Disruption of the 5-lipoxygenase pathway attenuates atherogenesis consequent to COX-2 deletion in mice

PGE2 synthesis and signaling in the liver physiology and pathophysiology: An update

The liver plays a central role in systemic metabolism and drug degradation. However, it is highly susceptible to damage due to various factors, including metabolic imbalances, excessive alcohol consumption, viral infections, and drug influences. These factors often result in conditions such as fatty liver, hepatitis, and acute or chronic liver injury. Failure to address these injuries could promptly lead to the development of liver cirrhosis and potentially hepatocellular carcinoma (HCC). Prostaglandin E2 (PGE2) is a metabolite of arachidonic acid that belongs to the class of polyunsaturated fatty acids (PUFA) and is synthesized via the cyclooxygenase (COX) pathway. By binding to its G protein coupled receptors (i.e., EP1, EP2, EP3 and EP4), PGE2 has a wide range of physiological and pathophysiology effects, including pain, inflammation, fever, cardiovascular homeostasis, etc. Recently, emerging studies showed that PGE2 plays an indispensable role in liver health and disease. This review focus on the research progress of the role of PGE2 synthase and its receptors in liver physiological and pathophysiological processes and discuss the possibility of developing liver protective drugs targeting the COXs/PGESs/PGE2/EPs axis.

Ferroptosis in age-related vascular diseases: Molecular mechanisms and innovative therapeutic strategies

Aging, an inevitable aspect of human existence, serves as one of the predominant risk factors for vascular diseases. Delving into the mystery of vascular disease's pathophysiology, the profound involvement of programmed cell death (PCD) has been extensively demonstrated. PCD is a fundamental biological process that plays a crucial role in both normal physiology and pathology, including a recently discovered form, ferroptosis. Ferroptosis is characterized by its reliance on iron and lipid peroxidation, and its significant involvement in vascular disease pathophysiology has been increasingly acknowledged. This phenomenon not only offers a promising therapeutic target but also deepens our understanding of the complex relationship between ferroptosis and age-related vascular diseases. Consequently, this article aims to thoroughly review the mechanisms that enable the effective control and inhibition of ferroptosis. It focuses on genetic and pharmacological interventions, with the goal of developing innovative therapeutic strategies to combat age-related vascular diseases.

Prostanoids in Cardiac and Vascular Remodeling

Prostanoids are biologically active lipids generated from arachidonic acid by the action of the COX (cyclooxygenase) isozymes. NSAIDs, which reduce the biosynthesis of prostanoids by inhibiting COX activity, are effective anti-inflammatory, antipyretic, and analgesic drugs. However, their use is limited by cardiovascular adverse effects, including myocardial infarction, stroke, hypertension, and heart failure. While it is well established that NSAIDs increase the risk of atherothrombotic events and hypertension by suppressing vasoprotective prostanoids, less is known about the link between NSAIDs and heart failure risk. Current evidence indicates that NSAIDs may increase the risk for heart failure by promoting adverse myocardial and vascular remodeling. Indeed, prostanoids play an important role in modulating structural and functional changes occurring in the myocardium and in the vasculature in response to physiological and pathological stimuli. This review will summarize current knowledge of the role of the different prostanoids in myocardial and vascular remodeling and explore how maladaptive remodeling can be counteracted by targeting specific prostanoids.

Effects of Atherogenic Factors on Endothelial Cells: Bioinformatics Analysis of Differentially Expressed Genes and Signaling Pathways

(1) Background: Atherosclerosis is a serious medical condition associated with high morbidity and mortality rates. It develops over many years as a complex chain of events in the vascular wall involving various cells and is influenced by many factors of clinical interest. (2) Methods: In this study, we performed a bioinformatic analysis of Gene Expression Omnibus (GEO) datasets to investigate the gene ontology of differentially expressed genes (DEGs) in endothelial cells exposed to atherogenic factors such as tobacco smoking, oscillatory shear, and oxidized low-density lipoproteins (oxLDL). DEGs were identified using the limma R package, and gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment, and protein-protein interaction (PPI) network analysis were performed. (3) Results: We studied biological processes and signaling pathways involving DEGs in endothelial cells under the influence of atherogenic factors. GO enrichment analysis demonstrated that the DEGs were mainly involved in cytokine-mediated signaling pathway, innate immune response, lipid biosynthetic process, 5-lipoxygenase activity, and nitric-oxide synthase activity. KEGG pathway enrichment analysis showed that common pathways included tumor necrosis factor signaling pathway, NF-κB signaling pathway, NOD-like receptor signaling pathway, lipid and atherosclerosis, lipoprotein particle binding, and apoptosis. (4) Conclusions: Atherogenic factors such as smoking, impaired flow, and oxLDL contribute to impaired innate immune response, metabolism, and apoptosis in endothelial cells, potentially leading to the development of atherosclerosis.

Macrophages use apoptotic cell-derived methionine and DNMT3A during efferocytosis to promote tissue resolution

Efferocytosis, the clearance of apoptotic cells (ACs) by macrophages, is critical for tissue resolution, with defects driving many diseases. Mechanisms of efferocytosis-mediated resolution are incompletely understood. Here, we show that AC-derived methionine regulates resolution through epigenetic repression of the extracellular signal-regulated kinase 1/2 (ERK1/2) phosphatase Dusp4. We focus on two key efferocytosis-induced pro-resolving mediators, prostaglandin E2 (PGE2) and transforming growth factor beta 1 (TGF-β1), and show that efferocytosis induces prostaglandin-endoperoxide synthase 2/cyclooxygenase 2 (Ptgs2/COX2), leading to PGE2 synthesis and PGE2-mediated induction of TGF-β1. ERK1/2 phosphorylation/activation by AC-activated CD36 is necessary for Ptgs2 induction, but this is insufficient owing to an ERK-DUSP4 negative feedback pathway that lowers phospho-ERK. However, subsequent AC engulfment and phagolysosomal degradation lead to Dusp4 repression, enabling enhanced p-ERK and induction of the Ptgs2-PGE2-TGF-β1 pathway. Mechanistically, AC-derived methionine is converted to S-adenosylmethionine, which is used by DNA methyltransferase-3A (DNMT3A) to methylate Dusp4. Bone-marrow DNMT3A deletion in mice blocks COX2/PGE2, TGF-β1, and resolution in sterile peritonitis, apoptosis-induced thymus injury and atherosclerosis. Knowledge of how macrophages use AC-cargo and epigenetics to induce resolution provides mechanistic insight and therapeutic options for diseases driven by impaired resolution.

