Nitric oxide donor-induced increase in permeability of the blood-brain barrier

Effects of Sodium Nitroprusside on Lipopolysaccharide-Induced Inflammation and Disruption of Blood-Brain Barrier

In various neurodegenerative conditions, inflammation plays a significant role in disrupting the blood-brain barrier (BBB), contributing to disease progression. Nitric oxide (NO) emerges as a central regulator of vascular function, with a dual role in inflammation, acting as both a pro- and anti-inflammatory molecule. This study investigates the effects of the NO donor sodium nitroprusside (SNP) in protecting the BBB from lipopolysaccharide (LPS)-induced inflammation, using bEnd.3 endothelial cells as a model system. Additionally, Raw 264.7 macrophages were employed to assess the effects of LPS and SNP on their adhesion to a bEnd.3 cell monolayer. Our results show that LPS treatment induces oxidative stress, activates the JAK2/STAT3 pathway, and increases pro-inflammatory markers. SNP administration effectively mitigates ROS production and IL-6 expression, suggesting a potential anti-inflammatory role. However, SNP did not significantly alter the adhesion of Raw 264.7 cells to bEnd.3 cells induced by LPS, probably because it did not have any effect on ICAM-1 expression, although it reduced VCAM expression. Moreover, SNP did not prevent BBB disruption. This research provides new insights into the role of NO in BBB disruption induced by inflammation.

Targeting Glutamate Neurotoxicity through Dietary Manipulation: Potential Treatment for Migraine

Glutamate, the main excitatory neurotransmitter in the central nervous system, is implicated in both the initiation of migraine as well as central sensitization, which increases the frequency of migraine attacks. Excessive levels of glutamate can lead to excitotoxicity in the nervous system which can disrupt normal neurotransmission and contribute to neuronal injury or death. Glutamate-mediated excitotoxicity also leads to neuroinflammation, oxidative stress, blood-brain barrier permeability, and cerebral vasodilation, all of which are associated with migraine pathophysiology. Experimental evidence has shown the protective effects of several nutrients against excitotoxicity. The current review focuses on the mechanisms behind glutamate's involvement in migraines as well as a discussion on how specific nutrients are able to work towards restoring glutamate homeostasis. Understanding glutamate's role in migraine is of vital importance for understanding why migraine is commonly comorbid with widespread pain conditions and for informing future research directions.

Argininosuccinate lyase deficiency causes blood-brain barrier disruption via nitric oxide-mediated dysregulation of claudin expression

Nitric oxide (NO) is a critical signaling molecule that has been implicated in the pathogenesis of neurocognitive diseases. Both excessive and insufficient NO production have been linked to pathology. Previously, we have shown that argininosuccinate lyase deficiency (ASLD) is a novel model system to investigate cell-autonomous, nitric oxide synthase-dependent NO deficiency. Humans with ASLD are at increased risk for developing hyperammonemia due to a block in ureagenesis. However, natural history studies have shown that individuals with ASLD have multisystem disease including neurocognitive deficits that can be independent of ammonia. Here, using ASLD as a model of NO deficiency, we investigated the effects of NO on brain endothelial cells in vitro and the blood-brain barrier (BBB) in vivo. Knockdown of ASL in human brain microvascular endothelial cells (HBMECs) led to decreased transendothelial electrical resistance, indicative of increased cell permeability. Mechanistically, treatment with an NO donor or inhibition of Claudin-1 improved barrier integrity in ASL-deficient HBMECs. Furthermore, in vivo assessment of a hypomorphic mouse model of ASLD showed increased BBB leakage, which was partially rescued by NO supplementation. Our results suggest that ASL-mediated NO synthesis is required for proper maintenance of brain microvascular endothelial cell functions as well as BBB integrity.

CXCR4-targeted nitric oxide nanoparticles deliver PD-L1 siRNA for immunotherapy against glioblastoma

While immunotherapy has emerged as a promising strategy to treat glioblastoma multiforme (GBM), the limited availability of immunotherapeutic agents in tumors due to the presence of the blood-brain barrier (BBB) and immunosuppressive tumor microenvironment dampens efficacy. Nitric oxide (NO) plays a role in modulating both the BBB and tumor vessels and could thus be delivered to disrupt the BBB and improve the delivery of immunotherapeutics into GBM tumors. Herein, we report an immunotherapeutic approach that utilizes CXCR4-targeted lipid‑calcium-phosphate nanoparticles with NO donors (LCP-NO NPs). The delivery of NO resulted in enhanced BBB permeability and thus improved gene delivery across the BBB. CXCR4-targeted LCP-NO NPs delivered siRNA against the immune checkpoint ligand PD-L1 to GBM tumors, silenced PD-L1 expression, increased cytotoxic T cell infiltration and activation in GBM tumors, and suppressed GBM progression. Thus, the codelivery of NO and PD-L1 siRNA by these CXCR4-targeted NPs may serve as a potential immunotherapy for GBM.

Harnessing Ultrasound for Targeting Drug Delivery to the Brain and Breaching the Blood–Brain Tumour Barrier

Despite significant advances in developing drugs to treat brain tumours, achieving therapeutic concentrations of the drug at the tumour site remains a major challenge due to the presence of the blood–brain barrier (BBB). Several strategies have evolved to enhance brain delivery of chemotherapeutic agents to treat tumours; however, most approaches have several limitations which hinder their clinical utility. Promising studies indicate that ultrasound can penetrate the skull to target specific brain regions and transiently open the BBB, safely and reversibly, with a high degree of spatial and temporal specificity. In this review, we initially describe the basics of therapeutic ultrasound, then detail ultrasound-based drug delivery strategies to the brain and the mechanisms by which ultrasound can improve brain tumour therapy. We review pre-clinical and clinical findings from ultrasound-mediated BBB opening and drug delivery studies and outline current therapeutic ultrasound devices and technologies designed for this purpose.

Factors influencing the blood-brain barrier permeability

The blood-brain barrier (BBB) is a dynamic structure that protects the brain from harmful blood-borne, endogenous and exogenous substances and maintains the homeostatic microenvironment. All constituent cell types play indispensable roles in the BBB's integrity, and other structural BBB components, such as tight junction proteins, adherens junctions, and junctional proteins, can control the barrier permeability. Regarding the need to exchange nutrients and toxic materials, solute carriers, ATP-binding case families, and ion transporter, as well as transcytosis regulate the influx and efflux transport, while the difference in localisation and expression can contribute to functional differences in transport properties. Numerous chemical mediators and other factors such as non-physicochemical factors have been identified to alter BBB permeability by mediating the structural components and barrier function, because of the close relationship with inflammation. In this review, we highlight recently gained mechanistic insights into the maintenance and disruption of the BBB. A better understanding of the factors influencing BBB permeability could contribute to supporting promising potential therapeutic targets for protecting the BBB and the delivery of central nervous system drugs via BBB permeability interventions under pathological conditions.

