The effect of a loading dose (300 mg) of clopidogrel on platelet function in patients with peripheral arterial disease

Construction and validation of a nomogram for predicting remission of migraine patients with patent foramen ovale after closure

OBJECTIVE

This study aimed to construct and validate a nomogram model that predicts the remission of migraine attacks by screening factors that affect the prognosis of migraine patients with patent foramen ovale (PFO) after closure.

METHOD

Retrospective analysis was conducted in migraine patients with PFO who underwent PFO closure in the Department of Cardiology of Jiangsu Province Hospital from September 2020 to April 2023. Based on the Migraine Disability Assessment (MIDAS) scores from the 1-year follow-up after PFO closure, all patients who met the inclusion criteria were categorized into a remission group and a non-remission group. The primary efficacy endpoint was remission of migraine headache. After collecting clinical data, transcranial doppler sonography (TCD) results and MIDAS scores, LASSO (least absolute shrinkage and selection operator) regression and multivariable logistic regression analysis were used to filter variables predictive to migraine remission and construct the nomogram model. The Nomogram's accuracy and consistency were respectively assessed through Receiver Operating Characteristic (ROC) curves and calibration curves. Additionally, an analysis of decision curves (DCA) was conducted to evaluate the clinical utility of this newly developed model.

RESULT

A total of 241 consecutive patients were included in the study. The remission group included 21 males and 93 females, with a median age of 39 (30.25,50) years. The non-remission group included 26 males and 101 females, with a median age of 35 (25.5,47.5) years. All Patients were randomly divided into a training cohort and a validation cohort. Multivariable logistic regression analysis showed that 5 independent predictors, including MIDAS before closure (p = 0.0002), mitigating factors (p = 0.0057), number of attacks/month (p = 0.0058), TCD (p = 0.0093) and Platelet Crit (PCT) (p = 0.0351), played a significant role in the prediction of remission of migraine patients with PFO after closure. Based on these independent predictors, the predictive nomogram model of migraine remission in PFO patients was constructed. The application of the nomogram in the training cohort exhibited good discrimination (area under the ROC curve was 0.7763[95% CI 0.7108-0.8418]), which was confirmed in the validation cohort (AUC was 0.704[95% CI 0.5533-0.8547]). The calibration curve showed that the nomogram model demonstrated good calibration performance. Additionally, the decision curve analysis indicated the clinical utility of the nomogram model.

CONCLUSION

The construction of the nomogram model had a considerable predictive accuracy for migraine remission in patients after PFO closure, which may provide constructive guidance for clinical decision making.

A Systematic Review of Clopidogrel Resistance in Vascular Surgery: Current Perspectives and Future Directions

BACKGROUND

Clopidogrel resistance is a well-described phenomenon that has been linked to adverse cardiovascular events in patients with coronary artery disease. The impact of clopidogrel resistance in patient outcomes after vascular and endovascular surgery is not well-established.

METHODS

Using preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines, a literature review with the medical subject headings (MeSH) terms "(clopidogrel resistance) and (vascular)", "(clopidogrel resistance) and (vascular surgery)", "(clopidogrel resistance) and (endovascular)", and "(clopidogrel resistance) and (endovascular surgery)" was performed in PubMed and Cochrane databases, to identify all peer-reviewed studies performed on clopidogrel resistance in vascular and endovascular surgery. Studies written in the English language from inception to 2022 were included. Case reports, studies with limited information, nonhuman studies, and studies not pertaining to vascular or endovascular surgery were excluded from analysis. Each study was independently reviewed by 2 qualified researchers to assess eligibility.

RESULTS

Of the 691 studies identified through the MeSH strategy, 16 studies met the inclusion criteria and were reviewed and summarized. These studies focused on extracranial cerebrovascular disease (n = 5) and peripheral arterial disease (PAD, n = 11), encompassing a total of 1,716 patients. The prevalence of clopidogrel resistance ranged from 0% to 83.3%, depending on the diagnostic assay and cutoff values used. In cerebrovascular disease, clopidogrel resistance may be associated with cerebral embolization, ischemic neurologic events, and vascular-related mortality. In PAD, clopidogrel resistance has been linked to recurrent stent thrombosis, target lesion revascularization, amputation-free survival, and all-cause mortality.

