Expression of a functional recombinant Phoneutria nigriventer toxin active on K+ channels

PnTx3-1 is a peptide isolated from the venom of the spider Phoneutria nigriventer that specifically inhibits A-type K(+) currents (I(A)) in GH(3) cells. Here we used a bacterial expression system to produce an NH(2)-extended mutant of PnTx3-1 (ISEF-PnTx3-1) and tested whether the toxin is functional. The recombinant toxin was purified from bacterial extracts by a combination of affinity and ion-exchange chromatography. The recombinant toxin blocked A-type K(+) currents in GH(3) cells in a fashion similar to that observed with the wild-type toxin purified from the spider venom. These results suggest that recombinant cDNA methods provide a novel source for the production of functional Phoneutria toxins. The recombinant ISEF-PnTx3-1 should be useful for further understanding of the role of A-type K(+) currents in biological processes.

Covalent structure and some pharmacological features of native and cleaved alpha-KTx12-1, a four disulfide-bridged toxin from Tityus serrulatus venom

A toxin with four disulfide bridges from Tityus serrulatus venom was able to compete with 125I-kaliotoxin on rat brain synaptosomal preparations, with an IC50 of 46 nM. The obtained amino acid sequence and molecular mass are identical to the previously described butantoxin. Enzymatic cleavages in the native peptide followed by mass spectrometry peptide mapping analysis were used to determine the disulfide bridge pattern of alpha-KTx12-1. Also, after the cleavage of the first six N-terminal residues, including the unusual disulfide bridge which forms an N-terminus ring, the potency of the cleaved peptide was found to decrease about 100 fold compared with the native protein.

Enzymes with gelatinolytic activity can be found in Tityus bahiensis and Tityus serrulatus venoms

Enzymes with gelatinolytic activity were detected in Tityus bahiensis and Tityus serrulatus venom. Their activity was optimal at pH 8.0 in SDS-PAGE-gelatin. They were inhibited by PMSF but not by iodoacetamide, pepstatin or phenantrolin in the assay conditions used. This suggests that these enzymes are serine proteases. The presence of metal ions did not affect the proteolytic activity of these enzymes. Several possible functions may be envisaged for these enzymes: in tissue permeabilization, pancreatitis and toxin processing.

Toxicity of South American snake venoms measured by an in vitro cell culture assay

Cytotoxicity of venoms from eight medically important South American Crotalidae snakes (Bothrops and Lachesis genera) was determined, based on a procedure originally described for the screening of cytotoxic agents in general. The assay, the conditions of which were adapted to snake venoms, determines the survival of viable cells in monolayer culture upon exposure to the toxic agent. Snake venom toxicity was expressed as the venom dose that killed 50% of the cells (CT(50)) under the assay conditions. Bothrops neuwieddi mattogrossensis (CT(50)=4.74+/-0.35 microg/ml) and Bothrops leucurus (CT(50)=4.95+/-0.51 microg/ml) were the most cytotoxic whereas Bothrops atrox (CT(50)=34.64+/-2.38 microg/ml) and Bothrops sp. (CT(50)=33.89+/-3.89 microg/ml) were the least cytotoxic venoms, respectively. The relationship between CT(50) and other biological activities of these snake venoms was evaluated.

A proposed 3D structure for crotamine based on homology building, molecular simulations and circular dichroism

Crotamine, isolated from the venom of the South American rattlesnake Crotalus durissus terrificus is a strongly basic 42-amino acid polypeptide belonging to the small basic myotoxin family. As no tridimensional structure is available for this myotoxin subfamily, despite its important pharmacological interest, we propose in this paper a theoretical 3D model for crotamine. Starting from a homology modelling procedure, followed by intensive molecular dynamics (MD) simulations in water and complementary CD experiments, the designed 3D model is the first example of a tridimensional structure in this family of small basic myotoxins. Crotamine, therefore, belongs to a newly identified structural family presenting a common fold also found in beta-defensin and antopleurine-B. The proposed 3D model will be used for future calculations about crotamine aggregation and interaction with membranes.

Induction of neutralizing antibodies against Tityus serrulatus scorpion toxins by immunization with a mixture of defined synthetic epitopes

We have used the Spot method of multiple peptide synthesis to prepare sets of immobilized overlapping peptides of uniform size (15 mer), covering the complete amino acid sequences of TsNTxP a non-toxic and immunogenic protein and TsIV, an alpha-type toxin that is the major lethal component of the venom of scorpion Tityus serrulatus. Anti-TsNTxP antibodies binding to peptides, revealed three antigenic regions, one in the N-terminal, the second in the central part and the other in the C-terminal part of TsNTxP. One peptide epitope in the C-terminal part of TsIV was identified with anti-TsIV neutralizing rabbit antibodies. Anti-peptide antibodies were raised against these four peptides all together covalently coupled to keyhole limpet hemocyanin (KLH) and found to neutralize in vitro the toxic effects of the T. serrulatus venom. Quantities of venom equivalent to 13.5 LD(50) were effectively neutralized by 1ml of the anti-peptide serum. The antigenic specificities of the anti-peptides were compared by an indirect enzyme-linked immunosorbent assay (ELISA) using synthetic peptides and crude venoms from T. serrulatus, T. bahiensis, T. cambridgei, T. stigmurus, Androctonus autralis Hector and Centruroides sculpturatus to coat the microtitration plates. The anti-peptide antibodies had a comparable high reactivity with the crude venom of T. serrulatus, moderate binding to T. bahiensis, T. cambridgei, T. stigmurus and Centruroides sculpturatus venoms but were unable to recognize the venom of Androctonus autralis Hector. These results show that by using peptides derived from the sequence of scorpion toxins, the generation of anti-peptide antibodies able to neutralize the cognate venom appears to be an alternative strategy for the easy preparation of antivenoms.

Fingerprinting of cell lines by directed amplification of minisatellite-region DNA (DAMD)

The development of in vitro propagation of cells has been an extraordinary technical advance for several biological studies. The correct identification of the cell line used, however, is crucial, as a mistaken identity or the presence of another contaminating cell may lead to invalid and/or erroneous conclusions. We report here the application of a DNA fingerprinting procedure (directed amplification of minisatellite-region DNA), developed by Heath et al. [Nucleic Acids Research (1993) 21: 5782-5785], to the characterization of cell lines. Genomic DNA of cells in culture was extracted and amplified by PCR in the presence of VNTR core sequences, and the amplicons were separated by agarose gel electrophoresis. After image capture with a digital camera, the banding profiles obtained were analyzed using a software (AnaGel) specially developed for the storage and analysis of electrophoretic fingerprints. The fingerprints are useful for construction of a data base for identification of cell lines by comparison to reference profiles as well as comparison of similar lines from different sources and periodic follow-up of cells in culture.

Inhibition of mutalysin II, a metalloproteinase from bushmaster snake venom by human alpha2-macroglobulin and rabbit immunoglobulin

Mutalysin II is a 22.5-kDa zinc endopeptidase isolated from Lachesis muta muta snake venom. In order to determine whether the inhibitors human alpha2-macroglobulin (alpha2-M) and rabbit antibody to mutalysin II share a common mechanism, we have investigated the inhibition of mutalysin II by these two different glycoproteins. The proteolytic activity of mutalysin II with dimethylcasein as substrate was completely inhibited by human alpha2-M and by a purified rabbit antibody to mutalysin II. The protection of fibrin(ogen) digestion by alpha2-M was slightly better than the protection offered by the antibody. In addition, the purified antibody reacted only with the metalloproteinase in bushmaster venom, as demonstrated by immunodiffusion. SDS-PAGE analysis of reduced samples showed that the interaction of mutalysin II with alpha2-M resulted in the formation of high molecular complex ( approximately 180000) and M(r) 90000 fragments generated by the venom enzyme. Also, fragments at 85 and 23 kDa were detected under non-reducing conditions after incubation of rabbit immunoglobulin with enzyme. Proteolysis of dimethylcasein as substrate revealed that the stoichiometry of inhibition was 1.0 mol of human alpha2-M and 1.5 mol of rabbit IgG antimutalysin II per mole of enzyme. Furthermore, dimethylcasein hydrolysis indicated that several viperid snake venoms, including Bothrops atrox, B. alternatus and Trimeresurus flavoviridis cross-reacted with the specific rabbit antibody to varying degrees.

