The case of low-dose aspirin for the prevention of myocardial infarction: but how low is low?

Simultaneous assay of activated platelet count and platelet-activating capacity by P-selectin detection using K2-EDTA-treated whole blood for antiplatelet agents

INTRODUCTION

It is well recognized that examinations of activated platelets (aPLTs) and platelet-activating capacity are very important to observe and prevent embolic diseases (events) such as ischemic stroke and myocardial infarction. Previously, we reported an appropriate measurement technique of aPLT for clinical assay. In this paper, we investigated stable conditions for measurement of activating capacity of platelets.

METHODS

Blood samples were taken from healthy volunteers using anticoagulants of 2K-EDTA, sodium citrate and heparin, and platelets were stimulated with adenosine diphosphate (ADP) or collagen. We demonstrated platelet-activating capacity by detection of scattering light, absorbance, microscopic observation, and P-selectin (CD62P) expression. We also performed basic experiments in seven healthy volunteers to test the clinical application of these assays with monitoring aspirin therapy.

RESULTS

We judged that samples of whole blood with 2K-EDTA were suitable for CD62P expression assay as functional assessments of platelet activity, because platelets treated with anticoagulants such as sodium citrate and heparin were extremely damaged after stimulation, and it was difficult to measure the CD62P expression by flow cytometry. For optimal results, samples should be tested within 1 h after the drawing of blood and stimulated with ADP or collagen for 10 min. The CD62P-positive platelet value of blood from volunteers who had taken aspirin was decreased, and platelet activation was inhibited as well.

CONCLUSION

The simultaneous assay of aPLT and platelet-activating capacity by CD62P detection using whole blood treated with the K2-EDTA anticoagulant was useful for the monitoring of antiplatelet drugs.

Combination antiplatelet therapy for secondary stroke prevention: enhanced efficacy or double trouble?

The evaluation of antithrombotic agents for secondary stroke prevention has focused on stroke reduction. The aim of this analysis was to focus specifically on the increase in bleeding risk. The annualized rates of total and major bleeding events in secondary stroke prevention trials of antithrombotics were assessed and cross compared. A Medline search for major randomized clinical studies with a follow-up duration of > or =1 year identified 13 studies. Pooled data sets were used to compare mean bleeding rates for aspirin (< or =325 mg/day), clopidogrel, anticoagulants (warfarin and other vitamin K antagonists), aspirin plus clopidogrel, and aspirin plus extended-release dipyridamole (ER-DP). Total bleeding occurred at mean rates of 4.8% with aspirin (< or =325 mg/day) alone, 2.9% with clopidogrel alone, 3.6% with aspirin plus ER-DP, 10.1% with aspirin plus clopidogrel, and 16.8% with anticoagulation. Major bleeding occurred at mean rates of 1% with aspirin (< or =325 mg/day) alone, 0.85% with clopidogrel, 0.93% with aspirin plus ER-DP, 1.7% with aspirin plus clopidogrel, and 2.5% with anticoagulation. In conclusion, the combination of aspirin and clopidogrel is associated with significantly greater bleeding than either aspirin (< or =325 mg/day) or clopidogrel alone. Aspirin plus ER-DP has a greater bleeding rate than clopidogrel but a lower rate than aspirin (< or =325 mg/day) alone.

Aspirin in cardiology--benefits and risks

AIMS

To review the current knowledge of the benefits and risks of long-term aspirin therapy for the prevention of cardiovascular disease.

METHODS

Relevant articles published in English between 1996 and 2006 were obtained from the Current Contents Science Edition, EMBASE and MEDLINE databases.

RESULTS

Secondary aspirin prophylaxis is effective in reducing the risk of ischaemic events in patients with cardiovascular disease. However, its utility in reducing primary ischaemic events is more controversial; it appears to reduce the incidence of ischaemic stroke, but increase the incidence of haemorrhagic stroke. Aspirin therapy can also lead to an increased risk of gastrointestinal ulcers, upper gastrointestinal bleeding and other haemorrhagic complications. Lower doses of aspirin are associated with a reduced risk of gastrointestinal side effects and are equally effective in reducing cardiovascular risk. Co-therapy with non-steroidal anti-inflammatory drugs, clopidogrel or warfarin increases the risk of gastrointestinal side effects, while co-therapy with proton pump inhibitors reduces it.

CONCLUSIONS

Both the benefits and risks need to be considered carefully when prescribing aspirin, particularly in primary prevention. Patients should be prescribed lower doses rather than higher doses of aspirin in line with prescribing guidelines. Co-prescription of a proton pump inhibitors may be necessary in patients at high risk for upper gastrointestinal complications.

New evidence for the spasm-of-resistance-vessel concept of ischemic diseases

The spasm of resistance vessel (S-RV) concept of ischemic diseases avers that S-RV representing vascular autoregulatory dysfunction directly induces symptoms in ischemic diseases. The most important ischemic diseases, ischemic heart disease (IHD) and stroke, generally are not attributed to S-RV, and new evidence will be provided in this communication that S-RV induces IHD and stroke. Hypertension and the ischemic disorders of migraine and Raynaud's disease have been attributed to S-RV and to vascular dysregulation, and this information was used to help structure the study. It was found that these disorders are closely associated with IHD and stroke, and this is consistent with S-RV and vascular dysregulation as the mechanism for IHD and stroke. Also, it was found that multiple risk factors for IHD foster S-RV and are risk factors for hypertension, migraine, Raynaud's disease, and stroke, and this supports S-RV as the mechanism for IHD and stroke.

Cyclooxygenases 1 and 2

Cyclooxygenase (COX), first purified in 1976 and cloned in 1988, is the key enzyme in the synthesis of prostaglandins (PGs) from arachidonic acid. In 1991, several laboratories identified a product from a second gene with COX activity and called it COX-2. However, COX-2 was inducible, and the inducing stimuli included pro-inflammatory cytokines and growth factors, implying a role for COX-2 in both inflammation and control of cell growth. The two isoforms of COX are almost identical in structure but have important differences in substrate and inhibitor selectivity and in their intracellular locations. Protective PGs, which preserve the integrity of the stomach lining and maintain normal renal function in a compromised kidney, are synthesized by COX-1. In addition to the induction of COX-2 in inflammatory lesions, it is present constitutively in the brain and spinal cord, where it may be involved in nerve transmission, particularly that for pain and fever. PGs made by COX-2 are also important in ovulation and in the birth process. The discovery of COX-2 has made possible the design of drugs that reduce inflammation without removing the protective PGs in the stomach and kidney made by COX-1. These highly selective COX-2 inhibitors may not only be anti-inflammatory but may also be active in colon cancer and Alzheimer's disease.

Aspirin protects endothelial cells from oxidative stress--possible synergism with vitamin E

A 24-h incubation with hydrogen peroxide (0.65 mM) markedly reduced viability of cultured endothelial cells. Preincubation with aspirin (3-30 microM) protected endothelial cells from hydrogen peroxide-induced toxicity and increased viability in a concentration-dependent fashion by up to 64% of control. A similar protection was observed with D-alpha-tocopherol acetate (vitamin E, 3-30 microM). The cytoprotective effects of aspirin and vitamin E against hydrogen peroxide were overadditive suggesting different mechanisms of antioxidant action. In agreement with this, cytotoxicity induced by iron, the main catalyst of oxygen radical formation, was substantially reduced by aspirin but not vitamin E. These results show that aspirin protects endothelial cells from oxidative stress possibly via binding or chelation of free cytosolic iron. Moreover, a combination of aspirin and vitamin E might be useful for the prevention of endothelial injury in cardiovascular disease, e.g. during atherogenesis.