Cyclooxygenase-1 deficiency in bone marrow cells increases early atherosclerosis in apolipoprotein E- and low-density lipoprotein receptor-null mice

The novel thromboxane prostanoid receptor mediates CTGF production to drive human nasal fibroblast self-migration through NF-κB and PKCδ-CREB signaling pathways

Chronic rhinosinusitis without nasal polyp (CRSsNP) is characterized by tissue repair/remodeling and the subepithelial stroma region in whose nasal mucosa has been reported by us to have thromboxane A2 (TXA2) prostanoid (TP) receptor and overexpress connective tissue growth factor (CTGF). Therefore, this study aimed to investigate the relationship between TP receptor activation and CTGF production/function in human CRSsNP nasal mucosa stromal fibroblasts. We found that TP agonists including U46619 and IBOP ([1S-[1α,2α(Z),3β(1E,3 S*),4α]]-7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid) could promote CTGF protein/messenger RNA expression and secretion. The pharmacological intervention and TP activation assay with U46619 identified the possible participation of PKCμ, PKCδ, nuclear factor-κB (NF-κB), and cyclic AMP response element-binding protein (CREB) phosphorylation/activation in the CTGF induction. Moreover, a phorbol ester-phorbol-12-myristate 13-acetate (PMA) exhibited a similar cellular signaling and CTGF production profile to that elicited by TP activation. However, further small interfering RNA interference analysis revealed that only NF-κB and PKCδ-CREB pathways were necessarily required for TP-mediated CTGF production, which could not be completely supported by those findings from PMA. Finally, in a functional assay, although CTGF did not affect fibroblast proliferation, TP-mediated CTGF could drive novel self-migration in fibroblasts both in the scratch/wound healing and transwell apparatus assays. Meanwhile, the overall staining for stress fibers and formation of the lamellipodia and filopodia-like structures was concomitantly increased in the treated migrating cells. Collectively, we provided here that novel TP mediates CTGF production and self-migration in human nasal fibroblasts through NF-κB and PKCδ-CREB signaling pathways. More importantly, we also demonstrated that thromboxane, TP receptor, CTGF, and stromal fibroblasts may act in concert in the tissue remodeling/repair process during CRSsNP development and progression.

Emerging Roles and Therapeutic Applications of Arachidonic Acid Pathways in Cardiometabolic Diseases

Cardiometabolic disease has become a major health burden worldwide, with sharply increasing prevalence but highly limited therapeutic interventions. Emerging evidence has revealed that arachidonic acid derivatives and pathway factors link metabolic disorders to cardiovascular risks and intimately participate in the progression and severity of cardiometabolic diseases. In this review, we systemically summarized and updated the biological functions of arachidonic acid pathways in cardiometabolic diseases, mainly focusing on heart failure, hypertension, atherosclerosis, nonalcoholic fatty liver disease, obesity, and diabetes. We further discussed the cellular and molecular mechanisms of arachidonic acid pathway-mediated regulation of cardiometabolic diseases and highlighted the emerging clinical advances to improve these pathological conditions by targeting arachidonic acid metabolites and pathway factors.

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.

Endothelium-dependent contraction: The non-classical action of endothelial prostacyclin, its underlying mechanisms, and implications

Although commonly thought to produce prostacyclin (prostaglandin I₂ ; PGI₂ ) that evokes vasodilatation and protects vessels from the development of diseases, the endothelial cyclooxygenase (COX)-mediated metabolism has also been found to release substance(s) called endothelium-derived contracting factor(s) (EDCF) that causes endothelium-dependent contraction and implicates in endothelial dysfunction of disease conditions. Various mechanisms have been proposed for the process; however, the major endothelial COX metabolite PGI₂ , which has been classically considered to activate the I prostanoid receptor (IP) that mediates vasodilatation and opposes the effects of thromboxane (Tx) A₂ produced by COX in platelets, emerges as a major EDCF in health and disease conditions. Our recent studies from genetically altered mice further suggest that vasomotor reactions to PGI₂ are collectively modulated by IP, the vasoconstrictor Tx-prostanoid receptor (TP; the prototype receptor of TxA₂ ) and E prostanoid receptor-3 (EP3; a vasoconstrictor receptor of PGE₂ ) although with differences in potency and efficacy; a contraction to PGI₂ reflects activities of TP and/or EP3 outweighing that of the concurrently activated IP. Here, we discuss the history of endothelium-dependent contraction, evidences that support the above hypothesis, proposed mechanisms for the varied reactions to endothelial PGI₂ synthesis as well as the relation of its dilator activity to the effect of another NO-independent vasodilator mechanism, the endothelium-derived hyperpolarizing factor. Also, we address the possible pathological and therapeutic implications as well as questions remaining to be resolved or limitations of our above findings obtained from genetically altered mouse models.

