Hemorrhage induced by snake venom metalloproteinases: biochemical and biophysical mechanisms involved in microvessel damage

Neuromuscular activity of BaTX, a presynaptic basic PLA2 isolated from Bothrops alternatus snake venom

We have previously isolated a Lys49 phospholipase A(2) homolog (BaTX) from Bothrops alternatus snake venom using a combination of molecular exclusion chromatography and reverse phase HPLC and shown its ability to cause neuromuscular blockade. In this work, we describe a one-step procedure for the purification of this toxin and provide further details of its neuromuscular activity. The toxin was purified by reverse phase HPLC and its purity and molecular mass were confirmed by SDS-PAGE, MALDI-TOF mass spectrometry, amino acid analysis and N-terminal sequencing. BaTX (0.007-1.4 microM) produced time-dependent, irreversible neuromuscular blockade in isolated mouse phrenic nerve-diaphragm and chick biventer cervicis preparations (time to 50% blockade with 0.35 microM toxin: 58+/-4 and 24+/-1 min, respectively; n=3-8; mean+/-S.E.) without significantly affecting the response to direct muscle stimulation. In chick preparations, contractures to exogenous acetylcholine (55 and 110 microM) or KCl (13.4 mM) were unaltered after complete blockade by all toxin concentrations. These results, which strongly suggested a presynaptic mechanism of action for this toxin, were reinforced by (1) the inability of BaTX to interfere with the carbachol-induced depolarization of the resting membrane, (2) a significant decrease in the frequency and amplitude of miniature end-plate potentials, and (3) a significant reduction (59+/-4%, n=12) in the quantal content of the end-plate potentials after a 60 min incubation with the toxin (1.4 microM). In addition, a decrease in the organ bath temperature from 37 degrees C to 24 degrees C and/or the replacement of calcium with strontium prevented the neuromuscular blockade, indicating a temperature-dependent effect possibly mediated by enzymatic activity.

cDNA Cloning and Some Additional Peptide Characterization of a Single-Chain Vascular Apoptosis-Inducing Protein, VAP2

Vascular apoptosis-inducing proteins (VAPs) from hemorrhagic snake venom are apoptosis-inducing toxins targeting vascular endothelial cells. Well-characterized VAPs consist of disulfide-bridged double chains (ddVAPs). The authors previously described a single-chain VAP (scVAP), VAP2 from Crotalus atrox, which also induces apoptosis in endothelial cells (Masuda et al., 1998, European Journal of Biochemistry, 253, 36-41). The authors report here the whole cDNA sequences and some additional peptide characteristics of VAP2. In addition to the apoptosis-inducing activity of VAP2, the toxin displays a cell-detaching activity after incubation in high-salt conditions. These observations indicate that the apoptosis and cell-detaching functions can be discriminated. Analysis of the cell-detaching activity also revealed that VAP2 consists of two similar peptides, VAP2A and VAP2B, which are members of the PIII-type snake venom metalloproteases (SVMPs). The VAP2A cDNA encodes a 609-amino acid protein. In contrast, the peptide sequences of VAP2B were identical to that of catrocollastatin, an inhibitor of platelet aggregation. VAP2A and VAP2B interact with each other to form a noncovalent dimer similar to the ddVAPs, which was detected by native polyacrylamide gel electrophoresis. These data show some new characteristics of VAPs, which are important to clarify the apoptotic pathways in vascular endothelial cells.

Inhibition of platelets and tumor cell adhesion by the disintegrin domain of human ADAM9 to collagen I under dynamic flow conditions

This work aimed to investigate the role of the disintegrin domain of the human ADAM9 (ADAM9D) on the adhesion of breast tumor cells and platelets to collagen I, in a dynamic flow assay to simulate in vivo shear conditions. Recombinant ADAM9D was able to support tumor cell adhesion through binding to the beta1 integrin subunit and also to inhibit the invasion through matrigel in vitro. In a dynamic flow assay ADAM9D inhibited about 75% and 65% of MDA-MB-231 tumor cells and platelet adhesion to collagen I, respectively. In addition, it was demonstrated that alphaVbeta3 integrin is new interacting partner for ADAM9D. In conclusion, these results suggest a role for the disintegrin domain of ADAM9 in the metastatic process. Also, ADAM9D may be a tool for investigating the role of ADAMs in metastasis and cancer progression and for the design of selective inhibitors against the adhesion and extravasation of cancer cells.

Structural basis of the autolysis of AaHIV suggests a novel target recognizing model for ADAM/reprolysin family proteins

AaHIV, a P-III-type snake venom metalloproteinase (SVMP), consists of metalloproteinase/disintegrin/cysteine-rich (MDC) domains and is homologous to a disintegrin and metalloproteinase (ADAM) family proteins. Similar to brevilysin H6 and jararhagin, AaHIV can easily autolyse to release a stable protein named acucetin, which contains disintegrin-like and cysteine-rich domains. In this study, we determined the crystal structure of AaHIV and investigated the autolysis mechanism. Based on the structure of AaHIV and the results from docking experiments, we present a new model for target recognition in which two protein molecules form a functional unit, and the DC domain of one molecule is used for target recognition while the M-domain of the other is used for target proteolysis. Our results shed new light on the mechanism of target recognition and processing in ADAM/reprolysin family proteins.

Prey envenomation does not improve digestive performance in Taiwanese pit vipers (Trimeresurus gracilis and T. stejnegeri stejnegeri)

It has been a common belief that snake venom may help in the digestion of its prey, although direct examples and supporting evidence have not been sufficient. To address this, the present study examined whether preinjecting natural amounts of pit viper venom into experimental mice may accelerate their digestion by the snakes or gain energy benefit as compared to the control without the envenomation. Live adults of two Asian pit viper species Trimeresurus gracilis and T. stejnegeri stejnegeri, which inhabit the cold and warm environment respectively, were the subjects studied herein. A natural dose of 1.2 mg of each of the pit viper venom in phosphate-buffered saline (PBS) was injected into the mouse (about 10% of the snake mass) before it was being fed to the same species of vipers, while the pit vipers in control group were given mouse injected with sterile PBS. The snakes were kept at 14 degrees C or 24 degrees C, and parameters of gut passage time, costs of digestion, and/or digestive efficiency were measured. The results did not support the hypotheses that envenomation facilitates prey digestion. The venom in fact caused longer first defecation time and lower assimilation energy at 14 degrees C. Besides, the time to reach the oxygen consumption peak, and the first defecation time of T. s. stejnegeri were longer than that of T. gracilis.

