ACE inhibitor effects on platelet function in stages I-II hypertension

Chronic venous disease, platelet and haemostatic abnormalities contribute to the pathogenesis of pigmented purpuric dermatoses

Background

To investigate the aetiology of pigmented purpuric dermatoses (PPD).

Methods

63 patients with a provisional diagnosis of PPD were assessed. Skin biopsies were performed to confirm the clinical diagnosis. Haemostasis was assessed using platelet function analyser-100 (PFA-100), light transmission aggregometry (LTA), impedance aggregometry (Multiplate) and measurement of clotting times and clotting factors. Chronic venous disease (CVD) was assessed by duplex ultrasound. When not contraindicated, patients were advised to discontinue haemostatic-modifying drugs or supplements for 4 weeks after which the laboratory measurements were repeated and the clinical resolution of PPD was assessed. Subsequently, a cohort of patients identified with CVD underwent endovenous interventions and further resolution of PPD was assessed.

Results

CVD was found in 48 patients (76.2%) while haemostatic abnormalities were found in 36 (57.1%). 30 patients (47.6%) had concurrent CVD and haemostatic abnormalities. Modifiable risk factors such as the intake of platelet inhibitors or other drugs and supplements such as fish oil were identified in 53 patients (84.1%). These could be ceased in 35 patients of whom 28 (80.0%) achieved either complete or partial resolution of PPD. Treatment of the underlying CVD was performed in 18 patients resulting in complete or partial resolution in 17 (94.4%). In seven patients (11.1%), no CVD or haemostatic abnormalities were identified, and the risk factors included dietary factors such as excessive caffeine or soft drink consumption.

Conclusion

Haemostatic abnormalities and CVD contribute to the pathogenesis of PPD. Resolution of PPD in the vast majority of patients may be achieved by cessation of modifiable risk factors and in particular platelet-modifying drugs or supplements and treatment of the underlying venous disease.

N-Terminal Pro-Brain Natriuretic Peptide and Right Ventricular Diameter Are Related to Aspirin Resistance in Coronary Artery Disease Patients

Background and Objectives: Resistance to ASA (ASAres) is a multifactorial phenomenon defined as insufficient reduction of platelet reactivity through incomplete inhibition of thromboxane A2 synthesis. The aim is to reassess the prevalence and predictors of ASAres in a contemporary cohort of coronary artery disease (CAD) patients (pts) on stable therapy with ASA, 75 mg o.d. Materials and Methods: We studied 205 patients with stable CAD treated with daily dose of 75 mg ASA for a minimum of one month. ASAres was defined as ARU (aspirin reaction units) ≥550 using the point-of-care VerifyNow Aspirin test. Results: ASAres was detected in 11.7% of patients. Modest but significant correlations were detected between ARU and concentration of N-terminal pro-brain natriuretic peptide (NT-proBNP) (r = 0.144; p = 0.04), body weight, body mass index, red blood cell distribution width, left ventricular mass, and septal end-systolic thickness, with trends for left ventricular mass index and prothrombin time. In multivariate regression analysis, log(NT-proBNP) was identified as the only independent predictor of ARU—partial r = 0.15, p = 0.03. Median concentrations of NT-proBNP were significantly higher in ASAres patients (median value 311.4 vs. 646.3 pg/mL; p = 0.046) and right ventricular diameter was larger, whereas mean corpuscular hemoglobin concentration was lower as compared to patients with adequate response to ASA. Conclusions: ASAres has significant prevalence in this contemporary CAD cohort and NT-proBNP has been identified as the independent correlate of on-treatment ARU, representing a predictor for ASAres, along with right ventricular enlargement and lower hemoglobin concentration in erythrocytes.

