The role of thrombin and thrombin receptors in ischemic, hemorrhagic and traumatic brain injury: deleterious or protective?

Thrombin enhances glioma growth

BACKGROUND

Our previous studies have demonstrated that argatroban, a specific thrombin inhibitor, reduces brain edema and neurological deficits in rat glioma models. The present study investigated whether or not thrombin enhances glioma growth in vivo and in vitro.

METHODS

There were two parts in this study. In the first part, rat C6 glioma cells were treated with or without thrombin. These cells were then injected into the right caudate of adult male Fischer 344 rats. Rats underwent behavioral testing prior to sacrifice 12 days later for tumor mass measurement. In the second part, C6 cells were incubated in serum-free medium for 24 hours and then treated with thrombin with or without argatroban, a thrombin inhibitor. DNA synthesis was examined using a 5-bromo-2'-deoxyuridine (BrdU) ELISA kit. Cell proliferation was determined using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay.

FINDINGS

Treatment of C6 cells with thrombin prior to intracerebral implantation resulted in a larger tumor mass and worse neurological deficits at dayl2. In vitro, thrombin increased DNA synthesis in C6 glioma cells, and this effect was blocked by argatroban. MTT assay showed that thrombin significantly increased glioma cell proliferation in vitro.

CONCLUSIONS

In summary, thrombin enhances C6 glioma growth in vivo and cell proliferation in vitro suggesting that thrombin may be a target of glioma therapy.

Concomitant intracerebral infusion of tissue plasminogen activator and thrombin leads to brain injury

Low doses of thrombin are neuroprotective while high doses are neurotoxic and lead to brain injury. However, evidence suggests that low doses of thrombin cause brain injury when infused concomitantly with tissue plasminogen activator (tPA), which is used clinically to facilitate evacuation of intracerebral hematomas. In this study, we examined the effects of intracerebral infusion of tPA and thrombin, individually and in combination. Rats were infused in the right basal ganglia with 50 microL saline solutions containing thrombin, tPA, or thrombin + tPA. In the first experiment, rats were used for blood-brain barrier (BBB) permeability measurements at 24 h after infusion. In the second experiment, animals were euthanized 3 days after infusion, and brain sections were stained with Fluoro-Jade to measure neuronal cell death. Behavioral tests were carried out before and after surgery. Infusion of thrombin + tPA markedly increased Evans blue tissue content in ipsilateral brain samples (p < 0.05). Fluoro-Jade-stained sections from thrombin + tPA group demonstrated significantly higher cell death counts (p < 0.01). Significant neurological deficit was revealed in thrombin + tPA group in forelimb-placing and corner-turn tests (p < 0.01). This study shows that tPA potentiates the neurotoxic effects of thrombin and leads to increased BBB permeability, neuronal cell death, and neurological deficit. Our results suggest that using tPA to lyse intracerebral hematomas has potential to produce neuronal cell death and disruption of BBB.

Hyperbaric oxygen preconditioning activates ribosomal protein S6 kinases and reduces brain swelling after intracerebral hemorrhage

BACKGROUND

New protein synthesis is key to ischemic tolerance induced by preconditioning and ribosomal protein S6 kinases (p70 S6 K) are important enzymes in protein synthesis. Hyperbaric oxygen preconditioning (HBOP) reduces ischemic brain damage. This study investigated if HBOP can activate p70 S6 K and increase new protein synthesis and if HBOP induces brain tolerance against brain swelling after intracerebral hemorrhage (ICH).

METHODS

There were two parts of the studies. 1) Rats received five consecutive sessions of HBOP. Twenty-four hours after HBOP, the rats had an ICH and were sacrificed one or three days later for brain edema measurement. 2) Rats received five sessions of HBOP or control pretreatment and were sacrificed for Western blot analysis and immunohistochemistry of activated p70 S6 K and heme oxygenase-1 (HO-1).

FINDINGS

Five sessions of HBOP significantly reduced brain edema in the ipsilateral basal ganglia after ICH. Western blot analysis showed that HBOP activated p70 S6 K and increased HO-1 levels in the basal ganglia. Strong activated p70 S6 K immunoreactivity was also found in the basal ganglia.

CONCLUSIONS

Our results suggest activation of p70 S6 K may have a role in heat shock protein synthesis after HBOP and may contribute to HBOP-induced brain protection.

PKC and Rho in vascular smooth muscle: activation by BOXes and SAH CSF

Cerebral vasospasm (CV) remains a significant cause of delayed neurological deficit and ischemic damage after subarachnoid hemorrhage (SAH), despite intensive research effort. The current lack of an effective therapeutic approach is somewhat due to our lack of understanding regarding the mechanism by which this pathological constriction develops. Recent evidence implicates bilirubin oxidation products (BOXes) in the etiology of CV after SAH: BOXes are found in cerebrospinal fluid from SAH patients with symptomatic or angiographically visible vasospasm (CSFV) but not in CSF from SAH patients with no vasospasm (CSFC). We have previously published research suggesting that the etiology of CV comprises two components: a physiological stimulation to constrict and a pathological failure to relax. Both these components are elicited by CSFV, but not CSFC, and BOXes synthesized in the laboratory potentiate physiological constriction in arterial smooth muscle in vitro, and elicit contraction in pial arteries in vivo. In this paper, we will present our results concerning the action of BOXes on arterial smooth muscle constriction, compared with CSFV. We will also present evidence implicating temporal changes in PKC isoforms and Rho expression in both BOXes- and CSFV-elicited smooth muscle responses.

Activation of protease-activated receptors in astrocytes evokes a novel neuroprotective pathway through release of chemokines of the growth-regulated oncogene/cytokine-induced neutrophil chemoattractant family

Activation of protease-activated receptors (PARs) is known to exert neuroprotection when low concentrations of the agonist protease thrombin are applied. However, the mechanism of protection is still unclear. Here, we showed that activation of multiple PARs, including PAR-1, PAR-2 and PAR-4, was able to elevate the release of the chemokine cytokine-induced neutrophil chemoattractant (CINC)-3 from rat astrocytes, in addition to evoking CINC-1 secretion. Different molecular mechanisms were identified as being involved in the secretion of CINC-1 and CINC-3, upon activation of different PARs. Importantly, we found that both CINC-1 and CINC-3 could signal to rat cortical neurons. Both chemokines acted via CXCR2 to prevent C2-ceramide-induced cytochrome c release from mitochondria. Consequently CINC-1 and CINC-3 protected neurons from apoptosis. We further revealed that conditioned media obtained from PAR-activated astrocytes similarly protected cortical neurons against C2-ceramide-induced cell death. The neuroprotection was considerably suppressed by a CXCR2 antagonist. CXCR2 is the cognate receptor for CINC. Therefore, our findings demonstrate that PAR-activated astrocytes are able to protect neurons against neurodegeneration and cell death via regulation of the secretion of chemokines CINC-1 and CINC-3. These data indicate a previously unknown mechanism for astrocyte-mediated neuroprotection achieved by PAR activation.

Antithrombin reduces ischemic volume, ameliorates neurologic deficits, and prolongs animal survival in both transient and permanent focal ischemia

BACKGROUND AND PURPOSE

Antithrombin (AT), a glycoprotein belonging to the serpin family, blocks thrombin formation and activity at several steps. Thrombin, beside its relevant role in the coagulation cascade, exerts neurodetrimental effects through the activation of a family of protease-activated receptors, which can be implicated in stroke pathophysiology. The aims of the present study were to evaluate whether AT could reduce brain damage, ameliorate neurologic deficits, and prolong animal survival.

METHODS

Two different doses of AT (10 and 30 IU/kg IP) were administered 3 hours, 6 hours, or 3 and 6 hours after an ischemic insult to mice and rats subjected to either transient or permanent focal ischemia. Ischemic volume was evaluated 24 hours or 7 days after the ischemic insult. Neurologic deficits were also scored.

