Different effects of calcium antagonists, nitrates, and beta-blockers on platelet function. Possible importance for the treatment of unstable angina

Beneficial Extracardiac Effects of Cardiovascular Medications

Cardiovascular diseases are the most common cause of death worldwide, with cardiovascular medications being amongst the most common medications prescribed. These medications have diverse effects on the heart, vascular system, as well as other tissues and organ systems. The extra cardiovascular effects have been found to be of use in the treatment of non-cardiovascular diseases and pathologies. Minoxidil is used to manage systemic hypertension with its well-known side effect of hirsutism used to treat alopecia and baldness. Sildenafil was originally investigated as a treatment option for systemic hypertension; however, its side effect of penile erection led to it being widely used for erectile dysfunction. Alpha-1 blockers such as terazosin are indicated to treat systemic hypertension but are more commonly used for benign prostatic hyperplasia and post-traumatic stress disorder. Beta blockers are the mainstay treatment for congestive heart failure and systemic hypertension but have been found useful to help in patients with intention tremors as well as prophylaxis of migraines. Similarly, calcium channel blockers are indicated in medical expulsion therapy for ureteric calculi in addition to their cardiovascular indications. Thiazides are commonly used for treating systemic hypertension and as diuretics. Thiazides can cause hypocalciuria and hypercalcemia. This side effect has led to thiazides being used to treat idiopathic hypercalciuria and associated nephrolithiasis. Spironolactone is commonly utilized in treating heart failure and as a diuretic for edema. It's well described anti-androgen side effects have been used for acne vulgaris and hirsutism in polycystic ovarian syndrome. This review article discusses how the various extracardiovascular effects of commonly used cardiovascular medications are put to use in managing non-cardiovascular conditions.

Platelet function in dogs with chronic liver disease

OBJECTIVES

To assess platelet function, buccal mucosal bleeding time and plasma von Willebrand factor concentration in dogs with chronic inflammatory and/or fibrotic liver disease and to compare results with those obtained in healthy dogs.

MATERIALS AND METHODS

Preliminary study including 18 dogs with chronic inflammatory and/or fibrotic liver disease undergoing liver biopsy and 18 healthy age-matched control dogs. Platelet function was assessed by measuring closure time with the PFA-100® analyser using adenosine diphosphate (ADP) as an agonist. Buccal mucosal bleeding time, closure time and plasma von Willebrand factor antigen were measured in dogs in both groups. After undergoing ultrasound-guided needle biopsy, dogs were monitored for haemorrhage to determine if there was an association of any measurement with post-biopsy bleeding.

RESULTS

The closure time was not different between the liver disease group (median 76.3; range 53 to 118.5 seconds) and control group (72.8; 57 to 89.5 seconds). The buccal mucosal bleeding time was longer in the liver disease group (median 138; range 95 to 229 seconds) than the control group (103; 63 to 200 seconds). The plasma von Willebrand factor antigen concentration was not different between the liver disease group (median 203; range 109 to 351%) and control group (165.5; 63 to 246%).

CLINICAL SIGNIFICANCE

In this study, dogs with chronic necroinflammatory and/or fibrotic liver disease did not have overt, clinically relevant derangements in platelet function as assessed by buccal mucosal bleeding time, closure time and von Willebrand factor analysis. In addition, none of the dogs undergoing percutaneous ultrasound-guided biopsy in the study exhibited bleeding complications post-biopsy procedure.

Factors Influencing Aspirin Hyporesponsiveness in Elderly Chinese Patients

Background

Aspirin hyporesponsiveness increases the risk of ischemic events. Therefore, it is important to investigate the factors influencing aspirin hyporesponsiveness.

Material/Methods

Patients aged 60 years or older who did not take aspirin before enrollment were included, with aspirin 100 mg/day administered after enrollment. The arachidonic acid-induced platelet aggregation rate (Ara) was measured by light transmission assay to evaluate aspirin responsiveness. Patients with Ara in the upper quartile after taking aspirin were assigned to the aspirin hyporesponsive group (Ara-Q4).

Results

A total of 292 elderly patients were included. The median value of Ara after taking aspirin was 5.87% (interquartile range 3.86–10.04%). Compared with the aspirin non-hyporesponsive group (Ara-Q1-3, Ara ≤10.04%, n=220), the level of uric acid (UA) (341.30 μmol/L vs. 299.10 μmol/L, p=0.027) and the ratios of β-blockers (9.72% vs. 2.27%, p=0.015) and diuretics (6.94% vs. 1.36%, p=0.036) were higher in the aspirin hyporesponsive group (Ara-Q4, Ara >10.04%, n=72). After multivariate adjustment, the results demonstrated baseline Ara (odds ratio [OR]: 1.030, 95% confidence interval [CI]: 1.004–1.056, p=0.021), UA level (OR: 1.003, 95% CI: 1.000–1.006, p=0.038), and β-blockers use (OR: 5.487, 95% CI: 1.515–19.870, p=0.010) were independently and positively associated with aspirin hyporesponsiveness.

