A dual-tracer method for differentiating transendothelial transport from paracellular leakage in vivo and in vitro

The Effect of Reduced Fibrinogen on Cerebrovascular Permeability during Traumatic Brain Injury in Fibrinogen Gene Heterozygous Knockout Mice

Vascular contribution to cognitive impairment and dementia (VCID) is a term referring to all types of cerebrovascular and cardiovascular disease-related cognitive decline, spanning many neuroinflammatory diseases including traumatic brain injury (TBI). This becomes particularly important during mild-to-moderate TBI (m-mTBI), which is characterized by short-term memory (STM) decline. Enhanced cerebrovascular permeability for proteins is typically observed during m-mTBI. We have previously shown that an increase in the blood content of fibrinogen (Fg) during m-mTBI results in enhanced cerebrovascular permeability. Primarily extravasated via a transcellular pathway, Fg can deposit into the parenchyma and exacerbate inflammatory reactions that can lead to neurodegeneration, resulting in cognitive impairment. In the current study, we investigated the effect of a chronic reduction in Fg concentration in blood on cerebrovascular permeability and the interactions of extravasated Fg with astrocytes and neurons. Cortical contusion injury (CCI) was used to generate m-mTBI in transgenic mice with a deleted Fg γ chain (Fg γ+/-), resulting in a low blood content of Fg, and in control C57BL/6J wild-type (WT) mice. Cerebrovascular permeability was tested in vivo. Interactions of Fg with astrocytes and neurons and the expression of neuronal nuclear factor-кB (NF-кB) were assessed via immunohistochemistry. The results showed that 14 days after CCI, there was less cerebrovascular permeability, lower extravascular deposition of Fg, less activation of astrocytes, less colocalization of Fg with neurons, and lower expression of neuronal pro-inflammatory NF-кB in Fg γ+/- mice compared to that found in WT mice. Combined, our data provide strong evidence that increased Fg extravasation, and its resultant extravascular deposition, triggers astrocyte activation and leads to potential interactions of Fg with neurons, resulting in the overexpression of neuronal NF-кB. These effects suggest that reduced blood levels of Fg can be beneficial in mitigating the STM reduction seen in m-mTBI.

A critical evaluation of "leakage" at the cochlear blood-stria-barrier and its functional significance

The blood-labyrinth-barrier (BLB) is a semipermeable boundary between the vasculature and three separate fluid spaces of the inner ear, the perilymph, the endolymph and the intrastrial space. An important component of the BLB is the blood-stria-barrier, which shepherds the passage of ions and metabolites from strial capillaries into the intrastrial space. Some investigators have reported increased "leakage" from these capillaries following certain experimental interventions, or in the presence of inflammation or genetic variants. This leakage is generally thought to be harmful to cochlear function, principally by lowering the endocochlear potential (EP). Here, we examine evidence for this dogma. We find that strial capillaries are not exclusive, and that the asserted detrimental influence of strial capillary leakage is often confounded by hair cell damage or intrinsic dysfunction of the stria. The vast majority of previous reports speculate about the influence of strial vascular barrier function on the EP without directly measuring the EP. We argue that strial capillary leakage is common across conditions and species, and does not significantly impact the EP or hearing thresholds, either on evidentiary or theoretical grounds. Instead, strial capillary endothelial cells and pericytes are dynamic and allow permeability of varying degrees in response to specific conditions. We present observations from mice and demonstrate that the mechanisms of strial capillary transport are heterogeneous and inconsistent among inbred strains.

Vascular Effects on Cerebrovascular Permeability and Neurodegeneration

Neurons and glial cells in the brain are protected by the blood brain barrier (BBB). The local regulation of blood flow is determined by neurons and signal conducting cells called astrocytes. Although alterations in neurons and glial cells affect the function of neurons, the majority of effects are coming from other cells and organs of the body. Although it seems obvious that effects beginning in brain vasculature would play an important role in the development of various neuroinflammatory and neurodegenerative pathologies, significant interest has only been directed to the possible mechanisms involved in the development of vascular cognitive impairment and dementia (VCID) for the last decade. Presently, the National Institute of Neurological Disorders and Stroke applies considerable attention toward research related to VCID and vascular impairments during Alzheimer's disease. Thus, any changes in cerebral vessels, such as in blood flow, thrombogenesis, permeability, or others, which affect the proper vasculo-neuronal connection and interaction and result in neuronal degeneration that leads to memory decline should be considered as a subject of investigation under the VCID category. Out of several vascular effects that can trigger neurodegeneration, changes in cerebrovascular permeability seem to result in the most devastating effects. The present review emphasizes the importance of changes in the BBB and possible mechanisms primarily involving fibrinogen in the development and/or progression of neuroinflammatory and neurodegenerative diseases resulting in memory decline.

Developing a transwell millifluidic device for studying blood-brain barrier endothelium

Blood-brain barrier (BBB) endothelial cell (EC) function depends on flow conditions and on supportive cells, like pericytes and astrocytes, which have been shown to be both beneficial and detrimental for brain EC function. Most studies investigating BBB EC function lack physiological relevance, using sub-physiological shear stress magnitudes and/or omitting pericytes and astrocytes. In this study, we developed a millifluidic device compatible with standard transwell inserts to investigate BBB function. In contrast to standard polydimethylsiloxane (PDMS) microfluidic devices, this model allows for easy, reproducible shear stress exposure without common limitations of PDMS devices such as inadequate nutrient diffusion and air bubble formation. In no-flow conditions, we first used the device to examine the impact of primary human pericytes and astrocytes on human brain microvascular EC (HBMEC) barrier integrity. Astrocytes, pericytes, and a 1-to-1 ratio of both cell types increased HBMEC barrier integrity via reduced 3 and 40 kDa fluorescent dextran permeability and increased claudin-5 expression. There were differing levels of low 3 kDa permeability in HBMEC-pericyte, HBMEC-astrocyte, and HBMEC-astrocyte-pericyte co-cultures, while levels of low 40 kDa permeability were consistent across co-cultures. The 3 kDa findings suggest that pericytes provide more barrier support to the BBB model compared to astrocytes, although both supportive cell types are permeability reducers. Incorporation of 24-hour 12 dynes per cm2 flow significantly reduced dextran permeability in HBMEC monolayers, but not in the tri-culture model. These results indicate that tri-culture may exert more pronounced impact on overall BBB permeability than flow exposure. In both cases, monolayer and tri-culture, flow exposure interestingly reduced HBMEC expression of both claudin-5 and occludin. ZO-1 expression, and localization at cell-cell junctions increased in the tri-culture but exhibited no apparent change in the HBMEC monolayer. Under flow conditions, we also observed HBMEC alignment in the tri-culture but not in HBMEC monolayers, indicating supportive cells and flow are both essential to observe brain EC alignment in vitro. Collectively, these results support the necessity of physiologically relevant, multicellular BBB models when investigating BBB EC function. Consideration of the roles of shear stress and supportive cells within the BBB is critical for elucidating the physiology of the neurovascular unit.

