Persistent production of platelet thromboxane A2 in patients chronically treated with aspirin

BACKGROUND: Patients treated with aspirin may have a reduced sensitivity to its antiplatelet effect. The mechanism accounting for such a reduced sensitivity might involve an impaired interaction of aspirin with cyclooxygenase-1 (COX)-1. OBJECTIVE: We sought to investigate whether platelets from patients under chronic treatment with aspirin still produce TxA2 and whether there is any relationship between the eventual persistent TxA2 formation and platelet aggregation. Finally, whether platelet-derived TxA2 can be inhibited by in vitro addition of aspirin. METHODS: Collagen-induced platelet aggregation and thromboxane-A2 (TxA2) were measured in 196 patients treated with aspirin (100-330 mg day(-1)) because of previous vascular events or presence of risk factors of atherosclerosis. RESULTS: Collagen-induced TxA2 production of the entire cohort was 128.7 +/- 21.6 pg 10(-8) cells, and was significantly correlated with platelet aggregation (Spearman's correlation coefficient = 0.44; P < 0.0001). Patients in the highest quartile of TxA2 showed higher platelet response to collagen (P < 0.0001) when compared with those in the lowest quartile. In a subgroup of 96 patients, platelets were treated in vitro with a TxA2 receptor antagonist (13-azaprostanoic acid) or aspirin before stimulation with collagen. 13-APA acid significantly inhibited platelet aggregation. Aspirin reduced (-72.9%) TxA2 production in patients with TxA2 values above the median but it was ineffective in those with TxA2 values below the median. CONCLUSION: In some patients chronically treated with aspirin platelet production of TxA2 may persist and account for enhanced platelet aggregation. Incomplete inhibition of COX-1 seems to be implicated in persistent TxA2 production.     

Residual platelet thromboxane A2 and prothrombotic effects of erythrocytes are important determinants of aspirin resistance in patients with vascular disease

Background: Permanent inactivation of cyclooxygenase‐1 and inhibition of platelet thromboxane A₂ (TxA₂) constitute the main mechanisms underlying the prevention of vascular disease by aspirin. Methods and Results: We studied platelet TxA₂ synthesis and its impact on platelet reactivity and platelet–erythrocyte [platelet‐rich plasma (PRP)–RBC] interactions in 533 aspirin‐treated patients with vascular disease. Seventy aspirin‐free and 16 aspirin‐treated normal subjects were evaluated as controls. Collagen (1 μg mL^?1)‐induced platelet activation (¹⁴C‐5HT release) and recruitment (proaggregatory activity of cell‐free releasates from activated platelets) were assessed in PRP, PRP + RBC, and whole blood (WB). TxA₂ was quantified in releasates from WB. Aspirin inhibited TxA₂ synthesis and platelet function in all patients, but to different degrees. Forty‐two patients (8%) displayed partial (<95%) inhibition of TxA₂ relative to that of aspirin‐free controls. They produced >3.5 ng mL^?1 TxA₂ and had higher platelet reactivity than 491 patients who had undetectable TxA₂ or produced residual TxA₂ (R‐TxA₂; ≤3.5 ng mL^?1). Patients with R‐TxA₂ were distributed into TxA₂ quartiles. Patients in the third and fourth quartiles had significantly elevated ¹⁴C‐5HT release in PRP, which was markedly amplified in PRP + RBC and WB. TxA₂ in the fourth quartile translated into increased platelet aggregation and recruitment. Significant correlations were found between R‐TxA₂ and platelet hyperfunction. Conclusion: Biochemical markers (TxA₂ synthesis, ¹⁴C‐5HT release) and biological assays (platelet aggregation and recruitment) used to monitor the aspirin effect in a large population of patients presenting with vascular disease have evidenced the importance of R‐TxA₂ and the prothrombotic effects of RBC in aspirin resistance.     

