Thrombin mediates severe neurovascular injury during ischemia

Thrombin and protein C pathway in peripheral nerve Schwann cells

Thrombin and activated protein C (aPC) bound to the endothelial protein C receptor (EPCR) both activate protease-activated receptor 1 (PAR1) generating either harmful or protective signaling respectively. In the present study we examined the localization of PAR-1 and EPCR and thrombin activity in Schwann glial cells of normal and crushed peripheral nerve and in Schwannoma cell lines. In the sciatic crush model nerves were excised 1h, 1, 4, and 7days after the injury. Schwannoma cell lines produced high levels of prothrombin which is converted to active thrombin and expressed both EPCR and PAR-1 which co-localized. In the injured sciatic nerve thrombin levels were elevated as early as 1h after injury, reached their peak 1day after injury which was significantly higher (24.4±4.1mU/ml) compared to contralateral uninjured nerves (2.6±7mU/ml, t-test p<0.001) and declined linearly reaching baseline levels by day 7. EPCR was found to be located at the microvilli of Schwann cells at the node of Ranvier and in cytoplasm surrounding the nucleus. Four days after sciatic injury, EPCR levels increased significantly (57,785±16602AU versus 4790±1294AU in the contralateral uninjured nerves, p<0.001 by t-test) mainly distal to the site of injury, where axon degeneration is followed by proliferation of Schwann cells which are diffusely stained for EPCR. EPCR seems to be located to cytoplasmic component of Schwann cells and not to compact myelin component, and is highly increased following injury.

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.

Nafamostat mesilate improves function recovery after stroke by inhibiting neuroinflammation in rats

Inflammation plays an important role in stroke pathology, making it a promising target for stroke intervention. Nafamostat mesilate (NM), a wide-spectrum serine protease inhibitor, is commonly used for treating inflammatory diseases, such as pancreatitis. However, its effect on neuroinflammation after stroke was unknown. Hence, the effects of NM on the inflammatory response post stroke were characterized. After transient middle cerebral artery occlusion (tMCAO) in rats, NM reduced the infarct size, improved behavioral functions, decreased the expression of proinflammatory mediators (TNF-α, IL-1β, iNOS and COX-2) in a time-dependent manner and promoted the expression of different anti-inflammatory factors (CD206, TGF-β, IL-10 and IL-4) at different time points. Furthermore, NM could inhibit the expression of proinflammatory mediators and promote anti-inflammatory mediators expression in rat primary microglia following exposure to thrombin combined with oxygen-glucose deprivation (OGD). The immune-modulatory effect of NM might be partly due to its inhibition of the NF-κB signaling pathway and inflammasome activation after tMCAO. In addition, NM significantly inhibited the infiltration of macrophage, neutrophil and T lymphocytes, which was partly mediated by the inhibition of monocyte chemotactic protein-1 (MCP-1), intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). Taken together, our results indicated that NM can provide long-term protection of the brain against tMCAO by modulating a broad components of the inflammatory response.

Upregulation of Thrombin/Matrix Metalloproteinase-1/Protease-Activated Receptor-1 Chain in Proliferative Diabetic Retinopathy

PURPOSE

Selective proteolytic activation of protease-activated receptor-1 (PAR1) by thrombin and matrix metalloproteinase-1 (MMP-1) plays a central role in enhancing angiogenesis. We investigated the expression levels of thrombin, MMP-1, and PAR1 and correlated these levels with vascular endothelial growth factor (VEGF) in proliferative diabetic retinopathy (PDR). In addition, we examined the expression of PAR1 and thrombin in the retinas of diabetic rats and PAR1 in human retinal microvascular endothelial cells (HRMEC) following exposure to high-glucose, the proinflammatory cytokines interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and the hypoxia mimetic agent cobalt chloride (CoCl₂).

METHODS

Vitreous samples from 32 PDR and 23 nondiabetic patients, epiretinal membranes from 10 patients with PDR, retinas of rats, and HRMEC were studied by enzyme-linked immunosorbent assay (ELISA), immunohistochemistry, and Western blot analysis. An assay for in vitro cell migration angiogenesis was performed in HRMEC.

RESULTS

In epiretinal membranes, PAR1 was expressed in vascular endothelial cells, CD45-expressing leukocytes, and myofibroblasts. ELISA and Western blot assays revealed significant increases in the expression levels of thrombin, MMP-1, and VEGF in vitreous samples from PDR patients compared to nondiabetic controls. Significant positive correlations were found between the levels of VEGF and the levels of thrombin (r = 0.41; p = 0.006) and MMP-1 (r = 0.66; p < 0.0001). Significant increases of cleaved PAR1 (approximately 50 kDa) and the proteolytically active thrombin (approximately 50 kDa) were detected in rat retinas after induction of diabetes. The proinflammatory cytokines IL-1β and TNF-α, but not high-glucose and CoCl₂, induced upregulation of cleaved PAR1 (approximately 30 kDa) in HRMEC. In addition, thrombin and MMP-1 induced VEGF in HRMEC and vorapaxar, a PAR1 inhibitor, inhibited thrombin-induced migration in HRMEC.

CONCLUSIONS

Interactions among thrombin, MMP-1, PAR1, and VEGF might facilitate angiogenesis in PDR.

The Alzheimer's disease peptide β-amyloid promotes thrombin generation through activation of coagulation factor XII

Essentials How the Alzheimer's disease (AD) peptide β-amyloid (Aβ) disrupts neuronal function in the disease is unclear. Factor (F) XII initiates blood clotting via FXI, and thrombosis has been implicated in AD. Aβ triggers FXII-dependent FXI and thrombin activation, evidence of which is seen in AD plasma. Aβ-triggered clotting could contribute to neuronal dysfunction in AD and be a novel therapeutic target.

