Adenosine Diphosphate-Induced Aggregation of Human Platelets in Flow Through Tubes: III. Shear and Extrinsic Fibrinogen-Dependent Effects

The effect of shear rate and fibrinogen concentration on adenosine diphosphate-induced aggregation of suspensions of washed human platelets in Poiseuille flow at 23°C was studied using a previously described double infusion technique and resistive particle counter size analysis (1). Using suspensions of multiple-centrifuged and -washed cells in Tyrodes-albumin [3 × 105 μl−1; (17)] with [fibrinogen] from 0 to 1.2μM, the, rate and extent of aggregation with 0.7 μM ADP in Tyrodes-albumin were measured over a range of mean transit times from 0.2 to 43 s, and at mean tube shear rates, Ḡ, = 41.9, 335 and 1,335 s−1. As measured by the decrease in singlet concentration, aggregation at 1.2 μM fibrinogen increased with increasing Ḡ up to 1,335 s1, in contrast to that previously reported in citratcd plasma, in which aggregation reached a maximum at Ḡ = 335 s−1. Without added fibrinogen, there was no aggregation at Ḡ = 41.9 s1; at Ḡ = 335 s1, there was significant aggregation but with an initial lag time, aggregation increasing further at Ḡ = 1,335 s−1. Without added fibrinogen, aggregation was abolished at all Ḡ upon incubation with the hexapeptide GRGDSP, but was almost unaffected by addition of an F(ab’)2 fragment of an antibody to human fibrinogen. Aggregation in the absence of added fibrinogen was also observed at 37°C. The activation of the multiple-washed platelets was tested using flow cytometry with the fluorescently labelled monoclonal antibodies FITC-PAC1 and FITC-9F9. It was shown that 57% of single cells in unactivated PRT expressed maximal GPIIb-IIIa fibrinogen receptors (MoAb PAC1) and 54% expressed pre-bound fibrinogen (MoAb 9F9), with further increases on ADP activation. However, incubation with GRGDSP and the F(ab’)2 fragment did not inhibit the prebound fibrinogen. Moreover, relatively unactivated cells (8% expressing receptor, 14% prebound fibrinogen), prepared from acidified cPRP by single centrifugation with 50 nM of the stable prostacyclin derivative, ZK 36 374, and resuspension in Tyrodes-albumin at 5 × 104 μl−1, aggregated with 2 and 5 μM ADP at Ḡ = 335 and 1,335 s−1 in the absence of added fibrinogen. We therefore postulate that a protein such as von Willebrand factor, secreted during platelet isolation or in flow at sufficiently high shear rates, may yield the observed shear-rate dependent aggregation without fibrinogen.

Inhibition of Platelet Aggregation by an SLE-Derived Human Hybridoma Autoantibody Against an Activation-Dependent Antigen

Anti-platelet autoantibodies may be responsible for hematological complications in patients with systemic lupus erythematosus (SLE), but the mechanisms by which these antibodies cause abnormal hemostasis remain unknown. In the present study, using fluorescence activated cell sorter (FACS) analysis, we demonstrate that an SLE-derived human hybridoma autoantibody, 9604, recognizes a surface antigen expressed on platelets activated by ADP, calcium ionophore A23187, or phorbol myristate acetate (PMA), showing saturation with approximately 2,000 antibody molecules bound per platelet and a Kd of 41 nM. The binding of 9604 to activated platelets was significantly inhibited by EDTA, indicating partial dependence on divalent cations. It did not appear to be dependent on platelet secretion, nor did it directly affect α-granule or dense granule secretion. The protein antigen responsible for the binding of 9604 to activated platelets was characterized by Western blot and immunoprccipitation and shown to have a native molecular weight (M. W.) of greater than 400,000, with a 32,000 M. W. subunit (p 32). Antibody 9604 had little or no effect on the shape change and the initial rate of primary aggregation of normal platelets. In contrast, 9604 inhibited secondary aggregation of stirred platelet suspensions (IC50 ≥1 nM) following activation by ADP, thromboxane A2 mimetic U46619, or calcium ionophore A23187, but not PMA or thrombin. The inhibition of large platelet aggregate formation (secondary aggregation), with a major shift to smaller microaggregates and singlets, was confirmed by direct particle count and sizing studies. The functional inhibition of platelet aggregation by an SLE-derived human hybridoma autoantibody in vitro suggests one potential mechanism that may play a role in the hemostatic disorders found in SLE.

