Effect of growth factors on human vascular endothelial cell prostacyclin production

TGFβ signaling and cardiovascular diseases

Transforming growth factor β (TGFβ) family members are involved in a wide range of diverse functions and play key roles in embryogenesis, development and tissue homeostasis. Perturbation of TGFβ signaling may lead to vascular and other diseases. In vitro studies have provided evidence that TGFβ family members have a wide range of diverse effects on vascular cells, which are highly dependent on cellular context. Consistent with these observations genetic studies in mice and humans showed that TGFβ family members have ambiguous effects on the function of the cardiovascular system. In this review we discuss the recent advances on TGFβ signaling in (cardio)vascular diseases, and describe the value of TGFβ signaling as both a disease marker and therapeutic target for (cardio)vascular diseases.

Apoptotic cells, through transforming growth factor-beta, coordinately induce anti-inflammatory and suppress pro-inflammatory eicosanoid and NO synthesis in murine macrophages

Apoptotic cells are rapidly engulfed by adjacent tissue cells or macrophages before they can release pro-inflammatory/proimmunogenic intracellular contents. In addition, recognition of the apoptotic cells is actively anti-inflammatory and anti-immunogenic with generation of anti-inflammatory mediators such as transforming growth factor-beta (TGF-beta) and anti-inflammatory eicosanoids. Here, we have investigated the role played by the induction of TGF-beta in the coordinate expression of anti-inflammatory eicosanoids or peroxisome proliferator-activated receptor-gamma and in the suppression of pro-inflammatory lipid mediators and nitric oxide (NO). By use of a dominant negative TGFbetaII receptor, TGF-beta signaling was blocked, and its participation in the consequences of apoptotic cell stimulation was determined. The induction of TGF-beta itself could be attributed to exposed phosphatidylserine on the apoptotic cells, which therefore appears to drive the balanced inflammatory mediator responses. Arachidonic acid release, COX-2, and prostaglandin synthase expression were shown to be significantly dependent on the TGF-beta production. On the other hand, a requirement for TGF-beta was also shown in the inhibition of thromboxane synthase and thromboxanes, of 5-lipoxygenase and sulfidopeptide leukotrienes, as well as of inducible nitric-oxide synthase and NO. TGF-beta-dependent induction of arginase was also found and would further limit the NO generation. Finally, apoptotic cells stimulated production of 15-lipoxygenase and 15-hydroxyeicosatetraenoic acid, a potentially anti-inflammatory pathway acting through peroxisome proliferator-activated receptor-gamma, and lipoxin A(4) production, which were also up-regulated by a TGF-beta-dependent pathway in this system. These results strongly suggest that the apoptotic cell inhibition of pro-inflammatory mediator production is pleiotropic and significantly dependent on the stimulation of TGF-beta production.

Soluble endoglin contributes to the pathogenesis of preeclampsia

Preeclampsia is a pregnancy-specific hypertensive syndrome that causes substantial maternal and fetal morbidity and mortality. Maternal endothelial dysfunction mediated by excess placenta-derived soluble VEGF receptor 1 (sVEGFR1 or sFlt1) is emerging as a prominent component in disease pathogenesis. We report a novel placenta-derived soluble TGF-beta coreceptor, endoglin (sEng), which is elevated in the sera of preeclamptic individuals, correlates with disease severity and falls after delivery. sEng inhibits formation of capillary tubes in vitro and induces vascular permeability and hypertension in vivo. Its effects in pregnant rats are amplified by coadministration of sFlt1, leading to severe preeclampsia including the HELLP (hemolysis, elevated liver enzymes, low platelets) syndrome and restriction of fetal growth. sEng impairs binding of TGF-beta1 to its receptors and downstream signaling including effects on activation of eNOS and vasodilation, suggesting that sEng leads to dysregulated TGF-beta signaling in the vasculature. Our results suggest that sEng may act in concert with sFlt1 to induce severe preeclampsia.

