Emanuela Falcinelli

Acute, short-term hyperglycemia enhances shear stress-induced platelet activation in patients with type II diabetes mellitus

OBJECTIVESnThe aim of our study was to assess whether acute, short-term hyperglycemia affects platelet reactivity in patients with Type II diabetes mellitus (T2DM).nnnBACKGROUNDnHyperglycemic spikes are thought to precipitate ischemic events in T2DM. Previous studies have shown in vivo platelet activation in diabetes; however, no studies have assessed whether acute in vivo hyperglycemia induces further activation of platelets.nnnMETHODSnIn a cross-over, randomized, double-blind study, 12 patients with T2DM underwent 4 h of either acute hyperglycemia (13.9 mmol/l, 250 mg/dl) or euglycemia (5.5 mmol/l, 100 mg/dl). Shear stress-induced platelet activation, P-selectin and lysosomal integral membrane protein (LIMP) expression on platelets in the bleeding-time blood, urinary 11-dehydro-thromboxane B(2) (TxB(2)) excretion, von Willebrand factor:antigen (vWF:Ag), and von Willebrand factor:activity (vWF:activity) were measured before and after hyperglycemia or euglycemia.nnnRESULTSnShear stress-induced platelet activation, P-selectin and LIMP expression on platelets in the bleeding-time blood, and urinary 11-dehydro-TxB(2) excretion increased significantly after hyperglycemic clamping, whereas no changes were observed after euglycemic clamping. Plasma vWF:Ag and vWF:activity increased strikingly in parallel fashion after hyperglycemic clamping, whereas no changes were observed after euglycemic clamping.nnnCONCLUSIONSnOur data demonstrate that acute, short-term hyperglycemia induces an increased activation of platelets exposed to high shear stress conditions in vitro (filtration method) or in vivo (bleeding time). In vivo platelet activation is reflected by an increased urinary excretion of 11-dehydro-TxB(2). The increased levels of vWF in the circulation correlate with the increase in platelet activation markers and may indicate some degree of causation. Acute, short-term hyperglycemia in T2DM may precipitate vascular occlusions by facilitating platelet activation.

Anti-platelet therapy: phosphodiesterase inhibitors

Inhibition of platelet aggregation can be achieved either by the blockade of membrane receptors or by interaction with intracellular signalling pathways. Cyclic adenosine 3,5-monophosphate (cAMP) and cyclic guanosine 3,5-monophosphate (cGMP) are two critical intracellular second messengers provided with strong inhibitory activity on fundamental platelet functions. Phosphodiesterases (PDEs), by catalysing the hydrolysis of cAMP and cGMP, limit the intracellular levels of cyclic nucleotides, thus regulating platelet function. The inhibition of PDEs may therefore exert a strong platelet inhibitory effect. Platelets possess three PDE isoforms (PDE2, PDE3 and PDE5), with different selectivity for cAMP and cGMP. Several nonselective or isoenzyme-selective PDE inhibitors have been developed, and some of them have entered clinical use as antiplatelet agents. This review focuses on the effect of PDE2, PDE3 and PDE5 inhibitors on platelet function and on the evidence for an antithrombotic action of some of them, and in particular of dipyridamole and cilostazol.

Matrix metalloproteinases and peripheral arterial disease

Matrix metalloproteinases (MMPs), a family of enzymes that degrade extracellular matrix, are emerging as important modulators of atherothrombosis. MMPs are produced by inflammatory cells; some of them are also released by activated platelets and play a crucial role in the remodeling processes, leading to atherosclerotic plaque formation, plaque rupture, arterial aneurysm development, and critical limb ischemia. Independent from their matrix degrading activity, MMPs also regulate some cell functions relevant to atherothrombosis, such as platelet activation, neutrophil activation, and vascular reactivity. Plasma levels of some MMPs are increasingly being recognized as a biomarker of atherosclerosis and cardiovascular risk. In peripheral arterial disease, MMPs have been shown to be involved in angiogenesis, arteriogenesis, and the development of arterial calcifications. Increased plasma levels of some MMPs (MMP-2, MMP-9) have been correlated with PAD development and severity. Single nucleotide polymorphisms of the genes encoding for some MMPs have also been associated with the risk of developing peripheral arterial disease and critical limb ischemia. Large prospective observational studies are needed to further demonstrate the role of MMPs in PAD. In perspective, pharmacologic targeting of the expression or activity of MMPs may represent a novel, attractive approach for the treatment of peripheral arterial disease.

