ORCID Profile
0000-0003-0904-677X
Current Organisation
Queen Mary University of London
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Publisher: Wiley
Date: 28-09-2021
DOI: 10.1111/BPH.15659
Abstract: P2Y 12 receptor antagonists reduce platelet aggregation and the incidence of arterial thrombosis. Adenosine signalling in platelets directly affects cyclic nucleotide tone, which we have shown to have a synergistic relationship with P2Y 12 inhibition. Several studies suggest that ticagrelor inhibits erythrocyte uptake of adenosine and that this could also contribute to its antiplatelet effects. We therefore examined the effects on platelet activation of adenosine signalling activators in combination with the P2Y 12 receptor antagonists ticagrelor and prasugrel. Human washed platelets, platelet‐rich plasma and whole blood were used to test the interactions between ticagrelor or prasugrel and adenosine or 5′‐ N ‐ethylcarboxamidoadenosine (NECA). Platelet reactivity to thrombin, protease‐activated receptor 1 (PAR‐1) activation or collagen was assessed by a combination of 96‐well plate aggregometry, light transmission aggregometry, whole blood aggregometry, ATP release assay and levels of cAMP. The inhibitory effects of ticagrelor and prasugrel on platelet aggregation and ATP release were enhanced in the presence of adenosine or NECA. Isobolographic analysis indicated a powerful synergy between P2Y 12 receptor inhibition and adenosine signalling activators. Increased levels of cAMP in platelets were also observed. In all cases, ticagrelor showed similar synergistic effects on platelet inhibition as prasugrel in the presence of adenosine or NECA. These results indicate that P2Y 12 antagonists have a synergistic relationship with adenosine signalling and that their efficacy may depend partly upon the presence of endogenous adenosine. This effect was common for prasugrel and ticagrelor despite reports of differences in their effects upon adenosine reuptake.
Publisher: BMJ
Date: 28-01-2015
Publisher: Informa UK Limited
Date: 12-10-2011
DOI: 10.3109/09537104.2011.592958
Abstract: Platelet reactivity testing is important for the diagnosis of bleeding disorders, and increasingly to optimise anti-platelet therapy. Traditional light transmission aggregometry is considered the gold standard, whilst 96-well plate aggregometry, founded on similar principles, provides a higher throughput screening method. Despite the widespread use of both, methodologies and outputs vary widely between laboratories. We report a methodological approach towards providing a standardised optical detection of platelet aggregation (optimul method) based upon 96-well plate aggregometry. In idual wells of half-area 96-well plates were coated with gelatine and one of seven concentrations of arachidonic acid (AA), adenosine diphosphate (ADP), collagen, epinephrine (EPI), ristocetin, TRAP-6 amide or U46619, before being lyophilised, vacuum-sealed, foil-packed and stored at room temperature for up to 24 weeks. For platelet testing, 40 µl of platelet-rich plasma was added to each well. Platelet aggregation was determined by changes in light absorbance, release of ATP/ADP by luminescence and release of thromboxane (TX) A(2) by ELISA. Some experiments were conducted in the presence of aspirin (30 µM) or prasugrel active metabolite (PAM 3 µM). Optimul plates stored for up to 12 weeks permitted reliable detection of concentration-dependent platelet aggregation, ATP/ADP release and TXA₂ production. PAM caused reductions in platelet responses to AA, ADP, collagen, EPI, TRAP-6 and U46619, whilst aspirin inhibited responses to AA, collagen and EPI. We conclude that the optimul method offers a viable, standardised approach, allowing platelet reactivity testing and could provide a broad platelet function analysis without the need for dedicated equipment.
