Conditionally immortalized cell lines as a new in vitro model for the study of barrier functions

Validation and characterization of a novel blood-brain barrier platform for investigating traumatic brain injury

The Blood-Brain Barrier (BBB) is a highly-selective physiologic barrier responsible for maintaining cerebral homeostasis. Innovative in vitro models of the BBB are needed to provide useful insights into BBB function with CNS disorders like traumatic brain injury (TBI). TBI is a multidimensional and highly complex pathophysiological condition that requires intrinsic models to elucidate its mechanisms. Current models either lack fluidic shear stress, or neglect hemodynamic parameters important in recapitulating the human in vivo BBB phenotype. To address these limitations in the field, we developed a fluid dynamic novel platform which closely mimics these parameters. To validate our platform, Matrigel-coated Transwells were seeded with brain microvascular endothelial cells, both with and without co-cultured primary human astrocytes and bone-marrow mesenchymal stem cells. In this article we characterized BBB functional properties such as TEER and paracellular permeability. Our platform demonstrated physiologic relevant decreases in TEER in response to an ischemic environment, while directly measuring barrier fluid fluctuation. These recordings were followed with recovery, implying stability of the model. We also demonstrate that our dynamic platform is responsive to inflammatory and metabolic cues with resultant permeability coefficients. These results indicate that this novel dynamic platform will be a valuable tool for evaluating the recapitulating BBB function in vitro, screening potential novel therapeutics, and establishing a relevant paradigm to evaluate the pathophysiology of TBI.

In Vitro Models of the Blood–Cerebrospinal Fluid Barrier and Their Applications in the Development and Research of (Neuro)Pharmaceuticals

The pharmaceutical research sector has been facing the challenge of neurotherapeutics development and its inherited high-risk and high-failure-rate nature for decades. This hurdle is partly attributable to the presence of brain barriers, considered both as obstacles and opportunities for the entry of drug substances. The blood–cerebrospinal fluid (CSF) barrier (BCSFB), an under-studied brain barrier site compared to the blood–brain barrier (BBB), can be considered a potential therapeutic target to improve the delivery of CNS therapeutics and provide brain protection measures. Therefore, leveraging robust and authentic in vitro models of the BCSFB can diminish the time and effort spent on unproductive or redundant development activities by a preliminary assessment of the desired physiochemical behavior of an agent toward this barrier. To this end, the current review summarizes the efforts and progresses made to this research area with a notable focus on the attribution of these models and applied techniques to the pharmaceutical sector and the development of neuropharmacological therapeutics and diagnostics. A survey of available in vitro models, with their advantages and limitations and cell lines in hand will be provided, followed by highlighting the potential applications of such models in the (neuro)therapeutics discovery and development pipelines.

[Development of Novel Methodology and Its Application for Clarifying the Transport Function of the Blood-brain Barrier]

The blood-brain barrier (BBB) consists of brain capillary endothelial cells linked by tight junctions and serves to regulate the transfer of endogenous compounds and xenobiotics between the circulating blood and brain interstitial fluid. We have developed a methodology to characterize brain-to-blood efflux transport in vivo, using the Brain Efflux Index and an in vitro culture model of the BBB, i.e., a conditionally immortalized cell line of the neurovascular unit. Employing these methods, we showed that the BBB plays an important role in protecting the brain by transporting neurotransmitters, neuromodulators, metabolites, uremic toxins, and xenobiotics together with atrial natriuretic peptide from the brain interstitial fluid to the circulating blood. We also developed a highly selective, sensitive LC-MS/MS method for simultaneous protein quantification. We found significant species differences in the expression amounts of various BBB transporter proteins among mice, rats, marmosets, cynomolgus monkeys, and humans. Among transporter proteins at the BBB, multidrug resistance protein 1 (Mdr1/Abcb1) is known to generate a concentration gradient of unbound substrate drugs between the blood and brain. Based on measurements of the intrinsic efflux transport rate of Mdr1 and the protein expression amounts of Mdr1 in mouse brain capillaries and Mdr1-expressing cell lines, we predicted the unbound drug concentration gradients of 7 drugs in the mouse brain in vivo. This was the first successful prediction of in vivo drug transport activity from in vitro experimental data and transporter protein concentration in tissues. This methodology and findings should greatly advance central nervous system barrier research.

Expression and Function of Organic Anion Transporting Polypeptides in the Human Brain: Physiological and Pharmacological Implications

The central nervous system (CNS) is an important pharmacological target, but it is very effectively protected by the blood–brain barrier (BBB), thereby impairing the efficacy of many potential active compounds as they are unable to cross this barrier. Among others, membranous efflux transporters like P-Glycoprotein are involved in the integrity of this barrier. In addition to these, however, uptake transporters have also been found to selectively uptake certain compounds into the CNS. These transporters are localized in the BBB as well as in neurons or in the choroid plexus. Among them, from a pharmacological point of view, representatives of the organic anion transporting polypeptides (OATPs) are of particular interest, as they mediate the cellular entry of a variety of different pharmaceutical compounds. Thus, OATPs in the BBB potentially offer the possibility of CNS targeting approaches. For these purposes, a profound understanding of the expression and localization of these transporters is crucial. This review therefore summarizes the current state of knowledge of the expression and localization of OATPs in the CNS, gives an overview of their possible physiological role, and outlines their possible pharmacological relevance using selected examples.

Pretreatment Effect of Inflammatory Stimuli and Characteristics of Tryptophan Transport on Brain Capillary Endothelial (TR-BBB) and Motor Neuron Like (NSC-34) Cell Lines

Tryptophan plays a key role in several neurological and psychiatric disorders. In this study, we investigated the transport mechanisms of tryptophan in brain capillary endothelial (TR-BBB) cell lines and motor neuron-like (NSC-34) cell lines. The uptake of [³H]l-tryptophan was stereospecific, and concentration- and sodium-dependent in TR-BBB cell lines. Transporter inhibitors and several neuroprotective drugs inhibited [³H]l-tryptophan uptake by TR-BBB cell lines. Gabapentin and baclofen exerted a competitive inhibitory effect on [³H]l-tryptophan uptake. Additionally, l-tryptophan uptake was time- and concentration-dependent in both NSC-34 wild type (WT) and mutant type (MT) cell lines, with a lower transporter affinity and higher capacity in MT than in WT cell lines. Gene knockdown of LAT1 (l-type amino acid transporter 1) and CAT1 (cationic amino acid transporter 1) demonstrated that LAT1 is primarily involved in the transport of [³H]l-tryptophan in both TR-BBB and NSC-34 cell lines. In addition, tryptophan uptake was increased by TR-BBB cell lines but decreased by NSC-34 cell lines after pro-inflammatory cytokine pre-treatment. However, treatment with neuroprotective drugs ameliorated tryptophan uptake by NSC-34 cell lines after inflammatory cytokines pretreatment. The tryptophan transport system may provide a therapeutic target for treating or preventing neurodegenerative diseases.

