Thrombin may contribute to the pathophysiology of central nervous system injury

Thrombomodulin as a new marker of lesion-induced astrogliosis: involvement of thrombin through the G-protein-coupled protease-activated receptor-1

Because injury of the CNS causes an astrogliosis, characterized by cell swelling and proliferation, similar to the effects of the serine protease thrombin on astrocytes, we hypothesized that a high level of thrombin at the site of injury might initially induce an astrocyte reaction and later increase the expression of its specific inhibitor, thrombomodulin. Thrombomodulin could then stabilize the astroglial scar through its adhesive properties. Here, we studied the in vivo injury response of astrocytes in the anterior medullary velum of adult rat by immunostaining and in situ hybridization of thrombomodulin. Thrombomodulin was poorly expressed on astrocytes in normal tissue, increased up to 2 d after injury, and was still highly expressed at 6 d. To check that thrombin had a direct effect on thrombomodulin expression by astrocytes, we used brain cortical astrocyte primary cultures treated with either thrombin or the agonist peptide thrombin receptor-activating peptide-6, known to activate directly the thrombin G-protein-coupled receptor (GPCR) protease-activated receptor-1 (PAR-1). Modification of thrombomodulin expression was studied by Western blotting and quantitative reverse transcription-PCR. There was a dose-dependent increase in thrombomodulin after 48 hr of treatment, with gene expression peaking at 24 hr but falling to control levels by 48 hr. Together, these results show the following: (1) injury increases astrocyte thrombomodulin expression; (2) thrombin might mediate thrombomodulin expression via the specific receptor PAR-1; and (3) serine proteases, their inhibitors, and the new family of GPCR, PARs, are active on astrogliosis.

Treatment of intraventricular hemorrhage with urokinase : effects on 30-Day survival

BACKGROUND AND PURPOSE

Intraventricular hemorrhage (IVH) remains associated with high morbidity and mortality. Therapy with external ventricular drainage alone has not modified outcome in these patients.

METHODS

Twelve pilot IVH patients who required external ventricular drainage were prospectively treated with intraventricular urokinase followed by the randomized, double-blinded allocation of 8 patients to either treatment or placebo. Observed 30-day mortality was compared with predicted 30-day mortality obtained by use of a previously validated method.

RESULTS

Twenty patients were enrolled; admission Glasgow Coma Scale score in 11 patients was </=8; 10 patients had pulse pressure <85 mm Hg. Mean+/-SD ICH volume in 16 patients was 6.21+/-7.53 cm(3) (range 0 to 23.88 cm(3)), and mean+/-SD intraventricular hematoma volume was 44.26+/-31.65 cm(3) (range 1.31 to 100.36 cm(3)). Four patients (20%) died within 30 days. Predicted mortality for these 20 patients was 68.42% (range 3% to 100%). Probability of observing </=4 deaths among 20 patients under a 68.42% expected mortality is 0.000012.

CONCLUSIONS

Intraventricular urokinase may significantly improve 30-day survival in IVH patients. On the basis of current evidence, a double-blinded, placebo-controlled, multicenter study that uses thrombolysis to treat IVH has received funding and began January 1, 2000.

Diffusion-weighted MRI and proton MR spectroscopic imaging in the study of secondary neuronal injury after intracerebral hemorrhage

BACKGROUND AND PURPOSE

Cerebral ischemia has been proposed as contributing mechanism to secondary neuronal injury after intracerebral hemorrhage (ICH). Possible tools for investigating this hypothesis are diffusion-weighted (DWI) and proton magnetic resonance spectroscopic imaging ((1)H-MRSI). However, magnetic field inhomogeneity induced by paramagnetic blood products may prohibit the application of such techniques on perihematoma tissue. We report on the feasibility of DWI and (1)H-MRSI in the study of human ICH and present preliminary data on their contribution to understanding perihematoma tissue functional and metabolic profiles.

METHODS

Patients with acute supratentorial ICH were prospectively evaluated using DWI and (1)H-MRSI. Obscuration of perihematoma tissue with both sequences was assessed. Obtainable apparent diffusion coefficient (Dav) and lactate spectra in perihematoma brain tissue were recorded and analyzed.

