Cochrane review: dipyridamole for preventing major vascular events in patients with vascular disease

Metabolic Interventions to Prevent Hypertrophy-Induced Alterations in Contractile Properties In Vitro

(1) Background: The exact mechanism(s) underlying pathological changes in a heart in transition to hypertrophy and failure are not yet fully understood. However, alterations in cardiac energy metabolism seem to be an important contributor. We characterized an in vitro model of adrenergic stimulation-induced cardiac hypertrophy for studying metabolic, structural, and functional changes over time. Accordingly, we investigated whether metabolic interventions prevent cardiac structural and functional changes; (2) Methods: Primary rat cardiomyocytes were treated with phenylephrine (PE) for 16 h, 24 h, or 48 h, whereafter hypertrophic marker expression, protein synthesis rate, glucose uptake, and contractile function were assessed; (3) Results: 24 h PE treatment increased expression of hypertrophic markers, phosphorylation of hypertrophy-related signaling kinases, protein synthesis, and glucose uptake. Importantly, the increased glucose uptake preceded structural and functional changes, suggesting a causal role for metabolism in the onset of PE-induced hypertrophy. Indeed, PE treatment in the presence of a PAN-Akt inhibitor or of a GLUT4 inhibitor dipyridamole prevented PE-induced increases in cellular glucose uptake and ameliorated PE-induced contractile alterations; (4) Conclusions: Pharmacological interventions, forcing substrate metabolism away from glucose utilization, improved contractile properties in PE-treated cardiomyocytes, suggesting that targeting glucose uptake, independent from protein synthesis, forms a promising strategy to prevent hypertrophy and hypertrophy-induced cardiac dysfunction.

Dual antiplatelet therapy after noncardioembolic ischemic stroke or transient ischemic attack: pros and cons

Dual antiplatelet therapy simultaneously blocks different platelet activation pathways and might thus be more potent at inhibiting platelet activation and more effective at reducing major ischemic vascular events compared to antiplatelet monotherapy. Aspirin plus clopidogrel dual therapy is now the standard therapy for patients with acute coronary syndrome and for those undergoing percutaneous coronary intervention. However, dual antiplatelet therapy carries an increased risk of bleeding. Patients with ischemic stroke or transient ischemic attack (TIA) are generally older and likely to have a fragile cerebrovascular bed, which further increases the risk of systemic major bleeding events and intracranial hemorrhage. Clinical trials and meta-analyses suggest that in comparison to antiplatelet monotherapy, dual antiplatelet therapy initiated early after noncardioembolic ischemic stroke or TIA further reduces the rate of recurrent stroke and major vascular events without significantly increasing the rate of major bleeding events. In contrast, studies of long-term therapy in patients with noncardioembolic ischemic stroke or TIA have yielded inconsistent data regarding the benefit of dual antiplatelet therapy over monotherapy. However, the harm associated with major bleeding events, including intracranial hemorrhage, which is generally more disabling and more fatal than ischemic stroke, is likely to increase with dual antiplatelet therapy. Physicians should carefully assess the benefits and risks of dual antiplatelet therapy versus antiplatelet monotherapy when managing patients with ischemic stroke or TIA.

A hybrid method for prediction and repositioning of drug Anatomical Therapeutic Chemical classes

In the Anatomical Therapeutic Chemical (ATC) classification system, therapeutic drugs are divided into 14 main classes according to the organ or system on which they act and their chemical, pharmacological and therapeutic properties. This system, recommended by the World Health Organization (WHO), provides a global standard for classifying medical substances and serves as a tool for international drug utilization research to improve quality of drug use. In view of this, it is necessary to develop effective computational prediction methods to identify the ATC-class of a given drug, which thereby could facilitate further analysis of this system. In this study, we initiated an attempt to develop a prediction method and to gain insights from it by utilizing ontology information of drug compounds. Since only about one-fourth of drugs in the ATC classification system have ontology information, a hybrid prediction method combining the ontology information, chemical interaction information and chemical structure information of drug compounds was proposed for the prediction of drug ATC-classes. As a result, by using the Jackknife test, the 1st prediction accuracies for identifying the 14 main ATC-classes in the training dataset, the internal validation dataset and the external validation dataset were 75.90%, 75.70% and 66.36%, respectively. Analysis of some samples with false-positive predictions in the internal and external validation datasets indicated that some of them may even have a relationship with the false-positive predicted ATC-class, suggesting novel uses of these drugs. It was conceivable that the proposed method could be used as an efficient tool to identify ATC-classes of novel drugs or to discover novel uses of known drugs.