SUMMARY

Background β-Amyloid (Aβ) is a key pathologic element in Alzheimer's disease (AD), but the mechanisms by which it disrupts neuronal function in vivo are not completely understood. AD is characterized by a prothrombotic state, which could contribute to neuronal dysfunction by affecting cerebral blood flow and inducing inflammation. The plasma protein factor XII triggers clot formation via the intrinsic coagulation cascade, and has been implicated in thrombosis. Objectives To investigate the potential for Aβ to contribute to a prothrombotic state. Methods and results We show that Aβ activates FXII, resulting in FXI activation and thrombin generation in human plasma, thereby establishing Aβ as a possible driver of prothrombotic states. We provide evidence for this process in AD by demonstrating decreased levels of FXI and its inhibitor C1 esterase inhibitor in AD patient plasma, suggesting chronic activation, inhibition and clearance of FXI in AD. Activation of the intrinsic coagulation pathway in AD is further supported by elevated fibrin levels in AD patient plasma. Conclusions The ability of Aβ to promote coagulation via the FXII-driven contact system identifies new mechanisms by which it could contribute to neuronal dysfunction and suggests potential new therapeutic targets in AD.

Nafamostat mesilate protects against acute cerebral ischemia via blood-brain barrier protection

Serine proteases, such as thrombin, are contributors to the disruption of the blood-brain barrier (BBB) and exacerbate brain damage during ischemic stroke, for which the current clinical therapy remains unsatisfactory. However, the effect of nafamostat mesilate (NM), a synthetic serine protease inhibitor, on BBB disruption following cerebral ischemia is unknown. Here, we investigated the in vivo effect of NM on BBB integrity in rats subjected to transient middle cerebral artery occlusion (MCAO) and explored the possible mechanism in an in vitro BBB model comprising rat brain microvascular endothelial cells and astrocytes after oxygen and glucose deprivation (OGD) in the presence of thrombin. The results showed that NM treatment remarkably attenuated transient MCAO-induced brain infarcts, brain oedema and motor dysfunction in addition to BBB disruption, which might be related to changes in tight junction protein expression and localization. Meanwhile, NM preserved BBB integrity and alleviated the changes in tight junction protein expression and localization and cytoskeleton rearrangement in rat brain microvascular endothelial cells via thrombin inhibition. Our findings suggest that NM treatment can preserve BBB integrity through the inhibition of thrombin, which might be correlated with the regulation of PKCα/RhoA/MLC2 pathway components.

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.

Pretreatment with baicalin attenuates hypoxia and glucose deprivation-induced injury in SH-SY5Y cells

OBJECTIVE

To explore the neuroprotective effects of baicalin against hypoxia and glucose deprivation-reperfusion (OGD/RO)-induced injury in SH-SY5Y cells.

METHODS

SH-SY5Y cells were divided into a control group, a OGD/RO group, which was subject to OGD/RO induction; and 3 baicalin groups subject to baicalin (1, 5, 25 μmol/L) for 2 h before induction of OGD/RO (low-, medium-, and high-dose baicalin groups). Cell viability was detected by thiazolyl blue tetrazolium bromide (MTT) assay and flow cytometric analysis was used to detect cell apoptosis. Real-time polymerase chain reaction was performed to determine the mRNA expression of caspase-3 gene. Western blot analysis was conducted to determine the expression of nuclear factor (NF)-κB and N-methyl-daspartic acid receptor-1 (NMDAR1).

RESULTS

Baicalin could significantly attenuate OGD/RO mediated apoptotic cell death in SH-SY5Y cells; the apoptosis rates in the low-, medium- and high-dose groups were 12.1%, 7.9%, and 5.4%, respectively. Western blot and real-time PCR analysis revealed that significant decrease in caspase-3 expression in the baicalin group compared with the OGD/RO group (P<0.01). Additionally, down-regulation of NF-κB and NMDAR1 was observed in the baicalin group compared with those obtained from the OGD/RO group. Compared with the low-dose baicalin group, remarkable decrease was noted in the medium- and high-dose groups (P<0.01).

CONCLUSION

Baicalin pre-treatment attenuates brain ischemia reperfusion injury by suppressing cellular apoptosis.

White matter hypoperfusion and damage in dementia: post-mortem assessment

Neuroimaging has revealed a range of white matter abnormalities that are common in dementia, some that predict cognitive decline. The abnormalities may result from structural diseases of the cerebral vasculature, such as arteriolosclerosis and amyloid angiopathy, but can also be caused by nonstructural vascular abnormalities (eg, of vascular contractility or permeability), neurovascular instability or extracranial cardiac or vascular disease. Conventional histopathological assessment of the white matter has tended to conflate morphological vascular abnormalities with changes that reflect altered interstitial fluid dynamics or white matter ischemic damage, even though the latter may be of extracranial or nonstructural etiology. However, histopathology is being supplemented by biochemical approaches, including the measurement of proteins involved in the molecular responses to brain ischemia, myelin proteins differentially susceptible to ischemic damage, vessel-associated proteins that allow rapid measurement of microvessel density, markers of blood-brain barrier dysfunction and axonal injury, and mediators of white matter damage. By combining neuroimaging with histopathology and biochemical analysis, we can provide reproducible, quantitative data on the severity of white matter damage, and information on its etiology and pathogenesis. Together these have the potential to inform and improve treatment, particularly in forms of dementia to which white matter hypoperfusion makes a significant contribution.

The pericyte: a forgotten cell type with important implications for Alzheimer's disease?

Pericytes are cells in the blood-brain barrier (BBB) that degenerate in Alzheimer's disease (AD), a neurodegenerative disorder characterized by early neurovascular dysfunction, elevation of amyloid β-peptide (Aβ), tau pathology and neuronal loss, leading to progressive cognitive decline and dementia. Pericytes are uniquely positioned within the neurovascular unit between endothelial cells of brain capillaries, astrocytes and neurons. Recent studies have shown that pericytes regulate key neurovascular functions including BBB formation and maintenance, vascular stability and angioarchitecture, regulation of capillary blood flow, and clearance of toxic cellular by-products necessary for normal functioning of the central nervous system (CNS). Here, we review the concept of the neurovascular unit and neurovascular functions of CNS pericytes. Next, we discuss vascular contributions to AD and review new roles of pericytes in the pathogenesis of AD such as vascular-mediated Aβ-independent neurodegeneration, regulation of Aβ clearance and contributions to tau pathology, neuronal loss and cognitive decline. We conclude that future studies should focus on molecular mechanisms and pathways underlying aberrant signal transduction between pericytes and its neighboring cells within the neurovascular unit, that is, endothelial cells, astrocytes and neurons, which could represent potential therapeutic targets to control pericyte degeneration in AD and the resulting secondary vascular and neuronal degeneration.

