Prothrombin activation induced by Ecarin - a prothrombin converting enzyme from Echis carinatus venom

High-throughput proteomics and in vitro functional characterization of the 26 medically most important elapids and vipers from sub-Saharan Africa

Venomous snakes are important parts of the ecosystem, and their behavior and evolution have been shaped by their surrounding environments over the eons. This is reflected in their venoms, which are typically highly adapted for their biological niche, including their diet and defense mechanisms for deterring predators. Sub-Saharan Africa is rich in venomous snake species, of which many are dangerous to humans due to the high toxicity of their venoms and their ability to effectively deliver large amounts of venom into their victims via their bite. In this study, the venoms of 26 of sub-Saharan Africa's medically most relevant elapid and viper species were subjected to parallelized toxicovenomics analysis. The analysis included venom proteomics and in vitro functional characterization of whole venom toxicities, enabling a robust comparison of venom profiles between species. The data presented here corroborate previous studies and provide biochemical details for the clinical manifestations observed in envenomings by the 26 snake species. Moreover, two new venom proteomes (Naja anchietae and Echis leucogaster) are presented here for the first time. Combined, the presented data can help shine light on snake venom evolutionary trends and possibly be used to further improve or develop novel antivenoms.

MOLECULAR MECHANISMS OF INTRAVASCULAR INHIBITION AND STIMULATION OF EXTRAVASCULAR THROMBOSIS

The hemostasis system is designed to maintain a balance between the processes of blood clotting, anticoagulation, as well as fibrinolysis, to ensure constant effective blood circulation in the body and rapid cessation of bleeding in the event of their occurrence. The procoagulant potential of the hemostasis system is based on molecular mechanisms that lead to the formation of fibrin in the bloodstream, which is the framework of the thrombus, and to the aggregation of platelets — the basis of the thrombus body. The anticoagulant potential of blood plasma is provided by mechanisms aimed at inhibiting blood coagulation processes. Thorough study and understanding of these mechanisms will open up numerous treatments for pathologies associated with both intravascular thrombosis and bleeding of various origins. The purpose of this review is to analyze ways to prevent intravascular thrombosis and stimulate extravascular thrombosis. The review describes and analyzes available and promising means of thrombosis prevention, in particular, direct and indirect anticoagulants and antiplatelets, as well as methods of effective stimulation of thrombosis, which is necessary in case of vascular damage. The result of this analysis is to determine the nodal points of the protein network of the hemostasis system, the action of which by specific molecular effectors will control the process of thrombosis.

Prokaryotic expression, evaluation, and prediction of the structure and function of the ecarin metalloproteinase domain

Ecarin is one of the most widely used drug compounds in blood clotting experiments and is used to monitor and treat many diseases such as cancer, liver, lupus, and cardiovascular disease. The metalloproteinase domain is known as the active site of ecarin. In this study, an ecarin metalloproteinase cassette was designed and synthesized in the pUC57 vector. The gene fragment was released and cloned into the pET-28a vector and expressed in Escherichia coli. The recombinant protein was confirmed by western blotting. Enzyme activity was estimated by a laboratory coagulation test, and prothrombin time and tertiary structure were determined by using the Iterative Threading ASSEmbly Refinement (I-TASSER) server. Data from blood clotting tests for the produced ecarin activity were analyzed using an independent t test. As per I-TASSER server prediction, model 1 with the highest confidence score 0.95, template modeling score (0.84 ± 0.08), and root mean square deviation (3.5 ± 2.4 Å) was considered as the best model, and the 2e3xA enzyme was more similar to the target protein. The predictive results helped to better understand the relationship between the structure and function of the ecarin metalloproteinase domain. Also, the production of this active site in the prokaryotic expression system, which is simpler and more cost-effective than the production of the eukaryotic system, showed that this recombinant ecarin could be used as a substitute for the raw snake venom of Echis carinatus because it converts prothrombin into thrombin, and its activity, as estimated using the prothrombin time test, was found to be faster than normal ecarin.

Ecarin based coagulation testing

Ecarin is derived from venom of Echis carinatus, and will activate prothrombin into meizothrombin which will then cleave fibrinogen to result in clot formation. Ecarin based testing has been described for decades, but these assays were typically restricted to reference or speciality coagulation laboratories. This test was initially described for the assessment of direct thrombin inhibitors (eg, bivalirudin lepirudin, or argatroban) and was not affected by heparins or heparinoids. Ecarin based assays were rarely used for anticoagulation monitoring until the emergence of the direct oral thrombin inhibitor dabigatran etexilate in 2010. As this test was mentioned in the prescribing information for dabigatran etexilate, there was increased interest for use by clinical laboratories as the preferred method for assessing the anticoagulant effect of this drug. The purpose of this document is to review the current status of ecarin based assays for assessing dabigatran. This is with the understanding that these methods can also be exploited for determining the anticoagulation effect of parenteral direct thrombin inhibitors, such as argatroban and bivalirudin.

High throughput screening and identification of coagulopathic snake venom proteins and peptides using nanofractionation and proteomics approaches

Snakebite is a neglected tropical disease that results in a variety of systemic and local pathologies in envenomed victims and is responsible for around 138,000 deaths every year. Many snake venoms cause severe coagulopathy that makes victims vulnerable to suffering life-threating haemorrhage. The mechanisms of action of coagulopathic snake venom toxins are diverse and can result in both anticoagulant and procoagulant effects. However, because snake venoms consist of a mixture of numerous protein and peptide components, high throughput characterizations of specific target bioactives is challenging. In this study, we applied a combination of analytical and pharmacological methods to identify snake venom toxins from a wide diversity of snake species that perturb coagulation. To do so, we used a high-throughput screening approach consisting of a miniaturised plasma coagulation assay in combination with a venom nanofractionation approach. Twenty snake venoms were first separated using reversed-phase liquid chromatography, and a post-column split allowed a small fraction to be analyzed with mass spectrometry, while the larger fraction was collected and dispensed onto 384-well plates. After fraction collection, any solvent present in the wells was removed by means of freeze-drying, after which it was possible to perform a plasma coagulation assay in order to detect coagulopathic activity. Our results demonstrate that many snake venoms simultaneously contain both procoagulant and anticoagulant bioactives that contribute to coagulopathy. In-depth identification analysis from seven medically-important venoms, via mass spectrometry and nanoLC-MS/MS, revealed that phospholipase A2 toxins are frequently identified in anticoagulant venom fractions, while serine protease and metalloproteinase toxins are often associated with procoagulant bioactivities. The nanofractionation and proteomics approach applied herein seems likely to be a valuable tool for the rational development of next-generation snakebite treatments by facilitating the rapid identification and fractionation of coagulopathic toxins, thereby enabling specific targeting of these toxins by new therapeutics such as monoclonal antibodies and small molecule inhibitors.