CONCLUSIONS

This systematic review provides an up-to-date summary of clopidogrel resistance in vascular and endovascular surgery. The impact of clopidogrel resistance remains incompletely investigated, and future studies are needed to clarify the role of resistance testing in patients with vascular disease.

Mean Platelet Volume: A Possible Predictor for Patients with Decompensated Chronic Heart Failure

Purpose

Despite all medical efforts and discoveries, heart failure (HF) remains one of the most important and common public health problems, with high mortality and hospitalization rates, due to decompensation of HF. In the present study, we aimed to identify a predictive factor through which we can evaluate the risk of readmission and mortality in the first year, given the initial admission of a patient with decompensated heart failure.

Patients and Methods

The parameter we have investigated is the mean platelet volume (MPV). Studies have shown that there is a significant correlation between the value of MPV and the risk of cardiovascular disease (CVD) and cardiovascular (CV) death. In this study, we enrolled 130 patients hospitalized for decompensated chronic HF (NYHA class IV HF or acute pulmonary edema) and analyzed whether there is a relationship between the value of the MPV at admission and 6-month rehospitalization, and 1-year mortality, respectively.

Results

The statistical analysis revealed significantly different values (p = 0.041) for MPV at admission between the group of patients without decompensated chronic HF compared to the group of patients with decompensated chronic HF (8.74 fl vs 9.08 fl). Also, the results of our study revealed that patients with decompensated chronic heart failure who were readmitted at 6 months and died at 1 year, respectively, had a higher MPV at admission (>9 fl), compared to those without the above-mentioned events, with a statistical significance.

Conclusion

A higher MPV at admission can be considered in our study as an independent predictor for rehospitalization and 1-year mortality of patients with decompensated chronic HF.

Relationship between mean platelet volume and metabolic syndrome in Chinese patients

Mean platelet volume (MPV) is a determinant of activation and variability of platelets (PLT). The focus of this study was to to investigate MPV values in patients with and without metabolic syndrome (MS). It also evaluates the association between them. There are close connections among MPV, MS, and cardiometabolic risk. We compiled age, body mass index, blood cell counts, MPV, and other data of 59976 self-reported healthy volunteers (28428 male, 31548 female), 24.65% of who have MS. The mean age of the group was 48.21 years old. The data was grouped by sex and values of data between men and women groups were analyzed by independent sample’s t-test. The relationship between sex and MS was evaluated by chi-square tests. Crude odd ratios of MS between MPV quartiles and 95% confidence intervals were analyzed by binary logistic regression in this study. We found women had higher levels of MPV (10.09 vs. 9.98, P < 0.01) and PLT (228.68 vs. 212.11, P < 0.01) than men. In females, the prevalence of MS was higher in low MPV group than in high MPV groups. The odds of having MS were significantly lower in higher MPV quartiles compared with MPV Quartile 1 in women (Adjusted OR < 1, P < 0.01). This study indicated that MS was inversely associated with MPV in females only.

Mean platelet volume and mortality risk in a national incident hemodialysis cohort

BACKGROUND

Higher mean platelet volume (MPV) is an indicator of larger, reactive platelets, and has been associated with a higher risk of thrombosis and cardiovascular events in the general population. Hemodialysis patients have a higher risk for cardiovascular death and predisposition to platelet dysfunction (thrombosis and bleeding diathesis), but the relationship between MPV and mortality in this population is unknown.

METHODS

Among a 5-year cohort (1/2007-12/2011) of 149,118 incident hemodialysis patients from a large national dialysis organization, we examined the association between MPV and all-cause mortality. In primary analyses, we granularly analyzed MPV across five categories: 7.2-7.5, >7.5-9.5, >9.5-11.5, >11.5-13.5, and >13.5-15.0fL. In secondary analyses, we examined MPV categorized as low, normal, and high based on thresholds in the general population: 7.2-7.5, >7.5-11.5, and >11.5fL, respectively. Associations between baseline and time-dependent MPV with mortality were estimated using traditional and time-dependent Cox models in order to determine long-term and short-term exposure-mortality associations, respectively, using three adjustment levels: unadjusted, case-mix, and case-mix+laboratory models.

