Involvement of the TP receptor in TNF-α-induced endothelial tissue factor expression

An autopsy case of intravascular large B-cell lymphoma showing a rapid transition to embolic strokes with occlusion of the major cerebral arteries

Intravascular large B-cell lymphoma can induce central nervous system manifestations, including strokes, due to small-vessel occlusion caused by lymphoma cells. However, involvement in large-sized vessels is rare. Here, we present an unusual autopsy case of an 88-year-old man showing a rapid transition from multiple strokes due to small vessel occlusion, typical of intravascular lymphoma, to progressive embolic strokes caused by the occlusion of major cerebral arteries. Magnetic resonance angiography demonstrated the major cerebral arteries associated with those multiple progressive strokes, including the right posterior cerebral artery, left anterior cerebral artery, and right middle cerebral artery, but the detectability was poor. A random skin biopsy at the abdomen confirmed the diagnosis of intravascular large B-cell lymphoma. The patient died 106 days after hospitalization despite intensive treatment. An autopsy revealed broad liquefactive necrosis in the area governed by the major cerebral arteries and multiple small infarctions caused by intravascular lymphoma cells in the small-sized vessels. In addition, the major cerebral arteries showed multiple thromboembolism with partial organization and clusters of intravascular lymphoma cells. Notably, those cells were shown aggregated and attached along the vascular wall of the basilar artery, which might have caused focal hypercoagulation in the near vessels. This aggregation might have disseminated widely in the other major cerebral arteries. Moreover, the cluster of intravascular lymphoma cells in the basilar artery was positive for tumor necrosis factor α, and similar histopathology findings were observed in the splenic veins. However, the pathogenesis of this rare phenomenon involving these cells remains unknown. From a clinical perspective, we should consider the possibility that intravascular lymphoma cells may provoke similar progressive embolic strokes.

Subacute administration of cilostazol modulates PLC-γ/PKC-α/p38/NF-kB pathway and plays vascular protective effects through eNOS activation in early stages of atherosclerosis development

AIMS

Hypercholesterolemia is an important risk factor for development of cardiovascular disturbances, such as atherosclerosis, and its treatment remains challenging in modern medicine. Cilostazol is a selective inhibitor of phosphodiesterase 3 clinically prescribed for intermittent claudication treatment. Due to its pleiotropic properties, such as lipid lowering, anti-inflammatory, and antioxidant effects, the therapeutic repurposing of cilostazol has become a strategic approach for atherosclerosis treatment. This study aimed to investigate the effects of subacute administration of cilostazol on the aortas of hypercholesterolemic rats, focusing on the signaling pathways involved in these actions.

MAIN METHODS

A murine model of hypercholesterolemia was employed to mimic the early stages of atherosclerosis development. Vascular reactivity assays were performed on thoracic aorta rings to assess the vascular response, as well as the non-invasive blood pressure was evaluated by plethysmography method. Pro-inflammatory markers and malondialdehyde (MDA) levels were measured to investigate the anti-inflammatory and antioxidant effects of cilostazol. Western Blot analysis was performed in aortas homogenates to evaluate the role of cilostazol on PLC-γ/PKC-α/p38-MAPK/IκB-α/NF-кB and PKA/eNOS/PKG pathways.

KEY FINDINGS

The hypercholesterolemic diet induced the production of pro-inflammatory mediators such as TNF-α, TXB2, VCAM, and worsened vascular function, marked by increased contractile response, decreased maximum relaxation, and elevated systolic and diastolic blood pressure. Cilostazol seems to counteract the deleterious effects promoted by hypercholesterolemic diet, showing important anti-inflammatory and vasculoprotective properties possibly through the inhibition of the PLC-γ/PKC-α/p38-MAPK/IκB-α/NF-кB pathway and activation of the PKA/eNOS/PKG pathway.

SIGNIFICANCE

Cilostazol suppressed hypercholesterolemia-induced vascular dysfunction and inflammation. Our data suggest the potential repurposing of cilostazol as a pharmacological treatment for atherosclerosis.