Drug Development for Central Nervous System Diseases Using In vitro Blood-brain Barrier Models and Drug Repositioning

An important goal of biomedical research is to translate basic research findings into practical clinical implementation. Despite the advances in the technology used in drug discovery, the development of drugs for central nervous system diseases remains challenging. The failure rate for new drugs targeting important central nervous system diseases is high compared to most other areas of drug discovery. The main reason for the failure is the poor penetration efficacy across the blood-brain barrier. The blood-brain barrier represents the bottleneck in central nervous system drug development and is the most important factor limiting the future growth of neurotherapeutics. Meanwhile, drug repositioning has been becoming increasingly popular and it seems a promising field in central nervous system drug development. In vitro blood-brain barrier models with high predictability are expected for drug development and drug repositioning. In this review, the recent progress of in vitro BBB models and the drug repositioning for central nervous system diseases will be discussed.

Effects of Cadmium on ZO-1 Tight Junction Integrity of the Blood Brain Barrier

Cadmium (Cd) is a highly toxic environmental pollutant released from the smelting and refining of metals and cigarette smoking. Oral exposure to cadmium may result in adverse effects on a number of tissues, including the central nervous system (CNS). In fact, its toxicity has been related to neurological disorders, as well as neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Under normal conditions, Cd barely reaches the brain in adults because of the presence of the blood-brain barrier (BBB); however, it has been demonstrated that Cd-dependent BBB alteration contributes to pathogenesis of neurodegeneration. However, the mechanism underlying Cd-dependent BBB alteration remain obscure. Here, we investigated the signaling pathway of Cd-induced tight junction (TJ), F-actin, and vimentin protein disassembly in a rat brain endothelial cell line (RBE4). RBE4 cells treated with 10 μM cadmium chloride (CdCl2) showed a dose- and time-dependent significant increase in reactive oxygen species (ROS) production. This phenomenon was coincident with the alteration of the TJ zonula occludens-1 (ZO-1), F-actin, and vimentin proteins. The Cd-dependent ROS increase elicited the upregulation of GRP78 expression levels, a chaperone involved in endoplasmic reticulum (ER) stress that induces caspase-3 activation. Further signal profiling by the pannexin-1 (PANX1) specific inhibitor 10Panx revealed a PANX1-independent increase in ATP spillage in Cd-treated endothelial cells. Our results point out that a ROS-dependent ER stress-mediated signaling pathway involving caspase-3 activation and ATP release is behind the BBB morphological alterations induced by Cd.

Recent advances in drug and nutrient transport across the blood-retinal barrier

INTRODUCTION

The blood-retinal barrier (BRB) is the barrier separating the blood and neural retina, and transport systems for low-weight molecules at the BRB are expected to be useful for developing drugs for the treatment of ocular neural disorders and maintaining a healthy retina. Areas covered: This review discusses blood-to-retina and retina-to-blood transport of drugs and nutrients at the BRB. In particular, P-gp (ABCB1/MDR1) has low impact on the transport of cationic drugs at the BRB, suggesting a significant role of novel organic cation transporters in influx and efflux transport of lipophilic cationic drugs between blood and the retina. The transport of pravastatin at the BRB involves transporters including organic anion transporting polypeptide 1a4 (Oatp1a4). Recent studies have shown the involvement of solute carrier transporters in the blood-to-retina transport of nutrients including riboflavin, L-ornithine, β-alanine, and L-histidine, implying that dipeptide transport at the BRB is minimal. Expert opinion: Novel organic cation transport systems and the elimination-dominant transport of pravastatin at the BRB are expected to be useful in systemic drug delivery to the neural retina without CNS side effects. The mechanism of nutrient transport at the BRB is expected to provide a new strategy for delivery of nutrient-mimetic drugs.

Imperatorin is Transported through Blood-Brain Barrier by Carrier-Mediated Transporters

Imperatorin, a major bioactive furanocoumarin with multifunctions, can be used for treating neurodegenerative diseases. In this study, we investigated the characteristics of imperatorin transport in the brain. Experiments of the present study were designed to study imperatorin transport across the blood-brain barrier both in vivo and in vitro. In vivo study was performed in rats using single intravenous injection and in situ carotid artery perfusion technique. Conditionally immortalized rat brain capillary endothelial cells were as an in vitro model of blood-brain barrier to examine the transport mechanism of imperatorin. Brain distribution volume of imperatorin was about 6 fold greater than that of sucrose, suggesting that the transport of imperatorin was through the blood-brain barrier in physiological state. Both in vivo and in vitro imperatorin transport studies demonstrated that imperatorin could be transported in a concentration-dependent manner with high affinity. Imperatorin uptake was dependent on proton gradient in an opposite direction. It was significantly reduced by pretreatment with sodium azide. However, its uptake was not inhibited by replacing extracellular sodium with potassium or N-methylglucamine. The uptake of imperatorin was inhibited by various cationic compounds, but not inhibited by TEA, choline and organic anion substances. Transfection of plasma membrane monoamine transporter, organic cation transporter 2 and organic cation/carnitine transporter 2/1 siRNA failed to alter imperatorin transport in brain capillary endothelial cells. Especially, tramadol, clonidine and pyrilamine inhibited the uptake of [³H]imperatorin competitively. Therefore, imperatorin is actively transported from blood to brain across the blood-brain barrier by passive and carrier-mediated transporter.

SLC and ABC Transporters: Expression, Localization, and Species Differences at the Blood-Brain and the Blood-Cerebrospinal Fluid Barriers

The blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB) separate the brain and cerebrospinal fluid (CSF) from the systemic circulation and represent a barrier to the uptake of both endogenous compounds and xenobiotics into the brain. For compounds whose passive diffusion is limited due to their ionization or hydrophilicity, membrane transporters can facilitate their uptake across the BBB or BCSFB. Members of the solute carrier (SLC) and ATP-binding case (ABC) families are present on these barriers. Differences exist in the localization and expression of transport proteins between the BBB and BCSFB, resulting in functional differences in transport properties. This review focuses on the expression, membrane localization, and different isoforms present at each barrier. Diseases that affect the central nervous system including brain tumors, HIV, Alzheimer's disease, Parkinson's disease, and stroke affect the integrity and expression of transporters at the BBB and BCSFB and will be briefly reviewed.