Best evidence for medical therapy for carotid artery stenosis

Carotid atheromatous disease is an important cause of stroke and represents a key target in stroke prevention. Randomized trials have shown the efficacy of carotid endarterectomy in secondary stroke prevention. Carotid stenting presents a less invasive alternative to surgical intervention. Advances in medical management, if compliance can be ensured, are leading to improvement in outcomes when implemented as sole therapy in the treatment of atherosclerotic carotid stenosis. This includes lifestyle modification, blood pressure control, and antiplatelet and statin therapy. Over the last 20 years, the annual rate of ipsilateral stroke associated with asymptomatic carotid stenosis has decreased from 2% to 4% to less than 1%. This is largely due to improvements in medical therapy. However, despite numerous trials and years of clinical research, the optimal management of symptomatic and asymptomatic carotid disease remains controversial. This article presents and summarizes the evidence supporting best medical treatment for carotid artery stenosis.

Secondary Stroke Prevention in Women

In a meta-analysis of results from 21 randomized trials comparing antiplatelet therapy with placebo in 18,270 patients with prior stroke or transient ischemic attack, antiplatelet therapy was associated with a 28% relative odds reduction in nonfatal strokes and a 16% reduction in fatal strokes, while another trial for secondary prevention with atorvastastin 80 mg showed a 16% risk reduction in time to first occurrence of stroke (adjusted hazard ratio: 0·84, 95% CI: 0·71–0·99). However, few studies have examined the sex differences regarding the efficacy of these treatments. Specifically, recent studies have reported higher rates of perioperative complications during endarterectomy in women. Nonetheless, to date, the data on the effects of carotid artery stenting in women, coming from diverse studies and meta-analyses, have been limited owing to the small number of female patients examined. Owing to this, the evidence of the benefit for women is unclear. Peculiar pathophysiological aspects of stroke, the higher stroke risk in some specific periods in life (e.g., pregnancy, puerperium and older age) and worse documented stroke outcome in women suggest that sex does matter in stroke management. Thus, future randomized controlled trials need to be sex-balanced, in order to better understand the efficacy of appropriate secondary stroke prevention therapy in women.

Intensive management of risk factors for accelerated atherosclerosis: the role of multiple interventions

Patients at high risk of vascular events can reduce their risk by 75% to 80% through a combination of lifestyle changes and medical therapy. These include smoking cessation, a Mediterranean diet, daily exercise, maintaining a fit weight, moderate consumption of alcohol, effective control of blood pressure and diabetes, intensive treatment with lipid-lowering drugs and antiplatelet agents, and perhaps treatment with vitamins to lower homocysteine. Much of this is achieved primarily by the patient; physicians need to become better at assisting their patients in making lifestyle changes. Effective control of treatment-resistant hypertension can be improved by individualizing medical therapy to the underlying cause, based on measurement of plasma renin and aldosterone. Measurement of carotid plaque may be useful by providing feedback on the success of therapy.

Current developments in anti-platelet therapy

Platelets play a life-saving role in hemostasis and blood clotting at sites of vascular injury and consequently are similarly involved in the pathological counterpart, namely thrombosis. Thus, anti-platelet therapy has become a mainstay in treatment and/or prophylaxis of conditions like myocardial infarction, stroke and other cardiovascular diseases. Acetyl-salicylic acid (ASA, aspirin) is still the most widely used agent and considered as the prototype antiplatelet drug. Since platelet activation occurs via several pathways that are not influenced by ASA, several other compounds have been developed to add to its beneficial effect. Currently four main classes of antiplatelet agents are available for clinical use: acetyl-salicylic acid (ASA), phosphodiesterase (PDE) inhibitors, thienopyridines and the intravenous GPIIb/IIIa antagonists. This article gives a concise review of these four classes of anti-platelet agents, using ASA as the reference standard.

