Search

We assessed the effect of the intercellular mediator of inflammation, platelet activating factor (PAF), on platelet function. The interaction between PAF and the platelet agonists ADP, thrombin and convulxin was analyzed in vitro in whole blood with the use of flow cytometry and was further characterized with the use of receptor antagonists to PAF (ABT-491), P2Y1 (MRS-2179), and P2Y12 (cangrelor) as well as a monoclonal anti-PSGL-1 antibody (anti-CD162). Low concentrations of PAF (0.1 nM) synergistically augmented platelet activation induced by other agonists (P < 0.01). Augmentation by PAF was receptor mediated and did not require platelet-leukocyte interaction. With >99% inhibition of P2Y receptor-mediated platelet activation, greater than additive activation was still observed with the combination of ADP plus PAF. Accordingly, PAF synergistically augments platelet activation in response to ADP and thrombin, and the extent of inhibition exerted by P2Y receptor antagonists is decreased in the presence of PAF.

Objectives: Both tirofiban and eptifibatide release rapidly from glycoprotein IIb-IIIa but have different dissociation constants (KD of tirofiban=15 nmol/l, of eptifibatide=120 nmol/l). Binding of fibrinogen to glycoprotein IIb-IIIa is biphasic, forming an initial reversible complex (KD=155-180 nmol/l) and a second more stable complex (KD=20-70 nmol/l). Diabetes is known to alter platelet function. To determine the influence of affinity on inhibitory effects in blood from patients with (n=20) and without (n=20) diabetes mellitus, we characterized the extent of inhibition as a function of time., Methods: Blood was added to reaction tubes containing tirofiban 100 ng/ml or eptifibatide 1.7 microg/ml (concentrations previously defined to be optimal) plus a platelet agonist (1 micromol/l adenosine diphosphate or 25 micromol/l thrombin receptor agonist peptide), and fluorochrome-labeled fibrinogen before analysis by flow cytometry., Results: The extent of inhibition early on (30 s to 3 min) was similar (>85%) with either agent in blood from those with and without diabetes mellitus, whereas the extent of inhibition 10-15 min later was maintained more effectively with tirofiban than with eptifibatide (difference in slope P<0.01). After 15 min, the extent of inhibition in response to adenosine diphosphate in those with diabetes mellitus was 95+/-6% for tirofiban and 70+/-15% for eptifibatide (P<0.001); in those without diabetes mellitus, it was 91+/-9% for tirofiban and 73+/-19% for eptifibatide (P<0.001)., Conclusion: For glycoprotein IIb-IIIa antagonists with a rapid rate of release, the biphasic binding of fibrinogen influences to a similar extent their ability to maintain inhibitory effects in blood from patients with and without diabetes mellitus.

Hyperglycemia has been linked to adverse outcomes after myocardial infarction. We characterized the effect of selected concentrations of glucose or mannitol on platelet function in whole blood samples from healthy volunteers and from patients with and without diabetes mellitus. Activation of platelet glycoprotein IIb/IIIa and P-selectin expression was increased similarly after addition of isosmotic concentrations of glucose and mannitol, suggesting that increased osmolarity associated with hyperglycemia increases platelet reactivity.