Emerging Roles of Microfluidics in Brain Research: From Cerebral Fluids Manipulation to Brain-on-a-Chip and Neuroelectronic Devices Engineering

Remarkable progress made in the past few decades in brain research enables the manipulation of neuronal activity in single neurons and neural circuits and thus allows the decipherment of relations between nervous systems and behavior. The discovery of glymphatic and lymphatic systems in the brain and the recently unveiled tight relations between the gastrointestinal (GI) tract and the central nervous system (CNS) further revolutionize our understanding of brain structures and functions. Fundamental questions about how neurons conduct two-way communications with the gut to establish the gut-brain axis (GBA) and interact with essential brain components such as glial cells and blood vessels to regulate cerebral blood flow (CBF) and cerebrospinal fluid (CSF) in health and disease, however, remain. Microfluidics with unparalleled advantages in the control of fluids at microscale has emerged recently as an effective approach to address these critical questions in brain research. The dynamics of cerebral fluids (i.e., blood and CSF) and novel in vitro brain-on-a-chip models and microfluidic-integrated multifunctional neuroelectronic devices, for example, have been investigated. This review starts with a critical discussion of the current understanding of several key topics in brain research such as neurovascular coupling (NVC), glymphatic pathway, and GBA and then interrogates a wide range of microfluidic-based approaches that have been developed or can be improved to advance our fundamental understanding of brain functions. Last, emerging technologies for structuring microfluidic devices and their implications and future directions in brain research are discussed.

Temporal Profile of Blood-Brain Barrier Breakdown in Reversible Cerebral Vasoconstriction Syndrome

Background and Purpose- Reversible cerebral vasoconstriction syndrome (RCVS) has a unique temporal course of vasoconstriction. Blood-brain barrier (BBB) breakdown is part of the pathophysiology of RCVS, but its temporal course is unknown. We aimed to investigate the temporal profile of BBB breakdown and relevant clinical profiles in a large sample size. Methods- In this prospective observatory bicenter study, patients who underwent contrast-enhanced fluid-attenuated inversion recovery magnetic resonance imaging within 2 months from onset were included. The presence and extent of BBB breakdown were evaluated using contrast-enhanced fluid-attenuated inversion recovery magnetic resonance imaging. Contrast-enhanced fluid-attenuated inversion recovery magnetic resonance imaging data were analyzed using a semiautomated segmentation technique to quantitatively measure the area of Gadolinium leakage into cerebrospinal fluid space. The univariable and multivariable linear regressions were performed to investigate the independent effect of time from onset with adjustment for other covariates. Results- In the 186 patients with angiogram-proven RCVS included in this analysis, BBB breakdown was observed in 52.6%, 56.8%, 30.3%, 40.0%, and 23.8% in the first, second, third, fourth, and ≥fifth week after onset. The extent of BBB breakdown peaked at first and second week, whereas the peak of vasoconstriction was observed at the third week after onset. Multivariable analysis showed the second week from onset (β, 3.35 [95% CI, 0.07-6.64]; P=0.046) and blood pressure surge (β, 3.84 [95% CI, 1.75-5.92]; P<0.001) were independently associated with a greater extent of BBB breakdown. A synergistic effect of time from onset and blood pressure surge was found (P for interaction=0.006). Conclusions- Frequency and extent of BBB breakdown are more prominent during the early stage in patients with RCVS, with an earlier peak than that of vasoconstriction. The temporal course of BBB breakdown may provide a pathophysiologic background of the temporal course of neurological complications of RCVS.

Sphenopalatine ganglion stimulation is a reversible and frequency-dependent modulator of the blood-brain barrier

BACKGROUND

The sphenopalatine ganglion (SPG) is a vasoactive mediator of the anterior intracranial circulation in mammals. SPG stimulation has been demonstrated to alter blood-brain barrier (BBB) permeability, although this phenomenon is not well characterized.

OBJECTIVE

To determine the effect of SPG stimulation on the BBB using rat models.

METHODS

Extravasation of fluorescent tracer 70 kDa FITC-dextran into rat brain specimens was measured across a range of stimulation parameters to assess BBB permeability. Tight junction (TJ) morphology was compared by assessing differences in the staining of proteins occludin and ZO-1 and analyzing ultrastructural changes on transmission electron microscopy (TEM) between stimulated and unstimulated specimens.

RESULTS

SPG stimulation at 10 Hz maximally increased BBB permeability, exhibiting a 6-fold increase in fluorescent traceruptake (1.66% vs 0.28%, p < 0.0001). This effect was reversed 4-hours after stimulation (0.36% uptake, p = 0.99). High-frequency stimulation at 20 Hz and 200 Hz did not increase tracer extravasation, (0.26% and 0.28% uptake, p = >0.999 and p = 0.998, respectively). Stimulation was associated a significant decrease in the colocalization of occludin and ZO-1 with endothelial markers in stimulated brains compared to control (74.6% vs. 39.7% and 67.2% vs. 60.4% colocalization, respectively, p < 0.0001), and ultrastructural changes in TJ morphology associated with increased BBB permeability were observed on TEM.

CONCLUSION

This study is the first to show a reversible, frequency-dependent increase in BBB permeability with SPG stimulation and introduces a putative mechanism of action through TJ disruption. Bypassing the BBB with SPG stimulation could enable new paradigms in delivering therapeutics to the CNS. Further study of this technology is needed.

Nitric oxide donor molsidomine promotes retrieval of object recognition memory in a model of cognitive deficit induced by 192 IgG-saporin

Nitric oxide (NO) plays a leading role in learning and memory processes. Previously, we showed its ability to modify the deleterious effect of immunotoxin 192 IgG-saporin (192-IgG-SAP) in the cholinergic system. The aim of this study was to analyze the potential of a NO donor (molsidomine, MOLS) to prevent the recognition memory deficits resulting from the septal cholinergic denervation by 192 IgG-SAP in rats. Quantification of neuronal and endothelial nitric oxide synthase (nNOS and eNOS, respectively) expression was evaluated in striatum, prefrontal cortex, and hippocampus. In addition, a choline acetyltransferase immunohistochemical analysis was performed in medial septum and assessed the effect of MOLS treatment on the spatial working memory of rats through a recognition memory test. Results showed that 192-IgG-SAP reduced the immunoreactivity of cholinergic septal neurons (41%), compared with PBS-receiving control rats (p < 0.05). Treatment with MOLS alone failed to antagonize the septal neuron population loss but prevented the progressive abnormal morphological changes of neurons. Those animals exposed to 192-IgG-SAP immunotoxin exhibited a reduction of cortical nNOS expression against the control group, whereas expression was enhanced in the 192-IgG-SAP + MOLS group. The most relevant finding was the recovering of the discrimination index exhibited by the 192-IgG-SAP + MOLS group. When compared with the rats exposed to the 192-IgG-SAP immunotoxin, they reached values similar to those observed in the PBS group. Our results show that although MOLS failed to block the cholinergic neurons loss induced by 192-IgG-SAP, it avoided the neuronal damage progression.

