Functional Testing for Heparin-Induced Thrombocytopenia Using Whole Blood Multiplate Impedance Aggregometry

Immune-mediated heparin-induced thrombocytopenia (HIT) occurs when heparin-dependent IgG antibodies bind to heparin/platelet factor 4 (H/PF4) complexes and activate platelets. There is a vast panoply of assays to investigate HIT which can be divided into two groups, antigen-based immunoassays that detect all antibodies against H/PF4 and are used as a first diagnostic step and functional assays that will identify only the antibodies capable of activating platelets and are mandatory to confirm a diagnosis of pathological HIT. The serotonin-release assay, known as SRA, has been the gold standard for decades, but in the last 10 years, other easier alternatives have been described. The current chapter will focus on whole blood multiple electrode aggregometry, a validated method for the functional diagnosis of HIT.

A pilot study assessing the implementation of 96-well plate-based aggregometry (Optimul) in Australia

Identification of disordered platelet function is important to guide peri-operative bleeding management as well as long term treatment and prognostic strategies in individuals with platelet bleeding disorders. Light transmission aggregometry (LTA), the current gold standard diagnostic test of platelet function is a time consuming technique almost exclusively performed in specialised laboratories and almost universally unavailable in regional centres in Australia, where there is an unmet need for access to specialised platelet function diagnostic services. 96-well plate-based aggregometry (Optimul, UK), has been utilised in research laboratories as a novel platform to investigate platelet function. We evaluated the Optimul assay at two centres in Australia, one regional and one tertiary metropolitan, to assess its feasibility as a screening test applicable to remote regional centres. Concentration-response curves were established from 45 healthy volunteers at the participating regional hospital and from 31 healthy volunteers at the tertiary institution. Optimul successfully detected anti-platelet effects in individuals taking aspirin (n=4), NSAID (n=2), clopidogrel (n=2) and dual therapy with aspirin and clopidogrel (n=1). When tested in parallel to LTA in individuals referred for the evaluation of abnormal bleeding symptoms there was overall a very good level of agreement between Optimul and LTA [Cohen's kappa (k₂)=0.84], supporting its role as a useful screening tool in the assessment of platelet function. Optimul assay performance was quick and the methodology simple, requiring no specialised training or resources to be implemented at either the regional or metropolitan laboratory. Widespread implementation, particularly in regional laboratories within Australia where specialised platelet function testing is unavailable, has the potential to drastically improve the inequity of access to such services.

The utility of flow cytometric platelet forward scatter as an alternative to mean platelet volume

The use of mean platelet diameter (MPD) to classify inherited thrombocytopenia (IT) has been demonstrated in several studies. Alternatively, the mean platelet volume (MPV) may be used, but in macrothrombocytopenia this may not be available. We hypothesized that platelet forward scatter (FSC) measurements using flow cytometry may be used for the size-based classification of IT. The study aimed to assess the ability of platelet FSC to measure platelet size and whether it could be used as an alternative to the MPD or MPV.Blood samples were obtained from individuals undergoing investigation for inherited platelet function disorders (IPFD, n = 40) or platelet number disorders (IPND, n = 46). A hematology analyzer was used to obtain MPV and platelet counts, flow cytometry to measure platelet FSC and ImageJ software to measure MPD from stained blood smears. The International Society of Thrombosis and Hemostasis (ISTH) Bleeding Assessment Tool (BAT) was used to calculate bleeding scores.Twenty-nine(63%) of IPND patients had an MPV that could not be reported. A significant correlation to platelet FSC was found to the MPD (p < .0001) and MPV (p < .0001) and an inverse correlation with platelet count (p < .0001). No significant correlation was found between FSC and bleeding history. In conclusion, platelet FSC is an alternative to MPV and may be used in macrothrombocytopenia where the MPV is not recorded.

Multicentre evaluation of 5B9, a monoclonal anti-PF4/heparin IgG mimicking human HIT antibodies, as an internal quality control in HIT functional assays: Communication from the ISTH SSC Subcommittee on Platelet Immunology

BACKGROUND

Functional tests for the diagnosis of heparin-induced thrombocytopenia (HIT) exhibit variable performance.

OBJECTIVES

We evaluated in a multicenter study whether 5B9, a monoclonal anti-PF4/heparin IgG mimicking human HIT antibodies, could be used as an internal quality control.

METHODS

5B9 was sent to 11 laboratories in seven countries, and six initial concentrations ranging from 10 to 400 μg/mL were tested by heparin-induced platelet activation assay (HIPA), serotonin release assay (SRA), platelet aggregation test (PAT), flow cytometry (FC), or heparin-induced multiple-electrode aggregometry (HIMEA). Each method was evaluated in three different laboratories using experimental procedures identical to those usually applied for the diagnosis of HIT by testing platelets from 10 different healthy donors.

RESULTS

The procedures used varied among the laboratories, particularly when platelet-rich plasma and whole blood were used. Nevertheless, positive results were obtained with at least 100 μg/ml of 5B9 for most donors tested by all centers (except one) performing HIPA, SRA, or HIMEA. FC and PAT results were more heterogeneous. FC results from one center that used washed platelets preincubated with PF4 were positive with all donors at 50 µg/ml 5B9, but at least 200 μg/ml of 5B9 were required to activate cells with most donors tested using PAT.

CONCLUSION

This study confirms that HIT functional tests are not well standardized and exhibit variable sensitivity for the detection of platelet-activating antibodies. However, 5B9 is a potentially useful tool to standardize functional tests, to select responding platelet donors, and consequently to improve the performance of these assays and comparability between laboratories.

Association of Global Coagulation Profiles With Cardiovascular Risk Factors and Atherosclerosis: A Sex Disaggregated Analysis From the BioHEART-CT Study

Background

Although the association between dysregulated coagulation and atherosclerosis is well recognized, individual assays have been of minimal value in understanding disease susceptibility. Here we investigated the association of global coagulation profiles with coronary artery disease with consideration of sex differences.

Methods and Results

The study included patients from the BioHEART‐CT (The BioHEART Study: Assessing Patients With Suspected Cardiovascular Disease for New Disease Markers and Risk Factors) biobank who had computed tomography coronary angiograms scored for coronary artery calcium score (CACS) and Gensini score. The cohort included 206 adult patients who were referred for clinically indicated computed tomography coronary angiography and had a median of 2 major cardiac risk factors; 50% were women and the average age was 62.6 years (±9.9 years). The overall hemostatic potential (OHP) and calibrated automated thrombography generation assays were performed on platelet‐poor plasma. CACS and Gensini score in men were significantly correlated in bivariate analysis with measures from the OHP assay, and regression models predicting disease severity by CACS or Gensini score were improved by adding the OHP assay variables in men but not in women. The calibrated automated thrombography generation assay demonstrated a more hypercoagulable profile in women than in men. The OHP assay showed hypercoagulable profiles in women with hyperlipidemia and men with obesity.

Conclusions

The OHP assay identified hypercoagulable profiles associated with different risk factors for each sex and was associated with CACS and Gensini score severity in men, emphasizing the associations between increased fibrin generation and reduced fibrinolysis with cardiac risk factors and early atherosclerosis.

Registration Information

www.anzctr.org.au. Identifier: ACTRN12618001322224.

Building platelet phenotypes: diaphanous-related formin 1 (DIAPH1)-related disorder

Variants of the Diaphanous-Related Formin 1 (DIAPH-1) gene have recently been reported causing inherited macrothrombocytopenia. The essential/"diagnostic" characteristics associated with the disorder are emerging; however, robust and complete criteria are not established. Here, we report the first cases of DIAPH1-related disorder in Australia caused by the autosomal dominant gain-of-function DIAPH1 R1213X variant formed by truncation of the protein within the diaphanous auto-regulatory domain (DAD) with loss of regulatory motifs responsible for autoinhibitory interactions within the DIAPH1 protein. We affirm phenotypic changes induced by the DIAPH1 R1213X variant to include macrothrombocytopenia, early-onset progressive sensorineural hearing loss, and mild asymptomatic neutropenia. High-resolution microscopy confirms perturbations of cytoskeletal dynamics caused by the DIAPH1 variant and we extend the repertoire of changes generated by this variant to include alteration of procoagulant platelet formation and possible dental anomalies.