RESULTS

In mice, 10 or 30 IU/kg AT administered twice, at 3 and 6 hours after transient ischemia, and 30 IU/kg AT administered 3 hours only after transient ischemia substantially reduced total ischemic volume, significantly improved neurologic deficits evaluated 24 hours after the insult, and prolonged animal survival. In rats, the same doses given at the same time intervals significantly reduced ischemic volume, evaluated 24 hours after permanent ischemia.

CONCLUSIONS

These results indicate that AT remarkably reduces infarct volume, ameliorates neurologic deficit scores, and prolongs animal survival in 2 rodent models of brain ischemia. Taken together, our data suggest that AT, delivered via systemic administration, an easily achievable route of administration and in a clinically useful time window, could represent a new therapeutic strategy to be validated for the clinical treatment of human stroke.

Learning and memory deficits in mice lacking protease activated receptor-1

The roles of serine proteases and protease activated receptors have been extensively studied in coagulation, wound healing, inflammation, and neurodegeneration. More recently, serine proteases have been suggested to influence synaptic plasticity. In this context, we examined the role of protease activated receptor 1 (PAR1), which is activated following proteolytic cleavage by thrombin and plasmin, in emotionally motivated learning. We were particularly interested in PAR1 because its activation enhances the function of NMDA receptors, which are required for some forms of synaptic plasticity. We examined several baseline behavioral measures, including locomotor activity, expression of anxiety-like behavior, motor task acquisition, nociceptive responses, and startle responses in C57Bl/6 mice in which the PAR1 receptor has been genetically deleted. In addition, we evaluated learning and memory in these mice using two memory tasks, passive avoidance and cued fear-conditioning. Whereas locomotion, pain response, startle, and measures of baseline anxiety were largely unaffected by PAR1 removal, PAR1-/- animals showed significant deficits in a passive avoidance task and in cued fear conditioning. These data suggest that PAR1 may play an important role in emotionally motivated learning.

Protease-activated receptors in the brain: receptor expression, activation, and functions in neurodegeneration and neuroprotection

Protease-activated receptors (PARs) are G protein-coupled receptors that regulate the cellular response to extracellular serine proteases, like thrombin, trypsin, and tryptase. The PAR family consists of four members: PAR-1, -3, and -4 as thrombin receptors and PAR-2 as the trypsin/tryptase receptor, which are abundantly expressed in the brain throughout development. Recent evidence has supported the direct involvement of PARs in brain development and function. The expression of PARs in the brain is differentially upregulated or downregulated under pathological conditions in neurodegenerative disorders, like Parkinson's disease, Alzheimer's disease, multiple sclerosis, stroke, and human immunodeficiency virus-associated dementia. Activation of PARs mediates cell death or cell survival in the brain, depending on the amplitude and the duration of agonist stimulation. Interference or potentiation of PAR activation is beneficial in animal models of neurodegenerative diseases. Therefore, PARs mediate either neurodegeneration or neuroprotection in neurodegenerative diseases and represent attractive therapeutic targets for treatment of brain injuries. Here, we review the abnormal expression of PARs in the brain under pathological conditions, the functions of PARs in neurodegenerative disorders, and the molecular mechanisms involved.

The role of calcium in protease-activated receptor-induced secretion of chemokine GRO/CINC-1 in rat brain astrocytes

Our recent data showed that activation of protease-activated receptor (PAR)-1 and PAR-2 in rat astrocytes not only evokes calcium signaling, but also regulates the release of the chemokine growth-regulated oncogene/cytokine-induced neutrophil chemoattractant-1 (GRO/CINC-1), a counterpart of the human GRO. This chemokine provides a feedback to protect astrocytes from toxic insults. Activated PAR-1 and PAR-2 were strong stimuli to induce the release of GRO/CINC-1. The effect was comparable to that induced by TNF-alpha. However, the role of calcium in the PAR-induced GRO/CINC-1 secretion remains unknown. Here, we found that the pharmacological blockade of either calcium release from the intracellular stores, or influx from the extracellular space, increased PAR-1- and PAR-2-induced GRO/CINC-1 secretion. Under calcium-free conditions, the basal mRNA level of GRO/CINC-1 was clearly increased. Further studies revealed that the intracellular GRO/CINC-1 protein level was slightly increased by treatment with thrombin or TRag in calcium-free conditions. However, the amount of protein synthesized was largely reduced in the absence of extracellular calcium as compared to that under normal calcium conditions. Importantly, we found that the intracellularly formed GRO/CINC-1 was not secreted into the cell culture supernatant under calcium-free conditions. These data suggest a dual role of calcium. On the one side, an increase in cytosolic calcium negatively regulates PAR-induced GRO/CINC-1 gene expression in rat astrocytes, but on the other side, the basal level of calcium is the pre-requisite for GRO/CINC-1 protein synthesis and secretion.

Thrombin potently enhances swelling-sensitive glutamate efflux from cultured astrocytes

High concentrations of thrombin (Thr) have been linked to neuronal damage in cerebral ischemia and traumatic brain injury. In the present study we found that Thr markedly enhanced swelling-activated efflux of (3)H-glutamate from cultured astrocytes exposed to hyposmotic medium. Thr (0.5-5 U/mL) elicited small (3)H-glutamate efflux under isosmotic conditions and increased the hyposmotic glutamate efflux by 5- to 10-fold, the maximum effect being observed at 15% osmolarity reduction. These Thr effects involve its protease activity and are fully mimicked by SFFLRN, the synthetic peptide activating protease-activated receptor-1. Thr potentiation of (3)H-glutamate efflux was largely dependent on a Thr-elicited increases in cytosolic Ca(2+) (Ca(2+) (i)) concentration ([Ca(2+)](i)). Preventing Ca(2+) (i) rise by treatment with EGTA-AM or with the phospholipase C blocker U73122 reduced the Thr-increased glutamate efflux by 68%. The protein kinase C blockers Go6976 or chelerythrine reduced the Thr effect by 19%-22%, while Ca/calmodulin blocker W7 caused a 63% inhibition. In addition to this Ca(2+)-sensitive pathway, Thr effect on glutamate efflux also involved activation of phosphoinositide-3 kinase (PI3K), since it was reduced by the PI3K inhibitor wortmannin (51% inhibition). Treating cells with EGTA-AM plus wortmannin essentially abolished Thr-dependent glutamate efflux. Thr-activated glutamate release was potently inhibited by the blockers of the volume-sensitive anion permeability pathway, NPPB (IC(50) 15.8 microM), DCPIB (IC(50) 4.2 microM), and tamoxifen (IC(50) 6.6 microM. These results suggest that Thr may contribute to the excitotoxic neuronal injury by elevating extracellular glutamate release from glial cells. Therefore, this work may aid in search of neuroprotective strategies for treating cerebral ischemia and brain trauma.

The effect of thrombin on a 6-hydroxydopamine model of Parkinson's disease depends on timing

Recent results in animal models suggest that thrombin may modulate brain injury in Parkinson's disease (PD). High doses of thrombin ( approximately 20U) can damage dopaminergic neurons, while we have found that low dose thrombin (1U), given several days before a brain insult (thrombin preconditioning), is protective in models of PD and stroke. However, the effects of such low levels of thrombin at the time of, or after, exposure to the dopamine neurotoxin 6-hydroxydopamine (6-OHDA) have not been examined and are the focus of this study. In the first set of experiments, rats received co-administration of thrombin (1U) or saline and 6-OHDA (5microg) into the medial forebrain bundle. 6-OHDA+thrombin resulted in striking increases in behavioral deficits, compared to 6-OHDA+saline. Similarly, co-administration of an agonist to protease-activated receptor (PAR)-1, a thrombin receptor, also resulted in significantly greater behavioral deficits. In a second set of experiments, thrombin (1U) or saline was administered 1 or 7 days after 6-OHDA to determine the effects of thrombin after 6-OHDA. Surprisingly, the rats that received saline had strikingly increased behavioral and neurochemical deficits resulting from the 6-OHDA lesion, while delayed thrombin administration prevented this effect. The results indicate that thrombin has differential effects in the 6-OHDA model, dependent on the time of administration. The ability of a second cannula insertion with saline infusion to increase dramatically deficits raises questions as to what role physical injury to already susceptible cells might play in the pathogenesis of some cases of PD.