Impact of Metabolic Syndrome on Neuroinflammation and the Blood-Brain Barrier

Metabolic syndrome, which includes diabetes and obesity, is one of the most widespread medical conditions. It induces systemic inflammation, causing far reaching effects on the body that are still being uncovered. Neuropathologies triggered by metabolic syndrome often result from increased permeability of the blood-brain-barrier (BBB). The BBB, a system designed to restrict entry of toxins, immune cells, and pathogens to the brain, is vital for proper neuronal function. Local and systemic inflammation induced by obesity or type 2 diabetes mellitus can cause BBB breakdown, decreased removal of waste, and increased infiltration of immune cells. This leads to disruption of glial and neuronal cells, causing hormonal dysregulation, increased immune sensitivity, or cognitive impairment depending on the affected brain region. Inflammatory effects of metabolic syndrome have been linked to neurodegenerative diseases. In this review, we discuss the effects of obesity and diabetes-induced inflammation on the BBB, the roles played by leptin and insulin resistance, as well as BBB changes occurring at the molecular level. We explore signaling pathways including VEGF, HIFs, PKC, Rho/ROCK, eNOS, and miRNAs. Finally, we discuss the broader implications of neural inflammation, including its connection to Alzheimer's disease, multiple sclerosis, and the gut microbiome.

Pharmacological manipulation of cGMP and NO/cGMP in CNS drug discovery

The development of small molecule modulators of NO/cGMP signaling for use in the CNS has lagged far behind the use of such clinical agents in the periphery, despite the central role played by NO/cGMP in learning and memory, and the substantial evidence that this signaling pathway is perturbed in neurodegenerative disorders, including Alzheimer's disease. The NO-chimeras, NMZ and Nitrosynapsin, have yielded beneficial and disease-modifying responses in multiple preclinical animal models, acting on GABA_A and NMDA receptors, respectively, providing additional mechanisms of action relevant to synaptic and neuronal dysfunction. Several inhibitors of cGMP-specific phosphodiesterases (PDE) have replicated some of the actions of these NO-chimeras in the CNS. There is no evidence that nitrate tolerance is a phenomenon relevant to the CNS actions of NO-chimeras, and studies on nitroglycerin in the periphery continue to challenge the dogma of nitrate tolerance mechanisms. Hybrid nitrates have shown much promise in the periphery and CNS, but to date only one treatment has received FDA approval, for glaucoma. The potential for allosteric modulation of soluble guanylate cyclase (sGC) in brain disorders has not yet been fully explored nor exploited; whereas multiple applications of PDE inhibitors have been explored and many have stalled in clinical trials.

Mechanisms of Blood Brain Barrier Disruption by Different Types of Bacteria, and Bacterial-Host Interactions Facilitate the Bacterial Pathogen Invading the Brain

This review aims to elucidate the different mechanisms of blood brain barrier (BBB) disruption that may occur due to invasion by different types of bacteria, as well as to show the bacteria-host interactions that assist the bacterial pathogen in invading the brain. For example, platelet-activating factor receptor (PAFR) is responsible for brain invasion during the adhesion of pneumococci to brain endothelial cells, which might lead to brain invasion. Additionally, the major adhesin of the pneumococcal pilus-1, RrgA is able to bind the BBB endothelial receptors: polymeric immunoglobulin receptor (pIgR) and platelet endothelial cell adhesion molecule (PECAM-1), thus leading to invasion of the brain. Moreover, Streptococcus pneumoniae choline binding protein A (CbpA) targets the common carboxy-terminal domain of the laminin receptor (LR) establishing initial contact with brain endothelium that might result in BBB invasion. Furthermore, BBB disruption may occur by S. pneumoniae penetration through increasing in pro-inflammatory markers and endothelial permeability. In contrast, adhesion, invasion, and translocation through or between endothelial cells can be done by S. pneumoniae without any disruption to the vascular endothelium, upon BBB penetration. Internalins (InlA and InlB) of Listeria monocytogenes interact with its cellular receptors E-cadherin and mesenchymal-epithelial transition (MET) to facilitate invading the brain. L. monocytogenes species activate NF-κB in endothelial cells, encouraging the expression of P- and E-selectin, intercellular adhesion molecule 1 (ICAM-1), and Vascular cell adhesion protein 1 (VCAM-1), as well as IL-6 and IL-8 and monocyte chemoattractant protein-1 (MCP-1), all these markers assist in BBB disruption. Bacillus anthracis species interrupt both adherens junctions (AJs) and tight junctions (TJs), leading to BBB disruption. Brain microvascular endothelial cells (BMECs) permeability and BBB disruption are induced via interendothelial junction proteins reduction as well as up-regulation of IL-1α, IL-1β, IL-6, TNF-α, MCP-1, macrophage inflammatory proteins-1 alpha (MIP1α) markers in Staphylococcus aureus species. Streptococcus agalactiae or Group B Streptococcus toxins (GBS) enhance IL-8 and ICAM-1 as well as nitric oxide (NO) production from endothelial cells via the expression of inducible nitric oxide synthase (iNOS) enhancement, resulting in BBB disruption. While Gram-negative bacteria, Haemophilus influenza OmpP2 is able to target the common carboxy-terminal domain of LR to start initial interaction with brain endothelium, then invade the brain. H. influenza type b (HiB), can induce BBB permeability through TJ disruption. LR and PAFR binding sites have been recognized as common routes of CNS entrance by Neisseria meningitidis. N. meningitidis species also initiate binding to BMECs and induces AJs deformation, as well as inducing specific cleavage of the TJ component occludin through the release of host MMP-8. Escherichia coli bind to BMECs through LR, resulting in IL-6 and IL-8 release and iNOS production, as well as resulting in disassembly of TJs between endothelial cells, facilitating BBB disruption. Therefore, obtaining knowledge of BBB disruption by different types of bacterial species will provide a picture of how the bacteria enter the central nervous system (CNS) which might support the discovery of therapeutic strategies for each bacteria to control and manage infection.

