Bradykinin antagonist decreases early disruption of the blood-spinal cord barrier after spinal cord injury in mice

Pharmacological interventions targeting the microcirculation following traumatic spinal cord injury

Traumatic spinal cord injury is a devastating disorder characterized by sensory, motor, and autonomic dysfunction that severely compromises an individual's ability to perform activities of daily living. These adverse outcomes are closely related to the complex mechanism of spinal cord injury, the limited regenerative capacity of central neurons, and the inhibitory environment formed by traumatic injury. Disruption to the microcirculation is an important pathophysiological mechanism of spinal cord injury. A number of therapeutic agents have been shown to improve the injury environment, mitigate secondary damage, and/or promote regeneration and repair. Among them, the spinal cord microcirculation has become an important target for the treatment of spinal cord injury. Drug interventions targeting the microcirculation can improve the microenvironment and promote recovery following spinal cord injury. These drugs target the structure and function of the spinal cord microcirculation and are essential for maintaining the normal function of spinal neurons, axons, and glial cells. This review discusses the pathophysiological role of spinal cord microcirculation in spinal cord injury, including its structure and histopathological changes. Further, it summarizes the progress of drug therapies targeting the spinal cord microcirculation after spinal cord injury.

Changes in blood-spinal cord barrier permeability and neuroimmune interactions in the underlying mechanisms of chronic pain

Advancing our understanding of the underlying mechanisms of chronic pain is instrumental to the identification of new potential therapeutic targets. Neuroimmune communication throughout the pain pathway is of crucial mechanistic importance and has been a major focus of preclinical chronic pain research over the last 2 decades. In the spinal cord, not only do dorsal horn neurons partake in mechanistically important bidirectional communication with resident immune cells such as microglia, but in some cases, they can also partake in bidirectional crosstalk with immune cells, such as monocytes/macrophages, which have infiltrated into the spinal cord from the circulation. The infiltration of immune cells into the spinal cord can be partly regulated by changes in permeability of the blood-spinal cord barrier (BSCB). Here, we discuss evidence for and against a mechanistic role for BSCB disruption and associated changes in neuroimmune crosstalk in preclinical chronic pain. We also consider recent evidence for its potential involvement in the vincristine model of chemotherapy-induced painful neuropathy. We conclude that current knowledge warrants further investigation to establish whether preventing BSCB disruption, or targeting the changes associated with this disruption, could be used for the development of novel approaches to treating chronic pain.

The effect of insomnia on development of Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia and a neurodegenerative disorder characterized by memory deficits especially forgetting recent information, recall ability impairment, and loss of time tracking, problem-solving, language, and recognition difficulties. AD is also a globally important health issue but despite all scientific efforts, the treatment of AD is still a challenge. Sleep has important roles in learning and memory consolidation. Studies have shown that sleep deprivation (SD) and insomnia are associated with the pathogenesis of Alzheimer's disease and may have an impact on the symptoms and development. Thus, sleep disorders have decisive effects on AD; this association deserves more attention in research, diagnostics, and treatment, and knowing this relation also can help to prevent AD through screening and proper management of sleep disorders. This study aimed to show the potential role of SD and insomnia in the pathogenesis and progression of AD.

Implication of the Kallikrein-Kinin system in neurological disorders: Quest for potential biomarkers and mechanisms

Neurological disorders represent major health concerns in terms of comorbidity and mortality worldwide. Despite a tremendous increase in our understanding of the pathophysiological processes involved in disease progression and prevention, the accumulated knowledge so far resulted in relatively moderate translational benefits in terms of therapeutic interventions and enhanced clinical outcomes. Aiming at specific neural molecular pathways, different strategies have been geared to target the development and progression of such disorders. The kallikrein-kinin system (KKS) is among the most delineated candidate systems due to its ubiquitous roles mediating several of the pathophysiological features of these neurological disorders as well as being implicated in regulating various brain functions. Several experimental KKS models revealed that the inhibition or stimulation of the two receptors of the KKS system (B1R and B2R) can exhibit neuroprotective and/or adverse pathological outcomes. This updated review provides background details of the KKS components and their functions in different neurological disorders including temporal lobe epilepsy, traumatic brain injury, stroke, spinal cord injury, Alzheimer's disease, multiple sclerosis and glioma. Finally, this work will highlight the putative roles of the KKS components as potential neurotherapeutic targets and provide future perspectives on the possibility of translating these findings into potential clinical biomarkers in neurological disease.

