Leptin-dependent platelet aggregation in healthy, overweight and obese subjects

Abstract

OBJECTIVE:To investigate the effects of leptin on platelet aggregation and platelet free calcium (Ca 2+ ) concentrations, and the role of the long form of leptin receptor (ObRb) and the phospholipase C (PLC) in mediating leptin effects on platelet function. DESIGN: Cross-sectional, clinical study. SETTING: Outpatient's Service for Prevention and Treatment of Obesity at the University Hospital of Messina, Italy. SUBJECTS: A total of 19 healthy, 14 overweight, and 16 obese male subjects. MEASUREMENTS: ADP-induced platelet aggregation and platelet Ca 2+ were measured after incubation of platelet-rich plasma with leptin alone 5-200 ng/ml, leptin 200 ng/ml and anti-human leptin receptor long-form antibody (ObRb-Ab) 5-10 ml, or leptin 200 ng/ml and PLC inhibitor U73122 0.5-1 nmol/l. RESULTS: Platelet stimulation with leptin lead to a significant and dose-dependent increase in platelet aggregation in healthy subjects. This effect was blunted in overweight, and strongly reduced in obese subjects. Similarly, the incubation with leptin induced a significant and dose-dependent increase in platelet free calcium, which was blunted in overweight and obese patients. The effect of leptin on platelet aggregation and platelet Ca 2+ was completely abated by the anti-ObRb-Ab and the PLC inhibitor U73122. CONCLUSIONS: Leptin produces a dose-dependent enhancement of ADP-induced platelet aggregation in humans. Platelet aggregation response to leptin is blunted, but not completely abolished in overweight/obese subjects, thus suggesting that platelet may represent a site of leptin resistance in human obesity. Leptin increases platelet free calcium in a dose-dependent manner. The inhibition of PLC completely abates the effect of leptin on both platelet aggregation and Ca 2+ levels. These findings suggest that signaling pathway other than JAK-STAT tyrosine phosphorylation (ie PLC and calcium) may be involved in mediating the prothrombotic action of leptin.

Relationship between metabolic syndrome and platelet responsiveness to leptin in overweight and obese patients

“…Leptin-induced platelet aggregation is blunted, but not completely abolished, in overweight and obese patients when compared to normal weight subjects, and this observation suggests that leptin receptor on platelet membrane may represent a site of leptin resistance in human obesity. 19 These findings have been recently extended by Canavan et al 39 by demonstrating that normal weight subjects undergoing complete caloric deprivation had greater sensitivity in hemostatic responses to leptin. The present study further confirms the existence of a differential sensitivity to the pro-thrombotic action of leptin effect based on total adiposity, and suggests the hypothesis that platelet resistance to leptin in overweight or obese patients could represent a finalistic protective mechanism against the excess pro-thrombotic stimulation that would be produced by obesity-related hyperleptinemia.…”

“…21 However, whether the platelet responsiveness to leptin really corresponds to a high-risk phenotype remains to be established. Indeed, the platelet aggregation response to leptin was blunted in patients with overweight or obesity in a former study, 19 thus suggesting that platelet from obese donors may be resistant to the pro-aggregating action of leptin.…”

“…19,20 Briefly, after an overnight fasting, a venous blood sample was obtained from each patient in the supine position from the cubital vein of the arm using a cannula that had been placed 30 min before sampling to avoid the stress of venipuncture, and maintained by slow infusion of saline solution (0.5 ml/min). Blood samples (25 ml) were collected in a conical polipropylene tube containing 3.33 ml/l of citric acid/sodium citrate/dextrose (ACD) (consisting of 64 mmol/l citric acid, 85 mmol/l sodium citrate and 111 mmol/l dextrose).…”

“…Furthermore, we previously reported that overweight and obesity are associated with a continuous progressive reduction of platelet leptin sensitivity. 19 Therefore, we judged that forcing the model to generate three clusters might be a good strategy according to the hypothesis that an intermediate level of platelet responsiveness would exist between nonresponders and responders.…”

“…Leptin also promotes thrombosis in the mouse, and it potentiates the aggregation of murine platelets in vitro in a leptin receptor-dependent manner. 15 Leptin also enhances the aggregation of human platelets, 14,[18][19][20] but it has recently been reported that the response varies significantly between donors, with platelets from some donors consistently responding to leptin (responders) and those from other donors never responding (non-responders). Although platelets from both responders and non-responders express the signaling form of the leptin receptor, platelets from responder donors express higher levels of this receptor than platelets from non-responders.…”