Prostacyclin Synthesis Research Articles

Endothelial cell COX-2 expression and activity in hypoxia

The clinical experience with selective cyclooxygenase (COX)-2 inhibitors reveals there are important protective roles for COX-2 in the cardiovascular system. This study examined the response to hypoxia of endothelial cell eicosanoid synthesis with respect to the role of COX-2 and its molecular regulation in hypoxia. Human umbilical vein endothelial cells (HUVEC) were exposed to hypoxia and the effects on COX-2, prostacyclin (PGI 2) and thromboxane (TXA 2) synthesis were examined. COX-2 promoter constructs were used to examine the role of Hypoxia Inducible Factors (HIFs) in COX-2 responses to hypoxia. Hypoxia caused an increase in PGI 2 synthesis, but not TXA 2 synthesis. PGI 2, but not TXA 2 synthesis, was absolutely dependent on upregulation of COX-2 by hypoxia. Mutations of transcription factor binding sites in the promoter showed a lack of involvement of NFκB in the response to hypoxia, but suggested involvement of HIFs. Transfection of HUVEC with HIF expression vectors increased activity of the promoter construct and increased native COX-2 expression in normoxia. EMSA showed HIF binding in nuclear extracts of hypoxic HUVEC to a region of the COX-2 promoter. The endothelial cell response to hypoxia involves increased production of the anti-thrombotic eicosanoid, PGI 2, which is dependent on COX-2 upregulation by a HIF-mediated process.

Contractile Hyporesponsiveness to Norepinephrine of Forearm Veins in Chronic Renal Failure

We recently reported that endothelium-dependent relaxation is impaired in forearm veins from patients with chronic renal failure. However, assessment of responses to norepinephrine remains controversial. We examined the contractile response to norepinephrine in forearm veins from patients on chronic hemodialysis and the role of nitric oxide (NO), prostanoids, and Ca(2+)-activated K(+) channels in this response. Isometric contraction curves were obtained in rings of forearm vein from 21 dialyzed patients and 12 multiorgan donors in response to norepinephrine (1 nmol/L to 10 micromol/L) or KCl (5 to 100 mmol/L). Veins from uremic patients were markedly less responsive to norepinephrine (7.6 +/- 0.6 g) and KCl (6.0 +/- 0.3 g) than those from organ donors (12.0 +/- 0.7 g and 10.4 +/- 0.5 g, respectively, P < .05). Treatment with N(G)-monomethyl-l-arginine (100 micromol/L), an inhibitor of NO synthase, or indomethacin (10 micromol/L), an inhibitor of prostacyclin synthesis, increased the response to norepinephrine in veins from control subjects but not in veins from dialyzed patients. Additional blockade of Ca(2+)-activated K(+) channels did not correct the hyporesponsiveness. In veins incubated in Ca(2+)-free solution containing either 100 mmol/L KCl or 1 micromol/L norepinephrine, addition of calcium chloride (0.1 to 30 mmol/L) elicited contractile responses that were significantly lower in veins from dialyzed patients. The results demonstrate that norepinephrine-mediated contractions of forearm veins are markedly decreased in dialyzed patients. Endothelium-derived relaxing factors are not involved in this effect. The reduced contractile response is most likely caused by a decreased calcium entry through voltage- and receptor-dependent calcium channels.

Cross Metathesis as a General Strategy for the Synthesis of Prostacyclin and Prostaglandin Analogues

[reaction: see text] A cross metathesis (CM) approach has been successfully applied to introduce fully functionalized omega-side chain appendages of various prostacyclin and prostaglandin analogues, resulting in high (E)-selectivities for the C13-C14 double bond and leading to the total syntheses of isocarbacyclin, 15R-TIC, carbacyclin, and PGF(2)(alpha) and the formal syntheses of 15-deoxy-TIC and PGJ(2).