Effects of Arachidonic Acid Metabolites on Cardiovascular Health and Disease

Arachidonic acid (AA) is an essential fatty acid that is released by phospholipids in cell membranes and metabolized by cyclooxygenase (COX), cytochrome P450 (CYP) enzymes, and lipid oxygenase (LOX) pathways to regulate complex cardiovascular function under physiological and pathological conditions. Various AA metabolites include prostaglandins, prostacyclin, thromboxanes, hydroxyeicosatetraenoic acids, leukotrienes, lipoxins, and epoxyeicosatrienoic acids. The AA metabolites play important and differential roles in the modulation of vascular tone, and cardiovascular complications including atherosclerosis, hypertension, and myocardial infarction upon actions to different receptors and vascular beds. This article reviews the roles of AA metabolism in cardiovascular health and disease as well as their potential therapeutic implication.

New horizons in the roles and associations of COX-2 and novel natural inhibitors in cardiovascular diseases

Age-related cardiovascular disease is the leading cause of death in elderly populations. Coxibs, including celecoxib, valdecoxib, etoricoxib, parecoxib, lumiracoxib, and rofecoxib, are selective cyclooxygenase-2 (COX-2) inhibitors used to treat osteoarthritis and rheumatoid arthritis. However, many coxibs have been discontinued due to adverse cardiovascular events. COX-2 contains cyclooxygenase (COX) and peroxidase (POX) sites. COX-2 inhibitors block COX activity without affecting POX activity. Recently, quercetin-like flavonoid compounds with OH groups in their B-rings have been found to serve as activators of COX-2 by binding the POX site. Galangin-like flavonol compounds serve as inhibitors of COX-2. Interestingly, nabumetone, flurbiprofen axetil, piketoprofen-amide, and nepafenac are ester prodrugs that inhibit COX-2. The combination of galangin-like flavonol compounds with these prodrug metabolites may lead to the development of novel COX-2 inhibitors. This review focuses on the most compelling evidence regarding the role and mechanism of COX-2 in cardiovascular diseases and demonstrates that quercetin-like compounds exert potential cardioprotective effects by serving as cofactors of COX-2.

Effects of nitro-butoxyl- and butyl-esters of non-steroidal anti-inflammatory drugs compared with parent compounds on the contractility of digital arterial smooth muscle from the fallow deer (Dama dama)

BACKGROUND

Non-steroidal anti-inflammatory drugs (NSAIDs) are a major cause of upper gastro-intestinal (GI) ulceration and bleeding as well as cardiovascular (CV) diseases (e.g., myocardial infarction and stroke). A feature common to both these adverse events is a variety of vascular reactions. One approach to overcome these side effects has been the development of nitric-oxide (NO)-donating NSAIDs. The NO is considered to overcome some of these vascular reactions caused by NSAIDs. Unfortunately, the NO-NSAIDs developed so far have not had the expected benefits compared with NSAIDs alone.

OBJECTIVES

Using in vitro preparations it is hoped to gain insight into the vascular and smooth muscle reactions induced by NO-NSAIDs compared with NSAIDs as a basis for improving the protective responses attributed to the NO-donating properties of these drugs.

METHODS

A range of NO-NSAIDs was synthesized based on the esterification of NSAIDs with the nitro-butoxylate as a prototype of an NO-donor. These compounds, as well as NO-donor agents and NSAIDS, were examined for their possible effects on isolated segments of digital arteries of fallow deer, which provide a robust model for determining the effects of vasodilator and vasoconstrictor activities, in comparison with those of standard pharmacological agents.

RESULTS

The NO-NSAIDs were found to antagonise the smooth muscle contractions produced by 5-hydroxytryptamine (serotonin, 5-HT). However, while almost all their parent NSAIDs had little or no effect, with the exception of the R-(-)-isomers of both ibuprofen and flurbiprofen, which caused vasodilatation, all the NO-NSAIDs tested antagonised the increase in tension produced by 5-HT.

CONCLUSIONS

R-(-)-ibuprofen and R-(-)-flurbiprofen, along with the nitro-butoxyl esters of the NSAIDs examined, produce relaxation of segments of deer digital artery smooth muscle in vitro. The evidence presented suggests that their mechanism involves the release of NO or its products.

Are NSAIDs Safe? Assessing the Risk-Benefit Profile of Nonsteroidal Anti-inflammatory Drug Use in Postoperative Pain Management

In this article, we review controversies in assessing the risk of serious adverse effects caused by administration of nonsteroidal anti-inflammatory drugs (NSAIDs). Our focus is upon NSAIDs used in short courses for the management of acute postoperative pain. In our review of the literature, we found that the risks of short-term NSAID use may be overemphasized. Specifically, that the likelihood of renal dysfunction, bleeding, nonunion of bone, gastric complications, and finally, cardiac dysfunction do not appear to be significantly increased when NSAIDs are used appropriately after surgery. The importance of this finding is that in light of the opioid epidemic, it is crucial to be aware of alternative analgesic options that are safe for postoperative pain control.

Mechanistic definition of the cardiovascular mPGES-1/COX-2/ADMA axis

AIMS

Cardiovascular side effects caused by non-steroidal anti-inflammatory drugs (NSAIDs), which all inhibit cyclooxygenase (COX)-2, have prevented development of new drugs that target prostaglandins to treat inflammation and cancer. Microsomal prostaglandin E synthase-1 (mPGES-1) inhibitors have efficacy in the NSAID arena but their cardiovascular safety is not known. Our previous work identified asymmetric dimethylarginine (ADMA), an inhibitor of endothelial nitric oxide synthase, as a potential biomarker of cardiovascular toxicity associated with blockade of COX-2. Here, we have used pharmacological tools and genetically modified mice to delineate mPGES-1 and COX-2 in the regulation of ADMA.

METHODS AND RESULTS

Inhibition of COX-2 but not mPGES-1 deletion resulted in increased plasma ADMA levels. mPGES-1 deletion but not COX-2 inhibition resulted in increased plasma prostacyclin levels. These differences were explained by distinct compartmentalization of COX-2 and mPGES-1 in the kidney. Data from prostanoid synthase/receptor knockout mice showed that the COX-2/ADMA axis is controlled by prostacyclin receptors (IP and PPARβ/δ) and the inhibitory PGE2 receptor EP4, but not other PGE2 receptors.

CONCLUSION

These data demonstrate that inhibition of mPGES-1 spares the renal COX-2/ADMA pathway and define mechanistically how COX-2 regulates ADMA.

