Acceleration of atherogenesis by COX-1-dependent prostanoid formation in low density lipoprotein receptor knockout mice

Prostaglandins and inflammation

Prostaglandins are lipid autacoids derived from arachidonic acid. They both sustain homeostatic functions and mediate pathogenic mechanisms, including the inflammatory response. They are generated from arachidonate by the action of cyclooxygenase isoenzymes, and their biosynthesis is blocked by nonsteroidal antiinflammatory drugs, including those selective for inhibition of cyclooxygenase-2. Despite the clinical efficacy of nonsteroidal antiinflammatory drugs, prostaglandins may function in both the promotion and resolution of inflammation. This review summarizes insights into the mechanisms of prostaglandin generation and the roles of individual mediators and their receptors in modulating the inflammatory response. Prostaglandin biology has potential clinical relevance for atherosclerosis, the response to vascular injury and aortic aneurysm.

Resistance artery mechanics and composition in angiotensin II-infused mice: effects of cyclooxygenase-1 inhibition

AIMS

The aim of this study was to investigate the role of cyclooxygenase (COX)-1 on vascular alterations in structure, mechanics, and extracellular matrix (ECM) components induced by angiotensin (Ang) II in mesenteric arteries from wild-type (WT) and COX-1 knockout (COX-1(-/-)) mice.

METHODS AND RESULTS

Animals were infused with vehicle or Ang II (400 ng/kg/min, s.c.) ± SC-560 (COX-1 inhibitor), DFU (COX-2 inhibitor), or SQ-29548 (TP receptor antagonist). After 2 weeks, vessels were isolated and exposed to intraluminal pressures (3-140 mmHg, pressurized myograph) to determine mechanical properties. Angiotensin II-induced vascular hypertrophic remodelling in WT was reversed by SC-560 or SQ-29548, but unaffected by DFU. Angiotensin II increased vessel stiffness (P< 0.01), this effect being ameliorated by SC-560 or SQ-29548, but unmodified by DFU. Angiotensin II failed to modify vessel elasticity in COX-1(-/-) mice. In WT vessels, Ang II enhanced COX-1 immunostaining, induced collagen and fibronectin depositions and decreased elastin content (P< 0.01). These effects were reversed by SC-560 or SQ-29548, but unaffected by DFU. In COX-1(-/-) mice, Ang II did not affect ECM contents. In WT, Ang II increased COX-1 and decreased COX-2 expression, and enhanced the vascular release of 6-keto-PGF1α which was prevented by COX-1 blockade. Human coronary artery smooth muscle cells, incubated with Ang II, showed an increased expression of procollagen I, which was abrogated by SC-560 or SQ-29548.

CONCLUSION

Angiotensin II-induced alterations of resistance arteries in structure, mechanics, and ECM composition were prevented by COX-1 inhibition and TP receptor antagonism, indicating that Ang II-mediated vascular damage is mediated by COX-1-derived prostanoid prostacyclin, activating TP receptors.

Thrombosis is reduced by inhibition of COX-1, but unaffected by inhibition of COX-2, in an acute model of platelet activation in the mouse

Background

Clinical use of selective inhibitors of cyclooxygenase (COX)-2 appears associated with increased risk of thrombotic events. This is often hypothesised to reflect reduction in anti-thrombotic prostanoids, notably PGI₂, formed by COX-2 present within endothelial cells. However, whether COX-2 is actually expressed to any significant extent within endothelial cells is controversial. Here we have tested the effects of acute inhibition of COX on platelet reactivity using a functional in vivo approach in mice.

Methodology/Principal Findings

A non-lethal model of platelet-driven thromboembolism in the mouse was used to assess the effects of aspirin (7 days orally as control) diclofenac (1 mg.kg⁻¹, i.v.) and parecoxib (0.5 mg.kg⁻¹, i.v.) on thrombus formation induced by collagen or the thromboxane (TX) A₂-mimetic, U46619. The COX inhibitory profiles of the drugs were confirmed in mouse tissues ex vivo. Collagen and U46619 caused in vivo thrombus formation with the former, but not latter, sensitive to oral dosing with aspirin. Diclofenac inhibited COX-1 and COX-2 ex vivo and reduced thrombus formation in response to collagen, but not U46619. Parecoxib inhibited only COX-2 and had no effect upon thrombus formation caused by either agonist.

Conclusions/Significance

Inhibition of COX-1 by diclofenac or aspirin reduced thrombus formation induced by collagen, which is partly dependent upon platelet-derived TXA₂, but not that induced by U46619, which is independent of platelet TXA₂. These results are consistent with the model demonstrating the effects of COX-1 inhibition in platelets, but provide no support for the hypothesis that acute inhibition of COX-2 in the circulation increases thrombosis.

Platelets participate in synovitis via Cox-1-dependent synthesis of prostacyclin independently of microparticle generation

In addition to the well-described role of platelets in thrombosis, a growing body of evidence implicates platelets in diverse inflammatory responses. We recently showed platelets can contribute to the pathophysiology of inflammatory arthritis via IL-1- containing microparticles. In this study, we demonstrate that platelets, and not platelet microparticles, actively contribute to synovitis via production of proinflammatory prostacyclin in an autoimmune arthritis model. Using both genetic and pharmacologic approaches, we establish that paracrine production of prostacyclin proceeds in the absence of cyclooxygenase-2. Furthermore, we also demonstrate that prostacyclin generation can arise via transcellular collaboration between platelets and fibroblast-like synoviocytes. In addition to shedding light on an unappreciated pathway of lipid synthesis in arthritis, we further delineate a novel effector activity by which platelets can contribute to inflammatory disease.

Pro-resolving actions and stereoselective biosynthesis of 18S E-series resolvins in human leukocytes and murine inflammation

E-series resolvins are antiinflammatory and pro-resolving lipid mediators derived from the ω-3 polyunsaturated fatty acid eicosapentaenoic acid (EPA) that actively clear inflammation to promote tissue homeostasis. Aspirin, in addition to exerting antithrombotic actions, also triggers the biosynthesis of these specialized pro-resolving mediators. Here, we used metabolomic profiling to investigate the biosynthesis of E-series resolvins with specific chiral chemistry in serum from human subjects and present evidence for new 18S series resolvins. Aspirin increased endogenous formation of 18S-hydroxyeicosapentaenoate (18S-HEPE) compared with 18R-HEPE, a known resolvin precursor. Human recombinant 5-lipoxygenase used both enantiomers as substrates, and recombinant LTA4 hydrolase (LTA4H) converted chiral 5S(6)-epoxide-containing intermediates to resolvin E1 and 18S-resolvin E1 (RvE1 and 18S-RvE1, respectively). 18S-RvE1 bound to the leukocyte GPCRs ChemR23 and BLT1 with increased affinity and potency compared with the R-epimer, but was more rapidly inactivated than RvE1 by dehydrogenase. Like RvE1, 18S-RvE1 enhanced macrophage phagocytosis of zymosan, E. coli, and apoptotic neutrophils and reduced both neutrophil infiltration and proinflammatory cytokines in murine peritonitis. These results demonstrate two parallel stereospecific pathways in the biosynthesis of E-series resolvins, 18R- and 18S-, which are antiinflammatory, pro-resolving, and non-phlogistic and may contribute to the beneficial actions of aspirin and ω-3 polyunsaturated fatty acids.