Fibrinogen, Fibrinogen-like 1 and Fibrinogen-like 2 Proteins, and Their Effects

Fibrinogen (Fg) and its derivatives play a considerable role in many diseases. For example, increased levels of Fg have been found in many inflammatory diseases, such as Alzheimer's disease, multiple sclerosis, traumatic brain injury, rheumatoid arthritis, systemic lupus erythematosus, and cancer. Although associations of Fg, Fg chains, and its derivatives with various diseases have been established, their specific effects and the mechanisms of actions involved are still unclear. The present review is the first attempt to discuss the role of Fg, Fg chains, its derivatives, and other members of Fg family proteins, such as Fg-like protein 1 and 2, in inflammatory diseases and their effects in immunomodulation.

Endothelial dysfunction in preterm infants: The hidden legacy of uteroplacental pathologies

Millions of infants are born prematurely every year worldwide. Prematurity, particularly at lower gestational ages, is associated with high mortality and morbidity and is a significant global health burden. Pregnancy complications and preterm birth syndrome strongly impact neonatal clinical phenotypes and outcomes. The vascular endothelium is a pivotal regulator of fetal growth and development. In recent years, the key role of uteroplacental pathologies impairing endothelial homeostasis is emerging. Conditions leading to very and extremely preterm birth can be classified into two main pathophysiological patterns or endotypes: infection/inflammation and dysfunctional placentation. The first is frequently related to chorioamnionitis, whereas the second is commonly associated with hypertensive disorders of pregnancy and fetal growth restriction. The nature, timing, and extent of prenatal noxa may alter fetal and neonatal endothelial phenotype and functions. Changes in the luminal surface, oxidative stress, growth factors imbalance, and dysregulation of permeability and vascular tone are the leading causes of endothelial dysfunction in preterm infants. However, the available evidence regarding endothelial physiology and damage is limited in neonates compared to adults. Herein, we discuss the current knowledge on endothelial dysfunction in the infectious/inflammatory and dysfunctional placentation endotypes of prematurity, summarizing their molecular features, available biomarkers, and clinical impact. Furthermore, knowledge gaps, shadows, and future research perspectives are highlighted.

Mechanism of Blood-Heart-Barrier Leakage: Implications for COVID-19 Induced Cardiovascular Injury

Although blood–heart-barrier (BHB) leakage is the hallmark of congestive (cardio-pulmonary) heart failure (CHF), the primary cause of death in elderly, and during viral myocarditis resulting from the novel coronavirus variants such as the severe acute respiratory syndrome novel corona virus 2 (SARS-CoV-2) known as COVID-19, the mechanism is unclear. The goal of this project is to determine the mechanism of the BHB in CHF. Endocardial endothelium (EE) is the BHB against leakage of blood from endocardium to the interstitium; however, this BHB is broken during CHF. Previous studies from our laboratory, and others have shown a robust activation of matrix metalloproteinase-9 (MMP-9) during CHF. MMP-9 degrades the connexins leading to EE dysfunction. We demonstrated juxtacrine coupling of EE with myocyte and mitochondria (Mito) but how it works still remains at large. To test whether activation of MMP-9 causes EE barrier dysfunction, we hypothesized that if that were the case then treatment with hydroxychloroquine (HCQ) could, in fact, inhibit MMP-9, and thus preserve the EE barrier/juxtacrine signaling, and synchronous endothelial-myocyte coupling. To determine this, CHF was created by aorta-vena cava fistula (AVF) employing the mouse as a model system. The sham, and AVF mice were treated with HCQ. Cardiac hypertrophy, tissue remodeling-induced mitochondrial-myocyte, and endothelial-myocyte contractions were measured. Microvascular leakage was measured using FITC-albumin conjugate. The cardiac function was measured by echocardiography (Echo). Results suggest that MMP-9 activation, endocardial endothelial leakage, endothelial-myocyte (E-M) uncoupling, dyssynchronous mitochondrial fusion-fission (Mfn2/Drp1 ratio), and mito-myocyte uncoupling in the AVF heart failure were found to be rampant; however, treatment with HCQ successfully mitigated some of the deleterious cardiac alterations during CHF. The findings have direct relevance to the gamut of cardiac manifestations, and the resultant phenotypes arising from the ongoing complications of COVID-19 in human subjects.

The Bradykinin B2 Receptor Agonist (NG291) Causes Rapid Onset of Transient Blood-Brain Barrier Disruption Without Evidence of Early Brain Injury

Background: The blood-brain barrier (BBB) describes the brain's highly specialized capillaries, which form a dynamic interface that maintains central nervous system (CNS) homeostasis. The BBB supports the CNS, in part, by preventing the entry of potentially harmful circulating molecules into the brain. However, this specialized function is challenging for the development of CNS therapeutics. Several strategies to facilitate drug delivery into the brain parenchyma via disruption of the BBB have been proposed. Bradykinin has proven effective in disrupting mechanisms across the blood-tumor barrier. Unfortunately, bradykinin has limited therapeutic value because of its short half-life and the undesirable biological activity elicited by its active metabolites. Objective: To evaluate NG291, a stable bradykinin analog, with selective agonist activity on the bradykinin-B2 receptor and its ability to disrupt the BBB transiently. Methods: Sprague Dawley rats and CD-1 mice were subjected to NG291 treatment (either 50 or 100 μg/kg, intravenously). Time and dose-dependent BBB disruption were evaluated by histological analysis of Evans blue (EB) extravasation. Transcellular and paracellular BBB leakage were assessed by infiltration of 99mTc-albumin (66.5 KDa) and 14C-sucrose (340 Da) radiolabeled probes into the brains of CD-1 mice treated with NG291. NG291 influence on P-glycoprotein (P-gp) efflux pump activity was evaluated by quantifying the brain accumulation of 3H-verapamil, a known P-gp substrate, in CD-1 mice. Results: NG291-mediated BBB disruption was localized, dose-dependent, and reversible as measured by EB extravasation. 99mTc-albumin leakage was significantly increased by 50 μg/kg of NG291, whereas 100 μg/kg of NG291 significantly augmented both 14C-sucrose and 99mTc-albumin leakage. NG291 enhanced P-gp efflux transporter activity and was unable to increase brain uptake of the P-gp substrate pralidoxime. NG291 did not evoke significant short-term neurotoxicity, as it did not increase brain water content, the number of Fluoro-Jade C positive cells, or astrocyte activation. Conclusion: Our findings strongly suggest that NG291 increases BBB permeability by two different mechanisms in a dose-dependent manner and increases P-gp efflux transport. This increased permeability may facilitate the penetration into the brain of therapeutic candidates that are not P-gp substrates.