Diagnosis of suspected inherited platelet function disorders: results of a worldwide survey

Diagnosis of inherited platelet function disorders (IPFDs) is important for appropriate management and to improve epidemiologic and clinical knowledge. However, there remains a lack of consensus on the diagnostic approach.

Intraplatelet signaling mechanisms of the priming effect of matrix metalloproteinase‐2 on platelet aggregation

Summary.u2002 Objective:u2002Platelets contain and release some matrix metalloproteinases (MMPs), enzymes involved in the degradation of extracellular matrix, and one of these (MMP‐2) exerts a proaggregatory effect. We explored the signal transduction mechanisms activated by MMP‐2 in human blood platelets. Methods and results:Recombinant, human MMP‐2, added before stimulation with subthreshold doses of different agonists, potentiated platelet activation, calcium influx, IP3 formation, and pleckstrin phosphorylation. Wortmannin and LY29400, two PI3‐K inhibitors, suppressed the potentiating effects of MMP‐2 and preincubation with MMP‐2 enhanced the thrombin‐induced association of the p85α PI3‐K subunit with the cytoskeleton and increased the phosphorylation of PKB. Protein tyrosine kinase inhibitors, MAP kinase inhibitors, PLA2 inhibitors, cyclooxygenase inhibitors and antagonists of the P2Y1 and P2Y12 receptors did not affect the potentiating activity of MMP‐2 on platelets. Conclusion:u2002Our data show that MMP‐2, at a concentration released by activated platelets, facilitates platelet activation acting at the level of a second messenger system common to different agonists and related to the activation of PI3‐K. Platelet‐released MMP‐2 may contribute to platelet activation in vivo.

Platelets release matrix metalloproteinase-2 in the coronary circulation of patients with acute coronary syndromes: possible role in sustained platelet activation

AIMSnTo investigate whether selected matrix metalloproteinases (MMPs) are released in the coronary circulation of patients with acute coronary syndrome (ACS), whether this release is related to platelet activation, and whether it contributes to sustained platelet activation.nnnMETHODS AND RESULTSnBlood from the aorta (Ao) and the coronary sinus (Cs) was obtained from 21 controls (non-cardiac chest pain), 24 stable angina (SA), and 30 ACS patients, before performing percutaneous transluminal coronary angioplasty. Selected MMPs, some platelet activation- and atheroma-related markers, and the platelet activation-potentiating activity of plasma were measured. Total MMP-2, active MMP-2, and MMP-9 were released in the coronary circulation of patients with ACS, but not of those with SA or controls. Similarly, transcoronary gradients of β-thromboglobulin (β-TG) and platelet factor 4, two platelet-specific proteins, and of soluble CD40L and secretory phospholipase A₂ (sPLA₂), markers of inflammation and platelet activation, were higher in ACS patients than in the other groups. In contrast, plasma monocyte chemoattractant protein-1, a platelet-unrelated marker of atherogenesis, was not increased in the Cs compared with Ao in any of the groups. Transcoronary gradients of both β-TG and sPLA₂ correlated with those of total and active MMP-2 in ACS, but not in controls or SA. Plasma from the Cs of ACS patients potentiated platelet activation, an effect suppressed by the specific MMP-2-inhibitor, tissue inhibitor of MMP-2 (TIMP-2).nnnCONCLUSIONnMatrix metalloproteinase-2 is released in the coronary circulation of ACS patients, derives in part from activated platelets, and may contribute to sustained intracoronary platelet activation.

