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

Carbon monoxide inhibits endothelin-1 release by human pulmonary artery smooth muscle cells

Endothelin-1 is a potent vasoconstrictor with mitogenic properties. This 21-amino-acid protein, released in the vasculature by endothelial and smooth muscle cells, has been implicated in pulmonary hypertension. More recently, evidence has accumulated for a role of the heme oxygenase system in pulmonary hypertension. Heme oxygenase catalyses the breakdown of heme to produce carbon monoxide, biliverdin and free iron. Here we show that a carbon monoxide-releasing molecule, but not biliverdin, inhibits endothelin-1 release from serum-stimulated human pulmonary artery smooth muscle cells. Under certain conditions, carbon monoxide appears to act as an endogenous break on endothelin-1 release.

Endogenously released endothelin-1 from human pulmonary artery smooth muscle promotes cellular proliferation: relevance to pathogenesis of pulmonary hypertension and vascular remodeling

Endothelin (ET)-1 is a potent vasoconstrictor and comitogen/ proliferation factor for vascular smooth muscle (VSM). As such, it has been implicated in the vascular wall remodeling observed in pulmonary hypertension (PH). Although the endothelium is considered the main source of ET-1, it can be released by other cells including VSM and may mediate proliferation in an autocrine manner. We investigated this possibility using human pulmonary artery smooth-muscle (HPASM) cells. Serum stimulated the release of ET-1 from HPASM cells in a concentration-dependent fashion and caused proliferation as determined by [(3)H]thymidine uptake and increase in cell number. Addition of an ET-A receptor antagonist (BQ123) or an inhibitor of ET-1 synthesis (phosphoramidon) reduced the proliferation induced by serum, confirming an autocrine role for ET-1. In addition, treatment of HPASM cells with two drug types used in the management of PH-cicaprost, a stable prostacyclin-mimetic; or diltiazem, a calcium-channel blocker-reduced ET-1 release from these cells. We conclude that ET-1 released from HPASM cells has an autocrine function in serum-induced proliferation, with important implications for the pathogenesis of human vascular remodeling. Drugs used in the treatment of PH may act, at least in part, by inhibiting this autocrine loop.

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.

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.

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.

Oestrogen and progesterone inhibit the stimulated production of endothelin-1

Important vascular proteins such as endothelin-1 (ET-1) promote the development of cardiovascular diseases. Oestrogen, and perhaps progesterone, prevent the development of vascular disease in women through incompletely understood cellular mechanisms. We hypothesized that oestradiol or progesterone might regulate the production of ET-1 as a potential novel mechanism. We found that serum and angiotensin II (AII) significantly stimulated ET-1 secretion from cultured bovine aortic endothelial cells, inhibited 50-75% by oestradiol or by progesterone. Serum and AII stimulated ET-1 mRNA levels, inhibited at least 70% by oestradiol and by progesterone. Serum stimulated ET-1 transcription mainly through the first 43 nucleotides of the ET-1 promoter, but oestradiol and progesterone did not inhibit this. In contrast, AII stimulated ET-1 transcription through nucleotides -143 to -98, specifically involving an activator protein-1 (AP-1) site at -102. Oestradiol and progesterone caused a 60-70% inhibition of AII-stimulated wild-type construct -. 143ET-1/CAT activity (CAT is chloramphenicol acyltransferase). AII-stimulation of ET-1 transcription was critically dependent on stimulation of mitogen-activated protein kinase (erk) activity, inhibited by oestradiol and progesterone. In summary, we found that sex steroids inhibit AII-induced erk signalling to the ET-1 transcriptional programme. This novel mechanism of negative transcriptional regulation by oestradiol and progesterone decreases the production of ET-1, potentially contributing to the vascular protective effects of these steroids.

