No abstract

Large inter-individual variation in platelet response to endogenous agonists and pharmacological agents, including resistance to antiplatelet therapy, prompts a search for novel platelet inhibitors and development new antithrombotic strategies. The present in vitro study evaluates the beneficial effects of three adenosine receptor (AR) agonists (regadenoson, LUF 5835 and NECA), different in terms of their selectivity for platelet adenosine receptors, when used alone and in combination with P2Y 12 inhibitors, such as cangrelor or prasugrel metabolite. The anti-platelet effects of AR agonists were evaluated in healthy subjects (in the whole group and after stratification of individuals into high-and low-responders to P2Y 12 inhibitors), using whole blood techniques, under flow (thrombus formation) and static conditions (study of platelet activation and aggregation). Compared to P2Y 12 antagonists, AR agonists were much less or not effective under static conditions, but demonstrated similar antiplatelet activity in flow. In most cases, AR agonists significantly enhanced the anti-platelet effect of P2Y 12 antagonists, despite possessing different selectivity profiles and antiplatelet activities. Importantly, their inhibitory effects in combination with P2Y 12 antagonists were similar in high-and low-responders to P2Y 12 inhibitors. In conclusion, a combination of anti-platelet agents acting via the P1 and P2 purinergic receptors represents a promising alternative to existing antithrombotic therapy.Molecules 2020, 25, 130 2 of 17 ADP is one of the key mediators of both physiological haemostasis and thrombosis, being not only a direct agonist of platelets, but also an important factor released from platelet intracellular structures, enhancing the platelet response initially induced by other activators. Platelets have two ADP receptors on their surface: the P2Y 1 receptor initiates platelet aggregation, while the P2Y 12 receptor enhances this process, eventually leading to the formation of a clot. Due to this fact, the P2Y 12 receptor is the main therapeutic target in anti-platelet therapy targeted at the ADP-dependent activation pathway [5]. Generally, the most commonly used clinically approved P2Y 12 inhibitors include the thienopyridine-class inhibitors (ticlopidine, clopidogrel and prasugrel), the ATP analogue cangrelor, and the cyclo-pentyl-triazolo-pyrimidine derivative ticagrelor [3,5]. Thienopyridines are prodrugs: their short-lived active metabolites irreversibly inactivate the receptor and consequently inhibit ADP-induced platelet activation. Cangrelor is the first (recently approved) intravenous P2Y 12 receptor inhibitor that reversibly and non-competitively blocks ADP signalling [6].Adenosine is an important purine metabolite, serving not only as a component of nucleic acids and ATP, the most important energy carrier in the cell, but also as a signalling molecule regulating many cell processes [7,8]. Adenosine receptors (AR) are a subfamily of highly conserved G protein-coupled receptors located in the membr...

Blood platelet dysfunctions are strongly involved in the development of the micro- and macrovascular complications in diabetes mellitus (DM). However, the molecular causes of abnormal platelet activation in DM remain unclear. Experimental data suggests that platelet mitochondria can regulate the prothrombotic phenotype of platelets, and changes in these organelles may influence platelet activation and modify platelet responses to stimulation. The present study evaluates the impact of DM on mitochondrial respiratory parameters and blood platelet activation/reactivity in a rat model of experimental diabetes following 1, 2.5 and 5 months of streptozotocin (STZ)-induced diabetes. Moreover, a mild inhibition of the mitochondrial respiratory chain with the use of metformin under in vitro and in vivo conditions was tested as a method to reduce platelet activation and reactivity. The platelets were studied with a combination of flow cytometry and advanced respirometry. Our results indicate that prolonged exposure of blood platelets to high concentrations of glucose, as in diabetes, can result in elevated blood platelet mitochondrial respiration; this may be an effect of cell adaptation to the high availability of energy substrates. However, as these alterations occur later than the changes in platelet activation/reactivity, they may not constitute the major reason for abnormal platelet functioning in DM. Moreover, metformin was not able to inhibit platelet activation and reactivity under in vitro conditions despite causing a decrease in mitochondrial respiration. This indicates that the beneficial effect of metformin on the coagulation system observed in vivo can be related to other mechanisms than via the inhibition of platelet activation.

1MeTIQ was shown to possess neuroprotective potential to the dopaminergic neurons damaged by 6-OHDA lesion. This compound has a protective effect but does not have neurorestorative capacity. It does not reverse damage already caused but will maintain the function and activity of undamaged dopamine neurons at physiological level.

Platelet biology owes to intravital studies not only a better understanding of platelets’ role in primary hemostasis but also findings that platelets are important factors in inflammation and atherosclerosis. Researchers who enter the field of intravital platelet studies may be confused by the heterogeneity of experimental protocols utilized. On the one hand, there are a variety of stimuli used to activate platelet response, and on the other hand there are several approaches to measure the outcome of the activation. A number of possible combinations of activation factors with measurement approaches result in the aforementioned heterogeneity. The aim of this review is to present the most often used protocols in a systematic way depending on the stimulus used to activate platelets. By providing examples of studies performed with each of the protocols, we attempt to explain why a particular combination of stimuli and measurement method was applied to study a given aspect of platelet biology.