Role Of Thromboxane A2 Research Articles

Thromboxane A2-TP axis promotes adipose tissue macrophages M1 polarization leading to insulin resistance in obesity

Aberrant arachidonic acid metabolism has been implicated in multiple pathophysiological conditions, and the downstream prostanoids levels are associated with adipocyte dysfunction in obesity. However, the role of thromboxane A2 (TXA2) in obesity remains unclear. We observed that TXA2, through its receptor TP, is a candidate mediator in obesity and metabolic disorders. Obese mice with upregulated TXA2 biosynthesis (TBXAS1) and TXA2 receptor (TP) expression in caused insulin resistance and macrophage M1 polarization in white adipose tissue (WAT), which can be prevented by treatment with aspirin. Mechanistically, the activation of TXA2-TP signaling axis leads to accumulation of protein kinase Cɛ (PKCɛ), thereby enhancing free fat acid (FFA) induced Toll-like receptor4 (TLR4) proinflammatory macrophage activation and the tumor necrosis factor–a (TNF-a) production in adipose tissues. Importantly, TP knockout mice reduced the accumulation of proinflammatory macrophages and adipocyte hypertrophy in WAT. Thus, our findings demonstrate that TXA2-TP axis plays a crucial role in obesity-induced adipose macrophage dysfunction, and rational targeting TXA2 pathway may improve obesity and its associated metabolic disorders in future. In this work, we establish previously unknown role of TXA2-TP axis in WAT. These findings might provide new insight into the molecular pathogenesis of insulin resistance, and indicate rational targeting TXA2 pathway to improve obesity and its associated metabolic disorders in future.

Effects of Fatty Acid Metabolites on Adipocytes Britening: Role of Thromboxane A2.

Obesity is a complex disease highly related to diet and lifestyle and is associated with low amount of thermogenic adipocytes. Therapeutics that regulate brown adipocyte recruitment and activity represent interesting strategies to fight overweight and associated comorbidities. Recent studies suggest a role for several fatty acids and their metabolites, called lipokines, in the control of thermogenesis. The purpose of this work was to analyze the role of several lipokines in the control of brown/brite adipocyte formation. We used a validated human adipocyte model, human multipotent adipose-derived stem cell model (hMADS). In the absence of rosiglitazone, hMADS cells differentiate into white adipocytes, but convert into brite adipocytes upon rosiglitazone or prostacyclin 2 (PGI2) treatment. Gene expression was quantified using RT-qPCR and protein levels were assessed by Western blotting. We show here that lipokines such as 12,13-diHOME, 12-HEPE, 15dPGJ2 and 15dPGJ3 were not able to induce browning of white hMADS adipocytes. However, both fatty acid esters of hydroxy fatty acids (FAHFAs), 9-PAHPA and 9-PAHSA potentiated brown key marker UCP1 mRNA levels. Interestingly, CTA2, the stable analog of thromboxane A2 (TXA2), but not its inactive metabolite TXB2, inhibited the rosiglitazone and PGI2-induced browning of hMADS adipocytes. These results pinpoint TXA2 as a lipokine inhibiting brown adipocyte formation that is antagonized by PGI2. Our data open new horizons in the development of potential therapies based on the control of thromboxane A2/prostacyclin balance to combat obesity and associated metabolic disorders.

Abstract 34: High urinary thromboxane B2 associates with lethal prostate cancer in African American men and inversely correlates with aspirin use