Effect of serotonin depletion on cortical spreading depression evoked cerebrovascular changes

Abstract Background: The cortical spreading depression (CSD) is a phenomenon associated with several pathological conditions including migraine. It can induce alterations in both neural and vascular compartments. Serotonin (5-HT) depletion is known as a condition involved in migraine pathophysiology. The hyper-excitability of the cortical neurons to the CSD activation in the low 5-HT state has been previously reported. However, the cerebrovascular responses to CSD activation in this condition have never been studied yet. Objectives: Determine the effect of 5-HT depletion on the cerebrovascular responses to CSD activation. Methods: Wistar rats (weighing 250-300 grams) were divided into three groups: control, CSD, and low 5-HT with CSD group (five rats per group). To induce the low 5-HT state, the para-chlorophenylalanine was injected intraperitoneally into the rats three days before the experiment. CSD was induced by the application of solid KCl (3 mg) on the parietal cortex. NaCl instead of KCl was applied to the control group. Cerebral cortical blood flow was monitored using Laser Doppler flowmetry. The ultrastructure of cerebral microvessels was examined using electron microscopy to determine the cerebral microcirculatory responses to CSD. Results: Depletion of serotonin induced a significant increase in the peak amplitude of CSD-evoked cerebral hyperaemia. This condition also enhanced the development of CSD-induced endothelial pinocytosis and microvillus formation in cerebrocortical microvessels. Conclusion: 5-HT was an important neurotransmitter involved in the control of cerebrovascular responses to CSD activation. The hypersensitivity of the cerebrovascular responses observed in the 5-HT depleted state may explain the relationship between headache and 5-HT depletion.

OGR1/GPR68 Modulates the Severity of Experimental Autoimmune Encephalomyelitis and Regulates Nitric Oxide Production by Macrophages

Ovarian cancer G protein-coupled receptor 1 (OGR1) is a proton-sensing molecule that can detect decreases in extracellular pH that occur during inflammation. Although OGR1 has been shown to have pro-inflammatory functions in various diseases, its role in autoimmunity has not been examined. We therefore sought to determine whether OGR1 has a role in the development of T cell autoimmunity by contrasting the development of experimental autoimmune encephalomyelitis between wild type and OGR1-knockout mice. OGR1-knockout mice showed a drastically attenuated clinical course of disease that was associated with a profound reduction in the expansion of myelin oligodendrocyte glycoprotein 35-55-reactive T helper 1 (Th1) and Th17 cells in the periphery and a reduced accumulation of Th1 and Th17 effectors in the central nervous system. We determined that these impaired T cell responses in OGR1-knockout mice associated with a reduced frequency and number of dendritic cells in draining lymph nodes during EAE and a higher production of nitric oxide by macrophages. Our studies suggest that OGR1 plays a key role in regulating T cell responses during autoimmunity.

Pharmacological modulation of dietary lipid-induced cerebral capillary dysfunction: Considerations for reducing risk for Alzheimer's disease

An increasing body of evidence suggests that cerebrovascular dysfunction and microvessel disease precede the evolution of hallmark pathological features that characterise Alzheimer's disease (AD), consistent with a causal association for onset or progression. Recent studies, principally in genetically unmanipulated animal models, suggest that chronic ingestion of diets enriched in saturated fats and cholesterol may compromise blood-brain barrier (BBB) integrity resulting in inappropriate blood-to-brain extravasation of plasma proteins, including lipid macromolecules that may be enriched in amyloid-β (Aβ). Brain parenchymal retention of blood proteins and lipoprotein bound Aβ is associated with heightened neurovascular inflammation, altered redox homeostasis and nitric oxide (NO) metabolism. Therefore, it is a reasonable proposition that lipid-lowering agents may positively modulate BBB integrity and by extension attenuate risk or progression of AD. In addition to their robust lipid lowering properties, reported beneficial effects of lipid-lowering agents were attributed to their pleiotropic properties via modulation of inflammation, oxidative stress, NO and Aβ metabolism. The review is a contemporary consideration of a complex body of literature intended to synthesise focussed consideration of mechanisms central to regulation of BBB function and integrity. Emphasis is given to dietary fat driven significant epidemiological evidence consistent with heightened risk amongst populations consuming greater amounts of saturated fats and cholesterol. In addition, potential neurovascular benefits associated with the use of hypolipidemic statins, probucol and fenofibrate are also presented in the context of lipid-lowering and pleiotropic properties.

Effects of nitric oxide on blood-brain barrier permeability in common carp (Cyprinus carpio L.)

OBJECTIVE

To determine in vivo effects of nitric oxide (NO) on blood-brain barrier (BBB) permeability in common carp (Cyprinus carpio L.).

ANIMALS

148 carp. PROCEDURES Carp received glyceryl trinitrate (1 mg/kg) as an NO donor or received no treatment (control group). Nitrite and nitrate concentrations in carp sera were determined 0.25, 1, 3, 6, 8, 12, and 24 hours after treatment. In control and treatment groups, BBB permeability was analyzed by assessment of leakage of Evans blue dye into various brain areas at 6, 12, and 24 hours after glyceryl trinitrate treatment. Brain edema was determined by means of the wet-dry weight method and assessed with light microscopy on H&E-stained preparations of tissues obtained 6 and 24 hours after glyceryl trinitrate treatment.

RESULTS

Treatment with glyceryl trinitrate induced endogenous synthesis of NO, which was upregulated 6 and 8 hours after treatment. Increased NO synthesis was associated with increased permeability of the BBB, which developed 6 hours after treatment with the NO donor. Although the BBB became impermeable again by 12 hours after glycerol trinitrate treatment, brain edema still persisted 24 hours after treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

In this study, treatment with an NO donor caused reversible opening of the BBB and brain edema in common carp. An intact BBB is important to prevent influx of potentially harmful substances into the brain. This investigation highlighted the possibility of BBB disarrangement caused by NO, a substance found in the CNS of all vertebrates evaluated.

TNF-like weak inducer of apoptosis promotes blood brain barrier disruption and increases neuronal cell death in MRL/lpr mice

Neuropsychiatric disease is one of the most common manifestations of human systemic lupus erythematosus, but the mechanisms remain poorly understood. In human brain microvascular endothelial cells in vitro, TNF-like weak inducer of apoptosis (TWEAK) decreases tight junction ZO-1 expression and increases the permeability of monolayer cell cultures. Furthermore, knockout (KO) of the TWEAK receptor, Fn14, in the MRL/lpr lupus mouse strain markedly attenuates neuropsychiatric disease, as demonstrated by significant reductions in depressive-like behavior and improved cognitive function. The purpose of the present study was to determine the mechanisms by which TWEAK signaling is instrumental in the pathogenesis of neuropsychiatric lupus (NPSLE). Evaluating brain sections of MRL/lpr Fn14WT and Fn14KO mice, we found that Fn14KO mice displayed significantly decreased cellular infiltrates in the choroid plexus. To evaluate the integrity of the blood brain barrier (BBB) in MRL/lpr mice, Western blot for fibronectin, qPCR for iNOS, and immunohistochemical staining for VCAM-1/ICAM-1 were performed. We found preserved BBB permeability in MRL/lpr Fn14KO mice, attributable to reduced brain expression of VCAM-1/ICAM-1 and iNOS. Additionally, administration of Fc-TWEAK intravenously directly increased the leakage of a tracer (dextran-FITC) into brain tissue. Furthermore, MRL/lpr Fn14KO mice displayed reduced antibody (IgG) and complement (C3, C6, and C4a) deposition in the brain. Finally, we found that MRL/lpr Fn14KO mice manifested reduced neuron degeneration and hippocampal gliosis. Our studies indicate that TWEAK/Fn14 interactions play an important role in the pathogenesis of NPSLE by increasing the accumulation of inflammatory cells in the choroid plexus, disrupting BBB integrity, and increasing neuronal damage, suggesting a novel target for therapy in this disease.