RESULTS

Nine patients with mean age of 63.4 (36 to 87) years were enrolled. Mean time from symptom onset to initial MRI was 3.4 (1 to 9) days; mean hematoma volume was 35.4 (5 to 80) cm(3). Perihematoma diffusion values were attainable in 9 of 9 patients, and (1)H-MRSI measures were obtainable in 5 of 9 cases. Dav in perihematoma regions was 172.5 (120.0 to 302.5)x10(-5) mm(2)/s and 87.6 (76.5 to 102.1)x10(-5) mm(2)/s in contralateral corresponding regions of interest (P=0.002). One patient showed an additional area of reduced Dav with normal T(2) intensity, which suggests ischemia. (1)H-MRSI revealed lactate surrounding the hematoma in 2 patients.

CONCLUSIONS

DWI and (1)H-MRSI can be used in the study of ICH patients. Our preliminary data are inconsistent with ischemia as the primary mechanism for perihematoma tissue injury. Further investigation with advanced MRI techniques will give a clearer understanding of the role that ischemia plays in tissue injury after ICH.

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

The effects of the thrombin inhibitor argatroban on the number of inflammatory cells and reactive astrocytes were investigated in a rat brain injury model. Gelatin sponge soaked with thrombin inhibitor (treatment group) or saline (control group) was placed in the brain defect to assess the infiltration of inflammatory cells by hematoxylin-eosin and immunohistochemical staining. Expression of polymorphonuclear leukocytes (PMNs) and monocyte/macrophage (Mo/Mo) cells, and vimentin (VIM)-positive astrocytes and glial fibrillary acidic protein (GFAP)-positive astrocytes were compared between groups. In the treatment group, infiltration of both PMNs and Mo/Mo cells, and the number of VIM-positive astrocytes were significantly reduced, but the number of GFAP-positive astrocytes was not different from the control group. Thrombin inhibitor suppresses the infiltration of inflammatory cells and excessive gliosis caused by VIM-positive astrocytes, but not expression of GFAP-positive astrocytes, suggesting minimization of secondary brain damage and promotion of the conditions required for neural regeneration.

Effects of alpha-thrombin on superoxide dismutase levels in human cerebral microvascular endothelial cells

BACKGROUND

Sequelae of traumatic brain injury include generation of oxygen-free radicals and fibrin deposition, which worsen the initial injury. Superoxide dismutases (SODs) scavenge and bind to the free-radical superoxide anion (O2-), potentially defending against oxidative stress. In the present study, we investigated the production of SOD within human cerebral microvascular endothelial (HCME) cells after exposure to alpha-thrombin, hypothesizing that manganese SOD (MnSOD) expression is increased. Our aims were to determine whether alterations in SOD are observed at the mRNA level, to examine whether a particular species is preferentially expressed, and to determine the requirement of the active site of alpha-thrombin.

METHODS

HCME cells were characterized and grown to confluence. Control cells and cells exposed to 10 nmol/L alpha-thrombin were harvested for mRNA isolation using reverse transcriptase-polymerase chain reaction. Quantitation of mRNA production determined the levels of copper-zinc SOD and MnSOD. Active site blocked alpha-thrombin was used as a negative control and determined the specificity of the response.

RESULTS

The cells in culture were identified as endothelial after fulfilling criteria, such as positive immunocytochemical staining for factor VIII/von Willebrand factor antigen and binding of Ulex europaeus agglutinin-1 lectin. Levels of MnSOD mRNA were elevated at all time points in response to alpha-thrombin, whereas the cytosolic form was undetectable. HCME cells that were exposed to active site-blocked alpha-thrombin produced mRNA levels of MnSOD that were increased above those of controls, but this increase was half that of mRNA levels of MnSOD produced by HCME cells that were exposed to alpha-thrombin.

CONCLUSION

Our study showed for the first time that alpha-thrombin partially modulates SOD in HCME cells, causing a preferential increase in MnSOD. Further investigation into secondary brain injury will provide insights into the role of alpha-thrombin in the mechanism of free radical-induced alterations, potentially improving the outcome of patients with head injury.

Effect of intracerebral and subdural hematomas on energy-dependent transport across the blood-brain barrier

