Glycoprotein IIb/IIIa inhibition attenuates platelet-activating factor-induced platelet activation by reducing protein kinase C activity

Hydrophobic Polystyrene-Modified Gelatin Enhances Fast Hemostasis and Tissue Regeneration in Traumatic Brain Injury

Hemostatic sealant is required to deal with blood loss, especially in the scenario of traumatic brain injury (TBI), which presents high rates of morbidity and disability. Hemostasis in surgery with traditional gelatin-based sealants often leads to blood loss and other issues in brain because of the hydrophilic gelatin swelling. Herein, hydrophobic effects on the hemostasis in TBI surgery are studied by tuning the chain length of polystyrene (PS) onto methylacrylated gelatin (Gel-MA). The hydrophobicity and hemostatic efficiency can be tuned by controlling the length of PS groups. The platelet activation of modified sealants Gel-MA-2P, Gel-MA-P, and Gel-MA-0.5P is as much as 17.5, 9.1, and 2.1 times higher than Gel-MA in vitro. The hemostatic time of Gel-MA-2P, Gel-MA-P, and Gel-MA-0.5P groups is 2.0-, 1.6-, and 1.1-folds faster than that in Gel-MA group in TBI mice. Increased formation of fibrins and platelet aggregation can also be observed in vitro by scanning electron microscopy. Animal's mortality is lowered by 46%, neurologic deficiency is reduced by 1.5 times, and brain edema is attenuated by 10%. Protein expression is further investigated to exhibit toxic iron-related processes caused by delayed hemostasis and activation of platelets via PI3K/PKC-α signaling. The hydrophobic Gel-MA has the potential in hemostatic TBI and promotes nervous system recovery in brain with the potentials in clinics.

Platelet-Leucocyte Aggregates as Novel Biomarkers in Cardiovascular Diseases

Simple Summary

Cardiovascular diseases are the most common cause of death worldwide. Hence, novel biomarkers are urgently needed to improve diagnosis and treatment. Platelet–leucocyte aggregates are conglomerates of platelets and leucocytes and are widely investigated as biomarkers in cardiovascular diseases. Platelet–leucocytes aggregates are present in health, but increase in patients with cardiovascular risk factors and acute or stable coronary syndromes, making them a potential diagnostic marker. Moreover, platelet–leucocyte aggregates predict outcomes after surgery or percutaneous treatment and could be used to monitor antiplatelet therapy. Emerging data about the participation of platelet–leucocyte aggregates in cardiovascular diseases pathogenesis make them an attractive target for novel therapies. Furthermore, simple detection with conventional flow cytometry provides accurate and reproducible results, although requires specific sample handling. The main task for the future is to determine the standardized protocol to measure blood concentrations of platelet–leucocyte aggregates and subsequently establish their normal range in health and disease.

Abstract

Platelet–leucocyte aggregates (PLA) are a formation of leucocytes and platelets bound by specific receptors. They arise in the condition of sheer stress, thrombosis, immune reaction, vessel injury, and the activation of leukocytes or platelets. PLA participate in cardiovascular diseases (CVD). Increased levels of PLA were revealed in acute and chronic coronary syndromes, carotid stenosis cardiovascular risk factors. Due to accessible, available, replicable, quick, and low-cost quantifying using flow cytometry, PLA constitute an ideal biomarker for clinical practice. PLA are promising in early diagnosing and estimating prognosis in patients with acute or chronic coronary syndromes treated by percutaneous coronary intervention (PCI) and coronary artery bypass grafting (CABG). PLA were also a reliable marker of platelet activity for monitoring antiplatelet therapy. PLA consist also targets potential therapies in CVD. All of the above potential clinical applications require further studies to validate methods of assay and proof clinical benefits.

Platelet-Activating Factor Promotes the Development of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is a multifaceted clinicopathological syndrome characterised by excessive hepatic lipid accumulation that causes steatosis, excluding alcoholic factors. Platelet-activating factor (PAF), a biologically active lipid transmitter, induces platelet activation upon binding to the PAF receptor. Recent studies have found that PAF is associated with gamma-glutamyl transferase, which is an indicator of liver disease. Moreover, PAF can stimulate hepatic lipid synthesis and cause hypertriglyceridaemia. Furthermore, the knockdown of the PAF receptor gene in the animal models of NAFLD helped reduce the inflammatory response, improve glucose homeostasis and delay the development of NAFLD. These findings suggest that PAF is associated with NAFLD development. According to reports, patients with NAFLD or animal models have marked platelet activation abnormalities, mainly manifested as enhanced platelet adhesion and aggregation and altered blood rheology. Pharmacological interventions were accompanied by remission of abnormal platelet activation and significant improvement in liver function and lipids in the animal model of NAFLD. These confirm that platelet activation may accompany a critical importance in NAFLD development and progression. However, how PAFs are involved in the NAFLD signalling pathway needs further investigation. In this paper, we review the relevant literature in recent years and discuss the role played by PAF in NAFLD development. It is important to elucidate the pathogenesis of NAFLD and to find effective interventions for treatment.