Venom variation in hemostasis of the southern Pacific rattlesnake (Crotalus oreganus helleri): isolation of hellerase

Envenomations by the southern Pacific rattlesnake (Crotalus oreganus helleri) are the most common snakebite accidents in southern California. Intraspecies venom variation may lead to unresponsiveness to antivenom therapy. Even in a known species, venom toxins are recognized as diverse in conformity with interpopulational, seasonal, ontogenetic and individual factors. Five venoms of individual C. oreganus helleri located in Riverside and San Bernardino counties of southern California were studied for their variation in their hemostatic activity. The results demonstrated that Riverside 2 and San Bernardino 1 venoms presented the highest lethal activity without hemorrhagic activity. In contrast, San Bernardino 2 and 3 venoms had the highest hemorrhagic and fibrinolytic activities with low lethal and coagulant activities. Riverside 1, Riverside 2 and San Bernardino 1 venoms presented a significant thrombin-like activity. San Bernardino 2 and 3 venoms presented an insignificant thrombin-like activity. In relation to the fibrinolytic activity, San Bernardino 3 venom was the most active on fibrin plates, which was in turn neutralized by metal chelating inhibitors. These results demonstrate the differences amongst C. oreganus helleri venoms from close localities. A metalloproteinase, hellerase, was purified by anionic and cationic exchange chromatographies from San Bernardino 3 venom. Hellerase exhibited the ability to break fibrin clots in vitro, which can be of biomedically importance in the treatment of heart attacks and strokes.

Determination of the structure form of the fourth ligand of zinc in Acutolysin A using combined quantum mechanical and molecular mechanical simulation

Acutolysin A, which is isolated from the snake venom of Agkistrodon acutus, is a member of the SVMPs subfamily of the metzincin family, and it is a snake venom zinc metalloproteinase possessing only one catalytic domain. The catalytic zinc ion, in the active site, is coordinated in a tetrahedral manner with three imidazole nitrogen atoms of histidine and one oxygen atom. It is uncertain whether this oxygen atom is a water molecule or a hydroxide ion just from the three-dimensional X-ray crystal structure. The identity of the fourth ligand of zinc is theoretically determined for the first time by performing both combined quantum mechanical and molecular mechanical (QM/MM) simulation and high-level quantum mechanical calculations. All of the results obtained indicate that the fourth ligand in the active site of the reported X-ray crystal structure is a water molecule rather than a hydroxide anion. On the basis of these theoretical results, we note that the experimental observed pH dependence of the proteolytic and hemorrhagic activity of Acutolysin A can be attributed to the deprotonation of the zinc-bound water to yield a better nucleophile, the hydroxide ion. Structural analyses revealed structural details useful for the understanding of acutolysin catalytic mechanism.

Effects of Bothrops asper snake venom on lymphatic vessels: insights into a hidden aspect of envenomation

BACKGROUND

Envenomations by the snake Bothrops asper represent a serious medical problem in Central America and parts of South America. These envenomations concur with drastic local tissue pathology, including a prominent edema. Since lymph flow plays a role in the maintenance of tissue fluid balance, the effect of B. asper venom on collecting lymphatic vessels was studied.

METHODOLOGY/PRINCIPAL FINDINGS

B. asper venom was applied to mouse mesentery, and the effects were studied using an intravital microscopy methodology coupled with an image analysis program. B. asper venom induced a dose-dependent contraction of collecting lymphatic vessels, resulting in a reduction of their lumen and in a halting of lymph flow. The effect was reproduced by a myotoxic phospholipase A(2) (PLA(2)) homologue isolated from this venom, but not by a hemorrhagic metalloproteinase or a coagulant thrombin-like serine proteinase. In agreement with this, treatment of the venom with fucoidan, a myotoxin inhibitor, abrogated the effect, whereas no inhibition was observed after incubation with the peptidomimetic metalloproteinase inhibitor Batimastat. Moreover, fucoidan significantly reduced venom-induced footpad edema. The myotoxic PLA(2) homologue, known to induce skeletal muscle necrosis, was able to induce cytotoxicity in smooth muscle cells in culture and to promote an increment in the permeability to propidium iodide in these cells.

CONCLUSIONS/SIGNIFICANCE

Our observations indicate that B. asper venom affects collecting lymphatic vessels through the action of myotoxic PLA(2)s on the smooth muscle of these vessels, inducing cell contraction and irreversible cell damage. This activity may play an important role in the pathogenesis of the pronounced local edema characteristic of viperid snakebite envenomation, as well as in the systemic biodistribution of the venom, thus representing a potential therapeutical target in these envenomations.

