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Background: Platelets, a type of anucleated cell, play a crucial role in cardiovascular diseases (CVDs). Therefore, targeting platelet activation is essential for mitigating CVDs. Endogenous agonists, such as collagen, activate platelets by initiating signal transduction through specific platelet receptors, leading to platelet aggregation. Eugenol, primarily sourced from clove oil, is known for its antibacterial, anticancer, and anti-inflammatory properties, making it a valuable medicinal agent. In our previous study, eugenol was shown to inhibit platelet aggregation induced by collagen and arachidonic acid. We concluded that eugenol exerts a potent inhibitory effect on platelet activation by targeting the PLCγ2–PKC and cPLA2-TxA2 pathways, thereby suppressing platelet aggregation. In our current study, we found that eugenol significantly inhibits NF-κB activation. This led us to investigate the relationship between the NF-κB and cPLA2 pathways to elucidate how eugenol suppresses platelet activation. Methods: In this study, we prepared platelet suspensions from the blood of healthy human donors to evaluate the inhibitory mechanisms of eugenol on platelet activation. We utilized immunoblotting and confocal microscopy to analyze these mechanisms in detail. Additionally, we assessed the anti-thrombotic effect of eugenol by observing fluorescein-induced platelet plug formation in the mesenteric microvessels of mice. Results: For immunoblotting and confocal microscopy studies, eugenol significantly inhibited NF-κB-mediated signaling events stimulated by collagen in human platelets. Specifically, it reduced the phosphorylation of IKK and p65 and prevented the degradation of IκBα. Additionally, CAY10502, a cPLA2 inhibitor, significantly reduced NF-κB-mediated signaling events. In contrast, BAY11-7082, an IKK inhibitor, did not affect collagen-stimulated cPLA2 phosphorylation. These findings suggest that cPLA2 acts as an upstream regulator of NF-κB activation during platelet activation. Furthermore, both BAY11-7082 and CAY10502 significantly reduced the collagen-induced rise in intracellular calcium levels. In the animal study, eugenol demonstrated potential as an anti-thrombotic agent by significantly reducing platelet plug formation in fluorescein-irradiated mouse mesenteric microvessels. Conclusion: Our study uncovered a novel pathway in platelet activation involving the cPLA2-NF-κB axis, which plays a key role in the antiplatelet effects of eugenol. These findings suggest that eugenol could serve as a valuable and potent prophylactic or therapeutic option for arterial thrombosis. [ABSTRACT FROM AUTHOR]

Acetaminophen and ibuprofen are widely used over-the-counter medications to reduce fever, pain, and inflammation. Although both drugs are safe in therapeutic concentrations, self-medication is practiced by millions of aged patients with comorbidities that decrease drug metabolism and/or excretion, thus raising the risk of overdosage. Mitochondrial dysfunction has emerged as an important pathomechanism underlying the organ toxicity of both drugs. Assessment of mitochondrial oxygen consumption in peripheral blood cells is a novel research field Cu several applications, including characterization of drug toxicity. The present study, conducted in human platelets isolated from blood donor-derived buffy coat, was aimed at assessing the acute, concentration-dependent effects of each drug on mitochondrial respiration. Using the high-resolution respirometry technique, a concentration-dependent decrease of oxygen consumption in both intact and permeabilized platelets was found for either drug, mainly by inhibiting complex I-supported active respiration. Moreover, ibuprofen significantly decreased the maximal capacity of the electron transport system already from the lowest concentration. In conclusion, platelets from healthy donors represents a population of cells easily available, which can be routinely used in studies assessing mitochondrial drug toxicity. Whether these results can be recapitulated in patients treated with these medications is worth further investigation as potential peripheral biomarker of drug overdose. [ABSTRACT FROM AUTHOR]

Hypercortisolism is known to affect platelet function. However, few studies have approached the effect of exogenous cortisol on human platelets, and the results obtained are conflicting and unconvincing. In this study, the effect of exogenous cortisol on several parameters indicative of oxidative status in human platelets has been analysed. We have found that cortisol stimulates ROS production, superoxide anion formation, and lipid peroxidation, with these parameters being in strict correlation. In addition, cortisol decreases GSH and membrane SH-group content, evidencing that the hormone potentiates oxidative stress, depleting platelet antioxidant defence. The involvement of src, syk, PI3K, and AKT enzymes in oxidative mechanisms induced by cortisol is shown. The main sources of ROS in cells can include uncontrolled increase of NADPH oxidase activity and uncoupled aerobic respiration during oxidative phosphorylation. Both mechanisms seem to be involved in ROS formation induced by cortisol, as the NADPH oxidase 1 inhibitor 2(trifluoromethyl)phenothiazine, and rotenone and antimycin A, complex I and III inhibitor, respectively, significantly reduce oxidative stress. On the contrary, the NADPH oxidase inhibitor gp91ds-tat, malate and NaCN, complex II and IV inhibitor, respectively, have a minor effect. It is likely that, in human platelets, oxidative stress induced by cortisol can be associated with venous and arterial thrombosis, greatly contributing to cardiovascular diseases. [ABSTRACT FROM AUTHOR]

Platelets assume a pivotal role in the pathogenesis of cardiovascular diseases (CVDs), emphasizing their significance in disease progression. Consequently, addressing CVDs necessitates a targeted approach focused on mitigating platelet activation. Eugenol, predominantly derived from clove oil, is recognized for its antibacterial, anticancer, and anti-inflammatory properties, rendering it a valuable medicinal agent. This investigation delves into the intricate mechanisms through which eugenol influences human platelets. At a low concentration of 2 μM, eugenol demonstrates inhibition of collagen and arachidonic acid (AA)-induced platelet aggregation. Notably, thrombin and U46619 remain unaffected by eugenol. Its modulatory effects extend to ATP release, P-selectin expression, and intracellular calcium levels ([Ca2+]i). Eugenol significantly inhibits various signaling cascades, including phospholipase Cγ2 (PLCγ2)/protein kinase C (PKC), phosphoinositide 3-kinase/Akt/glycogen synthase kinase-3β, mitogen-activated protein kinases, and cytosolic phospholipase A2 (cPLA2)/thromboxane A2 (TxA2) formation induced by collagen. Eugenol selectively inhibited cPLA2/TxA2 phosphorylation induced by AA, not affecting p38 MAPK. In ADP-treated mice, eugenol reduced occluded lung vessels by platelet thrombi without extending bleeding time. In conclusion, eugenol exerts a potent inhibitory effect on platelet activation, achieved through the inhibition of the PLCγ2–PKC and cPLA2-TxA2 cascade, consequently suppressing platelet aggregation. These findings underscore the potential therapeutic applications of eugenol in CVDs. [ABSTRACT FROM AUTHOR]

