Kinin B1 receptor expression and function on human brain endothelial cells

Brain Expression of CPB2 and Effects of Cpb2 Deficiency in Mouse Models of Behavior

BACKGROUND

 Procarboxypeptidase B2 (proCPB2 or TAFI) is a zymogen that after activation cleaves C-terminal basic residues from peptides or proteins with many identified targets. A splice variant of CPB2 has been found in the brain lacking essential residues for its carboxypeptidase function. The aim was to determine CPB2 expression in the brain and effects of CPB2 deficiency (Cpb2 -/-) on behavior.

MATERIALS AND METHODS

 Behavioral effects were tested by comparing Cpb2 -/- mice in short-term (open field and elevated zero maze tests) and long-term (Phenotyper) observations with wild-type (WT) controls.

RESULTS

 Long-term observation compared day 1 (acclimatizing to novel environment) to day 4 (fully acclimatized) with the inactive (day) and active (night) periods analyzed separately. Brain expression of CPB2 mRNA and protein was interrogated in publicly available databases. Long-term observation demonstrated differences between WT and Cpb2 -/- mice in several parameters. For example, Cpb2 -/- mice moved more frequently on both days 1 and 4, especially in the normally inactive periods. Cpb2 -/- mice spent more time on the shelter and less time in it. Differences were more pronounced on day 4 after the mice had fully acclimatized. In short-term observations, no differences were observed between Cpb2 -/- mice and WT mice. Brain expression of CBP2 was not detectable in the human protein atlas. Databases of single-cell RNAseq did not show expression of CPB2 mRNA in either human or mouse brain.

CONCLUSION

 Continuous observation of home-cage behavior suggests that Cpb2 -/- mice are more active than WT mice, show different day-night activity levels, and might have a different way of processing information.

Drug Penetration into the Central Nervous System: Pharmacokinetic Concepts and In Vitro Model Systems

Delivery of most drugs into the central nervous system (CNS) is restricted by the blood-brain barrier (BBB), which remains a significant bottleneck for development of novel CNS-targeted therapeutics or molecular tracers for neuroimaging. Consistent failure to reliably predict drug efficiency based on single measures for the rate or extent of brain penetration has led to the emergence of a more holistic framework that integrates data from various in vivo, in situ and in vitro assays to obtain a comprehensive description of drug delivery to and distribution within the brain. Coupled with ongoing development of suitable in vitro BBB models, this integrated approach promises to reduce the incidence of costly late-stage failures in CNS drug development, and could help to overcome some of the technical, economic and ethical issues associated with in vivo studies in animal models. Here, we provide an overview of BBB structure and function in vivo, and a summary of the pharmacokinetic parameters that can be used to determine and predict the rate and extent of drug penetration into the brain. We also review different in vitro models with regard to their inherent shortcomings and potential usefulness for development of fast-acting drugs or neurotracers labeled with short-lived radionuclides. In this regard, a special focus has been set on those systems that are sufficiently well established to be used in laboratories without significant bioengineering expertise.

Ca2+ homeostasis in brain microvascular endothelial cells

Blood brain barrier (BBB) is formed by the brain microvascular endothelial cells (BMVECs) lining the wall of brain capillaries. Its integrity is regulated by multiple mechanisms, including up/downregulation of tight junction proteins or adhesion molecules, altered Ca²⁺ homeostasis, remodeling of cytoskeleton, that are confined at the level of BMVECs. Beside the contribution of BMVECs to BBB permeability changes, other cells, such as pericytes, astrocytes, microglia, leukocytes or neurons, etc. are also exerting direct or indirect modulatory effects on BBB. Alterations in BBB integrity play a key role in multiple brain pathologies, including neurological (e.g. epilepsy) and neurodegenerative disorders (e.g. Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis etc.). In this review, the principal Ca²⁺ signaling pathways in brain microvascular endothelial cells are discussed and their contribution to BBB integrity is emphasized. Improving the knowledge of Ca²⁺ homeostasis alterations in BMVECa is fundamental to identify new possible drug targets that diminish/prevent BBB permeabilization in neurological and neurodegenerative disorders.

Polarized Proteins in Endothelium and Their Contribution to Function

Protein localization in endothelial cells is tightly regulated to create distinct signaling domains within their tight spatial restrictions including luminal membranes, abluminal membranes, and interendothelial junctions, as well as caveolae and calcium signaling domains. Protein localization in endothelial cells is also determined in part by the vascular bed, with differences between arteries and veins and between large and small arteries. Specific protein polarity and localization is essential for endothelial cells in responding to various extracellular stimuli. In this review, we examine protein localization in the endothelium of resistance arteries, with occasional references to other vessels for contrast, and how that polarization contributes to endothelial function and ultimately whole organism physiology. We highlight the protein localization on the luminal surface, discussing important physiological receptors and the glycocalyx. The protein polarization to the abluminal membrane is especially unique in small resistance arteries with the presence of the myoendothelial junction, a signaling microdomain that regulates vasodilation, feedback to smooth muscle cells, and ultimately total peripheral resistance. We also discuss the interendothelial junction, where tight junctions, adherens junctions, and gap junctions all convene and regulate endothelial function. Finally, we address planar cell polarity, or axial polarity, and how this is regulated by mechanosensory signals like blood flow.

Bradykinin receptor-1 activation induces inflammation and increases the permeability of human brain microvascular endothelial cells

Neuroinflammatory disorders such as Alzheimer's and Parkinson's diseases are characterised by chronic inflammation and loss of vascular integrity. Bradykinin 1 receptor (B1R) activation has been implicated in many neuroinflammatory diseases, but the contribution of B1R to inflammation and vascular breakdown is yet to be determined. As a result, the present study evaluated the effect of B1R stimulation using Des-Arg-9-BK on the cytokine profile and junctional properties of human cerebral microvascular endothelial cells (hCMVECs). Results showed that stimulation of B1R receptors increased secretion of pro-inflammatory cytokines, interleukin-6 (IL-6), IL-8, intracellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and monocyte chemoattractant protein-1 (MCP-1), but decreased the expression of vascular endothelial growth factor (VEGF), a cytokine and growth factor required for maintenance of the vasculature. B1R stimulation also resulted in the loss of occludin expression at tight junctions with no change in VE-cadherin expression. There was also a significant increase in permeability to Evans blue albumin, suggesting an increase of vascular permeability. Taken together, these results suggest that B1R activation that occurs in neuroinflammatory diseases may contribute to both the inflammation and loss of blood-brain barrier integrity that is characteristic of these diseases.

Peripheral white blood cell count as a screening tool for ventriculostomy-related infections

One of the most common complications following external ventricular drain (EVD) placement is infection. Routine cultures of cerebrospinal fluid (CSF) are often used to screen for infection, however several days may pass before infection is discovered. In this study, we compared the predictive value of daily recorded vital sign parameters and peripheral white blood count (WBC) in identifying ventriculostomy-related infections. Patients with EVDs who had CSF cultures for microorganisms performed between January 2011 and July 2017 were assigned to either an infected and/or uninfected study group. Clinical parameters were then compared using t-test, chi squared and multiple logistic regression analyses. Patients of any age and gender were included. One hundred seventy uninfected and 10 infected subjects were included in the study. Nine of the 10 infected patients had an elevated WBC (>10.4 × 10³/μL), with a significantly greater WBC (15.9 × 10³/μL) than the uninfected group (10.4 × 10³/μL) (p-value ≤ 0.0001). Using logistic regression, we found no association between patient vital signs and CSF infection except for WBC (p = .003). As a diagnostic marker for CSF infection, the sensitivity and specificity of WBC elevation greater than 15 × 10³/μL was 70% (7/10) and 90.2% (147/163), respectively. This study serves as a 'proof of concept' that WBC could be useful as potential screening tool for early detection of CSF infection post-EVD placement. Future investigation using a large, multicenter prospective study is needed to further assess the applicability of this parameter.