Characteristics of L-citrulline transport through blood-brain barrier in the brain capillary endothelial cell line (TR-BBB cells)

Background

_L-Citrulline is a neutral amino acid and a major precursor of _L-arginine in the nitric oxide (NO) cycle. Recently it has been reported that _L-citrulline prevents neuronal cell death and protects cerebrovascular injury, therefore, _L-citrulline may have a neuroprotective effect to improve cerebrovascular dysfunction. Therefore, we aimed to clarify the brain transport mechanism of _L-citrulline through blood-brain barrier (BBB) using the conditionally immortalized rat brain capillary endothelial cell line (TR-BBB cells), as an in vitro model of the BBB.

Methods

The uptake study of [¹⁴C] L-citrulline, quantitative real-time polymerase chain reaction (PCR) analysis, and rLAT1, system b^0,+, and CAT1 small interfering RNA study were performed in TR-BBB cells.

Results

The uptake of [¹⁴C] _L-citrulline was a time-dependent, but ion-independent manner in TR-BBB cells. The transport process involved two saturable components with a Michaelis–Menten constant of 30.9 ± 1.0 μM (Km₁) and 1.69 ± 0.43 mM (Km₂). The uptake of [¹⁴C] _L-citrulline in TR-BBB cells was significantly inhibited by neutral and cationic amino acids, but not by anionic amino acids. In addition, [¹⁴C]_L-citrulline uptake in the cells was markedly inhibited by 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH), which is the inhibitor of the large neutral amino acid transporter 1 (LAT1), B⁰, B^0,+ and harmaline, the inhibitor of system b^0,+. Gabapentin and _L-dopa as the substrates of LAT1 competitively inhibited the uptake of [¹⁴C] _L-citrulline. IC₅₀ values for _L-dopa, gabapentin, _L-phenylalanine and _L-arginine were 501 μM, 223 μM, 68.9 μM and 33.4 mM, respectively. The expression of mRNA for LAT1 was predominantly increased 187-fold in comparison with that of system b^0,+ in TR-BBB cells. In the studies of LAT1, system b^0,+ and CAT1 knockdown via siRNA transfection into TR-BBB cells, the transcript level of LAT1 and [¹⁴C] _L-citrulline uptake by LAT1 siRNA were significantly reduced compared with those by control siRNA in TR-BBB cells.

Conclusions

Our results suggest that transport of _L-citrulline is mainly mediated by LAT1 in TR-BBB cells. Delivery strategy for LAT1-mediated transport and supply of L-citrulline to the brain may serve as therapeutic approaches to improve its neuroprotective effect in patients with cerebrovascular disease.

Qualitative and quantitative structure-activity relationship modelling for predicting blood-brain barrier permeability of structurally diverse chemicals

In this study, structure-activity relationship (SAR) models have been established for qualitative and quantitative prediction of the blood-brain barrier (BBB) permeability of chemicals. The structural diversity of the chemicals and nonlinear structure in the data were tested. The predictive and generalization ability of the developed SAR models were tested through internal and external validation procedures. In complete data, the QSAR models rendered ternary classification accuracy of >98.15%, while the quantitative SAR models yielded correlation (r(2)) of >0.926 between the measured and the predicted BBB permeability values with the mean squared error (MSE) <0.045. The proposed models were also applied to an external new in vitro data and yielded classification accuracy of >82.7% and r(2) > 0.905 (MSE < 0.019). The sensitivity analysis revealed that topological polar surface area (TPSA) has the highest effect in qualitative and quantitative models for predicting the BBB permeability of chemicals. Moreover, these models showed predictive performance superior to those reported earlier in the literature. This demonstrates the appropriateness of the developed SAR models to reliably predict the BBB permeability of new chemicals, which can be used for initial screening of the molecules in the drug development process.

The alternative Epac/cAMP pathway and the MAPK pathway mediate hCG induction of leptin in placental cells

Pleiotropic effects of leptin have been identified in reproduction and pregnancy, particularly in the placenta, where it works as an autocrine hormone. In this work, we demonstrated that human chorionic gonadotropin (hCG) added to JEG-3 cell line or to placental explants induces endogenous leptin expression. We also found that hCG increased cAMP intracellular levels in BeWo cells in a dose-dependent manner, stimulated cAMP response element (CRE) activity and the cotransfection with an expression plasmid of a dominant negative mutant of CREB caused a significant inhibition of hCG stimulation of leptin promoter activity. These results demonstrate that hCG indeed activates cAMP/PKA pathway, and that this pathway is involved in leptin expression. Nevertheless, we found leptin induction by hCG is dependent on cAMP levels. Treatment with (Bu)₂cAMP in combination with low and non stimulatory hCG concentrations led to an increase in leptin expression, whereas stimulatory concentrations showed the opposite effect. We found that specific PKA inhibition by H89 caused a significant increase of hCG leptin induction, suggesting that probably high cAMP levels might inhibit hCG effect. It was found that hCG enhancement of leptin mRNA expression involved the MAPK pathway. In this work, we demonstrated that hCG leptin induction through the MAPK signaling pathway is inhibited by PKA. We observed that ERK1/2 phosphorylation increased when hCG treatment was combined with H89. In view of these results, the involvement of the alternative cAMP/Epac signaling pathway was studied. We observed that a cAMP analogue that specifically activates Epac (CPT-OMe) stimulated leptin expression by hCG. In addition, the overexpression of Epac and Rap1 proteins increased leptin promoter activity and enhanced hCG. In conclusion, we provide evidence suggesting that hCG induction of leptin gene expression in placenta is mediated not only by activation of the MAPK signaling pathway but also by the alternative cAMP/Epac signaling pathway.

Effect of acetazolamide on aquaporin-1 and fluid flow in cultured choroid plexus

Acetazolamide (AZA), used in treatment of early or infantile hydrocephalus, is effective in some cases, while its effect on the choroid plexus (CP) remains ill-defined. The drug reversibly inhibits aquaporin-4 (AQP4), the most ubiquitous "water pore" in the brain, and perhaps modulation of AQP1 (located apically on CP cells) by AZA may reduce cerebrospinal fluid (CSF) production. We sought to elucidate the effect of AZA on AQP1 and fluid flow in CP cell cultures.CP tissue culture from 10-day Sprague-Dawley rats and a TRCSF-B cell line were grown on Transwell permeable supports and treated with 100 μM AZA. Fluid assays to assess direction and extent of fluid flow, and AQP1 expression patterns by immunoblot, Immuncytochemistry (ICC), and quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) were performed.Immunoblots and ICC analyses showed a decrease in AQP1 protein shortly after AZA treatment (lowest at 12 h), with transient AQP1 reduction mediated by mRNA expression (lowest at 6 h). Transwell fluid assays indicated a fluid shift at 2 h, before significant changes in AQP1 mRNA or protein levels.Timing of AZA effect on AQP1 suggests the drug alters protein transcription, while affecting fluid flow by a concomitant method. It is plausible that other mechanisms account for these phenomena, as the processes may occur independently.

