trial was conducted from April 4, 2020, through July 31, 2022. The date of final follow-up was October 31, 2022. This was a multicenter trial. Eligible patients were adults with AIS who experienced END, which was defined as an increase of 2 or more points on the National Institutes of Health Stroke Scale within 48 hours from symptom onset. Patients who withdrew consent, experienced duplicate randomization, or were lost to follow-up were excluded from the study.

Interventions

Patients were randomly assigned to the argatroban group and control group within 48 hours of symptom onset. Both groups received standard therapy based on guidelines, including oral mono or dual antiplatelet therapy. The argatroban group received intravenous argatroban for 7 days (continuous infusion at a dose of 60 mg per day for 2 days, followed by 20 mg per day for 5 days) in addition to standard therapy.

Main Outcome and Measure

The primary end point was good functional outcome at 90 days, defined as a modified Rankin Scale score of 0 to 3.

Results

A total of 628 patients (mean [SD] age, 65 [11.9] years; 400 male [63.7%]) were included in this study (argatroban group, 314 [50%] and control group, 314 [50%]). Of these, 18 withdrew consent, 1 had duplicate randomization, and 8 were lost to follow-up. A total of 601 patients with stroke were included in the intention-to-treat analysis. Finally, 564 patients were included in the per-protocol analysis as 6 participants in the argatroban group and 31 participants in the control group did not follow the complete protocol. The number of patients with good functional outcome at 90 days was 240 (80.5%) in the argatroban group and 222 (73.3%) in the control group (risk difference, 7.2%; 95% CI, 0.6%-14.0%; risk ratio, 1.10; 95% CI, 1.01-1.20; P = .04). The proportion of symptomatic intracranial hemorrhage was 3 of 317 (0.9%) in the argatroban group and 2 of 272 (0.7%) in the control group (P = .78).

Conclusions and Relevance

Among patients with AIS with END, treatment with argatroban and antiplatelet therapy resulted in a better functional outcome at 90 days. This trial provided evidence to support the use of argatroban in reducing disability for patients with END.

Trial Registration

ClinicalTrials.gov Identifier: NCT04275180.

Argatroban promotes recovery of spinal cord injury by inhibiting the PAR1/JAK2/STAT3 signaling pathway

Argatroban is a synthetic thrombin inhibitor approved by U.S. Food and Drug Administration for the treatment of thrombosis. However, whether it plays a role in the repair of spinal cord injury is unknown. In this study, we established a rat model of T10 moderate spinal cord injury using an NYU Impactor Moder III and performed intraperitoneal injection of argatroban for 3 consecutive days. Our results showed that argatroban effectively promoted neurological function recovery after spinal cord injury and decreased thrombin expression and activity in the local injured spinal cord. RNA sequencing transcriptomic analysis revealed that the differentially expressed genes in the argatroban-treated group were enriched in the JAK2/STAT3 pathway, which is involved in astrogliosis and glial scar formation. Western blotting and immunofluorescence results showed that argatroban downregulated the expression of the thrombin receptor PAR1 in the injured spinal cord and the JAK2/STAT3 signal pathway. Argatroban also inhibited the activation and proliferation of astrocytes and reduced glial scar formation in the spinal cord. Taken together, these findings suggest that argatroban may inhibit astrogliosis by inhibiting the thrombin-mediated PAR1/JAK2/STAT3 signal pathway, thereby promoting the recovery of neurological function after spinal cord injury.

Argatroban as an Add-On to rtPA in Acute Ischemic Stroke: A Systematic Review and Meta-Analysis

Current treatment options for acute ischemic stroke, including intravenous thrombolysis (IVT) and mechanical thrombectomy, have undoubtedly revolutionized stroke care. The need for additional treatment options has brought into the light direct thrombin inhibitors (DTIs) and, specifically, argatroban as a promising candidate. However, there is uncertainty regarding the safety of adding argatroban to IVT, mainly due to the increased hemorrhagic risk. In this study, we performed a systematic review and meta-analysis examining the safety and efficacy of argatroban as an add-on treatment for IVT. The following databases were searched from inception until the 14th of May 2023: Pubmed/MEDLINE, ClinicalTrials.gov, the EU Clinical Trials Register, EMBASE/Scopus, and the Cochrane Library. Only randomized clinical trials (RCTs) enrolling patients with acute ischemic stroke who underwent IVT evaluating the add-on use of any DTIs were selected for the systematic review and further meta-analysis. The PRISMA guidelines were followed at all stages. Four studies with argatroban were included in the final analysis. Analysis of risk ratio and relative risk shows that the add-on therapy with argatroban seems to be effective and favors a good clinical outcome (mRS 0-2) at 90 days, similar to that of alteplase. All studies showed a low pooled incidence of symptomatic intracerebral hemorrhage (5%), parenchymal hematoma (3%), and other major bleeding (1%). Argatroban as an add-on treatment to IVT seems not to be associated with excessive bleeding risk; however, its efficacy remains unproven. According to this synopsis of the currently available evidence, it is premature to use argatroban as an add-on to IVT treatment outside the current clinical trial setting.

Effect of Argatroban Plus Intravenous Alteplase vs Intravenous Alteplase Alone on Neurologic Function in Patients With Acute Ischemic Stroke: The ARAIS Randomized Clinical Trial

IMPORTANCE

Previous studies suggested a benefit of argatroban plus alteplase (recombinant tissue-type plasminogen activator) in patients with acute ischemic stroke (AIS). However, robust evidence in trials with large sample sizes is lacking.

OBJECTIVE

To assess the efficacy of argatroban plus alteplase for AIS.

