Contribution of crotoxin for the inhibitory effect of Crotalus durissus terrificus snake venom on macrophage function

Previous work of our group demonstrated that Crotalus durissus terrificus venom has a dual effect on macrophage function: it inhibits spreading and phagocytosis and stimulates hydrogen peroxide and nitric oxide production, antimicrobial activity and glucose and glutamine metabolism of these cells. Crotalid venom also induces analgesia and this effect is mediated by opioid receptors. The involvement of opioidergic mechanism and the determination of the active component responsible for the inhibitory effect of crotalid venom on macrophage function were investigated. The venom reduced the spreading and phagocytic activities of peritoneal macrophages. This effect was observed in vitro, 2 h after incubation of resident peritoneal macrophages with the venom, and in vivo, 2 h after subcutaneous injection of the venom. The inhibition of phagocytosis was not modified by naloxone, an antagonist of opioid receptors. Venom neutralization with crotalid antivenom abolished the inhibitory effect of the venom, indicating that venom toxins are involved in this effect. Crotoxin, the main toxin of crotalid venom, s.c. injected to rats or added to the medium of peritoneal cell incubation, inhibited macrophage function in a similar manner to that observed for crude venom. The present results suggest that crotoxin causes a direct inhibition of macrophage spreading and phagocytic activities and may contribute to the inhibitory effect of crotalid venom on macrophage function.

Acute lung injury in experimental pancreatitis in rats: pulmonary protective effects of crotapotin and N-acetylcysteine

Respiratory complications are major factors contributing to death in acute pancreatitis. However, the mechanisms of these pulmonary complications are not completely elucidated. We studied the effects of pretreatment with purified crotapotin (a phospholipase A2 inhibitor), N-acetylcysteine (a reactive oxygen species inhibitor), and a combination of both on the pulmonary mechanical and morphometric changes secondary to severe acute necrohemorrhagic pancreatitis in Wistar rats. A total of 69 male Wistar rats were studied. Pancreatitis was induced by infusion of 0.5 mL of a 4% solution of sodium taurocholate into the biliopancreatic duct. Crotapotin, N-acetylcysteine, or a combination of both was given intraperitoneally 30 min before inducing pancreatitis. Data were compared with data from sham-operated animals with or without those pretreatments. The severity of pancreatic and pulmonary injuries was evaluated 4 h after inducing pancreatitis by morphometric and pulmonary mechanical studies. N-acetylcysteine prevented the development of alveolar edema, alveolar distention, and collapse. Crotapotin prevented alveolar distention and collapse, and pulmonary dynamic elastance increase. When used in combination, crotapotin and N-acetylcysteine prevented both pulmonary morphological and mechanical changes induced by acute pancreatitis, suggesting an increase in protective effect when these drugs are used together compared with individual effects. However, the severity of pancreatic necrosis and the increase in polymorphonuclear cells in alveolar septa induced by pancreatitis were not reduced by previous administration of crotapotin, N-acetylcysteine, or both. These results suggest that the protective effects of these drugs are probably due to an extra-pancreatic action in the circulation, or even directly in the lung.

Isolation and preliminary enzymatic characterization of a novel PLA2 from Crotalus durissus collilineatus venom

A crotoxin homolog was purified from the Crotalus durissus collilineatus venom using molecular exclusion and reverse-phase HPLC. This crotoxin contained one PLA2 (Cdcolli III F6) and four crotapotin isoforms, whereas crotoxin from Crotalus durissus terrificus venom had three PLA2 iso forms and two crotapotin isoforms. SDS-PAGE showed that the C. d. collilineatus PLA2 and crotapotin had relative molecular mass of 15 and 9 kDa, respectively. Neither the PLA2 (Cdcolli III F6) nor the crotapotins (Cdcolli III F3 and F4) had any neurotoxicity in mouse phrenic nerve-diaphragm preparations when tested alone. However, when PLA2 and crotapotin were coincubated before testing, the neurotoxicity was restored to a level similar to test in the venom in native crotoxin. The two crotapotins (Cdcolli III F3 and F4) differed in their ability to inhibit PLA2 activity, perhaps because of variations in their affinities for this enzyme. Cdcolli III F6 showed allosteric enzymatic behavior, with maximal activity at pH 8.3 and 36 degrees C. Full PLA2 activity required the presence of a low Ca2+ concentration and was inhibited by Cu2+ and Zn2+ and by Cu2+ and Mg2+ in the presence and absence of Ca2+, respectively. These results indicate that crotoxin from C. d. collineatus venom is very similar enzymatically to crotoxin from C. d. terrificus.