Bmal1 Deletion in Myeloid Cells Attenuates Atherosclerotic Lesion Development and Restrains Abdominal Aortic Aneurysm Formation in Hyperlipidemic Mice

OBJECTIVE

Although the molecular components of circadian rhythms oscillate in discrete cellular components of the vasculature and many aspects of vascular function display diurnal variation, the cellular connections between the molecular clock and inflammatory cardiovascular diseases remain to be elucidated. Previously we have shown that pre- versus postnatal deletion of Bmal1 (brain and muscle aryl hydrocarbon receptor nuclear translocator-like 1), the nonredundant core clock gene has contrasting effects on atherogenesis. Here we investigated the effect of myeloid cell Bmal1 deletion on atherogenesis and abdominal aortic aneurysm formation in mice. Approach and Results: Mice lacking Bmal1 in myeloid cells were generated by crossing Bmal1 flox/flox mice with lysozyme 2 promoter-driven Cre recombinase mice on a hyperlipidemic low-density lipoprotein receptor-deficient background and were fed on a high-fat diet to induce atherosclerosis. Atherogenesis was restrained, concomitant with a reduction of aortic proinflammatory gene expression in myeloid cell Bmal1 knockout mice. Body weight, blood pressure, blood glucose, triglycerides, and cholesterol were unaltered. Similarly, myeloid cell depletion of Bmal1 also restrained Ang II (angiotensin II) induced formation of abdominal aortic aneurysm in hyperlipidemic mice. In vitro, RNA-Seq analysis demonstrated a proinflammatory response in cultured macrophages in which there was overexpression of Bmal1.

CONCLUSIONS

Myeloid cell Bmal1 deletion retards atherogenesis and restrains the formation of abdominal aortic aneurysm and may represent a potential therapeutic target for inflammatory cardiovascular diseases.

Cold-Induced Browning of Inguinal White Adipose Tissue Is Independent of Adipose Tissue Cyclooxygenase-2

Previous studies using genetic mouse models have implicated COX-2 in the browning of white adipose tissues (WATs) in mice during cold exposure. However, COX-2 is important during development, and conventional knockouts (KOs) exhibit many defects, conditioned by genetic background. Similarly, the physiological relevance of transgenic overexpression of COX-2 is questionable. In the present study, we utilized mice in which COX-2 was deleted postnatally, bypassing the consequences of enzyme deficiency during development. Despite activation of thermogenesis and browning of inguinal WAT, cold exposure failed to increase COX-2 expression in the adipose tissues of mice with different genetic backgrounds, and the body temperature response to cold was unaltered in postnatal global COX-2 KOs. Selective disruption of COX-2 in adipose tissues also failed detectably to impact systemic prostaglandin biosynthesis. Browning of inguinal WATs induced by exposure to cold is independent of adipose tissue COX-2.

Cyclooxygenase-2, Asymmetric Dimethylarginine, and the Cardiovascular Hazard From Nonsteroidal Anti-Inflammatory Drugs

BACKGROUND

Large-scale, placebo-controlled trials established that nonsteroidal anti-inflammatory drugs confer a cardiovascular hazard: this has been attributed to depression of cardioprotective products of cyclooxygenase (COX)-2, especially prostacyclin. An alternative mechanism by which nonsteroidal anti-inflammatory drugs might constrain cardioprotection is by enhancing the formation of methylarginines in the kidney that would limit the action of nitric oxide throughout the vasculature.

METHODS

Targeted and untargeted metabolomics were used to investigate the effect of COX-2 deletion or inhibition in mice and in osteoarthritis patients exposed to nonsteroidal anti-inflammatory drugs on the l-arginine/nitric oxide pathway.

RESULTS

Analysis of the plasma and renal metabolome was performed in postnatal tamoxifen-inducible Cox-2 knockout mice, which exhibit normal renal function and blood pressure. This revealed no changes in arginine and methylarginines compared with their wild-type controls. Moreover, the expression of genes in the l-arginine/nitric oxide pathway was not altered in the renal medulla or cortex of tamoxifen inducible Cox-2 knockout mice. Therapeutic concentrations of the selective COX-2 inhibitors, rofecoxib, celecoxib, and parecoxib, none of which altered basal blood pressure or renal function as reflected by plasma creatinine, failed to elevate plasma arginine and methylarginines in mice. Finally, plasma arginine or methylarginines were not altered in osteoarthritis patients with confirmed exposure to nonsteroidal anti-inflammatory drugs that inhibit COX-1 and COX-2. By contrast, plasma asymmetrical dimethylarginine was increased in mice infused with angiotensin II sufficient to elevate blood pressure and impair renal function. Four weeks later, blood pressure, plasma creatinine, and asymmetrical dimethylarginine were restored to normal levels. The increase in asymmetrical dimethylarginine in response to infusion with angiotensin II in celecoxib-treated mice was also related to transient impairment of renal function.

CONCLUSIONS

Plasma methylarginines are not altered by COX-2 deletion or inhibition but rather are elevated coincident with renal compromise.

Tumor cell-intrinsic EPHA2 suppresses anti-tumor immunity by regulating PTGS2 (COX-2)

Resistance to immunotherapy is one of the biggest problems of current oncotherapeutics. WhileT cell abundance is essential for tumor responsiveness to immunotherapy, factors that define the T cell inflamed tumor microenvironment are not fully understood. We conducted an unbiased approach to identify tumor-intrinsic mechanisms shaping the immune tumor microenvironment(TME), focusing on pancreatic adenocarcinoma because it is refractory to immunotherapy and excludes T cells from the TME. From human tumors, we identified EPHA2 as a candidate tumor intrinsic driver of immunosuppression. Epha2 deletion reversed T cell exclusion and sensitized tumors to immunotherapy. We found that PTGS2, the gene encoding cyclooxygenase-2, lies downstream of EPHA2 signaling through TGFβ and is associated with poor patient survival. Ptgs2 deletion reversed T cell exclusion and sensitized tumors to immunotherapy; pharmacological inhibition of PTGS2 was similarly effective. Thus, EPHA2-PTGS2 signaling in tumor cells regulates tumor immune phenotypes; blockade may represent a novel therapeutic avenue for immunotherapy-refractory cancers. Our findings warrant clinical trials testing the effectiveness of therapies combining EPHA2-TGFβ-PTGS2 pathway inhibitors with anti-tumor immunotherapy, and may change the treatment of notoriously therapy-resistant pancreatic adenocarcinoma.

