Injections of blood, thrombin, and plasminogen more severely damage neonatal mouse brain than mature mouse brain

Monitoring neonatal brain hemorrhage progression by photoacoustic tomography

Neonatal brain hemorrhage (NBH) is the most common neurological disorder in neonates and its clinical interventions are very limited. Understanding the pathology of NBH by non-invasive in-vivo characterization of standardized animal models is essential for developing potential treatments. Currently, there is no suitable tool to provide non-invasive, non-ionizing dynamic imaging of neonatal mouse models with high resolution, high contrast, and deep imaging depth. In this study, we implemented a fast 3D photoacoustic tomography (PAT) system suitable for imaging neonatal mouse brains with good image quality and demonstrated its feasibility in non-invasive monitoring of the dynamic process of NBH in the whole neonatal mouse brain. The results present a high resolution and sensitivity for NBH detection. Both morphological and hemodynamic changes of the hematoma were accurately obtained. Our results demonstrated the potential of PAT as a powerful tool for the preclinical study of neonatal brain hemorrhage.

The Regulated Cell Death and Potential Interventions in Preterm Infants after Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) in preterm infants is one of the major co-morbidities of preterm birth and is associated with long-term neurodevelopmental deficits. There are currently no widely accepted treatments to prevent ICH or therapies for the neurological sequelae. With studies broadening the scope of cell death, the newly defined concept of regulated cell death has enriched our understanding of the underlying mechanisms of secondary brain injury after ICH and has suggested potential interventions in preterm infants. In this review, we will summarize the current evidence for regulated cell death pathways in preterm infants after ICH, including apoptosis, necroptosis, pyroptosis, ferroptosis, autophagy, and PANoptosis as well as several potential intervention strategies that may protect the immature brain from secondary injury after ICH through regulating regulated cell death.

Intracerebral hemorrhage and thrombin-induced alterations in cerebral microvessel matrix

Four phase III clinical trials of oral direct factor Xa or thrombin inhibitors demonstrated significantly lower intracranial hemorrhage compared to warfarin in patients with nonvalvular-atrial fibrillation. This is counter-intuitive to the principle that inhibiting thrombosis should increase hemorrhagic risk. We tested the novel hypothesis that anti-thrombin activity decreases the risk of intracerebral hemorrhage by directly inhibiting thrombin-mediated degradation of cerebral microvessel basal lamina matrix, responsible for preventing hemorrhage. Collagen IV, laminin, and perlecan each contain one or more copies of the unique α-thrombin cleavage site consensus sequence. In blinded controlled experiments, α-thrombin significantly degraded each matrix protein in vitro and in vivo in a concentration-dependent fashion. In vivo stereotaxic injection of α-thrombin significantly increased permeability, local IgG extravasation, and hemoglobin (Hgb) deposition together with microvessel matrix degradation in a mouse model. In all formats the direct anti-thrombin dabigatran completely inhibited matrix degradation by α-thrombin. Fourteen-day oral exposure to dabigatran etexilate-containing chow completely inhibited matrix degradation, the permeability to large molecules, and cerebral hemorrhage associated with α-thrombin. These experiments demonstrate that thrombin can degrade microvessel matrix, leading to hemorrhage, and that inhibition of microvessel matrix degradation by α-thrombin decreases cerebral hemorrhage. Implications for focal ischemia and other conditions are discussed.

Iron Neurotoxicity and Protection by Deferoxamine in Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is a subtype of stroke that is characterized by high morbidity and mortality, for which clinical outcome remains poor. An extensive literature indicates that the release of ferrous iron from ruptured erythrocytes in the hematoma is a key pathogenic factor in ICH-induced brain injury. Deferoxamine is an FDA-approved iron chelator that has the capacity to penetrate the blood-brain barrier after systemic administration and binds to iron. Previous animal studies have shown that deferoxamine attenuates ICH-induced brain edema, neuronal death, and neurological deficits. This review summarizes recent progress of the mechanisms by which deferoxamine may alleviate ICH and discusses further studies on its clinical utility.

Intracerebral haemorrhage: from clinical settings to animal models

Spontaneous intracerebral haemorrhage (ICH) is a devastating type of stroke with high mortality and morbidity and for which no effective treatments are available to date. Much experimental and clinical research have been performed to explore its mechanisms regard the subsequent inflammatory cascade and to seek the potential therapeutic strategies. The aim of this review is to discuss insights from clinical settings that have led to the development of numerous animal models of ICH. Some of the current and future challenges for clinicians to understand ICH are also surveyed.