Human vascular smooth muscle cells but not endothelial cells express prostaglandin E synthase

In a previous work, we postulated that endothelial cells possess only the following 2 enzymes involved in prostanoid synthesis: cyclooxygenase and prostacyclin synthase. The present work focused on investigating the expression of prostaglandin (PG) E synthase (PGES) in vascular cells. After incubation of vascular smooth muscle cells (SMCs) and human umbilical vein endothelial cells (HUVECs) with [(14)C]arachidonic acid, the profile of prostanoid synthesis was assessed by HPLC. Untransformed PGH(2) released by the cells was evaluated as the difference in the formation of PGF(2alpha) in the incubations performed in the presence and in the absence of SnCl(2). Resting SMCs and SMCs stimulated with phorbol 12-myristate 13-acetate (PMA), lipopolysaccharide (LPS), interleukin (IL)-1beta, and tumor necrosis factor (TNF)-alpha formed PGE(2) and PGI(2) (evaluated as 6-oxo-PGF(1alpha)), and in the presence of SnCl(2) only a small amount of PGE(2) was deviated toward PGF(2alpha). In contrast, resting and stimulated HUVECs produced PGI(2), PGE(2), PGF(2alpha), and PGD(2), and SnCl(2) completely diverted PGE(2) and PGD(2) toward PGF(2alpha). Reverse transcriptase-polymerase chain reaction analysis shows that mRNA encoding for PGES was not present in HUVECs and in endothelial cells from saphenous vein. Nevertheless, PGES was expressed in SMCs and induced by IL-1beta and TNF-alpha, and by PMA and LPS, although to a lesser extent. Whereas SMC stimulation led to an increase in the synthesis of PGE(2) and PGI(2) but not of untransformed PGH(2), stimulation of endothelial cells resulted in an enhanced release of the vasoconstricting prostanoid PGH(2).

Panax quinquefolium L. inhibits thrombin-induced endothelin release in vitro

Endothelial cell damage is considered to be the initial step in the genesis of thrombosis and arteriosclerosis, the common precursors of cardiovascular disorders. In this study, we evaluated the protective effects of American ginseng or Panax quinquefolium L. extracts on endothelial cell injury, and investigated effects of ginseng extracts on thrombin-induced endothelin release using cultured human umbilical vein endothelial cells. We observed that when endothelial cells pretreated with 1, 10, and 100 micrograms/ml of Panax quinquefolium L. extracts were incubated for 4 and 24 hr with thrombin, the concentration of endothelin was significantly decreased in a concentration dependent, time related manner (at 4 hr, IC50 = 5.1 micrograms/ml; at 24 hr, IC50 = 6.2 micrograms/ml). We further evaluated the effects of NG-nitro-L-arginine (NLA), a nitric oxide (NO) synthetase inhibitor, on the activity of Panax quinquefolium L. extracts. Following pretreatment of cultured endothelial cells with NLA, the inhibition of thrombin-induced endothelin release by Panax quinquefolium L. was significantly reduced (P < 0.05). This result suggests that the pharmacological action of Panax quinquefolium L. is, at least partially, due to NO release. Our data demonstrate that American ginseng may play a therapeutic role in facilitating the hemodynamic balance of vascular endothelial cells.

Effects of quercetin on the release of endothelin, prostacyclin and tissue plasminogen activator from human endothelial cells in culture