The sweet side of venom: Glycosylated prothrombin activating metalloproteases from Dispholidus typus (boomslang) and Thelotornis mossambicanus (twig snake)

Dispholidus typus and Thelotornis mossambicanus are closely related rear-fanged colubrid snakes that both possess strongly procoagulant venoms. However, despite similarities in overall venom biochemistry and resulting clinical manifestations, the underlying venom composition differs significantly between the two species. As a result, the only available antivenom-which is a monovalent antivenom for D. typus-has minimal cross reactivity with T. mossambicanus and is not a clinically viable option. It was hypothesised that this lack of cross reactivity is due to the additional large metalloprotease protein within T. mossambicanus venom, which may also be responsible for faster coagulation times. In this study, we found that T. mossambicanus venom is a more powerful activator of prothrombin than that of D. typus and that the SVMP transcripts from T. mossambicanus form a clade with those from D. typus. The sequences from D. typus and T. mossambicanus were highly similar in length, with the calculated molecular weights of the T. mossambicanus transcripts being significantly less than the molecular weights of some isoforms on the 1D SDS-PAGE gels. Analyses utilising degylcosylating enzymes revealed that T. mossambicanus SVMPs are glycosylated during post-translational modification, but that this does not lead to the different molecular weight bands observed in 1D SDS-PAGE gels. However, differences in glycosylation patterns may still explain some of the difference between the enzymatic activities and neutralization by antivenom that have been observed in these venoms. The results of this study provide new information regarding the treatment options for patients envenomated by T. mossambicanus as well as the evolution of these dangerous snakes.

Clinical implications of coagulotoxic variations in Mamushi (Viperidae: Gloydius) snake venoms

Snake bite is currently one of the most neglected tropical diseases affecting much of the developing world. Asian pit vipers are responsible for a considerable amount of envenomations annually and bites can cause a multitude of clinical complications resulting from coagulopathic and neuropathic effects. While intense research has been undertaken for some species of Asian pit viper, functional coagulopathic effects have been neglected for others. We investigated their effects upon the human clotting cascade using venoms of four species of Gloydius and Ovophis okinavensis, a species closely to Gloydius. All species of included within this investigation displayed varying fibrinogenolytic effects, resulting in a net anticoagulant outcome. Gloydius saxatilis and Gloydius ussuriensis displayed the most variable effects from differing localities, sampled from Russia and Korea. As this Gloydius investigation includes some geographical variation, notable results indicate key variations of these species that point to possible limitations in antivenom cross-reactivities, which may have implications for the clinical care of victims envenomed by these snakes.

The paraspecific neutralisation of snake venom induced coagulopathy by antivenoms

Snake envenoming causes several potentially lethal pathologies. The specific pathology is dictated by the toxin composition of venom, which varies by species, geography and ontogeny. This variation severely restricts the paraspecific efficacy of antivenoms used to treat snakebite victims. With a view to devising pathology-specific snakebite treatments, we assessed the procoagulant activity of 57 snake venoms and investigated the efficacy of various antivenoms. We find that procoagulant venoms act differentially on key steps of the coagulation cascade, and that certain monospecific antivenoms work in a previously unrecognised paraspecific manner to neutralise this activity, despite conventional assumptions of congener-restricted efficacy. Moreover, we demonstrate that the metal chelator EDTA is also capable of neutralising venom-induced lethality in vivo. This study illustrates the exciting potential of developing new, broad-spectrum, toxin-targeting antivenoms capable of treating key snakebite pathologies, and advocates a thorough re-examination of enzyme inhibiting compounds as alternative therapies for treating snakebite victims.

Proteomics and antivenomics of Echis carinatus carinatus venom: Correlation with pharmacological properties and pathophysiology of envenomation

The proteome composition of Echis carinatus carinatus venom (ECV) from India was studied for the first time by tandem mass spectrometry analysis. A total of 90, 47, and 22 distinct enzymatic and non-enzymatic proteins belonging to 15, 10, and 6 snake venom protein families were identified in ECV by searching the ESI-LC-MS/MS data against non-redundant protein databases of Viperidae (taxid 8689), Echis (taxid 8699) and Echis carinatus (taxid 40353), respectively. However, analysis of MS/MS data against the Transcriptome Shotgun Assembly sequences (87 entries) of conger E. coloratus identified only 14 proteins in ECV. Snake venom metalloproteases and snaclecs, the most abundant enzymatic and non-enzymatic proteins, respectively in ECV account for defibrinogenation and the strong in vitro pro-coagulant activity. Further, glutaminyl cyclase, aspartic protease, aminopeptidase, phospholipase B, vascular endothelial growth factor, and nerve growth factor were reported for the first time in ECV. The proteome composition of ECV was well correlated with its biochemical and pharmacological properties and clinical manifestations observed in Echis envenomed patients. Neutralization of enzymes and pharmacological properties of ECV, and immuno-cross-reactivity studies unequivocally point to the poor recognition of <20 kDa ECV proteins, such as PLA₂, subunits of snaclec, and disintegrin by commercial polyvalent antivenom.

Coagulating Colubrids: Evolutionary, Pathophysiological and Biodiscovery Implications of Venom Variations between Boomslang (Dispholidus typus) and Twig Snake (Thelotornis mossambicanus)

Venoms can deleteriously affect any physiological system reachable by the bloodstream, including directly interfering with the coagulation cascade. Such coagulopathic toxins may be anticoagulants or procoagulants. Snake venoms are unique in their use of procoagulant toxins for predatory purposes. The boomslang (Dispholidus typus) and the twig snakes (Thelotornis species) are iconic African snakes belonging to the family Colubridae. Both species produce strikingly similar lethal procoagulant pathologies. Despite these similarities, antivenom is only produced for treating bites by D. typus, and the mechanisms of action of both venoms have been understudied. In this study, we investigated the venom of D. typus and T. mossambicanus utilising a range of proteomic and bioactivity approaches, including determining the procoagulant properties of both venoms in relation to the human coagulation pathways. In doing so, we developed a novel procoagulant assay, utilising a Stago STA-R Max analyser, to accurately detect real time clotting in plasma at varying concentrations of venom. This approach was used to assess the clotting capabilities of the two venoms both with and without calcium and phospholipid co-factors. We found that T. mossambicanus produced a significantly stronger coagulation response compared to D. typus. Functional enzyme assays showed that T. mossambicanus also exhibited a higher metalloprotease and phospholipase activity but had a much lower serine protease activity relative to D. typus venom. The neutralising capability of the available boomslang antivenom was also investigated on both species, with it being 11.3 times more effective upon D. typus venom than T. mossambicanus. In addition to being a faster clotting venom, T. mossambicanus was revealed to be a much more complex venom composition than D. typus. This is consistent with patterns seen for other snakes with venom complexity linked to dietary complexity. Consistent with the external morphological differences in head shape between the two species, CT and MRI analyses revealed significant internal structural differences in skull architecture and venom gland anatomy. This study increases our understanding of not only the biodiscovery potential of these medically important species but also increases our knowledge of the pathological relationship between venom and the human coagulation cascade.

Peptidomimetic hydroxamate metalloproteinase inhibitors abrogate local and systemic toxicity induced by Echis ocellatus (saw-scaled) snake venom

The ability of two peptidomimetic hydroxamate metalloproteinase inhibitors, Batimastat and Marimastat, to abrogate toxic and proteinase activities of the venom of Echis ocellatus from Cameroon and Ghana was assessed. Since this venom largely relies for its toxicity on the action of zinc-dependent metalloproteinases (SVMPs), the hypothesis was raised that toxicity could be largely eliminated by using SVMP inhibitors. Both hydroxamate molecules inhibited local and pulmonary hemorrhagic, in vitro coagulant, defibrinogenating, and proteinase activities of the venoms in conditions in which venom and inhibitors were incubated prior to the test. In addition, the inhibitors prolonged the time of death of mice receiving 4 LD₅₀s of venom by the intravenous route. Lower values of IC₅₀ were observed for in vitro and local hemorrhagic activities than for systemic effects. When experiments were performed in conditions that simulated the actual circumstances of snakebite, i.e. by administering the inhibitor after envenoming, Batimastat completely abrogated local hemorrhage if injected immediately after venom. Moreover, it was also effective at inhibiting lethality and defibrinogenation when venom and inhibitor were injected by the intraperitoneal route. Results suggest that these, and possibly other, metalloproteinase inhibitors may become an effective adjunct therapy in envenomings by E. ocellatus when administered at the anatomic site of venom injection rapidly after the bite.

