Cultured endothelial cells increase their capacity to synthesize prostacyclin following the formation of a contact inhibited cell monolayer

TGF-beta2 inhibits AKT activation and FGF-2-induced corneal endothelial cell proliferation

The corneal endothelial cells form a boundary layer between anterior chamber and cornea. This single cell layer is important to maintain cornea transparency by eliciting net fluid transport into the anterior chamber. Injuries of the corneal endothelial layer in humans lead to corneal swelling and translucence. This hindrance is thought to be due to limited proliferative capacity of the endothelial layer. Fibroblast growth factor 2 (FGF-2) and transforming growth factor-beta 2 (TGF-beta2) are both found in aqueous humor, and these two cytokines promote and inhibit cell growth, respectively. The intracellular signaling mechanisms by which TGF-beta2 suppresses the mitogenic response to FGF-2, however, remain unclear. We have addressed this question by investigating potential crosstalk between FGF-2-induced and TGF-beta2-regulated intracellular signaling events in cultured bovine corneal endothelial (BCE) cells. We found that TGF-beta2 and FGF-2 oppositely affect BCE cell proliferation and TGF-beta2 can override the stimulating effects of FGF-2 by increasing COX-2 expression in these cells. Consistent with these findings, overexpression of COX-2 significantly reduced FGF-2-induced cell proliferation whereas a COX-2 specific inhibitor NS398 reversed the effect of TGF-beta2 on FGF-2-induced cell proliferation. The COX-2 product prostaglandin E2 (PGE-2) blocks FGF-2-induced cell proliferation. Whereas FGF-2 stimulates cell proliferation by activating the AKT pathway, TGF-beta2 and PGE-2 both inhibit this pathway. In accordance with the effect of PGE-2, cAMP also inhibits FGF-2-induced AKT activation. These findings suggest that the mitogenic response to FGF-2 in vivo in the corneal endothelial layer may be inhibited by TGF-beta2-induced suppression of the PI3-kinase/AKT signaling pathway.

Interleukin-8 stimulates placental prostacyclin production in preeclampsia

PROBLEM

Our purpose was to determine placental interleukin (IL)-8 production and its correlation with the prostacyclin production in normal and preeclamptic pregnancies and to evaluate the beneficial effect of IL-8 on prostacyclin production.

METHOD OF STUDY

We determined 1) the in vitro production of IL-8 and prostacyclin by placental villous tissues from normal and preeclamptic pregnancies and 2) the production of prostacyclin by villous tissues from preeclampsia treated with recombinant human IL-8 (rhIL-8). IL-8 levels were measured by enzyme-linked immunosorbent assay and prostacyclin by radioimmunoassay of 6-keto PGF1alpha, the stable metabolite of prostacyclin.

RESULTS

1) Placental production of IL-8 and 6-keto PGF1alpha were significantly less in preeclampsia than in normal pregnancies, P<0.05. 2) Placental production of 6-keto PGF1alpha and IL-8 was significantly correlated in preeclampsia, P<0.01. 3) Placental tissues treated with IL-8 exhibited a concentration-dependent increase in 6-keto PGF1alpha production.

CONCLUSIONS

Placental tissues from preeclampsia produce significantly less IL-8 than tissues from normal pregnancies, which correlates with decreased prostacyclin production. IL-8 improves placental prostacyclin production in preeclampsia.

Differential regulation of cyclooxygenase isoenzymes by cAMP-elevating agents

Bovine aortic endothelial cells produce prostacyclin as their major arachidonic acid metabolite. cAMP, in turn, is the second messenger for prostacyclin. In the present study, we investigated the effects of cAMP-elevating agents on prostacyclin production by bovine aortic endothelial cells. Treatment of resting bovine aortic endothelial cells with cAMP-elevating agents inhibited prostacyclin production and cyclooxygenase activity, without affecting arachidonic acid release. No change was detected in cyclooxygenase-1 protein expression. The specific inhibitor of protein kinase A, Rp-cAMPS (adenosine 3',5'-cyclic monophosphorothioate, Rp-isomer, triethylammonium salt), and the phosphatase inhibitor, okadaic acid, both suppressed cAMP-induced inhibition, suggesting that this inhibition is mediated by a phosphorylation-dephosphorylation cascade, which is possibly protein kinase A-dependent. In lipopolysaccharide-treated cyclooxygenase-2 expressing bovine aortic endothelial cells, where cyclooxygenase-1 activity was selectively inhibited, dibutyryl cAMP failed to inhibit cyclooxygenase-2 activity. Cyclooxygenase-2 protein was induced upon treatment with dibutyryl cAMP and further induction of cyclooxygenase-2 protein was effected by IBMX (3-isobutyl-1-methyl-xanthine) and dibutyryl cAMP in bacterial lipopolysaccharide-stimulated cells. These results suggest that increased cellular cAMP selectively inhibits cyclooxygenase-1 activity without altering cyclooxygenase-1 protein expression, and at the same time, up-regulates cyclooxygenase-2 protein. This complex regulation of cyclooxygenase activity and protein expression by cAMP may represent a prostacyclin-induced autoregulatory mechanism in bovine aortic endothelial cells.