Interactions between the Cyclooxygenase Metabolic Pathway and the Renin-Angiotensin-Aldosterone Systems: Their Effect on Cardiovascular Risk, from Theory to the Clinical Practice

Coronary artery disease (CAD) and stroke are the most common and serious long-term complications of hypertension. Acetylsalicylic acid (ASA) significantly reduces their incidence and cardiovascular mortality. The RAAS activation plays an important role in pathogenesis of CVD, resulting in increased vascular resistance, proliferation of vascular-smooth-muscle-cells, and cardiac hypertrophy. Drugs acting on the renin-angiotensin-aldosterone system (RAAS) are demonstrated to reduce cardiovascular events in population with cardiovascular disease (CVD). The cyclooxygenase inhibitors limit the beneficial effect of RAAS-inhibitors, which in turn may be important in subjects with hypertension, CAD, and congestive heart failure. These observations apply to most of nonsteroidal anti-inflammatory drugs and ASA at high doses. Nevertheless, there is no strong evidence confirming presence of similar effects of cardioprotective ASA doses. The benefit of combined therapy with low-doses of ASA is-in some cases-significantly higher than that of monotherapy. So far, the significance of ASA in optimizing the pharmacotherapy remains not fully established. A better understanding of its influence on the particular CVD should contribute to more precise identification of patients in whom benefits of ASA outweigh the complication risk. This brief review summarizes the data regarding usefulness and safety of the ASA combination with drugs acting directly on the RAAS.

Platelets and Cardiovascular Disease

Platelets play an important, but often under-recognized role in cardiovascular disease. For example, the normal response of the platelet can be altered, either by increased pro-aggregatory stimuli or by diminished anti-aggregatory substances to produce conditions of increased platelet activation/aggregation and occur in active cardiovascular disease states both on a chronic (e.g. stable angina pectoris) and acute basis (e.g. acute myocardial infarction). In addition, platelet hyperaggregability is also associated with the risk factors for coronary artery disease (e.g. smoking, hypertension, and hypercholesterolaemia). Finally, the utility of an increasing range of anti-platelet therapies in the management of the above disease states further emphasizes the pivotal role platelets play in the pathogenesis of cardiovascular disease. This paper provides a comprehensive overview of the normal physiologic role of platelets in maintain homeostasis, the pathophysiologic processes that contribute to platelet dysfunction in cardiovascular disease and the associated role and benefits of anti-platelet therapies.

Platelet hyperactivity and fibrin clot structure in transient ischemic attack individuals in the presence of metabolic syndrome: a microscopy and thromboelastography study

BACKGROUND

Strokes are commonly preceded by transient ischemic attacks (TIAs). TIA is often associated with metabolic syndrome (causing chronic inflammation), resulting in a proinflammatory- and procoagulant-environment. The aim of this study was to determine whether platelet- and fibrin network-morphology or coagulation profiles of individuals that suffered a TIA in the presence of metabolic syndrome was altered when compared to healthy individuals.

MATERIALS AND METHODS

The study consisted of 40 voluntary participants. Twenty individuals that suffered a TIA in the previous 48 h with at least two metabolic syndrome risk factors present and twenty healthy age-matched controls. Scanning electron- and atomic force microscopy was used to study platelet- and fibrin-morphology, atomic force microscopy was used to study platelet- and fibrin fiber-elasticity and thromboelastography for the study of coagulation profiles. Statistical analysis was performed to compare the two groups. In all cases a p-value of less than 0.05 was considered statistically significant.

RESULTS

Platelets of the control group appeared spherical with few pseudopodia present while the platelets of the TIA individuals presented with numerous pseudopodia and spreading, indicating activation. Platelet aggregation was also present. The fibrin networks of the healthy individuals consist of thick and thin fibers that form an organized network of fibers. The fibrin networks of the TIA individuals appeared less organized with less taut fibers. Fibrin fiber thickness was found to be significantly increased in the TIA group (p-value <0.001) when compared to healthy controls. The thicker fibers formed irregular networks with thick masses of fibrin fibers. Platelet and fibrin fiber elasticity was found to be significantly lower in the experimental group (p-value 0.0042 and p-value 0.0007 respectively). The hemostatic profiles of the diseased individuals did not differ significantly (p-value > 0.05) from the healthy controls, indicating a normal functioning coagulation cascade.