Platelets assume a pivotal role in the cardiovascular diseases (CVDs). Thus, targeting platelet activation is imperative for mitigating CVDs. Ginkgetin (GK), from Ginkgo biloba L, renowned for its anticancer and neuroprotective properties, remains unexplored concerning its impact on platelet activation, particularly in humans. In this investigation, we delved into the intricate mechanisms through which GK influences human platelets. At low concentrations (0.5–1 μM), GK exhibited robust inhibition of collagen and arachidonic acid (AA)‐induced platelet aggregation. Intriguingly, thrombin and U46619 remained impervious to GK's influence. GK's modulatory effect extended to ATP release, P‐selectin expression, intracellular calcium ([Ca2+]i) levels and thromboxane A2 formation. It significantly curtailed the activation of various signaling cascades, encompassing phospholipase Cγ2 (PLCγ2)/protein kinase C (PKC), phosphoinositide 3‐kinase/Akt/glycogen synthase kinase‐3β and mitogen‐activated protein kinases. GK's antiplatelet effect was not reversed by SQ22536 (an adenylate cyclase inhibitor) or ODQ (a guanylate cyclase inhibitor), and GK had no effect on the phosphorylation of vasodilator‐stimulated phosphoproteinSer157 or Ser239. Moreover, neither cyclic AMP nor cyclic GMP levels were significantly increased after GK treatment. In mouse studies, GK notably extended occlusion time in mesenteric vessels, while sparing bleeding time. In conclusion, GK's profound impact on platelet activation, achieved through inhibiting PLCγ2–PKC cascade, culminates in the suppression of downstream signaling and, ultimately, the inhibition of platelet aggregation. These findings underscore the promising therapeutic potential of GK in the CVDs. [ABSTRACT FROM AUTHOR]

Glycoprotein (GP) Ib-IX-V is the second most abundant platelet receptor for thrombin and other ligands crucial for hemostasis and thrombosis. Its activity is involved in platelet adhesion to vascular injury sites and thrombin-induced platelet aggregation. GPIb-IX-V is a heteromeric complex composed of four subunits, GPIbα, GPIbβ, GPV and GPIX, in a stoichiometric ratio that has been wildly debated. Despite its important physiological roles, the overall structure and molecular arrangement of GPIb-IX-V are not yet fully understood. Here, we purify stable and functional human GPIb-IX-V complex from reconstituted EXPi293F cells in high homogeneity, and perform biochemical and structural characterization of this complex. Single-particle cryo-electron microscopy structure of GPIb-IX-V is determined at ∼11 Å resolution, which unveils the architecture of GPIb-IX-V and its subunit organization. Size-exclusion chromatography-multi-angle static light scattering analysis reveals that GPIb-IX-V contains GPIb-IX and GPV at a 1:1 stoichiometric ratio and surface plasmon resonance assays show that association of GPV leads to slow kinetics of thrombin binding to GPIb-IX-V. Taken together, our results provide the first three-dimensional architecture of the intact GPIb-IX-V complex, which extends our understanding of the structure and functional mechanism of this complex in hemostasis and thrombosis. [ABSTRACT FROM AUTHOR]

Amperometry is arguably the most widely used technique for studying the exocytosis of biological amines. However, the scarcity of human tissues, particularly in the context of neurological diseases, poses a challenge for exocytosis research. Human platelets, which accumulate 90% of blood serotonin, release it through exocytosis. Nevertheless, single-cell amperometry with encapsulated carbon fibers is impractical due to the small size of platelets and the limited number of secretory granules on each platelet. The recent technological improvements in amperometric multi-electrode array (MEA) devices allow simultaneous recordings from several high-performance electrodes. In this paper, we present a comparison of three MEA boron-doped diamond (BDD) devices for studying serotonin exocytosis in human platelets: (i) the BDD-on-glass MEA, (ii) the BDD-on-silicon MEA, and (iii) the BDD on amorphous quartz MEA (BDD-on-quartz MEA). Transparent electrodes offer several advantages for observing living cells, and in the case of platelets, they control activation/aggregation. BDD-on-quartz offers the advantage over previous materials of combining excellent electrochemical properties with transparency for microscopic observation. These devices are opening exciting perspectives for clinical applications. [ABSTRACT FROM AUTHOR]

Background: Platelets, a type of anucleated cell, play a crucial role in cardiovascular diseases (CVDs). Therefore, targeting platelet activation is essential for mitigating CVDs. Endogenous agonists, such as collagen, activate platelets by initiating signal transduction through specific platelet receptors, leading to platelet aggregation. Eugenol, primarily sourced from clove oil, is known for its antibacterial, anticancer, and anti-inflammatory properties, making it a valuable medicinal agent. In our previous study, eugenol was shown to inhibit platelet aggregation induced by collagen and arachidonic acid. We concluded that eugenol exerts a potent inhibitory effect on platelet activation by targeting the PLCγ2–PKC and cPLA2-TxA2 pathways, thereby suppressing platelet aggregation. In our current study, we found that eugenol significantly inhibits NF-κB activation. This led us to investigate the relationship between the NF-κB and cPLA2 pathways to elucidate how eugenol suppresses platelet activation. Methods: In this study, we prepared platelet suspensions from the blood of healthy human donors to evaluate the inhibitory mechanisms of eugenol on platelet activation. We utilized immunoblotting and confocal microscopy to analyze these mechanisms in detail. Additionally, we assessed the anti-thrombotic effect of eugenol by observing fluorescein-induced platelet plug formation in the mesenteric microvessels of mice. Results: For immunoblotting and confocal microscopy studies, eugenol significantly inhibited NF-κB-mediated signaling events stimulated by collagen in human platelets. Specifically, it reduced the phosphorylation of IKK and p65 and prevented the degradation of IκBα. Additionally, CAY10502, a cPLA2 inhibitor, significantly reduced NF-κB-mediated signaling events. In contrast, BAY11-7082, an IKK inhibitor, did not affect collagen-stimulated cPLA2 phosphorylation. These findings suggest that cPLA2 acts as an upstream regulator of NF-κB activation during platelet activation. Furthermore, both BAY11-7082 and CAY10502 significantly reduced the collagen-induced rise in intracellular calcium levels. In the animal study, eugenol demonstrated potential as an anti-thrombotic agent by significantly reducing platelet plug formation in fluorescein-irradiated mouse mesenteric microvessels. Conclusion: Our study uncovered a novel pathway in platelet activation involving the cPLA2-NF-κB axis, which plays a key role in the antiplatelet effects of eugenol. These findings suggest that eugenol could serve as a valuable and potent prophylactic or therapeutic option for arterial thrombosis.

Human platelet 12-(S)-Lipoxygenase (12-LOX) is a fatty acid metabolizing oxygenase that plays an important role in platelet activation and cardiometabolic disease. ML355 is a specific 12-LOX inhibitor that has been shown to decrease thrombosis without prolonging hemostasis and protect human pancreatic islets from inflammatory injury. It has an amenable drug-like scaffold with nM potency and encouraging ADME and PK profiles, but its binding mode to the active site of 12-LOX remains unclear. In the current work, we combined computational modeling and experimental mutagenesis to propose a model in which ML355 conforms to the "U" shape of the 12-LOX active site, with the phenyl linker region wrapping around L407. The benzothiazole of ML355 extends into the bottom of the active site cavity, pointing towards residues A417 and V418. However, reducing the active site depth alone did not affect ML355 potency. In order to lower the potency of ML355, the cavity needed to be reduced in both length and width. In addition, H596 appears to position ML355 in the active site through an interaction with the 2-methoxy phenol moiety of ML355. Combined, this binding model suggested that the benzothiazole of ML355 could be enlarged. Therefore, a naphthyl-benzothiazole derivative of ML355, Lox12Slug001, was synthesized and shown to have 7.2-fold greater potency than ML355. This greater potency is proposed to be due to additional van der Waals interactions and pi-pi stacking with F414 and F352. Lox12Slug001 was also shown to be highly selective against 12-LOX relative to the other LOX isozymes and more importantly, it showed activity in rescuing human islets exposed to inflammatory cytokines with comparable potency to ML355. Further studies are currently being pursued to derivatize ML355 in order to optimize the additional space in the active site, while maintaining acceptable drug-like properties.