Publisher: Informa UK Limited
Date: 18-04-2023
Publisher: Cold Spring Harbor Laboratory
Date: 20-12-2021
DOI: 10.1101/2021.12.17.473131
Abstract: The proportion of young platelets, also known as newly formed or reticulated, within the overall platelet population has been clinically correlated with adverse cardiovascular outcomes. Our understanding of this is incomplete, however, because of limitations in the technical approaches available to study platelets of different ages. In this study we have developed and validated an in vivo ‘temporal labelling’ approach using injectable fluorescent anti-platelet antibodies to sub- ide platelets by age and assess differences in functional and molecular characteristics. With this approach we found that young platelets ( h old) in comparison to older platelets respond to stimuli with greater calcium flux and degranulation, and contribute more to the formation of thrombi in vitro and in vivo . Sequential s ling confirmed this altered functionality to be independent of platelet size with no size differences or changes relative to the global population seen at any age. The age associated decrease in thrombotic function was accompanied by significant decreases in the surface expression of GPVI and CD31 (PECAM-1) and an increase in CD9. Platelet mRNA content also decreased with age but at different rates for in idual mRNAs indicating apparent conservation of those encoding granule proteins. Our pulse-chase type approach to define circulating platelet age has allowed timely re-examination of commonly held beliefs regarding size and reactivity of young platelets whilst providing novel insights into the temporal regulation of receptor and protein expression. Overall, future application of this validated tool will inform on age-based platelet heterogeneity in physiology and disease.
Publisher: American Society of Hematology
Date: 03-09-2015
DOI: 10.1182/BLOOD-2015-01-621656
Abstract: Low-volume, high-throughput whole blood aggregometry will facilitate future mouse platelet function research. Application of this approach identifies ICAM-1 as a novel mediator of platelet-monocyte interaction through fibrinogen binding.
Publisher: Elsevier BV
Date: 09-2021
DOI: 10.1111/JTH.15470
Publisher: Wiley
Date: 19-04-2019
DOI: 10.1111/BPH.14196
Publisher: Elsevier BV
Date: 12-2021
DOI: 10.1111/JTH.15496
Publisher: Informa UK Limited
Date: 03-03-2015
DOI: 10.3109/09537104.2014.1001832
Abstract: In addition to adenosine diphosphate (ADP), a number of platelet function tests including the VerifyNow P2Y12 assay (VN-P2Y12) employ prostaglandin E1 (PGE1) to improve specificity for P2Y12 blockade by mitigating the contribution of the P2Y1 pathway on ADP-mediated platelet aggregation. Using short thromboelastography (s-TEG), we have previously shown that VN-P2Y12 overestimates the functional effect of clopidogrel in some in iduals. We investigated whether PGE1 systematically increases the inhibitory effects of P2Y12 blockade on ADP-mediated platelet aggregation in an in vitro model. Using s-TEG, we measured ADP-induced platelet aggregation either in the presence or absence of PGE1 (11 or 22 nM) in blood s les taken from healthy volunteers pre-incubated with prasugrel active metabolite (PAM 0, 1, 3 or 10 µM). In idually, both PGE1 (p < 0.02) and PAM (p < 0.0001) inhibited ADP-mediated platelet aggregation in a dose-dependent manner, as expected. Furthermore, inclusion of PGE1 augmented inhibition of ADP-mediated platelet aggregation in response to PAM (p < 0.02) in a dose-dependent manner such that a 10-fold higher dose of PAM was required to attain equivalent inhibition of ADP-mediated platelet aggregation to that achieved by 1 µM PAM in the presence of 11 nM PGE1. In conclusion, PGE1 potentiates the anti-aggregatory effects of P2Y12 blockade on ADP-mediated platelet aggregation. Assays that employ PGE1 with ADP may therefore overestimate therapeutic response to prasugrel in a proportion of in iduals, potentially making them unsuitable candidates for guiding delivery of personalized antiplatelet therapy.
Publisher: American Society of Hematology
Date: 17-06-2020
DOI: 10.1182/BLOODADVANCES.2020001776
Abstract: Trauma-induced coagulopathy (TIC) is a complex, multifactorial failure of hemostasis that occurs in 25% of severely injured patients and results in a fourfold higher mortality. However, the role of platelets in this state remains poorly understood. We set out to identify molecular changes that may underpin platelet dysfunction after major injury and to determine how they relate to coagulopathy and outcome. We performed a range of hemostatic and platelet-specific studies in blood s les obtained from critically injured patients within 2 hours of injury and collected prospective data on patient characteristics and clinical outcomes. We observed that, although platelet counts were preserved above critical levels, circulating platelets s led from trauma patients exhibited a profoundly reduced response to both collagen and the selective glycoprotein VI (GPVI) agonist collagen-related peptide, compared with those from healthy volunteers. These responses correlated closely with overall clot strength and mortality. Surface expression of the collagen receptors GPIbα and GPVI was reduced on circulating platelets in trauma patients, with increased levels of the shed ectodomain fragment of GPVI detectable in plasma. Levels of shed GPVI were highest in patients with more severe injuries and TIC. Collectively, these observations demonstrate that platelets experience a loss of GPVI and GPIbα after severe injury and translate into a reduction in the responsiveness of platelets during active hemorrhage. In turn, they are associated with reduced hemostatic competence and increased mortality. Targeting proteolytic shedding of platelet receptors is a potential therapeutic strategy for maintaining hemostatic competence in bleeding and improving the efficacy of platelet transfusions.
