Novel whole blood assay for phenotyping platelet reactivity in mice identifies ICAM-1 as a mediator of platelet-monocyte interaction

British Heart Foundation (PG/12/68/29779 and PG/14/48/30916) and the Wellcome Trust (101604/Z/13/Z to SN and TW, and 098291/Z/12/Z to S.N)

Ecto-5′-Nucleotidase: A Candidate Virulence Factor in Streptococcus sanguinis Experimental Endocarditis

Streptococcus sanguinis is the most common cause of infective endocarditis (IE). Since the molecular basis of virulence of this oral commensal bacterium remains unclear, we searched the genome of S. sanguinis for previously unidentified virulence factors. We identified a cell surface ecto-5′-nucleotidase (Nt5e), as a candidate virulence factor. By colorimetric phosphate assay, we showed that S. sanguinis Nt5e can hydrolyze extracellular adenosine triphosphate to generate adenosine. Moreover, a nt5e deletion mutant showed significantly shorter lag time (P<0.05) to onset of platelet aggregation than the wild-type strain, without affecting platelet-bacterial adhesion in vitro (P = 0.98). In the absence of nt5e, S. sanguinis caused IE (4 d) in a rabbit model with significantly decreased mass of vegetations (P<0.01) and recovered bacterial loads (log10CFU, P = 0.01), suggesting that Nt5e contributes to the virulence of S. sanguinis in vivo. As a virulence factor, Nt5e may function by (i) hydrolyzing ATP, a pro-inflammatory molecule, and generating adenosine, an immunosuppressive molecule to inhibit phagocytic monocytes/macrophages associated with valvular vegetations. (ii) Nt5e-mediated inhibition of platelet aggregation could also delay presentation of platelet microbicidal proteins to infecting bacteria on heart valves. Both plausible Nt5e-dependent mechanisms would promote survival of infecting S. sanguinis. In conclusion, we now show for the first time that streptococcal Nt5e modulates S. sanguinis-induced platelet aggregation and may contribute to the virulence of streptococci in experimental IE

Impact of Aspirin Dosing on the Effects of P2Y12 Inhibition in Patients with Acute Coronary Syndromes

The discovery of the antiplatelet effect of low-dose aspirin led to the hugely successful strategy of dual antiplatelet therapy in patients with acute coronary syndromes (ACS). Increasing the dose of aspirin beyond 75-100 mg has never been shown to offer additional efficacy in ACS patients but could possibly increase the risk of bleeding. In the Platelet Inhibition and Patients Outcome (PLATO) study, higher doses of aspirin appeared to neutralise the additional benefit of the potent P2Y12 inhibitor ticagrelor compared to clopidogrel (Circulation 124: 544-554, 2011). However, higher doses of aspirin have not been shown to have an adverse interaction with the potent P2Y12 inhibition provided by prasugrel and double-dose clopidogrel (Journal of the American College of Cardiology, 2013, in press; N Engl J Med 363: 930-942, 2010). This potentially suggests that the mechanism for this interaction is not related to the inhibition of platelet P2Y12 receptors or could simply be a chance finding.</p