Platelets as initiators and mediators of inflammation at the vessel wall

Platelets are dynamic cells with activities that extend beyond thrombosis including an important role in initiating and sustaining vascular inflammation. A role for platelets has been described in many physiologic and pathophysiologic processes such as atherosclerosis, stem cell trafficking, tumor metastasis, and arthritis. Platelet activation at sites of an intact inflamed endothelium contributes to vascular inflammation and vascular wall remodeling. Platelets secrete a wide array of preformed and synthesized inflammatory mediators upon activation that can exert significant local and systemic effects. This review will focus on the role of platelet derived mediators in vascular inflammation and vascular wall remodeling.

Pathophysiology of cyclooxygenases in cardiovascular homeostasis

Cyclooxygenase (COX) catalyzes the conversion of arachidonic acid into prostaglandin H(2) (PGH(2)), which is subsequently converted to the prostanoids PGE(2), PGI(2), PGF(2alpha), and thromboxane A(2). COX has 2 distinct membrane-anchored isoenzymes: COX-1 and COX-2. COX-1 is constitutively expressed in most normal tissues; COX-2 is highly induced by proinflammatory mediators in the setting of inflammation, injury, and pain. Inhibitors of COX activity include conventional nonselective nonsteroidal anti-inflammatory drugs and selective nonsteroidal anti-inflammatory drugs, such as COX-2 inhibitors. The adverse effects of COX inhibitors on the cardiovascular system have been addressed in the last few years. In general, COX inhibitors have many effects, but those most important to the cardiovascular system can be direct (through the effects of prostanoids) and indirect (through alterations in fluid dynamics). Despite reports of detrimental human cardiovascular events associated with COX inhibitors, short, long, and lifetime preclinical toxicology studies in rodents and nonrodents have failed to identify these risks. This article focuses on the expression and function of COX enzymes in normal and pathologic conditions of the cardiovascular system and discusses the cardiovascular pathophysiologic complications associated with COX inhibition.

Celecoxib combined with atorvastatin prevents progression of atherosclerosis

BACKGROUND

Increased expression of cyclooxygenase (COX-2) contributes to atherosclerosis. Recent studies suggest that COX-2 inhibitors prevent early plaque development but their effects on established lesions are less clear, while the statins promote plaque stability. The purpose of this study is to investigate whether administering a combination of a COX-2 inhibitor with a statin drug alters plaque progression in apo E-/- mice.

MATERIALS AND METHODS

Apo E-/- mice were fed a Western diet from 6 to 26 wk of age. At 26 wk, the Western diets supplemented with atorvastatin, celecoxib, or atorvastatin plus celecoxib were given for an additional 12 wk.

RESULTS

When the mice were 38 wk of age, the total area occupied by the atherosclerotic lesion was 53% less in the mice fed the combination of atorvastatin + celecoxib P ≤ 0.05) than that of the apo E-/- mice fed the Western diet alone, atorvastatin alone, or celecoxib alone. The decreased extent of atherosclerosis observed in the apo E-/- mice fed the combination of drugs was associated with reduced levels of prostaglandin (PG) E(2,) decreased protein expression of metalloproteinase (MMP)-9, macrophage chemotactic protein (MCP-1), and COX 2, and decreased staining for MMP-9, F4-80 (a marker for macrophages), and vascular cell adhesion molecule (VCAM).

CONCLUSION

This study indicates that using statins with a COX-2 inhibitor reduced the extent of atherosclerosis and inflammatory/cell adhesion molecule levels in the apo E-/- mouse model.

Tumor necrosis factor alpha signaling in the development of experimental murine pre-hepatic portal hypertension

The cytokine tumor necrosis factor alpha (TNFa) has previously been identified in the development of portal hypertension (PHT) by facilitating portal venous and systemic hyperemia. TNFa is reported to contribute to hyperemia via endothelial nitric oxide synthase (eNOS) induction and nitric oxide (NO) production. This study examines this hypothesis by utilizing TNFa receptor knockout mice and a murine model of pre-hepatic PHT. Plasma TNFa and NOx and tissue TNFa mRNA levels were determined in wild-type mice 0-7d post induction of pre-hepatic PHT by partial portal vein ligation (PVL). TNFa receptor knockout mice also received PVL or sham surgery and splenic pulp pressure, abdominal aortic flow and portal-systemic shunting were recorded 7d following. Portal pressure and systemic hyperemia developed rapidly following PVL. Plasma NOx was increased temporarily 2-3 days following PVL and returned to baseline by day 7. Circulating TNFa was below detectable limits of the ELISA used, as such no increase was observed. Hepatic and vascular TNFa mRNA levels were transiently changed after PVL otherwise there was no significant change. TNFa receptor targeted gene deletion did not ameliorate plasma NOx following PVL and had no effect on the development of PHT. TNFa receptor signaling plays no detectable role in the development of systemic hyperemia in the murine model of pre-hepatic PHT. Consequently, increased TNFa observed in intra-hepatic inflammatory models (CCl(4)) and in patients is probably related to inflammation associated with intra-hepatic pathology. Alternatively, TNFa may be signaling via a TNFa receptor independent mechanism.

Vascular biology of eicosanoids and atherogenesis

Atherosclerosis is a chronic and progressive inflammatory vascular disease that is characterized by a complex interplay between some components of the bloodstream and the arterial wall. The lipid derivatives eicosanoids have been identified as important mediators that contribute to mechanisms of atherogenesis. Prostaglandins and thromboxane A2 are members of the eicosanoid family synthesized from arachidonic acid by the combined action of cyclooxygenases and prostaglandins and thromboxane A2 synthase. Thromboxane A2, a potent platelet activator and vasoconstrictor and prostacyclin, a platelet inhibitor and vasodilator, are the most important in the development of cardiovascular diseases. Several pro-atherogenic biological effects have also been attributed to isoprostanes, a class of eicosanoid isomers formed via a free radical-mediated oxidation of fatty acids esterified in membrane phospholipids. Both groups of lipids manifest their biological activities by binding to specific receptors in target cells. In this article, we will describe the biological roles of prostacyclin, thromboxane A2 and isoprostanes in atherogenesis and discuss the latest pharmacological studies assessing the therapeutic effects of drugs that specifically target their biosynthesis and/or biological activities on vascular inflammation and atherosclerotic lesion development.

Oxidative risk for atherothrombotic cardiovascular disease

In the vasculature, reactive oxidant species, including reactive oxygen, nitrogen, or halogenating species, and thiyl, tyrosyl, or protein radicals may oxidatively modify lipids and proteins with deleterious consequences for vascular function. These biologically active free radical and nonradical species may be produced by increased activation of oxidant-generating sources and/or decreased cellular antioxidant capacity. Once formed, these species may engage in reactions to yield more potent oxidants that promote transition of the homeostatic vascular phenotype to a pathobiological state that is permissive for atherothrombogenesis. This dysfunctional vasculature is characterized by lipid peroxidation and aberrant lipid deposition, inflammation, immune cell activation, platelet activation, thrombus formation, and disturbed hemodynamic flow. Each of these pathobiological states is associated with an increase in the vascular burden of free radical species-derived oxidation products and, thereby, implicates increased oxidant stress in the pathogenesis of atherothrombotic vascular disease.

