Blood–brain-barriers in aging and in Alzheimer’s disease

The aging process correlates with a progressive failure in the normal cellular and organ functioning; these alterations are aggravated in Alzheimer’s disease (AD). In both aging and AD there is a general decrease in the capacity of the body to eliminate toxic compounds and, simultaneously, to supply the brain with relevant growth and nutritional factors. The barriers of the brain are targets of this age related dysfunction; both the endothelial cells of the blood–brain barrier and the choroid plexus epithelial cells of the blood-cerebrospinal fluid barrier decrease their secretory capacity towards the brain and their ability to remove toxic compounds from the brain. Additionally, during normal aging and in AD, the permeability of the brain barriers increase. As such, a greater contact of the brain parenchyma with the blood content alters the highly controlled neural environment, which impacts on neural function. Of interest, the brain barriers are more than mere obstacles to the passage of molecules and cells, and therefore active players in brain homeostasis, which is still to be further recognized and investigated in the context of health and disease. Herein, we provide a review on how the brain barriers change during aging and in AD and how these processes impact on brain function.     

Specific AHNAK expression in brain endothelial cells with barrier properties

The blood-brain barrier (BBB) is essential for maintaining brain homeostasis and low permeability. Because disruption of the BBB may contribute to many brain disorders, they are of considerable interests in the identification of the molecular mechanisms of BBB development and integrity. We here report that the giant protein AHNAK is expressed at the plasma membrane of endothelial cells (ECs) forming specific blood-tissue barriers, but is absent from the endothelium of capillaries characterized by extensive molecular exchanges between blood and extracellular fluid. In the brain, AHNAK is widely distributed in ECs with BBB properties, where it co-localizes with the tight junction protein ZO-1. AHNAK is absent from the permeable brain ECs of the choroid plexus and is down-regulated in permeable angiogenic ECs of brain tumors. In the choroid plexus, AHNAK accumulates at the tight junctions of the choroid epithelial cells that form the blood-cerebrospinal fluid (CSF) barrier. In EC cultures, the regulation of AHNAK expression and its localization corresponds to general criteria of a protein involved in barrier organization. AHNAK is up-regulated by angiopoietin-1 (Ang-1), a morphogenic factor that regulates brain EC permeability. In bovine cerebral ECs co-cultured with glial cells, AHNAK relocates from the cytosol to the plasma membrane when endothelial cells acquire BBB properties. Our results identify AHNAK as a protein marker of endothelial cells with barrier properties.     

Evidence for sex difference in the CSF/plasma albumin ratio in ~20 000 patients and 335 healthy volunteers

Given sex‐related differences in brain disorders, it is of interest to study if there is a sex difference in the permeability of the blood‐cerebrospinal fluid barrier (BCSFB) and the blood‐brain barrier (BBB). The CSF/serum albumin ratio (Q_Alb) is a standardized biomarker that evaluates the function of these barriers. In previous studies, contradictory results have been reported with respect to sex difference using this quotient, possibly because of small population sizes and heterogeneity with respect to ages. Q_Alb measurements in more than 20 000 patients between 1 and 90 years visiting our hospitals revealed a significant sex difference in all age groups also when excluding patients with pathologically high CSF albumin > 400 mg/L. Similar pattern was found in 335 healthy volunteers in similar age intervals. Although also other factors are likely important, our observation is consistent with lower integrity of the brain barriers in males. If the difference in Q_Alb is caused mainly by a difference in barrier function, this may require different drug doses and strategies for efficient central nervous system (CNS) delivery in males and females, as well as it may indicate differences in brain metabolism. Moreover, our study emphasizes that different reference values should be used both for different ages and sexes.     

