Role of the NO-GC/cGMP signaling pathway in platelet biomechanics

Cyclic guanosine monophosphate (cGMP) is a second messenger produced by the NO-sensitive guanylyl cyclase (NO-GC). The NO-GC/cGMP pathway in platelets has been extensively studied. However, its role in regulating the biomechanical properties of platelets has not yet been addressed and remains unknown. We therefore investigated the stiffness of living platelets after treatment with the NO-GC stimulator riociguat or the NO-GC activator cinaciguat using scanning ion conductance microscopy (SICM). Stimulation of human and murine platelets with cGMP-modulating drugs decreased cellular stiffness and downregulated P-selectin, a marker for platelet activation. We also quantified changes in platelet shape using deep learning-based platelet morphometry, finding that platelets become more circular upon treatment with cGMP-modulating drugs. To test for clinical applicability of NO-GC stimulators in the context of increased thrombogenicity risk, we investigated the effect of riociguat on platelets from human immunodeficiency virus (HIV)-positive patients taking abacavir sulfate (ABC)-containing regimens. Our results corroborate a functional role of the NO-GC/cGMP pathway in platelet biomechanics, indicating that biomechanical properties such as stiffness or shape could be used as novel biomarkers in clinical research.

Fibrinogen-mimicking, multiarm nanovesicles for human thrombus-specific delivery of tissue plasminogen activator and targeted thrombolytic therapy

Clinical use of tissue plasminogen activator (tPA) in thrombolytic therapy is limited by its short circulation time and hemorrhagic side effects. Inspired by fibrinogen binding to activated platelets, we report a fibrinogen-mimicking, multiarm nanovesicle for thrombus-specific tPA delivery and targeted thrombolysis. This biomimetic system is based on the lipid nanovesicle coated with polyethylene glycol (PEG) terminally conjugated with a cyclic RGD (cRGD) peptide. Our experiments with human blood demonstrated its highly selective binding to activated platelets and efficient tPA release at a thrombus site under both static and physiological flow conditions. Its clot dissolution time in a microfluidic system was comparable to that of free tPA. Furthermore, we report a purpose-built computational model capable of simulating targeted thrombolysis of the tPA-loaded nanovesicle and with a potential in predicting the dynamics of thrombolysis in physiologically realistic scenarios. This combined experimental and computational work presents a promising platform for development of thrombolytic nanomedicines.

Multiyear Evaluation of Fungicide Efficacy and Application Timing for Control of Southern Rust in Hybrid Corn in Arkansas

The efficacy and timing of eight foliar fungicides to manage southern rust of corn (caused by Puccinia polysora Underwood) was investigated over 4 years in three field experiments. Each experiment consisted of one-, two-, or three-fungicide application timings at tassel, milk, or dent growth stages with quinone outside inhibitor (QoI), demethylation inhibitor (DMI), or QoI + DMI fungicides. Each year trace amounts of southern rust were observed in the field at tassel, except in 2018, when rust was not observed until physiological maturity. Southern rust severity on ear leaf and two leaves above the ear leaf was approximately 50, 35, 75, and 0% at dent in 2015, 2016, 2017, and 2018, respectively. Applications that contained a QoI or QoI + DMI fungicide provided greater southern rust control than DMI fungicides, with little variation within fungicide classes. Applications of QoI or QoI + DMI fungicides applied at tassel provided greater disease control (52.5%) than those applied at milk (5.8%) or dent (1.4%), and greater yield protection (40.4%) than those applied at milk (23.7%) or dent (2.6%) when final rust development was severe (>40%). When rust development increased later in the season, after milk growth stage, a trend of better disease control was observed with fungicides applied at milk (57.8%) compared with tassel (35.2%), but grain yield protection was similar, with an average yield protection of 7.4%. There was no yield benefit with fungicides applied in the absence of disease or at the dent growth stage. Southern rust was most effectively managed with QoI or QoI + DMI fungicides applied at tassel when southern rust was present and environmental conditions favored rust development.

HIV Antivirals Affect Endothelial Activation and Endothelial-Platelet Crosstalk

RATIONALE

People living with HIV on effective antiretroviral therapy are at increased risk of cardiovascular complications, possibly due to off-target drug effects. Some studies have associated antiretroviral therapy with increased risk of myocardial infarction and endothelial dysfunction, but a link between endothelial function and antiretrovirals has not been established.

OBJECTIVE

To determine the effects of antiretrovirals in common clinical use upon in vitro endothelial function to better understand cardiovascular risk in people living with HIV.

METHODS AND RESULTS

Human umbilical cord vein endothelial cells or human coronary artery endothelial cells were pretreated with the antiretrovirals abacavir sulphate (ABC), tenofovir disoproxil fumarate, or tenofovir alafenamide. Expression of adhesion molecules, ectonucleotidases (CD39 and CD73), tissue factor (TF), endothelial-derived microparticle (EMP) numbers and phenotype, and platelet activation were evaluated by flow cytometry. TF and ectonucleotidase activities were measured using colourimetric plate-based assays. ABC-treated endothelial cells had higher levels of ICAM (intercellular adhesion molecule)-1 and TF expression following TNF (tumor necrosis factor)-α stimulation. In contrast, tenofovir disoproxil fumarate and tenofovir alafenamide treatment gave rise to greater populations of CD39⁺CD73⁺ cells. These cell surface differences were also observed within EMP repertoires. ABC-treated cells and EMP had greater TF activity, while tenofovir disoproxil fumarate- and tenofovir alafenamide-treated cells and EMP displayed higher ectonucleotidase activity. Finally, EMP isolated from ABC-treated cells enhanced collagen-evoked platelet integrin activation and α-granule release.

CONCLUSIONS

We report differential effects of antiretrovirals used in the treatment of HIV upon endothelial function. ABC treatment led to an inflammatory, prothrombotic endothelial phenotype that promoted platelet activation. In contrast, tenofovir disoproxil fumarate and tenofovir alafenamide conferred potentially cardioprotective properties associated with ectonucleotidase activity. These observations establish a link between antiretrovirals and specific functional effects that provide insight into cardiovascular disease in people living with HIV.

