A human-derived neurovascular unit in vitro model to study the effects of cellular cross-talk and soluble factors on barrier integrity.

The blood-brain barrier (BBB) restricts paracellular and transcellular diffusion of compounds and is part of a dynamic multicellular structure known as the "neurovascular unit" (NVU), which strictly regulates the brain homeostasis and microenvironment. Several neuropathological conditions (e.g., Parkinson's disease and Alzheimer's disease), are associated with BBB impairment yet the exact underlying pathophysiological mechanisms remain unclear. In total, 90% of drugs that pass animal testing fail human clinical trials, in part due to inter-species discrepancies. Thus, in vitro human-based models of the NVU are essential to better understand BBB mechanisms; connecting its dysfunction to neuropathological conditions for more effective and improved therapeutic treatments. Herein, we developed a biomimetic tri-culture NVU in vitro model consisting of 3 human-derived cell lines: human cerebral micro-vascular endothelial cells (hCMEC/D3), human 1321N1 (astrocyte) cells, and human SH-SY5Y neuroblastoma cells. The cells were grown in Transwell hanging inserts in a variety of configurations and the optimal setup was found to be the comprehensive tri-culture model, where endothelial cells express typical markers of the BBB and contribute to enhancing neural cell viability and neurite outgrowth. The tri-culture configuration was found to exhibit the highest transendothelial electrical resistance (TEER), suggesting that the cross-talk between astrocytes and neurons provides an important contribution to barrier integrity. Lastly, the model was validated upon exposure to several soluble factors [e.g., Lipopolysaccharides (LPS), sodium butyrate (NaB), and retinoic acid (RA)] known to affect BBB permeability and integrity. This in vitro biological model can be considered as a highly biomimetic recapitulation of the human NVU aiming to unravel brain pathophysiology mechanisms as well as improve testing and delivery of therapeutics.

High Levels of Receptor Tyrosine Kinases in CCM3-Deficient Cells Increase Their Susceptibility to Tyrosine Kinase Inhibition.

Cerebral cavernous malformations (CCMs) are vascular malformations that can be the result of the deficiency of one of the CCM genes. Their only present treatment is surgical removal, which is not always possible, and an alternative pharmacological strategy to eliminate them is actively sought. We have studied the effect of the lack of one of the CCM genes, CCM3, in endothelial and non-endothelial cells. By comparing protein expression in control and CCM3-silenced cells, we found that the levels of the Epidermal Growth Factor Receptor (EGFR) are higher in CCM3-deficient cells, which adds to the known upregulation of Vascular Endothelial Growth Factor Receptor 2 (VEGFR2) in these cells. Whereas VEGFR2 is upregulated at the mRNA level, EGFR has a prolonged half-life. Inhibition of EGFR family members in CCM3-deficient cells does not revert the known cellular effects of lack of CCM genes, but it induces significantly more apoptosis in CCM3-deficient cells than in control cells. We propose that the susceptibility to tyrosine kinase inhibitors of CCM3-deficient cells can be harnessed to kill the abnormal cells of these lesions and thus treat CCMs pharmacologically.

Anti-TNFR1 targeting in humanized mice ameliorates disease in a model of multiple sclerosis.

Tumour necrosis factor (TNF) signalling is mediated via two receptors, TNF-receptor 1 (TNFR1) and TNF-receptor 2 (TNFR2), which work antithetically to balance CNS immune responses involved in autoimmune diseases such as multiple sclerosis. To determine the therapeutic potential of selectively inhibiting TNFR1 in mice with experimental autoimmune encephalomyelitis, we used chimeric human/mouse TNFR1 knock-in mice allowing the evaluation of antagonistic anti-human TNFR1 antibody efficacy. Treatment of mice after onset of disease with ATROSAB resulted in a robust amelioration of disease severity, correlating with reduced central nervous system immune cell infiltration. Long-term efficacy of treatment was achieved by treatment with the parental mouse anti-human TNFR1 antibody, H398, and extended by subsequent re-treatment of mice following relapse. Our data support the hypothesis that anti-TNFR1 therapy restricts immune cell infiltration across the blood-brain barrier through the down-regulation of TNF-induced adhesion molecules, rather than altering immune cell composition or activity. Collectively, we demonstrate the potential for anti-human TNFR1 therapies to effectively modulate immune responses in autoimmune disease.