Cerebral microbleeds in a neonatal rat model

BACKGROUND

In adult humans, cerebral microbleeds play important roles in neurodegenerative diseases but in neonates, the consequences of cerebral microbleeds are unknown. In rats, a single pro-angiogenic stimulus in utero predisposes to cerebral microbleeds after birth at term, a time when late oligodendrocyte progenitors (pre-oligodendrocytes) dominate in the rat brain. We hypothesized that two independent pro-angiogenic stimuli in utero would be associated with a high likelihood of perinatal microbleeds that would be severely damaging to white matter.

METHODS

Pregnant Wistar rats were subjected to intrauterine ischemia (IUI) and low-dose maternal lipopolysaccharide (mLPS) at embryonic day (E) 19. Pups were born vaginally or abdominally at E21-22. Brains were evaluated for angiogenic markers, microhemorrhages, myelination and axonal development. Neurological function was assessed out to 6 weeks.

RESULTS

mRNA (Vegf, Cd31, Mmp2, Mmp9, Timp1, Timp2) and protein (CD31, MMP2, MMP9) for angiogenic markers, in situ proteolytic activity, and collagen IV immunoreactivity were altered, consistent with an angiogenic response. Vaginally delivered pups exposed to prenatal IUI+mLPS had spontaneous cerebral microbleeds, abnormal neurological function, and dysmorphic, hypomyelinated white matter and axonopathy. Pups exposed to the same pro-angiogenic stimuli in utero but delivered abdominally had minimal cerebral microbleeds, preserved myelination and axonal development, and neurological function similar to naïve controls.

CONCLUSIONS

In rats, pro-angiogenic stimuli in utero can predispose to vascular fragility and lead to cerebral microbleeds. The study of microbleeds in the neonatal rat brain at full gestation may give insights into the consequences of microbleeds in human preterm infants during critical periods of white matter development.

Post-hemorrhagic hydrocephalus: Recent advances and new therapeutic insights

Post-hemorrhagic hydrocephalus (PHH), also referred to as progressive ventricular dilatation, is caused by disturbances in cerebrospinal fluid (CSF) flow or absorption following hemorrhage in the brain. As one of the most serious complications of neonatal/adult intraventricular hemorrhage (IVH), subarachnoid hemorrhage (SAH), and traumatic brain injury (TBI), PHH is associated with increased morbidity and disability of these events. Common sequelae of PHH include neurocognitive impairment, motor dysfunction, and growth impairment. Non-surgical measures to reduce increased intracranial pressure (ICP) in PHH have shown little success and most patients will ultimately require surgical management, such as external ventricular drainage and shunting which mostly by inserting a CSF drainage shunt. Unfortunately, shunt complications are common and the optimum time for intervention is unclear. To date, there remains no comprehensive strategy for PHH management and it becomes imperative that to explore new therapeutic targets and methods for PHH. Over past decades, increasing evidence have indicated that hemorrhage-derived blood and subsequent metabolic products may play a key role in the development of IVH-, SAH- and TBI-associated PHH. Several intervention strategies have recently been evaluated and cross-referenced. In this review, we summarized and discussed the common aspects of hydrocephalus following IVH, SAH and TBI, relevant experimental animal models, clinical translation of in vivo experiments, and potential preventive and therapeutic targets for PHH.

Major remodeling of brain microvessels during neonatal period in the mouse: A proteomic and transcriptomic study

Preterm infants born before 29 gestation weeks incur major risk of subependymal/intracerebral/intraventricular hemorrhage. In mice, neonate brain endothelial cells are more prone than adult cells to secrete proteases under glutamate challenge, and invalidation of the Serpine 1 gene is accompanied by high brain hemorrhage risk up to five days after birth. We hypothesized that the structural and functional states of microvessels might account for age-dependent vulnerability in mice up to five days after birth and might represent a pertinent paradigm to approach the hemorrhage risk window observed in extreme preterms. Mass spectrometry proteome analyses of forebrain microvessels at days 5, 10 and in adult mice revealed 899 proteins and 36 enriched pathways. Microarray transcriptomic study identified 5873 genes undergoing at least two-fold change between ages and 93 enriched pathways. Both approaches pointed towards extracellular matrix, cell adhesion and junction pathways, indicating delayed microvascular strengthening after P5. Furthermore, glutamate receptors, proteases and their inhibitors exhibited convergent evolutions towards excitatory aminoacid sensitivity and low proteolytic control likely accounting for vascular vulnerability in P5 mice. Thus, age vascular specificities must be considered in future therapeutic interventions in preterms. Data are available on ProteomeXchange (identifier PXD001718) and NCBI Gene-Expression-Omnibus repository (identification GSE67870).