Dysregulation of oncogenic factors by GFI1B p32: investigation of a novel GFI1B germline mutation

GFI1B is a transcription factor essential for the regulation of erythropoiesis and megakaryopoiesis, and pathogenic variants have been associated with thrombocytopenia and bleeding. Analysing thrombocytopenic families by whole exome sequencing, we identified a novel GFI1B variant (c.648+5G>A), which causes exon 9 skipping and overexpression of a shorter p32 isoform. We report the clinical data of our patients and critically review the phenotype observed in individuals with different GFI1B variants leading to the same effect on the p32 expression. Since p32 is increased in acute and chronic leukemia cells, we tested the expression level of genes playing a role in various type of cancers, including hematological tumors and found that they are significantly dysregulated, suggesting a potential role for GFI1B in carcinogenesis regulation. Increasing the detection of individuals with GFI1B variants will allow us to better characterize this rare disease and determine whether it is associated with an increased risk of developing malignancies.

Ionotropic glutamate receptors in platelets: opposing effects and a unifying hypothesis

Ionotropic glutamate receptors include α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR), kainate receptors (KAR), and N-methyl-D-aspartate receptors (NMDAR). All function as cation channels; AMPAR and KAR are more permeable to sodium and NMDAR to calcium ions. Compared to the brain, receptor assemblies in platelets are unusual, suggesting distinctive functionalities.There is convincing evidence that AMPAR and KAR amplify platelet function and thrombus formation in vitro and in vivo. Transgenic mice lacking GluA1 and GluK2 (AMPAR and KAR subunits, respectively) have longer bleeding times and prolonged time to thrombosis in an arterial model. In humans, rs465566 KAR gene polymorphism associates with altered in vitro platelet responses suggesting enhanced aspirin effect. The NMDAR contribution to platelet function is less well defined. NMDA at low concentrations (≤10 μM) inhibits platelet aggregation and high concentrations (≥100 μM) have no effect. However, open NMDAR channel blockers interfere with platelet activation and aggregation induced by other agonists in vitro; anti-GluN1 antibodies interfere with thrombus formation under high shear rates ex vivo; and rats vaccinated with GluN1 develop iron deficiency anemia suggestive of mild chronic bleeding. In this review, we summarize data on glutamate receptors in platelets and propose a unifying model that reconciles some of the opposing effects observed.

Platelet-Reactive Antibodies in Patients after Ischaemic Stroke-An Epiphenomenon or a Natural Protective Mechanism

Ischaemic brain damage induces autoimmune responses, including the production of autoantibodies with potential neuroprotective effects. Platelets share unexplained similarities with neurons, and the formation of anti-platelet antibodies has been documented in neurological disorders. The aim of this study was to investigate the presence of anti-platelet antibodies in the peripheral blood of patients after ischaemic stroke and determine any clinical correlations. Using a flow cytometry-based platelet immunofluorescence method, we detected platelet-reactive antibodies in 15 of 48 (31%) stroke patients and two of 50 (4%) controls (p < 0.001). Western blotting revealed heterogeneous reactivities with platelet proteins, some of which overlapped with brain proteins. Stroke patients who carried anti-platelet antibodies presented with larger infarcts and more severe neurological dysfunction, which manifested as higher scores on the National Institutes of Health Stroke Scale (NIHSS; p = 0.009), but they had a greater recovery in the NIHSS by the time of hospital discharge (day 7 ± 2) compared with antibody-negative patients (p = 0.043). Antibodies from stroke sera reacted more strongly with activated platelets (p = 0.031) and inhibited platelet aggregation by up to 30.1 ± 2.8% (p < 0.001), suggesting the potential to interfere with thrombus formation. In conclusion, platelet-reactive antibodies can be found in patients soon after ischaemic stroke and correlate with better short-term outcomes, suggesting a potential novel mechanism limiting thrombosis.

The effect of metoprolol and aspirin on cardiovascular risk in bereavement: A randomized controlled trial

BACKGROUND

Bereavement is associated with an increased risk of cardiovascular disease; however, no reports exist of interventions to reduce risk. In a randomized, double-blind, placebo-controlled trial of 85 recently bereaved participants, we determined whether β-blocker (metoprolol 25 mg) and aspirin (100 mg) reduce cardiovascular risk markers and anxiety, without adversely affecting bereavement intensity.

METHODS

Participants were spouses (n = 73) or parents (n = 12) of deceased from 5 hospitals in Sydney, Australia, 55 females, 30 males, aged 66.1 ± 9.4 years. After assessment within 2 weeks of bereavement, subjects were randomized to 6 weeks of daily treatment or placebo, and the effect evaluated using ANCOVA, adjusted for baseline values (primary analysis).

RESULTS

Participants on metoprolol and aspirin had lower levels of home systolic pressure (P = .03), 24-hour average heart rate (P < .001) and anxiety (P = .01) platelet response to arachidonic acid (P < .001) and depression symptoms (P = .046) than placebo with no difference in standard deviation of NN intervals index (SDNNi), von Willebrand Factor antigen, platelet-granulocyte aggregates or bereavement intensity. No significant adverse safety impact was observed.

CONCLUSIONS

In early bereavement, low dose metoprolol and aspirin for 6 weeks reduces physiological and psychological surrogate measures of cardiovascular risk. Although further research is needed, results suggest a potential preventive benefit of this approach during heightened cardiovascular risk associated with early bereavement.

An integrated approach to inherited platelet disorders: results from a research collaborative, the Sydney Platelet Group

Inherited disorders of platelet function (IPFD) and/or number (IPND) are heterogeneous conditions that result in variable mucocutaneous bleeding symptoms as a result of deranged primary haemostasis caused by platelet dysfunction or thrombocytopenia. Diagnosis is important to guide post-operative bleeding prophylactic strategies, to avoid treatment with inappropriate medications, and inform prognosis. Achieving an accurate diagnosis has traditionally been hampered by the requirement of multiple, often complex, laboratory tests that are not always available at single centres. To improve the diagnosis of these disorders a research collaborative was established, the Sydney Platelet Group, that explored an integrated approach combining traditional and contemporary platelet phenotypic and genetic diagnostic platforms available at four Sydney tertiary hospitals. Herein we report the outcomes of the first 50 patients evaluated using this approach. The cohort included 22 individuals with suspected IPFD and 28 with thrombocytopenia. Bleeding scores were higher in individuals with IPFD (mean 5.75; SD 4.83) than those with IPNDs (mean 2.14; SD 2.45). In cases with suspected IPFD, diagnosis to the level of the defective pathway was achieved in 71% and four individuals were found not to have a definitive platelet function defect. Dense granule secretion disorders were the most common platelet pathway abnormality detected (n=5). Mean bleeding scores in these individuals were not significantly different to individuals with defects in other commonly detected platelet pathways (dense granules, signal transduction and 'undetermined'). A molecular diagnosis was achieved in 52% of individuals with IPNDs and 5% with IPFD. Likely pathogenic and pathogenic variants detected included variants associated with extra-haematological complications (DIAPH1, MYH9) and potential for malignancy (ANKRD26 and RUNX1). The level of platelet investigation undertaken by this initiative is currently not available elsewhere in Australia and initial results confirm the utility of this integrated phenotypic-genetic approach.

