Reduced inhibition of activated prothrombin by heparin and venous thromboembolism: heparin resistance revisited (original) (raw)
Related papers
Toxicon, 2010
Venom-induced consumption coagulopathy occurs in snake envenoming worldwide but the interaction between procoagulant snake venoms and human coagulation remains poorly understood. We aimed to evaluate an assay using endogenous thrombin potential (ETP) to investigate the procoagulant properties of a range of Australian whole venoms in human plasma and compared this to traditional clotting and prothrombinase activity studies. We developed a novel modification of ETP using procoagulant snake venoms to trigger thrombin production. This was used to characterise the relative potency, calcium and clotting factor requirements of five important Australian snake venoms and efficacy of commercial antivenom, and compared this to prothrombinase activity and clotting assays. All five venoms initiated thrombin generation in the absence and presence of calcium. Pseudonaja textilis (Brown snake; p < 0.0001), Hoplocephalus stephensii (Stephen's-banded snake; p < 0.0001) and Notechis scutatus (tiger snake; p ¼ 0.0073) all had statistically significant increases in ETP with calcium. Venom potency varied between assays, with ETP ranging from least potent with Oxyuranus scutellatus (Taipan) venom to intermediate with N. scutatus and H. stephensii venoms to most potent with P. textilis and Tropidechis carinatus (Rough-scale snake) venoms. ETPs for N. scutatus, T. carinatus and H. stephensii venoms were severely reduced with factor V deficient plasma. Antivenom neutralized the thrombin generating capacity but not prothrombin substrate cleaving ability of the venoms. Contrary to previous studies using clotting tests and factor Xa substrates, these venoms differ in calcium requirement. ETP is a useful assay to investigate mechanisms of other procoagulant venoms and is a robust method of assessing antivenom efficacy.
Anaesthesia and intensive care, 1992
The cardiovascular and haematological effects of purified prothrombin activator derived from the venom of the Australian Common Brown Snake (Pseudonaja textilis) were studied in anaesthetised, mechanically ventilated dogs. Severe depression of systemic blood pressure and cardiac output and a rise in central venous pressure were observed. Thrombocytopenia, prolongation of both prothrombin time and activated partial thromboplastin time and a reduction in serum fibrinogen were also observed. All of these observed effects were prevented by the prior administration of heparin--a naturally occurring anticoagulant. We conclude that the prothrombin activator in Pseudonaja textilis venom may cause cardiovascular depression due to myocardial dysfunction secondary to disseminated intravascular coagulation.
Thrombosis Research, 2016
Background: Animal models are used to test toxic effects of snake venoms/toxins and the antivenom required to neutralise them. However, venoms that cause clinically relevant coagulopathy in humans may have differential effects in animals. We aimed to investigate the effect of different procoagulant snake venoms on various animal plasmas. Methods: Prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen and D-dimer levels were measured in seven animal plasmas (human, rabbit, cat, guinea pig, pig, cow and rat). In vitro clotting times were then used to calculate the effective concentration (EC 50) in each plasma for four snake venoms with different procoagulant toxins: Pseudonaja textilis, Daboia russelli, Echis carinatus and Calloselasma rhodostoma. Results: Compared to human, PT and aPTT were similar for rat, rabbit and pig, but double for cat and cow, while guinea pig had similar aPTT but double PT. Fibrinogen and D-dimer levels were similar for all species. Human and rabbit plasmas had the lowest EC 50 for P. textilis (0.1 and 0.4 μg/ml), D. russelli (0.4 and 0.1 μg/ml), E. carinatus (0.6 and 0.1 μg/ml) venoms respectively, while cat plasma had the lowest EC 50 for C. rhodostoma (11 μg/ml) venom. Cow, rat, pig and guinea pig plasmas were highly resistant to all four venoms with EC 50 10-fold that of human. Conclusions: Different animal plasmas have varying susceptibility to procoagulant venoms, and excepting rabbits, animal models are not appropriate to test procoagulant activity. In vitro assays on human plasma should instead be adopted for this purpose.