Genetic Models Reveal cis and trans Immune-Regulatory Activities for lincRNA-Cox2

An inducible gene expression program is a hallmark of the host inflammatory response. Recently, long intergenic non-coding RNAs (lincRNAs) have been shown to regulate the magnitude, duration, and resolution of these responses. Among these is lincRNA-Cox2, a dynamically regulated gene that broadly controls immune gene expression. To evaluate the in vivo functions of this lincRNA, we characterized multiple models of lincRNA-Cox2-deficient mice. LincRNA-Cox2-deficient macrophages and murine tissues had altered expression of inflammatory genes. Transcriptomic studies from various tissues revealed that deletion of the lincRNA-Cox2 locus also strongly impaired the basal and inducible expression of the neighboring gene prostaglandin-endoperoxide synthase (Ptgs2), encoding cyclooxygenase-2, a key enzyme in the prostaglandin biosynthesis pathway. By utilizing different genetic manipulations in vitro and in vivo, we found that lincRNA-Cox2 functions through an enhancer RNA mechanism to regulate Ptgs2. More importantly, lincRNA-Cox2 also functions in trans, independently of Ptgs2, to regulate critical innate immune genes in vivo.

Cysteinyl-leukotriene pathway as a new therapeutic target for the treatment of atherosclerosis related to obstructive sleep apnea syndrome

AIMS

Obstructive sleep apnea (OSA) characterized by nocturnal intermittent hypoxia (IH) is associated with atherosclerosis and cysteinyl-leukotrienes (CysLT) pathway activation. We aimed to identify the determinants of CysLT pathway activation and the role of CysLT in OSA-related atherosclerosis.

METHODS AND RESULTS

Determinants of the urinary excretion of LTE₄ (U-LTE₄) including history of cardiovascular events, polysomnographic and biological parameters were studied in a cohort of 170 OSA patients and 29 controls, and in a subgroup of OSA patients free of cardiovascular event (n = 136). Mechanisms linking IH, the CysLT pathway and atherogenesis were investigated in Apolipoprotein E deficient (ApoE^-/-) mice exposed to 8-week IH. In the whole cohort, U-LTE₄ was independently influenced by age, minimal oxygen saturation, and a history of cardiovascular events, and correlated significantly with intima-media thickness. In the subgroup of OSA patients free of cardiovascular event, increased U-LTE₄ was increased compared to controls and independently related to hypoxia severity and traditional risk factors aggregated in the 10-year cardiovascular risk score of European Society of Cardiology. In IH mice, atherosclerosis lesion size and mRNA levels of 5-lipoxygenase, 5-lipoxygenase activating protein (FLAP) and CysLT₁ receptor were significantly increased. This transcriptional activation was associated with the binding of HIF-1 to the FLAP promoter and was strongly associated with atherosclerosis lesion size. CysLT₁ receptor antagonism (montelukast) significantly reduced atherosclerosis progression in IH mice.

CONCLUSIONS

IH-related CysLT pathway activation contributes to OSA-induced atherogenesis. In the era of personalized medicine, U-LTE₄ may be a useful biomarker to identify OSA patients for whom CysLT₁ blockade could represent a new therapeutic avenue for reducing cardiovascular risk.

Prostaglandin E2 promotes hepatic bile acid synthesis by an E prostanoid receptor 3-mediated hepatocyte nuclear receptor 4α/cholesterol 7α-hydroxylase pathway in mice

Prostaglandin E₂ (PGE₂ ) is an important lipid mediator of inflammation. However, whether and how PGE₂ regulates hepatic cholesterol metabolism remains unknown. We found that expression of the PGE₂ receptor, E prostanoid receptor 3 (EP3) expression is remarkably increased in hepatocytes in response to hyperlipidemic stress. Hepatocyte-specific deletion of EP3 receptor (EP3^hep-/- ) results in hypercholesterolemia and augments diet-induced atherosclerosis in low-density lipoprotein receptor knockout (Ldlr^-/- ) mice. Cholesterol 7α-hydroxylase (CYP7A1) is down-regulated in livers of EP3^hep-/- Ldlr^-/- mice, leading to suppressed hepatic bile acid (BA) biosynthesis. Mechanistically, hepatic-EP3 deficiency suppresses CYP7A1 expression by elevating protein kinase A (PKA)-dependent Ser143 phosphorylation of hepatocyte nuclear receptor 4α (HNF4α). Disruption of the PKA-HNF4α interaction and BA sequestration rescue impaired BA excretion and ameliorated atherosclerosis in EP3^hep-/- Ldlr^-/- mice.

CONCLUSION

Our results demonstrated an unexpected role of proinflammatory mediator PGE₂ in improving hepatic cholesterol metabolism through activation of the EP3-mediated PKA/HNF4α/CYP7A1 pathway, indicating that inhibition of this pathway may be a novel therapeutic strategy for dyslipidemia and atherosclerosis. (Hepatology 2017;65:999-1014).

Cardiovascular Consequences of Prostanoid I Receptor Deletion in Microsomal Prostaglandin E Synthase-1-Deficient Hyperlipidemic Mice

BACKGROUND

Inhibitors of cyclooxygenase-2 alleviate pain and reduce fever and inflammation by suppressing the biosynthesis of prostacyclin (PGI2) and prostaglandin E2. However, suppression of these prostaglandins, particularly PGI2, by cyclooxygenase-2 inhibition or deletion of its I prostanoid receptor also predisposes to accelerated atherogenesis and thrombosis in mice. By contrast, deletion of microsomal prostaglandin E synthase 1 (mPGES-1) confers analgesia, attenuates atherogenesis, and fails to accelerate thrombogenesis, while suppressing prostaglandin E2, but increasing biosynthesis of PGI2.

METHODS

To address the cardioprotective contribution of PGI2, we generated mice lacking the I prostanoid receptor together with mPges-1 on a hyperlipidemic background (low-density lipoprotein receptor knockouts).

RESULTS

mPges-1 depletion modestly increased thrombogenesis, but this response was markedly further augmented by coincident deletion of the I prostanoid receptor (n=10-18). By contrast, deletion of the I prostanoid receptor had no effect on the attenuation of atherogenesis by mPGES-1 deletion in the low-density lipoprotein receptor knockout mice (n=17-21).

CONCLUSIONS

Although suppression of prostaglandin E2 accounts for the protective effect of mPGES-1 deletion in atherosclerosis, augmentation of PGI2 is the dominant contributor to its favorable thrombogenic profile. The divergent effects on these prostaglandins suggest that inhibitors of mPGES-1 may be less likely to cause cardiovascular adverse effects than nonsteroidal anti-inflammatory drugs specific for inhibition of cyclooxygenase-2.