In vitro models of the blood-brain barrier

The chapter provides an introduction and brief overview of currently available in vitro blood-brain barrier models, pointing out the major advantages and disadvantages of the respective models and potential applications. Bovine brain microvessel endothelial cell isolation, culture, and transendothelial permeability measurement procedures are discussed in detail as a model system for a laboratory to begin brain vascular investigations.

Qualitative prediction of blood-brain barrier permeability on a large and refined dataset

The prediction of blood-brain barrier permeation is vitally important for the optimization of drugs targeting the central nervous system as well as for avoiding side effects of peripheral drugs. Following a previously proposed model on blood-brain barrier penetration, we calculated the cross-sectional area perpendicular to the amphiphilic axis. We obtained a high correlation between calculated and experimental cross-sectional area (r = 0.898, n = 32). Based on these results, we examined a correlation of the calculated cross-sectional area with blood-brain barrier penetration given by logBB values. We combined various literature data sets to form a large-scale logBB dataset with 362 experimental logBB values. Quantitative models were calculated using bootstrap validated multiple linear regression. Qualitative models were built by a bootstrapped random forest algorithm. Both methods found similar descriptors such as polar surface area, pKa, logP, charges and number of positive ionisable groups to be predictive for logBB. In contrast to our initial assumption, we were not able to obtain models with the cross-sectional area chosen as relevant parameter for both approaches. Comparing those two different techniques, qualitative random forest models are better suited for blood-brain barrier permeability prediction, especially when reducing the number of descriptors and using a large dataset. A random forest prediction system (n(trees) = 5) based on only four descriptors yields a validated accuracy of 88%.

Characterization and use of human brain microvascular endothelial cells to examine β-amyloid exchange in the blood-brain barrier

Alzheimer's disease (AD) is characterized by excessive cerebrovascular deposition of the β-amyloid peptide (Aβ). The investigation of Aβ transport across the blood-brain barrier (BBB) has been hindered by inherent limitations in the cellular systems currently used to model the BBB, such as insufficient barrier properties and poor reproducibility. In addition, many of the existing models are not of human or brain origin and are often arduous to establish and maintain. Thus, we characterized an in vitro model of the BBB employing human brain microvascular endothelial cells (HBMEC) and evaluated its utility to investigate Aβ exchange at the blood-brain interface. Our HBMEC model offers an ease of culture compared with primary isolated or coculture BBB models and is more representative of the human brain endothelium than many of the cell lines currently used to study the BBB. In our studies, the HBMEC model exhibited barrier properties comparable to existing BBB models as evidenced by the restricted permeability of a known paracellular marker. In addition, using a simple and rapid fluormetric assay, we showed that antagonism of key Aβ transport proteins significantly altered the bi-directional transcytosis of fluorescein-Aβ (1-42) across the HBMEC model. Moreover, the magnitude of these effects was consistent with reports in the literature using the same ligands in existing in vitro models of the BBB. These studies establish the HBMEC as a representative in vitro model of the BBB and offer a rapid fluorometric method of assessing Aβ exchange between the periphery and the brain.

Tanshinone IIA protects the human blood-brain barrier model from leukocyte-associated hypoxia-reoxygenation injury

To investigate the in vitro effect of tanshinone IIA on leukocyte-associated hypoxia-reoxygenation injury of human brain-blood barrier (BBB), we established the BBB model by culturing purified primary human brain microvascular endothelial cells (HBMVEC) to confluence on cell culture insert. BBB was identified by tight junction, transendothelial electrical resistance (TEER) and the permeability of BBB to horseradish peroxidase (HRP). The effect of tanshinone IIA on the permeability of BBB was tested at 2 h after hypoxia and 1h after reoxygenation with or without the supernatants of activated leukocytes. The effect of tanshinone IIA on leukocytes activation was analyzed by detection of MMP-9, cytokines and reactive oxygen species. The results showed that BBB formed by confluent HBMVECs had no cellular gap. Immunofluorescent staining for ZO-1 confirmed that the cells were connected by tight junction. Moreover, the BBB model had a higher TEER and a lower permeability for HRP than confluent HUVECs. The permeability of BBB for HRP was enhanced by hypoxia-reoxygenation and further greatly enhanced by adding the supernatants of activated leukocytes before reoxygenation. But such an effect was reversed by addition of tanshinone IIA before hypoxia. Moreover, tanshinone IIA could decrease the levels of MMP-9, TNF-α, IL-1α, IL-2, IFN-γ and reactive oxygen species in leukocytes. In conclusion, tanshinone IIA can protect BBB against leukocyte-associated hypoxia-reoxygenation injury by attenuating the activation of leukocytes and inhibiting the injury effects of leukocytic products. Tanshinone IIA may be a novel therapeutic agent for cerebral ischemia-reperfusion injury.

Fgf2 is expressed in human and murine embryonic choroid plexus and affects choroid plexus epithelial cell behaviour

Background

Although fibroblast growth factor (Fgf) signalling plays crucial roles in several developing and mature tissues, little information is currently available on expression of Fgf2 during early choroid plexus development and whether Fgf2 directly affects the behaviour of the choroid plexus epithelium (CPe). The purpose of this study was to investigate expression of Fgf2 in rodent and human developing CPe and possible function of Fgf2, using in vitro models. The application of Fgf2 to brain in vivo can affect the whole tissue, making it difficult to assess specific responses of the CPe.

Methods

Expression of Fgf2 was studied by immunohistochemistry in rodent and human embryonic choroid plexus. Effects of Fgf2 on growth, secretion, aggregation and gene expression was investigated using rodent CPe vesicles, a three-dimensional polarized culture model that closely mimics CPe properties in vivo, and rodent CPe monolayer cultures.

Results

Fgf2 was present early in development of the choroid plexus both in mouse and human, suggesting the importance of this ligand in Fgf signalling in the developing choroid plexus. Parallel analysis of Fgf2 expression and cell proliferation during CP development suggests that Fgf2 is not involved in CPe proliferation in vivo. Consistent with this observation is the failure of Fgf2 to increase proliferation in the tri-dimensional vesicle culture model. The CPe however, can respond to Fgf2 treatment, as the diameter of CPe vesicles is significantly increased by treatment with this growth factor. We show that this is due to an increase in cell aggregation during vesicle formation rather than increased secretion into the vesicle lumen. Finally, Fgf2 regulates expression of the CPe-associated transcription factors, Foxj1 and E2f5, whereas transthyretin, a marker of secretory activity, is not affected by Fgf2 treatment.