Protease-activated receptor signaling: new roles and regulatory mechanisms

PURPOSE OF REVIEW

Protease-activated receptors are G-protein-coupled receptors that transmit cellular responses to coagulant proteases in a variety of cell types in the vasculature and other tissues. Several other proteases can activate protease-activated receptors in vitro and may affect their function in vivo. While a role for these receptors in hemostasis and thrombosis has been established, their functions in inflammatory and other responses have yet to be fully elucidated. In addition, the mechanisms responsible for protease and cell type-specific signaling mediated by these receptors are largely undefined. Here, we highlight recent advances in understanding the roles and regulation of protease-activated receptor signaling.

RECENT FINDINGS

Recent studies have increased our knowledge of the function of protease-activated receptor signaling in platelets and its contribution to thrombosis. In other cell types, recent work has revealed new connections between these receptors and signaling effectors important for vascular development and inflammatory responses. Other studies have advanced our understanding of protease and cell type-specific responses as well as novel regulatory mechanisms for control of protease-activated receptor signaling.

SUMMARY

Thus, elucidating the signaling and regulatory mechanisms of protease-activated receptors in various tissues and cell types is important for understanding their biological function as well as for designing therapeutic strategies to control their function.

Preconditioning with hyperbaric oxygen attenuates brain edema after experimental intracerebral hemorrhage

OBJECT

Preconditioning with hyperbaric oxygen (HBO2) reduces ischemic brain damage. Activation of p44/42 mitogen-activated protein kinases (p44/42 MAPK) has been associated with preconditioning-induced brain ischemic tolerance. This study investigated if preconditioning with HBO2 protects against intracerebral hemorrhage (ICH)-induced brain edema formation and examined the role of p44/42 MAPK in such protection.

METHODS

The study had three experimental groups. In Group 1, Sprague-Dawley rats received two, three, or five consecutive sessions of preconditioning with HBO2 (3 ata, 100% oxygen, 1 hour daily). Twenty-four hours after preconditioning with HBO2, rats received an infusion of autologous blood into the caudate. They were killed 1 or 3 days later for brain edema measurement. Rats in Group 2 received either five sessions of preconditioning with HBO2 or control pretreatment and were killed 24 hours later for Western blot and immunohistochemical analyses. In Group 3, rats received an intracaudate injection of PD098059 (an inhibitor of p44/42 MAPK activation) before the first of five sessions of preconditioning with HBO2. Twenty-four hours after the final preconditioning with HBO2, rats received an intracaudate blood infusion. Brain water content was measured 24 hours after ICH.

RESULTS

Fewer than five sessions of preconditioning with HBO2 did not significantly attenuate brain edema after ICH. Five sessions of preconditioning with HBO2 reduced perihematomal edema 24 and 72 hours after ICH (p < 0.05). Strong p44/42 MAPK immunoreactivity was detected in the basal ganglia 24 hours after preconditioning with HBO2. Intracaudate infusion of PD098059 abolished HBO2 preconditioning-induced protection against ICH-induced brain edema formation.

CONCLUSIONS

Preconditioning with HBO2 protects against brain edema formation following ICH. Activation of the p44/42 MAPK pathway contributes to that protection. Preconditioning with HBO2 may be a way of limiting brain injury during invasive neurosurgical procedures that cause bleeding.

Thrombin-induced ischemic tolerance is prevented by inhibiting c-jun N-terminal kinase

We have studied ischemic tolerance induced by the serine protease thrombin in two different models of experimental ischemia. In organotypic hippocampal slice cultures, we demonstrate that incubation with low doses of thrombin protects neurons against a subsequent severe oxygen and glucose deprivation. L-JNKI1, a highly specific c-jun N-terminal kinase (JNK) inhibitor, and a second specific JNK inhibitor, SP600125, prevented thrombin preconditioning (TPC). We also show that the exposure to thrombin increases the level of phosphorylated c-jun, the major substrate of JNK. TPC, in vivo, leads to significantly smaller lesion sizes after a 30-min middle cerebral artery occlusion (MCAo), and the preconditioned mice were better off in the three tests used to evaluate functional recovery. In accordance with in vitro results, TPC in vivo was prevented by administration of L-JNKI1, supporting a role for JNK in TPC. These results, from two different TPC models and with two distinct JNK inhibitors, show that JNK is likely to be involved in TPC.

Astrocytic control of synaptic NMDA receptors

Astrocytes express a wide range of G-protein coupled receptors that trigger release of intracellular Ca2+, including P2Y, bradykinin and protease activated receptors (PARs). By using the highly sensitive sniffer-patch technique, we demonstrate that the activation of P2Y receptors, bradykinin receptors and protease activated receptors all stimulate glutamate release from cultured or acutely dissociated astrocytes. Of these receptors, we have utilized PAR1 as a model system because of favourable pharmacological and molecular tools, its prominent expression in astrocytes and its high relevance to neuropathological processes. Astrocytic PAR1-mediated glutamate release in vitro is Ca2+ dependent and activates NMDA receptors on adjacent neurones in culture. Activation of astrocytic PAR1 in hippocampal slices induces an APV-sensitive inward current in CA1 neurones and causes APV-sensitive neuronal depolarization in CA1 neurones, consistent with release of glutamate from astrocytes. PAR1 activation enhances the NMDA receptor-mediated component of synaptic miniature EPSCs, evoked EPSCs and evoked EPSPs in a Mg2+-dependent manner, which may reflect spine head depolarization and consequent reduction of NMDA receptor Mg2+ block during subsequent synaptic currents. The release of glutamate from astrocytes following PAR1 activation may also lead to glutamate occupancy of some perisynaptic NMDA receptors, which pass current following relief of tonic Mg2+ block during synaptic depolarization. These results suggest that astrocytic G-protein coupled receptors that increase intracellular Ca2+ can tune synaptic NMDA receptor responses.

SRC kinase inhibition improves acute outcomes after experimental intracerebral hemorrhage

BACKGROUND AND PURPOSE

The mechanisms by which intracerebral hemorrhages produce changes of blood flow and metabolism, cell death, and behavioral abnormalities are complex. In this study, we begin to test the hypothesis that intracerebral hemorrhage activates Src kinases that phosphorylate other molecules to produce cell injury and behavioral deficits after intracerebral hemorrhage (ICH).

METHODS

ICH was produced in adult Sprague Dawley rats by direct injection of autologous blood (50 microL) into striatum. Src kinase activity, glucose hypermetabolic areas around the ICH, TUNEL-stained cells, and apomorphine-induced rotational behaviors were assessed in animals with ICH pretreated with the Src kinase inhibitor, PP1, or with vehicle.

RESULTS

PP1 (3 mg/kg) blocked increases of Src kinase activity (5-fold) at 3 hours after ICH. PP1 also blocked the areas of glucose hypermetabolism and decreased the numbers of TUNEL-stained cells surrounding the ICH at 24 hours. Finally, apomorphine-induced (1 mg/kg) rotation at 24 hours after ICH was markedly attenuated by previous treatment with PP1 (3 mg/kg intraperitoneal).

CONCLUSIONS

PP1 decreases Src kinase activation, glucose metabolic activation, cell death, and behavioral abnormalities after ICH in striatum of adult rats. It is hypothesized that intracerebral hemorrhage, possibly via thrombin activation of protease-activated receptors, activates Src that phosphorylates NMDA receptors, matrix metalloproteinases, and other proteins that mediate injury after ICH.