The Effects of Fibrinogen's Interactions with Its Neuronal Receptors, Intercellular Adhesion Molecule-1 and Cellular Prion Protein

Neuroinflammatory diseases, such as Alzheimer's disease (AD) and traumatic brain injury (TBI), are associated with the extravascular deposition of the fibrinogen (Fg) derivative fibrin and are accompanied with memory impairment. We found that during the hyperfibrinogenemia that typically occurs during AD and TBI, extravasated Fg was associated with amyloid beta and astrocytic cellular prion protein (PrPC). These effects coincided with short-term memory (STM) reduction and neurodegeneration. However, the mechanisms of a direct Fg-neuron interaction and its functional role in neurodegeneration are still unclear. Cultured mouse brain neurons were treated with Fg in the presence or absence of function-blockers of its receptors, PrPC or intercellular adhesion molecule-1 (ICAM-1). Associations of Fg with neuronal PrPC and ICAM-1 were characterized. The expression of proinflammatory marker interleukin 6 (IL-6) and the generation of reactive oxygen species (ROS), mitochondrial superoxide, and nitrite in neurons were assessed. Fg-induced neuronal death was also evaluated. A strong association of Fg with neuronal PrPC and ICAM-1, accompanied with overexpression of IL-6 and enhanced generation of ROS, mitochondrial superoxide, and nitrite as well as the resulting neuronal death, was found. These effects were reduced by blocking the function of neuronal PrPC and ICAM-1, suggesting that the direct interaction of Fg with its neuronal receptors can induce overexpression of IL-6 and increase the generation of ROS, nitrite, and mitochondrial superoxide, ultimately leading to neuronal death. These effects can be a mechanism of neurodegeneration and the resultant memory reduction seen during TBI and AD.

Evaluation of Blood-Brain Barrier Integrity Using Vascular Permeability Markers: Evans Blue, Sodium Fluorescein, Albumin-Alexa Fluor Conjugates, and Horseradish Peroxidase

The blood-brain barrier (BBB) constituted by endothelial cells of brain microvessels is a dynamic interface, which controls and regulates the transport of various substances including peptides, proteins, ions, vitamins, hormones, and immune cells from the circulation into the brain parenchyma. Certain diseases/disorders such as Alzheimer's disease, sepsis, and hypertension can lead to varying degrees of BBB disruption. Moreover, impairment of BBB integrity has been implicated in the pathogenesis of various neurodegenerative diseases like epilepsy. In attempts to explore the wide spectrum of pathophysiologic mechanisms of these diseases/disorders, a variety of experimental insults targeted to the BBB integrity in vitro in cell culture models and in vivo in laboratory animals have been shown to alter BBB permeability causing enhanced transport of certain tracers such as sodium fluorescein, cadaverine-Alexa fluor, horseradish peroxidase, FITC-dextran, albumin-Alexa fluor conjugates, and Evans blue dye across the barrier. The permeability changes in barrier-type endothelial cells can be assessed by intravascular infusion of exogenous tracers and subsequent detection of the extravasated tracer in the brain tissue, which enable functional and structural analysis of BBB integrity. In this chapter, we aimed to highlight the current knowledge on the use of four most commonly performed tracers, namely, Evans blue, sodium fluorescein, albumin-Alexa fluor conjugates, and horseradish peroxidase. The experimental methodologies that we use in our laboratory for the detection of these tracers by macroscopy, spectrophotometry, spectrophotofluorometry, confocal laser scanning microscopy, and electron microscopy are also discussed. Tracing studies at the morphological level are mainly aimed at the identification of the tracers both in the barrier-related cells and brain parenchyma. In addition, BBB permeability to the tracers can be quantified using spectrophotometric and spectrophotofluorometric assays and image analysis by confocal laser scanning microscopy and electron microscopy. The results of our studies conducted under various experimental settings using the mentioned tracers indicate that barrier-type endothelial cells in brain microvessels orchestrate the paracellular and/or transcellular trafficking of substances across BBB. These efforts may not only contribute to designing approaches for the management of diseases/disorders associated with BBB breakdown but may also provide new insights for developing novel brain drug delivery strategies.

Effects of fibrinogen synthesis inhibition on vascular cognitive impairment during traumatic brain injury in mice

Traumatic brain injury (TBI) is associated with increased blood content of fibrinogen (Fg), called hyperfibrinogenemia (HFg), which results in enhanced cerebrovascular permeability and leads to short-term memory (STM) reduction. Previously, we showed that extravasated Fg was deposited in the vasculo-astrocyte interface and was co-localized with cellular prion protein (PrP^C) during mild-to-moderate TBI in mice. These effects were accompanied by neurodegeneration and STM reduction. However, there was no evidence presented that the described effects were the direct result of the HFg during TBI. We now present data indicating that inhibition of Fg synthesis can ameliorate TBI-induced cerebrovascular permeability and STM reduction. Cortical contusion injury (CCI) was induced in C57BL/6J mice. Then mice were treated with either Fg antisense oligonucleotide (Fg-ASO) or with control-ASO for two weeks. Cerebrovascular permeability to fluorescently labeled bovine serum albumin was assessed in cortical venules following evaluation of STM with memory assessement tests. Separately, brain samples were collected in order to define the expression of PrP^C via Western blotting while deposition and co-localization of Fg and PrP^C, as well as gene expression of inflammatory marker activating transcription factor 3 (ATF3), were characterized with real-time PCR. Results showed that inhibition of Fg synthesis with Fg-ASO reduced overexpression of AFT3, ameliorated enhanced cerebrovascular permeability, decreased expression of PrP^C and Fg deposition, decreased formation of Fg-PrP^C complexes in brain, and improved STM. These data provide direct evidence that a CCI-induced inflammation-mediated HFg could be a triggering mechanism involved in vascular cognitive impairment seen previously in our studies during mild-to-moderate TBI.