Inflammatory Mediators and Modulation of Blood–Brain Barrier Permeability

1. Unlike some interfaces between the blood and the nervous system (e.g., nerve perineurium), the brain endothelium forming the blood–brain barrier can be modulated by a range of inflammatory mediators. The mechanisms underlying this modulation are reviewed, and the implications for therapy of the brain discussed.2. Methods for measuring blood–brain barrier permeability in situ include the use of radiolabeled tracers in parenchymal vessels and measurements of transendothelial resistance and rate of loss of fluorescent dye in single pial microvessels. In vitro studies on culture models provide details of the signal transduction mechanisms involved.3. Routes for penetration of polar solutes across the brain endothelium include the paracellular tight junctional pathway (usually very tight) and vesicular mechanisms. Inflammatory mediators have been reported to influence both pathways, but the clearest evidence is for modulation of tight junctions.4. In addition to the brain endothelium, cell types involved in inflammatory reactions include several closely associated cells including pericytes, astrocytes, smooth muscle, microglia, mast cells, and neurons. In situ it is often difficult to identify the site of action of a vasoactive agent. In vitro models of brain endothelium are experimentally simpler but may also lack important features generated in situ by cell:cell interaction (e.g. induction, signaling).5. Many inflammatory agents increase both endothelial permeability and vessel diameter, together contributing to significant leak across the blood–brain barrier and cerebral edema. This review concentrates on changes in endothelial permeability by focusing on studies in which changes in vessel diameter are minimized.6. Bradykinin (Bk)² increases blood–brain barrier permeability by acting on B₂ receptors. The downstream events reported include elevation of [Ca²⁺]_i, activation of phospholipase A₂, release of arachidonic acid, and production of free radicals, with evidence that IL-1 potentiates the actions of Bk in ischemia.7. Serotonin (5HT) has been reported to increase blood–brain barrier permeability in some but not all studies. Where barrier opening was seen, there was evidence for activation of 5-HT₂ receptors and a calcium-dependent permeability increase.8. Histamine is one of the few central nervous system neurotransmitters found to cause consistent blood–brain barrier opening. The earlier literature was unclear, but studies of pial vessels and cultured endothelium reveal increased permeability mediated by H₂ receptors and elevation of [Ca²⁺]_i and an H₁ receptor-mediated reduction in permeability coupled to an elevation of cAMP.9. Brain endothelial cells express nucleotide receptors for ATP, UTP, and ADP, with activation causing increased blood–brain barrier permeability. The effects are mediated predominantly via a P_2U (P2Y₂) G-protein-coupled receptor causing an elevation of [Ca²⁺]_i; a P2Y₁ receptor acting via inhibition of adenyl cyclase has been reported in some in vitro preparations.10. Arachidonic acid is elevated in some neural pathologies and causes gross opening of the blood–brain barrier to large molecules including proteins. There is evidence that arachidonic acid acts via generation of free radicals in the course of its metabolism by cyclooxygenase and lipoxygenase pathways.11. The mechanisms described reveal a range of interrelated pathways by which influences from the brain side or the blood side can modulate blood–brain barrier permeability. Knowledge of the mechanisms is already being exploited for deliberate opening of the blood–brain barrier for drug delivery to the brain, and the pathways capable of reducing permeability hold promise for therapeutic treatment of inflammation and cerebral edema.     

Il1-β Involvement in Cognitive Impairment after Sepsis

Sepsis is defined as the host's reaction to infection and characterised by a systemic inflammatory response with important clinical implications. Central nervous system dysfunction secondary to sepsis is associated with local generation of pro- and anti-inflammatory cytokines, impaired cerebral microcirculation, an imbalance of neurotransmitters, apoptosis and cognitive impairment. It's known that the IL-1β is one of the first cytokines to be altered. Thus, the objective of this study was to evaluate the role of IL-1β in cognitive parameters in brain tissue through the use of an IL-1β (IL-1ra) receptor antagonist up to 10 days and to assess blood–brain barrier permeability, cytokine levels, oxidative parameters and energetic metabolism up to 24 h, after sepsis induction. To this aim, we used sham-operated Wistar rats or submitted to the cecal ligation and perforation (CLP) procedure. Immediately after, the animals received one dose of 10 μg of IL-1ra. After 24 h, the rats were killed and were evaluated for biochemical parameters in the pre-frontal cortex, hippocampus and striatum. After 10 days, the animals were submitted to the habituation to the open field and step-down inhibitory avoidance task. We observed that the use of IL-1ra reverted the increase of blood–brain barrier permeability in the pre-frontal cortex, hippocampus and striatum; the increase of IL-1β, IL1-6 and TNF-α levels in the pre-frontal cortex and striatum; the decrease of complex I activity in the pre-frontal, hippocampus and striatum; the increase of oxidative parameters in pre-frontal cortex, hippocampus and striatum; and cognitive impairment. In conclusion, the results observed in this study reinforce the role of acute brain inflammatory response, in particular, the IL1β response, in the cognitive impairment associated with sepsis.     