Coagulopathy Caused by the Main Anticoagulant Fractions of Echis carinatus Snake Venom on Blood
Background: The venom of Viperidae snakes is a compound liquid rich in medicinally active proteins and peptides. It is an invasive weapon for preys immobilization, killing and digestion. Materials and Methods: With a combination of gel and ion exchange chromatography ten sub-fractions were isolated from the E.carinatus venom. Three sub-fractions as anticoagulant sub-fractions were then intravenously injected to mice. Blood sampling was taken before and after injecting these three sub-fractions. The PT, PTT and FT were recorded. Results: Comparison of the PT before and after injecting three sub-fractions, showed that the blood coagulation time after injection is more than the blood normal coagulation time and also more than the coagulation time after the crude venom injection. This coagulation time difference shows the intense coagulation activity of these sub-fractions which thus significantly decrease the rate of coagulation cascade activity and lead to slow blood coagulation. Conclusion: Comparison of the PT and PTT after injecting three sub-fractions with this test normal time respectively showed that the rate of the mice blood coagulation extrinsic and intrinsic system activity rate considerably decreases. By comparing the FT after injecting with this test normal time, coagulation cascade intense inactivation and the nonproduction of fibrin can be inferred. Keywords: Snake Venom; Chromatography; Anticoagulants; Echis Carinatus; Blood Coagulation.
Toxicon, 1994
III and antivenom reversal of coagulopathy in rats envenomated with Malayan pit viper venom. Toxicon 32, 97-103, 1994.-The therapeutic effects of antithrombin III (AT-III) and unrefined equine antivenom in the treatment of coagulopathy induced by Malayan pit viper (Calloselasma rhodostoma) venom were assessed in 42 adult Wistar rats . Following intramuscular venom injection (2 pg/g body weight), serial blood samples were taken from the femoral vein for measurement of whole blood clotting time and AT-III activity. There was progressive depletion of AT-III and blood ceased to clot a mean (S.E.) of 164 (8.3) min after venom injection. Coagulopathy was reversed by a high dose antivenom (10 hg/g) or a lower dose of antivenom (5 hg/g) in combination with AT-III (z0.1 U/g; P < 0.01) but not 5 hg/g antivenom or AT-III alone. Following successful treatment, the mean plasma AT-III activity remained above 90% . In this animal model, systemic envenomation by the Malayan pit viper causes uncoagulable blood associated with AT-III consumption. The dose of antivenom required to reverse this coagulopathy can be reduced by half by the addition of AT-III su~3cient to maintain blood concentrations within the normal range.
Toxicology In Vitro
Venom can affect any part of the body reachable via the bloodstream. Toxins which specifically act upon the coagulation cascade do so either by anticoagulant or procoagulant mechanisms. Here we investigated the coagulotoxic effects of six species within the medically important pit viper genus Protobothrops (Habu) from the Chinese mainland and Japanese islands, a genus known to produce hemorrhagic shock in envenomed patients. Differential coagulotoxicity was revealed: P. jerdonii and P. mangshanensis produced an overall net anticoagulant effect through the pseudo-procoagulant clotting of fibrinogen; P. flavoviridis and P. tokarensis exhibit a strong anticoagulant activity through the destructive cleavage of fibrinogen; and while P. elegans and P. mucrosquamatus both cleaved the A-alpha and B-beta chains of fibrinogen they did not exhibit strong anticoagulant activity. These variations in coagulant properties were congruent with phylogeny, with the closest relatives exhibiting similar venom effects in their action upon fibrinogen. Ancestral state reconstruction indicated that anticoagulation mediated by pseudo-procoagulant cleavage of fibrinogen is the basal state, while anticoagulation produced by destructive cleavage of fibrinogen is the derived state within this genus. This is the first in depth study of its kind highlighting extreme enzymatic variability, functional diversification and clotting diversification within one genus surrounding one target site, governed by variability in co-factor dependency. The documentation that the same net overall function, anticoagulation, is mediated by differential underlying mechanics suggests limited antivenom cross-reactivity, although this must be tested in future work. These results add to the body of knowledge necessary to inform clinical management of the envenomed patient.