The endothelial cyclooxygenase pathway: Insights from mouse arteries

To date, cyclooxygenase-2 (COX-2) is commonly believed to be the major mediator of endothelial prostacyclin (prostaglandin I2; PGI2) synthesis that balances the effect of thromboxane (Tx) A2 synthesis mediated by the other COX isoform, COX-1 in platelets. Accordingly, selective inhibition of COX-2 is considered to cause vasoconstriction, platelet aggregation, and hence increase the incidence of cardiovascular events. This idea has been claimed to be substantiated by experiments on mouse models, some of which are deficient in one of the two COX isoforms. However, results from our studies and those of others using similar mouse models suggest that COX-1 is the major functional isoform in vascular endothelium. Also, although PGI2 is recognized as a potent vasodilator, in some arteries endothelial COX activation causes vasoconstrictor response. This has again been recognized by studies, especially those performed on mouse arteries, to result largely from endothelial PGI2 synthesis. Therefore, evidence that supports a role for COX-1 as the major mediator of PGI2 synthesis in mouse vascular endothelium, reasons for the inconsistency, and results that elucidate underlying mechanisms for divergent vasomotor reactions to endothelial COX activation will be discussed in this review. In addition, we address the possible pathological implications and limitations of findings obtained from studies performed on mouse arteries.

Timing of expression of the core clock gene Bmal1 influences its effects on aging and survival

The absence of Bmal1, a core clock gene, results in a loss of circadian rhythms, an acceleration of aging, and a shortened life span in mice. To address the importance of circadian rhythms in the aging process, we generated conditional Bmal1 knockout mice that lacked the BMAL1 protein during adult life and found that wild-type circadian variations in wheel-running activity, heart rate, and blood pressure were abolished. Ocular abnormalities and brain astrogliosis were conserved irrespective of the timing of Bmal1 deletion. However, life span, fertility, body weight, blood glucose levels, and age-dependent arthropathy, which are altered in standard Bmal1 knockout mice, remained unaltered, whereas atherosclerosis and hair growth improved, in the conditional adult-life Bmal1 knockout mice, despite abolition of clock function. Hepatic RNA-Seq revealed that expression of oscillatory genes was dampened in the adult-life Bmal1 knockout mice, whereas overall gene expression was largely unchanged. Thus, many phenotypes in conventional Bmal1 knockout mice, hitherto attributed to disruption of circadian rhythms, reflect the loss of properties of BMAL1 that are independent of its role in the clock. These findings prompt reevaluation of the systemic consequences of disruption of the molecular clock.

Role of cyclooxygenase-1 and -2 in endothelium-dependent contraction of atherosclerotic mouse abdominal aortas

The objective of this study was to determine the role of cyclooxygenase (COX)-1 or -2 in endothelium-dependent contraction under atherosclerotic conditions. Atherosclerosis was induced in apoE knockout (apoE(-/-)) mice and those with COX-1(-/-) (apoE(-/-)-COX-1(-/-)) by feeding with high fat and cholesterol food. Aortas (abdominal or the whole section) were isolated for functional and/or biochemical analyses. As in non-atherosclerotic conditions, the muscarinic receptor agonist acetylcholine (ACh) evoked an endothelium-dependent, COX-mediated contraction following NO synthase (NOS) inhibition in abdominal aortic rings from atherosclerotic apoE(-/-) mice. Interestingly, COX-1 inhibition not only abolished such a contraction in rings showing normal appearance, but also diminished that in rings with plaques. Accordingly, only a minor contraction (<30% that of apoE(-/-) counterparts) was evoked by ACh (following NOS inhibition) in abdominal aortic rings of atherosclerotic apoE(-/-)-COX-1(-/-) mice with plaques, and none was evoked in those showing normal appearance. Also, the contraction evoked by ACh in apoE(-/-)-COX-1(-/-) abdominal aortic rings with plaques was abolished by non-selective COX inhibition, thromboxane-prostanoid (TP) receptor antagonism, or endothelial denudation. Moreover, it was noted that ACh evoked a predominant production of the prostacyclin (PGI2, which mediates abdominal aortic contraction via TP receptors in mice) metabolite 6-keto-PGF1α, which was again sensitive to COX-1 inhibition or COX-1(-/-). Therefore, in atherosclerotic mouse abdominal aortas, COX-1 can still be the major isoform mediating endothelium-dependent contraction, which probably results largely from PGI2 synthesis as in non-atherosclerotic conditions. In contrast, COX-2 may have only a minor role in such response limited to areas of plaques under the same pathological condition.

PGE2, Kidney Disease, and Cardiovascular Risk: Beyond Hypertension and Diabetes

An important measure of cardiovascular health is obtained by evaluating the global cardiovascular risk, which comprises a number of factors, including hypertension and type 2 diabetes, the leading causes of illness and death in the world, as well as the metabolic syndrome. Altered immunity, inflammation, and oxidative stress underlie many of the changes associated with cardiovascular disease, diabetes, and the metabolic syndrome, and recent efforts have begun to elucidate the contribution of PGE2 in these events. This review summarizes the role of PGE2 in kidney disease outcomes that accelerate cardiovascular disease, highlights the role of cyclooxygenase-2/microsomal PGE synthase 1/PGE2 signaling in hypertension and diabetes, and outlines the contribution of PGE2 to other aspects of the metabolic syndrome, particularly abdominal adiposity, dyslipidemia, and atherogenesis. A clearer understanding of the role of PGE2 could lead to new avenues to improve therapeutic options and disease management strategies.

The role of lipoxygenases in pathophysiology; new insights and future perspectives

Lipoxygenases (LOXs) are dioxygenases that catalyze the formation of corresponding hydroperoxides from polyunsaturated fatty acids such as linoleic acid and arachidonic acid. LOX enzymes are expressed in immune, epithelial, and tumor cells that display a variety of physiological functions, including inflammation, skin disorder, and tumorigenesis. In the humans and mice, six LOX isoforms have been known. 15-LOX, a prototypical enzyme originally found in reticulocytes shares the similarity of amino acid sequence as well as the biochemical property to plant LOX enzymes. 15-LOX-2, which is expressed in epithelial cells and leukocytes, has different substrate specificity in the humans and mice, therefore, the role of them in mammals has not been established. 12-LOX is an isoform expressed in epithelial cells and myeloid cells including platelets. Many mutations in this isoform are found in epithelial cancers, suggesting a potential link between 12-LOX and tumorigenesis. 12R-LOX can be found in the epithelial cells of the skin. Defects in this gene result in ichthyosis, a cutaneous disorder characterized by pathophysiologically dried skin due to abnormal loss of water from its epithelial cell layer. Similarly, eLOX-3, which is also expressed in the skin epithelial cells acting downstream 12R-LOX, is another causative factor for ichthyosis. 5-LOX is a distinct isoform playing an important role in asthma and inflammation. This isoform causes the constriction of bronchioles in response to cysteinyl leukotrienes such as LTC4, thus leading to asthma. It also induces neutrophilic inflammation by its recruitment in response to LTB4. Importantly, 5-LOX activity is strictly regulated by 5-LOX activating protein (FLAP) though the distribution of 5-LOX in the nucleus. Currently, pharmacological drugs targeting FLAP are actively developing. This review summarized these functions of LOX enzymes under pathophysiological conditions in mammals.