Conclusions

This study found that baseline Ara, UA level, and β-blockers use were independently and positively associated with aspirin hyporesponsiveness in elderly Chinese patients, which needs to be validated in large-scale studies.

Potential Protective Role of Blood Pressure-Lowering Drugs on the Balance between Hemostasis and Fibrinolysis in Hypertensive Patients at Rest and During Exercise

In patients with hypertension, the triad represented by endothelial dysfunction, platelet hyperactivity, and altered fibrinolytic function disturbs the equilibrium between hemostasis and fibrinolysis and translates into a hypercoagulable state, which underlies the risk of thrombotic complications. This article reviews the scientific evidence regarding some biological effects of antihypertensive drugs, which can protect patients from the adverse consequences of hypertensive disease, improving endothelial function, enhancing antioxidant activity, and restoring equilibrium between hemostatic and fibrinolytic factors. These protective effects appear not to be mediated through blood pressure reduction and are not shared by all molecules of the same pharmacological class.

Platelets Activation in Patients Undergoing PTCA and Their Responsiveness After in vitro Stimulation

We evaluated expression of platelet activation markers in blood samples of 15 patients who underwent percutaneous transluminal coronary angioplasty (PTCA) by flow cytometry. Analysis was performed before the beginning of PTCA, during initial coronary angiography and after the end of PTCA or after a stent placement, respectively. We evaluated platelet-derived microparticles, platelet-leukocyte aggregates, platelet aggregates and a membrane expression of CD62P and CD63 molecules. Responsiveness of platelets to the activationin vitrowith thrombin-receptor activating protein – 6 (TRAP-6) was tested simultaneously. Statistically significant differences between patient samples were found only in the expression of the activation markers CD62P (before PTCA 0.22 %, during 0.39 %, after 0.67 %), CD63 (0.26 %/ 0.45 %/ 0.85 %) and platelet-leukocyte aggregates (13.57 %/ 18.39 %/ 23.63 %).In the same group the expression of all constitutive membrane markers was statistically significantly decreased: in patients undergoing PTCA was the expression of CD9:87.98 % (in comparison with control group 94.98 %), CD31: 87.10 % (92.78 %), CD36: 87.37 % (90.98 %), CD41: 88.09 % (95.62 %), CD42a: 88.54 % (94.98 %), CD42a: 88.31 % (94.13 %).

Thromboelastography After Murine TBI and Implications of Beta-Adrenergic Receptor Knockout

BACKGROUND

The source of coagulopathy in traumatic brain injury (TBI) is multifactorial and may include adrenergic stimulation. The aim of this study was to assess coagulopathy after TBI using thromboelastography (TEG), and to investigate the implications of β-adrenergic receptor knockout.

METHODS

Adult male wild type c57/bl6 (WT) and β1/β2-adrenergic receptor knockout (BKO) mice were assigned to either TBI (WT-TBI, BKO-TBI) or sham injury (WT-sham, BKO-sham). Mice assigned to TBI were subject to controlled cortical impact (CCI). At 24 h post-injury, whole blood samples were obtained and taken immediately for TEG.

RESULTS

At 24 h after injury, a trend toward increased fibrinolysis was seen in WT-TBI compared to WT-sham although this did not reach significance (EPL 8.1 vs. 0 %, p = 0.18). No differences were noted in fibrinolysis in BKO-TBI compared to BKO-sham (LY30 2.6 vs. 2.5 %, p = 0.61; EPL 3.4 vs. 2.9 %, p = 0.61). In addition BKO-TBI demonstrated increased clot strength compared to BKO-sham (MA 76.6 vs. 68.6, p = 0.03; G 18.2 vs. 11.3, p = 0.03).

CONCLUSIONS

In a mouse TBI model, WT mice sustaining TBI demonstrated a trend toward increased fibrinolysis at 24 h after injury while BKO mice did not. These findings suggest β-blockade may attenuate the coagulopathy of TBI and minimize progression of intracranial hemorrhage by reducing fibrinolysis and increasing clot strength.

Antiplatelet resistance and the role of associated variables in stable patients treated with stenting

Introduction

Nowadays, clopidogrel and acetylsalicylic acid (ASA) have become routinely applied therapies in percutaneous coronary interventions (PCI) with stenting.