Cyclooxygenase-1 haplotype modulates platelet response to aspirin

BACKGROUND: Aspirin (acetylsalicylic acid) irreversibly inhibits platelet cyclooxygenase (COX)-1, the enzyme that converts arachidonic acid (AA) to the potent platelet agonist thromboxane (TX) A2. Despite clear benefit from aspirin in patients with cardiovascular disease (CAD), evidence of heterogeneity in the way individuals respond has given rise to the concept of 'aspirin resistance.'AIMS: To evaluate the hypothesis that incomplete suppression of platelet COX as a consequence of variation in the COX-1 gene may affect aspirin response and thus contribute to aspirin resistance. PATIENTS AND METHODS: Aspirin response, determined by serum TXB2 levels and AA-induced platelet aggregation, was prospectively studied in patients (n = 144) with stable CAD taking aspirin (75-300 mg). Patients were genotyped for five single nucleotide polymorphisms in COX-1 [A-842G, C22T (R8W), G128A (Q41Q), C644A (G213G) and C714A (L237M)]. Haplotype frequencies and effect of haplotype on two platelet phenotypes were estimated by maximum likelihood. The four most common haplotypes were considered separately and less common haplotypes pooled. RESULTS: COX-1 haplotype was significantly associated with aspirin response determined by AA-induced platelet aggregation (P = 0.004; 4 d.f.). Serum TXB2 generation was also related to genotype (P = 0.02; 4 d.f.). CONCLUSION: Genetic variability in COX-1 appears to modulate both AA-induced platelet aggregation and thromboxane generation. Heterogeneity in the way patients respond to aspirin may in part reflect variation in COX-1 genotype.     

The recovery of platelet cyclooxygenase activity explains interindividual variability in responsiveness to low‐dose aspirin in patients with and without diabetes

See also Lordkipanidze M, Harrison P. Aspirin twice a day keeps new COX‐1 at bay. This issue, pp 1217–9. Summary Background. Interindividual variability in response to aspirin has been popularized as ‘resistance’. We hypothesized that faster recovery of platelet cyclooxygenase‐1 activity may explain incomplete thromboxane (TX) inhibition during the 24‐h dosing interval. Objective. To characterize the kinetics and determinants of platelet cyclooxygenase‐1 recovery in aspirin‐treated diabetic and non‐diabetic patients. Patients/Methods. One hundred type 2 diabetic and 73 non‐diabetic patients on chronic aspirin 100 mg daily were studied. Serum TXB₂ was measured every 3 h, between 12 and 24 h after a witnessed aspirin intake, to characterize the kinetics of platelet cyclooxygenase‐1 recovery. Patients with the fastest TXB₂ recovery were randomized to aspirin 100 mg once daily, 200 mg once daily or 100 mg twice daily, for 28 days and TXB₂ recovery was reassessed. Results and Conclusions. Platelet TXB₂ production was profoundly suppressed at 12 h in both groups. Serum TXB₂ recovered linearly, with a large interindividual variability in slope. Diabetic patients in the third tertile of recovery slopes (≥ 0.10 ng mL^?1 h^?1) showed significantly higher mean platelet volume and body mass index, and younger age. Higher body weight was the only independent predictor of a faster recovery in non‐diabetics. Aspirin 100 mg twice daily completely reversed the abnormal TXB₂ recovery in both groups. Interindividual variability in the recovery of platelet cyclooxygenase activity during the dosing interval may limit the duration of the antiplatelet effect of low‐dose aspirin in patients with and without diabetes. Inadequate thromboxane inhibition can be easily measured and corrected by a twice daily regimen.     

Aspirin and the in vitro linear relationship between thromboxane A2‐mediated platelet aggregation and platelet production of thromboxane A2

