Detection of Fibrin Deposits in Tissues from Horses with Severe Gastrointestinal Disorders

Activated platelets and platelet-leukocyte aggregates in the equine systemic inflammatory response syndrome

In humans, activated platelets contribute to sepsis complications and to multiple organ failure. In our prospective analytical study of cases of the equine systemic inflammatory response syndrome (SIRS), we adapted a standard human protocol for the measurement of activated platelets and platelet-leukocyte aggregates (PLAs) in equine platelet-leukocyte-rich plasma (PLRP) by flow cytometry, and we investigated the hypothesis that activated platelets and PLAs are increased in clinical cases of SIRS. We included 17 adult horses and ponies fulfilling at least 2 SIRS criteria, and 10 healthy equids as controls. Activation of platelets was determined by increased expression of CD62P on platelets. Activated platelets and PLAs were measured before and after in vitro activation of platelets with collagen. Median expression of CD62P on platelets was significantly increased after activation in the control group: 1.45% (interquartile range [IQR]: 1.08-1.99%) initially versus 8.78% (IQR: 6.79-14.78%, p = 0.002) after activation. The equids with SIRS had significantly more activated platelets and PLAs in native PLRP than controls: CD62P 4.92% (median, IQR: 2.21-12.41%) versus 1.45% in controls (median, IQR: 1.08-1.99%, p = 0.0007), and PLAs 4.16% (median, IQR: 2.50-8.58%) versus 2.95% in controls (median, IQR: 1.57-3.22%, p = 0.048). To our knowledge, increased platelet activation and PLAs have not been demonstrated previously with flow cytometry in clinical cases of equine SIRS.

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.

Clinical, hematologic, hemostatic, and serum biochemical findings related to survival in Arabian horses with colic

BACKGROUND

The efficacy of clinical examinations, and hematologic, hemostatic, and serum biochemical assessments to determine appropriate early medical or surgical therapy in Arabian horses with colic have not been well-described.

OBJECTIVES

We aimed to evaluate clinical and hematologic findings, coagulation-fibrinolytic parameters, and organ dysfunction markers in association with survival in horses with colic.

METHODS

Seventeen Arabian horses with colic and ten healthy horses were enrolled. After clinical examinations, including heart rates (HRs), capillary refill times (CRTs), abdominal sounds, rectal palpations, and nasogastric (NG) reflux assessments in both healthy and diseased horses, blood samples were collected and hematologic parameters, coagulation indices such as the prothrombin time (PT), activated partial thromboplastin time (APTT), plasma d-dimer (PDD), platelet count, fibrinogen, and hepatorenal biomarkers were measured. Based on the outcomes, horses with colic were divided into survival (10) and nonsurvival (7) groups, and all mentioned parameters were compared with the control group horses.

RESULTS

Unlike HRs, CRTs, and abdominal sounds, rectal palpations (57.1%) and NG reflux (28.6%) findings were least sensitive in being able to determine survival. At least three of the five coagulation indices were significantly abnormal (prolonged PT, increased PDD, and decreased plasma fibrinogen) in 71.4% of the horses in the nonsurvival group compared with the control and survival groups. Significantly increased urea, creatinine, and bilirubin levels, and AST activities were also observed in the survival group compared with the control and nonsurvival groups.

CONCLUSIONS

The combination of prolonged PT, increased PDD, and hypofibrinogenemia could be a reliable predictor of survival in horses with colic. The significant renal and hepatic dysfunctions in nonsurviving horses with colic appeared to be consistent with disseminated intravascular coagulation (DIC) and a grave prognosis.

Evaluating continuous blood coagulopathy in assessing the severity of acute colitis in Thoroughbred racehorses

Although severe blood coagulopathy in horses with acute colitis causes multiple organ failure, which may be fatal, few studies have focused on the correlation between the fluctuations of coagulation parameters and severity of colitis. In this study, we evaluated the fluctuations of coagulation parameters in 14 Thoroughbred racehorses with acute colitis for 5 days from the day of hospitalization and compared them between 5 survivors and 9 non-survivors. Noteworthy features in the non-survivors were that antithrombin activity and fibrin degradation products continuously decreased and increased, respectively, for 4 days or more and that thrombin-antithrombin complexes increased in the last 2 days before death. Thus, these parameters should be continuously monitored to observe these fluctuations in assessing the severity of acute colitis.