Conclusion

Fgf2 expression early in the development of both human and rodent choroid plexus, and its ability to modulate behaviour and gene expression in CPe, supports the view that Fgf signalling plays a role in the maintenance of integrity and function of this specialized epithelium, and that this role is conserved between rodents and humans.

The low density lipoprotein receptor-related protein 1 mediates uptake of amyloid beta peptides in an in vitro model of the blood-brain barrier cells

The metabolism of amyloid beta peptide (A beta) in the brain is crucial to the pathogenesis of Alzheimer disease. A body of evidence suggests that A beta is actively transported from brain parenchyma to blood across the blood-brain barrier (BBB), although the precise mechanism remains unclear. To unravel the cellular and molecular mechanism of A beta transport across the BBB, we established a new in vitro model of the initial internalization step of A beta transport using TR-BBB cells, a conditionally immortalized endothelial cell line from rat brain. We show that TR-BBB cells rapidly internalize A beta through a receptor-mediated mechanism. We also provide evidence that A beta internalization is mediated by LRP1 (low density lipoprotein receptor-related protein 1), since administration of LRP1 antagonist, receptor-associated protein, neutralizing antibody, or small interference RNAs all reduced A beta uptake. Despite the requirement of LRP1-dependent internalization, A beta does not directly bind to LRP1 in an in vitro binding assay. Unlike TR-BBB cells, mouse embryonic fibroblasts endogenously expressing functional LRP1 and exhibiting the authentic LRP1-mediated endocytosis (e.g. of tissue plasminogen activator) did not show rapid A beta uptake. Based on these data, we propose that the rapid LRP1-dependent internalization of A beta occurs under the BBB-specific cellular context and that TR-BBB is a useful tool for analyzing the molecular mechanism of the rapid transport of A beta across BBB.

Growth of choroid plexus epithelium vesicles in vitro depends on secretory activity

Although a number of models have been used to study choroid plexus epithelium (CPe) function, analysis in physiological conditions of this polarised epithelium which produces the majority of the cerebrospinal fluid (CSF) and is one of the key barriers between blood and CSF in the brain remains challenging. As CPe cells form polarised CPe vesicles when cultured in Matrigel, we have assessed their behaviour and potential use for pharmacological studies. Like CPe cells in vivo, CPe vesicles express transthyretin, E2f5, Fox-j1 and p73, and contain tight junctions, as indicated by ZO-1 expression and electron microscopy analysis. Time-lapse microscopy shows that CPe cells plated in Matrigel are highly migratory and rapidly form homotypic cell aggregates, which then reorganise to form vesicles whose size increases linearly overtime. Neither aggregate nor vesicle size is affected by AraC treatment, though this inhibitor significantly reduces proliferation in CPe monolayers. Increase in size of vesicles, which have reached a growth plateau is observed following addition of fluorescently-labelled CPe cells, which become incorporated into the vesicle walls. Significantly, treatment with secretion inhibitors blocks vesicle formation and their expansion. These results show that secretion, rather than cell division, controls vesicle growth, consistent with low levels of proliferation and thinning of the CPe observed both in growing vesicles and during CPe development. Therefore, changes in vesicle size can be used to evaluate the effect of putative molecules involved in the regulation of secretion.

Porcine brain microvessel endothelial cells as an in vitro model to predict in vivo blood-brain barrier permeability

The objective of the study was to establish primary cultured porcine brain microvessel endothelial cells (PBMECs) as an in vitro model to predict the blood-brain barrier (BBB) permeability in vivo. The intercellular tight junction formation of PBMECs was examined by electron microscopy and measured by transendothelial electrical resistance (TEER). The mRNA expression of several BBB transporters in PBMECs was determined by reverse transcriptionpolymerase chain reaction analysis. The in vitro permeability of 16 structurally diverse compounds, representing a range of passive diffusion and transporter-mediated mechanisms of brain penetration, was determined in PBMECs. Except for the perfusion flow rate marker diazepam, the BBB permeability of these compounds was determined either in our laboratory or as reported in literature using in situ brain perfusion technique in rats. Results in the present study showed that PBMECs had a high endothelium homogeneity, an mRNA expression of several BBB transporters, and high TEER values. Culturing with rat astrocyte-conditioned medium increased the TEER of PBMECs, but had no effect on the permeability of sucrose, a paracellular diffusion marker. The PBMEC permeability of lipophilic compounds measured under stirred conditions was greatly increased compared with that measured under unstirred conditions. The PBMEC permeability of the 15 test compounds, determined under the optimized study conditions, correlated with the in situ BBB permeability with an r2 of 0.60. Removal of the three system L substrates increased the r2 to 0.89. In conclusion, the present PBMEC model may be used to predict or rank the in vivo BBB permeability of new chemical entities in a drug discovery setting.

Establishment and characterization of conditionally immortalized endothelial cell lines from the thoracic duct and inferior vena cava of tsA58/EGFP double-transgenic rats

The basic biology of blood vascular endothelial cells has been well documented. However, little is known about that of lymphatic endothelial cells, despite their importance under normal and pathological conditions. The lack of a lymphatic endothelial cell line has hampered progress in this field. The objective of this study has been to establish and characterize lymphatic and venous endothelial cell lines derived from newly developed tsA58/EGFP transgenic rats harboring the temperature-sensitive simian virus 40 (SV40) large T-antigen and enhanced green fluorescent protein (EGFP). Endothelial cells were isolated from the transgenic rats by intraluminal enzymatic digestion. The cloned cell lines were named TR-LE (temperature-sensitive rat lymphatic endothelial cells from thoracic duct) and TR-BE (temperature-sensitive rat blood-vessel endothelial cells from inferior vena cava), respectively, and cultured on fibronectin-coated dishes in HuMedia-EG2 supplemented with 20% fetal bovine serum and Endothelial Mitogen at a permissive temperature, 33 degrees C. A temperature shift to 37 degrees C resulted in a decrease in proliferation with degradation of the large T-antigen and cleavage of poly (ADP-ribose) polymerase. TR-LE cells expressed lymphatic endothelial markers VEGFR-3 (vascular endothelial growth factor receptor), LYVE-1 (a lymphatic endothelial receptor), Prox-1 (a homeobox gene product), and podoplanin (a glomerular podocyte membrane mucoprotein), together with endothelial markers CD31, Tie-2, and VEGFR-2, whereas TR-BE cells expressed CD31, Tie-2, and VEGFR-2, but no lymphatic endothelial markers. Thus, these conditionally immortalized and EGFP-expressing lymphatic and vascular endothelial cell lines might represent an important tool for the study of endothelial cell functions in vitro.