Fibrinogen and Neuroinflammation During Traumatic Brain Injury

Many neurodegenerative diseases such as Alzheimer's disease (AD), multiple sclerosis, and traumatic brain injury (TBI) are associated with systemic inflammation. Inflammation itself results in increased blood content of fibrinogen (Fg), called hyperfibrinogenemia (HFg). Fg is not only considered an acute phase protein and a marker of inflammation, but has been shown that it can cause inflammatory responses. Fibrin deposits have been associated with memory reduction in neuroinflammatory diseases such as AD and TBI. Reduction in short-term memory has been seen during the most common form of TBI, mild-to-moderate TBI. Fibrin deposits have been found in brains of patients with mild-to-moderate TBI. The vast majority of the literature emphasizes the role of fibrin-activated microglia as the mediator in the neuroinflammation pathway. However, the recent discovery that astrocytes, which constitute approximately 30% of the cells in the mammalian central nervous system, manifest different reactive states warrants further investigations in the causative role of HFg in astrocyte-mediated neuroinflammation. Our previous study showed that Fg deposited in the vasculo-astrocyte interface-activated astrocytes. However, little is known of how Fg directly affects astrocytes and neurons. In this review, we summarize studies that show the effect of Fg on different types of cells in the vasculo-neuronal unit. We will also discuss the possible mechanism of HFg-induced neuroinflammation during TBI.

Fibrinogen-cellular prion protein complex formation on astrocytes

Traumatic brain injury (TBI) is one of the most common neurological disorders causing memory reduction, particularly short-term memory (STM). We showed that, during TBI-induced inflammation, increased blood content of fibrinogen (Fg) enhanced vascular protein transcytosis and deposition of extravasated Fg in vasculo-astrocyte interfaces. In addition, we found that deposition of cellular prion protein (PrP^C) was also increased in the vasculo-astrocyte endfeet interface. However, association of Fg and PrP^C was not confirmed. Presently, we aimed to define whether Fg can associate with PrP^C on astrocytes and cause their activation. Cultured mouse brain astrocytes were treated with medium alone (control), Fg (2 mg/mL or 4 mg/mL), 4 mg/mL of Fg in the presence of a function-blocking anti-PrP^C peptide or anti-mouse IgG, function-blocking anti-PrP^C peptide, or anti-mouse IgG alone. After treatment, either cell lysates were collected and analyzed via Western blot or coimmunoprecipitation was performed, or astrocytes were fixed and their activation was assessed with immunohistochemistry. Results showed that Fg dose-dependently activated astrocytes, increased expressions of PrP^C and tyrosine (tropomyosin) receptor kinase B (TrkB), and PrP gene. Blocking the function of PrP^C reduced these effects. Coimmunoprecipitation demonstrated Fg and PrP^C association. Since it is known that prion protein has a greater effect on memory reduction than amyloid beta, and that activation of TrkB is involved in neurodegeneration, our findings confirming the possible formation of Fg-PrP^C and Fg-induced overexpression of TrkB on astrocytes suggest a possible triggering mechanism for STM reduction that was seen previously during mild-to-moderate TBI.NEW & NOTEWORTHY For the first time we showed that fibrinogen (Fg) can associate with cellular prion protein (PrP^C) on the surface of cultured mouse brain astrocytes. At high levels, Fg causes upregulation of astrocyte PrP^C and astrocyte activation accompanied with overexpression of tyrosine receptor kinase B (TrkB), which results in nitric oxide (NO) production and generation of reactive oxygen species (ROS). Fg/PrP^C interaction can be a triggering mechanism for TrkB-NO-ROS axis activation and the resultant astrocyte-mediated neurodegeneration.

Lung Endothelial Transcytosis

Transcytosis of macromolecules through lung endothelial cells is the primary route of transport from the vascular compartment into the interstitial space. Endothelial transcytosis is mostly a caveolae-dependent process that combines receptor-mediated endocytosis, vesicle trafficking via actin-cytoskeletal remodeling, and SNARE protein directed vesicle fusion and exocytosis. Herein, we review the current literature on caveolae-mediated endocytosis, the role of actin cytoskeleton in caveolae stabilization at the plasma membrane, actin remodeling during vesicle trafficking, and exocytosis of caveolar vesicles. Next, we provide a concise summary of experimental methods employed to assess transcytosis. Finally, we review evidence that transcytosis contributes to the pathogenesis of acute lung injury. © 2020 American Physiological Society. Compr Physiol 10:491-508, 2020.

Vascular and non-vascular contributors to memory reduction during traumatic brain injury

Traumatic brain injury (TBI) is an increasing health problem. It is a complex, progressive disease that consists of many factors affecting memory. Studies have shown that increased blood-brain barrier (BBB) permeability initiates pathological changes in neuro-vascular network but the role of cerebrovascular dysfunction and its mediated mechanisms associated with memory reduction during TBI are still not well understood. Changes in BBB, inflammation, extravasation of blood plasma components, activation of neuroglia lead to neurodegeneration. Extravasated proteins such as amyloid-beta, fibrinogen, and cellular prion protein may form degradation resistant complexes that can lead to neuronal dysfunction and degeneration. They also have the ability to activate astrocytes, and thus, can be involved in memory impairment. Understanding the triggering mechanisms and the places they originate in vasculature or in extravascular tissue may help to identify potential therapeutic targets to ameliorate memory reduction during TBI. The goal of this review is to discuss conceptual mechanisms that lead to short-term memory reduction during non-severe TBI considering distinction between vascular and non-vascular effects on neurons. Some aspects of these mechanisms need to be confirmed further. Therefore, we hope that the discussion presented bellow may lead to experiments that may clarify the triggering mechanisms of memory reduction after head trauma.

