Tihana Kurtović

Ammodytagin, a heterodimeric metalloproteinase from Vipera ammodytes ammodytes venom with strong hemorrhagic activity

Ammodytagin, a hemorrhagic Zn(2+)-dependent metalloproteinase from Vipera ammodytes ammodytes (Vaa) venom, is a glycosylated heterodimer of 108 kDa, as determined by MALDI mass spectrometry. Partial amino acid sequencing by Edman degradation and MS/MS analysis identified sequences belonging to metalloproteinase, disintegrin-like and cysteine-rich domains, which in addition to its heterodimeric nature allows classification into the P-IIIc group of snake venom metalloproteinases (SVMPs). Only few members of that group have been described so far. Ammodytagin possesses potent azocaseinolytic activity which can be inhibited by Na(2)EDTA, Zn(2+) and DTT. It cleaves insulin B-chain, hydrolysing it at positions Gln(4)-His(5), His(10)-Leu(11) and Tyr(16)-Leu(17). Furthermore, ammodytagin acts as a strong hemorrhagin in both rats and mice. Investigation of a substrate specificity revealed that the hemorrhagic activity of the novel SVMP might be the result of its involvement in cleavage of basal membrane components and depletion of fibrinogen, prothrombin and factor X in blood circulation. Finally, antiserum raised against ammodytagin was able to completely neutralise the hemorrhagic activity of the whole venom, suggesting it might be one of the key molecules towards which effective Vaa specific antivenom should be directed.

Identification of proteins interacting with ammodytoxins in Vipera ammodytes ammodytes venom by immuno-affinity chromatography.

In order to perform their function, proteins frequently interact with other proteins. Various methods are used to reveal protein interacting partners, and affinity chromatography is one of them. Snake venom is composed mostly of proteins, and various protein complexes in the venom have been found to exhibit higher toxicity levels than respective components separately. Complexes can modulate envenomation activity of a venom and/or potentiate its effect. Our previous data indicate that the most toxic components of the Vipera ammodytes ammodytes (Vaa) venom isolated so far—ammodytoxins (Atxs)—are contributing to the venom’s toxicity only moderately; therefore, we aimed to explore whether they have some interacting partner(s) potentiating toxicity. For screening of possible interactions, immuno-affinity chromatography combined with identification by mass spectrometry was used. Various chemistries (epoxy, carbonyldiimidazole, ethylenediamine) as well as protein G functionality were used to immobilize antibodies on monolith support, a Convective Interaction Media disk. Monoliths have been demonstrated to better suit the separation of large biomolecules. Using such approach, several proteins were indicated as potential Atx-binding proteins. Among these, the interaction of Atxs with a Kunitz-type inhibitor was confirmed by far-Western dot-blot and surface plasmon resonance measurement. It can be concluded that affinity chromatography on monolithic columns combined with mass spectrometry identification is a successful approach for screening of protein interactions and it resulted with detection of the interaction of Atx with Kunitz-type inhibitor in Vaa venom for the first time.

VaH3, one of the principal hemorrhagins in Vipera ammodytes ammodytes venom, is a homodimeric P-IIIc metalloproteinase

Hemorrhage is the most potent manifestation of envenomation by Vipera ammodytes ammodytes (V. a. ammodytes) venom in man. A detailed description of the venom components contributing to this effect is thus medically very important. We have characterized a novel component, termed here VaH3, as a potently hemorrhagic snake venom metalloproteinase (SVMP). Its proteolytic activity and overall stability depend on the presence of Zn(2+) and Ca(2+) ions. The molecular mass of this slightly acidic molecule, determined by MALDI/TOF analysis, is 104 kDa. Chemical reduction and S-carbamoylmethylation result in a single monomer of 53.7 kDa. N-deglycosylation decreased this mass by 4.6 kDa. The complete amino acid sequence of VaH3 was determined by protein and cDNA sequencing, showing that each of the identical glycoprotein subunits comprise a metalloproteinase, a disintegrin-like domain and a cysteine-rich domain, VaH3 belongs to the P-IIIc class of SVMPs. It shows strong sequence similarity to vascular endothelial cell apoptosis-inducing reprolysins. Anti-ammodytagin antibodies strongly cross-reacted with VaH3 and completely neutralized its hemorrhagic activity in rat, despite the fact that the two hemorrhagic P-III SVMPs from V. a. ammodytes venom do not share a very high degree of amino acid sequence identity. In spite of its narrow proteolytic specificity, VaH3 rapidly cleaved some basal membrane and extracellular matrix proteins, such as collagen IV, fibronectin and nidogen. Moreover, it also hydrolyzed plasma proteins involved in blood coagulation. It is an effective α-fibrinogenase that cleaves prothrombin and factor X without activating them. The degradation of these proteins likely contributes to the hemorrhagic activity of VaH3. A three-dimensional model of VaH3 was built to help explain structure-function relationships in ADAM/ADAMTS, a family of proteins having significant therapeutic potential and substantial sequence similarity to VaH3.