Immunobiology of spinal cord injuries and potential therapeutic approaches

The incidence of spinal cord injuries (SCI) is high every year. As the spinal cord is the highway that allows for the brain to control the rest of the body, spinal cord injuries greatly impact the quality of life of the patients. The SCI include the primary response consisting of the initial accident-induced damage and the secondary response that is characterized by damage due to inflammation and biological responses. Astrocytes are the first to act at the site of the injury, forming a glial scar and attracting immune cells. The immune system plays a role in cleaning out the debris caused by the injury, as well as preventing neurons to grow and heal. The secondary injury caused by the inflammatory response is the major target to combat SCI. This article critically reviews the key players in the inflammatory SCI response and potential therapies, specifically targeting astrocytes, neutrophils, and macrophages. These cells are both beneficial and detrimental following SCI, depending on the released molecules and the types of cells infiltrated to the site of injury. Indeed, depending on the subtype of macrophages, M1 or M2, beneficial or detrimental response could be incited. Therapeutic strategies to regulate and manipulate the immune cells via increasing or decreasing their recruitment to the site of injury could be developed together with upregulating and downregulating the release of certain chemicals from the infiltrated cells.

Modulatory and plastic effects of kinins on spinal cord networks

KEY POINTS

Inflammatory kinins are released following spinal cord injury or neurotrauma. The effects of these kinins on ongoing locomotor activity of central pattern generator networks are unknown. In the present study, kinins were shown to have short- and long-term effects on motor networks. The short-term effects included direct depolarization of interneurons and motoneurons in the ventral horn accompanied by modulation of transient receptor potential vanilloid 1-sensitive nociceptors in the dorsal horn. Over the long-term, we observed a bradykinin-mediated effect on promoting plasticity in the spinal cord. In a model of spinal cord injury, we observed an increase in microglia numbers in both the dorsal and ventral horn and, in a microglia cell culture model, we observed bradykinin-induced expression of glial-derived neurotrophic factor.

ABSTRACT

The expression and function of inflammatory mediators in the developing spinal cord remain poorly characterized. We discovered novel, short and long-term roles for the inflammatory nonapeptide bradykinin (BK) and its receptor bradykinin receptor B2 (B2R) in the neuromodulation of developing sensorimotor networks following a spinal cord injury (SCI), suggesting that BK participates in an excitotoxic cascade. Functional expression of B2R was confirmed by a transient disruptive action of BK on fictive locomotion generated by a combination of NMDA, 5-HT and dopamine. The role of BK in the dorsal horn nociceptive afferents was tested using spinal cord attached to one-hind-limb (HL) preparations. In the HL preparations, BK at a subthreshold concentration induced transient disruption of fictive locomotion only in the presence of: (1) noxious heat applied to the hind paw and (2) the heat sensing ion channel transient receptor potential vanilloid 1 (TRPV1), known to be restricted to nociceptors in the superficial dorsal horn. BK directly depolarized motoneurons and ascending interneurons in the ventrolateral funiculus. We found a key mechanism for BK in promoting long-term plasticity within the spinal cord. Using a model of neonatal SCI and a microglial cell culture model, we examined the role of BK in inducing activation of microglia and expression of glial-derived neurotrophic factor (GDNF). In the neonatal SCI model, we observed an increase in microglia numbers and increased GDNF expression restricted to microglia. In the microglia cell culture model, we observed a BK-induced increased expression of GDNF via B2R, suggesting a novel mechanism for BK spinal-mediated plasticity.