Summary. Background: Currently, ‘aspirin resistance’, the anti‐platelet effects of non‐steroid anti‐inflammatory drugs (NSAIDs) and NSAID‐aspirin interactions are hot topics of debate. It is often held in this debate that the relationship between platelet activation and thromboxane (TX) A₂ formation is non‐linear and TXA₂ generation must be inhibited by at least 95% to inhibit TXA₂‐dependent aggregation. This relationship, however, has never been rigorously tested. Objectives: To characterize, in vitro and ex vivo, the concentration‐dependent relationships between TXA₂ generation and platelet activity. Method: Platelet aggregation, thrombi adhesion and TXA₂ production in response to arachidonic acid (0.03–1 mmol L^?1), collagen (0.1–30 μg mL^?1), epinephrine (0.001–100 μmol L^?1), ADP, TRAP‐6 amide and U46619 (all 0.1‐30 μmol L^?1), in the presence of aspirin or vehicle, were determined in 96‐well plates using blood taken from naïve individuals or those that had taken aspirin (75 mg, o.d.) for 7 days. Results: Platelet aggregation, adhesion and TXA₂ production induced by either arachidonic acid or collagen were inhibited in concentration‐dependent manners by aspirin, with logIC₅₀ values that did not differ. A linear relationship existed between aggregation and TXA₂ production for all combinations of arachidonic acid or collagen and aspirin (P < 0.01; R² 0.92; n = 224). The same relationships were seen in combinations of aspirin‐treated and naïve platelets, and in blood from individuals taking an anti‐thrombotic dose of aspirin. Conculsions: These studies demonstrate a linear relationship between inhibition of platelet TXA₂ generation and TXA₂‐mediated aggregation. This finding is important for our understanding of the anti‐platelet effects of aspirin and NSAIDs, NSAID–aspirin interactions and ‘aspirin resistance’.     

A randomized trial to assess the pharmacodynamics and pharmacokinetics of a single dose of an extended-release aspirin formulation

Aims. Low-dose acetylsalicylic acid (ASA; aspirin) for secondary prevention reduces cardiovascular disease mortality risk. ASA acetylates cyclooxygenase in the portal circulation and is rapidly (half-life, 20 min) hydrolyzed. Certain patients with cardiovascular disease may exhibit high on-therapy platelet reactivity as a result of high platelet turnover, a process whereby platelets are produced and are active beyond the duration of antiplatelet coverage provided by once-daily immediate-release (IR) ASA. A once-daily, extended-release (ER) ASA formulation using ER microcapsule technology was developed to release ASA over the 24-h dosing interval and reduce maximal plasma concentrations to spare peripheral endogenous endothelial prostacyclin production. Methods. Healthy adults (n = 50) were randomized in a crossover study to receive two different ER-ASA single doses (up to 325 mg) and two different IR-ASA single doses (up to 81 mg) in four periods, each separated by ≥14 days. Pharmacodynamics was assessed by measuring serum thromboxane B₂ (TXB₂), urine 11-dehydro-TXB₂, and arachidonic acid-induced platelet aggregation. Pharmacokinetics was determined for ASA and salicylic acid (SA). Results: Both formulations produced dose-dependent inhibition on all pharmacodynamic parameters. Marked inhibition of TXB₂ and 11-dehydro-TXB₂ was maintained over the 24-h dosing interval after a dose of ≥81 mg ER-ASA or ≥40 mg IR-ASA. The dose required to achieve 50% of maximum TXB₂ inhibition with ER-ASA was 49.9 mg versus 29.6 mg for IR-ASA, for a similar maximum pharmacodynamic effect (98.9% TXB₂ inhibition). This suggests that an approximately twofold greater ER-ASA dose (162.5 mg) is necessary to obtain the same response as that of IR-ASA 81 mg. Peak ASA concentrations were lower and T_max was longer with ER-ASA versus IR-ASA. Administration of IR-ASA resulted in a dose-normalized mean C_max of ASA that was approximately sixfold higher than that for ER-ASA and a C_max of SA approximately two- to threefold higher than that for ER-ASA. Conclusion. Both ASA formulations showed dose-dependent antiplatelet activity. Compared with the IR-ASA, ER-ASA released active drug more slowly, resulting in prolonged absorption and lower systemic drug concentrations, which is expected for an ER (24-h) formulation.     

The endocannabinoid 2‐arachidonoylglycerol activates human platelets through non‐CB1/CB2 receptors