Structural and functional characterization of basic PLA2 isolated from Crotalus durissus terrificus venom

The venom of Crotalus durissus terrificus was fractionated by reverse-phase HPLC to obtain crotapotins (F5 and F7) and PLA2 (F15, F16, and F17) of high purity. The phospholipases A2 (PLA2S) and crotapotins showed antimicrobial activity against Xanthomonas axonopodis pv. passiflorae, although the unseparated crotoxin did not. The F17 of the PLA2 also revealed significant anticoagulant activity, althrough for this to occur the presence of Glu 53 and Trp 61 is important. The F17 of the PLA2 showed allosteric behavior in the presence of a synthetic substrate. The amino acid sequence of this PLA2 isoform, determined by automatic sequencing, was HLLQFNKMLKFETRK NAVPFYAFGCYCGWGGQRRPKDATDRCCFVHDCCYEKVTKCNTKWDFYRYSLKSGY ITCGKGTWCKEQICECDRVAAECLRRSLSTYKNEYMFYPDSRCREPSETC. Analysis showed that the sequence of this PLA2 isoform differed slightly from the amino acid sequence of the basic crotoxin subunit reported in the literature. The homology with other crotalid PLA2 cited in the literature varied from 60% to 90%. The pL was estimated to be 8.15, and the calculated molecular weight was 14664.14 as determined by Tricine SDS-PAGE, two-dimensional electrophoresis, and MALDI-TOFF. These results also suggested that the enzymatic activity plays an important role in the bactericidal effect of the F17 PLA2 as well as that of anticoagulation, although other regions of the molecule may also be involved in this biological activity.

Inhibition of crotoxin phospholipase A(2) activity by manoalide associated with inactivation of crotoxin toxicity and dissociation of the heterodimeric neurotoxic complex

Crotoxin (CACB complex) is a convulsant heterodimeric neurotoxic phospholipase A(2) (PLA(2)). The role of phospholipid hydrolysis in its epileptogenic properties remains unresolved. We, thus, studied the effect of manoalide (MLD), a PLA(2) inhibitor, on the toxin catalytic activity and its central and peripheral toxicity. Incubation of crotoxin with MLD fully and irreversibly inactivated its enzymatic activity. Interestingly, crotoxin also lost its central neurotoxicity after intracerebroventricular injection and peripheral toxicity after intravenous administration. MLD-treated crotoxin prevented the high affinity binding of [125I]-radiolabeled crotoxin on rat cortex synaptic plasma membranes. Further analysis of MLD-treated crotoxin by non-denaturing PAGE and surface plasmon resonance indicated that the crotoxin complex was dissociated after MLD treatment. Although the loss of MLD-treated crotoxin peripheral neurotoxicity could not be attributed to this dissociation, the presence of free CA subunit might explain the observed competition in binding experiments. In conclusion, the dissociation of the crotoxin complex by MLD, as demonstrated in this study, did not permit to specify the role of the enzymatic activity in crotoxin epileptogenic properties. Other approaches would be required to resolve this question.

30-day intravenous administration of VRCTC-310-ONCO in rabbits

VRCTC-310-ONCO, an agent based on the snake phospholipase A2 (crotoxin), is currently under clinical development. After phase I study in patients by intramuscular administration, the interest of intravenous (IV) dosing arose. To evaluate IV administration of VRCTC-310-ONCO in rabbits, ten animals were subjected to surgical implant of fixed jugular catheter, by which they received daily IV doses of 0.03 mg/kg body weight of VRCTC-310-ONCO for 30 days (n = 8) or saline (n = 2). The procedure was well tolerated in all rabbits. One of the animals died after the sixth dose of VRCTC-310-ONCO with CNS involvement; two additional rabbits required dose-reduction. All other rabbits achieved 30 days of treatment and were sacrificed. All rabbits (even controls) developed lymphocytosis and mild anaemia, without changes in blood neutrophils. No changes were found in serum transaminases (GOT and GPT), cholesterol, triglycerides, and y-glutamyl transpeptidase. At necropsy, chronic granulation tissue was found surrounding the implant in all rabbits. VRCTC-3 10-ONCO-treated rabbits presented generalised and marked swelling of hepatocytes, with areas of cytoplasmic vacuolisation. No abnormalities were found in kidney, heart, lung, spleen, adrenal gland, uterus, testes and ovary. Additional studies with IV route for VRCTC-310-ONCO, including humans, are required to define its toxicity in the clinical setting.

