Measurement of platelet function in dogs using a novel impedance aggregometer

P2Y1 and P2Y12 Receptors Mediate Aggregation of Dog and Cat Platelets: A Comparison to Human Platelets

Thrombosis is one of the most prevalent and serious health issues amongst humans. A key component of thrombotic events is the activation and aggregation of platelets, of which the P2Y1 and P2Y12 receptors play a crucial role in this process. Despite a breadth of knowledge on thrombosis and its mechanisms and treatment in various disorders in humans, there is less of an understanding of the expression and exact role of these receptors in companion animals such as dogs and cats. Therefore, this study aimed to investigate P2Y1 and P2Y12 receptors on dog and cat platelets in platelet-rich plasma and compare them to human platelets. Immunoblotting revealed the presence of P2Y1 and P2Y12 receptor proteins on dog and cat platelets, although relative amounts of each receptor appeared to contrast those of human platelets, with increased amounts of P2Y1 compared to P2Y12 receptors in dogs and cats. Using a modified 384-well plate aggregation assay, designed for use with small volumes, the human P2Y1 and P2Y12 receptor agonists adenosine 5'-diphosphate and 2-methylthio-adenosine 5'-diphosphate caused aggregation of dog and cat platelets. This aggregation was near-completely inhibited by the selective P2Y12 antagonist ticagrelor. Aggregation of dog and cat platelets was partly inhibited by the human P2Y1 receptor antagonist MRS2179. The agonist and antagonist responses in dog and cat platelets were like those of human platelets. In contrast, the aggregation of dog platelets in the absence of added nucleotides was two-fold greater than that of cats and humans. This study indicates that platelets of cats and dogs possess functional P2Y1 and P2Y12 receptors that can be inhibited by human antagonists. The data presented suggest differing roles or responses of the platelet P2Y receptors in dogs and cats compared to humans but also highlight the potential of using currently available P2Y1 or P2Y12 antiplatelet drugs such as ticagrelor for the treatment of thrombosis in these companion animals.

The effect of concurrent clopidogrel and omeprazole administration on clopidogrel metabolism and platelet function in healthy cats

BACKGROUND

Some studies in humans show that the concurrent use of clopidogrel and omeprazole decreases plasma clopidogrel active metabolite (CAM) concentrations and clopidogrel antiplatelet effects. Whether this drug interaction occurs in cats is unknown.

HYPOTHESIS

We hypothesized that administration of clopidogrel with omeprazole would decrease plasma CAM concentrations and decrease clopidogrel antiplatelet effects in healthy cats.

ANIMALS

Ten domestic cats.

METHODS

In this 2-sequence, 2-period, 2-treatment randomized crossover study, healthy cats were randomly assigned to receive clopidogrel only (18.75 mg PO q24h) or clopidogrel with omeprazole (1 mg/kg PO q12h) for 10 days, followed by a 2-week washout period, and then the opposite treatment for another 10 days. Blood was collected by jugular venipuncture on days 0, 5, and 10. Plasma CAM concentrations were measured using high-performance liquid chromatography-tandem mass spectrometry. Platelet function was evaluated using Plateletworks, Multiplate Analyzer, and Platelet Function Analyzer-100 (PFA-100).

RESULTS

Multiplate Analyzer and PFA-100 detected no difference in platelet function between days or treatment groups. Plateletworks detected a significant difference (P < .001) in platelet function from day 0 to 5 and day 0 to 10 in both treatment groups but no difference between treatment groups. Plasma CAM concentrations were significantly lower on day 10 (P < .02) in cats receiving both medications versus clopidogrel only.

CONCLUSIONS AND CLINICAL IMPORTANCE

Concurrent omeprazole and clopidogrel administration was associated with altered pharmacokinetics on day 10, but no difference in pharmacodynamics between the 2 treatment groups. The short-term use of clopidogrel and omeprazole does not seem to alter platelet function significantly.