RESULTS

In primary analyses, higher baseline and time-dependent MPV levels were associated with incrementally higher death risk in case-mix+laboratory analyses (reference: >9.5-11.5fL). In secondary analyses, high baseline and time-dependent MPV levels were associated with higher mortality, whereas low MPV was associated with lower death risk across all multivariable models (reference: normal MPV).

CONCLUSIONS

Hemodialysis patients with higher MPV have heightened mortality risk. Further studies are needed to determine the pathophysiologic basis for the higher risk, and if modification of MPV ameliorates mortality in this population.

Platelet Activation in Bypass Surgery for Critical Limb Ischemia

Platelet activation contributes to graft occlusion after bypass surgery. This study investigated platelet activation status before, during, and after bypass. Blood was taken preoperatively from patients undergoing femoro-popliteal bypass and at incision, after dissection, after ischemia, after reperfusion, 24 hours after surgery, and almost 2 years after bypass (and given aspirin or warfarin). Platelet aggregation was measured using a turbidimetric method and platelet activation with flow cytometry. Statistical analysis was performed using Mann-Whitney U and Wilcoxon's tests. Resting platelet activation was similar between controls and patients undergoing bypass. Platelet activation decreased at incision but remained highly reactive. Platelet aggregation increased after dissection and the ischemic phase but significantly decreased after reperfusion. Platelet aggregation and activation were increased at 24 hours and subsequently after bypass. Platelets in critical limb ischemia exist in the primed state and become activated by minimum stimuli. Increased platelet activation occurs after bypass grafting for critical limb ischemia despite adjunctive therapy.

Approach to the Assessment of Platelet Function: Comparison between Optical-based Platelet-rich Plasma and Impedance-based Whole Blood Platelet Aggregation Methods

Platelet aggregation studies play an important role in the assessment of hereditary and acquired platelet function defects. The first aggregation test introduced into laboratory practice used platelet-rich plasma (PRP) where aggregation was detected by an optical method. The assessment of platelet function using whole blood (WB) aggregation by an impedance method followed up nearly 20 years later. The WB impedance aggregation assay appears to be superior to the optical method because it 1) evaluates platelets in a physiologic milieu in the presence of red and white blood cells, which are known to modulate platelet function; 2) is faster; 3) has higher sensitivity; and 4) does not require centrifugation, thus avoiding injury to platelets and loss of giant thrombocytes. These two assays were compared. Clearly, the WB impedance aggregation methodology has many advantages over the optical PRP assay for the assessment of the hyperactive platelet syndrome and the effects of anti-platelet drugs.

Effect of Clopidogrel on Platelet Aggregation and Intimal Hyperplasia following Carotid Endarterectomy in the Rat

Intimal hyperplasia results in significant morbidity and mortality following vascular intervention. Both platelets and elevated homocysteine have been implicated in the development of intimal hyperplasia. We previously demonstrated that a locally applied antiplatelet agent decreases the development of intimal hyperplasia. We were therefore interested in a systemic antiplatelet agent, clopidogrel. We hypothesized that clopidogrel would decrease platelet aggregation and activity and intimal hyperplasia. Male Sprague-Dawley rats underwent carotid endarterectomy (CEA) and treatment with either placebo or varying regimens of clopidogrel, including chronic, pre-CEA bolus, chronic plus pre-CEA bolus, and chronic plus post-CEA bolus; a homocystine diet was used to elevate both plasma homocysteine and the degree of intimal hyperplasia. Platelet aggregation, platelet activity, and intimal hyperplasia were then assessed. Platelet aggregation was not decreased with chronic clopidogrel; however, it was decreased with pre-CEA bolus clopidogrel. Similarly, platelet activity was not inhibited by chronic clopidogrel but was inhibited by pre-CEA and chronic plus pre-CEA bolus clopidogrel. Neither chronic, pre-CEA bolus, chronic plus pre-CEA bolus, nor chronic plus post-CEA bolus clopidogrel resulted in a decrease in intimal hyperplasia. Although pre-CEA bolus clopidogrel resulted in a decrease in both platelet aggregation and activity, it was unable to decrease the development of intimal hyperplasia at any dose. Additional factors must therefore contribute to the pathologic development of intimal hyperplasia.

