Urinary Thromboxane Research Articles

“Aspirin Resistance”: Low Prevalence and Assay Discordance in a Pediatric Cohort.

“Aspirin resistance” (i.e., inadequate platelet inhibition as suggested by ex vivo assays in patients on aspirin) has been reported to occur commonly in adults and has been linked to an increased risk of adverse clinical events in this age group. However, its prevalence and clinical significance are largely unknown in children, with only limited pediatric data available. We have studied 22 children (ages 1 to 17 years) started on aspirin therapy for various indications (12 with a history of ischemic stroke, 6 after intervention via cardiac catheterization or surgery, 3 with a primary rheumatologic diagnosis, 1 with thrombocytosis) using a variety of measures of platelet inhibition, including optical aggregometry, PFA-100® and urinary thromboxane B2 concentration. We considered previously published definitions of aspirin resistance in adults, including ≥ 70% aggregation to 10 μM adenosine diphosphate (ADP) and ≥ 20% aggregation to 0.5 mg/mL arachidonic acid (AA), normal PFA-100 closure time (collagen/epinephrine cartridge) and normal urinary thromboxane B2 concentration (normal range defined by healthy pediatric controls). Subjects had received aspirin for a minimum of one week (range 1 to 249 weeks) prior to testing and mean aspirin dose was 3.4 mg/kg/d (range 1.3 to 7.9). Only 1 of 22 pediatric subjects (5%) met any of the pre-specified definitions for aspirin resistance; this single subject exhibited a normal PFA-100 closure time while receiving aspirin but was not aspirin resistant according to optical aggregometry or urinary thromboxane B2 criteria. Two other subjects on aspirin exhibited inappropriately “normal” aggregation to either ADP or AA (but not both). Each subject on aspirin excreted low levels of urinary thromboxane B2 compared with healthy non-medicated controls. To confirm an aspirin effect, five subjects were studied prior to initiation of aspirin therapy; each demonstrated pronounced changes in measured parameters after aspirin dosing (e.g. mean aggregation to AA decreased from 83 to 7%, p<.001). The small number of subjects who demonstrated any evidence of aspirin resistance did not differ from fully aspirin responsive subjects in terms of age, gender, race, platelet count, or aspirin dose, indication or therapy duration. Nor was there significant correlation between any of the measures of aspirin resistance we studied. In this initial prevalence study of a clinically diverse group of pediatric patients, laboratory evidence of aspirin resistance was not commonly encountered, despite our utilization of a broad panel of assays previously reported to identify aspirin resistance in adults. The prevalence of aspirin resistance in children thus appears low, and possibly less than that in adults. However, for the minority of pediatric patients who demonstrate laboratory evidence of aspirin resistance, this finding may hold clinical relevance; clinical follow-up of this cohort is ongoing. Finally, the lack of correlation we observed between assays previously linked to adverse clinical outcomes in patients taking aspirin supports that multiple molecular mechanisms contribute to the clinical phenotype of aspirin treatment failure.

The Paradox of Platelet Activation and Impaired Function: Platelet-von Willebrand Factor Interactions, and the Etiology of Thrombotic and Hemorrhagic Manifestations in Essential Thrombocythemia and Polycythemia Vera