Design, synthesis and biological evaluation of hydrogen sulfide releasing derivatives of 3-n-butylphthalide as potential antiplatelet and antithrombotic agents

In the present study, a series of hydrogen sulfide (H2S) releasing derivatives (8a–g and 9a–f) of 3-n-butylphthalide (NBP) were designed, synthesized and biologically evaluated. The most promising compound 8e significantly inhibited the adenosine diphosphate (ADP) and arachidonic acid (AA)-induced platelet aggregation in vitro, superior to NBP, ticlopidine hydrochloride and aspirin. Furthermore, 8e could slowly produce moderate levels of H2S in vitro, which could be beneficial for improving cardiovascular and cerebral circulation. Most importantly, 8e protected against the collagen and adrenaline induced thrombosis in mice, and exhibited greater antithrombotic activity than NBP and aspirin in rats. Overall, 8e could warrant further investigation for the treatment of thrombosis-related ischemic stroke.

Progesterone attenuates thrombin-induced endothelial barrier disruption in the brain endothelial cell line bEnd.3: The role of tight junction proteins and the endothelial protein C receptor

This study examines the effects of progesterone on blood-brain barrier (BBB) integrity following thrombin administration. Thrombin is expressed in many diseases which affect neural tissue and is associated with breakdown of the BBB. Progesterone has shown protective effects on the BBB in stroke and traumatic brain injury.

METHODS

Mouse brain endothelial (bEnd.3) cells were treated with progesterone (20 μmol/l) for 24h before thrombin administration (60 U/ml). BBB permeability was measured by transendothelial electrical resistance (TEER), because TEER decrease is associated with BBB compromise. Tight junction (TJ) proteins (occludin, claudin-5, and zonula occludens-1) and endothelial protein C receptor (EPCR) were analyzed.

RESULTS

Thrombin decreased TEER and progesterone prevented that decrease. TJ proteins and EPCR were also decreased after thrombin treatment and progesterone treatment blocked that effect.

CONCLUSION

Progesterone can attenuate thrombin-induced BBB disruption by blocking the degradation of TJ proteins and EPCR in bEnd.3 cells.

Brain tissue responses to neural implants impact signal sensitivity and intervention strategies

Implantable biosensors are valuable scientific tools for basic neuroscience research and clinical applications. Neurotechnologies provide direct readouts of neurological signal and neurochemical processes. These tools are generally most valuable when performance capacities extend over months and years to facilitate the study of memory, plasticity, and behavior or to monitor patients’ conditions. These needs have generated a variety of device designs from microelectrodes for fast scan cyclic voltammetry (FSCV) and electrophysiology to microdialysis probes for sampling and detecting various neurochemicals. Regardless of the technology used, the breaching of the blood–brain barrier (BBB) to insert devices triggers a cascade of biochemical pathways resulting in complex molecular and cellular responses to implanted devices. Molecular and cellular changes in the microenvironment surrounding an implant include the introduction of mechanical strain, activation of glial cells, loss of perfusion, secondary metabolic injury, and neuronal degeneration. Changes to the tissue microenvironment surrounding the device can dramatically impact electrochemical and electrophysiological signal sensitivity and stability over time. This review summarizes the magnitude, variability, and time course of the dynamic molecular and cellular level neural tissue responses induced by state-of-the-art implantable devices. Studies show that insertion injuries and foreign body response can impact signal quality across all implanted central nervous system (CNS) sensors to varying degrees over both acute (seconds to minutes) and chronic periods (weeks to months). Understanding the underlying biological processes behind the brain tissue response to the devices at the cellular and molecular level leads to a variety of intervention strategies for improving signal sensitivity and longevity.

Thrombin induces ischemic LTP (iLTP): implications for synaptic plasticity in the acute phase of ischemic stroke

Acute brain ischemia modifies synaptic plasticity by inducing ischemic long-term potentiation (iLTP) of synaptic transmission through the activation of N-Methyl-D-aspartate receptors (NMDAR). Thrombin, a blood coagulation factor, affects synaptic plasticity in an NMDAR dependent manner. Since its activity and concentration is increased in brain tissue upon acute stroke, we sought to clarify whether thrombin could mediate iLTP through the activation of its receptor Protease-Activated receptor 1 (PAR1). Extracellular recordings were obtained in CA1 region of hippocampal slices from C57BL/6 mice. In vitro ischemia was induced by acute (3 minutes) oxygen and glucose deprivation (OGD). A specific ex vivo enzymatic assay was employed to assess thrombin activity in hippocampal slices, while OGD-induced changes in prothrombin mRNA levels were assessed by (RT)qPCR. Upon OGD, thrombin activity increased in hippocampal slices. A robust potentiation of excitatory synaptic strength was detected, which occluded the ability to induce further LTP. Inhibition of either thrombin or its receptor PAR1 blocked iLTP and restored the physiological, stimulus induced LTP. Our study provides important insights on the early changes occurring at excitatory synapses after ischemia and indicates the thrombin/PAR1 pathway as a novel target for developing therapeutic strategies to restore synaptic function in the acute phase of ischemic stroke.

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.

Cytoprotective-selective activated protein C therapy for ischaemic stroke

Despite years of research and efforts to translate stroke research to clinical therapy, ischaemic stroke remains a major cause of death, disability, and diminished quality of life. Primary and secondary preventive measures combined with improved quality of care have made significant progress. However, no novel drug for ischaemic stroke therapy has been approved in the past decade. Numerous studies have shown beneficial effects of activated protein C (APC) in rodent stroke models. In addition to its natural anticoagulant functions, APC conveys multiple direct cytoprotective effects on many different cell types that involve multiple receptors including protease activated receptor (PAR) 1, PAR3, and the endothelial protein C receptor (EPCR). Application of molecular engineered APC variants with altered selectivity profiles to rodent stroke models demonstrated that the beneficial effects of APC primarily require its cytoprotective activities but not its anticoagulant activities. Extensive basic, preclinical, and clinical research provided a compelling rationale based on strong evidence for translation of APC therapy that has led to the clinical development of the cytoprotective-selective APC variant, 3K3A-APC, for ischaemic stroke. Recent identification of non-canonical PAR1 and PAR3 activation by APC that give rise to novel tethered-ligands capable of inducing biased cytoprotective signalling as opposed to the canonical signalling provides a mechanistic explanation for how APC-mediated PAR activation can selectively induce cytoprotective signalling pathways. Collectively, these paradigm-shifting discoveries provide detailed insights into the receptor targets and the molecular mechanisms for neuroprotection by cytoprotective-selective 3K3A-APC, which is currently a biologic drug in clinical trials for ischaemic stroke.