Salts of Clopidogrel: Investigation to Ensure Clinical Equivalence: A 12-Month Randomized Clinical Trial

BACKGROUND

In the present clinical trial, we compared the efficacy and safety of the generic clopidogrel besylate (CB) with the innovator clopidogrel hydrogen sulfate (CHS) salt in patients eligible to receive clopidogrel.

METHODS

A prospective 2-arm, multicenter, open-label, phase 4 clinical trial. Consecutive patients (n = 1864) were screened and 1800 were enrolled in the trial and randomized to CHS or CB. Primary efficacy end point was the composite of myocardial infarction, stroke, or death from vascular causes, and primary safety end point was rate of bleeding events as defined by Bleeding Academic Research Consortium criteria.

RESULTS

At 12-month follow-up, no differences were observed between CB (n = 759) and CHS (n = 798) in primary efficacy and safety end points (age, sex, history of percutaneous coronary intervention adjusted odds ratio [OR], 0.70; 95% confidence interval [CI], 0.41-1.21 and OR, 0.81; 95% CI, 0.51-1.29, respectively) between CHS and CB. Analyses of efficacy and safety in subgroups that were defined according to the qualifying diagnosis revealed that there was no difference between CHS and CB.

CONCLUSION

The efficacy and safety of CB administered for 12 months for the secondary prevention of atherothrombotic events are similar to that of CHS. (Salts of Clopidogrel: Investigation to ENsure Clinical Equivalence, SCIENCE trial; ClinicalTrials.gov Identifier:NCT02126982).

The Prognostic Impact of In-Hospital Change in Mean Platelet Volume in Patients With Non-ST-Segment Elevation Myocardial Infarction

It is unclear whether changes in mean platelet volume (MPV) are associated with total mortality in acute coronary syndromes. We investigated whether the change in MPV predicts total mortality in patients with non-ST-segment elevation myocardial infarction (NSTEMI). We retrospectively analyzed 419 consecutive patients (19 patients were excluded). The remaining patients were categorized as survivors (n = 351) or nonsurvivors (n = 49). Measurements of MPV were performed at admission and after 24 hours. The difference between the 2 measurements was considered as the MPV change (ΔMPV). The end point of the study was total mortality at 1-year follow-up. During the follow-up, there were 49 deaths (12.2%). Admission MPV was comparable in the 2 groups. However, both MPV (9.6 ± 1.4 fL vs 9.2 ± 1.0 fL, P = .044) and ΔMPV (0.40 [0.10-0.70] fL vs 0.70 [0.40-1.20] fL, P < .001) at the first 24 hours were higher in nonsurvivors than survivors. In multivariate analysis, ΔMPV was an independent predictor of total mortality (odds ratio: 1.84, 95% confidence interval: 1.28-2.65, P = .001). An early increase in MPV after admission was independently associated with total mortality in patients with NSTEMI. Such patients may need more effective antiplatelet therapy.

Platelet function testing: state of the art

Platelet function testing has evolved from crude tests, such as the bleeding time, to tests that permit a relatively sophisticated evaluation of platelet activity. Nonetheless, these tests are hampered by lack of specificity and sensitivity, and poor standardization of methods and techniques. The bleeding time, which has long been a staple of hemostasis testing, has been dropped from the test menu at many laboratories. In its place, tests such as the Platelet Function Analyzer-100 are increasingly used to screen patients with possible bleeding disorders. Older tests, such as platelet aggregometry and lumiaggregometry, are still used frequently because they provide insight into receptor, signaling pathway and granule release mechanisms. Flow cytometry is available in some specialized laboratories and allows for quantitative and qualitative assessment of some platelet functions, although the expense of testing is often prohibitive. Finally, the wider availability of platelet function testing has stimulated interest and demand for monitoring the effect of platelet inhibitory drugs, such as aspirin and clopidogrel. As platelet function pathways become better understood, the demand for these type of monitoring tests is likely to increase.

Could mean platelet volume among complete blood count parameters be a surrogate marker of metabolic syndrome in pre-pubertal children?

