Transendothelial movement of liposomes in vitro mediated by cancer cells, neutrophils or histamine

A two-chamber culture system has been used to examine the ability of small liposomes to cross an endothelial cell barrier in response to various stimuli. Transendothelial transit of liposomes was almost negligible in the presence of intact, healthy endothelial cells (EC). Addition of histamine induced a concentration-dependent increase in the movement of liposomes across the EC monolayer. In the presence of polymorphonuclear neutrophils (PMNs), migrating in response to a chemotactic gradient of N-Formil-Met-Leu-Phe (fMLP), both liposomes and IgG crossed EC monolayer by a paracellular pathway, largely independent of an association with the PMNs. The presence of cancer cell, growing in the lower chamber or the presence of cancer cell-conditioned media, also resulted in the passage of liposome across the EC. We conclude that EC monolayers are sufficiently disrupted by several physiologically relevant stimuli to allow for the transendothelial passage of liposomes. These results have important implications for the therapeutic use of liposome in the treatment of cancer or other inflammatory processes.     

The effects of pro- and anti-atherosclerotic factors on intracellular nucleotide concentration in murine endothelial cells

Abstract

Endothelial cell activation and dysfunction could lead to endothelial injury that is an important factor in the development of vascular diseases. Vascular injury is strongly associated with disturbed endothelial cell energetics and pyridine nucleotide pool. This study aimed to evaluate the effects of inflammatory stimuli (IL-6, LPS), uric acid, hyperglycemia, fatty acids, flavonoids, statins and nonsteroidal anti-inflammatory drugs on cellular concentration of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and nicotinamide adenine dinucleotide (NAD⁺) in cultured endothelial cells. Murine-immortalized heart endothelial cells (H5V cells) were treated with different concentrations of pro- and anti-atherosclerotic factors and intracellular concentration of nucleotides were measured using high performance liquid chromatography. Intracellular ATP concentration in H5V cells was not changed by inflammatory stimuli (IL-6 and LPS), uric acid, glucose, atorvastatin, acetylsalicylic acid, monounsaturated and polyunsaturated fatty acids. Only high concentration of palmitic acid (1?mM) and kaempferol (>0.1?mM) decreased intracellular ATP concentration. The concentration of intracellular ADP has not been altered by any of tested compounds. In turn, intracellular NAD⁺ pool was modified only by polyunsaturated fatty acids and atorvastatin. Linoleic acid, docosahexaenoic acid and atorvastatin increased cellular NAD⁺ concentration. Tested compounds have a small influence on murine endothelial cell energetics, but polyunsaturated fatty acids and atorvastatin increased intracellular NAD⁺ concentration that could be an important protective mechanism against endothelial cell injury.     

On-Chip Endothelial Inflammatory Phenotyping

Atherogenesis is potentiated by metabolic abnormalities that contribute to a heightened state of systemic inflammation resulting in endothelial dysfunction. However, early functional changes in endothelium that signify an individual''s level of risk are not directly assessed clinically to help guide therapeutic strategy. Moreover, the regulation of inflammation by local hemodynamics contributes to the non-random spatial distribution of atherosclerosis, but the mechanisms are difficult to delineate in vivo. We describe a lab-on-a-chip based approach to quantitatively assay metabolic perturbation of inflammatory events in human endothelial cells (EC) and monocytes under precise flow conditions. Standard methods of soft lithography are used to microfabricate vascular mimetic microfluidic chambers (VMMC), which are bound directly to cultured EC monolayers.¹ These devices have the advantage of using small volumes of reagents while providing a platform for directly imaging the inflammatory events at the membrane of EC exposed to a well-defined shear field. We have successfully applied these devices to investigate cytokine-,² lipid-^{3, 4} and RAGE-induced⁵ inflammation in human aortic EC (HAEC). Here we document the use of the VMMC to assay monocytic cell (THP-1) rolling and arrest on HAEC monolayers that are conditioned under differential shear characteristics and activated by the inflammatory cytokine TNF-α. Studies such as these are providing mechanistic insight into atherosusceptibility under metabolic risk factors.     