Publisher: Cold Spring Harbor Laboratory
Date: 12-01-2022
DOI: 10.1101/2022.01.11.475814
Abstract: Prostacyclin is one of the bodies fundamental signalling pathways. It has long been considered principally anti-thrombotic hormone derived from the vascular endothelium. The role of non-vascular sources in prostacyclin synthesis has not been systematically evaluated, however, due to a lack of tools resulting in an underappreciation of its role in other contexts. Here we used cellspecific knockout mice and human tissues to show that lung, and other tissues, are powerful producers of prostacyclin independent of their vascular components. Instead, in mice and humans, lung prostacyclin synthesis is associated with fibroblasts. The fibroblast-derived prostaglandins enter the circulation and provide systemic anti-thrombotic protection. These observations define a new paradigm in prostacyclin biology in which fibroblast/non-vascular-derived prostacyclin works in parallel with endothelium-derived prostaglandins to control cardiovascular health and potentially a broad range of other biology. These results may explain how local diseases of the lung and elsewhere result in cardiovascular risk.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 10-2015
DOI: 10.1161/ATVBAHA.115.306219
Abstract: Reduced antiplatelet drug efficacy occurs in conditions of increased platelet turnover, associated with increased proportions of drug-free, that is, uninhibited, platelets. Here, we detail mechanisms by which drug-free platelets promote platelet aggregation in the face of standard antiplatelet therapy. To model standard antiplatelet therapy, platelets were treated in vitro with aspirin, the P2Y 12 receptor blocker prasugrel active metabolite, or aspirin plus prasugrel active metabolite. Different proportions of uninhibited platelets were then introduced. Light transmission aggregometry analysis demonstrated clear positive associations between proportions of drug-free platelets and percentage platelet aggregation in response to a range of platelet agonists. Using differential platelet labeling coupled with advanced flow cytometry and confocal imaging we found aggregates formed in mixtures of aspirin-inhibited platelets together with drug-free platelets were characterized by intermingled platelet populations. This distribution is in accordance with the ability of drug-free platelets to generate thromboxane A 2 and so drive secondary platelet activation. Conversely, aggregates formed in mixtures of prasugrel active metabolite–inhibited or aspirin plus prasugrel active metabolite–inhibited platelets together with drug-free platelets were characterized by distinct cores of drug-free platelets. This distribution is consistent with the ability of drug-free platelets to respond to the secondary activator ADP. These experiments are the first to image the interactions of inhibited and uninhibited platelets in the formation of platelet aggregates. They demonstrate that a general population of platelets can contain subpopulations that respond strikingly differently to overall stimulation of the population and so act as the seed for platelet aggregation.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 05-2009
DOI: 10.1161/ATVBAHA.108.183160
Abstract: Objectives— Statins and fibrates are hypolipidemic drugs which decrease cardiac events in in iduals without raised levels of cholesterol. These drugs inhibit platelet function, but the mechanisms by which this pleiotropic effect is exerted are not known. Methods and Results— We used a range of approaches to show statins inhibit human platelet activation in vitro while engaging PPARα and PPARγ. The effects of simvastatin were prevented by the PPARγ antagonist GW9662 or the PPARα antagonist GW6471. In a small-scale human study fluvastatin activated PPARα and PPARγ in platelets and reduced aggregation in response to arachidonic acid ex vivo. The effects of fenofibrate were prevented by PPARα antagonism with GW6471. Fenofibrate increased bleeding time in wild-type, but not in PPARα −/− mice. The inhibitory effect of fenofibrate, but not simvastatin, on aggregation was prevented by deletion of PPARα in murine platelets. PKCα, which influences platelet activation, associated and immune-precipitated with PPARγ in platelets stimulated with statins and with PPARα in platelets stimulated with fenofibrate. Conclusions— This study is the first to provide a unifying explanation of how fibrates and statins reduce thrombotic and cardiovascular risk. Our findings that PPARs associate with PKCα in platelets also provide a mechanism by which these effects are mediated.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 27-10-2015
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 09-2011
DOI: 10.1161/ATVBAHA.111.226241