My health: whose responsibility? Low-dose aspirin and older people

The benefit of aspirin as a prophylactic after a thrombotic event was first observed 30 years ago. Its use after coronary or cerebral thrombosis, and in patients judged to be at increased risk of a thrombotic event, is now virtually mandatory, unless there are signs of intolerance. The present policy in the UK for cardiovascular protection by low-dose aspirin is dependent upon the identification of people at high vascular risk. The policy has had only very limited success, partly owing to the fact that only a relatively small proportion of people with levels of vascular risk factors that would justify aspirin prophylaxis are identified. In fact, it has been demonstrated that the application of accepted guidelines for aspirin prophylaxis to risk factor data in representative UK population samples gives a cost-effective evidence-base for a reasonable extension of prophylaxis to all people aged over approximately 50 years. It is possible that reductions in both dementia and cancer incidence could also follow the wider use of low-dose aspirin but further research on these outcomes is urgently required. The evidence on possible benefits and harm from low-dose aspirin should therefore be publicized widely, and everything possible should be done to stimulate discussion involving the general public. In the end, however, the preservation of health is one's own responsibility and, therefore, people should generally be encouraged to evaluate the evidence on health-promotion measures, including low-dose aspirin, and take responsibility for their own health.

Aspirin plus dipyridamole versus aspirin alone after cerebral ischaemia of arterial origin (ESPRIT): randomised controlled trial

BACKGROUND

Results of trials of aspirin and dipyridamole combined versus aspirin alone for the secondary prevention of vascular events after ischaemic stroke of presumed arterial origin are inconsistent. Our aim was to resolve this uncertainty.

METHODS

We did a randomised controlled trial in which we assigned patients to aspirin (30-325 mg daily) with (n=1363) or without (n=1376) dipyridamole (200 mg twice daily) within 6 months of a transient ischaemic attack or minor stroke of presumed arterial origin. Our primary outcome event was the composite of death from all vascular causes, non-fatal stroke, non-fatal myocardial infarction, or major bleeding complication, whichever happened first. Treatment was open, but auditing of outcome events was blinded. Primary analysis was by intention to treat. This study is registered as an International Standard Randomised Controlled Trial (number ISRCTN73824458) and with (NCT00161070).

FINDINGS

Mean follow-up was 3.5 years (SD 2.0). Median aspirin dose was 75 mg in both treatment groups (range 30-325); extended-release dipyridamole was used by 83% (n=1131) of patients on the combination regimen. Primary outcome events arose in 173 (13%) patients on aspirin and dipyridamole and in 216 (16%) on aspirin alone (hazard ratio 0.80, 95% CI 0.66-0.98; absolute risk reduction 1.0% per year, 95% CI 0.1-1.8). Addition of the ESPRIT data to the meta-analysis of previous trials resulted in an overall risk ratio for the composite of vascular death, stroke, or myocardial infarction of 0.82 (95% CI 0.74-0.91). Patients on aspirin and dipyridamole discontinued trial medication more often than those on aspirin alone (470 vs 184), mainly because of headache.

INTERPRETATION

The ESPRIT results, combined with the results of previous trials, provide sufficient evidence to prefer the combination regimen of aspirin plus dipyridamole over aspirin alone as antithrombotic therapy after cerebral ischaemia of arterial origin.

Recent advance in antiplatelet therapy: the mechanisms, evidence and approach to the problems

Antiplatelet therapy has been established as a preventive medicine for ischemic cardiovascular diseases both at acute and chronic phases. This therapy is also crucial for the prevention of thrombotic events after coronary stent implantation. So far, many lines of clinical evidence have demonstrated the beneficial effects of aspirin (an irreversible cyclooxygenase inhibitor) and thienopyridine derivatives (adenosine diphosphate (ADP)-receptor P2Y12 inhibitors). Recently, it has been reported that the cardiovascular risk is elevated in patients with platelets resistant to these drugs, compared to the good responders. One of the current problems to be solved in antiplatelet therapy is to find out patients resistant to the antiplatelet therapy and improve its preventive effects. In addition to aspirin and thienopyridines, several types of drugs with antiplatelet effects are currently available in clinical practice. Clinical evidence has recently been accumulating for these drugs that can be potential alternatives in patients with aspirin or thienopyridine resistance. In this review, the mechanisms, evidence and approach to the present problems of drugs with antiplatelet effects are discussed.

Dipyridamole bioavailability in subjects with reduced gastric acidity

Dipyridamole (DP) is an antiplatelet agent that shows decreased oral bioavailability with increased gastric pH that occurs with commonly prescribed antacids. An extended-release (ER) formulation of DP that employs tartaric acid to improve bioavailability of DP in the presence of elevated gastric pH was developed as a combination antiplatelet product with immediate-release aspirin. This crossover-designed study examined the relative bioavailability of DP from the composite product compared to conventional DP tablets during reduced gastric acidity. Gastric pH was increased (pH > 4.0) in 20 healthy subjects with lansoprazole (30 mg/d for 5 days). Dipyridamole systemic exposure over 12 hours was compared after oral administration of a single composite ER capsule (200 mg DP + 25 mg aspirin) versus two 100-mg conventional DP tablets given 6 hours apart combined with 81 mg aspirin. DP relative bioavailability was reduced 53% with conventional tablets compared to the composite buffered ER capsule in reduced gastric acid conditions. Peak DP plasma concentrations were 57% lower with immediate-release tablets compared to the composite formulation with high stomach pH. Substituting generic DP plus low-dose aspirin may be less effective than the buffered DP composite product in patients with concomitant antacid therapies.

