Thrombin inhibitor ameliorates secondary damage in rat brain injury: suppression of inflammatory cells and vimentin-positive astrocytes

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.

Therapeutic Anticoagulation with Argatroban and Heparins Reduces Granulocyte Migration: Possible Impact on ECLS-Therapy?

Introduction

Anticoagulants such as argatroban and heparins (low-molecular-weight and unfractionated) play an immense role in preventing thromboembolic complications in clinical practice. Nevertheless, they can also have a negative effect on the immune system. This study is aimed at investigating the influence of these substances on polymorphonuclear neutrophils (PMNs), whose nonspecific defense mechanisms can promote thrombogenesis.

Methods

Blood samples from 30 healthy volunteers were investigated, whereby PMNs were isolated by density gradient centrifugation and incubated with 0.8 μg/mL of argatroban, 1.0 U/mL of low-molecular-weight heparin (LMWH), 1.0 U/mL of unfractionated heparin (UFH), or without drug (control). A collagen-cell mixture was prepared and filled into 3D μ-slide chemotaxis chambers (IBIDI® GmbH, Germany). Stimulation was initiated by using a chemokine gradient of n-formyl-methionine-leucyl-phenylalanine (fMLP), and microscopic observation was conducted for 4.5 hours. The cells' track length and track straightness, as well as the number of attracted granulocytes, level of ROS (reactive oxygen species) production, and NET (neutrophil extracellular traps) formation, were analyzed and categorized into migration distances and time periods.

Results

All three anticoagulants led to significantly reduced PMN track lengths, with UFH having the biggest impact. The number of tracks observed in the UFH group were significantly reduced compared to the control group. Additionally, the UFH group demonstrated a significantly lower track straightness compared to the control. ROS production and NET formation were unaffected.

Conclusion

Our data provide evidence that anticoagulants have an inhibitory effect on the extent of PMN migration and chemotactic migration efficiency, thus indicating their potential immune-modulatory and prothrombotic effects.

The action of thrombin in intracerebral hemorrhage induced brain damage is mediated via PKCα/PKCδ signaling

The present study investigates the role of protein kinase C alpha/delta (PKCα/PKCδ) in brain injury induced by intracerebral hemorrhage (ICH) by utilizing a rat model that received intracerebral injections of autologous blood and thrombin (TM). The activation and expression of PKC and PKCδ were analyzed by Western blot and immunohistochemistry. A PKC inhibitor, dihydrochloride (H7), was administrated intraperitoneally after injury to evaluate the effect of inhibition of PKC on ICH and TM induced brain damage. Our data indicate that both ICH and TM increased the expression of PKCα/PKCδ in the brain tissue, and PKCα expression peaked at 6h, while PKCδ expression reached its maximum value at 72h post-injury. Administration of H7 significantly reduced the inflammatory cells infiltrate, permeability of brain-blood barrier (BBB), brain edema, and neuronal death. We conclude that both PKCα and PKCδ play important roles in ICH and TM-induced brain injury, and dihydrochloride (H7) can attenuate brain damage after ICH.

Serum inflammatory adhesion molecules and high-sensitivity C-reactive protein correlates with delayed ischemic neurologic deficits after subarachnoid hemorrhage

BACKGROUND

The purpose of the present study was to investigate the relationship between serum concentrations of the immunoglobulin-like superfamily, selectins, hsCRP, and the development of DIND in patients with aneurysmal SAH.

METHODS

Serum ICAM-1, VCAM-1, E-selectin, P-selectin, L-selectin, and hsCRP were measured in 33 patients with SAH who underwent aneurysmal clipping within 48 hours of the onset of symptoms. Serum samples were obtained during the early period (day 0) and the late period (day 7).

RESULTS

The serum concentrations of ICAM-1 (P = .009), VCAM-1 (P = .0383) and hsCRP (P = .0014) during the early period were significantly higher in patients with SAH than in control patients. Further, serum hsCRP concentration during the late period was significantly higher in patients with SAH than in control patients (P = 0033). Finally, serum concentrations of ICAM-1, VCAM-1, and hsCRP during the early (P = .0055, P = .0266, and P = .0266) and late (P = .0423, P = .0041, and P = .0004) period were significantly higher in patients with DIND than in patients without DIND.

CONCLUSIONS

Serum levels of ICAM-1, VCAM-1 and hsCRP during the early and late period following SAH correlate with DIND.