Interest in childhood metabolic syndrome (MetS) has increased substantially due to the increasing prevalence of childhood obesity on a global scale. Early recognition of MetS is critical in order to delay the development of cardiovascular disease (CVD). In this study, we evaluated the relationship between complete blood count (CBC) parameters and MetS among pre-pubertal children which may provide evidence in support of using low cost, readily available clinical haematological parameters for the detection of MetS. A retrospective analysis was carried out on 330 (125 lean vs. 205 overweight) Turkish pre-pubertal children who attend to a paediatric outpatient clinic. Age, gender, puberty, body mass index, CBC parameters, cardiometabolic risk factors including lipid profiles, high sensitive serum reactive protein (hsCRP) and insulin resistance index calculated by homeostasis model assessment (HOMA-IR) were evaluated and compared among lean, overweight children and children with MetS. The mean age of the study population was 7.4 ± 1.9 years. In both gender, the mean values of mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) were significantly lower and red blood cell (RBC), platelet (PLT) counts were significantly higher in overweight children. Overall, 8.4% (n = 28) of patients met the criteria of MetS. Children with MetS had higher levels of PLT and lower levels of mean platelet volume (MPV). Of all the haematological parameters analysed, PLT was positively, whereas MPV was negatively correlated with MetS in girls. In addition, MPV was inversely correlated with fasting blood glucose, HOMA-IR, low density lipoprotein-cholesterol (LDL-C) and low density lipoprotein-cholesterol/high density lipoprotein-cholesterol (LDL-C/HDL-C) ratio in girls after adjusting for confounding factors. The risk analyses of MetS in terms of MPV quartiles showed that the adjusted OR (95% CI) for the lowest vs. the highest quartile was 7.71 (1.45-40.89) in girls. These data might suggest that MPV could be another feature of MetS in pre-pubertal girls and might be used as a surrogate marker for MetS in clinical settings.

Antiplatelet Treatment in the Secondary Prevention of Coronary and Cerebrovascular Disease

Ischemic heart disease and cerebrovascular disease remain major health problems with associated mortality and quality-of-life consequences. Antiplatelet agents, including thienopyridines and the new P2Y12 inhibitors, have been shown to improve survival in the secondary prevention setting. We review the available evidence on the effectiveness and safety of previous established as well as novel antithrombotic agents in the secondary prevention of cardiovascular disease with a special focus on cerebrovascular disease.

Decreased mean platelet volume and platelet distribution width are associated with mild cognitive impairment and Alzheimer's disease

Neuroinflammation is a critical driving force underlying mild cognitive impairment (MCI) and Alzheimer's disease (AD) pathologies. Activated platelets play an important role in neuroinflammation and have been implicated in AD pathogenic mechanisms. Mean platelet volume (MPV), a marker of platelet activation, is involved in the pathophysiology of a variety of pro-inflammatory diseases. However, little research has been conducted to investigate the relationship between platelet indices and MCI and AD pathogenesis. In this cross-sectional study, we investigated the levels of platelet count, MPV and platelet distribution width (PDW) in 120 AD patients, 120 MCI patients, and 120 non-demented controls. Our study showed that MPV and PDW were significantly lower in patients with AD as compared with either MCI or controls. Moreover, MCI patients had lower MPV and PDW values compared with the controls (P < 0.001). In addition, there is a positive correlation between mini-mental state examination (MMSE) and MPV and PDW, after adjusting age, gender, and body mass index (r = 0.576, P < 0.001 for MPV; r = 0.465, P < 0.001 for PDW, respectively). Multivariate analysis showed that MPV and PDW were significantly associated with MMSE (β = 0.462; P < 0.001 for MPV; β = 0.245; P < 0.001 for PDW; respectively). In conclusion, MPV and PDW were decreased in MCI and AD patients. Further prospective research is warranted to determine the potential clinical application of MPV and PDW as biomarkers in the early diagnosis of AD.

Pharmacotherapeutic Considerations for the Use of Prasugrel and Ticagrelor to Reduce Stent Thrombosis in Patients With Acute Coronary Syndrome

Despite the improvement in stent technology, stent thrombosis (ST), a potentially catastrophic event, still occurs. Among several risk factors for ST, high on-treatment platelet reactivity to clopidogrel has been demonstrated to play a role, occurring in about one-third of the patients. In order to overcome this limitation, prasugrel and ticagrelor, newer P2Y12 inhibitors, have been developed and approved for clinical use. Two large clinical trials, TRial to assess Improvement in Therapeutic Outcomes by optimizing platelet inhibitioN with prasugrel-thrombolysis in myocardial infarction (TRITON-TIMI) 38 and Study of Platelet Inhibition and Patient Outcomes (PLATO), evaluated these drugs in patients with acute coronary syndrome (ACS), showing a significant improvement in efficacy end points (including a prominent reduction in ST occurrence) compared to clopidogrel. In contrast, the TRILOGY ACS trial found no benefit with prasugrel compared to clopidogrel in patients with medically treated ACS. The aim of this review is to consider decision-making strategies between prasugrel and ticagrelor in daily clinical practice.