A role for VEGFR2 activation in endothelial responses caused by barrier disruptive OxPAPC concentrations

Introduction

Oxidation products of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphatidylcholine (OxPAPC) differentially modulate endothelial cell (EC) barrier function in a dose-dependent fashion. Vascular endothelial growth factor receptor-2 (VEGFR2) is involved in the OxPAPC-induced EC inflammatory activation. This study examined a role of VEGFR2 in barrier dysfunction caused by high concentrations of OxPAPC and evaluated downstream signaling mechanisms resulting from the effect of OxPAPC in EC from pulmonary and systemic circulation.

Methods

EC monolayer permeability in human pulmonary artery endothelial cells (HPAEC) and human aortic endothelial cells (HAEC) was monitored by changes in transendothelial electrical resistance (TER) across EC monolayers. Actin cytoskeleton was examined by immunostaining with Texas Red labeled phalloidin. Phosphorylation of myosin light chains (MLC) and VE-Cadherin was examined by Western blot and immunofluorescence techniques. The role of VEGFR2 in OxPAPC-induced permeability and cytoskeletal arrangement were determined using siRNA-induced VEGFR2 knockdown.

Results

Low OxPAPC concentrations (5–20 µg/ml) induced a barrier protective response in both HPAEC and HAEC, while high OxPAPC concentrations (50–100 µg/ml) caused a rapid increase in permeability ; actin stress fiber formation and increased MLC phosphorylation were observed as early as 30 min after treatment. VEGFR2 knockdown dramatically decreased the amount of MLC phosphorylation and stress fiber formation caused by high OxPAPC concentrations with modest effects on the amount of VE-cadherin phosphorylation at Y⁷³¹. We present evidence that activation of Rho is involved in the OxPAPC/VEGFR2 mechanism of EC permeability induced by high OxPAPC concentrations. Knockdown of VEGFR2 did not rescue the early drop in TER but prevented further development of OxPAPC-induced barrier dysfunction.

Conclusions

This study shows that VEGFR2 is involved in the delayed phase of EC barrier dysfunction caused by high OxPAPC concentrations and contributes to stress fiber formation and increased MLC phosphorylation.     

In vitro concentration dependent transport of phenytoin and phenobarbital,but not ethosuximide,by human P-glycoprotein

AimsOne possible mechanism for epilepsy drug resistance is overexpression of P-glycoprotein in the blood–brain barrier, but whether (or which) antiepileptic drugs (AEDs) are transported by P-gp remains unclear. We evaluated AEDs as P-gp substrates using cell monolayers.Main methodsBi-directional transport assays and concentration equilibrium transport assays (CETAs) were performed for phenytoin (PHT), phenobarbital (PB), and ethosuximide (ESM) using wildtype Madin–Darby Canine Kidney II cell line MDCKII and porcine renal endothelial cell line LLC–PK1 cells and these cells transfected with human MDR1 cDNA to express P-gp.Key findingsWildtype cells demonstrated no efflux transport of PHT, PB, or ESM. In CETAs, both MDR1-transfected cell lines transported PHT from basolateral to apical when PHT loading concentrations were 5 or 10, but not 20 µg/ml. MDCK–MDR1 cells transported PB when initial concentrations were 10 or 20, but not 5 µg/ml. LLC–MDR1 did not transport PB. P-gp inhibitor verapamil blocked efflux transport. MDR1-transfected cells did not transport ESM at 5.6 or 56 µg/ml. Bi-directional transport assays demonstrated weak transport for PHT but not PB or ESM.SignificanceHuman P-gp transports PHT and PB, but not ESM, in a concentration dependent manner. CETA may be more sensitive than bi-directional assays to detect transport of drugs with high passive diffusion. Potential P-gp substrates should be tested at clinically relevant concentration ranges.     