Antiinflammatory and neuroprotective actions of COX2 inhibitors in the injured brain

Overexpression of COX2 appears to be both a marker and an effector of neural damage after a variety of acquired brain injuries, and in natural or pathological aging of the brain. COX2 inhibitors may be neuroprotective in the brain by reducing prostanoid and free radical synthesis, or by directing arachidonic acid down alternate metabolic pathways. The arachidonic acid shunting hypothesis proposes that COX2 inhibitors' neuroprotective effects may be mediated by increased formation of potentially beneficial eicosanoids. Under conditions where COX2 activity is inhibited, arachidonic acid accumulates or is converted to eicosanoids via lipoxygenases and cytochrome P450 (CYP) epoxygenases. Several P450 eicosanoids have been demonstrated to have beneficial effects in the brain and/or periphery. We suspect that arachidonic acid shunting may be as important to functional recovery after brain injuries as altered prostanoid formation per se. Thus, COX2 inhibition and arachidonic acid shunting have therapeutic implications beyond the suppression of prostaglandin synthesis and free radical formation.

Effects of Recombinant Activated Factor VII in Traumatic Nonsurgical Intracranial Hemorrhage

OBJECTIVE

To determine whether treatment with recombinant activated factor VII (rFVIIa) will prevent progression of bleeding in nonsurgical hemorrhagic traumatic brain injury (TBI).

METHODS

Chart review from the trauma registry of a level 1 trauma center between January 1, 2002 and December 31, 2004 identified 2 patients who received rFVIIa for progressive hemorrhagic TBI. These patients were given a single dose of rFVIIa (120 mcg/kg) after a repeat head computed tomography (CT) scan showed worsening of intracranial bleeding. Pre-rFVIIa and post-rFVIIa coagulation parameters and postintervention CT scans were performed. A matched convenience sample was drawn from the institution's trauma registry reflecting similar injury patterns.

RESULTS

The 2 patients who received rFVIIa were ages 61 and 79 years; the patients in the matched convenience sample were 57 and 63 years. Both sets of patients comprised 1 man and 1 woman who had suffered blunt trauma, including hemorrhagic TBI, and were matched according to age, gender, and injury severity score (ISS). During their hospital course, repeat CT scans documented worsening of intracranial hemorrhage in both cohorts. In the rFVIIa patients, follow-up CT showed overall improvement of head injury compared with the convenience sample. The rFVIIa patients also saw an appreciable decrease in both prothrombin time (PT) and international normalized ratio (INR).

CONCLUSIONS

In hemorrhagic TBI, rFVIIa has the potential to limit or even halt the progression of bleeding that would otherwise place growing pressure on the brain. A prospective, randomized multicenter trial is planned to elucidate this hypothesis.

The injury response of oligodendrocyte precursor cells is induced by platelets, macrophages and inflammation-associated cytokines

Oligodendrocyte precursor cells recognized with the NG2 antibody respond rapidly to CNS injuries with hypertrophy and upregulation of the NG2 chondroitin sulfate proteoglycan within 24 h. These cells participate in glial scar formation, remaining around the injury site for several weeks. After injury, reactive oligodendrocyte precursor cells increase their production of several chondroitin sulfate proteoglycans, including NG2: this cell type thus represents a component of the inhibitory environment that prevents regeneration of axons in the injured CNS. This study analyzes factors that activate oligodendrocyte precursor cells. Both microglia and astrocytes become reactive around motor neurons following peripheral nerve lesions. We show that oligodendrocyte precursor cells do not hypertrophy or increase NG2 levels after these lesions. Those lesions that cause an oligodendrocyte precursor cell reaction generally open the blood-brain barrier. We therefore opened the blood-brain barrier with microinjections of vascular endothelial growth factor or lipopolysaccharide to the rat and mouse brain, and examined oligodendrocyte precursor cell reactivity after 24 h. Both treatments led to increases in NG2 and hypertrophy of oligodendrocyte precursor cells. Of directly injected blood components serum and thrombin were without effect, while platelets and macrophages activated oligodendrocyte precursor cells. We tested the effects of a range of injury-related cytokines, of which tumor necrosis factor alpha; interleukin-1; transforming growth factor beta; interferon gamma had effects on oligodendrocyte precursor cells. Oligodendrocyte precursor cell chemokines, and mitogens did not increase NG2 levels.

Does thrombin play a role in the pathogenesis of brain damage after periventricular hemorrhage?