P-III hemorrhagic metalloproteinases from Russell's viper venom: cloning, characterization, phylogenetic and functional site analyses

Two homologous P-III hemorrhagic metalloproteinases were purified from Russell's viper venoms from Myanmar and Kolkata (eastern India), and designated as daborhagin-M and daborhagin-K, respectively. They induced severe dermal hemorrhage in mice at a minimum hemorrhagic dose of 0.8-0.9 microg. Daborhagin-M specifically hydrolyzed an Aalpha-chain of fibrinogen, fibronectin, and type IV collagen in vitro. Analyses of its cleavage sites on insulin chain B and kinetic specificities toward oligopeptides suggested that daborhagin-M prefers hydrophobic residues at the P(1), P(1)', and P(2)' positions on the substrates. Of the eight Daboia geographic venom samples analyzed by Western blotting, only those from Myanmar and eastern India showed a strong positive band at 65kDa, which correlated with the high risk of systemic hemorrhagic symptoms elicited by Daboia envenoming in both regions. The full sequence of daborhagin-K was determined by cDNA cloning and sequencing, and then confirmed by peptide mass fingerprinting. Furthermore, molecular phylogenetic analyses based on 27 P-IIIs revealed the co-evolution of two major P-III classes with distinct hemorrhagic potencies, and daborhagin-K belongs to the most hemorrhagic subclass. By comparing the absolute complexity profiles between these two classes, we identified four structural motifs probably responsible for the phylogenetic subtyping and hemorrhagic potencies of P-III SVMPs.

Assessment of metalloproteinase inhibitors clodronate and doxycycline in the neutralization of hemorrhage and coagulopathy induced by Bothrops asper snake venom

Snake venom metalloproteinases (SVMPs) play a prominent role in the local and systemic manifestations of viperid snakebite envenomations. Thus, the possibility of using metalloproteinase inhibitors in the treatment of these envenomations is a promising therapeutic alternative. This study assessed the ability of two metalloproteinase inhibitors, the biphosphonate clodronate and the tetracycline doxycycline, to inhibit proteolytic, hemorrhagic, coagulant and defibrinogenating effects of Bothrops asper venom. Both compounds were able to inhibit these activities, at concentrations in the mM range, when incubated with venom prior to testing. However, when inhibition of hemorrhage was assessed in assays involving independent injection of venom and drug, inhibition was poor, even when these compounds were injected immediately after envenomation. These findings support the concept that the effectiveness of compounds, such as clodronate and doxycycline, whose inhibitory action on SVMPs is based on zinc chelation alone, is limited, and stress the view that more specific molecules are required for an effective inhibition of SVMPs in vivo.

Skin pathology induced by snake venom metalloproteinase: acute damage, revascularization, and re-epithelization in a mouse ear model

Viperid snakebite envenomation induces blistering and dermonecrosis. The pathological alterations induced by a snake venom metalloproteinase in the skin were investigated in a mouse ear model. Metalloproteinase BaP1, from Bothrops asper, induced rapid edema, hemorrhage, and blistering; the latter two effects were abrogated by preincubation with the metalloproteinase inhibitor batimastat. Neutrophils did not play a role in the pathology, as depletion of these cells resulted in a similar histological picture. Blisters are likely to result from the direct proteolytic activity of BaP1 of proteins at the dermal-epidermal junction, probably at the lamina lucida, as revealed by immunostaining for type IV collagen and laminin. Widespread apoptosis of keratinocytes was detected by the TUNEL assay, whereas no apoptosis of capillary endothelial cells was observed. BaP1 induced a drastic reduction in the microvessel density, revealed by immunostaining for the endothelial marker vascular endothelial growth factor receptor-2. This was followed by a rapid angiogenic response, leading to a partial revascularization. Skin damage was followed by inflammation and granulation tissue formation. Then, a successful re-epithelization process occurred, and the skin of the ear regained its normal structure by 2 weeks. Venom metalloproteinase-induced skin damage reproduces the pathological changes described in snakebitten patients.

Bothrops snakebite on the head: case report and review of the literature

A previously healthy, 21-year-old female was admitted 5 h after being bitten in the occipital region by a pitviper presumed to be Bothrops jararaca. Physical examination revealed marked cranial and facial oedema extending to the neck and dorsum, bilateral eyelid ecchymosis, and local conjunctival and gingival bleeding. The patient was alert and complained of mild, local pain and nausea. There were no signs of neurological involvement. The main laboratory findings on admission included incoagulable blood, a platelet count of 4000/microl, and an ELISA-estimated serum venom concentration of 62.6 ng/ml. Sequential serum creatinine, urea nitrogen, sodium and potassium concentrations were normal. The case was classified as severe and, after the intravenous administration of ranitidine, chlorpheniramine and hydrocortisone, the intravenous infusion of 12 vials of undiluted bothropic equine antivenom [F(ab)(2); 10 ml/vial] was initiated. The antivenom infusion was halted after 10 vials because the patient developed a severe early reaction, although this was successfully treated with subcutaneous adrenaline and intravenous hydrocortisone. Platelet replacement (seven units) was performed and 24 h after the antivenom infusion, normal results in blood-coagulation tests and an increase in the platelet count (to 100,000/microl) were observed. No circulating venom was detected in blood samples collected 6, 12, 24 or 48 h post-admission. The patient was discharged after 4 days, with clinical improvement and no signs of local infection, and subsequent follow-up revealed no sequelae.

Collagen binding is a key factor for the hemorrhagic activity of snake venom metalloproteinases

Snake venom metalloproteinases (SVMPs) are multifunctional enzymes involved in several symptoms following snakebite, such as severe local hemorrhage. Multidomain P-III SVMPs are strongly hemorrhagic, whereas single domain P-I SVMPs are not. This indicates that disintegrin-like and cysteine-rich domains allocate motifs that enable catalytic degradation of ECM components leading to disruption of capillary vessels. Interestingly, some P-III SVMPs are completely devoid of hemorrhagic activity despite their highly conserved disintegrin-like and cysteine-rich domains. This observation was approached in the present study by comparing the effects of jararhagin, a hemorrhagic P-III SVMP, and berythractivase, a pro-coagulant and non-hemorrhagic P-III SVMP. Both toxins inhibited collagen-induced platelet aggregation, but only jararhagin was able to bind to collagen I with high affinity. The monoclonal antibody MAJar 3, that neutralizes the hemorrhagic effect of Bothrops venoms and jararhagin binding to collagen, did not react with berythractivase. The three-dimensional structures of jararhagin and berythractivase were compared to explain the differential binding to collagen and MAJar 3. Thereby, we pinpointed a motif within the Da disintegrin subdomain located opposite to the catalytic domain. Jararhagin binds to both collagen I and IV in a triple helix-dependent manner and inhibited in vitro fibrillogenesis. The jararhagin-collagen complex retained the catalytic activity of the toxin as observed by hydrolysis of fibrin. Thus, we suggest that binding of hemorrhagic SVMPs to collagens I and IV occurs through a motif located in the Da subdomain. This allows accumulation of toxin molecules at the site of injection, close to capillary vessels, where their catalytic activity leads to a local hemorrhage. Toxins devoid of this motif would be more available for vascular internalization leading to systemic pro-coagulant effects. This reveals a novel function of the disintegrin domain in hemorrhage formation.