Serotonin depletion can enhance the cerebrovascular responses induced by cortical spreading depression via the nitric oxide pathway

Serotonin (5-HT) is an important neurotransmitter involved in the control of neural and vascular responses. 5-HT depletion can induce several neurological disorders, including migraines. Studies on a cortical spreading depression (CSD) migraine animal model showed that the cortical neurons sensitivity, vascular responses, and nitric oxide (NO) production were significantly increased in 5-HT depletion. However, the involvement of NO in the cerebrovascular responses in 5-HT depletion remains unclear. This study aimed to investigate the role of NO in the CSD-induced alterations of cerebral microvessels in 5-HT depletion. Rats were divided into four groups: control, control with L-NAME treatment, 5-HT depleted, and 5-HT depleted with L-NAME treatment. 5-HT depletion was induced by intraperitoneal injection with para-chlorophenylalanine (PCPA) 3 days before the experiment. The CSD was triggered by KCl application. After the second wave of CSD, N-nitro-l-arginine methyl ester (L-NAME) or saline was intravenously injected into the rats with or without L-NAME treatment groups, respectively. The intercellular adhesion molecules-1 (ICAM-1), cell adhesion molecules-1 (VCAM-1), and the ultrastructural changes of the cerebral microvessels were examined. The results showed that 5-HT depletion significantly increased ICAM-1 and VCAM-1 expressions in the cerebral cortex. The number of endothelial pinocytic vesicles and microvilli was higher in the 5-HT depleted group when compared to the control. Interestingly, L-NAME treatment significantly reduced the abnormalities observed in the 5-HT depleted group. The results of this study demonstrated that an increase of NO production is one of the mechanisms involved in the CSD-induced alterations of the cerebrovascular responses in 5-HT depletion.

C-type natriuretic peptide modulates permeability of the blood-brain barrier

C-type natriuretic peptide (CNP) is abundant in brain and is reported to exert autocrine function in vascular cells, but its effect on blood-brain barrier (BBB) permeability has not been clarified yet. Here, we examined this effect. Transendothelial electrical resistance (TEER) of in vitro BBB model, composed of bovine brain microvascular endothelial cells and astrocytes, was significantly dose dependently decreased by CNP (1, 10, and 100 nmol/L). C-type natriuretic peptide treatment reduced both the messenger RNA (mRNA) and protein expressions of tight junction (TJ) protein zonula occludens-1 (ZO-1). The effects on TEER, mRNA, and protein expressions of ZO-1 were mimicked by cyclic GMP (cGMP) analog 8-bromo-cGMP (1 μmol/L) and reversed by protein kinase G (PKG) inhibitor Rp-8-CPT-cGMPS (100 μmol/L), thus implying the role of PKG and cGMP signaling in BBB function. Transcription factor JunD knockdown by small interfering RNA resulted in no change of permeability by CNP. In vivo study of mouse brain by fluorimetric analysis with intravenous administration of sodium fluorescein (40 mg/kg) also showed a significant increase in BBB permeability by CNP (10 nmol/kg, intravenously). These findings suggest that CNP modulates the BBB permeability by altering ZO-1 expression.

Inhibition of matrix metalloproteinases-2 and -9 prevents cognitive impairment induced by pneumococcal meningitis in Wistar rats

Pneumococcal meningitis is a relevant clinical disease characterized by an intense inflammatory reaction into the subarachnoid and ventricular spaces, leading to blood–brain barrier breakdown, hearing loss, and cognitive impairment. Matrix metalloproteinases (MMPs) are capable of degrading components of the basal laminin, thus contributing to BBB damage and neuronal injury. In the present study, we evaluated the effects of MMP-2, MMP-9, and MMP-2/9 inhibitors on BBB integrity, learning, and memory in Wistar rats subjected to pneumococcal meningitis. The animals underwent a magna cistern tap and received either 10 µL sterile saline as a placebo or an equivalent volume of a Streptococcus pneumoniae suspension at a concentration of 5 × 109 cfu/mL. The rats were randomized into different groups that received adjuvant treatment with MMP-2, MMP-9 or MMP-2/9 inhibitors. The BBB integrity was evaluated, and the animals were habituated to open-field and object recognition tasks 10 days after meningitis induction. Adjuvant treatments with inhibitors of MMP-2 or MMP-2/9 prevented BBB breakdown in the hippocampus, and treatments with inhibitors of MMP-2, MMP-9 or MMP-2/9 prevented BBB breakdown in the cortex. Ten days after meningitis induction, the animals that received adjuvant treatment with the inhibitor of MMP-2/9 demonstrated that animals habituated to the open-field task faster and enhanced memory during short-term and long-term retention test sessions in the object recognition task. Further investigation is necessary to provide support for MMP inhibitors as an alternative treatment for bacterial meningitis; however, these findings suggest that the meningitis model could be a good research tool for studying the biological mechanisms involved in the behavioral alterations associated with pneumococcal meningitis.

Molsidomine, a nitric oxide donor, modulates rotational behavior and monoamine metabolism in 6-OHDA lesioned rats treated chronically with L-DOPA

Some biochemical and histological studies of Parkinson's disease patients' brains and 6-OHDA-lesioned rats suggest that dopaminergic dennervation of the striatum leads to the nitrergic system hypofunction in this structure. Hence, recently the modulation of nitric oxide (NO)- soluble guanylyl cyclase-cyclic GMP signaling is considered to be a new target for the treatment of Parkinson's disease. The aim of our study was to examine the impact of chronic combined treatment with low doses of the NO donor molsidomine (2 and 4mg/kg) and L-DOPA (12.5 and 25mg/kg) on rotational behavior and monoamine metabolism in the striatum (STR) and substantia nigra (SN) of unilaterally 6-OHDA-lesioned rats. Chronic administration of molsidomine at a dose of 2mg/kg jointly with 25mg/kg of L-DOPA significantly decreased the number of contralateral rotations when compared to L-DOPA alone. Other combinations of the examined drug doses were less effective. The tissue DA levels in the ipsilateral STR and SN after the last chronic doses of molsidomine (2mg/kg) and L-DOPA (12.5 or 25mg/kg), were significantly higher than after L-DOPA alone. Chronic L-DOPA treatment alone or jointly with a lower dose of molsidomine decreased 5-HT levels and accelerated its catabolism in the examined structures. However, combination of a higher dose of molsidomine with L-DOPA (25mg/kg) did not reduce 5-HT content while its catabolism was less intensive. The obtained results show that low doses of molsidomine can modulate rotational behavior and tissue DA and 5-HT concentrations in the STR and SN of 6-OHDA-lesioned rats treated chronically with L-DOPA.