Abstract Background Platelets play a crucial role in cardiovascular diseases (CVDs) and are activated by endogenous agonists like collagen. These agonists initiate signal transduction through specific platelet receptors, resulting in platelet aggregation. Glabridin, a prenylated isoflavonoid found in licorice root, is known for its significance in metabolic abnormalities. Glabridin has been observed to inhibit collagen-induced platelet aggregation, but the precise mechanisms, specifically concerning NF-κB activation and integrin αIIbβ3 signaling, are not yet fully understood. Methods In this study, platelet suspensions were prepared from healthy human blood donors, and the aggregation ability was observed using a lumi-aggregometer. The inhibitory mechanisms of glabridin in human platelets were evaluated through immunoblotting and confocal microscopy. The anti-thrombotic effects of glabridin were assessed by histological analysis of lung sections in acute pulmonary thromboembolism and by examining fluorescein-induced platelet plug formation in mesenteric microvessels in mice. Results Glabridin inhibited integrin αIIbβ3 inside-out signals such as Lyn, Fyn, Syk, and integrin β3 activation and NF-κB-mediated signal events, with similar potency to classical inhibitors BAY11-7082 and Ro106-9920. Glabridin and BAY11-7082 inhibited IKK, IκBα, and p65 phosphorylation and reversed IκBα degradation, while Ro106-9920 only reduced p65 phosphorylation and reversed IκBα degradation. BAY11-7082 reduced Lyn, Fyn, Syk, integrin β3, phospholipase Cγ2 and protein kinase C activation. Glabridin reduced platelet plug formation in mesenteric microvessels and occluded vessels in thromboembolic lungs of mice. Conclusion Our study revealed a new pathway for activating integrin αIIbβ3 inside-out signals and NF-κB, which contributes to the antiplatelet aggregation effect of glabridin. Glabridin could be a valuable prophylactic or clinical treatment option for CVDs.

About 90% of blood serotonin is stored in secretory granules of platelets and is released by exocytosis [...]

This document explores the phosphorylation of apolipoprotein A-I (apoA-I) by platelet tyrosine kinases. The study identifies several Src family kinases (SFKs) involved in the tyrosine phosphorylation of apoA-I in platelets, specifically at Tyr42. The authors suggest that this phosphorylation may impact apoA-I's role in platelet signaling and lipid binding, but further research is needed to determine the specific kinase responsible and understand the functional implications. The study was conducted ethically and received support from the Open Access Publication Fund of Martin-Luther-University Halle-Wittenberg. [Extracted from the article]

Platelets play a vital role in the formation of dangerous arterial thrombosis. Platelets are activated by adhesive proteins or soluble agonists through their specific receptors. The receptor-mediated signaling pathways lead to common signaling events, which result in shape changes and inside–out signaling, leading fibrinogen binding to glycoprotein IIb/IIIa complex (integrin αIIbβ3). This interaction initiates integrin αIIbβ3-mediated outside-in signaling, subsequently culminating in granule secretion and aggregation. Myricetin is a flavonoid that occurs in a variety of plants. Although myricetin has been demonstrated to have several bioactive properties, its role in platelet activation has not been extensively studied. The present study demonstrated the ability of myricetin to inhibit platelet aggregation stimulated by collagen, thrombin, and U46619. Myricetin reduced the ATP-release, cytosolic Ca2+ mobilization, and P-selectin expression and the activation of PLCγ2/PKC, PI3K/Akt/GSK3β, and MAPK. Myricetin exerted a direct inhibitory effect on the activation of integrin αIIbβ3 by disrupting the binding between FITC-PAC-1 and the integrin. Moreover, myricetin suppressed integrin αIIbβ3-mediated outside–in signaling, such as integrin β3, Src, and Syk phosphorylation on immobilized fibrinogen. In animal studies, myricetin significantly prolonged the occlusion time of thrombotic platelet plug formation in mesenteric microvessels without extending bleeding time. This study concludes that myricetin is a natural integrin αIIbβ3 inhibitor and a novel antithrombotic agent.

Background: Platelets play a crucial role in cardiovascular diseases (CVDs) and are activated by endogenous agonists like collagen. These agonists initiate signal transduction through specific platelet receptors, resulting in platelet aggregation. Glabridin, a prenylated isoflavonoid found in licorice root, is known for its significance in metabolic abnormalities. Glabridin has been observed to inhibit collagen-induced platelet aggregation, but the precise mechanisms, specifically concerning NF-κB activation and integrin αIIbβ3 signaling, are not yet fully understood. Methods: In this study, platelet suspensions were prepared from healthy human blood donors, and the aggregation ability was observed using a lumi-aggregometer. The inhibitory mechanisms of glabridin in human platelets were evaluated through immunoblotting and confocal microscopy. The anti-thrombotic effects of glabridin were assessed by histological analysis of lung sections in acute pulmonary thromboembolism and by examining fluorescein-induced platelet plug formation in mesenteric microvessels in mice. Results: Glabridin inhibited integrin αIIbβ3 inside-out signals such as Lyn, Fyn, Syk, and integrin β3 activation and NF-κB-mediated signal events, with similar potency to classical inhibitors BAY11-7082 and Ro106-9920. Glabridin and BAY11-7082 inhibited IKK, IκBα, and p65 phosphorylation and reversed IκBα degradation, while Ro106-9920 only reduced p65 phosphorylation and reversed IκBα degradation. BAY11-7082 reduced Lyn, Fyn, Syk, integrin β3, phospholipase Cγ2 and protein kinase C activation. Glabridin reduced platelet plug formation in mesenteric microvessels and occluded vessels in thromboembolic lungs of mice. Conclusion: Our study revealed a new pathway for activating integrin αIIbβ3 inside-out signals and NF-κB, which contributes to the antiplatelet aggregation effect of glabridin. Glabridin could be a valuable prophylactic or clinical treatment option for CVDs. [ABSTRACT FROM AUTHOR]

Amperometry is arguably the most widely used technique for studying the exocytosis of biological amines. However, the scarcity of human tissues, particularly in the context of neurological diseases, poses a challenge for exocytosis research. Human platelets, which accumulate 90% of blood serotonin, release it through exocytosis. Nevertheless, single-cell amperometry with encapsulated carbon fibers is impractical due to the small size of platelets and the limited number of secretory granules on each platelet. The recent technological improvements in amperometric multi-electrode array (MEA) devices allow simultaneous recordings from several high-performance electrodes. In this paper, we present a comparison of three MEA boron-doped diamond (BDD) devices for studying serotonin exocytosis in human platelets: (i) the BDD-on-glass MEA, (ii) the BDD-on-silicon MEA, and (iii) the BDD on amorphous quartz MEA (BDD-on-quartz MEA). Transparent electrodes offer several advantages for observing living cells, and in the case of platelets, they control activation/aggregation. BDD-on-quartz offers the advantage over previous materials of combining excellent electrochemical properties with transparency for microscopic observation. These devices are opening exciting perspectives for clinical applications.

