Analysis of platelet function and dysfunction

Advances in Platelet-Dysfunction Diagnostic Technologies

The crucial role of platelets in hemostasis and their broad implications under various physiological conditions underscore the importance of accurate platelet-function testing. Platelets are key to clotting blood and healing wounds. Therefore, accurate diagnosis and management of platelet disorders are vital for patient care. This review outlines the significant advancements in platelet-function testing technologies, focusing on their working principles and the shift from traditional diagnostic methods to more innovative approaches. These improvements have deepened our understanding of platelet-related disorders and ushered in personalized treatment options. Despite challenges such as interpretation of complex data and the costs of new technologies, the potential for artificial-intelligence integration and the creation of wearable monitoring devices offers exciting future possibilities. This review underscores how these technological advances have enhanced the landscape of precision medicine and provided better diagnostic and treatment options for platelet-function disorders.

The Impact of Perioperative Morbidities, Lack of Discharge Aspirin, and Lack of Discharge Statin on Long Term Survival Following EVAR

OBJECTIVE

Adverse perioperative events and discharge medications both have the potential to impact survival following endovascular abdominal aortic aneurysm repair (EVAR). We hypothesize that variables such as blood loss, reoperation in the same hospital admission, and lack of discharge statin/aspirin have significant effect on long term survival following EVAR. Similarly, other perioperative morbidities, are hypothesized to affect long term mortality. Quantifying the mortality effect of perioperative events and treatment emphasizes to physicians the critical nature of preoperative optimization, case planning, operative execution and postoperative patient management.

METHODS

All EVAR in the Vascular Quality Initiative between 2003 and 2021 were queried. Exclusions were: ruptured/symptomatic aneurysm; concomitant renal artery or supra-renal intervention at the time of EVAR; conversion to open aneurysm repair at the time of initial operation; and undocumented mortality status at the 5 year mark postoperatively. 18,710 patients met inclusion criteria. Multivariable Cox regression time dependent analysis was performed to investigate the strength of mortality association of the exposure variables. Standard demographic variables and pre-existing major co-morbidities were included in the regression analysis to account for disproportionate, deleterious co-variables amongst those experiencing the various morbidities. Kaplan-Meier survival analysis was performed to provide survival curves for the key variables.

RESULTS

Mean follow up was 5.99 years and 5-year survival for included patients was 69.2%. Cox regression revealed increased long term mortality to be associated with the following perioperative events: reoperation during the index hospital admission (HR 1.21, P = .034), perioperative leg ischemia (HR 1.34, P = .014), perioperative acute renal insufficiency (HR 1.24, P = .013), perioperative myocardial infarction (HR 1.87, P < .001), perioperative intestinal ischemia (HR 2.13, P < .001), perioperative respiratory failure (HR 2.15, P < .001), lack of discharge aspirin (HR 1.26, P < .001), and lack of discharge statin (HR 1.26, P < .001). The following pre-existing co-morbidities correlated with increased long term mortality (P < .001 for all) : body mass index under 20 kg/m2, hypertension, diabetes, coronary artery disease, reported history congestive heart failure, chronic obstructive pulmonary disease, peripheral artery disease, advancing age, baseline renal insufficiency and left ventricular ejection fraction less than 50%. Females were more likely to have EBL >300 mL, reoperation, perioperative MI, limb ischemia and acute renal insufficiency than males (P < .01 for all). Female sex trended but was not associated with increased long term mortality risk (HR 1.06, 95% CI .995-1.14, P = .072).

CONCLUSIONS

Survival after EVAR is improved with optimal operative planning to facilitate evading the need for reoperation and ensuring patients without contra-indication are discharged with aspirin and statin medications. Females and patients with pre-existing co-morbidity are at particularly higher risk for perioperative limb ischemia, renal insufficiency, intestinal ischemia and myocardial ischemia necessitating appropriate preparation and preventative measures.