Although both intracerebral and subdural hematomas induce brain edema, previous studies have indicated that they may have different cerebrovascular effects. Our own investigations have demonstrated that while subdural hematomas (SDH) are associated with ischemia this is not the case following intracerebral hematomas (ICH). Previous studies have demonstrated a decrease in energy-dependent transport of glutamine across the blood-brain barrier (BBB) following focal cerebral ischemia. The present study investigates this further by examining the effects of SDH, ICH, and intracerebral thrombin injections, an agent involved in ICH-induced injury, on blood to brain glutamine transport. The injection of 200 microL of blood into the subdural space induced a marked reduction in glutamine transport (Ki, influx rate constant) into the cerebral cortex at 4 and 24 h following SDH (sham, 105+/-4% of contralateral cortex; SDH 4 h, 63+/-5%, p<0.01; SDH 24 h, 47+/-12%, p<0.05). There were no significant changes in glutamine Ki in subcortical areas following SDH. Following ICH (200-microL clot); however, there were only modest decreases in glutamine Ki in subcortical areas (sham, 98+/-2% of right cortex; ICH 4 h, 91+/-5%, p<0.01; ICH 24 h, 91+/-2%, p<0.05). Intracerebral injection of thrombin (5U) had minimal effect on glutamine Ki, in subcortical areas, at 4 h and induced a modest decrease in transport at 24 h (sham, 98+/-2% of right cortex; thrombin 4 h, 98+/-2%; thrombin 24 h, 86+/-2%, p<0.05). The present studies demonstrate marked differences in the effects of ICH and SDH on BBB function.

Thrombin and mast cell tryptase regulate guinea-pig myenteric neurons through proteinase-activated receptors-1 and -2

1. Proteases regulate cells by cleaving proteinase-activated receptors (PARs). Thrombin and trypsin cleave PAR-1 and PAR-2 on neurons and astrocytes of the brain to regulate morphology, growth and survival. We hypothesized that thrombin and mast cell tryptase, which are generated and released during trauma and inflammation, regulate enteric neurons by cleaving PAR-1 and PAR-2. 2. We detected immunoreactive PAR-1 and PAR-2 in > 60 % of neurons from the myenteric plexus of guinea-pig small intestine in primary culture. A large proportion of neurons that expressed substance P, vasoactive intestinal peptide or nitric oxide synthase also expressed PAR-1 and PAR-2. We confirmed expression of PAR-1 and PAR-2 in the myenteric plexus by RT-PCR using primers based on sequences of cloned guinea-pig receptors. 3. Thrombin, trypsin, tryptase, a filtrate from degranulated mast cells, and peptides corresponding to the tethered ligand domains of PAR-1 and PAR-2 increased [Ca2+]i in > 50 % of cultured myenteric neurons. Approximately 60 % of neurons that responded to PAR-1 agonists responded to PAR-2 agonists, and > 90 % of PAR-1 and PAR-2 responsive neurons responded to ATP. 4. These results indicate that a large proportion of myenteric neurons that express excitatory and inhibitory neurotransmitters and purinoceptors also express PAR-1 and PAR-2. Thrombin and tryptase may excite myenteric neurons during trauma and inflammation when prothrombin is activated and mast cells degranulate. This novel action of serine proteases probably contributes to abnormal neurotransmission and motility in the inflamed intestine.

Attenuation of thrombin-induced brain edema by cerebral thrombin preconditioning

BACKGROUND AND PURPOSE

Edema formation after intracerebral hemorrhage has been linked to thrombin toxicity induced by the clot. However, thrombin at low concentrations actually protects neurons and astrocytes in culture from hypoglycemic and ischemic cell death. It is also known that a brief episode of brain ischemia increases neuronal tolerance to a subsequent severe ischemic episode. The objective of this study was to investigate whether pretreatment of the brain with low-dose thrombin induces tolerance to a subsequent large dose of thrombin injected into brain parenchyma.

METHODS

The rat brain was preconditioned with 1 U thrombin by direct infusion into the right caudate nucleus. After thrombin pretreatment, the effects of a large dose (5 U) of thrombin on brain edema formation were studied at different intervals. We examined whether heat-shock protein (HSP) 27, HSP32, and HSP70 were induced by Western blot analysis, immunocytochemistry, and immunofluorescent double staining.

RESULTS

Thrombin pretreatment significantly attenuated the brain edema that normally follows the infusion of a large dose of thrombin (79.2+/-0.4 versus 84.0+/-0.3; P<0.01). This effect was abolished by the thrombin inhibitor hirudin. Time course studies showed that the maximal effect of thrombin preconditioning (TPC) on brain edema formation was 7 days after pretreatment. This time course corresponded to marked upregulation of HSP27 in the ipsilateral brain. TPC also induced HSP32, but this effect occurred earlier than the effect on edema formation. TPC had no effect on HSP70. Immunocytochemistry and immunofluorescent double labeling showed that HSP27 and HSP32 were expressed in astrocytes after TPC.

CONCLUSIONS

OFF phenomenon of thrombin-induced tolerance of the brain to edema formation may be related to HSP27 induction.