Diminished expression of β2-GPI is associated with a reduced ability to mitigate complement activation in anti-GPIIb/IIIa-mediated immune thrombocytopenia

Anti-GPIIb/IIIa-mediated complement activation has been reported to be important in the pathogenesis of immune thrombocytopenia (ITP). However, the role of the complement system and the involved regulatory mechanism remain equivocal. Beta2-glycoprotein I (β2-GPI), known as the main target for antiphospholipid autoantibodies, has been demonstrated as a complement regulator. Here, we investigated the complement-regulatory role of β2-GPI in anti-GPIIb/IIIa-mediated ITP. Plasma complement activation and enhanced complement activation capacity (CAC) were found in ITP patients with anti-GPIIb/IIIa antibodies in vivo and in vitro. Diminished plasma levels of β2-GPI were shown in patients of this group, which was inversely correlated with C5b-9 deposition. C5b-9 generation was inhibited by approximate physiological concentrations of β2-GPI, in a dose-dependent manner. Inhibition of C3a generation by β2-GPI and the existence of β2-GPI/C3 complexes in plasma indicated a regulation on the level of the C3 convertase. Furthermore, β2-GPI down-regulated the phosphorylation levels of c-Jun N-terminal kinase (JNK) and cleavage of BH3 interacting domain death agonist (Bid) and ultimately harbored platelet lysis. Our findings may provide a novel link between diminished plasma levels of β2-GPI and enhanced complement activation, indicating β2-GPI as a potential diagnostic biomarker and therapeutic target in the treatment of anti-GPIIb/IIIa-mediated ITP.

The Marine-Derived Kinase Inhibitor Fascaplysin Exerts Anti-Thrombotic Activity

Background: The marine-derived kinase inhibitor fascaplysin down-regulates the PI3K pathway in cancer cells. Since this pathway also plays an essential role in platelet signaling, we herein investigated the effect of fascaplysin on thrombosis. Methods: Fascaplysin effects on platelet activation, platelet aggregation and platelet-leukocyte aggregates (PLA) formation were analyzed by flow cytometry. Mouse dorsal skinfold chambers were used to determine in vivo the effect of fascaplysin on photochemically induced thrombus formation and tail-vein bleeding time. Results: Pre-treatment of platelets with fascaplysin reduced the activation of glycoprotein (GP)IIb/IIIa after protease-activated receptor-1-activating peptide (PAR-1-AP), adenosine diphosphate (ADP) and phorbol-12-myristate-13-acetate (PMA) stimulation, but did not markedly affect the expression of P-selectin. This was associated with a decreased platelet aggregation. Fascaplysin also decreased PLA formation after PMA but not PAR-1-AP and ADP stimulation. This may be explained by an increased expression of CD11b on leukocytes in PAR-1-AP- and ADP-treated whole blood. In the dorsal skinfold chamber model of photochemically induced thrombus formation, fascaplysin-treated mice revealed a significantly extended complete vessel occlusion time when compared to controls. Furthermore, fascaplysin increased the tail-vein bleeding time. Conclusion: Fascaplysin exerts anti-thrombotic activity, which represents a novel mode of action in the pleiotropic activity spectrum of this compound.

Platelets regulate CD4⁺ T-cell differentiation via multiple chemokines in humans

Atherosclerosis is an inflammatory and thrombotic disease. Both platelets and lymphocytes play important roles in atherogenesis. However, information on their interaction is limited. We therefore studied how platelets regulate CD4+ T cell activation and differentiation. Human CD4+ T cells and autologous platelets were co-cultured. Platelets concentration-dependently enhanced anti-CD3/CD28-induced IFNγ production by CD4+ T cells, but attenuated their proliferation. Abrogation of heterotypic cell-cell contact partially reversed the enhancement, and supernatant from activated platelets partially mimicked the enhancement, suggesting that platelets exert their effects via both soluble mediators and direct cell-cell contact. Platelets enhanced the production of IL-10 and cytokines characteristic for type 1 T helper (TH1) (IFNγ/TNFα) and TH17 (IL-17) cells, but influenced TH2 cytokines (IL-4/IL-5) little. The cytokine responses were accompanied by enhanced TH1/TH17/TReg differentiation. Using neutralising antibodies and recombinant PF4, RANTES, and TGFβ, we found that platelet-derived PF4 and RANTES enhanced both pro- and anti-inflammatory cytokine production, whilst recombinant TGFβ enhanced IL-10 but not TNFα production. In conclusion, platelets enhance the differentiation and cytokine production of anti-CD3/CD28-stimulated CD4+ T cells via both multiple chemokines and direct cell-cell contact. Our study provides new insights into the cross-talk between thrombosis and adaptive immunity, and indicates that platelets can enhance T-effector cell development.