Changes in blood-brain barrier permeability and ultrastructure, and protein expression in a rat model of cerebral hypoperfusion

Cerebral hypoperfusion involved a reduction in cerebral blood flow, leading to neuronal dysfunction, microglial activation and white matter degeneration. The effects on the blood-brain barrier (BBB) however, have not been well-documented. Here, two-vessel occlusion model was adopted to mimic the condition of cerebral hypoperfusion in Sprague-Dawley rats. The BBB permeability to high and low molecular weight exogenous tracers i.e. Evans blue dye and sodium fluorescein respectively, showed marked extravasation of the Evans blue dye in the frontal cortex, posterior cortex and thalamus-midbrain at day 1 following induction of cerebral hypoperfusion. Transmission electron microscopy revealed brain endothelial cell and astrocyte damages including increased pinocytotic vesicles and formation of membrane invaginations in the endothelial cells, and swelling of the astrocytes' end-feet. Investigation on brain microvessel protein expressions using two-dimensional (2D) gel electrophoresis coupled with LC-MS/MS showed that proteins involved in mitochondrial energy metabolism, transcription regulation, cytoskeleton maintenance and signaling pathways were differently expressed. The expression of aconitate hydratase, heterogeneous nuclear ribonucleoprotein, enoyl Co-A hydratase and beta-synuclein were downregulated, while the opposite observed for calreticulin and enhancer of rudimentary homolog. These findings provide insights into the BBB molecular responses to cerebral hypoperfusion, which may assist development of future therapeutic strategies.

Derangement of the endothelial glycocalyx in sepsis

The vascular endothelial surface is coated by the glycocalyx, a ubiquitous gel-like layer composed of a membrane-binding domain that contains proteoglycans, glycosaminoglycan side-chains, and plasma proteins such as albumin and antithrombin. The endothelial glycocalyx plays a critical role in maintaining vascular homeostasis. However, this component is highly vulnerable to damage and is also difficult to examine. Recent advances in analytical techniques have enabled biochemical, visual and computational investigation of this vascular component. The glycocalyx modulates leukocyte-endothelial interactions, thrombus formation and other processes that lead to microcirculatory dysfunction and critical organ injury in sepsis. It also acts as a regulator of vascular permeability and contains mechanosensors as well as receptors for growth factors and anticoagulants. During the initial onset of sepsis, the glycocalyx is damaged and circulating levels of glycocalyx components, including syndecans, heparan sulfate and hyaluronic acid, can be measured and are reportedly useful as biomarkers for sepsis. Also, a new methodology using side-stream dark-field imaging is now clinically available for assessing the glycocalyx. Multiple factors including hypervolemia and hyperglycemia are toxic to the glycocalyx, and several agents have been proposed as therapeutic modalities, although no single treatment has been proven to be clinically effective. In this article, we review the derangement of the glycocalyx in sepsis. Despite the accumulated knowledge regarding the important roles of the glycocalyx, the relationship between derangement of the endothelial glycocalyx and severity of sepsis or disseminated intravascular coagulation has not been adequately elucidated and further work is needed.

Nutlin-loaded magnetic solid lipid nanoparticles for targeted glioblastoma treatment

Aim

Glioblastoma multiforme is one of the deadliest forms of cancer, and current treatments are limited to palliative cares. The present study proposes a nanotechnology-based solution able to improve both drug efficacy and its delivery efficiency.

Materials & methods

Nutlin-3a and superparamagnetic nanoparticles were encapsulated in solid lipid nanoparticles, and the obtained nanovectors (nutlin-loaded magnetic solid lipid nanoparticle [Nut-Mag-SLNs]) were characterized by analyzing both their physicochemical properties and their effects on U-87 MG glioblastoma cells.

Results

Nut-Mag-SLNs showed good colloidal stability, the ability to cross an in vitro blood–brain barrier model, and a superior pro-apoptotic activity toward glioblastoma cells with respect to the free drug.

Conclusion

Nut-Mag-SLNs represent a promising multifunctional nanoplatform for the treatment of glioblastoma multiforme.

Hyperfibrinogenemia-mediated astrocyte activation

Fibrinogen (Fg)-containing plaques are associated with memory loss during various inflammatory neurodegenerative diseases such as Alzheimer's disease, multiple sclerosis, stroke, and traumatic brain injury. However, mechanisms of its action in neurovascular unit are not clear. As Fg is a high molecular weight blood protein and cannot translocate far from the vessel after extravasation, we hypothesized that it may interact with astrocytes first causing their activation. Cultured mouse cortical astrocytes were treated with Fg in the presence or absence of function-blocking anti-mouse intercellular adhesion molecule 1 (ICAM-1) antibody, or with medium alone (control). Expressions of ICAM-1 and tyrosine receptor kinase B (TrkB) as markers of astrocyte activation, and phosphorylation of TrkB (pTrkB) were assessed. Fg dose-dependently increased activation of astrocytes defined by their shape change, retraction of processes, and enhanced expressions of ICAM-1 and TrkB, and increased pTrkB. Blocking of ICAM-1 function ameliorated these Fg effects. Data suggest that Fg interacts with astrocytes causing overexpression of ICAM-1 and TrkB, and TrkB phosphorylation, and thus, astrocyte activation. Since TrkB is known to be involved in neurodegeneration, interaction of Fg with astrocytes and the resultant activation of TrkB can be a possible mechanism involved in memory reduction, which were observed in previous studies and were associated with formation of complexes of Fg deposited in extravascular space with proteins such as Amyloid beta or prion, the proteins involved in development of dementia.

Inhibition of mTOR protects the blood-brain barrier in models of Alzheimer's disease and vascular cognitive impairment

An intact blood-brain barrier (BBB) limits entry of proinflammatory and neurotoxic blood-derived factors into the brain parenchyma. The BBB is damaged in Alzheimer's disease (AD), which contributes significantly to the progression of AD pathologies and cognitive decline. However, the mechanisms underlying BBB breakdown in AD remain elusive, and no interventions are available for treatment or prevention. We and others recently established that inhibition of the mammalian/mechanistic target of rapamycin (mTOR) pathway with rapamycin yields significant neuroprotective effects, improving cerebrovascular and cognitive function in mouse models of AD. To test whether mTOR inhibition protects the BBB in neurological diseases of aging, we treated hAPP(J20) mice modeling AD and low-density lipoprotein receptor-null (LDLR-/-) mice modeling vascular cognitive impairment with rapamycin. We found that inhibition of mTOR abrogates BBB breakdown in hAPP(J20) and LDLR-/- mice. Experiments using an in vitro BBB model indicated that mTOR attenuation preserves BBB integrity through upregulation of specific tight junction proteins and downregulation of matrix metalloproteinase-9 activity. Together, our data establish mTOR activity as a critical mediator of BBB breakdown in AD and, potentially, vascular cognitive impairment and suggest that rapamycin and/or rapalogs could be used for the restoration of BBB integrity. NEW & NOTEWORTHY This report establishes mammalian/mechanistic target of rapamycin as a critical mediator of blood-brain barrier breakdown in models of Alzheimer's disease and vascular cognitive impairment and suggests that drugs targeting the target of rapamycin pathway could be used for the restoration of blood-brain barrier integrity in disease states.