Role of blood clot formation on early edema development after experimental intracerebral hemorrhage

BACKGROUND AND PURPOSE

Blood "toxicity" is hypothesized to induce edema and brain tissue injury following intracerebral hemorrhage (ICH). Lobar ICH in pigs produces rapidly developing, marked perihematomal edema (>10% increase in water content) associated with clot-derived plasma protein accumulation. Coagulation cascade activation and, specifically, thrombin itself contribute to edema development during the first 24 hours after gray matter ICH in rats. In the present study, we sought to determine whether blood clot formation is necessary for edema development by comparing intracerebral infusions of heparinized and unheparinized blood in pig (white matter) and in rat (gray matter). We also examined heparin's effect on thrombin-induced gray matter edema.

METHODS

In pigs, we infused autologous blood (with or without heparin) into the cerebral white matter to produce lobar hematomas and froze the brains in situ at 1, 4, or 24 hours after ICH. We determined hematomal and perihematomal edema volumes on coronal sections by computer-assisted morphometry. In rats, we infused either blood or thrombin (with or without heparin) into the basal ganglia and measured water, sodium, and potassium contents at 24 hours after ICH.

RESULTS

In pigs, unheparinized blood induced rapid (at 1 hour) and prolonged (24 hours) perihematomal edema (average volume, 1.29+/-0. 20 mL; n=6). No perihematomal edema was present following heparinized blood infusions (n=6). In rats, unheparinized blood produced significantly greater edema than heparinized blood infusions. As with whole blood, thrombin-induced gray matter edema at 24 hours was significantly reduced by coinjection of heparin.

CONCLUSIONS

After ICH, blood clot formation is required for rapid and prolonged edema development in perihematomal white and gray matter. Thrombin also contributes to prolonged edema in gray matter.

Thrombin induced inhibition of neurite outgrowth from dorsal root ganglion neurons

Thrombin is a multifunctional protease. Recent studies on cultured neuronal cells have suggested a function for thrombin in the development and maintenance of the nervous system. Thrombin has been found to induce neurite retraction and reverse stellation in neuroblastoma cell lines and rat astrocytes, respectively. The major focus of our study was to investigate the potential role of thrombin in peripheral nervous system development using the rat embryonic dorsal root ganglion model. We found a dose dependent inhibition of neurite outgrowth from explant dorsal root ganglion cultures upon exposure to 2 to 200 nM thrombin. This effect was reversed by the specific thrombin inhibitor, hirudin. A synthetic peptide that imitates the fully active receptor, thrombin receptor activating peptide, was also found to inhibit neurite outgrowth from dorsal root ganglia. bis-Benzimide stained neuronal cultures did not show any evidence of cell death after exposure to thrombin or thrombin receptor activating peptides. Immunohistochemical studies revealed specific staining of the thrombin receptor on neurons, with intense labeling along neurites. Enriched neuronal cultures exposed to thrombin and thrombin receptor activating peptides revealed rapid activation of phospholipase Cgamma-1, a second messenger associated with the thrombin receptor. These findings are the first to describe the localization of the thrombin receptor to dorsal root ganglion neurons. We propose that receptor activation is associated with thrombin induced inhibition of neurite outgrowth.

Signaling pathways involved in thrombin-induced cell protection

This study examined the signal transduction pathways involved in thrombin-induced neuroprotection and compares these results with those of a similar study of thrombin-induced neuronal death. In thrombin-induced protection of astrocytes from hypoglycemia, pretreatment of astrocytes with tyrosine or serine/threonine kinase inhibitors, cytochalasin D, or exoenzyme C3, a potent inhibitor of the small GTPase RhoA, attenuated thrombin-induced protection. These same inhibitors were previously shown to block thrombin-induced cell death, implying a similarity in the cell death and cell-protective pathways. Biochemical assays determined that thrombin increased available RhoA activity, although more slowly and to a lesser extent than occurs in thrombin-induced cell death. A clear difference in these pathways was revealed when a time course study of thrombin-induced cell death indicated that unlike thrombin-induced protection, cells must be exposed to thrombin for >16 h to irreversibly enter the cell death pathway. Addition of lower doses of thrombin every 24 h also induced cell death. These studies indicate that exposure of cells to micromolar concentrations of thrombin alone does not induce cell death, but the continued exposure to thrombin is required. Thus the cell death and protective pathways may share initial signaling proteins, but differences in the amplitude as well as the duration of the signal may result in different final pathways.

