Cerebrospinal fluid transthyretin in the neonate and blood-cerebrospinal fluid barrier permeability

We measured transthyretin levels in the cerebrospinal fluid (CSF) of newborn infants, older children, patients with viral and bacterial meningitis, and adults with increased CSF protein levels. Neonatal CSF transthyretin levels are elevated disproportionately in comparison to levels in the other groups. We conclude that increased levels of transthyretin in the CSF of neonates are not explained by increased permeability of the blood-CSF barrier.     

Disruption of the blood-cerebrospinal fluid barrier by transient cerebral ischemia

The influence of transient cerebral ischemia on blood-brain and blood-cerebrospinal fluid (CSF) barrier permeability was studied sequentially by magnetic resonance imaging (MRI) contrast enhancement using gadolinium-diethylene triamine pentacetic acid (Gd-DTPA) in rats. The unilateral internal carotid and middle cerebral arteries were transiently occluded by inserting a nylon thread into the carotid artery and removing it following a variable interval of 5 to 60 min. Contrast enhancement of the lateral ventricle on the affected side was seen in the enhanced T1-weighted image at the early stage of reperfusion 6 h after the start of ischemia in most of the rats subjected to 30- and 60-min ischemia, and in 3 of 6 rats in the 15-min ischemia group. Autoradiograms of Gd-[¹⁴C]DTPA in rats subjected to 60-min ischemia demonstrated that the tracer strongly accumulated in the choroid plexus, the wall of the lateral ventricle and its surrounding brain tissue. On the other hand, parenchymal enhancement of the striatum was seen only in the 60-min ischemia group and appeared later on Day 1 or Day 7. These results indicate that ventricular enhancement on MRI in this model is caused by disruption of the blood-CSF barrier at the choroid plexus of the lateral ventricle. This is the first reported study to demonstrate blood-CSF barrier disruption by transient ischemia.     

Racial variation in the blood-cerebrospinal fluid barrier of normal children

Conclusion The normal bromide permeability quotient variation of the negro covers a distinctly lower range than that of the white.Financed through Child Neurology Research by the Friedsam Foundation. This is a preliminary report. The full report including complete tabulations and critical analysis of data will appear in the volume of collected reports of Child Neurology Research soon to be published.     

Pro-inflammatory cytokines modulate matrix metalloproteinase secretion and organic anion transport at the blood-cerebrospinal fluid barrier

Neuroinflammation and neuroinfection trigger cytokine-mediated responses that include an increase in the cerebrospinal fluid (CSF) levels of pro-inflammatory matrix metalloproteinases (MMPs) and organic anions such as leukotrienes and prostaglandins. The choroid plexus (CP) epithelium forming the interface between the blood and the CSF regulates the CSF concentration of bioactive organic anions and is involved in neuro-immune regulation. We demonstrated that both fourth and lateral ventricle CPs are a source of pro- and active MMP-2 and MMP-9 in the brain. Using a cellular model of the blood-CSF barrier, we showed that a pro-inflammatory cytokine treatment leads to an increase in the choroidal MMP secretion at either the apical or the basolateral membrane, depending on the ventricular origin of the choroidal cells. This effect was not concomitant with an alteration in the structural blood-CSF barrier. Neither was the pool of antioxidant sulfhydryls in the choroidal cells challenged. In contrast, the efficiency of the choroidal epithelium to clear the CSF from organic anions was highly reduced. Thus, during inflammation, the CPs could be one source of MMPs found in the CSF facilitate leucocyte migration by secreting MMPs into the choroidal stroma, and promote the inflammatory process by failing in its ability to clear deleterious compounds from the brain.     

