Aspirin and thrombinogenesis

Comprehensive Quality Control of the Regenerative Therapy Using Platelet Concentrates: The Current Situation and Prospects in Japan

Platelet concentrates (PCs), represented by platelet-rich plasma (PRP), have been widely applied in the fields of regenerative and aesthetic therapies. PCs' mechanisms of action, however, are too complicated, and it is not easy to present the whole picture; besides, clinical outcomes are hardly reproducible in many cases. Therefore, several medically advanced countries seemingly intend to regulate PC therapies weakly or strictly because of the increasing popularity. Japan established laws and regulations for PC therapy in the "Act on the Safety of Regenerative Medicine" along with the "Pharmaceuticals, Medical Devices and Other Therapeutic Products Act" in 2014, which, to our knowledge, represent the strictest regulatory framework for production and therapeutic use of PCs in the world. According to these laws and regulations, PCs produced for topical use should be prepared as cell-based medicinal products, essentially as should stem cells, in accordance with their registered ("licensed" under actual conditions) standard operating procedures. Nonetheless, criteria for their quality are not standardized. In this review, we discuss the quality of PC preparations by focusing on the basic concept and regulatory framework of regenerative medicine in Japan. Within the new framework, PC therapy is regulated by a specific notification and registration system, as is stem cell therapy. In comparison with the latter, however, risk factors that hamper successful PC therapy are much fewer. Via appropriate evaluation of patients' conditions and whole-blood samples by simple and sensitive but not yet fully standardized assays, it is theoretically possible that PC quality will be controlled nearly completely. In addition to or instead of standardization of preparation protocols, standardization of preoperative examination of individual PC preparations is an urgent task for improving and guaranteeing the safety and efficacy of PC therapy.

High glucose contributes to aspirin insensitivity in streptozotocin-diabetic rats: a multiparametric aggregation study

The effect of chronic hyperglycaemia on blood platelet response to acetylsalicylic acid was studied in rats with experimental diabetes. Platelet aggregation was determined in non-diabetic and streptozotocin-diabetic rats treated orally with 4 or 40 mg aspirin (ASA)/kg per day (for 8 weeks from the eighth day of diabetes) using whole blood impedance aggregometry with arachidonic acid or ADP as platelet agonists. The dose-dependent effect of ASA 'therapy' on ADP-agonized platelets was significant only in non-diabetic animals, while in diabetic rats both doses were ineffective in reducing ADP-stimulated platelet aggregation. ASA-mediated increased acetylation of platelet proteins favoured reduced platelet aggregation and slower platelet disaggregation (Pr < 0.025 or less). Interestingly, however, the occupation of platelet protein-free amino groups was significantly higher in control rats compared with diabetic rats (P < 0.001), pointing out that proteins of platelets in non-diabetic animals were more vulnerable for the ASA-induced acetylation. We conclude that chronic hyperglycaemia interferes with preventive effects of ASA on platelet reactivity. Our data validate the suggestion that the relationship between aspirin ineffectiveness and poor metabolic control, first revealed in humans, concerns also other animals' platelets and holds regardless of the model or type of diabetes.

Pharmacological basis of different targets for the treatment of atherosclerosis

The development of atherosclerotic plaque is a highly regulated and complex process which occurs as a result of structural and functional alterations in endothelial cells, smooth muscle cells (SMCs), monocytes/macrophages, T-lymphocytes and platelets. The plaque formation in the coronary arteries or rupture of the plaque in the peripheral vasculature in latter stages of atherosclerosis triggers the onset of acute ischemic events involving myocardium. Although lipid lowering with statins has been established as an important therapy for the treatment of atherosclerosis, partially beneficial effects of statins beyond decreasing lipid levels has shifted the focus to develop newer drugs that can affect directly the process of atherosclerosis. Blockade of renin angiotensin system, augmentation of nitric oxide availability, reduction of Ca(2+) influx, prevention of oxidative stress as well as attenuation of inflammation, platelet activation and SMC proliferation have been recognized as targets for drug treatment to control the development, progression and management of atherosclerosis. A major challenge for future drug development is to formulate a combination therapy affecting different targets to improve the treatment of atherosclerosis.

Aspirin resistance

Treatment failures occur with any drug and aspirin is no exception. Evidence is growing to indicate that there are subpopulations that do not respond to antithrombotic action of aspirin. The term 'aspirin resistance' has been used to describe a number of different phenomena, including inability of aspirin to: (i) protect against cardiovascular events despite its regular intake; (ii) to affect various laboratory tests, reflecting platelet activity. Research on aspirin resistance yielded interesting results in clinical pharmacology and pharmacogenetics. Future studies will show whether genotyping for polymorphisms might be of value in everyday clinical use of aspirin. Present data indicate that in survivors of recent myocardial infarction or unstable angina, patients receiving coronary artery bypass grafts, as well as in subjects with hypercholesterolemia, aspirin resistance has to be considered when implementing antithrombotic therapy. However, in individual patients the available laboratory tests are of no particular use to predict reliably the clinical outcome or to guide in making therapeutic decision. Prospective clinical trials seem necessary to reach such conclusions.