In vitro evaluation of electrostatic endothelial cell transplantation onto 4 mm interior diameter expanded polytetrafluoroethylene grafts

PURPOSE

To perform an in vitro evaluation of electrostatic endothelial cell transplantation of human umbilical vein endothelial cells (HUVEC) onto segments of 4 mm internal diameter expanded polytetrafluoroethylene (ePTFE) vascular prostheses.

METHODS

This evaluation consisted of exposing vascular graft segments that had been subjected to either electrostatic or gravitation transplantation with HUVEC to a physiologic shear stress (15 dynes/cm2) under steady flow conditions within a flow loop system. Biochemical assays were performed on freshly transplanted grafts by means of radioimmunoassay for prostacyclin and thromboxane A2.

RESULTS

There was a 30% loss of HUVEC after 30 minutes of shear stress exposure from the grafts subjected to gravitational transplantation with no additional significant (alpha = 0.05) loss after 120 minutes. Grafts subjected to electrostatic transplantation had no significant (alpha = 0.05) loss of HUVEC during exposure to physiologic shear stress. Furthermore, after 120 minutes of shear-stress exposure, the grafts subjected to electrostatic transplantation (78,420 +/- 6274 HUVEC/cm2) retained 2.3 times more HUVEC than the counterparts subjected to gravitational transplantation (34,427 +/- 4637 HUVEC/cm2). The biochemical assay results indicated no significant (alpha = 0.05) production of prostacyclin or thromboxane A2 regardless of the method of cell transplantation.

CONCLUSIONS

(1) The electrostatic transplantation technique was superior to the gravitational transplantation technique in terms of cellular retention when the ePTFE grafts were exposed to physiologic shear stress. (2) Production of prostacyclin and thromboxane A2 did not differ between transplanted HUVEC subjected to gravitational or electrostatic procedures.

Interendothelial junctions: structure, signalling and functional roles

Endothelial cell-cell adhesive junctions are formed by transmembrane adhesive proteins linked to a complex cytoskeletal network. These structures are important not only for maintaining adhesion between endothelial cells and, as a consequence, for the control of vascular permeability, but also for intracellular signalling properties. The establishment of intercellular junctions might affect the endothelial functional phenotype by the downregulation or upregulation of endothelial-specific activities.

Heterogeneity of endothelial cells. Specific markers

During embryonic development, endothelial cells differentiate from a common precursor called angioblast and acquire organ-specific properties. One of the important determinants of endothelial cell differentiation is the local environment, and especially the interaction with surrounding cells. This interaction may occur through the release of soluble cytokines, cell-to-cell adhesion and communication, and the synthesis of matrix proteins on which the endothelium adheres and grows. The acquisition and maintenance of specialized properties by endothelial cells is important in the functional homeostasis of the different organs. For instance, in the brain, alteration of the blood-brain barrier properties may have important consequences on brain functional integrity. One of the major limitations to the study of endothelial cell heterogeneity is the fact that these cells are still difficult to isolate and culture from the microcirculation of different organs, and once in culture, they tend to lose their specialized properties. This finding suggests that we have to develop new culture systems, which possibly include coculture with other cell types. An important issue is to develop tools that can help in recognizing endothelial cells and their differentiated phenotype both in vivo and in tissue culture. In this review we give a short overview of the differentiated properties of the endothelium, considering a few examples of highly specialized endothelial cells, such as the brain or bone marrow microcirculation or high endothelial venules. We made a particular effort to list the most common markers of endothelial cell phenotypes. These molecules and related antibodies may be valuable tools for endothelial cell isolation and characterization.

Density-dependent endothelial cell production of an inhibitor of smooth muscle cell growth

Embryonic data and ultrastructural analyses suggest that the primitive endothelium signals undifferentiated mesenchymal cells to migrate to the forming blood vessel and subsequently regulates mural cell growth and behavior. Upon maturation of the blood vessel, chemotactic and mitogenic signals are apparently diminished and differentiated smooth muscle cells normally remain quiescent. This homeostasis is seemingly upset in conditions which lead to pathologies characterized by smooth muscle cell hyperplasia such as atherosclerosis. By culturing endothelial cells at different densities, we attempted to re-create the various stages of vascular development. Whereas media conditioned by sparse endothelial cells stimulate smooth muscle cells, media conditioned by dense endothelial cell cultures are inhibitory. Culture of sparse smooth muscle cells in media conditioned for 3 days by postconfluent endothelial cell cultures leads to dose-dependent and reversible smooth muscle cell inhibition. Furthermore, in the presence of the endothelial cell-derived inhibitor, smooth muscle cells are rendered refractory to mitogens such as fibroblast growth factor and platelet-derived growth factor. The inhibitory activity is not attributable to the well-characterized inhibitors of smooth muscle cell growth, transforming growth factor type-beta, prostaglandin I2, or heparan sulfate proteoglycan. Partial characterization of the inhibitory conditioned media suggests that the active molecule is smaller than 1,000 da, and stable to boiling as well as proteinase K and heparinase digestion. These findings support the concept that there is intercellular communication between endothelial cells and smooth muscle cells and provide evidence for a novel endothelial cell-derived smooth muscle cell growth inhibitor.

