Long-term serial cultivation of arterial and capillary endothelium from adult bovine brain

Dissecting gene expression at the blood-brain barrier

The availability of genome-wide expression data for the blood-brain barrier is an invaluable resource that has recently enabled the discovery of several genes and pathways involved in the development and maintenance of the blood-brain barrier, particularly in rodent models. The broad distribution of published data sets represents a viable starting point for the molecular dissection of the blood-brain barrier and will further direct the discovery of novel mechanisms of blood-brain barrier formation and function. Technical advances in purifying brain endothelial cells, the key cell that forms the critical barrier, have allowed for greater specificity in gene expression comparisons with other central nervous system cell types, and more systematic characterizations of the molecular composition of the blood-brain barrier. Nevertheless, our understanding of how the blood-brain barrier changes during aging and disease is underrepresented. Blood-brain barrier data sets from a wider range of experimental paradigms and species, including invertebrates and primates, would be invaluable for investigating the function and evolution of the blood-brain barrier. Newer technologies in gene expression profiling, such as RNA-sequencing, now allow for finer resolution of transcriptomic changes, including isoform specificity and RNA-editing. As our field continues to utilize more advanced expression profiling in its ongoing efforts to elucidate the blood-brain barrier, including in disease and drug delivery, we will continue to see rapid advances in our understanding of the molecular mediators of barrier biology. We predict that the recently published data sets, combined with forthcoming genomic and proteomic blood-brain barrier data sets, will continue to fuel the molecular genetic revolution of blood-brain barrier biology.

The biocompatibility of a polyelectrolyte vitreous body substitute on a high resistance in vitro model of the blood-retinal barrier

The vitreous body can be regarded as a fascinating simple but important tissue, since it represents the main compartment of the eye and plays a crucial role for proper vision. Several diseases require its removal with following substitution using a liquid artificial vitreous body replacement. We explore the biocompatibility of a poly(AMPS-Na+)-graft-poly(NIPAAm) polyelectrolyte following the innovative concept of thermo-responsive behaviour, exhibiting enhanced shear viscosity at physiological temperatures. As a powerful model for the blood-retinal barrier, we use the well-established in vitro cell culture model based on highly differentiated porcine brain capillary endothelial cells. Via the quantification of the transendothelial electrical resistance and immunocytochemical staining of tight junction proteins, we are able to show that a barrier integrity affecting impact of the polyelectrolyte was only transient and nearly reversible. Furthermore, the polyelectrolyte hydrogel is characterized by the absence of any acute cell morphology, cell vitality or proliferation affecting impacts. It does not trigger acute apoptotic processes, as can be substantiated via caspase-3 activity and DNA fragmentation assays. In view of the results of this study, it is shown that the polyelectrolyte does not affect the vitality parameters of our porcine brain capillary endothelial cells. It can be suggested that the tested thermo-responsive polyelectrolyte does not affect the sensitive retinal barrier integrity. Thus from the cellular tolerance it might serve as a potential liquid artificial vitreous body replacement to overcome the most prominent difficulties of common vitreal endotamponades.

A model for transport studies of the blood-brain barrier

The blood-brain barrier (BBB) is the cellular structure between the blood flowing through the brain and the parenchymal tissues of the brain. This physiological barrier is formed by the endothelial cells of the capillary walls. It exquisitely regulates the passage of substances into and out of the brain. Astrocytes (astroglial cells) signal the endothelial cells to adopt BBB characteristics. An in vitro BBB model can be very useful for the study of the nutrition, physiology, and pharmacology of the brain. We took advantage of numerous advances made by previous researchers in this field to develop a co-culture BBB model. Capillary endothelial cells and astrocytes are isolated from the brains of miniature swine and grown on permeable membranes suspended between two chambers of media: analogous to the capillary lumen and the interstitium of the brain, respectively. The endothelial cell isolation procedure includes mechanical and enzymatic digestion of the brain tissue followed by separation of the capillary fragments, based on size and density, from other brain cells. Astrocytes are purified from these "other" cells. The endothelial cells of the capillary fragments proliferate in culture flasks and are then seeded onto the upper surface of a polycarbonate semi-permeable membrane suspended between two chambers of fluid. Astrocytes are seeded on the underside of the membranes. Their close proximity enables the astrocytes to communicate with the endothelial cells and encourage their expression of BBB characteristics without disrupting the endothelial cell monolayer. Transport studies across the monolayer can be conducted by introducing test compounds into the media on one side and observing its appearance on the other side. Mechanisms of transport can also be studied.

