Optimization of coagulometric tests that incorporate human plasma for determination of coagulation factor activities in canine plasma

UV-Triggered Hydrogel Coating of the Double Network Polyelectrolytes for Enhanced Endothelialization

The left atrial appendage (LAA) occluder is an important medical device for closing the LAA and preventing stroke. The device-related thrombus (DRT) prevents the implantation of the occluder in exerting the desired therapeutic effect, which is primarily caused by the delayed endothelialization of the occluder. Functional coatings are an effective strategy for accelerating the endothelialization of occluders. However, the occluder surface area is particularly large and structurally complex, and the device is subjected to a large shear friction in the sheath during implantation, which poses a significant challenge to the coating. Herein, a hydrogel coating by the in situ UV-triggered polymerization of double-network polyelectrolytes is reported. The findings reveal that the double network and electrostatic interactions between the networks resulted in excellent mechanical properties of the hydrogel coating. The sulfonate and Arg-Gly-Asp (RGD) groups in the coating promoted hemocompatibility and endothelial growth of the occluder, respectively. The coating significantly accelerated the endothelialization of the LAA occluder in a canine model is further demonstrated. This study has potential clinical benefits in reducing both the incidence of DRT and the postoperative anticoagulant course for LAA closure.

Coagulation factor activity patterns of venom-induced consumption coagulopathy in naturally occurring tiger snake (Notechis scutatus) envenomed dogs treated with antivenom

BACKGROUND

Venom-induced consumption coagulopathy (VICC) from tiger snake (Notechis scutatus) envenomation results in a dose-dependent coagulopathy that is detectable on coagulometry. However, individual coagulation factor activities in dogs with tiger snake envenomation have not been determined. This study aimed to characterise VICC and the time course of recovery in tiger snake envenomed dogs and to investigate an association between tiger snake venom (TSV) concentrations and factor activity.

METHODS

This was a prospective, observational, cohort study. The study cohort was 11 dogs of any age, breed, sex, body weight >10 kg, confirmed serum TSV on ELISA and treated with antivenom. Blood was collected at enrolment before antivenom administration, then at 3, 12 and 24 h after antivenom administration. Tiger snake venom concentrations were detected with a sandwich ELISA. Fibrinogen was measured using a modified Clauss method, and coagulation factors (F) II, V, VII, VIII and X were measured with factor-deficient human plasma using a modified prothrombin (PT) and activated partial thromboplastin (aPTT) method. Linear mixed models, with multiple imputations of censored observations, were used to determine the effect of time and TSV concentration on the coagulation times and factor activity. This cohort was compared to 20 healthy controls.

RESULTS

At enrolment, there were severe deficiencies in fibrinogen, FV and FVIII, with predicted recovery by 10.86, 11.75 and 13.14 h after antivenom, respectively. There were modest deficiencies in FX and FII, with predicted recovery by 20.57 and 32.49 h after antivenom, respectively. No changes were detected in FVII. Prothrombin time and aPTT were markedly prolonged with predicted recovery of aPTT by 12.58 h. Higher serum TSV concentrations were associated with greater deficiencies in FII, FV and FVIII, and greater prolongations in coagulation times. The median (range) serum TSV concentration was 57 (6-2295) ng/mL.

CONCLUSIONS

In tiger snake envenomed dogs, we detected a profound, TSV-concentration-related consumption of select coagulation factors, that rapidly recovered toward normal. These findings allowed further insight into tiger snake VICC in dogs.

Heparin in Vitro Sensitivity of the Activated Partial Thromboplastin Time in Canine Plasma Depends on Reagent

The in vitro heparin sensitivity of 6 different commercial activated partial thromboplastin time (APTT) reagents was investigated based on artificial plasma samples prepared by addition of sodium heparin at different activities (0—1.5 IU/ml) to pooled normal canine plasma. Statistical analysis using 2-way analysis of variance was based on APTT ratios (APTT/mean APTT control). Significant differences between the APTT ratios of different APTT reagents ( P < 0.00001) were found, which also depended on heparin activity (interaction between the factors; P < 0.00001). For example, mean APTT ratio at 0.7 IU/ml heparin varied between 1.2 and 2.5. The results of this study indicate that recommendations for the control of heparin therapy in dogs by APTT ratio should be reagent specific.

Purification of protein C from canine plasma

Background

In order to characterize the functional properties of canine protein C (CnPC), the zymogen needs to be purified from plasma. The goals of this study were (1) to purify protein C from fresh frozen canine plasma by barium chloride and ammonium sulphate precipitation, followed by immunoaffinity chromatography using a monoclonal mouse antibody against human protein C (HPC4) and (2) to characterize this protein’s structure.