Absence of myeloid COX-2 attenuates acute inflammation but does not influence development of atherosclerosis in apolipoprotein E null mice

OBJECTIVE

The role of myeloid cell cyclooxygenase-2 (COX-2) in the progression of atherosclerosis has not been clearly defined.

METHODS AND RESULTS

We investigated the role of COX-2 expressed in the myeloid lineage in the development of atherosclerosis using a myeloid-specific COX-2(-/-) (COX-2(-M/-M)) mouse on a hyperlipidemic apolipoprotein (apo) E(-/-) background (COX-2(-M/-M)/apoE(-/-)). Myeloid COX-2 depletion resulted in significant attenuation of acute inflammation corresponding with decreased PGE(2) levels in an air pouch model. COX-2 depletion in myeloid cells did not influence development of atherosclerosis in COX-2(-M/-M)/apoE(-/-) when compared to apoE(-/-) littermates fed either chow or western diets. The unanticipated lack of contribution of myeloid COX-2 to the development atherosclerosis is not attributable to altered maintenance, differentiation, or mobilization of myeloid and lymphoid populations. Moreover, myeloid COX-2 depletion resulted in unaltered serum prostanoid levels and cellular composition of atherosclerotic lesions of COX-2(-M/-M)/apoE(-/-) mice.

CONCLUSIONS

Our results suggest that COX-2 expression in myeloid cells, including macrophages, does not influence the development of atherosclerosis in mice.

Platelet dysfunction in central obesity

Central obesity is a relevant risk factor for major cardiovascular events due to the atherosclerotic involvement of coronary, cerebral and lower limb arterial vessels. A major role in the increased cardiovascular risk is played by platelets, which show an increased activation and a reduced sensitivity to the physiological and pharmacological antiaggregating agents. This review focuses on platelet dysfunction in central obesity. The mechanisms involved are related to: i) the reduced sensitivity to insulin and other substances acting via intracellular cyclic nucleotides, such as nitrates and prostacyclin; ii) the altered intracellular ionic milieu with elevated cytosolic Ca(2+); and iii) the increased oxidative stress, which elicits isoprostane production from arachidonic acid. Therapeutic guidelines recommend a multifactorial prevention of cardiovascular disease including antiplatelet drugs in high risk patients, even though, at present, the protective effect of antiplatelet therapy in obese, insulin resistant subjects has not been evaluated by specific trials. Some reports, however, suggest a decreased sensitivity to the antiaggregating effects of both acetylsalicylic acid (aspirin) and thienopyridines in human obesity. Platelet defects may play a pivotal role in the reduced efficacy of antiplatelet therapy in obese subjects in the setting of cardiovascular prevention and acute coronary syndrome treatment. Thus, a specifically tailored antiaggregating therapy is likely necessary in obese, insulin resistant subjects, especially in the presence of type 2 diabetes mellitus.

Inhibition of 11beta-hydroxysteroid dehydrogenase type II selectively blocks the tumor COX-2 pathway and suppresses colon carcinogenesis in mice and humans

Colorectal cancer (CRC) is a leading cause of cancer death, yet primary prevention remains the best approach to reducing overall morbidity and mortality. Studies have shown that COX-2-derived PGE2 promotes CRC progression, and both nonselective COX inhibitors (NSAIDs) and selective COX-2 inhibitors (such as glucocorticoids) reduce the number and size of colonic adenomas. However, increased gastrointestinal side effects of NSAIDs and increased cardiovascular risks of selective COX-2 inhibitors limit their use in chemoprevention of CRC. We found that expression of 11beta-hydroxysteroid dehydrogenase type II (11betaHSD2), which converts active glucocorticoids to inactive keto-forms, increased in human colonic and Apc+/min mouse intestinal adenomas and correlated with increased COX-2 expression and activity. Furthermore, pharmacologic inhibition or gene silencing of 11betaHSD2 inhibited COX-2-mediated PGE2 production in tumors and prevented adenoma formation, tumor growth, and metastasis in mice. Inhibition of 11betaHSD2 did not reduce systemic prostacyclin production or accelerate atherosclerosis in mice, thereby avoiding the major cardiovascular side effects seen with systemic COX-2 inhibitors. Therefore, 11betaHSD2 inhibition represents what we believe to be a novel approach for CRC chemoprevention and therapy by increasing tumor glucocorticoid activity, which in turn selectively blocks local COX-2 activity.

Cyclooxygenase inhibitors repress vascular hyaluronan-synthesis in murine atherosclerosis and neointimal thickening

Hyaluronan (HA) is a key molecule of the extracellular matrix that is thought to be critically involved in both atherosclerosis and restenosis. Recently, it has been demonstrated that the cyclooxygenase (COX) products, prostacyclin and prostaglandin E(2), induce HA synthesis in vitro by transcriptional up-regulation of HA-synthase 2 (HAS2) and HAS1. The relative roles in atherosclerotic and restenotic artery disease of tissue specifically expressed COX-1 and COX-2 are still under debate. Thus, the present study aimed to investigate the effect of COX isoform inhibition on HA-accumulation and regulation of HAS isoform expression in two models of pathologic artery remodelling in vivo. Firstly, ApoE-deficient mice were treated with a prototypic isoform non-selective inhibitor, indomethacin or with a prototypic COX-2 selective inhibitor, rofecoxib, for 8 weeks. Aortic HAS mRNA expression and HA-accumulation in atherosclerotic aortic root lesions were analyzed. Secondly, neointimal hyperplasia was induced by carotid artery ligation in ApoE-deficient mice on a high fat diet and the effects of the COX inhibitors were determined after 4 weeks of treatment. Intimal HA-accumulation was markedly reduced in both models by indomethacin and rofecoxib. This coincided with a strong inhibition of HAS1 mRNA expression in both models and with decreased HAS2 mRNA in the aorta of ApoE-deficient mice. HAS3 was not affected. The repression of HA-accumulation by both COX-2 selective and non-selective COX inhibition implicates COX-2 in the regulation of HA synthesis via stimulation of HAS1 and HAS2 expression in vivo. Modulation of vascular HA-accumulation might play a role in chronic effects of COX inhibitors on the progression of atherosclerosis.