Propitious Therapeutic Modulators to Prevent Blood-Spinal Cord Barrier Disruption in Spinal Cord Injury

The blood-spinal cord barrier (BSCB) is a specialized protective barrier that regulates the movement of molecules between blood vessels and the spinal cord parenchyma. Analogous to the blood-brain barrier (BBB), the BSCB plays a crucial role in maintaining the homeostasis and internal environmental stability of the central nervous system (CNS). After spinal cord injury (SCI), BSCB disruption leads to inflammatory cell invasion such as neutrophils and macrophages, contributing to permanent neurological disability. In this review, we focus on the major proteins mediating the BSCB disruption or BSCB repair after SCI. This review is composed of three parts. Section 1. SCI and the BSCB of the review describes critical events involved in the pathophysiology of SCI and their correlation with BSCB integrity/disruption. Section 2. Major proteins involved in BSCB disruption in SCI focuses on the actions of matrix metalloproteinases (MMPs), tumor necrosis factor alpha (TNF-α), heme oxygenase-1 (HO-1), angiopoietins (Angs), bradykinin, nitric oxide (NO), and endothelins (ETs) in BSCB disruption and repair. Section 3. Therapeutic approaches discusses the major therapeutic compounds utilized to date for the prevention of BSCB disruption in animal model of SCI through modulation of several proteins.

From blood to brain through BBB and astrocytic signaling

In this Festschrift, I discuss the career and guiding principles to which Abba J. Kastin has adhered during the last 20 years we worked together. I briefly describe the history of our joint laboratory group, the context of studies of peptide permeation across the blood-brain barrier (BBB), and newer developments in the BBB Group as Abba steps down after serving 35 years as the founding Editor-in-Chief for Peptides. Abba's BBB studies on peptides have contributed to concepts in the neuroendocrinology of feeding and developed information on molecular trafficking across BBB cells. The astroglial leptin signaling studies and the interactions of sleep and BBB are two major directions, whereas the long-term MIF-1 project demarcates a tortuous road on translational research.

Roles of kinins in the nervous system

The kallikrein-kinin system (KKS) is an endogenous pathway involved in many biological processes. Although primarily related to blood pressure control and inflammation, its activation goes beyond these effects. Neurogenesis and neuroprotection might be stimulated by bradykinin being of great interest for clinical applications following brain injury. This peptide is also an important player in spinal cord injury pathophysiology and recovery, in which bradykinin receptor blockers represent substantial therapeutic potential. Here, we highlight the participation of kinin receptors and especially bradykinin in mediating ischemia pathophysiology in the central and peripheral nervous systems. Moreover, we explore the recent advances on mechanistic and therapeutic targets for biological, pathological, and neural repair processes involving kinins.

Sleep restriction impairs blood-brain barrier function

The blood-brain barrier (BBB) is a large regulatory and exchange interface between the brain and peripheral circulation. We propose that changes of the BBB contribute to many pathophysiological processes in the brain of subjects with chronic sleep restriction (CSR). To achieve CSR that mimics a common pattern of human sleep loss, we quantified a new procedure of sleep disruption in mice by a week of consecutive sleep recording. We then tested the hypothesis that CSR compromises microvascular function. CSR not only diminished endothelial and inducible nitric oxide synthase, endothelin1, and glucose transporter expression in cerebral microvessels of the BBB, but it also decreased 2-deoxy-glucose uptake by the brain. The expression of several tight junction proteins also was decreased, whereas the level of cyclooxygenase-2 increased. This coincided with an increase of paracellular permeability of the BBB to the small tracers sodium fluorescein and biotin. CSR for 6 d was sufficient to impair BBB structure and function, although the increase of paracellular permeability returned to baseline after 24 h of recovery sleep. This merits attention not only in neuroscience research but also in public health policy and clinical practice.

