Methods for microcarrier culture of bovine pulmonary artery endothelial cells avoiding the use of enzymes

An ultrafast enzyme-free acoustic technique for detaching adhered cells in microchannels

Adherent cultured cells are widely used biological tools for a variety of biochemical and biotechnology applications, including drug screening and gene expression analysis. One critical step in culturing adherent cells is the dissociation of cell monolayers into single-cell suspensions. Different enzymatic and non-enzymatic methods have been proposed for this purpose. Trypsinization, the most common enzymatic method for dislodging adhered cells, can be detrimental to cells, as it can damage cell membranes and ultimately cause cell death. Additionally, all available techniques require a prolonged treatment duration, typically on the order of minutes (5-10 min). Dissociation of cells becomes even more challenging in microfluidic devices, where, due to the nature of low Reynolds number flow and reduced mixing efficiency, multiple washing steps and prolonged trypsinization may be necessary to treat all cells. Here, we report a novel acoustofluidic method for the detachment of cells adhered onto a microchannel surface without exposing the cells to any enzymatic or non-enzymatic chemicals. This method enables a rapid (i.e., on the order of seconds), cost-effective, and easy-to-operate cell detachment strategy, yielding a detachment efficiency of ∼99% and cellular viability similar to that of the conventional trypsinization method. Also, as opposed to biochemical-based techniques (e.g., enzymatic), in our approach, cells are exposed to the dissociating agent (i.e., substrate-mediated acoustic excitation and microstreaming flow) only for as long as they remain attached to the substrate. After dissociation, the effect of acoustic excitation is reduced to microstreaming flow, therefore, minimizing unwanted effects of the dissociating agent on the cell phenotype. Additionally, our results suggest that cell excitation at acoustic powers lower than that required for complete cell detachment can potentially be employed for probing the adhesion strength of cell-substrate attachment. This novel approach can, therefore, be used for a wide range of lab-on-a-chip applications.

Culture and purification of SD rat corpus cavernosum endothelial cells by enzymatic digestion combined with mechanical extrusion and fixed-point digestion

To explore a new method of in vitro culture and purification of rat corpus cavernosum endothelial cells (CCECs). Male Sprague-Dawley rats' penile tissue were digested with elastase or collagenase combined with mechanical extrusion to isolate and culture the CCECs. The fixed-point digestion method was used to purify the primary cells. High-purity CCECs were successfully isolated. Following the digestion of the primary CCECs by elastase or collagenase coupled with mechanical extrusion, the cells were paving stone- and cobblestone-shaped over 10 days. The cell purity yielded in the second generation (P2) CCECs after using the fixed-point digestion method was significantly high. Compared with primary CCECs extracted by elastase digestion combined with the mechanical extrusion method, CCECs cultured by collagenase digestion yielded higher purity and a more stable morphology after fixed-point digestion and purification. Immunofluorescence staining of the third generation CCECs and the expression results of endothelial cell-associated marker antibodies CD31 and VWF were positive, and flow cytometry showed the purity of CCECs was 96.9%. Enzymatic digestion combined with mechanical extrusion and fixed-point digestion is a simple, economical method for in vitro culture and purification of CCECs, which is conducive to studying the pathophysiological mechanisms of endothelial dysfunction and erectile dysfunction.

In VitroModels to Study Mechanisms of Lung Toxicity

Several functioning in vitro systems of varying complexity are currently in use for the study of mechanisms of lung toxicity. The isolated perfused lung is the model closest to the in vivo situation. It is a suitable model for combining metabolic and functional studies. It is, for instance, possible to relate changes in lung mechanics and lung perfusion flow to the release of various mediators during exposure of the lung to various agents. A simpler model may be constructed from lung slices which are less viable but suitable for uptake as well as metabolism studies.

Specific lung cells such as Clara cells and type II pneumocytes have been isolated and cultured and are valuable tools for studies of the molecular mechanisms of lung toxicity, particularly in cases of cell-specific toxicity. There is, however, a great need to develop techniques for the isolation and culture of other types of lung cells and also to improve the culturing techniques for those already isolated.

Atrial fibrillation in pigs induces left atrial endocardial transcriptional remodelling

The leading cause of cardioembolic stroke is atrial fibrillation (AF), which predisposes to atrial thrombus formation. Although rheological alterations promote a hypercoagulable environment, as yet undefined factors contribute to thrombogenesis. The role of the endocardium has barely been explored. To approach this topic, rapid atrial pacing (RAP) was applied in four pigs to mimic A F. Left and right endocardial cells were isolated separately and their gene expression pattern was compared with that of four control pigs. The AF-characteristic rhythm disorders and endothelial nitric oxide synthase down-regulation were successfully reproduced, and validated RAP to mimic A F. A change was observed in the transcriptomic endocardial profile after RAP: the expression of 364 genes was significantly altered (p<0.01), 29 of them having passed the B>0 criteria. The left atrial endocardium [325 genes (7 genes, B>0)] was largely responsible for such alterations. Blood coagulation, blood vessel morphogenesis and inflammatory response are among the most significant altered functions, and help to explain the activation of coagulation observed after RAP: D-dimer, 0.49 (1.63) vs. 0.23 (0.24) mg/l [median (interquartile range)] in controls, p=0.02. Furthermore, three genes directly related to thrombotic processes were differentially expressed after RAP: FGL2 [fold change (FC)=0.85; p=0.007], APLP2 (FC=-0.47; p=0.005) and ADAMTS-18 (FC=-0.69; p=0.004). We demonstrate for the first time that AF induces a global expression change in the left atrial endocardium associated with an activation of blood coagulation. The nature of some of the altered functions and genes provides clues to identify new therapeutic targets.

Methods for the Initiation and Maintenance of Human Endothelial Cell Culture

The culture of human endothelial cells for the in vitro investigation of the metabolic, synthetic, and physiologic functions of these cells has grown increas ingly common. Model systems investigating the pathogenesis of atherosclerosis are being developed. Methods for the initiation and maintenance of human en dothelial cell cultures are described. The roles of cryopreservation, microcar rier culturing, and roller bottle mass culturing are discussed.