Differential Inhibition of the Platelet Activation Sequence: Shape Change, Micro- and Macro-Aggregation, by a Stable Prostacyclin Analogue (lloprost)

The relative sensitivities of adenosine diphosphate (ADP)-induced activation, and of prostaglandin-mediated inhibition, were determined for rates of platelet shape change (SC [Vs]), early platelet recruitment measured by electronic platelet counting (PA [PA3]), and turbidometrically-measured aggregation (TA[Va]). Studies were performed in stirred citrated platelet-richplasma from 9 healthy human donors. The [ADP]1/2, ([ADP]giving half maximal rate) was determined for the sequence of activation steps: unactivated platelets → SC → PA → TA. Distinct ADP sensitivities were obtained from log dose-responsestudies, with a relative dose dependency for rates of change in the order of [ADP]1/2 TA > [ADP]1/2 PA > [ADP]1/2 SC of ~4:3:1.Differential inhibition of the above activation scheme was evalu-ated from log dose-response curves for lloprost (ZK 36374), astable carbacyclin analogue of prostacyclin (PGI2), with greaterpotency than PGI2 for the same platelet receptors. IC50 valuescorresponding to lloprost concentrations causing 50% inhibitionof rates of TA (Va), PA (PA3) and SC (Vs) were found in therelative ratios of 1: ~3: ~5, when measured at a common ADPconcentration for all three parameters, or 1: ~2: ~3 when deter-mined at respective [ADP]1/2 values for each parameter. Thus, about 3-5 times more lloprost is required to respectively inhibitthe rates of shape change (Vs) and early platelet recruitment(PA3), than that needed to inhibit the rate of turbidometrically-measured aggregation (Va).

What do Key Stakeholders Think About HIV Self-Testing in Canada? Results from a Cross-Sectional Survey

Human immunodeficiency virus (HIV) self-testing presents an empowering alternative to facility-based testing for reaching undiagnosed HIV infected individuals, but is not currently available in Canada. We surveyed stakeholders (clinical providers, public health professionals, researchers) engaged in HIV testing initiatives nationwide to identify the concerns, opportunities and challenges to implementing HIV self-testing in Canada. An online cross-sectional survey was disseminated by the Canadian Institutes of Health Research Centre for REACH 2.0 National HIV & sexually transmitted and blood borne infections working group to stakeholders nationwide, with a target sample size of 200. Quantitative and qualitative data were analyzed using a mixed-methods, respondent-informed approach, to inform subsequent HIV self-testing in a country where self-testing is not yet accessible. A total of 183 responses were received. A majority (70.7%) (128/181) felt that self-testing was a necessary investment to reach the undiagnosed. 64.6% (117/181) felt that self-tests should be made available to their clients and 71.5% (128/179) of respondents agreed that self-test instructions required improvements. However, 50% (90/180) felt that self-testing will pose an economic challenge to current HIV testing models. Regardless, 21% urged for timely action and availability of HIV self-tests. Thematic analyses reflected the following concerns: (a) need for affordable self-tests, (b) need for expedited, customized, and accessible linkages to counselling, (c) concern for patients to cope with positive self-test results, (d) accuracy of self-tests to detect acute HIV and (e) liability in the context of non-disclosure. Stakeholders agreed to the provision of an option of HIV self-testing to reach the undiagnosed individuals. Concerns regarding costs and accuracy of self-tests, expedited linkages to counselling, and integration of self-test within prevailing HIV testing models, will need to be addressed before their widespread implementation.

Contact Force and Atrial Fibrillation Ablation

Catheters able to measure the force and vector of contact between the catheter tip and myocardium are now available. Pre-clinical work has established that the degree of contact between the radiofrequency ablation catheter and myocardium correlates with the size of the delivered lesion. Excess contact is associated with steam pops and perforation. Catheter contact varies within the left atrium secondary to factors including respiration, location, atrial rhythm and the trans-septal catheter delivery technology used. Compared with procedures performed without contact force (CF)-sensing, the use of this technology has, in some studies, been found to improve complication rates, procedure and fluoroscopy times, and success rates. However, for each of these parameters there are also studies suggesting a lack of difference from the availability of CF data. Nevertheless, CF-sensing technology has been adopted as a standard of care in many institutions. It is likely that use of CF-sensing technology will allow for the optimization of each individual radiofrequency application to maximize efficacy and procedural safety. Recent work has attempted to define what these optimal targets should be, and approaches to do this include assessing for sites of pulmonary vein reconnection after ablation, or comparing the impedance response to ablation. Based on such work, it is apparent that factors including mean CF, force time integral (the area under the force-time curve) and contact stability are important determinants of ablation efficacy. Multicenter prospective randomized data are lacking in this field and required to define the CF parameters required to produce optimal ablation.

Decline in Decreased Cephalosporin Susceptibility and Increase in Azithromycin Resistance in Neisseria gonorrhoeae, Canada

Antimicrobial resistance profiles were determined for Neisseria gonorrhoeae strains isolated in Canada during 2010–2014. The proportion of isolates with decreased susceptibility to cephalosporins declined significantly between 2011 and 2014, whereas azithromycin resistance increased significantly during that period. Continued surveillance of antimicrobial drug susceptibilities is imperative to inform treatment guidelines.

The Utility of Point-of-Care Ultrasound in Detecting Distal Forearm Buckle Fractures in Paediatric Patients

BACKGROUND: Distal forearm fractures are common paediatric injuries. The use of plain radiographs is almost universal for diagnosis but this technology can be painful and time consuming. It is well known that children’s pain in the emergency department (ED) is both under-recognized and suboptimally managed. Point-of-care ultrasound (POCUS) has demonstrated good accuracy in detecting cortical disruption in adults but test characteristics in the most common paediatric fracture type (buckle or torus fractures) have not been explored. POCUS may also lead to quicker assessment and be associated with less pain and improved caregiver satisfaction compared to plain radiographs. Our results may provide support an alternative diagnostic strategy for centres where plain radiographs are not readily accessible and where severe pain is an issue.