DESIGN, SETTING, AND PARTICIPANTS

This multicenter, open-label, blinded end point randomized clinical trial including 808 patients with AIS was conducted at 50 hospitals in China with enrollment from January 18, 2019, through October 30, 2021, and final follow-up on January 24, 2022.

INTERVENTIONS

Eligible patients were randomly assigned within 4.5 hours of symptom onset to the argatroban plus alteplase group (n = 402), which received intravenous argatroban (100 μg/kg bolus over 3-5 minutes followed by an infusion of 1.0 μg/kg per minute for 48 hours) within 1 hour after alteplase (0.9 mg/kg; maximum dose, 90 mg; 10% administered as 1-minute bolus, remaining infused over 1 hour), or alteplase alone group (n = 415), which received intravenous alteplase alone. Both groups received guideline-based treatments.

MAIN OUTCOMES AND MEASURES

The primary end point was excellent functional outcome, defined as a modified Rankin Scale score (range, 0 [no symptoms] to 6 [death]) of 0 to 1 at 90 days. All end points had blinded assessment and were analyzed on a full analysis set.

RESULTS

Among 817 eligible patients with AIS who were randomized (median [IQR] age, 65 [57-71] years; 238 [29.1%] women; median [IQR] National Institutes of Health Stroke Scale score, 9 [7-12]), 760 (93.0%) completed the trial. At 90 days, 210 of 329 participants (63.8%) in the argatroban plus alteplase group vs 238 of 367 (64.9%) in the alteplase alone group had an excellent functional outcome (risk difference, -1.0% [95% CI, -8.1% to 6.1%]; risk ratio, 0.98 [95% CI, 0.88-1.10]; P = .78). The percentages of participants with symptomatic intracranial hemorrhage, parenchymal hematoma type 2, and major systemic bleeding were 2.1% (8/383), 2.3% (9/383), and 0.3% (1/383), respectively, in the argatroban plus alteplase group and 1.8% (7/397), 2.5% (10/397), and 0.5% (2/397), respectively, in the alteplase alone group.

CONCLUSIONS AND RELEVANCE

Among patients with acute ischemic stroke, treatment with argatroban plus intravenous alteplase compared with alteplase alone did not result in a significantly greater likelihood of excellent functional outcome at 90 days.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03740958.

Thrombin induces ACSL4-dependent ferroptosis during cerebral ischemia/reperfusion

Ischemic stroke represents a significant danger to human beings, especially the elderly. Interventions are only available to remove the clot, and the mechanism of neuronal death during ischemic stroke is still in debate. Ferroptosis is increasingly appreciated as a mechanism of cell death after ischemia in various organs. Here we report that the serine protease, thrombin, instigates ferroptotic signaling by promoting arachidonic acid mobilization and subsequent esterification by the ferroptotic gene, acyl-CoA synthetase long-chain family member 4 (ACSL4). An unbiased multi-omics approach identified thrombin and ACSL4 genes/proteins, and their pro-ferroptotic phosphatidylethanolamine lipid products, as prominently altered upon the middle cerebral artery occlusion in rodents. Genetically or pharmacologically inhibiting multiple points in this pathway attenuated outcomes of models of ischemia in vitro and in vivo. Therefore, the thrombin-ACSL4 axis may be a key therapeutic target to ameliorate ferroptotic neuronal injury during ischemic stroke.

Cerebroprotection for Acute Ischemic Stroke: Looking Ahead

We search for ischemic stroke treatment knowing we have failed-intensely and often-to translate mechanistic knowledge into treatments that alleviate our patients' functional impairments. Lessons can be derived from our shared failures that may point to new directions and new strategies. First, the principle criticisms of both preclinical and clinical assessments are summarized. Next, previous efforts to develop single-mechanism treatments are reviewed. Finally, new definitions, novel approaches, and different directions are presented. In previous development efforts, the basic science and preclinical assessment of candidate treatments often lacked rigor and sufficiency; the clinical trials may have lacked power, rigor, or rectitude; or most likely both preclinical and clinical investigations were flawed. Single-target agents directed against specific molecular mechanisms proved unsuccessful. The term neuroprotection should be replaced as it has become ambiguous: protection of the entire neurovascular unit may be called cerebral cytoprotection or cerebroprotection. Success in developing cerebroprotection-either as an adjunct to recanalization or as stand-alone treatment-will require new definitions that recognize the importance of differential vulnerability in the neurovascular unit. Recent focus on pleiotropic multi-target agents that act via multiple mechanisms of action to interrupt ischemia at multiple steps may be more fruitful. Examples of pleiotropic treatments include therapeutic hypothermia and 3K3A-APC (activated protein C). Alternatively, the single-target drug NA-1 triggers multiple downstream signaling events. Renewed commitment to scientific rigor is essential, and funding agencies and journals may enforce quality principles of rigor in preclinical science. Appropriate animal models should be selected that are suited to the purpose of the investigation. Before clinical trials, preclinical assessment could include subjects that are aged, of both sexes, and harbor comorbid conditions such as diabetes or hypertension. With these new definitions, novel approaches, and renewed attention to rigor, the prospect for successful cerebroprotective therapy should improve.