Establishment of a microcarrier culture system with serial sub-cultivation for functionally active human endothelial cells

A microcarrier culture system was established for a large-scale production of functional human endothelial cells. It has been difficult to cultivate human endothelial cells in large quantities for the reasons that specific growth factor and extracellular matrix are required for the survival and proliferation of the cells and the life span of the primary cells are limited. A lot of studies have reported that the shear stress gives significant influences on the structure, growth rate and biological functions of endothelial cells. We aimed to develop a convenient microcarrier culture system for human endothelial cells which can reproduce the flow effects experienced in vivo or in vitro. In 200 mL volume culture, human umbilical vein endothelial cells (HUVEC) could be serially sub-cultivated by optimizing the culture conditions such as shear strength, growth factor, beads and seeding cell concentration, serum concentration, and passage timing. The growth rate was enhanced depending on the shear strength and the life span of the cells was elongated until over 43PDL which is much longer than those of monolayer cultures. The cells maintained the diploidy of over 80% without obvious abnormal changes in the chromosomes. The serially sub-cultured microcarrier cells maintained various endothelial cell functions such as the syntheses of von Willebrand factor (vWf), prostacyclin and other biological substances, the expression of CD31, and the VEGF(165) dependent growth characteristic. The synthesis of biological products was affected by shear strength. In the case of prostacyclin, a different synthesis response was observed between steady flow and transiently reduced shear strength. The synthesis of endothelin-1 (ET-1) was down-regulated by increase of shear strength different from those of other products. The culture system was scaled up until 2 L volume under the optimum DO control. The cells synthesized IL-6 in response to shear strength. These results indicate that the established microcarrier system might be able to contribute to the supply of functional human endothelial cells for various medical applications such as the reconstruction of injured blood vessels caused by atherosclerosis or restenosis of coronary arteries after angioplasty, and the construction of an anti-coagulable artificial blood vessel or an artificial skin with good transplant-ability.

Characterization of aggregation and protein expression of bovine corneal endothelial cells as microcarrier cultures in a rotating-wall vessel

Rotating-wall vessels are beneficial to tissue engineering in that the reconstituted tissue formed in these low-shear bioreactors undergoes extensive three-dimensional growth and differentiation. In the present study, bovine corneal endothelial (BCE) cells were grown in a high-aspect rotating-wall vessel (HARV) attached to collagen-coated Cytodex-3 beads as a representative monolayer culture to investigate factors during HARV cultivation which affect three-dimensional growth and protein expression. A collagen type I substratum in T-flask control cultures increased cell density of BCE cells at confluence by 40% and altered the expression of select proteins (43, 50 and 210 kDa). The low-shear environment in the HARV facilitated cell bridging between microcarrier beads to form aggregates containing upwards of 23 beads each, but it did not promote multilayer growth. A kinetic model of microcarrier aggregation was developed which indicates that the rate of aggregation between a single bead and an aggregate was nearly 10 times faster than between two aggregate and 60 times faster than between two single beads. These differences reflect changes in collision frequency and cell bridge formation. HARV cultivation altered the expression of cellular proteins (43 and 70 kDa) and matrix proteins (50, 73, 89 and 210 kDa) relative to controls perhaps due to hypoxia, fluid flow or distortion of cell shape. In addition to the insight that this work has provided into rotating-wall vessels, it could be useful in modeling aggregation in other cell systems, propagating human corneal endothelial cells for eye surgery and examining the response of endothelial cells to reduced shear.

Fine-tuning of a three-dimensional microcarrier-based angiogenesis assay for the analysis of endothelial-mesenchymal cell co-cultures in fibrin and collagen gels

A prerequisite for successful tissue engineering is the existence of a functional microvascular network. We hypothesized that such networks can be created and quantified in an in vitro setting by co-culturing endothelial cells (ECs) with tissue-specific 'bystander cells' in 3-D gel matrices. To test this hypothesis we adapted a previously described in vitro microcarrier-based angiogenesis assay (V. Nehls and D. Drenckhahn, 1995, Microvasc Res 50: 311-322). On optimizing this assay, we noted that the initial EC-microcarrier coverage depended on EC type and seeding technique employed to coat the microcarrier beads with the ECs. A confluent EC monolayer on the microcarrier surfaces formed only when bovine aortic endothelial cells (BAECs) were admixed to the beads under gentle agitation on an orbital shaker. After embedding BAEC-covered microcarrier beads into a sandwich-like arrangement of collagen or fibrin gels, we assessed cellular outgrowth at different serum concentrations in terms of migration distance and sprout formation. Quantifiable sprout formation was highest at 1% fetal bovine serum (FBS) in collagen matrices and at 0.1% FBS in fibrin matrices. At higher serum concentration, excess cell migration and formation of clusters prevented quantitative analysis of sprouting. Following the fine-tuning of this angiogenesis assay, we co-cultured BAECs with adipose tissue-derived fibroblasts (FBs) and vascular smooth muscle cells (SMCs). While FBs were able to increase the average migration distance of BAECs in both matrices, SMCs enhanced BAEC migration in fibrin, but not in collagen gels. By contrast, the number of newly formed sprouts in fibrin gels was increased by both cell types. We conclude that in this model bystander cells enhance EC network formation in a matrix-dependent manner. Additionally, these results stress the importance of carefully selecting the experimental parameters of a given in vitro angiogenesis model.

Microbeads and anchorage-dependent eukaryotic cells: the beginning of a new era in biotechnology

Modern methods for the mass cultivation of anchorage-dependent mammalian cells started with the advent of microcarrier technology. Largely for reasons pertaining to their mode of preparation and ease of cultivation, 150-230 microns microbeads have been overwhelmingly adopted and the technology around them developed. To meet high biomass, macroporous microbeads have been developed. Also, the chemistry of the microsupport has been adapted in order to afford better protection of fragile cells to mechanical wear while simultaneously reorienting their differentiation towards the sought aims (production of cytokines, enzymes etc. ...). Future progress depends upon solutions being brought to problems inherent to this new technology (maintenance of steady state conditions of growth etc. ...) as well as to requirements arising from animal cell culture in general (biosensors, bioreactor's design etc. ...). Besides such technical implementations, biology at large is also expected to benefit from the advent of microcarriers in fields as diverse as the preparation of metaphasic chromosomes in bulk, toxicity testing, organ reconstitution following cell transplantation etc.