CONCLUSION

The findings indicate that pathological clot formation is not caused by alterations in the coagulation cascade but rather by the premature activation of platelets (as a result of chronic inflammation) that in turn causes altered fibrin formation.

Hypertension as a Risk Factor for Aspirin and Clopidogrel Resistance in Patients With Stable Coronary Artery Disease

Background:

Platelets play an important role in the pathogenesis of coronary artery disease (CAD). The importance of dual antiplatelet therapy to prevent recurrent ischemic events in patients who have acute coronary syndrome and who will undergo percutaneous coronary intervention (PCI) is well known and widely accepted as a gold standard. However, despite this apparently effective therapy, incidence of adverse ischemic events could not be decreased enough. Resistance to aspirin/clopidogrel is an important risk factor for adverse ischemic clinical events. Up-to-date studies revealed many risk factors for antiplatelet resistance, one of which is hypertension (HT). Currently, there is no sufficient number of studies evaluating the association between HT and antiplatelet resistance, which is the aim of this study.

Methods:

We enrolled 145 consecutive patients (19 female [13.1%], 126 male [86.9%], mean age 55 ± 10) with stable CAD receiving regular antiplatelet therapy composed of 100 mg/d aspirin and 75 mg/d clopidogrel. All patients had been implanted nondrug-eluting coronary stent and/or stents at least 1 month ago. The HT was diagnosed by 24-hour blood pressure (BP) monitoring. Clopidogrel and aspirin resistance was measured by impedance aggregometry method.

Results:

We included 49 patients with HT and 96 nonhypertensive patients with stable CAD. Aspirin resistance was detected in 22 (16.4%) of 134 patients who received aspirin. Clopidogrel resistance was detected in 55 (37.9%) of 145 patients who received clopidogrel. Prevalance of aspirin and clopidogrel resistance was significantly higher in the hypertensive group than in the nonhypertensive group ( P = .030 and P = .007, respectively). Correlation analysis revealed weak but significantly positive correlation between clopidogrel resistance and serum uric acid levels, mean platelet volume, platelet count, and 24-hour mean systolic BP ( r = −.180, P = .030; r = .189, P = .016; r = .226, P = .006; and r = .200, P = .016, respectively).

Conclusion:

We demonstrated higher incidence of antiplatelet resistance in patients with HT. Upon this finding, which is emerged from an actual group of patients with HT, cardioprotective effect of antiplatelet therapy in patients with HT should be argued.

Aspirin for the prevention of cardiovascular events in patients without clinical cardiovascular disease: a meta-analysis of randomized trials

BACKGROUND

The benefit of aspirin to prevent cardiovascular events in subjects without clinical cardiovascular disease relative to the increased risk of bleeding is uncertain.

METHODS

A meta-analysis of randomized trials of aspirin versus placebo/control to assess the effect of aspirin on major cardiovascular events (MCEs) (nonfatal myocardial infarction, nonfatal stroke, or cardiovascular death), individual components of the MCE, stroke subtype, all-cause mortality, and major bleeding. Nine trials involving 102,621 patients were included: 52,145 allocated to aspirin and 50,476 to placebo/control.

RESULTS

Over a mean follow-up of 6.9 years, aspirin was associated with a reduction in MCE (risk ratio [RR] 0.90, 95% CI 0.85-0.96, P < .001). There was no significant reduction for myocardial infarction, stroke, ischemic stroke, or all-cause mortality. Aspirin was associated with hemorrhagic stroke (RR 1.35, 95% CI 1.01-1.81, P = .04) and major bleeding (RR 1.62, 95% CI 1.31-2.00, P < .001). In meta-regression, the benefits and bleeding risks of aspirin were independent of baseline cardiovascular risk, background therapy, age, sex, and aspirin dose. The number needed to treat to prevent 1 MCE over a mean follow-up of 6.9 years was 253 (95% CI 163-568), which was offset by the number needed to harm to cause 1 major bleed of 261 (95% CI 182-476).