Sandwich-ELISA detection of venom antigens in envenoming by Phoneutria nigriventer spider

Enzyme linked immunosorbent assays (ELISA) were developed to detect antigens from Phoneutria nigriventer spider venom. Horse anti-P. nigriventer immunoglobulins were prepared by immunoaffinity chromatography and used to set up a sandwich-type ELISA. The specificity of the assay was demonstrated by its capacity to correctly discriminate between the circulating antigens in mice that were experimentally inoculated with P. nigriventer venom from those in mice inoculated with Lycosa sp. and Loxosceles intermedia spider venoms, Tityus serrulatus scorpion venom and Apis mellifera bee venom. Measurable absorbance signals were obtained with 0.8ng of venom per assay. The ELISA was used to follow the kinetic distribution of antigens in experimentally envenomed mice and to detect antigens in the sera of patients envenomed by P. nigriventer.

Spider neurotoxins block the beta scorpion toxin-induced calcium uptake in rat brain cortical synaptosomes

In this paper we describe the effects of the beta scorpion toxin Tityus gamma (TiTX gamma) and spider neurotoxins Tx3-3 and Tx3-4 in the (45)Ca(2+) uptake in synaptosomes. The TiTX gamma-stimulatory effect on (45)Ca(2+) uptake in synaptosomes was inhibited omega-Conotoxin MVIIC (omega-CgTX MVIIC) (0.1 microM) and omega-Agatoxin IVA (0.1 microM) by 70% and 41%, respectively. omega-CgTX MVIIC (1.0 microM) almost completely blocked the TiTX gamma-induced (45)Ca(2+) uptake in synaptosomes. Verapamil (1.0 microM) and omega-Conotoxin GVIA (0.1 microM) had no effect in the scorpion toxin-induced (45)Ca(2+) influx. The spider neurotoxins Tx3-3 and Tx3-4 inhibited the TiTX gamma-induced calcium uptake with an IC(50) of 10.0 and 30.0 nM, respectively. It is suggested that spider neurotoxins Tx3-3 and Tx3-4 blocking effect in the TiTX gamma-induced calcium uptake involves P/Q-type calcium channels.

Purification and amino acid sequence of a highly insecticidal toxin from the venom of the brazilian spider Phoneutria nigriventer which inhibits NMDA-evoked currents in rat hippocampal neurones

A new insecticidal toxin Tx4(5-5) was isolated from the fraction PhTx4 of the venom of the spider Phoneutria nigriventer by reverse phase high performance liquid chromatography (HPLC) and anion exchange HPLC. The complete amino acid sequence determined by automated Edman degradation showed that Tx4(5-5) is a single chain polypeptide composed of 47 amino acid residues, including 10 cysteines, with a calculated molecular mass of 5175 Da. Tx4(5-5) shows 64% of sequence identity with Tx4(6-1), another insecticidal toxin from the same venom. Tx4(5-5) was highly toxic to house fly (Musca domestica), cockroach (Periplaneta americana) and cricket (Acheta domesticus ), producing neurotoxic effects (knock-down, trembling with uncoordinated movements) at doses as low as 50 ng/g (house fly), 250 ng/g (cockroach) and 150 ng/g (cricket). In contrast, intracerebroventricular injections (30 microg) into mice induced no behavioural effects. Preliminary electrophysiological studies carried out on whole-cell voltage-clamped rat hippocampal neurones indicated that Tx4(5-5) (at 1 microM) reversibly inhibited the N-methyl-D-aspartate-subtype of ionotropic glutamate receptor, while having little or no effect on kainate-, alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid- or gamma-aminobutyric acid-activated currents.

Crotoxin, the major toxin from the rattlesnake Crotalus durissus terrificus, inhibits 3H-choline uptake in guinea pig ileum

We examined the effect of crotoxin, the neurotoxic complex from the venom of the South American rattlesnake Crotalus durissus terrificus, on the uptake of 3H-choline in minces of smooth muscle myenteric plexus from guinea pig ileum. In the concentration range used (0. 03-1 microM) and up to 10 min of treatment, crotoxin decreased 3H-choline uptake by 50-75% compared to control. This inhibition was time dependent and did not seem to be associated with the disruption of the neuronal membrane, because at least for the first 20 min of tissue exposure to the toxin (up to 1 microM) the levels of lactate dehydrogenase (LDH) released into the supernatant were similar to those of controls. Higher concentrations of crotoxin or more extensive incubation times with this toxin resulted in elevation of LDH activity detected in the assay supernatant. The inhibitory effect of crotoxin on 3H-choline uptake seems to be associated with its phospholipase activity since the equimolar substitution of Sr2+ for Ca2+ in the incubation medium or the modification of the toxin with p-bromophenacyl bromide substantially decreased this effect. Our results show that crotoxin inhibits 3H-choline uptake with high affinity (EC25 = 10 +/- 5 nM). We suggest that this inhibition could explain, at least in part, the blocking effect of crotoxin on neurotransmission.

Action of metalloproteinases mutalysin I and II on several components of the hemostatic and fibrinolytic systems

The zinc endopeptidases mutalysin I (100 kDa) and mutalysin II (22.5 kDa) have been previously isolated from bushmaster (Lachesis muta muta) snake venom. Hemorrhagic activity was observed with as little as 0.5 microg (2000 units/mg) and 17.8 microg (56.2 units/mg) for mutalysin I and II, respectively. Additionally, the proteases hydrolyse the Aalpha>Bbeta chain of fibrinogen without clot formation. The specific fibrinogenolytic activity was estimated as 5. 25 and 16.3 micromol fibrinogen/min/micromol protein for mutalysin I and II, respectively. In vitro, the enzymes act directly on fibrin and are not inhibited by serine proteinase inhibitors (SERPINS). Analysis by SDS-PAGE of fibrin hydrolysis by both enzymes showed that mutalysin II (0.22 microM) completely digested the alpha- and gamma-gamma chains and partially the beta-chain (in 120 min incubation). In contrast, mutalysin I (three fold higher concentration than mutalysin II) hydrolyzed selectively the alpha-chain of fibrin leaving the beta and gamma-gamma chains unaffected. Unlike with the plasminogen activator-based thrombolytic agents (e.g., streptokinase), mutalysins do not activate plasminogen. Neither enzyme had an effect on protein C activation. Mutalysin II does not inhibit platelet aggregation in human PRP induced by collagen or ADP. However, mutalysin I showed a selective inhibitory effect on collagen-induced aggregation of human PRP; it did not affect platelet aggregation with ADP as the agonist. The present investigation demonstrates that both native and EDTA-inactivated mutalysin I dose dependently blocked aggregation of human PRP elicited by 10 microg/mL of collagen with an IC(50) of 180 and 580 nM, respectively. These studies suggest that, in addition to the metalloprotease region of mutalysin I, the disintegrin-like domain also participates in the inhibitory effect. The proteolytic activity of mutalysin II against dimethylcasein and fibrin was completely abolished by alpha2-macroglobulin (alpha2-M). The stoichiometry of inhibition was 1.0 mol of enzyme per mol of alpha2-M. In contrast, the proteolytic effect of mutalysin I against the same substrates was not significantly inhibited by alpha2-M. Therefore, the data explain why mutalysin I contributes significantly not only to local but also to systemic bleeding associated with the observed pathological effects of the venom.

