Species difference in the fibrinogenolytic effects of alpha- and beta-fibrinogenases from Trimeresurus mucrosquamatus snake venom

The Royal Armoury: Venomics and antivenomics of king cobra (Ophiophagus hannah) from the Indian Western Ghats

Despite being famous as 'the king' of the snake world, the king cobra (Ophiophagus hannah) has remained a mysterious species, particularly with respect to its venom ecology. In contrast, venom research has largely focussed on the 'big four' snakes that are greatly responsible for the burden of snakebite in the Indian subcontinent. This study aims to bridge the current void in our understanding of the O. hannah venom by investigating its proteomic, biochemical, pharmacological, and toxinological profiles via interdisciplinary approaches. Considering their physical resemblance, the king cobra is often compared to the spectacled cobra (Naja naja). Comparative venomics of O. hannah and N. naja in this study provided interesting insights into their venom compositions, activities, and potencies. Our findings suggest that the O. hannah venom, despite being relatively less complex than the N. naja venom, is equally potent. Finally, our in vitro and in vivo assays revealed that both Indian polyvalent and Thai Red Cross monovalent antivenoms completely fail to neutralise the O. hannah venom. Our findings provide guidelines for the management of bites from this clinically important yet neglected snake species in India.

Thrombolytic Effects of Philippine Pit Viper (Trimeresurus flavomaculatus) Venom in Human Blood In Vitro and Ferric Chloride-Induced Cardiac Thrombosis on Swiss Webster Mice In Vivo

INTRODUCTION

 Thrombosis is one of the leading causes of mortality worldwide. Thrombolytic agents are used to reduce this burden. Studies pointed out that certain proteins in the venom of several snake species may have potential thrombolytic properties. Trimeresurus flavomaculatus, known as the Philippine pit viper, is found along damp localities in the Philippines. Venoms of closely related species have been shown to exhibit thrombolytic effects in vitro and in vivo. However, no extensive studies yet have been conducted about the thrombolytic effect of T. flavomaculatus venom. Thus, this two-phased study aimed to determine the thrombolytic effect of T. flavomaculatus venom on human blood and ferric chloride-induced cardiac thrombosis in mice.

METHODOLOGY

Phase 1 was done using clot lysis method to measure thrombolytic activity in vitro. Venom dilutions of 3:4, 1:2, 2:3, and 1:0, positive control (streptokinase), and negative control (normal saline solution) were inoculated to different samples of human blood. Phase 2 measured the thrombolytic activity in vivo. Ferric chloride-saturated filter paper was applied over the cardiac wall for the induction of thrombus formation. Venom dilutions of 1:64, 1:16, 1:4, and 1:1, positive control (streptokinase), and negative control (normal saline solution) were then injected through the dorsal tail vein of mice. After 1 hour, the cardiac tissues were excised for histologic examination.

RESULTS

Phase 1 results showed that the venom had significant thrombolytic activity in vitro. Dilutions of 1:0 and 3:4 had no significant differences with streptokinase in vitro. Phase 2 results showed significant lysis in vivo at 1:1, 1:4, and 1:64 venom dilutions.

CONCLUSION

 The results indicated that T. flavomaculatus has a potential thrombolytic activity both in vitro and in vivo.

Fangs in the Ghats: Preclinical Insights into the Medical Importance of Pit Vipers from the Western Ghats

The socioeconomic impact of snakebites in India is largely attributed to a subset of snake species commonly known as the 'big four'. However, envenoming by a range of other clinically important yet neglected snakes, a.k.a. the 'neglected many', also adds to this burden. The current approach of treating bites from these snakes with the 'big four' polyvalent antivenom is ineffective. While the medical significance of various species of cobras, saw-scaled vipers, and kraits is well-established, the clinical impact of pit vipers from regions such as the Western Ghats, northeastern India, and the Andaman and Nicobar Islands remains poorly understood. Amongst the many species of snakes found in the Western Ghats, the hump-nosed (Hypnale hypnale), Malabar (Craspedocephalus malabaricus), and bamboo (Craspedocephalus gramineus) pit vipers can potentially inflict severe envenoming. To evaluate the severity of toxicity inflicted by these snakes, we characterised their venom composition, biochemical and pharmacological activities, and toxicity- and morbidity-inducing potentials, including their ability to damage kidneys. Our findings highlight the therapeutic inadequacies of the Indian and Sri Lankan polyvalent antivenoms in neutralising the local and systemic toxicity resulting from pit viper envenomings.