Rat brain endothelial cell lines for the study of blood-brain barrier permeability and transport functions

(1) In vitro models of the BBB have been developed from cocultures between bovine, porcine, rodent or human brain capillary endothelial cells with rodent or human astrocytes. Since most in vivo BBB studies have been performed with small laboratory animals, especially rats, it is important to establish a rat brain endothelial (RBE) cell culture system that will allow correlations between in vitro and in vivo results. The present review will constitute a brief description of the best characterized RBE cell lines (RBE4, GP8/3.9, GPNT, RBEC1, TR-BBBs and rBCEC4 cell lines) and will summarize their recent and important contribution to our current knowledge of the BBB transport functions and permeability to blood-borne solutes, drugs, and cells. (2) In most cases, primary cultures of RBE cells were transduced with an immortalizing gene (SV40 or polyoma virus large T-antigen or adenovirus E1A), either by transfection of plasmid DNA or by infection using retroviral vectors. In one case however, the conditionally immortalized TR-BBB cell line was derived from primary cultures of brain endothelial cells of SV40-T-expressing transgenic rats. (3) All cell lines appear to have an endothelial morphology. The absence of foci formation would mean that the cells are not transformed. The endothelial origin is shown by the expression of Factor VIII-related antigen. Immortalized RBE cells express all the enzymes and transporters that are considered as specific for the blood-brain barrier endothelium, with similar characteristics to those expected from in vivo analyses, but at a significantly lower level. Some RBE cell lines are responsive to astroglial factors, such as RBE4 cells, rBEC4, and TR-BBB cells. None of the immortalized RBE cell lines appear to generate the necessary restrictive paracellular barrier properties that would allow to use them in transendothelial permeability screening. (4) RBE cell lines have been used to demonstrate that transporters such as organic cation transporter/carnitine transporter, serotonin transporter, and the ATA2 system A isoform are expressed in rat brain endothelium. When the transporter is shown to be expressed with the same properties in the immortalized RBE cells as in vivo, regulation studies may be initiated even if the transporter is down-regulated. Pharmacological applications have been proposed with well-characterized transporters such as monocarboxylic acid transporter-1, large neutral amino acid tansporter-1, nucleoside carrier systems, and P-glycoprotein. RBE cell monolayers have also been used to investigate the mechanism of the transendothelial transport of large molecules, such as immunoliposomes or nanoparticles, potentially useful as drug delivery vectors to the brain. (5) RBE4 and GP8 cell lines have been extensively used to demonstrate that intercellular adhesion molecule-1 (ICAM-1) engagement in brain endothelial cells triggers multiple signal transduction pathways. Using functional assays, it was established that ICAM-1 signaling is intimately and actively involved in facilitating lymphocyte infiltration. (6) Several RBE cell lines have been described, which constitute tentative in vitro models of the rat BBB. The major limitation of these models generally appears to be due to their relatively high paracellular permeability to small molecules, thus limiting their use for permeability studies. The strategies developed for the production of these RBE cell lines will enable the characterization of still more efficient permeability models, as well as the immortalization of human brain endothelial cells.

Permeability studies on in vitro blood-brain barrier models: physiology, pathology, and pharmacology

(1) The specifically regulated restrictive permeability barrier to cells and molecules is the most important feature of the blood-brain barrier (BBB). The aim of this review was to summarize permeability data obtained on in vitro BBB models by measurement of transendothelial electrical resistance and by calculation of permeability coefficients for paracellular or transendothelial tracers. (2) Results from primary cultures of cerebral microvascular endothelial cells or immortalized cell lines from bovine, human, porcine, and rodent origin are presented. Effects of coculture with astroglia, neurons, mesenchymal cells, blood cells, and conditioned media, as well as physiological influence of serum components, hormones, growth factors, lipids, and lipoproteins on the barrier function are discussed. (3) BBB permeability results gained on in vitro models of pathological conditions including hypoxia and reoxygenation, neurodegenerative diseases, or bacterial and viral infections have been reviewed. Effects of cytokines, vasoactive mediators, and other pathogenic factors on barrier integrity are also detailed. (4) Pharmacological treatments modulating intracellular cyclic nucleotide or calcium levels, and activity of protein kinases, protein tyrosine phosphatases, phospholipases, cyclooxygenases, or lipoxygenases able to change BBB integrity are outlined. Barrier regulation by drugs involved in the metabolism of nitric oxide and reactive oxygen species, as well as influence of miscellaneous treatments are also listed and evaluated. (5) Though recent advances resulted in development of improved in vitro BBB model systems to investigate disease modeling, drug screening, and testing vectors targeting the brain, there is a need for checking validity of permeability models and cautious interpretation of data.

Advances in the cell biology of transport via the inner blood-retinal barrier: establishment of cell lines and transport functions

The retinal capillary endothelial cells are connected to each other by tight junctions that play a key role in permeability as the inner blood-retinal barrier (inner BRB). Thus, understanding the inner BRB transport mechanism is an important step towards drug targeting of the retina. Nevertheless, inner BRB transport studies have been very limited in number since it is not easy to use the retinal capillaries, which are very small in size, for in vitro transport studies. Conditionally immortalized rat retinal capillary endothelial cells (TR-iBRB), pericytes (TR-rPCT) and Müller cell lines (TR-MUL) have been established from transgenic rats harboring the temperature-sensitive simian virus 40 large T-antigen gene. These cell lines possess respective cell type markers and maintain certain in vivo functions. Using a combination of newly developed cell lines and in vivo studies, we have elucidated the mechanism whereby vitamin C, L-cystine, and creatine are supplied to the retina. TR-iBRB cells are also able to identify transporters and apply to study regulation of transporters under pathophysiological conditions. Furthermore, these cell lines permit the investigation of cell-to-cell interactions and the expression of inner BRB-specific genes between TR-iBRB and other cell lines.