Role of oxidative stress in the pathophysiology of pneumococcal meningitis

Pneumococcal meningitis is a life-threatening disease characterized by an acute purulent infection affecting the pia mater, the arachnoid, and the subarachnoid spaces. Streptococcus pneumoniae crosses the blood-brain barrier (BBB) by both transcellular traversal and disruption of the intraepithelial tight junctions to allow intercellular traversal. During multiplication, pneumococci release their bacterial products, which are highly immunogenic and may lead to an increased inflammatory response in the host. Thus, these compounds are recognized by antigen-presenting cells through the binding of toll-like receptors. These receptors induce the activation of myeloid differentiation factor 88 (MyD88), which interacts with various protein kinases, including IL-1 receptor-associated kinase-4 (IRAK4), which is phosphorylated and dissociated from MyD88. These products also interact with tumor necrosis factor receptor-associated factor 6 dependent signaling pathway (TRAF6). This cascade provides a link to NF-κB-inducing kinase, resulting in the nuclear translocation of NF-κB leading to the production of cytokines, chemokines, and other proinflammatory molecules in response to bacterial stimuli. Consequently, polymorphonuclear cells are attracted from the bloodstream and then activated, releasing large amounts of NO^•, O₂^•, and H₂O₂. This formation generates oxidative and nitrosative stress, subsequently, lipid peroxidation, mitochondrial damage, and BBB breakdown, which contributes to cell injury during pneumococcal meningitis.

Hemoglobin-induced nitric oxide synthase overexpression and nitric oxide production contribute to blood-brain barrier disruption in the rat

Hemoglobin (Hb) released from extravasated erythrocytes may have a critical role in the process of blood-brain barrier (BBB) disruption and subsequent edema formation after intracerebral hemorrhage (ICH). Excessive nitric oxide (NO) production synthesized by nitric oxide synthase (NOS) has been well documented to contribute to BBB disruption. However, considerably less attention has been focused on the role of NO in Hb-induced BBB disruption. This study was designed to examine the hypothesis that Hb-induced NOS overexpression and excessive NO production may contribute to the changes of tight junction (TJ) proteins and subsequent BBB dysfunction. Hemoglobin was infused with stereotactic guidance into the right caudate nucleus of male Sprague Dawley rats. Then, we investigated the effect of Hb on the BBB permeability, changes of TJ proteins (claudin-5, occludin, zonula occludens-1 (ZO-1), and junctional adhesion molecule-1 (JAM-1)), iron deposition, expression of inducible NOS (iNOS) and endothelial NOS (eNOS), as well as NO production. Hb injection caused a significant increase in BBB permeability. Significant reduction of claudin-5, ZO-1, and JAM-1 was observed after Hb injection as evidenced by PCR and immunofluorescence. After a decrease at early stage, occludin showed a fivefold increase in mRNA level at 7 days. Significant iron deposition was detectable from 48 h to 7 days in a time-dependent manner. The iNOS and eNOS levels dramatically increased after Hb injection concomitantly with large quantities of NO released. Furthermore, enhanced iNOS or eNOS immunoreactivity was co-localized with diffused or diminished claudin-5 staining. We concluded that overexpressed NOS and excessive NO production induced by Hb may contribute to BBB disruption, which may provide an important potential therapeutic target in the treatment of ICH.

Inhaled nitric oxide reduces secondary brain damage after traumatic brain injury in mice

Ischemia, especially pericontusional ischemia, is one of the leading causes of secondary brain damage after traumatic brain injury (TBI). So far efforts to improve cerebral blood flow (CBF) after TBI were not successful because of various reasons. We previously showed that nitric oxide (NO) applied by inhalation after experimental ischemic stroke is transported to the brain and induces vasodilatation in hypoxic brain regions, thus improving regional ischemia, thereby improving brain damage and neurological outcome. As regional ischemia in the traumatic penumbra is a key mechanism determining secondary posttraumatic brain damage, the aim of the current study was to evaluate the effect of NO inhalation after experimental TBI. NO inhalation significantly improved CBF and reduced intracranial pressure after TBI in male C57 Bl/6 mice. Long-term application (24 hours NO inhalation) resulted in reduced lesion volume, reduced brain edema formation and less blood-brain barrier disruption, as well as improved neurological function. No adverse effects, e.g., on cerebral auto-regulation, systemic blood pressure, or oxidative damage were observed. NO inhalation might therefore be a safe and effective treatment option for TBI patients.

Nitric oxide (NO) and asymmetric dimethylarginine (ADMA): their pathophysiological role and involvement in intracerebral hemorrhage

OBJECTIVE

Nitric oxide (NO) has a variety of functions in physiological systems, particularly in the vasculature and the central nervous system. Currently, the imbalance of the pathway involving nitric oxide, nitric oxide synthase, and asymmetric dimethylarginine (NO-NOS-ADMA) is increasingly discussed in connection with endothelial dysfunction. Knowledge about the role of this pathway in intracerebral hemorrhage (ICH), which represents the most devastating stroke subtype, is increasing but still sparse. This article aims to review the current knowledge about the role and metabolism of NO and ADMA. It will also address the role of the NO-NOS-ADMA pathway in ICH and delineate some questions that should be addressed by future studies.

METHODS

A literature search regarding the data about NO, NOS, and ADMA and its role in ICH was conducted in PubMed.

RESULTS

Experimental data from cell culture and animal models indicate that, after the occurrence of ICH, neuronal and inducible nitric oxide synthases (nNOS and iNOS) are both overexpressed and uncoupled through the induction of blood compound metabolites, including thrombin and inflammatory mediators. ADMA, the most potent endogenous inhibitor of NOS, is also overproduced following dysregulation of its metabolizing enzymes. Dysfunction of the NO-NOS-ADMA pathway results in cell death, blood-brain barrier (BBB) disruption, and brain edema via different pathological mechanisms. However, the available data from clinical studies are still rare and partially contradictory.

CONCLUSION

Experimental data suggest an important role for the NO-NOS-ADMA pathway for secondary injury after ICH. Since the literature shows contradictory results, further studies are needed to address current confusion.

Perfusion-CT assessment of blood-brain barrier permeability in patients with aneurysmal subarachnoid hemorrhage

BACKGROUND

The goal of this study was to determine which clinical and radiographic variables in patients with subarachnoid hemorrhage (SAH) are associated with in vivo blood-brain barrier permeability (BBBP) assessments obtained using perfusion-CT (PCT) technology.

