Ultrastructural alterations in mouse capillary blood vessels after experimental injection of venom from the snake Bothrops asper (Terciopelo)

Stingray Venom Proteins: Mechanisms of Action Revealed Using a Novel Network Pharmacology Approach

Animal venoms offer a valuable source of potent new drug leads, but their mechanisms of action are largely unknown. We therefore developed a novel network pharmacology approach based on multi-omics functional data integration to predict how stingray venom disrupts the physiological systems of target animals. We integrated 10 million transcripts from five stingray venom transcriptomes and 848,640 records from three high-content venom bioactivity datasets into a large functional data network. The network featured 216 signaling pathways, 29 of which were shared and targeted by 70 transcripts and 70 bioactivity hits. The network revealed clusters for single envenomation outcomes, such as pain, cardiotoxicity and hemorrhage. We carried out a detailed analysis of the pain cluster representing a primary envenomation symptom, revealing bibrotoxin and cholecystotoxin-like transcripts encoding pain-inducing candidate proteins in stingray venom. The cluster also suggested that such pain-inducing toxins primarily activate the inositol-3-phosphate receptor cascade, inducing intracellular calcium release. We also found strong evidence for synergistic activity among these candidates, with nerve growth factors cooperating with the most abundant translationally-controlled tumor proteins to activate pain signaling pathways. Our network pharmacology approach, here applied to stingray venom, can be used as a template for drug discovery in neglected venomous species.

Bleeding and Thrombosis: Insights into Pathophysiology of Bothrops Venom-Related Hemostasis Disorders

Toxins from Bothrops venoms targeting hemostasis are responsible for a broad range of clinical and biological syndromes including local and systemic bleeding, incoagulability, thrombotic microangiopathy and macrothrombosis. Beyond hemostais disorders, toxins are also involved in the pathogenesis of edema and in most complications such as hypovolemia, cardiovascular collapse, acute kidney injury, myonecrosis, compartmental syndrome and superinfection. These toxins can be classified as enzymatic proteins (snake venom metalloproteinases, snake venom serine proteases, phospholipases A₂ and L-amino acid oxidases) and non-enzymatic proteins (desintegrins and C-type lectin proteins). Bleeding is due to a multifocal toxicity targeting vessels, platelets and coagulation factors. Vessel damage due to the degradation of basement membrane and the subsequent disruption of endothelial cell integrity under hydrostatic pressure and tangential shear stress is primarily responsible for bleeding. Hemorrhage is promoted by thrombocytopenia, platelet hypoaggregation, consumption coagulopathy and fibrin(ogen)olysis. Onset of thrombotic microangiopathy is probably due to the switch of endothelium to a prothrombotic phenotype with overexpression of tissue factor and other pro-aggregating biomarkers in association with activation of platelets and coagulation. Thrombosis involving large-caliber vessels in B. lanceolatus envenomation remains a unique entity, which exact pathophysiology remains poorly understood.

Qualitative and Quantitative Study of the Changes in the Ultrastructure of Mammalian Adrenal Cortex Caused by the Venezuelan Tigra Mariposa (Bothrops venezuelensis) Snake Venom

The damage of the adrenal gland by snake venoms needs to be clarified. Lethality (LD₅₀) of Bothrops venezuelensis (Bv) venom was established by intraperitoneally mice injections. Preparation of specimens for transmission electron microscopy samples from cortex adrenal gland biopsies at 3, 6, and 24 h was processed. The quantitative description by the principal component analysis (PCA) of the adrenal gland was as follows: thickening of the capillary endothelium, area of the capillary lumen, cell nucleus area, enlargement of the perinuclear space, number of mitochondria, area of the mitochondria, number of mitochondrial cristae, number of cristae per mitochondrial unit, and tubular diameter of the smooth endoplasmic reticulum (SER). Sections of the adrenal cortex, after 3 h postinjection with Bv venom showed in the cortical cells: mitochondria with tubular cristae and slightly swollen SER cisternae, nucleus with variable heterochromatin content, irregular edges, and swollen nuclear envelope. After 6 h, cells with swollen nucleus envelope, electron dense lipids and mitochondria with loss of their cristae were observed. Myelin figures, close to the microvilli of the cortical cell, multivesicular bodies, swollen profiles of the SER, and electron dense lipid drops were noticed. After 24 h, thickening of the endothelial wall, fenestrae and projections into the capillary lumen, loss of the mitochondrial cristae, destruction of the capillary and the plasma membrane of the cortical cell, multivesicular body, SER loss, and an enlargement of the perinuclear space were detected. In the quantitative PCA, there were significant changes after the venom treatments.

Structurally Robust and Functionally Highly Versatile-C-Type Lectin (-Related) Proteins in Snake Venoms

Snake venoms contain an astounding variety of different proteins. Among them are numerous C-type lectin family members, which are grouped into classical Ca²⁺- and sugar-binding lectins and the non-sugar-binding snake venom C-type lectin-related proteins (SV-CLRPs), also called snaclecs. Both groups share the robust C-type lectin domain (CTLD) fold but differ in a long loop, which either contributes to a sugar-binding site or is expanded into a loop-swapping heterodimerization domain between two CLRP subunits. Most C-type lectin (-related) proteins assemble in ordered supramolecular complexes with a high versatility of subunit numbers and geometric arrays. Similarly versatile is their ability to inhibit or block their target molecules as well as to agonistically stimulate or antagonistically blunt a cellular reaction triggered by their target receptor. By utilizing distinct interaction sites differentially, SV-CLRPs target a plethora of molecules, such as distinct coagulation factors and receptors of platelets and endothelial cells that are involved in hemostasis, thrombus formation, inflammation and hematogenous metastasis. Because of their robust structure and their high affinity towards their clinically relevant targets, SV-CLRPs are and will potentially be valuable prototypes to develop new diagnostic and therapeutic tools in medicine, provided that the molecular mechanisms underlying their versatility are disclosed.

Preclinical Evaluation of the Efficacy of Antivenoms for Snakebite Envenoming: State-of-the-Art and Challenges Ahead

Animal-derived antivenoms constitute the mainstay in the therapy of snakebite envenoming. The efficacy of antivenoms to neutralize toxicity of medically-relevant snake venoms has to be demonstrated through meticulous preclinical testing before their introduction into the clinical setting. The gold standard in the preclinical assessment and quality control of antivenoms is the neutralization of venom-induced lethality. In addition, depending on the pathophysiological profile of snake venoms, the neutralization of other toxic activities has to be evaluated, such as hemorrhagic, myotoxic, edema-forming, dermonecrotic, in vitro coagulant, and defibrinogenating effects. There is a need to develop laboratory assays to evaluate neutralization of other relevant venom activities. The concept of the 3Rs (Replacement, Reduction, and Refinement) in Toxinology is of utmost importance, and some advances have been performed in their implementation. A significant leap forward in the study of the immunological reactivity of antivenoms against venoms has been the development of “antivenomics”, which brings the analytical power of mass spectrometry to the evaluation of antivenoms. International partnerships are required to assess the preclinical efficacy of antivenoms against snake venoms in different regions of the world in order to have a detailed knowledge on the neutralizing profile of these immunotherapeutics.