Advances in Platelet-Dysfunction Diagnostic Technologies

The crucial role of platelets in hemostasis and their broad implications under various physiological conditions underscore the importance of accurate platelet-function testing. Platelets are key to clotting blood and healing wounds. Therefore, accurate diagnosis and management of platelet disorders are vital for patient care. This review outlines the significant advancements in platelet-function testing technologies, focusing on their working principles and the shift from traditional diagnostic methods to more innovative approaches. These improvements have deepened our understanding of platelet-related disorders and ushered in personalized treatment options. Despite challenges such as interpretation of complex data and the costs of new technologies, the potential for artificial-intelligence integration and the creation of wearable monitoring devices offers exciting future possibilities. This review underscores how these technological advances have enhanced the landscape of precision medicine and provided better diagnostic and treatment options for platelet-function disorders.

Whole blood platelet impedance aggregometry with the ROTEM platelet device: comparison of 2 anticoagulants and storage times for the establishment of canine reference intervals

The ROTEM platelet device, a point-of-care whole blood platelet impedance aggregometer, is an add-on to the rotational thromboelastometry ROTEM delta device. The latter has been validated in dogs. We examined whether canine whole blood is suited for analysis with the ROTEM platelet device using adenosine-5'-diphosphate (ADP) and arachidonic acid (ARA) as agonists for platelet activation, and if there are significant differences between sample storage times and anticoagulants used. Subsequently, we determined canine reference intervals (RIs) for the ROTEM platelet device for ADP and ARA. In a pilot study, we examined whole blood from 7 dogs after 15-min and 60-min storage of lithium-heparinized samples and 40-min and 80-min storage of hirudinized samples. Statistical analysis showed no significant differences between ROTEM platelet device results for both ADP and ARA in lithium-heparin and hirudin anticoagulated canine whole blood. Lithium-heparinized blood samples analyzed after 15-min storage had the lowest coefficient of variation. RIs were determined for heparinized whole blood samples from 49 dogs after 15 min of storage.

The canine activated platelet secretome (CAPS): A translational model of thrombin-evoked platelet activation response

BACKGROUND

Domestic dogs represent a translational animal model to study naturally occurring human disease. Proteomics has emerged as a promising tool for characterizing human platelet pathophysiology; thus a detailed characterization of the core canine activated platelet secretome (CAPS) will enhance utilization of the canine model. The objectives of this study were development of a robust, high throughput, label-free approach for proteomic identification and quantification of the canine platelet (i) thrombin releasate proteins, and (ii) the protein subgroup that constitutes CAPS.

METHODS

Platelets were isolated from 10 healthy dogs and stimulated with 50 nmol/L of γ-thrombin or saline. Proteins were in-solution trypsin-digested and analyzed by nano-liquid chromatography-tandem spectrometry. Core releasate proteins were defined as those present in 10 of 10 dogs, and CAPS defined as releasate proteins with a significantly higher abundance in stimulated versus saline controls (corrected P < .05).

RESULTS

A total of 2865 proteins were identified; 1126 releasate proteins were present in all dogs, 650 were defined as CAPS. Among the differences from human platelets were a canine lack of platelet factor 4 and vascular endothelial growth factor C, and a 10- to 20-fold lower concentration of proteins such as haptoglobin, alpha-2 macroglobulin, von Willebrand factor, and amyloid-beta A4. Twenty-eight CAPS proteins, including cytokines, adhesion molecules, granule proteins, and calcium regulatory proteins have not previously been attributed to human platelets.

CONCLUSIONS

CAPS proteins represent a robust characterization of a large animal platelet secretome and a novel tool to model platelet physiology, pathophysiology, and to identify translational biomarkers of platelet-mediated disease.

Abnormal platelet activity in dogs and cats - impact and measurement

Abnormal platelet activity can either lead to bleeding tendencies or inappropriate thrombus formation and can occur secondarily to a wide variety of disease processes, with a range of clinical consequences and severity. This article will discuss the pathophysiology of platelet function abnormalities and consider a logical diagnostic approach applicable to veterinary practice. Recent advances in platelet function testing will then be discussed, with regards to detection of platelet dysfunction and tailoring of pharmacological manipulation. Although many of these tests are still confined to research or academic institutions, techniques for indirectly assessing platelet function are starting to become more widely available. Although we still require further research to develop guidelines for the use of these tests in clinical decision-making, the recent advances in this field are an exciting step forward in being able to detect and manage platelet dysfunction in both primary care and referral practice.