Neonatal periventricular hemorrhage (PVH) is a devastating complication of prematurity in the human infant. Based upon observations made primarily in adult rodents and the fact that the immature brain uses proteolytic systems for cell migration and growth, we hypothesized that thrombin and plasmin enzyme activities contribute to the brain damage after PVH. The viability of mixed brain cells derived from newborn rat periventricular region was suppressed by whole blood and thrombin, but not plasmin. Following injection of autologous blood into the periventricular region of newborn rat brain, proteolytic activity was detected in a halo around the hematoma using membrane overlays impregnated with thrombin and plasmin fluorogenic substrates. Two-day old rats received periventricular injection of blood, thrombin, and plasminogen. After 2 days, thrombin and blood were associated with significantly greater damage than saline or plasminogen. Two-day old mice received intracerebral injections of blood in combination with saline or the proteolytic inhibitors hirudin, alpha2macroglobulin, or plasminogen activator inhibitor-1. After 2 days, hirudin significantly reduced brain cell death and inflammation. Two-day-old mice then received low and high doses of hirudin mixed with blood after which behavioral testing was conducted repeatedly. At 10 weeks there was no statistically significant evidence for behavioral or structural brain protection. These results indicate that thrombin likely plays a role in neonatal periventricular brain damage following PVH. However, additional factors are likely important in the recovery from this result.

Priorities for clinical research in intracerebral hemorrhage: report from a National Institute of Neurological Disorders and Stroke workshop

BACKGROUND AND PURPOSE

Spontaneous intracerebral hemorrhage (ICH) is one of the most lethal stroke types. In December 2003, a National Institute of Neurological Disorders and Stroke (NINDS) workshop was convened to develop a consensus for ICH research priorities. The focus was clinical research aimed at acute ICH in patients.

METHODS

Workshop participants were divided into 6 groups: (1) current state of ICH research; (2) basic science; and (3) imaging, (4) medical, (5) surgical, and (6) clinical methodology. Each group formulated research priorities before the workshop. At the workshop, these were discussed and refined.

RESULTS

Recent progress in management of hemorrhage growth, intraventricular hemorrhage, and limitations in the benefit of open craniotomy were noted. The workshop identified the importance of developing animal models to reflect human ICH, as well as the phenomena of rebleeding. More human ICH pathology is needed. Real-time, high-field magnets and 3-dimensional imaging, as well as high-resolution tissue probes, are ICH imaging priorities. Trials of acute blood pressure-lowering in ICH and coagulopathy reversal are medical priorities. The exact role of edema in human ICH pathology and its treatment requires intensive study. Trials of minimally invasive surgical techniques including mechanical and chemical surgical adjuncts are critically important. The methodologic challenges include establishing research networks and a multi-specialty approach. Waiver of consent issues and standardizing care in trials are important issues. Encouragement of young investigators from varied backgrounds to enter the ICH research field is critical.

CONCLUSIONS

Increasing ICH research is crucial. A collaborative approach is likely to yield therapies for this devastating form of brain injury.

Effect of Vimentin on Reactive Gliosis:In VitroandIn VivoAnalysis

Reactive gliosis is a prominent result of many types of insult to the central nervous system (CNS) and leads to the formation of glial scar that impedes the regeneration of axons. The intermediate filament protein vimentin is found in pathology of the CNS, mainly in the vicinity of injuries to the CNS. In the present study we investigated the role of vimentin in the formation of glial scars in vitro and in vivo by using immunohistochemistry, Western blot analysis, and in situ hybridization. In vitro experiments showed that the intensity of immunofluorescent labeling for vimentin and glial fibrillary acidic protein (GFAP) was consistently decreased in astrocytes after transfection with a retrovirus carrying antisense complementary DNA (cDNA) for vimentin. Transfection also inhibited the growth of astrocytes and decreased the expression of vimentin mRNA. In vivo studies demonstrated that transfection with the retrovirus carrying the antisense cDNA vimentin inhibited the upregulation of vimentin and GFAP in stab wounds in rat cerebrum. These results suggest that vimentin may play a key role in the formation of glial scars in the CNS.

Cerebral microvessel responses to focal ischemia

Cerebral microvessels have a unique ultrastructure form, which allows for the close relationship of the endothelium and blood elements to the neurons they serve, via intervening astrocytes. To focal ischemia, the cerebral microvasculature rapidly displays multiple dynamic responses. Immediate events include breakdown of the primary endothelial cell permeability barrier, with transudation of plasma, expression of endothelial cell-leukocyte adhesion receptors, loss of endothelial cell and astrocyte integrin receptors, loss of their matrix ligands, expression of members of several matrix-degrading protease families, and the appearance of receptors associated with angiogenesis and neovascularization. These events occur pari passu with neuron injury. Alterations in the microvessel matrix after the onset of ischemia also suggest links to changes in nonvascular cell viability. Microvascular obstruction within the ischemic territory occurs after occlusion and reperfusion of the feeding arteries ("focal no-reflow" phenomenon). This can result from extrinsic compression and intravascular events, including leukocyte(-platelet) adhesion, platelet-fibrin interactions, and activation of coagulation. All of these events occur in microvessels heterogeneously distributed within the ischemic core. The panorama of acute microvessel responses to focal cerebral ischemia provide opportunities to understand interrelationships between neurons and their microvascular supply and changes that underlie a number of central nervous system neurodegenerative disorders.

