Objectives Platelet activation seems to be implicated in the cardiovascular events occurring in patients with community-acquired pneumonia (CAP) but the underlying mechanism is still unclear. Aim of the study was to assess the mechanism involved in platelet activation in CAP patients. Methods Two-hundred-seventy-eight consecutive patients hospitalized for CAP were recruited and followed-up until discharge. Hospitalized patients matched for sex, age and comorbidities but without acute infectious diseases were used as controls. Results At hospital admission patients disclosed enhanced plasma levels of sP-selectin, a maker of in-vivo platelet activation, serum sNOX2-dp, a marker of NADPH-oxidase activation, serum Lipopolysaccharide (LPS) and serum zonulin, a marker of gut permeability, compared to controls (p < 0.001). Baseline sP-selectin was independently associated to serum LPS, sNOX2-sp and Pneumonia Severity Index score (p < 0.001). Plasma sP-selectin, serum sNOX2-dp, LPS and zonulin coincidentally decreased at hospital discharge (p < 0.001). An in vitro study showed that LPS, at concentration similar to that found in CAP patients, induced sP-selectin release by agonist-activated platelets, a phenomenon that was counteract by treating cells with gp91ds-tat, a specific inhibitor of NOX2. Conclusions CAP patients display enhanced platelet activation, which is related to LPS-mediated NOX2 activation. Enhanced gut permeability seems be implicated in enhancing circulating levels of LPS.
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