Patients with essential thrombocythemia (ET) and polycythemia vera (PV), complicated by microvascular ischemic or thrombotic events, have shortened platelet survival, increased beta-thromboglobulin, platelet factor 4, and thrombomodulin levels, and increased urinary thromboxane B2 excretion. These are all reversible by inhibition of platelet cyclooxygenase 1 with aspirin, and are therefore indicative of platelet activation and platelet-mediated thrombotic processes. The thrombotic tendency persists as long as platelet counts are above the upper limit of normal (400 x 10 (9)/L). Despite strong evidence of in vivo platelet activation, the ex vivo platelet function tests are impaired. Platelet dysfunction in ET and PV typically is characterized by a missing second-wave adrenaline aggregation, an increased adenosine diphosphate aggregation threshold, and reduced secretion products, but a normal arachidonic acid or collagen-induced aggregation. The proposed concept is that platelets in thrombocythemia (ET and PV) are hypersensitive. Due to the existing high shear stress in the microvasculature (end-arterial circulation), platelets spontaneously activate, secrete their products, form aggregates mediated by von Willebrand factor (vWF) that transiently plug the microcirculation, deaggregate, and then recirculate as exhausted defective platelets with secondary storage pool disease on ex vivo analysis. At increasing platelet counts from below to above 1000 x 10 (9)/L, the thrombotic condition changes into an overt spontaneous bleeding tendency as a result of a functional vWF deficiency that is caused by proteolysis of large vWF multimers. This is consistent with acquired type 2 von Willebrand syndrome (AvWS). AvWS is reversible by reduction of the platelet count to normal. The acquired JAK2 V617F gain of function mutation is the cause of trilinear myeloproliferative disease with the sequential occurrence of ET and PV. Heterozygous JAK2 V617F mutation with slightly increased kinase activity is enough for the induction of spontaneous megakaryopoiesis and erythropoiesis, and an increase of hypersensitive platelets is the cause of aspirin-sensitive, platelet-mediated microvascular ischemic and thrombotic complications in ET and early PV mimicking ET. Homozygous JAK2 mutation with pronounced increase of kinase activity is associated with pronounced trilinear megakaryocyte, erythroid, and granulocytic myeloproliferation, with the most frequent clinical picture of classical PV complicated by major thrombosis, in addition to the platelet-mediated microvascular thrombotic syndrome of thrombocythemia.

Relation Between Atherosclerosis Risk Factors and Aspirin Resistance in a Primary Prevention Population

Resistance to inhibition of platelet function by aspirin may contribute to future myocardial infarction and stroke. Adverse cardiovascular outcomes have been associated with aspirin resistance on several different platelet function assays, including the level of urinary 11-dehydro thromboxane B2 (Tx-M), platelet aggregation to arachidonic acid and adenosine diphosphate, and closure time on the platelet function analyzer-100. We examined the concordance of these aspirin-resistance assays and their relation to cardiovascular risk factors in a primary prevention population. Asymptomatic patients (n = 1,311) at increased risk for coronary heart disease were evaluated before and after 2 weeks of aspirin (81 mg/day). Aspirin resistance was defined according to published criteria for these 3 assays of platelet function. Subjects were characterized for the presence of atherosclerosis risk factors. Agreement among the 3 assays was poor. Only 5 patients met aggregation criteria for aspirin resistance. Attenuated suppression of urinary Tx-M by aspirin was associated with a greater atherosclerotic risk profile and Framingham risk score in multivariable regression analysis. Aspirin resistance by platelet function analyzer-100 was associated only with increased von Willebrand factor levels and not with atherosclerotic risk profile. In conclusion, in a primary prevention population, different published criteria for aspirin resistance classify distinct groups of patients as aspirin resistant with very little overlap. Higher Tx-M, which reflects decreased suppression of thromboxane production in vivo, is the only criterion associated with atherosclerosis risk factors, suggesting that this measurement may represent the most relevant approach for identifying asymptomatic subjects whose aspirin treatment will "fail."

Clinical and Laboratory Features, Pathobiology of Platelet-Mediated Thrombosis and Bleeding Complications, and the Molecular Etiology of Essential Thrombocythemia and Polycythemia Vera: Therapeutic Implications