Summary. Background: The endocannabinoid 2‐arachidonoylglycerol (2‐AG) is an endogenous lipid that acts through the activation of G‐protein‐coupled cannabinoid receptors and plays essential roles in many physiological contexts. In the cardiovascular system 2‐AG is generated by both activated endothelial cells and platelets, and participates in the regulation of inflammation and thrombosis. Although human platelets actively metabolize endocannabinoids, 2‐AG also binds to platelet surface and leads to cell activation. Objective: To investigate the biological consequence of 2‐AG interactions with human platelets and to clarify the role of cannabinoid receptors. Methods: Gel‐filtered platelets were stimulated with 2‐AG in the presence or absence of various inhibitors. Platelet aggregation and secretion were measured in a lumiaggregometer. Calcium ion movements were measured in FURA‐2 loaded platelets. Thromboxane A₂ (TxA₂) generation was evaluated as Thromboxane B₂ accumulation with a commercial EIA assay. Results: 2‐AG induced platelet shape change, aggregation and secretion with a dose‐dependent mechanism that required engagement of platelet TxA₂ receptors. 2‐AG caused also cytosolic calcium increase; however, it was totally dependent on availability of TxA₂. Indeed 2‐AG was able to induce a robust generation of TxA₂ through the cyclooxygenase pathway. Treatment of platelets with inhibitors of monoacylglycerol lipase and fatty acid amide hydrolase did not affect the activation induced by 2‐AG. Moreover, neither CB₁ and CB₂ proteins nor CB₁/CB₂ mRNAs were detected in platelets. Conclusions: 2‐AG can be considered a new physiologic platelet agonist able to induce full platelet activation and aggregation with a non‐CB₁/CB₂ receptor‐mediated mechanism.     

Pyrazolinone analgesics prevent the antiplatelet effect of aspirin and preserve human platelet thromboxane synthesis.

BACKGROUND: Anti-inflammatory analgesics, including ibuprofen and naproxen, are known to interfere with the antiplatelet effect of aspirin, presumably as a result of a drug-drug interaction at the level of platelet cyclooxygenase-1 (COX-1). OBJECTIVE: We studied whether dipyrone, which has recently been reported to inhibit COX isoforms by a mechanism different from conventional non-steroidal anti-inflammatory drugs (NSAIDs), also interferes with the antiplatelet effect of aspirin. METHODS: Arachidonic acid- and collagen-induced aggregation, as well as thromboxane formation, were measured in human platelet-rich plasma. Platelet P-selectin expression was determined by flow cytometry and cell-free COX enzyme activity was quantified by luminol-enhanced luminescence of human platelet microsomes. In addition, computerized docking was performed based on the crystal structure of COX-1. RESULTS: 4-Methylaminoantipyrine (MAA), the active metabolite of dipyrone, largely attenuated or even completely abolished the inhibition of arachidonic acid-induced platelet aggregation, thromboxane formation and P-selectin expression by aspirin. Similar results were obtained for other pyrazolinones, as well as for the conventional NSAIDs ibuprofen and naproxen. Moreover, MAA attenuated the effect of aspirin on COX activity of platelet microsomes, suggesting a competition with aspirin at the COX-1 enzyme. This was confirmed by docking studies, which revealed that MAA forms a strong hydrogen bond with serine 530 within the COX-1, thereby preventing enzyme acetylation by aspirin. CONCLUSION: This study demonstrates for the first time that dipyrone and other pyrazolinones have a high potential to attenuate or prevent the antiplatelet effect of aspirin. This should be considered if pyrazolinone analgesics are administered to patients with cardiovascular disease requiring antiplatelet aspirin therapy.     

Differences in the effects of extended-release aspirin and plain-formulated aspirin on prostanoids and nitric oxide in healthy volunteers

This study was designed to evaluate the effects of extended-release aspirin on platelet aggregation and the production of prostanoids and nitric oxide. The participants in this double blind, randomized and crossover study were 20 healthy volunteers. Interventions were 150 mg of plain-formulated aspirin (PFASA) and 150 mg of extended-release aspirin (ERASA). Blood samples were collected before and 10, 20, 60, 120, 240, 480 and 1440 min after the first dose; 3, 7 and 14 days after daily administration and 24 h after the last dose. The main measures were platelet aggregometry, thromboxane B2, 6-keto-prostaglandin (PG) F1alpha and nitric oxide in each control. Platelet aggregation was inhibited by 50% with ERASA, and by 77% with PFASA. No differences were found in chronic treatment. Thromboxane B2 was inhibited more by the latter (51-67%), but 90% inhibition was observed in both groups after 3 days. The levels of 6-keto-PGF1alpha was reduced by 20% with ERASA and by 58% with PFASA. Nitric oxide production increased in both groups, but after 24 h, and 7-14 days, elevated concentrations of nitric oxide were found only in the ERASA. The antiplatelet effects of ERASA provide pharmacological advantages (greater prostacyclin synthesis and prolonged increase in nitric oxide production) over those provided by the plain formulation.     