Effects of caspase-1 knockout on chronic neural recording quality and longevity: insight into cellular and molecular mechanisms of the reactive tissue response

Chronic implantation of microelectrodes into the cortex has been shown to lead to inflammatory gliosis and neuronal loss in the microenvironment immediately surrounding the probe, a hypothesized cause of neural recording failure. Caspase-1 (aka Interleukin 1β converting enzyme) is known to play a key role in both inflammation and programmed cell death, particularly in stroke and neurodegenerative diseases. Caspase-1 knockout (KO) mice are resistant to apoptosis and these mice have preserved neurologic function by reducing ischemia-induced brain injury in stroke models. Local ischemic injury can occur following neural probe insertion and thus in this study we investigated the hypothesis that caspase-1 KO mice would have less ischemic injury surrounding the neural probe. In this study, caspase-1 KO mice were implanted with chronic single shank 3 mm Michigan probes into V1m cortex. Electrophysiology recording showed significantly improved single-unit recording performance (yield and signal to noise ratio) of caspase-1 KO mice compared to wild type C57B6 (WT) mice over the course of up to 6 months for the majority of the depth. The higher yield is supported by the improved neuronal survival in the caspase-1 KO mice. Impedance fluctuates over time but appears to be steadier in the caspase-1 KO especially at longer time points, suggesting milder glia scarring. These findings show that caspase-1 is a promising target for pharmacologic interventions.

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.

Deferoxamine attenuates acute hydrocephalus after traumatic brain injury in rats

Acute post-traumatic ventricular dilation and hydrocephalus are relatively frequent consequences of traumatic brain injury (TBI). Several recent studies have indicated that high iron levels in brain may relate to hydrocephalus development after intracranial hemorrhage. However, the role of iron in the development of post-traumatic hydrocephalus is still unclear. This study was to determine whether or not iron has a role in hydrocephalus development after TBI. TBI was induced by lateral fluid-percussion in male Sprague-Dawley rats. Some rats had intraventricular injection of iron. Acute hydrocephalus was measured by magnetic resonance T2-weighted imaging and brain hemorrhage was determined by T2* gradient-echo sequence imaging and brain hemoglobin levels. The effect of deferoxamine on TBI-induced hydrocephalus was examined. TBI resulted in acute hydrocephalus at 24 h (lateral ventricle volume: 24.1 ± 3.0 vs. 9.9 ± 0.2 mm(3) in sham group). Intraventricular injection of iron also caused hydrocephalus (25.7 ± 3.4 vs. 9.0 ± 0.6 mm(3) in saline group). Deferoxamine treatment attenuated TBI-induced hydrocephalus and heme oxygenase-1 upregulation. In conclusion, iron may contribute to acute hydrocephalus after TBI.

Mannose-binding lectin promotes local microvascular thrombosis after transient brain ischemia in mice

BACKGROUND AND PURPOSE

Several lines of evidence support the involvement of mannose-binding lectin (MBL) in stroke brain damage. The lectin pathway of the complement system facilitates thrombin activation and clot formation under certain experimental conditions. In the present study, we examine whether MBL promotes thrombosis after ischemia/reperfusion and influences the course and prognosis of ischemic stroke.

METHODS

Middle cerebral artery occlusion/reperfusion was performed in MBL-deficient (n=85) and wild-type (WT; n=83) mice, and the brain lesion was assessed by MRI at days 1 and 7. Relative cerebral blood flow was monitored up to 6 hours after middle cerebral artery occlusion with laser speckle contrast imaging. Fibrin(ogen) was analyzed in the brain vasculature and plasma, and the effects of thrombin inhibitor argatroban were evaluated to assess the role of MBL in thrombin activation.

RESULTS

Infarct volumes and neurological deficits were smaller in MBL knockout mice than in WT mice. Relative cerebral blood flow values during middle cerebral artery occlusion and at reperfusion were similar in both groups, but decreased during the next 6 hours in the WT group only. Also, the WT mice showed more fibrin(ogen) in brain vessels and a better outcome after argatroban treatment. In contrast, argatroban did not improve the outcome in MBL knockout mice.

CONCLUSIONS

MBL promotes brain damage and functional impairment after brain ischemia/reperfusion in mice. These effects are secondary to intravascular thrombosis and impaired relative cerebral blood flow during reperfusion. Argatroban protects WT mice, but not MBL knockout mice, emphasizing a role of MBL in local thrombus formation in acute ischemia/reperfusion.

Pericyte function in the physiological central nervous system

Damage to the central nervous system (CNS) leads to disruption of the vascular network, causing vascular dysfunction. Vascular dysfunction is the major event in the pathogenesis of CNS diseases and is closely associated with the severity of neuronal dysfunction. The suppression of vascular dysfunction has been considered a promising avenue to limit damage to the CNS, leading to efforts to clarify the cellular and molecular basis of vascular homeostasis maintenance. A reduction of trophic support and oxygen delivery due to circulatory insufficiency has long been regarded as a major cause of vascular damage. Moreover, recent studies provide a new perspective on the importance of the structural stability of blood vessels in CNS diseases. This updated article discusses emerging information on the key role of vascular integrity in CNS diseases, specially focusing on pericyte function.