Effect of gamma interferon on phospholipid hydrolysis and fatty acid incorporation in L929 cells infected with Rickettsia prowazekii

Treatment of Rickettsia prowazekii-infected L929 cells with gamma interferon (IFN-gamma) immediately after infection altered the lipid metabolism of the host cells as determined by measurement of phospholipid hydrolysis and oleic acid incorporation into phospholipids and neutral lipids. At 48 h postinfection, there was increased phospholipid hydrolysis in infected cultures relative to mock-infected cultures and a further increase in radiolabeled phospholipid hydrolysis in IFN-gamma-treated infected cultures. Oleic acid, the radiolabeled product of hydrolysis, was found in both the free fatty acid and neutral lipid fractions. None of the mock-infected cultures demonstrated increased hydrolysis of their radiolabeled phospholipids in response to treatment with IFN-gamma. Most of the radiolabeled oleic acid incorporated into cultures in the interval between 24 and 48 h after infection and IFN-gamma treatment was present in the phospholipid fraction. However, the neutral lipid fraction from the infected cultures that had been IFN-gamma treated was labeled to a greater extent than that from the untreated cultures. Thin-layer chromatographic analysis of the neutral lipid fractions from both the hydrolysis and incorporation experiments demonstrated that most of the radiolabel was in triglycerides. The infected cultures at 30 h were intact as assessed by the exclusion of trypan blue, but at 48 h postinfection in the IFN-gamma-treated infected cultures more than half of the cells were unable to exclude trypan blue. In no case did the mock-infected cells show substantial damage as a result of IFN-gamma treatment.

Intracellular free calcium concentration and thromboxane A2 formation of vascular smooth muscle cells are influenced by fish oil and n-3 eicosapentaenoic acid

The effect of fish oil and n-3 eicosapentaenoic acid (EPA) on intracellular free calcium concentration ([Ca2+]i) and thromboxane B2 (TXB2) formation in resting and stimulated cultured rat vascular smooth muscle cells (VSMC) was examined. In resting control cells [Ca2+]i was 147 +/- 15 nmol l-1 (mean +/- SEM, n = 4). After pretreatment of the cells with fish oil or EPA for 24 days the resting [Ca2+]i was decreased to 126 +/- 10 nmol l-1 and 84 +/- 8 nmol-1, respectively. After stimulation of untreated control cells with either 100 nmol l-1 angiotensin II (AII), 40 micrograms ml-1 low-density lipoprotein (LDL), or 100 ng ml-1 of recombinant platelet-derived growth factor (PDGFAB), [Ca2+]i was (in nmol l-1) 306 +/- 31, 217 +/- 25 and 213 +/- 16. Treatment of cells with fish oil or EPA reduced the stimulatory effect of the agonists, and the following [Ca2+]i values (in nmol l-1) were found: 199 +/- 21, 131 +/- 10, 148 +/- 13; and 175 +/- 11, 98 +/- 12, and 103 +/- 6, respectively. PDGFAB induced a four fold increase in TXB2-generation (270 +/- 28 pg mg-1 cell protein compared with 61 +/- 8.2 pg mg-1 in unstimulated control cells) within 6 min. In cells pretreated with fish oil or EPA, TXB2-formation was reduced by 54% and 44%, respectively.

IN CONCLUSION

in rat VSMC stimulated by a variety of vasoactive agonist, fish oil and EPA can markedly attenuate intracellular mechanisms related to changes of cytosolic calcium concentration and eicosanoid production.(ABSTRACT TRUNCATED AT 250 WORDS)

Adhesion and spreading of corneal endothelial cells on collagens type I and IV in vitro: a model to study mechanisms of endothelial repair

In vitro assays using endothelial cells (EC, bovine corneal) were performed to study adhesion and spreading on collagen types I and IV. Adhesion was quantitatively analyzed by counting the EC under a light microscope. Spreading was determined by measuring cell area using a scanning electron microscope (SEM). Collagen types I, IV, and IV-F, a mixture of 70, 120, and 140 KD fragments of type IV, all promoted EC adhesion, Types IV and IV-F showed evidence of giving a more marked adhesion than type I. A study of cell area, carried out under identical conditions, such as those in the adhesion assay, showed that types I and IV-F, but not type IV, promoted cell spreading. This provides evidence that cell adhesion and spreading are indeed separate biological phenomena. Furthermore, the ability of fragments of type IV collagen to promote both cell adhesion and spreading may represent an inherent repair mechanism in damaged endothelium.

Unique sequences in the env gene of avian hemangioma retrovirus are responsible for cytotoxicity and endothelial cell perturbation

An avian retrovirus isolated from spontaneous cavernous hemangiomas of layer hens codes for an env protein that induces a cytopathic effect on a wide variety of cultured avian and mammalian cells and also causes thrombogenicity of endothelial cells. Sequence analysis of the avian hemangioma inducing virus revealed unique elements in both its env gene and its LTR. We propose that these elements are responsible for the biological and pathogenic characteristics of the virus.

