Measurements of endogenous thrombin potential using the CAT method in cats: Reference values and influence of the direct factor Xa inhibitor apixaban

Assessment of thrombin generation in horses using a calibrated automated thrombogram

BACKGROUND

The amount of thrombin generated reflects the endogenous thrombin potential (ETP), which depends on the balance of pro- and anticoagulant factors. The calibrated automated thrombogram (CAT) allows for the direct measurement of thrombin generation during the clotting process.

OBJECTIVES

(1) To describe the results of the CAT assay in horses, (2) to establish intra-assay and intra- and interindividual variation of thrombin generation in healthy horses, and (3) to compare in vitro low-molecular-weight heparin (LMWH) sensitivity between healthy and sick horses. The hypothesis for the last objective is that inhibition of thrombin generation in sick horses requires higher heparin concentrations.

METHODS

The plasma of 10 healthy mixed breed horses was used for the determination of normal thrombin generation parameters (lag time, time to peak, peak thrombin concentration, and ETP). Five of the healthy horses were compared with five horses with systemic inflammatory response syndrome (SIRS). In vitro heparin sensitivity was determined using LMWH.

RESULTS

The intra-assay variation was small (<5%) for all parameters. Relatively large intra- and interindividual variation were observed in healthy horses. Four of the five sick horses with SIRS had a thrombogram compatible with a hypercoagulable state. The in vitro heparin sensitivity test suggested decreased sensitivity to LMWH in hypercoagulable states.

CONCLUSIONS

The CAT assay could detect coagulopathy in horses. In vivo experiments are needed to confirm that it can be used to monitor responses to LMWH therapy.

A pilot study evaluating the Calibrated Automated Thrombogram assay and application of plasma-thromboelastography for detection of hemostatic aberrations in horses with gastrointestinal disease

Background

Critically ill horses, such as horses with gastrointestinal (GI) disease, often suffer from hemostatic aberrations. Global hemostatic tests examining the initiation of coagulation, clot strength and fibrinolysis, such as the Calibrated Automated Thrombogram (CAT) and plasma-thromboelastography (TEG) have not been evaluated in horses. This study aimed to evaluate CAT and apply plasma-TEG in horses.

Test performance of CAT was evaluated on equine platelet poor plasma with intra- and inter-assay variability (CV) and a heparin dilution curve. To examine clinical performance of both tests, group comparisons were assessed comparing healthy horses, horses with mild and severe GI disease with both CAT and plasma-TEG.

Results

For CAT, intra- and inter-assay CVs were established for lag-time (1.7, 4.7%), endogenous thrombin potential (1.6, 4.6%), peak (2.6, 3.9%) and time to peak (ttPeak) (1.9, 3.4%). Increasing heparin concentrations led to the expected decrease in thrombin generation. In the group comparison analysis, CAT showed significant higher peak (p = 0.04) and ttPeak (p = 0.008) in the severe GI disease group compared to horses with mild GI disease and healthy horses, respectively. Plasma-TEG showed an increased angle (p = 0.032), maximum amplitude (p = 0.017) and shear elastic force (G) (p = 0.017) in the severe GI disease group compared to healthy horses.

Conclusions

CAT performed well in horses. Both CAT and plasma-TEG identified hemostatic aberrations in horses with severe GI disease compared to healthy horses. Further studies including more horses, are needed to fully appreciate the use of CAT and plasma-TEG in this species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03058-7.

Cutaneous Vasculopathy and Pulmonary Thromboembolism in an Unstable Diabetic Cat

A 6-year-old, male-neutered, domestic short-haired cat was referred for further management of a 3-month history of uncontrolled diabetes mellitus. The cat visited the hospital on 3 occasions during a 3-week time period. Hyperglycemia was documented at all visits. The cat initially presented with evidence of hypovolemia, cranial abdominal pain, and dehydration. Moderate hyperglycemia, mild ketonemia, and severe hypokalemia were documented. A 3 × 2 cm skin lesion with associated alopecia and erythema was first noticed at a routine follow-up examination (visit 2) 1 week later. A diagnosis of diabetic ketoacidosis was made 6 days later. The previously identified skin lesion now measured 6 × 2.5 cm. Two episodes of respiratory distress were identified at this visit, with no evidence of cardiac or pulmonary pathology. The cat developed a moderate anemia (packed cell volume 16 %, total solids 7.9 g/dL) on the fifth day of hospitalization. Fluid therapy, electrolyte supplementation, regular insulin, anti-emetic, and analgesia medications were administered during visits 1 and 3. Due to development of anemia, suspected pulmonary thromboembolism events and progression of skin lesions, euthanasia was elected. A diagnosis of cutaneous vasculopathy with secondary ischemic necrosis was made postmortem and pulmonary thromboembolism was confirmed. To the authors' knowledge, this is the first report of cutaneous vasculopathy and pulmonary thromboembolism in a cat with confirmed diabetes mellitus, warranting further research to assess if hypercoagulability is common in this patient population, as routine thromboprophylaxis and anticoagulation may be potentially indicated.

Thrombin Aptamer-Modified Metal-Organic Framework Nanoparticles: Functional Nanostructures for Sensing Thrombin and the Triggered Controlled Release of Anti-Blood Clotting Drugs

This paper features the synthesis of thrombin-responsive, nucleic acid-gated, UiO-68 metal-organic framework nanoparticles (NMOFs) loaded with the drug Apixaban or rhodamine 6G as a drug model. Apixaban acts as an inhibitor of blood clots formation. The loads in the NMOFs are locked by duplex nucleic acids that are composed of anchor nucleic acids linked to the NMOFs that are hybridized with the anti-thrombin aptamer. In the presence of thrombin, the duplex gating units are separated through the formation of thrombin-aptamer complexes. The unlocking of the NMOFs releases the drug (or the drug model). The release of the drug is controlled by the concentration of thrombin. The Apixaban-loaded NMOFs revealed improved inhibition, as compared to free Apixaban, toward blood clot formation. This is reflected by their longer time intervals for inducing clot formation and the decreased doses of the drug required to affect clots formation. The beneficial effects of the Apixaban-loaded NMOFs are attributed to the slow-release mechanism induced by the NMOFs carriers, where the inhibition of factor Xa in the blood clotting cycle retards the formation of thrombin, which slows down the release of the drug.