Plasma proteins in edematous white matter after intracerebral hemorrhage confound immunoblots: an ELISA to quantify contamination

Intracerebral hemorrhage (ICH) and traumatic brain injury can induce brain tissue edema (i.e., interstitial and/or vasogenic), containing high concentrations of plasma proteins. To understand biochemical processes in edema development following these insults, it would be useful to examine alterations in various proteins (e.g., transcription factors, signaling). However, determining altered protein responses in edematous brain tissue using standard immunoblotting techniques is problematic due to contaminating plasma proteins. To solve this problem, we developed an enzyme-linked immunosorbent assay (ELISA) method to quantify the two major plasma proteins, albumin and immunoglobulin G (IgG), that comprise about 80% of the total plasma proteins. We tested our method on edematous white matter samples from our porcine ICH model. To induce ICH, we infused autologous arterial whole blood (3 mL) into frontal hemispheric white matter of pentobarbital- anesthetized pigs ( approximately 20 kg) over 15 min. We froze brains in situ at various times up to 24 h post- ICH and sampled white matter adjacent and contralateral to hematomas. We prepared cytoplasmic extracts that we subjected to ELISA and immunoblotting analyses. Our results demonstrate that this ELISA method is accurate, reproducible, and enables the concentrations of albumin and IgG in edematous brain tissue samples to be accurately determined. By using this correction method, equal amounts of cellular protein can be loaded onto gels during immunoblotting procedures. This method is applicable to edematous tissue samples in brain injury models in which high plasma protein concentrations result from interstitial or vasogenic edema development.

Brain Injury After Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is a subtype of stroke with high morbidity and mortality. The mechanisms underlying ICH-induced brain injury have become better understood during the past decade. Experimental investigations have indicated that thrombin formation, red blood cell lysis, and iron toxicity play a major role in ICH-induced injury and that these mechanisms may provide new therapeutic targets. This article reviews the role of thrombin and iron in ICH-induced injury.

Proteinase-activated receptor-1 and -2 induce the release of chemokine GRO/CINC-1 from rat astrocytes via differential activation of JNK isoforms, evoking multiple protective pathways in brain

Activation of both PAR-1 (proteinase-activated receptor-1) and PAR-2 resulted in release of the chemokine GRO (growth-regulated oncogene)/CINC-1 (cytokine-induced neutrophil chemoattractant-1), a functional counterpart of human interleukin-8, from rat astrocytes. Here, we investigate whether the two PAR receptor subtypes can signal separately. PAR-2-induced GRO/CINC-1 release was independent of protein kinase C, phosphoinositide 3-kinase and MEK (mitogen-activated protein kinase kinase)-1/2 activation, whereas these three kinases were involved in PAR-1-induced GRO/CINC-1 release. Despite such clear differences between PAR-1 and PAR-2 signalling pathways, JNK (c-Jun N-terminal kinase) was identified in both signalling pathways to play a pivotal role. By isoform-specific loss-of-function studies using small interfering RNA against JNK1-3, we demonstrate that different JNK isoforms mediated GRO/CINC-1 secretion, when it was induced by either PAR-1 or PAR-2 activation. JNK2 and JNK3 isoforms were both activated by PAR-1 and essential for chemokine GRO/CINC-1 secretion, whereas PAR-1-mediated JNK1 activation was mainly responsible for c-Jun phosphorylation, which was not involved in GRO/CINC-1 release. In contrast, PAR-2-induced JNK1 activation, which failed to phosphorylate c-Jun, uniquely contributed to GRO/CINC-1 release. Therefore our results show for the first time that JNK-mediated chemokine GRO/CINC-1 release occurred in a JNK isoform-dependent fashion and invoked PAR subtype-specific mechanisms. Furthermore, here we demonstrate that activation of PAR-2, as well as PAR-1, rescued astrocytes from ceramide-induced apoptosis via regulating chemokine GRO/CINC-1 release. Taken together, our results suggest that PAR-1 and PAR-2 have overlapping functions, but can activate separate pathways under certain pathological conditions to rescue neural cells from cell death. This provides new functional insights into PAR/JNK signalling and the protective actions of PARs in brain.

Protease-activated receptor-1 induces generation of new microglia in the dentate gyrus of traumatised hippocampal slice cultures

The protease thrombin is not only known as a major component in the blood coagulation cascade but is also involved in proinflammatory processes in the central nervous system (CNS). Here we used an in vitro model, to investigate the effect of thrombin and protease-activated receptor-1 (PAR-1) on proliferation and microgliosis after traumatic injury. A 5-day exposure to thrombin after cutting the Schaffer collaterals induced a proliferation and microgliosis in the dentate gyrus of organotypic slice cultures. This effect is at least partially mediated by PAR-1 since the selective peptide agonist TRag shows similar effects. Thus, thrombin effects after injury might involve microglial proliferation.

Thrombin induces striatal neurotoxicity depending on mitogen-activated protein kinase pathways in vivo

Intracerebral hemorrhage represents stroke characterized by formation and expansion of hematoma within brain parenchyma. Blood-derived factors released from hematoma are considered to be involved in poor prognosis of this disorder. We previously reported that thrombin, a blood-derived serine protease, induced cytotoxicity in the cerebral cortex and the striatum in organotypic slice cultures, which depended on mitogen-activated protein kinase (MAPK) pathways. Here we investigated the mechanisms of thrombin cytotoxicity in the striatum in vivo. Thrombin microinjected into the striatum of adult rats induced neuronal death and microglial activation around the injection site. Neuronal loss without any sign of nuclear fragmentation was observed as early as 4 h after thrombin injection, which was followed by gradual neuronal death exhibiting nuclear fragmentation. Thrombin-induced damage assessed at 72 h after injection was partially but significantly reduced by concomitant administration of inhibitors of MAPK pathways. Activation of extracellular signal-regulated kinase (ERK) and p38 MAPK in response to thrombin was verified by Western blot analysis. Moreover, phosphorylated ERK and p38 MAPK were localized prominently in reactive microglia, and inhibition of microglial activation by minocycline attenuated thrombin-induced damage, suggesting that reactive microglia were responsible for thrombin-induced neuronal death. Thus, MAPK pathways and microglial activation may serve as therapeutic targets of pathogenic conditions associated with hemorrhagic stroke.

Innate immunity and protective neuroinflammation: new emphasis on the role of neuroimmune regulatory proteins

Brain inflammation due to infection, hemorrhage, and aging is associated with activation of the local innate immune system as expressed by infiltrating cells, resident glial cells, and neurons. The innate immune response relies on the detection of "nonself" and "danger-self" ligands behaving as "eat me signals" by a plethora of pattern recognition receptors (PRRs) expressed by professional and amateur phagocytes to promote the clearance of pathogens, toxic cell debris (amyloid fibrils, aggregated synucleins, prions), and apoptotic cells accumulating within the brain parenchyma and the cerebrospinal fluid (CSF). These PRRs (e.g., complement, TLR, CD14, scavenger receptors) are highly conserved between vertebrates and invertebrates and may represent the most ancestral innate scavenging system involved in tissue homeostasis. However, in some diseases, these protective mechanisms lead to neurodegeneration on the ground that several innate immune molecules have neurocytotoxic activities. The response is a "double-edged sword" representing a fine balance between protective and detrimental effects. Several key regulatory mechanisms have now been evidenced in the control of CNS innate immunity, and these could be harnessed to explore novel therapeutic avenues. We will herein provide new emphasis on the role of neuroimmune regulatory proteins (NIRegs), such as CD95L, TNF, CD200, CD47, sialic acids, CD55, CD46, fH, C3a, HMGB1, which are involved in silencing innate immunity at the cellular and molecular levels and suppression of inflammation. For instance, NIRegs may play an important role in controlling lymphocyte/macrophage/microglia hyperinflammatory responses, while sparing host defense and repair mechanisms. Moreover, NIRegs have direct beneficial effects on neurogenesis and contributing to brain tissue remodeling.

