Impaired anti-platelet effect of aspirin, inflammation and platelet turnover in cardiac surgery

Antithrombotic strategies for preventing graft failure in coronary artery bypass graft

Coronary artery bypass graft (CABG) procedures face challenges related to graft failure, driven by factors such as acute thrombosis, neointimal hyperplasia, and atherosclerotic plaque formation. Despite extensive efforts over four decades, the optimal antithrombotic strategy to prevent graft occlusion while minimizing bleeding risks remains uncertain, relying heavily on expert opinions rather than definitive guidelines. To address this uncertainty, we conducted a review of randomized clinical trials and meta-analyses of antithrombotic therapy for patients with CABG. These studies examined various antithrombotic regimens in CABG such as single antiplatelet therapy (aspirin or P2Y12 inhibitors), dual antiplatelet therapy, and anticoagulation therapy. We evaluated outcomes including the patency of grafts, major adverse cardiovascular events, and bleeding complications and also explored future perspectives to enhance long-term outcomes for CABG patients. Early studies established aspirin as a key component of antithrombotic pharmacotherapy after CABG. Subsequent randomized controlled trials focused on adding a P2Y12 inhibitor (such as clopidogrel, ticagrelor, or prasugrel) to aspirin, yielding mixed results. This article aims to inform clinical decision-making and guide the selection of antithrombotic strategies after CABG.

Circulating Thrombomodulin: Release Mechanisms, Measurements, and Levels in Diseases and Medical Procedures

Thrombomodulin (TM) is a type-I transmembrane protein that is mainly expressed on endothelial cells and plays important roles in many biological processes. Circulating TM of different forms are also present in biofluids, such as blood and urine. Soluble TM (sTM), comprised of several domains of TM, is the major circulating TM which is generated by either enzymatic or chemical cleavage of the intact protein under different conditions. Under normal conditions, sTM is present in low concentrations (<10 ng/mL) in the blood but is elevated in several pathological conditions associated with endothelial dysfunction such as cardiovascular, inflammatory, infection, and metabolic diseases. Therefore, sTM level has been examined for monitoring disease development, such as disseminated intravascular coagulation (DIC), sepsis and multiple organ dysfunction syndrome in patients with novel coronavirus disease 2019 (COVID-19) recently. In addition, microvesicles (MVs) that contain membrane TM (MV-TM) have been found to be released from activated cells which also contribute to levels of circulating TM in certain diseases. Several release mechanisms of sTM and MV-TM have been reported, including enzymatic, chemical, and TM mutation mechanisms. Measurements of sTM and MV-TM have been developed and explored as biomarkers in many diseases. In this review, we summarize all these advances in three categories as follows: (1) release mechanisms of circulating TM, (2) methods for measuring circulating TM in biological samples, and (3) correlation of circulating TM with diseases. Altogether, it provides a whole picture of recent advances on circulating TM in health and disease.

Platelet Apoptotic Response May Be Associated With the Capacity of Aspirin to Inhibit Platelets

An inadequate platelet response to aspirin (ASA) has been identified in some patients under chronic ASA treatment. The aim of this study was to analyze if ASA-sensitive and ASA-resistant platelets have differences in their apoptotic capability. Clinically stable ischemic coronary patients who had been taking ASA (100 mg/d) for at least 9 months before inclusion were divided into ASA-resistant (n = 11) and ASA-sensitive (n = 13) groups as defined by the PFA-100 test. Platelets from ASA-sensitive patients showed higher expression of the proapoptotic proteins Bak and Bax than those from ASA-resistant patients, although only Bak protein remained different when the results were adjusted by age. In resting platelets, neither caspase-3 activity nor cytosolic cytochrome C levels were different between both experimental groups. Stimulation of platelets with calcium ionophore (10 nmol/L, A23187) increased caspase-3 activity (1.91-fold higher; P < 0.05) and cytosolic cytochrome C levels (1.84-fold higher; P < 0.05) to a higher degree in ASA-sensitive than in ASA-resistant platelets. In conclusion, ASA-sensitive platelets seem to be better prepared to undergo apoptosis during robust platelet activation.