In the effort to obtain multitarget compound interfering with inflammation, oxidative stress, and tumorigenesis, we synthesized a small library of pyrazole compounds, selecting 4a, 4f, and 4g as the most noteworthy being IC50 against platelet ROS production induced by thrombin of about 10 µM. The in vitro antioxidant potential of the three molecules was evaluated, and since they show a remarkable antioxidative activity, their effect on several parameter indicative of oxidative status and on the efficiency of the aerobic metabolism was tested. The three molecules strongly inhibit superoxide anion production, lipid peroxidation, NADPH oxidase activity and almost restore the oxidative phosphorylation efficiency in thrombin-stimulated platelet, demonstrating a protective effect against oxidative stress. This effect was confirmed in endothelial cell in which 4a, 4f, and 4g show an interesting inhibition activity on H2O2-stimulated EA.hy926 cells. At last, antiproliferative activity of 4a, 4f, and 4g was submitted to a large screening at the NCI. The molecules show interesting anticancer activity, among them the most remarkable is 4g able to strongly inhibit the proliferation of both solid tumor and leukemia cells lines. In conclusion, all the three newly synthetized pyrazoles show remarkable antioxidant and antiproliferative effect worthy of further study. [ABSTRACT FROM AUTHOR]

Jyotsna Kailashiya, Debabrata Dash Centre for Advanced Research on Platelet Signalling & Thrombosis Biology, Department of Biochemistry, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, IndiaCorrespondence: Debabrata DashCentre for Advanced Research on Platelet Signalling & Thrombosis Biology, Department of Biochemistry, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India, Email ddash.biochem@gmail.comPurpose: Cerium oxide nanoparticles (nanoceria) exist in either 3+ or 4+ oxidation state with interesting redox properties and exhibit both oxidant and antioxidant attributes based on concentration, environment and pH. Thanks to their wide spread use in fuel, cosmetics and other industries as well as in biomedical field, nanoceria particles get released into environment with risk of significant human exposure, and thus necessitate careful examination and optimization of their biomedical applications.Methods: This research was planned to explore effects of nanoceria on human platelet functions and whole blood coagulation. Platelets and whole blood from volunteer healthy donors were treated with different doses of nanoceria and various platelet functions, fibrin polymerization and blood coagulation were tested.Results: Nanoceria particles were found to reduce platelet aggregation and secretion of granule contents in a dose-dependent manner, impaired fibrin polymerization and retraction of fibrin-rich thrombi, associated with reduced cytosolic filamentous actin. Remarkably, nanoceria instigated early clot formation in whole blood attributable to putative activation of coagulation cascade.Conclusion: Above observations provide cautionary framework to critically re-evaluate and accordingly plan biomedical applications of nanoceria.Keywords: cerium oxide nanoparticles, fibrin polymerization, human platelets, platelet aggregation, thromboelastogram

Fucosylated glycosaminoglycan (FG) from sea cucumbers has been reported to have anticoagulant effects via targeting intrinsic tenase. However, FG from natural source also potentially poses risks due to its FXIIa activation and platelet aggregating effects. Here, we found that the effect of FG on human platelet aggregation depended on both the sulfation pattern and chain length. FGs with higher content of Fuc2S4S and larger molecular weight (≥14 kD) had stronger activity. Both platelet aggregation and P-selectin expression induced by TaFG (an FG from Thelenota ananas) were decreased as the molecular weight reduced. Ticagrelor, aspirin and wortmannin completely blocked the secretion (ADP) but only partially blocked the aggregation induced by TaFG. Tirofiban an αIIbβ3 antagonist however potently inhibited both the secretion and aggregation, with IC50 of 6.01 ± 1.1.97 nM. Furthermore, TaFG could bind to human αIIbβ3 with high affinity, and the affinities of two FGs were paralleled with their activity in platelet aggregation or activation. These results indicated that αIIbβ3 played an important role in TaFG-induced platelet aggregation which was mediated by PI3K, and that platelet secretion was required for the amplification of aggregation.

Platelets from neonates have been shown to exhibit a reduced response to physiological agonists, such as thrombin; however, the mechanism behind these findings is poorly understood. Berna‐Erro et al. now provide differences in SARAF and pannexin‐1 expression and function between neonatal and maternal platelets that might shed some light on the underlying mechanism. Commentary on: Berna‐Erro. SARAF overexpression impairs thrombin‐induced Ca2+ homeostasis in neonatal platelets. Br J Haematol 2024;204:988‐1004. [ABSTRACT FROM AUTHOR]

Metformin is widely used as first-line medication for type 2 diabetes (T2D), the main disease comorbid with kidney disease, cardiovascular diseases (CVDs), and retinopathy. Platelets are crucial in platelet-dependent arterial thrombosis, which causes CVDs and cerebrovascular diseases. Research indicates that metformin may improve these diseases; metformin reportedly reduced platelet activation in rats. However, no reports have included human platelets. We investigated the mechanisms underlying metformin's effects on platelet activation by using human platelets and evaluated its in vivo effectiveness in experimental mice. Metformin inhibited platelet aggregation stimulated by collagen but not by arachidonic acid, U46619, or thrombin. Metformin suppressed ATP release, [Ca2+]i mobilization, and P-selectin expression, as well as phospholipase C (PLC)γ2/protein kinase C (PKC), p38 mitogen-activated protein kinase (MAPK), and phosphoinositide 3-kinase (PI3K)/Akt/glycogen synthase kinase-3β (GSK3β) phosphorylation. Metformin did not affect vasodilator-stimulated phosphoprotein (VASP) phosphorylation. In the animal studies, metformin reduced acute pulmonary thromboembolism mortality without increasing bleeding times. These results provide insights into the role and mechanisms of metformin in human platelet activation. Metformin decreased platelet activation by interfering with the PLCγ2/PKC, PI3K/Akt/GSK3β, and p38 MAPK pathways through a VASP-independent mechanism. Metformin demonstrates promise as a new class of antiplatelet agent that can inhibit platelet activation. [ABSTRACT FROM AUTHOR]

Human platelets were identified in tumors by Trousseau in 1865, although their roles in tumor microenvironments have only recently attracted the attention of cancer researchers. In this study we exploit and enhance platelet interactions in tumor microenvironments by introducing tumor-targeting and imaging functions. The first step in repurposing human platelets as vehicles for tumor-targeting was to inhibit platelet-aggregation by cytoplasmic-loading of kabiramide (KabC), a potent inhibitor of actin polymerization and membrane protrusion. KabC-Platelets can accumulate high levels of other membrane-permeable cytoxins and probes, including epidoxorubicin, carboxyfluorescein di-ester and chlorin-e6. Finally, mild reaction conditions were developed to couple tumor-targeting proteins and antibodies to KabC-platelets. Fluorescence microscopy studies showed KabC-platelets, surface-coupled with transferrin and Cy5, bind specifically to RPMI8226 and K562 cells, both of which over-express the transferrin receptor. Repurposed platelets circulate for upto 9-days a feature that increases their chance of interacting with target cells. KabC-platelets, surface-coupled with transferrin and Cy7, or chlorin-e6, and injected in immuno-compromised mice were shown to accumulate specifically in sub-cutaneous and intra-cranial myeloma xenotransplants. The high-contrast, in vivo fluorescence images recorded from repurposed platelets within early-stage myeloma is a consequence in part of their large size (φ~2µm), which allows them to transport 100 to 1000-times more targeting-protein and probe molecules respectively. Human platelets can be configured with a plurality of therapeutic and targeting antibodies to help stage tumor environments for an immunotherapy, or with combinations of therapeutic antibodies and therapeutic agents to target and treat cardiovascular and neurologic diseases.