Mesotrypsin, a brain trypsin, activates selectively proteinase-activated receptor-1, but not proteinase-activated receptor-2, in rat astrocytes

Proteinase-activated receptors (PARs), a subfamily of G protein-coupled receptors, which are activated by serine proteases, such as trypsin, play pivotal roles in the CNS. Mesotrypsin (trypsin IV) has been identified as a brain-specific trypsin isoform. However, its potential physiological role concerning PAR activation in the brain is largely unknown. Here, we show for the first time that mesotrypsin, encoded by the PRSS3 (proteinase, serine) gene, evokes a transient and pronounced Ca(2+) mobilization in both primary rat astrocytes and retinal ganglion RGC-5 cells, suggesting a physiological role of mesotrypsin in brain cells. Mesotrypsin mediates Ca(2+) responses in rat astrocytes in a concentration-dependent manner, with a 50% effective concentration (EC(50)) value of 25 nm. The maximal effect of mesotrypsin on Ca(2+) mobilization in rat astrocytes is much higher than that observed in 1321N1 human astrocytoma cells, indicating that the activity of mesotrypsin is species-specific. The pre-treatment of cells with thrombin or the PAR-1-specific peptide TRag (Ala-pFluoro-Phe-Arg-Cha-HomoArg-Tyr-NH(2), synthetic thrombin receptor agonist peptide), but not the PAR-2-specific peptide, reduces significantly the mesotrypsin-induced Ca(2+) response. Treatment with the PAR-1 antagonist SCH79797 confirms that mesotrypsin selectively activates PAR-1 in rat astrocytes. Unlike mesotrypsin, the two other trypsin isoforms, cationic and anionic trypsin, activate multiple PARs in rat astrocytes. Therefore, our data suggest that brain-specific mesotrypsin, via the regulation of PAR-1, is likely to be involved in multiple physiological/pathological processes in the brain.

Modulation of hippocampal neuron survival by thrombin and factor Xa

Effects of thrombin, factor Xa (FXa), and protease-activated receptor 1 and 2 agonist peptides (PAR1-AP and PAR2-AP) on survival and intracellular Ca2+ homeostasis in hippocampal neuron cultures treated with cytotoxic doses of glutamate were investigated. It is shown that at low concentrations (<or=10 nM) thrombin and FXa protect neurons from glutamate-induced excitotoxicity. Inactivation of the proteases blocked the neuroprotective effect. Using PAR1-AP, PAR2-AP, and PAR1 antagonist, we have demonstrated that the neuroprotective effect of thrombin is mediated through activation of PAR1, whereas the effect of FXa may involve novel subtype(s) of PARs. Unlike FXa, thrombin induced transient intracellular calcium signal in hippocampal neurons, which was mainly mediated via IP(3) receptors of the endoplasmic reticulum. Both of the serine proteases improved the recovery of neuronal Ca2+ homeostasis after glutamate treatment.

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.

Protease-activated receptor-1 mediates protection elicited by thrombin preconditioning in a rat 6-hydroxydopamine model of Parkinson's disease

The etiology of Parkinson's disease remains poorly understood, and current treatment options do not slow disease progression. Recently, chemical (thrombin) preconditioning (TPC) was found to be protective in a 6-hydroxydopamine (6-OHDA) model of the disease. It is important to understand the mechanisms behind these thrombin-induced protective effects. The current study was conducted in the rat to determine whether the protective effects of TPC are mediated via activation of protease-activated receptors (PARs). Preconditioning with specific local infusion of agonist peptides for PAR-1 and PAR-4 3 days before unilateral 6-OHDA administration (10 microg into the medial forebrain bundle) was tested. In addition, co-administration of a PAR-1 antagonist with TPC was examined. In a neurobehavioral assessment battery, PAR-1 agonist preconditioning provided protection in a vibrissae-elicited forelimb placing test, a forelimb-use asymmetry test, and a corner turn test. In addition, inclusion of a PAR-1 antagonist prevented the protective effects elicited by TPC. In contrast to the effects of the PAR-1 agonist, PAR-4 agonist preconditioning afforded no such protection. Indeed, in a lower-dose model of 6-OHDA (5 microg), PAR-4 preconditioning significantly increased behavioral deficits. These results indicate that the protective effects of TPC in this model are mediated through PAR-1 activation. Neither the effects of PAR-1 nor TPC on later 6-OHDA-induced behavioral deficits appeared to be mediated through (DA) content sparing. Further mechanistic studies on the actions of PAR-1 and PAR-4 as detrimental in experimental models of Parkinson's disease are warranted.

Astrogliosis is delayed in type 1 interleukin-1 receptor-null mice following a penetrating brain injury

The cytokines IL-1α and IL-1β are induced rapidly after insults to the CNS, and their subsequent signaling through the type 1 IL-1 receptor (IL-1R1) has been regarded as essential for a normal astroglial and microglial/macrophage response. To determine whether abrogating signaling through the IL-1R1 will alter the cardinal astrocytic responses to injury, we analyzed molecules characteristic of activated astrocytes in response to a penetrating stab wound in wild type mice and mice with a targeted deletion of IL-1R1. Here we show that after a stab wound injury, glial fibrillary acidic protein (GFAP) induction on a per cell basis is delayed in the IL-1R1-null mice compared to wild type counterparts. However, the induction of chondroitin sulfate proteoglycans, tenascin, S-100B as well as glutamate transporter proteins, GLAST and GLT-1, and glutamine synthetase are independent of IL-1RI signaling. Cumulatively, our studies on gliosis in the IL-1R1-null mice indicate that abrogating IL-1R1 signaling delays some responses of astroglial activation; however, many of the important neuroprotective adaptations of astrocytes to brain trauma are preserved. These data recommend the continued development of therapeutics to abrogate IL-1R1 signaling to treat traumatic brain injuries. However, astroglial scar related proteins were induced irrespective of blocking IL-1R1 signaling and thus, other therapeutic strategies will be required to inhibit glial scarring.

Deferoxamine reduces CSF free iron levels following intracerebral hemorrhage

Iron overload occurs in brain after intracerebral hemorrhage (ICH). Deferoxamine, an iron chelator, attenuates perihematomal edema and oxidative stress in brain after ICH. We investigated the effects of deferoxamine on cerebrospinal fluid (CSF) free iron and brain total iron following ICH. Rats received an infusion of 100-microL autologous whole blood into the right basal ganglia, then were treated with either deferoxamine (100 mg/kg, i.p., administered 2 hours after ICH and then at 12-hour intervals for up to 7 days) or vehicle. The rats were killed at different time points from 1 to 28 days for measurement of free and total iron. Behavioral tests were also performed. Free iron levels in normal rat CSF were very low (1.1 +/- 0.4 micromol). After ICH, CSF free iron levels were increased at all time points. Levels of brain total iron were also increased after ICH (p < 0.05). Deferoxamine given 2 hours after ICH reduced free iron in CSF at all time points. Deferoxamine also reduced ICH-induced neurological deficits (p < 0.05), but did not reduce total brain iron. In conclusion, CSF free iron levels increase after ICH and do not clear for at least 28 days. Deferoxamine reduces free iron levels and improves functional outcome in the rat, indicating that it may be a potential therapeutic agent for ICH patients.

Protease-activated receptor-1 protects rat astrocytes from apoptotic cell death via JNK-mediated release of the chemokine GRO/CINC-1

Thrombin at low doses is an endogenous mediator of protection in ischaemic and haemorrhagic models of stroke. However, the mechanism of thrombin-induced protection remains unclear. Recently accumulating evidence has shown that astrocytes play an important role in the brain after injury. We report that thrombin and thrombin receptor agonist peptide (TRag) up-regulated secretion of the chemokine growth-regulated oncogene/cytokine-induced neutrophil chemoattractant-1 (GRO/CINC-1) in primary rat astrocytes in a concentration-dependent manner. However, we found no increase of interleukin (IL)-6, IL-1beta and tumour necrosis factor-alpha secretion. Protease-activated receptor 1 (PAR-1)-induced GRO/CINC-1 release was mainly mediated by c-Jun N-terminal kinase (JNK) activation. Extracellular signal-regulated kinase 1/2 might be partially involved, but not p38 mitogen-activated protein kinase. Further studies demonstrated that PAR-1 activation, as well as application of recombinant GRO/CINC-1, protected astrocytes from C(2)-ceramide-induced cell death. Protection occurred with suppression of cytochrome c release from mitochondria. The inhibition of cytochrome c release was largely reduced by the antagonist of chemokine receptor CXCR2, SB-332235. Importantly, a specific JNK inhibitor significantly abolished the protective action of PAR-1. These results demonstrate for the first time that PAR-1 plays an important role in anti-apoptosis in the brain by regulating the release of chemokine GRO/CINC-1, which gives a feedback through its receptor CXCR2 to preserve astrocytes from toxic insults.