Studying disulfide bond rearrangement by MALDI‐RTOF PSD and MALDI‐TOF/RTOF high‐energy CID (20 keV) experiments of peptides derived from ammodytoxins

Ammodytoxins (Atxs) are presynaptically neurotoxic phospholipases present in Vipera ammodytes ammodytes snake venom. Atxs show a high sequence homology and contain 14 cysteines which form seven biologically relevant disulfide bridges-connecting non-neighboring cysteines. Formic acid cleavage was performed to confirm protein sequences by MALDI RTOF MS and resulted in 95.6% sequence coverage exhibiting only few formylations. Cysteine-containing peptides showed adjacent signals 2 and/or 4 Da lower (according to the number of cysteines present in the peptide) than the theoretical molecular weight indicating disulfide bridge rearrangement. Post-source decay (PSD) and high-energy collision-induced dissociation (CID) at 20 keV experiments showed fragmentation pattern unique for the reduced, thiol group containing and the oxidized, disulfide bridge harboring peptides. Besides typical low-energy fragment ions observed during PSD experiments (a-, b-, y-type ions), additional high-energy fragment ions (c-, x-, w-, d-type and internal fragments) of significant intensity were generated during fragmentation at 20 keV. In the case of charge directing N- and C-termini, x- and w-type ions were also observed during PSD. Good and up to complete sequence coverage was achieved for all studied peptides from Atxs in the case of high-energy CID, whereas PSD lacked information particularly for larger peptides.

The standard mouse assay of anti-venom quality does not measure antibodies neutralising the haemorrhagic activity of Vipera ammodytes venom

The venom of Vipera ammodytes ammodytes (Vaa), like the venoms of other Viperinae snakes, is largely haemorrhagic and necrotising, and only to a lesser extent neurotoxic to humans. The components most extensively studied so far, and most probably involved in generating the observed pathologies, are haemorrhagins (H), members of the metalloproteinase group of enzymes, and neurotoxic ammodytoxins (Atxs), that belong to the secretory phospholipases A2. Rabbit antisera were prepared containing functional antibodies specific for each class of pathology-inducing venom constituents and for both classes together. The involvement of these antibodies in neutralising the toxicity of whole Vaa venom was assessed using the ED50 assay in mice. This assay is the only regulatorily approved assay for estimating anti-venom potency and as such has the task to quantify the active compound neutralising venom-induced pathology of the anti-venom. Fully functional anti-Atx antibodies were shown to be responsible for neutralising the portion of venom toxicity, while anti-H antibodies were not protective in this assay. Thus, the mouse ED50 assay, intended to measure the active principle of the anti-venom, does not measure antibodies specific for Vaa venom haemorrhagins, and consequently does not fulfil its primary task from the regulatory point of view.

Ammodytoxin content of Vipera ammodytes ammodytes venom as a prognostic factor for venom immunogenicity.

Venoms are complex mixtures of proteins, peptides and other compounds whose biochemical and biological variability has been clearly demonstrated. These molecules have been used as antigens for immunization of anti-venom-producing animals (horses or sheep). Ammodytoxins (Atx) are potently neurotoxic compounds, and the most toxic compounds isolated so far from the Vipera ammodytes ammodytes (Vaa) venom. Recently we have shown that the level of antibodies specific to Vaa venoms most toxic component, ammodytoxin A (AtxA), (anti-AtxA IgG) in Vaa venom immunized rabbit sera highly correlated to the venom toxicity-neutralization potential of these sera. Here we investigated whether Atx content of Vaa venom could influence the outcome of immunization procedure. The novel ELISA was developed for precise determination of Atx content and Atx was quantified in venom samples used for immunization of rabbits. We clearly showed that animals immunized with the venom containing lower amount of Atx produced sera with significantly lower venom toxicity-neutralizing power and, vice versa, animals immunized with venoms containing higher amount of Atx produced sera with higher venom toxicity-neutralizing ability. Thus, the content of Atx in Vaa venom is a relevant parameter of its suitability in the production of highly protective Vaa anti-venom.

Vipera ammodytes bites treated with antivenom ViperaTAb: a case series with pharmacokinetic evaluation

Abstract Context: In clinical practice it is difficult to differentiate between V. berus and V. ammodytes venomous bites. In the past this was not a concern, but due to the current shortage in Viperfav™ and European viper venom antiserum availability, V. a. ammodytes venomous bites have recently been treated with ViperaTAb®, which is a pharmaceutical formulation containing a monospecific ovine Fab fragments against the venom of V. berus. Objective: To evaluate ViperaTAb® in V. a. ammodytes envenomations. Materials and methods: This is a prospective case series of three consecutive patients envenomed by V. a. ammodytes snakebite treated with ViperaTAb®. V. ammodytes venom, neurotoxic ammodytoxins, and Fab fragment levels were determined in serum samples and a pharmacokinetic analysis of the antivenom Fab fragments was carried out. Results: Three patients bitten by V. a. ammodytes with extensive local swelling, neurological symptoms and recurrent thrombocytopenia were treated with ViperaTAb®. V. ammodytes venom was detected in serum of all three patients. Ammodytoxins were detected in the serum of only the most severely envenomed patient who developed neurological symptoms. In the presented moderate cases, a dose of 8 mL of ViperaTAb® reduced swelling and improved systemic effects, such as thrombocytopenia. However, this dose of ViperaTAb® was not effective in the most severely envenomed patient with the highest serum values of V. ammodytes venom. In this case ViperaTAb® did not stop local swelling and it had no effect on neurological signs. ViperaTAb®’s systemic clearance, distribution and elimination half-lives were 4.3–13.4 mL/h/kg, 1.2–3.2 h and 14.1–55.4 h, respectively. Conclusions: In patients envenomed by V. a. ammodytes venom, ViperaTAb® reduces moderate swelling and temporarily improves systemic effects, except neurological symptoms. ViperaTAb® application induces a decrement of V. ammodytes venom level in the blood, but did not affect serum concentration of neurotoxic ammodytoxins in the one patient with measurable concentrations.