Uptake of 36Cl and 22Na by the Brain-Cerebrospinal Fluid System: Comparison of the Permeability of the Blood-Brain and Blood-Cerebrospinal Fluid Barriers

Abstract: Transport and permeability properties of the blood-brain and blood-CSF barriers were determined by kinetic analysis of radioisotope uptake from the plasma into the CNS of the adult rat. Cerebral cortex and cerebellum uptake curves for ³⁶Cl and ²²Na were resolved into two components. The fast component (t_½ 0.02–0.05 h, fractional volume 0.04–0.08) is comprised of the vascular compartment and a small perivascular space whereas the slow component (t_½ 1.06–1.69 h, fractional volume 0.92–0.96) represents isotope movement across the blood-brain barrier into the brain extracellular and cellular compartments. Uptake curves of both ³⁶Cl and ²²Na into the CSF were also resolved into two components, a fast component (t_½ 0.18 h, fractional volume 0.24) and a slow component (t_½ 1.2 h, fractional volume 0.76). Evidence suggests that the fast component represents isotope movement across the blood-CSF barrier, i.e., the choroid plexuses, whereas the CSF slow component probably reflects isotope penetration primarily from the brain extracellular fluid into the CSF. The extracellular fluid volume of the cerebral cortex and cerebellum was estimated as ?13% from the initial slope of the curve of brain space versus CSF space curve for both ³⁶Cl and ²²Na. Like the choroid plexuses, the glial cell compartment of the brain appears to accumulate Cl from 2 to 6 times that predicted for passive distribution. The relative permeability of the blood-CSF and blood-brain barriers to ³⁶Cl, ²²Na, and [³H]mannitol was determined by calculating permeability surface-area products (PA). Analysis of the PA values for all three isotopes indicates that the effective permeability of the choroidal epithelium (blood/CSF barrier) is significantly greater than that of the capillary endothelium in the cerebral cortex and cerebellum (blood-brain barrier).     

The blood-CSF barrier explained: when development is not immaturity

It is often suggested that during development the brain barriers are immature. This argument stems from teleological interpretations and experimental observations of the high protein concentrations in fetal cerebrospinal fluid (CSF) and decreases in apparent permeability of passive markers during development. We argue that the developmental blood-CSF barrier restricts the passage of lipid-insoluble molecules by the same mechanism as in the adult (tight junctions) rendering the paracellular pathway an unlikely route of entry. Instead, we suggest that both protein and passive markers are transferred across the epithelium through a transcellular route. We propose that changes in volume of distribution can largely explain the decrease in apparent permeability for passive markers and that developmentally regulated cellular transfer explains changes in CSF protein concentrations. The blood-CSF tight junctions are functionally mature from very early in development, and it appears that transfer from blood into embryonic brain occurs predominately via CSF rather than the vasculature.     

血脑屏障与脑血管疾病的相关研究

血脑屏障（blood brain barrier,BBB）的主要结构包括：脑毛细血管内皮细胞及其间的紧密连接（tight junction,TJ）、基底膜、基 底膜下星型胶质细胞终足。血脑屏障是存在于血液和脑组织之间的一层屏障系统,在许多大脑疾患的病理过程中,BBB 的破坏导 致通透性增高都是不可避免的一个环节。BBB是保证中枢神经系统的正常生理功能的重要屏障系统。目前已有大量关于血脑屏 障通透性在脑血管疾病中的变化研究。本文分别从血脑屏障的结构和功能,药物通过血脑屏障的方法和功能,脑缺血损伤、阿尔 茨海默病、帕金森病和多发性硬化症等不同的脑病变与血脑屏障通透性的变化及中医药应用等方面做一综述。有针对性地对 BBB和大脑疾病进行进一步的研究与探索,将会为临床治疗相关疾病带来新的视角与机遇。     