Muscle Tissue Damage Induced by the Venom of Bothrops asper: Identification of Early and Late Pathological Events through Proteomic Analysis

The time-course of the pathological effects induced by the venom of the snake Bothrops asper in muscle tissue was investigated by a combination of histology, proteomic analysis of exudates collected in the vicinity of damaged muscle, and immunodetection of extracellular matrix proteins in exudates. Proteomic assay of exudates has become an excellent new methodological tool to detect key biomarkers of tissue alterations for a more integrative perspective of snake venom-induced pathology. The time-course analysis of the intracellular proteins showed an early presence of cytosolic and mitochondrial proteins in exudates, while cytoskeletal proteins increased later on. This underscores the rapid cytotoxic effect of venom, especially in muscle fibers, due to the action of myotoxic phospholipases A2, followed by the action of proteinases in the cytoskeleton of damaged muscle fibers. Similarly, the early presence of basement membrane (BM) and other extracellular matrix (ECM) proteins in exudates reflects the rapid microvascular damage and hemorrhage induced by snake venom metalloproteinases. The presence of fragments of type IV collagen and perlecan one hour after envenoming suggests that hydrolysis of these mechanically/structurally-relevant BM components plays a key role in the genesis of hemorrhage. On the other hand, the increment of some ECM proteins in the exudate at later time intervals is likely a consequence of the action of endogenous matrix metalloproteinases (MMPs) or of de novo synthesis of ECM proteins during tissue remodeling as part of the inflammatory reaction. Our results offer relevant insights for a more integrative and systematic understanding of the time-course dynamics of muscle tissue damage induced by B. asper venom and possibly other viperid venoms.

Efficacy of IgG and F(ab')2 antivenoms to neutralize snake venom-induced local tissue damage as assessed by the proteomic analysis of wound exudate

Proteomic analysis of wound exudates represents a valuable tool to investigate tissue pathology and to assess the therapeutic success of various interventions. In this study, the ability of horse-derived IgG and F(ab')(2) antivenoms to neutralize local pathological effects induced by the venom of the snake Bothrops asper in mouse muscle was investigated by the proteomic analysis of exudates collected in the vicinity of affected tissue. In experiments involving the incubation of venom and antivenom prior to injection in mice, hemorrhagic activity was completely abolished and local muscle-damaging activity was significantly reduced by the antivenoms. In these conditions, the relative amounts of several intracellular and extracellular matrix proteins were reduced by the action of antivenoms, whereas the relative amounts of various plasma proteins were not modified. Because not all intracellular proteins were reduced, it is likely that there is a residual cytotoxicity not neutralized by antivenoms. In experiments designed to more closely reproduce the actual circumstances of envenoming, that is, when antivenom is administered after envenomation, the number of proteins whose amounts in exudates were reduced by antivenoms decreased, underscoring the difficulty in neutralizing local pathology due to the very rapid onset of venom-induced pathology. In these experiments, IgG antivenom was more efficient than F(ab')(2) antivenom when administered after envenomation, probably as a consequence of differences in their pharmacokinetic profiles.

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.

Local and systemic pathophysiological alterations induced by a serine proteinase from the venom of the snake Bothrops jararacussu

The local and systemic pathophysiological alterations induced by BjussuSP-I, a thrombin-like serine proteinase from the venom of the snake Bothrops jararacussu, were assessed in mice. BjussuSP-I induced a mild edema but no local myonecrosis or hemorrhage. It did not induce any microvascular alteration in the cremaster muscle. Intramuscular injection of BjussuSP-I promoted an increase in the expression of proMMP-9, but it did not induce the activation of proMMP-2 or proMMP-9 synthesized in muscle tissue injected with a myotoxic phospholipase A(2) homolog. BjussuSP-I induced defibrin(ogen)ation upon intravenous and intramuscular injections, with reduction in plasma fibrinogen concentration and increments in the levels of fibrin degradation products and D-dimer. When compared with animals having normal coagulation, mice defibrin(ogen)ated by BjussuSP-I developed a slightly larger hemorrhagic lesion in the skin when injected with metalloproteinase BaP1. Intravenous injection of sublethal doses of BjussuSP-I promoted a series of behavioral and motor changes similar to those previously described for 'gyroxin', i.e. opisthotonus and a circular body movement along the longitudinal axis.

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

Zinc-dependent metalloproteinases are responsible for the hemorrhagic activity characteristic of viperid snake venoms. Snake venom metalloproteinases (SVMPs) are classified in various groups (P-I-IV), according to their domain composition. P-III SVMPs, comprising metalloproteinase, disintegrin-like and cysteine-rich domains, exert more potent hemorrhagic activity than P-I SVMPs, which present only the metalloproteinase domain. SVMPs degrade various components of the basement membrane and are also able to hydrolyze endothelial cell membrane proteins, such as integrins and cadherins, involved in cell-matrix and cell-cell adhesion. In addition, disintegrin-like and cysteine-rich domains interact with endothelial cell integrins, interfering with their adhesion to extracellular matrix. Hemorrhage induced by SVMPs is an extremely rapid event in vivo, with capillary endothelial cells showing drastic structural alterations within few minutes. In contrast, observations in cell culture conditions do not evidence such rapid endothelial cell damage. Instead, the main effect is detachment and rounding of these cells; it is only after several hours of incubation that cells show evidence of apoptotic damage. This apparent discrepancy between in vivo and in vitro observations can be explained if biophysical forces operating on microvessels in vivo are taken into consideration. It is proposed that SVMP-induced hemorrhage occurs in vivo by a 'two-step' mechanism. Initially, SVMPs degrade basement membrane and adhesion proteins, thus weakening the capillary wall and perturbing the interactions between endothelial cells and the basement membrane. Then, transmural pressure acting on the weakened capillary wall causes distention. As a consequence, endothelial cells become very thin, until the integrity of the capillary wall is lost at some points, where extravasation occurs. In addition, endothelial cells become more susceptible to blood flow-dependent shear stress, which further contributes to capillary wall disruption.