Models for Angiogenesis in Gliomas

During the last decades a lot of attention has been focussed on mechanisms of glioma vascularization, particularly in terms of investigating vascular growth factors and receptors. Recently, these efforts resulted in various approaches for antiangiogenic treatment strategies using in vitro cell culture systems as well as experimental orthotopic and non-orthotopic brain tumors. These basic science and preclinical trials need an assortment of models, which should allow investigating a variety of questions. Several objectives concerning basic endothelial cell (EC) characteristics can adequately be studied in vitro using EC monolayer assays. Three-dimensional spheroid techniques respect the more complex cell-cell and cell-environment interplay within a 3-dimensional culture. Recent advances in molecular genetic techniques offer a wide access to the genome of EC. Using these micro array or chip methods differences between micro- and macromolecular EC as well as variations within the gene pool of different organ specific EC can be assessed. To optimize the imitation of the crucial interaction of human gliomas with host endothelial cells, immunological cells and extracellular matrix, animal models are mandatory. An essential rule is to utilize an orthotopic model, since tumor-host-interaction is organ specific. To avoid alloimmunogenic responses, it is desirable to use weak or non-immunogenic glioma grafts, which is best accomplished in a syngeneic model. However, since rat gliomas poorly resemble human glioma growth patterns, human glioma xenografting into immunocompromized animals should be considered. In vivo-monitoring techniques like videoscopy via a cranial window or magnetic resonance imaging (MRI) allow for functional studies and improve the validity of the model employed. Finally, it is essentially to recognize the limitations of each model considered and to select that model which seems to be most appropriate for the objectives to be investigated.

Antiangiogenic therapy against experimental glioblastoma using genetically engineered cells producing interferon-alpha, angiostatin, or endostatin

Inhibition of angiogenesis has been considered among the most promising approaches to treat highly vascularized solid tumors such as glioblastoma. In this study, we designed and validated a new in vitro assay system based on the implantation of tumor cells into organotypic brain slice cultures. We evaluated the effects of local production of three endogenous inhibitors of angiogenesis, angiostatin, endostatin, and interferon (IFN)-alpha(1), using stably transfected rat (9L) and human (GL15) glioblastoma cells on tumor vascularization and growth. Despite similar effectiveness of the three proteins in a classic in vitro endothelial cell migration assay, IFN-alpha(1) demonstrated the most potent antiangiogenic effect in organotypic brain slice cultures. In vivo, after intracerebral implantation of such genetically modified glioblastoma cells, IFN-alpha(1) caused a dramatic decrease in tumor volume revealed by magnetic resonance imaging and by postmortem histology. The mechanisms of this antitumor effect were most likely caused by the major antiangiogenic action of the cytokine, because IFN-alpha(1) expression provoked a pronounced decrease in blood vessel density, which was accompanied by extensive necrosis in the body mass of the tumors. The median survival time of rats implanted intracerebrally with IFN-alpha-expressing 9L cells tripled, and was still significantly increased when these constituted only 1% of transplanted tumor cells. A similar effect was seen when 50% of the transplanted cells were replaced by IFN-alpha-expressing bone marrow stromal cells. These data point to the local delivery of IFN-alpha(1) using cell vectors as a potent tool for the inhibition of tumor-induced angiogenesis.

Adrenomedullin, an autocrine mediator of blood-brain barrier function

Since the discovery that adrenomedullin gene expression is 20- to 40-fold higher in endothelial cells than even in the adrenal medulla, this peptide has been regarded as an important secretory product of the vascular endothelium, together with nitric oxide, eicosanoids, endothelin-1, and other vasoactive metabolites. Cerebral endothelial cells secrete an exceptionally large amount of adrenomedullin, and the adrenomedullin concentration is about 50% higher in the cerebral circulation than in the peripheral vasculature. The adrenomedullin production of cerebral endothelial cells is induced by astrocyte-derived factors. Adrenomedullin causes vasodilation in the cerebral circulation, may participate in the maintenance of the resting cerebral blood flow, and may be protective against ischemic brain injury. Recent data from our laboratory indicate that adrenomedullin, as an endothelium-derived autocrine/paracrine hormone, plays an important role in the regulation of specific blood-brain barrier properties. Adrenomedullin is suggested to be one of the physiological links between astrocyte-derived factors, cyclic adenosine 3'5'-monophosphate (cAMP), and the induction and maintenance of the blood-brain barrier. Moreover, the role of adrenomedullin in the differentiation and proliferation of endothelial cells and in angiogenesis suggests a more complex function for adrenomedullin in the cerebral circulation and in the development of the blood-brain barrier.

Cellular mechanisms of microbial proteins contributing to invasion of the blood-brain barrier

One of the least understood issues in the pathogenesis and pathophysiology of microbial infection of the central nervous system (CNS) is how microorganisms cross the blood-brain barrier (BBB), which separates brain interstitial space from blood and is formed by the tight junctions of brain microvascular endothelial cells (BMEC). BMEC monolayer and bilayer culture systems have been developed as in vitro models to dissect the mechanisms of adhesion and invasion involved in pathogenesis of CNS infection caused by microbes. Viral, bacterial, fungal and parasitic pathogens may breach the BBB and enter the CNS through paracellular, transcellular and/or Trojan horse mechanisms. Conceivable evidence suggests that microbial proteins are the major genetic determinants mediating penetration across the BBB. Several bacterial proteins including IbeA, IbeB, AslA,YijP, OmpA, PilC and InlB contribute to transcellular invasion of BMEC. Viral proteins such as gp120 of HIV have been shown to play a role in penetration of the BBB. Fungal and parasitic pathothogens may follow similar mechanisms. SAG1 of Toxoplasma gondii has been suggested as a ligand to mediate host-cell invasion. Understanding the fundamental mechanisms of microbial penetration of the BBB may help develop novel approaches to prevent the mortality and morbidity associated with central nervous system (CNS) infectious diseases.