The Middle Eastern Cousin: Comparative Venomics of Daboia palaestinae and Daboia russelii

Among the medically most important snakes in the world, the species belonging to the genus Daboia have been attributed to the highest number of human envenomings, deaths and disabilities. Given their significant clinical relevance, the venoms of Russell's vipers (D. russelii and D. siamensis) have been the primary focus of research. In contrast, the composition, activity, ecology and evolution of venom of its congener, the Palestine viper (D. palaestinae), have remained largely understudied. Therefore, to unravel the factors responsible for the enhanced medical relevance of D. russelii in comparison to D. palaestinae, we comparatively evaluated their venom proteomes, biochemical activities, and mortality and morbidity inflicting potentials. Furthermore, the synthesis and regulation of venom in snakes have also remained underinvestigated, and the relative contribution of each venom gland remains unclear. We address this knowledge gap by sequencing the tissue transcriptomes of both venom glands of D. palaestinae, and comparatively evaluating their contribution to the secreted venom concoction. Our findings highlight the disparity in the venom composition, function and toxicities of the two Daboia species. We also show that toxin production is not partitioned between the two venom glands of D. palaestinae.

Venomics of the Enigmatic Andaman Cobra (Naja sagittifera) and the Preclinical Failure of Indian Antivenoms in Andaman and Nicobar Islands

The Andaman and Nicobar Islands are an abode to a diversity of flora and fauna, including the many endemic species of snakes, such as the elusive Andaman cobra (Naja sagittifera). However, the ecology and evolution of venomous snakes inhabiting these islands have remained entirely uninvestigated. This study aims to bridge this knowledge gap by investigating the evolutionary history of N. sagittifera and its venom proteomic, biochemical and toxicity profile. Phylogenetic reconstructions confirmed the close relationship between N. sagittifera and the Southeast Asian monocellate cobra (N. kaouthia). Overlooking this evolutionary history, a polyvalent antivenom manufactured using the venom of the spectacled cobra (N. naja) from mainland India is used for treating N. sagittifera envenomations. Comparative evaluation of venoms of these congeners revealed significant differences in their composition, functions and potencies. Given the close phylogenetic relatedness between N. sagittifera and N. kaouthia, we further assessed the cross-neutralising efficacy of Thai monovalent N. kaouthia antivenom against N. sagittifera venoms. Our findings revealed the inadequate preclinical performance of the Indian polyvalent and Thai monovalent antivenoms in neutralising N. sagittifera venoms. Moreover, the poor efficacy of the polyvalent antivenom against N. naja venom from southern India further revealed the critical need to manufacture region-specific Indian antivenoms.

Remarkable intrapopulation venom variability in the monocellate cobra (Naja kaouthia) unveils neglected aspects of India's snakebite problem