Inhibition of neuronal high-voltage activated calcium channels by the omega-phoneutria nigriventer Tx3-3 peptide toxin

We have investigated the effect of omega-PnTx3-3 (referred to in previous papers simply as Tx3-3), a peptide toxin from the venom of the spider Phoneutria nigriventer, on neuronal high-voltage activated (HVA) Ca(2+) channels, using whole-cell patch-clamp. omega-PnTx3-3 (120 nM) blocked 74+/-8% of the total HVA Ca(2+) currents of cerebellar granule neurones, without affecting the low-voltage activated (LVA) current. P/Q/R-type currents in cerebellar granule neurones, isolated using 4 microM nicardipine and 100 nM omega-conotoxin GVIA, were markedly (79+/-6%) inhibited by 60 nM omega-PnTx3-3. R-type currents, isolated either by additional application of 0.5-1 microM of omega-agatoxin IVA or by pre-incubation with 5 microM omega-conotoxin MVIIC were inhibited almost totally by 120 nM of omega-PnTx3-3. omega-PnTx3-3 reversibly altered the kinetics of the P/Q/R current, increasing the degree of inactivation that occurred during a 50 ms pulse from 20% to 40%. N-type currents, recorded from neuroblastoma N18 cells, were partially (34+/-2%) inhibited by 320 nM omega-PnTx3-3. L-type currents, recorded from GH3 cells, were partially (45+/-12%) inhibited by 80 nM omega-PnTx3-3. We conclude that omega-PnTx3-3 inhibits all known HVA Ca(2+) channels, and most effectively the P/Q- and R-type currents.

Inhibition of glutamate uptake by Tx3-4 is dependent on the redox state of cysteine residues

Glutamate transporters are essential for the homeostasis of glutamate and normal function of glutamatergic synapses. Their function was shown to be regulated by redox agents and dimerizations that involves redox changes of cysteine residues. Peptide neurotoxins are also known to be rich in cysteine residues that contribute to their activity and stability. Among them is the toxin Tx3-4, from the spider Phoneutria nigriventer, which is able to inhibit glutamate uptake in rat hippocampal synaptosomes. Based on results obtained with manipulation of the redox state of cysteine residues in synaptosomes and in Tx3-4, we suggest that the effect of this toxin on glutamate uptake is due to interactions that involve cysteines both in the toxin and in the transporters.

Isolation of a proteinase with plasminogen-activating activity from Lachesis muta muta (bushmaster) snake venom

A plasminogen activator enzyme (LV-PA) from Lachesis muta muta venom was purified to homogeneity using gel filtration and anion exchange chromatography. SDS-PAGE under reducing conditions showed a single protein band with an Mr of 33,000 Da. It is an acidic glycoprotein which activates plasminogen to plasmin indirectly, functioning via prior formation of a molecular complex, known as plasminogen activator. The purified preparation catalyzes the hydrolysis of several p-nitroanilide peptide substrates containing Lys at the scissile bond. In contrast, no hydrolysis was detected on the synthetic substrates TAME and BAPNA, which contain arginine. By the use of the plasmin-specific chromogenic substrate Tos-Gly-Pro-Lys-pNA, the preparation had a plasmin-like activity of 0.68 U/mg, which was 35.8-fold higher than that of the crude venom from which it was prepared. In vitro, fibrin hydrolysis using LV-PA as plasminogen activator displayed more similarity with the effect produced by streptokinase (SK). SDS-PAGE (10%) analysis showed a 115-kDa complex formation after incubation of plasminogen with either LV-PA or SK. At a molar ratio of 50:1 (fibrinogen:enzyme), the preparation exhibited weakly fibrinogenolytic activity. However, LV-PA is distinguished from thrombin in that it does not clot fibrinogen. After incubation of LV-PA with platelet-rich plasma, the enzyme (2 microM) showed no effect on platelet aggregation induced by ADP, epinephrine, or collagen. Comparison of the N-terminal sequence of LV-PA with other snake venom plasminogen activators revealed that LV-PA exhibits a high degree of sequence identity with the TsVPA from Trimeresurus stejnegeri (90%) and with the Haly-PA from Agkistrodon halys (85%). LV-PA also has homology with other snake venom serine proteinases such as the thrombin-like/gyroxin analogue (38%) from bushmaster venom and with other coagulation serine proteases. The proteinase was readily inhibited by treatment with p-nitrophenyl p-guanidinebenzoate, p-aminobenzamidine, and phenylmethanesulfonyl fluoride but was not affected by metal chelators.

Induction of neutralizing antibodies against Tityus serrulatus toxins by immunization with a recombinant nontoxic protein

An immunogenic nontoxic protein (TsNTxP) was purified from the venom of the scorpion Tityus serrulatus (Ts). This peptide is composed of 63 amino acid residues with a high degree of structural homology with the toxins isolated from Ts. The nucleotide sequence of the gene that encodes TsNTxP was obtained and also showed a high degree of similarity with genes encoding Tityus toxins [Guatimosim, S.C.F., Prado, V.F., Diniz, C.R., Chávez-Olórtegui, C.. Kalapothakis, E., 1999. Molecular cloning and genomic analysis of TsNTxP; an immunogenic protein from Tityus serrulatus scorpion venom. Toxicon 37, 507-517]. In the present study the TsNTxP gene was expressed in E. coli BL21DE3 cells as a fusion protein with maltose-binding protein. The recombinant protein (TsNTxPrec) was purified by affinity chromatography and used as an immunogen in rabbits. The antigenic specificity of anti-TsNTxPrec antibodies was compared by an enzyme-linked immunosorbent assay using TsNTxP, TstFG50 (the fraction of Ts venom that represents most of the toxicity of the crude venom) and the crude venom, to coat microtitration plates. Anti-TsNTxPrec antibodies had a comparable high cross-reactivity for all antigens tested. Concentrations of Ts venom equivalent to 20 LD50 were effectively neutralized by 1 ml of the anti-TsNTxPrec serum. This result provides basic data for the use of such recombinant scorpion protein as an immunogen in the development of antivenoms for clinical use.

Neutralization of the hemorrhagic activity of Bothrops and Lachesis snake venoms by a monoclonal antibody against mutalysin-II

One mAb reactive with mutalysin-II, a hemorrhagic metalloproteinase isolated from Lachesis muta muta venom, was produced in mice immunized with L. m. muta venom. Indirect ELISA was employed to compare the antigenic cross-reactivity among the venoms from Bothrops snakes. The mAb anti-mutalysin-II efficiently neutralized the hemorrhagic effect of both mutalysin-II and L. m. muta crude venom. Furthermore, the mAb were cross-reactive with B. alternatus, B. atrox, B. itapetiningae, B. jararaca and B. neuwiedii and showed variable potencies in neutralizing the hemorrhagic activity of several bothropic venoms.