Aim

Numerous variables can interfere with antiplatelet responsiveness, so we aimed to investigate the role of different variables associated with ASA or clopidogrel resistance in stable coronary artery disease.

Material and methods

A total of 207 patients undergoing elective PCI were included in the analysis. All patients received a loading dose of clopidogrel and ASA during PCI procedure and followed by dual antiplatelet therapy. Clopidogrel and ASA resistance were measured by impedance aggregometry method.

Results

Of the patients, 19.8% had clopidogrel resistance, 18.8% had ASA resistance, 9.2% had both clopidogrel and ASA resistance, and 71.5% were responsive to both drugs. In multivariate analysis, platelet count, angiotensin receptor blocker (ARB) use, and ASA resistance were independent variables associated with clopidogrel resistance, and clopidogrel resistance was the only variable associated with ASA resistance. In differentiating whether clopidogrel resistance exists or not, optimum ASA aggregometry response cut-off values were specified, and in differentiating whether ASA resistance exists or not, optimum clopidogrel aggregometry response cut-off values were specified.

Conclusions

In this study, there was a higher incidence of low responsiveness to ASA when there was a low response to clopidogrel, and vice versa. Angiotensin receptor blocker use, platelet count, and ASA resistance were independent variables associated with clopidogrel resistance. Clopidogrel resistance was the only independent variable associated with ASA resistance. Angiotensin receptor blocker use seems to an independent risk factor for clopidogrel resistance in this study, but this result needs to be verified in other studies.

Glucose intolerance and insulin resistance as predictors of low platelet response to clopidogrel in patients with minor ischemic stroke or TIA

The relation between high on-treatment platelet reactivity (HPR), and the level of glucose intolerance and insulin resistance (IR) was studied in clopidogrel-treated patients with minor ischemic stroke or TIA. The cohort consisted of 66 patients, 11 of which had known type 2 diabetes mellitus (DM). Platelet aggregation in whole blood (Multiplate™) and metabolic variables were measured 1 month after acute onset of neurological symptoms. Glucose tolerance was measured by Oral Glucose Tolerance Test (OGTT). IR was estimated by homeostasis model assessment HOMA-IR. Patients were categorized as "responders" (R) or "non-responders" (NR) to clopidogrel according to an established cut-off in platelet aggregation induced by adenosine diphosphate (ADP). In total, 14/66 (21%) patients were NR. Impaired glucose tolerance (IGT), impaired fasting glucose (IFG) or DM was seen in 13/14 NR (93%), while for R this was the case in 25/52 (48%), p = 0.001. The percentage of NR was 33% in patients with DM and 35% in patients with IGT or IFG. In the group with normal glucose tolerance (NGT) the percentage of NR was low, 4% (1/28). Fasting plasma glucose (f-PG) was higher for NR than for R, 6.0 (5.5-6.7) mM vs. 5.3 (5.0-6.0) mM, p = 0.023. Glycated hemoglobin (HbA1c) did not differ between NR and R. NR also had higher arachidonic acid-induced platelet aggregation than R, and a tendency towards higher aggregation induced by thrombin receptor agonist peptide (TRAP), indicating that HPR reflects a global platelet hyper-reactivity. HOMA-IR was calculated for 52 of the patients above without known diabetes, 9 of which were NR (17%). NR were significantly more insulin resistant than R, with median HOMA-IR 4.5 (3.0-7.4) compared to 2.1 (1.5-3.2) for R, p = 0.001. HOMA-IR and fasting plasma insulin were the only metabolic variables with significant relationships to ADP-induced platelet aggregation. The results suggest that HPR develops in the pre-diabetic phase. A metabolic disturbance with glucose intolerance and/or high level of IR was a pre-requisite for HPR in the tested cohort. Conversely, normal glucose tolerance combined with normal or mildly elevated HOMA-IR excluded HPR. NR are likely to constitute a high-risk group among patients with ischemic cerebrovascular disease. Measurement of f-PG or HbA1c is insufficient to identify NR, while OGTT and HOMA-IR are more predictive.

Serial change in platelet activation markers with aspirin and clopidogrel after acute ischemic stroke

OBJECTIVES

Antiplatelet drugs are widely used for secondary prevention after cerebral ischemia of noncardioembolic origin and different antiplatelet drugs exert different pharmacologic effects. This study investigated differences in platelet activation markers in patients taking either aspirin or clopidogrel after acute ischemic stroke.

METHODS

A prospective randomized case-control study evaluated 70 patients with noncardioembolic stroke treated with either aspirin (100 mg/d) or clopidogrel (75 mg/d) after acute ischemic stroke. Platelet activation markers (CD62P, CD63, and CD40L) were measured by flow cytometry at different time points (<48 hours and days 7, 30, and 90 after stroke). The markers were also evaluated in 30 at-risk control subjects.