Activated macrophages and the blood-brain barrier: inflammation after CNS injury leads to increases in putative inhibitory molecules

The cellular responses to spinal cord or brain injury include the production of molecules that modulate wound healing. This study examined the upregulation of chondroitin sulfate proteoglycans, a family of molecules present in the wound healing matrix that may inhibit axon regeneration in the central nervous system (CNS) after trauma. We have demonstrated increases in these putative inhibitory molecules in brain and spinal cord injury models, and we observed a close correlation between the tissue distribution of their upregulation and the presence of inflammation and a compromised blood-brain barrier. We determined that the presence of degenerating and dying axons injured by direct trauma does not provide a sufficient signal to induce the increases in proteoglycans observed after injury. Activated macrophages, their products, or other serum components that cross a compromised blood-brain barrier may provide a stimulus for changes in extracellular matrix molecules after CNS injury. While gliosis is associated with increased levels of proteoglycans, not all reactive astrocytes are associated with augmented amounts of these extracellular matrix molecules, which suggests a heterogeneity among glial cells that exhibit a reactive phenotype. Chondroitin sulfate also demarcates developing cavities of secondary necrosis, implicating these types of boundary molecules in the protective response of the CNS to trauma.

Hirudin suppresses the invasion of inflammatory cells and the appearance of vimentin-positive astrocytes in the rat cerebral ablation model

Hirudin is a specific and direct-acting thrombin inhibitor superior to heparin as an anticoagulant. Thrombin is a multifunctional molecule that acts as a serine protease locally generated from prothrombin during blood coagulation related to injury and/or inflammation. We previously reported that thrombin might be involved in the inflammatory response, glial reaction, and scar formation that occurred in central nervous system (CNS). Here we studied the suppressive effects of hirudin on the inflammation, vimentin-positive astrocytes, and glial fibrillary acidic protein (GFAP)-positive astrocytes using rat cerebral ablation models. Hirudin and vehicle solution soaked in Gelform were administered to the cavity of the traumatic brain defect. Brains were examined by conventional histologic and immunohistologic technique. Antibodies for monocytes/macrophages, GFAP, and vimentin were used to assess the infiltration of inflammatory cells and reaction of astrocytes. The number of the inflammatory cells, vimentin-positive astrocytes, and GFAP-positive astrocytes were quantitatively analyzed. Hirudin suppressed the infiltration of inflammatory cells and the increase in vimentin-positive astrocytes, but had no effects on the increase in GFAP-positive astrocytes. These data suggest that thrombin may play an important role in inflammatory and glial responses to CNS injury, and that hirudin can be a candidate for the therapeutic agent that minimizes the secondary brain damage following the inflammation, and the glial reaction mediated by vimentin-positive astrocytes near the lesion site.

Thrombin induces apoptosis in cultured neurons and astrocytes via a pathway requiring tyrosine kinase and RhoA activities

Thrombin activity is a factor in acute CNS trauma and may contribute to such chronic neurodegenerative diseases as Alzheimer's disease. Thrombin is a multifunctional serine protease that catalyses the final steps in blood coagulation. However, increasing evidence indicates that thrombin also elicits a variety of cellular and inflammatory responses, including responses from neural cells. Most recently, high concentrations of thrombin were shown to cause cell death in both astrocyte and hippocampal neuron cultures. The purpose of this study was to determine the mechanisms underlying thrombin-induced cell death. Our data show that thrombin appears to cause apoptosis as evidenced by cleavage of DNA into oligonucleosomal-sized fragments, fragmentation of nuclei, and prevention of death by inhibition of protein synthesis. Synthetic peptides that directly activate the thrombin receptor also induced apoptosis, indicating that thrombin-induced cell death occurred via activation of the thrombin receptor. The signal transduction cascade involves tyrosine and serine/threonine kinases and an intact actin cytoskeleton. Additional study revealed the involvement of the small GTP-binding protein RhoA. Thrombin induced RhoA activity in both astrocytes and hippocampal neurons, and inhibition of RhoA activity with exoenzyme C3 attenuated cell death, indicating that thrombin activation of RhoA was necessary for thrombin-induced cell death. Tyrosine kinase inhibitors blocked thrombin induction of RhoA, indicating that tyrosine kinase activity was required upstream of RhoA. These data suggest a sequential linkage of cellular events from which we propose a model for the second messenger cascade induced by thrombin in neural cells that can lead to apoptosis.