Binding sites and actions of Tx1, a neurotoxin from the venom of the spider Phoneutria nigriventer, in guinea pig ileum

Tx1, a neurotoxin isolated from the venom of the South American spider Phoneutria nigriventer, produces tail elevation, behavioral excitation and spastic paralysis of the hind limbs after intracerebroventricular injection in mice. Since Tx1 contracts isolated guinea pig ileum, we have investigated the effect of this toxin on acetylcholine release, as well as its binding to myenteric plexus-longitudinal muscle membranes from the guinea pig ileum. [125I]-Tx1 binds specifically and with high affinity (Kd = 0.36 +/- 0.02 nM) to a single, non-interacting (nH = 1.1), low capacity (Bmax 1.1 pmol/mg protein) binding site. In competition experiments using several compounds (including ion channel ligands), only PhTx2 and PhTx3 competed with [125I]-Tx1 for specific binding sites (K0.5 apparent = 7.50 x 10(-4) g/l and 1.85 x 10(-5) g/l, respectively). PhTx2 and PhTx3, fractions from P. nigriventer venom, contain toxins acting on sodium and calcium channels, respectively. However, the neurotoxin PhTx2-6, one of the isoforms found in the PhTx2 pool, did not affect [125I]-Tx1 binding. Tx1 reduced the [3H]-ACh release evoked by the PhTx2 pool by 33%, but did not affect basal or KCl-induced [3H]-ACh release. Based on these results, as well as on the homology of Tx1 with toxins acting on calcium channels (omega-Aga IA and IB) and its competition with [125I]-omega-Cono GVIA in the central nervous system, we suggest that the target site for Tx1 may be calcium channels.

Primary culture of venom gland cells from the South American rattlesnake (Crotalus durissus terrificus)

Primary cultures of venom gland cells from the South American rattlesnake (Crotalus durissus terrificus) were attempted. At first, six different cell types were obtained including potentially secreting epithelial-like cells. Nonepithelial cell cultures were later invaded by fibroblast-like cells. Cultures of epithelial-like gland cells were successfully maintained, after testing different culture conditions by varying the media, incubation temperature, use of dissociating agents and adhesion substrates. The best results were achieved using plates precoated with rattlesnake skin collagen and incubation in CMRL 1415 modified for snake gland cells plus 10% fetal calf serum at 30 degrees C. The presence of venom could be demonstrated in the supernatant of five out of six epithelial-like gland cell cultures tested by ELISA, in the very first passages. After the third passage, however, venom amounts dropped to undetectable values. A total of 23 venom gland cell lines were obtained and are kept frozen in the laboratory; among them, five epithelial-like gland cell lines with up to 12 passages, that were continuously cultured for more than 30 weeks. The methodology described here was successfully applied to C. d. terrificus kidney cells culturing, developed to be used as negative control.

Studies on the specificity of CNF, a phospholipase A2 inhibitor isolated from the blood plasma of the South American rattlesnake (Crotalus durissus terrificus). I. Interaction with PLA2 from Lachesis muta muta snake venom

A phospholipase A2 inhibitor has been previously purified and cloned from the blood plasma of the South American rattlesnake, Crotalus durissus terrificus. This inhibitor, named CNF for Crotalus neutralizing factor, interacts with crotoxin, the main neurotoxin from C. d. terrificus venom, abolishing its phospholipase A2 activity. Crotoxin is a heterodimer of an acidic subunit (CA) and a basic phospholipase A2 (CB). CNF acts by forming a stable non-toxic complex with CB, replacing CA in the toxic CA-CB of crotoxin. In the present investigation, we have shown that CNF has a broader specificity. It is able to inhibit the PLA2 activity of the whole venom from the bushmaster snake (Lachesis muta muta), a species evolutionary related to Crotalus. Inhibition experiments have been carried out with four PLA2 active components isolated from L. m. muta venom, one basic and three acidic ones. CNF inhibition is not restricted to the basic PLA2, but extended to the three acidic forms as well.

Inhibition of glutamate uptake by a polypeptide toxin (phoneutriatoxin 3-4) from the spider Phoneutria nigriventer

Glutamate concentration increases significantly in the extracellular compartment during brain ischaemia and anoxia. This increase has an important Ca(2+)-independent component, which is due in part to the reversal of glutamate transporters of the plasma membrane of neurons and glia. The toxin phoneutriatoxin 3-4 (Tx3-4) from the spider Phoneutria nigriventer has been reported to decrease the evoked glutamate release from synaptosomes by inhibiting Ca(2+) entry via voltage-dependent Ca(2+) channels. However, we report here that Tx3-4 is also able to inhibit the uptake of glutamate by synaptosomes in a time-dependent manner and that this inhibition in turn leads to a decrease in the Ca(2+)-independent release of glutamate. No other polypeptide toxin so far described has this effect. Our results suggest that Tx3-4 can be a valuable tool in the investigation of function and dysfunction of glutamatergic neurotransmission in diseases such as ischaemia.

PhTx4, a new class of toxins from Phoneutria nigriventer spider venom, inhibits the glutamate uptake in rat brain synaptosomes

We report the characterization of a new class of glutamate uptake inhibitors isolated from Phoneutria nigriventer venom. Glutamate transport activity was assayed in rat cerebrocortical synaptosomes by using [(3)H]-L-glutamate. PhTx4 inhibited glutamate uptake in a dose dependent manner. The IC(50) value obtained was 2.35+/-0.9 microg/ml which is in the observed range reported for glutamate uptake blockers. Tx4-7, one of PhTx4 toxins, showed the strongest inhibitory activity (50.3+/-0.69%, n=3).

Phoneutria nigriventer toxin Tx3-1 blocks A-type K+ currents controlling Ca2+ oscillation frequency in GH3 cells

GH3 cells present spontaneous Ca2+ action potentials and oscillations of intracellular Ca2+, which can be modified by altering the activity of K+ or Ca2+ channels. We took advantage of this spontaneous activity to screen for effects of a purified toxin (Tx3-1) from the venom of Phoneutria nigriventer on ion channels. We report that Tx3-1 increases the frequency of Ca2+ oscillations, as do two blockers of potassium channels, 4-aminopyridine and charybdotoxin. Whole-cell patch clamp experiments show that Tx3-1 reversibly inhibits the A-type K+ current (I(A)) but does not block other K+ currents (delayed-rectifying, inward-rectifying, and large-conductance Ca2+-sensitive) or Ca2+ channels (T and L type) in these cells. In addition, we describe the sequence of a full cDNA clone of Tx3-1, which shows that Tx3-1 has no homology to other known blockers of K+ channels and gives insights into the processing of this neurotoxin. We conclude that Tx3-1 is a selective inhibitor of I(A), which can be used to probe the role of this channel in the control of cellular function. Based on the effect of Tx3-1, we suggest that I(A) is an important determinant of the frequency of Ca2+ oscillations in unstimulated GH3 cells.

Molecular cloning and genomic analysis of TsNTxp: an immunogenic protein from Tityus serrulatus scorpion venom

A non-toxic protein (TsNTxP) from Tityus serrulatus scorpion venom has been shown to be an efficient immunogen and anti-TsNTxP antibodies recognize and neutralize the effect of Tityus serrulatus venom [Chávez-Olórtegui et al., 1997. Toxicon 35, 213-221]. With the purpose of studying the organization of the gene that code for this protein, we have isolated a full length cDNA clone for TsNTxP from a cDNA expression library using anti-TsNTxP antibodies. The nucleotide sequence of the gene that encodes TsNTxP was also obtained and it reveals the presence of an intron within the signal peptide sequence. The TsNTxP gene showed high degree of similarity with genes encoding toxins from scorpions of the genus Tityrus.