Endothelium-derived relaxing factors. A perspective from in vivo data

We review below published studies of endothelium-dependent vasodilation in vivo. Endothelium-dependent vasodilation has been demonstrated in conduit arteries in vivo and in the cerebral, coronary, mesenteric, and femoral vascular beds as well as in the microcirculation of the brain and the microcirculation of cremaster muscle. The available evidence, although not complete, strongly suggests that the endothelium-derived relaxing factor generated by acetylcholine in the cerebral microcirculation is a nitrosothiol. The endothelium-derived relaxing factor generated by bradykinin in this vascular bed is an oxygen radical generated in association with enhanced arachidonate metabolism via cyclooxygenase. In the microcirculation of skeletal muscle, on the other hand, the vasodilation from bradykinin is mediated partly by prostacyclin and partly by an endothelium-derived relaxing factor similar to that generated by acetylcholine. Basal secretion of endothelium-derived relaxing factor is controversial in vivo but is usually present in vitro. On the other hand, it appears that endothelium-derived relaxing factor mediates flow-dependent vasodilation in both large vessels and in the microcirculation in vivo. The generation and release of endothelium-derived relaxing factor from endothelium may be abnormal in a variety of conditions including acute and chronic hypertension, atherosclerosis, and ischemia followed by reperfusion. Several mechanisms for these abnormalities have been identified. These include inability to generate endothelium-derived relaxing factor or destruction of endothelium-derived relaxing factor by oxidants after its release in the extracellular space. These abnormalities in endothelium-dependent relaxation may contribute to the vascular abnormalities in these conditions.

In vitro studies on the expansion of endothelial cell monolayers on components of the basement membrane

The purpose of the present study was to observe the expansion of a monolayer of endothelial cells over specific components of the basement membrane. This was performed in vitro in a monolayer expansion assay over 5 days. The control surface was uncoated glass in the form of coverslips. Test substances were coated at a concentration of 10 micrograms/ml. The highest expansion was obtained with a high molecular weight fragment mixture of collagen type IV (IV-F, consisting of 75, 120 and 140 KD fragments), followed by fibronectin. Collagens type I, III and IV tetramer gave similar results, less than fibronectin or collagen type IV-F, although all of the above basement membrane coatings promoted expansion significantly above that of the control (P less than 0.01). The poorest expansion was obtained with laminin, which was significantly less than the control. The pentapeptide GRGDS, related to the fibronectin cell binding region, gave expansion significantly below that of the intact fibronectin molecule, as did the intact collagen type IV molecule compared with type IV-F (P less than 0.025). This indicates that sequences of the fibronectin molecule other than the cell binding sequence may be involved in promoting endothelial cell expansion. In addition, the integrity of the collagen type IV molecule does not appear necessary for this effect. On the contrary, the higher movement on IV-F may represent an inherent repair mechanism in damaged endothelium. Autoradiographic studies show that endothelial cell proliferation at the expanding front is involved in the migration assay.

Modulation of phospholipase A2 lytic activity by actin and myosin

Prostacyclin (PGI2) production is closely coupled with endothelial cell shape and F-actin distribution in vitro. These findings may implicate cytoskeletal constituents in a mechanism regulating eicosanoid metabolism. To determine the potential for such a regulatory mechanism, cytoskeletal protein effects on the rate-limiting eicosanoid cascade enzyme (phospholipase A2; PLA2) were studied. Membrane phospholipid degradation was indirectly determined by spectrophotometric measurement of PLA2-induced rat red blood cell ghost (RBC-G) hemolysis. PLA2 was incubated with actin (skeletal, smooth, or nonmuscle cell) at a nonmuscle cell concentration (100 microM) and then exposed to the RBC-G. Comparisons in the presence or absence of actin revealed that F-actin stimulated whereas G-actin suppressed PLA2 lytic behavior significantly (P less than 0.05). When a 10: or 100:1 F-actin to myosin ratio was used, the F-actin stimulatory effect was significantly (P less than 0.05) reduced. These findings suggest that the in vitro correlation between PGI2 production and endothelial cell shape may be the result of PLA2 regulation by cytoskeletal elements that impart cellular form.

Evaluation of long-term cultured endothelial cells as a model system for studying vascular ageing

Long-term cultures of human umbilical endothelial cells were examined for changes in cell growth, cell density, cell volume, occurrence of multinucleated cells, prostacyclin production and negative charge of the cell surface during in vitro cellular ageing. The changes observed were consistent with the previously described changes in vascular endothelial cells during in vivo ageing. Therefore, we conclude that cumulative cell division is deeply involved in in vivo ageing of endothelial cells and that this in vitro system is suitable for investigating in vivo ageing of vascular endothelial cells.