The ARRIVE guidelines 2.0: Updated guidelines for reporting animal research

Reproducible science requires transparent reporting. The ARRIVE guidelines (Animal Research: Reporting of In Vivo Experiments) were originally developed in 2010 to improve the reporting of animal research. They consist of a checklist of information to include in publications describing in vivo experiments to enable others to scrutinise the work adequately, evaluate its methodological rigour, and reproduce the methods and results. Despite considerable levels of endorsement by funders and journals over the years, adherence to the guidelines has been inconsistent, and the anticipated improvements in the quality of reporting in animal research publications have not been achieved. Here, we introduce ARRIVE 2.0. The guidelines have been updated and information reorganised to facilitate their use in practice. We used a Delphi exercise to prioritise and divide the items of the guidelines into 2 sets, the "ARRIVE Essential 10," which constitutes the minimum requirement, and the "Recommended Set," which describes the research context. This division facilitates improved reporting of animal research by supporting a stepwise approach to implementation. This helps journal editors and reviewers verify that the most important items are being reported in manuscripts. We have also developed the accompanying Explanation and Elaboration document, which serves (1) to explain the rationale behind each item in the guidelines, (2) to clarify key concepts, and (3) to provide illustrative examples. We aim, through these changes, to help ensure that researchers, reviewers, and journal editors are better equipped to improve the rigour and transparency of the scientific process and thus reproducibility.

The ARRIVE guidelines 2.0: updated guidelines for reporting animal research

Reproducible science requires transparent reporting. The ARRIVE guidelines (Animal Research: Reporting of In Vivo Experiments) were originally developed in 2010 to improve the reporting of animal research. They consist of a checklist of information to include in publications describing in vivo experiments to enable others to scrutinise the work adequately, evaluate its methodological rigour, and reproduce the methods and results. Despite considerable levels of endorsement by funders and journals over the years, adherence to the guidelines has been inconsistent, and the anticipated improvements in the quality of reporting in animal research publications have not been achieved. Here, we introduce ARRIVE 2.0. The guidelines have been updated and information reorganised to facilitate their use in practice. We used a Delphi exercise to prioritise and divide the items of the guidelines into 2 sets, the 'ARRIVE Essential 10,' which constitutes the minimum requirement, and the 'Recommended Set,' which describes the research context. This division facilitates improved reporting of animal research by supporting a stepwise approach to implementation. This helps journal editors and reviewers verify that the most important items are being reported in manuscripts. We have also developed the accompanying Explanation and Elaboration document, which serves (1) to explain the rationale behind each item in the guidelines, (2) to clarify key concepts, and (3) to provide illustrative examples. We aim, through these changes, to help ensure that researchers, reviewers, and journal editors are better equipped to improve the rigour and transparency of the scientific process and thus reproducibility.

The ARRIVE guidelines 2.0: Updated guidelines for reporting animal research

Reproducible science requires transparent reporting. The ARRIVE guidelines (Animal Research: Reporting of In Vivo Experiments) were originally developed in 2010 to improve the reporting of animal research. They consist of a checklist of information to include in publications describing in vivo experiments to enable others to scrutinise the work adequately, evaluate its methodological rigour, and reproduce the methods and results. Despite considerable levels of endorsement by funders and journals over the years, adherence to the guidelines has been inconsistent, and the anticipated improvements in the quality of reporting in animal research publications have not been achieved. Here, we introduce ARRIVE 2.0. The guidelines have been updated and information reorganised to facilitate their use in practice. We used a Delphi exercise to prioritise and divide the items of the guidelines into 2 sets, the "ARRIVE Essential 10," which constitutes the minimum requirement, and the "Recommended Set," which describes the research context. This division facilitates improved reporting of animal research by supporting a stepwise approach to implementation. This helps journal editors and reviewers verify that the most important items are being reported in manuscripts. We have also developed the accompanying Explanation and Elaboration document, which serves (1) to explain the rationale behind each item in the guidelines, (2) to clarify key concepts, and (3) to provide illustrative examples. We aim, through these changes, to help ensure that researchers, reviewers, and journal editors are better equipped to improve the rigour and transparency of the scientific process and thus reproducibility.

The ARRIVE guidelines 2.0: Updated guidelines for reporting animal research

Reproducible science requires transparent reporting. The ARRIVE guidelines (Animal Research: Reporting of In Vivo Experiments) were originally developed in 2010 to improve the reporting of animal research. They consist of a checklist of information to include in publications describing in vivo experiments to enable others to scrutinise the work adequately, evaluate its methodological rigour, and reproduce the methods and results. Despite considerable levels of endorsement by funders and journals over the years, adherence to the guidelines has been inconsistent, and the anticipated improvements in the quality of reporting in animal research publications have not been achieved. Here, we introduce ARRIVE 2.0. The guidelines have been updated and information reorganised to facilitate their use in practice. We used a Delphi exercise to prioritise and divide the items of the guidelines into 2 sets, the "ARRIVE Essential 10," which constitutes the minimum requirement, and the "Recommended Set," which describes the research context. This division facilitates improved reporting of animal research by supporting a stepwise approach to implementation. This helps journal editors and reviewers verify that the most important items are being reported in manuscripts. We have also developed the accompanying Explanation and Elaboration (E&E) document, which serves (1) to explain the rationale behind each item in the guidelines, (2) to clarify key concepts, and (3) to provide illustrative examples. We aim, through these changes, to help ensure that researchers, reviewers, and journal editors are better equipped to improve the rigour and transparency of the scientific process and thus reproducibility.

The ARRIVE guidelines 2.0: updated guidelines for reporting animal research

Reproducible science requires transparent reporting. The ARRIVE guidelines (Animal Research: Reporting of In Vivo Experiments) were originally developed in 2010 to improve the reporting of animal research. They consist of a checklist of information to include in publications describing in vivo experiments to enable others to scrutinise the work adequately, evaluate its methodological rigour and reproduce the methods and results. Despite considerable levels of endorsement by funders and journals over the years, adherence to the guidelines has been inconsistent, and the anticipated improvements in the quality of reporting in animal research publications have not been achieved. Here, we introduce ARRIVE 2.0. The guidelines have been updated and information reorganised to facilitate their use in practice. We used a Delphi exercise to prioritise and divide the items of the guidelines into two sets, the 'ARRIVE Essential 10', which constitutes the minimum requirement, and the 'Recommended Set', which describes the research context. This division facilitates improved reporting of animal research by supporting a stepwise approach to implementation. This helps journal editors and reviewers verify that the most important items are being reported in manuscripts. We have also developed the accompanying Explanation and Elaboration document, which serves (1) to explain the rationale behind each item in the guidelines, (2) to clarify key concepts and (3) to provide illustrative examples. We aim, through these changes, to help ensure that researchers, reviewers and journal editors are better equipped to improve the rigour and transparency of the scientific process and thus reproducibility.