Microvascular disturbances in essential thrombocythemia (ET) and polycythemia vera (PV), including erythromelalgia, and atypical and typical transient cerebral, ocular, and coronary ischemic attacks, are caused by platelet-mediated transient and occlusive thrombosis in the end-arterial circulation. ET patients with microvascular disturbances have shortened platelet survival, increased beta-thromboglobulin (beta-TG), platelet factor 4 (PF4), and thrombomodulin (TM) levels, and increased urinary thromboxane B2 (TXB2) excretion, indicating platelet-mediated thrombotic processes. Inhibition of platelet cyclooxygenase-1 by aspirin is followed by relief of microvascular disturbances; correction of shortened platelet survival; correction of increased plasma beta-TG, PF4, and TM levels; and correction of increased TXB2 excretion to normal. In PV associated with thrombocythemia, increased hematocrit and whole blood viscosity aggravate the platelet-mediated microvascular syndrome of thrombocythemia to produce major arterial and venous thrombotic complications. Correction of hematocrit to normal by phlebotomy will reduce the major arterial and venous thrombotic complications, but fails to prevent the platelet-mediated microvascular circulation disturbances in PV patients because thrombocythemia persists. Complete relief and prevention of microvascular and major thrombosis in ET and PV patients, in addition to phlebotomy, are obtained by treatment with aspirin and not with coumarin. The discovery of JAK2 V617F gain of function mutation in patients with myeloproliferative disorders (MPDs) expands our insights into the molecular etiology and biological features of ET, PV, and chronic idiopathic myelofibrosis (CIMF). The current concept is that heterozygous JAK2 V617F mutation with increased kinase activity is enough for megakaryocyte proliferation and increased hypersensitive platelets with no or slightly increased erythropoiesis in ET and in early PV mimicking ET. Homozygous JAK2 mutation with pronounced kinase activity is associated with trilinear megakaryocyte, erythroid, and granulocytic myeloproliferation, myeloid metaplasia, and secondary myelofibrosis (MF), with the most frequent clinical picture of classical PV complicated by major thrombosis in addition to the platelet-mediated microvascular thrombotic syndrome of thrombocythemia. The positive predictive value of a JAK2 V617F polymerase chain reaction test for the diagnosis of MPDs is high (near to 100%), but only half of ET and MF (sensitivity 50%) and the majority of PV (sensitivity 85 to 97%) are JAK2 V617F positive. Bone marrow histopathology, when used in combination with specific markers such as serum erythropoietin, PRV-1, endogenous erythroid colony formation, peripheral blood parameters and red cell mass, has a high sensitivity and specificity (near 100%) to detect the early and overt stages of the MPDs and to differentiate between ET, PV, and CIMF in both JAK2 V617F-positive and -negative MPDs.

Influence of Natural Honey on Biochemical and Hematological Variables in AIDS: A case study

Honey lowers prostaglandins and elevates nitric oxide (NO) in various biological fluids in normal persons. NO and prostaglandin play a role in pathogenesis of AIDS. The study was designed to assess the effect of natural honey on prostaglandins and NO levels, blood indices and biochemical tests in a 40 year-old woman with AIDS. This presentation is a case story of a 40 year-old women with a long history of AIDS treated with 80g of natural honey. Plasma and urinary prostaglandin F2 alpha and thromboxane B2 levels, plasma, urine and saliva content of NO-end product (total nitrite) and hematological tests were estimated before and 3 hours after oral consumption of 80g of natural honey. These variables, in addition to biochemical tests, were re-estimated after 21 days of daily consumption of 80g of natural honey. Results showed that prostaglandins level compared with normal subjects were elevated in patient with AIDS. Natural honey decreased prostaglandins levels, and elevated NO-end product, percentage of lymphocytes, platelet count, and serum protein, albumin and copper levels. It might be concluded that natural honey decreased prostaglandins level, elevated NO production and improved hematological and biochemical tests in a patient with a long history of AIDS.

Platelet-mediated erythromelalgic, cerebral, ocular and coronary microvascular ischemic and thrombotic manifestations in patients with essential thrombocythemia and polycythemia vera: A distinct aspirin-responsive and coumadin-resistant arterial thrombophilia

Microvascular circulation disturbances including erythromelalgia, its microvascular ischemic complications, and migraine-like atypical or typical transient ischemic cerebral, ocular, and coronary ischemic attacks are specific clinical manifestations in patients with essential thrombocythemia (ET), and polycythemia vera (PV) associated with thrombocythemia. Thrombocythemia (ET and PV) patients with microvascular disturbances have shortened platelet survival, increased β-thromboglobulin (β-tg), platelet factor 4 (PF4), and thrombomoduline (TM) levels, and increased urinary thromboxane B2 (TxB2) excretion indicating platelet-mediated processes in vivo. Inhibition of platelet cyclooxygenase (COX 1) by aspirin is followed by relief of microvascular disturbances, correction of shortened platelet survival, and return of plasma levels of β-tg, PF4, TM levels and TxB2 excretion to normal. The transient ischemic attacks and thrombotic complications in thrombocythemia are very likely caused by hypersensitive platelets produced by spontaneously proliferating enlarged megakaryocytes in the bone marrow of ET and PV patients. In contrast to normal platelets in healthy individuals the circulating hypersensitive thrombocythemic platelets spontaneously activate and secrete their products, thus forming aggregates that transiently plug the microcirculation, or result in occlusive platelet thrombi in arterioles or small arteries. Clear evidence is presented that the microvascular transient ischemic and occlusive thrombotic complications in thrombocythemia patients are relieved by treatment with aspirin and by reduction of platelet counts to normal (<400 × 109/l), but not by coumadin. In patients with thrombocythemia associated with PV, increased hematocrit and whole blood viscosity aggravate the platelet-mediated microvascular ischemic and thrombotic syndrome of thrombocythemia to major arterial and venous thrombotic complications. Correction of hematocrit and blood viscosity by phlebotomy significantly reduces the major arterial and venous thrombotic complications, but fails to prevent the platelet-mediated microvascular circulation disturbances in PV patients because thrombocythemia persists. Complete relief and prevention of microvascular and major thrombosis in PV patients are obtained by treatment with low-dose aspirin on top of phlebotomy or by treatment with the platelet lowering agents, anagrelide, interferon or hydroxyurea.