Interpopulation venom variation has been widely documented in snakes across large geographical distances. This variability is known to markedly influence the effectiveness of snakebite therapy, as antivenoms manufactured against one population may not be effective against others. In contrast, the extent of intrapopulation venom variability, especially at finer geographical scales, remains largely uninvestigated. Moreover, given the historical focus on the 'big four' Indian snakes, our understanding of venom variation in medically important yet neglected snakes, such as the monocellate cobra (Naja kaouthia), remains unclear. To address this shortcoming, we investigated N. kaouthia venoms sampled across a small spatial scale (<50 km) in Eastern India. An interdisciplinary approach employed in this study unveiled considerable intrapopulation differences in the venom proteomic composition, pharmacological and biochemical activities, and toxicity profiles. Documentation of stark differences in venoms at such a finer geographical scale, despite the influence of similar ecological and environmental conditions, is intriguing. Furthermore, evaluation of in vitro and in vivo venom recognition and neutralisation potential of Indian polyvalent 'big four' antivenoms and Thai monovalent N. kaouthia antivenom revealed concerning deficiencies. These results highlight the negative impact of phylogenetic divergence and intrapopulation snake venom variation on the effectiveness of conventional antivenom therapy. SIGNIFICANCE: In contrast to our understanding of snake venom variation across large distances, which is theorised to be shaped by disparities in ecology and environment, intrapopulation variation at finer geographic scales remains scarcely investigated. Assessment of intrapopulation venom variability in Naja kaouthia at a small spatial scale (<50 km) in Eastern India unravelled considerable differences in venom compositions, activities and potencies. While the influence of subtle differences in prey preference and local adaptations cannot be ruled out, these findings, perhaps, also emphasise the role of accelerated molecular evolutionary regimes that rapidly introduce variations in evolutionarily younger lineages, such as advanced snakes. The inability of 'big four' Indian antivenoms and Thai N. kaouthia monovalent antivenom in countering these variations highlights the importance of phylogenetic considerations for the development of efficacious snakebite therapy. Thus, we provide valuable insights into the venoms of one of the most medically important yet neglected Indian snakes.

Biogeographic venom variation in Russell's viper (Daboia russelii) and the preclinical inefficacy of antivenom therapy in snakebite hotspots

BACKGROUND

Snakebite in India results in over 58,000 fatalities and a vast number of morbidities annually. The majority of these clinically severe envenomings are attributed to Russell's viper (Daboia russelii), which has a near pan-India distribution. Unfortunately, despite its medical significance, the influence of biogeography on the composition and potency of venom from disparate D. russelii populations, and the repercussions of venom variation on the neutralisation efficacy of marketed Indian antivenoms, remain elusive.

METHODS

Here, we employ an integrative approach comprising proteomic characterisation, biochemical analyses, pharmacological assessment, and venom toxicity profiling to elucidate the influence of varying ecology and environment on the pan-Indian populations of D. russelii. We then conducted in vitro venom recognition experiments and in vivo neutralisation assays to evaluate the efficacy of the commercial Indian antivenoms against the geographically disparate D. russelii populations.

FINDINGS

We reveal significant intraspecific variation in the composition, biochemical and pharmacological activities and potencies of D. russelii venoms sourced from five distinct biogeographic zones across India. Contrary to our understanding of the consequences of venom variation on the effectiveness of snakebite therapy, commercial antivenom exhibited surprisingly similar neutralisation potencies against the majority of the investigated populations, with the exception of low preclinical efficacy against the semi-arid population from northern India. However, the ability of Indian antivenoms to counter the severe morbid effects of Daboia envenoming remains to be evaluated.

CONCLUSION

The concerning lack of antivenom efficacy against the north Indian population of D. russelii, as well as against two other 'big four' snake species in nearby locations, underscores the pressing need to develop pan-India effective antivenoms with improved efficacy in high snakebite burden locales.

Biogeographical venom variation in the Indian spectacled cobra (Naja naja) underscores the pressing need for pan-India efficacious snakebite therapy

Background

Snake venom composition is dictated by various ecological and environmental factors, and can exhibit dramatic variation across geographically disparate populations of the same species. This molecular diversity can undermine the efficacy of snakebite treatments, as antivenoms produced against venom from one population may fail to neutralise others. India is the world’s snakebite hotspot, with 58,000 fatalities and 140,000 morbidities occurring annually. Spectacled cobra (Naja naja) and Russell’s viper (Daboia russelii) are known to cause the majority of these envenomations, in part due to their near country-wide distributions. However, the impact of differing ecologies and environment on their venom compositions has not been comprehensively studied.

Methods

Here, we used a multi-disciplinary approach consisting of venom proteomics, biochemical and pharmacological analyses, and in vivo research to comparatively analyse N. naja venoms across a broad region (>6000 km; seven populations) covering India’s six distinct biogeographical zones.