Resistance to Water Diffusion in the Stratum Corneum Is Depth-Dependent

The stratum corneum (SC) provides a permeability barrier that limits the inflow and outflow of water. The permeability barrier is continuously and dynamically formed, maintained, and degraded along the depth, from the bottom to the top, of the SC. Naturally, its functioning and structure also change dynamically in a depth-dependent manner. While transepidermal water loss is typically used to assess the function of the SC barrier, it fails to provide any information about the dynamic mechanisms that are responsible for the depth-dependent characteristics of the permeability barrier. This paper aims to quantitatively characterize the depth-dependency of the permeability barrier using in vivo non-invasive measurement data for understanding the underlying mechanisms for barrier formation, maintenance, and degradation. As a framework to combine existing experimental data, we propose a mathematical model of the SC, consisting of multiple compartments, to explicitly address and investigate the depth-dependency of the SC permeability barrier. Using this mathematical model, we derive a measure of the water permeability barrier, i.e. resistance to water diffusion in the SC, from the measurement data on transepidermal water loss and water concentration profiles measured non-invasively by Raman spectroscopy. The derived resistance profiles effectively characterize the depth-dependency of the permeability barrier, with three distinct regions corresponding to formation, maintenance, and degradation of the barrier. Quantitative characterization of the obtained resistance profiles allows us to compare and evaluate the permeability barrier of skin with different morphology and physiology (infants vs adults, different skin sites, before and after application of oils) and elucidates differences in underlying mechanisms of processing barriers. The resistance profiles were further used to predict the spatial-temporal effects of skin treatments by in silico experiments, in terms of spatial-temporal dynamics of percutaneous water penetration.     

Alteration of sphingolipid metabolism as a putative mechanism underlying LPS‐induced BBB disruption

Septic encephalopathy with confusion and agitation occurs early during sepsis and contributes to the severity of the disease. A decrease in the sphingosine‐1‐phosphate (S1P) blood levels has been shown in patients and in animal models of sepsis. The lipid mediator S1P is known to be involved in endothelial barrier function in a context‐dependent manner. We utilized lipopolysaccharide (LPS )‐injected mice as a model for septic encephalopathy and first performed tracer permeability assays to assess the blood–brain barrier (BBB ) breakdown in vivo. At time points corresponding to the BBB breakdown post LPS injection, we aimed to characterize the regulation of the sphingolipid signaling pathway at the BBB during sepsis. We measured sphingolipid concentrations in blood, in mouse brain microvessels (MBMV s), and brain tissue. We also analyzed the expression of S1P receptors, transporters, and metabolizing enzymes in MBMV s and brain tissue. Primary mouse brain microvascular endothelial cells (MBMEC s) were isolated to evaluate the effects of LPS on transendothelial electrical resistance (TEER ) as a measure of permeability in vitro . We observed a relevant decrease in S1P levels after LPS injection in all three compartments (blood, MBMV s, brain tissue) that was accompanied by an increased expression of the S1P receptor type 1 and of sphingosine kinase 1 on one hand and of the S1P degrading enzymes lipid phosphate phosphatase 1 (LPP 1) and S1P phosphatase 1 on the other hand, as well as a down‐regulation of sphingosine kinase 2. Application of LPS to a monolayer of primary MBMEC s did not alter TEER , but serum from LPS ‐treated mice lead to a breakdown of the barrier compared to serum from vehicle‐treated mice. We observed profound alterations of the sphingolipid metabolism at the BBB after LPS injection that point toward a therapeutic potential of drugs interfering with this pathway as novel approach for the detrimental overwhelming immune response in sepsis.

Read the Editorial Highlight for this article on page 115 . Cover Image for this Issue: doi. 10.1111/jnc.14161 .