Lysophosphatidylcholine enhances superoxide anions production via endothelial NADH/NADPH oxidase

Reactive oxygen species (ROS) including superoxide anions (O2(-)) play a key role in atherogenesis, and endothelial cells have the ability to generate ROS. To investigate the enzymatic sources of ROS and the effects of lysophosphatidylcholine (LPC), an atherogenic lipid, we measured ROS production in cultured bovine aortic endothelial cells (BAECs) by the lucigenin-enhanced chemiluminescence (CL) method and electron spin resonance (ESR). BAEC homogenates had the enzymatic activity of NADH/NADPH oxidase. BAECs cultured on microcarrier beads generated O2(-) under basal conditions. The inhibition of NADH/ NADPH oxidase by diphenylene iodonium (DPI) significantly attenuated O2(-) production, whereas no inhibitors of other oxidases suppressed it. Although LPC enhanced O2(-) production approximately 3.1-fold, its action was suppressed by DPI. Tyrosine kinase inhibitors significantly attenuated LPC-induced O2(-) production. ESR with DMPO demonstrated that LPC increased the formation of the DMPO-hydroxyl adduct in dose- and time-dependent manners. These data suggest that the basal production of O2(-) in endothelial cells is mainly mediated by the NADH/NADPH oxidase system and that LPC activates this oxidase to enhance O2(-) production through a tyrosine kinase-dependent pathway. The enhancement of ROS production by LPC is probably involved in its atherogenic property.

O2-dependent prostanoid synthesis activates functional PGE receptors on corpus cavernosum smooth muscle

We have previously demonstrated that decreased O2 tension inhibits prostaglandin synthesis from human corpus cavernosum smooth muscle cells in static culture over 8-18 h (R. B. Moreland et al., Molecular Urology 2: 41-47, 1998). In this report, an experimental system was designed that allowed determination of the effects of O2 tension changes over the time frame of physiological penile erection. Human corpus cavernosum smooth muscle cells were cultured on microcarrier beads in enclosed stirrer flasks so that rapid changes of O2 tension could be modulated. After 18 h of equilibration at 30-40 mmHg to simulate blood PO2 at penile flaccidity, O2 tension was increased to 100 mmHg for 1 h and then returned to 30-40 mmHg. Media samples were withdrawn for prostanoid synthesis and cell samples were taken for cAMP determinations. After 18 h of 30-40 mmHg PO2 values, prostanoid synthesis by human corpus cavernosum smooth muscle cells was low (0.1-0.7 pmol/10(6) cells). When PO2 was increased to 100 mmHg, a rapid increase in PGE2 >> PGF2alpha > PGD2 was observed (thromboxane A2 was undetectable), which peaked at 5.7 pmol PGE2/10(6) cells. Increased O2 tension correlated with increased PGE2 and increased intracellular synthesis of cAMP. The prostaglandin G/H synthase inhibitor indomethacin or the E prostanoid (EP2)-selective antagonist AH-6809 each inhibited the O2-tension-dependent increases in cAMP. These data support a role of differential O2 tension in the penis in the smooth muscle synthesis of PGE2, which in turn increases cAMP synthesis via EP2 receptors.

Changes of endothelial nitric oxide synthase level and activity during endothelial cell proliferation

The goal of this study was to investigate the effect of endothelial cell proliferation on the expression and activity of endothelial nitric oxide synthase (eNOS). Bovine atrial endothelial cells (BAtEC) were studied between day 1 and 6 after seeding. During this period the number of cells in S-phase decreased progressively, while cell number and protein content increased, reaching a maximum at confluence (day 4). Expression of eNOS (determined by ELISA) and eNOS activity (determined by L-arginine to L-citrulline conversion) increased with culture duration with a maximum at confluence. Nitric oxide (*NO) release from BAtEC was determined after stimulation with Ca2+ ionophore A23187 (10 microM, 30 min) by .NO chemiluminescence in the absence of a chemical reduction system. Total *NO release (measured in the presence of 100 U/ml superoxide dismutase) did not change with state of cell proliferation/growth, whereas "bioavailable" *NO (measured in the absence of superoxide dismutase) was low in highly proliferating BAtEC. Relative eNOS activity (.NO and L-citrulline production per eNOS protein) was highest in proliferating BAtEC. The novel finding of this study is that the specific eNOS activity is upregulated in proliferating BAtEC and downregulated in quiescent BAtEC. The amount of "bioavailable" *NO is determined by eNOS activity and *NO inactivation (probably by superoxide), both high in proliferating BAtEC.

Isolation and culture of capillary endothelial cells from the eel, Anguilla rostrata

There has been little development of endothelial cell cultures from vertebrates other than mammals. In this report the isolation of capillary endothelial cells from the rete mirabile of the eel, Anguilla rostrata, is described. The cells are isolated with collagenase H and dispase II. The cells are plated into fibronectin-hyaluronic acid coated flasks. The culture medium is M199 with Earle's salts supplemented with NaCl, HEPES, NaHCO(3), glutamine, pyruvate, heparin, antibiotics, endothelial cell growth supplement, and 20% serum. Cultures are incubated at 25 degrees C in humidified air. The rete mirabile contains pericytes in addition to endothelial cells. Variations in plating time, serum concentrations, and growth matrices were tried to separate the two cell types. The total number of endothelial cells and the ratio of endothelial cells to pericytes are the most important factors in obtaining pure cultures of capillary endothelial cells. Endothelial cells are isolated also from the endocardium, bulbus arteriosus, and large vessels. The initial isolates usually take 3-6 weeks to grow to confluence with subcultures taking about 2 weeks to confluence.

Effect of coacervated alpha-elastin on proliferation of vascular smooth muscle and endothelial cells

The arterial wall injury associated with arterial graft implantation causes smooth muscle cells (SMCs) in the media to migrate and proliferate in the intima at the graft-artery junction resulting in anastomotic intimal hyperplasia (AIH). An important step in developing a small-diameter prosthesis may be to stimulate endothelialization and thereby inhibit AIH. In this study, we investigated the effect of coacervated and crosslinked alpha-elastin on proliferation of SMCs and endothelial cells (ECs) in vitro. Coacervation is an important step in the conversion of proelastin to make an elastin fiber in vivo. SMCs and ECs were prepared from porcine aortic media and endothelium, respectively. SMCs and ECs (three to five passages, 4 x 10[4] cells/well) were seeded onto 12 well plates, coated and crosslinked with 0 or 10 mg/mL of coacervated alpha-elastin. After the 1st, 2nd, or 3rd day of cultivation, proliferation was assayed by scintillation counting of [3H]-thymidine incorporation. For the 4th day only, 0, 0.1, 1, 10 mg/mL concentration of coacervated alpha-elastin was coated and crosslinked. SMC proliferation (1st, 2nd day: p<0.005; 3rd, 4th day: p<0.0001) was significantly inhibited over time and dose dependently, eg, 0.1 mg/mL (45.7+/-2.3%: % of control p<0.005), 1 mg/mL (5.9+/-0.7%, p<0.0005), 10 mg/mL (2.8+/-0.4%, p<0.0005). EC proliferation was inhibited over time by 10 mg/mL of coacervated alpha-elastin (2nd, 3rd day: p<0.005; 4th day: p<0.0001), but proliferation (132.8+/-9.9%: % of control p=NS) was stimulated by 0.1 mg/mL of coacervated alpha-elastin. These results suggest that coating and crosslinking a coacervated alpha-elastin into the structure of arterial prosthesis may inhibit AIH and stimulate endothelialization.