Endothelial and Antithrombotic Actions of HDL

It is well recognized that high-density lipoprotein (HDL)-cholesterol is antiatherogenic and serves a role in mediating cholesterol efflux from cells. However, HDL has multiple additional endothelial and antithrombotic actions that may also afford cardiovascular protection. HDL promotes the production of the atheroprotective signaling molecule nitric oxide (NO) by upregulating endothelial NO synthase (eNOS) expression, by maintaining the lipid environment in caveolae where eNOS is colocalized with partner signaling molecules, and by stimulating eNOS as a result of kinase cascade activation by the high-affinity HDL receptor scavenger receptor class B type I (SR-BI). HDL also protects endothelial cells from apoptosis and promotes their growth and their migration via SR-BI-initiated signaling. As importantly, there is evidence of a variety of mechanisms by which HDL is antithrombotic and thereby protective against arterial and venous thrombosis, including through the activation of prostacyclin synthesis. The antithrombotic properties may also be related to the abilities of HDL to attenuate the expression of tissue factor and selectins, to downregulate thrombin generation via the protein C pathway, and to directly and indirectly blunt platelet activation. Thus, in addition to its cholesterol-transporting properties, HDL favorably regulates endothelial cell phenotype and reduces the risk of thrombosis. With further investigation and resulting greater depth of understanding, these mechanisms may be harnessed to provide new prophylactic and therapeutic strategies to combat atherosclerosis and thrombotic disorders.

Thromboxane Receptor Stimulation Suppresses Guanylate Cyclase-Mediated Relaxation of Radial Arteries

The internal mammary artery (IMA) and the radial artery (RA) are routinely used in coronary artery bypass grafting. However, RA grafts have a higher incidence of postoperative vasospasm and comparatively poor patency rates. The present study was undertaken to investigate the signaling pathways mediating contraction and relaxation in the IMA and RA with the aim of better understanding the mechanism underlying the propensity of RA grafts to spasm. We examined the contractile responses of the IMA and RA to KCl (a depolarizing agent), phenylephrine (an alpha-adrenergic agonist), and U46619 (a thromboxane analogue). Contractions induced by KCl or U46619 did not significantly differ in IMA and RA. By contrast, phenylephrine evoked significantly greater contraction of the IMA than the RA. Contractions induced by both phenylephrine and U46619 were dose-dependently inhibited by nifedipine (an L-type calcium channel blocker). Estimation of thromboxane A2 (TxA2) and prostacyclin (PGI2) synthesis revealed that the TxA2 to PGI2 ratio in the RA was twice that in the IMA. Moreover, acetylcholine-induced and nitroglycerin-induced relaxation of RA precontracted with U46619 was significantly impaired, as compared with RA precontracted with phenylephrine. These data suggest that inhibition of nitroglycerin-induced soluble guanylate cyclase activity by U46619 was at least partially responsible for the diminished vasodilatory response of RA to nitric oxide. Our findings suggest that by reducing nitric oxide-stimulated soluble guanylate cyclase activity, the higher TxA2 to PGI2 ratios in RA, and the elevated serum TxA2 levels seen during coronary artery bypass grafting operations, may underlie the vasospasm and poor patency rates seen with the RA.

Cyclooxygenase-2 Inhibition and Coagulation

Selective inhibitors of cyclooxygenase-2 (COX-2) have come under scrutiny because of a possibly increased thrombotic risk observed in retrospective studies and comparatively small cancer trials. Indeed, inhibition of COX-2 may favor a prothrombotic environment by suppressing endothelial prostacyclin synthesis while leaving COX-1-dependent platelet thromboxane (TX) A2 synthesis unopposed. However, in vitro studies have shown that the effect of coxibs on coagulation is dependent on several variables; for example, the coxib celecoxib reduces endothelial tissue factor expression, a key initiator of the coagulation cascade. Furthermore, animal studies are inconclusive as some studies investigating the effect of COX-2 inhibition in atherosclerosis imply a detrimental effect of coxibs, whereas others suggest a beneficial effect on plaque progression and stability. In healthy human subjects and in patients with atherosclerotic vascular diseases, the effect of COX-2 inhibition on coagulation is equally unclear as no prospective, randomized, double-blinded studies sufficiently powered to investigate cardiovascular endpoints have been performed to directly investigate a potentially cardiotoxic effect of coxibs. Here, we review the effect of COX-2 inhibition on the coagulation system; we discuss the molecular mechanisms involved and summarize important clinical trials in which an increased frequency of thrombotic complications coxibs was observed.