Differential Inhibition of Platelet Reactivity by Dual Therapy With Aspirin and Low-Dose Rivaroxaban in Peripheral Arterial Disease: A Pilot Study

Patients with peripheral arterial disease (PAD) benefit from combination therapy with acetylsalicylic acid (ASA, 100 mg, one time per day) plus low-dose rivaroxaban (2.5 mg, two times per day) compared to ASA monotherapy. In particular, major adverse cardiac and limb events were significantly reduced after peripheral endovascular revascularization (EVR). In this pilot study, the platelet activation status in vivo and platelet reactivity in vitro were longitudinally analyzed by flow cytometric assays and calibrated automated thrombography in platelet-rich plasma (PRP) from 10 patients with PAD receiving ASA (100 mg, one time per day) before EVR, ASA plus clopidogrel (75 mg, one time per day) after EVR, and ASA plus rivaroxaban (2.5 mg, two times per day) during a long-term follow-up. Platelet responsiveness to clopidogrel was compared to additional 10 patients with stable PAD and clopidogrel (75 mg, one time per day) monotherapy. ASA plus rivaroxaban treatment resulted in a significantly decreased thrombin peak in PRP for two triggers, namely, low concentration of tissue factor (TF) and thrombin, compared to ASA monotherapy. TF-controlled thrombin generation was additionally characterized by a significantly prolonged lag time in PRP and platelet-free plasma during ASA plus rivaroxaban combination therapy. In comparison, ASA plus clopidogrel treatment presented a significant reduction of the thrombin peak in PRP, which was less pronounced than during subsequent ASA plus rivaroxaban therapy. Platelet responsiveness to clopidogrel was observed for 60% of patients receiving ASA plus clopidogrel and clopidogrel monotherapy, respectively. Blocking of CD36 on the platelet surface further reduced the thrombin peak in PRP induced by TF for all three therapy regimes. Platelet activation in vivo and in response to the GPVI-agonist convulxin or thrombin in vitro was similar, whereas integrin αIIbβ3 activation and α-granule release induced by the PAR-1 activating peptide TRAP-6 were significantly diminished during ASA plus rivaroxaban treatment compared to ASA monotherapy. In conclusion, the data of this pilot study indicate an inhibitory effect of rivaroxaban on the thrombin propagation phase of CD36-sensitive platelet thrombin formation in patients with PAD treated with ASA plus rivaroxaban combination therapy, which is associated with decreased PAR-1 but not thrombin-mediated platelet activation.

Implication of Platelets in Immuno-Thrombosis and Thrombo-Inflammation

In addition to their well-described hemostatic function, platelets are active participants in innate and adaptive immunity. Inflammation and immunity are closely related to changes in platelet reactions and enhanced platelet function in thrombo-inflammation, as well as in microbial and virus infections. A platelet’s immune function is incompletely understood, but an important balance exists between its protective and pathogenic responses and its thrombotic and inflammatory functions. As the mediator of vascular homeostasis, platelets interact with neutrophils, bacteria and virus by expressing specific receptors and releasing granules, transferring RNA, and secreting mitochondria, which controls hemostasis and thrombosis, infection, and innate and adaptive immunity. This review focuses on the involvement of platelets during immuno-thrombosis and thrombo-inflammation.

Effects of Clopidogrel, Prasugrel and Ticagrelor on Microvascular Function and Platelet Reactivity in Patients With Acute Coronary Syndrome Undergoing Coronary Artery Stenting. A Randomized, Blinded, Parallel Group Trial

Aims: In this pre-specified analysis of the "endothelium, stent and antiplatelet therapy" study, we investigate the impact of antiplatelet therapies on microvascular function in patients undergoing stenting for an acute coronary syndrome. Methods and Results: Fifty-six patients [age: 63(55-67) years, males, 10 diabetics, 27 non-ST-elevation myocardial infarction] were randomized to receive clopidogrel, ticagrelor or prasugrel in form of oral loading 2 h before stenting followed by oral therapy. Investigators were blinded to the allocation. Laser-Doppler microvascular function and ADP-induced platelet aggregation capacity were measured at baseline, 2 h after oral antiplatelet loading, and 1 day, 1 week and 1 month after stenting during chronic therapy with the same antiplatelet agent. Platelet aggregation decreased in all groups 2 h after oral loading, with a significantly larger effect in the prasugrel group (P = 0.009). Similarly, prasugrel and ticagrelor loading was followed by an increase in microvascular reactive hyperemia (P = 0.007 and P = 0.042 compared to clopidogrel). This effect disappeared one day after coronary intervention, with a significant decrease in the prasugrel group (P = 0.026). Similarly, analysis of microvascular conductance showed a larger increase in the prasugrel group 2 h after loading (P = 0.022 among groups), and a decrease in all groups after stenting. Conclusions: Oral loading with prasugrel (and less consistently ticagrelor) is associated with improved microvascular function and stronger platelet inhibition in acute coronary syndrome patients. The microvascular effect was however lost 1 day after stenting and during subsequent follow-up. Further studies are necessary to clarify the the long-term effects and potential benefits of P2Y12 inhibitors on microvascular damage. ClINICALTRIALS.gov N°: NCT01700322 EUDRACT-N°: 2011-005305-73.