Nitroxides increase the detectable amount of nitric oxide released from endothelial cells

Nitroxides are known to exert superoxide dismutase-mimetic properties and to decrease O-2- and H2O2-mediated cytotoxicity. However, the effect of nitroxides on .NO homeostasis has not been studied yet. The present study investigates the effect of nitroxides on the detectable amount of .NO released by 3-morpholinosydnonimine (SIN-1) and cultured endothelial cells. Cultured bovine aortic and atrial endothelial cells stimulated with 10 microM A23187 released a stable flux of .NO, as detected by .NO chemiluminescence. Addition of 100 units/ml SOD or 10 microM of the nitroxides 4-hydroxy-2,2,6, 6-tetramethylpiperidine-N-oxyl (TEMPOL), 3-carboxy-proxyl, and 3-ethoxycarbonyl-proxyl, increased the chemiluminescence signal. The effect of these nitroxides on the amount of .NO released from cell monolayers was dose-dependent, with the highest efficacy between 30 and 100 microM. EPR spin trapping in SIN-1 solutions revealed the formation of .OH adducts from spontaneous dismutation of O-2 and concomitant reaction with H2O2. Both SOD and TEMPOL increased the signal intensity of the .OH adduct by accelerating the dismutation of O-2. The results of this study demonstrate that the SOD-mimetic activity of nitroxides increases the amount of bioavailable .NO in vitro.

Inhibitory effect of type 1 collagen gel containing alpha-elastin on proliferation and migration of vascular smooth muscle and endothelial cells

The purpose of this study was to investigate in vitro the potential effect of type 1 collagen gel containing alpha-elastin on the proliferation of vascular smooth muscle cells and vascular endothelial cells, and on smooth muscle cell migration. Vascular smooth muscle cell and endothelial cell were cultured in 12-well plates precoated with collagen gels and alpha-elastin. Cell proliferation rates were measured by monitoring [3H]-thymidine incorporation. After 2, 3 or 4 days of culture, the proliferation rate of both smooth muscle cells and endothelial cells was significantly decreased on collagen gel containing 10 mg/ml alpha-elastin compared with collagen gel only as control. Smooth muscle cell proliferation on collagen gel containing alpha-elastin on the 4th day of culture was decreased dose-dependently, e.g. 1 mg/ml of alpha-elastin (74.8(2.3)% of control, P=n.s.); 5 mg/ml (56.7(2.1)%; P<0.05); 10 mg/ml (30.3(3.1)%; P<0.005). In the case of cultured endothelial cells, however, [3H]-thymidine incorporation was not decreased significantly in the presence of 5 mg/ml alpha-elastin (83.1(7.9)%, P=n.s.). After stimulation by platelet-derived growth factor, the smooth muscle cell migration rate on collagen gel containing alpha-elastin (5 mg/ml) was decreased over time. The area of migration on the 6th day of culture was also significantly decreased dose-dependently in the presence of alpha-elastin, e.g. 1 mg/ml (72.6(3.4)% of control, P<0.05), 5 mg/ml (56.9%(1.5)%; P<0.05); 10 mg/ml (37.3(2.7)%; P<0.0005). In conclusion, alpha-elastin inhibited the proliferation and migration of smooth muscle cell in a dose-dependent manner on collagen gel culture, however, at high concentrations of alpha-elastin (10 mg/ml), the endothelial cell proliferation rate was also inhibited. At 5 mg/ml, alpha-elastin significantly inhibited smooth muscle cell proliferation and migration but did not significantly inhibit endothelial cell proliferation. Incorporation of collagen gel containing alpha-elastin into the structure of arterial prosthesis offers the possibility of inhibiting smooth muscle cell hyperplasia without significant effect on endothelial cell formation.

Bioassay of prostacyclin and endothelium-derived relaxing factor (EDRF) from porcine aortic endothelial cells. 1985

A cascade superfusion technique has been developed for the differential bioassay of prostacyclin and endothelium-derived relaxing factor (EDRF) released from porcine aortic endothelial cells cultured on microcarriers, packed into a column and perfused.

Bradykinin (Bk; 20–100 Nm) released prostacyclin (9.6 ± 1.5 Nm per 10⁶ cells; mean ± s.e.mean, n = 9) and prostaglandin E₂ (PGE₂; 2.1 ± 0.6 Nm per 10° cells) from the column measured by relaxation of strips of bovine coronary artery (BCA) and rabbit mesenteric or coeliac artery, respectively. The presence of these prostanoids in the effluent was confirmed by specific radioimmunoassays.

A23187 (500–2000 Nm) also released both prostacyclin and PGE₂ from the cells. This release was long-lasting and not reproducible.

Bk (20–100 Nm) and A23187 (30–300 Nm) released EDRF from the column. This was detected in a cascade of four rabbit aortic strips (RbA), denuded of endothelium and contracted with U46619 or phenylephrine. The relaxation of the RbA strips caused by EDRF was progressively attenuated down the cascade (half-life < 7 s) and was not affected by indomethacin.

EDRF and prostacyclin could be differentially bioassayed in a cascade of alternating RbAs and BCAs as prostacyclin did not relax RbAs and the time delay to the BCAs destroys EDRF. EDRF could be bioassayed on its own when the endothelial cells were treated with indomethacin.

5-Hydroxytryptamine 0.2, noradrenaline 1.0, platelet-activating factor (Paf-acether) 1.0, formylmethionyl-leucyl-phenylalanine 1.0, acetylcholine 0.5, bethanecol 0.5, adenosine diphosphate 0.25 and angiotensin II 0.1 μm did not release either prostanoids or EDRF from the column.