Evaluation of an oral direct factor Xa inhibitor anticoagulant in healthy adult horses

OBJECTIVE

To assess whether an oral direct factor Xa inhibitor (DiXaI) anticoagulant drug used at the low end of the recommended dose in people achieves presumed prophylactic plasma concentrations and does not induce bleeding in horses.

DESIGN

Experimental study.

SETTING

Field study.

ANIMALS

Ten healthy adult horses.

INTERVENTIONS

A DiXaI was administered at a dose of 0.125 mg/kg every 24 h orally for 4 days. Following a wash-out period of 2 weeks, 8 of 10 horses received daily subcutaneous doses of a low molecular weight heparin (dalteparin) for 4 consecutive days at 50 IU/kg. In both trials, antifactor Xa activity was measured at baseline time and 3 hours after each dose administration. Activated partial thromboplastin time, prothrombin time, hematocrit, erythrocyte agglutination, and platelet aggregation were monitored throughout the study. In addition, an in vitro spiking experiment was performed to demonstrate anticoagulant activity of this DiXaI in horse plasma.

MAIN RESULTS

When treated with the DiXaI, this group of horses did not achieve the suggested thromboprophylactic plasma range of antifactor Xa activity (0.1-0.2 IU/mL), except for 1 horse after the first administration of the drug. In contrast, median values of plasma antifactor Xa activity 3 hours after receiving dalteparin were within the prophylactic range (0.16 IU/mL). No hemorrhagic events or erythrocyte agglutination were observed. In vitro addition of this DiXaI caused a concentration-dependent effect in antifactor Xa activity.

CONCLUSIONS

At the low end of the recommended dose in people this oral formulation of DiXaI did not reach prophylactic plasma antifactor Xa activity in this group of healthy adult horses. Further studies are warranted in order to establish the prophylactic dose for horses.

Association Between Necropsy Evidence of Disseminated Intravascular Coagulation and Hemostatic Variables Before Death in Horses With Colic

Background

Disseminated intravascular coagulation (DIC) is frequent in horses with severe gastrointestinal disorders. Postmortem studies have found fibrin microthrombi in tissues of these horses, but studies relating these histopathological findings with antemortem hemostatic data are lacking.

Hypothesis

Antemortem classification of coagulopathy is related to the presence and severity of fibrin deposits observed postmortem in horses with severe gastrointestinal disorders.

Animals

Antemortem hemostatic profile data and postmortem tissue samples (kidney, lung, liver) from 48 horses with colic.

Methods

Tissue samples were stained with phosphotungstic acid hematoxylin and immunohistochemical methods for histological examination. A fibrin score (grades 0–4) was assigned for each technique, tissue and horse, as well as the presence or absence of DIC at postmortem examination. D‐dimer concentration, prothrombin time (PT), activated partial thromboplastin time (aPTT), and antithrombin (AT) activity, as well as the clinicopathological evidence of coagulopathy, were determined from plasma samples collected 0–24 hours before death or euthanasia. Histologic and clinicopathologic data from the same horses were compared retrospectively.

Results

No association was found between antemortem classification of coagulopathy and postmortem diagnosis of DIC based on tissue fibrin deposition. None of the hemostatic parameters was significantly different between horses with or without postmortem diagnosis of DIC. There was no association between horses with fibrin in tissues or different cut‐offs for D‐dimer concentration and postmortem evidence of DIC.

Conclusions and Clinical Importance

Abnormalities of the routine clotting profile, including D‐dimer concentration, were not useful in predicting histologic evidence of DIC at necropsy in horses with severe gastrointestinal disorders.

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.

The use of nonsteroidal anti-inflammatory drugs in critically ill horses

OBJECTIVE

To review the physiology of the cyclooxygenase (COX) enzymes with reference to the beneficial effects of nonsteroidal anti-inflammatory drugs (NSAIDs) related to their analgesic and antiendotoxic properties as well as the mechanisms responsible for adverse gastrointestinal, renal, and coagulation effects.