Leuko-platelet index predicts thrombotic events in patients with acute coronary syndrome

PURPOSE

To evaluate the predictive value of a bedside index in hospitalized patients with acute coronary syndromes (ACS).

METHODS

We studied the association of leuko-platelet index (LPI: platelet count * leukocyte count/10⁸) with risk of mortality, shock, or heart failure (combined end point-CEP), and with the response to antiplatelet therapy, measured by light transmission aggregometry.

RESULTS

In the derivation cohort we included 1100 patients with non STEM-ACS, GRACE score of 133 ± 52, Crusade score 24,3 ± 14, 66% male, 65 + 11 years. LPI was 17 (12-24). LPI was higher (19 (13-25)) in patients with MI than in patients with unstable angina (16 (12-22) in (p < 0.001)). A total of 115 patients (10.5%) had the CEP. CEP was associated to LPI (OR 1.04 (1.002-1.08), p = 0.03), age (OR 1.01 (0.97-1.05), p = 0.62) and GRACE>140 (OR 8.1 (2.2-29), p = 0.02). LPI (OR 1.04 (1.004-1.07) p = 0.03) and GRACE score (OR 1.02 (1.01-1.03) p < 0.01) were associated to cardiovascular mortality. We confirmed these results in the validation cohort #1 (686 patients, 61 + 11 years old, 47% nonST-ACS, 53% ST-ACS, 21% had CEP) and in validation cohort #2 (218 patients, 56.8% males, 73 + 7 years old, 79% nonST-ACS, GRACE score 136 + 30) and 8.3% with CEP. We used the cutoff points of LPI obtained in the derivation cohort (>24).

CONCLUSIONS

LPI > 24 was associated to CEP (OR (1.7-5.2), p 0.01), independently of age (OR 1 (0.98-1.02), p = 0.8), and GRACE score (OR 1.01 (0.99-1.01), p 0.69), and It was associated to antiplatelet resistance (OR 1.03 (95% CI 1.00-1.06) p = 0.05).

Randomized trial of ticagrelor vs. aspirin in patients after coronary artery bypass grafting: the TiCAB trial

Aims

The antiplatelet treatment strategy providing optimal balance between thrombotic and bleeding risks in patients undergoing coronary artery bypass grafting (CABG) is unclear. We prospectively compared the efficacy of ticagrelor and aspirin after CABG.

Methods and results

We randomly assigned in double-blind fashion patients scheduled for CABG to either ticagrelor 90 mg twice daily or 100 mg aspirin (1:1) once daily. The primary outcome was the composite of cardiovascular death, myocardial infarction (MI), repeat revascularization, and stroke 12 months after CABG. The main safety endpoint was based on the Bleeding Academic Research Consortium classification, defined as BARC ≥4 for periprocedural and hospital stay-related bleedings and BARC ≥3 for post-discharge bleedings. The study was prematurely halted after recruitment of 1859 out of 3850 planned patients. Twelve months after CABG, the primary endpoint occurred in 86 out of 931 patients (9.7%) in the ticagrelor group and in 73 out of 928 patients (8.2%) in the aspirin group [hazard ratio 1.19; 95% confidence interval (CI) 0.87–1.62; P = 0.28]. All-cause mortality (ticagrelor 2.5% vs. aspirin 2.6%, hazard ratio 0.96, CI 0.53–1.72; P = 0.89), cardiovascular death (ticagrelor 1.2% vs. aspirin 1.4%, hazard ratio 0.85, CI 0.38–1.89; P = 0.68), MI (ticagrelor 2.1% vs. aspirin 3.4%, hazard ratio 0.63, CI 0.36–1.12, P = 0.12), and stroke (ticagrelor 3.1% vs. 2.6%, hazard ratio 1.21, CI 0.70–2.08; P = 0.49), showed no significant difference between the ticagrelor and aspirin group. The main safety endpoint was also not significantly different (ticagrelor 3.7% vs. aspirin 3.2%, hazard ratio 1.17, CI 0.71–1.92; P = 0.53).