Inhibition of endothelial nitric oxide synthase activity by protein kinase C

Nitric oxide (NO) is an important molecular messenger accounting for endothelium-derived relaxing factor. Recently, NO synthase (NOS) from cultured endothelial cells has been purified and molecularly cloned. To evaluate the effect of phosphorylation by protein kinase C (PKC) and cyclic AMP-dependent protein kinase (PKA) on endothelial constitutive NOS catalytic activity, we incubated purified endothelial NOS with PKC or PKA. Endothelial NOS was stoichiometrically phosphorylated by PKC and PKA. In intact bovine aortic endothelial cells (BAECs), NOS was phosphorylated by stimulation with 12-O-tetradecanoylphorbol-13-acetate (TPA). NOS activity measured by the conversion of [3H]arginine to [3H]citrulline in homogenates of BAECs treated with TPA or phorbol 12,13-dibutyrate was reduced by 30%, whereas dibutylyl cyclic AMP did not affect NOS activity. Moreover, we measured NO release from cultured BAECs by a chemiluminescence method to examine the effect of PKC and PKA on endothelial NOS activity. In cultured BAECs, ATP gamma S and A23187 induced NO release in time- and dose-dependent manners. Phorbol esters such as TPA and phorbol 12,13-dibutyrate dose dependently inhibited NO release stimulated by A23187 as well as ATP gamma S. Reduction of NO release by TPA was almost completely prevented by pretreatment with staurosporine, an inhibitor of PKC. NO release by A23187 was increased in PKC-downregulated BAECs. In contrast, dibutylyl cyclic AMP or 8-bromo cyclic GMP had no effect on NO release from BAECs induced by A23187 or ATP gamma S. These results indicate that phosphorylation of NOS by PKC is associated with a reduction of its catalytic activity in vascular endothelial cells.

Influence of anti-inflammatory drugs on adhesion of neutrophils to endothelial cells cultured on microcarriers: a novel in vitro system as an alternative to animal experimentation

Pharmacological control of inflammation by steroidal (SAIDs) and nonsteroidal (NSAIDs) antiinflammatory drugs is of substantial clinical importance. To reduce the number of animals used in pharmacological and toxicological evaluation of these drugs we developed a novel assay to determine adhesion of bovine neutrophils (PMN) to bovine aortic endothelial cells (BAEC) cultured on microcarriers in a flow-through system. Pretreatment of BAEC with thrombin (10(-7)-10(-4) M) led to a dose-dependent increase of PMN-adhesion (10(-6)-10(-4) M:P < 0.05); platelet-activating factor (10(-9) M) and 1:200 diluted zymosan-activated serum (ZAS) had similar effects (P < 0.001). Pretreatment of PMN with SAIDs (50.9 and 509 microM dexamethasone, 12.2 and 24.4 microM flumethasone) did inhibit adhesion to ZAS-treated BAEC dose-dependently. Pretreatment of PMN with NSAIDs had a less consistent influence on adhesion to ZAS-stimulated BAEC. While phenylbutazone (0.33 and 3.3 mM), diclofenac (0.392 and 0.574 mM), indomethacine (0.436 and 0.872 mM), and acetylsalicylic acid (3.47 and 16.94 mM) induced dose-dependent inhibition of PMN-adhesion to ZAS-treated BAEC, piroxicam (0.377 and 0.754 mM) inhibited PMN-adhesion strongly (P < 0.001) but not dose-dependently, and ketoprofene (0.614 and 1.228 mM) had no effect on PMN-adhesion. The method presented here is efficient for evaluating the pharmacological modulation of PMN interaction with endothelial cells, and useful for studying further aspects of endothelial cell biology.

Reorganization of endothelial cord-like structures on basement membrane complex (Matrigel): involvement of transforming growth factor beta 1

The formation of capillary-like network structures by cultured vascular endothelial cells on reconstituted basement membrane matrix, Matrigel, models endothelial cell differentiation, the final step of angiogenesis (Kubota et al., 1988; Grant et al., 1989). When endothelial cells derived from bovine aorta and brain capillaries were plated on Matrigel, DNA synthesis was suppressed and a network of capillary-like structures rapidly formed in 8-12 h. With time, the network broke down, resulting in dense cellular cords radiating from multiple cellular clusters in 16-24 h. Finally, multicellular aggregates of cells were formed as the network underwent further retraction. Network regression was prevented when either dithiothreitol (DTT) or anti-TGF-beta 1 antibodies were added during the assay. The addition of exogenous TGF-beta 1 promoted the regression of endothelial cells into the clusters. This response to TGF-beta 1 was blocked by potent serine threonine protein kinase inhibitors, H-7 and HA100. TGF-beta 1 was released from polymerized Matrigel by incubation with Dulbecco's modified eagle's medium (DMEM) in the absence of cells. The Matrigel-conditioned DMEM inhibited endothelial DNA synthesis even in the presence of anti-TGF-beta 1 antibodies. These results suggest that TGF-beta 1 and possibly other soluble factors from Matrigel may be important for differentiation and remodeling of endothelial cells in a capillary network with possible implications for wound healing and development.

Characterization of cultured rat aortic endothelial cells

We describe a new method to obtain rat aortic endothelial cells without contamination by vascular smooth muscle cells. The endothelial cells were characterized up to the 20th passage by low density lipoprotein incorporation, the absence of alpha-smooth muscle actin, the production of endothelium derived relaxing factor, and an elevation in intracellular free calcium concentration in response to bradykinin and ATP but not to AMP and angiotensin II.

The diffusional transport of water and small solutes in isolated endothelial cells and erythrocytes

The diffusional permeability coefficients, PD, for tritiated water (3HHO) 14C-antipyrine (AP) and 14C-iodoantipyrine (IAP) in isolated calf pulmonary artery endothelial cells and dog erythrocytes are measured with the linear diffusion technique at 11.5, 15, 20 and 37 degrees C. The PD values for both cell populations follow the sequence 3HHO > IAP > AP at each of the temperatures. PD for water is higher in the erythrocyte compared to the endothelial cells. The differences in PD for AP and IAP in the erythrocytes and endothelial cells are not dramatic and are similar to the differences seen in comparing permeation of the same solute through bilayers of different composition. A comparison of the values of PD calculated for the endothelial cells with those for isolated capillaries and the structured endothelium in whole lungs validates the use of the isolated cells as models for the endothelial cells in situ. Incubation of the endothelial cells with cis-vaccenic acid or cholesterol produces a reduction in PD for water and antipyrine. These data are analyzed in terms of Stokesian and non-Stokesian diffusion. The interpretation which best accommodates the data is that the phospholipid area of the membrane, rather than the hydrocarbon core, provides the greatest resistance to permeation for these solutes.