Abstract Background: Systemic low-grade inflammation is a candidate risk factor for prostate cancer (PC) in African American (AA) men, potentially contributing to lethal PC development. We previously reported that regular aspirin use is associated with a decreased risk of advanced stage disease and disease recurrence in AA patients with PC. The cancer-preventive benefits of aspirin have been attributed to inhibition of the cyclooxygenase (COX) pathway. Thromboxane A2 (TXA2) is an eicosanoid produced by the COX1 enzyme in platelets. Aspirin can inhibit metastasis by inhibiting COX1 activity and TXA2 synthesis. Hence, we assessed the role of TXA2 in the development of lethal PC. Because TXA2 is unstable, we measured its corresponding primary metabolite, urinary thromboxane B2 (TXB2), to examine the relationship of TXA2 with PC. Method: TXB2 was measured in cases (977) and controls (1022) from the NCI-MD PC Case-Control study using a mass-spectrometry-based assay. TXB2 levels were modeled into low (≤median) and high (>median) levels. We calculated risk factor-adjusted odds ratios (ORs) and 95% confidence intervals (CI) using unconditional logistic regression, adjusted hazard ratios (HR) using Cox regression and sub hazard ratios (SHR) using the Fine-Gray model. Results: We observed increased TXB2 levels in cases and an inverse relationship between levels of TXB2 and aspirin use in both cases and controls. For cases who used aspirin, the odds of having high TXB2 were reduced when compared to non-users (OR 0.46 95%CI, 0.34-0.61). This observation remained significant when stratified by race/ethnicity (AA: OR 0.36 95%CI, 0.23-0.54; EA: OR 0.58 95%CI, 0.38-0.88), indicating significant inhibition of TXB2 formation by aspirin, most notably in AA men. Further analysis showed that high TXB2 is associated with a PC case status in AA men (OR 1.44 95%CI, 1.08-1.93) but not EA men (OR 1.07 95%CI, 0.83-1.93), indicating increased TXA2 synthesis in AA men with PC compared to AA men without the disease. Also, men with high TXB2 were more likely to be diagnosed with metastasis compared to men with low TXB2 (OR 4.27 95%CI, 1.48-12.29), indicating more aggressive disease for cases with high TXB2. Furthermore, high TXB2 was associated with all-cause mortality (HR 1.56 95%CI, 1.05-2.33) and PC mortality (HR 4.02 95%CI, 1.46-11.07; SHR 2.89 95%CI, 1.03-8.11) in AA men only. Our findings indicate a distinct association between TXA2 and PC outcomes in AA men. Conclusion: Aspirin use inversely associates with high TXB2. This is of clinical interest as we report that increased TXB2 associates with PC in AA men, with aggressive PC, and with PC death which disproportionally affects AA men. This is consistent with our previous findings that aspirin may reduce lethal PC in AA men and highlights the potential benefit of aspirin for prevention of lethal PC in this high-risk group of men through inhibition of TXA2 synthesis. Citation Format: Maeve Bailey-Whyte, Ginger Milne, Tsion Z. Minas, Tiffany H. Dorsey, Wei Tang, Cheryl J. Smith, Michael B. Cook, Clayton Yates, Stefan Ambs. High urinary thromboxane B2 associates with lethal prostate cancer in African American men and inversely correlates with aspirin use [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 34.

血栓素A2在支气管哮喘中的作用

血栓素A2在支气管哮喘中的作用

Abstract PO-157: High urinary thromboxane B2 associates with aggressive prostate cancer and inversely correlates with aspirin use