Inhibition of Snake Venom Metalloproteinase by β-Lactoglobulin Peptide from Buffalo (Bubalus bubalis) Colostrum

Bioactive peptide research has experienced considerable therapeutic interest owing to varied physiological functions, efficacy in excretion, and tolerability of peptides. Colostrum is a rich natural source of bioactive peptides with many properties elucidated such as anti-thrombotic, anti-hypertensive, opioid, immunomodulatory, etc. In this study, a variant peptide derived from β-lactoglobulin from buffalo colostrum was evaluated for the anti-ophidian property by targeting snake venom metalloproteinases. These are responsible for rapid local tissue damages that develop after snakebite such as edema, hemorrhage, myonecrosis, and extracellular matrix degradation. The peptide identified by LC-MS/MS effectively neutralized hemorrhagic activity of the Echis carinatus venom in a dose-dependent manner. Histological examinations revealed that the peptide mitigated basement membrane degradation and accumulation of inflammatory leucocytes at the venom-injected site. Inhibition of proteolytic activity was evidenced in both casein and gelatin zymograms. Also, inhibition of fibrinolytic and fibrinogenolytic activities was seen. The UV-visible spectral study implicated Zn²⁺ chelation, which was further confirmed by molecular docking and dynamic studies by assessing molecular interactions, thus implicating the probable mechanism for inhibition of venom-induced proteolytic and hemorrhagic activities. The present investigation establishes newer vista for the BLG-col peptide with anti-ophidian efficacy as a promising candidate for therapeutic interventions.

Albizia lebbeck seed methanolic extract as a complementary therapy to manage local toxicity of Echis carinatus venom in a murine model

CONTEXT AND OBJECTIVE

Viperid venom-induced chronic local-toxicity continues even after anti-snake venom treatment. Therefore, traditional antidote Albizia lebbeck L. (Fabaceae) seed extract was tested against Echis carinatus S. (Viperidae) venom (ECV)-induced local toxicity to evaluate its complementary remedy.

MATERIALS AND METHODS

Soxhlet extraction of A. lebbeck seeds was performed with the increasing polarity of solvents (n-hexane to water); the extract was screened for phytochemicals (alkaloids, anthraquinones, flavonoids, glycosides, phenolics, saponins, steroids and tannins). In preliminary in vitro analysis, A. lebbeck methanolic extract (ALME) demonstrated significant inhibition of ECV proteases, the major enzyme-toxin responsible for local- toxicity. Therefore, in vitro neutralizing potential of ALME was further evaluated against hyaluronidases and phospholipase A₂ (1:1-1:100 w/w). In addition, alleviation of ECV induced characteristic local- toxicity [haemorrhage (i.d.) and myotoxicity (i.m.)] was determined in mice.

RESULTS

ALME contained high concentrations of phenolics and flavonoids and demonstrated significant in vitro inhibition of ECV protease (IC₅₀=36.32 μg, p < 0.0001) and hyaluronidase (IC₅₀=91.95 μg, p < 0.0001) at 1:100 w/w. ALME significantly neutralized ECV induced haemorrhage (ED₅₀=26.37 μg, p < 0.0001) and myotoxicity by significantly reducing serum creatinine kinase (ED₅₀=37.5 μg, p < 0.0001) and lactate dehydrogenase (ED₅₀=31.44 μg, p = 0.0021) levels at 1:50 w/w.

DISCUSSION AND CONCLUSION

ALME demonstrated significant neutralization of ECV enzymes that contribute in local tissue damage and haemostatic alterations. The study scientifically supports the anecdotal use of A. lebbeck in complementary medicine and identifies ALME as principle fraction responsible for antivenom properties.

Metalloproteases Affecting Blood Coagulation, Fibrinolysis and Platelet Aggregation from Snake Venoms: Definition and Nomenclature of Interaction Sites

Snake venom metalloproteases, in addition to their contribution to the digestion of the prey, affect various physiological functions by cleaving specific proteins. They exhibit their activities through activation of zymogens of coagulation factors, and precursors of integrins or receptors. Based on their structure–function relationships and mechanism of action, we have defined classification and nomenclature of functional sites of proteases. These metalloproteases are useful as research tools and in diagnosis and treatment of various thrombotic and hemostatic conditions. They also contribute to our understanding of molecular details in the activation of specific factors involved in coagulation, platelet aggregation and matrix biology. This review provides a ready reference for metalloproteases that interfere in blood coagulation, fibrinolysis and platelet aggregation.

NETosis and lack of DNase activity are key factors in Echis carinatus venom-induced tissue destruction

Indian Echis carinatus bite causes sustained tissue destruction at the bite site. Neutrophils, the major leukocytes in the early defence process, accumulate at the bite site. Here we show that E. carinatus venom induces neutrophil extracellular trap (NET) formation. The NETs block the blood vessels and entrap the venom toxins at the injection site, promoting tissue destruction. The stability of NETs is attributed to the lack of NETs-degrading DNase activity in E. carinatus venom. In a mouse tail model, mice co-injected with venom and DNase 1, and neutropenic mice injected with the venom, do not develop NETs, venom accumulation and tissue destruction at the injected site. Strikingly, venom-induced mice tail tissue destruction is also prevented by the subsequent injection of DNase 1. Thus, our study suggests that DNase 1 treatment may have a therapeutic potential for preventing the tissue destruction caused by snake venom.

The saw-scaled viper venom causes continued tissue damage that may cause death. Here the authors show that the venom attracts neutrophils to the bite site and induces neutrophil extracellular traps that capture venom components causing tissue damage, which can be prevented by enzymatic DNA degradation.

Purification and characterization of five snake venom metalloproteinases from Egyptian Echis pyramidum pyramidum venom

New five P-III snake venom metalloproteinases (SVMPs): EpyB2 (62 kDa), EpyB3 (62+23 kDa), EpyB4 (60 kDa), EpyB5 (67 kDa) and EpyB6 (66 kDa) of the most dangerous viper, Echis pyramidum pyramidum (Epy), were purified and characterized in a set of biochemical assays. The SVMPs were purified by applying a protocol of two successive chromatographic steps. Three purified SVMPs "EpyB2, EpyB4, and EpyB5" have hemorrhagic activity with MHDs, 7 μg, 7.6 μg and 15 μg, respectively; furthermore, they have high preference towards fibronectin, collagen, gelatin, fibrin and hemoglobin substrates compared with non-hemorrhagic SVMPs (EpyB3 and EpyB6). All the purified SVMPs showed remarkable thermal and pH stability, inhibited by metalloproteinase inhibitors and Zn(2+), Mn(2+), Ni(2+), Co(2+), Cu(2+), and Hg(2+). The purified SVMPs act as α-fibrinogenases, prothrombin activators and procoagulants. In conclusion, Epy venom has multiple SVMPs that are responsible for hemorrhagic events and thus represent a significant health hazard for victims of envenomation, however, they may be useful for treating diseases involving abnormal blood clot formation.