The dual cyclooxygenase/5-lipoxygenase inhibitor licofelone attenuates p-glycoprotein-mediated drug resistance in the injured spinal cord

There are currently no proven effective treatments that can improve recovery of function in spinal cord injury (SCI) patients. Many therapeutic compounds have shown promise in pre-clinical studies, but clinical trials have been largely unsuccessful. P-glycoprotein (Pgp, Abcb1b) is a drug efflux transporter of the blood-spinal cord barrier that limits spinal cord penetration of blood-borne xenobiotics. Pathological Pgp upregulation in diseases such as cancer causes heightened resistance to a broad variety of therapeutic drugs. Importantly, several drugs that have been evaluated for the treatment of SCI, such as riluzole, are known substrates of Pgp. We therefore examined whether Pgp-mediated pharmacoresistance diminishes delivery of riluzole to the injured spinal cord. Following moderate contusion injury at T10 in male Sprague-Dawley rats, we observed a progressive, spatial spread of increased Pgp expression from 3 days to 10 months post-SCI. Spinal cord uptake of i.p.-delivered riluzole was significantly reduced following SCI in wild type but not Abcb1a-knockout rats, highlighting a critical role for Pgp in mediating drug resistance following SCI. Because inflammation can drive Pgp upregulation, we evaluated the ability of the new generation dual anti-inflammatory drug licofelone to promote spinal cord delivery of riluzole following SCI. We found that licofelone both reduced Pgp expression and enhanced riluzole bioavailability within the lesion site at 72 h post-SCI. This work highlights Pgp-mediated drug resistance as an important obstacle to therapeutic drug delivery for SCI, and suggests licofelone as a novel combinatorial treatment strategy to enhance therapeutic drug delivery to the injured spinal cord.

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.

Kinin receptor antagonists as potential neuroprotective agents in central nervous system injury

Injury to the central nervous system initiates complex physiological, cellular and molecular processes that can result in neuronal cell death. Of interest to this review is the activation of the kinin family of neuropeptides, in particular bradykinin and substance P. These neuropeptides are known to have a potent pro-inflammatory role and can initiate neurogenic inflammation resulting in vasodilation, plasma extravasation and the subsequent development of edema. As inflammation and edema play an integral role in the progressive secondary injury that causes neurological deficits, this review critically examines kinin receptor antagonists as a potential neuroprotective intervention for acute brain injury, and more specifically, traumatic brain and spinal cord injury and stroke.

Cytokine transport across the injured blood-spinal cord barrier

Spinal cord injury (SCI) induces dynamic changes of the blood-spinal cord barrier and even the more distant blood-brain barrier. Besides an immediate increase of paracellular permeability resulting from the direct impact of the injury, the transport systems for selective cytokines undergo regulatory changes. Since many of the transported molecules play essential roles in neuroregeneration, we propose that this altered peripheral tissue / CNS interaction benefits remodeling of the spinal cord and functional recovery after SCI. This review examines the transport of cytokines and neurotrophic factors into the spinal cord, emphasizing the upregulation of two cytokines--tumor necrosis factor alpha (TNF) and leukemia inhibitory factor (LIF)--during the course of SCI. The increased transport of TNF and LIF after SCI remains saturable and does not coincide with generalized BBB disruption, highlighting a pivotal regulatory role for the blood-spinal cord barrier.

