Effects of aspirin dose escalation on platelet function and urinary thromboxane and prostacyclin levels in normal dogs

Aspirin 15cH has Different Effects on Morphology and Function of Lipopolysaccharide-Challenged RAW 264.7 Macrophages In Vitro Compared to a Pharmacological Dose of Aspirin

INTRODUCTION

 Aspirin is one of the most commonly used drugs worldwide. It is known to present antipyretic, anti-inflammatory and anti-thrombotic actions, making it extremely useful in a wide range of clinical contexts. Interestingly, homeopathically prepared Aspirin 15cH has been found to have a pro-thrombotic effect in rats, raising the hypothesis that Aspirin 15cH could also modulate the activity of inflammatory cells in different pathological processes.

OBJECTIVE

 Our objective was to assess what effect Aspirin 15cH has on RAW 264.7 macrophages in vitro.

METHODS

 The effects of Aspirin 15cH on biochemical and morphological activities of lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages were evaluated. These effects were compared with unchallenged macrophages (negative control), untreated LPS-stimulated macrophages, macrophages treated with succussed water (vehicle control), or aspirin 200 µg/mL (pharmacological inhibitor of LPS activity). Cell morphology (adhered cell area and cytoskeleton arrangements), cell viability, toll-like receptor-4 (TLR-4) expression, and the production of nitric oxide, cytokines and intracellular reactive oxygen species were assessed.

RESULTS

 Aspirin 15cH reduced the number of cells expressing TLR-4 on the surface (p = 0.03) and induced a "columnar" morphology of macrophage pseudopods, indicating changes in cytoskeleton arrangement. When cells were treated with both Aspirin 15cH and LPS, cell morphology became heterogeneous, suggesting that sub-populations of cells had differing sensitivities to LPS or Aspirin 15cH. Exposure of the cells to LPS alone, succussed water or aspirin 200 µg/mL produced effects consistent with the literature.

CONCLUSION

 Aspirin 15cH, aspirin 200 µg/mL, LPS and succussed water appear to act as independent stimuli able to induce different patterns of macrophage response. Aspirin 15cH induced changes suggestive of M2 polarization of the macrophages (i.e., toward a wound healing or tissue repair, rather than inflammatory, phenotype). These preliminary findings need to be confirmed in further specific studies.

Functionalization of in vivo tissue-engineered living biotubes enhance patency and endothelization without the requirement of systemic anticoagulant administration

Vascular regeneration and patency maintenance, without anticoagulant administration, represent key developmental trends to enhance small-diameter vascular grafts (SDVG) performance. In vivo engineered autologous biotubes have emerged as SDVG candidates with pro-regenerative properties. However, mechanical failure coupled with thrombus formation hinder translational prospects of biotubes as SDVGs. Previously fabricated poly(ε-caprolactone) skeleton-reinforced biotubes (PBs) circumvented mechanical issues and achieved vascular regeneration, but orally administered anticoagulants were required. Here, highly efficient and biocompatible functional modifications were introduced to living cells on PB lumens. The 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-N-methoxy (DMPE)-PEG-conjugated anti-coagulant bivalirudin (DPB) and DMPE-PEG-conjugated endothelial progenitor cell (EPC)-binding TPS-peptide (DPT) modifications possessed functionality conducive to promoting vascular graft patency. Co-modification of DPB and DPT swiftly attained luminal saturation without influencing cell viability. DPB repellent of non-specific proteins, DPB inhibition of thrombus formation, and DPB protection against functional masking of DPT's EPC-capture by blood components, which promoted patency and rapid endothelialization in rat and canine artery implantation models without anticoagulant administration. This strategy offers a safe, facile, and fast technical approach to convey additional functionalization to living cells within tissue-engineered constructs.

Effectiveness of aspirin vs. clopidogrel in dogs with immune mediated haemolytic anaemia evaluated by serial thromboelastography and platelet mapping