Cyclooxygenase-2 Induction and Prostacyclin Release by Protease-activated Receptors in Endothelial Cells Require Cooperation between Mitogen-activated Protein Kinase and NF-κB Pathways

The functional significance of protease-activated receptors (PARs) in endothelial cells is largely undefined, and the intracellular consequences of their activation are poorly understood. Here, we show that the serine protease thrombin, a PAR-1-selective peptide (TFLLRN), and SLIGKV (PAR-2-selective peptide) induce cyclooxygenase-2 (COX-2) protein and mRNA expression in human endothelial cells without modifying COX-1 expression. COX-2 induction was accompanied by sustained production of 6-keto-PGF1alpha, the stable hydrolysis product of prostacyclin, and this was inhibited by indomethacin and the COX-2-selective inhibitor NS398. PAR-1 and PAR-2 stimulation rapidly activated both ERK1/2 and p38MAPK, and pharmacological blockade of MEK with either PD98059 or U0126 or of p38MAPK by SB203580 or SB202190 strongly inhibited thrombin- and SLIGKV-induced COX-2 expression and 6-keto-PGF1alpha formation. Thrombin and peptide agonists of PAR-1 and PAR-2 increased luciferase activity in human umbilical vein endothelial cells infected with an NF-kappaB-dependent luciferase reporter adenovirus, and this, as well as PAR-induced 6-keto-PGF1alpha synthesis, was inhibited by co-infection with adenovirus encoding wild-type or mutated (Y42F) IkappaBalpha. Thrombin- and SLIGKV-induced COX-2 expression and 6-keto-PGF1alpha generation were markedly attenuated by the NF-kappaB inhibitor PG490 and partially inhibited by the proteasome pathway inhibitor MG-132. Activation of PAR-1 or PAR-2 promoted nuclear translocation and phosphorylation of p65-NF-kappaB, and thrombin-induced but not PAR-2-induced p65-NF-kappaB phosphorylation was reduced by inhibition of MEK or p38MAPK. Activation of PAR-4 by AYPGKF increased phosphorylation of ERK1/2 and p38MAPK without modifying NF-kappaB activation or COX-2 induction. Our data show that PAR-1 and PAR-2, but not PAR-4, are coupled with COX-2 expression and sustained endothelial production of vasculoprotective prostacyclin by mechanisms that depend on ERK1/2, p38MAPK, and IkappaBalpha-dependent NF-kappaB activation.

Vasomotor action of insulin on the rabbit normal cavernous smooth muscle

Investigations on the effects of insulin on the normal vasculature have produced conflicting results. This study was aimed at establishing the vasomotor actions of insulin on normal cavernous smooth muscle. Insulin produced dose-dependent (10 − 10 –10 − 5 M) relaxation of the norepinephrine-precontracted strips of cavernosum, and of Bay K8644 [methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-2(trifluoromethylphenyl)pyridine-5-carboxylate]-precontracted strips. Endothelial denudation or indomethacin (10 μM) pre-treatment significantly reduced these insulin-induced relaxations, whereas N G-nitro- l-arginine methyl ester (L-NAME, 5 mM) did not. Moreover, the pre-treatment of the cavernosum strips with a prostacyclin synthesis inhibitor [9,11-diazo-15-deoxy-prostaglandin H 2 (U-51605), 10 μM] significantly reduced insulin-induced response, whereas pretreatment with a cyclooxygenase-2 (COX-2) inhibitor (NS-398, 10 μM) did not. In addition, responses to insulin were not inhibited by K + channel blockers, i.e., tetraethylammonium (TEA, 10 mM) or 4-aminopyridine (4-AP, 10 μM). Moreover, L-type Ca 2+ currents were reduced by prostacyclin (2 μM) but not by insulin (10 μM). We conclude that insulin induces the endothelium-dependent relaxation of cavernous smooth muscles and that this relaxation response may emanate from the direct inhibition of L-type Ca 2+ channels by prostacyclin.