Local and systemic toxicity of Echis carinatus venom: neutralization by Cassia auriculata L. leaf methanol extract

Viper bites cause high morbidity and mortality especially in tropical and subtropical regions, affecting a large number of the rural population in these areas. Even though anti-venoms are available, in most cases they fail to tackle viper venom-induced local manifestations that persist even after anti-venom administration. Several studies have been reported the use of plant products and approved drugs along side anti-venom therapy for efficient management of local tissue damage. In this regard, the present study focuses on the protective efficacy of Cassia auriculata L. (Leguminosae) against Echis carinatus venom (ECV) induced toxicity. C. auriculata is a traditional medicinal plant, much valued in alternative medicine for its wide usage in ayurveda, naturopathy, and herbal therapy. Further, it has been used widely by traditional healers for treatment of snake and scorpion bites in the Western Ghats of Karnataka, India. In the present study, C. auriculata leaf methanol extract (CAME) significantly inhibited enzymatic activities of ECV proteases (96 ± 1 %; P = 0.001), PLA2 (45 ± 5 %; P = 0.01) and hyaluronidases (100 %; P = 0.0003) in vitro and hemorrhage, edema and myotoxicity in vivo. Further, CAME effectively reduced the lethal potency of ECV and increased the survival time of mice by ~6 times (17 vs 3 h). These inhibitory potentials of CAME towards hydrolytic enzymes, mortal and morbid symptoms of ECV toxins clearly substantiates the use by traditional healers of C. auriculata as a folk medicinal remedy for snakebite.

Hemostatic interference of Indian king cobra (Ophiophagus hannah) Venom. Comparison with three other snake venoms of the subcontinent

Unlike Naja naja, Bungarus caeruleus, Echis carinatus, and Daboia/Vipera russellii venoms, Ophiophagus hannah venom is medically ignored in the Indian subcontinent. Being the biggest poisonous snake, O. hannah has been presumed to inject several lethal doses of venom in a single bite. Lack of therapeutic antivenom to O. hannah bite in India makes any attempt to save the victim a difficult exercise. This study was initiated to compare O. hannah venom with the above said venoms for possible interference in hemostasis. Ophiophagus hannah venom was found to actively interfere in hemostatic stages such as fibrin clot formation, platelet activation/aggregation, and fibrin clot dissolution. It decreased partial thromboplastin time (aPTT), prothrombin time (PT), and thrombin clotting time (TCT). These activities are similar to that shown by E. carinatus and D. russellii venoms, and thus O. hannah venom was found to exert procoagulant activity through the common pathway of blood coagulation, while N. naja venom increased aPTT and TCT but not PT, and hence it was found to exert anticoagulant activity through the intrinsic pathway. Venoms of O. hannah, E. carinatus, and D. russellii lack plasminogen activation property as they do not hydrolyze azocasein, while they all show plasmin-like activity by degrading the fibrin clot. Although N. naja venom did not degrade azocasein, unlike other venoms, it showed feeble plasmin-like activity on fibrin clot. Venom of E. carinatus induced clotting of human platelet rich plasma (PRP), while the other three venoms interfered in agonist-induced platelet aggregation in PRP. Venom of O. hannah least inhibited the ADP induced platelet aggregation as compared to D. russellii and N. naja venoms. All these three venoms showed complete inhibition of epinephrine-induced aggregation at varied doses. However, O. hannah venom was unique in inhibiting thrombin induced aggregation.

Measurement of the new anticoagulants

New oral anticoagulants are given at fixed daily doses without laboratory dose adjustment for prevention of venous thromboembolism following elective total knee- and hip replacement, for treatment and prevention of recurrent events of acute venous thromboembolism, and for prevention of embolic events in atrial fibrillation. However, it may be necessary to determine the anticoagulant effect of new oral anticoagulants in special patient populations such as in elderly, for renal impairment, before operation, bleeding or thrombotic episodes and to monitor self-compliance. Oral factor Xa and oral thrombin inhibitors influence dose dependently global and specific coagulation assays. Standardization of assays is currently undertaken. Determination of the new oral anticoagulants in serum samples would facilitate blood sampling and analysis from samples taken and stored for creatinine or other biochemical parameters. Point of care methods from plasma or urine for the new oral anticoagulants would improve patient care. First data demonstrate the feasibility of such assays in urine.

Snake venom metalloproteinases

Recent proteomic analyses of snake venoms show that metalloproteinases represent major components in most of the Crotalid and Viperid venoms. In this chapter we discuss the multiple activities of the SVMPs. In addition to hemorrhagic activity, members of the SVMP family also have fibrin(ogen)olytic activity, act as prothrombin activators, activate blood coagulation factor X, possess apoptotic activity, inhibit platelet aggregation, are pro-inflammatory and inactivate blood serine proteinase inhibitors. Clearly the SVMPs have multiple functions in addition to their well-known hemorrhagic activity. The realization that there are structural variations in the SVMPs and the early studies that led to their classification represents an important event in our understanding of the structural forms of the SVMPs. The SVMPs were subdivided into the P-I, P-II and P-III protein classes. The noticeable characteristic that distinguished the different classes was their size (molecular weight) differences and domain structure: Class I (P-I), the small SVMPs, have molecular masses of 20-30 kDa, contain only a pro domain and the proteinase domain; Class II (P-II), the medium size SVMPs, molecular masses of 30-60 kDa, contain the pro domain, proteinase domain and disintegrin domain; Class III (P-III), the large SVMPs, have molecular masses of 60-100 kDa, contain pro, proteinase, disintegrin-like and cysteine-rich domain structure. Another significant advance in the SVMP field was the characterization of the crystal structure of the first P-I class SVMP. The structures of other P-I SVMPs soon followed and the structures of P-III SVMPs have also been determined. The active site of the metalloproteinase domain has a consensus HEXXHXXGXXHD sequence and a Met-turn. The "Met-turn" structure contains a conserved Met residue that forms a hydrophobic basement for the three zinc-binding histidines in the consensus sequence.

Neutralisation of Local Haemorrhage Induced by the Saw-Scaled Viper Echis carinatus sochureki Venom Using Ethanolic Extract of Hibiscus aethiopicus L

The objective of the study is to investigate the anti-snake venom activities of a local plant, Hibiscus aethiopicus L. The H. aethiopicus was dried and extracted with ethanol. Different assays were performed according to standard techniques, to evaluate the plant's acute toxicity and its antivenom activities. The results of evaluating the systemic acute toxicity of the H. aethiopicus extract using “oral and intra-peritoneal” route were normal even at the highest dose (24 g/kg) tested. All guinea pigs (n = 3) when treated with venoms E. c. sochureki (75 μg) alone induced acute skin haemorrhage. In contrast, all guinea pigs (n = 18) treated with both venom and the plant extract at a concentration between 500 and 1000 mg/kg showed no signs of haemorrhage. Moreover, all guinea pigs (n = 18) treated with venom and the plant extract below 400 mg/kg showed acute skin haemorrhage. All guinea pigs treated with venom E. c. sochureki (75 μg) alone induced acute skin haemorrhage after both 24 and 32 hours. In contrast, all guinea pigs treated with both venom and the plant extract (administered independently) at concentrations between 500 and 1000 mg/kg showed no signs of haemorrhage after 32 hours. However, after 24 hours all tested guinea pigs showed less inhibition (<60%) compared to that obtained after 32 hours. The outcome of this study reflects that the extract of H. aethiopicus plant may contain an endogenous inhibitor of venom induced local haemorrhage.

Acute renal failure in acute poisoning: prospective study from a tertiary care centre of South India

BACKGROUND

Cases of people presenting with poisoning are likely to develop acute renal failure (ARF), which may be due to multiple mechanisms/aetiologies. These cases need careful observation and appropriate treatment.

OBJECTIVE

To find the risk of ARF among acute poisoning cases, identify the underlying causes and to analyse the outcome.