Results

The purified protein contained three glycosylated forms of a heavy chain (~49 kDa) and a glycosylated light chain (~25 kDa). Tandem mass spectra of the peptides obtained following trypsin digestion and liquid chromatography identified this protein to be protein C (vitamin K-dependent protein C precursor, gi|62078422) with 100% probability. Three glycosylation sites (Asn139, Asn202, and Asn350) were identified by detection of peptides containing an N-linked glycosylation consensus sequon with a 3-dalton increase in mass following incubation of the protein with PNGase F in ¹⁸O-labeled water. Following incubation with Protac (a specific activator of protein C), the heavy chain showed a slight decrease in molecular size and amidolytic activity measured by a synthetic chromogenic substrate containing an amide bond [H-D-(γ-carbobenzoxyl)-lysyl-prolyl-arginine-paranitroanilide diacetate salt]. The amidolytic activity was increased by ~303-fold in the final protein preparation compared to that in plasma. The purified protein showed concentration-dependent anti-factor V and anti-factor VIII activities in canine plasma in coagulometric factor assays.

Conclusions

These studies showed that CnPC could be purified from plasma using HPC4 and that this protein showed amidolytic and anti-coagulant properties upon activation with Protac.

Monitoring unfractionated heparin therapy in dogs by measuring thrombin generation

BACKGROUND

The calibrated automated thrombogram (CAT), an assay that permits measurement of thrombin generation in plasma, may be useful in studying hemostatic disorders and anticoagulant therapy in animals.

OBJECTIVES

The aims of the study were to measure thrombin generation in healthy Beagle dogs and to evaluate the potential use of the CAT assay for monitoring therapy with unfractionated heparin (UFH).

METHODS

Individual platelet-poor plasma samples and a plasma pool from 20 healthy adult Beagles were prepared. Serial UFH plasma dilutions were used to establish an in vitro heparin-sensitivity curve. The pharmacodynamic effects of heparin in vivo were evaluated in Beagles using the CAT assay to measure thrombin generation with tissue factor at a concentration of 5 pM for initiation.

RESULTS

In healthy Beagles, the range of endogenous thrombin potential (ETP) was 238.7-414.0 nM/min (mean ± SD, 340.4 ± 63.1 nM/min). ETP intra-assay and interassay variations were 7.1% and 12.9%, respectively. In vitro, a UFH concentration ≥0.4 U/mL resulted in total inhibition of thrombin generation. In vivo, the maximal effect of UFH on ETP was observed at 170 ± 36 minutes (range, 120-210 minutes) and resulted in a decrease in ETP of 38.5 ± 7.8% (range, 26.5-50.3%). In 210-420 minutes, ETP returned to baseline in 5 dogs.

CONCLUSION

Our study demonstrates that thrombin generation can be measured in canine plasma and may be useful in assessing the degree of anticoagulation provided by UFH.

Canine specific ELISA for coagulation factor VII

Canine coagulation factor VII (FVII) deficiency can be hereditary or acquired and may cause life threatening bleeding episodes if untreated. FVII procoagulant activity can be measured by FVII activity (FVII:C), but assays for measurement of canine specific FVII antigen (FVII:Ag) have not been available to date. In this study, a canine specific ELISA for measurement of FVII:Ag in plasma was developed and validated. The FVII:Ag ELISA correctly diagnosed homozygous and heterozygous hereditary FVII deficiency. Together with activity based assays, such as FVII:C, the FVII:Ag ELISA should be valuable in the diagnosis of hereditary canine FVII deficiency.

Characterization of canine coagulation factor VII and its complex formation with tissue factor: canine-human cross-species compatibility

BACKGROUND

Canine models have been good predictors of efficacy of hemophilia treatments, including recombinant human coagulation factor (F)VIIa (hFVIIa). However, canine FVIIa and tissue factor (TF) have remained incompletely characterized.

OBJECTIVE

 To explore canine-human cross-species FVIIa-TF compatibility in order to strengthen the predictive value of canine models in research on FVIIa and TF.

METHODS

Canine FVIIa (cFVIIa) and canine TF((1-217)) [cTF((1-217))] were produced by recombinant techniques, and canine-human cross-species FVIIa-TF interactions were characterized in vitro.