Findings

By generating the most comprehensive pan-Indian proteomic and toxicity profiles to date, we unveil considerable differences in the composition, pharmacological effects and potencies of geographically-distinct venoms from this species and, through the use of immunological assays and preclinical experiments, demonstrate alarming repercussions on antivenom therapy. We find that commercially-available antivenom fails to effectively neutralise envenomations by the pan-Indian populations of N. naja, including a complete lack of neutralisation against the desert Naja population.

Conclusion

Our findings highlight the significant influence of ecology and environment on snake venom composition and potency, and stress the pressing need to innovate pan-India effective antivenoms to safeguard the lives, limbs and livelihoods of the country’s 200,000 annual snakebite victims.

Annually, India is burdened by the highest number of snake envenomations across the globe, with over 58,000 fatalities and three times the number of morbidities, predominantly affecting the rural agrarian communities. The spectacled cobra (Naja naja) and Russell’s viper (Daboia russelii) are responsible for the vast majority of envenomations in the country, in part, due to their near country-wide distributions. In this study, we unveil the astounding differences in venom composition of N. naja from six different biogeographical zones across the country (>6000 km). We provide a comprehensive account of their disparate venom proteomic profiles, biochemical and pharmacological effects, and the associated potencies. Our study uncovers alarming differences in the efficacy of the marketed polyvalent antivenoms in neutralising these venoms, thereby, emphasising the pressing need to develop dose-efficacious and pan-India effective antivenoms for the treatment of snakebites in the country. This study also highlights the significant influence of ecology and diverse environments on the venom variability, insinuating the necessity for innovating cost-effective and pan-India efficacious solutions to safeguard the lives, limbs and livelihoods of India’s two hundred thousand annual snakebite victims.

Toxicological comparison of Crotalus ruber lucasensis venom from different ecoregions of the Baja California Peninsula

The Baja California Peninsula possesses a mosaic of ecoregions that offers a wide variety of environments for the species that here inhabit. Here we report biological variations in. Crotalus ruber lucasensis venom from arid, semiarid and tropical eco-regions. Lethal (1.4-6.8 mg/kg), edematogenic (0.3-0.5 μg) and defibrinogenating (from non-detectable to 20 μg) activities were found to have significant differences among eco-regions.

Beyond the 'big four': Venom profiling of the medically important yet neglected Indian snakes reveals disturbing antivenom deficiencies

Background

Snakebite in India causes the highest annual rates of death (46,000) and disability (140,000) than any other country. Antivenom is the mainstay treatment of snakebite, whose manufacturing protocols, in essence, have remained unchanged for over a century. In India, a polyvalent antivenom is produced for the treatment of envenomations from the so called ‘big four’ snakes: the spectacled cobra (Naja naja), common krait (Bungarus caeruleus), Russell’s viper (Daboia russelii), and saw-scaled viper (Echis carinatus). In addition to the ‘big four’, India is abode to many other species of venomous snakes that have the potential to inflict severe clinical or, even, lethal envenomations in their human bite victims. Unfortunately, specific antivenoms are not produced against these species and, instead, the ‘big four’ antivenom is routinely used for the treatment.

Methods

We characterized the venom compositions, biochemical and pharmacological activities and toxicity profiles (mouse model) of the major neglected yet medically important Indian snakes (E. c. sochureki, B. sindanus, B. fasciatus, and two populations of N. kaouthia) and their closest ‘big four’ congeners. By performing WHO recommended in vitro and in vivo preclinical assays, we evaluated the efficiencies of the commercially marketed Indian antivenoms in recognizing venoms and neutralizing envenomations by these neglected species.

Findings

As a consequence of dissimilar ecologies and diet, the medically important snakes investigated exhibited dramatic inter- and intraspecific differences in their venom profiles. Currently marketed antivenoms were found to exhibit poor dose efficacy and venom recognition potential against the ‘neglected many’. Premium Serums antivenom failed to neutralise bites from many of the neglected species and one of the ‘big four’ snakes (North Indian population of B. caeruleus).