Quercetin and related flavonoids are naturally occurring polyphenolic compounds with multiple pharmacological activities. Using cultured human umbilical vein endothelial cells, we investigated the effects of quercetin on endothelin (ET-1) and tissue plasminogen activator (t-PA) release induced by thrombin. We observed that when endothelial cells pretreated with 5 or 50 microM of quercetin were incubated for 4 and 24 h with thrombin, ET-1 concentration-dependently decreased (n = 6, P < 0.01, at 4 h IC50 = 1.54 microM, at 24 h IC50 = 2.78 microM). Under the same experimental conditions, quercetin significantly increased t-PA (n = 6, P < 0.01, at 4 h EC50 = 0.71 microM and at 24 hrs EC50 = 0.74 microM). In the same preparation, we evaluated prostacyclin (PGI2) release, induced by thrombin activated platelets, as determined by a 6-Keto-PGF1alpha radioimmunoassay. Following the treatment of cultured endothelial cells with activated platelets, the concentration of 6-Keto-PGF1alpha was significantly increased (P < 0.01). Quercetin (1, 5, and 20 microM) inhibited PGI2, in a concentration-dependent manner (n = 6, P < 0.05). Our data indicate that quercetin modulates the release of ET-1, t-PA, and PGI2 from vascular endothelial cells.

Effects of angiogenic growth factors on endothelium-derived prostacyclin production by ovine uterine and placental arteries

Uteroplacental and fetoplacental arteries produce substantial amounts of prostacyclin (PGI2). Because angiogenic growth factors such as basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), and epidermal growth factor (EGF) are increased in pregnancy, we hypothesized that treatment of uterine and fetoplacental arteries with bFGF, VEGF, and EGF would further enhance the pregnancy-induced increase in PGI2 production. Duplicate uterine (UA) and fetoplacental (PA) artery (primary branch off of the umbilical cord = pPA; cotyledonary or tertiary = tPA) explants from seven late gestation sheep were placed in tissue culture (RPMI; 37 degrees C) for 24 h alone or with (1-100 ng/mL) bFGF, VEGF, or EGF. To evaluate the endothelial contribution to basal and stimulated PGI2 production and to determine whether it is de novo, arteries with and without endothelium from three additional late gestation ewes, tissues were incubated in the absence or presence of growth factors with or without meclofenamate (1 microM). The stable metabolite of PGI2, 6-keto-PGF1 alpha, was measured in culture media and expressed as ng/mg wet wt 24 h. PGI2 production by UA increased (p < 0.05) from 5.43 +/- 0.26 at control to 8.93 +/- 0.99 with 100 ng/mL bFGF. Although VEGF produced a similar response, EGF did not increase PGI2 production in UA. In pPA, 100 ng/mL bFGF induced a 2.2-fold increase (p < 0.01) in PGI2 production from 1.94 +/- 0.14 to 4.20 +/- 0.31; VEGF and EGF were without effect. In tPA, 50 and 100 ng/mL bFGF increased PGI2 production from 1.98 +/- 0.14 to 3.5 +/- 1.05 and 3.96 +/- 0.46 (p < 0.02). In tPA, VEGF did not increase PGI2 production; however, 10, 50, and 100 ng/mL EGF, enhanced (p < 0.03) PGI2 production from 1.98 +/- 0.14 to 3.39 +/- 0.62, 3.62 +/- 0.26, and 2.93 +/- 0.20. Endothelium removal and meclofenamate treatment caused a 90% and 100% decrease, respectively, in basal PGI2 production, with no recovery after treatment with growth factors. We conclude that PGI2 production is augmented by bFGF in UA, pPA and tPA, by VEGF in UA, and by EGF in tPA during ovine pregnancy. Basal and stimulated PGI2 secretion is endothelium-derived via de novo synthesis. bFGF, VEGF, and EGF, in addition to angiogenesis, may modulate PGI2 production, further enhancing blood flow to the growing uteroplacental bed.