MATERIAL AND METHODS

In this prospective study with nested case control, 1,250 cases admitted to the Poison Control, Training and Research Centre of Government General Hospital, Madras Medical College were monitored and evaluated for development of ARF. Patients with history of diabetes/hypertension, known chronic kidney disease, chronic NSAID therapy, those on drugs that increase serum creatinine by inhibiting creatinine secretion and other co-morbid illnesses were excluded. Data were interpreted after subjecting them to bivariate logistic regression and then step wise multivariate analysis.

RESULTS

Thirty-two cases developed ARF. Twenty-four were due to snake bite, the rest due to chemical poisons. Chances of developing ARF were greater (6.15%) among the poisoning due to bites and stings than chemical poisoning (0.9%). Five in the former and seven in the latter expired. Among cases bitten by snakes, only 22 (7%) cases bitten by Russell Viper Daboia russelii developed renal failure. Copper sulphate and rat killer poisonings were the commonest causes of chemical induced ARF, dichromate, indigenous medicines and vasmol 33 (paraphenelyne diamine) were the least causes for ARF. None of the patients with organophosphate developed ARF nor did any of the 150 admitted for overdose of medicines developed ARF.

CONCLUSION

The risk of ARF among the cases of poisoning was 2.5%. The outcome of ARF among bites and stings was better than chemical poisoning, and the difference was highly significant (p= 0.005, OR = 0.04-1.0, 95% CI = 0.004-0.38). Early recognition and appropriate measures reduce the occurrence of ARF.

Procoagulant properties of bare and highly PEGylated vinyl-modified silica nanoparticles

AIMS

Undesired alterations of the blood clotting balance may follow the intravascular injection of nanotherapeutics/diagnostics. Here, we tested the procoagulant activity of synthetic amorphous silica (SAS) and organically modified silica (ORMOSIL) nanoparticles (NPs) and whether a high-density polyethylene glycol coating minimizes these effects.

MATERIALS & METHODS

Hageman factor- and tissue factor-dependent activation of human blood/plasma coagulation, and binding to human monocytes, endothelial cells and platelets were quantified in vitro using naked and PEGylated ORMOSIL-NPs. Their effects were compared with those of SAS-NPs, present in many industrial products, and of poly(lactic-co-glycolic acid)- and small unilamellar vesicles-NPs, already approved for use in humans.

RESULTS

Both SAS-NPs and ORMOSIL-NPS presented a significant procoagulant activity. However, highly PEGylated ORMOSIL-NPs were particularly averse to the interaction with the soluble factors and cellular elements that may lead to intravascular blood coagulation.

CONCLUSION

Stealth, highly PEGylated ORMOSIL-NPs with a poor procoagulant activity can be used as starting blocks to design hemocompatible nanomedical-devices.

Local tissue destruction and procoagulation properties of Echis carinatus venom: inhibition by Vitis vinifera seed methanol extract

Plant extracts are extensively used against snakebites in Indian folk medicine. In this study, one such traditionally used plant, Vitis vinifera L. (Vitaceae) seed methanol extract has been studied for its ability to neutralize Indian Echis carinatus (saw-scaled viper) venom. The extract effectively inhibited toxic effects, such as oedema, haemorrhage, myonecrosis and coagulation of citrated human plasma. Further, the extract inhibited the caseinolytic, hyaluronolytic and fibrinogenolytic activities of the venom. The extract caused dose dependent inhibition of the toxic activities studied, suggesting venom inhibition. Thus, the anti-snake venom property of the extract appears to be highly promising for further investigation in order to achieve better neutralization of Indian E. carinatus venom poisoning.

Role of the acidic hirudin-like COOH-terminal amino acid region of factor Va heavy chain in the enhanced function of prothrombinase

Prothrombinase activates prothrombin through initial cleavage at Arg(320) followed by cleavage at Arg(271). This pathway is characterized by the generation of an enzymatically active, transient intermediate, meizothrombin, that has increased chromogenic substrate activity but poor clotting activity. The heavy chain of factor Va contains an acidic region at the COOH terminus (residues 680-709). We have shown that a pentapeptide from this region (DYDYQ) inhibits prothrombin activation by prothrombinase by inhibiting meizothrombin generation. To ascertain the function of these regions, we have created a mutant recombinant factor V molecule that is missing the last 30 amino acids from the heavy chain (factor V(Delta680-709)) and a mutant molecule with the (695)DYDY (698) --> AAAA substitutions (factor V(4A)). The clotting activities of both recombinant mutant factor Va molecules were impaired compared to the clotting activity of wild-type factor Va (factor Va (Wt)). Using an assay employing purified reagents, we found that prothrombinase assembled with factor Va(Delta680-709) displayed an approximately 39% increase in k cat, while prothrombinase assembled with factor Va(4A) exhibited an approximately 20% increase in k cat for the activation of prothrombin as compared to prothrombinase assembled with factor Va(Wt). Gel electrophoresis analyzing prothrombin activation by prothrombinase assembled with the mutant molecules revealed a delay in prothrombin activation with persistence of meizothrombin. Our data demonstrate that the COOH-terminal region of factor Va heavy chain is indeed crucial for coordinated prothrombin activation by prothrombinase because it regulates meizothrombin cleavage at Arg(271) and suggest that this portion of factor Va is partially responsible for the enhanced procoagulant function of prothrombinase.

Characterization of a novel protein from Proatheris superciliaris venom: proatherocytin, a 34-kDa platelet receptor PAR1 agonist

Many toxins from viperid venoms have been characterised as powerful activators of platelets. Here, the venom from the East African Lowland viper, Proatheris superciliaris, was investigated for its effect on platelets and the coagulation system. Whole P. superciliaris venom stimulated platelet shape change and aggregation; however, the stimulation of platelet activation was unaffected by the structurally distinct Src family kinase inhibitors PP1 and PD0173952, suggesting that platelet activation was mediated by a G protein-coupled receptor. A platelet reactive 34-kDa protein was isolated from P. superciliaris venom which we have designated proatherocytin. This protein induced Src kinase-independent aggregation of both human and mouse platelets that was inhibited by the serine protease inhibitor AEBSF. Proatherocytin did not clot bovine or human fibrinogen, degrade fibrinogen or hydrolyse the serine protease substrate benzoyl-FVR-pNA. It activated human PAR1 on stably transfected rat kidney epithelial cells, whereas no activation of the trypsin receptor PAR2 was shown. Surprisingly, Edman degradation of proatherocytin revealed sequence identity with existing disintegrin-like domains of snake venom metalloproteinases. These results suggest that proatherocytin is a highly selective PAR1 agonist that also causes mouse platelet aggregation, probably through cleavage of PAR4.

Distribution of the heterogeneity of des-gamma-carboxyprothrombin in patients with hepatocellular carcinoma

BACKGROUND AND AIM

Our aim was to evaluate the heterogeneity of des-gamma-carboxyprothrombin (DCP) in the plasma of patients with hepatocellular carcinoma (HCC), benign liver diseases, and normal controls and compare the DCP values by enzyme-linked immunosorbent assay (ELISA) for two types monoclonal antibodies (MU-3 and 19B7).

METHODS

We purified DCP from the plasma of 17 patients with HCC, three patients with metastatic liver tumors (MTLT), 12 with acute hepatitis (AH), five with chronic hepatitis (CH), nine with liver cirrhosis (LC), and 10 normal controls (NC). The DCP was analyzed by using immunoaffinity chromatography, reversed-phase high-performance liquid chromatography and measured by using an ELISA.