Fine-Tuning of Platelet Responses by Serine/Threonine Protein Kinases and Phosphatases-Just the Beginning

Comprehensive proteomic analyses of human and murine platelets established an extraordinary intracellular repertoire of signaling components, which control crucial functions. The spectrum of platelet serine/threonine protein kinases (more than 100) includes the AGC family (protein kinase A, G, C [PKA, PKG, PKC]), the mitogen-activated protein kinases (MAPKs), and others. PKA and PKG have multiple significantly overlapping substrates in human platelets, which possibly affect functions with clear "signaling nodes" of regulation by multiple protein kinases/phosphatases. Signaling nodes are intracellular Ca²⁺ stores, the contractile system (myosin light chains), and other signaling components such as G-proteins, protein kinases, and protein phosphatases. An example for this fine-tuning is the tyrosine kinase Syk, a crucial component of platelet activation, which is controlled by several serine/threonine and tyrosine protein kinases as well as phosphatases. Other protein kinases including PKA/PKG modulate protein phosphatase 2A, which may be a master regulator of MAPK signaling in human platelets. Protein kinases and in particular MAPKs are targeted by an increasing number of clinically used inhibitors. However, the precise regulation and fine-tuning of these protein kinases and their effects on other signaling components in platelets are only superficially understood-just the beginning. However, promising future approaches are in sight.

Effects of clopidogrel vs. prasugrel vs. ticagrelor on endothelial function, inflammatory parameters, and platelet function in patients with acute coronary syndrome undergoing coronary artery stenting: a randomized, blinded, parallel study

AIMS

In a randomized, parallel, blinded study, we investigate the impact of clopidogrel, prasugrel, or ticagrelor on peripheral endothelial function in patients undergoing stenting for an acute coronary syndrome.

METHODS AND RESULTS

The primary endpoint of the study was the change in endothelium-dependent flow-mediated dilation (FMD) following stenting. A total of 90 patients (age 62 ± 9 years, 81 males, 22 diabetics, 49 non-ST elevation myocardial infarctions) were enrolled. There were no significant differences among groups in any clinical parameter. Acutely before stenting, all three drugs improved FMD without differences between groups (P = 0.73). Stenting blunted FMD in the clopidogrel and ticagrelor group (both P < 0.01), but not in the prasugrel group. During follow-up, prasugrel was superior to clopidogrel [mean difference 2.13, 95% confidence interval (CI) 0.68-3.58; P = 0.0047] and ticagrelor (mean difference 1.57, 95% CI 0.31-2.83; P = 0.0155), but this difference was limited to patients who received the study therapy 2 h before stenting. Ticagrelor was not significantly superior to clopidogrel (mean difference 0.55, 95% CI -0.73 to 1.82; P = 0.39). No significant differences were seen among groups for low-flow-mediated dilation. Plasma interleukin (IL)-6 (P = 0.02 and P = 0.01, respectively) and platelet aggregation reactivity in response to adenosine diphosphate (P = 0.002 and P = 0.035) were lower in the prasugrel compared to clopidogrel and ticagrelor group.

CONCLUSION

As compared to ticagrelor and clopidogrel, therapy with prasugrel in patients undergoing stenting for an acute coronary syndrome is associated with improved endothelial function, stronger platelet inhibition, and reduced IL-6 levels, all of which may have prognostic implications. This effect was lost in patients who received the study medication immediately after stenting.

EUDRACT-NO

2011-005305-73.

Age-Dependent Control of Collagen-Dependent Platelet Responses by Thrombospondin-1-Comparative Analysis of Platelets from Neonates, Children, Adolescents, and Adults