A Structural/Functional Domain on Human CD36 Is Involved in the Binding of Anti-Nakα Antibodies

The human CD36 antigen is an integral membrane glycoprotein expressed by platelets, monocytes, endothelial cells and various tumor cell lines. CD36 acts as a receptor for thrombospondin, collagen, Plasmodium falciparum-infected erythrocytes and oxidized low- density lipoprotein. Individuals possessing the Naka-negative phenotype do not express CD36 and risk developing anti-CD36 isoantibodies upon blood transfusion or during pregnancy. In the present study, we have examined the interaction of an anti-Naka serum with recombinantly expressed CD36. Results obtained show that five functional CD36 monoclonal antibodies (OKM5, FA6-152, L103, ESIV-C7 and 10/5) prevent the binding of the anti-Naka serum whereas a single monoclonal antibody (13/10) has no effect. Consistent with this result, an epitope map of CD36 generated using cross-blocking experiments, indicates that the inhibitory monoclonal antibodies recognize closely- related epitopes whereas 13/10 reacts with a distinct CD36 determinant. Furthermore, we have demonstrated, in a recent study, that OKM5, FA6-152, L103 and 10/5 bind to the same CD36 domain defined by amino acids 155 to 183. Taken together, our results indicate that the 155-183 sequence is important for the binding of the anti-Naka serum to CD36 and may represent a surface-exposed, immunogenic and presumably functional region on human CD36.

N-methyl-d-aspartate receptor mediated calcium influx supports in vitro differentiation of normal mouse megakaryocytes but proliferation of leukemic cell lines

Background

N-methyl-d-aspartate receptors (NMDARs) contribute calcium influx in megakaryocytic cells but their roles remain unclear; both pro- and anti-differentiating effects have been shown in different contexts.

Objectives

The aim of this study was to clarify NMDAR contribution to megakaryocytic differentiation in both normal and leukemic cells.

Methods

Meg-01, Set-2, and K-562 leukemic cell lines were differentiated using phorbol-12-myristate-13-acetate (PMA, 10 nmol L^-1) or valproic acid (VPA, 500 μmol L^-1). Normal megakaryocytes were grown from mouse marrow-derived hematopoietic progenitors (lineage-negative and CD41a-enriched) in the presence of thrombopoietin (30-40 nmol L^-1). Marrow explants were used to monitor proplatelet formation in the native bone marrow milieu. In all culture systems, NMDARs were inhibited using memantine and MK-801 (100 μmol L^-1); their effects compared against appropriate controls.

Results

The most striking observation from our studies was that NMDAR antagonists markedly inhibited proplatelet formation in all primary cultures employed. Proplatelets were either absent (in the presence of memantine) or short, broad and intertwined (with MK-801). Earlier steps of megakaryocytic differentiation (acquisition of CD41a and nuclear ploidy) were maintained, albeit reduced. In contrast, in leukemic Meg-01 cells, NMDAR antagonists inhibited differentiation in the presence of PMA and VPA but induced differentiation when applied by themselves.

Conclusions

NMDAR-mediated calcium influx is required for normal megakaryocytic differentiation, in particular proplatelet formation. However, in leukemic cells, the main NMDAR role is to inhibit differentiation, suggesting diversion of NMDAR activity to support leukemia growth. Further elucidation of the NMDAR and calcium pathways in megakaryocytic cells may suggest novel ways to modulate abnormal megakaryopoiesis.

A Naturally Occurring Point Mutation in the β3 Integrin MIDAS-like Domain Affects Differently αvβ3 and αIIbβ3 Receptor Function

We have investigated the effect of a new Leu196Pro mutation, identified in the MIDAS-like domain of the β3 integrin subunit in a patient with type II Glanzmann thrombasthenia, on β3 integrin receptor function. Expression of the mutant β3Pro196 subunit in CHO cells, either associated with recombinant human αIIb or αv, resulted in normal biosynthesis of β3 and heterodimerization with αv or IIb, but selectively interfered with αIIbβ3 maturation and transport to the cell surface. Functional analysis of the β3 mutant receptors revealed strong inhibition of αvβ3-mediated cell spreading on immobilized fibrinogen, focal contact formation, p125FAK phosphorylation and fibrin clot retraction, as opposed to normal αIIbβ3-mediated cell interaction with immobilized fibrinogen, focal contact translocation and signaling. In contrast, antibody- or DTT-activated mutant αIIbβ3 was unable to bind soluble fibrinogen or the ligand mimetic PAC-1 monoclonal antibody, but underwent a conformational change following RGD peptide binding as demonstrated by AP5-LIBS epitope expression. These results suggest that (1) the highly conserved TL196T motif in the β3 integrin subunit is located in a domain structurally important for the exposure of a functional binding site for soluble fibrinogen; and (2) that the MIDAS-like contact site in β3 is not involved in αIIbβ3-mediated cell adhesion to immobilized fibrinogen, while it is essential for αvβ3-mediated interaction with this ligand.

Heterozygous loss of platelet glycoprotein (GP) Ib-V-IX variably affects platelet function in velocardiofacial syndrome (VCFS) patients

Velocardiofacial syndrome (VCFS) is a common, phenotypically heterogeneous developmental disorder caused by an interstitial microdeletion within human chromosome 22q11. The deleted chromosomal region in >90% of VCFS patients includes the GPIbβ gene, encoding for one subunit of the platelet GPIb-V-IX receptor, which is critical for platelet adhesion under shear, and important in aggregation and thrombin-mediated activation. Complete loss of GPIb-V-IX due to autosomal recessive inheritance of two GPIbα,Ibβ or GP9 gene mutations,results in a severe bleeding disorder,Bernard-Soulier syndrome (BSS). In this study, twenty-one confirmedVCFS patients were analyzed for platelet morphological and functional alterations, resulting from the heterozygous loss of one GPIbβ gene allele. Compared to unaffected family members,VCFS patients showed a significant decrease in platelet count; VCFS platelet size and mean platelet volume were increased, but not as markedly as in BSS. As expected from obligatory heterozygotes for GPIbβ deficiency, VCFS patients showed reduced platelet GPIb-V-IX surface expression and total GPIb content, but with considerable variation between cases. Platelet function tested using the PFA-100™ analyzer was impaired in 70% of patients. Platelet aggregation was reduced in response to a GPIb-dependent agonist, ristocetin, in 50% ofVCFS patients, with 35% showing a reduced response to thrombin receptor activating peptide. Genomic screening was performed to exclude mutations of the subunit genes, indicating that these platelet abnormalities were due to GPIbβ heterozygosity and not spontaneous BSS. In conclusion, many VCFS patients have in-vitro defects in platelet function that may increase their risk of bleeding during surgery.

Diurnal changes and levels of fibrin generation are not altered by continuous positive airway pressure (CPAP) in obstructive sleep apnoea (OSA)

Obstructive sleep apnoea (OSA) is associated with increased cardiovascular disease (CVD) risk. In the general population, CVD events peak at 9:00–10:00 AM, associated with diurnal changes in thrombotic potential. However in OSA, these CVD events occur frequently at night. Measuring thrombotic potential across the sleep-wake cycle may provide insight into the temporal association of OSA with CVD. This study aimed to determine diurnal changes in fibrin generation in OSA and whether treatment of OSA with continuous positive airway pressure (CPAP) alters fibrin generation across the sleep-wake cycle. In a randomised placebo-controlled crossover trial, patients with OSA were assigned to two months each of therapeutic CPAP and placebo. After each treatment period, fibrin generation was determined by overall haemostatic potential assay at seven time points over 24 hours (h). Twenty-eight patients (25 men, 3 women) with severe OSA (Apnoea Hypopnoea Index = 37.9 ± 23.9/h, Oxygen Desaturation Index 31.3 ± 22.4/h) completed the study. All parameters, except lag time to fibrin generation, showed significant diurnal changes, both on CPAP and placebo. Compared to 9:00 AM, fibrin generation parameters were significantly lower at midnight and 3:00 AM for overall coagulation potential (OCP), overall haemostasis potential (OHP), maximum optical density, and maximum slope (all p≤0.001). CPAP produced no change in fibrin generation parameters compared to placebo. In severe OSA patients, fibrin generation peaked at 6:00 AM and 9:00 AM rather than during the sleep period (midnight and 3:00 AM). These findings suggest a prothrombotic shift in the morning similar to individuals without OSA. There was no difference between CPAP and placebo on fibrin generation.