Endothelial cyclooxygenase-1 paradoxically drives local vasoconstriction and atherogenesis despite underpinning prostacyclin generation

Endothelial cyclooxygenase-1-derived prostanoids, including prostacyclin, have clear cardioprotective roles associated with their anti-thrombotic potential but have also been suggested to have paradoxical pathological activities within arteries. To date it has not been possible to test the importance of this because no models have been available that separate vascular cyclooxygenase-1 products from those generated elsewhere. Here, we have used unique endothelial-specific cyclooxygenase-1 knockout mice to show that endothelial cyclooxygenase-1 produces both protective and pathological products. Functionally, however, the overall effect of these was to drive pathological responses in the context of both vasoconstriction in vitro and the development of atherosclerosis and vascular inflammation in vivo. These data provide the first demonstration of a pathological role for the vascular cyclooxygenase-1 pathway, highlighting its potential as a therapeutic target. They also emphasize that, across biology, the role of prostanoids is not always predictable due to unique balances of context, products, and receptors.

Rare earth element lanthanum protects against atherosclerosis induced by high-fat diet via down-regulating MAPK and NF-κB pathways

Rare earth elements, which are extensively used in environmental protection, medicine, food, aerospace and other fields, have attracted widespread attention in recent years. However, the effect on atherosclerosis and its biological mechanism remains unclear. To elucidate these problems, here we performed a study that Apolipoprotein E-deficient mice were fed with high-fat diet to promote the development of atherosclerosis, meanwhile, mice were received 0.1, 0.2, 1.0, 2.0 mg/kg lanthanum nitrate (La(NO₃)₃) for 12 weeks. The results showed that La(NO₃)₃ prominently inhibited aorta morphological alternations by histopathological examination. Meanwhile, La(NO₃)₃ regulated serum lipids, including reducing total cholesterol and increasing high-density lipoprotein. Moreover, the oxidative stress was alleviated by La(NO₃)₃ intervention through enhancing superoxide dismutase and glutathione, and decreasing malondialdehyde levels. In addition, enzyme-linked immunosorbent assay analysis showed La(NO₃)₃ could ameliorate the dysfunction of vascular endothelium with declined endothelin-1 and increased prostacyclin. Furthermore, Western blot analysis indicated that La(NO₃)₃ significantly down-regulated inflammation-mediated proteins including phosphorylated p38 mitogen-activated protein kinases (p-p38 MAPK), monocyte chemo-attractant protein, intercellular adhesion molecule-1, nuclear factor-kappa B p65 (NF-κB p65), tumor necrosis factor-α, interleukin-6 and interleukin-1β, whereas up-regulated the inhibitor of NF-κB protein. In conclusion, La(NO₃)₃ ameliorates atherosclerosis by regulating lipid metabolism, oxidative stress, endothelial dysfunction and inflammatory response in mice. The potential mechanism associates with the inhibition of MAPK and NF-κB signaling pathways.

Cardiovascular Biology of Prostanoids and Drug Discovery

Prostanoids are a group of bioactive lipids that are synthesized de novo from membrane phospholipid-released arachidonic acid and have diverse functions in normal physiology and disease. NSAIDs (non-steroidal anti-inflammatory drugs), which are among the most commonly used medications, ameliorate pain, fever, and inflammation by inhibiting COX (cyclooxygenase), which is the rate-limiting enzyme in the biosynthetic cascade of prostanoids. The use of NSAIDs selective for COX-2 inhibition increases the risk of a thrombotic event (eg, myocardial infarction and stroke). All NSAIDs are associated with an increased risk of heart failure. Substantial variation in clinical responses to aspirin exists and is associated with cardiovascular risk. Limited clinical studies suggest the involvement of prostanoids in vascular restenosis in patients who received angioplasty intervention. mPGES (microsomal PG [prostaglandin] E synthase)-1, an alternative target downstream of COX, has the potential to be therapeutically targeted for inflammatory disease, with diminished thrombotic risk relative to selective COX-2 inhibitors. mPGES-1-derived PGE₂ critically regulates microcirculation via its receptor EP (receptor for prostanoid E) 4. This review summarizes the actions and associated mechanisms for modulating the biosynthesis of prostanoids in thrombosis, vascular remodeling, and ischemic heart disease as well as their therapeutic relevance.