Abstract: Therapeutic hypothermia is successfully used, for ex le, in cardiac surgery to protect organs from ischemia. Cardiosurgical procedures, especially in combination with extracorporeal circulation, and hypothermia itself are potentially prothrombotic. Despite the obvious need, the long half-life of antiplatelet drugs and thus the risk of postoperative bleedings have restricted their use in cardiac surgery. We describe here the design and testing of a unique recombinant hypothermia-controlled antiplatelet fusion protein with the aim of providing increased safety of hypothermia, as well as cardiac surgery. An elastin-mimetic polypeptide was fused to an activation-specific glycoprotein (GP) IIb/IIIa-blocking single-chain antibody. In silico modeling illustrated the sterical hindrance of a β-spiral conformation of elastin-mimetic polypeptide preventing the single-chain antibody from inhibiting GPIIb/IIIa at 37°C. Circular dichroism spectra demonstrated reverse temperature transition, and flow cytometry showed binding to and blocking of GPIIb/IIIa at hypothermic body temperature (≤32°C) but not at normal body temperature. In vivo thrombosis in mice was selectively inhibited at hypothermia but not at 37°C. This is the first description of a broadly applicable pharmacological strategy by which the activity of a potential drug can be controlled by temperature. In particular, this drug steerability may provide substantial benefits for antiplatelet therapy.
Publisher: Public Library of Science (PLoS)
Date: 23-05-2011
Publisher: American Society of Hematology
Date: 30-11-2022
DOI: 10.1182/BLOODADVANCES.2022007099
Abstract: The proportion of young platelets, also known as newly formed or reticulated, within the overall platelet population has been clinically correlated with adverse cardiovascular outcomes. However, our understanding of this is incomplete because of limitations in the technical approaches available to study platelets of different ages. In this study, we have developed and validated an in vivo temporal labeling approach using injectable fluorescent antiplatelet antibodies to sub ide platelets by age and assess differences in functional and molecular characteristics. With this approach, we found that young platelets (& hours old) in comparison with older platelets respond to stimuli with greater calcium flux and degranulation and contribute more to the formation of thrombi in vitro and in vivo. Sequential s ling confirmed this altered functionality to be independent of platelet size, with distribution of sizes of tracked platelets commensurate with the global platelet population throughout their 5-day lifespan in the circulation. The age-associated decrease in thrombotic function was accompanied by significant decreases in the surface expression of GPVI and CD31 (PECAM-1) and an increase in CD9. Platelet messenger RNA (mRNA) content also decreased with age but at different rates for in idual mRNAs indicating apparent conservation of those encoding granule proteins. Our pulse-chase–type approach to define circulating platelet age has allowed timely reexamination of commonly held beliefs regarding size and reactivity of young platelets while providing novel insights into the temporal regulation of receptor and protein expression. Overall, future application of this validated tool will inform age-based platelet heterogeneity in physiology and disease.
Publisher: Elsevier BV
Date: 07-2020
DOI: 10.1111/JTH.14826
Publisher: Georg Thieme Verlag KG
Date: 2012
DOI: 10.1160/TH11-10-0727
Abstract: From the discovery of the platelet glycoprotein (GP) IIb/IIIa and identification of its central role in haemostasis, the integrin GPIIb/IIIa (αIIbβ3, CD41/CD61) was destined to be an anti-thrombotic target. The subsequent successful development of intravenous ligand-mimetic inhibitors occurred during a time of limited understanding of integrin physiology. Although efficient inhibitors of ligand binding, they also mimic ligand function. In the case of GPIIb/IIIa inhibitors, despite strongly inhibiting platelet aggregation, paradoxical fibrinogen binding and platelet activation can occur. The quick progression to development of small-molecule orally available inhibitors meant that this approach inherited many potential flaws, which together with a short half-life resulted in an increase in mortality and a halt to the numerous pharmaceutical development programs. Limited clinical benefits, together with the success of other anti-thrombotic drugs, in particular P2Y12 ADP receptor blockers, have also led to a restrictive use of intravenous GPIIb/ IIIa inhibitors. However, with a greater understanding of this key platelet-specific integrin, GPIIb/IIIa remains a potentially attractive target and future drug developments will be better informed by the lessons learnt from taking the current inhibitors back to the bench. This overview will review the physiology behind the inherent problems of a ligand-based integrin inhibitor design and discuss novel promising approaches for GPIIb/IIIa inhibition.