RESULTS

In HCC, the synthesis of the 1-, 3-, and 4-Gla (gamma-carboxyglutamic acid) DCP variants markedly increased, and those levels accounted for more than 50% of the DCP. The synthesis of the 3-, and 4-Gla DCP gradually increased in order of AH, CH, and LC patients. The MU-3 antibody reacted with the 1-, 3- and 4-Gla DCP variants, whereas the 19B7 antibody reacted with the 6-, 7- and 8-Gla variants. The DCP was measured by ELISA, markedly increased in order of NC, AH, CH, LC, and HCC cases. The correlation of the ratios (1 + 3 + 4)-Gla/(6 + 7 + 8)-Gla DCP and MU-3/19B7 was positive and statistically significant (r = 0.786, n = 56).

CONCLUSIONS

According to the severity of liver damages, the synthesis of the 1-, 3- and 4-Gla DCP variants that lost the Ca binding from the outside of the Gla-domain of the prothrombin molecule increases and the MU-3/19B7 ratio is believed to reflect this.

Comparison of Two Different Ecarin Clotting Time Methods

BACKGROUND

Ecarin Clotting Time (ECT) assay specifically determines the inhibition of meizothrombin by direct thrombin inhibitors (DTI). Blood coagulation factor levels lowered by vitamin K antagonists (VKA) may prolong ECT. Concomitant treatment of VKA with DTI may influence differently the two published ECT methods.

METHODS

Lepirudin (100-3,000 ng/ml), argatroban (300--3,000 ng/ml) and melagatran (30--1000 ng/ml) were added to normal plasma (NP; n=12) samples and to plasma of patients on stable vitamin K antagonist therapy with warfarin (VKAP; n=12). ECT assays were performed according to [5] (method 1) and according to [6] (method 2). Data were subjected to multifactorial variance analysis.

RESULTS

Normal ranges were 35.5+/-2.8 s in NP versus 31.8+/-1.2 s in VKAP with method 1 (p< 0.001) and 44.3+/-3.9 s in NP vs. 51.4+/-8.3 s in VKAP with method 2 (p< 0.004). Besides the inhibitors (p<0.0001), the method used (p<0.0001) and the group (NP vs. VKAP, p=0.003) had an influence on the ECT. Inhibitors (p< 0.02) or method used (p< 0.03) and the group (NP vs. VKAP, p=0.0001) influenced also the ECT ratio.

DISCUSSION

Both ECT methods are suitable for monitoring different DTIs over a large linear range with both methods during concomitant treatments with vitamin K antagonists. The ECT ratio improves but not abolishes the differences between the methods. Additive effects of vitamin K antagonists on ECT methods have to be taken into consideration in clinical routine.

Structural considerations of the snake venom metalloproteinases, key members of the M12 reprolysin family of metalloproteinases

The importance of proteinases in the pathologies associated with Viperid envenoming has long been appreciated. Over the past 40 years substantial research has clearly implicated metalloproteinases in the venom (snake venom metalloproteinases; SVMPs) as playing key roles in the development of such symptoms as hemorrhage, edema, hypotension, hypovolemia, inflammation and necrosis. In spite of this wealth of information there are still many unresolved questions pertaining to the structural basis for the various SVMPS giving rise to the diversity of activities. In this short review we will not attempt to provide an exhaustive collation of structural studies on the SVMPs; however, we will give a brief outline of the structural classification of the SVMPs; as well as relate them to the other members of the reprolysin family of metalloproteinases, the ADAMs. The information put forth in the text does not allow specific conclusions to be drawn on the structural basis for SVMP functional diversity, but it is our goal that it will allow for the development of testable hypotheses that can be experimentally pursued. What the reader will observe is that there are very interesting structural features displayed by the various SVMP classes and subclasses that provide insight into their functional characteristics.

The intriguing world of prothrombin activators from snake venom

Activation of prothrombin to mature thrombin occurs by the proteolytic action of the prothrombinase complex consisting of a serine proteinase factor Xa, and cofactors factor Va, Ca(2+) ions and phospholipids. Several exogenous prothrombin activators are found in snake venom. They are classified into four groups based on their cofactor requirements. Group A and B prothrombin activators are metalloproteinases whereas group C and D prothrombin activators are serine proteinases. Group C prothrombin activators resemble the mammalian factor Xa-factor Va complex, while Group D activators are structurally and functionally similar to factor Xa. This review provides a detailed description of the current knowledge on all prothrombin activators and highlights several intriguing questions that are yet to be answered.

Effects of three novel metalloproteinases from the venom of the West African saw-scaled viper, Echis ocellatus on blood coagulation and platelets

Two metalloproteinases, a 24-kDa P-I EoVMP1 and a 56-kDa P-III EoVMP2, have recently been isolated from the venom of the West African saw-scaled viper Echis ocellatus. We now reveal a new 65-kDa haemorrhagic group P-III metalloproteinase which we have designated EoVMP3. The aim of this study was to determine whether these three snake venom metalloproteinases (SVMPs) affect platelets and blood coagulation. EoVMP1 had no effect on the aggregation of washed human platelets, whereas EoVMP2 inhibited collagen-induced platelet aggregation. In contrast, EoVMP3 did not inhibit the aggregation of platelets by collagen but instead activated platelets in the absence of any additional co-factors. All three SVMPs were capable of activating prothrombin to varying degrees and can therefore be described as procoagulants. EoVMP1, EoVMP2 and EoVMP3 share sequence identity with other members of the reprolysin family, but differ greatly in their effects on some of the components that control haemostasis.

A secreted metallo protease from Aeromonas hydrophila exhibits prothrombin activator activity

Detection, purification, and partial characterization of a protease from Aeromonas hydrophila capable of cleaving prothrombin into active thrombin is described. The protease has been characterized with respect to enzymatic characteristics such as optimum reaction conditions for prothrombin activation, usage of additional substrates, as well as sensitivity against inhibitors. The protease activity can reversibly be inhibited by Me2+ chelating agents like ethylenediamine tetraacetic acid. The enzyme exhibits a pI value of 4.4 and can withstand temperatures up to 55 degrees C without loss of activity. With respect to prothrombin the enzyme exhibits a K(M) value of 1.47 micromol/l and a vmax value of 1.66 mol/min per mol enzyme. Amino terminal sequence analysis as well as mass spectrometry of fragments obtained by trypsin digest showed identity to a recently described elastase type protease from the same organism and homology to known proteases from other procaryotes (e.g. Aeromonas caviae, Vibrio proteolytica, Pseudomonas aeruginosa).