The ARRIVE guidelines 2.0: Updated guidelines for reporting animal research

Reproducible science requires transparent reporting. The ARRIVE guidelines (Animal Research: Reporting of In Vivo Experiments) were originally developed in 2010 to improve the reporting of animal research. They consist of a checklist of information to include in publications describing in vivo experiments to enable others to scrutinise the work adequately, evaluate its methodological rigour, and reproduce the methods and results. Despite considerable levels of endorsement by funders and journals over the years, adherence to the guidelines has been inconsistent, and the anticipated improvements in the quality of reporting in animal research publications have not been achieved. Here, we introduce ARRIVE 2.0. The guidelines have been updated and information reorganised to facilitate their use in practice. We used a Delphi exercise to prioritise and divide the items of the guidelines into 2 sets, the "ARRIVE Essential 10," which constitutes the minimum requirement, and the "Recommended Set," which describes the research context. This division facilitates improved reporting of animal research by supporting a stepwise approach to implementation. This helps journal editors and reviewers verify that the most important items are being reported in manuscripts. We have also developed the accompanying Explanation and Elaboration document, which serves (1) to explain the rationale behind each item in the guidelines, (2) to clarify key concepts, and (3) to provide illustrative examples. We aim, through these changes, to help ensure that researchers, reviewers, and journal editors are better equipped to improve the rigour and transparency of the scientific process and thus reproducibility.

Reporting animal research: Explanation and elaboration for the ARRIVE guidelines 2.0

Improving the reproducibility of biomedical research is a major challenge. Transparent and accurate reporting is vital to this process; it allows readers to assess the reliability of the findings and repeat or build upon the work of other researchers. The ARRIVE guidelines (Animal Research: Reporting In Vivo Experiments) were developed in 2010 to help authors and journals identify the minimum information necessary to report in publications describing in vivo experiments. Despite widespread endorsement by the scientific community, the impact of ARRIVE on the transparency of reporting in animal research publications has been limited. We have revised the ARRIVE guidelines to update them and facilitate their use in practice. The revised guidelines are published alongside this paper. This explanation and elaboration document was developed as part of the revision. It provides further information about each of the 21 items in ARRIVE 2.0, including the rationale and supporting evidence for their inclusion in the guidelines, elaboration of details to report, and examples of good reporting from the published literature. This document also covers advice and best practice in the design and conduct of animal studies to support researchers in improving standards from the start of the experimental design process through to publication.

The ARRIVE guidelines 2.0: Updated guidelines for reporting animal research

Reproducible science requires transparent reporting. The ARRIVE guidelines (Animal Research: Reporting of In Vivo Experiments) were originally developed in 2010 to improve the reporting of animal research. They consist of a checklist of information to include in publications describing in vivo experiments to enable others to scrutinise the work adequately, evaluate its methodological rigour, and reproduce the methods and results. Despite considerable levels of endorsement by funders and journals over the years, adherence to the guidelines has been inconsistent, and the anticipated improvements in the quality of reporting in animal research publications have not been achieved. Here, we introduce ARRIVE 2.0. The guidelines have been updated and information reorganised to facilitate their use in practice. We used a Delphi exercise to prioritise and divide the items of the guidelines into 2 sets, the "ARRIVE Essential 10," which constitutes the minimum requirement, and the "Recommended Set," which describes the research context. This division facilitates improved reporting of animal research by supporting a stepwise approach to implementation. This helps journal editors and reviewers verify that the most important items are being reported in manuscripts. We have also developed the accompanying Explanation and Elaboration (E&E) document, which serves (1) to explain the rationale behind each item in the guidelines, (2) to clarify key concepts, and (3) to provide illustrative examples. We aim, through these changes, to help ensure that researchers, reviewers, and journal editors are better equipped to improve the rigour and transparency of the scientific process and thus reproducibility.

Radiolabelling and immunohistochemistry reveal platelet recruitment into lungs and platelet migration into airspaces following LPS inhalation in mice

INTRODUCTION

Platelets are under investigation for their role in host defence and inflammatory lung diseases and have been demonstrated to be recruited to the lung. However, the mechanisms and consequences of platelet recruitment into lungs are poorly understood. We have utilised a murine model to investigate the mechanisms of platelet involvement in lung inflammation induced by intranasal administration of LPS.

OBJECTIVES

Our aim was to characterise lung platelet recruitment following LPS inhalation in mice using immunohistochemistry, and non-invasive and invasive radiolabelled platelet tracking techniques.

RESULTS

Intranasal administration of LPS caused an increase in lung platelet staining in lung tissue and elicited the recruitment of radiolabelled platelets into the lung. Prior to these responses in the lung, we observed an earlier decrease in blood platelet counts, temporally associated with platelet recruitment to the liver and spleen. Non-invasive measurements of thoracic radioactivity reflected changes in blood counts rather than extravascular lung platelet recruitment. However, both in situ counting of radiolabelled platelets and immunostaining for platelet surface markers showed LPS-induced increases in extravascular platelets into lung airspaces suggesting that some of the platelets recruited to the lung enter air spaces.

CONCLUSIONS

Intranasal administration of LPS activates the innate immune response which includes a fall in peripheral blood platelet counts with subsequent platelet recruitment to the lung, spleen and liver, measured by immunohistochemistry and radiolabelling techniques.

Pharmacological impact of antiretroviral therapy on platelet function to investigate human immunodeficiency virus-associated cardiovascular risk

BACKGROUND AND PURPOSE

Some clinical studies have reported increased myocardial infarction in people living with human immunodeficiency virus (HIV) taking the antiretroviral abacavir sulphate (ABC). Given that clinical studies contain confounding variables (e.g., HIV-associated factors), we investigated the pharmacological effects of antiretrovirals on platelet function in HIV-negative volunteers in order to identify mechanisms of increased cardiovascular risk.