Role of cyclooxygenase isoforms in prostacyclin biosynthesis and murine prehepatic portal hypertension

Portal hypertension (PHT) is a common complication of liver cirrhosis and significantly increases morbidity and mortality. Abrogation of PHT using NSAIDs has demonstrated that prostacyclin (PGI(2)), a direct downstream metabolic product of cyclooxygenase (COX) activity, is an important mediator in the development of experimental and clinical PHT. However, the role of COX isoforms in PGI(2) biosynthesis and PHT is not fully understood. Prehepatic PHT was induced by portal vein ligation (PVL) in wild-type, COX-1(-/-), and COX-2(-/-) mice treated with and without COX-2 (NS398) or COX-1 (SC560) inhibitors. Hemodynamic measurements and PGI(2) biosynthesis were determined 1-7 days after PVL or sham surgery. Gene deletion or pharmacological inhibition of COX-1 or COX-2 attenuated but did not ameliorate PGI(2) biosynthesis after PVL or prevent PHT. In contrast, treatment of COX-1(-/-) mice with NS398 or COX-2(-/-) mice with SC560 restricted PGI(2) biosynthesis and abrogated the development of PHT following PVL. In conclusion, either COX-1 or COX-2 can mediate elevated PGI(2) biosynthesis and the development of experimental prehepatic PHT. Consequently, PGI(2) rather then COX-selective drugs are indicated in the treatment of PHT. Identification of additional target sites downstream of COX may benefit the >27,000 patients whom die annually from cirrhosis in the United States alone.

Cyclooxygenase-2 inhibition increases lipopolysaccharide-induced atherosclerosis in mice

AIMS

The risk of adverse cardiovascular events in humans is increased with chronic use of cyclooxygenase-2 (COX-2) inhibitors. However, the role of COX-2 in animal models of cardiovascular disease has been controversial. In humans and animal models, cardiovascular disease is increased by bacterial infection of the supporting tissue of the teeth, a condition known as periodontal disease. Periodontal disease may result in chronic exposure to pro-inflammatory mediators, such as bacterial lipopolysaccharide (LPS), thereby producing a systemic inflammatory response. The current study examined the role of COX-2 in atherosclerosis induced by LPS derived from the periodontal disease pathogen Porphyromonas gingivalis (P. gingivalis).

METHODS AND RESULTS

Porphyromonas gingivalis LPS was administered by chronic infusion for 28 days and atherosclerosis development was examined in the aortic root of ApoE (apolipoprotein E)-deficient mice. The extent of atherosclerosis was compared between mice receiving control diet or diet containing the COX-2 inhibitor celecoxib. The role of COX-2 in P. gingivalis LPS-induced inflammatory cell activation was examined in peritoneal macrophages. Porphyromonas gingivalis LPS infusion significantly increased atherosclerosis development. In mice infused with P. gingivalis LPS, administration of the COX-2 inhibitor celecoxib further increased the extent of atherosclerotic lesion area. In peritoneal macrophages, P. gingivalis LPS increased the expression of COX-2 mRNA (messenger ribonucleic acid) and the production of prostaglandin (PG) E(2) (PGE(2)), the latter of which was inhibited by celecoxib. Porphyromonas gingivalis LPS-induced expression of tumour necrosis factor alpha (TNFalpha) was enhanced by inactivation of COX-2 and was attenuated by treatment with PGE(2).

CONCLUSION

The inhibition of COX-2-derived PGE(2) may enhance P. gingivalis LPS-induced atherosclerosis by increasing macrophage production of TNFalpha.

Modulation of enzymatic activities by n-3 polyunsaturated fatty acids to support cardiovascular health

Epidemiological evidence from Greenland Eskimos and Japanese fishing villages suggests that eating fish oil and marine animals can prevent coronary heart disease. Dietary studies from various laboratories have similarly indicated that regular fish oil intake affects several humoral and cellular factors involved in atherogenesis and may prevent atherosclerosis, arrhythmia, thrombosis, cardiac hypertrophy and sudden cardiac death. The beneficial effects of fish oil are attributed to their n-3 polyunsaturated fatty acid (PUFA; also known as omega-3 fatty acids) content, particularly eicosapentaenoic acid (EPA; 20:5, n-3) and docosahexaenoic acid (DHA; 22:6, n-3). Dietary supplementation of DHA and EPA influences the fatty acid composition of plasma phospholipids that, in turn, may affect cardiac cell functions in vivo. Recent studies have demonstrated that long-chain omega-3 fatty acids may exert beneficial effects by affecting a wide variety of cellular signaling mechanisms. Pathways involved in calcium homeostasis in the heart may be of particular importance. L-type calcium channels, the Na+-Ca2+ exchanger and mobilization of calcium from intracellular stores are the most obvious key signaling pathways affecting the cardiovascular system; however, recent studies now suggest that other signaling pathways involving activation of phospholipases, synthesis of eicosanoids, regulation of receptor-associated enzymes and protein kinases also play very important roles in mediating n-3 PUFA effects on cardiovascular health. This review is therefore focused on the molecular targets and signaling pathways that are regulated by n-3 PUFAs in relation to their cardioprotective effects.

Prostanoid function and cardiovascular disease

Prostanoids, including prostaglandins (PGs) and thromboxanes (TXs) are synthesized from arachidonic acid by the combined action of cyclooxygenases (COXs) and PG and TX synthases. Finally after their synthesis, prostanoids are quickly released to the extracellular medium exerting their effects upon interaction with prostanoid receptors present in the neighbouring cells. These agents exert important actions in the cardiovascular system, modulating vascular homeostasis and participating in the pathogenesis of vascular diseases as thrombosis and atherosclerosis. Among prostanoids, Tromboxane (TX)A(2), a potent platelet activator and vasoconstrictor and prostacyclin (PGI2), a platelet inhibitor and vasodilator, are the most important in controlling vascular homeostasis. Although multiple studies using pharmacological inhibitors and genetically deficient mice have demonstrated the importance of prostanoid-mediated actions on cardiovascular physiology, further analysis on the prostanoid mediated actions in the vascular system are required to better understand the benefits and risks for the use of COX inhibitors in cardiovascular diseases.

Selective cyclooxygenase inhibitors prevent the growth of Chlamydia pneumoniae in HL cells

The effects of the selective cyclooxygenase (COX) inhibitors SC-560 and PTPBS were studied in Chlamydia pneumoniae-infected HL cell cultures. Chlamydia pneumoniae growth and viability were assessed by quantifying inclusions and re-passages. COX-1 and COX-2 mRNA expression in HL cells during chlamydial infection was quantified with real-time polymerase chain reaction. SC-560 (10 microg/mL) and PTPBS (18 microg/mL) completely inhibited the growth of C. pneumoniae and the effect was dose-dependent between 4-9 microg/mL and 2-16 microg/mL, respectively. Inclusion size was reduced from 11.5+/-1.3 microm to 1.9+/-0.7 microm in the presence of the drugs. Removing the drugs returned the size to normal and increased the number of inclusions. Selective COX inhibitors appear to have a chlamydiostatic but not chlamydiacidic effect; they inhibit the growth of C. pneumoniae in vitro but do not prevent infection or eradicate C. pneumoniae from host cells.

Celecoxib and ankylosing spondylitis

It is now over 100 years since the arrival of aspirin and, from the mid-20th Century onwards, we have seen numerous attempts at providing society with safer and more efficacious nonsteroidal drugs. Ironically, while aspirin went from strength to strength with an ever-increasing pharmaceutical profile, new nonsteroidal anti-inflammatory drugs arrived and disappeared with rapid succession. Finally, there appears to have been a breakthrough with the development of the coxibs but concern has recently developed because of potential toxic cardiovascular reactions. Although originally studied in rheumatoid arthritis and degenerative arthropathy, the coxibs have now been investigated in ankylosing spondylitis and efficacy appears to be favorable and, to date, there is little evidence of toxicity, although problems in the nonspondylarthropathic arena may spill over into the seronegative spondylarthritides.