Adenosine receptors regulate gap junction coupling of the human cerebral microvascular endothelial cells hCMEC/D3 by Ca2+ influx through cyclic nucleotide-gated channels.

KEY POINTS: Gap junction channels are essential for the formation and regulation of physiological units in tissues by allowing the lateral cell-to-cell diffusion of ions, metabolites and second messengers. Stimulation of the adenosine receptor subtype A2B increases the gap junction coupling in the human blood-brain barrier endothelial cell line hCMEC/D3. Although the increased gap junction coupling is cAMP-dependent, neither the protein kinase A nor the exchange protein directly activated by cAMP were involved in this increase. We found that cAMP activates cyclic nucleotide-gated (CNG) channels and thereby induces a Ca2+ influx, which leads to the increase in gap junction coupling. The report identifies CNG channels as a possible physiological link between adenosine receptors and the regulation of gap junction channels in endothelial cells of the blood-brain barrier. ABSTRACT: The human cerebral microvascular endothelial cell line hCMEC/D3 was used to characterize the physiological link between adenosine receptors and the gap junction coupling in endothelial cells of the blood-brain barrier. Expressed adenosine receptor subtypes and connexin (Cx) isoforms were identified by RT-PCR. Scrape loading/dye transfer was used to evaluate the impact of the A2A and A2B adenosine receptor subtype agonist 2-phenylaminoadenosine (2-PAA) on the gap junction coupling. We found that 2-PAA stimulated cAMP synthesis and enhanced gap junction coupling in a concentration-dependent manner. This enhancement was accompanied by an increase in gap junction plaques formed by Cx43. Inhibition of protein kinase A did not affect the 2-PAA-related enhancement of gap junction coupling. In contrast, the cyclic nucleotide-gated (CNG) channel inhibitor l-cis-diltiazem, as well as the chelation of intracellular Ca2+ with BAPTA, or the absence of external Ca2+ , suppressed the 2-PAA-related enhancement of gap junction coupling. Moreover, we observed a 2-PAA-dependent activation of CNG channels by a combination of electrophysiology and pharmacology. In conclusion, the stimulation of adenosine receptors in hCMEC/D3 cells induces a Ca2+ influx by opening CNG channels in a cAMP-dependent manner. Ca2+ in turn induces the formation of new gap junction plaques and a consecutive sustained enhancement of gap junction coupling. The report identifies CNG channels as a physiological link that integrates gap junction coupling into the adenosine receptor-dependent signalling of endothelial cells of the blood-brain barrier.

Effect of cigarette smoke on monocyte procoagulant activity: Focus on platelet-derived brain-derived neurotrophic factor (BDNF).

Cigarette smoke (CS) activates platelets, promotes vascular dysfunction, and enhances Tissue Factor (TF) expression in blood monocytes favoring pro-thrombotic states. Brain-derived neurotrophic factor (BDNF), a member of the family of neurotrophins involved in survival, growth, and maturation of neurons, is released by activated platelets (APLTs) and plays a role in the cardiovascular system. The effect of CS on circulating levels of BDNF is controversial and the function of circulating BDNF in atherothrombosis is not fully understood. Here, we have shown that human platelets, treated with an aqueous extract of CS (CSE), released BDNF in a dose-dependent manner. In addition, incubation of human monocytes with BDNF or with the supernatant of platelets activated with CSE increased TF activity by a Tropomyosin receptor kinase B (TrkB)-dependent mechanism. Finally, comparing serum and plasma samples of 12 male never smokers (NS) and 29 male active smokers (AS) we observed a significant increase in microparticle-associated TF activity (MP-TF) as well as BDNF in AS, while in serum, BDNF behaved oppositely. Taken together these findings suggest that platelet-derived BDNF is involved in the regulation of TF activity and that CS plays a role in this pathway by favoring a pro-atherothrombotic state.

Pivotal Role for CD16+ Monocytes in Immune Surveillance of the Central Nervous System.