Role of reactive oxygen species in atherosclerosis: Lessons from murine genetic models

Atherosclerosis is a multifactorial chronic and inflammatory disease of medium and large arteries, and the major cause of cardiovascular morbidity and mortality worldwide. The pathogenesis of atherosclerosis involves a number of risk factors and complex events including hypercholesterolemia, endothelial dysfunction, increased permeability to low density lipoproteins (LDL) and their sequestration on extracellular matrix in the intima of lesion-prone areas. These events promote LDL modifications, particularly by oxidation, which generates acute and chronic inflammatory responses implicated in atherogenesis and lesion progression. Reactive oxygen species (ROS) (which include both free radical and non-free radical oxygen intermediates), play a key-role at each step of atherogenesis, in endothelial dysfunction, LDL oxidation, and inflammatory events involved in the initiation and development of atherosclerosis lesions. Most advanced knowledge supporting the "oxidative theory of atherosclerosis" i.e. the nature and the cellular sources of ROS and antioxidant defences, as well as the mechanisms involved in the redox balance, is based on the use of genetically engineered animals, i.e. transgenic, genetically modified, or altered for systems producing or neutralizing ROS in the vessels. This review summarizes the results obtained from animals genetically manipulated for various sources of ROS or antioxidant defences in the vascular wall, and their relevance (advance or limitation), for understanding the place and role of ROS in atherosclerosis.

Role of thromboxane A2 signaling in endothelium-dependent contractions of arteries

Thromboxane A₂ (TxA₂) plays a very important role in various cardiovascular diseases through its action on platelet aggregation, vasoconstriction, and proliferation. The present article focuses on the role of TxA₂ signaling in endothelium-dependent contractions of arteries. Arachidonic acid (AA) is metabolized by cyclooxygenase (COX) to form the unstable prostaglandin H₂ which is further converted into TxA₂. After being produced by thromboxane synthase (TxAS), TxA₂ ultimately stimulates TxA₂/prostanoid (TP) receptor to induce vasoconstriction. The calcium ionophore A23187, the prostanoid precursor AA, or the muscarinic receptor agonist acetylcholine (ACh) can evoke endothelium-dependent contractions associated with TxA₂. The endothelium-dependent contractions shown in hypertension, diabetes, atherogenesis, and other cardiovascular diseases have been significantly reduced by antagonism of COX, TxAS, or TP receptor. So inhibition of the bioavailability and/or effect of TxA₂ may be promising therapeutic targets to prevent these diseases. Especially some bioactive compounds isolated from medicinal plants will provide new pharmacological approaches to promote vascular health.

Recommendation on Design, Execution, and Reporting of Animal Atherosclerosis Studies: A Scientific Statement From the American Heart Association

Animal studies are a foundation for defining mechanisms of atherosclerosis and potential targets of drugs to prevent lesion development or reverse the disease. In the current literature, it is common to see contradictions of outcomes in animal studies from different research groups, leading to the paucity of extrapolations of experimental findings into understanding the human disease. The purpose of this statement is to provide guidelines for development and execution of experimental design and interpretation in animal studies. Recommendations include the following: (1) animal model selection, with commentary on the fidelity of mimicking facets of the human disease; (2) experimental design and its impact on the interpretation of data; and (3) standard methods to enhance accuracy of measurements and characterization of atherosclerotic lesions.

Recommendation on Design, Execution, and Reporting of Animal Atherosclerosis Studies: A Scientific Statement From the American Heart Association

Animal studies are a foundation for defining mechanisms of atherosclerosis and potential targets of drugs to prevent lesion development or reverse the disease. In the current literature, it is common to see contradictions of outcomes in animal studies from different research groups, leading to the paucity of extrapolations of experimental findings into understanding the human disease. The purpose of this statement is to provide guidelines for development and execution of experimental design and interpretation in animal studies. Recommendations include the following: (1) animal model selection, with commentary on the fidelity of mimicking facets of the human disease; (2) experimental design and its impact on the interpretation of data; and (3) standard methods to enhance accuracy of measurements and characterization of atherosclerotic lesions.