Aim In acute medicine, we occasionally treat life‐threatening conditions such as sepsis and trauma, which cause severe thrombocytopenia. Serum thrombopoietin levels have been reported to increase under the condition of thrombocytopenia related to severity. Collagen is a crucial activator of platelets, and Rho family members, such as Rho/Rho‐kinase and Rac, play roles as active molecules involved in the intracellular signaling pathways in platelet activation. The present study aimed to elucidate the effects of thrombopoietin (TPO) on subthreshold low‐dose collagen‐stimulated human platelets in terms of Rho/Rho‐kinase and Rac. Methods Platelet‐rich plasma donated from healthy volunteers was stimulated by the subthreshold low‐dose of collagen after pretreatment with TPO and/or NSC23766, an inhibitor of the Rac‐guanine nucleotide exchange factor interaction, or Y27632, an inhibitor of Rho‐kinase. Platelet aggregation was measured using an aggregometer based on laser‐scattering methods. Proteins involved in intracellular signaling were analyzed using western blotting, and the secretion of platelet‐derived growth factor‐AB from activated platelets was determined using an enzyme‐linked immunosorbent assay. Results Under the existence of TPO, the low dose of collagen remarkably elicited the aggregation and platelet‐derived growth factor‐AB secretion of platelets, which were suppressed by NSC23766 and Y27632. The combination of TPO and collagen considerably induced a transient increase of guanosine triphosphate (GTP)‐binding Rac and GTP‐binding Rho followed by an increase of phosphorylated cofilin, a Rho‐kinase substrate. Conclusion These results strongly suggest that TPO and collagen in low doses cooperatively potentiate human platelet activation through both Rac and Rho/Rho‐kinase mediated pathways.

In the effort to obtain multitarget compound interfering with inflammation, oxidative stress, and tumorigenesis, we synthesized a small library of pyrazole compounds, selecting 4a, 4f, and 4g as the most noteworthy being IC50 against platelet ROS production induced by thrombin of about 10 µM. The in vitro antioxidant potential of the three molecules was evaluated, and since they show a remarkable antioxidative activity, their effect on several parameter indicative of oxidative status and on the efficiency of the aerobic metabolism was tested. The three molecules strongly inhibit superoxide anion production, lipid peroxidation, NADPH oxidase activity and almost restore the oxidative phosphorylation efficiency in thrombin-stimulated platelet, demonstrating a protective effect against oxidative stress. This effect was confirmed in endothelial cell in which 4a, 4f, and 4g show an interesting inhibition activity on H2O2-stimulated EA.hy926 cells. At last, antiproliferative activity of 4a, 4f, and 4g was submitted to a large screening at the NCI. The molecules show interesting anticancer activity, among them the most remarkable is 4g able to strongly inhibit the proliferation of both solid tumor and leukemia cells lines. In conclusion, all the three newly synthetized pyrazoles show remarkable antioxidant and antiproliferative effect worthy of further study.

Fucosylated glycosaminoglycan (FG) from sea cucumbers has been reported to have anticoagulant effects via targeting intrinsic tenase. However, FG from natural source also potentially poses risks due to its FXIIa activation and platelet aggregating effects. Here, we found that the effect of FG on human platelet aggregation depended on both the sulfation pattern and chain length. FGs with higher content of Fuc2S4S and larger molecular weight (≥14 kD) had stronger activity. Both platelet aggregation and P-selectin expression induced by TaFG (an FG from Thelenota ananas) were decreased as the molecular weight reduced. Ticagrelor, aspirin and wortmannin completely blocked the secretion (ADP) but only partially blocked the aggregation induced by TaFG. Tirofiban an αIIbβ3 antagonist however potently inhibited both the secretion and aggregation, with IC50 of 6.01 ± 1.1.97 nM. Furthermore, TaFG could bind to human αIIbβ3 with high affinity, and the affinities of two FGs were paralleled with their activity in platelet aggregation or activation. These results indicated that αIIbβ3 played an important role in TaFG-induced platelet aggregation which was mediated by PI3K, and that platelet secretion was required for the amplification of aggregation. [ABSTRACT FROM AUTHOR]

Myocardial infarction and cerebral ischemic stroke are prominent causes of death worldwide. Platelets play major roles in these diseases, although they are anucleated cells, but also express the NF-κB. Pterostilbene (PTE) possesses some intriguing pharmacological properties, including the capacity to inhibit platelet activation. We investigated the inhibitory role of PTE in NF-κB-mediated signal events and compared the relative potency with that of classical NF-κB inhibitors. PTE and IκB kinase (IKK) inhibitor, BAY11-7082, and proteasome inhibitor, Ro106-9920, inhibited platelet aggregation; the activity of BAY11-7082 and PTE were similar, but Ro106-9920 was weak in this reaction. PTE and BAY11-7082 diminished NF-κB signaling molecules, including IKK, IκBα, and p65 phosphorylation, and reversed IκBα degradation. However, Ro106-9920 was only effective in diminishing p65 phosphorylation and reversing IκBα degradation. In investigating the role of Akt and NF-κB in cell signaling events, MK-2206 (an inhibitor of Akt) markedly abolished IKK and p65 phosphorylation; BAY11-7082 also reduced Akt phosphorylation. PTE exhibited more potent activity in vivo than did BAY11-7082 in acute pulmonary thromboembolism. In conclusion, we identified a distinctive activation pathway of NF-κB and Akt involved in PTE-mediated antiplatelet aggregation, and PTE demonstrated powerful activity as a prophylactic and as clinical therapy for cardiovascular diseases. [ABSTRACT FROM AUTHOR]

Abstract Background Commercial herbal medicines (CHMs) marketed as immune boosters are gaining wide popularity in South Africa, in the absence of control and regulatory guidelines. These commercially packaged and labelled herbal preparations, acquired in various retail outlets, are used without consulting either a conventional health provider or a traditional health practitioner. Although they are indicated for immune-boosting purposes, they might exert many other beneficial and unwanted effects on physiological systems. Platelets are crucial in haemostasis and important for the immunological system. The aim was to investigate the effect of the CHMs used to strengthen the immune system on the activity of human platelets. Methods Six CHMs commonly used as African traditional medicines in Pretoria, South Africa, were tested for their effects on healthy, isolated human platelets, using a bioluminescence method. The tested herbal medicines were Intlamba Zifo™, Maphilisa™ Herbal medicine, Matla™ African medicine for all diseases, Ngoma™ Herbal Tonic Immune Booster, Stametta™ Body Healing Liquid, and Vuka Uphile™ Immune Booster and serial-diluted standards of each from 10 to 10,000 times. The luminol-enhanced luminescence activity of the platelets was measured after incubation with the herbal medicines and activation with phorbol myristate acetate (PMA) or N-formyl-methionyl-leucyl-phenylalanine (fMLP). Results Five herbal medicines, namely Intlamba Zifo™, Maphilisa™ Herbal medicine, Matla™ African medicine for all diseases, Stametta™ Body Healing Liquid, and Vuka Uphile™ Immune Booster exerted comparable weak inhibitory effects on both PMA and fMLP-induced platelets, which were concentration dependent at high doses, and inversely related to concentration at low doses. Intlamba Zifo™, Matla™ African medicine for all diseases, Stametta™ Body Healing Liquid, and Vuka Uphile™ exhibited weak, but non-systematic stimulatory effects at low doses, which were not statistically significant. Ngoma™ Herbal Tonic Immune Booster had weak, inhibitory effects at high doses and weak stimulatory effects that were inversely related to concentration at low doses. Conclusion The findings suggest a potential beneficial role of the CHMs in the suppression of platelets’ reactivity and in enhancing the immune system. Caution, however, should be exercised as platelet inhibition and stimulation predispose to the risk of bleeding and thrombosis, respectively.