A fluorescent version of the bradykinin B2 receptor antagonist B-9430: pharmacological characterization and use in live cell imaging

B-9430 (d-Arg-[Hyp3, Igl5, D-Igl7, Oic8]-bradykinin), where Hyp is trans-4-hydroxyproline, Igl is alpha-(2-indanyl)glycine and Oic is (3as, 7as)-octahydroindol-2-yl-carbonyl is a high affinity bradykinin B2 receptor antagonist with effects extended to the B1 receptors at high concentrations. The N-terminus of B-9430 has been extended with d-biotinyl (B-10330) or 5(6)-carboxyfluorescein-epsilon-aminocaproyl (B-10380) to derive fluorescent receptor probes. The pharmacological profile of B-10380 was similar to that of B-9430 with a minor loss of potency (a competitive antagonist of bradykinin at the B2 receptors of the human isolated umbilical vein, pA2 6.83; an insurmountable antagonist at the B2 receptors in the rabbit jugular vein; a weak competitive antagonist of the B1 receptors in the rabbit aorta, pA2 5.95). B-10330 and B-10380 displaced the binding of [3H]bradykinin from rabbit B2 receptors with a potency slightly inferior to that of B-9430 (larger gap at the rat B2 receptor). Treatment with B-10330 and fluorescent streptavidin did not support imaging of recombinant B2 receptors. However, the plasma membrane of HEK 293a cells that transiently expressed recombinant rabbit B2 receptors, but not B1 receptors, was labeled with 5-50 nM B-10380 (epifluorescence microscopy). B-10380 staining was not observed in nontransfected cells and was abolished by co-treating receptor-expressing cells with a nonpeptide antagonist. The N-terminal extension of a potent peptide antagonist of the bradykinin B2 receptor with a fluorophore produced a fluorescent probe suitable for live cell imaging and other applications at the expense of a minor loss of affinity.

B-9972 (D-Arg-[Hyp3,Igl5,Oic7,Igl8]-bradykinin) Is an Inactivation-Resistant Agonist of the Bradykinin B2Receptor Derived from the Peptide Antagonist B-9430 (D-Arg-[Hyp3,Igl5,D-Igl7,Oic8]-bradykinin): Pharmacologic Profile and Effective Induction of Receptor Degradation

The bradykinin B(2) receptor is a heptahelical receptor regulated by a cycle of phosphorylation, endocytosis, and extensive recycling at the cell surface following agonist stimulation. B-9430 (d-Arg-[Hyp(3),Igl(5),D-Igl(7),Oic(8)]-bradykinin) is a second generation peptide antagonist found to be competitive at the human B(2) receptor and insurmountable at the rabbit B(2) receptor (contractility assays, isolated human umbilical and rabbit jugular veins). Two isomers of this peptide were prepared: B-10344 (D-Arg-[Hyp(3),Igl(5),Oic(7),D-Igl(8)]-bradykinin; inverted sequence Oic(7), D-Igl(8)) and B-9972 (D-Arg-[Hyp(3),Igl(5),Oic(7),Igl(8)]-bradykinin); they are low- and high-potency agonists, respectively, in vascular preparations. The potency gap between bradykinin and B-9972 is narrow in contractility assays, despite the fact that B-9972 affinity is 7-fold inferior at the rabbit B(2) receptor (radioligand binding competition assay). The effects of agonists on receptors were compared using two chimerical constructions based on rabbit B(2) receptors: conjugate of the B(2) receptor with green fluorescent protein (B(2)R-GFP) and the N-terminally tagged conjugate of the myc epitope with the B(2) receptor. Imaging and immunoblotting showed that B-9972 induced a persistent endocytosis of cell surface B(2) receptors in human embryonic kidney 293 cells with slow receptor degradation (weak after 3 h of treatment, important at 12 h) and B(2)R-GFP desensitization ([(3)H]bradykinin endocytosis and extracellular signal-regulated kinase 1/2 phosphorylation assays). Bradykinin was not active in this respect but when combined with captopril, induced some degradation. B-9430 reduced the endocytosis and degradation of B(2) receptors by the agonists. The results illustrate the agonist-antagonist transition in B(2) receptor peptide ligands with a constrained C-terminal structure, the importance of species in their pharmacological profile, and the possibility of selectively degrading receptors using a peptidase-resistant agonist.