Third trimester-equivalent ethanol exposure causes micro-hemorrhages in the rat brain

Exposure to ethanol during fetal development produces long-lasting neurobehavioral deficits caused by functional alterations in neuronal circuits across multiple brain regions. Therapeutic interventions currently used to treat these deficits are only partially efficacious, which is a consequence of limited understanding of the mechanism of action of ethanol. Here, we describe a novel effect of ethanol in the developing brain. Specifically, we show that exposure of rats to ethanol in vapor chambers during the equivalent to the third trimester of human pregnancy causes brain micro-hemorrhages. This effect was observed both at low and high doses of ethanol vapor exposure, and was not specific to this exposure paradigm as it was also observed when ethanol was administered via intra-esophageal gavage. The vast majority of the micro-hemorrhages were located in the cerebral cortex but were also observed in the hypothalamus, midbrain, olfactory tubercle, and striatum. The auditory, cingulate, insular, motor, orbital, retrosplenial, somatosensory, and visual cortices were primarily affected. Immunohistochemical experiments showed that the micro-hemorrhages caused neuronal loss, as well as reactive astrogliosis and microglial activation. Analysis with the Catwalk test revealed subtle deficits in motor function during adolescence/young adulthood. In conclusion, our study provides additional evidence linking developmental ethanol exposure with alterations in the fetal cerebral vasculature. Given that this effect was observed at moderate levels of ethanol exposure, our findings lend additional support to the recommendation that women abstain from consuming alcoholic beverages during pregnancy.

Impaired adult hippocampal neurogenesis and cognitive ability in a mouse model of intrastriatal hemorrhage

Thrombin released by hematoma is an important mediator of the secondary injury of intracerebral hemorrhage (ICH), however, the effect of thrombin on adult neurogenesis and cognitive ability remains elusive. In this study, intrastriatal injection of 0.05 U thrombin didn't affect the neurogenesis at the subgranular zone (SGZ), which was distal to the injection site. 0.1 U thrombin increased the 5-bromo-2-deoxyuridine(+) (BrdU(+), S-phase proliferating cells)/doublecortin(+) (DCX(+), immature neurons) double labelled neurons, but decreased BrdU(+)/NeuN(+) double labelled mature neurons. Higher doses of thrombin (1 U, 2 U, and 5 U) significantly decreased the BrdU(+)/DCX(+) and BrdU(+)/NeuN(+) double labelled cells. After 1 U thrombin injection, cell apoptosis was found at the dentate gyrus of hippocampus at 3-24 h, but not 5 d post-injury. Thrombin infusion (1 U) induced spatial memory deficits in Morris water maze test; whereas, hirudin, the thrombin antagonist, significantly reversed both neurogenesis loss and spatial learning and memory impairment. In conclusion, at least at short term (5 days) after striatum ICH, the effect of high dose of thrombin on neurogenesis of SGZ, and the spatial learning and memory ability, is detrimental.

Interference with protease-activated receptor 1 does not reduce damage to subventricular zone cells of immature rodent brain following exposure to blood or blood plasma

BACKGROUND

Prior work showed that whole blood, plasma, and serum injections are damaging to the neonatal rodent brain in a model of intracerebral/periventricular hemorrhage. Thrombin alone is also damaging. In adult animal models of hemorrhagic stroke, the protease-activated (thrombin) receptor PAR1 mediates some of the brain damage. We hypothesized that PAR1 interference will reduce the adverse effects of blood products on immature rodent brain and cells.

RESULTS

Cultured oligodendrocyte precursor cells from rats and mice were exposed to blood plasma with and without the PAR1 antagonists SCH-79797 or BMS-200261. In concentrations previously shown to have activity on brain cells, neither drug showed evidence of protection against the toxicity of blood plasma. Newborn mice (wild type, heterozygous, and PAR1 knockout) were subjected to intracerebral injection of autologous whole blood into the periventricular region of the frontal lobe. Cell proliferation, measured by Ki67 immunoreactivity in the subventricular zone, was suppressed at 1 and 2 days, and was not normalized in the knockout mice. Cell apoptosis, measured by activated caspase 3 immunoreactivity, was not apparent in the subventricular zone. Increased apoptosis in periventricular striatal cells was not normalized in the knockout mice.