11,12-EET suppressed LPS induced TF expression and thrombus formation by accelerating mRNA degradation rate via strengthening PI3K-Akt signaling pathway and inhibiting p38-TTP pathway

Epoxyeicosatrienoic acids (EETs), which are synthesized from arachidonic acid by cytochrome P450 epoxygenases, function primarily as autocrine and paracrine effectors in the cardiovascular system. So far, most research has focused on the vasodilatory, anti-inflammatory, anti-apoptotic and mitogenic properties of EETs in the systemic circulation. However, whether EETs could suppress tissue factor (TF) expression and prevent thrombus formation remains unknown. Here we utilized in vivo and in vitro models to investigate the effects and underlying mechanisms of exogenously EETs on LPS induced TF expression and inferior vein cava ligation induced thrombosis. We observed that the thrombus formation rate and the size of the thrombus were greatly reduced in 11,12-EET treated mice，accompanied by decreased TF and inflammatory cytokines expression. Further in vitro studies showed that by enhancing p38 MAPK activation and subsequent tristetraprolin (TTP) phosphorylation, LPS strengthened the stability of TF mRNA and induced increased TF expression. However, by strengthening PI3K-dependent Akt phosphorylation, which acted as a negative regulator of p38-TTP signaling pathway，11,12-EET reduced LPS-induced TF expression in monocytes. In addition, 11,12-EET inhibited LPS-induced NF-κB nuclear translocation by activating the PI3K/Akt pathway. Further study indicated that the inhibitory effect of 11,12-EET on TF expression was mediated by antagonizing LPS-induced activation of thromboxane prostanoid receptor. In conclusion, our study demonstrated that 11,12-EET prevented thrombosis by reducing TF expression and targeting the CYP2J2 epoxygenase pathway may represent a novel approach to mitigate thrombosis related diseases.

Thrombo-Inflammation in COVID-19 and Sickle Cell Disease: Two Faces of the Same Coin

People with sickle cell disease (SCD) are at greater risk of severe illness and death from respiratory infections, including COVID-19, than people without SCD (Centers for Disease Control and Prevention, USA). Vaso-occlusive crises (VOC) in SCD and severe SARS-CoV-2 infection are both characterized by thrombo-inflammation mediated by endothelial injury, complement activation, inflammatory lipid storm, platelet activation, platelet-leukocyte adhesion, and activation of the coagulation cascade. Notably, lipid mediators, including thromboxane A2, significantly increase in severe COVID-19 and SCD. In addition, the release of thromboxane A2 from endothelial cells and macrophages stimulates platelets to release microvesicles, which are harbingers of multicellular adhesion and thrombo-inflammation. Currently, there are limited therapeutic strategies targeting platelet-neutrophil activation and thrombo-inflammation in either SCD or COVID-19 during acute crisis. However, due to many similarities between the pathobiology of thrombo-inflammation in SCD and COVID-19, therapies targeting one disease may likely be effective in the other. Therefore, the preclinical and clinical research spurred by the COVID-19 pandemic, including clinical trials of anti-thrombotic agents, are potentially applicable to VOC. Here, we first outline the parallels between SCD and COVID-19; second, review the role of lipid mediators in the pathogenesis of these diseases; and lastly, examine the therapeutic targets and potential treatments for the two diseases.

Activated factor XI is associated with increased factor VIIa - Antithrombin complexes in stable coronary artery disease: Impact on cardiovascular outcomes

BACKGROUND

Coronary artery disease (CAD) is associated with a prothrombotic tendency including increased factor (F) VIIa-antithrombin (FVIIa-AT) complexes, a measure of tissue factor (TF) exposure, and activated FXI (FXIa). We investigated whether increased FVIIa-AT complexes are associated with FXIa and active TF and if major adverse clinical outcomes are predicted by the complexes in CAD.

METHODS

In 120 CAD patients, we assessed FVIIa-AT complex concentrations and the presence of circulating FXIa and active TF. Levels of 8-iso-prostaglandin F2α (8-iso-PGF2α), interleukin-6, high-sensitivity C reactive protein, prothrombin fragment 1 + 2, and free Tissue Factor Pathway Inhibitor were determined. Myocardial infarction (MI), ischemic stroke, systemic thromboembolism (SE), and cardiovascular (CV) death were recorded separately and as a composite endpoint, during follow-up.