EXPERIMENTAL APPROACH

Platelets were isolated from healthy volunteers and HIV-negative subjects enrolled on a Phase I clinical trial and platelet function evaluated using aggregometry and flow cytometry. In vivo platelet thromboembolism was monitored in anaesthetized mice.

KEY RESULTS

Human platelet aggregation was unaffected by all antiretrovirals tested, but ABC treatment led uniquely to increased platelet granule release. ABC also interrupted NO-mediated inhibition of platelet aggregation and increased in vivo aggregation in mice. Another antiretroviral, tenofovir, did not affect platelet function. Furthermore, aggregation and activation of platelets isolated from 20 subjects taking clinically relevant doses of tenofovir were comparable to baseline samples.

CONCLUSIONS AND IMPLICATIONS

ABC can enhance platelet activation, independently of variables that confound clinical studies, suggesting a potential pharmacological effect that is absent with tenofovir. Mechanistically, we propose that ABC enhances platelet degranulation and interrupts NO-mediated platelet inhibition. The interaction of ABC with NO signalling is demonstrated by ABC-mediated enhancement of aggregation in vivo and in vitro that persisted in the presence of NO. Although an association between ABC and platelet activation has not been confirmed in patients, these findings provide evidence of a mechanistic link between platelet activation and antiretroviral therapy.

The isothiocyanate sulforaphane modulates platelet function and protects against cerebral thrombotic dysfunction

BACKGROUND AND PURPOSE

Platelet activation provides a critical link between inflammation and thrombosis. Sulforaphane (SFN), a naturally occurring isothiocyanate, has been shown to display both anti-inflammatory and anti-thrombotic actions in the systemic microvasculature. As inflammation promotes thrombosis and vice versa, in this study we investigated whether SFN is able to reduce inflammatory potentiation of thrombotic events, suppress platelet activation and thrombus formation in the cerebral microvasculature.

EXPERIMENTAL APPROACH

Thrombosis was induced in the murine brain using the light/dye-injury model, in conjunction with LPS treatment, with and without SFN treatment. In vitro and in vivo platelet assays (aggregation, flow and other functional tests) were also employed, using both human and murine platelets.

KEY RESULTS

SFN was found to reduce LPS-mediated enhancement of thrombus formation in the cerebral microcirculation. In tail-bleed experiments, LPS treatment prolonged bleeding time, and SFN treatment was found to protect against this LPS-induced derangement of platelet function. SFN inhibited collagen-mediated platelet aggregation in vitro and in vivo and the associated adhesion and impaired calcium signalling. Furthermore, glycoprotein VI was shown to be involved in the protective effects observed with SFN treatment.

CONCLUSIONS AND IMPLICATIONS

The data presented here provide evidence for the use of SFN in preventing stroke in selected high-risk patient cohorts.

Refinement of a mouse cardiovascular model: Development, application and dissemination

European and UK legislation requires all animal procedures to be conducted with consideration to reduction, refinement and replacement. In this review, 3Rs developments are discussed in the field of platelet biology and thromboembolism. Platelet research requires the use of animal models, and mice are widely used in the field. When working in vitro, conventional light transmission techniques have been scaled down allowing reduction in animal numbers. In vivo, vascular injury models are widely used and work is ongoing to develop ex vivo approaches that use fewer animals. Thromboembolic mortality models, which inflict considerable pain and suffering, have also been used widely. A published and characterised refinement of this mortality model allows real-time monitoring of radiolabelled platelets under general anaesthesia and reduces both the severity level and the numbers of mice used in a typical experiment. This technique is more sensitive than the mortality approach and has opened up new avenues of research, which would not have been feasible by using death as an end-point. To drive uptake of real-time monitoring, a more simplistic approach has been developed involving micro-sampling and cell counting. Thromboembolic mortality models should therefore be considered obsolete due to the emergence of 3Rs models with improved scientific outcomes and that can be implemented relatively easily.

Revision of the ARRIVE guidelines: rationale and scope

In 2010, the NC3Rs published the Animal Research: Reporting of In Vivo Experiments (ARRIVE) guidelines to improve the reporting of animal research. Despite considerable levels of support from the scientific community, the impact on the quality of reporting in animal research publications has been limited. This position paper highlights the strategy of an expert working group established to revise the guidelines and facilitate their uptake. The group's initial work will focus on three main areas: prioritisation of the ARRIVE items into a tiered system, development of an explanation and elaboration document, and revision of specific items.

Endogenous Nitric Oxide Acts as a Natural Antithrombotic Agent In Vivo by Inhibiting Platelet Aggregation in the Pulmonary Vasculature

Nitric oxide (NO) is a powerful vasodilator and an inhibitor of platelet aggregation in vitro. While the ability of NO to modulate vascular tone in vivo has been proven, only a few studies have assessed its platelet inhibitory activity in vivo.

We have employed two complementary animal models of pulmonary platelet thromboembolism to assess the antithrombotic activity of endogenous NO in vivo. The inhibition of nitric oxide synthase (NOS) by L-NAME significantly potentiated while the administration of the NOS substrate L-arginine significantly reduced the accumulation of 111In-labelled platelets in the pulmonary vasculature of rabbits induced by intravenous collagen plus epinephrine. L-NAME or L-arginine did not, however, modify 111In-labelled erythrocyte distribution in lungs and phenylephrine had no effect on platelet accumulation following collagen + adrenaline, suggesting that the effects of L-NAME were not due to vasoconstriction but rather to a direct modification of platelet function. In mice, L-NAME significantly reduced the dose of collagen + adrenaline required to induce thromboembolic mortality, increased the fall in circulating platelets and increased the % of pulmonary vessels occluded by platelet thrombi. The effects of L-NAME were reversed by L-arginine but not by a dose of nicardipine exerting maximal vasodilatation. Phenylephrine did not potentiate collagen + adrenaline-induced mortality.

In the pulmonary vasculature in vivo, endogenous NO inhibits collagen + adrenaline-induced aggregation and enhances platelet disaggregation. This natural modulator function of NO is exerted via a direct effect on platelets and not as a result of haemodynamic changes.