Conclusions

This study unravels disturbing deficiencies in dose efficacy and neutralisation capabilities of the currently marketed Indian antivenoms, and emphasises the pressing need to develop region-specific snakebite therapy for the ‘neglected many’.

Snakebite is a ‘neglected tropical disease’ that majorly affects the rural populations in developing countries. India bears the brunt of snakebites with over 46,000 deaths and 140,000 disabilities, annually. A significant number of these bites are attributed to the widely distributed ‘big four’ snakes, namely spectacled cobra (Naja naja), common krait (Bungarus caeruleus), Russell’s viper (Daboia russelii), and saw-scaled viper (Echis carinatus). The commercial antivenoms marketed in India are only manufactured against these four species, while neglecting many other medically relevant snakes with restricted geographic distribution. Snakebite pathology is dependent on the venom composition of the population/species, which can, in turn, vary intra- and inter-specifically. Though this variation severely limits the cross-population/species antivenom efficacy, envenomations by the neglected snakes in India are treated with the ‘big four’ antivenom. Therefore, to unravel the underlying venom variability, we investigated venom proteomic, biochemical/pharmacological and toxicity profiles of the major neglected Indian snakes and their ‘big four’ relatives. To assess the effectiveness of the ‘big four’ antivenom in treating bites from these neglected snakes, we performed preclinical experiments, which revealed alarming inadequacies of the commercial antivenoms. Our findings accentuate the compelling necessity for the innovation of highly efficacious next-generation snakebite therapy in India.

Characterization of a fibrinolytic enzyme (ussurenase) from Agkistrodon blomhoffii ussurensis snake venom: Insights into the effects of Ca2+ on function and structure

Fibrino(geno)lytic enzymes from snake venoms have been identified as high quality therapeutic agents for treatment of blood clots and strokes. They act on fibrinogen and fibrin, leading to defibrinogenation of blood, lysis of fibrin, and a consequent decrease in blood viscosity. In this work, a fibrinolytic enzyme (ussurenase) from China Agkistrodon blomhoffii Ussurensis snake venom, was purified to homogeneity, identified as a stable 23,367.8 Da monomeric protein, and was identified as a new kind of snake venom metalloproteinase. Ussurenase reacts optimally with fibrin clots at pH 7.5-8.3 and a temperature of 33-41 degrees C. Although many fibrinolytic enzymes are known to be zinc-dependent, measurements from inductively coupled plasma-atomic emission spectroscopy (ICP-AES) reveal that ussurenase is a Ca2+-containing protein with a molar ratio of 1:1 ([Ca2+]:[enzyme]). Ca2+ is crucial to the fibrin clot hydrolysis by ussurenase but also plays an important role in maintaining the structural integrity of the enzyme. The addition of Ca2+ to the apoenzyme induces a conformational change making the environments surrounding the Trp residues of the enzyme more hydrophobic. The presence of Ca2+ also increases the structural stability of ussurenase, so that higher concentrations of the denaturant guanidine hydrochloride are required to denature the native ussurenase compared to the apo-form. UV absorption and CD spectroscopy experiments show that Ca2+ increases the thermostability and changes the secondary structure of ussurenase. All these data suggest that Ca2+ is crucial for the correct folding and activity of ussurenase.