RESULTS

FVIIa-AT complexes were positively associated with current smoking and multivessel CAD. Elevated FVIIa-AT complexes characterized patients with circulating FXIa and/or active TF in association with increased plasma isoprostanes but not with thrombin generation or inflammatory markers. During a median follow-up of 106 months (interquartile range 95-119), high baseline levels of FVIIa-AT complexes predicted ischemic stroke/SE (HR 4.61 [95% CI 1.48-18.42]) and a composite endpoint of MI, stroke/SE, and CV death (HR 7.47 [95% CI 2.81-19.87]).

CONCLUSIONS

This study is the first to show that high FVIIa-AT complexes characterize advanced CAD patients with detectable FXIa and active TF, which is, in part, driven by oxidative stress. High FVIIa-AT complexes were associated with the risk of ischemic stroke/SE during long-term follow-up, highlighting the need for effective antithrombotic agents in CAD.

Ramatroban for chemoprophylaxis and treatment of COVID-19: David takes on Goliath

INTRODUCTION

In COVID-19 pneumonia, there is a massive increase in fatty acid levels and lipid mediators with a predominance of cyclooxygenase metabolites, notably TxB2 ≫ PGE2 > PGD2 in the lungs, and 11-dehydro-TxB2, a TxA2 metabolite, in the systemic circulation. While TxA2 stimulates thromboxane prostanoid (TP) receptors, 11-dehydro-TxB2 is a full agonist of DP2 (formerly known as the CRTh2) receptors for PGD2. Anecdotal experience of using ramatroban, a dual receptor antagonist of the TxA2/TP and PGD2/DP2 receptors, demonstrated rapid symptomatic relief from acute respiratory distress and hypoxemia while avoiding hospitalization.

AREAS COVERED

Evidence supporting the role of TxA2/TP receptors and PGD2/DP2 receptors in causing rapidly progressive lung injury associated with hypoxemia, a maladaptive immune response and thromboinflammation is discussed. An innovative perspective on the dual antagonism of TxA2/TP and PGD2/DP2 receptor signaling as a therapeutic approach in COVID-19 is presented. This paper examines ramatroban an anti-platelet, immunomodulator, and antifibrotic agent for acute and long-haul COVID-19.

EXPERT OPINION

Ramatroban, a dual blocker of TP and DP2 receptors, has demonstrated efficacy in animal models of respiratory dysfunction, atherosclerosis, thrombosis, and sepsis, as well as preliminary evidence for rapid relief from dyspnea and hypoxemia in COVID-19 pneumonia. Ramatroban merits investigation as a promising antithrombotic and immunomodulatory agent for chemoprophylaxis and treatment.

Kidney in the net of acute and long-haul coronavirus disease 2019: a potential role for lipid mediators in causing renal injury and fibrosis

PURPOSE OF REVIEW

Severe COVID-19 disease is often complicated by acute kidney injury (AKI), which may transition to chronic kidney disease (CKD). Better understanding of underlying mechanisms is important in advancing therapeutic approaches.

RECENT FINDINGS

SARS-CoV-2-induced endothelial injury initiates platelet activation, platelet-neutrophil partnership and release of neutrophil extracellular traps. The resulting thromboinflammation causes ischemia-reperfusion (I/R) injury to end organs. Severe COVID-19 induces a lipid-mediator storm with massive increases in thromboxane A2 (TxA2) and PGD2, which promote thromboinflammation and apoptosis of renal tubular cells, respectively, and thereby enhance renal fibrosis. COVID-19-associated AKI improves rapidly in the majority. However, 15-30% have protracted renal injury, raising the specter of transition from AKI to CKD.

SUMMARY

In COVID-19, the lipid-mediator storm promotes thromboinflammation, ischemia-reperfusion injury and cytotoxicity. The thromboxane A2 and PGD2 signaling presents a therapeutic target with potential to mitigate AKI and transition to CKD. Ramatroban, the only dual antagonist of the thromboxane A2/TPr and PGD2/DPr2 signaling could potentially mitigate renal injury in acute and long-haul COVID. Urgent studies targeting the lipid-mediator storm are needed to potentially reduce the heavy burden of kidney disease emerging in the wake of the current pandemic.