Effects of clopidogrel and prednisone on platelet function in healthy dogs

Background

Glucocorticoids cause hypercoagulability, but it is unknown if they counteract clopidogrel's antiplatelet effects.

Hypothesis/Objectives

Determine the effects of clopidogrel and prednisone on platelet function.

Animals

Twenty‐four healthy dogs.

Methods

Double‐blinded, placebo‐controlled randomized trial. Platelet function was evaluated using a platelet function analyzer and impedance aggregometry (days 0, 14, and 28) for dogs treated with placebo, clopidogrel (2‐3 mg/kg/d), prednisone (2 mg/kg/d), or prednisone with clopidogrel PO for 28 days. Results were categorized as nonresponder versus responder (platelet function analyzer), and inadequate, ideal, or excessive response (aggregometry). Results were compared using mixed model, split‐plot repeated measures analysis of variance and generalized estimating equation proportional odds models. P < .05 was considered significant.

Results

Closure times differed by treatment (F [3, 20] = 10.5; P < .001), time (F [2, 40] = 14.3; P < .001), and treatment‐by‐time (F [6, 40] = 3.4; P = .01). Area under the curve (AUC) differed by treatment (F [3, 20] = 19.6; P < .001), time (F [2, 40] = 35.4; P < .001), and treatment‐by‐time (F [6, 40] = 13.5; P < .001). Based on closure times, 5/6 dogs each in the clopidogrel and prednisone/clopidogrel groups were responders. All dogs in the prednisone/clopidogrel group were overcontrolled based on AUC (days 14 and 28), whereas 5/6 (day 14) and 2/6 (day 28) dogs treated with clopidogrel were overcontrolled. Compared to clopidogrel, dogs receiving prednisone/clopidogrel were 11 times (P = .03) more likely to have an excessive response.

Conclusions and Clinical Importance

Administration of clopidogrel/prednisone increases platelet dysfunction in healthy dogs.

Effects of Aspirin and Prednisone on Platelet Function and Thromboxane Synthesis in Healthy Dogs

Glucocorticoid administration is a risk factor for thromboembolism in hypercoagulable dogs, and it is unknown if aspirin counteracts glucocorticoid-induced hypercoagulability. The objective was to determine the effects of sustained aspirin and prednisone administration on platelet function and thromboxane synthesis. Our hypothesis was that aspirin would consistently inhibit platelet function and thromboxane synthesis when administered with or without prednisone. In 24 healthy dogs, platelet aggregometry and urine 11-dehydro-thromboxane-B₂ (11-dTXB₂)-to-creatinine ratios were measured on days 0, 14, and 28. Dogs were administered placebos, aspirin (2 mg/kg/d), prednisone (2 mg/kg/d), or prednisone/aspirin combination therapy PO for 28 days in a randomized double-blinded study. Aspirin response was based on a >25% reduction in platelet aggregation compared to pre-treatment values. Results were compared using mixed model, split-plot repeated measures ANOVAs. P < 0.05 was considered significant. AUC differed significantly by time [F_(2,40) = 10.2, P < 0.001] but not treatment or treatment-by-time. On day 14, 2 dogs were aspirin responders (aspirin, 1; placebo, 1). On day 28, 3 dogs were aspirin responders (aspirin, 2; prednisone/aspirin, 1). Urine 11-dTXB₂-to-creatinine ratios differed significantly by group [F_(3,20) = 3.9, P = 0.024] and time [F_(2,40) = 8.7, P < 0.001), but not treatment-by-time. Post-hoc analysis revealed significant differences between aspirin and placebo groups (P=0.008), aspirin and prednisone/aspirin groups (P = 0.030), and placebo and prednisone groups (P = 0.030). In healthy dogs, sustained aspirin, prednisone, and combination therapy do not inhibit platelet aggregation, and when used as individual therapies, aspirin and prednisone decreased thromboxane synthesis. Additional studies using varied platelet function methodologies in hypercoagulable dogs are necessary.