Effects of HIV-1 Tat and Methamphetamine on Blood-Brain Barrier Integrity and Function In Vitro

Human immunodeficiency (HIV) infection results in neurocognitive deficits in about one half of infected individuals. Despite systemic effectiveness, restricted antiretroviral penetration across the blood-brain barrier (BBB) is a major limitation in fighting central nervous system (CNS)-localized infection. Drug abuse exacerbates HIV-induced cognitive and pathological CNS changes. This study's purpose was to investigate the effects of the HIV-1 protein Tat and methamphetamine on factors affecting drug penetration across an in vitro BBB model. Factors affecting paracellular and transcellular flux in the presence of Tat and methamphetamine were examined. Transendothelial electrical resistance, ZO-1 expression, and lucifer yellow (a paracellular tracer) flux were aspects of paracellular processes that were examined. Additionally, effects on P-glycoprotein (P-gp) and multidrug resistance protein 1 (MRP-1) mRNA (via quantitative PCR [qPCR]) and protein (via immunoblotting) expression were measured; Pgp and MRP-1 are drug efflux proteins. Transporter function was examined after exposure of Tat with or without methamphetamine using the P-gp substrate rhodamine 123 and also using the dual P-gp/MRP-1 substrate and protease inhibitor atazanavir. Tat and methamphetamine elicit complex changes affecting transcellular and paracellular transport processes. Neither Tat nor methamphetamine significantly altered P-gp expression. However, Tat plus methamphetamine exposure significantly increased rhodamine 123 accumulation within brain endothelial cells, suggesting that treatment inhibited or impaired P-gp function. Intracellular accumulation of atazanavir was not significantly altered after Tat or methamphetamine exposure. Atazanavir accumulation was, however, significantly increased by simultaneous inhibition of P-gp and MRP. Collectively, our investigations indicate that Tat and methamphetamine alter aspects of BBB integrity without affecting net flux of paracellular compounds. Tat and methamphetamine may also affect several aspects of transcellular transport.

Cancer Immunotherapy Getting Brainy: Visualizing the Distinctive CNS Metastatic Niche to Illuminate Therapeutic Resistance

The advent of cancer immunotherapy (CIT) and its success in treating primary and metastatic cancer may offer substantially improved outcomes for patients. Despite recent advancements, many malignancies remain resistant to CIT, among which are brain metastases, a particularly virulent disease with no apparent cure. The immunologically unique niche of the brain has prompted compelling new questions in immuno-oncology such as the effects of tissue-specific differences in immune response, heterogeneity between primary tumors and distant metastases, and the role of spatiotemporal dynamics in shaping an effective anti-tumor immune response. Current methods to examine the immunobiology of metastases in the brain are constrained by tissue processing methods that limit spatial data collection, omit dynamic information, and cannot recapitulate the heterogeneity of the tumor microenvironment. In the current review, we describe how high-resolution, live imaging tools, particularly intravital microscopy (IVM), are instrumental in answering these questions. IVM of pre-clinical cancer models enables short- and long-term observations of critical immunobiology and metastatic growth phenomena to potentially generate revolutionary insights into the spatiotemporal dynamics of brain metastasis, interactions of CIT with immune elements therein, and influence of chemo- and radiotherapy. We describe the utility of IVM to study brain metastasis in mice by tracking the migration and growth of fluorescently-labeled cells, including cancer cells and immune subsets, while monitoring the physical environment within optical windows using imaging dyes and other signal generation mechanisms to illuminate angiogenesis, hypoxia, and/or CIT drug expression within the metastatic niche. Our review summarizes the current knowledge regarding brain metastases and the immune milieu, presents the current status of CIT and its prospects in targeting brain metastases to circumvent therapeutic resistance, and proposes avenues to utilize IVM to study CIT drug delivery and therapeutic efficacy in preclinical models that will ultimately facilitate novel drug discovery and innovative combination therapies.

Primary Porcine Brain Endothelial Cells as In Vitro Model to Study Effects of Ultrasound and Microbubbles on Blood-Brain Barrier Function

Focused ultrasound (FUS) in the presence of microbubbles transiently and reversibly opens the blood-brain barrier (BBB) in rodents and humans, thereby providing a time window for increased drug delivery into brain tissue. To get insight into the underlying mechanisms that govern ultrasound (US)-mediated opening of the BBB, in vitro models are a useful alternative. In this paper, we have utilized an in vitro BBB model that consists of primary porcine brain endothelial cells (PBECs). PBEC monolayers are grown on permeable membranes, which allow assessment of key features of BBB function as well as US treatment. This experimental model is characterized by low permeability for both small molecules and proteins, has a high transendothelial electrical resistance, and expresses tight junctions and efflux pumps. Here, we compare the effects of inertial and stable cavitation in the presence of SonoVue microbubbles on PBEC monolayers' electrical resistance and permeability properties. Our results point out the fragility of PBEC monolayers, which enhances results variability. In particular, we show that handling of the inserts, such as medium change and transfer to the US setup, modifies the cellular response, and immunostaining of the monolayers introduces damage and cell detachment within the US-exposed monolayers. Our results indicate that stable cavitation might have a more pronounced impact on cell permeability as compared with inertial cavitation in vitro. This paper might contribute to further development of experimental setups that are suitable to characterize the impact of FUS and microbubbles on BBB properties in vitro.

Cerebrovascular disorders caused by hyperfibrinogenaemia

KEY POINTS

Hyperfibrinogenaemia (HFg) results in vascular remodelling, and fibrinogen (Fg) and amyloid β (Aβ) complex formation is a hallmark of Alzheimer's disease. However, the interconnection of these effects, their mechanisms and implications in cerebrovascular diseases are not known. Using a mouse model of HFg, we showed that at an elevated blood level, Fg increases cerebrovascular permeability via mainly caveolar protein transcytosis. This enhances deposition of Fg in subendothelial matrix and interstitium making the immobilized Fg a readily accessible substrate for binding Aβ and cellular prion protein (PrP^C ), the protein that is thought to have a greater effect on memory than Aβ. We showed that enhanced formation of Fg-Aβ and Fg-PrP^C complexes are associated with reduction in short-term memory. The present study delineates a new mechanistic pathway for vasculo-neuronal dysfunctions found in inflammatory cardiovascular and cerebrovascular diseases associated with an elevated blood level of Fg.