Abstract Background: Systemic low-grade inflammation is a candidate risk factor for prostate cancer (PC) in African-American (AA) men potentially contributing to aggressive disease and mortality. Regular use of the anti-inflammatory drug aspirin is associated with decreased risk of advanced stage PC and increased disease-free survival in AA men. The chemopreventive benefits of aspirin have been attributed to inhibition of the cyclooxygenase (COX) pathway. Thromboxane A2 is an eicosanoid produced by the COX 1 enzyme in platelets. Aspirin inhibits cancer metastasis by inhibiting COX1 activity and thromboxane A2 synthesis. Hence, we assessed the role of thromboxane A2 in the development of lethal PC. Because thromboxane A2 is highly unstable, we measured its corresponding primary metabolite, urinary thromboxane b2 (TXB2), to examine the relationship of thromboxane A2 levels with PC. Method: TXB2 was measured in cases (977) and controls (1023) from the NCI-MD PC Case Control study using a mass-spectrometry-based assay. We estimated odds ratios (ORs) and 95% confidence intervals (CI) using unconditional logistic regression, with TXB2 levels modeled by quartiles. Multivariable models were adjusted for PC risk factors. Results: We observed an inverse relationship between aspirin use and levels of TXB2 in both cases and controls. For cases who used aspirin, the odds of having TXB2 urinary levels in the highest quartile (Q4) were significantly reduced when compared to non-users (adjusted OR = 0.29 95%CI 0.19-0.4) and this observation remained significant when stratified by race/ethnicity (AA men: OR 0.21 95%CI 0.11-0.38) (EA men: OR 0.34 95%CI 0.19-0.61), indicating significant inhibition of TXB2 formation by aspirin. The adjusted OR for PC was 1.42 (95%CI 1.09-1.85) for men in Q4 compared to Q1 (P trend 0.002). There was an association between TXB2 and PC in AA men (Q4 adjusted OR 1.95 95%CI 1.31-2.91, P trend <0.000) but not EA men (Q4 adjusted OR 1.04 95%CI 0.72-1.49, P trend 0.58), indicating increased thromboxane A2 synthesis in AA men with PC when compared to AA men without the disease. Also, men with Q4 levels of TXB2 were more likely to be diagnosed with metastasis compared to men with Q1 levels of TXB2 (adjusted OR 6.98 95%CI 1.51-32.32, P trend 0.014), indicating more aggressive disease for cases with the highest levels of TXB2. Conclusion: Aspirin use is protective against high levels of urinary TXB2. This is of clinical interest as we report increased urinary TXB2 associates with PC in AA men as well as with more aggressive PC which disproportionally affects AA men. These findings are consistent with our previous findings that aspirin inhibits aggressive disease in AA men and highlights the potential benefit of aspirin as a chemoprotective agent for this population through inhibition of thromboxane A2 synthesis. Citation Format: Maeve Kiely, Ginger Milne, Tsion Z. Minas, Tiffany H. Dorsey, Wei Tang, Cheryl J. Smith, Michael B. Cook, Clayton Yates, Stefan Ambs. High urinary thromboxane B2 associates with aggressive prostate cancer and inversely correlates with aspirin use [abstract]. In: Proceedings of the AACR Virtual Conference: Thirteenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2020 Oct 2-4. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(12 Suppl):Abstract nr PO-157.

The role of thromboxane A2 in complement activation-related pseudoallergy

AbstractComplement activation-related pseudoallergy (CARPA) is a hypersensitivity reaction occurring upon intravenous administration of numerous liposomal therapeutics, other nonbiological complex drugs and biologicals. It has a complex molecular and cellular mechanism that involves the production, actions and interactions of numerous vasoactive mediators in blood, including thromboxane A

Lack of Thromboxane Synthase Prevents Hypertension and Fetal Growth Restriction after High Salt Treatment during Pregnancy.

Preeclampsia (PE) is a potentially fatal pregnancy-related hypertensive disorder characterized by poor placenta development that can cause fetal growth restriction. PE-associated pathologies, including thrombosis, hypertension, and impaired placental development, may result from imbalances between thromboxane A2 (TXA2) and prostacyclin. Low-dose aspirin, which selectively inhibits TXA2 production, is used to prevent high-risk PE. However, the role of TXA2 in aspirin-mediated protective effects in women with PE is not understood fully. In this study, we examined the role of prostanoids in PE using human samples and an induced PE mouse model. We demonstrated that the administration of salted drinking water (2.7% NaCl) to wild-type mice resulted in elevated placental TXA2 synthase (TXAS) and plasma TXA2, but not prostacyclin, levels, which was also found in our clinical PE placenta samples. The high salt-treated wild-type pregnant mice had shown unchanged maternal body weight, hypertension (MAP increase 15 mmHg), and decreased pup weight (~50%) and size (~24%), but these adverse effects were ameliorated in TXAS knockout (KO) mice. Moreover, increased expression of interleukin-1β and downstream phosphorylated-p38-mitogen-activated protein kinase were concordant with apoptosis induction in the placentas of salt water-treated wild-type mice. These alterations were not observed in TXAS KO mice. Together, our data suggest that TXA2 depletion has anti-PE effects due to the prevention of hypertension and placental damage through downregulation of the interleukin-1β pathway.

Possible role of thromboxane A2 in remote hind limb preconditioning-induced cardioprotection.