Atrial natriuretic peptide reduces ischemia/reperfusion-induced spinal cord injury in rats by enhancing sensory neuron activation

We recently demonstrated that calcitonin gene-related peptide (CGRP) released from sensory neurons reduces spinal cord injury (SCI) by inhibiting neutrophil activation through an increase in the endothelial production of prostacyclin (PGI(2)). Carperitide, a synthetic alpha-human atrial natriuretic peptide (ANP), reduces ischemia/reperfusion (I/R)-induced tissue injury. However, its precise therapeutic mechanism(s) remains to be elucidated. In the present study, we examined whether ANP reduces I/R-induced spinal cord injury by enhancing sensory neuron activation using rats. ANP increased CGRP release and cellular cAMP levels in dorsal root ganglion neurons isolated from rats in vitro. The increase in CGRP release induced by ANP was reversed by pretreatment with capsazepine, an inhibitor of vanilloid receptor-1 activation, or with (9S, 10S, 12R)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i][1,6]-benzodiazocine-10-carboxylic acid hexyl ester (KT5720), an inhibitor of protein kinase A (PKA), suggesting that ANP might increase CGRP release from sensory neurons by activating PKA through an increase in the cellular cAMP level. Spinal cord ischemia was induced in rats using a balloon catheter placed in the aorta. ANP reduced mortality and motor disturbances by inhibiting reduction of the number of motor neurons in animals subjected to SCI. ANP significantly enhanced I/R-induced increases in spinal cord tissue levels of CGRP and 6-keto-prostaglandin F(1alpha). a stable metabolite of PGI(2). ANP inhibited I/R-induced increases in spinal cord tissue levels of tumor necrosis factor and myeloperoxidase. Pretreatment with 4'-chloro-3-methoxycinnamanilide (SB366791), a specific vanilloid receptor-1 antagonist, and indomethacin reversed the effects of ANP. These results strongly suggest that ANP might reduce I/R-induced SCI in rats by inhibiting neutrophil activation through enhancement of sensory neuron activation.

Activation of sensory neurons contributes to reduce spinal cord injury in rats

We previously demonstrated that activation of sensory neurons increases endothelial prostaglandin I(2) (PGI(2)) production by releasing calcitonin gene-related peptide (CGRP). Since PGI(2) reduces post-traumatic spinal cord injury (SCI) by inhibiting tumor necrosis factor (TNF) production, activation of sensory neurons in the spinal cord tissue may ameliorate spinal cord injury. This study examines these possibilities using rat models of compression trauma-induced SCI. Both SB366791, a specific vanilloid receptor antagonist, and CGRP (8-37), a CGRP receptor antagonist, significantly inhibited trauma-induced increases in spinal cord tissue 6-keto-PGF(1alpha) levels. SB366791, CGRP (8-37) and indomethacin (IM) enhanced increases in spinal cord tissue TNF levels at 2h after trauma and exacerbated motor disturbances. Administration of CGRP significantly reduced motor disturbances and inhibited increases in spinal cord tissue TNF levels through enhancement of increases in tissue levels of 6-keto-PGF(1alpha). These observations strongly suggest that activation of sensory neurons might ameliorate compression trauma-induced SCI, inhibiting TNF production through enhancement of endothelial PGI(2) production. Thus, although the spinal cord sensory neurons function as nociceptive neurons, they could also be critically involved in the cytoprotective system that attenuates SCI development and, thus, pharmacological stimulation of spinal cord sensory neurons might contribute to reduce spinal cord injury.