Prostacyclin production in cultured endothelial cells is highly sensitive to low doses of ionizing radiation

In an attempt to detect if low doses of ionizing radiation affect the physiological function of blood vessels, the effect of prostacyclin production was examined using cultured endothelial cells. Irradiation with 5 cGy suppressed the production to 53% of the levels in unirradiated control cells. The PGI2 production decreased with an increase in the dose, showing a maximal decrease at 100 cGy without further decrease at 200 cGy. The suppressive effect lasted for 15 min after irradiation and disappeared later. Preincubation with alpha-tocopherol abrogated the suppressive effect completely, although preincubation with ascorbic acid showed little effect. These results suggest that low dose irradiation inhibits the prostacyclin production by changing the cellular membranes transiently.

Effective stabilization of ethanol levels in multiple-well tissue culture plates

Underestimation of ethanol (EtOH) volatility in vitro is a potential source of experimental error. EtOH (0-5% in culture medium) was added to 24- or 96-well tissue culture plates with standard low evaporation lids and incubated at 37 degrees C in humidified 7.5% CO2 and 92.5% air. After 72 hours, approximately 70% of the initial EtOH had disappeared from the aqueous phase of the plate (EtOH volatilization). EtOH concentrations gradually decreased in high-concentration wells (1-5%) and increased in low-concentration wells (0-0.1%) over time. This temporal redistribution of EtOH (EtOH diffusion) was detected after only 1 hour of incubation. Parafilm, Blenderm surgical tape, and ELISA plate-sealing tape barriers inconsistently or inadequately prevented EtOH volatilization and diffusion, but a newly designed plate-sealing clamp (PSC) apparatus inhibited this phenomenon. Rat hepatic sinusoidal endothelial cells cultured with the PSC apparatus maintained intact cell membranes for 72 hours and stable levels of monolayer permeability for at least 48 hours. By stabilizing in vitro EtOH concentrations, the PSC apparatus eliminates a potential source of major experimental error.

Lysophosphatidylcholine inhibits bradykinin-induced phosphoinositide hydrolysis and calcium transients in cultured bovine aortic endothelial cells

Vascular endothelium, which produces endothelium-derived relaxing and constricting factors, plays an important role in regulating the vascular tone. We recently demonstrated that oxidized low density lipoprotein inhibited endothelium-dependent relaxation and that lysophosphatidylcholine accumulated during the oxidative modification of low density lipoprotein was the essential substance for the inhibition of endothelium-dependent relaxation. To clarify the mechanisms of the inhibitory effect of lysophosphatidylcholine, we used a bioassay system to investigate the effect of lysophosphatidylcholine on the production and/or release of endothelium-derived relaxing factor and its effect on the cytosolic Ca2+ level ([Ca2+]i) and phosphoinositide hydrolysis in cultured bovine aortic endothelial cells. [Ca2+]i was monitored by the fura 2 method, and the accumulation of inositol phosphates in cells labeled with myo-[2-3H]inositol was measured. Bioassay experiments showed that lysophosphatidylcholine inhibited the production and/or release of endothelium-derived relaxing factor from cultured endothelial cells. Lysophosphatidylcholine (5-20 micrograms/ml) induced a biphasic increase in [Ca2+]i, which consisted of a rapid increase followed by a sustained increase, and the initial component was a result of mobilization from intracellular Ca2+ stores without detectable synthesis of inositol 1,4,5-trisphosphates. Furthermore, lysophosphatidylcholine (5-20 micrograms/ml) dose-dependently inhibited both phosphoinositide hydrolysis and the increases in [Ca2+]i evoked by bradykinin. These results indicate that the impairment of endothelium-dependent relaxation induced by lysophosphatidylcholine is due to the inhibition of phosphoinositide hydrolysis and the subsequent increases in [Ca2+]i in endothelial cells. Lysophosphatidylcholine that accumulates in oxidized low density lipoprotein and atherosclerotic arteries may play an important role in the modification of endothelial function.

Interleukin-2 directly increases albumin permeability of bovine and human vascular endothelium in vitro

The direct effects of interleukin-2 (IL-2) on albumin permeability of cultured bovine pulmonary artery endothelial cell (BPAEC) and human arterial endothelial cell (HAEC) monolayers were studied. BPAEC were exposed to IL-2 (500 to 25,000 U/ml) for 4 h. The steady-state transfer rate of [125I]albumin across the BPAEC monolayer was 3.3 +/- 0.4%/h (n = 10) in control BPAEC (diluent alone), was significantly increased in BPAEC exposed to 500 U/ml of IL-2 (72 +/- 3% above control values, n = 6, P less than 0.02), and further increased in BPAEC exposed to 5,000 U/ml (60 +/- 2% increase above 500 U/ml values, n = 5, P less than 0.02). No further increase was noted after exposure to 25,000 U/ml of IL-2. Additionally, no further increase in [125I]albumin transfer rates was noted in BPAEC exposed to 5,000 U/ml of IL-2 for 24 versus 4 h. Similar changes were found using HAEC. Preincubation of HAEC with an anti-IL-2 low-affinity receptor antibody (anti-IL-2R alpha) inhibited the IL-2-induced permeability increase. Expression of IL-2R alpha receptors in HAEC incubated with 5,000 U/ml of IL-2 for 4 h was also found. Thus, IL-2 appears to have a direct effect on cultural arterial endothelial monolayers not requiring the presence of other cell types or serum proteins. IL-2-induced increases in endothelial macromolecular permeability may play an important role in the pathogenesis of the IL-2-induced vascular leak syndrome seen in vivo.

Role of endothelial cells in the proliferative response of cultured pulmonary vascular smooth muscle cells to reduced oxygen tension

The development of pulmonary hypertension in a wide variety of human disease states and experimental animal models characterized by chronic alveolar hypoxia is mediated by two pathologic vascular processes, a) vasoconstriction and b) vasoconstruction (structural remodeling). The anatomic changes seen within the pulmonary circulation include a) increased deposition of collagen and elastin in the adventitial layer and b) aberrant pulmonary vascular smooth muscle cell proliferation and maturation in the medial segments. Despite the demonstrated ability of pharmacologic manipulation in the experimental animal to ameliorate both the structural and hemodynamic changes, the actual etiologic mechanisms are only beginning to be explored. Using the cell culture technique of co-cultivation, we have investigated the potential role of bovine pulmonary arterial endothelial cell-derived factors in mediating abnormal bovine smooth muscle cell growth under conditions of reduced oxygen tension. We have demonstrated that these cultured endothelial cells exposed in vitro to reduced levels of atmospheric oxygen concentrations of 5.0% and 2.5% O2 for durations of 24 to 72 h produce and secrete soluble growth factor(s) which stimulate smooth muscle cell proliferation when compared to cells maintained under standard tissue culture oxygen conditions of 95% room air. This growth-stimulatory effect required the concomitant presence of serum factors (0.5% fetal bovine serum), was inhibited by heparin, was distinct from platelet-derived growth factor, and seemed to have a molecular weight greater than 14,000 Da. We conclude that reduced levels of oxygen tension in vitro can selectively induce pulmonary arterial endothelial cells to release mitogen(s) which can stimulate vascular smooth muscle replication. Furthermore, we speculate that this in vitro finding may be of importance as an etiologic mechanism to explain the accelerated smooth muscle cell growth characteristic of hypoxic pulmonary arteriopathy.