Release of arachidonic acid from vascular endothelial cells: fatty acyl specificity is observed with receptor-mediated agonists and with the calcium ionophore A23187 but not with melittin

Vascular endothelial cells respond to a variety of physiological and pharmacological stimuli by releasing free arachidonic acid from membrane phospholipids, thus initiating synthesis of prostacyclin. Previous work in our laboratory has demonstrated that the thrombin-stimulated deacylation is specific for arachidonate and structurally similar polyunsaturated fatty acids that contain a delta-5 double bond. We now report that histamine, bradykinin, and the calcium ionophore A23187 exhibit the same fatty acid specificity as does thrombin. Experiments with both human umbilical vein and calf pulmonary artery endothelial cells indicate that these agonists stimulate the release of previously incorporated [14C]arachidonate but not 8,11,14-[14C]eicosatrienoate or [14C]docosatetraenoate. By contrast, melittin stimulates the release of 8,11,14-eicosatrienoate, docosatetraenoate, and oleate as well as arachidonate. These results suggest that histamine, bradykinin, and A23187 activate a common calcium-dependent phospholipase A2. Melittin appears either to alter the substrate specificity of the receptor-linked phospholipase A2 activity or to activate additional enzymes as well.

The lupus anticoagulant stimulates the release of prostacyclin from human endothelial cells

Decreased endothelial cell production of prostacyclin (PGI2) in response to the lupus anticoagulant has been previously demonstrated and postulated to have a causal relationship to the thrombotic events associated with the lupus anticoagulant. Five patients who exhibited the anticoagulant were studied in an effort to determine if a relationship exists between exposure of endothelial cells to the lupus anticoagulant and decreased production of PGI2. Human endothelial cells derived from human umbilical vein grown in culture were exposed to IgG fractions of patient plasmas containing the lupus anticoagulant. PGI2 released per 10(6) cells was determined by radioimmunoassay for 6-keto-PGF-1-alpha. The overall means for the patient and control groups are given by 47 pM/10(6) cells and 12 pM/10(6) cells respectively. This is a statistically significant difference (F = 10.65, p = 0.017) when the effects of different batches of endothelial cells and thrombin stimulation are adjusted for in the analysis of variance model. These results demonstrate that in this homologous human system exposure of endothelial cells to the lupus anticoagulant leads to stimulation rather than inhibition of PGI2 release.

Regulation of prostaglandin synthesis in human vascular cells

Prostacyclin (PGI2) synthesis in human vascular tissue is mainly regulated by the activity of enzymes that metabolize arachidonic acid, and especially by the activity of cyclooxygenase. The activity of this enzyme depends upon the balance between its synthesis and its inactivation by peroxidated metabolites or drugs. Cyclooxygenase in vascular endothelial cells is strongly inhibited by aspirin, but is rapidly resynthesized. The resynthesis proceeds more rapidly in endothelium than in smooth muscle cells. Growth factors for vascular cells strongly influence cyclooxygenase production and activity. PDGF both releases arachidonate and stimulates cyclooxygenase synthesis in fibroblasts and smooth muscle cells, and ECGF enhances new enzyme synthesis. By contrast, we find that the endothelial growth factor depresses PGI2 synthesis in human endothelial cells in a time and concentration-dependent manner. This inhibitory effect is potentiated by heparin. The inhibition correlates with a decrease in the content of immunoreactive cyclooxygenase within the endothelial cells when they are grown in the presence of ECGF and heparin. These findings suggest that proliferation selectively suppresses the function of prostaglandin synthesis in endothelial cells.

Recovery of prostacyclin capacity of irradiated endothelial cells and the protective effect of vitamin C

Ionizing irradiation has been reported to affect prostacyclin (PGI2) production by intact blood vessels and cultured endothelial cells (EC) due to damage of enzymes of the arachidonate cascade. In the present study, we investigated whether EC can recover from radiation injury and regain their capacity to produce PGI2. Bovine aortic EC were exposed to radiation doses of 3 and 6 Gy and their capacity to produce PGI2 in response to stimulation with arachidonic acid was tested, at various times after irradiation. The results of these experiments showed clearly that EC exposed to single or fractionated irradiation could recover their capacity to produce PGI2 depending on the radiation dose and the time period following radiation. Radiation damage is associated with oxidant stress and the production of free radicals. We therefore tested the ability of an oxygen radical scavenger, vitamin C, to protect the capacity of irradiated EC to produce PGI2. Pretreatment of EC with low concentrations of vitamin C inhibited the radiation induced release of PGI2 to the culture medium. Vitamin C also enhanced the capacity of irradiated EC to produce PGI2 following short stimulation with arachidonic acid. Treatment with this scavenger however, did not protect the cells against the cytopathic effects of radiation.