CONCLUSIONS

The current totality of evidence provides only modest support for a benefit of aspirin in patients without clinical cardiovascular disease, which is offset by its risk. For every 1,000 subjects treated with aspirin over a 5-year period, aspirin would prevent 2.9 MCE and cause 2.8 major bleeds.

Increased platelet cholesterol and decreased percentage volume of platelets as a secondary risk factor for coronary artery disease

Platelet hyperactivity is likely to contribute to the progression of atherogenesis and organized thrombus formation on vascular surfaces. The purpose of this study was to examine the effect of hypercholesterolemia on the cholesterol content of platelets, on platelet responsiveness and other platelet indices using platelets from 5 groups of age-matched subjects (n = 30 each), which includes healthy controls. All groups except controls had a high plasma lipid profile. While subjects in group I had only hyperlipidemia, those in groups II and III had hyperlipidemia in conjunction with diabetes mellitus and hypertension, respectively. The fourth group consisted of patients with confirmed coronary artery disease (CAD). The parameters studied include packed cell volume of platelets (platelet crit), platelet distribution width (PDW), platelet cholesterol and platelet aggregation in response to adenosine diphosphate and collagen. All the patient groups showed increased platelet aggregation (p < 0.05) and low platelet crit compared with controls (p < 0.05). In addition, platelet cholesterol was increased in patients with coronary disease, hyperlipidemia and diabetes mellitus (p < 0.05) but not in patients with hypertension (p > 0.05); PDW was high only in CAD (p < 0.05). A higher PDW indicated a prothrombotic tendency in CAD patients. Our data suggest that hyperlipidemia increases the lipid content in platelets and enhances their reactivity. Hyperactive platelets with increased platelet cholesterol may contribute to accelerated atherogenesis associated with CAD.

Ebelactone B, an Inhibitor of Extracellular Cathepsin A-Type Enzyme, Suppresses Platelet Aggregation Ex Vivo in Renovascular Hypertensive Rats

The present study was undertaken to investigate whether ebelactone B, an inhibitor of bradykinin and angiotensin I hydrolysis by serine carboxypeptidase Y-like enzymes, could influence platelet aggregation ex vivo in renovascular hypertensive rats (2-kidney, 1-clip Goldblatt model, 2K1C). We found that ebelactone B (5 mg/kg) administrated subcutaneously once a day for 5 days, 5 weeks after the development of hypertension, or a single dose of ebelactone B (0.5 mg/kg) injected intravenously into 2K1C hypertensive rats before the induction of arterial thrombosis, both markedly suppressed collagen-induced platelet aggregation in whole blood. In contrast, inhibition of collagen-induced platelet aggregation was not evident in vitro after pretreatment of the blood with ebelactone B, indicating that ex vivo the antiaggregatory action of this compound can proceed through an indirect mechanism. The injection of ebelactone B did not affect the mean blood pressure of 2K1C hypertensive rats but lowered an elevated extracellular serine carboxypeptidase cathepsin A-like activity. Thus, the data indicate that ebelactone B may be a promising antiaggregatory agent in renovascular hypertension and suggest that 1 of the possible mechanisms through which it exerts this effect may be related to the suppression of cathepsin A-like activity released locally during the development of renovascular hypertension.

Effect of amlodipine and cilazapril treatment on platelet Ca2+ handling in spontaneously hypertensive rats

