Auswahl der wissenschaftlichen Literatur zum Thema „Pseudonoja textilis“

The efficacy of antivenom in prevention of cardiovascular depression and coagulopathy induced by Brown Snake species (Pseudonaja textilis, Pseudonaja affinis) was investigated in anaesthetised mechanically ventilated dogs. Venom and antivenom in variable amounts were incubated together at 37°C for 30 minutes prior to intravenous injection. The dose of antivenom required to prevent severe cardiovascular depression and coagulopathy induced by Pseudonaja textilis venom was 25 times the current recommended dose for clinical use. A tenfold dose of antivenom was required to neutralise similar effects induced by Pseudonaja affinis venom. Large amounts of antivenom may be required in clinical use if coagulopathy or cardiovascular depression are present after envenomation by species of the Brown Snake genus.

The cardiovascular and haematological effects of purified prothrombin activator derived from the venom of the Australian Common Brown Snake (Pseudonaja textilis) were studied in anaesthetised, mechanically ventilated dogs. Severe depression of systemic blood pressure and cardiac output and a rise in central venous pressure were observed. Thrombocytopenia, prolongation of both prothrombin time and activated partial thromboplastin time and a reduction in serum fibrinogen were also observed. All of these observed effects were prevented by the prior administration of heparin — a naturally occurring anticoagulant. We conclude that the prothrombin activator in Pseudonaja textilis venom may cause cardiovascular depression due to myocardial dysfunction secondary to disseminated intravascular coagulation.

The efficacy of heparin therapy after subcutaneous injection of Common Brown Snake (Pseudonaja textilis) venom was studied in anaesthetised, mechanically ventilated dogs. Intravenous heparin (100 U/kg), administered fifteen minutes after envenomation, neither prevented nor hastened the recovery from cardiovascular depression and coagulopathy observed after venom administration. Heparin therapy is not recommended for the treatment of established human envenomation.

Most reptiles exhibit no parental care and aggressive behaviour towards heterospecific predators has rarely been recorded in the natural environment. Several species of the subfamily Egerniinae are amongst the most highly social of all squamate reptiles, exhibiting stable social aggregations and high levels of long-term social and genetic monogamy. We have examined Cunningham’s skinks, Egernia cunninghami, over a three-year period during late January and early February (total 32 days) in the alpine region of New South Wales using video and thermal imaging. Four birthing sessions were witnessed during our field studies of social aggregations of skinks. Our observations monitored skink encounters, in the presence of offspring, with an eastern brown snake, Pseudonaja textilis (two separate encounters, one recorded by video/imaging) and 12 encounters with the Australian magpie, Gymnorhina tibicen. All events were associated with aggressive chasing and/or attack by adult skinks. The first snake encounter involved the active targeting of a recently born juvenile with the mother of the juvenile attacking the snake (running towards the snake, biting and remaining attached for several seconds). The second encounter (the following year) comprised two adult skinks attacking and biting a snake, Pseudonaja textilis. All magpie encounters resulted in chases by adult skinks.

An Australian common brown snake, Pseudonaja textilis, is known to contain highly lethal neurotoxins. Among them, a long-chain α-neurotoxin, pseudonajatoxin b, has been identified. In this report, while presenting evidence for the presence of at least four such long-chain α-neurotoxins in the venom of P. textilis, we describe the characteristics of both the mRNA and the gene responsible for the synthesis of these neurotoxins. A precursor toxin synthesized from the gene has been identified as being capable of producing the isoforms possibly by post-translational modifications at its C-terminal end. Recombinant toxins corresponding to the precursor and its product have been found to possess similar binding affinities for muscular acetylcholine receptors (IC50 = 3×10−8 M) and a lethality, LD50, of 0.15μg/g in mice.

The haemodynanic effects of Brown Snake (Pseudonaja) species (textilis, nuchalis, affinis) were investigated in anaesthetised, mechanically ventilated dogs. Blood pressure decreased to minimal levels five minutes after intravenous envenomation. Hypotension was accompanied by significant decrements in cardiac output and stroke volume and a rise in peripheral vascular resistance. Heart rate increased transiently during 0.5-2.0 minutes after envenomation but had declined below resting levels five minutes after envenomation. No statistically significant change was recorded in central venous pressure. Depression of myocardial contractility is postulated as the mechanism of venom induced hypotension.