Cloning, cDNA sequence analysis and patch clamp studies of a toxin from the venom of the armed spider (Phoneutria nigriventer)

The cDNAs (Tx3-2 and Pn3A) encoding precursor of toxin Tx3-2 and an isoform called Pn3A have been isolated from a library constructed from stimulated venom glands of the spider Phoneutria nigriventer. The cDNA of Tx3-2 reveals the presence of a signal peptide of 21 amino acids and of an intervening propeptide (with 16 amino acids) preceding the toxin sequence, which was followed by additional amino acid residues at the C-terminus (C-terminal peptide), implying post-translational modifications of the synthesised peptide. The deduced amino acid sequence for the mature toxin confirms the previous sequence published. In addition, by using the whole-cell patch clamp technique, we have determined that purified Tx3-2 decreases L-type currents present in GH3 cells. Finally, the presence of the cDNA Pn3A, with high sequence identity with Tx3-2, reveals the existence of a putative new toxin showing, at the cDNA level, 85.4% identity in its whole segment.

Pathological changes induced by PhTx1 from Phoneutria nigriventer spider venom in mouse skeletal muscle in vitro

The 'armed' spider Phoneutria nigriventer is responsible for most human accidents involving spiders in Brazil. The effects of fraction Tx1 (PhTx1) from the venom of this spider were investigated by physiological and morphological methods using the mouse phrenic nerve-diaphragm preparation. PhTx1 (1 and 5 microg) did not affect the twitch tension of muscle fibers under indirect electrical stimulation. At this same concentration, PhTx1 also did not alter the miniature end-plate potential (mepp) frequency and amplitude, nor did it change the resting membrane potential 60 min after addition to the preparation. Light microscopy (LM) revealed that in muscles incubated with PhTx1 a number of fibers were morphologically altered, as evidenced by microvacuolization and myofibril hypercontraction and loss within 15 min after toxin administration. Transmission electron microscopy (TEM) showed sarcoplasmic reticulum swelling, disorganization of the sarcomeres and mitochondrial damage, and occasionally, sarcolemmal discontinuities with a persisting basal membrane. The intra-muscular fascicles of the phrenic nerve showed myelinated axons with vacuolated myelin sheaths as well as peri- and intra-axoplasmic vacuoles. The neuromuscular junction changes were variable, but were rarely severe. Thus, although PhTx1 did not depolarize or hyperpolarize the neuromuscular junction, it was nevertheless toxic to a restricted number of muscle fibers and nerve structures. The site of action of PhTx1 may involve the sarcolemma and axolemma as suggested by the morphological abnormalities which could reflect hydroelectrolytic disturbances.

Investigation of the effect of PhTx2, from the venom of the spider Phoneutria nigriventer, on the release of [3H]-acetylcholine from rat cerebrocortical synaptosomes

Venoms from spiders are an important source of toxins that can help on the dissection of mechanisms involved in neurotransmission. Among them is the venom of the spider Phoneutria nigriventer that contains several toxic fractions with different targets in mammals and/or insects. We here report that one of these fractions (PhTx2) is able to evoke acetylcholine release from rat cortical synaptosomes and that this effect is dependent on extracellular calcium and is inhibited by the sodium channel blocker tetrodotoxin.

Phoneutria nigriventer toxins block tityustoxin-induced calcium influx in synaptosomes

Neurotoxins can help the understanding of mechanisms involved in neurotransmission. We here report that two neurotoxin isoforms, Tx3-3 and Tx3-4 obtained from the venom of the spider Phoneutria nigriventer inhibited the 45Ca2+ influx in rat cortical synaptosomes induced by the scorpion venom tityustoxin. The IC50 for Tx3-3 and Tx3-4 were 0.32 and 7.9 nM, respectively. The neurotoxins Tx3-3 and Tx3-4 are very effective in inhibiting 45Ca2+ influx and they should be useful in studies involving Ca(2+)-dependent processes.

In vivo protection against Tityus serrulatus scorpion toxins by immunization of mice with a non-toxic protein

The possibility of inducing a humoral immune response able to produce neutralizing antibodies against the lethal effects of scorpion toxins was evaluated in the mouse model. A non-toxic protein (TsNTxP) was purified from the venom of the Brazilian scorpion Tityus serrulatus by combining gel filtration, ion exchange and reverse phase HPLC chromatographic steps. After four injections of TsNTxP the mice developed an IgG response. The anti-TsNTxP antibodies had a comparable high cross-reactivity for the crude venom, toxic fraction (toxic fraction of venom that represents most of the toxicity of the crude venom -- TsTFG50) and TsIV, a representative alpha-type toxin of T. serrulatus, and moderate binding capacity for TsVII, a representative beta-type toxin. In vitro neutralization assays indicated that preincubation of a lethal dose of the toxic fraction with immune serum strongly reduced its toxicity. In vivo protection assays showed that mice immunized with TsNTxP resisted a challenge of 10 LD50 (s.c.) of the toxic fraction of T. serrulatus venom.

A toxin from the spider Phoneutria nigriventer that blocks calcium channels coupled to exocytosis

1. The aim of the present experiments was to investigate the pharmacological action of a toxin from the spider Phoneutria nigriventer, Tx3-3, on the function of calcium channels that control exocytosis of synaptic vesicles. 2. Tx3-3, in confirmation of previous work, diminished the intracellular calcium increase induced by membrane depolarization with KCl (25 mM) in rat cerebrocortical synaptosomes. The toxin was very potent (IC50 0.9 nM) at inhibiting calcium channels that regulate calcium entry in synaptosomes. In addition, Tx3-3 blocked the exocytosis of synaptic vesicles, as measured with the fluorescent dye FM1-43. 3. Using omega-toxins that interact selectively with distinct neuronal calcium channels, we investigated whether the target of Tx3-3 overlaps with known channels that mediate exocytosis. The results indicate that the main population of voltage-sensitive calcium channels altered by Tx3-3 can also be inhibited by omega-agatoxin IVA, an antagonist of P/Q calcium channels. Omega-conotoxin GVIA, which inhibits N type calcium channels did not decrease significantly the entry of calcium or exocytosis of synaptic vesicles in depolarized synaptosomes. 4. It is concluded that Tx3-3 potently inhibits omega-agatoxin IVA-sensitive calcium channels, which are involved in controlling exocytosis in rat brain cortical synaptosomes.

Induction of neutralizing antibodies in mice immunized with scorpion toxins detoxified by liposomal entrapment

The possibility of producing neutralizing antibodies against the lethal effects of scorpion toxins was evaluated in the mouse model by immunization with an immunogen devoid of toxicity. A toxic fraction (5 mg) from the venom of the scorpion Tityus serrulatus was entrapped in sphingomyelin-cholesterol liposomes. The liposomes were treated for 1 h at 37 degrees C with a 1% (w/w) trypsin solution in 0.2 M sodium carbonate buffer, pH 8.3. This treatment led to a strong reduction in venom toxicity. Immunization was performed as follows: mice were injected s.c. with 20 micrograms of the liposome-entrapped toxic fraction on days 1 and 21 and a final injection (20 micrograms) was administered i.p. on day 36. After injection of the immunogen, all mice developed an IgG response which was shown to be specific for the toxic antigen. The antibodies were measured 10 days after the end of the immunization protocol. In an in vitro neutralization assay we observed that pre-incubation of a lethal dose of the toxic fraction with immune serum strongly reduced its toxicity. In vivo protection assays showed that mice with anti-toxin antibodies could resist the challenge with the toxic fraction, which killed, 30 min after injection, all non-immune control mice.