Effect of atrial natriuretic factor on permeability of the blood-cerebrospinal fluid barrier

Summary The demonstration of ¹²⁵I-labelled atrial natriuretic factor (ANF)-binding sites on choroid plexus suggests a physiological role of ANF on the blood-cerebrospinal fluid barrier. This ultrastructural study was undertaken to determine whether ANF (0.5 g) alters the permeability of rat blood-cerebrospinal fluid barrier under steady states. Horseradish peroxidase (HRP) was used as a marker of protein permeability and ionic lanthanum as a marker of ionic permeability. HRP was not observed in the walls of choroid plexus vessels of control rats at 3 or 6 min, while at 12 min HRP was present in vessel walls and occasionally in continuity in the adjacent intercellular space between choroidal epithelial cells. In ANF-treated rats, HRP was observed in vessel walls and in the intercellular space between the choroidal epithelial cells up to the apical tight junctions at 3 min, indicating an accelerated passage of tracer. Although HRP was never observed beyond the apical tight junctions in control or test animals, at 6 min test rats showed ionic lanthanum within these junctions in focal areas and in continuity in the adjacent ventricular cavity. These studies demonstrate that ANF causes accelerated passage of both HRP and ionic lanthanum from blood into choroid plexuses with passage of ionic lanthanum into the ventricular cavity through the apical tight junctions of choroidal epithelial cells. The latter is in keeping with the known function of ANF in regulating water and electrolyte fluxes.Supported by Heart and Stroke Foundation of Ontario, Grant T.1324     

SPARC/osteonectin, an endogenous mechanism for targeting albumin to the blood-cerebrospinal fluid interface during brain development

Specialized populations of choroid plexus epithelial cells have previously been shown to be responsible for the transfer of individual plasma proteins from blood to the cerebrospinal fluid (CSF), contributing to their characteristically high concentrations in CSF of the developing brain. The mechanism of this protein transfer remains elusive. Using a marsupial, Monodelphis domestica, we demonstrate that the albumin-binding protein SPARC (osteonectin/BM-40/culture-shock protein) is present in a subset of choroid plexus epithelial cells from its first appearance, throughout development, and into adulthood. The synthesis of SPARC by the lateral ventricular plexus was confirmed with real-time PCR. The expression level of SPARC was higher in plexuses of younger than older animals. Western blot analysis of the gene product confirmed the quantitative PCR results. The co-localization of SPARC and albumin shown by immunocytochemistry and its cellular location indicate that this glycoprotein may act as a recognition site for albumin. In addition, the numbers of SPARC-immunopositive cells and its expression were responsive to experimental changes of albumin concentration in the blood. It is suggested that SPARC may be one of the molecules that govern the uptake and delivery of proteins from blood to the CSF. The results also confirm that protein transfer across the blood-CSF barrier is developmentally and physiologically regulated.     

Soluble intercellular adhesion molecule-1 in cerebrospinal fluid: An indicator for the inflammatory impairment of the blood-cerebrospinal fluid barrier

A soluble form of the intercellular adhesion molecule- (sICAM-1) was measured in paired cerebrospinal fluid (CSF)/blood samples from 123 patients with differenr neurological diseases. Mean levels of circulating ICAM-1 in the blod were mean ±SD = 423 ± 184.6 ng ml⁻¹ (range 44–1115 ng ml⁻¹). Considerable differences of sICAM-1 in the CSF of patients wre observed between disease groups. In accute bacterial maningitis, sICAM-1 levels as high as of the serum concentration were detected in the CSF (n = 24; mean ± SD = 33.0 ± 23.7 ng ml⁻¹; range: 4.8–93.9 ng ml⁻¹). These changes coincided with a sever blood-CSF barrier dysfunction as indicated by a high CSF/blood ration for albumin (mean ± SD = 46.7 ± 52.2; range: 16.8–249.3). In patients with polyradiculitits (n = 9; mean ± SD = 14.5 ± 11.9 ng ml⁻¹; range: 2.6–43.7 ng ml⁻¹) a similar convariation between the albumin and sICAM CSF/blood ratios was detected. In patients with multiple sclerosis (n = 9; mean ± SD = 5 ± 4.3; arange: 0–12.7 ng ml⁻¹ or HIV infection with neurological symptoms (n = 18; mean ± SD = 4.9 ± 3.2; range; 1–11.9 ng ml⁻¹) low levels of sICAM-1 were detected in the CSG associated with intact blood-CSF barrier function in most patients. Among 13 patients with viral meningitis, only four had detectable levels of sICAM-1 in their CSF (mean ± SD = 1.0 ± 1.5 ng ml⁻¹; range: 0–3.7). Interestingly, in a groupof patients with non-inflammatory disorders of the CNS soluble ICAM-1 was present only in three out of 50 CSF samples despite indication for blood-CSF barrier dysfunction in most cases. Repeated lumbar punctures revealed that persistent high CSF/serum ratios for sICAM-1 were associated with poor outcome. In patients with inflammatory diseases of the CNS, a signoficant correlation was observed between CSF/serumratios for albumin and sICAM-1 ([ifn = 169; r = 0.67; P < 0.001), whereas no relation between these parameters was detected in patients with non-inflammatory diseases These results indicate that sICAM-1 is a reliable marker for an inflammatory process within non-inflammatory process within the CNS which is associated with blood-CSF barrier distrubance.     