Publisher: Public Library of Science (PLoS)
Date: 28-04-2011
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 05-2017
DOI: 10.1161/ATVBAHA.116.308763
Abstract: Aspirin together with thienopyridine P2Y 12 inhibitors, commonly clopidogrel, is a cornerstone of antiplatelet therapy. However, many patients receiving this therapy display high on-treatment platelet reactivity, which is a major therapeutic hurdle to the prevention of recurrent thrombotic events. The emergence of uninhibited platelets after thrombopoiesis has been proposed as a contributing factor to high on-treatment platelet reactivity. Here, we investigate the influences of platelet turnover on platelet aggregation in the face of different dual-antiplatelet therapy strategies. Traditional light transmission aggregometry, cytometry, advanced flow cytometric imaging, and confocal microscopy were used to follow the interactions of populations of platelets from healthy volunteers and patients with stable cardiovascular disease. Newly formed, reticulated platelets overproportionately contributed to, and clustered at, the core of forming aggregates. This phenomenon was particularly observed in s les from patients treated with aspirin plus a thienopyridine, but was absent in s les taken from patients treated with aspirin plus ticagrelor. Reticulated platelets are more reactive than older platelets and act as seeds for the formation of platelet aggregates even in the presence of antiplatelet therapy. This is coherent with the emergence of an uninhibited subpopulation of reticulated platelets during treatment with aspirin plus thienopyridine, explained by the short pharmacokinetic half-lives of these drugs. This phenomenon is absent during treatment with ticagrelor, because of its longer half-life and ability to act as a circulating inhibitor. These data highlight the important influences of pharmacokinetics on antiplatelet drug efficacies, especially in diseases associated with increased platelet turnover.
Publisher: American Society for Clinical Investigation
Date: 02-11-2018
Publisher: American Society for Clinical Investigation
Date: 25-03-2019
DOI: 10.1172/JCI121985
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 12-10-2023
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 2022
DOI: 10.1161/ATVBAHA.121.317113
Abstract: Platelets are central to acute myocardial infarction (MI). How the platelet proteome is altered during MI is unknown. We sought to describe changes in the platelet proteome during MI and identify corresponding functional consequences. Platelets from patients experiencing ST-segment–elevation MI (STEMI) before and 3 days after treatment (n=30) and matched patients with severe stable coronary artery disease before and 3 days after coronary artery bypass grafting (n=25) underwent quantitative proteomic analysis. Elevations in the proteins S100A8 and S100A9 were detected at the time of STEMI compared with stable coronary artery disease (S100A8: FC, 2.00 false discovery rate, 0.05 S100A9: FC, 2.28 false discovery rate, 0.005). During STEMI, only S100A8 mRNA and protein levels were correlated in platelets ( R =0.46, P =0.012). To determine whether de novo protein synthesis occurs, activated platelets were incubated with 13C-labeled amino acids for 24 hours and analyzed by mass spectrometry. No incorporation was confidently detected. Platelet S100A8 and S100A9 was strongly correlated with neutrophil abundance at the time of STEMI. When isolated platelets and neutrophils were coincubated under quiescent and activated conditions, release of S100A8 from neutrophils resulted in uptake of S100A8 by platelets. Neutrophils released S100A8/A9 as free heterodimer, rather than in vesicles or extracellular traps. In the community-based Bruneck study (n=338), plasma S100A8/A9 was inversely associated with platelet reactivity—an effect abrogated by aspirin. Leukocyte-to-platelet protein transfer may occur in a thromboinflammatory environment such as STEMI. Plasma S100A8/A9 was negatively associated with platelet reactivity. These findings highlight neutrophils as potential modifiers for thrombotic therapies in coronary artery disease.