Refinement of Mouse Protocols for the Study of Platelet Thromboembolic Responses In Vivo

Mouse models of thromboembolism are frequently used to investigate platelet function in vivo and, according to European Union (EU) legislation, must be conducted in the context of replacement, refinement and reduction. We have previously developed a refined real-time mouse model of thromboembolism as an alternative to models of thromboembolic mortality which inflict considerable pain and suffering. Real-time monitoring involves infusion of radiolabelled platelets into the circulation of anaesthetized mice, and platelet aggregation is measured as increases in platelet-associated counts in the pulmonary vasculature following injection of platelet agonists. This gives a definitive data set on the tissue localization and extent of platelet activation. We developed an additional, more simplistic alternative to mortality models based on blood microsampling which entails the measurement of circulating platelet counts following agonist stimulation. Blood microsamples were collected from the tail vein of anaesthetized mice at three different time points leading to a reduction in animal numbers. Platelet counts significantly dropped 1 minute after stimulation with collagen or thrombin and were restored over 10 minutes. These results correlate with those obtained via real-time monitoring and were confirmed by immunohistochemistry. Pre-treatment of mice with aspirin significantly inhibited the decrease in platelet counts following collagen. These data suggest that blood microsampling may be implemented as a simplistic refined alternative to mortality models of thromboembolism when specialized monitoring equipment, or use of radioactive isotopes for real-time monitoring, which remains the ‘gold standard’, is not feasible. Microsampling refines and reduces animal procedures in compliance with current EU legislation.

Influence of inflammation and nitric oxide upon platelet aggregation following deposition of diesel exhaust particles in the airways

Background and Purpose

Exposure to nanoparticulate pollution has been implicated in platelet‐driven thrombotic events such as myocardial infarction. Inflammation and impairment of NO bioavailability have been proposed as potential causative mechanisms. It is unclear, however, whether airways exposure to combustion‐derived nanoparticles such as diesel exhaust particles (DEP) or carbon black (CB) can augment platelet aggregation in vivo and the underlying mechanisms remain undefined. We aimed to investigate the effects of acute lung exposure to DEP and CB on platelet activation and the associated role of inflammation and endothelial‐derived NO.

Experimental Approach

DEP and CB were intratracheally instilled into wild‐type (WT) and eNOS^−/− mice and platelet aggregation was assessed in vivo using an established model of radio‐labelled platelet thromboembolism. The underlying mechanisms were investigated by measuring inflammatory markers, NO metabolites and light transmission aggregometry.

Key Results

Platelet aggregation in vivo was significantly enhanced in WT and eNOS^−/− mice following acute airways exposure to DEP but not CB. CB exposure, but not DEP, was associated with significant increases in pulmonary neutrophils and IL‐6 levels in the bronchoalveolar lavage fluid and plasma of WT mice. Neither DEP nor CB affected plasma nitrate/nitrite concentration and DEP‐induced human platelet aggregation was inhibited by an NO donor.

Conclusions and Implications

Pulmonary exposure to DEP and subsequent platelet activation may contribute to the reports of increased cardiovascular risk, associated with exposure to airborne pollution, independent of its effects on inflammation or NO bioavailability.

Hydrogen Sulfide and Platelets: A Possible Role in Thrombosis

Platelets are circulating blood elements with key roles in haemostasis and thrombosis. Platelets are activated by a range of stimuli including exposed subendothelial components. Haemostasis also depends upon the effects of inhibitory substances, including the gasotransmitter nitric oxide whose effects on platelets are well documented. Evidence is also emerging to suggest that H2S is generated enzymatically by platelets and can impact their function. Exposure of platelets to H2S from slow-release compounds inhibits aggregation and exerted anti-thrombotic effects in vivo. The mechanisms by which H2S impacts platelet function and the importance of interactions between H2S and other gasotransmitters remain unclear. H2S is therefore emerging as a potentially important regulator of platelet activation and thrombosis. Further study is required to evaluate its importance as a regulator of platelet physiology and associated pathological conditions such as myocardial infarction and stroke.

Role of inorganic nitrate and nitrite in driving nitric oxide-cGMP-mediated inhibition of platelet aggregation in vitro and in vivo

BACKGROUND

Nitric oxide (NO) is a critical negative regulator of platelets that is implicated in the pathology of thrombotic diseases. Platelets generate NO, but the presence and functional significance of NO synthase (NOS) in platelets is unclear. Inorganic nitrate/nitrite is increasingly being recognized as a source of bioactive NO, although its role in modulating platelets during health and vascular dysfunction is incompletely understood.

METHODS

We investigated the functional significance and upstream sources of NO-cGMP signaling events in platelets by using established methods for assessing in vitro and in vivo platelet aggregation, and assessed the bioconversion of inorganic nitrate to nitrite during deficiency of endothelial NOS (eNOS).

RESULTS

The phosphodiesterase 5 (PDE5) inhibitor sildenafil inhibited human platelet aggregation in vitro. This inhibitory effect was abolished by a guanylyl cyclase inhibitor and NO scavengers, but unaffected by NOS inhibition. Inorganic nitrite drove cGMP-mediated inhibition of human platelet aggregation in vitro and nitrate inhibited platelet function in eNOS(-/-) mice in vivo in a model of thromboembolic radiolabeled platelet aggregation associated with an enhanced plasma nitrite concentration as compared with wild-type mice.

CONCLUSIONS

Platelets generate transient, endogenous cGMP signals downstream of NO that are primarily independent of NOS and may be enhanced by inhibition of PDE5. Furthermore, nitrite can generate transient NO-cGMP signals in platelets. The absence of eNOS leads to enhanced plasma nitrite levels following nitrate administration in vivo, which negatively impacts on platelet function. Our data suggest that inorganic nitrate exerts an antiplatelet effect during eNOS deficiency, and, potentially, that dietary nitrate may reduce platelet hyperactivity during endothelial dysfunction.

Integrin-linked kinase regulates the rate of platelet activation and is essential for the formation of stable thrombi

BACKGROUND

Integrin-linked kinase (ILK) and its associated complex of proteins are involved in many cellular activation processes, including cell adhesion and integrin signaling. We have previously demonstrated that mice with induced platelet ILK deficiency show reduced platelet activation and aggregation, but only a minor bleeding defect. Here, we explore this apparent disparity between the cellular and hemostatic phenotypes.