Inhibition of NMDA receptor function with an anti-GluN1-S2 antibody impairs human platelet function and thrombosis

GluN1 is a mandatory component of N-methyl-D-aspartate receptors (NMDARs) best known for their roles in the brain, but with increasing evidence for relevance in peripheral tissues, including platelets. Certain anti-GluN1 antibodies reduce brain infarcts in rodent models of ischaemic stroke. There is also evidence that human anti-GluN1 autoantibodies reduce neuronal damage in stroke patients, but the underlying mechanism is unclear. This study investigated whether anti-GluN1-mediated neuroprotection involves inhibition of platelet function. Four commercial anti-GluN1 antibodies were screened for their abilities to inhibit human platelet aggregation. Haematological parameters were examined in rats vaccinated with GluN1. Platelet effects of a mouse monoclonal antibody targeting the glycine-binding region of GluN1 (GluN1-S2) were tested in assays of platelet activation, aggregation and thrombus formation. The epitope of anti-GluN1-S2 was mapped and the mechanism of antibody action modelled using crystal structures of GluN1. Our work found that rats vaccinated with GluN1 had a mildly prolonged bleeding time and carried antibodies targeting mostly GluN1-S2. The monoclonal anti-GluN1-S2 antibody (from BD Biosciences) inhibited activation and aggregation of human platelets in the presence of adrenaline, adenosine diphosphate, collagen, thrombin and a protease-activated receptor 1-activating peptide. When human blood was flowed over collagen-coated surfaces, anti-GluN1-S2 impaired thrombus growth and stability. The epitope of anti-GluN1-S2 was mapped to α-helix H located within the glycine-binding clamshell of GluN1, where the antibody binding was computationally predicted to impair opening of the NMDAR channel. Our results indicate that anti-GluN1-S2 inhibits function of human platelets, including dense granule release and thrombus growth. Findings add to the evidence that platelet NMDARs regulate thrombus formation and suggest a novel mechanism by which anti-GluN1 autoantibodies limit stroke-induced neuronal damage.

Effect of Frailty and Age on Platelet Aggregation and Response to Aspirin in Older Patients with Atrial Fibrillation: A Pilot Study

INTRODUCTION

Frailty is associated with changes in inflammation, coagulation, and possibly platelet function. Aspirin is still prescribed for stroke prevention in older patients with atrial fibrillation, although not recommended by current guidelines. In frail older people, it is unclear whether platelet aggregability and response to aspirin are altered. This study aims to investigate the effects of frailty and chronological age on platelet aggregability and on responses to aspirin in older patients with atrial fibrillation.

METHODS

Inpatients with atrial fibrillation aged ≥65 years were recruited from a tertiary referral hospital in Sydney, Australia. Frailty was determined using the Reported Edmonton Frail Scale. Platelet aggregation studies were performed using whole blood impedance aggregometry.

RESULTS

Data from 115 participants were analyzed (mean age 85 ± 6 years, 41% female, 52% frail). Spearman correlation coefficients found no significant associations of platelet aggregation with chronological age or with frailty score. Comparison between frail and non-frail groups showed that there was no impact of frailty status on aggregation assays amongst participants who were not taking any antiplatelet drugs. Amongst participants taking aspirin, the frail had higher adjusted arachidonic acid agonist (ASPI) test measures (AU per platelet) than the non-frail (0.11 ± 0.11 vs. 0.05 ± 0.04; p = 0.04), suggesting that in frail participants, platelet aggregation is less responsive to aspirin than in non-frail.

CONCLUSIONS

We found no effect of chronological age or frailty status on platelet aggregation amongst older patients with atrial fibrillation in this pilot study. However, frailty could be associated with reduced aspirin responsiveness among older patients with atrial fibrillation.

Differentiation between dogs with thrombosis and normal dogs using the overall hemostasis potential assay

OBJECTIVE

To determine whether the overall hemostasis potential (OHP) and calibrated automated thrombogram (CAT) were significantly different between dogs with thrombosis and normal dogs.

ANIMALS

Ten dogs with clinical evidence of thromboembolic disease had both OHP and CAT performed. Forty healthy control dogs had OHP performed, and 23 of these also had CAT performed.

MEASUREMENTS AND MAIN RESULTS

Dogs with thrombosis had significantly higher OHP (P = 0.003), overall coagulation potential (P = 0.0001), and maximum optical density (Max OD, P < 0.0001) than normal dogs, and a significantly longer delay in the start of clot formation (P = 0.01). Max OD was higher than established reference intervals in 80% of the dogs with thrombosis. Using the CAT assay, dogs with thrombosis had a significantly longer lag time than normal dogs (P < 0.001). Plasma fibrinogen concentration correlated positively with overall coagulation potential, OHP, Max OD, and the slope of the OHP curve (P < 0.05), and was increased in 90% of dogs with thrombosis.

CONCLUSIONS

The OHP assay findings were significantly different between normal dogs and those with thrombosis. CAT did not detect any significant differences between these populations of dogs, other than the lag time of the assay.

Role of Nongenomic Signaling Pathways Activated by Aldosterone During Cardiac Reperfusion Injury

Aldosterone (Aldo) activates both genomic and nongenomic signaling pathways in the cardiovascular system. Activation of genomic signaling pathways contributes to the adverse cardiac actions of Aldo during reperfusion injury; however, the extent nongenomic signaling pathways contribute has been difficult to identify due to lack of a specific ligand that activates only nongenomic signaling pathways. Using a pegylated aldosterone analog, aldosterone-3-carboxymethoxylamine-TFP ester conjugated to methoxypegylated amine (Aldo-PEG), we are able for the first time to distinguish between nongenomic and genomic cardiac actions of Aldo. We confirm Aldo-PEG activates phosphorylation of ERK1/2 in rat cardiomyocyte H9c2 cells similar to Aldo and G protein-coupled receptor 30 (GPR30 or GPER) agonist G1. GPER antagonist, G36, but not mineralocorticoid receptor (MR) antagonist spironolactone, prevented ERK1/2 phosphorylation by Aldo, Aldo-PEG, and G1. The selective nongenomic actions of Aldo-PEG are confirmed, with Aldo-PEG increasing superoxide production in H9c2 cells to similar levels as Aldo but having no effect on subcellular localization of MR. Striatin serves as a scaffold for GPER and MR, with GPER antagonist G36, but not spironolactone, restoring MR-striatin complexes. Aldo-PEG had no effect on MR-dependent transcriptional activation, whereas Aldo increased transcript levels of serum-regulated kinase 1 and plasminogen activator inhibitor-1. Using our ex vivo experimental rat model of myocardial infarction, we found aggravated infarct size and apoptosis by Aldo but not Aldo-PEG. Our studies confirm that in the heart, activation of nongenomic signaling pathways alone are not sufficient to trigger the deleterious effects of aldosterone during myocardial reperfusion injury.

Inhibition of glutamate regulated calcium entry into leukemic megakaryoblasts reduces cell proliferation and supports differentiation

Human megakaryocytes release glutamate and express glutamate-gated Ca(2+)-permeable N-methyl-D-aspartate receptors (NMDARs) that support megakaryocytic maturation. While deregulated glutamate pathways impact oncogenicity in some cancers, the role of glutamate and NMDARs in megakaryocytic malignancies remains unknown. The aim of this study was to determine if NMDARs participate in Ca(2+) responses in leukemic megakaryoblasts and if so, whether modulating NMDAR activity could influence cell growth. Three human cell lines, Meg-01, Set-2 and K-562 were used as models of leukemic megakaryoblasts. NMDAR components were examined in leukemic cells and human bone marrow, including in megakaryocytic disease. Well-established NMDAR modulators (agonists and antagonists) were employed to determine NMDAR effects on Ca(2+) flux, cell viability, proliferation and differentiation. Leukemic megakaryoblasts contained combinations of NMDAR subunits that differed from normal bone marrow and the brain. NMDAR agonists facilitated Ca(2+) entry into Meg-01 cells, amplified Ca(2+) responses to adenosine diphosphate (ADP) and promoted growth of Meg-01, Set-2 and K-562 cells. Low concentrations of NMDAR inhibitors (riluzole, memantine, MK-801 and AP5; 5-100μM) were weakly cytotoxic but mainly reduced cell numbers by suppressing proliferation. The use-dependent NMDAR inhibitor, memantine (100μM), reduced numbers and proliferation of Meg-01 cells to less than 20% of controls (IC50 20μM and 36μM, respectively). In the presence of NMDAR inhibitors cells acquired morphologic and immunophenotypic features of megakaryocytic differentiation. In conclusion, NMDARs provide a novel pathway for Ca(2+) entry into leukemic megakaryoblasts that supports cell proliferation but not differentiation. NMDAR inhibitors counteract these effects, suggesting a novel opportunity to modulate growth of leukemic megakaryoblasts.