Identification of a saturable uptake system for deoxyribonucleosides at the blood-brain and blood-cerebrospinal fluid barriers

Substances can enter the brain either directly across the blood-brain barrier or indirectly across the choroid plexuses and arachnoid membrane (blood-CSF barrier) into the CSF and then by diffusion into the brain. Earlier studies have demonstrated a saturable thymidine uptake across the blood-CSF barrier, but not across the blood-brain barrier. In this study transport of [³H]thymidine across both barriers was measured in vivo by means of a bilateral vascular brain perfusion technique in the anaesthetised guinea-pig. This method allows simultaneous and quantitative measurement of slowly penetrating solutes into both brain and CSF, under controlled conditions of arterial inflow. The results of the present study carried out over perfusion periods of up to 30 min indicated a progressive uptake of [³H]thymidine into brain and CSF, which was found to be significantly greater than the transport ofd-[¹⁴C]mannitol (a plasma space marker). Furthermore, the addition of 1 mM unlabelled thymidine in the perfusate caused saturation of [³H]thymidine uptake into both brain and CSF. In conclusion, these findings suggest that thymidine can cross both the blood-brain and blood-CSF barriers in the guinea-pig by carrier-mediated transport systems.     

Amyloid beta peptide as a vaccine for Alzheimer's disease involves receptor-mediated transport at the blood-brain barrier.

Much research is now focused on a potential vaccine for Alzheimer's disease (AD). Current studies involve administering the amyloid beta peptide (Abeta) in Freund's complete adjuvant, which cannot be used in humans. Our studies show that the immune complex of Abeta is taken up by a receptor-mediated process at the blood-brain barrier (BBB). The success of immunization for AD, therefore, may be critically dependent on circulating Abeta levels which are lower in AD patients compared to AD transgenic mice. Moreover, we have found that modifying the antibody with polyamine increases its BBB permeability and may provide a better approach to passive immunization for Alzheimer's disease.     

The choroid plexus-cerebrospinal fluid interface in Alzheimer's disease:more than just a barrier

The choroid plexus is a complex structure which hangs inside the ventricles of the brain and consists mainly of choroid plexus epithelial(CPE) cells surrounding fenestrated capillaries.These CPE cells not only form an anatomical barrier,called the blood-cerebrospinal fluid barrier(BCSFB),but also present an active interface between blood and cerebrospinal fluid(CSF).CPE cells perform indispensable functions for the development,maintenance and functioning of the brain.Indeed,the primary role of the choroid plexus in the brain is to maintain homeostasis by secreting CSF which contains different molecules,such as nutrients,neurotrophins,and growth factors,as well as by clearing toxic and undesirable molecules from CSF.The choroid plexus also acts as a selective entry gate for leukocytes into the brain.Recent findings have revealed distinct changes in CPE cells that are associated with aging and Alzheimer's disease.In this review,we review some recent findings that highlight the importance of the CPE-CSF system in Alzheimer's disease and we summarize the recent advances in the regeneration of brain tissue through use of CPE cells as a new therapeutic strategy.     