Conclusion

In this prematurely terminated and thus underpowered randomized trial of ticagrelor vs. aspirin in patients after CABG no significant differences in major cardiovascular events or major bleeding could be demonstrated.

ClinicalTrials.gov Identifier

NCT01755520.

Very-low-dose twice-daily aspirin maintains platelet inhibition and improves haemostasis during dual-antiplatelet therapy for acute coronary syndrome

Higher aspirin doses may be inferior in ticagrelor-treated acute coronary syndrome (ACS) patients and reducing bleeding risk whilst maintaining antithrombotic benefits could improve outcomes. We characterized the pharmacodynamics of a novel dual-antiplatelet-therapy regimen consisting of very-low-dose twice-daily (BD) aspirin with standard-dose ticagrelor. A total of 20 ticagrelor-treated ACS patients entered a randomized crossover to take aspirin 20 mg BD (12-hourly) during one 14-day period and 75 mg once-daily (OD) in the other. After 14 days of treatment, serum thromboxane (TX)B2 and light-transmittance aggregometry were assessed pre- and 2 h post-morning-dose, bleeding time was measured post-dose, and TXA2 and prostacyclin stable metabolites were measured in urine collected 2 h post-morning-dose. Data are expressed as mean ± SD. After 14 days treatment, serum TXB2 levels were significantly greater 2 h post-dosing with aspirin 20 mg BD vs. 75 mg OD (3.0 ± 3.6 ng/mL vs. 0.8 ± 1.9 ng/mL; p = 0.018) whereas pre-dosing levels were not significantly different (3.5 ± 4.1 ng/mL vs. 2.5 ± 3.1 ng/mL, p = 0.23). 1-mmol/L arachidonic acid-induced platelet aggregation was similarly inhibited by both regimens pre-dose (8.5 ± 14.3% vs. 5.1 ± 3.6%, p = 0.24) and post-dose (8.7 ± 14.2% vs. 6.6 ± 5.3%; p = 0.41). Post-dose bleeding time was shorter with 20 mg BD (680 ± 306 s vs. 834 ± 386 s, p = 0.02). Urinary prostacyclin and TX metabolite excretion were not significantly different. In conclusion, compared to aspirin 75 mg OD, aspirin 20 mg BD provided consistent inhibition of platelet TXA2 release and aggregation, and improved post-dose hemostasis, in ticagrelor-treated ACS patients. Further studies are warranted to assess whether this regimen improves the balance of clinical efficacy and safety.

Perioperative urinary thromboxane metabolites and outcome of coronary artery bypass grafting: a nested case-control study

OBJECTIVE

As a marker of in vivo thromboxane generation, high-level urinary thromboxane metabolites (TXA-M) increase the occurrence of cardiovascular events in high-risk patients. To investigate whether perioperative urinary TXA-M level is associated with major adverse cardiac and cerebrovascular events (MACCE) after coronary artery bypass graft (CABG) surgery, we designed a nested case-control study.

DESIGN

Observational, nested case-control study.

SETTING

Single-centre outcomes research in Fuwai Hospital, Beijing, China.

PARTICIPANTS

One thousand six hundred and seventy Chinese patients undergoing CABG surgery from September 2011 to October 2013.

METHODS

We obtained urinary samples from 1670 Chinese patients undergoing CABG 1 hour before surgery (pre-CABG), and 6 hours (post-CABG 6 hours) and 24 hours after surgery (post-CABG 24 hours). Patients were followed up for 1 year, and we observed 56 patients had MACCE. For each patient with MACCE, we matched three control subjects. Perioperative urinary TXA-M of the three time spots was detected in these 224 patients.