Most dogs with immune mediated haemolytic anaemia (IMHA) are hypercoagulable, as measured by thromboelastography (TEG). Thromboelastography-platelet mapping (TEG-PM) has been used to assess platelet function in human patients treated with aspirin or clopidogrel. The aim of this study was to compare platelet thromboxane A₂-receptor inhibition (TXA_2-RI) and platelet adenosine diphosphate (ADP)-receptor inhibition (ADP-RI) as measured by TEG-PM in dogs with primary IMHA receiving aspirin or clopidogrel to determine if TEG-PM might be useful to monitor treatment. Eighteen client-owned dogs with IMHA were enroled in a prospective double blinded study. Dogs were randomised to receive aspirin or clopidogrel in addition to standard therapy. Thromboelastography was measured before, and 1 and 4 days after commencing treatment. Thromboelastography-PM was performed on days 1 and 4. Non-responders were defined as < 50 % platelet thromboxane A₂-receptor inhibition (TXA_2-RI) in the aspirin group and < 50 % platelet adenosine diphosphate (ADP)-receptor inhibition (ADP-RI) in the clopidogrel group, on day 4. Mean platelet TXA₂-RI and platelet ADP-RI were not significantly different between groups at any timepoint (P > 0.05). The overall mean percentage inhibition of TXA₂-receptor was 25 % (aspirin 33 %, clopidogrel 15 %), and of ADP-receptor was 82 % (aspirin 83 %, clopidogrel 80 %). On day 4, 6/9 dogs (66 %) in the aspirin group and 2/8 dogs (25 %) in the clopidogrel group were non-responders (P = 0.086). Two dogs defined as responders based on TEG-PM developed thromboembolism. Overall, there was no significant difference in efficacy between aspirin and clopidogrel based on measurement of receptor inhibition using TEG-PM (P > 0.05), and routine TEG was not reliable for monitoring treatment response in dogs with IMHA. In some dogs, there was a discrepancy between TEG-PM results and clinical response. Further investigation of TEG-PM use in dogs, including its usefulness to monitor treatment response and adjust treatment in individual dogs and any effect of anaemia, is warranted.

Urinary 11-dehydrothromboxane B2 concentrations in 20 dogs with primary immune-mediated hemolytic anemia

BACKGROUND

Thromboembolic disease is a major cause of mortality in dogs with immune-mediated hemolytic anemia (IMHA). At present, no reliable biomarkers of individual patient thrombotic risk are available. In human medicine, increased urinary thromboxane concentrations have utility as markers of prothrombotic tendency in various situations.

HYPOTHESIS/OBJECTIVES

First, to determine if urinary 11-dehydrothromboxane B2 (u11-dTXB) concentrations are increased in dogs with primary IMHA compared to normal dogs; second, to assess whether u11-dTXB concentration is associated with survival, known prognostic indicators, or frequency of thrombosis in dogs with IMHA.

ANIMALS

Twenty client-owned dogs diagnosed with primary IMHA and 17 healthy dogs volunteered by hospital staff.

METHODS

Prospective case-control study. A previously validated ELISA was used to measure urine 11-dTXB concentrations, which were normalized to urine creatinine concentration (u11-dTXB:Cr). Samples were obtained at presentation from patients with primary IMHA. Standard clincopathological data at baseline and survival data were collected. Urinary 11-dTXB:Cr was compared between outcome subgroups, and correlated with known markers of disease severity.

RESULTS

Baseline u11-dTXB:Cr was significantly higher in dogs with IMHA than in healthy dogs (median, 3.75; range, 0.83-25.36 vs 0.65; 0.24-2.57; P = .003) but did not differ between dogs with IMHA that survived and did not survive to 30 days after presentation, nor between dogs with and without clinical suspicion of thrombotic disease.

CONCLUSIONS AND CLINICAL IMPORTANCE

Urinary 11-dTXB:Cr is increased in dogs with IMHA compared to healthy controls, consistent with a prothrombotic state. However, in this IMHA population u11-dTXB:Cr was not associated with survival or suspected thrombosis.

The use of impedance aggregometry to evaluate platelet function after the administration of DDAVP in healthy dogs treated with aspirin or clopidogrel

OBJECTIVE

To evaluate the effect of 1-Desamino-8-d-arginine vasopressin (DDAVP; desmopressin acetate) on platelet aggregation in healthy dogs receiving aspirin or clopidogrel.

ANIMALS

7 healthy staff-owned dogs.

PROCEDURES

In this randomized double-blinded crossover study, impedance aggregometry was performed on samples of lithium-heparinized whole blood samples from dogs before (T0) treatment with aspirin (1 mg/kg, PO, q 24 h for 4 days; ASP group) or clopidogrel (1 mg/kg, PO, q 24 h for 4 days; CLP group) and then before (T1) and after (T2) treatment with DDAVP (0.3 μg/kg, IV, once). There was a 14-day washout period before the crossover component. Aggregometry was performed with 4 different assays, each of which involved a different agonist reagent to stimulate platelet function: ADP, thrombin receptor activating peptide-6, arachidonic acid, or collagen type 1.