Factors affecting delivery of antiviral drugs to the brain

Although the CNS is in part protected from peripheral insults by the blood-brain barrier and the blood-cerebrospinal fluid barrier, a number of human viruses gain access to the brain, replicate within this organ, or sustain latent infection. The efficacy of antiviral drugs towards the cerebral viral load is often limited as both blood-brain interfaces impede their cerebral distribution. For polar compounds, the major factor restricting their entry lies in the tight junctions that occlude the paracellular pathway across these barriers. For compounds with more favourable lipid solubility properties, CNS penetration will be function of a number of physicochemical factors that include the degree of lipophilicity, size and ability to bind to protein or red blood cells, as well as other factors inherent to the vascular and choroidal systems, such as the local cerebral blood flow and the surface area available for exchange. In addition, influx and efflux transport systems, or metabolic processes active in both capillary endothelial cells and choroid plexus epithelial cells, can greatly change the bioavailability of a drug in one or several compartments of the CNS. The relative importance of these various factors with respect to the CNS delivery of the different classes of antiviral drugs is illustrated and discussed.

mRNA expression of the ATP-binding cassette transporter subfamily A (ABCA) in rat and human brain capillary endothelial cells

The ATP-binding cassette transporter subfamily A (ABCA) consists of the transporters mediating cholesterol release and regulated by cholesterol. As about 25% of total body cholesterol exists in the brain, sterol homeostasis is an important issue as far as central nervous system function is concerned. The purpose of this study was to clarify the mRNA expression of ABCA subtypes at the blood-brain barrier (BBB) using cultured rat and human brain capillary endothelial cells, TR-BBB and hBME cells, respectively. mRNA expression of ABCA1, 2, 3, 4, 5, 6, 7 and 8/9 was detected in TR-BBB cells. In the brain capillary-rich fraction, mRNA expression of ABCA1, 2, 3, 4, 5, 7 and 8/9 was detected. ABCA2 and 5 mRNA were also detected in hBME cells. These results demonstrate, for the first time, that ABCA subtypes are expressed at the rat and/or human BBB. The expression of ABCA subtypes at the BBB is likely to contribute to sterol homeostasis in the central nervous system.

Accessibility of endothelial and inducible nitric oxide synthase to the intracellular citrulline-arginine regeneration pathway

This study investigates our hypothesis that argininosuccinate synthase (AS), the rate-limiting enzyme for arginine (L-arg) regeneration from citrulline (L-cit), plays a pivotal role in supplying L-arg to endothelial (eNOS), but not inducible (iNOS) nitric oxide synthase, for nitric oxide (NO) production. Transgenic rat blood-brain barrier (TR-BBB) endothelial cells were used as a model to elucidate the accessibility of the L-arg compartments for NOS isozymes. NO production via eNOS or iNOS, with or without alpha-methyl-DL-aspartic acid (MDLA), an AS inhibitor, was measured by a fluorometric method. NO production via eNOS was activated by the calcium ionophore A23187, while via iNOS was induced by cytokines. AS activity was assayed by the amount of argininosuccinate regenerated from radioactive aspartic acid from cell extracts. Upon increased AS activity (5.9-fold) in cells grown in L-arg-free/L-cit-supplemented medium, A23187-activated NO production also significantly increased, however cytokine-induced NO production was not detected. A23187-activated NO production was observed not only in L-arg containing medium, but also L-arg-free and L-arg-free/L-cit-supplemented medium, and was abolished by MDLA regardless of medium type. Cytokine-induced NO production was only observed in L-arg containing medium, not in L-arg-free or L-arg-free/L-cit-supplemented medium, and it was not inhibited by MDLA in the L-arg containing medium. Our results indicate that extracellular L-arg was the only L-arg pool for cytokine-induced NO production and intracellular L-arg regenerated from L-cit via AS pathway was the major L-arg pool for A23187-activated NO production in TR-BBB endothelial cells. Therefore, modulation of AS activity could be a promising strategy to selectively alter NO production via eNOS, but not iNOS.

The Choroid Plexus‐Cerebrospinal Fluid System: From Development to Aging

The function of the cerebrospinal fluid (CSF) and the tissue that secretes it, the choroid plexus (CP), has traditionally been thought of as both providing physical protection to the brain through buoyancy and facilitating the removal of brain metabolites through the bulk drainage of CSF. More recent studies suggest, however, that the CP-CSF system plays a much more active role in the development, homeostasis, and repair of the central nervous system (CNS). The highly specialized choroidal tissue synthesizes trophic and angiogenic factors, chemorepellents, and carrier proteins, and is strategically positioned within the ventricular cavities to supply the CNS with these biologically active substances. Through polarized transport systems and receptor-mediated transcytosis across the choroidal epithelium, the CP, a part of the blood-CSF barrier (BCSFB), controls the entry of nutrients, such as amino acids and nucleosides, and peptide hormones, such as leptin and prolactin, from the periphery into the brain. The CP also plays an important role in the clearance of toxins and drugs. During CNS development, CP-derived growth factors, such as members of the transforming growth factor-beta superfamily and retinoic acid, play an important role in controlling the patterning of neuronal differentiation in various brain regions. In the adult CNS, the CP appears to be critically involved in neuronal repair processes and the restoration of the brain microenvironment after traumatic and ischemic brain injury. Furthermore, recent studies suggest that the CP acts as a nursery for neuronal and astrocytic progenitor cells. The advancement of our knowledge of the neuroprotective capabilities of the CP may therefore facilitate the development of novel therapies for ischemic stroke and traumatic brain injury. In the later stages of life, the CP-CSF axis shows a decline in all aspects of its function, including CSF secretion and protein synthesis, which may in themselves increase the risk for development of late-life diseases, such as normal pressure hydrocephalus and Alzheimer's disease. The understanding of the mechanisms that underlie the dysfunction of the CP-CSF system in the elderly may help discover the treatments needed to reverse the negative effects of aging that lead to global CNS failure.

A pericyte-derived angiopoietin-1 multimeric complex induces occludin gene expression in brain capillary endothelial cells through Tie-2 activation in vitro

Although tight-junctions (TJs) at the blood-brain barrier (BBB) are important to prevent non-specific entry of compounds into the CNS, molecular mechanisms regulating TJ maintenance remain still unclear. The purpose of this study was therefore to identify molecules, which regulate occludin expression, derived from astrocytes and pericytes that ensheathe brain microvessels by using conditionally immortalized adult rat brain capillary endothelial (TR-BBB13), type II astrocyte (TR-AST4) and brain pericyte (TR-PCT1) cell lines. Transfilter co-culture with TR-AST4 cells, and exposure to conditioned medium of TR-AST4 cells (AST-CM) or TR-PCT1 cells (PCT-CM) increased occludin mRNA in TR-BBB13 cells. PCT-CM-induced occludin up-regulation was significantly inhibited by an angiopoietin-1-neutralizing antibody, whereas the up-regulation by AST-CM was not. Immunoprecipitation and western blot analyses confirmed that multimeric angiopoietin-1 is secreted from TR-PCT1 cells, and induces occludin mRNA, acting through tyrosine phosphorylation of Tie-2 in TR-BBB13 cells. A fractionated AST-CM study revealed that factors in the molecular weight range of 30-100 kDa led to occludin induction. Conversely, occludin mRNA was reduced by transforming growth factor beta 1, the mRNA of which was up-regulated in TR-AST4 cells following hypoxic treatment. In conclusion, in vitro BBB model studies revealed that the pericyte-derived multimeric angiopoietin-1/Tie-2 pathway induces occludin expression.