Thrombin receptor on rat primary hippocampal neurons: coupled calcium and cAMP responses

We have tested the hypothesis that hippocampal neurons respond to thrombin via a neuronal thrombin receptor. A human neuroblastoma cell line, SK-N-SH, known to be thrombin responsive morphologically, responded both to thrombin and thrombin receptor agonist peptide (TRAP 42-55) with elevation of intracellular calcium. In Western blots of membranes from SK-N-SH cells and cultured rat hippocampal neurons using an antibody against the N-terminal peptide of the human thrombin receptor, putative receptor proteins of 66 and 47 kDa were detected in both cells. Neurons were treated with thrombin and TRAP 42-55 (TRAP-14) to determine their effects on intracellular levels of calcium and cAMP. Only 10% of the neurons showed a rapid response to thrombin, but most responded rapidly to agonist peptide with a prolonged elevation of intracellular free calcium. Neuronal cAMP levels were decreased by 40% after 24 h thrombin treatment. This decrease in cAMP level could be blocked by both the Gi-protein inhibitor, pertussis toxin, and the thrombin inhibitor, hirudin, suggesting a possible involvement of Gi-protein-coupled receptor activation. Furthermore, rapid calcium and cAMP responses were apparently induced by pre-treatment of neurons with thrombin for 24 h and subsequent washout. In summary, these data indicate that rat primary hippocampal neurons have thrombin receptors whose responses to thrombin apparently are up-regulated by 24 h thrombin pre-treatment. These results may have implications for synaptic remodeling, learning and memory.

Experimental intracerebral hemorrhage in rats. Magnetic resonance imaging and histopathological correlates

BACKGROUND AND PURPOSE

Intracerebral hemorrhage is associated with a considerable proportion of strokes and head injuries. The mechanism of brain cell injury associated with hemorrhage may be different from that due to pure ischemia. Therefore, it is essential that models of intracerebral hemorrhage be developed and well characterized. The purpose of this study was to obtain high-field MR images of rat brain at progressive times after induction of intracerebral hemorrhage and to correlate the images with behavior and histological evolution.

METHODS

Intracerebral hemorrhage was induced in rats by injection of bacterial collagenase and heparin into the caudate nucleus. Histopathological changes and corresponding MR images were studied from 30 minutes to 3 weeks after injection. Behavioral changes were also followed for 3 weeks.

RESULTS

Histological correlation showed that MR is capable of resolving the accumulation and degeneration of the hematoma, a centripetal wave of neutrophils infiltrating from the surrounding tissue beginning at 12 hours, and centripetal invasion of macrophages beginning at 48 hours. Widespread white matter edema was clearly evident on MR images for 1 week after the hemorrhage. Medium-sized striatal neurons were lost in the tissue surrounding the hematoma. Behavioral improvement was rapid during resolution of the edema but incomplete at 3 weeks.

CONCLUSIONS

MR images correlate very well with histological changes in this experimental model of intracerebral hemorrhage and can therefore be used to follow changes due to drug treatments in vivo. The intense neutrophilic response to this lesion may contribute to neuronal injury at the periphery of the hematoma.

Bromodeoxyuridine: a diagnostic tool in biology and medicine, Part III. Proliferation in normal, injured and diseased tissue, growth factors, differentiation, DNA replication sites and in situ hybridization

This paper is a continuation of parts I (history, methods and cell kinetics) and II (clinical applications and carcinogenesis) published previously (Dolbeare, 1995 Histochem. J. 27, 339, 923). Incorporation of bromodeoxyuridine (BrdUrd) into DNA is used to measure proliferation in normal, diseased and injured tissue and to follow the effect of growth factors. Immunochemical detection of BrdUrd can be used to determine proliferative characteristics of differentiating tissues and to obtain birth dates for actual differentiation events. Studies are also described in which BrdUrd is used to follow the order of DNA replication in specific chromosomes, DNA replication sites in the nucleus and to monitor DNA repair. BrdUrd incorporation has been used as a tool for in situ hybridization experiments.

Thrombin-soaked gelatin sponge and brain edema in rats

Previous work from this laboratory has shown that injection of thrombin into rat basal ganglia causes brain edema. This study investigates the effect on rat brain of thrombin-soaked gelatin sponge (used for intraoperative hemostasis in clinical situations) at a concentration similar to that used in humans. Three models were developed to evaluate this effect. In the first model, a gelatin sponge soaked with vehicle or thrombin (100 U/cm3) was placed on the intact pia of the right frontal lobe in rats without cortical lesions. In the second model, frontal cortex was excised (3 mm3) and the exposed brain was cauterized with electrocoagulation. Gelatin sponge was soaked with vehicle or thrombin (1000, 100, 10, or 1 U/cm3) and placed in the lesion site. In the third model, hirudin, a specific thrombin antagonist, was added to the thrombin-soaked gelatin sponge and placed in a similar cortical lesion to determine if the observed effects were specific to thrombin. The dose-response range for thrombin was determined qualitatively by magnetic resonance (MR) imaging and quantitatively by brain edema formation 24 hours after exposure. We found no edema in the cortically intact rats. The rats given cortical lesions developed significant edema when subjected to 1000, 100, and 10 U/cm3 thrombin as seen on MR imaging and at 100 and 10 U/cm3 thrombin as revealed by wet/dry weight and ion studies of brain tissue. Topical hirudin prevented thrombin-induced edema. It is concluded that thrombin-soaked gelatin sponges cause or enhance significant brain edema in rats at concentrations typically used for human neurosurgery.