Metformin is widely used as first-line medication for type 2 diabetes (T2D), the main disease comorbid with kidney disease, cardiovascular diseases (CVDs), and retinopathy. Platelets are crucial in platelet-dependent arterial thrombosis, which causes CVDs and cerebrovascular diseases. Research indicates that metformin may improve these diseases; metformin reportedly reduced platelet activation in rats. However, no reports have included human platelets. We investigated the mechanisms underlying metformin’s effects on platelet activation by using human platelets and evaluated its in vivo effectiveness in experimental mice. Metformin inhibited platelet aggregation stimulated by collagen but not by arachidonic acid, U46619, or thrombin. Metformin suppressed ATP release, [Ca2+]i mobilization, and P-selectin expression, as well as phospholipase C (PLC)γ2/protein kinase C (PKC), p38 mitogen-activated protein kinase (MAPK), and phosphoinositide 3-kinase (PI3K)/Akt/glycogen synthase kinase-3β (GSK3β) phosphorylation. Metformin did not affect vasodilator-stimulated phosphoprotein (VASP) phosphorylation. In the animal studies, metformin reduced acute pulmonary thromboembolism mortality without increasing bleeding times. These results provide insights into the role and mechanisms of metformin in human platelet activation. Metformin decreased platelet activation by interfering with the PLCγ2/PKC, PI3K/Akt/GSK3β, and p38 MAPK pathways through a VASP-independent mechanism. Metformin demonstrates promise as a new class of antiplatelet agent that can inhibit platelet activation.

Platelets from neonates have been shown to exhibit a reduced response to physiological agonists, such as thrombin; however, the mechanism behind these findings is poorly understood. Berna-Erro et al. now provide differences in SARAF and pannexin-1 expression and function between neonatal and maternal platelets that might shed some light on the underlying mechanism. Commentary on: Berna-Erro. SARAF overexpression impairs thrombin-induced Ca 2+ homeostasis in neonatal platelets. Br J Haematol 2024;204:988-1004., (© 2023 The Authors. British Journal of Haematology published by British Society for Haematology and John Wiley & Sons Ltd.)

Previously we have shown that wheat germ agglutinin (WGA) and, with minor potency, Phaseolus vulgaris agglutinin (PHA), but not lens culinarian agglutinin (LCA), induce platelet aggregation, through the PLCƴ2 activation by the concerted action of src/syk and PI3K/BTK pathways. In this study, we have investigated platelet oxidative stress induced by lectins. Several parameters indicative of oxidative stress, such as reactive oxygen species (ROS), superoxide anion, lipid peroxidation and the efficiency of the aerobic metabolism, have been measured. It was found that ROS, superoxide anion formation and lipid peroxidation are significantly increased upon platelet treatment with WGA and PHA while LCA is ineffective. WGA is always more effective than PHA in all experimental conditions tested. In addition, the involvement of NADPH oxidase 1, syk and PI3K in oxidative stress induced by WGA and PHA has been shown. Concerning the lectins effect on aerobic metabolism, WGA and PHA, but not LCA, act as uncoupling agents, determining an increase of oxygen consumption and a decrease of ATP synthesis, with a consequent decrease of P/O value. These results are confirmed by the impairment of platelets proton gradient formation, evaluated by membrane potential, in platelets treated with WGA and PHA. In conclusion lectins, especially WGA, induce oxidative stress in platelets and decrease energy availability through modifications of membrane structure leading to the inefficiency of the aerobic machinery that steers platelets toward death as suggested by the decreased metabolic activity of platelets and the increased lactic dehydrogenase release.

Platelets play a critical role in arterial thrombosis. Rutaecarpine (RUT) was purified from Tetradium ruticarpum, a well-known Chinese medicine. This study examined the relative activity of RUT with NF-κB inhibitors in human platelets. BAY11-7082 (an inhibitor of IκB kinase [IKK]), Ro106-9920 (an inhibitor of proteasomes), and RUT concentration-dependently (1–6 μM) inhibited platelet aggregation and P-selectin expression. RUT was found to have a similar effect to that of BAY11-7082; however, it exhibits more effectiveness than Ro106-9920. RUT suppresses the NF-κB pathway as it inhibits IKK, IκBα, and p65 phosphorylation and reverses IκBα degradation in activated platelets. This study also investigated the role of p38 and NF-κB in cell signaling events and found that SB203580 (an inhibitor of p38) markedly reduced p38, IKK, and p65 phosphorylation and reversed IκBα degradation as well as p65 activation in a confocal microscope, whereas BAY11-7082 had no effects in p38 phosphorylation. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay shows that RUT and BAY11-7082 did not exhibit free radical scavenging activity. In the in vivo study, compared with BAY11-7082, RUT more effectively reduced mortality in adenosine diphosphate (ADP)-induced acute pulmonary thromboembolism without affecting the bleeding time. In conclusion, a distinctive pathway of p38-mediated NF-κB activation may involve RUT-mediated antiplatelet activation, and RUT could act as a strong prophylactic or therapeutic drug for cardiovascular diseases.

Abstract Background Metformin is the most common pharmacological treatment for type 2 diabetes. It is considered safe but has been associated with the development of lactic acidosis under circumstances where plasma concentrations exceed therapeutic levels. Metformin-induced lactic acidosis has been linked to the drug’s toxic effect on mitochondrial function. Current treatment strategies aim to remove the drug and correct for the acidosis. With a mortality of 20%, complementary treatment strategies are needed. In this study, it was investigated whether targeting mitochondria with pharmacological agents that bypass metformin-induced mitochondrial dysfunction can counteract the energetic deficit linked to toxic doses of metformin. Methods The redox agent methylene blue and the cell-permeable succinate prodrug NV118 were evaluated by measuring mitochondrial respiration and lactate production of human platelets exposed to metformin and co-treated with either of the two pharmacological bypass agents. Results The cell-permeable succinate prodrug NV118 increased mitochondrial respiration which was linked to phosphorylation by the ATP-synthase and alleviated the increase in lactate production induced by toxic doses of metformin. The redox agent methylene blue, in contrast, failed to mitigate the metformin-induced changes in mitochondrial respiration and lactate generation. Conclusions The cell-permeable succinate prodrug NV118 bypassed the mitochondrial dysfunction and counteracted the energy deficit associated with toxic doses of metformin. If similar effects of NV118 prove translatable to an in vivo effect, this pharmacological strategy presents as a promising complementary treatment for patients with metformin-induced lactic acidosis.

Background: Cyclic AMP is a powerful inhibitor of platelet aggregation. In the present study we examined the effect of platelet aggregation modulators on cyclic AMP content in human thrombocytes. Of the agents we tested, lactoferrin, wortmannin, quercetin and amiloride are platelet aggregation inhibitors, whereas ouabain is a platelet activator.

Abstract Background The leaves of Annona purpurea have yielded several alkaloids with anti-aggregation activities against rabbit platelets. This is promising in the search for agents that might act against platelets and reduce the incidence of cardiovascular diseases. Since significant differences in platelet function have been reported between human and animal platelets, a study focusing on the effect of A. purpurea extracts against human platelet activation is necessary. Methods The compounds in an A. purpurea ethanolic extract underwent bio-guided fractionation and were used for in vitro human platelet aggregation assays to isolate the compounds with anti-platelet activity. The bioactive compounds were identified by spectroscopic analysis. Additional platelet studies were performed to characterize their action as inhibitors of human platelet activation. Results The benzylisoquinoline alkaloid norpurpureine was identified as the major anti-platelet compound. The IC50 for norpurpureine was 80 μM against platelets when stimulated with adenosine 5′-diphosphate (ADP), collagen and thrombin. It was pharmacologically effective from 20 to 220 μM. Norpurpureine (220 μM) exhibited its in vitro effectiveness in samples from 30 healthy human donors who did not take any drugs during the 2 weeks prior to the collection. Norpurpureine also gradually inhibited granule secretion and adhesion of activated platelets to immobilized fibrinogen. At the intra-platelet level, norpurpureine prevented agonist-stimulated calcium mobilization and cAMP reduction. Structure–activity relationship analysis indicates that the lack of a methyl group at the nitrogen seems to be key in the ability of the compound to interact with its molecular target. Conclusion Norpurpureine displays a promising in vitro pharmacological profile as an inhibitor of human platelet activation. Its molecular target could be a common effector between Ca2+ and cAMP signaling, such as the PLC-PKC-Ca2+ pathway and PDEs. This needs further evaluation at the protein isoform level.