Recanalisation therapies for acute ischaemic stroke in patients on direct oral anticoagulants

Direct oral anticoagulants (DOACs) have emerged as primary therapeutic option for stroke prevention in patients with atrial fibrillation. However, patients may have ischaemic stroke despite DOAC therapy and there is uncertainty whether those patients can safely receive intravenous thrombolysis or mechanical thrombectomy. In this review, we summarise and discuss current knowledge about different approaches to select patient. Time since last DOAC intake-as a surrogate for anticoagulant activity-is easy to use but limited by interindividual variability of drug pharmacokinetics and long cut-offs (>48 hours). Measuring anticoagulant activity using drug-specific coagulation assays showed promising safety results. Large proportion of patients at low anticoagulant activity seem to be potentially treatable but there remains uncertainty about exact safe cut-off values and limited assay availability. The use of specific reversal agents (ie, idarucizumab or andexanet alfa) prior to thrombolysis is a new emerging option with first data reporting safety but issues including health economics need to be elucidated. Mechanical thrombectomy appears to be safe without any specific selection criteria applied. In patients on DOAC therapy with large vessel occlusion, decision for intravenous thrombolysis should not delay thrombectomy (eg, direct thrombectomy or immediate transfer to a thrombectomy-capable centre recommended). Precision medicine using a tailored approach combining clinicoradiological information (ie, penumbra and vessel status), anticoagulant activity and use of specific reversal agents only if necessary seems a reasonable choice.

Reperfusion failure despite recanalization in stroke: New translational evidence

Current treatment for acute ischemic stroke aims at recanalizing the occluded blood vessel to reperfuse ischemic brain tissue. Clot removal can be achieved pharmacologically with a thrombolytic drug, such as recombinant tissue plasminogen activator, or with mechanical thrombectomy. However, reopening the occluded vessel does not guarantee full tissue reperfusion, which has been referred to as reperfusion failure. When it occurs, reperfusion failure significantly attenuates the beneficial effect of recanalization therapy and severely affects functional recovery of stroke patients. The mechanisms of reperfusion failure are somewhat complex and not fully understood. Briefly, after stroke, capillaries show stalls, constriction and luminal narrowing, being crowded with neutrophils, and fibrin–platelet deposits. Furthermore, after recanalization in stroke patients, a primary clot can break, dislodge, and occlude distal arterial branches further downstream. In this review, we highlight a rodent model that allows studying the pathophysiological mechanisms underlying reperfusion failure after stroke. We also describe the vascular and intravascular changes involved in reperfusion, which may provide relevant therapeutic targets for improving treatment of stroke patients.

Alteplase and Adjuvant Therapies for Acute Ischemic Stroke

Acute ischemic stroke (AIS) is a time sensitive medical emergency and a leading cause of morbidity and mortality worldwide. Intravenous (IV) recombinant tissue plasminogen activator (IV alteplase) is currently the only proven effective medication for the treatment of AIS with promising adjuvant medications currently under investigation. Recent advances in endovascular thrombectomy have broadened therapeutic options in specific patient populations, with modern treatment strategies utilizing advanced imaging modalities to extend the window for treatment. In all cases, rapid treatment remains a priority. The future of IV alteplase and the changing standard for treatment of AIS remain unwritten with the increasing evidence for imaging selection for both endovascular thrombectomy and IV alteplase, while novel adjuncts are under investigation. In this article, we review the history of IV alteplase investigations for stroke, evidence for thrombectomy as an adjunct to IV alteplase, and the potential of novel adjuvant therapeutics currently under investigation.

Thrombin inhibitor argatroban modulates bone marrow stromal cells behaviors and promotes osteogenesis through canonical Wnt signaling

AIMS

Coagulation is a common event that play a double-edged role in physiological and pathological process. Anti-coagulation methods were applied in joint surgery or scaffolds implantation to encourage new vascular formation and avoid coagulation block. However, whether anti-coagulation drug perform regulatory roles in bone structure is unknown. This study aims to explore a direct thrombin inhibitor, argatroban, effects on bone marrow stromal cells (BMSCs) and decipher the underlying mechanisms.

MATERIALS AND METHODS

Argatroban effects on BMSCs were investigated in vivo and in vitro. The drug was applied in periodontal disease model mice and bone loss was evaluated by μCT and histology. BMSCs were treated with different doses argatroban or vehicle. Cellular reactions were analyzed using wound healing assay, qRT-PCR, Alizarin Red S staining and western blotting.

KEY FINDINGS

We demonstrated that local injection of argatroban can rescue bone loss in periodontal disease in vivo. To explore the underlying mechanism, we examined that cell proliferation and differentiation capability. Proliferation and migration of BMSCs were both inhibited by applying lower dose of argatroban. Interestingly, without affecting osteoclastogenesis, osteogenic differentiation was significantly induced by argatroban, which were shown by extracellular mineralization and upregulation of early osteoblastic differentiation markers, alkaline phosphatase, Osteocalcin, transcription factors RUNX2 and Osterix. In addition, molecular analysis revealed that argatroban promoted β-catenin nuclear translocation and led to an increase of osteogenesis through activating canonical Wnt signaling.

SIGNIFICANCE

Taken together, our results show the novel application of the anti-coagulation compound argatroban in the commitment of BMSCs-based alveolar bone regeneration and remodeling.

Effects of Thrombin on the Neurovascular Unit in Cerebral Ischemia

Cerebral ischemia is a cerebrovascular disease with high morbidity and mortality that poses a significant burden on society and the economy. About 60% of cerebral ischemia is caused by thrombus, and the formation of thrombus proceeds from insoluble fibrin, following its transformation from liquid fibrinogen. In thrombus-induced ischemia, increased permeability of the blood-brain barrier (BBB), followed by the extravasation of blood components into the brain results in an altered brain microenvironment. Changes in the brain microenvironment affect brain function and the neurovascular unit (NVU), the working unit of the brain. Recent studies have reported that coagulation factors interact with the NVU and its components, but the specific function of this interaction is highly speculative and warrants further investigations. In this article, we reviewed the role of coagulation factors in cerebral ischemia and the role of coagulation factors in thrombosis. Additionally, the influence of thrombin on the NVU is introduced, as well as in the function of NVU, which may help to explore part of brain injury mechanism during ischemia. Lastly, we propose some novel therapeutic approaches on ischemic stroke by reducing the risk of coagulation.