Role of TNF-α, IL-1β and IL-6 in the local tissue damage induced by Bothrops asper snake venom: an experimental assessment in mice

The role of the cytokines TNF-alpha, IL-1beta and IL-6 in the acute local pathological effects induced by Bothrops asper snake venom was assessed in mice. Intramuscular injection of this venom induced increments in IL-1beta and IL-6 in muscle, but no elevations of TNF-alpha were detected. Pentoxifylline (PTX), a methylxanthine derivative that inhibits the synthesis of TNF-alpha, and antibodies against these three cytokines were used to assess the role of these cytokines in venom-induced effects. As a control, PTX pretreatment was effective at abrogating lethality and serum TNF-alpha increments in mice subjected to endotoxemia induced by injection of Escherichia coli lipopolysaccharide, although it did not affect the increment in IL-1beta and IL-6 in such endotoxic model. PTX failed to reduce lethality, hemorrhage, myonecrosis, dermonecrosis and edema induced by B. asper venom. Moreover, pretreatment with anti-cytokine antibodies was also ineffective at reducing venom-induced myonecrosis and hemorrhage. It is concluded that TNF-alpha, IL-1beta and IL-6 do not have a significant role in the pathogenesis of the acute local pathological effects induced by B. asper venom in mice, although this does not exclude the possibility that these cytokines play a role in other aspects of venom-induced local pathology, as well as in the reparative and regenerative responses that take place after the onset of tissue damage.

Feeding behavior and venom toxicity of coral snake Micrurus nigrocinctus (Serpentes: Elapidae) on its natural prey in captivity

The feeding behavior and venom toxicity of the coral snake Micrurus nigrocinctus (Serpentes: Elapidae) on its natural prey in captivity were investigated. Coral snakes searched for their prey (the colubrid snake Geophis godmani) in the cages. Once their preys were located, coral snakes stroke them with a rapid forward movement, biting predominantly in the anterior region of the body. In order to assess the role of venom in prey restraint and ingestion, a group of coral snakes was 'milked' in order to drastically reduce the venom content in their glands. Significant differences were observed between snakes with venom, i.e., 'nonmilked' snakes, and 'milked' snakes regarding their behavior after the bite. The former remained hold to the prey until paralysis was achieved, whereas the latter, in the absence of paralysis, moved their head towards the head of the prey and bit the skull to achieve prey immobilization by mechanical means. There were no significant differences in the time of ingestion between these two groups of coral snakes. Susceptibility to the lethal effect of coral snake venom greatly differed in four colubrid species; G. godmani showed the highest susceptibility, followed by Geophis brachycephalus, whereas Ninia psephota and Ninia maculata were highly resistant to this venom. In addition, the blood serum of N. maculata, but not that of G. brachycephalus, prolonged the time of death of mice injected with 2 LD(50)s of M. nigrocinctus venom, when venom and blood serum were incubated before testing. Subcutaneous injection of coral snake venom in G. godmani induced neurotoxicity and myotoxicity, without causing hemorrhage and without affecting heart and lungs. It is concluded that (a) M. nigrocinctus venom plays a role in prey immobilization, (b) venom induces neurotoxic and myotoxic effects in colubrid snakes which comprise part of their natural prey, and (c) some colubrid snakes of the genus Ninia present a conspicuous resistance to the toxic action of M. nigrocinctus venom.

Effect of the metalloproteinase inhibitor batimastat in the systemic toxicity induced by Bothrops asper snake venom: understanding the role of metalloproteinases in envenomation

The peptidomimetic hydroxamate metalloproteinase inhibitor batimastat (BB-94) was assessed for its ability to neutralize the systemic effects (lethality, hemorrhage and coagulopathy) induced by the venom of Bothrops asper, the most important snake from a medical standpoint in Central America. Batimastat inhibited lethality when a venom challenge dose of two LD(50)s was used by intraperitoneal and intravenous routes, with ED(50)s of 250 and 22 microM, respectively. With a challenge dose of three LD(50)s, lethality was not abrogated, but a conspicuous and dose-dependent delay in the time of death was observed in mice injected with mixtures of venom plus batimastat. Upon incubation with 500 microM batimastat, venom LD(50) increased 2.86-fold (intraperitoneal route) and 2.37-fold (intravenous route), when compared with LD(50) of venom alone. Batimastat also inhibited the hemorrhagic effect induced by venom in the lungs after intravenous injection. Moreover, batimastat exerted a significant inhibition of in vitro coagulant and in vivo defibrinogenating effects of venom, evidencing that metalloproteinases play a key role in the coagulopathy characteristic of B. asper envenomation. The remaining uninhibited coagulant effect is due to serine proteinases, i.e. thrombin-like enzymes, since this effect was completely abrogated by the combination of batimastat and PMSF. Our results stress the view that metalloproteinases play a relevant role in the systemic pathophysiology of B. asper envenomation and that metalloproteinase inhibitors may become a therapeutic alternative in this pathology.

Pharmacokinetic-pharmacodynamic relationships of immunoglobulin therapy for envenomation

Parenteral administration of horse- and sheep-derived antivenoms constitutes the cornerstone in the therapy of envenomations induced by animal bites and stings. Depending on the type of neutralising molecule, antivenoms are made of: (i) whole IgG molecules (150 kDa), (ii) F(ab')(2) immunoglobulin fragments (100 kDa) or (iii) Fab immunoglobulin fragments (50 kDa). Because of their variable molecular mass, these three types of antivenoms have different pharmacokinetic profiles. Fab fragments have the largest volume of distribution and readily reach extravascular compartments. They are catabolised mainly by the kidney, having a more rapid clearance than F(ab')(2) fragments and IgG. On the other hand, IgG molecules have a lower volume of distribution and a longer elimination half-life, showing the highest cycling through the interstitial spaces in the body. IgG elimination occurs mainly by extrarenal mechanisms. F(ab')(2) fragments display a pharmacokinetic profile intermediate between those of Fab fragments and IgG molecules. Such diverse pharmacokinetic properties have implications for the pharmacodynamics of these immunobiologicals, since a pronounced mismatch has been described between the pharmacokinetics of venoms and antivenoms. Some venoms, such as those of scorpions and elapid snakes, are rich in low-molecular-mass neurotoxins of high diffusibility and large volume of distribution that reach their tissue targets rapidly after injection. In contrast, venoms rich in high-molecular-mass toxins, such as those of viperid snakes, have a pharmacokinetic profile characterised by a rapid initial absorption followed by a slow absorption process from the site of venom injection. Such delayed absorption has been linked with recurrence of envenomation when antibody levels in blood decrease. This heterogeneity in pharmacokinetics and mechanism of action of venom components requires a detailed analysis of each venom-antivenom system in order to determine the most appropriate type of neutralising molecule for each particular venom. Besides having a high affinity for toxicologically relevant venom components, an ideal antivenom should possess a volume of distribution as similar as possible to that of the toxins being neutralised. Moreover, high levels of neutralising antibodies should remain in blood for a relatively prolonged time to assure neutralisation of toxins reaching the bloodstream later in the course of envenomation, and to promote redistribution of toxins from extravascular compartments to blood. Additional studies are required on different venoms and antivenoms in order to further understand the pharmacokinetic-pharmacodynamic relationships of antibodies and their fragments and to optimise the immunotherapy of envenomations.