Platelet function is developmentally regulated. Healthy neonates do not spontaneously bleed, but their platelets are hypo-reactive to several agonists. The mechanisms underlying immature platelet function in neonates are incompletely understood. This critical issue remains challenging for the establishment of age-specific reference ranges. In this study, we evaluated platelet reactivity of five pediatric age categories, ranging from healthy full-term neonates up to adolescents (11–18 years) in comparison to healthy adults (>18 years) by flow cytometry. We confirmed that platelet hypo-reactivity detected by fibrinogen binding, P-selectin, and CD63 surface expression was most pronounced in neonates compared to other pediatric age groups. However, maturation of platelet responsiveness varied with age, agonist, and activation marker. In contrast to TRAP and ADP, collagen-induced platelet activation was nearly absent in neonates. Granule secretion markedly remained impaired at least up to 10 years of age compared to adults. We show for the first time that neonatal platelets are deficient in thrombospondin-1, and exogenous platelet-derived thrombospondin-1 allows platelet responsiveness to collagen. Platelets from all pediatric age groups normally responded to the C-terminal thrombospondin-1 peptide RFYVVMWK. Thus, thrombospondin-1 deficiency of neonatal platelets might contribute to the relatively impaired response to collagen, and platelet-derived thrombospondin-1 may control distinct collagen-induced platelet responses.

Anticoagulation in Patients with Platelet Disorders

Platelet disorders comprise heterogeneous diseases featured by reduced platelet counts and/or impaired platelet function causing variable bleeding symptoms. Despite their bleeding diathesis, patients with platelet disorders can develop transient or permanent prothrombotic conditions that necessitate prophylactic or therapeutic anticoagulation. Anticoagulation in patients with platelet disorders is a matter of concern because the bleeding risk could add to the hemorrhagic risk related to the platelet defect. This review provides an overview on the evidence on anticoagulation in patients with acquired and inherited thrombocytopenia and/or platelet dysfunction. We summarize tools to evaluate and balance bleeding- and thrombotic risks and describe a practical approach on how to manage these patients if they have an indication for prophylactic or therapeutic anticoagulation.

Platelet Phenotyping and Function Testing in Thrombocytopenia

Patients who suffer from inherited or acquired thrombocytopenia can be also affected by platelet function defects, which potentially increase the risk of severe and life-threatening bleeding complications. A plethora of tests and assays for platelet phenotyping and function analysis are available, which are, in part, feasible in clinical practice due to adequate point-of-care qualities. However, most of them are time-consuming, require experienced and skilled personnel for platelet handling and processing, and are therefore well-established only in specialized laboratories. This review summarizes major indications, methods/assays for platelet phenotyping, and in vitro function testing in blood samples with reduced platelet count in relation to their clinical practicability. In addition, the diagnostic significance, difficulties, and challenges of selected tests to evaluate the hemostatic capacity and specific defects of platelets with reduced number are addressed.

The Cell Cycle Checkpoint System MAST(L)-ENSA/ARPP19-PP2A is Targeted by cAMP/PKA and cGMP/PKG in Anucleate Human Platelets

The cell cycle is controlled by microtubule-associated serine/threonine kinase-like (MASTL), which phosphorylates the cAMP-regulated phosphoproteins 19 (ARPP19) at S62 and 19e/α-endosulfine (ENSA) at S67and converts them into protein phosphatase 2A (PP2A) inhibitors. Based on initial proteomic data, we hypothesized that the MASTL-ENSA/ARPP19-PP2A pathway, unknown until now in platelets, is regulated and functional in these anucleate cells. We detected ENSA, ARPP19 and various PP2A subunits (including seven different PP2A B-subunits) in proteomic studies of human platelets. ENSA-S109/ARPP19–S104 were efficiently phosphorylated in platelets treated with cAMP- (iloprost) and cGMP-elevating (NO donors/riociguat) agents. ENSA-S67/ARPP19-S62 phosphorylations increased following PP2A inhibition by okadaic acid (OA) in intact and lysed platelets indicating the presence of MASTL or a related protein kinase in human platelets. These data were validated with recombinant ENSA/ARPP19 and phospho-mutants using recombinant MASTL, protein kinase A and G. Both ARPP19 phosphorylation sites S62/S104 were dephosphorylated by platelet PP2A, but only S62-phosphorylated ARPP19 acted as PP2A inhibitor. Low-dose OA treatment of platelets caused PP2A inhibition, diminished thrombin-stimulated platelet aggregation and increased phosphorylation of distinct sites of VASP, Akt, p38 and ERK1/2 MAP kinases. In summary, our data establish the entire MASTL(like)–ENSA/ARPP19–PP2A pathway in human platelets and important interactions with the PKA, MAPK and PI3K/Akt systems.