L'hémostase humaine est régulée par l'activité de complexes enzyme-cofacteurs macromoléculaires qui nécessitent une surface membranaire chargée négativement pour leur assemblage. Outre l'organisation spatiale des réactions de coagulation lors de lésions vasculaires, la formation du complexe FX / FV à la surface phospholipidique permet l'amplification de la conversion de la FIl en Flla. Cependant, les connaissances sur les mécanismes moléculaires précis du phénomène d'amplification de l'hémostase à la surface de membrane lipidique sont incomplètes. L'objectif est de préciser les connaissances des mécanismes moléculaires du peptide d'activation sur le FX, le rôle du domaine Gla de la sérine protéase le FXa et du variant résistant aux anticoagulants oraux directs (AOD) qui régulent l'assemblage des complexes enzyme-cofacteur, complexes conduisant à la coagulation sanguine. En particulier, dans ce travail de thèse est étudié : 1/ le rôle dans l'évolution de la longueur du peptide d'activation du FX du venin de serpent et notamment un rôle potentiel dans la vitesse d'activation du FX et de l'amplification du phénomène de coagulation. 2/ le rôle du domaine GLA de la sérine protéase le FXa lié à la surface des phospholipides, qui associé au facteur Va convertit la Flla en FIl, une étape clé de la coagulation sanguine. Des variantes de ces protéines présentant des propriétés procoagulantes améliorées peuvent être trouvées dans la nature, avec, comme exemple le plus frappant, les protéines FVa-Xa exprimées dans le venin du serpent commun australien Pseudonaja textilis
Human hemostasis is regulated by the activity of enzyme-cofactor complexes macromolecular molecules that require a negatively charged membrane surface for their assembly. In addition to the spatial organization of coagulation reactions during vascular lesions, the formation of the FX/FV complex on the phospholipid surface allows the amplification of the conversion of FIl to Flla. However, the knowledge on the precise molecular mechanisms of the phenomenon of amplification of hemostasis on the lipid membrane surface are incomplete. The objective is to clarify the knowledge of the molecular mechanisms of the peptide activation on FX, the role of the Gla domain of the serine protease Fa and the variant resistant to direct oral anticoagulants (DOACs) that regulate the assembly of enzyme-cofactor complexes, complexes leading to blood clotting. In this thesis is studied 1/ the role in the evolution of the length of the FX activation peptide of the venom of snake and in particular a potential role in the speed of activation of the FX and the amplification of the coagulation phenomenon. 2/ the role of the GLA domain of the serine protease FXa linked to the surface of phospholipids, which associated with factor Va converts Flla into Fil, a key step in blood clotting. Variants of these proteins exhibiting properties Enhanced procoagulants can be found in nature, with, as an example most strikingly, the FVa-Xa proteins expressed in common snake venom Australian Pseudonaja textilis

I used surgically implanted miniature radio-transmitters to conduct a broad behavioural ecology study of the eastern brownsnake, Pseudonaja textilis, a large (to 2 m), slender, fast-moving elapid snake responsible for most snakebite fatalities in Australia. In order to minimise trauma to the snake, I modified anaesthesia (use of nitrous oxide to relax the animal prior to induction of surgical—level anaesthesia with halothane); implantation techniques (reliance on “blunt” dissection rather than cutting of tissues after the initial incision; placement of antenna in the peritoneal cavity rather than subcutaneously; anchoring the transmitter in place to avoid slippage in a position anterior to the incision), and removal (use of a "disposable" silicon casing to eliminate problems associated with tissue adhesion to the antenna). Comparisons of changes in body mass of telemetered versus non— telemetered snakes indicated that the transmitters had no detectable effects on growth rate, even in a drought year when such effects might be most obvious. Encounters between humans and dangerously venomous snakes put both participants at serious risk, so the determinants of such encounters warrant attention. I set out to identify factors influencing the probability that a human walking in agricultural land near the town of Leeton (in the Murrumbidgee Irrigation Area in south-eastem Australia) would come into close proximity to a brownsnake. My study area is typical of many of the agricultural landscapes occupied by B. texiis. Over a three-year period, I walked regular transects to quantify the number and rate of snake encounters, and the proportion of snakes above-ground which could be seen. The rate of encounters depended upon a series of factors, including season, time of day, habitat type, weather conditions (wind and air temperature) and shade of the observer’s clothing (light versus dark).