RESULTS

Post-CABG 24 hours TXA-M is significantly higher than that of patients without MACCE (11 101vs8849 pg/mg creatine, P=0.007). In addition, patients in the intermediate tertile and upper tertile of post-CABG 24 hours urinary TXA-M have a 2.2 times higher (HR 2.22, 95% CI 1.04 to 4.71, P=0.038) and a 2.8 times higher (HR 2.81, 95% CI 1.35 to 5.85, P=0.006) risk of 1 year MACCE than those in the lower tertile, respectively.

CONCLUSIONS

In conclusion, post-CABG 24 hours urinary TXA-M elevation is associated with an increase of 1 year adverse events after CABG, indicating that the induction of cyclo-oxygenase-2 by surgery-related inflammatory stimuli or platelet turnover may be responsible for the high levels of post-CABG urinary TXA-M.

TRIAL REGISTRATION NUMBER

NCT01573143.

Haemodialysis impairs clopidogrel but not aspirin responsiveness in patients with end-stage renal disease

Dual antiplatelet therapy (DAPT) with aspirin (ASA) and clopidogrel (Clp) is the standard treatment to reduce ischaemic coronary events, but in patients with end-stage renal disease (ESRD) the efficacy of Clp remains unclear. Patients with ESRD are at higher risk for coronary artery disease (CAD) and also their post-interventional outcome is worse compared to patients with normal renal function. Little is known about the influence of haemodialysis (HD) on ASA and Clp responsiveness. To assess the effect of HD on ASA- and Clp-responsiveness in patients with documented CAD and ESRD, 31 patients with ESRD (mean age 66.5 ± 1.8 years, 23 male ) on DAPT were evaluated for their ASA and Clp responsiveness with the Verify Now System (Accumetrics Inc.) We measured the antiplatelet effect in all ESRD patients at three time points: T1: just before HD; T2: directly after HD; T3: steady state on a HD free day one week after T1. In our study at baseline 10 (32.3%) patients were ASA-low responder (ASA-LR) and 14 (45.2%) patients Clp-low responder (Clp-LR). There was a significant difference in the PRU values before ( T1) and immediately after HD (T2) [PRU T1=234 (169; 274) vs PRUT2= 247 (199; 278); pT1,2=0.036; ]. Results were shown as median ARU T1 (25th, 75th percentile) or median PRU T1 (25th, 75th percentile). Hence HD seems to impair responsiveness to Clp, resulting in an increase of 6.5 % Clp-LR. No significant differences in the ARU values at the different time-points were found.

Once versus twice daily aspirin after coronary bypass surgery: a randomized trial

Essentials Coronary artery bypass graft (CABG) failure is associated with myocardial infarction and death. We tested whether more frequent dosing improves aspirin (ASA) response following CABG surgery. Twice-daily compared with once-daily dosing reduces ASA hyporesponsiveness after CABG surgery. The efficacy of twice-daily ASA needs to be tested in a trial powered for clinical outcomes.