METHODS

The impact of ILK inhibition on integrin αII b β3 activation and degranulation was assessed with the ILK-specific inhibitor QLT0267, and a conditional ILK-deficient mouse model was used to assess the impact of ILK deficiency on in vivo platelet aggregation and thrombus formation.

RESULTS

Inhibition of ILK reduced the rate of both fibrinogen binding and α-granule secretion, but was accompanied by only a moderate reduction in the maximum extent of platelet activation or aggregation in vitro. The reduction in the rate of fibrinogen binding occurred prior to degranulation or translocation of αII b β3 to the platelet surface. The change in the rate of platelet activation in the absence of functional ILK led to a reduction in platelet aggregation in vivo, but did not change the size of thrombi formed following laser injury of the cremaster arteriole wall in ILK-deficient mice. It did, however, result in a marked decrease in the stability of thrombi formed in ILK-deficient mice.

CONCLUSION

Taken together, the findings of this study indicate that, although ILK is not essential for platelet activation, it plays a critical role in facilitating rapid platelet activation, which is essential for stable thrombus formation.

First Report of Sclerotinia Blight of Peanut Caused by Sclerotinia minor in Arkansas

In September, 2013, symptoms similar to Sclerotinia blight caused by Sclerotinia minor were observed on Runner peanut (cv. FloRun 107) in a commercial field near Pocahontas, Arkansas, in Randolph County (2). Blighted plants with wilted leaves were observed in several small (30 × 30 cm) clustered foci located near the end of a 20-ha, furrow-irrigated field. Peanut stems within the lower canopy of symptomatic plants had straw-colored lesions, with white fluffy mycelium and small (<2.0 mm diam.), black, irregularly shaped sclerotia. Stems on plants with severe symptoms were shredded in appearance, with small black sclerotia inside the stem tissue (2). Final disease incidence near harvest in mid-October was less than 1% of the field. Sclerotinia blight symptoms were also observed in 2013 on Runner (cvs. FloRun 107, Georgia 09B, and Florida 07) and Spanish peanut (cvs. OLin and OL06) research plots near Newport, AR, in Jackson County. Disease incidence among cultivars in these research plots was <1% for all cultivars except FloRun 107, which had a disease incidence of 2.6% for a 849.8 m² plot. Isolations from surface-disinfected leaves on potato dextrose agar (PDA) consistently yielded white, fluffy mycelia with small (0.5 to 2.0 mm diam.), black, irregularly shaped sclerotia typical of S. minor (2). Six-week-old peanut plants (cv. FloRun 107) growing in pots were used to test pathogenicity. Each plant was inoculated by placing an agar plug (5 mm diam.), collected from the edge of an actively growing S. minor culture, on the main peanut stem. Plants (n = 5) were incubated for 8 days in a humidity chamber where temperatures ranged from 24 to 30°C and relative humidity remained >95%. Characteristic symptoms of Sclerotia blight were observed on all inoculated peanut plants whereas none of the plants (n = 3) inoculated with sterile PDA agar plugs expressed symptoms. Pathogenicity tests were repeated on peanut cvs. Flavor Runner 458 and Georgia 09B with similar results. S. minor was consistently isolated from symptomatic tissue on PDA, fulfilling Koch's postulates. To our knowledge, this is the first report of S. minor on peanut or any host in Arkansas or the Mid-South region. The two peanut fields with Sclerotinia blight had a history of soybean production, and S. minor may have gone undetected on soybean or one of many host weed species (1). Since S. minor is a major economic pathogen of peanut, commonly causing yield losses of 10% (2), it will likely be a significant factor in Arkansas and Mid-South peanut production. References: (1) M. S. Melzer et al. Can. J. Plant Pathol. 19:272, 1997. (2) D. M. Porter and H. A. Melouk. Sclerotinia blight. Page 34 in: Compendium of Peanut Diseases, 2nd ed. N. Kokalis-Burelle et al., eds. The American Phytopathological Society, St. Paul, MN, 1997.

Improving Bioscience Research Reporting: The ARRIVE Guidelines for Reporting Animal Research

In the last decade the number of bioscience journals has increased enormously, with many filling specialised niches reflecting new disciplines and technologies. The emergence of open-access journals has revolutionised the publication process, maximising the availability of research data. Nevertheless, a wealth of evidence shows that across many areas, the reporting of biomedical research is often inadequate, leading to the view that even if the science is sound, in many cases the publications themselves are not “fit for purpose”, meaning that incomplete reporting of relevant information effectively renders many publications of limited value as instruments to inform policy or clinical and scientific practice [1–21]. A recent review of clinical research showed that there is considerable cumulative waste of financial resources at all stages of the research process, including as a result of publications that are unusable due to poor reporting [22]. It is unlikely that this issue is confined to clinical research [2–14,16–20].

Induction of platelet aggregation after a direct physical interaction with diesel exhaust particles

BACKGROUND

There is a proven link between exposure to traffic-derived particulate air pollution and the incidence of platelet-driven cardiovascular diseases. It is suggested that inhalation of small, nanosized particles increases cardiovascular risk via toxicological and inflammatory processes and translocation of nanoparticles into the bloodstream has been shown in experimental models. We therefore investigated the ability of diesel exhaust particles (DEP) to interact physically and functionally with platelets.

METHODS

The interaction of DEP and carbon black (CB) with platelets was examined by transmission electron microscopy (TEM), whereas the functional consequences of exposure were assessed by measuring in vitro and in vivo platelet aggregation via established methods.

RESULTS

Both DEP and CB were internalized and seen in proximity with the open canalicular system in platelets. DEP induced platelet aggregation in vitro whereas CB had no effect. DEP induced Ca(2+) release, dense granule secretion and surface P-selectin expression, but not toxicologic membrane disruption. Low concentrations of DEP potentiated agonist-induced platelet aggregation in vitro and in vivo.

CONCLUSIONS

DEP associate physically with platelets in parallel with a Ca(2+) -mediated aggregation response displaying the conventional features of agonist-induced aggregation. The ability of DEP to enhance the aggregation response to platelet stimuli would be expected to increase the incidence of platelet-driven cardiovascular events should they be inhaled and translocate into the blood. This study provides a potential mechanism for the increased thrombotic risk associated with exposure to ambient particulate air pollution.