Estrogen and postmenopausal estrogen/progestin therapy: effect on endothelium-dependent prostacyclin, nitric oxide and endothelin-1 production

It is well documented that postmenopausal estrogen/progestin therapy (HRT) protects women against cardiovascular disorders. However, the mechanism(s) by which this protection is mediated remains largely unresolved, because beneficial effects of estrogen on the blood lipid profile account for only 20-30% of the overall protection. Growing evidence suggests that estrogen has direct effects on the blood vessel wall indicating that vascular endothelium may play a key role in mediating these effects by producing vasoactive factors, such as prostacyclin (PGI2), nitric oxide (NO) and endothelin-1 (ET-1). In vitro estrogen stimulates endothelial PGI2 and NO production, whereas ET-1 production is not affected. Moreover, in vivo studies indicate that estrogen and HRT increase PGI2 and NO production, whereas ET-1 production decreases. These effects are evidently mediated through estrogen receptors in endothelial cells. Thus, estrogen and HRT lead to the dominance of vasodilatory and antiaggregatory agents released by the endothelial cells. This may be an important new mechanism in the cardiovascular protection mediated by estrogen and HRT.

Prostaglandin I2 analog enhances the expression of urokinase-type plasminogen activator and wound healing in cultured human fibroblast

This study examines the effects of prostaglandin I2 (PGI2) on urokinase-type plasminogen activator (uPA) production and wound healing by human fibroblasts. Employing fibrin autography, it was found that beraprost sodium, a stable PGI2 analog, enhanced the fibrinolytic activity in media conditioned by human fibroblasts, TIG-3-20 cells. Fibrin zymography, ELISA, and Northern blot analysis confirmed that the enhanced activity was caused by an increase in uPA synthesis and secretion and a decrease in type-1 plasminogen activator inhibitor. While cycloheximide and 2',5'-dideoxyadenosine, an adenylate cyclase inhibitor, suppressed the effect of PGI2, dibutyryl cyclic AMP increased the fibrinolytic activity and uPA mRNA. These findings indicate that PGI2 promotes uPA production in TIG-3-20 cells via direct stimulation of the cyclic AMP intracellular pathway. A similar effect was observed in two other fibroblast cell lines, TIG-7-20 and TIG-7-30. Although PGI2 itself did not affect cellular proliferation, it promoted in vitro repopulation of the denuded area in a wounded monolayer. These observations suggest that PGI2 can stimulate wound healing through the enhanced production of uPA.

Effect of serum on vascular smooth muscle function

Serum contains many biologically active factors influencing cell growth and is commonly used as a culture medium supplement. It has not generally been appreciated that serum can affect vascular tone. We have observed that the contractile response of aortic rings previously exposed to 10% fetal bovine serum (FBS) for 24 hours and then stimulated with phenylephrine (0.01-1microM) or angiotensin II (1microM) is significantly diminished compared to 1) rings incubated in FBS for only 6 hours, 2) aortic rings previously incubated in 1% FBS or 3) aortic rings incubated in 10% bovine serum albumin for 24 hours. A similar attenuated response was also seen when the vascular aortic rings were incubated in heat inactivated adult bovine serum. To test whether prostaglandins might be induced by factors contained in serum and account for the diminished stimulated contractile response, rings were incubated for 24 hours in media containing 10% FBS with either indomethacin 10microM, corticosterone 100nM or 11-dehydrocorticosterone 100nM. These agents are known to affect prostaglandin synthesis. Contractile responses were then measured accordingly. In each series, the previously attenuated contractile response to phenylephrine and to angiotensin II was fully restored with prostaglandin synthesis inhibition. Thus, factors contained in serum are capable of blunting the stimulated contractile response of rat aortic vessels. These serum factors appear to act by inducing prostaglandin synthesis in vascular tissue.

Hormone replacement therapy modifies the capacity of plasma and serum to regulate prostacyclin and endothelin-1 production in human vascular endothelial cells

OBJECTIVE

To determine if hormone replacement therapy (HRT) modifies the ability of plasma or serum to regulate the synthesis of vasodilatory prostacyclin and that of vasoconstrictive endothelin-1 by cultured human umbilical vein endothelial cells.

DESIGN

Plasma and serum collected before and during the sixth treatment cycle of HRT from 13 healthy postmenopausal women were added to cultured endothelial cells.

SETTING

Helsinki University Central Hospital, Department of Obstetrics and Gynecology, Helsinki, Finland.