SUMMARY

Background Acetyl-salicylic acid (ASA) hyporesponsiveness occurs transiently after coronary artery bypass graft (CABG) surgery and may compromise the effectiveness of ASA in reducing thrombotic graft failure. A reduced response to ASA 81 mg once-daily after CABG surgery is overcome by four times daily ASA dosing. Objectives To determine whether ASA 325 mg once-daily or 162 mg twice-daily overcomes a reduced response to ASA 81 mg once-daily after CABG surgery. Methods Adults undergoing CABG surgery were randomized to ASA 81 mg once-daily, 325 mg once-daily or 162 mg twice-daily. The primary outcome was median serum thromboxane B2 (TXB2 ) level on postoperative day 4. We pooled the results with those of our earlier study to obtain better estimates of the effect of ASA 325 mg once-daily or in divided doses over 24 h. Results We randomized 68 patients undergoing CABG surgery. On postoperative day 4, patients randomized to receive ASA 81 mg once-daily had a median day 4 TXB2 level of 4.2 ng mL-1 (Q1, Q3: 1.5, 7.5 ng mL-1 ), which was higher than in those randomized to ASA 162 mg twice-daily (1.1 ng mL-1 ; Q1, Q3: 0.7, 2.7 ng mL-1 ) and similar to those randomized to ASA 325 mg once-daily (1.9 ng mL-1 ; Q1, Q3: 0.9, 4.7 ng mL-1 ). Pooled data showed that the median TXB2 level on day 4 in groups receiving ASA 162 mg twice-daily or 81 mg four times daily was 1.1 ng mL-1 compared with 2.2 ng mL-1 in those receiving ASA 325 mg once-daily. Conclusions Multiple daily dosing of ASA is more effective than ASA 81 mg once-daily or 325 mg once-daily at suppressing serum TXB2 formation after CABG surgery. A twice-daily treatment regimen needs to be tested in a clinical outcome study.

The Prevalence and Clinical Relevance of ASA Nonresponse After Cardiac Surgery: A Prospective Bicentric Study

We aimed to identify the prevalence of acetylsalicylic acid (ASA) nonresponse in patients after coronary artery bypass graft (CABG) surgery and the possible consequences for the rate of major cardiovascular events. This prospective, observational, bicentric cohort study was conducted in two German University hospitals. A total of 400 patients (200 in each study center) undergoing elective CABG surgery were enrolled after written informed consent. Platelet function was analyzed on day 3 (d3) and day 5 (d5) postoperatively following stimulation with arachidonic acid (ASPItest) and with thrombin receptor-activating peptide 6 (TRAPtest) using multiple electrode aggregometry (Multiplate). Individuals with an ASPItest ≥40 AU·min were categorized as ASA nonresponders. A 1-year follow-up recorded the combined end point of cardiovascular events, hospital admissions, or deaths related to cardiovascular disease. The prevalence of ASA nonresponse was 51.5% on d3, and it significantly increased to 71.3% on d5 ( P = .0049). The area under the aggregation curve in the TRAPtest ( P < .0001), the platelet count on d5 ( P = .009), and the cardiopulmonary bypass time ( P = .01) were identified as independent predictors of an ASA nonresponse. A 1-year follow-up recorded 54 events fulfilling criteria for the combined end point with no difference between ASA responders and nonresponders. This study indicates a high incidence of perioperative ASA nonresponse in patients following CABG. No effect on the incidence of cardiovascular events was recorded in the 1-year follow-up. Therefore, a randomized dosage adjustment trial should elucidate whether a tailored ASA treatment after CABG surgery represents a useful concept.

Early platelet recovery following cardiac surgery with cardiopulmonary bypass

Coronary artery bypass grafting (CABG) with cardiopulmonary bypass (CPB) is frequently associated with low platelet count (PC) and disturbed platelet function (PF). While PC is easy to measure, PF is more difficult to assess. Moreover, the time-related platelet dysfunction and recovery after CPB is not fully elucidated. Platelet dysfunction could lead to bleeding but also to coronary graft failure. Laboratory tests could provide more insights into PF after CABG. The aim of the current study was to investigate the time-related PF induced by CPB. Blood samples of 20 patients with a preoperative PC of more than 250 × 10⁹/L were collected before incision, after weaning from CPB, and 24 h postoperative. Platelet contribution to coagulation was quantified by PLTEM (calculated by means of EXTEM and FIBTEM results). PF was assessed by multiple electrode impedance aggregometry (MEIA) in whole blood and by light transmission aggregometry (LTA) in platelet-rich plasma after stimulation with arachidonic acid (AA), adenosine diphosphate, collagen, and thrombin-receptor-activating peptide. LTA and MEIA analysis demonstrated significant platelet dysfunction after CPB, with partial recovery within 24 h after surgery. AA-induced platelet aggregation increased to higher levels within 24 h after surgery compared to baseline values as measured by LTA. PLTEM maximum clot firmness remained unchanged throughout the study. Correlation analyses revealed that MEIA and rotational thromboelastometry (ROTEM), but not LTA, were dependent on PC and hematocrit. No correlations were found between LTA, MEIA, ROTEM, PC, and clinical outcome parameters. Our results demonstrate a reversible platelet dysfunction recovering within 24 h after CPB. Interestingly, AA-induced platelet aggregation increases to higher levels during the first 24 h postoperatively, which might be important for early initiation of antiplatelet therapy after CABG. MEIA as POC test is able to detect platelet dysfunction during cardiac surgery with a PC of ≥150 × 10⁹/L.