Release of sphingosine‐1‐phosphate from human platelets is dependent on thromboxane formation

Summary. Background: Platelets release the immune‐modulating lipid sphingosine‐1‐phosphate (S1P). However, the mechanisms of platelet S1P secretion are not fully understood. Objectives: The present study investigates the function of thromboxane (TX) for platelet S1P secretion during platelet activation and the consequences for monocyte chemotaxis. Methods: S1P was detected using thin‐layer chromatography in [³H]sphingosine‐labeled platelets and by mass spectrometry. Monocyte migration was measured in modified Boyden chamber chemotaxis assays. Results: Release of S1P from platelets was stimulated with protease‐activated receptor‐1‐activating peptide (PAR‐1‐AP, 100 μm ). Acetylsalicylic acid (ASA) and two structurally unrelated reversible cyclooxygenase inhibitors diclofenac and ibuprofen suppressed S1P release. Oral ASA (500‐mg single dose or 100 mg over 3 days) attenuated S1P release from platelets in healthy human volunteers ex vivo. This was paralleled by inhibition of TX formation. S1P release was increased by the TX receptor (TP) agonist U‐46619, and inhibited by the TP antagonist ramatroban and by inhibitors of ABC‐transport. Furthermore, thrombin‐induced release of S1P was attenuated in platelets from TP‐deficient mice. Supernatants from PAR‐1‐AP‐stimulated human platelets increased the chemotactic capacity of human peripheral monocytes in a S1P‐dependent manner via S1P receptors‐1 and ‐3. These effects were inhibited by ASA‐pretreatment of platelets. Conclusions: TX synthesis and TP activation mediate S1P release after thrombin receptor activation. Inhibition of this pathway may contribute to the anti‐inflammatory actions of ASA, for example by affecting activity of monocytes at sites of vascular injury.     

Identifying determinants of variability to tailor aspirin therapy

Once-daily, low-dose aspirin is a cornerstone in the prophylaxis and treatment of cardiovascular diseases. Aspirin ‘resistance’ still lacks definition, a standardized reference assay, underlying mechanisms, clinical impact or efficacy of alternative antiplatelet drugs. Aspirin response in several studies has been measured by different platelet function tests, not always reflecting aspirin pharmacodynamics, thus generating significantly heterogeneous results. The EMA indicated serum thromboxane B₂ as the only valid surrogate assay to study different aspirin formulations. Rather than resistance, recent studies focused on sources of intra- and inter-individual variability in response to aspirin, based on pharmacokinetic and/or pharmacodynamic mechanisms. Drug interactions, diabetes, conditions of increased platelet output, obesity and aging can potentially increase the variability of aspirin response. Preliminary studies testing different aspirin regimens showed that twice-daily low doses were more effective than once-daily higher aspirin doses on surrogate end points of platelet inhibition. Large studies are needed to test new disease-tailored, low-dose aspirin regimens.     

Biological effects of aspirin and clopidogrel in a randomized cross-over study in 96 healthy volunteers

BACKGROUND: Some data suggest that biological 'resistance' to aspirin or clopidogrel may influence clinical outcome. OBJECTIVE: The aim of this study was to evaluate the relationship between aspirin and clopidogrel responsiveness in healthy subjects. METHODS: Ninety-six healthy subjects were randomly assigned to receive a 1-week course of aspirin 100 mg day(-1) followed by a 1-week course of clopidogrel (300 mg on day 1, then 75 mg day(-1)), or the reverse sequence, separated by a 2-week wash-out period. The drug effects were assessed by means of serum TxB2 assay, platelet aggregation tests, and the PFA -100 and Ultegra RPFA -Verify Now methods. RESULTS: Only one subject had true aspirin resistance, defined as a serum TxB2 level > 80 pg microL(-1) at the end of aspirin administration and confirmed by platelet incubation with aspirin. PFA-100 values were normal in 29% of the subjects after aspirin intake, despite a drastic reduction in TxB2 production; these subjects were considered to have aspirin pseudo-resistance. Clopidogrel responsiveness was not related to aspirin pseudo-resistance. Selected polymorphisms of platelet receptor genes were not associated with either aspirin or clopidogrel responsiveness. CONCLUSIONS: In healthy subjects, true aspirin resistance is rare and aspirin pseudo-resistance is not related to clopidogrel responsiveness.     