The facilitatory actions of snake venom phospholipase A(2) neurotoxins at the neuromuscular junction are not mediated through voltage-gated K(+) channels

Electrophysiological investigations have previously suggested that phospholipase A(2) (PLA(2)) neurotoxins from snake venoms increase the release of acetylcholine (Ach) at the neuromuscular junction by blocking voltage-gated K(+) channels in motor nerve terminals. We have tested some of the most potent presynaptically-acting neurotoxins from snake venoms, namely beta-bungarotoxin (BuTx), taipoxin, notexin, crotoxin, ammodytoxin C and A (Amotx C & A), for effects on several types of cloned voltage-gated K(+) channels (mKv1.1, rKv1.2, mKv1.3, hKv1.5 and mKv3.1) stably expressed in mammalian cell lines. By use of the whole-cell configuration of the patch clamp recording technique and concentrations of toxins greater than those required to affect acetylcholine release, these neurotoxins have been shown not to block any of these voltage-gated K(+) channels. In addition, internal perfusion of the neurotoxins (100 microg/ml) into mouse B82 fibroblast cells that expressed rKv1.2 channels also did not substantially depress K(+) currents. The results of this study suggest that the mechanism by which these neurotoxins increase the release of acetylcholine at the neuromuscular junction is not related to the direct blockage of voltage-activated Kv1.1, Kv1.2, Kv1.3, Kv1.5 and Kv3.1 K(+) channels.

Effects of chemical modifications of crotoxin B, the phospholipase A(2) subunit of crotoxin from Crotalus durissus terrificus snake venom, on its enzymatic and pharmacological activities

Crotoxin B, the basic Asp49-PLA(2) subunit from crotoxin, the main component of Crotalus durissus terrificus venom, displays myotoxic, edema-inducing, bactericidal (upon Escherichia coli), liposomal-disrupting and anticoagulant activities. Chemical modifications of His (with 4-bromophenacyl bromide, BPB), Tyr (with 2-nitrobenzenesulphonyl fluoride, NBSF), Trp (with o-nitrophenylsulphenyl chloride, NPSC) and Lys (with acetic anhydride) residues of this protein, in addition to cleavage with cyanogen bromide (CNBr) and inhibition with ethylenediaminetetraacetic acid (EDTA), were carried out in order to study their effects on enzymatic and pharmacological activities. Lethality was reduced after modification of His or Lys residues, as well as after cleavage with CNBr, while enzymatic activity was completely abolished after modification of His or incubation with EDTA. Modification of Lys or Tyr, or cleavage with CNBr, partially reduced enzymatic activity. Anticoagulant activity was modified similarly to enzymatic activity, evidencing the dependency of this pharmacological effect on catalytic activity. Myotoxicity was reduced after modification of His or Lys, as well as after cleavage with CNBr, whereas EDTA reduced this effect to a lesser extent. Bactericidal effect was significantly reduced only after modification of Lys and after cleavage with CNBr. Edema-inducing activity was partially inhibited after treatment with EDTA and strongly reduced after acetylation of Lys residues and cleavage with CNBr, being only partially reduced after His alkylation. On the other hand, liposome disrupting activity was only partially reduced after modification of His and Tyr or after cleavage with CNBr. Modification of Trp residue partially reduced lethality and myotoxicity but did not affect enzymatic or anticoagulant activities. These data indicate that enzymatic activity is relevant for some pharmacological effects induced by crotoxin B (mainly lethal, myotoxic and anticoagulant activities), and also evidence that this subunit of crotoxin displays regions different from the active catalytic site which are involved in some of the toxic and pharmacological effects induced by this phospholipase A(2).