Errata

The FEBS JournalVolume 273, Issue 3 p. 669-671 Free Access Errata First published: 17 January 2006 https://doi.org/10.1111/j.1742-4658.2006.05113.xAboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat The paper by Fauti et al.[[1]] contains errors on pages 174-176. Figures 4-6 and their legends should appear as follows: Figure 4Open in figure viewerPowerPoint Raf induction does not activate PPARβ transcriptional activity. PPARβ-LBD mediated transcriptional activity was determined in untreated and 4-OHT-treated RafER3T3 cells in the presence of 20 mm arachidonic acid. Cells were transiently transfected with an expression vector encoding the LexA-PPARβ fusion protein (Lex-PPARb-LBD) or the empty vector (pcDNA3.1) together with a lexA-luciferase reporter plasmid (7 L-TATAi). Luciferase activity was determined 48 h after transfection; 4-OHT treatment was for 24 h. As a positive control, cells were also treated with 1 mm GW501516 for 24 h. Values represent the average of triplicates; error bars show the standard deviation. Significant differences from untreated cells are indicated by an asterisk (paired t-test: P < 0.003). Figure 5Open in figure viewerPowerPoint Immunolocalization of BgVgR in ovaries of B . germanica. (A,B) Oocytes from 2-day-old, sixth instar nymphs; BgVgR does not accumulate in the cortex of basal oocytes. (C,D) Oocytes from 5-day-old, sixth instar nymphs; BgVgR accumulates in the cortex of basal oocytes. E- F. Oocytes from 3-day-old adult females showing BgVgR accumulated in the cortex of basal oocytes. (G,H) Basal oocytes of an adult female on the first day of the period of ootheca transport, showing BgVgR in the cortex. Scale bars: 50 μm. Figure 6Open in figure viewerPowerPoint Overexpression of Cox-2 and PGIS does not induce PPARβ transcriptional activity. HEK293 cells were transiently transfected with expression vectors for Cox-2, PGIS or both. Forty-eight hours later, PPARβ-LBD mediated transcriptional activity and 6-kPGF1α accumulation in the cell culture supernatant were determined. For experimental details see legend to Fig. 4. Values represent the average of triplicates; error bars show the standard deviation. Significant differences from untreated cells are indicated by an asterisk (paired t-test: P = 0.01). The paper by Ciudad et al.[[2]] contains an error on page 330. Figure 5 should be in colour: Figure 5Open in figure viewerPowerPoint Induction of PPARβ transcriptional activity by AA is not dependent on PGI2 synthesis. (A) Stimulation of PPARβ-LBD mediated transcriptional activity in NIH3T3 cells by polyunsaturated fatty acids and the synthetic agonists carbaprostacyclin (cPGI) and GW01516. For experimental details see legend to Fig. 4. Values represent the average of triplicates; error bars show the standard deviation. Significant differences from untreated cells are indicated by an asterisk (paired t-test: P = 0.01). (B) Effect of the PGIS inhibitor U51605 on 6-kPGF1α accumulation in the cell culture supernatant as a measure of PGI2 synthesis (bar graph) and on PPARβ-LBD mediated transcriptional activity (bottom row). PPAR activities are shown as the average of triplicates and standard deviation. The publisher apologises for these errors. References 1 Fauti T, Müller-Brüsselbach S, Kreutzer M, Rieck M, Meissner W, Rapp U, Schweer H, Kömhoff M & Müller R (2006) Induction of PPARβ and prostacyclin (PGI2) synthesis by Raf signaling: failure of PGI2 to activate PPARβ. FEBS Journal 273, 170– 179. Wiley Online LibraryCASPubMedWeb of Science®Google Scholar 2 Ciudad L, Piulachs M-D & Bellés X (2006) Systemic RNAi of the cockroach vitellogenin receptor results in a phenotype similar to that of the Drosophila yolkless mutant. FEBS Journal 273, 325– 335. Wiley Online LibraryCASPubMedWeb of Science®Google Scholar Volume273, Issue3February 2006Pages 669-671 FiguresReferencesRelatedInformation

Induction of PPARβ and prostacyclin (PGI2) synthesis by Raf signaling: failure of PGI2 to activate PPARβ

A role for the nuclear receptor peroxisome proliferator-activated receptor-beta (PPARbeta) in oncogenesis has been suggested by a number of observations but its precise role remains elusive. Prostaglandin I2 (PGI2, prostacyclin), a major arachidonic acid (AA) derived cyclooxygenase (Cox) product, has been proposed as a PPARbeta agonist. Here, we show that the 4-hydroxytamoxifen (4-OHT) mediated activation of a C-Raf-estrogen receptor fusion protein leads to the induction of both the PPARbeta and Cox-2 genes, concomitant with a dramatic increase in PGI2 synthesis. Surprisingly, however, 4-OHT failed to activate PPARbeta transcriptional activity, indicating that PGI2 is insufficient for PPARbeta activation. In agreement with this conclusion, the overexpression of ectopic Cox-2 and PGI2 synthase (PGIS) resulted in massive PGI2 synthesis but did not activate the transcriptional activity of PPARbeta. Conversely, inhibition of PGIS blocked PGI2 synthesis but did not affect the AA mediated activation of PPARbeta. Our data obtained with four different cell types and different experimental strategies do not support the prevailing opinion that PGI2 plays a significant role in the regulation of PPARbeta.