Time course of changes in concentration of intracellular free calcium in cultured cerebrovascular smooth muscle cells exposed to oxyhemoglobin

A culture of smooth muscle cells obtained from monkey middle cerebral arteries was developed to allow quantitative assessment of intracellular calcium and immunofluorescence analysis after various periods of exposure to oxyhemoglobin. Intracellular calcium concentration was examined for up to 7 days after a single exposure to oxyhemoglobin. Intracellular calcium concentrations were measured with the fluorescent dye fura-2 and were significantly elevated for 7 days after exposure to oxyhemoglobin (P less than 0.01). Less than 2 minutes after application of oxyhemoglobin, there was marked elevation of intracellular calcium from the control value of 75 +/- 2 nmol/L to 240 +/- 28 nmol/L (P less than 0.01 by analysis of variance). Intracellular calcium concentration of cells exposed for 24 hours to oxyhemoglobin and then grown in normal oxyhemoglobin-free medium fell close to normal levels on Days 3 and 7. On Day 3, the increase in intracellular calcium that followed repeated daily exposure to oxyhemoglobin was greater than that resulting from a single application of oxyhemoglobin (P less than 0.01 by Student's t test), but by Day 7 the elevation produced by these different approaches was similar. Smooth muscle cells exposed to oxyhemoglobin showed a reduction in immunoreactivity to alpha-actin. These data support the hypothesis that disruption of intracellular calcium regulation and calcium overloading may be important in the process of cell injury, which results in vasoconstriction and sometimes cell death, after exposure to oxyhemoglobin.

Chloride-selective channels of large conductance in bovine aortic endothelial cells

Single-channel currents of an anionic channel in the plasma membrane of cultured bovine aortic endothelial cells have been recorded with the patch-clamp technique. The channel is selective for chloride over cations, and has an average single channel conductance of 382 picosiemens in symmetric 140 millimoles of chloride. In addition to the main conductance state it shows well-defined subconductance states of about 50, 100, 150 and 200 picosiemens. The channel is very active at membrane potentials close to 0 mV, but steps to either positive or negative membrane potentials above +/- 20 millivolt lead to a rapid inactivation of the channel. Changes in the concentrations of free calcium or adenosine tri-phosphate on the cytosolic surface do not influence channel activity. The chloride channel rarely opens at resting membrane potential, but it may help repolarize endothelial cells following depolarizing stimuli.

The cerebral microvessels in culture, an update

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

Differential protective effects of O-phenanthroline and catalase on H2O2-induced DNA damage and inhibition of protein synthesis in endothelial cells

The respective roles of H2O2 and .OH radicals was assessed from the protective effects of catalase and the iron chelator o-phenanthroline on 1) the inhibition of protein synthesis, and 2) DNA damage and the related events (activation of the DNA repairing enzyme poly(ADP)ribose polymerase with the associated depletion of NAD and ATP stores) in cultured endothelial cells exposed to the enzyme reaction hypoxanthine-xanthine oxidase (HX-XO) or pure H2O2. Catalase added in the extracellular phase completely prevented all of these oxidant-induced changes. O-phenanthroline afforded a complete protective effect against DNA strand breakage and the associated activation of the enzyme poly(ADP)ribose polymerase. By contrast, iron chelation was only partially effective in maintaining the cellular NAD and ATP contents, as well as the protein synthetic activity. In addition, the ATP depletion following oxidant injury was much more profound than NAD depletion. These results indicate that: 1) .OH radical was most likely the ultimate O2 species responsible for DNA damage and activation of poly(ADP)ribose polymerase; 2) both H2O2 and .OH radicals were involved in the other cytotoxic effects (inhibition of protein synthesis and reduction of NAD and ATP stores); and 3) NAD and ATP depletion did not result solely from activation of poly(ADP)ribose polymerase, but other mechanisms are likely to be involved. These observations are also compatible with the existence of a compartmentalized intracellular iron pool.

Oxidized low density lipoprotein inhibits bradykinin-induced phosphoinositide hydrolysis in cultured bovine aortic endothelial cells

Vascular endothelial cells, in response to various neurohumoral and physical stimuli, produce an endothelium-derived relaxing factor, a substance which regulates vascular tone. We have demonstrated that oxidized low density lipoprotein (LDL) inhibits endothelium-dependent relaxation. We studied the effect of oxidized LDL on inositol phosphates formation stimulated with bradykinin (BK) in cultured bovine aortic endothelial cells. BK elicited a rapid generation of inositol phosphates from inositol phospholipids. Accumulation of inositol 1,4,5-trisphosphate (IP3) stimulated with BK (0.1 microM) was markedly inhibited by oxidized LDL. However, native LDL had little effect on BK-induced accumulation of IP3. From these results, oxidized LDL inhibits receptor-mediated phosphoinositides hydrolysis and modulates the endothelial function.

In situ pulmonary vascular perfusion for improved recovery of pulmonary intravascular macrophages

The microcirculation contains mononuclear phagocytes, with features characteristic of macrophages, adhered to luminal capillary surfaces by intercellular adhesion plaques. These pulmonary intravascular macrophages may play an important role in regulating lung vascular tone and capillary permeability, and may modulate capillary endothelial cell growth and replication by the secretion of soluble mediators (i.e., arachidonate metabolites, cytokines). This study describes a technique which utilizes in situ lung perfusion to remove intravascular macrophages in large numbers from the microcirculation of porcine lung (n = 26). This technique yielded 3.8 +/- 0.5 x 10(8) (mean +/- SEM) mononuclear cells which were highly phagocytic toward particulate carbon (phagocytic index, 80 +/- 6%). Harvested mononuclear phagocytes reestablished intercellular adhesion plaques when placed on small vessel porcine pulmonary artery endothelial cell monolayers and exhibited histochemical characteristics typical of monocyte/macrophage lineage cells. Mononuclear cells obtained from lung microcirculation displayed size heterogeneity varying from 10.4 to 16.5 microns in diameter. Both large and small cell populations phagocytosed particulate carbon. Morphometric studies performed on collagenase-treated lung demonstrated that in situ perfusion removed significant numbers of intravascular macrophages in lung capillaries. The technique described permits the rapid removal of anchored mononuclear phagocytes from lung capillaries with minimal postmortem delay.