Fatores associados à incoagulabilidade sangüínea no envenenamento por serpentes do gênero Bothrops

Com o objetivo de conhecer fatores associados à incoagulabilidade sangüínea no envenenamento botrópico, foram obtidas informações de 2.991 prontuários médicos de pacientes atendidos no Instituto Butantan de 1981 a 1990. Associaram-se positivamente à incoagulabilidade sangüínea (p<0,05): picadas no final do ano e em extremidades dos membros inferiores; dor, edema e equimose local; hemorragia e choque; dose de antiveneno; tempo do acidente à chegada ao Instituto Butantan. Associaram-se negativamente à incoagulabilidade (p<0,05): tamanho de Bothrops jararaca; uso de torniquete; tempo entre a chegada ao Instituto Butantan e o início da administração do antiveneno. Não se associaram à incoagulabilidade (p>0,05): horário do acidente; presença de presa recém-deglutida no tubo digestivo da serpente; sexo e idade do paciente; ocorrência de bolha, necrose, abscesso e incisão local, amputação, insuficiência renal e óbito. Pode-se concluir que, embora a incoagulabilidade sangüínea apresente associação com manifestações precoces do envenenamento, não tem boa associação com a evolução clínica do paciente.

Neutrophils do not contribute to local tissue damage, but play a key role in skeletal muscle regeneration, in mice injected withBothrops aspersnake venom

Local tissue damage induced by crotaline snake venoms includes edema, myonecrosis, hemorrhage, and an inflammatory response associated with a prominent cellular infiltrate. The role of neutrophils in the local tissue damage induced by Bothrops asper snake venom and by myotoxin I, a phospholipase A2 isolated from this venom, was investigated. Male Swiss mice were pretreated with either an antimouse granulocyte rat monoclonal immunoglobulin G (IgG) antibody or with isotype-matched control antibody. No significant differences in these local effects were observed between mice pretreated with antigranulocyte antibodies and those receiving control IgG. Moreover, myotoxicity induced by B. asper myotoxin I was similar in neutrophil-depleted and control mice. The role of neutrophils in the process of skeletal muscle regeneration was also assessed. Muscle regeneration was assessed by quantifying the muscle levels of creatine kinase and by morphometric histological analysis of the area comprised by regenerating cells in damaged regions of skeletal muscle. Mice depleted of neutrophils and then injected with B. asper venom showed a more deficient regenerative response than mice pretreated with control IgG. Moreover, a drastic difference in the regenerative response was observed in mice injected with myotoxin I, because animals pretreated with control IgG showed a successful regeneration, whereas those depleted of neutrophils had abundant areas of necrotic tissue that had not been removed 7 days after injection, associated with reduced contents of creatine kinase. It is concluded that (1) neutrophils do not play a significant role in the acute local pathological alterations induced by the venom of B. asper, and (2) neutrophils play a prominent role in the process of skeletal muscle regeneration after injection of B. asper venom and myotoxin I, probably related to the phagocytosis of necrotic material and the recruitment of other inflammatory cells, two events directly associated with a successful muscle regenerative response.

Intramuscular administration of antivenoms in experimental envenomation by Bothrops asper: comparison between Fab and IgG

The efficacy of intramuscular (im) administration of sheep Fab and IgG antivenoms was assessed in a mouse experimental model of envenomation by Bothrops asper, in order to test if the more rapid absorption of Fab improves neutralization. Both antivenoms were adjusted to have a similar neutralizing potency in assays involving preincubation of venom and antivenom. Neither antivenom was effective in neutralizing lethality, nor in prolonging the time of death, in mice injected with either 3, 2 or 1.5 LD(50)s of venom by the intraperitoneal (ip) route, in experiments in which antivenoms were administered im immediately after envenomation. Antivenoms were effective in the neutralization of defibrinating activity, even if treatment was performed 30 min after envenomation, with no differences between IgG and Fab. Regarding neutralization of local effects, i.e. myonecrosis and hemorrhage, im administration of antivenoms at a site distant from the venom-injection site was completely ineffective in reducing the extent of local tissue damage. However, partial neutralization of these effects was achieved if antivenoms were administered im at the same site of venom injection, provided treatment was performed immediately after envenomation. Fab antivenom was slightly more effective than IgG antivenom in the neutralization of myotoxicity under these conditions, although a similar efficacy was observed between these antivenoms regarding neutralization of hemorrhagic effect. Our observations do not evidence major differences in the neutralizing ability of Fab and IgG antivenoms when applied by the im route, and do not support the hypothesis that im administration of Fab antivenoms constitutes an effective alternative to treat B. asper envenomations.

Increments in cytokines and matrix metalloproteinases in skeletal muscle after injection of tissue-damaging toxins from the venom of the snake Bothrops asper

Envenomations by the snake Bothrops asper are characterized by prominent local tissue damage (i.e. myonecrosis), blistering, hemorrhage and edema. Various phospholipases A2 and metalloproteinases that induce local pathological alterations have been purified from this venom. Since these toxins induce a conspicuous inflammatory response, it has been hypothesized that inflammatory mediators may contribute to the local pathological alterations described. This study evaluated the local production of cytokines and matrix metalloproteinases (MMPs) as a consequence of intramuscular injections of an Asp-49 myotoxic phospholipase A2 (myotoxin III (MT-III)) and a P-I type hemorrhagic metalloproteinase (BaP1) isolated from B. asper venom. Both enzymes induced prominent tissue alterations and conspicuous increments in interleukin (IL)-1beta, IL-6 and a number of MMPs, especially gelatinase MMP-9, rapidly after injection. In contrast, no increments in tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma were detected. In agreement, MT-III and BaP1 did not induce the synthesis of TNF-alpha by resident peritoneal macrophages in vitro. Despite the conspicuous expression of latent forms of MMPs in muscle, evidenced by zymography, there were no increments in activated MMP-2 and only a small increase in activated MMP-9, as detected by a functional enzymatic assay. This suggests that MMP activity was regulated by a highly controlled activation of latent forms and, probably, by a concomitant synthesis of MMP inhibitors. Since no hemorrhage nor dermonecrosis were observed after injection of MT-III, despite a prominent increase in MMP expression, and since inflammatory exudate did not enhance hemorrhage induced by BaP1, it is suggested that endogenous MMPs released in the tissue are not responsible for the dermonecrosis and hemorrhage characteristic of B. asper envenomation. Moreover, pretreatment of mice with the peptidomimetic MMP inhibitor batimastat did not reduce myotoxic nor edema-forming activities of MT-III, suggesting that MMPs do not play a prominent role in the pathogenesis of these effects in this experimental model. It is concluded that MT-III and BaP1 induce a local inflammatory response associated with the synthesis of IL-1beta, IL-6 and MMPs. MMPs do not seem to play a prominent role in the acute local pathological alterations induced by these toxins in this experimental model.