Platelet hyperprocoagulant activity in Type 2 diabetes mellitus: attenuation by glycoprotein IIb/IIIa inhibition

BACKGROUND

Platelets are hyperactive in Type 2 diabetes mellitus (T2DM), and antiplatelet treatment with glycoprotein (GP) IIb/IIIa inhibitors provides better thrombotic protection in DM than in non-diabetic subjects.

OBJECTIVE

We hypothesized that diabetic platelets are hyperprocoagulant, and that this hyperactivity can be inhibited by GPIIb/IIIa blockade.

METHODS

Patients with T2DM and gender/age/body mass index-matched non-diabetic controls were recruited (n = 12 for both) to study the effect of GPIIb/IIIa blockade on platelet procoagulant activity. Platelet phosphotidylserine (PS), factor (F) Va expression, and platelet-derived microparticle (PDMP) generation were measured by whole blood flow cytometry. Platelet-dependent thrombin generation and plasma clotting time were monitored in recalcified platelet-rich plasma.

RESULTS

Compared to controls, basal platelet activation was similar, while thrombin receptor activating peptide stimulated activation was enhanced in patients with T2DM. Diabetic platelets also displayed more profound elevations of platelet PS exposure, FVa binding, and PDMP generation upon stimulation. These alterations resulted in a hyperprocoagulant state, as evidenced by a marked increase in the platelet procoagulant index, enhanced thrombin generation, and a shortened plasma clotting time. GPIIb/IIIa blockade by c7E3 or SR121566 decreased platelet PS exposure and FVa binding, and diminished platelet procoagulant activity in patients with T2DM.

CONCLUSIONS

Platelets have increased procoagulant activity in patients with T2DM. The hyperprocoagulant activity is counteracted by GPIIb/IIIa blockade.

Inverse agonist-induced signaling and down-regulation of the platelet-activating factor receptor

Platelet-activating factor (PAF) is a potent phospholipid mediator involved in several diseases such as allergic asthma, atherosclerosis and psoriasis. The human PAF receptor (PAFR) is a member of the G-protein-coupled receptor family. Following stimulation, PAFR becomes rapidly desensitized; this refractory state is dependent on PAFR phosphorylation, internalization and down-regulation. In this report, we show that the PAFR inverse agonist, WEB2086, can induce phosphorylation and down-regulation of PAFR. Using selective inhibitors, we determined that the agonist, PAF, and WEB2086 could induce phosphorylation of PAFR by PKC. Moreover, dominant-negative (DN) mutant of PKC isoforms beta inhibited WEB2086-stimulated PAFR phosphorylation, whereas PAF-stimulated phosphorylation was inhibited by DN PKCalpha and delta. WEB2086 also induced PAFR down-regulation which could be blocked by PKC inhibitors and by DN PKCbeta. WEB2086-induced down-regulation was dynamin-dependent but arrestin-independent. Unlike PAF, WEB2086-stimulated intracellular trafficking of PAFR was independent of Rab5. Specific inhibitors of lysosomal proteases and of proteasomes were both effective in reducing WEB2086-induced PAFR down-regulation, indicating the importance of receptor targeting to both lysosomes and proteasomes in long-term cell desensitization to WEB2086. These results indicate that although both agonists and inverse agonists induce receptor PAFR down-regulation, this may be accomplished through different signal transduction and trafficking pathways.

High glucose levels enhance platelet activation: involvement of multiple mechanisms

Diabetes mellitus (DM) and hyperglycaemia are associated with platelet activation. The present study was designed to investigate how high glucose levels influence platelet function. Fasting human blood was incubated with different concentrations of D-glucose (5, 15 and 30 mmol/l) and other sugars without or with in vitro stimuli. Platelet activation was monitored by whole blood flow cytometry. High glucose levels enhanced adenosine diphosphate (ADP)- and thrombin receptor-activating peptide (TRAP)-induced platelet P-selectin expression, and TRAP-induced platelet fibrinogen binding. Similar effects were seen with 30 mmol/l L-glucose, sucrose and galactose. Hyperglycaemia also increased TRAP-induced platelet-leucocyte aggregation. Protein kinase C (PKC) blockade did not counteract the enhancement of platelet P-selectin expression, but abolished the enhancement of TRAP-induced platelet fibrinogen binding by hyperglycaemia. Superoxide anion scavenging by superoxide dismutase (SOD) attenuated the hyperglycaemic enhancement of platelet P-selectin expression, but did not counteract the enhancement of TRAP-induced platelet fibrinogen binding. Hyperglycaemia did not alter platelet intracellular calcium responses to agonist stimulation. Blockade of cyclo-oxygenase (COX), phosphotidylinositol-3 (PI3) kinase, or nitric oxide synthase, or the addition of insulin did not influence the effect of hyperglycaemia. In conclusion, high glucose levels enhanced platelet reactivity to agonist stimulation through elevated osmolality. This occurred via superoxide anion production, which enhanced platelet P-selectin expression (secretion), and PKC signalling, which enhanced TRAP-induced fibrinogen binding (aggregablity).