Atorvastatin downregulates tissue plasminogen activator-aggravated genes mediating coagulation and vascular permeability in single cerebral endothelial cells captured by laser microdissection

The effects of statins on gene expression of cerebral endothelial cells (ECs) in vivo have not been investigated after stroke. We developed a rapid double immunofluorescent staining protocol with antibodies against von Willebrand factor (a marker for endothelium) and glial fibrillary acidic protein (a marker for astrocytes) for laser capture microdissection to isolate single ECs in brain tissue of the rat. Using this protocol in combination with real-time PCR, we found that stroke significantly increased mRNA levels of protease-activated receptor 1 (PAR-1) and tissue factor (TF) in ECs isolated from ischemic cerebral microvessels compared with nonischemic vessels. Treatment of embolic stroke with recombinant human tissue plasminogen activator (rht-PA) 4 h after stroke further elevated PAR-1 mRNA levels nearly 1000-fold in the core and 500-fold in the boundary above the nonstroke group 30 h after stroke, while TF mRNA levels were elevated approximately 10 fold above the nonstroke group. Furthermore, stroke significantly increased matrix metalloproteinase (MMP) 2 and 9 mRNA levels in the ischemic core and boundary regions 6 and 30 h after stroke. Treatment with rht-PA-upregulated MMP2 expression in the ischemic boundary and core. Atorvastatin completely blocked rht-PA upregulation of the above genes, when atorvastatin in combination with rht-PA was administered 4 h after stroke. Monotherapy of atorvastatin 4 h after stroke did not significantly reduce expression of genes examined in the present study. These data provide evidence that atorvastatin reduces exogenous tPA-aggravated cerebral endothelial genes that mediate thrombosis and blood-brain barrier permeability, which could contribute to the beneficial effects of statins on thrombolytic treatment of acute stroke.

Nitric oxide-producing microglia mediate thrombin-induced degeneration of dopaminergic neurons in rat midbrain slice culture

Activated microglia are considered to play important roles in degenerative processes of midbrain dopaminergic neurons. Here we examined mechanisms of neurotoxicity of thrombin, a protease known to trigger microglial activation, in organotypic midbrain slice cultures. Thrombin induced a progressive decline in the number of dopaminergic neurons, an increase in nitric oxide (NO) production, and whole tissue injury indicated by lactate dehydrogenase release and propidium iodide uptake. Microglia expressed inducible NO synthase (iNOS) in response to thrombin, and inhibition of iNOS rescued dopaminergic neurons without affecting whole tissue injury. Inhibitors of mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase (ERK), p38 MAPK and c-Jun N-terminal kinase (JNK) attenuated thrombin-induced iNOS induction and dopaminergic cell death. Whole tissue injury was also attenuated by inhibition of ERK and p38 MAPK. Moreover, depletion of resident microglia from midbrain slices abrogated thrombin-induced NO production and dopaminergic cell death, but did not inhibit tissue injury. Finally, antioxidative drugs prevented thrombin-induced dopaminergic cell death without affecting whole tissue injury. Hence, NO production resulting from MAPK-dependent microglial iNOS induction is a crucial event in thrombin-induced dopaminergic neurodegeneration, whereas damage of other midbrain cells is MAPK-dependent but is NO-independent.

Mechanisms of brain injury after intracerebral haemorrhage

The past decade has resulted in a rapid increase in knowledge of mechanisms underlying brain injury induced by intracerebral haemorrhage (ICH). Animal studies have suggested roles for clot-derived factors and the initial physical trauma and mass effect as a result of haemorrhage. The coagulation cascade (especially thrombin), haemoglobin breakdown products, and inflammation all play a part in ICH-induced injury and could provide new therapeutic targets. Human imaging has shown that many ICH continue to expand after the initial ictus. Rebleeding soon after the initial haemorrhage is common and forms the basis of a current clinical trial using factor VIIa to prevent rebleeding. However, questions about mechanisms of injuries remain. There are conflicting data on the role of ischaemia in ICH and there is uncertainty over the role of clot removal in ICH therapy. The next decade should bring further information about the underlying mechanisms of ICH-induced brain injury and new therapeutic interventions for this severe form of stroke. This review addresses our current understanding of the mechanisms underlying ICH-induced brain injury.

Brain genomics of intracerebral hemorrhage

After intracerebral hemorrhage (ICH), many changes of gene transcription occur that may be important because they will contribute to understanding mechanisms of injury and recovery. Therefore, gene expression was assessed using Affymetrix microarrays in the striatum and the overlying cortex at 24 h after intracranial infusions of blood into the striatum of adult rats. Intracerebral hemorrhage regulated 369 of 8,740 transcripts as compared with saline-injected controls, with 104 regulated genes shared by the striatum and cortex. There were 108 upregulated and 126 downregulated genes in striatum, and 170 upregulated and 69 downregulated genes in the cortex. Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) confirmed upregulation of IL-1-beta, Lipcortin 1 (annexin) and metallothionein 1,2, and downregulation of potassium voltage-gated channel, shaker-related subfamily, beta member 2 (Kcnab2). Of the functional groups of genes modulated by ICH, many metabolism and signal-transduction-related genes decreased in striatum but increased in adjacent cortex. In contrast, most enzyme, cytokine, chemokine, and immune response genes were upregulated in both striatum and in the cortex after ICH, likely in response to foreign proteins from the blood. A number of these genes may contribute to brain edema and cellular apoptosis caused by ICH. In addition, downregulation of growth factor pathways and the phosphatidylinositol 3-kinase (PI3K)/Akt pathway could also contribute to perihematoma cell death/apoptosis. Intracerebral hemorrhage-related downregulation of GABA-related genes and potassium channels might contribute to perihematoma cellular excitability and increased risk of post-ICH seizures. These genomic responses to ICH potentially provide new therapeutic targets for treatment.

Focal ischemia induces expression of protease-activated receptor1 (PAR1) and PAR3 on microglia and enhances PAR4 labeling in the penumbra

Thrombin significantly influences neurodegenerative processes after ischemia. The current literature suggests that the effects are mediated via protease-activated receptors 1, 3 and 4 (PAR1, 3, 4). Therefore, we investigated with immunohistochemical methods whether focal cerebral ischemia altered the expression of PARs in the rodent brain. For this purpose, we used the model of endothelin-induced occlusion of the middle cerebral artery and the model of transcranial permanent occlusion of the middle cerebral artery in mice. In contrast to the exclusively neuronal staining in the brain parenchyma of naïve animals, PAR1 and PAR3 occurred in addition on microglial cells in the penumbra after transient and after permanent focal ischemia. Although microglia activation could be detected for several weeks after the insult, PAR1 and PAR3 were traceable on microglia only 12 and 48 h after the insult, but not on day 7 post-ischemia. PAR4 was expressed, both in naïve and in ischemic animals, exclusively in neuronal cells. However, at the border zone and within the infarct area, enhanced immunohistochemical PAR4 signals were recognized. From our data, we conclude that PAR1 and PAR3 could be involved in thrombin-modulated initiation of post-ischemic inflammation and PAR4 may be associated with neuronal degeneration.

Thrombin-induced delayed injury involves multiple and distinct signaling pathways in the cerebral cortex and the striatum in organotypic slice cultures

Thrombin, a serine protease essential for blood coagulation, also plays an important role in cellular injury associated with intracerebral hemorrhage. Here, we show that, in organotypic cortico-striatal slice cultures, thrombin evoked delayed neuronal injury in the cerebral cortex and shrinkage of the striatum. These effects were prevented by cycloheximide and actinomycin D but not by a caspase-3 inhibitor. Thrombin-induced shrinkage of the striatum was abolished by a thrombin inhibitor argatroban or prior heat inactivation of thrombin, and significantly attenuated by a protease-activated receptor-1 antagonist FR171113. However, thrombin-induced cortical injury was not prevented either by heat inactivation or by FR171113, and was only partially inhibited by argatroban. In addition, inhibition of extracelluar signal-regulated kinase (ERK), Src tyrosine kinase and protein kinase C prevented both neuronal injury in the cortex and shrinkage of the striatum, whereas inhibition of p38 mitogen-activated protein kinase and c-Jun N-terminal kinase prevented shrinkage of the striatum only. Thrombin treatment promptly induced phosphorylation of ERK, which was not prevented by inhibition of Src and protein kinase C. Thus, thrombin induces cellular injury in the cerebral cortex and the striatum, by recruiting multiple and distinct signaling pathways in protease activity-independent as well as dependent manner.