Isolation and enzymatic characterization of a basic phospholipase A2 from Bothrops jararacussu snake venom

A novel basic phospholipase A2 (PLA2) isoform was isolated from Bothrops jararacussu snake venom and partially characterized. The venom was fractionated by HPLC ion-exchange chromatography in ammonium bicarbonate buffer, followed by reverse-phase HPLC to yield the protein Bj IV. Tricine SDS-PAGE in the presence or absence of dithiothreitol showed that Bj IV had a molecular mass of 15 and 30 kDa, respectively. This enzyme was able to form multimeric complexes (30, 45, and 60 kDa). Amino acid analysis showed a high content of hydrophobic and basic amino acids as well as 14 half-cysteine residues. The N-terminal sequence (DLWSWGQMIQETGLLPSYTTY...) showed a high degree of homology with basic D49 PLA2 myotoxins from other Bothrops venoms. Bj IV had high PLA2 activity and produced moderate myonecrosis in skeletal muscle, but showed no neuromuscular activity in mouse phrenic nerve-diaphragm preparations. Bj IV showed allosteric enzymatic behavior, with maximal activity at pH 8.2 and 35-45 degrees C. Full PLA2 activity required Ca2+ but was inhibited by Cu2+ and Zn2+, and by Cu2+ and Mg2+ in the presence and absence of Ca2+, respectively. Crotapotins from Crotalus durissus terrificus rattlesnake venom significantly inhibited the enzymatic activity of Bj IV. The latter observation suggested that the binding site for crotapotin in this PLA2 was similar to that in the basic PLA2 of the crotoxin complex from C. d. terrificus venom. The presence of crotapotin-like proteins capable of inhibiting the catalytic activity of D49 PLA2 could partly explain the low PLA2 activity of Bothrops venoms.

In vivo effect of snake phospholipase A2 (crotoxin+cardiotoxin) on serum IL-1alpha, TNF-alpha and IL-1ra level in humans

VRCTC-310-Onco (crotoxin, a secretory phospholipase A2+cardiotoxin) is under development as an anti-neoplastic agent. Pro-inflammatory cytokines TNF-alpha and interleukin 1 alpha (IL-1alpha) and anti-inflammatory cytokine IL-1 receptor antagonist (IL-1ra) were measured with commercial ELISA kits in sera corresponding to 23 cycles with doses between 0.0025 and 0.023 microg/kg body weight, obtained during the phase I trial of VRCTC-310-Onco. Neither serum TNF-alpha nor IL-1alpha did change significantly after VRCTC-310-Onco. Basal IL-1ra was 794 +/- 97 pg/ml, by 3 h it was similar, 651 +/- 99 pg/ml and at 24 h p.i. it increased to 1197 +/- 122 pg/ml (P<0.001). The increase was dose-dependent. The addition of dexamethasone (required to reduce pain with the highest doses) inhibited IL-1alpha and enhanced the induction of IL-1ra by VRCTC-310-Onco. Summing up, in vivo, in humans, in the dose range tested, VRCTC-310-Onco induces IL-1ra, and does not consistently modify IL-1alpha or TNF-alpha serum levels.

Enzymatic characterization of a novel phospholipase A2 from Crotalus durissus cascavella rattlesnake (Maracambóia) venom

The PLA2 and crotapotin subunits of crotoxin from Crotalus durissus cascavella venom were purified by a combination of high-performance liquid chromatography (HPLC) molecular exclusion (Protein Pack 300SW column) and reverse-phase HPLC (RP-HPLC). Tricine SDS-PAGE showed that the PLA2 and crotapotins migrated as single bands with estimated molecular masses of 15 and 9 kDa, respectively. The amino acid composition of the PLA2 showed the presence of 14 half-cysteines and a high content of basic residues (Lys, Arg, His), whereas the crotapotins were rich in hydrophobic, negatively charged residues and half-cysteines. The PLA2 showed allosteric behavior, with maximal activity at pH 8.3 and 35-40 degrees C. C. d. cascavella PLA2 required Ca2+ for activity but was inhibited by Cu2+ and Zn2+ and by Cu2+ and Mg2+ in the presence and absence of Ca2+, respectively. Crotapotin (F3) and heparin inhibited the catalytic activity of the PLA2 by acting as allosteric inhibitors.

