- Email: [email protected]
Evolution of the envenomations caused by Arachnida
1116
Report and Abstracts
co-oxidation process with prostaglandin synthetases. Antioxidant agents such as SOD and catalase, vitamins A and E, or inhibitors of prostaglandin synthetases such as piroxicam, indomethacin and aspirin are efficient at preventing tissue and D N A lesions due to oxidative pathways. Glucuronides and sulfoconjugates of O T A are eliminated in urine. G S H conjugates have not been identified, although N-acetylcystein (NAC) modifies the O T A D N A - a d d u c t formation profile. A combination of m a n y of these substances can be useful in the prevention of toxic effects of ochratoxin A. Scorpion toxins: recent data in moleeular immunology. C. Devaux (CNRS U R A 1455, Facult6 de M~decine-Nord, Bd P. Dramard, 13916 Marseille Cedex 20, France). Scorpion stings have powerful toxic effects that cause significant health problems in many areas of the world. The lethal effect of scorpion venom is due to neurotoxins that act on sodium channels of excitable cells. The sequence variability of these molecules gives rise to antigenic polymorphism. 3D structure analysis suggests that conserved hydrophobic residues contribute to the c o m m o n pharmacological properties. We systematically re-examined the antigenicity of one toxin (toxin II from Androctonus australis hector) by the Pepscan method, and thereby identified a new linear epitope. This epitope corresponds to the highly conserved N-terminal sequence (residues 1-8). Polyclonal sera raised against a peptide that mimics this region recognize the native toxin II and also several other toxins that show a sequence similarity in their N-terminal part, but belong to different immunological groups. In addition, these sera are able to neutralize toxin II and inhibit its binding to rat brain synaptosomes. The possibility of raising a humoral immune response able to induce protection from the lethal effects of toxins was evaluated in the mouse model. Preliminary results, using non-toxic or detoxified immunogens, are discussed. Evolution o f the envenomations caused by Arachnida. M. Goyffon (L.E.R.A.I., M u s 6 u m National d'Histoire Naturelle, 57 Rue Cuvier, F-75005 Paris, France). The spiders and the scorpions are the two important venomous Arachnida orders, in particular the scorpions which are the most dangerous in the venomous fauna if the ratio number deaths/number stings is the criterion retained. Araneism can be neurotoxic (Latrodectus) or necrotic (Loxosceles). Considering the Latrodectus genus, cyclic peaks of envenomations corresponding to cyclic peaks of the spider populations are often observed. The variety of subspecies, and the difficulties in identifying some similar species in the genus explain the variability of the symptomatologies described. The geographic variations of necrotic power of the Loxosceles venoms are more surprising: some species harmless in Europe, as L. rufescens, are toxic in the New World, where this species was imported recently. The same observations were reported with Tegenaria agrestis, but no explanation can be given. Some similar facts are known for the scorpions: Buthus oecitanus is not really dangerous in Europe, but it is responsible for deaths in North Africa. More interesting are the epidemiological modifications of scorpionism due to the extension of the distribution of some dangerous species, which are capable of adapting to an urban environment, such as Centruroides exilicauda (U.S.A.) or Tityus serrulatus. Moreover, when public hygiene is neglected, commensal insects such as cockroaches proliferate, and scorpions, which easily find prey, also proliferate. A similar observation was recently reported with a dangerous snake, Eehis ocellatus, in tropical Africa. Therefore, an increase in venomous stings or bites in tropical countries could signify a deterioration in urban sanitary conditions. Molecular studies on bacterial toxins: towards" new generation ~raccines. C. Locht (Laboratoire de Microbiologie G~n6tique et Mol6culaire, Institut Pasteur de Lille, 1 Rue du Prof. Calmette, F-59019 Lille Cedex, France). Many bacterial pathogens express their virulence by the action of protein toxins. Consequently, protection against these diseases can be achieved by vaccination using the toxins as immunogens. Typical examples are tetanus toxin and diphtheria toxin. Because of their inherent activity, native forms cannot be used directly, but must first be detoxified. Genetic engineering provides a very powerful way to inactivate protein toxins without abolishing their immunoprotective potential. Pertussis toxin is one of the most complex protein toxins known to date and clinical tests have demonstrated its immunoprotectivity against whooping cough in children. The toxin is composed of five dissimilar subunits, named St to $5, that are arranged in an A B structure. A, composed of SI, is an enzymatically active moiety, and B, composed of $2 $5, is a receptor-binding moiety. The molecular steps of toxin action are (1) the binding of the toxin to the target cells, (2) the membrane translocation of the enzymatically active SI subunit, and (3) expression of ADP-ribosyltransferase activity by the internalized Sl subunit. The Sl-catatysed ADP-ribosylation of signal transducing G proteins causes signal transduction arrest, which is responsible for most of the biological activities of pertussis toxin. We have cloned the structural genes of each of the five toxin subunits and studied the enzyme mechanism of the SI subunit. This has provided information about the involvement of individual amino acid residues in substrate binding and catalysis. Site-directed alteration of these residues yielded toxin analogues, with dramatically reduced enzyme activity. However, not all biological activities were affected by the reduction of the enzyme activity. Therefore, we also studied the residues involved in the binding activities of the B moiety of the toxin, especially subunits $2 and