Primary hemostatic function in dogs with acute kidney injury

BACKGROUND

Bleeding tendencies can occur with uremia.

OBJECTIVES

To characterize primary hemostatic function in dogs with acute kidney injury (AKI).

ANIMALS

Ten dogs with International Renal Interest Society AKI grade III or above and 10 healthy controls.

METHODS

Prospective study comparing PCV, platelet count, platelet aggregometry (Multiplate), and von Willebrand factor antigen to collagen binding activity ratio (vWF:Ag:vWF:CBA) in 2 groups of dogs (AKI group versus controls). Buccal mucosal bleeding time was measured in the AKI group only. Data are presented as median [25th, 75th percentile] unless otherwise stated. Significance was set at P < .05.

RESULTS

Mean PCV was significantly lower in the AKI (34.7%; ±SD, 8.8) than in the control (46.1%; ±SD, 3.6; P < .001) group. Platelet count was significantly higher in the AKI (350.5 × 103 /μL [301, 516]) than in the control (241 × 103 /μL [227, 251]; P = .01) group. Collagen-activated platelet aggregometry measured as area under the curve was significantly lower in the AKI (36.9 ± 17.7) than in the control (54.9 ± 11.2; P = .05) group. vWF:Ag:vWF:CBA was significantly higher in the AKI (2.2 [1.9, 2.6]) than in the control (1.1 [1.1, 1.2]; P = .01) group. There was a strong correlation between vWF:Ag:vWF:CBA and creatinine (r = 0.859; P < .001), but no other variables.

CONCLUSIONS AND CLINICAL IMPORTANCE

Dogs with AKI had decreased collagen-activated platelet aggregation and appear to have a type II von Willebrand disease-like phenotype as indicated by the high vWF:Ag:vWF:CBA.

Comparison of Multiplate, Platelet Function Analyzer-200, and Plateletworks in Healthy Dogs Treated with Aspirin and Clopidogrel

BACKGROUND

Platelet function testing may be warranted to assess response to aspirin and clopidogrel.

HYPOTHESIS/OBJECTIVES

To evaluate the effects of aspirin, clopidogrel, or combination therapy using 3 platelet function tests: Multiplate Analyzer (MP), Platelet Function Analyzer-200 (PFA), and Plateletworks (PW).

ANIMALS

Six healthy laboratory Beagles.

METHODS

Randomized double-blind placebo-controlled study (crossover design). Dogs were given aspirin 1 mg/kg, clopidogrel 2 mg/kg, or combination therapy for 1 week each, with a washout period of 2 weeks. Platelet function was assessed on days 0 and 7 of each phase using MP (adenosine diphosphate [ADP], arachidonic acid [AA], collagen [COL] agonists), PFA (P2Y, COL-ADP [CADP], COL-Epinephrine [CEPI] cartridges), and PW (ADP, AA, COL agonists). Platelet counts were obtained with impedance and optical counters.

RESULTS

For MP, mean aggregation was decreased for COL and AA with combination therapy and for ADP with all treatments. For PFA, mean CT was increased for the CEPI cartridge with aspirin; and for the P2Y and CADP cartridges with clopidogrel or combination therapy. More dogs receiving clopidogrel showed an increase in PFA CT using the P2Y than the CADP cartridge. For PW, mean aggregation was decreased for AA with all treatments; for ADP with clopidogrel or combination therapy; and for COL with clopidogrel. The PW results with the 2 hematology counters showed almost perfect agreement.

CONCLUSION AND CLINICAL IMPORTANCE

All platelet function tests detected treatment effects in some dogs and may have utility for monitoring therapy.