Role of adenosine and nitric oxide on the mechanisms of action of dipyridamole

BACKGROUND AND PURPOSE

The combination of dipyridamole and aspirin has been shown to be more effective than aspirin alone in the secondary prevention of stroke. Dipyridamole may act by inhibiting adenosine uptake, thus potentiating its actions. Dipyridamole also inhibits cGMP-specific phosphodiesterases (PDE) and, through this mechanism, could potentiate cGMP-mediated actions of nitric oxide.

METHODS

To define the mechanism of action of dipyridamole, we studied the local vascular effects of adenosine, acetylcholine (NO-mediated dilation), and nitroprusside (cGMP-mediated dilation) in a double-blind study after treatment with dipyridamole/aspirin (200 mg dipyridamole/25 mg aspirin twice a day) or aspirin control for 7 days in 6 normal volunteers. Vasodilators were administered into the brachial artery in the nondominant arm in random order and forearm blood flow (FBF) was measured by venous occlusion plethysmography.

RESULTS

Adenosine at a dosage of 125 mug/min increased FBF from 4.6+/-0.9 to 29.4+/-5.3 (539% increase) with dipyridamole/aspirin and from 3.9+/-0.8 to 12+/-2.5 mL/100 mL forearm/min (208% increase) with aspirin alone (P=0.007). In contrast, dipyridamole/aspirin did not alter the response to acetylcholine or to nitroprusside. The magnitude of adenosine-induced vasodilation correlated with plasma dipyridamole concentrations (r2=0.6); no correlation was observed with acetylcholine- or nitroprusside-induced vasodilation. Similar potentiation of adenosine, but not acetylcholine or nitroprusside, was observed in 7 additional subjects when adenosine, acetylcholine, and nitroprusside were given in random order before and 2 hours after a single dose of dipyridamole/aspirin.

CONCLUSIONS

The effects of dipyridamole on resistance vessels are preferentially explained by potentiation of adenosine mechanisms rather than potentiation of nitric oxide or other cGMP-mediated actions.

Preventable stroke and stroke prevention

Stroke is a major cause of death and disability in the world. The main causes of stroke are atherothromboembolism and cardiogenic embolism. The main causal and treatable risk factors for atherothromboembolic ischemic stroke are increasing blood pressure (BP), increasing cholesterol, cigarette smoking and diabetes; and the main risk factors for cardiogenic ischemic stroke are atrial fibrillation (AF) and ischemic heart disease. Strategies to reduce the incidence of stroke include prevention of first-ever and recurrent stroke, and treatment of patients with acute stroke to reduce death and disability. The two main strategies of stroke prevention are the 'population' (or 'mass') approach and the 'high risk' approach. The 'population' approach aims to reduce stroke by lowering the prevalence and mean level of causal risk factors in the community, by means of public education and government legislation. The 'high risk' approach aims to reduce stroke by identifying individuals at high risk of stroke, and lowering their risk by means of optimal medical therapies. Level 1 evidence from randomized controlled trials indicates that effective treatments for high risk patients include control of causal risk factors (lowering BP, lowering blood cholesterol), antithrombotic therapy (antiplatelet therapy with aspirin, clopidogrel, or the combination of aspirin and dipyridamole for patients in sinus rhythm, and anticoagulation with warfarin or ximelagatran for patients in AF) and, where appropriate, carotid revascularization for patients with severe carotid stenosis.

Dipyridamole for Preventing Recurrent Ischemic Stroke and Other Vascular Events

Background and Purpose— Results from randomized controlled trials of dipyridamole, given with or without aspirin, for secondary prevention after ischemic stroke or transient ischemic attack (TIA) have given conflicting results. We performed a meta-analysis using individual patient data from relevant randomized controlled trials.