PATIENTS

Thirteen postmenopausal women (> or = 1 year since their last menstruation, FSH level > 40 mIU/mL [conversion factor to SI unit, 1.00], clear vasomotor symptoms) that suffered from incapacitating menopausal symptoms necessitating the initiation of HRT were studied.

INTERVENTIONS

A combined regimen consisting of 2 mg oral E2 for 12 days followed by 2.0 mg oral E2 + 1.0 mg norethisterone acetate for 10 days and 1.0 mg E2 for 6 days.

MAIN OUTCOME MEASURES

The releases of prostacyclin, as assessed by its metabolite 6-keto-prostaglandin F1 alpha, and that of endothelin-1 by cultured human umbilical vein endothelial cells in the presence of 10% plasma or 10% serum collected from the study subjects.

RESULTS

Hormone replacement therapy enhanced the ability of plasma to stimulate prostacyclin production by 21% +/- 6% (mean +/- SEM) during the E2 + norethisterone acetate phase and tended to do so also during the E2-only phase (11% +/- 10%) but caused no change in endothelin-1 release. In contrast, HRT decreased the ability of serum to stimulate prostacyclin production by 12% +/- 5% during the E2-only phase and increased that of endothelin-1 by 8% +/- 4% during the E2 + norethisterone acetate phase.

CONCLUSION

Because plasma flushes endothelial cells in vivo, our data on the HRT-induced stimulation of the capacity of plasma to enhance the production of vasoprotective prostacyclin without a concomitant change in endothelin-1 release in cultured human umbilical vein endothelial cells may provide one new explanation for the cardiovascular protection of HRT.

Inhibition of platelet aggregation by endocardial endothelial cells

We assessed the anti-platelet properties of endocardial endothelial cells (EECs) by measuring platelet aggregation after brief interaction with EECs isolated from the right ventricles of porcine hearts. Platelet aggregation in response to thrombin was significantly inhibited by brief incubation of platelet suspensions over EEC monolayers. Pretreatment of EECs with indomethacin restored platelet reaction but that with L-NAME and hemoglobin (Hb) did not. The PGI2 content of platelet suspensions after interaction with cultured EECs was significantly correlated with the inhibition of platelet aggregation. These results suggest that EECs inhibit platelet aggregation by releasing PGI2.

Hirudin stimulates prostacyclin but not endothelin-1 production in cultured human vascular endothelial cells

To study the effect of hirudin on endothelial cell prostacyclin (PGI2) and endothelin-1 (ET-1) production, we cultured human umbilical vein endothelial cells (HUVECs), stimulated them with 0.00001-10 kU/l of hirudin for 12-24 hours, and measured by radioimmunoassays the concentrations of 6-ketoprostaglandinF1 alfa (6-keto, a metabolite of PGI2) and ET-1 in the incubation medium. In incubation medium containing 10% serum hirudin stimulated PGI2-production dose-dependently. The lowest stimulatory hirudin concentration was 0.001 kU/l, which increased the concentration of 6-keto by 10.8 +/- 4.4% (mean +/- S.E) (p < 0.01). The greatest stimulation rate (28.6 +/- 6.2%, p < 0.001) was obtained with the highest hirudin concentration (10 kU/l), when the culture medium contained 10% human serum. The PGI2-stimulating activity was exaggerated in the absence of serum, when 1 kU/l of hirudin increased PGI2-production by 59.7 +/- 6.2% (p < 0.001, n = 14). Stimulation of PGI2 appeared after 12 hour incubation. Hirudin had no effect on the conversion of exogenous arachidonic acid to 6-keto or on the production of ET-1. We thus conclude that hirudin stimulates PGI2-production through de novo protein synthesis. Stimulation of PGI2-production by hirudin may contribute to its antithrombotic activity, since PGI2 favours vasodilatation and attenuates platelet aggregation.