Clinical implications of aspirin resistance

Aspirin (acetylsalicylic acid) is one of the main therapeutic medications used in the prevention of thromboembolic vascular events. Aspirin exhibits its antiplatelet action by irreversibly inhibiting platelet cyclooxygenase-1 enzyme, thus preventing the production of thromboxane A₂ (TXA₂). Aspirin resistance, as measured in vitro, is the inability of aspirin to reduce platelet activation and aggregation by failure to suppress the platelet production of TXA₂. Laboratory tests of platelet TXA₂ production or platelet function dependent on TXA₂can detect aspirin resistance in vitro. The clinical implication of this laboratory definition has not yet been elucidated via prospective trials that have controlled for confounders, such as hypertension, diabetes and dyslipidemia. Large meta-analyses have found low-dose aspirin to be as effective as high-dose aspirin in preventing vascular events, making a dose-dependent improvement in laboratory response clinically irrelevant. Possible causes of aspirin resistance include poor compliance, inadequate dose, drug interactions, genetic polymorphisms of cyclooxygenase-1, increased platelet turnover and upregulation of nonplatelet pathways of thromboxane production. However, there is currently no standardized approach to the diagnosis and no proven effective treatment for aspirin resistance. Further research exploring the mechanisms of aspirin resistance is needed in order to better define aspirin resistance, as well as to develop a standardized laboratory test that is specific and reliable, and can correlate with the clinical risk of vascular events. The intent of this paper is to review the literature discussing possible mechanisms, diagnostic testing and clinical trials of aspirin resistance and to discuss its clinical relevance as it pertains to cerebrovascular and cardiovascular disease.     

吲哚美辛对喉癌细胞Hep-2增殖与凋亡及COX-2蛋白表达的影响

目的探索吲哚美辛对喉癌细胞增殖与凋亡的作用以及对细胞COX-2蛋白表达的影响。方法Hep-2细胞暴露于含吲哚美辛（125，250，500μM）的培养基中，培养24小时，用MTT方法检测各组药物与溶剂对照组相比对细胞增殖的影响；用台盼蓝染色法检测吲哚美辛对细胞活力的影响；吖啶橙染色法观察吲哚美辛（250μM）对细胞形态的影响；流式细胞仪分析法检测吲哚美辛（250μM）对细胞周期和细胞凋亡的影响，Western blot检测吲哚美辛对细胞COX-2蛋白表达的影响。结果吲哚美辛使Hep-2细胞增殖及细胞活力明显降低，细胞形态发生明显变化，细胞质萎缩而细胞核相对较大，S期细胞分数明显增加，细胞出现凋亡峰，而COX-2蛋白表达量增加。结论吲哚美辛强烈抑制Hep-2细胞增殖与细胞活力，明显改变细胞初始形态，阻滞细胞从S期向G2／M期转化，并诱导其凋亡，吲哚美辛对Hep-2细胞的上述作用机制与COX-2的特异性抑制途径无关。     

Thromboxane and prostacyclin biosynthesis in heart failure of ischemic origin: effects of disease severity and aspirin treatment