Effects of specific COX-2-inhibition on renin release and renal and systemic prostanoid synthesis in healthy volunteers

The renin-angiotensin system plays a critical role in cardiovascular function, but little is known about the effects of specific cyclooxygenase 2 (COX-2) inhibition on this system in healthy humans under physiologic conditions. Twenty-one healthy female volunteers received, in a randomized, double-blind, crossover study, celecoxib 200 mg twice a day, indomethacin 50 mg three times a day, or placebo for 4 days and a single dose, each, on day 5. On day 5 of each treatment, the following parameters were assessed with subjects in an upright position before and after administration of 20 mg furosemide intravenously: plasma renin activity (PRA), plasma aldosterone, serum and urine electrolytes, and creatinine. Index metabolites of prostanoids were analyzed by gas chromatography-tandem mass spectrometry in 24-hour urine on day 4 and in 2-hour urines before and after furosemide administration. Baseline and furosemide-stimulated PRA were reduced to a similar degree by celecoxib and indomethacin. Plasma aldosterone and urinary excretion of potassium showed changes consistent with the alteration of PRA. Urinary excretion rates of prostaglandin E(2), (PGE(2)), 7alpha-hydroxy-5, 11-diketotetranor-prosta-1,16-dioic acid (PGE-M), and 2,3-dinor-thromboxane B(2) (TxB(2)) were not reduced by celecoxib, whereas indomethacin led to a decrease of 40%, 45%, and 80%, respectively. Both active treatments inhibited urinary excretion of 2,3-dinor-6-keto-PGF(1alpha) and 6-keto-PGF(1alpha) by 60% and 40%, respectively. Renin-release in healthy humans with normal salt intake is COX-2 dependent. While COX-1 is critical for renal and systemic PGE(2) production, renal prostacyclin synthesis is apparently COX-2 dependent. Finally, the previously demonstrated shift of the thromboxane-prostacyclin balance toward prothrombotic thromboxane by specific COX-2 inhibition is confirmed.

Involvement of phosphoinositide-3-kinase and phospholipase C transduction systems in the non-genomic action of progesterone in vascular tissue

We investigate the participation of tyrosine kinase, phosphatidylinositol-3-kinase, phospholipase C systems in the intracellular transduction pathways involved in the non-genomic stimulation of vasodilators compounds synthesis induced by progesterone (Pg). Using aortic strips isolated from female fertile Wistar rats, we showed that physiological concentrations of progesterone markedly increase prostacyclin synthesis in a very short time interval (45 s to 10 min) as well as nitric oxide release (5–30 min). The stimulatory action of progesterone on nitric oxide synthase (NOS) activity was maintained even in the presence of an antagonist of progesterone receptor, compound RU486. In contrast, in the presence of tyrosine kinase inhibitor (1 μM genistein) or phosphatidylinositol-3-kinase inhibitor (1 μM LY294002), the enhancement of nitric oxide elicited by 10–100 nM progesterone was completely suppressed. The steroid stimulates phopholipase C activity, inducing significant increase in diacylglycerol generation (5–15-min treatment). The presence of an inhibitor of protein kinase C (PKC) impaired the anti-aggregatory action of the hormone. Due to the fact that phospholipase C activation implies calcium mobilization, we investigate the role of changes in calcium fluxes on progesterone nitric oxide generation. We found that calcium influx from extracellular medium and calcium mobilization from internal pools was required. The present results suggest that, tyrosine kinase and phosphatidylinositol-3-kinase cascades are involved in progesterone nitric oxide synthase stimulation and that diacilglicerol/protein kinase C system may be relevant for physiological regulation of platelet aggregation process.