The Role of Thrombin in Brain Injury After Hemorrhagic and Ischemic Stroke

Thrombin is increased in the brain after hemorrhagic and ischemic stroke primarily due to the prothrombin entry from blood either with a hemorrhage or following blood-brain barrier disruption. Increasing evidence indicates that thrombin and its receptors (protease-activated receptors (PARs)) play a major role in brain pathology following ischemic and hemorrhagic stroke (including intracerebral, intraventricular, and subarachnoid hemorrhage). Thrombin and PARs affect brain injury via multiple mechanisms that can be detrimental or protective. The cleavage of prothrombin into thrombin is the key step of hemostasis and thrombosis which takes place in every stroke and subsequent brain injury. The extravascular effects and direct cellular interactions of thrombin are mediated by PARs (PAR-1, PAR-3, and PAR-4) and their downstream signaling in multiple brain cell types. Such effects include inducing blood-brain-barrier disruption, brain edema, neuroinflammation, and neuronal death, although low thrombin concentrations can promote cell survival. Also, thrombin directly links the coagulation system to the immune system by activating interleukin-1α. Such effects of thrombin can result in both short-term brain injury and long-term functional deficits, making extravascular thrombin an understudied therapeutic target for stroke. This review examines the role of thrombin and PARs in brain injury following hemorrhagic and ischemic stroke and the potential treatment strategies which are complicated by their role in both hemostasis and brain.

Argatroban Increased the Basal Vein Drainage and Improved Outcomes in Acute Paraventricular Ischemic Stroke Patients

Background

Since venous drainage in acute arterial ischemic stroke has not been thoroughly researched, we evaluate the effect of argatroban, a selective direct thrombin inhibitor, as a therapy to increase the rate of basal vein Rosenthal (BVR) drainage and improve patients’ post-stroke outcomes.

Material/Methods

In this multicenter clinical trial, 60 eligible patients at 4.5 to 48 hours after the stroke onset were recruited. After being randomly allocated into 2 groups, they were treated with standard therapy either alone or with argatroban.

Results

Compared to the contralateral brain hemisphere, the mean flow velocity (MFV) in BVR drainage was significantly reduced in the stroke-afflicted ipsilateral hemisphere. After treatment with argatroban for 7 days, the MFV from BVR of the ipsilateral hemisphere in the argatroban treated group was significantly increased when compared to the control group. At 90 days after the onset of stroke, the MFV of BVR in the ipsilateral hemisphere was similar in both groups. Compared with controls, the argatroban-treated patients had smaller lesions from baseline to 7 days. Argatroban also improved National Institutes of Health Stroke Scale (NIHSS) scores on day 7 after the onset of stroke. Furthermore, the argatroban group’s neurological functions were superior to those of their untreated counterparts after 90 days. No difference was found in the incidence of adverse reactions between the 2 groups.

Conclusions

These observations indicate that vein drainage change may contribute to the acute phase of brain edema and the outcomes of ischemic stroke patients.

Clinical Trial Registration

URL-http://www.chictr.org

Unique identifier: ChiCTR-IPR-16008663

Interactions of antithrombotic herbal medicines with Western cardiovascular drugs

Thrombotic events act as a critical factor that interferes with Cardiovascular Diseases (CVDs), and antithrombotic herbal medicine is a long-standing controversial issue. Although a dispute is involved in their clinical application, all parties unanimously agree that herbal products have been widely used in folk medicine, and their interactions with conventional drugs are of high concern. This study aims to investigate how antithrombotic herbal medicines interact with Western cardiovascular drugs on the molecular level by taking an example of the most frequently used herbal pair, Danshen-Chuanxiong (DS-CX), and to discover more scientific evidence on their potential herb-drug interactions. Network pharmacology (NP), as an analytical approach of a complex system, is used to visualize and compare target profiles of DS-CX and Western cardiovascular drugs, which can be applied to predict common herb-drug targets and to construct a solid context for discussing herb-drug interactions. These interactions are further validated by in vitro assays, while in vivo zebrafish model employed for evaluating an overall pharmacological efficacy of herbal pairs in specific combination ratios. The study finds that DS could react directly to the Western cardiovascular drug targets relevant to antithrombotic pathways (i.e., thrombin, coagulation factor Xa and cyclooxygenase-1), whereas CX could not react directly and can synergistically affect antithrombotic effects with DS in specific combination ratios. Moreover, it is indicated that DS-CX may generate wide biological functions by a complicated mechanism of "neuro-immune-metabolism/endocrine" (NIM), which can further cause multiple direct and indirect interactions with Western cardiovascular drugs. From the clinical perspective, herb-drug interactions should be given high attention, especially when multiple herbs are used simultaneously.