Thromboxane-prostanoid receptor activation blocks ATP-sensitive potassium channels in rat aortas

K+ channel activation is one of the major mechanisms involved in vasodilation. Vasoconstrictor agonists such as angiotensin II promote ATP-dependent potassium channels (KATP ) dysfunction. This study evaluates whether thromboxane-prostanoid (TP receptor) activation by the agonist U46619 increases reactive oxygen species (ROS) production in rat aortas, which could contribute to KATP channel dysfunction and impaired NO-dependent vasodilation. TP receptor activation with the selective agonist U46619 increased ROS in endothelial cells (ECs) and vascular smooth muscle cells (VSMCs), but the TP receptor antagonist SQ29548 abolished this effect. ECs and VSMCs incubation with ROS scavengers like Tiron or PEG-Catalase impaired U46619-induced ROS production. U46619 at the concentrations of 0.1 and 1 µmol/L induced contractions with similar amplitude. KATP channel activation with pinacidil-induced relaxation was lower for the contractions induced with 0.1 or 1 µmol/L U46619 than with 10 nmol/L U46619. Acetylcholine-induced relaxation provided similar results. In aortas pre-contracted with 10 nmol/L U46619, neither Tiron (100 µmol/L) nor catalase (300 U/mL) affected pinacidil-induced relaxation. However, in aortas pre-contracted with 0.1 µmol/L U46619, catalase potentiated pinacidil-induced relaxation. Pinacidil potentiated acetylcholine-induced relaxation in aortas pre-contracted with 0.1 and 1 µmol/L U46619. Incubation with 10 nmol/L U46619 increased NO concentration in ECs. Taken together, these results show that high concentrations of the TP receptor agonist U46619 impair KATP channels, which is probably due to ROS production. It is likely that hydrogen peroxide is the ROS.

Modulation by antenatal therapies of cardiovascular and renal programming in male and female offspring of preeclamptic rats

Morbidity and mortality risks are enhanced in preeclamptic (PE) mothers and their offspring. Here, we asked if sexual dimorphism exists in (i) cardiovascular and renal damage evolved in offspring of PE mothers, and (ii) offspring responsiveness to antenatal therapies. PE was induced by administering N^G-nitro-L-arginine methyl ester (L-NAME, 50 mg/kg/day, oral gavage) to pregnant rats for 7 days starting from gestational day 14. Three therapies were co-administered orally with L-NAME, atrasentan (endothelin ETA receptor antagonist), terutroban (thromboxane A2 receptor antagonist, TXA2), or α-methyldopa (α-MD, central sympatholytic drug). Cardiovascular and renal profiles were assessed in 3-month-old offspring. Compared with offspring of non-PE rats, PE offspring exhibited elevated systolic blood pressure and proteinuria and reduced heart rate and creatinine clearance (CrCl). Apart from a greater bradycardia in male offspring, similar PE effects were noted in male and female offspring. While terutroban, atrasentan, or α-MD partially and similarly blunted the PE-evoked changes in CrCl and proteinuria, terutroban was the only drug that virtually abolished PE hypertension. Rises in cardiorenal inflammatory (tumor necrosis factor alpha, TNFα) and oxidative (isoprostane) markers were mostly and equally eliminated by all therapies in the two sexes, except for a greater dampening action of atrasentan, compared with α-MD, on tissue TNFα in female offspring only. Histopathologically, antenatal terutroban or atrasentan was more effective than α-MD in rectifying cardiac structural damage, myofiber separation, and cytoplasmic alterations, in PE offspring. The repair by antenatal terutroban or atrasentan of cardiovascular and renal anomalies in PE offspring is mostly sex-independent and surpasses the protection offered by α-MD, the conventional PE therapy.