Remote hind limb preconditioning (RIPC) is a protective strategy in which short episodes of ischemia and reperfusion in a remote organ (hind limb) protects the target organ (heart) against sustained ischemic reperfusion injury. The present study was designed to investigate the possible role of thromboxane A2 in RIPC-induced cardioprotection in rats. Remote hind limb preconditioning was performed by four episodes of 5 min of inflation and 5 min of deflation of pressure cuff. Occlusion of the hind limb with blood pressure cuff is most feasible, non-invasive, clinically relevant, and safe method for inducing RIPC. Isolated rat hearts were perfused on Langendorff apparatus and were subjected to global ischemia for 30 min followed by 120-min reperfusion. The levels of lactate dehydrogenase (LDH) and creatine kinase (CK) were measured in coronary effluent to assess the degree of myocardial injury. The extent of myocardial infarct size along with the functional parameters including left ventricular developed pressure (LVDP), dp/dtmax, and dp/dtmin were also measured. Ozagrel (thromboxane synthase inhibitor) and seratrodast (thromboxane A2 receptor antagonist) were employed as pharmacological modulators of thromboxane A2. Remote hind limb preconditioning significantly attenuated ischemia/reperfusion-induced myocardial injury and produced cardioprotective effects. However, administration of ozagrel and seratrodast completely abolished the cardioprotective effects of RIPC suggesting the key role of thromboxane A2 in RIPC-induced cardioprotection. It may be concluded that brief episodes of preconditioning ischemia and reperfusion activates the thromboxane synthase enzyme that produces thromboxane A2, which may elicit cardioprotection either involving humoral or neurogenic pathway.

Thromboxane A2 stimulates neurite outgrowth in cerebral cortical neurons via mitogen activated protein kinase signaling

Thromboxane A2 (TXA2) is a central prostanoid in the cardiovascular system and is a crucial mediator of vascular homeostasis and platelet aggregation. In this study, we report a novel role for TXA2 in neurite outgrowth. TXA2 receptor is expressed in rat cortical neurons, and treatment with the TXA2 agonist U-46619 promotes neurite outgrowth in a concentration-dependent manner. We investigated the molecular mechanism underlying U-46619-induced neurite outgrowth in cortical neurons. Blockade of the phosphorylation of mitogen activated protein kinase (MAPK) prevents U-46619-mediated neurite outgrowth. These data indicates that TXA2 functions as a positive regulator of neurite outgrowth via a mechanism dependent on MAPKs in cortical neurons.

Selective Deficiency Of Prostaglandin E2 Uncovers A Dominant Effector Role For Thromboxane A2 In Allergen-induced Pulmonary Inflammation And Vascular Remodeling

S U N D A Y 550 Selective Deficiency Of Prostaglandin E2 Uncovers A Dominant Effector Role For Thromboxane A2 In Allergeninduced Pulmonary Inflammation And Vascular Remodeling T. Liu, C. Feng, T. M. Laidlaw, W. Xing, S. Shen, G. Milne, J. A. Boyce; Department of Medicine, Harvard Medical School, Boston, MA, Jeff and Penny Vinik Center for Allergic Disease Research, Division of Rheumatology, Immunology and Allergy, Brigham and Women’s Hospital, Boston, MA, Department of Medicine and Pediatrics, Harvard Medical School, Boston, MA, Department of Pharmacology, Vanderbilt University, Nashville, TN. RATIONALE: Prostaglandin E2 (PGE2) has prominent anti-inflammatory and anti-fibrotic actions in the lung. Ptges mice are deficient in PGE2 and developed exaggerated pulmonary eosinophilia and hyperplasia of the pulmonary arteriolar smooth muscle compared with PGE2-sufficient controls when challenged intranasally with low doses of a house dust mite extract (Df). We hypothesized that both pulmonary eosinophilia and remodeling observed in the setting of selective PGE2 deficiency depend on thromboxane A2 (TXA2). METHODS: Double knockout mice lacking both ptges and T prostanoid (TP) receptor (ptges/tpr mice) were generated. After six challenges with Df, bronchial alveolar lavage fluid was collected and cell differential was counted; parabronchial lymph nodewas harvested and restimulated for cytokine generation analysis; and pulmonary pathological datawas collected. E prostanoid (EP) receptor-dependent blockade of intracellular adhesion molecule (ICAM)-1 induction by TP receptor stimulation was studied in vitro using human umbilical vein endothelial cells and antibody blocking of ICAM-1 was performed in vivo. RESULTS: The deletion of the TP receptor completely eliminated the increments in inflammation, vascular remodeling, effector cytokine generation, and ICAM-1 induction observed in the ptgesmice.Dysregulation of TP-dependent ICAM-1 induction was essential for the effects of PGE2 deficiency in vivo. In vitro studies demonstrated that TP receptor signaling was controlled hierarchically by EP1 and EP2 receptor-dependent pathways involving separate protein kinases. CONCLUSIONS: PGE2-mediated bronchoprotection involves prominent control of TP-dependent effector functions through a novel heterologous mechanism. TP receptor antagonism could be useful therapeutically in asthma associated with low levels of PGE2 production.