Neuron-generated thrombin induces a protective astrocyte response via protease activated receptors

Astrocytes protect neurons during cerebral injury through several postulated mechanisms. Recent therapeutic attention has focused on enhancing or augmenting the neuroprotective actions of astrocytes but in some instances astrocytes can assume a neurotoxic phenotype. The signaling mechanisms that drive astrocytes toward a protective versus toxic phenotype are not fully known but cell-cell signaling via proteases acting on cell-specific receptors underlies critical mechanistic steps in neurodevelopment and disease. The protease activated receptor (PAR), resides in multiple brain cell types, and most PARs are found on astrocytes. We asked whether neuron-generated thrombin constituted an important astrocyte activation signal because our previous studies have shown that neurons contain prothrombin gene and transcribed protein. We used neuron and astrocyte mono-cell cultures exposed to oxygen-glucose deprivation and a model of middle cerebral artery occlusion. We found that ischemic neurons secrete thrombin into culture media, which leads to astrocyte activation; such astrocyte activation can be reproduced with low doses of thrombin. Media from prothrombin-deficient neurons failed to activate astrocytes and adding thrombin to such media restored activation. Astrocytes lacking PAR1 did not respond to neuron-generated thrombin. Induced astrocyte activation was antagonized dose-dependently with thrombin inhibitors or PAR1 antagonists. Ischemia-induced astrocyte activation in vivo was inhibited after neuronal prothrombin knockout, resulting in larger strokes. Restoring prothrombin to neurons with a lentiviral gene vector restored astrocyte activation and reduced stroke damage. We conclude that neuron-generated thrombin, released during ischemia, acts via PAR1 and may cause astrocyte activation and paracrine neuroprotection.

Neuroprotection and vasculoprotection using genetically targeted protease-ligands

Thrombin and activated protein C (APC) are known coagulation factors that exhibit profound effects in brain by acting on the protease activated receptor (PAR). The wild type (WT) proteases appear to impact cell survival powerfully, and therapeutic forms of APC are under development. Engineered recombinant thrombin or APC were designed to separate their procoagulant or anticoagulant effects from their cytoprotective properties. We measured vascular disruption and neuronal degeneration after a standard rodent filament stroke model. For comparison to a robust anticoagulant, we used a GpIIb/IIIa inhibitor, GR144053. During 2 h MCAo both WT murine APC and its mutant, 5A-APC, significantly decreased neuronal death 30 min after reperfusion. During 4 h MCAo, only 5A-APC significantly protected neurons but both WT-APC and 5A-APC exacerbated vascular disruption during 4 h MCAo. Human APC mutants appeared to reduce 24 h neuronal injury significantly when given after 2 h delay after MCAo. In contrast, 24 h vascular damage was worsened by high doses of WT and mutant APCs, although only statistically significantly for high dose 3K3A-APC. Mutated thrombin worsened vascular damage significantly without affecting neuron damage. GR144053 failed to ameliorate vascular disruption or neuronal injury despite significant anticoagulation. Differential effects on neurons and the vasculature were demonstrated using wild-type and mutated proteases. The mutants murine 3K3A-APC and 5A-APC protected neurons in this rodent model but in high doses worsened vascular leakage. Cytoactive effects of plasma proteases may be separated from their coagulation effects. Further studies should explore impact of dose and timing on cytoactive and vasculoactive properties of these drugs.

Safety and Feasibility of Argatroban, Recombinant Tissue Plasminogen Activator, and Intra-Arterial Therapy in Stroke (ARTSS-IA Study)

BACKGROUND

A randomized trial of concurrent recombinant tissue-type plasminogen activator (r-tPA) + thrombin-inhibition with Argatroban in stroke patients recently demonstrated safety and signal of efficacy compared to r-tPA alone, but patients having endovascular therapy (EVT) were excluded. The current study intended to study feasibility and safety of concurrent r-tPA and Argatroban in patients undergoing EVT.

METHODS

We conducted a single-arm, feasibility, and safety study of patients that received standard-dose r-tPA, had intracranial large vessel occlusions, and underwent EVT within 6 hours of stroke onset. During r-tPA, a 100 μg/kg Argatroban bolus, followed by 12-hour infusion, targeted an activated Partial Thromboplastin Time (aPTT) 2.25 timesbaseline. Feasibility was defined as ability to combine treatments without EVT time-metric delays, compared to cotemporaneous r-tPA + EVT treatments. Safety was incidence of symptomatic intracerebral hemorrhage (sICH), systemic hemorrhage, or EVT complications.

RESULTS

All preplanned 10 patients were enrolled. Arterial occlusions were middle cerebral artery (n = 8), internal carotid artery (n = 1), and posterior cerebral artery (n = 1). All received Argatroban before EVT and completed infusions. There were no delays in time-metrics compared to nonstudy patients during the same period. Nine patients achieved excellent angiographic reperfusion (Thrombolysis In Cerebral Ischemia [TICI] ≥2b); with 7 complete (TICI = 3). There were no sICH, systemic hemorrhage, or EVT complications. At 90 days, 6 (60%) patients had a modified Rankin Scale of 0-2 and none died.

CONCLUSIONS

In patients treated with r-tPA and EVT, concomitant Argatroban is feasible, does not delay EVT provision, produces high rates of recanalization, is probably safe, and warrants further study.

Intracerebral Hemorrhagic Expansion Occurs in Patients Using Non-Vitamin K Antagonist Oral Anticoagulants Comparable with Patients Using Warfarin

BACKGROUND

Non-vitamin K antagonist oral anticoagulant (NOAC) use has significantly reduced intracerebral hemorrhagic (ICH) risk compared with standard anticoagulant treatment. Hematoma expansion (HE) is a known predictor of mortality in warfarin-associated ICH. Little is known about HE in patients using NOACs.

METHODS

We conducted a retrospective chart review of patients with ICH admitted to Cedars-Sinai Medical Center from October 2010 to June 2016. We identified patients with concomitant administration of an oral anticoagulant and collected data including evidence of HE on imaging and modified Rankin Scale (mRS) at discharge. We defined HE as relative (≥33% increase) or absolute expansion (≥12 mL). We compared outcomes of patients with and without HE.