Anti-inflammatory therapies for atherosclerosis

The view of atherosclerosis as an inflammatory disease has emerged from observations of immune activation and inflammatory signalling in human atherosclerotic lesions, from the definition of inflammatory biomarkers as independent risk factors for cardiovascular events, and from evidence of low-density lipoprotein-induced immune activation. Studies in animal models of hyperlipidaemia have also supported the beneficial effects of countering inflammation to delay atherosclerosis progression. Specific inflammatory pathways with relevance to human diseases have been identified, and inhibitors of these pathways are either already in use for the treatment of other diseases, or are under development and evaluation. These include 'classic' drugs (such as allopurinol, colchicine, and methotrexate), biologic therapies (for example tumour necrosis factor inhibitors and IL-1 neutralization), as well as targeting of lipid mediators (such as phospholipase inhibitors and antileukotrienes) or intracellular pathways (inhibition of NADPH oxidase, p38 mitogen-activated protein kinase, or phosphodiesterase). The evidence supporting the use of anti-inflammatory therapies for atherosclerosis is mainly based on either observational or small interventional studies evaluating surrogate markers of disease activity. Nevertheless, these data are crucial to understand the role of inflammation in atherosclerosis, and to design randomized controlled studies to evaluate the effect of specific anti-inflammatory strategies on cardiovascular outcomes.

COX-2 protects against atherosclerosis independently of local vascular prostacyclin: identification of COX-2 associated pathways implicate Rgl1 and lymphocyte networks

Cyxlo-oxygenase (COX)-2 inhibitors, including traditional nonsteroidal anti-inflammatory drugs (NSAIDs) are associated with increased cardiovascular side effects, including myocardial infarction. We and others have shown that COX-1 and not COX-2 drives vascular prostacyclin in the healthy cardiovascular system, re-opening the question of how COX-2 might regulate cardiovascular health. In diseased, atherosclerotic vessels, the relative contribution of COX-2 to prostacyclin formation is not clear. Here we have used apoE(-/-)/COX-2(-/-) mice to show that, whilst COX-2 profoundly limits atherosclerosis, this protection is independent of local prostacyclin release. These data further illustrate the need to look for new explanations, targets and pathways to define the COX/NSAID/cardiovascular risk axis. Gene expression profiles in tissues from apoE(-/-)/COX-2(-/-) mice showed increased lymphocyte pathways that were validated by showing increased T-lymphocytes in plaques and elevated plasma Th1-type cytokines. In addition, we identified a novel target gene, rgl1, whose expression was strongly reduced by COX-2 deletion across all examined tissues. This study is the first to demonstrate that COX-2 protects vessels against atherosclerotic lesions independently of local vascular prostacyclin and uses systems biology approaches to identify new mechanisms relevant to development of next generation NSAIDs.

Myeloid cell microsomal prostaglandin E synthase-1 fosters atherogenesis in mice

Microsomal prostaglandin E synthase-1 (mPGES-1) in myeloid and vascular cells differentially regulates the response to vascular injury, reflecting distinct effects of mPGES-1-derived PGE2 in these cell types on discrete cellular components of the vasculature. The cell selective roles of mPGES-1 in atherogenesis are unknown. Mice lacking mPGES-1 conditionally in myeloid cells (Mac-mPGES-1-KOs), vascular smooth muscle cells (VSMC-mPGES-1-KOs), or endothelial cells (EC-mPGES-1-KOs) were crossed into hyperlipidemic low-density lipoprotein receptor-deficient animals. En face aortic lesion analysis revealed markedly reduced atherogenesis in Mac-mPGES-1-KOs, which was concomitant with a reduction in oxidative stress, reflective of reduced macrophage infiltration, less lesional expression of inducible nitric oxide synthase (iNOS), and lower aortic expression of NADPH oxidases and proinflammatory cytokines. Reduced oxidative stress was reflected systemically by a decline in urinary 8,12-iso-iPF2α-VI. In contrast to exaggeration of the response to vascular injury, deletion of mPGES-1 in VSMCs, ECs, or both had no detectable phenotypic impact on atherogenesis. Macrophage foam cell formation and cholesterol efflux, together with plasma cholesterol and triglycerides, were unchanged as a function of genotype. In conclusion, myeloid cell mPGES-1 promotes atherogenesis in hyperlipidemic mice, coincident with iNOS-mediated oxidative stress. By contrast, mPGES-1 in vascular cells does not detectably influence atherogenesis in mice. This strengthens the therapeutic rationale for targeting macrophage mPGES-1 in inflammatory cardiovascular diseases.

Cyclooxygenase-2 in endothelial and vascular smooth muscle cells restrains atherogenesis in hyperlipidemic mice

BACKGROUND

Placebo-controlled trials of nonsteroidal anti-inflammatory drugs selective for inhibition of cyclooxygenase-2 (COX-2) reveal an emergent cardiovascular hazard in patients selected for low risk of heart disease. Postnatal global deletion of COX-2 accelerates atherogenesis in hyperlipidemic mice, a process delayed by selective enzyme deletion in macrophages.

METHODS AND RESULTS

In the present study, selective depletion of COX-2 in vascular smooth muscle cells and endothelial cells depressed biosynthesis of prostaglandin I2 and prostaglandin E2, elevated blood pressure, and accelerated atherogenesis in Ldlr knockout mice. Deletion of COX-2 in vascular smooth muscle cells and endothelial cells coincided with an increase in COX-2 expression in lesional macrophages and increased biosynthesis of thromboxane. Increased accumulation of less organized intimal collagen, laminin, α-smooth muscle actin, and matrix-rich fibrosis was also apparent in lesions of the mutants.

CONCLUSIONS

Although atherogenesis is accelerated in global COX-2 knockouts, consistent with evidence of risk transformation during chronic nonsteroidal anti-inflammatory drug administration, this masks the contrasting effects of enzyme depletion in macrophages versus vascular smooth muscle cells and endothelial cells. Targeting delivery of COX-2 inhibitors to macrophages may conserve their efficacy while limiting cardiovascular risk.