Culture of human corpus cavernosum endothelium

Summary A method for culturing endothelial cells (HCC-EC) from surgical specimens of human corpus cavernosum has been developed. The approach involves selective endothelial outgrowth from explants and may be generally applicable to tissue whose endothelium is not amenable to isolation by routine mechanical or enzymatic methods. The tissue is minced into pieces which are placed onto gelatin-or fibronectin-coated tissue culture plastic, and grown in medium suitable for microvascular endothelial cell growth (Carson and Haudenschild, In Vitro 22:344–354, 1986). By Days 5 to 7 EC colonies are found. Within a day or two after the appearance of the EC colonies, a non-EC cell type appears and, if undisturbed, quickly overgrows the EC. An exploitable temporal separation between the emergence of EC and non-EC is obtained when both conditioned medium (from bovine aortic endothelium) and retinal extract are present during the outgrowth period. Explants are removed by pipetting at the first sign of the emergence of the non-EC cell type. Once isolated, HCC-EC do not require conditioned medium but do require either retinal extract or acidic fibroblast growth factor for survival and growth. Approximately 60% of the first passage cultures are at least 80% EC as judged by DiI-Ac-LDL labeling. One corpus (0.3×0.3×0.5 cm) usually produces 120 cm² of primary culture within 2 wk. These EC form contact-inhibited monolayers and stain positively for Factor VIII. They have a doubling time at 6th passage of 48 h and a plateau density of 5 to 7×10⁴ cells/cm². The availability of such cultures should facilitate the study of endothelium-mediated responses which play an important role in the erectile function of human penile corpus cavernosum. Supported by NIH R01 HL23567-09, DK-39080-01, DK40025-01, DK40487-01.     

Generation of an Immortalized Murine Brain Microvascular Endothelial Cell Line as an In Vitro Blood Brain Barrier Model

Epithelial and endothelial cells (EC) are building paracellular barriers which protect the tissue from the external and internal environment. The blood-brain barrier (BBB) consisting of EC, astrocyte end-feet, pericytes and the basal membrane is responsible for the protection and homeostasis of the brain parenchyma. In vitro BBB models are common tools to study the structure and function of the BBB at the cellular level. A considerable number of different in vitro BBB models have been established for research in different laboratories to date. Usually, the cells are obtained from bovine, porcine, rat or mouse brain tissue (discussed in detail in the review by Wilhelm et al. ¹). Human tissue samples are available only in a restricted number of laboratories or companies ^2,3. While primary cell preparations are time consuming and the EC cultures can differ from batch to batch, the establishment of immortalized EC lines is the focus of scientific interest.Here, we present a method for establishing an immortalized brain microvascular EC line from neonatal mouse brain. We describe the procedure step-by-step listing the reagents and solutions used. The method established by our lab allows the isolation of a homogenous immortalized endothelial cell line within four to five weeks. The brain microvascular endothelial cell lines termed cEND ⁴ (from cerebral cortex) and cerebEND ⁵ (from cerebellar cortex), were isolated according to this procedure in the Förster laboratory and have been effectively used for explanation of different physiological and pathological processes at the BBB. Using cEND and cerebEND we have demonstrated that these cells respond to glucocorticoid- ^4,6-9 and estrogen-treatment ¹⁰ as well as to pro-infammatory mediators, such as TNFalpha ^5,8. Moreover, we have studied the pathology of multiple sclerosis ¹¹ and hypoxia ^12,13 on the EC-level. The cEND and cerebEND lines can be considered as a good tool for studying the structure and function of the BBB, cellular responses of ECs to different stimuli or interaction of the EC with lymphocytes or cancer cells.     