RESULTS

Out of 814 patients with ICH who were admitted, we identified 9 patients with recent NOAC use and 18 intentionally matched controls on warfarin. We found no significant differences in National Institutes of Health Stroke Scale or ICH score on presentation (median [interquartile range] 15 [5,21] versus 7 [1.25,19.5] [P = .41] and 2 [1,4] versus 1 [1,3] [P = .33]) between patients on NOACs and those on warfarin. Four out of the 9 patients on NOAC and 5 of the 18 patients on warfarin demonstrated HE, with no significant difference (P = .42). There were no significant differences in mRS on discharge between groups (P = .52).

CONCLUSIONS

In our coagulopathic NOAC patient population, HE occurs within 6 hours in 44% of patients. This case series did not have sufficient statistical power to detect significant differences between the groups. To our knowledge, this is one of the largest case series reporting on HE with concomitant NOAC use.

Randomized, Multicenter Trial of ARTSS-2 (Argatroban With Recombinant Tissue Plasminogen Activator for Acute Stroke)

BACKGROUND AND PURPOSE

We conducted a randomized exploratory study to assess safety and the probability of a favorable outcome with adjunctive argatroban, a direct thrombin-inhibitor, administered to recombinant tissue-type plasminogen activator (r-tPA)-treated ischemic stroke patients.

METHODS

Patients treated with standard-dose r-tPA, not receiving endovascular therapy, were randomized to receive no argatroban or argatroban (100 μg/kg bolus) followed by infusion of either 1 (low dose) or 3 μg/kg per minute (high dose) for 48 hours. Safety was incidence of symptomatic intracerebral hemorrhage. Probability of clinical benefit (modified Rankin Scale score 0-1 at 90 days) was estimated using a conservative Bayesian Poisson model (neutral prior probability centered at relative risk, 1.0 and 95% prior intervals, 0.33-3.0).

RESULTS

Ninety patients were randomized: 29 to r-tPA alone, 30 to r-tPA+low-dose argatroban, and 31 to r-tPA+high-dose argatroban. Rates of symptomatic intracerebral hemorrhage were similar among control, low-dose, and high-dose arms: 3/29 (10%), 4/30 (13%), and 2/31 (7%), respectively. At 90 days, 6 (21%) r-tPA alone, 9 (30%) low-dose, and 10 (32%) high-dose patients were with modified Rankin Scale score 0 to 1. The relative risks (95% credible interval) for modified Rankin Scale score 0 to 1 with low, high, and either low or high dose argatroban were 1.17 (0.57-2.37), 1.27 (0.63-2.53), and 1.34 (0.68-2.76), respectively. The probability that adjunctive argatroban was superior to r-tPA alone was 67%, 74%, and 79% for low, high, and low or high dose, respectively.

CONCLUSIONS

In patients treated with r-tPA, adjunctive argatroban was not associated with increased risk of symptomatic intracerebral hemorrhage and provides evidence that a definitive effectiveness trial is indicated.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique Identifier: NCT01464788.

A Linear Temporal Increase in Thrombin Activity and Loss of Its Receptor in Mouse Brain following Ischemic Stroke

BACKGROUND

Brain thrombin activity is increased following acute ischemic stroke and may play a pathogenic role through the protease-activated receptor 1 (PAR1). In order to better assess these factors, we obtained a novel detailed temporal and spatial profile of thrombin activity in a mouse model of permanent middle cerebral artery occlusion (pMCAo).

METHODS

Thrombin activity was measured by fluorescence spectroscopy on coronal slices taken from the ipsilateral and contralateral hemispheres 2, 5, and 24 h following pMCAo (n = 5, 6, 5 mice, respectively). Its spatial distribution was determined by punch samples taken from the ischemic core and penumbra and further confirmed using an enzyme histochemistry technique (n = 4). Levels of PAR1 were determined using western blot.

RESULTS

Two hours following pMCAo, thrombin activity in the stroke core was already significantly higher than the contralateral area (11 ± 5 vs. 2 ± 1 mU/ml). At 5 and 24 h, thrombin activity continued to rise linearly (r = 0.998, p = 0.001) and to expand in the ischemic hemisphere beyond the ischemic core reaching deleterious levels of 271 ± 117 and 123 ± 14 mU/ml (mean ± SEM) in the basal ganglia and ischemic cortex, respectively. The peak elevation of thrombin activity in the ischemic core that was confirmed by fluorescence histochemistry was in good correlation with the infarcts areas. PAR1 levels in the ischemic core decreased as stroke progressed and thrombin activity increased.

CONCLUSION

In conclusion, there is a time- and space-related increase in brain thrombin activity in acute ischemic stroke that is closely related to the progression of brain damage. These results may be useful in the development of therapeutic strategies for ischemic stroke that involve the thrombin-PAR1 pathway in order to prevent secondary thrombin related brain damage.

Identification of berberine as a direct thrombin inhibitor from traditional Chinese medicine through structural, functional and binding studies

Thrombin acts as a key enzyme in the blood coagulation cascade and represents a potential drug target for the treatment of several cardiovascular diseases. The aim of this study was to identify small-molecule direct thrombin inhibitors from herbs used in traditional Chinese medicine (TCM). A pharmacophore model and molecular docking were utilized to virtually screen a library of chemicals contained in compositions of traditional Chinese herbs, and these analyses were followed by in vitro bioassay validation and binding studies. Berberine (BBR) was first confirmed as a thrombin inhibitor using an enzymatic assay. The BBR IC₅₀ value for thrombin inhibition was 2.92 μM. Direct binding studies using surface plasmon resonance demonstrated that BBR directly interacted with thrombin with a K_D value of 16.39 μM. Competitive binding assay indicated that BBR could bind to the same argartroban/thrombin interaction site. A platelet aggregation assay demonstrated that BBR had the ability to inhibit thrombin-induced platelet aggregation in washed platelets samples. This study proved that BBR is a direct thrombin inhibitor that has activity in inhibiting thrombin-induced platelet aggregation. BBR may be a potential candidate for the development of safe and effective thrombin-inhibiting drugs.