Bacterial invasion and transcytosis in transfected human brain microvascular endothelial cells

Most cases of neonatal bacterial meningitis develop as a result of a hematogenous spread, but it is not clear how circulating bacteria cross the blood-brain barrier. Attempts to answer these questions have been hampered by the lack of a reliable model of the human blood-brain barrier. Human brain microvascular endothelial cells (HBMEC) were isolated and transfected with a pBR322 based plasmid containing simian virus 40 large T antigen (SV40-LT). The transfected HBMEC exhibited similar brain endothelial cell characteristics as the primary HBMEC, i.e. gamma glutamyl transpeptidase and a high transendothelial electrical resistance. Escherischia coli and Citrobacter spp, two important Gram-negative bacilli causing neonatal meningitis, were found to transcytose across primary and transfected HBMEC, without affecting the integrity of the monolayer. In addition, E. coli and C. freundii invaded transfected HBMEC as shown previously with primary HBMEC. We conclude that E. coli and C. freundii are able to invade and transcytose HBMEC and these bacterial-HBMEC interactions are similar between primary and transfected HBMEC. Therefore, our transfected HBMEC should be useful for studying pathogenesis of CNS infections.

Models for assessment of angiogenesis in gliomas

In the last two decades, much attention has been focussed on mechanisms of glioma vascularization including the investigation of growth factors and receptors involved. Recently, these efforts resulted in various approaches for antiangiogenic treatment of experimental brain tumors. These basic science and preclinical trials need an assortment of models, which should allow investigating a variety of questions. Several objectives concerning basic endothelial cell (EC) characteristics can adequately be studied in vitro using EC monolayer assays. Three-dimensional spheroid techniques respect the more complex cell-cell and cell-environment interplay within a three-dimensional culture. To optimize the imitation of the crucial interaction of human gliomas with host endothelial cells, immunological cells and extracellular matrix, animal models are mandatory. An essential rule is to utilize an orthotopic model, since tumor-host interaction is organ specific. To avoid alloimmunogenic responses, it is desirable to use weakly or not immunogenic glioma grafts, what is best accomplished in a syngeneic model. However, since rat gliomas poorly resemble human glioma growth patterns, human glioma xenografting into immunocompromized animals should be considered. In vivo monitoring techniques like videoscopy via a cranial window or magnetic resonance imaging (MRI) allow for functional studies and improve the validity of the model employed. Finally, it is essentially to recognize the limitations of each model considered and to select that model, which seems to be most appropriate for the objectives to be investigated.

Bacterial penetration across the blood-brain barrier during the development of neonatal meningitis

Bacterial pathogens may breach the blood-brain barrier (BBB) and invade the central nervous system through paracellular and/or transcellular mechanisms. Transcellular penetration, e.g., transcytosis across the BBB has been demonstrated for Escherichia coli K1, group B streptococcus, Listeria monocytogenes, Citrobacter freundii and Streptococcus pneumonia strains. Genes contributing to invasion of brain microvascular endothelial cells include E. coli K1 genes ompA, ibeA, ibeB, and yijP. Understanding the mechanisms of bacterial penetration across the BBB may help develop novel approaches to preventing bacterial meningitis.

Reoxygenation injury of human brain capillary endothelial cells

1. Many studies have demonstrated that endothelial cells from several species can generate oxygen free radicals when subjected to anoxia and reoxygenation. However, due to the heterogeneity of the endothelium within different organs and species, the effects of superoxide dismutase (SOD), catalase, and allopurinol on reoxygenated cultured cells remain quite controversial. 2. This review outlines the possible sources of oxygen free radicals within brain endothelial cells. 3. We examine the aspects of the effects of SOD catalase and allopurinol on cultured human brain capillary endothelial cells upon reoxygenation. 4. Also, we introduce briefly a method of culturing human brain capillary endothelial cells and present our experimental results on the effects of SOD, catalase, and allopurinol in these cultured cells following anoxia and reoxygenation.

Identification of chondromodulin I as a novel endothelial cell growth inhibitor. Purification and its localization in the avascular zone of epiphyseal cartilage

Cartilage is unique among tissues of mesenchymal origin in that it is resistant to vascular invasion due to an intrinsic angiogenic inhibitor. During endochondral bone formation, however, calcified cartilage formed in the center of the cartilaginous bone rudiment allows vascular invasion, which initiates the replacement of cartilage by bone. The transition of cartilage from the angioresistant to the angiogenic status thus plays a key role in bone formation. However, the molecular basis of this phenotypic transition of cartilage has been obscure. We report here purification of an endothelial cell growth inhibitor from a guanidine extract of bovine epiphyseal cartilage. The N-terminal amino acid sequence indicated that the inhibitor was identical to chondromodulin I (ChM-I), a cartilage-specific growth-modulating factor. Purified ChM-I inhibited DNA synthesis and proliferation of vascular endothelial cells as well as tube morphogenesis in vitro. Expression of ChM-I cDNA in COS7 cells indicated that mature ChM-I molecules were secreted from the cells after post-translational modifications and cleavage from the transmembrane precursor at the predicted processing signal. Recombinant ChM-I stimulated DNA synthesis and proteoglycan synthesis of cultured growth plate chondrocytes, but inhibited tube morphogenesis of endothelial cells. In situ hybridization and immunohistochemical studies indicated that ChM-I is specifically expressed in the avascular zone of cartilage in developing bone, but not present in calcifying cartilage. These results suggest a regulatory role of ChM-I in vascular invasion during endochondral bone formation.