Drugs for the prevention and treatment of thrombosis in patients with heparin-induced thrombocytopenia

Most patients with heparin-induced thrombocytopenia (HIT), a serious adverse effect of heparin mediated by platelet-activating heparin-dependent antibodies, require alternative anticoagulation. This is because HIT is highly prothrombotic and is characterized by markedly increased thrombin generation. Unfractionated heparins seem to induce HIT more often than low molecular weight heparins. There are three anticoagulants for which there is an emerging consensus for their efficacy in management of HIT, and which are currently approved for treatment of HIT in several countries: the recombinant hirudin, lepirudin, a direct thrombin inhibitor; the synthetic direct thrombin inhibitor, argatroban; and the heparinoid, danaparoid sodium, mainly exhibiting antifactor-Xa activity. Recommendations for optimal use of these drugs in HIT are given in this review stressing the need for immediate treatment of patients with HIT without awaiting laboratory diagnosis. Hirudin, the drug for which most data from prospective trials exists, can be safely and effectively used in patients with HIT, its dramatically increased elimination half-life in patients with renal failure being the most important drawback. Argatroban, which is mainly eliminated by the liver, could be used preferentially in such patients with renal impairment. Interference with the international normalized ratio makes oral anticoagulation, which is necessary in many patients with HIT, problematic. Activated partial thromboplastin time is sufficient to monitor lepirudin and argatroban treatment in most cases. Danaparoid sodium, with an antifactor-X activity half-life of about 24 hours seems to be best suited for thrombosis prophylaxis in patients with HIT. In some patients monitoring by determining antifactor-Xa activity is necessary. No antidote is available for any of the drugs discussed, and bleeding complications are the most important adverse effects. In situations such as hemodialysis or cardiopulmonary bypass, not only the characteristics of the drug in use itself, but also availability of monitoring methods play an important role. Adjunctive treatments have not been systematically evaluated and should be used cautiously. Recent data suggest that re-exposure of patients with a history of HIT with heparin, for example during cardiopulmonary bypass, can be well tolerated provided no circulating HIT antibodies are detectable at the time of re-exposure, and heparin is strictly avoided pre- and postoperatively.

Management of lepirudin therapy for a patient with antiphospholipid antibody syndrome using the whole blood ecarin clot time and activated partial thromboplastin time

A patient with antiphospholipid antibody syndrome (APS) and a history of heparin-induced thrombocytopenia required lepirudin therapy. The patient had an abnormal baseline activated partial thromboplastin time (aPTT), complicating management of his therapy. We investigated whether an alternative monitoring system, using a dry reagent technology [Thrombolytic Assessment System (TAS)], could be used to monitor the patient's whole blood ecarin clot time (ECT) and aPTT. Baseline values for the ECT and aPTT were normal with this system. During a continuous infusion of lepirudin, the patient's whole blood ECT was maintained between a desired range of 150-200 s for 73% of the time. Similarly, his whole blood aPTT was maintained between 60 and 80 s for 80% of the time. In contrast, the patient's plasma-based aPTT by standard methods was consistently > 150 s. The patient underwent surgical procedures without complications. To further investigate the finding that the patient's antibody did not affect the aPTT with this system, we performed the ECT and the aPTT assays on the TAS Analyzer with plasma samples from 10 patients with APS and abnormal aPTTs. All 10 samples had plasma ECT values within the normal range. Four patients had normalization of the aPTT, suggesting that a subset of patients with APS may benefit from the TAS aPTT assay when monitoring heparin or other anticoagulation therapy.

The purification and partial characterisation of two novel metalloproteinases from the venom of the West African carpet viper, Echis ocellatus

Separation of previously uncharacterised Echis ocellatus venom by phenyl-Superose FPLC (Fast Liquid Protein Chromatography) yielded eight protein fractions. Three of these displayed high proteolytic activity when assayed by in vivo and in vitro assays (including enzyme linked immunosorbant assay), and were further separated using Superdex 75 and Mono-Q FPLC. This resulted in the purification of a non-haemorrhagic 24 kDa metalloproteinase (EoVMP1, pI 7.0), and a haemorrhagic 56 kDa metalloproteinase (EoVMP2, pI 5.5). Following tryptic digest, short amino acid sequences of EoVMP1 and EoVMP2 were obtained using Edman degradation. Both sequences displayed homology when aligned with existing snake venom metalloproteinases (SVMPs). The strong homology observed among previously well-characterised SVMPs suggests that principles governing the interaction of substrates and inhibitors are likely to be similar for EoVMP1, EoVMP2 and all members of the reprolysin family.

A prothrombin activator from Bothrops erythromelas (jararaca-da-seca) snake venom: characterization and molecular cloning

A novel prothrombin activator enzyme, which we have named 'berythractivase', was isolated from Bothrops erythromelas (jararaca-da-seca) snake venom. Berythractivase was purified by a single cation-exchange-chromatography step on a Resource S (Amersham Biosciences) column. The overall purification (31-fold) indicates that berythractivase comprises about 5% of the crude venom. It is a single-chain protein with a molecular mass of 78 kDa. SDS/PAGE of prothrombin after activation by berythractivase showed fragment patterns similar to those generated by group A prothrombin activators, which convert prothrombin into meizothrombin, independent of the prothrombinase complex. Chelating agents, such as EDTA and o -phenanthroline, rapidly inhibited the enzymic activity of berythractivase, like a typical metalloproteinase. Human fibrinogen A alpha-chain was slowly digested only after longer incubation with berythractivase, and no effect on the beta- or gamma-chains was observed. Berythractivase was also capable of triggering endothelial proinflammatory and procoagulant cell responses. von Willebrand factor was released, and the surface expression of both intracellular adhesion molecule-1 and E-selectin was up-regulated by berythractivase in cultured human umbilical-vein endothelial cells. The complete berythractivase cDNA was cloned from a B. erythromelas venom-gland cDNA library. The cDNA sequence possesses 2330 bp and encodes a preproprotein with significant sequence similarity to many other mature metalloproteinases reported from snake venoms. Berythractivase contains metalloproteinase, desintegrin-like and cysteine-rich domains. However, berythractivase did not elicit any haemorrhagic response. These results show that, although the primary structure of berythractivase is related to that of snake-venom haemorrhagic metalloproteinases and functionally similar to group A prothrombin activators, it is a prothrombin activator devoid of haemorrhagic activity. This is a feature not observed for most of the snake venom metalloproteinases, including the group A prothrombin activators.

SSR182289A, a novel, orally active thrombin inhibitor: in vitro profile and ex vivo anticoagulant activity

SSR182289A competitively inhibits human thrombin (K(i) = 0.031 +/- 0.002 microM) and shows good selectivity with respect to other human proteases, e.g., trypsin (K(i) = 54 +/- 2 microM), factor Xa (K(i) = 167 +/- 9 microM), and factor VIIa, factor IXa, plasmin, urokinase, tPA, kallikrein, and activated protein C (all K(i) values >250 microM). In human plasma, SSR182289A demonstrated anticoagulant activity in vitro as measured by standard clotting parameters (EC100 thrombin time 96 +/- 7 nM) and inhibited tissue factor-induced thrombin generation (IC50 of 0.15 +/- 0.02 microM). SSR182289A inhibited thrombin-induced aggregation of human platelets with an IC50 value of 32 +/- 9 nM, but had no effect on aggregation induced by other platelet agonists. The anticoagulant effects of SSR182289A were studied by measuring changes in coagulation markers ex vivo after i.v. or oral administration in several species. In dogs, SSR182289A (0.1-1 mg/kg i.v. and 1-5 mg/kg p.o.) produced dose-related increases in clotting times. After oral dosing, maximum anticoagulant effects were observed 2 h after administration with increases in thrombin time, 2496 +/- 356%; ecarin clotting time (ECT), 1134 +/- 204%; and activated partial thromboplastin time (aPTT), 91 +/- 20% for the dose of 3 mg/kg p.o., and thrombin time, 3194 +/- 425%; ECT, 2017 +/- 341%; and aPTT, 113 +/- 9% after 5 mg/kg p.o. Eight hours after administration of 3 or 5 mg/kg SSR182289A, clotting times were still elevated. SSR182289A also showed oral anticoagulant activity in rat, rabbit, and macaque. Hence, SSR182289A is a potent, selective, and orally active thrombin inhibitor.