ABSTRACT

Many cardiovascular diseases are associated with inflammation and as such are accompanied by an increased blood level of fibrinogen (Fg). Besides its well-known prothrombotic effects Fg seems to have other destructive roles in developing microvascular dysfunction that include changes in vascular reactivity and permeability. Increased permeability of brain microvessels has the most profound effects as it may lead to cerebrovascular remodelling and result in memory reduction. The goal of the present study was to define mechanisms of cerebrovascular permeability and associated reduction in memory induced by elevated blood content of Fg. Genetically modified, transgenic hyperfibrinogenic (HFg) mice were used to study cerebrovascular transcellular and paracellular permeability in vivo. The extent of caveolar formation and the role of caveolin-1 signalling were evaluated by immunohistochemistry (IHC) and Western blot (WB) analysis in brain samples from experimental animals. Formation of Fg complexes with amyloid β (Aβ) and with cellular prion protein (PrP^C ) were also assessed with IHC and WB analysis. Short-term memory of mice was assessed by novel object recognition and Y-maze tests. Caveolar protein transcytosis was found to have a prevailing role in overall increased cerebrovascular permeability in HFg mice. These results were associated with enhanced formation of caveolae. Increased formation of Fg-PrP^C and Fg-Aβ complexes were correlated with reduction in short-term memory in HFg mice. Using the model of hyperfibrinogenaemia, the present study shows a novel mechanistic pathway of inflammation-induced and Fg-mediated reduction in short-term memory.

Ablation of matrix metalloproteinase-9 gene decreases cerebrovascular permeability and fibrinogen deposition post traumatic brain injury in mice

Traumatic brain injury (TBI) is accompanied with enhanced matrix metalloproteinase-9 (MMP-9) activity and elevated levels of plasma fibrinogen (Fg), which is a known inflammatory agent. Activation of MMP-9 and increase in blood content of Fg (i.e. hyperfibrinogenemia, HFg) both contribute to cerebrovascular disorders leading to blood brain barrier disruption. It is well-known that activation of MMP-9 contributes to vascular permeability. It has been shown that at an elevated level (i.e. HFg) Fg disrupts blood brain barrier. However, mechanisms of their actions during TBI are not known. Mild TBI was induced in wild type (WT, C57BL/6 J) and MMP-9 gene knockout (Mmp9(-/-)) homozygous, mice. Pial venular permeability to fluorescein isothiocyanate-conjugated bovine serum albumin in pericontusional area was observed 14 days after injury. Mice memory was tested with a novel object recognition test. Increased expression of Fg endothelial receptor intercellular adhesion protein-1 and formation of caveolae were associated with enhanced activity of MMP-9 causing an increase in pial venular permeability. As a result, an enhanced deposition of Fg and cellular prion protein (PrP(C)) were found in pericontusional area. These changes were attenuated in Mmp9(-/-) mice and were associated with lesser loss of short-term memory in these mice than in WT mice. Our data suggest that mild TBI-induced increased cerebrovascular permeability enhances deposition of Fg-PrP(C) and loss of memory, which is ameliorated in the absence of MMP-9 activity. Thus, targeting MMP-9 activity and blood level of Fg can be a possible therapeutic remedy to diminish vasculo-neuronal damage after TBI.

Ablation of MMP9 gene ameliorates paracellular permeability and fibrinogen-amyloid beta complex formation during hyperhomocysteinemia

Increased blood level of homocysteine (Hcy), called hyperhomocysteinemia (HHcy) accompanies many cognitive disorders including Alzheimer's disease. We hypothesized that HHcy-enhanced cerebrovascular permeability occurs via activation of matrix metalloproteinase-9 (MMP9) and leads to an increased formation of fibrinogen-β-amyloid (Fg-Aβ) complex. Cerebrovascular permeability changes were assessed in C57BL/6J (wild type, WT), cystathionine-β-synthase heterozygote (Cbs+/-, a genetic model of HHcy), MMP9 gene knockout (Mmp9-/-), and Cbs and Mmp9 double knockout (Cbs+/-/Mmp9-/-) mice using a dual-tracer probing method. Expression of vascular endothelial cadherin (VE-cadherin) and Fg-Aβ complex formation was assessed in mouse brain cryosections by immunohistochemistry. Short-term memory of mice was assessed with a novel object recognition test. The cerebrovascular permeability in Cbs+/- mice was increased via mainly the paracellular transport pathway. VE-cadherin expression was the lowest and Fg-Aβ complex formation was the highest along with the diminished short-term memory in Cbs+/- mice. These effects of HHcy were ameliorated in Cbs+/-/Mmp9-/- mice. Thus, HHcy causes activation of MMP9 increasing cerebrovascular permeability by downregulation of VE-cadherin resulting in an enhanced formation of Fg-Aβ complex that can be associated with loss of memory. These data may lead to the identification of new targets for therapeutic intervention that can modulate HHcy-induced cerebrovascular permeability and resultant pathologies.

Role of microRNA29b in blood-brain barrier dysfunction during hyperhomocysteinemia: an epigenetic mechanism

Although blood-brain barrier (BBB) integrity is maintained by the cross-talk of endothelial cells, junction proteins, and neurogliovascular network, the epigenetic mechanisms behind BBB permeability are largely unknown. We are reporting for the first time miR29b-mediated regulation of BBB, which is a novel mechanism underlying BBB integrity. We hypothesize that miR29b regulates BBB dysfunction by regulating DNMT3b, which consequently regulates the levels of metalloproteinases, that can eat up the membrane and junction proteins leading to leaky vasculature. In addition, 5'-azacytidine (5'-aza) was used to test its efficacy on BBB permeability. Blood-brain barrier disruption model was created by using homocysteine, and in the models miR29b was identified to be most affected, by using microRNA RT(2)-qPCR array. MiR29b mimics and inhibitors also confirmed that miR29b regulates the levels DNMT3b and MMP9. In hyperhomocysteinemic cystathionine-β-synthase deficient (CBS(+/-)) mice with high brain vessel permeability, miR29b levels were also high as compared with wild-type (WT) mice. Interestingly, 5'-aza improved BBB permeability by decreasing the expression of miR29b. In conclusion, our data suggested miR29b-mediated regulation of BBB dysfunction through DNMT3b and MMP9. It also potentiates the use of microRNAs as candidates for future epigenetic therapies in the improvement of BBB integrity.