Prognostic Value of Mean Platelet Volume in Patients With Non-ST-Elevation Acute Coronary Syndrome

The aim of this study is to determine mean platelet volume (MPV) in a population with non-ST-elevation acute coronary syndrome (nSTEACS) and explore its relation with prognosis. Patients (n = 329) with a diagnosis of nSTEACS at admission were recruited, with a determination of MPV in the first 12 hours at admission. We also collected blood from 87 healthy controls. A composite end point of cardiovascular death and new ACS was assessed at 6-month follow-up. Patients with nSTEACS showed larger platelets (MPV: 11.0 [10.3-11.8] vs 9.2 [8.6-10.0] fL; P < .001.). In Cox regression analysis, MPV at admission was a significant predictor of cardiovascular adverse events in univariate analysis, hazard ratio (HR) 1.4 95% confidence interval (CI) 1.1-1.8; P = .018; but after adjustment with clinical variables, MPV lost its statistical significance. In conclusion, patients with nSTEACS present with larger platelets than healthy controls, however this parameter did not show an independent prognostic significance at 6-month follow-up.

Review: Antiplatelet Drugs: What Comes Next?

Antiplatelet drugs are important components in the management of atherothrombotic vascular disease. However, several limitations restrict the safety and efficacy of current antiplatelet therapy in clinical practice. Interpatient variability and resistance to aspirin and/or clopidogrel has spurred efforts for the development of novel agents. Indeed, several antiplatelet drugs are at various stages of evaluation; those at advanced stage of development are the focus of this review.

New antiplatelet drugs: beyond aspirin and clopidogrel

Antiplatelet therapy remains a cornerstone of modern management of atherothrombotic vascular disease. For many years, aspirin has been the mainstay of initial antiplatelet drug management in coronary heart disease, while the need for inhibition of other platelet activation pathways has led to the development of various other antiplatelet drugs, such as clopidogrel. An improved understanding of the underlying mechanisms involved in thrombogenesis has paved the way for further development of newer antiplatelet drug therapies. Various clinical studies have probed the effectiveness and risk profile of the newer antiplatelet drugs, such as prasugrel, in comparison with currently available drugs. Some newer agents such as prasugrel are close to being approved for clinical use, whereas other agents such as cangrelor and AZD6140 are in phase 3 clinical trials. New drug classes, such as the thromboxane receptor antagonists (such as NCX-4016 and S18886), as well as platelet adhesion antagonists and thrombin receptor antagonists are similarly being evaluated for their efficacy and risk profile in phase I and II trials.

Effects of clopidogrel on survival of rat skin flaps

Clopidogrel is a thienopyridine derivative that is chemically related to ticlopidine, which irreversibly inhibits platelet aggregation by selectively binding to adenylate cyclase-coupled adenosine diphosphate receptors on the platelet's surface. In animal models, clopidogrel has been shown to reduce the incidence of both arterial and venous thrombi. In the present study the effects of clopidogrel on the survival of rat epigastric island flaps was researched. Epigastric island flaps of 7x7cm were raised from symphisis pubis to arcus costa with the panniculus carnosus. The experimental group received seven doses of 25mg/kg clopidogrel postoperatively, the first dose given immediately after the suturing of the flaps. The rats were anaesthetised on postoperative day 7 to assess the survival of flaps. The difference between the clopidogrel and the control group was significant (P<0.005). The full-thickness skin samples obtained after the calculation of survival percentages revealed thinning of the epidermis layer and active chronic inflammation in both groups. However, diffuse dilated vessels, extravasated eritrocytes were seen in the clopidogrel group flaps. The results indicated a significant increase in flap survival in rats given clopidogrel. Further research is needed to assess the critical doses of clopidogrel to create optimal flap survival improvement.