Methods— Randomized controlled trials involving dipyridamole in patients with previous ischemic stroke or TIA were sought from searches of the Cochrane Library, other electronic databases, references lists, earlier reviews, and contact with the manufacturer of dipyridamole. Individual patient data were merged from 5 of 7 relevant trials involving 11 459 patients. Results were adjusted for age, gender, qualifying event, and history of previous hypertension.

Results— Recurrent stroke was reduced by dipyridamole as compared with control (OR, 0.82; 95% CI, 0.68 to 1.00), and by combined aspirin and dipyridamole versus aspirin alone (OR, 0.78; 95% CI, 0.65 to 0.93), dipyridamole alone (OR, 0.74; 95% CI, 0.60 to 0.90), or control (OR, 0.61; 95% CI, 0.51 to 0.71). The point estimates obtained for the comparisons of aspirin and dipyridamole versus control (OR, 0.63; significant) or versus aspirin (OR, 0.88; nonsignificant) were similar if the data from the largest trial, ESPS II (which provided 57% of data), were excluded. Similar findings were observed for nonfatal stroke. The combination of aspirin and dipyridamole also significantly reduced the composite outcome of nonfatal stroke, nonfatal myocardial infarction, and vascular death as compared with aspirin alone (OR, 0.84; 95% CI, 0.72 to 0.97), dipyridamole alone (OR, 0.76; 95% CI, 0.64 to 0.90), or control (OR, 0.66; 95% CI, 0.57 to 0.75). Vascular death was not altered in any group.

Conclusions— Dipyridamole, given alone or with aspirin, reduces stroke recurrence in patients with previous ischemic cerebrovascular disease. The combination of aspirin and dipyridamole also reduces the composite of nonfatal stroke, nonfatal myocardial infarction, and vascular death as compared with aspirin alone.

Adenosine uptake inhibitors

Adenosine is a purine nucleoside and modulates a variety of physiological functions by interacting with cell-surface adenosine receptors. Under several adverse conditions, including ischemia, trauma, stress, seizures and inflammation, extracellular levels of adenosine are increased due to increased energy demands and ATP metabolism. Increased adenosine could protect against excessive cellular damage and organ dysfunction. Indeed, several protective effects of adenosine have been widely reported (e.g., amelioration of ischemic heart and brain injury, seizures and inflammation). However, the effects of adenosine itself are insufficient because extracellular adenosine is rapidly taken up into adjacent cells and subsequently metabolized. Adenosine uptake inhibitors (nucleoside transport inhibitors) could retard the disappearance of adenosine from the extracellular space by blocking adenosine uptake into cells. Therefore, it is expected that adenosine uptake inhibitors will have protective effects in various diseases, by elevating extracellular adenosine levels. Protective or ameliorating effects of adenosine uptake inhibitors in ischemic cardiac and cerebral injury, organ transplantation, seizures, thrombosis, insomnia, pain, and inflammatory diseases have been reported. Preclinical and clinical results indicate the possibility of therapeutic application of adenosine uptake inhibitors.

Dipyridamole alters cardiac substrate preference by inducing translocation of FAT/CD36, but not that of GLUT4

In cardiac myocytes, uptake rates of glucose and long-chain fatty acids (FA) are regulated by translocation of GLUT4 and FA translocase (FAT)/CD36, respectively, from intracellular stores to the sarcolemma. Insulin and contractions are two major physiological stimuli able to induce translocation of both transporters and therefore enhance the uptake of both substrates. Interestingly, the cardiovascular drug dipyridamole was able to enhance FA uptake but had no effect on glucose uptake. The selective stimulatory effect of dipyridamole on FA uptake was unrelated to its effects on phosphodiesterase inhibition and on nucleoside transport inhibition. However, dipyridamole-stimulated FA uptake was abolished in the presence of sulfo-N-succinimidylpalmitate, which indicated that FAT/CD36 is involved in the uptake process. Furthermore, the effect was additive to that of insulin but not to that of the AMP-elevating agent oligomycin, indicating that dipyridamole stimulates FAT/CD36-mediated FA uptake by activating the AMP-activated protein kinase (AMPK) signaling pathway. Dipyridamole, however, neither influenced the intracellular AMP content nor induced activation of AMPK. Finally, dipyridamole was able to induce FAT/CD36 translocation from intracellular storage sites to the sarcolemma but had no effect on the subcellular distribution of GLUT4. It is concluded that beyond AMP-activated protein kinase the contraction-induced and AMPK-mediated signal branches off into separate mobilization of GLUT4 and of FAT/CD36, and that dipyridamole activates a yet unidentified target in the FAT/CD36 mobilizing branch.