Preparation of a crotoxin neutralizing monoclonal antibody

South American snake venoms with abundant neurotoxic components. Composition and toxicological properties. A literature review

In South America there are three snake genera with predominantly neurotoxic venoms: Crotalus, Micrurus and Hydrophis, which include nine species/subspecies, 97 species and a single marine species, respectively. Although accidents with neurotoxic venoms are less frequent than those with anticoagulant, cytotoxic or necrotic venoms (e.g. from Bothrops), they are of major public health importance. Venoms from genus Crotalus have been extensively studied, while data on the venoms from the other two genera are very limited, especially for Hydrophis. The venoms of North and South American Crotalus species show biochemical and physiopathological differences. The former species cause bothrops-like envenomation symptoms, while the latter mainly have neurotoxic and myotoxic effects, leading to respiratory paralysis and, occasionally, renal failure by myoglobinuria and death, often with no local lesions. Micrurus and Hydrophis also cause neurotoxic envenomations. Many studies have isolated, identified and characterized new enzymes and toxins, thus expanding the knowledge of snake venom composition. The present review summarizes the currently available information on neurotoxic venoms from South American snakes, with a focus on protein composition and toxicological properties. It also includes some comments concerning potential medical applications of elapid and crotalic toxins.

Immunotherapeutic potential of Crotoxin: anti-inflammatory and immunosuppressive properties

For the past 80 years, Crotoxin has become one of the most investigated isolated toxins from snake venoms, partially due to its major role as the main toxic component in the venom of the South American rattlesnake Crotalus durissus terrificus. However, in the past decades, progressive studies have led researchers to shift their focus on Crotoxin, opening novel perspectives and applications as a therapeutic approach. Although this toxin acts on a wide variety of biological events, the modulation of immune responses is considered as one of its most relevant behaviors. Therefore, the present review describes the scientific investigations on the capacity of Crotoxin to modulate anti-inflammatory and immunosuppressive responses, and its application as a medicinal immunopharmacological approach. In addition, this review will also discuss its mechanisms, involving cellular and molecular pathways, capable of improving pathological alterations related to immune-associated disorders.

Antibodies to a fragment of the Bothrops moojenil-amino acid oxidase cross-react with snake venom components unrelated to the parent protein

It is widely accepted that immunological cross-reactivity of snake venoms is mediated by antibodies that recognize venom components bearing either amino acid sequence homology or similar biological functions. However, here we demonstrate that polyspecific Bothrops antivenom is a source of cross-reactive antibodies that interact with venom proteins of distinctive primary structures and biological functions. The homoserine lactone derivative of the undecapeptide IQRWSLDKYAM (Ile1-Hse11), excised from the l-amino acid oxidase (LAAO) of the Bothrops moojeni venom, was the ligand of an affinity resin used to isolate specific anti-Ile1-Hse11 antibodies which were instrumental in revealing immunological cross-reactivity among unrelated venom proteins. We examined the extent of the cross-reactivity of these antibodies by probing electroblots of venoms from representative snakes of genera Bothrops, Lachesis, Crotalus and Micrurus, and by unambiguous structural characterization of the affinity-purified proteins of B. moojeni venom recovered from an agarose-anti-Ile1-Hse11 column. Our results indicate that all venoms tested had at least three reactive components toward anti-Ile1-Hse11 antibodies, among which we identified two serine proteases, one phospholipase A2 homologue, and LAAO. We hypothesize that the cross-reactivity of the anti-Ile1-Hse11 antibodies to unrelated venom proteins derives from their mechanism of antigen recognition, whereby complementarity is achieved through reciprocal conformational adaptation of the reacting molecules. Also, we believe these findings have implications both in the development of improved antivenoms and the preparation of immunochemical reagents for diagnostic and scientific investigation purposes in the field of snake venoms.