Molecular and functional characterization of a natural homozygous Arg67His mutation in the prothrombin gene of a patient with a severe procoagulant defect contrasting with a mild hemorrhagic phenotype

In a patient who presented with a severe coagulation deficiency in plasma contrasting with a very mild hemorrhagic diathesis a homozygous Arg67His mutation was identified in the prothrombin gene. Wild-type (factor IIa [FIIa]-WT) and mutant Arg67His thrombin (FIIa-MT67) had similar amidolytic activity. By contrast, the k(cat)/K(m) value of fibrinopeptide A hydrolysis by FIIa-WT and FIIa-MT67 was equal to 2.1 x 10(7) M(-1)s(-1) and 9 x 10(5) M(-1)s(-1). Decreased activation of protein C (PC) correlated with the 33-fold decreased binding affinity for thrombomodulin (TM; K(d) = 65.3 nM vs 2.1 nM, in FIIa-MT67 and in FIIa-WT, respectively). In contrast, hydrolysis of PC in the absence of TM was normal. The Arg67His mutation had a dramatic effect on the cleavage of protease-activated G protein-coupled receptor 1 (PAR-1) 38-60 peptide (k(cat/)K(m) = 4 x 10(7) M(-1)s(-1) to 1.2 x 10(6) M(-1)s(-1)). FIIa-MT67 showed a weaker platelet activating capacity, attributed to a defective PAR-1 interaction, whereas the interaction with glycoprotein Ib was normal. A drastic decrease (up to 500-fold) of the second-order rate constant pertaining to heparin cofactor II (HCII) interaction, especially in the presence of dermatan sulfate, was found for the FIIa-MT67 compared with FIIa-WT, suggesting a severe impairment of thrombin inhibition by HCII in vivo. Finally, the Arg67His mutation was associated with a 5-fold decrease of prothrombin activation by the factor Xa-factor Va complex, perhaps through impairment of the prothrombin-factor Va interaction. These experiments show that the Arg67His substitution affects drastically both the procoagulant and the anticoagulant functions of thrombin as well as its inhibition by HCII. The mild hemorrhagic phenotype might be explained by abnormalities that ultimately counterbalance each other.

Separation and purification of Echis coloratus venom and some biological and biochemical effects of the proteins

Crude venom of Echis coloratus was separated into seven protein fractions using 7% preparative native polyacrylamide gel electrophoresis. The effect of crude venom and seven venom protein fractions (F1-F7) from Echis coloratus on key metabolic activities of fibroblast cultures was investigated. Confluent cultures were incubated with the venom proteins for 3 h at 37 degrees C. The specific activity of phosphofructokinase, was significantly lowered upon incubation with the crude venom and with fractions 2, 3, 4 and 6. Citrate synthase activity was significantly lowered by the crude venom and by fractions 2 and 3. Glycogen phosphorylase activity was significantly increased by the crude venom and by fractions 2, 3, 4 and 6 leading to a significant concurrent drop in glycogen content. Creatine kinase activity was significantly increased by the crude venom and by fractions 3, 4, 5 and 6. Cellular ATP levels rose significantly upon incubation with the crude venom and with fractions 3, 4, 5 and 6. Incubation of cell sonicates with all the venom proteins did not significantly alter the activity or content of any of the studied parameters.

Preliminary characteristics of the prothrombin converting enzyme from venom of Stephen's banded snake (Hoplocephalus stephensii)

Stephen's banded snake (Hoplocephalus stephensii) is an infrequently encountered Australian elapid species. The crude venom contains coagulant activity and the component responsible is a prothrombin activator requiring factor V for activity. SDS-PAGE of the isolated native protein revealed two bands at 23 and 36 kDa. These findings indicate that the procoagulant is similar to that found in the Australian tiger snake (Notechis scutatus) and thus resembles factor Xa.

Drug-induced and drug-dependent immune thrombocytopenias

Thrombocytopenia is a frequent comorbid condition in many in hospital patients. In some patients, drugs are the cause of low platelet counts. While cytotoxic effects of anti-tumor therapy are the most frequent cause, immune mechanisms should also be considered. This review addresses thrombocytopenias in four groups. Heparin-dependent thrombocytopenia (HIT), by far the most frequent drug-induced immune-mediated type of thrombocytopenia, has a unique pathogenesis and clinical consequences. HIT is a clinicopathological syndrome in which antibodies mostly directed against a multimolecular complex of platelet factor 4 and heparin cause paradoxical thromboembolic complications. The mechanisms through which heparin can enhance thrombin generation are discussed and treatment alternatives for affected patients are presented in detail. It is of primary importance to recognize these patients as early as possible and to substitute heparin with a compatible anticoagulatory drug, such as hirudin, danaparoid or argatroban. Patients seem to benefit from therapeutic doses of alternative treatment rather than from low-dose prophylactic doses. With the increasing use of glycoprotein (GP) IIb/IIIa inhibitors in patients with acute coronary syndromes, thrombocytopenias are increasingly recognized as an adverse effect of these drugs. Up to 4% of treated patients are affected. Most important, pseudothrombocytopenia, a laboratory artefact, is as frequent as real drug-induced thrombocytopenia and must be excluded before changes in treatment are considered. The pathogenesis of these thrombocytopenias is still debated; an immune mechanism involving preformed antibodies is likely. However, since these antibodies are also detectable in a high percentage of normal controls and of patients not developing thrombocytopenia, their impact is still unclear. Patients with real thrombocytopenia are at an increased risk of bleeding; treatment consists of cessation of the GP IIb/IIIa inhibitor and platelet transfusions in cases of severe hemorrhage. Classic immune thrombocytopenia can be induced by some drugs, e.g. gold, which trigger anti-platelet antibodies indistinguishable from platelet autoantibodies found in autoimmune thrombocytopenia. Drug-induced and drug-dependent immune thrombocytopenia is induced by antibodies recognizing an epitope on platelet GP formed after binding of a drug to a platelet glycoprotein. Still unresolved is whether antibody binding is the consequence of a conformational change of the antigen, the antibody, or both. These antibodies typically react with monomorphic epitopes on platelet GP, but only in the presence of the drug or a metabolite. Although several platelet GP have been identified as antibody target (GPIb/IX, GPV, GP IIb/IIIa), antibodies in an individual patient are highly specific for a single GP. Clinically, these patients present with very low platelet counts and acute, sometimes severe, hemorrhage. Treatment is restricted to withdrawal of the drug and symptomatic treatment of bleeding.

Vitamin K deficiency in diarrhoea

The study was undertaken to determine the frequency of occurrence of vitamin K deficiency in infants with diarrhoeal illness. Infants were categorized into four groups as follows: A(acute diarrhoea), B(protracted diarrhoea) C(intractable diarrhoea) and D(healthy controls). Screening coagulation tests, PT and PTTK along with estimation of functional activity and total antigenic levels of prothrombin were performed. The ratio of functional to total prothrombin was calculated. PT was prolonged in 30% (24/75) of all infants with diarrhoea as compared to controls where the abnormality was observed in 11.1% infants (2/18). The ratio of functional to total prothrombin was significantly lower in infants with diarrhoea, the mean +/- SD values being 0.65 +/- 0.41 vs 1.1 +/- 0.26. This difference was statistically highly significant (p < 0.001). Low ratio was observed in 57.3% (43/75) infants with diarrhoea. Thus functional to total prothrombin ratio identified approximately twice as many diarrhoeal infants with vitamin K deficiency as compared to PT alone. There was no significant correlation with breast feeding as the only mode of diet, or the prior administration of antibiotics in infants with diarrhoea. The inherent malabsorptive state in diarrhoea may be a major contributory factor.