Therapeutic window of bradykinin B2 receptor inhibition after focal cerebral ischemia in rats

Following cerebral ischemia bradykinin/kinin B(2) receptors mediate inflammatory responses resulting in edema formation and secondary brain damage. However, the therapeutic window for B(2) receptor inhibition determining its potential clinical use has not been investigated so far. The aim of the current study was therefore to investigate the effect of delayed B(2) receptor inhibition on morphological and functional outcome following experimental stroke. Rats were subjected to 90 min of middle cerebral artery occlusion (MCAo) by an intraluminal filament. Animals received 0.9% NaCl or 1.0mg/kg/day Anatibant (LF 16-0687 Ms), a selective bradykinin B(2) receptor antagonist, for 3 days beginning at different time points after MCAo: 1, 2.5, 4.5, or 6.5h (n=10 per group). Neurological recovery was examined daily, infarct volume on day 7 after MCAo. Animal physiology was not influenced by B(2) receptor inhibition. Significant improvement of functional outcome was observed when treatment was delayed up to 4.5h after ischemia (p<0.05 versus vehicle). Inhibition of B(2) receptors during ischemia, i.e. when the inhibitor was given 1h after MCAo, reduced infarct volume in the basal ganglia and in the cortex by 49% (p<0.05) and 26% (p<0.05), respectively. Inhibition of B(2) receptors at later time points (2.5, 4.5, or 6.5 after MCAo) reduced penumbral damage, i.e. cortical infarction, by 19-26% (p<0.05). In conclusion, the current study shows that the therapeutic window of B(2) receptor inhibition extends for up to 6.5h after MCAo. Our data therefore suggest that inhibition of kinin B(2) receptors represents a treatment strategy for ischemic stroke which may warrant clinical validation.

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.

Release of bradykinin and expression of kinin B2 receptors in the brain: role for cell death and brain edema formation after focal cerebral ischemia in mice

Pharmacological studies using bradykinin B2 receptor antagonists suggest that bradykinin, an early mediator of inflammation and the main metabolite of the kallikrein-kinin system, is involved in secondary brain damage after cerebral ischemia. However, the time-course of bradykinin production and kinin receptor expression as well as the conclusive role of bradykinin B2 receptors for brain damage after experimental stroke have not been elucidated so far. C57/Bl6 mice were subjected to 45 mins of middle cerebral artery occlusion (MCAO) and 2, 4, 8, 24, and 48 h later brains were removed for the analysis of tissue bradykinin concentration and kinin B2 receptor mRNA and protein expression. Brain edema, infarct volume, functional outcome, and long-term survival were assessed in WT and B2-/- mice 24 h or 7 days after MCAO. Tissue bradykinin was maximally increased 12 h after ischemia (three-fold), while kinin B2 receptor mRNA upregulation peaked 24 to 48 h after MCAO (10- to 12-fold versus naïve brain tissue). Immunohistochemistry revealed that kinin B2 receptors were constitutively and widely expressed in mouse brain, were upregulated 2 h after ischemia in cells showing signs of ischemic damage, and remained upregulated in the penumbra up to 24 h after ischemia. B2-/- mice had improved motor function (P<0.05), smaller infarct volumes (-38%; P<0.01), developed less brain edema (-87%; P<0.05), and survived longer (P<0.01) as compared with wild-type controls. The current results show that bradykinin is produced in the brain, kinin B2 receptors are upregulated on dying cells, and B2 receptors are involved in cell death and brain edema formation after experimental stroke.

The blood-brain barrier: an overview: structure, regulation, and clinical implications

The blood-brain barrier (BBB) is a diffusion barrier, which impedes influx of most compounds from blood to brain. Three cellular elements of the brain microvasculature compose the BBB-endothelial cells, astrocyte end-feet, and pericytes (PCs). Tight junctions (TJs), present between the cerebral endothelial cells, form a diffusion barrier, which selectively excludes most blood-borne substances from entering the brain. Astrocytic end-feet tightly ensheath the vessel wall and appear to be critical for the induction and maintenance of the TJ barrier, but astrocytes are not believed to have a barrier function in the mammalian brain. Dysfunction of the BBB, for example, impairment of the TJ seal, complicates a number of neurologic diseases including stroke and neuroinflammatory disorders. We review here the recent developments in our understanding of the BBB and the role of the BBB dysfunction in CNS disease. We have focused on intraventricular hemorrhage (IVH) in premature infants, which may involve dysfunction of the TJ seal as well as immaturity of the BBB in the germinal matrix (GM). A paucity of TJs or PCs, coupled with incomplete coverage of blood vessels by astrocyte end-feet, may account for the fragility of blood vessels in the GM of premature infants. Finally, this review describes the pathogenesis of increased BBB permeability in hypoxia-ischemia and inflammatory mechanisms involving the BBB in septic encephalopathy, HIV-induced dementia, multiple sclerosis, and Alzheimer disease.