Selective Cyclooxygenase-2 Inhibitors Development in Cardiovascular Medicine

At the end of September 2004, Merck & Co announced the voluntary withdrawal of rofecoxib (Vioxx) worldwide because of an increased risk of cardiovascular events. Since its approval in 1999, Vioxx, a selective cyclooxygenase-2 (COX-2) inhibitor, has been Merck & Co’s leading drug for control of acute pain and chronic pain associated with osteoarthritis, rheumatoid arthritis, and menstruation. Last year, worldwide sales of rofecoxib reached US $2.5 billion, and it is estimated that the drug was prescribed ≈10 million times per month in the United States.1 Thus, given the number of patients involved and the serious nature of the side effects, the withdrawal raised serious concerns about the safety of other selective COX-2 inhibitors, collectively called coxibs, that are on the market and those currently under development. Celecoxib (Celebrex) and rofecoxib were the first 2 coxibs approved by the US Food and Drug Administration (FDA) and launched in 1999 by Pfizer and Merck & Co, respectively. Since then, a second generation of these drugs has emerged onto the market. Valdecoxib (Bextra) was approved by the FDA and launched in 2002. In that same year, the European regulatory authority approved 2 other coxibs: etoricoxib (Arcoxia) and parecoxib sodium (Dynastat), the prodrug of valdecoxib. Today, etoricoxib and a fifth coxib, lumiracoxib (Prexige), are under consideration for FDA approval. In view of the rapid development in this area, the main concern is whether the reported cardiovascular effects of rofecoxib are a class effect applicable to all coxibs that were initially designed to reduce the gastric toxicity of nonselective COX inhibitors. Although most of the data accumulated so far would suggest a class effect related to the general mode of action of all coxibs and the physiological role of COX-2, recent in vitro data would theoretically support the hypothesis that the cardiovascular side …

Neuronal Prostacyclin Is an Autocrine Regulator of Arterial Baroreceptor Activity

We tested the hypothesis that neuronal prostacyclin is an autocrine regulator of arterial baroreceptor neuronal activity. In isolated rat aortic nodose baroreceptor neurons, mechanical stimulation depolarized 12 neurons by 13.1+/-3.4 mV and triggered action potentials in 5 of them, averaging 18.2+/-9.5 spikes. Current injections depolarized 21 neurons by 29.9+/-8.0 mV and triggered action potentials averaging 17.0+/-2.4 spikes. After a period of prolonged neuronal activation with pulses of 1 nA at 20 Hz for 1 minute, the action potential responses to mechanical stimulation and to current injections were first markedly suppressed (0.2+/-0.2 and 2.1+/-0.7 spikes, respectively) and then enhanced, reaching levels above control (29.0+/-8.0 and 21.7+/-2.6 spikes, respectively) over the subsequent 15 minutes. In contrast, there was no inhibition of the depolarizations caused by mechanical stimulation or current injections. The recovery and enhancement of action potentials, which reached 150+/-5.4% of control values at 15 minutes (n=13), were abrogated by 10 micromol/L of indomethacin and replaced by sustained inhibition for over 15 minutes. Carbacyclin (10 micromol/L) reversed the inhibition and restored action potential responses. Prostacyclin production by cultured nodose neurons was enhanced by arachidonic acid and electrical field stimulation and inhibited by indomethacin. We conclude that prostacyclin provides an autocrine feedback that restores and enhances the responsiveness of arterial baroreceptor neurons after their inhibition from excessive neuronal activation. We speculate that reduced synthesis of neuronal prostacyclin contributes to the resetting phenomenon and the suppressed activity of arterial baroreceptors in hypertension.

Inhibiting Long-Chain Fatty Acyl CoA Synthetase Does Not Increase Agonist-Induced Release of Arachidonate Metabolites from Human Endothelial Cells

Background: Triacsin C, a fatty acid analog, inhibits endothelial nitric oxide synthetase (eNOS) palmitoylation, increases nitric oxide synthesis and enhances methacholine-induced relaxation of vascular rings. The experiments presented here tested the hypothesis that triacsin C increases the synthesis of PGI₂ and/or endothelial-derived hyperpolarizing factor. Methods: Long-chain fatty acyl CoA synthetase activity (LCFACoAS), agonist-induced prostacyclin synthesis and agonist-induced release of radioactivity in endothelial cells labeled with [³H]arachidonic acid were measured in the presence and absence of triacsin C. Results: Inhibition by triacsin C of palmitoyl CoA formation was significantly greater than inhibition of arachidonoyl CoA formation in solubilized endothelial cell preparations. While 24-hour triacsin C treatment significantly reduced basal 6-keto synthesis, it had no effect on agonist-stimulated synthesis. The release of arachidonic acid metabolites was examined in [³H]arachidonate-labeled cells. Triacsin C treatment had no effect on basal or vasopressin-, angiotensin-II-, bradykinin- or ionomycin-induced release of radioactivity, but significantly reduced release in response to isoproterenol or phenylephrine. Expression of neither immunoreactive eNOS nor immunoreactive inducible nitric oxide synthetase (iNOS) was changed by triacsin C treatment, but the fraction of immunoreactive eNOS in the cytoplasm of treated cells was significantly greater as compared to vehicle control cells. Phorbol myristoyl acetate or fenofibrate significantly increased in vitro LCFACoAS activity, and significantly decreased the nitrite/eNOS ratio. Conclusions: These data indicate that, while triacsin C can inhibit arachidonoyl CoA synthetase in endothelial cells, it does not increase the availability of endogenous substrate for basal or agonist-induced PGI₂ synthesis, nor does it enhance release of arachidonic acid or its metabolites.