     

Nowhere to run: semi-permeable barriers affect pronghorn space use

Animal movement can mediate the ecological consequences of fragmentation; however, barriers such as fences, roads, and railways are becoming a pervasive threat to wildlife. Pronghorn (Antilocapra americana) habitat in western North America has been fragmented by roads, railways, and fences. Although pronghorn are sensitive to barriers, neither the relative permeability of different barriers to crossing nor their influence on space use have been quantified. We used a large global positioning system (GPS)-collar dataset of pronghorn (n = 1,010 animal-years) in Wyoming, USA, to first quantify the likelihood that pronghorn cross each of 5 different anthropogenic barriers, including fences, county roads, railroads, state highways, and interstate highways (i.e., interstates). Next, we assessed how each barrier influenced pronghorn space use during the winter as indexed by the area occupied, and daily displacement relative to the density of barriers on an individual's winter range. The semi-permeability of the 5 barriers varied substantially, with the interstate being the most severe barrier to pronghorn movement. Pronghorn were >300 times less likely to cross interstates compared to state highways. Although pronghorn space use was rarely influenced by barriers within individual core winter ranges, pronghorn space use was constrained by barriers on the buffered periphery of individual winter ranges. Despite their different permeability to movement, the density of fences and combined interstates and railroads had similarly negative effects on pronghorn space use. Our results illustrate that the degree to which pronghorn avoid crossing barriers may scale up to affect access to habitat. Additionally, our results indicate that the effects of barriers on habitat access are not proportional to their permeability. Our results add to a growing consensus that effective management of mobile species depends on understanding how different kinds of semi-permeable barriers influence access and use of habitats.     

Dysregulation of focal adhesion kinase upon Toxoplasma gondii infection facilitates parasite translocation across polarised primary brain endothelial cell monolayers

The apicomplexan parasite Toxoplasma gondii invades tissues and traverses non‐permissive biological barriers in infected humans and other vertebrates. Following ingestion, the parasite penetrates the intestinal wall and disseminates to immune‐privileged sites such as the brain parenchyma, after crossing the blood–brain barrier. In the present study, we have established a protocol for high‐purification of primary mouse brain endothelial cells to generate stably polarised monolayers that allowed assessment of cellular barrier traversal by T. gondii. We report that T. gondii tachyzoites translocate across polarised monolayers of mouse brain endothelial cells and human intestinal Caco2 cells without significantly perturbing barrier impermeability and with minimal change in transcellular electrical resistance. In contrast, challenge with parasite lysate or LPS increased barrier permeability by destabilising intercellular tight junctions (TJs) and accentuated transmigration of T. gondii. Conversely, reduced phosphorylation of the TJ‐regulator focal adhesion kinase (FAK) was observed dose‐dependently upon challenge of monolayers with live T. gondii but not with parasite lysate or LPS. Pharmacological inhibition of FAK phosphorylation reversibly altered barrier integrity and facilitated T. gondii translocation. Finally, gene silencing of FAK by shRNA facilitated transmigration of T. gondii across epithelial and endothelial monolayers. Jointly, the data demonstrate that T. gondii infection transiently alters the TJ stability through FAK dysregulation to facilitate transmigration. This work identifies the implication of the TJ regulator FAK in the transmigration of T. gondii across polarised cellular monolayers and provides novel insights in how microbes overcome the restrictiveness of biological barriers.     

Evaluation of chronic lead effects in the blood brain barrier system by DCE-CT

BackgroundLead (Pb) is an environmental factor has been suspected of contributing to the dementia including Alzheimer’s disease (AD). Our previous studies have shown that Pb exposure at the subtoxic dose increased brain levels of beta-amyloid (Aβ) and amyloid plaques, a pathological hallmark for AD, in amyloid precursor protein (APP) transgenic mice, and is hypothesized to inhibit Aβ clearance in the blood- cerebrospinal fluid (CSF) barrier. However, it remains unclear how different levels of Pb affect Aβ clearance in the whole blood-brain barrier system. This study was designed to investigate whether chronic exposure of Pb affected the permeability of the blood-brain barrier system by using the Dynamic Contrast-Enhanced Computerized Tomography (DCE-CT) method.MethodsDEC-CT was used to investigate whether chronic exposure of toxic Pb affected the permeability of the real-time blood brain barrier system.ResultsData showed that Pb exposure increased permeability surface area product, and also significantly induced brain perfusion. However, Pb exposure did not alter extracellular volumes or fractional blood volumes of mouse brain.ConclusionOur data suggest that Pb exposure at subtoxic and toxic levels directly targets the brain vasculature and damages the blood brain barrier system.     