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.

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.

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.

CD36-dependent 7-ketocholesterol accumulation in macrophages mediates progression of atherosclerosis in response to chronic air pollution exposure

RATIONALE

Air pollution exposure has been shown to potentiate plaque progression in humans and animals. Our previous studies have suggested a role for oxidized lipids in mediating adverse vascular effect of air pollution. However, the types of oxidized lipids formed in response to air pollutants and how this occurs and their relevance to atherosclerosis are not fully understood.

OBJECTIVE

To investigate the mechanisms by which particulate matter <2.5 μm (PM2.5) induces progression of atherosclerosis.

METHODS AND RESULTS

Atherosclerosis-prone ApoE(-/-) or LDLR(-/-) mice were exposed to filtered air or concentrated ambient PM2.5 using a versatile aerosol concentrator enrichment system for 6 months. PM2.5 increased 7-ketocholesterol (7-KCh), an oxidatively modified form of cholesterol, in plasma intermediate density lipoprotein/low-density lipoprotein fraction and in aortic plaque concomitant with progression of atherosclerosis and increased CD36 expression in plaque macrophages from PM2.5-exposed mice. Macrophages isolated from PM2.5-exposed mice displayed increased uptake of oxidized lipids without alterations in their efflux capacity. Consistent with these finding, CD36-positive macrophages displayed a heightened capacity for oxidized lipid uptake. Deficiency of CD36 on hematopoietic cells diminished the effect of air pollution on 7-KCh accumulation, foam cell formation, and atherosclerosis.

CONCLUSIONS

Our results suggest a potential role for CD36-mediated abnormal accumulations of oxidized lipids, such as 7-KCh, in air pollution-induced atherosclerosis progression.

Impact of hematopoietic cyclooxygenase-1 deficiency on obesity-linked adipose tissue inflammation and metabolic disorders in mice

OBJECTIVE

Adipose tissue (AT)-specific inflammation is considered to mediate the pathological consequences of obesity and macrophages are known to activate inflammatory pathways in obese AT. Because cyclooxygenases play a central role in regulating the inflammatory processes, we sought to determine the role of hematopoietic cyclooxygenase-1 (COX-1) in modulating AT inflammation in obesity.

MATERIALS/METHODS

Bone marrow transplantation was performed to delete COX-1 in hematopoietic cells. Briefly, female wild type (wt) mice were lethally irradiated and injected with bone marrow (BM) cells collected from wild type (COX-1+/+) or COX-1 knock-out (COX-1-/-) donor mice. The mice were fed a high fat diet for 16 weeks.

RESULTS

The mice that received COX-1-/- bone marrow (BM-COX-1-/-) exhibited a significant increase in fasting glucose, total cholesterol and triglycerides in the circulation compared to control (BM-COX-1+/+) mice. Markers of AT-inflammation were increased and were associated with increased leptin and decreased adiponectin in plasma. Hepatic inflammation was reduced with a concomitant reduction in TXB2 levels. The hepatic mRNA expression of genes involved in lipogenesis and lipid transport was increased while expression of genes involved in regulating hepatic glucose output was reduced in BM-COX-1-/- mice. Finally, renal inflammation and markers of renal glucose release were increased in BM-COX-1-/- mice.

CONCLUSION

Hematopoietic COX-1 deletion results in impairments in metabolic homeostasis which may be partly due to increased AT inflammation and dysregulated adipokine profile. An increase in renal glucose release and hepatic lipogenesis/lipid transport may also play a role, at least in part, in mediating hyperglycemia and dyslipidemia, respectively.

Antagonism of the antithrombotic and anti-atherosclerotic actions of aspirin by rofecoxib in the cholesterol-fed rabbit

BACKGROUND AND PURPOSE

Most patients at elevated cardiovascular risk receive long-term aspirin (ASA) anti-platelet treatment. The present study specifically addresses the pharmacological interactions between selective COX-2 inhibitors and ASA and the possible consequences for the thrombotic risk during long-term treatment.