Report and Abstracts
co-oxidation process with prostaglandin synthetases. Antioxidant agents such as SOD and catalase, vitamins A and E, or inhibitors of prostaglandin synthetases such as piroxicam, indomethacin and aspirin are efficient at preventing tissue and D N A lesions due to oxidative pathways. Glucuronides and sulfoconjugates of O T A are eliminated in urine. G S H conjugates have not been identified, although N-acetylcystein (NAC) modifies the O T A D N A - a d d u c t formation profile. A combination of m a n y of these substances can be useful in the prevention of toxic effects of ochratoxin A. Scorpion toxins: recent data in moleeular immunology. C. Devaux (CNRS U R A 1455, Facult6 de M~decine-Nord, Bd P. Dramard, 13916 Marseille Cedex 20, France). Scorpion stings have powerful toxic effects that cause significant health problems in many areas of the world. The lethal effect of scorpion venom is due to neurotoxins that act on sodium channels of excitable cells. The sequence variability of these molecules gives rise to antigenic polymorphism. 3D structure analysis suggests that conserved hydrophobic residues contribute to the c o m m o n pharmacological properties. We systematically re-examined the antigenicity of one toxin (toxin II from Androctonus australis hector) by the Pepscan method, and thereby identified a new linear epitope. This epitope corresponds to the highly conserved N-terminal sequence (residues 1-8). Polyclonal sera raised against a peptide that mimics this region recognize the native toxin II and also several other toxins that show a sequence similarity in their N-terminal part, but belong to different immunological groups. In addition, these sera are able to neutralize toxin II and inhibit its binding to rat brain synaptosomes. The possibility of raising a humoral immune response able to induce protection from the lethal effects of toxins was evaluated in the mouse model. Preliminary results, using non-toxic or detoxified immunogens, are discussed. Evolution o f the envenomations caused by Arachnida. M. Goyffon (L.E.R.A.I., M u s 6 u m National d'Histoire Naturelle, 57 Rue Cuvier, F-75005 Paris, France). The spiders and the scorpions are the two important venomous Arachnida orders, in particular the scorpions which are the most dangerous in the venomous fauna if the ratio number deaths/number stings is the criterion retained. Araneism can be neurotoxic (Latrodectus) or necrotic (Loxosceles). Considering the Latrodectus genus, cyclic peaks of envenomations corresponding to cyclic peaks of the spider populations are often observed. The variety of subspecies, and the difficulties in identifying some similar species in the genus explain the variability of the symptomatologies described. The geographic variations of necrotic power of the Loxosceles venoms are more surprising: some species harmless in Europe, as L. rufescens, are toxic in the New World, where this species was imported recently. The same observations were reported with Tegenaria agrestis, but no explanation can be given. Some similar facts are known for the scorpions: Buthus oecitanus is not really dangerous in Europe, but it is responsible for deaths in North Africa. More interesting are the epidemiological modifications of scorpionism due to the extension of the distribution of some dangerous species, which are capable of adapting to an urban environment, such as Centruroides exilicauda (U.S.A.) or Tityus serrulatus. Moreover, when public hygiene is neglected, commensal insects such as cockroaches proliferate, and scorpions, which easily find prey, also proliferate. A similar observation was recently reported with a dangerous snake, Eehis ocellatus, in tropical Africa. Therefore, an increase in venomous stings or bites in tropical countries could signify a deterioration in urban sanitary conditions. Molecular studies on bacterial toxins: towards" new generation ~raccines. C. Locht (Laboratoire de Microbiologie G~n6tique et Mol6culaire, Institut Pasteur de Lille, 1 Rue du Prof. Calmette, F-59019 Lille Cedex, France). Many bacterial pathogens express their virulence by the action of protein toxins. Consequently, protection against these diseases can be achieved by vaccination using the toxins as immunogens. Typical examples are tetanus toxin and diphtheria toxin. Because of their inherent activity, native forms cannot be used directly, but must first be detoxified. Genetic engineering provides a very powerful way to inactivate protein toxins without abolishing their immunoprotective potential. Pertussis toxin is one of the most complex protein toxins known to date and clinical tests have demonstrated its immunoprotectivity against whooping cough in children. The toxin is composed of five dissimilar subunits, named St to $5, that are arranged in an A B structure. A, composed of SI, is an enzymatically active moiety, and B, composed of $2 $5, is a receptor-binding moiety. The molecular steps of toxin action are (1) the binding of the toxin to the target cells, (2) the membrane translocation of the enzymatically active SI subunit, and (3) expression of ADP-ribosyltransferase activity by the internalized Sl subunit. The Sl-catatysed ADP-ribosylation of signal transducing G proteins causes signal transduction arrest, which is responsible for most of the biological activities of pertussis toxin. We have cloned the structural genes of each of the five toxin subunits and studied the enzyme mechanism of the SI subunit. This has provided information about the involvement of individual amino acid residues in substrate binding and catalysis. Site-directed alteration of these residues yielded toxin analogues, with dramatically reduced enzyme activity. However, not all biological activities were affected by the reduction of the enzyme activity. Therefore, we also studied the residues involved in the binding activities of the B moiety of the toxin, especially subunits $2 and