Plasma kallikrein modulates immune cell trafficking during neuroinflammation via PAR2 and bradykinin release

Blood-brain barrier (BBB) disruption and transendothelial trafficking of immune cells into the central nervous system (CNS) are pathophysiological hallmarks of neuroinflammatory disorders like multiple sclerosis (MS). Recent evidence suggests that the kallikrein-kinin and coagulation system might participate in this process. Here, we identify plasma kallikrein (KK) as a specific direct modulator of BBB integrity. Levels of plasma prekallikrein (PK), the precursor of KK, were markedly enhanced in active CNS lesions of MS patients. Deficiency or pharmacologic blockade of PK renders mice less susceptible to experimental autoimmune encephalomyelitis (a model of MS) and is accompanied by a remarkable reduction of BBB disruption and CNS inflammation. In vitro analysis revealed that KK modulates endothelial cell function in a protease-activated receptor-2-dependent manner, leading to an up-regulation of the cellular adhesion molecules Intercellular Adhesion Molecule 1 and Vascular Cell Adhesion Molecule 1, thereby amplifying leukocyte trafficking. Our study demonstrates that PK is an important direct regulator of BBB integrity as a result of its protease function. Therefore, KK inhibition can decrease BBB damage and cell invasion during neuroinflammation and may offer a strategy for the treatment of MS.

The Coagulation Factors Fibrinogen, Thrombin, and Factor XII in Inflammatory Disorders-A Systematic Review

Background

The interaction of coagulation factors has been shown to go beyond their traditional roles in hemostasis and to affect the development of inflammatory diseases. Key molecular players, such as fibrinogen, thrombin, or factor XII have been mechanistically and epidemiologically linked to inflammatory disorders like multiple sclerosis (MS), rheumatoid arthritis (RA), and colitis.

Objectives

To systematically review the evidence for a role of coagulation factors, especially factor XII, fibrinogen, and thrombin in inflammatory disorders like MS, RA, and bowel disorders.

Methods

A systematic literature search was done in the PubMed database to identify studies about coagulation factors in inflammatory diseases. Original articles and reviews investigating the role of the kallikrein–kinin and the coagulation system in mouse and humans were included.

Results

We identified 43 animal studies dealing with inflammatory disorders and factors of the kallikrein–kinin or the coagulation system. Different immunological influences are described and novel molecular mechanisms linking coagulation and inflammation are reported.

Conclusion

A number of studies have highlighted coagulation factors to tip the balance between hemostasis and thrombosis and between protection from infection and extensive inflammation. To optimize the treatment of chronic inflammatory disorders by these factors, further studies are necessary.

[Coagulation factors and multiple sclerosis : Key factors in the pathogenesis?]

Environmental factors and genetic predisposition influence the individual risk to develop multiple sclerosis (MS). Preclinical results in animal models of MS, such as experimental autoimmune encephalomyelitis (EAE), prove a significant contribution of the corpuscular and plasmatic coagulation system for the severity of MS. It was recently shown that key molecules of the coagulation cascade, such as fibrinogen, thrombin and factor XII can influence neuroinflammatory disorders such as MS. The inhibition of both fibrinogen and factor XII led to a significantly improved disease course in animal models. Furthermore, in patients suffering from MS a dysregulation of diverse coagulation factors was demonstrated. The precise role of these changes for the pathogenesis of MS remains to be clarified. Nonetheless, the identification of molecular mechanisms between inflammation and the coagulation cascade might provide completely new perspectives for the therapy of MS; however, as most of the currently available data were obtained from animal models, this knowledge must be interpreted with an adequate degree of caution.

Localization and Interaction between Kinin B1 Receptor and NADPH Oxidase in the Vascular System of Diabetic Rats

Kinin B1 receptor (B1R) enhanced superoxide anion (O2•-) production in the vasculature of diabetic rats. This study investigates the induction and distribution of B1R in diabetic blood vessels and addresses the hypothesis that B1R is co-localized with NADPH oxidase (NOX1 and NOX2) and produces its activation via protein kinase C (PKC). Diabetes was induced in rats with streptozotocin (STZ 65 mg.kg⁻¹, i.p.). Two weeks later, the production of O2•- was measured in aorta rings in response to the B1R agonist (Sar[D-Phe⁸]-des-Arg⁹-BK, 20 μM) by the method of lucigenin-enhanced chemiluminescence. Various inhibitors were added (10 μM) to block PKC_total (Ro-31-8220), PKCβ1/2 (LY333531), or NADPH oxidase (Diphenyleneiodonium). The cellular localization of B1R was studied in the aorta, popliteal artery, and renal glomerulus/arteries by immunofluorescence and confocal microscopy with markers of endothelial cells (anti-RECA-1), macrophages (anti-CD11), vascular smooth muscle cells (anti-SMA), and NADPH oxidase (anti-NOX1 and NOX2). Although B1R was largely distributed in resistant vessels, it was sparsely expressed in the aorta's endothelium. The greater basal production of O2•- in STZ-diabetic aorta was significantly enhanced by the B1R agonist (15–45 min). The peak response to the agonist (30 min) was inhibited by all inhibitors. Immunofluorescent staining for B1R, NOX1, and NOX2 was significantly increased in endothelial cells, vascular smooth muscle cells, and macrophages of STZ-diabetic aorta on which they were found co-localized. Data showed that B1R enhanced O2•- by activating vascular NADPH oxidase through PKCβ1/2. This was substantiated by the cellular co-localization of B1R with NOX1 and NOX2 and opens the possibility that B1R-enhanced oxidative stress is derived from vascular and infiltrating immune cells in diabetes.

Neurovascular Unit Dysfunction and Blood-Brain Barrier Hyperpermeability Contribute to Schizophrenia Neurobiology: A Theoretical Integration of Clinical and Experimental Evidence

Schizophrenia is a psychotic disorder characterized by delusions, hallucinations, negative symptoms, as well as behavioral and cognitive dysfunction. It is a pathoetiologically heterogeneous disorder involving complex interrelated mechanisms that include oxidative stress and neuroinflammation. Neurovascular endothelial dysfunction and blood-brain barrier (BBB) hyperpermeability are established mechanisms in neurological disorders with comorbid psychiatric symptoms such as epilepsy, traumatic brain injury, and Alzheimer's disease. Schizophrenia is frequently comorbid with medical conditions associated with peripheral vascular endothelial dysfunction, such as metabolic syndrome, cardiovascular disease, and diabetes mellitus. However, the existence and etiological relevance of neurovascular endothelial dysfunction and BBB hyperpermeability in schizophrenia are still not well recognized. Here, we review the growing clinical and experimental evidence, indicating that neurovascular endotheliopathy and BBB hyperpermeability occur in schizophrenia patients. We present a theoretical integration of human and animal data linking oxidative stress and neuroinflammation to neurovascular endotheliopathy and BBB breakdown in schizophrenia. These abnormalities may contribute to the cognitive and behavioral symptoms of schizophrenia via several mechanisms involving reduced cerebral perfusion and impaired homeostatic processes of cerebral microenvironment. Furthermore, BBB disruption can facilitate interactions between brain innate and peripheral adaptive immunity, thereby perpetuating harmful neuroimmune signals and toxic neuroinflammatory responses, which can also contribute to the symptoms of schizophrenia. Taken together, these findings support the "mild encephalitis" hypothesis of schizophrenia. If neurovascular abnormalities prove to be etiologically relevant to the neurobiology of schizophrenia, then targeting these abnormalities may represent a promising therapeutic strategy.