Monocytes represent a heterogeneous population of primary immune effector cells. At least three different subsets can be distinguished based on expression of the low-affinity FcγRIII: CD14(++)CD16 -: classical monocytes, CD14(++)CD16(+) intermediate monocytes, and CD14(+)CD16 ++: non-classical monocytes. Whereas CD16 -: classical monocytes are considered key players in multiple sclerosis (MS), little is known on CD16(+) monocytes and how they contribute to the disease. In this study, we examined the frequency and phenotype of monocyte subpopulations in peripheral blood, cerebrospinal fluid (CSF), and brain biopsy material derived from MS patients and controls. Furthermore, we addressed a possible monocyte dysfunction in MS and analyzed migratory properties of monocyte subsets using human brain microvascular endothelial cells. Our ex vivo studies demonstrated that CD16(+) monocyte subpopulations are functional but numerically reduced in the peripheral blood of MS patients. CD16(+) monocytes with an intermediate-like phenotype were found to be enriched in CSF and dominated the CSF monocyte population under noninflammatory conditions. In contrast, an inversed CD16(+) to CD16 -: CSF monocyte ratio was observed in MS patients with relapsing-remitting disease. Newly infiltrating, hematogenous CD16(+) monocytes were detected in a perivascular location within active MS lesions, and CD16(+) monocytes facilitated CD4(+) T cell trafficking in a blood -: brain barrier model. Our findings support an important role of CD16(+) monocytes in the steady-state immune surveillance of the CNS and suggest that CD16(+) monocytes shift to sites of inflammation and contribute to the breakdown of the blood-brain barrier in CNS autoimmune diseases.

Serotype O18 avian pathogenic and neonatal meningitis Escherichia coli strains employ similar pathogenic strategies for the onset of meningitis.

Neonatal meningitis Escherichia coli K1 (NMEC) are thought to be transmitted from mothers to newborns during delivery or by nosocomial infections. However, the source of E. coli K1 causing these infections is not clear. Avian pathogenic E. coli (APEC) have the potential to cause infection in humans while human E. coli have potential to cause colibacillosis in poultry, suggesting that these strains may lack host specificity. APEC strains are capable of causing meningitis in newborn rats; however, it is unclear whether these bacteria use similar mechanisms to that of NMEC to establish disease. Using four representative APEC and NMEC strains that belong to serotype O18, we demonstrate that these strains survive in human serum similar to that of the prototypic NMEC strain E44, a derivative of RS218. These bacteria also bind and enter both macrophages and human cerebral microvascular endothelial cells (HCMEC/D3) with similar frequency as that of E44. The amino acid sequences of the outer membrane protein A (OmpA), an important virulence factor in the pathogenesis of meningitis, are identical within these representative APEC and NMEC strains. Further, these strains also require FcγRI-α chain (CD64) and Ecgp96 as receptors for OmpA in macrophages and HCMEC/D3, respectively, to bind and enter these cells. APEC and NMEC strains induce meningitis in newborn mice with varying degree of pathology in the brains as assessed by neutrophil recruitment and neuronal apoptosis. Together, these results suggest that serotype O18 APEC strains utilize similar pathogenic mechanisms as those of NMEC strains in causing meningitis.

Abnormal megakaryopoiesis and platelet function in cyclooxygenase-2-deficient mice.