BnP1, a novel P-I metalloproteinase from Bothrops neuwiedi venom: biological effects benchmarking relatively to jararhagin, a P-III SVMP

Snake venom metalloproteinases (SVMPs) have been extensively studied and their effects associated with the local bleeding observed in human accidents by viper snakes. Representatives of P-I and P-III classes of SVMPs similarly hydrolyze extracellular matrix proteins or coagulation factors while only P-III SVMPs induce significant hemorrhage in experimental models. In this work, the effects of P-I and P-III SVMPs on plasma proteins and cultures of muscle and endothelial cells were compared in order to enlighten the mechanisms involved in venom-induced hemorrhage. To reach this comparison, BnP1 was isolated from B. neuwiedi venom and used as a weakly hemorrhagic P-I SVMPs and jararhagin was used as a model of potently hemorrhagic P-III SVMP. BnP1 was isolated by size exclusion and anion-exchange chromatographies, showing apparent molecular mass of approximately 24kDa and sequence similarity with other members of SVMPs, which allowed its classification as a group P-I SVMP. The comparison of local effects induced by SVMPs showed that BnP1 was devoid of significant myotoxic and hemorrhagic activities and jararhagin presented only hemorrhagic activity. BnP1 and jararhagin were able to hydrolyze fibrinogen and fibrin, although the latter displayed higher activity in both systems. Using HUVEC primary cultures, we observed that BnP1 induced cell detachment and a decrease in the number of viable endothelial cells in levels comparable to those observed by treatment with jararhagin. Moreover, both BnP1 and jararhagin induced apoptosis in HUVECs while only a small increase in LDH supernatant levels was observed after treatment with jararhagin, suggesting that the major mechanism involved in endothelial cell death is apoptosis. Jararhagin and BnP1 induced little effects on C2C12 muscle cell cultures, characterized by a partial detachment 24h after treatment and a mild necrotic effect as evidenced by a small increase in the supernatants LDH levels. Taken together, our data show that P-I and P-III SVMPs presented comparable effects except for the hemorrhagic activity, suggesting that hydrolysis of coagulation factors or damage to endothelial cells are not sufficient for induction of local bleeding.

Molecular and functional characterization of a new non-hemorrhagic metalloprotease from Bothrops jararacussu snake venom with antiplatelet activity

BjussuMP-II is an acidic low molecular weight metalloprotease (Mr approximately 24,000 and pI approximately 6.5), isolated from Bothrops jararacussu snake venom. The chromatographic profile in RP-HPLC and its N-terminal sequence confirmed its high purity level. Its complete cDNA was obtained by RT-PCR and the 615bp codified for a mature protein of 205 amino acid residues. The multiple alignment of its deduced amino acid sequence and those of other snake venom metalloproteases showed a high structural similarity, mainly among class P-I proteases. The molecular modeling analysis of BjussuMP-II showed also conserved structural features with other SVMPs. BjussuMP-II did not induce hemorrhage, myotoxicity and lethality, but displayed dose-dependent proteolytic activity on fibrinogen, collagen, fibrin, casein and gelatin, keeping stable at different pHs, temperatures and presence of several divalent ions. BjussuMP-II did not show any clotting or anticoagulant activity on human citrated plasma, in contrast to its inhibitory effects on platelet aggregation. The aspects broached, in this work, provide data on the relationship between structure and function, in order to better understand the effects elicited by snake venom metalloproteases.

‘Partitagin’ a hemorrhagic metalloprotease from Hippasa partita spider venom: Role in tissue necrosis

The poisonous bite by Hippasa partita, a funnel web spider from the Indian subcontinent has been demonstrated to give rise to severe dermo- and myonecrosis. In this work a hemorrhagic metalloprotease, Partitagin was purified from H. partita venom by successive chromatography on Sephadex G-100, DEAE Sephadex A-50 and Biosep DEAE columns. SDS-PAGE, reversed phase HPLC on a C(4) column, N-terminal amino acid sequencing and MALDI-TOF mass spectrometry confirmed the homogeneity. Partitagin was assayed using fat free casein as substrate. EDTA, 1,10-phenanthroline and cyanide, inactivated it irreversibly while, EGTA, PMSF, leupeptin, pepstatin and aprotinin did not inhibit. The presence of Zn(+2) was confirmed by atomic absorption spectrometry. Partitagin caused hemorrhage when tested in a mouse model. Light microscopy of skin tissue sections at the site of injection revealed extensive damage of extracellular matrix (ECM) in which the basement membrane surrounding blood vessels and capillaries showing signs of extensive destruction and also loss of vessel wall integrity. Similar intense damage was also noticed in the ECM of muscle tissue sections but with no damage caused to myocytes. Partitagin showed specificity of action on the components of ECM and degraded collagen type-IV and fibronectin but not collagen type-I. Partitagin was devoid of edema, myotoxicity and lethality. This is the first report on the isolation and characterization of a toxin from spider venom in the Indian subcontinent.