New approaches to in vitro models of blood-brain barrier drug transport

The pharmaceutical industry has been searching for an in vitro blood-brain barrier (BBB) model that preserves in vivo transporter functions in CNS drug discovery and development. The application of conditionally immortalized cell lines derived from transgenic animals harboring temperature-sensitive SV40 large T-antigen gene, is a rational and promising approach to such a workable in vitro BBB model. The established brain capillary endothelial cell lines retain the in vivo transport rate of several compounds and various forms of gene expression. Furthermore, this new approach has enabled the development of stable and reproducible co-culture models with a pericyte cell line and/or an astrocyte cell line.

Recombinant arginine deiminase as a differential modulator of inducible (iNOS) and endothelial (eNOS) nitric oxide synthetase activity in cultured endothelial cells

Modulation of the extracellular level of arginine, substrate for nitric oxide synthetases, is a promising modality to alleviate certain pathological conditions where excess nitric oxide (NO) is produced. However, complications arise, as only preferential inhibition of the inducible nitric oxide synthetase (iNOS), but not endothelial nitric oxide synthetase (eNOS), is desired for the treatment of NO over-production. We investigated the effect of arginine deprivation mediated by a recombinant arginine deiminase (rADI) on the activity of iNOS and eNOS in an endothelial cell line, TR-BBB. Our results demonstrated that cytokine-induced NO production depends on the extracellular arginine as substrate. However, if sufficient citrulline is present in the medium, A23187-activated NO production by eNOS does not rely on extracellular arginine. Treatment with rADI can markedly inhibit cytokine-induced NO production via iNOS, but not A23187-activated NO production via eNOS. Our results also showed that the decrease of NO production by iNOS could be achieved by depleting arginine from the medium even under the conditions that would up-regulate iNOS expression. Thus, rADI appears to be a novel selective modulator of iNOS activity that may be a used as a tool in the study of pathological disorders where NO over-production plays a key role.

Expression and regulation of L-cystine transporter, system xc-, in the newly developed rat retinal Müller cell line (TR-MUL)

The purpose of the present study was to elucidate the expression and regulation of the L-cystine transporter, system x(c) (-), in Müller cells. In this study, newly developed conditionally immortalized rat Müller cell lines (TR-MUL) from transgenic rats harboring the temperature-sensitive SV 40 large T-antigen gene were used as an in vitro model. TR-MUL cells express large T-antigen and grow well at 33 degrees C with a doubling time of 30 h, but do not grow at 39 degrees C. TR-MUL cells express typical Müller cell markers such as S-100, glutamine synthetase, and EAAT1/GLAST, whereas EAAT2/GLT-1 and EAAT5 are not detected. TR-MUL cells also exhibit little or no expression of glial fibrillary acidic protein. We found that TR-MUL5 cells exhibited [(14)C]L-cystine uptake activity and expressed xCT and 4F2hc, which involve system x(c) (-). The uptake of [(14)C]L-cystine was significantly inhibited by L-glutamic acid and L-aspartic acid, whereas L-leucine had no effect. Following diethyl maleate (DEM) treatment, the glutathione concentration in TR-MUL5 cells was reduced in the first 24 h, then gradually recovered for more than 24 h. The L-cystine uptake rate and the xCT expression level in TR-MUL5 cells were enhanced by DEM treatment. In contrast, the 4F2hc expression level was unchanged. In conclusion, TR-MUL cells have the properties of Müller cells and exhibit system x(c) (-)-mediated L-cystine uptake activity. The oxidative stress conditions following DEM treatment activate L-cystine transport in TR-MUL cells due to the enhanced transcription of the xCT gene.

Interleukin-10 as a CNS therapeutic: the obstacle of the blood-brain/blood-spinal cord barrier

Interleukin (IL)-10 exerts beneficial effects on the central nervous system (CNS) after peripheral administration, but its penetration across the blood-brain barrier (BBB) has not been quantified. We show that 125I-IL-10 is stable in circulating blood but does not cross the intact BBB after intravenous delivery. Thus, peripheral IL-10 probably can serve as a CNS therapeutic only when the BBB is disrupted.

Establishment of conditionally immortalized rat retinal pericyte cell lines (TR-rPCT) and their application in a co-culture system using retinal capillary endothelial cell line (TR-iBRB2)

The purpose of this study was to establish and characterize a retinal pericyte cell line from retinal capillaries of transgenic rats harboring the temperature-sensitive simian virus 40 large T-antigen gene (tsA58 Tg rat), and to apply this to the co-culture with a retinal capillary endothelial cell line. The conditionally immortalized rat retinal pericyte cell lines (TR-rPCTs), which express a temperature-sensitive large T-antigen, were obtained from two tsA58 Tg rats. These cell lines had a multicellular nodule morphology and reacted positively with von Kossa staining, a marker of calcification. TR-rPCTs cells expressed mRNA of pericyte markers such as rat intercellular adhesion molecule-1, platelet-derived growth factor-receptor beta, angiopoietin-1, and osteopontin. Western blot analysis indicated that alpha-smooth muscle actin (alpha-SMA) was expressed in TR-rPCT3 and 4 cells. In contrast, alpha-SMA was induced by transforming growth factor-beta1 and its enhancement was reduced by basic fibroblast growth factor in TR-rPCT1 and 2 cells. When TR-rPCT1 cells were cultured with a rat retinal endothelial cell line (TR-iBRB2) in a contact co-culture system, the number of TR-iBRB2 cells were significantly reduced in comparison with that of a single culture of TR-iBRB2 cells, suggesting that physical contact between pericytes and retinal endothelial cells is important for the growth of retinal endothelial cells. In conclusion, conditionally immortalized retinal pericyte cell lines were established from tsA58 Tg rats. These cell lines exhibited the properties of retinal pericytes and can be applied in co-culture systems with a retinal capillary endothelial cell line.

Screening of Tanzanian plant extracts for their potential inhibitory effect on P-glycoprotein mediated efflux

For years, many efforts have been made to discover new drugs using plants as natural screening libraries. In this study, extracts of 43 Tanzanian medicinal plants were screened for their potential inhibitory effect on P-gp, using the secretory transport of Cyclosporin A (CsA) in the Caco-2 system as a measure of the functionality of P-gp efflux. Two out of these 43 plant extracts (extracts of Annickia kummeriae and Acacia nilotica) appeared to have a modulatory effect on P-gp related efflux carriers. In presence of the extract of Annickia kummeriae, a concentration dependent decrease on the polarity in transport of CsA was observed; the inhibitory effect of this extract on P-gp was comparable to that of valspodar, a known P-gp inhibiting agent. The exact nature of the active components of these botanicals remains to be identified.