CONCLUSION

Interference with the thrombin-PAR1 system does not reduce the adverse effects of blood on germinal cells of the immature rodent brain. PAR1 interference is unlikely to be a useful treatment for reducing the brain damage that accompanies periventricular (germinal matrix) hemorrhage, a common complication of premature birth.

Warfarin pretreatment reduces cell death and MMP-9 activity in experimental intracerebral hemorrhage

Little is known about the pathophysiology of oral anticoagulation-associated intracerebral hemorrhage (OAC-ICH). We compared hematoma volume, number of terminal deoxynucleotidyl dUTP nick-end labeling (TUNEL)-positive cells (indicating cell death), MMP-9 levels, and perilesional edema formation between warfarin-treated mice and controls. Intracerebral hemorrhage was induced by an injection of collagenase into the right striatum. Twenty-four hours later, hematoma volume was measured using a photometric hemoglobin assay. Cell death was quantified using TUNEL staining. MMP-9 levels were determined by zymography, and edema formation was assessed via the wet-dry method. Warfarin increased hematoma volume by 2.6-fold. The absolute number of TUNEL-positive cells in the perihematomal zone was lower in warfarin-treated animals (300.5 ± 39.8 cells/mm2) than in controls (430.5 ± 38.9 cells/mm2; p = 0.034), despite the larger bleeding volume. MMP-9 levels were reduced in anticoagulated mice as compared to controls (p = 0.018). Perilesional edema formation was absent in warfarin mice and modestly present in controls. Our results suggest differences in the pathophysiology of OAC-ICH compared to intracerebral hemorrhage occurring under normal coagulation. A likely explanation is that thrombin, a strong inductor of apoptotic cell death and blood-brain barrier disruption, is produced to a lesser extent in OAC-ICH. In humans, however, we assume that the detrimental effects of a larger hematoma volume in OAC-ICH by far outweigh potential protective effects of thrombin deficiency.

Thrombin Causes Neuronal Atrophy and Acute but not Chronic Cell Death

BACKGROUND

Brain injury after intracerebral hemorrhage (ICH) arises from numerous contributors, of which some also play essential roles. Notably, thrombin production, needed to stop bleeding, also causes acute cell death and edema. In some rodent models of ICH, peri-hematoma neurons die over weeks. Hence we evaluated whether thrombin is responsible for this chronic degeneration. Functional impairments after ICH also result from sub-lethal damage to neurons, especially the loss of dendrites. Thus, we evaluated whether thrombin infusion alone, a reductionist model of ICH, causes similar injury.

METHODS

Adult rats had a modest intra-striatal infusion of thrombin (1 U) or saline followed by a behavioral test, to verify impairment, 7 days later. After this they were euthanized and tissue stained with Golgi-Cox solution to allow the assessment of dendritic morphology in striatal neurons. In a second experiment, rats survived 7 or 60 days after thrombin infusion in order to histologically determine lesion volume.

RESULTS

Thrombin caused early cell death and considerable atrophy in surviving peri-lesion neurons, which had less than half of their usual numbers of branches. However, total tissue loss was comparable at 7 (24.1 mm3) and 60 days (25.6 mm3).

CONCLUSION

Thrombin infusion causes early cell death and neuronal atrophy in nearby surviving striatal neurons but thrombin does not cause chronic tissue loss. Thus, the chronic degeneration found after ICH in rats is not simply and solely due to acute thrombin production. Nonetheless, thrombin is an important contributor to behavioral dysfunction because it causes cell death and substantial dendritic injury.