Abnormal Ca2+ handling and enhanced aggregation response have been reported in platelets from spontaneously hypertensive rats (SHR) and patients with essential hypertension, and thought to be involved in the progression of target organ damage of hypertension. It is important to examine whether antihypertensive therapy can improve the abnormal platelet response in hypertension. We investigated the effect of antihypertensive treatment such as amlodipine and cilazapril on Ca2+ handling and aggregation response in SHR platelets. Four-week-old male SHR were divided into three groups. Each group was treated with amiodipine (A: 10 mg/kg/day), cilazapril (C: 10 mg/kg/day) or vehicle (V) for 8 weeks by gavage. At 12-week-old, platelet [Ca2+]i was measured with fura-2 in each group of SHR and age-matched Wistar-Kyoto rats (WKY) as normal control. Systolic blood pressure in amlodipine and cilazapril treated groups were similar with WKY and significantly lower than vehicle treated group (A: 124 +/- 9, C: 126 +/- 9, WKY: 122 +/- 10 and V: 180 +/- 9 mmHg, respectively). The basal [Ca2+]i in the three groups of SHR were similar and higher than WKY (A: 47 +/- 1.7, C: 47 +/- 1.2, V: 48 +/- 3.9 and WKY: 40 +/- 4.0 nmol/l, respectively). There were no significant differences in thrombin (0.1 U/ml)-stimulated [Ca2+]i rise in the presence or absence of extracellular Ca2+ among the three groups of SHR and these were higher than WKY. Intracellular Ca2+ discharge capacity, assessed by the ionomycinstimulation was similar in the all groups. Thrombin-induced maximum platelet aggregation responses in the three groups of SHR were similar and higher than WKY. The antihypertensive treatment of Ca2+ antagonist or ACE inhibitor gave no change in intraplatelet Ca2+ metabolism in SHR. These results support the hypothesis that an abnormal Ca2+ handling in SHR platelet is genetically determined and not improved by hypotensive therapy.

Perindopril augments ecto-ATP diphosphohydrolase activity and enhances endothelial anti-platelet function in human umbilical vein endothelial cells

OBJECTIVES

Recent clinical trials have demonstrated that angiotensin-converting enzyme inhibitors (ACEIs) reduce thrombotic events by unknown mechanisms in patients with atherosclerotic cardiovascular diseases.

DESIGN

We studied the in-vitro effects of perindopril, an ACEI, on the ability of human umbilical vein endothelial cells (HUVEC) to inhibit platelet aggregation.

METHODS

Platelet aggregation in the presence of HUVEC and endothelial surface expression and activities of ecto-ATP diphosphohydrolase (ecto-ADPase), CD39, were determined. The capability of HUVEC to release prostacyclin and nitric oxide (NO) was also investigated.

RESULTS

Perindoprilat (an active metabolite of perindopril) significantly enhanced the surface expression and activities of ecto-ADPase and prostacyclin release, resulting in enhancement of ability to inhibit platelet aggregation by HUVEC. These effects of perindoprilat were also observed in HUVEC activated by tumour necrosis factor (TNF)-alpha, which increased the expression of intracellular adhesion molecule-1 (ICAM-1), CD54, and, despite up-regulation of prostacyclin release, attenuated endothelial anti-platelet properties by decreasing ecto-ADPase activity. Perindoprilat partially restored this capability, but failed to reduce enhanced expression of ICAM-1. By contrast, the role of NO as a platelet inhibitor appeared minimal in HUVEC. Candesartan, an angiotensin II receptor (AT(1)) blocker, did not affect endothelial anti-platelet property.

CONCLUSIONS

Perindoprilat was found to augment endothelial capability to inhibit platelet aggregation by increasing ecto-ADPase activity and prostacyclin release in HUVEC. This beneficial effect of perindoprilat appeared to be preserved in the activated cells exposed to TNF-alpha, although no evidence was found to support that it could reverse the inflammation process induced by cytokines.

Inhibition of platelet aggregability by losartan in essential hypertension

Most clinical events associated with hypertension have a thrombotic component. Losartan is a selective, competitive antagonist of the thromboxane A2 receptor in experiments performed in isolated vascular strips and in human and rat platelet-enriched plasma. In this study, we investigated for the first time whether losartan at therapeutic doses has an effect on platelet aggregability and indexes of fibrinolysis in essential hypertensive subjects. Changes in the dose-response curve to platelet aggregation induced by the thrombin receptor-activating peptide SFLRRN-NH2 were determined in 9 patients (56% men, 72% white; mean age 52.8 years) with stage I or II essential hypertension and in 9 untreated healthy volunteers. After a 4-week washout period, hypertensive subjects received 2 weeks of placebo followed by 4 weeks of losartan 50 mg/day. Both subjects and end points were blinded for treatment assignment. In addition, plasminogen activator inhibitor type 1 antigen and von Willebrand antigen were studied in all patients and controls. Four weeks of losartan produced a statistically significant (p <0.05) increase in the concentration of SFLRRN-NH2 required to induce a half-maximal response in platelet aggregation extent and rate 4 weeks after initiation of treatment. The decrease in platelet aggregability was independent of blood pressure control and the effects of gender and age. Losartan had no effect on plasma concentrations of plasminogen activator inhibitor-1 and von Willebrand factor in hypertensive subjects. These data demonstrate for the first time a novel antiplatelet effect of losartan at therapeutic doses, which was independent of changes in blood pressure, plasma markers of fibrinolytic activity, and endothelial perturbation.