Enzymatic characterization of a novel phospholipase A2 from Crotalus durissus cascavella rattlesnake (Maracambóia) venom

The PLA2 and crotapotin subunits of crotoxin from Crotalus durissus cascavella venom were purified by a combination of HPLC molecular exclusion (Protein Pack 300SW column) and reverse-phase HPLC (RP-HPLC). Tricine SDS-PAGE showed that the PLA2 and crotapotins migrated as single bands with estimated molecular masses of 15 and 9 kDa, respectively. The amino acid composition of the PLA2 showed the presence of 14 half-cysteines and a high content of basic residues (Lys, Arg, His), whereas the crotapotins were rich in hydrophobic, negatively charged residues and half-cysteines. The PLA2 showed allosteric behavior, with maximal activity at pH 8.3 and 35-40 degrees C. The C. d. cascavella PLA2 required Ca2+ for activity, but was inhibited by Cu2+ and Zn2+ and by Cu2+ and Mg2+ in the presence and absence of Ca2+, respectively. Crotapotin (F3) and heparin inhibited the catalytic activity of the PLA2 by acting as allosteric inhibitors.

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.

Nature of the postsynaptic action of crotoxin at guinea-pig diaphragm end-plates

Crotoxin is known to desensitize the nicotinic receptor of Torpedo marmorata and Electrophorus electricus electroplaques. The aim of the present study was to elucidate whether the postsynaptic effect of crotoxin at a mammalian muscle end-plate is also caused by receptor desensitization or results from a curaremimetic action. For this purpose, we investigated the action of 4-aminopyridine (4-AP) on crotoxin-induced blockade of miniature end-plate potentials (m.e.p.p.s) and of the depolarization of end-plates produced by carbachol. The experiments were carried out in guinea-pig diaphragms bathed in Tyrode solution at 37 degrees C and gassed with 95% O2, 5% CO2. The potentials were measured with conventional techniques using glass microelectrodes. Even at low concentrations, crotoxin blocked the m.e.p.p.s and this blockade was antagonized by 4-AP. Neostigmine was without effect. 4-AP did not restore the m.e.p.p.s blocked by either d-tubocurarine (dTc) or beta-bungarotoxin (beta-BTX). 4-AP also antagonized the crotoxin-induced blockade of the end-plate depolarization produced by carbachol. These results show that the postsynaptic effect of crotoxin at the guinea-pig muscle end-plate also results from nicotinic receptor desensitization.

Effect of crotapotin and heparin on the rat paw oedema induced by different secretory phospholipases A2

The effects of crotapotin (a non-toxic and non-enzymatic acid polypeptide naturally complexed with phospholipase A2) and heparin on rat paw edema induced by different secretory phospholipases A2 (sPLA2) have been investigated. The ability of crotapotin to affect the enzymatic activity of the sPLA2(s) have also been evaluated. Secretory PLA2(s) obtained from both snake (Naja naja, Naja mocambique mocambique, Crotalus adamanteus and Crotalus durissus terrificus) and bee (Apis mellifera) venoms as well as that from bovine pancreas were used in this study. Rat paw oedema was induced by a single subplantar injection of the sPLA2s (5-30 microg/paw) in absence and presence of either crotapotin (10-100 microg/paw) or heparin (50 U/paw). Paw volume was measured using a hydroplethysmometer. Phospholipase A2 from Naja naja, Naja mocambique mocambique, Apis mellifera venoms and the basic component of Crotalus durissus terrificus venom all induced dose-dependent rat paw oedema whereas those from Crotalus adamanteus venom and bovine pancreas were ineffective. Paw oedema induced by PLA2(s) from both Naja naja and Apis mellifera venoms was significantly (P < 0.05) inhibited by crotapotin (0.1-100 microg/site) whereas the Naja mocambique mocambique venom PLA2-induced oedema was significantly potentiated (P < 0.05) by this polypeptide (40 microg/site). On the other hand, heparin (50 U/paw) had no effect on the paw oedema induced by PLA2 from Naja naja and Apis mellifera venoms but significantly inhibited the Naja mocambique mocambique venom PLA2-induced oedema. The measurement of the in vitro phospholipasic activity revealed that crotapotin inhibited by 60-70% the enzymatic activities of PLA2(s) from Crotalus adamanteus, Naja mocambique mocambique, Apis mellifera venoms and bovine pancreas. Our results suggest that despite the great homology between the various types of sPLA2 they interact with crotapotin on cell surfaces in different ways leading to either inhibition or potentiation of the paw oedema by a mechanism unrelated to their enzymatic activities. Since heparin reduced paw oedema induced by PLA2 from Naja mocambique mocambique venom it is likely that this sPLA2 is similar to the novel heparin-sensitive PLA2 found in mast cells.