Feedback Regulation of Syk by Protein Kinase C in Human Platelets

The spleen tyrosine kinase (Syk) is essential for immunoreceptor tyrosine-based activation motif (ITAM)-dependent platelet activation, and it is stimulated by Src-family kinase (SFK)-/Syk-mediated phosphorylation of Y352 (interdomain-B) and Y525/526 (kinase domain). Additional sites for Syk phosphorylation and protein interactions are known but remain elusive. Since Syk S297 phosphorylation (interdomain-B) was detected in platelets, we hypothesized that this phosphorylation site regulates Syk activity via protein kinase C (PKC)-and cyclic adenosine monophosphate (cAMP)-dependent pathways. ADP, the GPVI-agonist convulxin, and the GPIbα-agonist echicetin beads (EB) were used to stimulate human platelets with/without effectors. Platelet aggregation and intracellular messengers were analyzed, along with phosphoproteins, by immunoblotting using phosphosite-specific antibodies or phos-tags. ADP, convulxin, and EB upregulated Syk S297 phosphorylation, which was inhibited by iloprost (cAMP pathway). Convulxin-stimulated Syk S297 phosphorylation was stoichiometric, transient, abolished by the PKC inhibitor GF109203X, and mimicked by the PKC activator PDBu. Convulxin/EB stimulated Syk S297, Y352, and Y525/526 phosphorylation, which was inhibited by SFK and Syk inhibitors. GFX and iloprost inhibited convulxin/EB-induced Syk S297 phosphorylation but enhanced Syk tyrosine (Y352/Y525/526) and substrate (linker adaptor for T cells (LAT), phospholipase γ2 (PLC γ2)) phosphorylation. GFX enhanced convulxin/EB-increases of inositol monophosphate/Ca²⁺. ITAM-activated Syk stimulates PKC-dependent Syk S297 phosphorylation, which is reduced by SFK/Syk/PKC inhibition and cAMP. Inhibition of Syk S297 phosphorylation coincides with enhanced Syk activation, suggesting that S297 phosphorylation represents a mechanism for feedback inhibition in human platelets.

cAMP- and cGMP-elevating agents inhibit GPIbα-mediated aggregation but not GPIbα-stimulated Syk activation in human platelets

Background

The glycoprotein (GP) Ib-IX-V complex is a unique platelet plasma membrane receptor, which is essential for platelet adhesion and thrombus formation. GPIbα, part of the GPIb-IX-V complex, has several physiological ligands such as von Willebrand factor (vWF), thrombospondin and distinct coagulation factors, which trigger platelet activation. Despite having an important role, intracellular GPIb-IX-V signaling and its regulation by other pathways are not well defined. Our aim was to establish the intracellular signaling response of selective GPIbα activation in human platelets, in particular the role of the tyrosine kinase Syk and its regulation by cAMP/PKA and cGMP/PKG pathways, respectively. We addressed this using echicetin beads (EB), which selectively bind to GPIbα and induce platelet aggregation.

Methods

Purified echicetin from snake Echis carinatus venom was validated by mass spectrometry. Washed human platelets were incubated with EB, in the presence or absence of echicetin monomers (EM), Src family kinase (SFK) inhibitors, Syk inhibitors and the cAMP- and cGMP-elevating agents iloprost and riociguat, respectively. Platelet aggregation was analyzed by light transmission aggregometry, protein phosphorylation by immunoblotting. Intracellular messengers inositolmonophosphate (InsP1) and Ca²⁺_i were measured by ELISA and Fluo-3 AM/FACS, respectively.

Results

EB-induced platelet aggregation was dependent on integrin α_IIbβ₃ and secondary mediators ADP and TxA₂, and was antagonized by EM. EB stimulated Syk tyrosine phosphorylation at Y352, which was SFK-dependent and Syk-independent, whereas Y525/526 phosphorylation was SFK-dependent and partially Syk-dependent. Furthermore, phosphorylation of both Syk Y352 and Y525/526 was completely integrin α_IIbβ₃-independent but, in the case of Y525/526, was partially ADP/TxA₂-dependent. Syk activation, observed as Y352/ Y525/Y526 phosphorylation, led to the phosphorylation of direct substrates (LAT Y191, PLCγ2 Y759) and additional targets (Akt S473). PKA/PKG pathways inhibited EB-induced platelet aggregation and Akt phosphorylation but, surprisingly, enhanced Syk and LAT/PLCγ2 tyrosine phosphorylation. A similar PKA/PKG effect was confirmed with convulxin−/GPVI-stimulated platelets. EB-induced InsP1 accumulation/InsP3 production and Ca²⁺-release were Syk-dependent, but only partially inhibited by PKA/PKG pathways.