Inflammatory Mechanisms Contributing to Endothelial Dysfunction

Maintenance of endothelial cell integrity is an important component of human health and disease since the endothelium can perform various functions including regulation of vascular tone, control of hemostasis and thrombosis, cellular adhesion, smooth muscle cell proliferation, and vascular inflammation. Endothelial dysfunction is encompassed by complex pathophysiology that is based on endothelial nitric oxide synthase uncoupling and endothelial activation following stimulation from various inflammatory mediators (molecular patterns, oxidized lipoproteins, cytokines). The downstream signaling via nuclear factor-κB leads to overexpression of adhesion molecules, selectins, and chemokines that facilitate leukocyte adhesion, rolling, and transmigration to the subendothelial space. Moreover, oscillatory shear stress leads to pro-inflammatory endothelial activation with increased monocyte adhesion and endothelial cell apoptosis, an effect that is dependent on multiple pathways and flow-sensitive microRNA regulation. Moreover, the role of neutrophil extracellular traps and NLRP3 inflammasome as inflammatory mechanisms contributing to endothelial dysfunction has recently been unveiled and is under further investigation. Consequently, and following their activation, injured endothelial cells release inflammatory mediators and enter a pro-thrombotic state through activation of coagulation pathways, downregulation of thrombomodulin, and an increase in platelet adhesion and aggregation owing to the action of von-Willebrand factor, ultimately promoting atherosclerosis progression.

The key contribution of platelet and vascular arachidonic acid metabolism to the pathophysiology of atherothrombosis

Arachidonic acid is one of the most abundant and ubiquitous ω-6 polyunsaturated fatty acid, present in esterified form in the membrane phospholipids of all mammalian cells and released from phospholipids by several phospholipases in response to various activating or inhibitory stimuli. Arachidonic acid is the precursor of a large number of enzymatically and non-enzymatically derived, biologically active autacoids, including prostaglandins (PGs), thromboxane (TX) A2, leukotrienes, and epoxyeicosatetraenoic acids (collectively called eicosanoids), endocannabinoids and isoprostanes, respectively. Eicosanoids are local modulators of the physiological functions and pathophysiological roles of blood vessels and platelets. For example, the importance of cyclooxygenase (COX)-1-derived TXA2 from activated platelets in contributing to primary haemostasis and atherothrombosis is demonstrated in animal and human models by the bleeding complications and cardioprotective effects associated with low-dose aspirin, a selective inhibitor of platelet COX-1. The relevance of vascular COX-2-derived prostacyclin (PGI2) in endothelial thromboresistance and atheroprotection is clearly shown by animal and human models and by the adverse cardiovascular effects exerted by COX-2 inhibitors in humans. A vast array of arachidonic acid-transforming enzymes, downstream synthases and isomerases, transmembrane receptors, and specificity in their tissue expression make arachidonic acid metabolism a fine-tuning system of vascular health and disease. Its pharmacological regulation is central in human cardiovascular diseases, as demonstrated by biochemical measurements and intervention trials.

Peach Kernel Oil Downregulates Expression of Tissue Factor and Reduces Atherosclerosis in ApoE knockout Mice

Atherosclerosis is the pathological process in arteries due to the plaque formation that is responsible for several diseases like heart disease, stroke and peripheral arterial disease. In this study, we performed in vitro and in vivo assays to evaluate the potential anti-atherosclerosis activity of peach kernel oil. For the in vitro assay, we incubated human umbilical vein endothelial cells (HUVEC) with tumor necrosis factor-α (TNF-α) to induce tissue factors (TF, an essential mediator of hemostasis and trigger of thrombosis) elevation. We found that TNF-α-induced TF elevation was suppressed by peach kernel oil in a dose-dependent manner at both mRNA and protein levels. Peach kernel oil can significantly improve HUVEC viability, protect the endothelial cells, which achieved the goal of prevention of thrombotic diseases. For the in vivo assay, we investigated the effect and mechanism of peach kernel oil on preventing atherosclerotic lesion formation in ApoE knockout mice. Results show that peach kernel oil could reduce total cholesterol, triglyceride, low-density lipoprotein cholesterol levels, elevate the high-density lipoprotein cholesterol level in serum, and reduce the area of the aortic atherosclerotic lesions in high-fat diet fed ApoE knockout mice. Moreover, peach kernel oil treatment can significantly down regulate the expression of TF protein to inhibit the formation of atherosclerotic plaque. In conclusion, peach kernel oil may be a potential health food to prevent atherosclerosis in cardiovascular diseases.