Platelets enhance contractility in perfused rat mesenteric arteries: involvement of endothelin-1

We investigated the effects of platelet supernatant on pressor responses to norepinephrine in isolated perfused rat mesenteric arteries. Perfusion of the arteries with platelet supernatant for 2 h markedly enhanced the pressor responses to norepinephrine (10(-6) and 3 x 10(-6) M). This enhancement was significantly inhibited by phosphoramidon (10(-4) M), an endothelin converting enzyme inhibitor. Both BQ788 [N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D -1-methoxycarbonyltryptophanyl-D-norleucine] (10(-6) M), an endothelin ET(B) receptor antagonist, and bosentan (Ro47-0203, 4-tert-butyl-N-[6-(2-hydroxy-ethoxy)-5-(2-methoxy-phenoxy)-2,2-bipyri midin-4-yl]-benzenesulfonamide) (10(-5) M), a nonselective endothelin receptor antagonist, also prevented the potentiation of responses to norepinephrine evoked by platelet supernatant, but FR 139317 ((R)2-[(R)-2-[(S)-2-[[1-(hexahydro-1H-azepinyl)]carbonyl]amino-4-+ ++methylpentanoyl] amino-3-[3-(1-methyl-1H-indoyl)]propionyl]amino-3-(2-pyridyl) propionic acid) (10-6 M), an endothelin ET(A) receptor antagonist, had little effect. Suppressor doses of endothelin-1 (3 x 10(-10) M) or sarafotoxin S6c (S6c) (3 x 10(-10) M) potentiated significantly the norepinephrine-induced vasoconstriction, in the same preparation. Moreover, supernatant-induced enhancement of pressor responses to norepinephrine was markedly suppressed by TGF-beta1 neutralizing antibody. Transforming growth factor-beta1 (TGF-beta1) (40 pM) also significantly enhanced the pressor responses to norepinephrine (10(-6) M) and this enhancement was significantly inhibited by phosphoramidon. These results suggest that platelet-derived TGF-beta1 stimulates the vascular production of endothelin-1 and thereby enhances vasoconstrictor responses to norepinephrine. Platelet-induced enhancement of vasoconstrictor responses to norepinephrine seems to be mainly mediated by endothelin ET(B) receptor, in rat mesenteric arteries.

Effect of physiological concentrations of estradiol on PGI2 and NO in endothelial cells

OBJECTIVES

To elucidate the mechanisms by which estrogens protect against occlusive vascular disorders, we studied the effect of 17 beta-estradiol on the production of prostacyclin (PGI2) and nitric oxide (NO) in primary cultures of human umbilical vein endothelial cells (HUVECs).

METHODS

To study the effect of 17 beta-estradiol on PGI2 production, HUVECs were incubated in the absence and presence of 17 beta-estradiol (0.01-10 nmol/l) encapsulated within beta-cyclodextrin for 12 h in serum-free medium. To study the effect of 17 beta-estradiol (100 nmol/l) on maximal calcium-dependent NO production, we used different approaches. First, HUVECs were incubated with 2 mumol/l calcium ionophore A23187 with or without 17 beta-estradiol (100 nmol/l) for 24 h in serum-free medium. Second, HUVECs were preincubated with or without 17 beta-estradiol (100 nmol/l) for 12 h in medium supplemented with 2% fetal calf serum, and thereafter incubated in serum-free medium with 2 mumol/l of A23187 and with 100 nmol/l of 17 beta-estradiol (cells which contained 17 beta-estradiol during the preincubation period as well as cells which did not) or without it (only cells which did not contain 17 beta-estradiol during the preincubation period) for 6 h or 24 h.

RESULTS

17 beta-Estradiol (0.1 nmol/l) increased the concentration of 6-keto-prostaglandin F1 alpha, a stable metabolite of PGI2 in the incubation medium, by 16%, and no further increase occurred with higher 17 beta-estradiol concentrations. The stimulation was prevented by tamoxifen. 17 beta-Estradiol did not affect NO production in any of our experiments measured as accumulation of nitrate and nitrite in the experimental medium.