Solid Supported Vesicles for Bactericide Delivery

Abstract

Cationic and anionic liposomes have been prepared by extrusion from dipalmitoylphosphatidylcholine (DPPC) and its mixtures with cholesterol and dimethyldioctadecyltrimethylammonium bromide (DDAB) and with phosphatidylinositol (PI) respectively covering a range of composition from 0 to 19 mole % DDAB and PI. The adsorption of liposomal lipid from the liposome dispersion onto particles of silica and titanium dioxide in suspension has been studied as a function of liposome composition and concentration. The adsorption isotherms have been fitted using a Langmuir equation from which the binding constants and maximum surface coverage were obtained. The Gibbs energies of adsorption for the cationic liposomes were on average -61.0 ± 2.1 kJ mol^?1 (on silica) and -50.6 ± 2.9 kJ mol^?1 (on titanium dioxide). On average saturation adsorption is equivalent to 3 to 10 lipid monolayers on silica and 3 to 7 on titanium dioxide. Using liposomes encapsulating D-glucose it is demonstrated that there is almost no release of glucose on adsorption of the lipid, indicating that the liposomes are adsorbed intact to form a liposome monolayer on the particle surfaces. Adsorption of intact liposomes to form a close-packed liposome monolayer of solid supported vesicles (SSV) is shown to be equivalent to on average 7.0 ± 0.2 phospholipid monolayers. The SSVs are shown to have increased stability to disruption by surfactants and when carrying the oil-soluble bactericide, Triclosan?, to be capable of inhibiting the growth of oral bacteria from immobilised biofilms.     

Endothelial Cell E- and P-Selectin and Vascular Cell Adhesion Molecule-1 Function as Signaling Receptors

Previous studies have shown that polymorphonuclear leukocyte (PMN) adherence to endothelial cells (EC) induces transient increases in EC cytosolic free calcium concentration ([Ca²⁺]_i) that are required for PMN transit across the EC barrier (Huang, A.J., J.E. Manning, T.M. Bandak, M.C. Ratau, K.R. Hanser, and S.C. Silverstein. 1993. J. Cell Biol. 120:1371–1380). To determine whether stimulation of [Ca²⁺]_i changes in EC by leukocytes was induced by the same molecules that mediate leukocyte adherence to EC, [Ca²⁺]_i was measured in Fura2-loaded human EC monolayers. Expression of adhesion molecules by EC was induced by a pretreatment of the cells with histamine or with Escherichia coli lipopolysaccharide (LPS), and [Ca²⁺]_i was measured in single EC after the addition of mAbs directed against the EC adhesion proteins P-selectin, E-selectin, intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), or platelet/endothelial cell adhesion molecule-1 (PECAM-1). Both anti–P- and anti–E-selectin mAb, as well as anti–VCAM-1 mAb, induced transient increases in EC [Ca²⁺]_i that were comparable to those induced by 200 μM histamine. In contrast, no effect was obtained by mAbs directed against the endothelial ICAM-1 or PECAM-1. PMN adherence directly stimulated increases in [Ca²⁺]_i in histamine- or LPS-treated EC. mAbs directed against leukocyte CD18 or PECAM-1, the leukocyte counter-receptors for endothelial ICAM-1 and PECAM-1, respectively, did not inhibit PMN-induced EC activation. In contrast, mAb directed against sialyl Lewis x (sLe^x), a PMN ligand for endothelial P- and E-selectin, completely inhibited EC stimulation by adherent PMN. Changes in EC [Ca²⁺]_i were also observed after adherence of peripheral blood monocytes to EC treated with LPS for 5 or 24 h. In these experiments, the combined addition of mAbs to sLe^x and VLA-4, the leukocyte counter-receptor for endothelial VCAM-1, inhibited [Ca²⁺]_i changes in the 5 h–treated EC, whereas the anti–VLA-4 mAb alone was sufficient to inhibit [Ca²⁺]_i changes in the 24 h-treated EC. Again, no inhibitory effect was observed with an anti-CD18 or anti–PECAM-1 mAb. Of note, the conditions that induced changes in EC [Ca²⁺]_i, i.e., mAbs directed against endothelial selectins or VCAM-1, and PMN or monocyte adhesion to EC via selectins or VCAM-1, but not via ICAM-1 or PECAM-1, also induced a rearrangement of EC cytoskeletal microfilaments from a circumferential ring to stress fibers. We conclude that, in addition to their role as adhesion receptors, endothelial selectins and VCAM-1 mediate endothelial stimulation by adhering leukocytes.     