Astrocyte-endothelial interactions and blood-brain barrier permeability

The blood-brain barrier (BBB) is formed by brain endothelial cells lining the cerebral microvasculature, and is an important mechanism for protecting the brain from fluctuations in plasma composition, and from circulating agents such as neurotransmitters and xenobiotics capable of disturbing neural function. The barrier also plays an important role in the homeostatic regulation of the brain microenvironment necessary for the stable and co-ordinated activity of neurones. The BBB phenotype develops under the influence of associated brain cells, especially astrocytic glia, and consists of more complex tight junctions than in other capillary endothelia, and a number of specific transport and enzyme systems which regulate molecular traffic across the endothelial cells. Transporters characteristic of the BBB phenotype include both uptake mechanisms (e.g. GLUT-1 glucose carrier, L1 amino acid transporter) and efflux transporters (e.g. P-glycoprotein). In addition to a role in long-term barrier induction and maintenance, astrocytes and other cells can release chemical factors that modulate endothelial permeability over a time-scale of seconds to minutes. Cell culture models, both primary and cell lines, have been used to investigate aspects of barrier induction and modulation. Conditioned medium taken from growing glial cells can reproduce some of the inductive effects, evidence for involvement of diffusible factors. However, for some features of endothelial differentiation and induction, the extracellular matrix plays an important role. Several candidate molecules have been identified, capable of mimicking aspects of glial-mediated barrier induction of brain endothelium; these include TGFbeta, GDNF, bFGF, IL-6 and steroids. In addition, factors secreted by brain endothelial cells including leukaemia inhibitory factor (LIF) have been shown to induce astrocytic differentiation. Thus endothelium and astrocytes are involved in two-way induction. Short-term modulation of brain endothelial permeability has been shown for a number of small chemical mediators produced by astrocytes and other nearby cell types. It is clear that endothelial cells are involved in both long- and short-term chemical communication with neighbouring cells, with the perivascular end feet of astrocytes being of particular importance. The role of barrier induction and modulation in normal physiology and in pathology is discussed.

Upregulation of the transport system for TNFalpha at the blood-brain barrier

The transport system for the cytokine tumor necrosis factor-alpha (TNFalpha) at the blood-brain barrier (BBB) enables an enhanced yet saturable entry of TNFalpha from blood to the CNS. This review focuses on the selective upregulation of the transport system for TNFalpha at the BBB that is specific for type of pathology, region, and time. The upregulation is reflected by increased CNS tissue uptake of radiolabeled TNFalpha after iv injection in mice and by inhibition of this increase with excess non-radiolabeled TNFalpha. (1) Spinal cord injury (SCI): upregulation of TNFalpha uptake after thoracic transection is seen in the delayed phase of BBB disruption at the lumbar spinal cord. Thoracic SCI by compression, however, has a longer lasting impact on TNFalpha transport that involves thoracic and lumbar spinal cord, in contrast to the upregulation confined to the lumbar region in lumbar SCI by compression. Regardless, the uptake of TNFalpha by spinal cord does not parallel BBB disruption as measured by the leakage of radiolabeled albumin. (2) Experimental autoimmune encephalomyelitis (EAE): the increase in the differential permeability to TNFalpha is seen in all CNS regions (brain and cervical, thoracic, and lumbar spinal cord) and has a distinct time course and reversibility. Exogenous TNFalpha has biphasic effects in modulating functional scores. The BBB, a dynamically regulated barrier, is actively involved in disease processes.