Different degrees of NADPH oxidase 2 regulation and in vivo platelet activation: lesson from chronic granulomatous disease.

Background: In vitro study showed that NADPH oxidase (NOx), the most important enzyme producing reactive oxygen species (ROS), plays a role in the process of platelet activation. However, it is unclear if changes in its activity affect platelet activation in vivo. Methods and Results: In vivo and ex vivo experiments assessing platelet activation were investigated in healthy subjects, obese patients, and subjects with different low rates of NOx2 activity, namely X-linked chronic granulomatous disease (X-CGD) patients and X-CGD carriers. We included 27 X-CGD patients, 31 women carriers of hereditary deficiency of NOx2, 31 obese women, and 62 healthy subjects matched for sex and age. Plasma levels of soluble sCD40 L (sCD40L) and soluble P (sP)-selectin, 2 markers of in vivo platelet activation, were reduced in X-CGD patients (sCD40L=-55%; sP-selectin=-51%, P < 0.001) and in X-CGD carriers (sCD40L=-41%; sP-selectin=-57%, P < 0.001) compared with respective controls. Conversely, obese women, who disclosed NOx2 upregulation, had significantly higher plasma levels of sCD40L (+47%, P < 0.001) and sP-selectin (+70%, P < 0.001) compared with controls. Ex vivo study showed platelet isoprostane downexpression and enhanced platelet NO generation in both X-CGD patients and X-CGD carriers compared with controls; opposite findings were observed in obese patients. Correlation analysis showed that platelet NOx2 regulation was directly associated with plasma levels of sCD40L (R=0.336, P < 0.001) and sP-selectin (R=0.441; P < 0.001). Conclusions: The study provides the first evidence that in vivo platelet activation is significantly and directly associated with NOx2 activity. Platelet NOx2 may be a novel target for platelet activation inhibition.