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Adenosine diphosphate receptors on blood platelets - potential new targets for antiplatelet therapy

100%
Rozalski M., Nocun M., Watala C.
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2005
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vol. 52
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issue 2
411-415
EN
Platelets play a key role not only in physiological haemostasis, but also under pathological conditions such as thrombosis. Platelet activation may be initiated by a variety of agonists including thrombin, collagen, thromboxane or adenosine diphosphate (ADP). Although ADP is regarded as a weak agonist of blood platelets, it remains an important mediator of platelet activation evoked by other agonists, which induce massive ADP release from dense granules, where it occurs in molar concentrations. Thus, ADP action underlies a positive feedback that facilitates further platelet aggregation and leads to platelet plug formation. Additionally, ADP acts synergistically to other, even weak, agonists such as serotonin, adrenaline or chemokines. Blood platelets express two types of P2Y ADP receptors: P2Y_1 and P2Y_12. ADP-dependent platelet aggregation is initiated by the P2Y1 receptor, whereas P2Y_12 receptor augments the activating signal and promotes platelet release reaction. Stimulation of P2Y_12 is also essential for ADP-mediated complete activation of GPIIb-IIIa and GPIa-IIa, and further stabilization of platelet aggregates. The crucial role in blood platelet biology makes P2_Y12 an ideal candidate for pharmacological approaches for anti-platelet therapy.
2
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Inhibition of collagen-induced platelet reactivity by DGEA peptide.

88%
Luzak B., Golanski J., Rozalski M., Boncler M. A., Watala C.
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2003
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vol. 50
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issue 4
1119-1128
EN
Direct interactions between collagen, the most thrombogenic component of the extracellular matrix, and platelet surface membrane receptors mediate platelet adhesion and induce platelet activation and aggregation. In this process two glycoproteins are crucial: integrin α2β1, an adhesive receptor, and GPVI, which is especially responsible for signal transduction. Specific antagonists of the collagen receptors are useful tools for investigating the complexity of platelet-collagen interactions. In this work we assessed the usefulness of DGEA peptide (Asp-Gly-Glu-Ala), the shortest collagen type I-derived motif recognised by the collagen-binding integrin α2β1, as a potential antagonist of collagen receptors. We examined platelet function using several methods including platelet adhesion under static conditions, platelet function analyser PFA-100TM, whole blood electric impedance aggregometry (WBEA) and flow cytometry. We found that DGEA significantly inhibited adhesion, aggregation and release reaction of collagen activated blood platelets. The inhibitory effect of DGEA on static platelet adhesion reached sub-maximal values at millimolar inhibitor concentrations, whereas the specific blocker of α2β1 - monoclonal antibodies Gi9, when used at saturating concentrations, had only a moderate inhibitory effect on platelet adhesion. Considering that 25-30% of total collagen binding to α2β1 is specific, we conclude that DGEA is a strong antagonist interfering with a variety of collagen-platelet interactions, and it can be recognised not only by the primary platelet adhesion receptor α2β1 but also by other collagen receptors.
3
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Effects of 1-methylnicotinamide and its metabolite N-methyl-2-pyridone-5-carboxamide on streptozotocin-induced toxicity in murine insulinoma MIN6 cell line

88%
Przygodzki T., Slominska E., Polakowska E., Mlynarski W., Watala C.
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2011
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vol. 58
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issue 1
75-77
EN
1-methylnicotinamide (MNA) is a primary metabolite of nicotinamide. In recent years several activities of MNA have been described, such as anti-inflammatory activity in skin diseases, induction of prostacyclin synthesis via COX-2, aortal endothelium protection in diabetes and hypertriglyceridaemia and increased survival rate of diabetic rats. 1-methylnicotinamide was also suggested to protect pancreatic cells from streptozotocin in vivo. Streptozotocin toxicity is known to be mediated by poly-ADP-ribose polymerase. Nicotinamide and its derivatives have been shown to ameliorate poly-ADP-ribose polymerase-dependent nucleotide pool reduction. We aimed to verify if 1-methylnicotinamide and its metabolite, N-methyl-2-pyridone-5-carboxamide, can protect insulinoma cells from streptozotocin-induced toxicity. We found that N-methyl-2-pyridone-5-carboxamide, but not 1-methylnicotinamide, restores the pool of ATP and NAD+ in streptozotocin-treated cells, but neither compound improved the cell viability. We conclude that inhibition of poly-ADP-ribose polymerase-dependent nucleotide pool reduction may not be sufficient to protect cells from streptozotocin toxicity.
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