Endothelium-derived relaxing factor in cultured cells

Many vasoactive agents stimulate release of an endothelium-derived relaxing factor (EDRF). EDRF stimulates cyclic guanosine 3',5'-monophosphate (cGMP) accumulation and relaxation of vascular smooth muscle in a manner similar to that produced by sodium nitroprusside. Endothelium and vascular smooth muscle were isolated from porcine, bovine, and rat thoracic aorta. The capacity of sodium nitroprusside to stimulate cGMP accumulation in cultured bovine, porcine, and rat vascular smooth muscle was found to increase with time in culture to a maximum of 12 to 14 days after plating. In addition, bovine and porcine vascular smooth muscle, but not rat vascular smooth muscle, lost the sodium nitroprusside-stimulated cGMP response after the fifth passage. Cultured endothelial cells did not respond to endothelium-dependent vasodilators or sodium nitroprusside with increased cGMP levels. Vascular smooth muscle cells responded only to sodium nitroprusside. Mixed cultures of porcine and bovine endothelium and vascular smooth muscle and bovine endothelium and rat vascular smooth muscle responded to endothelium-dependent vasodilators with increased cGMP levels. Short-term (4 hours) coculture experiments using bovine endothelium grown on microcarriers to assess the need for long-term contact between the two cell types produced similar results. Release of EDRF from bovine endothelium was studied by loading endothelium-covered microcarrier beads into a column superfused with physiological buffer. Treatment of the column with bradykinin, the calcium ionophore A23187, melittin, and arachidonate released EDRF from the column as measured by cGMP changes in denuded aortic rings and vascular smooth muscle cells and by relaxation of rings when bathed in column effluent. The time course of cGMP changes and relaxation were similar and could be reversed by hydroquinone.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation among endothelial cell shape, F-actin arrangement, and prostacyclin synthesis

Though many factors have been identified which modulate prostacyclin (PGI2) synthesis, there is little information on cellular mechanisms whereby endothelial cells (EC) regulate their basal eicosanoid metabolism. Using substrates of various adhesive capacities, bovine and porcine aortic EC shape and cytoskeletal F-actin arrangement could be modulated. Staining with rhodamine-phalloidin (R-P) permitted analysis of F-actin arrangement, while differences in cell shape were determined by measurement of cell perimeter surface area (CPSA). Spectrophotoflurometric measurements were used to quantitate the R-P binding capacity of the cultures. Cultures of reduced CPSA (225.2 +/- 13.5 mu2) generated the highest levels of basal PGl2 (6.14 +/- 0.51 pg/ug cell protein); had a diffuse arrangement of F-actin and an increased binding capacity for R-P (463.55 +/- 50.58 nmoles/ug cell protein). Cultures of enlarged CPSA (1399.3 +/- 148.3 mu2), with many actin cables and a significantly reduced (p less than 0.001) R-P binding capacity (74.941 +/- 11.79 nmoles/ug of cell protein) produced significantly smaller (p less than 0.001) basal quantities of PGl2 (1.33 +/- 0.14 pg/ug cell protein). Similarly, arachidonic acid stimulation of cultures of reduced CPSA resulted in an increased synthesis of PGl2 when compared to stimulated cultures of enlarged cells. These findings suggest a role for cell shape and the cytoskeleton in the mechanism controlling PGl2 production and indicate that alteration of the arrangement of F-actin may be of importance in regulation of EC eicosanoid metabolism.

A blood vessel model constructed from collagen and cultured vascular cells

A model of a blood vessel was constructed in vitro. Its multilayered structure resembled that of an artery and it withstood physiological pressures. Electron microscopy showed that the endothelial cells lining the lumen and the smooth muscle cells in the wall were healthy and well differentiated. The lining of endothelial cells functioned physically, as a permeability barrier, and biosynthetically, producing von Willebrand's factor and prostacyclin. The strength of the model depended on its multiple layers of collagen integrated with a Dacron mesh.

Production of platelet-activating factor by human vascular endothelial cells: evidence for a requirement for specific agonists and modulation by prostacyclin

Primary cultures of confluent endothelial cells derived from human umbilical veins produce platelet-activating factor (PAF) (1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) when stimulated with appropriate agonists. Highly purified human thrombin and calcium ionophore A23187 stimulate the incorporation of [3H] acetate into a lipid product that has been identified as PAF by its behavior in thin-layer chromatographic and high-performance liquid chromatographic systems, the presence of characteristic biologic activity, and appropriate response to phospholipases. A number of other humoral mediators, examined because they directly influence the activity of vascular cells or because they may mediate endothelial injury, do not stimulate PAF production by endothelial cells. This indicates that the synthesis of PAF by cultured human endothelial cells is a response to specific agonists and is not an unregulated event that occurs as a result of nonspecific cellular perturbation. The PAF produced by thrombin-treated endothelial cells is a potent stimulus for platelet activation, as assayed by the aggregation of human platelets in autologous plasma. The production of PAF by endothelial monolayers is attenuated by prostacyclin, another product of stimulated endothelial cells. Conversely, PAF production is enhanced by treatment of the endothelial cells with indomethacin, an inhibitor of prostacyclin synthesis from arachidonic acid, indicating that endogenously generated prostacyclin may modulate PAF synthesis. The potential to synthesize PAF, a unique lipid autocoid that stimulates the activation of both platelets and polymorphonuclear leukocytes, suggests that endothelial cells can directly influence the activity of these circulating effector cells. This biologic potential may be important in the interaction of the endothelium with circulating blood cells in physiologic conditions and in syndromes of vascular injury.