Time factor in the detection of circulating whole venom and crotoxin and efficacy of antivenom therapy in patients envenomed by Crotalus durissus

Thirty-seven patients envenomed by Crotalus durissus were classified into three groups according to the interval between the bite and hospital admission (delta T): group 1 (n = 14, delta T < 4 hr), group 2 (n = 14, delta T > 4 hr < 8 hr) and group 3 (n = 9, delta T > 8 hr). Venous blood from these patients was sampled for biochemical and hematological analysis and for whole venom, crotoxin and antivenom enzyme-linked immunosorbent assays before antivenom treatment (T0) and at 1 hr (T1), 6 hr (T6), 12 hr (T12) and 24 hr (T24) after the start of antivenom therapy. The patients were treated with 100-200 ml (10-20 ampules) of C. durissus antivenom. Whole venom and crotoxin were detected in 13 (92.8%) and 11 (78.6%) of 14 group 1 patients, respectively, in 11 (78.6%) and six (42.9%) of 14 group 2 patients, respectively, and in two (22.2%) and one (11.1%) of nine group 3 patients, respectively, before antivenom treatment. Data from this study show that whole venom and crotoxin were not detected in most of patients when the time elapsed between the bite and hospital admission was greater than 8 hr, and crotoxin was not detected in most of the patients who were admitted to the hospital at times ranging from 4 to 8 hr after the snakebite. Plasma whole venom, crotoxin and antivenom levels measured over time in these patients show the efficacy of antivenom treatment, since circulating venom and crotoxin were no longer detected 1 hr after antivenom therapy and high antivenom titers persisted for at least 24 hr after serotherapy.

Epidemiological and clinical aspects of snakebite in Belo Horizonte, southeast Brazil

Epidemiologic and clinical aspects of 310 hospitalized snakebite patients and 310 matched controls were described, over a seven years period, from an emergency hospital in Belo Horizontal, Southeast Brazil. The diagnosis was based upon clinical picture or actual snake identification. Fifty six percent of victims were bitten by the snakes of genus Bothrops, 32.0% by Crotalus, 1.0% by Lachesis and 10.0% undetermined. During the study period, stable number of cases and marked seasonal variation were noted. In comparing cases of snakebite and controls, those from a rural area or who were involved in agricultural labor activity were identified as a high risk group, with an odds ratio (OR) of 14.7 and 6.7, respectively, in favor of being bitten. Upon treatment, snakebite patients were 13.5 times more likely to have had early anaphylactic reactions than their controls, with a higher association in the age group > or = 20 years (OR = 30.3). Increased risks were also detected for pyrexia (OR = 11.7), with a marked association in the group under 19 years old (OR = 16.6). Severe cases of snakebite are an important treatable cause of morbidity in Brazil but therapy may be potentially life threatening. The higher case-fatality ratio encountered, compared to national statistics may be due the representativeness of the more severe cases who sought hospitalization. Preventing snakebite and early referral of those who are bitten is proposed.

An enzyme-linked immunosorbent assay (ELISA) that discriminates between the venoms of Brazilian Bothrops species and Crotalus durissus

Enzyme-linked immunosorbent assays (ELISAs) were developed to detect specific antigens from Bothrops sp. and Crotalus durissus snake venoms in Brazil. Cross-reactive immunoglobulins from hyperimmune horse anti-Bothrops and anti-Crotalus sera were removed by immunoaffinity chromatography. Specific IgGs for Bothrops sp. and C. durissus venom antigens were prepared and used to set up a sandwich-type ELISA. The specificity of the assay was demonstrated by its capacity to identify correctly the circulating antigens in mice experimentally inoculated with both venoms. Measurable absorbance signals were obtained with 5 ng of venom per assay. The ELISA was also used to identify circulating antigens in the sera of humans bitten by Bothrops sp. and C. durissus. These ELISAs could be valuable for clinicians and epidemiologists if they prove to have both the high sensitivity and specificity required for such tests.

Neutralizing capacity of antibodies elicited by a non-toxic protein purified from the venom of the scorpion Tityus serrulatus

Polyclonal rabbit antibodies raised against a non-toxic protein (TsNTxP) purified from the toxic fraction of the crude venom of Tityus serrulatus can neutralize the effects of the venom. The antigenic specificities of anti-TsNTxP were compared by an indirect enzyme-linked immunosorbent assay using TsNTxP, TstFG50 (toxic fraction of venom that represents most of the toxicity of the crude venom), and crude venoms from T. serrulatus, T. bahiensis, T. cambridgei, T. stigmurus, Androctonus australis Hector and Centruroides sculpturatus to coat microtitration plates. The anti-TsNTxP antibodies had a comparable high cross-reactivity with the toxic fraction and crude venom of T. serrulatus, moderate binding capacity for T. bahiensis, T. cambridgei, T. stigmurus and were unable to recognize the venoms of A. australis Hector and C. sculpturatus. Quantities of venom equivalent to 20 LD50 were effectively neutralized by 1 ml of the anti-TsNTxP serum. This result shows that this protein may be of interest in the production of antivenoms for clinical use.

Acetylcholine release from rat brain cortical slices evoked by the fraction P4 of the venom of the spider Phoneutria nigriventer has Ca2+ and temperature independent components

Fractionation of the venom of the spider Phoneutria nigriventer revealed that it was a mixture of several neurotoxic peptides. The peptides so far characterized either inhibited or induced neurotransmitter release. These effects were mediated by Ca2+ channels or increasing Na+ permeability through voltage sensitive Na(+)-channels, respectively. The pooled toxic components (fraction P4) showed stimulatory effects on acetylcholine release from brain cortical slices. In addition, a component of the observed effects resembling that of alpha-latrotoxin was identified, which was characterized by the ability to provoke release of acetylcholine (ACh) at low temperature and in a manner independent of extracellular Ca2+ and of voltage sensitive Na(+)-channels.

Body distribution of Tityus serrulatus scorpion venom in mice and effects of scorpion antivenom

In the present study we report the distribution of Tityus serrulatus scorpion venom in serum and various tissues of CFI mice and the efficacy of antivenom in reducing venom concentration. The animals were injected s.c. with 10 micrograms of scorpion venom, divided into groups of four animals and killed at different times from 15 min to 24 hr. Blood samples and samples of different tissues (heart, lung, liver, kidney, spleen, brain and injection site) were collected. Maximum venom levels occurred at 15 min in the kidney and liver and at 30 min in serum, lung, heart and spleen. After 2 hr the venom decreased rapidly in serum and in all other organs until venom levels were no longer detectable after 8 hr. No venom was detected in the central nervous system. In another experiment, 10 microliters of scorpion antivenom was injected i.v. together with the venom, and a rapid reduction of venom concentration was observed in the blood and tissues. In the third experiment, anti-scorpion venom was injected i.v. 1 hr after venom administration, and partial reduction of venom concentration was detected in tissues (lung and kidney). These studies contribute to the elaboration of more objective treatment that may result in a more economic, efficient and controlled use of scorpion antivenom in stings involving humans.

Pharmacokinetics of Tityus serrulatus scorpion venom determined by enzyme-linked immunosorbent assay in the rat

Experiments were performed in two groups of anaesthetized rats to study the genesis of pulmonary oedema and to determine the pharmacokinetic parameters following a subcutaneous (s.c.) injection of Tityus serrulatus scorpion venom. In group I, the rats were anaesthetized with pentobarbital (4 mg/100 g, i.p.); the s.c. injection of scorpion venom at the dose of 50 micrograms/100 g did not induce arterial hypertension, but unilateral pulmonary oedema was observed in three of six rats. The injection of a higher dose of venom (200 micrograms/100 g, N = 6) induced arterial hypertension and bilateral (N = 3) or unilateral (N = 1) pulmonary oedema. These data indicate that it is possible to evoke unilateral pulmonary oedema without previous arterial hypertension induced by the venom. For the study of pharmacokinetic parameters a second group of six rats was anaesthetized with urethane (140 mg/ 100 g, i.p.) and the venom injected at a dose of 200 micrograms/100 g, s.c. The plasma concentrations of venom were determined by enzyme-linked immunosorbent assay, at times 0, 5, 30, 60, 180, 360, and 720 min after venom injection. A biphasic curve was obtained with an ascending phase followed by a descending phase. The maximum plasma scorpion venom concentration was reached at 60 min. The pharmacokinetic parameters showed a fast absorption rate (Ka = 0.058 min-1), a fast and high distribution of venom to tissues (t1/2 alpha = 31.50 min and Vdarea = 6800.47 ml.kg-1, respectively), a great affinity of the venom for the tissues (KCT = 0.056 min-1 and KTC = 0.002 min-1) and a slow elimination half-life (t1/2 beta = 173.25 min).