DATA SOURCES

Human and veterinary peer reviewed literature

VETERINARY DATA SYNTHESIS

NSAIDs are frequently administered to critically ill horses for their analgesic and anti-inflammatory effects. However, NSAIDs have significant side effects principally on the gastrointestinal mucosa and kidneys. These side effects may be exacerbated in critically ill horses if they have gastrointestinal damage or are volume depleted

CONCLUSIONS

This review provides important information for equine veterinarians and criticalists on the advantages and disadvantages of using traditional NSAIDs and newer equine COX-2 selective NSAIDs for the management of different conditions in critically ill horses.

Coagulopathies in horses

Although primary coagulopathies are rare in horses, changes in coagulation and fibrinolysis are commonly associated with inflammatory diseases. A clear understanding of the pathophysiology of normal and abnormal hemostasis is required to be able to choose and interpret diagnostic tests evaluating coagulation and fibrinolysis. After diagnosis, treatment of the underlying disease must occur regardless of whether clinical manifestations (excessive bleeding or thrombosis) of the coagulopathy are present or not. Specific treatment may be initiated if there are clinical signs of coagulopathy.

Pharmacodynamics of multi-dose low molecular weight heparin in healthy horses

OBJECTIVES

To compare the pharmacodynamics of once daily and twice daily administration of low molecular weight heparin (LMWH) administration in horses.

STUDY DESIGN

Randomized cross over study.

ANIMALS

Adult mixed breed healthy mares (n = 6).

METHODS

LMWH (dalteparin) was administered (50 U/kg subcutaneously) either every 12 or 24 hours for 3 consecutive days. Anti-factor Xa activity was measured before and at select time points after LMWH administration. Packed cell volume (PCV), platelet count, partial thromboplastin time (PTT), and anti-thrombin (AT) activity were monitored throughout the study.

RESULTS

No changes in PCV, platelet count, or AT activity were detected with either frequency of daily LMWH administration. Values for PTT increased throughout the study but never exceeded the normal reference interval. Anti-factor Xa activity was maintained within or above the suggested thromboprophylactic range (0.1-0.2 U/mL) when LMWH was administered twice daily, but fell below this range ≈ 16 hours after administration when given once daily. For both once and twice daily LMWH administration, the area under the curve was significantly greater after the last dose of LMWH when compared to the first dose.

CONCLUSIONS

Administration of LMWH once or twice daily for 3 consecutive days appears to be safe in healthy adult horses. Anti-factor Xa activity was maintained within or above the suggested thromboprophylactic range for 24 hours with twice daily LMWH administration but not with once daily administration.

Intravenous and oral administrations of DD2 [7-Amino-2-(sulfanylmethyl)heptanoic acid] produce thrombolysis through inhibition of plasma TAFIa in rats with tissue factor-induced microthrombosis

Thrombin-activatable fibrinolysis inhibitor (TAFI) is a plasma zymogen that is activated by thrombin in plasma. In fibrinolytic processes, carboxy-terminal lysine (Lys) residues in partially degraded fibrin are important sites for plasminogen binding and activation, and an active form of TAFI (TAFIa) inhibits fibrinolysis by eliminating these residues proteolytically. We synthesized DD2 [7-Amino-2-(sulfanylmethyl)heptanoic acid], a Lys analogue containing sulfur, as an inhibitor of TAFIa and investigated its pharmacological profile and pathophysiological role in thrombolysis via in vitro and in vivo studies. DD2 specifically inhibited plasma TAFIa activity with an apparent IC(50) (50% inhibitory concentration) value of 3.4×10(-8)M under the present experimental condition and enhanced tissue plasminogen activator-mediated clot lysis in a concentration-dependent manner. In order to study tissue factor (TF)-induced microthrombosis in an animal model, rats were given intravenous injection (2.5mg/kg and higher) or oral administration (10mg/kg and higher) of DD2. This attenuated TF-induced glomerular fibrin deposition and increased the plasma levels of fibrin degradation products and D-dimer in a dose-dependent manner. A DD2 dose approximately 4X higher than the dose used in intravenous injections was required to achieve an equivalent thrombolytic effect to that seen following oral administration. Moreover, the oral absorption efficiency of DD2 into the vasculature was 29.8%. These results indicate that both intravenous and oral administration of DD2 enhanced endogenous fibrinolysis and reduced thrombi in a TF-induced microthrombosis model.