Predictive value of serum bradykinin and desArg9-bradykinin levels for chemotherapeutic responses in active tuberculosis patients: A retrospective case series

BACKGROUND

There is an urgent need for methods that can rapidly and accurately assess therapeutic responses in patients with active tuberculosis (TB) in order to predict treatment outcomes. Exposure to bacterial pathogens can rapidly activate the plasma contact system, triggering the release of bradykinin (BK) and its metabolite desArg⁹-bradykinin (DABK) to induce inflammation and innate immune responses. We hypothesized that serum BK and DABK levels might act as sensitive immune response signatures for changes in Mycobacterium tuberculosis (Mtb) burden, and therefore examined how serum levels of these markers corresponded with anti-TB therapy in a small cohort of active TB cases.

METHODS

Nanotrap Mass-Spectrometry (MS) was used to analyze serial blood specimens from 13 HIV-negative adults with microbiologically confirmed active TB who were treated with first-line anti-TB chemotherapy. MS signal for BK (m/z 1060.5) and DABK (m/z 904.5) serum peptides were evaluated at multiple time-points (before, during, and after treatment) to evaluate how BK and DABK levels corresponded with disease status.

RESULTS

Serum BK levels declined from pretreatment baseline levels during the early stage anti-TB therapy (induction phase) and tended to remain below baseline levels during extended treatment (consolidation phase) and after therapy completion. BK levels were consistent with induction phase sputum culture conversions indicative of decreased Mtb burden reflecting good treatment responses. Serum DABK levels tended to increase during the induction phase and decrease at consolidation and post-therapy time points, which may indicate a shift from active disease to chronic inflammation to a disease free state. Elevated BK and DABK levels after treatment completion in one patient may be related to the subsequent recurrent TB disease.

CONCLUSIONS

Our pilot data suggests that changes in the circulating BK and DABK levels in adult TB patients can be used as potential surrogate markers of the host response both early and late in anti-TB treatment for both pulmonary and extrapulmonary TB patients. We will further exploit these host-response signatures in the future as biomarkers in combination with other clinical and microbiologic tools which may improve treatment efficacy and facilitate the development of host-directed therapy.

Blood coagulation factor XII drives adaptive immunity during neuroinflammation via CD87-mediated modulation of dendritic cells

Aberrant immune responses represent the underlying cause of central nervous system (CNS) autoimmunity, including multiple sclerosis (MS). Recent evidence implicated the crosstalk between coagulation and immunity in CNS autoimmunity. Here we identify coagulation factor XII (FXII), the initiator of the intrinsic coagulation cascade and the kallikrein-kinin system, as a specific immune cell modulator. High levels of FXII activity are present in the plasma of MS patients during relapse. Deficiency or pharmacologic blockade of FXII renders mice less susceptible to experimental autoimmune encephalomyelitis (a model of MS) and is accompanied by reduced numbers of interleukin-17A-producing T cells. Immune activation by FXII is mediated by dendritic cells in a CD87-dependent manner and involves alterations in intracellular cyclic AMP formation. Our study demonstrates that a member of the plasmatic coagulation cascade is a key mediator of autoimmunity. FXII inhibition may provide a strategy to combat MS and other immune-related disorders.

In vitro models of the blood-brain barrier: An overview of commonly used brain endothelial cell culture models and guidelines for their use

The endothelial cells lining the brain capillaries separate the blood from the brain parenchyma. The endothelial monolayer of the brain capillaries serves both as a crucial interface for exchange of nutrients, gases, and metabolites between blood and brain, and as a barrier for neurotoxic components of plasma and xenobiotics. This "blood-brain barrier" function is a major hindrance for drug uptake into the brain parenchyma. Cell culture models, based on either primary cells or immortalized brain endothelial cell lines, have been developed, in order to facilitate in vitro studies of drug transport to the brain and studies of endothelial cell biology and pathophysiology. In this review, we aim to give an overview of established in vitro blood-brain barrier models with a focus on their validation regarding a set of well-established blood-brain barrier characteristics. As an ideal cell culture model of the blood-brain barrier is yet to be developed, we also aim to give an overview of the advantages and drawbacks of the different models described.

Kinin B2 receptor can play a neuroprotective role in Alzheimer's disease

Alzheimer's disease (AD) is characterized by cognitive decline, presence of amyloid-beta peptide (Aβ) aggregates and neurofibrillary tangles. Kinins act through B1 and B2 G-protein coupled receptors (B1R and B2R). Chronic infusion of Aβ peptide leads to memory impairment and increases in densities of both kinin receptors in memory processing areas. Similar memory impairment was observed in C57BL/6 mice (WTAβ) but occurred earlier in mice lacking B2R (KOB2Aβ) and was absent in mice lacking B1R (KOB1Aβ). Thus, the aim of this study was to evaluate the participation of B1R and B2R in Aβ peptide induced cognitive deficits through the evaluation of densitiesof kinin receptors, synapses, cell bodies and number of Aβ deposits in brain ofWTAβ, KOB1Aβ and KOB2Aβ mice. An increase in B2R density was observed in both WTAβ and KOB1Aβ in memory processing related areas. KOB1Aβ showed a decrease in neuronal density and an increase in synaptic density and, in addition, an increase in Aβ deposits in KOB2Aβ was observed. In conclusion, memory preservation in KOB1Aβ, could be due to the increase in densities of B2R, suggesting a neuroprotective role for B2R, reinforced by the increased number of Aβ plaques in KOB2Aβ. Our data point to B2R as a potential therapeutic target in AD.

Modulation of the kallikrein/kinin system by the angiotensin-converting enzyme inhibitor alleviates experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS). Bradykinin is the end-product of the kallikrein/kinin system, which has been recognized as an endogenous target for combating CNS inflammation. Angiotensin-converting enzyme (ACE) inhibitors influence the kallikrein/kinin system and reportedly have immunomodulatory characteristics. The objectives of this study were to determine whether bradykinin is involved in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an animal model of MS, and whether bradykinin control by the ACE inhibitor could be a therapeutic target in MS. The ACE inhibitor enalapril (1·0 or 0·2 mg/kg/day) was administered orally to EAE mice and the serum levels of bradykinin and cytokines in EAE mice were analysed. As a result, the administration of enalapril increased serum bradykinin levels, decreased the clinical and pathological severity of EAE and attenuated interleukin-17-positive cell invasion into the CNS. Additionally, bradykinin receptor antagonist administration reduced the favourable effects of enalapril. Our results suggest that bradykinin is involved in the pathomechanism underlying CNS inflammation in EAE, possibly through inhibiting cell migration into CNS. Control of the kallikrein/kinin system using ACE inhibitors could be a potential therapeutic strategy in MS.

Differential regulation of astrocyte prostaglandin response by kinins: possible role for mitogen activated protein kinases

The role of kinins, well known as peripheral inflammatory mediators, in the modulation of brain inflammation is not completely understood. The present data show that bradykinin, a B2 receptor agonist, enhanced both basal and lipopolysaccharide (LPS)-induced cyclooxygenase-2 mRNA and protein levels and prostaglandin E2 synthesis in primary rat astrocytes. By contrast, Lys-des-Arg(9)-bradykinin, which is a bradykinin breakdown product and a selective kinin B1 receptor agonist, attenuated both basal and LPS-induced astrocyte cyclooxygenase-2 mRNA levels and prostaglandin E2 production. Pre-treating the cells with p42/p44 MAPK but not with JNK or p38 inhibitors completely abrogated PGE2 synthesis in cells stimulated with LPS in the presence of bradykinin or bradykinin B1 receptor agonist. Bradykinin, but not the bradykinin B1 receptor agonist, augmented p42/p44 MAPK phosphorylation. The phosphorylation of JNK and p38 was not altered upon exposure to Bradykinin or the bradykinin B1 receptor agonist. These results suggest that the dual delayed effect of kinins on PGE2 synthesis may be due to differential regulation of COX-2 and signaling molecules such as p42/p44 MAPKs. Thus, kinins may exert opposing actions on brain inflammation and neurodegenerative diseases.