The effect of arachidonic acid on airway and pulmonary vasculature--the possible role of thromboxane A2 (author's transl)

The effect of arachidonic acid on airway and pulmonary vasculature--the possible role of thromboxane A2 (author's transl)

Effect of Pharmaceutical Interventions Targeting Thromboxane Receptors and Thromboxane Synthase in Cardiovascular and Renal Diseases

The present review focuses on the roles of thromboxane A2 (TxA2) in arterial thrombosis, atherogenesis, vascular stent-related ischemic events and renal proteinuria. Particular emphasis is laid on therapeutic interventions targeting the TxA2 (TP) receptors and TxA2 synthase (TS), including dual TP-receptor antagonists and TS inhibitors. Their significant inhibitory efficacies on arterial thrombogenesis, atherogenesis, restenosis after stent placement, vasoconstriction and proteinuria indicate novel and improved treatments for cardiovascular and selected renal diseases. New therapeutic interventions of the TxA2 pathway may also be beneficial for patients with poor biological antiplatelet drug response, for example, to aspirin and/or clopidogrel. These new TP/TS agents offer novel improved treatments to efficiently and simultaneously interfere with thrombogenesis and atherogenesis, and to enlarge the existing panel of platelet inhibitors for efficient prophylaxis and treatment of arterial thrombosis and renal proteinuria.

W1556 Pathogenic Importance of Thromboxane A2 in Ischemia/Reperfusion-Induced Gastric Injury in Mice

Background/Aim: Eicosanoids are involved in the regulatorymechanism of the gastricmucosal integrity under various conditions. We previously reported that COX-2/PGI2 plays a protective role in the gastric mucosal defense under ischemia/reperfusion (I/R)induced conditions, while indomethacin worsens these lesions, partly mediated by the up-regulation of leukotrienes and their receptors. However, it remains unknown whether thromboxane A2 (TXA2) plays any role in the pathogenesis of I/R-induced gastric injury. In the present study, we examined the role of TXA2 in the ulcerogenic response in the mouse stomach under I/Rinduced conditions. Methods: Under urethane anesthesia, the celiac artery was clamped (ischemia) for 30 min, followed by reperfusion by removal of the clamp. After reperfusion for 60 min, the area (mm2) of macroscopically visible lesions in the stomach was measured. SC-560 (COX-1 inhibitor: 5 mg/kg), rofecoxib (COX-2 inhibitor: 5 mg/kg), ozagrel [TX synthase (TXS) inhibitor: 200 mg/kg] or seratrodast [TXA2 receptor (TP) antagonist: 1-30 mg/kg] was administered PO 60 min before the onset of ischemia. Iloprost (PGI2 analogue: 1 μg/kg) was given IV 5 min before reperfusion. TXB2 and 6-keto-PGF1a contents in the gastric mucosa were measured by enzyme immunoassay. The expression of TP and TXS mRNAs were examined by RT-PCR. Results: I/R produced hemorrhagic lesions in the gastric mucosa, the lesion score being 9.3±2.1 mm2. The severity of I/R-induced gastric lesions was significantly decreased by the pretreatment with ozagrel, seratrodast or iloprost. By contrast, the gastric ulcerogenic response under I/R conditions was markedly worsened by pretreatment with rofecoxib, and this response was abrogated by co-administration of iloprost. The expressions of TP and TXS mRNAs were observed in the normal mouse stomach, and these expressions remained unchanged under I/R-induced conditions. I/R significantly increased both TXB2 and 6-keto-PGF1a contents in the gastric mucosa. The increase of TXB2 content under I/R conditions was significantly attenuated by SC-560 but not rofecoxib, while the increased PGI2 biosynthetic response was totally attenuated by rofecoxib but not SC-560. I/R by itself had no effect on the TXB2/ 6-keto-PGF1a ratio in the gastric mucosa, yet the ratio was markedly increased by rofecoxib and decreased by ozagrel, respectively. Conclusion: These results suggest that 1) COX-1/TXA2 plays a crucial role in the development of I/R-induced gastric lesions, in addition to COX-2/PGI2, and 2) the aggravation by rofecoxib of I/R-induced gastric lesions may be accounted partly for by the imbalance of TXA2/PGI2 ratio in the stomach.