Purification and characterization of a fibrinogen-clotting enzyme from the venom of jararacuçu (Bothrops jararacussu)

A clotting enzyme of the venom of Bothrops jararacussu, denoted FC-Bj, was purified by gel chromatography on Sephadex G-100 followed by HPLC on DEAE-5PW-PAK and gel filtration on Sephacryl S-200HR. The enzyme was identified as an acidic glycoprotein which probably consists of a single polypeptide chain with isoelectric point values in the range 3.3-4.4 and containing approx. 19% carbohydrates. On polyacrylamide gel electrophoresis (PAGE) at pH 8.3, the enzyme presented a diffuse protein band. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the enzyme showed two protein bands corresponding to mol. wts of 50,600 and 60,000. After treatment of the enzyme with neuraminidase, a strongly stained band and a band weaker in staining intensity were observed on SDS-PAGE, thereby reducing the mol. wts to 44,500 and 56,300, respectively. The clotting factor possessed N-alpha-benzoyl-DL-arginine p-nitroanilide hydrolysing activity and coagulated fibrinogen to fibrin. These activities were 0.548 units/mg and 50.55 NIH thrombin units/mg, respectively. The proteinase was of the serine type, as indicated by sensitivity to phenylmethanesulfonyl fluoride and benzamidine. However, the amidolytic activity of this enzyme was resistant to inhibitors such as heparin, aprotinin, agmatine, EDTA, I-2581 and TLCK. The importance of disulfide bridges for the structural integrity of the purified enzyme was indicated by the loss of amidolytic activity in the presence of beta-mercaptoethanol and dithiothreitol. SDS-PAGE of fibrinogen degraded with this enzyme revealed the disappearance of the A alpha and B beta chains and the appearance of lower mol. wt fragments. The enzyme was able to hydrolyse synthetic chromogenic substrates with arginine as the C-terminal residue, and the kinetic parameters were determined. It hydrolysed the plasma kallikrein substrate H-D-Pro-Phe-Arg-pNA (S-2302) and produced kinin-releasing activity causing ileum contraction. In addition, hypotension and bradycardia were observed in urethane-anesthetized rats upon i.v. injection of the enzyme.

A novel tool for the investigation of glutamate release from rat cerebrocortical synaptosomes: the toxin Tx3-3 from the venom of the spider Phoneutria nigriventer

The present experiments investigated the effect of some of the toxic components present in the venom of the spider Phoneutria nigriventer on the release of neurotransmitter. The toxic fraction, Phoneutria nigriventer toxin-3 (PhTx3), abolished Ca2+-dependent glutamate release, but did not alter Ca2+-independent secretion of glutamate when rat brain cortical synaptosomes were depolarized with 33 mM KCl. This effect was most likely due to interference with the entry of calcium through voltage-gated calcium channels, because PhTx3 reduced by 50% the increase in intrasynaptosomal free calcium induced by membrane depolarization, and did not affect the release of glutamate evoked by a calcium ionophore (ionomycin). A polypeptide (Tx3-3) present in the PhTx3 fraction reproduced the effects of the PhTx3 fraction on transmitter release and intrasynaptosomal free calcium in the low nanomolar range. We compared the alterations produced by the Tx3-3 with the actions of toxins known to block calcium channels coupled to exocytosis: the results indicated that the Tx3-3 inhibition of glutamate release and intrasynaptosomal calcium resemble that observed with omega-conotoxin MVIIC. We suggest that the Tx3-3 is a calcium-channel antagonist that blocked glutamate exocytosis.

Characterization of a hemorrhagic factor, LHF-I, isolated from the bushmaster snake (Lachesis muta muta) venom

Hemorrhagic factor I (LHF-I) was previously purified from the venom of the bushmaster snake (Lachesis muta muta). In terms of biochemical and immunological properties, LHF-I is a glycoprotein (mol. wt 100,000, pI 4.7) consisting of two subunits; it loses its activity following mercaptoethanol treatment. LHF-I contains 0.7 g-atom zinc and 1.2 g-atom calcium per mole protein. The hemorrhagic and the proteinase activities are inhibited by EDTA; subsequent addition of Ca2+ or Mg2+ does not reverse the EDTA-induced inhibition of the hemorrhagic activity. The metalloenzyme does not hyrolyze arginine esters and is devoid of phospholipase A2 activity. It hydrolyzes the A alpha- > B beta-chain of fibrinogen without clot formation and hydrolyzes selectively the alpha-chain of fibrin, leaving the B beta- and tau-chains unaffected. Antibodies to the hemorrhagic factor in bushmaster venom were produced by immunizing rabbits with the purified protein. The antibody was purified by protein-A affinity chromatography. This antibody was also used to screen other Crotalinae venom samples for immunologically similar epitopes by ELISA assay. The purified antibody reacted only with LHF-I and two samples of bushmaster venom from different geographical locations.

The effect of PhTx3 on the release of 3H-acetylcholine induced by tityustoxin and potassium in brain cortical slices and myenteric plexus

The venom of the Brazilian spider Phoneutria nigriventer possesses several neurotoxic polypeptidic fractions. Previous work has established that one of the toxic components, PhTx3, inhibited Ca(2+)-dependent glutamate release and the increase in cytosolic free Ca2+ in response to membrane depolarization. In the present work, we investigated the effect of PhTx3 on the release of acetylcholine (ACh) from brain and peripheral neurons. PhTx3 decreased the release of [3H]-ACh induced by tityustoxin and KCl in brain cortical slices and myenteric plexus. The inhibitory effect of myenteric plexus had the same magnitude as that obtained in the absence of extracellular Ca2+. However, in brain PhTx3 was less efficient at decreasing the evoked release of ACh. These experiments suggest that the target of PhTx3 is coupled to the process of release of ACh in brain and autonomic nervous system.

Proteolytic specificity of two hemorrhagic factors, LHF-I and LHF-II, isolated from the venom of the bushmaster snake (Lachesis muta muta)

Two hemorrhagic metalloproteinases (LHF-I and LHF-II) were previously isolated from Lachesis muta muta (bushmaster snake) venom. The proteolytic activities of these hemorrhagic factors and of the crude venom were investigated using as substrate the oxidized B-chain of bovine insulin. LHF-II cleaves the Ala14-Leu15 bond of insulin B-chain very rapidly and the Phe24-Phe25, His10-Leu11 and His5-Leu6 more slowly, whereas LHF-I hydrolyzed only the Ala14-Leu15 bond. Both hemorrhagic factors cleaved the Leu-Leu bond in the fluorogenic peptide Abz-Pro-Leu-Gly-Leu-Leu-Gly-Arg-EDDnp. When the insulin B-chain was incubated with crude venom previously treated with 2.5 mM PMSF, the Ala14-Leu15 bond was also rapidly cleaved. In addition, the hemorrhagic activity and the digestion of casein remained unaltered. Both hemorrhagic and proteolytic activities were inhibited when the crude venom was treated with EDTA, confirming that only metalloproteinases are responsible for these activities. The hydrolysis of insulin B-chain and the fluorogenic heptapeptide by these proteinases was found to be in inverse relationship to their hemorrhagic activities.