Neurovascular unit dysfunction with blood-brain barrier hyperpermeability contributes to major depressive disorder: a review of clinical and experimental evidence

About one-third of people with major depressive disorder (MDD) fail at least two antidepressant drug trials at 1 year. Together with clinical and experimental evidence indicating that the pathophysiology of MDD is multifactorial, this observation underscores the importance of elucidating mechanisms beyond monoaminergic dysregulation that can contribute to the genesis and persistence of MDD. Oxidative stress and neuroinflammation are mechanistically linked to the presence of neurovascular dysfunction with blood-brain barrier (BBB) hyperpermeability in selected neurological disorders, such as stroke, epilepsy, multiple sclerosis, traumatic brain injury, and Alzheimer’s disease. In contrast to other major psychiatric disorders, MDD is frequently comorbid with such neurological disorders and constitutes an independent risk factor for morbidity and mortality in disorders characterized by vascular endothelial dysfunction (cardiovascular disease and diabetes mellitus). Oxidative stress and neuroinflammation are implicated in the neurobiology of MDD. More recent evidence links neurovascular dysfunction with BBB hyperpermeability to MDD without neurological comorbidity. We review this emerging literature and present a theoretical integration between these abnormalities to those involving oxidative stress and neuroinflammation in MDD. We discuss our hypothesis that alterations in endothelial nitric oxide levels and endothelial nitric oxide synthase uncoupling are central mechanistic links in this regard. Understanding the contribution of neurovascular dysfunction with BBB hyperpermeability to the pathophysiology of MDD may help to identify novel therapeutic and preventative approaches.

Spatial reference memory deficits precede motor dysfunction in an experimental autoimmune encephalomyelitis model: the role of kallikrein-kinin system

Multiple sclerosis (MS) is a progressive T cell-mediated autoimmune demyelinating inflammatory disease of the central nervous system (CNS). Although it is recognized that cognitive deficits represent a manifestation of the disease, the underlying pathogenic mechanisms remain unknown. Here we provide evidence of spatial reference memory impairments during the pre-motor phase of experimental autoimmune encephalomyelitis (EAE) in mice. Specifically, these cognitive deficits were accompanied by down-regulation of choline acetyltransferase (ChAT) mRNA expression on day 5 and 11 post-immunization, and up-regulation of inflammatory cytokines in the hippocampus and prefrontal cortex. Moreover, a marked increase in B1R mRNA expression occurred selectively in the hippocampus, whereas protein level was up-regulated in both brain areas. Genetic deletion of kinin B1R attenuated cognitive deficits and cholinergic dysfunction, and blocked mRNA expression of both IL-17 and IFN-γ in the prefrontal cortex, lymph node and spleen of mice subjected to EAE. The discovery of kinin receptors, mainly B1R, as a target for controlling neuroinflammatory response, as well as the cognitive deficits induced by EAE may foster the therapeutic exploitation of the kallikrein-kinin system (KKS), in particular for the treatment of autoimmune disorders, such as MS, mainly during pre-symptomatic phase.

The bradykinin B1 receptor regulates Aβ deposition and neuroinflammation in Tg-SwDI mice

The deposition of amyloid-β peptides (Aβ) in the cerebral vasculature, a condition known as cerebral amyloid angiopathy, is increasingly recognized as an important component leading to intracerebral hemorrhage, neuroinflammation, and cognitive impairment in Alzheimer disease (AD) and related disorders. Recent studies demonstrated a role for the bradykinin B1 receptor (B1R) in cognitive deficits induced by Aβ in mice; however, its involvement in AD and cerebral amyloid angiopathy is poorly understood. Herein, we investigated the effect of B1R inhibition on AD-like neuroinflammation and amyloidosis using the transgenic mouse model (Tg-SwDI). B1R expression was found to be up-regulated in brains of Tg-SwDI mice, specifically in the vasculature, neurons, and astrocytes. Notably, administration of the B1R antagonist, R715, to 8-month-old Tg-SwDI mice for 8 weeks resulted in higher Aβ40 levels and increased thioflavin S-positive fibrillar Aβ deposition. Moreover, blockage of B1R inhibited neuroinflammation, as evidenced by the decreased accumulation of activated microglia and reactive astrocytes, diminished NF-κB activation, and reduced cytokine and chemokine levels. Together, our results indicate that B1R activation plays an important role in limiting the accumulation of Aβ in AD-like brain, likely through the regulation of activated glial cell accumulation and release of pro-inflammatory mediators. Therefore, the modulation of the receptor may represent a novel therapeutic approach for AD.

Induction of selective blood-tumor barrier permeability and macromolecular transport by a biostable kinin B1 receptor agonist in a glioma rat model

Treatment of malignant glioma with chemotherapy is limited mostly because of delivery impediment related to the blood-brain tumor barrier (BTB). B1 receptors (B1R), inducible prototypical G-protein coupled receptors (GPCR) can regulate permeability of vessels including possibly that of brain tumors. Here, we determine the extent of BTB permeability induced by the natural and synthetic peptide B1R agonists, LysdesArg⁹BK (LDBK) and SarLys[dPhe⁸]desArg⁹BK (NG29), in syngeneic F98 glioma-implanted Fischer rats. Ten days after tumor inoculation, we detected the presence of B1R on tumor cells and associated vasculature. NG29 infusion increased brain distribution volume and uptake profiles of paramagnetic probes (Magnevist and Gadomer) at tumoral sites (T₁-weighted imaging). These effects were blocked by B1R antagonist and non-selective cyclooxygenase inhibitors, but not by B2R antagonist and non-selective nitric oxide synthase inhibitors. Consistent with MRI data, systemic co-administration of NG29 improved brain tumor delivery of Carboplatin chemotherapy (ICP-Mass spectrometry). We also detected elevated B1R expression in clinical samples of high-grade glioma. Our results documented a novel GPCR-signaling mechanism for promoting transient BTB disruption, involving activation of B1R and ensuing production of COX metabolites. They also underlined the potential value of synthetic biostable B1R agonists as selective BTB modulators for local delivery of different sized-therapeutics at (peri)tumoral sites.

Why dapsone stops seizures and may stop neutrophils' delivery of VEGF to glioblastoma

Lopez-Gomez et al. recently published remarkable but mechanistically unexplained empirical evidence that the old antibiotic dapsone has antiepileptic activity. We addressed the question "Why should a sulfone antibiotic reduce seizures?". We report here our conclusions based on data from past studies that seizures are associated with elevated interleukin-8 (IL-8) and that dapsone inhibits IL-8 release and function in several different clinical and experimental contexts. Diverse CNS insults cause an increase in CNS IL-8. Thus, the pro-inflammatory environment generated by increase IL-8 leads to a lower seizure threshold. Together this evidence indicates dapsone exerts anti-seizure activity by diminishing IL-8 signalling. Since IL-8 is clearly upregulated in glioblastoma and contributes to the florid angiogenesis of that disease, and since interference with IL-8 function has been shown to inhibit glioblastoma invasion and growth in several experimental models, and dapsone has been repeatedly been shown to clinically inhibit IL-8 function when used to treat human neutrophilic dermatoses, we believe that dapsone thereby reduces seizures by countering IL-8 function and may similarly retard glioblastoma growth by such anti-IL-8 function.