Contribution of cyclooxygenase-1 to thromboxane formation, platelet-vessel wall interactions and atherosclerosis in the ApoE null mouse

OBJECTIVE

Prostaglandin and thromboxane (TXA(2)) generation is increased in atherosclerosis. Studies with selective inhibitors attribute the enhanced prostacyclin (PGI(2)) generation to both cyclooxygenase-1 (COX-1) and COX-2 whereas the increased TXA(2) generation reflects platelet COX-1 expression. However, TXA(2) formation remains elevated in patients with cardiovascular disease on doses of aspirin that fully suppress platelet COX-1, suggesting other tissue sources for TXA(2) formation. Disruption of the thromboxane receptor gene suppresses the development of atherosclerosis. Notwithstanding this, the role of COX-1 in atherosclerosis is unclear, as it is widely distributed and contributes to a number of products, including those that potentially contribute to the resolution of inflammation.

METHODS AND RESULTS

We examined the role of COX-1 on prostaglandin generation, development of atherosclerosis and platelet-vessel wall interactions in the apoE(-/-) murine model by disrupting the COX-1 gene. ApoE(-/-)/COX-1(+/+), ApoE(-/-)/COX-1(+/-) and ApoE(-/-)/COX-1(-/-), were administered a 1% cholesterol diet for 8 weeks. Stable urinary metabolites of PGI(2) and TXA(2), which were markedly increased in the ApoE(-/-)/COX-1(+/+) were reduced by disruption of COX-1. Deletion of one or both copies of the COX-1 gene suppressed lesion formation. Assessment of platelet-vessel wall interactions by intravital microscopy showed a significant decrease in firm adhesion of platelets in the apoE/COX-1 double knockout (DKO).

CONCLUSION

COX-1 contributes to the enhanced formation of both PGI(2) and TXA(2) in atherosclerosis, and to the development of the disease. Non-platelet sources of COX-1 and TXA(2) that are inaccessible to standard doses of aspirin may contribute to the development of atherosclerosis.

Absence of cyclooxygenase-2 exacerbates hypoxia-induced pulmonary hypertension and enhances contractility of vascular smooth muscle cells

BACKGROUND

Cyclooxygenase-2 (COX-2) is upregulated in pulmonary artery smooth muscle cells (PASMCs) during hypoxia and may play a protective role in the response of the lung to hypoxia. Selective COX-2 inhibition may have detrimental pulmonary vascular consequences during hypoxia.

METHODS AND RESULTS

To investigate the role of COX-2 in the pulmonary vascular response to hypoxia, we subjected wild-type and COX-2-deficient mice to a model of chronic normobaric hypoxia. COX-2-null mice developed severe pulmonary hypertension with exaggerated elevation of right ventricular systolic pressure, significant right ventricular hypertrophy, and striking vascular remodeling after hypoxia. Pulmonary vascular remodeling in COX-2-deficient mice was characterized by PASMC hypertrophy but not increased proliferation. Furthermore, COX-2-deficient mice had significant upregulation of the endothelin-1 receptor (ET(A)) in the lung after hypoxia. Similarly, selective pharmacological inhibition of COX-2 in wild-type mice exacerbated hypoxia-induced pulmonary hypertension and resulted in PASMC hypertrophy and increased ET(A) receptor expression in pulmonary arterioles. The absence of COX-2 in vascular smooth muscle cells during hypoxia in vitro augmented traction forces and enhanced contractility of an extracellular matrix. Treatment of COX-2-deficient PASMCs with iloprost, a prostaglandin I(2) analog, and prostaglandin E(2) abrogated the potent contractile response to hypoxia and restored the wild-type phenotype.

CONCLUSIONS

Our findings reveal that hypoxia-induced pulmonary hypertension and vascular remodeling are exacerbated in the absence of COX-2 with enhanced ET(A) receptor expression and increased PASMC hypertrophy. COX-2-deficient PASMCs have a maladaptive response to hypoxia manifested by exaggerated contractility, which may be rescued by either COX-2-derived prostaglandin I(2) or prostaglandin E(2).

Correlation between rises in Chlamydia pneumoniae-specific antibodies, platelet activation and lipid peroxidation after percutaneous coronary intervention

We recently showed that Chlamydia pneumoniae activates platelets in vitro, with an associated oxidation of low-density lipoproteins. The aim of this study was to investigate whether C. pneumoniae is released during percutaneous coronary intervention (PCI) and, thereby, causes platelet activation and lipid peroxidation. Seventy-three patients undergoing coronary angiography and following PCI or coronary artery bypass graft (CABG) and 57 controls were included in the study. C. pneumoniae antibodies, serotonin and lipid peroxidation were measured before and 24 h, 1 month and 6 months after angiography. The results show that serum C. pneumoniae IgA concentrations were significantly higher in patients than in the controls. Furthermore, in 38% of the C. pneumoniae IgG positive patients, the C. pneumoniae IgG concentration increased 1 month after PCI. The levels of C. pneumoniae IgG antibodies 1 month after PCI correlated with plasma-lipid peroxidation (r = 0.91, P < 0.0001) and platelet-derived serotonin (r = 0.62, P = 0.02). There was no elevation in the total serum IgG 1 month after PCI. In conclusion, the present results suggest that PCI treatment of coronary stenosis releases C. pneumoniae from the atherosclerotic lesions, which leads to platelet activation and lipid peroxidation.

The select cyclooxygenase-2 inhibitor celecoxib reduced the extent of atherosclerosis in apo E-/- mice

Many investigators have suggested that immune activation may trigger the atherosclerotic process. The benefits of aspirin in preventing myocardial infarction have been attributed, in part, to its anti-inflammatory effects. Several reports have documented that cyclooxygenase (COX)-2 is up-regulated in human and mouse atherosclerotic lesions. To clarify the role of COX-2 in atherosclerosis, we conducted a study to test whether the COX-2 inhibitor, celecoxib, prevents the development and progression of the atherosclerotic process. We have used the apo E-/- mouse, a relevant animal model of atherosclerosis that develops fibrofatty lesions similar to human atherosclerosis. Treatment of 4-wk old apo E-/- mice with a standard rodent no. 5020 diet supplemented with 900 ppm of celecoxib for 16 wk led to an 81% reduction in lesion size. The mean lesion area per section (mean +/- SD) of proximal aorta from the apo E-/- mice fed the diet with celecoxib (33,991 +/- 7863 microm2, P < 0.001) was significantly less than that of the untreated apo E-/- mice (183,401 +/- 36,212 microm2). There were no lesions detected in the C57B1/6 mice. Immunohistochemistry of the ileum revealed that there was 80% reduction in staining for intercellular adhesion molecule and 60% reduction in staining for vascular cell adhesion molecule in the celecoxib treated mice. The protective effect of celecoxib was not maintained when the mice were switched after feeding the celecoxib-supplemented diet to the control 5020 diet for an additional 10 wk. These findings demonstrate that selective inhibition of the COX-2 enzyme with celecoxib prevented the development of atherosclerotic lesions in the proximal aortas from apo E-/- mice. One of the possible mechanisms is reduction in expression of the endothelial cell adhesion cell molecules intercellular adhesion molecule and vascular cell adhesion molecule, which plays a key role in the recruitment of inflammatory cells during the early stages of atherogenesis.