Publisher: Georg Thieme Verlag KG
Date: 2009
DOI: 10.1160/TH09-04-0215
Abstract: Aspirin and clopidogrel are key anti-thrombotic therapies. Results from platelet reactivity testing during therapy, have been shown to correlate with future events and would allow for the optimisation of therapy. However, there is little agreement among current tests and there remains a clear clinical need for a universal standardised test. It was the objective of this study to explore the potential of 96-well plate aggregometry as a definitive clinical test of platelet reactivity with respect to aspirin and clopidogrel.A small non-blinded trial of 16 healthy male volunteers assigned to seven days of aspirin (75mg/day) or clopidogrel (75mg/day) therapy. Blood was collected before and on day 7 of treatment. Platelet aggregation was measured using a 96-well plate based aggregation method, and thrombi adhesion measured by colourimetric assay. Platelet agonists used were ADP (0.1–30µM), arachidonic acid (0.03–1.3mM), collagen (0.1–30µg/ml), adrenaline (0.001–100µM), ristocetin (0.2–3mg/ ml),TRAP6 amide (0.130µM) and U46619 (0.130µM). Concentration response curves were constructed to each agonist under the various conditions and used to extract data such as log EC50, Hill slope, and area under the curve. These demonstrated low intraand inter-assay variability and strong discrimination of drug effects.This study demonstrates the ability of the 96-well plate based aggregation and adhesion method to detect and differentiate between stable aspirin and clopidogrel treatment in healthy volunteers.Moreover,this assay marries the ability to test subjects or patients using a range of platelet agonists with more rapidity and ease than the current gold standard platelet assay, traditional light transmission aggregometry, making it a serious alternative assay for use in clinical settings.
Publisher: Wiley
Date: 19-01-2018
DOI: 10.1111/APHA.13028
Abstract: The current guidelines following an acute coronary syndrome recommend dual-antiplatelet therapy (DAPT) (aspirin plus a P2Y To explore how exercise-induced improvements in vascular and platelet function affect the efficacy of DAPT, in a cross-sectional study of men with different physical activity levels (training status). A total of 42 healthy, normal-weight, middle-aged men were ided into 3 groups: untrained, moderately trained and well-trained. Their platelet reactivity (agonist-induced % aggregation) was investigated in platelet-rich plasma at rest and after inhibition with aspirin and ticagrelor and/or prostacyclin and nitric oxide added to the blood in vitro, and after physiological tests of vascular function passive movement of the leg, flow-mediated dilation and one-leg knee-extensor exercise. Vascular function of the femoral artery (changes in arterial blood flow) was assessed by ultrasound Doppler. Platelets from the well-trained subjects had lower basal reactivity, a higher sensitivity to the anti-aggregatory effects of prostacyclin and were more potently inhibited by DAPT compared to the untrained subjects. The moderately trained and well-trained subjects had a superior vascular function compared to untrained subjects, and their platelets were more inhibited by the passive movement, flow-mediated dilation and one-leg knee-extensor exercise. A habitually active lifestyle leads to an increased platelet sensitivity to pharmacological and physiological platelet inhibitors. We suggest that physical activity habits (training status) should be considered when personalizing and optimizing antithrombotic treatment strategies.