Summary. Background: Thromboembolism is a relatively common complication of chronic heart failure (HF) and the place of antiplatelet therapy is uncertain. Objectives: We characterized the rate of thromboxane and prostacyclin biosynthesis in chronic HF of ischemic origin, with the aim of separating the influence of HF on platelet activation from that of the underlying ischemic heart disease (IHD). Patients and Methods: We compared urinary 11‐dehydro‐thromboxane (TX)B₂, 2,3 dinor 6‐keto‐PGF_1α, 8‐iso‐prostaglandin (PG)F_2α, and plasma N‐terminal pro‐brain natriuretic peptide (NT‐pro‐BNP), asymmetric dimethylarginine (ADMA), and soluble CD40 ligand (sCD40L), in 84 patients with HF secondary to IHD, 61 patients with IHD without HF and 42 healthy subjects. Results: HF patients not on aspirin had significantly higher urinary 11‐dehydro‐TXB₂ as compared with healthy subjects (P < 0.0001) and IHD patients not on aspirin (P = 0.028). They also showed significantly higher 8‐iso‐PGF_2α (P = 0.018), NT‐pro‐BNP (P = 0.021) and ADMA (P < 0.0001) than IHD patients not on aspirin. HF patients on low‐dose aspirin had significantly lower 11‐dehydro‐TXB₂ (P < 0.0001), sCD40L (P = 0.007) and 2,3‐dinor‐6‐keto‐PGF_1α (P = 0.005) than HF patients not treated with aspirin. HF patients in NYHA classes III and IV had significantly higher urinary 11‐dehydro‐TXB₂ than patients in classes I and II, independently of aspirin treatment (P < 0.05). On multiple linear regression analysis, higher NT‐pro‐BNP levels, lack of aspirin therapy and sCD40L, predicted 11‐dehydro‐TXB₂ excretion rate in HF patients (R² = 0.771). Conclusions: Persistent platelet activation characterizes HF patients. This phenomenon is related to disease severity and is largely suppressable by low‐dose aspirin. The homeostatic increase in prostacyclin biosynthesis is impaired, possibly contributing to enhanced thrombotic risk in this setting.     

COX-2和MMP-2在乳腺癌中的表达及意义

目的探讨环氧化酶-2（cyclooxygenase,COX-2）和基质金属蛋白酶-2（matrix metalloproteinase-2,MMP-2）在乳腺癌中表达的意义和相互关系。方法免疫组化方法（S-P法）观察70例乳腺癌,15例乳腺良性肿瘤与15例正常乳腺组织的COX-2和MMP-2的表达。结果正常乳腺组织和良性肿瘤中COX-2和MMP-2无表达,乳腺癌组织中COX-2和MMP-2的阳性表达率分别为57.14%和61.43%（P〈0.05）,cyclinE和p53的阳性表达与乳腺癌的临床分期密切相关（P〈0.05）;cyclinE和p53在乳腺癌的阳性表达具有相关（P〈0.05）,共同阳性表达的患者5年生存率明显低于阴性者（P〈0.05）。结论COX-2和MMP-2在乳腺癌中均有高表达,在乳腺癌的发病过程中它们的高表达具有协同效应,共同促进乳腺癌的发生和发展。     

还氧合酶-2和肝细胞生长因子的表达在早期胃癌发生中的意义

目的通过检测正常胃组织、不典型增生胃组织和早期胃癌组织中还氧合酶-2（Cyclooxygenase-2,COX-2）和肝细胞生长因子（Hepatocyte growth factor,HGF）蛋白表达,探讨二者在早期胃癌发生中的意义。方法运用免疫组化方法检测50例不同胃组织COX-2和HGF蛋白表达情况。结果 1.在由正常胃粘膜到不典型增生到早期胃癌的演进过程中,COX-2和HGF蛋白表达呈上升趋势,COX-2和HGF的蛋白表达在正常胃组织、不典型增生胃组织和早期胃癌组织之间具有显著的差异性。2.HGF与COX-2在胃癌组织中的表达具有显著的相关性。结论 1.COX-2及HGF均参与了早期胃癌的发生。2.HGF与COX-2之间的相互作用在早期胃癌的发生中有一定的意义。     

Aspirin ‘resistance’: role of pre‐existent platelet reactivity and correlation between tests