Effect of the angiotensin-converting enzyme inhibitor perindopril on haemostasis in essential hypertension

Endothelial damage, platelet hyperactivity and other changes of blood coagulation may play a role in the vascular complications of essential hypertension. Undesirable changes of haemostasis induced by some anti-hypertensive drugs can encourage the acceleration of atherogenesis. Therefore, the effect of angiotensin-converting enzyme (ACE)-inhibitors on haemostasis is of interest. The therapeutic dose of perindopril was previously shown to reduce platelet aggregation. In the present study, selected parameters of haemostasis were investigated in 23 patients with first and second stage of non-treated essential hypertension. The measurements were carried out before therapy, after 1 week of placebo administration, and after 1 week and after 1 month of ACE-inhibitor perindopril therapy in a once-daily dose of 4 mg. Plasma prothrombin time, activated partial thromboplastin time, fibrinogen level, plasminogen and antithrombin III activities, protein C and free protein S antigens, total fibrinolytic activity as well as fibrin monomers and D-dimers were assayed. There were no significant changes in any haemostasis variables investigated following placebo administration or perindopril therapy. On the basis of this study, no unfavourable effects on haemostasis induced by this therapy were found. The platelet-inhibitory effect of perindopril, without any harmful effects on coagulation or fibrinolytic activity and coagulation inhibitors, is desirable in the new approach to hypertension treatment. These properties of perindopril may be important in terms of the beneficial role of anti-hypertensive drugs in cardiovascular morbidity.

Captopril administration reduces thrombus formation and surface expression of platelet glycoprotein IIb/IIa in early postmyocardial infarction stage

Long-term administration of the angiotensin-converting enzyme inhibitor captopril in survivors of myocardial infarction (MI) reduces the risk of cardiovascular death, recurrence of MI, and unstable angina, suggesting that captopril may possess antithrombotic properties that have not been clearly elucidated. We assessed the short-term antithrombotic effects of captopril on platelet aggregation, platelet-subendothelium interaction, and the expression of major glycoproteins on platelet surface. A double-blind study was carried out in 25 patients with MI. Blood samples were taken before (baseline) and 12 days after treatment in both the control and captopril groups. Platelet aggregation was tested by conventional aggregometry using common activating agents. Platelet interaction with deeply damaged subendothelial surface was evaluated in a perfusion model, with blood maintained under flow conditions. Deposition of platelets was quantified by using computer-assisted morphometric techniques on histological sections, and it was expressed as a percentage of total vessel surface covered by platelets (CS) and as a ratio between large aggregates (T) and surface covered by platelets (100XT/CS). Glycoprotein expression was measured using flow cytometric techniques. Aggregometric responses showed no significant variations; however, in the captopril group, 100XT/CS decreased after 12 days of treatment (100XT/CS: 36+/-12.1% captopril versus 64+/-8.0% baseline; P=0.005). This parameter was also significantly decreased from that found in control group patients (100XT/CS:67=/-4.5%, P=0.008). Flow cytometry showed a 30% reduction in glycoprotein IIb/IIIa expression (P=0.02). Captopril reduced the formation of large aggregates in a perfusion system, which might be related to a down-regulation of glycoprotein IIb/IIIa complex on the platelet surface. These results suggest that captopril exerts an antiplatelet effect that may contribute to its beneficial action in MI.