RESULTS

 Recombinant cFVIIa and soluble cTF((1-217)) were produced and purified to homogeneity. hFVIIa and cFVIIa bound with comparably high affinities to cTF((1-217)) (K(D)=6.0±0.7 nm and K(D)=6.0±0.3 nm, respectively) and to cell surface-expressed cTF (K(D)=8.4±0.4 nm and K(D)=7.2±1.2 nm, for (125) I-labeled hFVIIa and cFVII, respectively). In contrast, cFVIIa bound to human TF (hTF) with decreased affinity, both in solution and on cell surfaces. The decreased binding resulted in reduced activity of cFVIIa in functional assays with hTF((1-209)) . In direct comparison, cFVIIa was more active than hFVIIa, both in the absence and the presence of cognate TF.

CONCLUSION

The present finding that hFVIIa binds to cTF essentially as it does to hTF substantiates the hypothesis that human FVIIa-TF biology can be reliably recapitulated in canine models on administration of hFVIIa to dogs.

G244E in the canine factor IX gene leads to severe haemophilia B in Rhodesian Ridgebacks

Haemophilia B in Rhodesian Ridgebacks is currently the most important canine haemophilia in Germany. The aim of this study was to define the underlying genetic defect. Genetic studies were performed including six phenotypically affected male dogs (factor IX activity: approximately 1%), four suspected carriers (factor IX activity 48-69%, one confirmed by affected offspring), and 12 healthy dogs. Comparison of the entire coding region of the canine factor IX DNA sequences and exon-intron junctions from affected dogs with the wild type canine factor IX DNA revealed a G-A missense mutation in exon 7. This mutation results in a glycine (GGA) to glutamic acid (GAA) exchange in the catalytic domain of the haemophilic factor IX. All affected dogs were hemizygous for the detected mutation and carriers were heterozygous, whereas none of the Rhodesian Ridgebacks with normal factor IX activity showed the mutation. No further alterations in the sequences between affected dogs and the healthy control group could be observed. None of the Rhodesian Ridgebacks with undefined haemophilia B status (n=30) and no individual of three other dog breeds (Doberman Pinscher: n=20; German Wire haired Pointer: n=20; Labrador: n=25) showed the presence of the mutation. Amino acid sequence alignment and protein structural modelling analysis indicate that the detected mutation causes a relevant functional defect. The results of this study suggest that the detected mutation is responsible for a severe form of haemophilia B in Rhodesian Ridgebacks.

Reference Intervals and Method Optimization for Variables Reflecting Hypocoagulatory and Hypercoagulatory States in Dogs using the STA Compact® Automated Analyzer

Reference intervals for coagulation parameters have been rarely determined in dogs for the STA Compact® automated coagulation analyzer, so it is the aim of the current study to validate assays and establish reference ranges for its use in canine specimens. Coagulation parameters were assessed in 56 healthy dogs with a median age of 2 years and evenly distributed sex. The 95% reference intervals were as follows: 1-stage prothrombin time = 5.7–8.0 sec; activated partial thromboplastin time (APTT) = 10.0–14.3 sec; thrombin time (TT) = 11.9–18.3 sec; fibrinogen = 1.3–3.1 g/1; antithrombin (AT) = 107.9–128.0%; D-dimer = 0.023–0.65 μg/ml; anti-factor Xa = 0.04–0.26 IU/1; and activated protein C (APC) ratio = 2.0–3.0. Protein C and S activity was markedly below (<-20%) and factor VIII was 2- to 11-fold above the human calibration standard, so a standard curve had to be prepared from canine pooled plasma. Reference intervals for protein C, protein S, and factor VIII were 75.5–118.9%, 74.4–160.5%, and 70.9–136.4%, respectively, compared with a canine standard curve. Streptokinase-activated plasminogen assay was not suitable for dogs. There was no significant impact of sex on hemostasis test results. Factor VIII activity, AT, protein C, protein S, and APC ratio were overestimated in hemolytic plasma, whereas fibrinogen, TT, and APTT were underestimated. Lipemia resulted only in false-high D-dimers. This study provided useful reference intervals for dogs, but some human tests (i.e., protein C, protein S, factor VIII, and plasminogen) required modification.

Coagulation disorders in dogs with hepatic disease

Liver disease has been associated with abnormalities in haemostasis. In this study, coagulation times, platelet counts, platelet activity parameters, activities of individual coagulation factors, D-dimers, antithrombin (AT) and protein C activity were measured in 42 dogs with histologically confirmed liver disease. Outcome was correlated with histological diagnosis. One or more coagulation abnormalities were present in 57% of dogs with hepatic disease. Activated partial thromboplastin time was significantly prolonged in dogs with chronic hepatitis (CH), with or without cirrhosis. Mean platelet numbers, AT and factor IX activity were significantly lower in dogs with CH plus cirrhosis, compared to dogs with other hepatopathies. D-dimers were not significantly increased in any group. Only three dogs, all with different histological diagnoses, satisfied the criteria for disseminated intravascular coagulation (DIC). Haemostatic abnormalities were primarily seen in dogs with cirrhosis and this may be due to reduced synthesis rather than increased consumption of coagulation factors.

