Platelet microparticles and soluble P selectin in peripheral artery disease: Relationship to extent of disease and platelet activation markers

Background. There is increased platelet activation in many cardiovascular diseases. This observation may explain the presence of increased levels of platelet microparticles (PMP) in these diseases. However, whether or not levels of PMPs inter-relate with other markers of platelet activation, such as soluble P-selectin, or with disease severity, is unknown. We therefore hypothesized raised PMP levels in stable peripheral artery disease (PAD) intermittent claudication (IC), with an additional increase in severe PAD critical limb ischaemia (CLI). Furthermore, we tested the hypothesis that PMP levels are correlated with other markers of platelet activation, such as soluble P-selectin, membrane bound P-selectin (CD62P) and CD63. Methods. Patients with PAD were recruited from the vascular outpatient and inpatient facilities at a teaching hospital. Age and sex-matched controls were also recruited from healthy volunteers. Venous blood was obtained from 23 patients with severe disease (CLI), 36 with moderate disease (IC), and from 30 healthy controls. The percentage of platelets positive for CD62P and CD63, as well as the numbers of PMPs were defined by flow cytometry. Plasma soluble P selectin was measured by enzyme-linked immunosorbent assay (ELISA). Results. PMPs were increased relative to healthy controls in patients with IC, with a further increase in CLI (P<0.001). Soluble P selectin and CD62+ve platelets were raised in both patient groups, but there was no difference amongst the two patient groups. CD63+ve cells were raised only in CLI compared to healthy controls. In multivariate analysis, only PMP and soluble P selectin independently predicted disease severity, and the two markers correlated modestly (r=0.345, P<0.001). Conclusion. Increased PMP and soluble P selectin are both related to the severity of symptomatic PAD. However, it is uncertain if this relationship is a cause or effect of atherosclerosis. This finding may have clinical implications as PMPs have the potential to influence the progression of atheroma as well as promote thrombosis.