In vitro effect of blood cell counts on multiple-electrode impedance aggregometry in dogs

OBJECTIVE To assess the effect of decreased platelet and WBC counts on platelet aggregation as measured by a multiple-electrode impedance aggregometer in dogs. ANIMALS 24 healthy dogs. PROCEDURES From each dog, 9 mL of blood was collected into a 10-mL syringe that contained 1 mL of 4% sodium citrate solution to yield a 10-mL sample with a 1:9 citrate-to-blood ratio. Each sample was then divided into unmanipulated and manipulated aliquots with progressively depleted buffy-coat fractions such that 2 to 3 blood samples were evaluated per dog. The Hct for manipulated aliquots was adjusted with autologous plasma so that it was within 2% of the Hct for the unmanipulated aliquot for each dog. All samples were analyzed in duplicate with a multiple-electrode impedance aggregometer following the addition of ADP as a platelet agonist. The respective effects of platelet count, plateletcrit, Hct, and WBC count on platelet aggregation area under the curve (AUC), aggregation, and velocity were analyzed with linear mixed models. RESULTS WBC count was positively associated with platelet AUC, aggregation, and velocity; blood samples with leukopenia had a lower AUC, aggregation, and velocity than samples with WBC counts within the reference range. Platelet count, plateletcrit, and Hct did not have an independent effect on AUC, aggregation, or velocity. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that WBC count was positively associated with platelet aggregation when ADP was used to activate canine blood samples for impedance aggregometry. That finding may be clinically relevant and needs to be confirmed by in vivo studies.

Suspected aspirin resistance in individual healthy adult warmblood horses

The reasons for this prospective experimental study were to determine a dosing scheme with loading and maintenance dose of aspirin inducing inhibition of platelet function measured by whole blood impedance aggregometry. Ten horses received aspirin orally in the morning with one loading dose of 4.7-5 mg/kg and maintenance doses of 1-1.3 mg/kg daily the following 4 days. Aggregometries (COLtest, ASPItest, ADPtest) and serum salicylic acid were measured. ASPItest showed significant difference in inhibition at 24 and 48 hr (p < .05) and 96 hr (p < .01). Significant change for ADPtest and COLtest couldn't be detected. Serum salicylic acid concentrations were significantly (p < .01) increased at 6 and 12 hr. Despite this, three horses failed any inhibitory effect of platelet function, suspecting an aspirin resistance. Regarding the other seven horses platelet aggregation induced by ASPItest was reduced between 37% and 100% from baseline at 6 and 12 hr and between 0 and 98% during the next 4 days. Correlations of serum concentration of salicylic acid and aggregometries couldn't be detected. It can be presumed that equine platelets are less susceptible to aspirin what may compromise eventually the anticoagulatory effects and efficacy in preventing and treating diseases with increased platelet activation as endotoxaemia or laminitis.

Establishment of reference ranges and evaluation of in vitro concentration-dependent platelet inhibition by acetylsalicylic acid for multiple electrode impedance aggregometry in healthy dogs

Acetylsalicylic acid (ASA, aspirin) is an antiplatelet medication used for prevention of thromboembolism. Effects of ASA appear to vary widely between dogs, but the underlying mechanisms are not understood. The Multiplate analyzer is a newer form of whole-blood impedance aggregometry recently validated for use in healthy dogs. A method utilizing this instrument to measure ASA effects on platelet function has not been established. The goals of this study were to establish reference ranges for the Multiplate in healthy dogs and secondly, to develop a technique to determine the in vitro concentration of ASA needed to cause 50% inhibition of platelet aggregation (IC50). Reference ranges established from 40 dogs at multiple test times for three agonists were consistent with previously published values. In vitro IC50 values were calculated using the sigmoid E_max model in 20 healthy dogs on two occasions to determine individual repeatability. Calculated in vitro IC50 demonstrated four ASA response groups: responder (n = 16), poor responder (n = 1), variable responder (n = 2), and nonresponder (n = 1). Multiplate within-assay variability was  <10% for area under the curve (AUC), and between-assay baseline AUC variability was  <15%. The described technique allowed for determination of an in vitro IC50 for ASA in dogs using a multiple electrode impedance aggregometer.