BM-520, an original TXA2 modulator, inhibits the action of thromboxane A2 and 8-iso-prostaglandin F2α in vitro and in vivo on human and rodent platelets, and aortic vascular smooth muscles from rodents

Thromboxane A(2) (TXA(2)) and 8-iso-PGF(2alpha) are two prostanoid agonists of the thromboxane A(2) receptor (TP), whose activation has been involved in platelet aggregation and atherosclerosis. Agents able to counteract the actions of these agonists are of great interest in the treatment and prevention of cardiovascular events. Here, we investigated in vitro and in vivo the pharmacological profile of BM-520, a new TP antagonist. In our experiments, this compound showed a great binding affinity for human washed platelets TP receptors, and prevented human platelet activation and aggregation induced by U-46619, arachidonic acid and 8-iso-PGF(2alpha). The TP receptor antagonist property of BM-520 was confirmed by its relaxing effect on rat aorta smooth muscle preparations precontracted with U-46619 and 8-iso-PGF(2alpha). Further, its TP antagonism was also demonstrated in vivo in guinea pig after a single intravenous injection (10 mg kg(-1)). We conclude that this novel TP antagonist could be a promising therapeutic tool in pathologies such as atherosclerosis where an increased production of TXA(2) and 8-iso-PGF(2alpha), as well as TP activation are well-established pathogenic events.

Drug-induced immunomodulation to affect the development and progression of atherosclerosis: a new opportunity?

Inflammation and cytokine pathways are crucial for the development and progression of atherosclerotic lesions. In this review, the hypothesis that immunomodulatory drugs provide a possible therapeutic modality for cardiovascular disease is evaluated. Therefore, after a short overview of the specific inflammatory pathways involved in atherosclerosis, literature on the effect of several immunomodulatory drugs, such as nonsteroidal anti-inflammatory drugs, specific cyclooxygenase inhibitors and immunosuppressive drugs, used currently in the prevention of rejection after organ transplant, on the development and progression of atherosclerosis is reviewed. In addition, the pleiotropic immunomodulatory effect of two established cardiovascular drugs (angiotensin-converting enzyme inhibitors and statins) is discussed.

The effects of COX-2 selective and non-selective NSAIDs on the initiation and progression of atherosclerosis in ApoE−/− mice

In this study, we investigated the effects of prolonged administration of the selective COX-2 inhibitors celecoxib and rofecoxib and the non-selective NSAID naproxen on the initiation and progression of atherosclerosis. ApoE(-/-) mice, as well as corresponding wild-type mice, were fed either a normal chow or a high fat Western diet with or without addition of the respective drugs over a period of 16 weeks. Thereafter, aortic lesion size, plasma lipid levels, and COX-2 expression in the plaques were determined. The results showed that neither the COX-2 selective inhibitors nor naproxen had a significant impact on the initiation and progression of atherosclerosis in diet-fed ApoE(-/-) mice, although both celecoxib and rofecoxib showed a tendency to reduce plaque size. This slight effect may be due to selective inhibition of COX-2 activity because the COX-2 expression was not altered in the plaque. Plasma lipid levels were also not significantly influenced by these drugs. Interestingly, in ApoE(-/-) mice that have been fed with normal chow, we found an increased incidence of plaque formation after treatment with celecoxib and rofecoxib, indicating that coxibs may promote the initiation of atherosclerosis. This effect was probably masked in diet-fed mice by the more pronounced effects of the high cholesterol diet. In conclusion, the reduction in diet-induced plaque size in animals fed a high fat diet and the promotion of atherosclerosis in mice on a normal diet indicate a dual role of the coxibs. In advanced stages of atherosclerosis, they may exert antithrombotic properties due to their COX-2 inhibiting activity, whereas in very early stages they may favor the initiation of atherogenesis. However, because these results were only observed in ApoE(-/-) and not in wild-type animals, coxibs may increase the risk of thrombosis in patients with a predisposition for thrombotic complications.

A novel thromboxane receptor antagonist and synthase inhibitor, BM-573, reduces development and progression of atherosclerosis in LDL receptor deficient mice

Atherosclerosis is a chronic inflammatory disease of the vasculature influenced by a variety of mediators. Among them, prostanoids, which include prostacyclin and thromboxane (Tx) A(2), have recently received a lot of attention. Previous studies demonstrated that antagonism or deletion of the receptor for TxA(2) retards early atherogenesis in apolipoprotein E-deficient mice, but no data are available in low-density lipoprotein (LDL) receptor deficient mice. In our study, we tested the effect of a novel TxA(2) receptor (TP) antagonist and synthase inhibitor, BM-573, on atherosclerosis development and progression in LDL receptor deficient mice. To this end, the effect of 12 weeks treatment with BM-573 on early or established aortic atherosclerotic lesions of these mice was assessed. In both treatments, while BM-573 did not affect body weight, systolic blood pressure, total plasma cholesterol or triglycerides levels, it partially reduced TxA(2) but did not affect prostacyclin biosynthesis. Moreover, BM-573 significantly decreased early atherogenesis and prevented progression of established atherosclerotic lesions. These results show for the first time that this dual Tx inhibitor is effective in reducing atherogenesis in the LDL receptor deficient mice. They also demonstrate the novel concept that this therapeutic approach halts the progression of the disease and influences the cellular composition of the atherosclerotic plaques.

Double-label expression studies of prostacyclin synthase, thromboxane synthase and COX isoforms in normal aortic endothelium

We have performed double-label immunofluorescence microscopy studies to evaluate the extent of co-localization of prostacyclin synthase (PGIS) and thromboxane synthase (TXS) with cyclooxygenase (COX)-1 and COX-2 in normal aortic endothelium. In dogs, COX-2 expression was found to be restricted to small foci of endothelial cells while COX-1, PGIS and TXS were widely distributed throughout the endothelium. Quantification of the total cross-sectioned aortic endothelium revealed a 6- to 7-fold greater expression of COX-1 relative to COX-2 (55 vs. 8%) and greater co-distribution of PGIS with COX-1 compared to COX-2 (19 vs. 3%). These results are in contrast to the extensive co-localization of PGIS and COX-2 in bronchiolar epithelium. In rat and human aortas, immunofluorescence studies also showed significant COX-1 and PGIS co-localization in the endothelium. Only minor focal COX-2 expression was detected in rat endothelium, similar to the dog, while COX-2 was not detected in human specimens. Inhibition studies in rats showed that selective COX-1 inhibition caused a marked reduction of 6-keto-PGF(1alpha) and TXB(2) aortic tissue levels, while COX-2 inhibition had no significant effect, providing further evidence for a functionally larger contribution of COX-1 to the synthesis of prostacyclin and thromboxane in aortic tissue. The data suggest a major role for COX-1 in the production of both prostacyclin and thromboxane in normal aortic tissue. The extensive co-localization of PGIS and COX-2 in the lung also indicates significant tissue differences in the co-expression patterns of these two enzymes.