Lipid peroxide and transition metals are required for the toxicity of oxidized low density lipoprotein to cultured endothelial cells

The toxicity of oxidized low density lipoprotein (Ox-LDL) to cultured vascular endothelial cells was investigated. The modification of low density lipoprotein (LDL) by copper led to the production of thiobarbituric acid-reacting substance (TBARS) and lipid hydroperoxide (LPO). TBARS was distributed not only in lipoprotein, but also in the aqueous phase, whereas LPO was observed only in the lipoprotein particle. During the incubation of LDL with copper, the copper bound to lipoprotein and formed a complex. The toxicity of products resulting from the oxidation of LDL to endothelial cells was recognized in Ox-LDL particles, not in the aqueous phase. Following dialysis of Ox-LDL against EDTA, copper which had bound to the Ox-LDL particle was released and the toxicity of Ox-LDL disappeared. The addition of copper to the dialyzed Ox-LDL restored the cytotoxicity. To a lesser extent this effect was also observed with the addition of iron. A study of the time-course of LDL oxidation showed that the toxicity of Ox-LDL depends upon the level of LPO, not upon the content of TBARS, the extent of negative charge or the protein adduct of aldehydes. These results demonstrate that transition metal is required for Ox-LDL toxicity and that the toxic moiety of the products resulting from LDL oxidation is LPO associated with the Ox-LDL particle.

Macro- and microvascular endothelial cells in vitro: maintenance of biochemical heterogeneity despite loss of ultrastructural characteristics

Microvascular endothelial cells from bovine adrenal medulla and brain and macrovessel endothelial cells from bovine aorta were isolated and cultured under similar conditions in order to determine morphologic and biochemical heterogeneity in vitro. All three cell types exhibited nearly identical ultrastructural morphology and two-dimensional gel protein patterns of 35S-methionine-labeled whole cells. Two-dimensional gel analysis of 35S-methionine-labeled plasma membrane proteins however, revealed two-dimensional gel protein patterns unique to the tissue type from which the endothelial cells were isolated. This suggests that the functional significance of these specific endothelial cell types is manifested primarily in surface-associated proteins and that many of the differences are sustained in culture. To determine the potential of aorta, brain, and adrenal medulla endothelial cell (EC) cultures to respond to developmentally significant signals, morphology, growth pattern, and cell surface proteins were monitored in the presence and absence of growth factors. A 17 to 26% increase in cell density as well as an increase in the number of elongated and overlapping cells resulted when all three EC types were exposed to a mitogenic medium. Additionally, expression of specific glycoprotein profiles, as determined by Concanavalin A Western blotting of two-dimensional gels, was dependent on the presence or absence of growth factors in the medium. The ability to induce this morphologic and biochemical variation in the three endothelial cell types was maintained into later passage. Taken together, these data imply that endothelial cells isolated from different tissues exhibit and maintain biochemical heterogeneity and do not completely dedifferentiate into a common endothelial cell type in culture. Furthermore, expression of specific subsets of cell surface proteins is dependent on environmental conditions, and in some cases is both cell-type and media-type dependent. Thus, even though endothelial cells are considered terminally differentiated cells, there exists additional or "latent" heterogeneity in the ability of these different cells to respond to "developmental signals" (i.e. mitogenic medium) in vitro.

The use of microcarrier beads in the production of endothelium-derived relaxing factor by freshly harvested endothelial cells

This study is concerned with the use of freshly harvested bovine endothelial cells attached to microcarrier beads in the production of the endothelium-derived relaxing factor (EDRF). The results are compared to production of EDRF by endothelial cells grown in tissue cultures. We found that freshly harvested cells attach themselves to microcarrier beads within minutes. This results in large surface/area volume ratio and permits superfusion of cells suspension on a filter (pore size of 25-30 microns), resulting in cell free filtrate. When superfusing an endothelium-deprived pulmonary artery strip, the effluent causes relaxation; the response depends on the number of superfused endothelial cells. The number of viable freshly harvested cells attached to microcarrier beads in 5 ml Krebs-Henseleit solution is small (30%), as compared to almost 100% for cultured cells. Despite this difference, percent relaxation induced for the same number of viable cells is identical for both groups. Scanning electromicrographs confirm anchorage of endothelial cells to microcarrier beads. While cultured cells cover the entire surface and are individually attached, freshly harvested cells are anchored as cell aggregates leaving some of the surface free. Attachment of freshly harvested endothelial cells to microcarrier beads offers an alternative for the study of the role of endothelial cells in the production of vasoactive substances.

Effect of long-term hypoxia on cultured aortic and pulmonary arterial endothelial cells

In a previous study, we found a marked difference in the release of a cytokine, neutrophil chemoattractant activity (NCA), from cultured endothelial cells exposed to acute decreases in ambient oxygen, depending on the vascular bed of origin. In the current study, we used this cytokine to evaluate the effect of long-term exposure to decreased oxygen on endothelial cell function. We found that, in aortic and pulmonary arterial endothelial cells maintained for months in decreased ambient oxygen (10 or 3% oxygen), exposure to acute decreases in ambient oxygen caused a change in the pattern of NCA release; however, the differential response between the two cell types persisted. Aortic endothelial cells release NCA when exposed acutely to a level of oxygen below that in which they have been chronically maintained. In contrast, pulmonary arterial endothelial cells release NCA only when exposed to 0% oxygen acutely, but only if grown chronically in 10% oxygen; otherwise there was no release of NCA. As another indicator of endothelial cell function, we evaluated the effects of acute hypoxic exposure on prostacyclin production by endothelial cells maintained in 21 or 3% oxygen. If grown in 21% oxygen, both cell types decreased prostacyclin production upon exposure to 0% oxygen. However, when grown in 3% oxygen, only aortic endothelial cells decreased prostacyclin production when exposed acutely to 0% oxygen; pulmonary arterial endothelial cell prostacyclin production did not change. This study demonstrating the persistence of a differential pattern of NCA release and the appearance of a differential pattern of prostacyclin production after a long-term decrease in environmental oxygen suggests that the capacity of certain vascular endothelial cells to respond to decreases in oxygen concentration is carried by the cell throughout its existence. Thus, in certain situations, vascular endothelial cells may be important in sensing acute decreases in ambient oxygen.