Summary. Background: Aspirin ‘resistance’ is a widely used term for hyporesponsiveness to aspirin in a platelet function test. Serum thromboxane (TX) B₂ is the most specific test of aspirin’s effect on platelets. Objectives: (i) To examine the role of pre‐existent platelet hyperreactivity in aspirin ‘resistance’. (ii) To determine the correlation between aspirin resistance defined by serum TXB₂ and other assays of platelet function. Methods: To enable pre‐aspirin samples to be drawn, platelet function was measured in normal subjects (n = 165) before and after aspirin 81 mg daily for seven days. Results: The proportion of the post‐aspirin platelet function predicted by the pre‐aspirin platelet function was 28.3 ± 7.5% (mean ± asymptotic standard error) for serum TXB₂, 39.3 ± 6.8% for urinary 11‐dehydro TXB₂, 4.4 ± 7.7% for arachidonic acid‐induced platelet aggregation, 40.4 ± 7.1% for adenosine diphosphate‐induced platelet aggregation, 26.3 ± 9.2% for the VerifyNow Aspirin Assay^®, and 45.0 ± 10.9% for the TEG^® PlateletMapping? System with arachidonic acid. There was poor agreement between aspirin‐resistant subjects identified by serum TXB₂ vs. aspirin‐resistant subjects identified by the other five assays, irrespective of whether the analysis was based on categorical or continuous variables. Platelet count correlated with pre‐aspirin serum TXB₂ and VerifyNow Aspirin Assay, but not with any post‐aspirin platelet function test. Conclusions: (i) Aspirin ‘resistance’ (i.e. hyporesponsiveness to aspirin in a laboratory test) is in part unrelated to aspirin but is the result of underlying platelet hyperreactivity prior to the institution of aspirin therapy. (ii) Aspirin resistance defined by serum TXB₂ shows a poor correlation with aspirin resistance defined by other commonly used assays.     

膀胱癌中COX-2、Survivin的表达及临床意义

目的检测COX-2和Survivin在膀胱癌中的表达,分析它们与不同临床病理因素及预后的关系。方法应用免疫组织化学方法对手术切除的56例膀胱癌COX-2,Survivin蛋白表达进行检测。结果膀胱癌中COX-2、Survivin蛋白阳性表达率分别为55.3%,62.5%,随着肿瘤分级、分期的升高,COX-2、Survivin表达阳性率增加(P<0.05),差别有显著性(P<0.05)。经Spearman等级相关性分析表明,COX-2表达水平与Survivin表达水平之间成正相关关系(rs=0.324,P=0.001)。Kaplan-Meier生存分析表明COX-2,Survivin表达阳性组的生存时间明显低于阴性组,二者差异显著。结论COX-2和Survivin可作为膀胱癌早期诊断、治疗和判断预后的新靶点。     

Enhanced antiplatelet effect of clopidogrel in patients whose platelets are least inhibited by aspirin: a randomized crossover trial

Summary. Objective: We aimed to determine whether adding clopidogrel to aspirin in patients at high risk of future cardiovascular events would suppress laboratory measures of the antiplatelet effects of aspirin; and have greater platelet inhibitory effects in patients with the least inhibition of platelets by aspirin. Methods: We performed a randomized, double‐blind, placebo‐controlled, crossover trial, comparing clopidogrel 75 mg day^?1 versus placebo, in 36 aspirin‐treated patients with symptomatic objectively confirmed peripheral arterial disease. Results: The addition of clopidogrel to aspirin did not suppress platelet aggregation induced by arachidonic acid, urinary 11 dehydro thromboxane B₂ concentrations, or soluble markers of platelet activation markers (P‐selectin, CD40‐ligand) and inflammation (high sensitivity serum C‐reactive protein, interleukin‐6). Clopidogrel significantly inhibited platelet aggregation induced by ADP (reduction 26.2%; 95% CI: 21.3–31.1%, P < 0.0001) and collagen (reduction 6.2%; 95% CI: 3.2–9.3%, P = 0.0003). The greatest inhibition of collagen‐induced platelet aggregation by clopidogrel was seen in patients with the least inhibition of arachidonic acid induced aggregation by aspirin [lower tertile of arachidonic acid‐induced platelet aggregation: 2.8% (95% CI: ?0.8 to 6.3%) reduction in mean collagen‐induced aggregation by clopidogrel; middle tertile: 4.0% (95% CI: 0.4–7.6%); upper tertile 12.6% (95% CI: 4.5–20.8%); P‐value for interaction 0.01]. Conclusions: The greatest platelet inhibitory effect of clopidogrel occurs in patients with the least inhibition of arachidonic acid‐induced platelet aggregation by aspirin. This raises the possibility that the clinical benefits of adding clopidogrel to aspirin may be greatest in patients whose platelets are least inhibited by aspirin. Confirmation in clinical outcome studies may allow these patients to be targeted with antiplatelet drugs that inhibit the ADP receptor, thereby overcoming the problem of laboratory aspirin resistance.