W1560 Involvement of Aquaporin-1 in Epithelial Cell Migration During Wound Healing

Background/Aim: Eicosanoids are involved in the regulatorymechanism of the gastricmucosal integrity under various conditions. We previously reported that COX-2/PGI2 plays a protective role in the gastric mucosal defense under ischemia/reperfusion (I/R)induced conditions, while indomethacin worsens these lesions, partly mediated by the up-regulation of leukotrienes and their receptors. However, it remains unknown whether thromboxane A2 (TXA2) plays any role in the pathogenesis of I/R-induced gastric injury. In the present study, we examined the role of TXA2 in the ulcerogenic response in the mouse stomach under I/Rinduced conditions. Methods: Under urethane anesthesia, the celiac artery was clamped (ischemia) for 30 min, followed by reperfusion by removal of the clamp. After reperfusion for 60 min, the area (mm2) of macroscopically visible lesions in the stomach was measured. SC-560 (COX-1 inhibitor: 5 mg/kg), rofecoxib (COX-2 inhibitor: 5 mg/kg), ozagrel [TX synthase (TXS) inhibitor: 200 mg/kg] or seratrodast [TXA2 receptor (TP) antagonist: 1-30 mg/kg] was administered PO 60 min before the onset of ischemia. Iloprost (PGI2 analogue: 1 μg/kg) was given IV 5 min before reperfusion. TXB2 and 6-keto-PGF1a contents in the gastric mucosa were measured by enzyme immunoassay. The expression of TP and TXS mRNAs were examined by RT-PCR. Results: I/R produced hemorrhagic lesions in the gastric mucosa, the lesion score being 9.3±2.1 mm2. The severity of I/R-induced gastric lesions was significantly decreased by the pretreatment with ozagrel, seratrodast or iloprost. By contrast, the gastric ulcerogenic response under I/R conditions was markedly worsened by pretreatment with rofecoxib, and this response was abrogated by co-administration of iloprost. The expressions of TP and TXS mRNAs were observed in the normal mouse stomach, and these expressions remained unchanged under I/R-induced conditions. I/R significantly increased both TXB2 and 6-keto-PGF1a contents in the gastric mucosa. The increase of TXB2 content under I/R conditions was significantly attenuated by SC-560 but not rofecoxib, while the increased PGI2 biosynthetic response was totally attenuated by rofecoxib but not SC-560. I/R by itself had no effect on the TXB2/ 6-keto-PGF1a ratio in the gastric mucosa, yet the ratio was markedly increased by rofecoxib and decreased by ozagrel, respectively. Conclusion: These results suggest that 1) COX-1/TXA2 plays a crucial role in the development of I/R-induced gastric lesions, in addition to COX-2/PGI2, and 2) the aggravation by rofecoxib of I/R-induced gastric lesions may be accounted partly for by the imbalance of TXA2/PGI2 ratio in the stomach.