Neutralizing human anti crotoxin scFv isolated from a nonimmunized phage library

Combinatorial phage display technology offers a new possibility for making human antibodies which could be used in immune therapy. We explored the use of this technology to make human scFvs specific for crotoxin, the main toxic component of the venom of the South-American rattlesnake Crotalus durissus terrificus. Crotoxin, a phospholipase A2 neurotoxin constituted by the association of two subunits, exerts its lethal action by blocking neuromuscular transmission. This is the first report of human anticrotoxin scFvs (scFv 1, scFv 6 and scFv 8) isolated from a naive library of more than 1010 scFv clones with in vivo neutralizing activity. Nevertheless, differences are observed at the level of biological and immunological effects. Only scFv 8 is able to reduce the myotoxicity induced by crotoxin and scFv 1 is capable of altering the in vitro enzymatic activity of this toxin. All three scFvs recognize a region of one subunit located at the junction with the other one. Moreover these scFvs share strong amino acid homologies at the level of either the heavy or the light chain. Taken together, our results suggest that the use of human anticrotoxin scFvs may lead to a new and less aggressive passive immune therapy against poisoning by the venom of Crotalus durissus terrificus.

Influence of ionizing radiation on crotoxin: biochemical and immunological aspects

Irradiation of crotoxin and its subunits with 2000 Gy of gamma-rays from 60Co source leads to aggregation and generation of lower mol. wt breakdown products. Aggregates separated by gel filtration retain at least part of their higher-ordered structure, based on their reactivity with monoclonal antibodies known to react with conformational epitopes in native crotoxin. These same aggregates can serve as antigens to raise antisera that cross-react and neutralize crotoxin. Compared with native crotoxin, aggregates appear less myotoxic, are largely devoid of phospholipase activity, and are virtually non-toxic in mice. These results indicate that irradiation of toxic proteins can promote significant detoxification, but still retain many of the original antigenic and immunological properties of native crotoxin.

Specificity and binding affinity of an anti-crotoxin combinatorial antibody selected from a phage-displayed library

A crotoxin-specific, monoclonal, high-affinity, single-chain antibody variable region (scFv) was generated by combinatorial methods using Pharmacia's Recombinant Phage Antibody System. A high-affinity clone, designated A10G, was selected, and its DNA sequence was determined. Protein A10G showed high reaction specificity, with only the closely related rattlesnake neurotoxins, concolor toxin and Mojave toxin, showing cross-reactivity out of eleven group II phospholipase A2s (PLA2s) screened. No group I PLA2s cross-reacted in enzyme-linked immunosorbent assays. The gene coding for A10G was subcloned into an expression vector, and the resulting expressed nonfusion protein, designated A10GPE, was renatured and purified to apparent homogeneity. Dissociation constants of A10G with intact crotoxin and crotoxin basic subunit were determined to be 7 x 10(-10) and 6.8 x 10(-9) M, respectively. When A10GPE was preincubated with either the basic subunit or intact crotoxin at molar ratios of up to 5:1, no inhibition of phospholipase activity was observed. Expressed protein, however, could partially neutralize the lethality of Mojave toxin, a crotoxin homolog, in mice.

Monoclonal antibodies to VRV-PL-VIIIa, a basic multitoxic phospholipase A2 from Vipera russelli venom

VRV-PL-VIIIa, the most basic phospholipase A2 (PLA2) from the venom of Vipera russelli, induces multiple toxic effects, including neurotoxicity, myotoxicity, edema and hemorrhage. Rabbit polyclonal anti-serum was raised against VRV-PL-VIIIa. The antiserum cross-reacted in enzyme-linked immunosorbant assay (ELISA) with two other PLA2 from the same venom, VRV-PL-V and VRV-PL-VI, and with ammodytoxin A, caudoxin and crotoxin. Twenty-two hybridoma cell lines secreting monoclonal antibodies against VRV-PL-VIIIa were isolated. The monoclonal antibodies exhibited apparent binding affinities in ELISA with VRV-PL-VIIIa ranging over two orders of magnitude. Most of the monoclonal antibodies cross-reacted moderately with VRV-PL-V and weakly with VRV-PL-VI. None of the antibodies cross-reacted with ammodytoxin, caudoxin or crotoxin. Reducing the disulfide bonds of VRV-PL-VIIIa lowered the ELISA signals of each monoclonal antibody to nonspecific levels, suggesting that all the antibodies recognize conformational epitopes. Four of the 22 antibodies neutralized the enzymatic activity of VRV-PL-VIIIa. Interestingly, two of the four exhibited the lowest affinities of the monoclonal antibody library for VRV-PL-VIIIa in ELISA, while the other two exhibited the highest. Each of the monoclonal antibodies was biotinylated and spatial binding relationships were evaluated by competition ELISA.