Kinin-mediated inflammation in neurodegenerative disorders

The mediatory role of kinins in both acute and chronic inflammation within nervous tissues has been widely described. Bradykinin, the major representative of these bioactive peptides, is one of a few mediators of inflammation that directly stimulates afferent nerves due to the broad expression of specific kinin receptors in cell types in these tissues. Moreover, kinins may be delivered to a site of injury not only after their production at the endothelium surface but also following their local production through the enzymatic degradation of kininogens at the surface of nerve cells. A strong correlation between inflammatory processes and neurodegeneration has been established. The activation of nerve cells, particularly microglia, in response to injury, trauma or infection initiates a number of reactions in the neuronal neighborhood that can lead to cell death after the prolonged action of inflammatory substances. In recent years, there has been a growing interest in the effects of kinins on neuronal destruction. In these studies, the overexpression of proteins involved in kinin generation or of kinin receptors has been observed in several neurologic disorders including neurodegenerative diseases such Alzheimer's disease and multiple sclerosis as well as disorders associated with a deficiency in cell communication such as epilepsy. This review is focused on recent findings that provide reliable evidence of the mediatory role of kinins in the inflammatory responses associated with different neurological disorders. A deeper understanding of the role of kinins in neurodegenerative diseases is likely to promote the future development of new therapeutic strategies for the control of these disorders. An example of this could be the prospective use of kinin receptor antagonists.

The role of kinin receptors in preventing neuroinflammation and its clinical severity during experimental autoimmune encephalomyelitis in mice

Background

Multiple sclerosis (MS) is a demyelinating and neuroinflammatory disease of the human central nervous system (CNS). The expression of kinins is increased in MS patients, but the underlying mechanisms by which the kinin receptor regulates MS development have not been elucidated.

Methodology/Principal Findings

Experimental autoimmune encephalomyelitis (EAE) was induced in female C57BL/6 mice by immunization with MOG_35–55 peptide emulsified in complete Freund's adjuvant and injected with pertussis toxin on day 0 and day 2. Here, we report that blockade of the B₁R in the induction phase of EAE markedly suppressed its progression by interfering with the onset of the immune response. Furthermore, B₁R antagonist suppressed the production/expression of antigen-specific T_H1 and T_H17 cytokines and transcription factors, both in the periphery and in the CNS. In the chronic phase of EAE, the blockade of B₁R consistently impaired the clinical progression of EAE. Conversely, administration of the B₁R agonist in the acute phase of EAE suppressed disease progression and inhibited the increase in permeability of the blood-brain barrier (BBB) and any further CNS inflammation. Of note, blockade of the B₂R only showed a moderate impact on all of the studied parameters of EAE progression.

Conclusions/Significance

Our results strongly suggest that kinin receptors, mainly the B₁R subtype, play a dual role in EAE progression depending on the phase of treatment through the lymphocytes and glial cell-dependent pathways.

Human brain endothelial cells endeavor to immunoregulate CD8 T cells via PD-1 ligand expression in multiple sclerosis

Background

Multiple sclerosis (MS), an inflammatory disease of the central nervous system (CNS), is characterized by blood-brain barrier (BBB) disruption and massive infiltration of activated immune cells. Engagement of programmed cell death-1 (PD-1) expressed on activated T cells with its ligands (PD-L1 and PD-L2) suppresses T cell responses. We recently demonstrated in MS lesions elevated PD-L1 expression by glial cells and absence of PD-1 on many infiltrating CD8 T cells. We have now investigated whether human brain endothelial cells (HBECs), which maintain the BBB, can express PD-L1 or PD-L2 and thereby modulate T cells.

Methods

We used primary cultures of HBECs isolated from non-tumoral CNS tissue either under basal or inflamed conditions. We assessed the expression of PD-L1 and PD-L2 using qPCR and flow cytometry. Human CD8 T cells were isolated from peripheral blood of healthy donors and co-cultured with HBECs. Following co-culture with HBECs, proliferation and cytokine production by human CD8 T cells were measured by flow cytometry whereas transmigration was determined using a well established in vitro model of the BBB. The functional impact of PD-L1 and PD-L2 provided by HBECs was determined using blocking antibodies. We performed immunohistochemistry for the detection of PD-L1 or PD-L2 concurrently with caveolin-1 (a cell specific marker for endothelial cells) on post-mortem human brain tissues obtained from MS patients and normal controls.

Results

Under basal culture conditions, PD-L2 is expressed on HBECs, whilst PD-L1 is not detected. Both ligands are up-regulated under inflammatory conditions. Blocking PD-L1 and PD-L2 leads to increased transmigration and enhanced responses by human CD8 T cells in co-culture assays. Similarly, PD-L1 and PD-L2 blockade significantly increases CD4 T cell transmigration. Brain endothelium in normal tissues and MS lesions does not express detectable PD-L1; in contrast, all blood vessels in normal brain tissues are PD-L2-positive, while only about 50% express PD-L2 in MS lesions.

Conclusions

Our observations suggest that brain endothelial cells contribute to control T cell transmigration into the CNS and immune responses via PD-L2 expression. However, such impact is impaired in MS lesions due to downregulation of endothelium PD-L2 levels.

Central nervous system recruitment of effector memory CD8+ T lymphocytes during neuroinflammation is dependent on α4 integrin

Clonally expanded CD8⁺ T lymphocytes are present in multiple sclerosis lesions, as well as in the cerebrospinal fluid of patients with multiple sclerosis. In experimental autoimmune encephalomyelitis, CD8⁺ T lymphocytes are found in spinal cord and brainstem lesions. However, the exact phenotype of central nervous system-infiltrating CD8⁺ T lymphocytes and the mechanism by which these cells cross the blood–brain barrier remain largely unknown. Using cerebrospinal fluid from patients with multiple sclerosis, spinal cord from experimental autoimmune encephalomyelitis and coronavirus-induced encephalitis, we demonstrate that central nervous system-infiltrating CD8⁺ T lymphocytes are mostly of the effector memory phenotype (CD62L⁻ CCR7⁻ granzymeB^hi). We further show that purified human effector memory CD8⁺ T lymphocytes transmigrate more readily across blood-brain barrier-endothelial cells than non-effector memory CD8⁺ T lymphocytes, and that blood-brain barrier endothelium promotes the selective recruitment of effector memory CD8⁺ T lymphocytes. Furthermore, we provide evidence for the recruitment of interferon-γ- and interleukin-17-secreting CD8⁺ T lymphocytes by human and mouse blood-brain barrier endothelium. Finally, we show that in vitro migration of CD8⁺ T lymphocytes across blood-brain barrier-endothelial cells is dependent on α4 integrin, but independent of intercellular adhesion molecule-1/leucocyte function-associated antigen-1, activated leucocyte cell adhesion molecule/CD6 and the chemokine monocyte chemotactic protein-1/CCL2. We also demonstrate that in vivo neutralization of very late antigen-4 restricts central nervous system infiltration of CD8⁺ T lymphocytes in active immunization and adoptive transfer experimental autoimmune encephalomyelitis, and in coronavirus-induced encephalitis. Our study thus demonstrates an active role of the blood-brain barrier in the recruitment of effector memory CD8⁺ T lymphocytes to the CNS compartment and defines α4 integrin as a major contributor of CD8⁺ T lymphocyte entry into the brain.