Potentiation and priming of platelet activation: a potential target for antiplatelet therapy

Ischemic cardiovascular events represent the leading cause of mortality and morbidity worldwide, and platelet aggregation and thrombus formation are the main effectors of acute arterial ischemic events. Although antiplatelet therapy is the cornerstone of antithrombotic treatment of ischemic cardiovascular disorders, available antiplatelet agents have less than satisfactory efficacy; thus, the identification of novel potential target candidates for antiplatelet therapy is highly warranted. Recent evidence suggests that several molecules that amplify the aggregation response of platelets to activating stimuli, which are either released by platelets (potentiating molecules) or present in the milieu before platelets get activated (primers), play a major role in pathologic thrombus formation without being significantly involved in primary haemostasis. These molecules appear to be a particularly appealing novel potential pharmacologic target for antiplatelet therapy. Here, we review the present knowledge on some molecules acting as potentiators or primers of platelet activation and discuss their possible pharmacologic modulation for antithrombotic purposes.

Loss of matrix metalloproteinase 2 in platelets reduces arterial thrombosis in vivo

1. 1. Momi, 2. et aln . 2009. J. Exp. Med. doi: 10.1084/jem.20090687n [OpenUrl][1][Abstract/FREE Full Text][2]nn [1]: {openurl}?query=rft_id%253Dinfo%253Adoi%252F10.1084%252Fjem.20090687%26rft_id%253Dinfo%253Apmid%252F19808257%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%

Dominant inheritance of a novel integrin β3 mutation associated with a hereditary macrothrombocytopenia and platelet dysfunction in two Italian families

Glanzmann’s thrombasthenia is a bleeding disorder caused by mutations of the ITGA2B or ITGB3 genes. This paper describes two Italian families with moderate thrombocytopenia with large platelets, defective platelet function and moderate/severe mucocutaneous bleeding, transmitted as an autosomal dominant trait and associated with a novel mutation in the ITGB3 gene, encoding the integrin β chain β3. This report adds to previous studies of mutant alleles which illustrate the importance of signaling via this integrin for platelet function as well as for platelet formation. Background Defects of integrin αIIbβ3 are typical of Glanzmann’s thrombasthenia, an inherited autosomal recessive bleeding disorder characterized by the failure of platelets to aggregate in response to all physiological agonists, but with no abnormalities in the number or size of platelets. Although large heterogeneity has been described for Glanzmann’s thrombasthenia, no family has so far been described as having an autosomal dominant form of this disease. Design and Methods We describe two Italian families with moderate thrombocytopenia with large platelets, defective platelet function and moderate/severe mucocutaneous bleeding, transmitted as an autosomal dominant trait and associated with a novel integrin β3-gene (ITGB3) mutation. Results The characteristics of our families are moderate macrothrombocytopenia and defective platelet function associated with a mild reduction of surface αIb β3, impaired platelet aggregation to physiological agonists but not to ristocetin, normal clot retraction, reduced fibrinogen binding and expression of activated αIIbβ3 upon stimulation, normal platelet adhesion to immobilized fibrinogen but reduced platelet spreading and tyrosine phosphorylation, indicating defective αIIbβ3-mediated outside-in signaling. Molecular analysis revealed a novel mutation of ITGB3 that determines an in-frame deletion producing the loss of amino acids 647–686 of the βTD ectodomain of integrin β3. Haplotype analysis indicated that the two families inherited the mutation from a common ancestral chromosome. Conclusions This novel autosomal dominant macrothrombocytopenia associated with platelet dysfunction raises interesting questions about the role of integrin β3, and its βTD domain, in platelet formation and function.

Endothelial and platelet function alterations in HIV-infected patients

The HIV epidemic has huge dimensions: in 2009, 33.3million people worldwide, including 2.5million children, were affected by human immunodeficiency virus (HIV) infection. The introduction of Highly Active Anti-Retroviral Therapy (HAART) has significantly modified the course of HIV disease, with longer survival and improved quality of life, but it has simultaneously lead to the appearance of previously unrecognized complications, such as ischemic cardiovascular events. Many studies have shown a higher rate of premature atherosclerosis in patients with HIV infection, leading to coronary, cerebrovascular, or peripheral arterial disease. However, it is still debated whether cardiovascular complications are a consequence of HIV infection itself or of the long-term use of HAART. In particular, myocardial infarction has been suggested to be associated with the use of abacavir. Endothelial dysfunction and platelet activation are markers of atherosclerosis and of increased cardiovascular risk. Here we review the evidence that endothelial dysfunction and platelet alterations are associated with chronic HIV infection, the possible role of different HAARTs, and the possible pathophysiologic mechanisms. Potential therapeutic implications are also discussed.