The effect of omega-3 polyunsaturated fatty acids on fibrin and thrombin generation in healthy subjects and subjects with cardiovascular disease

Hypercoagulability plays a key role in the progression of cardiovascular disease (CVD). Although omega-3 polyunsaturated fatty acid (PUFA) intake has been inversely related to the risk of cardiovascular events, the mechanisms are not fully understood. The aim of this study was to investigate the effects of omega-3 on novel markers of global coagulation. The generation of fibrin and thrombin, measured via overall hemostasis potential (OHP) assay and calibrated automated thrombography, respectively, was determined in 40 healthy subjects and 16 patients with CVD at baseline and after 4 weeks of 640 mg/day omega-3 PUFA. In healthy subjects, fibrin generation was significantly reduced, as measured by overall coagulation potential (p = 0.013), OHP (p < 0.001), velocity of fibrin polymerization (p = 0.002), and significant increase in delay to fibrin generation (p = 0.002). The peak of generated thrombin was significantly reduced (p = 0.043). In subjects with CVD, omega-3 PUFA significantly reduced OHP and significantly increased the lag time to thrombin generation (both p < 0.001). Treatment with omega-3 PUFA had no effect on other fibrin and thrombin generation parameters in CVD patients. Four-week omega-3 PUFA supplementation reduced thrombotic potential in healthy subjects, as shown by reduced fibrin generation and peak thrombin. There was a greater effect on fibrin generation in healthy subjects compared with those with CVD.

Spectrum of the mutations in Bernard-Soulier syndrome

Bernard-Soulier syndrome (BSS) is a rare autosomal recessive bleeding disorder characterized by defects of the GPIb-IX-V complex, a platelet receptor for von Willebrand factor (VWF). Most of the mutations identified in the genes encoding for the GP1BA (GPIbα), GP1BB (GPIbβ), and GP9 (GPIX) subunits prevent expression of the complex at the platelet membrane or more rarely its interaction with VWF. As a consequence, platelets are unable to adhere to the vascular subendothelium and agglutinate in response to ristocetin. In order to collect information on BSS patients, we established an International Consortium for the study of BSS, allowing us to enrol and genotype 132 families (56 previously unreported). With 79 additional families for which molecular data were gleaned from the literature, the 211 families characterized so far have mutations in the GP1BA (28%), GP1BB (28%), or GP9 (44%) genes. There is a wide spectrum of mutations with 112 different variants, including 22 novel alterations. Consistent with the rarity of the disease, 85% of the probands carry homozygous mutations with evidence of founder effects in some geographical areas. This overview provides the first global picture of the molecular basis of BSS and will lead to improve patient diagnosis and management.

N-methyl-D-aspartate receptors amplify activation and aggregation of human platelets

BACKGROUND

Glutamate is stored in platelet dense granules and large amounts (>400 μM) are released during thrombus formation. N-methyl-d-aspartate glutamate receptors (NMDARs) have been shown in platelets but their roles are unclear.

MATERIALS AND METHODS

Platelet activation indices (CD62P expression and PAC-1 binding) and platelet aggregation were tested in the presence of well-characterized agonists (glutamate, NMDA, glycine) and antagonists (MK-801, memantine, AP5) of neuronal NMDARs. Expression of NMDAR subunits in platelets was determined.

RESULTS

NMDAR agonists facilitated and NMDAR antagonists inhibited platelet activation and aggregation. Low concentrations (100 μM) of MK-801 and memantine reduced adrenaline-induced CD62P expression by 47 ± 5 and 42 ± 3%, respectively, and inhibited adrenaline-induced platelet aggregation by 17 ± 6 and 25 ± 5%, respectively (P<0.05). AP5 caused less inhibition of platelet function, requiring concentrations of at least 250 μM to inhibit aggregation. NMDAR agonists did not aggregate platelets by themselves but enhanced aggregation initiated by low concentrations of ADP. Exogenous glutamate helped reverse inhibition of platelet aggregation by riluzole (inhibitor of glutamate release). Compared with seven possible NMDAR subunits in neurons, human platelets contained four: GluN1, GluN2A, GluN2D and GluN3A, a combination rarely seen in neurons. The presence of NMDAR transcripts in platelets implied platelet ability to regulate NMDAR expression presumably 'on demand'. Flow cytometry and electron microscopy demonstrated that in non-activated platelets, NMDAR subunits were contained inside platelets but relocated onto platelet blebs, filopodia and microparticles after platelet activation.

CONCLUSIONS

Our results support an active role for NMDARs in platelets, in a process that involves activation-dependent receptor relocation towards the platelet surface.

Detection of hypofibrinolysis in stable coronary artery disease using the overall haemostatic potential assay

INTRODUCTION

Patients with stable coronary artery disease (CAD) are at risk of arterial thrombosis causing myocardial infarction. Detection of global haemostatic markers of hypercoagulability and hypofibrinolysis may be important for risk stratification and individualised treatment. We examined overall haemostatic potential (OHP) and thrombin generation in a group of stable CAD patients. We also sought to investigate associations between fibrinolytic inhibitors and abnormal global fibrinolysis in these patients.

MATERIALS AND METHODS

Blood samples were collected from 56 patients defined by coronary anatomy as symptomatically stable CAD. Medications were recorded. Samples were analysed using the global coagulation assays OHP and thrombin generation (calibrated automated thrombogram, CAT), platelet aggregometry measured by Multiplate®, and levels of plasminogen activator inhibitor-1 (PAI-1) antigen measured by ELISA. Results were compared with a reference group of healthy controls.

RESULTS

Stable CAD patients displayed increased fibrin and thrombin generation and impaired fibrinolysis (decreased overall fibrinolytic potential, OFP, and increased clot lysis time) compared with healthy controls. No effect of antiplatelet agents or other medications on these parameters was observed using platelet-poor plasma. After multivariate adjustment, OFP of healthy individuals was significantly associated with fibrinogen, but in CAD patients PAI-1 became an important determinant.

CONCLUSIONS

Hypercoagulability of plasma is observed in stable CAD, with both increased thrombin generation and reduced fibrinolytic potential making a significant contribution. The OHP assay may provide a simple method of identifying hypercoagulability in individual patients.

Effects of omega-3 polyunsaturated fatty acids on platelet function in healthy subjects and subjects with cardiovascular disease

Hyperactivation and aggregation of platelets play a major role in thrombosis and hemostasis. The aims of this study were to investigate the effects of omega-3 polyunsaturated fatty acids (PUFAs) on platelet function. Light transmission aggregometry and flow cytometric analyses of platelet activation and platelet-leukocyte aggregates were determined at baseline and after 4 weeks of omega-3 (docosahexaenoic acid 520 mg and eicosapentaenoic acid 120 mg) supplementation. In total, 40 healthy subjects and 16 patients with a history of cardiovascular disease (CVD) completed the study. In healthy subjects, omega-3 PUFA significantly reduced adenosine diphosphate (ADP)-induced (maximum amplitude, 77.0% ± 3.2% vs. 71.6% ± 3.4%, p = 0.036; maximum slope, 86.3 ± 1.8 vs. 80.7 ± 2.1, p = 0.014) and adrenaline-induced platelet aggregation (maximum slope, 42.8 ± 2.7 vs. 37.4 ± 3.0, p = 0.013; lag time, 00:21 ± 00:02 vs. 00:31 ± 00:03 s, p = 0.002). Omega-3 PUFA also reduced P-selectin expression (40.5% ± 2.9% vs. 34.4% ± 2.4%, p = 0.049) on platelets and platelet-monocyte aggregates (38.5% ± 2.6% vs. 31.4% ± 2.5%, p = 0.022) after activation with ADP 0.5 µM. There were fewer changes in platelet aggregation and activation found in subjects with CVD. Nevertheless, there was a reduction in the slope of arachidonic acid-induced platelet aggregation (13.21 ± 6.41 vs. 4.88 ± 3.01, p = 0.009) and increased lag time for U46619 (00:16 ± 00:00 vs. 00:29 ± 00:07 s, p = 0.018) induced platelet aggregation. Thus, 4-week supplementation of 640 mg omega-3 PUFA reduced measures of platelet aggregation and activation in healthy subjects but effects were less evident in patients with existing CVD. Our findings support the recommendation that the omega-3 PUFA dose be higher in CVD than among healthy subjects.