Assessment of platelet aggregation responses in vivo in the mouse

Platelet aggregation responses are conventionally assessed in cuvette-based systems using either isolated platelets or whole blood. Unfortunately, in vitro aggregometry poorly predicts in vivo functionality, since mediators derived from the vascular endothelium are major regulators of platelet function. There is a need, therefore, for functional assays that assess platelet responsiveness in vivo in the presence of an intact and functional vascular endothelium. We have developed methodology for monitoring aggregation responses of freely circulating radiolabelled platelets using external detection probes in the anaesthetised mouse. Intravenous injection of platelet agonists induces reversible, dose-dependent aggregation responses that are sensitive to anti-platelet therapies and modification of the vascular endothelium. The technique provides a means of determining the effects of pharmacological and genetic manipulation upon platelet function in vivo.

Plasma membrane calcium pump (PMCA4)-neuronal nitric-oxide synthase complex regulates cardiac contractility through modulation of a compartmentalized cyclic nucleotide microdomain

Identification of the signaling pathways that regulate cyclic nucleotide microdomains is essential to our understanding of cardiac physiology and pathophysiology. Although there is growing evidence that the plasma membrane Ca(2+)/calmodulin-dependent ATPase 4 (PMCA4) is a regulator of neuronal nitric-oxide synthase, the physiological consequence of this regulation is unclear. We therefore tested the hypothesis that PMCA4 has a key structural role in tethering neuronal nitric-oxide synthase to a highly compartmentalized domain in the cardiac cell membrane. This structural role has functional consequences on cAMP and cGMP signaling in a PMCA4-governed microdomain, which ultimately regulates cardiac contractility. In vivo contractility and calcium amplitude were increased in PMCA4 knock-out animals (PMCA4(-/-)) with no change in diastolic relaxation or the rate of calcium decay, showing that PMCA4 has a function distinct from beat-to-beat calcium transport. Surprisingly, in PMCA4(-/-), over 36% of membrane-associated neuronal nitric-oxide synthase (nNOS) protein and activity was delocalized to the cytosol with no change in total nNOS protein, resulting in a significant decrease in microdomain cGMP, which in turn led to a significant elevation in local cAMP levels through a decrease in PDE2 activity (measured by FRET-based sensors). This resulted in increased L-type calcium channel activity and ryanodine receptor phosphorylation and hence increased contractility. In the heart, in addition to subsarcolemmal calcium transport, PMCA4 acts as a structural molecule that maintains the spatial and functional integrity of the nNOS signaling complex in a defined microdomain. This has profound consequences for the regulation of local cyclic nucleotide and hence cardiac β-adrenergic signaling.

Thrombosis is reduced by inhibition of COX-1, but unaffected by inhibition of COX-2, in an acute model of platelet activation in the mouse

Background

Clinical use of selective inhibitors of cyclooxygenase (COX)-2 appears associated with increased risk of thrombotic events. This is often hypothesised to reflect reduction in anti-thrombotic prostanoids, notably PGI₂, formed by COX-2 present within endothelial cells. However, whether COX-2 is actually expressed to any significant extent within endothelial cells is controversial. Here we have tested the effects of acute inhibition of COX on platelet reactivity using a functional in vivo approach in mice.

Methodology/Principal Findings

A non-lethal model of platelet-driven thromboembolism in the mouse was used to assess the effects of aspirin (7 days orally as control) diclofenac (1 mg.kg⁻¹, i.v.) and parecoxib (0.5 mg.kg⁻¹, i.v.) on thrombus formation induced by collagen or the thromboxane (TX) A₂-mimetic, U46619. The COX inhibitory profiles of the drugs were confirmed in mouse tissues ex vivo. Collagen and U46619 caused in vivo thrombus formation with the former, but not latter, sensitive to oral dosing with aspirin. Diclofenac inhibited COX-1 and COX-2 ex vivo and reduced thrombus formation in response to collagen, but not U46619. Parecoxib inhibited only COX-2 and had no effect upon thrombus formation caused by either agonist.

Conclusions/Significance

Inhibition of COX-1 by diclofenac or aspirin reduced thrombus formation induced by collagen, which is partly dependent upon platelet-derived TXA₂, but not that induced by U46619, which is independent of platelet TXA₂. These results are consistent with the model demonstrating the effects of COX-1 inhibition in platelets, but provide no support for the hypothesis that acute inhibition of COX-2 in the circulation increases thrombosis.

Refinement, reduction and replacement approaches to in vivo cardiovascular research

In this review, the justification and benefits of refinement, reduction and replacement (3Rs) approaches to cardiovascular research are examined using the field of platelet biology and arterial thrombosis as an example. Arterial thrombosis is a platelet-driven condition and platelets are regulated by autologous signals, but also by external factors such as the vascular endothelium. In vitro assays using isolated platelets therefore poorly reflect in vivo platelet function and human disease. As a consequence, animal models, including mouse models, are frequently used. In particular, models of thromboembolic mortality have been successfully employed to determine the role of the vascular endothelium in regulating platelet function and thrombosis in vivo. Such models raise both scientific and ethical concerns and have recently been refined permitting the use of fewer mice at a lower severity level. These refinements have been scientifically beneficial in permitting analysis of the development and progression of thrombotic diseases and in improving our understanding of the role of the vascular endothelium in regulating platelet function and thrombosis. For many, the ultimate goal in 3Rs-driven science is replacement of animal models with non-animal alternatives; this is exemplified, in the platelet field, by the development of in vitro flow systems. The development of 3Rs approaches to cardiovascular research is shown to have led to improved scientific models. Further characterization and use of these models will likely contribute to increased understanding of thrombotic disease processes and facilitate drug development in the cardiovascular field.

The plasma membrane calcium ATPase modulates calcium homeostasis, intracellular signaling events and function in platelets

BACKGROUND

The plasma membrane calcium ATPase (PMCA) regulates localized signaling events in a variety of cell types, although its functional role in platelets remains undefined.

OBJECTIVES

To investigate the role of PMCA in determining platelet intracellular calcium concentration ([Ca²(+) ](i) ) at rest and following agonist stimulation, and to define the corresponding effects upon different stages of platelet activation.

METHODS

[Ca²(+) ](i) was continuously measured in Fura-2-loaded platelets and in vitro and in vivo functional analyses performed in the presence of the PMCA inhibitor carboxyeosin (CE).