Comparison between IgG and F(ab')(2) polyvalent antivenoms: neutralization of systemic effects induced by Bothrops asper venom in mice, extravasation to muscle tissue, and potential for induction of adverse reactions

Whole IgG and F(ab')(2) equine-derived polyvalent (Crotalinae) antivenoms, prepared from the same batch of hyperimmune plasma, were compared in terms of neutralization of the lethal and defibrinating activities induced by Bothrops asper venom, their ability to reach the muscle tissue compartment in envenomated mice, and their potential for the induction of adverse reactions. Both preparations were adjusted to the same potency against the lethal effect of B. asper venom in experiments involving preincubation of venom and antivenom. Then, "rescue" experiments were performed, i.e. antivenom was administered either intravenously or intramuscularly at various times after envenomation. IgG and F(ab')(2) antivenoms were equally effective in the neutralization of lethality, both being more effective when administered i.v. than after i.m. injection. Neutralization decreased as the time lapse between envenomation and treatment increased. No significant differences were observed in the ability of antivenoms to neutralize defibrinating activity of B. asper venom in experiments involving independent injection of venom and antivenoms. There was a much higher accumulation of equine antibodies in muscle tissue that had been injected with B. asper venom than in non-envenomated tissue, indicating that venom-induced microvessel damage probably favors a prominent and similar extravasation of both IgG and F(ab')(2) antibodies. This may explain the similar effectiveness of both types of antivenom in previously reported studies on the neutralization of venom-induced local tissue damage. Both IgG and F(ab')(2) antivenoms activate human complement in vitro and induce an anti-equine immunoglobulin response in mice, indicating that Fc removal per se does not eliminate the potential for inducing adverse reactions. However, IgG antivenom had higher anticomplementary activity and induced a stronger anti-immunoglobulin response than F(ab')(2) antivenom.

Skeletal muscle necrosis and regeneration after injection of Thalassophryne nattereri (niquim) fish venom in mice

Stings by Thalassophryne nattereri are responsible for envenomation of fishermen in north-eastern Brazil. Its venom induces prominent local tissue damage, characterized by pain, oedema and necrosis. The pathogenesis of acute muscle damage induced by T. nattereri venom was studied in mice. Intramuscular injection induced myonecrosis within the first hours. Some muscle cells presented a hypercontracted morphology, but most necrotic fibres were not hypercontracted, being instead characterized by a disorganization of myofibrils, with Z line loss, mitochondrial swelling and sarcolemmal disruption. In addition, thrombosis was observed histologically in venules and veins, together with vascular congestion and stasis, evidenced by intravital microscopy. Venom induced a rapid increment in serum creatine kinase (CK) levels, concomitant with a reduction in gastrocnemius muscle CK activity, whereas no increments in muscle lactic acid were detected. A rapid cytolytic effect was induced by the venom on C2C12 murine myoblasts in culture. The inflammatory reaction in affected muscle was characterized by oedema and scarce cellular infiltrate of polymorphonuclear leucocytes and macrophages, with a consequent delay in the removal of necrotic material. Skeletal muscle regeneration was partially impaired, as evidenced by the presence of regenerating fibres of variable size and by the increase of fibrotic tissue in endomysium and perimysium. It is suggested that T. nattereri venom affects muscle fibres by a direct cytotoxic effect, and that the vascular alterations described preclude a successful regenerative process.

Snake venom metalloproteinases: their role in the pathogenesis of local tissue damage

The biochemical characteristics of hemorrhagic metalloproteinases isolated from snake venoms are reviewed, together with their role in the pathogenesis of the local tissue damage characteristic of crotaline and viperine snake envenomations. Venom metalloproteinases differ in their domain structure. Some enzymes comprise only the metalloproteinase domain, others have disintegrin-like and high cysteine domains and others present, besides these domains, an additional lectin-like subunit. All of them are zinc-dependent enzymes with highly similar zinc binding environments. Some metalloproteinases induce hemorrhage by directly affecting mostly capillary blood vessels. It is suggested that hemorrhagic enzymes cleave, in a highly selective fashion, key peptide bonds of basement membrane components, thereby affecting the interaction between basement membrane and endothelial cells. As a consequence, these cells undergo a series of morphological and functional alterations in vivo, probably associated with biophysical hemodynamic factors such as tangential fluid shear stress. Eventually, gaps are formed in endothelial cells through which extravasation occurs. In addition to hemorrhage, venom metalloproteinases induce skeletal muscle damage, myonecrosis, which seems to be secondary to the ischemia that ensues in muscle tissue as a consequence of bleeding and reduced perfusion. Microvessel disruption by metalloproteinases also impairs skeletal muscle regeneration, being therefore responsible of fibrosis and permanent tissue loss after snakebites. Moreover, venom metalloproteinases participate in the degradation of extracellular matrix components and play a relevant role in the prominent local inflammatory response that characterizes snakebite envenomations, since they induce edema, activate endogenous matrix metalloproteinases (MMPs) and are capable of releasing TNF-alpha from its membrane-bound precursor. Owing to their protagonic role in the pathogenesis of local tissue damage, snake venom metalloproteinases constitute relevant targets for natural and synthetic inhibitors which may complement antivenoms in the neutralization of these effects.

Effectiveness of batimastat, a synthetic inhibitor of matrix metalloproteinases, in neutralizing local tissue damage induced by BaP1, a hemorrhagic metalloproteinase from the venom of the snake bothrops asper

Batimastat (BB-94), a synthetic hydroxamate peptidomimetic matrix metalloproteinase inhibitor, was tested for its ability to inhibit proteolytic and toxic effects induced by BaP1, a 24-kDa hemorrhagic metalloproteinase isolated from the venom of Bothrops asper, the medically most important snake species in Central America and southern Mexico. Batimastat inhibited proteolytic activity on biotinylated casein, with anIC(50) of 80 nM. In addition, batimastat was effective in inhibiting hemorrhagic, dermonecrotic, and edema-forming activities of this metalloproteinase if incubated with the enzyme prior to the assays. When the inhibitor was administered i.m. at the site of the toxin injection without preincubation, rapidly after metalloproteinase administration, it totally abrogated the hemorrhagic and dermonecrotic effects of BaP1. Inhibition was less effective as the time lapse between toxin and batimastat injection increased, due to the extremely rapid development of BaP1-induced local tissue damage in this experimental model. On the other hand, batimastat was ineffective if administered by the i.p. route immediately after toxin injection. It is concluded that batimastat, and probably other synthetic metalloproteinase inhibitors, may become useful therapeutic tools aimed at the in situ inhibition of venom metalloproteinases, when injected at the site of the bite rapidly after envenomation.