Prognostic Significance of Blood Brain Barrier Permeability in Acute Hemorrhagic Stroke

BACKGROUND

Blood brain barrier (BBB) disruption is accompanied by edema in the surrounding areas of the intracerebral hemorrhage (ICH). The aim of the study was to clarify the correlation between BBB breakdown and outcome in ICH.

PATIENTS

Twenty-seven patients with primary ICH were included in the study. Each patient underwent CT and DTPA-SPECT, and the National Institutes of Health (NIH) and modified Rankin score were performed as well.

RESULTS

DTPA-SPECT had a significant correlation with the modified Rankin score after 3 months (p = 0.008) and 6 months (p = 0.01). The CT scan was directly correlated with the NIH score on days 1, 7 and 30 (p = 0.01, p = 0.01 and p = 0.04, respectively). No correlation was found between DTPA-SPECT and CT scan data.

CONCLUSIONS

The degree of BBB breakdown, as imaged by the DTPA-SPECT technique, was directly correlated with the late functional outcome. The CT scan has an inverse correlation with the NIH score. These findings may have broad clinical implications.

Study of neurotrophic activity of thrombin on the model of regenerating mouse nerve

Experiments demonstrated a dose-dependent facilitating effect of thrombin and peptide thrombin receptor agonist PAR1 (TRAP6) on regeneration of mouse peripheral nerve after its crushing. The maximum neurotrophic effect was observed at low concentrations of thrombin (10 nM) and TRAP6 (10 microM).

The role of thrombin in gliomas

BACKGROUND

In a previous study we found that intracerebral infusion of argatroban, a specific thrombin inhibitor, reduces brain edema and neurologic deficits in a C6 glioma model.

OBJECTIVES

To examine the role of thrombin in gliomas and whether systemic argatroban administration can reduce glioma mass and neurologic deficits and extend survival time in C6 and F98 gliomas.

METHODS

The presence of thrombin in human glioblastoma samples and rat C6 glioma cells (in vitro and in vivo) was assessed using immunohistochemistry. The effect of thrombin on C6 cell proliferation in vitro was assessed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide assay. The role of thrombin in vivo was assessed in rat C6 and F98 glioma cell models using argatroban, a thrombin inhibitor. The effects of argatroban on tumor mass, neurologic deficits and survival time were investigated.

RESULTS

Thrombin immunoreactivity was found in cultured rat C6 glioma cells and human glioblastomas. Thrombin induced C6 cell proliferation in vitro. In C6 glioma, argatroban reduced glioma mass (P < 0.05) and neurologic deficits (P < 0.05) at day 9. In F98 glioma, argatroban prolonged survival time (P < 0.05).

CONCLUSION

These results suggest that thrombin plays an important role in glioma growth. Thrombin may be a new therapeutic target for gliomas.

Hypoxic preconditioning protects against ischemic brain injury

Animals exposed to brief periods of moderate hypoxia (8% to 10% oxygen for 3 hours) are protected against cerebral and cardiac ischemia between 1 and 2 days later. This hypoxia preconditioning requires new RNA and protein synthesis. The mechanism of this hypoxia-induced tolerance correlates with the induction of the hypoxia-inducible factor (HIF), a transcription factor heterodimeric complex composed of inducible HIF-1alpha and constitutive HIF-1beta proteins that bind to the hypoxia response elements in a number of HIF target genes. Our recent studies show that HIF-1alpha correlates with hypoxia induced tolerance in neonatal rat brain. HIF target genes, also induced following hypoxia-induced tolerance, include vascular endothelial growth factor, erythropoietin, glucose transporters, glycolytic enzymes, and many other genes. Some or all of these genes may contribute to hypoxia-induced protection against ischemia. HIF induction of the glycolytic enzymes accounts in part for the Pasteur effect in brain and other tissues. Hypoxia-induced tolerance is not likely to be equivalent to treatment with a single HIF target gene protein since other transcription factors including Egr-1 (NGFI-A) have been implicated in hypoxia regulation of gene expression. Understanding the mechanisms and genes involved in hypoxic tolerance may provide new therapeutic targets to treat ischemic injury and enhance recovery.

Subnanomolar concentrations of thrombin enhance the volume-sensitive efflux of taurine from human 1321N1 astrocytoma cells

The ability of subnanomolar concentrations of thrombin to protect both neurons and glia from ischemia and other metabolic insults has recently been reported. In this study, we demonstrate an additional neuroprotective property of thrombin; its ability to promote the release of the organic osmolyte, taurine, in response to hypoosmotic stress. Incubation of human 1321N1 astrocytoma cells with hypo-osmolar buffers (320-227 mOsM) resulted in a time-dependent release of taurine. Inclusion of thrombin (EC(50) = 60 pM) resulted in a marked increase in taurine efflux that, although evident under isotonic conditions (340 mOsM), was maximal at an osmolarity of 270 mOsM (3-4-fold stimulation). Thrombin-stimulated taurine efflux was dependent upon its protease activity and could be mimicked by addition of the peptide SFLLRN, a proteinase activated receptor-1 (PAR-1) subtype-specific ligand. Inclusion of anion channel blockers known to inhibit the volume-sensitive organic osmolyte anion channel attenuated thrombin-stimulated taurine release. Depletion of intracellular Ca(2+) with either 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) or thapsigargin, or alternatively, inhibition of protein kinase C (PKC) with bisindolylmaleimide or chelerythrine resulted in a 30 to 50% inhibition of thrombin-stimulated taurine efflux. Under conditions in which intracellular Ca(2+) was depleted and PKC activity inhibited, thrombin-stimulated taurine efflux was reduced by >85%. The results indicate that activation of PAR-1 receptors by thrombin facilitates the ability of 1321N1 astrocytoma cells to release osmolytes in response to a reduction in osmolarity via a mechanism that is dependent on intracellular Ca(2+) and PKC activity.

The deleterious or beneficial effects of different agents in intracerebral hemorrhage: think big, think small, or is hematoma size important?

BACKGROUND AND PURPOSE

Thrombin, heme oxygenase, complement, microglia activation, and leukocyte infiltration are all actively upregulated in intracerebral hemorrhage (ICH). Experimental evidence suggests that all these factors are involved in ICH-induced brain injury. This suggests a scenario whereby ICH actively (through gene and protein upregulation) induces pathways that result in brain injury.

SUMMARY OF REVIEW

In this comment, we suggest a potential answer to this conundrum. The upregulation of these factors may have been an evolutionary adaptation to limit brain injury during small hematomas (microbleeds). There is evidence that low levels of thrombin and heme oxygenase limit brain injury. In contrast, the excessive upregulation of these same factors may have a harmful effect after a large hematoma.

CONCLUSIONS

The mechanisms upregulated to limit brain injury after microbleeds may also induce injury after large hematomas. The effect of hematoma size on the mechanisms involved in ICH-induced brain injury and the implications of any such effect on clinical therapies merit further investigation.