The effect of fibrin on endothelial cell migration in vitro

Endothelial cells are known to migrate and come into contact with fibrin during numerous physiological processes, such as in wound healing and in tumor growth. The present study was initiated to investigate the effect of fibrin on endothelial cell migration in vitro. Endothelial cell migration was assayed by wounding confluent monolayers of bovine aortic endothelial cells with a razor blade and counting the number of cells crossing the wound per unit time. Wound-induced proliferation of endothelial cells was inhibited by mitomycin C-treatment without affecting endothelial cell migration, indicating that in this assay migration could be measured independent of proliferation. Migration of endothelial cells in vitro was inhibited by fibrin in a concentration dependent manner. Endothelial cell migration under fibrin was further reduced by plasminogen depletion of the serum, and fibrin still inhibited the migration of mitomycin C-treated endothelial cells. Kadish et al. (Tissue and Cell, 11, 99, 1979) previously reported that fibrin did not affect EC migration in vitro. The inability to inhibit EC migration with fibrin appears to be due to their assay system which employed agarose, since pre-treating the wounded monolayer with agarose eliminated the inhibition of EC migration by fibrin. The present results indicate that EC migration in vitro can be used as a model system for studying the interaction of fibrin with EC.     

The involvement of parenchymal,Kupffer and endothelial liver cells in the hepatic uptake of intravenously injected liposomes effects of lanthanum and gadolinium salts

¹²⁵I-labeled albumin or poly(vinyl pyrrolidone) encapsulated in intermediate size multilamellar or unilamellar liposomes with 30–40% of cholesterol were injected intravenously into rats. In other experiments liposomes containing phosphatidyl[Me-¹⁴C]choline were injected. 1 h after injection parenchymal or non-parenchymal cells were isolated. Non-parenchymal cells were separated by elutriation centrifugation into a Kupffer cell fraction and an endothelial cell fraction. From the measurements of radioactivities in the various cell fractions it was concluded that the liposomes are almost exclusively taken up by the Kupffer cells. Endothelial cells did not contribute at all and hepatocytes only to a very low extent to total hepatic uptake of the ¹²⁵I-labels. Of the ¹⁴C-label, which orginates from the phosphatidylcholine moiety of the liposomes, much larger proportions were recovered in the hepatocytes. A time-dependence study suggested that besides the involvement of phosphatidylcholine exchange between liposomes and high density lipoprotein, a process of intercellular transfer of lipid label from Kupffer cells to the hepatocytes may be involved in this phenomenon. Lanthanum or gadolinium salts, which effectively block Kupffer cell activity, failed to accomplish an increase in the fraction of liposomal material recovered in the parenchymal cells. This is compatible with the notion that liposomes of the type used in these experiments have no, or at most very limited, access to the liver parenchyma following their intravenous administration to rats.     

Cytotoxicity to a Tumor Cell Line of Epoxy-Phosphatidylinositol Liposomes

Abstract

Selective cytotoxicity of tumor cells induced by liposomal plant phosphatidylinositol (Ptdlns) has been studied. We could not always obtain cytotoxic plant Ptdlns liposomes in a series of experiments. Moreover, animal Ptdlns occasionally showed cytotoxicity towards tumor cells. By ¹H nuclear magnetic resonance analysis of non-and cytotoxic Ptdlns, it has been suggested that oxidized acyl residues, such as hydroperoxide or dioxetan, may have been present in the cytotoxic Ptdlns. We have prepared epoxy-Ptdlns, as an analogous compound of the oxidized lipid, from noncytotoxic Ptdlns by chemical synthesis. the epoxy-PtdIns liposomes showed cytotoxicity towards tumor cells. In the presence of 100 µM epoxy-Ptdlns liposomes, normal human peripheral lymphocytes survived for 3 days, but Raji human lymphoblastoid-like cells were almost all killed. However, at higher concentrations, epoxy-PtdIns liposomes were also cytotoxic to normal cells.     