B cell-derived IL-15 enhances CD8 T cell cytotoxicity and is increased in multiple sclerosis patients

Multiple lines of evidence suggest that CD8 T cells contribute to the pathogenesis of multiple sclerosis (MS). However, the sources and involvement of cytokines such as IL-15 in activating these cells is still unresolved. To investigate the role of IL-15 in enhancing the activation of CD8 T cells in the context of MS, we determined cell types expressing the bioactive surface IL-15 in the peripheral blood of patients and evaluated the impact of this cytokine on CD8 T cell cytotoxicity and migration. Flow cytometric analysis showed a significantly greater proportion of B cells and monocytes from MS patients expressing IL-15 relative to controls. We established that CD40L activation of B cells from healthy donors increased their IL-15 levels, reaching those of MS patients. We also demonstrated an enhanced cytotoxic profile in CD8 T cells from MS patients upon stimulation with IL-15. Furthermore, we showed that IL-15 expressed by B cells and monocytes is sufficient and functional, enhancing granzyme B production by CD8 T cells upon coculture. Exposure of CD8 T cells to this cytokine enhanced their ability to kill glial cells as well as to migrate across an in vitro inflamed human blood-brain barrier. The elevated levels of IL-15 in patients relative to controls, the greater susceptibility of CD8 T cells from patients to IL-15, in addition to the enhanced cytotoxic responses by IL-15-exposed CD8 T cells, stresses the potential of therapeutic strategies to reduce peripheral sources of IL-15 in MS.

Blockade of the kinin receptor B1 protects from autoimmune CNS disease by reducing leukocyte trafficking

Disruption of the blood brain barrier (BBB) and transendothelial trafficking of immune cells into the central nervous system (CNS) are pathophysiological hallmarks of Multiple Sclerosis (MS) and its animal model, Experimental Autoimmune Encephalomyelitis (EAE). Kinins are proinflammatory peptides which are released during tissue injury including EAE. They increase vascular permeability and enhance inflammation by acting on distinct bradykinin receptors, B1R and B2R. We studied the expression of B1R and B2R and the effect of their inhibition on the disease course, BBB integrity and T cell migration following myelin oligodendrocyte glycoprotein (MOG(35-55))-induced EAE. B1R, but not B2R expression was markedly enhanced in inflammatory CNS lesions in mice and humans. Brain endothelial cells could be identified as major source of B1R protein. The severity of EAE was significantly alleviated in B1R(-/-) mice compared with wild-type (WT) controls (P<0.05). Treatment of WT mice with the B1R antagonist R715 before and after disease onset was equally effective (P<0.05) while B1R activation by R838 promoted EAE (P<0.05). B1R inhibition was accompanied by a remarkable reduction of BBB disruption and tissue inflammation. In vitro analyses revealed that B1R suppression reverses the upregulation of ICAM-I and VCAM-I at the inflamed BBB thereby limiting T cell transmigration. In contrast, blocking B2R had no significant impact on EAE. We conclude that B1R inhibition can reduce BBB damage and cell invasion during autoimmune CNS disease and may offer a novel anti-inflammatory strategy for the treatment of MS.

Brain endothelial cell-cell junctions: how to "open" the blood brain barrier

The blood-brain barrier (BBB) is a highly specialized structural and biochemical barrier that regulates the entry of blood-borne molecules into brain, and preserves ionic homeostasis within the brain microenvironment. BBB properties are primarily determined by junctional complexes between the cerebral endothelial cells. These complexes are comprised of tight and adherens junctions. Such restrictive angioarchitecture at the BBB reduces paracellular diffusion, while minimal vesicle transport activity in brain endothelial cells limits transcellular transport. Under normal conditions, this largely prevents the extravasation of large and small solutes (unless specific transporters are present) and prevents migration of any type of blood-borne cell. However, this is changed in many pathological conditions. There, BBB disruption (“opening”) can lead to increased paracellular permeability, allowing entry of leukocytes into brain tissue, but also contributing to edema formation. In parallel, there are changes in the endothelial pinocytotic vesicular system resulting in the uptake and transfer of fluid and macromolecules into brain parenchyma. This review highlights the route and possible factors involved in BBB disruption in a variety of neuropathological disorders (e.g. CNS inflammation, Alzheimer’s disease, Parkinson’s disease, epilepsy). It also summarizes proposed signal transduction pathways that may be involved in BBB “opening”.

Role of kinin B1 and B2 receptors in memory consolidation during the aging process of mice

Under physiological conditions, elderly people present memory deficit associated with neuronal loss. This pattern is also associated with Alzheimer's disease but, in this case, in a dramatically intensified level. Kinin receptors have been involved in neurodegeneration and increase of amyloid-beta concentration, associated with Alzheimer's disease (AD). Considering these findings, this work evaluated the role of kinin receptors in memory consolidation during the aging process. Male C57Bl/6 (wt), knock-out B1 (koB1) or B2 (koB2) mice (3, 6, 12 and 18-month-old - mo; n=10 per group) were submitted to an acquisition session, reinforcement to learning (24h later: test 1) and final test (7days later: test 2), in an active avoidance apparatus, to evaluate memory. Conditioned avoidance responses (CAR, % of 50 trials) were registered. In acquisition sessions, similar CAR were obtained among age matched animals from all strains. However, a significant decrease in CAR was observed throughout the aging process (3mo: 8.8+/-2.3%; 6mo: 4.1+/-0.6%; 12mo: 2.2+/-0.6%, 18mo: 3.6+/-0.6%, P<0.01), indicating a reduction in the learning process. In test 1, as expected, memory retention increased significantly (P<0.05) in all 3- and 6-month-old animals as well as in 12-month-old-wt and 12-month-old-koB1 (P<0.01), compared to the training session. However, 12-month-old-koB2 and all 18-month-old animals did not show an increase in memory retention. In test 2, 3- and 6-month-old wt and koB1 mice of all ages showed a significant improvement in memory (P<0.05) compared to test 1. However, 12-month-old wt and koB2 mice of all ages showed no difference in memory retention. We suggest that, during the aging process, the B1 receptor could be involved in neurodegeneration and memory loss. Nevertheless, the B2 receptor is apparently acting as a neuroprotective factor.

Participation of kinin receptors on memory impairment after chronic infusion of human amyloid-beta 1-40 peptide in mice

Chronic infusion of human amyloid-beta 1-40 (Abeta) in the lateral ventricle (LV) of rats is associated with memory impairment and increase of kinin receptors in cortical and hippocampal areas. Deletion of kinin B1 or B2 receptors abolished memory impairment caused by an acute single injection of Abeta in the LV. As brain tissue and kinin receptors could unlikely react to acute or chronic administration of a similar quantity of Abeta, we evaluated the participation of B1 or B2 receptors in memory impairment after chronic infusion of Abeta. Male C57Bl/6J (wt), knock-out B1 (koB1) or B2 (koB2) mice (12weeks of age) previously trained in a two-way shuttle-box and achieving conditioned avoidance responses (CAR, % of 50 trials) were infused with AB (550pmol, 0.12microL/h, 28days) or vehicle in the LV using a mini-osmotic pump. They were tested before the surgery (T0), 7 and 35days after the infusion started (T7; T35). In T0, no difference was observed between CAR of the control (Cwt=59.7+/-6.7%; CkoB1=46.7+/-4.0%; CkoB2=64.4+/-5.8%) and Abeta (Abetawt=66.0+/-3.0%; AbetakoB1=66.8+/-8.2%; AbetakoB2=58.7+/-5.9%) groups. In T7, AbetakoB2 showed a significant decrease in CAR (41.0+/-8.6%) compared to the control-koB2 (72.8+/-2.2%, P<0.05). In T35, a significant decrease (P<0.05) was observed in Abetawt (40.7+/-3.3%) and AbetakoB2 (41.2+/-10.7%) but not in the AbetakoB1 (64.0+/-14.0%) compared to their control groups. No changes were observed in the controls at T35. We suggest that in chronic infusion of BA, B1 receptors could play an important role in the neurodegenerative process. Conversely, the premature memory impairment of koB2 suggests that it may be a protective factor.