RESULTS

Ischemic stroke patients had significantly increased circulating CD62P, CD63, and CD40L in the acute stage compared with the control group. Levels of CD62P, CD63, and CD40L were more significantly reduced in the clopidogrel group than in the aspirin group in the first week after stroke. Furthermore, differences in CD62P and CD63 levels were significant even at 1 month after stroke.

CONCLUSIONS

Patients treated with clopidogrel have lower platelet activity than those taking aspirin after acute ischemic stroke. The stronger effect of clopidogrel is notable 1 week after stroke and persists for at least 1 month. Further large-scale trials are warranted to clarify optimal treatment.

Levels and value of platelet activation markers in different subtypes of acute non-cardio-embolic ischemic stroke

INTRODUCTION

Platelet activation and its interaction with leukocytes are important in the pathophysiology of ischemic stroke. This study aimed to evaluate the value of platelet activation and platelet-leukocyte interaction in different subtypes of acute, non-cardio-embolic ischemic stroke.

METHODS

Fifty-four patients with acute, non-cardio-embolic ischemic stroke, including 32 small-vessel and 22 large-vessel diseases, were evaluated. Platelet activation markers (CD62P, CD63, and CD40L) and platelet-leukocyte interaction were measured by flow cytometry at different time points (<48 hours and Days 7, 30, and 90 post-ischemic stroke). Markers were also evaluated in 28 other stroke patients in the convalescent stage (3 to 9 months after acute stroke) and in 28 control subjects.

RESULTS

Patients with ischemic stroke had significantly increased circulating CD62P, CD63, platelet-monocyte interaction, and platelet-lymphocyte interaction in the acute stage compared with the convalescent stage and control groups. Levels of CD62P and CD63 were significantly higher in the large-vessel disease group than in the small-vessel disease group, and differences in CD62P were significant even at one month. The CD40L level in the poor outcome group was significantly higher than that in the good outcome group. Stroke patients with diabetes mellitus and large-vessel disease were associated with poor outcome.

CONCLUSIONS

Patients with large-vessel cerebral infarction elicit higher platelet activation and platelet-leukocyte interaction compared to small-vessel infarction. Further large scale trials are warranted to evaluate the relationship between platelet activation markers and outcome in stroke patients under different anti-platelet therapies, and to clarify optimal treatment.

Effect of amlodipine on exercise-induced platelet activation in patients affected by chronic stable angina

BACKGROUND

Literature concerning exercise-induced platelet activation in chronic stable angina is somewhat confusing. The reason lies in the type of exercise as well as in methodological problems. A powerful, recently introduced procedure to detect platelet activation is flow cytometry. Platelet response to activating factors is mediated by calcium uptake; however, calcium antagonist effect on platelet activity is still unclear.

HYPOTHESIS

The study was undertaken to investigate exercise-induced platelet activation before and after treatment with amlodipine in chronic stable angina.

METHODS

Twenty patients with chronic stable angina were entered into the study. Each subject underwent a symptom-limited cycloergometer stress test following a washout period of 2 weeks. Blood samples were collected before and immediately after exercise. All subjects were then randomized into two groups of 10 patients each, with Group 1 and Group 2 taking amlodipine 10 mg/day, and placebo for 4 weeks, respectively. They subsequently underwent a second exercise stress test, and blood samples were obtained before and immediately after exercise. Flow-cytometric evaluation of platelet activity was performed in order to recognize GMP-140 expression on platelet membrane.

RESULTS

Strenuous exercise induced a significant increase in platelet activation in all subjects prior to therapy. No significant differences were observed in platelet activity at rest between Groups 1 and 2, whereas a significant decrease in exercise-induced platelet activation was demonstrated in Group 1 compared with Group 2.

CONCLUSION

Our data provide evidence of the favorable effect of amlodipine on exercise-induced platelet activation in patients affected by chronic stable angina.

Dipyridamole Decreases Protease-Activated Receptor and Annexin-V Binding on Platelets of Poststroke Patients with Aspirin Nonresponsiveness

BACKGROUND

Although controversial, the phenomenon of aspirin resistance (AR) has been correlated in some small studies with poor clinical outcomes in patients with coronary artery disease. Even less is known regarding the role of AR in the post stroke population. The reason for and the underlying mechanism of AR is unknown. We hypothesized that excessive formation of thrombin on the platelet surface may contribute to this phenomenon and assessed how dipyridamole affects multiple platelet and thrombin generation biomarkers in AR patients after ischemic stroke.