Pathophysiology and therapeutic potential of purinergic signaling

The concept of a purinergic signaling system, using purine nucleotides and nucleosides as extracellular messengers, was first proposed over 30 years ago. After a brief introduction and update of purinoceptor subtypes, this article focuses on the diverse pathophysiological roles of purines and pyrimidines as signaling molecules. These molecules mediate short-term (acute) signaling functions in neurotransmission, mechanosensory transduction, secretion and vasodilatation, and long-term (chronic) signaling functions in cell proliferation, differentiation, and death involved in development and regeneration. Plasticity of purinoceptor expression in pathological conditions is frequently observed, including an increase in the purinergic component of autonomic cotransmission. Recent advances in therapies using purinergic-related drugs in a wide range of pathological conditions will be addressed with speculation on future developments in the field.

Increased platelet purinergic sensitivity in peripheral arterial disease--a pilot study

Peripheral arterial disease (PAD) is associated with platelet hyperaggregability as well as an increase in morbidity and mortality from myocardial infarction (MI) and stroke. Purinergic signaling has been shown, both experimentally and clinically, to play an important role in the activation of platelets. Platelets express three different purinergic receptors: P2Y1, P2Y12 and P2X1. We assessed the hypothesis that the hyperaggregability associated with PAD is partly due to an increased P2 receptor expression at the transcriptional and/or translational level. Patients with PAD (n=8) and controls (n=8) were studied. Using a high-resolution channelyzer, platelet shape change (PSC) was assessed by measuring the median platelet volume (MPV). The fall in free platelet count following the addition of ADP was also assessed. Real-time PCR was used to quantify the mRNA expression and Western blots to quantify the protein expression of P2 receptors in platelets. The median (and range) fall in free platelet count after adding ADP was significantly (P=0.02) greater for patients [11% (5-24); n=8] than for controls [0.5% (0-10); n=8] despite using a lower concentration of ADP for the patient samples. The MPV did not differ significantly. The mRNA levels for the three P2 receptors were similar in PAD patients and controls. Western blot detected no significant differences in protein expression between these groups. Thus, platelets from PAD patients show an increased activation after stimulation with ADP (even though all patients were on aspirin). This hyperactivity was neither due to an obvious up-regulation of the mRNA levels nor to altered protein levels of P2 receptors in the platelets. It is suggested that the increased sensitivity to ADP in PAD is caused by post-receptor mechanisms.

The effect of clopidogrel, aspirin and both antiplatelet drugs on platelet function in patients with peripheral arterial disease

Peripheral arterial disease (PAD) is associated with platelet hyperactivity. Aspirin and clopidogrel, two platelet inhibitors, act by different mechanisms. Aspirin inhibits thromboxane A2 synthesis and clopidogrel acts on the P2Y12 platelet ADP receptor. We evaluated the effect of clopidogrel (75 mg/day), aspirin (75 mg/day) and then both drugs on several platelet function indices in patients with PAD (n = 20). There was a significant (P = 0.0001) decrease in ADP-induced aggregation, after clopidogrel but not after taking aspirin. Clopidogrel plus aspirin significantly decreased spontaneous platelet aggregation (SPA) (P = 0.01 to P = 0.002) but SPA was not significantly altered by either aspirin or clopidogrel monotherapy. Similarly, monotherapy did not inhibit serotonin (5HT)-induced aggregation but there was a sigificant inhibition (P = 0.03 to P < 0.02) after combination therapy. ADP (0.8 microM)-induced platelet shape change (PSC) was significantly inhibited by clopidogrel (P = 0.004) or aspirin (P = 0.01). This was also true for 5HT-induced PSC (clopidogrel, P = 0.01; aspirin, P = 0.03). Soluble P-selectin decreased significantly (from 32 +/- 24 to 25 +/- 17 ng/ml, P = 0.04) with combination therapy. Plasma platelet-derived growth factor and intraplatelet 5HT levels were not altered by combination therapy. In PAD, clopidogrel is a more potent inhibitor of ADP-induced platelet activation than aspirin; combination therapy is more effective than clopidogrel or aspirin monotherapy. These potentially clinically relevant findings should be evaluated in appropriately designed trials.