Selective expression of adhesion molecules on human brain microvascular endothelial cells

Human microvascular endothelial cells were isolated from children's brain and examined for their morphological characteristics and upregulation of cell adhesion molecules in response to TNF alpha. Our human brain microvascular endothelial cells (HBMEC) were positive for factor VIII-Rag, carbonic anhydrase IV, Ulex Europeus Agglutinin I, took up fluorescently labeled acetylated low density lipoprotein and expressed gamma glutamyl transpeptidase, demonstrating their brain endothelial cell characteristics. Upon treatment with TNF alpha. VCAM and ICAM but little ELAM was expressed on HBMEC, while VCAM, ICAM and ELAM were clearly evident on HUVEC. This selective expression of cell adhesion molecules was also demonstrated by in situ stimulation of brain tissues. In conclusion, microvascular endothelial cells from childrens brains display selective expression of cell adhesion molecules, which differ from macrovascular endothelial cells. This may have consequences for leukocyte trafficking into the central nervous system.

Isolation and culture of bovine intracranial arterial endothelial cells

We report a simple explant technique to isolate and propagate endothelial cells from bovine cerebral arteries. The endothelial nature of the cells was confirmed by the presence of Factor VIII/von Willebrand antigen, the ability to phagocytize low-density lipoprotein, and the ability to be induced to express E-selectin. The lack of expression of the CD11c antigen and the absence of smooth muscle alpha-actin immunofluorescence suggested that the cultures were not contaminated with macrophages or smooth muscle cells, respectively. This technique yields pure cerebral arterial endothelial cell cultures, which will be of value for in vitro investigation of cerebrovascular physiology and disease processes.

Bactericidal/permeability-increasing protein protects vascular endothelial cells from lipopolysaccharide-induced activation and injury

Bactericidal/permeability-increasing protein (BPI), a human neutrophil granule protein, has been shown to bind lipopolysaccharide (LPS) and neutralize LPS-mediated cytokine production in adherent monocytes and the whole-blood system. In this study we investigated the ability of recombinant human BPI (rBPI) to inhibit LPS-induced vascular endothelial cell (EC) injury and activation. rBPI inhibited significantly both rough and smooth LPS-mediated injury for cultured bovine brain microvessel ECs, as measured by lactic dehydrogenase release, and blocked the LPS-induced interleukin-6 (IL-6) release from human umbilical vein ECs in a dose-dependent manner. BPI was able to inhibit LPS-mediated EC injury or activation whether it was added before or at the same time with LPS, but delaying the time of addition of rBPI resulted only in a partial inhibition. BPI also inhibited LPS-induced tumor necrosis factor alpha, IL-1 beta, and IL-6 release from human whole blood. This inhibition of tumor necrosis factor alpha, IL-1 beta, and IL-6 release from whole blood was maximal when BPI was premixed with LPS before addition to blood and was partial when BPI was added simultaneously with LPS, but no inhibition was observed when the addition of rBPI was delayed for 5 min. These findings suggest that rBPI is a potent inhibitor of LPS-mediated responses in ECs and whole blood and underscore the potential use of BPI in treatment or prevention of endotoxic shock. In contrast, the anti-lipid A monoclonal antibodies HA-1A and E5 were ineffective in inhibiting LPS-mediated EC injury and activation as well as LPS-induced cytokine release in whole blood.

Biochemical characteristics of primary and passaged cultures of primate brain microvessel endothelial cells

Rhesus macaque monkey brain microvessel endothelial cells (BMECs) were isolated and grown in culture in an effort to establish an appropriate primate in vitro model of the endothelial component of the blood-brain barrier. The presence of Factor VIII antigen, alkaline phosphatase, gamma-glutamyl transpeptidase, lactate dehydrogenase, total protein, and the passive permeability properties was documented for both primary and passaged cultures. Primate BMECs were shown to exhibit similar morphological and biochemical properties described for other BMEC culture systems derived from other species. In addition, the passaged primate BMECs were particularly notable for the changes in enzyme activities and total protein that parallel age-dependent changes in brain capillary endothelia. This study provides further support for the possible application of BMEC culture systems in investigations of blood-brain barrier functions under normal, aging, and diseased conditions.

Characterization of a gamma-glutamyl transpeptidase positive subpopulation of endothelial cells in a spontaneous tube-forming clone of rat cerebral resistance-vessel endothelium