RESULTS

Median results for platelet aggregometry with agonist reagents ADP, arachidonic acid, or thrombin receptor activating peptide-6 significantly decreased between T0 and T1 for the CLP group; however, no meaningful difference in platelet aggregation was detected in the ASP group. Results for platelet aggregometry did not differ substantially between T1 and T2 regardless of treatment group or assay.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings suggested that administration of DDAVP may have no effect on platelet aggregation (measured with platelet aggregometry) in healthy dogs treated with clopidogrel. Because no inhibition of platelet aggregation was detected for dogs in the ASP group, no conclusion could be made regarding the effects of DDAVP administered to dogs treated with aspirin.

Effects of pentoxifylline on canine platelet aggregation

BACKGROUND

Pentoxifylline can decrease platelet function in humans, but the anti-platelet effects of pentoxifylline in dogs is unknown. The addition of a luciferin-luciferase reagent during platelet aggregometry can induce a dose-dependent potentiation of platelet aggregation.

OBJECTIVE

To determine if exposure to pentoxifylline, without the addition of a luciferin-luciferase reagent during aggregometry, causes canine platelet dysfunction. Our hypotheses were that pentoxifylline would inhibit platelet function, and that the addition of a luciferin-luciferase reagent would obscure detection of pentoxifylline-induced platelet dysfunction as measured via aggregometry.

METHODS

Seven healthy Walker hound dogs. Platelet-rich plasma (PRP) and whole blood were treated for 30 minutes with pentoxifylline: 0 (control), 1 and 2 μg/mL. The platelet aggregation was determined using optical (maximum amplitude) and impedance (ohms) aggregometry using collagen as the agonists, with and without a luciferin-luciferase reagent. Four samples were analysed per concentration and the results were averaged.

RESULTS

Based on optical aggregometry, there was no difference (p = 0.964) in the mean maximum amplitude at any pentoxifylline concentration, with and without the luciferin-luciferase reagent. During impedance aggregometry, the addition of a luciferin-luciferase reagent was associated with significantly (p < 0.001) greater platelet aggregation in response to a collagen agonist, regardless of the presence or absence of pentoxifylline.

CONCLUSIONS

Pentoxifylline does not exert an in vitro anti-platelet effect on canine platelet aggregation when collagen is used as an agonist, but it is unknown if long-term oral drug administration will inhibit platelet aggregation. The addition of a luciferin-luciferase reagent during platelet aggregometry can artificially enhance canine platelet aggregation.

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.

Platelet aggregometry testing during aspirin or clopidogrel treatment and measurement of clopidogrel metabolite concentrations in dogs with protein-losing nephropathy

Background

Dogs with protein‐losing nephropathy (PLN) are treated with antiplatelet drugs for thromboprophylaxis but no standardized method exists to measure drug response. It is also unknown if clopidogrel metabolite concentrations [CM] differ between healthy and PLN dogs.

Objectives

Assess response to aspirin or clopidogrel in PLN dogs using platelet aggregometry (PA) and compare [CM] between healthy and PLN dogs.

Animals

Six healthy and 14 PLN dogs.

Methods

Platelet aggregometry using adenosine diphosphate (ADP), arachidonic acid (AA), and saline was performed in healthy dogs at baseline and 1‐week postclopidogrel administration to identify responders or nonresponders. A decrease of ≥60% for ADP or ≥30% for AA at 1 or 3 hours postpill was used to define a responder. At 1 and 3 hours postclopidogrel, [CM] and PA were measured in healthy and PLN dogs. Platelet aggregometry was performed in PLN dogs at baseline, 1, 6, and 12 weeks after clopidogrel or aspirin administration.

Results

In PLN dogs receiving clopidogrel, PA differed from baseline at all time points for ADP but not for AA at any time point. Most dogs responded at 1 or both time points except for 1 dog that showed no response. For PLN dogs receiving aspirin, no differences from baseline were observed at any time point for either ADP or AA. No differences in [CM] were found at either time point between healthy and PLN dogs.

Conclusions and Clinical Importance

Platelet aggregometry may represent an objective method to evaluate response to clopidogrel or aspirin treatment and PLN dogs appear to metabolize clopidogrel similarly to 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.

Clinical, clinicopathologic, and gastrointestinal changes from administration of clopidogrel, prednisone, or combination in healthy dogs: A double-blind randomized trial

Background

Dogs with immune‐mediated disease often receive glucocorticoids with clopidogrel, but ulcerogenic effects of current protocols are unknown.

