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Metallic nanoparticles are attractive candidates as MRI contrast agents and mediators for drug delivery, diagnostics, and therapy. Direct contact and exposure to blood circulation is common in many such applications. The consequent thrombotic response may therefore be important to study. The main objective of the present work was to study how platelet functions were changed in the presence of different nano-surface or surface capping, which may provide a measure for the safety of a nanoparticle, and also assess the use of such nanoparticles in platelet modulation. Aggregometry, ATP release reaction, flow cytometry and immune-blotting studies were performed to study platelet response to different nano-particles (iron oxide, gold and silver). For each nanoparticle surface conjugation (capping) was varied. It was found that citric acid functionalized iron oxide nanoparticles have anti-platelet activity, with a decrease in aggregation, tyrosine phosphorylation level, and granule release. On the other hand in other cases (e.g. gold nanoparticles) pro-aggregatory response was observed in the presence of nanoparticles and, in some cases, the nanoparticles behaved neutrally (e.g. for starch-coated iron oxide nanoparticles). Therefore, nanoparticles can induce antiplatelet or a pro-aggregatory response, or remain neutral depending on surface capping. A related observation is that antiplatelet drugs can be made more potent by nanoparticle conjugation.

Acute coronary syndrome (ACS) covers a spectrum of clinical conditions ranging from unstable angina, Non-ST segment elevation myocardial infarction (NSTEMI), or ST segment elevation myocardial infarction (STEMI). This study encompasses patients with acute coronary syndrome, who were receiving the dual antiplatelet therapy of aspirin and clopidogrel. The focus of the study was to gain insight into the role of selective P2Y1 antagonism using MRS2179 in such cases as well as its effects, if any, on collagen-epinephrine interaction. All the cases showed greater potency of inhibition of the interaction when yohimbine hydrochloride (YH), a blocker of alpha2A-adrenoreceptor, was used compared to MRS2179, a P2Y1 antagonist, although there was variability in responsiveness to the antiplatelet drugs. These findings indicate that alpha2A-adrenoreceptors of platelets in this group play a major role in precipitating the interactive effect of collagen and epinephrine. The dose-response effect as studied by platelet aggregometry showed that the required molar concentration to block the interactive effect in the case of YH was less than that of MRS2179. Hence, it is postulated that although there may be an impairment of collagen-induced aggregation by MRS2179, the interactive effect of collagen-epinephrine may not be impaired by MRS2179 as efficaciously as YH.