A spontaneous tube-forming clone of rat cerebral resistance-vessel endothelium was characterized in long-term serial culture. In this study, a clone, RV-150 ECT, of cerebral resistance vessel endothelial cells in long-term culture has been shown to have a subpopulation of gamma-GTP positive cells that are present in all cultures regardless of confluency status or tube-forming stages. In pre-confluent and confluent cultures, the gamma-GTP positive cells are few in number, stain weakly, and are randomly distributed in the monolayers. In monolayer post-confluent cultures, gamma-GTP positive cells increase in number, stain strongly, and begin to show signs of non-random distributions. In early post-confluent cultures that have become a mixture of monolayer and multilayer cells, there is a further increase in gamma-GTP positive cells which begin to form distinct groupings. In mid post-confluent cultures, the multilayered areas of the culture have begun clustering to form clear multicellular aggregates. The gamma-GTP positive cells at this stage are reduced in number and are predominantly associated with the cell clusters. In late post-confluent cultures, the multicellular clusters develop clear cell cords between/among the clusters. At this stage the gamma-GTP positive cells are associated exclusively with cell clusters. With cord development, the gamma-GTP positive cells are associated with both clusters and cords, and are reduced in number apparently because of selective degeneration of these cells. The results of this study demonstrate that a phenotypically distinct subpopulation of endothelial cells exhibits characteristic features of the blood-brain barrier, namely gamma-GTP. The ability of these cells to express this property in long-term serial culture suggests that this may represent a useful in vitro model to study the growth and differentiation of blood-brain barrier vessels.

Endotoxin-mediated endothelial cell injury and activation: role of soluble CD14

Vascular endothelial cell (EC) injury by lipopolysaccharides (LPS) plays a major role in the pathogenesis of gram-negative bacterial sepsis and endotoxic shock. The studies described here were performed to define further the molecular mechanisms involved in the EC responses to LPS. We showed that serum was required for LPS-mediated cytotoxicity for bovine brain microvessel, pulmonary, and aortic ECs and that anti-human CD14 antibodies completely blocked LPS-mediated cytotoxicity for ECs in the presence of human serum. The addition of a recombinant soluble form of human CD14 to serum-free medium restored the LPS-mediated cytotoxicity, whereas the addition of LPS binding protein (LBP), a serum protein that potentiates LPS-induced responses to monocytes, had no effect. A similar dependency on serum or recombinant soluble CD14 (under serum-free conditions) was observed for LPS-induced secretion of interleukin-6 by human umbilical vein ECs. These findings indicate that soluble CD14 is required for LPS-mediated EC responses independently of LPB, suggesting that serum soluble CD14 represents a naturally occurring agonist for EC responses to LPS.

The cerebral microvessels in culture, an update

Recent advances in our knowledge of the blood-brain barrier (BBB) have in part been made by studying the properties and function of cerebral endothelial cells in vitro. After an era of working with a fraction, enriched in cerebral microvessels by centrifugation, the next generation of in vitro BBB model systems was introduced, when the conditions for routinely culturing the endothelial cells were established. This review summarizes the results obtained from this rapidly growing field. It can be stated with certainty that, in addition to providing a better insight into the chemical composition of cerebral endothelial cells, much has been learned from these studies about the characteristics of transport processes and cell-to-cell interactions during the last 12 years. With the application of new technologies, the approach offers a new means of investigation, applicable not only to biochemistry and physiology but also to the drug research, and may improve the transport of substances through the BBB. The in vitro approach has been and should remain an excellent model of the BBB to help unravel the complex molecular interactions underlying and regulating the permeability of the cerebral endothelium.

A histological and flow cytometric study of dog brain endothelial cell injuries in delayed radiation necrosis

The pathogenesis of delayed cerebral radiation necrosis was studied histologically and biochemically in 25 dogs with special attention to vascular endothelial cell injuries. The dogs were sacrificed 3 to 30 months after irradiation with a single dose of 15 Gy to the head. Brain specimens were appropriately fixed for light and electron microscopic studies, and capillary endothelial cells were isolated for flow cytometric study. The endothelial cells were stained with acridine orange, then the cell ratios in the reproductive phase (S + G2 + M) were investigated with flow cytometry. Thereafter, Feulgen hydrolysis and computer analysis of the hydrolysis curves were performed to examine the qualitative changes in deoxyribonucleic acid (DNA) of endothelial cells after irradiation. Under light microscopy, spongy degeneration with small cell infiltration was observed, especially in the frontal white matter, at 6 months after irradiation. At 9 months, necrotic foci appeared and developed until 15 months after irradiation. Blood vessels around the necrotic area showed luminal narrowing with endothelial hyperplasia and proliferation. At 30 months, no fresh necrotic lesions were observed. Under electron microscopy, endothelial cells of capillaries and small vessels around the necrotic area showed an increase of pinocytosis, and in the nuclei there was an increase of infoldings and euchromatin. The cell ratios in the reproductive phase were 14.5% to 23.3% (maximum at 9 months) in the irradiated group compared to 6.4% in the control group. The rate constant of apurinic acid production, a parameter correlating with DNA transcriptional activity, was minimum at 3 months and maximum at 9 months after irradiation. The data suggest that impairment of the microcirculation plays an important role in the pathogenesis of delayed radiation necrosis, and that the time of necrosis occurrence closely correlates with the cell cycle of vascular endothelial cells.

Blood-brain barrier: transport studies in isolated brain capillaries and in cultured brain endothelial cells

The development of in vitro BBB models consisting of isolated brain capillaries and cultured brain microvessel endothelial cells has made possible the study of BBB transport phenomena at the cellular level. Basic characteristics of BBB transport of endogenous and exogenous solutes and their biochemical, pharmacological, ontogenic, and pathological regulation mechanisms have been investigated. This information has led not only to a better understanding of BBB transport but also to the construction of strategies for improving drug delivery to the CNS for diagnosis and therapeutics. To elucidate the complexity of BBB transport, in vivo studies are always necessary at some point; however, in vitro systems can be useful complements to the in vivo systems. The tissue culture systems seem to be especially important in the clarification of cellular, biochemical and molecular features of BBB transport. Appropriate systems should be selected or combined, depending on the purpose of the investigation.

