Mechanisms linking leptin to arterial and venous thrombosis: potential pharmacological targets.

Epidemiological evidence strongly links excess body weight with an increased risk to develop atherothrombotic complications. Obesity is frequently associated with systemic and local inflammation as well as elevated circulating leptin levels, and clinical studies found hyperleptinemia to correlate not only with measures of adiposity, but also with circulating biomarkers of an increased metabolic and cardiovascular risk or surrogate markers of subclinical atherosclerosis. Moreover, experimental studies in mice with systemic disruption of the leptin-leptin receptor system as well as after administration or neutralization of the adipokine demonstrated that leptin promotes both arterial and venous thrombosis. In addition to directly binding to and activating platelets and thus potentiating their aggregation in response to agonist stimulation, leptin enhances the expression of prothrombotic and anti-fibrinolytic proteins in vascular and inflammatory cells. On the other hand, its ability to mobilize and recruit vascular progenitor cells from the bone marrow to sites of vascular injury was found to be impaired in hyperleptinemic, obese humans and rodents. Thus, leptin promotes thrombus formation and resolution by several different mechanisms involving primary hemostasis, the coagulation cascade as well as the integrity of the vessel wall. Dissection of the molecular mechanisms underlying each of its actions may pave the road for novel therapeutic options in targeting the increased risk of thrombosis associated with obesity, keeping in mind unresolved issues of a cell-specific leptin resistance as well as individual differences in the responsiveness to leptin.