Cytoskeletal rearrangement and cell death induced by Bothrops alternatus snake venom in cultured Madin–Darby canine kidney cells

Bothrops snake venoms cause renal damage, with renal failure being the main cause of death in humans bitten by these snakes. In this work, we investigated the cytoskeletal rearrangement and cytotoxicity caused by Bothrops alternatus venom in cultured Madin–Darby canine kidney (MDCK) cells. Incubation with venom (10 and 100 µg/mL) significantly (p <0.05) decreased the cellular uptake of neutral red dye after 1 and 3 h. Venom (100 µg/mL) also markedly decreased the transepithelial electrical resistance (RT) across MDCK monolayers. Staining with rhodamine-conjugated phalloidin revealed disarray of the cytoskeleton that involved the stress fibers at the basal cell surface and focal adhesion-associated F-actin in the cell–matrix contact region. Feulgen staining showed a significant decrease in the number of cells undergoing mitosis and an increase in the frequency of altered nuclei. Scanning electron microscopy revealed a decrease in the number of microvilli and the presence of cells with a fusiform format. Flow cytometry with annexin V and propidium iodide showed that cell death occurred by necrosis, with little apoptosis, a conclusion supported by the lack of DNA fragmentation characteristic of apoptosis. Pretreating the cells with catalase significantly attenuated the venom-induced loss of viability, indicating a possible involvement of H2O2 in the cellular damage; less protection was observed with superoxide dismutase or Nω-nitro-l-arginine methyl ester. These results indicate that Bothrops alternatus venom is cytotoxic to cultured MDCK cells, possibly via the action of reactive oxygen species. This cytotoxicity could contribute to nephrotoxicity after envenoming by this species.

Use of SILAC for exploring sheddase and matrix degradation of fibroblasts in culture by the PIII SVMP atrolysin A: Identification of two novel substrates with functional relevance

Snake venom metalloproteinases (SVMPs) in Viperid venoms primarily function to give rise to local and systemic hemorrhage following snake envenomation. Years of research on these toxins, both in vitro and in vivo, indicate that they function by disrupting capillary basement membranes, stromal matrix and cell-cell and cell-matrix contacts to allow escape of capillary contents under pressure. However, most of these studies used either defined substrates in vitro or were limited by relevant antibodies for detection of sites of action in vivo. In this investigation we use stable isotope-labeled amino acids in culture (SILAC) to determine novel proteolytic activities for exogenously added atrolysin A, a hemorrhagic PIII SVMP isolated from Crotalus atrox venom. When comparing the solubilized products of SILAC-labeled cultured human fibroblasts treated with atrolysin A to that of untreated fibroblasts using LC/MS/MS, several proteins were identified as being released into the culture media specifically due to atrolysin A proteolytic activity. These included collagen VI, fibronectin, fibulin 2 and annexin V. Of particular interest was the observation of collagen VI and annexin V in that the release of these substrates could play a role in altering hemostasis and promote hemorrhage caused by the more typical actions of atrolysin A. In summary, this study demonstrates the utility of SILAC for exploring sheddase activity with cells in culture and suggests the presence of two novel substrates for SVMPs that may play a pathological role in altering host hemostasis during envenomation.

Molecular cloning of albolatin, a novel snake venom metalloprotease from green pit viper (Trimeresurus albolabris), and expression of its disintegrin domain

Disintegrins are snake venom-derived, RGD- or KGD-containing peptides that can inhibit integrin-mediated platelet aggregation and cell-matix interactions. The aim of this study is to analyze the full-length cDNA sequence of a snake venom metalloprotease (SVMP) from green pit viper (Trimeresurus albolabris) venom and characterize functions of its disintegrin domain on human platelets. From the primary cDNA library of venom glands, a partial sequence of a novel SVMP (Albolatin) was obtained. Using the 5'-RACE, the 2040bp full-length sequence of albolatin mRNA was derived. The deduced amino acid sequence revealed a type P-II SVMP of 484 amino acid residues comprising a signal region, pro-peptide, inactive metalloprotease domain and a disintegrin domain. It showed 85% amino acid identical to Trimeresurus jerdonii jerdonitin and 81% to Gloydius halys agkistin. Sequence alignment revealed that all cysteines were conserved except for an extra cysteine in the protease domain of albolatin. The disintegrin domain of albolatin, which comprised 76 amino acids with a KGDW sequence, was expressed in Pichia pastoris with the yield of 3.3mg/L of culture medium. The molecular weights were 11kDa in reduced and 22kDa in non-reduced states indicating a homodimer. It can inhibit collagen-induced platelet aggregation with IC(50) of 976nM and, therefore, should be investigated for a potential to be a novel therapeutic agent.

Evaluation of three Brazilian antivenom ability to antagonize myonecrosis and hemorrhage induced by Bothrops snake venoms in a mouse model

Despite preventing death after snakebites, there is little evidence that polyvalent antivenoms (PAVs) protect against myotoxicity and local damages. We evaluated antibothropic Brazilian PAVs from three manufacturers against the myotoxicity and hemorrhagic activity of Bothrops jararacussu and B. jararaca venoms, respectively, by using two protocols: preincubation of PAVs with venom, and i.v. pretreatment with PAVs, prior to the venom inoculation. In this investigation, we used doses of PAVs ranging from 0.4 to 4.0mL/mg of venom equivalent up to 10 times the amount recommended by the producers for the clinical practice in Brazil. In our preincubation protocol in vivo, PAVs antagonized myotoxicity of B. jararacussu venom by 40-95%, while our pretreatment protocol antagonized myotoxic activity by 0-60%. Preincubation of antivenoms with B. jararaca venom antagonized its hemorrhagic activity by 70-95%, while pretreatment antagonized hemorrhagic activity by 10-50%. Although all PAVs demonstrated partial antagonism against both venoms, the magnitude of these effects varied greatly among the manufactures. The results suggest that the current clinical doses of these PAVs may have negligible antimyotoxic effect.