Quantitative detection of blood-brain barrier-associated enzymes in cultured endothelial cells of porcine brain microvessels

The present study deals with a rapid and convenient assay for blood-brain barrier (BBB)-associated enzymes, gamma-glutamyl transpeptidase (gamma-GTP) and alkaline phosphatase (ALP), in cultured endothelial cells and other cells. These enzyme activities in cultured cells could be efficiently measured by direct incubation of each substrate in the culture plates without pretreatment of the cells. This new direct in situ-in plate assay was more rapid and convenient than conventional ex-plate assays, and these assays gave similar values for specific enzyme activities. gamma-GTP and ALP activities could be detected by this in situ method in primary-cultured endothelial cells of porcine brain microvessels, but their levels were lower than those before culture. The degree of loss due to culture differed between gamma-GTP and ALP; a relatively large amount of ALP remained but the gamma-GTP level decreased greatly. In this direct in situ-in plate assay, cultured porcine aortic endothelial cells exhibited negligibly small activities for both enzymes, whereas cultured astroglial cells of neonatal porcine brain showed moderate gamma-GTP activity and a trace of ALP activity. This direct in situ-in plate assay can be used for microculture and automatic measurement and offers a convenient means for studying the possible regulatory mechanisms of the expression of the BBB-associated enzymes.

Human cerebral endothelium: isolation and characterization of cells derived from microvessels of non-neoplastic and malignant glial tissue

Human microvessels were isolated and cultured from non-neoplastic cerebral tissue specimens resected for the treatment of seizure disorders and from malignant glial tumors. After 1-2 weeks, cobblestone patterned plaques of cells were isolated and cultured from these microvessels. Cell lines positive for Factor VIII antigen and negative for glial fibrillary acidic protein were designated as endothelium. Endothelium from both tissue sources produced gamma-glutamyl transpeptidase in response to glial cell conditioned media. Tumor derived microvessel endothelium had decreased longevity in culture when compared to normal microvessel endothelium. Tumor derived endothelium also formed less extensive intercellular junctional complexes in vitro. The isolation and characterization of human cerebral microvessel endothelium derived from non-neoplastic tissue and glial tumors may lead to a further understanding of the role of endothelium in tumor growth and vascular permeability alterations.

The use of cultured epithelial and endothelial cells for drug transport and metabolism studies

In an effort to develop novel strategies for delivery of drug candidates arising from rational drug design and recombinant DNA technology, pharmaceutical scientists have begun to employ the techniques of cell culture to study drug transport and metabolism at specific biological barriers. This review describes some of the general factors that should be considered in developing a cell culture model for transport studies and metabolism studies. In addition, we review in detail the recent progress that has been made in establishing, validating, and using cell cultures of epithelial barriers (e.g., cells that constitute the intestinal, rectal, buccal, sublingual, nasal, and ophthalmic mucosa as well as the epidermis of the skin) and the endothelial barriers (e.g., brain microvessel endothelial cells).

Production of basic fibroblast growth factor-like factor by cultured human cholangiocellular carcinoma cells

An extract of cultured human cholangiocellular carcinoma cells (HuCC-T1) was found to contain high mitogenic activity for BALB/c3T3 cells. The growth factor eliciting most of the mitogenic activity was purified and concluded to be identical with basic fibroblast growth factor (bFGF)-like factor on the basis of its molecular weight and heparin-Sepharose elution profile, and the results of immunoblotting and radioimmunoassay. HuCC-T1 cells also secreted bFGF-like factor into serum-free medium. A combination of insulin and transferrin or bovine serum albumin stimulated the growth of HuCC-T1 cells in serum-free medium. However, bFGF did not stimulate their growth in the presence and absence of these supplements. Neutralizing monoclonal antibody against bFGF did not inhibit growth. These results indicate that bFGF-like factor is not a growth factor for this cell line.

Isolation and characterization of endothelial cells from bovine cerebral arteries

For our laboratory's investigation into the role of the endothelial cells in vasospasm following subarachnoid hemorrhage and in inflammatory diseases, we found it necessary to devise a modified method of cell culture, which would be appropriate for studying human endothelial cells from lobectomized brain. We report our techniques to increase cell harvest and ensure reproducibility, our method of culturing endothelial cells from bovine major cerebral arteries, and our morphologic and immunocytochemical characterization of these cells. To increase the harvest of endothelial cells, the blood cells were washed from the lumen of the major cerebral arteries at the slaughterhouse and a modified reversed vessel technique was employed. The monolayer of cultured endothelial cells displayed a cobblestone appearance when it reached confluency and transmission electron microscopy revealed junctional complexes and interdigitation of cytoplasm at Passages 10 and 17. The cells stained positively for Factor VIII-related antigen at Passages 3, 5, 7, 10, and 15. Also the cells metabolized acetylated low-density lipoprotein at Passage 8. To determine the purify of the cultured endothelial cells, an immunocytochemical study of the cytoskeleton was performed on Passage 5 cells using either rhodamine-phalloidin or antibodies against smooth muscle myosin, desmin, and vimentin.