A protease-activated receptor 1 antagonist protects against global cerebral ischemia/reperfusion injury after asphyxial cardiac arrest in rabbits

Cerebral ischemia/reperfusion injury is partially mediated by thrombin, which causes brain damage through protease-activated receptor 1 (PAR1). However, the role and mechanisms underlying the effects of PAR1 activation require further elucidation. Therefore, the present study investigated the effects of the PAR1 antagonist SCH79797 in a rabbit model of global cerebral ischemia induced by cardiac arrest. SCH79797 was intravenously administered 10 minutes after the model was established. Forty-eight hours later, compared with those administered saline, rabbits receiving SCH79797 showed markedly decreased neuronal damage as assessed by serum neuron specific enolase levels and less neurological dysfunction as determined using cerebral performance category scores. Additionally, in the hippocampus, cell apoptosis, polymorphonuclear cell infiltration, and c-Jun levels were decreased, whereas extracellular signal-regulated kinase phosphorylation levels were increased. All of these changes were inhibited by the intravenous administration of the phosphoinositide 3-kinase/Akt pathway inhibitor LY29004 (3 mg/kg) 10 minutes before the SCH79797 intervention. These findings suggest that SCH79797 mitigates brain injury via anti-inflammatory and anti-apoptotic effects, possibly by modulating the extracellular signal-regulated kinase, c-Jun N-terminal kinase/c-Jun and phosphoinositide 3-kinase/Akt pathways.

Thrombin-induced apoptosis in neurons through activation of c-Jun-N-terminal kinase

CONTEXT

Studies have shown that thrombin activation played a central role in cell injuries associated with intracerebral hemorrhage (ICH).

OBJECTIVE

Here, our study investigated the cytotoxicity of thrombin on neurons, and determined the involvement of JNK pathways in thrombin-induced neuronal apoptosis.

MATERIALS AND METHODS

Primary cultured neurons were treated with different doses of thrombin. Some neurons were given either SP600125 or vehicle. LDH release assay and flow cytometry were used to measure neuronal apoptosis caused by thrombin. The activation of JNK and capases-3 were measured by Western blot.

RESULTS

Our results showed large doses of thrombin that increased the LDH release, the level of cleaved caspase-3 and apoptosis rate of neurons. JNK was activated by thrombin in a time-dependent manner. Administration of SP600125 protects neurons from thrombin-induced apoptosis.

CONCLUSION

These data indicate that the activation of JNK is crucial for thrombin-induced neuronal apoptosis, and inhibition of JNK may be a potential therapeutic target for ICH.

Targeting the thrombin receptor modulates inflammation and astrogliosis to improve recovery after spinal cord injury

The deregulation of serine protease activity is a common feature of neurological injury, but little is known regarding their mechanisms of action or whether they can be targeted to facilitate repair. In this study we demonstrate that the thrombin receptor (Protease Activated Receptor 1, (PAR1)) serves as a critical translator of the spinal cord injury (SCI) proteolytic microenvironment into a cascade of pro-inflammatory events that contribute to astrogliosis and functional decline. PAR1 knockout mice displayed improved locomotor recovery after SCI and reduced signatures of inflammation and astrogliosis, including expression of glial fibrillary acidic protein (GFAP), vimentin, and STAT3 signaling. SCI-associated elevations in pro-inflammatory cytokines such as IL-1β and IL-6 were also reduced in PAR1-/- mice and co-ordinate improvements in tissue sparing and preservation of NeuN-positive ventral horn neurons, and PKCγ corticospinal axons, were observed. PAR1 and its agonist's thrombin and neurosin were expressed by perilesional astrocytes and each agonist increased the production of IL-6 and STAT3 signaling in primary astrocyte cultures in a PAR1-dependent manner. In turn, IL-6-stimulated astrocytes increased expression of PAR1, thrombin, and neurosin, pointing to a model in which PAR1 activation contributes to increased astrogliosis by feedforward- and feedback-signaling dynamics. Collectively, these findings identify the thrombin receptor as a key mediator of inflammation and astrogliosis in the aftermath of SCI that can be targeted to reduce neurodegeneration and improve neurobehavioral recovery.

A novel histochemical method for the visualization of thrombin activity in the nervous system

Although thrombin has an important role in both central and peripheral nerve diseases, characterization of the anatomical distribution of its proteolytic activity has been limited by available methods. This study presents the development, challenges, validation and implementation of a novel histochemical method for visualization of thrombin activity in the nervous system. The method is based on the cleavage of the substrate, Boc-Asp(OBzl)-Pro-Arg-4MβNA by thrombin to liberate free 4-methoxy-2-naphthylamine (4MβNA). In the presence of 5-nitrosalicylaldehyde, free 4MβNA is captured, yielding an insoluble yellow fluorescent precipitate which marks the site of thrombin activity. The sensitivity of the method was determined in vitro using known concentrations of thrombin while the specificity was verified using a highly specific thrombin inhibitor. Using this method we determined the spatial distribution of thrombin activity in mouse brain following transient middle cerebral artery occlusion (tMCAo) and in mouse sciatic nerve following crush injury. Fluorescence microscopy revealed well-defined thrombin activity localized to the right ischemic hemisphere in cortical areas and in the striatum compared to negligible thrombin activity contralaterally. The histochemical localization of thrombin activity following tMCAo was in good correlation with the infarct areas per triphenyltetrazolium chloride staining and to thrombin activity measured biochemically in tissue punches (85 ± 35 and 20 ± 3 mU/ml, in the cortical and striatum areas respectively, compared to 7 ± 2 and 13 ± 2 mU/ml, in the corresponding contralateral areas; mean ± SEM; p<0.05). In addition, 24 h following crush injury, focal areas of highly elevated thrombin activity were detected in teased sciatic fibers. This observation was supported by the biochemical assay and western blot technique. The histochemical method developed in this study can serve as an important tool for studying the role of thrombin in physiological and pathological conditions.