Multiple non-aggregatory functions of human platelets (PLT) are widely acknowledged, yet their functional examination is limited mainly due to a lack of standardized isolation and analytic methods. Platelet apheresis (PA) is an established clinical method for PLT isolation aiming at the treatment of bleeding diathesis in severe thrombocytopenia. On the other hand, density gradient centrifugation (DC) is an isolation method applied in research for the analysis of the mitochondrial metabolic profile of oxidative phosphorylation (OXPHOS) in PLT obtained from small samples of human blood. We studied PLT obtained from 29 healthy donors by high-resolution respirometry for comparison of PA and DC isolates. ROUTINE respiration and electron transfer capacity of living PLT isolated by PA were significantly higher than in the DC group, whereas plasma membrane permeabilization resulted in a 57% decrease of succinate oxidation in PA compared to DC. These differences were eliminated after washing the PA platelets with phosphate buffer containing 10 mmol·L−1 ethylene glycol-bis (2-aminoethyl ether)-N,N,N′,N′-tetra-acetic acid, suggesting that several components, particularly Ca2+ and fuel substrates, were carried over into the respiratory assay from the serum in PA. A simple washing step was sufficient to enable functional mitochondrial analysis in subsamples obtained from PA. The combination of the standard clinical PA isolation procedure with PLT quality control and routine mitochondrial OXPHOS diagnostics meets an acute clinical demand in biomedical research of patients suffering from thrombocytopenia and metabolic diseases.

Myocardial infarction and cerebral ischemic stroke during the process of arterial thrombosis are prominently causes of death worldwide. Platelets are anucleated cells and play a critical factor in these diseases. Columbianadin (CBN), a coumarin derivative from plants, inhibits effective platelet activation. In this study, platelet function analysis revealed that the closure time of the platelet plug in human whole blood significantly prolonged by CBN, whereas CBN did not pointedly prolong the bleeding time in mice. BAY11-7082 (an inhibitor of IκB kinase) and MG-132 (an inhibitor of proteasome) inhibited collagen-stimulated platelet aggregation and ATP-release in human platelets, BAY11-7082 exhibited a higher potency than MG-132. Moreover, CBN markedly reduced NF-κB activation (e.g., IκBα and p65 phosphorylation) and reversed IκBα degradation in activated platelets. We investigated intercellular signaling events between mitogen-activated protein kinases and NF-κB, and found that BAY11-7082 abolished JNK1/2 and ERK1/2 phosphorylation. Interestingly, SP600125 (an inhibitor of JNK) but not PD98059 (an inhibitor of ERK) had no effect in NF-κB activation in activated platelets. Moreover, CBN but not BAY11-7082 significantly reduced hydroxyl radical (HO●) formation in platelets. Therefore, we propose that CBN inhibits NF-κB activation in human platelets and could present a potent clinical treatment for thromboembolic diseases. [ABSTRACT FROM AUTHOR]

Human platelets aggregate at sites of blood vessel damage in response to a rise in their cytosolic calcium concentration. Controlling these cytosolic calcium rises would provide a method to inhibit platelet activation and prevent the unwanted blood clots that causes heart attack and strokes. Previously we have predicted that calcium accumulation within the lumen of an infolded portion of the platelet plasma membrane called the open canalicular system (OCS) is essential for maintaining this cytosolic calcium rise. Due to its nanometer dimensions of the OCS, it has been difficult to measure or interfere with the predicted luminal calcium accumulation. Here we utilise iron oxide magnetic nanoparticles coated with the known calcium chelator, citrate, to create calcium-binding nanoparticles. These were used to assess whether an OCS calcium store plays a role in controlling the dynamics of human platelet activation and aggregation. We demonstrate that citrate-coated nanoparticles are rapidly and selectively uptaken into the OCS of activated human platelets, where they act to buffer the accumulation of calcium there. Treatment with these calcium-binding nanoparticles reduced thrombin-evoked cytosolic calcium rises, and slowed platelet aggregation and clot retraction in human platelets. In contrast, nanoparticles that cannot bind calcium have no effect. This study demonstrates that the OCS acts as a key source of calcium for maintaining cytosolic calcium rises and accelerating platelet aggregation, and that calcium-binding nanoparticles targeted to the OCS could provide an anti-platelet therapy to treat patients at risk of suffering heart attacks or strokes. [ABSTRACT FROM AUTHOR]

Myocardial infarction and cerebral ischemic stroke are prominent causes of death worldwide. Platelets play major roles in these diseases, although they are anucleated cells, but also express the NF-κB. Pterostilbene (PTE) possesses some intriguing pharmacological properties, including the capacity to inhibit platelet activation. We investigated the inhibitory role of PTE in NF-κB-mediated signal events and compared the relative potency with that of classical NF-κB inhibitors. PTE and IκB kinase (IKK) inhibitor, BAY11-7082, and proteasome inhibitor, Ro106-9920, inhibited platelet aggregation; the activity of BAY11-7082 and PTE were similar, but Ro106-9920 was weak in this reaction. PTE and BAY11-7082 diminished NF-κB signaling molecules, including IKK, IκBα, and p65 phosphorylation, and reversed IκBα degradation. However, Ro106-9920 was only effective in diminishing p65 phosphorylation and reversing IκBα degradation. In investigating the role of Akt and NF-κB in cell signaling events, MK-2206 (an inhibitor of Akt) markedly abolished IKK and p65 phosphorylation; BAY11-7082 also reduced Akt phosphorylation. PTE exhibited more potent activity in vivo than did BAY11-7082 in acute pulmonary thromboembolism. In conclusion, we identified a distinctive activation pathway of NF-κB and Akt involved in PTE-mediated antiplatelet aggregation, and PTE demonstrated powerful activity as a prophylactic and as clinical therapy for cardiovascular diseases.

The healthy vascular endothelium constantly releases autacoids which cause an increase of intracellular cyclic nucleotides to tame platelets from inappropriate activation. Elevating cGMP and cAMP, in line with previous reports, cooperated in the inhibition of isolated human platelet intracellular calcium-mobilization, dense granules secretion, and aggregation provoked by thrombin. Further, platelet alpha granules secretion and, most relevant, integrin α IIa β 3 activation in response to thrombin are shown to be prominently affected by the combined elevation of cGMP and cAMP. Since stress-related sympathetic nervous activity is associated with an increase in thrombotic events, we investigated the impact of epinephrine in this setting. We found that the assessed signalling events and functional consequences were to various extents restored by epinephrine, resulting in full and sustained aggregation of isolated platelets. The restoring effects of epinephrine were abolished by either interfering with intracellular calcium-elevation or with PI3-K signalling. Finally, we show that in our experimental setting epinephrine likewise reconstitutes platelet aggregation in heparinized whole blood, which may indicate that this mechanism could also apply in vivo. • Elevated cyclic nucleotides synergize in precluding platelet responses provoked by 0.3 U/ml thrombin. • Adrenoceptor α 2A -signalling reconstitutes molecular and functional responses by repressing the effects of cGMP/cAMP. • Inhibitory Gαz signalling appears to be refractory towards PKG/PKA-signalling. • The reconstitution of aggregation by epinephrine likewise applies for platelets in heparinized whole blood. [ABSTRACT FROM AUTHOR]