Mechanisms of hydrocephalus after neonatal and adult intraventricular hemorrhage

Intraventricular hemorrhage (IVH) is a cause of significant morbidity and mortality and is an independent predictor of a worse outcome in intracerebral hemorrhage (ICH) and germinal matrix hemorrhage (GMH). IVH may result in both injuries to the brain as well as hydrocephalus. This paper reviews evidence on the mechanisms and potential treatments for IVH-induced hydrocephalus. One frequently cited theory to explain hydrocephalus after IVH involves obliteration of the arachnoid villi by microthrombi with subsequent inflammation and fibrosis causing CSF outflow obstruction. Although there is some evidence to support this theory, there may be other mechanisms involved, which contribute to the development of hydrocephalus. It is also unclear whether the causes of acute and chronic hydrocephalus after hemorrhage occur via different mechanisms; mechanical obstruction by blood in the former, and inflammation and fibrosis in the latter. Management of IVH and strategies for prevention of brain injury and hydrocephalus are areas requiring further study. A better understanding of the pathogenesis of hydrocephalus after IVH, may lead to improved strategies to prevent and treat post-hemorrhagic hydrocephalus.

Microglia activation in the extremely preterm human brain

BACKGROUND

The periventricular white matter (PVWM) of the immature preterm brain is selectively vulnerable to a spectrum of injury. Although essential for normal brain development, the presence of resident microglia may exacerbate PVWM injury.

METHODS

We used immunohistochemistry to investigate microglia profile in human preterm noninjured control brains and in brains with evidence of germinal matrix hemorrhage/intraventricular hemorrhage (GMH/IVH), with median gestational age (GA) of 24.1 and 25.4 wk, respectively.

RESULTS

The number of microglia in the PVWM was higher than the other brain regions in both the control and GMH/IVH groups. Microglial density increased further in the PVWM of GMH/IVH brains, regardless of hemorrhage severity and despite normal macroscopic and imaging appearances to the PVWM. This was due to an increase in activated Iba1/CD68- and not Iba/CD45-immunopositive microglia. However, there were very few CD68/Ki67 colocalized cells, suggesting that the source of this increase may be due to a quick transformation of CD45-immunopositive hematopoietic microglia into CD68-immunopositive microglia. There was also increased apoptosis in the PVWM of all cases of GMH/IVH, with axonal injury and increased tumor necrosis factor-α (TNF-α) expression evident in the most severe cases.

CONCLUSION

Isolated GMH/IVH may influence ongoing brain development, with a significant role played by microglial activation.

Time course of upregulation of inflammatory mediators in the hemorrhagic brain in rats: correlation with brain edema

Intracerebral hemorrhage (ICH) can cause secondary brain damage through inflammation-related pathways. Thrombin and one of its receptors, protease activated receptor-1 (PAR-1); matrix metalloproteinase (MMP)-9; and aquaporin (AQP)-4 are stroke-related inflammatory mediators that have been implicated in ICH pathology. To further characterize the inflammatory response after ICH, we studied the temporal profile of the expression of these inflammatory mediators and assessed their potential correlation with brain edema formation after brain hemorrhage in rats. ICH was modeled by infusing autologous blood into the striatum. Then mRNA and protein expression was assessed over the course of 5 days. We found that the mRNA and/or protein expression of thrombin, PAR-1, AQP-4, and MMP-9 was upregulated between 2h and 5 days after ICH. Each reached a maximal level at day 2, except for AQP-4 protein, which peaked at day 5. Brain water content after ICH presented a similar trend; it was increased at 2h, peaked at day 2, and then decreased but remained elevated at day 5. Our data provide novel evidence that upregulation of these selected inflammatory mediators occurs very early and persists for several days after ICH, and that temporal patterns of expression of thrombin and AQP-4 are associated with brain edema formation. These findings have important implications for efforts to reduce secondary brain damage after ICH.

Mechanisms of injury to white matter adjacent to a large intraventricular hemorrhage in the preterm brain

The purpose of this article is to investigate the hyperechoic lesion seen adjacent to a lateral ventricle that contains blood but is not distended. The literature on ependymal barrier dysfunction was reviewed in search of mechanisms of injury to the white matter adjacent to an intraventricular hemorrhage. The clinical literature on the clinical diagnosis of periventricular hemorrhagic infarction was also reviewed to find out how frequently this diagnosis was made. Support was found for the possibility that the ventricular wall does not always function as an efficient barrier, allowing ventricular contents to gain access to the white matter where they cause damage. Hemorrhagic infarction may not be the only or the most frequent mechanism of white matter damage adjacent to a large intraventricular hemorrhage.