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.

Regulation of epidermal growth factor receptor activity by crotoxin, a snake venom phospholipase A2 toxin. A novel growth inhibitory mechanism

Crotoxin (CT), a phospholipase A2 (PLA2) derived from the venom of Crotalus durissus terrificus, is a heterodimeric protein composed of subunit B with enzymatic activity and a binding regulatory subunit (A) without enzyme activity. Although the PLA2 activity of CT may be important in its anti-proliferative activity, its cytostatic mechanism is unknown. In this study, we examined the cytostatic effect of PLA2-associated CT activity on squamous carcinoma cells expressing distinct levels of epidermal growth factor receptor (EGFr). CT was most effective in suppressing growth on cells expressing high intrinsic levels of EGFr. Cardiotoxin, another membrane active toxin with no intrinsic PLA2 activity, had no differential anti-proliferative activity on cells expressing high EGFr levels, suggesting a correlation between EGFr expression and CT-directed anti-proliferative activity. Both chemically modified CT (MCT) devoid of PLA2 activity and covalently cross-linked CT (CCT), which is functionally unable to utilize cellular membranes as PLA2 substrate, were also without growth inhibitory activity. No evidence for direct binding of CT to EGFr was found, although pretreatment with EGF was able to partially suppress the anti-proliferative activity of CT. Tyrosine phosphorylation of EGFr, however, was stimulated by CT in intact A431 cells. Tyrosine phosphorylation of EGFr was concentration-dependently stimulated (3- to 8-fold) in cellular membranes of A431 cells treated in vitro with CT but not with anti-proliferatively inactive MCT or CCT. The data provide evidence for transmembrane receptors involved in growth signaling (namely EGFr) as cellular targets and potential effectors of PLA2-mediated anti-proliferative activity of snake venom.

Crotoxin-induced behavioral effects in rats

Crotoxin is the major component of Crotalus durissus terrificus venom. In view of the presence of high-affinity specific binding sites for crotoxin in the brain, the objective of this work was to investigate whether crotoxin induces behavioral effects in the open-field and hole-board tests. Adult male Wistar rats (180-220 g) treated with crotoxin, 100, 250 and 500 micrograms/kg, ip, administered 2 h before the test, presented statistically significant behavioral alterations (ANOVA for one-way classification complemented with Dunnet test, P < 0.05). In the open-field test, 250 and 500 micrograms/kg of crotoxin increased freezing (from 3.22 sec to 10.75 sec and 11.2 sec) and grooming (from 13.44 sec to 22.75 sec and 21.22 sec) and decreased ambulation (from 64.8 to 39.38 and 45.8). The dose of 500 micrograms/kg also decreased rearing (from 24.9 to 17.5). In the hole-board test, 500 micrograms/kg of crotoxin decreased head-dip count (from 6.33 to 4.00). All the crotoxin-induced behavioral effects were antagonized by an anxiolytic dose of diazepam (1.5 mg/kg, ip. 30 min before the tests). These results show that crotoxin reduced open-field activity and exploratory behavior as well. We suggest that these effects express an increased emotional state induced by this toxin.

Molecular cloning and characterization of a neurotoxic phospholipase A2 from the venom of Taiwan habu (Trimeresurus mucrosquamatus)