Acidic and basic fibroblast growth factors have comparable effects on the haemostatic function of vascular endothelium

Acidic and basic fibroblast growth factor (aFGF and bFGF respectively) are closely related mitogens (55% homology) of the heparin binding growth factor family. Reports of the relative potency of these growth factors and the ability of heparin to potentiate the activity of bFGF are conflicting. We have examined the effect of heparin and human recombinant aFGF and bFGF on basal and thrombin challenged release of metabolites from cultured human umbilical vein endothelial cells (HUVEC). Culture supernatant was assayed for thrombospondin, prostacyclin and PAI-1 and cell lysates were analysed for t-PA. aFGF and bFGF were equipotent in regulating ther release of all metabolites studied, except thrombin stimulated release of PGI2 where bFGF was more potent than aFGF in the absence of heparin. Heparin potentiated the mitogenic and metabolic effects of both bFGF and aFGF. However, heparin was not essential for the expression of the biological activity of FGF.

Growth-promoting effects of substance P on endothelial cells in vitro. Synergism with calcitonin gene-related peptide, insulin, and plasma factors

The purpose of this study was to determine the effects of the vasoactive perivascular neuropeptide substance P (SP) on the growth and function of vascular endothelial cells in serum-free culture conditions with cells quiescent in the G0-G1 phase of the cell cycle and to characterize the response. In addition, interactions between SP and other growth factors and neuropeptides including insulin, platelet factors, neurokinin A, neurokinin B, and calcitonin gene-related peptide (CGRP) were studied on endothelial cell growth and compared. Growth effects were determined by stimulation of tritiated thymidine incorporation into DNA and cell proliferation. SP exhibited differential effects on cell growth that were a function of concentration, incubation time, interaction with other growth factors, and cell culture conditions. DNA synthesis in response to SP showed a bell-shaped distribution with a maximal effect that was 10.5-fold over control at 500 micrograms/mL of SP after 48 hours of incubation. The effect showed marked synergism with insulin (10 micrograms/mL) and with CGRP (0.01 to 10 micrograms/mL), which is colocalized with SP in vivo. Insulin and CGRP alone had no significant effect on endothelial cell growth. Furthermore, no synergism was observed between SP and platelet-derived growth factor or platelet-derived endothelial cell growth factor. Endothelial cell proliferation increased in response to SP to 2.6-fold over control at 48 hours, was maximal at 10 micrograms/mL SP, and also demonstrated synergism with insulin (10 micrograms/mL). Our studies indicate that neuropeptides play a significant role in regulating endothelial cell growth and proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

Proliferation-dependent changes in release of arachidonic acid from endothelial cells

Stimulation of endothelial cells resulted in release of arachidonic acid from phospholipids. The magnitude of this response decreased as the cells became confluent and the change coincided with a decrease in the percentage of cells in growth phases (G2+M); this was not a consequence of time in culture or a factor in the growth medium. Preconfluent cells released approximately 30% of arachidonic acid; confluent cells released only 6%. The decreasing release of arachidonic acid was demonstrated using metabolic labeling, mass measurements of arachidonic acid, and measurement of PGI2. The decrease was not due to a changing pool of arachidonic acid, and mass measurements showed no depletion of arachidonic acid. Release from each phospholipid and from each phospholipid class decreased with confluence. Conversion of confluent cells to the proliferative phenotype by mechanical wounding of the monolayer caused increased release of arachidonic acid. Potential mechanisms for these changes were investigated using assays of phospholipase activity. Phospholipase A2 activity changed in concert with the alteration in release, a consequence of changes in phosphorylation of the enzyme. The increased release of arachidonic acid from preconfluent, actively dividing cells may have important physiologic implications and may help elucidate mechanisms regulating release of arachidonic acid.