Activation of kinin receptor B1 limits encephalitogenic T lymphocyte recruitment to the central nervous system

Previous proteomic and transcriptional analyses of multiple sclerosis lesions revealed modulation of the renin-angiotensin and the opposing kallikrein-kinin pathways. Here we identify kinin receptor B1 (Bdkrb1) as a specific modulator of immune cell entry into the central nervous system (CNS). We demonstrate that the Bdkrb1 agonist R838 (Sar-[D-Phe]des-Arg(9)-bradykinin) markedly decreases the clinical symptoms of experimental autoimmune encephalomyelitis (EAE) in SJL mice, whereas the Bdkrb1 antagonist R715 (Ac-Lys-[D-betaNal(7), Ile(8)]des-Arg(9)-bradykinin) resulted in earlier onset and greater severity of the disease. Bdkrb1-deficient (Bdkrb1(-/-)) C57BL/6 mice immunized with a myelin oligodendrocyte glycoprotein fragment, MOG(35-55), showed more severe disease with enhanced CNS-immune cell infiltration. The same held true for mixed bone marrow-chimeric mice reconstituted with Bdkrb1(-/-) T lymphocytes, which showed enhanced T helper type 17 (T(H)17) cell invasion into the CNS. Pharmacological modulation of Bdkrb1 revealed that in vitro migration of human T(H)17 lymphocytes across blood-brain barrier endothelium is regulated by this receptor. Taken together, these results suggest that the kallikrein-kinin system is involved in the regulation of CNS inflammation, limiting encephalitogenic T lymphocyte infiltration into the CNS, and provide evidence that Bdkrb1 could be a new target for the treatment of chronic inflammatory diseases such as multiple sclerosis.

Increases of kinin B1 and B2 receptors binding sites after brain infusion of amyloid-beta 1–40 peptide in rats

Although numerous inflammation pathways have been implicated in Alzheimer's disease, the involvement of the kallikrein-kinin system is still under investigation. We anatomically localized and quantified the density of kinin B(1) and B(2) receptors binding sites in the rat brain after the infusion of amyloid-beta (Abeta) peptide in the right lateral brain ventricle for 5 weeks. The conditioned avoidance test showed a significant reduction of memory consolidation in rats infused with Abeta (68.6+/-20.9%, P<0.05) when compared to control group (90.8+/-4.1%; infused with vehicle). Autoradiographic studies performed in brain samples of both groups using [(125)I]HPP-[des-Arg(10)]-Hoe-140 (150pM, 90min, 25 degrees C) showed a significant increase in density of B(1) receptor binding sites in the ventral hippocampal commissure (1.23+/-0.07fmol/mg), fimbria (1.31+/-0.05fmol/mg), CA1 and CA3 hippocampal areas (1.05+/-0.03 and 1.24+/-0.02fmol/mg, respectively), habenular nuclei (1.30+/-0.04fmol/mg), optical tract (1.30+/-0.05fmol/mg) and internal capsule (1.26+/-0.05fmol/mg) in Abeta group. For B(2) receptors ([(125)I]HPP-Hoe-140, 200pM, 90min, 25 degrees C), a significant increase in density of binding sites was observed in optical tract (2.04+/-0.08fmol/mg), basal nucleus of Meynert (1.84+/-0.18fmol/mg), lateral septal nucleus - dorsal and intermediary portions (1.66+/-0.29fmol/mg), internal capsule (1.74+/-0.19fmol/mg) and habenular nuclei (1.68+/-0.11fmol/mg). In control group, none of these nuclei showed [(125)I]HPP-Hoe-140 labeling. This significant increase in densities of kinin B(1) and B(2) receptors in animals submitted to Abeta infusion was observed mainly in brain regions related to cognitive behavior, suggesting the involvement of the kallikrein-kinin system in Alzheimer's disease in vivo.

Roles of the kallikrein/kinin system in the adaptive immune system

This review deals with the effects of kinins, a family of octa- to decapeptides structurally related to bradykinin (BK), in adaptive immune responses. Herein, we discuss the experimental evidence that kinins may exert influence on multiple players of the immune system (i.e. macrophages, dendritic cells, T and B lymphocytes), and modulate the activation, proliferation, migration and effector functions of these cells. We also give an overview of the possible impact of kinins in human autoimmune diseases and corresponding animal models, with special emphasis on autoimmune neuroinflammation and arthritis. These studies indicate a possible immunomodulatory capacity of kinins beyond our current knowledge of kinin actions regarding the vascular system, and thus the way towards future therapeutic approaches.

Death receptor expression and function at the human blood brain barrier

The blood brain barrier (BBB) is composed of specialized endothelial cells tightly anastomosed to one another and surrounded by a thick extracellular matrix, the basement membrane. Together these components restrict the diffusion of cells and molecules from the periphery into the central nervous system (CNS), providing immune privilege and homeostasis. Dysregulation of the BBB and trans-endothelial migration of immune cells are amongst the earliest CNS changes partaking in lesion formation in multiple sclerosis (MS). Death receptors are members of the tumor necrosis factor receptor (TNFR) super-family. They are expressed on a variety of tissues including endothelium, but the consequence of their triggering appears to be cell type specific. In this study, we describe the expression of death receptors TNFR1, Fas and DR5 on primary cultures of human BBB-derived endothelial cells (ECs), as well as the effects of receptor activation on human brain endothelial cell (HBEC) function. We show that HBECs are resistant to cell death mediated via TNFalpha, FasL and TRAIL and that neither receptor ligation induces cellular proliferation of HBECs. TNFR1 ligation induces NFkappaB activation and the upregulation of chemokines MCP-1 and IL-8, as well as adhesion molecules ICAM-1 and VCAM-1, while Fas and DR5 triggering activate the extracellular signal regulated kinases-1 and -2 (Erk 1/2, p42/44 MAPK) inducing the release of matrix metalloproteinase 9 (MMP9) by BBB-derived ECs.

Statins reduce human blood-brain barrier permeability and restrict leukocyte migration: Relevance to multiple sclerosis

OBJECTIVE

Dysregulation of the blood-brain barrier (BBB) and transendothelial migration of immune cells are among the earliest central nervous system changes partaking in lesion formation in both multiple sclerosis (MS) and its early clinical form, the clinically isolated syndrome. Evidence for the anti-inflammatory effects of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors within the central nervous system arose from studies demonstrating that statins improve clinical signs in the animal model of MS and reduce the number of gadolinium-enhancing lesions in MS.

METHODS

We sought to describe the impact of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor treatment on the physiology and immunology of human BBB-derived endothelial cells (ECs).

RESULTS

We demonstrate that lovastatin and simvastatin induce a 50 to 60% reduction in the diffusion rates of bovine serum albumin and [(14)C]-sucrose across human BBB-ECs in vitro through abrogation of isoprenylation processes, but independent of the expression of the tight junction molecules occludin, VE-cadherin, JAM-1, zonula occluden-1, and zonula occluden-2. Simvastatin and lovastatin were equipotent in reducing BBB permeability in vitro, with median effective concentration (EC(50)) of 9.5 x 10(-8) and 1.0 x 10(-7)M, respectively. We further demonstrate that lovastatin and simvastatin treatment of BBB-ECs significantly restricts the migration of clinically isolated syndrome-derived and MS-derived monocytes and lymphocytes across the human BBB in vitro, through a specific reduction in the secretion of the chemokines monocyte chemotactic protein-1/CCL2 and interferon-gamma-inducible protein-10/CXCL10 by BBB-ECs.

INTERPRETATION

Our data parallel the previously reported magnetic resonance imaging-based radiological findings and suggest an effect of statins that could be beneficial in early MS, restricting the diffusion of molecular tracers and the migration of immune cells across the human BBB.