As toxinas de veneno de serpentes têm como principal função alterar a homeostase das presas para fins de alimentação ou defesa. O estudo aprofundado da composição do veneno de serpentes é importante para a produção de soros antiofídicos mais eficientes, para a descoberta de novos fármacos e na compreensão de processos biológicos, ecológicos e evolutivos. As pesquisas com toxinas têm mostrado uma versatilidade natural, refinada pela evolução, na diversificação de funções em famílias de proteínas recrutadas de suas funções endógenas, por meio de sucessivas duplicações e acumulo de mutações levando a uma evolução acelerada. A miríade de toxinas disponíveis e sua diversidade de funções ainda não foram completamente descritas. A combinação das análises em larga escala do transcriptoma de novo da glândula de veneno e do proteoma do veneno permite elaborar um perfil mais completo do toxinoma do veneno, permitindo inclusive um aumento na sensibilidade da detecção de toxinas pouco representadas e inesperadas nos venenos. O objetivo geral deste estudo foi analisar o toxinoma do veneno de uma das mais perigosas espécies australianas, a Pseudonaja textilis (Elapidae). Foi possível identificar no veneno as toxinas: fatores de coagulação de veneno do complexo protrombinase, subunidades de fosfolipases A2 (PLA2) da neurotoxina textilotoxin e PLA2 de atividade procoagulante, neurotoxinas tipo three-finger toxin (3FTx), inibidores de protease do tipo-kunitz textilinin, e pela primeira vez, uma nova variante de 3FTx, lectinas tipo C, CRiSP além de indícios de toxinas de lagarto Heloderma e outras proteínas candidatas a toxinas como calreticulin e dipeptidase 2. Metaloproteinases, pouco estudadas em Elapidae, foram clonadas e detectadas no veneno por ensaios de fracionamento e imunoreatividade. A análise do transcriptoma identificou novas isoformas e variantes de toxinas, principalmente das 3FTx e dos inibidores de serinoproteases, assim como transcritos de toxinas que não foram detectadas no veneno e que merecem mais investigações. O quadro de sintomas com acidentes em humanos é bem explicado pelas toxinas identificadas, porém, em seu habitat natural, as toxinas pouco conhecidas e até então não descritas devem ter funções importantes e específicas na predação. Identificar esta diversidade de variantes é importante para entender o modo de ação das toxinas.
Snake venom toxins alter prey homeostasis for feeding or defense. In depth studies of venom composition are important for better antivenom production, for new drugs lead and discovery and for better understanding of biological, ecological and evolutionary processes. Research on toxins have shown the natures way of innovating, refined by evolution, diversifying functions of protein families recruited from their endogenous function to the venom gland by successive gene duplication and mutation accumulation, leading to an accelerated evolution. A myriad of available toxins and diversity of functions is still available for discovery. Combining high throughput techniques such as venom gland de novo transcriptomics and venom proteomics, one can assess and observe a more complete profile of the snake toxinome, additionally allowing an upscale in low represented and unexpected toxin detection. The aim of this project was to investigate the venom toxinome of one of the most dangerous Australian species, Pseudonaja textilis (Elapidae). The toxins identified in it venom was: protrombinase complex coagulation factors, neurotoxic textilotoxin phospholipase A2 (PLA2) subunits and procoagulant PLA2, neurotoxic three-finger toxins (3FTx), Kunitz-type protease inhibitor textilinin, and for the first time, a new long 3FTx, C-type lectins, CRiSPs, as well as evidences of lizard toxins from Heloderma genus and other toxin candidates calreticulin and dipeptidase 2. Metalloproteinases, little investigated in Elapidae, was cloned and detected in the venom after fractionation and immunoassay. The transcriptome revealed new toxin variants and isoforms, specially 3FTx and serine protease inhibitors, as well as transcripts from toxins not detected in the venom that deserves further investigation. Human accident symptoms are well explained by the identified toxins, however, in its natural environment, little known and undescribed toxins must have specific and important role in predation. Identifying this diversity is important to better understand toxins ways of action.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
FAPESP:09/10305-8

Abstract Textilotoxin is the main neurotoxin responsible for the high lethality of the venom of P. textilis textilis. This elapid snake was the cause of nine snake bite fatalities in Australia in the period 1981 to 1991 (Sutherland 1992). The toxin possesses phospholipase A2 (PLA2) activity, like other ,β-neurotoxins from elapid, crotalid, and viperid snakes. Studies on the mechanism of action using electromyography in the mouse demonstrated a use-dependent rate of development of neuromuscular blockade (Lloyd et al. 1991), in which the development of such blockade in vivo was accelerated by increasing rates of nerve stimulation.