Augmentation of interleukin-1 induced prostacyclin production by endothelial cell growth factor: implications for chronic synovitis

Interleukin-1 (IL-1) is a key inflammatory cytokine that has important effects both on endothelial cell (EC) growth and synthetic function. Fibroblast growth factors (FGF's), including endothelial cell growth factor (ECGF), are important regulators of EC growth, and their role in the pannus formation and synovial proliferation seen in chronic arthritis has been emphasized recently. While ECGF mediated EC proliferation is inhibited by IL-1, potential interaction of these peptides on other aspects of EC function has not been described. As both IL-1 and FGF may be important disease mediators in rheumatoid arthritis, we studied their combined effects on EC prostacyclin production. While ECGF alone had no measurable effects, it enhanced rIL-1 alpha induced prostacyclin production in a dose and time dependent fashion. Both pertussis and cholera toxins blocked the augmentation, suggesting a role for G proteins in mediating the synergism. These studies demonstrate that ECGF can alter certain effects of IL-1 on the endothelium, and point to an additional role that this family of growth factors may play in some inflammatory disorders.

Human serum, plasma, and platelets stimulate prostacyclin and endothelin-1 synthesis in human vascular endothelial cells

Prostacyclin (PGI2), a powerful vasodilatory prostanoid, and endothelin-1 (ET-1), a potent vasoconstrictive peptide, are produced by vascular endothelial cells. We show that human serum (10%) caused a 3.2-fold stimulation both in PGI2 and ET-1 synthesis in human endothelial cells cultured from umbilical veins, and human plasma (10%) stimulated productions of both 1.6- and 1.7-fold, respectively. In addition, releasates from thrombin-activated platelets (20 x 10(9) platelets/l) caused a 1.9-fold increase in PGI2 and a 1.4-fold increase in the ET-1 synthesis. Releasates from frozen-thawed and sonicated platelets (20 x 10(9) platelets/l) caused a 3.6-fold increase in PGI2 release but did not affect ET-1 production. We thus conclude that, in normal situation, endothelial stimulating activity present in plasma perhaps plays a role in the regulation of endothelial function, whereas platelet-derived activity in serum may be important at site of thrombosis.

Modulation of prostacyclin production by cytokines in vascular endothelial cells

The data presented in this review clearly show that many different cytokines regulate the synthesis of PGI2 in vascular EC (Tables 1 & 2). Since these agents are synthesized, stored, and/or released from platelets, leukocytes and cells present in the vascular wall (Fig.), they are to be found at sites of vascular injury and may, through their effect on the synthesis of PGI2 and other prostanoids, regulate thrombogenesis and atherogenesis. Despite the mass of detailed data, the picture is still fragmentary. Very little, for instance, is known about the 'orchestral effects' of different combinations of cytokines. In addition, it seems that the regulation of PGI2 synthesis by cytokines varies with the species and with the type of vasculature from which the cells originated. However, discrepancies may also be due to the use of different culture conditions. Moreover, we must remember that the present data are almost exclusively from in vitro studies, and the representativeness of these results in in vivo situations remains to be clarified.

Transforming growth factor-beta opposes the stimulatory effects of interleukin-1 and tumor necrosis factor on amnion cell prostaglandin E2 production: implication for preterm labor

OBJECTIVE

In preterm labor increased concentrations of interleukin-1 and tumor necrosis factor are present in amniotic fluid. These cytokines may promote labor by stimulating the production of prostaglandins by intrauterine tissues. In many biologic processes, transforming growth factor-beta modifies the actions of cytokines. We studied the effect of transforming growth factor-beta on the cytokine-induced prostaglandin E2 production by amnion cells.

STUDY DESIGN

Human amnion cells in monolayer culture were treated with interleukin-1, tumor necrosis factor, or vehicle in the presence or absence of transforming growth factor-beta. The prostaglandin E2 production was measured.

RESULTS

Transforming growth factor-beta decreased the interleukin-1- or tumor necrosis factor-induced prostaglandin E2 production by 70% to 80% and the basal prostaglandin E2 synthesis by 27%. The synergistic stimulation of prostaglandin E2 production by the combination of interleukin-1 with tumor necrosis factor was inhibited by 80% in cells treated with transforming growth factor-beta. Transforming growth factor-beta 1, -beta 2, and -beta 1,2 were equipotent.