W1559 Pathogenic Importance of Endothelial Isozyme of Nitric Oxide Synthase (eNOS) in Aggravation of Gastric Lesions Induced By Indomethacin and Cold-Restraint Stress in Adjuvant-Induced Arthritic Rats

Background/Aim: Eicosanoids are involved in the regulatorymechanism of the gastricmucosal integrity under various conditions. We previously reported that COX-2/PGI2 plays a protective role in the gastric mucosal defense under ischemia/reperfusion (I/R)induced conditions, while indomethacin worsens these lesions, partly mediated by the up-regulation of leukotrienes and their receptors. However, it remains unknown whether thromboxane A2 (TXA2) plays any role in the pathogenesis of I/R-induced gastric injury. In the present study, we examined the role of TXA2 in the ulcerogenic response in the mouse stomach under I/Rinduced conditions. Methods: Under urethane anesthesia, the celiac artery was clamped (ischemia) for 30 min, followed by reperfusion by removal of the clamp. After reperfusion for 60 min, the area (mm2) of macroscopically visible lesions in the stomach was measured. SC-560 (COX-1 inhibitor: 5 mg/kg), rofecoxib (COX-2 inhibitor: 5 mg/kg), ozagrel [TX synthase (TXS) inhibitor: 200 mg/kg] or seratrodast [TXA2 receptor (TP) antagonist: 1-30 mg/kg] was administered PO 60 min before the onset of ischemia. Iloprost (PGI2 analogue: 1 μg/kg) was given IV 5 min before reperfusion. TXB2 and 6-keto-PGF1a contents in the gastric mucosa were measured by enzyme immunoassay. The expression of TP and TXS mRNAs were examined by RT-PCR. Results: I/R produced hemorrhagic lesions in the gastric mucosa, the lesion score being 9.3±2.1 mm2. The severity of I/R-induced gastric lesions was significantly decreased by the pretreatment with ozagrel, seratrodast or iloprost. By contrast, the gastric ulcerogenic response under I/R conditions was markedly worsened by pretreatment with rofecoxib, and this response was abrogated by co-administration of iloprost. The expressions of TP and TXS mRNAs were observed in the normal mouse stomach, and these expressions remained unchanged under I/R-induced conditions. I/R significantly increased both TXB2 and 6-keto-PGF1a contents in the gastric mucosa. The increase of TXB2 content under I/R conditions was significantly attenuated by SC-560 but not rofecoxib, while the increased PGI2 biosynthetic response was totally attenuated by rofecoxib but not SC-560. I/R by itself had no effect on the TXB2/ 6-keto-PGF1a ratio in the gastric mucosa, yet the ratio was markedly increased by rofecoxib and decreased by ozagrel, respectively. Conclusion: These results suggest that 1) COX-1/TXA2 plays a crucial role in the development of I/R-induced gastric lesions, in addition to COX-2/PGI2, and 2) the aggravation by rofecoxib of I/R-induced gastric lesions may be accounted partly for by the imbalance of TXA2/PGI2 ratio in the stomach.

Roles of thromboxane A2 and 5-hydroxytryptamine in endotoxin-induced digital vasoconstriction in horses

To evaluate the roles of 5-hydroxytryptamine (5-HT), thromboxane A2 (TxA2), and platelet-activating factor (PAF) in endotoxin-induced digital hypoperfusion in horses. 6 healthy adult Thoroughbreds. Horses were treated with IV administration of saline (0.9% NaCl) solution (control treatment) or the 5-HT 1B/D selective antagonist, GR55562 (0.3 mg/kg), prior to tryptamine infusion (1.6 microg/kg/min for 30 minutes) to establish an effective GR55562 dose. In a crossover study, horses were treated with IV administration of saline solution (control treatment), aspirin (4 mg/kg, 2 hours or 4 days before lipopolysaccharide [LPS] infusion), GR55562 (0.3 mg/kg), the PAF antagonist WEB2086 (3 mg/kg), or aspirin plus GR55562 prior to LPS infusion (30 ng/kg for 30 minutes). Digital blood flow was measured by use of Doppler ultrasonography. Concomitant measurements of hoof wall and coronary band surface temperatures were made. Serial blood samples were collected and plasma 5-HT and TxA2 concentrations determined. GR55562 abolished tryptamine-induced digital hypoperfusion. Neither WEB2086 nor GR55562 affected LPS-induced alterations in digital perfusion or plasma mediator concentrations. Aspirin given 2 hours before LPS administration abolished the increase in plasma TxA2 concentration and significantly attenuated LPS-induced digital hypoperfusion. Aspirin given 4 days before LPS significantly attenuated the increase in plasma TxA2 concentration and digital hypothermia. Aspirin plus GR55562 had a greater effect on LPS-induced digital hypothermia than aspirin alone. Thromboxane A2 and 5-HT played a role in mediating LPS-induced digital hypoperfusion in horses. Platelet-activating factor appeared unimportant in mediating LPS-induced 5-HT or TxA2 release or digital hypoperfusion.