A novel missense mutation responsible for factor VII deficiency in research Beagle colonies

BACKGROUND

Canine factor VII (cFVII) deficiency, an autosomal recessive trait originally identified in research Beagles, is associated with a mild to moderate bleeding tendency.

OBJECTIVE

Our aim was to identify and characterize the mutation causing cFVII deficiency.

METHODS

In order to sequence the coding regions of the cFVII gene, we cloned the cFVII cDNA. Genomic DNA and plasma from FVII-deficient Beagles and obligate carriers were utilized.

RESULTS

In all FVII-deficient dogs, we identified a single causative G to A missense mutation in exon 5, encoding the second epidermal growth factor-like domain, resulting in substitution of glycine 96 by glutamic acid, with plasma FVII coagulant activity of

CONCLUSIONS

We have identified a single causative mutation for cFVII deficiency that may have implications for pharmacotoxicologic research, because reduced FVII coagulant activity may alter hemostatic and/or cardiovascular endpoints in this commonly used animal species.

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Key Words Collapse

MESH Headings

• Amino Acid Sequence
• Animals
• Blood Coagulation
• Cell Line
• Cloning, Molecular
• DNA Mutational Analysis
• Dog Diseases/blood
• Dog Diseases/genetics
• Dogs
• Factor VII/genetics
• Factor VII/metabolism
• Factor VII Deficiency/blood
• Factor VII Deficiency/genetics
• Factor VII Deficiency/veterinary
• Gene Frequency
• Heterozygote
• Homozygote
• Humans
• Molecular Sequence Data
• Mutation, Missense
• Polymerase Chain Reaction
• Prothrombin Time
• Recombinant Proteins/metabolism
• Sequence Alignment
• Sequence Analysis, Protein
• Thrombelastography
• Transfection

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Grants

• RR02512 NCRR NIH HHS
• U01 HL66948 NHLBI NIH HHS

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Affiliation(s)

M B Callan School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA
M N Aljamali
P Margaritis
M E Griot-Wenk
E S Pollak
P Werner
U Giger
K A High

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Efficacy of low molecular weight heparin in a canine model of thromboplastin-induced acute disseminated intravascular coagulation

The aim of this study was to test the efficacy of different dosages of low molecular weight heparin (LMWH) in acute DIC which was induced in anaesthetised dogs by 4 h infusions of a canine lung thromboplastin extract. In all animals during the first 2 h, development of acute DIC was characterised by decreasing fibrinogen concentrations, platelet numbers, factor V- and antithrombin activities. Two hours after starting the thromboplastin infusion, intravenous LMWH treatment in different dosages started in groups 2 and 3 to achieve plasma levels between 0.27+/-0.01 and 0.36+/-0.02 anti-FXaUml(-1) or 0.62+/-0.08 and 0.90+/-0.07 antiFXaUml(-1) (mean+/-SD), respectively, during the time period of parallel administration of thromboplastin and LMWH (group 1=control; 4 dogs/group). In this time period, changes in factor V activity and fibrinogen concentration did not differ between group 2 and the control group. This was in contrast to group 3. The results of this study indicate that an efficacious interruption of the consumption reaction in cases of severe canine DIC requires high plasma heparin levels.

Acute haemostatic changes in accidentally traumatised dogs

Alterations of the haemostatic system were studied in 30 dogs within 24 h following natural injury. No other exclusion criteria were considered. Most dogs had bone fractures, thoracic and/or abdominal trauma. Compared to the controls, the platelet count and activities of all individual coagulation factors, inhibitors of the blood coagulation system (antithrombin, protein C) and plasminogen were significantly decreased (P < 0.01). The only exceptions were alpha2-plasmin inhibitor activity, which did not differ from the control group (P > 0.05), and an increased fibrinogen concentration (P = 0.0113). Deficiencies in the coagulation system were reflected by frequent abnormal results of the screening tests. In most of the animals, the concentrations of soluble fibrin and/or fibrin(ogen) degradation products were above the reference values (P < 0.0001). The absence of a decrease in fibrinogen and alpha2-plasmin inhibitor reflects their role as acute phase reactants. The results of this study indicate the high frequency of decompensated consumption of haemostatic components in acutely traumatised dogs.