Differential Impact of Serial Measurement of Nonplatelet Thromboxane Generation on Long-Term Outcome After Cardiac Surgery

BACKGROUND

Systemic thromboxane generation, not suppressible by standard aspirin therapy and likely arising from nonplatelet sources, increases the risk of atherothrombosis and death in patients with cardiovascular disease. In the RIGOR (Reduction in Graft Occlusion Rates) study, greater nonplatelet thromboxane generation occurred early compared with late after coronary artery bypass graft surgery, although only the latter correlated with graft failure. We hypothesize that a similar differential association exists between nonplatelet thromboxane generation and long-term clinical outcome.

METHODS AND RESULTS

Five-year outcome data were analyzed for 290 RIGOR subjects taking aspirin with suppressed platelet thromboxane generation. Multivariable modeling was performed to define the relative predictive value of the urine thromboxane metabolite, 11-dehydrothromboxane B₂ (11-dhTXB₂), measured 3 days versus 6 months after surgery on the composite end point of death, myocardial infarction, revascularization or stroke, and death alone. 11-dhTXB₂ measured 3 days after surgery did not independently predict outcome, whereas 11-dhTXB₂ >450 pg/mg creatinine measured 6 months after surgery predicted the composite end point (adjusted hazard ratio, 1.79; P=0.02) and death (adjusted hazard ratio, 2.90; P=0.01) at 5 years compared with lower values. Additional modeling revealed 11-dhTXB₂ measured early after surgery associated with several markers of inflammation, in contrast to 11-dhTXB₂ measured 6 months later, which highly associated with oxidative stress.

CONCLUSIONS

Long-term nonplatelet thromboxane generation after coronary artery bypass graft surgery is a novel risk factor for 5-year adverse outcome, including death. In contrast, nonplatelet thromboxane generation in the early postoperative period appears to be driven predominantly by inflammation and did not independently predict long-term clinical outcome.

Effects of Aspirin on Endothelial Function and Hypertension

PURPOSE OF REVIEW

Endothelial dysfunction is intimately related to the development of various cardiovascular diseases, including hypertension, and is often used as a target for pharmacological treatment. The scope of this review is to assess effects of aspirin on endothelial function and their clinical implication in arterial hypertension.

RECENT FINDINGS

Emerging data indicate the role of platelets in the development of vascular inflammation due to the release of proinflammatory mediators, for example, triggered largely by thromboxane. Vascular inflammation further promotes oxidative stress, diminished synthesis of vasodilators, proaggregatory and procoagulant state. These changes translate into vasoconstriction, impaired circulation and thrombotic complications. Aspirin inhibits thromboxane synthesis, abolishes platelets activation and acetylates enzymes switching them to the synthesis of anti-inflammatory substances. Aspirin pleiotropic effects have not been fully elucidated yet. In secondary prevention studies, the decrease in cardiovascular events with aspirin outweighs bleeding risks, but this is not the case in primary prevention settings. Ongoing trials will provide more evidence on whether to expand the use of aspirin or stay within current recommendations.

Role of thromboxane-dependent platelet activation in venous thrombosis: Aspirin effects in mouse model