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.

Meal‐induced platelet activation in Type 2 diabetes mellitus: effects of treatment with repaglinide and glibenclamide

To compare the effects of treatment with repaglinide and glibenclamide on platelet function and endothelial markers in patients with Type 2 diabetes mellitus, before and after a standardized meal. Fifteen patients with Type 2 diabetes were investigated on three occasions: at baseline without oral hypoglycaemic drug treatment, and after 6 weeks' treatment with repaglinide or glibenclamide, respectively, in an open randomized cross-over study. Agonist-induced platelet P-selectin expression and platelet aggregation, urinary thromboxane, soluble P-selectin, von Willebrand factor (VWF), soluble E-selectin, intercellular adhesion molecule (ICAM-1) and C-reactive protein (CRP) were measured. In addition, pre-meal data were compared with non-diabetic control subjects (n = 15), matched for sex, age and BMI. Adenosine diphosphate (ADP)-induced platelet P-selectin expression increased post-meal in Type 2 diabetic patients both at baseline and after treatment with repaglinide and glibenclamide (P < 0.01 for all; repeated measures anova). Repaglinide treatment reduced fasting ADP-induced P-selectin expression compared with baseline (P = 0.01), but did not influence meal-induced platelet hyper-reactivity (P = 0.32). No significant anti-platelet effects of glibenclamide treatment were found. Plasma concentrations of VWF and ICAM-1 were elevated in patients with Type 2 diabetes compared with control subjects (P < 0.05 for both) and were reduced during treatment with repaglinide (P < 0.01 for both) but did not change during glibenclamide treatment. The post-meal state is associated with enhanced platelet reactivity in patients with Type 2 diabetes mellitus. Pre-meal treatment with repaglinide or glibenclamide does not inhibit postprandial platelet activation, but repaglinide treatment is associated with attenuated platelet and endothelial activity in the fasting state.

Lumiracoxib Does Not Affect the Ex Vivo Antiplatelet Aggregation Activity of Low‐Dose Aspirin in Healthy Subjects

This randomized, double-blind, placebo-controlled study evaluated the pharmacodynamic effects of concomitant low-dose aspirin and lumiracoxib in healthy subjects. Participants received lumiracoxib 400 mg once daily (n = 14) or placebo (n = 14) for 11 days, with concomitant low-dose aspirin (75 mg once daily) from days 5 to 11. Ex vivo pharmacodynamic assessments included assays of platelet aggregation and urinary thromboxane and prostacyclin metabolite profile. Arachidonic acid-stimulated platelet aggregation was reduced from 76.3% on day 4 to 4.8% on day 11 in the placebo group and from 75.8% on day 4 to 5.1% on day 11 in the lumiracoxib group. Collagen-induced platelet aggregation was reduced from 77.5% on day 4 to 52.8% on day 11 in the placebo group and from 79.5% on day 4 to 55.9% on day 11 in the lumiracoxib group. Urinary thromboxane and prostacyclin were unaffected by lumiracoxib. In conclusion, concomitant lumiracoxib did not interfere with the cyclooxygenase-1-mediated antiplatelet effects of low-dose aspirin.