Comparative study on the ability of IgG and Fab sheep antivenoms to neutralize local hemorrhage, edema and myonecrosis induced by Bothrops asper (terciopelo) snake venom

The ability of sheep antivenoms, consisting of whole IgG molecules or Fab fragments, to neutralize local hemorrhage, edema and myonecrosis induced by Bothrops asper venom was comparatively studied in mice. The two antivenoms were produced from the same batch of hyperimmune plasma and were adjusted to the same neutralizing potency against these effects in assays where venom and antivenoms were incubated prior to injection. Thus, if differences are observed in experiments involving independent injection of venom and antivenoms, they would depend on the pharmacokinetic profiles of the products. Despite the observation that both antivenoms neutralized the three effects if preincubated with venom, neutralization was only partial when antivenoms were administered i.v. at various time intervals after envenomation. No significant differences were observed between IgG and Fab antivenoms concerning neutralization of hemorrhagic and edema-forming activities, whereas IgG antivenom was slightly more effective in neutralizing myotoxic activity in experiments involving independent injection of venom and antivenom. These results do not support the hypothesis that Fab fragments are more effective than whole IgG molecules in the neutralization of locally-acting toxins from B. asper venom.

Local haemorrhage induced by Bothrops jararaca venom: relationship to neurogenic inflammation

We investigated morphological alterations induced by s.c. injection of 2.5 microg of Bothrops jararaca venom in rats. Intense disorganisation of collagen fibres was observed 1 min after the venom injection, particularly at regions near vessels and nerves. Mast cells were degranulated, and erythrocytes were seen leaving venules throughout the endothelial junctions. At this time, damaged endothelial cells were not observed. In rats envenomed as above, but immediately after cardiorespiratory failure induced by deep ether anaesthesia, alterations in the connective tissue structures, as previously described, were not observed. The mediation of this haemorrhage was investigated by injecting the venom into the foot pad of mice and compared to the mediation of oedema. Local haemorrhage was significantly reduced in mice pre-treated with capsaicin or guanethidine or submitted to a surgical section of sciatic and saphenous nerves. In these animals, oedema was not affected. Groups treated with methysergide or morphine showed both haemorrhage and oedema significantly reduced. Indomethacin or dexamethasone pre-treatments significantly reduced the oedema, but not the haemorrhage. Moreover, in animals treated with promethazine or mepyramine, oedema and haemorrhage were not affected. These data suggest that local haemorrhage induced by Bothrops jararaca venom is partially controlled by serotonin and neurohumoral mediators. Furthermore, results indicate that haemorrhage and oedema are mediated by different pharmacological systems.

Purification and characterization of BaH4, a hemorrhagic metalloproteinase from the venom of the snake Bothrops asper

A hemorrhagic metalloproteinase, named BaH4, was isolated from the venom of the snake Bothrops asper by a combination of ion-exchange chromatography on DEAE-Sepharose and gel filtration on Sephacryl S-200. BaH4 is a 69 kDa protein with a pI of 5.3. It was recognized by antibodies raised against hemorrhagic metalloproteinase BaH1 isolated from B. asper venom, with a reaction of partial immunologic identity. BaH4 shows proteolytic activity on biotinylated casein, hide powder azure and fibrin, although having lower activity than crude B. asper venom and metalloproteinase BaP1 isolated from the same venom. BaH4 hydrolyzed fibronectin, laminin and type IV collagen in vitro, albeit at a relatively high enzyme:substrate ratio. Proteolytic activity was inhibited by chelating agents and 2-mercaptoethanol, but not by soybean trypsin inhibitor. Prominent hemorrhage developed in gastrocnemius and cremaster muscles after administration of BaH4. Moreover, it induced lethality in mice after intravenous injection, with an LD50 of 0.37 microg/g. Histological observations showed conspicuous pulmonary hemorrhage when the enzyme was injected intravenously. BaH4 is a hemorrhagic metalloproteinase which may play a relevant role in local and systemic bleeding characteristic of B. asper envenomations.

Comparative study of the venoms of three subspecies of Lachesis muta (bushmaster) from Brazil, Colombia and Costa Rica

A comparative study was performed on the pharmacology and biochemistry of venoms from three subspecies of Lachesis muta (L. m. stenophrys, L. m. muta and L. m. rhombeata) from Brazil, Colombia and Costa Rica. All venoms induced lethal, hemorrhagic, edema-forming, myotoxic, coagulant and defibrinating effects, showing also proteolytic and indirect hemolytic activities. The venoms of L. m. stenophrys from Costa Rica and L. m. muta from Cascalheira, Brazil, had the highest lethal and hemorrhagic activities and the venom of L. m. rhombeata showed the highest coagulant activity, whereas no significant differences were observed in myotoxic and edema-forming activities at most of the time intervals studied. In addition, venoms showed similar electrophoretic patterns on SDS-polyacrylamide gel electrophoresis. In conclusion, despite quantitative differences in toxic and enzymatic activities, together with subtle variations in electrophoretic patterns, our results indicate that experimental envenomation by these venoms induce a qualitatively similar pathophysiological profile.

Neutralization of local tissue damage induced by Bothrops asper (terciopelo) snake venom

Local tissue damage represents a serious consequence of Bothrops asper envenomations. It encompasses a complex series of alterations, including myonecrosis, dermonecrosis, hemorrhage and edema. Due to its rapid development it is difficult to neutralize by antivenoms, especially if there is a delay in serotherapy. Experimental studies with this venom and the polyvalent (Crotalinae) antivenom produced in Costa Rica indicate that antivenom is effective in neutralizing these toxic activities when incubated with the venom prior to injection. However, if venom and antivenom are injected independently in mice, neutralization of these effects is only partial. Moreover, neutralization is not complete even if homologous or heterologous antibodies are present in the circulation before venom is injected. Despite differences in their pharmacokinetic profiles, equine whole IgG and F(ab')2 antivenoms show similar efficacy in the neutralization of edema, hemorrhage and myonecrosis induced by B. asper venom, suggesting that the use of antivenoms made of antibody fragments may not improve neutralization of these effects. This is due, at least in part, to the fact that microvessel disruption by venom components favors a similar antibody concentration in the affected tissues. Recent advances in the development of neutralizing substances of rapid diffusion, that could be injected locally in the field, may contribute to the neutralization of metalloproteinases and phospholipases A2. In addition, the rapid administration of antivenoms with high antibody titers against locally-acting toxins is very important in the treatment of these effects.