Epitope mapping of snake venom phospholipases A2 with pseudexin monoclonal antibodies

Fifteen different monoclonal antibodies, developed against a pseudexin A, B, and C mixture, were screened for linear epitope recognition. Peptides (9-mers) spanning pseudexin B were synthesized on alanine-derivatized polyethylene pins and subsequently probed with antibody. Four antibodies recognized linear epitopes of pseudexin A, pseudexin B, and also nonidentical sequences found in other phospholipases A2 (PLA2S) as determined by enzyme-linked immunosorbent assays. Three antibodies recognized a highly conserved site important in calcium binding and the interlocking of dimeric forms of PLA2. Antibodies neutralizing lethal or enzymatic effects of PLA2 did not recognize linear epitopes.

Immunological studies of the toxic site in ammodytoxin A

Two monoclonal antibodies against the native ammodytoxin A and four site-directed polyclonal antibodies against synthetic peptides derived from the primary structure of the toxin were prepared in order to estimate the localization of its toxic site. Some of the antibodies neutralized the lethal toxicity of the toxin, thus indicating an approximate position of the toxic or receptor binding site on the molecule that is different from those predicted by comparison with a number of known sequences.

Specific binding of crotoxin to brain synaptosomes and synaptosomal membranes

Crotoxin, the presynaptic neurotoxin from Crotalus durissus terrificus, was iodinated and used to demonstrate high affinity, specific binding to guinea-pig (Cavia porcellus) brain synaptosomes and synaptosomal membrane fragments. 125I-crotoxin binding to the membrane fragments displays two binding plateaus, (Kd1 = 4 nM and Kd2 = 87 nM, Bmax1 = 2 and Bmax2 = 4 pmoles/mg membrane protein), but binding to whole synaptosomes revealed only one plateau (Kd = 2 nM and Bmax = 5 pmoles/mg membrane protein). Rosenthal analyses of Scatchard plots yielded similar binding constants in the presence or absence of 0.025% Triton X-100. In addition to equilibrium analyses, kinetic analyses of 125I-crotoxin binding to synaptosomal membrane fragments gave a Kd-value of 3 nM. The Kd value was not significantly changed by the exclusion of added calcium, but the binding site number was lowered. Crotoxin binding was inhibited by the acidic subunit of crotoxin and several presynaptic neurotoxins, which were classified according to their inhibitory properties as, strong (acidic subunit of crotoxin, Mojave toxin, concolor toxin, taipoxin and pseudexin), moderate (ammodytoxin A and textilotoxin), weak (notexin and scutoxin A), very weak (notechis II-5) and non-inhibitory (basic subunit of crotoxin, beta-bungarotoxin, Crotalus atrox and porcine pancreatic phospholipases A2, dendrotoxin, and notechis III-4). Purified acidic subunit of crotoxin, the most potent competitor of crotoxin binding, was somewhat more competitive than intact crotoxin and the other strong inhibitors on a molar basis. Strong, moderate and weak inhibitor groups each differed from the preceding group by requiring about a ten fold increase in concentration to effect a 50% inhibition of crotoxin binding. The weak group was therefore at least two-orders of magnitude less effective than the strong inhibition shown by the acidic subunit of crotoxin. Treatment of synaptosomal membranes with protease K lowered 125I-crotoxin binding, whereas treatment with trypsin did not. Iodinated, phospholipase A2 from C. atrox venom showed no specific binding to whole synaptosomes. Our results demonstrate the presence and describe some of the properties of high affinity, specific binding sites in brain tissue for crotoxin and related presynaptic neurotoxins.

Preparation and characterization of monoclonal antibodies against pseudexin

Fifteen hybridoma cell lines secreting monoclonal antibodies against pseudexin were developed. The cell lines were grown as ascites tumors and the resulting antibodies were purified by Protein A affinity-chromatography. Several of the antibodies exhibited extensive ELISA cross-reactions with different phospholipase A2 toxins from various snake venoms, while other of the antibodies reacted only with the pseudexins. Three of the antibodies neutralized pseudexin A and B, but none of the 10 other phospholipase A2 toxins tested. These same three antibodies inhibited the enzymatic activity of pseudexin A and B and also that of notexin. After each antibody was labeled with biotin, competition experiments were carried out to determine the binding relationships among the antibodies and the pseudexins. Competitions were frequently observed, with a low of zero to a high of eight out of the 14 possibilities. Competition experiments were also carried out with biotin-labeled rabbit IgG against the pseudexins. Some of the monoclonal antibodies had no effect on rabbit IgG binding to pseudexin, while others blocked up to 50% of the binding.