METHODS

SAH patients with confirmed aneurysm etiology and with PCT and angiogram within 24 hours of each other were included, and relationships between clinical and imaging variables were analyzed using random-effects generalized linear models.

RESULTS

One thousand one hundred and sixty two vascular territories from 83 patients were evaluated in this study. The mean BBBP increased by severity of vasospasm on DSA, however, in multivariate analysis, only mean transit time (MTT), cerebral blood volume (CBV), and severity of hydrocephalus were significantly associated with BBBP. Increased BBBP was not associated with angiographic vasospasm severity in multivariate analysis.

CONCLUSION

Perfusion-CT assessment of BBBP may serve as a unique and useful biomarker in conjunction with angiography, additional perfusion-CT parameters, and clinical assessments, especially in characterizing microvascular dysfunction, or even in targeting treatments. However, future prospective studies will be required to definitively establish its clinical utility in the care of SAH patients.

Review: molecular pathogenesis of blood-brain barrier breakdown in acute brain injury

Historically, the blood-brain barrier (BBB) was considered to be at the level of cerebral endothelium. Currently, the interaction of endothelium with other components of the vessel wall and with neurones and glial cells is considered to constitute a functional unit, termed the neurovascular unit that maintains cerebral homeostasis in steady states and brain injury. The emphasis of this review is on cerebral endothelium, the best-studied component of the neurovascular unit, and its permeability mechanisms in health and acute brain injury. Major advances have been made in unravelling the molecular structure of caveolae and tight junctions, both of which are components of the structural barrier to the entry of plasma proteins into brain. Time course studies suggest that caveolar changes precede junctional changes in acute brain injury. Additional factors modulating BBB permeability in acute brain injury are matrix metalloproteinases-2 and 9 and angiogenic factors, the most notable being vascular endothelial growth factor-A and angiopoietins (Ang) 1 and 2. Vascular endothelial growth factor-A and Ang2 have emerged as potent inducers of BBB breakdown while Ang1 is a potent anti-leakage factor. These factors have the potential to modulate permeability in acute brain injury and this is an area of ongoing research. Overall, a combination of haemodynamic, structural and molecular alterations affecting brain endothelium results in BBB breakdown in acute brain injury.

Morphology and properties of brain endothelial cells

The molecular advances in various aspects of brain endothelial cell function in steady states are considerable and difficult to summarize in one chapter. Therefore, this chapter focuses on endothelial permeability mechanisms in steady states and disease namely vasogenic edema. The morphology and properties of caveolae and tight junctions that are involved in endothelial permeability to macromolecules are reviewed. Endothelial transport functions are briefly reviewed. Diseases with alterations of endothelial permeability are mentioned and details are provided of the molecular alterations in caveolae and tight junctions in vasogenic edema. Other factors involved in increased endothelial permeability such as the matrix metalloproteinases are briefly discussed. Of the modulators of endothelial permeability, angioneurins such as the vascular endothelial growth factors and angiopoietins are discussed. The chapter concludes with a brief discussion on delivery of therapeutic substances across endothelium.

Neuroprotective effect of inhaled nitric oxide on excitotoxic-induced brain damage in neonatal rat

Background

Inhaled nitric oxide (iNO) is one of the most promising therapies used in neonates. However, little information is known about its impact on the developing brain submitted to excitotoxic challenge.

Methodology/Principal Findings

We investigated here the effect of iNO in a neonatal model of excitotoxic brain lesions. Rat pups and their dams were placed in a chamber containing 20 ppm NO during the first week of life. At postnatal day (P)5, rat pups were submitted to intracranial injection of glutamate agonists. At P10, rat pups exposed to iNO exhibited a significant decrease of lesion size in both the white matter and cortical plate compared to controls. Microglia activation and astrogliosis were found significantly decreased in NO-exposed animals. This neuroprotective effect was associated with a significant decrease of several glutamate receptor subunits expression at P5. iNO was associated with an early (P1) downregulation of pCREB/pAkt expression and induced an increase in pAkt protein concentration in response to excitotoxic challenge (P7).

Conclusion

This study is the first describe and investigate the neuroprotective effect of iNO in neonatal excitotoxic-induced brain damage. This effect may be mediated through CREB pathway and subsequent modulation of glutamate receptor subunits expression.

Looking at the blood-brain barrier: molecular anatomy and possible investigation approaches

The blood-brain barrier (BBB) is a dynamic and complex interface between blood and the central nervous system that strictly controls the exchanges between the blood and brain compartments, therefore playing a key role in brain homeostasis and providing protection against many toxic compounds and pathogens. In this review, the unique properties of brain microvascular endothelial cells and intercellular junctions are examined. The specific interactions between endothelial cells and basement membrane as well as neighboring perivascular pericytes, glial cells and neurons, which altogether constitute the neurovascular unit and play an essential role in both health and function of the central nervous system, are also explored. Some relevant pathways across the endothelium, as well as mechanisms involved in the regulation of BBB permeability, and the emerging role of the BBB as a signaling interface are addressed as well. Furthermore, we summarize some of the experimental approaches that can be used to monitor BBB properties and function in a variety of conditions and have allowed recent advances in BBB knowledge. Elucidation of the molecular anatomy and dynamics of the BBB is an essential step for the development of new strategies directed to maintain or restore BBB integrity and barrier function and ultimately preserve the delicate interstitial brain environment.

Decreased brain edema after collagenase-induced intracerebral hemorrhage in mice lacking the inducible nitric oxide synthase gene. Laboratory investigation

OBJECT

Hematoma size and brain edema after intracerebral hemorrhage (ICH) are important prognostic factors. Inducible nitric oxide synthase (iNOS) is induced after cerebral ischemia and is known to be involved in secondary neuronal injury, but its significance in ICH is unknown. The authors tested whether iNOS would influence hematoma size and brain edema after ICH.

METHODS

The authors used C57BL/6 and iNOS knockout mice for all the experiments. Experimental ICH was induced by the intrastriatal stereotactic administration of bacterial collagenase. Brain tissue was obtained at 72 hours after ICH. The volume of hematoma was quantified by spectrophotometric assay, and the brain water content was measured. The investigators also measured blood-brain barrier permeability using Evans blue dye.

RESULTS

There was no significant difference in hematoma size between the 2 groups. The brain water content of the lesional hemisphere was higher in C57BL/6 mice than in iNOS knockout mice. More Evans blue leakage in the brain was observed in C57BL/6 control mice than in iNOS knockout mice. Immunohistochemistry showed iNOS immunoreactivity in the perihematoma areas of C57BL/6 mice but not in the iNOS knockout mice.

CONCLUSIONS

When hematoma size was similar, iNOS knockout mice had significantly less brain edema than their littermates. These results suggest that iNOS modulation might become an antiedematous therapy for ICH.