Recent trials suggest that Aspirin (ASA) reduces the incidence of venous thromboembolism in human. However, the molecular mechanisms underlying this effect are still unclear. In this study we assessed the effects of ASA in venous thrombosis mouse model induced by inferior vena cava (IVC) ligation and we investigated the mechanisms responsible for this effect. ASA (3mg/kg daily for 2 days) treatment decreased the thrombus size, the amounts of tissue factor activity in plasma microvesicles (TF-MP) and the levels of 2,3-dinor Thromboxane B2 (TXB-M) in urine compared to control mice. Interestingly, the thrombus size positively correlated with both TF-MP activity and TXB-M. In addition, positive correlation was observed between TF-MP activity and TXB-M. A reduced number of neutrophils and monocytes, and of TF-positive cells accompanied to a lower amount of fibrin and neutrophil extracellular traps (NETs) were also found in thrombi of ASA-treated mice. Similar results were obtained when mice were treated 24h before IVC ligation with SQ29548 (1mg/kg), a selective thromboxane receptor antagonist. In addition, transfusion of platelets in SQ29548 treated-mice excluded the likelihood of a redundant role of platelet-TP receptor in this context. Finally, incubation of macrophages and neutrophils with SQ29548 prevented TF activity and/or NETs formation induced by supernatant of activated platelets or by IBOP, a selective thromboxane analogue. In conclusion, ASA, suppressing TXA2, prevents macrophages and neutrophils activation and markedly reduces thrombus size with a mechanism most likely dependent of the inhibition of TF activity and NETs formation. These results provide a new link between platelet-produced thromboxane and the occurrence of venous thrombosis.

Risk Factors for Nonplatelet Thromboxane Generation After Coronary Artery Bypass Graft Surgery

Background

Persistent thromboxane (TX) generation while receiving aspirin therapy is associated with an increased risk of cardiovascular events. The Reduction in Graft Occlusion Rates (RIGOR) study found that aspirin‐insensitive TXA₂ generation, indicated by elevated urine 11‐dehydro‐TXB₂ (UTXB₂) 6 months after coronary artery bypass graft surgery, was a potent risk factor for vein graft thrombosis and originated predominantly from nonplatelet sources. Our goal was to identify risks factors for nonplatelet TXA₂ generation.

Methods and Results

Multivariable modeling was performed by using clinical and laboratory variables obtained from 260 RIGOR subjects with verified aspirin‐mediated inhibition of platelet TXA₂ generation. The strongest variable associated with UTXB₂ 6 months after surgery, accounting for 47.2% of the modeled effect, was urine 8‐iso‐prostaglandin (PG)F_2α, an arachidonic acid metabolite generated nonenzymatically by oxidative stress (standardized coefficient 0.442, P<0.001). Age, sex, race, lipid therapy, creatinine, left ventricular ejection fraction, and aspirin dose were also significantly associated with UTXB₂ (P<0.03), although they accounted for only 4.8% to 10.2% of the modeled effect. Urine 8‐iso‐PGF_2α correlated with risk of vein graft occlusion (odds ratio 1.67, P=0.001) but was not independent of UTXB₂. In vitro studies revealed that endothelial cells generate TXA₂ in response to oxidative stress and direct exposure to 8‐iso‐PGF_2α.

Conclusions

Oxidative stress–induced formation of 8‐iso‐PGF_2α is strongly associated with nonplatelet thromboxane formation and early vein graft thrombosis after coronary artery bypass graft surgery. The endothelium is potentially an important source of oxidative stress–induced thromboxane generation. These findings suggest therapies that reduce oxidative stress could be useful in reducing cardiovascular risks associated with aspirin‐insensitive thromboxane generation.

Acanthoic acid inhibits LPS-induced inflammatory response by activating LXRα in human umbilical vein endothelial cells

Acanthoic acid, a pimaradiene diterpene isolated from Acanthopanax koreanum, has been reported to have anti-inflammatory activities. However, the effect of acanthoic acid on vascular inflammation has not been investigated. The aim of this study was to investigate the anti-inflammatory effects of acanthoic acid on lipopolysaccharide (LPS)-induced inflammatory response in human umbilical vein endothelial cells (HUVECs). The production of cytokines TNF-α and IL-8 was detected by ELISA. The expression of VCAM-1, ICAM-1, E-selectin, NF-κB and LXRα were detected by Western blotting. Adhesion of monocytes to HUVECs was detected by monocytic cell adhesion assay. The results showed that acanthoic acid dose-dependently inhibited LPS-induced TNF-α and IL-8 production. Acanthoic acid also inhibited TNF-α-induced IL-8 and IL-6 production. LPS-induced endothelial cell adhesion molecules, VCAM-1 and ICAM-1 were also inhibited by acanthoic acid. Acanthoic acid inhibited LPS-induced NF-κB activation. Furthermore, acanthoic acid dose-dependently up-regulated the expression of LXRα. In addition, our results showed that the anti-inflammatory effect of acanthoic acid was attenuated by transfection with LXRα siRNA. In conclusion, the anti-inflammatory effect of acanthoic acid is due to its ability to activate LXRα. Acanthoic acid may be a therapeutic agent for inflammatory cardiovascular disease.