Evidence for endothelium-derived relaxing factor in cultured cells

Intracellular cyclic GMP concentration was used as a biochemical indicator of endothelium-dependent and organonitrate-induced responses to these vasodilators in cultured porcine aortic smooth muscle and endothelial cells. Sodium nitroprusside (10(-6) M) caused a rapid increase in cyclic GMP levels in confluent smooth muscle cell cultures but not in confluent endothelial monolayers. Adenosine triphosphate (10(-4) M) and methacholine (10(-5) M), two agents that elicit endothelium-dependent relaxation in intact vessels, failed to raise cyclic GMP concentrations in muscle or endothelial cultures alone. When the cell types were grown together in mixed culture, however, treatment with adenosine triphosphate or methacholine induced an elevation in intracellular cyclic GMP levels. These findings suggest that mixed cultures of arterial smooth muscle and endothelial cells can be used to study the phenomenon of endothelium-dependent responses in arterial smooth muscle.

Interferon induction by viruses. XIV. Development of interferon inducibility and its inhibition in chick embryo cells "aged" in vitro

Studies with a number of viruses revealed a time-dependent acquisition of interferon (IFN) inducibility in primary chick embryo cells as they "aged" in vitro for 2-12 days at a confluent cell density without a medium change. The time-course for the development of IFN inducibility was established by generating and analyzing a family of dose (multiplicity)-response (IFN yield) curves, using Newcastle disease virus (NDV, strain LaSota) as the inducer. Cells produced little or no IFN for the first 4-5 days. Between 5 and 6 days the cells gradually developed the capacity to respond to NDV (and other viruses). Maximal yields of IFN were inducible by day 10. This time-dependent development of IFN inducibility was abrogated almost completely when "aging" was carried out in the presence of drugs that inhibited the synthesis of cyclic derivatives of C20 oxygenated unsaturated fatty acids, i.e., inhibitors of prostaglandin/leukotriene synthesis and the arachidonic acid cascade. Of the prostaglandin synthesis inhibitors, indomethacin was particularly effective. Cells treated on day 0 with 10 micrograms/ml of indomethacin produced 100- to 1000-fold less IFN than controls when induced on day 8. To prevent maximally the development of IFN inducibility, indomethacin must be added within the first 2 days of seeding. After about 2 days, the cells begin to escape the action of the drug. Indomethacin added at the time of induction had no effect on the yield of IFN. IFN inducibility was partially restored when indomethacin was removed during the aging process. "Aging" chick cells in low concentrations of cycloheximide (0.5 micrograms/ml) produced results comparable to incubation with indomethacin. Neither reagent had any marked effect on the rate of total protein or RNA synthesis, nor did their action prevent the induction of stress (heat shock) proteins. Cells "aged" in indomethacin were threefold less efficient in responding to the action of IFN, whereas aging in cycloheximide had no effect on IFN's action. Plaque formation on drug-treated cells was normal for viruses that were poor inducers of IFN. However, both the plaquing efficiency and plaque size of Sindbis virus (an excellent IFN inducer) were enhanced markedly on cells treated with indomethacin or low concentrations of cycloheximide during the aging process. These data implicate a family of fatty acid derivatives of arachadonic acid, including prostaglandins and leukotrienes, in the development of IFN inducibility in primary chick embryo cells "aged" in vitro.

Correlation between trypsin binding to a specific receptor and prostacyclin production in cultured vascular endothelial cells

The correlation between the binding and processing of trypsin and its effect on prostacyclin (PGI2) production in cultured adult bovine aortic endothelial (ABAE) cells was studied. ABAE cells demonstrated an ability to produce PGI2 in a dose-response manner to trypsin at the range of 0.1-2.0 micrograms/ml with a saturation at a concentration of 1 microgram/ml. Likewise, 125I-trypsin binding to the cultured cells increased in a dose-response way and reached saturation at a concentration of about 1 microgram/ml; 125I-trypsin was bound to a specific high-affinity cell-surface receptor with a dissociation constant (Kd) of 1.5 X 10(-8) M and each of the confluent ABAE cells has about 1.2 X 10(5) such receptors sites. The cell-surface receptor for trypsin displayed specific characteristics and an excess amount of unlabeled trypsin successfully abolished 125I-trypsin binding while thrombin in excess failed to compete for 125I-trypsin binding. Only a small fraction of the cell-surface-bound 125I-trypsin was internalized and subsequently degraded by ABAE cells as compared to the process of 125I-trypsin internalization by human skin fibroblasts (HSF). This study demonstrated that the stimulatory effect of trypsin on prostacyclin production and release by ABAE cells might be mediated by a specific cell-surface receptor for trypsin on these cells distinct from the thrombin receptor.

Regulation of production of a platelet-derived growth factor-like protein by cultured bovine aortic endothelial cells