Reprint of “Oxidative alterations of cyclooxygenase during atherogenesis” [Prostag. Oth. Lipid. M. 80 (2006) 1–14]

Nitric oxide (*NO) and eicosanoids are critical mediators of physiological and pathophysiological processes. They include inflammation and atherosclerosis. *NO production and eicosanoid synthesis become disrupted during atherosclerosis and thus, it is important to understand the mechanisms that may contribute to this outcome. We, and others, have shown that nitrogen oxide (NOx) species modulate cyclooxygenase (COX; also known as prostaglandin H2 synthase) activity and alter eicosanoid production. We have determined that peroxynitrite (ONOO-) has multiple effects on COX activity. ONOO- can provide the peroxide tone necessary for COX activation, such that simultaneous exposure of COX to its arachidonic acid substrate and ONOO- results in increased eicosanoid production. Alternatively, in the absence of arachidonic acid, ONOO- can modify COX through nitration of an essential tyrosine residue (Tyr385) such that it is incapable of catalysis. In this regard, we have shown that COX nitration occurs in human atherosclerotic tissue and in aortic lesions from ApoE-/- mice kept on a high fat diet. Additionally, we have demonstrated that Tyr nitration in ApoE-/- mice is dependent on the inducible form of NO synthase (iNOS). Under conditions where ONOO- persists and arachidonic acid is not immediately available, the cell may try to correct the situation by responding to ONOO- and releasing arachidonic acid via a signaling pathway to favor COX activation. Other post-translational modifications of COX by NOx species include S-nitrosation of cysteine (Cys) residues (which may have an activating effect) and Cys oxidation. The central focus of this review will include a discussion of how NOx species alter COX activity at the molecular level and how these modifications may contribute to altered eicosanoid output during atherosclerosis and lesion development.

Thromboxane receptor blockade improves the antiatherogenic effect of thromboxane A2 suppression in LDLR KO mice

Suppression of thromboxane (Tx) A(2) biosynthesis retards atherogenesis. In this setting, the coincidental presence of nonconventional ligands for the TxA(2) receptor (TP), such as isoprostanes, could still induce a proatherogenic vascular phenotype. However, no data are available on the effect of combining suppression of TxA(2) formation with blockade of TP in atherogenesis. To this end, we tested the effect of a selective COX-1 inhibitor, SC560, a TP antagonist, BM-573, or a combination of both in low-density lipoprotein receptor-deficient mice on a high-fat diet. None of the treatments affected body weight or plasma cholesterol or triglycerides levels. Although SC-560 suppressed TxA(2) biosynthesis, BM-573 reduced its levels by 35%; in contrast, the 2 drugs, alone or in combination, did not significantly affect prostacyclin levels. At the end of the study, SC560 and BM-573 reduced atherogenesis; however, a further significant decrease was observed in mice receiving both drugs. This effect was associated with a further significant reduction of vascular inflammation, a decrease in macrophages, and an increase in the content of collagen and smooth muscle cells of the atherosclerotic lesions. These results show for the first time that the addition of a TP antagonist increases the antiatherogenic effect of COX-1-dependent TxA(2) suppression.

The PGH-synthase system and isozyme-selective inhibition

Virtually all human cell types can express both cyclooxygenase (COX)-1 and COX-2 under appropriate circumstances. Both isoforms can subserve physiologic and pathophysiologic roles when coupled with the appropriate stimuli and downstream prostaglandin (PG)H2-isomerases and prostanoid receptors. Although the ratio of maximal biosynthetic capacity of human platelets to the basal rate of production of thromboxane A2 is approximately 5000, this ratio is much lower in the case of PGI2, thus dictating quite different requirements for the extent and duration of COX inhibition in human platelets and vascular endothelial cells to detect functional and clinical effects. The development of low-dose aspirin as an antiplatelet agent has been instrumental in characterizing the role of platelet COX-1 in atherothrombosis. Similarly, though quite unexpectedly, the development of coxibs as anti-inflammatory agents has been instrumental in elucidating the role of endothelial COX-2 in vascular occlusion. Because of differential requirements for the inhibition of thromboxane A2 versus PGI2 biosynthesis in vivo, most traditional nonsteroidal anti-inflammatory drugs tend to mimic the effects of coxibs, rather than aspirin, on prostanoid-dependent cardiovascular homeostasis.

Aging associated with mild dyslipidemia reveals that COX-2 preserves dilation despite endothelial dysfunction

The endothelial function declines with age, and dyslipidemia (DL) has been shown to hasten this process by favoring the generation of reactive oxygen species (ROS). Cyclooxygenase-2 (COX-2) can be induced by ROS, but its contribution to the regulation of the endothelial function is unknown. Since COX-2 inhibitors may be deleterious to the cardiovascular system, we hypothesized that DL leads to ROS-dependent endothelial damage and a protective upregulation of COX-2. Dilations to acetylcholine (ACh) of renal arteries isolated from 3-, 6-, and 12-mo-old wild-type (WT) and DL mice expressing the human ApoB-100 were recorded with or without COX inhibitors and the antioxidant N-acetyl-l-cystein (NAC). Nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) were inhibited using N(omega)-nitro-l-arginine (l-NNA) and a depolarizing solution, respectively. In WT mice, the dilation to ACh declined at 12 mo but was insensitive to COX-1/2 inhibition alone or with NAC. DL led to an early endothelial dysfunction at 6 mo, normalized, however, by NAC. At 12 mo, vascular sensitivity to ACh was further reduced by DL. At this age, selective COX-2 inhibition reduced the dilation, whereas addition of NAC improved it. In 3- and 6-mo-old WT mice, l-NNA significantly reduced the dilation, whereas it limited the dilation only in 3-mo-old DL mice. EDHF-dependent dilation remains identical in both groups. These data suggest that COX-2 activity confers endothelium-dependent vasodilatory function in aged DL mice in the face of a pro-oxidative environment. Upregulation of this pathway compensates for the early loss of the contribution of NO in DL mice.

Oxidative alterations of cyclooxygenase during atherogenesis

Nitric oxide (*NO) and eicosanoids are critical mediators of physiological and pathophysiological processes. They include inflammation and atherosclerosis. *NO production and eicosanoid synthesis become disrupted during atherosclerosis and thus, it is important to understand the mechanisms that may contribute to this outcome. We, and others, have shown that nitrogen oxide (NO(x)) species modulate cyclooxygenase (COX; also known as prostaglandin H(2) synthase) activity and alter eicosanoid production. We have determined that peroxynitrite (ONOO(-)) has multiple effects on COX activity. ONOO(-) can provide the peroxide tone necessary for COX activation, such that simultaneous exposure of COX to its arachidonic acid substrate and ONOO(-) results in increased eicosanoid production. Alternatively, in the absence of arachidonic acid, ONOO(-) can modify COX through nitration of an essential tyrosine residue (Tyr385) such that it is incapable of catalysis. In this regard, we have shown that COX nitration occurs in human atherosclerotic tissue and in aortic lesions from ApoE(-/-) mice kept on a high fat diet. Additionally, we have demonstrated that Tyr nitration in ApoE(-/-) mice is dependent on the inducible form of NO synthase (iNOS). Under conditions where ONOO(-) persists and arachidonic acid is not immediately available, the cell may try to correct the situation by responding to ONOO(-) and releasing arachidonic acid via a signaling pathway to favor COX activation. Other post-translational modifications of COX by NO(x) species include S-nitrosation of cysteine (Cys) residues (which may have an activating effect) and Cys oxidation. The central focus of this review will include a discussion of how NO(x) species alter COX activity at the molecular level and how these modifications may contribute to altered eicosanoid output during atherosclerosis and lesion development.