Previous studies suggest that cyclooxygenase-2 (COX-2) might influence megakaryocyte (MK) maturation and platelet production in vitro. Using a gene deletion model, we analysed the effect of COX-2 deficiency on megakaryopoiesis and platelet function. COX-2-/- mice (10-12 weeks old) have hyper-responsive platelets as suggested by their enhanced aggregation, TXA2 biosynthesis, CD62P and CD41/CD61 expression, platelet-fibrinogen binding, and increased thromboembolic death after collagen/epinephrine injection compared to wild-type (WT). Moreover, increased platelet COX-1 expression and reticulated platelet fraction were observed in COX-2-/- mice while platelet count was similar to WT. MKs were significantly reduced in COX-2-/- bone marrows (BMs), with high nuclear/cytoplasmic ratios, low ploidy and poor expression of lineage markers of maturation (CD42d, CD49b). However, MKs were significantly increased in COX-2-/- spleens, with features of MK maturation markers which were not observed in MKs of WT spleens. Interestingly, the expression of COX-1, prostacyclin and PGE2 synthases and prostanoid pattern were modified in BMs and spleens of COX-2-/- mice. Moreover, COX-2 ablation reduced the percentage of CD49b+ cells, the platelet formation and the haematopoietic stem cells in bone marrow and increased their accumulation in the spleen. Splenectomy decreased peripheral platelet number, reverted their hyper-responsive phenotype and protected COX-2-/- mice from thromboembolism. Interestingly, fibrosis was observed in spleens of old COX-2-/- mice (28 weeks old). In conclusion, COX-2 deletion delays BM megakaryopoiesis promoting a compensatory splenic MK hyperplasia, with a release of hyper-responsive platelets and increased thrombogenicity in vivo. COX-2 seems to contribute to physiological MK maturation and pro-platelet formation.

Production of prostaglandin E2 induced by cigarette smoke modulates tissue factor expression and activity in endothelial cells.

Cigarette smoke (CS) increases the incidence of atherothrombosis, the release of prostaglandin (PG) E2, and the amount of tissue factor (TF). The link between PGE2 and TF, and the impact of this interaction on CS-induced thrombosis, is unknown. Plasma from active smokers showed higher concentration of PGE2, TF total antigen, and microparticle-associated TF (MP-TF) activity compared with never smokers. Similar results were obtained in mice and in mouse cardiac endothelial cells (MCECs) after treatment with aqueous CS extracts (CSEs) plus IL-1ß [CSE (6.4 puffs/L)/IL-1ß (2 µg/L)]. A significant correlation between PGE2 and TF total antigen or MP-TF activity were observed in both human and mouse plasma or tissue. Inhibition of PGE synthase reduced TF in vivo and in vitro and prevented the arterial thrombosis induced by CSE/IL-1ß. Only PG E receptor 1 (EP1) receptor antagonists (SC51089:IC50 ∼ 1 µM, AH6809:IC50 ∼ 7.5 µM) restored the normal TF and sirtuin 1 (SIRT1) levels in MCECs before PGE2 (EC50 ∼ 2.5 mM) or CSE/IL-1ß exposure. Similarly, SIRT1 activators (CAY10591: IC50 ∼ 10 µM, resveratrol: IC50 ∼ 5 µM) or prostacyclin analogs (IC50 ∼ 5 µM) prevented SIRT1 inhibition and reduced TF induced by CSE/IL-1ß or by PGE2. In conclusion, PGE2 increases both TF expression and activity through the regulation of the EP1/SIRT1 pathway. These findings suggest that EP1 may represent a possible target to prevent prothrombotic states.

Inflammatory response of endothelial cells to a human endogenous retrovirus associated with multiple sclerosis is mediated by TLR4.

The MSRV (multiple sclerosis-associated retrovirus) belongs to the human endogenous retrovirus HERV-W family. The envelope protein originating from the MSRV has been found in most patients with multiple sclerosis (MS). This protein (Env-ms) has pro-inflammatory properties for several types of immune cells and could therefore play a role in MS pathogenesis by promoting the leukocyte diapedesis observed in the central nervous system of patients. Our study aims to analyze the effects of Env-ms on the blood-brain barrier (BBB) at a molecular and functional level. We demonstrate that the recombinant MSRV envelope is able to stimulate several inflammatory parameters in a human BBB in vitro model, the HCMEC/D3 brain endothelial cell line. Indeed, Env-ms induces over-expression of ICAM-1, a major mediator of leukocyte adhesion to endothelial cells, in a dose-dependent manner as well as a strong dose-dependent production of the pro-inflammatory cytokines IL-6 and IL-8. Furthermore, using a silencing approach with siRNAs, we show that Env-ms is recognized via the Toll-like receptor 4 receptor, a pattern recognition receptor of innate immunity present on endothelial cells. We also show, using functional assays, that treatment of brain endothelial cells with Env-ms significantly stimulated the adhesion and the transmigration of activated immune cells through a monolayer of endothelial cells. These findings support the hypothesis that MSRV could be involved in the pathogenesis of MS disease or at least in maintenance of inflammatory conditions, thus fueling the auto-immune disorder. MSRV could also play a role in other chronic inflammatory diseases.