Genetic ablation of 12/15-lipoxygenase but not 5-lipoxygenase protects against denervation-induced muscle atrophy

Skeletal muscle atrophy is a debilitating outcome of a number of chronic diseases and conditions associated with loss of muscle innervation by motor neurons, such as aging and neurodegenerative diseases. We previously reported that denervation-induced loss of muscle mass is associated with activation of cytosolic phospholipase A2 (cPLA2), the rate-limiting step for the release of arachidonic acid from membrane phospholipids, which then acts as a substrate for metabolic pathways that generate bioactive lipid mediators. In this study, we asked whether 5- and 12/15-lipoxygenase (LO) lipid metabolic pathways downstream of cPLA2 mediate denervation-induced muscle atrophy in mice. Both 5- and 12/15-LO were activated in response to surgical denervation; however, 12/15-LO activity was increased ~2.5-fold versus an ~1.5-fold increase in activity of 5-LO. Genetic and pharmacological inhibition of 12/15-LO (but not 5-LO) significantly protected against denervation-induced muscle atrophy, suggesting a selective role for the 12/15-LO pathway in neurogenic muscle atrophy. The activation of the 12/15-LO pathway (but not 5-LO) during muscle atrophy increased NADPH oxidase activity, protein ubiquitination, and ubiquitin-proteasome-mediated proteolytic degradation. In conclusion, this study reveals a novel pathway for neurogenic muscle atrophy and suggests that 12/15-LO may be a potential therapeutic target in diseases associated with loss of innervation and muscle atrophy.

The adverse effect of selective cyclooxygenase-2 inhibitor on random skin flap survival in rats

BACKGROUND

Cyclooxygenase-2(COX-2) inhibitors provide desired analgesic effects after injury or surgery, but evidences suggested they also attenuate wound healing. The study is to investigate the effect of COX-2 inhibitor on random skin flap survival.

METHODS

The McFarlane flap model was established in 40 rats and evaluated within two groups, each group gave the same volume of Parecoxib and saline injection for 7 days. The necrotic area of the flap was measured, the specimens of the flap were stained with haematoxylin-eosin(HE) for histologic analysis. Immunohistochemical staining was performed to analyse the level of VEGF and COX-2 .

RESULTS

7 days after operation, the flap necrotic area ratio in study group (66.65 ± 2.81)% was significantly enlarged than that of the control group(48.81 ± 2.33)%(P <0.01). Histological analysis demonstrated angiogenesis with mean vessel density per mm(2) being lower in study group (15.4 ± 4.4) than in control group (27.2 ± 4.1) (P <0.05). To evaluate the expression of COX-2 and VEGF protein in the intermediate area II in the two groups by immunohistochemistry test .The expression of COX-2 in study group was (1022.45 ± 153.1), and in control group was (2638.05 ± 132.2) (P <0.01). The expression of VEGF in the study and control groups were (2779.45 ± 472.0) vs (4938.05 ± 123.6)(P <0.01).In the COX-2 inhibitor group, the expressions of COX-2 and VEGF protein were remarkably down-regulated as compared with the control group.

CONCLUSION

Selective COX-2 inhibitor had adverse effect on random skin flap survival. Suppression of neovascularization induced by low level of VEGF was supposed to be the biological mechanism.

Cardiovascular disease and non-steroidal anti-inflammatory drug prescribing in the midst of evolving guidelines

RATIONALE, AIMS AND OBJECTIVES

Responding to safety concerns, the American Heart Association (AHA) published guidelines for non-steroidal anti-inflammatory drug (NSAID) use in patients with pre-existing cardiovascular disease (CVD) during 2005 and revised them in 2007. In the revision, a stepped approach to pain management recommended non-selective NSAIDs over highly selective NSAIDs. This research evaluated NSAID prescribing during and after guideline dissemination.

METHOD

A cross-sectional sample of 8666 adult, community-based practice visits with one NSAID prescription representing approximately 305 million visits from the National Ambulatory Medical Care Survey (NAMCS) from 2005 to 2010 was studied. Multivariable logistic regression controlling for patient, provider and visit characteristics assessed the associations between diagnosis of CVD and NSAID type prescribed during each calendar year. Visits were stratified by arthritis diagnosis to model short-term/intermittent and long-term NSAID use.

RESULTS

Approximately one-third (36.8%) of visits involving a NSAID prescription included at least one of four diagnoses for CVD (i.e. hypertension, congestive heart failure, ischaemic heart disease or cerebrovascular disease). Visits involving a CVD diagnosis had increased odds of a prescription for celecoxib, a highly selective NSAIDs, overall [adjusted odds ratio (AOR) = 1.29, 95% confidence interval (CI): 1.06-1.57] and in the subgroup of visits without an arthritis diagnosis (AOR = 1.45, 95% CI: 1.11-1.89). Results were not statistically significant for visits with an arthritis diagnosis (AOR = 1.10, 95% CI: 0.47-2.57). When analysed by year, the relationship was statistically significant in 2005 and 2006, but not statistically significant in each subsequent year.

CONCLUSION

National prescribing trends suggest partial implementation of AHA guidelines for NSAID prescribing in CVD from 2005 to 2010.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Targeting leukotriene B4 in inflammation

INTRODUCTION

Leukotriene (LT) B(4) is a powerful proinflammatory lipid mediator and triggers adherence to the endothelium, activates and recruits leukocytes to the site of injury. When formed in excess, LTB(4) plays a pathogenic role and may sustain chronic inflammation in diseases such as asthma, rheumatoid arthritis, and inflammatory bowel disease. Recent investigations have also indicated that LTB(4) is involved in cardiovascular diseases.

AREAS COVERED

As the 5-lipoxygenase pathway involves several discrete, tightly coupled, enzymes, which convert the substrate, 'step by step', into bioactive products, several different strategies have been used to target LTB(4) as a means to treat inflammation. Here, we discuss recent findings regarding the development of selective enzyme inhibitors and antagonists for LTB(4) receptors, as well as their application in preclinical and clinical studies.

EXPERT OPINION

Components of the 5-lipoxygenase pathway have received considerable attention as candidate drug targets resulting in one new class of medications against asthma, that is, the antileukotrienes. However, efforts to specifically target LTB(4) have not yet been fruitful in the clinical setting, in spite of very promising preclinical data. Recently, crystal structures along with hitherto unknown functions of key enzymes in the leukotriene cascade have emerged, offering new opportunities for drug development and, with time, pharmacological intervention in LTB(4)-mediated pathologies.