Cytotoxic, thrombolytic and edematogenic activities of leucurolysin-a, a metalloproteinase from Bothrops leucurus snake venom

Leucurolysin-a (leuc-a), a 23 kDa non-hemorrhagic metalloproteinase, is found in venom of the viper Bothrops leucurus. Here, we examine the biological consequences of leuc-a, including thrombolytic activity, direct effects on endothelial cells in culture and edematogenic activity in vivo. We demonstrate fibrinolytic activity of leuc-a, in which the protease specifically degrades alpha, beta, and gamma-gamma chains. While not causing hemorrhaging, leuc-a does cause thrombolytic activities in whole blood clots. Endothelial cells are highly resistant to leuc-a in culture. Cell viability suffered only when cells were exposed to large quantities of the protease. Nevertheless, leuc-a induces changes in cell morphology. The impact of leuc-a on cell adhesion was confirmed by an adhesion assay, in which cell adhesion to fibronectin decreased due to leuc-a. This mild cellular impact is unlike that of crude venom, where lower concentrations triggered cell death and a greater reduction in cell adhesion. Also, leuc-a increased microvessel permeability with marked edema in mice peritoneum and foot pads. These effects are similar to those of other P-I class SVPMs. These in vivo effects were weaker when crude venom was tested. In conclusion, albeit not showing significant hemorrhagic activity, leuc-a can induce a prominent edema which appears to be significant in the local effects observed after B. leucurus venom accidents.

Molecular characterization and phylogenetic analysis of BjussuMP-I: A RGD-P-III class hemorrhagic metalloprotease from Bothrops jararacussu snake venom

Snake venom metalloproteases (SVMPs) embody zinc-dependent multidomain enzymes responsible for a relevant pathophysiology in envenomation, including local and systemic hemorrhage. The molecular features responsible for hemorrhagic potency of SVMPs have been associated with their multidomains structures which can target these proteins them to several receptors of different tissues and cellular types. BjussuMP-I, a SVMP isolated from the Bothrops jararacussu venom, has been characterized as a P-III hemorrhagic metalloprotease. The complete cDNA sequence of BjussuMP-I with 1641bp encodes open reading frames of 547 amino acid residues, which conserve the common domains of P-III high molecular weight hemorrhagic metalloproteases: (i) pre-pro-peptide, (ii) metalloprotease, (iii) disintegrin-like and (iv) rich cysteine domain. BjussuMP-I induced lyses in fibrin clots and inhibited collagen- and ADP-induced platelet aggregation. We are reporting, for the first time, the primary structure of an RGD-P-III class snake venom metalloprotease. A phylogenetic analysis of the BjussuMP-I metalloprotease/catalytic domain was performed to get new insights into the molecular evolution of the metalloproteases. A theoretical molecular model of this domain was built through folding recognition (threading) techniques and refined by molecular dynamics simulation. Then, the final BjussuMP-I catalytic domain model was compared to other SVMPs and Reprolysin family proteins in order to identify eventual structural differences, which could help to understand the biochemical activities of these enzymes. The presence of large hydrophobic areas and some conserved surface charge-positive residues were identified as important features of the SVMPs and other metalloproteases.

Purification and characterization of patagonfibrase, a metalloproteinase showing α-fibrinogenolytic and hemorrhagic activities, from Philodryas patagoniensis snake venom

Venoms of Colubridae snakes are a rich source of novel compounds, which may have applications in medicine and biochemistry. In the present study, we describe the purification and characterization of a metalloproteinase (patagonfibrase), the first protein to be isolated from Philodryas patagoniensis (Colubridae) snake venom. Patagonfibrase is a single-chain protein, showing a molecular mass of 53,224 Da and an acidic isoelectric point (5.8). It hydrolyzed selectively the Aalpha-chain of fibrinogen and when incubated with fibrinogen or plasma, the thrombin clotting time was prolonged. Prominent hemorrhage developed in mouse skin after intradermal injection of patagonfibrase. When administered into mouse gastrocnemius muscle, it induced local hemorrhage and necrosis, and systemic bleeding in lungs. Patagonfibrase showed proteolytic activity toward azocasein, which was enhanced by Ca(2+) and inhibited by Zn(2+), cysteine, dithiothreitol and Na(2)EDTA. Patagonfibrase impaired platelet aggregation induced by collagen and ADP. Thus, patagonfibrase may play a key role in the pathogenesis of disturbances that occur in P. patagoniensis envenomation, and may be used as a biological tool to explore many facets of hemostasis.

Crystal structures of catrocollastatin/VAP2B reveal a dynamic, modular architecture of ADAM/adamalysin/reprolysin family proteins

Catrocollastatin/vascular apoptosis-inducing protein (VAP)2B is a metalloproteinase from Crotalus atrox venom, possessing metalloproteinase/disintegrin/cysteine-rich (MDC) domains that bear the typical domain architecture of a disintegrin and metalloproteinase (ADAM)/adamalysin/reprolysin family proteins. Here we describe crystal structures of catrocollastatin/VAP2B in three different crystal forms, representing the first reported crystal structures of a member of the monomeric class of this family of proteins. The overall structures show good agreement with both monomers of atypical homodimeric VAP1. Comparison of the six catrocollastatin/VAP2B monomer structures and the structures of VAP1 reveals a dynamic, modular architecture that may be important for the functions of ADAM/adamalysin/reprolysin family proteins.