Permeability of PEGylated immunoarsonoliposomes through in vitro blood brain barrier-medulloblastoma co-culture models for brain tumor therapy.

PURPOSE: Owing to restricted access of pharmacological agents into the brain due to blood brain barrier (BBB) there is a need: 1. to develop a more representative 3-D-co-culture model of tumor-BBB interaction to investigate drug and nanoparticle transport into the brain for diagnostic and therapeutic evaluation. 2. to address the lack of new alternative methods to animal testing according to replacement-reduction-refinement principles. In this work, in vitro BBB-medulloblastoma 3-D-co-culture models were established using immortalized human primary brain endothelial cells (hCMEC/D3). METHODS: hCMEC/D3 cells were cultured in presence and in absence of two human medulloblastoma cell lines on Transwell membranes. In vitro models were characterized for BBB formation, zonula occludens-1 expression and permeability to dextran. Transferrin receptors (Tfr) expressed on hCMEC/D3 were exploited to facilitate arsonoliposome (ARL) permeability through the BBB to the tumor by covalently attaching an antibody specific to human Tfr. The effect of anticancer ARLs on hCMEC/D3 was assessed. RESULTS: In vitro BBB and BBB-tumor co-culture models were established successfully. BBB permeability was affected by the presence of tumor aggregates as suggested by increased permeability of ARLs. There was a 6-fold and 8-fold increase in anti-Tfr-ARL uptake into VC312R and BBB-DAOY co-culture models, respectively, compared to plain ARLs. CONCLUSION: The three-dimensional models might be appropriate models to study the transport of various drugs and nanocarriers (liposomes and immunoarsonoliposomes) through the healthy and diseased BBB. The immunoarsonoliposomes can be potentially used as anticancer agents due to good tolerance of the in vitro BBB model to their toxic effect.

The poorly membrane permeable antipsychotic drugs amisulpride and sulpiride are substrates of the organic cation transporters from the SLC22 family.

Variations in influx transport at the blood-brain barrier might affect the concentration of psychotropic drugs at their site of action and as a consequence might alter therapy response. Furthermore, influx transporters in organs such as the gut, liver and kidney may influence absorption, distribution, and elimination. Here, we analyzed 30 commonly used psychotropic drugs using a parallel artificial membrane permeability assay. Amisulpride and sulpiride showed the lowest membrane permeability (P e < 1.5 × 10(-6) cm/s) and will require influx transport to penetrate the blood-brain barrier and other physiological barriers. We then studied the uptake of amisulpride and sulpiride by the organic cation transporters of the SLC22 family OCT1, OCT2, OCT3, OCTN1, and OCTN2 Amisulpride was found to be transported by all five transporters studied. In contrast, sulpiride was only transported by OCT1 and OCT2. OCT1 showed the highest transport ability both for amisulpride (CLint = 1.9 ml/min/mg protein) and sulpiride (CLint = 4.2 ml/min/mg protein) and polymorphisms in OCT1 significantly reduced the uptake of both drugs. Furthermore, we observed carrier-mediated uptake that was inhibitable by known OCT inhibitors in the immortalized human brain microvascular endothelial cell line hCMEC/D3. In conclusion, this study demonstrates that amisulpride and sulpiride are substrates of organic cation transporters of the SLC22 family. SLC22 transporters may play an important role in the distribution of amisulpride and sulpiride, including their ability to penetrate the blood-brain barrier.

Synthesis and in vitro evaluation of BBB permeability, tumor cell uptake, and cytotoxicity of a series of carboranylporphyrin conjugates.