Drug delivery and therapeutic impact of extended-release acetylsalicylic acid

Current treatment guidelines recommend once-daily, low-dose acetylsalicylic acid (ASA; aspirin) for secondary prevention of cardiovascular events. However, the anti-thrombotic benefits of traditional ASA formulations may not extend over a 24-h period, especially in patients at high risk for a recurrent cardiovascular event. A next-generation, extended-release ASA formulation (ER-ASA) has been developed to provide 24-h anti-thrombotic coverage with once-daily dosing. The pharmacokinetics of ER-ASA indicates slower absorption and prolonged ASA release versus immediate-release ASA, with a favorable safety profile. ER-ASA minimizes systemic ASA absorption and provides sustained antiplatelet effects over a 24-h period.

Multiple daily doses of acetyl-salicylic acid (ASA) overcome reduced platelet response to once-daily ASA after coronary artery bypass graft surgery: a pilot randomized controlled trial

BACKGROUND

The efficacy of ASA for prevention of graft failure following CABG surgery may be limited by incomplete platelet inhibition due to increased post-operative platelet turnover.

OBJECTIVES

To determine whether acetyl-salicylic acid (ASA) 325 mg once-daily or 81 mg four-times daily overcomes the impaired response to ASA 81 mg once-daily in post-operative coronary artery bypass graft (CABG) patients.

METHODS

We randomized 110 patients undergoing CABG surgery to either ASA 81 mg once-daily, 81 mg four times daily or 325 mg once-daily and compared their effects on serum thromboxane B2 (TXB2 ) suppression and arachidonate-induced platelet aggregation.

RESULTS

One hundred patients were included in the final analysis. Platelet counts fell after surgery, reached a nadir on day 2, and then gradually increased. Although there was near complete suppression of TXB2 on the second or third post-operative day, TXB2 levels increased in parallel with the rise in platelet count on subsequent days. This increase was most marked in patients receiving ASA 81 mg once-daily and less evident in those receiving ASA four times daily. On post-operative day 4, (i) median TXB2 levels were lower with four times daily ASA than with either ASA 81 mg once-daily (1.1 ng/mL; Quartile(Q) Q1,Q3: 0.5, 2.4 and 13.3 ng/mL; Q1,Q3: 7.8, 30.8 ng/mL, respectively; P < 0.0001) or ASA 325 mg once-daily (3.4 ng/mL; Q1,Q3: 2.0, 8.2 ng/mL; P = 0.002), and (ii) ASA given four times daily was more effective than ASA 81 mg once-daily and 325 mg once-daily at suppressing platelet aggregation.

CONCLUSIONS

Four times daily ASA is more effective than ASA 81 and 325 mg once-daily at suppressing serum TXB2 formation and platelet aggregation immediately following CABG surgery.

Evaluation of laboratory methods routinely used to detect the effect of aspirin against new reference methods

BACKGROUND

Aspirin, a commonly used antiplatelet agent, blocks platelet thromboxane A₂ (TXA₂) formation from arachidonic acid (AA) by acetylating platelet cyclooxygenase-1 (COX-1). Laboratory methods currently used to detect this antiplatelet effect of aspirin provide variable results. We have reported three methods that assess platelet COX-1 acetylation (inactivation) by aspirin and its direct consequences. The first and second assays use monoclonal anti-human-COX-1 antibodies that only detect acetylated (inactivated) COX-1 and active (non-acetylated) COX-1, respectively. The third method measures platelet production of TXB₂ (the stable metabolite of TXA₂) in vitro in response to AA. We compared the results of these three reference methods with other routinely used methods for assessing the functional consequences aspirin treatment.