Platelet function in baboons and humans - A comparative study of whole blood using impedance platelet aggregometry (Multiplate®)

BACKGROUND

Platelets play a pivotal role in coagulation, inflammation and wound healing. Suitable animal models that have the potential to mimic human platelet function are limited. The objective of the current study was to compare platelet aggregation response in the whole blood of baboons and humans using impedance aggregometry.

METHODS

Blood was drawn from 24 anesthetised male baboons and 25 healthy volunteers. The platelet aggregation response was determined by impedance aggregometry (Multiplate®). Platelets in the hirudinised whole blood samples were stimulated with four different activators: adenosine diphosphate (ADP), collagen (COL), thrombin receptor activating peptide-6 (TR1AP), and activation of PAR-4 thrombin receptor subtype (TR4AP) at standard concentrations. Higher than standard concentrations were tested in a subgroup of the animals.

RESULTS

The cell counts showed no differences between baboons and humans. The platelet aggregation response was significantly lower in baboons compared to humans when stimulated with the platelet agonists ADP (p<0.0001), COL (p=0.021) and TR4AP (p<0.0001). TR1AP did not stimulate platelet aggregation in the baboon blood. Doubling the concentration of ADP and of TR4AP significantly increased the AUC compared to the standard concentration. In contrast, increased COL levels did not further increase the AUC.

CONCLUSION

The current study revealed that testing the platelet function in baboon blood by impedance aggregometry is feasible with ADP, COL and TR4AP, but not with TR1AP. Compared to humans, the aggregation response is lower in baboons. Considering the limitations in accordance to these results, baboons might represent a potential species for further platelet research.

Influence of a low dosage of clopidogrel on platelet function in cats as measured by the platelet function analyser PFA-100 and the multiplate analyser

The antiplatelet drug clopidogrel is widely used for prophylaxis of arterial thromboses in cats in a standard dosage of 18.75mg per cat once daily. The aim of the study was to verify if a reduced daily dose of 10mg clopidogrel per cat has a similar antiplatelet effect as the standard dosage. Platelet function was measured with the platelet function analyser PFA-100^® and a novel impedance aggregometer. Suitability of the platelet function analyser was tested in citrated blood samples of 59 healthy cats and reference ranges were established. In addition, agonist concentrations for impedance aggregometry were optimised. In the main experiment two groups of 6 healthy cats received clopidogrel either in a dosage of 10 or 18.75mg per cat over a period of seven days. Analyses were performed on days 1, 2, 3, 5, and 7. In comparison to baseline both clopidogrel dosages showed an inhibitory effect on results of the platelet function analyser and velocity of ADP-induced platelet aggregation. Values at all times were different from baseline, with the exception of day 1 in cats receiving 10mg clopidogrel where the closure time of the platelet function analysis and part of ADP-induced aggregation did not show a significant difference. Significant differences were not found between the two doses. In conclusion, our study indicates that 10mg clopidogrel per day may be as effective as 18.75mg although the latter may be advantageous as an initial loading dosage to achieve effective levels more rapidly.

Evaluation of platelet function using multiple electrode platelet aggregometry in dogs with septic peritonitis

OBJECTIVE

To assess platelet function via multiple electrode platelet aggregometry (MEPA) in dogs with septic peritonitis and in healthy dogs. The secondary aim was to determine if there is prognostic significance to changes in platelet function observed in septic dogs.

DESIGN

Prospective, observational cohort study conducted from January 2012 to March 2014.

SETTING

University teaching hospital.

ANIMALS

Twenty dogs with septic peritonitis and 23 healthy dogs.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

MEPA using arachidonic acid, adenosine diphosphate, and collagen (COL) as agonists was measured within 24 hours of diagnosis of sepsis. Compared to healthy dogs, platelet aggregation was reduced in dogs with septic peritonitis for all agonists (P < 0.01). Overall mortality rate was 40%. MEPA in response to COL was significantly reduced in nonsurvivors compared to survivors (P = 0.019). Using receiver-operating characteristic curve statistics, a COL-activated MEPA less than 43.5 aggregation units had a sensitivity and specificity of 85.7% and 90.9%, respectively, for predicting nonsurvival in dogs with septic peritonitis.