A portable microchip for ultrasensitive and high-throughput assay of thrombin by rolling circle amplification and hemin/G-quadruplex system

In this work, a convenient and high-throughput colorimetric assay was developed on an aptamer-modified microchip for ultrasensitive detection of thrombin using rolling circle amplification and G-quadruplex DNAzyme. This system consisted of an aptamer-modified microchip and a secondary aptamer. The secondary aptamer contained a thrombin aptamer and a primer with a G-quadruplex circular template. RCA technology was used to improve the sensitivity by producing the multiple G-quadruplex units. To generate colorimetric signal, G-quadruplex DNAzyme was used to catalyze the H2O2-mediated oxidation of 2,2'-azinobis (3-ethylbenzothiozoline)-6-sulfonic acid. At the optimal conditions, the linear range for thrombin was 0.100-50.000 pg/mL, and the limit of detection was down to 0.083 pg/mL. Moreover, the developed method was successfully applied to detect thrombin from human plasma and serum, indicating that this approach has great potential in clinical diagnosis and medical investigation.

Activated protein C analog protects from ischemic stroke and extends the therapeutic window of tissue-type plasminogen activator in aged female mice and hypertensive rats

BACKGROUND AND PURPOSE

3K3A-activated protein C (APC) protects young, healthy male rodents after ischemic stroke. 3K3A-APC is currently under development as a neuroprotectant for acute ischemic stroke in humans. Stroke Therapy Academic Industry Roundtable recommends that after initial studies in young, healthy male animals, further studies should be performed in females, aged animals, and animals with comorbid conditions. Here, we studied the effects of delayed 3KA-APC therapy alone and with tissue-type plasminogen activator (tPA) in aged female mice and spontaneously hypertensive rats.

METHODS

We used Stroke Therapy Academic Industry Roundtable recommendations for ensuring good scientific inquiry. Murine recombinant 3K3A-APC (0.2 mg/kg) alone or with recombinant tPA (10 mg/kg) was given intravenously 4 hours after transient middle cerebral artery occlusion in aged female mice and rats and after embolic stroke in spontaneously hypertensive rat. 3K3A-APC was additionally administered within 3 to 7 days after stroke. The neuropathological analysis and neurological scores, foot-fault, forelimb asymmetry, and adhesive removal tests were performed within 7 and 28 days of stroke.

RESULTS

In all models, tPA alone had no effects on the infarct volume or behavior. 3K3A-APC alone or with tPA reduced the infarct volume 7 days after the middle cerebral artery occlusion in aged female mice and embolic stroke in spontaneously hypertensive rat by 62% to 66% and 50% to 53%, respectively, significantly improved (P<0.05) behavior, and eliminated tPA-induced intracerebral microhemorrhages. In aged female mice, 3K3A-APC was protective within 4 weeks of stroke.

CONCLUSIONS

3K3A-APC protects from ischemic stroke and extends the therapeutic window of tPA in aged female mice and in spontaneously hypertensive rat with a comorbid condition.

Thrombin-induced cerebral hemorrhage: role of protease-activated receptor-1

Thrombin causes blood-brain barrier disruption, and this study examined whether thrombin can cause brain hemorrhage through protease-activated receptor-1 (PAR-1). Male wild type and PAR-1 knockout mice had an intracerebral injection of thrombin or saline. Mice then underwent serial T2 magnetic resonance imaging and were euthanized for brain hemoglobin, iron, and interleukin-1β measurements. Thrombin caused massive T2 lesions and brain hemorrhage in wild type mice. These effects were markedly reduced in PAR-1 knockout mice. Thrombin also increased brain interleukin-1β, and this was absent in PAR-1 knockout mice. In conclusion, thrombin increases interleukin-1β levels and induces intracerebral hemorrhage through PAR-1 activation.

Quantitative detection of thrombin activity in an ischemic stroke model

Thrombin, a central factor in thrombogenesis, affects cells in the brain through protease activated receptors. Low levels of thrombin activity are neuroprotective while higher levels are deleterious, and we have therefore developed a new method for its direct quantitative measurement in brain slices following stroke. Thrombin activity was measured by a fluorescent substrate on fresh coronal slices taken from the ipsilateral and contralateral hemispheres 24-72 h following permanent right middle cerebral artery occlusion. Prolyl endopeptidase and aminopeptidases were inhibited as a critical step to insure the specificity of the assay for thrombin detection. Infarct volume was assessed using TTC staining. Thrombin activity in the right ischemic hemisphere was significantly higher compared to the contralateral hemisphere (32 ± 6 and 27 ± 10 mU/ml, mean ± SE in the two most affected slices from the ischemic hemisphere vs. 21 ± 6 and 8 ± 2 mU/ml in corresponding contralateral slices; p < 0.05). Thrombin levels in the ischemic and contralateral hemispheres were significantly higher compared to healthy control mice and were above the range known to be protective to brain cells. A significant correlation was found between thrombin activity in the ischemic hemisphere and the infarct volume. Results of studies based on this method may translate into potential thrombin based therapies.

Thrombin, a mediator of cerebrovascular inflammation in AD and hypoxia

Considerable evidence implicates hypoxia and vascular inflammation in Alzheimer's disease (AD). Thrombin, a multifunctional inflammatory mediator, is demonstrable in the brains of AD patients both in the vessel walls and senile plaques. Hypoxia-inducible factor 1α (HIF-1α), a key regulator of the cellular response to hypoxia, is also upregulated in the vasculature of human AD brains. The objective of this study is to investigate inflammatory protein expression in the cerebrovasculature of transgenic AD mice and to explore the role of thrombin as a mediator of cerebrovascular inflammation and oxidative stress in AD and in hypoxia-induced changes in brain endothelial cells. Immunofluorescent analysis of the cerebrovasculature in AD mice demonstrates significant (p < 0.01–0.001) increases in thrombin, HIF-1α, interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), matrix metalloproteinases (MMPs), and reactive oxygen species (ROS) compared to controls. Administration of the thrombin inhibitor dabigatran (100 mg/kg) to AD mice for 34 weeks significantly decreases expression of inflammatory proteins and ROS. Exposure of cultured brain endothelial cells to hypoxia for 6 h causes an upregulation of thrombin, HIF-1α, MCP-1, IL-6, and MMP2 and ROS. Treatment of endothelial cells with the dabigatran (1 nM) reduces ROS generation and inflammatory protein expression (p < 0.01–0.001). The data demonstrate that inhibition of thrombin in culture blocks the increase in inflammatory protein expression and ROS generation evoked by hypoxia. Also, administration of dabigatran to transgenic AD mice diminishes ROS levels in brain and reduces cerebrovascular expression of inflammatory proteins. Taken together, these results suggest that inhibiting thrombin generation could have therapeutic value in AD and other disorders where hypoxia, inflammation, and oxidative stress are involved.