Snake venom fibrin(ogen)olytic enzymes

Snake venoms contain a number of serine and metalloproteinases and included among these are the fibrin(ogen)olytic proteinases. Some years ago it was postulated that the fibrin(ogen)olytic enzymes may be clinically useful. Over the past 150 years a substantial body of literature has been generated on the identification and characterization of fibrin(ogen)olytic enzymes from a broad spectrum of snake species. In this review we describe the two different classes of fibrin(ogen)olytic enzymes isolated from snake venom and we summarize a number of studies aimed at characterizing the purified enzymes and/or their derivatives. Two distinct classes of venom fibrin(ogen)olytic enzymes have been previously identified, the metalloproteinases and serine proteinases. These two classes of proteinases differ in their mechanism of action and they target different amino acid sequences in fibrin(ogen), but each perform the same role in nature. When a snake envenomates its prey it needs a mechanism to facilitate the spread of the toxic components throughout the circulation. Fibrin(ogen)olytic enzymes break down fibrin rich clots and help to prevent further clot formation by their action on fibrinogen. This characteristic feature has led to development of fibrin(ogen)olytic snake venom enzymes as potential clinical agents to treat occlusive thrombi. Fibrolase, a fibrinolytic metalloproteinase isolated from Agkistrodon contortrix contortrix venom and the serine beta-fibrinogenolytic proteinase from Vipera lebetina have been chosen as representative enzymes from the two classes, and their biochemical and physiochemical properties will be described in detail. Finally, the characterization and development of alfimeprase, a recombinant fibrinolytic enzyme derived from fibrolase, as a clinical agent is described citing the progression from the laboratory bench to its current status as having successfully completed Phase II clinical trials.

Lonofibrase, a novel alpha-fibrinogenase from Lonomia obliqua caterpillars

Envenomation caused by Lonomia obliqua caterpillars is an increasing problem in Southern Brazil. The clinical profile is characterized by a profound hemorrhagic disorder. In the present study, we describe the characterization of a fibrin(ogen)olytic factor (lonofibrase) isolated from a venomous secretion of the caterpillars. The crude extract showed a dose-dependent inhibitory effect in the rate of thrombin-induced fibrinogen clotting and produced fragmentation of fibrinogen. Isolation of the fibrin(ogen)olytic enzyme was achieved by combining ion exchange chromatography followed by gel filtration in a fast protein liquid chromatography (FPLC) system. A single 35-kDa band was identified and the isolated enzyme named lonofibrase. Lonofibrase rapidly degrades Aalpha and Bbeta chains of fibrinogen, also being able to cleave fibrin in a distinct way from that observed with plasmin. The presence of lonofibrase with both fibrinogenolytic and fibrinolytic activities in L. obliqua secretion is coherent with the severe hemorrhagic clinical profile resulting from envenomation caused by these insects.

A non-toxic anticoagulant metalloprotease: purification and characterization from Indian cobra (Naja naja naja) venom

A non-toxic potent anticoagulant metalloprotease NN-PF(3) has been purified to homogeneity from the Indian cobra (Naja naja naja) venom through a combination of column chromatography and electrophoresis. NN-PF(3) is a single chain protein with a molecular weight of 68 kDa by SDS-PAGE. It hydrolysed casein, gelatin, haemoglobin and bovine fibrinogen, but did not hydrolyse bovine serum albumin or synthetic substrates such as TAME, BAEE and BAPNA. EDTA, EGTA and cyanide inhibited the enzymatic activity while 1,10-phenanthroline, PMSF, leupetin and pepstatin did not show any effect. NN-PF(3) is a metalloprotease containing Ca(2+) and Zn(2+) at a molar ratio of 1:1.2 and 1:0.4, respectively, as revealed by atomic absorption spectroscopy. NN-PF(3) was non-lethal up to an i.p. dose of 15 mg/kg body weight of mice and is devoid of myotoxicity, cytotoxicity and haemorrhagic activity. It is weakly oedematic, but strongly anticoagulant in property and the effect observed was both dose and time dependent.