CONCLUSIONS

Circulating platelets from dogs with septic peritonitis have diminished aggregation in response to multiple platelet agonists. MEPA may serve as an assessment tool for illness severity in this patient population.

Assessment of platelet function in healthy sedated cats using three whole blood platelet function tests

The objectives of this study were to establish feline references intervals for 3 commercial whole blood platelet function test analyzer systems: Multiplate analyzer (MP; Roche Diagnostics International Ltd., Rotkreuz, Switzerland), Platelet Function Analyzer-100 (PF: Siemens Canada, Mississauga, Ontario, Canada), and Plateletworks Combo-25 kit (PW; Helena Laboratories, Beaumont, TX). Venipuncture was performed on 55 healthy sedated cats, and platelet aggregation in response to adenosine diphosphate (ADP), collagen (COL), and arachidonic acid (AA; MP only) was assessed using citrated blood. For the MP analyzer, median (95% confidence intervals [CIs]) area under curve (Units) for ADP, COL, and AA agonists were 87 (11-176), 81 (32-129), and 91 (59-129), respectively. For the PF analyzer, median (95% CIs) closure time, using COL-ADP cartridges, was 69 (46-89) sec. For the PW assay, median (95% CIs) percent aggregations for ADP and COL agonists were 71 (18-92) and 49 (9-96), respectively, using impedance hematology analyzer platelet counts, and 94 (25-98) and 68 (14-119), respectively, using flow cytometry hematology analyzer platelet counts. There were low correlations between the PF analyzer (COL-ADP cartridge) and MP analyzer (COL agonist; ρ = 0.11), and between the PF analyzer (COL-ADP cartridge) and PW assay (COL agonist using impedance platelet counts; ρ = 0.14). The PW assay percent aggregations using impedance and flow cytometric platelet counts were correlated for both ADP (ρ = 0.64) and COL (ρ = 0.64) agonists. Platelet function testing using these tests are feasible in cats, but 95% CIs are wide, so single results may be difficult to interpret. Platelet counting by impedance or flow cytometry may be used for the PW assay but are not interchangeable.

Inhibition of platelet function with clopidogrel, as measured with a novel whole blood impedance aggregometer in horses

This study aimed to validate a loading and maintenance clopidogrel dosing scheme for the inhibition of platelet function, measured by whole blood impedance aggregometry in healthy adult horses. Ten Warmblood horses received oral clopidogrel once daily. Doses were based on 50 kg weight categories and resulted in one loading dose of 6-6.5 mg/kg bodyweight and maintenance doses of 1.2-1.4 mg/kg over the next 4 days. Platelet function was measured via whole blood multiple electrode impedance aggregometry prior to (T0) and at 6, 12, 24, 48, 72, 96, 144, 192 and 240 h following the loading dose. Aggregometries for collagen (COLtest), arachidonic acid (ASPItest), adenosine diphosphate (ADPtest) and ADP with prostaglandin E1 (ADPtestHS) were performed. Statistical analyses included one way repeated measures ANOVAs and subsequent Dunnett's tests. Platelet aggregation induced by collagen remained unchanged. There were significant inhibitions in the ASPItest (P <0.01 at 192 h, and P <0.05 at 240 h) and the ADPtest and ADPtestHS (P < 0.01, with the exception of 240 h). The loading dose of clopidogrel induced rapid inhibition of platelet function within hours, and the low dose was suitable for maintaining the inhibition over the 4 days of therapy. Recovery of platelet function was restored 6 days after the cessation of medication, determined with the ADPtest and ADPtestHS, but remained inhibited with the ASPItest. The prolonged effect of clopidogrel may indicate differences in the activation of platelets between horses and humans that were previously unknown.