A series of tri[(p-carboranylmethylthio)tetrafluorophenyl]porphyrin conjugates of linear and branched polyamines, glucose, arginine, tri(ethylene glycol), and Tyr-D-Arg-Phe-ß-Ala (YRFA) peptide were synthesized. These conjugates were investigated for their BBB permeability in human hCMEC/D3 brain endothelial cells, and their cytotoxicity and uptake were assessed using human glioma T98G cells. For comparison purposes, a symmetric tetra[(p-carboranylmethylthio)tetrafluorophenyl]porphyrin was also synthesized, and its crystal structure was obtained. All porphyrin conjugates show low dark cytotoxicity (IC50>400 µM) and low phototoxicity (IC50>100 µM at 1.5 J/cm2) toward T98G cells. All conjugates were efficiently taken up by T98G cells, particularly the cationic polyamine and arginine conjugates, and were localized in multiple cellular organelles, including mitochondria and lysosomes. All compounds showed relatively low in vitro BBB permeability compared with that of lucifer yellow because of their higher molecular weight, hydrophobicity, and tendency for aggregation in solution. Within this series, the branched polyamine and YRFA conjugates showed the highest permeability coefficient, whereas the glucose conjugate showed the lowest permeability coefficient.

Oxidative and pro-inflammatory impact of regular and denicotinized cigarettes on blood brain barrier endothelial cells: is smoking reduced or nicotine-free products really safe?

BACKGROUND: Both active and passive tobacco smoke (TS) potentially impair the vascular endothelial function in a causative and dose-dependent manner, largely related to the content of reactive oxygen species (ROS), nicotine, and pro-inflammatory activity. Together these factors can compromise the restrictive properties of the blood-brain barrier (BBB) and trigger the pathogenesis/progression of several neurological disorders including silent cerebral infarction, stroke, multiple sclerosis and Alzheimer's disease. Based on these premises, we analyzed and assessed the toxic impact of smoke extract from a range of tobacco products (with varying levels of nicotine) on brain microvascular endothelial cell line (hCMEC/D3), a well characterized human BBB model. RESULTS: Initial profiling of TS showed a significant release of reactive oxygen (ROS) and reactive nitrogen species (RNS) in full flavor, nicotine-free (NF, "reduced-exposure" brand) and ultralow nicotine products. This release correlated with increased oxidative cell damage. In parallel, membrane expression of endothelial tight junction proteins ZO-1 and occludin were significantly down-regulated suggesting the impairment of barrier function. Expression of VE-cadherin and claudin-5 were also increased by the ultralow or nicotine free tobacco smoke extract. TS extract from these cigarettes also induced an inflammatory response in BBB ECs as demonstrated by increased IL-6 and MMP-2 levels and up-regulation of vascular adhesion molecules, such as VCAM-1 and PECAM-1. CONCLUSIONS: In summary, our results indicate that NF and ultralow nicotine cigarettes are potentially more harmful to the BBB endothelium than regular tobacco products. In addition, this study demonstrates that the TS-induced toxicity at BBB ECs is strongly correlated to the TAR and NO levels in the cigarettes rather than the nicotine content.

Endotoxin-induced monocytic microparticles have contrasting effects on endothelial inflammatory responses.

Septic shock is a severe disease state characterised by the body's life threatening response to infection. Complex interactions between endothelial cells and circulating monocytes are responsible for microvasculature dysfunction contributing to the pathogenesis of this syndrome. Here, we intended to determine whether microparticles derived from activated monocytes contribute towards inflammatory processes and notably vascular permeability. We found that endotoxin stimulation of human monocytes enhances the release of microparticles of varying phenotypes and mRNA contents. Elevated numbers of LPS-induced monocytic microparticles (mMP) expressed CD54 and contained higher levels of transcripts for pro-inflammatory cytokines such as TNF, IL-6 and IL-8. Using a prothrombin time assay, a greater reduction in plasma coagulation time was observed with LPS-induced mMP than with non-stimulated mMP. Co-incubation of mMP with the human brain endothelial cell line hCMEC/D3 triggered their time-dependent uptake and significantly enhanced endothelial microparticle release. Unexpectedly, mMP also modified signalling pathways by diminishing pSrc (tyr416) expression and promoted endothelial monolayer tightness, as demonstrated by endothelial impedance and permeability assays. Altogether, these data strongly suggest that LPS-induced mMP have contrasting effects on the intercellular communication network and display a dual potential: enhanced pro-inflammatory and procoagulant properties, together with protective function of the endothelium.