VaSP1, catalytically active serine proteinase from Vipera ammodytes ammodytes venom with unconventional active site triad

VaSP1, a serine proteinase from Vipera ammodytes ammodytes venom, is a glycosylated monomer of 31.5 kDa, as determined by MALDI mass spectrometry, showing multiple isoelectric points between pH 6.5 and pH 8.5. Partial amino acid sequencing of VaSP1 by Edman degradation and MS/MS analysis identified sequences which allowed its classification among the so-called snake venom serine proteinase homologues, members of the peptidase S1 family, however being devoid of the canonical catalytic triad. Only few representatives of this group have been identified so far with just two of them characterised in detail at the protein level. Despite substitution of His57 with Arg, VaSP1 possesses proteolytic activity which can be inhibited by Pefabloc, benzamidine, Zn²⁺ ions, DTT and trypsin inhibitor II, a Kunitz/BPTI group member. It hydrolyses N(α)-benzoyl-Phe-Val-Arg-p-NA, exhibiting Michaelis-Menten behaviour with K(m) = 48.2 μM and V(m) = 0.019 nM s⁻¹. The pH for optimal activity on tested substrate is around 9.0. VaSP1 also cleaves insulin B-chain, digesting it at positions His¹⁰-Leu¹¹, Ala¹⁴-Leu¹⁵ and Tyr¹⁶-Leu¹⁷. Furthermore, the novel serine proteinase is active towards wide array of proteins involved in haemostasis where its degradation of fibrinogen, fibrin, prothrombin, factor X and plasminogen in vivo probably results in depletion of coagulation factors in blood circulation. The possibility that VaSP1 possesses anticoagulant properties has been further indicated by its ability to prolong prothrombin time and activated partial thromboplastin time.

Chromatography, mass spectrometry, and molecular modeling studies on ammodytoxins

The ammodytoxins (Atxs) are neurotoxic phospholipases which occur in Vipera ammodytes ammodytes (Vaa) snake venom. There are three Atx isoforms, A, B, and C, which differ in only five amino acid positions at the C-terminus but differ substantially in their toxicity. The objective of this study was to establish an analytical method for unambiguous identification of all three isoforms and to use the method to assess a procedure for purification of the most toxic phospholipase, AtxA, from the venom. Isolation procedure for AtxA consisted of isolation of Atx-cross-reactive material (proteins recognized by anti-Atx antibodies), by use of an affinity column, then cation exchange on CIM (Convective Interaction Media) disks. The purification procedure was monitored by means of reversed-phase chromatography (RPC) and mass spectrometry (MS). Although previous cation exchange of the pure isoforms enabled separate elution of AtxA from B and C, separation of AtxA from Atxs mixture was not accomplished. RPC was not able to separate the Atx isoforms, whereas an MS based approach proved to be more powerful. Peptides resulting from tryptic digestion of Atxs which enable differentiation between the three isoforms were successfully detected and their sequences were confirmed by post-source decay (PSD) fragmentation. Separation of Atx isoforms by ion-exchange chromatography is most presumably prevented by Atxs heterodimer formation. The tendency of Atxs to form homodimers and heterodimers of similar stability was confirmed by molecular modeling.

A Single Dose of ViperfavTM May Be Inadequate for Vipera ammodytes Snake Bite: A Case Report and Pharmacokinetic Evaluation

ViperfavTM is a commercial F(ab’)2 antivenom prepared against European vipers venom. It is safe and effective for treating envenomation caused by Vipera aspis and Vipera berus. Therapeutic efficacy for treating Vipera ammodytes ammodytes (V. a. ammodytes) envenoming has not been yet described, although protective efficacy has been demonstrated in preclinical studies. We report on a 32-year-old man bitten by V. a. ammodytes who was treated with Viperfav™. Viperfav™ promptly reduced local extension and improved systemic pathological signs, but 24 h after the incident a recurrence of thrombocytopenia occurred despite a favorable pharmacokinetic profile with systemic clearance (1.64 (mL·h−1)·kg−1) and elimination half-life (97 h) among the highest ever reported. The recommended dose of Viperfav™ for V. aspis and V. berus bites may be inadequate for serious V. a. ammodytes envenomations. Following V. a. ammodytes bite, serial blood counts and coagulation profiles should be performed to help guide Viperfav™ treatment, along with supplemental administration as indicated.