Homepage bandeau_genéral
  Venin


  Director : BON Cassian (cbon@pasteur.fr)


  abstract

 

Antivenom therapy is the only specific treatment of envenomations. Although much used, it is often contentious because of a lack of suitably controlled studies that demonstrate its efficacy and rigorously establish the conditions for its use. We gathered clinical and laboratory data on over one hundred and fifty cases of viper envenomation in a multicentre study in France. This investigation was completed by an experimental study of the effects of antivenom therapy on venom toxicokinetics in the rabbit, with and without antivenom therapy. We found that viper venom is quickly absorbed from the injection site and diffuses throughout the body, but is eliminated slowly in the absence of antivenom therapy. The intravenous administration of "specific antivenom serum", i.e. F(ab)'2 fragments of purified equine immunoglobulins, induces redistribution of the venom from the tissues to the vascular compartment, where the toxic antigens are neutralised by antibodies and then eliminated. These results prompted French physicians to reconsider their negative stance regarding "antivenom serum" and to use it again under stricter conditions. This has led to substantial reductions in mortality, morbidity and hospitalisation times.



  report

cale

We have used the same methodology to study other types of envenomation, notably by scorpions from North Africa. This work has shown that scorpion venom is assimilated and then eliminated much faster than viper venom. This means that antivenom therapy must be implemented much more promptly after scorpion envenomation than after a viper bite.

VENOMS AND HAEMOSTASIS(G. Faure, M. Leduc, R. Maroun, B. Saliou, A. Wisner)

Numerous components in snake venoms activate or inhibit haemostatic mechanisms. Several from various venoms have been characterised in the Unité des Venins: bothrojaracin, a thrombin inhibitor; TSV-PA, a plasminogen activator; and convulxin, a platelet activator.

Bothrojaracin, discovered in the venom of Bothrops jararaca, is a specific and potent inhibitor of human thrombin. It has an original action mechanism since it interacts with exosites I and II, which are necessary for thrombin's interaction with its macromolecular substrates (fibrinogen, platelet receptors, thrombomodulin, etc.) and physiological inhibitors (antithrombin III and heparin), but does not affect the enzyme's catalytic site. Having cloned and sequenced the cDNA encoding the subunits of bothrojaracin, we expressed bothrojaracin as a recombinant fusion protein combining bothrojaracin with the enzyme acetylcholinesterase (AChE), isolated from the venom of the banded krait, Bungarus fasciatus. We are currently using site-directed mutagenesis to study the bothrojaracin-thrombin interaction, with a view to screening for novel antithrombotic agents.

We have identified a specific activator of plasminogen, TSV-PA, in the venom of the Chinese green tree viper, Trimeresurus stejnegeri. This serine proteinase has a catalytic domain homologous to that of human plasminogen activator, t-PA. The cDNA encoding TSV-PA has been cloned, sequenced and expressed in E. coli. The 3D structure of TSV-PA has been established by crystallography. Unlike t-PA, TSV-PA is insensitive to physiological inhibitors. It may therefore prove to be a more active thrombolytic agent than t-PA in the treatment of stroke, because of its longer in vivo half-life. We have investigated the molecular mechanism of TSV-PA's insensitivity to t-PA inhibitors by site-directed mutagenesis.

Convulxin, extracted from the South American rattlesnake, Crotalus durissus terrificus, activates blood platelets by specifically binding to their collagen receptor, glycoprotein VI (GPVI), which plays a determinant role in the triggering and control of primary haemostasis. Convulxin has proved to be a precious pharmacological tool and we have used it to identify, purify and characterise GPVI and to study its structural and functional properties. Convulxin is a trimer of dimers (ab)3. The cDNAs encoding the two subunits have been cloned, sequenced and expressed in the form of a fusion protein combining acetylcholinesterase of snake venom (AChE) and a monomer of convulxin ab. This recombinant protein (AChE-ab) binds to GPVI and we are currently investigating its functional properties.

Lastly, we have shown that human type II PLA2 (sPLA2grII), secreted by activated blood platelets, inhibits plasma coagulation. sPLA2grII therefore exerts negative feedback control on the procoagulant action of activated platelets. This regulatory loop may enable us to enhance understanding of the mechanisms of haemostasis and how they are regulated. We have shown that the anticoagulant activity of sPLA2grII does not involve its enzymatic activity but rather direct activity on coagulation factor Xa. Site-directed mutagenesis and a comparative study with anticoagulant PLA2 of snake venoms has enabled us to identify one of the regions of human sPLA2grII responsible for its anticoagulant activity. Using this region, peptides could be prepared for use as molecular models in the development of novel antithrombotic agents.



  publications

puce Publications of the unit on Pasteur's references database


  personnel

  Office staff Researchers Scientific trainees Other personnel
 

COUEILLE Solange, coueille@pasteur.fr

CHOUMET Valérie, IP

FAURE Grazyna, IP

LEDUC Mireille, Paris XI University

MAROUN Rachid C., INSERM

GHADIRI Ataallah, Postdoctoral fellow

GOWDA Verabasappa, Trainee on leave

GUILLEMIN Isabelle, IP, Postdoctoral fellow

HENEINE Luiz, Trainee on leave

JAN Virginie, PhD student

FERQUEL Elisabeth, IP

MAZARS Séverine, IP

ROBBE-VINCENT Annie, IP

SALIOU Bernard, IP

WISNER Anne, IP


filet

Page Top research Institut Pasteur homepage

If you have problems with this Web page, please write to rescom@pasteur.fr.