Effects of continuous positive airway pressure on coagulability in obstructive sleep apnoea: a randomised, placebo-controlled crossover study

INTRODUCTION

Obstructive sleep apnoea (OSA) is associated with increased cardiovascular risk, however the mechanisms are not well established.

OBJECTIVES

This study aimed to determine whether treatment of OSA with nasal continuous positive airway pressure (CPAP) would favourably alter coagulability across the sleep-wake cycle.

METHODS

In a randomised crossover trial, 28 patients received therapeutic or placebo CPAP, each for 2 months with a 1 month washout between treatments. After each treatment period, a 24 h coagulation study was conducted in the laboratory. Plasminogen activator inhibitor-1 (PAI-1), D-dimer, fibrinogen, von Willebrand Factor (vWF), factor VIII (FVIII), factor VII (FVII) and factor V (FV) were determined at seven time points over the day and night.

RESULTS

At baseline, patients had severe OSA (Apnoea Hypopnoea Index 37.9 ± 23.9 events/h). Treatment of OSA with CPAP compared with placebo resulted in lower 24 h levels of vWF (-3.9%, p=0.013), FVIII (-6.2%, p=0.007) and FV (-4.2%, p<0.001). The greatest difference occurred during the nocturnal and early morning periods. In contrast, fibrinogen, D-dimer, FVII and PAI-1 did not differ between treatments, however all markers displayed diurnal variability independent of treatment.

CONCLUSIONS

In this randomised, placebo-controlled crossover trial, treatment of OSA with CPAP reduced the early morning level of vWF, and nocturnal levels of FVIII and FV. These findings suggest that CPAP may reduce cardiovascular risk in OSA, in part through reducing risk of thrombosis.

Evaluating heparin-induced thrombocytopenia: the old and the new

Heparin-induced thrombocytopenia (HIT) is a rare but potentially serious complication of heparin use. Prompt diagnosis is crucial and requires the integration of clinical assessment and laboratory testing. Pretest clinical scoring systems (i.e., 4 Ts) have been established. Immunoassays can detect the presence of antibodies directed toward heparin-platelet factor 4 (H-PF4) complexes, but provide no information about their ability to activate platelets. A low clinical score, when combined with a negative immunoassay result obviates the need for further testing. However, immunoassays and 4 Ts scores have only modest specificity. Functional testing (serotonin release assay or heparin-induced platelet activation) remain important in confirming the presence of pathogenic H-PF4 antibodies, but are technically demanding to perform and limited in guiding clinical decisions in the acute setting. This review evaluates current immuno- and functional assays available in the laboratory diagnosis of HIT, and describes recent attempts to improve the specificity of enzyme immunoassays, including adopting an immunoglobulin G-specific assay and raising the optical density value cutoff for a positive result. The importance of donor selection and newer functional assays, including flow cytometry-based assays, are also discussed. A current approach to integrating clinical scoring, immunoassays, and functional testing for HIT is also outlined.

Validation of whole blood impedance aggregometry as a new diagnostic tool for HIT: results of a large Australian study

Heparin-induced thrombocytopenia (HIT) remains a challenge, with diagnosis confirmed only by functional assays. The gold standard 14C-serotonin release assay (SRA) is highly sensitive but technically challenging and unsuitable for routine use. We conducted a large study to validate whole blood impedance aggregometry (WBIA) as a suitable diagnostic tool for HIT. WBIA and SRA were used to test 181 samples positive for H-PF4 antibodies by PaGIA or ELISA. Using the same high responder donor, 77 samples were positive by WBIA (aggregation with low-dose but not high-dose heparin). Using the strict definition for SRA positivity, 72 samples were true HIT. In nine samples, serotonin release with high-dose heparin dropped by > 50% but was still >20%; these were retested after a one-half dilution and 8/9 became positive. Ten other samples were discrepant between the two assays: one strongly positive (89% release) and six weakly positive samples by SRA (average release 56%) were WBIA negative. When these samples were retested using a random donor, only two remained SRA positive. Three samples were strongly WBIA positive but SRA negative; two were retested by SRA with 0.5IU/ml heparin and one became positive. Under controlled conditions, using the same selected high-responder donor, WBIA and SRA performed similarly with slightly increased sensitivity of the WBIA when using the strict definition of SRA positivity. WBIA is easy to perform with rapid turn-around time and warrants a multi-laboratory trial to complete its validation as a confirmatory assay for platelet-activating HIT antibodies.

Effect of omega-3 fish oil on cardiovascular risk in diabetes

PURPOSE

Diabetes and cardiovascular disease are major public health concerns worldwide and are leading causes of morbidity and mortality. People with type 2 diabetes are at an increased risk for cardiovascular disease. Diet has a substantial affect on the progression of many diseases, including diabetes, cardiovascular disease, osteoporosis, and arthritis. Omega-3 polyunsaturated fatty acids (long-chain polyunsaturated fatty acids [LC-PUFA]) have long been attributed to the maintenance of health and may be of benefit in reducing cardiovascular risk. The purpose of this review is to investigate the possible roles of omega-3 in reducing cardiovascular risk in patients with diabetes.

METHODS

A literature search was conducted from the Medline, EBSCO, and EMBASE databases. Articles that addressed diabetes, cardiovascular disease, or omega-3 were included.

RESULTS

Reviews and studies reported an association with fish and omega-3 LC-PUFA consumption and decreased total cardiovascular mortality (approximately 15%-19%), along with decreased platelet activation and aggregation, improved lipid profiles, including reduction of triglycerides and very low-density lipoprotein (VLDL), decreased inflammation, and lowered blood pressure.

CONCLUSION

Diets higher in fish and omega-3 LC-PUFA may reduce cardiovascular risk in diabetes by inhibiting platelet aggregation, improving lipid profiles, and reducing cardiovascular mortality. Fish and omega-3 LC-PUFA can be recommended to people with diabetes and included into a diabetes management program.

Whole blood impedance aggregometry detects heparin-induced thrombocytopenia antibodies

Heparin-induced thrombocytopenia (HIT) is a serious complication of heparin use. IgG antibodies to complexes of platelet factor 4 (PF4) and heparin trigger the clinical manifestations of HIT. Only a subset of these antibodies will activate platelets and these can only be identified with platelet aggregation (functional) assays. Heparin-induced platelet aggregation (HIPA) and (14)C-serotonin release (SRA) assays for HIT are time-consuming and complex to perform. We have developed a whole blood impedance (WBI) test using the new Multiplate analyser. All samples referred to our laboratory over a 10 month period were screened for heparin-PF4 antibodies by an ELISA method (Zymutest HIA IgG). The 4T's score was used to assess HIT pretest probability. Twenty antibody positive samples were further tested by all three functional assays: light transmission aggregometry (LTA), SRA and WBI. Thirteen out of twenty samples were positive by LTA (10 patients) and 15 by WBI (11 patients). SRA, considered to be the gold standard, was used as a confirmatory test and 11 were found to be positive (10 patients); four discrepant samples were weakly positive by WBI. The prevalence of a positive functional test was strongly correlated with the 4T's clinical risk score, but a small number of low-risk patients had positive functional assays. In this study, the WBI assay detected all SRA positive patients and was positive for two others suggesting greater sensitivity. The rapid and easy to perform assay may be a useful tool for haematology laboratories to detect platelet-activating HIT antibodies.