Infection-associated platelet dysfunction of canine platelets detected in a flow chamber model

BACKGROUND

In the present study, the influence of bacterial infection, lipopolysacharides (LPS) and hydroxyethyl starch (HES) on platelet function in a parallel plate flow chamber were measured. Experiments were performed with non-activated and protease-activating-receptor (PAR) 4 agonist activated platelets. Comparative measurements were in vivo capillary bleeding time, platelet function analyzer and impedance aggregometry.

RESULTS

PAR 4 agonist did not increase platelet adhesion of platelets from dogs with bacterial inflammation in the flow chamber in contrast to platelets of healthy dogs. Except from impedance aggregometry with lower sensitivity and specificity, PFA did not detect platelet dysfunctions in dogs with infection. In vitro addition of LPS or HES significantly reduced platelet covered area after PAR-activation.

CONCLUSIONS

The flow chamber detects platelet dysfunctions in dogs with inflammatory diseases. In vitro addition of LPS highlights the inhibiting effect of bacterial wall components on platelet function. Platelet dysfunction induced by infection could possibly also be diagnosed after treatment of sepsis with colloids has commenced. The flow chamber could be a useful tool to detect sepsis associated platelet dysfunction given that larger prospective trials confirm these findings from a proof of concept study.

Platelet-neutrophil aggregate formation in blood samples from dogs with systemic inflammatory disorders

OBJECTIVE

To evaluate platelet-neutrophil aggregate (PNA) formation and neutrophil shape as indicators of neutrophil activation in dogs with systemic inflammatory diseases and after blood sample incubation with various platelet and neutrophil agonists.

ANIMALS

20 dogs with systemic inflammatory response syndrome (SIRS) and 10 healthy Beagles.

PROCEDURES

Neutrophils were isolated from blood samples directly after blood sample collection and after incubation of blood samples with phorbol myristate acetate, collagen, adenosine diphosphate, epinephrine, or various concentrations of lipopolysaccharide or arachidonic acid. CD61+ neutrophils as an indicator of PNA formation were evaluated, and neutrophil size and granularity were assessed via flow cytometry.

RESULTS

Dogs with SIRS had more PNA formation, larger neutrophil size, and less granularity relative to control dogs, but no differences were evident when these dogs were grouped by whether they had sepsis (n = 6) or disseminated intravascular coagulation (12). A significant increase in PNA formation occurred after neutrophil incubation with all agonists, and incubation with phorbol myristate acetate elicited the strongest response. Neutrophils increased in size and decreased in granularity after incubation with all agonists except epinephrine. Incubation with lipopolysaccharide or arachidonic acid resulted in a dose-dependent effect on PNA formation and neutrophil shape.

CONCLUSIONS AND CLINICAL RELEVANCE

SIRS appeared to increase the degree of PNA formation and neutrophil shape change. Similar changes after neutrophil incubation with platelet agonists suggested that platelet activation has a role in PNA formation. Additional studies are necessary to determine the clinical importance and diagnostic value of PNA formation in dogs with SIRS and sepsis.

Optimization of Multiplate(®) whole blood platelet aggregometry in the Beagle dog and Wistar rat for ex vivo drug toxicity testing

This study was performed to optimize and standardize the use of the Multiplate(®) whole blood impedance aggregometer in the Beagle dog and Wistar rat for use in a research laboratory environment. The anticoagulants citrate, heparin and hirudin were compared and platelet aggregation responses to ADP, collagen, arachidonic acid and Par-4 agonist were evaluated to determine their half maximal effective concentrations (EC(50)) in blood containing low concentrations of a drug solvent (0.1% DMSO). The results indicate that citrate anticoagulation is not suitable for Multiplate(®) whole blood aggregometry because of the presence of spontaneous aggregation. ADP and collagen were found to be appropriate agonists for both species, whereas in the Beagle dog Par-4 agonist failed to induce aggregation and arachidonic acid induced platelet aggregation showed a high interindividual variability. The agonists EC(50) calculated in hirudin blood were 2.70 μM ADP, 0.85 μg/ml collagen, 0.03 mM arachidonic acid and 165.7 μM Par-4 agonist in the Wistar rat, and 0.95 μM ADP and 0.23 μg/ml collagen in the Beagle dog.