Damaging effects of ethylenediaminetetra-acetate and penicillins on permeability barriers in Gram-negative bacteria

1. The permeability barrier against benzylpenicillin has been found to be passive in four strains of penicillinase-producing Gram-negative bacteria (three of Klebsiella aerogenes and one of Escherichia coli). 2. If the three K. aerogenes strains are grown in the presence of sub-inhibitory concentrations of benzylpenicillin, ampicillin or phenethicillin the resultant bacterial cells have deficient permeability barriers. Concentrations of ampicillin or benzylpenicillin less than one-tenth of those required to inhibit growth cause destruction of more than half the permeability barrier in these strains. 3. Benzylpenicillin, ampicillin and phenethicillin have no effect upon the permeability barriers of resting cells from the three K. aerogenes strains. 4. Treatment of resting cells with trisodium EDTA, although failing to sensitize K. aerogenes to lysozyme, severely damages permeability barriers in this species. 5. The magnesium and calcium salts of EDTA do not have the same capacity as the sodium salt for causing damage to permeability barriers in K. aerogenes and E. coli. Damage caused by trisodium EDTA can be at least partially reversed by treatment with Ca(2+) or Mg(2+) ions. It is suggested that EDTA damage is caused by removal of either Ca(2+) or Mg(2+) ions, or both, from the bacterial cell envelope. 6. Bacterial cells with deficient permeability barriers as a result of either growth in the presence of a penicillin or treatment with EDTA remain viable, and revert to their usual permeability after growth in nutrient broth.     

TGF-β1-mediated exosomal lnc-MMP2-2 increases blood–brain barrier permeability via the miRNA-1207-5p/EPB41L5 axis to promote non-small cell lung cancer brain metastasis

Brain metastases remain a major problem in patients with advanced non-small cell lung cancer (NSCLC). The permeability of the blood–brain barrier (BBB) is highly increased during lung cancer brain metastasis; however, the underlying mechanism remains largely unknown. We previously found that lnc-MMP2-2 is highly enriched in tumor growth factor (TGF)-β1-mediated exosomes and regulates the migration of lung cancer cells. This study aimed to explore the role of exosomal lnc-MMP2-2 in the regulation of BBB and NSCLC brain metastasis. Here, using endothelial monolayers and mouse models, we found that TGF-β1-mediated NSCLC-derived exosomes efficiently destroyed tight junctions and the integrity of these natural barriers. Overexpression of lnc-MMP2-2 in human brain microvascular endothelial cells increased vascular permeability in endothelial monolayers, whereas inhibition of lnc-MMP2-2 alleviated these effects. Furthermore, lnc-MMP2-2 knockdown markedly reduced NSCLC brain metastasis in vivo. Mechanistically, through luciferase reporter assays, RNA pull-down assay, and Ago2 RNA immunoprecipitation assay, we showed that lnc-MMP2-2 served as a microRNA sponge or a competing endogenous RNA for miR-1207-5p and consequently modulated the derepression of EPB41L5. In conclusion, TGF-β1-mediated exosomal lnc-MMP2-2 increases BBB permeability to promote NSCLC brain metastasis. Thus, exosomal lnc-MMP2-2 may be a potential biomarker and therapeutic target against lung cancer brain metastasis.Subject terms: Lung cancer, Metastasis     

Natriuretic peptides differentially attenuate thrombin-induced barrier dysfunction in pulmonary microvascular endothelial cells