Delayed argatroban treatment reduces edema in a rat model of intracerebral hemorrhage

BACKGROUND AND PURPOSE

Studies indicate that thrombin plays an important role in intracerebral hemorrhage (ICH)-induced edema formation. Although thrombin is produced as the blood clots, it may be bound to fibrin and only gradually released from the clot. The time window for administration of a thrombin inhibitor to reduce ICH-induced edema is unknown. Whether this time window extends beyond the period when a thrombin inhibitor might exacerbate rebleeding is also unknown.

METHODS

This study examines (1) whether argatroban, an inhibitor of both free and fibrin-bound thrombin, can reduce edema formation after intracerebral infusion of 100 micro L of blood in the rat; (2) the therapeutic time window for argatroban; and (3) whether argatroban promotes rebleeding in a model in which ICH was induced by intracerebral injection of collagenase.

RESULTS

Intracerebral infusion of blood caused a marked increase in perihematomal water content. Intracerebral injection of argatroban 3 hours after ICH caused a significant reduction in edema measured at 48 hours (80.9+/-1.0% versus 82.6+/-0.8%; P<0.01). The systemic administration of high-dose argatroban (0.9 mg/h) starting 6 hours after ICH also significantly reduced edema (80.3+/-1.1% versus 82.0+/-1.3% in vehicle controls; P<0.05). There was no protection when the onset of argatroban administration was delayed to 24 hours after ICH or if a lower dose of argatroban (0.3 mg/h) was used. Argatroban did not increase collagenase-induced hematoma volume when given into the clot after 3 hours or given systemically at 6 hours.

CONCLUSIONS

Our data suggest that argatroban may be an effective therapy for ICH-induced edema.

Signal transduction through tyrosine-phosphorylated carboxy-terminal fragments of APP via an enhanced interaction with Shc/Grb2 adaptor proteins in reactive astrocytes of Alzheimer's disease brain

The processing of the amyloid precursor protein (APP) through the formation of C-terminal fragments (CTFs) and the production of beta-amyloid, are events likely to influence the development and the progression of Alzheimer's disease (AD). APP is a transmembrane protein similar to a cell-surface receptor with the intraluminal NPTY motif in the cytosolic C terminus. Although APP holoprotein can be bound to intracellular proteins like Fe65, X11, and mDab, the ultimate function and the mechanisms through which this putative receptor transfers its message are unclear. Here it is shown that in human brain, a subset of tyrosine-phosphorylated CTFs represent docking sites for the adaptor protein ShcA. ShcA immunoreactivity is greatly enhanced in Alzheimer's patients; it is mainly localized to glial cells and occurs at reactive astrocytes surrounding cerebral vessels and amyloid plaques. Grb2 also is involved in complexes with ShcA and tyrosine-phosphorylated CTFs, and in AD brain the interaction between Grb2-ShcA and CTFs is enhanced. Also, a higher amount of phospho-ERK1,2 is present in AD brain in comparison with control cases, likely as a result of the ShcA activation. In vitro experiments show that the ShcA-CTFs interaction is strictly confined to glial cells when treated with thrombin, which is a well-known ShcA and ERK1,2 activator, mitogen, and regulator of APP cleavage. In untreated cells ShcA does not interact with either APP or CTFs, although they are normally produced. Altogether these data suggest that CTFs are implicated in cell signaling via Shc transduction machinery, likely influencing MAPK activity and glial reaction in AD patients.