Marked Interindividual Variability in the Response to Selective Inhibitors of Cyclooxygenase-2

Variability in response to drugs may influence both efficacy and safety. Cyclooxygenase (COX)-2 inhibitors pose a cardiovascular risk by potentially increasing the likelihood of thrombosis, hypertension, and atherogenesis. Differences between individuals in the response to COX-2 inhibitors would be expected to influence their susceptibility to cardiovascular complications. We examined the variability in degree and selectivity of COX-2 inhibition in humans in response to celecoxib and rofecoxib. Fifty healthy volunteers received placebo, rofecoxib (25 mg), and celecoxib (200 mg), randomized by order. COX-1 and COX-2 inhibition was determined using ex vivo and in vivo indices of enzymatic activity. A subset of 5 individuals underwent 5 replicate studies to estimate variability in drug response both within and between subjects. Despite the higher COX-2 selectivity of rofecoxib in vitro, the average selectivity attained by 25 mg rofecoxib and 200 mg celecoxib in vivo were not different. However, there was considerable variability at an individual level in the degree of COX-2 inhibition and selectivity attained by both drugs. Approximately one third of the variability was attributable to differences between individuals, suggesting the contribution of genetic sources of variance, such as candidate polymorphisms detected in COX-1 and CYP2C9. The actual degree of selectivity for inhibition of COX-2 achieved by the coxibs relates both to chemical properties of the drug and to factors within an individual that modulate drug response. These sources of variability might be exploited to identify patients uniquely susceptible to benefit or at developing risk of cardiovascular complications.

Tu-P7:47 Roles of thromboxane A2 and prostacyclin in the development of atherosclerosis in ApoE-deficient mice

Tu-P7:47 Roles of thromboxane A2 and prostacyclin in the development of atherosclerosis in ApoE-deficient mice

Role of thromboxane A2 in muscle injury following ischaemia.

The effect of a thromboxane A2 receptor antagonist (GR32191) on gastrocnemius muscle blood flow, oedema and viability was assessed in a rodent model of 6-h unilateral hindlimb ischaemia and 4-h reperfusion, and the results compared with those in control and normal groups, and in animals undergoing 6-h ischaemia alone. Control animals demonstrated reduced muscle blood flow throughout reperfusion (at 10 min, P < 0.01 versus normal, P not significant versus ischaemia; at 120 min, P < 0.05 versus normal and ischaemia; at 240 min, P < 0.01 versus normal, P not significant versus ischaemia), and the development of muscle oedema (P < 0.01 versus normal and ischaemia) and muscle necrosis (P < 0.01 versus normal and ischaemia). In contrast, the thromboxane A2 receptor antagonist enhanced muscle blood flow (at 10 min, P < 0.01 versus control; at 120 min, P < 0.05 versus control; at 240 min, P < 0.01 versus control) and preserved muscle viability (P < 0.01 versus control; P not significant versus normal and ischaemia). These results indicate that thromboxane A2 is an important mediator of skeletal muscle reperfusion injury and suggest that administration of a thromboxane A2 receptor antagonist may improve limb salvage rates after surgery for acute ischaemia.

Role of Thromboxane A2 in the Induction of Apoptosis of Immature Thymocytes by Lipopolysaccharide

Role of Thromboxane A2 in the Induction of Apoptosis of Immature Thymocytes by Lipopolysaccharide