Correlation between octanol/water and liposome/water distribution coefficients and drug absorption of a set of pharmacologically active compounds

Abstract

Absorption and consequent therapeutic action are key issues in the development of new drugs by the pharmaceutical industry. In this sense, different models can be used to simulate biological membranes to predict the absorption of a drug. This work compared the octanol/water and the liposome/water models. The parameters used to relate the two models were the distribution coefficients between liposomes and water and octanol and water and the fraction of drug orally absorbed. For this study, 66 drugs were collected from literature sources and divided into four groups according to charge and ionization degree: neutral; positively charged; negatively charged; and partially ionized/zwitterionic. The results show a satisfactory linear correlation between the octanol and liposome systems for the neutral (R^2?=?0.9324) and partially ionized compounds (R^2?=?0.9367), contrary to the positive (R^2?=?0.4684) and negatively charged compounds (R^2?=?0.1487). In the case of neutral drugs, results were similar in both models because of the high fraction orally absorbed. However, for the charged drugs (positively, negatively, and partially ionized/zwitterionic), the liposomal model has a more-appropriate correlation with absorption than the octanol model. These results show that the neutral compounds only interact with membranes through hydrophobic bonds, whereas charged drugs favor electrostatic interactions established with the liposomes. With this work, we concluded that liposomes may be a more-appropriate biomembrane model than octanol for charged compounds.     

Changes in Morphology,Anatomy, and Photosynthetic Capacity of Needles of Japanese Larch (Larix kaempferi) Seedlings Grown in High CO2 Concentrations

Photosynthetic traits of two-year-old Japanese larch seedlings (Larix kaempferi Carr.) grown at elevated CO₂ concentrations were studied in relation to structural changes in the needles. Seedlings were grown at two CO₂ concentrations, 360 (AC) and 720 (EC) mol mol^–1 at high and low nutrient supply rates, high N (HN) and low N (LN). The photosynthetic capacity fell significantly in EC+LN, but increased significantly in EC+HN. Since the mesophyll surface area exposed to intercellular space per unit leaf area (A^mes/A) is correlated with the photosynthetic rate, we measured A^mes/A for larch needles growing in EC. Changes of A^mes/A in both EC+HN and EC+LN were very similar to the changes in photosynthetic capacity. This suggests that the changes of A^mes/A in EC probably caused the changes in the photosynthetic capacity. The changes of A^mes/A in EC were attributed to changes in the mesophyll cell size and mesophyll cell number. The photosynthetic capacity in EC can be explained by taking morphological and structural adaptations into account as well as biochemical factors.     

Endothelial Cell Permeability during Hantavirus Infection Involves Factor XII-Dependent Increased Activation of the Kallikrein-Kinin System

Hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS) are diseases caused by hantavirus infections and are characterized by vascular leakage due to alterations of the endothelial barrier. Hantavirus-infected endothelial cells (EC) display no overt cytopathology; consequently, pathogenesis models have focused either on the influx of immune cells and release of cytokines or on increased degradation of the adherens junction protein, vascular endothelial (VE)-cadherin, due to hantavirus-mediated hypersensitization of EC to vascular endothelial growth factor (VEGF). To examine endothelial leakage in a relevant in vitro system, we co-cultured endothelial and vascular smooth muscle cells (vSMC) to generate capillary blood vessel-like structures. In contrast to results obtained in monolayers of cultured EC, we found that despite viral replication in both cell types as well as the presence of VEGF, infected in vitro vessels neither lost integrity nor displayed evidence of VE-cadherin degradation. Here, we present evidence for a novel mechanism of hantavirus-induced vascular leakage involving activation of the plasma kallikrein-kinin system (KKS). We show that incubation of factor XII (FXII), prekallikrein (PK), and high molecular weight kininogen (HK) plasma proteins with hantavirus-infected EC results in increased cleavage of HK, higher enzymatic activities of FXIIa/kallikrein (KAL) and increased liberation of bradykinin (BK). Measuring cell permeability in real-time using electric cell-substrate impedance sensing (ECIS), we identified dramatic increases in endothelial cell permeability after KKS activation and liberation of BK. Furthermore, the alterations in permeability could be prevented using inhibitors that directly block BK binding, the activity of FXIIa, or the activity of KAL. Lastly, FXII binding and autoactivation is increased on the surface of hantavirus-infected EC. These data are the first to demonstrate KKS activation during hantavirus infection and could have profound implications for treatment of hantavirus infections.     