Morphologic plasticity and periodicity: porcine cerebral microvascular cells in culture

Porcine cerebral microvascular (PCMV) endothelial cell cultures and pericyte-endothelial cell cocultures were established and the self-organizational properties of the cells were examined in various culture conditions. Cultured PCMV endothelial cells were characterized by the capacity to produce prostacyclin in response to bradykinin. Cultured PCMV pericytes were identified with a smooth muscle actin-specific stain. PCMV endothelial cells organized into cord structures when left in culture for several weeks without passage. Lumina were observed in cross sections of these cords and appeared to form through a process of cell-selective autolysis. PCMV endothelial cells required three dimensions for self-organization, forming suspended cords in planes that either intersected or paralleled the culture vessel floor. After formation, suspended cords continued to exhibit a morphologic plasticity punctuated by the coordinated migrations of PCMV endothelial cells en masse. Sequential propagation of PCMV endothelial cell monolayers and development of suspended capillarylike cords recurred cyclically when cells were left in culture without passage for several weeks. Cord development was also observed in PCMV pericyte-endothelial cell cocultures with large proportions of pericytes. However, pericytes were not located in cross sections of suspended cords formed in coculture. Apparently, in some conditions of PCMV coculture, populations of PCMV endothelial cells and pericytes segregate. Retina-derived growth factor (RDGF) promoted this cell-type segregation and the subsequent formation of suspended cords in PCMV cocultures, although its exact mode of action is unclear. These results indicate that cultured cerebral microvascular endothelial cells and pericytes have capacities for complex, temporal self-organization that varies according to culture conditions.

Monoclonal antibodies against heparin-binding growth factor II/basic fibroblast growth factor that block its biological activity: invalidity of the antibodies for tumor angiogenesis

Two monoclonal antibodies (mAbs) against bovine heparin-binding growth factor II (HBGF-II)/basic fibroblast growth factor (bFGF) were obtained from mouse hybridoma cell lines. They were highly specific for bFGF from bovine, human, and mouse sources and did not cross-react with bovine heparin-binding growth factor I (HBGF-I)/acidic fibroblast growth factor (aFGF). The immunoglobulin class and subclass of these mAbs were IgG1, K. The apparent dissociation constant (Kd) for bFGF of these mAbs ranged from 10(-9) to 10(-10) M. One mAb (bFM-2) also cross-reacted with heat-inactivated bFGF, while the other mAb (bFM-1) did not, suggesting that bFM-1 recognized the conformation of the bFGF molecule necessary for its biological activity. These mAbs inhibited growth of cultured bovine capillary endothelial cells in both the presence and absence of exogenous bFGF, indicating the autocrine action of this growth factor in in vitro growth of these cells. On the other hand, injection of these hybridoma cell lines s.c. into the backs of athymic mice resulted in development of highly vascularized solid tumors and a sustained high level of anti-bFGF activity in the blood of the tumor-bearing mice. These findings suggest that bFGF is not essential as an autocrine or paracrine growth factor for angiogenesis in vivo. These mAbs should be useful in further studies on the physiological role and the conformation-function relationship of bFGF because they block its biological activity.

Heterogeneity in endothelial cells from large vessels and microvessels

The successful isolation and culture of vascular endothelial cells has led to an upsurge of interest in their role in such diverse processes as thrombogenesis, atherosclerosis and tumour growth. In this article we have outlined methods for the culture and characterization of endothelial cells from large vessels, capillary and post-capillary venules of lymph nodes. Comparison of their immunological and metabolic properties illustrates the heterogeneity within the vasculature. The effect of growth and angiogenic factors on these cells and the efficacy of their use in culture medium is considered.

Functional heterogeneity of vascular endothelial cells

This review has highlighted some of the well-described differences in endothelial cells derived from different sites of the vascular tree. In presenting a select group of endothelial properties, there was no intention to imply that these are the only properties of endothelial cells that exhibit heterogeneity. Nonetheless, having described endothelial heterogeneity in regard to a number of defined properties, we are left with persistent questions including: Are these divergent properties of endothelial cells fixed? Alternatively, can we alter the properties of endothelial cells by affecting the signals from the environment? A number of reports strongly suggest that endothelial cells are capable of acquiring new properties. Stewart and Wiley investigated the role of the neural tissue environment on the differentiation of brain capillary endothelial cells. These authors transplanted ectopic sites, i.e. vascular segments of brain from very young quail embryos to chick coeliac cavity, and a quail somites to chick brain ventricles. The distinctive morphology of quail cells provided a cell marker to differentiate host from graft. The results of this study demonstrated that mesenteric or somatic vessels growing into grafted brain developed functional, structural and histochemical features specific for neural capillaries. Conversely, capillaries in mesodermal tissue that had been grafted to the brain were devoid of the neural capillary characteristics, indicating that brain vessels do not form a barrier when they are made to vascularize non-neural tissue. Milici and Carley reported that bovine adrenal capillary cells cultured on plastic exhibited occasional diaphragmed fenestrations and no transendothelial channels. However, if these same cells were cultured on a basement membrane (matrix) laid down by MDCK cells (a canine nephron epithelial cell line), the cells responded by increasing the number of diaphragmed fenestrations and transendothelial channels. This cell culture study supported an earlier whole animal study in which the importance of the epithelium and/or epithelial basal lamina in the maintenance of endothelial ultrastructure was demonstrated in a developmental study of rat intestinal capillaries. In this earlier study, it was noted that epithelial development coincided with the formation of fenestrations by the endothelium. Enzymatic activities of endothelial cells can also be altered by environmental signals. For example, primary cerebral microvascular endothelial cells exhibit barrier features and are enriched in gamma-glutamyl transpeptidase activity, yet rapidly lose the activity when subcultured.(ABSTRACT TRUNCATED AT 400 WORDS)