EXPERIMENTAL APPROACH

New Zealand white rabbits were fed a standard laboratory diet supplemented with 1% cholesterol (CON) for 12 weeks. Age-matched control rabbits were fed the same standard diet without addition of cholesterol (SD). Rabbits were randomly assigned to one of the following groups: rofecoxib (ROFE, 25 mg·kg⁻¹, bid), acetylsalicylic acid (ASA, 5 mg·kg⁻¹, bid) or a combination of both (ASA + ROFE). At the end of the feeding period, the severity of atherosclerotic plaque formation was assessed in the aorta. Thrombus formation was assessed in the left carotid artery using a modified Folts procedure.

KEY RESULTS

Treatment of cholesterol-fed rabbits with ASA significantly reduced plaque formation. This reduction in lesion size was not observed in animals treated with the combination of rofecoxib and ASA. In the modified Folts model, treatment with either rofecoxib or ASA increased the total blood flow above that of untreated animals. This increase was statistically significant in the case of ASA, while cotreatment with rofecoxib abolished this ASA effect completely and reduced the total flow rate to the levels seen in untreated hypercholesterolaemic controls.

CONCLUSIONS

COX-2 inhibition by rofecoxib attenuates the antithrombotic and anti-atherosclerotic effects of ASA during long-term treatment in cholesterol-fed rabbits.

[Effects of Chinese herbal medicine Guanxinkang on lipid metabolism and serum C-reactive protein, amyloid A protein and fibrinogen in apolipoprotein E-knockout mice with atherosclerosis]

OBJECTIVE

To observe the effects of Guanxinkang (GXK) decoction, a compound traditional Chinese herbal medicine, on serum lipids and apolipoprotein A I (ApoA I), apolipoprotein B (ApoB), apolipoprotein E (ApoE), C-reactive protein (CRP), serum amyloid A protein (SAA) and fibrinogen (Fbg) concentrations of ApoE-knockout mice with atherosclerosis, and to explore the mechanism of GXK decoction in anti-atherosclerosis.

METHODS

Seventy 6-week-old ApoE-knockout mice receiving a high-cholesterol diet were used to induce atherosclerosis and were randomly divided into 5 groups: untreated group, simvastatin group and low- (drug concentration is 0.864 g/mL), medium- (1.728 g/mL), and high-dose (3.456 g/mL) GXK groups. Another fourteen 6-week-old C57BL/6J mice were used as the normal control. Two 12-week-old mice were randomly selected from the normal control and the ApoE-knockout mice respectively to observe vulnerable plaque in the mouse's aortic by hematoxylin-eosin staining. Blood was collected from venous plexus of eye socket after gavage of corresponding drugs once daily for 8 weeks continuously, and then the serum was separated. Triglyceride (TAG) and total cholesterol (TC) were measured by enzyme-coupled assay; low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) were measured by selective precipitation method. Serum levels of ApoA I and ApoB were determined by turbidimetry. Double-antibody sandwich enzyme-linked immunosorbent assay was used to detect ApoE, CRP, SAA and Fbg concentrations in serum.

RESULTS

Compared with the normal control group, the levels of serum TC, TAG, LDL-C, ApoB, CRP, SAA and Fbg in the untreated group were increased (P<0.05), and the serum concentrations of HDL-C, ApoA I and ApoE in the untreated group were decreased (P<0.05). After treatment, GXK decoction and simvastatin improved the dyslipidemia by increasing the concentrations of ApoA I and HDL-C and decreasing the concentrations of TC, TAG, LDL-C, ApoB, CRP, SAA and Fbg (P<0.05). The high-dose GXK decoction had the most marked effects on SAA and Fbg and the serum lipids compared with the low-dose and medium-dose GXK and simvastatin.

CONCLUSION

GXK decoction may not only provide an active effect on hyperlipidemia, but also down-regulate the levels of serum CRP, SAA and Fbg. GXK decoction exerts an anti-atherosclerosis effect in ApoE-knockout mice.

Cytosolic phospholipase A2alpha contributes to blood pressure increases and endothelial dysfunction under chronic NO inhibition

OBJECTIVE

Nitric oxide (NO) is an important modulator of cardiovascular function. In this study, we examined whether cytosolic phospholipase A2α (cPLA2α), an initial enzyme in the arachidonic acid pathway, is involved in blood pressure (BP) elevation in a murine model of chronic NO inhibition.