Screening for fibrinolytic activity in eight Viperid venoms

Snake venoms contain direct-acting fibrinolytic metalloproteinases (MMP) that could have important applications in medicine. Fibrinolytic enzymes isolated from venom can induce in vitro clot lysis by directly acting on a fibrin clot. The most ideal fibrinolytic enzyme would have high affinity for clots, dissolve clots directly without causing hemorrhage, and would not be neutralized in vivo by endogenous metalloproteinase inhibitors. The purpose of this study was to compare DEAE/HPLC venom profiles from Viperid snakes and identify fractions that contain fibrinolytic activity with no hemorrhagic activity and are not neutralized by animal sera. The sera selected were from four (Virginia opossum, Gray woodrat, Mexican ground squirrel, and Hispid cottonrat) animals known to neutralize hemorrhagic activity in snake venoms. Nineteen fractions from the Viperid venoms had fibrinolytic activity. Agkistrodon venom fractions contained the highest specific fibrinolytic activities. A. piscivorus leucostoma fraction 4 contained a high specific fibrinolytic activity, no hemorrhagic activity, and the fibrinolytic activity was not neutralized by the proteinase inhibitors of the four animal sera. A. contortrix laticinctus fraction 1 also had a high specific fibrinolytic activity and no hemorrhagic activity. However, the fibrinolytic activity was neutralized by Didelphis virginiana (Virginia opossum) serum.

Snake venoms and the hemostatic system

Snake venoms are complex mixtures containing many different biologically active proteins and peptides. A number of these proteins interact with components of the human hemostatic system. This review is focused on those venom constituents which affect the blood coagulation pathway, endothelial cells, and platelets. Only highly purified and well characterized snake venom proteins will be discussed in this review. Hemostatically active components are distributed widely in the venom of many different snake species, particularly from pit viper, viper and elapid venoms. The venom components can be grouped into a number of different categories depending on their hemostatic action. The following groups are discussed in this review: (i) enzymes that clot fibrinogen; (ii) enzymes that degrade fibrin(ogen); (iii) plasminogen activators; (iv) prothrombin activators; (v) factor V activators; (vi) factor X activators; (vii) anticoagulant activities including inhibitors of prothrombinase complex formation, inhibitors of thrombin, phospholipases, and protein C activators; (viii) enzymes with hemorrhagic activity; (ix) enzymes that degrade plasma serine proteinase inhibitors; (x) platelet aggregation inducers including direct acting enzymes, direct acting non-enzymatic components, and agents that require a cofactor; (xi) platelet aggregation inhibitors including: alpha-fibrinogenases, 5'-nucleotidases, phospholipases, and disintegrins. Although many snake venoms contain a number of hemostatically active components, it is safe to say that no single venom contains all the hemostatically active components described here. Several venom enzymes have been used clinically as anticoagulants and other venom components are being used in pre-clinical research to examine their possible therapeutic potential. The disintegrins are an interesting group of peptides that contain a cell adhesion recognition motif, Arg-Gly-Asp (RGD), in the carboxy-terminal half of their amino acid sequence. These agents act as fibrinogen receptor (integrin GPIIb/IIIa) antagonists. Since this integrin is believed to serve as the final common pathway leading to the formation of platelet-platelet bridges and platelet aggregation, blockage of this integrin leads to inhibition of platelet aggregation regardless of the stimulating agent. Clinical trials suggest that platelet GPIIb/IIIa blockade is an effective therapy for the thrombotic events and restenosis frequently accompanying cardiovascular and cerebrovascular disease. Therefore, because of their clinical poten tial, a large number of disintegrins have been isolated and characterized.

Characterization of snake venom components acting on blood coagulation and platelet function

Snake venoms can affect blood coagulation and platelet function in various ways. The physicochemical properties and the mechanisms of actions of the snake venom components affecting blood coagulation and platelet function are discussed.

Species specific sensitivity towards the hemorrhagin of Ophiophagus hannah (Elapidae)

The filtration pattern of Ophiophagus hannah venom on Sephadex G-75 shows several peaks. The first peak, S1, includes high molecular weight proteins and contains the hemorrhagic and proteolytic activities. The proteolytic fractions overlap the hemorrhagic fractions, but are not identical with them. The crude venom and the high molecular weight peak have caseinase, benzoyl-L-arginine ethyl ester hydrolase and kallikrein-like activities, but not collagenase, gelatinase, thrombin, plasmin or urokinase-like activities. The hemorrhagin of Ophiophagus hannah shows species specific differences in its hemorrhagic effects: it causes hemorrhages in rabbits and hares (Lagomorpha), but not in rats, mice or guinea-pigs (Rodentia).