Ciclooxigenasa 2: ¿una nueva diana terapéutica en la aterosclerosis?

It is now widely accepted that atherosclerosis is a complex chronic inflammatory disorder of the arterial tree associated with several risk factors. From the initial phases to eventual rupture of vulnerable atherosclerotic plaques, a low-grade inflammation, also termed microinflammation, appears to play a key pathogenetic role. Systemic inflammatory markers (C reactive protein, cytokines adhesion molecules) also play a role in this process. Experimental and clinical evidence suggests that cyclooxygenase-2 (COX-2), an enzyme which catalyzes the generation of prostaglandins from arachidonic acid, also contributes to lesion formation. Recent reports by our group have demonstrated increased monocyte COX-2 activity and the production of prostaglandin E2 in relation to cardiovascular risk factors and subclinical atherosclerosis in asymptomatic subjects. Our findings support the notion that the COX-2/prostaglandin E2 axis may have a role, raising the question as to whether its selective inhibition might be an attractive therapeutic target in atherosclerosis. COX-2 inhibitors, collectively called "coxibs" (celecoxib, rofecoxib, valdecoxib, lumiracoxib, etc), held a promise as anti-inflammatory drugs without the some of the side effects of aspirin or non steroidal antiinflammatory agents. However, clinical studies raise several clinically relevant questions as to their beneficial role in atherosclerosis prevention, because of increased thrombogenicity and cardiovascular risk, and therefore coxibs should be restricted in atherosclerosis-prone patients.

Cyclooxygenase-2 inhibition: Vascular inflammation and cardiovascular risk

The inducible isoform of cyclooxygenase-2 (COX-2) plays a role in pathophysiologic processes like inflammation and pain but is also constitutively expressed in tissues such as the kidney or vascular endothelium, where it exerts important physiologic functions. Although much evidence exists that implicates COX-2 in atherosclerosis, its role in this setting remains substantially uncertain. This observation is also confirmed by the results of clinical trials of selective COX-2 inhibitors. Treatment with these drugs, developed with the assumption that they would be as effective as nonselective COX inhibitors but without their gastrointestinal side effects, has been reported to be associated with an increased cardiovascular risk. In this article, we review the pattern of expression of COX-2 in the cellular players of atherothrombosis, its role as a determinant of plaque vulnerability, and the vascular effects on prostanoid inhibition by COX-2 inhibitors.

Manipulation of inflammation modulates hyperlipidemia in apolipoprotein E-deficient mice: a possible role for interleukin-6

There are increasing evidences showing that inflammation participates in atherosclerosis. Therefore, the therapeutic use of anti-inflammatory agents should be considered. We have induced chronic, aseptic inflammation upon the injection of turpentine and tested the effect of dexamethasone on lipoprotein metabolism and, consequently, atherosclerosis in apolipoprotein E-deficient mice. Aseptic inflammation caused a significant decrease in hyperlipidemia. Treatment with dexamethasone elicited the opposite effect increasing hyperlipidemia through mechanisms related to the increase in the synthesis of triglyceride-rich lipoproteins. Changes in plasma lipids correlated with those observed in the size of atherosclerotic lesions. Our data suggest the presence of a common mechanism present in both observations and which is probably related to the cytokine secretion. Among the candidates, we chose to test the effect of interleukin-6 because it is involved in both processes, atherosclerosis and inflammation, and its expression is efficiently repressed by corticosteroids. The injection of recombinant interleukin-6 in our mice elicited the same effects observed in our model of inflammation. We conclude that manipulation of inflammation-related mechanisms modulates lipid homeostasis and development of atherosclerotic plaque in rodents.

Cardiovascular risk with cyclooxygenase inhibitors: general problem with substance specific differences?

Randomised clinical trials and observational studies have shown an increased risk of myocardial infarction, stroke, hypertension and heart failure during treatment with cyclooxygenase inhibitors. Adverse cardiovascular effects occurred mainly, but not exclusively, in patients with concomitant risk factors. Cyclooxygenase inhibitors cause complex changes in renal, vascular and cardiac prostanoid profiles thereby increasing vascular resistance and fluid retention. The incidence of cardiovascular adverse events tends to increase with the daily dose and total exposure time. A comparison of individual selective and unselective cyclooxygenase inhibitors suggests substance-specific differences, which may depend on differences in pharmacokinetic parameters or inhibitory potency and may be contributed by prostaglandin-independent effects. Diagnostic markers such as N-terminal pro brain natriuretic peptide (NT-proBNP) or high-sensitive C-reactive protein might help in the early identification of patients at risk, thus avoiding the occurrence of serious cardiovascular toxicity.

Inducible nitric oxide synthase mediates prostaglandin h2 synthase nitration and suppresses eicosanoid production

Nitric oxide (NO) modulates the biological levels of arachidonate-derived cell signaling molecules by either enhancing or suppressing the activity of prostaglandin H(2) isoforms (PGHS-1 and PGHS-2). Whether NO activates or suppresses PGHS activity is determined by alternative protein modifications mediated by NO and NO-derived species. Here, we show that inducible NO synthase (iNOS) and PGHS-1 co-localize in atherosclerotic lesions of ApoE(-/-) mouse aortae. Immunoblotting and immunohistochemistry revealed Tyr nitration in PGHS-1 in aortic lesions but markedly less in adjacent nonlesion tissue. PGHS-2 was also found in lesions, but 3-nitrotyrosine incorporation was not detected. 3-Nitrotyrosine formation in proteins is considered a hallmark reaction of peroxynitrite, which can form via NO-superoxide reactions in an inflammatory setting. That iNOS-derived NO is essential for 3-nitrotyrosine modification of PGHS-1 was confirmed by the absence of 3-nitrotyrosine in lesions from ApoE(-/-)iNOS(-/-) mice. Mass spectrometric studies specifically identified the active site residue Tyr385 as a 3-nitrotyrosine modification site in purified PGHS-1 exposed to peroxynitrite. PGHS-mediated eicosanoid (PGE(2)) synthesis was more than fivefold accelerated in cultured iNOS(-/-) versus iNOS-expressing mouse aortic smooth muscle cells, suggesting that iNOS-derived NO markedly suppresses PGHS activity in vascular cells. These results further suggest a regulatory role of iNOS in eicosanoid biosynthesis in human atherosclerotic lesions.