METHODS

108 healthy volunteers were treated with low-dose aspirin for 7 days. On day 7 following aspirin treatment COX-1 in the platelets was fully acetylated whereas only non-acetylated COX-1 was present in the day 0 platelets. Further, TXB2 production by day 7 platelets was completely blocked. The following tests were performed on the samples obtained from study participants before and after seven days of aspirin treatment: PFA-100 closure time with collagen/epinephrine cartridge, VerifyNow (VN) Aspirin Assay, platelet aggregation and ATP secretion using AA, ADP, epinephrine and collagen as agonists.

RESULTS

Comparing the pre-treatment and day 7 values, methods that use AA as platelet agonist (AA-induced platelet aggregation/secretion and VN Aspirin Assay) showed high discriminative power. In contrast, results of the other tests showed considerable overlap between day 7 and day 0 values.

CONCLUSIONS

Only assays that clearly distinguish between acetylated and non-acetylated platelet COX-1 are useful for establishing the antiplatelet effect of aspirin. The other tests are not suitable for this purpose.

Thrombomodulin and the vascular endothelium: insights into functional, regulatory, and therapeutic aspects

Thrombomodulin (TM) is a 557-amino acid protein with a broad cell and tissue distribution consistent with its wide-ranging physiological roles. When expressed on the lumenal surface of vascular endothelial cells in both large vessels and capillaries, its primary function is to mediate endothelial thromboresistance. The complete integral membrane-bound protein form displays five distinct functional domains, although shorter soluble (functional) variants comprising the extracellular domains have also been reported in fluids such as serum and urine. TM-mediated binding of thrombin is known to enhance the specificity of the latter serine protease toward both protein C and thrombin activatable fibrinolysis inhibitor (TAFI), increasing their proteolytic activation rate by almost three orders of magnitude with concomitant anticoagulant, antifibrinolytic, and anti-inflammatory benefits to the vascular wall. Recent years have seen an abundance of research into the cellular mechanisms governing endothelial TM production, processing, and regulation (including flow-mediated mechanoregulation)--from transcriptional and posttranscriptional (miRNA) regulation of TM gene expression, to posttranslational processing and release of the expressed protein--facilitating greater exploitation of its therapeutic potential. The goal of the present paper is to comprehensively review the endothelial/TM system from these regulatory perspectives and draw some fresh conclusions. This paper will conclude with a timely examination of the current status of TM's growing therapeutic appeal, from novel strategies to improve the clinical efficacy of recombinant TM analogs for resolution of vascular disorders such as disseminated intravascular coagulation (DIC), to an examination of the complex pleiotropic relationship between statin treatment and TM expression.

Aspirin resistance: current status and role of tailored therapy

Aspirin is integral in the primary and secondary prevention of coronary artery disease and acute coronary syndrome. Given the high clinical importance of aspirin in the management of coronary artery disease, much attention has been directed towards the concept of "aspirin resistance." Unfortunately, the term aspirin resistance is ill-defined in the literature, leading to a large variance in the reported prevalence of this phenomenon. In this review, the current understanding of aspirin resistance is discussed. Commonly used functional and diagnostic tests of platelet function, including their strengths and weakness, are reviewed. We next discuss several proposed mechanisms of aspirin resistance and special high-risk groups at risk for aspirin treatment failure. We then discuss optimal dosing and diagnostic strategies for those populations at risk for aspirin resistance with a focus on tailored aspirin therapy for high-risk groups. Finally, future topics of interest in the field of aspirin resistance are considered.