Previous studies have described a protective effect of atrial natriuretic peptide (ANP) against agonist-induced permeability in endothelial cells derived from various vascular beds. In the current study, we assessed the effects of the three natriuretic peptides on thrombin-induced barrier dysfunction in rat lung microvascular endothelial cells (LMVEC). Both ANP and brain natriuretic peptide (BNP) attenuated the effect of thrombin on increased endothelial monolayer permeability and significantly enhanced the rate of barrier restoration. C-type natriuretic peptide (CNP) had no effect on the degree of thrombin-induced monolayer permeability, but did enhance the restoration of the endothelial barrier, similar to ANP and BNP. In contrast, the non-guanylyl cyclase-linked natriuretic peptide receptor specific ligand, cyclic-atrial natriuretic factor (c-ANF), delayed the rate of barrier restoration following exposure to thrombin. All three natriuretic peptides promoted cGMP production in the endothelial cells; however, 8-bromo-cGMP alone did not significantly affect thrombin modulation of endothelial barrier function. ANP and BNP, but not CNP or c-ANF, blunted thrombin-induced RhoA GTPase activation. We conclude that ANP and BNP protect against thrombin-induced barrier dysfunction in the pulmonary microcirculation by a cGMP-independent mechanism, possibly by attenuation of RhoA activation.     

Neurodegenerative Evidence in Mice Brains with Cecal Ligation and Puncture-Induced Sepsis: Preventive Effect of the Free Radical Scavenger Edaravone

Sepsis is a major clinical challenge and septic encephalopathy is its nasty complication. The pathogenesis and underlying mechanisms of septic encephalopathy are not well understood. This study sought to fully characterize sepsis-associated biochemical and histopathological changes in brains of mice after cecal ligation and puncture, regarded as a highly clinically relevant animal model of polymicrobial sepsis. Real-time PCR analysis showed that gene expression levels of proinflammatory cytokines, including tumor necrosis factor-α and interleukin-1β, were significantly up-regulated in brain tissues from septic mice, but to a much lesser extent when compared with those in peripheral tissues such as lungs. Blood-brain barrier (BBB) permeability was significantly increased in septic mice, as determined by the measurement of sodium fluorescein and Evans blue content. Sepsis resulted in increases in NADPH oxidase activity and expression of p47^phox and p67^phox and up-regulation of inducible nitric oxide (NO) synthase in brains, indicating that superoxide, produced by NADPH oxidase, reacts with NO to form peroxynitrite, that maybe lead to the loss of BBB integrity. Light and electron microscopic examination of septic mouse brain showed serious neuronal degeneration, as indicated by hyperchromatic, shrunken, pyknotic, and electron-dense neurons. These histopathogical changes were prevented by treatment with the free radical scavenger edaravone. Together, these results suggest that sepsis can lead to rapid neurodegenerative changes in brains via free radical species production and possibly subsequent injury to the BBB. We may also provide a potentially useful therapeutic tool for treating septic encephalopathy.     

Engaging neuroscience to advance translational research in brain barrier biology

The delivery of many potentially therapeutic and diagnostic compounds to specific areas of the brain is restricted by brain barriers, of which the most well known are the blood-brain barrier (BBB) and the blood-cerebrospinal fluid (CSF) barrier. Recent studies have shown numerous additional roles of these barriers, including an involvement in neurodevelopment, in the control of cerebral blood flow, and--when barrier integrity is impaired--in the pathology of many common CNS disorders such as Alzheimer's disease, Parkinson's disease and stroke.     

Determinants of Passive Drug Entry into the Central Nervous System

1. The blood–brain barriers restrict the passive diffusion of many drugs into the brain and constitute a significant obstacle in the pharmacological treatment of central nervous system diseases and disorders. The degree of restriction they impose is variable, with some lipid-insoluble drugs effectively excluded from the brain, while many lipid-soluble drugs do not appear to be subject to any restriction.2. The ease with which any particular drug diffuses across the blood–brain barrier is determined largely by the number and strength of intermolecular forces holding it to surrounding water molecules. By quantifying the molecular features that contribute to these forces, it is possible to predict the in vivo blood–brain barrier permeability of a drug from its molecular structure. Dipolarity, polarizability, and hydrogen bonding ability are factors that appear to reduce permeability, whereas molecular volume (size) and molar refraction are associated with increased permeability.3. Increasing the passive entry of restricted drugs into the central nervous system can be achieved by disrupting the blood–brain barrier (increased paracellular diffusion) or by modifying the structure of restricted drugs to temporarily or permanently increase their lipid solubility (increased transcellular permeability).4. Competitive inhibition of outwardly directed active efflux mechanisms (P-glycoprotein and MRP, the multidrug resistance-related protein) can also significantly increase the accumulation of certain drugs within the central nervous system.