Inhibition by CaNa2EDTA of local tissue damage induced by Bothrops asper (terciopelo) venom: application in horse immunization for antivenom production

The ability of the chelating agent CaNa2EDTA to inhibit local tissue damage induced by Bothrops asper venom was studied in mice and in horses used for polyvalent (Crotalinae) antivenom production. CaNa2EDTA was devoid of toxicity when injected i.m. or s.c. inducing only a mild edema. Preincubation of B. asper venom with CaNa2EDTA inhibited hemorrhagic and dermonecrotic activities, but did not reduce edema-forming and myotoxic effects. A group of horses initially immunized with native venoms developed less severe local tissue reactions when injected with booster doses of venom and CaNa2EDTA than when receiving booster injections of venom alone, although they showed a similar antivenom response. Moreover, antivenoms produced from plasmas of horses that received booster injections of either venom alone or venom plus CaNa2EDTA had similar neutralizing activity against lethal, hemorrhagic and coagulant effects induced by B. asper venom. The similar antibody response was corroborated by Western blotting using crude venom and by an ELISA that estimates anti-myotoxin titer. It is concluded that the chelating agent CaNa2EDTA reduces the extent of local tissue damage induced by B. asper venom, without affecting the immune response of horses against pharmacologically-relevant venom components.

Immunoglobulin G and F(ab')2 polyvalent antivenoms do not differ in their ability to neutralize hemorrhage, edema and myonecrosis induced by Bothrops asper (terciopelo) snake venom

The ability of whole immunoglobulin G (IgG) and F(ab')2 polyvalent (Crotalinae) antivenoms to neutralize the hemorrhagic, edema-forming and myotoxic activities of Bothrops asper venom was studied. Both antivenoms were adjusted to the same neutralizing potency against lethal and hemorrhagic activities in experiments where venom and antivenoms were incubated before injection. Thus, in these experimental conditions, differences in the neutralizing ability in experiments involving independent injection of venom and antivenoms would depend mainly on the different pharmacokinetic profiles of whole IgG and F(ab')2 antivenoms. Experiments involving local injection of venom followed by intravenous administration of antivenom at either 0, 15 or 30 min after envenomation did not reveal any significant difference between whole IgG and F(ab')2 products concerning neutralization of hemorrhage, edema and myonecrosis induced by B. asper venom. The three effects were neutralized by antivenoms only to a partial extent and neutralization decreased as the time-lapse between envenomation and antivenom administration increased. Moreover, with the exception of one time-interval, no significant differences in the neutralization of hemorrhage were observed when antivenom was administered by the intramuscular or intraperitoneal route. The results do not support the assumption that F(ab')2 antivenom is more effective than whole IgG antivenom in the neutralization of local hemorrhage, edema and myonecrosis induced by B. asper venom in mice.

Snakes and snakebite in Central America

This review treats the general biology, taxonomy, distribution and venom apparatus of the venomous snakes of Central America. Consideration has been given to the chemistry, pharmacology and immunology of the venom, and particular attention is dispensed to the clinical problem, including the treatment, of envenomations by these reptiles.

Inhibition of the hemorrhagic activity of Bothrops asper venom by a novel neutralizing mixture

This study screened 25 sera, 19 synthetic products and five antivenoms obtained after immunization for their ability to neutralize the hemorrhagic activity of venom from the snake Bothrops asper. Among the sera screened, the homologous serum of B. asper itself was found to possess the highest neutralizing capacity, abolishing the hemorrhagic effect of the venom at weight ratio of 3:1. It was more efficient than the antisera obtained by immunization. Among the synthetic compounds tested, only O-phenanthroline and EDTA salts inhibited the hemorrhagic activity at concentrations of 0.5-10 mM; however, only CaNa2EDTA was non-toxic at the concentrations studied. Intravenous injections and in situ administration of the non-toxic inhibitors revealed that a fraction of B. asper serum, the horse polyvalent antivenom and CaNa2EDTA were the most potent antihemorrhagic materials against B. asper venom, especially when administered in situ as a mixture. This work suggests that this neutralizing mixture could be highly useful in the neutralization of local and systemic hemorrhage developing after B. asper envenomation.

Isolation, characterization and mode of neutralization of a potent antihemorrhagic factor from the serum of the snake Bothrops asper

A potent antihemorrhagic factor (BaSAH1) was isolated from the serum of the snake Bothrops asper by ammonium sulfate precipitation at 40-60%, Sephacryl S-200 and Sephadex G-50 gel filtration, DEAE-Sepharose, and hydrophobic Phenyl-Sepharose chromatography. The purified protein showed one band with an isoelectric point of 5.2 and a molecular weight of 66 kDa. 4 micrograms of the purified factor BaSAH were needed to neutralize the hemorrhagic dose of B. asper whole venom compared to 60 micrograms of the clinically used horse polyvalent immunoglobulins. Moreover, 0.35 microgram of BaSAH were sufficient to achieve complete neutralization of the main hemorrhagic toxin (BaH1), with a molar ratio of 2:1. The antihemorrhagic activity was stable between pH 1.5-9 and up to 60 degrees C but lost activity completely after 30 min of heating at 70 degrees C. BaSAH did not digest the hemorrhagic toxin BaH1 or formed a precipitin line with it, nor with the whole venom. Both ELISA experiments and chromatography of BaSAH after incubation with the 125I-labeled hemorrhagic toxin BaH1 demonstrated that the mechanism of the neutralization involves a formation of an inactive soluble complex between the natural antihemorrhagin and the main hemorrhagin of B. asper venom.

In vitro activity of BaH1, the main hemorrhagic toxin of Bothrops asper snake venom on bovine endothelial cells

Incubation of BaH1, the main hemorrhagic toxin purified from the venom of Bothrops asper, with endothelial cells caused the appearance of spaces among the cells. This effect became more noticeable with increasing hemorrhagin concentration and longer incubation time. Later, the cells became rounded and detached from the substrate into the medium. Augmentation of Trypan blue did not stain the detached cells, indicating their viability. Moreover, after washing the floating cells from the toxin they could be recultivated: they again spread on the substrate and proliferated, demonstrating that BaHl is not directly cytotoxic to the endothelial cells.

A potent antihemorrhagin in the serum of the non-poisonous water snake Natrix tessellata: isolation, characterization and mechanism of neutralization

The main natural antihemorrhagic factor (NtAH), which inhibits the hemorrhagic activity of Bothrops asper snake venom, was isolated from the serum of the non-poisonous water snake Natrix tessellata by ammonium sulfate precipitation at 35-55%, Sephadex G-75 gel filtration, ion exchange chromatography on DEAE-Sepharose and CM-Sepharose and hydrophobic Phenyl-Sepharose chromatography. The purified protein showed one band with an isoelectric point of 4.5 and a molecular mass of about 880 kDa. The antihemorrhagic activity was stable between pH 5.5-11.7 and up to 50 degrees C, but lost activity after 20 min at 60 degrees C. It did not form a precipitin line with the main hemorrhagin of Bothrops asper snake venom (BaH1), nor with the whole venom, which suggests that the antihemorrhagic factor is not an immunoglobulin. The mechanism of neutralization by the isolated antihemorrhagic factor NtAH did not include digestion of the hemorrhagic toxin BaH1. Chromatography of NtAH with active 125I-labeled BaH1 toxin as well as ELISA experiments demonstrated that the mechanism of neutralization involves formation of an inactive soluble complex between the natural NtAH of the non-poisonous water snake and the main hemorrhagin of Bothrops asper venom.