Elevated level of fibrinogen increases caveolae formation; role of matrix metalloproteinase-9

The role of the inflammatory agent fibrinogen (Fg) in increased pial venular permeability has been shown previously. It was suggested that an activation of matrix metalloproteinase-9 (MMP-9) is involved in Fg-induced enhanced transcytosis through endothelial cells (ECs). However, direct link between Fg, caveolae formation, and MMP-9 activity has never been shown. We hypothesized that at an elevated level, Fg enhances formation of functional caveolae through activation of MMP-9. Male wild-type (WT, C57BL/6J) or MMP-9 gene knockout (MMP9-/-) mice were infused with Fg (4 mg/ml, final blood concentration) or equal volume of phosphate buffered saline (PBS). After 2 h, mice were sacrificed and brains were collected for immunohistochemical analyses. Mouse brain ECs were treated with 4 mg/ml of Fg or PBS in the presence or absence of MMP-9 activity inhibitor, tissue inhibitor of metalloproteinases-4 (TIMP-4, 12 ng/ml). Formation of functional caveolae was assessed by confocal microscopy. Fg-induced increased formation of caveolae, which was defined by an increased co-localization of caveolin-1 (Cav-1) and plasmalemmal vesicle-associated protein-1 and was associated with an increased phosphorylation of Cav-1, was ameliorated in the presence of TIMP-4. These results suggest that at high levels, Fg enhances formation of functional caveolae that may involve Cav-1 signaling and MMP-9 activation.

Sphingolipids affect fibrinogen-induced caveolar transcytosis and cerebrovascular permeability

Inflammation-induced vascular endothelial dysfunction can allow plasma proteins to cross the vascular wall, causing edema. Proteins may traverse the vascular wall through two main pathways, the paracellular and transcellular transport pathways. Paracellular transport involves changes in endothelial cell junction proteins, while transcellular transport involves caveolar transcytosis. Since both processes are associated with filamentous actin formation, the two pathways are interconnected. Therefore, it is difficult to differentiate the prevailing role of one or the other pathway during various pathologies causing an increase in vascular permeability. Using a newly developed dual-tracer probing method, we differentiated transcellular from paracellular transport during hyperfibrinogenemia (HFg), an increase in fibrinogen (Fg) content. Roles of cholesterol and sphingolipids in formation of functional caveolae were assessed using a cholesterol chelator, methyl-β-cyclodextrin, and the de novo sphingolipid synthesis inhibitor myriocin. Fg-induced formation of functional caveolae was defined by association and colocalization of Na+-K+-ATPase and plasmalemmal vesicle-associated protein-1 with use of Förster resonance energy transfer and total internal reflection fluorescence microscopy, respectively. HFg increased permeability of the endothelial cell layer mainly through the transcellular pathway. While MβCD blocked Fg-increased transcellular and paracellular transport, myriocin affected only transcellular transport. Less pial venular leakage of albumin was observed in myriocin-treated HFg mice. HFg induced greater formation of functional caveolae, as indicated by colocalization of Na+-K+-ATPase with plasmalemmal vesicle-associated protein-1 by Förster resonance energy transfer and total internal reflection fluorescence microscopy. Our results suggest that elevated blood levels of Fg alter cerebrovascular permeability mainly by affecting caveolae-mediated transcytosis through modulation of de novo sphingolipid synthesis.

Curcumin-primed exosomes mitigate endothelial cell dysfunction during hyperhomocysteinemia

AIM

Exosomes, the nano-units (<200 nm), released from diverse cell types in the extracellular body fluid, possess non-immunogenic property and ability to cross the blood-brain barrier (BBB). Since exosomes carry biological information from their cells of origin, we hypothesize that priming cells with potential therapeutic agents release improved cellular contents through exosomes. Curcumin possesses anti-oxidative and anti-inflammatory properties and provides a promising treatment for cerebral diseases and therefore, the aim of the study is to establish that mouse brain endothelial cells (MBECs) when primed with curcumin (7.5 μM), release an alleviated exosome population that can help recover the endothelial cell (EC) layer permeability.

MAIN METHODS

Homocysteine is a well-known causative factor of BBB disruption; therefore, homocysteine-treated ECs were used as a model of BBB disruption and curcumin-primed exosomes were utilized to check their potential for mitigating EC disruption. MBECs were treated with curcumin and exosomes were isolated by using ultracentrifugation and immunoprecipitation. Expression levels of junction proteins were detected by Western blot and immunocytochemistry assays. Endothelial cell permeability was analyzed with Fluorescein isothiocyanate-Bovine serum albumin (FITC-BSA) leakage assay using transwell permeable supports.

KEY FINDINGS

Exosomes derived from curcumin-treated (primed) cells (CUR-EXO) alleviated oxidative stress, tight junctions (ZO-1, claudin-5, occludin), adherent junction (VE-cadherin) proteins and EC layer permeability induced during EC damage due to high homocysteine levels (hyperhomocysteinemia).

SIGNIFICANCE

In conclusion, the study potentiates the use of CUR-EXO for cerebral diseases where drug delivery is still a challenge. The results also pave the way to novel translational therapies for cerebral diseases by maintaining and establishing therapeutic conservatories via primed exosomes.

Role of fibrinogen in cerebrovascular dysfunction after traumatic brain injury

Traumatic brain injury (TBI) has been associated with various neurological disorders. However, the role of cerebrovascular dysfunction and its mechanisms associated with TBI are still not well understood. Inflammation is the main cause of vascular dysfunction. It affects properties of blood components and the vascular wall leading to changes in blood flow and in interaction of blood components and vascular endothelium exacerbating microcirculatory complications during inflammatory diseases. One of the markers of inflammation is a plasma adhesion protein, fibrinogen (Fg). At elevated levels, Fg can also cause inflammatory responses. One of the manifestations of inflammatory responses is an increase in microvascular permeability leading to accumulation of plasma proteins in the subendothelial matrix and causing vascular remodelling. This has a most devastating effect on cerebral circulation after TBI that is accompanied with an elevation of plasma level of Fg and with an increased cerebrovascular permeability in injury penumbra impairing the normal healing process. This study reviews cerebrovascular alterations after TBI, considers the consequences of increased blood-brain barrier permeability, defines the role of elevated level of Fg and discusses the potential mechanisms of its action leading to vascular dysfunction, which subsequently can cause impairment in neuronal function. Thus, possible mechanisms of vasculo-neuronal dysfunction after TBI are considered.