Platelet-derived growth factor (PDGF) is a potent mitogen for cultured cells of mesenchymal origin. Known sources of PDGF or PDGF-like protein are blood platelets, several transformed cell lines, and cultured endothelial cells (EC). We have examined the regulation of production of a PDGF-like protein in cultures of bovine aortic EC using a specific radioreceptor assay for PDGF. EC constitutively secreted PDGF-like protein into serum-containing or serum-free medium. The rate of production of PDGF-like protein was constant for at least 3 weeks and was not due to release of an internal store, since cell lysis by repeated freeze/thaw cycles did not release significant amounts of the protein. Synthesis of PDGF-like protein was sensitive to changes in the pH of the media and was maximal at pH 8.5. Production of PDGF-like protein was independent of EC growth rate: rapidly dividing cells and confluent, quiescent cells produced equal amounts per cell. However, sparse, quiescent EC produced more PDGF-like protein per cell than did confluent, quiescent cells. Several phorbol esters stimulated production of PDGF-like protein. At a concentration of 10(-6) M, a twofold stimulation was observed upon addition of the tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) and nearly a fourfold stimulation upon addition of the nonpromoting analog, methyl TPA. Incubation of EC with endotoxin (10 micrograms/ml) resulted in a twofold stimulation of PDGF-like protein production. In all experiments with endotoxin and phorbol esters, an increase in the production of PDGF-like protein was accompanied by morphological changes in the EC cultures. The cells appeared elongated and fibroblastic and exhibited low viability. A mathematical model was developed in which PDGF-like protein production was shown to consist of two separate components--production at a constant rate by healthy cells and a large burst of synthesis and secretion by dying cells. These results suggest that injurious agents may be capable of stimulating production of a growth factor by the endothelium.

Human vascular endothelial cells synthesize and release 24- and 26-carbon polyunsaturated fatty acids

Vascular endothelial cells from human umbilical vein readily incorporate [14C]eicosatrienoate (20:3 (n - 6) and desaturate it to synthesize [14C]arachidonate (20:4) and [14C]docosatetraenoate (22:4). Both substrate and metabolites are extensively esterified in cellular phospholipids and triacylglycerol. After these cells are incubated for 24-48 h with 4.5 microM [14C]20:3 in culture medium plus 10% fetal bovine serum, the medium contains a number of radiolabeled free fatty acids. In addition to arachidonate and docosatetraenoate, these include still longer-chain polyunsaturated fatty acids. We have identified these as 24:4, 24:5, 26:4 and 26:5 by both radio-gas chromatography and HPLC. Although the 24- and 26-carbon polyunsaturated fatty acids represent a negligible percentage of cellular 14C-labeled fatty acids, they are each present in the medium at a concentration of 10-40 nM, whereas [14C]arachidonate is 60-100 nM. In particular, products of delta 4 desaturation are a significant component of radiolabeled polyunsaturated fatty acids in medium but not in the cells. Since docosapolyenoic fatty acids have recently been shown to give rise to biologically active oxygenated derivatives, the selective release and possible subsequent metabolism of even longer polyunsaturated fatty acids warrants further investigation.

Interferon enhances prostacyclin production by cultured vascular endothelial cells

The effects of interferon (IFN) on the arachidonate metabolism and physiological functions of cultured endothelial cells and blood platelets have been examined. Cultured bovine aortic endothelial cells were found to be sensitive to the antiviral and antiproliferative activities of human leukocyte (alpha) IFN and to increase their capacity to synthesize prostacyclin (PGI2) upon exposure to IFN. Several observations indicate that IFN stimulates PGI2 synthesis at the level of the enzymes phospholipase A2 and cyclooxygenase: (a) PGI2 production was dependent upon the supply of exogenous arachidonic acid or the liberation of endogenous cellular arachidonate by ionophore A23187, but was not observed when IFN-treated cells were exposed to the endoperoxide prostaglandin H2. (b) IFN had no effect on the spontaneous release of PGI2 into the culture medium during the incubation period (24-72 h). (c) The stimulatory effect of IFN on PGI2 production was inhibited by both glucocorticoids and indomethacin. The effect of IFN on platelet prostaglandin metabolism was also investigated. Incubation of platelet-rich plasma with IFN had no effect on platelet aggregation and thromboxane A2 production. The biological significance of the findings presented in this paper may be considered in view of the protective role of PGI2 in the vessel wall and the fact that infection with certain viruses induces endothelial damage both in man and experimental animal models.

The effect of radiation on prostacyclin (PGI2) production by cultured endothelial cells

The effect of ionizing irradiation on the synthesis of prostacyclin (PGI2) by cultured bovine aortic endothelial cells was determined. PGI2 was measured in the culture medium by a radioimmunoassay for 6-Keto PGF1 alpha. Two phenomena were observed following irradiation: a) Cells which suffered an immediate radiation damage (1000-5000 rads) released high quantities of PGI2 to the culture medium. This was due to a de novo synthesis of PGI2 stimulated by radiation induced cellular damage, since pretreatment with aspirin of the endothelial cell monolayers resulted in a marked inhibition of PGI2 release following irradiation. b) Metabolically active cells which remained confluent and firmly attached to the culture dish following single, low and intermediate doses (200-1200 rads) radiation, exhibited a marked decrease in their capacity to synthesize PGI2 upon exposure to various stimuli of the arachidonic acid cascade (arachidonic acid, melittin, ionophore A23187 and PGH2). Similar results were observed with cells treated with fractionated radiation. The quantities of PGI2 produced by the endothelial cells decreased as a function of the dose of radiation and time interval between irradiation and subsequent stimulation. Radiation had a minimal effect on the nonthrombogenic properties of the endothelial cells, as evidenced by the small increase in platelet adherence to the endothelial cells. The effect of radiation on PGI2 production by the vascular endothelium may be relevant to the development of radiation induced capillary occlusions, and the enhancement of atherosclerotic lesions in large vessels.