RESULTS

Concentrations of CE that selectively inhibited Ca²(+) extrusion through PMCA were established in human platelets. [Ca²(+) ](i) was elevated by CE in resting platelets, although collagen-stimulated Ca²(+) release was reduced. Impaired Ca²(+) mobilization upon agonist stimulation was accompanied by reduced dense granule secretion and impaired platelet aggregation. Platelet aggregation responses were also reduced in PMCA4(-/-) mice and in an in vivo mouse model of platelet thromboembolism. Conversely, inhibition of PMCA promoted the early and later stages of platelet activation, observed as enhanced adhesion to fibrinogen, and accelerated clot retraction. Investigations into the signaling mechanisms underlying CE-mediated inhibition of platelet aggregation implicated cGMP-independent vasodilator-stimulated phosphoprotein phosphorylation.

CONCLUSIONS

Disruption of PMCA activity perturbs platelet Ca²(+) homeostasis and function in a time-dependent manner, demonstrating that PMCA differentially regulates Ca²(+) -dependent signaling events, and hence function, throughout the platelet activation process.

Distinct role and location of the endothelial isoform of nitric oxide synthase in regulating platelet aggregation in males and females in vivo

The role of endogenous nitric oxide in regulating platelet function in vivo is incompletely understood. The enzymic and anatomic sources of bioactive NO remain unclear and the consequences of the differences in endothelial function between males and females to platelet responsiveness are not known. We employed a mouse model of platelet thromboembolism to assess platelet aggregation in vivo along with supporting in vitro studies to investigate these issues. Pharmacological nitric oxide synthase (NOS) inhibition protracted the duration of thromboembolic responses to ADP (adenosine diphosphate) and enhanced in vivo platelet aggregation following activation of the coagulation cascade. Collagen induced in vivo platelet aggregation was enhanced in female eNOS(-/-) mice and the NOS inhibitor L-NAME (Nω-Nitro-l-arginine methyl ester hydrochloride) potentiated collagen induced thromboembolism although selective iNOS and nNOS antagonists had no effect. None of the NOS inhibitors tested had significant effects on platelet aggregation in isolated whole blood. In conclusion, endogenous NO derived from eNOS in the vascular endothelium is a critical regulator of platelet function in vivo in both males and females with negligible roles of iNOS and nNOS. Despite the expression of NOS enzymes in circulating blood elements, there is no evidence of a functional role of endogenous NO from these cells in regulating platelets. eNOS and its up- and down-stream mediators are therefore potential anti-thrombotic targets.

The teacher as observer and experimenter in the modification of disputing and talking-out behaviors

Disputing and talking-out behaviors of individual pupils and entire classroom groups in special education classes and regular classes from white middle-class areas and from all black poverty areas ranging from the first grade to junior high school were studied. The classroom teacher in each case acted as the experimenter and as an observer. Various means of recording behaviors were used and reliability of observation was checked by an outside observer, another teacher, a teacher-aide, a student, or by using a tape recorder. Observation sessions varied from 15 min to an entire school day. After baseline rates were obtained, extinction of inappropriate disputing or talking-out behaviors and reinforcement of appropriate behavior with teacher attention, praise and in some cases a desired classroom activity or a surprise at the end of the week brought a decrease in undesired verbalizations. A reversal of contingencies brought a return to high levels of inappropriate talking with a return to low levels when reinforcement for appropriate talking was reinstated. The experiments demonstrated that teachers in a variety of classroom settings could obtain reliable observational records and carry out experimental manipulations successfully using resources available in most schools.

Plasma membrane calcium ATPase proteins as novel regulators of signal transduction pathways

Emerging evidence suggests that plasma membrane calcium ATPases (PMCAs) play a key role as regulators of calcium-triggered signal transduction pathways via interaction with partner proteins. PMCAs regulate these pathways by targeting specific proteins to cellular sub-domains where the levels of intracellular free calcium are kept low by the calcium ejection properties of PMCAs. According to this model, PMCAs have been shown to interact functionally with the calcium-sensitive proteins neuronal nitric oxide synthase, calmodulin-dependent serine protein kinase, calcineurin and endothelial nitric oxidase synthase. Transgenic animals with altered expression of PMCAs are being used to evaluate the physiological significance of these interactions. To date, PMCA interactions with calcium-dependent partner proteins have been demonstrated to play a crucial role in the pathophysiology of the cardiovascular system via regulation of the nitric oxide and calcineurin/nuclear factor of activated T cells pathways. This new evidence suggests that PMCAs play a more sophisticated role than the mere ejection of calcium from the cells, by acting as modulators of signaling transduction pathways.

Functional regulation of vascular and platelet activity during thrombosis by nitric oxide and endothelial nitric oxide synthase

Nitric oxide (NO) regulates both vascular tone and platelet function. Since thrombotic diseases and their animal models consist of both vascular and platelet components, the functional mechanisms by which NO and endothelial nitric oxide synthase (eNOS) regulate thrombotic events are unclear. Experiments were conducted by measuring collagen-induced aggregation of freely circulating radio-labelled platelets in the pulmonary vasculature of anaesthetised mice via external detection probes. In addition, cardiac haemodynamic function was assessed by invasive catheterisation during thrombotic stimulation. Platelet aggregation responses were shown to occur independently of changes in vessel tone induced by pharmacological vasoconstriction or vasodilatation. Acute NOS inhibition significantly potentiated the amplitude and duration of platelet aggregation and an NO donor had an inhibitory effect. In contrast, in eNOS-/- mice, the amplitude of platelet aggregation was not affected although the response was protracted following moderate thrombotic stimulation. Thrombosis induced changes in haemodynamic performance were sensitive to vasomodulation and were potentiated by both NOS inhibition and in eNOS-/- mice. In conclusion, endogenous NO and exogenously applied NO donors exert an antithrombotic effect in vivo through a direct suppression of platelet aggregation. In contrast, eNOS exerts a powerful antithrombotic effect upon the vascular components of thrombosis but has a more subtle effect on the duration of thrombotic responses that are platelet-mediated. Our data demonstrate the differential roles of eNOS and general NO bioavailability in regulating vascular and platelet activity during thrombosis.