Endothelial cell control of thrombosis

Hemostasis encompasses a set of tightly regulated processes that govern blood clotting, platelet activation, and vascular repair. Upon vascular injury, the hemostatic system initiates a series of vascular events and activates extravascular receptors that act in concert to seal off the damage. Blood clotting is subsequently attenuated by a plethora of inhibitors that prevent excessive clot formation and eventual thrombosis. The endothelium which resides at the interface between the blood and surrounding tissues, serves an integral role in the hemostatic system. Depending on specific tissue needs and local stresses, endothelial cells are capable of evoking either antithrombotic or prothrombotic events. Healthy endothelial cells express antiplatelet and anticoagulant agents that prevent platelet aggregation and fibrin formation, respectively. In the face of endothelial dysfunction, endothelial cells trigger fibrin formation, as well as platelet adhesion and aggregation. Finally, endothelial cells release pro-fibrinolytic agents that initiate fibrinolysis to degrade the clot. Taken together, a functional endothelium is essential to maintain hemostasis and prevent thrombosis. Thus, a greater understanding into the role of the endothelium can provide new avenues for exploration and novel therapies for the management of thromboembolisms.

Constrictor prostanoids and uridine adenosine tetraphosphate: vascular mediators and therapeutic targets in hypertension and diabetes

Vascular dysfunction plays a pivotal role in the development of systemic complications associated with arterial hypertension and diabetes. The endothelium, or more specifically, various factors derived from endothelial cells tightly regulate vascular function, including vascular tone. In physiological conditions, there is a balance between endothelium-derived factors, that is, relaxing factors (endothelium-derived relaxing factors; EDRFs) and contracting factors (endothelium-derived contracting factors; EDCFs), which mediate vascular homeostasis. However, in disease states, such as diabetes and arterial hypertension, there is an imbalance between EDRF and EDCF, with a reduction of EDRF signalling and an increase of EDCF signalling. Among EDCFs, COX-derived vasoconstrictor prostanoids play an important role in the development of vascular dysfunction associated with hypertension and diabetes. Moreover, uridine adenosine tetraphosphate (Up4 A), identified as an EDCF in 2005, also modulates vascular function. However, the role of Up4 A in hypertension- and diabetes-associated vascular dysfunction is unclear. In the present review, we focused on experimental and clinical evidence that implicate these two EDCFs (vasoconstrictor prostanoids and Up4 A) in vascular dysfunction associated with hypertension and diabetes.

Regulation of tissue factor gene expression in monocytes and endothelial cells: Thromboxane A2 as a new player

Tissue factor (TF) is the primary activator of the coagulation cascade. Under normal conditions, endothelial cells (ECs) and blood cells, such as monocytes, do not express TF. However, bacterial lipopolysaccharide (LPS) induces TF expression in monocytes and this leads to disseminated intravascular coagulation during endotoxemia and sepsis. A variety of stimuli induce TF expression in ECs in vitro, although it is unclear how much TF is expressed by the endothelium in vivo. LPS induction of TF gene expression in monocytic cells and ECs is mediated by various intracellular signaling pathways and the transcription factors NF-ĸB, AP-1 and Egr-1. In contrast, vascular endothelial cell growth factor (VEGF) induces TF gene expression in ECs via the transcription factors NFAT and Egr-1. Similarly, oxidized phospholipids (such as 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine) induce TF expression in ECs and possibly monocytes via NFAT and Egr-1. Thromboxane A2 (TXA2) can now be added to the list of stimuli that induce TF gene expression in both monocytes and ECs. Interestingly, inhibition of the TX-prostanoid (TP) receptor also reduces TF expression in with tumor necrosis factor (TNF)-α stimulated ECs and LPS stimulated monocytes, which suggests that TP receptor antagonist may be useful in reducing pathologic TF expression in the vasculature and blood.