The CXCR1/2 ligand NAP-2 promotes directed intravascular leukocyte migration through platelet thrombi

Thrombosis promotes leukocyte infiltration into inflamed tissues, leading to organ injury in a broad range of diseases; however, the mechanisms by which thrombi guide leukocytes to sites of vascular injury remain ill-defined. Using mouse models of endothelial injury (traumatic or ischemia reperfusion), we demonstrate a distinct process of leukocyte recruitment, termed "directed intravascular migration," specifically mediated by platelet thrombi. Single adherent platelets and platelet aggregates stimulated leukocyte shape change at sites of endothelial injury; however, only thrombi were capable of inducing directed intravascular leukocyte migration. Leukocyte recruitment and migration induced by platelet thrombi occurred most prominently in veins but could also occur in arteries following ischemia-reperfusion injury. In vitro studies demonstrated a major role for platelet-derived NAP-2 (CXCL-7) and its CXCR1/2 receptor in regulating leukocyte polarization and motility. In vivo studies demonstrated the presence of an NAP-2 chemotactic gradient within the thrombus body. Pharmacologic blockade of CXCR1/2 as well as genetic deletion of NAP-2 markedly reduced leukocyte shape change and intrathrombus migration. These studies define a distinct process of leukocyte migration that is initiated by homotypic adhesive interactions between platelets, leading to the development of an NAP-2 chemotactic gradient within the thrombus body that guides leukocytes to sites of vascular injury.

Thrombin regulation of synaptic plasticity: implications for physiology and pathology

Thrombin, a serine protease involved in the coagulation cascade has been recently shown to affect neuronal function following blood-brain barrier breakdown. Several lines of evidence have shown that thrombin may exist in the brain parenchyma under normal physiological conditions, yet its role in normal brain functions and synaptic transmission has not been established. In an attempt to shed light on the physiological functions of thrombin and Protease Activated Receptor 1 (PAR1) in the brain, we studied the effects of thrombin and a PAR1 agonist on long term potentiation (LTP) in mice hippocampal slices. Surprisingly, different concentrations of thrombin affect LTP through different molecular routes converging on PAR1. High thrombin concentrations induced an NMDA dependent, slow onset LTP, whereas low concentrations of thrombin promoted a VGCCs, mGluR-5 dependent LTP through activated Protein C (aPC). Remarkably, aPC facilitated LTP by activating PAR1 through an Endothelial Protein C Receptor (EPCR)-mediated mechanism which involves intracellular calcium stores. These findings reveal a novel mechanism by which PAR1 may regulate the threshold for synaptic plasticity in the hippocampus and provide additional insights into the role of this receptor in normal and pathological conditions.

PHLPP1 gene deletion protects the brain from ischemic injury

A recently discovered protein phosphatase PHLPP (PH domain Leucine-rich repeat Protein Phosphatase) has been shown to dephosphorylate Akt on its hydrophobic motif (Ser473) thereby decreasing Akt kinase activity. We generated PHLPP1 knockout (KO) mice and used them to explore the ability of enhanced in vivo Akt signaling to protect the brain against ischemic insult. Brains from KO mice subjected to middle cerebral artery occlusion (MCAO) for 2 hours showed significantly greater increases in Akt activity and less neurovascular damage after reperfusion than wild-type (WT) mice. Remarkably, infarct volume in the PHLPP1 KO was significantly reduced compared with WT (12.7±2.7% versus 22.9±3.1%) and this was prevented by Akt inhibition. Astrocytes from KO mice and neurons in which PHLPP1 was downregulated showed enhanced Akt activation and diminished cell death in response to oxygen-glucose deprivation. Thus, deletion of PHLPP1 can enhance Akt activation in neurons and astrocytes, and can significantly increase cell survival and diminish infarct size after MCAO. Inhibition of PHLPP could be a therapeutic approach to minimize damage after focal ischemia.

Concurrent middle cerebral artery occlusion and intra-arterial drug infusion via ipsilateral common carotid artery catheter in the rat

Pre-clinical development of therapy for acute ischemic stroke requires robust animal models; the rodent middle cerebral artery occlusion (MCAo) model using a nylon filament inserted into the internal carotid artery is the most popular. Drug screening requires targeted delivery of test substance in a controlled manner. To address these needs, we developed a novel method for delivering substances directly into the ischemic brain during MCAo in the awake rat. An indwelling catheter is placed in the common carotid artery ipsilateral to the occlusion at the time of the surgical placement of the occluding filament. The internal and common carotid arteries are left patent to allow superfusion anterograde. The surgeries can be completed quickly to allow rapid recovery from anesthesia; tests substances can be infused at any given time for any given duration. To simulate clinical scenarios, the occluding filament can be removed minutes or hours later (reperfusion) followed by therapeutic infusions. By delivering drug intra-arterially to the target tissue, "first pass" loss in the liver is reduced and drug effects are concentrated in the ischemic zone. To validate our method, rats were infused with Evans blue dye either intra-arterially or intravenously during a 4 h MCAo. After a 30 min reperfusion period, the dye was extracted from each hemisphere and quantitated with a spectrophotometer. Significantly more dye was measured in the ischemic hemispheres that received the dye intra-arterially.