Toxic effect of blood components on perinatal rat subventricular zone cells and oligodendrocyte precursor cell proliferation, differentiation and migration in culture

The germinal matrix of human brain gives rise to oligodendrocytes and astrocytes after mid-gestation. Hemorrhage in the germinal matrix of premature infants is associated with suppressed cell proliferation. We hypothesize that soluble blood constituents have an adverse effect on the proliferation of cultured rat subventricular zone (SVZ) cells and the proliferation, migration, and differentiation of oligodendrocyte progenitor cells (OPC). Using caspase 3 activation and lactate dehydrogenase release assays, rat plasma, serum, thrombin, and kallikrein killed SVZ cells when grown in the presence (but not absence) of platelet derived growth factor. Plasma and serum killed OPC at 1:1 to 1:100 dilutions. Using a bromodeoxyuridine incorporation assay OPC proliferation was reduced by plasma, serum, thrombin and plasmin. Blood proteins also suppressed OPC migration in a concentration dependent manner. However, differentiation of OPC into myelin basic protein expressing cells was suppressed only by thrombin. We conclude that soluble blood components, particularly thrombin, have an adverse effect on maturing SVZ cells and OPC derived from newborn rat brain.

Contributions of multiple proteases to neurotoxicity in a mouse model of intracerebral haemorrhage

Proteases such as matrix metalloproteinases (MMPs) and thrombin are implicated in intracerebral haemorrhage (ICH) but their interactions amongst one another and interdependency remain to be defined. The latter is important since proteases acting through different mechanisms to inflict neurotoxicity would require separate targeting compared with proteases acting through the same cascade. We reported recently that MMP-9 and thrombin combined to promote neurotoxicity in ICH; however, as there was still substantial injury when both MMP-9 and thrombin were inhibited, we sought other factors that also contribute to ICH pathology. MMP-3, another member of the MMP family, has been correlated with poor prognosis in ICH in humans and it has been shown to increase rapidly after ICH in animals. Moreover, MMP-3 can convert the MMP-9 zymogen to its active form. Thus, we have examined whether MMP-3 is neurotoxic and addressed whether its potential effect in ICH is dependent on, or additional to, damage inflicted by MMP-9 and thrombin. We report that cultured neurons are killed by MMP-3 and that neuronal death is most marked when all three proteases, MMP-3, MMP-9 and thrombin, are combined. In vivo, the injection of autologous blood into the right striatum to produce ICH injury resulted in MMP-3 expression within 3 h. The blood-induced lesion and neuronal death was significantly reduced in MMP-3 or MMP-9 null mice compared with wild-type counterparts, and MMP-3 and -9 double null mice had even less brain damage. Significantly, pathological destruction after ICH was least in MMP-3 and -9 double null mice treated with a thrombin antagonist, hirudin. These results provide insights into molecules that inflict neurotoxicity in ICH and demonstrate that multiple proteases would need to be targeted simultaneously to successfully reduce ICH neurotoxicity.

The expression and the role of protease nexin-1 on brain edema after intracerebral hemorrhage

Brain edema is one of the most frequent and serious complications of intracerebral hemorrhage (ICH), but how the ICH cause brain edema is unknown. Our studies were designed to investigate the regulation and distribution of protease nexin-1 (PN-1), thrombin and aquaporin-4 (AQP-4) in brain edema after ICH in rat and human brain in vivo. Our result showed that the severity of cerebral edema resulted from an acute stage of ICH. The PN-1-thrombin system modulated cerebral edema after ICH. Thrombin and AQP-4 increased to aggregate cerebral edema after ICH. In order to control the deleterious effect of thrombin's overexpression, PN-1 appeared quickly and abundantly to inhibit thrombin and lessen the cerebral edema. PN-1 was distributed in neurons and glial cells of cerebral cortex, hippocampus, thalamencephalon, basal ganglia, cerebellum and circum-encephalocoele in rat and human brain. The expression of AQP-4 is different between human and rat. Thus, we demonstrated that the animal experimental approach was, however, not sufficient by itself and needed to be corroborated by observations on human brains.