Effect of various Viperidae and Crotalidae snake venoms on endothelial cells in vitro

The effect of various crotalid and viperid venoms at 10, 50 and 100 micrograms/ml was examined on bovine and murine endothelial cells in vitro. The venoms caused the cells to lose their processes, leading to the appearance of spaces which were gradually enlarged between clusters of cells. The cells became round and finally detached from the substrate. This effect was more pronounced on bovine normal cells than on murine transformed cells. Most of the venoms did not affect the viability of the cells even after 24 hr of incubation, as determined by the trypan blue dye exclusion procedure. Moreover, after the cells were washed from the venoms and transferred into fresh medium, they regained their original morphology after spreading on the substrate and they then proliferated normally. This reversible effect shows that most of the crotalid and viperid venoms examined were not directly cytotoxic to the endothelial cells at the concentrations tested.

Pathological changes induced by BaH1, a hemorrhagic proteinase isolated from Bothrops asper (Terciopelo) snake venom, on mouse capillary blood vessels

The pathological changes induced in capillaries by BaH1, a hemorrhagic metalloproteinase isolated from the venom of Bothrops asper, were studied after i.m. injection in mouse gastrocnemius. Hemorrhage was observed macroscopically, and corroborated histologically, within the first 5 min. At the ultrastructural level, the earliest changes in endothelial cells, observed 1 min after toxin administration, consisted of a decrease in the number of pinocytotic vesicles, the presence of blebs and cytoplasmic projections pinching off to the vascular lumen and the detachment of endothelial cells from the surrounding basal lamina. These processes occurred concomitantly with a thinning of endothelial cells. In capillaries undergoing more advanced degenerative stages, there were gaps or breaks in endothelial cells through which erythrocytes were escaping to the extravascular space. In these cells, the basal lamina was usually absent. Throughout this process, intercellular junctions remained apparently intact and no evidence was found of extravasation through widened intercellular junctions. In addition to this morphological pattern of degeneration, some capillaries presented swollen endothelial cells with dilated endoplasmic reticulum and lacking pinocytotic vesicles. Many capillaries contained platelet plugs and fibrin. Thus, hemorrhage induced by BaH1 occurs per rhexis, as has been also described for other venoms and hemorrhagic toxins.

Activity of hemorrhagic metalloproteinase BaH-1 and myotoxin II from Bothrops asper snake venom on capillary endothelial cells in vitro

In vivo, hemorrhagic toxins isolated from snake venoms cause a disorganization of the basal lamina of capillaries, with a concomitant degenerative process of endothelial cells. In this study we investigated the effects of BaH-1, a hemorrhagic metalloproteinase purified from the venom of Bothrops asper, on a murine endothelial cell line of capillary origin. A quantitative cytotoxicity assay based on the release of lactic dehydrogenase was utilized. BaH-1, despite its potent hemorrhagic activity, did not exert direct cytolytic activity on the endothelial cells, even at concentrations as high as 65 micrograms/ml. The only visible effect of BaH-1 on the cultured cells was a relatively slow, moderate detachment of cells, interpreted as a consequence of proteolytic degradation of extracellular matrix components. In contrast, myotoxin II, a lysine-49 phospholipase A2 from the same venom, was clearly cytotoxic to this cell type, albeit being devoid of hemorrhagic activity. These findings suggest that the ability of venom metalloproteinases to induce hemorrhage is not related to a direct cytotoxic action on endothelial cells, and that the rapid degenerative changes of endothelium observed in vivo are probably the result of an indirect mechanism.

The dynamics of local tissue damage induced by Bothrops asper snake venom and myotoxin II on the mouse cremaster muscle: an intravital and electron microscopic study

The acute tissue damaging effects of Bothrops asper snake venom and a myotoxic Lys-49 phospholipase A2 (myotoxin II) on the mouse cremaster muscle were studied by intravital and electron microscopy. Both venom and myotoxin induced local contractions of the muscle fibres within 10-60 sec after exposure, which disappeared after 1-2 min. This observation is consistent with the hypothesis that Bothrops myotoxins act initially at the sarcolemma by affecting its permeability and allowing an influx of calcium. The venom also induced an early but transient vasoconstriction of arterioles. The development of edema was monitored using i.v. FITC-dextran as a marker. Plasma leakage started after about 2 min of exposure to venom or myotoxin, was extensive by 4-5 min, and originated from small venules and their adjoining capillary segments. The venom induced formation of thrombi and emboli in venules, but not in arterioles. Haemorrhage appeared after 4-6 min of exposure, the bleedings always originating from capillaries and small venules. The microbleedings were explosive, appearing as rapid bursts of erythrocytes into the extravascular space, and suggesting a per rhexis type of haemorrhage. This was confirmed by electron microscopy evaluation of the same microvessels observed intravitally, which showed erythrocyte extravasation through gaps in damaged endothelial cells. Other phenomena in the microcirculation included blood-flow disturbances, crenation and sphering of erythrocytes, and stasis with dense packing of cells in capillary networks. Muscle necrosis, caused by either venom or myotoxin, started 3-4 min after application. The first sign of damage in the fibres was the development of a narrow, transverse band with local loss of striation. This was followed by slow retraction of myofibrils until there was a complete transverse rupture of the fibre. This process was often repeated along the same fibre, leaving a row of fragments separated by spaces apparently devoid of myofibrillar material. The results confirm the rapid tissue damaging effects of B. asper venom, implying that potentially useful blocking agents must be administered early and have the ability to diffuse rapidly into the tissues.

Isolation and characterization of synergistic hemorrhagins from the venom of the snake Bothrops asper

Three hemorrhagic factors (BaH1, BH2 and BH3) were isolated from the venom of Bothrops asper by gel filtration on Sephacryl S-200, DEAE-Sepharose chromatography, metal chelate affinity chromatography and hydrophobic interaction chromatography. They contain 55% of the total hemorrhagic activity of the whole venom when they are mixed, but lose almost half of the activity if they are separated, indicating a synergism between the three. The main hemorrhagin is BaH1 (Bothrops asper hemorrhagin 1); the other two are weak hemorrhagins but contribute to the synergism. They are acidic proteins with a pI of 4.5, 5.2 and 5; their mol. wt is 64,000, 26,000 and 55,000 respectively. The minimal hemorrhagic dose (MHD) of BaH1, BH2 and BH3 is 0.18, 2 and 1.6 micrograms, with a specific activity 55, 5 and 6.25 higher than that of the whole venom. The hemorrhagic activity of all three factors was inhibited by EDTA and ortho-phenathroline, indicating that the hemorrhagic activity is metal dependent. Phosphoramidon, soybean trypsin inhibitor, PMSF, pepstatin and aprotinin did not affect the hemorrhagic activity of the isolated factors.