Using gel-filtration chromatography and reverse-phase (RP) HPLC we have purified a presynaptic neurotoxin (designated as trimucrotoxin) from the crude venom of Taiwan habu (Trimeresurus mucrosquamatus). Its complete primary structure was solved by an automated N-terminal sequencing and cDNA sequencing method. The enzyme inhibited the twitch of the chick biventer cervicis muscle at 0.1-1 micrograms/ml and showed lethality in mice (LD50 = 1.2 micrograms/g, when given intravenously). Trimucrotoxin exists mainly as a homodimer of 14 kDa subunits as shown by a gel-filtration experiment, and dissociates into monomers during SDS/PAGE in the absence of Ca2+. However, most of trimucrotoxin migrated as slowly as a trimer during nondenaturing SDS/PAGE in the presence of Ca2+ or Sr2+. Its amino acid sequence identity to crotoxin B and agkistrodotoxin is about 75%, and its cDNA sequence is 82% identical to that of crotoxin B. Rabbit antiserum against trimucrotoxin also cross-reacted with the other crotalid neurotoxic phospholipases A2. Furthermore, the purified acidic subunit of crotoxin potentiated the neurotoxicity of trimucrotoxin. A comparison of the sequences of these crotalid neurotoxins revealed some common features of the possible neurotoxic sites, including residues 6, 11, 76-81 and 119-125.

Neutralization of the effect of Crotalus durissus terrificus venom by gangliosides

We determined the ability of a mixture of gangliosides (16% GD1b, 19% GT1b, 21% GM1, 40% GD1a) to neutralize the effect of Crotalus durissus terrificus (Cdt) venom in vitro and in vivo. Protection was indicated by the absence of muscular contractions, hind limb paralysis or death of BALB/c mice (16-18 g) after receiving Cdt venom (1 microgram Cdt venom containing 0.6 microgram protein) at the doses indicated. A dose of Cdt venom above 0.9 microgram (ip) or 1 microgram (im) induced muscular contraction and above 1.2 micrograms (ip) or 5.5 micrograms (im) the venom induced muscular contraction and hind limb paralysis. Cdt venom above 2.5 micrograms (ip) or 9 micrograms (im) induced all these symptoms and 95 to 100% death in experimental animals. The lethal dose 50% of the Cdt venom used was 8 micrograms (im) and 1.5 micrograms (ip). In in vitro studies, 4 mg gangliosides neutralized the effect of up to 1.5 micrograms Cdt venom. Quantities as low as 0.2 mg gangliosides were capable of neutralizing 0.9 microgram of Cdt venom in vitro. Intramuscular treatment with 1 mg gangliosides performed 60 min after the intramuscular injection of 5 micrograms Cdt venom protected 100% of the animals. In contrast, no protection was achieved with intraperitoneal treatment with gangliosides. The data show that gangliosides were effective in neutralizing the toxic effects induced by Crotalus durissus terrificus venom both in vitro and in vivo and that post-exposure intramuscular treatment with gangliosides could protect animals experimentally inoculated with the venom.

Inhibition of carrageenin-induced rat paw oedema by crotapotin, a polypeptide complexed with phospholipase A2

1. The effect of purified crotapotin, a non-toxic non-enzymatic chaperon protein normally complexed to a phospholipase A2 (PLA2) in South America rattlesnake venom, was studied in the acute inflammatory response induced by carrageenin (1 mg/paw), compound 48/80 (3 micrograms/paw) and 5-hydroxytryptamine (5-HT) (3 micrograms/paw) in the rat hind-paw. The effects of crotapotin on platelet aggregation, mast cell degranulation and eicosanoid release from guinea-pig isolated lung were also investigated. 2. Subplantar co-injection of crotapotin (1 and 10 micrograms/paw) with carrageenin or injection of crotapotin (10 micrograms/paw) into the contralateral paw significantly inhibited the carrageenin-induced oedema. This inhibition was also observed when crotapotin (10-30 micrograms/paw) was administered either intraperitoneally or orally. Subplantar injection of heated crotapotin (15 min at 60 degrees C) failed to inhibit carrageenin-induced oedema. Subplantar injection of crotapotin (10 micrograms/paw) also significantly inhibited the rat paw oedema induced by compound 48/80, but it did not affect 5-HT-induced oedema. 3. In adrenalectomized animals, subplantar injection of crotapotin markedly inhibited the oedema induced by carrageenin. The inhibitory effect of crotapotin was also observed in rats depleted of histamine and 5-HT stores. 4. Crotapotin (30 micrograms/paw) had no effect on either the histamine release induced by compound 48/80 in vitro or on the platelet aggregation induced by both arachidonic acid (1 nM) and platelet activating factor (1 microM) in human platelet-rich plasma. The platelet aggregation and thromboxane B2 (TXB2) release induced by thrombin (100 mu ml-1) in washed human platelets were also not affected by crotapotin. In addition, crotapotin (10 microg/paw) did not affect the release of 6-oxo-prostaglandin Fla, and TXB2 induced by ovalbumin in sensitized guinea-pig isolated lungs.5. Our results indicate that the anti-inflammatory activity of crotapotin is not due to endogenous corticosteroid release or inhibition of cyclo-oxygenase activity. It is possible that crotapotin may interact with extracellular PLA2 generated during the inflammatory process thereby reducing its hydrolytic activity.