Hypothesis/Objectives

To compare gastrointestinal endoscopic findings among dogs administered clopidogrel, prednisone, and combination treatment.

Animals

Twenty‐four healthy research dogs.

Methods

Double‐blinded, placebo‐controlled randomized trial. Dogs received placebo, clopidogrel (2–3 mg/kg q24h), prednisone (2 mg/kg q24h), or prednisone with clopidogrel PO for 28 days. Attitude, food intake, vomiting, and fecal score were determined daily. Clinicopathologic testing was performed at baseline and on day 28. Gastrointestinal hemorrhages, erosions, and ulcers were numerated by 2 blinded investigators for endoscopies performed on days 0, 14, and 28, and endoscopic mucosal lesion scores were calculated. Results were compared using mixed model, split‐plot repeated measures ANOVAs and generalized estimating equation proportional odds models as appropriate. P < .05 was considered significant.

Results

Clinical signs of gastrointestinal bleeding were not noted. Endoscopic mucosal lesion scores differed significantly by group (F[3, 20] = 12.8, P < .001) and time (F[2, 40] = 8.3, P < .001). Posthoc analysis revealed higher lesion scores in the prednisone‐receiving groups (P ≤ .006 for each) and on day 14 (P ≤ .007 for each). Ulcers were identified in 4 dogs administered prednisone and 3 dogs administered prednisone/clopidogrel. Odds of having endoscopic mucosal lesion scores ≥4 were 7‐times higher for dogs in prednisone (95%CI 1.1, 43.0; P = .037) and prednisone‐clopidogrel (95%CI 1.1, 43.4; P = .037) groups than those in the placebo group.

Conclusions and Clinical Importance

Gastrointestinal bleeding and ulceration occur commonly in healthy dogs administered prednisone or prednisone/clopidogrel treatment, but not clopidogrel monotherapy. Though lesions are severe in many cases, they are not accompanied by clinical signs.

Clinical, clinicopathologic, and gastrointestinal changes from aspirin, prednisone, or combination treatment in healthy research dogs: A double-blind randomized trial

Background

Dogs with immune‐mediated disease are often coadministered glucocorticoids and aspirin, but ulcerogenic effects of current protocols are unknown.

Objectives

To compare gastrointestinal changes among dogs administered aspirin, prednisone, and combination treatment.

Animals

Twenty‐four healthy research dogs.

Methods

Double‐blinded, placebo‐controlled randomized trial of dogs administered placebo, aspirin (2 mg/kg q24h), prednisone (2 mg/kg q24h), or combination treatment PO for 28 days. Clinical signs were recorded daily, with laboratory work performed at baseline and day 28. Gastrointestinal mucosal hemorrhages, erosions, and ulcers were numerated for endoscopic studies performed on days 0, 14, and 28; endoscopic mucosal lesion scores were calculated. Results were compared using mixed model repeated‐measures analyses of variance and generalized estimating equation proportional odds models. P < .05 was considered significant.

Results

Gastric mucosal lesion scores differed by treatment‐by‐time (F[6, 40] = 4.4, P = .002), treatment (F[3, 20] = 7.1, P = .002), and time (F[2, 40] = 18.9, P < .001). Post hoc analysis revealed increased scores in the aspirin (day 14 only), prednisone, and prednisone/aspirin groups during treatment. Ulcers were identified on 14 studies, representing 10 dogs. Dogs receiving prednisone and prednisone/aspirin had 11.1 times (95% CI, 1.7‐73.6) and 31.5 times (95% CI, 3.5‐288.0) higher odds, respectively, of having endoscopic mucosal lesion scores ≥4 than dogs receiving placebo (P ≤ .01).

Conclusions and Clinical Importance

Gastrointestinal bleeding occurs commonly in dogs administered aspirin, prednisone, or prednisone/aspirin treatment, with higher lesion scores for dogs receiving combination treatment. Even severe lesions are not accompanied by clinical signs.