CONCLUSIONS

The stimulatory effect on PGI2 production of physiological concentrations of 17 beta-estradiol, shown now for the first time, may provide one explanation for the ability of 17 beta-estradiol to protect against occlusive vascular disorders.

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.

Racial and gender differences in endothelin-1

In summary, ET-1 levels were significantly increased in black men compared with white men. This racial difference could have important research implications if increased ET-1 levels are linked to left ventricular hypertrophy and other cardiovascular diseases, and it may serve as a foundation for future studies.

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.

Endothelin and endothelin antagonists: pharmacology and clinical implications

Endothelins (ET) are a family of peptides with potent biological properties. Endothelial cells produce exclusively ET-1 while other tissues produce ET-2 and ET-3. The production of ET requires an increase in intracellular Ca2+. This increase can be induced by physical chemicals (i.e. hypoxia) or receptor-operated stimuli (i.e. thrombin, angiotensin II, arginine vasopressin, transforming growth factor beta 1, interleukin-1). Most of ET is released abluminally towards vascular smooth muscle and less luminally. The main vascular effect of ET are vasodilation (transient), profound and sustained vasoconstriction as well as proliferation of vascular smooth muscle. These biological effects are mediated by distinct receptors. Three ET receptors have been cloned, i.e. ETA-, ETB- and ETC-receptors. In vascular tissue ETA-receptors are expressed on vascular smooth muscle and responsible for vasoconstriction. ETB-receptors are expressed on endothelium and linked to nitric oxide and/or prostacyclin release. Activation of these receptors explains the transient vasodilation with intraluminal application of ET. Vascular smooth muscle cells can express ETB-receptors which contribute to ET-induced vasoconstriction particularly at lower concentrations. The role of the recently cloned ETC-receptor in the vasculature is still uncertain. ET production is increased (as judged from circulating plasma levels) in vascular disease and atherosclerosis in particular, in myocardial infarction and heart failure, pulmonary hypertension and renal disease. ET production is increased in arterial hypertension remains controversial. Non-peptidic ET antagonists have been developed which either block ETA- receptors or ETA- and ETB-receptors simultaneously. The advantage of ETA-receptors is that they leave the endothelium-dependent vasodilation to ET (via ETB-receptor) intact. However, ETB-mediated contraction remains unaffected by these antagonists. In contrast ETA-/ETB-antagonists fully prevent ET-induced vasoconstriction, however, they also inhibit the endothelial effects of the peptide. ET antagonists interfere with the effects of ET in isolated vascular tissue (including that obtained from humans) as well as in vivo. In humans, ETA as well as ETA-/ETB-antagonists inhibit endothelin-induced vasoconstriction. Hence in summary ET are a family of potent peptides with profound effects in the vasculature. Several studies suggest a role of ET in cardiovascular disease. The newly developed ET-antagonists are potent and selective tools to delineate the (patho-)physiological roles of ET and may become a new class of cardiovascular drugs.

Involvement of transforming growth factor-beta 1 for platelets-induced stimulation of endothelin-1 production

1. Possible mechanisms by which platelets stimulate the production of endothelin-1 (ET-1) in vascular endothelial cells (EC) were investigated. 2. A supernatant of platelets stimulated the expression of prepro ET-1 mRNA, followed by an increased secretion of ET-1 from cultured EC. These responses were markedly enhanced by pretreatment of the platelets with thrombin, at a concentration which did not influence the ET-1 production in EC. A platelet suspension, separated from cultured EC by a permeable nylon membrane, also markedly stimulated the ET-1 secretion from EC. 3. Endothelin-1 production enhanced by the platelet supernatant, with or without thrombin pretreatment, correlated with the active transforming growth factor-beta 1 (TGF-beta 1) concentrations in the supernatant. The supernatant-induced increase in ET-1 secretion from the EC was markedly suppressed by TGF-beta 1 neutralizing antibody. 4. We tentatively conclude that platelets stimulate the endothelial ET-1 production by releasing a bioactive diffusible substance, mainly TGF-beta 1.