Myocardial infarction and cerebral ischemic stroke during the process of arterial thrombosis are prominently causes of death worldwide. Platelets are anucleated cells and play a critical factor in these diseases. Columbianadin (CBN), a coumarin derivative from plants, inhibits effective platelet activation. In this study, platelet function analysis revealed that the closure time of the platelet plug in human whole blood significantly prolonged by CBN, whereas CBN did not pointedly prolong the bleeding time in mice. BAY11-7082 (an inhibitor of IκB kinase) and MG-132 (an inhibitor of proteasome) inhibited collagen-stimulated platelet aggregation and ATP-release in human platelets, BAY11-7082 exhibited a higher potency than MG-132. Moreover, CBN markedly reduced NF-κB activation (e.g., IκBα and p65 phosphorylation) and reversed IκBα degradation in activated platelets. We investigated intercellular signaling events between mitogen-activated protein kinases and NF-κB, and found that BAY11-7082 abolished JNK1/2 and ERK1/2 phosphorylation. Interestingly, SP600125 (an inhibitor of JNK) but not PD98059 (an inhibitor of ERK) had no effect in NF-κB activation in activated platelets. Moreover, CBN but not BAY11-7082 significantly reduced hydroxyl radical (HO●) formation in platelets. Therefore, we propose that CBN inhibits NF-κB activation in human platelets and could present a potent clinical treatment for thromboembolic diseases.

Platelets play a vital role in the formation of dangerous arterial thrombosis. Platelets are activated by adhesive proteins or soluble agonists through their specific receptors. The receptor-mediated signaling pathways lead to common signaling events, which result in shape changes and inside-out signaling, leading fibrinogen binding to glycoprotein IIb/IIIa complex (integrin α IIb β 3 ). This interaction initiates integrin α IIb β 3 -mediated outside-in signaling, subsequently culminating in granule secretion and aggregation. Myricetin is a flavonoid that occurs in a variety of plants. Although myricetin has been demonstrated to have several bioactive properties, its role in platelet activation has not been extensively studied. The present study demonstrated the ability of myricetin to inhibit platelet aggregation stimulated by collagen, thrombin, and U46619. Myricetin reduced the ATP-release, cytosolic Ca 2+ mobilization, and P-selectin expression and the activation of PLCγ2/PKC, PI3K/Akt/GSK3β, and MAPK. Myricetin exerted a direct inhibitory effect on the activation of integrin α IIb β 3 by disrupting the binding between FITC-PAC-1 and the integrin. Moreover, myricetin suppressed integrin α IIb β 3 -mediated outside-in signaling, such as integrin β 3 , Src, and Syk phosphorylation on immobilized fibrinogen. In animal studies, myricetin significantly prolonged the occlusion time of thrombotic platelet plug formation in mesenteric microvessels without extending bleeding time. This study concludes that myricetin is a natural integrin α IIb β 3 inhibitor and a novel antithrombotic agent., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors.)

The objective of this study was to determine whether adenosine 5′ monophosphate (AMP)‐activated protein kinase (AMPK) is activated by anandamide (AEA) and is involved in endothelial nitric oxide synthase (eNOS) activation. We found that AEA stimulates and activates AMPKα through a Ca2+‐dependent/Calmodulin (CaM)‐dependent pathway as the specific inhibitor of the Ca2+/Calmodulin kinase kinase β (CaMKKβ) STO‐609 abolishes the AMPK phosphorylation/activation. The same inhibiting effect is shown in platelets pretreated with LY294002, an inhibitor of phosphatidylinositol 3 kinase (PI3K), or with MK2206, an inhibitor of protein kinase B (AKT), suggesting that AMPK is downstream of the PI3K/AKT pathway. Moreover, the AEA‐induced eNOS activation and the consequent nitric oxide (NO) and guanosine 3′‐5′ cyclic monophosphate (cGMP) increase are mediated by the CaMKKβ/AMPKα pathway as STO‐609 significantly inhibits these parameters. In contrast, liver kinase B1 (LKB1) seems to be very poorly involved. One crucial effect of NO and cGMP elevation is the activation of protein kinase G that can phosphorylate the vasodilator‐stimulated phosphoprotein (VASP). We have demonstrated that AEA stimulates VASP phosphorylation on both thr278 and ser239 that is strongly inhibited by STO‐609, LY294002, and MK2206. Finally, AMPK phosphorylation/activation and VASP phosphorylation are significantly reduced by SR141716, the specific inhibitor of type 1 cannabinoid receptor (CB1). SR144528, an antagonist of type 2 cannabinoid receptor (CB2), has a less‐potent effect, suggesting that the CB1 receptor is overall involved in the AEA effect. In conclusion, we show that the CaMKKβ/AMPKα pathway, downstream of the PI3K/AKT pathway, is activated by AEA in human platelets and leads to increase NO levels producing beneficial effects during ischemic conditions and contributing to extend platelet survival. [ABSTRACT FROM AUTHOR]

We have compared the effect of three legume lectins, wheat germ agglutinin (WGA), Phaseolus vulgaris agglutinin (PHA) and Lens culinaris agglutinin (LCA), on the function of human platelets. We have found that WGA is more active than PHA in stimulating platelet activation/aggregation, while LCA has no effect. Studies on the mechanisms involved show that WGA and PHA induce phosphorylation/activation of PLCγ² and increase [Ca2+]i. For the first time, it has been shown that Src/Syk pathway, the adapter protein SLP-76 and the exchange protein VAV, participate in the PLCγ² activation by these lectins. Moreover WGA and PHA stimulate the PI3K/AKT pathway. PI3K, through its product phosphatidylinositol-3,4,5-trisphosphate activates Bruton's tyrosine kinase (BTK) and contributes to PLCγ² activation. In conclusion, our findings suggest that PLCγ² activation induced by WGA and PHA is regulated by Src/Syk and by PI3K/BTK pathways through their concerted action. [ABSTRACT FROM AUTHOR]

The study investigated effect of substrate supplementation with Se alone or in combination with Cu or/and Zn Se on (1) the growth of Pleurotus ostreatus and Pleurotus eryngii; (2) elements accumulation in mushrooms; (3) the antioxidant activities of bio-enriched mushroom extracts in human platelets. The accumulation of elements generally increased over concentration gradient reaching its maximum at 1.2 mM for P. ostreatus and P. eryngii: (1) over 100 and 80 mg kg of Se, respectively (Se supplementation); (2) over 15 and 30 mg kg of Cu, respectively (Se+Cu); (3) over 30 and 85 mg kg of Zn, respectively. Se was predominantly accumulated as an organic fraction. Contrary to P. eryngii, the P. ostreatus biomass decreased with substrate elements concentration but was satisfactory up to 0.9 mM of Se, Se+Cu and Se+Zn. The Se+Cu+Zn model yielded low biomass and elements accumulation. Extracts from mushrooms bio-enriched with Se and Se+Zn (0.6-1.2 mM) revealed significant antioxidant activities in human platelets by ameliorating reactive oxygen species (ROS) and preventing lipid peroxidation. The study demonstrated the potential application of Pleurotus mushrooms as functional food products bio-enriched with essential elements. ROS inhibition by extracts of these mushrooms may be useful in control of platelets activation cascade. [ABSTRACT FROM AUTHOR]