METHODS

Whole blood samples from 20 post stroke AR patients were pretreated with dipyridamole, simulating the therapeutic range, and then incubated for 45 min at 37 degrees C. Platelet characteristics were assessed by aggregometry, cartridge-based analyzer, and receptor expression by flow cytometry. Markers of thrombin generation were measured in the autologous plasma by ELISA.

RESULTS

Pretreatment of blood with dipyridamole resulted in 22-26% diminished expression of intact PAR-1 receptor (p=0.021 and p=0.024) and 28-31% decrease of annexin V binding (p=0.031 and p=0.02) after incubation with 2 microg/ml and 4 microg/ml of dipyridamole, respectively. Platelet aggregation and thrombin generation markers were not affected in vitro by dipyridamole.

CONCLUSIONS

Dipyridamole may be capable of overcoming increased prothrombinase complex formation and be in part able to compensate for AR in patients with moderate carotid stenosis. This phenomenon may explain the clinical advantages of Aggrenox, known to reduce ischemic events in post stroke patients as proven in clinical trials, though an additional antithrombotic benefit beyond the platelet inhibition by aspirin alone.

Differential associations of beta-blockers with hemorrhagic events for chronic heart failure patients on warfarin

PURPOSE

Beta-blockers have many different physiologic effects that could potentially influence the risk of hemorrhagic events in chronic heart failure patients (CHF) on warfarin. We examined how different beta-blockers vary in their associated risk of a hemorrhagic event.

METHODS

We used databases from the Department of Veterans Affairs (VA) that contain information on medications prescribed, diagnoses, and hospitalizations. We identified patients with CHF on warfarin and either metoprolol, carvedilol, atenolol, or no beta-blocker during 1999-2001. We modeled time to first hemorrhagic event using a Cox proportional hazards model, adjusting for age, ethnicity, comorbidities, and other factors. INR levels were examined in a subsample of 3546 patients.

RESULTS

We identified 66,988 CHF patients on warfarin. Hemorrhagic events occurred in 15.3% of the sample and, in 3.8% of the sample, the hemorrhage was considered severe. Compared to patients on carvedilol, the hazards ratio for a new hemorrhagic event was 1.25 (1.17, 1.34) for no beta-blocker, 1.27 (1.18, 1.38) for atenolol, and 1.38 (1.28, 1.48) for metoprolol. No differences in INR levels were evident among the four groups.

CONCLUSIONS

The risk for a hemorrhagic event among CHF patients on warfarin may be affected by beta-blocker use and varies depending on which beta-blocker is prescribed.

Lack of depression effect on platelet activation in patients with heart failure

P-selectin is a marker of platelet activation. Previous studies have reported elevated P-selectin in patients with congestive heart failure (CHF) and depression as separate disorders. We examined if comorbid depression had an effect on platelet activation in CHF patients. Soluble (s)P-selectin was measured in 108 CHF patients; 24 with comorbid depression. There were no significant differences in age, cardiac parameters or (s)P-selectin levels between CHF-only patients and patients with comorbid depression. Our data show no group differences in P-selectin values, which suggests that comorbid depression has no additive effect on platelet activation in CHF patient.

Effects of diltiazem on platelet activation and cytosolic calcium during percutaneous transluminal coronary angioplasty

AIMS

To evaluate effects of diltiazem on platelet hyper-reactivity in situations associated with endothelial injury and their possible relationship to cytosolic calcium concentration.

METHODS

Blood samples were collected at seven time points from 35 patients undergoing percutaneous transluminal coronary angioplasty (PTCA) who received combined diltiazem and aspirin/ticlopidine therapy or aspirin/ticlopidine therapy alone. Platelet expression of glycoprotein IIb/IIIa and P-selectin, production of thromboxane B(2), and cytosolic calcium concentration were measured, respectively, by whole blood flow cytometry, radioimmunoassay, and fluorospectrophotometry. The effects of diltiazem of different concentrations on expression of glycoprotein IIb/IIIa and P-selectin were also studied in vitro in blood samples from patients with chronic stable angina.

RESULTS

Of the two treatments, aspirin/ticlopidine therapy did not prevent an acute increase of expression of glycoprotein IIb/IIIa and P-selectin and plasma thromboxane B(2) five minutes and 10 minutes after first inflation and 10 minutes after PTCA, whereas combined diltiazem and aspirin/ticlopidine therapy had a significant inhibitory effect. In the group receiving aspirin/ticlopidine therapy, there was a short term increase of platelet [Ca(2+)](i) immediately after PTCA which was significantly reduced by diltiazem treatment. Expression of glycoprotein IIb/IIIa and P-selectin was significantly inhibited in vitro by diltiazem in the concentration of 200 ng/ml or higher, but not 50 ng/ml.