Conclusion

EB and EM are specific agonists and antagonists, respectively, of GPIbα-mediated Syk activation leading to platelet aggregation. The cAMP/PKA and cGMP/PKG pathways do not inhibit but enhance GPIbα−/GPVI-initiated, SFK-dependent Syk activation, but strongly inhibit further downstream responses including aggregation. These data establish an important intracellular regulatory network induced by GPIbα.

Graphical abstract

Electronic supplementary material

The online version of this article (10.1186/s12964-019-0428-1) contains supplementary material, which is available to authorized users.

Coronary thrombosis in acute pancreatitis

The incidence of acute myocardial infarction in the setting of acute pancreatitis is very rare. The recognition of such complex diagnosis may be clinically challenging, as the symptoms of both conditions are often indistinguishable. We report a case in which we encountered both conditions concurrently, and hypothesize that the ambient inflammatory and pro-thrombotic milieu of acute pancreatitis resulted in acute coronary thrombosis despite the absence of significant coronary atherosclerosis. Among multiple coronary imaging modalities currently in use, optimal cohesion tomography provided a unique capability for direct visualization of the coronary thrombus. (1) Inflammatory processes such as acute pancreatitis promote a thrombogenic state. (2) Presentation of acute myocardial infarction is variable and can mimic a variety of medical conditions. (3) Intravascular imaging is emerging as a useful tool in delineating details of intra-coronary pathology not clear on standard fluoroscopy. (4) The above case highlights the likely concurrence of pathologies that follow common pathways such as system-wide inflammation and coagulation. Clinicians must be aware of this uncommon yet very likely possibility and keep a low threshold to perform ECG and cardiac biomarker testing if symptoms are suggestive of a myocardial infarction, even in the presence of a clear alternative diagnosis.

Effects of the NO/soluble guanylate cyclase/cGMP system on the functions of human platelets

Platelets are circulating sentinels of vascular integrity and are activated, inhibited, or modulated by multiple hormones, vasoactive substances or drugs. Endothelium- or drug-derived NO strongly inhibits platelet activation via activation of the soluble guanylate cyclase (sGC) and cGMP elevation, often in synergy with cAMP-elevation by prostacyclin. However, the molecular mechanisms and diversity of cGMP effects in platelets are poorly understood and sometimes controversial. Recently, we established the quantitative human platelet proteome, the iloprost/prostacyclin/cAMP/protein kinase A (PKA)-regulated phosphoproteome, and the interactions of the ADP- and iloprost/prostacyclin-affected phosphoproteome. We also showed that the sGC stimulator riociguat is in vitro a highly specific inhibitor, via cGMP, of various functions of human platelets. Here, we review the regulatory role of the cGMP/protein kinase G (PKG) system in human platelet function, and our current approaches to establish and analyze the phosphoproteome after selective stimulation of the sGC/cGMP pathway by NO donors and riociguat. Present data indicate an extensive and diverse NO/riociguat/cGMP phosphoproteome, which has to be compared with the cAMP phosphoproteome. In particular, sGC/cGMP-regulated phosphorylation of many membrane proteins, G-proteins and their regulators, signaling molecules, protein kinases, and proteins involved in Ca²⁺ regulation, suggests that the sGC/cGMP system targets multiple signaling networks rather than a limited number of PKG substrate proteins.

Changes in Platelet Count and Size Indices in Adolescent Patients With Anorexia Nervosa

The significance of platelet size indices has not been widely analyzed in anorexia nervosa (AN). It seems important to get more knowledge on the easily available indices of platelet function obtained by routine complete blood count analysis in patients with AN. We analyzed platelet count (PLT), platelet distribution width (PDW), and mean platelet volume using an automated blood cell counter in 25 females with AN and healthy age- and gender-matched nonatopic controls. Mean PLT was significantly lower in patients with AN than in the control group. Platelet distribution width values in patients with AN were significantly higher than those in the controls. Platelet distribution width values significantly correlated with the disease duration and rate of body weight loss in the anorectic patients. Anorexia nervosa in adolescents is associated with a decrease in PLT along with an increased PDW, which may be an indicator of dysregulated thrombopoiesis.