OBJECTIVES: The objectives of this study were to: (i) evaluate the diagnostic accuracy POCUS in detecting suspected non-angulated distal forearm fractures in children presenting to the ED compared to AP and lateral plain film x-rays of the forearm, (ii) determine the length of time required to complete a POCUS evaluation for a suspected distal forearm non-angulated fracture in children in the ED, (iii) explore the differences in caregiver satisfaction with POCUS evaluation compared to plain radiography, and (iv) explore differences in associated pain between POCUS and plain radiography.

DESIGN/METHODS: This was a prospective cohort study designed to test the hypothesis that POCUS provides comparable sensitivity and specificity to plain radiography and is associated with less pain and greater caregiver satisfaction. We included children aged 4-17 years who presented to the paediatric ED with a suspected non-angulated distal forearm fracture based on a typical mechanism of injury. The patient underwent an x-ray and a POCUS evaluation of the affected region by a Canadian Emergency Ultrasound (CEUS)-trained physician who was blinded to the x-ray results. Caregivers were asked to complete a satisfaction questionnaire using a five-point Likert scale and children were asked to complete the Faces Pain Scale – Revised (FPS-R) reflecting discomfort associated with the diagnostic modality. The primary POCUS diagnosis made by the physician was compared to the x-ray diagnosis made by the staff paediatric radiologist. All POCUS images were independently interpreted by a second expert POCUS sonographer blinded to the original POCUS interpretation, x-ray, and final diagnosis. The primary outcomes were sensitivity of POCUS and pain score using the FPS-R.

RESULTS: Eighty-five participants were enrolled, of whom 33 (39%) sustained a buckle fracture. The mean (SD) age of the participants was 11 (3.4) years and 52 (61%) were male. Sensitivity and sensitivity of POCUS for detecting any cortical disruption was 97% [95% CI: 84.2, 99.9] and 96% [95% CI: 86.8, 99.5], respectively. Agreement (kappa) between sonographers was 0.74 [95% CI: 0.64, 0.87] representing substantial agreement. POCUS was associated with significantly lower mean (SD) pain scores compared to plain radiography [2.3 (2.5) vs 3.6 (3.0), p < 0.01]. The median (IQR) time to perform POCUS was significantly lower that plain radiography [68 (42) vs 1200 (1440) seconds, p < 0.01]. POCUS was associated with comparable mean caregiver satisfaction compared to plain radiography [4.7 (0.7) vs 4.4 (1.0), p = 0.15].

CONCLUSION: This prospective study of POCUS for non-angulated distal forearm injuries in children suggests that POCUS is associated with excellent sensitivity and specificity for the detection of cortical disruption. Furthermore, POCUS is associated with significantly less pain and procedure time compared to plain radiography. The results suggest that POCUS could be a useful diagnostic strategy in resource-limited settings for children with suspected forearm injuries and has the added benefit of lower associated pain.

Combined aerobic exercise and enzyme replacement therapy rejuvenates the mitochondrial-lysosomal axis and alleviates autophagic blockage in Pompe disease

A unifying feature in the pathogenesis of aging, neurodegenerative disease, and lysosomal storage disorders is the progressive deposition of macromolecular debris impervious to enzyme catalysis by cellular waste disposal mechanisms (e.g., lipofuscin). Aerobic exercise training (AET) has pleiotropic effects and stimulates mitochondrial biogenesis, antioxidant defense systems, and autophagic flux in multiple organs and tissues. Our aim was to explore the therapeutic potential of AET as an ancillary therapy to mitigate autophagic buildup and oxidative damage and rejuvenate the mitochondrial-lysosomal axis in Pompe disease (GSD II/PD). Fourteen weeks of combined recombinant acid α-glucosidase (rhGAA) and AET polytherapy attenuated mitochondrial swelling, fortified antioxidant defense systems, reduced oxidative damage, and augmented glycogen clearance and removal of autophagic debris/lipofuscin in fast-twitch skeletal muscle of GAA-KO mice. Ancillary AET potently augmented the pool of PI4KA transcripts and exerted a mild restorative effect on Syt VII and VAMP-5/myobrevin, collectively suggesting improved endosomal transport and Ca(2+)- mediated lysosomal exocytosis. Compared with traditional rhGAA monotherapy, AET and rhGAA polytherapy effectively mitigated buildup of protein carbonyls, autophagic debris/lipofuscin, and P62/SQSTM1, while enhancing MnSOD expression, nuclear translocation of Nrf-2, muscle mass, and motor function in GAA-KO mice. Combined AET and rhGAA therapy reactivates cellular clearance pathways, mitigates mitochondrial senescence, and strengthens antioxidant defense systems in GSD II/PD. Aerobic exercise training (or pharmacologic targeting of contractile-activity-induced pathways) may have therapeutic potential for mitochondrial-lysosomal axis rejuvenation in lysosomal storage disorders and related conditions (e.g., aging and neurodegenerative disease).