Snake venoms are rich in valuable substances that have medical potential in the diagnosis and treatment of hemostatic diseases. The present paper was aimed at the purification and functional characterization basis of a thrombinlike enzyme and its role in the functioning of the coagulation cascade and platelet aggregation pathway. A thrombin-like serine protease was purified from the Iranian Echis carinatus venom (TLIECV), employing a one-step chromatographic procedure. This peptide was collected in high yield and purity by a single chromatographic step using RP-HPLC equipped with a C18 column. This peptide showed a 3000 Da molecular weight in gelelectrophoresis. Evidence in the SDS-PAGE gel has confirmed high recovery of fraction in optimal terms. Subsequently, this peptide was identified via its intact molecular mass and peptide mass fingerprint (PMF) using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS). Multiple sequence alignments were performed by ClustalW, the Bioedit software. Molegro Data Modeller (MDM) 3.0 software was used to predict the putative tertiary structure of the peptide. The enzyme possessed fibrinogenolytic, procoagulant, and aggregation inducer properties. Moreover, the SDS-PAGE (12%) was applied to examine fibrinogenolytic function. The purified enzyme degraded the Aα chain of fibrinogen while the Bβ and γ chains were not digested. According to that, the deficient human plasma in factor X and normal human plasma were also coagulated by TLIECV, it takes part in the common and intrinsic routes of the coagulation cascade. These findings proved that TLIECV is a serine protease identical to procoagulant thrombinlike snake venom proteases; however, it specifically releases the Aα chain of bovine fibrinogen. Because of its function to make up for the deficiency of factor X and its platelet aggregation inducer property, TLIECV could be considered a molecular impact to reveal the hemostasis mechanisms.
Toxicon, 1999
Green pit viper (Trimeresurus albolabris and Trimeresurus macrops) venom was found to have a thrombin-like eect in vitro but cause a de®brination syndrome in vivo. The eects of venom on ®brinolytic system have not been well characterized. This knowledge can help to de®ne the roles of anti®brinolytic therapy, give insights in ®brinolytic system regulation and potentially lead to identi®cation of a new pro®brinolytic agent from this venom. Fortysix cases of green pit viper bites were studied for various coagulation and ®brinolytic parameters and correlated with serum venom levels measured by ELISA. Fibrinolytic system activation is very common as indicated by low plasminogen (50%), low antiplasmin (56.5%) and elevated ®brin±®brinogen degradation products (FDPs, 97.4%) levels. FDP test is very sensitive and a normal level is useful for exclusion of systemic envenomation. In contrast to some other models of de®brination syndrome, such as Russell viper (Daboia russelli siamensis), elevation of plasminogen activator activity (PA) was found indicating a hyper®brinolytic state. De®nite increase in tissue-type plasminogen activator (t-PA) antigen ( p = 0.00075) with a modest elevation of its inhibitor plasminogen activator inhibitor-1 (PAI-1) ( p = 0.27) probably contributes to this eect. This supports the idea that the balance between plasminogen activators and inhibitors can determine ®brinolytic responses in pathologic states. Fibrinopeptide A levels were markedly elevated (68.432 51.57 ng/ml in Toxicon 37 (1999) 743±755 cases and 2.83 2 3.80 ng/ml in control, p < 0.0001) and correlated well with clinical severity suggesting that the ®brin deposition from the thrombin-like eect is the main mechanism of ®brinolysis. Therefore, anti®brinolytic agents probably have no role in treatment. However, the components of green pit viper venom that have these pro®brinolytic eects in human are interesting and should be further identi®ed. #