Participation of Prostacyclin in Endothelial Dysfunction Induced by Aldosterone in Normotensive and Hypertensive Rats

The aim of the present study was to analyze the possible involvement of vasoconstrictors prostanoids on the reduced endothelium-dependent relaxations produced by chronic administration of aldosterone in Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). For this purpose, acetylcholine (ACh) relaxations in aortic segments from both strains were analyzed in absence and presence of the cyclooxygenase-1 (COX-1) and COX-2 inhibitor indomethacin, the specific COX-2 inhibitor NS-398, the TP receptor antagonist (SQ 29 548), the thromboxane A2 (TXA2) synthase inhibitor furegrelate, and the prostacyclin (PGI2) synthesis inhibitor tranylcypromine (TCP). In addition, COX-2 protein expression was studied by Western blot analysis. Release of prostaglandin E2 (PGE2) and the metabolites of PGF2alpha, TXA2, and PGI2, 13,14-dihydro-15-keto PGF2a, TXB2, and 6-keto-PGF1alpha, respectively, were measured. Treatment with aldosterone did not modify blood pressure levels in any strain. However, aldosterone markedly reduced (P<0.05) ACh-induced relaxations in segments from both strains in a similar extent. Indomethacin, NS-398, SQ 29 548, and TCP enhanced (P<0.05) ACh relaxations in both strains treated with aldosterone. Aortic COX-2 protein expression was higher in both strains of rats treated with aldosterone. In normotensive animals, aldosterone increases the ACh-stimulated aortic production of 13,14-dihydro-15-keto PGF2a, PGE2, and 6-keto-PGF1alpha (P<0.05). In SHR, ACh only increased the 6-keto-PGF1alpha production (P<0.05). It could be concluded that chronic treatment with aldosterone was able to produce endothelial dysfunction through COX-2 activation in normotensive and hypertensive conditions. PGI2 seems to be the main factor accounting for endothelial dysfunction in hypertensive rats, whereas other prostanoids besides PGI2 appear to be involved in endothelial dysfunction under normotensive conditions.

Drug Insight: cyclo-oxygenase 2 inhibitors and cardiovascular risk—where are we now?

Cyclo-oxygenase (COX) 1 mediates the production of thromboxane A2 in platelets, leading to platelet aggregation and vasoconstriction. Conversely, COX2 catalyzes endothelial prostacyclin synthesis, which effectively counteracts thromboxane A2, triggering vasodilation and platelet inhibition. Selective COX2 inhibitors decrease prostacyclin production, potentially disrupting homeostasis and creating a prothrombotic state. The VIGOR study findings of increased cardiovascular risk with rofecoxib were subsequently confirmed by large meta-analyses, observational studies and recent APPROVe trial publication. The APC trial findings of increased cardiovascular risk with Celebrex (celecoxib) conflict with those in the ADAPT trial, the upcoming PreSAP publication, a case-control study by Graham et al. and prior large clinical trials, meta-analyses and observational studies of this drug. Therefore, while an adverse class effect is a possibility for COX2 inhibitors, the published data are inconsistent. Baseline cardiovascular risk in patients might contribute significantly to these findings. In light of the negative Vioxx (rofecoxib) publicity, however, COX2 inhibitors might forever remain underinvestigated. The relative selectivity of these compounds for COX2 is extremely variable, casting significant doubt on the class-effect hypothesis. Improved endothelial function has also been reported with celecoxib, leading to endothelium-dependent vasodilation, and associated decreases in C-reactive protein and LDL cholesterol. The addition of meloxicam to low-dose aspirin and heparin has improved clinical outcomes after acute coronary syndromes. These are the first studies suggesting improvement in endothelial function and reduction of inflammation with COX2 inhibition. Thus, more randomized controlled trials are needed to study the relative cardiovascular effects of different COX2 inhibitors, alone and in combination with aspirin.