CXCL1/CXCL8 (GROα/IL-8) in human diabetic ketoacidosis plasma facilitates leukocyte recruitment to cerebrovascular endothelium in vitro.

Diabetic ketoacidosis (DKA) in children is associated with intracranial vascular complications, possibly due to leukocyte-endothelial interactions. Our aim was to determine whether DKA-induced inflammation promoted leukocyte adhesion to activated human cerebrovascular endothelium. Plasma was obtained from children with type 1 diabetes either in acute DKA or in an insulin-controlled state (CON). Plasma concentrations of 21 inflammatory analytes were compared between groups. DKA was associated with altered circulating levels of ↑CXCL1 (GROα), ↑CXCL8 (IL-8), ↑IL-6, ↑IFNα2, and ↓CXCL10 (IP-10) compared with CON. These plasma analyte measurements were then used to create physiologically relevant cytokine mixtures (CM). Human cerebral microvascular endothelial cells (hCMEC/D3) were stimulated with either plasma (DKA-P or CON-P) or CM (DKA-CM or CON-CM) and assessed for polymorphonuclear leukocyte (PMN) adhesion. Stimulation of hCMEC/D3 with DKA-P or DKA-CM increased PMN adhesion to hCMEC/D3 under "flow" conditions. PMN adhesion to hCMEC/D3 was suppressed with neutralizing antibodies to CXCL1/CXCL8 or their hCMEC/D3 receptors CXCR1/CXCR2. DKA-P, but not DKA-CM, initiated oxidative stress in hCMEC/D3. Expression of ICAM-1, VCAM-1, and E-selectin were unaltered on hCMEC/D3 by either DKA-P or DKA-CM. In summary, DKA elicits inflammation in children associated with changes in circulating cytokines/chemokines. Increased CXCL1/CXCL8 instigated PMN adhesion to hCMEC/D3, possibly contributing to DKA-associated intracranial vascular complications.

Differences in amyloid-ß clearance across mouse and human blood-brain barrier models: kinetic analysis and mechanistic modeling.

Alzheimer's disease (AD) has a characteristic hallmark of amyloid-ß (Aß) accumulation in the brain. This accumulation of Aß has been related to its faulty cerebral clearance. Indeed, preclinical studies that used mice to investigate Aß clearance showed that efflux across blood-brain barrier (BBB) and brain degradation mediate efficient Aß clearance. However, the contribution of each process to Aß clearance remains unclear. Moreover, it is still uncertain how species differences between mouse and human could affect Aß clearance. Here, a modified form of the brain efflux index method was used to estimate the contribution of BBB and brain degradation to Aß clearance from the brain of wild type mice. We estimated that 62% of intracerebrally injected (125)I-Aß40 is cleared across BBB while 38% is cleared by brain degradation. Furthermore, in vitro and in silico studies were performed to compare Aß clearance between mouse and human BBB models. Kinetic studies for Aß40 disposition in bEnd3 and hCMEC/D3 cells, representative in vitro mouse and human BBB models, respectively, demonstrated 30-fold higher rate of (125)I-Aß40 uptake and 15-fold higher rate of degradation by bEnd3 compared to hCMEC/D3 cells. Expression studies showed both cells to express different levels of P-glycoprotein and RAGE, while LRP1 levels were comparable. Finally, we established a mechanistic model, which could successfully predict cellular levels of (125)I-Aß40 and the rate of each process. Established mechanistic model suggested significantly higher rates of Aß uptake and degradation in bEnd3 cells as rationale for the observed differences in (125)I-Aß40 disposition between mouse and human BBB models. In conclusion, current study demonstrates the important role of BBB in the clearance of Aß from the brain. Moreover, it provides insight into the differences between mouse and human BBB with regards to Aß clearance and offer, for the first time, a mathematical model that describes Aß clearance across BBB.

Oligodendrocyte progenitor cells promote neovascularization in glioma by disrupting the blood-brain barrier.