Captopril effect on prostaglandin E2, thromboxane B2 and proteinuria in lupus nephritis patients

Objective High urinary Prostaglandin E2 (PGE2) and thromboxane B2 (TxB2) levels have been reported in lupus nephritis (LN). Captopril diminishes proteinuria and improves glomerular filtration rate (GFR), and may have effect on immune function. We evaluate captopril effect on urinary PGE2, and TxB2. Methods Eighteen LN patients were randomly assigned to two groups. Group 1 received only prednisone plus cyclophosphamide. Group 2 received also captopril. Serum creatinine, GFR, RPF, urinary proteins, PGE2 and TxB2, were assessed. Results There were no differences between the initial and final assessments in Group 1. Group 2 showed a significant decrement in proteinuria ( p = 0.003) and serum creatinine ( p = 0.01) at the end of the study. PGE2 decreased significantly when compared with the initial value ( p = 0.02). Conclusion Captopril plus usual treatment, improved serum creatinine and decreased proteinuria in parallel with prostaglandin E2 reduction. This effect is not related to changes in GFR or RPF. Captopril may have an immunomodulatory effect on local inflammatory processes in lupus nephritis.

Increased Susceptibility to Pulmonary Hypertension in Heterozygous BMPR2-Mutant Mice

Bone morphogenetic protein receptor-2 (BMPR2)-heterozygous, mutant (BMPR2(+/-)) mice have a genetic trait similar to that of certain patients with idiopathic pulmonary arterial hypertension (IPAH). To understand the role of BMPR2 in the development of IPAH, we examined the phenotype of BMPR2(+/-) mice and their response to inflammatory stress. BMPR2(+/-) mice were found to have the same life span, right ventricular systolic pressure (RVSP), and lung histology as those of wild-type mice under unstressed conditions. However, when treated with recombinant adenovirus expressing 5-lipoxygenase (Ad5LO), BMPR2(+/-) mice exhibited significantly higher RVSP than wild-type mice. The increase of RVSP occurred in the first 2 weeks after Ad5LO delivery. Modest but significant muscularization of distal pulmonary arterioles appeared in BMPR2(+/-) mice 4 weeks after Ad5LO treatment. Measurement of urinary metabolites of vasoactive molecules showed that cysteinyl leukotrienes, prostacyclin metabolites, and PGE2 were all increased to a similar degree in both BMPR2(+/-) and wild-type mice during 5LO transgene expression, whereas urinary endothelin-1 remained undetectable. Urinary thromboxane A2 metabolites, in contrast, were significantly higher in BMPR2(+/-) than in wild-type mice and paralleled the increase in RVSP. Platelet activation markers, serotonin, and soluble P-selectin showed a trend toward higher concentrations in BMPR2(+/-) than wild-type mice. Cell culture studies found that BMP treatment reduced interleukin-1beta-stimulated thromboxane A2 production in the pulmonary epithelial cell line A549. BMPR2(+/-) mice do not develop pulmonary hypertension spontaneously; however, under inflammatory stress, they are more susceptible to an increase in RVSP, thromboxane A2 production, and vascular remodeling than wild-type mice.

Nocturnal rise of urinary thromboxane B2 in patients with coronary artery disease

Nocturnal rise of urinary thromboxane B2 in patients with coronary artery disease

Comparison of Three Different Platelet Function Assays to Determine Aspirin Sensitivity.

In large studies of patients with cardiac disease, it was observed that up to 9% are ASA resistant (ASAR) and 23% are ASA semi responders using the platelet function analyzer (PFA-100), which measures whole blood platelet adhesion and aggregation under high shear. The prevalence of ASAR is of great clinical importance. With an estimated 20 million patients in the USA taking ASA for prevention of atherosclerotic events, even a 10% incidence equates to more than two million patients receiving inadequate anti-platelet therapy. Given the widespread use of ASA, more reliable and rapid methods to measure aspirin sensitivity are needed. Importantly, future large scale studies to determine the effect of monitoring ASA sensitivity to optimize therapy are compromised due to current lack of uniformity in assessing ASAR from center to center. The classical method of platelet aggregometry is labor-intensive and not readily adaptable to the clinical setting. Moreover, platelet aggregometry measures platelet responses under low shear, which does not simulate the high shear conditions expected to be involved in arterial thrombosis. In contrast, the PFA-100 does measure thrombus formation under high shear. The new TEG platelet coagulation assay uses whole blood, includes high shear, and is a point of care method. We compared these three techniques to assess aspirin effects on platelet function and clot formation: PFA-100 with collagen-epinephrine cartridges, TEG platelet coagulation assay, and standard optical aggregation in platelet rich plasma using arachidonic acid (AA) and adenosine diphosphate (ADP) as agonists. RESULTS: We found significant differences between the PFA-100, TEG platelet function, and standard optical aggregation. Twelve normal individuals previously defined as ASA sensitive or ASAR, using the PFA-100, were studied at baseline and following three days of oral aspirin at 81mg/day. We found that all four patients determined to be ASAR by PFA-100 were found to be sensitive in TEG and aggregometer assays when using AA as the agonist. Furthermore, some participants showed a gain of platelet function following ASA when studied on the TEG and aggregometer using ADP as the agonist. Currently, it is unclear which response to ASA treatment is most important to predict cardiovascular complications in normal individuals or patients placed on aspirin. Gum et al, showed that increased urinary secrection of thromboxane metabolites, suggesting ASA insensitivity, is associated with a higher incidence of cardiovascular events. Unfortunately, this test may simply indicate poor patient compliance rather than true ASAR, so a clear demonstration of platelet sensitivity will also be necessary. Our data confirms the need for a collaborative trial comparing different platelet assays to assess true ASA sensitivity together with concurrent measurements of urinary thromboxane metabolite levels. Knowing which assay best links aspirin sensitivity to disease outcome will allow physicians to better manage normal individuals and patients at risk for significant cardiovascular disease.