Purification and functional characterization of AAV1, a novel P-III metalloproteinase, from Formosan Agkistrodon acutus venom

AAV1, an alkaline glycoprotein (GP), was purified from Agkistrodon acutus venom by two chromatographic steps on successive DEAE-Sephadex A-50 and Superdex 75 FPLC columns. AAV1 on SDS-PAGE under non-reducing conditions migrated as a monomeric and a polymeric forms with apparent molecular mass of 57 and 180 kDa, respectively. Upon reduction, it appeared as a single broad band with a mass of 50.3 kDa corresponding to the size of a typical P-III metalloproteinase acurhagin. The N-terminal sequence of an autoproteolytical 30 kDa-fragment of AAV1 showed a high homology to that of venom proteins with Metalloproteinase, Disintegrin-like, and Cysteine-rich (MDC) domains. Although it was devoid of cleaving activity toward gelatin, fibronectin and prothrombin, AAV1 preferentially digested the Aalpha chain of fibrinogen and followed by the Bbeta chain, leading to the inhibition of fibrinogen-induced platelet aggregation in elastase-treated human platelets. However, the proteolytic activity of AAV1 was completely inactivated by the chelating agent but not serine proteinase inhibitor. Furthermore, AAV1 could concentration-dependently inhibit platelet aggregation and suppress tyrosine phosphorylation of intracellular proteins in collagen- and convulxin-stimulated platelets, respectively. The interaction of MDC domains in AAV1 molecule with platelet GPVI was responsible for the inhibitory effect of AAV1 on collagen- and convulxin-induced platelet aggregation. Taken together, these pieces of evidence suggest that AAV1 from Formosan viper venom belongs to a new member of high-molecular mass metalloproteinase family and functions as a GPVI antagonist.

Novel insights into capillary vessel basement membrane damage by snake venom hemorrhagic metalloproteinases: a biochemical and immunohistochemical study

The hemorrhagic activity characteristic of viperid snake envenomations is due to the action of venom metalloproteinases (SVMPs) on the capillary vessel basement membrane (BM). This study compared the action of two SVMPs on BM in vitro (degradation of Matrigel) and in vivo (immunohistochemical assessment of BM markers in mouse gastrocnemius muscle). SVMPs BaP1 (belonging to the P-I class) and jararhagin (of the P-III class) had a similar proteolytic activity on azocasein and degraded Matrigel with a slightly different cleavage pattern, since BaP1 exerted a limited proteolysis of both laminin and nidogen, whereas jararhagin predominantly degraded nidogen. In contrast with this pattern of limited proteolysis of BM proteins observed in vitro, immunohistochemical analysis of laminin, nidogen and type IV collagen, as well as of the endothelial cell marker VEGFR-2, in the hemorrhagic areas in the muscle, revealed a pronounced reduction in the immunostaining of these three BM components, associated with a loss of the endothelial cell marker. BM of muscle fibers was affected to a lesser extent. In conclusion, in vitro results demonstrated that SVMPs induce a pattern of limited proteolysis on BM components. The drastic loss of these antigens in affected capillaries in vivo is likely to depend on the combination of limited proteolysis of BM and the action of hemodynamic biophysical forces, previously shown to play a role in SVMP-induced capillary damage, which may cause a mechanical disruption of BM structure.

Systemic pathological alterations caused by Philodryas patagoniensis colubrid snake venom in rats

Very little is known about the systemic effects caused by Philodryas patagoniensis colubrid snake venom. In this work, this venom was tested for its ability to induce histopathological changes in rats after its intramuscular, subcutaneous or intravenous administration, by light microscopic examination of some organs (cerebellum, cerebrum, lung, liver, kidney and heart). Four rats were used for each dose of 0.23, 0.45 and 0.90 mg of venom in 0.3 ml of phosphate-buffered saline solution (pH 7.4). Aliquots of blood were withdrawn at different time intervals for enzymatic determination of alanine aminotransferase, aspartate aminotransferase and creatine kinase levels. After 2h the animals were killed by an overdose of anesthetic, and samples of kidney, heart, liver, lung, cerebrum and cerebellum were taken to microscopic examination (hematoxylin and eosin stain). Histologically, no abnormality was observed in heart tissue, in none of the administration routes of the venom used. However, histological observations showed multifocal hemorrhage in cerebellum, cerebrum and lung sections, severe peritubular capillary congestion in kidney sections and hydropic degeneration in liver sections, when venom was administrated intravenously. The subcutaneous route showed similar results to the previous one, with the exception of cerebellar hemorrhage. Intramuscularly, neither cerebral nor cerebellar hemorrhage was observed. Plasma alanine aminotransferase and aspartate aminotransferase increased levels were demonstrated, mainly when venom was administered intravenously or subcutaneously. Our results suggest that P. patagoniensis venom induces moderate histopathological changes in vital organs of rats. These changes are initiated at early stages of the envenomation and may be associated with a behavioral or functional abnormality of those organs during envenoming.

A randomized, double-blind, placebo-controlled trial of antivenom for local effects of green pit viper bites

Although systemic administration of antivenom can promptly reverse coagulopathy, efficacy on local effects of viper venom remains to be determined. Currently, there has been no proven specific treatment for snakebite patients with severe local effects. This study is a randomized, double-blind, placebo-controlled trial. Patients bitten by green pit vipers (Trimeresurus albolabris or T. macrops) with marked limb swelling, but no severe coagulopathy requiring antivenom, were randomized to receive either equine F(ab')2 antivenom, or placebo. Twenty-eight cases were included, 14 in each group, and they had their limb circumferences measured on days 1, 2, 4 and 6 after interventions. The percentage reduction in limb circumference was significantly better in the antivenom group compared with the placebo group (ANOVA, P = 0.03), especially in the first 24 h (1.14 vs. 3.62%, in placebo and antivenom group, respectively, P = 0.014). The reduction in pain score was similar. The plasma venom levels were not different at presentation but lower in the antivenom group 24h after intervention (P = 0.033). These data suggest that intravenous antivenom could accelerate local oedema resolution in humans. However, the degree is not clinically significant, and, therefore, general use is not recommended.

Venom gland EST analysis of the saw-scaled viper, Echis ocellatus, reveals novel α9β1 integrin-binding motifs in venom metalloproteinases and a new group of putative toxins, renin-like aspartic proteases

Echis ocellatus is the most medically important snake in West Africa. However, the composition of its venom and the differential contribution of these venom components to the severe haemorrhagic and coagulopathic pathology of envenoming are poorly understood. To address this situation we assembled a toxin transcriptome based upon 1000 expressed sequence tags (EST) from a cDNA library constructed from pooled venom glands of 10 individual E. ocellatus. We used a variety of bioinformatic tools to construct a fully annotated venom-toxin transcriptome that was interrogated with a combination of BLAST annotation, gene ontology cataloguing and disintegrin-motif searching. The results of these analyses revealed an unusually abundant and diverse expression of snake venom metalloproteinases (SVMP) and a broad toxin-expression profile including several distinct isoforms of bradykinin-potentiating peptides, phospholipase A(2), C-type lectins, serine proteinases and l-amino oxidases. Most significantly, we identified for the first time a conserved alpha(9)beta(1) integrin-binding motif in several SVMPs, and a new group of putative venom toxins, renin-like aspartic proteases.