Proinflammatory cytokine production by cultured neonatal rat microglia after exposure to blood products

Periventricular germinal matrix hemorrhage is a devastating complication of preterm birth. Inflammation appears to play a role in brain damage after premature birth and hypoxia. The effects of rat blood plasma and serum on cytokine expression by cultured rat microglial cells were investigated. We analyzed mRNA expression levels of tumor necrosis factor (TNF)-alpha, interleukin-6 and protease activated receptor-1 and -4 by quantitative RT-PCR. Protein expression for TNFalpha was done using immunocytochemistry and ELISPOT assays. Plasma and serum had dose dependent toxic effects on microglia as measured by lactate dehydrogenase release assay and activated caspase-3 immunocytochemistry. High concentrations of plasma enhanced TNFalpha mRNA expression and protein production, while high concentrations of serum enhanced IL-6 mRNA expression. This study suggests that soluble components of blood might be differentially responsible for up regulating production of the cytokines TNFalpha and IL-6 by microglia from immature rodent brain.

Plasminogen potentiates thrombin cytotoxicity and contributes to pathology of intracerebral hemorrhage in rats

Thrombin and plasmin are serine proteases involved in blood coagulation and fibrinolysis, whose precursors are circulating in blood stream. These blood-derived proteases might play important roles in the pathogenesis of intracerebral hemorrhage by acting on brain parenchymal cells. We previously reported that thrombin induced delayed neuronal injury through extracellular signal-regulated kinase (ERK)-dependent pathways. Here, we investigated potential cytotoxic actions of plasminogen, a precursor protein of plasmin, using slice cultures prepared from neonatal rat brain and intracortical microinjection model in adult rats. Although plasminogen alone did not evoke prominent neuronal injury, plasminogen caused significant neuronal injury when combined with a moderate concentration of thrombin (30 U/mL) in the cerebral cortex of slice cultures. The cortical injury was prevented by tranexamic acid and aprotinin. The combined neurotoxicity of thrombin and plasminogen was also prevented by PD98059, an inhibitor of ERK pathway, as well as by other agents that have been shown to prevent cortical injury induced by a higher concentration (100 U/mL) of thrombin alone. Extracellular signal-regulated kinase phosphorylation after plasminogen exposure was localized in cortical astrocytes. Moreover, microinjection of plasminogen in vivo potentiated thrombin-induced cortical injury, and inhibition of plasmin ameliorated hemorrhage-induced neuronal loss in the cerebral cortex. These results suggest that plasminogen/plasmin system augmenting thrombin neurotoxicity participates in hemorrhagic cortical injury.

Combination of thrombin and matrix metalloproteinase-9 exacerbates neurotoxicity in cell culture and intracerebral hemorrhage in mice

The rapid loss of neurons is a major pathological outcome of intracerebral hemorrhage (ICH). Several mechanisms may produce the neurotoxicity observed in ICH, and these include proteolytic enzymes such as thrombin and matrix metalloproteinase-9 (MMP-9). We tested the hypothesis that thrombin and MMP-9 combine to injure neurons in culture and that they interact to promote the acute neurotoxicity that occurs in ICH in vivo. We report that human fetal neurons die when exposed to thrombin or MMP-9 in isolation and that a combination of these two enzymes increased neurotoxicity. The toxicity of thrombin involved protease-activated receptor-1 and the conversion of proMMP-9 to active MMP-9. In ICH, which was induced in mice by the intracerebral injection of autologous blood, significant areas of brain damage, neuronal death, microglia/macrophage activation, and neutrophil accumulation occurred by 24 h of injury. Importantly, these neuropathological features were reduced in MMP-9 null mice compared with wild-type controls, and the concordant antagonism of thrombin using hirudin also alleviated the injury found in MMP-9 null mice. Our collective results demonstrate that thrombin and MMP-9 collaborate to promote neuronal death in culture and in ICH. To improve the prognosis of ICH, the neurotoxic actions of thrombin and MMP-9 must be inhibited early and simultaneously after injury.

Animal models of germinal matrix hemorrhage

Germinal matrix hemorrhage refers to bleeding that arises from the subependymal (or periventricular) germinal region of the immature brain. Clinical studies have shown that infants who experience germinal matrix hemorrhage can develop hydrocephalus or suffer from long-term neurologic dysfunction, including cerebral palsy, seizures, and learning disabilities. Understanding the causative factors and the pathogenesis of subsequent brain damage is important if germinal matrix hemorrhage is to be prevented or treated. Appropriate animal models are necessary to achieve this understanding. A number of animal species, including mice, rats, rabbits, sheep, pigs, dogs, cats, and primates, have been used to model germinal matrix hemorrhage. This literature review critically evaluates the animal models of germinal matrix hemorrhage. Each model has its own advantages and disadvantages; no single model is suitable for the study of all aspects of brain damage.

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

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