Peroxynitrite provides the peroxide tone for PGHS‐2‐dependent prostacyclin synthesis in vascular smooth muscle cells

Endotoxin-treated vascular smooth muscle cells (VSMCs) were recently shown to release high amounts of prostacyclin (PGI2) dependent on the induction of prostaglandin endoperoxide synthase-2 (PGHS-2). In contrast to endothelial PGI2-synthase, for which nitration and inhibition by peroxynitrite was reported, addition of SIN-1 as a peroxynitrite-generating system did not cause inhibition but rather doubled PGI2 release by VSMC. The hypothesis of peroxynitrite supplementing an unsaturated peroxide tone for PGHS-2 was supported by H2O2 exerting the same effect. Studies performed with purified PGHS-2 revealed maximal elevation of enzyme activity in the presence of equimolar concentrations of *NO and *O2-, which together form peroxynitrite, while excessive production of either one radical was inhibitory. Most importantly, 6-keto-PGF1alpha formation by intact VSMC depended on a nearly equimolar generation of *NO and *O2- for providing the endogenous peroxide tone. These findings, together with the observation that an excess of exogenously added *NO, as well as uric acid as a scavenger of peroxynitrite potently reduced PGI2 release, underlined the role of peroxynitrite as the dominating and rate-limiting intracellular mediator of peroxide tone in VSMC. The results allow us to postulate a new cross-talk between the *NO and the prostanoid pathways with a crucial role for peroxynitrite in providing the peroxide tone for a continuous activation of PGHS-2.

Effect of Enhanced Prostacyclin Synthesis by Adenovirus‐Mediated Transfer on Lipopolysaccharide Stimulation in Neuron‐Glia Cultures

Prostacyclin (PGI2) is known as a short-lived, potent vasodilator and platelet anti-aggregatory eicosanoid. This work attempts to selectively augment PGI2 synthesis in neuron-glia cultures by adenoviral (Ad) gene transfer of PGI synthase (PGIS) or bicistronic cyclooxygenase 1 (COX-1)/PGIS and examines whether PGI2 confers protection against lipopolysaccharide (LPS) stimulation. Cultures released low levels of eicosanoids. Upon Ad-PGIS or Ad-COX-1/PGIS infection, cultures selectively increased prostacyclin release. Both PGIS- and COX-1/PGIS-overexpressed cultures contained fewer microglial numbers. Further, they significantly attenuated LPS-induced iNOS expression and lactate, nitric oxide, and TNF-alpha production. Taken together, enhanced prostacyclin synthesis in neuron-glial cultures reduced microglia number and suppressed LPS stimulation.

Endothelin B receptor-deficient mice develop endothelial dysfunction independently of salt loading

Rodents without a functional endothelin B (ETB) receptor develop salt-sensitive hypertension. The underlying mechanisms, however, are so far unknown. The ETB receptor is involved in endothelial function by modulating the activity of the endothelial nitric oxide synthesis as well as contributing to the control of endothelial prostacyclin synthesis. In the present study, we analysed whether salt alters endothelial function in rescued ETB receptor-deficient mice. We used mice with a rescue of the lethal phenotype of an ETB knockout. These mice were generated by crossbreeding ETB mice with dopamine-hydroxylase ETB transgenic mice. Adult rescued ETB-deficient mice were kept in parallel with wild-type control animals for 15 days on standard (0.2% NaCl) or salt-enriched (4% NaCl) chow, respectively. Systolic blood pressure was measured by the tail cuff method and endothelium-dependent and endothelium-independent vascular function was assessed in isolated aortic rings under isometric conditions. Systolic blood pressure increased on salt-enriched chow in ETB receptor-deficient mice (166 +/- 12 mmHg), but neither in wild-type mice on high-salt diet (128 +/- 11 mmHg; P < 0.05) nor in ETB receptor-deficient mice on standard chow. The heart rate was similar in all groups at any point of time. Endothelium-dependent relaxation was impaired in ETB receptor-deficient mice (74 +/- 3 versus 96 +/- 5% of preconstriction for wild-type mice; P < 0.05) and was not significantly affected by a salt-enriched diet. Endothelium-independent relaxation was similar among all groups. Contractions to endothelin-1 were not significantly influenced by preincubation with the ETB receptor antagonist BQ-788, but were completely blunted by preincubation with the ETA receptor antagonist BQ-123 in all animals. Rescued ETB receptor-deficient mice develop salt-sensitive hypertension. Nevertheless, in this animal model of ETB receptor deficiency, endothelial function is impaired independent of salt-enriched diet or hypertension. This indicates that, in this model, salt-induced hypertension is not mediated by endothelial dysfunction.