Nitric oxide/cGMP signalling induces Escherichia coli K1 receptor expression and modulates the permeability in human brain endothelial cell monolayers during invasion

Escherichia coli K1 invasion of human brain microvascular endothelial cells (HBMEC) mediated by outer membrane protein A (OmpA) results in the leakage of HBMEC monolayers. Despite the influence of nitric oxide (NO) in endothelial cell tight junction integrity, its role in E. coli-induced HBMEC monolayer permeability is poorly defined. Here, we demonstrate that E. coli invasion of HBMEC stimulates NO production by increasing the inducible nitric oxide synthase (iNOS) expression. Exposure to NO-producing agents enhanced the invasion of OmpA(+)E. coli and thereby increased the permeability of HBMEC. OmpA(+)E. coli-induced NO production lead to increased generation of cGMP and triggered the expression of OmpA receptor, Ec-gp96 in HBMEC. Pre-treatment of HBMEC with iNOS inhibitors or by introducing siRNA to iNOS, but not to eNOS or cGMP inhibitors abrogated the E. coli-induced expression of Ec-gp96. Overexpression of the C-terminal truncated Ec-gp96 in HBMEC prevented NO production and its downstream effector, cGMP generation and consequently, the invasion of OmpA(+)E. coli. NO/cGMP production also activates PKC-alpha, which is previously shown to be involved in HBMEC monolayer leakage. These results indicate that NO/cGMP signalling pathway plays a novel role in OmpA(+)E. coli invasion of HBMEC by enhancing the surface expression of Ec-gp96.

PPAR-gamma agonist rosiglitazone reverses increased cerebral venous hydraulic conductivity during hypertension

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists have been shown to protect the cerebral vasculature, including the blood-brain barrier. In the present study, we investigated the effect of the PPAR-gamma agonist rosiglitazone on changes in venous permeability during chronic hypertension induced by nitric oxide synthase inhibition. Female Sprague-Dawley rats were either treated with N(G)-nitro-L-arginine methyl ester (L-NAME; 0.5 g/l in drinking water) for 5 wk (HTN; n = 8), L-NAME for 5 wk plus the PPAR-gamma agonist rosiglitazone (20 mg/kg in food) for the last 3 wk (HTN + Rosi; n = 5), L-NAME for 5 wk plus the superoxide dismutase mimetic Tempol (1 mmol/l in drinking water) for the last 3 wk (HTN + Tempol; n = 8), or were untreated controls (n = 9). Fluid filtration (J(v)/S) and hydraulic conductivity (L(p)) of cerebral veins were compared in vitro between groups after a step increase in pressure from 10 to 25 mmHg to mimic the change in hydrostatic pressure during acute hypertension. Hypertension increased J(v)/S by 2.2-fold and L(p) by 3.2-fold. Rosiglitazone treatment after 2 wk of hypertension completely reversed the increased J(v)/S and L(p) that occurred during hypertension, whereas Tempol had no effect. These results demonstrate that rosiglitazone was effective at reversing changes in venous permeability that occurred during chronic hypertension, an effect that does not appear to be related to its antioxidant properties. Our findings suggest that PPAR-gamma may be a key regulator of blood-brain barrier permeability and a potential therapeutic target during hypertension.

Pathology and new players in the pathogenesis of brain edema

Brain edema continues to be a major cause of mortality after diverse types of brain pathologies such as major cerebral infarcts, hemorrhages, trauma, infections and tumors. The classification of edema into vasogenic, cytotoxic, hydrocephalic and osmotic has stood the test of time although it is recognized that in most clinical situations there is a combination of different types of edema during the course of the disease. Basic information about the types of edema is provided for better understanding of the expression pattern of some of the newer molecules implicated in the pathogenesis of brain edema. These molecules include the aquaporins, matrix metalloproteinases and growth factors such as vascular endothelial growth factors A and B and the angiopoietins. The potential of these agents in the treatment of edema is discussed. Since many molecules are involved in the pathogenesis of brain edema, effective treatment cannot be achieved by a single agent but will require the administration of a "magic bullet" containing a variety of agents released at different times during the course of edema in order to be successful.

Cyclic guanosine monophosphate signaling cascade mediates pigment aggregation in freshwater shrimp chromatophores

The cell signaling cascades that mediate pigment movements in crustacean chromatophores are not yet well established, although Ca(2+) and cyclic nucleotide second messengers are involved. Here, we examine the participation of cyclic guanosine monophosphate (cGMP) in pigment aggregation triggered by red pigment concentrating hormone (RPCH) in the red ovarian chromatophores of freshwater shrimp. In Ca(2+)-containing (5.5 mmol l(-1)) saline, 10 micromol l(-1) dibutyryl cGMP alone produced complete pigment aggregation with the same time course ( approximately 20 min) and peak velocity ( approximately 17 microm/min) as 10(-8) mol l(-1) RPCH; however, in Ca(2+)-free saline (9 x 10(-11) mol l(-1) Ca(2+)), db-cGMP was without effect. The soluble guanylyl cyclase (GC-S) activators sodium nitroprusside (SNP, 0.5 micromol l(-1)) and 3-morpholinosydnonimine (SIN-1, 100 micromol l(-1)) induced moderate aggregation by themselves ( approximately 35%-40%) but did not affect RPCH-triggered aggregation. The GC-S inhibitors zinc protoporphyrin IX (ZnPP-XI, 30 micromol l(-1)) and 6-anilino-5,8-quinolinedione (LY83583, 10 micromol l(-1)) partially inhibited RPCH-triggered aggregation by approximately 35%. Escherichia coli heat-stable enterotoxin (STa, 1 micromol l(-1)), a membrane-receptor guanylyl cyclase stimulator, did not induce or affect RPCH-triggered aggregation. We propose that the binding of RPCH to an unknown membrane-receptor type activates a Ca(2+)-dependent signaling cascade coupled via cytosolic guanylyl cyclase and cGMP to protein kinase G-phosphorylated proteins that regulate aggregation-associated, cytoskeletal molecular motor activity. This is a further example of a cGMP signaling cascade mediating the effect of a crustacean X-organ neurosecretory peptide.

Inhaled nitric oxide for preterm neonates

The evidence for the benefits of inhaled nitric oxide (iNO) on gas exchange, cytokine-induced lung inflammation, and vascular dysfunction has been demonstrated by several animal and human studies. The use of iNO in extremely low birth weight neonates for the prevention of adverse outcomes like chronic lung disease and neurologic injury has been investigated, but the findings remain inconclusive. This review briefly outlines the biologic rationale for the use of iNO in preterm neonates and the results on the outcome measures of bronchopulmonary dysplasia and brain injury from the recent clinical trials. This article focuses on the potential toxicities, persistent controversies, and unanswered questions regarding the use of this treatment modality in this patient population at high risk for adverse outcomes.