Breakdown of the blood brain barrier and blood-cerebrospinal fluid barrier is associated with differential leukocyte migration in distinct compartments of the CNS during the course of murine NCC

Brain homeostasis is normally protected by the blood brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCB), barriers that function in distinct CNS compartments and consist of different types of blood vessels including pial (subarachnoid spaces, leptomeninges), parenchymal (cerebral cortex) and ventricular vessels. In this study, a mouse model of neurocysticercosis was used to distinguish between changes in the permeability of the BBB and the BCB and determine the association of such alterations on leukocyte infiltration. Mice were intracranially infected with the parasite Mesocestoides corti and sacrificed at various times post infection. Different anatomical areas of infected brain were analyzed by three color immunofluoresence utilizing antibodies against serum proteins to assess brain barrier permeability, glial fibrillary acidic protein (GFAP) to detect astrocytes, and specific cell surface markers to determine the subpopulations of leukocytes infiltrating the CNS at particular sites. The results indicate increased permeability of all three types of vessels/structural sites as a result of infection evidenced by serum proteins and leukocyte extravasation but with considerable differences in the timing and extent of these permeability changes. Parenchymal vessels were the most resilient to changes in permeability whereas pial vessels were the least. Choroid plexus vessels of the ventricles also appeared less susceptible to increased permeability compared with pial vessels. In addition, parenchymal vessels appeared impermeable to particular types of immune cells even after extended periods of infection. Additionally, alterations in reactive astrocytes juxtaposed to blood vessels that exhibited increased permeability displayed increased expression of cytokines known to regulate brain barrier function. The results suggest that access of leukocytes and serum derived factors into the infected brain depend on several parameters including the anatomical area, type of vascular bed, cell phenotype and cytokine microenvironment.     

Breakdown of the blood-cerebrospinal fluid barrier to immunoglobulin in mice injected intracerebrally with a neurotropic influenza A virus : Post-exposure treatment with monoclonal antibody promotes recovery

Mice may be protected from the invariably fatal consequences of intracerebral (i.c.) inoculation of A/WSN influenza virus by intravenous injection with 0.5 mg of virus-specific monoclonal anti-hemagglutinin antibody given 2 days after i.c. challenge. The integrity of the blood-cerebrospinal fluid (CSF) barrier in such mice has been examined by comparing specific immunoglobulin (Ig) titers in serum and CSF. It seems that the process of virus growth results directly in substantial breakdown of the blood-CSF barrier at some time between 63 and 96 h after i.c. exposure to virus. The exogenously administered, virus-specific monoclonal antibody is not obviously involved either in abrogating the integrity of this physiological barrier system or in promoting inflammation. In fact, higher Ig titers are found in CSF for an antibody that does not bind to the virus. This presumably reflects the fact that virus-infected cells in the central nervous system are adsorbing specific Ig from the CSF.     

Demonstration of a coupled metabolism-efflux process at the choroid plexus as a mechanism of brain protection toward xenobiotics.

Brain homeostasis depends on the composition of both brain interstitial fluid and CSF. Whereas the former is largely controlled by the blood-brain barrier, the latter is regulated by a highly specialized blood-CSF interface, the choroid plexus epithelium, which acts either by controlling the influx of blood-borne compounds, or by clearing deleterious molecules and metabolites from CSF. To investigate mechanisms of brain protection at the choroid plexus, the blood-CSF barrier was reconstituted in vitro by culturing epithelial cells isolated from newborn rat choroid plexuses of either the fourth or the lateral ventricle. The cells grown in primary culture on semipermeable membranes established a pure polarized monolayer displaying structural and functional barrier features, (tight junctions, high electric resistance, low permeability to paracellular markers) and maintaining tissue-specific markers (transthyretin) and specific transporters for micronutriments (amino acids, nucleosides). In particular, the high enzymatic drug metabolism capacity of choroid plexus was preserved in the in vitro blood-CSF interface. Using this model, we demonstrated that choroid plexuses can act as an absolute blood-CSF barrier toward 1-naphthol, a cytotoxic, lipophilic model compound, by a coupled metabolism-efflux mechanism. This compound was metabolized in situ via uridine diphosphate glururonosyltransferase-catalyzed conjugation, and the cellular efflux of the glucurono-conjugate was mediated by a transporter predominantly located at the basolateral, i.e., blood-facing membrane. The transport process was temperature-dependent, probenecid-sensitive, and recognized other glucuronides. Efflux of 1-naphthol metabolite was inhibited by intracellular glutathione S-conjugates. This metabolism-polarized efflux process adds a new facet to the understanding of the protective functions of choroid plexuses.