Coagulopathies in horses with colic

The most common coagulopathy in horses with colic is a hypercoagulable state associated with disseminated intravascular coagulation. The intensity of this coagulopathy depends on the severity and duration of the gastrointestinal lesion, with the ischemic and inflammatory problems and peritonitis being the most frequently affected by coagulopathies. Early initiation of prophylactic therapy significantly reduces the severe hypercoagulable state in horses with intestinal conditions which are recognized to be at high risk for disseminated intravascular coagulation. In addition to the systemic coagulopathy observed in horses with colic, a peritoneal coagulopathy independent from that occurring in blood has been observed, and its recognition and assessment may have clinical usefulness in the diagnosis of the gastrointestinal diseases and outcome.

Peritoneal D-dimer concentration for assessing peritoneal fibrinolytic activity in horses with colic

BACKGROUND

Plasma D-dimer concentration is a useful marker to assess systemic coagulation and fibrinolytic activities in humans, dogs, and horses. Peritoneal fibrinolytic activity increases in horses with colic, especially in horses with endotoxin in the peritoneal fluid.

HYPOTHESIS/OBJECTIVES

Peritoneal D-dimer concentration can be used to assess peritoneal fibrinolytic activity in horses with severe gastrointestinal (GI) disorders and altered peritoneal fluid.

ANIMALS

Two hundred and twenty-one colic horses and 15 control horses.

METHODS

Prospective observational clinical study. Blood and peritoneal fluid were collected on admission. Horses were grouped according to diagnosis, peritoneal fluid analysis, and outcome. Peritoneal D-dimer concentration was determined, together with peritoneal tissue-plasminogen activator (t-PA) and plasminogen activator inhibitor (PAI-1) activities. Plasma D-dimer concentration also was measured.

RESULTS

Peritoneal D-dimer concentration was significantly higher in all colic groups compared with controls, and in horses with enteritis, peritonitis, and ischemic disorders compared with horses with large intestinal obstructions. Peritoneal D-dimer concentration was significantly higher in horses with altered peritoneal fluid (modified transudate and exudate) compared with horses with normal peritoneal fluid analysis. Plasma D-dimer concentration also was significantly higher in the peritonitis group, and in horses with altered peritoneal fluid analysis. Peritoneal and plasma D-dimer concentrations also were significantly higher in nonsurvivors. Peritoneal d-dimer concentration was significantly correlated with decreased peritoneal t-PA activity and increased peritoneal PAI-1 activity.

CONCLUSIONS AND CLINICAL IMPORTANCE

Peritoneal D-dimer concentration is markedly higher in severe GI disorders, and it can be used to assess peritoneal fibrinolytic activity in horses with colic.

Fibrin deposits and organ failure in newborn foals with severe septicemia

BACKGROUND

Septicemia in human neonates frequently is complicated by activation of the coagulation system, disseminated intravascular coagulation (DIC) and multiple organ failure syndrome, which may contribute to high mortality. In adult horses with DIC, the lung has been the organ most frequently affected by fibrin deposits. In addition, in vivo studies suggest that hemostatic mechanisms may be immature in foals < 1-day old.

HYPOTHESIS

Newborn foals with severe septicemia have fibrin deposits in their tissues independently of their age, and these fibrin deposits are associated with organ failure.

ANIMALS

Thirty-two septic and 4 nonseptic newborn foals euthanized for poor prognosis.

METHODS

Tissue samples (kidney, lung, and liver) collected on postmortem examination were stained with phosphotungstic acid hematoxylin (PTAH) and immunohistochemistry (IHC) for blind histologic examination. A fibrin score (grades 0-4) was established for each tissue sample and for each foal. Medical records were reviewed for assessing clinical evidence of organ failure during hospitalization.

RESULTS

Fibrin deposits were found in most septic foals (28/32 when using IHC and 21/32 when using PTAH), independently of the age of the foal. The lung was the most affected tissue (97% of the septic foals). Additionally, organ failure was diagnosed in 18/32 septic foals (8 with respiratory failure, 14 with renal failure), although a statistical association with severe fibrin deposition was not identified.

CONCLUSIONS AND CLINICAL IMPORTANCE

Nonsurviving septic foals have fibrin deposits in their tissues, a finding consistent with capillary microthrombosis and DIC.