Studies on the enantiomers of ZJM-289: synthesis and biological evaluation of antiplatelet, antithrombotic and neuroprotective activities

ZJM-289 is a potent racemic agent which inhibits both platelet aggregation and thrombosis superior to a known anti-ischemic stroke drug 3-n-butylphthalide (NBP). Herein, the enantiomers of ZJM-289, (S)-ZJM-289 and (R)-ZJM-289, were synthesized and evaluated for their biological activities. It was observed that the two enantiomers appeared to be almost as effective as ZJM-289 in inhibiting platelet aggregation in vitro and thrombus formation in vivo. Moreover, like ZJM-289, its enantiomers could regulate the ratio of thromboxane B(2) (TXB(2)) and 6-keto-prostaglandin F(1α), and enhanced levels of nitric oxide (NO), cAMP and cGMP, suggesting that the anti-platelet and antithrombotic activities of the enantiomers and ZJM-289 are associated with both the arachidonic acid cascade and cGMP-NO signal pathway. Furthermore, it was found that oral administration of the enantiomers and ZJM-289 for three days significantly reduced the infarct size, brain water content and neurological deficit in rats after cerebral ischemia reperfusion. Importantly, the two enantiomers equally improved blood flow in the ischemic stroke model and modulated endothelial function through releasing moderate levels of NO, which might, at least partially, contribute to their neuroprotection. Collectively, the present study demonstrates that the two enantiomers are as potent as ZJM-289 in inhibition of platelet aggregation and thrombosis and in neuroprotection, and (S)-ZJM-289 shows somewhat better effects than (R)-ZJM-289 and ZJM-289 in a few cases. These findings may provide new insights into the development of therapeutic agents like ZJM-289 for the intervention of thrombosis-related ischemic stroke.

PAR-1 antagonist SCH79797 ameliorates apoptosis following surgical brain injury through inhibition of ASK1-JNK in rats

Neurosurgical procedures inevitably produce intraoperative hemorrhage. The subsequent entry of blood into the brain parenchyma results in the release of large amounts of thrombin, a known contributor to perihematomal edema formation and apoptosis after brain injury. The present study seeks to test 1) the effect of surgically induced brain injury (SBI) on thrombin activity, expression of thrombin's receptor PAR-1, and PAR-1 mediated apoptosis; 2) the effect of thrombin inhibition by argatroban and PAR-1 inhibition by SCH79797 on the development of secondary brain injury in the SBI model on rats. A total of 88 Sprague-Dawley male rats were randomly divided into sham, vehicle-, argatroban-, or SCH79797-treated groups. SBI involved partial resection of the right frontal lobe under inhalation isoflurane anesthesia. Sham-operated animals received only craniotomy. Thrombin activity, brain water content, and neurological deficits were measured at 24 h following SBI. Involvement of the Ask1/JNK pathway in PAR-1-induced post-SBI apoptosis was characterized by using Ask1 or JNK inhibitors. We observed that SBI increased thrombin activity, yet failed to demonstrate any effect on PAR-1 expression. Argatroban and SCH79797 reduced SBI-induced brain edema and neurological deficits in a dose-dependent manner. SBI-induced apoptosis seemed mediated by the PAR-1/Ask1/JNK pathways. Administration of SCH79797 ameliorated the apoptosis following SBI. Our findings indicate that PAR-1 antagonist protects against secondary brain injury after SBI by decreasing both brain edema and apoptosis by inactivating PAR-1/Ask1/JNK pathway. The anti-apoptotic effect of PAR-1 antagonists may provide a promising path for therapy following SBI.

Thrombin activity associated with neuronal damage during acute focal ischemia

Mechanisms of ischemic neuronal and vascular injury remain obscure. Here we test the hypothesis that thrombin, a blood-borne coagulation factor, contributes to neurovascular injury during acute focal ischemia. Stroke was induced in adult Sprague Dawley rats by occluding the middle cerebral artery. Intra-arterial thrombin infusion during ischemia significantly increased vascular disruption and cellular injury. Intravenous infusion of argatroban, a direct thrombin inhibitor, alleviated neurovascular injury. Immunostaining showed thrombin on neurons in the ischemic core. Using an activatable cell-penetrating peptide engineered to detect thrombin activity, we discovered that thrombin proteolytic activity was specifically associated with neuronal damage during ischemia. Protease activated receptor-1, the presumptive thrombin receptor, appeared to mediate ischemic neurovascular injury. Furthermore, rats receiving thrombin during ischemia showed cognitive deficit, whereas rats receiving argatroban retained intact learning and memory. These results suggest a potential role for thrombin contributing to neurovascular injury and several potential avenues for neuroprotection.

Role of protease-activated receptor-1 in brain injury after experimental global cerebral ischemia

BACKGROUND AND PURPOSE

Evidence suggests that the protease-activated receptor-1 (PAR-1), a thrombin receptor, mediates neuronal injury in experimental cerebral ischemia. The present study investigated whether PAR-1 plays a role in brain injury after global cerebral ischemia.

METHODS

Adult male wild-type or PAR-1 knockout mice underwent a 20-minute bilateral common carotid artery occlusion or a sham operation. Behavior tests were performed before ischemia and 1, 2, and 3 days after bilateral common carotid artery occlusion. Mice were euthanized at different time points for thrombin activity, brain edema, Western blot analysis, and brain histology.

RESULTS

Thrombin activity and PAR-1 expression were increased in the brain after bilateral common carotid artery occlusion. Compared with wild-type mice, PAR-1 knockout mice had less brain edema formation, neuronal death, and behavior impairment after bilateral common carotid artery occlusion. In addition, bilateral common carotid artery occlusion-induced activation of mitogen-activated protein kinases was absent in PAR-1 knockout mice.

CONCLUSIONS

PAR-1 contributes to the brain injury induced by global cerebral ischemia, which may be related to activation of mitogen-activated protein kinases.

Tissue plasminogen activator induced delayed edema in experimental porcine intracranial hemorrhage: reduction with plasminogen activator inhibitor-1 administration

Hematoma puncture and subsequent clot lysis with recombinant tissue plasminogen activator (rtPA) emerged as an alternative therapy for spontaneous intracerebral hemorrhage (ICH) and is associated with delayed edema possibly counteracting the beneficial effects of hematoma volume reduction. We hypothesized that immediate reversal of rtPA activity after clot lysis and hematoma drainage diminishes edema formation. To test this hypothesis, we administered plasminogen activator inhibitor (PAI)-1 after rtPA lysis of experimentally induced ICH. A right frontal ICH was placed through a twist drill burr hole and autologous blood injection. Following creation of the frontal ICH, pigs received no further treatment (n = 5), lysis with rtPA (n = 7), or lysis with rtPA followed by administration of PAI-1 (n = 6). Hematoma and edema volumes were assessed with magnetic resonance imaging on days 0, 4, and 10. The rtPA significantly reduced hematoma volume and contributed to edema on day 10 after experimentally induced ICH. Administration of PAI-1 attenuated the rtPA-induced edema volume on day 10, but the hematoma volume reduction was less pronounced. In conclusion, PAI-1 attenuated delayed cerebral edema after rtPA lysis of experimental ICH but also reduced the lytic activity of rtPA. The combination of rtPA clot lysis with PAI-1 might have the potential to further improve the effect of the lytic therapy of ICH, but additional studies to define the optimum time point for PAI-1 administration are required.