BLOOD COAGULATION TESTS IN TOXICOLOGICAL STUDIES-REVIEW OF METHODS AND THEIR SIGNIFICANCE FOR DRUG SAFETY ASSESSMENT-

In general toxicological studies, prothrombin time and activated partial thromboplastin time are routinely measured to assess blood coagulation. Special (problem-driven) tests for blood coagulation are of significance to detect abnormalities and investigate the mechanism of toxicity in detail. In this review, we compiled widely scattered information on blood coagulation testing from different fields in the biological area, and reviewed the methods available and their significance in toxicological studies. The relevant literature cited here reports large species differences in platelet aggregation, coagulation factors or fibrinolysis, and technical limitations. However, the following tests are basically applicable to laboratory animals; (1) assays for individual coagulation factors and protein induced by vitamin K absence or antagonists (PIVKA) to investigate coagulation factor abnormalities; (2) platelet aggregation-, platelet adhesion-, platelet release-tests and von Willebrand factor assay to screen and/or investigate platelet dysfunction; (3) fibrin/fibrinogen degradation products (FDP), D-dimer and thromboelastogram to detect fibrinolitic abnormalities, and assays for plasminogen, plasmin and their activator/inhibitor to investigate fibrinolysis in detail; and (4) bleeding-time to grossly evaluate blood coagulation capability in vivo. An appropriate battery of these tests provides significant information for risk assessment of drugs.

Sensitivity of different prothrombin time assays to factor VII deficiency in canine plasma

The factor VII sensitivity of prothrombin time (PT) in dogs was tested using five different PT reagents and a commercial PT variant. The five PT reagents were used according to manufacturers' instructions (standard test, PT([ST])) and also using a modified test instruction (modified test, PT([MT])). Plasma samples with defined factor VII levels (10-100%) were prepared by adding increasing quantities of canine factor VII deficient plasma to the pooled plasma of healthy dogs. Statistical comparison based on prothrombin time ratios (PTR = PT sample: PT measured for 100% factor VII activity level) revealed significant differences between different reagents for PT([ST]) and also for PT([MT]). Factor VII activity at which PT was prolonged to the upper limit of the reference values (FVII([X(0.975)])) was 16-39% (PT([ST])) and 23-35% (PT([MT])). Factor VII sensitivity measured by PTR and also by FVII([X(0.975)]) values, was higher in four of five PT reagents using PT([MT]) when compared with PT([ST]). The results of this study indicate the importance of selecting a sensitive reagent and method for PT measurement and for careful interpretation of PT test results using canine plasma.

Commercial variants of the prothrombin time test as a screening test of acquired coagulation factor II, VII, and X deficiencies in dogs

The aim of this study was to acquire the single factor sensitivity of three commercial variants of the prothrombin time test (PT(Va1)-Thrombotest, PT(Va2)-Normotest, PT(Va3)-Hepato Quick) for canine plasma. For this purpose, 38 samples from animals with coumarin intoxication followed by vitamin K(1) treatment who had a reduced activity of the coagulation factors II, VII, and/or X (experiment 1) as well as 25 plasma samples from animals with moderately reduced activity of the coagulation factors II, V, VII, and/or X caused by a hepatogenic synthesis disorder or disseminated intravascular coagulation (experiment 2), were examined. Measurements for all tests were performed according to the instructions of the manufacturer and also with higher plasma dilution. Furthermore, control measurements were performed with the conventional prothrombin time test (standard test; PT(ST)). The prothrombin time measured with the PT(Va3), which was prolonged in all samples from experiments 1 and 2, especially reflected with high sensitivity the reduced activity of the coagulation factors. The measurements with PT(Va2) and PT(Va1) showed only an insignificantly lower sensitivity (> or =0.88) with a maximum of 1 (experiment 1) and 3 (experiment 2) false negative test results, respectively. Compared to the already high sensitivity, a higher dilution of the sample material did not lead to a significantly higher sensitivity (P>0.05) for any of the tested commercial variants of the prothrombin time assay. While there was no significant difference (P>0.05) between the number of false negative test results in the variants of the prothrombin time assay, in both experiments a significantly higher number of false negative test results was found for the PT(ST) (P<0.001). The results show that, in contrast to the PT(ST), all three tested commercial prothrombin time variants are suitable for the detection of deficiencies of coagulation factors II, VII, and X in canine plasma.