Beneficial effect of aspirin on renal function post-cardiopulmonary bypass.

Urine thromboxane, plasma creatinine, and creatinine clearance were determined perioperatively in 20 patients undergoing coronary bypass surgery. Ten patients took aspirin until the day of surgery, and 10 discontinued aspirin at least one week before surgery. A significant increase in urine thromboxane following establishment of cardiopulmonary bypass was observed only in the control group. Plasma creatinine increased in the control group on the 1st postoperative day (from 81.9 +/- 13.2 to 97.6 +/- 13.2 micromol.L(-1), p = 0.02) and decreased next day to the preoperative level (82.7 +/- 9 micromol.L(-1), p = 0.03). In the aspirin group, creatinine remained unchanged on the 1st postoperative day (89.4 +/- 14.2 vs. 87.2 +/- 7.7 micromol.L(-1), p = 0.6), and increased significantly on the 2nd day (101.4 +/- 8.5 micromol.L(-1), p = 0.01). The aspirin group had higher creatinine levels (p < 0.0001) and lower creatinine clearance (60.2 +/- 16.5 vs. 82 +/- 25.7 mL.min(-1), p < 0.0001) than the control group on the 2nd postoperative day. A significant positive correlation was seen between urine thromboxane and creatinine on day 2 in both groups (r = 0.6). Aspirin administrated before coronary surgery may have a beneficial effect on renal function, probably mediated by its antiplatelet activity and thromboxane inhibition.

Cyclooxygenase isoforms and platelet vessel wall interactions in the apolipoprotein E knockout mouse model of atherosclerosis.

Cyclooxygenase (COX) activity is induced in human atherosclerosis, and the products formed may modify the disease directly or through an effect on platelets. We examined the role of COX-1 and -2 on platelet vessel wall interactions and development of atherosclerosis in a murine model. Apolipoprotein E-deficient (apoE-/-) mice fed a 1% cholesterol diet were treated with a selective COX-1 inhibitor (SC-560), a selective COX-2 inhibitor (SC-236), or vehicle. Urinary prostacyclin and thromboxane metabolites (2,3-dinor-6-keto-PGF1alpha and 2,3-dinor-TXB2) were increased in the apoE-/- knockout mouse. There was also induction of both COX isoforms in the vascular lesions formed, which stained for CD41, a platelet-specific marker, and for CD40L. Selective inhibition of COX-2 had no effect on lesion formation and, despite selective reduction in prostacyclin generation, had no effect on platelet activity, as measured by thromboxane formation or platelet deposition. Selective inhibition of COX-1 reduced 2,3-dinor-TXB2 generation and lesion formation. However, platelet deposition on the vessel wall persisted, with well-defined monolayers seen. There was also persistent expression of the macrophage marker CD68 and increased expression of the cell death protein Bax. In contrast to lesion development, the selective COX-1 inhibitor had no effect on the regression of evolving lesions. COX-1 plays an important role in the early stages of lesion development in the apoE-/- knockout model of atherosclerosis, preventing gross lesion formation in the face of continued vascular injury and inflammation. Despite the inhibition of prostacyclin, COX-2 inhibition had no effect on lesion development or platelet-vessel wall interactions.

L-arginine reverses p47phox and gp91phox expression induced by high salt in Dahl rats.