The role of the coagulation cascade in brain edema formation after intracerebral hemorrhage

The coagulation cascade has a potential role in brain edema formation due to intracerebral hemorrhage. In this study blood and other solutions were injected stereotactically into the right basal ganglia in rats. Twenty-four hours following injection, brain water and ion contents were measured to determine the amount of brain edema. Intracerebral blood resulted in an increase in brain water content. The amount of brain edema surrounding the intracerebral hematoma was reduced by a thrombin inhibitor N alpha-(2-Naphthalenesulfonylglycyl)-4-amidino-DL-phenylalaninep iperidide, (alpha-NAPAP) infused into the hematoma after the clot had been allowed to solidify. The inhibitor did not alter the actual size of the clot mass. An artificial clot composed of fibrinogen, thrombin, and styrene microspheres also produced brain edema. A fibrin clot led to edema formation even in the absence of mass effect provided by the microspheres. The single component responsible for production of brain edema in all these models was thrombin. The edema was formed in response to a fibrinogen-independent pathway. These results indicate that the coagulation cascade is involved in brain edema that develops adjacent to an intracerebral hematoma.

Dual effects of thrombin and a 14-amino acid peptide agonist of the thrombin receptor on septal cholinergic neurons

We have compared the effects of thrombin and of the 14-amino acid peptide agonist (TRAP-14) of the thrombin protease activated receptor (PAR) on cholinergic neurons in pure cultures of rat septal neurons and in co-cultures of septal neurons and glial cells. In pure septal cultures, low concentrations of thrombin (up to 10 nM) did not affect choline acetyltransferase (ChAT) activity, a marker of cholinergic neurons, or 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) reduction, an index of cell viability. However, 100 nM thrombin decreased ChAT activity and MTT reduction by 44 and 17%, respectively. In co-cultures, a low concentration of thrombin (1 nM) increased ChAT activity (+75%), whereas a high concentration (100 nM) decreased it (-83%). At this high concentration, thrombin was neurotoxic, as indicated by a large decrease in MTT reduction (-80%). Thrombin effects on ChAT activity were mimicked by TRAP-14 both in pure septal cultures (no effect at 0.1 microM and -63% at 100 microM) and in co-cultures (+25% at 0.1 microM and -28% at 100 microM). In contrast, this peptide did not affect MTT reduction. These dual effects of thrombin and TRAP-14 on ChAT activity in co-cultures, were also observed on pure cultures of septal cells supplied with NGF. The activation and inhibition by TRAP-14 of the expression of ChAT activity in septal neuron/glial cell cultures were inhibited by a 9-amino acid peptide antagonist of thrombin PAR. Thus, the effects of thrombin on cholinergic neurons seem to be mainly mediated by thrombin PAR and glial cells seem to play a major role in these thrombin actions.

Redistribution and degeneration of retinal astrocytes in experimental murine cerebral malaria: relationship to disruption of the blood-retinal barrier

To determine whether astrocytes play a critical role in the pathogenesis of experimental murine cerebral malaria (EMCM), we examined changes in astrocyte morphology and distribution, using retinal wholemounts, in three models: a fatal cerebral malaria (CM) model, in which mice die showing cerebral symptoms; a "resolving" model, in which mice exhibit mild cerebral symptoms, but then recover; and a non-CM model, in which cerebral symptoms are not seen. In the fatal model, retinal astrocytes lost their even distribution from day 3 post-inoculation (p.i.) with malaria parasites, progressing to gliosis (day 5 p.i.), well before the onset of cerebral symptoms on day 6-7 p.i. At the terminal stage of the disease there was a loss of astrocyte processes contacting retinal vessels, often along vessel segments containing adherent monocytes. These features occurred in a mild form in the resolving model and were absent in the non-CM models. To investigate the mechanisms underlying these astrocytic changes, we carried out two experimental manipulations. Firstly, since dexamethasone ameliorates cerebral complications in the fatal CM model, the astrocytic response was monitored after dexamethasone treatment on days 0 and 1 p.i., or days 3 and 4 p.i. Second, to determine whether increased blood-retinal barrier (BRB) permeability initiates the astrocyte changes, breakdown of the BRB was induced experimentally by intra-carotid injection of arabinose and astrocyte morphology and distribution were examined 12, 24, and 48 h later. Retinal astrocytes in both the dexamethasone- and the arabinose-treated groups showed loss of even astrocyte distribution but no loss of astrocyte ensheathment of vessels. It is concluded that: i) astrocytes are involved in the pathogenesis of EMCM, since these changes are only prominent in the fatal model and occur substantially before the onset of cerebral symptoms; ii) the initial changes in astrocyte distribution may be a consequence of the increase in BRB permeability; and iii) the immune response triggered by the malaria parasite may be responsible for the loss of astrocyte ensheathment of vessel segments.