Mesenchymal stem cells: isolation, characterisation and in vivo fluorescent dye tracking

Cell therapies have been used to regenerate the heart by direct myocardial delivery, by coronary infusion and by surface attached scaffolds. Multipotent mesenchymal stem cells (MSC) with capacity to differentiate into cardiomyocytes and other cell lines have been predominantly trialled in rodents. However, large animal models are increasingly needed to translate basic research into new, safe regenerative therapies. Understanding the mode of action of cell therapies in the mammalian heart has been limited by cell tracking capability. This study examined the ability to track the fate of allogeneic MSC in sheep using various fluorescent dyes. MSC isolated from sheep bone marrow were grown in culture following extraction and flow cytometric characterisation. After labelling with fluorescent tracking dyes (e.g. CFSE and DiI) cells were tested for in vitro and in vivo signal up to six weeks. Labelling effect on cell division and differentiation was studied. Several dyes lost fluorescence and slowed cell division. However, the thiol reactive dye CM-DiI showed detectable in vivo fluorescence in labelled MSC six weeks after injection into sheep skeletal muscle and two weeks after implantation of an MSC coated biomaterial scaffold. CM-DiI labelled MSC differentiated in vitro showed label retention over four weeks. The fluorescent membrane dye CM-DiI tracks implanted sheep MSC and provides an alternative to traditional cell markers such as gene modified GFP.

Heterozygous loss of platelet glycoprotein (GP) Ib-V-IX variably affects platelet function in velocardiofacial syndrome (VCFS) patients

Velocardiofacial syndrome (VCFS) is a common, phenotypically heterogeneous developmental disorder caused by an interstitial microdeletion within human chromosome 22q11. The deleted chromosomal region in >90% of VCFS patients includes the GPIb beta gene, encoding for one subunit of the platelet GPIb-V-IX receptor, which is critical for platelet adhesion under shear, and important in aggregation and thrombin-mediated activation. Complete loss of GPIb-V-IX due to autosomal recessive inheritance of two GPIb alpha, Ib beta or GP9 gene mutations, results in a severe bleeding disorder, Bernard-Soulier syndrome (BSS). In this study, twenty-one confirmedVCFS patients were analyzed for platelet morphological and functional alterations, resulting from the heterozygous loss of one GPIb beta gene allele. Compared to unaffected family members, VCFS patients showed a significant decrease in platelet count; VCFS platelet size and mean platelet volume were increased, but not as markedly as in BSS. As expected from obligatory heterozygotes for GPIb beta deficiency, VCFS patients showed reduced platelet GPIb-V-IX surface expression and total GPIb content, but with considerable variation between cases. Platelet function tested using the PFA-100 trade mark analyzer was impaired in 70% of patients. Platelet aggregation was reduced in response to a GPIb-dependent agonist, ristocetin, in 50% of VCFS patients, with 35% showing a reduced response to thrombin receptor activating peptide. Genomic screening was performed to exclude mutations of the subunit genes, indicating that these platelet abnormalities were due to GPIb beta heterozygosity and not spontaneous BSS. In conclusion, many VCFS patients have in-vitro defects in platelet function that may increase their risk of bleeding during surgery.

Can the blood pressure effects of COX-2 selective inhibitors be explained by changes in plasma aldosterone levels?

OBJECTIVE

The increased cardiovascular risk associated with rofecoxib may relate to differential effects on blood pressure (BP) in comparison with other cyclooxygenase-2 (COX-2) selective inhibitors. Rofecoxib is uniquely metabolized by cytosol reductase and may compete with aldosterone for metabolism. We hypothesized that the effect of rofecoxib on BP may be due to an increase in aldosterone levels.

DESIGN

Prospective, randomized, cross-over study.

SETTING

Tertiary institution.

PATIENTS

Eleven patients (all female, age 65 +/- 11 years) with osteoarthritis and hypertension.

INTERVENTIONS

Patients received rofecoxib 50 mg once/day or celecoxib 400 mg once/day for 8 weeks, followed by cross-over after a 2-week wash-out period.

OUTCOME MEASURES

Office BP, heart rate (HR), plasma aldosterone and aldosterone related-markers, markers of sympathetic and parasympathetic activity, catecholamines and heart rate variability (HRV) were measured.

RESULTS

Rofecoxib caused an increase in BP compared to celecoxib; a change in recumbent systolic BP +/- SD (6.1 +/- 11.0 versus -7.0 +/- 12.5 mmHg, P < 0.05) and recumbent diastolic BP +/- SD (3.6 +/- 7.6 versus -1.7 +/- 5.7 mmHg). There was no difference in median change in plasma aldosterone levels between rofecoxib and celecoxib (-31 +/- 171.5 versus 43 +/- 147 pg/ml, P = 0.173). The other parameters measured were not different between the two agents.

CONCLUSIONS

Rofecoxib therapy results in a significant increase in systolic BP compared to celecoxib. As plasma aldosterone levels were not different between the two drugs, the differential effect of rofecoxib on BP compared to celecoxib appears to be unlikely due to competition by rofecoxib for aldosterone metabolism.

The relationship between cotinine and periodontal disease

Smoking is a risk factor for periodontitis but there are conflicting reports about the relationship between the severity of periodontitis and smoking behaviour, in part because self-reported smoking status may be inaccurate. Cotinine, a major metabolite of nicotine with a longer half-life (17 h versus 30 min), may be a more useful biochemical marker of smoking status. Smoking behaviour, plasma cotinine levels, and measures of periodontitis severity in 135 adults with moderate-advanced periodontitis were studied. Smokers had comparable periodontitis at a younger age than non-smokers. Smoking, as measured by cigarettes smoked per day and plasma cotinine levels, was significantly related to the severity of periodontitis.

A common ancestral glycoprotein (GP) 9 1828A>G (Asn45Ser) gene mutation occurring in European families from Australia and Northern Europe with Bernard-Soulier Syndrome (BSS)

Bernard-Soulier syndrome (BSS) is an extremely rare hereditary bleeding disorder, caused by mutations occurring in the Glycoprotein (GP) Ibalpha, GPIbbeta and GP9 genes that encode for the corresponding subunits of platelet GPIb-V-IX adhesion receptor complex. BSS has been reported in many populations, mostly behaving in an autosomal-recessive manner.While the great majority of BSS mutations are unique to a single individual or family, the GP9 1828A>G Asn45Ser mutation, which we have identified in an undocumented Australian Caucasian, has already been reported in multiple unrelated Caucasian families from various Northern and Central European countries. Haplotype analysis of 19 BSS patients from 15 unrelated Northern European families (including 2 compound heterozygote siblings from a British family previously published, and 17 1828A>G Asn45Ser homozygotes), showed that 14 of these BSS patients from 11 of the 1828A>G Asn45Ser homozygote families share a common haplotype at the chromosomal region 3' to the GP9 gene. Hence, the results suggest that the GP9 1828A>GAsn45Ser mutation in these families is ancient, and its frequent emergence in the European population is the result of a founder effect rather than recurrent mutational events. Association of the 1828A>G Asn45Ser mutation with variant haplotypes in 4 other Northern European BSS families raised the possibility of a second founder event, or rare recombinations in these families. Additional members from these 'atypical' lineages would need to be screened to resolve this question.

Eleven human platelet systems studied in the Vietnamese and Ma'ohis Polynesian populations

The frequencies of human platelet antigens (HPA) are variable among different ethnic groups. Platelet phenotyping and genotyping in different populations are important to the clinical implications of antiplatelet alloimmunization. No report on HPA prevalence has been published concerning the Vietnamese Kinh and Ma'ohis Polynesian populations. Recent anthropological and genetic marker studies suggest that these two groups have a common origin in East Asia, so we have conducted a combined study concerning the frequency of HPA-1 to HPA-11w systems (excluding HPA-8w) and Gov in these two populations. The results demonstrate a similar pattern of prevalence between Ma'ohis and most of the Asian populations. However, it should be noted that the frequency of HPA-2 is closer to northern Caucasian frequencies than to Asian frequencies. The population of Kinh shows an HPA distribution that is closer to the Chinese population than to the northeastern Thais except for HPA-3, closer to the Indonesian population. Given HPA-3 gene frequency distribution fetomaternal incompatibility could occur more frequently with the risk of alloantibody production.