Crotoxin induces aggregation of human washed platelets

Crotoxin, the main toxic component isolated from the venom of the South American rattlesnake Crotalus durissus terrificus, is a reversible protein complex composed of a non-toxic non-enzymatic acidic polypeptide (crotapotin) and a toxic basic phospholipase A2 (PLA2). In this study, we have evaluated the ability of crotoxin to induced aggregation in human washed platelets. Human washed platelet aggregation was monitored in a Payton aggregometer and thromboxane B2 (TXB2) release measured by direct radioimmunoassay (RIA). Crotoxin (15-50 micrograms/ml) produced dose-dependent and irreversible human washed platelet aggregation, which was inhibited by pre-incubation of the platelets with sodium nitroprusside (50-500 microM) or iloprost (8-80 nM). Crotoxin also induced TXB2 release (207 +/- 8 ng/ml, n = 6), and although indomethacin significantly reduced the release of TXB2 (to 23.5 +/- 5 ng/ml, P < 0.001, n = 6), it did not inhibit crotoxin-induced aggregation. Our results clearly demonstrate that crotoxin induces human washed platelet aggregation and that this phenomenon is independent of the formation of pro-aggregatory arachidonic acid metabolites.

Effects of crotoxin on the action potential kinetics of frog skeletal muscle

1. The effect of crotoxin on the action potential kinetics of frog (Rana catesbeiana; 60-80 g) skeletal muscle was studied using a modified Ringer solution containing 1.6 mM KCl. 2. Crotoxin affected the kinetics of the action potential in a dose-dependent manner (90 to 460 nM). At 230 nM, crotoxin prolonged the duration of the action potential (from 1.1 +/- 0.1 to 1.6 +/- 0.1 ms) and slowed the rates of depolarization (from 282.0 +/- 7.3 to 196.0 +/- 13.2 V/s) and repolarization (from -81.4 +/- 6.9 to -55.6 +/- 3.8 V/s), in a dose-dependent manner. Its phospholipase subunit (component B) was five times less effective. 3. No effect of crotoxin was observed in the presence of 2.5 mM KCl or when SrCl2 was substituted for CaCl2. Lowering the muscle temperature to 12 degrees C did not reduce the effect of crotoxin. 4. No effect on the passive membrane response to hyperpolarizing current pulses was observed, which implies no major effect on the membrane resistance and capacitance. 5. It is concluded that crotoxin reduces the Na+ current and slows down the repolarization mechanism. This effect is probably not dependent on the phospholipase A2 activity of crotoxin and is inhibited by the substitution of Sr2+ for Ca2+.

VRCTC-310--a novel compound of purified animal toxins separates antitumor efficacy from neurotoxicity

Two purified animal venom toxins, crotoxin and cardiotoxin, have been combined to produce a unique natural product (VRCTC-310) currently under investigation as an antitumor agent by the National Cancer Institute. In vitro, it has demonstrated cytotoxic disease specificity and a unique mechanism of action when submitted to COMPARE analysis. In vivo, tolerance was developed to the neurotoxic properties of crotoxin which allowed comparison of several schedules of fixed and escalating daily i.m. doses to mice bearing s.c. Lewis Lung carcinoma. An 83% inhibition of tumor growth was achieved using an escalating dose schedule starting at 1.8 mg/kg and reaching 6.3 mg/kg/day on day 20. Although some irritation around the sites of i.m. injection was noted, animal weight loss was negligible and there were no other signs of adverse toxicity. This natural product represents a new, membrane interactive anticancer agent which produces a unique spectrum of cytotoxicity in vitro and which has demonstrated interesting in vivo antitumor efficacy.