Edema from intracerebral hemorrhage: the role of thrombin

The mechanism by which intracerebral hemorrhage leads to the formation of brain edema is unknown. This study assesses the components of blood to determine if any are toxic to surrounding brain. Various solutions were infused stereotactically into the right basal ganglia of rats. The animals were sacrificed 24 hours later; brain edema and ion contents were measured. Whole blood caused an increase in brain water content and ion changes consistent with brain edema. Concentrated blood cells, serum from clotted blood, and plasma from unclotted blood all failed to provoke edema formation when infused directly into the brain. On the other hand, activation of the coagulation cascade by adding prothrombinase to plasma did produce brain edema. The edema response to whole blood could be prevented by adding a specific thrombin inhibitor, hirudin, to the injected blood. This study indicates that thrombin plays an important role in edema formation from an intracerebral blood clot.

Intracerebral infusion of thrombin as a cause of brain edema

Purified thrombin from an exogenous source is a hemostatic agent commonly used in neurosurgical procedures. The toxicity of thrombin in the brain, however, has not been examined. This study was performed to assess the effect of thrombin on brain parenchyma, using the formation of brain edema as an indicator of injury. Ten microliters of test solution was infused stereotactically into the right basal ganglia of rats. The animals were sacrificed 24 hours later, and the extent of brain edema and ion content were measured. Concentrations of human thrombin as low as 1 U/microliter resulted in a significant increase in brain water content. Rats receiving 10 U/microliters had a mortality rate of 33% compared to no mortality in the groups receiving smaller doses. Thrombin-induced brain edema was inhibited by a specific and potent thrombin inhibitor, hirudin. A medical grade of bovine thrombin commonly used in surgery also caused brain edema when injected at a concentration of 2 U/microliters. Edema formation was prevented by another highly specific thrombin inhibitor, N alpha-(2-Naphthalenesulfonylglycyl)-4-DL-phenylalaninepiperidid e (alpha-NAPAP). Thrombin-induced brain edema was accompanied by increases in brain sodium and chloride contents and a decrease in brain potassium content. Changes in brain ions were inhibited by both hirudin and alpha-NAPAP, corresponding to the inhibition of brain water accumulation. This study shows that thrombin causes brain edema when infused into the brain at concentrations as low as 1 U/microliter, an amount within the range of concentrations used for topical hemostasis in neurosurgery.

Protease nexin-1, a potent thrombin inhibitor, is reduced around cerebral blood vessels in Alzheimer's disease

The clotting protease thrombin might contribute to the pathophysiology of central nervous system (CNS) injury and certain diseases by its ability to retract processes on neurons and astrocytes and to stimulate astrocyte proliferation. Protease nexin-1 (PN-1) is a 43 kDa thrombin inhibitor found predominantly in the brain where much of it resides around capillaries and large blood vessels. This location of PN-1 prompted the hypothesis that it may play a protective role against extravasated thrombin released following cerebrovascular injury or under certain pathological conditions. Recent studies indicated that the levels of PN-1 are markedly reduced in the postmortem brains of patients with Alzheimer's disease (AD). It was suggested that this reduction in PN-1 levels was due to the sequestration of PN-1 by extravasated thrombin. In the present study we examined the specific nature of this reduction by immunohistochemical staining of sections from control and AD brains using PN-1 specific antibodies. We show that the levels of PN-1 immunoreactivity around blood vessels and the number of blood vessels exhibiting PN-1 immunoreactivity were markedly reduced in the brains of patients with AD compared to age-matched controls; this reduction was reflected by a decrease in the levels of PN-1 activity and PN-1 protein. Thus an imbalance between PN-1 and thrombin may be a contributing factor in the pathology of AD.