Derangements in the production and degradation of reactive oxygen species (ROS) as well as nitric oxide (NO) have been implicated in cardiovascular diseases. We explored how supplementation with l-arginine, an NO synthase substrate, restores such derangements of ROS/NO systems in Dahl salt-sensitive, hypertensive (DS) rats. We detected an increase of NADPH oxidase activity, a key enzyme that produces superoxide, in the membrane fraction of the renal cortex derived from DS rats loaded with high salt for 4 weeks; high salt loading also remarkably increased urinary H2O2, 8-isoprostane, and thromboxane B2 excretion and decreased plasma NO end products. These changes from high salt loading were counteracted by oral l-arginine supplementation. We further examined expression patterns of NADPH oxidase subunits in renal cortex derived from these animals. High salt loading increased gp91phox and p47phox but not p22phox or Rac1 or mRNA abundance, which were counteracted with L-arginine supplementation. Western blot analyses after subcellular fractionation revealed that l-arginine supplementation distinctly decreases membrane localization of p47phox protein, as it decreases total expression of Rac1 protein in DS rats with high salt loading. These results disclose that high salt loading causes a deficiency in available L-arginine amounts for NO synthases and induces NADPH oxidase activation in the renal cortex of DS rats, which l-arginine supplementation markedly restores. Since superoxide rapidly eliminates NO, which inhibits sodium reabsorption in the cortical collecting duct, superoxide production caused by upregulated NADPH oxidase activity in the renal cortex of high salt-loaded DS rats may accelerate sodium reabsorption and hypertension.

Thromboxane inhibition improves renal perfusion and excretory function in severe congestive heart failure

ObjectivesThe aim of this study was to evaluate whether thromboxane inhibition can favorably affect renal perfusion and clinical conditions in patients affected by severe heart failure. BackgroundThe renal formation of the vasoconstrictor thromboxane A2(TxA2) is increased during cardiac failure. MethodsBy oral administration of picotamide (a renal TxA2synthase and TxA2/prostaglandin H2receptor inhibitor), we blocked renal TxA2. Fourteen patients in New York Heart Association functional class IV were studied according to a randomized, double-blinded, cross-over design. Each of the two eight-day periods of testing was preceded by a three-day period during which certain vasoactive medications were stopped. ResultsDaily 24-h total urinary thromboxane B2(TxB2), the stable metabolite of TxA2, dropped at the end of picotamide treatment (p < 0.01 vs. baseline). Compared with placebo, effective renal plasma flow and the glomerular filtration rate increased (p < 0.01 and p < 0.05, respectively), thus leading to a significant decrease in the filtration fraction (p < 0.01). Renal vascular resistance decreased consistently (p < 0.01). In all patients, picotamide treatment was associated with an increase in diuresis and natriuresis (p < 0.001 vs. baseline). Plasma creatinine decreased (p < 0.05 vs. baseline). Patients also showed improvement in several clinical parameters, including a significant decrease in both pulmonary and venous pressure (p < 0.01 vs. baseline). ConclusionsThese results indicate that renal thromboxane formation plays an important role in renal vascular resistance in patients with severe heart failure, such as those described in the present study. Inhibition of TxA2improves renal hemodynamics and kidney function and favorably affects indexes of cardiac performance.

Aspirin and clopidogrel in acute coronary syndromes: therapeutic insights from the CURE study.

Platelet adhesion, activation, and aggregation are central to thrombus formation, which follows atherosclerotic plaque disruption and causes acute coronary syndromes. Aspirin and clopidogrel exert their antiplatelet effects by inhibiting thromboxane A2 production and adenosine diphosphate-induced platelet aggregation pathways, respectively. Aspirin has proven benefits in primary and secondary prevention of coronary artery disease. Clopidogrel, an alternative antiplatelet agent used in patients with aspirin intolerance, is especially useful in combination with aspirin after coronary stent procedures. The CURE (Clopidogrel in Unstable Angina to Prevent Recurrent Events) study demonstrates for the first time the benefit of adding clopidogrel to aspirin rather than using aspirin alone in patients having acute coronary syndromes without ST-segment elevation myocardial infarction. Patients who are resistant to aspirin (up to 10%) have higher rates of cardiovascular events and may derive special benefit from the combination therapy. Aspirin resistance can be assessed through platelet aggregometry testing, measurement of urinary thromboxane metabolites, and, possibly, genomic testing in the future.