The Importance of Thrombin in Cerebral Injury and Disease

There is increasing evidence that prothrombin and its active derivative thrombin are expressed locally in the central nervous system. So far, little is known about the physiological and pathophysiological functions exerted by thrombin in the human brain. Extra-hepatic prothrombin expression has been identified in neuronal cells and astrocytes via mRNA measurement. The actual amount of brain derived prothrombin is expected to be 1% or less compared to that in the liver. The role in brain injury depends upon its concentration, as higher amounts cause neuroinflammation and apoptosis, while lower concentrations might even be cytoprotective. Its involvement in numerous diseases like Alzheimer’s, multiple sclerosis, cerebral ischemia and haemorrhage is becoming increasingly clear. This review focuses on elucidation of the cerebral thrombin expression, local generation and its role in injury and disease of the central nervous system.

Emergency and critical care management of acute ischaemic stroke

Ischaemic stroke is a devastating condition that is the leading cause of disability in the USA. Over the last 2 decades, the focus of management has shifted from secondary stroke prevention to acute treatment. Coordinated care starts in the field with the emergency medical service providers and continues in the ambulance and the emergency department through to the intensive care unit. After diagnosis and stabilization, a major goal is reperfusion therapy with intravenous fibrinolytics. Neuroimaging research is focused on improving patient selection, expanding treatment windows, and increasing the safety of therapeutic intervention. The role of adjunctive intra-arterial and mechanical thrombectomy remains undefined, and methods to improve reperfusion using sonolysis and new-generation fibrinolytics are currently investigational. Treatment in the intensive care unit targets prevention of secondary brain injury through optimization of blood pressure, cerebral perfusion, glucose, and temperature management, ventilation, and oxygenation. The most feared complications include malignant cerebral edema and symptomatic hemorrhagic transformation. Decompressive craniectomy is life saving, but questions regarding patient selection and timing remain. Hyperosmolar agents are currently used to mitigate cerebral edema, but newer agents to prevent the formation of cerebral edema at the molecular level are being studied. We outline a practical approach to current emergency and intensive care management based on consensus guidelines and the best available evidence.

Protease activated receptor-1 mediates cytotoxicity during ischemia using in vivo and in vitro models

Protease activated receptors (PARs) populate neurons and astrocytes in the brain. The serine protease thrombin, which activates PAR-1 during the first hours after stroke, appears to be associated with the cytotoxicity. Thrombin antagonists and PAR-1 inhibitors have been correlated with reduced cell death and behavioral protection after stroke, but no data yet support a mechanistic link between PAR-1 action and benefit. We sought to establish the essential role of PAR-1 in mediating ischemic damage. Using a short hairpin mRNA packaged with green fluorescent protein in a lentivirus vector, we knocked downPAR-1 in the medial caudate nucleus prior to rat middle cerebral artery occlusion (MCAo) and in rat neurons prior to oxygen-glucose deprivation. We also compared aged PAR-1 knockout mice with aged PAR-3, PAR-4 mice and young wild-type mice in a standard MCAo model. Silencing PAR-1 significantly reduced neurological deficits, reduced endothelial barrier leakage, and decreased neuronal degeneration in vivo during MCAo. PAR-1 knock-down in the ischemic medial caudate allowed cells to survive the ischemic injury; infected cells were negative for terminal deoxynucleotidyl transferase mediated dUTP Nick End Labeling (TUNEL) and c-Fos injury markers. Primary cultured neurons infected with PAR-1 short hairpin ribonucleic acid (shRNA) showed increased neuroprotection during hypoxic/aglycemic conditions with or without added thrombin. The aged PAR-1 knockout mice showed decreased infarction and vascular disruption compared to aged controls or young wild types. We demonstrated an essential role for PAR-1 during ischemia. Silencing or removing PAR-1 significantly protected neurons and astrocytes. Further development of agents that act at PAR-1 or its downstream pathways could yield powerful stroke therapy.

Nafamostat mesilate attenuates neuronal damage in a rat model of transient focal cerebral ischemia through thrombin inhibition

Evidence suggests that thrombin, a blood coagulation serine protease, mediates neuronal injury in experimental cerebral ischemia. Here, we test the hypothesis that nafamostat mesilate, a serine protease inhibitor, may ameliorate ischemia-induced neuronal damage through thrombin inhibition after ischemic stroke. Focal ischemia was induced in adult Sprague-Dawley rats by occlusion of the middle cerebral artery for 2 hours followed by 22 hours of reperfusion. The administration of nafamostat mesilate during ischemia and reperfusion reduced the brain infarct volume, edema volume and neurological deficit. Thrombin expression and activity in the ipsilateral striatum were increased after ischemia, whereas the administration of nafamostat mesilate significantly inhibited thrombin expression and activity. Immunostaining showed that the majority of thrombin was expressed in neurons. TUNEL staining showed that nafamostat mesilate reduced the number of dying cells during ischemia. A rat behavioral test showed that nafamostat mesilate treatment significantly improved the learning ability of ischemic rats. These results suggest that nafamostat mesilate may have a potential therapeutic role for neuroprotection against focal cerebral ischemia through thrombin inhibition.