Platelet Inhibition by Insulin Is Absent in Type 2 Diabetes Mellitus

Abstract

Objective-ADP-induced P2y 12 signaling is crucial for formation and stabilization of an arterial thrombus. We demonstrated recently in platelets from healthy subjects that insulin interferes with Ca 2ϩ increases induced by ADP-P2y 1 contact through blockade of the G-protein G i , and thereby with P2y 12 -mediated suppression of cAMP. Methods and Results-Here we show in patients with type 2 diabetes mellitus (DM2) that platelets have lost responsiveness to insulin leading to increased adhesion, aggregation, and procoagulant activity on contact with collagen. Using Ser 473 phosphorylation of protein kinase B as output for insulin signaling, a 2-fold increase is found in insulin-stimulated normal platelets, but in DM platelets there is no significant response. In addition, DM2 platelets show increased P2y 12 -mediated suppression of cAMP and decreased P2y 12 inhibition by the receptor antagonist AR-C69931MX. Key Words: P2y 12 receptor Ⅲ Ca 2ϩ regulation Ⅲ clopidogrel Ⅲ protein kinase B/Akt Ⅲ IRS-1 P latelet activation leads to release of components that initiate formation of a thrombus and start inflammatory responses that contribute to atherosclerosis. 1 Signaling through the P2y 12 receptor is crucial for formation and stabilization of a thrombus. 2,3 Inhibition of the P2y 12 receptor reduces collagen-induced adhesion, aggregation and thrombin generation. 3,4 Subjects with a P2y 12 deficiency have a bleeding tendency 3,5 and individuals with an increased P2y 12 receptor copy number have platelets with an increased responsiveness to agonists, and these subjects experience peripheral arterial thrombosis. 6 The CAPRIE trial shows that long-term administration of the P2y 12 antagonist clopidogrel is more effective than aspirin in reducing the combined risk of ischemic stroke, myocardial infarction, or vascular death in subjects with a prothrombotic condition such as diabetes mellitus type 2 (DM2). 7 These findings illustrate the crucial role of P2y 12 signaling in platelet activation in vitro and in vivo. Conclusion-TheThe importance of P2y 12 signaling is explained by its capacity to initiate 2 pathways that directly interfere with platelet activating or inhibiting mechanisms. First, there is the activation of the G-protein subunit G i ␣, which inhibits adenylyl cyclase and thereby formation of the platelet inhibitor cAMP. 8 This property is particularly evident after treatment with prostacyclin, 9 and also in the absence of cAMP elevating agents, P2y 12 signaling controls cAMP production through adenylyl cyclase. 10,11 cAMP inhibits platelets through cAMPdependent protein kinase (protein kinase A [PKA]), 12 which inhibits almost all platelet functions through blockade of multiple steps in platelet activation cascades including receptor activation, signaling through the mitogen-activated protein kinases pathway, formation of thromboxane A 2 (TxA 2 ), and the activation of key enzymes such as phospholipase C ␤ and protein kinase C (PKC). 13 Second, there is the release of the G i ␤␥ dimer leading to the activation ...

Greater Clinical Benefit of More Intensive Oral Antiplatelet Therapy With Prasugrel in Patients With Diabetes Mellitus in the Trial to Assess Improvement in Therapeutic Outcomes by Optimizing Platelet Inhibition With Prasugrel–Thrombolysis in Myocardial Infarction 38

“…6 Physiologically, insulin reduces platelet aggregation by inhibiting the P2Y 12 receptor, although this inhibition is absent in subjects with DM and insulin resistance. 32,33 In previous mechanistic studies, insulin-treated subjects had higher levels of platelet aggregation after dual antiplatelet therapy than subjects with DM not treated with insulin, indicating that treatment with insulin may identify a group of subjects at particular risk for poor response to clopidogrel. 22 We did not collect age of onset (juvenile versus adult) or duration of diabetes, both factors that may influence insulin use.…”

Prevalence and Risk Factors for Aspirin and Clopidogrel Resistance in Cerebrovascular Stenting

“…There is accumulating evidence that platelet hyperactivity in patients with diabetes 32 is mediated by insulin resistance and increased P2Y12 signaling. 33 Other potential mechanisms include increased platelet turnover, altered platelet membrane structure, increased intracellular calcium, and abnormal glycation. 32,34,35 A recent study suggested that 150-mg daily maintenance dosage of clopidogrel resulted in greater platelet inhibition than conventional 75-mg daily dosing in patients with diabetes.…”

Induction of insulin resistance by the adipokines resistin, leptin, plasminogen activator inhibitor-1 and retinol binding protein 4 in human megakaryocytes

“…2,5 Under laboratory conditions, type 2 diabetes platelets adhere better to a thrombogenic surface, form bigger aggregates at lower agonist concentration and produce more thromboxane A2 than do control platelets. 6 The hyperactivity correlates with loss of insulin sensitivity and intensive insulin treatment partly normalizes aggregation. 7 Inhibition of platelet responsiveness with aspirin therapy reduces the relative risk of myocardial infarction and stroke by about 10%.…”

“…Insulin also inhibits splicing of tissue factor pre-mRNA in platelets adhering to prothrombotic proteins and the loss of insulin responsiveness in type 2 diabetes might well contribute to the thrombogenicity of the platelet plug that forms upon plaque rupture. 6,11 Weight gain and appearance of insulin resistance go hand in hand and are thought to be caused by abnormal adipokine release by visceral fat. 12 Adipocytes release resistin, leptin, plasminogen activator inhibitor-1 (PAI-1), retinol binding protein 4 (RBP4) and visfatin and their plasma levels are elevated in individuals with abdominal obesity.…”