Reduced platelet hyper-reactivity and platelet-leukocyte aggregation after periodontal therapy

Background

Platelets from untreated periodontitis patients are hyper-reactive and form more platelet-leukocyte complexes compared to cells from individuals without periodontitis. It is not known whether the improvement of the periodontal condition achievable by therapy has beneficial effects on the platelet function. We aimed to assess the effects of periodontal therapy on platelet reactivity.

Methods

Patients with periodontitis (n = 25) but unaffected by any other medical condition or medication were included and donated blood before and after periodontal therapy. Reactivity to ADP or oral bacteria was assessed by flow cytometric analysis of membrane markers (binding of PAC-1, P-selectin, CD63) and platelet-leukocyte complex formation. Reactivity values were expressed as ratio between the stimulated and unstimulated sample. Plasma levels of soluble (s) P-selectin were determined by enzyme-linked immunosorbent assay (ELISA).

Results

Binding of PAC-1, the expression of P-selectin and CD63 in response to the oral bacterium P. gingivalis were lower at recall (1.4 ± 1.1, 1.5 ± 1.2, and 1.0 ± 0.1) than at baseline (2.7 ± 4.1, P = 0.026, 6.0 ± 12.5, P = 0.045, and 2.7 ± 6.7, P = 0.042, respectively). Formation of platelet-leukocyte complexes in response to P. gingivalis was also reduced at recall compared to baseline (1.2 ± 0.7 vs. 11.4 ± 50.5, P = 0.045). sP-selectin levels were significantly increased post-therapy.

Conclusions

In periodontitis patients, the improvement of the periodontal condition is paralleled by a reduction in platelet hyper-reactivity. We suggest that periodontal therapy, as an intervention for improved oral health, can facilitate the management of thrombotic risk, and on the long term can contribute to the prevention of cardiovascular events in patients at risk.

Trial registration

Current Controlled Trials identifier ISRCTN36043780. Retrospectively registered 25 September 2013.

Electronic supplementary material

The online version of this article (doi:10.1186/s12959-016-0125-x) contains supplementary material, which is available to authorized users.

Nanoparticles camouflaged in platelet membrane coating as an antibody decoy for the treatment of immune thrombocytopenia

Immune thrombocytopenia purpura (ITP) is characterized by the production of pathological autoantibodies that cause reduction in platelet counts. The disease can have serious medical consequences, leading to uncontrolled bleeding that can be fatal. Current widely used therapies for the treatment of ITP are non-specific and can, at times, result in complications that are more burdensome than the disease itself. In the present study, the use of platelet membrane-coated nanoparticles (PNPs) as a platform for the specific clearance of anti-platelet antibodies is explored. The nanoparticles, whose outer layer displays the full complement of native platelet surface proteins, act as decoys that strongly bind pathological anti-platelet antibodies in order to minimize disease burden. Here, we study the antibody binding properties of PNPs and assess the ability of the nanoparticles to neutralize antibody activity both in vitro and in vivo. Ultimately, we leverage the neutralization capacity of PNPs to therapeutically treat a murine model of antibody-induced thrombocytopenia and demonstrate considerable efficacy as shown in a bleeding time assay. PNPs represent a promising platform for the specific treatment of antibody-mediated immune thrombocytopenia by acting as an alternative target for anti-platelet antibodies, thus preserving circulating platelets with the potential of leaving broader immune function intact.

A review and discussion of platelet nitric oxide and nitric oxide synthase: do blood platelets produce nitric oxide from L-arginine or nitrite?

The NO/sGC/cGMP/PKG system is one of the most powerful mechanisms responsible for platelet inhibition. In numerous publications, expression of functional NO synthase (NOS) in human and mouse platelets has been reported. Constitutive and inducible NOS isoforms convert L-arginine to NO and L-citrulline. The importance of this pathway in platelets and in endothelial cells for the regulation of platelet function is discussed since decades. However, there are serious doubts in the literature concerning both expression and functionality of NOS in platelets. In this review, we aim to present and critically evaluate recent data concerning NOS expression and function in platelets, and to especially emphasise potential pitfalls of detection of NOS proteins and measurement of NOS activity. Prevailing analytical problems are probably the main sources of contradictory data on occurrence, activity and function of NOS in platelets. In this review we also address issues of how these problems can be resolved. NO donors including organic nitrites (RONO) and organic nitrate (RONO2) are inhibitors of platelet activation. Endogenous inorganic nitrite (NO2 (-)), the product of NO autoxidation, and exogenous inorganic nitrite are increasingly investigated as NO donors in the circulation. The role of platelets in the generation of NO from nitrite is also discussed.