CONCLUSION

Transforming growth factor-beta suppresses the cytokine-induced prostaglandin E2 production by amnion cells and may be an important factor in maintaining pregnancy in the face of labor-promoting cytokines.

Cyclical strain effects on production of vasoactive materials in cultured endothelial cells

Mechanical forces due to fluid flow and cyclical strain can alter endothelial cell morphology and function, including the release of vasoactive materials endothelin, prostacyclin (PGI2), and tissue plasminogen activator (t-PA). In this study, effects of cyclical strain were modeled by culturing bovine aortic endothelial cells on fibronectin-coated elastic membranes of silicone rubber (Silastic) or poly-etherurethane urea (Mitrathane). After growing to confluence under static conditions of 37 degrees C in humidified air with 5% CO2, cells were strained cyclically at membrane elongations of 5% or 10% for 24 hours at 1 Hz. Controls were maintained under static conditions or were exposed to fluid motions similar to the strained cells but without stretching. Secretion rates were constant throughout experiments in the strain chamber with no initial burst in metabolism associated with the initiation of strain. Secretion rates were not altered by choice of elastic membrane. At a physiological level of 10% cyclical strain, prostacyclin and endothelian secretion rates were increased by 2.5-fold and 1.7-fold, respectively, above stationary controls. Endothelin production demonstrated a dose-dependent response with cyclical strain, while PGI2 appeared to require a threshold strain before an increase in secretion occurred. No significant differences in t-PA levels were seen in cyclically strained cells compared with controls. These results indicate that endothelial cells respond metabolically to cyclical strain and suggest that mechanical strain may modulate secretion of selective vasoactive materials by vascular endothelial cells.

Platelet-derived growth factor receptors on macrovascular endothelial cells mediate relaxation via nitric oxide in rat aorta

The effects of platelet-derived growth factor (PDGF) were studied in isolated rings of rat aorta contracted submaximally to phenylephrine. The BB isoform of PDGF elicited relaxation in rings with endothelium and further contraction in rings without endothelium. Both the endothelium-dependent relaxation and endothelium-independent contraction occurred at concentrations known to induce PDGF receptor-mediated responses in cultured cells. Furthermore, the relaxation was isoform specific. This conclusion is supported by the unique ability of PDGF-BB to induce endothelium-dependent relaxations, as well as by studies showing isoform specific, concentration-dependent desensitization of PDGF-BB relaxation. The relaxation induced by PDGF-BB was prevented by N omega-nitro-L-arginine. It was also observed that endothelium-independent contractions to the AB and AA isoforms of PDGF were less than those to PDGF-BB. Contrary to the widely held view that PDGF receptors are not present on the endothelium of macrovessels, these studies provide evidence for an endothelium-dependent, nitric oxide mediated relaxation of rat aorta caused by PDGF via PDGF beta beta-receptors.

Human serum stimulates endothelin-1 synthesis more potently than prostacyclin production by cultured vascular endothelial cells

Human serum stimulated the synthesis of a vasoconstrictive peptide, endothelin-1 (ET-1), and a vasodilatory prostanoid, prostacyclin (PGI2), by cultured human umbilical vein endothelial cells in a concentration- and time-dependent manner. Incubation in 20% concentration of the serum for 24 h stimulated ET-1 synthesis almost six-fold while PGI2 production increased two-fold. In addition, a tumor-promoting phorbol ester, phorbol 12-myristate 13-acetate (PMA), inhibited the serum-induced ET-1 production and stimulated PGI2 synthesis in a concentration- and time-dependent manner. Our results suggest that human serum derived factor(s) stimulate the production of vasoconstrictive ET-1 more potently than the synthesis of vasodilatory PGI2 by human vascular endothelial cells and that the production of these agents is differentially regulated by PMA.