ACVIM consensus statement on the treatment of immune-mediated hemolytic anemia in dogs

Immune‐mediated hemolytic anemia (IMHA) causes severe anemia in dogs and is associated with considerable morbidity and mortality. Treatment with various immunosuppressive and antithrombotic drugs has been described anecdotally and in previous studies, but little consensus exists among veterinarians as to the optimal regimen to employ and maintain after diagnosis of the disease. To address this inconsistency and provide evidence‐based guidelines for treatment of IMHA in dogs, we identified and extracted data from studies published in the veterinary literature. We developed a novel tool for evaluation of evidence quality, using it to assess study design, diagnostic criteria, explanation of treatment regimens, and validity of statistical methods. In combination with our clinical experience and comparable guidelines for humans afflicted with autoimmune hemolytic anemia, we used the conclusions of this process to make a set of clinical recommendations regarding treatment of IMHA in dogs, which we refined subsequently by conducting several iterations of Delphi review. Additionally, we considered emerging treatments for IMHA in dogs and highlighted areas deserving of future research. Comments were solicited from several professional bodies to maximize clinical applicability before the recommendations were submitted for publication. The resulting document is intended to provide clinical guidelines for management of IMHA in dogs. These guidelines should be implemented pragmatically, with consideration of animal, owner, and veterinary factors that may vary among cases.

Consensus on the Rational Use of Antithrombotics in Veterinary Critical Care (CURATIVE): Domain 3-Defining antithrombotic protocols

OBJECTIVES

To systematically examine the evidence for use of a specific protocol (dose, frequency, route) of selected antithrombotic drugs, in comparisons to no therapy or to other antithrombotic therapies, to reduce the risk of complications or improve outcomes in dogs and cats at risk for thrombosis.

DESIGN

Standardized, systematic evaluation of the literature, categorization of relevant articles according to level of evidence (LOE) and quality (Good, Fair, or Poor), and development of consensus on conclusions via a Delphi-style survey for application of the concepts to clinical practice.

SETTINGS

Academic and referral veterinary medical centers.

RESULTS

Databases searched included Medline via PubMed and CAB abstracts. Eight different antithrombotic drugs were investigated using a standardized Patient, Intervention, Comparison, Outcome (PICO) question format both for dogs and cats, including aspirin, clopidogrel, warfarin, unfractionated heparin (UFH), dalteparin, enoxaparin, fondaparinux, and rivaroxaban, generating a total of 16 worksheets. Most studies identified were experimental controlled laboratory studies in companion animals (LOE 3) with only four randomized controlled clinical trials in companion animals (LOE 1).

CONCLUSIONS

Overall, evidence-based recommendations concerning specific protocols could not be formulated for most antithrombotic drugs evaluated, either because of the wide range of dosage reported (eg, aspirin in dogs) or the lack of evidence in the current literature. However, clopidogrel administration in dogs and cats at risk of arterial thrombosis, notably in cats at risk of cardiogenic thromboembolism, is supported by the literature, and specific protocols were recommended. Comparably, aspirin should not be used as a sole antithrombotic in cats with cardiomyopathy. Using the available safety profile information contained in the literature, the panel reached consensus on suggested dosage schemes for most antithrombotics. Significant knowledge gaps were highlighted, which will hopefully drive novel research.

Investigation into the causes of aspirin resistance in healthy dogs

Antiplatelet effects of acetylsalicylic acid (ASA, aspirin) may be poor in some individuals. Additionally, no method exists for predicting poor ASA response (resistance) in individual dogs. This study's main objective was to determine whether poor ASA response results from pharmacodynamic or pharmacokinetic causes. ASA concentrations causing 50% inhibition of platelet aggregation (in vitro IC50) were determined using whole blood collected from 21 drug-free healthy dogs to evaluate intrinsic sensitivity of platelets to ASA. Dogs were then administered ASA at 4 mg/kg once orally. Percent decrease in platelet aggregation from baseline, and plasma ASA and salicylic acid (SA) concentrations (expressed as AUC values) were measured for up to 3 hr. By 3 hr, 13/21 (62%) dogs showed >50% aggregation inhibition, while 8/21 (38%) dogs showed <50% inhibition. Aggregation inhibition values were negatively correlated with in vitro IC50 values (Rs = -0.49; p = 0.028) and positively correlated with ASA concentrations (Rs = 0.48; p = 0.03). Furthermore, ASA concentrations were strongly negatively correlated (Rs = -0.88; p < 0.001) with SA/ASA concentration ratios, an index of ASA metabolism to SA by esterase enzymes. Multiple linear regression analysis indicated that 59% (p < 0.001) of interindividual variability in aggregation inhibition was explained by in vitro IC50 values (29% of variability) and ASA concentrations (29% of variability). Consequently, poor in vivo ASA response in these dogs resulted from both pharmacodynamic (decreased platelet sensitivity) and pharmacokinetic (lower ASA concentrations) causes. Lower ASA concentrations may be explained by reduced bioavailability associated with higher esterase activities.