Enhanced platelet-derived growth factor (PDGF) signaling in glioma drives its development and progression. In this study, we define a unique role for stroma-derived PDGF signaling in maintaining tumor homeostasis within the glioma microenvironment. Large numbers of PDGF receptor-α (PDGFRα)-expressing stromal cells derived from oligodendrocytes progenitor cells (OPC) were discovered at the invasive front of high-grade gliomas, in which they exhibited a unique perivascular distribution. In PDGFRα-deficient host mice, in which orthotopic Gl261 tumors displayed reduced outgrowth, we found that tumor-associated blood vessels displayed smaller lumens and normalized vascular morphology, with tumors in host animals injected with the vascular imaging agent gadolinium also being enhanced less avidly by MRI. Notably, glioma-associated OPC promoted endothelial sprouting and tubule formation, in part by abrogating the inhibitory effect that perivascular astrocytes exert on vascular endothelial conjunctions. Stromal-derived PDGF-CC was crucial for the recruitment and activation of OPC, insofar as mice genetically deficient in PDGF-CC phenocopied the glioma/vascular defects observed in PDGFRα-deficient mice. Clinically, we showed that higher levels of PDGF-CC in glioma specimens were associated with more rapid disease recurrence and poorer overall survival. Our findings define a PDGFRα/PDGF-CC signaling axis within the glioma stromal microenvironment that contributes to vascular remodeling and aberrant tumor angiogenesis in the brain.

A recombinant inhibitory isoform of vascular endothelial growth factor164/165 aggravates ischemic brain damage in a mouse model of focal cerebral ischemia.

Vascular endothelial growth factors (VEGF) are a Janus-faced family of growth factors exerting both neuroprotective and maladaptive effects on the blood-brain barrier. For example, VEGFs are beneficial in promoting postischemic brain angiogenesis, but the newly formed vessels are leaky. We investigated the role of the naturally occurring murine inhibitory VEGF isoform VEGF165b in a mouse model of focal cerebral ischemia by middle cerebral artery occlusion and reperfusion (I/R) in male C57BL/6 mice. We investigated the roles of VEGF164/165 and VEGF165b in both brain and nonbrain endothelial barrier, angiogenesis, and neutrophil migration using oxygen glucose deprivation and reoxygenation as in vitro model. We investigated the role of VEGF165b in brain edema, neutrophil infiltration, ischemic brain damage, and neuronal death in vivo using an adenovirus encoding a recombinant VEGF164b isoform. Neither VEGF164/165 nor VEGF165b significantly altered brain endothelial barrier or angiogenesis in vitro. However, treatment of brain endothelial cells with VEGF165b increased neutrophil migration in vitro and exacerbated stroke injury by aggravating neutrophil infiltration and neurodegeneration in vivo. Our results indicate that alterations in the delicate balance in the relative levels of pro- and antiangiogenic VEGF isoforms can result in either adaptive or detrimental effects, depending on the VEGF isoform levels and on the duration and extent of injury.

Somatostatin preserved blood brain barrier against cytokine induced alterations: possible role in multiple sclerosis.

Multiple sclerosis (MS) is an inflammatory neurological disorder associated with demyelination, impaired blood brain barrier (BBB), axonal damage and neuronal loss. In the present study, we measured somatostatin (SST) and tumor necrosis factor-α (TNF-α) like immunoreactivity in CSF samples from MS and non-MS patients. We also examined the role of SST in cytokines and lipopolysaccharide (LPS)-induced damage to the BBB using human brain endothelial cells in culture. Most of the cerebrospinal fluid (CSF) samples studied from definite MS patients exhibited lower somatostatin (SST)-like immunoreactivity and higher expression of TNF-α in comparison to non-MS patients. Treatment of cells with cytokines and LPS blocked SST secretion and decreased SST expression. Human brain endothelial cells expressed all five somatostatin receptors (SSTRs) with increased expression of SSTR2 and 4 upon treatment with cytokines and LPS. Cytokines and LPS-induced disruption of the tight junction proteins Zonula occludens (ZO-1) organization was restored in presence of SST, SSTR2 or SSTR4 selective agonists. Furthermore, inflammation induced changes in extracellular signal-regulated kinases (ERK1/2 and ERK5) signaling and altered expression of endothelial and inducible nitric oxide synthase are modulated in presence of SST. These data indicate that decreased levels of SST contribute to failure of the BBB in MS.