CONCLUSIONS

Combined diltiazem and aspirin/ticlopidine therapy significantly inhibited platelet activation that continued in the presence of conventional aspirin/ticlopidine treatment. Antiplatelet effects of diltiazem were probably a consequence of reduction of platelet [Ca(2+)](i) and may only be achieved in higher than therapeutic concentrations.

Impact of calcium antagonists on bleeding time in patients with chronic renal failure

Haemorrhagic diathesis develops in chronic renal failure, in which calcium antagonists are used widely as antihypertensive agents. Although calcium antagonists are reported to impair platelet function, it has not been examined whether calcium antagonists alter bleeding time. The present study was conducted to clarify whether calcium antagonists affect bleeding time in chronic renal failure. Patients with chronic renal failure without and with calcium antagonists were enrolled (n = 156), and bleeding time (Ivy's method) as well as blood parameters (BUN, creatinine, platelet counts, and haemoglobin) were compared in patients with normal and prolonged bleeding time. Among patients not taking calcium antagonists (n = 34), three cases manifested prolonged bleeding time, whereas abnormal bleeding time was observed in 31 patients out of 122. Positive correlations were observed between bleeding time and BUN in both calcium antagonist-untreated (r = 0.46) and -treated groups (r = 0.25). The odds ratio for prolongation of bleeding time in patients taking calcium antagonists was 3.52 (95% CI, 1.01-12.33). In 12 calcium antagonist-treated patients with prolonged bleeding time, the withdrawal of calcium antagonists markedly shortened bleeding time (from 11.3 +/- 0.8 to 5.4 +/- 0.8 min, P < 0.05, n = 12). In contrast, in the additional group (n = 9), the continued treatment with calcium antagonists had no effect on bleeding time (from 11.7 +/- 0.9 to 10.0 +/- 1.0 min). Despite the inhibitory effect of calcium antagonists on bleeding time, no clinically serious events associated with haemorrhagic diathesis developed. In conclusion, calcium antagonists prolong bleeding time in patients with chronic renal failure. The subclinical (laboratory) effect of calcium antagonists however is not necessarily associated with haemorrhagic events of clinical significance.

Cilnidipine more highly attenuates cold pressor stress-induced platelet activation in hypertension than does amlodipine

The clinical significance of N-type calcium channel blockade has not been fully examined. We here compared the effects of the N-type calcium channel blockers cilnidipine and amlodipine on the sympathetic nervous system and platelet function in hypertension under resting and stressed conditions. Thirty-two patients with hypertension (58+/-9 years) received cilnidipine or amlodipine for 4 weeks in this crossover study. On day 28 of each treatment, plasma levels of epinephrine (EP), norepinephrine (NEP), and beta-thromboglobulin (BTG), and EC50 of ADP-induced platelet aggregation (ADPE50) were determined at rest and after a cold pressor test. On day 29, the group receiving cilnidipine was switched to amlodipine treatment, and vice versa. At rest, the blood pressure, heart rates, EP, NEP, ADPEC50, and BTG, were similar in both treatments. After the cold pressor test, increases in EP (35+/-17 to 44+/-25 pg/ml; p<0.05) and BTG (40+/-13 to 49+/-22 ng/ml; p<0.01) and a decrease in ADPEC50 (32+/-26 to 27+/-24 micromol; p<0.05) were observed in the amlodipine treatment, but not in the cilnidipine treatment. In addition, the increase in NEP was significantly greater (p<0.05) in the amlodipine (276+/-78 to 318+/-87 pg/ml; p<0.01) than in the cilnidipine treatment (273+/-88 to 291+/-100 pg/ml; p<0.05). Cilnidipine more highly attenuates the activation of platelet function in response to cold pressor stress than does amlodipine. Attenuated activation of the sympathetic nervous system via N-type calcium channel blockade may contribute to this phenomenon.

Fluorescence spectroscopic analysis of circulating platelet activation during coronary angioplasty

BACKGROUND AND OBJECTIVE

Platelet activation during percutaneous transluminal coronary angioplasty (PTCA) initiates thrombus formation and plaque regrowth at sites of arterial injury, limiting procedure efficacy. We have developed a simple assay for circulating platelet activation based on fluorescence analysis of membrane fluidity and intracellular calcium concentration and light scattering analysis of platelet aggregation.

STUDY DESIGN/MATERIALS AND METHODS

Platelet activation state was measured in 45 patients undergoing angioplasty, before and after treatment with platelet inhibitors.