Efficacy of antivenom therapy for neutralizing circulating venom antigens in patients stung by Tityus serrulatus scorpions

Enzyme-linked immunosorbent assays for detection of Tityus serrulatus venom antigen and of horse anti-T. serrulatus venom antibodies were carried out before antivenom treatment and at 1, 6, 12, and 24 hr after antivenom therapy in 18 patients with systemic manifestations following T. serrulatus scorpion sting. Increased levels of circulating venom antigens were detected in the patients before antivenom treatment, but were no longer detected 1 hr after specific antivenom therapy. High titers of antivenom persisted for at least 24 hr after treatment with antivenom. The evolution of clinical and laboratory manifestations of envenoming showed that vomiting and local pain decreased within 1 hr and hyperglycemia was no longer detected 12 hr after antivenom therapy. The cardiorespiratory manifestations disappeared 6-24 hr after the administration of antivenom and all patients recovered completely. This study demonstrates the efficacy of antivenom therapy in neutralizing circulating venom antigens and supports the prompt administration of a potent antivenom to patients with systemic manifestations of envenoming.

Purification and amino acid sequence of the insecticidal neurotoxin Tx4(6-1) from the venom of the 'armed' spider Phoneutria nigriventer (Keys)

An insecticidal peptide referred to as Tx4(6-1) was purified from the venom of the spider Phoneutria nigriventer by a combination of gel filtration, reverse-phase fast liquid chromatography on Pep-RPC, reverse-phase high performance liquid chromatography (HPLC) on Vydac C18 and ion-exchange HPLC on cationic columns. Tx4(6-1) is highly toxic to house flies. At levels of 0.5 ng/house fly it caused excitatory symptoms immediately after intrathoracical injection. However, in mice injections of 0.03 mg of the toxin intracerebroventricularly resulted in no apparent symptoms of intoxication. These results demonstrate that Tx4(6-1) of P. nigriventer has no toxicity for mice, and suggest that it is a specific anti-insect toxin. The mol. wt (5244.6) and purity of the toxin were determined by desorption mass spectroscopy. The complete amino acid sequence of this toxin was established by direct automated Edman degradation and manual 4-N,N'-dimethylaminoazobenzene-4'isothiocyanate/phenyl-isothiocyanate microsequence analyses of peptides obtained from digests with various proteases. The protein contains 48 amino acids including 10 Cys and 6 Lys. The N-terminal and C-terminal residues were Cys. The Tx4(6-1) sequence differs from that of previously characterized neurotoxins found in the same and other venom spiders, but exhibited sequence similarities in the location of the Cys residues.

ELISA for the detection of toxic antigens in experimental and clinical envenoming by Tityus serrulatus scorpion venom

An ELISA was developed for identification of circulating toxic antigens from Tityus serrulatus scorpion venom. The toxic fraction from the scorpion venom was purified by Sephadex G-50 chromatography and immunoaffinity techniques were used for identifying antibodies that reacted with this fraction. These antibodies were used to develop a sandwich-type ELISA. The specificity of the assay was demonstrated by its capacity for identifying mice that were experimentally inoculated with T. serrulatus venom from those inoculated with Phoneutria nigriventer spider venom, Apis mellifera bee venom and Bothrops atrox, Crotalus durissus terrificus, Lachesis muta muta and Micrurus frontalis snake venoms. Measurable absorbance signals were obtained with 0.1 ng of venom per assay. The ELISA also detected antigens in the sera of patients systemically envenomed by T. serrulatus. Therefore, this ELISA could be a valuable tool for clinicians and epidemiologists, owing to its sensitivity and specificity.

Partial purification and pharmacological characterization of a neurotoxic fraction isolated from the venom of the spider Lycosa erythrognatha

The effect of the venom of the spider Lycosa erythrognatha on the frog sciatic nerve was investigated with the single sucrose-gap method. Solutions containing the crude venom (40 micrograms protein/ml) markedly increased the duration of compound action potentials and caused the appearance of long-lasting depolarizing post-potentials. These effects were only partially (20%) reversed by extensive washing with control solution. The active material was sensitive to proteolytic treatments with pronase or trypsin and was separated with 20% acetonitrile and 0.1% trifluoroacetic acid by reverse phase chromatography. The effect of this fraction (LycIV) on the post-potential amplitude was concentration-dependent, and was fitted with a quadratic hyperbola having a half maximal effect of 0.9 microgram protein/ml. SDS-polyacrylamide gel electrophoresis of LycIV showed an enriched polypeptide band with apparent molecular weight of approximately 8 kDa. The observed effects were similar to those of toxins that inhibit sodium channel inactivation and different from the effects of potassium channel blockers. Pore formation or membrane disruption could be ruled out. It was concluded that the venom contains a neurotoxic polypeptide that alters the repolarization of action potentials, probably by inhibiting sodium channel inactivation.

A phospholipase A2 inhibitor from the plasma of the South American rattlesnake (Crotalus durissus terrificus). Protein structure, genomic structure, and mechanism of action

The lethal toxicity of the South American rattlesnake (Crotalus durissus terrificus) venom can be attributed mainly to the presence of a pre-synaptic neurotoxin, crotoxin, with phospholipase A2 activity. Crotoxin is a heterodimer of an acidic protein (CA) and a basic phospholipase A2 (CB). An anti-toxic protein of subunit molecular mass 23.6 kDa that neutralizes both lethal and PLA2 activity of crotalid venom and crotoxin has been previously purified from the plasma of this snake (Fortes-Dias, C., Fonseca, B. C. B., Kochva, E., and Diniz, C. R. (1991) Toxicon 29, 997-1008). The protein has been named CNF for Crotalus neutralizing factor. In the present study, we have shown that CNF exists as an oligomeric aggregate of (CNF)n, where n = 6-8, and when it interacts with crotoxin, it replaces the acidic protein CA of crotoxin to form a stable near stoichiometric complex of CNF.CB. The CNF.CB complex no longer exhibits PLA2 activity and is inert in vivo. Thus, the exchange reaction between CA.CB of crotoxin and CNF to form CNF.CB and free CA is reminiscent of the interaction of crotoxin with its target receptor at the neuromuscular transmission site in the presynaptic cells. A cDNA encoding CNF has been isolated from a liver cDNA library using an appropriate nucleotide probe. The nucleotide sequence codes for a 19-residue signal peptide, followed by a 181-residue protein of which 16 are half-cystines. Calculated molecular mass is 20.06 kDa, and there is a putative N-linked carbohydrate site at Asn157.

Biochemical, pharmacological and genomic characterisation of Ts IV, an alpha-toxin from the venom of the South American scorpion Tityus serrulatus

The venom of the scorpion, Tityus serrulatus, was fractionated to investigate the chemical and pharmacological properties of its alpha-toxin content. Three alpha-toxins (Ts III, Ts IV and Ts V) were purified by conventional chromatography (gel filtration and ion-exchange chromatography), followed by immunoaffinity chromatography. Competition experiments using reference alpha- and beta-toxins suggested that these alpha-toxins were contaminated with around 0.01% of beta-toxin. The sequence of the first 30 amino acids of Ts IV was established. Using an oligonucleotide probe, a cDNA encoding its precursor was cloned from a venom gland cDNA library. The primary structure deduced from the cDNA nucleotide sequence provides possible explanations for the polymorphism of these three molecules.