Thrombin induces an inflammatory phenotype in a human brain endothelial cell line

In this study, we utilized the human brain endothelial cell line, hCMEC/D3, to determine the effects of the coagulation factor, thrombin, on the human blood-brain barrier (BBB). We show that thrombin increased the mRNA and cell surface levels of ICAM-1 and VCAM-1 in hCMEC/D3 cells. Thrombin similarly upregulated several chemokines implicated in human neurological conditions. Additionally, the paracellular permeability of the human BBB in vitro was also increased following thrombin treatment. Overall, this study demonstrates that thrombin can effectively induce an inflamed phenotype in an in vitro human BBB.

Introduction to haemostasis from a pharmacodynamic perspective

Biochemical characterization of the haemostatic system has advanced significantly in the past decades. Sub-systems, such as coagulation, fibrinolysis, blood cells and platelets and the vessel wall have been studied by specialists, mostly separately and independently. The time has come to integrate the approaches, and, in particular, to develop tests to document the state of the whole system and to have available adequate pharmacodynamic tests to evaluate treatments. Many examples are available to show that traditional general methods of clotting and lysis do not provide the information that is desired. The present tendency is to use specific methods for specific factors or effects which are very limited in pharmacological information. There is also increasing awareness of the occurrence of rather broad interindividual variability in the haemostatic system. This suggests that individually tailored treatments are required. This is the more relevant since haemostasis is a balance and treatment should be positioned between efficacy and safety. The conclusion is reached that there is a need for integrated or global methods or sets of methods that reflect the complexity and individual status appropriately and allow the practitioner to judge the effects of interventions and their individual aspects.

Linking inflammation and coagulation: novel drug targets to treat organ ischemia

PURPOSE OF REVIEW

Activation of the coagulation system during ischemia/reperfusion injury is an unavoidable event and even further augmented during cardiovascular surgery. Clotting not only leads to disturbance of blood rheology but also enhances the inflammatory response. We aim to highlight the inflammatory properties of the coagulation system and novel potential therapeutic approaches targeting both features.

RECENT FINDINGS

Heparin, a thrombin inhibitor, is still the drug of choice for preventing coagulation following, for example, cardiovascular surgery. On the contrary, much effort is done to evaluate the utilization of direct thrombin inhibitors to prevent ischemia/reperfusion injury. Furthermore, targeting the inflammatory potential of the coagulation system seems to be very promising. Fibrin(ogen) and its degradation products modulate the inflammatory response, especially by inducing leukocyte migration. Inhibiting these pro-inflammatory effects, for example, by administration of Bβ15-42 was recently shown to be beneficial under various inflammatory conditions.

SUMMARY

Ischemia and reperfusion are common activators of coagulation that is also accompanied by inflammation. Therefore, targeting this well orchestrated system might be of therapeutic benefit, as its mode of action is dual: clotting inhibition and anti-inflammation. This novel therapeutic approach might at least be of benefit in the treatment of systemic inflammatory syndromes following, that is, cardiovascular surgery.

Neurovascular pathways to neurodegeneration in Alzheimer's disease and other disorders

The neurovascular unit (NVU) comprises brain endothelial cells, pericytes or vascular smooth muscle cells, glia and neurons. The NVU controls blood-brain barrier (BBB) permeability and cerebral blood flow, and maintains the chemical composition of the neuronal 'milieu', which is required for proper functioning of neuronal circuits. Recent evidence indicates that BBB dysfunction is associated with the accumulation of several vasculotoxic and neurotoxic molecules within brain parenchyma, a reduction in cerebral blood flow, and hypoxia. Together, these vascular-derived insults might initiate and/or contribute to neuronal degeneration. This article examines mechanisms of BBB dysfunction in neurodegenerative disorders, notably Alzheimer's disease, and highlights therapeutic opportunities relating to these neurovascular deficits.

Central nervous system pericytes in health and disease

Pericytes are uniquely positioned within the neurovascular unit to serve as vital integrators, coordinators and effectors of many neurovascular functions, including angiogenesis, blood-brain barrier (BBB) formation and maintenance, vascular stability and angioarchitecture, regulation of capillary blood flow and clearance of toxic cellular byproducts necessary for proper CNS homeostasis and neuronal function. New studies have revealed that pericyte deficiency in the CNS leads to BBB breakdown and brain hypoperfusion resulting in secondary neurodegenerative changes. Here we review recent progress in understanding the biology of CNS pericytes and their role in health and disease.

Thrombin as a multi-functional enzyme. Focus on in vitro and in vivo effects

Thrombin is the central protease in the coagulation cascade and one of the most extensively studied of all enzymes. In addition to its recognised role in the coagulation cascade and haemostasis, thrombin is known to have multiple pleiotropic effects, which mostly have been shown only in in vitro studies: it plays a role in inflammation and cellular proliferation and displays a mitogen activity on smooth muscle cells and endothelial cells, predominantly by activation of angiogenesis. In vivo , thrombin effects were examined in animal models of intravenous or intraarterial thrombin infusion. An extensive literature search regarding in vivo data showed that i) thrombin administered as a bolus causes microembolism, ii) thrombin infused slowly at steady-state conditions (up to 1.6 U/kg/min) leads to bleeds but not to intravascular clotting, iii) large quantity of thrombin infused at low rates (0.05 U/kg/min) does not have any measurable effect, and iv) thrombin increases vascular permeability leading to tissue damage. Although several decades of research on thrombin functions have provided a framework for understanding the biology of thrombin, animal and human studies with use of newer laboratory techniques are still needed to confirm the pleiotropic thrombin functions shown in in vitro studies.