Publisher: Proceedings of the National Academy of Sciences
Date: 12-08-2019
Abstract: Membrane ballooning is a fundamental mechanism by which platelets contribute to thrombin generation. However, this process has not previously been described in human disease. In this study, we demonstrated the presence of ballooning procoagulant platelets free in the circulation of critically injured humans, a phenomenon which results in systemic generation of thrombin and contributes to an acute coagulopathy. The surfaces of ballooning platelets were decorated with the damage-associated molecular pattern histone H4, and exposure of healthy platelets to histone caused membrane disruption and recapitulated the phenotypic changes in injured patients. These findings provide a description of platelet ballooning contributing to human disease and identify histone release from injured tissues as a driver of the procoagulant ballooning process.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 26-06-2012
DOI: 10.1161/CIRCULATIONAHA.111.030312
Abstract: Molecular imaging is a fast emerging technology allowing noninvasive detection of vascular pathologies. However, imaging modalities offering high resolution currently do not allow real-time imaging. We hypothesized that contrast-enhanced ultrasound with microbubbles (MBs) selectively targeted to activated platelets would offer high-resolution, real-time molecular imaging of evolving and dissolving arterial thrombi. Lipid-shell based gas-filled MBs were conjugated to either a single-chain antibody specific for activated glycoprotein IIb/IIIa via binding to a Ligand-Induced Binding Site (LIBS-MBs) or a nonspecific single-chain antibody (control MBs). Successful conjugation was assessed in flow cytometry and immunofluorescence double staining. LIBS-MBs but not control MBs strongly adhered to both immobilized activated platelets and microthrombi under flow. Thrombi induced in carotid arteries of C57Bl6 mice in vivo by ferric chloride injury were then assessed with ultrasound before and 20 minutes after MB injection through the use of gray-scale area intensity measurement. Gray-scale units converted to decibels demonstrated a significant increase after LIBS-MB but not after control MB injection (9.55±1.7 versus 1.46±1.3 dB P .01). Furthermore, after thrombolysis with urokinase, LIBS-MB ultrasound imaging allows monitoring of the reduction of thrombus size ( P .001). We demonstrate that glycoprotein IIb/IIIa–targeted MBs specifically bind to activated platelets in vitro and allow real-time molecular imaging of acute arterial thrombosis and monitoring of the success or failure of pharmacological thrombolysis in vivo.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 17-02-2015
DOI: 10.1161/CIRCULATIONAHA.114.011591
Abstract: Cardiovascular side effects associated with cyclooxygenase-2 inhibitor drugs dominate clinical concern. Cyclooxygenase-2 is expressed in the renal medulla where inhibition causes fluid retention and increased blood pressure. However, the mechanisms linking cyclooxygenase-2 inhibition and cardiovascular events are unknown and no biomarkers have been identified. Transcriptome analysis of wild-type and cyclooxygenase-2 −/− mouse tissues revealed 1 gene altered in the heart and aorta, but genes altered in the renal medulla, including those regulating the endogenous nitric oxide synthase inhibitors asymmetrical dimethylarginine (ADMA) and monomethyl- l -arginine. Cyclo-oxygenase-2 −/− mice had increased plasma levels of ADMA and monomethyl- l -arginine and reduced endothelial nitric oxide responses. These genes and methylarginines were not similarly altered in mice lacking prostacyclin receptors. Wild-type mice or human volunteers taking cyclooxygenase-2 inhibitors also showed increased plasma ADMA. Endothelial nitric oxide is cardio-protective, reducing thrombosis and atherosclerosis. Consequently, increased ADMA is associated with cardiovascular disease. Thus, our study identifies ADMA as a biomarker and mechanistic bridge between renal cyclooxygenase-2 inhibition and systemic vascular dysfunction with nonsteroidal anti-inflammatory drug usage. We identify the endogenous endothelial nitric oxide synthase inhibitor ADMA as a biomarker and mechanistic bridge between renal cyclooxygenase-2 inhibition and systemic vascular dysfunction.
Publisher: BMJ
Date: 18-10-2010
Abstract: Aspirin is now widely accepted as the first-line antithrombotic platelet therapy for at-risk in iduals. During the last decade or so it has also become established that co-administering antagonists of the ADP receptor P2Y(12) with aspirin further reduces the risk of acute thrombotic events. By the nature of its evolution, this therapeutic approach assumes that P2Y(12) receptor antagonists will be added to aspirin, and this therefore dominates the design of clinical trials. This strategy has resulted in the generation of a large body of clinical evidence showing the benefit of aspirin plus P2Y(12) receptor antagonists, largely from studies with clopidogrel and more recently from those with prasugrel and ticagrelor, but with obvious limitations in terms of residual ischaemic event rates and bleeding complications. It is our hypothesis, however, that when administered in the presence of potent P2Y(12) receptor antagonists, aspirin could actually increase total cardiovascular risk, although this has never been tested in large outcome studies. Clearly, this potentially negative interaction could be of relevance to millions of patients.
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: Start date not available
End Date: End date not available
Funder: British Heart Foundation
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