RESULTS

PTCA alone produced a decrease in pyrene dimer formation (P0.0083) and an increase in light scattering at 650 nm (P0.0128). Treatment with ADP and GPIIb/IIIa receptor antagonists reduced PTCA induced changes in pyrene dimer formation. An unexpected decrease in pyrene dimer formation (P0.05) was detected when the GPIIb/IIIa receptor antagonist was given together with an ADP receptor antagonist.

CONCLUSIONS

1) Analysis of membrane fluidity provides a sensitive marker for platelet activation state. 2) Reduced membrane fluidity after combined platelet inhibitor treatments suggests reduced antiplatelet efficacy.

Platelet inhibition by sertraline and N-desmethylsertraline: a possible missing link between depression, coronary events, and mortality benefits of selective serotonin reuptake inhibitors

Recently, clinical depression has been identified as an independent risk factor for increased mortality in patients following acute coronary events. Although the underlying mechanisms of this link remain uncertain, increased platelet activity has been suggested but never proven as the mechanism responsible for this association. Sertraline hydrochloride is a selective serotonin reuptake inhibitor (SSRI), and is an effective antidepressant agent. Its major liver metabolite, N-desmethylsertraline (NDMS), is known to be neurologically inactive. We assessed the in vitro effects of escalating concentrations of sertraline and NDMS on human platelets by aggregometry in plasma and whole blood, by expression of major surface receptors with flow cytometry in washed cells and in the whole blood, and quantitatively by various platelet function analysers in healthy volunteers and patients with coronary artery disease. Pretreatment of blood samples with sertraline and NDMS resulted in a dose-dependent inhibition of platelet-rich plasma aggregation induced by 5 microM ADP (P =, 0.002), by 10 microM ADP (P = 0.0017), by collagen (P = 0.008), and by thrombin (P = 0.026). Whole blood platelet aggregability was also significantly reduced when induced by 20 microM ADP (P = 0.006), and by collagen (P = 0.01). Surface expression of CD9 (P = 0.004), GP Ib (P = 0.0001), GP IIb/IIIa (P = 0.007), VLA-2 (P = 0.01), P-selectin (P = 0.02), and PECAM-1 (P = 0.01), but not the vitronectin receptor, was also reduced in sertraline and NDMS pretreated washed platelets. Whole blood flow cytometry revealed significant inhibition of GP IIb/IIIa (P = 0.008), and P-selectin expression (P = 0.0001) in NDMS treated samples. Closure time was delayed for the collagen-ADP cartridge (P = 0.009), and for the collagen-epinephrin cartridge (P = 0.01), indicating platelet inhibition in whole blood under high shear conditions. Rapid platelet-function assay revealed a decreased (P = 0.002) ability of platelets to agglutinate fibrinogen-coated beads, suggesting GP IIb/IIIa inhibition. Both sertraline, and its neurologically inactive metabolite NDMS, exhibited significant dose-dependent inhibition of human platelets. The documented anti-platelet effects of sertraline and NDMS may be directly related to the mortality benefits of SSRIs after ischemic events including myocardial infarction and stroke.

Effects of a novel calcium antagonist, benidipine hydrochloride, on platelet responsiveness to mental stress in patients with essential hypertension

The effects of a novel calcium antagonist, benidipine hydrochloride, on responses of platelets to mental stress were evaluated in nine patients with essential hypertension. Before and 12 weeks after the monotherapy with benidipine (2-4 mg/day), platelet aggregability and plasma beta-thromboglobulin were determined during rest and after a 10-min arithmetic stress. Before the treatment, arithmetic stress significantly increased platelet aggregability in response to adenosine diphosphate (ADP) and plasma beta-thromboglobulin level. Blood pressure, pulse rate, and plasma catecholamines also increased during arithmetic stress. The treatment with benidipine did not affect resting values of platelet functions, but attenuated significantly stress-induced alterations in primary aggregation to 1.0 microM ADP (34 +/- 4% to 40 +/- 3% before treatment vs. 32 +/- 2% to 34 +/- 3% after benidipine), ADP threshold for biphasic aggregation (2.2 +/- 0.4 to 1.8 +/- 0.3 microM before treatment vs. 2.2 +/- 0.3 to 2.2 +/- 0.4 microM after benidipine) and plasma beta-thromboglobulin level (74 +/- 16 to 104 +/- 15 ng/ml before treatment vs. 60 +/- 10 to 52 +/- 8 ng/ml after benidipine; p < 0.05 for Stress x Treatment interactions in all values). The pretreatment elevations in blood pressure and sympathetic activity with stress were not modified by benidipine treatment. In conclusion, the monotherapy with benidipine did not affect platelet function during the resting condition, but significantly suppressed the platelet activation induced by arithmetic stress in patients with essential hypertension.