A naturally occurring point mutation in the beta3 integrin MIDAS-like domain affects differently alphavbeta3 and alphaIIIbbeta3 receptor function

We have investigated the effect of a new Leu196Pro mutation, identified in the MIDAS-like domain of the beta3 integrin subunit in a patient with type II Glanzmann thrombasthenia, on beta3 integrin receptor function. Expression of the mutant beta3Pro196 subunit in CHO cells, either associated with recombinant human alphaIIb or alphav, resulted in normal biosynthesis of beta3 and heterodimerization with alphav or alphaIIb, but selectively interfered with alphaIIbbeta3 maturation and transport to the cell surface. Functional analysis of the beta3 mutant receptors revealed strong inhibition of alphavbeta3-mediated cell spreading on immobilized fibrinogen, focal contact formation, p125FAK phosphorylation and fibrin clot retraction, as opposed to normal alphaIIbbeta3-mediated cell interaction with immobilized fibrinogen, focal contact translocation and signaling. In contrast, antibody- or DTT-activated mutant aIIbbeta3 was unable to bind soluble fibrinogen or the ligand mimetic PAC-1 monoclonal antibody, but underwent a conformational change following RGD peptide binding as demonstrated by AP5-LIBS epitope expression. These results suggest that (1) the highly conserved TL196T motif in the beta3 integrin subunit is located in a domain structurally important for the exposure of a functional binding site for soluble fibrinogen; and (2) that the MIDAS-like contact site in beta3 is not involved in alphaIIbbeta3-mediated cell adhesion to immobilized fibrinogen, while it is essential for alphavbeta3-mediated interaction with this ligand.

Green fluorescent protein (GFP) tagged to the cytoplasmic tail of alphaIIb or beta3 allows the expression of a fully functional integrin alphaIIb(beta3): effect of beta3GFP on alphaIIb(beta3) ligand binding

Using green fluorescent protein (GFP) as an autofluorescent tag, we report the first successful visualization of a beta3 integrin in a living cell. GFP fused in frame to the cytoplasmic tail of either alphaIIb or beta3 allowed normal expression, heterodimerization, processing and surface exposure of alphaIIbGFPbeta3 and alphaIIb(beta3)GFP receptors in Chinese hamster ovary (CHO) cells. Direct microscopic observation of the autofluorescent cells in suspension following antibody-induced alphaIIb(beta3) capping revealed an intense autofluorescent cap corresponding to unlabelled immunoclustered GFP-tagged alphaIIb(beta3). GFP-tagged alphaIIbbeta3 receptors mediated fibrinogen-dependent cell adhesion, were readily detectable in focal adhesions of unstained living cells and triggered p125(FAK) tyrosine phosphorylation similar to wild-type alphaIIb(beta3) (where FAK corresponds to focal adhesion kinase). However, GFP tagged to beta3, but not to alphaIIb, induced spontaneous CHO cell aggregation in the presence of soluble fibrinogen, as well as binding of the fibrinogen mimetic monoclonal antibody PAC1 in the absence of alphaIIb(beta3) receptor activation. Time-lapse imaging of living transfectants revealed a characteristic redistribution of GFP-tagged alphaIIb(beta3) during the early stages of cell attachment and spreading, starting with alphaIIb(beta3) clustering at the rim of the cell contact area, that gradually overlapped with the boundary of the attached cell, and, with the onset of cell spreading, to a reorganization of alphaIIb(beta3) in focal adhesions. Taken together, our results demonstrate that (1) fusion of GFP to the cytoplasmic tail of either alphaIIb or beta3 integrin subunits allows normal cell surface expression of a functional receptor, and (2) structural modification of the beta3 integrin cytoplasmic tail, rather than the alphaIIb subunit, plays a major role in alphaIIb(beta3) affinity modulation. With the successful direct visualization of functional alphaIIb(beta3) receptors in living cells, the generation of autofluorescent integrins in transgenic animals will become possible, allowing new approaches to study the dynamics of integrin functions.

Oxaliplatin-induced fever and release of IL-6

BACKGROUND

Oxaliplatin is a novel cytotoxic agent with documented activity in colorectal cancer. Side effects are generally moderate, and include peripheral neuropathy along with mild bone marrow suppression and gastrointestinal side effects. To our knowledge, induction of febrile episodes by this agents has not been described in the literature.

CASE REPORT

We present the case of a 74-year-old male patient admitted to our institution for palliative treatment of metastatic colorectal carcinoma. Due to progression during treatment with 5-fluorouracil and leucovorin, chemotherapy consisting of oxaliplatin 85 mg/m(2) on days 1 + 15 plus mitomycin C 8 mg/m(2) on day 1 repeated every 28 days was initiated. The first cycle of this combination was tolerated without side effects, but the patient experienced fever up to 39 degrees C starting 2 h after oxaliplatin administration on day 15 of the second cycle, which persisted for 3 days. Fever again recurred at the same interval following administration of oxaliplatin on day 1 of the next cycle. Blood samples taken at regular intervals disclosed an increase in IL-6 serum levels parallel to the body temperature curve, with the peak corresponding to the highest temperature, while C-reactive protein values remained unchanged. In spite of intensive premedication with steroids, antipyretics and clarithromycin, fever promptly recurred during the third cycle of treatment.

CONCLUSION

Our data suggest a clear- cut correlation between fever, the release of IL-6 and oxaliplatin administration. Whether IL-6 release is directly triggered by the application of oxaliplatin or is a bystander phenomenon, however, remains unclear at the moment.

A three amino acid deletion in glycoprotein IIIa is responsible for type I Glanzmann's thrombasthenia: importance of residues Ile325Pro326Gly327 for beta3 integrin subunit association

Glanzmann's thrombasthenia (GT) is a recessive autosomal bleeding disorder characterized by abnormal platelet aggregation due to a qualitative or quantitative defect of the glycoprotein (GP) IIb-IIIa complex (integrin alphaIIb beta3). We describe a new mutation in the GPIIIa gene responsible for type I GT in a consanguineous Algerian family. A discordance between phenotyping and genotyping of the GPIIIa-related HPA-1 platelet alloantigen system in three family members heterozygous for the disease suggested a genetic defect in the GPIIIa gene and a normal GPIIb gene. Sequence analysis of amplified genomic DNA fragments showed a 6-bp deletion in exon 7 of the GPIIIa gene resulting in the amino acid deletion/substitution (Ile325pro326Gly327 --> Met) and creating a new BspHI restriction site. Expression of the mutated integrin beta3 subunit cDNA in Chinese hamster ovary cells showed that the cDNA gene was transcribed into a full-length beta3 protein with an apparent molecular weight identical to wild-type beta3 and accumulated as a single-chain molecule in the cell cytoplasm. The absence of heterodimeric complex formation of the mutant beta3 protein with endogenous alpha v was shown by immunoprecipitation experiments, intracellular immunofluorescent labeling, and a semiquantitative enzyme-linked immunosorbent assay using the alpha vbeta3 complex-specific monoclonal antibodies LM609 and 23C6. Substitution of the methionine residue by a proline, present at position 326 of wild-type beta3, did not restore the ability of the recombinant mutant beta3 protein to associate with alpha v , suggesting that the Ile-Pro-Gly motif is located in a beta3 domain important for integrin subunit interaction. The association of a BspHI restriction site with this newly identified mutation has allowed allele-specific restriction analysis of Algerian GT individuals and the identification of two new unrelated type I patients exhibiting the same mutation, suggesting that the described mutation might be significant in this population and that BspHI restriction analysis will provide a useful screening assay for antenatal diagnosis and genetic counselling.