Signal transduction through tyrosine-phosphorylated C-terminal fragments of amyloid precursor protein via an enhanced interaction with Shc/Grb2 adaptor proteins in reactive astrocytes of Alzheimer's disease brain

The proteolytic processing of amyloid precursor protein (APP) through the formation of membrane-bound C-terminal fragments (CTFs) and of soluble beta-amyloid peptides likely influences the development of Alzheimer's disease (AD). We show that in human brain a subset of CTFs are tyrosine-phosphorylated and form stable complexes with the adaptor protein ShcA. Grb2 is also part of these complexes, which are present in higher amounts in AD than in control brains. ShcA immunoreactivity is also greatly enhanced in patients with AD and occurs at reactive astrocytes surrounding cerebral vessels and amyloid plaques. A higher amount of phospho-ERK1,2, likely as result of the ShcA activation, is present in AD brains. In vitro experiments show that the ShcA-CTFs interaction is strictly confined to glial cells when treated with thrombin, which is a well known ShcA and ERK1,2 activator and a regulator of APP cleavage. In untreated cells ShcA does not interact with either APP or CTFs, although they are normally generated. Altogether these data suggest that CTFs are implicated in cell signaling via Shc transduction machinery, likely influencing MAPK activity and glial reaction in AD patients.

Thrombin and PAR-1 activating peptide increase iNOS expression in cytokine-stimulated C6 glioma cells

Thrombin (THR) plays a key role in the brain under physiological and pathological conditions. Several of the biological activities of thrombin have been shown to be mainly driven through activation of protease-activated receptor-1 (PAR-1)-type thrombin receptor. Here we have studied the effect of THR and PAR-1-activating peptide (PAR1-AP), SFLLRN, on cytokine-induced expression of inducible nitric oxide (iNOS), a prominent marker of astroglial activation using the rat C6 glioma cells. In this cell line, THR (1-10 U/mL) and PAR1-AP (1-100 microM) induced a significant concentration-dependent increase both of IFN-gamma- (250 U/mL) or TNF-alpha- (500 U/mL) induced NO release. The observed increase of NO production was related to an enhancement of iNOS expression as measured in cell lysates prepared from different treatments by using SDS-PAGE followed by western blot analysis. The effect of THR, but not that of PAR1-AP, was significantly inhibited by hirulog(TM) (60 microg/mL), a specific and stochiometric THR inhibitor or by cathepsin-G (40 mU/mL), an inhibitor of PAR-1. In conclusion our data suggest a role for THR through activation of PAR-1 in the induction of astroglial iNOS, and further support the hypothesis that THR may function as an important pathophysiological modulator of the inflammatory response.

Acute tissue damage after injections of thrombin and plasmin into rat striatum

BACKGROUND AND PURPOSE

Extravasation of blood is associated with intracerebral hemorrhage and head trauma. The mechanism of brain cell injury associated with hemorrhage differs from that due to pure ischemia. The purpose of this study was to investigate the acute changes after intracerebral injections of proteins that are involved in blood clotting and clot lysis.

METHODS

Sixty-eight adult rats were subjected to stereotaxic intrastriatal injections of normal saline (5 microL), low- (2.5 U/5 microL) and high-dose (25 U/5 microL) thrombin, low- (0.1 microgram/5 microL) and high-dose (1 microgram/5 microL) tissue plasminogen activator, low- (0.05 U/5 microL) and high-dose (0.5 U/5 microL) plasminogen, and low- (0.335 U/5 microL) and high-dose (3.35 U/5 microL) plasmin. Forty-eight hours later rats were perfusion fixed. Brain damage area, eosinophilic neurons, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL)-positive cells, infiltrating neutrophils, CD8a immunoreactive leukocytes, and reactive microglia were quantified.

RESULTS

Damage area in striatum, dying cells, inflammatory cells, and microglial reaction were significantly greater after the high-dose plasminogen, plasmin, and thrombin injections. Tissue plasminogen activator injections were associated with mild inflammation.

CONCLUSIONS

These results suggested that thrombin and plasmin are harmful to brain cells in vivo. Although the doses required to cause damage are relatively great in consideration of the plasma content of these proteins, their pathological effect might be enhanced through synergism with other mechanisms.

Thrombin attenuation is neuroprotective in the injured rat optic nerve

The functional loss that often follows injury of the mammalian CNS has been attributed not only to the immediate neural loss, but also to secondary neuronal degeneration caused by toxic biochemical mediators in the environment of the injured nerve. We report here that a high thrombin content, produced as a result of injury-induced activation of prothrombin, appears to be an important mediator of secondary damage. Measurement of post-traumatic neuronal survival in vivo revealed that post-traumatic local application of the thrombin inhibitor N-alpha-(2-naphthylsulphonylglycyl)-4-(D,L)-amidinophenylalanine piperidide acetate in the rat optic nerve subjected to mild partial crush injury left twice as many retinal ganglion cells with functioning axons as in controls. Thus, by readjusting thrombin activity, thereby possibly obtaining a moderate post-traumatic increase and thus gaining the benefit of thrombin without its toxic effects, it may be possible to create an environment that is more favourable for post-traumatic survival.