METHODS AND RESULTS

cPLA2α gene-deficient mice (cPLA2α-/-) and wild-type mice (WT) were administered the NO synthesis inhibitor Nω-nitro-L-arginine methyl ester (L-NAME) for 4 weeks. Before treatment, BP was comparable in both groups; it increased significantly in the WT but not in the cPLA2α-/- after treatment. Bone marrow transplantation experiments showed that cPLA2α in blood cells and plasma eicosanoid concentrations were not involved in BP elevation by L-NAME treatment. Activation of cPLA2α and subsequent production of eicosanoids in the aortic endothelium but not in aortic smooth muscle cell, heart, or kidney was observed after L-NAME treatment. Aortic ring assays revealed that endothelial function was comparable in both groups of mice before treatment. L-NAME treatment disturbed endothelial function in WT but not in cPLA2α-/-.

CONCLUSIONS

These results suggest that endothelial cPLA2α may play a principal role in L-NAME-induced hypertension and may be a target molecule for maintaining endothelial function under NO inhibition.

The cyclooxygenase-2 selective inhibitor, etodolac, but not aspirin reduces neovascularization in a murine ischemic hind limb model

Cyclooxygenase inhibitors are often prescribed to relieve severe ischemic leg pain in critical ischemic limb patients. Prescription of high doses of aspirin and selective cyclooxygenase-2 inhibitors is reported to increase cardiovascular events through suppression of the vasodilative prostanoid prostaglandin I(2) in endothelium. Here, we evaluated the influence of aspirin and etodolac, a selective cyclooxygenase-2 inhibitor, on neovascularization using a murine ischemia hind limb model. C57BL/6J mice were treated with aspirin or etodolac for twenty-eight days after induction of ischemia. We exploited a concentration of the agents that suppressed cyclooxygenase activity efficiently, especially in prostaglandin I(2) production. Recovery of limb blood perfusion and capillary density in ischemic limbs was significantly suppressed by etodolac treatment when compared to the aspirin treated group and untreated group. Production of 6-keto prostaglandin F(1alpha) and prostaglandin E(2) was lower in the aspirin treated group when compared with the etodolac-treated group. Also, these concentrations were lower in both treatment groups compared with the untreated group. Immunohistochemical analysis suggested cyclooxygenase-2 was expressed in endothelium but not in inflammatory cells in ischemic tissue from the acute to chronic phase. Cyclooxygenase-1 was expressed strongly in inflammatory cells in the acute phase. Furthermore, bone marrow-derived mononuclear cell transplantation improved neovascularization, whereas aspirin and etodolac did not inhibit these effects. Production of arachidonic acid metabolites by transplanted cells was independent of the improvement of neovascularization. In conclusion, cyclooxygenase-2 inhibition reduces ischemia-induced neovascularization.

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.

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.

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.

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.

Protection of atherogenesis in thromboxane A2 receptor-deficient mice is not associated with thromboxane A2 receptor in bone marrow-derived cells

In the previous study, we generated mice lacking thromboxane A2 receptor (TP) and apolipoprotein E, apoE(-/-)TP(-/-) mice, and reported that the double knockout mice developed markedly smaller atherosclerotic lesions than those in apoE(-/-) mice. To investigate the mechanism responsible for reduced atherosclerosis in apoE(-/-)TP(-/-) mice, we examined the role of TP in bone marrow (BM)-derived cells in the development of the atherosclerotic lesions. When we compared the function of macrophages in apoE(-/-) and in apoE(-/-)TP(-/-) mouse in vitro, there was no difference in the expression levels of cytokines and chemokines after stimulation with lipopolysaccharide. We then transplanted the BM from either apoE(-/-) or apoE(-/-)TP(-/-) mice to either apoE(-/-) or apoE(-/-)TP(-/-) mice after sublethal irradiation. After 12 weeks with high fat diet, we analyzed the atherosclerotic lesion of aortic sinus. When the BM from apoE(-/-) or apoE(-/-)TP(-/-) mice was transplanted to apoE(-/-) mice, the lesion size was almost the same as that of apoE(-/-) mice without BM transplantation. In contrast, when the BM from apoE(-/-) or apoE(-/-)TP(-/-) mice was transplanted to apoE(-/-)TP(-/-) mice, the lesion size was markedly reduced. These results indicate that the protection of atherogenesis in TP(-/-) mice is not associated with TP in BM-derived cells.