Amino acid sequence of the basic subunit of Mojave toxin from the venom of the Mojave rattlesnake (Crotalus s. scutulatus)

The complete sequence of the basis subunit of Mojave toxin from the venom of the Mojave rattlesnake (Crotalus s. scutulatus) is presented. It is shown to have great similarity to the basic subunits of related toxins from the venoms of the South American and midget faded rattlesnakes.

Effects of subunit cross-linking on the properties of crotoxin

Crotoxin was cross-linked using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride. Cross-linked crotoxin had the expected amino-terminal amino acids, amino acid composition, behavior on SDS-PAGE and an 80% reduction of reactable lysine residues. It was also non-toxic, had reduced immunological cross-reactivity toward both poly- and monoclonal antibodies raised to the basic subunit of crotoxin and had lost greater than 95% of its phospholipase activity. Loss of toxicity is due to either subunit cross-linking or the modification of essential residues.

Isolation of a crotoxin-like protein from the venom of a South American rattlesnake (Crotalus durissus collilineatus)

1. A crotoxin-like protein was isolated from the venom of a South American rattlesnake Crotalus durissus collilineatus. 2. Many of its properties are similar to those of crotoxin, including its non-covalent heterodimeric structure, electrophoretic mobility on SDS-PAGE, isoelectric focusing properties, toxicity in mice, immunological reactivity, multiple isoforms, phospholipase activity, peptide map, and instability on an anion-exchange column. 3. Results indicate that "collilineatus toxin" is strongly homologous with crotoxin, found in the venom of Crotalus durissus terrificus, and all other characterized rattlesnake neurotoxins.

Neutralization of lethal potency and inhibition of enzymatic activity of a phospholipase A2 neurotoxin, crotoxin, by non-precipitating antibodies (Fab)

Rabbit antibodies were prepared against both purified catalytic (component-B) and purified non-catalytic (component-A) subunits of crotoxin, the major phospholipase A2 neurotoxin from the South American rattlesnake. They cross-react with crotoxin-like toxins from the venom of several Crotalus species as well as with single-chain phospholipase A2 neurotoxins from Crotalid and Viperid venoms (agkistrodontoxin and ammodytoxin A) but not from Elapid venoms (notexin). Immunological cross-reactions of anti-component-A and anti-component-B sera with crotoxin and with its isolated components A and B showed that component-A exposes determinants of low immunogenicity which are present on component-B, whereas the major antigenic determinants of component-B are not present on component-A. Anti-component-B antibodies, but not anti-component-A antibodies, neutralize the lethal potency of crotoxin and inhibit its enzymatic activity. Furthermore, non-precipitating anti-component-B Fab fragments were as potent as antibodies, indicating that crotoxin neutralization results from the binding of the antibodies to the catalytic subunit, rather than the formation of an immunoprecipitate.

A gyroxin analog from the venom of the bushmaster (Lachesis muta muta)

Clinical observations of possible neurotoxic activity in bushmaster (Lachesis muta muta) envenomations, coupled with the accepted ancestral relationship of Lachesis to other crotalids, suggested that Lachesis venom might contain a crotoxin-like molecule. Crude venom and gel-filtration fractions showed modest reactivity in enzyme-linked immunosorbent assays using rabbit polyclonal antibodies raised against the basic subunit of crotoxin, but no reaction was detected with a murine monoclonal antibody raised against the same antigen. Phospholipase assays, LD50 determinations and SDS-polyacrylamide gel electrophoresis indicated the presence of non-toxic phospholipases, but no crotoxin homologs. A higher mol.wt, toxic protein (60,000) with an LD50 of 0.07 micrograms/g in mice was isolated and purified, which induced gyroxin-like, rapid rolling motions in mice. Its amino terminal sequence shows considerable amino acid sequence identity with gyroxin from the venom of Crotalus durissus terrificus and other serine proteases.