The anti-snake venom properties ofTamarindus indica(leguminosae) seed extract

In Indian traditional medicine, various plants have been used widely as a remedy for treating snake bites. The aim of this study was to evaluate the effect of Tamarindus indica seed extract on the pharmacological as well as the enzymatic effects induced by V. russelli venom. Tamarind seed extract inhibited the PLA(2), protease, hyaluronidase, l-amino acid oxidase and 5'-nucleotidase enzyme activities of venom in a dose-dependent manner. These are the major hydrolytic enzymes responsible for the early effects of envenomation, such as local tissue damage, inflammation and hypotension. Furthermore, the extract neutralized the degradation of the Bbeta chain of human fibrinogen and indirect hemolysis caused by venom. It was also observed that the extract exerted a moderate effect on the clotting time, prolonging it only to a small extent. Edema, hemorrhage and myotoxic effects including lethality, induced by venom were neutralized significantly when different doses of the extract were preincubated with venom before the assays. On the other hand, animals that received extract 10 min after the injection of venom were protected from venom induced toxicity. Since it inhibits hydrolytic enzymes and pharmacological effects, it may be used as an alternative treatment to serum therapy and, in addition, as a rich source of potential inhibitors of PLA(2), metalloproteinases, serine proteases, hyaluronidases and 5 cent-nucleotidases, the enzymes involved in several physiopathological human and animal diseases.

Bothrops jararaca venom gland transcriptome: analysis of the gene expression pattern

Bothrops jararaca is a pit viper responsible for the majority of snake envenoming accidents in Brazil. As an attempt to describe the transcriptional activity of the venom gland, ESTs of a cDNA library constructed from B. jararaca venom gland were generated and submitted to bioinformatics analysis. The results showed a clear predominance of transcripts coding for toxins instead of transcripts coding for proteins involved in cellular functions. Among toxins, the most frequent transcripts were from metalloproteinases (52.6%), followed by serine-proteinases (28.5%), C-type lectins (8.3%) and bradykinin-potentiating peptides (BPPs) (6.2%). Results were similar to that obtained from the transcriptome analysis of B. insularis, a phylogenetically close sister of B. jararaca, though some differences were observed and are pointed out, such as a higher amount of the hypotensive BPPs in B. insularis transcriptome (19.7%). Another striking difference observed is that PIII and PII-classes of metalloproteinases are similarly represented in B. jararaca in contrast to B. insularis, in which a predominance of PIII-class metalloproteinase, which present a more intense hemorrhagic action, is observed. These features may, in part, explain the higher potency of B. insularis venom. The results obtained can help in proteome studies, and the clones can be used to directly probe the genetic material from other snake species or to investigate differences in gene expression pattern in response to factors such as diet, aging and geographic localization.

Crystallization and preliminary X-ray crystallographic analysis of two vascular apoptosis-inducing proteins (VAPs) from Crotalus atrox venom

VAPs are haemorrhagic snake-venom toxins belonging to the reprolysin family of zinc metalloproteinases. In vitro, VAPs induce apoptosis specifically in cultured vascular endothelial cells. VAPs have a modular structure that bears structural homology to mammalian ADAMs (a disintegrin and metalloproteinases). VAP1 is a homodimer with a MW of 110 kDa in which the monomers are connected by a single disulfide bridge. VAP2 is homologous to VAP1 and exists as a monomer with a MW of 55 kDa. In the current study, several crystal forms of VAP1 and VAP2 were obtained using the vapour-diffusion method and diffraction data sets were collected using SPring-8 beamlines. The best crystals of VAP1 and VAP2 generated data sets to 2.5 and 2.15 angstroms resolution, respectively.

Functional characterization of a basic D49 phospholipase A2 (LmTX-I) from the venom of the snake Lachesis muta muta (bushmaster)

The whole venom of Lachesis muta muta is preponderantly neurotoxic but moderately myotoxic on the chick biventer cervicis preparation (BCp). We have now examined these toxic activities of a basic phospholipase A(2), LmTX-I, isolated from the whole venom. LmTX-I caused a significant concentration-dependent neuromuscular blockade in the BCp. The time to produce 50% neuromuscular blockade was 14.7+/-0.75 min (30 microg/ml), 23.6+/-0.9 min (10 microg/ml), 34+/-1.7 min (2.5 microg/ml) and 39.2+/-3.6 min (1 microg/ml), (n=5/concentration; p<0.05). Complete blockade with all tested concentrations was not accompanied by inhibition of the response to ACh. At the highest concentration, LmTX-I (30 microg/ml) significantly reduced contractures elicited by exogenous KCl (20mM), increased the release of creatine kinase (1542.5+/-183.9 IU/L vs 442.7+/-39.8 IU/L for controls after 120 min, p<0.05), and induced the appearance of degenerating muscle fibers ( approximately 15%). Quantification of myonecrosis indicated 14.8+/-0.8 and 2.0+/-0.4%, with 30 and 10 microg/mlvenom concentration, respectively, against 1.07+/-0.4% for control preparations. The findings indicate that the basic PLA(2) present on venom from L. m. muta (LmTX-I) possesses a dominant neurotoxic action on isolated chick nerve-muscle preparations, whereas myotoxicity was mainly observed at the highest concentration used (30 microg/ml). These effects of LmTX-I closely reproduce the effects of the whole venom of L. m. muta in chick neuromuscular preparations.