Short-Term Shear Stress Induces Rapid Actin Dynamics in Living Endothelial Cells

Hemodynamic shear stress guides a variety of endothelial phenotype characteristics, including cell morphology, cytoskeletal structure, and gene expression profile. The sensing and processing of extracellular fluid forces may be mediated by mechanotransmission through the actin cytoskeleton network to intracellular locations of signal initiation. In this study, we identify rapid actin-mediated morphological changes in living subconfluent and confluent bovine aortic endothelial cells (ECs) in response to onset of unidirectional steady fluid shear stress (15 dyn/cm²). After flow onset, subconfluent cells exhibited dynamic edge activity in lamellipodia and small ruffles in the downstream and side directions for the first 12 min; activity was minimal in the upstream direction. After 12 min, peripheral edge extension subsided. Confluent cell monolayers that were exposed to shear stress exhibited only subtle increases in edge fluctuations after flow onset. Addition of cytochalasin D to disrupt actin polymerization served to suppress the magnitude of flow-mediated actin remodeling in both subconfluent confluent EC monolayers. Interestingly, when subconfluent ECs were exposed to two sequential flow step increases (1 dyn/cm² followed by 15 dyn/cm² 12 min later), actin-mediated edge activity was not additionally increased after the second flow step. Thus, repeated flow increases served to desensitize mechanosensitive structural dynamics in the actin cytoskeleton.     

Enhanced permeability across Caco-2 cell monolayers by specific mannosylating ligand of buserelin acetate proliposomes

Context: Oral delivery of peptide and protein drugs still remains the area of challenges due to their low stability and permeability across GI tract. Among numerous attempts, the receptor-mediated drug targeting is a promising approach to enhance GI permeability.

Objective: The aim of this study was to prepare mannosylated buserelin acetate (MANS-BA) proliposome powders grafted with N-octadecyl-d-mannopyranosylamine (SAMAN) as targeting moiety and evaluate their permeability across Caco-2 cell monolayers.

Materials and methods: The MANS-BA proliposome powders were prepared by coprecipitation method. The targeting moiety SAMAN was synthesized in-house and confirmed by characterization using Fourier transform infrared (FTIR) and differential scanning calorimeter (DSC).

Results: The MANS-BA liposomes reconstituted from proliposome powders exhibited the oligolamellar vesicular structure of phospholipid bilayer. Their size, zeta potential and entrapment efficiency were in the ranges of 93.11–218.95?nm, ?24.03 to ?37.15?mV and 21.12–33.80%, respectively. The permeability of reconstituted MANS-BA liposomes across Caco-2 cell monolayers was significantly enhanced to about 1.2- and 2.2-fold over those of conventional BA liposomes and solution, respectively.

Discussion: Increase in dicetylphosphate, cholesterol and SAMAN contents resulted in significant increase in size and zeta potential of reconstituted MAN-BA liposomes. The entrapment efficiency was increased with increasing dicetylphosphate and mannitol contents in liposomes containing cholesterol.

Conclusions: The significantly enhanced permeability across Caco-2 cell monolayers of MANS-BA liposomes might be due to the role of mannose receptor on intestinal enterocytes.     