Optimized medium for clonal growth of human microvascular endothelial cells with minimal serum

An optimized basal nutrient medium, MCDB 131, has been developed that supports clonal growth of human microvascular endothelial cells (HMVEC) with as little as 0.7% dialyzed fetal bovine serum (dFBS) when also supplemented with 10 ng/ml epidermal growth factor (EGF) and 1 microgram/ml hydrocortisone. An extensive initial survey of available media showed that MCDB 402, a medium optimized for low-serum growth of Swiss 3T3 cells, supported the best clonal growth of HMVEC with 10% dFBS. Quantitative adjustment of the composition of MCDB 402 for improved clonal growth of HMVEC with reduced amounts of dFBS resulted in development of MCDB 131. Although many different adjustments contributed to the optimal properties of MCDB 131 for growth of HMVEC, the most unusual feature of this medium is its high magnesium concentration. A major benefit was achieved by increasing Mg2+ from 0.8 mM in MCDB 402 to 10.0 mM in MCDB 131. In the absence of defined supplements, MCDB 131 supports good clonal growth of HMVEC with 2% dFBS. This can be reduced to 0.7% by adding EGF and hydrocortisone, which act synergistically to improve growth with low levels of dFBS.

Synthesis of acetylcholine by endothelial cells isolated from rat brain cortex capillaries

Choline acetyltransferase (ChAT) activity was measured in a fraction of endothelial cells obtained by collagenase digestion from previously isolated rat brain cortex capillaries. ChAT specific activity in the dissociated cells (0.264 nmol X mg protein-1 X min-1) was nearly 7 times higher than the activity measured in 'capillary-forming' cells (0.038 nmol X mg protein-1 X min-1). It is not known whether this increase was caused by ChAT enrichment of the former cellular fraction, and/or by a change in the specific activity of the enzyme during the isolation procedure, but the finding would be in favor of the intrinsic localization of cerebrovascular ChAT in endothelial cells. This would support the hypothesis of a role for locally synthesized ACh in the vasodilating response to noxious stimuli.

Primary cultures of rat aortic endothelial and smooth muscle cells: I. An in vitro model to study xenobiotic-induced vascular cytotoxicity

Primary cultures of rat vascular endothelial and smooth muscle cells were developed as models to study xenobiotic-induced cytotoxicity. Endothelial and smooth muscle cells were isolated by enzymatic digestion and mechanical dissociation of rat thoracic aortae. Optimal cell growth and minimal fibroblast contamination in cultures of both cell types were obtained in Medium 199 supplemented with 10% fetal bovine serum. Cultured cells were characterized by distinctive morphologic features and growth patterns. Intercellular endothelial cell junctions were selectively stained with silver nitrate. Endothelial cells also exhibited a nonthrombogenic surface, as reflected by platelet-binding studies. Confluent cultures of smooth muscle cells, but not endothelial cells, contracted in response to norepinephrine (10 microM). Cultures of both cell types were exposed to acrolein (2, 5 or 50 ppm), an environmental pollutant, for 4 and 24 h. Morphologic damage, lactate dehydrogenase release, and cellular thiol content were used as indices of cytotoxicity. Acrolein-induced enzyme leakage and morphologic alterations were dose- and time-dependent and more pronounced in cultures of smooth muscle cells than in endothelial cells. The total thiol content of endothelial cells exposed to acrolein (50 ppm) for 24 h was not significantly different from that of respective controls. In contrast, the content of treated smooth muscle cells was higher than that of controls. These observations show that primary cultures of vascular cells provide a useful model to evaluate xenobiotic-induced cytotoxicity. The information obtained using a cell culture system may be complemented by the use of other in vivo and in vitro models to determine the mechanisms by which xenobiotics cause vascular cell injury.

Specific antigen and organelle expression of a long-term rhesus endothelial cell line

A long-term culture of a spontaneously transformed endothelial cell line derived from the choroid-retina of a rhesus macaque fetus is reported. It has been carried in vitro by serial propagation more than 548 passages in 17 yr. Cells were identified as being of endothelial origin by cellular morphology, growth pattern, ultrastructure, immunocytochemistry (immunofluorescence and immunoperoxidase), and immunodiffusion. The transformants are characterized by an infinite life span, a changed expression of Factor VIII-related antigen, and chromosomal aberrations. Throughout long-term serial passages and after repeated freeze-storage, thawing, and reculture the cells retain the specific organelles, Weibel-Palade bodies, and most of the other characteristic morphologic features. For this long-term cultured endothelial cell line, Weibel-Palade bodies seem to be a more reliable marker than Factor VIII-related antigen.