Management of high-risk subsets in unstable angina

This article focuses on the optimal treatment of postinfarction, refractory, or recurrent angina based on the results of recent clinical trials. Many of our recommendations hold true for the general management of unstable angina, but special considerations for the high-risk subsets are emphasized. Specifically, we discuss acute medical management and suggest that an early aggressive strategy that leads to early coronary angiography with the goal of revascularization when feasible best serves this subset. A special emphasis on the emerging role of glycoprotein IIb-IIIa antagonists is made because the important role of platelets in coronary thrombosis has dominated recent views on the pathophysiology of unstable angina.

Shear-induced platelet adhesion and aggregation on subendothelium are increased in diabetic patients

Increased platelet aggregation has been suggested to play a role in the accelerated atherosclerosis of diabetics. However the physiological relevance of the aggregation tests has been questioned. The purpose of this study was to determine platelet activation in diabetic patients, using a novel device--the cone and plate(let) analyzer--to measure shear-induced platelet adhesion and aggregation on extracellular matrix (ECM). Whole blood platelet adhesion and aggregation in patients with noninsulin-dependent diabetes mellitus (n=82) and in nondiabetic controls (n=71) were compared. Clinical and laboratory characteristics of the diabetic patients were analyzed for possible correlation with parameters of platelet activity. Patients with diabetes had a significantly increased platelet activation compared to nondiabetic subjects, demonstrated by an increased adhesion to the ECM (surface coverage, 23% [95% confidence interval, 22-25%] vs. 19% [95% confidence interval, 18-20%], respectively) and an increased average size of the ECM-bound aggregates (54 microm2 [95% confidence interval, 51-57 microm2] vs. 47 microm2 [95% confidence interval, 43-51 microm2], respectively). Platelet adhesion in the diabetic group was found to correlate with triglyceride levels (r=0.36) and hematocrit values (r=0.31) and inversely with high-density lipoprotein cholesterol levels (r=0.30). There were no correlation, however, between parameters of platelet reactivity and duration of diabetes, vascular complications and low-density lipoprotein levels. Our data demonstrate an increased platelet adhesion and aggregation in diabetic patients and suggest a modulatory role of diabetic dyslipidemia.

Effects of prior aspirin and anti-ischemic therapy on outcome of patients with unstable angina. TIMI 7 Investigators. Thrombin Inhibition in Myocardial Ischemia

Both aspirin and beta-adrenergic blocking drugs have been shown to reduce the risk of death or acute myocardial infarction (AMI) in patients with unstable angina, but their effect during chronic use on the presentation of acute coronary syndromes is less well defined. Calcium antagonists and oral nitrates are also widely prescribed for patients with coronary disease, but their effect on presentation of acute myocardial ischemia is unknown. We retrospectively examined the effects of prior aspirin and anti-ischemic medical therapy on clinical events in 410 patients hospitalized for unstable angina. Ischemic pain occurred at rest for a duration of 5 to 60 minutes. During hospitalization, 97% of patients received aspirin and all received the direct thrombin inhibitor bivalirudin for at least 72 hours. Despite being older and more likely to have risk factors for coronary disease and poor outcome, patients receiving aspirin before admission were less likely to present with non-Q-wave AMI (5% vs 14% in patients not on aspirin, p = 0.004). Prior beta blocker, calcium antagonist, or nitrate administration did not appear to modify presentation as unstable angina or non-Q-wave AMI. In a multivariate model, the combined incidence of death, AMI not present at enrollment, or recurrent angina was best predicted by age (adjusted odds ratio [95% confidence interval] 2.38 [1.14 to 3.98]) and presence of electrocardiographic changes with pain on presentation (adjusted odds ratio 2.83 [1.50 to 5.35]) but was not related to prior or in-hospital medical therapy. Thus, aspirin but not anti-ischemic therapy before hospitalization of patients with unstable angina was associated with a decreased incidence of non-Q-wave AMI on admission.

The assessment of platelet derived growth factor concentration in post myocardial infarction and stable angina patients

Platelet derived growth factor (PDGF) has been implicated in the pathogenesis of atherosclerosis. PDGF is released by aggregating platelets and monocytes which gather around sites of arterial injury. In the study reported here the concentration of plasma PDGF was measured in post myocardial infarction (MI) patients (n = 28), angina patients (n = 25), and control subjects (n = 27). Venous blood samples were taken and the concentration of PDGF determined by an enzyme linked immunosorbent assay (ELISA). Plasma PDGF concentrations were significantly higher in the post MI group compared to both the control and angina groups (P < or = 0.05). The increase in PDGF concentration may be due to increased activation of platelets or monocytes since these two cells are major sources of plasma PDGF. High concentrations of PDGF in the circulation could further accelerate the progression of the disease.