LC-MS/MS confirms that COX-1 drives vascular prostacyclin whilst gene expression pattern reveals non-vascular sites of COX-2 expression

There are two schools of thought regarding the cyclooxygenase (COX) isoform active in the vasculature. Using urinary prostacyclin markers some groups have proposed that vascular COX-2 drives prostacyclin release. In contrast, we and others have found that COX-1, not COX-2, is responsible for vascular prostacyclin production. Our experiments have relied on immunoassays to detect the prostacyclin breakdown product, 6-keto-PGF_1α and antibodies to detect COX-2 protein. Whilst these are standard approaches, used by many laboratories, antibody-based techniques are inherently indirect and have been criticized as limiting the conclusions that can be drawn. To address this question, we measured production of prostanoids, including 6-keto-PGF_1α, by isolated vessels and in the circulation in vivo using liquid chromatography tandem mass spectrometry and found values essentially identical to those obtained by immunoassay. In addition, we determined expression from the Cox2 gene using a knockin reporter mouse in which luciferase activity reflects Cox2 gene expression. Using this we confirm the aorta to be essentially devoid of Cox2 driven expression. In contrast, thymus, renal medulla, and regions of the brain and gut expressed substantial levels of luciferase activity, which correlated well with COX-2-dependent prostanoid production. These data are consistent with the conclusion that COX-1 drives vascular prostacyclin release and puts the sparse expression of Cox2 in the vasculature in the context of the rest of the body. In doing so, we have identified the thymus, gut, brain and other tissues as target organs for consideration in developing a new understanding of how COX-2 protects the cardiovascular system.

Effect of zileuton and celecoxib on urinary LTE4 and PGE-M levels in smokers

COX-2 and 5-lipoxygenase (5-LO) use arachidonic acid for the synthesis of eicosanoids that have been implicated in carcinogenesis and cardiovascular disease. The ability of celecoxib, a selective COX-2 inhibitor, to redirect arachidonic acid into the 5-LO pathway can potentially reduce its efficacy as a chemopreventive agent and increase the risk of cardiovascular complications. Levels of urinary prostaglandin E metabolite (PGE-M) and leukotriene E4 (LTE4), biomarkers of the COX and 5-LO pathways, are elevated in smokers. Here, we investigated the effects of zileuton, a 5-LO inhibitor, versus zileuton and celecoxib for 6 ± 1 days on urinary PGE-M and LTE4 levels in smokers. Treatment with zileuton led to an 18% decrease in PGE-M levels (P = 0.03); the combination of zileuton and celecoxib led to a 62% reduction in PGE-M levels (P < 0.001). Levels of LTE4 decreased by 61% in subjects treated with zileuton alone (P < 0.001) and were unaffected by the addition of celecoxib. Although zileuton use was associated with a small overall decrease in PGE-M levels, increased PGE-M levels were found in a subset (19 of 52) of subjects. Notably, the addition of celecoxib to the 5-LO inhibitor protected against the increase in urinary PGE-M levels (P = 0.03). In conclusion, zileuton was an effective inhibitor of 5-LO activity resulting in marked suppression of urinary LTE4 levels and possible redirection of arachidonic acid into the COX-2 pathway in a subset of subjects. Combining celecoxib and zileuton was associated with inhibition of both the COX-2 and 5-LO pathways manifested as reduced levels of urinary PGE-M and LTE4.

Myeloid cell 5-lipoxygenase activating protein modulates the response to vascular injury

RATIONALE

Human genetics have implicated the 5-lipoxygenase enzyme in the pathogenesis of cardiovascular disease, and an inhibitor of the 5-lipoxygenase activating protein (FLAP) is in clinical development for asthma.

OBJECTIVE

Here we determined whether FLAP deletion modifies the response to vascular injury.

METHODS AND RESULTS

Vascular remodeling was characterized 4 weeks after femoral arterial injury in FLAP knockout mice and wild-type controls. Both neointimal hyperplasia and the intima/media ratio of the injured artery were significantly reduced in the FLAP knockouts, whereas endothelial integrity was preserved. Lesional myeloid cells were depleted and vascular smooth muscle cell (VSMC) proliferation, as reflected by bromodeoxyuridine incorporation, was markedly attenuated by FLAP deletion. Inflammatory cytokine release from FLAP knockout macrophages was depressed, and their restricted ability to induce VSMC migration ex vivo was rescued with leukotriene B(4). FLAP deletion restrained injury and attenuated upregulation of the extracellular matrix protein, tenascin C, which affords a scaffold for VSMC migration. Correspondingly, the phenotypic modulation of VSMC to a more synthetic phenotype, reflected by morphological change, loss of α-smooth muscle cell actin, and upregulation of vascular cell adhesion molecule-1 was also suppressed in FLAP knockout mice. Transplantation of FLAP-replete myeloid cells rescued the proliferative response to vascular injury.

CONCLUSIONS

Expression of lesional FLAP in myeloid cells promotes leukotriene B(4)-dependent VSMC phenotypic modulation, intimal migration, and proliferation.

Vascular COX-2 modulates blood pressure and thrombosis in mice

Prostacyclin (PGI(2)) is a vasodilator and platelet inhibitor, properties consistent with cardioprotection. More than a decade ago, inhibition of cyclooxygenase-2 (COX-2) by the nonsteroidal anti-inflammatory drugs (NSAIDs) rofecoxib and celecoxib was found to reduce the amount of the major metabolite of PGI(2) (PGI-M) in the urine of healthy volunteers. This suggested that NSAIDs might cause adverse cardiovascular events by reducing production of cardioprotective PGI(2). This prediction was based on the assumption that the concentration of PGI-M in urine likely reflected vascular production of PGI(2) and that other cardioprotective mediators, especially nitric oxide (NO), were not able to compensate for the loss of PGI(2). Subsequently, eight placebo-controlled clinical trials showed that NSAIDs that block COX-2 increase adverse cardiovascular events. We connect tissue-specific effects of NSAID action and functional correlates in mice with clinical outcomes in humans by showing that deletion of COX-2 in the mouse vasculature reduces excretion of PGI-M in urine and predisposes the animals to both hypertension and thrombosis. Furthermore, vascular disruption of COX-2 depressed expression of endothelial NO synthase and the consequent release and function of NO. Thus, suppression of PGI(2) formation resulting from deletion of vascular COX-2 is sufficient to explain the cardiovascular hazard from NSAIDs, which is likely to be augmented by secondary mechanisms such as suppression of NO production.

Cyclooxygenase-1, not cyclooxygenase-2, is responsible for physiological production of prostacyclin in the cardiovascular system

Prostacyclin is an antithrombotic hormone produced by the endothelium, whose production is dependent on cyclooxygenase (COX) enzymes of which two isoforms exist. It is widely believed that COX-2 drives prostacyclin production and that this explains the cardiovascular toxicity associated with COX-2 inhibition, yet the evidence for this relies on indirect evidence from urinary metabolites. Here we have used a range of experimental approaches to explore which isoform drives the production of prostacyclin in vitro and in vivo. Our data show unequivocally that under physiological conditions it is COX-1 and not COX-2 that drives prostacyclin production in the cardiovascular system, and that urinary metabolites do not reflect prostacyclin production in the systemic circulation. With the idea that COX-2 in endothelium drives prostacyclin production in healthy individuals removed, we must seek new answers to why COX-2 inhibitors increase the risk of cardiovascular events to move forward with drug discovery and to enable more informed prescribing advice.