Delivery of negatively charged liposomes into the atherosclerotic plaque of apolipoprotein E-deficient mouse aortic tissue

Liposomes have been used to diagnose and treat cancer and, to a lesser extent, cardiovascular disease. We previously showed the uptake of anionic liposomes into the atheromas of Watanabe heritable hyperlipidemic rabbits within lipid pools. However, the cellular distribution of anionic liposomes in atherosclerotic plaque remains undescribed. In addition, how anionic liposomes are absorbed into atherosclerotic plaque is unclear. We investigated the uptake and distribution of anionic liposomes in atherosclerotic plaque in aortic tissues from apolipoprotein E-deficient (ApoE^–/–) mice. To facilitate the tracking of liposomes, we used liposomes containing fluorescently labeled non-silencing small interfering RNA. Confocal microscopy analysis showed the uptake of anionic liposomes into atherosclerotic plaque and colocalization with macrophages. Transmission electron microscopy analysis revealed anionic liposomal accumulation in macrophages. To investigate how anionic liposomes cross the local endothelial barrier, we examined the role of clathrin-mediated endocytosis in human coronary artery endothelial cells (HCAECs) treated with or without the inflammatory cytokine tumor necrosis factor (TNF)-α. Pretreatment with amantadine, an inhibitor of clathrin-mediated endocytosis, significantly decreased liposomal uptake in HCAECs treated with or without TNF-α by 77% and 46%, respectively. Immunoblot analysis showed that endogenous clathrin expression was significantly increased in HCAECs stimulated with TNF-α but was inhibited by amantadine. These studies indicated that clathrin-mediated endocytosis is partly responsible for the uptake of liposomes by endothelial cells. Our results suggest that anionic liposomes target macrophage-rich areas of vulnerable plaque in ApoE^–/– mice; this finding may lead to the development of novel diagnostic and therapeutic strategies for treating vulnerable plaque in humans.     

Interferon-γ and high glucose-induced opening of Cx43 hemichannels causes endothelial cell dysfunction and damage

Both IFN-γ or high glucose have been linked to systemic inflammatory imbalance with serious repercussions not only for endothelial function but also for the formation of the atherosclerotic plaque. Although the uncontrolled opening of connexin hemichannels underpins the progression of various diseases, whether they are implicated in endothelial cell dysfunction and damage evoked by IFN-γ plus high glucose remains to be fully elucidated. In this study, by using live cell imaging and biochemical approaches, we demonstrate that IFN-γ plus high glucose augment endothelial connexin43 hemichannel activity, resulting in the increase of ATP release, ATP-mediated Ca²⁺ dynamics and production of nitric oxide and superoxide anion, as well as impaired insulin-mediated uptake and intercellular diffusion of glucose and cell survival. Based on our results, we propose that connexin 43 hemichannel inhibition could serve as a new approach for tackling the activation of detrimental signaling resulting in endothelial cell dysfunction and death caused by inflammatory mediators during atherosclerosis secondary to diabetes mellitus.     

Statin therapy influences endothelial cell morphology and F-actin cytoskeleton structure when exposed to static and laminar shear stress conditions

AimsTo determine how statin drugs (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) affect endothelial cell (EC) shape and F-actin cytoskeleton arrangement in the presence of physiologically relevant wall shear stress (WSS) of 12.5 dyn/cm².Main methodsHuman abdominal aortic endothelial cells (HAAECs) were cultured to a confluent monolayer within three dimensional tissue culture models and presheared for 6 h at 12.5 dyn/cm² within a continuous flow loop. Statins were added to the perfusion media and the perfusion was continued for a further 24 h. ECs were then analyzed for morphology and F-actin cytoskeleton arrangement using light microscopy and laser scanning confocal microscopy.Key findingsECs became rounded with a significantly higher shape index with the addition of 10 μM simvastatin under both static and flow conditions. F-actin cytoskeleton structure was disorganized and fragmented with statin treatment under static and flow conditions. Neither of these findings were observed with the addition of both simvastatin and 200 μM mevalonate, confirming regulation through the cholesterol biosynthesis pathway.SignificanceEC morphology and F-actin cytoskeleton arrangement are regulated through the cholesterol biosynthesis pathway and are therefore impacted by statin treatment. ECs treated with statins became rounded, which is usually associated with unhealthy cells in regions of the vasculature prone to developing atherosclerotic plaques.