Two types of protease-activated receptors (PAR-1 and PAR-2) mediate calcium signaling in rat retinal ganglion cells RGC-5

Protease-activated receptors (PARs), G-protein-coupled receptors, are widely expressed in various tissues, where they participate in physiological and pathological processes, such as hemostasis, proliferation, tissue repair, and inflammation. Recently, we found that PARs were upregulated in the rat retina following optic nerve crush injury. However, the role of PAR in retinal ganglion cells following optic nerve crush still remains unknown. Here, we studied PAR-mediated calcium signaling in retinal ganglion cells, RGC-5. Using reverse transcription-polymerase chain reaction, we demonstrate that RGC-5 cells mainly express PAR-1 and to a lower extent PAR-2, which was further confirmed by indirect immunofluorescence. Short-term stimulation of RGC-5 cells with thrombin (0.001-1 U/ml) and trypsin (1-100 nM) concentration-dependently induced a transient increase in intracellular calcium concentration ([Ca(2+)](i)). An increase in [Ca(2+)](i) was also induced by both TRag (PAR-1 activating peptide) and PAR-2 activating peptide (PAR-2 AP). The EC(50) values were 0.3 nM for thrombin, 12.0 nM for trypsin, 1.3 microM for TRag, and 1.6 microM for PAR-2 AP, respectively. Desensitization was studied using two successive pulses of agonists. The thrombin-induced calcium response was significantly reduced by PAR-1 desensitization caused by pre-challenging RGC-5 cells with thrombin or TRag, but not by PAR-2 desensitization. On the other hand, pretreatment with trypsin, TRag or PAR-2 AP desensitized the cells since the calcium response to a second exposure to trypsin was significantly reduced. Calcium source studies revealed that PAR-induced [Ca(2+)](i) rise mainly comes from intracellular stores in RGC-5 cells. Thus, we demonstrate that PAR-1 and PAR-2 are functionally expressed in retinal ganglion cells, mediating calcium mobilization mainly from intracellular stores.

Expression of Myelencephalon-Specific Protease after Cryogenic Lesioning of the Rat Parietal Cortex

The gene for myelencephalon-specific protease (MSP) is a member of the kallikrein gene family and in rats is expressed mainly in the central nervous system. Its function and alteration in brain injury have not yet been clarified. We examined the expression of MSP after cryogenic injury (CI) using in situ hybridization, immunohistochemistry, and Western blotting. Analysis of MSP mRNA by in situ hybridization revealed a higher level of expression around the cryogenic area than on the contralateral side at 2-7 days after CI, with peak expression occurring 7 days after CI. Immunohistochemical analysis demonstrated expression of MSP protein at 1 day after CI, in the same region in which MSP mRNA was observed, with peak expression again at 7 days after CI, in the area around the lesion. Double immunohistochemical labeling revealed that MSP was expressed mainly in oligodendrocytes. These results suggest that expression of MSP may be related to the turnover of myelin-associated proteins and extracellular matrix proteins after CI. The regulation of active MSP may be important in the physiological or pathological changes involved in remyelination or demyelination.

Tissue plasminogen activator and glial function

Tissue plasminogen activator (tPA) is the only FDA-approved treatment of thrombotic stroke and is a major parenchymal serine protease in the brain. However, it has been implicated in a plethora of brain pathologies, raising concern about its use as a safe therapeutic. tPA is thought to regulate physiological processes that entail tissue remodeling and plasticity, purportedly due to its ability to initiate the degradation of extracellular matrix proteins and possibly other substrates. Understanding the physiological role(s) of tPA promises to both elucidate important aspects of brain function and improve the available therapies for neurological disease. In this context, the effects of tPA on glial cells, mainly microglial cells, but also astrocytes and Schwann cells, appear to be of particular importance, given the increasing awareness of the significance of glia in brain physiology and pathology

Ischemia and ischemic tolerance in the brain: an overview

Stroke is the third leading cause of death and the leading cause of adult disability in the United States. This review outlines the pathways that lead to cell death following stroke, and also summarizes the current literature on the phenomenon of ischemic tolerance. Ischemic tolerance is an endogenous neuroprotective mechanism by which neurons are protected from the deleterious effects of brain ischemia that occur during and after stroke. A better understanding of the processes that lead to cell death after stroke and endogenous neuroprotective mechanisms like ischemic tolerance could help in the development of new treatment strategies for this devastating neurological disease.

Holo-transferrin and thrombin can interact to cause brain damage

BACKGROUND AND PURPOSE

Previous studies have suggested that delayed release of hemoglobin degradation products, particularly iron, is involved in intracerebral hemorrhage (ICH)-induced brain injury. However, a recent study found evidence of iron-induced brain injury soon after ICH. This study, therefore, examined whether another iron-containing component of blood, holo-transferrin (holo-Tf), might also induce brain injury either alone or in combination with thrombin, another factor involved in early ICH-induced brain injury.

METHODS

Male Sprague-Dawley rats received an intracerebral infusion of holo-Tf, apo (noniron-loaded)-Tf, thrombin, or a combination of Tf with thrombin into the right basal ganglia. The rats were euthanized 24 hours later for measurement of brain edema and assessment of DNA damage (single- and double-strand breaks and 8-hydroxyl-2'-deoxyguanosine immunohistochemistry). Iron distribution was examined histochemically.

RESULTS

Holo-Tf, apo-Tf, and the dose of thrombin used (1 U) all failed to induce brain edema when administered alone. However, the combination of holo-Tf with thrombin (but not apo-Tf with thrombin) caused brain edema, DNA damage, and intracellular iron accumulation in the ipsilateral basal ganglia.

CONCLUSIONS

These results suggest that in addition to hemoglobin-bound iron, Tf-bound iron may contribute to ICH-induced brain injury and that thrombin may contribute to the latter by facilitating cellular iron uptake.

Complement inhibition attenuates brain edema and neurological deficits induced by thrombin

The present study examined whether thrombin activates the complement cascade in the brain and whether N-acetylheparin, an inhibitor of complement activation, attenuates brain injury induced by thrombin. There were three sets of studies. In the first set, rats had an intracerebral infusion of either five-unit thrombin or a needle insertion. Brains were sampled at 24 hours for Western blot analysis and immuno-histochemistry. In the second set, rats received either five-unit thrombin+saline, five-unit thrombin+25 microg N-acetylheparin or five-unit thrombin+100 microg N-acetylheparin infusion. Brains were sampled 24 hours later for water content measurement. In the third set, rats received either five-unit thrombin+saline or five-unit thrombin+ 100 microg N-acetylheparin. Behavioral tests sensitive to unilateral striatal damage were carried out for two weeks. Western blotting demonstrated that complement C9 and clusterin levels increase 24 hours after thrombin infusion (P < 0.01). Both C9 and clusterin positive cells were found around the injection site. High-dose (100-microg) but not low-dose (25-microg) N-acetylheparin attenuated thrombin-induced brain edema (81.5 +/- 0.4% vs. 83.7 +/- 0.3% in the vehicle, P < 0.05). Behavior was also significantly improved by N-acetylheparin (P < 0.05). In conclusion, thrombin-induced edema formation and neurological deficits were both reduced by N-acetylheparin. This suggests that inhibition may be a novel treatment for the thrombin-induced brain injury that occurs in intracerebral hemorrhage.

Thrombin preconditioning provides protection in a 6-hydroxydopamine Parkinson's disease model

Low-dose thrombin given several days before lesioning is neuroprotective in ischemic and hemorrhagic models of stroke, an effect termed thrombin preconditioning (TPC). Here, the ability of TPC to provide protection in a 6-hydroxydopamine (6-OHDA) model of Parkinson's disease (PD) was evaluated. All animals received 10 microg 6-OHDA into the right medial forebrain bundle. Three days prior to 6-OHDA, the animals received either 1 U rat thrombin (n=17) or saline (n=14) 1 mm above the site of neurotoxin delivery. The animals were then evaluated for neurobehavioral deficits until 21 days post-injection. TPC animals performed significantly better on both a vibrissae-elicited forelimb placing test and a forelimb-use asymmetry test than the saline controls. The animals were then sacrificed for either catecholamine determination by HPLC with electrochemical detection or for histopathology to determine lateral ventricular volume or striatal tyrosine hydroxylase immunoreactivity. Although TPC did not protect against the dopamine depletion associated with this severe model, it did reduce dopaminergic terminal loss and ventricular enlargement as compared to saline-treated animals. This report presents the new finding that preconditioning (and TPC in particular) provides protection in a 6-OHDA PD model. Understanding the mechanisms involved in TPC-mediated protection may stimulate innovative therapeutic regimens.