Platelet-mediated microvascular inflammation and thrombosis in thrombocythemia vera: a distinct aspirin-responsive arterial thrombophilia, which transforms into a bleeding diathesis at increasing platelet counts

Erythromelalgia is the main, pathognomonic and presenting symptom in patients with essential thrombocythemia and thrombocythemia associated with polycythemia vera. Complete relief from erythromelalgic and acrocyanotic pain is obtained with the cyclooxygenase inhibitors aspirin and indomethacin, but not with sodiumsalicylate, dipyridamol, sulfinpyrozone and ticlopedine. Thus, cyclooxygenase metabolites are necessary for erythromelalgia to develop. Local platelet consumption in erythromelalgic areas became evident by the demonstration of arteriolar fibromuscular intimal proliferation and occlusions by platelet-rich thrombi in skin biopsies, by the findings of shortened platelet survival times, significant higher levels of platelet activation markers β-thromboglobulin, thrombomoduline and increased urinary thromboxane B2 excretion in thrombocythemia patients suffering from erythromelalgia. Aspirin treatment of erythromelalgia in thrombocythemia patients resulted in the disappearance of the erythromelalgic, thrombotic signs and symptoms, correction of the shortened platelet survival times, and a significant reduction of the increased levels of β-TG, PF4, TM and urinary TxB2 excretion to normal. Erythromelalgia is frequently preceded or followed by atypical transient neurologic, ocular or coronary ischemic symptoms, which specifically respond to low-dose aspirin or reduction of platelet counts to normal. The broad spectrum of acropareshesias, erythromelalgia and acrocyanotic ischemia together with the episodic and transient atypical TIAs and ocular or coronary ischemic symptoms are caused by spontaneous activation and aggregation of hypersensitive platelets in the end-arterial microvasculature involving the peripheral, cerebral and coronary circulation of thrombocythemia patients. These microvacular circulation ischemic disturbances in thrombocythemia vera already occur at platelet counts in excess of 400 × 10 9 l –1. Low-dose aspirin is highly effective and safe in the cure and prevention of thrombotic and ischemic events and does not elicit bleedings at platelet counts below 1000 × 10 9 l –1. Spontaneous hemorrhages usually occur at very high platelet counts far in excess of 1000 × 10 9 l –1 (HT) due to an acquired von Willebrand factor deficiency at increasing platelet counts. At platelet counts between 1000 and 2000 × 10 9 l –1, thrombosis and bleeding (ETT and HT) frequently occur in sequence or paradoxically and low-dose aspirin does prevent thrombotic complications but aggravates or may elicit bleeding symptoms. Reduction of the platelet count to below 1000 × 10 9 l –1 by platelet lowering agents usually results in the disappearance of the bleeding tendency and improvement of the von Willebrand syndrome, but the thrombotic tendency persists as long as platelet counts are above the upper limit of normal.

Cocaine decreases urinary prostacyclin release in pregnancy: correlation with uterine and umbilical Doppler velocimetry

Objective: The purpose of this study was to determine maternal urinary prostacyclin and thromboxane excretion in patients with recent cocaine use, compared to cocaine-free controls, and correlate the findings with Doppler velocimetry.Study design: Seventeen patients admitted withpremature rupture of membranes between the gestational ages of 24 and 34 weeks were tested for urinary cocaine metabolites. Eleven patients had positive screening and six patients were negative and served as controls. After initial stabilization, 24-hurine collections were obtained and were assayed for the prostacyclin metabolite 2,3-dinor-6-keto-PGF1α, and the thromboxane metabolite 2,3-dinor TXB2. These patients underwent uterine and umbilical arterial Doppler velocimetry expressed as the pulsatility index. Statistical analysis was performed by the SPSS statistical package using the non-paired Student ttest, and Spearman correlation coefficient with p < 0.05 being considered significant.Results: Compared withcontrols, urinary excretion of prostacyclin in pregnant women with recent cocaine use was significantly lower. The pulsatility index of the uterine arteries of the cocaine-positive individuals was higher than in controls and had a significant inverse correlation withprostacyclin metabolite excretion. Umbilical arterial velocimetry was similar in the two groups.Conclusion: Recent cocaine ingestion in pregnant women decreases production of prostacyclin and negatively affects the pulsatility index of the uterine artery.