High glucose increases B1-kinin receptor expression and signaling in endothelial cells

The loss of endothelial function is the initiating factor in the development of diabetic vascular disease. Kinins control endothelial function by the activation of two receptors: the B2 which is constitutively expressed, and the B1 which is highly induced in pathological conditions. In the present study, we observed that the levels of B1-receptor mRNA and protein are induced in endothelial cells incubated in high glucose. An increase in B1-receptor was also observed in the endothelial layer of aortas, from 4-week diabetic rats. When cells were grown in high glucose, the B1 agonist des-Arg9-BK increased nitrite levels, whereas in normal glucose nitrite levels were unchanged. Nitrite increase was blocked by L-NAME and 1400W indicating the participation of the inducible Nitric Oxide Synthase (iNOS). iNOS protein levels were also increased in high glucose. These results demonstrate the participation of the B1 receptor in the signaling pathways mediated by kinins in high glucose.

The kallikrein-kinin system: current and future pharmacological targets

The kallikrein-kinin system is an endogenous metabolic cascade, triggering of which results in the release of vasoactive kinins (bradykinin-related peptides). This complex system includes the precursors of kinins known as kininogens and mainly tissue and plasma kallikreins. The pharmacologically active kinins, which are often considered as either proinflammatory or cardioprotective, are implicated in many physiological and pathological processes. The interest of the various components of this multi-protein system is explained in part by the multiplicity of its pharmacological activities, mediated not only by kinins and their receptors, but also by their precursors and their activators and the metallopeptidases and the antiproteases that limit their activities. The regulation of this system by serpins and the wide distribution of the different constituents add to the complexity of this system, as well as its multiple relationships with other important metabolic pathways such as the renin-angiotensin, coagulation, or complement pathways. The purpose of this review is to summarize the main properties of this kallikrein-kinin system and to address the multiple pharmacological interventions that modulate the functions of this system, restraining its proinflammatory effects or potentiating its cardiovascular properties.

Autocrine peptide mediators of cerebral endothelial cells and their role in the regulation of blood-brain barrier

A unique feature of cerebral endothelial cells (CECs) is the formation of the blood-brain barrier (BBB), which contributes to the stability of the brain microenvironment. CECs are capable of producing several substances mediating endothelium-dependent vasorelaxation or vasoconstriction, regulating BBB permeability, and participating in the regulation of cell-cell interactions during inflammatory and immunological processes. The chemical nature of these mediators produced by CECs ranges from gaseous anorganic molecules (e.g. nitric oxide) through lipid mediators (e.g. prostaglandins) to peptides. Peptide mediators are a large and diverse family of bioactive molecules which can elicit multiple effects on cerebral endothelial functions. In this review, we summarize current knowledge of peptide mediators produced by CECs, such as adrenomedullin, angiotensin, endothelin and several others and their role in the regulation of BBB functions.

Th1 and Th2 lymphocyte migration across the human BBB is specifically regulated by interferon beta and copolymer-1

Lymphocyte migration into the central nervous system is a central event in lesion formation in MS. Both interferon beta (IFNbeta) and copolymer-1 (Cop-1) reduce the overall lymphocyte entry into the brain through the blood-brain barrier (BBB) as judged by MRI based studies. In this study, we used a modified Boyden chamber assay in which human brain microvascular endothelial cell (HBEC) monolayers are grown on a fibronectin coated transwell membrane to evaluate in vitro migration of allo-antigen Th1 and Th2 lymphocytes across brain endothelium. We confirmed previous observations showing that migration rates of Th2 lymphocytes across HBECs were higher than migration rates of Th1 cells. When HBECs were pre-treated with IFNbeta (100 U/ml) 30 min prior to migration, the migration rate of Th1 was significantly decreased (45% reduction) while the migration of Th2 remained unchanged. Addition of Cop-1 (30 microg/ml) to HBEC monolayers 30 min prior to migration significantly increased the migration rate of Th2 cells and did not affect the migration of Th1 cells. We did not observe any changes in (1) the expression of adhesion molecules on the surface of HBECs and (2) the pattern of chemokine production by HBECs after IFNbeta or Cop-1 treatment. The changes in cellular migration rates were not paralleled with changes in diffusion of large molecular weight tracers across brain ECs. Our data support the notion that immuno-modulators used for the treatment of MS selectively and differentially regulate the migration of T helper lymphocyte subsets and that Cop-1 promotes trans-endothelial migration of Th2 cells across the BBB.

Human immunodeficiency virus type 1 transport across the in vitro mouse brain endothelial cell monolayer

Human immunodeficiency virus type 1 (HIV-1) is associated with a neuroinflammatory dementia. Cognitive impairment remains a common complication of late-stage HIV-1 infection. Previous studies have shown that entry of HIV-1 into the central nervous system (CNS) occurs soon after infection. For these reasons, it is important to understand how HIV-1 crosses the BBB. We used primary mouse brain microvessel endothelial cell (MBEC) monolayer models to study interactions between brain endothelial cells and radioactively labeled HIV-1 CL4 (131I-HIV-1), which had been rendered noninfectious with aldithiol, and compared to radioactively labeled bovine serum albumin (131I-BSA or 125I-BSA) and detected HIV-1 on MBEC monolayer with electron microscopic analysis. The permeability of the monolayers to HIV-1 was measured by determining the percent material transported (PMT). Luminal to abluminal PMT of 131I-HIV-1 was 4.65 times greater than that of the much smaller 131I-BSA, showing that the MBEC monolayer is more permeable to HIV-1 than to BSA. Electron microscopy showed that HIV-1 was transported through a trans-cellular pathway from luminal side to basolateral space with some virus associated with the nucleus. Unlabeled HIV-1 did not affect the transport of 131I-HIV-1 or break down the MBEC monolayer. Wheatgerm agglutinin (WGA) increased 131I-HIV-1 penetration across the MBEC monolayer, consistent with absorptive endocytosis as the mechanism for HIV-1 penetration. The enhanced transport of HIV-1 was unidirectional, as the abluminal to luminal PMT of 131I-HIV-1 was not different from that of BSA nor enhanced by WGA. Characterization of the radioactivity transported from the luminal to abluminal chamber on Sepharose 4B-200 columns showed the transported radioactivity represented intact virus. MBEC monolayers preloaded from the luminal surface with 131I-HIV-1 showed most of the virus was retained by the endothelial cells, while the remainder was effluxed mainly to the luminal surface. MBEC monolayers preloaded from the abluminal surface with 131I-HIV-1 retained little virus and most of the virus was effluxed mainly to the abluminal surface. In conclusion, cell-free, intact 131I-HIV-1 crossed brain endothelial cell monolayers unidirectionally in the luminal to abluminal direction through an adsorptive endocytotic pathway. HIV-1 taken up from luminal side by monolayers of brain endothelial cells was mainly released to the luminal side. HIV-1 efflux mechanisms are different from influx mechanisms.

Dualité fonctionnelle des récepteurs des kinines en physiopathologie

Kinins are autacoid peptides and central neuromediators involved in cardiovascular regulation, inflammation and pain. Their effects are mediated by two transmembrane G-protein-coupled receptors denoted as B1 and B2. While the B2 receptor is constitutive, the B1 receptor is inducible and up-regulated in the presence of cytokines, endotoxins or during tissue injury. The B2 receptor is believed to play an important role in the beneficial effects of angiotensin-1 converting enzyme inhibitors used in the treatment of cardiovascular diseases, yet it is involved in the acute phase of inflammation and of somatic and visceral pain. Conversely, the B1 receptor participates in the chronic phase of these responses and is likely to play a strategic role in diseases with a strong immune component such as rheumatoid arthritis, multiple sclerosis, septic shock and diabetes. A dual function for the B1 receptor is also reported in some pathologies in which it can exert either a protective (multiple sclerosis and septic shock) or harmful (pain and inflammation) effect. Therefore, the use of antagonists for these receptors as clinical therapeutic agents requires a rigorous evaluation of the potential side effects.